STRUCTURES AND PROPERTIES OF SILICA-GELS PREPARED BY THE SOL-GEL METHOD

Abstract

Apparent density, nitrogen adsorption, SEM and IR spectroscopy have been employed in a study of structures and properties of gels prepared by the acid- and base-catalyzed reactions of TEOS. The gel made from a low water content sol contains residual organic groups caused by incomplete hydrolysis, which contributes to the formation of micropores during heat treatment. According to the results of volume vs. thickness data, the acid-catalyzed gels have slit-shaped micropores. The base-catalyzed gels, however, have cylindrical pores. An acid-catalyzed particle has shown fibrous or plate-like structure in the SEM, whereas base-catalyzed gels have shown spherical particles distributed over the gel. The acidic gel made from higher water content (molar ratio of water to TEOS, R > 4) sol has shown coarse microstructures when compared with that from lower water content (R < 4) sol.