The microwave technique has been developed for ceramic sintering in recent ten more years. In this paper the difference between microwave sintering and conventional sintering is investigated by means of XRD, SEM, and TEM. Three kinds of ceramic materials are prepared for two sintering method respectively, while pure-Al_2O_3 and Al_2O_3 (90%wt.)+Cr_2O_3 (10%wt.) are selected to stand for solid sintering and Si_3N_4 (5%wt.Al_2O_3+4%wt.Y_2O_3) stands for liquid sintering. The results from comparing with the rate of linear contraction, microstructure change and grain growth, solid solubility of Cr_2O_3 in Al_2O_3, and the appearance of liquid phase and α→β phase in Si_3N_4 of sintered specimen show that microwave sintering needs less energy, has quicker sintering speed and lower sintering temperature. The size of grain is smaller and evenner and the way of its growth is collection in microwave sintering. These are mainly because that microwave promotes volumn diffusion in solid sintering and decreased viscosity and forming temperature of liquid phase in liquid sintering. By studying of the intrinstic characteristics of surface and interface of ceramic material and the coupling mechanism microwave to ceramic, the Higher Temperature Microzone Model is set up, and the mechanism of microwave promots volumn diffusion and decreases viscosity and forming temperature of liquid phase is theoretical discussed.
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