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References

Tungsten, also called wolfram, is a chemical element that has the symbol W (German: wolfram) 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, especially the fact that it has the highest melting point of all the non-alloyed metals and the second highest of all the elements after carbon. 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, in X-ray tubes (as both the filament and target), and in superalloys. Tungsten is the only metal from the third transition series that is known to occur in biomolecules.

Notable characteristics

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, extruding, or sintering. Of all metals at temperatures above 1650 °C (3000 °F), this element has the highest melting point (3422 °C) (6192 °F), lowest vapor pressure and the highest tensile strength. Tungsten has the lowest coefficient of thermal expansion of any pure metal. Its corrosion resistance is excellent and most mineral acids can attack it only slightly. Tungsten metal forms a protective oxide when exposed to air but can be oxidized at high temperature. Steel alloyed with small quantities of tungsten greatly increases its toughness.

Application

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 hard metals) 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 wire with a high melting point.

Other uses:
Its high melting point makes tungsten suitable for aerospace 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 armament, heat sinks, and high density applications, such as weights, counterweights, ballast keels for yachts and tail ballast for commercial aircraft. The high density makes it an ideal ingredient for darts, normally 80% and sometimes up to 97%. This allows darts containing tungsten to have a smaller diameter than those of other metals at the same weight, permitting tighter groupings.
High-speed steel contains tungsten and some tungsten steels contain as much as 18% tungsten.
Super alloys containing tungsten are used in turbine blades and wear resistant parts and coatings. Tungsten powder is used as a filler material in plastic composites, which are used as a nontoxic substitute for lead, in bullets, shot, and radiation shields.
Tungsten chemical compounds are used in catalysts, inorganic pigments, and tungsten disulfide high-temperature lubricants which are 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 heavy alloys, used as an alternative to depleted uranium.
Tungsten is used as an interconnect material in integrated circuits. Contact holes are etched in silicon dioxide dielectric material, filled with tungsten and polished to form connections to transistors. Typical contact holes can be as small as 65 nm. Tungsten carbide is one of the hardest carbides and is used in machine tools such as make milling and turning tools, and used together with cobalt and carbon is often the best choice for such applications.
Used extensively for shielding in the radiopharmaceutical industry. It is often employed when transporting individual FDG doses (called 'pigs') - the high energy of fluorine-18 makes lead much less effective.
Tungsten is used in the emitters of focused ion beam and electron microscopes.
Tungsten is also beginning to be used in jewelry. Its hardness makes it ideal for rings that will never scratch, are hypoallergenic and will not need polishing. This property is especially useful in designs with a brushed finish.
Also used in fishing lures like the Mormyshka.
Miscellaneous: Oxides are used in ceramic glazes and calcium/magnesium tungstates are used widely in fluorescent lighting. Crystal tungstates are used as scintillation detectors in nuclear physics and nuclear medicine. 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. Some types of strings for musical instruments are wound with tungsten wire.

Biological role

Tungsten is an essential nutrient for some organisms.
Enzymes called oxidoreductases use tungsten in a way that is similar to molybdenum by using it in a tungsten-pterin complex.
On August 20, 2002, officials representing the U.S.-based Centers for Disease Control and Prevention announced that urine tests on leukemia patient families and control group families in the Fallon, Nevada area had shown elevated levels of the metal tungsten in the bodies of both groups.[4] Sixteen recent cases of cancer in children were discovered in the Fallon area which has now been identified as a cancer cluster, (it should be noted, however, that the majority of the cancer victims are not long time residents of Fallon). Dr. Carol H. Rubin, a branch chief at the CDC, said data demonstrating a link between tungsten and leukemia is not available at present.

Isotopes

Naturally occurring tungsten consists of five isotopes whose half-lives are so long that they can be considered stable. All can decay into isotopes of element 72 (hafnium) by alpha emission; 180W has been observed to have a half life of 1.8 ± 0.2 Ea. The other naturally occurring isotopes have not been observed to decay, constraining their half-lives to be: 182W, T1/2 > 8.3 Ea; 184W, T1/2 > 29 Ea; 185W, T1/2 > 13 Ea; 186W, T1/2 > 27 Ea. [7] On average, two alpha decays of 180W occur in one gram of natural tungsten per year.
27 artificial radioisotopes of tungsten have been characterized, the most stable of which are 181W with a half-life of 121.2 days, 185W with a half-life of 75.1 days, 188W with a half-life of 69.4 days and 178W with a half-life of 21.6 days. All of the remaining radioactive isotopes have half-lives of less than 24 hours, and most of these have half-lives that are less than 8 minutes. Tungsten also has 4 meta states, the most stable being 179mW (t½ 6.4 minutes).