Tungsten

Notable Characteristics

Pure tungsten is a steel-gray to tin-white hard metal. Tungsten can be cut with a hacksaw when it is very pure (it is brittle and hard to work when impure) and is otherwise worked by forging, drawning, or extruding. This element has the highest melting point (3422 °C), lowest vapor pressure and the highest tensile strength at temperatures above 1650 °C of all metals. Its corrosion resistance is excellent and it can only be attacked slightly by most mineral acids. Common oxidation states of tungsten are +2, +3, +4, +5, +6, but it exhibits all oxidation states from -2 to 6. Tungsten metal forms a protective oxide when exposed to air. When alloyed in small quantities with steel, it greatly increases its hardness.

Applications

Tungsten is a metal with a wide range of uses, the largest of which is as tungsten carbide (W₂C, WC) in cemented carbides. Cemented carbides (also called hardmetals) are wear-resistant materials used by the metalworking, mining, and petroleum and construction industries. Tungsten is widely used in light bulb and television tube filaments, as well as electrodes, because it can be drawn into very thin metal wires that have have a high melting point. Other uses;

• A high melting point also makes tungsten suitable for space-oriented and high temperature uses which include electrical, heating, and welding applications.
• Hardness and density properties make this metal ideal for making heavy metal alloys that are used in armaments, heat sinks[?], and high-density applications, such as weights and counterweights.
• High speed tool steels (Hastelloy ®, Stellite ®) are often alloyed with tungsten, with tungsten steels containing as much as 18% tungsten.
• Superalloys containing this metal are used in turbine blades, tool steels, and wear-resistant alloy parts and coatings.
• Composites are used as a substitute for lead in bullets and shot.
• Tungsten chemical compounds are used in catalysts, inorganic pigments, and tungsten disulfide high-temperature lubricants which is stable to 500 °C.
• Since this element's thermal expansion is similar to borosilicate glass, it is used for making glass-to-metal seals.

Miscellaneous: Oxides are used in ceramic glazes and calcium/magnesium tungstates are used widely in fluorescent lighting. The metal is also used in X-ray targets, heating elements for electrical furnaces. Salts that contain tungsten are used in the chemical and tanning industries. Tungsten 'bronzes' (so called due to the colour of the tungsten oxides) along with other compounds are used in paints.

History

Tungsten (Swedish tung sten meaning "heavy stone") was first hypothesized to exist by Peter Woulfe[?] in 1779 who examined wolframite[?] (which was later named for Woulfe) and concluded that it must contain a new substance. In 1781 Carl Wilhelm Scheele ascertained that a new acid could be made from tungstenite. Scheele and Berman suggested that it could be possible to obtain a new metal by reducing tungstic acid. José[?] and Fausto Elhuyar[?] found an acid in wolframite that was identical to the tungstic acid in 1783. In Spain later that year the brothers succeeded in isolating tungsten through reduction of this acid with charcoal. They are credited for the discovery of the element.

Biological Role

Enzymes called oxidoreductases[?] use tungsten in a way that is similar to molybdenum by using it in a tungsten-pterin[?] complex.

Occurrence

Tungsten is found in the minerals wolframite (iron-manganese tungstate, FeWO₄/MnWO₄) , scheelite[?] (calcium tungstate, CaWO₄), ferberite[?] and huebnerite[?]. Important deposits of these minerals are in Bolivia, California, China, Colorado, Portugal, Russia, and South Korea (with China producing about 75% of the world's supply). The metal is commercially produced by reducing tungsten oxide with hydrogen or carbon.

Isotopes

Naturally occurring tungsten is made of three stable isotopes and two radioisotopes that have such absurdly long half lifes that for most practical purposes are considered stable. In addition to this, there are twenty-one unstable isotopes with W-181 being the longest lived (t_½ = 121.2 days).

External Links

• WebElements.com - Tungsten (http://www.webelements.com/webelements/elements/text/W/index.html)
• EnvironmentalChemistry.com - Tungsten (http://environmentalchemistry.com/yogi/periodic/W.html)

Common misspelling and questions (FAQ)

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