CoachThe sol–gel process makes an oxide by hydrolysis and condensation of molecular precursors, usually alkoxides, in solution: the solution becomes a sol of small oxide clusters, then a gel, a continuous solid network filled with liquid. Dried by evaporation, the gel shrinks into a dense xerogel; dried above the critical point of the liquid, which removes it without a liquid–gas interface, it keeps its volume as an aerogel.
