Microstructural evolution of Ti4+-doped calcium hexaaluminate ceramics

Calcium hexaaluminate (CaAl12O19 or CA(6)) ceramics were fabricated by solid-state reaction sintering of Al2O3 and CaCO3 powder mixtures. The influence of Ti-4(+) doping on microstructural development of CA(6) ceramics was investigated. After doping Ti-4(+), the lengths and widths of the CA(6) grains increased, and the aspect ratios decreased significantly. Al vacancies (V-Al) in mirror planes of CA(6) are created by substituting Ti-4(+) for Al3+. As more V-Al generates in the mirror planes, vacancy concentration varies considerably between mirror planes and spinel blocks. Combined with the fact that the ionic radius of Ti-4(+) is larger than that of Al3+, the crystal growth of CA(6) along c axis is more promoted than that along basal plane. CaTiO3 and residual Al2O3 were observed in Ti-4(+)-doped samples because of the reactions between CaO and TiO2.