Process for the production of high purity silicon

Abstract

Abstract <PICT:0907855/III/1> High-purity silicon is recovered from a solution of silicon and impurities in molten antimony, silver, bismuth, cadmium, gallium, indium, or zinc obtained by dissolving already produced silicon in the molten metal or by producing silicon in the presence of the molten metal, by distilling off the metal and the impurities under vacuum, e.g. at 1 micron of mercury. Already produced silicon may have a purity of 92-93%. Silicon may be produced by reducing a fluorosilicate of an alkali metal or an alkaline earth metal with sodium, potassium, calcium or magnesium. The reduction may be effected in the presence of a fluoride of an alkali metal or an alkaline earth metal as flux at 480 DEG -550 DEG C. Dissolution may be completed at 1200 DEG -1300 DEG C. Reduction and dissolution may be effected in a graphite crucible in an atmosphere of argon. Most of the solvent metal may be removed before the final distillation by filtration, chemical treatment, or pre-distillation. The chemical treatment may be effected with aqua regia, hydrochloric acid, or nitric acid. The final distillation may be effected in a silica crucible. Silica fragments may be removed from the product by treatment with boiling hydrofluoric acid. The product may then be washed with distilled water and alcohol and dried at 100 DEG C.

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