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Si
SILICON

History

Silicon is all around us as the element in quartz and silica sand. Early in the 19th century, Scottish chemist Thomas Thomson surveyed the work of several well-known colleagues investigating silica. None had yet isolated the element, and chemists disagreed as to whether it would be a metal (silicium) or an earth (silicon). Thomson believed the evidence favored an earth, a nonmetal, and his name stuck. In 1823, Swedish chemist Jöns Jakob Berzelius finally produced the pure element.

Mining and Production

quartzSilicon forms a major portion of the Earth's crust. Silica, which is silicon dioxide, is quarried and excavated in large amounts world-wide to be used as-is. Quartz (right), sandstone, and other building stone are used in construction with no chemical processing. Sand goes into glassmaking.

Silicon in elemental form is also desired, though. It can be prepared from silica by heating with coal in a furnace. Carbon combines with oxygen as carbon monoxide, and silicon drains off. Solar power wafers demand purer silicon, which can be obtained through electrolysis of molten silica.

In recent decades, ultra-pure silicon crystals have replaced germanium in electronics. Extreme purity ("9 9s" or 99.9999999%) has been achieved by more and more efficient methods involving iterated cycles of melting and freezing or crystalizing and dissolving.

The amount of silica stone excavated each year isn't reported. The production of silicon in 2013 was 7.7 million tonnes, of which China produced 2/3.

Properties and Uses

Silicon is a grey and lustrous semiconductor. It conducts heat well and electricity marginally. Although it may look like a metal, it is brittle. Silicon can be a crystal or a powder.

Chemically, the element forms long molecular chains in the same way as carbon, though not as stable or complex. The best-known compound is silicon dioxide, which is quartz and the basis for ordinary glass.

The major use of elemental silicon is in metallurgy. It is added to blast furnaces containing ferrous alloys or ores. The silicon removes oxygen and reduces the metal in the same way that carbon (coke or coal) would. This avoids seeing the oxygen combine with existing carbon in the ore, for carbon is desirable in ferrous metals.

solar panelsPure silicon wafers are used in all kinds of electronics, including solar cells and integrated circuits.

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