Blot's theory of acoustic propagation in porous media applied to aerogels and alcogels

Comparison of acoustic propagation in alcogels and aerogels presents an interesting difference for the high porosity: in alcogels, longitudinal wave velocity remains around the velocity in alcohol while, in aerogels, it is significantly lower than the velocity in air. In this paper, Blot's model of acoustic propagation in porous media is applied. We find a good agreement with measurements in terms of velocity that validates this theory for both alcogel and aerogel cases. Qualitative agreement is obtained for absorption but further comparisons are needed to test quantitative agreement. The theory allows explanation of behaviour differences observed by distinguishing the influence of the solid and fluid phases from that of the gel network. (C) 1998 Elsevier Science B.V. All rights reserved.