Preparation of an aluminium titanate-25 vol% mullite composite by sintering of gel-coated powders

A gel-coated powder processing, i.e. mullite precursor gel coating synthesised Al2TiO5 solid solution (with 2.5 wt% MgO) particles, was used to prepare an Al2TiO5-25 vol% mullite composite precursor. The mullitisation, densification, mechanical and thermal properties of the composite have been investigated. It was found that direct mullitisation occurred at 988 degrees C in the composite precursor this being attributed to the presence of Al2TiO5 particles. Two different mullite morphologies with near isometric and acicular shapes were observed. The formation of acicular mullite is ascribed to the presence of a liquid phase at the firing temperature as a consequence of composition alterations due to segregation of Al2O3 and SiO2. Good dispersion of the mullite grains along the grin boundaries was observed in samples that attained high densification. The thermal expansion coefficient of the composite was still relatively low (similar to 2.7 x 10(-6) K-1). During long-term (100 h at 100 degrees C) decomposition tests the Al2TiO5 chemical stability was maintained. (C) 1996 Elsevier Science Limited.