The Action of Sulphur Dioxide and of Water on Glass Surfaces

JSGT 1949 V33 T289-T335

The removal of alkali from glass by the reaction with water or with sulphur dioxide has been investigated theoretically and experimentally. Both these reactions have been shown to be controlled by diffusion processes within the glass. The type of diffusion process involved is governed by the condition that the electrical neutrality of the glass must be maintained. It is concluded that : (a) the reaction with water involves the exchange of sodium ions by hydrogen ions and that the reaction is limited by the rate of diffusion of sodium ions to the surface; (b) the reaction with sulphur dioxide at 20-100° in gas saturated with water vapour involves the same process and proceeds at the same speed as the reaction with water; (c) at 100-600° (and 'in atmospheres not saturated with water vapour below 100°) the sulphur-dioxide reaction is limited by the rate of diffusion of sodium through a compacted layer of glass at the surface which arises from a secondary dehydration process; (d) with anhydrous reagents the sulphur-dioxide reaction involves the simultaneous diffusion of sodium ions and oxygen ions to the glass surface, and the speed is limited by the rate of diffusion of oxygen ions; above about 700° this process predominates over ion exchange.

R. W. Douglas & J. O. Isard