EFFECTS OF TEMPERATURE ON FORMATION OF SILICA-GEL

The gelation of solutions containing mixtures of tetramethoxysilane with methanol or tetraethoxysilane with ethanol, H//2O and HCl or HF as a catalyst was studied at various temperatures in closed systems. Large differences in gelation rates were observed between HCl and HF at all temperatures. At 25, 50 and 70 degree C, the gelation times were 9. 2, 1. 25 and 0. 30 h for HF and 380, 70 and 20 h for HCl, for the TEOS systems. The apparent activation energies for the two TEOS systems were almost identical. Apparent activation energies are attributed to the process of polymerization. This was justified by investigating the dependence of gelation time on the water concentration. The bulk density, apparent density and porosity were studied for the TEOS systems.