tungsten

—tungstenic /tung sten"ik/, adj.

/tung"steuhn/, n. Chem.

a rare, metallic element having a bright-gray color, a metallic luster, and a high melting point, 3410° C, and found in wolframite, tungstite, and other minerals: used in alloys of high-speed cutting tools, electric-lamp filaments, etc. Symbol: W; at. wt.: 183.85; at. no.: 74; sp. gr.: 19.3. Also called wolfram.

[1760-70; < Sw, equiv. to tung heavy + sten stone]

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or wolfram

Metallic chemical element, one of the transition elements, chemical symbol W, atomic number 74.

Exceptionally strong, white to grayish, and brittle, it has the highest melting point (6,170 °F [3,410 °C]), greatest high-temperature strength, and lowest thermal expansion coefficient of any metal. Its chief uses are in steels to increase hardness and strength and in lightbulb filaments (see incandescent lamp). It is also used in electrical contacts, rocket nozzles, chemical apparatus, high-speed rotors, and solar-energy devices. Tungsten is relatively inert, but compounds (in which it has various valences) are known. The most important, tungsten carbide, noted for its hardness, is used to increase the wear-resistance of cast iron and of tools' cutting edges.

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▪ chemical element

Introduction

also called  wolfram 

 chemical element, 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 (Elhuyar, Fausto) by charcoal reduction of the oxide (WO₃) derived from the mineral wolframite. Earlier (1781) the Swedish chemist Carl Wilhelm Scheele (Scheele, Carl Wilhelm) had discovered tungstic acid in a mineral now known as scheelite, and his countryman Torbern Bergman (Bergman, Torbern Olof) had 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' symbol W prevails. In British and American usage tungsten is preferred; in Germany and a number of other European countries wolfram is accepted.

Occurrence, properties, and uses

      The amount of tungsten in the Earth's crust is estimated to be 1.5 parts per million, or about 1.5 grams per ton of rock. It does not occur as a free metal. Tungsten 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, 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). 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 (filament lamp) 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 (26.3 percent), tungsten-183 (14.28 percent), tungsten-184 (30.7 percent), and tungsten-186 (28.6 percent). Tungsten crystals are isometric and, by X-ray analysis, are seen to be body-centric-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). 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.

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 g/cm³ (20° C)

oxidation states

+2, +3, +4, +5, +6

electronic config.

[Xe]4f¹⁴5d⁴6s²

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