GB834383A - Improvements in or relating to methods of removing impurities from silica - Google Patents

Abstract

Silica is purified by heating to 1100-1500 DEG C. in a gaseous atmosphere comprising Cl2, HCl gas or mixtures thereof in a chamber having inlet and exit orifices provided for introduction and removal of the gaseous atmosphere, whereby the impurities diffuse outward from the bulk of the silica to the surface thereof where they are reacted on by the gaseous atmosphere, reaction products being expelled in the form of vapours through the exit orifice. A silica, graphite or zirconia chamber 6 containing silica to be purified is filled with a gaseous atmosphere supplied from cylinders 1 through valves 2, gauges 3, mixing chamber 4 and inlet orifice 5, CCl4, sometimes used to assist the purification, by acting as a reducing agent at the reaction temperatures, may be introduced as a vapour by bubbling the gases <PICT:0834383/III/1> through CCl4 liquid, contained in vessel 7, before entering chamber 6. The chamber is heated electrically to 1100-1500 DEG C. and impurities diffusing outwardly to the surface of the silica, react with the gaseous atmosphere to form reaction product vapours which are removed through exit orifice 18. Silica to be treated may be in a granular form or in the form of a finished crucible. When silica in a granular form is to be treated, the chamber 6 may be rotated, in order to agitate the granules and to ensure uniform heating thereof, by means of ring gears 11 driven by motor 13 through pinions 12, power being supplied to heating element 10 by slip rings 14 in contact wth stationary brushes 15.