ABSTRACT
Besides most homogeneous precursors, various authors also noted segregation in the phase evolution process of some monophasic gels during heating, which resulted in spinel formation along with tetragonal mullite formation. A great number of combinations of silicon and aluminum components have been used for both aqueous and nonaqueous ways of synthesis of mullite precursors. Mullitization temperature is considered an important criterion to assess the mixing scale or the degree of aluminosilicate bonds present in the precursor system. The primary attempt is to synthesize a chemically homogeneous high-purity mullite precursor by cogelation or coprecipitation techniques. The fourth approach is to control the hydrolysis of components by varying the use of water/alcohol as to avoid preferential hydrolysis of either the silica component or the alumina component. Homogeneity was achieved by Bhattacharya et al. in a stepwise manner, as follows: by the colloidal sol-gel route, inorganic components were found to develop diphasic or inhomogeneous gel withparticle sizes inthe range of 50–100 nm.
