Transition metal
Tungsten (also called wolfram) is a chemical element; it has symbol W (from German: Wolfram) and atomic number 74. It is a metal found naturally on Earth almost exclusively in compounds with other elements. It was identified as a distinct element in 1781 and first isolated as a metal in 1783. Its important ores include scheelite and wolframite, the latter lending the element its alternative name.
The free element is remarkable for its robustness, especially the fact that it has the highest melting point of all known elements, at 3,422 °C (6,192 °F; 3,695 K). It also has the highest boiling point, at 5,930 °C (10,706 °F; 6,203 K). Its density is 19.254 g/cm3, comparable with that of uranium and gold, and much higher (about 1.7 times) than that of lead. Polycrystalline tungsten is an intrinsically brittle and hard material (under standard conditions, when uncombined), making it difficult to work into metal. However, pure single-crystalline tungsten is more ductile and can be cut with a hard-steel hacksaw.
Tungsten occurs in many alloys, which have numerous applications, including incandescent light bulb filaments, X-ray tubes, electrodes in gas tungsten arc welding, superalloys, and radiation shielding. Tungsten's hardness and high density make it suitable for military applications in penetrating projectiles. Tungsten compounds are often used as industrial catalysts. …
In 1781, Carl Wilhelm Scheele discovered that a new acid, tungstic acid, could be made from scheelite (at the time called tungsten). Scheele and Torbern Bergman suggested that it might be possible to obtain a new metal by reducing this acid. In 1783, José and Fausto Elhuyar found an acid made from wolframite that was identical to tungstic acid. Later that year, at the Royal Basque Society in the town of Bergara, Spain, the brothers succeeded in isolating tungsten by reduction of this acid with charcoal, and they are credited with the discovery of the element (they called it "wolfram" or "volfram").
The strategic value of tungsten came to notice in the early 20th century. British authorities acted in 1912 to free the Carrock mine from the German owned Cumbrian Mining Company and, during World War I, restrict German access elsewhere. In World War II, tungsten played a more 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 at Panasqueira. Tungsten's desirable properties such as resistance to high temperatures, its hardness and density, and its strengthening of alloys made it an important raw material for the arms industry, both as a constituent of weapons and equipment and employed in production itself, e.g., in tungsten carbide cutting tools for machining steel. …
In its raw form, tungsten is a hard steel-grey metal that is often brittle and hard to work. Purified, monocrystalline tungsten retains its hardness (which exceeds that of many steels), and becomes malleable enough that it can be worked easily. It can be worked by forging, drawing, rolling, or extruding. Most materials based on tungsten are formed by sintering tungsten powder along with additives, though this results in a more porous final product.
Of all metals in pure form, tungsten has the highest melting point (3,422 °C, 6,192 °F), lowest vapor pressure (at temperatures above 1,650 °C, 3,000 °F), and the highest tensile strength. Although carbon remains solid at higher temperatures than tungsten, carbon sublimes at atmospheric pressure instead of melting, so it has no melting point. Moreover, tungsten's most stable crystal phase does not exhibit any high-pressure-induced structural transformations for pressures up to at least 364 gigapascals. Tungsten has the lowest coefficient of thermal expansion of any pure metal. The low thermal expansion and high melting point and tensile strength of tungsten originate from strong covalent bonds formed between tungsten atoms by the 5d electrons. Alloying small quantities of tungsten with steel greatly increases its toughness.
Tungsten exists in two major crystalline forms: α and β. The former has a body-centered cubic structure and is the more stable form. …
Tungsten is found mainly in the minerals wolframite, scheelite, tuneptite (tungstite) and stolzite. Wolframite is iron–manganese tungstate (Fe,Mn)WO4, a solid solution of the two minerals ferberite (FeWO4) and hübnerite (MnWO4), while scheelite is calcium tungstate (CaWO4). Tungstite is produced through weathering of other tungsten minerals. Stolzite is nominally tetragonal lead tungstate (PbWO4), but often forms clusters with molybdenum. Tungsten ore deposits are predominantly magmatic or hydrothermal in origin and are associated with felsic igneous intrusions. Pure tungsten has thus far not been found in nature.
Even though minerals such as wolframite and scheelite are considered tungsten's main ores, their composition is rarely more than 1.5% tungsten oxide. Tungsten is separated from scheelite ore by froth flotation or gravity separation, since the crystals have a tendency to break apart into fine particles; wolfram is weakly magnetic, and so can be separated by a combination of gravity and magnetic separation methods.
Tungsten is used in pure form and as alloys and compounds for a wide range of purposes. Tungsten carbide and other cemented tungsten carbides make up 60 to 70% of global tungsten usage, and steels and other alloys make up roughly 20 to 30%. The rest of its products in other chemical compounds make up less than 10% of total tungsten usage. Because of the high ductile-brittle transition temperature of tungsten, its products are conventionally manufactured through powder metallurgy, spark plasma sintering, chemical vapor deposition, hot isostatic pressing, and thermoplastic routes. A more flexible manufacturing alternative is selective laser melting, which is a form of 3D printing and allows creating complex three-dimensional shapes.
Tungsten is mainly used in the production of hard materials based on tungsten carbide (WC), one of the hardest carbides. WC is an efficient electrical conductor, but W2C is less so. WC is used to make wear-resistant abrasives, and "carbide" cutting tools such as knives, drills, circular saws, dies, milling and turning tools used by the metalworking, woodworking, mining, petroleum and construction industries. Carbide tooling is actually a ceramic/metal composite, where metallic cobalt acts as a binding (matrix) material to hold the WC particles in place. This type of industrial use accounts for about 60% of current tungsten consumption. …
Naturally occurring tungsten consists of four stable isotopes (182W, 183W, 184W, and 186W) and one very long-lived radioisotope, 180W. Theoretically, all five can decay into isotopes of element 72 (hafnium) by alpha emission, but only 180W has been observed to do so, with a half-life of (1.8±0.2)×1018 years; on average, this yields about two alpha decays of 180W per gram of natural tungsten per year.
Another 34 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, 178W with a half-life of 21.6 days, and 187W with a half-life of 23.72 h. All of the remaining radioactive isotopes have half-lives of less than 3 hours, and most of these have half-lives below 8 minutes. Tungsten also has 12 meta states, with the most stable being 179mW (t1/2 6.4 minutes).
Tungsten, at atomic number Z = 74, is the heaviest element known to be biologically functional. It is used by some bacteria and archaea, but not in eukaryotes. 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. 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 molybdopterin-requiring enzymes. 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. Acetylene hydratase is an unusual metalloenzyme in that it catalyzes a hydration reaction. Two reaction mechanisms have been proposed, in one of which there is a direct interaction between the tungsten atom and the C≡C triple bond. 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.
In soil, tungsten metal oxidizes to the tungstate anion. …