GB728919A - Improvements in the preparation of silicon tetrachloride - Google Patents

Abstract

Silicon tetrachloride is prepared by passing chlorine over silicon or an alloy thereof at temperatures not higher than 150 DEG C. in the presence of a catalyst comprising one or more "activated metals" selected from the group consisting of cobalt, copper, nickel, chromium, manganese, iron, silver, titanium, tin, antimony, vanadium and molybdenum. The "activated metals" are produced (i) by reduction of the oxides, hydroxides or nitrates with hydrogen or ammonia, (ii) by decomposing an organic salt such as the oxalate or formate of the metal in an inert or reducing atmosphere, (iii) by reduction of the metal chloride with silicon, (iv) by precipitation from a metal salt solution by the action of another metal such as zinc, cadmium or manganese, or (v) by selective attack of an alloy of the metal, such as the caustic soda attack on a cobalt-tin, cobalt-aluminium or cobalt-silicon alloy. According to examples (i) cobalt chloride was mixed with silicon in a proportion of 1 : 10 by weight and reacted at 460 DEG C. to produce cobalt and silicon tetrachloride. Chlorine was passed over the resultant mixture of silicon and the cobalt catalyst at 136 DEG C., temperature control being effected by cooling or adding an inert gas. The activity of the cobalt catalyst was restored by discontinuing the chlorine supply and heating the silicon cobalt mass to which further silicon may be added, to at least 380 DEG C.; (ii) cobalt hydroxide was reduced with hydrogen at 560 DEG C., optionally in the presence of silicon. The resulting mass, with added silicon, was treated with chlorine at 150 DEG C. after initiation at 230 DEG C.; (iii) copper carbonate was slowly dissolved in concentrated ammonia solution which was then mixed with ferrosilicon and diatomaceous earth. After evaporation of water, the dry cake was packed into a reaction chamber and reduced with hydrogen at 200 DEG C. The resulting mass was then reacted with chlorine at ordinary temperatures. Further examples refer to copper and mixed cobalt-manganese catalysts. Specifications 141,908 and 176,811, [both in Class 1 (ii)], are referred to.