Mullite/SiAlON/alumina composites by infiltration processing

The formation of mullite/SiAlON/alumina composites was studied by infiltrating a SiAlON/alumina-base composite with two different solutions, followed by thermal treatment, The base composite was prepared from a mixture of tabular Al2O3 grains, fume SiO2, and aluminum powders, The mixture was pressed into test bars and nitrided in a nitrogen-gas (N-2) atmosphere at 1480 degrees C. The infiltrants were prehydrolyzed ethyl polysilicate solution and ethyl polysilicate-aluminum nitrate solution, The composites were infiltrated under vacuum, cured at 100 degrees C, and precalcined in air at 700 degrees C. This infiltration process was repeated several times to produce bars that had been subjected to multiple infiltrations, then the bars were calcined in a N-2 atmosphere at 1480 degrees C to obtain mullite/SiAlON/alumina composites. The infiltration process increased the percentage of nitrogenous crystalline and mullite phases in the matrix; therefore, a decrease of the composite microporosity was observed, The infiltration increased the mechanical strength of the composites, Of the two composites, the one produced using prehydrolyzed ethyl polysilicate as the infiltrant had a higher mechanical strength, before and after being subjected to a severe thermal shock.