Mullite precursor part I. Characterization of mullite precursor formed by a reaction of monosilicic acid on aluminum hydroxide

By adsorption of monosilicic acid on aluminum hydroxide, an amorphous aluminosilicate (AAS) of Si/Al ratio of 1/3 was formed. When the AAS was heated to 1000°C, mullite (3Al₂O₃ · 2SiO₂) crystallized directly without the formation of a spinel phase. It was clearly evidenced that correct adjustment of three factors, the Si/Al ratio, the proportion of 4- and 6-coordinated aluminums, and the single environment of a SiO^4-₄ unit (no Si-O-Si bond), is important for the direct mullitization from AAS.