GB794641A - Improvements in or relating to processes for the production of pure germanium and silicon - Google Patents

Abstract

Impurities in a germanium or silicon halide are converted into substances having a different volatility from said halide by one or more chemical or electrochemical methods of reduction which affect the germanium or silicon halide either not at all or only to a negligible extent, the germanium or silicon halide is separated from the converted impurity substances, and the purified halide is reduced to give pure germanium or silicon. Typically tin, magnesium, or zinc, e.g. as chips, are added to germanium tetrachloride which has not been subjected to special drying procedures and contains arsenic, antimony and iron chlorides as impurities, whereby arsenic and antimony are reduced to elementary form and deposited on the added metal, some of which is oxidized to its chloride, while the ferric chloride is reduced to ferrous chloride. Alternatively, nascent hydrogen produced by the addition of zinc and hydrochloric acid or by the addition of hydrochloric or hydrobromic acid and electrolysis is used to reduce the arsenic and antimony impurities to the gaseous hydrides, which escape aided by the passage of an inert gas through the reaction vessel, while ferric and cupric chlorides are reduced to the lower chlorides or the metals. Silicon halides may be similarly treated. In a further method, germanium tetrachloride containing trace impurities of iron, cobalt, nickel and copper is dehydrated and purified by addition of one or more alkali or alkaline earth metal carbonates which remove hydrochloric acid present due to hydrolysis of the germanium tetrachloride and is subsequently or simultaneously distilled off. Typically the impure germanium tetrachloride is boiled with anhydrous sodium carbonate. In each case the treated tetrachloride is distilled off and is reduced to elementary form, as by hydrolysing to the oxide followed by reduction with hydrogen.