Effect of heat treatment on the pore structure properties of silica gel powders derived from water glass

For silica gel powders prepared by azeotropic distillation of gels derived from water glass, nitrogen adsorption was employed to investigate the pore structure properties during heat treatment. It was shown that both the BET and micropore specific surface areas increased up to the temperature range 300–500°C; the collapse of micro and meso pores occurred above 500°C, which caused a reduction of specific surface area and total pore volume as well as a shift of pore size distributions to larger size. Heat treating at 1200°C caused the BET specific surface area to be reduced to 1.4 m2/g, and no pores existed in the powders as a result of formation of cristobalite.