Influence of CaO on microstructure and properties of MgAl2O4 transparent ceramics

Transparent magnesium aluminate spinel (MgAl2O4) ceramics were successfully fabricated from commercial spinel powders via air presintering and hot isostatic pressing (HIP) using CaO as sintering additive. The influence of the CaO content on microstructure, densification process and optical quality of MgAl2O4 ceramics were investigated. It was found that using CaO as sintering additive would prompt the sintering process significantly. The relative densities of MgAl2O4 ceramics presintered at 1525.C change from 92.1% to 97.8% with the amount of CaO increasing from 0 to 0.15 wt%, and the average grain sizes of presintered MgAl2O4 ceramics increase from 0.4 mu m to 0.8 mu m, correspondingly. However, when the CaO content increases to 0.15 wt%, the secondary phase grains (calcium aluminate) occur in MgAl2O4 ceramics, which severely reduces the optical quality. The transparent MgAl2O4 ceramic with 0.125 wt% CaO presintered at 1525 degrees C for 3 h and HIP post-treated at 1600 degrees C for 3 h shows the best in-line transmittance of 86.3% at 1100 nm and 83.7% at 600 nm, the average grain size of 2.9 mu m.