DENSIFICATION KINETICS AND STRUCTURAL EVOLUTION DURING SINTERING OF SILICA AEROGEL

A silica aerogel was sintered at 1050 degrees C, and the effect of den sification on the pore structure was determined by nitrogen sorption. Based on the initial pore size distribution (psd) of the aerogel, the kinetics of densification and the evolution of the psd were calculated using the theory of viscous sintering. If the psd is ignored, and the sintering behavior is predicted using the average pore size, then the agreement with measurements is not very good. However, when the actua l psd is used in the calculation, then the predictions are excellent f or density versus time, surface area and mean pore size versus density , and psd versus time. The quality of the fit depends on the constitut ive laws describing the response of the porous material to stresses; t he best results are obtained using the laws originally derived for the cylinder model. The power-laws that describe the density dependence o f the elastic modulus of aerogels do not seem to apply to the viscosit y; reasons for this dependence are discussed. (C) 1998 Published by El sevier Science B.V. All rights reserved.