EFFECT OF PRECURSOR PARTICLE-SIZE ON THE DENSIFICATION AND CRYSTALLIZATION BEHAVIOR OF MULLITE

Stoichiometric mullite, 3Al2O3.2SiO2, has been prepared from a variety of colloidal and solution precursors. In order to change the level of mixing, the size of the silica particles has been varied while keepin g the alumina (boehmite) particle size constant. The effect of varying particle size on the crystallization and densification behavior has b een studied. Densification behavior was characterized by measuring the bulk density of pellets as a function of heat treatment temperature a nd by dilatometry. Phase development was examined by thermal analysis and X-ray diffraction. Results showed that the formation of crystallin e phases including mullite inhibited densification. The formation of m ullite was controlled by the initial segregation of alumina and silica in the gel. A heat treatment time-temperature profile designed to opt imize the densification of the colloidal powders was investigated in o rder to compare the ability of the different gels to densify.