Densification behaviour and microstructure of gel-derived phase-pure mullite in the presence of sinter additives

Gels with high pure mullite composition have been synthesized using aluminu m nitrate nanohydrate and ethyl silicate. Pure mullite has been sintered to 88.5% of the T.D., when sintered at 1600 degreesC for 3 h. Suitable sinter ing aids such as SrO (0.5 wt.%) and clay (2 wt.%) have tremendous effect in promoting the densification behavior of mullite to attain density to 98 an d 95% of T.D. respectively at relatively low temperatures by pressureless s intering. SrO promotes the densification of pure mullite via liquid phase s intering and also does clay assist the viscous flow sintering. Clear differ ences found in the microstructures of mullite could be related to the diffe rent sintering aids, which have apparent effect on the densification behavi or. SrO doped samples show a duplex microstructure of fine equiaxed and elo ngated grain morphology, while the clay doped samples show equiaxed and aci cular morphology. (C) 2001 Elsevier Science Ltd. All rights reserved.