Sustainable Processing of High-Temperature Ceramics Using Microwave Energy

 

Processing of industrial ceramics for use in high-temperature service environments is currently accomplished by conventional heating that is energy-intensive and polluting. Microwave renders thermal and non-thermal effects that significantly benefit processing of ceramics. Microwave processing is adopted in industrial applications for realizing time, energy and cost savings, and for improving the end product quality and uniformity.

The heating mechanisms are different in conventional and microwave processing of materials. Conventional methods heat the surface and then rely on conduction, convection and radiation for transfer of heat into the material. Microwave, on the other hand, directly interacts with the material across its volume. Given the surface heat losses, heat transport under microwave radiation is from the core towards surface. The specific mechanisms and efficiency of microwave heating depend upon the material type. Microwave radiation also renders non-thermal effects that benefit diffusion, chemical reaction and densification phenomena.

Some advantages of microwave processing are: (i) reduced processing time, temperature and power consumption, and enhanced diffusion and reaction rates; (ii) finer, more uniform and nearly fault-free microstructures, yielding improved and more consistent physical and mechanical properties; (iii) reduced thermal stresses and heat-affected zones; and (iv) improved interfacial qualities resulting from selective hating of phases with higher microwave absorption. These advantages can reduce the energy demand and the corresponding polluting effects of processing ceramics by the currently prevalent conventional heating.