Tungsten (W)
Tungsten (W) is a chemical element known for its remarkable hardness and high melting point, making it an essential material in various industrial applications. It is primarily found in combination with other elements, with significant deposits located in China, Canada, Russia, and the United States. Tungsten boasts the highest melting point of any metal, at 3,410°C, and is characterized as a dense, brittle metal with a unique set of properties, including excellent thermal and electrical conductivity.
The element is utilized extensively in cutting tools, wear-resistant materials, and as filaments in incandescent light bulbs, highlighting its practical importance in everyday technology. Additionally, tungsten forms part of high-speed steel and tungsten carbide, which are crucial for manufacturing durable tools and machinery. With minimal biological activity and limited environmental concerns, tungsten's industrial uses extend to applications in paints, rubber, and as catalysts in the petroleum industry. Overall, tungsten's diverse functionality and resilience underscore its significance across multiple sectors.
Tungsten (W)
Where Found
Tungsten is always found in combination with other elements. Although it is found on every continent, a majority of the known reserves are in China. Other major sources include Canada, Russia, and the United States.
Primary Uses
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.
Technical Definition
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.
Description, Distribution, and Forms
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.
History
Tungsten was discovered twice. In 1781, the Swedish chemistCarl 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.
Obtaining Tungsten
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.
Uses of Tungsten
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.
Bibliography
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