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

Calcium–hexaluminate/magnesium–aluminum spinel ceramic composites were synthesized at 1450 °C for 3 h 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 3 h 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 142.7 MPa. However, composites from hydrothermal treatment at 25 °C exhibited a weaker diffraction peak of calcium hexaluminate and an uncompleted crystal appearance.