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Copper is a chemical element with the symbol Cu (from Latin: cuprum) and atomic number 29. It is a ductile metal with very high thermal and electrical conductivity. Pure copper is soft and malleable; a freshly exposed surface has a reddish-orange color. It is used as a conductor of heat and electricity, a building material, and a constituent of various metal alloysSony VAIO VPCF135Z1E/B battery.

The metal and its alloys have been used for thousands of years. In the Roman era, copper was principally mined on Cyprus, hence the origin of the name of the metal as сyprium (metal of Cyprus), later shortened to сuprum. Its compounds are commonly encountered as copper(II) salts, which often impart blue or green colors to minerals such as turquoise and have been widely used historically as pigmentsSony VAIO VPCF137HG/BI battery. Architectural structures built with copper corrode to give green verdigris (or patina). Decorative art prominently features copper, both by itself and as part of pigments.

Copper(II) ions are water-soluble, where they function at low concentration as bacteriostatic substances, fungicides, and wood preservatives. In sufficient amounts, they are poisonous to higher organisms; at lower concentrations it is an essential trace nutrient to all higher plant and animal life. The main areas where copper is found in animals are liver, muscle and boneSony VAIO VPCF136FG/BI battery.

Characteristics

[edit]Physical

A copper disc (99.95% pure) made by continuous casting and etching.

Copper just above its melting point keeps its pink luster color when enough light outshines the orange incandescence color.

Copper, silver and gold are in group 11 of the periodic table, and they share certain attributes: they have one s-orbital electron on top of a filled d-electron shell and are characterized by high ductility and electrical conductivitySony VAIO VPCF135FG/B battery. The filled d-shells in these elements do not contribute much to the interatomic interactions, which are dominated by the s-electrons through metallic bonds. Contrary to metals with incomplete d-shells, metallic bonds in copper are lacking a covalent character and are relatively weak. This explains the low hardness and high ductility of single crystals of copperSony VAIO VPCF127HG/BI battery.[2] At the macroscopic scale, introduction of extended defects to the crystal lattice, such as grain boundaries, hinders flow of the material under applied stress thereby increasing its hardness. For this reason, copper is usually supplied in a fine-grained polycrystalline form, which has greater strength than monocrystalline formsSony VAIO VPCF11Z1E battery.[3]

The low hardness of copper partly explains its high electrical (59.6×106 S/m) and thus also high thermal conductivity, which are the second highest among pure metals at room temperature.[4] This is because the resistivity to electron transport in metals at room temperature mostly originates from scattering of electrons on thermal vibrations of the latticeSony VAIO VPCF11S1E battery, which are relatively weak for a soft metal.[2] The maximum permissible current density of copper in open air is approximately 3.1×106 A/m2 of cross-sectional area, above which it begins to heat excessively.[5] As with other metals, if copper is placed against another metal, galvanic corrosion will occur.[6]

Together with osmium (bluish), and gold (yellow), copper is one of only three elemental metals with a natural color other than gray or silverSony VAIO VPCF11M1E/H battery.[7] Pure copper is orange-red and acquires a reddish tarnish when exposed to air. The characteristic color of copper results from the electronic transitions between the filled 3d and half-empty 4s atomic shells – the energy difference between these shells is such that it corresponds to orange light. The same mechanism accounts for the yellow color of goldSony VAIO VPCF11M1E battery.[2]

[edit]Chemical

Unoxidized copper wire (left) and oxidized copper wire (right).

Copper forms a rich variety of compounds with oxidation states +1 and +2, which are often called cuprous and cupric, respectively.[8] It does not react with water, but it slowly reacts with atmospheric oxygen forming a layer of brown-black copper oxide. In contrast to the oxidation of iron by wet air, this oxide layer stops the further, bulk corrosionSony VAIO VPCF11JFX/B battery. A green layer of verdigris (copper carbonate) can often be seen on old copper constructions, such as the Statue of Liberty, the largest copper statue in the world built using repoussé and chasing.[9] Hydrogen sulfides and sulfides react with copper to form various copper sulfides on the surface. In the latter case, the copper corrodes, as is seen when copper is exposed to air containing sulfur compoundsSony VAIO VPCF119FJ battery.[10] Oxygen-containing ammonia solutions give water-soluble complexes with copper, as do oxygen and hydrochloric acid to form copper chlorides and acidified hydrogen peroxide to form copper(II) salts. Copper(II) chloride and copper comproportionate to form copper(I) chloride.[11]

[edit]Isotopes

Main article: Isotopes of copper

There are 29 isotopes of copper. 63Cu and 65Cu are stable, with 63Cu comprising approximately 69% of naturally occurring copper; they both have a spin of 3/2Sony VAIO VPCF119FC/BI battery.[12] The other isotopes are radioactive, with the most stable being 67Cu with a half-life of 61.83 hours.[12] Seven metastable isotopes have been characterized, with 68mCu the longest-lived with a half-life of 3.8 minutes. Isotopes with a mass number above 64 decay by β-, whereas those with a mass number below 64 decay by β+. 64Cu, which has a half-life of 12.7 hours, decays both waysSony VAIO VPCF119FC battery.[13]

62Cu and 64Cu have significant applications. 64Cu is a radiocontrast for X-ray imaging, and complexed with a chelate can be used for treating cancer. 62Cu is used in 62Cu-PTSM that is a radioactive tracer for positron emission tomography.[14]

[edit]Occurrence

Copper can be found as either native copper or as part of minerals. Native copper is a polycrystal, with the largest described single crystal measuring 4.4×3.2×3.2 cm.[15] The largest mass of elemental copper weighed 420 tonnes and was found in 1857 on the Keweenaw Peninsula in Michigan, US. Sony VAIO VPCF117HG/BI battery There are many examples of copper-containing minerals: chalcopyrite and chalcocite are copper sulfides, azurite and malachite are copper carbonates and cuprite is a copper oxide.[4] Copper is present in the Earth's crust at a concentration of about 50 parts per million (ppm),[16] and is also synthesized in massive stars.[17]

[edit]Production

Chuquicamata in Chile is one of the world's largest open pit copper minesSony VAIO VPCF116FG/BI battery.

World production trend

Copper output in 2005

Copper prices 2003–2011 in USD per tonne

See also: List of countries by copper production

Most copper is mined or extracted as copper sulfides from large open pit mines in porphyry copper deposits that contain 0.4 to 1.0% copper. Examples include Chuquicamata in Chile, Bingham Canyon Mine in Utah, United States and El Chino Mine in New Mexico, United States. According to the British Geological Survey, in 2005, Chile was the top mine producer of copper with at least one-third world share followed by the United StatesSony VAIO VPCF115FG/B battery, Indonesia and Peru.[4] The amount of copper in use is increasing and the quantity available is barely sufficient to allow all countries to reach developed world levels of usage.[18]

[edit]Reserves

See also: Peak copper#Reserves

Copper has been in use at least 10,000 years, but more than 95% of all copper ever mined and smelted has been extracted since 1900. As with many natural resources, the total amount of copper on Earth is vast (around 1014 tons just in the top kilometer of Earth's crust, or about 5 million years worth at the current rate of extraction) Sony VAIO VPCF21ZHJ battery. However, only a tiny fraction of these reserves is economically viable, given present-day prices and technologies. Various estimates of existing copper reserves available for mining vary from 25 years to 60 years, depending on core assumptions such as the growth rate.[19] Recycling is a major source of copper in the modern world.[20] Because of these and other factorsSony VAIO VPCF21Z1E/BI battery, the future of copper production and supply is the subject of much debate, including the concept of Peak copper, analogous to Peak Oil.

The price of copper has historically been unstable,[21] and it quintupled from the 60-year low of US$0.60/lb (US$1.32/kg) in June 1999 to US$3.75 per pound (US$8.27/kg) in May 2006. It dropped to US$2.40/lb (US$5.29/kg) in February 2007, then rebounded to US$3.50/lb (US$7.71/kg) in April 2007Sony VAIO VPCF21AHJ battery.[22] In February 2009, weakening global demand and a steep fall in commodity prices since the previous year's highs left copper prices at US$1.51/lb.[23]

[edit]Methods

Main article: Copper extraction techniques

The concentration of copper in ores averages only 0.6%, and most commercial ores are sulfides, especially chalcopyrite (CuFeS2) and to a lesser extent chalcocite (Cu2S).[24] These minerals are concentrated from crushed ores to the level of 10–15% copper by froth flotation or bioleachingSony VAIO VPCF21AGJ battery.[25] Heating this material with silica in flash smelting removes much of the iron as slag. The process exploits the greater ease of converting iron sulfides into its oxides, which in turn react with the silica to form the silicate slag, which floats on top of the heated mass. The resulting copper matte consisting of Cu2S is then roasted to convert all sulfides into oxidesSony VAIO VPCF21AFJ battery:[24]

2 Cu2S + 3 O2 → 2 Cu2O + 2 SO2

The cuprous oxide is converted to blister copper upon heating:

2 Cu2O → 4 Cu + O2

The Sudbury matte process converted only half the sulfide to oxide and then used this oxide to remove the rest of the sulfur as oxide. It was then electrolytically refined and the anode mud exploited for the platinum and gold it contained. This step exploits the relatively easy reduction of copper oxides to copper metal. Natural gas is blown across the blister to remove most of the remaining oxygen and electrorefining is performed on the resulting material to produce pure copperSony VAIO VPCF219FJ/BI battery:[26]

Cu2+ + 2 e– → Cu

[edit]Recycling

Copper, like aluminium, is 100% recyclable without any loss of quality whether in a raw state or contained in a manufactured product. In volume, copper is the third most recycled metal after iron and aluminium. It is estimated that 80% of the copper ever mined is still in use today.[27] According to the International Resource Panel's Metal Stocks in Society reportSony VAIO VPCF217HG/BI battery, the global per capita stock of Copper in use in society is 35–55 kg. Much of this is in more-developed countries (140–300 kg per capita) rather than less-developed countries (30–40 kg per capita).

The process of recycling copper follows roughly the same steps as is used to extract copper, but requires fewer steps. High purity scrap copper is melted in a furnace and then reduced and cast into billets and ingots; lower purity scrap is refined by electroplating in a bath of sulfuric acid. Sony VAIO VPCF217HG battery

[edit]Compounds

A sample of copper(I) oxide.

See also: Category:Copper compounds

[edit]Binary compounds

As for other elements, the simplest compounds of copper are binary compounds, i.e. those containing only two elements. The principal ones are the oxides, sulfides and halides. Both cuprous and cupric oxides are known. Among the numerous copper sulfides, important examples include copper(I) sulfide and copper(II) sulfideSony VAIO VPCF14ZHJ battery.

The cuprous halides with chlorine, bromine, and iodine are known, as are the cupric halides with fluorine, chlorine, and bromine. Attempts to prepare copper(II) iodide give cuprous iodide and iodine.[8]

2 Cu2+ + 4 I− → 2 CuI + I2

[edit]Coordination chemistry

Copper(II) gives a deep blue coloration in the presence of ammonia ligands. The one used here is tetramminecopper(II) sulfateSony VAIO VPCF14AHJ battery.

Copper, like all metals, forms coordination complexes with ligands. In aqueous solution, copper(II) exists as [Cu(H2O)6]2+. This complex exhibits the fastest water exchange rate (speed of water ligands attaching and detaching) for any transition metal aquo complex. Adding aqueous sodium hydroxide causes the precipitation of light blue solid copper(II) hydroxide. A simplified equation isSony VAIO VPCF14AGJ battery:

Cu2+ + 2 OH− → Cu(OH)2

Aqueous ammonia results in the same precipitate. Upon adding excess ammonia, the precipitate dissolves, forming tetraamminecopper(II):

Cu(H2O)4(OH)2 + 4 NH3 → [Cu(H2O)2(NH3)4]2+ + 2 H2O + 2 OH−

Many other oxyanions form complexes; these include copper(II) acetate, copper(II) nitrate, and copper(II) carbonate. Copper(II) sulfate forms a blue crystalline pentahydrate, which is the most familiar copper compound in the laboratory. It is used in a fungicide called the Bordeaux mixtureSony VAIO VPCF14AFJ battery.[29]

Ball-and-stick model of the complex [Cu(NH3)4(H2O)2]2+, illustrating the octahedral coordination geometry common for copper(II).

Polyols, compounds containing more than one alcohol functional group, generally interact with cupric salts. For example, copper salts are used to test for reducing sugars. Specifically, using Benedict's reagent and Fehling's solution the presence of the sugar is signaled by a color change from blue Cu(II) to reddish copper(I) oxideSony VAIO VPCF149FJ/BI battery.[30] Schweizer's reagent and related complexes with ethylenediamine and other amines dissolve cellulose.[31] Amino acids form very stable chelate complexes with copper(II). Many wet-chemical tests for copper ions exist, one involving potassium ferrocyanide, which gives a brown precipitate with copper(II) saltsSony VAIO VPCF148FJ/B battery.

[edit]Organocopper chemistry

Main article: Organocopper compound

Compounds that contain a carbon-copper bond are known as organocopper compounds. They are very reactive towards oxygen to form copper(I) oxide and have many uses in chemistry. They are synthesized by treating copper(I) compounds with Grignard reagents, terminal alkynes or organolithium reagents;[32] in particular, the last reaction described produces a Gilman reagentSony VAIO VPCF13ZHJ battery. These can undergo substitution with alkyl halides to form coupling products; as such, they are important in the field of organic synthesis. Copper(I) acetylide is highly shock-sensitive but is an intermediate in reactions such as the Cadiot-Chodkiewicz coupling[33] and the Sonogashira coupling.[34] Conjugate addition to enones[35] and carbocupration of alkynes[36] can also be achieved with organocopper compoundsSony VAIO VPCF13Z0E/B battery. Copper(I) forms a variety of weak complexes with alkenes and carbon monoxide, especially in the presence of amine ligands.[37]

[edit]Copper(III) and copper(IV)

Complexes of copper(III) are frequent intermediates in reactions of organocopper compounds. Dicopper oxo complexes also feature copper(III).[38] Fluoride ligands, being highly basic, stabilize metal ions in high oxidation states; indeed, representative copper(III) and copper(IV) complex are fluorides. These include K3CuF6 and Cs2CuF6.[8] With di- and tripeptidesSony VAIO VPCF13M8E/B battery, purple-colored complexes of copper(III) have been observed, this high oxidation state being stabilized by the deprotonated amide ligands.[39]

History

Copper Age

Main article: Copper Age

A corroded copper ingot from Zakros, Crete, shaped in the form of an animal skin typical for that era.

Copper occurs naturally as native copper and was known to some of the oldest civilizations on record. It has a history of use that is at least 10,000 years old, and estimates of its discovery place it at 9000 BC in the Middle East;[40] a copper pendant was found in northern Iraq that dates to 8700 BCSony VAIO VPCF13AHJ battery.[41] There is evidence that gold and meteoric iron (but not iron smelting) were the only metals used by humans before copper.[42] The history of copper metallurgy is thought to have followed the following sequence: 1) cold working of native copper, 2) annealing, 3) smelting, and 4) the lost wax method. In southeastern Anatolia, all four of these metallurgical techniques appears more or less simultaneously at the beginning of the Neolothic c. 7500 BCSony VAIO VPCF13AGJ battery.[43] However, just as agriculture was independently invented in several parts of the world (including Pakistan, China, and the Americas) copper smelting was invented locally in several different places. It was probably discovered independently in China before 2800 BC, in Central America perhaps around 600 AD, and in West Africa about the 9th or 10th century ADSony VAIO VPCF13AFJ battery.[44] Investment casting was invented in 4500–4000 BC in Southeast Asia[40] and carbon dating has established mining at Alderley Edge in Cheshire, UK at 2280 to 1890 BC.[45] Ötzi the Iceman, a male dated from 3300–3200 BC, was found with an axe with a copper head 99.7% pure; high levels of arsenic in his hair suggest his involvement in copper smeltingSony VAIO VPCF138FJ/BI battery.[46] Experience with copper has assisted the development of other metals; in particular, copper smelting led to the discovery of iron smelting.[46] Production in the Old Copper Complex in Michigan and Wisconsin is dated between 6000 and 3000 BC.[47][48] Natural bronze, a type of copper made from ores rich in silicon, arsenic, and (rarely) tin, came into general use in the Balkans around 5500 BCSony VAIO VPCF138FJ/B battery. Previously the only tool made of copper had been the awl, used for punching holes in leather and gouging out peg-holes for wood joining. However, the introduction of a more robust form of copper led to the widespread use, and large-scale production of heavy metal tools, including axes, adzes, and axe-adzes. Sony VAIO VPCF138FC/BI battery

[edit]Bronze Age

Main article: Bronze Age

Alloying copper with tin to make bronze was first practiced about 4000 years after the discovery of copper smelting, and about 2000 years after "natural bronze" had come into general use. Bronze artifacts from Sumerian cities and Egyptian artifacts of copper and bronze alloys date to 3000 BC.[49] The Bronze Age began in Southeastern Europe around 3700 - 3300 BCSony VAIO VPCF135FG battery, in Northwestern Europe about 2500 BC. It ended with the beginning of the Iron Age, 2000-1000 BC in the Near East, 600 BC in Northern Europe. The transition between the Neolithic period and the Bronze Age was formerly termed the Chalcolithic period (copper-stone), with copper tools being used with stone tools. This term has gradually fallen out of favor because in some parts of the world the Calcholithic and Neolithic are coterminous at both endsSony VAIO VPCF12AHJ battery. Brass, an alloy of copper and zinc, is of much more recent origin. It was known to the Greeks, but became a significant supplement to bronze during the Roman Empire.[49]

Antiquity and Middle Ages

In alchemy the symbol for copper was also the symbol for the goddess and planet Venus.

Chalcolithic copper mine in Timna Valley, Negev Desert, Israel.

In Greece, copper was known by the name chalkos (χαλκός). It was an important resource for the Romans, Greeks and other ancient peoples. In Roman times, it was known as aes Cyprium, aes being the generic Latin term for copper alloys and Cyprium from Cyprus, where much copper was minedSony VAIO VPCF12AGJ battery. The phrase was simplified to cuprum, hence the English copper. Aphrodite and Venus represented copper in mythology and alchemy, due to its lustrous beauty, its ancient use in producing mirrors, and its association with Cyprus, which was sacred to the goddess. The seven heavenly bodies known to the ancients were associated with the seven metals known in antiquity, and Venus was assigned to copperSony VAIO VPCF12AFJ battery.[50]

Britain's first use of brass occurred around the 3rd–2nd century BC. In North America, copper mining began with marginal workings by Native Americans. Native copper is known to have been extracted from sites on Isle Royale with primitive stone tools between 800 and 1600.[51] Copper metallurgy was flourishing in South America, particularly in Peru around 1000 ADSony VAIO VPCF129FJ/BI battery; it proceeded at a much slower rate on other continents. Copper burial ornamentals from the 15th century have been uncovered, but the metal's commercial production did not start until the early 20th century.

The cultural role of copper has been important, particularly in currency. Romans in the 6th through 3rd centuries BC used copper lumps as money. At first, the copper itself was valued, but gradually the shape and look of the copper became more importantSony VAIO VPCF128FJ/B battery. Julius Caesar had his own coins made from brass, while Octavianus Augustus Caesar's coins were made from Cu-Pb-Sn alloys. With an estimated annual output of around 15,000 t, Roman copper mining and smelting activities reached a scale unsurpassed until the time of the Industrial Revolution; the provinces most intensely mined were those of Hispania, Cyprus and in Central Europe. Sony VAIO VPCF127FJ/W battery

The gates of the Temple of Jerusalem used Corinthian bronze made by depletion gilding. It was most prevalent in Alexandria, where alchemy is thought to have begun.[54] In ancient India, copper was used in the holistic medical science Ayurveda for surgical instruments and other medical equipment. Ancient Egyptians (~2400 BC) used copper for sterilizing wounds and drinking waterSony VAIO VPCF11ZHJ battery, and later on for headaches, burns, and itching. The Baghdad Battery, with copper cylinders soldered to lead, dates back to 248 BC to AD 226 and resembles a galvanic cell, leading people to believe this was the first battery; the claim has not been verified.[55]

[edit]Modern period

Acid mine drainage affecting the stream running from the disused Parys Mountain copper mines

The Great Copper Mountain was a mine in Falun, Sweden, that operated from the 10th century to 1992. It produced two thirds of Europe's copper demand in the 17th century and helped fund many of Sweden's wars during that timeSony VAIO VPCF11AHJ battery.[56] It was referred to as the nation's treasury; Sweden had a copper backed currency.[57]

The uses of copper in art were not limited to currency: it was used by Renaissance sculptors, in photographic technology known as the daguerreotype, and the Statue of Liberty. Copper plating and copper sheathing for ships' hulls was widespread; the ships of Christopher Columbus were among the earliest to have this featureSony VAIO VPCF11AGJ battery.[58] The Norddeutsche Affinerie in Hamburg was the first modern electroplating plant starting its production in 1876.[59] The German scientist Gottfried Osann invented powder metallurgy in 1830 while determining the metal's atomic mass; around then it was discovered that the amount and type of alloying element (e.g., tin) to copper would affect bell tones. Flash smelting was developed by Outokumpu in Finland and first applied at Harjavalta in 1949Sony VAIO VPCF11AFJ battery; the energy-efficient process accounts for 50% of the world’s primary copper production.[60]

The Intergovernmental Council of Copper Exporting Countries, formed in 1967 with Chile, Peru, Zaire and Zambia, played a similar role for copper as OPEC does for oil. It never achieved the same influence, particularly because the second-largest producer, the United States, was never a member; it was dissolved in 1988Sony VAIO VPCF118FJ battery.[61]

Applications

Assorted copper fittings

The major applications of copper are in electrical wires (60%), roofing and plumbing (20%) and industrial machinery (15%). Copper is mostly used as a metal, but when a higher hardness is required it is combined with other elements to make an alloy (5% of total use) such as brass and bronze.[16] A small part of copper supply is used in production of compounds for nutritional supplements and fungicides in agriculture. Sony VAIO VPCF117FJ battery Machining of copper is possible, although it is usually necessary to use an alloy for intricate parts to get good machinability characteristics.

[edit]Electronics and related devices

Copper electrical busbars distributing power to a large building

The electrical properties of copper are exploited in copper wires and devices such as electromagnets. Integrated circuits and printed circuit boards increasingly feature copper in place of aluminium because of its superior electrical conductivity (see Copper interconnect for main article); heat sinks and heat exchangers use copper as a result of its superior heat dissipation capacity to aluminiumSony VAIO VGN-CS33H battery. Vacuum tubes, cathode ray tubes, and the magnetrons in microwave ovens use copper, as do wave guides for microwave radiation.[63]

[edit]Electric motors

Main article: Copper in energy efficient motors

Copper’s greater conductivity versus other metallic materials enhances the electrical energy efficiency of motors.[64] This is important because motors and motor-driven systems account for 43%-46% of all global electricity consumption and 69% of all electricity used by industry.[65] Increasing the mass and cross section of copper in a coil increases the electrical energy efficiency of the motorSony VAIO VGN-CS33H/Z battery. Copper motor rotors, a new technology designed for motor applications where energy savings are prime design objectives,[66][67] are enabling general-purpose induction motors to meet and exceed National Electrical Manufacturers Association (NEMA) premium efficiency standards.[68]

[edit]Architecture and industry

Copper roof on the Minneapolis City Hall, coated with patina

Old copper utensils in a Jerusalem restaurant

Because of the waterproof nature of copper, it has been used as the roofing material of many buildings since ancient timesSony VAIO VGN-CS33H/B battery. The green color on these buildings is due to a long-term chemical reaction: copper is first oxidized to copper(II) oxide, then to cuprous and cupric sulfide and finally to copper(II) carbonate, also called verdigris, which is highly corrosion-resistant.[69] The copper used in this application is phosphorus deoxidized copper (Cu-DHP).[70] Lightning rods use copper as a means to divert electric current throughout the ground instead of destroying the main structureSony VAIO VGN-CS31Z/Q battery.[71] Copper has excellent brazing and soldering properties and can be welded; the best results are obtained with gas metal arc welding.[72]

[edit]Copper in alloys

See also: List of copper alloys

Numerous copper alloys exist, many with important uses. Brass is an alloy of copper and zinc and bronze usually refers to copper-tin alloys, but can refer to any alloy of copper such as aluminium bronze. Copper is one of the most important constituents of carat silver and gold alloys and carat solders used in the jewelry industry, modifying the color, hardness and melting point of the resulting alloysSony VAIO VGN-CS31S/W battery.[73]

The alloy of copper and nickel, called cupronickel, is used in low-denomination statuary coins, often for the outer cladding. The US 5-cent coin called nickel consists of 75% copper and 25% nickel and has a homogeneous composition. The 90% copper/10% nickel alloy is remarkable by its resistance to corrosion and is used in various parts being exposed to seawaterSony VAIO VGN-CS31S/V battery. Alloys of copper with aluminium (about 7%) have a pleasant golden color and are used in decorations.[16] Copper alloys with tin are part of lead-free solders.[74]

[edit]Antibiofouling applications

Main articles: Copper alloys in aquaculture and Copper sheathing

Copper has long been used as a biostatic surface to line parts of ships to protect against barnacles and mussels. It was originally used pure, but has since been superseded by Muntz metal. Bacteria will not grow on a copper surface because it is biostatic. Similarly, as discussed in copper alloys in aquacultureSony VAIO VGN-CS31S/T battery, copper alloys have become important netting materials in the aquaculture industry for the fact that they are antimicrobial and prevent biofouling even in extreme conditions[75] and have strong structural and corrosion-resistant[76] properties in marine environments.

[edit]Other uses

Copper compounds in liquid form are used as a wood preservative, particularly in treating original portion of structures during restoration of damage due to dry rot. Together with zincSony VAIO VGN-CS31S/R battery, copper wires may be placed over non-conductive roofing materials to discourage the growth of moss. Textile fibers use copper to create antimicrobial protective fabrics,[77] as do ceramic glazes, stained glass and musical instruments. Electroplating commonly uses copper as a base for other metals such as nickel.

Copper is one of three metals, along with lead and silver, used in a museum materials testing procedure called the Oddy testSony VAIO VGN-CS31S/P battery. In this procedure, copper is used to detect chlorides, oxides, and sulfur compounds.

Copper is also commonly found in jewelry, and folklore states that copper bracelets relieve arthritis symptoms, though this is not proven.[78]

[edit]Biological role

Main article: Copper in health

Rich sources of copper include oysters, beef and lamb liver, Brazil nuts, blackstrap molasses, cocoa, and black pepper. Good sources include lobster, nuts and sunflower seeds, green olives, avocados, and wheat branSony VAIO VGN-CS28 battery.

Copper proteins have diverse roles in biological electron transport and oxygen transportation, processes that exploit the easy interconversion of Cu(I) and Cu(II).[79] The biological role for copper commenced with the appearance of oxygen in earth's atmosphere.[80] The protein hemocyanin is the oxygen carrier in most mollusks and some arthropods such as the horseshoe crab (Limulus polyphemus) Sony VAIO VGN-CS28/Q battery.[81] Because hemocyanin is blue, these organisms have blue blood, not the red blood found in organisms that rely on hemoglobin for this purpose. Structurally related to hemocyanin are the laccases and tyrosinases. Instead of reversibly binding oxygen, these proteins hydroxylate substrates, illustrated by their role in the formation of lacquersSony VAIO VGN-CS27 battery.[79]

Copper is also a component of other proteins associated with the processing of oxygen. In cytochrome c oxidase, which is required for aerobic respiration, copper and iron cooperate in the reduction of oxygen. Copper is also found in many superoxide dismutases, proteins that detoxify superoxides, by converting it (by disproportionation) to oxygen and hydrogen peroxideSony VAIO VGN-CS27/W battery:

2 HO2 → H2O2 + O2

Several copper proteins, such as the "blue copper proteins", do not interact directly with substrates, hence they are not enzymes. These proteins relay electrons by the process called electron transfer.[79]

Silicon ( /ˈsɪlɨkən/ sil-ə-kən or /ˈsɪlɨkɒn/ sil-ə-kon) is a chemical element with the symbol Si and atomic number 14. A tetravalent metalloid, it is less reactive than its chemical analog carbonSony VAIO VGN-CS27/R battery, the nonmetal directly above it in the periodic table, but more reactive than germanium, the metalloid directly below it in the table. Controversy about silicon's character dates to its discovery: silicon was first prepared and characterized in pure form in 1824, and given the name silicium (from Latin: silicis, flints), with an -ium word-ending to suggest a metalSony VAIO VGN-CS27/P battery, a name which the element retains in several non-English languages. However, its final English name, suggested in 1831, reflects the more physically similar elements carbon and boron.

Silicon is the eighth most common element in the universe by mass, but very rarely occurs as the pure free element in nature. It is most widely distributed in dusts, sands, planetoids, and planets as various forms of silicon dioxide (silica) or silicates. Over 90% of the Earth's crust is composed of silicate mineralsSony VAIO VGN-CS27/C battery, making silicon the second most abundant element in the earth's crust (about 28% by mass) after oxygen.[5]

Most silicon is used commercially without being separated, and indeed often with little processing of compounds from nature. These include direct industrial building-use of clays, silica sand and stone. Silica is used in ceramic brick. Silicate goes into Portland cement for mortar and stucco, and when combined with silica sand and gravel, to make concreteSony VAIO VGN-CS26T/W battery. Silicates are also in whiteware ceramics such as porcelain, and in traditional quartz-based soda-lime glass. More modern silicon compounds such as silicon carbide form abrasives and high-strength ceramics. Silicon is the basis of the ubiquitous synthetic silicon-based polymers called silicones.

Elemental silicon also has a large impact on the modern world economy. Although most free silicon is used in the steel refiningSony VAIO VGN-CS26T/V battery, aluminum-casting, and fine chemical industries (often to make fumed silica), the relatively small portion of very highly purified silicon that is used in semiconductor electronics (< 10%) is perhaps even more critical. Because of wide use of silicon in integrated circuits, the basis of most computers, a great deal of modern technology depends on itSony VAIO VGN-CS26T/T battery.

Silicon is an essential element in biology, although only tiny traces of it appear to be required by animals,[6] however various sea sponges need silicon in order to have structure. It is much more important to the metabolism of plants, particularly many grasses, and silicic acid (a type of silica) forms the basis of the striking array of protective shells of the microscopic diatomsSony VAIO VGN-CS26T/R battery.

Characteristics

[edit]Physical

Silicon crystallizes in a diamond cubic crystal structure

Further information: Monocrystalline silicon

Silicon is a solid at room temperature, with relatively high melting and boiling points of approximately 1,400 and 2,800 degrees Celsius respectively.[7] Interestingly, silicon has a greater density in a liquid state than a solid state. Therefore, it does not contract when it freezes like most substancesSony VAIO VGN-CS26T/Q battery, but expands, similar to how ice is less dense than water and has less mass per unit of volume than liquid water. With a relatively high thermal conductivity of 149 W·m−1·K−1, silicon conducts heat well and as a result is not often used to insulate hot objects.

In its crystalline form, pure silicon has a gray color and a metallic luster. Like germanium, silicon is rather strong, very brittle, and prone to chipping. Silicon, like carbon and germanium, crystallizes in a diamond cubic crystal structure, with a lattice spacing of approximately 0.5430710 nm (5.430710 Å). Sony VAIO VGN-CS26T/P battery

The outer electron orbital of silicon, like that of carbon, has four valence electrons. The 1s,2s,2p and 3s subshells are completely filled while the 3p subshell contains two electrons out of a possible six.

Silicon is a semiconductor. It has a negative temperature coefficient of resistance, since the number of free charge carriers increases with temperatureSony VAIO VGN-CS26T/C battery. The electrical resistance of single crystal silicon significantly changes under the application of mechanical stress due to the piezoresistive effect.[9]

[edit]Chemical

Silicon powder

Silicon is a metalloid, readily either donating or sharing its four outer electrons, allowing for many forms of chemical bonding. Even though it is relatively inert like carbon, silicon still reacts with halogens and dilute alkalis, but most acids (except for some hyper-reactive combinations of nitric acid and hydrofluoric acid) have no known effect on itSony VAIO VGN-CS25H battery. However, having four bonding electrons gives it, like carbon, many opportunities to combine with other elements or compounds under the right circumstances.

[edit]Isotopes

Main article: isotopes of silicon

Naturally occurring silicon is composed of three stable isotopes, silicon-28, silicon-29, and silicon-30, with silicon-28 being the most abundant (92% natural abundance).[10] Out of these, only silicon-29 is of use in NMR and EPR spectroscopy.[11] Twenty radioisotopes have been characterized, with the most stable being silicon-32 with a half-life of 170 yearsSony VAIO VGN-CS25H/W battery, and silicon-31 with a half-life of 157.3 minutes.[10] All of the remaining radioactive isotopes have half-lives that are less than seven seconds, and the majority of these have half-lives that are less than one tenth of a second.[10] Silicon does not have any known nuclear isomers.[10]

The isotopes of silicon range in mass number from 22 to 44.[10] The most common decay mode of six isotopes with mass numbers lower than the most abundant stable isotope, silicon-28Sony VAIO VGN-CS25H/R battery, is β+

, primarily forming aluminium isotopes (13 protons) as decay products.[10] The most common decay mode(s) for 16 isotopes with mass numbers higher than silicon-28 is β−

, primarily forming phosphorus isotopes (15 protons) as decay products.[10]

[edit]Occurrence

Quartz crystal cluster from Tibet. The naturally-occurring mineral is a network solid with the formula SiO2Sony VAIO VGN-CS25H/Q battery.

See also: Silicate minerals

Measured by mass, silicon makes up 27.7% of the Earth's crust and is the second most abundant element in the crust, with only oxygen having a greater abundance.[12] Silicon is usually found in the form of complex silicate minerals, and less often as silicon dioxide (silica, a major component of common sand). Pure silicon crystals are very rarely found in natureSony VAIO VGN-CS25H/P battery.

The silicate minerals—various minerals containing silicon, oxygen and reactive metals—account for 90% of the mass of the Earth's crust. This is due to the fact that at the high temperatures characteristic of the formation of the inner solar system, silicon and oxygen have a great affinity for each other, forming networks of silicon and oxygen in chemical compounds of very low volatilitySony VAIO VGN-CS25H/C battery. Since oxygen and silicon were the most common non-gaseous and non-metallic elements in the debris from supernova dust which formed the protoplanetary disk in the formation and evolution of the Solar System, they formed many complex silicates which accreted into larger rocky planetesimals that formed the terrestrial planets. Here, the reduced silicate mineral matrix entrapped the metals reactive enough to be oxidized (aluminum, calcium, sodium, potassium and magnesium) Sony VAIO VGN-CS23T/W battery. After loss of volatile gases, as well as carbon and sulfur via reaction with hydrogen, this silicate mixture of elements formed most of the Earth's crust. These silicates were of relatively low density with respect to iron, nickel, and other metals non-reactive to oxygen and thus a residuum of uncombined iron and nickel sank to the planet's core, leaving a thick mantle consisting mostly of magnesium and iron silicates aboveSony VAIO VGN-CS23T/Q battery.

Examples of silicate minerals in the crust include those in the pyroxene, amphibole, mica, and feldspar groups. These minerals occur in clay and various types of rock such as granite and sandstone.

Silica occurs in minerals consisting of very pure silicon dioxide in different crystalline forms, quartz, agate amethyst, rock crystal, chalcedony, flint, jasper, and opal. The crystals have the empirical formula of silicon dioxideSony VAIO VGN-CS23H battery, but do not consist of separate silicon dioxide molecules in the manner of solid carbon dioxide. Rather, silica is structurally a network-solid consisting of silicon and oxygen in three-dimensional crystals, like diamond. Less pure silica forms the natural glass obsidian. Biogenic silica occurs in the structure of diatoms, radiolaria and siliceous spongesSony VAIO VGN-CS23H/S battery.

Silicon is also a principal component of many meteorites, and is a component of tektites, a silicate mineral of possibly lunar origin, or (if Earth-derived) which has been subjected to unusual temperatures and pressures, possibly from meteorite strike.

[edit]Production

Ferrosilicon alloy

Ferrosilicon, an iron-silicon alloy that contains varying ratios of elemental silicon and iron, accounts for about 80% of the world's production of elemental silicon, with China, the leading supplier of elemental siliconSony VAIO VGN-CS23H/B battery, providing 4.6 million tonnes (or 2/3 of the world output) of silicon, most of which is in the form of ferrosilicon. It is followed by Russia (610,000 t), Norway (330,000 t), Brazil (240,000 t) and the United States (170,000 t).[13] Ferrosilicon is primarily used by the steel industry (see below).

Aluminum-silicon alloys are heavily used in the aluminum alloy casting industry, where silicon is the single most important additive to aluminum to improve its casting propertiesSony VAIO VGN-CS23G battery. Since cast aluminum is widely used in the automobile industry, this use of silicon is thus the single largest industrial use of "metallurgical grade" pure silicon (as this purified silicon is added to pure aluminum, whereas ferrosilicon is never purified before being added to steel).[14]

[edit]Metallurgical grade

Elemental silicon not alloyed with significant quantities of other elements, and usually > 95% is often referred to loosely as silicon metalSony VAIO VGN-CS23G/W battery. It makes up about 20% of the world total elemental silicon production, with less than 1 to 2% of total elemental silicon (5–10% of metallurgical grade silicon) ever purified to higher grades for use in electronics. Metallurgical grade silicon is commercially prepared by the reaction of high-purity silica with wood, charcoal, and coal in an electric arc furnace using carbon electrodesSony VAIO VGN-CS23G/Q battery. At temperatures over 1,900 °C (3,450 °F), the carbon in the aforementioned materials and the silicon undergo the chemical reaction SiO2 + 2 C → Si + 2 CO. Liquid silicon collects in the bottom of the furnace, which is then drained and cooled. The silicon produced via this process is called metallurgical grade silicon and is at least 98% pure. Using this method, silicon carbide (SiC) may also form from an excess of carbon in one or both of the following waysSony VAIO VGN-CS23G/P battery: SiO2 + C → SiO + CO or SiO + 2 C → SiC + CO. However, provided the concentration of SiO2 is kept high, the silicon carbide can be eliminated by the chemical reaction 2 SiC + SiO2 → 3 Si + 2 CO.

As noted above, metallurgical grade silicon "metal" has its primary use in the aluminum casting industry to make aluminum-silicon alloy parts. The remainder (about 45%) is used by the chemical industry, where it is primarily employed to make fumed silicaSony VAIO VGN-CS21Z/Q battery.[15]

As of September 2008, metallurgical grade silicon costs about US$1.45 per pound ($3.20/kg),[16] up from $0.77 per pound ($1.70/kg) in 2005.[17]

[edit]Electronic grade

Monocrystalline silicon ingot grown by the Czochralski process

The use of silicon in semiconductor devices demands a much greater purity than afforded by metallurgical grade silicon. Very pure silicon (>99.9%) can be extracted directly from solid silica or other silicon compounds by molten salt electrolysis. Sony VAIO VGN-CS21S/W battery This method, known as early as 1854[20] (see also FFC Cambridge process), has the potential to directly produce solar-grade silicon without any carbon dioxide emission at much lower energy consumption.

Solar grade silicon cannot be used for semiconductors, where purity must be extreme to properly control the process. Bulk silicon wafers used at the beginning of the integrated circuit making process must first be refined to "nine nines" purity (99.9999999%)Sony VAIO VGN-CS21S/V battery, a process which requires repeated applications of refining technology.

The majority of silicon crystals grown for device production are produced by the Czochralski process, (CZ-Si) since it is the cheapest method available and it is capable of producing large size crystals. However, single crystals grown by the Czochralski process contain impurities because the crucible containing the melt often dissolvesSony VAIO VGN-CS21S/T battery. Historically, a number of methods have been used to produce ultra-high-purity silicon.

Early silicon purification techniques were based on the fact that if silicon is melted and re-solidified, the last parts of the mass to solidify contain most of the impurities. The earliest method of silicon purification, first described in 1919 and used on a limited basis to make radar components during World War IISony VAIO VGN-CS21S/R battery, involved crushing metallurgical grade silicon and then partially dissolving the silicon powder in an acid. When crushed, the silicon cracked so that the weaker impurity-rich regions were on the outside of the resulting grains of silicon. As a result, the impurity-rich silicon was the first to be dissolved when treated with acid, leaving behind a more pure productSony VAIO VGN-CS21S/P battery.

In zone melting, also called zone refining, the first silicon purification method to be widely used industrially, rods of metallurgical grade silicon are heated to melt at one end. Then, the heater is slowly moved down the length of the rod, keeping a small length of the rod molten as the silicon cools and re-solidifies behind itSony VAIO VGN-CS215J/R battery. Since most impurities tend to remain in the molten region rather than re-solidify, when the process is complete, most of the impurities in the rod will have been moved into the end that was the last to be melted. This end is then cut off and discarded, and the process repeated if a still higher purity is desired. Sony VAIO VGN-CS215J/Q battery

A polycrystalline silicon rod made by the Siemens process

At one time, DuPont produced ultra-pure silicon by reacting silicon tetrachloride with high-purity zinc vapors at 950 °C, producing silicon by SiCl4 + 2 Zn → Si + 2 ZnCl2. However, this technique was plagued with practical problems (such as the zinc chloride byproduct solidifying and clogging lines) and was eventually abandoned in favor of the Siemens processSony VAIO VGN-CS19/W battery. In the Siemens process, high-purity silicon rods are exposed to trichlorosilane at 1150 °C. The trichlorosilane gas decomposes and deposits additional silicon onto the rods, enlarging them because 2 HSiCl3 → Si + 2 HCl + SiCl4. Silicon produced from this and similar processes is called polycrystalline silicon. Polycrystalline silicon typically has impurity levels of less than one part per billion. Sony VAIO VGN-CS19/R battery

In 2006 REC announced construction of a plant based on fluidized bed (FB) technology using silane: 3 SiCl4 + Si + 2 H2 → 4 HSiCl3, 4 HSiCl3 → 3 SiCl4 + SiH4, SiH4 → Si + 2 H2.[25] The advantage of fluid bed technology is that processes can be run continuously, yielding higher yields than Siemens Process, which is a batch processSony VAIO VGN-CS19/Q battery.

Today, silicon is purified by converting it to a silicon compound that can be more easily purified by distillation than in its original state, and then converting that silicon compound back into pure silicon. Trichlorosilane is the silicon compound most commonly used as the intermediate, although silicon tetrachloride and silane are also used. When these gases are blown over silicon at high temperature, they decompose to high-purity siliconSony VAIO VGN-CS19/P battery.

In addition, there is the Schumacher process, which utilizes tribromosilane in place of trichlorosilane and fluid bed technology. It requires lower deposition temperatures, lower capital costs to build facilities and operate, no hazardous polymers nor explosive material, and produces no amorphous silicon dust waste, all of which are drawbacks of the Siemens processSony VAIO VGN-CS17H/W battery.[26] However, there are yet to be any major factories built using this process.

Compounds

PDMS – a silicone compound

Silicon forms binary compounds called silicides with many metallic elements whose properties range from reactive compounds, e.g. magnesium silicide, Mg2Si through high melting refractory compounds such as molybdenum disilicide, MoSi2.[27]

Silicon carbide, SiC (carborundum) is a hard, high melting solid and a well known abrasive. It may also be sintered into a type of high-strength ceramic used in armorSony VAIO VGN-CS17H/Q battery.

Silane, SiH4, is a pyrophoric gas with a similar tetrahedral structure to methane, CH4. When pure, it does not react with pure water or dilute acids; however, even small amounts of alkali impurities from the laboratory glass can result in a rapid hydrolysis.[28] There is a range of catenated silicon hydrides that form a homologous series of compounds, SinH2n+2 where n = 2–8 (analogous to the alkanes) Sony VAIO VGN-CS16T/W battery. These are all readily hydrolyzed and are thermally unstable, particularly the heavier members.[29][30]

Disilenes contain a silicon-silicon double bond (analogous to the alkenes) and are generally highly reactive requiring large substituent groups to stabilize them.[31] A disilyne with a silicon-silicon triple bond was first isolated in 2004; although as the compound is non-linear, the bonding is dissimilar to that in alkynesSony VAIO VGN-CS16T/T battery.[32]

Tetrahalides, SiX4, are formed with all the halogens.[33] Silicon tetrachloride, for example, reacts with water, unlike its carbon analogue, carbon tetrachloride.[34] Silicon dihalides are formed by the high temperature reaction of tetrahalides and silicon; with a structure analogous to a carbene they are reactive compounds. Silicon difluoride condenses to form a polymeric compound, (SiF2)n. Sony VAIO VGN-CS16T/R battery

Silicon dioxide is a high melting solid with a number of crystal forms; the most familiar of which is the mineral quartz. In quartz each silicon atom is surrounded by four oxygen atoms that bridge to other silicon atoms to form a three dimensional lattice.[34] Silica is soluble in water at high temperatures forming a range of compounds called monosilicic acid, Si(OH)4. Sony VAIO VGN-CS16T/Q battery

Under the right conditions monosilicic acid readily polymerizes to form more complex silicic acids, ranging from the simplest condensate, disilicic acid (H6Si2O7) to linear, ribbon, layer and lattice structures which form the basis of the many silicate minerals and are called polysilicic acids {Six(OH)4–2x}n. Sony VAIO VGN-CS16T/P battery

With oxides of other elements the high temperature reaction of silicon dioxide can give a wide range of glasses with various properties.[36] Examples include soda lime glass, borosilicate glass and lead crystal glass.

Silicon sulfide, SiS2 is a polymeric solid (unlike its carbon analogue the liquid CS2).[37]

Silicon forms a nitride, Si3N4 which is a ceramic.[38] Silatranes, a group of tricyclic compounds containing five-coordinate silicon, may have physiological properties. Sony VAIO VGN-CS13T/W battery

Many transition metal complexes containing a metal-silicon bond are now known, which include complexes containing SiHnX3−n ligands, SiX3 ligands, and Si(OR)3 ligands.[39]

Silicones are large group of polymeric compounds with an (Si-O-Si) backbone. An example is the silicone oil PDMS (polydimethylsiloxane). These polymers can be crosslinked to produce resins and elastomers. Sony VAIO VGN-CS13H/W battery

Many organosilicon compounds are known which contain a silicon-carbon single bond. Many of these are based on a central tetrahedral silicon atom, and some are optically active when central chirality exists. Long chain polymers containing a silicon backbone are known, such as polydimethysilylene (SiMe2)n.[41] Polycarbosilane, [(SiMe2)2CH2]n with a backbone containing a repeating -Si-Si-C unit, is a precursor in the production of silicon carbide fibers. Sony VAIO VGN-CS13H/R battery

[edit]History

Attention was first drawn to quartz as the possible oxide of a fundamental chemical element by Antoine Lavoisier, in 1787. In 1811, Gay-Lussac and Thénard are thought to have prepared impure amorphous silicon, through the heating of recently isolated potassium metal with silicon tetrafluoride, but they did not purify and characterize the productSony VAIO VGN-CS13H/Q battery, nor identify it as a new element. In 1824, Berzelius prepared amorphous silicon using approximately the same method as Gay-Lussac (potassium metal and potassium fluorosilicate), but purifying the product to a brown powder by repeatedly washing it. He named the product silicium from the Latin silex, silicis for flint, flints, and adding the "-ium" ending because he believed it was a metalSony VAIO VGN-CS13H/P battery. As a result he is usually given credit for element's discovery.[42][43] Silicon was given its present name in 1831 by Scottish chemist Thomas Thomson. He retained part of Berzelius's name but added "-on" because he believed silicon a nonmetal more similar to boron and carbon.

Silicon in its more common crystalline form was not prepared until 31 years later, by Deville.[44] By electrolyzing impure sodium-aluminum chloride containing approximately 10% silicon, he was able to obtain a slightly impure allotrope of silicon in 1854Sony VAIO VGN-CS11Z/T battery.[45] Later, more cost-effective methods have been developed to isolate silicon in several allotrope forms, the most recent being silicene.

Because silicon is an important element in semiconductors and high-technology devices, many places in the world bear its name. For example, Silicon Valley in California, since it is the base for a number of technology-related industriesSony VAIO VGN-CS11Z/R battery, bears the name silicon. Other geographic locations with connections to the industry have since been named after silicon as well. Examples include Silicon Forest in Oregon, Silicon Hills in Austin, Texas, Silicon Saxony in Germany, Silicon Valley in India, Silicon Border in Mexicali, Mexico, Silicon Fen in Cambridge, England, and Silicon Gorge in Bristol, EnglandSony VAIO VGN-CS11S/W battery.

Applications

Compounds

Most silicon is used industrially without being separated into the element, and indeed often with comparatively little processing from natural occurrence. Over 90% of the Earth's crust is composed of silicate minerals. Many of these have direct commercial uses, such as clays, silica sand and most kinds of building stone. Thus, the vast majority of uses for silicon are as structural compoundsSony VAIO VGN-CS11S/Q battery, either as the silicate minerals or silica (crude silicon dioxide). For example, silica is an important part of ceramic brick. Silicates are used in making Portland cement which is used in building mortar and stucco, but more importantly combined with silica sand, and gravel (usually containing silicate minerals like granite), to make the concrete that is the basis of most of the very largest industrial building projects of the modern world. Sony VAIO VGN-CS11S/P battery

Silicate minerals are also in whiteware ceramics, an important class of products usually containing various types of fired clay (natural aluminum silicate). An example is porcelain which is based on silicate mineral kaolinite. Ceramics include art objects, and domestic, industrial and building products. Traditional quartz-based soda-lime glass also functions in many of the same roles(Sony VAIO VGN-AW11M/H battery).

More modern silicon compounds also function as high-technology abrasives and new high-strength ceramics based upon (silicon carbide), and in superalloys.

Alternating silicon-oxygen chains with hydrogen attached to the remaining silicon bonds form the ubiquitous silicon-based polymeric materials known as silicones. These compounds containing silicon-oxygen and occasionally silicon-carbon bonds have the capability to act as bonding intermediates between glass and organic compounds(Sony VAIO VGN-AW11S/B battery), and to form polymers with useful properties such as impermeability to water, flexibility and resistance to chemical attack. Silicones are often used in waterproofing treatments, molding compounds, mold-release agents, mechanical seals, high temperature greases and waxes, and caulking compounds. Silicone is also sometimes used in breast implants, contact lenses, explosives and pyrotechnics(Sony VAIO VGN-AW11Z/B battery).[47] Silly Putty was originally made by adding boric acid to silicone oil.[48]

[edit]Alloys

Elemental silicon is added to molten cast iron as ferrosilicon or silicocalcium alloys to improve performance in casting thin sections, and to prevent the formation of cementite where exposed to outside air. The presence of elemental silicon in molten iron acts as a sink for oxygen, so that the steel carbon content, which must be kept within narrow limits for each type of steel(Sony VAIO VGN-AW170C battery), can be more closely controlled. Ferrosilicon production and use is a monitor of the steel industry, and although this form of elemental silicon is impure, it accounts for 80% of the world's use of free silicon.

The properties of silicon itself can be used to modify alloys. Silicon's importance in aluminum casting is that a significantly high amount (12%) of silicon in aluminum forms a eutectic mixture which solidifies with very little thermal contraction(Sony VAIO VGN-AW19/Q battery). This greatly reduces tearing and cracks formed from stress as casting alloys cool to solidity. Silicon also significantly improves the hardness and thus wear-resistance of aluminum.[14] Silicon is an important constituent of electrical steel, modifying its resistivity and ferromagnetic properties.

Metallurgical grade silicon is silicon of 95–99% purity. About 55% of the world consumption of metallurgical purity silicon goes for production of aluminum-silicon alloys for aluminum part casts(Sony VAIO VGN-AW19 battery), mainly for use in the automotive industry. The reason for the high silicon use in these alloys is noted above.[15] Much of the rest of metallurgical-grade silicon is used by the chemical industry for production of the important industrial product fumed silica. The remainder is used in production of other fine chemicals such as silanes and some types of silicones(Sony VAIO VGN-AW21M/H battery).

[edit]Electronics

Main article: Semiconductor device fabrication

Silicon wafer with mirror finish

Since most elemental silicon produced remains as ferrosilicon alloy, only a relatively small amount (20%) of the elemental silicon produced is refined to metallurgical grade purity (a total of 1.3–1.5 million metric tons/year). The fraction of silicon metal which is further refined to semiconductor purity is estimated at only 15% of the world production of metallurgical grade silicon. (Sony VAIO VGN-AW21S/B battery) However, the economic importance of this small very high-purity fraction (especially the ~ 5% which is processed to monocrystalline silicon for use in integrated circuits) is disproportionately large.

Pure monocrystalline silicon is used to produce silicon wafers used in the semiconductor industry, in electronics and in some high-cost and high-efficiency photovoltaic applications. In terms of charge conduction, pure silicon is an intrinsic semiconductor which means that unlike metals it conducts electron holes and electrons which may be released from atoms within the crystal by heat(Sony VAIO VGN-AW21VY/Q battery), and thus increase silicon's electrical conductance with higher temperatures. Pure silicon has too low a conductance to be used as a circuit element in electronics without being doped with small concentrations of certain other elements. This process greatly increases its conductivity and adjusts its electrical response by controlling the number and charge (positive or negative) (Sony VAIO VGN-AW21XY/Q battery) of activated carriers. Such control is necessary for transistors, solar cells, semiconductor detectors and other semiconductor devices, which are used in the computer industry and other technical applications. For example, in silicon photonics, silicon can be used as a continuous wave Raman laser medium to produce coherent light, though it is ineffective as an everyday light source(Sony VAIO VGN-AW21Z/B battery).

In common integrated circuits, a wafer of monocrystalline silicon serves as a mechanical support for the circuits, which are created by doping, and insulated from each other by thin layers of silicon oxide, an insulator which is easily produced by exposing the element to oxygen under the proper conditions. Silicon has become the most popular material to build both high power semiconductors and integrated circuits(Sony VAIO VGN-AW230J/H battery), because of all the elements, silicon is the semiconductor which can withstand the highest powers and temperatures without becoming dysfunctional due to avalanche breakdown, a process in which an electron avalanche is created by a chain reaction process where heat produces free electrons and holes, which in turn produce more current which produces more heat(Sony VAIO VGN-AW235J/B battery). In addition, the insulating oxide of silicon is not soluble in water, which gives it an advantage over germanium (an element with similar properties which can also be used in semiconductor devices) in certain type of fabrication techniques.[49]

Monocrystalline silicon is expensive to produce, and is usually only justified in production of integrated circuits, where tiny crystal imperfections can interfere with tiny circuit paths. For other uses, other types of pure silicon which do not exist as single crystals may be employed(Sony VAIO VGN-AW270Y/Q battery). These include hydrogenated amorphous silicon and upgraded metallurgical-grade silicon (UMG-Si) which are used in the production of low-cost, large-area electronics in applications such as liquid crystal displays, and of large-area, low-cost, thin-film solar cells. Such semiconductor grades of silicon which are either slightly less pure than those used in integrated circuits, or which are produced in polycrystalline rather than monocrystalline form(Sony VAIO VGN-AW31M/H battery), make up roughly similar amount of silicon as are produced for the monocrystalline silicon semiconductor industry, or 75,000 to 150,000 metric tons per year. However, production of such materials is growing more quickly than silicon for the integrated circuit market. By 2013 polycrystalline silicon production, used mostly in solar cells, is projected to reach 200,000 metric tons per year(Sony VAIO VGN-AW31S/B battery), while monocrystalline semiconductor silicon production (used in computer microchips) remains below 50,000 tons/year.[15]

[edit]Biological role

Silica skeletons of radiolaria in false color.

Although silicon is readily available in the form of silicates, very few organisms have a use for it. Diatoms, radiolaria and siliceous sponges use biogenic silica as a structural material to construct skeletons. In more advanced plants, the silica phytoliths (opal phytoliths) are rigid microscopic bodies occurring in the cell; some plants, for example rice(Sony VAIO VGN-AW41MF battery), need silicon for their growth.[50][51][52] Although silicon was proposed to be an ultra trace nutrient, its exact function in the biology of animals is still under discussion. Higher organisms are only known to use it in very limited occasions in the form of silicic acid and soluble silicates.

Silicon is currently under consideration for elevation to the status of a "plant beneficial substance by the Association of American Plant Food Control Officials (AAPFCO) (Sony VAIO VGN-AW41XH/Q battery)."[53][54] Silicon has been shown in university and field studies to improve plant cell wall strength and structural integrity,[55] improve drought and frost resistance, decrease lodging potential and boost the plant's natural pest and disease fighting systems.[56] Silicon has also been shown to improve plant vigor and physiology by improving root mass and density, and increasing above ground plant biomass and crop yields(Sony VAIO VGN-AW41XH battery).[55]

Hypothetical silicon-based lifeforms are the subject of silicon biochemistry, by analogy with carbon-based lifeforms. Silicon, being below carbon in the periodic table, is thought to have similar enough properties that would make silicon-based life possible, but much different from life as we know it(Sony VAIO VGN-AW41ZF/B battery).

 
Iron is a chemical element with the symbol Fe (from Latin: ferrum) and atomic number 26. It is a metal in the first transition series. It is the most common element (by mass) forming the planet Earth as a whole, forming much of Earth's outer and inner core. It is the fourth most common element in the Earth's crustSony VAIO VPCF135Z1E/B battery. Iron's very common presence in rocky planets like Earth is due to its abundant production as a result of fusion in high-mass stars, where the production of nickel-56 (which decays to the most common isotope of iron) is the last nuclear fusion reaction that is exothermic. This causes radioactive nickel to become the last element to be produced before collapse of a supernova leads to the explosive events that scatter this precursor radionuclide of iron abundantly into spaceSony VAIO VPCF137HG/BI battery.

Like other group 8 elements, iron exists in a wide range of oxidation states, −2 to +8, although +2 and +3 are the most common. Elemental iron occurs in meteoroids and other low oxygen environments, but is reactive to oxygen and water. Fresh iron surfaces appear lustrous silvery-gray, but oxidize in normal air to give iron oxidesSony VAIO VPCF136FG/BI battery, also known as rust. Unlike many other metals which form passivating oxide layers, iron oxides occupy more volume than iron metal, and thus iron oxides flake off and expose fresh surfaces for corrosion.

Iron metal has been used since ancient times, though lower-melting copper alloys were used first in history. Pure iron is soft (softer than aluminium), but is unobtainable by smelting. The material is significantly hardened and strengthened by impurities from the smelting processSony VAIO VPCF135FG/B battery, such as carbon. A certain proportion of carbon (between 0.2% and 2.1%) produces steel, which may be up to 1000 times harder than pure iron. Crude iron metal is produced in blast furnaces, where ore is reduced by coke to cast iron, which has a high carbon content. Further refinement with oxygen reduces the carbon content to the correct proportion to make steelSony VAIO VPCF127HG/BI battery. Steels and low carbon iron alloys with other metals (alloy steels) are by far the most common metals in industrial use, due to their great range of desirable properties.

Iron chemical compounds, which include ferrous and ferric compounds, have many uses. Iron oxide mixed with aluminium powder can be ignited to create a thermite reaction, used in welding and purifying ores. It forms binary compounds with the halogens and the chalcogens. Among its organometallic compounds is ferrocene, the first sandwich compound discoveredSony VAIO VPCF11Z1E battery.

Iron plays an important role in biology, forming complexes with molecular oxygen in hemoglobin and myoglobin; these two compounds are common oxygen transport proteins in vertebrates. Iron is also the metal used at the active site of many important redox enzymes dealing with cellular respiration and oxidation and reduction in plants and animalsSony VAIO VPCF11S1E battery.

Characteristics

Mechanical properties

The mechanical properties of iron and its alloys can be evaluated using a variety of tests, including the Brinell test, Rockwell test and the Vickers hardness test. The data on iron is so consistent that it is often used to calibrate measurements or to compare tests.[5][6] However, the mechanical properties of iron are significantly affected by the sample's puritySony VAIO VPCF11M1E/H battery: pure research-purpose single crystals of iron are actually softer than aluminium,[4] and the purest industrially produced iron (99.99%) has a hardness of 20–30 Brinell.[7] An increase in the carbon content of the iron will initially cause a significant corresponding increase in the iron's hardness and tensile strength. Maximum hardness of 65 Rc is achieved with a 0.6% carbon content, although this produces a metal with a low tensile strength. Sony VAIO VPCF11M1E battery

[edit]Phase diagram and allotropes

Main article: Allotropes of iron

Iron represents an example of allotropy in a metal. There are at least four allotropic forms of iron, known as α, γ, δ, and ε; at very high pressures, some controversial experimental evidence exists for a phase β stable at very high pressures and temperatures.[9]

Low-pressure phase diagram of pure iron

As molten iron cools down it crystallizes at 1538 °C into its δ allotrope, which has a body-centered cubic (bcc) crystal structureSony VAIO VPCF11JFX/B battery. As it cools further its crystal structure changes to face-centered cubic (fcc) at 1394 °C, when it is known as γ-iron, or austenite. At 912 °C the crystal structure again becomes bcc as α-iron, or ferrite, is formed, and at 770 °C (the Curie point, Tc) iron becomes magnetic. As the iron passes through the Curie temperature there is no change in crystalline structure, but there is a change in "domain structure"Sony VAIO VPCF119FJ battery, where each domain contains iron atoms with a particular electronic spin. In unmagnetized iron, all the electronic spins of the atoms within one domain are in the same direction; the neighboring domains point in various directions and thus cancel out. In magnetized iron, the electronic spins of all the domains are aligned, so that the magnetic effects of neighboring domains reinforce each otherSony VAIO VPCF119FC/BI battery. Although each domain contains billions of atoms, they are very small, about 10 micrometres across.[10] At pressures above approximately 10 GPa and temperatures of a few hundred kelvin or less, α-iron changes into a hexagonal close-packed (hcp) structure, which is also known as ε-iron; the higher-temperature γ-phase also changes into ε-iron, but does so at higher pressure. The β-phase, if it exists, would appear at pressures of at least 50 GPa and temperatures of at least 1500 KSony VAIO VPCF119FC battery; it has been thought to have an orthorhombic or a double hcp structure.[9]

Iron is of greatest importance when mixed with certain other metals and with carbon to form steels. There are many types of steels, all with different properties, and an understanding of the properties of the allotropes of iron is key to the manufacture of good quality steels.

α-iron, also known as ferrite, is the most stable form of iron at normal temperaturesSony VAIO VPCF117HG/BI battery. It is a fairly soft metal that can dissolve only a small concentration of carbon (no more than 0.021% by mass at 910 °C).[11]

Above 912 °C and up to 1400 °C α-iron undergoes a phase transition from bcc to the fcc configuration of γ-iron, also called austenite. This is similarly soft and metallic but can dissolve considerably more carbon (as much as 2.04% by mass at 1146 °C). This form of iron is used in the type of stainless steel used for making cutlery, and hospital and food-service equipmentSony VAIO VPCF116FG/BI battery.[10]

The high-pressure phases of iron are important as endmember models for the solid parts of planetary cores. The inner core of the Earth is generally assumed to consist essentially of an iron-nickel alloy with ε (or β) structure.

The melting point of iron is experimentally well constrained for pressures up to approximately 50 GPa. For higher pressures, different studies placed the γ-ε-liquid triple point at pressures differing by tens of gigapascals and yielded differences of more than 1000 K for the melting pointSony VAIO VPCF115FG/B battery. Generally speaking, molecular dynamics computer simulations of iron melting and shock wave experiments suggest higher melting points and a much steeper slope of the melting curve than static experiments carried out in diamond anvil cells.[12]

[edit]Isotopes

Main article: Isotopes of iron

Naturally occurring iron consists of four stable isotopes: 5.845% of 54Fe, 91.754% of 56Fe, 2.119% of 57Fe and 0.282% of 58Fe. Of these stable isotopes, only 57Fe has a nuclear spin (−1/2). The nuclide 54Fe is predicted to undergo double beta decaySony VAIO VPCF21ZHJ battery, but this process had never been observed experimentally for these nuclei, and only the lower limit on the half-life was established: t1/2>3.1×1022 years.

60Fe is an extinct radionuclide of long half-life (2.6 million years).[13] It is not found on Earth, but its ultimate decay product is the stable nuclide nickel-60.

Much of the past work on measuring the isotopic composition of Fe has focused on determining 60Fe variations due to processes accompanying nucleosynthesis (i.e., meteorite studies) and ore formation. In the last decade howeverSony VAIO VPCF21Z1E/BI battery, advances in mass spectrometry technology have allowed the detection and quantification of minute, naturally occurring variations in the ratios of the stable isotopes of iron. Much of this work has been driven by the Earth and planetary science communities, although applications to biological and industrial systems are beginning to emerge. Sony VAIO VPCF21AHJ battery

The most abundant iron isotope 56Fe is of particular interest to nuclear scientists as it represents the most common endpoint of nucleosynthesis. It is often cited, falsely, as the isotope of highest binding energy, a distinction which actually belongs to nickel-62.[15] Since 56Ni is easily produced from lighter nuclei in the alpha process in nuclear reactions in supernovae (see silicon burning process), Sony VAIO VPCF21AGJ battery nickel-56 (14 alpha particles) is the endpoint of fusion chains inside extremely massive stars, since addition of another alpha particle would result in zinc-60, which requires a great deal more energy. This nickel-56, which has a half-life of about 6 days, is therefore made in quantity in these stars, but soon decays by two successive positron emissions within supernova decay products in the supernova remnant gas cloud, first to radioactive cobalt-56Sony VAIO VPCF21AFJ battery, and then stable iron-56. This last nuclide is therefore common in the universe, relative to other stable metals of approximately the same atomic weight.

In phases of the meteorites Semarkona and Chervony Kut a correlation between the concentration of 60Ni, the daughter product of 60Fe, and the abundance of the stable iron isotopes could be found which is evidence for the existence of 60Fe at the time of formation of the Solar System. Possibly the energy released by the decay of 60Fe contributedSony VAIO VPCF219FJ/BI battery, together with the energy released by decay of the radionuclide 26Al, to the remelting and differentiation of asteroids after their formation 4.6 billion years ago[citation needed]. The abundance of 60Ni present in extraterrestrial material may also provide further insight into the origin of the Solar System and its early historySony VAIO VPCF217HG/BI battery.

Nuclei of iron atoms have some of the highest binding energies per nucleon, surpassed only by the nickel isotope 62Ni. This is formed by nuclear fusion in stars. Although a further tiny energy gain could be extracted by synthesizing 62Ni, conditions in stars are unsuitable for this process to be favored. Elemental distribution on Earth greatly favors iron over nickel, and also presumably in supernova element production. Sony VAIO VPCF217HG battery

Iron-56 is the heaviest stable isotope produced by the alpha process in stellar nucleosynthesis; elements heavier than iron and nickel require a supernova for their formation. Iron is the most abundant element in the core of red giants, and is the most abundant metal in iron meteorites and in the dense metal cores of planets such as EarthSony VAIO VPCF14ZHJ battery.

Nucleosynthesis

Iron is created by extremely large, extremely hot (over 2.5 billion kelvin) stars, through a process called the silicon burning process. It is the heaviest stable element to be produced in this manner. The process starts with the second largest stable nucleus created by silicon burning: calcium. One stable nucleus of calcium fuses with one helium nucleus, creating unstable titaniumSony VAIO VPCF14AHJ battery. Before the titanium decays, it can fuse with another helium nucleus, creating unstable chromium. Before the chromium decays, it can fuse with another helium nucleus, creating unstable iron. Before the iron decays, it can fuse with another helium nucleus, creating unstable nickel-56. Any further fusion of nickel-56 consumes energy instead of producing energy, so after the production of nickel-56Sony VAIO VPCF14AGJ battery, the star does not produce the energy necessary to keep the core from collapsing. Eventually, the nickel-56 decays to unstable cobalt-56 which, in turn decays to stable iron-56. When the core of the star collapses, it creates a Supernova. Supernovas also create additional forms of stable iron via the r-process.

OccurrenceSony VAIO VPCF14AFJ battery

See also Category: Iron minerals

Planetary occurrence

Iron meteorites of similar composition of Earth's inner and outer core

Iron is the sixth most abundant element in the Universe, and the most common refractory element.[17] It is formed as the final exothermic stage of stellar nucleosynthesis, by silicon fusion in massive stars. Metallic iron is rarely found on the surface of the Earth because it tends to oxidize, but its oxides are pervasive and represent the primary oresSony VAIO VPCF149FJ/BI battery. While it makes up about 5% of the Earth's crust, both the Earth's inner and outer core are believed to consist largely of an iron-nickel alloy constituting 35% of the mass of the Earth as a whole. Iron is consequently the most abundant element on Earth, but only the fourth most abundant element in the Earth's crust.[18][19] Most of the iron in the crust is found combined with oxygen as iron oxide minerals such as hematite and magnetiteSony VAIO VPCF148FJ/B battery. Large deposits of iron are found in banded iron formations. These geological formations are a type of rock consisting of repeated thin layers of iron oxides, either magnetite (Fe3O4) or hematite (Fe2O3), alternating with bands of iron-poor shale and chert. The banded iron formations are common in the time between 3,700 million years ago and 1,800 million years agoSony VAIO VPCF13ZHJ battery

About 1 in 20 meteorites consist of the unique iron-nickel minerals taenite (35–80% iron) and kamacite (90–95% iron). Although rare, iron meteorites are the main form of natural metallic iron on the Earth's surface.[22] It was proven by Mössbauer spectroscopy that the red color of the surface of Mars is derived from an iron oxide-rich regolith. Sony VAIO VPCF13Z0E/B battery

Stocks in use in society

According to the International Resource Panel's Metal Stocks in Society report, the global per capita stock of iron in use in society is 2200 kg. Much of this is in more-developed countries (7000–14000 kg per capita) rather than less-developed countries (2000 kg per capita).

Chemistry and compounds

Iron forms compounds mainly in the +2 and +3 oxidation states. Traditionally, iron(II) compounds are called ferrous, and iron(III) compounds ferricSony VAIO VPCF13M8E/B battery. Iron also occurs in higher oxidation states, an example being the purple potassium ferrate (K2FeO4) which contains iron in its +6 oxidation state. Iron(IV) is a common intermediate in many in biochemical oxidation reactions.[24][25] Numerous organometallic compounds contain formal oxidation states of +1, 0, −1, or even −2. The oxidation states and other bonding properties are often assessed using the technique of Mössbauer spectroscopySony VAIO VPCF13AHJ battery.[26] There are also many mixed valence compounds that contain both iron(II) and iron(III) centers, such as magnetite and Prussian blue (Fe4(Fe[CN]6)3).[25] The latter is used as the traditional "blue" in blueprints.[27]

Hydrated iron(III) chloride, also known as ferric chloride

The iron compounds produced on the largest scale in industry are iron(II) sulfate (FeSO4·7H2O) and iron(III) chloride (FeCl3). The former is one of the most readily available sources of iron(II), but is less stable to aerial oxidation than Mohr's salt ((NH4)2Fe(SO4)2·6H2O) Sony VAIO VPCF13AGJ battery. Iron(II) compounds tend to be oxidized to iron(III) compounds in the air.[25]

Unlike many other metals, iron does not form amalgams with mercury. As a result, mercury is traded in standardized 76 pound flasks (34 kg) made of iron.[28]

[edit]Binary compounds

Iron reacts with oxygen in the air to form various oxide and hydroxide compounds; the most common are iron(II,III) oxide (Fe3O4), and iron(III) oxide (Fe2O3). Iron(II) oxide also exists, though it is unstable at room temperatureSony VAIO VPCF13AFJ battery. These oxides are the principal ores for the production of iron (see bloomery and blast furnace). They are also used in the production of ferrites, useful magnetic storage media in computers, and pigments. The best known sulfide is iron pyrite (FeS2), also known as fool's gold owing to its golden luster.[25]

The binary ferrous and ferric halides are well known, with the exception of ferric iodideSony VAIO VPCF138FJ/BI battery. The ferrous halides typically arise from treating iron metal with the corresponding binary halogen acid to give the corresponding hydrated salts.[25]

Fe + 2 HX → FeX2 + H2

Iron reacts with fluorine, chlorine, and bromine to give the corresponding ferric halides, ferric chloride being the most common:

2 Fe + 3 X2 → 2 FeX3 (X = F, Cl, Br)

Coordination and organometallic compounds

See also: organoiron chemistry

Prussian blue

Several cyanide complexes are known. The most famous example is Prussian blue, (Fe4(Fe[CN]6)3). Potassium ferricyanide and potassium ferrocyanide are also known; the formation of Prussian blue upon reaction with iron(II) and iron(III) respectively forms the basis of a "wet" chemical test.[25] Prussian blue is also used as an antidote for thallium and radioactive caesium poisoning. Sony VAIO VPCF138FJ/B batteryPrussian blue can be used in laundry bluing to correct the yellowish tint left by ferrous salts in water.[31]

Ferrocene

Several carbonyl compounds of iron are known. The premier iron(0) compound is iron pentacarbonyl, Fe(CO)5, which is used to produce carbonyl iron powder, a highly reactive form of metallic iron. Thermolysis of iron pentacarbonyl gives the trinuclear cluster, triiron dodecacarbonyl. Collman's reagent, disodium tetracarbonylferrateSony VAIO VPCF138FC/BI battery, is a useful reagent for organic chemistry; it contains iron in the −2 oxidation state. Cyclopentadienyliron dicarbonyl dimer contains iron in the rare +1 oxidation state.[32]

Ferrocene is an extremely stable complex. The first sandwich compound, it contains an iron(II) center with two cyclopentadienyl ligands bonded through all ten carbon atoms. This arrangement was a shocking novelty when it was first discovered, Sony VAIO VPCF135FG battery but the discovery of ferrocene has led to a new branch of organometallic chemistry. Ferrocene itself can be used as the backbone of a ligand, e.g. dppf. Ferrocene can itself be oxidized to the ferrocenium cation (Fc+); the ferrocene/ferrocenium couple is often used as a reference in electrochemistry. Sony VAIO VPCF12AHJ battery

History

Main article: History of ferrous metallurgy

Wrought iron

The symbol for Mars has been used since antiquity to represent iron.

The Delhi iron pillar is an example of the iron extraction and processing methodologies of India. The iron pillar at Delhi has withstood corrosion for the last 1600 years.

Iron objects of great age are much rarer than objects made of gold or silver due to the ease of corrosion of iron.[35] Beads made of meteoric iron in 3500 B.C. or earlier were found in Gerzah, Egypt by G. A. WainwrightSony VAIO VPCF12AGJ battery.[36] The beads contain 7.5% nickel, which is a signature of meteoric origin since iron found in the Earth's crust has very little to no nickel content. Meteoric iron was highly regarded due to its origin in the heavens and was often used to forge weapons and tools or whole specimens placed in churches.[36] Items that were likely made of iron by Egyptians date from 2500 to 3000 BCSony VAIO VPCF12AFJ battery.[35] Iron had a distinct advantage over bronze in warfare implements. It was much harder and more durable than bronze, although susceptible to rust. However, this is contested. Hittitologist Trevor Bryce argues that before advanced iron-working techniques were developed in India, cast-iron weapons used by early Mesopotamian armies had a tendency to shatter in combat, due to their high carbon content. Sony VAIO VPCF129FJ/BI battery

The first iron production started in the Middle Bronze Age but it took several centuries before iron displaced bronze. Samples of smelted iron from Asmar, Mesopotamia and Tall Chagar Bazaar in northern Syria were made sometime between 2700 and 3000 BC.[38] The Hittites appear to be the first to understand the production of iron from its ores and regard it highly in their society. Sony VAIO VPCF128FJ/B battery They began to smelt iron between 1500 and 1200 BC and the practice spread to the rest of the Near East after their empire fell in 1180 BC.[38] The subsequent period is called the Iron Age. Iron smelting, and thus the Iron Age, reached Europe two hundred years later and arrived in Zimbabwe, Africa by the 8th century.[38]

Artifacts from smelted iron occur in India from 1800 to 1200 BC,[39] and in the Levant from about 1500 BC (suggesting smelting in Anatolia or the Caucasus). Sony VAIO VPCF127FJ/W battery

The Book of Genesis, fourth chapter, verse 22 contains the first mention of iron in the Old Testament of the Bible; "Tubal-cain, an instructor of every artificer in brass and iron."[35] Other verses allude to iron mining (Job 28:2), iron used as a stylus (Job 19:24), furnace (Deuteronomy 4:20), chariots (Joshua 17:16), nails (I Chron. 22:3), saws and axes (II Sam. 12:31) Sony VAIO VPCF11ZHJ battery, and cooking utensils (Ezekiel 4:3).[42] The metal is also mentioned in the New Testament, for example in Acts chapter 12 verse 10, "[Peter passed through] the iron gate that leadeth unto the city" of Antioch.[43] The Quran referred to Iron 1400 years ago.

Iron working was introduced to Greece in the late 11th century BC.[44] The spread of ironworking in Central and Western Europe is associated with Celtic expansion. According to Pliny the Elder, iron use was common in the Roman era. Sony VAIO VPCF11AHJ battery The annual iron output of the Roman Empire is estimated at 84,750 t,[45] while the similarly populous Han China produced around 5,000 t.[46]

During the Industrial Revolution in Britain, Henry Cort began refining iron from pig iron to wrought iron (or bar iron) using innovative production systems. In 1783 he patented the puddling process for refining iron ore. It was later improved by others including Joseph HallSony VAIO VPCF11AGJ battery.

Cast iron

Cast iron was first produced in China about 550 BC,[47] but was hardly in Europe until the medieval period.[48][49] During the medieval period, means were found in Europe of producing wrought iron from cast iron (in this context known as pig iron) using finery forges. For all these processes, charcoal was required as fuelSony VAIO VPCF11AFJ battery.

Coalbrookdale by Night, 1801. Blast furnaces light the iron making town of Coalbrookdale.

Medieval blast furnaces were about 10 feet (3.0 m) tall and made of fireproof brick; forced air was usually provided by hand-operated bellows.[49] Modern blast furnaces have grown much biggerSony VAIO VPCF118FJ battery.

In 1709, Abraham Darby I established a coke-fired blast furnace to produce cast iron. The ensuing availability of inexpensive iron was one of the factors leading to the Industrial Revolution. Toward the end of the 18th century, cast iron began to replace wrought iron for certain purposes, because it was cheaper. Carbon content in iron wasn't implicated as the reason for the differences in properties of wrought iron, cast iron and steel until the 18th centurySony VAIO VPCF117FJ battery.[38]

Since iron was becoming cheaper and more plentiful, it also became a major structural material following the building of the innovative first iron bridge in 1778.

Steel

See also: Steelmaking

Steel (with smaller carbon content than pig iron but more than wrought iron) was first produced in antiquity by using a bloomery. Blacksmiths in Luristan in western Iran were making good steel by 1000 BC.[38] Then improved versionsSony VAIO VGN-CS33H battery, Wootz steel by India and Damascus steel by China were developed around 300 B.C. and 500 A.D. respectively. These methods were specialized, and so steel did not become a major commodity until the 1850s.[50]

New methods of producing it by carburizing bars of iron in the cementation process were devised in the 17th century AD. In the Industrial Revolution, new methods of producing bar iron without charcoal were devised and these were later applied to produce steelSony VAIO VGN-CS33H/Z battery. In the late 1850s, Henry Bessemer invented a new steelmaking process, involving blowing air through molten pig iron, to produce mild steel. This made steel much more economical, thereby leading to wrought iron no longer being produced.[citation needed]

Foundations of modern chemistry

Antoine Lavoisier used the reaction of water steam with metallic iron inside an incandescent iron tube to produce hydrogen in his experiments leading to the demonstration of the mass conservationSony VAIO VGN-CS33H/B battery. Anaerobic oxidation of iron at high temperature can be schematically represented by the following reactions:

Fe +    H2O → FeO + H2

2 Fe + 3 H2O → Fe2O3 + 3 H2

3 Fe + 4 H2O → Fe3O4 + 4 H2

Recent discoveries

discovery of Mössbauer effect

many enzymes use iron in the catalytic center

Nickel-56 is the natural end product of silicon burning in massive stars. However Nickel-56 decays to cobalt-56 and then to stable iron-56, ultimately making iron the most abundant heavy element produced by that nucleosynthesis.[51]

superconductivity?

magnetic effect

ferrocene

Industrial production

See also: Iron ore

The production of iron or steel is a process containing two main stages, unless the desired product is cast iron. The first stage is to produce pig iron in a blast furnace. Alternatively, it may be directly reducedSony VAIO VGN-CS31Z/Q battery. The second is to make wrought iron or steel from pig iron by a further process.

The fining process of smelting iron ore to make wrought iron from pig iron, with the right illustration displaying men working a blast furnace, from the Tiangong Kaiwu encyclopedia, published in 1637 by Song Yingxing.

How iron was extracted in the 19th century

For a few limited purposes like electromagnet cores, pure iron is produced by electrolysis of a ferrous sulfate solutionSony VAIO VGN-CS31S/W battery

Blast furnace

Main article: Blast furnace

Ninety percent of all mining of metallic ores is for the extraction of iron[citation needed]. Industrially, iron production involves iron ores, principally hematite (nominally Fe2O3) and magnetite (Fe3O4) in a carbothermic reaction (reduction with carbon) in a blast furnace at temperatures of about 2000 °C. In a blast furnace, iron oreSony VAIO VGN-CS31S/V battery, carbon in the form of coke, and a flux such as limestone (which is used to remove silicon dioxide impurities in the ore which would otherwise clog the furnace with solid material) are fed into the top of the furnace, while a massive blast of heated air, about 4 tons per ton of iron,[49] is forced into the furnace at the bottomSony VAIO VGN-CS31S/T battery.

Iron output in 2005

In the furnace, the coke reacts with oxygen in the air blast to produce carbon monoxide:

2 C + O2 → 2 CO

The carbon monoxide reduces the iron ore (in the chemical equation below, hematite) to molten iron, becoming carbon dioxide in the process:

Fe2O3 + 3 CO → 2 Fe + 3 CO2

Some iron in the high-temperature lower region of the furnace reacts directly with the coke:

2 Fe2O3 + 3 C → 4 Fe + 3 CO2Sony VAIO VGN-CS31S/R battery

The flux is present to melt impurities in the ore, principally silicon dioxide sand and other silicates. Common fluxes include limestone (principally calcium carbonate) and dolomite (calcium-magnesium carbonate). Other fluxes may be used depending on the impurities that need to be removed from the ore. In the heat of the furnace the limestone flux decomposes to calcium oxide (also known as quicklime) Sony VAIO VGN-CS31S/P battery:

CaCO3 → CaO + CO2

Then calcium oxide combines with silicon dioxide to form a liquid slag.

CaO + SiO2 → CaSiO3

The slag melts in the heat of the furnace. In the bottom of the furnace, the molten slag floats on top of the denser molten iron, and apertures in the side of the furnace are opened to run off the iron and the slag separately. The iron, once cooled, is called pig iron, while the slag can be used as a material in road construction or to improve mineral-poor soils for agricultureSony VAIO VGN-CS28 battery

This heap of iron ore pellets will be used in steel production.

In 2005, approximately 1,544 million metric tons of iron ore were produced worldwide. According to the British Geological Survey, China was the top producer of iron ore with at least one quarter world share, followed by Brazil, Australia and India.

Direct iron reduction

Since coke is becoming more regulated due to environmental concerns, alternative methods of processing iron have been developedSony VAIO VGN-CS28/Q battery. One of them is known as direct iron reduction.[49] It reduces iron ore to a powder substance called sponge iron, which is suitable for steelmaking. There are two main reactions that go on in the direct reduction process:

Natural gas is partially oxidized (with heat and a catalyst):

2 CH4 + O2 → 2 CO + 4 H2

These gases are then treated with iron ore in a furnace, producing solid sponge iron:

Fe2O3 + CO + 2 H2 → 2 Fe + CO2 + 2 H2O

Silica is removed by adding a flux, i.e. limestone, later.

Further processes

Pig iron is not pure iron, but has 4–5% carbon dissolved in it with small amounts of other impurities like sulfurSony VAIO VGN-CS27 battery, magnesium, phosphorus and manganese. As the carbon is the major impurity, the iron (pig iron) becomes brittle and hard. This form of iron, also known as cast iron, is used to cast articles in foundries such as stoves, pipes, radiators, lamp-posts and rails.

Alternatively pig iron may be made into steel (with up to about 2% carbon) or wrought iron (commercially pure iron). Various processes have been used for this, including finery forges, puddling furnaces, Bessemer convertersSony VAIO VGN-CS27/W battery, open hearth furnaces, basic oxygen furnaces, and electric arc furnaces. In all cases, the objective is to oxidize some or all of the carbon, together with other impurities. On the other hand, other metals may be added to make alloy steels.

The hardness of the steel depends upon its carbon content: the higher the percentage of carbon, the greater the hardness and the lesser the malleability. The properties of the steel can also be changed by several methodsSony VAIO VGN-CS27/R battery.

Annealing involves the heating of a piece of steel to 700–800 °C for several hours and then gradual cooling. It makes the steel softer and more workable.

Steel may be hardened by cold working. The metal is bent or hammered into its final shape at a relatively cool temperature. Cold forging is the stamping of a piece of steel into shape by a heavy press. Wrenches are commonly made by cold forgingSony VAIO VGN-CS27/P battery. Cold rolling, which involves making a thinner but harder sheet, and cold drawing, which makes a thinner but stronger wire, are two other methods of cold working. To harden the steel, it is heated to red-hot and then cooled by quenching it in the water. It becomes harder and more brittle. If it is too hardened, it is then heated to a required temperature and allowed to cool. The steel thus formed is less brittleSony VAIO VGN-CS27/C battery.

Heat treatment is another way to harden steel. The steel is heated red-hot, then cooled quickly. The iron carbide molecules are decomposed by the heat, but do not have time to reform. Since the free carbon atoms are stuck, it makes the steel much harder and stronger than before.[49]

Sometimes both toughness and hardness are desired. A process called case hardening may be usedSony VAIO VGN-CS26T/W battery. Steel is heated to about 900 °C then plunged into oil or water. Carbon from the oil can diffuse into the steel, making the surface very hard. The surface cools quickly, but the inside cools slowly, making an extremely hard surface and a durable, resistant inner layer.

Iron may be passivated by dipping it into a concentrated nitric acid solution. This forms a protective layer of oxide on the metal, protecting it from further corrosionSony VAIO VGN-CS26T/V battery.[52]

Applications

Metallurgical

Photon mass attenuation coefficient for iron.

Iron is the most widely used of all the metals, accounting for 95% of worldwide metal production.[citation needed] Its low cost and high strength make it indispensable in engineering applications such as the construction of machinery and machine tools, automobiles, the hulls of large ships, and structural components for buildings. Since pure iron is quite soft, it is most commonly used in the form of steelSony VAIO VGN-CS26T/T battery.

Commercially available iron is classified based on purity and the abundance of additives. Pig iron has 3.5–4.5% carbon[53] and contains varying amounts of contaminants such as sulfur, silicon and phosphorus. Pig iron is not a saleable product, but rather an intermediate step in the production of cast iron and steel from iron ore. Cast iron contains 2–4% carbonSony VAIO VGN-CS26T/R battery, 1–6% silicon, and small amounts of manganese. Contaminants present in pig iron that negatively affect material properties, such as sulfur and phosphorus, have been reduced to an acceptable level. It has a melting point in the range of 1420–1470 K, which is lower than either of its two main components, and makes it the first product to be melted when carbon and iron are heated togetherSony VAIO VGN-CS26T/Q battery. Its mechanical properties vary greatly, dependent upon the form carbon takes in the alloy.

"White" cast irons contain their carbon in the form of cementite, or iron carbide. This hard, brittle compound dominates the mechanical properties of white cast irons, rendering them hard, but unresistant to shock. The broken surface of a white cast iron is full of fine facets of the broken carbide, a very pale, silvery, shiny material, hence the appellationSony VAIO VGN-CS26T/P battery.

In gray iron the carbon exists free as fine flakes of graphite, and also renders the material brittle due to the stress-raising nature of the sharp edged flakes of graphite. A newer variant of gray iron, referred to as ductile iron is specially treated with trace amounts of magnesium to alter the shape of graphite to spheroids, or nodules, vastly increasing the toughness and strength of the materialSony VAIO VGN-CS26T/C battery.

Wrought iron contains less than 0.25% carbon.[53] It is a tough, malleable product, but not as fusible as pig iron. If honed to an edge, it loses it quickly. Wrought iron is characterized by the presence of fine fibers of slag entrapped in the metal. Wrought iron is more corrosion resistant than steel. It has been almost completely replaced by mild steel for traditional "wrought iron" products and blacksmithingSony VAIO VGN-CS25H battery.

Mild steel corrodes more readily than wrought iron, but is cheaper and more widely available. Carbon steel contains 2.0% carbon or less,[54] with small amounts of manganese, sulfur, phosphorus, and silicon. Alloy steels contain varying amounts of carbon as well as other metals, such as chromium, vanadium, molybdenum, nickel, tungsten, etcSony VAIO VGN-CS25H/W battery. Their alloy content raises their cost, and so they are usually only employed for specialist uses. One common alloy steel, though, is stainless steel. Recent developments in ferrous metallurgy have produced a growing range of microalloyed steels, also termed 'HSLA' or high-strength, low alloy steels, containing tiny additions to produce high strengths and often spectacular toughness at minimal costSony VAIO VGN-CS25H/R battery.

Apart from traditional applications, iron is also used for protection from ionizing radiation. Although it is lighter than another traditional protection material, lead, it is much stronger mechanically. The attenuation of radiation as a function of energy is shown in the graph.

The main disadvantage of iron and steel is that pure iron, and most of its alloys, suffer badly from rust if not protected in some waySony VAIO VGN-CS25H/Q battery. Painting, galvanization, passivation, plastic coating and bluing are all used to protect iron from rust by excluding water and oxygen or by cathodic protection.

Of compounds

Although its metallurgical role is dominant in terms of amounts, iron compounds are pervasive in industry as well being used in many niche uses. Iron catalysts are traditionally used in the Haber-Bosch Process for the production of ammonia and the Fischer-Tropsch process for conversion of carbon monoxide to hydrocarbons for fuels and lubricantsSony VAIO VGN-CS25H/P battery.[55] Powdered iron in an acidic solvent was used in the Bechamp reduction the reduction of nitrobenzene to aniline.[56]

Iron(III) chloride finds use in water purification and sewage treatment, in the dyeing of cloth, as a coloring agent in paints, as an additive in animal feed, and as an etchant for copper in the manufacture of printed circuit boards.[57] It can also be dissolved in alcohol to form tincture of iron.[31] The other halides tend to be limited to laboratory usesSony VAIO VGN-CS25H/C battery.

Iron(II) sulfate is used as a precursor to other iron compounds. It is also used to reduce chromate in cement. It is used to fortify foods and treat iron deficiency anemia. These are its main uses. Iron(III) sulfate is used in settling minute sewage particles in tank water. Iron(II) chloride is used as a reducing flocculating agent, in the formation of iron complexes and magnetic iron oxides, and as a reducing agent in organic synthesisSony VAIO VGN-CS23T/W battery.

Biological role

Iron is abundant in biology. Iron-proteins are found in all living organisms, ranging from the evolutionarily primitive archaea to humans. The color of blood is due to the hemoglobin, an iron-containing protein. As illustrated by hemoglobin, iron often is bound to cofactors, e.g. in hemes. The iron-sulfur clusters are pervasive and include nitrogenaseSony VAIO VGN-CS23T/Q battery, the enzymes responsible for biological nitrogen fixation. Influential theories of evolution have invoked a role for iron sulfides in the iron-sulfur world theory.

Structure of Heme b, in the protein additional ligand(s) would be attached to Fe.

Iron is a necessary trace element found in nearly all living organisms. Iron-containing enzymes and proteins, often containing heme prosthetic groups, participate in many biological oxidations and in transportSony VAIO VGN-CS23H battery. Examples of proteins found in higher organisms include hemoglobin, cytochrome (see high-valent iron), and catalase.[58]

[edit]Bioinorganic compounds

The most commonly-known and studied "bioinorganic" compounds of iron (i.e., iron compounds used in biology) are the heme proteins: examples are hemoglobin, myoglobin, and cytochrome P450. These compounds can transport gases, build enzymes, and be used in transferring electrons. Metalloproteins are a group of proteins with metal ion cofactorsSony VAIO VGN-CS23H/S battery. Some examples of iron metalloproteins are ferritin and rubredoxin. Many enzymes vital to life contain iron, such as catalase, lipoxygenases, and IRE-BP.

Health and diet

Main articles: Iron deficiency (medicine) and Human iron metabolism

Iron is pervasive, but particularly rich sources of dietary iron include red meat, lentils, beans, poultry, fish, leaf vegetables, watercress, tofu, chickpeas, black-eyed peas, blackstrap molasses, fortified bread, and fortified breakfast cereals. Iron in low amounts is found in molasses, teff and farina. Iron in meat (heme iron) is more easily absorbed than iron in vegetablesSony VAIO VGN-CS23H/B battery.[59] Although some studies suggest that heme/hemoglobin from red meat has effects which may increase the likelihood of colorectal cancer,[60][61] there is still some controversy,[62] and even a few studies suggesting that there is not enough evidence to support such claims.[63]

Iron provided by dietary supplements is often found as iron(II) fumarate, although iron sulfate is cheaper and is absorbed equally well. Elemental iron, or reduced iron, despite being absorbed at only one third to two thirds the efficiency (relative to iron sulfate) Sony VAIO VGN-CS23G battery,[64] is often added to foods such as breakfast cereals or enriched wheat flour. Iron is most available to the body when chelated to amino acids[65] and is also available for use as a common iron supplement. Often the amino acid chosen for this purpose is the cheapest and most common amino acid, glycine, leading to "iron glycinate" supplements.[66] The Recommended Dietary Allowance (RDA) for iron varies considerably based on age, gender, and source of dietary iron (heme-based iron has higher bioavailability) Sony VAIO VGN-CS23G/W battery.[67] Infants may require iron supplements if they are bottle-fed cow's milk.[68] Blood donors and pregnant women are at special risk of low iron levels and are often advised to supplement their iron intake.[69]

Uptake and storage

Iron acquisition poses a problem for aerobic organisms, because ferric iron is poorly soluble near neutral pH. Thus, bacteria have evolved high-affinity sequestering agents called siderophores.

After uptake, in cells, iron storage is carefully regulated; "free" iron ions do not exist as suchSony VAIO VGN-CS23G/Q battery. A major component of this regulation is the protein transferrin, which binds iron ions absorbed from the duodenum and carries it in the blood to cells.[73] In animals, plants, and fungi, iron is often the metal ion incorporated into the heme complex. Heme is an essential component of cytochrome proteins, which mediate redox reactions, and of oxygen carrier proteins such as hemoglobin, myoglobin, and leghemoglobinSony VAIO VGN-CS23G/P battery.

Inorganic iron contributes to redox reactions in the iron-sulfur clusters of many enzymes, such as nitrogenase (involved in the synthesis of ammonia from nitrogen and hydrogen) and hydrogenase. Non-heme iron proteins include the enzymes methane monooxygenase (oxidizes methane to methanol), ribonucleotide reductase (reduces ribose to deoxyriboseSony VAIO VGN-CS21Z/Q battery; DNA biosynthesis), hemerythrins (oxygen transport and fixation in marine invertebrates) and purple acid phosphatase (hydrolysis of phosphate esters).

Iron distribution is heavily regulated in mammals, partly because iron ions have a high potential for biological toxicity.[74]

Regulation of uptake

Main article: Hepcidin

Iron uptake is tightly regulated by the human body, which has no regulated physiological means of excreting iron. Only small amounts of iron are lost daily due to mucosal and skin epithelial cell sloughing, so control of iron levels is mostly by regulating uptakeSony VAIO VGN-CS21S/W battery.[75] Regulation of iron uptake is impaired in some people as a result of a genetic defect that maps to the HLA-H gene region on chromosome 6. In these people, excessive iron intake can result in iron overload disorders, such as hemochromatosis. Many people have a genetic susceptibility to iron overload without realizing it or being aware of a family history of the problem. For this reasonSony VAIO VGN-CS21S/V battery, it is advised that people do not take iron supplements unless they suffer from iron deficiency and have consulted a doctor. Hemochromatosis is estimated to cause disease in between 0.3 and 0.8% of Caucasians.[76]

MRI finds that iron accumulates in the hippocampus of the brains of those with Alzheimer's disease and in the substantia nigra of those with Parkinson diseaseSony VAIO VGN-CS21S/T battery.[77]

[edit]Permeable reactive barriers

Zero-valent iron is the main reactive material for permeable reactive barriers.[citation needed]

[edit]Precautions

NFPA 704

101

Fire diamond for powdered iron metal

Main article: Iron poisoning

Large amounts of ingested iron can cause excessive levels of iron in the blood. High blood levels of free ferrous iron react with peroxides to produce free radicals, which are highly reactive and can damage DNA, proteins, lipids, and other cellular components. Thus, iron toxicity occurs when there is free iron in the cell, which generally occurs when iron levels exceed the capacity of transferrin to bind the ironSony VAIO VGN-CS21S/R battery. Damage to the cells of the gastrointestinal tract can also prevent them from regulating iron absorption leading to further increases in blood levels. Iron typically damages cells in the heart, liver and elsewhere, which can cause significant adverse effects, including coma, metabolic acidosis, shock, liver failure, coagulopathy, adult respiratory distress syndrome, long-term organ damage, and even deathSony VAIO VGN-CS21S/P battery.[78] Humans experience iron toxicity above 20 milligrams of iron for every kilogram of mass, and 60 milligrams per kilogram is considered a lethal dose.[79] Overconsumption of iron, often the result of children eating large quantities of ferrous sulfate tablets intended for adult consumption, is one of the most common toxicological causes of death in children under sixSony VAIO VGN-CS215J/R battery.[79] The Dietary Reference Intake (DRI) lists the Tolerable Upper Intake Level (UL) for adults as 45 mg/day. For children under fourteen years old the UL is 40 mg/day.

The medical management of iron toxicity is complicated, and can include use of a specific chelating agent called deferoxamine to bind and expel excess iron from the body.[78][80]

Nickel is a chemical element with the chemical symbol Ni and atomic number 28. It is a silvery-white lustrous metal with a slight golden tingeSony VAIO VGN-CS215J/Q battery. Nickel belongs to the transition metals and is hard and ductile. Pure nickel shows a significant chemical activity that can be observed when nickel is powdered to maximize the exposed surface area on which reactions can occur, but larger pieces of the metal are slow to react with air at ambient conditions due to the formation of a protective oxide surfaceSony VAIO VGN-CS19/W battery. Even then, nickel is reactive enough with oxygen so that native nickel is rarely found on Earth's surface, being mostly confined to the interiors of larger nickel–iron meteorites that were protected from oxidation during their time in space. On Earth, such native nickel is always found in combination with iron, a reflection of those elements' origin as major end products of supernova nucleosynthesis. An iron–nickel mixture is thought to compose Earth's inner coreSony VAIO VGN-CS19/R battery.[3]

The use of nickel (as a natural meteoric nickel–iron alloy) has been traced as far back as 3500 BC. Nickel was first isolated and classified as a chemical element in 1751 by Axel Fredrik Cronstedt, who initially mistook its ore for a copper mineral. The element name comes from a mischievous sprite of German miner's mythology, Nickel (similar to Old Nick) Sony VAIO VGN-CS19/Q battery, that personified the fact that copper-nickel ores resisted refinement into copper. Nickel's most important modern ore minerals are laterites, including limonite, garnierite, and pentlandite. Major production sites include Sudbury region in Canada (which is thought to be of meteoric origin), New Caledonia in the Pacific and Norilsk in Russia.

Because of nickel's slow rate of oxidation at room temperature, it is considered corrosion-resistantSony VAIO VGN-CS19/P battery. Historically this has led to its use for plating metals such as iron and brass, to its use for chemical apparatus, and its use in certain alloys that will retain a high silvery polish, such as German silver. About 6% of world nickel production is still used for corrosion-resistant pure-nickel plating. Nickel was once a common component of coins, but has largely been replaced by cheaper iron for this purpose, especially since the metal has proven to be a skin allergen for some peopleSony VAIO VGN-CS17H/W battery.

Nickel is one of the four elements that are ferromagnetic around room temperature. Alnico permanent magnets based partly on nickel are of intermediate strength between iron-based permanent magnets and rare-earth magnets. The metal is chiefly valuable in the modern world for the alloys it forms; about 60% of world production is used in nickel-steels (particularly stainless steel) Sony VAIO VGN-CS17H/Q battery. Other common alloys, as well as some new superalloys, make up most of the remainder of world nickel use, with chemical uses for nickel compounds consuming less than 3% of production.[4] As a compound, nickel has a number of niche chemical manufacturing uses, such as a catalyst for hydrogenation. Enzymes of some microorganisms and plants contain nickel as an active center, which makes the metal an essential nutrient for themSony VAIO VGN-CS16T/W battery.

Characteristics

Atomic and physical properties

Nickel is a silvery-white metal with a slight golden tinge that takes a high polish. It is one of only four elements that are magnetic at or near room temperature, the others being iron, cobalt and gadolinium. Its Curie temperature is 355 °C, meaning that bulk nickel is non-magnetic above this temperatureSony VAIO VGN-CS16T/T battery.[5] The unit cell of nickel is a face centered cube with the lattice parameter of 0.352 nm giving an atomic radius of 0.124 nm. Nickel belongs to the transition metals and is hard and ductile.

Electron configuration dispute

The nickel atom has two electron configurations, [Ar] 4s2 3d8 and [Ar] 4s1 3d9, which are very close in energy, where the symbol [Ar] refers to the argon-like core structure. There is some disagreement as to which should be considered the lowest energy configuration.[6] Chemistry textbooks quote the electron configuration of nickel as [Ar] 4s2 3d8Sony VAIO VGN-CS16T/R battery,[7] or equivalently as [Ar] 3d8 4s2.[8] This configuration agrees with the Madelung energy ordering rule, which predicts that 4s is filled before 3d. It is supported by the experimental fact that the lowest energy state of the nickel atom is a 4s2 3d8 energy level, specifically the 3d8(3F) 4s2 3F, J=4 level.[9]

However each of these two configurations in fact gives rise to a set of states at different energiesSony VAIO VGN-CS16T/Q battery.[9] The two sets of energies overlap, and the average energy of states having configuration [Ar] 4s1 3d9 is in fact lower than the average energy of states having configuration [Ar] 4s2 3d8. For this reason the research literature on atomic calculations quotes the ground state configuration of nickel as 4s1 3d9Sony VAIO VGN-CS16T/P battery.[6]

Isotopes

Main article: Isotopes of nickel

Naturally occurring nickel is composed of 5 stable isotopes; 58Ni, 60Ni, 61Ni, 62Ni and 64Ni with 58Ni being the most abundant (68.077% natural abundance). 62Ni is the most stable nuclide of all the existing elements, with binding energy greater than both 56Fe, often incorrectly cited as most stable, and 58FeSony VAIO VGN-CS13T/W battery.[10] 18 radioisotopes have been characterised with the most stable being 59Ni with a half-life of 76,000 years, 63Ni with a half-life of 100.1 years, and 56Ni with a half-life of 6.077 days. All of the remaining radioactive isotopes have half-lives that are less than 60 hours and the majority of these have half-lives that are less than 30 seconds. This element also has one meta stateSony VAIO VGN-CS13H/W battery.[11]

Nickel-56 is produced by the silicon burning process and later set free in large quantities during type Ia supernovae. The shape of the light curve of these supernovae at intermediate to late-times corresponds to the decay via electron capture of nickel-56 to cobalt-56 and ultimately to iron-56.[12] Nickel-59 is a long-lived cosmogenic radionuclide with a half-life of 76,000 yearsSony VAIO VGN-CS13H/R battery. 59Ni has found many applications in isotope geology. 59Ni has been used to date the terrestrial age of meteorites and to determine abundances of extraterrestrial dust in ice and sediment. Nickel-60 is the daughter product of the extinct radionuclide 60Fe, which decays with a half-life of 2.6 million years. Because 60Fe has such a long half-life, its persistence in materials in the solar system at high enough concentrations may have generated observable variations in the isotopic composition of 60NiSony VAIO VGN-CS13H/Q battery. Therefore, the abundance of 60Ni present in extraterrestrial material may provide insight into the origin of the solar system and its early history. Nickel-62 has the highest binding energy per nucleon of any isotope for any element (8.7946 Mev/nucleon).[13] Isotopes heavier than 62Ni cannot be formed by nuclear fusion without losing energy. 48Ni, discovered in 1999, is the most proton-rich heavy element isotope knownSony VAIO VGN-CS13H/P battery. With 28 protons and 20 neutrons 48Ni is "double magic" (like 208Pb) and therefore unusually stable.[11][14]

The isotopes of nickel range in atomic weight from 48 u (48Ni) to 78 u (78Ni). Nickel-78's half-life was recently measured to be 110 milliseconds and is believed to be an important isotope involved in supernova nucleosynthesis of elements heavier than ironSony VAIO VGN-CS11Z/T battery.[15]

Occurrence

See also: Ore genesis and Category:Nickel minerals

Widmanstätten pattern showing the two forms of nickel-iron, Kamacite and Taenite, in an octahedrite meteorite

On Earth, nickel occurs most often in combination with sulfur and iron in pentlandite, with sulfur in millerite, with arsenic in the mineral nickeline, and with arsenic and sulfur in nickel galena.[16] Nickel is commonly found in iron meteorites as the alloys kamacite and taeniteSony VAIO VGN-CS11Z/R battery.

The bulk of the nickel mined comes from two types of ore deposits. The first are laterites where the principal ore minerals are nickeliferous limonite: (Fe, Ni)O(OH) and garnierite (a hydrous nickel silicate): (Ni, Mg)3Si2O5(OH)4. The second are magmatic sulfide deposits where the principal ore mineral is pentlandite: (Ni, Fe)9S8Sony VAIO VGN-CS11S/W battery.

In terms of supply, the Sudbury region of Ontario, Canada, produces about 30% of the world's supply of nickel. The Sudbury Basin deposit is theorized to have been created by a meteorite impact event early in the geologic history of Earth. Russia contains about 40% of the world's known resources at the Norilsk deposit in Siberia. The Russian mining company MMC Norilsk Nickel obtains the nickel and the associated palladium for world distributionSony VAIO VGN-CS11S/Q battery. Other major deposits of nickel are found in New Caledonia, France, Australia, Cuba, and Indonesia. Deposits found in tropical areas typically consist of laterites, which are produced by the intense weathering of ultramafic igneous rocks and the resulting secondary concentration of nickel bearing oxide and silicate mineralsSony VAIO VGN-CS11S/P battery.

Based on geophysical evidence, most of the nickel on Earth is postulated to be concentrated in the Earth's outer core and inner core. Kamacite and taenite are naturally occurring alloys of iron and nickel. For kamacite the alloy is usually in the proportion of 90:10 to 95:5 although impurities such as cobalt or carbon may be present, while for taenite the nickel content is between 20% and 65%. Kamacite and taenite occur in nickel iron meteorites(Sony VAIO VGN-AW11M/H battery).[17]

Compounds

See also Category: Nickel compounds

Tetracarbonyl nickel

The most common oxidation state of nickel is +2, but compounds of Ni0, Ni+, and Ni3+ are well known, and Ni4+ has been demonstrated.[18]

[edit]Nickel(0)

Tetracarbonylnickel (Ni(CO)4), discovered by Ludwig Mond,[19] is a volatile liquid at room temperature. On heating, the complex decomposes back to nickel and carbon monoxide:

Ni(CO)4 a Ni + 4 CO

This behavior is exploited in the Mond process for purifying nickel, as described above. The related nickel(0) complex bis(cyclooctadiene)nickel(0) is a useful catalyst in organonickel chemistry due to the easily displaced cod ligands(Sony VAIO VGN-AW11S/B battery).

Nickel(II)

Nickel sulfate crystals

Nickel(II) forms compounds with all common anions, i.e. the sulfide, sulfate, carbonate, hydroxide, carboxylates, and halides. Nickel(II) sulfate is produced in large quantities by dissolving nickel metal or oxides in sulfuric acid. It exists as both a hexa- and heptahydrates.[20] This compound is useful for electroplating nickel(Sony VAIO VGN-AW11Z/B battery).

The four halogens form nickel compounds, all of which adopt octahedral geometries. Nickel(II) chloride is most common, and its behavior is illustrative of the other halides. Nickel(II) chloride is produced by dissolving nickel residues in hydrochloric acid. The dichloride is usually encountered as the green hexahydrate, but it can be dehydrated to give the yellow anhydrous NiCl2(Sony VAIO VGN-AW170C battery). Some tetracoordinate nickel(II) complexes form both tetrahedral and square planar geometries. The tetrahedral complexes are paramagnetic and the square planar complexes are diamagnetic. This equilibrium as well as the formation of octahedral complexes contrasts with the behavior of the divalent complexes of the heavier group 10 metals, palladium(II) and platinum(II), which tend to adopt only square-planar complexes(Sony VAIO VGN-AW19/Q battery).[18]

Nickelocene is known; it has an electron count of 20, making it relatively unstable.

Nickel(III) antimonide

Nickel(I), (III), and (IV)

For simple compounds, nickel(III) and nickel(IV) only occurs with fluoride and oxides. Nickel(III) oxide is used as the cathode in many rechargeable batteries, including nickel-cadmium, nickel-iron, nickel hydrogen, and nickel-metal hydride, and used by certain manufacturers in Li-ion batteries(Sony VAIO VGN-AW19 battery).[21]

History

Because the ores of nickel are easily mistaken for ores of silver, understanding of this metal and its use dates to relatively recent times. However, the unintentional use of nickel is ancient, and can be traced back as far as 3500 BC. Bronzes from what is now Syria had contained up to 2% nickel.[22] Further, there are Chinese manuscripts suggesting that "white copper" (Sony VAIO VGN-AW21M/H battery) (cupronickel, known as baitung) was used there between 1700 and 1400 BC. This Paktong white copper was exported to Britain as early as the 17th century, but the nickel content of this alloy was not discovered until 1822.[23]

In medieval Germany, a red mineral was found in the Erzgebirge (Ore Mountains) that resembled copper ore. However, when miners were unable to extract any copper from it, they blamed a mischievous sprite of German mythology(Sony VAIO VGN-AW21S/B battery), Nickel (similar to Old Nick), for besetting the copper. They called this ore Kupfernickel from the German Kupfer for copper. This ore is now known to be nickeline or niccolite, a nickel arsenide. In 1751, Baron Axel Fredrik Cronstedt was attempting to extract copper from kupfernickel and obtained instead a white metal that he named after the spirit which had given its name to the mineral, nickel(Sony VAIO VGN-AW21VY/Q battery).[28] In modern German, Kupfernickel or Kupfer-Nickel designates the alloy cupronickel.

After its discovery, the only source for nickel was the rare Kupfernickel, but, from 1824 on, the nickel was obtained as byproduct of cobalt blue production. The first large-scale producer of nickel was Norway, which exploited nickel-rich pyrrhotite from 1848 on. The introduction of nickel in steel production in 1889 increased the demand for nickel(Sony VAIO VGN-AW21XY/Q battery), and the nickel deposits of New Caledonia, which were discovered in 1865, provided most of the world's supply between 1875 and 1915. The discovery of the large deposits in the Sudbury Basin, Canada in 1883, in Norilsk-Talnakh, Russia in 1920, and in the Merensky Reef, South Africa in 1924 made large-scale production of nickel possible. (Sony VAIO VGN-AW21Z/B battery)

Dutch coins made of pure nickel

Nickel has been a component of coins since the mid-19th century. In the United States, the term "nickel" or "nick" was originally applied to the copper-nickel Flying Eagle cent, which replaced copper with 12% nickel 1857–58, then the Indian Head cent of the same alloy from 1859–1864. Still later in 1865, the term designated the three-cent nickel(Sony VAIO VGN-AW230J/H battery), with nickel increased to 25%. In 1866, the five-cent shield nickel (25% nickel, 75% copper) appropriated the designation. Along with the alloy proportion, this term has been used to the present in the United States. Coins of nearly pure nickel were first used in 1881 in Switzerland, and more notably 99.9% nickel five-cent coins were struck in Canada (Sony VAIO VGN-AW235J/B battery) (the world's largest nickel producer at the time) during non-war years from 1922–1981, and their metal content made these coins magnetic.[29] During the wartime period 1942–45, more or all nickel was removed from Canadian and U.S. coins, due to nickel's war-critical use in armor.[25][30] Canada switched alloys again to plated steel during the Korean war, but was forced to stop making pure nickel "nickels" in 1981(Sony VAIO VGN-AW270Y/Q battery), reserving the pure 99.9% nickel alloy after 1968 only to its higher-value coins. Finally, in the 21st century, with rising nickel prices, most countries that formerly used nickel in their coins have abandoned the metal for cost reasons, and the U.S. five cents remains one of the few coins in which the metal is still used, save for exterior plating. (Sony VAIO VGN-AW31M/H battery)

[edit]Production

World nickel production in metric tons, in 2005. The Russian Federation is the largest producer, followed by Canada.

In 2005, Russia was the largest producer of nickel with about one-fifth world share closely followed by Canada, Australia, and Indonesia, as reported by the British Geological Survey. A nickel deposit in western Turkey had been exploited(Sony VAIO VGN-AW31S/B battery), with this location being especially convenient for European smelters, steelmakers, and factories. The one locality in the United States where nickel was commercially mined is Riddle, Oregon, where several square miles of nickel-bearing garnierite surface deposits are located. The mine closed in 1987. The Eagle mine project is a proposed new nickel mine in Michigan's upper peninsula(Sony VAIO VGN-AW31XY/Q battery).

[edit]Extraction and purification

Nickel is recovered through extractive metallurgy. Nickel is extracted from its ores by conventional roasting and reduction processes that yield a metal of greater than 75% purity. In many stainless steel applications, 75% pure nickel can be used without further purification, depending on the composition of the impurities(Sony VAIO VGN-AW31ZJ/B battery).

Most sulfide ores have traditionally been processed using pyrometallurgical techniques to produce a matte for further refining. Recent advances in hydrometallurgy have resulted in significant nickel purification using these processes. Most sulfide deposits have traditionally been processed by concentration through a froth flotation process followed by pyrometallurgical extraction.(Sony VAIO VGN-AW41JF/H battery) In hydrometallurgical processes, nickel sulfide ores undergo flotation (differential flotation if Ni/Fe ratio is too low) and then smelted. After producing the nickel matte, further processing is done via the Sherritt-Gordon process. First, copper is removed by adding hydrogen sulfide, leaving a concentrate of only cobalt and nickel. Then, solvent extraction is used to separate the cobalt and nickel, with the final nickel concentration greater than 99%(Sony VAIO VGN-AW41JF battery).

Electrolytically refined nickel nodule, with visible green, crystallized nickel-electrolyte salts in the pores.

[edit]Electrorefining

A second common form of further refining involves the leaching of the metal matte into a nickel salt solution, followed by the electro-winning of the nickel from solution by plating it onto a cathode as electrolytic nickel(Sony VAIO VGN-AW41MF/H battery).

[edit]Mond process

Highly purified nickel spheres made in the Mond process.

Main article: Mond process

Purification of nickel oxides to obtain the purest metal is performed via the Mond process, which increases the nickel concentrate to greater than 99.99% purity.[34] This process was patented by L. Mond and has been in industrial use since before the beginning of the 20th century. In the process, nickel is reacted with carbon monoxide at around 40–80 °C to form nickel carbonyl in the presence of a sulfur catalyst(Sony VAIO VGN-AW41MF battery). Iron gives iron pentacarbonyl too, but this reaction is slow. If necessary, it may be separated by distillation. Dicobalt octacarbonyl is also formed in this process, but it decomposes to tetracobalt dodecacarbonyl at the reaction temperature to give a non-volatile solid.[4]

Nickel is re-obtained from the nickel carbonyl by one of two processes. It may be passed through a large chamber at high temperatures in which tens of thousands of nickel spheres(Sony VAIO VGN-AW41XH/Q battery), called pellets, are constantly stirred. It then decomposes depositing pure nickel onto the nickel spheres. Alternatively, the nickel carbonyl may be decomposed in a smaller chamber at 230 °C to create fine nickel powder. The resultant carbon monoxide is re-circulated and reused through the process. The highly pure nickel produced by this process is known as "carbonyl nickel".(Sony VAIO VGN-AW41XH battery)

[edit]Metal value

The market price of nickel surged throughout 2006 and the early months of 2007; as of April 5, 2007, the metal was trading at 52,300 USD/tonne or 1.47 USD/oz.[36] The price subsequently fell dramatically from these peaks, and as of 19 January 2009 the metal was trading at 10,880 USD/tonne. (Sony VAIO VGN-AW41ZF/B battery)

The US nickel coin contains 0.04 oz (1.25 g) of nickel, which at the April 2007 price was worth 6.5 cents, along with 3.75 grams of copper worth about 3 cents, making the metal value over 9 cents. Since the face value of a nickel is 5 cents, this made it an attractive target for melting by people wanting to sell the metals at a profit. However, the United States Mint(Sony VAIO VGN-AW41ZF battery), in anticipation of this practice, implemented new interim rules on December 14, 2006, subject to public comment for 30 days, which criminalize the melting and export of cents and nickels.[37] Violators can be punished with a fine of up to $10,000 and/or imprisoned for a maximum of five years.

As of September 16, 2011, the melt value of a U.S. nickel is $0.0600409, which is 20% higher than the face value. (SONY Vaio VGN-NS38M Battery)

Applications

Nickel superalloy jet engine (RB199) turbine blade

The fraction of global nickel production presently used for various applications is as follows: 60% for making nickel steels; 14% in nickel-copper alloys and nickel silver; 9% to make malleable nickel, nickel clad, Inconel, and other superalloys; 6% in plating; 3% for nickel cast irons; 3% in heat and electric resistance alloys, such as Nichrome; 2% for nickel brasses and bronzes; 3% in all other applications combined. (SONY Vaio VGN-NS31S Battery)

Nickel is used in many specific and recognizable industrial and consumer products, including stainless steel, alnico magnets, coinage, rechargeable batteries, electric guitar strings, microphone capsules, and special alloys. It is also used for plating and as a green tint in glass. Nickel is preeminently an alloy metal, and its chief use is in the nickel steels and nickel cast irons(SONY Vaio VGN-NS31M Battery), of which there are many varieties. It is also widely used in many other alloys, such as nickel brasses and bronzes, and alloys with copper, chromium, aluminium, lead, cobalt, silver, and gold (Inconel, Incoloy, Monel, Nimonic).[41]

A "horseshoe magnet" made of alnico nickel alloy. The composition of alnico alloys is typically 8–12% Al, 15–26% Ni, 5–24% Co, up to 6% Cu, up to 1% Ti, and the balance is Fe(SONY Vaio VGN-NS31Z Battery). The development of alnico began in 1931 when it was discovered that an alloy of iron, nickel, and aluminum had a coercivity double that of the best magnet steels of the time. Alnico magnets are now being replaced by rare earth magnets in many applications

Because of its resistance to corrosion, nickel has been occasionally used historically as a substitute for decorative silver(SONY Vaio VGN-NS21Z Battery). Nickel was also occasionally used in some countries after 1859 as a cheap coinage metal (see above) but beginning the later years of the 20th century has largely replaced by cheaper stainless steel (i.e., iron) alloys, except notably in the United States.

Nickel is an excellent alloying agent for certain other precious metals, and so used in the so-called fire assay, as a collector of platinum group elements (PGE). As such, nickel is capable of full collection of all 6 PGE elements from ores(SONY Vaio VGN-NS21M Battery), in addition to partial collection of gold. High-throughput nickel mines may also engage in PGE recovery (primarily platinum and palladium); examples are Norilsk in Russia and the Sudbury Basin in Canada.

Nickel foam or nickel mesh is used in gas diffusion electrodes for alkaline fuel cells.[42][43]

Nickel and its alloys are frequently used as catalysts for hydrogenation reactions. Raney nickel, a finely-divided nickel-aluminium alloy, is one common form(SONY Vaio VGN-NS21S Battery), however related catalysts are also often used, including related 'Raney-type' catalysts.

Nickel is a naturally magnetostrictive material, meaning that, in the presence of a magnetic field, the material undergoes a small change in length.[44] In the case of nickel, this change in length is negative (contraction of the material), which is known as negative magnetostriction and is on the order of 50 ppm(SONY Vaio VGN-NS12S Battery).

Nickel is used as a binder in the cemented tungsten carbide or hardmetal industry and used in proportions of six to 12% by weight. Nickel can make the tungsten carbide magnetic and adds corrosion-resistant properties to the cemented tungsten carbide parts, although the hardness is lower than those of parts made with cobalt binder. (SONY Vaio VGN-NS12M Battery)

Biological role

Although not recognized until the 1970s, nickel plays important roles in the biology of microorganisms and plants.[46] In fact, urease (an enzyme that assists in the hydrolysis of urea) contains nickel. The NiFe-hydrogenases contain nickel in addition to iron-sulfur clusters. Such [NiFe]-hydrogenases characteristically oxidise H2. A nickel-tetrapyrrole coenzyme(SONY Vaio VGN-NS11Z Battery), Cofactor F430, is present in the methyl coenzyme M reductase, which powers methanogenic archaea. One of the carbon monoxide dehydrogenase enzymes consists of an Fe-Ni-S cluster.[47] Other nickel-containing enzymes include a rare bacterial class of superoxide dismutase[48] and glyoxalase I enzymes in bacteria and several parasitic eukaryotic trypanosomal parasites (this enzyme in higher organisms, including yeast and mammals, uses divalent zinc, Zn2+)(SONY Vaio VGN-NS11M Battery).

[edit]Toxicity

In the US, the minimal risk level of nickel and its compounds is set to 0.2 µg/m3 for inhalation during 15–364 days.[55] Nickel sulfide fume and dust are believed to be carcinogenic, and various other nickel compounds may be as well. Nickel carbonyl, [Ni(CO)4], is an extremely toxic gas. The toxicity of metal carbonyls is a function of both the toxicity of the metal as well as the carbonyl's ability to give off highly toxic carbon monoxide gas(SONY Vaio VGN-NS11L Battery), and this one is no exception; nickel carbonyl is also explosive in air.[58][59] Sensitized individuals may show an allergy to nickel, affecting their skin, also known as dermatitis. Sensitivity to nickel may also be present in patients with pompholyx. Nickel is an important cause of contact allergy, partly due to its use in jewellery intended for pierced ears(SONY Vaio VGN-NS11J Battery).[60] Nickel allergies affecting pierced ears are often marked by itchy, red skin. Many earrings are now made nickel-free due to this problem. The amount of nickel allowed in products that come into contact with human skin is regulated by the European Union. In 2002, researchers found amounts of nickel being emitted by 1 and 2 Euro coins far in excess of those standards. This is believed to be due to a galvanic reaction. (SONY Vaio VGN-NS11E Battery)

Nickel was voted Allergen of the Year in 2008 by the American Contact Dermatitis Society.[62]

Reports also showed that both the nickel-induced activation of hypoxia-inducible factor (HIF-1) and the up-regulation of hypoxia-inducible genes are due to depleted intracellular ascorbate levels. The addition of ascorbate to the culture medium increased the intracellular ascorbate level and reversed both the metal-induced stabilization of HIF-1- and HIF-1α-dependent gene expression. (SONY Vaio VGN-NS10L Battery)

 
Manganese is a chemical element, designated by the symbol Mn. It has the atomic number 25. It is found as a free element in nature (often in combination with iron), and in many minerals. As a free element, manganese is a metal with important industrial metal alloy uses, particularly in stainless steels(Dell 1691P battery).

Historically, manganese is named for various black minerals (such as pyrolusite) from the same region of Magnesia in Greece which gave names to similar-sounding magnesium, Mg, and magnetite, an ore of the element iron, Fe. By the mid-18th century, Swedish chemist Carl Wilhelm Scheele had used pyrolusite to produce chlorine(Dell 310-6321 battery). Scheele and others were aware that pyrolusite (now known to be manganese dioxide) contained a new element, but they were not able to isolate it. Johan Gottlieb Gahn was the first to isolate an impure sample of manganese metal in 1774, by reducing the dioxide with carbon.

Manganese phosphating is used as a treatment for rust and corrosion prevention on steel. Depending on their oxidation state(Dell 312-0068 battery), manganese ions have various colors and are used industrially as pigments. The permanganates of alkali and alkaline earth metals are powerful oxidizers. Manganese dioxide is used as the cathode (electron acceptor) material in standard and alkaline disposable dry cells and batteries.

In biology, manganese(II) ions function as cofactors for a large variety of enzymes with many functions(Dell 312-0078 battery). Manganese enzymes are particularly essential in detoxification of superoxide free radicals in organisms that must deal with elemental oxygen. Manganese also functions in the oxygen-evolving complex of photosynthetic plants. The element is a required trace mineral for all known living organisms. In larger amounts, and apparently with far greater activity by inhalation(Dell 312-0079 battery), manganese can cause a poisoning syndrome in mammals, with neurological damage which is sometimes irreversible.

Characteristics

[edit]Physical properties

Electrolytically refined manganese chips and 1 cm3 cube

Manganese is a silvery-gray metal resembling iron. It is hard and very brittle, difficult to fuse, but easy to oxidize.[1] Manganese metal and its common ions are paramagnetic.[2]

[edit]Isotopes

Main article: Isotopes of manganese

Naturally occurring manganese is composed of one stable isotope, 55Mn. Eighteen radioisotopes have been characterized(Dell 312-0305 battery), with the most stable being 53Mn with a half-life of 3.7 million years, 54Mn with a half-life of 312.3 days, and 52Mn with a half-life of 5.591 days. All of the remaining radioactive isotopes have half-lives that are less than three hours and the majority of these have half-lives that are less than one minute. This element also has three meta states(Dell 312-0326 battery).[3]

Manganese is part of the iron group of elements, which are thought to be synthesized in large stars shortly before the supernova explosion. 53Mn decays to 53Cr with a half-life of 3.7 million years. Because of its relatively short half-life, 53Mn occurs only in tiny amounts due to the action of cosmic rays on iron in rocks.[4] Manganese isotopic contents are typically combined with chromium isotopic contents and have found application in isotope geology and radiometric dating(Dell 312-0518 battery). Mn–Cr isotopic ratios reinforce the evidence from 26Al and 107Pd for the early history of the solar system. Variations in 53Cr/52Cr and Mn/Cr ratios from several meteorites indicate an initial 53Mn/55Mn ratio that suggests Mn–Cr isotopic composition must result from in situ decay of 53Mn in differentiated planetary bodies. Hence 53Mn provides additional evidence for nucleosynthetic processes immediately before coalescence of the solar system(Dell 312-0566 battery).[3]

The isotopes of manganese range in atomic weight from 46 u (46Mn) to 65 u (65Mn). The primary decay mode before the most abundant stable isotope, 55Mn, is electron capture and the primary mode after is beta decay.[3]

[edit]Chemical properties

The most common oxidation states of manganese are +2, +3, +4, +6 and +7, though oxidation states from −3 to +7 are observed. Mn2+ often competes with Mg2+ in biological systems. Manganese compounds where manganese is in oxidation state +7(Dell 312-0585 battery), which are restricted to the unstable oxide Mn2O7 and compounds of the intensely purple permanganate anion MnO4−, are powerful oxidizing agents.[1] Compounds with oxidation states +5 (blue) and +6 (green) are strong oxidizing agents and are vulnerable to disproportionation.

Manganese chloride crystals - the pale pink color of Mn (II) salts is due to a spin-forbidden 3d transition, which is rare(Dell 312-0831 battery).

Aqueous solution of KMnO4 illustrating the deep purple of Mn(VII) as it occurs in permanganate

The most stable oxidation state for manganese is +2, which has a pale pink color, and many manganese(II) compounds are known, such as manganese(II) sulfate (MnSO4) and manganese(II) chloride (MnCl2). This oxidation state is also seen in the mineral rhodochrosite, (manganese(II) carbonate) (Dell BAT30WL battery). The +2 oxidation state is the state used in living organisms for essential functions; other states are toxic for the human body. The +2 oxidation of Mn results from removal of the two 4s electrons, leaving a "high spin" ion in which all five of the 3d orbitals contain a single electron. Absorption of visible light by this ion is accomplished only by a spin-forbidden transition in which one of the d electrons must pair with another(Dell D6400 battery), to give the atom a change in spin of two units. The unlikeliness of such a transition is seen in the uniformly pale and almost colorless nature of Mn(II) compounds relative to other oxidation states of manganese.[5]

The +3 oxidation state is known in compounds like manganese(III) acetate, but these are quite powerful oxidizing agents and also prone to disproportionation in solution to manganese(II) and manganese(IV) (Dell HF674 battery). Solid compounds of manganese(III) are characterized by their preference for distorted octahedral coordination due to the Jahn-Teller effect and its strong purple-red color.

The oxidation state 5+ can be obtained if manganese dioxide is dissolved in molten sodium nitrite.[7] Manganate (VI) salts can also be produced by dissolving Mn compounds, such as manganese dioxide, in molten alkali while exposed to air(Dell N3010 battery).

Permanganate (+7 oxidation state) compounds are purple, and can give glass a violet color. Potassium permanganate, sodium permanganate and barium permanganate are all potent oxidizers. Potassium permanganate, also called Condy's crystals, is a commonly used laboratory reagent because of its oxidizing properties and finds use as a topical medicine (for example, in the treatment of fish diseases) (Dell Inspiron N4010 battery). Solutions of potassium permanganate were among the first stains and fixatives to be used in the preparation of biological cells and tissues for electron microscopy.[8]

[edit]History

The origin of the name manganese is complex. In ancient times, two black minerals from Magnesia in what is now modern Greece, were both called magnes from their place of origin, but were thought to differ in gender(Dell INSPIRON 1100 battery). The male magnes attracted iron, and was the iron ore we now know as lodestone or magnetite, and which probably gave us the term magnet. The female magnes ore did not attract iron, but was used to decolorize glass. This feminine magnes was later called magnesia, known now in modern times as pyrolusite or manganese dioxide. Neither this mineral nor manganese itself is magnetic(Dell Inspiron 1200 battery). In the 16th century, manganese dioxide was called manganesum (note the two n's instead of one) by glassmakers, possibly as a corruption and concatenation of two words, since alchemists and glassmakers eventually had to differentiate a magnesia negra (the black ore) from magnesia alba (a white ore, also from Magnesia, also useful in glassmaking). Michele Mercati called magnesia negra manganesa(Dell Inspiron 1420 battery), and finally the metal isolated from it became known as manganese (German: Mangan). The name magnesia eventually was then used to refer only to the white magnesia alba (magnesium oxide), which provided the name magnesium for that free element, when it was eventually isolated, much later.[9]

Some of the cave paintings in Lascaux, France, use manganese-based pigments.[10]

Several oxides of manganese(Dell Inspiron 1464 battery), for example manganese dioxide, are abundant in nature, and owing to their color, these oxides have been used as since the Stone Age. The cave paintings in Gargas contain manganese as pigments and these cave paintings are 30,000 to 24,000 years old.[11]

Manganese compounds were used by Egyptian and Roman glassmakers, to either remove color from glass or add color to it.[12] The use as "glassmakers soap" continued through the Middle Ages until modern times and is evident in 14th-century glass from Venice(Dell Inspiron 1564 battery).[13]

Credit for first isolating manganese is usually given to Johan Gottlieb Gahn.

Because of the use in glassmaking, manganese dioxide was available to alchemists, the first chemists, and was used for experiments. Ignatius Gottfried Kaim (1770) and Johann Glauber (17th century) discovered that manganese dioxide could be converted to permanganate, a useful laboratory reagent.[14] By the mid-18th century(Dell Inspiron 1764 battery), the Swedish chemist Carl Wilhelm Scheele used manganese dioxide to produce chlorine. First, hydrochloric acid, or a mixture of dilute sulfuric acid and sodium chloride was made to react with manganese dioxide, later hydrochloric acid from the Leblanc process was used and the manganese dioxide was recycled by the Weldon process. The production of chlorine and hypochlorite containing bleaching agents was a large consumer of manganese ores(Dell Inspiron 1520 battery).

Scheele and other chemists were aware that manganese dioxide contained a new element, but they were not able to isolate it. Johan Gottlieb Gahn was the first to isolate an impure sample of manganese metal in 1774, by reducing the dioxide with carbon.

The manganese content of some iron ores used in Greece led to the speculations that the steel produced from that ore contains inadvertent amounts of manganese, making the Spartan steel exceptionally hard. (Dell Inspiron 1521 battery)Around the beginning of the 19th century, manganese was used in steelmaking and several patents were granted. In 1816, it was noted that adding manganese to iron made it harder, without making it any more brittle. In 1837, British academic James Couper noted an association between heavy exposures to manganese in mines with a form of Parkinson's disease(Dell inspiron 1525 battery).[16] In 1912, manganese phosphating electrochemical conversion coatings for protecting firearms against rust and corrosion were patented in the United States, and have seen widespread use ever since.[17]

The invention of the Leclanché cell in 1866 and the subsequent improvement of the batteries containing manganese dioxide as cathodic depolarizer increased the demand of manganese dioxide. Until the introduction of the nickel-cadmium battery and lithium-containing batteries(Dell inspiron 1526 battery), most batteries contained manganese. The zinc-carbon battery and the alkaline battery normally use industrially produced manganese dioxide, because natural occurring manganese dioxide contains impurities. In the 20th century, manganese dioxide has seen wide commercial use as the chief cathodic material for commercial disposable dry cells and dry batteries of both the standard (zinc-carbon) and alkaline types. (Dell Inspiron 1720 battery)

[edit]Occurrence and production

See also: Category:Manganese minerals

Manganese makes up about 1000 ppm (0.1%) of the Earth's crust, making it the 12th most abundant element there.[19] Soil contains 7–9000 ppm of manganese with an average of 440 ppm.[19] Seawater has only 10 ppm manganese and the atmosphere contains 0.01 µg/m3.[19] Manganese occurs principally as pyrolusite (MnO2), braunite, (Mn2+Mn3+6)(SiO12),[20] psilomelane (Ba,H2O)2Mn5O10, and to a lesser extent as rhodochrosite (MnCO3) (Dell Inspiron 2000 battery).

The most important manganese ore is pyrolusite (MnO2). Other economically important manganese ores usually show a close spatial relation to the iron ores.[1] Land-based resources are large but irregularly distributed. About 80% of the known world manganese resources are found in South Africa; other important manganese deposits are in Ukraine, Australia, India, China, Gabon and Brazil(Dell INSPIRON 2600 battery).[21] In 1978, 500 billion tons of manganese nodules were estimated to exist on the ocean floor.[22] Attempts to find economically viable methods of harvesting manganese nodules were abandoned in the 1970s.[23]

Manganese is mined in South Africa, Australia, China, Brazil, Gabon, Ukraine, India and Ghana and Kazakhstan. US Import Sources (1998–2001): Manganese ore: Gabon, 70%; South Africa, 10%; Australia, 9%; Mexico, 5%; and other, 6%(Dell INSPIRON 3800 battery). Ferromanganese: South Africa, 47%; France, 22%; Mexico, 8%; Australia, 8%; and other, 15%. Manganese contained in all manganese imports: South Africa, 31%; Gabon, 21%; Australia, 13%; Mexico, 8%; and other, 27%.[21][24]

For the production of ferromanganese, the manganese ore is mixed with iron ore and carbon, and then reduced either in a blast furnace or in an electric arc furnace.[25] The resulting ferromanganese has a manganese content of 30 to 80%(Dell INSPIRON 4000 battery).[1] Pure manganese used for the production of noniron alloys is produced by leaching manganese ore with sulfuric acid and a subsequent electrowinning process.[26]

[edit]Applications

Manganese has no satisfactory substitute in its major applications, which are related to metallurgical alloy use.[21] In minor applications, (e.g., manganese phosphating), zinc and sometimes vanadium are viable substitutes. In disposable battery manufacture, standard and alkaline cells using manganese will be generally replaced in the future with lithium battery technology(Dell Inspiron 5000 battery).

[edit]Steel

US Marine Corps steel helmet

Manganese is essential to iron and steel production by virtue of its sulfur-fixing, deoxidizing, and alloying properties. Steelmaking,[27] including its ironmaking component, has accounted for most manganese demand, presently in the range of 85% to 90% of the total demand.[26] Among a variety of other uses, manganese is a key component of low-cost stainless steel formulations. (Dell INSPIRON 500M battery)

Small amounts of manganese improve the workability of steel at high temperatures, because it forms a high melting sulfide and therefore prevents the formation of a liquid iron sulfide at the grain boundaries. If the manganese content reaches 4%, the embrittlement of the steel becomes a dominant feature. The embrittlement decreases at higher manganese concentrations and reaches an acceptable level at 8%(Dell INSPIRON 5100 battery). Steel containing 8 to 15% of manganese can have a high tensile strength of up to 863 MPa.[29][30] Steel with 12% manganese was used for British steel helmets. This steel composition was discovered in 1882 by Robert Hadfield and is still known as Hadfield steel.[31]

[edit]Aluminium alloys

Main article: Aluminium alloy

The second large application for manganese is as alloying agent for aluminium. Aluminium with a manganese content of roughly 1.5% has an increased resistance against corrosion due to the formation of grains absorbing impurities which would lead to galvanic corrosion(Dell INSPIRON 510M battery).[32] The corrosion-resistant aluminium alloys 3004 and 3104 with a manganese content of 0.8 to 1.5% are the alloys used for most of the beverage cans.[33] Before year 2000, in excess of 1.6 million tonnes have been used of those alloys; with a content of 1% manganese, this amount would need 16,000 tonnes of manganese.[33]

[edit]Other uses

World-War-II-era nickel (1942-5 identified by mint mark P,D or S above dome) made from a 56% copper-35% silver-9% manganese alloy(Dell INSPIRON 6000 battery)

Methylcyclopentadienyl manganese tricarbonyl is used as an additive in unleaded gasoline to boost octane rating and reduce engine knocking. The manganese in this unusual organometallic compound is in the +1 oxidation state.[34]

Manganese(IV) oxide (manganese dioxide, MnO2) is used as a reagent in organic chemistry for the oxidation of benzylic alcohols (i.e. adjacent to an aromatic ring). Manganese dioxide has been used since antiquity to oxidatively neutralize the greenish tinge in glass caused by trace amounts of iron contamination(Dell INSPIRON 600M battery).[13] MnO2 is also used in the manufacture of oxygen and chlorine, and in drying black paints. In some preparations, it is a brown pigment that can be used to make paint and is a constituent of natural umber.

Manganese(IV) oxide was used in the original type of dry cell battery as an electron acceptor from zinc, and is the blackish material found when opening carbon–zinc type flashlight cells. The manganese dioxide is reduced to the manganese oxide-hydroxide MnO(OH) during discharging, preventing the formation of hydrogen at the anode of the batter(Dell Inspiron 6400 battery)y.[35]

MnO2 + H2O + -

e → MnO(OH) + OH−

The same material also functions in newer alkaline batteries (usually battery cells), which use the same basic reaction, but a different electrolyte mixture. In 2002, more than 230,000 tons of manganese dioxide was used for this purpose.[18][35]

The metal is very occasionally used in coins; until 2000, the only United States coin to use manganese was the "wartime" nickel from 1942–1945. (Dell INSPIRON 7000 battery) An alloy of 75% copper and 25% nickel was traditionally used for the production of nickel coins. However, because of shortage of nickel metal during the war, it was substituted by more available silver and manganese, thus resulting in an alloy of 56% copper, 35% silver and 9% manganese. Since 2000, dollar coins, for example the Sacagawea dollar and the Presidential $1 coins, are made from a brass containing 7% of manganese with a pure copper core(Dell INSPIRON 700M battery).[37] In both cases of nickel and dollar, the use of manganese in the coin was to duplicate the electromagnetic properties of a previous identically sized and valued coin, for vending purposes. In the case of the later U.S. dollar coins, the manganese alloy was an attempt to duplicate properties of the copper/nickel alloy used in the previous Susan B. Anthony dollar.

Manganese compounds have been used as pigments and for the coloring of ceramics and glass(Dell Inspiron 710m battery). The brown color of ceramic is sometimes based on manganese compounds.[38] In the glass industry, manganese compounds are used for two effects. Manganese(III) reacts with iron(II) to induce a strong green color in glass by forming less-colored iron(III) and slightly pink manganese(II), compensating for the residual color of the iron(III).[13] Larger amounts of manganese are used to produce pink colored glass(Dell INSPIRON 8200 battery).

[edit]Biological role

Reactive center of arginase with boronic acid inhibitor - the manganese atoms are shown in yellow.

Manganese is an essential trace nutrient in all forms of life.[19] The classes of enzymes that have manganese cofactors are very broad, and include oxidoreductases, transferases, hydrolases, lyases, isomerases, ligases, lectins, and integrins. The reverse transcriptases of many retroviruses (though not lentiviruses such as HIV) contain manganese(Dell INSPIRON 8600 battery). The best-known manganese-containing polypeptides may be arginase, the diphtheria toxin, and Mn-containing superoxide dismutase (Mn-SOD).[39]

Mn-SOD is the type of SOD present in eukaryotic mitochondria, and also in most bacteria (this fact is in keeping with the bacterial-origin theory of mitochondria). The Mn-SOD enzyme is probably one of the most ancient, for nearly all organisms living in the presence of oxygen use it to deal with the toxic effects of superoxide, formed from the 1-electron reduction of dioxygen(Dell INSPIRON 9100 battery). Exceptions include a few kinds of bacteria, such as Lactobacillus plantarum and related lactobacilli, which use a different nonenzymatic mechanism, involving manganese (Mn2+) ions complexed with polyphosphate directly for this task, indicating how this function possibly evolved in aerobic life.

The human body contains about 12 mg of manganese, which is stored mainly in the bones; in the tissue, it is mostly concentrated in the liver and kidneys(Dell INSPIRON 9200 battery).[19] In the human brain, the manganese is bound to manganese metalloproteins, most notably glutamine synthetase in astrocytes.[40]

Manganese is also important in photosynthetic oxygen evolution in chloroplasts in plants. The oxygen-evolving complex (OEC) is a part of photosystem II contained in the thylakoid membranes of chloroplasts; it is responsible for the terminal photooxidation of water during the light reactions of photosynthesis, and has a metalloenzyme core containing four atoms of manganese.[41] For this reason, most broad-spectrum plant fertilizers contain manganese(Dell INSPIRON 9300 battery).

[edit]Precautions

Manganese compounds are less toxic than those of other widespread metals, such as nickel and copper.[42] However, exposure to manganese dusts and fumes should not exceed the ceiling value of 5 mg/m3 even for short periods because of its toxicity level.[43] Manganese poisoning has been linked to impaired motor skills and cognitive disorders(Dell Inspiron 9400 battery).[44]

The permanganate exhibits a higher toxicity than the manganese(II) compounds. The fatal dose is about 10 g, and several fatal intoxications have occurred. The strong oxidative effect leads to necrosis of the mucous membrane. For example, the esophagus is affected if the permanganate is swallowed. Only a limited amount is absorbed by the intestines, but this small amount shows severe effects on the kidneys and on the liver. (Dell Inspiron E1505 battery)

In 2005, a study suggested a possible link between manganese inhalation and central nervous system toxicity in rats.[47]

Manganese exposure in United States is regulated by Occupational Safety and Health Administration.[48]

Generally, exposure to ambient Mn air concentrations in excess of 5 μg Mn/m3 can lead to Mn-induced symptoms. Increased ferroportin protein expression in human embryonic kidney (HEK293) cells is associated with decreased intracellular Mn concentration and attenuated cytotoxicity(Dell Inspiron E1705 battery), characterized by the reversal of Mn-reduced glutamate uptake and diminished lactate dehydrogenase leakage.[49]

[edit]Environmental health concerns

[edit]Manganese in drinking water

Waterborne manganese has a greater bioavailability than dietary manganese. According to results from a 2010 study,[50] higher levels of exposure to manganese in drinking water are associated with increased intellectual impairment and reduced intelligence quotients in school-age children. It is hypothesized that long-term exposure to the naturally occurring manganese in shower water puts up to 8.7 million Americans at risk. (Dell Inspiron Mini 9 battery)

[edit]Manganese in gasoline

Methylcyclopentadienyl manganese tricarbonyl (MMT) is a gasoline additive used to replace lead compounds for unleaded gasolines, to improve the octane number in low octane number petrol distillates. It functions as an antiknock agent by the action of the carbonyl groups. Fuels containing manganese tend to form manganese carbides(Dell Latitude D400 battery), which damage exhaust valves. The need to use lead or manganese compounds is merely historic, as the availability of reformation processes which create high-octane rating fuels increased. The use of such fuels directly or in mixture with non-reformed distillates is universal in developed countries (EU, Japan, etc.) (Dell STUDIO 1450 battery). In USA the imperative to provide the lowest possible price per volume on motor fuels (low fuel taxation rate) and lax legistation of fuel content (before 2000) caused refineries to use MMT. Compared to 1953, levels of manganese in air have dropped.[53] Many racing competitions specifically ban manganese compounds in racing fuel (cart, minibike). MMT contains 24.4-25.2% manganese. There is strong correlation between elevated atmospheric manganese concentrations and automobile traffic density(Dell Vostro 1400 battery).

Role in neurological disorders

Manganism

Manganese overexposure is most frequently associated with manganism, a rare neurological disorder associated with excessive manganese ingestion or inhalation. Historically, persons employed in the production or processing of manganese alloys have been at risk for developing manganism; however, current health and safety regulations protect workers in developed nations. (Dell Vostro 1500 battery) The disorder was first described in 1837 by British academic James Couper, who studied two patients who were manganese grinders.[56]

Manganism is a biphasic disorder. In its early stages, an intoxicated person may experience depression, mood swings, compulsive behaviors, and psychosis. Early neurological symptoms give way to late-stage manganism, which resembles Parkinson's disease(Dell XPS GEN 2 battery). Symptoms include weakness, monotone and slowed speech, an expressionless face, tremor, forward-leaning gait, inability to walk backwards without falling, rigidity, and general problems with dexterity, gait and balance.[56][57] Unlike Parkinson's disease, manganism is not associated with loss of smell and patients are typically unresponsive to treatment with L-DOPA. (Dell XPS M1210 battery) Symptoms of late-stage manganism become more severe over time even if the source of exposure is removed and brain manganese levels return to normal.[57]

[edit]Childhood developmental disorders

Several recent studies attempt to examine the effects of chronic low-dose manganese overexposure on development in children. The earliest study of this kind was conducted in the Chinese province of Shanxi. Drinking water there had been contaminated through improper sewage irrigation and contained 240-350 µg Mn/L(Dell XPS M1330 battery). Although WMn concentrations at or below 300 µg Mn/L are considered safe by the US EPA and 500 µg Mn/L are considered safe by the WHO, the 92 children sampled (between 11 and 13 years of age) from this province displayed lower performance on tests of manual dexterity and rapidity, short-term memory, and visual identification when compared to children from an uncontaminated area(Dell XPS 1340 battery). More recently, a study of 10-year-old children in Bangladesh showed a relationship between WMn concentration in well water and diminished IQ scores. A third study conducted in Quebec examined school children between the ages of 6 and 15 living in homes that received water from a well containing 610 µg Mn/L; controls lived in homes that received water from a 160 µg Mn/L well(Dell XPS M1530 battery). Children in the experimental group showed increased hyperactive and oppositional behaviours.[50]

[edit]Neurodegenerative diseases

Chronic low-dose manganese intoxication is strongly implicated in a number of neurodegenerative disorders, including Alzheimer's disease, Parkinson's disease, and amyotrophic lateral sclerosis. It may also play a role in the development of multiple sclerosis, restless leg syndrome, and Huntington's disease(Dell XPS M170 battery). A protein called DMT1 is the major transporter involved in manganese absorption from the intestine, and may be the major transporter of manganese across the blood-brain barrier. DMT1 also transports inhaled manganese across the nasal epithelium. The putative mechanism of action is that manganese overexposure and/or dysregulation leads to oxidative stress, mitochondrial dysfunction, glutamate-mediated excitoxicity, and aggregates of protein(Dell XPS M1710 battery).

Cobalt ( /ˈkoʊbɒlt/ koh-bolt or /ˈkoʊbɔːlt/ koh-bawlt)[3] is a chemical element with symbol Co and atomic number 27. It is found naturally only in chemically combined form. The free element, produced by reductive smelting, is a hard, lustrous, silver-gray metal.

Cobalt-based blue pigments have been used since ancient times for jewelry and paints, and to impart a distinctive blue tint to glass, but the color was later thought by alchemists to be due to the known metal bismuth(Dell XPS M1730 battery). Miners had long used the name kobold ore (German for goblin ore) for some of the blue-pigment producing minerals; they were named because they were poor in known metals and gave poisonous arsenic-containing fumes upon smelting. In 1735, such ores were found to be reducible to a new metal (the first discovered since ancient times), and this was ultimately named for the kobold(Dell XPS M2010 battery).

Today, some cobalt is produced specifically from various metallic-lustered ores, for example cobaltite (CoAsS), but the main source of the element is as a by-product of copper and nickel mining. The copper belt in the Democratic Republic of the Congo and Zambia yields most of the cobalt metal mined worldwide(Dell Latitude E5400 battery).

Cobalt is used in the preparation of magnetic, wear-resistant and high-strength alloys. Cobalt silicate and cobalt(II) aluminate (CoAl2O4, cobalt blue) give a distinctive deep blue color to glass, smalt, ceramics, inks, paints and varnishes. Cobalt occurs naturally as only one stable isotope, cobalt-59. Cobalt-60 is a commercially important radioisotope, used as a radioactive tracer and in the production of gamma rays(Dell Latitude E5500 battery).

Cobalt is the active center of coenzymes called cobalamins, the most common example of which is vitamin B12. As such it is an essential trace dietary mineral for all animals. Cobalt in inorganic form is also an active nutrient for bacteria, algae and fungi.

Characteristics

A block of electrolytically refined cobalt (99.9% purity) cut from a large plate

Cobalt is a ferromagnetic metal with a specific gravity of 8.9. Pure cobalt is not found in nature, but compounds of cobalt are common(Dell Latitude E6400 battery). Small amounts of it are found in most rocks, soil, plants and animals. The Curie temperature is 1115 °C[4] and the magnetic moment is 1.6–1.7 Bohr magnetons per atom.[5] In nature, it is frequently associated with nickel, and both are characteristic minor components of meteoric iron. Cobalt has a relative permeability two thirds that of iron.[6] Metallic cobalt occurs as two crystallographic structures(Dell Latitude E6500 battery): hcp and fcc. The ideal transition temperature between the hcp and fcc structures is 450 °C, but in practice, the energy difference is so small that random intergrowth of the two is common.[7][8][9]

Cobalt is a weakly reducing metal that is protected from oxidation by a passivating oxide film. It is attacked by halogens and sulfur. Heating in oxygen produces Co3O4 which loses oxygen at 900 °C to give the monoxide CoO. (Dell Inspiron Mini 12 battery)

[edit]Compounds

See also Category: Cobalt compounds

Common oxidation states of cobalt include +2 and +3, although compounds with oxidation states ranging from −3 to +4 are also known. A common oxidation state for simple compounds is +2. Cobalt(II) salts form the red-pink [Co(H2O)6]2+ complex in aqueous solution. Addition of chloride gives the intensely blue [CoCl4]2−.(Dell XPS M140 battery)

[edit]Oxygen and chalcogen compounds

Several oxides of cobalt are known. Green cobalt(II) oxide (CoO) has rocksalt structure. It is readily oxidized with water and oxygen to brown cobalt(III) hydroxide (Co(OH)3). At temperatures of 600–700 °C, CoO oxidizes to the blue cobalt(II,III) oxide (Co3O4), which has a spinel structure.[2] Black cobalt(III) oxide (Co2O3) is also known.[11] Cobalt oxides are antiferromagnetic at low temperature(Dell XPS 13 battery): CoO (Neel temperature 291 K) and Co3O4 (Neel temperature: 40 K), which is analogous to magnetite (Fe3O4), with a mixture of +2 and +3 oxidation states.[12]

The principal chalcogenides of cobalt include the black cobalt(II) sulfides, CoS2, which adopts a pyrite-like structure, and Co2S3. Pentlandite (Co9S8) is metal-rich.[2]

[edit]Halides

Cobalt(II) chloride hexahydrate

Four dihalides of cobalt(II) are known: cobalt(II) fluoride (CoF2, pink), cobalt(II) chloride (CoCl2, blue), cobalt(II) bromide (CoBr2, green), cobalt(II) iodide (CoI2, blue-black). These halides exist in anhydrous and hydrated forms(Dell XPS 16 battery). Whereas the anhydrous dichloride is blue, the hydrate is red.[13]

The reduction potential for the reaction

Co3+ + -

e → Co2+

is +1.92 V, beyond that for chlorine to chloride, +1.36 V. As a consequence cobalt(III) and chloride would result in the cobalt(III) being reduced to cobalt(II). Because the reduction potential for fluorine to fluoride is so high, +2.87 V, cobalt(III) fluoride is one of the few simple stable cobalt(III) compounds. Cobalt(III) fluoride, which is used in some fluorination reactions, reacts vigorously with water. (Dell XPS 1640 battery)

[edit]Coordination compounds

As for all metals, molecular compounds of cobalt are classified as coordination complexes, that is molecules or ions that contain cobalt linked to several ligands. The principles of electronegativity and hardness–softness of a series of ligands can be used to explain the usual oxidation state of the cobalt. For example Co+3 complexes tend to have ammine ligands(Dell XPS 1645 battery). As phosphorus is softer than nitrogen, phosphine ligands tend to feature the softer Co2+ and Co+, an example being tris(triphenylphosphine)cobalt(I) chloride ((P(C6H5)3)3CoCl). The more electronegative (and harder) oxide and fluoride can stabilize Co4+ derivatives, e.g. caesium hexafluorocobaltate (Cs2CoF6) and potassium percobaltate (K3CoO4). (Dell XPS 1647 battery)

Alfred Werner, a Nobel-prize winning pioneer in coordination chemistry, worked with compounds of empirical formula CoCl3(NH3)6. One of the isomers determined was cobalt(III) hexammine chloride. This coordination complex, a "typical" Werner-type complex, consists of a central cobalt atom coordinated by six ammine ligands orthogonal to each other and three chloride counteranions(Dell Latitude 131L battery). Using chelating ethylenediamine ligands in place of ammonia gives tris(ethylenediamine)cobalt(III) chloride ([Co(en)3]Cl3), which was one of the first coordination complexes that was resolved into optical isomers. The complex exists as both either right- or left-handed forms of a "three-bladed propeller". This complex was first isolated by Werner as yellow-gold needle-like crystals. (Dell Latitude C400 battery)

[edit]Organometallic compounds

Main article: Organocobalt chemistry

Cobaltocene is a structural analog to ferrocene, where cobalt substitutes for iron. Cobaltocene is sensitive to oxidation, much more than ferrocene.[16] Cobalt carbonyl (Co2(CO)8) is a catalyst in carbonylation reactions.[17] Vitamin B12 (see below) is an organometallic compound found in nature and is the only vitamin to contain a metal atom. (Dell Latitude C500 battery)

[edit]Isotopes

Main article: Isotopes of cobalt

59Co is the only stable cobalt isotope and the only isotope to exist in nature. 22 radioisotopes have been characterized with the most stable being 60Co with a half-life of 5.2714 years, 57Co with a half-life of 271.79 days, 56Co with a half-life of 77.27 days, and 58Co with a half-life of 70.86 days. All of the remaining radioactive isotopes have half-lives that are shorter than 18 hours, and the majority of these are shorter than 1 second(Dell Latitude C510 battery). This element also has 4 meta states, all of which have half-lives shorter than 15 minutes.[19]

The isotopes of cobalt range in atomic weight from 50 u (50Co) to 73 u (73Co). The primary decay mode for isotopes with atomic mass unit values less than that of the most abundant stable isotope, 59Co, is electron capture and the primary mode of decay for those of greater than 59 atomic mass units is beta decay. The primary decay products before 59Co are element 26 (iron) isotopes and the primary products after are element 28 (nickel) isotopes. (Dell Latitude C540 battery)

[edit]History

Early Chinese blue and white porcelain, manufactured circa 1335

Cobalt compounds have been used for centuries to impart a rich blue color to glass, glazes and ceramics. Cobalt has been detected in Egyptian sculpture and Persian jewelry from the third millennium BC, in the ruins of Pompeii (destroyed in 79 AD), and in China dating from the Tang dynasty (618–907 AD) and the Ming dynasty (1368–1644 AD). (Dell Latitude C600 battery)

Cobalt has been used to color glass since the Bronze Age. The excavation of the Uluburun shipwreck yielded an ingot of blue glass, which was cast during the 14th century BC.[21][22] Blue glass items from Egypt are colored with copper, iron, or cobalt. The oldest cobalt-colored glass was from the time of the Eighteenth dynasty in Egypt (1550–1292 BC). The location where the cobalt compounds were obtained is unknown. (Dell Latitude C610 battery)

The word cobalt is derived from the German kobalt, from kobold meaning "goblin", a superstitious term used for the ore of cobalt by miners. The first attempts at smelting these ores to produce metals such as copper or nickel failed, yielding simply powder (cobalt(II) oxide) instead. Also, because the primary ores of cobalt always contain arsenic(Dell Latitude C640 battery), smelting the ore oxidized the arsenic content into the highly toxic and volatile arsenic oxide, which also decreased the reputation of the ore for the miners.[25]

Swedish chemist Georg Brandt (1694–1768) is credited with discovering cobalt circa 1735, showing it to be a new previously unknown element different from bismuth and other traditional metals, and calling it a new "semi-metal."[26][27] He was able to show that compounds of cobalt metal were the source of the blue color in glass(Dell Latitude C800 battery), which previously had been attributed to the bismuth found with cobalt. Cobalt became the first metal to be discovered since the pre-historical period, during which all the known metals (iron, copper, silver, gold, zinc, mercury, tin, lead and bismuth) had no recorded discoverers.[28]

During the 19th century, a significant part of the world's production of cobalt blue (a dye made with cobalt compounds and alumina) and smalt (cobalt glass powdered for use for pigment purposes in ceramics and painting) was carried out at the Norwegian Blaafarveværket. (Dell Latitude C810 battery) The first mines for the production of smalt in the 16th to 18th century were located in Norway, Sweden, Saxony and Hungary. With the discovery of cobalt ore in New Caledonia in 1864 the mining of cobalt in Europe declined. With the discovery of ore deposits in Ontario, Canada in 1904 and the discovery of even larger deposits in the Katanga Province in the Congo in 1914 the mining operations shifted again(Dell Latitude C840 battery).[25] With the Shaba conflict starting in the 1978 the main source for cobalt the copper mines of Katanga Province nearly stopped their production.[31][32] The impact on the world cobalt economy from this conflict was smaller than expected, because industry established effective ways for recycling cobalt materials and in some cases was able to change to cobalt-free alternatives. (Dell Latitude CPI battery)

In 1938, John Livingood and Glenn T. Seaborg discovered cobalt-60.[33] This isotope was famously used at Columbia University in the 1950s to establish parity violation in radioactive beta decay.[34][35]

After World War Two, the US wanted to be sure it was never short of the ore needed for cobalt like the German's were and went exploring for a supply with the US border. A good supply of the ore needed was found in Idaho near Blackbird canyon in the side of a mountain(Dell Latitude D410 battery). The firm Calera Mining Company got production started at the site. [36]

[edit]Occurrence

The stable form of cobalt is created in supernovas via the r-process.[37] It comprises 0.0029% of the Earth's crust and is one of the first transition metal series.

Cobalt occurs in copper and nickel minerals and in combination with sulfur and arsenic in the sulfidic cobaltite (CoAsS), safflorite (CoAs2) and skutterudite (CoAs3) minerals.[10] The mineral cattierite is similar to pyrite and occurs together with vaesite in the copper deposits of the Katanga Province. (Dell Latitude D420 battery)Upon contact with the atmosphere, weathering occurs and the sulfide minerals oxidize to form pink erythrite ("cobalt glance": Co3(AsO4)2·8H2O) and sphaerocobaltite (CoCO3).[39][40]

Cobalt is not found as a native metal but is mainly obtained as a by-product of nickel and copper mining activities. The main ores of cobalt are cobaltite, erythrite, glaucodot and skutterudite(Dell Latitude D430 battery).

[edit]Production

Cobalt ore

Cobalt output in 2005

World production trend

See also: Cobalt extraction techniques

In 2005, the copper deposits in the Katanga Province (former Shaba province) of the Democratic Republic of the Congo were the top producer of cobalt with almost 40% world share, reports the British Geological Survey.[43] The political situation in the Congo influences the price of cobalt significantly. (Dell Latitude D500 battery)

The Mukondo Mountain project, operated by the Central African Mining and Exploration Company in Katanga, may be the richest cobalt reserve in the world. It is estimated to be able to produce about one third of total global production of cobalt in 2008.[45] In July 2009 CAMEC announced a long term agreement under which CAMEC would deliver its entire annual production of cobalt in concentrate from Mukondo Mountain to Zhejiang Galico Cobalt & Nickel Materials of China. (Dell Latitude D505 battery)

Several methods exist for the separation of cobalt from copper and nickel. They depend on the concentration of cobalt and the exact composition of the used ore. One separation step involves froth flotation, in which surfactants bind to different ore components, leading to an enrichment of cobalt ores. Subsequent roasting converts the ores to the cobalt sulfate(Dell Latitude D510 battery), whereas the copper and the iron are oxidized to the oxide. The leaching with water extracts the sulfate together with the arsenates. The residues are further leached with sulfuric acid yielding a solution of copper sulfate. Cobalt can also be leached from the slag of the copper smelter.[47]

The products of the above-mentioned processes are transformed into the cobalt oxide (Co3O4). This oxide is reduced to the metal by the aluminothermic reaction or reduction with carbon in a blast furnace(Dell Latitude D520 battery).[10]

[edit]Applications

The main application of cobalt is as the metal in alloys.[41][42]

[edit]Alloys

Cobalt-based superalloys consume most of the produced cobalt.[41][42] The temperature stability of these alloys makes them suitable for use in turbine blades for gas turbines and jet aircraft engines, though nickel-based single crystal alloys surpass them in this regard.[48] Cobalt-based alloys are also corrosion and wear-resistant(Dell Latitude D600 battery). This makes them useful in the medical field, where cobalt is often used (along with titanium) for orthopedic implants that do not wear down over time. The development of the wear-resistant cobalt alloys started in the first decade of the 19th century with the stellite alloys, which are cobalt-chromium alloys with varying tungsten and carbon content. The formation of chromium and tungsten carbides makes them very hard and wear resistant(Dell Latitude D610 battery).[49] Special cobalt-chromium-molybdenum alloys like Vitallium are used for prosthetic parts such as hip and knee replacements.[50] Cobalt alloys are also used for dental prosthetics, where they are useful to avoid allergies to nickel.[51] Some high speed steels also use cobalt to increase heat and wear-resistance. The special alloys of aluminium, nickel, cobalt and iron, known as Alnico(Dell Latitude D620 battery), and of samarium and cobalt (samarium-cobalt magnet) are used in permanent magnets.[52] It is also alloyed with 95% platinum for jewelry purposes, yielding an alloy that is suitable for fine detailed casting and is also slightly magnetic.[53]

[edit]Batteries

Lithium cobalt oxide (LiCoO2) is widely used in lithium ion battery cathodes. The material is composed of cobalt oxide layers in which the lithium is intercalated. During discharging the lithium intercalated between the layers is set free as lithium ion(Dell Latitude D630 battery).[54] Nickel-cadmium [55] (NiCd) and nickel metal hydride[56] (NiMH) batteries also contain significant amounts of cobalt; the cobalt improves the oxidation capabilities of nickel in the battery.[55]

[edit]Catalysis

Several cobalt compounds are used in chemical reactions as oxidation catalysts. Cobalt acetate is used for the conversion of xylene to terephthalic acid, the precursor to the bulk polymer polyethylene terephthalate(Dell Latitude D800 battery). Typical catalysts are the cobalt carboxylates (known as cobalt soaps). They are also used in paints, varnishes, and inks as "drying agents" through the oxidation of drying oils.[54] The same carboxylates are used to improve the adhesion of the steel to rubber in steel-belted radial tires.

Cobalt-based catalysts are also important in reactions involving carbon monoxide. Steam reforming, useful in hydrogen production, uses cobalt oxide-base catalysts. Cobalt is also a catalyst in the Fischer–Tropsch process(Dell Latitude D810 battery), used in the hydrogenation of carbon monoxide into liquid fuels.[57] The hydroformylation of alkenes often rely on cobalt octacarbonyl as the catalyst,[58] although such processes have been partially displaced by more efficient iridium- and rhodium-based catalysts, e.g. the Cativa process.

The hydrodesulfurization of petroleum uses a catalyst derived from cobalt and molybdenum. This process helps to rid petroleum of sulfur impurities that interfere with the refining of liquid fuels. (Dell Latitude D820 battery)

[edit]Pigments and coloring

Cobalt blue glass

Cobalt-colored glass

Before the 19th century, the predominant use of cobalt was as pigment. Since the Middle Ages, it has been involved in the production of smalt, a blue colored glass. Smalt is produced by melting a mixture of the roasted mineral smaltite, quartz and potassium carbonate, yielding a dark blue silicate glass which is ground after the production(Dell Latitude D830 battery).[59] Smalt was widely used for the coloration of glass and as pigment for paintings.[60] In 1780, Sven Rinman discovered cobalt green and in 1802 Louis Jacques Thénard discovered cobalt blue.[61] The two varieties of cobalt blue, cobalt aluminate and cobalt green (a mixture of cobalt(II) oxide and zinc oxide), were used as pigments for paintings because of their superior stability. (Dell Latitude 2100 battery)

[edit]Radioisotopes

Cobalt-60 (Co-60 or 60Co) is useful as a gamma ray source because it can be produced in predictable quantity and high activity by bombarding cobalt with neutrons. It produces two gamma rays with energies of 1.17 and 1.33 MeV.[19][64]

Its uses include external beam radiotherapy, sterilization of medical supplies and medical waste, radiation treatment of foods for sterilization (cold pasteurization),[65] industrial radiography (e.g. weld integrity radiographs) (Dell Latitude 2110 battery), density measurements (e.g. concrete density measurements), and tank fill height switches. The metal has the unfortunate habit of producing a fine dust, causing problems with radiation protection. Cobalt from radiotherapy machines has been a serious hazard when not disposed of properly, and one of the worst radiation contamination accidents in North America occurred in 1984(Dell Latitude E4300 battery), after a discarded radiotherapy unit containing cobalt-60 was mistakenly disassembled in a junkyard in Juarez, Mexico.[66][67]

Cobalt-60 has a radioactive half-life of 5.27 years. This decrease in activity requires periodic replacement of the sources used in radiotherapy and is one reason why cobalt machines have been largely replaced by linear accelerators in modern radiation therapy.[68]

Cobalt-57 (Co-57 or 57Co) is a cobalt radioisotope most often used in medical tests, as a radiolabel for vitamin B12 uptake(Dell Vostro 1310 battery), and for the Schilling test. Cobalt-57 is used as a source in Mössbauer spectroscopy and is one of several possible sources in X-ray fluorescence devices.[69][70]

Nuclear weapon designs could intentionally incorporate 59Co, some of which would be activated in a nuclear explosion to produce 60Co. The 60Co, dispersed as nuclear fallout, creates what is sometimes called a cobalt bomb. (Dell Vostro 1320 battery)

[edit]Other uses

Other uses of cobalt are in electroplating, owing to its attractive appearance, hardness and resistance to oxidation,[72] and as ground coats for porcelain enamels.[73]

[edit]Biological role

Cobalt is essential to all animals, including humans. It is a key constituent of cobalamin, also known as vitamin B12, which is the primary biological reservoir of cobalt as an "ultratrace" element. Bacteria in the guts of ruminant animals convert cobalt salts into vitamin B12(Dell Vostro 1510 battery), a compound which can only be produced by bacteria. The minimum presence of cobalt in soils therefore markedly improves the health of grazing animals, and an uptake of 0.20 mg/kg a day is recommended for them, as they can obtain vitamin B12 in no other way.[74] In the early 20th century during the development for farming of the North Island Volcanic Plateau of New Zealand(Dell Vostro 1520 battery), cattle suffered from what was termed "bush sickness". It was discovered that the volcanic soils lacked cobalt salts, which was necessary for cattle.[75] The ailment was cured by adding small amounts of cobalt to fertilisers.

Non-ruminant herbivores produce vitamin B12 from bacteria in their colons which again make the vitamin from simple cobalt salts. However the vitamin cannot be absorbed from the colon(Dell Vostro 2510 battery), and thus non-ruminants must ingest feces to obtain the nutrient. Animals that do not follow these methods of getting vitamin B12 from their own gastrointestinal bacteria or that of other animals, must obtain the vitamin pre-made in other animal products in their diet, and they cannot benefit from ingesting simple cobalt salts.

The cobalamin-based proteins use corrin to hold the cobalt(Dell Vostro 1014 battery). Coenzyme B12 features a reactive C-Co bond, which participates in its reactions.[76] In humans, B12 exists with two types of alkyl ligand: methyl and adenosyl. MeB12 promotes methyl (-CH3) group transfers. The adenosyl version of B12 catalyzes rearrangements in which a hydrogen atom is directly transferred between two adjacent atoms with concomitant exchange of the second substituent, X, which may be a carbon atom with substituents(Dell Inspiron 1410 battery), an oxygen atom of an alcohol, or an amine. Methylmalonyl coenzyme A mutase (MUT) converts MMl-CoA to Su-CoA, an important step in the extraction of energy from proteins and fats.[77]

Although far less common than other metalloproteins (e.g. those of zinc and iron), cobaltoproteins are known aside from B12. These proteins include methionine aminopeptidase 2 an enzyme that occurs in humans and other mammals which does not use the corrin ring of B12(Dell Vostro 1014N battery), but binds cobalt directly. Another non-corrin cobalt enzyme is nitrile hydratase, an enzyme in bacteria that are able to metabolize nitriles.[78]

[edit]Precautions

Main article: Cobalt poisoning

Cobalt is an essential element for life in minute amounts. The LD50 value for soluble cobalt salts has been estimated to be between 150 and 500 mg/kg. Thus, for a 100 kg person the LD50 would be about 20 grams(Dell Vostro 1015 battery).[79]

After nickel and chromium, cobalt is a major cause of contact dermatitis.[80] In 1966, the addition of cobalt compounds to stabilize beer foam in Canada led to cardiomyopathy, which came to be known as beer drinker's cardiomyopathy. (Dell Vostro A840 battery)

 
Titanium is a chemical element with the symbol Ti and atomic number 22. It has a low density and is a strong, lustrous, corrosion-resistant (including sea water, aqua regia and chlorine) transition metal with a silver color. Sony VAIO VPCF135Z1E/B battery

Titanium was discovered in Cornwall, Great Britain, by William Gregor in 1791 and named by Martin Heinrich Klaproth for the Titans of Greek mythology. The element occurs within a number of mineral deposits, principally rutile and ilmenite, which are widely distributed in the Earth's crust and lithosphere, and it is found in almost all living things, rocks, water bodies, and soilsSony VAIO VPCF137HG/BI battery.[2] The metal is extracted from its principal mineral ores via the Kroll process[3] or the Hunter process. Its most common compound, titanium dioxide, is a popular photocatalyst and is used in the manufacture of white pigments.[4] Other compounds include titanium tetrachloride (TiCl4), a component of smoke screens and catalysts; and titanium trichloride (TiCl3), which is used as a catalyst in the production of polypropyleneSony VAIO VPCF136FG/BI battery.[2]

Titanium can be alloyed with iron, aluminium, vanadium, molybdenum, among other elements, to produce strong lightweight alloys for aerospace (jet engines, missiles, and spacecraft), military, industrial process (chemicals and petro-chemicals, desalination plants, pulp, and paper), automotive, agri-food, medical prostheses, orthopedic implants, dental and endodontic instruments and filesSony VAIO VPCF135FG/B battery, dental implants, sporting goods, jewelry, mobile phones, and other applications.[2]

The two most useful properties of the metal form are corrosion resistance and the highest strength-to-weight ratio of any metal.[5] In its unalloyed condition, titanium is as strong as some steels, but 45% lighter.[6] There are two allotropic forms[7] and five naturally occurring isotopes of this element, 46Ti through 50Ti, with 48Ti being the most abundant (73.8%).Sony VAIO VPCF127HG/BI battery Titanium's properties are chemically and physically similar to zirconium, because both of them have the same number of valence electrons and are in the same group in the periodic table.

Characteristics

[edit]Physical properties

A metallic element, titanium is recognized for its high strength-to-weight ratio.[7] It is a strong metal with low density that is quite ductile (especially in an oxygen-free environment),[2] lustrous, and metallic-white in color.[9] The relatively high melting point (more than 1,650 °C or 3,000 °F) makes it useful as a refractory metal. It is paramagnetic and has fairly low electrical and thermal conductivity. Sony VAIO VPCF11Z1E battery

Commercial (99.2% pure) grades of titanium have ultimate tensile strength of about 63,000 psi (434 MPa), equal to that of common, low-grade steel alloys, but are 45% lighter.[6] Titanium is 60% more dense than aluminium, but more than twice as strong[6] as the most commonly used 6061-T6 aluminium alloy. Certain titanium alloys (e.g., Beta C) achieve tensile strengths of over 200,000 psi (1,400 MPa). Sony VAIO VPCF11S1E battery However, titanium loses strength when heated above 430 °C (806 °F).[11]

It is fairly hard (although not as hard as some grades of heat-treated steel), non-magnetic and a poor conductor of heat and electricity. Machining requires precautions, as the material will soften and gall if sharp tools and proper cooling methods are not used. Like those made from steel, titanium structures have a fatigue limit which guarantees longevity in some applicationsSony VAIO VPCF11M1E/H battery.[9] Titanium alloys specific stiffnesses are also usually not as good as other materials such as aluminium alloys and carbon fiber, so it is used less for structures which require high rigidity.

The metal is a dimorphic allotrope whose hexagonal alpha form changes into a body-centered cubic (lattice) β form at 882 °C (1,620 °F).[11] The specific heat of the alpha form increases dramatically as it is heated to this transition temperature but then falls and remains fairly constant for the β form regardless of temperatureSony VAIO VPCF11M1E battery.[11] Similar to zirconium and hafnium, an additional omega phase exists, which is thermodynamically stable at high pressures, but is metastable at ambient pressures. This phase is usually hexagonal (ideal) or trigonal (distorted) and can be viewed as being due to a soft longitudinal acoustic phonon of the β phase causing collapse of (111) planes of atoms.[12]

[edit]Chemical properties

The Pourbaix diagram for titanium in pure water, perchloric acid or sodium hydroxideSony VAIO VPCF11JFX/B battery

The most noted chemical property of titanium is its excellent resistance to corrosion; it is almost as resistant as platinum, capable of withstanding attack by dilute sulfuric acid and hydrochloric acid as well as chlorine gas, chloride solutions, and most organic acids.[3] However, it is soluble in concentrated acids.[14] The Pourbaix diagram in the image shows that titanium is actually thermodynamically a very reactive metalSony VAIO VPCF119FJ battery.

However, it is slow to react with water and air, because it forms a passive and protective oxide coating that protects it from further reaction.[2] When it first forms, this protective layer is only 1–2 nm thick but continues to slowly grow; reaching a thickness of 25 nm in four years.[15]

Titanium readily reacts with oxygen at 1,200 °C (2,190 °F) in air, and at 610 °C (1,130 °F) in pure oxygen, forming titanium dioxideSony VAIO VPCF119FC/BI battery.[7] As a result, the metal cannot be melted in open air since it burns before the melting point is reached. Melting is only possible in an inert atmosphere or in a vacuum. At 550 °C (1,022 °F), it combines with chlorine.[3] It also reacts with the other halogens and absorbs hydrogen.[4]

Titanium is one of the few elements that burns in pure nitrogen gas, reacting at 800 °C (1,470 °F) to form titanium nitride, which causes embrittlementSony VAIO VPCF119FC battery.[16]

Experiments have shown that natural titanium becomes radioactive after it is bombarded with deuterons, emitting mainly positrons and hard gamma rays.[3]

[edit]Compounds

See also categories: Titanium compounds and Titanium minerals

TiN coated drill bit

The +4 oxidation state dominates titanium chemistry,[17] but compounds in the +3 oxidation state are also common.[18] Because of this high oxidation state, many titanium compounds have a high degree of covalent bondingSony VAIO VPCF117HG/BI battery.

Star sapphires and rubies get their asterism from the titanium dioxide impurities present in them.[15] Titanates are compounds made with titanium dioxide. Barium titanate has piezoelectric properties, thus making it possible to use it as a transducer in the interconversion of sound and electricity.[7] Esters of titanium are formed by the reaction of alcohols and titanium tetrachloride and are used to waterproof fabrics. Sony VAIO VPCF116FG/BI battery

Titanium nitride (TiN), having a hardness equivalent to sapphire and carborundum (9.0 on the Mohs Scale),[19] is often used to coat cutting tools, such as drill bits.[20] It also finds use as a gold-colored decorative finish, and as a barrier metal in semiconductor fabrication.[21]

Titanium tetrachloride (titanium(IV) chloride, TiCl4, sometimes called "tickle"[22]) is a colorless liquid which is used as an intermediate in the manufacture of titanium dioxide for paintSony VAIO VPCF115FG/B battery.[23] It is widely used in organic chemistry as a Lewis acid, for example in the Mukaiyama aldol condensation.[24] Titanium also forms a lower chloride, titanium(III) chloride (TiCl3), which is used as a reducing agent.[25]

Titanocene dichloride is an important catalyst for carbon-carbon bond formation. Titanium isopropoxide is used for Sharpless epoxidation. Other compounds include titanium bromide (used in metallurgy, superalloys, and high-temperature electrical wiring and coatings) and titanium carbide (found in high-temperature cutting tools and coatings) Sony VAIO VPCF21ZHJ battery.[4]

[edit]Occurrence

Titanium is always bonded to other elements in nature. It is the ninth-most abundant element in the Earth's crust (0.63% by mass)[27] and the seventh-most abundant metal. It is present in most igneous rocks and in sediments derived from them (as well as in living things and natural bodies of water).[2][3] Of the 801 types of igneous rocks analyzed by the United States Geological Survey, 784 contained titaniumSony VAIO VPCF21Z1E/BI battery.[27] Its proportion in soils is approximately 0.5 to 1.5%.[27]

It is widely distributed and occurs primarily in the minerals anatase, brookite, ilmenite, perovskite, rutile, titanite (sphene), as well in many iron ores.[15] Of these minerals, only rutile and ilmenite have any economic importance, yet even they are difficult to find in high concentrations. Significant titanium-bearing ilmenite deposits exist in western AustraliaSony VAIO VPCF21AHJ battery, Canada, China, India, Mozambique, New Zealand, Norway, and Ukraine.[15] Large quantities of rutile are also mined in North America and South Africa and help contribute to the annual production of 90,000 tonnes of the metal and 4.3 million tonnes of titanium dioxide.[15] Total reserves of titanium are estimated to exceed 600 million tonnesSony VAIO VPCF21AGJ battery.[15]

Titanium is contained in meteorites and has been detected in the sun and in M-type stars;[3] the coolest type of star with a surface temperature of 3,200 °C (5,790 °F).[28] Rocks brought back from the moon during the Apollo 17 mission are composed of 12.1% TiO2.[3] It is also found in coal ash, plants, and even the human bodySony VAIO VPCF21AFJ battery.

[edit]Isotopes

Main article: Isotopes of titanium

Naturally occurring titanium is composed of 5 stable isotopes: 46Ti, 47Ti, 48Ti, 49Ti, and 50Ti, with 48Ti being the most abundant (73.8% natural abundance). Eleven radioisotopes have been characterized, with the most stable being 44Ti with a half-life of 63 years, 45Ti with a half-life of 184.8 minutes, 51Ti with a half-life of 5.76 minutes, and 52Ti with a half-life of 1.7 minutesSony VAIO VPCF219FJ/BI battery. All of the remaining radioactive isotopes have half-lives that are less than 33 seconds and the majority of these have half-lives that are less than half a second.[8]

The isotopes of titanium range in atomic weight from 39.99 u (40Ti) to 57.966 u (58Ti). The primary decay mode before the most abundant stable isotope, 48Ti, is electron capture and the primary mode after is beta emission. The primary decay products before 48Ti are element 21 (scandium) isotopes and the primary products after are element 23 (vanadium) isotopesSony VAIO VPCF217HG/BI battery.[8]

[edit]History

Martin Heinrich Klaproth named titanium for the Titans of Greek mythology.

Titanium was discovered included in a mineral in Cornwall, United Kingdom, in 1791 by amateur geologist and pastor William Gregor, then vicar of Creed parish.[29] He recognized the presence of a new element in ilmenite[4] when he found black sand by a stream in the nearby parish of Manaccan and noticed the sand was attracted by a magnetSony VAIO VPCF217HG battery.[29] Analysis of the sand determined the presence of two metal oxides; iron oxide (explaining the attraction to the magnet) and 45.25% of a white metallic oxide he could not identify.[27] Gregor, realizing that the unidentified oxide contained a metal that did not match the properties of any known element, reported his findings to the Royal Geological Society of Cornwall and in the German science journal Crell's AnnalenSony VAIO VPCF14ZHJ battery.[29]

Around the same time, Franz-Joseph Müller von Reichenstein produced a similar substance, but could not identify it.[4] The oxide was independently rediscovered in 1795 by German chemist Martin Heinrich Klaproth in rutile from Hungary.[29] Klaproth found that it contained a new element and named it for the Titans of Greek mythology.[28] After hearing about Gregor's earlier discovery, he obtained a sample of manaccanite and confirmed it contained titaniumSony VAIO VPCF14AHJ battery.

The processes required to extract titanium from its various ores are laborious and costly; it is not possible to reduce in the normal manner, by heating in the presence of carbon, because that produces titanium carbide.[29] Pure metallic titanium (99.9%) was first prepared in 1910 by Matthew A. Hunter at Rensselaer Polytechnic Institute by heating TiCl4 with sodium at 700–800 °C in the Hunter processSony VAIO VPCF14AGJ battery.[3] Titanium metal was not used outside the laboratory until 1932 when William Justin Kroll proved that it could be produced by reducing titanium tetrachloride (TiCl4) with calcium.[30] Eight years later he refined this process by using magnesium and even sodium in what became known as the Kroll process.[30] Although research continues into more efficient and cheaper processes (e.g., FFC Cambridge), the Kroll process is still used for commercial productionSony VAIO VPCF14AFJ battery.

Titanium sponge, made by the Kroll process

Titanium of very high purity was made in small quantities when Anton Eduard van Arkel and Jan Hendrik de Boer discovered the iodide, or crystal bar, process in 1925, by reacting with iodine and decomposing the formed vapors over a hot filament to pure metal.[31]

In the 1950s and 1960s the Soviet Union pioneered the use of titanium in military and submarine applications (Alfa Class and Mike Class)[32] as part of programs related to the Cold WarSony VAIO VPCF149FJ/BI battery.[33] Starting in the early 1950s, titanium began to be used extensively for military aviation purposes, particularly in high-performance jets, starting with aircraft such as the F100 Super Sabre and Lockheed A-12.

In the USA, the Department of Defense realized the strategic importance of the metal[34] and supported early efforts of commercialization.[35] Throughout the period of the Cold War, titanium was considered a Strategic Material by the U.S. governmentSony VAIO VPCF148FJ/B battery, and a large stockpile of titanium sponge was maintained by the Defense National Stockpile Center, which was finally depleted in 2005.[36] Today, the world's largest producer, Russian-based VSMPO-Avisma, is estimated to account for about 29% of the world market share.[37]

In 2006, the U.S. Defense Agency awarded $5.7 million to a two-company consortium to develop a new process for making titanium metal powder. Under heat and pressure, the powder can be used to create strong, lightweight items ranging from armor plating to components for the aerospace, transport, and chemical processing industries. Sony VAIO VPCF13ZHJ battery

Production and fabrication

Titanium (mineral concentrate)

The processing of titanium metal occurs in 4 major steps:[39] reduction of titanium ore into "sponge", a porous form; melting of sponge, or sponge plus a master alloy to form an ingot; primary fabrication, where an ingot is converted into general mill products such as billet, bar, plate, sheet, strip, and tube; and secondary fabrication of finished shapes from mill productsSony VAIO VPCF13Z0E/B battery.

Because the metal reacts with oxygen at high temperatures it cannot be produced by reduction of its dioxide.[9] Titanium metal is therefore produced commercially by the Kroll process, a complex and expensive batch process. (The relatively high market value of titanium is mainly due to its processing, which sacrifices another expensive metal, magnesiumSony VAIO VPCF13M8E/B battery.[40]) In the Kroll process, the oxide is first converted to chloride through carbochlorination, whereby chlorine gas is passed over red-hot rutile or ilmenite in the presence of carbon to make TiCl4. This is condensed and purified by fractional distillation and then reduced with 800 °C molten magnesium in an argon atmosphere.[7]

A more recently developed method, the FFC Cambridge process,[41] may eventually replace the Kroll processSony VAIO VPCF13AHJ battery. This method uses titanium dioxide powder (which is a refined form of rutile) as feedstock to make the end product which is either a powder or sponge. If mixed oxide powders are used, the product is an alloy manufactured at a much lower cost than the conventional multi-step melting process. The FFC Cambridge process may render titanium a less rare and expensive material for the aerospace industry and the luxury goods marketSony VAIO VPCF13AGJ battery, and could be seen in many products currently manufactured using aluminium and specialist grades of steel.

Common titanium alloys are made by reduction. For example, cuprotitanium (rutile with copper added is reduced), ferrocarbon titanium (ilmenite reduced with coke in an electric furnace), and manganotitanium (rutile with manganese or manganese oxides) are reduced.[42]

2 FeTiO3 + 7 Cl2 + 6 C → 2 TiCl4 + 2 FeCl3 + 6 CO (900 °C)

TiCl4 + 2 Mg → 2 MgCl2 + Ti (1100 °C) Sony VAIO VPCF13AFJ battery

About 50 grades of titanium and titanium alloys are designated and currently used, although only a couple of dozen are readily available commercially.[43] The ASTM International recognizes 31 Grades of titanium metal and alloys, of which Grades 1 through 4 are commercially pure (unalloyed). These four are distinguished by their varying degrees of tensile strengthSony VAIO VPCF138FJ/BI battery, as a function of oxygen content, with Grade 1 being the most ductile (lowest tensile strength with an oxygen content of 0.18%), and Grade 4 the least (highest tensile strength with an oxygen content of 0.40%).[15] The remaining grades are alloys, each designed for specific purposes, be it ductility, strength, hardness, electrical resistivity, creep resistance, resistance to corrosion from specific media, or a combination thereofSony VAIO VPCF138FJ/B battery.[44]

The grades covered by ASTM and other alloys are also produced to meet Aerospace and Military specifications (SAE-AMS, MIL-T), ISO standards, and country-specific specifications, as well as proprietary end-user specifications for aerospace, military, medical, and industrial applications. Sony VAIO VPCF138FC/BI battery

In terms of fabrication, all welding of titanium must be done in an inert atmosphere of argon or helium in order to shield it from contamination with atmospheric gases such as oxygen, nitrogen, or hydrogen.[11] Contamination will cause a variety of conditions, such as embrittlement, which will reduce the integrity of the assembly welds and lead to joint failureSony VAIO VPCF135FG battery. Commercially pure flat product (sheet, plate) can be formed readily, but processing must take into account the fact that the metal has a "memory" and tends to spring back. This is especially true of certain high-strength alloys.[46][47] Titanium cannot be soldered without first pre-plating it in a metal that is solderable.[48] The metal can be machined using the same equipment and via the same processes as stainless steelSony VAIO VPCF12AHJ battery.[11]

[edit]Applications

A titanium cylinder, "Grade 2" quality

Titanium is used in steel as an alloying element (ferro-titanium) to reduce grain size and as a deoxidizer, and in stainless steel to reduce carbon content.[2] Titanium is often alloyed with aluminium (to refine grain size), vanadium, copper (to harden), iron, manganese, molybdenum, and with other metals.[49] Applications for titanium mill products (sheet, plate, bar, wire, forgings, castings) can be found in industrial, aerospace, recreational, and emerging marketsSony VAIO VPCF12AGJ battery. Powdered titanium is used in pyrotechnics as a source of bright-burning particles.

Pigments, additives and coatings

Titanium dioxide is the most commonly used compound of titanium

About 95% of titanium ore extracted from the Earth is destined for refinement into titanium dioxide (TiO2), an intensely white permanent pigment used in paints, paper, toothpaste, and plastics.[50] It is also used in cement, in gemstones, as an optical opacifier in paper,[51] and a strengthening agent in graphite composite fishing rods and golf clubsSony VAIO VPCF12AFJ battery.

TiO2 powder is chemically inert, resists fading in sunlight, and is very opaque: this allows it to impart a pure and brilliant white color to the brown or gray chemicals that form the majority of household plastics.[4] In nature, this compound is found in the minerals anatase, brookite, and rutile.[2] Paint made with titanium dioxide does well in severe temperaturesSony VAIO VPCF129FJ/BI battery, and stands up to marine environments.[4] Pure titanium dioxide has a very high index of refraction and an optical dispersion higher than diamond.[3] In addition to being a very important pigment, titanium dioxide is also used in sunscreens due to its ability to protect skin by itself.[9] Recently, titanium oxide has been put to use in air purifiers (as a filter coating), or in film used to coat windows on buildings so that when titanium oxide becomes exposed to UV lightSony VAIO VPCF128FJ/B battery (either solar or artificial) and moisture in the air, reactive redox species like hydroxyl radicals are produced so that they can purify the air or keep window surfaces clean.[52]

[edit]Aerospace and marine

Due to their high tensile strength to density ratio,[7] high corrosion resistance,[3] fatigue resistance, high crack resistance,[53] and ability to withstand moderately high temperatures without creeping, titanium alloys are used in aircraft, armor plating, naval ships, spacecraftSony VAIO VPCF127FJ/W battery, and missiles.[3][4] For these applications titanium alloyed with aluminium, vanadium, and other elements is used for a variety of components including critical structural parts, fire walls, landing gear, exhaust ducts (helicopters), and hydraulic systems. In fact, about two thirds of all titanium metal produced is used in aircraft engines and frames.[54] The SR-71 "Blackbird" was one of the first aircraft to make extensive use of titanium within its structureSony VAIO VPCF11ZHJ battery, paving the way for its use in modern military and commercial aircraft. An estimated 59 metric tons (130,000 pounds) are used in the Boeing 777, 45 in the Boeing 747, 18 in the Boeing 737, 32 in the Airbus A340, 18 in the Airbus A330, and 12 in the Airbus A320. The Airbus A380 may use 146 metric tons, including about 26 tons in the engines.[55] In engine applications, titanium is used for rotors, compressor blades, hydraulic system components, and nacellesSony VAIO VPCF11AHJ battery. The titanium 6AL-4V alloy accounts for almost 50% of all alloys used in aircraft applications.[56]

Due to its high corrosion resistance to sea water, titanium is used to make propeller shafts and rigging and in the heat exchangers of desalination plants;[3] in heater-chillers for salt water aquariums, fishing line and leader, and for divers' knives. Titanium is used to manufacture the housings and other components of ocean-deployed surveillance and monitoring devices for scientific and military useSony VAIO VPCF11AGJ battery. The former Soviet Union developed techniques for making submarines largely out of titanium.[57]

[edit]Industrial

High-purity (99.999%) titanium with visible crystal structure

Welded titanium pipe and process equipment (heat exchangers, tanks, process vessels, valves) are used in the chemical and petrochemical industries primarily for corrosion resistance. Specific alloys are used in downhole and nickel hydrometallurgy applications due to their high strength (e. g.: titanium Beta C alloy), corrosion resistance, or combination of bothSony VAIO VPCF11AFJ battery. The pulp and paper industry uses titanium in process equipment exposed to corrosive media such as sodium hypochlorite or wet chlorine gas (in the bleachery).[58] Other applications include: ultrasonic welding, wave soldering,[59] and sputtering targets.[60]

Titanium tetrachloride (TiCl4), a colorless liquid, is important as an intermediate in the process of making TiO2 and is also used to produce the Ziegler-Natta catalyst, and is used to iridize glass and because it fumes strongly in moist air it is also used to make smoke screensSony VAIO VPCF118FJ battery.[9]

[edit]Consumer and architectural

Titanium metal is used in automotive applications, particularly in automobile or motorcycle racing, where weight reduction is critical while maintaining high strength and rigidity.[61] The metal is generally too expensive to make it marketable to the general consumer market, other than high-end products, particularly for the racing/performance market. Late model Corvettes have been available with titanium exhaustsSony VAIO VPCF117FJ battery.[62]

Titanium is used in many sporting goods: tennis rackets, golf clubs, lacrosse stick shafts; cricket, hockey, lacrosse, and football helmet grills; and bicycle frames and components. Although not a mainstream material for bicycle production, titanium bikes have been used by race teams and adventure cyclists.[63] Titanium alloys are also used in spectacle framesSony VAIO VGN-CS33H battery.[64] This results in a rather expensive, but highly durable and long lasting frame which is light in weight and causes no skin allergies. Many backpackers use titanium equipment, including cookware, eating utensils, lanterns, and tent stakes.[64] Though slightly more expensive than traditional steel or aluminium alternatives, these titanium products can be significantly lighter without compromising strength. Titanium is also favored for use by farriers, since it is lighter and more durable than steel when formed into horseshoesSony VAIO VGN-CS33H/Z battery.[64]

Titanium has occasionally been used in architectural applications: the 40 m (131 foot) memorial to Yuri Gagarin, the first man to travel in space, in Moscow, is made of titanium for the metal's attractive color and association with rocketry.[65] The Guggenheim Museum Bilbao and the Cerritos Millennium Library were the first buildings in Europe and North AmericaSony VAIO VGN-CS33H/B battery, respectively, to be sheathed in titanium panels.[54] Other construction uses of titanium sheathing include the Frederic C. Hamilton Building in Denver, Colorado[66] and the 107 m (350 foot) Monument to the Conquerors of Space in Moscow.[67]

Because of its superior strength and light weight when compared to other metals traditionally used in firearms (steel, stainless steel, and aluminium), and advances in metalworking techniques, the use of titanium has become more widespread in the manufacture of firearmsSony VAIO VGN-CS31Z/Q battery. Primary uses include pistol frames and revolver cylinders. For these same reasons, it is also used in the body of laptop computers (for example, in Apple's PowerBook line).[68]

Some upmarket categories of tools made to be lightweight and corrosion-resistant, such as shovels and flashlights, are made of titanium or titanium alloys as well.

[edit]Jewelry

Because of its durability, titanium has become more popular for designer jewelry (particularly, titanium rings).[64] Its inertness makes it a good choice for those with allergies or those who will be wearing the jewelry in environments such as swimming poolsSony VAIO VGN-CS31S/W battery. Titanium is also alloyed with gold to produce an alloy that can be marketed as 24-carat gold, as the 1% of alloyed Ti is insufficient to require a lesser mark. The resulting alloy is roughly the hardness of 14-carat gold and thus is more durable than a pure 24-carat gold item would be.[69]

Titanium's durability, light weight, dent- and corrosion resistance makes it useful in the production of watch cases.[64] Some artists work with titanium to produce artworks such as sculptures, decorative objects and furnitureSony VAIO VGN-CS31S/V battery.[70]

The inertness and ability to be attractively colored makes titanium a popular metal for use in body piercing.[71] Titanium may be anodized to produce various colors, which varies the thickness of the surface oxide layer and causes interference fringes.[72]

[edit]Medical

Because it is biocompatible (non-toxic and is not rejected by the body), titanium is used in a gamut of medical applications including surgical implements and implants, such as hip balls and sockets (joint replacement) that can stay in place for up to 20 yearsSony VAIO VGN-CS31S/T battery.[29] The titanium is often alloyed with about 4% aluminium[73] or 6% Al and 4% vanadium.

Titanium has the inherent property to osseointegrate, enabling use in dental implants that can remain in place for over 30 years. This property is also useful for orthopedic implant applications.[29] These benefit from titanium's lower modulus of elasticity (Young's modulus) to more closely match that of the bone that such devices are intended to repairSony VAIO VGN-CS31S/R battery. As a result, skeletal loads are more evenly shared between bone and implant, leading to a lower incidence of bone degradation due to stress shielding and periprosthetic bone fractures which occur at the boundaries of orthopedic implants. However, titanium alloys' stiffness is still more than twice that of bone so adjacent bone bears a greatly reduced load and may deteriorateSony VAIO VGN-CS31S/P battery.[74]

Since titanium is non-ferromagnetic, patients with titanium implants can be safely examined with magnetic resonance imaging (convenient for long-term implants). Preparing titanium for implantation in the body involves subjecting it to a high-temperature plasma arc which removes the surface atoms, exposing fresh titanium that is instantly oxidizedSony VAIO VGN-CS28 battery.[29]

Titanium is also used for the surgical instruments used in image-guided surgery, as well as wheelchairs, crutches, and any other products where high strength and low weight are desirable.

Precautions

Nettle contains up to 80 parts per million of titanium.

Titanium is non-toxic even in large doses and does not play any natural role inside the human body.[28] An estimated quantity of 0.8 milligrams of titanium is ingested by humans each day, but most passes through without being absorbedSony VAIO VGN-CS28/Q battery.[28] It does, however, have a tendency to bio-accumulate in tissues that contain silica. An unknown mechanism in plants may use titanium to stimulate the production of carbohydrates and encourage growth. This may explain why most plants contain about 1 part per million (ppm) of titanium, food plants have about 2 ppm, and horsetail and nettle contain up to 80 ppmSony VAIO VGN-CS27 battery.[28]

As a powder or in the form of metal shavings, titanium metal poses a significant fire hazard and, when heated in air, an explosion hazard.[75] Water and carbon dioxide–based methods to extinguish fires are ineffective on burning titanium; Class D dry powder fire fighting agents must be used insteadSony VAIO VGN-CS27/W battery.[4]

When used in the production or handling of chlorine, care must be taken to use titanium only in locations where it will not be exposed to dry chlorine gas which can result in a titanium/chlorine fire.[76] A fire hazard exists even when titanium is used in wet chlorine due to possible unexpected drying brought about by extreme weather conditionsSony VAIO VGN-CS27/R battery.

Titanium can catch fire when a fresh, non-oxidized surface comes in contact with liquid oxygen.[77] Such surfaces can appear when the oxidized surface is struck with a hard object, or when a mechanical strain causes the emergence of a crack. This poses the possible limitation for its use in liquid oxygen systems, such as those found in the aerospace industrySony VAIO VGN-CS27/P battery.

Chromium ( /ˈkroʊmiəm/ kroh-mee-əm) is a chemical element which has the symbol Cr and atomic number 24. It is the first element in Group 6. It is a steely-gray, lustrous, hard metal that takes a high polish and has a high melting point. It is also odorless, tasteless, and malleable. The name of the element is derived from the Greek word "chrōma" (χρώμα) Sony VAIO VGN-CS27/C battery, meaning colour,[2] because many of its compounds are intensely coloured. Chromium oxide was used by the Chinese in the Qin dynasty over 2,000 years ago to coat weapons such as bronze crossbow bolts and steel swords found at the Terracotta Army. It later came to the attention of the West when it was discovered by Louis Nicolas Vauquelin in the mineral crocoite (lead(II) chromate) in 1797Sony VAIO VGN-CS26T/W battery. Crocoite was used as a pigment, and after the discovery that the mineral chromite also contains chromium, this mineral was used to produce pigments as well.

Chromium was regarded with great interest because of its high corrosion resistance and hardness. A major development was the discovery that steel could be made highly resistant to corrosion and discoloration by adding chromium to form stainless steel. This application, along with chrome plating Sony VAIO VGN-CS26T/V battery (electroplating with chromium) are currently the highest-volume uses of the metal. Chromium and ferrochromium are produced from the single commercially viable ore, chromite, by silicothermic or aluminothermic reaction or by roasting and leaching processes.

Although trivalent chromium (Cr(III)) is required in trace amounts for sugar and lipid metabolism, few cases have been reported where its complete removal from the diet has caused chromium deficiency. In larger amounts and in different forms, chromium can be toxic and carcinogenicSony VAIO VGN-CS26T/T battery. The most prominent example of toxic chromium is hexavalent chromium (Cr(VI)). Abandoned chromium production sites often require environmental cleanup.

Characteristics

[edit]Physical

Chromium is remarkable for its magnetic properties: it is the only elemental solid which shows antiferromagnetic ordering at room temperature (and below). Above 38 °C, it transforms into a paramagnetic state.[1]

[edit]Passivation

Chromium metal left standing in air is passivated by oxygen, forming a thin protective oxide surface layer. This layer is a spinel structure only a few atoms thickSony VAIO VGN-CS26T/R battery. It is very dense, and prevents the diffusion of oxygen into the underlying material. This barrier is in contrast to iron or plain carbon steels, where the oxygen migrates into the underlying material and causes rusting.[3] The passivation can be enhanced by short contact with oxidizing acids like nitric acid. Passivated chromium is stable against acidsSony VAIO VGN-CS26T/Q battery. The opposite effect can be achieved by treatment with a strong reducing agent that destroys the protective oxide layer on the metal. Chromium metal treated in this way readily dissolves in weak acids.[4]

Chromium, unlike metals such as iron and nickel, does not suffer from hydrogen embrittlement. However, it does suffer from nitrogen embrittlement, reacting with nitrogen from air and forming brittle nitrides at the high temperatures necessary to work the metal partsSony VAIO VGN-CS26T/P battery.[5]

[edit]Occurrence

Crocoite (PbCrO4)

Chromite ore

Chromium is the 21st most abundant element in Earth's crust with an average concentration of 100 ppm.[6] Chromium compounds are found in the environment, due to erosion of chromium-containing rocks and can be distributed by volcanic eruptions. The concentrations range in soil is between 1 and 3000 mg/kg, in sea water 5 to 800 µg/literSony VAIO VGN-CS26T/C battery, and in rivers and lakes 26 µg/liter to 5.2 mg/liter.[7] Chromium is mined as chromite (FeCr2O4) ore.[8] About two-fifths of the chromite ores and concentrates in the world are produced in South Africa, while Kazakhstan, India, Russia, and Turkey are also substantial producers. Untapped chromite deposits are plentiful, but geographically concentrated in Kazakhstan and southern AfricaSony VAIO VGN-CS25H battery.[9]

Although rare, deposits of native chromium exist.[10][11] The Udachnaya Pipe in Russia produces samples of the native metal. This mine is a kimberlite pipe, rich in diamonds, and the reducing environment helped produce both elemental chromium and diamond.[12]

The relation between Cr(III) and Cr(VI) strongly depends on pH and oxidative properties of the location, but in most cases, the Cr(III) is the dominating speciesSony VAIO VGN-CS25H/W battery,[7] although in some areas the ground water can contain up to 39 µg/liter of total chromium of which 30 µg/liter is present as Cr(VI).[13]

Isotopes

Main article: Isotopes of chromium

Naturally occurring chromium is composed of three stable isotopes; 52Cr, 53Cr and 54Cr with 52Cr being the most abundant (83.789% natural abundance). 19 radioisotopes have been characterized with the most stable being 50Cr with a half-life of (more than) 1.8×1017 years, and 51Cr with a half-life of 27.7 daysSony VAIO VGN-CS25H/R battery. All of the remaining radioactive isotopes have half-lives that are less than 24 hours and the majority of these have half-lives that are less than 1 minute. This element also has 2 meta states.[14]

53Cr is the radiogenic decay product of 53Mn. Chromium isotopic contents are typically combined with manganese isotopic contents and have found application in isotope geology. Mn-Cr isotope ratios reinforce the evidence from 26Al and 107Pd for the early history of the solar systemSony VAIO VGN-CS25H/Q battery. Variations in 53Cr/52Cr and Mn/Cr ratios from several meteorites indicate an initial 53Mn/55Mn ratio that suggests Mn-Cr isotopic composition must result from in-situ decay of 53Mn in differentiated planetary bodies. Hence 53Cr provides additional evidence for nucleosynthetic processes immediately before coalescence of the solar systemSony VAIO VGN-CS25H/P battery.[15]

The isotopes of chromium range in atomic mass from 43 u (43Cr) to 67 u (67Cr). The primary decay mode before the most abundant stable isotope, 52Cr, is electron capture and the primary mode after is beta decay.[14] 53Cr has been posited as a proxy for atmospheric oxygen concentrationSony VAIO VGN-CS25H/C battery.[16]

[edit]Compounds

Chromium is a member of the transition metals, in group 6. Chromium(0) has an electronic configuration of 4s13d5, owing to the lower energy of the high spin configuration. Chromium exhibits a wide range of possible oxidation states, where the +3 state is most stable energetically; the +3 and +6 states are most commonly observed in chromium compounds, whereas the +1, +4 and +5 states are rareSony VAIO VGN-CS23T/W battery.[17]

The following is the Pourbaix diagram for chromium in pure water, perchloric acid or sodium hydroxide:[7][18]

Chromium(III)

Chromium(III) chloride hexahydrate ([CrCl2(H2O)4]Cl·2H2O)

Anhydrous chromium(III) chloride (CrCl3)

A large number of chromium(III) compounds are known. Chromium(III) can be obtained by dissolving elemental chromium in acids like hydrochloric acid or sulfuric acid. The Cr3+ ion has a similar radius (63 pm) to the Al3+ ion (radius 50 pm), so they can replace each other in some compounds, such as in chrome alum and alum. When a trace amount of Cr3+ replaces Al3+ in corundum (aluminium oxide, Al2O3), the red-colored ruby is formedSony VAIO VGN-CS23T/Q battery.

Chromium(III) ions tend to form octahedral complexes. The colors of these complexes is determined by the ligands attached to the Cr centre. The commercially available chromium(III) chloride hydrate is the dark green complex [CrCl2(H2O)4]Cl. Closely related compounds have different colours: pale green [CrCl(H2O)5]Cl2 and the violet [Cr(H2O)6]Cl3Sony VAIO VGN-CS23H battery. If water-free green chromium(III) chloride is dissolved in water then the green solution turns violet after some time, due to the substitution of water by chloride in the inner coordination sphere. This kind of reaction is also observed with solutions of chrome alum and other water-soluble chromium(III) saltsSony VAIO VGN-CS23H/S battery.

Chromium(III) hydroxide (Cr(OH)3) is amphoteric, dissolving in acidic solutions to form [Cr(H2O)6]3+, and in basic solutions to form [Cr(OH)6]3−. It is dehydrated by heating to form the green chromium(III) oxide (Cr2O3), which is the stable oxide with a crystal structure identical to that of corundumSony VAIO VGN-CS23H/B battery.[4]

[edit]Chromium(VI)

Chromium(VI) oxide

Chromium(VI) compounds are powerful oxidants at low or neutral pH. Most important are chromate anion (CrO2−

4) and dichromate (Cr2O72-) anions, which exist in equilibrium:

2 [CrO4]2- + 2 H+  [Cr2O7]2- + 2 H2O

Chromium(VI) halides are known also and include hexafluoride CrF6 and chromyl chloride (CrO2Cl2).[4]

Sodium chromate is produced industrially by the oxidative roasting of chromite ore with calcium or sodium carbonateSony VAIO VGN-CS23G battery. The dominant species is therefore, by the law of mass action, determined by the pH of the solution. The change in equilibrium is visible by a change from yellow (chromate) to orange (dichromate), such as when an acid is added to a neutral solution of potassium chromate. At yet lower pH values, further condensation to more complex oxyanions of chromium is possibleSony VAIO VGN-CS23G/W battery.

Both the chromate and dichromate anions are strong oxidizing reagents at low pH:[4]

Sodium chromate (Na2CrO4)

Cr2O2−

7 + 14 H3O+ + 6 e− → 2 Cr3+ + 21 H2O (ε0 = 1.33 V)

They are, however, only moderately oxidizing at high pH:[4]

CrO2−

4 + 4 H2O + 3 e− → Cr(OH)3 + 5 OH− (ε0 = −0.13 V)

Chromium(VI) compounds in solution can be detected by adding an acidic hydrogen peroxide solution. The unstable dark blue chromium(VI) peroxide (CrO5) is formed, which can be stabilized as an ether adduct CrO5·OR2.[4]

Chromic acid has the hypothetical formula H2CrO4. It is a vaguely described chemical, despite many well-defined chromates and dichromates are known. The dark red chromium(VI) oxide CrO3, the acid anhydride of chromic acid, is sold industrially as "chromic acid".Sony VAIO VGN-CS23G/Q battery It can be produced by mixing sulfuric acid with dichromate, and is a strong oxidizing agent.

[edit]Chromium(V) and chromium(IV)

The oxidation state +5 is only realized in few compounds but are intermediates in many reactions involving oxidations by chromate. The only binary compound is the volatile chromium(V) fluoride (CrF5). This red solid has a melting point of 30 °C and a boiling point of 117 °C. It can be synthesized by treating chromium metal with fluorine at 400 °C and 200 bar pressureSony VAIO VGN-CS23G/P battery. The peroxochromate(V) is another example of the +5 oxidation state. Potassium peroxochromate (K3[Cr(O2)4]) is made by reacting potassium chromate with hydrogen peroxide at low temperatures. This red brown compound is stable at room temperature but decomposes spontaneously at 150–170 °C.[19]

Compounds of chromium(IV) (in the +4 oxidation state) are slightly more common than those of chromium(V) Sony VAIO VGN-CS21Z/Q battery. The tetrahalides, CrF4, CrCl4, and CrBr4, can be produced by treating the trihalides (CrX3) with the corresponding halogen at elevated temperatures. Such compounds are susceptible to disproportionation reactions and are not stable in water.

[edit]Chromium(II) and chromium(I)

Many chromium(II) compounds are known, including the water-stable chromium(II) chloride, CrCl2, which can be made by reduction of chromium(III) chloride with zinc. The resulting bright blue solution is only stable at neutral pH.[4] Many chromous carboxylates are also known, most famously, the red chromous acetate (Cr2(O2CCH3)4), which features a quadruple bondSony VAIO VGN-CS21S/W battery.

[edit]Chromium(I)

Most Cr(I) compounds are obtained by oxidation of electron-rich, octahedral Cr(0) complexes. Other Cr(I) complexes contain cyclopentadienyl ligands. As verified by X-ray diffraction, a Cr-Cr quintuple bond (length 183.51(4)  pm) has also been described.[20] Extremely bulky monodentate ligands stabilize this compound by shielding the quintuple bond from further reactionsSony VAIO VGN-CS21S/V battery.

Chromium compound determined experimentally to contain a Cr-Cr quintuple bond

[edit]Chromium(0) and chromium(I)

Main article: organochromium chemistry

Many chromium(0) compounds are known. Most are derivatives of chromium hexacarbonyl or bis(benzene)chromium.

[edit]History

Weapons found in burial pits dating from the late 3rd century BC Qin Dynasty of the Terracotta Army near Xi'an, China have been analyzed by archaeologists. Although buried more than 2,000 years ago, the ancient bronze tips of crossbow bolts and swords found at the site showed no sign of corrosion, because the bronze was coated with chromiumSony VAIO VGN-CS21S/T battery.[21]

Chromium later came to the attention of westerners in the 18th century. On 26 July 1761, Johann Gottlob Lehmann found an orange-red mineral in the Beryozovskoye mines in the Ural Mountains which he named Siberian red lead. Though misidentified as a lead compound with selenium and iron components, the mineral was Crocoite (lead chromate) with a formula of PbCrO4Sony VAIO VGN-CS21S/R battery.[22]

In 1770, Peter Simon Pallas visited the same site as Lehmann and found a red lead mineral that had useful properties as a pigment in paints. The use of Siberian red lead as a paint pigment developed rapidly. A bright yellow pigment made from crocoite also became fashionable.[22]

The red colour of rubies is from a small amount of chromium(III) Sony VAIO VGN-CS21S/P battery.

In 1797, Louis Nicolas Vauquelin received samples of crocoite ore. He produced chromium trioxide (CrO3) by mixing crocoite with hydrochloric acid. In 1798, Vauquelin discovered that he could isolate metallic chromium by heating the oxide in a charcoal oven.[23] He was also able to detect traces of chromium in precious gemstones, such as ruby or emerald. Sony VAIO VGN-CS215J/R battery

During the 1800s, chromium was primarily used as a component of paints and in tanning salts. At first, crocoite from Russia was the main source, but in 1827, a larger chromite deposit was discovered near Baltimore, United States. This made the United States the largest producer of chromium products till 1848 when large deposits of chromite where found near Bursa, TurkeySony VAIO VGN-CS215J/Q battery.[8]

Chromium is also known for its luster when polished. It is used as a protective and decorative coating on car parts, plumbing fixtures, furniture parts and many other items, usually applied by electroplating. Chromium was used for electroplating as early as 1848, but this use only became widespread with the development of an improved process in 1924Sony VAIO VGN-CS19/W battery.[25]

Metal alloys now account for 85% of the use of chromium. The remainder is used in the chemical industry and refractory and foundry industries.

[edit]Production

Approximately 4.4 million metric tons of marketable chromite ore were produced in 2000, and converted into ~3.3 million tons of ferro-chrome with an approximate market value of 2.5 billion United States dollars.[26] The largest producers of chromium ore have been South Africa (44%) India (18%), Kazakhstan (16%) Zimbabwe (5%), Finland (4%) Iran (4%) and Brazil (2%) with several other countries producing the rest of less than 10% of the world productionSony VAIO VGN-CS19/R battery.[26]

The two main products of chromium ore refining are ferrochromium and metallic chromium. For those products the ore smelter process differs considerably. For the production of ferrochromium, the chromite ore (FeCr2O4) is reduced in large scale in electric arc furnace or in smaller smelters with either aluminium or silicon in an aluminothermic reactionSony VAIO VGN-CS19/Q battery.[27]

Chromium ore output in 2002[26]

For the production of pure chromium, the iron has to be separated from the chromium in a two step roasting and leaching process. The chromite ore is heated with a mixture of calcium carbonate and sodium carbonate in the presence of air. The chromium is oxidized to the hexavalent form, while the iron forms the stable Fe2O3Sony VAIO VGN-CS19/P battery. The subsequent leaching at higher elevated temperatures dissolves the chromates and leaves the insoluble iron oxide. The chromate is converted by sulfuric acid into the dichromate.[27]

4 FeCr2O4 + 8 Na2CO3 + 7 O2 → 8 Na2CrO4 + 2 Fe2O3 + 8 CO2

2 Na2CrO4 + H2SO4 → Na2Cr2O7 + Na2SO4 + H2O

The dichromate is converted to the chromium(III) oxide by reduction with carbon and then reduced in an aluminothermic reaction to chromium.[27]

Na2Cr2O7 + 2 C → Cr2O3 + Na2CO3 + CO

Cr2O3 + 2 Al → Al2O3 + 2 Cr

Applications

Metallurgy

Decorative chrome plating on a motorcycle.

The strengthening effect of forming stable metal carbides at the grain boundaries and the strong increase in corrosion resistance made chromium an important alloying material for steel. The high speed tool steels contain between 3 and 5% chromium. Stainless steelSony VAIO VGN-CS17H/W battery, the main corrosion-proof metal alloy, is formed when chromium is added to iron in sufficient concentrations, usually above 11%. For its formation, ferrochromium is added to the molten iron. Also nickel-based alloys increase in strength due to the formation of discrete, stable metal carbide particles at the grain boundaries. For example, Inconel 718 contains 18.6% chromiumSony VAIO VGN-CS17H/Q battery. Because of the excellent high temperature properties of these nickel superalloys, they are used in jet engines and gas turbines in lieu of common structural materials.[28]

The relative high hardness and corrosion resistance of unalloyed chromium makes it a good surface coating, being still the most "popular" metal coating with unparalleled combined durability. A thin layer of chromium is deposited on pretreated metallic surfaces by electroplating techniques. There are two deposition methods: Thin, below 1 µm thicknessSony VAIO VGN-CS16T/W battery, layers are deposited by chrome plating, and are used for decorative surfaces. If wear-resistant surfaces are needed then thicker chromium layers are deposited. Both methods normally use acidic chromate or dichromate solutions. To prevent the energy consuming change in oxidation state, the use of Chromium(III) sulfate is under development, but for most applications, the established process is usedSony VAIO VGN-CS16T/T battery.[25]

In the chromate conversion coating process, the strong oxidative properties of chromates are used to deposit a protective oxide layer on metals like aluminium, zinc and cadmium. This passivation and the self healing properties by the chromate stored in the chromate conversion coating, which is able to migrate to local defects, are the benefits of this coating methodSony VAIO VGN-CS16T/R battery.[29] Because of environmental and health regulations on chromates, alternative coating method are under development.[30]

Anodizing of aluminium is another electrochemical process, which does not lead to the deposition of chromium, but uses chromic acid as electrolyte in the solution. During anodization, an oxide layer is formed on the aluminium. The use of chromic acid, instead of the normally used sulfuric acid, leads to a slight difference of these oxide layersSony VAIO VGN-CS16T/Q battery.[31] The high toxicity of Cr(VI) compounds, used in the established chromium electroplating process, and the strengthening of safety and environmental regulations demand a search for substitutes for chromium or at least a change to less toxic chromium(III) compounds.[25]

[edit]Dye and pigment

School bus painted in chrome yellow[32]

The mineral crocoite (lead chromate PbCrO4) was used as a yellow pigment shortly after its discoverySony VAIO VGN-CS16T/P battery. After a synthesis method became available starting from the more abundant chromite, chrome yellow was, together with cadmium yellow, one of the most used yellow pigments. The pigment does not photo degrade but it tends to darken due to the formation of chromium(III) oxide. It has a strong color, and was used for school buses in the US and for Postal Service (for example Deutsche Post) in EuropeSony VAIO VGN-CS13T/W battery. The use of chrome yellow declined due to environmental and safety concerns and was replaced by organic pigments or alternatives free from lead and chromium. Other pigments based on chromium are, for example, the bright red pigment chrome red, which is a basic lead chromate (PbCrO4·Pb(OH)2). A very important chromate pigment, which was used widely in metal primer formulations was zinc chromateSony VAIO VGN-CS13H/W battery, now replaced by zinc phosphate. A wash primer was formulated to replace the dangerous practice of pretreating aluminium aircraft bodies with a phosphoric acid solution. This used zinc tetroxychromate dispersed in a solution of polyvinyl butyral. An 8% solution of phosphoric acid in solvent was added just before applicationSony VAIO VGN-CS13H/R battery. It was found that an easily oxidized alcohol was an essential ingredient. A thin layer of about 10–15 microns was applied, which turned from yellow to dark green when it was cured. There is still a question as to the correct mechanism. Chrome green is a mixture of Prussian blue and chrome yellow, while the chrome oxide green is Chromium(III) oxide.[33]

A red color is achieved by doping chromium(III) into the crystals of corundum, which are then called ruby. Therefore, chromium is used in producing synthetic rubiesSony VAIO VGN-CS13H/Q battery.[34]

Chromium oxides are also used as a green color in glassmaking and as a glaze in ceramics.[35] Green chromium oxide is extremely light-fast and as such is used in cladding coatings. It is also the main ingredient in IR reflecting paints, used by the armed forces, to paint vehicles, to give them the same IR reflectance as green leavesSony VAIO VGN-CS13H/P battery.[36]

[edit]Wood preservative

Because of their toxicity, chromium(VI) salts are used for the preservation of wood. For example, chromated copper arsenate (CCA) is used in timber treatment to protect wood from decay fungi, wood attacking insects, including termites, and marine borers.[37] The formulations contain chromium based on the oxide CrO3 between 35.3% and 65.5%. In the United States, 65,300 metric tons of CCA solution have been used in 1996Sony VAIO VGN-CS11Z/T battery.[37]

[edit]Tanning

Main article: Tanning

Chromium(III) salts, especially chrome alum and chromium(III) sulfate, are used in the tanning of leather. The chromium(III) stabilizes the leather by cross linking the collagen fibers.[38] Chromium tanned leather can contain between 4 and 5% of chromium, which is tightly bound to the proteins.[8] Although the form of chromium used for tanning is not the toxic hexavalent varietySony VAIO VGN-CS11Z/R battery, there remains interest in management of chromium in the tanning industry such as recovery and reuse, direct/indirect recycling,[39] use of less chromium or "chrome-less" tanning are practiced to better manage chromium in tanning.

[edit]Refractory material

The high heat resistivity and high melting point makes chromite and chromium(III) oxide a material for high temperature refractory applications, like blast furnaces, cement kilns, molds for the firing of bricks and as foundry sands for the casting of metalsSony VAIO VGN-CS11S/W battery. In these applications, the refractory materials are made from mixtures of chromite and magnesite. The use is declining because of the environmental regulations due to the possibility of the formation of chromium(VI).[27]

[edit]Catalysts

Several chromium compounds are used as catalysts for processing hydrocarbons. For example the Phillips catalysts for the production of polyethylene are mixtures of chromium and silicon dioxide or mixtures of chromium and titanium and aluminium oxide.[40] Fe-Cr mixed oxides are employed as high-temperature catalysts for the water gas shift reaction. Copper chromite is a useful hydrogenation catalystSony VAIO VGN-CS11S/Q battery.[43]

[edit]Other use

Chromium(IV) oxide (CrO2) is a magnetic compound. Its ideal shape anisotropy, which imparts high coercivity and remnant magnetization, made it a compound superior to the γ-Fe2O3. Chromium(IV) oxide is used to manufacture magnetic tape used in high-performance audio tape and standard audio cassettes.[44] Chromates can prevent corrosion of steel under wet conditions, and therefore chromates are added to drilling muds. Sony VAIO VGN-CS11S/P battery

Chromium(III) oxide is a metal polish known as green rouge.

Chromic acid is a powerful oxidizing agent and is a useful compound for cleaning laboratory glassware of any trace of organic compounds. It is prepared in situ by dissolving potassium dichromate in concentrated sulfuric acid, which is then used to wash the apparatus. Sodium dichromate is sometimes used because of its higher solubility (50 g/L versus 200 g/L respectively) (Sony VAIO VGN-AW11M/H battery). Potassium dichromate is a chemical reagent, used in cleaning laboratory glassware and as a titrating agent. It is also used as a mordant (i.e., a fixing agent) for dyes in fabric.

[edit]Biological role

Chromium has no verified biological role and has been classified as not essential for mammals.[46] (Cr(III) or Cr3+) occurs in trace amounts and appears to be benign.[47] Chromium deficiency is controversial or is at least extremely rare. It has been attributed to only three people on parenteral nutrition(Sony VAIO VGN-AW11S/B battery), which is when a patient is fed a liquid diet through intravenous drips.[48] In contrast, hexavalent chromium (Cr(VI) or Cr6+) is very toxic and mutagenic when inhaled. Cr(VI) has not been established as a carcinogen when in solution, although it may cause allergic contact dermatitis (ACD).[49] Although no biological role for chromium has ever been demonstrated, dietary supplements for chromium include chromium(III) picolinate, chromium(III) polynicotinate, and related materials(Sony VAIO VGN-AW11Z/B battery). The benefit of those supplements is questioned by some studies.[50]

The use of chromium-containing dietary supplements is controversial owing to the absence of any verified biological role, the expense of these supplements, and the complex effects of their use.[51] The popular dietary supplement chromium picolinate complex generates chromosome damage in hamster cells (due to the picolinate ligand) (Sony VAIO VGN-AW170C battery).[52] In the United States the dietary guidelines for daily chromium uptake were lowered from 50–200 µg for an adult to 35 µg (adult male) and to 25 µg (adult female).[53]

[edit]Precautions

Main article: Chromium toxicity

Water insoluble chromium(III) compounds and chromium metal are not considered a health hazard, while the toxicity and carcinogenic properties of chromium(VI) have been known for a long time.[54] Because of the specific transport mechanisms, only limited amounts of chromium(III) enter the cells(Sony VAIO VGN-AW19/Q battery). Several in vitro studies indicated that high concentrations of chromium(III) in the cell can lead to DNA damage.[55] Acute oral toxicity ranges between 1.5 and 3.3 mg/kg.[56] The proposed beneficial effects of chromium(III) and the use as dietary supplements yielded some controversial results, but recent reviews suggest that moderate uptake of chromium(III) through dietary supplements poses no risk(Sony VAIO VGN-AW19 battery).[55]

[edit]Cr(VI)

The acute oral toxicity for chromium(VI) ranges between 50 and 150 µg/kg.[56] In the body, chromium(VI) is reduced by several mechanisms to chromium(III) already in the blood before it enters the cells. The chromium(III) is excreted from the body, whereas the chromate ion is transferred into the cell by a transport mechanism(Sony VAIO VGN-AW21M/H battery), by which also sulfate and phosphate ions enter the cell. The acute toxicity of chromium(VI) is due to its strong oxidational properties. After it reaches the blood stream, it damages the kidneys, the liver and blood cells through oxidation reactions. Hemolysis, renal and liver failure are the results of these damages. Aggressive dialysis can improve the situation(Sony VAIO VGN-AW21S/B battery).[57]

The carcinogenity of chromate dust is known for a long time, and in 1890 the first publication described the elevated cancer risk of workers in a chromate dye company.[58][59] Three mechanisms have been proposed to describe the genotoxicity of chromium(VI). The first mechanism includes highly reactive hydroxyl radicals and other reactive radicals which are by products of the reduction of chromium(VI) to chromium(III) (Sony VAIO VGN-AW21VY/Q battery). The second process includes the direct binding of chromium(V), produced by reduction in the cell, and chromium(IV) compounds to the DNA. The last mechanism attributed the genotoxicity to the binding to the DNA of the end product of the chromium(III) reduction.[60]

Chromium salts (chromates) are also the cause of allergic reactions in some people. Chromates are often used to manufacture, amongst other things, leather products(Sony VAIO VGN-AW21XY/Q battery), paints, cement, mortar and anti-corrosives. Contact with products containing chromates can lead to allergic contact dermatitis and irritant dermatitis, resulting in ulceration of the skin, sometimes referred to as "chrome ulcers". This condition is often found in workers that have been exposed to strong chromate solutions in electroplating, tanning and chrome-producing manufacturers. (Sony VAIO VGN-AW21Z/B battery)

[edit]Environmental issues

As chromium compounds were used in dyes and paints and the tanning of leather, these compounds are often found in soil and groundwater at abandoned industrial sites, now needing environmental cleanup and remediation per the treatment of brownfield land. Primer paint containing hexavalent chromium is still widely used for aerospace and automobile refinishing applications. (Sony VAIO VGN-AW31M/H battery)

In 2010, the Environmental Working Group studied the drinking water in 35 American cities. The study was the first nationwide analysis measuring the presence of the chemical in U.S. water systems. The study found measurable hexavalent chromium in the tap water of 31 of the cities sampled, with Norman, Oklahoma, at the top of list(Sony VAIO VGN-AW31S/B battery); 25 cities had levels that exceeded California's proposed limit.[64] Note: Concentrations of Cr VI in US municipal drinking water supplies reported by EWG are within likely, natural background levels for the areas tested and not necessarily indicative of industrial pollution (CalEPA Fact Sheet), as asserted by EWG. This factor was not taken into consideration in their report(Sony VAIO VGN-AW41MF battery).

 
Potassium is the chemical element with the symbol K (from Neo-Latin kalium) and atomic number 19. Elemental potassium is a soft silvery-white alkali metal that oxidizes rapidly in air and is very reactive with water, generating sufficient heat to ignite the hydrogen emitted in the reaction(SONY PCG-5G2L battery).

Because potassium and sodium are chemically very similar, it took a long time before their salts were differentiated. The existence of multiple elements in their salts was suspected from 1702,[1] and this was proven in 1807 when potassium and sodium were individually isolated from different salts by electrolysis. Potassium in nature occurs only in ionic salts(SONY PCG-5G3L battery). As such, it is found dissolved in seawater (which is 0.04% potassium by weight[2][3]), and is part of many minerals.

Most industrial chemical applications of potassium employ the relatively high solubility in water of potassium compounds, such as potassium soaps. Potassium metal has only a few special applications, being replaced in most chemical reactions with sodium metal.

Potassium ions are necessary for the function of all living cells(SONY PCG-F305 battery). Potassium ion diffusion is a key mechanism in nerve transmission, and potassium depletion in animals, including humans, results in various cardiac dysfunctions. Potassium is found in especially high concentrations within plant cells, and in a mixed diet it is mostly concentrated in fruits. The high concentration of potassium in plants(SONY PCG-5J1L battery), associated with comparatively low amounts of sodium there, resulted in potassium's being first isolated from potash, the ashes of plants, giving the element its name. For the same reason, heavy crop production rapidly depletes soils of potassium, and agricultural fertilizers consume 95% of global potassium chemical production(SONY PCG-5J2L battery).[4]

Properties

Physical

The flame test of potassium

Potassium atoms have 19 electrons, which is one more than the extremely stable configuration of argon. A potassium atom is thus much more likely to lose the "extra" electron than to gain one; however, the alkalide ions, K–, are known.[5] Because of the low first ionization energy (418.8 kJ/mol) the potassium atom easily loses an electron and oxidizes into the monopositive cation, K+(SONY PCG-5K2L battery).[6] This process requires so little energy that potassium is readily oxidized by atmospheric oxygen. In contrast, the second ionization energy, is very high (3052 kJ/mol), because removal of two electrons breaks the stable noble gas electronic configuration.[6] Potassium therefore does not readily form compounds with the oxidation state of +2 (or higher) (SONY PCG-5L1L battery).[5]

Potassium is the second least dense metal after lithium. It is a soft solid that has a low melting point and can easily be cut with a knife. Freshly cut potassium is silvery in appearance, but it begins to tarnish toward gray immediately after being exposed to air.[7][8] In a flame test, potassium and its compounds emit a lilac color with a peak emission wavelength of 766.5 nm (see movie below). (SONY PCG-6S2L battery)

Chemical

Potassium is an extremely active metal, which reacts violently with oxygen and water in air. With oxygen, it converts to potassium peroxide and with water potassium hydroxide. The reaction of potassium with water is dangerous because of its violent exothermic character and the production of hydrogen gas. Hydrogen reacts again with atmospheric oxygen, producing water, which reacts with the remaining potassium(SONY PCG-6S3L battery).[8] This reaction requires only traces of water; because of this, potassium and its liquid alloy with sodium — NaK — are potent desiccants that can be used to dry solvents prior to distillation.[8][10]

Because of the sensitivity of potassium to water and air, the reactions are possible only in inert atmosphere, such as argon gas using air-free techniques. Potassium does not react with most hydrocarbons, such as mineral oil or kerosene(SONY PCG-6V1L battery).[8] It readily dissolves in liquid ammonia, up to 480 g per 1000 g of ammonia at 0 °C. Depending on the concentration, the ammonia solutions are blue to yellow, and their electrical conductivity is similar to that of liquid metals. In a pure solution, potassium slowly reacts with ammonia to form KNH2, but this reaction is accelerated by minute amounts of transition metal salts.[11] It can reduce the salts to the metal(SONY PCG-6W1L battery); potassium is often used as the reductant in the preparation of finely divided metals from their salts by the Rieke method.[12] For example, the preparation of Rieke magnesium employs potassium as the reductant:

MgCl2 + 2 K → Mg + 2 KCl

Compounds

The only common oxidation state for potassium is +1. Potassium metal is a powerful reducing agent that is easily oxidized to the monopositive cation, K+. Once oxidized, it is very stable and difficult to reduce back to the metal(SONY PCG-7111L battery).[5]

Potassium hydroxide reacts readily with carbon dioxide to produce potassium carbonate, and is used to remove traces of the gas from air. In general, potassium compounds have excellent water solubility, owing to the high hydration energy of the K+ ion. The potassium ion is colorless in water and is very difficult to precipitate; possible precipitation methods include reactions with sodium tetraphenylborate, hexachloroplatinic acid, and sodium cobaltinitrite(SONY PCG-71511M battery).[8]

Potassium oxidizes faster than most metals and forms oxides with oxygen-oxygen bonds, as do all alkali metals except lithium. Three species are formed during the reaction: potassium oxide, potassium peroxide, and potassium superoxide,[13] which contain three different oxygen-based ions: oxide (O2−), peroxide (O2−

2), and superoxide (O−

2) (SONY PCG-6W3L battery). The last two species, especially the superoxide, are rare and are formed only in reaction with very electropositive metals; these species contain oxygen—oxygen bonds.[11] All potassium—oxygen binary compounds are known to react with water violently, forming potassium hydroxide. This compound is a very strong alkali, and 1.21 kg of it can dissolve as much as a liter of water.

Structure of solid potassium superoxide (KO2) (SONY PCG-7113L battery).

In aqueous solution

Potassium compounds are typically highly ionic and thus most of them are soluble in water. The main species in water are the aquo complexes [K(H2O)n]+ where n = 6 and 7.[16] Some of the few salts that are poorly soluble include potassium tetraphenylborate, potassium hexachloroplatinate, and potassium cobaltinitrite. (SONY PCG-7133L battery)

Isotopes

Main article: isotopes of potassium

There are 24 known isotopes of potassium, three of which occur naturally: 39K (93.3%), 40K (0.0117%), and 41K (6.7%). Naturally occurring 40K has a half-life of 1.250×109 years. It decays to stable 40Ar by electron capture or positron emission (11.2%) or to stable 40Ca by beta decay (88.8%).[18] The decay of 40K to 40Ar enables a commonly used method for dating rocks(SONY PCG-7Z1L battery). The conventional K-Ar dating method depends on the assumption that the rocks contained no argon at the time of formation and that all the subsequent radiogenic argon (i.e., 40Ar) was quantitatively retained. Minerals are dated by measurement of the concentration of potassium and the amount of radiogenic 40Ar that has accumulated. The minerals that are best suited for dating include biotite, muscovite(SONY PCG-7Z2L battery)     , metamorphic hornblende, and volcanic feldspar; whole rock samples from volcanic flows and shallow instrusives can also be dated if they are unaltered.[18][19] Outside of dating, potassium isotopes have been used as tracers in studies of weathering and for nutrient cycling studies because potassium is a macronutrient required for life. (SONY PCG-8Y1L battery)

40K occurs in natural potassium (and thus in some commercial salt substitutes) in sufficient quantity that large bags of those substitutes can be used as a radioactive source for classroom demonstrations. In healthy animals and people, 40K represents the largest source of radioactivity, greater even than 14C. In a human body of 70 kg mass, about 4,400 nuclei of 40K decay per second.[21] The activity of natural potassium is 31 Bq/g. (SONY PCG-8Y2L battery)

Creation and occurrence

See also categories: Potassium minerals and Potassium compounds

Potassium in feldspar

Potassium is formed in the universe by nucleosynthesis from lighter atoms. The stable form of potassium is created in supernovas via the explosive Oxygen-burning process.[23]

Elemental potassium does not occur in nature because it reacts violently with water (see section Precautions below).[8] As various compounds, potassium makes up about 2.6% of the weight of the Earth's crust and is the seventh most abundant element, similar in abundance to sodium at approximately 1.8% of the crust(SONY PCG-8Z2L battery).[24] In seawater, potassium at 0.39 g/L[2] (0.039 wt/v%) is far less abundant than sodium at 10.8 g/L (1.08 wt/v%).[25][26]

Orthoclase (potassium feldspar) is a common rock-forming mineral. Granite for example contains 5% potassium, which is well above the average in the Earth's crust. Sylvite (KCl), carnallite (KCl·MgCl2·6(H2O)), kainite (MgSO4·KCl·3H2O) and langbeinite (MgSO4·K2SO4)) are the minerals found in large evaporite deposits worldwide(SONY PCG-8Z1L battery). The deposits often show layers starting with the least soluble at the bottom and the most soluble on top.[26] Deposits of niter (potassium nitrate) are formed by decomposition of organic material in contact with atmosphere, mostly in caves; because of the good water solubility of niter the formation of larger deposits requires special environmental conditions(SONY PCG-7112L battery).[27]

History

Neither elemental potassium nor potassium salts (as separate entities from other salts) were known in Roman times, and the Latin name of the element is not Classical Latin but rather neo-Latin. The Latin name kalium was taken from the word "alkali", which in turn came from Arabic: القَلْيَه‎ al-qalyah "plant ashes." The similar-sounding English term alkali is from this same root (potassium in Modern Standard Arabic is بوتاسيوم būtāsyūm) (SONY PCG-6W2L battery).

Humphry Davy

The English name for the element potassium comes from the word "potash",[28] referring to the method by which potash was obtained – leaching the ash of burnt wood or tree leaves and evaporating the solution in a pot. Potash is primarily a mixture of potassium salts because plants have little or no sodium content, and the rest of a plant's major mineral content consists of calcium salts of relatively low solubility in water(SONY PCG-5K1L battery). While potash has been used since ancient times, it was not understood for most of its history to be a fundamentally different substance from sodium mineral salts. Georg Ernst Stahl obtained experimental evidence that led him to suggest the fundamental difference of sodium and potassium salts in 1702,[1] and Henri Louis Duhamel du Monceau was able to prove this difference in 1736(SONY PCGA-BP2E battery).[29] The exact chemical composition of potassium and sodium compounds, and the status as chemical element of potassium and sodium, was not known then, and thus Antoine Lavoisier did include the alkali in his list of chemical elements in 1789.[30][31]

Potassium metal was first isolated in 1807 in England by Sir Humphry Davy, who derived it from caustic potash (KOH), by the use of electrolysis of the molten salt with the newly discovered voltaic pile. Potassium was the first metal that was isolated by electrolysis(SONY PCGA-BP2EA battery).[32] Later in the same year, Davy reported extraction of the metal sodium from a mineral derivative (caustic soda, NaOH, or lye) rather than a plant salt, by a similar technique, demonstrating that the elements, and thus the salts, are different. Although the production of potassium and sodium metal should have shown that both are elements, it took some time before this view was universally accepted(SONY VGP-BPS2 battery).[31]

For a long time the only significant applications for potash were the production of glass, bleach, and soap.[35] Potassium soaps from animal fats and vegetable oils were especially prized, as they tended to be more water-soluble and of softer texture, and were known as soft soaps.[4] The discovery by Justus Liebig in 1840 that potassium is a necessary element for plants and that most types of soil lack potassium[36] caused a steep rise in demand for potassium salts(SONY VGP-BPS3 battery). Wood-ash from fir trees was initially used as a potassium salt source for fertilizer, but, with the discovery in 1868 of mineral deposits containing potassium chloride near Staßfurt, Germany, the production of potassium-containing fertilizers began at an industrial scale. Other potash deposits were discovered, and by the 1960s Canada became the dominant producer. (SONY VGP-BPS4 battery)

Commercial production

Sylvite from New Mexico

Potassium salts such as carnallite, langbeinite, polyhalite, and sylvite form extensive deposits in ancient lake and seabeds,[25] making extraction of potassium salts in these environments commercially viable. The principal source of potassium – potash – is mined in Canada, Russia, Belarus, Germany, Israel, United States, Jordan, and other places around the world. (SONY VGP-BPS5 battery) The first mined deposits were located near Staßfurt, Germany, but the deposits span from Great Britain over Germany into Poland. They are located in the Zechstein and were deposited in the Middle to Late Permian. The largest deposits ever found lie 1000 meters (3000 feet) below the surface of the Canadian province of Saskatchewan. The deposits are located in the Elk Point Group produced in the Middle Devonian(SONY VGP-BPS5A battery). Saskatchewan, where several large mines have operated since the 1960s, pioneered the use of freezing of wet sands (the Blairmore formation) in order to drive mine shafts through them. The main potash mining company in Saskatchewan is the Potash Corporation of Saskatchewan.[46] The water of the Dead Sea is used by Israel and Jordan as a source for potash, while the concentration in normal oceans is too low for commercial production(SONY VGP-BPS8 battery).

Mining and beneficiation waste heaps from potash mining in Germany, consisting mostly of sodium chloride.

Several methods are applied to separate the potassium salts from the present sodium and magnesium compounds. The most-used method is to precipitate some compounds relying on the solubility difference of the salts at different temperatures. Electrostatic separation of the ground salt mixture is also used in some mines(SONY VGP-BPS8A battery). The resulting sodium and magnesium waste is either stored underground or piled up in slag heaps. Most of the mined potassium minerals end up as potassium chloride after processing. The mineral industry refers to potassium chloride either as potash, muriate of potash, or simply MOP.[26]

Pure potassium metal can be isolated by electrolysis of its hydroxide in a process that has changed little since Davy(SONY VGP-BPL8 battery). Although the electrolysis process was developed and used in industrial scale in the 1920s the thermal method by reacting sodium with potassium chloride in a chemical equilibrium reaction became the dominant method in the 1950s. The production of sodium potassium alloys is possible by changing the reaction time and the amount of sodium used in the reaction. The Griesheimer process employing the reaction of potassium fluoride with calcium carbide was also used to produce potassium. (SONY VGP-BPS9 battery)

Na + KCl → NaCl + K                      (Thermal method)

2 KF + CaC2 → 2K + CaF2 + 2 C       (Griesheimer process)

Reagent-grade potassium metal cost about $10.00/pound ($22/kg) in 2010 when purchased in tonne quantities. Lower purity metal is considerably cheaper. The market is volatile due to the difficulty of the long-term storage of the metal. It must be stored under a dry inert gas atmosphere or anhydrous mineral oil to prevent the formation of a surface layer of potassium superoxide(SONY VGP-BPS9/S battery). This superoxide is a pressure-sensitive explosive that will detonate when scratched. The resulting explosion will usually start a fire that is difficult to extinguish.[48][49]

Biological role

Main article: Potassium in biology

Biochemical function

Main article: Action potential

The action of the sodium-potassium pump is an example of primary active transport. The two carrier proteins on the left are using ATP to move sodium out of the cell against the concentration gradient. The proteins on the right are using secondary active transport to move potassium into the cell(SONY VGP-BPS9A battery).

Potassium is the eighth or ninth most common element by mass (0.2%) in the human body, so that a 60 kg adult contains a total of about 120 g of potassium.[50] The body has about as much potassium as sulfur and chlorine, and only the major minerals calcium and phosphorus are more abundant. (SONY VGP-BPS9A/B battery)

Potassium cations are important in neuron (brain and nerve) function, and in influencing osmotic balance between cells and the interstitial fluid, with their distribution mediated in all animals (but not in all plants) by the so-called Na+/K+-ATPase pump.[52] This ion pump uses ATP to pump three sodium ions out of the cell and two potassium ions into the cell(SONY VGP-BPS9/B battery), thus creating an electrochemical gradient over the cell membrane. In addition, the highly selective potassium ion channels (which are tetramers) are crucial for the hyperpolarization, in for example neurons, after an action potential is fired. The most recently resolved potassium ion channel is KirBac3.1, which gives a total of five potassium ion channels (KcsA, KirBac1.1, KirBac3.1, KvAP, and MthK) with a determined structure(SONY VGP-BPS9A/S battery).[53] All five are from prokaryotic species.

Potassium can be detected by taste because it triggers three of the five types of taste sensations, according to concentration. Dilute solutions of potassium ions taste sweet, allowing moderate concentrations in milk and juices, while higher concentrations become increasingly bitter/alkaline, and finally also salty to the taste. The combined bitterness and saltiness of high-potassium solutions makes high-dose potassium supplementation by liquid drinks a palatability challenge. (SONY VGP-BPL9 battery)

Membrane polarization

Potassium is also important in preventing muscle contraction and the sending of all nerve impulses in animals through action potentials. By nature of their electrostatic and chemical properties, K+ ions are larger than Na+ ions, and ion channels and pumps in cell membranes can distinguish between the two types of ions, actively pumping or passively allowing one of the two ions to pass, while blocking the other. (SONY VGP-BPS10 battery)

A shortage of potassium in body fluids may cause a potentially fatal condition known as hypokalemia, typically resulting from vomiting, diarrhea, and/or increased diuresis.[57] Deficiency symptoms include muscle weakness, paralytic ileus, ECG abnormalities, decreased reflex response and in severe cases respiratory paralysis, alkalosis and cardiac arrhythmia. (SONY VGP-BPL10 battery)

Filtration and excretion

Potassium is an essential mineral micronutrient in human nutrition; it is the major cation (positive ion) inside animal cells, and it is thus important in maintaining fluid and electrolyte balance in the body. Sodium makes up most of the cations of blood plasma at a reference range of about 145 mmol/L (3.345 g)(1mmol/L = 1mEq/L), and potassium makes up most of the cell fluid cations at about 150 mmol/L (4.8 g) (SONY VGP-BPS11 battery). Plasma is filtered through the glomerulus of the kidneys in enormous amounts, about 180 liters per day.[59] Thus 602 g of sodium and 33 g of potassium are filtered each day. All but the 1–10 g of sodium and the 1–4 g of potassium likely to be in the diet must be reabsorbed. Sodium must be reabsorbed in such a way as to keep the blood volume exactly right and the osmotic pressure correct(SONY VGP-BPL11 battery); potassium must be reabsorbed in such a way as to keep serum concentration as close as possible to 4.8 mmol/L (about 0.190 g/L).[60] Sodium pumps in the kidneys must always operate to conserve sodium. Potassium must sometimes be conserved also, but, as the amount of potassium in the blood plasma is very small and the pool of potassium in the cells is about thirty times as large(SONY VGP-BPL12 battery), the situation is not so critical for potassium. Since potassium is moved passively[61][62] in counter flow to sodium in response to an apparent (but not actual) Donnan equilibrium,[63] the urine can never sink below the concentration of potassium in serum except sometimes by actively excreting water at the end of the processing. Potassium is secreted twice and reabsorbed three times before the urine reaches the collecting tubules.[64] At that point(SONY VGP-BPS12 battery), it usually has about the same potassium concentration as plasma. At the end of the processing, potassium is secreted one more time if the serum levels are too high.

If potassium were removed from the diet, there would remain a minimum obligatory kidney excretion of about 200 mg per day when the serum declines to 3.0–3.5 mmol/L in about one week,[65] and can never be cut off completely, resulting in hypokalemia and even death(SONY VGP-BPS13 battery).[66]

The potassium moves passively through pores in the cell membrane. When ions move through pumps there is a gate in the pumps on either side of the cell membrane and only one gate can be open at once. As a result, approximately 100 ions are forced through per second. Pores have only one gate, and there only one kind of ion can stream through(SONY VGP-BPS13Q battery), at 10 million to 100 million ions per second.[67] The pores require calcium in order to open[68] although it is thought that the calcium works in reverse by blocking at least one of the pores.[69] Carbonyl groups inside the pore on the amino acids mimic the water hydration that takes place in water solution[70] by the nature of the electrostatic charges on four carbonyl groups inside the pore(SONY VGP-BPS13A/Q battery).[71]

In diet

Adequate intake

A potassium intake sufficient to support life can in general be guaranteed by eating a variety of foods. Clear cases of potassium deficiency (as defined by symptoms, signs and a below-normal blood level of the element) are rare in healthy individuals. Foods rich in potassium include parsley, dried apricots, dried milk, chocolate, various nuts (especially almonds and pistachios) (SONY VGP-BPS13B/Q battery), potatoes, bamboo shoots, bananas, avocados, soybeans, and bran, although it is also present in sufficient quantities in most fruits, vegetables, meat and fish.[72]

Optimal intake

Epidemiological studies and studies in animals subject to hypertension indicate that diets high in potassium can reduce the risk of hypertension and possibly stroke (by a mechanism independent of blood pressure), and a potassium deficiency combined with an inadequate thiamine intake has produced heart disease in rats(SONY VGP-BPS13/B battery).[73] There is some debate regarding the optimal amount of dietary potassium. For example, the 2004 guidelines of the Institute of Medicine specify a DRI of 4,000 mg of potassium (100 mEq), though most Americans consume only half that amount per day, which would make them formally deficient as regards this particular recommendation.[74] Likewise, in the European Union, in particular in Germany and Italy, insufficient potassium intake is somewhat common(SONY VGP-BPS13B/B battery).[75] Italian researchers reported in a 2011 meta-analysis that a 1.64 g higher daily intake of potassium was associated with a 21% lower risk of stroke.[76]

Medical supplementation and disease

Supplements of potassium in medicine are most widely used in conjunction with loop diuretics and thiazides, classes of diuretics that rid the body of sodium and water, but have the side-effect of also causing potassium loss in urine. A variety of medical and non-medical supplements are available. Potassium salts such as potassium chloride may be dissolved in water(SONY VGP-BPS13A/S battery), but the salty/bitter taste of high concentrations of potassium ion make palatable high concentration liquid supplements difficult to formulate.[54] Typical medical supplemental doses range from 10 mmol (400 mg, about equal to a cup of milk or 6 US fl oz (180 ml). of orange juice) to 20 mmol (800 mg) per dose. Potassium salts are also available in tablets or capsules(SONY VGP-BPS21A/B battery), which for therapeutic purposes are formulated to allow potassium to leach slowly out of a matrix, as very high concentrations of potassium ion (which might occur next to a solid tablet of potassium chloride) can kill tissue, and cause injury to the gastric or intestinal mucosa. For this reason, non-prescription supplement potassium pills are limited by law in the US to only 99 mg of potassium. (SONY VGP-BPS21B battery)

Individuals suffering from kidney diseases may suffer adverse health effects from consuming large quantities of dietary potassium. End stage renal failure patients undergoing therapy by renal dialysis must observe strict dietary limits on potassium intake, as the kidneys control potassium excretion, and buildup of blood concentrations of potassium (hyperkalemia) may trigger fatal cardiac arrhythmia(SONY VGP-BPS21 battery).

Applications

Fertilizer

Potassium and magnesium sulfate fertilizer

Potassium ions are an essential component of plant nutrition and are found in most soil types.[4] They are used as a fertilizer in agriculture, horticulture, and hydroponic culture in the form of chloride (KCl), sulfate (K2SO4), or nitrate (KNO3). Agricultural fertilizers consume 95% of global potassium chemical production, and about 90% of this potassium is supplied as KCl(SONY VGP-BPS21/S battery).[4] The potassium content of most plants range from 0.5% to 2% of the harvested weight of crops, conventionally expressed as amount of K2O. Modern high-yield agriculture depends upon fertilizers to replace the potassium lost at harvest. Most agricultural fertilizers contain potassium chloride, while potassium sulfate is used for chloride-sensitive crops or crops needing higher sulfur content(SONY VGP-BPS13AS battery). The sulfate is produced mostly by decomposition of the complex minerals kainite (MgSO4·KCl·3H2O) and langbeinite (MgSO4·K2SO4). Only a very few fertilizers contain potassium nitrate.[77] In 2005, about 93% of world potassium production was consumed by the fertilizer industry.[45]

Food

The potassium cation is a nutrient necessary for human life and health. Potassium chloride is used as a substitute for table salt by those seeking to reduce sodium intake so as to control hypertension(SONY VGP-BPS13S battery). The USDA lists tomato paste, orange juice, beet greens, white beans, potatoes, bananas and many other good dietary sources of potassium, ranked in descending order according to potassium content.[78]

Potassium sodium tartrate (KNaC4H4O6, Rochelle salt) is the main constituent of baking powder; it is also used in the silvering of mirrors. Potassium bromate (KBrO3) is a strong oxidizer (E924), used to improve dough strength and rise height(SONY VGP-BPS13B/S battery). Potassium bisulfite (KHSO3) is used as a food preservative, for example in wine and beer-making (but not in meats). It is also used to bleach textiles and straw, and in the tanning of leathers.[79][80]

Industrial

Major potassium chemicals are potassium hydroxide, potassium carbonate, potassium sulfate, and potassium chloride. Megatons of these compounds are produced annually(SONY VGP-BPS13B/G battery).[81]

Potassium hydroxide KOH is a strong base, which is used in industry to neutralize strong and weak acids, to control pH and to manufacture potassium salts. It is also used to saponify fats and oils, in industrial cleaners, and in hydrolysis reactions, for example of esters.[82][83]

Potassium nitrate (KNO3) or saltpeter is obtained from natural sources such as guano and evaporites or manufactured via the Haber process(SONY VGP-BPS14 battery); it is the oxidant in gunpowder (black powder) and an important agricultural fertilizer. Potassium cyanide (KCN) is used industrially to dissolve copper and precious metals, in particular silver and gold, by forming complexes. Its applications include gold mining, electroplating, and electroforming of these metals; it is also used in organic synthesis to make nitriles(SONY VGP-BPL14 battery). Potassium carbonate (K2CO3 or potash) is used in the manufacture of glass, soap, color TV tubes, fluorescent lamps, textile dyes and pigments.[84] Potassium permanganate (KMnO4) is an oxidizing, bleaching and purification substance and is used for production of saccharin. Potassium chlorate (KClO3) is added to matches and explosives. Potassium bromide (KBr) was formerly used as a sedative and in photography(SONY VGP-BPS14/B battery).[4]

Potassium chromate (K2CrO4) is used in inks, dyes, stains (bright yellowish-red color); in explosives and fireworks; in the tanning of leather, in fly paper and safety matches,[85] but all these uses are due to the properties of chromate ion containment rather than potassium ions(SONY VGP-BPS14/S battery).

Niche uses

Potassium compounds are so pervasive that thousands of small uses are in place. The superoxide KO2 is an orange solid that acts as a portable source of oxygen and a carbon dioxide absorber. It is widely used in respiration systems in mines, submarines and spacecraft as it takes less volume than the gaseous oxygen.[86][87]

4 KO2 + 2 CO2 → 2 K2CO3 + 3 O2

Potassium cobaltinitrite K3[Co(NO2)6] is used as artist's pigment under the name of Aureolin or Cobalt yellow. (SONY VGP-BPS14B battery)

Laboratory uses

An alloy of sodium and potassium, NaK is a liquid used as a heat-transfer medium and a desiccant for producing dry and air-free solvents. It can also be used in reactive distillation.[89] The ternary alloy of 12% Na, 47% K and 41% Cs has the lowest melting point of −78 °C of any metallic compound.[7]

Metallic potassium is used in several types of magnetometers(SONY VGP-BPS22 battery).[90]

Precautions

A reaction of potassium metal with water. Hydrogen is liberated that burns with a pink or lilac flame, the flame color owing to burning potassium vapor. Strongly alkaline potassium hydroxide is formed in solution.

Potassium reacts very violently with water producing potassium hydroxide (KOH) and hydrogen gas.

2 K (s) + 2 H2O (l) → 2 KOH (aq) + H2↑ (g) (SONY VGP-BPS22 battery)

This reaction is exothermic and releases enough heat to ignite the resulting hydrogen. It in turn may explode in the presence of oxygen. Potassium hydroxide is a strong alkali that causes skin burns. Finely divided potassium will ignite in air at room temperature. The bulk metal will ignite in air if heated. Because its density is 0.89 g/cm3, burning potassium floats in water that exposes it to atmospheric oxygen(SONY VGP-BPS18 battery). Many common fire extinguishing agents, including water, either are ineffective or make a potassium fire worse. Nitrogen, argon, Sodium chloride (table salt), sodium carbonate (soda ash), and silicon dioxide (sand) are effective if they are dry. Some Class D dry powder extinguishers designed for metal fires are also effective. These agents deprive the fire of oxygen and cool the potassium metal(SONY VGP-BPS22/A battery).[91]

Potassium reacts violently with halogens and will detonate in the presence of bromine. It also reacts explosively with sulfuric acid. During combustion potassium forms peroxides and superoxides. These peroxides may react violently with organic compounds such as oils. Both peroxides and superoxides may react explosively with metallic potassium(SONY VGP-BPS22A battery).[92]

Because potassium reacts with water vapor present in the air, it is usually stored under anhydrous mineral oil or kerosene. Unlike lithium and sodium, however, potassium should not be stored under oil for longer than 6 months, unless in an inert (oxygen free) atmosphere, or under vacuum. After prolonged storage in air dangerous shock-sensitive peroxides can form on the metal and under the lid of the container, and can detonate upon opening(SONY Vaio VGN-CR120E/W battery).[93]

Because of the highly reactive nature of potassium metal, it must be handled with great care, with full skin and eye protection and preferably an explosion-resistant barrier between the user and the metal. Ingestion of large amounts of potassium compounds can lead to hyperkalemia strongly influencing the cardiovascular system.[94][95] Potassium chloride is used in the United States for death penalty via lethal injection(SONY Vaio VGN-CR120E/R battery).[94]

Calcium ( /ˈkælsiəm/ kal-see-əm) is the chemical element with the symbol Ca and atomic number 20. It has an atomic mass of 40.078 amu. Calcium is a soft gray alkaline earth metal, and is the fifth-most-abundant element by mass in the Earth's crust. Calcium is also the fifth-most-abundant dissolved ion in seawater by both molarity and mass, after sodium, chloride, magnesium, and sulfate(SONY Vaio VGN-CR120E/P battery).[2]

Calcium is essential for living organisms, in particular in cell physiology, where movement of the calcium ion Ca2+ into and out of the cytoplasm functions as a signal for many cellular processes. As a major material used in mineralization of bones and shells, calcium is the most abundant metal by mass in many animals(SONY Vaio VGN-CR120E/L battery).

Notable characteristics

Flame test. Brick-red color originates from calcium.

In chemical terms, calcium is reactive and soft for a metal (though harder than lead, it can be cut with a knife with difficulty). It is a silvery metallic element that must be extracted by electrolysis from a fused salt like calcium chloride.[3] Once produced, it rapidly forms a gray-white oxide and nitride coating when exposed to air. In bulk form (typically as chips or "turnings"), the metal is somewhat difficult to ignite(SONY Vaio VGN-CR120E battery), more so even than magnesium chips; but, when lit, the metal burns in air with a brilliant high-intensity orange-red light. Calcium metal reacts with water, evolving hydrogen gas at a rate rapid enough to be noticeable, but not fast enough at room temperature to generate much heat. In powdered form, however, the reaction with water is extremely rapid, as the increased surface area of the powder accelerates the reaction with the water(SONY Vaio VGN-CR120 battery). Part of the slowness of the calcium-water reaction results from the metal being partly protected by insoluble white calcium hydroxide. In water solutions of acids, where this salt is soluble, calcium reacts vigorously.

Calcium, with a density of 1.55 g/cm3, is the lightest of the alkaline earth metals; magnesium (specific gravity 1.74) and beryllium (1.84) are more dense, although lighter in atomic mass. From strontium onward, the alkali earth metals become more dense with increasing atomic mass(SONY Vaio VGN-CR11H/B battery).

It has two allotropes.[4]

Calcium has a higher electrical resistivity than copper or aluminium, yet weight-for-weight, due to its much lower density, it is a rather better conductor than either. However, its use in terrestrial applications is usually limited by its high reactivity with air.

Calcium salts are colorless from any contribution of the calcium, and ionic solutions of calcium (Ca2+) are colorless as well. As with magnesium salts and other alkaline earth metal salts, calcium salts are often quite soluble in water(SONY Vaio VGN-CR116E battery). Notable exceptions include the hydroxide, the sulfate (unusual for sulfate salts), the carbonate and the phosphates. With the exception of the sulfate, even the insoluble ones listed are in general more soluble than its transition metal counterparts. When in solution, the calcium ion to the human taste varies remarkably, being reported as mildly salty, sour, "mineral like" or even "soothing." It is apparent that many animals can taste, or develop a taste(SONY Vaio VGN-CR116 battery), for calcium, and use this sense to detect the mineral in salt licks or other sources.[5] In human nutrition, soluble calcium salts may be added to tart juices without much effect to the average palate.

Calcium is the fifth-most-abundant element by mass in the human body, where it is a common cellular ionic messenger with many functions, and serves also as a structural element in bone(SONY Vaio VGN-CR115E battery). It is the relatively high-atomic-number calcium in the skeleton that causes bone to be radio-opaque. Of the human body's solid components after drying and burning of organics (as for example, after cremation), about a third of the total "mineral" mass remaining, is the approximately one kilogram of calcium that composes the average skeleton (the remainder being mostly phosphorus and oxygen) (SONY Vaio VGN-CR115 battery).

H and K lines

Visible spectra of many stars, including the Sun, exhibit strong absorption lines of singly ionized calcium. Prominent among these are the H-line at 3968.5 Å and the K line at 3933.7 Å of singly ionized calcium, or Ca II. For the Sun and stars with low temperatures, the prominence of the H and K lines can be an indication of strong magnetic activity in the chromosphere(SONY Vaio VGN-CR110EW battery). Measurement of periodic variations of these active regions can also be used to deduce the rotation periods of these stars.[6]

Compounds

Calcium, combined with phosphate to form hydroxylapatite, is the mineral portion of human and animal bones and teeth. The mineral portion of some corals can also be transformed into hydroxylapatite.

Calcium hydroxide (slaked lime) is used in many chemical refinery processes and is made by heating limestone at high temperature (above 825 °C) and then carefully adding water to it(Sony VAIO VGN-FZ11S battery). When lime is mixed with sand, it hardens into a mortar and is turned into plaster by carbon dioxide uptake. Mixed with other compounds, lime forms an important part of Portland cement.

Calcium carbonate (CaCO3) is one of the common compounds of calcium. It is heated to form quicklime (CaO), which is then added to water (H2O). This forms another material known as slaked lime (Ca(OH)2), which is an inexpensive base material used throughout the chemical industry. Chalk, marble, and limestone are all forms of calcium carbonate(Sony VAIO VGN-FZ15T battery).

When water percolates through limestone or other soluble carbonate rocks, it partially dissolves the rock and causes cave formation and characteristic stalactites and stalagmites and also forms hard water. Other important calcium compounds are calcium nitrate, calcium sulfide, calcium chloride, calcium carbide, calcium cyanamide and calcium hypochlorite.

A few calcium compounds in the oxidation state +1 have also been investigated recently(Sony VAIO VGN-FZ15G battery).[1]

Nucleosynthesis

This section requires expansion with:

information on other calcium isotopes.

Calcium-40 is created in extremely large and hot (over 2.5 × 109 K) stars, as part of the silicon-burning process in which alpha particles are added to silicon atoms. The process fuses an atom of argon and an atom of helium:

36Ar + 4He = 40Ca

Isotopes

Main article: Isotopes of calcium

Calcium has four stable isotopes (40Ca, 42Ca, 43Ca and 44Ca), plus two more isotopes (46Ca and 48Ca) that have such long half-lives that for all practical purposes they also can be considered stable(Sony VAIO VGN-FZ11L battery). The 20% range in relative mass among naturally occurring calcium isotopes is greater than for any element except hydrogen and helium. Calcium also has a cosmogenic isotope, radioactive 41Ca, which has a half-life of 103,000 years. Unlike cosmogenic isotopes that are produced in the atmosphere, 41Ca is produced by neutron activation of 40Ca. Most of its production is in the upper metre or so of the soil column(Sony VAIO VGN-FZ11Z battery), where the cosmogenic neutron flux is still sufficiently strong. 41Ca has received much attention in stellar studies because it decays to 41K, a critical indicator of solar-system anomalies.

Ninety-seven percent of naturally occurring calcium is in the form of 40Ca. 40Ca is one of the daughter products of 40K decay, along with 40Ar. While K-Ar dating has been used extensively in the geological sciences, the prevalence of 40Ca in nature has impeded its use in dating. Techniques using mass spectrometry and a double spike isotope dilution have been used for K-Ca age dating(Sony VAIO VGN-FZ11M battery).

The most abundant isotope, 40Ca, has a nucleus of 20 protons and 20 neutrons. This is the heaviest stable isotope of any element that has equal numbers of protons and neutrons. In supernova explosions, calcium is formed from the reaction of carbon with various numbers of alpha particles (helium nuclei), until the most common calcium isotope (containing 10 helium nuclei) has been synthesized. (Sony VAIO VGN-FZ18M battery)

Isotope fractionation

As with the isotopes of other elements, a variety of processes fractionate, or alter the relative abundance of, calcium isotopes.[7] The best studied of these processes is the mass dependent fractionation of calcium isotopes that accompanies the precipitation of calcium minerals, such as calcite, aragonite and apatite, from solution. Isotopically light calcium is preferentially incorporated into minerals(Sony VAIO VGN-FZ18 battery), leaving the solution from which the mineral precipitated enriched in isotopically heavy calcium. At room temperature the magnitude of this fractionation is roughly 0.25‰ (0.025%) per atomic mass unit (AMU). Mass-dependent differences in calcium isotope composition conventionally are expressed the ratio of two isotopes (usually 44Ca/40Ca) in a sample compared to the same ratio in a standard reference material(Sony VAIO VGN-FZ210CE battery). 44Ca/40Ca varies by about 1% among common earth materials.[8]

Calcium isotope fractionation during mineral formation has led to several applications of calcium isotopes. In particular, the 1997 observation by Skulan and DePaolo[9] that calcium minerals are isotopically lighter than the solutions from which the minerals precipitate is the basis of analogous applications in medicine and in paleooceanography(Sony VAIO VGN-FZ31S battery). In animals with skeletons mineralized with calcium the calcium isotopic composition of soft tissues reflects the relative rate of formation and dissolution of skeletal mineral. In humans changes in the calcium isotopic composition of urine have been shown to be related to changes in bone mineral balance. When the rate of bone formation exceeds the rate of bone resorption, soft tissue 44Ca/40Ca rises(Sony VAIO VGN-FZ31Z battery). Soft tissue 44Ca/40Ca falls when bone resorption exceeds bone formation. Because of this relationship, calcium isotopic measurements of urine or blood may be useful in the early detection of metabolic bone diseases like osteoporosis.[10]

A similar system exists in the ocean, where seawater 44Ca/40Ca tends to rise when the rate of removal of Ca2+ from seawater by mineral precipitation exceeds the input of new calcium into the ocean, and fall when calcium input exceeds mineral precipitation(Sony VAIO VGN-FZ31E battery). It follows that rising 44Ca/40Ca corresponds to falling seawater Ca2+ concentration, and falling 44Ca/40Ca corresponds to rising seawater Ca2+ concentration. In 1997 Skulan and DePaolo presented the first evidence of change in seawater 44Ca/40Ca over geologic time, along with a theoretical explanation of these changes. More recent papers have confirmed this observation, demonstrating that seawater Ca2+ concentration is not constant(Sony VAIO VGN-FZ31J battery), and that the ocean probably never is in “steady state” with respect to its calcium input and output.[11][12] This has important climatological implications, as the marine calcium cycle is closely tied to the carbon cycle (see below).

Geochemical cycling

Calcium provides an important link between tectonics, climate and the carbon cycle. In the simplest terms, uplift of mountains exposes Ca-bearing rocks to chemical weathering and releases Ca2+ into surface water(Sony VAIO VGN-FZ31M battery). This Ca2+ eventually is transported to the ocean where it reacts with dissolved CO2 to form limestone. Some of this limestone settles to the sea floor where it is incorporated into new rocks. Dissolved CO2, along with carbonate and bicarbonate ions, are referred to as dissolved inorganic carbon (DIC).

Travertine terraces Pamukkale, Turkey

The actual reaction is more complicated and involves the bicarbonate ion (HCO3-) that forms when CO2 reacts with water at seawater pH(Sony VAIO VGN-FZ31B battery):

Ca2+ + 2HCO−

3 → CaCO3 (limestone) + CO2 + H2O

Note that at ocean pH most of the CO2 produced in this reaction is immediately converted back into HCO3−. The reaction results in a net transport of one molecule of CO2 from the ocean/atmosphere into the lithosphere.[13]

The result is that each Ca2+ ion released by chemical weathering ultimately removes one CO2 molecule from the surficial system (atmosphere, ocean, soils and living organisms), storing it in carbonate rocks where it is likely to stay for hundreds of millions of years(Sony VAIO VGN-FZ32 battery). The weathering of calcium from rocks thus scrubs CO2 from the ocean and atmosphere, exerting a strong long-term effect on climate.[14] Analogous cycles involving magnesium, and to a much smaller extent strontium and barium, have the same effect.

As the weathering of limestone (CaCO3) liberates equimolar amounts of Ca2+ and CO2, it has no net effect on the CO2 content of the atmosphere and ocean(Sony VAIO VGN-FZ410 battery). The weathering of silicate rocks like granite, on the other hand, is a net CO2 sink because it produces abundant Ca2+ but very little CO2.

History

Lime as building material was used since prehistoric times going as far back as 7000 to 14000 BC.[15] The first dated lime kiln dates back to 2500 BC and was found in Khafajah mesopotamia.[16][17] Calcium (from Latin calx, genitive calcis, meaning "lime")[18] was known as early as the first century when the Ancient Romans prepared lime as calcium oxide(Sony VAIO VGN-FZ21 battery). Literature dating back to 975 AD notes that plaster of paris (calcium sulfate), is useful for setting broken bones. It was not isolated until 1808 in England when Sir Humphry Davy electrolyzed a mixture of lime and mercuric oxide.[19] Davy was trying to isolate calcium; when he heard that Swedish chemist Jöns Jakob Berzelius and Pontin prepared calcium amalgam by electrolyzing lime in mercury, he tried it himself(Sony VAIO VGN-FZ21S battery). He worked with electrolysis throughout his life and also discovered/isolated sodium, potassium, magnesium, boron and barium. Calcium metal was not available in large scale until the beginning of the 20th century.

Occurrence

See also Category: Calcium minerals

Calcium is not naturally found in its elemental state. Calcium occurs most commonly in sedimentary rocks in the minerals calcite, dolomite and gypsum. It also occurs in igneous and metamorphic rocks chiefly in the silicate minerals: plagioclases, amphiboles, pyroxenes and garnets(Sony VAIO VGN-FZ21M battery).

Applications

Calcium is used[20]

as a reducing agent in the extraction of other metals, such as uranium, zirconium, and thorium.

as a deoxidizer, desulfurizer, or decarbonizer for various ferrous and nonferrous alloys.

as an alloying agent used in the production of aluminium, beryllium, copper, lead, and magnesium alloys.

in the making of cements and mortars to be used in construction.

in the making of cheese, where calcium ions influence the activity of rennin in bringing about the coagulation of milk(Sony VAIO VGN-FZ38M battery).

Calcium compounds

See also Category: Calcium compounds

Calcium carbonate (CaCO3) is used in manufacturing cement and mortar, lime, limestone (usually used in the steel industry) and aids in production in the glass industry. It also has chemical and optical uses as mineral specimens in toothpastes, for example.

Calcium hydroxide solution (Ca(OH)2) (also known as limewater) is used to detect the presence of carbon dioxide by being bubbled through a solution. It turns cloudy where CO2 is present(Sony VAIO VGN-S battery).

Calcium arsenate (Ca3(AsO4)2) is used in insecticides.

Calcium carbide (CaC2) is used to make acetylene gas (for use in acetylene torches for welding) and in the manufacturing of plastics.

Calcium chloride (CaCl2) is used in ice removal and dust control on dirt roads, in conditioner for concrete, as an additive in canned tomatoes, and to provide body for automobile tires.

Calcium cyclamate (Ca(C6H11NHSO3)2) was used as a sweetening agent but is no longer permitted for use because of suspected cancer-causing properties(Sony VAIO VGN-SZ battery).

Calcium gluconate (Ca(C6H11O7)2) is used as a food additive and in vitamin pills.

Calcium hypochlorite (Ca(OCl)2) is used as a swimming pool disinfectant, as a bleaching agent, as an ingredient in deodorant, and in algaecide and fungicide.

Calcium permanganate (Ca(MnO4)2) is used in liquid rocket propellant, textile production, as a water sterilizing agent and in dental procedures.

Calcium phosphate (Ca3(PO4)2) is used as a supplement for animal feed, fertilizer, in commercial production for dough and yeast products, in the manufacture of glass, and in dental products(Sony VGN-NR11S/S Battery).

Calcium phosphide (Ca3P2) is used in fireworks, rodenticide, torpedoes and flares.

Calcium stearate (Ca(C18H35O2)2) is used in the manufacture of wax crayons, cements, certain kinds of plastics and cosmetics, as a food additive, in the production of water resistant materials and in the production of paints.

Calcium sulfate (CaSO4·2H2O) is used as common blackboard chalk, as well as, in its hemihydrate form better known as Plaster of Paris(Sony VGN-NR11M/S Battery).

Calcium tungstate (CaWO4) is used in luminous paints, fluorescent lights and in X-ray studies.

Hydroxylapatite (Ca5(PO4)3(OH), but is usually written Ca10(PO4)6(OH)2) makes up seventy percent of bone. Also carbonated-calcium deficient hydroxylapatite is the main mineral of which dental enamel and dentin are comprised.

Nutrition

Calcium is an important component of a healthy diet and a mineral necessary for life. The National Osteoporosis Foundation says, "Calcium plays an important role in building stronger(Sony VGN-NR11Z/S Battery), denser bones early in life and keeping bones strong and healthy later in life." Approximately 99 percent of the body's calcium is stored in the bones and teeth.[23] The rest of the calcium in the body has other important uses, such as some exocytosis, especially neurotransmitter release, and muscle contraction. In the electrical conduction system of the heart, calcium replaces sodium as the mineral that depolarizes the cell(Sony VGN-NR11Z/T Battery), proliferating the action potential. In cardiac muscle, sodium influx commences an action potential, but during potassium efflux, the cardiac myocyte experiences calcium influx, prolonging the action potential and creating a plateau phase of dynamic equilibrium. Long-term calcium deficiency can lead to rickets and poor blood clotting and in case of a menopausal woman, it can lead to osteoporosis(Sony VAIO VGN-FZ21E battery), in which the bone deteriorates and there is an increased risk of fractures. While a lifelong deficit can affect bone and tooth formation, over-retention can cause hypercalcemia (elevated levels of calcium in the blood), impaired kidney function and decreased absorption of other minerals.[24][25] Several sources suggest a correlation between high calcium intake (2000 mg per day, or twice the U.S. recommended daily allowance(Sony VAIO VGN-FZ21Z battery), equivalent to six or more glasses of milk per day) and prostate cancer.[26] High calcium intakes or high calcium absorption were previously thought to contribute to the development of kidney stones. However, a high calcium intake has been associated with a lower risk for kidney stones in more recent research. Vitamin D is needed to absorb calcium(Sony VAIO VGN-FZ21J battery).

Dairy products, such as milk and cheese, are a well-known source of calcium. Some individuals are allergic to dairy products and even more people, in particular those of non Indo-European descent, are lactose-intolerant, leaving them unable to consume non-fermented dairy products in quantities larger than about half a liter per serving. Others, such as vegans, avoid dairy products for ethical and health reasons(Sony VAIO VGN-FW11 battery).

Many good sources of calcium exist, including seaweeds such as kelp, wakame and hijiki; nuts and seeds like almonds, hazelnuts, sesame, pistachio; blackstrap molasses; beans; figs; quinoa; okra; rutabaga; broccoli; dandelion leaves; kale; and fortified products such as orange juice and soy milk(Sony VAIO VGN-FW11M battery).

Numerous vegetables, notably spinach, chard and rhubarb have a high calcium content, but they may also contain varying amounts of oxalic acid that binds calcium and reduces its absorption. The same problem may to a degree affect the absorption of calcium from amaranth, collard greens, chicory greens. This process may also be related to the generation of calcium oxalate(Sony VAIO VGN-FW11S battery).

An overlooked source of calcium is eggshell, which can be ground into a powder and mixed into food or a glass of water.

The calcium content of most foods can be found in the USDA National Nutrient Database.[33]

Dietary calcium supplements

500 milligram calcium supplements made from calcium carbonate

Calcium supplements are used to prevent and to treat calcium deficiencies. Most experts recommend that supplements be taken with food and that no more than 600 mg should be taken at a time because the percent of calcium absorbed decreases as the amount of calcium in the supplement increases(Sony VAIO VGN-FW21E battery).[21] It is recommended to spread doses throughout the day. Recommended daily calcium intake for adults ranges from 1000 to 1500 mg. It is recommended to take supplements with food to aid in absorption.

Vitamin D is added to some calcium supplements. Proper vitamin D status is important because vitamin D is converted to a hormone in the body, which then induces the synthesis of intestinal proteins responsible for calcium absorption(Sony VAIO VGN-FW21J battery).[34]

The absorption of calcium from most food and commonly used dietary supplements is very similar.[35] This is contrary to what many calcium supplement manufacturers claim in their promotional materials.

Milk is an excellent source of dietary calcium for those whose bodies tolerate it because it has a high concentration of calcium and the calcium in milk is excellently absorbed.[35]

Soymilk and other vegetable milks are usually sold with calcium added so that their calcium concentration is as high as in milk(Sony VAIO VGN-FW21L battery)

Also different kind of juices boosted with calcium are widely available.

Calcium carbonate is the most common and least expensive calcium supplement. It should be taken with food. It depends on low pH levels for proper absorption in the intestine.[36] Some studies suggests that the absorption of calcium from calcium carbonate is similar to the absorption of calcium from milk.[37][38] While most people digest calcium carbonate very well(Sony VAIO VGN-FW41M battery), some might develop gastrointestinal discomfort or gas. Taking magnesium with it can help to avoid constipation. Calcium carbonate is 40% elemental calcium. 1000 mg will provide 400 mg of calcium. However, supplement labels will usually indicate how much calcium is present in each serving, not how much calcium carbonate is present.

Antacids frequently contain calcium carbonate, and are a commonly used, inexpensive calcium supplement(Sony VAIO VGN-FW41M/H battery)

Coral calcium is a salt of calcium derived from fossilized coral reefs. Coral calcium is composed of calcium carbonate and trace minerals.

Calcium citrate can be taken without food and is the supplement of choice for individuals with achlorhydria or who are taking histamine-2 blockers or proton-pump inhibitors.[39]Calcium citrate is about 21% elemental calcium. 1000 mg will provide 210 mg of calcium. It is more expensive than calcium carbonate and more of it must be taken to get the same amount of calcium(Sony VAIO VGN-FW21M battery).

Calcium phosphate costs more than calcium carbonate, but less than calcium citrate. Microcrystalline hydroxyapatite (MH) is one of several forms of calcium phosphate used as a dietary supplement. Hydroxyapatite is about 40% calcium.

Calcium lactate has similar absorption as calcium carbonate,[40] but is more expensive. Calcium lactate and calcium gluconate are less concentrated forms of calcium and are not practical oral supplements. (Sony VAIO VGN-FW21Z battery)

Calcium chelates are synthetic calcium compounds, with calcium bound to an organic molecule, such as malate, aspartate, or fumarate. These forms of calcium may be better absorbed on an empty stomach. However, in general they are absorbed similarly to calcium carbonate and other common calcium supplements when taken with food(Sony VAIO VGN-FW32J battery).[41] The 'chelate' mimics the action that natural food performs by keeping the calcium soluble in the intestine. Thus, on an empty stomach, in some individuals, chelates might, in theory, be absorbed better.

In July 2006, a report citing research from Fred Hutchinson Cancer Research Center in Seattle, Washington claimed that women in their 50s gained 5 pounds (2.3 kg) less in a period of 10 years by taking more than 500 mg of calcium supplements than those who did not(Sony VAIO VGN-FW17W battery). However, the doctor in charge of the study, Dr. Alejandro J. Gonzalez also noted it would be "going out on a limb" to suggest calcium supplements as a weight-limiting aid.[42]

Prevention of fractures due to osteoporosis

Such studies often do not test calcium alone, but rather combinations of calcium and vitamin D. Randomized controlled trials found both positive[43][44] and negative effects. The different results may be explained by doses of calcium and underlying rates of calcium supplementation in the control groups(Sony VAIO VGN-FW31E battery).[49] However, it is clear that increasing the intake of calcium promotes deposition of calcium in the bones, where it is of more benefit in preventing the compression fractures resulting from the osteoporotic thinning of the dendritic web of the bodies of the vertebrae, than it is at preventing the more serious cortical bone fractures that happen at hip and wrist. (Sony VAIO VGN-FW139E battery)

Possible cancer prevention

A meta-analysis[44] by the international Cochrane Collaboration of two randomized controlled trials[50][51] found that calcium "might contribute to a moderate degree to the prevention of adenomatous colonic polyps".

More recent studies were conflicting, and one that was positive for effect (Lappe, et al.) did control for a possible anti-carcinogenic effect of vitamin D, which was found to be an independent positive influence from calcium-alone on cancer risk (see second study below) (Sony VAIO VGN-FW139E/H battery).[52]

A randomized controlled trial found that 1000 mg of elemental calcium and 400 IU of vitamin D3 had no effect on colorectal cancer[53]

A randomized controlled trial found that 1400–1500 mg supplemental calcium and 1100 IU vitamin D3 reduced aggregated cancers with a relative risk of 0.402.[54]

An observational cohort study found that high calcium and vitamin D intake was associated with "lower risk of developing premenopausal breast cancer." (Sony VAIO VGN-FW31M battery)

Hazards and toxicity

Compared with other metals, the calcium ion and most calcium compounds have low toxicity. This is not surprising given the very high natural abundance of calcium compounds in the environment and in organisms. Calcium poses few serious environmental problems, with kidney stones the most common side-effect in clinical studies. Acute calcium poisoning is rare, and difficult to achieve unless calcium compounds are administered intravenously(Sony VAIO VGN-FW31J battery). For example, the oral median lethal dose (LD50) for rats for calcium carbonate and calcium chloride are 6.45 [56] and 1.4 g/kg,[57] respectively.

Calcium metal is hazardous because of its sometimes-violent reactions with water and acids. Calcium metal is found in some drain cleaners, where it functions to generate heat and calcium hydroxide that saponifies the fats and liquefies the proteins (e.g., hair) that block drains(Sony VAIO VGN-FW31Z battery). When swallowed calcium metal has the same effect on the mouth, esophagus and stomach, and can be fatal.[58]

Excessive consumption of calcium carbonate antacids/dietary supplements (such as Tums) over a period of weeks or months can cause milk-alkali syndrome, with symptoms ranging from hypercalcemia to potentially fatal renal failure. What constitutes “excessive” consumption is not well known and, it is presumed, varies a great deal from person to person(Sony VGN-NR11Z Battery). Persons consuming more than 10 grams/day of CaCO3 (=4 g Ca) are at risk of developing milk-alkali syndrome,[59] but the condition has been reported in at least one person consuming only 2.5 grams/day of CaCO3 (=1 g Ca), an amount usually considered moderate and safe(Sony VGN-NR11S Battery).[60]

Oral calcium supplements diminish the absorption of thyroxine when taken within four to six hours of each other.[61] Thus, people taking both calcium and thyroxine run the risk of inadequate thyroid hormone replacement and thence hypothyroidism if they take them simultaneously or near-simultaneously(Sony VGN-CR11Z Battery).

 
Chlorine is the chemical element with atomic number 17 and symbol Cl. It is the second lightest halogen, with fluorine being the lightest. Chlorine is found in the periodic table in group 17. The element forms diatomic molecules under standard conditions, called dichlorine. It has the highest electron affinity and the third highest electronegativity of all the elementsSony VAIO VPCF135Z1E/B battery; for this reason, chlorine is a strong oxidizing agent.

The most common compound of chlorine, sodium chloride, has been known since ancient times; however, around 1630, chlorine gas was obtained by the Belgian chemist and physician Jan Baptist van Helmont. The synthesis and characterization of elemental chlorine occurred in 1774 by Swedish chemist Carl Wilhelm ScheeleSony VAIO VPCF137HG/BI battery, who called it "dephlogisticated muriatic acid air," having thought he synthesized the oxide obtained from the hydrochloric acid. Because acids were thought at the time to necessarily contain oxygen, a number of chemists, including Claude Berthollet, suggested that Scheele's dephlogisticated muriatic acid air must be a combination of oxygen and the yet undiscovered elementSony VAIO VPCF136FG/BI battery, and Scheele named the supposed new element within this oxide as muriaticum. The suggestion that this newly discovered gas was a simple element was made in 1809 by Joseph Louis Gay-Lussac and Louis-Jacques. This was confirmed by Sir Humphry Davy in 1810, who named it chlorine, from the Greek word χλωρος (chlōros), meaning "green-yellow."

Chlorine is a component of various compoundsSony VAIO VPCF135FG/B battery, including table salt. It is the second most abundant halogen and 21st most abundant chemical element in Earth's crust. The great oxidizing potential of chlorine led it to its bleaching and disinfectant uses, as well as uses of an essential reagent in the chemical industry. As a common disinfectant, chlorine compounds are used in swimming pools to keep them clean and sanitarySony VAIO VPCF127HG/BI battery. In the upper atmosphere, chlorine-containing molecules such as chlorofluorocarbons have been implicated in ozone depletion. Elemental chlorine is extremely dangerous and poisonous for all lifeforms; however, chlorine is necessary to most forms of life, including humans, in form of chloride ions.

Characteristics

Physical characteristics

Chlorine, liquified under a pressure of 7.4 bar at room temperature, displayed in a quartz ampule embedded in acrylic glassSony VAIO VPCF11Z1E battery.

At standard temperature and pressure, two chlorine atoms form the diatomic molecule Cl2.[3] This is a yellow-green gas that has a distinctive strong odor, familiar to most from common Household bleach.[4] The bonding between the two atoms is relatively weak (only 242.580 ± 0.004 kJ/mol), which makes the Cl2 molecule highly reactive. The boiling point at regular atmosphere is around −34 ˚CSony VAIO VPCF11S1E battery, but it can be liquefied at room temperature with pressures above 740 kPa.[5]

Chemical characteristics

Along with fluorine, bromine, iodine, and astatine, chlorine is a member of the halogen series that forms the group 17 (formerly VII, VIIA, or VIIB) of the periodic table. Chlorine forms compounds with almost all of the elements to give compounds that are usually called chlorides. Chlorine gas reacts with most organic compounds, and will even sluggishly support the combustion of hydrocarbonsSony VAIO VPCF11M1E/H battery.[6]

Hydrolysis

At 25 °C and atmospheric pressure, one liter of water dissolves 3.26 g or 1.02 L of gaseous chlorine.[7] Solutions of chlorine in water contain chlorine (Cl2), hydrochloric acid, and hypochlorous acid:

Cl2 + H2O  HCl + HClO

This conversion to the right is called disproportionation, because the ingredient chlorine both increases and decreases in formal oxidation state. The solubility of chlorine in water is increased if the water contains dissolved alkali hydroxide, and in this way, chlorine bleach is producedSony VAIO VPCF11M1E battery.[8]

Cl2 + 2 OH– → ClO– + Cl– + H2O

Chlorine gas only exists in a neutral or acidic solution.

Compounds

See also Category: Chlorine compounds

Chlorine exists in all odd numbered oxidation states from −1 to +7, as well as the elemental state of zero and four in chlorine dioxide (see table below, and also structures in chlorite).[9] Progressing through the states, hydrochloric acid can be oxidized using manganese dioxide, or hydrogen chloride gas oxidized catalytically by air to form elemental chlorine gasSony VAIO VPCF11JFX/B battery.[10]

Chlorine oxides

Chlorine forms a variety of oxides, as seen above: chlorine dioxide (ClO2), dichlorine monoxide (Cl2O), dichlorine hexoxide (Cl2O6), dichlorine heptoxide (Cl2O7). The anionic derivatives of these same oxides are also well known including chlorate (ClO−

3), chlorite (ClO−

2), hypochlorite (ClO−), and perchlorate (ClO−

4). The acid derivatives of these anions are hypochlorous acid (HOCl), chloric acid (HClO3) and perchloric acid (HClO4) Sony VAIO VPCF119FJ battery. The chloroxy cation chloryl (ClO2+) is known and has the same structure as chlorite but with a positive charge and chlorine in the +5 oxidation state.[11] The compound "chlorine trioxide", rather than being the expected +6 oxidation state, is instead a mixture of +5 and +7 states, occurring as the ionic compound chloryl perchlorate, [ClO2]+[ClO4]− commonly called dichlorine hexoxide.[12]

In hot concentrated alkali solution hypochlorite disproportionatesSony VAIO VPCF119FC/BI battery:

2 ClO− → Cl− + ClO−2

ClO− + ClO−2 → Cl− + ClO−3

Sodium chlorate and potassium chlorate can be crystallized from solutions formed by the above reactions. If their crystals are heated, they undergo a further, final disproportionation:

4 ClO−3 → Cl− + 3 ClO−4

This same progression from chloride to perchlorate can be accomplished by electrolysis. The anode reaction progression is:[13]

Each step is accompanied at the cathode by

2 H2O + 2 e− → 2 OH− + H2 (−0.83 volts) Sony VAIO VPCF119FC battery

Interhalogen compounds

Chlorine oxidizes bromide and iodide salts to bromine and iodine, respectively. However, it cannot oxidize fluoride salts to fluorine. It makes a variety of interhalogen compounds such as the chlorine fluorides, chlorine monofluoride (ClF), chlorine trifluoride (ClF3), chlorine pentafluoride (ClF5). Chlorides of bromine and iodine are also knownSony VAIO VPCF117HG/BI battery.[14]

Organochlorine compounds

Main article: Organochloride

Chlorine is used extensively in organic chemistry in substitution and addition reactions. Chlorine often imparts many desired properties to an organic compound, in part owing to its electronegativity. Some organochlorine compounds are also serious pollutants, either as side products of industrial processes or as persistent pesticidesSony VAIO VPCF116FG/BI battery.

Many important industrial products are produced via organochlorine intermediates. Examples include polycarbonates, polyurethanes, silicones, polytetrafluoroethylene, carboxymethyl cellulose, and propylene oxide. Like the other halogens, chlorine participates in free-radical substitution reactions with hydrogen-containing organic compoundsSony VAIO VPCF115FG/B battery. When applied to organic substrates, reaction is often—but not invariably—non-regioselective, and, hence, may result in a mixture of isomeric products. It is often difficult to control the degree of substitution as well, so multiple substitutions are common. If the different reaction products are easily separated, e.g., by distillation, substitutive free-radical chlorination (in some cases accompanied by concurrent thermal dehydrochlorination) may be a useful synthetic routeSony VAIO VPCF21ZHJ battery. Industrial examples of this are the production of methyl chloride, methylene chloride, chloroform, and carbon tetrachloride from methane, allyl chloride from propylene, and trichloroethylene, and tetrachloroethylene from 1,2-dichloroethane.

Like the other halides, chlorine undergoes electrophilic addition reactions, the most notable one being the chlorination of alkenes and aromatic compounds with a Lewis acid catalyst. Organic chlorine compounds tend to be less reactive in nucleophilic substitution reactions than the corresponding bromine or iodine derivatives, but they tend to be cheaperSony VAIO VPCF21Z1E/BI battery. They may be activated for reaction by substituting with a tosylate group, or by the use of a catalytic amount of sodium iodide.[citation needed]

Chlorides

Main article: Chloride

Chlorine combines with almost all elements to give chlorides. Compounds with oxygen, nitrogen, xenon, and krypton are known, but do not form by direct reaction of the elements.[15] Chloride is one of the most common anions in nature. Hydrogen chloride and its aqueous solution, hydrochloric acid, are produced on megaton scale annually both as valued intermediates but sometimes as undesirable pollutantsSony VAIO VPCF21AHJ battery.

Occurrence

See also Category: Halide minerals

In nature, chlorine is found primarily as the chloride ion, a component of the salt that is deposited in the earth or dissolved in the oceans — about 1.9% of the mass of seawater is chloride ions. Even higher concentrations of chloride are found in the Dead Sea and in underground brine deposits. Most chloride salts are soluble in water, thusSony VAIO VPCF21AGJ battery, chloride-containing minerals are usually only found in abundance in dry climates or deep underground. In the Earth's crust, chlorine is present at average concentrations of about 126 parts per million,[16] predominantly in such minerals as halite (sodium chloride), sylvite (potassium chloride), and carnallite (potassium magnesium chloride hexahydrate). Over 2000 naturally occurring organic chlorine compounds are knownSony VAIO VPCF21AFJ battery.[17]

In the interstellar medium, chlorine is produced in supernovae via the r-process.[18]

Isotopes

Main article: Isotopes of chlorine

Chlorine has a wide range of isotopes. The two stable isotopes are 35Cl (75.77%) and 37Cl (24.23%).[19] Together they give chlorine an atomic weight of 35.4527 g/mol. The half-integer value for chlorine's weight caused some confusion in the early days of chemistry, when it had been postulated that atoms were composed of even units of hydrogen (see Proust's law), and the existence of chemical isotopes was unsuspectedSony VAIO VPCF219FJ/BI battery.[20]

Trace amounts of radioactive 36Cl exist in the environment, in a ratio of about 7x10−13 to 1 with stable isotopes. 36Cl is produced in the atmosphere by spallation of 36Ar by interactions with cosmic ray protons. In the subsurface environment, 36Cl is generated primarily as a result of neutron capture by 35Cl or muon capture by 40Ca. 36Cl decays to 36S and to 36ArSony VAIO VPCF217HG/BI battery, with a combined half-life of 308,000 years. The half-life of this hydrophilic nonreactive isotope makes it suitable for geologic dating in the range of 60,000 to 1 million years. Additionally, large amounts of 36Cl were produced by irradiation of seawater during atmospheric detonations of nuclear weapons between 1952 and 1958. The residence time of 36Cl in the atmosphere is about 1 weekSony VAIO VPCF217HG battery. Thus, as an event marker of 1950s water in soil and ground water, 36Cl is also useful for dating waters less than 50 years before the present. 36Cl has seen use in other areas of the geological sciences, including dating ice and sediments.[19]

History

The most common compound of chlorine, sodium chloride, has been known since ancient times; archaeologists have found evidence that rock salt was used as early as 3000 BC and brine as early as 6000 BCSony VAIO VPCF14ZHJ battery.[21] Around 1630, chlorine was recognized as a gas by the Belgian chemist and physician Jan Baptist van Helmont.[22]

Carl Wilhelm Scheele

Elemental chlorine was first prepared and studied in 1774 by Swedish chemist Carl Wilhelm Scheele, and, therefore, he is credited for its discovery.[23] He called it "dephlogisticated muriatic acid air" since it is a gas (then called "airs") and it came from hydrochloric acid (then known as "muriatic acid")Sony VAIO VPCF14AHJ battery.[23] However, he failed to establish chlorine as an element, mistakenly thinking that it was the oxide obtained from the hydrochloric acid (see phlogiston theory). [23] He named the new element within this oxide as muriaticum.[23] Regardless of what he thought, Scheele did isolate chlorine by reacting MnO2 (as the mineral pyrolusite) with HCl:[22]

4 HCl + MnO2 → MnCl2 + 2 H2O + Cl2

Scheele observed several of the properties of chlorine: the bleaching effect on litmus, the deadly effect on insects, the yellow green color, and the smell similar to aqua regiaSony VAIO VPCF14AGJ battery.[24]

At the time, common chemical theory was: any acid is a compound that contains oxygen (still sounding in the German and Dutch names of oxygen: sauerstoff or zuurstof, both translating into English as acid stuff), so a number of chemists, including Claude Berthollet, suggested that Scheele's dephlogisticated muriatic acid air must be a combination of oxygen and the yet undiscovered element, muriaticum. Sony VAIO VPCF14AFJ battery

In 1809, Joseph Louis Gay-Lussac and Louis-Jacques Thénard tried to decompose dephlogisticated muriatic acid air by reacting it with charcoal to release the free element muriaticum (and carbon dioxide).[23] They did not succeed and published a report in which they considered the possibility that dephlogisticated muriatic acid air is an element, but were not convinced.Sony VAIO VPCF149FJ/BI battery

In 1810, Sir Humphry Davy tried the same experiment again, and concluded that it is an element, and not a compound.[23] He named this new element as chlorine, from the Greek word χλωρος (chlōros), meaning green-yellow.[29] The name halogen, meaning salt producer, was originally defined for chlorine (in 1811 by Johann Salomo Christoph Schweigger) Sony VAIO VPCF148FJ/B battery, and later in 1842, at a suggestion by Jöns Jakob Berzelius, this term was applied to the rest of the elements in this family.[30][31] In 1823, Michael Faraday liquefied chlorine for the first time,[32][33] and demonstrated that what was then known as "solid chlorine" had a structure of chlorine hydrate (Cl2·H2O).[22]

Chlorine was first used by Claude Berthollet to bleach textiles in 1785. In 1826, silver chloride was used to produce photographic images for the first timeSony VAIO VPCF13ZHJ battery.[34] Chloroform was first used as an anesthetic in 1847.[34] An elemental chlorine solution in water (which was expensive), then the less expensive chlorine gas dissolved in lime-water (calcium hypochlorite) was first used as an antiseptic to prevent the spread of puerperal fever in the maternity wards of Vienna General Hospital in Austria in 1847. Sony VAIO VPCF13Z0E/B battery In 1850, chlorine in lime-water was used by John Snow to purify the water supply in London after an outbreak of cholera. (Both uses preceded the germ theory of disease, and were based on destruction of odors and "putrid matter").

The US Department of Treasury called for all water to be disinfected with chlorine by 1918.[34] Polyvinyl chloride (PVC) was invented in 1912Sony VAIO VPCF13M8E/B battery, initially without a purpose.[34] Chlorine gas was first introduced as a weapon on April 22, 1915, at Ypres by the German Army,[36][37] and the results of this weapon were disastrous because gas masks had not been mass distributed and were tricky to get on quickly.

Production

Liquid chlorine analysis

Main article: Chlorine production

In industry, elemental chlorine is usually produced by the electrolysis of sodium chloride dissolved in water.[38] Along with chlorine, this chloralkali process yields hydrogen gas and sodium hydroxide, according to the following chemical equationSony VAIO VPCF13AHJ battery:[10]

2 NaCl + 2 H2O → Cl2 + H2 + 2 NaOH

The electrolysis of chloride solutions all proceed according to the following equations:

Cathode: 2 H+ (aq) + 2 e− → H2 (g)

Anode: 2 Cl− (aq) → Cl2 (g) + 2 e−

Overall process: 2 NaCl (or KCl) + 2 H2O → Cl2 + H2 + 2 NaOH (or KOH) In diaphragm cell electrolysis, an asbestos (or polymer-fiber) diaphragm separates a cathode and an anode, preventing the chlorine forming at the anode from re-mixing with the sodium hydroxide and the hydrogen formed at the cathodeSony VAIO VPCF13AGJ battery.[39] The salt solution (brine) is continuously fed to the anode compartment and flows through the diaphragm to the cathode compartment, where the caustic alkali is produced and the brine is partially depleted. Diaphragm methods produce dilute and slightly impure alkali but they are not burdened with the problem of preventing mercury discharge into the environment and they are more energy efficientSony VAIO VPCF13AFJ battery. Membrane cell electrolysis employ permeable membrane as an ion exchanger. Saturated sodium (or potassium) chloride solution is passed through the anode compartment, leaving at a lower concentration.[40] This method is more efficient than the diaphragm cell and produces very pure sodium (or potassium) hydroxide at about 32% concentration, but requires very pure brineSony VAIO VPCF138FJ/BI battery.

Laboratory methods

Small amounts of chlorine gas can be made in the laboratory by combining hydrochloric acid and manganese dioxide. Alternatively a strong acid such as sulfuric acid or hydrochloric acid reacts with sodium hypochlorite solution to release chlorine gas but reacts with sodium chlorate to produce chlorine gas and chlorine dioxide gas as wellSony VAIO VPCF138FJ/B battery. In the home, accidents occur when hypochlorite bleach solutions are combined with certain acidic drain-cleaners.

Applications

Production of industrial and consumer products

Principal applications of chlorine are in the production of a wide range of industrial and consumer products.[41][42] For example, it is used in making plastics, solvents for dry cleaning and metal degreasing, textiles, agrochemicals and pharmaceuticals, insecticides, dyestuffs, household cleaning products, etcSony VAIO VPCF138FC/BI battery. Quantitatively, about 63% and 18% of all chlorine are used in the manufacture of organic and inorganic chlorine compounds, respectively,[38] and about 15,000 chlorine compounds are being used commercially.[24] The remaining 19% is used for bleaches and disinfection products.[38] The most significant of organic compounds in terms of production volume are 1,2-dichloroethane and vinyl chloride, intermediates in the production of PVCSony VAIO VPCF135FG battery. Other particularly important organochlorines are methyl chloride, methylene chloride, chloroform, vinylidene chloride, trichloroethylene, perchloroethylene, allyl chloride, epichlorohydrin, chlorobenzene, dichlorobenzenes, and trichlorobenzenes. The major inorganic compounds include HCl, Cl2O, HOCl, NaClO3, chlorinated isocyanurates, AlCl3, SiCl4, SnCl4, PCl3, PCl5, POCl3, AsCl3, SbCl3, SbCl5, BiCl3, S2Cl2, SCl2, SOCI2, CIF3, ICl, ICl3, TiCl3, TiCl4, MoCl5, FeCl3, ZnCl2, etc. Sony VAIO VPCF12AHJ battery

Purification and disinfection

Main article: Chlorination

Chlorine is an important chemical for water purification (such as water treatment plants), in disinfectants, and in bleach. Chlorine in water is more than three times as effective as a disinfectant against Escherichia coli than an equivalent concentration of bromine, and is more than six times more effective than an equivalent concentration of iodineSony VAIO VPCF12AGJ battery.[44]

Chlorine is usually used (in the form of hypochlorous acid) to kill bacteria and other microbes in drinking water supplies and public swimming pools. In most private swimming pools, chlorine itself is not used, but rather sodium hypochlorite, formed from chlorine and sodium hydroxide, or solid tablets of chlorinated isocyanurates. The drawback of using chlorine in swimming pools is that the chlorine reacts with a human's hair and skin because hair and skin are made from proteinSony VAIO VPCF12AFJ battery.(Reaction with protein amino groups) Even small water supplies are now routinely chlorinated.[6]

It is often impractical to store and use poisonous chlorine gas for water treatment, so alternative methods of adding chlorine are used. These include hypochlorite solutions, which gradually release chlorine into the water, and compounds like sodium dichloro-s-triazinetrione (dihydrate or anhydrous), sometimes referred to as "dichlor", and trichloro-s-triazinetrioneSony VAIO VPCF129FJ/BI battery, sometimes referred to as "trichlor". These compounds are stable while solid and may be used in powdered, granular, or tablet form. When added in small amounts to pool water or industrial water systems, the chlorine atoms hydrolyze from the rest of the molecule forming hypochlorous acid (HOCl), which acts as a general biocide, killing germs, micro-organisms, algae, and so on. Sony VAIO VPCF128FJ/B battery

Use as a weapon

World War I

Main article: Poison gas in World War I

Chlorine gas, also known as bertholite, was first used as a weapon in World War I by Germany on April 22, 1915 in the Second Battle of Ypres [47]. As described by the soldiers it had a distinctive smell of a mixture between pepper and pineapple. It also tasted metallic and stung the back of the throat and chest. Chlorine can react with water in the mucosa of the lungs to form hydrochloric acid, an irritant that can be lethalSony VAIO VPCF127FJ/W battery. The damage done by chlorine gas can be prevented by a gas mask, or other filtration method, which makes the overall chance of death by chlorine gas much lower than those of other chemical weapons. It was pioneered by a German scientist later to be a Nobel laureate, Fritz Haber of the Kaiser Wilhelm Institute in Berlin, in collaboration with the German chemical conglomerate IG FarbenSony VAIO VPCF11ZHJ battery, who developed methods for discharging chlorine gas against an entrenched enemy. It is alleged that Haber's role in the use of chlorine as a deadly weapon drove his wife, Clara Immerwahr, to suicide.[48] After its first use, chlorine was utilized by both sides as a chemical weapon, but it was soon replaced by the more deadly phosgene and mustard gasSony VAIO VPCF11AHJ battery.[49]

Iraq War

Main article: 2007 chlorine bombings in Iraq

Chlorine "attack" on an acetal resin plumbing joint.

Chlorine gas has also been used by insurgents against the local population and coalition forces in the Iraq War in the form of chlorine bombs. On March 17, 2007, for example, three chlorine filled trucks were detonated in the Anbar province killing two and sickening over 350.[50] Other chlorine bomb attacks resulted in higher death tollsSony VAIO VPCF11AGJ battery, with more than 30 deaths on two separate occasions.[51] Most of the deaths were caused by the force of the explosions rather than the effects of chlorine, since the toxic gas is readily dispersed and diluted in the atmosphere by the blast. The Iraqi authorities have tightened up security for chlorine, which is essential for providing safe drinking water for the populationSony VAIO VPCF11AFJ battery.

Chlorine cracking

The element is widely used for purifying water owing to its powerful oxidizing properties, especially potable water supplies and water used in swimming pools. Several catastrophic collapses of swimming pool ceilings have occurred owing to stress corrosion cracking of stainless steel rods used to suspend them.[52] Some polymers are also sensitive to attackSony VAIO VPCF118FJ battery, including acetal resin and polybutene. Both materials were used in hot and cold water domestic supplies, and stress corrosion cracking caused widespread failures in the USA in the 1980s and 1990s. One example shows an acetal joint in a water supply system, which, when it fractured, caused substantial physical damage to computers in the labs below the supply. The cracks started at injection molding defects in the joint and grew slowly until finally triggeredSony VAIO VPCF117FJ battery. The fracture surface shows iron and calcium salts that were deposited in the leaking joint from the water supply before failure.[53]

Health effects

NFPA 704

030OX

Chlorine is a toxic gas that irritates the respiratory system. Because it is heavier than air, it tends to accumulate at the bottom of poorly ventilated spaces. Chlorine gas is a strong oxidizer, which may react with flammable materials.[54]

Chlorine is detectable with measuring devices in concentrations of as low as 0.2 parts per million (ppm), and by smell at 3 ppm. Coughing and vomiting may occur at 30 ppm and lung damage at 60 ppm. About 1000 ppm can be fatal after a few deep breaths of the gasSony VAIO VGN-CS33H battery.[24] Breathing lower concentrations can aggravate the respiratory system, and exposure to the gas can irritate the eyes.[55] The toxicity of chlorine comes from its oxidizing power. When chlorine is inhaled at concentrations above 30 ppm, it begins to react with water and cells, which change it into hydrochloric acid (HCl) and hypochlorous acid (HClO) Sony VAIO VGN-CS33H/Z battery.

When used at specified levels for water disinfection, the reaction of chlorine with water is not a major concern for human health. However, other materials present in the water may generate disinfection by-products that can damage human health.

Argon ( /ˈɑrɡɒn/ ar-gon) is a chemical element represented by the symbol Ar. Argon has atomic number 18 and is the third element in group 18 of the periodic table (noble gases) Sony VAIO VGN-CS33H/B battery. Argon is the third most common gas in the Earth's atmosphere, at 0.93% (9,300 ppm), making it approximately 23.8 times more abundant than carbon dioxide (390 ppm). Nearly all of this argon is radiogenic argon-40 derived from the decay of potassium-40 in the Earth's crust. In the universe, argon-36 is by far the most common argon isotope, being the preferred argon isotope produced by stellar nucleosynthesis in supernovasSony VAIO VGN-CS31Z/Q battery.

The name "argon" is derived from the Greek word αργον meaning "lazy" or "the inactive one", a reference to the fact that the element undergoes almost no chemical reactions. The complete octet (eight electrons) in the outer atomic shell makes argon stable and resistant to bonding with other elements. Its triple point temperature of 83.8058 K is a defining fixed point in the International Temperature Scale of 1990Sony VAIO VGN-CS31S/W battery.

Argon is produced industrially by the fractional distillation of liquid air. Argon is mostly used as an inert shielding gas in welding and other high-temperature industrial processes where ordinarily non-reactive substances become reactive; for example, an argon atmosphere is used in graphite electric furnaces to prevent the graphite from burning. Argon gas also has uses in incandescent and fluorescent lighting, and other types of gas discharge tubesSony VAIO VGN-CS31S/V battery. Argon makes a distinctive blue-green gas laser.

Characteristics

A small piece of rapidly melting solid argon.

Argon has approximately the same solubility in water as oxygen and is 2.5 times more soluble in water than nitrogen. Argon is colorless, odorless, and nontoxic as a solid, liquid, and gas. Argon is chemically inert under most conditions and forms no confirmed stable compounds at room temperatureSony VAIO VGN-CS31S/T battery.

Although argon is a noble gas, it has been found to have the capability of forming some compounds. For example, the creation of argon fluorohydride (HArF), a marginally stable compound of argon with fluorine and hydrogen, was reported by researchers at the University of Helsinki in 2000.[2] Although the neutral ground-state chemical compounds of argon are presently limited to HArFSony VAIO VGN-CS31S/R battery, argon can form clathrates with water when atoms of it are trapped in a lattice of the water molecules.[3] Argon-containing ions and excited state complexes, such as ArH+ and ArF, respectively, are known to exist. Theoretical calculations have predicted several argon compounds that should be stable,[4] but for which no synthesis routes are currently knownSony VAIO VGN-CS31S/P battery.

[edit]History

Lord Rayleigh's method for the isolation of argon, based on an experiment of Henry Cavendish's. The gases are contained in a test-tube (A) standing over a large quantity of weak alkali (B), and the current is conveyed in wires insulated by U-shaped glass tubes (CC) passing through the liquid and round the mouth of the test-tube. The inner platinum ends (DD) of the wire receive a current from a battery of five Grove cells and a Ruhmkorff coil of medium sizeSony VAIO VGN-CS28 battery.

Argon (αργος, Greek meaning "inactive", in reference to its chemical inactivity)[5][6] was suspected to be present in air by Henry Cavendish in 1785 but was not isolated until 1894 by Lord Rayleigh and Sir William Ramsay in Scotland in an experiment in which they removed all of the oxygen, carbon dioxide, water and nitrogen from a sample of clean air. Sony VAIO VGN-CS28/Q battery They had determined that nitrogen produced from chemical compounds was one-half percent lighter than nitrogen from the atmosphere. The difference seemed insignificant, but it was important enough to attract their attention for many months. They concluded that there was another gas in the air mixed in with the nitrogen.[10] Argon was also encountered in 1882 through independent research of H. F. Newall and W.N. HartleySony VAIO VGN-CS27 battery. Each observed new lines in the color spectrum of air but were unable to identify the element responsible for the lines. Argon became the first member of the noble gases to be discovered. The symbol for argon is now Ar, but up until 1957 it was A.[11]

[edit]Occurrence

Argon constitutes 0.934% by volume and 1.28% by mass of the Earth's atmosphere, and air is the primary raw material used by industry to produce purified argon productsSony VAIO VGN-CS27/W battery. Argon is isolated from air by fractionation, most commonly by cryogenic fractional distillation, a process that also produces purified nitrogen, oxygen, neon, krypton and xenon.[12]

Isotopes

Main article: Isotopes of argon

The main isotopes of argon found on Earth are 40Ar (99.6%), 36Ar (0.34%), and 38Ar (0.06%). Naturally occurring 40K with a half-life of 1.25×109 years, decays to stable 40Ar (11.2%) by electron capture or positron emission, and also to stable 40Ca (88.8%) via beta decaySony VAIO VGN-CS27/R battery. These properties and ratios are used to determine the age of rocks by the method of K-Ar dating.[13]

In the Earth's atmosphere, 39Ar is made by cosmic ray activity, primarily with 40Ar. In the subsurface environment, it is also produced through neutron capture by 39K or alpha emission by calcium. 37Ar is created from the neutron spallation of 40Ca as a result of subsurface nuclear explosions. It has a half-life of 35 daysSony VAIO VGN-CS27/P battery.[13]

Argon is notable in that its isotopic composition varies greatly between different locations in the solar system. Where the major source of argon is the decay of 40K in rocks, 40Ar will be the dominant isotope, as it is on earth. Argon produced directly by stellar nucleosynthesis, in contrast, is dominated by the alpha process nuclide, 36Ar. Correspondingly, solar argon contains 84.6% 36Ar based on solar wind measurements. Sony VAIO VGN-CS27/C battery

The predominance of radiogenic 40Ar is responsible for the fact that the standard atomic weight of terrestrial argon is greater than that of the next element, potassium. This was puzzling at the time when argon was discovered, since Mendeleev had placed the elements in his periodic table in order of atomic weight, although the inertness of argon implies that it must be placed before the reactive alkali metal potassiumSony VAIO VGN-CS26T/W battery. Henry Moseley later solved this problem by showing that the periodic table is actually arranged in order of atomic number. (See History of the periodic table).

The much greater atmospheric abundance of argon relative to the other noble gases is also due to the presence of radiogenic 40Ar. Primordial 36Ar has an abundance of only 31.5 ppmv (= 9340 ppmv x 0.337%), comparable to that of neon (18.18 ppmv)Sony VAIO VGN-CS26T/V battery.

The Martian atmosphere contains 1.6% of 40Ar and 5 ppm of 36Ar. The Mariner space probe fly-by of the planet Mercury in 1973 found that Mercury has a very thin atmosphere with 70% argon, believed to result from releases of the gas as a decay product from radioactive materials on the planet. In 2005, the Huygens probe also discovered the presence of 40Ar on Titan, the largest moon of Saturn. Sony VAIO VGN-CS26T/T battery

[edit]Compounds

See also: Van der Waals molecule

Argon’s complete octet of electrons indicates full s and p subshells. This full outer energy level makes argon very stable and extremely resistant to bonding with other elements. Before 1962, argon and the other noble gases were considered to be chemically inert and unable to form compounds; however, compounds of the heavier noble gases have since been synthesizedSony VAIO VGN-CS26T/R battery. In August 2000, the first argon compound was formed by researchers at the University of Helsinki. By shining ultraviolet light onto frozen argon containing a small amount of hydrogen fluoride, argon fluorohydride (HArF) was formed.[2][16] It is stable up to 40 kelvin (−233 °C). The ArCF2+

2 metastable dication, which is valence isoelectronic with carbonyl fluoride, was observed in 2010Sony VAIO VGN-CS26T/Q battery.[17]

Production

Industrial

Argon is produced industrially by the fractional distillation of liquid air in a cryogenic air separation unit; a process that separates liquid nitrogen, which boils at 77.3 K, from argon, which boils at 87.3 K and liquid oxygen, which boils at 90.2 K. About 700,000 tonnes of argon are produced worldwide every yearSony VAIO VGN-CS26T/P battery.[18]

[edit]In radioactive decays

40Ar, the most abundant isotope of argon, is produced by the decay of 40K with a half-life of 1.25×109 years by electron capture or positron emission. Because of this, it is used in potassium-argon dating to determine the age of rocks.

[edit]Applications

Cylinders containing argon gas for use in extinguishing fire without damaging server equipment

There are several different reasons argon is used in particular applications:

An inert gas is needed. In particular, argon is the cheapest alternative when nitrogen is not sufficiently inertSony VAIO VGN-CS26T/C battery.

Low thermal conductivity is required.

The electronic properties (ionization and/or the emission spectrum) are necessary.

Other noble gases would probably work as well in most of these applications, but argon is by far the cheapest. Argon is inexpensive since it is a byproduct of the production of liquid oxygen and liquid nitrogen from a cryogenic air separation unit, both of which are used on a large industrial scale. The other noble gases (except helium) are produced this way as wellSony VAIO VGN-CS25H battery, but argon is the most plentiful since it has the highest concentration in the atmosphere. The bulk of argon applications arise simply because it is inert and relatively cheap.

[edit]Industrial processes

Argon is used in some high-temperature industrial processes, where ordinarily non-reactive substances become reactive. For example, an argon atmosphere is used in graphite electric furnaces to prevent the graphite from burningSony VAIO VGN-CS25H/W battery.

For some of these processes, the presence of nitrogen or oxygen gases might cause defects within the material. Argon is used in various types of arc welding such as gas metal arc welding and gas tungsten arc welding, as well as in the processing of titanium and other reactive elements. An argon atmosphere is also used for growing crystals of silicon and germaniumSony VAIO VGN-CS25H/R battery.

See also: shielding gas

Argon is an asphyxiant in the poultry industry, either for mass culling following disease outbreaks, or as a means of slaughter more humane than the electric bath. Argon's relatively high density causes it to remain close to the ground during gassing. Its non-reactive nature makes it suitable in a food product, and since it replaces oxygen within the dead bird, argon also enhances shelf lifeSony VAIO VGN-CS25H/Q battery.[19]

Argon is sometimes used for extinguishing fires where damage to equipment is to be avoided.

[edit]Scientific research

Argon is used, primarily in liquid form, as the target for direct dark matter searches. The interaction of a hypothetical WIMP particle with the argon nucleus produces scintillation light that is then detected by photomultiplier tubes. Two-phase detectors also use argon gas to detect the ionized electrons produced during the WIMP-nucleus scatteringSony VAIO VGN-CS25H/P battery. As with most other liquefied noble gases, argon has a high scintillation lightyield (~ 51 photons / keV[20]), is transparent to its own scintillation light, and is relatively easy to purify. Compared to xenon, argon is cheaper and has a distinct scintillation time profile which allows the separation of electronic recoils from nuclear recoils. On the other hand, its intrinsic gamma-ray background is larger due to 39Ar contaminationSony VAIO VGN-CS25H/C battery, unless one uses underground argon sources with a low level of radioactivity. Dark matter detectors currently operating with liquid argon include WArP, ArDM, microCLEAN and DEAP-I.

Preservative

A sample of caesium is packed under argon to avoid reactions with air

Argon is used to displace oxygen- and moisture-containing air in packaging material to extend the shelf-lives of the contents (argon has the European food additive code of E938). Aerial oxidation, hydrolysisSony VAIO VGN-CS23T/W battery, and other chemical reactions which degrade the products are retarded or prevented entirely. Bottles of high-purity chemicals and certain pharmaceutical products are available in sealed bottles or ampoules packed in argon. In wine making, argon is used to top-off barrels to avoid the aerial oxidation of ethanol to acetic acid during the aging process.

Argon is also available in aerosol-type cans, which may be used to preserve compounds such as varnish, polyurethane, paint, etc. for storage after openingSony VAIO VGN-CS23T/Q battery.[21]

Since 2001, the American National Archives stores important national documents such as the Declaration of Independence and the Constitution within argon-filled cases to retard their degradation. Using argon reduces gas leakage, compared with the helium used in the preceding five decadesSony VAIO VGN-CS23H battery.[22]

Laboratory equipment

Gloveboxes are often filled with argon, which recirculates over scrubbers to maintain an oxygen-, nitrogen-, and moisture-free atmosphere

See also: Air-free technique

Argon may be used as the inert gas within Schlenk lines and gloveboxes. The use of argon over comparatively less expensive nitrogen is preferred where nitrogen may react with the experimental reagents or apparatusSony VAIO VGN-CS23H/S battery.

Argon may be used as the carrier gas in gas chromatography and in electrospray ionization mass spectrometry; it is the gas of choice for the plasma used in ICP spectroscopy. Argon is preferred for the sputter coating of specimens for scanning electron microscopy. Argon ions are also used for sputtering in microelectronicsSony VAIO VGN-CS23H/B battery.

[edit]Medical use

Cryosurgery procedures such as cryoablation use liquefied argon to destroy cancer cells. In surgery it is used in a procedure called "argon enhanced coagulation" which is a form of argon plasma beam electrosurgery. The procedure carries a risk of producing gas embolism in the patient and has resulted in the death of one person via this type of accidentSony VAIO VGN-CS23G battery.[23] Blue argon lasers are used in surgery to weld arteries, destroy tumors, and to correct eye defects.[24] It has also been used experimentally to replace nitrogen in the breathing or decompression mix, to speed the elimination of dissolved nitrogen from the blood.[25] See Argox.

Lighting

Argon gas-discharge lamp forming the symbol for argon "Ar". Small amounts of mercury are sometimes added to argon to produce an electric blue color, as in this pictureSony VAIO VGN-CS23G/W battery.

Incandescent lights are filled with argon, to preserve the filaments at high temperature from oxidation. It is used for the specific way it ionizes and emits light, such as in plasma globes and calorimetry in experimental particle physics. Gas-discharge lamps filled with argon provide blue light. Argon is also used for the creation of blue and green laser lightSony VAIO VGN-CS23G/Q battery.

[edit]Miscellaneous uses

It is used for thermal insulation in energy efficient windows.[26] Argon is also used in technical scuba diving to inflate a dry suit, because it is inert and has low thermal conductivity.[27]

Compressed argon is allowed to expand, to cool the seeker heads of the AIM-9 Sidewinder missile, and other missiles that use cooled thermal seeker heads. The gas is stored at high pressureSony VAIO VGN-CS23G/P battery.[28]

Argon-39, with a half-life of 269 years, has been used for a number of applications, primarily ice core and ground water dating. Also, potassium-argon dating is used in dating igneous rocks.

Safety

Although argon is non-toxic, it does not satisfy the body's need for oxygen and is thus an asphyxiant. Argon is 25% more dense than air and is considered highly dangerous in closed areasSony VAIO VGN-CS21Z/Q battery. It is also difficult to detect because it is colorless, odorless, and tasteless. A 1994 incident in which a man was asphyxiated after entering an argon filled section of oil pipe under construction in Alaska highlights the dangers of argon tank leakage in confined spaces, and emphasizes the need for proper use, storage and handlingSony VAIO VGN-CS21S/W battery.

 
Silicon is a chemical element with the symbol Si and atomic number 14. A tetravalent metalloid, it is less reactive than its chemical analog carbon, the nonmetal directly above it in the periodic table, but more reactive than germanium, the metalloid directly below it in the table. Controversy about silicon's character dates to its discoveryHP Pavilion DV9000 Battery: silicon was first prepared and characterized in pure form in 1824, and given the name silicium (from Latin: silicis, flints), with an -ium word-ending to suggest a metal, a name which the element retains in several non-English languages. However, its final English name, suggested in 1831, reflects the more physically similar elements carbon and boronHP Pavilion DV9500 Battery.

Silicon is the eighth most common element in the universe by mass, but very rarely occurs as the pure free element in nature. It is most widely distributed in dusts, sands, planetoids, and planets as various forms of silicon dioxide (silica) or silicates. Over 90% of the Earth's crust is composed of silicate minerals, making silicon the second most abundant element in the earth's crust (about 28% by mass) after oxygenHP Pavilion DV9700t Battery.[5]

Most silicon is used commercially without being separated, and indeed often with little processing of compounds from nature. These include direct industrial building-use of clays, silica sand and stone. Silica is used in ceramic brick. Silicate goes into Portland cement for mortar and stucco, and when combined with silica sand and gravel, to make concreteHP Pavilion dv9000T Battery. Silicates are also in whiteware ceramics such as porcelain, and in traditional quartz-based soda-lime glass. More modern silicon compounds such as silicon carbide form abrasives and high-strength ceramics. Silicon is the basis of the ubiquitous synthetic silicon-based polymers called siliconesHP Pavilion dv9000Z Battery.

Elemental silicon also has a large impact on the modern world economy. Although most free silicon is used in the steel refining, aluminum-casting, and fine chemical industries (often to make fumed silica), the relatively small portion of very highly purified silicon that is used in semiconductor electronics (< 10%) is perhaps even more critical. Because of wide use of silicon in integrated circuits, the basis of most computers, a great deal of modern technology depends on itHP Pavilion dv9001EA Battery.

Silicon is an essential element in biology, although only tiny traces of it appear to be required by animals,[6] however various sea sponges need silicon in order to have structure. It is much more important to the metabolism of plants, particularly many grasses, and silicic acid (a type of silica) forms the basis of the striking array of protective shells of the microscopic diatomsHP Pavilion dv9001TX Battery.

Characteristics

[edit]Physical

Silicon crystallizes in a diamond cubic crystal structure

Further information: Monocrystalline silicon

Silicon is a solid at room temperature, with relatively high melting and boiling points of approximately 1,400 and 2,800 degrees Celsius respectively.[7] Interestingly, silicon has a greater density in a liquid state than a solid state. Therefore, it does not contract when it freezes like most substances, but expandsHP Pavilion dv9001XX Battery, similar to how ice is less dense than water and has less mass per unit of volume than liquid water. With a relatively high thermal conductivity of 149 W·m−1·K−1, silicon conducts heat well and as a result is not often used to insulate hot objects.

In its crystalline form, pure silicon has a gray color and a metallic luster. Like germanium, silicon is rather strong, very brittle, and prone to chipping. Silicon, like carbon and germanium, crystallizes in a diamond cubic crystal structure, with a lattice spacing of approximately 0.5430710 nm (5.430710 Å). HP Pavilion dv9002EA Battery

The outer electron orbital of silicon, like that of carbon, has four valence electrons. The 1s,2s,2p and 3s subshells are completely filled while the 3p subshell contains two electrons out of a possible six.

Silicon is a semiconductor. It has a negative temperature coefficient of resistance, since the number of free charge carriers increases with temperature. The electrical resistance of single crystal silicon significantly changes under the application of mechanical stress due to the piezoresistive effectHP Pavilion dv9002TX Battery.[9]

[edit]Chemical

Silicon powder

Silicon is a metalloid, readily either donating or sharing its four outer electrons, allowing for many forms of chemical bonding. Even though it is relatively inert like carbon, silicon still reacts with halogens and dilute alkalis, but most acids (except for some hyper-reactive combinations of nitric acid and hydrofluoric acid) have no known effect on itHP Pavilion dv9002XX Battery. However, having four bonding electrons gives it, like carbon, many opportunities to combine with other elements or compounds under the right circumstances.

[edit]Isotopes

Main article: isotopes of silicon

Naturally occurring silicon is composed of three stable isotopes, silicon-28, silicon-29, and silicon-30, with silicon-28 being the most abundant (92% natural abundance).[10] Out of these, only silicon-29 is of use in NMR and EPR spectroscopyHP Pavilion dv9003EA Battery.[11] Twenty radioisotopes have been characterized, with the most stable being silicon-32 with a half-life of 170 years, and silicon-31 with a half-life of 157.3 minutes.[10] All of the remaining radioactive isotopes have half-lives that are less than seven seconds, and the majority of these have half-lives that are less than one tenth of a second.[10] Silicon does not have any known nuclear isomersHP Pavilion dv9003TX Battery.[10]

The isotopes of silicon range in mass number from 22 to 44.[10] The most common decay mode of six isotopes with mass numbers lower than the most abundant stable isotope, silicon-28, is β+

, primarily forming aluminium isotopes (13 protons) as decay products.[10] The most common decay mode(s) for 16 isotopes with mass numbers higher than silicon-28 is β−HP Pavilion dv9003XX Battery

, primarily forming phosphorus isotopes (15 protons) as decay products.[10]

[edit]Occurrence

Quartz crystal cluster from Tibet. The naturally-occurring mineral is a network solid with the formula SiO2.

See also: Silicate minerals

Measured by mass, silicon makes up 27.7% of the Earth's crust and is the second most abundant element in the crust, with only oxygen having a greater abundance.[12] Silicon is usually found in the form of complex silicate minerals, and less often as silicon dioxide (silica, a major component of common sand). Pure silicon crystals are very rarely found in natureHP Pavilion dv9004TX Battery.

The silicate minerals—various minerals containing silicon, oxygen and reactive metals—account for 90% of the mass of the Earth's crust. This is due to the fact that at the high temperatures characteristic of formation of the inner solar system, silicon and oxygen have a great affinity for each other, forming networks of silicon and oxygen in chemical compounds of very low volatilityHP Pavilion dv9005CA Battery. Since oxygen and silicon were the most common non-gaseous and non-metallic elements in the debris from supernova dust which formed the protoplanetary disk in the formation and evolution of the Solar System, they formed many complex silicates which accreted into larger rocky planetesimals that formed the terrestrial planets. Here, the reduced silicate mineral matrix entrapped the metals reactive enough to be oxidized (aluminum, calcium, sodium, potassium and magnesium) HP Pavilion dv9005EA Battery. After loss of volatile gases, as well as carbon and sulfur via reaction with hydrogen, this silicate mixture of elements formed most of the Earth's crust. These silicates were of relatively low density with respect to iron, nickel, and other metals non-reactive to oxygen and thus a residuum of uncombined iron and nickel sank to the planet's core, leaving a thick mantle consisting mostly of magnesium and iron silicates aboveHP Pavilion dv9005TX Battery.

Examples of silicate minerals in the crust include those in the pyroxene, amphibole, mica, and feldspar groups. These minerals occur in clay and various types of rock such as granite and sandstone.

Silica occurs in minerals consisting of very pure silicon dioxide in different crystalline forms, quartz, agate amethyst, rock crystal, chalcedony, flint, jasper, and opal. The crystals have the empirical formula of silicon dioxideHP Pavilion dv9005US Battery, but do not consist of separate silicon dioxide molecules in the manner of solid carbon dioxide. Rather, silica is structurally a network-solid consisting of silicon and oxygen in three-dimensional crystals, like diamond. Less pure silica forms the natural glass obsidian. Biogenic silica occurs in the structure of diatoms, radiolaria and siliceous spongesHP Pavilion dv9006TX Battery.

Silicon is also a principal component of many meteorites, and is a component of tektites, a silicate mineral of possibly lunar origin, or (if Earth-derived) which has been subjected to unusual temperatures and pressures, possibly from meteorite strike.

[edit]Production

[edit]Alloys

Ferrosilicon alloy

Ferrosilicon, an iron-silicon alloy that contains varying ratios of elemental silicon and iron, accounts for about 80% of the world's production of elemental silicon, with ChinaHP Pavilion dv9007TX Battery, the leading supplier of elemental silicon, providing 4.6 million tonnes (or 2/3 of the world output) of silicon, most of which is in the form of ferrosilicon. It is followed by Russia (610,000 t), Norway (330,000 t), Brazil (240,000 t) and the United States (170,000 t).[13] Ferrosilicon is primarily used by the steel industry (see below).

Aluminum-silicon alloys are heavily used in the aluminum alloy casting industry, where silicon is the single most important additive to aluminum to improve its casting propertiesHP Pavilion dv9008TX Battery. Since cast aluminum is widely used in the automobile industry, this use of silicon is thus the single largest industrial use of "metallurgical grade" pure silicon (as this purified silicon is added to pure aluminum, whereas ferrosilicon is never purified before being added to steel).[14]

[edit]Metallurgical grade

Elemental silicon not alloyed with significant quantities of other elements, and usually > 95% is often referred to loosely as silicon metal. It makes up about 20% of the world total elemental silicon productionHP Pavilion dv9010CA Battery, with less than 1 to 2% of total elemental silicon (5–10% of metallurgical grade silicon) ever purified to higher grades for use in electronics. Metallurgical grade silicon is commercially prepared by the reaction of high-purity silica with wood, charcoal, and coal in an electric arc furnace using carbon electrodes. At temperatures over 1,900 °C (3,450 °F), the carbon in the aforementioned materials and the silicon undergo the chemical reaction SiO2 + 2 C → Si + 2 COHP Pavilion dv9010TX Battery. Liquid silicon collects in the bottom of the furnace, which is then drained and cooled. The silicon produced via this process is called metallurgical grade silicon and is at least 98% pure. Using this method, silicon carbide (SiC) may also form from an excess of carbon in one or both of the following ways: SiO2 + C → SiO + CO or SiO + 2 C → SiC + CO. However, provided the concentration of SiO2 is kept high, the silicon carbide can be eliminated by the chemical reaction 2 SiC + SiO2 → 3 Si + 2 COHP Pavilion dv9010US Battery.

As noted above, metallurgical grade silicon "metal" has its primary use in the aluminum casting industry to make aluminum-silicon alloy parts. The remainder (about 45%) is used by the chemical industry, where it is primarily employed to make fumed silica.[15]

As of September 2008, metallurgical grade silicon costs about US$1.45 per pound ($3.20/kg),[16] up from $0.77 per pound ($1.70/kg) in 2005HP Pavilion dv9011TX Battery.[17]

[edit]Electronic grade

Monocrystalline silicon ingot grown by the Czochralski process

The use of silicon in semiconductor devices demands a much greater purity than afforded by metallurgical grade silicon. Very pure silicon (>99.9%) can be extracted directly from solid silica or other silicon compounds by molten salt electrolysis.[18][19] This method, known as early as 1854[20] (see also FFC Cambridge process), has the potential to directly produce solar-grade silicon without any carbon dioxide emission at much lower energy consumptionHP Pavilion dv9012TX Battery.

Solar grade silicon cannot be used for semiconductors, where purity must be extreme to properly control the process. Bulk silicon wafers used at the beginning of the integrated circuit making process must first be refined to "nine nines" purity (99.9999999%), a process which requires repeated applications of refining technologyHP Pavilion dv9013CA Battery.

The majority of silicon crystals grown for device production are produced by the Czochralski process, (CZ-Si) since it is the cheapest method available and it is capable of producing large size crystals. However, single crystals grown by the Czochralski process contain impurities because the crucible containing the melt often dissolves. Historically, a number of methods have been used to produce ultra-high-purity siliconHP Pavilion dv9013CL Battery.

Early silicon purification techniques were based on the fact that if silicon is melted and re-solidified, the last parts of the mass to solidify contain most of the impurities. The earliest method of silicon purification, first described in 1919 and used on a limited basis to make radar components during World War II, involved crushing metallurgical grade silicon and then partially dissolving the silicon powder in an acidHP Pavilion dv9013TX Battery. When crushed, the silicon cracked so that the weaker impurity-rich regions were on the outside of the resulting grains of silicon. As a result, the impurity-rich silicon was the first to be dissolved when treated with acid, leaving behind a more pure product.

In zone melting, also called zone refining, the first silicon purification method to be widely used industrially, rods of metallurgical grade silicon are heated to melt at one end. Then, the heater is slowly moved down the length of the rodHP Pavilion dv9014EA Battery, keeping a small length of the rod molten as the silicon cools and re-solidifies behind it. Since most impurities tend to remain in the molten region rather than re-solidify, when the process is complete, most of the impurities in the rod will have been moved into the end that was the last to be melted. This end is then cut off and discarded, and the process repeated if a still higher purity is desiredHP Pavilion dv9014TX Battery.[21]

A polycrystalline silicon rod made by the Siemens process

At one time, DuPont produced ultra-pure silicon by reacting silicon tetrachloride with high-purity zinc vapors at 950 °C, producing silicon by SiCl4 + 2 Zn → Si + 2 ZnCl2. However, this technique was plagued with practical problems (such as the zinc chloride byproduct solidifying and clogging lines) and was eventually abandoned in favor of the Siemens processHP Pavilion dv9015EA Battery. In the Siemens process, high-purity silicon rods are exposed to trichlorosilane at 1150 °C. The trichlorosilane gas decomposes and deposits additional silicon onto the rods, enlarging them because 2 HSiCl3 → Si + 2 HCl + SiCl4. Silicon produced from this and similar processes is called polycrystalline silicon. Polycrystalline silicon typically has impurity levels of less than one part per billion. HP Pavilion dv9015TX Battery

In 2006 REC announced construction of a plant based on fluidized bed (FB) technology using silane: 3 SiCl4 + Si + 2 H2 → 4 HSiCl3, 4 HSiCl3 → 3 SiCl4 + SiH4, SiH4 → Si + 2 H2.[25] The advantage of fluid bed technology is that processes can be run continuously, yielding higher yields than Siemens Process, which is a batch processHP Pavilion dv9016EA Battery.

Today, silicon is purified by converting it to a silicon compound that can be more easily purified by distillation than in its original state, and then converting that silicon compound back into pure silicon. Trichlorosilane is the silicon compound most commonly used as the intermediate, although silicon tetrachloride and silane are also used. When these gases are blown over silicon at high temperature, they decompose to high-purity siliconHP Pavilion dv9016TX Battery.

In addition, there exists the Schumacher process, which utilizes tribromosilane in place of trichlorosilane and fluid bed technology. It requires lower deposition temperatures, lower capital costs to build facilities and operate, no hazardous polymers nor explosive material, and no amorphous silicon dust waste, all of which are drawbacks of the Siemens Process.[26] However, there are yet to be any major factories built on this processHP Pavilion dv9017TX Battery.

[edit]Compounds

PDMS – a silicone compound

Silicon forms binary compounds called silicides with many metallic elements whose properties range from reactive compounds, e.g. magnesium silicide, Mg2Si through high melting refractory compounds such as molybdenum disilicide, MoSi2.[27]

Silicon carbide, SiC (carborundum) is a hard, high melting solid and a well known abrasive. It may also be sintered into a type of high-strength ceramic used in armorHP Pavilion dv9018EA Battery.

Silane, SiH4, is a pyrophoric gas with a similar tetrahedral structure to methane, CH4. When pure, it does not react with pure water or dilute acids; however, even small amounts of alkali impurities from the laboratory glass can result in a rapid hydrolysis.[28] There is a range of catenated silicon hydrides that form a homologous series of compounds, SinH2n+2 where n = 2–8 (analogous to the alkanes) HP Pavilion dv9018TX Battery. These are all readily hydrolyzed and are thermally unstable, particularly the heavier members.[29][30]

Disilenes contain a silicon-silicon double bond (analogous to the alkenes) and are generally highly reactive requiring large substituent groups to stabilize them.[31] A disilyne with a silicon-silicon triple bond was first isolated in 2004; although as the compound is non-linear, the bonding is dissimilar to that in alkynesHP Pavilion dv9019EA Battery.[32]

Tetrahalides, SiX4, are formed with all the halogens.[33] Silicon tetrachloride, for example, reacts with water, unlike its carbon analogue, carbon tetrachloride.[34] Silicon dihalides are formed by the high temperature reaction of tetrahalides and silicon; with a structure analogous to a carbene they are reactive compounds. Silicon difluoride condenses to form a polymeric compound, (SiF2)n. HP Pavilion dv9019TX Battery

Silicon dioxide is a high melting solid with a number of crystal forms; the most familiar of which is the mineral quartz. In quartz each silicon atom is surrounded by four oxygen atoms that bridge to other silicon atoms to form a three dimensional lattice.[34] Silica is soluble in water at high temperatures forming a range of compounds called monosilicic acid, Si(OH)4HP Pavilion dv9020TX Battery.[35]

Under the right conditions monosilicic acid readily polymerizes to form more complex silicic acids, ranging from the simplest condensate, disilicic acid (H6Si2O7) to linear, ribbon, layer and lattice structures which form the basis of the many silicate minerals and are called polysilicic acids {Six(OH)4–2x}nHP Pavilion dv9021TX Battery.[35]

With oxides of other elements the high temperature reaction of silicon dioxide can give a wide range of glasses with various properties.[36] Examples include soda lime glass, borosilicate glass and lead crystal glass.

Silicon sulfide, SiS2 is a polymeric solid (unlike its carbon analogue the liquid CS2).[37]

Silicon forms a nitride, Si3N4 which is a ceramic.[38] Silatranes, a group of tricyclic compounds containing five-coordinate silicon, may have physiological propertiesHP Pavilion dv9022EA Battery.[39]

Many transition metal complexes containing a metal-silicon bond are now known, which include complexes containing SiHnX3−n ligands, SiX3 ligands, and Si(OR)3 ligands.[39]

Silicones are large group of polymeric compounds with an (Si-O-Si) backbone. An example is the silicone oil PDMS (polydimethylsiloxane). These polymers can be crosslinked to produce resins and elastomersHP Pavilion dv9022TX Battery.[40]

Many organosilicon compounds are known which contain a silicon-carbon single bond. Many of these are based on a central tetrahedral silicon atom, and some are optically active when central chirality exists. Long chain polymers containing a silicon backbone are known, such as polydimethysilylene (SiMe2)n.[41] Polycarbosilane, [(SiMe2)2CH2]n with a backbone containing a repeating -Si-Si-C unit, is a precursor in the production of silicon carbide fibersHP Pavilion dv9024EA Battery.[41]

[edit]History

Attention was first drawn to quartz as the possible oxide of a fundamental chemical element by Antoine Lavoisier, in 1787. In 1811, Gay-Lussac and Thénard are thought to have prepared impure amorphous silicon, through the heating of recently isolated potassium metal with silicon tetrafluoride, but they did not purify and characterize the product, nor identify it as a new elementHP Pavilion dv9030EA Battery. In 1824, Berzelius prepared amorphous silicon using approximately the same method as Gay-Lussac (potassium metal and potassium fluorosilicate), but purifying the product to a brown powder by repeatedly washing it. He named the product silicium from the Latin silex, silicis for flint, flints, and adding the "-ium" ending because he believed it was a metal. As a result he is usually given credit for element's discovery. HP Pavilion dv9030US Battery Silicon was given its present name in 1831 by Scottish chemist Thomas Thomson. He retained part of Berzelius's name but added "-on" because he believed silicon a nonmetal more similar to boron and carbon.

Silicon in its more common crystalline form was not prepared until 31 years later, by Deville.[44] By electrolyzing impure sodium-aluminum chloride containing approximately 10% silicon, he was able to obtain a slightly impure allotrope of silicon in 1854.[45] Later, more cost-effective methods have been developed to isolate silicon in several allotrope forms, the most recent being siliceneHP Pavilion dv9033CL Battery.

Because silicon is an important element in semiconductors and high-technology devices, many places in the world bear its name. For example, Silicon Valley in California, since it is the base for a number of technology-related industries, bears the name silicon. Other geographic locations with connections to the industry have since been named after silicon as wellHP Pavilion dv9035EA Battery. Examples include Silicon Forest in Oregon, Silicon Hills in Austin, Texas, Silicon Saxony in Germany, Silicon Valley in India, Silicon Border in Mexicali, Mexico, Silicon Fen in Cambridge, England, and Silicon Gorge in Bristol, England.

Applications

Compounds

Most silicon is used industrially without being separated into the element, and indeed often with comparatively little processing from natural occurrence. Over 90% of the Earth's crust is composed of silicate minerals. Many of these have direct commercial uses, such as claysHP Pavilion dv9035NR Battery, silica sand and most kinds of building stone. Thus, the vast majority of uses for silicon are as structural compounds, either as the silicate minerals or silica (crude silicon dioxide). For example, silica is an important part of ceramic brick. Silicates are used in making Portland cement which is used in building mortar and stucco, but more importantly combined with silica sand, and gravel (usually containing silicate minerals like granite) HP Pavilion dv9036EA Battery, to make the concrete that is the basis of most of the very largest industrial building projects of the modern world. [46]

Silicate minerals are also in whiteware ceramics, an important class of products usually containing various types of fired clay (natural aluminum silicate). An example is porcelain which is based on silicate mineral kaolinite. Ceramics include art objects, and domestic, industrial and building products. Traditional quartz-based soda-lime glass also functions in many of the same rolesHP Pavilion dv9700t Battery.

More modern silicon compounds also function as high-technology abrasives and new high-strength ceramics based upon (silicon carbide), and in superalloys.

Alternating silicon-oxygen chains with hydrogen attached to the remaining silicon bonds form the ubiquitous silicon-based polymeric materials known as silicones. These compounds containing silicon-oxygen and occasionally silicon-carbon bonds have the capability to act as bonding intermediates between glass and organic compoundsHP Pavilion dv9700/CT Battery, and to form polymers with useful properties such as impermeability to water, flexibility and resistance to chemical attack. Silicones are often used in waterproofing treatments, molding compounds, mold-release agents, mechanical seals, high temperature greases and waxes, and caulking compounds. Silicone is also sometimes used in breast implants, contact lensesHP Pavilion dv9605TX Battery, explosives and pyrotechnics.[47] Silly Putty was originally made by adding boric acid to silicone oil.[48]

[edit]Alloys

Elemental silicon is added to molten cast iron as ferrosilicon or silicocalcium alloys to improve performance in casting thin sections, and to prevent the formation of cementite where exposed to outside air. The presence of elemental silicon in molten iron acts as a sink for oxygen, so that the steel carbon content, which must be kept within narrow limits for each type of steelHP Pavilion dv9604TX Battery, can be more closely controlled. Ferrosilicon production and use is a monitor of the steel industry, and although this form of elemental silicon is impure, it accounts for 80% of the world's use of free silicon.

The properties of silicon itself can be used to modify alloys. Silicon's importance in aluminum casting is that a significantly high amount (12%) of silicon in aluminum forms a eutectic mixture which solidifies with very little thermal contraction. This greatly reduces tearing and cracks formed from stress as casting alloys cool to solidityHP Pavilion dv9600 Battery. Silicon also significantly improves the hardness and thus wear-resistance of aluminum.[14] Silicon is an important constituent of electrical steel, modifying its resistivity and ferromagnetic properties.

Metallurgical grade silicon is silicon of 95–99% purity. About 55% of the world consumption of metallurgical purity silicon goes for production of aluminum-silicon alloys for aluminum part casts, mainly for use in the automotive industryHP Pavilion dv9535us Battery. The reason for the high silicon use in these alloys is noted above.[15] Much of the rest of metallurgical-grade silicon is used by the chemical industry for production of the important industrial product fumed silica. The remainder is used in production of other fine chemicals such as silanes and some types of siliconesHP Pavilion dv9525us Battery.

[edit]Electronics

Main article: Semiconductor device fabrication

Silicon wafer with mirror finish

Since most elemental silicon produced remains as ferrosilicon alloy, only a relatively small amount (20%) of the elemental silicon produced is refined to metallurgical grade purity (a total of 1.3–1.5 million metric tons/year). The fraction of silicon metal which is further refined to semiconductor purity is estimated at only 15% of the world production of metallurgical grade silicon. HP Pavilion dv9500z Battery However, the economic importance of this small very high-purity fraction (especially the ~ 5% which is processed to monocrystalline silicon for use in integrated circuits) is disproportionately large.

Pure monocrystalline silicon is used to produce silicon wafers used in the semiconductor industry, in electronics and in some high-cost and high-efficiency photovoltaic applications. In terms of charge conduction, pure silicon is an intrinsic semiconductor which means that unlike metals it conducts electron holes and electrons which may be released from atoms within the crystal by heatHP Pavilion dv9500t Battery, and thus increase silicon's electrical conductance with higher temperatures. Pure silicon has too low a conductance to be used as a circuit element in electronics without being doped with small concentrations of certain other elements. This process greatly increases its conductivity and adjusts its electrical response by controlling the number and charge (positive or negative) of activated carriersHP Pavilion dv9500/CT Battery. Such control is necessary for transistors, solar cells, semiconductor detectors and other semiconductor devices, which are used in the computer industry and other technical applications. For example, in silicon photonics, silicon can be used as a continuous wave Raman laser medium to produce coherent light, though it is ineffective as an everyday light sourceHP Pavilion dv9500 Battery.

In common integrated circuits, a wafer of monocrystalline silicon serves as a mechanical support for the circuits, which are created by doping, and insulated from each other by thin layers of silicon oxide, an insulator which is easily produced by exposing the element to oxygen under the proper conditions. Silicon has become the most popular material to build both high power semiconductors and integrated circuits, because of all the elementsHP Pavilion dv9299XX Battery, silicon is the semiconductor which can withstand the highest powers and temperatures without becoming dysfunctional due to avalanche breakdown, a process in which an electron avalanche is created by a chain reaction process where heat produces free electrons and holes, which in turn produce more current which produces more heat. In addition, the insulating oxide of silicon is not soluble in waterHP Pavilion dv9299EA Battery, which gives it an advantage over germanium (an element with similar properties which can also be used in semiconductor devices) in certain type of fabrication techniques.[49]

Monocrystalline silicon is expensive to produce, and is usually only justified in production of integrated circuits, where tiny crystal imperfections can interfere with tiny circuit paths. For other uses, other types of pure silicon which do not exist as single crystals may be employedHP Pavilion dv9297EA Battery. These include hydrogenated amorphous silicon and upgraded metallurgical-grade silicon (UMG-Si) which are used in the production of low-cost, large-area electronics in applications such as Liquid crystal displays, and of large-area, low-cost, thin-film solar cells. Such semiconductor grades of silicon which are either slightly less pure than those used in integrated circuitsHP Pavilion dv9296EU Battery, or which are produced in polycrystalline rather than monocrystalline form, make up roughly similar amount of silicon as are produced for the monocrystalline silicon semiconductor industry, or 75,000 to 150,000 metric tons per year. However, production of such materials is growing more quickly than silicon for the integrated circuit market. By 2013 polycrystalline silicon production, used mostly in solar cells, is projected to reach 200,000 metric tons per year, while monocrystalline semiconductor silicon production (used in computer microchips) remains below 50,000 tons/year. HP Pavilion dv9296EA Battery

[edit]Biological role

Silica skeletons of radiolaria in false color.

Although silicon is readily available in the form of silicates, very few organisms have a use for it. Diatoms, radiolaria and siliceous sponges use biogenic silica as a structural material to construct skeletons. In more advanced plants, the silica phytoliths (opal phytoliths) are rigid microscopic bodies occurring in the cell; some plants, for example riceHP Pavilion dv9295EA Battery, need silicon for their growth.[50][51][52] Although silicon was proposed to be an ultra trace nutrition its exact function in the biology of animals is still under discussion. Higher organisms are only known to use it in very limited occasions in the form of silicic acid and soluble silicates.

Silicon is currently under consideration for elevation to the status of a "plant beneficial substance by the Association of American Plant Food Control Officials (AAPFCO)." HP Pavilion dv9295EA BatterySilicon has been shown in university and field studies to improve plant cell wall strength and structural integrity,[55] improve drought and frost resistance, decrease lodging potential and boost the plant's natural pest and disease fighting systems.[56] Silicon has also been shown to improve plant vigor and physiology by improving root mass and density, and increasing above ground plant biomass and crop yieldsHP Pavilion dv9294EU Battery.[55]

Hypothetical silicon-based lifeforms are the subject of silicon biochemistry, in analogy with carbon-based lifeforms. Silicon, being below carbon in the periodic table, is thought to have similar enough properties that would make silicon-based life possible, but much different from life as we know itHP Pavilion dv9294EA Battery.

Phosphorus ( /ˈfɒsfərəs/ fos-fər-əs) is the chemical element that has the symbol P and atomic number 15. A multivalent nonmetal of the nitrogen group, phosphorus as a mineral is almost always present in its maximally oxidized state, as inorganic phosphate rocks. Elemental phosphorus exists in two major forms—white phosphorus and red phosphorus—but due to its high reactivity, phosphorus is never found as a free element on EarthHP Pavilion dv9292EU Battery.

The first form of elemental phosphorus to be produced (white phosphorus, in 1669) emits a faint glow upon exposure to oxygen – hence its name given from Greek mythology, Φωσφόρος meaning "light-bearer" (Latin Lucifer), referring to the "Morning Star", the planet Venus. The term "phosphorescence", meaning glow after illumination, originally derives from this property of phosphorusHP Pavilion dv9291EA Battery, although this word has since been used for a different physical process that produces a glow. The glow of phosphorus itself originates from oxidation of the white (but not red) phosphorus— a process now termed chemiluminescence.

The vast majority of phosphorus compounds are consumed as fertilizers. Other applications include the role of organophosphorus compounds in detergents, pesticides and nerve agents, and matchesHP Pavilion dv9289EA Battery.[4]

Phosphorus is essential for life. As phosphate, it is a component of DNA, RNA, ATP, and also the phospholipids that form all cell membranes. Demonstrating the link between phosphorus and life, elemental phosphorus was historically first isolated from human urine, and bone ash was an important early phosphate source. Phosphate minerals are fossilsHP Pavilion dv9288EA Battery. Low phosphate levels are an important limit to growth in some aquatic systems. The chief commercial use of phosphorus compounds for production of fertilizers is due to the need to replace the phosphorus that plants remove from the soil.

Characteristics

Main article: Allotropes of phosphorus

Physical

P4 molecule

Phosphorus exists as several forms (allotropes) that exhibit strikingly different properties.[5] The two most common allotropes are white phosphorus and red phosphorus. Another form, scarlet phosphorusHP Pavilion dv9287CL Battery, is obtained by allowing a solution of white phosphorus in carbon disulfide to evaporate in sunlight. Black phosphorus is obtained by heating white phosphorus under high pressures (about 12,000 standard atmospheres or 1.2 gigapascals). In appearance, properties, and structure, it resembles graphite, being black and flaky, a conductor of electricity, and has puckered sheets of linked atoms. Another allotrope is diphosphorusHP Pavilion dv9286EA Battery; it contains a phosphorus dimer as a structural unit and is highly reactive.[6]

White phosphorus

White phosphorus exposed to air glows in the darkness

White phosphorus and related molecular forms

The most important form of elemental phosphorus from the perspective of applications and chemical literature is white phosphorus. It consists of tetrahedral P4 molecules, in which each atom is bound to the other three atoms by a single bond. This P4 tetrahedron is also present in liquid and gaseous phosphorus up to the temperature of 800 °C when it starts decomposing to P2 moleculesHP Pavilion dv9285EA Battery.[7] Solid white exists in two forms. At low-temperatures, the β form is stable. At high-temperatures α form is predominant. These forms differ in terms of the relative orientations of the constituent P4 tetrahedra.

White phosphorus is the least stable, the most reactive, more volatile, less dense, and more toxic than the other allotropes. White phosphorus gradually changes to red phosphorus. This transformation, which is accelerated by light and heatHP Pavilion dv9283EA Battery, and samples of white phosphorus almost always contain some red phosphorus and therefore appear yellow. For this reason, it is also called yellow phosphorus. It glows in the dark (when exposed to oxygen) with a very faint tint of green and blue, is highly flammable and pyrophoric (self-igniting) upon contact with air as well as toxic (causing severe liver damage on ingestion) HP Pavilion dv9276EA Battery. Because of pyrophoricity, white phosphorus is used as an additive in napalm. The odour of combustion of this form has a characteristic garlic smell, and samples are commonly coated with white "(di)phosphorus pentoxide", which consists of P4O10 tetrahedra with oxygen inserted between the phosphorus atoms and at their vertices. White phosphorus is insoluble in water but soluble in carbon disulfideHP Pavilion dv9275LA Battery.[8]

Thermolysis (cracking) of P4 at 1100 kelvin) gives diphosphorus, P2. This species is not stable as a solid or liquid. The dimeric unit contains a triple bond and is analogous to N2. It can also be generated as a transient intermediate in solution by thermolysis of organophosphorus precursor reagents.[9] At still higher temperatures, P2 dissociates into atomic PHP Pavilion dv9275EA Battery.

Although the term phosphorescence is derived from phosphorus, the reaction that gives phosphorus its glow is properly called chemiluminescence (glowing due to a cold chemical reaction), not phosphorescence (re-emitting light that previously fell onto a substance and excited it) HP Pavilion dv9274EU Battery.

Crystal structure of red phosphorus

red phosphorus

Red phosphorus

Red phosphorus is polymeric in structure. It can be viewed as a derivative of P4 wherein one P-P bond is broken, and one additional bond is formed between the neighbouring tetrahedron resulting in a chain-like structure. Red phosphorus may be formed by heating white phosphorus to 250 °C (482 °F) or by exposing white phosphorus to sunlightHP Pavilion dv9273EA Battery.[10] Phosphorus after this treatment is amorphous. Upon further heating, this material crystallises. In this sense, red phosphorus is not an allotrope, but rather an intermediate phase between the white and violet phosphorus, and most of its properties have a range of values. For example, freshly prepared, bright red phosphorus is highly reactive and ignites at about 300 °C,[11] though it is still more stable than white phosphorusHP Pavilion dv9272EA Battery, which ignites at about 30 °C.[12] After prolonged heating or storage, the color darkens (see infobox images); the resulting product is more stable and does not spontaneously ignite in air.[13]

Violet phosphorus

Violet phosphorus is a form of phosphorus that can be produced by day-long annealing of red phosphorus above 550 °C. In 1865, Hittorf discovered that when phosphorus was recrystallized from molten lead, a red/purple form is obtained. Therefore this form is sometimes known as "Hittorf's phosphorus" (or violet or α-metallic phosphorus) HP Pavilion dv9271EA Battery.[6]

Crystal structure of black phosphorus

Black phosphorus

Black phosphorus is the least reactive allotrope and the thermodynamically stable form below 550 °C. It is also known as β-metallic phosphorus and has a structure somewhat resembling that of graphite.[14][15] High pressures are usually required to produce black phosphorus, but it can also be produced at ambient conditions using metal salts as catalystsHP Pavilion dv9269EA Battery.[16]

Isotopes

Main article: Isotopes of phosphorus

Twenty-three isotopes of phosphorus are known,[17] including all possibilities from 24P up to 46P). Only 31P is stable and is therefore present at 100% abundance. The half-integer nuclear spin and high abundance of 31P make phosphorus-31 NMR spectroscopy a very useful analytical tool in studies of phosphorus-containing samplesHP Pavilion dv9268EA Battery.

Two radioactive isotopes of phosphorus have half-lives that make them useful for scientific experiments. 32P has a half-life of 14.262 days and 33P has a half-life of 25.34 days. Biomolecules can be "tagged" with a radioisotope to allow for the study of very dilute samples.

Radioactive isotopes of phosphorus include

32P, a beta-emitter (1.71 MeV) with a half-life of 14.3 days, which is used routinely in life-science laboratories, primarily to produce radiolabeled DNA and RNA probesHP Pavilion dv9267EA Battery, e.g. for use in Northern blots or Southern blots. Because the high energy beta particles produced penetrate skin and corneas, and because any 32P ingested, inhaled, or absorbed is readily incorporated into bone and nucleic acids, Occupational Safety and Health Administration in the United States, and similar institutions in other developed countries require that a lab coatHP Pavilion dv9266EU Battery, disposable gloves and safety glasses or goggles be worn when working with 32P, and that working directly over an open container be avoided in order to protect the eyes. Monitoring personal, clothing, and surface contamination is also required. In addition, due to the high energy of the beta particles, shielding this radiation with the normally used dense materials (e.g. lead) HP Pavilion dv9266EA Battery, gives rise to secondary emission of X-rays via Bremsstrahlung (braking radiation). Therefore shielding must be accomplished with low density materials, e.g. Plexiglas (Lucite), other plastics, water, or (when transparency is not required), even wood.[18]

33P, a beta-emitter (0.25 MeV) with a half-life of 25.4 days. It is used in life-science laboratories in applications in which lower energy beta emissions are advantageous such as DNA sequencingHP Pavilion dv9265LA Battery.

Occurrence

See also Category: Phosphate minerals

In terms of stellar nucleosynthesis, stable forms of phosphorus are produced in large (greater than 3 solar masses) stars by fusing two oxygen atoms together.[citation needed] This requires temperatures above 1,000 megakelvins.

Phosphorus is not found free in nature, but it is widely distributed in many minerals, mainly phosphates. Phosphate rock, which is partially made of apatite (an impure tri-calcium phosphate mineral), is an important commercial source of this elementHP Pavilion dv9260US Battery. About 50 percent of the global phosphorus reserves are in the Arab nations.[19] Large deposits of apatite are located in China, Russia, Morocco, Florida, Idaho, Tennessee, Utah, and elsewhere. Albright and Wilson in the United Kingdom and their Niagara Falls plant, for instance, were using phosphate rock in the 1890s and 1900s from the Îles du Connétable, Tennessee and Florida; by 1950 they were using phosphate rock mainly from Tennessee and North AfricaHP Pavilion dv9260NR Battery.[20] In the early 1990s Albright and Wilson's purified wet phosphoric acid business was being adversely affected by phosphate rock sales by China and the entry of their long-standing Moroccan phosphate suppliers into the purified wet phosphoric acid business.[21]

Scarcity

Recent reports suggest that production of phosphorus may have peaked, leading to the possibility of global shortages by 2040.[22] In 2007, at the rate of consumption, the supply of phosphorus was estimated to run out in 345 yearsHP Pavilion dv9255EA Battery.[23] However, some scientists now believe that a "Peak phosphorus" will occur in 30 years and that "At current rates, reserves will be depleted in the next 50 to 100 years."[24]

Production

Main article: phosphoric acid

The majority of phosphorus-containing compounds are produced for use as fertilisers. For this purpose, phosphate-containing minerals are converted to phosphoric acid. Two distinct routes are employed, the main one being treatment of phosphate minerals with sulfuric acidHP Pavilion dv9254EU Battery. The other process utilises white phosphorus, which may be produced by reaction and distillation from very low grade phosphate sources. The white phosphorus is then oxidised to phosphoric acid and subsequently neutralised with base to give phosphate salts. Phosphoric acid obtained via white phosphorus is relatively pure and is the main source of phosphates used in detergents and other non-fertiliser applicationsHP Pavilion dv9253EA Battery.

Elemental phosphorus

About 1,000,000 short tons (910,000 t) of elemental phosphorus is produced annually. Calcium phosphate (phosphate rock), mostly mined in Florida and North Africa, can be heated to 1,200–1,500 °C with sand, which is mostly SiO2, and coke (impure carbon) to produce vaporized P4. The product is subsequently condensed into a white powder under water to prevent oxidation by airHP Pavilion dv9252EU Battery. Even under water, white phosphorus is slowly converted to the more stable red phosphorus allotrope. The chemical equation for this process when starting with fluoroapatite, a common phosphate mineral, is:

4 Ca5(PO4)3F + 18 SiO2 + 30 C → 3 P4 + 30 CO + 18 CaSiO3 + 2 CaF2

Side products from this production include ferrophosphorus, a crude form of Fe2P, resulting from iron impurities in the mineral precursors. The silicate slag is a useful construction material. The fluoride is sometimes recovered for use in water fluoridationHP Pavilion dv9248EA Battery. More problematic is a "mud" containing significant amounts of white phosphorus. Production of white phosphorus is conducted in large facilities in part because it is energy intensive. The white phosphorus is transported in molten form. Some major accidents have occurred during transportation, train derailments at Brownston, Nebraska and Miamisburg, Ohio led to large firesHP Pavilion dv9244EU Battery. The worst incident in recent times was an environmental one in 1968 when the sea became contaminated due to spillages and/or inadequately treated sewage from a white phosphorus plant at Placentia Bay, Newfoundland.[25]

Another process by which elemental phosphorus is extracted includes applying at high temperatures (1500 °C):[26]

2 Ca3(PO4)2 + 6 SiO2 + 10 C → 6CaSiO3 + 10 CO + P4

Thermphos International is Europe's only producer of elemental phosphorus with the annual capacity of 80,000 t provided by a plant at Vlissingen, the NetherlandsHP Pavilion dv9244EA Battery.[27]

Compounds

See also Category: Phosphorus compounds

Oxyacids of phosphorus

Phosphorous oxyacids are extensive, often commercially important, and sometimes structurally complicated. They all have acidic protons bound to oxygen atoms and some have nonacidic protons that are bonded directly to phosphorus. Although many oxyacids of phosphorus are formed, only six are important, and three of them, hypophosphorous acid, phosphorous acid and phosphoric acid are particularly important onesHP Pavilion dv9243EA Battery.

Phosphorus(V) compounds

Oxides

The most prevalent compounds of phosphorus are derivatives of phosphate (PO43-), a tetrahedral anion.[28] Phosphate is the conjugate base of phosphoric acid, which is produced on a massive scale for use in fertilizers. Being triprotic, phosphoric acid converts stepwise to three conjugate basesHP Pavilion dv9237EU Battery:

H3PO4 + H2O  H3O+ + H2PO4−       Ka1= 7.25×10−3

H2PO4− + H2O  H3O+ + HPO42−       Ka2= 6.31×10−8

HPO42− + H2O  H3O+ +  PO43−        Ka3= 3.98×10−13

Phosphate exhibits the tendency to form chains and rings with P-O-P bonds. Many polyphosphates are known, including ATP. Polyphosphates arise by dehydration of hydrogen phosphates such as HPO42- and H2PO4-. For example, the industrially important trisodium triphosphate (also known as sodium tripolyphosphate, STPP) is produced industrially on a megatonne scale via this condensation reactionHP Pavilion dv9235NR Battery:

2 Na2[(HO)PO3] + Na[(HO)2PO2] → Na5[O3P-O-P(O)2-O-PO3] + 2 H2O

Phosphorus pentoxide (P4O10) is the acid anhydride of phosphoric acid, but several intermediates are known between the two. This waxy white solid reacts vigorously with water.

The tetrahedral structure of P4O10 and P4S10.

With metal cations, phosphate forms a variety of salts. These solids are polymeric, featuring P-O-M linkages. When the metal cation has a charge of 2+ or 3+, the salts are generally insoluble, hence they exist as common minerals. Many phosphate salts are derived from hydrogen phosphate (HPO42-)HP Pavilion dv9233EU Battery.

PCl5 and PF5 are common compounds. Both are volatile and pale or colourless. The other two halides, PBr5 and PI5PI5 are unstable. The pentachloride and pentafluoride adopt trigonal bipyramid molecular geometry and are Lewis acids. With fluoride, PF5 forms PF6–, an anion that is isoelectronic with SF6. The most important oxyhalide is phosphorus oxychloride (POCl3), which is tetrahedralHP Pavilion dv9233CL Battery.

Before extensive computer calculations were feasible, it was proposed that bonding in phosphorus(V) compounds involved d orbitals. It is now accepted that the bonding can be better explained by molecular orbital theory and involves only s- and p-orbitals on phosphorus.[29]

Nitrides

Compounds of the formula (PNCl2)n exist mainly as rings such as the trimer hexachlorophosphazeneHP Pavilion dv9233CA Battery. The phosphazenes arise by treatment of phosphorus pentachloride with ammonium chloride: PCl5 + NH4Cl → 1/n (NPCl2)n + 4 HCl The chloride groups can be replaced by alkoxide (RO-) to give rise to a family of polymers with potentially useful properties.[30]

Sulfides

Main article: phosphorus sulfide

Phosphorus forms a wide range of sulfides, where phosphorus can be P(V), P(III) or other oxidation states. Most famous is the three-fold symmetric P4S3 used in strike-anywhere matches. P4S10 and P4O10 have analogous structuresHP Pavilion dv9232EU Battery.

Phosphorus(III) compounds

Phosphine (PH3) and its organic derivatives (PR3) are structural analogues with ammonia (NH3) but the angles at phosphorus are closer to 90° for phosphine and its organic derivatives. It is an ill-smelling, toxic compound. Phosphine is produced by hydrolysis of calcium phosphide, Ca3P2. Unlike ammonia, phosphine is oxidised by air. Phosphine is also far less basic than ammoniaHP Pavilion dv9231CA Battery.

All four symmetrical trihalides are well known: gaseous PF3, the yellowish liquids PCl3 and PBr3, and the solid PI3. These materials are moisture sensitive, hydrolysing to give phosphorus acid. The trichloride, a common reagent, is produced by chlorination of white phosphorus:

P4 + 6 Cl2 → 4 PCl3

The trifluoride is produced by from the trichloride by halide exchange. PF3 is toxic because it binds to haemoglobinHP Pavilion dv9225US Battery.

Phosphorus(III) oxide, P4O6 (also called tetraphosphorus hexoxide) is the anhydride of P(OH)3, the minor tautomer of phosphorous acid. The structure of P4O6 is like that of P4O10 less the terminal oxide groups.

Mixed oxyhalides and oxyhydrides of phosphorus(III) are almost unknown.

Organophosphorus compounds

Main article: organophosphorus compounds

Compounds with P-C and P-O-C bonds are often classified as organophosphorus compounds. They are widely used commerciallyHP Pavilion dv9221TX Battery. The PCl3 serves as a source of P3+ in routes to organophosphorus(III) compounds. For example it is the precursor to triphenylphosphine:

PCl3 + 6 Na + 3 C6H5Cl → P(C6H5)3 + 6 NaCl

Treatment of phosphorus trihalides with alcohols and phenols gives phosphites, e.g. triphenylphosphite:

PCl3 + 3 C6H5OH → P(OC6H5)3 + 3 HCl

Similar reactions occur for phosphorus oxychloride, affording triphenylphosphate:

OPCl3 + 3 C6H5OH → OP(OC6H5)3 + 3 HCl

Phosphorus(I) and phosphorus(II) compounds

These compounds generally feature P-P bonds.[8] Examples include catenated derivatives of phosphine and organophosphinesHP Pavilion dv9221TX Battery. The highly flammable gas diphosphine (P2H4) is the first of a series of derivatives of this type. Diphosphine is an analogue of hydrazine. Compounds containing P=P double bonds have also been observed, although they are rare.

A stable diphosphene, a derivative of phosphorus(I).

Phosphides

The phosphide ion is P3-. Phosphides arise by reaction of metals with red phosphorus. Salts of P3- do not exist in solution and these derivatives are refractory, reflecting their high lattice energy. Illustrated by the behaviour calcium phosphide, many metal phosphides hydrolyse in water with release of phosphineHP Pavilion dv9220US Battery:

Ca3P2 + 6 H2O → 2 PH3 + 3 Ca(OH)2

Schreibersite is a naturally occurring phosphide found in meteorites. Many polyphosphides are known such as derivatives of OsP2. These can be structurally complex ranging from Na3P7 and derivatives of P264-. Often these species adopt cage-like structures that resemble fragments of violet phosphorusHP Pavilion dv9220TX Battery.

Spelling and etymology

The name Phosphorus in Ancient Greece was the name for the planet Venus and is derived from the Greek words (φως = light, φέρω = carry), which roughly translates as light-bringer or light carrier.[10] (In Greek mythology and tradition, Augerinus (Αυγερινός = morning star, in use until today), Hesperus or Hesperinus (΄Εσπερος or Εσπερινός or Αποσπερίτης = evening star, in use until today) and EosphorusHP Pavilion dv9220TX Battery (Εωσφόρος = dawnbearer, not in use for the planet after Christianity) are close homologues, and also associated with Phosphorus-the-planet).

According to the Oxford English Dictionary, the correct spelling of the element is phosphorus. The word phosphorous is the adjectival form of the P3+ valence: so, just as sulfur forms sulfurous and sulfuric compounds, phosphorus forms phosphorous compounds (e.g., phosphorous acid) and P5+ valence phosphoric compounds (e.g., phosphoric acids and phosphates) HP Pavilion dv9220EU Battery.

History and discovery

Phosphorus was the 13th element to be discovered. For this reason, and also due to its use in explosives, poisons and nerve agents, it is sometimes referred to as "the Devil's element".[32] The discovery of phosphorus is credited to the German alchemist Hennig Brand in 1669, although other chemists might have discovered phosphorus around the same timeHP Pavilion dv9220CA Battery.[33] Brand experimented with urine, which contains considerable quantities of dissolved phosphates from normal metabolism.[10] Working in Hamburg, Brand attempted to create the fabled philosopher's stone through the distillation of some salts by evaporating urine, and in the process produced a white material that glowed in the dark and burned brilliantly. It was named phosphorus mirabilis HP Pavilion dv9219TX Battery ("miraculous bearer of light").[34] His process originally involved letting urine stand for days until it gave off a terrible smell. Then he boiled it down to a paste, heated this paste to a high temperature, and led the vapours through water, where he hoped they would condense to gold. Instead, he obtained a white, waxy substance that glowed in the dark. Brand had discovered phosphorusHP Pavilion dv9219EA Battery, the first element discovered since antiquity. We now know that Brand produced ammonium sodium hydrogen phosphate, (NH4)NaHPO4. While the quantities were essentially correct (it took about 1,100 L of urine to make about 60 g of phosphorus), it was unnecessary to allow the urine to rot. Later scientists would discover that fresh urine yielded the same amount of phosphorusHP Pavilion dv9218TX Battery.

Robert Boyle

Brand at first tried to keep the method secret,[35] but later sold the recipe for 200 thalers to D Krafft from Dresden,[10] who could now make it as well, and toured much of Europe with it, including England, where he met with Robert Boyle. The secret that it was made from urine leaked out and first Johann Kunckel (1630–1703) in Sweden (1678) and later Boyle in London (1680) also managed to make phosphorusHP Pavilion dv9218EA Battery. Boyle states that Krafft gave him no information as to the preparation of phosphorus other than that it was derived from "somewhat that belonged to the body of man". This gave Boyle a valuable clue, however, so that he, too, managed to make phosphorus, and published the method of its manufacture.[10] Later he improved Brand's process by using sand in the reaction (still using urine as base material) HP Pavilion dv9217TX Battery,

4 NaPO3 + 2 SiO2 + 10 C → 2 Na2SiO3 + 10 CO + P4

Robert Boyle was the first to use phosphorus to ignite sulfur-tipped wooden splints, forerunners of our modern matches, in 1680.

In 1769 Johan Gottlieb Gahn and Carl Wilhelm Scheele showed that calcium phosphate (Ca3(PO4)2) is found in bones, and they obtained phosphorus from bone ash. Antoine Lavoisier recognized phosphorus as an element in 1777. HP Pavilion dv9217EA Battery Bone ash was the major source of phosphorus until the 1840s. Phosphate rock, a mineral containing calcium phosphate, was first used in 1850 and following the introduction of the electric arc furnace in 1890, this became the only source of phosphorus. Phosphorus, phosphates and phosphoric acid are still obtained from phosphate rock. Phosphate rock is a major feedstock in the fertilizer industryHP Pavilion dv9217EA Battery.

White phosphorus was first made commercially, for the match industry in the 19th century, by distilling off phosphorus vapour from precipitated phosphates, mixed with ground coal or charcoal, which was heated in an iron pot, in retort.[37] The precipitated phosphates were made from ground-up bones that had been de-greased and treated with strong acidsHP Pavilion dv9216TX Battery. Carbon monoxide and other flammable gases produced during the reduction process were burnt off in a flare stack. This process became obsolete when the submerged-arc furnace for phosphorus production was introduced to reduce phosphate rock.[38][39] The electric furnace method allowed production to increase to the point where phosphorus could be used in weapons of warHP Pavilion dv9216TX Battery.[40][41] In World War I it was used in incendiaries, smoke screens and tracer bullets.[41] A special incendiary bullet was developed to shoot at hydrogen-filled Zeppelins over Britain (hydrogen being highly flammable if it can be ignited).[41] During World War II, Molotov cocktails of benzene and phosphorus were distributed in Britain to specially selected civilians within the British resistance operation, for defenceHP Pavilion dv9216EA Battery; and phosphorus incendiary bombs were used in war on a large scale. Burning phosphorus is difficult to extinguish and if it splashes onto human skin it has horrific effects.[8]

Early matches used white phosphorus in their composition, which was dangerous due to its toxicity. Murders, suicides and accidental poisonings resulted from its use. (An apocryphal tale tells of a woman attempting to murder her husband with white phosphorus in his food, which was detected by the stew's giving off luminous steam) HP Pavilion dv9215TX Battery.[40] In addition, exposure to the vapours gave match workers a severe necrosis of the bones of the jaw, the infamous "phossy jaw". When a safe process for manufacturing red phosphorus was discovered, with its far lower flammability and toxicity, laws were enacted, under the Berne Convention (1906), requiring its adoption as a safer alternative for match manufactureHP Pavilion dv9214TX Battery.[42] The toxicity of white phosphorus led to discontinuation of it use in matches.[43] In a historical coincidence, the Allies used phosphorus incendiary bombs in World War II to destroy Hamburg, the place where the "miraculous bearer of light" was first discovered.[34]

The glow, the explanation, and the term derived from it

It was known from early times that the green glow emanating from white phosphorus would persist for a time in a stoppered jar, but then cease. Robert Boyle in the 1680s ascribed it to "debilitation" of the air; in fact, it is oxygen being consumedHP Pavilion dv9214EA Battery. By the 18th century, it was known that in pure oxygen, phosphorus does not glow at all;[44] there is only a range of partial pressure at which it does. Heat can be applied to drive the reaction at higher pressures.[45]

In 1974, the glow was explained by R. J. van Zee and A. U. Khan.[40] A reaction with oxygen takes place at the surface of the solid (or liquid) phosphorus, forming the short-lived molecules HPO and P2O2 that both emit visible lightHP Pavilion dv9213TX Battery. The reaction is slow and only very little of the intermediates are required to produce the luminescence, hence the extended time the glow continues in a stoppered jar.

Since that time, phosphors and phosphorescence were used loosely to describe substances that shine in the dark without burning. However, as mentioned above, even though the term phosphorescence was originally coined as a term by analogy with the glow from oxidation of elemental phosphorus, is now reserved for another fundamentally different process—re-emission of light after illuminationHP Pavilion dv9213EA Battery.

Applications

Fertiliser

The dominant application of phosphorus is in fertilisers, which provides phosphate as required for all life and is often a limiting nutrient for crops. Phosphorus, being an essential plant nutrient, finds its major use as a constituent of fertilizers for agriculture and farm production in the form of concentrated phosphoric acids, which can consist of 70% to 75% P2O5HP Pavilion dv9212TX Battery. Global demand for fertilisers led to large increase in phosphate (PO43–) production in the second half of the 20th century. Due to the essential nature of phosphorus to living organisms, the low solubility of natural phosphorus-containing compounds, and the slow natural cycle of phosphorus, the agricultural industry is heavily reliant on fertilisers that contain phosphateHP Pavilion dv9212EA Battery, mostly in the form of superphosphate of lime. Superphosphate of lime is a mixture of two phosphate salts, calcium dihydrogen phosphate Ca(H2PO4)2 and calcium sulfate dihydrate CaSO4·2H2O produced by the reaction of sulfuric acid and water with calcium phosphate.

Organophosphorus compounds

White phosphorus is widely used to make organophosphorus compounds, through the intermediates phosphorus chlorides and two phosphorus sulfides, phosphorus pentasulfide, and phosphorus sesquisulfideHP Pavilion dv9211TX Battery.[46] Organophosphorus compounds have many applications, including in plasticizers, flame retardants, pesticides, extraction agents, and water treatment.[8] in particular the herbicide glyphosate sold under the brand name Roundup.

Metallurgical aspects

Phosphorus is also an important component in steel production, in the making of phosphor bronze, and in many other related products. Phosphorus is added to metallic copper during its smelting process to react with oxygen present as an impurity in copper and to produce oxygen-free copper or phosphorus-containing copper HP Pavilion dv9211EA Battery (CuOFP) alloys with a higher thermal and electrical conductivity than normal copper.

Matches

Match striking surface made of a mixture of red phosphorus, glue and ground glass. The glass powder is used to increase the friction.

Main article: Match

Phosphorus-contained matches were first produced in 1830s and contained a mixture of white phosphorus, an oxygen-releasing compound (potassium chlorate, lead dioxide or some nitrate) and a binder in their heads. They were rather sensitive to storage conditions, toxic and unsafe, as they could be lit by striking on any rough surfaceHP Pavilion dv9210US Battery. Therefore, their production was gradually banned between 1872 and 1925 in different countries.[47] The international Berne Convention, adopted in 1906, prohibited the use of white phosphorus in matches. As a consequence, the 'strike-anywhere' matches were gradually replaced by 'safety matches' where white phosphorus was substituted by phosphorus sesquisulfide (P4S3) HP Pavilion dv9210TX Battery, sulfur or antimony sulfide. Such matches are hard to ignite on an arbitrary surface and require a special strip. The strip contains red phosphorus which heats up upon striking, reacts with the oxygen-releasing compound in the head and ignites the flammable material of the head.[11][46]

Water softening

Sodium tripolyphosphate made from phosphoric acid is used in laundry detergents in some countries, but banned for this use in others.[13] It is useful for softening water to enhance the performance of the detergents and to prevent pipe/boiler tube corrosionHP Pavilion dv9210CA Battery.

Niche applications

Phosphates are utilized in the making of special glasses that are used for sodium lamps.[13]

Bone-ash, calcium phosphate, is used in the production of fine china.[13]

Phosphoric acid made from elemental phosphorus is used in food applications such as some soda beverages. The acid is also a starting point to make food grade phosphates.[46] These include mono-calcium phosphate that is employed in baking powder and sodium tripolyphosphate and other sodium phosphatesHP Pavilion dv9209TX Battery.[46] Among other uses these are used to improve the characteristics of processed meat and cheese. Others are used in toothpaste.[46]

White phosphorus, called "WP" (slang term "Willie Peter") is used in military applications as incendiary bombs, for smoke-screening as smoke pots and smoke bombs, and in tracer ammunition. It is also a part of an obsolete M34 White Phosphorus US hand grenade. This multipurpose grenade was mostly used for signalling, smoke screens and inflammationHP Pavilion dv9208TX Battery; it could also cause severe burns and had a psychological impact on the enemy.[48][49] Military uses of white phosphorus are constrained by international law [50]

In trace amounts, phosphorus is used as a dopant for n-type semiconductors.

32P and 33P are used as radioactive tracers in biochemical laboratories.

Phosphate is a strong complexing agent for the hexavalent uranyl (UO22+) species and this is the reason why apatite and other natural phosphates can often be very rich in uranium.

Tributylphosphate is an organophosphate soluble in kerosene and used to extract uranium in the Purex process applied in the reprocessing of spent nuclear fuelHP Pavilion dv9208NR Battery.

Biological role

Inorganic phosphorus in the form of the phosphate PO3−

4 is required for all known forms of life,[51] playing a major role in biological molecules such as DNA and RNA where it forms part of the structural framework of these molecules. Living cells also use phosphate to transport cellular energy in the form of adenosine triphosphate (ATP). Nearly every cellular process that uses energy obtains it in the form of ATPHP Pavilion dv9207TX Battery. ATP is also important for phosphorylation, a key regulatory event in cells. Phospholipids are the main structural components of all cellular membranes. Calcium phosphate salts assist in stiffening bones.[8]

Living cells are defined by a membrane that separates it from its surroundings. Biological membranes are made from a phospholipid matrix and proteins, typically in the form of a bilayer. Phospholipids are derived from glycerol, such that two of the glycerol hydroxyl (OH) protons have been replaced with fatty acids as an esterHP Pavilion dv9206TX Battery, and the third hydroxyl proton has been replaced with phosphate bonded to another alcohol.[52]

An average adult human contains about 0.7 kg of phosphorus, about 85–90% of which is present in bones and teeth in the form of apatite, and the remainder in soft tissues and extracellular fluids (~1%). The phosphorus content increases from about 0.5 weight% in infancy to 0.65–1.1 weight% in adultsHP Pavilion dv9206EU Battery. Average phosphorus concentration in the blood is about 0.4 g/L, about 70% of that is organic and 30% inorganic phosphates.[53] A well-fed adult in the industrialized world consumes and excretes about 1–3 grams of phosphorus per day, with consumption in the form of inorganic phosphate and phosphorus-containing biomolecules such as nucleic acids and phospholipids; and excretion almost exclusively in the form of phosphate ions such as H2PO−HP Pavilion dv9205US Battery

4 and HPO2−

4. Only about 0.1% of body phosphate circulates in the blood, and this amount reflects the amount of phosphate available to soft tissue cells.

Bone and teeth enamel

The main component of bone is hydroxyapatite as well as amorphous forms of calcium phosphate, possibly including carbonate. Hydroxyapatite is the main component of tooth enamel. Water fluoridation enhances the resistance of teeth to decay by the partial conversion of this mineral to the still harder material called fluoroapatite: HP Pavilion dv9205TX Battery

Ca5(PO4)3OH + F− → Ca5(PO4)3F + OH−

Phosphorus deficiency

In medicine, low-phosphate syndromes are caused by malnutrition, by failure to absorb phosphate, and by metabolic syndromes that draw phosphate from the blood (such as re-feeding after malnutrition) or pass too much of it into the urine. All are characterized by hypophosphatemia, which is a condition of low levels of soluble phosphate levels in the blood serum, and therefore inside cellsHP Pavilion dv9205EU Battery. Symptoms of hypophosphatemia include muscle and neurological dysfunction, and disruption of muscle and blood cells due to lack of ATP. Too much phosphate can lead to diarrhoea and calcification (hardening) of organs and soft tissue, and can interfere with the body's ability to use iron, calcium, magnesium, and zincHP Pavilion dv9205CA Battery.[54]

Phosphorus is an essential macromineral for plants, which is studied extensively in edaphology in order to understand plant uptake from soil systems. In ecological terms, phosphorus is often a limiting factor in many environments; i.e. the availability of phosphorus governs the rate of growth of many organisms. In ecosystems an excess of phosphorus can be problematicHP Pavilion dv9204TX Battery, especially in aquatic systems, resulting in eutrophication which sometimes lead to algal blooms.

Food sources

The main food sources of phosphorus are kinds of food containing protein, for example, milk and meat. As a rule, if one holds a meal plan providing sufficient amount of protein and calcium then amount of phosphorus is also sufficient.[55]

Precautions

Organic compounds of phosphorus form a wide class of materials, many are required for life, but some are extremely toxicHP Pavilion dv9203TX Battery. Fluorophosphate esters are among the most potent neurotoxins known. A wide range of organophosphorus compounds are used for their toxicity to certain organisms as pesticides (herbicides, insecticides, fungicides, etc.) and weaponised as nerve agents. Most inorganic phosphates are relatively nontoxic and essential nutrientsHP Pavilion dv9202TX Battery.[8]

The white phosphorus allotrope presents a significant hazard because it ignites in air and produces phosphoric acid residue. Chronic white phosphorus poisoning leads to necrosis of the jaw called "phossy jaw". Ingestion of white phosphorus may cause a medical condition known as "Smoking Stool Syndrome".HP Pavilion dv9202EA Battery

Phosphorus explosion

Upon exposure to elemental phosphorus, in the past it was suggested to wash the affected area with 2% copper sulfate solution to form harmless compounds that can be washed away. According to the recent US Navy's Treatment of Chemical Agent Casualties and Conventional Military Chemical Injuries: FM8-285: Part 2 Conventional Military Chemical InjuriesHP Pavilion dv9201TX Battery, "Cupric (copper(II)) sulfate has been used by U.S. personnel in the past and is still being used by some nations. However, copper sulfate is toxic and its use will be discontinued. Copper sulfate may produce kidney and cerebral toxicity as well as intravascular hemolysis."[57]

The manual suggests instead "a bicarbonate solution to neutralize phosphoric acid, which will then allow removal of visible white phosphorus. Particles often can be located by their emission of smoke when air strikes themHP Pavilion dv9201CA Battery, or by their phosphorescence in the dark. In dark surroundings, fragments are seen as luminescent spots. Promptly debride the burn if the patient's condition will permit removal of bits of WP (white phosphorus) that might be absorbed later and possibly produce systemic poisoning. DO NOT apply oily-based ointments until it is certain that all WP has been removedHP Pavilion dv9200XX Battery. Following complete removal of the particles, treat the lesions as thermal burns."[note 1] As white phosphorus readily mixes with oils, any oily substances or ointments are not recommended until the area is thoroughly cleaned and all white phosphorus removed.

US DEA List I status

Phosphorus can reduce elemental iodine to hydroiodic acid, which is a reagent effective for reducing ephedrine or pseudoephedrine to methamphetamineHP Pavilion dv9105EU Battery.[58] For this reason, red and white phosphorus were designated by the United States Drug Enforcement Administration as List I precursor chemicals under 21 CFR 1310.02 effective on November 17, 2001.[59] As a result, in the United States, handlers of red or white phosphorus are subject to stringent regulatory controlsHP Pavilion dv9100 Battery.

 
Sodium is a chemical element with the symbol Na (from Latin: natrium) and atomic number 11. It is a soft, silvery-white, highly reactive metal and is a member of the alkali metals; its only stable isotope is 23Na. The free metal does not occur in nature, but instead must be prepared from its compoundsSony VAIO VPCF135Z1E/B battery; it was first isolated by Humphry Davy in 1807 by the electrolysis of sodium hydroxide. Sodium is the sixth most abundant element in the Earth's crust, and exists in numerous minerals such as feldspars, sodalite and rock salt. Many salts of sodium are highly water-soluble, and their sodium has been leached by the action of water so that chloride and sodium are the most common dissolved elements by weight in the Earth's bodies of oceanic waterSony VAIO VPCF137HG/BI battery.

Many sodium compounds are useful, such as sodium hydroxide (lye) for soapmaking, and sodium chloride for use as a deicing agent and a nutrient. Sodium is an essential element for all animals and some plants. In animals, sodium ions are used against potassium ions to build up charges on cell membranes, allowing transmission of nerve impulses when the charge is dissipatedSony VAIO VPCF136FG/BI battery. The consequent need of animals for sodium causes it to classified as a dietary inorganic macro-mineral.

Physical

Emission spectrum for sodium, showing the D line.

A positive flame test for sodium has a bright yellow color.

Sodium at standard temperature and pressure is a soft metal that can be readily cut with a knife and is a good conductor of electricity. Freshly exposed, sodium has a bright, silvery luster that rapidly tarnishes, forming a white coating of sodium hydroxide and sodium carbonate. These properties change at elevated pressures: at 1.5 Mbar, the color changes to blackSony VAIO VPCF135FG/B battery, then to red transparent at 1.9 Mbar, and finally clear transparent at 3 Mbar. All of these allotropes are insulators and electrides.[2]

When sodium or its compounds are introduced into a flame, they turn it yellow,[3] because the excited 3s electrons of sodium emit a photon when they fall from 3p to 3s; the wavelength of this photon corresponds to the D line at 589.3 nm. Spin-orbit interactions involving the electron in the 3p orbital split the D line into two; hyperfine structures involving both orbitals cause many more linesSony VAIO VPCF127HG/BI battery.[4]

[edit]Chemical

Sodium is generally less reactive than potassium and more reactive than lithium.[5] Like all the alkali metals, it reacts exothermically with water, to the point that sufficiently large pieces melt to a sphere and may explode; this reaction produces caustic sodium hydroxide and flammable hydrogen gasSony VAIO VPCF11Z1E battery. When burned in dry air, it mainly forms sodium peroxide as well as some sodium oxide. In moist air, sodium hydroxide results.[6] Sodium metal is highly reducing, with the reduction of sodium ions requiring −2.71 volts[7] but potassium and lithium have even more negative potentials.[8] Hence, the extraction of sodium metal from its compounds (such as with sodium chloride) uses a significant amount of energySony VAIO VPCF11S1E battery.[6]

[edit]Isotopes

Main article: Isotopes of sodium

20 isotopes of sodium are known, but only 23Na is stable. Two radioactive, cosmogenic isotopes are the byproduct of cosmic ray spallation: 22Na with a half-life of 2.6 years and 24Na with a half-life of 15 hours; all other isotopes have a half-life of less than one minute.[9] Two nuclear isomers have been discovered, the longer-lived one being 24mNa with a half-life of around 20.2 microsecondsSony VAIO VPCF11M1E/H battery. Acute neutron radiation, such as from a nuclear criticality accident, converts some of the stable 23Na in human blood to 24Na; by measuring the concentration of 24Na in relation to 23Na, the neutron radiation dosage of the victim can be calculated.[10]

[edit]Occurrence

23Na is created in the carbon-burning process by fusing two carbon atoms together; this requires temperatures above 600 megakelvins and a star with at least three solar masses.[11] The Earth's crust has 2.6% sodium by weight, making it the sixth most abundant element thereSony VAIO VPCF11M1E battery.[12] Because of its high reactivity, it is never found as a pure element. It is found in many different minerals, some very soluble, such as halite and natron, others much less soluble such as amphibole, and zeolite. The insolubility of certain sodium minerals such as cryolite and feldspar arises from their polymeric anions, which in the case of feldspar is a polysilicateSony VAIO VPCF11JFX/B battery. In the interstellar medium, sodium is identified by the D line; though it has a high vaporization temperature, its abundance allowed it to be detected by Mariner 10 in Mercury's atmosphere.[13]

[edit]Compounds

See also Category: Sodium compounds

Structure of sodium chloride, showing octahedral coordination around Na+ and Cl- centres. This framework disintegrates upon dissolution in water and reassembles upon evaporation.

Sodium compounds are of immense commercial importance, being particularly central to industries producing glass, paper, soap, and textilesSony VAIO VPCF119FJ battery.[14] The sodium compounds that are the most important are common salt (NaCl), soda ash (Na2CO3), baking soda (NaHCO3), caustic soda (NaOH), sodium nitrate (NaNO3), di- and tri-sodium phosphates, sodium thiosulfate (Na2S2O3·5H2O), and borax (Na2B4O7·10H2O).[15] In its compounds, sodium is usually ionically bonded to water and anions, and is viewed as a hard Lewis acidSony VAIO VPCF119FC/BI battery.[16]

[edit]Aqueous solutions

Sodium tends to form water-soluble compounds, such as halides, sulfates, nitrates, carboxylates and carbonates. The main aqueous species are the aquo complexes [Na(H2O)n]+, where n = 4–6.[17] The high affinity of sodium for oxygen-based ligands is the basis of crown ethers; macrolide antibiotics, which interfere with Na+ transport in the infecting organism, are functionally related and more complexSony VAIO VPCF119FC battery.

Direct precipitation of sodium salts from aqueous solutions is rare, because sodium salts typically have a high affinity for water; an exception is sodium bismuthate (NaBiO3).[18] Because of this, sodium salts are usually isolated as solids by evaporation or by precipitation with an organic solvent, such as ethanol; for example, only 0.35 g/L of sodium chloride will dissolve in ethanol.[19] Crown ethers, like 15-crown-5, may be used as a phase-transfer catalystSony VAIO VPCF117HG/BI battery.[20]

Sodium content in bulk may be determined by treating with a large excess of uranyl zinc acetate; the hexahydrate (UO2)2ZnNa(CH3CO2)·6H2O precipitates, which can be weighed. Caesium and rubidium do not interfere with this reaction, but potassium and lithium do.[21] Lower concentrations of sodium may be determined by atomic absorption spectrophotometry[22] or by potentiometry using ion-selective electrodesSony VAIO VPCF116FG/BI battery.[23]

[edit]Electrides and sodides

Like the other alkali metals, sodium dissolves in ammonia and some amines to give deeply coloured solutions; evaporation of these solutions leaves a shiny film of metallic sodium. The solutions contain the coordination complex (Na(NH3)6)+, whose positive charge is counterbalanced by electrons as anions; cryptands permit the isolation of these complexes as crystalline solidsSony VAIO VPCF115FG/B battery. Cryptands, like crown ethers and other ionophores, have a high affinity for the sodium ion; derivatives of the alkalide Na- are obtainable[24] by the addition of cryptands to solutions of sodium in ammonia via disproportionation.[25]

[edit]Organosodium compounds

The structure of the complex of sodium (Na+, shown in yellow) and the antibiotic monensin-A.

Many organosodium compounds have been prepared. Because of the high polarity of the C-Na bonds, they behave like sources of carbanions (salts with organic anions) Sony VAIO VPCF21ZHJ battery. Some well known derivatives include sodium cyclopentadienide (NaC5H5) and trityl sodium ((C6H5)3CNa).[26]

[edit]History

Salt has been an important commodity in human activities, as shown by the English word salary, which derives from salarium, the wafers of salt sometimes given to Roman soldiers along with their other wages. In medieval Europe, a compound of sodium with the Latin name of sodanum was used as a headache remedy. The name sodium is thought to originate from the Arabic sudaSony VAIO VPCF21Z1E/BI battery, meaning headache, as the headache-alleviating properties of sodium carbonate or soda were well known in early times.[27] The chemical abbreviation for sodium was first published by Jöns Jakob Berzelius in his system of atomic symbols,[28] and is a contraction of the element's new Latin name natrium, which refers to the Egyptian natronSony VAIO VPCF21AHJ battery,[27] a natural mineral salt primarily made of hydrated sodium carbonate. Natron historically had several important industrial and household uses, later eclipsed by other sodium compounds. Although sodium, sometimes called soda, had long been recognised in compounds, the metal itself was not isolated until 1807 by Sir Humphry Davy through the electrolysis of sodium hydroxide. Sony VAIO VPCF21AGJ battery

Sodium imparts an intense yellow color to flames. As early as 1860, Kirchhoff and Bunsen noted the high sensitivity of a sodium flame test, and stated in Annalen der Physik und Chemie:[31]

“In a corner of our 60 m3 room farthest away from the apparatus, we exploded 3 mg. of sodium chlorate with milk sugar while observing the nonluminous flame before the slit. After a while, it glowed a bright yellow and showed a strong sodium line that disappeared only after 10 minutesSony VAIO VPCF21AFJ battery. From the weight of the sodium salt and the volume of air in the room, we easily calculate that one part by weight of air could not contain more than 1/20 millionth weight of sodium.     ”

[edit]Commercial production

Enjoying rather specialized applications, only about 100,000 tonnes of metallic sodium are produced annually.[14] Metallic sodium was first produced commercially in 1855 by carbothermal reduction of sodium carbonate at 1100 °C, in what is known as the Deville process: Sony VAIO VPCF219FJ/BI battery

Na2CO3 + 2 C → 2 Na + 3 CO

A related process based on the reduction of sodium hydroxide was developed in 1886.[32]

Sodium is now produced commercially through the electrolysis of molten sodium chloride, based on a process patented in 1924.[35][36] This is done in a Downs Cell in which the NaCl is mixed with calcium chloride to lower the melting point below 700 °C. As calcium is less electropositive than sodium, no calcium will be formed at the anodeSony VAIO VPCF217HG/BI battery. This method is less expensive than the previous Castner process of electrolyzing sodium hydroxide.

Reagent-grade sodium in tonne quantities sold for about US$3.30/kg in 2009; lower purity metal sells for considerably less. The market for sodium is volatile due to the difficulty in its storage and shipping; it must be stored under a dry inert gas atmosphere or anhydrous mineral oil to prevent the formation of a surface layer of sodium oxide or sodium superoxideSony VAIO VPCF217HG battery. These oxides can react violently in the presence of organic materials. Sodium will also burn violently when heated in air.[37] Smaller quantities of sodium cost far more, in the range of US$165/kg; the high cost is partially due to the expense of shipping hazardous material.[38]

[edit]Applications

Though metallic sodium has some important uses, the major applications of sodium use it in its many compounds; millions of tons of the chloride, hydroxide, and carbonate are produced annuallySony VAIO VPCF14ZHJ battery.

[edit]Free element

Metallic sodium is mainly used for the production of sodium borohydride, sodium azide, indigo, and triphenylphosphine. Previous uses were for the making of tetraethyllead and titanium metal; because applications for these chemicals were discontinued, the production of sodium declined after 1970.[14] Sodium is also used as an alloying metal, an anti-scaling agentSony VAIO VPCF14AHJ battery,[39] and as a reducing agent for metals when other materials are ineffective. Sodium vapor lamps are often used for street lighting in cities and give colours ranging from yellow-orange to peach as the pressure increases.[40] By itself or with potassium, sodium is a desiccant; it gives an intense blue colouration with benzophenone when the desiccate is dry.[41] In organic synthesisSony VAIO VPCF14AGJ battery, sodium is used in various reactions such as the Birch reduction, and the sodium fusion test is conducted to qualitatively analyse compounds.[42] Lasers emitting light at the D line, utilising sodium, are used to create artificial laser guide stars that assist in the adaptive optics for land-based visible light telescopes. Sony VAIO VPCF14AFJ battery

[edit]Heat transfer

Liquid sodium is used as a heat transfer fluid in some fast reactors,[44] due to its high thermal conductivity and low neutron absorption cross section, which is required to achieve a high neutron flux; the high boiling point allows the reactor to operate at ambient pressure. Drawbacks of using sodium include its opacity, which hinders visual maintenanceSony VAIO VPCF149FJ/BI battery, and its explosive properties. Radioactive sodium-24 may be formed by neutron activation during operation, posing a slight radiation hazard; the radioactivity stops within a few days after removal from the reactor. If a reactor needs to be frequently shut down, NaK is used; due to it being liquid at room temperature, cooling pipes do not freeze. In this case, the pyrophoricity of potassium means extra precautions against leaks need to be takenSony VAIO VPCF148FJ/B battery. Another heat transfer application is in high-performance internal combustion engines with poppet valves, where valve stems partially filled with sodium are used as a heat pipe to cool the valves.

[edit]Compounds

Two equivalent images of the chemical structure of sodium stearate, a typical soap.

Most soaps are sodium salts of fatty acids. Sodium soaps are harder (higher melting) soaps than potassium soaps.[15] Sodium chloride is extensively used for anti-icing and de-icing and as a preservative; sodium bicarbonate is mainly used for cookingSony VAIO VPCF13ZHJ battery. Along with potassium, many important medicines have sodium added to improve their bioavailability; although in most cases potassium is the better ion, sodium is selected for its lower price and atomic weight.[45] Sodium hydride is used as a base for various reactions (such as the aldol reaction) in organic chemistry, and as a reducing agent in inorganic chemistry. Sony VAIO VPCF13Z0E/B battery

[edit]Biological role

Main article: Sodium in biology

Sodium is an essential nutrient that regulates blood volume, blood pressure, osmotic equilibrium and pH; the minimum physiological requirement for sodium is 500 milligrams per day.[47] Sodium chloride is the principal source of sodium in the diet, and is used as seasoning and preservative, such as for pickling and jerky; most of it comes from processed foodsSony VAIO VPCF13M8E/B battery.[48] The DRI for sodium is 2.3 grams per day,[49] but on average people in the United States consume 3.4 grams per day,[50] the minimum amount that promotes hypertension;[51] this in turn causes 7.6 million premature deaths worldwide.[52]

The renin-angiotensin system regulates the amount of fluids and sodium in the body. Reduction of blood pressure and sodium concentration in the kidney result in the production of renin, which in turn produces aldosterone and angiotensinSony VAIO VPCF13AHJ battery, retaining sodium in the urine. Because of the increase in sodium concentration, the production of renin decreases, and the sodium concentration returns to normal.[53] Sodium is also important in neuron function and osmoregulation between cells and the extracellular fluid, their distribution mediated in all animals by Na+/K+-ATPase;[54] hence, sodium is the most prominent cation in extracellular fluidSony VAIO VPCF13AGJ battery.[55]

In C4 plants, sodium is a micronutrient that aids in metabolism, specifically in regeneration of phosphoenolpyruvate and synthesis of chlorophyll.[56] In others, it substitutes for potassium in several roles, such as maintaining turgor pressure and aiding in the opening and closing of stomata.[57] Excess sodium in the soil limits the uptake of water due to decreased water potentialSony VAIO VPCF13AFJ battery, which may result in wilting; similar concentrations in the cytoplasm can lead to enzyme inhibition, which in turn causes necrosis and chlorosis.[58] To avoid these problems, plants developed mechanisms that limit sodium uptake by roots, store them in cell vacuoles, and control them over long distances;[59] excess sodium may also be stored in old plant tissue, limiting the damage to new growthSony VAIO VPCF138FJ/BI battery.

[edit]Precautions

Care is required in handling elemental sodium, as it is potentially explosive and generates flammable hydrogen and caustic sodium hydroxide upon contact with water; powdered sodium may combust spontaneously in air or oxygen.[60] Excess sodium can be safely removed by hydrolysis in a ventilated cabinet; this is typically done by sequential treatment with isopropanolSony VAIO VPCF138FJ/B battery, ethanol and water. Isopropanol reacts very slowly, generating the corresponding alkoxide and hydrogen.[61] Fire extinguishers based on water accelerate sodium fires; those based on carbon dioxide and bromochlorodifluoromethane lose their effectiveness when they dissipate. An effective extinguishing agent is Met-L-X, which comprises approximately 5% Saran in sodium chloride together with flow agentsSony VAIO VPCF138FC/BI battery; it is most commonly hand-applied with a scoop. Other materials include Lith+, which has graphite powder and an organophosphate flame retardant, and dry sand.

Magnesium ( /mæɡˈniːziəm/ mag-nee-zee-əm) is a chemical element with the symbol Mg, atomic number 12, and common oxidation number +2. It is an alkaline earth metal and the eighth most abundant element in the Earth's crust [2] and ninth in the known universe as a whole.[3][4] Magnesium is the fourth most common element in the Earth as a whole Sony VAIO VPCF135FG battery (behind iron, oxygen and silicon), making up 13% of the planet's mass and a large fraction of the planet's mantle. The relative abundance of magnesium is related to the fact that it is easily built up in supernova stars from a sequential addition of three helium nuclei to carbon (which in turn is made from three helium nuclei). Due to magnesium ion's high solubility in water, it is the third most abundant element dissolved in seawaterSony VAIO VPCF12AHJ battery.[5]

The free element (metal) is not found naturally on Earth, as it is highly reactive (though once produced, it is coated in a thin layer of oxide (see passivation), which partly masks this reactivity). The free metal burns with a characteristic brilliant white light, making it a useful ingredient in flares. The metal is now mainly obtained by electrolysis of magnesium salts obtained from brineSony VAIO VPCF12AGJ battery. Commercially, the chief use for the metal is as an alloying agent to make aluminium-magnesium alloys, sometimes called "magnalium" or "magnelium". Since magnesium is less dense than aluminium, these alloys are prized for their relative lightness and strength.

In human biology, magnesium is the eleventh most abundant element by mass in the human body; its ions are essential to all living cells, where they play a major role in manipulating important biological polyphosphate compounds like ATP, DNA, and RNASony VAIO VPCF12AFJ battery. Hundreds of enzymes thus require magnesium ions to function. Magnesium compounds are used medicinally as common laxatives, antacids (e.g., milk of magnesia), and in a number of situations where stabilization of abnormal nerve excitation and blood vessel spasm is required (e.g., to treat eclampsia). Magnesium ions are sour to the taste, and in low concentrations they help to impart a natural tartness to fresh mineral watersSony VAIO VPCF129FJ/BI battery.

In vegetation magnesium is the metallic ion at the center of chlorophyll, and is thus a common additive to fertilizers.[6]

Origin and characteristics

[edit]Physical and chemical properties

Elemental magnesium is a fairly strong, silvery-white, light-weight metal (two thirds the density of aluminium). It tarnishes slightly when exposed to air, although unlike the alkali metals, storage in an oxygen-free environment is unnecessary because magnesium is protected by a thin layer of oxide that is fairly impermeable and difficult to removeSony VAIO VPCF128FJ/B battery. Like its lower periodic table group neighbor calcium, magnesium reacts with water at room temperature, though it reacts much more slowly than calcium. When submerged in water, hydrogen bubbles will almost unnoticeably begin to form on the surface of the metal, though if powdered it will react much more rapidly. The reaction will occur faster with higher temperatures (see precautions) Sony VAIO VPCF127FJ/W battery. Magnesium's ability to react with water can be harnessed to produce energy and run a magnesium-based engine. Magnesium also reacts exothermically with most acids, such as hydrochloric acid (HCl). As with aluminium, zinc and many other metals, the reaction with hydrochloric acid produces the chloride of the metal and releases hydrogen gasSony VAIO VPCF11ZHJ battery.

Magnesium is a highly flammable metal, but while it is easy to ignite when powdered or shaved into thin strips, it is difficult to ignite in mass or bulk. Once ignited, it is difficult to extinguish, being able to burn in nitrogen (forming magnesium nitride), carbon dioxide (forming magnesium oxide and carbon) and water (forming magnesium oxide and hydrogen) Sony VAIO VPCF11AHJ battery. This property was used in incendiary weapons used in the firebombing of cities in World War II, the only practical civil defense being to smother a burning flare under dry sand to exclude the atmosphere. On burning in air, magnesium produces a brilliant white light which includes strong ultraviolet. Thus magnesium powder (flash powder) was used as a source of illumination in the early days of photographySony VAIO VPCF11AGJ battery. Later, magnesium ribbon was used in electrically ignited flash bulbs. Magnesium powder is used in the manufacture of fireworks and marine flares where a brilliant white light is required. Flame temperatures of magnesium and magnesium alloys can reach 3,100 °C (3,370 K; 5,610 °F),[7] although flame height above the burning metal is usually less than 300 mm (12 in) Sony VAIO VPCF11AFJ battery.[8] Magnesium may be used as an ignition source for thermite, an otherwise difficult to ignite mixture of aluminium and iron oxide powder.

Magnesium compounds are typically white crystals. Most are soluble in water, providing the sour-tasting magnesium ion Mg2+. Small amounts of dissolved magnesium ion contribute to the tartness and taste of natural waters. Magnesium ion in large amounts is an ionic laxative, and magnesium sulfate (common name: Epsom salt) is sometimes used for this purposeSony VAIO VPCF118FJ battery. So-called "milk of magnesia" is a water suspension of one of the few insoluble magnesium compounds, magnesium hydroxide. The undissolved particles give rise to its appearance and name. Milk of magnesia is a mild base commonly used as an antacid, which has some laxative side effectSony VAIO VPCF117FJ battery.

[edit]Isotopes

Magnesium has three stable isotopes: 24Mg, 25Mg and 26Mg. All are present in significant amounts (see table of isotopes above). About 79% of Mg is 24Mg. The isotope 28Mg is radioactive and in the 1950s to 1970s was made commercially by several nuclear power plants for use in scientific experiments. This isotope has a relatively short half-life (21 hours) and so its use was limited by shipping timesSony VAIO VGN-CS33H battery.

26Mg has found application in isotopic geology, similar to that of aluminium. 26Mg is a radiogenic daughter product of 26Al, which has a half-life of 717,000 years. Large enrichments of stable 26Mg have been observed in the Ca-Al-rich inclusions of some carbonaceous chondrite meteorites. The anomalous abundance of 26Mg is attributed to the decay of its parent 26Al in the inclusionsSony VAIO VGN-CS33H/Z battery. Therefore, the meteorite must have formed in the solar nebula before the 26Al had decayed. Hence, these fragments are among the oldest objects in the solar system and have preserved information about its early history.

It is conventional to plot 26Mg/24Mg against an Al/Mg ratio. In an isochron dating plot, the Al/Mg ratio plotted is27Al/24Mg. The slope of the isochron has no age significance, but indicates the initial 26Al/27Al ratio in the sample at the time when the systems were separated from a common reservoirSony VAIO VGN-CS33H/B battery.

[edit]Creation

Magnesium is produced in stars larger than 3 solar masses by fusing helium and neon in the alpha process at temperatures above 600 megakelvins.

[edit]Occurrence

Although magnesium is found in over 60 minerals, only dolomite, magnesite, brucite, carnallite, talc, and olivine are of commercial importance.

The Mg2+ cation is the second most abundant cation in seawater (occurring at about 12% of the mass of sodium there), which makes seawater and sea-salt an attractive commercial source of Mg. To extract the magnesium, calcium hydroxide is added to seawater to form magnesium hydroxide precipitateSony VAIO VGN-CS31Z/Q battery.

MgCl2 + Ca(OH)2 → Mg(OH)2 + CaCl2

Magnesium hydroxide (brucite) is insoluble in water so it can be filtered out, and reacted with hydrochloric acid to obtain concentrated magnesium chloride.

Mg(OH)2 + 2 HCl → MgCl2 + 2 H2O

From magnesium chloride, electrolysis produces magnesium.

In the United States, magnesium is principally obtained by electrolysis of fused magnesium chloride from brines, wells, and sea water. At the cathode, the Mg2+ ion is reduced by two electrons to magnesium metalSony VAIO VGN-CS31S/W battery:

Mg2+ + 2 e−

→ Mg

At the anode, each pair of Cl− ions is oxidized to chlorine gas, releasing two electrons to complete the circuit:

2 Cl− → Cl2 (g) + 2 e−

The United States has traditionally been the major world supplier of this metal, supplying 45% of world production even as recently as 1995. Today, the US market share is at 7%, with a single domestic producer left, US Magnesium, a Renco Group company in Utah born from now-defunct Magcorp. Sony VAIO VGN-CS31S/V battery

As of 2005, China has taken over as the dominant supplier, pegged at 60% world market share, which increased from 4% in 1995. Unlike the above-described electrolytic process, China is almost completely reliant on a different method of obtaining the metal from its ores, the silicothermic Pidgeon process (the reduction of the oxide at high temperatures with silicon). Sony VAIO VGN-CS31S/T battery

[edit]History

Sir Humphry Davy

The name magnesium originates from the Greek word for a district in Thessaly called Magnesia. It is related to magnetite and manganese, which also originated from this area, and required differentiation as separate substances. See manganese for this history.

Magnesium is the seventh most abundant element in the Earth's crust by mass or molarity.[2] It is found in large deposits of magnesiteSony VAIO VGN-CS31S/R battery, dolomite, and other minerals, and in mineral waters, where magnesium ion is soluble. In 1618, a farmer at Epsom in England attempted to give his cows water from a well there. The cows refused to drink because of the water's bitter taste, but the farmer noticed that the water seemed to heal scratches and rashes. The substance became known as Epsom salts and its fame spread; it was eventually recognized to be hydrated magnesium sulfate, MgSO4Sony VAIO VGN-CS31S/P battery.

The metal itself was first produced by Sir Humphry Davy in England in 1808 using electrolysis of a mixture of magnesia and mercuric oxide.[11] Antoine Bussy prepared it in coherent form in 1831. Davy's first suggestion for a name was magnium,[11] but the name magnesium is now usedSony VAIO VGN-CS28 battery.

[edit]Applications

[edit]As metal

An unusual application of magnesium as an illumination source while wakeskating in 1931

Magnesium is the third most commonly used structural metal, following iron and aluminium. It has been called the lightest useful metal by The Periodic Table of Videos.[12]

The main applications of magnesium are, in order: component of aluminium alloys, in die-casting (alloyed with zinc),[13] to remove sulfur in the production of iron and steel, the production of titanium in the Kroll processSony VAIO VGN-CS28/Q battery.[14]

Magnesium, in its purest form, can be compared with aluminium, and is strong and light, so it is used in several high volume part manufacturing applications, including automotive and truck components. Specialty, high-grade car wheels of magnesium alloy are called "mag wheels", although the term is often more broadly misapplied to include aluminum wheelsSony VAIO VGN-CS27 battery. In 1957, a Chevrolet Corvette SS, designed for racing, was constructed with magnesium body panels. An earlier Mercedes-Benz race car model, the Mercedes-Benz 300 SLR, had a body made from Elektron, a magnesium alloy; these cars ran (with successes) at Le Mans, the Mille Miglia, and other world-class race events in 1955 (though one was involved in the single worst accident in auto racing historySony VAIO VGN-CS27/W battery, in terms of human casualties, at the Le Mans race.) Porsche's all-out quest to decrease the weight of their race cars led to the use of magnesium frames in the famous 917/053 that won Le Mans in 1971, and still holds the absolute distance record. The 917/30 Can-Am car also featured a magnesium frame, helping it to make the most of its prodigious 1100–1500 hpSony VAIO VGN-CS27/R battery. Volkswagen Group has used magnesium in its engine components for many years. For a long time, Porsche used magnesium alloy for its engine blocks due to the weight advantage. There is renewed interest in magnesium engine blocks, as featured in the 2006 BMW 325i and 330i models. The BMW engine uses an aluminium alloy insert for the cylinder walls and cooling jackets surrounded by a high-temperature magnesium alloy AJ62ASony VAIO VGN-CS27/P battery. The application of magnesium AE44 alloy in the 2006 Corvette Z06 engine cradle has advanced the technology of designing robust automotive parts in magnesium. Both these alloys are recent developments in high-temperature low creep magnesium alloys. Mitsubishi Motors also uses magnesium (branded magnesium alloy) for its paddle shifters. The general strategy for such alloys is to form intermetallic precipitates at the grain boundariesSony VAIO VGN-CS27/C battery, for example by adding mischmetal or calcium.[15] New alloy development and lower costs, which are becoming competitive to aluminium, will further the number of automotive applications.[citation needed]

Products made of magnesium: firestarter and shavings, sharpener, magnesium ribbon

The second application field of magnesium is electronic devices. Because of low weight, good mechanical and electrical properties, magnesium is widely used for manufacturing of mobile phones, laptop computers, cameras, and other electronic componentsSony VAIO VGN-CS26T/W battery.

Historically, magnesium was one of the main aerospace construction metals and was used for German military aircraft as early as World War I and extensively for German aircraft in World War II. The Germans coined the name 'Elektron' for magnesium alloy. The term is still used today. Because of perceived hazards with magnesium parts in the event of fireSony VAIO VGN-CS26T/V battery, the application of magnesium in the commercial aerospace industry was generally restricted to engine related components. Currently the use of magnesium alloys in aerospace is increasing, mostly driven by the increasing importance of fuel economy and the need to reduce weight.[citation needed] The development and testing of new magnesium alloys continues, notably Elektron 21Sony VAIO VGN-CS26T/T battery, which has successfully undergone extensive aerospace testing for suitability in engine, internal and airframe components. The European Community runs three R&D magnesium projects in the Aerospace priority of Six Framework Program.

[edit]Niche uses of the metal

Magnesium, being available and relatively nontoxic, has variety of uses:

Magnesium is flammable, burning at a temperature of approximately 3,100 °C (3,370 K; 5,610 °F),[7] and the autoignition temperature of magnesium ribbon is approximately 473 °C (746 K; 883 °F). Sony VAIO VGN-CS26T/R battery It produces intense, bright, white light when it burns. Magnesium's high burning temperature makes it a useful tool for starting emergency fires during outdoor recreation. Other uses include flash photography, flares, pyrotechnics and fireworks sparklers.

Magnesium firestarter (in left hand), used with a pocket knife and flint to create sparks that ignite the shavingsSony VAIO VGN-CS26T/Q battery

In the form of turnings or ribbons, to prepare Grignard reagents, which are useful in organic synthesis.

As an additive agent in conventional propellants and the production of nodular graphite in cast iron.

As a reducing agent for the production of uranium and other metals from their salts.

As a sacrificial (galvanic) anode to protect underground tanks, pipelines, buried structures, and water heatersSony VAIO VGN-CS26T/P battery.

Alloyed with zinc to produce the zinc sheet used in photoengraving plates in the printing industry, dry-cell battery walls, and roofing.[13]

As a metal, this element's principal use is as an alloying additive to aluminium with these aluminium-magnesium alloys being used mainly for beverage cans.

[edit]In magnesium compounds

Magnesium compounds, primarily magnesium oxide (MgO), are used as refractory a material in furnace linings for producing iron, steel, nonferrous metals, glass and cementSony VAIO VGN-CS26T/C battery. Magnesium oxide and other magnesium compounds are also used in the agricultural, chemical, and construction industries.

Magnesium reacted with an alkyl halide gives a Gringard reagent, which is a very useful tool for preparing alcohols.

In agriculture and biology, the magnesium ion is necessary for all life (see magnesium in biology), so magnesium salts are frequently included in various foods, fertilizers (magnesium is a component of chlorophyll), and culture mediaSony VAIO VGN-CS25H battery.

[edit]Niche and illustrative uses of magnesium compounds

[edit]Biological

Magnesium sulfate, as the heptahydrate called Epsom salts, is used as bath salts, as a laxative, and as a highly soluble fertilizer.

Magnesium hydroxide, suspended in water, is used in milk of magnesia antacids and laxatives.

Magnesium chloride, oxide, gluconate, malate, orotate, glycinate and citrate are all used as oral magnesium supplements. Oral magnesium supplements have been claimed to be therapeutic for some individuals who suffer from Restless Leg Syndrome (RLS). Sony VAIO VGN-CS25H/W battery

Magnesium borate, magnesium salicylate, and magnesium sulfate are all used as antiseptics.

Magnesium bromide is used as a mild sedative (this action is due to the bromide, not the magnesium).

Magnesium stearate is a slightly flammable white powder with lubricating properties. In pharmaceutical technology, it is used in the manufacturing of numerous kinds of tablets to prevent the tablets from sticking to the equipment during the tablet compression process Sony VAIO VGN-CS25H/R battery (i.e., when the tablet's substance is pressed into tablet form).

Magnesium carbonate powder is used by athletes such as gymnasts, weightlifters and climbers to eliminate moisture and improving the grip on a gymnastic apparatus, lifting bar and climbing rocks.

[edit]Non biological

Dead-burned magnesite (magnesium carbonate) is used for refractory purposes such as brick and liners in furnaces and converters.

Magnesium sulfite is used in the manufacture of paper (sulfite process).

Magnesium phosphate is used to fireproof wood used in construction.

Magnesium hexafluorosilicate is used in mothproofing of textilesSony VAIO VGN-CS25H/Q battery.

[edit]Biological role

Main article: Magnesium in biology

Because of the important interaction between phosphate and magnesium ions, magnesium ions are essential to the basic nucleic acid chemistry of life, and thus are essential to all cells of all known living organisms. Over 300 enzymes require the presence of magnesium ions for their catalytic action, including all enzymes utilizing or synthesizing ATP, or those that use other nucleotides to synthesize DNA and RNASony VAIO VGN-CS25H/P battery. ATP exists in cells normally as a chelate of ATP and a magnesium ion.

Plants have an additional use for magnesium in that chlorophylls are magnesium-centered porphyrins. Magnesium deficiency in plants causes late-season yellowing between leaf veins, especially in older leaves, and can be corrected by applying Epsom salts (which is rapidly leached), or else crushed dolomitic limestone to the soilSony VAIO VGN-CS25H/C battery.

Examples of food sources of magnesium

Magnesium is a vital component of a healthy human diet. Human magnesium deficiency (including conditions that show few overt symptoms) is relatively rare[17] although only 32% of the United States meet the RDA-DRI;[18] low levels of magnesium in the body has been associated with the development of a number of human illnesses such as asthma, diabetesSony VAIO VGN-CS23T/W battery, and osteoporosis.[19] Taken in the proper amount magnesium plays a role in preventing both stroke and heart attack. The symptoms of people with fibromyalgia, migraines, and girls going through their premenstrual syndrome are less severe and magnesium can shorten the length of the migraine symptoms. Sony VAIO VGN-CS23T/Q battery

Adult human bodies contain about 24 grams of magnesium, with 60% in the skeleton, 39% intracellular (20% in skeletal muscle), and 1% extracellular. Serum levels are typically 0.7–1.0 mmol/L or 1.8–2.4 mEq/L. Serum magnesium levels may appear normal even in cases of underlying intracellular deficiency, although no known mechanism maintains a homeostatic level in the blood other than renal excretion of high blood levelsSony VAIO VGN-CS23H battery.

Intracellular magnesium is correlated with intracellular potassium. Magnesium is absorbed in the gastrointestinal tract, with more absorbed when status is lower. In humans, magnesium appears to facilitate calcium absorption[citation needed]. Low and high protein intake inhibit magnesium absorption, and other factors such as phosphate, phytate, and fat affect absorptionSony VAIO VGN-CS23H/S battery. Absorbed dietary magnesium is largely excreted through the urine, although most magnesium "administered orally" is excreted through the feces.[22] Magnesium status may be assessed roughly through serum and erythrocyte Mg concentrations and urinary and fecal excretion, but intravenous magnesium loading tests are likely the most accurate and practical in most peopleSony VAIO VGN-CS23H/B battery.[23] In these tests, magnesium is injected intravenously; a retention of 20% or more indicates deficiency.[24] Other nutrient deficiencies are identified through biomarkers, but none are established for magnesium.[25]

Spices, nuts, cereals, coffee, cocoa, tea, and vegetables are rich sources of magnesium[26]. Green leafy vegetables such as spinach are also rich in magnesium as they contain chlorophyllSony VAIO VGN-CS23G battery. Observations of reduced dietary magnesium intake in modern Western countries compared to earlier generations may be related to food refining and modern fertilizers that contain no magnesium.[22]

Numerous magnesium dietary supplements are available. Magnesium oxide, one of the most common because it has high magnesium content per weight, has been reported to be the least bioavailable.[27][28] Magnesium citrate has been reported as more bioavailable than oxide or amino-acid chelate (glycinate) formsSony VAIO VGN-CS23G/W battery.[29]

Excess magnesium in the blood is freely filtered at the kidneys, and for this reason it is difficult to overdose on magnesium from dietary sources alone.[19] With supplements, overdose is possible, however, particularly in people with poor renal function; occasionally, with use of high cathartic doses of magnesium salts, severe hypermagnesemia has been reported to occur even without renal dysfunction.[30] Alcoholism can produce a magnesium deficiencySony VAIO VGN-CS23G/Q battery, which is easily reversed by oral or parenteral administration, depending on the degree of deficiency.[31]

[edit]Detection in biological fluids

Magnesium concentrations in plasma or serum may be measured to monitor for efficacy and safety in those receiving the drug therapeutically, to confirm the diagnosis in potential poisoning victims or to assist in the forensic investigation in a case of fatal overdosage. The newborn children of mothers who received parenteral magnesium sulfate during labor may exhibit toxicity at serum magnesium levels that were considered appropriate for the mothersSony VAIO VGN-CS23G/P battery.[32]

[edit]Magnesium in treatment-resistant depression (TRD)

There has been some speculation that magnesium deficiency can lead to depression. Cerebral spinal fluid (CSF) magnesium has been found low in treatment-resistant suicidal depression and in patients that have attempted suicide. Brain magnesium has been found low in TRD using phosphorus nuclear magnetic resonance spectroscopySony VAIO VGN-CS21Z/Q battery, an accurate means for measuring brain magnesium. Blood and CSF magnesium do not appear well-correlated with major depression.[33] Magnesium chloride in relatively small doses was found to be as effective in the treatment of depressed elderly type 2 diabetics with hypomagnesemia as imipramine 50 mg daily. Sony VAIO VGN-CS21S/W battery

[edit]Safety precautions for magnesium metal

The magnesium-bodied Honda RA302 of Jo Schlesser crashes and burns during the 1968 French Grand Prix. Schlesser was killed. The magnesium car body did not cause the fire or the death, but it greatly hindered attempts to douse the fire with water.

[citation needed]

Magnesium metal and its alloys are explosive hazards; they are highly flammable in their pure form when molten or in powder or ribbon form. Burning or molten magnesium metal reacts violently with water. When working with powdered magnesiumSony VAIO VGN-CS21S/V battery, safety glasses with welding eye protection are employed, because the bright white light produced by burning magnesium contains ultraviolet light that can permanently damage the retinas of the eyes.[35]

Magnesium is capable of reducing water to the highly flammable hydrogen gas:[36]

Mg (s) + 2 H2O (l) → Mg(OH)2 (s) + H2 (g)

As a result, water cannot be used to extinguish magnesium fires; the hydrogen gas produced will only intensify the fire. Dry sand is an effective smothering agent but is usable only on relatively level and flat surfacesSony VAIO VGN-CS21S/T battery.

Magnesium also reacts with carbon dioxide to form magnesium oxide and carbon:

2 Mg (s) + CO2 → 2 MgO (s) + C (s)

hence, carbon dioxide fire extinguishers cannot be used for extinguishing magnesium fires either.[37]

Burning magnesium is usually quenched by using a Class D dry chemical fire extinguisher, or by covering the fire with sand or magnesium foundry flux to remove its air sourceSony VAIO VGN-CS21S/R battery.

 
Carbon is the chemical element with symbol C and atomic number 6. As a member of group 14 on the periodic table, it is nonmetallic and tetravalent—making four electrons available to form covalent chemical bonds. There are three naturally occurring isotopes, with 12C and 13C being stable, while 14C is radioactive, decaying with a half-life of about 5,730 yearsSony VAIO VPCF135Z1E/B battery.[9] Carbon is one of the few elements known since antiquity.

There are several allotropes of carbon of which the best known are graphite, diamond, and amorphous carbon.[12] The physical properties of carbon vary widely with the allotropic form. For example, diamond is highly transparent, while graphite is opaque and black. Diamond is among the hardest materials knownSony VAIO VPCF137HG/BI battery, while graphite is soft enough to form a streak on paper (hence its name, from the Greek word "to write"). Diamond has a very low electrical conductivity, while graphite is a very good conductor. Under normal conditions, diamond has the highest thermal conductivity of all known materials.

All carbon allotropes are solids under normal conditions with graphite being the most thermodynamically stable formSony VAIO VPCF136FG/BI battery. They are chemically resistant and require high temperature to react even with oxygen. The most common oxidation state of carbon in inorganic compounds is +4, while +2 is found in carbon monoxide and other transition metal carbonyl complexes. The largest sources of inorganic carbon are limestones, dolomites and carbon dioxide, but significant quantities occur in organic deposits of coal, peatSony VAIO VPCF135FG/B battery, oil and methane clathrates. Carbon forms more compounds than any other element, with almost ten million pure organic compounds described to date, which in turn are a tiny fraction of such compounds that are theoretically possible under standard conditions.[13]

Carbon is the 15th most abundant element in the Earth's crust, and the fourth most abundant element in the universe by mass after hydrogen, helium, and oxygen. It is present in all known life formsSony VAIO VPCF127HG/BI battery, and in the human body carbon is the second most abundant element by mass (about 18.5%) after oxygen.[14] This abundance, together with the unique diversity of organic compounds and their unusual polymer-forming ability at the temperatures commonly encountered on Earth, make this element the chemical basis of all known lifeSony VAIO VPCF11Z1E battery.

Characteristics

The different forms or allotropes of carbon (see below) include the hardest naturally occurring substance, diamond, and also one of the softest known substances, graphite. Moreover, it has an affinity for bonding with other small atoms, including other carbon atoms, and is capable of forming multiple stable covalent bonds with such atomsSony VAIO VPCF11S1E battery. As a result, carbon is known to form almost ten million different compounds; the large majority of all chemical compounds.[13] Carbon also has the highest sublimation point of all elements. At atmospheric pressure it has no melting point as its triple point is at 10.8 ± 0.2 MPa and 4,600 ± 300 K (~4,330 °C or 7,820 °F),[2][3] so it sublimates at about 3,900 K. Sony VAIO VPCF11M1E/H battery

Carbon sublimes in a carbon arc which has a temperature of about 5,800 K (5,530 °C; 9,980 °F). Thus, irrespective of its allotropic form, carbon remains solid at higher temperatures than the highest melting point metals such as tungsten or rhenium. Although thermodynamically prone to oxidation, carbon resists oxidation more effectively than elements such as iron and copper that are weaker reducing agents at room temperatureSony VAIO VPCF11M1E battery.

Carbon compounds form the basis of all known life on Earth, and the carbon-nitrogen cycle provides some of the energy produced by the Sun and other stars. Although it forms an extraordinary variety of compounds, most forms of carbon are comparatively unreactive under normal conditions. At standard temperature and pressure, it resists all but the strongest oxidizersSony VAIO VPCF11JFX/B battery. It does not react with sulfuric acid, hydrochloric acid, chlorine or any alkalis. At elevated temperatures carbon reacts with oxygen to form carbon oxides, and will reduce such metal oxides as iron oxide to the metal. This exothermic reaction is used in the iron and steel industry to control the carbon content of steel:

Fe3O4 + 4 C(s) → 3 Fe(s) + 4 CO(g)

with sulfur to form carbon disulfide and with steam in the coal-gas reactionSony VAIO VPCF119FJ battery:

C(s) + H2O(g) → CO(g) + H2(g).

Carbon combines with some metals at high temperatures to form metallic carbides, such as the iron carbide cementite in steel, and tungsten carbide, widely used as an abrasive and for making hard tips for cutting tools.

As of 2009, graphene appears to be the strongest material ever tested.[17] However, the process of separating it from graphite will require some technological development before it is economical enough to be used in industrial processesSony VAIO VPCF119FC/BI battery.[18]

The system of carbon allotropes spans a range of extremes:

Allotropes

Main article: Allotropes of carbon

Atomic carbon is a very short-lived species and, therefore, carbon is stabilized in various multi-atomic structures with different molecular configurations called allotropes. The three relatively well-known allotropes of carbon are amorphous carbon, graphite, and diamond. Once considered exotic, fullerenes are nowadays commonly synthesized and used in researchSony VAIO VPCF119FC battery; they include buckyballs,[24][25] carbon nanotubes,[26] carbon nanobuds[27] and nanofibers.[28][29] Several other exotic allotropes have also been discovered, such as lonsdaleite,[30] glassy carbon,[31] carbon nanofoam[32] and linear acetylenic carbon (carbyne).[33]

The amorphous form is an assortment of carbon atoms in a non-crystalline, irregular, glassy state, which is essentially graphite but not held in a crystalline macrostructure. It is present as a powderSony VAIO VPCF117HG/BI battery, and is the main constituent of substances such as charcoal, lampblack (soot) and activated carbon. At normal pressures carbon takes the form of graphite, in which each atom is bonded trigonally to three others in a plane composed of fused hexagonal rings, just like those in aromatic hydrocarbons.[34] The resulting network is 2-dimensional, and the resulting flat sheets are stacked and loosely bonded through weak van der Waals forcesSony VAIO VPCF116FG/BI battery. This gives graphite its softness and its cleaving properties (the sheets slip easily past one another). Because of the delocalization of one of the outer electrons of each atom to form a π-cloud, graphite conducts electricity, but only in the plane of each covalently bonded sheet. This results in a lower bulk electrical conductivity for carbon than for most metals. The delocalization also accounts for the energetic stability of graphite over diamond at room temperatureSony VAIO VPCF115FG/B battery.

Some allotropes of carbon: a) diamond; b) graphite; c) lonsdaleite; d–f) fullerenes (C60, C540, C70); g) amorphous carbon; h) carbon nanotube.

At very high pressures carbon forms the more compact allotrope diamond, having nearly twice the density of graphite. Here, each atom is bonded tetrahedrally to four others, thus making a 3-dimensional network of puckered six-membered rings of atomsSony VAIO VPCF21ZHJ battery. Diamond has the same cubic structure as silicon and germanium and because of the strength of the carbon-carbon bonds, it is the hardest naturally occurring substance in terms of resistance to scratching. Contrary to the popular belief that "diamonds are forever", they are in fact thermodynamically unstable under normal conditions and transform into graphiteSony VAIO VPCF21Z1E/BI battery.[12] However, due to a high activation energy barrier, the transition into graphite is so extremely slow at room temperature as to be unnoticeable. Under some conditions, carbon crystallizes as lonsdaleite. This form has a hexagonal crystal lattice where all atoms are covalently bonded. Therefore, all properties of lonsdaleite are close to those of diamondSony VAIO VPCF21AHJ battery.[30]

Fullerenes have a graphite-like structure, but instead of purely hexagonal packing, they also contain pentagons (or even heptagons) of carbon atoms, which bend the sheet into spheres, ellipses or cylinders. The properties of fullerenes (split into buckyballs, buckytubes and nanobuds) have not yet been fully analyzed and represent an intense area of research in nanomaterialsSony VAIO VPCF21AGJ battery. The names "fullerene" and "buckyball" are given after Richard Buckminster Fuller, popularizer of geodesic domes, which resemble the structure of fullerenes. The buckyballs are fairly large molecules formed completely of carbon bonded trigonally, forming spheroids (the best-known and simplest is the soccerball-shaped C60 buckminsterfullerene).[24] Carbon nanotubes are structurally similar to buckyballsSony VAIO VPCF21AFJ battery, except that each atom is bonded trigonally in a curved sheet that forms a hollow cylinder.[25][26] Nanobuds were first reported in 2007 and are hybrid bucky tube/buckyball materials (buckyballs are covalently bonded to the outer wall of a nanotube) that combine the properties of both in a single structureSony VAIO VPCF219FJ/BI battery.[27]

Of the other discovered allotropes, carbon nanofoam is a ferromagnetic allotrope discovered in 1997. It consists of a low-density cluster-assembly of carbon atoms strung together in a loose three-dimensional web, in which the atoms are bonded trigonally in six- and seven-membered rings. It is among the lightest known solids, with a density of about 2 kg/m3Sony VAIO VPCF217HG/BI battery.[35] Similarly, glassy carbon contains a high proportion of closed porosity,[31] but contrary to normal graphite, the graphitic layers are not stacked like pages in a book, but have a more random arrangement. Linear acetylenic carbon[33] has the chemical structure[33] -(C:::C)n-. Carbon in this modification is linear with sp orbital hybridization, and is a polymer with alternating single and triple bondsSony VAIO VPCF217HG battery. This type of carbyne is of considerable interest to nanotechnology as its Young's modulus is forty times that of the hardest known material – diamond.[36]

Occurrence

Graphite ore

Raw diamond crystal.

"Present day" (1990s) sea surface dissolved inorganic carbon concentration (from the GLODAP climatology)

Carbon is the fourth most abundant chemical element in the universe by mass after hydrogen, helium, and oxygen. Carbon is abundant in the Sun, stars, comets, and in the atmospheres of most planets. Some meteorites contain microscopic diamonds that were formed when the solar system was still a protoplanetary diskSony VAIO VPCF14ZHJ battery. Microscopic diamonds may also be formed by the intense pressure and high temperature at the sites of meteorite impacts.[37]

In combination with oxygen in carbon dioxide, carbon is found in the Earth's atmosphere (approximately 810 gigatonnes of carbon) and dissolved in all water bodies (approximately 36,000 gigatonnes of carbon). Around 1,900 gigatonnes of carbon are present in the biosphereSony VAIO VPCF14AHJ battery. Hydrocarbons (such as coal, petroleum, and natural gas) contain carbon as well—coal "reserves" (not "resources") amount to around 900 gigatonnes, and oil reserves around 150 gigatonnes. Proven sources of natural gas are about 175 1012 cubic metres (representing about 105 gigatonnes carbon), but it is estimated that there are also about 900 1012 cubic metres of "unconventional" gas such as shale gasSony VAIO VPCF14AGJ battery, representing about 540 gigatonnes of carbon.[38] (In the past, quantities of hydrocarbons were greater. In the period from 1751 to 2008 about 347 gigatonnes of carbon were released as carbon dioxide to the atmosphere from burning of fossil fuels.[39]) Carbon is also locked up as methane and methane hydrates in polar regions. It is estimated that at least 1,400 Gt of carbon is in this form just in (and under) the submarine permafrost of the Siberian ShelfSony VAIO VPCF14AFJ battery.[40]

Carbon is a major component in very large masses of carbonate rock (limestone, dolomite, marble and so on). Coal is the largest commercial source of mineral carbon, accounting for 4,000 gigatonnes or 80% of fossil carbon fuel.[41] It is also rich in carbon – for example, anthracite contains 92–98%Sony VAIO VPCF149FJ/BI battery.[42]

As for individual carbon allotropes, graphite is found in large quantities in the United States (mostly in New York and Texas), Russia, Mexico, Greenland, and India. Natural diamonds occur in the rock kimberlite, found in ancient volcanic "necks," or "pipes". Most diamond deposits are in Africa, notably in South Africa, Namibia, Botswana, the Republic of the Congo, and Sierra LeoneSony VAIO VPCF148FJ/B battery. There are also deposits in Arkansas, Canada, the Russian Arctic, Brazil and in Northern and Western Australia. Diamonds are now also being recovered from the ocean floor off the Cape of Good Hope. However, though diamonds are found naturally, about 30% of all industrial diamonds used in the U.S. are now made synthetically.

Carbon-14 is formed in upper layers of the troposphere and the stratosphereSony VAIO VPCF13ZHJ battery, at altitudes of 9–15 km, by a reaction that is precipitated by cosmic rays.[43] Thermal neutrons are produced that collide with the nuclei of nitrogen-14, forming carbon-14 and a proton.

Isotopes

Main article: Isotopes of carbon

Isotopes of carbon are atomic nuclei that contain six protons plus a number of neutrons (varying from 2 to 16). Carbon has two stable, naturally occurring isotopes.[9] The isotope carbon-12 (12C) forms 98.93% of the carbon on Earth, while carbon-13 (13C) forms the remaining 1.07%.Sony VAIO VPCF13Z0E/B battery [9] The concentration of 12C is further increased in biological materials because biochemical reactions discriminate against 13C.[44] In 1961 the International Union of Pure and Applied Chemistry (IUPAC) adopted the isotope carbon-12 as the basis for atomic weights.[45] Identification of carbon in NMR experiments is done with the isotope 13C.

Carbon-14 (14C) is a naturally occurring radioisotope which occurs in trace amounts on Earth of up to 1 part per trillion (0.0000000001%)Sony VAIO VPCF13M8E/B battery, mostly confined to the atmosphere and superficial deposits, particularly of peat and other organic materials.[46] This isotope decays by 0.158 MeV β- emission. Because of its relatively short half-life of 5730 years, 14C is virtually absent in ancient rocks, but is created in the upper atmosphere (lower stratosphere and upper troposphere) by interaction of nitrogen with cosmic raysSony VAIO VPCF13AHJ battery.[47] The abundance of 14C in the atmosphere and in living organisms is almost constant, but decreases predictably in their bodies after death. This principle is used in radiocarbon dating, invented in 1949, which has been used extensively to determine the age of carbonaceous materials with ages up to about 40,000 years.[48][49]

There are 15 known isotopes of carbon and the shortest-lived of these is 8C which decays through proton emission and alpha decay and has a half-life of 1.98739x10−21 s. Sony VAIO VPCF13AGJ batteryThe exotic 19C exhibits a nuclear halo, which means its radius is appreciably larger than would be expected if the nucleus were a sphere of constant density.[51]

Formation in stars

Main articles: Triple-alpha process and CNO cycle

Formation of the carbon atomic nucleus requires a nearly simultaneous triple collision of alpha particles (helium nuclei) within the core of a giant or supergiant star which is known as the triple-alpha process, as the products of further nuclear fusion reactions of helium with hydrogen or another helium nucleus produce lithium-5 and beryllium-8 respectivelySony VAIO VPCF13AFJ battery, both of which are highly unstable and decay almost instantly back into smaller nuclei.[52] This happens in conditions of temperatures over 100 megakelvin and helium concentration that the rapid expansion and cooling of the early universe prohibited, and therefore no significant carbon was created during the Big Bang. Instead, the interiors of stars in the horizontal branch transform three helium nuclei into carbon by means of this triple-alpha processSony VAIO VPCF138FJ/BI battery.[53] In order to be available for formation of life as we know it, this carbon must then later be scattered into space as dust, in supernova explosions, as part of the material which later forms second, third-generation star systems which have planets accreted from such dust.[54] The Solar System is one such third-generation star system. Another of the fusion mechanisms powering stars is the CNO cycle, in which carbon acts as a catalyst to allow the reaction to proceedSony VAIO VPCF138FJ/B battery.

Rotational transitions of various isotopic forms of carbon monoxide (for example, 12CO, 13CO, and C18O) are detectable in the submillimeter wavelength range, and are used in the study of newly forming stars in molecular clouds.[55]

Carbon cycle

Main article: Carbon cycle

Diagram of the carbon cycle. The black numbers indicate how much carbon is stored in various reservoirs, in billions tonnes ("GtC" stands for gigatonnes of carbon; figures are circa 2004). The purple numbers indicate how much carbon moves between reservoirs each yearSony VAIO VPCF138FC/BI battery. The sediments, as defined in this diagram, do not include the ~70 million GtC of carbonate rock and kerogen.

Under terrestrial conditions, conversion of one element to another is very rare. Therefore, the amount of carbon on Earth is effectively constant. Thus, processes that use carbon must obtain it somewhere and dispose of it somewhere else. The paths that carbon follows in the environment make up the carbon cycleSony VAIO VPCF135FG battery. For example, plants draw carbon dioxide out of their environment and use it to build biomass, as in carbon respiration or the Calvin cycle, a process of carbon fixation. Some of this biomass is eaten by animals, whereas some carbon is exhaled by animals as carbon dioxide. The carbon cycle is considerably more complicated than this short loop; for example, some carbon dioxide is dissolved in the oceansSony VAIO VPCF12AHJ battery; dead plant or animal matter may become petroleum or coal, which can burn with the release of carbon, should bacteria not consume it.[56][57]

Compounds

Organic compounds

Main article: Organic compound

Structural formula of methane, the simplest possible organic compound.

Correlation between the carbon cycle and formation of organic compounds. In plants, carbon dioxide formed by carbon fixation can join with water in photosynthesis (green) to form organic compounds, which can be used and further converted by both plants and animalsSony VAIO VPCF12AGJ battery.

Carbon has the ability to form very long chains of interconnecting C-C bonds. This property is called catenation. Carbon-carbon bonds are strong, and stable. This property allows carbon to form an almost infinite number of compounds; in fact, there are more known carbon-containing compounds than all the compounds of the other chemical elements combined except those of hydrogen (because almost all organic compounds contain hydrogen too) Sony VAIO VPCF12AFJ battery.

The simplest form of an organic molecule is the hydrocarbon—a large family of organic molecules that are composed of hydrogen atoms bonded to a chain of carbon atoms. Chain length, side chains and functional groups all affect the properties of organic molecules. By IUPAC's definition, all the other organic compounds are functionalized compounds of hydrocarbons.Sony VAIO VPCF129FJ/BI battery

Carbon occurs in all known organic life and is the basis of organic chemistry. When united with hydrogen, it forms various hydrocarbons which are important to industry as refrigerants, lubricants, solvents, as chemical feedstock for the manufacture of plastics and petrochemicals and as fossil fuelsSony VAIO VPCF128FJ/B battery.

When combined with oxygen and hydrogen, carbon can form many groups of important biological compounds including sugars, lignans, chitins, alcohols, fats, and aromatic esters, carotenoids and terpenes. With nitrogen it forms alkaloids, and with the addition of sulfur also it forms antibiotics, amino acids, and rubber productsSony VAIO VPCF127FJ/W battery. With the addition of phosphorus to these other elements, it forms DNA and RNA, the chemical-code carriers of life, and adenosine triphosphate (ATP), the most important energy-transfer molecule in all living cells.

Inorganic compounds

Main article: Compounds of carbon

Commonly carbon-containing compounds which are associated with minerals or which do not contain hydrogen or fluorine, are treated separately from classical organic compounds; however the definition is not rigid (see reference articles above) Sony VAIO VPCF11ZHJ battery. Among these are the simple oxides of carbon. The most prominent oxide is carbon dioxide (CO2). This was once the principal constituent of the paleoatmosphere, but is a minor component of the Earth's atmosphere today.[58] Dissolved in water, it forms carbonic acid (H2CO3), but as most compounds with multiple single-bonded oxygens on a single carbon it is unstableSony VAIO VPCF11AHJ battery.[59] Through this intermediate, though, resonance-stabilized carbonate ions are produced. Some important minerals are carbonates, notably calcite. Carbon disulfide (CS2) is similar.

The other common oxide is carbon monoxide (CO). It is formed by incomplete combustion, and is a colorless, odorless gas. The molecules each contain a triple bond and are fairly polar, resulting in a tendency to bind permanently to hemoglobin molecules, displacing oxygen, which has a lower binding affinity.[60][61] Cyanide (CN–), has a similar structureSony VAIO VPCF11AGJ battery, but behaves much like a halide ion (pseudohalogen). For example it can form the nitride cyanogen molecule ((CN)2), similar to diatomic halides. Other uncommon oxides are carbon suboxide (C3O2),[62] the unstable dicarbon monoxide (C2O),[63][64] carbon trioxide (CO3),[65][66] cyclopentanepentone (C5O5)[67] cyclohexanehexone (C6O6),[67] and mellitic anhydride (C12O9) Sony VAIO VPCF11AFJ battery.

With reactive metals, such as tungsten, carbon forms either carbides (C4–), or acetylides (C2−

2) to form alloys with high melting points. These anions are also associated with methane and acetylene, both very weak acids. With an electronegativity of 2.5,[68] carbon prefers to form covalent bonds. A few carbides are covalent lattices, like carborundum (SiC), which resembles diamondSony VAIO VPCF118FJ battery.

Organometallic compounds

Main article: Organometallic chemistry

Organometallic compounds by definition contain at least one carbon-metal bond. A wide range of such compounds exist; major classes include simple alkyl-metal compounds (for example, tetraethyllead), η2-alkene compounds (for example, Zeise's salt), and η3-allyl compounds (for example, allylpalladium chloride dimer); metallocenes containing cyclopentadienyl ligands Sony VAIO VPCF117FJ battery (for example, ferrocene); and transition metal carbene complexes. Many metal carbonyls exist (for example, tetracarbonylnickel); some workers consider the carbon monoxide ligand to be purely inorganic, and not organometallic.

While carbon is understood to exclusively form four bonds, an interesting compound containing an octahedral hexacoordinated carbon atom has been reported. The cation of the compound is [(Ph3PAu)6C]2+Sony VAIO VGN-CS33H battery. This phenomenon has been attributed to the aurophilicity of the gold ligands.[69]

History and etymology

Antoine Lavoisier in his youth

The English name carbon comes from the Latin carbo for coal and charcoal,[70] whence also comes the French charbon, meaning charcoal. In German, Dutch and Danish, the names for carbon are Kohlenstoff, koolstof and kulstof respectively, all literally meaning coal-substance.

Carbon was discovered in prehistory and was known in the forms of soot and charcoal to the earliest human civilizationsSony VAIO VGN-CS33H/Z battery. Diamonds were known probably as early as 2500 BCE in China, while carbon in the form of charcoal was made around Roman times by the same chemistry as it is today, by heating wood in a pyramid covered with clay to exclude air.[71][72]

Carl Wilhelm Scheele

In 1722, René Antoine Ferchault de Réaumur demonstrated that iron was transformed into steel through the absorption of some substance, now known to be carbon.[73] In 1772, Antoine Lavoisier showed that diamonds are a form of carbonSony VAIO VGN-CS33H/B battery; when he burned samples of charcoal and diamond and found that neither produced any water and that both released the same amount of carbon dioxide per gram. In 1779,[74] Carl Wilhelm Scheele showed that graphite, which had been thought of as a form of lead, was instead identical with charcoal but with a small admixture of iron, and that it gave "aerial acid" Sony VAIO VGN-CS31Z/Q battery (his name for carbon dioxide) when oxidized with nitric acid.[75] In 1786, the French scientists Claude Louis Berthollet, Gaspard Monge and C. A. Vandermonde confirmed that graphite was mostly carbon by oxidizing it in oxygen in much the same way Lavoisier had done with diamond.[76] Some iron again was left, which the French scientists thought was necessary to the graphite structureSony VAIO VGN-CS31S/W battery. However, in their publication they proposed the name carbone (Latin carbonum) for the element in graphite which was given off as a gas upon burning graphite. Antoine Lavoisier then listed carbon as an element in his 1789 textbook.[77]

A new allotrope of carbon, fullerene, that was discovered in 1985[78] includes nanostructured forms such as buckyballs and nanotubes.[24] Their discoverers – Robert Curl, Harold Kroto and Richard Smalley – received the Nobel Prize in Chemistry in 1996Sony VAIO VGN-CS31S/V battery.[79] The resulting renewed interest in new forms lead to the discovery of further exotic allotropes, including glassy carbon, and the realization that "amorphous carbon" is not strictly amorphous.[31]

Production

Graphite

Main article: Graphite

Commercially viable natural deposits of graphite occur in many parts of the world, but the most important sources economically are in China, India, Brazil and North Korea. Graphite deposits are of metamorphic origin, found in association with quartz, mica and feldspars in schistsSony VAIO VGN-CS31S/T battery, gneisses and metamorphosed sandstones and limestone as lenses or veins, sometimes of a meter or more in thickness. Deposits of graphite in Borrowdale, Cumberland, England were at first of sufficient size and purity that, until the 19th century, pencils were made simply by sawing blocks of natural graphite into strips before encasing the strips in woodSony VAIO VGN-CS31S/R battery. Today, smaller deposits of graphite are obtained by crushing the parent rock and floating the lighter graphite out on water.[80]

There are three types of natural graphite—amorphous, flake or crystalline flake, and vein or lump. Amorphous graphite is the lowest quality and most abundant. Contrary to science, in industry "amorphous" refers to very small crystal size rather than complete lack of crystal structureSony VAIO VGN-CS31S/P battery. Amorphous is used for lower value graphite products and is the lowest priced graphite. Large amorphous graphite deposits are found in China, Europe, Mexico and the United States. Flake graphite is less common and of higher quality than amorphous; it occurs as separate plates that crystallized in metamorphic rock. Flake graphite can be four times the price of amorphousSony VAIO VGN-CS28 battery. Good quality flakes can be processed into expandable graphite for many uses, such as flame retardants. The foremost deposits are found in Austria, Brazil, Canada, China, Germany and Madagascar. Vein or lump graphite is the rarest, most valuable, and highest quality type of natural graphite. It occurs in veins along intrusive contacts in solid lumps, and it is only commercially mined in Sri LankaSony VAIO VGN-CS28/Q battery.[80]

According to the USGS, world production of natural graphite was 1.1 million tonnes in 2010, to which China contributed 800,00 t, India 130,000 t, Brazil 76,000 t, North Korea 30,000 t and Canada 25,000 t. No natural graphite was reported mined in the United States, but 118,000 t of synthetic graphite with an estimated value of $998 million was produced in 2009Sony VAIO VGN-CS27 battery.[80]

Diamond

Main article: Diamond

Diamond output in 2005

The diamond supply chain is controlled by a limited number of powerful businesses, and is also highly concentrated in a small number of locations around the world (see figure).

Only a very small fraction of the diamond ore consists of actual diamonds. The ore is crushed, during which care has to be taken in order to prevent larger diamonds from being destroyed in this process and subsequently the particles are sorted by densitySony VAIO VGN-CS27/W battery. Today, diamonds are located in the diamond-rich density fraction with the help of X-ray fluorescence, after which the final sorting steps are done by hand. Before the use of X-rays became commonplace, the separation was done with grease belts; diamonds have a stronger tendency to stick to grease than the other minerals in the oreSony VAIO VGN-CS27/R battery.[81]

Historically diamonds were known to be found only in alluvial deposits in southern India.[82] India led the world in diamond production from the time of their discovery in approximately the 9th century BCE[83] to the mid-18th century AD, but the commercial potential of these sources had been exhausted by the late 18th century and at that time India was eclipsed by Brazil where the first non-Indian diamonds were found in 1725. Sony VAIO VGN-CS27/P battery

Diamond production of primary deposits (kimberlites and lamproites) only started in the 1870s after the discovery of the Diamond fields in South Africa. Production has increased over time and now an accumulated total of 4.5 billion carats have been mined since that date.[85] Interestingly 20% of that amount has been mined in the last 5 years alone and during the last ten years 9 new mines have started production while 4 more are waiting to be opened soonSony VAIO VGN-CS27/C battery. Most of these mines are located in Canada, Zimbabwe, Angola, and one in Russia.[85]

In the United States, diamonds have been found in Arkansas, Colorado and Montana.[86][87] In 2004, a startling discovery of a microscopic diamond in the United States[88] led to the January 2008 bulk-sampling of kimberlite pipes in a remote part of MontanaSony VAIO VGN-CS26T/W battery.[89]

Today, most commercially viable diamond deposits are in Russia, Botswana, Australia and the Democratic Republic of Congo.[90] In 2005, Russia produced almost one-fifth of the global diamond output, reports the British Geological Survey. Australia has the richest diamantiferous pipe with production reaching peak levels of 42 metric tons (41 long tons; 46 short tons) per year in the 1990sSony VAIO VGN-CS26T/V battery.[86] There are also commercial deposits being actively mined in the Northwest Territories of Canada, Siberia (mostly in Yakutia territory; for example, Mir pipe and Udachnaya pipe), Brazil, and in Northern and Western Australia.

Applications

Pencil leads for mechanical pencils are made of graphite (often mixed with a clay or synthetic binder) Sony VAIO VGN-CS26T/T battery.

Sticks of vine and compressed charcoal.

A cloth of woven carbon filaments

Silicon carbide single crystal

The C60 fullerene in crystalline form

Tungsten carbide milling bits

Carbon is essential to all known living systems, and without it life as we know it could not exist (see alternative biochemistry). The major economic use of carbon other than food and wood is in the form of hydrocarbons, most notably the fossil fuel methane gas and crude oil (petroleum). Crude oil is used by the petrochemical industry to produce, amongst other things, gasoline and kerosene, through a distillation process, in refineriesSony VAIO VGN-CS26T/R battery. Cellulose is a natural, carbon-containing polymer produced by plants in the form of cotton, linen, and hemp. Cellulose is mainly used for maintaining structure in plants. Commercially valuable carbon polymers of animal origin include wool, cashmere and silk. Plastics are made from synthetic carbon polymers, often with oxygen and nitrogen atoms included at regular intervals in the main polymer chainSony VAIO VGN-CS26T/Q battery. The raw materials for many of these synthetic substances come from crude oil.

The uses of carbon and its compounds are extremely varied. It can form alloys with iron, of which the most common is carbon steel. Graphite is combined with clays to form the 'lead' used in pencils used for writing and drawing. It is also used as a lubricant and a pigment, as a molding material in glass manufactureSony VAIO VGN-CS26T/P battery, in electrodes for dry batteries and in electroplating and electroforming, in brushes for electric motors and as a neutron moderator in nuclear reactors.

Charcoal is used as a drawing material in artwork, for grilling, and in many other uses including iron smelting. Wood, coal and oil are used as fuel for production of energy and space heating. Gem quality diamond is used in jewelry, and Industrial diamonds are used in drillingSony VAIO VGN-CS26T/C battery, cutting and polishing tools for machining metals and stone. Plastics are made from fossil hydrocarbons, and carbon fiber, made by pyrolysis of synthetic polyester fibers is used to reinforce plastics to form advanced, lightweight composite materials. Carbon fiber is made by pyrolysis of extruded and stretched filaments of polyacrylonitrile (PAN) and other organic substancesSony VAIO VGN-CS25H battery. The crystallographic structure and mechanical properties of the fiber depend on the type of starting material, and on the subsequent processing. Carbon fibers made from PAN have structure resembling narrow filaments of graphite, but thermal processing may re-order the structure into a continuous rolled sheet. The result is fibers with higher specific tensile strength than steelSony VAIO VGN-CS25H/W battery.[91]

Carbon black is used as the black pigment in printing ink, artist's oil paint and water colours, carbon paper, automotive finishes, India ink and laser printer toner. Carbon black is also used as a filler in rubber products such as tyres and in plastic compounds. Activated charcoal is used as an absorbent and adsorbent in filter material in applications as diverse as gas masksSony VAIO VGN-CS25H/R battery, water purification and kitchen extractor hoods and in medicine to absorb toxins, poisons, or gases from the digestive system. Carbon is used in chemical reduction at high temperatures. Coke is used to reduce iron ore into iron. Case hardening of steel is achieved by heating finished steel components in carbon powder. Carbides of silicon, tungsten, boron and titaniumSony VAIO VGN-CS25H/Q battery, are among the hardest known materials, and are used as abrasives in cutting and grinding tools. Carbon compounds make up most of the materials used in clothing, such as natural and synthetic textiles and leather, and almost all of the interior surfaces in the built environment other than glass, stone and metalSony VAIO VGN-CS25H/P battery.

Diamonds

The diamond industry can be broadly separated into two basically distinct categories: one dealing with gem-grade diamonds and another for industrial-grade diamonds. While a large trade in both types of diamonds exists, the two markets act in dramatically different ways.

A large trade in gem-grade diamonds exists. Unlike precious metals such as gold or platinum, gem diamonds do not trade as a commoditySony VAIO VGN-CS25H/C battery: there is a substantial mark-up in the sale of diamonds, and there is not a very active market for resale of diamonds.

The market for industrial-grade diamonds operates much differently from its gem-grade counterpart. Industrial diamonds are valued mostly for their hardness and heat conductivity, making many of the gemological characteristics of diamond, including clarity and color, mostly irrelevant. This helps explain why 80% of mined diamonds Sony VAIO VGN-CS23T/W battery (equal to about 100 million carats or 20 tonnes annually), unsuitable for use as gemstones and known as bort, are destined for industrial use.[92] In addition to mined diamonds, synthetic diamonds found industrial applications almost immediately after their invention in the 1950s; another 3 billion carats (600 tonnes) of synthetic diamond is produced annually for industrial useSony VAIO VGN-CS23T/Q battery.[93] The dominant industrial use of diamond is in cutting, drilling, grinding, and polishing. Most uses of diamonds in these technologies do not require large diamonds; in fact, most diamonds that are gem-quality except for their small size, can find an industrial use. Diamonds are embedded in drill tips or saw blades, or ground into a powder for use in grinding and polishing applicationsSony VAIO VGN-CS23H battery.[94] Specialized applications include use in laboratories as containment for high pressure experiments (see diamond anvil cell), high-performance bearings, and limited use in specialized windows.[95][96] With the continuing advances being made in the production of synthetic diamonds, future applications are beginning to become feasible. Garnering much excitement is the possible use of diamond as a semiconductor suitable to build microchips from, or the use of diamond as a heat sink in electronicsSony VAIO VGN-CS23H/S battery.[97]

Precautions

Worker at carbon black plant in Sunray, Texas (photo by John Vachon, 1942)

Pure carbon has extremely low toxicity to humans and can be handled and even ingested safely in the form of graphite or charcoal. It is resistant to dissolution or chemical attack, even in the acidic contents of the digestive tract, for example. Consequently once it enters into the body's tissues it is likely to remain there indefinitelySony VAIO VGN-CS23H/B battery. Carbon black was probably one of the first pigments to be used for tattooing, and Ötzi the Iceman was found to have carbon tattoos that survived during his life and for 5200 years after his death.[98] However, inhalation of coal dust or soot (carbon black) in large quantities can be dangerous, irritating lung tissues and causing the congestive lung disease coalworker's pneumoconiosisSony VAIO VGN-CS23G battery. Similarly, diamond dust used as an abrasive can do harm if ingested or inhaled. Microparticles of carbon are produced in diesel engine exhaust fumes, and may accumulate in the lungs.[99] In these examples, the harmful effects may result from contamination of the carbon particles, with organic chemicals or heavy metals for example, rather than from the carbon itself.

Carbon generally has low toxicity to almost all life on Earth; however, to some creatures it can still be toxic – for instance, carbon nanoparticles are a deadly toxins to DrosophilaSony VAIO VGN-CS23G/W battery.[100]

Carbon may also burn vigorously and brightly in the presence of air at high temperatures, as in the Windscale fire, which was caused by sudden release of stored Wigner energy in the graphite core. Large accumulations of coal, which have remained inert for hundreds of millions of years in the absence of oxygen, may spontaneously combust when exposed to air, for example in coal mine waste tipsSony VAIO VGN-CS23G/Q battery.

The great variety of carbon compounds include such lethal poisons as tetrodotoxin, the lectin ricin from seeds of the castor oil plant Ricinus communis, cyanide (CN−) and carbon monoxide; and such essentials to life as glucose and protein.

Nitrogen ( /ˈnaɪtrɵdʒən/ ny-trə-jən) is a chemical element that has the symbol N, atomic number of 7 and atomic mass 14.00674 u. Elemental nitrogen is a colorless, odorless, tasteless, and mostly inert diatomic gas at standard conditionsSony VAIO VGN-CS23G/P battery, constituting 78.09% by volume of Earth's atmosphere.[1] The element nitrogen was discovered as a separable component of air, by Scottish physician Daniel Rutherford, in 1772.

Nitrogen is a common element in the universe, estimated at about seventh in total abundance in our galaxy and the solar system. Its occurrence there is thought to be entirely due to synthesis by fusion from carbon and hydrogen in supernovasSony VAIO VGN-CS21Z/Q battery. Due to the volatility of elemental nitrogen and its common compounds with hydrogen and oxygen, nitrogen is far less common on the rocky planets of the inner solar system, and it is a relatively rare element on Earth as a whole. However, as is the case on Earth, nitrogen and its compounds occur commonly as gases in the atmospheres of planets and moons that have atmospheresSony VAIO VGN-CS21S/W battery.

Many industrially important compounds, such as ammonia, nitric acid, organic nitrates (propellants and explosives), and cyanides, contain nitrogen. The extremely strong bond in elemental nitrogen dominates nitrogen chemistry, causing difficulty for both organisms and industry in breaking the bond to convert the N2 into useful compoundsSony VAIO VGN-CS21S/V battery, but at the same time causing release of large amounts of often useful energy when the compounds burn, explode, or decay back into nitrogen gas.

Nitrogen occurs in all living organisms, primarily in amino acids and thus proteins and in the nucleic acids (DNA and RNA). The human body contains about 3% by weight of nitrogen, the fourth most abundant element after oxygen, carbon, and hydrogen. Nitrogen resides in the chemical structure of almost all neurotransmittersSony VAIO VGN-CS21S/T battery, and is a defining component of alkaloids, biological molecules produced as secondary metabolites by many organisms. The nitrogen cycle describes movement of the element from the air into the biosphere and organic compounds, then back into the atmosphere. Synthetically produced nitrates are key ingredients of industrial fertilizers,[1] and key pollutants in causing the eutrophication of water systemsSony VAIO VGN-CS21S/R battery.

History and etymology

Nitrogen is formally considered to have been discovered by Scottish physician Daniel Rutherford in 1772, who called it noxious air or fixed air.[2] The fact that there was an element of air that does not support combustion was clear to Rutherford. Nitrogen was also studied at about the same time by Carl Wilhelm Scheele, Henry Cavendish, and Joseph PriestleySony VAIO VGN-CS21S/P battery, who referred to it as burnt air or phlogisticated air. Nitrogen gas was inert enough that Antoine Lavoisier referred to it as "mephitic air" or azote, from the Greek word ἄζωτος (azotos) meaning "lifeless".[3] In it, animals died and flames were extinguished. Lavoisier's name for nitrogen is used in many languages (French, Polish, Russian, etc.) and still remains in English in the common names of many compounds, such as hydrazine and compounds of the azide ionSony VAIO VGN-CS215J/R battery.

The English word nitrogen (1794) entered the language [4] from the French nitrogène, coined in 1790 by French chemist Jean-Antoine Chaptal (1756–1832), from "nitre" + Fr. gène "producing" (from Gk. -γενής means "forming" or "giving birth to."). The gas had been found in nitric acid. Chaptal's meaning was that nitrogen gas is the essential part of nitric acidSony VAIO VGN-CS215J/Q battery, in turn formed from saltpetre (potassium nitrate), then known as nitre. This word in the more ancient world originally described sodium salts that did not contain nitrate, and is a cognate of natron.

Nitrogen compounds were well known during the Middle Ages. Alchemists knew nitric acid as aqua fortis (strong water). The mixture of nitric and hydrochloric acids was known as aqua regia (royal water), celebrated for its ability to dissolve gold (the king of metals) Sony VAIO VGN-CS19/W battery. The earliest military, industrial, and agricultural applications of nitrogen compounds used saltpetre (sodium nitrate or potassium nitrate), most notably in gunpowder, and later as fertilizer. In 1910, Lord Rayleigh discovered that an electrical discharge in nitrogen gas produced "active nitrogen", an allotrope considered to be monatomic. The "whirling cloud of brilliant yellow light" produced by his apparatus reacted with quicksilver to produce explosive mercury nitrideSony VAIO VGN-CS19/R battery.[5]

[edit]Production

Nitrogen gas is an industrial gas produced by the fractional distillation of liquid air, or by mechanical means using gaseous air (i.e., pressurized reverse osmosis membrane or Pressure swing adsorption). Commercial nitrogen is often a byproduct of air-processing for industrial concentration of oxygen for steelmaking and other purposes. When supplied compressed in cylinders it is often called OFN (oxygen-free nitrogen) Sony VAIO VGN-CS19/Q battery.[6]

In a chemical laboratory it is prepared by treating an aqueous solution of ammonium chloride with sodium nitrite.

NH4Cl(aq) + NaNO2(aq) → N2(g) + NaCl(aq) + 2 H2O (l)

Small amounts of impurities NO and HNO3 are also formed in this reaction. The impurities can be removed by passing the gas through aqueous sulfuric acid containing potassium dichromate. Very pure nitrogen can be prepared by the thermal decomposition of barium or sodium azideSony VAIO VGN-CS19/P battery.

2 NaN3 → 2 Na + 3 N2

[edit]Properties

Nitrogen is a nonmetal, with an electronegativity of 3.04. It has five electrons in its outer shell and is, therefore, trivalent in most compounds. The triple bond in molecular nitrogen (N2) is one of the strongest. The resulting difficulty of converting N2 into other compounds, and the ease (and associated high energy release) of converting nitrogen compounds into elemental N2Sony VAIO VGN-CS17H/W battery, have dominated the role of nitrogen in both nature and human economic activities.

At atmospheric pressure molecular nitrogen condenses (liquefies) at 77 K (−195.79 °C) and freezes at 63 K (−210.01 °C)[1] into the beta hexagonal close-packed crystal allotropic form. Below 35.4 K (−237.6 °C) nitrogen assumes the cubic crystal allotropic form (called the alpha-phase). Liquid nitrogen, a fluid resembling water in appearanceSony VAIO VGN-CS17H/Q battery, but with 80.8% of the density (the density of liquid nitrogen at its boiling point is 0.808 g/mL), is a common cryogen.

Unstable allotropes of nitrogen consisting of more than two nitrogen atoms have been produced in the laboratory, like N3 and N4.[7] Under extremely high pressures (1.1 million atm) and high temperatures (2000 K), as produced using a diamond anvil cell, nitrogen polymerizes into the single-bonded cubic gauche crystal structure. This structure is similar to that of diamondSony VAIO VGN-CS16T/W battery, and both have extremely strong covalent bonds. N4 is nicknamed "nitrogen diamond."[8]

Other (as yet unsynthesized) allotropes include hexazine (N6, a benzene analog)[9] and octaazacubane (N8, a cubane analog).[10] The former is predicted to be highly unstable, while the latter is predicted to be kinetically stable, for reasons of orbital symmetrySony VAIO VGN-CS16T/T battery.[11]

[edit]Isotopes

See also: Isotopes of nitrogen

There are two stable isotopes of nitrogen: 14N and 15N. By far the most common is 14N (99.634%), which is produced in the CNO cycle in stars. Of the ten isotopes produced synthetically, 13N has a half-life of ten minutes and the remaining isotopes have half-lives on the order of seconds or less. Biologically mediated reactions (e.g., assimilation, nitrification, and denitrification) strongly control nitrogen dynamics in the soilSony VAIO VGN-CS16T/R battery. These reactions typically result in 15N enrichment of the substrate and depletion of the product.

A small part (0.73%) of the molecular nitrogen in Earth's atmosphere is the isotopologue 14N15N, and almost all the rest is 14N2.

Radioisotope 16N is the dominant radionuclide in the coolant of pressurized water reactors or boiling water reactors during normal operation. It is produced from 16O (in water) via (n,p) reactionSony VAIO VGN-CS16T/Q battery. It has a short half-life of about 7.1 s, but during its decay back to 16O produces high-energy gamma radiation (5 to 7 MeV).

Because of this, the access to the primary coolant piping in a pressurized water reactor must be restricted during reactor power operation.[12] 16N is one of the main means used to immediately detect even small leaks from the primary coolant to the secondary steam cycleSony VAIO VGN-CS16T/P battery.

In similar fashion, access to any of the steam cycle components in a boiling water reactor nuclear power plant must be restricted during operation. Condensate from the condenser is typically retained for 10 minutes to allow for decay of the 16N. This eliminates the need to shield and restrict access to any of the feed water piping or pumpsSony VAIO VGN-CS13T/W battery.

[edit]Electromagnetic spectrum

Nitrogen discharge (spectrum) tube

Molecular nitrogen (14N2) is largely transparent to infrared and visible radiation because it is a homonuclear molecule and, thus, has no dipole moment to couple to electromagnetic radiation at these wavelengths. Significant absorption occurs at extreme ultraviolet wavelengths, beginning around 100 nanometers. This is associated with electronic transitions in the molecule to states in which charge is not distributed evenly between nitrogen atomsSony VAIO VGN-CS13H/W battery. Nitrogen absorption leads to significant absorption of ultraviolet radiation in the Earth's upper atmosphere and the atmospheres of other planetary bodies. For similar reasons, pure molecular nitrogen lasers typically emit light in the ultraviolet range.

Nitrogen also makes a contribution to visible air glow from the Earth's upper atmosphere, through electron impact excitation followed by emissionSony VAIO VGN-CS13H/R battery. This visible blue air glow (seen in the polar aurora and in the re-entry glow of returning spacecraft) typically results not from molecular nitrogen but rather from free nitrogen atoms combining with oxygen to form nitric oxide (NO).

Nitrogen gas also exhibits scintillation.

[edit]Reactions

Structure of dinitrogen, N2

Structure of [Ru(NH3)5(N2)]2+

In general, nitrogen is unreactive at standard temperature and pressure. N2 reacts spontaneously with few reagents, being resilient to acids and bases as well as oxidants and most reductants. When nitrogen reacts spontaneously with a reagent, the net transformation is often called nitrogen fixationSony VAIO VGN-CS13H/Q battery.

Nitrogen reacts with elemental lithium.[13] Lithium burns in an atmosphere of N2 to give lithium nitride:

6 Li + N2 → 2 Li3N

Magnesium also burns in nitrogen, forming magnesium nitride.

3 Mg + N2 → Mg3N2

N2 forms a variety of adducts with transition metals. The first example of a dinitrogen complex is [Ru(NH3)5(N2)]2+ (see figure at right). However, it is interesting to note that the N2 ligand was obtained by the decomposition of hydrazine, and not coordination of free dinitrogen. Such compounds are now numerous, other examples include IrCl(N2)(PPh3)2Sony VAIO VGN-CS13H/P battery, W(N2)2(Ph2PCH2CH2PPh2)2, and [(η5-C5Me4H)2Zr]2(μ2, η2,η2-N2). These complexes illustrate how N2 might bind to the metal(s) in nitrogenase and the catalyst for the Haber process.[14] A catalytic process to reduce N2 to ammonia with the use of a molybdenum complex in the presence of a proton source was published in 2005.[13]

The starting point for industrial production of nitrogen compounds is the Haber processSony VAIO VGN-CS11Z/T battery, in which nitrogen is fixed by reacting N2 and H2 over an iron(II, III) oxide (Fe3O4) catalyst at about 500 °C and 200 atmospheres pressure. Biological nitrogen fixation in free-living cyanobacteria and in the root nodules of plants also produces ammonia from molecular nitrogen. The reaction, which is the source of the bulk of nitrogen in the biosphere, is catalyzed by the nitrogenase enzyme complex that contains Fe and Mo atomsSony VAIO VGN-CS11Z/R battery, using energy derived from hydrolysis of adenosine triphosphate (ATP) into adenosine diphosphate and inorganic phosphate (−20.5 kJ/mol).

[edit]Occurrence

See also Category: Nitrate minerals

See also Category: Ammonium minerals

Nitrogen is the largest constituent of the Earth's atmosphere (78.082% by volume of dry air, 75.3% by weight in dry air). However, this high concentration does not reflect nitrogen's overall low abundance in the makeup of the Earth, from which most of the element escaped by solar evaporation, early in the planet's formationSony VAIO VGN-CS11S/W battery.

Nitrogen is a common element in the universe, and is estimated to be approximately seventh most abundant chemical element by mass in the universe, our galaxy and the solar system. Its occurrence there is thought to be entirely due to synthesis by fusion from carbon and hydrogen in supernovas. In these places it was originally created by fusion processes from carbon and hydrogen in supernovasSony VAIO VGN-CS11S/Q battery.[15]Molecular nitrogen and nitrogen compounds have been detected in interstellar space by astronomers using the Far Ultraviolet Spectroscopic Explorer.[16]

Due to the volatility of elemental nitrogen and also its common compounds with hydrogen and oxygen, nitrogen and its compounds were driven out of the planetesimals in the early solar system by the heat of the Sun, and in the form of gases, were lost to the rocky planets of the inner solar system. Nitrogen is therefore a relatively rare element on these inner planetsSony VAIO VGN-CS11S/P battery, including Earth, as a whole. In this, nitrogen resembles neon, which has a similar abundance in the universe, but is also rare in the inner solar system. Nitrogen is estimated at 30th of the elements in crustal abundance. There exist some relatively uncommon nitrogen minerals, such as saltpetre (potassium nitrate), Chile saltpetre (sodium nitrate) and sal ammoniac (ammonium chloride) (Sony VAIO VGN-AW11M/H battery). Even these are known mainly as concentrated from evaporative ocean beds, on account of their ready solubility of most naturally-occurring nitrogen compounds in water. A similar pattern occurs with the water solubility of the uncommon light element boron.

However, nitrogen and its compounds occur far more commonly as gases in the atmospheres of planets and moons that are large enough to have atmospheres.[17] For example, molecular nitrogen is a major constituent of not only Earth's atmosphere(Sony VAIO VGN-AW11S/B battery), but also the Saturnian moon Titan's thick atmosphere. Also, due to retension by gravity at colder temperatures, nitrogen and its compounds occur in appreciable to trace amounts in planetary atmospheres of the gas giant planets.[18]

Nitrogen is present in all living organisms, in proteins, nucleic acids, and other molecules. It typically makes up around 4% of the dry weight of plant matter, and around 3% of the weight of the human body(Sony VAIO VGN-AW11Z/B battery). It is a large component of animal waste (for example, guano), usually in the form of urea, uric acid, ammonium compounds, and derivatives of these nitrogenous products, which are essential nutrients for all plants that cannot fix atmospheric nitrogen.

[edit]Compounds

See also Category: Nitrogen compounds

The main neutral hydride of nitrogen is ammonia (NH3), although hydrazine (N2H4) is also commonly used. Ammonia is more basic than water by 6 orders of magnitude. In solution ammonia forms the ammonium ion (Sony VAIO VGN-AW170C battery)(NH+4). Liquid ammonia (boiling point 240 K) is amphiprotic (displaying either Brønsted-Lowry acidic or basic character) and forms ammonium and the less common amide ions (NH−

2); both amides and nitride (N3−) salts are known, but decompose in water. Singly, doubly, triply and quadruply substituted alkyl compounds of ammonia are called amines (four substitutions, to form commercially and biologically important quaternary amines, results in a positively charged nitrogen, and thus a water-soluble, or at least amphiphilic, compound) (Sony VAIO VGN-AW19/Q battery). Larger chains, rings and structures of nitrogen hydrides are also known, but are generally unstable.

Other classes of nitrogen anions (negatively charged ions) are the poisonous azides (N−

3), which are linear and isoelectronic to carbon dioxide, but which bind to important iron-containing enzymes in the body in a manner more resembling cyanide. Another molecule of the same structure is the colorless and relatively inert anesthetic gas Nitrous oxide (dinitrogen monoxide, N2O), also known as laughing gas(Sony VAIO VGN-AW19 battery). This is one of a variety of nitrogen oxides that form a family often abbreviated as NOx. Nitric oxide (nitrogen monoxide, NO), is a natural free radical used in signal transduction in both plants and animals, for example, in vasodilation by causing the smooth muscle of blood vessels to relax. The reddish and poisonous nitrogen dioxide NO2 contains an unpaired electron and is an important component of smog(Sony VAIO VGN-AW21M/H battery). Nitrogen molecules containing unpaired electrons show a tendency to dimerize (thus pairing the electrons), and are, in general, highly reactive. The corresponding acids are nitrous HNO2 and nitric acid HNO3, with the corresponding salts called nitrites and nitrates.

The higher oxides dinitrogen trioxide N2O3, dinitrogen tetroxide N2O4 and dinitrogen pentoxide N2O5, are unstable and explosive, a consequence of the chemical stability of N2. Nearly every hypergolic rocket engine uses N2O4 as the oxidizer(Sony VAIO VGN-AW21S/B battery); their fuels, various forms of hydrazine, are also nitrogen compounds. These engines are extensively used on spacecraft such as the space shuttle and those of the Apollo Program because their propellants are liquids at room temperature and ignition occurs on contact without an ignition system, allowing many precisely controlled burns. Some launch vehicles such as the Titan II and Ariane 1 through 4 also use hypergolic fuels(Sony VAIO VGN-AW21VY/Q battery), although the trend is away from such engines for cost and safety reasons. N2O4 is an intermediate in the manufacture of nitric acid HNO3, one of the few acids stronger than hydronium and a fairly strong oxidizing agent.

Nitrogen is notable for the range of explosively unstable compounds that it can produce. Nitrogen triiodide NI3 is an extremely sensitive contact explosive. Nitrocellulose, produced by nitration of cellulose with nitric acid, is also known as guncotton(Sony VAIO VGN-AW21XY/Q battery). Nitroglycerin, made by nitration of glycerin, is the dangerously unstable explosive ingredient of dynamite. The comparatively stable, but less powerful explosive trinitrotoluene (TNT) is the standard explosive against which the power of nuclear explosions are measured.[19]

Nitrogen can also be found in organic compounds. Common nitrogen functional groups include: amines, amides, nitro groups, imines, and enamines(Sony VAIO VGN-AW21Z/B battery). The amount of nitrogen in a chemical substance can be determined by the Kjeldahl method.

[edit]Applications

Nitrogen gas has a variety of applications, including serving as an inert replacement for air where oxidation is undesirable;

As a modified atmosphere, pure or mixed with carbon dioxide, to preserve the freshness of packaged or bulk foods (by delaying rancidity and other forms of oxidative damage)

In ordinary incandescent light bulbs as an inexpensive alternative to argon.[20]

The production of electronic parts such as transistors, diodes, and integrated circuits

Dried and pressurized, as a dielectric gas for high-voltage equipment(Sony VAIO VGN-AW230J/H battery)

The manufacturing of stainless steel[21]

Used in military aircraft fuel systems to reduce fire hazard, (see inerting system)

On top of liquid explosives as a safety measure

Filling automotive and aircraft tires[22] due to its inertness and lack of moisture or oxidative qualities, as opposed to air. The difference in N2 content between air and pure N2 is 20%[23][24]

Used as a propellant for draft wine, and as an alternative to or together with carbon dioxide for other beverages(Sony VAIO VGN-AW235J/B battery).

Nitrogen is commonly used during sample preparation procedures for chemical analysis. It is used to concentrate and reduce the volume of liquid samples. Directing a pressurized stream of nitrogen gas perpendicular to the surface of the liquid allows the solvent to evaporate while leaving the solute(s) and un-evaporated solvent behind(Sony VAIO VGN-AW270Y/Q battery).[25]

Nitrogen tanks are also replacing carbon dioxide as the main power source for paintball guns. Nitrogen must be kept at higher pressure than CO2, making N2 tanks heavier and more expensive.

[edit]Nitrogenated beer

Nitrogen can be used instead of carbon dioxide to pressurize kegs of some beers, in particular, stouts and British ales, due to the smaller bubbles it produces, which makes the dispensed beer smoother and headier(Sony VAIO VGN-AW31M/H battery). A pressure sensitive nitrogen capsule known commonly as a "widget" allows nitrogen charged beers to be packaged in cans and bottles.[26]

A mixture of nitrogen and carbon dioxide can be used for this purpose as well, to maintain the saturation of beer with carbon dioxide.[27]

[edit]Liquid nitrogen

Air balloon submerged in liquid nitrogen

Main article: Liquid nitrogen

Liquid nitrogen is a cryogenic liquid. At atmospheric pressure, it boils at −195.8 °C. When insulated in proper containers such as Dewar flasks, it can be transported without much evaporative loss(Sony VAIO VGN-AW31S/B battery).[28]

Like dry ice, the main use of liquid nitrogen is as a refrigerant. Among other things, it is used in the cryopreservation of blood, reproductive cells (sperm and egg), and other biological samples and materials. It is used in the clinical setting in cryotherapy to remove cysts and warts on the skin.[29] It is used in cold traps for certain laboratory equipment and to cool infrared detectors or X-ray detectors(Sony VAIO VGN-AW31XY/Q battery). It has also been used to cool central processing units and other devices in computers that are overclocked, and that produce more heat than during normal operation.[30]

[edit]Applications of nitrogen compounds

Molecular nitrogen (N2) in the atmosphere is relatively non-reactive due to its strong bond, and N2 plays an inert role in the human body, being neither produced nor destroyed. In nature, nitrogen is converted into biologically (and industrially) useful compounds by lightning, and by some living organisms, notably certain bacteria(Sony VAIO VGN-AW31ZJ/B battery) (i.e., nitrogen fixing bacteria—see Biological role below). Molecular nitrogen is released into the atmosphere in the process of decay, in dead plant and animal tissues.

The ability to combine, or fix, molecular nitrogen is a key feature of modern industrial chemistry, where nitrogen and natural gas are converted into ammonia via the Haber process. Ammonia, in turn, can be used directly (primarily as a fertilizer, and in the synthesis of nitrated fertilizers) (Sony VAIO VGN-AW41JF/H battery),[1] or as a precursor of many other important materials including explosives, largely via the production of nitric acid by the Ostwald process.

The organic and inorganic salts of nitric acid have been important historically as convenient stores of chemical energy. They include important compounds such as potassium nitrate (or saltpeter used in gunpowder) and ammonium nitrate(Sony VAIO VGN-AW41JF battery), an important fertilizer and explosive (see ANFO). Various other nitrated organic compounds, such as nitroglycerin, trinitrotoluene, and nitrocellulose, are used as explosives and propellants for modern firearms. Nitric acid is used as an oxidizing agent in liquid fueled rockets. Hydrazine and hydrazine derivatives find use as rocket fuels and monopropellants. In most of these compounds(Sony VAIO VGN-AW41MF/H battery), the basic instability and tendency to burn or explode is derived from the fact that nitrogen is present as an oxide, and not as the far more stable nitrogen molecule (N2), which is a product of the compounds' thermal decomposition. When nitrates burn or explode, the formation of the powerful triple bond in the N2 produces most of the energy of the reaction(Sony VAIO VGN-AW41MF battery).

Nitrogen is a constituent of molecules in every major drug class in pharmacology and medicine. Nitrous oxide (N2O) was discovered early in the 19th century to be a partial anesthetic, though it was not used as a surgical anesthetic until later. Called "laughing gas", it was found capable of inducing a state of social disinhibition resembling drunkenness(Sony VAIO VGN-AW41XH/Q battery). Other notable nitrogen-containing drugs are drugs derived from plant alkaloids, such as morphine (there exist many alkaloids known to have pharmacological effects; in some cases, they appear as natural chemical defenses of plants against predation). Drugs that contain nitrogen include all major classes of antibiotics and organic nitrate drugs like nitroglycerin and nitroprusside that regulate blood pressure and heart action by mimicking the action of nitric oxide(Sony VAIO VGN-AW41XH battery).

[edit]Biological role

See also: Nitrogen cycle and Human impacts on the nitrogen cycle

Nitrogen is an essential building block of amino and nucleic acids, essential to life on Earth.

Elemental nitrogen in the atmosphere cannot be used directly by either plants or animals, and must be converted to a reduced (or 'fixed') state to be useful for higher plants and animals. Precipitation often contains substantial quantities of ammonium and nitrate, thought to result from nitrogen fixation by lightning and other atmospheric electric phenomena(Sony VAIO VGN-AW41ZF/B battery).[31] This was first proposed by Liebig in 1827 and later confirmed.[31] However, because ammonium is preferentially retained by the forest canopy relative to atmospheric nitrate, most fixed nitrogen reaches the soil surface under trees as nitrate. Soil nitrate is preferentially assimilated by tree roots relative to soil ammonium[citation needed].

Specific bacteria (e.g., Rhizobium trifolium) (Sony VAIO VGN-AW41ZF battery) possess nitrogenase enzymes that can fix atmospheric nitrogen (see nitrogen fixation) into a form (ammonium ion) that is chemically useful to higher organisms. This process requires a large amount of energy and anoxic conditions. Such bacteria may live freely in soil (e.g., Azotobacter) but normally exist in a symbiotic relationship in the root nodules of leguminous plants (SONY Vaio VGN-NS38M Battery) (e.g. clover, Trifolium, or soybean plant, Glycine max). Nitrogen-fixing bacteria are also symbiotic with a number of unrelated plant species such as alders (Alnus) spp., lichens, Casuarina, Myrica, liverworts, and Gunnera.[32]

As part of the symbiotic relationship, the plant converts the 'fixed' ammonium ion to nitrogen oxides and amino acids to form proteins and other molecules, (e.g., alkaloids). In return for the 'fixed' nitrogen, the plant secretes sugars to the symbiotic bacteria(SONY Vaio VGN-NS31S Battery).[32] Legumes maintain an anaerobic (oxygen free) environment for their nitrogen-fixing bacteria.

Plants are able to assimilate nitrogen directly in the form of nitrates that may be present in soil from natural mineral deposits, artificial fertilizers, animal waste, or organic decay (as the product of bacteria, but not bacteria specifically associated with the plant). Nitrates absorbed in this fashion are converted to nitrites by the enzyme nitrate reductase(SONY Vaio VGN-NS31M Battery), and then converted to ammonia by another enzyme called nitrite reductase.[32]

Nitrogen compounds are basic building blocks in animal biology as well. Animals use nitrogen-containing amino acids from plant sources as starting materials for all nitrogen-compound animal biochemistry, including the manufacture of proteins and nucleic acids. Plant-feeding insects are dependent on nitrogen in their diet(SONY Vaio VGN-NS31Z Battery), such that varying the amount of nitrogen fertilizer applied to a plant can affect the reproduction rate of insects feeding on fertilized plants.[33]

Soluble nitrate is an important limiting factor in the growth of certain bacteria in ocean waters.[34] In many places in the world, artificial fertilizers applied to crop-lands to increase yields result in run-off delivery of soluble nitrogen to oceans at river mouths(SONY Vaio VGN-NS21Z Battery). This process can result in eutrophication of the water, as nitrogen-driven bacterial growth depletes water oxygen to the point that all higher organisms die. Well-known "dead zone" areas in the U.S. Gulf Coast and the Black Sea are due to this important polluting process.

Many saltwater fish manufacture large amounts of trimethylamine oxide to protect them from the high osmotic effects of their environment; conversion of this compound to dimethylamine is responsible for the early odor in unfresh saltwater fish(SONY Vaio VGN-NS21M Battery).[35] In animals, free radical nitric oxide (NO) (derived from an amino acid), serves as an important regulatory molecule for circulation.[34]

Animal metabolism of NO results in production of nitrite. Animal metabolism of nitrogen in proteins, in general, results in excretion of urea, while animal metabolism of nucleic acids results in excretion of urea and uric acid. The characteristic odor of animal flesh decay is caused by the creation of long-chain, nitrogen-containing amines, such as putrescine and cadaverine(SONY Vaio VGN-NS21S Battery), which are breakdown products of the amino acids ornithine and lysine, respectively, in decaying proteins.[36]

Decay of organisms and their waste products may produce small amounts of nitrate, but most decay eventually returns nitrogen content to the atmosphere, as molecular nitrogen. The circulation of nitrogen from atmosphere, to organic compounds, then back to the atmosphere, is referred to as the nitrogen cycle(SONY Vaio VGN-NS12S Battery).[32]

[edit]Safety

Rapid release of nitrogen gas into an enclosed space can displace oxygen, and therefore represents an asphyxiation hazard. This may happen with few warning symptoms, since the human carotid body is a relatively slow and a poor low-oxygen (hypoxia) sensing system.[37] An example occurred shortly before the launch of the first Space Shuttle mission in 1981(SONY Vaio VGN-NS12M Battery), when two technicians lost consciousness (and one of them died) after they walked into a space located in the Shuttle's Mobile Launcher Platform that was pressurized with pure nitrogen as a precaution against fire. The technicians would have been able to exit the room if they had experienced early symptoms from nitrogen-breathing(SONY Vaio VGN-NS11Z Battery).

When inhaled at high partial pressures (more than about 4 bar, encountered at depths below about 30 m in scuba diving), nitrogen begins to act as an anesthetic agent. It can cause nitrogen narcosis, a temporary semi-anesthetized state of mental impairment similar to that caused by nitrous oxide. (SONY Vaio VGN-NS11M Battery)

Nitrogen also dissolves in the bloodstream and body fats. Rapid decompression (in particular, in the case of divers ascending too quickly, or astronauts decompressing too quickly from cabin pressure to spacesuit pressure) can lead to a potentially fatal condition called decompression sickness (formerly known as caisson sickness or the bends) (SONY Vaio VGN-NS11L Battery), when nitrogen bubbles form in the bloodstream, nerves, joints, and other sensitive or vital areas.[40][41] Other "inert" gases (those gases other than carbon dioxide and oxygen) cause the same effects from bubbles composed of them, so replacement of nitrogen in breathing gases may prevent nitrogen narcosis, but does not prevent decompression sickness(SONY Vaio VGN-NS11J Battery).[42]

Direct skin contact with liquid nitrogen will cause severe frostbite (cryogenic "burns"). This may happen almost instantly on contact, or after a second or more, depending on the form of liquid nitrogen. Bulk liquid nitrogen causes less rapid freezing than a spray of nitrogen mist (such as is used to freeze certain skin growths in the practice of dermatology) (SONY Vaio VGN-NS11E Battery). The extra surface area provided by nitrogen-soaked materials is also important, with soaked clothing or cotton causing far more rapid damage than a spill of direct liquid to skin. Full "contact" between naked skin and large collected-droplets or pools of liquid nitrogen may be prevented for a second or two, by a layer of insulating gas from the Leidenfrost effect(SONY Vaio VGN-NS10L Battery). This may give the skin a second of protection from nitrogen bulk liquid. However, liquid nitrogen applied to skin in mists, and on fabrics, bypasses this effect, and causes local frostbite immediately.

Oxygen sensors are sometimes used as a safety precaution when working with liquid nitrogen to alert workers of gas spills into a confined space(SONY Vaio VGN-NS10J Battery).