Effect of Resistive Coupled Microwave Sintering on the Micro Hardness and Thermal Properties of Infrared Transparent Nano Yttria

摘要

Resistive coupled microwave sintering technique which couples the resistive heating and microwave heating effectively is employed to sinter infrared transparent yttria to 99.2% of the theoretical density. The pellets fabricated from the ultra-fine nano powder with average particle size ~15nm synthesized by combustion technique and sintered at 1450℃ with an average grain size of 0.22μm. For a comparative study of the hardness and thermal properties two other variants of sintering strategies, conventional sintering and susceptor assisted microwave sintering are also employed. A comprehensive analysis on the hardness reveals that the hardness of the pellets sintered via resistive coupled microwave heating is 8.85 GPa and is superior to the pellets sintered using the other two techniques. The microhardness of the pellets sintered via resistive heating is found to be 6.64 GPa and that for pellets sintered via susceptor assisted microwave heating is 7.88 GPa. The thermal properties of the pellets like thermal conductivity, thermal diffusivity and the specific heat capacity are also analyzed in detail. The results clearly indicate that the yttria ultra fine nanophase powder synthesised by the single step combustion method and sintered via resistive coupled microwave heating shows better mechanical and thermal properties which can be used very effectively for the fabrication of infrared transparent windows and domes.