Mullite/Alumina Particulate Composites by Infiltration Processing

A method has been developed for incorporating mullite into alumina by infiltrating an alumina preform with a prehydrolyzed ethyl silicate solution, followed by heating to decompose the infiltrant, form mullite, and densify the mullite/alumina composite. It has been found that the major portion of the weight loss of gelled ethyl silicate sols occurs in the 250° to 350°C range. Mullite formed in infiltrated bodies at ∼1475°C and specimens containing 12 to 15 vol% mullite reached 98.5% of the theoretical density after heating for 2 h at 1650°C. The mullite was found to be well dispersed within the alumina matrix and its presence decreased grain growth in the alumina by more than an order of magnitude.