Microwave Hybrid Heating for Advanced Ceramic Sintering Processing

The fabrication process of engineering ceramics involves a tricky, time-consuming and energy-demanding sintering step which is conventionally performed using electrical or gas furnaces. A huge amount of recent research focuses on the use of microwave-assisted heating, mostly as microwave hybrid heating (MHH) using ceramic radiation susceptors for carrying out the sintering process. Microwave irradiation with a frequency and power range of 2.45 - 28.00 GHz and 0.5 – 6.0 kW, respectively, has been applied to a wide range of ceramic materials (oxides, nitrides, carbides, calcium-phosphates and hydrides) for the production of sintered near dense and even porous products. The literature review reveals that MHH hinders grain growth during the last step of the sintering process, eventually enhancing mechanical properties of the final engineering ceramic piece. The main advantage of MHH in ceramic sintering is the substantial lower amount of energy consumed. Mathematical modelling of the microwave-assisted sintering of ceramic materials has been reviewed and it is shown that prediction of grain and pore morphology evolution during sintering is still at its infancy. Accordingly, up-scaling problems and high initial costs are the main challenges to be overcome for the industrialization of MHH for ceramic sintering processes.