On the relationship between microstructure and densification of silica gels

Sol-gel is an interesting technique for the substitution of the traditional methods (melting, chemical vapor deposition) employed by industry for production of glasses and coatings. Several sol-gel recipes for silica or doped silica glasses have been reported in the literature, but only a few of them have found industrial application, mainly because of the difficulties with obtaining glassy monoliths in the decimetre range. In this work, we investigate the role of the gel microstructure, mainly porosity, in determining the possibility to obtain large monoliths. Several xerogels and one aerogel have been investigated by gas adsorption isotherms and thermal analyses. We confirm that aerogels can likely lead to a glass without fractures, while this is not always true for xerogels. We point out that a proper tailoring of pores dimensions and surface area can lead to a successful densification of xerogels.