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This article is about the chemical element. For other uses, seeTungsten (disambiguation).
Tungsten,74W
Tungsten
Pronunciation/ˈtʌŋstən/​(TUNG-stən)
Alternative nameWolfram, pronounced:/ˈwʊlfrəm/(WUUL-frəm)
Allotropesα-tungsten (common), β-tungsten
AppearanceGrayish white, lustrous
Standard atomic weightAr°(W)
Tungsten in theperiodic 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
tantalum←tungsten→rhenium
Atomic number(Z)74
Groupgroup 6
Periodperiod 6
Blockd-block
Electron configuration[Xe] 4f145d46s2[3]
Electrons per shell2, 8, 18, 32, 12, 2
Physical properties
PhaseatSTPsolid
Melting point3695K​(3422 °C, ​6192 °F)
Boiling point6203 K ​(5930 °C, ​10706 °F)
Density(at 20° C)19.254 g/cm3 [4]
when liquid (atm.p.)17.6 g/cm3
Heat of fusion52.31kJ/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
atT(K) 3477 3773 4137 4579 5127 5823
Atomic properties
Oxidation states−4, −2, −1, 0, +1, +2, +3,+4,+5,+6(a mildlyacidicoxide)
ElectronegativityPauling scale: 2.36
Ionization energies
  • 1st: 770 kJ/mol
  • 2nd: 1700 kJ/mol
Atomic radiusempirical: 139pm
Covalent radius162±7 pm
Color lines in a spectral range
Spectral linesof tungsten
Other properties
Natural occurrenceprimordial
Crystal structure​body-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+59.0×10−6cm3/mol (298 K)[8]
Young's modulus411 GPa
Shear modulus161 GPa
Bulk modulus310 GPa
Speed of soundthin rod4620 m/s (atr.t.) (annealed)
Poisson ratio0.28
Mohs hardness7.5
Vickers hardness3430–4600 MPa
Brinell hardness2000–4000 MPa
CAS Number7440-33-7
History
Discoveryand first isolationJuan José ElhuyarandFausto Elhuyar[9](1783)
Named byTorbern Bergman(1781)
Symbol"W": fromWolfram,originally fromMiddle High Germanwolf-rahm'wolf's foam' describing the mineralwolframite[10]
Isotopes of tungsten
Main isotopes Decay
abun­dance half-life(t1/2) mode pro­duct
180W 0.120% 1.8×1018y 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(also calledwolfram)[11][12]is achemical element;it hassymbolWandatomic number74. Tungsten is arare metalfound naturally onEarthalmost exclusively as compounds with other elements. It was identified as a new element in 1781 and first isolated as a metal in 1783. Its importantoresincludescheeliteandwolframite,the latter lending the element its alternative name.

Thefree elementis remarkable for its robustness, especially the fact that it has the highestmelting pointof all known elements, melting at 3,422 °C (6,192 °F; 3,695 K). It also has the highestboiling point,at 5,930 °C (10,706 °F; 6,203 K).[13]Its density is 19.254 g/cm3,[4]comparable with that ofuraniumandgold,and much higher (about 1.7 times) than that oflead.[14]Polycrystalline tungsten is an intrinsicallybrittle[15][16][17]andhardmaterial (under standard conditions, when uncombined), making it difficult towork into metal.However, pure single-crystalline tungsten is moreductileand can be cut with a hard-steelhacksaw.[18]

Tungsten occurs in many alloys, which have numerous applications, including incandescentlight bulbfilaments,X-ray tubes,electrodes ingas tungsten arc welding,superalloys,andradiation shielding.Tungsten's hardness and highdensitymake it suitable for military applications inpenetrating projectiles.Tungsten compounds are often used as industrialcatalysts.Its largest use is intungsten carbide,a wear-resistant metal used inmetalworking,mining,andconstruction.[19]About 50% of tungsten is used in tungsten carbide, with the remaining major use being alloys and steels: less than 10% is used other compounds.[20]

Tungsten is the only metal in the thirdtransitionseries that is known to occur inbiomolecules,being found in a few species of bacteria andarchaea.However, tungsten interferes withmolybdenumandcoppermetabolism and is somewhat toxic to most forms of animal life.[21][22]

Characteristics

Physical properties

In its raw form, tungsten is a hard steel-greymetalthat is oftenbrittleand hard towork.Purified, monocrystalline tungsten retains itshardness(which exceeds that of many steels), and becomesmalleableenough that it can be worked easily.[18]It is worked byforging,drawing,orextrudingbut it is more commonly formed bysintering.

Of all metals in pure form, tungsten has the highestmelting point(3,422 °C, 6,192 °F), lowestvapor pressure(at temperatures above 1,650 °C, 3,000 °F), and the highesttensile strength.[23]Althoughcarbonremains solid at higher temperatures than tungsten, carbonsublimesatatmospheric pressureinstead of melting, so it has no melting point. Moreover, tungsten's most stablecrystal phasedoes not exhibit any high-pressure-induced structural transformations for pressures up to at least 364 gigapascals.[24]Tungsten has the lowestcoefficient of thermal expansionof any pure metal. The low thermal expansion and high melting point andtensile strengthof tungsten originate from strongcovalent bondsformed between tungsten atoms by the 5d electrons.[25] Alloying small quantities of tungsten withsteelgreatly increases itstoughness.[14]

Tungsten exists in two majorcrystallineforms: α and β. The former has abody-centered cubicstructure and is the more stable form. The structure of theβ phaseis calledA15 cubic;it ismetastable,but can coexist with the α phase at ambient conditions owing to non-equilibrium synthesis or stabilization by impurities. Contrary to the α phase which crystallizes in isometric grains, the β form exhibits a columnarhabit.The α phase has one third of theelectrical resistivity[26]and a much lowersuperconducting transition temperatureTCrelative to the β phase: ca. 0.015 K vs. 1–4 K; mi xing the two phases allows obtaining intermediate TCvalues.[27][28]The TCvalue can also be raised byalloyingtungsten with another metal (e.g. 7.9 K for W-Tc).[29]Such tungsten alloys are sometimes used in low-temperature superconducting circuits.[30][31][32]

Isotopes

Main article:Isotopes of tungsten

Naturally occurring tungsten consists of four stableisotopes(182W,183W,184W, and186W) and one very long-lived radioisotope,180W. Theoretically, all five can decay into isotopes of element 72 (hafnium) byAlpha emission,but only180W has been observed to do so, with a half-life of(1.8±0.2)×1018years;[33][34]on average, this yields about two Alpha decays of180W per gram of natural tungsten per year.[35]This rate is equivalent to aspecific activityof roughly 63 micro-becquerelper kilogram. This rate of decay is orders of magnitude lower than that observed in carbon or potassium as found on earth, which likewise contain small amounts of long-lived radioactive isotopes.Bismuthwas long thought to be non-radioactive, but209
Bi(its longest lived isotope) actually decays with a half life of2.01×1019years or about a factor 10 slower than180
W.However, due to naturally occurring bismuth being 100%209
Bi,its specific activity is actually higher than that of natural tungsten at 3 milli-becquerel per kilogram. The other naturally occurring isotopes of tungsten have not been observed to decay, constraining their half-lives to be at least4×1021years.

Another 34 artificialradioisotopesof tungsten have been characterized, the most stable of which are181W 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, and187W with a half-life of 23.72 h.[35]All of the remainingradioactiveisotopes have half-lives of less than 3 hours, and most of these have half-lives below 8 minutes.[35]Tungsten also has 11meta states,with the most stable being179mW (t1/26.4 minutes).

Chemical properties

Tungsten is a mostly non-reactive element: it does not react with water, is immune to attack by most acids and bases, and does not react with oxygen or air at room temperature. At elevated temperatures (i.e., when red-hot) it reacts with oxygen to form thetrioxidecompound tungsten(VI), WO3.It will, however, react directly with fluorine (F2) at room temperature to formtungsten(VI) fluoride(WF6), a colorless gas. At around 250 °C it will react with chlorine or bromine, and under certain hot conditions will react with iodine. Finely divided tungsten ispyrophoric.[36][37]

The most common formaloxidation stateof tungsten is +6, but it exhibits all oxidation states from −2 to +6.[37][38]Tungsten typically combines with oxygen to form the yellowtungstic 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 withchlorineto formtungsten hexachloride(WCl6).[14]

In aqueous solution, tungstate gives theheteropoly acidsandpolyoxometalateanionsunder neutral and acidic conditions. Astungstateis progressively treated with acid, it first yields the soluble,metastable"paratungstate A"anion,W
7O6−
24,which over time converts to the less soluble "paratungstate B" anion,H
2W
12O10−
42.[39]Further acidification produces the very soluble metatungstate anion,H
2W
12O6−
40,after which equilibrium is reached. The metatungstate ion exists as a symmetric cluster of twelve tungsten-oxygenoctahedraknown as theKegginanion. Many other polyoxometalate anions exist as metastable species. The inclusion of a different atom such asphosphorusin place of the two centralhydrogensin metatungstate produces a wide variety of heteropoly acids, such asphosphotungstic acidH3PW12O40.

Tungsten trioxide can formintercalationcompounds with alkali metals. These are known asbronzes;an example issodium tungsten bronze.

In gaseous form, tungsten forms the diatomic species W2.These molecules feature asextuple bondbetween tungsten atoms — the highest known bond order amongstableatoms.[40][41]

History

In 1781,Carl Wilhelm Scheelediscovered that a newacid,tungstic acid,could be made fromscheelite(at the time called tungsten).[42][43]Scheele andTorbern Bergmansuggested that it might be possible to obtain a new metal by reducing this acid.[44]In 1783,JoséandFausto Elhuyarfound an acid made fromwolframitethat was identical to tungstic acid. Later that year, at theRoyal Basque Societyin the town ofBergara,Spain, the brothers succeeded in isolating tungsten by reduction of this acid withcharcoal,and they are credited with the discovery of the element (they called it "wolfram" or "volfram" ).[45][46][47][48][49]

The strategic value of tungsten came to notice in the early 20th century. British authorities acted in 1912 to free theCarrock minefrom the German owned Cumbrian Mining Company and, duringWorld War I,restrict German access elsewhere.[50]InWorld War II,tungsten played a more significant role inbackground political dealings.Portugal, as the main European source of the element, wasput under pressure from both sides,because of its deposits of wolframite ore atPanasqueira.Tungsten's desirable properties such as resistance to high temperatures, its hardness and density, and its strengthening of alloys made it an important raw material for the arms industry,[51][52]both as a constituent of weapons and equipment and employed in production itself, e.g., intungsten carbidecutting tools for machining steel. Now tungsten is used in many more applications such as aircraft and motorsport ballast weights, darts, anti-vibration tooling, and sporting equipment.

Tungsten is unique amongst the elements in that it has been the subject of patent proceedings. In 1928, a US court rejectedGeneral Electric's attempt to patent it, overturningU.S. patent 1,082,933granted in 1913 toWilliam D. Coolidge.[53][54][55]

Etymology

The nametungsten(which means'heavy stone'inSwedishand was the old Swedish name for the mineralscheeliteand other minerals of similar density) is used in English, French, and many other languages as the name of the element, butwolfram(orvolfram) is used in most European (especially Germanic, Spanish and Slavic) languages and is derived from the mineralwolframite,which is the origin of the chemical symbolW.[18]The namewolframiteis derived fromGermanwolf rahm('wolf soot, wolf cream'), the name given to tungsten byJohan Gottschalk Walleriusin 1747. This, in turn, derives fromLatinlupi spuma,the nameGeorg Agricolaused for the mineral in 1546, which translates into English as'wolf's froth'and is a reference to the large amounts oftinconsumed by the mineral during its extraction, as though the mineral devoured it like a wolf.[10]This naming follows a tradition of colorful names miners from theOre Mountainswould give various minerals, out of a superstition that certain ones that looked as if they contained then-known valuable metals but when extracted were somehow "hexed".Cobalt(cf.Kobold),pitchblende(cf. Germanblendenfor'to blind, to deceive') andnickel(cf. "Old Nick" ) derive their names from the same miners' idiom.

Occurrence

Wolframite mineral, with a scale in cm

Tungsten has thus far not been found in nature in its pure form.[56]Instead, tungsten is found mainly in the mineralswolframiteandscheelite.[56]Wolframite isiron–manganesetungstate(Fe,Mn)WO4,a solid solution of the two mineralsferberite(FeWO4) andhübnerite(MnWO4), whilescheeliteiscalciumtungstate (CaWO4). Other tungsten minerals range in their level of abundance from moderate to very rare, and have almost no economic value.

Chemical compounds

See also:Category:Tungsten compounds
Structure of W6Cl18( "tungsten trichloride" )

Tungsten forms chemical compounds in oxidation states from -II to VI. Higher oxidation states, always as oxides, are relevant to its terrestrial occurrence and its biological roles, mid-level oxidation states are often associated withmetal clusters,and very low oxidation states are typically associated withCO complexes.The chemistries of tungsten andmolybdenumshow strong similarities to each other, as well as contrasts with their lighter congener,chromium.The relative rarity of tungsten(III), for example, contrasts with the pervasiveness of the chromium(III) compounds. The highest oxidation state is seen intungsten(VI) oxide(WO3).[57]Tungsten(VI) oxide is soluble in aqueousbase,forming tungstate (WO42−). Thisoxyanioncondenses at lowerpHvalues, formingpolyoxotungstates.[58]

The broad range ofoxidation statesof tungsten is reflected in its various chlorides:[57]

Organotungsten compoundsare numerous and also span a range of oxidation states. Notable examples include the trigonal prismaticW(CH3)6and octahedralW(CO)6.

Production

Tungsten mining inRwandaforms an important part of the country's economy.[citation needed]
Tungsten concentrate production, 1946

Reserves

The world's reserves of tungsten are 3,200,000 tonnes; they are mostly located inChina(1,800,000 t),Canada(290,000 t),[59]Russia(160,000 t),Vietnam(95,000 t) andBolivia.As of 2017, China, Vietnam and Russia are the leading suppliers with 79,000, 7,200 and 3,100 tonnes, respectively. Canada had ceased production in late 2015 due to the closure of its sole tungsten mine. Meanwhile, Vietnam had significantly increased its output in the 2010s, owing to the major optimization of its domestic refining operations, and overtook Russia and Bolivia.[60]

China remains the world's leader not only in production, but also in export and consumption of tungsten products. Tungsten production is gradually increasing outside China because of the rising demand. Meanwhile, its supply by China is strictly regulated by the Chinese Government, which fights illegal mining and excessive pollution originating from mining and refining processes.[61]

There is a large deposit of tungsten ore on the edge ofDartmoorin theUnited Kingdom,which was exploited duringWorld War IandWorld War IIas theHemerdon Mine.Following increases in tungsten prices, this mine was reactivated in 2014,[62]but ceased activities in 2018.[63]

Within theEU,theAustrianFelbertal scheelite deposit is one of the few producing tungsten mines.[64]Portugalis one of Europe's main tungsten producers, with 121 kt of contained tungsten in mineral concentrates from 1910 to 2020, accounting for roughly 3.3% of the global production.[65]

Tungsten is considered to be aconflict mineraldue to the unethical mining practices observed in theDemocratic Republic of the Congo.[66][67]

Extraction

Tungsten is extracted from its ores in several stages. The ore is eventually converted totungsten(VI) oxide(WO3), which is heated withhydrogenor carbon to produce powdered tungsten.[44]Because of tungsten's high melting point, it is not commercially feasible to cast tungsteningots.Instead, powdered tungsten is mixed with small amounts of powdered nickel or other metals, andsintered.During the sintering process, the nickel diffuses into the tungsten, producing an alloy.

Tungsten can also be extracted by hydrogen reduction ofWF6:

WF6+ 3 H2→ W + 6 HF

orpyrolytic decomposition:[68]

WF6→ W + 3 F2(ΔHr= +)

Tungsten is not traded as a futures contract and cannot be tracked on exchanges like theLondon Metal Exchange.The tungsten industry often uses independent pricing references such asArgus MediaorMetal Bulletinas a basis for contracts.[69]The prices are usually quoted for tungsten concentrate or WO3.[60]

Applications

Close-up of a tungsten filament inside ahalogen lamp
Tungsten carbidejewelry

Approximately half of the tungsten is consumed for the production of hard materials – namelytungsten carbide– with the remaining major use being in alloys and steels. Less than 10% is used in otherchemical compounds.[20]Because of the high ductile-brittle transition temperature of tungsten, its products are conventionally manufactured throughpowder metallurgy,spark plasma sintering,chemical vapor deposition,hot isostatic pressing,andthermoplasticroutes. A more flexible manufacturing alternative isselective laser melting,which is a form of3D printingand allows creating complex three-dimensional shapes.[70]

Industrial

Tungsten is mainly used in the production of hard materials based ontungsten carbide(WC), one of the hardestcarbides.WC is an efficientelectrical conductor,but W2C is less so. WC is used to make wear-resistantabrasives,and "carbide" cutting tools such as knives, drills,circular saws,dies,millingandturningtools used by the metalworking, woodworking,mining,petroleumand construction industries.[14]Carbide tooling is actually a ceramic/metal composite, where metallic cobalt acts as a binding(matrix) materialto hold the WC particles in place. This type of industrial use accounts for about 60% of current tungsten consumption.[71]

Thejewelryindustry makes rings of sinteredtungsten carbide,tungsten carbide/metal composites, and also metallic tungsten.[72]WC/metal composite rings use nickel as the metal matrix in place ofcobaltbecause it takes a higher luster when polished. Sometimes manufacturers or retailers refer totungsten carbideas a metal, but it is aceramic.[73]Because of tungsten carbide's hardness, rings made of this material are extremely abrasion resistant, and will hold a burnished finish longer than rings made of metallic tungsten. Tungsten carbide rings are brittle, however, and may crack under a sharp blow.[74]

Alloys

Further information:Tantalum–tungsten alloys

The hardness and heat resistance of tungsten can contribute to usefulalloys.A good example ishigh-speed steel,which can contain as much as 18% tungsten.[75]Tungsten's high melting point makes tungsten a good material for applications likerocket nozzles,for example in theUGM-27 Polarissubmarine-launched ballistic missile.[76]Tungsten alloys are used in a wide range of applications, including the aerospace and automotive industries and radiation shielding.[77]Superalloyscontaining tungsten, such asHastelloyandStellite,are used inturbineblades and wear-resistant parts and coatings.

Tungsten's heat resistance makes it useful inarc weldingapplications when combined with another highly-conductive metal such as silver or copper. The silver or copper provides the necessary conductivity and the tungsten allows the welding rod to withstand the high temperatures of the arc welding environment.[78]

Permanent magnets

Quenched (martensitic) tungsten steel (approx. 5.5% to 7.0% W with 0.5% to 0.7% C) was used for making hard permanent magnets, due to its highremanenceandcoercivity,as noted byJohn Hopkinson(1849–1898) as early as 1886. The magnetic properties of a metal or an alloy are very sensitive to microstructure. For example, while the element tungsten is not ferromagnetic (butironis), when it is present in steel in these proportions, it stabilizes themartensitephase, which has greater ferromagnetism than theferrite (iron)phase due to its greater resistance tomagnetic domain wall motion.

Military

Tungsten, usually alloyed withnickel,iron,orcobaltto form heavy alloys, is used inkinetic energy penetratorsas an alternative todepleted uranium,in applications where uranium'sradioactivityis problematic even in depleted form, or where uranium's additionalpyrophoricproperties are not desired (for example, in ordinary small arms bullets designed to penetrate body armor). Similarly, tungsten alloys have also been used inshells,grenades,andmissiles,to create supersonic shrapnel. Germany used tungsten during World War II to produce shells for anti-tank gun designs using the Gerlichsqueeze boreprinciple to achieve very high muzzle velocity and enhanced armor penetration from comparatively small caliber and light weight field artillery. The weapons were highly effective but a shortage of tungsten used in the shell core, caused in part by theWolfram Crisis,limited their use.[citation needed]

Tungsten has also been used indense inert metal explosives,which use it as dense powder to reduce collateral damage while increasing the lethality of explosives within a small radius.[79]

Chemical applications

Tungsten(IV) sulfideis a high temperaturelubricantand is a component of catalysts forhydrodesulfurization.[80]MoS2is more commonly used for such applications.[81]

Tungstenoxidesare used inceramicglazes andcalcium/magnesiumtungstates are used widely influorescent lighting.Crystaltungstatesare used asscintillation detectorsinnuclear physicsandnuclear medicine.Other salts that contain tungsten are used in the chemical andtanningindustries.[23] Tungsten oxide (WO3) is incorporated intoselective catalytic reduction(SCR) catalysts found in coal-fired power plants. These catalysts convertnitrogen 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.[82]Tungsten containing catalysts are promising for epoxidation,[83]oxidation,[84]and hydrogenolysis reactions.[85]Tungsten heteropoly acids are key component of multifunctional catalysts.[86]Tungstates can be used as photocatalyst,[87]while the tungsten sulfide as electrocatalyst.[88]

Niche uses

Applications requiring its high density include weights,counterweights,ballast keels for yachts, tail ballast for commercial aircraft, rotor weights for civil and military helicopters, and as ballast in race cars forNASCARandFormula One.[89]Being slightly less than twice the density, tungsten is seen as an alternative (albeit more expensive) to leadfishing sinkers.Depleted uraniumis also used for these purposes, due to similarly high density. Seventy-five-kg blocks of tungsten were used as "cruise balance mass devices" on the entry vehicle portion of the 2012Mars Science Laboratoryspacecraft. It is an ideal material to use as adollyforriveting,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-qualitydarts[90](to allow for a smaller diameter and thus tighter groupings) or forartificial flies(tungsten beads allow the fly to sink rapidly). Tungsten is also used as a heavy bolt to lower the rate of fire of theSWD M11/9sub-machine gun from 1300 RPM to 700 RPM. Tungsten has seen use recently in nozzles for3D printing;the high wear resistance and thermal conductivity of tungsten carbide improves the printing of abrasive filaments.[91]Somestring instrumentstrings incorporates tungsten.[92][93]Tungsten is used as an absorber on the electron telescope on theCosmic Ray Systemof the twoVoyager spacecraft.[94]

Gold substitution

Its density, similar to that of gold, allows tungsten to be used in jewelry as an alternative togoldorplatinum.[18][95]Metallic tungsten ishypoallergenic,and is harder than gold alloys (though not as hard as tungsten carbide), making it useful forringsthat will resist scratching, especially in designs with abrushed finish.

Because the density is so similar to that of gold (tungsten is only 0.36% less dense), and its price of the order of one-thousandth, tungsten can also be used incounterfeitingofgold bars,such as by plating a tungsten bar with gold,[96][97][98]which has been observed since the 1980s,[99]or taking an existing gold bar, drilling holes, and replacing the removed gold with tungsten rods.[100]The densities are not exactly the same, and other properties of gold and tungsten differ, but gold-plated tungsten will pass superficial tests.[96]

Gold-plated tungsten is available commercially from China (the main source of tungsten), both in jewelry and as bars.[101]

Electronics

Because it retains its strength at high temperatures and has a highmelting point,elemental tungsten is used in many high-temperature applications,[102]such asincandescent light bulb,cathode-ray tube,andvacuum tubefilaments,heating elements,androcket enginenozzles.[18]Its high melting point also makes tungsten suitable for aerospace and high-temperature uses such as electrical, heating, and welding applications, notably in thegas tungsten arc weldingprocess (also called tungsten inert gas (TIG) welding).[103]

Tungsten electrode used in agas tungsten arc weldingtorch
Tungsten filament is used in incandescent lightbulbs, where it is heated until it glows

Because of its conductive properties and relative chemical inertness, tungsten is also used inelectrodes,and in the emitter tips in electron-beam instruments that usefield emission guns,such aselectron microscopes.In electronics, tungsten is used as an interconnect material inintegrated circuits,between thesilicon dioxidedielectricmaterial and the transistors. It is used in metallic films, which replace the wiring used in conventional electronics with a coat of tungsten (ormolybdenum) onsilicon.[68]

The electronic structure of tungsten makes it one of the main sources forX-raytargets,[104][105]and also for shielding from high-energyradiations(such as in theradiopharmaceuticalindustry for shielding radioactive samples ofFDG). It is also used in gamma imaging as a material from which coded apertures are made, due to its excellent shielding properties. Tungsten powder is used as a filler material inplasticcomposites, which are used as a nontoxic substitute forleadinbullets,shot,and radiation shields. Since this element's thermal expansion is similar toborosilicate glass,it is used for making glass-to-metal seals.[23]In addition to its high melting point, when tungsten is doped with potassium, it leads to an increased shape stability (compared with non-doped tungsten). This ensures that the filament does not sag, and no undesired changes occur.[106]

Tungsten is used in producing vibration motors, also known as mobile vibrators.[107]These motors are integral components that provide tactile feedback to users, alerting them to incoming calls, messages, and notifications.[108]Tungsten’s high density, hardness, and wear resistance property helps to endure the high-speed rotational vibrations these motors generate.[109][110]

Nanowires

Through top-downnanofabricationprocesses, tungstennanowireshave been fabricated and studied since 2002.[111]Due to a particularly high surface to volume ratio, the formation of a surface oxide layer and the single crystal nature of such material, the mechanical properties differ fundamentally from those of bulk tungsten.[112]Such tungsten nanowires have potential applications innanoelectronicsand importantly as pH probes and gas sensors.[113]In similarity tosilicon nanowires,tungsten nanowires are frequently produced from a bulk tungsten precursor followed by athermal oxidationstep to control morphology in terms of length and aspect ratio.[114]Using theDeal–Grove modelit is possible to predict the oxidation kinetics of nanowires fabricated through such thermal oxidation processing.[115]

Fusion power

Due to its high melting point and good erosion resistance, tungsten is a lead candidate for the most exposed sections of the plasma-facing inner wall ofnuclear fusionreactors.It will be used as theplasma-facing materialof thedivertorin theITERreactor,[116]and is currently in use in theJETtest reactor.

Biological role

Tungsten, at atomic numberZ= 74, is the heaviest element known to be biologically functional. It is used by some bacteria andarchaea,[117]but not ineukaryotes.For example,enzymescalledoxidoreductasesuse tungsten similarly tomolybdenumby using it in a tungsten-pterincomplex withmolybdopterin(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.[118]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 molybdopterin-requiring enzymes.[119]One of the enzymes in the oxidoreductase family which sometimes employ tungsten (bacterialformate dehydrogenaseH) is known to use a selenium-molybdenum version of molybdopterin.[120]Acetylene hydrataseis an unusualmetalloenzymein that it catalyzes a hydration reaction. Two reaction mechanisms have been proposed, in one of which there is a direct interaction between the tungsten atom and the C≡C triple bond.[121]Although a tungsten-containingxanthine dehydrogenasefrom bacteria has been found to contain tungsten-molydopterin and also non-protein bound selenium, a tungsten-selenium molybdopterin complex has not been definitively described.[122]

In soil, tungsten metal oxidizes to thetungstateanion. It can be selectively or non-selectively imported by someprokaryotic organismsand may substitute formolybdatein certainenzymes.Its effect on the action of these enzymes is in some cases inhibitory and in others positive.[123]The soil's chemistry determines how the tungsten polymerizes;alkalinesoils cause monomeric tungstates;acidicsoils cause polymeric tungstates.[124]

Sodium tungstateandleadhave been studied for their effect onearthworms.Lead was found to be lethal at low levels and sodium tungstate was much less toxic, but the tungstate completely inhibited theirreproductive ability.[125]

Tungsten has been studied as a biological copper metabolicantagonist,in a role similar to the action of molybdenum. It has been found thattetrathiotungstate[zh]salts may be used as biological copperchelationchemicals, similar to thetetrathiomolybdates.[126]

In archaea

Tungsten is essential for some archaea. The following tungsten-utilizing enzymes are known:

Awtpsystem is known to selectively transport tungsten in archaea:

Health factors

Because tungsten is a rare metal[128]and its compounds are generally inert, the effects of tungsten on the environment are limited.[129]The abundance of tungsten in the Earth's crust is thought to be about 1.5 parts per million. It is one of the rarer elements.

It was at first believed to be relatively inert and an only slightly toxic metal, but beginning in the year 2000, the risk presented by tungsten alloys, its dusts and particulates to induce cancer and several other adverse effects in animals as well as humans has been highlighted from in vitro and in vivo experiments.[130][131] Themedian lethal doseLD50depends strongly on the animal and the method of administration and varies between 59 mg/kg (intravenous, rabbits)[132][133]and 5000 mg/kg (tungsten metal powder,intraperitoneal,rats).[134][135]

People can be exposed to tungsten in the workplace by breathing it in, swallowing it, skin contact, and eye contact. TheNational Institute for Occupational Safety and Health(NIOSH) has set arecommended exposure limit(REL) of 5 mg/m3over an 8-hour workday and a short term limit of 10 mg/m3.[136]

In popular culture

Tungsten and tungsten alloys gained popularity through tungsten cubes and spheres. This popularity started in October 2021, and rose again in January 2023, through social media.[137]

The main reason that tungsten cubes, spheres and other forms became popular is for their novelty as an item, due to their density. No other element comes close to the same density with regards to cost and availability, with some being radioactive as well.

See also

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