Tungsten

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Tungsten, 74W
Tungsten
Pronunciation/ˈtʌŋstən/ (TUNG-stən)
Alternative nameWolfram, pronounced: /ˈwʊlfrəm/ (WUUL-frəm)
Allotropesα-tungsten (common), β-tungsten
AppearanceGrayish white, lustrous
Standard atomic weight Ar°(W)
Tungsten in the periodic table
Hydrogen Helium
Lithium Beryllium Boron Carbon Nitrogen Oxygen Fluorine Neon
Sodium Magnesium Aluminium Silicon Phosphorus Sulfur Chlorine Argon
Potassium Calcium Scandium Titanium Vanadium Chromium Manganese Iron Cobalt Nickel Copper Zinc Gallium Germanium Arsenic Selenium Bromine Krypton
Rubidium Strontium Yttrium Zirconium Niobium Molybdenum Technetium Ruthenium Rhodium Palladium Silver Cadmium Indium Tin Antimony Tellurium Iodine Xenon
Caesium Barium Lanthanum Cerium Praseodymium Neodymium Promethium Samarium Europium Gadolinium Terbium Dysprosium Holmium Erbium Thulium Ytterbium Lutetium Hafnium Tantalum Tungsten Rhenium Osmium Iridium Platinum Gold Mercury (element) Thallium Lead Bismuth Polonium Astatine Radon
Francium Radium Actinium Thorium Protactinium Uranium Neptunium Plutonium Americium Curium Berkelium Californium Einsteinium Fermium Mendelevium Nobelium Lawrencium Rutherfordium Dubnium Seaborgium Bohrium Hassium Meitnerium Darmstadtium Roentgenium Copernicium Nihonium Flerovium Moscovium Livermorium Tennessine Oganesson
Mo

W

Sg
tantalumtungstenrhenium
Atomic number (Z)74
Groupgroup 6
Periodperiod 6
Block  d-block
Electron configuration[Xe] 4f14 5d4 6s2[3]
Electrons per shell2, 8, 18, 32, 12, 2
Physical properties
Phase at STPsolid
Melting point3695 K ​(3422 °C, ​6192 °F)
Boiling point6203 K ​(5930 °C, ​10706 °F)
Density (at 20° C)19.254 g/cm3[4]
when liquid (at m.p.)17.6 g/cm3
Heat of fusion52.31 kJ/mol[5][6]
Heat of vaporization774 kJ/mol
Molar heat capacity24.27 J/(mol·K)
Vapor pressure
P (Pa) 1 10 100 1 k 10 k 100 k
at T (K) 3477 3773 4137 4579 5127 5823
Atomic properties
Oxidation states−4, −2, −1, 0, +1, +2, +3, +4, +5, +6 (a mildly acidic oxide)
ElectronegativityPauling scale: 2.36
Ionization energies
  • 1st: 770 kJ/mol
  • 2nd: 1700 kJ/mol
Atomic radiusempirical: 139 pm
Covalent radius162±7 pm
Color lines in a spectral range
Spectral lines of tungsten
Other properties
Natural occurrenceprimordial
Crystal structurebody-centered cubic (bcc) (cI2)
Lattice constant
Body-centered cubic crystal structure for tungsten
a = 316.52 pm (at 20 °C)[4]
Thermal expansion4.42×10−6/K (at 20 °C)[4]
Thermal conductivity173 W/(m⋅K)
Electrical resistivity52.8 nΩ⋅m (at 20 °C)
Magnetic orderingparamagnetic[7]
Molar magnetic susceptibility+59.0×10−6 cm3/mol (298 K)[8]
Young's modulus411 GPa
Shear modulus161 GPa
Bulk modulus310 GPa
Speed of sound thin rod4620 m/s (at r.t.) (annealed)
Poisson ratio0.28
Mohs hardness7.5
Vickers hardness3430–4600 MPa
Brinell hardness2000–4000 MPa
CAS Number7440-33-7
History
Discovery and first isolationJuan José Elhuyar and Fausto Elhuyar[9] (1783)
Named byTorbern Bergman (1781)
Symbol"W": from Wolfram, originally from Middle High German wolf-rahm 'wolf's foam' describing the mineral wolframite[10]
Isotopes of tungsten
Main isotopes Decay
abun­dance half-life (t1/2) mode pro­duct
180W 0.120% 1.8×1018 y α 176Hf
181W synth 121.2 d ε 181Ta
182W 26.5% stable
183W 14.3% stable
184W 30.6% stable
185W synth 75.1 d β 185Re
186W 28.4% stable
188W synth 69.78 d β 188Re
 Category: Tungsten
| references

Tungsten (/[invalid input: 'icon']ˈtʌŋstən/), also known as wolfram (/[invalid input: 'icon']ˈwʊlfrəm/ WOOL-frəm), is a chemical element with the chemical symbol W and atomic number 74.

ok lets put numbers like this.A steel-gray metal under standard conditions when uncombined, tungsten is found naturally on Earth only in chemical compounds. It was identified as a new element in 1781, 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 gold, and much higher (about 1.7 times) than that of lead.[11] Tungsten with minor amounts of impurities is often brittle[12] and hard, making it difficult to work. However, very pure tungsten is more ductile, and can be cut with a hacksaw.[13]

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 superalloys. 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. However, tungsten interferes with molybdenum and copper metabolism, and is somewhat toxic to animal life.[14][15]

History

In 1781, Carl Wilhelm Scheele discovered that a new acid, tungstic acid, could be made from scheelite (at the time named tungstenite). Scheele and Torbern Bergman suggested that it might be possible to obtain a new metal by reducing this acid.[16] In 1783, José and Fausto Elhuyar found an acid made from wolframite that was identical to tungstic acid. 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.[17][18]

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. Tungsten's resistance to high temperatures and its strengthening of alloys made it an important raw material for the arms industry.[19]

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"), 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.[13] 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 1546, 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.[10]

Characteristics

Physical properties

In tungsten's raw form, it is a steel-gray metal that is often brittle and hard to work, but if pure, it can be worked easily.[13] 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.[20] Tungsten has the lowest coefficient of thermal expansion of any pure metal. The low thermal expansion and high melting point and strength of tungsten are due to strong covalent bonds formed between tungsten atoms by the 5d electrons.[21] Alloying small quantities of tungsten with steel greatly increases its toughness.[11]

Isotopes

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[22] to do so with a half-life of (1.8 ± 0.2)×1018 yr; on average, this yields about two alpha decays of 180W in one gram of natural tungsten per year.[23] The other naturally occurring isotopes have not been observed to decay, constraining their half-lives to be[23]

182W, T1/2 > 8.3×1018 years
183W, T1/2 > 29×1018 years
184W, T1/2 > 13×1018 years
186W, T1/2 > 27×1018 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.[23] All of the remaining radioactive isotopes have half-lives of less than 3 hours, and most of these have half-lives below 8 minutes.[23] Tungsten also has 4 meta states, the most stable being 179mW (T½ 6.4 minutes).

Chemical properties

Main article: Tungsten compounds

Elemental tungsten resists attack by oxygen, acids, and alkalis.[24]

The most common formal oxidation state of tungsten is +6, but it exhibits all oxidation states from −2 to +6.[24][25] Tungsten typically combines with oxygen to form the yellow tungstic oxide, WO3, which dissolves in aqueous alkaline solutions to form tungstate ions, WO2−
4
.

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).[11]

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, W
7
O
6–
24
, which over time converts to the less soluble "paratungstate B" anion, H
2
W
12
O
10–
42
.[26] Further acidification produces the very soluble metatungstate anion, H
2
W
12
O
6–
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 species. 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 over 75% of this total in 2000, with most of the remaining production coming from Austria, Bolivia, Portugal, Russia, and Colombia.[27] Significant reserves in nations other than the aforementioned producers exist in the United States (3.2% of the estimated global reserve base), Canada (7.9% of the estimated global reserve base), and North Korea (0.56% of the estimated global reserve base).[28]

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 (molybdopterin, 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.[29] However, 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.[30] One 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.[31] 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.[32]

Other effects on biochemistry

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.[33] It is thought that a tungstate-containing enzyme in eukaryotes would be inert.[citation needed] The soil's chemistry determines how the tungsten polymerizes; alkaline soils cause monomeric tungstates; acidic soils cause polymeric tungstates.[34]

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.[35]

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.[36]

Production

Wolframite
Tungsten output in 2005

About 37,400 tonnes of tungsten concentrates were produced in the year 2000.[27] 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.[16] Because of tungsten's high melting point, it is not commercially feasible to cast tungsten ingots. 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:[37]

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.[38]

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 (tungsten carbide), with the remaining major use being its use in alloys and steels. Less than 10% is used in chemical compounds.[39]

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 °C. 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[11] and accounts for about 60% of current tungsten consumption.[40]

The jewelry industry makes rings of sintered tungsten carbide, tungsten carbide/metal composites, and also simply metallic tungsten. Sometimes manufacturers or retailers refer to tungsten carbide as a metal, but it is actually a ceramic. 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 tungsten. Tungsten carbide rings are brittle, however, and may crack if dropped.

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.[41] 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.[42] Superalloys containing tungsten, such as Hastelloy and Stellite, are used in turbine blades and wear-resistant parts and coatings.

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). 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.[43]

Chemical applications

Tungsten(IV) sulfide is a high temperature lubricant and is a component of catalysts for hydrodesulfurization. MoS2 is more commonly used for such applications.

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.[20]

Niche uses

Applications requiring its high density include heat sinks, weights, counterweights, ballast keels for yachts, tail ballast for commercial aircraft, and as ballast in race cars for NASCAR and Formula One. It is an ideal material to use as a dolly for riveting, 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[44] (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 wires.

Its density, similar to that of gold, allows tungsten to be used in jewelry as an alternative to gold or platinum.[13][45] 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 finish.[46]

Electronics

Because it retains its strength at high temperatures and has a high melting point, elemental tungsten is used in many high-temperature applications,[47] such as light bulb, cathode-ray tube, and vacuum tube filaments, heating elements, and rocket engine nozzles.[13] 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 inertia, tungsten is also used in electrodes, and in the emitter tips in electron-beam instruments that use field emission guns, such as electron microscopes. 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.[37]

The electronic structure of tungsten makes it one of the main sources for X-ray targets,[48] and also for shielding from high-energy radiations (such as in the radiopharmaceutical industry for shielding radioactive samples of FDG). 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.[20]

Precautions

Because tungsten is rare and its compounds generally inert, the effects of tungsten on the environment are limited.[49] The median lethal dose LD50 depends strongly on the animal and the method of administration and varies between 59 mg/kg (intravenous, rabbit)[50][51] and 5000 mg/kg (tungsten metal powder, intraperitoneal, rats).[52][53]

See also

References

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