Low-temperature synthesis of calcium–hexaluminate/magnesium–aluminum spinel composite ceramics

Abstract

Calcium–hexaluminate/magnesium–aluminum spinel ceramic composites were synthesized at 1450°C for 3h using a precursor from dolomite and industrial aluminium hydroxide through a 200°C hydrothermal treatment, which was 100°C lower than the traditional process. The main reason for this treatment was to initiate a phase transformation from gibbsite to boehmite. The morphology of calcium hexaluminate was determined by the crystal structure of aluminium hydroxide. Loosely stacked platelets were caused by tabular gibbsite, and cross-distribution flakes were due to cross-sheet boehmite. The porosity and compressive strength of composites synthesized at 1500°C for 3h increased with increasing hydrothermal temperature. CA6 of composites from hydrothermal treatment at 200°C had a more regular hexagonal plate-like morphology, total porosity of 72.2%, and compressive strength of 142.7MPa. However, composites from hydrothermal treatment at 25°C exhibited a weaker diffraction peak of calcium hexaluminate and an uncompleted crystal appearance.