Influence of presintering temperature on magnesium aluminate spinel transparent ceramics fabricated by solid‐state reactive sintering

Transparent magnesium aluminate spinel (MgO·1.1Al2O3) ceramics were successfully prepared by the solid-state reactive sintering method using commercial γ-Al2O3 and MgO powders as raw material. The extra alumina compared with stoichiometric spinel was found efficient to improve the optical quality of transparent spinel ceramics. The influence of presintering temperature on the phase formation, densification process, microstructure evolution, and optical quality of MgO·1.1Al2O3 was systematically investigated. The α-Al2O3 phase was found in the ceramics calcined at 800°C. With the calcination temperature exceeding 1000°C, the magnesium aluminate spinel ceramics were all pure spinel phase. The density increased from 3.05 to 3.53 g/cm3 and the average grain size increased from 0.5 to 1.9 μm with the increase of presintering temperature from 1450°C to 1600°C. The transparent MgO·1.1Al2O3 ceramic sample presintered at 1550°C for 3 h and hot isostatic pressing posttreated at 1600°C for 3 h showed the best in-line transmittance of 86.5% at 1100 nm and 84.3% at 800 nm.