EFFECT OF MICROSTRUCTURE ON THERMAL DEHYDROXYLATION OF SILICA-GELS

Dehydroxylation of gels is important for the preparation of high quali ty glasses and for the application of the porous gel materials at high temperatures. In this report, the effect of changing the microstructu re of silica aerogels on the thermal dehydroxylation of the gels in va cuum is presented. Surface area, density and IR spectra of the aerogel s were determined after heat treatment to 1100 degrees C in vacuum. Th e two different microstructures have been obtained by aging one set of gels in a water/ethanol solution to promote coarsening of the wet gel prior to supercritical drying. Network coarsening causes a larger por e size and less concave neck curvature of this type of aerogels. Coars ening of the network was shown to facilitate dehydroxylation of the ae rogels.