Sintering behaviour of porous ceramic kaolin–corundum composites: Phase evolution and densification

Kaolinite–corundum (derived from bauxite) associations were assessed as candidate matrices in the field of porous ceramics composites. Particles of corundum were expected to behave as non reactive second phase, deflecting the matrix cracks and increasing the toughness. Porosity and densification were monitored by developing coarse grains (67 wt.% of grains <1 mm and 33 wt.% of grains between 1 and 4 mm) of bauxite-based chamotte with corundum as principal phase. The main features resulting from the use of bauxite-based chamotte were the increase of softening point, the absence of vitrification in the temperature range of refractory composites in service and the achievement of a good thermal stability. For temperatures ranging between 1200 and 1300 °C, flint kaolin matrix did not show any reaction with the red corundum grains. Refractory composites elaborated with more than 30% of corundum exhibited typical final characteristics which satisfied ASTM C155 and ISO 1109 standards for refractory materials, namely: the chemical composition (Al2O3 > 56 wt.%), the secondary expansion (<0.1%), the total porosity (∼45 vol.%) and the bulk density (1.9 g/cm3). Such materials are promising low-cost solutions for the production of porous ceramics composites.