Energy flow during microwave sintering of zirconia in the presence of a SiC susceptor

We present a theoretical model which examines the energy conversion during ceramic sintering in the presence of a susceptor. Zirconia (ZrO/sub 2/) as other low-loss materials couples very poorly to microwaves at low temperatures but since the loss increases with the temperature significantly, the coupling improves dramatically at high temperatures. In order to improve the heat transfer at low temperature, SiC susceptor is introduced; its relatively high losses facilitate good coupling with the microwave field (2.45 GHz). Three mechanisms are considered in the energy flow process: microwave absorption due to losses, black body radiation and heat convection. Computer simulation indicates that silicon carbide is heated rapidly when compared to zirconia, whereas zirconia reaches higher temperatures after a prolonged period of microwave exposure. It is shown that at low temperatures (<800 C) the main heating mechanism is the black-body radiation which emerges from the SiC. Above this temperature the microwave radiation is the main mechanism which contributes to the temperature increase of the zirconia. The simulation results are in agreement with experimental data.