![]() This rate is equivalent to a specific activity of roughly 63 micro- becquerel per kilogram. 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 ☐.2) ×10 18 years on average, this yields about two alpha decays of 180W per gram of natural tungsten per year. Naturally occurring tungsten consists of four stable isotopes ( 182W, 183W, 184W, and 186W) and one very long-lived radioisotope, 180W. Such tungsten alloys are sometimes used in low-temperature superconducting circuits. The T C value can also be raised by alloying tungsten with another metal (e.g. 1–4 K mixing the two phases allows obtaining intermediate T C values. The α phase has one third of the electrical resistivity and a much lower superconducting transition temperature T C relative to the β phase: ca. Contrary to the α phase which crystallizes in isometric grains, the β form exhibits a columnar habit. The structure of the β phase is called A15 cubic it is metastable, but can coexist with the α phase at ambient conditions owing to non-equilibrium synthesis or stabilization by impurities. The former has a body-centered cubic structure and is the more stable form. Tungsten exists in two major crystalline forms: α and β. Īlloying small quantities of tungsten with steel greatly increases its toughness. The low thermal expansion and high melting point and tensile strength of tungsten originate from strong metallic bonds formed between tungsten atoms by the 5d electrons. Tungsten has the lowest coefficient of thermal expansion of any pure metal. Moreover, tungsten's most stable crystal phase does not exhibit any high-pressure-induced structural transformations for pressures up to at least 364 gigapascals. Although carbon remains solid at higher temperatures than tungsten, carbon sublimes at atmospheric pressure instead of melting, so it has no melting point. Of all metals in pure form, tungsten has the highest melting point (3,422 ☌, 6,192 ☏), lowest vapor pressure (at temperatures above 1,650 ☌, 3,000 ☏), and the highest tensile strength. It is worked by forging, drawing, or extruding but it is more commonly formed by sintering. Purified, monocrystalline tungsten retains its hardness (which exceeds that of many steels), and becomes malleable enough that it can be worked easily. In its raw form, tungsten is a hard steel-grey metal that is often brittle and hard to work. However, tungsten interferes with molybdenum and copper metabolism and is somewhat toxic to most forms of animal life. Tungsten is the only metal in the third transition series that is known to occur in biomolecules, being found in a few species of bacteria and archaea. Tungsten compounds are often used as industrial catalysts. Tungsten's hardness and high density make it suitable for military applications in penetrating projectiles. 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. However, pure single-crystalline tungsten is more ductile and can be cut with a hard-steel hacksaw. ![]() Polycrystalline tungsten is an intrinsically brittle and hard material (under standard conditions, when uncombined), making it difficult to work into metal. Its density is 19.30 grams per cubic centimetre (0.697 lb/cu in), comparable with that of uranium and gold, and much higher (about 1.7 times) than that of lead. The free element is remarkable for its robustness, especially the fact that it has the highest melting point of all known elements, melting at 3,422 ☌ (6,192 ☏ 3,695 K). Its important ores include scheelite and wolframite, the latter lending the element its alternate name. It was identified as a new element in 1781 and first isolated as a metal in 1783. Tungsten is a rare metal found naturally on Earth almost exclusively as compounds with other elements. Tungsten (also called wolfram) is a chemical element with the symbol W and atomic number 74.
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