Mullite Alumina Particulate Composites by Infiltration Processing: II, Infiltration and Characterization

Mullite/alumina composites were fabricated by infiltrating porous alumina preforms with a hydrolyzed ethyl silicate sol. Evidence is presented which suggests that initial infiltration occurred without complete filling of the porosity by the sol. Multiple infiltrations were used to increase the amount of SiO2 introduced but led to blockage of the pores in the surface of the preform. Sintered bodies had concentration gradients, SiO2 decreasing from the surface inward. Although mullite limited grain growth in alumina, in partially modified bodies large grains (>1 mm) with a preferred orientation were observed at the interface between the two zones.