THE INCREASE IN PH DURING AGING OF POROUS SOL-GEL SILICA SPHERES

The increase in pH in the hydrothermal fluid is studied after hydrothermal aging of porous silica gel spheres of 1-3 mm diameter. The porous silica spheres are formed by the sol-gel process from a supersaturated silica solution. The increase of the pH of the hydrothermal solution affects the silica solubility. A model to explain the increase in pH assumes condensation of sodium complexed silanol groups and the release of ionized monosilicic acid in the fluid. The existence of sodium complexed silanol groups is demonstrated by surface titration experiments.