Textural properties of densified aerogels

Silica aerogels were subjected to isostatic pressure using a Hg porosimeter. Nitrogen adsorption experiments were performed to estimate specific surface area, porous volume and pore size distribution. In a same way, gas permeability measurements have been carried out. During the first stages of compression, the specific surface area seems to be constant. The difference between the total pore volume and that measured by the BJH method (using the desorption part of the isotherm) is less important in compressed aerogels than in sintered ones. Permeability decrease with densification is faster in partially compressed aerogels. This behavior is correlated to disappearance of largest pores and has been associated to the evolution of the pore size distribution which evolves toward smaller pore diameters. (C) 1998 Elsevier Science B.V. All rights reserved.