Mullite formation from highly homogeneous mixtures of Al2O3 and SiO2

Mullite, 3A12O3 · 2SiO2, was synthesized by heat-treating homogeneous sol-gel-derived mixtures of A12O3 and SiO2 taken in stoichiometric amounts. To reduce the mullitization temperature, sols containing γ-AlOOH and SiO2 nanoparticles (2 to 20 nm) were used in the preparation of the mullite precursors. A few samples were made using the products of hydrolysis of aluminum salts instead of the γ-AlOOH sol. The process parameters determining the homogeneity of the precursor mixtures were revealed. The preparation conditions ensuring mullite crystallization at temperatures between 1200 and 1250°C were found. The results are discussed in terms of the reaction between A12O3 and SiO2 during mullitization.