Iron And Nickel

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)