Properties and Uses

Pure tungsten is a shiny white metal and in its purest form is quite pliant and can easily be processed. Usually, however, it contains small amounts of carbon and oxygen, which give tungsten metal its considerable hardness and brittleness.

Today, the main use of tungsten is in the manufacture of cemented carbides.

Cemented carbides, or hardmetals as they are often called, are materials made by "cementing" very hard tungsten monocarbide (WC) grains in a binder matrix of tough cobalt metal by liquid phase sintering which results in a hardness close to diamond.

Tungsten features the lowest vapour pressure of all metals, very high moduli of compression and elasticity, very high thermal creep resistance, high thermal and electrical conductivity and, last but not least, a very high coefficient of electron emission. The latter can even be improved by alloying tungsten with certain metal oxides.

Most of these unusual properties are due to the half-filled 5d electron shell with a very high binding energy of the tungsten metal lattice. Based on these properties, tungsten, tungsten alloys and some tungsten compounds cannot be substituted in many important applications in different fields of modern technology.

Tungsten occurs in the natural state only in the form of chemical compounds with other elements. Although more than 20 tungsten bearing minerals are known, only two of them are important for industrial use, namely wolframite and scheelite.

Pure scheelite has blue-white fluorescence in ultraviolet light, a property which is utilised in prospecting.

Wolframite is a general term for iron and manganese tungstates where the iron/manganese ratio can vary. A mineral with more than 80% FeWO4 is called Ferberite and a mineral with more than 80% MnWO4 is called Hübnerite.

Fast facts

  • Tungsten is the heaviest engineering material with a density of 19.25 g/cm3.
  • It has the highest melting point of all metals at around 3400°C with a boiling point of 5700°C.
  • It has the lowest vapour pressure of all metals.
  • It has the highest modulus of elasticity of the metals (E = 400GPa).
  • It is the hardest pure metal.
  • Excellent high temperature strength characteristics.
  • It has the highest tensile strength at temperatures above 1650°C.
  • It has a low thermal expansion co-efficient (4.4x10-6 m/m/°C) similar to that of borosilicate glass, and therefore makes it useful for glass to metal seals.
  • It does not oxidise in air and needs no protection from oxidation at elevated temperatures.
  • Its corrosion resistance is excellent, and it is not attacked by nitric, hydrofluoric, or sulphuric acid solutions.

Uses

  • Tungsten has many diverse commercial, industrial, and military applications. The most memorable for the layman would be the light bulb filament.
  • The largest use, accounting for more than 50% of demand is in cemented carbide (or hardmetals as they are often called) – wear resistant materials used by the metalworking, mining, oil, and construction industries.
  • Steels and alloys represent approximately 25% of global tungsten consumption and tungsten is found in tool, stainless and full alloy steels, as well as super alloys.
  • Mill products manufactured from tungsten metal are mainly used in the lamp industry and for electrical and electronic contacts.
  • Chemical applications and products, such as catalysts and pigments, account for the remaining  tungsten demand.