DENSIFICATION OF ACID-CATALYZED SILICA XEROGELS

Wet acid-catalysed gels prepared by hydrolysis and condensation of tet ramethylorthosilicate (TMOS) can be dried without the occurrence of fr actures or cracks when drying conditions are appropriate. Furthermore, the resultant dried gel monoliths can be converted to silica glass on heating to 1100 degrees C and holding there for 30 min when the compo sition of the starting solution is appropriate. The xerogel to glass t ransformation was followed by scanning electron microscopy (SEM), smal l-angle X-ray scattering, Brunauer-Emmett-Teller (BET) measurements, l ow-frequency Raman scattering and dilatometric measurements and reveal s that the densification process is different from the one described f or base-catalysed xerogels.