tungsten ore - 06

A steel-gray metal under standard conditions when uncombined, tungsten is found naturally on Earth only combined in chemical compounds. Its important ores include wolframite and scheelite. The free element 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. Also remarkable is its very high density of 19.3 times that of water. This density is slightly more than that of uranium and 71% more than that of lead.[3] Tungsten with minor amounts of impurities is often brittle[4] and hard, making it difficult to work. However, very pure tungsten is more ductile, and can be cut with a hacksaw.[5]

Detailed description

This density is slightly more than that of uranium and 71% more than that of lead.[3] Tungsten with minor amounts of impurities is often brittle[4] and hard, making it difficult to work. However, very pure tungsten is more ductile, and can be cut with a hacksaw.[5]
The unalloyed elemental form is used mainly in electrical applications. Tungsten's many alloys have numerous applications, most notably in incandescent light bulb filaments, X-ray tubes (as both the filament and target), and superalloys. Tungsten's hardness and high density give it military applications in penetrating projectiles. Tungsten compounds are most often used industrially as catalysts.
Tungsten is the only metal from the third transition series that is known to occur in biomolecules, and is the heaviest element known to be used by living organisms.[6][7]

History
In 1781, Carl Wilhelm Scheele discovered that a new acid, tungstic acid, could be made from scheelite (at the time named tungstenite). Scheele and Torbern Bergman suggested that it might be possible to obtain a new metal by reducing this acid.[8] In 1783, José and Fausto Elhuyar found an acid made from wolframite that was identical to tungstic acid. Later that year, in Spain, the brothers succeeded in isolating tungsten by reduction of this acid with charcoal, and they are credited with the discovery of the element.[9][10]
In World War II, tungsten played a significant role in background political dealings. Portugal, as the main European source of the element, was put under pressure from both sides, because of its deposits of wolframite ore. Tungsten's resistance to high temperatures and its strength in alloys made it an important raw material for the weaponry industry.[11]
Characteristics
Physical properties
In its raw form, tungsten is a steel-gray metal that is often brittle and hard to work, but, if pure, it can be worked easily.[5] It is worked by forging, drawing, extruding or sintering. Of all metals in pure form, tungsten has the highest melting point (3,422 °C, 6,192 °F), lowest vapor pressure and (at temperatures above 1,650 °C, 3,000 °F) the highest tensile strength.[13] Tungsten has the lowest coefficient of thermal expansion of any pure metal. The low thermal expansion and high melting point and strength of tungsten are due to strong covalent bonds formed between tungsten atoms by the 5d electrons.[14] Alloying small quantities of tungsten with steel greatly increases its toughness.[3]
Occurrence
Tungsten is found in the minerals wolframite (iron-manganese tungstate, (Fe,Mn)WO4), scheelite (calcium tungstate, (CaWO4), ferberite (FeWO4) and hübnerite (MnWO4). China produced over 75% of this total, with most of the remaining production coming from Austria, Bolivia, Portugal, Russia, and Colombia.[20] Wolframite is also considered to be a conflict mineral due to the unethical mining practices observed in the Democratic Republic of the Congo.[citation needed]
Biological role
Tungsten, at atomic number 74, is the heaviest element known to be biologically functional, with the next heaviest being iodine (Z = 53). Although not in eukaryotes, tungsten is used by some bacteria. For example, enzymes called oxidoreductases use tungsten similarly to molybdenum by using it in a tungsten-pterin complex with molybdopterin (molybdopterin, despite its name, does not contain molybdenum, but may complex with either molybdenum or tungsten in use by living organisms). Tungsten-using enzymes typically reduce carboxylic acids to aldehydes.[21] However, the tungsten oxidoreductases may also catalyse oxidations. The first tungsten-requiring enzyme to be discovered also requires selenium, and in this case the tungsten-selenium pair may function analogously to the molybdenum-sulfur pairing of some molybdenum cofactor-requiring enzymes.[22] One of the enzymes in the oxidoreductase family which sometimes employ tungsten (bacterial formate dehydrogenase H) is known to use a selenium-molybdenum version of molybdopterin.[23] Although a tungsten-containing xanthine dehydrogenase from bacteria has been found to contain tungsten-molydopterin and also non-protein bound selenium, a tungsten-selenium molybdopterin complex has not been definitively described.[24]
Other effects on biochemistry
In soil, tungsten metal oxidizes to the tungstate anion. It may substitute for molybdenum in certain enzymes, and in such cases the resulting enzyme in eukaryotes would presumably be inert. The soil's chemistry determines how the tungsten polymerizes; alkaline soils cause monomeric tungstates; acidic soils cause polymeric tungstates.[25]
Sodium tungstate and lead have been studied for their effect on earthworms. Lead was found to be lethal at low levels and sodium tungstate was much less toxic, but the tungstate completely inhibited their reproductive ability.[26]
Production
From its ores, about 37,400 tonnes of tungsten concentrates are produced per year in 2000.[20] Tungsten is extracted from its ores in several stages. The ore is eventually converted to tungsten(VI) oxide (WO3), which is heated with hydrogen or carbon to produce powdered tungsten.[8] It can be used in that state or pressed into solid bars.
Tungsten can also be extracted by hydrogen reduction of WF6:
WF6 + 3 H2 → W + 6 HF
or pyrolytic decomposition:[28]
WF6 → W + 3 F2 (ΔHr = +)
Tungsten is not traded as a futures contract and cannot be tracked on exchanges like the London Metal Exchange. The price for pure metal is around $20,075 per tonne as of October 2008.[29]
Applications

Approximately half of the tungsten is consumed for the production of hard materials (tungsten carbide), with the remaining major use being its use in alloys and steels. Less than 10% is used in chemical compounds.[30]
Hard materials
Tungsten is mainly used in the production of hard materials based on tungsten carbide, one of the hardest carbides, with a melting point of 2770 °C for. WC is an efficient electrical conductor, but W2C is less so. WC is used to make wear-resistant abrasives and cutters and knives for drills, circular saws, milling and turning tools used by the metalworking, woodworking, mining, petroleum and construction industries[3] and accounts for about 60% of current tungsten consumption.[31]
Alloys
The hardness and density of tungsten are applied in obtaining heavy metal alloys. A good example is high speed steel, which can contain as much as 18% tungsten.[32] Tungsten's high melting point makes tungsten a good material for applications like rocket nozzles, for example in the UGM-27 Polaris Submarine-launched ballistic missile.[33] Superalloys containing tungsten, such as Hastelloy and Stellite, are used in turbine blades and wear-resistant parts and coatings.
In armaments, tungsten, usually alloyed with nickel and iron or cobalt to form heavy alloys, is used in kinetic energy penetrators as an alternative to depleted uranium, in applications where uranium's additional pyrophoric properties are not required (for example, in ordinary small arms bullets designed to penetrate body armor). Similarly, tungsten alloys have also been used in cannon shells, grenades and missiles, to create supersonic shrapnel.