**4. Conclusions**

22 Sintering of Ceramics – New Emerging Techniques

Fig. 12. SEM micrographs of the fracture surface of MHFS zirconia (Tosoh TZ-3Y) processed

It is difficult to process zirconia in a 2.45GHz microwave furnace because the dielectric properties of this material change rapidly with temperature (see Figure 2) and its thermal conductivity is very low. Therefore, the use of hybrid heating is very important to produce

at 2.45GHz with power level of 1.8kW for 20min (99% density), a) internal region,

b) near-surface region.

Studies by our research group confirm that microwave hybrid fast sintering can be employed successfully to sinter low and high dielectric loss ceramics, producing highly dense ceramics and suppressing grain growth in the final stages of sintering. Controlled heating schedules and the use of suitably designed susceptor materials yield uniform microstructures without stress-related cracking or the development of incipient fusion, hot spots or thermal runaway. Thus, successful microwave fast sintering depends on the strict control of sintering conditions, striking an adequate balance between power and time or temperature and time to obtain highly dense and homogeneous microstructures.
