Plastic densification in silica aerogels

Under isostatic pressure aerogels display an irreversible shrinkage caused by plastic deformation. As a consequence of this plastic shrinkage it is possible to densify, and thus to modify the elastic properties of aerogels. We show that the elasticity of the material is strongly influenced by structural transformation, and we observe a weakening of the network during the first stage of densification. The structural evolution, followed by Small Angle X-ray Scattering, shows that the densification mechanism is different from the one obtained by a sintering at high temperature. The densification mechanism induces a textural change at the periphery of the constitutive clusters but not inside, in contrast to viscous sintering.