Preparation of Fine SiO2-Al2O3 Powders by Hydrolysis of Mixed Alkoxides

Abstract

Mixtures of Al(OC₃H₇ⁱ)₃ and Si(OC₂H₅)₄ corresponding to xAl₂O₃⋅2SiO₂(x=1, 2, 3, 4) were dissolved in benzene and refluxed (81°-83°C) under a dried N₂ flow. Hydrolysis with equivalent amount of distilled water to formation of SiO₂ and Al(OH)₃ gave amorphous powders showing an exothermic peak at 980°C in DTA connected with crystallization to Al-Si spinel and mullite. Phases produced in the powders and disks heated at 800°-1620°C were compared with a phase diagram of the SiO₂-Al₂O₃ system. Compositions of mullite formed at 1400°C and 1550°C were estimated from the lattice constant a₀. Average particle size of the SiO₂-Al₂O₃ powders heat-treated at 1400°C for 3h, which showed narrow size distributions, were ≈0.15μm for x=1 and 2, and 0.082-0.089μm for x=3 and 4, respectively.