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Wednesday, 28 January 2015

Tungsten

Tungsten


The metal tungsten [vɔlfram] is a chemical Substance with the symbol W and atomic number 74. It is a shiny white metal that is ranked among the transition metals. Tungsten has the highest of all pure metals, melting and boiling point.

In the 16th century Freiberg mineralogist Georgius Agricola described That, the occurrence of a mineral in Saxon tin ore, which greatly complicated the tin production by slugging of the tin content. Whether it acted to wolf ramite, is still controversial, as he spoke of the "lightness" of the mineral. He named the mineral lupi spuma, which translated from Latin means "wolf (s) foam" means. Later, from Wolf foam Wolfrahm. And finally came to the now famous words of tungsten.

The common word in English and French Tungsten derives (Swedish for "heavy stone") Tung Sten (calcium tungstate) from. In this realized in 1781, the Swedish chemist Carl Wilhelm Scheele, a hitherto unidentified salt. Pure tungsten was the first time in 1783 by the Spanish brothers Fausto and Juan José Elhuyar (who worked under the direction of Scheele) by decrease of tungsten trioxide, which is obtained from wolframite made.

The tungsten ores are first concentrated by flotation. Thereafter, the digestion of the ground ore with soda takes place by melting at about 800 ° C, or with sodium hydroxide solution under pressure (roasting), said first soluble sodium tungstate is formed. After precipitation and filtering off impurities, the sodium tungstate (Na2WO4 • 2 H2O) is converted with calcium chloride to calcium tungstate with hydrochloric acid to tungsten trioxide (WO3 * H2O) reacts, which is filtered off. By adding an ammoniacal solution forms a complex called ammonium para tungstate (APT). This is also collected by filtration and subsequently transferred at 600 ° C in relatively pure tungsten trioxide. By annealing to obtain tungsten (VI) oxide (WO3), which is reduced at 800 ° C under a hydrogen atmosphere to steel gray tungsten:

This process produces gray powder; this is frequently compacted into sintered electrically panels. At temperatures above 3400 ° C, in special electric furnaces with a reducing atmosphere of hydrogen a compact tungsten metal are melted (Zone melting process).