Where Found (Encyclopedia of Global Resources)
Primary Uses (Encyclopedia of Global Resources)
Tungsten’s hardness and ability to impart that hardness to alloys makes it widely used in cutting materials and wear-resistant materials. Tungsten’s high density, high melting point, high thermal and electrical conductivities, and resistance to corrosion also make it useful in many military and industrial applications. Perhaps its most widely known use, however, is as a filament in incandescent lightbulbs.
(The entire section is 61 words.)
Technical Definition (Encyclopedia of Global Resources)
Tungsten (chemical element W, atomic number 74) belongs to Group VIB as a transition element in the periodic table of the elements. It has five naturally occurring isotopes: 180 (0.14 percent), 182 (25.41 percent), 183 (14.40 percent), 184 (30.64 percent), and 186 (28.41 percent). It has an average atomic weight of 183.85. Tungsten resembles the other members of the Group VIB family, chromium and especially molybdenum, in its chemical and physical properties. A hard, brittle metal, tungsten has a density of 19.3 grams per cubic centimeter. It has the highest melting point of any metal at 3,410° Celsius and a boiling point of 5,930° Celsius.
(The entire section is 90 words.)
Description, Distribution, and Forms (Encyclopedia of Global Resources)
Tungsten makes up about 0.01 percent of the Earth’s crust, ranking twenty-sixth in abundance. Although about 60 percent of the known reserves are in China, tungsten is mined in many countries, including the United States, Russia, and Canada. The four main tungsten ores—scheelite, ferberite, huebnerite, and wolframite—are all found in igneous rock. Tungsten is usually found as a trioxide combined with oxides of iron, manganese, calcium, and to a lesser extent lead or copper. Scheelite is calcium tungstate (CaWO4), while the other three are combinations of iron tungstate (FeWO4) and manganese tungstate (MnWO4).
Tungsten has no known biological activity in humans or in animals. In some bacteria, such as C. thermoaceticum and C. formicoaceticum, enzymes incorporate tungsten. In E. coli tungsten acts as an antagonist of molybdenum. However, tungsten in general has minimal effect on living tissue. Because of its limited biological impact, there is little concern for the impact of tungsten on the environment. In 2008, about 55,000 metric tons of tungsten were produced. The United States consumed more than 14,000 metric tons.
(The entire section is 172 words.)
History (Encyclopedia of Global Resources)
Tungsten was discovered twice. In 1781, the Swedish chemist Carl Wilhelm Scheele found tungstic acid in the mineral now called scheelite. Scheelite had been called tungsten after the Swedish words tung (heavy) and sten (stone). In 1783, the Spanish brothers Juan José and Fausto Elhuyar isolated a metal from the mineral wolframite, and its name became wolfram. The symbol W comes from wolfram. The name wolframite apparently comes from its wolflike nature—in that it devours tin during the tin-smelting process. Wolframite inhibits the reduction of tin oxides to tin during smelting. The brothers later showed that their wolfram and Scheele’s tungsten were the same.
Although tungsten’s hardness was noticed, and experimentation that led to hard alloys was begun by the Elhuyar brothers, tungsten tool steel came to public notice only in 1900, and cemented tungsten carbide only in the 1920’s. By 1909 a powder metallurgy had been developed to form tungsten filaments for electric lamps.
(The entire section is 154 words.)
Obtaining Tungsten (Encyclopedia of Global Resources)
Tungsten metal is produced in a reduction of tungsten trioxide by heating with hydrogen at 850° Celsius. The tungsten trioxide is formed from tungstic acid (hydrous tungsten trioxide) by roasting. Tungstic acid is produced by different methods determined by the ore to be refined. Wolframite is converted to soluble alkali tungstate either by fusing with sodium hydroxide and leaching the cooled product with water or by protracted boiling with aqueous alkali. Tungstic acid is then precipitated by reaction with hydrochloric acid. Another method begins with scheelite, which is converted to insoluble tungstic acid by treatment with hydrochloric acid and then separated from the soluble salts of other metals.
(The entire section is 107 words.)
Uses of Tungsten (Encyclopedia of Global Resources)
Perhaps the most important use of tungsten to the everyday person in the United States is as incandescent lamp filaments. Since 1908, tungsten has been the most used material for lamp filaments. Because of its high melting point, it can be used at higher temperature than other elements and thus has a greater luminosity. Other properties that make tungsten a good filament are a favorable radiation range (the light given off is in the range detectable by the human eye), low vapor pressure (which means that the filament will be long lasting), and high shock resistance.
Another important use of tungsten is in tungsten steel, including high-speed steel, shock-resistant steel, some stainless steels, heat-resistant steel, and magnet steel. The tungsten adds corrosion resistance and strength at high temperatures. The uses of tungsten carbides are numerous, varied, and easily understood because they are among the hardest materials in existence. Uses include cutting tools, mining drills, armor-piercing projectiles, and spray nozzles.
Tungsten is also used in paint pigments, inks, plastics, and rubber. Calcium and magnesium tungstates are used as phosphors in fluorescent lights and television tubes. The petroleum industry uses certain tungsten compounds such as ammonium tungstate, tungsten trioxide, and tungsten disulfide as catalysts.
(The entire section is 201 words.)
Further Reading (Encyclopedia of Global Resources)
Evans, Anthony M. Ore Geology and Industrial Minerals: An Introduction. 3d ed. Boston: Blackwell Scientific, 1993.
Greenwood, N. N., and A. Earnshaw. “Chromium, Molybdenum, and Tungsten.” In Chemistry of the Elements. 2d ed. Boston: Butterworth-Heinemann, 1997.
Lassner, Erik, and Wolf-Dieter Schubert. Tungsten: Properties, Chemistry, Technology of the Element, Alloys, and Chemical Compounds. New York: Kluwer Academic/Plenum, 1999.
Sigel, Astrid, and Helmut Sigel, eds. Molybdenum and Tungsten: Their Roles in Biological Processes. New York: Marcel Dekker, 2002.
Silva, J. J. R. Fraústo da, and R. J. P. Williams. “Molybdenum, Tungsten, Vanadium, and Chromium.” In The Biological Chemistry of the Elements: The Inorganic Chemistry of Life. 2d ed. New York: Oxford University Press, 2001.
Weeks, Mary Elvira. Discovery of the Elements. 7th ed. New material added by Henry M. Leicester. Easton, Pa.: Journal of Chemical Education, 1968.
Yih, Stephen W. H., and Chun T. Wang. Tungsten: Sources, Metallurgy, Properties, and Applications. New York: Plenum Press, 1979.
Natural Resources Canada. Canadian Minerals Yearbook, Mineral and Metal Commodity Reviews. http://www.nrcan-rncan.gc.ca/mms-smm/busi-indu/cmy-amc/com-eng.htm
U.S. Geological Survey. Tungsten: Statistics and Information....
(The entire section is 186 words.)
Tungsten (Chemical Elements)
Tungsten is a transition metal. The transition metals are a group of elements found in the middle of the periodic table. They occupy the boxes in Rows 4 through 7 between Groups 2 and 13. The periodic table is a chart that shows how chemical elements are related to one another.
These metals have very similar physical and chemical properties. One of tungsten's unusual properties is its very high melting point of 3,410°C (6,170°F). This is the highest melting point of any metal. Another of its important properties is its ability to retain its strength at very high temperatures. These properties account for tungsten's primary application, the manufacture of alloys. An alloy is made by melting and mixing two or more metals. The mixture has properties different from those of the individual metals.
Credit for the discovery of tungsten is often divided among three...
(The entire section is 1248 words.)