The characteristics of the microwave sintering for alumina and ZTA ceramics in a domestic 2.45 GHz microwave oven was investigated. Alumina and ZTA were successfully sintered without thermal runaway by using an insulation box composed of alumina fiber insulator, zirconia fiber insulator, and SiC plate. To compare with the microwave sintering a series of comparative expeiments were performed in which alumina and ZTA were conventionally sintered and rapid-heated by using an identical heating profile to the microwave sintering in a conventional tube furnace.
In the microwave sintering alumina was sintered at a lower temperature in a shorter time and exibit a higher ratio of densification rate to grain growth rate than the conventional sintering. As a result microwave-sintered alumina showed a higher density and a smaller grain size. ZTA was also densified more rapidly and showed higher density for the case of microwave sintering than that of conventional sintering and rapid heating. These results could be explained by "microwave effect" that the diffusion rate is enhanced in a microwave field.
In ZTA system the microwave effect resulted in a distinctive densification behavior. Because of the faster microwave coupling of zirconia than that of alumina due to its higher dielectric loss factor at a lower temperature, relative density of ZTA sintered in the microwave field continuously increased with zirconia content contrary to the conventional sintering.
