Chemical Processing of Composite Precursors with CordieriteMullite Composition by Copolymerization of Alko x ides

Abstract

Composite precursor powders with cordierite-mullite composition were prepared by copolymerization of metal alkoxides. Cordierite (2 MgO.2 Al₂O₃.5 SiO₂) precursor solution was prepared by copolymerization between partially hydrolyzed tetraethyl silicate (TEOS) and Mg-Al double alkoxide. On the other hand, alminium iso-propoxide was refluxed in isobutyl alcohol followed by copolymerization with partially hydrolyzed TEOS so as to prepare homogeneous mullite (3Al₂O₃.2SiO₂) precursor solution. By mixing cordierite and mullite precursor solutions, composite precursor solutions were obtained. Excess amount of water was added to the composite precursor solutions to precipitate homogeneous composite precursor powders. The precursor powders were heat-treated up to 1400°C. Mullite phase was identified at temperature as low as 900°C. α-cordierite phase was formed at 1200°C through a reaction between sapphirine (4 MgO.5 Al₂O₃. 2SiO₂) and amorphous silica. The calcined composite precursor compacts could be sintered into dense bodies by 1300°C firing. From the results, the chemical processing of the composite precursor was considered to be effective to prepare homogeneous cordierite-mullite composite at low temperature.