ABSTRACT
Hoffman and Komarneni first synthesized a diphasic gel, consisting of two discrete silica and alumina phases, each noncrystalline in nature in some cases and one component pseudocrystalline in other cases. Hamano et al. mixed boehmite and silica sols to prepare mullite powders so that the stoichiometric composition of mullite was maintained. The boehmite sol was prepared from aluminum ethoxide by hydrolysis/condensation reactions, using HCl as a catalyst. Transformation of mullite powder prepared from aluminum sulfate and fumed silica is given by Mizuno and Sato. The silica sol was prepared by hydrolysis/ condensation of methyl silicate. The two sols were then mixed and subsequently dried by slowly adding the mixture to a hot petroleum bath. The gel monoliths were air-dried very slowly for a considerable length of time at room temperature in covered molds with pinhole vents to a prevent cracking.
