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Tungsten, or wolfram, is a
chemical element 400px, The periodic table of the chemical elements In chemistry, an element is a pure substance consisting only of atoms that all have the same numbers of protons in their atomic nuclei. Unlike chemical compounds, chemical elements cannot be br ...
with the
symbol A symbol is a mark, sign, or word that indicates, signifies, or is understood as representing an idea, object, or relationship. Symbols allow people to go beyond what is known or seen by creating linkages between otherwise very different concep ...
W and
atomic number 300px, The Rutherford–Bohr model of the hydrogen atom () or a hydrogen-like ion (). In this model it is an essential feature that the photon energy (or frequency) of the electromagnetic radiation emitted (shown) when an electron jumps from one ...
74. Tungsten is a
rare metal Precious metals are rare, naturally occurring metallic chemical elements of high economic value. Chemically, the precious metals tend to be less reactive than most elements (see noble metal). They are usually ductile and have a high lustre. H ...
found naturally on Earth almost exclusively as compounds with other elements. It was identified as a new element in 1781 and first isolated as a metal in 1783. Its important ores include
tungsten Tungsten, or wolfram, is a chemical element with the symbol W and atomic number 74. Tungsten is a rare metal found naturally on Earth almost exclusively as compounds with other elements. It was identified as a new element in 1781 and first isolate ...
,
scheelite Scheelite is a calcium tungstate mineral with the chemical formula CaWO4. It is an important ore of tungsten (wolfram). Well-formed crystals are sought by collectors and are occasionally fashioned into gemstones when suitably free of flaws. Scheel ...
, and
wolframite Wolframite, (Fe,Mn)WO4, is an iron manganese tungstate mineral that is the intermediate between ferberite (Fe2+ rich) and hübnerite (Mn2+ rich). Along with scheelite, the wolframite series are the most important tungsten ore minerals. Wolframite i ...
, the last lending the element its alternate name. The
free element In chemistry, a free element is a chemical element that is not combined with or chemically bonded to other elements. Examples of elements which can occur as free elements include the oxygen molecule (O) and carbon.A. Earnshaw and Norman Greenwood. ...
is remarkable for its robustness, especially the fact that it has the highest
melting point#REDIRECT Melting point#REDIRECT Melting point {{Redirect category shell, 1= {{R from other capitalisation ...
{{Redirect category shell, 1= {{R from other capitalisation ...
of all the elements discovered, melting at . It also has the highest
boiling point The boiling point of a substance is the temperature at which the vapor pressure of a liquid equals the pressure surrounding the liquid and the liquid changes into a vapor. The boiling point of a liquid varies depending upon the surrounding enviro ...
, at . Its density is 19.25 grams per cubic centimetre, comparable with that of
uranium Uranium is a chemical element with the symbol U and atomic number 92. It is a silvery-grey metal in the actinide series of the periodic table. A uranium atom has 92 protons and 92 electrons, of which 6 are valence electrons. Uranium is weak ...
and
gold Gold is a chemical element with the symbol Au (from la, aurum) and atomic number 79, making it one of the higher atomic number elements that occur naturally. In a pure form, it is a bright, slightly reddish yellow, dense, soft, malleable, and ...
, and much higher (about 1.7 times) than that of
lead Lead is a chemical element with the symbol Pb (from the Latin ) and atomic number 82. It is a heavy metal that is denser than most common materials. Lead is soft and malleable, and also has a relatively low melting point. When freshly cut, lead ...
. Polycrystalline tungsten is an intrinsically
brittle tensile testpieces A material is brittle if, when subjected to stress (physics), stress, it fractures with little elastic deformation and without significant plastic deformation. Brittle materials absorb relatively little energy prior to fractur ...
and hard material (under standard conditions, when uncombined), making it difficult to
work Work may refer to: * Work (human activity), intentional activity people perform to support themselves, others, or the community ** Manual labour, physical work done by humans ** House work, housework, or homemaking * Work (physics), the product of ...
. However, pure single-crystalline tungsten is more
ductile Ductility is a mechanical property commonly described as a material's amenability to drawing (e.g. into wire). In materials science, ductility is defined by the degree to which a material can sustain plastic deformation under tensile stress befo ...

ductile
and can be cut with a hard-steel
hacksaw A hacksaw is a fine-toothed saw, originally and mainly made for cutting metal. The equivalent saw for cutting wood is usually called a bow saw. Most hacksaws are hand saws with a C-shaped walking frame that holds a blade under tension. Such h ...

hacksaw
. Tungsten occurs in many alloys, which have numerous applications, including incandescent
light bulb An electric light is a device that produces visible light from electric power. It is the most common form of artificial lighting and is essential to modern society, providing interior lighting for buildings and exterior light for evening and n ...

light bulb
filaments,
X-ray tubeAn X-ray tube is a vacuum tube that converts electrical input power into X-rays. The availability of this controllable source of X-rays created the field of radiography, the imaging of partly opaque objects with penetrating radiation. In contrast to ...
s, electrodes in
gas tungsten arc welding Gas tungsten arc welding (GTAW), also known as tungsten inert gas (TIG) welding, is an arc welding process that uses a non-consumable tungsten electrode to produce the weld. The weld area and electrode are protected from oxidation or other atmosph ...
,
superalloys Nickel superalloy jet engine (RB199) turbine blade A superalloy, or high-performance alloy, is an alloy with the ability to operate at a high fraction of its melting point. Several key characteristics of a superalloy are excellent mechanical stren ...
, and
radiation shielding Radiation protection, also known as radiological protection, is defined by the International Atomic Energy Agency (IAEA) as "The protection of people from harmful effects of exposure to ionizing radiation, and the means for achieving this". Exposure ...
. Tungsten's hardness and high
density The density (more precisely, the volumetric mass density; also known as specific mass), of a substance is its mass per unit volume. The symbol most often used for density is ''ρ'' (the lower case Greek letter rho), although the Latin letter '' ...
make it suitable for military applications in penetrating
projectile A projectile is any object thrown by the exertion of a force. It can also be defined as an object launched into the space and allowed to move free under the influence of gravity and air resistance. Although any object in motion through space (for e ...
s. Tungsten compounds are often used as industrial
catalyst that utilizes a low-temperature oxidation catalyst to convert carbon monoxide to less toxic carbon dioxide at room temperature. It can also remove formaldehyde from the air. Catalysis () is the process of increasing the reaction rate, rate of a ...

catalyst
s. Tungsten is the only metal in the third transition series that is known to occur in
biomolecule , showing alpha helices, represented by ribbons. This poten was the first to have its suckture solved by X-ray crystallography by Max Perutz and Sir John Cowdery Kendrew in 1958, for which they received a Nobel Prize in Physics A biomolecule o ...
s, being found in a few species of bacteria and
archaea Archaea ( ; singular archaeon ) constitute a domain of single-celled organisms. These microorganisms lack cell nuclei and are therefore prokaryotes. Archaea were initially classified as bacteria, receiving the name archaebacteria (in the Archae ...
. However, tungsten interferes with
molybdenum Molybdenum is a chemical element with the symbol Mo and atomic number 42. The name is from Neo-Latin ''molybdaenum'', which is based on Ancient Greek ', meaning lead, since its ores were confused with lead ores. Molybdenum minerals have been known ...
and
copper Copper is a chemical element with the symbol Cu (from la, cuprum) and atomic number 29. It is a soft, malleable, and ductile metal with very high thermal and electrical conductivity. A freshly exposed surface of pure copper has a pinkish-orang ...

copper
metabolism and is somewhat toxic to most forms of animal life.


Characteristics


Physical properties

In its raw form, tungsten is a hard steel-grey
metal A metal (from Greek μέταλλον ''métallon'', "mine, quarry, metal") is a material that, when freshly prepared, polished, or fractured, shows a lustrous appearance, and conducts electricity and heat relatively well. Metals are typically ...
that is often
brittle tensile testpieces A material is brittle if, when subjected to stress (physics), stress, it fractures with little elastic deformation and without significant plastic deformation. Brittle materials absorb relatively little energy prior to fractur ...
and hard to
work Work may refer to: * Work (human activity), intentional activity people perform to support themselves, others, or the community ** Manual labour, physical work done by humans ** House work, housework, or homemaking * Work (physics), the product of ...
. If made very pure, tungsten retains its
hardness Hardness is a measure of the resistance to localized plastic deformation induced by either mechanical indentation or abrasion. In general, different materials differ in their hardness; for example hard metals such as titanium and beryllium are ha ...
(which exceeds that of many steels), and becomes
malleable Ductility is a mechanical property commonly described as a material's amenability to drawing (e.g. into wire). In materials science, ductility is defined by the degree to which a material can sustain plastic deformation under tensile stress befo ...
enough that it can be worked easily. It is worked by
forging Forging is a manufacturing process involving the shaping of metal using localized compressive forces. The blows are delivered with a hammer (often a power hammer) or a die. Forging is often classified according to the temperature at which it i ...
,
drawing Drawing is a form of visual art in which an artist uses instruments to mark paper or other two-dimensional surface. Drawing instruments include graphite pencils, pen and ink, various kinds of paints, inked brushes, colored pencils, crayons, char ...
, or
extruding allow bars to be joined with special connectors. Extrusion is a process used to create objects of a fixed cross section (geometry), cross-sectional profile. A material is pushed through a die of the desired cross-section. The two main advantages ...
but it is more commonly formed by
sintering Clinker nodules produced by sintering Sintering or frittage is the process of compacting and forming a solid mass of material by heat or pressure without melting it to the point of liquefaction. Sintering happens naturally in mineral deposits or ...
. Of all metals in pure form, tungsten has the highest
melting point#REDIRECT Melting point#REDIRECT Melting point {{Redirect category shell, 1= {{R from other capitalisation ...
{{Redirect category shell, 1= {{R from other capitalisation ...
(), lowest
vapor pressure#REDIRECT Vapor pressure#REDIRECT Vapor pressure {{R from other capitalisation ...
{{R from other capitalisation ...
(at temperatures above ), and the highest
tensile strength In physics, tension is described as the pulling force transmitted axially by the means of a string, a cable, chain, or similar one-dimensional continuous object, or by each end of a rod, truss member, or similar three-dimensional object; tension mig ...
. Although
carbon Carbon (from la, carbo "coal") is a chemical element with the symbol C and atomic number 6. It is nonmetallic and tetravalent—making four electrons available to form covalent chemical bonds. It belongs to group 14 of the periodic table. Car ...
remains solid at higher temperatures than tungsten, carbon sublimes at
atmospheric pressure Atmospheric pressure, also known as barometric pressure (after the barometer), is the pressure within the atmosphere of Earth. The standard atmosphere (symbol: atm) is a unit of pressure defined as , which is equivalent to 760mm Hg, 29.9212inchesH ...
instead of melting, so it has no melting point. Tungsten has the lowest
coefficient of thermal expansion Thermal expansion is the tendency of matter to change its shape, area, volume, and density in response to a change in temperature, usually not including phase transitions. Temperature is a monotonic function of the average molecular kinetic e ...
of any pure metal. The low thermal expansion and high melting point and
tensile strength In physics, tension is described as the pulling force transmitted axially by the means of a string, a cable, chain, or similar one-dimensional continuous object, or by each end of a rod, truss member, or similar three-dimensional object; tension mig ...
of tungsten originate from strong
metallic bond Metallic bonding is a type of chemical bonding that arises from the electrostatic attractive force between conduction electrons (in the form of an electron cloud of delocalized electrons) and positively charged metal ions. It may be describe ...
s formed between tungsten atoms by the 5d electrons. Alloying small quantities of tungsten with
steel Steel is an alloy of iron with typically a few tenths of a percent of carbon to improve its strength and fracture resistance compared to iron. Many other elements may be present or added. Stainless steels that are corrosion- and oxidation-resis ...
greatly increases its
toughness In materials science and metallurgy, toughness is the ability of a material to absorb energy and plastically deform without fracturing. Tungsten exists in two major
crystalline A crystal or crystalline solid is a solid material whose constituents (such as atoms, molecules, or ions) are arranged in a highly ordered microscopic structure, forming a crystal lattice that extends in all directions. In addition, macrosco ...
forms: α and β. The former has a
body-centered cubic 200px, A network model of a primitive cubic system In crystallography, the cubic (or isometric) crystal system is a crystal system where the unit cell is in the shape of a cube. This is one of the most common and simplest shapes found in crystals an ...
structure and is the more stable form. The structure of the β phase is called A15 cubic; it is
metastable In physics, metastability is a stable state of a dynamical system other than the system's state of least energy. A ball resting in a hollow on a slope is a simple example of metastability. If the ball is only slightly pushed, it will settle back ...
, 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 columnar Crystal habit, habit. The α phase has one third of the electrical resistivity and a much lower superconductivity, superconducting transition temperature TC relative to the β phase: ca. 0.015 K vs. 1–4 K; mixing the two phases allows obtaining intermediate TC values. The TC value can also be raised by alloying tungsten with another metal (e.g. 7.9 K for W-technetium, Tc). Such tungsten alloys are sometimes used in low-temperature superconducting circuits.


Isotopes

Naturally occurring tungsten consists of four stable isotopes (182W, 183W, 184W, and 186W) and one very long-lived radioisotope, 180W. Theoretically, all five can decay into isotopes of element 72 (hafnium) by alpha emission, but only 180W has been observed to do so, with a half-life of years; on average, this yields about two alpha decays of 180W per gram of natural tungsten per year. The other naturally occurring isotopes have not been observed to decay, constraining their half-lives to be at least 4 × 1021 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. All of the remaining radioactive isotopes have half-lives of less than 3 hours, and most of these have half-lives below 8 minutes. Tungsten also has 11 meta states, with the most stable being 179mW (''t''1/2 6.4 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 the trioxide compound tungsten(VI), WO3. It will, however, react directly with fluorine (F2) at room temperature to form tungsten hexafluoride, tungsten(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 is pyrophoric. The most common formal oxidation state of tungsten is +6, but it exhibits all oxidation states from −2 to +6. Tungsten typically combines with oxygen to form the yellow tungsten trioxide, tungstic oxide, WO3, which dissolves in aqueous alkaline solutions to form tungstate ions, . Tungsten carbides (W2C and WC) are produced by heating powdered tungsten with
carbon Carbon (from la, carbo "coal") is a chemical element with the symbol C and atomic number 6. It is nonmetallic and tetravalent—making four electrons available to form covalent chemical bonds. It belongs to group 14 of the periodic table. Car ...
. W2C is resistant to chemical attack, although it reacts strongly with chlorine to form tungsten hexachloride (WCl6). 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 In physics, metastability is a stable state of a dynamical system other than the system's state of least energy. A ball resting in a hollow on a slope is a simple example of metastability. If the ball is only slightly pushed, it will settle back ...
"paratungstate A" anion, , which over time converts to the less soluble "paratungstate B" anion, . Further acidification produces the very soluble metatungstate anion, , after which equilibrium is reached. The metatungstate ion exists as a symmetric cluster of twelve tungsten-oxygen octahedron, octahedra known as the Keggin structure, 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 (chemistry), intercalation compounds with alkali metals. These are known as ''bronzes''; an example is sodium tungsten bronze.


History

In 1781, Carl Wilhelm Scheele discovered that a new acid, tungstic acid, could be made from
scheelite Scheelite is a calcium tungstate mineral with the chemical formula CaWO4. It is an important ore of tungsten (wolfram). Well-formed crystals are sought by collectors and are occasionally fashioned into gemstones when suitably free of flaws. Scheel ...
(at the time tungsten). Scheele and Torbern Bergman suggested that it might be possible to obtain a new metal by reducing this acid. In 1783, Juan José Elhuyar, José and Fausto Elhuyar found an acid made from
wolframite Wolframite, (Fe,Mn)WO4, is an iron manganese tungstate mineral that is the intermediate between ferberite (Fe2+ rich) and hübnerite (Mn2+ rich). Along with scheelite, the wolframite series are the most important tungsten ore minerals. Wolframite i ...
that was identical to tungstic acid. Later that year, at the Real Sociedad Bascongada de Amigos del País, Royal Basque Society in the town of Bergara, Spain, the brothers succeeded in isolating tungsten by reduction of this acid with charcoal, and they are credited with the discovery of the element (they called it "wolfram" or "volfram"). The strategic value of tungsten came to notice in the early 20th century. British authorities acted in 1912 to free the Carrock Fell, Carrock mine from the German owned Cumbrian Mining Company and, during World War I, restrict German access elsewhere. In World War II, tungsten played a more significant role in background political dealings. Portugal, as the main European source of the element, was Portugal during World War II#Wolfram, put under pressure from both sides, because of its deposits of wolframite ore at Panasqueira. 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, both as a constituent of weapons and equipment and employed in production itself, e.g., in tungsten carbide cutting tools for machining steel. Now tungsten is used in many more applications such as aircraft & motorsport ballast weights, darts, anti-vibration tooling, and sporting equipment.


Etymology

The name "tungsten" (which means "heavy stone" in Swedish language, Swedish) is used in English, French, and many other languages as the name of the element, but not in the Nordic countries. "Tungsten" was the old Swedish name for the mineral
scheelite Scheelite is a calcium tungstate mineral with the chemical formula CaWO4. It is an important ore of tungsten (wolfram). Well-formed crystals are sought by collectors and are occasionally fashioned into gemstones when suitably free of flaws. Scheel ...
. "Wolfram" (or "volfram") is used in most European (especially Germanic, Spanish and Slavic) languages and is derived from the mineral
wolframite Wolframite, (Fe,Mn)WO4, is an iron manganese tungstate mineral that is the intermediate between ferberite (Fe2+ rich) and hübnerite (Mn2+ rich). Along with scheelite, the wolframite series are the most important tungsten ore minerals. Wolframite i ...
, which is the origin of the chemical symbol W. 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 Latin "''lupi spuma''", the name Georg Agricola used for the element in 1546, which translates into English as "wolf's froth" and is a reference to the large amounts of tin consumed by the mineral during its extraction.


Occurrence

Tungsten is found mainly in the minerals
wolframite Wolframite, (Fe,Mn)WO4, is an iron manganese tungstate mineral that is the intermediate between ferberite (Fe2+ rich) and hübnerite (Mn2+ rich). Along with scheelite, the wolframite series are the most important tungsten ore minerals. Wolframite i ...
(iron–manganese tungstate (Fe,Mn)WO4, which is a solid solution of the two minerals ferberite FeWO4, and hübnerite MnWO4) and
scheelite Scheelite is a calcium tungstate mineral with the chemical formula CaWO4. It is an important ore of tungsten (wolfram). Well-formed crystals are sought by collectors and are occasionally fashioned into gemstones when suitably free of flaws. Scheel ...
(calcium tungstate (CaWO4). Other tungsten minerals range in their level of abundance from moderate to very rare, and have almost no economical value.


Chemical compounds

image:JAFYAQ.png, upStructure 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 with metal clusters, and very low oxidation states are typically associated with metal carbonyl, CO complexes. The chemistries of tungsten and
molybdenum Molybdenum is a chemical element with the symbol Mo and atomic number 42. The name is from Neo-Latin ''molybdaenum'', which is based on Ancient Greek ', meaning lead, since its ores were confused with lead ores. Molybdenum minerals have been known ...
show 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 in tungsten(VI) oxide (WO3). Tungsten(VI) oxide is soluble in aqueous base (chemistry), base, forming tungstate (WO42−). This oxyanion condenses at lower pH values, forming polyoxometalate, polyoxotungstates. The broad range of oxidation states of tungsten is reflected in its various chlorides: * Tungsten(II) chloride, which exists as the hexamer W6Cl12 * Tungsten(III) chloride, which exists as the hexamer W6Cl18 * Tungsten(IV) chloride, WCl4, a black solid, which adopts a polymeric structure. * Tungsten(V) chloride WCl5, a black solid which adopts a dimeric structure. * Tungsten(VI) chloride WCl6, which contrasts with the instability of MoCl6. Organomolybdenum, Organotungsten compounds are numerous and also span a range of oxidation states. Notable examples include the trigonal prismatic hexamethyltungsten, W(CH3)6 and octahedral tungsten hexacarbonyl, W(CO)6.


Production

The world's reserves of tungsten are 3,200,000 tonnes; they are mostly located in China (1,800,000 t), Canada (290,000 t), Russia (160,000 t), Vietnam (95,000 t) and Bolivia. 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. 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.Tungsten
''Mineral Commodity Summaries''. USGS (2018)
Tungsten is considered to be a conflict mineral due to the unethical mining practices observed in the Democratic Republic of the Congo. There is a large deposit of tungsten ore on the edge of Dartmoor in the United Kingdom, which was exploited during World War I and World War II as the Hemerdon Mine. Following increases in tungsten prices, this mine was reactivated in 2014, but ceased activities in 2018. 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 Carbon (from la, carbo "coal") is a chemical element with the symbol C and atomic number 6. It is nonmetallic and tetravalent—making four electrons available to form covalent chemical bonds. It belongs to group 14 of the periodic table. Car ...
to produce powdered tungsten. 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 Sintering, sintered. During the sintering process, the nickel diffuses into the tungsten, producing an alloy. Tungsten can also be extracted by hydrogen reduction of Tungsten hexafluoride, WF6: :WF6 + 3 H2 → W + 6 HF or pyrolysis, pyrolytic decomposition: :WF6 → W + 3 F2 (heat of reaction, Δ''H''r = +) Tungsten is not traded as a futures contract and cannot be tracked on exchanges like the London Metal Exchange. The tungsten industry often uses independent pricing references such as Argus Media or Metal Bulletin as a basis for contracts. The prices are usually quoted for tungsten concentrate or WO3.Shedd, Kim B. (December 2018
Tungsten
''2016 Minerals Yearbook''. USGS


Applications

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. Because of the high ductile-brittle transition temperature of tungsten, its products are conventionally manufactured through powder metallurgy, spark plasma sintering, chemical vapor deposition, hot isostatic pressing, and thermoplastic routes. A more flexible manufacturing alternative is selective laser melting, which is a form of 3D printing and allows creating complex three-dimensional shapes.


Hard materials

Tungsten is mainly used in the production of hard materials based on tungsten carbide, one of the hardest carbides. WC is an efficient electrical conductor, but W2C is less so. WC is used to make wear-resistant abrasives, and "carbide" cutting tools such as knives, drills, circular saws, reloading ammunition Die (manufacturing), dies, Milling machine, milling and Lathe (metal), turning tools used by the metalworking, woodworking, mining, petroleum and construction industries. Carbide tooling is actually a ceramic/metal composite, where metallic cobalt acts as a binding Metal matrix composite, (matrix) material to hold the WC particles in place. This type of industrial use accounts for about 60% of current tungsten consumption. The jewelry industry makes rings of sintered tungsten carbide, tungsten carbide/metal composites, and also metallic tungsten. WC/metal composite rings use nickel as the metal matrix in place of cobalt because it takes a higher luster when polished. Sometimes manufacturers or retailers refer to tungsten carbide as a metal, but it is a ceramic. 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.


Alloys

The hardness and heat resistance of tungsten can contribute to useful alloys. A good example is high speed steel, which can contain as much as 18% tungsten. Tungsten's high melting point makes tungsten a good material for applications like Rocket engine nozzle, rocket nozzles, for example in the UGM-27 Polaris submarine-launched ballistic missile. Tungsten alloys are used in a wide range of applications, including the aerospace and automotive industries and radiation shielding. Superalloys containing tungsten, such as Hastelloy and Stellite, are used in turbine blades and wear-resistant parts and coatings. Tungsten's heat resistance makes it useful in arc welding applications 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.


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 high remanence and coercivity, as noted by John 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 (but iron is), when it is present in steel in these proportions, it stabilizes the martensite phase, which has greater ferromagnetism than the Allotropes of iron, ferrite (iron) phase due to its greater resistance to Domain wall (magnetism), magnetic domain wall motion.


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 radioactivity is problematic even in depleted form, or where uranium's additional pyrophoric properties are not desired (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. Germany used tungsten during World War II to produce shells for anti-tank gun designs using the Gerlich squeeze bore principle 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 the Wolfram Crisis, limited that effectiveness. 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.


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 scintillator, scintillation detectors in nuclear physics and nuclear medicine. Other salts that contain tungsten are used in the chemical and Tanning (leather), tanning industries. Tungsten oxide (WO3) is incorporated into selective catalytic reduction (SCR) catalysts found in coal-fired power plants. These catalysts convert nitrogen oxides (NOx, 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.


Niche uses

Applications requiring its high density include weights, Mallory metal, counterweights, ballast keels for yachts, tail ballast for commercial aircraft, rotor weights for civil and military helicopters, and as ballast in race cars for NASCAR and Formula One. Depleted uranium is 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 2012 Mars Science Laboratory spacecraft. It is an ideal material to use as a dolly (tool), 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 (to allow for a smaller diameter and thus tighter groupings) or for Fly tying, artificial flys (tungsten beads allow the fly to sink rapidly). Tungsten is also used as a heavy bolt to lower the rate of fire of the Cobray Company, SWD M11/9 sub-machine gun from 1300 RPM to 700 RPM. Tungsten has seen use recently in nozzles for 3D printing; the high wear resistance and thermal conductivity of tungsten carbide improves the printing of abrasive filaments. Some cello C strings are wound with tungsten. The extra density gives this string more projection and often cellists will buy just this string and use it with three strings from a different set. Tungsten is used as an absorber on the electron telescope on the Cosmic Ray System of the two Voyager program, Voyager spacecraft.


Gold substitution

Its density, similar to that of gold, allows tungsten to be used in jewelry as an alternative to
gold Gold is a chemical element with the symbol Au (from la, aurum) and atomic number 79, making it one of the higher atomic number elements that occur naturally. In a pure form, it is a bright, slightly reddish yellow, dense, soft, malleable, and ...
or platinum. Metallic tungsten is hypoallergenic, and is harder than gold alloys (though not as hard as tungsten carbide), making it useful for ring (finger), rings that will resist scratching, especially in designs with a brushed 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 in counterfeiting of gold bars, such as by plating a tungsten bar with gold, which has been observed since the 1980s, or taking an existing gold bar, drilling holes, and replacing the removed gold with tungsten rods. The densities are not exactly the same, and other properties of gold and tungsten differ, but gold-plated tungsten will pass superficial tests. Gold-plated tungsten is available commercially from China (the main source of tungsten), both in jewelry and as bars.


Electronics

Because it retains its strength at high temperatures and has a high
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, elemental tungsten is used in many high-temperature applications, such as Incandescent light bulb, cathode-ray tube, and vacuum tube filaments, heating elements, and rocket engine nozzles. 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 Gas tungsten arc welding (GTAW), also known as tungsten inert gas (TIG) welding, is an arc welding process that uses a non-consumable tungsten electrode to produce the weld. The weld area and electrode are protected from oxidation or other atmosph ...
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 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 Molybdenum is a chemical element with the symbol Mo and atomic number 42. The name is from Neo-Latin ''molybdaenum'', which is based on Ancient Greek ', meaning lead, since its ores were confused with lead ores. Molybdenum minerals have been known ...
) on silicon. The electronic structure of tungsten makes it one of the main sources for X-ray targets,Hasz, Wayne Charles ''et al.'' (August 6, 2002) "X-ray target" and also for shielding from high-energy radiations (such as in the radiopharmaceutical industry for shielding radioactive samples of Fludeoxyglucose (18F), FDG). 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 in plastic composites, which are used as a nontoxic substitute for
lead Lead is a chemical element with the symbol Pb (from the Latin ) and atomic number 82. It is a heavy metal that is denser than most common materials. Lead is soft and malleable, and also has a relatively low melting point. When freshly cut, lead ...
in bullets, lead shot, shot, and radiation shields. Since this element's thermal expansion is similar to borosilicate glass, it is used for making glass-to-metal seals. 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.


Nanowires

Through top-down nanofabrication processes, tungsten nanowires have been fabricated and studied since 2002. 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. Such tungsten nanowires have potential applications in nanoelectronics and importantly as pH probes and gas sensors. In similarity to silicon nanowires, tungsten nanowires are frequently produced from a bulk tungsten precursor followed by a thermal oxidation step to control morphology in terms of length and aspect ratio. Using the Deal–Grove model it is possible to predict the oxidation kinetics of nanowires fabricated through such thermal oxidation processing.


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 of nuclear fusion Fusion power, reactors. It will be used as the plasma-facing material of the divertor in the ITER reactor, and is currently in use in the Joint European Torus, JET test reactor.


Biological role

Tungsten, at atomic number ''Z'' = 74, is the heaviest element known to be biologically functional. It is used by some bacteria and
archaea Archaea ( ; singular archaeon ) constitute a domain of single-celled organisms. These microorganisms lack cell nuclei and are therefore prokaryotes. Archaea were initially classified as bacteria, receiving the name archaebacteria (in the Archae ...
, but not in eukaryotes. For example, enzymes called oxidoreductases use tungsten similarly to
molybdenum Molybdenum is a chemical element with the symbol Mo and atomic number 42. The name is from Neo-Latin ''molybdaenum'', which is based on Ancient Greek ', meaning lead, since its ores were confused with lead ores. Molybdenum minerals have been known ...
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. 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. 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. Acetylene hydratase is an unusual metalloenzyme in 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. 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. In soil, tungsten metal oxidizes to the tungstate anion. It can be selectively or non-selectively imported by some Prokaryote, prokaryotic organisms and may substitute for molybdenum, molybdate in certain enzymes. Its effect on the action of these enzymes is in some cases inhibitory and in others positive. The soil's chemistry determines how the tungsten polymerizes; alkaline soils cause monomeric tungstates; acidic soils cause polymeric tungstates. Sodium tungstate and
lead Lead is a chemical element with the symbol Pb (from the Latin ) and atomic number 82. It is a heavy metal that is denser than most common materials. Lead is soft and malleable, and also has a relatively low melting point. When freshly cut, 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 Reproduction, reproductive ability. Tungsten has been studied as a biological copper metabolic Receptor antagonist, antagonist, in a role similar to the action of molybdenum. It has been found that salts may be used as biological copper chelation chemicals, similar to the tetrathiomolybdates.


In archaea

Tungsten is essential for some archaea. The following tungsten-utilizing enzymes are known: * Aldehyde ferredoxin oxidoreductase (AOR) in ''Thermococcus'' strain ES-1 * Formaldehyde ferredoxin oxidoreductase (FOR) in ''Thermococcus litoralis'' * Glyceraldehyde-3-phosphate ferredoxin oxidoreductase (GAPOR) in ''Pyrococcus furiosus'' A ''wtp'' system is known to selectively transport tungsten in archaea: * WtpA is tungsten-binding protein of ABC transporter, ABC family of transporters * WptB is a permease * WtpC is ATPase


Health factors

Because tungsten is a rare metal and its compounds are generally inert, the effects of tungsten on the environment are limited. 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. The median lethal dose LD50 depends strongly on the animal and the method of administration and varies between 59 mg/kg (intravenous, rabbits) and 5000 mg/kg (tungsten metal powder, Intraperitoneal injection, intraperitoneal, rats). People can be exposed to tungsten in the workplace by breathing it in, swallowing it, skin contact, and eye contact. The National Institute for Occupational Safety and Health (NIOSH) has set a recommended exposure limit (REL) of 5 mg/m3 over an 8-hour workday and a short term limit of 10 mg/m3.


Patent claim

Tungsten is unique amongst the elements in that it has been the subject of patent proceedings. In 1928, a US court rejected General Electric's attempt to patent it, overturning granted in 1913 to William D. Coolidge.


See also

* Field emission gun * Tungsten oxide * List of chemical element name etymologies, List of chemical elements name etymologies * List of chemical elements naming controversies


References


External links


Properties, Photos, History, MSDS




at ''The Periodic Table of Videos'' (University of Nottingham)
Picture in the collection from Heinrich Pniok

Elementymology & Elements Multidict by Peter van der Krogt – Tungsten

International Tungsten Industry Association
{{Authority control Tungsten, Chemical elements Transition metals Biology and pharmacology of chemical elements Refractory metals