Reactions of vitreous silicates and aluminosilicates with aqueous solutions Communication I. Reactions of vitreous sodium silicates with water and with hydrochloric acid solutions

Abstract

1. A study has been made of the action of water and hydrochloric acid sol~utions on vitreous, sodium silicates having compositions correspondlng to the invariant points on the phase diagram of the system Na2O-SiO2, to intermediate points, and also to points representing high silica contents. 2. The process of interaction of sodium silicates with water can be broken down into two stages: exchange of sodium ions of the glass for hydrogen ions of the solution, resulting in the formation of a residual layer of silica acid, which together with the silica of the original glass comprises a protective film on the surface; and reaction of the protective layer with the alkaline solution that has been formed, resulting in removal of silicic acid from the surface by dissolution 3. In the case of sodium silicates having a low silica content, a kinetic equilibriumi s established between the primary and secondary reactions, so that dissolution of the glass appears to take place. In the case of sodium silicates of high silica content, the main process is the leaching of Na2O from the glass. 4. When sodium silicates are treated with hydrochloric acid solutions, transfer to the solution of SiO2 lags behind that of Na2O to a greater extent than in the case of water treatments. In the case of glasses having a silica content greater than that of disilicate, no SiO2 could be detected in the solution. 5. The relation between the logarithms of the amounts of components passing into solution and the molecular percentage of silica the glass is represented over the range of compositions examined by smooth curves or (in the case of acid treatment) by straight lines, without appreciable deviations at compositions corresponding to invariant points on the phase diagram of Na2O-SiO2. 6. With rise in temperature the amounts of the components passing into solution increase considerably, and at the same time the boundary of the region of soluble silicates moves in the direction of glasses of higher original silica content.