The thermal behavior of the silanol of silica gel has been studied by quantitative infrared spectroscopy. Transparent and glass-like plates of silica gel of high purity, after they had been heat-treated at various temperatures below 680 °C, were used for the measurement of OH stretching vibrations ranging from 3100 to 3800 cm−1. These absorption bands were analysed into the several component bands by the simulation method using a Dupont Co. Curve Resolver. The intensity of these bands in area were proportional to the OH concentrations as measured by the thermal method. Each component band disappeared at a temperature which was roughly equal to that obtained from the dielectric and conductivity measurements. From these results, assignment was attempted on the basis of these bands.
The effects of various kinds of inorganic salts upon the physical properties of silica gel heated in the range up to 1200°C were studied. We measured the polymorphic behavior by means of X-ray diffraction, the simultaneous measurement of the differential thermal analysis, and the thermogravimetric analysis, and the specific surface area by means of the BET N2 method and by means of studying the water-adsorption capacity. The cationic impurities which were found to have strong effects upon the physical properties mentioned above are Na+, K+, Ca2+, Pb2+, Cd2+, Zn2+, and Sb3+. Cations such as Al3+, Cr3+, Mn3+, and Co2+ were shown to have weak but positive effects upon the physical properties of silica gel.
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.
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