Structural characterization and phase development of sol-gel-derived mullite and its precursors

In this study single phase gels from alcoholic solutions of silicon alkoxide and chelated aluminium alkoxide or aluminium salt with similar primary particle size were investigated. The influence of water content, dilution, and precursor reactivity on gelation behaviour and phase segregation was studied in order to understand the origin of an intermediate spinel-like phase during the crystalline phase development. It is shown that the high temperature phase development is related to two important process parameters. One is the reactivity difference between silicon and aluminium alkoxide, the other is the water content of the precursor solution. Both parameters influence the homogeneity of the gels.