Tungsten, or Wolfram, a silver-white metallic chemical element. Tungsten is the name for the element in the United States and Great Britain; wolfram is the name used in most of the rest of the world.
Tungsten is one of the densest and hardest of the metals; it has the highest melting point of any pure metal. It can be drawn out into fine wire. Annealed tungsten wire has extremely high tensile strength. Chemically, tungsten is relatively inert. At ordinary temperatures it is not easily attacked by alkalies or acids, including aqua regia. It does not oxidize at temperatures of less than 750 F. (400 C.).
Pure tungsten is used in the filaments of light bulbs and for the targets in X-ray tubes. Most tungsten, however, is used in the production of extremely hard tool steels, sometimes called tungsten steels. Nonferrous alloys composed of various percentages of tungsten, copper, and nickel are used in radiation shielding. Tungsten carbide is used as an abrasive and in the manufacture of drill bits. A minor use of tungsten is in chemical compounds, such as sodium tungstate, used to flameproof cloth.
The primary tungsten ores are wolframite, a mineral composed of tungsten, iron, manganese, and oxygen; and scheelite, a mineral composed of tungsten, calcium, and oxygen. Wolframite is treated with sodium carbonate to produce soluble sodium tungstate, which is then converted into tungstic acid. Scheelite is converted directly into tungstic acid by being treated with hydrochloric acid. Further metallurgical treatments convert the tungstic acid into tungstic oxide. Reduction at 1,500 to 1,800 F. (800 to 1,000 C.) in a hydrogen atmosphere produces purified tungsten metal in powdered form.
Because of its extremely high melting point, tungsten is difficult to melt and cast like other metals. It is worked primarily with the techniques of powder metallurgy. More than half of the world's estimated reserves of tungsten are in China, which is also the leading producer. Normally, China accounts for more than half of the world's output. the list of other leading producers changes often as the world price of tungsten changes. It usually includes Russia, Austria, Portugal, Peru, South Korea, and Bolivia.
Tungsten was discovered in 1783 by the D'Elhuyar brothers, Spanish mineralogists working in Germany.
Symbol: W. Atomic number: 74. Atomic weight: 183.85. Specific gravity: 19.3. Melting point: 6,170 F. (3,410 C.). Boiling point: 10,220 F. (5,660 C.). Tungsten has five stable isotopes—W-180, W-182, W-183, W-184, and W-186. It belongs to Group VI-B of the Periodic Table and has a valence of +2, 3, 4, 5, or 6.