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

Transparent magnesium aluminate spinel (MgO center dot 1.1Al(2)O(3)) ceramics were successfully prepared by the solid-state reactive sintering method using commercial gamma-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 center dot 1.1Al(2)O(3) was systematically investigated. The alpha-Al2O3 phase was found in the ceramics calcined at 800 degrees C. With the calcination temperature exceeding 1000 degrees C, the magnesium aluminate spinel ceramics were all pure spinel phase. The density increased from 3.05 to 3.53 g/cm(3) and the average grain size increased from 0.5 to 1.9 mu m with the increase of presintering temperature from 1450 degrees C to 1600 degrees C. The transparent MgO center dot 1.1Al(2)O(3) ceramic sample presintered at 1550 degrees C for 3 h and hot isostatic pressing posttreated at 1600 degrees C for 3 h showed the best in-line transmittance of 86.5% at 1100 nm and 84.3% at 800 nm.