Tungsten - Definition
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Tungsten - Description :
Tungsten (formerly wolfram) is a chemical element in the periodic table that has the symbol W (L. wolframium) and atomic number 74. A very hard, heavy, steel-gray to white transition metal, tungsten is found in several ores including wolframite and scheelite and is remarkable for its robust physical properties. The pure form is used mainly in electrical applications but its many compounds and alloys are widely used in many applications (most notably in light bulb filaments and in space-age superalloys).
Pure tungsten is steel-gray to tin-white and is a 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, drawing, or extruding. This element has the highest melting point (3422 °C) (6192 °F) , lowest vapor pressure and the highest tensile strength at temperatures above 1650 °C (3000 °F) of all metals. Its corrosion resistance is excellent and it can only be attacked slightly by most mineral acids. Tungsten metal forms a protective oxide when exposed to air but can be oxidized at high temperature. 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, petroleum and construction industries. Tungsten is widely used in light bulb and vacuum tube filaments, as well as electrodes, because it can be drawn into very thin metal wires that 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, notably in the GTAW process (also called TIG welding).
* 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.
* The high density makes it an ideal ingredient for darts, sometimes up to 80%.
* 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 (930 °F).
* Since this element's thermal expansion is similar to borosilicate glass, it is used for making glass-to-metal seals.
* It is used in kinetic energy penetrators, usually alloyed with nickel and iron or cobalt to form tungsten heavy alloys, as an alternative to depleted uranium.
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 and 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. Tungsten Carbide has recently been used in the fashioning of jewelry due to its hypoallergenic nature and the fact that due to its extreme hardness it is not apt to lose its luster like other polished metals. |
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