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 po ssible to densify, and thus to modify the elastic properties of aerogels. W e show that the elasticity of the material is strongly influenced by struct ural transformation, and we observe a weakening of the network during the f irst stage of densification. The structural evolution, followed by Small An gle X-ray Scattering, shows that the densification mechanism is different f rom the one obtained by a sintering at high temperature. The densification mechanism induces a textural change at the periphery of the constitutive cl usters but not inside, in contrast to viscous sintering.