Aerogels of Inorganic Oxides

Abstract

A highly-divided state (small particles, high surface area, porosity) of an inorganic material, like an oxide, cannot be created by a mechanical process (e.g. grinding) applied to a coarse material. The divided state must be induced during the chemical preparation of the material. The divided solid finds then use as adsorbent, filler, support for catalysts and catalyst itself, reinforcing agent, pigment, thermal and phonic insulator, gellifying agent, etc. This chemical procedure is, in particular, a condition which must be fulfilled for the preparation of binary (or ternary) mixed oxides (or salts) where the mechanical process is not able to achieve a good dispersion of one phase onto the second phase. This paper deals mainly with the preparation and some properties of oxides or hydroxides (hydrated oxides) from a historical perspective. The new applications of silica aerogels and their unique physical properties are the main topic of this Symposium. Other aerogels and mixed oxides or metal on oxide aerogels are less known. In the case of binary or ternary oxides the less refractory one (e.g. NiO) may be reduced to the metallic state, whose particles are stabilized in the divided form by the other oxide (or oxides), like silica or alumina, which is the support of the metal.