Isolation, production and industrial uses

Silicon (96-99% pure) is now invariably made by the reduction of quartzite or sand with high purity coke in an electric arc furnace the Si02 is kept in excess to prevent the accumulation of SiC (p. 334)  

The reaction is frequently carried out in the presence of scrap iron (with low P and S content) to produce ferrosilicon alloys these are used in the metallurgical industry to deoxidize steel, to manufacture high-Si corrosion-resistant Fe, and Si/steel laminations for electric motors. The scale of operations can be gauged from the 1980 world production figures which were in excess of 5 megatonnes. Consumption of high purity (semiconductor grade) Si leapt from less than 10 tonnes in 1955 to 2800 tonnes in 1980. 

Silicon for the chemical industry is usually purified to 98.5% by leaching the powdered 96-97% material with water. Very pure Si for semiconductor applications is obtained either from SiCU (made from the chlorination of scrap Si) or from SiHCls (a byproduct of the silicone industry, p. 338). These volatile compounds are 

Geochemistry, Pergamon Press, Oxford, 1982, 372 pp. S. R. Aston (ed.), Silicon Geochemistry and Biogeochemistry, Academic Press, 1983, 272 pp. 

Hyperflne Si is one of the purest materials ever made on an industrial scale the production of transistors (p. 332) requires the routine preparation of crystals with impurity levels below 1 atom in 10 , and levels below 1 atom in 10 can be attained in special cases. 

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