Drying of silica alcogels by liquid and supercritical CO2

Gels dried in supercritical conditions give a new class of materials called aerogels. The process of silica aerogel production in which extraction with liquid (or supercritical) carbon dioxide is used, consists of four main stages: elution, diffusion, heating and evacuation. Aerogel production from silica gels prepared from tetraethoxysilane is described. The autoclave process which started with alcohol-liquid carbon dioxide exchange was followed by supercritical evacuation. Some important technical aspects of the process are considered. The effect of elution rate, temperature and duration of diffusion is investigated.