Tungsten

From ArticleWorld

Tungsten is a chemical element with the symbol W, atomic number 74 and atomic weight 183.85. It is a hard, grey element occurring in the transition series of the periodic table. Since it is a metallic substance, it is lustrous and heavy with a specific gravity of 19.3 – almost twice that of lead. The pure form of tungsten is used in many electrical devices.

Characteristics of tungsten metal

Greyish and hard, this metal can be worked on by forging or extrusion. The impure form is brittle. The melting point is 3422°C and the boiling point is 5555°C. Of all metals, this has the highest values of melting and boiling points. The vapour pressure is the lowest and the tensile strength is highest among all metals. Tungsten is highly resistant to corrosion since an oxide layer that forms on its surface prevents attacks by mineral acids.

Uses of tungsten

Tungsten has a great number of applications. It is used in metal-working, mining and construction as tungsten carbide (W2C or WC), which is used to make wear-resistant materials called cement carbides. The most common use of tungsten is as the filament of a light bulb. It is also used in electrical furnaces. High-density applications such as those in military technology require tungsten to be used.

Turbine blades and certain coatings on heavy-equipment surfaces are made using tungsten. Other important uses of tungsten include glass-to-metal sealing (since tungsten expands at the same rate as glass), jewellery (because of its lustre) and as calcium or magnesium tungstate in fluorescent lighting.

History of tungsten

Tungsten was discovered by Peter Woulfe in 1779, although sometimes Carl Scheel is also credited with the discovery in 1781. It was found to be present in wolframite, an important ore of the element. In 1783, Spanish chemists Jose and Fausto Elhugar claimed to have isolated the element from the ore. Tungsten was widely used for the manufacture of armaments and in World War – II. Apart from wolframite, tungsten was discovered in scheelite (calcium tungstate), huebnerite and ferberite. Huge deposits of these ores have been located in the United States, China, Russia and Australia.

Today, tungsten is obtained from its ores by an initial reaction with sodium carbonate. The resulting sodium tungstate is treated with hydrochloric acid to form tungstic acid. Tungstic acid is then washed and dried to yield the oxide, which is further reduced to pure tungsten by heating in an atmosphere of hydrogen.