[47] Tungsten(VI) oxide is soluble in aqueous base, forming tungstate (WO42−). Tungsten is extracted from its ores in several stages. The National Institute for Occupational Safety and Health (NIOSH) has set a recommended exposure limit (REL) of 5 mg/m3 over an 8-hour workday and a short term limit of 10 mg/m3. Tungsten, or wolfram,[8][9] is a chemical element with the symbol W and atomic number 74. Another 30 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.[30] All of the remaining radioactive isotopes have half-lives of less than 3 hours, and most of these have half-lives below 8 minutes. Electrode facings for the welding of stainless steel. Finely divided tungsten is pyrophoric.[31][32]. [19] Although carbon remains solid at higher temperatures than tungsten, carbon sublimes at atmospheric pressure instead of melting, so it has no melting point. 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 radioactivity is problematic even in depleted form, or where uranium's additional pyrophoric properties are not desired (for example, in ordinary small arms bullets designed to penetrate body armor). This, in turn, derives from Latin "lupi spuma", the name Georg Agricola used for the element in 1546, which translates into English as "wolf's froth" and is a reference to the large amounts of tin consumed by the mineral during its extraction.[46]. The values of all these properties are higher for tungsten than they are in the case of molybdenum. The metatungstate ion exists as a symmetric cluster of twelve tungsten-oxygen octahedra known as the Keggin anion. Following increases in tungsten prices, this mine was reactivated in 2014,[54] but ceased activities in 2018.[55]. At elevated temperatures (i.e., when red-hot) it reacts with oxygen to form the trioxide compound tungsten(VI), WO3. [105] The abundance of tungsten in the Earth's crust is thought to be about 1.5 parts per million. [43] In World War II, tungsten played a more significant role in background political dealings. It is also used in gamma imaging as a material from which coded apertures are made, due to its excellent shielding properties. [61] WC/metal composite rings use nickel as the metal matrix in place of cobalt because it takes a higher luster when polished. Its chemical symbol is W. Tungsten has the highest melting point of all metals (3,422± 15°C). The chemistries of tungsten and molybdenum show strong similarities to each other, as well as contrasts with their lighter congener, chromium. [64] 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. WC is used to make wear-resistant abrasives, and "carbide" cutting tools such as knives, drills, circular saws, reloading ammunition dies, milling and turning tools used by the metalworking, woodworking, mining, petroleum and construction industries. As of 2017, China, Vietnam and Russia are the leading suppliers with 79,000, 7,200 and 3,100 tonnes, respectively. [11] Its density is 19.30 times that of water, comparable with that of uranium and gold, and much higher (about 1.7 times) than that of lead. [87] Due to a particularly high surface to volume ratio, the formation of a surface oxide layer and the single crystal nature of such material, the mechanical properties differ fundamentally from those of bulk tungsten. Because the density is so similar to that of gold (tungsten is only 0.36% less dense), and its price of the order of one-thousandth, tungsten can also be used in counterfeiting of gold bars, such as by plating a tungsten bar with gold,[77][78][79] which has been observed since the 1980s,[80] or taking an existing gold bar, drilling holes, and replacing the removed gold with tungsten rods. [12], Tungsten exists in two major crystalline forms: α and β. [101], Tungsten has been studied as a biological copper metabolic antagonist, in a role similar to the action of molybdenum. Tungsten-using enzymes typically reduce carboxylic acids to aldehydes. [37] In 1783, José and Fausto Elhuyar found an acid made from wolframite that was identical to tungstic acid. 0.015 K vs. 1–4 K; mixing the two phases allows obtaining intermediate TC values. Tungsten compounds are also often used as industrial catalysts. [59], 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. [19] Lead was found to be lethal at low levels and sodium tungstate was much less toxic, but the tungstate completely inhibited their reproductive ability. Tungsten features the lowest vapour pressure of all metals, very high moduli of compression and elasticity, very high thermal creep resistance and high thermal and electrical conductivity. Less than 10% is used in other chemical compounds. [113][114][115], This article is about the chemical element. Its electrical conductivity at 0°C is about 28% of that of silver, which itself has the highest conductivity, and its coefficient of thermal expansion is the lowest of all metals. [81] The densities are not exactly the same, and other properties of gold and tungsten differ, but gold-plated tungsten will pass superficial tests.

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