Abstract
This chapter describes the different steps of the transformations of a gel into an aerogel and into glass and the physical properties of the different materials derived from sintered silica aerogels. Silica glasses can be synthesized by sintering silica aerogels at temperatures ranging from 900 to 1,200 °C close to half the temperatures used for the glass melting process. The heat treatment can be taillored to obtain fully densified or porous glasses. Supercritical drying also enables the synthesis of aerogels from a wide range of binary compositions giving rise to binary or ternary silicate glasses after sintering. Another interesting application of aerogels is as a host matrix for the synthesis of multi-phase materials, doped material glasses, or composites. Their large pore volume is used as a sponge to incorporate chemical species in such a way as to form a two-phase material. The chemical species are first processed in liquid form and can be dried after the pores are filled. The result is a nanocomposite material composed of salt oxide embedded in the silica matrix.