ENHANCING THE MICROHARDNESS OF MAGNESIUM ALUMINATE SPINEL BY RESISTIVE COUPLED MICROWAVE SINTERING FOR INFRARED TRANSPARENT WINDOW APPLICATION

A novel resistive coupled microwave sintering technique which couples the resistive heating and microwave heating was effectively employed to sinter infrared transparent magnesium aluminate spinel to 99.3% of the theoretical density. The pellets fabricated from the fine nano powder with average particle size ~15 nm synthesized by combustion technique was sintered at 1420oC with an average grain size of 0.18 µm. A comprehensive analysis on the hardness revealed that the hardness of the pellets sintered via resistive coupled microwave heating is 16.07 GPa and was superior to the pellets sintered using two other variants of sintering strategies, resistive heating and susceptor assisted microwave heating. The results clearly indicate that the magnesium aluminate spinel ultra fine nanophase powder synthesised by the single step combustion method and sintered via resistive coupled microwave heating yields better hardness without compromising the transmittance can be used very effectively for the fabrication of high quality futuristic infrared transparent windows and domes.