EFFECT OF EXCESS SIO2 ON THE REACTION SINTERING OF ALUMINUM TITANATE-25 VOL-PERCENT MULLITE COMPOSITES

A stepwise alkoxide hydrolysis processing was used to prepare aluminiu m titanate-25 vol% mullite composite powders. The effect of three leve ls of excess SiO2 (1, 3 and 5 wt%, expressed relative to Al2TiO5) on d ensification, microstructure, mechanical strength and thermal expansio n has been investigated. The addition of excess SiO2 reduced the const rained effect caused by the formation of Al2TiO5 and mullite. After th e formation of Al2TiO5 and mullite, the densification rate was enhance d for the samples containing excess SiO2. These effects can be attribu ted to the presence of a liquid phase at the firing temperatures. The presence of liquid phases during sintering promoted grain growth of Al 2TiO5 and also the formation of acicular mullite, The mechanical stren gth of the composition with 3 wt% excess SiO2 showed a three-fold impr ovement over the sample without excess SiO2, whereas the corresponding thermal expansion was still relatively low (similar to 1.3 x 10(-6) K -1 from 20 to 1000 degrees C). The reduced porosity was believed to be the predominant factor contributing to the improvement of the mechani cal strength (C) 1998 Elsevier Science Limited and Techna S.r.l.