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Tungsten

Tungsten

Gist

Tungsten (symbol W) is a rare, hard, refractory metal with the highest melting point of all elements, making it useful for high-temperature applications like light bulb filaments, heating elements, and tool bits. Also known as wolfram, it is a Group 6 element found naturally in minerals such as wolframite and scheelite. The metal is used in alloys like tungsten carbide, a very hard and wear-resistant material found in industrial cutting tools, drill tips, and even some jewelry.

Tungsten is used in products where extreme heat resistance, hardness, and density are needed. Key applications include light bulb filaments, cutting tools and drill bits made of tungsten carbide, X-ray tubes, electronic components, high-temperature furnace parts, radiation shielding, and alloys for aerospace and automotive components. Its high density and ability to strengthen other metals also make it useful for ballast weights, darts, and jewelry.

Summary

Tungsten (also called wolfram) is a chemical element; it has symbol W (from Latin: Wolframium). Its atomic number is 74. It is a metal found naturally on Earth almost exclusively in compounds with other elements. It was identified as a distinct element in 1781 and first isolated as a metal in 1783. Its important ores include scheelite and wolframite, the latter lending the element its alternative name.

The free element is remarkable for its robustness, especially the fact that it has the highest melting point of all known elements, melting at 3,422 °C (6,192 °F; 3,695 K). It also has the highest boiling point, at 5,930 °C (10,706 °F; 6,203 K). Its density is 19.254 g/{cm}^{3}, comparable with that of uranium and gold, and much higher (about 1.7 times) than that of lead. Polycrystalline tungsten is an intrinsically brittle and hard material (under standard conditions, when uncombined), making it difficult to work into metal. However, pure single-crystalline tungsten is more ductile and can be cut with a hard-steel hacksaw.

Tungsten occurs in many alloys, which have numerous applications, including incandescent light bulb filaments, X-ray tubes, electrodes in gas tungsten arc welding, superalloys, and radiation shielding. Tungsten's hardness and high density make it suitable for military applications in penetrating projectiles. Tungsten compounds are often used as industrial catalysts. Its largest use is in tungsten carbide, a wear-resistant material used in metalworking, mining, and construction. About 50% of tungsten is used in tungsten carbide, with the remaining major use being alloys and steels: less than 10% is used in other compounds.

Tungsten is the only metal in the third transition series that is known to occur in biomolecules, being found in a few species of bacteria and archaea. However, tungsten interferes with molybdenum and copper metabolism and is somewhat toxic to most forms of animal life.

Details

Tungsten (W), chemical element, is an exceptionally strong refractory metal of Group 6 (VIb) of the periodic table, used in steels to increase hardness and strength and in lamp filaments.

Tungsten metal was first isolated (1783) by the Spanish chemists and mineralogists Juan José and Fausto Elhuyar by charcoal reduction of the oxide (WO3) derived from the mineral wolframite. Earlier (1781) the Swedish chemist Carl Wilhelm Scheele had discovered tungstic acid in a mineral now known as scheelite, and his countryman Torbern Bergman concluded that a new metal could be prepared from the acid. The names tungsten and wolfram have been used for the metal since its discovery, though everywhere Jön Jacob Berzelius’s symbol W prevails. In British and American usage, tungsten is preferred; in Germany and a number of other European countries, wolfram is accepted.

Element Properties

atomic number  :  74
atomic weight  :  183.85
melting point  :  3,410 °C (6,152 °F)
boiling point  :  5,660 °C (10,220 °F)
density  :  19.3 grams/{cm}^{3} at 20 °C (68 °F)
oxidation states  :  +2, +3, +4, +5, +6

Occurrence, properties, and uses

The amount of tungsten in Earth’s crust is estimated to be 1.5 parts per million, or about 1.5 grams per ton of rock. China is the dominant producer of tungsten; in 2016 it produced over 80 percent of total tungsten mined, and it contained nearly two-thirds of the world’s reserves. Vietnam, Russia, Canada, and Bolivia produce most of the remainder. Tungsten does not occur as a free metal. It is about as abundant as tin or as molybdenum, which it resembles, and half as plentiful as uranium. Although tungsten occurs as tungstenite—tungsten disulfide, WS2—the most important ores in this case are the tungstates such as scheelite (calcium tungstate, CaWO4), stolzite (lead tungstate, PbWO4), and wolframite—a solid solution or a mixture or both of the isomorphous substances ferrous tungstate (FeWO4) and manganous tungstate (MnWO4).

For tungsten the ores are concentrated by magnetic and mechanical processes, and the concentrate is then fused with alkali. The crude melts are leached with water to give solutions of sodium tungstate, from which hydrous tungsten trioxide is precipitated upon acidification, and the oxide is then dried and reduced to metal with hydrogen.

Tungsten is rather resistant to attack by acids, except for mixtures of concentrated nitric and hydrofluoric acids, and it can be attacked rapidly by alkaline oxidizing melts, such as fused mixtures of potassium nitrate and sodium hydroxide or sodium peroxide; aqueous alkalies, however, are without effect. It is inert to oxygen at normal temperature but combines with it readily at red heat, to give the trioxides, and is attacked by fluorine at room temperature, to give the hexafluorides.

Tungsten metal has a nickel-white to grayish lustre. Among metals it has the highest melting point, at 3,410 °C (6,170 °F), the highest tensile strength at temperatures of more than 1,650 °C (3,002 °F), and the lowest coefficient of linear thermal expansion (4.43 × {10}^{-6} per °C at 20 °C [68 °F]). Tungsten is ordinarily brittle at room temperature. Pure tungsten can, however, be made ductile by mechanical working at high temperatures and can then be drawn into very fine wire. Tungsten was first commercially employed as a lamp filament material and thereafter used in many electrical and electronic applications. It is used in the form of tungsten carbide for very hard and tough dies, tools, gauges, and bits. Much tungsten goes into the production of tungsten steels, and some has been used in the aerospace industry to fabricate rocket-engine nozzle throats and leading-edge reentry surfaces. (For information on the mining, recovery, and applications of tungsten, see tungsten processing.)

Natural tungsten is a mixture of five stable isotopes: tungsten-180 (0.12 percent), tungsten-182 (26.50 percent), tungsten-183 (14.31 percent), tungsten-184 (30.64 percent), and tungsten-186 (28.43 percent). Tungsten crystals are isometric and, by X-ray analysis, are seen to be body-centred cubic.

Compounds

Chemically, tungsten is relatively inert. Compounds have been prepared, however, in which the element has oxidation states from 0 to +6. The states above +2, especially +6, are most common. In the +4, +5, and +6 states, tungsten forms a variety of complexes.

The most important tungsten compound is tungsten carbide (WC), which is noted for its hardness (9.5 on the Mohs scale, where the maximum, diamond, is 10). It is used alone or in combination with other metals to impart wear-resistance to cast iron and the cutting edges of saws and drills. Tungsten also forms hard, refractory, and chemically inert interstitial compounds with boron, nitrogen, and silicon upon direct reaction with those elements at high temperatures.

Additional Information:

Appearance

A shiny, silvery-white metal.

Uses

Tungsten was used extensively for the filaments of old-style incandescent light bulbs, but these have been phased out in many countries. This is because they are not very energy efficient; they produce much more heat than light.

Tungsten has the highest melting point of all metals and is alloyed with other metals to strengthen them. Tungsten and its alloys are used in many high-temperature applications, such as arc-welding electrodes and heating elements in high-temperature furnaces.

Tungsten carbide is immensely hard and is very important to the metal-working, mining and petroleum industries. It is made by mixing tungsten powder and carbon powder and heating to 2200°C. It makes excellent cutting and drilling tools, including a new ‘painless’ dental drill which spins at ultra-high speeds.

Calcium and magnesium tungstates are widely used in fluorescent lighting.

Biological role

Tungsten is the heaviest metal to have a known biological role. Some bacteria use tungsten in an enzyme to reduce carboxylic acids to aldehydes.

Natural abundance

The principal tungsten-containing ores are scheelite and wolframite. The metal is obtained commercially by reducing tungsten oxide with hydrogen or carbon.

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