Improvement of translucency in Al2O3 ceramics by two-step sintering technique

Pure, 140, 500, and 2500 ppm MgO-doped Al2O3 specimens were sintered at 1700 °C in a vacuum with and without pre-sintering heat treatment (HT) at 800 °C for 50 h in air. Pre-sintering HT improved the transmittance in the visible (400–700 nm) range significantly. This enhanced transmittance was explained in terms of the removal of residual pores and the homogenization of the microstructure due to the lowering of the boundary mobility as a result of the MgO addition and the suppression of local densification through a pre-coarsening step.