Effect of seeds on the formation of sol-gel mullite

Mullite precursor gels have been prepared from a mixture of particulate boehmite sol and tetraethoxysilane at a pH of 4. The sol has been seeded with submicron size α-Al 2O 3, γ-Al 2O 3 and mullite limited to two percent by weight of the mullite phase. These gels have been invesitgated with respect to phase formation, densification and microstructural development. Dilatometric studies on the seeded precursor gels indicate marked shrinkage in their profiles. Of the different seed nuclei, fine mullite particles have shown excellent influence in the early ceramic phase formation as well as densification. Further they induce complete transformation of the precursor gel to the high temperature phase as well as a uniform fine-grained microstructure.