Microstructure development in calcium hexaluminate

Calcium hexaluminate (CA6) was prepared from alumina and calcium carbonate powders. The influence of processing method and firing temperature on calcium hexaluminate grain morphology was studied. A significant correlation was found between grain morphology and green density, porosity distribution and presence of agglomerates. Platelet grains were observed for low green densities and large pores, while more equiaxed grains were found when green density was increased. A model is proposed for the formation of equiaxed or platelet grains. The model is based on the number of contact areas between alumina and calcium carbonate grains in green specimens as well as on the free space available for calcium hexaluminate to grow.