Aerogels

Abstract

The first aerogels were made by S. S. Kistler in 1931. Aerogels are produced by a sol–gel process followed by supercritical drying of the wet gel in an autoclave. Their porosity extends from about 1 to 100 nm, which is the reason why properly made aerogels are highly transparent. Aerogels have a spongelike, open‐pore structure with a large inner surface. Monolithic aerogels are used in Cerenkov detectors in high‐energy physics; several houses have been insulated with layers of translucent granular aerogels for the purpose of passive solar energy usage; opacified aerogel powders are being tested as substitutes for chlorofluoro‐carbon‐blown polyurethane foams and as thermal superinsulations in heat‐storage systems; experiments have been performed with aerogels as catalytic substrates, acoustic impedance matching layers, precursors for high‐quality glasses, containment for fusion fuels, and gas filters; and aerogels are used in radioluminescent light and energy sources. The attraction that these low‐density materials exert on physicists, chemists, and material scientists is recognized from the upsurge of publications on aerogels: about 200 papers are currently published per year. Recently, the periodical Science has rated aerogels as one of the top ten scientific and technological developments.