Aerogels — the so-called 'Fourth State of Matter'

Allahabad University, Allahabad-211 002 Manuscript received 23 December 1992 Extremely low density gels of silica and other metal oxides can be prepared by the removal of the water/alcohols from the aqua- or alco-gels under supercritical conditions. The use of alkyl orthosilicates suggested by Teichner as precursors, has made the technology of preparing aerogels much simpler. In this article a very brief account is presented for the preparation of simple and heterometal alkoxides, developed in the laboratories of Mehrotra, and their applications for the preparation of novel aerogels by the sol-gel process