This study used monocalcium aluminate (CaAl2O4, CA) to produce ceramic composites with duplex microstructures by hydration and gelation reactions of the aluminate, and compared the properties with those made by a die-pressing process with mixed powders. The microstructure of sintered bodies, the fracture strengths and toughness of the composites with and without thermal shock was characterized by different techniques. Experimental results show that the composites with the addition of CA resulted in the formation of CA6 (CaO*6Al2O3) platelets, so as to reveal two types of microstructures, either in a cluster of agglomerated platelets or with a uniform distribution of platelet CA6 grains. The former, which appeared as a duplex microstructure consisted of a dense matrix and distributed clusters of CA6 platelets, gave an improvement in toughness and thermal shock resistance. The toughness mechanisms of the samples with duplex microstructures are discussed.

Keywords: calcium aluminate, composite, platelets, duplex, microstructure