Effects of calcination temperature on powder state and pre-sintering structure of transparent MgAl2O4 ceramics

The powder state of MgAl 2 O 4 strongly affects the densification and optical properties of transparent ceramics. In this work, MgAl 2 O 4 powders with different calcination-induced powder states were obtained by gradient calcination of a nanosized co-precipitated precursor. The densification behavior during pre-sintering and the final transmittance after HIP were systematically investigated. With elevated calcination temperature, the primary particle size increased from 38 to 63 nm (from SEM analysis) and the specific surface area decreased from 76.49 to 36.25 m 2 /g. Coarsened powders require a higher pre-sintering temperature to convert interconnected pores into closed pores. An empirical relation was established between the optimal pre-sintering temperature and calcination temperature: T p r e ≈ T c a l / 4 + 1200 $T_{pre}\approx T_{cal}/4+1200$ . The best MgAl 2 O 4 transparent ceramic exhibited an in-line transmittance of about 81% at 1400 nm.