PREPARATION OF AN ALUMINUM TITANATE-25 VOL-PERCENT MULLITE COMPOSITE BY SINTERING OF GEL-COATED POWDERS

A gel-coated powder processing, i.e. mullite precursor gel coating syn thesised Al2TiO5 solid solution (with 2.5 wt% MgO) particles, was used to prepare an Al2TiO5-25 vol% mullite composite precursor. The mullit isation, densification, mechanical and thermal properties of the compo site have been investigated. It was found that direct mullitisation oc curred at 988 degrees C in the composite precursor this being attribut ed to the presence of Al2TiO5 particles. Two different mullite morphol ogies with near isometric and acicular shapes were observed. The forma tion 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 composit e 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.