EVOLUTION OF THE ACOUSTICAL PROPERTIES OF SILICA ALCOGELS DURING THEIR FORMATION

Silica aerogels are materials of very high porosity obtained through a sol-gel process. Since their structural properties greatly influence their acoustical and mechanical properties, it is important to follow how the different chemical reactions occur in this process. We present a study of this evolution for two different types of alcogels through acoustical measurements in an ultrasonic range. These samples have be en chosen because of the significantly different behaviour of aerogels which have the same structure. The data obtained during the gelation show fluctuations of velocity that can be interpreted as chemical chan ges. These chemical changes give information about the evolution and t he kind of structures one can expect from different catalyses. (C) 199 8 Elsevier Science B.V.