Tungsten, is a chemical element with the chemical symbol W and atomic number 74. The word tungsten comes from the Swedish language tung sten directly translatable to heavy stone.[3]
A hard, rare metal under standard conditions when uncombined, tungsten is found naturally on Earth only in chemical compounds. It was identified as a new element in 1781Sony VPCEH3T9E battery, and first isolated as a metal in 1783. Its important ores include wolframite and scheelite. The free element is remarkable for its robustness, especially the fact that it has the highest melting point of all the non-alloyed metals and the second highest of all the elements after carbon. Also remarkable is its high density of 19.3 times that of water, comparable to that of uranium and goldSony VPCEH3N6E battery, and much higher (about 1.7 times) than that of lead.[4] Tungsten with minor amounts of impurities is often brittle[5] and hard, making it difficult to work. However, very pure tungsten, though still hard, is more ductile, and can be cut with a hard-steel hacksaw.[6]
The unalloyed elemental form is used mainly in electrical applications. Tungsten's many alloys have numerous applications, most notably in incandescent light bulb filaments, X-ray tubes (as both the filament and target), and superalloysSony VPCEH3N1E battery. Tungsten's hardness and high density give it military applications in penetrating projectiles. Tungsten compounds are most often used industrially as catalysts.
Tungsten is the only metal from the third transition series that is known to occur in biomolecules, where it is used in a few species of bacteria. It is the heaviest element known to be used by any living organism. Tungsten interferes with molybdenum and copper metabolism, and is somewhat toxic to animal lifeSony VPCEH3D0E battery.
History
In 1781, Carl Wilhelm Scheele discovered that a new acid, tungstic acid, could be made from scheelite (at the time named tungsten). Scheele and Torbern Bergman suggested that it might be possible to obtain a new metal by reducing this acid.[9] In 1783, José and Fausto Elhuyar found an acid made from wolframite that was identical to tungstic acidSony VPCEH3B1E battery. Later that year, in Spain, the brothers succeeded in isolating tungsten by reduction of this acid with charcoal, and they are credited with the discovery of the element.[10][11]
In World War II, tungsten played a significant role in background political dealings. Portugal, as the main European source of the element, was put under pressure from both sides, because of its deposits of wolframite ore at PanasqueiraSony VPCEH2Z1E battery. Tungsten's resistance to high temperatures and its strengthening of alloys made it an important raw material for the arms industry.[12]
[edit]Etymology
The name "tungsten" (from the Nordic tung sten, meaning "heavy stone") is used in English, French, and many other languages as the name of the element. Tungsten was the old Swedish name for the mineral scheelite. The other name "wolfram" (or "volfram")Sony VPCEH2S9E battery, used for example in most European (especially Germanic and Slavic) languages, is derived from the mineral wolframite, and this is also the origin of its chemical symbol, W.[6] The name "wolframite" is derived from German "wolf rahm" ("wolf soot" or "wolf cream"), the name given to tungsten by Johan Gottschalk Wallerius in 1747. This, in turn, derives from "Lupi spuma", the name Georg Agricola used for the element in 1546Sony VPCEH2Q1E battery, which translates into English as "wolf's froth" or "cream" (the etymology is not entirely certain), and is a reference to the large amounts of tin consumed by the mineral during its extraction.[13]
Characteristics
Physical properties
In tungsten's raw form, it is a hard steel-gray metal that is often brittle and hard to work. If made very pure, tungsten retains its hardness (which exceeds that of many steels), and becomes malleable enough that it can be worked easily. Sony VPCEH2P0E battery It is worked by forging, drawing, extruding or sintering.
Of all metals in pure form, tungsten has the highest melting point (3,422 °C, 6,192 °F), lowest vapor pressure (at temperatures above 1,650 °C, 3,000 °F) and the highest tensile strength.[14] Tungsten has the lowest coefficient of thermal expansion of any pure metal. The low thermal expansion and high melting point and strength of tungsten originate from strong covalent bonds formed between tungsten atoms by the 5d electrons. Sony VPCEH2N1E battery Alloying small quantities of tungsten with steel greatly increases its toughness.[4]
Tungsten exists in two major crystalline forms: α and β. The former has a body-centered cubic structure and is the most stable form. The structure of the β phase is called A15 cubic; it is metastable, but can coexist with the α phase at ambient conditions owing to non-equilibrium synthesis or stabilization by impuritiesSony VPCEH2M9E battery. Contrary to the α phase which crystallizes in isometric grains, the β form exhibits a columnar habit. The α phase has a three times lower electrical resistivity[16] and a much lower superconducting transition temperature TC than the β phase: ca. 0.015 K vs. 1–4 K; mixing the two phases allows obtaining intermedicate TC values.[17][18] The TC value can also be raised by alloying tungsten with another metal (e.g. 7.9 K for W-Tc). Sony VPCEH2M1E batterySuch tungsten alloys are sometimes used in low-temperature superconducting circuits.[20][21][22]
[edit]Isotopes
Main article: Isotopes of tungsten
Naturally occurring tungsten consists of five isotopes whose half-lives are so long that they can be considered stable. Theoretically, all five can decay into isotopes of element 72 (hafnium) by alpha emission, but only 180W has been observed[23] to do so with a half-life of (1.8 ± 0.2)×1018 yearsSony VPCEH2L9E battery; on average, this yields about two alpha decays of 180W in one gram of natural tungsten per year.[24] The other naturally occurring isotopes have not been observed to decay, constraining their half-lives to be[24]
182W, T1/2 > 8.3×1018 years
183W, T1/2 > 2.9×1019 years
184W, T1/2 > 1.3×1019 years
186W, T1/2 > 2.7×1019 years
Another 30 artificial radioisotopes of tungsten have been characterized, the most stable of which are 181W with a half-life of 121.2 days, 185W with a half-life of 75.1 days, 188W with a half-life of 69.4 days, 178W with a half-life of 21.6 days, and 187W with a half-life of 23.72 h.[24] All of the remaining radioactive isotopes have half-lives of less than 3 hoursSony VPCEH2J1E battery, and most of these have half-lives below 8 minutes.[24] Tungsten also has 4 meta states, the most stable being 179mW (T½ 6.4 minutes).
[edit]Chemical properties
Main article: Tungsten compounds
Elemental tungsten resists attack by oxygen, acids, and alkalis.[25]
The most common formal oxidation state of tungsten is +6, but it exhibits all oxidation states from −2 to +6.[25][26] Tungsten typically combines with oxygen to form the yellow tungstic oxide, WO3, which dissolves in aqueous alkaline solutions to form tungstate ions, WO2−
4Sony VPCEH2H1E battery.
Tungsten carbides (W2C and WC) are produced by heating powdered tungsten with carbon. W2C is resistant to chemical attack, although it reacts strongly with chlorine to form tungsten hexachloride (WCl6).[4]
In aqueous solution, tungstate gives the heteropoly acids and polyoxometalate anions under neutral and acidic conditions. As tungstate is progressively treated with acid, it first yields the soluble, metastable "paratungstate A" anion, W7O6–Sony VPCEH2F1E battery
24, which over time converts to the less soluble "paratungstate B" anion, H2W12O10–
42.[27] Further acidification produces the very soluble metatungstate anion, H2W12O6–
40, after which equilibrium is reached. The metatungstate ion exists as a symmetric cluster of twelve tungsten-oxygen octahedra known as the Keggin anion. Many other polyoxometalate anions exist as metastable speciesSony VPCEH2E0E battery. The inclusion of a different atom such as phosphorus in place of the two central hydrogens in metatungstate produces a wide variety of heteropoly acids, such as phosphotungstic acid H3PW12O40.
Tungsten trioxide can form intercalation compounds with alkali metals. These are known as bronzes; an example is sodium tungsten bronze.
Occurrence
Tungsten is found in the minerals wolframite (iron-manganese tungstate, (Fe,Mn)WO4), scheelite (calcium tungstate, (CaWO4), ferberite (FeWO4) and hübnerite (MnWO4). China produced 51,000 tonnes of tungsten concentrate in 2009Sony VPCEH2D0E battery, which was 83% of the world output. In the prelude to WWII China's production of tungsten played a role as China could use this leverage to demand material assistance from the US government.[28] Most of the remaining production originated from Russia (2,500 t), Canada (1,964 t), Bolivia (1,023 t), Austria (900 t), Portugal (900 t), Thailand (600 t), Brazil (500 t), Peru (500 t) and Rwanda (500 t). Sony VPCEH2C0E battery Tungsten is also considered to be a conflict mineral due to the unethical mining practices observed in the Democratic Republic of the Congo.[30][31]
[edit]Biological role
Tungsten, at atomic number 74, is the heaviest element known to be biologically functional, with the next heaviest being iodine (Z = 53). Although not in eukaryotes, tungsten is used by some bacteria. For example, enzymes called oxidoreductases use tungsten similarly to molybdenum by using it in a tungsten-pterin complex with molybdopterin (molybdopterinSony VPCEH29FJ/W battery, despite its name, does not contain molybdenum, but may complex with either molybdenum or tungsten in use by living organisms). Tungsten-using enzymes typically reduce carboxylic acids to aldehydes.[32] The tungsten oxidoreductases may also catalyse oxidations. The first tungsten-requiring enzyme to be discovered also requires selenium, and in this case the tungsten-selenium pair may function analogously to the molybdenum-sulfur pairing of some molybdenum cofactor-requiring enzymes. Sony VPCEH29FJ/P batteryOne of the enzymes in the oxidoreductase family which sometimes employ tungsten (bacterial formate dehydrogenase H) is known to use a selenium-molybdenum version of molybdopterin.[34] Although a tungsten-containing xanthine dehydrogenase from bacteria has been found to contain tungsten-molydopterin and also non-protein bound selenium, a tungsten-selenium molybdopterin complex has not been definitively described. Sony VPCEH29FJ/B battery
In soil, tungsten metal oxidizes to the tungstate anion. It can be selectively or non-selectively imported by some prokaryotic organisms and may substitute for molybdate in certain enzymes. Its effect on the action of these enzymes is in some cases inhibitory and in others positive.[36] The soil's chemistry determines how the tungsten polymerizes; alkaline soils cause monomeric tungstates; acidic soils cause polymeric tungstates. Sony VPCEH28FN/L battery
Sodium tungstate and lead have been studied for their effect on earthworms. Lead was found to be lethal at low levels and sodium tungstate was much less toxic, but the tungstate completely inhibited their reproductive ability.[38]
Tungsten has been studied as a biological copper metabolic antagonist, in a role similar to the action of molybdenum. It has been found that tetrathiotungstates may be used as biological copper chelation chemicals, similar to the tetrathiomolybdates.Sony VPCEH28FJ/W battery
[edit]Production
Wolframite
Tungsten output in 2005
About 61,300 tonnes of tungsten concentrates were produced in the year 2009.[29] Tungsten is extracted from its ores in several stages. The ore is eventually converted to tungsten(VI) oxide (WO3), which is heated with hydrogen or carbon to produce powdered tungsten.[9] Because of tungsten's high melting point, it is not commercially feasible to cast tungsten ingotsSony VPCEH28FJ/P battery. Instead, powdered tungsten is mixed with small amounts of powdered nickel or other metals, and sintered. During the sintering process, the nickel diffuses into the tungsten, producing an alloy.
Tungsten can also be extracted by hydrogen reduction of WF6:
WF6 + 3 H2 → W + 6 HF
or pyrolytic decomposition:[40]
WF6 → W + 3 F2 (ΔHr = +)
Tungsten is not traded as a futures contract and cannot be tracked on exchanges like the London Metal Exchange. The price for pure metal is around $20,075 per tonne as of October 2008. Sony VPCEH28FJ/B battery
Applications
Close-up of a tungsten filament inside a halogen lamp
Tungsten carbide ring (jewelry)
Approximately half of the tungsten is consumed for the production of hard materials — namely tungsten carbide — with the remaining major use being in alloys and steels. Less than 10% is used in other chemical compounds.[42]
[edit]Hard materials
Tungsten is mainly used in the production of hard materials based on tungsten carbide, one of the hardest carbides, with a melting point of 2770 °CSony VPCEH28FH/B battery. WC is an efficient electrical conductor, but W2C is less so. WC is used to make wear-resistant abrasives and cutters and knives for drills, circular saws, milling and turning tools used by the metalworking, woodworking, mining, petroleum and construction industries[4] and accounts for about 60% of current tungsten consumption. Sony VPCEH28FG/P battery
The jewelry industry makes rings of sintered tungsten carbide, tungsten carbide/metal composites, and also metallic tungsten. Sometimes manufacturers or retailers refer to tungsten carbide as a metal, but it is a ceramic.[44] Because of tungsten carbide's hardness, rings made of this material are extremely abrasion resistant, and will hold a burnished finish much longer than rings made of metallic tungstenSony VPCEH28FG/B battery. Tungsten carbide rings are brittle, however, and may crack under a sharp blow.[45]
[edit]Alloys
The hardness and density of tungsten are applied in obtaining heavy metal alloys. A good example is high speed steel, which can contain as much as 18% tungsten.[46] Tungsten's high melting point makes tungsten a good material for applications like rocket nozzles, for example in the UGM-27 Polaris submarine-launched ballistic missile. Sony VPCEH28FF/B battery Superalloys containing tungsten, such as Hastelloy and Stellite, are used in turbine blades and wear-resistant parts and coatings.
[edit]Armaments
Tungsten, usually alloyed with nickel and iron or cobalt to form heavy alloys, is used in kinetic energy penetrators as an alternative to depleted uranium, in applications where uranium's additional pyrophoric properties are not required (for example, in ordinary small arms bullets designed to penetrate body armor) Sony VPCEH28FA/B battery. Similarly, tungsten alloys have also been used in cannon shells, grenades and missiles, to create supersonic shrapnel. Tungsten has also been used in Dense Inert Metal Explosives, which use it as dense powder to reduce collateral damage while increasing the lethality of explosives within a small radius.[48]
[edit]Chemical applications
Tungsten(IV) sulfide is a high temperature lubricant and is a component of catalysts for hydrodesulfurization.[49] MoS2 is more commonly used for such applicationsSony VPCEH27FG/W battery.[50]
Tungsten oxides are used in ceramic glazes and calcium/magnesium tungstates are used widely in fluorescent lighting. Crystal tungstates are used as scintillation detectors in nuclear physics and nuclear medicine. Other salts that contain tungsten are used in the chemical and tanning industries. Sony VPCEH26FJ/W battery
Tungsten oxide (WO3) is incorporated into selective catalytic reduction (SCR) catalysts found in coal-fired power plants. These catalysts convert nitrogen oxides (NOx) to nitrogen (N2) and water (H2O) using ammonia (NH3). The tungsten oxide helps with the physical strength of the catalyst and extends catalyst life. Sony VPCEH26EN/B battery
[edit]Niche uses
Applications requiring its high density include weights, counterweights, ballast keels for yachts, tail ballast for commercial aircraft, and as ballast in race cars for NASCAR and Formula One; depleted uranium is also used for these purposes, due to similarly high density. It is an ideal material to use as a dolly for rivetingSony VPCEH26EH/P battery, where the mass necessary for good results can be achieved in a compact bar. High-density alloys of tungsten with nickel, copper or iron are used in high-quality darts[52] (to allow for a smaller diameter and thus tighter groupings) or for fishing lures (tungsten beads allow the fly to sink rapidly). Some types of strings for musical instruments are wound with tungsten wiresSony VPCEH26EG/P battery.
[edit]Gold substitution
Its density, similar to that of gold, allows tungsten to be used in jewelry as an alternative to gold or platinum.[6][53] Metallic tungsten is harder than gold alloys (though not as hard as tungsten carbide), and is hypoallergenic, making it useful for rings that will resist scratching, especially in designs with a brushed finishSony VPCEH26EF/B battery.
Because the density is so similar to gold (tungsten is only 0.36% less dense), tungsten can also be used in counterfeiting of gold bars, such as by plating a tungsten bar with gold, which has been observed since the 1980s,[57] or taking an existing gold bar, drilling holes, and replacing the removed gold with tungsten rods.[58] The densities are not exactly the same, and other properties of gold and tungsten differ, but gold-plated tungsten will pass superficial tests. Sony VPCEH26EA/W battery
Gold-plated tungsten is available commercially from China (the main source of tungsten), both in jewelry and as bars.[59]
[edit]Electronics
Because it retains its strength at high temperatures and has a high melting point, elemental tungsten is used in many high-temperature applications,[60] such as light bulb, cathode-ray tube, and vacuum tube filaments, heating elements, and rocket engine nozzles. Sony VPCEH25EN/W battery Its high melting point also makes tungsten suitable for aerospace and high-temperature uses such as electrical, heating, and welding applications, notably in the gas tungsten arc welding process (also called tungsten inert gas (TIG) welding).
Because of its conductive properties and relative chemical inertness, tungsten is also used in electrodes, and in the emitter tips in electron-beam instruments that use field emission guns, such as electron microscopesSony VPCEH25EG/B battery. In electronics, tungsten is used as an interconnect material in integrated circuits, between the silicon dioxide dielectric material and the transistors. It is used in metallic films, which replace the wiring used in conventional electronics with a coat of tungsten (or molybdenum) on silicon.[40]
The electronic structure of tungsten makes it one of the main sources for X-ray targets,[61][62] and also for shielding from high-energy radiations (such as in the radiopharmaceutical industry for shielding radioactive samples of FDG) Sony VPCEH24FX/W battery. Tungsten powder is used as a filler material in plastic composites, which are used as a nontoxic substitute for lead in bullets, shot, and radiation shields. Since this element's thermal expansion is similar to borosilicate glass, it is used for making glass-to-metal seals.[14]
Precautions
Because tungsten is rare and its compounds are generally inert, the effects of tungsten on the environment are limited. The median lethal dose LD50 depends strongly on the animal and the method of administration and varies between 59 mg/kg (intravenous, rabbit) and 5000 mg/kg (tungsten metal powder, intraperitoneal, ratsSony VPCEH24FX/P battery).
Patent claim
Tungsten is unique amongst the elements in that it has been the subject of legal proceedings. In 1928, a US court rejected General Electric's attempt to patent it, overturning U.S. Patent 1,082,933 granted in 1913 to William D. Coolidge.
Platinum ( /ˈplætɨnəm/ or /ˈplætənəm/) is a chemical element with the chemical symbol Pt and an atomic number of 78.
Its name is derived from the Spanish term platina, which is literally translated into "little silver".[1][2] It is a dense, malleable, ductile, precious, gray-white transition metalSony VPCEH24FX/L battery.
Even though it has six naturally occurring isotopes, platinum is one of the rarest elements in the Earth's crust and has an average abundance of approximately 5 μg/kg. It is the least reactive metal. It occurs in some nickel and copper ores along with some native deposits, mostly in South Africa, which accounts for 80% of the world productionSony VPCEH24FX/B battery.
As a member of the platinum group of elements, as well as of the group 10 of the periodic table of elements, platinum is generally non-reactive. It exhibits a remarkable resistance to corrosion, even at high temperatures, and as such is considered a noble metal. As a result, platinum is often found chemically uncombined as native platinumSony VPCEH1Z1E battery. Because it occurs naturally in the alluvial sands of various rivers, it was first used by pre-Columbian South American natives to produce artifacts. It was referenced in European writings as early as 16th century, but it was not until Antonio de Ulloa published a report on a new metal of Colombian origin in 1748 that it became investigated by scientistsSony VPCEH1S9E battery.
Platinum is used in catalytic converters, laboratory equipment, electrical contacts and electrodes, platinum resistance thermometers, dentistry equipment, and jewelry. Because only a few hundred tonnes are produced annually, it is a scarce material, and is highly valuable and is a major precious metal commodity. Being a heavy metal, it leads to health issues upon exposure to its salts, but due to its corrosion resistance, it is not as toxic as some metals. Sony VPCEH1S8E battery Its compounds, most notably cisplatin, are applied in chemotherapy against certain types of cancer.[4]
Characteristics
Physical
As a pure metal, platinum is silvery-white, lustrous, ductile, and malleable.[5] Platinum is more ductile than gold, silver and copper, thus being the most ductile of pure metals, but gold is still more malleable than platinum [6][7] It does not oxidize at any temperature, although it is corroded by halogens, cyanides, sulfur, and caustic alkalis. Platinum is insoluble in hydrochloric and nitric acid, but dissolves in hot aqua regia to form chloroplatinic acid, H2PtCl6. Sony VPCEH1S1E battery
Platinum's resistance to wear and tarnish is well suited for making fine jewelry. The metal has an excellent resistance to corrosion and high temperature and has stable electrical properties. All of these characteristics have been used for industrial applications.[9]
Chemical
See also: Platinum group
Platinum dissolves in hot aqua regia
The most common oxidation states of platinum are +2 and +4. The +1 and +3 oxidation states are less common, and are often stabilized by metal bonding in bimetallic (or polymetallic) speciesSony VPCEH1S0E battery. As is expected, tetracoordinate platinum(II) compounds tend to adopt 16-electron square planar geometries. While elemental platinum is generally unreactive, it dissolves in hot aqua regia to give soluble hexachloroplatinic acid ("H2PtCl6", formally (H3O)2PtCl6·nH2O ):[10]
Pt + 4 HNO3 + 6 HCl → H2PtCl6 + 4 NO2 + 4 H2O
As a soft acid, platinum has a great affinity for sulfur, such as on dimethyl sulfoxide (DMSO); numerous DMSO complexes have been reported and care should be taken in the choice of reaction solvent. Sony VPCEH1M9E battery
Isotopes
Main article: Isotopes of platinum
Platinum has six naturally occurring isotopes: 190Pt, 192Pt, 194Pt, 195Pt, 196Pt, and 198Pt. The most abundant of these is 195Pt, comprising 33.83% of all platinum. It is the only stable isotope with a non-zero spin; with a spin of 1/2, 195Pt satellite peaks are often observed in 1H and 31P NMR spectroscopy (i.e. Pt-phosphine and Pt-alkyl complexes) Sony VPCEH1M1E battery. 190Pt is the least abundant at only 0.01%. Of the naturally occurring isotopes, only 190Pt is unstable, though it decays with a half-life of 6.5×1011 years. 198Pt can undergo alpha decay, but its decay had never been observed (the half-life is known to be longer than 3.2×1014 years), therefore it is considered stable. Platinum also has 31 synthetic isotopes ranging in atomic mass from 166 to 202, making the total number of known isotopes 37Sony VPCEH1L9E battery. The least stable of these is 166Pt with a half-life of 300 µs, while the most stable is 193Pt with a half-life of 50 years. Most platinum isotopes decay by some combination of beta decay and alpha decay. 188Pt, 191Pt, and 193Pt decay primarily by electron capture. 190Pt and 198Pt have double beta decay paths. Sony VPCEH1L8E battery
Occurrence
A native platinum nugget, Kondyor mine, Khabarovsk Krai
Platinum output in 2005
Platinum is an extremely rare metal,[13] occurring at a concentration of only 0.005 ppm in the Earth's crust. It is sometimes mistaken for silver (Ag). Platinum is often found chemically uncombined as native platinum and alloyed with iridium as platiniridium. Most often the native platinum is found in secondary deposits; platinum is combined with the other platinum group metals in alluvial depositsSony VPCEH1L0E battery. The alluvial deposits used by pre-Columbian people in the Chocó Department, Colombia are still a source for platinum group metals. Another large alluvial deposit is in the Ural Mountains, Russia, and it is still mined.[8]
In nickel and copper deposits, platinum group metals occur as sulfides (e.g., (Pt,Pd)S), tellurides (e.g., PtBiTe), antimonides (PdSb), and arsenides (e.g., PtAs2), and as end alloys with nickel or copper. Platinum arsenide, sperrylite (PtAs2) Sony VPCEH1J8E battery, is a major source of platinum associated with nickel ores in the Sudbury Basin deposit in Ontario, Canada. At Platinum, Alaska, about 545,000 troy ounces had been mined between 1927 and 1975. The mine ceased operations in 1990.[16] The rare sulfide mineral cooperite, (Pt,Pd,Ni)S, contains platinum along with palladium and nickel. Cooperite occurs in the Merensky Reef within the Bushveld complex, Gauteng, South Africa. Sony VPCEH1J1E battery
In 1865, chromites were identified in the Bushveld region of South Africa, followed by the discovery of platinum in 1906.[18] The largest known primary reserves are in the Bushveld complex in South Africa.[19] The large copper–nickel deposits near Norilsk in Russia, and the Sudbury Basin, Canada, are the two other large depositsSony VPCEH1E1E battery. In the Sudbury Basin, the huge quantities of nickel ore processed make up for the fact platinum is present as only 0.5 ppm in the ore. Smaller reserves can be found in the United States,[19] for example in the Absaroka Range in Montana.[20] In 2009, South Africa was the top producer of platinum, with an almost 80% share, followed by Russia at 11%; world production in 2009 was 178,000 kg.Sony VPCEH1AJ battery
In 2010 July its been announced that Platinum is present in the state of Tamil Nadu, India[22] and a MOU has been signed between Geological Survey of India with TAMIN – Tamil Nadu Minerals Ltd.[23]
Platinum exists in higher abundances on the Moon and in meteorites. Correspondingly, platinum is found in slightly higher abundances at sites of bolide impact on the Earth that are associated with resulting post-impact volcanism, and can be mined economically; the Sudbury Basin is one such example. Sony VPCEH19FJ/W battery
Compounds
Halides
Hexachloroplatinic acid mentioned above is probably the most important platinum compound, as it serves as the precursor for many other platinum compounds. By itself, it has various applications in photography, zinc etchings, indelible ink, plating, mirrors, porcelain coloring, and as a catalyst. Sony VPCEH19FJ/P battery
Treatment of hexachloroplatinic acid with an ammonium salt, such as ammonium chloride, gives ammonium hexachloroplatinate,[10] which is relatively insoluble in ammonium solutions. Heating this ammonium salt in the presence of hydrogen reduces it to elemental platinum. Potassium hexachloroplatinate is similarly insoluble, and hexachloroplatinic acid has been used in the determination of potassium ions by gravimetry. Sony VPCEH19FJ/B battery
When hexachloroplatinic acid is heated, it decomposes through platinum(IV) chloride and platinum(II) chloride to elemental platinum, although the reactions do not occur stepwise:[27]
(H3O)2PtCl6·nH2O PtCl4 + 2 HCl + (n + 2) H2O
PtCl4 PtCl2 + Cl2
PtCl2 Pt + Cl2
All three reactions are reversible. Platinum(II) and platinum(IV) bromides are known as well. Platinum hexafluoride is a strong oxidizer capable of oxidizing oxygenSony VPCEH18FJ/W battery.
[edit]Oxides
Platinum(IV) oxide, PtO2, also known as Adams' catalyst, is a black powder which is soluble in KOH solutions and concentrated acids.[28] PtO2 and the less common PtO both decompose upon heating.[5] Platinum(II,IV) oxide, Pt3O4, is formed in the following reaction:
2 Pt2+ + Pt4+ + 4 O2− → Pt3O4
Platinum also forms a trioxide, where it is present in the +4 oxidation state.
[edit]Other compounds
Unlike palladium acetate, platinum(II) acetate is not commercially available. Where a base is desired, the halides have been used in conjunction with sodium acetate.[11] The use of platinum(II) acetylacetonate has also been reported. Sony VPCEH18FJ/P battery
Several barium platinides have been synthesized in which platinum exhibits negative oxidation states ranging from −1 to −2. These include BaPt, Ba3Pt2, and Ba2Pt.[30] Caesium platinide, Cs2Pt, a dark-red transparent crystalline compound[31] has been shown to contain Pt2−
anions.[32] Platinum also exhibits negative oxidation states at surfaces reduced electrochemically. Sony VPCEH18FJ/B batteryThe negative oxidation states exhibited by platinum are unusual for metallic elements, and they are attributed to the relativistic stabilization of the 6s orbitals.[32]
Zeise's salt, containing an ethylene ligand, was one of the first organometallic compounds discovered. Dichloro(cycloocta-1,5-diene)platinum(II) is a commercially available olefin complex, which contains easily displaceable cod ligands ("cod" being an abbreviation of 1,5-cyclooctadiene). The cod complex and the halides are convenient starting points to platinum chemistry.Sony VPCEH18FH/P battery
Cisplatin, or cis-diamminedichloroplatinum(II) is the first of a series of square planar platinum(II)-containing chemotherapy drugs, including carboplatin and oxaliplatin. These compounds are capable of crosslinking DNA, and kill cells by similar pathways to alkylating chemotherapeutic agents. Sony VPCEH18FG/L battery
The hexachloroplatinate ion
The anion of Zeise's salt
Dichloro(cycloocta-1,5-diene)platinum(II)
Cisplatin
History
Platinum occurs naturally in the alluvial sands of various rivers, though there is little evidence of its use by ancient people. However, the metal was used by pre-Columbian Americans near modern-day Esmeraldas, Ecuador to produce artifacts of a white gold-platinum alloy. The first European reference to platinum appears in 1557 in the writings of the Italian humanist Julius Caesar Scaliger as a description of an unknown noble metal found between Darién and MexicoSony VPCEH18FF/B battery, "which no fire nor any Spanish artifice has yet been able to liquefy."[35]
This alchemical symbol for platinum was made by joining the symbols of silver and gold.
Antonio de Ulloa is credited with the discovery of platinum.
In 1741, Charles Wood,[36] a British metallurgist, found various samples of Colombian platinum in Jamaica, which he sent to William Brownrigg for further investigation. Antonio de Ulloa, also credited with the discovery of platinum, returned to Spain from the French Geodesic Mission in 1746 after having been there for eight yearsSony VPCEH18FA/B battery. His historical account of the expedition included a description of platinum as being neither separable nor calcinable. Ulloa also anticipated the discovery of platinum mines. After publishing the report in 1748, Ulloa did not continue to investigate the new metal. In 1758, he was sent to superintend mercury mining operations in Huancavelica. Sony VPCEH17FJ/W battery
In 1750, after studying the platinum sent to him by Wood, Brownrigg presented a detailed account of the metal to the Royal Society, mentioning that he had seen no mention of it in any previous accounts of known minerals.[37] Brownrigg also made note of platinum's extremely high melting point and refractoriness toward borax. Other chemists across Europe soon began studying platinum, including Andreas Sigismund Marggraf[38] Torbern BergmanSony VPCEH17FG/W battery, Jöns Jakob Berzelius, William Lewis, and Pierre Macquer. In 1752, Henrik Scheffer published a detailed scientific description of the metal, which he referred to as "white gold", including an account of how he succeeded in fusing platinum ore with the aid of arsenic. Scheffer described platinum as being less pliable than gold, but with similar resistance to corrosion. Sony VPCEH17FG/P battery
Carl von Sickingen researched platinum extensively in 1772. He succeeded in making malleable platinum by alloying it with gold, dissolving the alloy in hot aqua regia, precipitating the platinum with ammonium chloride, igniting the ammonium chloroplatinate, and hammering the resulting finely divided platinum to make it cohere. Franz Karl Achard made the first platinum crucible in 1784Sony VPCEH17FG/L battery. He worked with the platinum by fusing it with arsenic, then later volatilizing the arsenic.[35]
Since the other platinum family members were not discovered yet (platinum was the first in the list), Scheffer and Sickingen made the false assumption that due to its hardness – which is slightly more than for pure iron – platinum was a relatively non pliable material, even brittle at times, when in fact its ductility and malleability are close to that of goldSony VPCEH17FG/B battery. Their assumptions could not be avoided since the platinum they experimented with was highly contaminated with minute amounts of the platinum family elements such as Osmium and Iridium amongst others, which embrittled the platinum alloy. Alloying this impure platinum residue called "plyoxen" with gold was the only solution at the time to obtain a pliable compound, but nowadaysSony VPCEH16EN/B battery, very pure platinum is available and extremely long wire can be drawn from pure platinum, very easily, due to its crystalline structure which is similar to that of many soft metals.[39]
In 1786, Charles III of Spain provided a library and laboratory to Pierre-François Chabaneau to aid in his research of platinum. Chabaneau succeeded in removing various impurities from the ore, including gold, mercury, lead, copper, and iron. This led him to believe he was working with a single metal, but in truth the ore still contained the yet-undiscovered platinum group metalsSony VPCEH16EH/W battery. This led to inconsistent results in his experiments. At times, the platinum seemed malleable, but when it was alloyed with iridium, it would be much more brittle. Sometimes the metal was entirely incombustible, but when alloyed with osmium, it would volatilize. After several months, Chabaneau succeeded in producing 23 kilograms of pure, malleable platinum by hammering and compressing the sponge form while white-hotSony VPCEH16EG/W battery. Chabeneau realized the infusibility of platinum would lend value to objects made of it, and so started a business with Joaquín Cabezas producing platinum ingots and utensils. This started what is known as the "platinum age" in Spain.[35]
In 2007, Gerhard Ertl won the Nobel Prize in Chemistry for determining the detailed molecular mechanisms of the catalytic oxidation of carbon monoxide over platinum (catalytic converter). Sony VPCEH16EF/B battery
Production
1,000 cubic centimeters of 99.9% pure platinum, worth about US$910,000 at 30 October 2009 prices
Platinum, along with the rest of the platinum metals, is obtained commercially as a by-product from nickel and copper mining and processing. During electrorefining of copper, noble metals such as silver, gold and the platinum group metals as well as selenium and tellurium settle to the bottom of the cell as "anode mud"Sony VPCEH16EA/P battery, which forms the starting point for the extraction of the platinum group metals.[41][42]
If pure platinum is found in placer deposits or other ores, it is isolated from them by various methods of subtracting impurities. Because platinum is significantly denser than many of its impurities, the lighter impurities can be removed by simply floating them away in a liquid. Platinum is also nonmagnetic, while nickel and iron are both magneticSony VPCEH15EN/W battery. These two impurities are thus removed by running an electromagnet over the mixture. Because platinum has a higher melting point than most other substances, many impurities can be burned or melted away without melting the platinum. Finally, platinum is resistant to hydrochloric and sulfuric acids, while other substances are readily attacked by them. Metal impurities can be removed by stirring the mixture in either of the two acids and recovering the remaining platinumSony VPCEH15EG/B battery.[43]
One suitable method for purification for the raw platinum, which contains platinum, gold, and the other platinum group metals, is to process it with aqua regia, in which palladium, gold and platinum are dissolved, while osmium, iridium, ruthenium and rhodium stay unreacted. The gold is precipitated by the addition of iron(III) chloride and after filtering off the goldSony VPCEH13FX/W battery, the platinum is precipitated as ammonium chloroplatinate by the addition of ammonium chloride. Ammonium chloroplatinate can be converted to the metal by heating.[44]
Applications
Cross section of a metal-core catalytic converter
Of the 239 tonnes of platinum sold in 2006, 130 tonnes were used for vehicle emissions control devices, 49 tonnes for jewelry, 13.3 tonnes in electronics, and 11.2 tonnes in the chemical industry as a catalyst. The remaining 35.5 tonnes went to various other minor applications, such as electrodes, anticancer drugs, oxygen sensors, spark plugs and turbine engines. Sony VPCEH13FX/P battery
[edit]Catalysis
The most common use of platinum is as a catalyst in chemical reactions, many times as platinum black. It has been employed in this application since the early 19th century, when platinum powder was used to catalyze the ignition of hydrogen. Its most important application is in automobiles as a catalytic converterSony VPCEH13FX/L battery, which allows the complete combustion of low concentrations of unburned hydrocarbons from the exhaust into carbon dioxide and water vapor. Platinum is also used in the petroleum industry as a catalyst in a number of separate processes, but especially in catalytic reforming of straight run naphthas into higher-octane gasoline which becomes rich in aromatic compoundsSony VPCEH13FX/B battery. PtO2, also known as Adams' catalyst, is used as a hydrogenation catalyst, specifically for vegetable oils.[25] Platinum metal also strongly catalyzes the decomposition of hydrogen peroxide into water and oxygen gas.[46]
Standard
International Prototype Meter bar
From 1889 to 1960, the meter was defined as the length of a platinum-iridium (90:10) alloy bar, known as the International Prototype Meter bar. The previous bar was made of platinum in 1799. The International Prototype Kilogram remains defined by a cylinder of the same platinum-iridium alloy made in 1879. Sony VPCCA3SFX/R battery
The standard hydrogen electrode also uses a platinized platinum electrode due to its corrosion resistance, and other attributes.[48]
Precious metal
Platinum Eagle
Main articles: Platinum as an investment and Platinum coin
Platinum is a precious metal commodity; its bullion has the ISO currency code of XPT. Coins, bars, and ingots are traded or collected. Platinum finds use in jewelry, usually as a 90–95% alloy, due to its inertness and shine. Jewelry trade publications advise jewelers to present minute surface scratches (which they term patina) as a desirable feature. Sony VPCCA3S1E battery
In watchmaking, Vacheron Constantin, Patek Philippe, Rolex, Breitling, and other companies use platinum for producing their limited edition watch series. Watchmakers appreciate the unique properties of platinum, as it neither tarnishes nor wears out (relative to gold).[51]
Average price of platinum from 1991 to 2007 in US$ per troy ounce (~$20/g)[52]
The price of platinum, like other industrial commodities, is more volatile than that of gold. In 2008, the price of platinum dropped from $2,252 to $774 per oz, Sony VPCCA3E1E battery a loss of nearly 2/3 of its value. By contrast, the price of gold dropped from ~$1,000 to ~$700/oz during the same time frame, a loss of only 1/3 of its value.
During periods of sustained economic stability and growth, the price of platinum tends to be as much as twice the price of gold, whereas during periods of economic uncertainty,[54] the price of platinum tends to decrease due to reduced industrial demand, falling below the price of gold. Gold prices are more stable in slow economic timesSony VPCCA38EC/R battery, as gold is considered a safe haven and gold demand is not driven by industrial uses. In the 18th century, platinum's rarity made King Louis XV of France declare it the only metal fit for a king.[55]
[edit]Other uses
In the laboratory, platinum wire is used for electrodes; platinum pans and supports are used in thermogravimetric analysis because of the stringent requirements of chemical inertness upon heating to high temperatures (~1000 °C) Sony VPCCA38EC battery. Platinum is used as an alloying agent for various metal products, including fine wires, noncorrosive laboratory containers, medical instruments, dental prostheses, electrical contacts, and thermocouples. Platinum-cobalt, an alloy of roughly three parts platinum and one part cobalt, is used to make relatively strong permanent magnets.[25] Platinum-based anodes are used in ships, pipelines, and steel piers. Sony VPCCA37EC/B battery
[edit]Symbol of prestige
See also: Platinum album and Platinum (color)
An assortment of native platinum nuggets
Platinum's rarity as a metal has caused advertisers to associate it with exclusivity and wealth. "Platinum" debit cards have greater privileges than do "gold" ones.[56] "Platinum awards" are the second highest possible, ranking above "gold", "silver" and "bronze", but below diamond. For example, in the United States, a musical album that has sold more than 1 million copiesSony VPCCA37EC battery, will be credited as "platinum", whereas an album that sold more than 10 million copies will be certified as "diamond".[57] Some products, such as blenders and vehicles, with a silvery-white color are identified as "platinum". Platinum is considered a precious metal, although its use is not as common as the use of gold or silver. The frame of the Crown of Queen Elizabeth the Queen MotherSony VPCCA36FW/W battery, manufactured for her coronation as Consort of King George VI, is made of platinum. It was the first British crown to be made of this particular metal.[58]
[edit]Health issues
According to the Centers for Disease Control and Prevention, short-term exposure to platinum salts may cause irritation of the eyes, nose, and throat, and long-term exposure may cause both respiratory and skin allergies. The current OSHA standard is 2 micrograms per cubic meter of air averaged over an 8-hour work shift. Sony VPCCA36FW/B battery
Certain platinum complexes are used in chemotherapy, and show good activity against some tumors. Cisplatin is particularly effective against testicular cancer; the cure rate was improved from 10% to 85%.[60] However, the side effects are severe. Cisplatin causes cumulative, irreversible kidney damage and deafness.[61] As with other ototoxic agents, deafness may be secondary to interactions with melanin in the stria vascularisSony VPCCA36FH/W battery. Binding of platinum to RNA has been reviewed.[62]
As platinum is a catalyst in the manufacture of the silicone rubber and gel components of several types of medical implants (breast implants, joint replacement prosthetics, artificial lumbar discs, vascular access ports, etc.), the possibility platinum could enter the body and cause adverse effects has merited studySony VPCCA36FG/B battery. The Food and Drug Administration and other institutions have reviewed the issue and found no evidence to suggest toxicity in vivo.
A hard, rare metal under standard conditions when uncombined, tungsten is found naturally on Earth only in chemical compounds. It was identified as a new element in 1781Sony VPCEH3T9E battery, and first isolated as a metal in 1783. Its important ores include wolframite and scheelite. The free element is remarkable for its robustness, especially the fact that it has the highest melting point of all the non-alloyed metals and the second highest of all the elements after carbon. Also remarkable is its high density of 19.3 times that of water, comparable to that of uranium and goldSony VPCEH3N6E battery, and much higher (about 1.7 times) than that of lead.[4] Tungsten with minor amounts of impurities is often brittle[5] and hard, making it difficult to work. However, very pure tungsten, though still hard, is more ductile, and can be cut with a hard-steel hacksaw.[6]
The unalloyed elemental form is used mainly in electrical applications. Tungsten's many alloys have numerous applications, most notably in incandescent light bulb filaments, X-ray tubes (as both the filament and target), and superalloysSony VPCEH3N1E battery. Tungsten's hardness and high density give it military applications in penetrating projectiles. Tungsten compounds are most often used industrially as catalysts.
Tungsten is the only metal from the third transition series that is known to occur in biomolecules, where it is used in a few species of bacteria. It is the heaviest element known to be used by any living organism. Tungsten interferes with molybdenum and copper metabolism, and is somewhat toxic to animal lifeSony VPCEH3D0E battery.
History
In 1781, Carl Wilhelm Scheele discovered that a new acid, tungstic acid, could be made from scheelite (at the time named tungsten). Scheele and Torbern Bergman suggested that it might be possible to obtain a new metal by reducing this acid.[9] In 1783, José and Fausto Elhuyar found an acid made from wolframite that was identical to tungstic acidSony VPCEH3B1E battery. Later that year, in Spain, the brothers succeeded in isolating tungsten by reduction of this acid with charcoal, and they are credited with the discovery of the element.[10][11]
In World War II, tungsten played a significant role in background political dealings. Portugal, as the main European source of the element, was put under pressure from both sides, because of its deposits of wolframite ore at PanasqueiraSony VPCEH2Z1E battery. Tungsten's resistance to high temperatures and its strengthening of alloys made it an important raw material for the arms industry.[12]
[edit]Etymology
The name "tungsten" (from the Nordic tung sten, meaning "heavy stone") is used in English, French, and many other languages as the name of the element. Tungsten was the old Swedish name for the mineral scheelite. The other name "wolfram" (or "volfram")Sony VPCEH2S9E battery, used for example in most European (especially Germanic and Slavic) languages, is derived from the mineral wolframite, and this is also the origin of its chemical symbol, W.[6] The name "wolframite" is derived from German "wolf rahm" ("wolf soot" or "wolf cream"), the name given to tungsten by Johan Gottschalk Wallerius in 1747. This, in turn, derives from "Lupi spuma", the name Georg Agricola used for the element in 1546Sony VPCEH2Q1E battery, which translates into English as "wolf's froth" or "cream" (the etymology is not entirely certain), and is a reference to the large amounts of tin consumed by the mineral during its extraction.[13]
Characteristics
Physical properties
In tungsten's raw form, it is a hard steel-gray metal that is often brittle and hard to work. If made very pure, tungsten retains its hardness (which exceeds that of many steels), and becomes malleable enough that it can be worked easily. Sony VPCEH2P0E battery It is worked by forging, drawing, extruding or sintering.
Of all metals in pure form, tungsten has the highest melting point (3,422 °C, 6,192 °F), lowest vapor pressure (at temperatures above 1,650 °C, 3,000 °F) and the highest tensile strength.[14] Tungsten has the lowest coefficient of thermal expansion of any pure metal. The low thermal expansion and high melting point and strength of tungsten originate from strong covalent bonds formed between tungsten atoms by the 5d electrons. Sony VPCEH2N1E battery Alloying small quantities of tungsten with steel greatly increases its toughness.[4]
Tungsten exists in two major crystalline forms: α and β. The former has a body-centered cubic structure and is the most stable form. The structure of the β phase is called A15 cubic; it is metastable, but can coexist with the α phase at ambient conditions owing to non-equilibrium synthesis or stabilization by impuritiesSony VPCEH2M9E battery. Contrary to the α phase which crystallizes in isometric grains, the β form exhibits a columnar habit. The α phase has a three times lower electrical resistivity[16] and a much lower superconducting transition temperature TC than the β phase: ca. 0.015 K vs. 1–4 K; mixing the two phases allows obtaining intermedicate TC values.[17][18] The TC value can also be raised by alloying tungsten with another metal (e.g. 7.9 K for W-Tc). Sony VPCEH2M1E batterySuch tungsten alloys are sometimes used in low-temperature superconducting circuits.[20][21][22]
[edit]Isotopes
Main article: Isotopes of tungsten
Naturally occurring tungsten consists of five isotopes whose half-lives are so long that they can be considered stable. Theoretically, all five can decay into isotopes of element 72 (hafnium) by alpha emission, but only 180W has been observed[23] to do so with a half-life of (1.8 ± 0.2)×1018 yearsSony VPCEH2L9E battery; on average, this yields about two alpha decays of 180W in one gram of natural tungsten per year.[24] The other naturally occurring isotopes have not been observed to decay, constraining their half-lives to be[24]
182W, T1/2 > 8.3×1018 years
183W, T1/2 > 2.9×1019 years
184W, T1/2 > 1.3×1019 years
186W, T1/2 > 2.7×1019 years
Another 30 artificial radioisotopes of tungsten have been characterized, the most stable of which are 181W with a half-life of 121.2 days, 185W with a half-life of 75.1 days, 188W with a half-life of 69.4 days, 178W with a half-life of 21.6 days, and 187W with a half-life of 23.72 h.[24] All of the remaining radioactive isotopes have half-lives of less than 3 hoursSony VPCEH2J1E battery, and most of these have half-lives below 8 minutes.[24] Tungsten also has 4 meta states, the most stable being 179mW (T½ 6.4 minutes).
[edit]Chemical properties
Main article: Tungsten compounds
Elemental tungsten resists attack by oxygen, acids, and alkalis.[25]
The most common formal oxidation state of tungsten is +6, but it exhibits all oxidation states from −2 to +6.[25][26] Tungsten typically combines with oxygen to form the yellow tungstic oxide, WO3, which dissolves in aqueous alkaline solutions to form tungstate ions, WO2−
4Sony VPCEH2H1E battery.
Tungsten carbides (W2C and WC) are produced by heating powdered tungsten with carbon. W2C is resistant to chemical attack, although it reacts strongly with chlorine to form tungsten hexachloride (WCl6).[4]
In aqueous solution, tungstate gives the heteropoly acids and polyoxometalate anions under neutral and acidic conditions. As tungstate is progressively treated with acid, it first yields the soluble, metastable "paratungstate A" anion, W7O6–Sony VPCEH2F1E battery
24, which over time converts to the less soluble "paratungstate B" anion, H2W12O10–
42.[27] Further acidification produces the very soluble metatungstate anion, H2W12O6–
40, after which equilibrium is reached. The metatungstate ion exists as a symmetric cluster of twelve tungsten-oxygen octahedra known as the Keggin anion. Many other polyoxometalate anions exist as metastable speciesSony VPCEH2E0E battery. The inclusion of a different atom such as phosphorus in place of the two central hydrogens in metatungstate produces a wide variety of heteropoly acids, such as phosphotungstic acid H3PW12O40.
Tungsten trioxide can form intercalation compounds with alkali metals. These are known as bronzes; an example is sodium tungsten bronze.
Occurrence
Tungsten is found in the minerals wolframite (iron-manganese tungstate, (Fe,Mn)WO4), scheelite (calcium tungstate, (CaWO4), ferberite (FeWO4) and hübnerite (MnWO4). China produced 51,000 tonnes of tungsten concentrate in 2009Sony VPCEH2D0E battery, which was 83% of the world output. In the prelude to WWII China's production of tungsten played a role as China could use this leverage to demand material assistance from the US government.[28] Most of the remaining production originated from Russia (2,500 t), Canada (1,964 t), Bolivia (1,023 t), Austria (900 t), Portugal (900 t), Thailand (600 t), Brazil (500 t), Peru (500 t) and Rwanda (500 t). Sony VPCEH2C0E battery Tungsten is also considered to be a conflict mineral due to the unethical mining practices observed in the Democratic Republic of the Congo.[30][31]
[edit]Biological role
Tungsten, at atomic number 74, is the heaviest element known to be biologically functional, with the next heaviest being iodine (Z = 53). Although not in eukaryotes, tungsten is used by some bacteria. For example, enzymes called oxidoreductases use tungsten similarly to molybdenum by using it in a tungsten-pterin complex with molybdopterin (molybdopterinSony VPCEH29FJ/W battery, despite its name, does not contain molybdenum, but may complex with either molybdenum or tungsten in use by living organisms). Tungsten-using enzymes typically reduce carboxylic acids to aldehydes.[32] The tungsten oxidoreductases may also catalyse oxidations. The first tungsten-requiring enzyme to be discovered also requires selenium, and in this case the tungsten-selenium pair may function analogously to the molybdenum-sulfur pairing of some molybdenum cofactor-requiring enzymes. Sony VPCEH29FJ/P batteryOne of the enzymes in the oxidoreductase family which sometimes employ tungsten (bacterial formate dehydrogenase H) is known to use a selenium-molybdenum version of molybdopterin.[34] Although a tungsten-containing xanthine dehydrogenase from bacteria has been found to contain tungsten-molydopterin and also non-protein bound selenium, a tungsten-selenium molybdopterin complex has not been definitively described. Sony VPCEH29FJ/B battery
In soil, tungsten metal oxidizes to the tungstate anion. It can be selectively or non-selectively imported by some prokaryotic organisms and may substitute for molybdate in certain enzymes. Its effect on the action of these enzymes is in some cases inhibitory and in others positive.[36] The soil's chemistry determines how the tungsten polymerizes; alkaline soils cause monomeric tungstates; acidic soils cause polymeric tungstates. Sony VPCEH28FN/L battery
Sodium tungstate and lead have been studied for their effect on earthworms. Lead was found to be lethal at low levels and sodium tungstate was much less toxic, but the tungstate completely inhibited their reproductive ability.[38]
Tungsten has been studied as a biological copper metabolic antagonist, in a role similar to the action of molybdenum. It has been found that tetrathiotungstates may be used as biological copper chelation chemicals, similar to the tetrathiomolybdates.Sony VPCEH28FJ/W battery
[edit]Production
Wolframite
Tungsten output in 2005
About 61,300 tonnes of tungsten concentrates were produced in the year 2009.[29] Tungsten is extracted from its ores in several stages. The ore is eventually converted to tungsten(VI) oxide (WO3), which is heated with hydrogen or carbon to produce powdered tungsten.[9] Because of tungsten's high melting point, it is not commercially feasible to cast tungsten ingotsSony VPCEH28FJ/P battery. Instead, powdered tungsten is mixed with small amounts of powdered nickel or other metals, and sintered. During the sintering process, the nickel diffuses into the tungsten, producing an alloy.
Tungsten can also be extracted by hydrogen reduction of WF6:
WF6 + 3 H2 → W + 6 HF
or pyrolytic decomposition:[40]
WF6 → W + 3 F2 (ΔHr = +)
Tungsten is not traded as a futures contract and cannot be tracked on exchanges like the London Metal Exchange. The price for pure metal is around $20,075 per tonne as of October 2008. Sony VPCEH28FJ/B battery
Applications
Close-up of a tungsten filament inside a halogen lamp
Tungsten carbide ring (jewelry)
Approximately half of the tungsten is consumed for the production of hard materials — namely tungsten carbide — with the remaining major use being in alloys and steels. Less than 10% is used in other chemical compounds.[42]
[edit]Hard materials
Tungsten is mainly used in the production of hard materials based on tungsten carbide, one of the hardest carbides, with a melting point of 2770 °CSony VPCEH28FH/B battery. WC is an efficient electrical conductor, but W2C is less so. WC is used to make wear-resistant abrasives and cutters and knives for drills, circular saws, milling and turning tools used by the metalworking, woodworking, mining, petroleum and construction industries[4] and accounts for about 60% of current tungsten consumption. Sony VPCEH28FG/P battery
The jewelry industry makes rings of sintered tungsten carbide, tungsten carbide/metal composites, and also metallic tungsten. Sometimes manufacturers or retailers refer to tungsten carbide as a metal, but it is a ceramic.[44] Because of tungsten carbide's hardness, rings made of this material are extremely abrasion resistant, and will hold a burnished finish much longer than rings made of metallic tungstenSony VPCEH28FG/B battery. Tungsten carbide rings are brittle, however, and may crack under a sharp blow.[45]
[edit]Alloys
The hardness and density of tungsten are applied in obtaining heavy metal alloys. A good example is high speed steel, which can contain as much as 18% tungsten.[46] Tungsten's high melting point makes tungsten a good material for applications like rocket nozzles, for example in the UGM-27 Polaris submarine-launched ballistic missile. Sony VPCEH28FF/B battery Superalloys containing tungsten, such as Hastelloy and Stellite, are used in turbine blades and wear-resistant parts and coatings.
[edit]Armaments
Tungsten, usually alloyed with nickel and iron or cobalt to form heavy alloys, is used in kinetic energy penetrators as an alternative to depleted uranium, in applications where uranium's additional pyrophoric properties are not required (for example, in ordinary small arms bullets designed to penetrate body armor) Sony VPCEH28FA/B battery. Similarly, tungsten alloys have also been used in cannon shells, grenades and missiles, to create supersonic shrapnel. Tungsten has also been used in Dense Inert Metal Explosives, which use it as dense powder to reduce collateral damage while increasing the lethality of explosives within a small radius.[48]
[edit]Chemical applications
Tungsten(IV) sulfide is a high temperature lubricant and is a component of catalysts for hydrodesulfurization.[49] MoS2 is more commonly used for such applicationsSony VPCEH27FG/W battery.[50]
Tungsten oxides are used in ceramic glazes and calcium/magnesium tungstates are used widely in fluorescent lighting. Crystal tungstates are used as scintillation detectors in nuclear physics and nuclear medicine. Other salts that contain tungsten are used in the chemical and tanning industries. Sony VPCEH26FJ/W battery
Tungsten oxide (WO3) is incorporated into selective catalytic reduction (SCR) catalysts found in coal-fired power plants. These catalysts convert nitrogen oxides (NOx) to nitrogen (N2) and water (H2O) using ammonia (NH3). The tungsten oxide helps with the physical strength of the catalyst and extends catalyst life. Sony VPCEH26EN/B battery
[edit]Niche uses
Applications requiring its high density include weights, counterweights, ballast keels for yachts, tail ballast for commercial aircraft, and as ballast in race cars for NASCAR and Formula One; depleted uranium is also used for these purposes, due to similarly high density. It is an ideal material to use as a dolly for rivetingSony VPCEH26EH/P battery, where the mass necessary for good results can be achieved in a compact bar. High-density alloys of tungsten with nickel, copper or iron are used in high-quality darts[52] (to allow for a smaller diameter and thus tighter groupings) or for fishing lures (tungsten beads allow the fly to sink rapidly). Some types of strings for musical instruments are wound with tungsten wiresSony VPCEH26EG/P battery.
[edit]Gold substitution
Its density, similar to that of gold, allows tungsten to be used in jewelry as an alternative to gold or platinum.[6][53] Metallic tungsten is harder than gold alloys (though not as hard as tungsten carbide), and is hypoallergenic, making it useful for rings that will resist scratching, especially in designs with a brushed finishSony VPCEH26EF/B battery.
Because the density is so similar to gold (tungsten is only 0.36% less dense), tungsten can also be used in counterfeiting of gold bars, such as by plating a tungsten bar with gold, which has been observed since the 1980s,[57] or taking an existing gold bar, drilling holes, and replacing the removed gold with tungsten rods.[58] The densities are not exactly the same, and other properties of gold and tungsten differ, but gold-plated tungsten will pass superficial tests. Sony VPCEH26EA/W battery
Gold-plated tungsten is available commercially from China (the main source of tungsten), both in jewelry and as bars.[59]
[edit]Electronics
Because it retains its strength at high temperatures and has a high melting point, elemental tungsten is used in many high-temperature applications,[60] such as light bulb, cathode-ray tube, and vacuum tube filaments, heating elements, and rocket engine nozzles. Sony VPCEH25EN/W battery Its high melting point also makes tungsten suitable for aerospace and high-temperature uses such as electrical, heating, and welding applications, notably in the gas tungsten arc welding process (also called tungsten inert gas (TIG) welding).
Because of its conductive properties and relative chemical inertness, tungsten is also used in electrodes, and in the emitter tips in electron-beam instruments that use field emission guns, such as electron microscopesSony VPCEH25EG/B battery. In electronics, tungsten is used as an interconnect material in integrated circuits, between the silicon dioxide dielectric material and the transistors. It is used in metallic films, which replace the wiring used in conventional electronics with a coat of tungsten (or molybdenum) on silicon.[40]
The electronic structure of tungsten makes it one of the main sources for X-ray targets,[61][62] and also for shielding from high-energy radiations (such as in the radiopharmaceutical industry for shielding radioactive samples of FDG) Sony VPCEH24FX/W battery. Tungsten powder is used as a filler material in plastic composites, which are used as a nontoxic substitute for lead in bullets, shot, and radiation shields. Since this element's thermal expansion is similar to borosilicate glass, it is used for making glass-to-metal seals.[14]
Precautions
Because tungsten is rare and its compounds are generally inert, the effects of tungsten on the environment are limited. The median lethal dose LD50 depends strongly on the animal and the method of administration and varies between 59 mg/kg (intravenous, rabbit) and 5000 mg/kg (tungsten metal powder, intraperitoneal, ratsSony VPCEH24FX/P battery).
Patent claim
Tungsten is unique amongst the elements in that it has been the subject of legal proceedings. In 1928, a US court rejected General Electric's attempt to patent it, overturning U.S. Patent 1,082,933 granted in 1913 to William D. Coolidge.
Platinum ( /ˈplætɨnəm/ or /ˈplætənəm/) is a chemical element with the chemical symbol Pt and an atomic number of 78.
Its name is derived from the Spanish term platina, which is literally translated into "little silver".[1][2] It is a dense, malleable, ductile, precious, gray-white transition metalSony VPCEH24FX/L battery.
Even though it has six naturally occurring isotopes, platinum is one of the rarest elements in the Earth's crust and has an average abundance of approximately 5 μg/kg. It is the least reactive metal. It occurs in some nickel and copper ores along with some native deposits, mostly in South Africa, which accounts for 80% of the world productionSony VPCEH24FX/B battery.
As a member of the platinum group of elements, as well as of the group 10 of the periodic table of elements, platinum is generally non-reactive. It exhibits a remarkable resistance to corrosion, even at high temperatures, and as such is considered a noble metal. As a result, platinum is often found chemically uncombined as native platinumSony VPCEH1Z1E battery. Because it occurs naturally in the alluvial sands of various rivers, it was first used by pre-Columbian South American natives to produce artifacts. It was referenced in European writings as early as 16th century, but it was not until Antonio de Ulloa published a report on a new metal of Colombian origin in 1748 that it became investigated by scientistsSony VPCEH1S9E battery.
Platinum is used in catalytic converters, laboratory equipment, electrical contacts and electrodes, platinum resistance thermometers, dentistry equipment, and jewelry. Because only a few hundred tonnes are produced annually, it is a scarce material, and is highly valuable and is a major precious metal commodity. Being a heavy metal, it leads to health issues upon exposure to its salts, but due to its corrosion resistance, it is not as toxic as some metals. Sony VPCEH1S8E battery Its compounds, most notably cisplatin, are applied in chemotherapy against certain types of cancer.[4]
Characteristics
Physical
As a pure metal, platinum is silvery-white, lustrous, ductile, and malleable.[5] Platinum is more ductile than gold, silver and copper, thus being the most ductile of pure metals, but gold is still more malleable than platinum [6][7] It does not oxidize at any temperature, although it is corroded by halogens, cyanides, sulfur, and caustic alkalis. Platinum is insoluble in hydrochloric and nitric acid, but dissolves in hot aqua regia to form chloroplatinic acid, H2PtCl6. Sony VPCEH1S1E battery
Platinum's resistance to wear and tarnish is well suited for making fine jewelry. The metal has an excellent resistance to corrosion and high temperature and has stable electrical properties. All of these characteristics have been used for industrial applications.[9]
Chemical
See also: Platinum group
Platinum dissolves in hot aqua regia
The most common oxidation states of platinum are +2 and +4. The +1 and +3 oxidation states are less common, and are often stabilized by metal bonding in bimetallic (or polymetallic) speciesSony VPCEH1S0E battery. As is expected, tetracoordinate platinum(II) compounds tend to adopt 16-electron square planar geometries. While elemental platinum is generally unreactive, it dissolves in hot aqua regia to give soluble hexachloroplatinic acid ("H2PtCl6", formally (H3O)2PtCl6·nH2O ):[10]
Pt + 4 HNO3 + 6 HCl → H2PtCl6 + 4 NO2 + 4 H2O
As a soft acid, platinum has a great affinity for sulfur, such as on dimethyl sulfoxide (DMSO); numerous DMSO complexes have been reported and care should be taken in the choice of reaction solvent. Sony VPCEH1M9E battery
Isotopes
Main article: Isotopes of platinum
Platinum has six naturally occurring isotopes: 190Pt, 192Pt, 194Pt, 195Pt, 196Pt, and 198Pt. The most abundant of these is 195Pt, comprising 33.83% of all platinum. It is the only stable isotope with a non-zero spin; with a spin of 1/2, 195Pt satellite peaks are often observed in 1H and 31P NMR spectroscopy (i.e. Pt-phosphine and Pt-alkyl complexes) Sony VPCEH1M1E battery. 190Pt is the least abundant at only 0.01%. Of the naturally occurring isotopes, only 190Pt is unstable, though it decays with a half-life of 6.5×1011 years. 198Pt can undergo alpha decay, but its decay had never been observed (the half-life is known to be longer than 3.2×1014 years), therefore it is considered stable. Platinum also has 31 synthetic isotopes ranging in atomic mass from 166 to 202, making the total number of known isotopes 37Sony VPCEH1L9E battery. The least stable of these is 166Pt with a half-life of 300 µs, while the most stable is 193Pt with a half-life of 50 years. Most platinum isotopes decay by some combination of beta decay and alpha decay. 188Pt, 191Pt, and 193Pt decay primarily by electron capture. 190Pt and 198Pt have double beta decay paths. Sony VPCEH1L8E battery
Occurrence
A native platinum nugget, Kondyor mine, Khabarovsk Krai
Platinum output in 2005
Platinum is an extremely rare metal,[13] occurring at a concentration of only 0.005 ppm in the Earth's crust. It is sometimes mistaken for silver (Ag). Platinum is often found chemically uncombined as native platinum and alloyed with iridium as platiniridium. Most often the native platinum is found in secondary deposits; platinum is combined with the other platinum group metals in alluvial depositsSony VPCEH1L0E battery. The alluvial deposits used by pre-Columbian people in the Chocó Department, Colombia are still a source for platinum group metals. Another large alluvial deposit is in the Ural Mountains, Russia, and it is still mined.[8]
In nickel and copper deposits, platinum group metals occur as sulfides (e.g., (Pt,Pd)S), tellurides (e.g., PtBiTe), antimonides (PdSb), and arsenides (e.g., PtAs2), and as end alloys with nickel or copper. Platinum arsenide, sperrylite (PtAs2) Sony VPCEH1J8E battery, is a major source of platinum associated with nickel ores in the Sudbury Basin deposit in Ontario, Canada. At Platinum, Alaska, about 545,000 troy ounces had been mined between 1927 and 1975. The mine ceased operations in 1990.[16] The rare sulfide mineral cooperite, (Pt,Pd,Ni)S, contains platinum along with palladium and nickel. Cooperite occurs in the Merensky Reef within the Bushveld complex, Gauteng, South Africa. Sony VPCEH1J1E battery
In 1865, chromites were identified in the Bushveld region of South Africa, followed by the discovery of platinum in 1906.[18] The largest known primary reserves are in the Bushveld complex in South Africa.[19] The large copper–nickel deposits near Norilsk in Russia, and the Sudbury Basin, Canada, are the two other large depositsSony VPCEH1E1E battery. In the Sudbury Basin, the huge quantities of nickel ore processed make up for the fact platinum is present as only 0.5 ppm in the ore. Smaller reserves can be found in the United States,[19] for example in the Absaroka Range in Montana.[20] In 2009, South Africa was the top producer of platinum, with an almost 80% share, followed by Russia at 11%; world production in 2009 was 178,000 kg.Sony VPCEH1AJ battery
In 2010 July its been announced that Platinum is present in the state of Tamil Nadu, India[22] and a MOU has been signed between Geological Survey of India with TAMIN – Tamil Nadu Minerals Ltd.[23]
Platinum exists in higher abundances on the Moon and in meteorites. Correspondingly, platinum is found in slightly higher abundances at sites of bolide impact on the Earth that are associated with resulting post-impact volcanism, and can be mined economically; the Sudbury Basin is one such example. Sony VPCEH19FJ/W battery
Compounds
Halides
Hexachloroplatinic acid mentioned above is probably the most important platinum compound, as it serves as the precursor for many other platinum compounds. By itself, it has various applications in photography, zinc etchings, indelible ink, plating, mirrors, porcelain coloring, and as a catalyst. Sony VPCEH19FJ/P battery
Treatment of hexachloroplatinic acid with an ammonium salt, such as ammonium chloride, gives ammonium hexachloroplatinate,[10] which is relatively insoluble in ammonium solutions. Heating this ammonium salt in the presence of hydrogen reduces it to elemental platinum. Potassium hexachloroplatinate is similarly insoluble, and hexachloroplatinic acid has been used in the determination of potassium ions by gravimetry. Sony VPCEH19FJ/B battery
When hexachloroplatinic acid is heated, it decomposes through platinum(IV) chloride and platinum(II) chloride to elemental platinum, although the reactions do not occur stepwise:[27]
(H3O)2PtCl6·nH2O PtCl4 + 2 HCl + (n + 2) H2O
PtCl4 PtCl2 + Cl2
PtCl2 Pt + Cl2
All three reactions are reversible. Platinum(II) and platinum(IV) bromides are known as well. Platinum hexafluoride is a strong oxidizer capable of oxidizing oxygenSony VPCEH18FJ/W battery.
[edit]Oxides
Platinum(IV) oxide, PtO2, also known as Adams' catalyst, is a black powder which is soluble in KOH solutions and concentrated acids.[28] PtO2 and the less common PtO both decompose upon heating.[5] Platinum(II,IV) oxide, Pt3O4, is formed in the following reaction:
2 Pt2+ + Pt4+ + 4 O2− → Pt3O4
Platinum also forms a trioxide, where it is present in the +4 oxidation state.
[edit]Other compounds
Unlike palladium acetate, platinum(II) acetate is not commercially available. Where a base is desired, the halides have been used in conjunction with sodium acetate.[11] The use of platinum(II) acetylacetonate has also been reported. Sony VPCEH18FJ/P battery
Several barium platinides have been synthesized in which platinum exhibits negative oxidation states ranging from −1 to −2. These include BaPt, Ba3Pt2, and Ba2Pt.[30] Caesium platinide, Cs2Pt, a dark-red transparent crystalline compound[31] has been shown to contain Pt2−
anions.[32] Platinum also exhibits negative oxidation states at surfaces reduced electrochemically. Sony VPCEH18FJ/B batteryThe negative oxidation states exhibited by platinum are unusual for metallic elements, and they are attributed to the relativistic stabilization of the 6s orbitals.[32]
Zeise's salt, containing an ethylene ligand, was one of the first organometallic compounds discovered. Dichloro(cycloocta-1,5-diene)platinum(II) is a commercially available olefin complex, which contains easily displaceable cod ligands ("cod" being an abbreviation of 1,5-cyclooctadiene). The cod complex and the halides are convenient starting points to platinum chemistry.Sony VPCEH18FH/P battery
Cisplatin, or cis-diamminedichloroplatinum(II) is the first of a series of square planar platinum(II)-containing chemotherapy drugs, including carboplatin and oxaliplatin. These compounds are capable of crosslinking DNA, and kill cells by similar pathways to alkylating chemotherapeutic agents. Sony VPCEH18FG/L battery
The hexachloroplatinate ion
The anion of Zeise's salt
Dichloro(cycloocta-1,5-diene)platinum(II)
Cisplatin
History
Platinum occurs naturally in the alluvial sands of various rivers, though there is little evidence of its use by ancient people. However, the metal was used by pre-Columbian Americans near modern-day Esmeraldas, Ecuador to produce artifacts of a white gold-platinum alloy. The first European reference to platinum appears in 1557 in the writings of the Italian humanist Julius Caesar Scaliger as a description of an unknown noble metal found between Darién and MexicoSony VPCEH18FF/B battery, "which no fire nor any Spanish artifice has yet been able to liquefy."[35]
This alchemical symbol for platinum was made by joining the symbols of silver and gold.
Antonio de Ulloa is credited with the discovery of platinum.
In 1741, Charles Wood,[36] a British metallurgist, found various samples of Colombian platinum in Jamaica, which he sent to William Brownrigg for further investigation. Antonio de Ulloa, also credited with the discovery of platinum, returned to Spain from the French Geodesic Mission in 1746 after having been there for eight yearsSony VPCEH18FA/B battery. His historical account of the expedition included a description of platinum as being neither separable nor calcinable. Ulloa also anticipated the discovery of platinum mines. After publishing the report in 1748, Ulloa did not continue to investigate the new metal. In 1758, he was sent to superintend mercury mining operations in Huancavelica. Sony VPCEH17FJ/W battery
In 1750, after studying the platinum sent to him by Wood, Brownrigg presented a detailed account of the metal to the Royal Society, mentioning that he had seen no mention of it in any previous accounts of known minerals.[37] Brownrigg also made note of platinum's extremely high melting point and refractoriness toward borax. Other chemists across Europe soon began studying platinum, including Andreas Sigismund Marggraf[38] Torbern BergmanSony VPCEH17FG/W battery, Jöns Jakob Berzelius, William Lewis, and Pierre Macquer. In 1752, Henrik Scheffer published a detailed scientific description of the metal, which he referred to as "white gold", including an account of how he succeeded in fusing platinum ore with the aid of arsenic. Scheffer described platinum as being less pliable than gold, but with similar resistance to corrosion. Sony VPCEH17FG/P battery
Carl von Sickingen researched platinum extensively in 1772. He succeeded in making malleable platinum by alloying it with gold, dissolving the alloy in hot aqua regia, precipitating the platinum with ammonium chloride, igniting the ammonium chloroplatinate, and hammering the resulting finely divided platinum to make it cohere. Franz Karl Achard made the first platinum crucible in 1784Sony VPCEH17FG/L battery. He worked with the platinum by fusing it with arsenic, then later volatilizing the arsenic.[35]
Since the other platinum family members were not discovered yet (platinum was the first in the list), Scheffer and Sickingen made the false assumption that due to its hardness – which is slightly more than for pure iron – platinum was a relatively non pliable material, even brittle at times, when in fact its ductility and malleability are close to that of goldSony VPCEH17FG/B battery. Their assumptions could not be avoided since the platinum they experimented with was highly contaminated with minute amounts of the platinum family elements such as Osmium and Iridium amongst others, which embrittled the platinum alloy. Alloying this impure platinum residue called "plyoxen" with gold was the only solution at the time to obtain a pliable compound, but nowadaysSony VPCEH16EN/B battery, very pure platinum is available and extremely long wire can be drawn from pure platinum, very easily, due to its crystalline structure which is similar to that of many soft metals.[39]
In 1786, Charles III of Spain provided a library and laboratory to Pierre-François Chabaneau to aid in his research of platinum. Chabaneau succeeded in removing various impurities from the ore, including gold, mercury, lead, copper, and iron. This led him to believe he was working with a single metal, but in truth the ore still contained the yet-undiscovered platinum group metalsSony VPCEH16EH/W battery. This led to inconsistent results in his experiments. At times, the platinum seemed malleable, but when it was alloyed with iridium, it would be much more brittle. Sometimes the metal was entirely incombustible, but when alloyed with osmium, it would volatilize. After several months, Chabaneau succeeded in producing 23 kilograms of pure, malleable platinum by hammering and compressing the sponge form while white-hotSony VPCEH16EG/W battery. Chabeneau realized the infusibility of platinum would lend value to objects made of it, and so started a business with Joaquín Cabezas producing platinum ingots and utensils. This started what is known as the "platinum age" in Spain.[35]
In 2007, Gerhard Ertl won the Nobel Prize in Chemistry for determining the detailed molecular mechanisms of the catalytic oxidation of carbon monoxide over platinum (catalytic converter). Sony VPCEH16EF/B battery
Production
1,000 cubic centimeters of 99.9% pure platinum, worth about US$910,000 at 30 October 2009 prices
Platinum, along with the rest of the platinum metals, is obtained commercially as a by-product from nickel and copper mining and processing. During electrorefining of copper, noble metals such as silver, gold and the platinum group metals as well as selenium and tellurium settle to the bottom of the cell as "anode mud"Sony VPCEH16EA/P battery, which forms the starting point for the extraction of the platinum group metals.[41][42]
If pure platinum is found in placer deposits or other ores, it is isolated from them by various methods of subtracting impurities. Because platinum is significantly denser than many of its impurities, the lighter impurities can be removed by simply floating them away in a liquid. Platinum is also nonmagnetic, while nickel and iron are both magneticSony VPCEH15EN/W battery. These two impurities are thus removed by running an electromagnet over the mixture. Because platinum has a higher melting point than most other substances, many impurities can be burned or melted away without melting the platinum. Finally, platinum is resistant to hydrochloric and sulfuric acids, while other substances are readily attacked by them. Metal impurities can be removed by stirring the mixture in either of the two acids and recovering the remaining platinumSony VPCEH15EG/B battery.[43]
One suitable method for purification for the raw platinum, which contains platinum, gold, and the other platinum group metals, is to process it with aqua regia, in which palladium, gold and platinum are dissolved, while osmium, iridium, ruthenium and rhodium stay unreacted. The gold is precipitated by the addition of iron(III) chloride and after filtering off the goldSony VPCEH13FX/W battery, the platinum is precipitated as ammonium chloroplatinate by the addition of ammonium chloride. Ammonium chloroplatinate can be converted to the metal by heating.[44]
Applications
Cross section of a metal-core catalytic converter
Of the 239 tonnes of platinum sold in 2006, 130 tonnes were used for vehicle emissions control devices, 49 tonnes for jewelry, 13.3 tonnes in electronics, and 11.2 tonnes in the chemical industry as a catalyst. The remaining 35.5 tonnes went to various other minor applications, such as electrodes, anticancer drugs, oxygen sensors, spark plugs and turbine engines. Sony VPCEH13FX/P battery
[edit]Catalysis
The most common use of platinum is as a catalyst in chemical reactions, many times as platinum black. It has been employed in this application since the early 19th century, when platinum powder was used to catalyze the ignition of hydrogen. Its most important application is in automobiles as a catalytic converterSony VPCEH13FX/L battery, which allows the complete combustion of low concentrations of unburned hydrocarbons from the exhaust into carbon dioxide and water vapor. Platinum is also used in the petroleum industry as a catalyst in a number of separate processes, but especially in catalytic reforming of straight run naphthas into higher-octane gasoline which becomes rich in aromatic compoundsSony VPCEH13FX/B battery. PtO2, also known as Adams' catalyst, is used as a hydrogenation catalyst, specifically for vegetable oils.[25] Platinum metal also strongly catalyzes the decomposition of hydrogen peroxide into water and oxygen gas.[46]
Standard
International Prototype Meter bar
From 1889 to 1960, the meter was defined as the length of a platinum-iridium (90:10) alloy bar, known as the International Prototype Meter bar. The previous bar was made of platinum in 1799. The International Prototype Kilogram remains defined by a cylinder of the same platinum-iridium alloy made in 1879. Sony VPCCA3SFX/R battery
The standard hydrogen electrode also uses a platinized platinum electrode due to its corrosion resistance, and other attributes.[48]
Precious metal
Platinum Eagle
Main articles: Platinum as an investment and Platinum coin
Platinum is a precious metal commodity; its bullion has the ISO currency code of XPT. Coins, bars, and ingots are traded or collected. Platinum finds use in jewelry, usually as a 90–95% alloy, due to its inertness and shine. Jewelry trade publications advise jewelers to present minute surface scratches (which they term patina) as a desirable feature. Sony VPCCA3S1E battery
In watchmaking, Vacheron Constantin, Patek Philippe, Rolex, Breitling, and other companies use platinum for producing their limited edition watch series. Watchmakers appreciate the unique properties of platinum, as it neither tarnishes nor wears out (relative to gold).[51]
Average price of platinum from 1991 to 2007 in US$ per troy ounce (~$20/g)[52]
The price of platinum, like other industrial commodities, is more volatile than that of gold. In 2008, the price of platinum dropped from $2,252 to $774 per oz, Sony VPCCA3E1E battery a loss of nearly 2/3 of its value. By contrast, the price of gold dropped from ~$1,000 to ~$700/oz during the same time frame, a loss of only 1/3 of its value.
During periods of sustained economic stability and growth, the price of platinum tends to be as much as twice the price of gold, whereas during periods of economic uncertainty,[54] the price of platinum tends to decrease due to reduced industrial demand, falling below the price of gold. Gold prices are more stable in slow economic timesSony VPCCA38EC/R battery, as gold is considered a safe haven and gold demand is not driven by industrial uses. In the 18th century, platinum's rarity made King Louis XV of France declare it the only metal fit for a king.[55]
[edit]Other uses
In the laboratory, platinum wire is used for electrodes; platinum pans and supports are used in thermogravimetric analysis because of the stringent requirements of chemical inertness upon heating to high temperatures (~1000 °C) Sony VPCCA38EC battery. Platinum is used as an alloying agent for various metal products, including fine wires, noncorrosive laboratory containers, medical instruments, dental prostheses, electrical contacts, and thermocouples. Platinum-cobalt, an alloy of roughly three parts platinum and one part cobalt, is used to make relatively strong permanent magnets.[25] Platinum-based anodes are used in ships, pipelines, and steel piers. Sony VPCCA37EC/B battery
[edit]Symbol of prestige
See also: Platinum album and Platinum (color)
An assortment of native platinum nuggets
Platinum's rarity as a metal has caused advertisers to associate it with exclusivity and wealth. "Platinum" debit cards have greater privileges than do "gold" ones.[56] "Platinum awards" are the second highest possible, ranking above "gold", "silver" and "bronze", but below diamond. For example, in the United States, a musical album that has sold more than 1 million copiesSony VPCCA37EC battery, will be credited as "platinum", whereas an album that sold more than 10 million copies will be certified as "diamond".[57] Some products, such as blenders and vehicles, with a silvery-white color are identified as "platinum". Platinum is considered a precious metal, although its use is not as common as the use of gold or silver. The frame of the Crown of Queen Elizabeth the Queen MotherSony VPCCA36FW/W battery, manufactured for her coronation as Consort of King George VI, is made of platinum. It was the first British crown to be made of this particular metal.[58]
[edit]Health issues
According to the Centers for Disease Control and Prevention, short-term exposure to platinum salts may cause irritation of the eyes, nose, and throat, and long-term exposure may cause both respiratory and skin allergies. The current OSHA standard is 2 micrograms per cubic meter of air averaged over an 8-hour work shift. Sony VPCCA36FW/B battery
Certain platinum complexes are used in chemotherapy, and show good activity against some tumors. Cisplatin is particularly effective against testicular cancer; the cure rate was improved from 10% to 85%.[60] However, the side effects are severe. Cisplatin causes cumulative, irreversible kidney damage and deafness.[61] As with other ototoxic agents, deafness may be secondary to interactions with melanin in the stria vascularisSony VPCCA36FH/W battery. Binding of platinum to RNA has been reviewed.[62]
As platinum is a catalyst in the manufacture of the silicone rubber and gel components of several types of medical implants (breast implants, joint replacement prosthetics, artificial lumbar discs, vascular access ports, etc.), the possibility platinum could enter the body and cause adverse effects has merited studySony VPCCA36FG/B battery. The Food and Drug Administration and other institutions have reviewed the issue and found no evidence to suggest toxicity in vivo.
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