Abstract
Addition of calcium, strontium or barium nitrates to alumina powders promotes the crystallization “in situ” of calcium, strontium and barium hexaluminates during the sintering of green compacts. Calcium and strontium hexaluminates develop platelike structures randomly dispersed in the alumina matrix whereas barium hexaluminate does not. The strength and toughness of as-fired samples containing calcium or strontium hexaluminates are greater than those of the matrix. Materials containing barium hexaluminate have lower values. These composites maintain the same properties after aging for 30d at 35°C in aqueous or physiological solution and no chemical reaction between the ageing media and the hexaluminates was observed on examination by scanning electron microscope.
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