Properties and Uses
Pure tungsten is a shiny white metal and in its purest form is quite pliant and can easily be processed. However, it usually contains small amounts of carbon and oxygen, which give tungsten metal its considerable hardness and brittleness.
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 (Manganese Tungstate) is called Hübnerite.
Tungsten is the heaviest engineering material with a density of 19.25 g/cm3.
It has the highest melting point of all metals at 3410∞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 (4.4 x 10-6 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.
Environmentally friendly, does not break down or decompose.
Due to the unique properties of tungsten, tungsten alloys and some tungsten compounds listed above, the metal cannot be substituted in many important applications in different fields of modern technology.
Tungsten is an additive in the production of specialty alloys; filament wire for lighting (2%); and specialty uses for mobile phone handsets, military, ballistics (defense equipment) automotive parts, aerospace components, drilling, boring & cutting equipment, logging equipment, electrical & electron- ics appliances, chemical applications and other end-uses.
Today, the majority of tungsten is used in manufacturing cemented carbides or hard metals. These are materials made by cementing tungsten carbide grains in a binder matrix of a tough nickel or cobalt alloy using the process of sintering. Tungsten carbide is the most popularly used form of the product which has hardness close to diamond. It is denser than steel and titanium, twice as hard as any steel grade, and has extremely high wear resistance. Due to these characteristics, the product is widely used in construction, metalworking applications and mining. The global mining industry’s usage of tungsten carbide as drilling, boring, and cutting tools will likely propel the tungsten market growth as the demand for precious metals in China and other developing countries increases.
Also, pure tungsten metal products used in the electronics industry such as electrodes, lighting filaments, electrical and electronic contacts, sheets, wires, rods, etc. will be a major factor driving the mill tungsten market growth, not to mention, future applications of tungsten that are being developed as an alternative to lead.
Filaments for electric lamps – electrical and electronic contacts, wire, rods and so on.
Inert gas welding electrodes.
Metal evaporation work.
As an alloy (steels) it is used for high-speed steel tools, weights and counterbalances, radiation shielding, cutting/grinding tools.
Electronic applications such as electric contacts points for automobile distributors, heat sinks, electrochemical machining and electrodes for electrical-discharge machining (EDM).
Windings and heating elements for electric furnaces.
Space missiles, rocket nozzles and high-temperature applications as a coating.
As yarn it is used for reinforcement in metal, ceramic and plastic composites.
Magnetrons for microwave ovens.
Metalworking, mining, cutting tools bits, heat- and erosion-resistant parts, coatings, seal rings and petroleum.
Calcium and magnesium tungstates are widely used in fluorescent lighting.
Other tungsten salts are used in tanning industries.
Tungsten disulphide is used as a dry high temperature lubricant (stable to 500∞C).
Tungsten bronzes and other compounds are used as pigments for paints.