Microstructure and properties of MgAl2O4 transparent ceramics fabricated by hot isostatic pressing

Transparent magnesium aluminate spinet (MgAl2O4) ceramics were successfully fabricated by presintering in air and hot isostatic pressing (HIP) with commercial spinet and calcium oxide powders as raw materials. Due to the liquid phase formation of calcium aluminate in the presintering process, small amount of CaO (0.1 wt%) is found to be very effective for the densification of the ceramics. The influence of presintering temperature on the microstructure, densification process, optical quality and mechanical properties of MgAl2O4 ceramics were investigated. It is found that the relative density of presintered MgAl2O4 ceramics changes from 86.3% to 99.4% when the presintering temperature increases from 1450 degrees C to 1550 degrees C. The average grain size of MgAl2O4 ceramics increases from 0.7 mu m to 4.5 mu m with the increase of presintering temperature from 1450 to 1650 degrees C. The transparent MgAl2O4 ceramic sample presintered at 1525 degrees C for 3 h and HIP post-treated at 1600 degrees C for 3 h shows high in-line transmittances of 86.3% at 1100 nm and 82.5% at 600 nm, the average grain size of 1.5 mu m, the high flexural strength of 281 +/- 16 MPa and hardness of 13.23 +/- 0.07 GPa.