Method of preparation of very pure chemical elements, in particular, the silicon from their halides

摘要

PICT:0799876/III/1 A mixture of silicon tetrachloride and hydrogen is passed through a high-temperature reaction zone so as to cause the production of silicon and hydrogen chloride to a substantial extent, the silicon is allowed to deposit in said zone the gaseous reaction product, which consists of a mixture of hydrogen chloride and unreacted silicon tetrachloride and hydrogen, is removed from the reaction zone, the hydrogen chloride is removed from said mixture and further silicon tetrachloride and hydrogen added thereto to replace that used in the reaction, and the resulting mixture of silicon tetrachloride and hydrogen is recycled to the high temperature reaction zone. The silicon may be produced at a temperature of 1100-1300 DEG C., preferably 1200 DEG C. Removal of hydrogen chloride and addition of hydrogen may be effected simultaneously by reaction of the hydrogen chloride with vaporized zinc at a temperature of 600-800 DEG C., preferably 650 DEG C. As illustrated, silicon tetrachloride is introduced from reservoir 30 into the cyclic system after the high temperature reaction zone 31. Zinc vapour is then introduced into the system from zinc boiler 33. The zinc chloride thereby produced is removed by means of a cooling and settling chamber 34 and filter 35 of glass wool. The remaining hydrogen and silicon tetrachloride pass via pump 36 to reaction zone 31. Before passing to zone 31, a portion of the gases may pass continuously or intermittently through an analyser 37 consisting of an infra-red analysis unit or a thermal conductivity cell. Hydrogen for commencing the reaction, and for subsequent supplementary addition, if necessary, may be added via reaction tube 32. Silicon tetra chloride for use in the process may be purified by admixing with a solvent, e.g. dichloromethane, trichloromonofluoromethane, or trichlorotriflorethane, passing through activated alumina boiling off, condensing, and recycling the solvent (Fig. 2, not shown).