Fast pressureless sintering of highly infrared-transparent MgAlON ceramics at a low temperature using CaCO3-doped coarse bimodal powder

By doping CaCO₃ as sintering additive into the coarse MgAlON powder characterized by bimodal particle size distribution (D₅₀=0.9 µm), highly infrared-transparent MgAlON ceramics were successfully fabricated by pressureless sintering at 1790 °C for 90 min. The transmittance of 2 mm thick samples reaches 83.6% at 3750 nm. The fabricated MgAlON ceramics exhibit better transparency than those sintered at 1880 °C for 150 min, which were prepared via doping with Y₂O₃ as additive or using fine unimodal MgAlON powder (D₅₀=0.5 µm). Furthermore, using the coarse bimodal powder, transmittance of the CaCO₃-doped MgAlON can be enhanced by increasing temperature and holding time, with 87.6% (at 3750 nm) transmittance achieved when sintered at 1880 °C for 150 min. Both the robust sintering additive of CaCO₃ and the bimodal particle size distribution of the MgAlON powder, contribute to the fast densification and excellent transparency of the fabricated MgAlON ceramics.