SINTERING AND MICROSTRUCTURAL INVESTIGATIONS ON COMBUSTION PROCESSED MULLITE

Various grades of mullite have been prepared by the combustion route u sing different fuels and silica sources of the redox mixture. Sinterin g behaviour and microstructure of combustion processed mullite have be en investigated. Pure mullite sintered at 1650 degrees C showed 3% shr inkage and was porous. The microstructure shows the presence of equiax ed grains. Hot isostatic pressing (100 MPa, 1500 degrees C 30 min) fol lowed by sintering at 1700 degrees C yielded >95% theoretical density. Mullite with 5 wt% of Y2O3 ol MgO sintered at 1650 degrees C achieved high density (approximate to 95% theoretical density) with a shrinkag e of 18 and 22% respectively. The microstructure showed the presence o f anisotropic elongated mullite grains and corundum particles. The enh anced densification of mullite with additives is attributed to the for mation of liquid phase which facilitates diffusion.