The Surface Structure of Silica Gel Studied by Dielectric Dispersion

The effect of water adsorption and heat treatment at various temperatures between 200 and 1100°C on the dielectric dispersions of silica gel was measured in the frequency range from 50 to 3×106 Hz and 9.81 GHz and in the temperature range from −196°C to 180°C. Two anomalous dispersions (Dispersion I and II) and one anomaly (Anomaly III) were found. The mechanisms of those anomalies were discussed in relation to some physical properties and silica crystal structures. Dispersion I, having activation energy ΔE equal to 11 to 14 kcal/mol, can be ascribed to the monomolecular layer of adsorbed water. Dispersion II, with activation energy of about 5 to 7 kcal/mol, can be attributed to proton diffusion through hydrogen-bond chain of surface silanol groups. Anomaly III, having activation energy of about 3 kcal/mol, may be assigned to dipolar rotation of free silanol.