The polymerization of silicic acid obtained by the hydrothermal treatment of quartz and the solubility of amorphous silica

Abstract

The polymerization of silicic acid in the solution obtained by treating quartz with water at temperature 400℃ and under a specific volume of water 1.6ml/g was investigated from the changes in the concentration of molecular silica, the results were compared with those already reported, in which the silicic acid prepared from sodium silicate solution was used. The rate of the polymerization of silicic acid showed the maximum at about pH 7.5, and became lower on the both sides of this pH. The polymerization reaction seemed to be the second order on the acid side and the third order on the alkaline side with respect to the concentration of molecular silica. The effect of temperature was observed at temperatures from 0 to 100℃, and it was ascertained that the rate of the polymerization increased with temperature. The activation energy was estimated to be 9.8 kcal/mol in the original solution (pH 6.0). The solubility curve of amorphous silica was obtained by determining the concentrations of monomeric silica in the equilibrium state of polymerization, and the results were compared with those already obtained by the author and his co-worker and others. The heat of solution of amorphous silica was estimated to be 3.2kcal/mol.