Tungsten
Tungsten is a transition metal element denoted by the atomic symbol, W. It has an atomic number of 74 and the average atomic weight of its isotopes is 183.85. Tungsten's greatest assets are its high melting point 6,170 ± 68°F (3,410 ± 20°C), which is higher than that of any other metal, and its ability to retain its strength at very high temperatures. These properties make tungsten, which has been given atomic number 74, extremely useful in the manufacture and use of many alloys, which are mixtures of metals.
In nature, tungsten is mainly found in the minerals scheelite and wolframite. Scheelite, which was named after Carl Wilhelm Scheele, was originally called tung sten, which is Swedish for "heavy stone." In 1781 Scheele examined this mineral and found that a new acid could be produced from it. The acid Scheele had prepared was actually tungstic acid. In 1783 Spanish mineralogist Don Fausto d'Elhuyar (1755-1833) and his older brother, Juan Jose d'Elhuyar (1754-1804), obtained tungstic acid from wolframite. Recognizing that this was the same acid that Scheele had produced just two years earlier, the d'Elhuyar brothers reduced the acid and discovered the new metal, tungsten. Because it was first obtained from wolframite, tungsten is also called wolfram.
Tungsten's chief use is as a filament for electric light bulbs. Originally, light bulb filaments were made of carbon and various other materials, and a vacuum was created inside the bulb to preserve the fragile filament. Scientists knew that tungsten, because of its high melting point, would perform better. But because the metal is brittle, no one could figure out how to draw it into the fine wire needed for filaments.
Researchers at General Electric's laboratory began working on the problem. In 1909 American physicist William D. Coolidge (1873-1975) perfected a revolutionary process for making tungsten ductile, or capable of being drawn into wire. Tungsten filaments greatly improved the durability and efficiency of incandescent light bulbs. Coolidge also invented an X-ray tube using tungsten that allowed for greater precision and could conduct higher voltages. With these advances, X-ray technology was introduced to the worlds of industry and medicine.
One of Coolidge's colleagues at GE, American chemist Irving Langmuir (1881-1957), discovered that tungsten filaments would last much longer if light bulbs were filled with a nonreactive gas such as nitrogen or argon. He also improved the tungsten filament by coating it with a single layer of thorium atoms, and he found that filaments are more efficient when tightly coiled. Since then, most modern light bulbs have been made in essentially the same way. One exception is the tungsten halogen lamp, in which a small amount of iodine, bromine, or other halogen is added to the bulb's gas filling. This prevents evaporated tungsten from blackening the inside of the bulb and dimming its light.
In the late 1800s scientists found that unlike most metals, which soften when heated, steel alloys made with tungsten would remain hard at very high temperatures. This discovery anticipated the start of today's high-speed tool industry. Being hard and tough, tungsten is more durable than ordinary steel and is used to make tools that can operate at higher temperatures. Other tungsten alloys are used in automobile ignition systems, electric furnaces, vacuum tubes, and space missiles. Tungsten carbide, an extremely hard compound, is used in mining, oil drilling, dental drills, and ball point pens while other tungsten compounds are used in fluorescent lamps.
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