Nonthermal effects on microwave radiation on ionic diffusion in ionic crystalline ceramics

Summary form only given, as follows. Numerous claims have been made of observations that microwave heating of ceramics promotes faster processing or solid state reactions (e.g., sintering, bonding, tracer ion diffusion) than conventional furnace heating. These claims are controversial due to the absence of a verifiable theoretical explanation as well as questions on the interpretation of sample temperature measurements obtained in the presence of microwave fields or during microwave heating. A recent experimental investigation has clearly established that intense microwave fields can yield enhanced ion (or vacancy) diffusion in ionic crystalline ceramics. The results are in qualitative agreement with a model in which the microwave fields exert a ponderomotive or radiation pressure acting near the surfaces of NaCl crystals or grains. It is believed that this phenomenon explains the observations of microwave-enhanced tracer ion diffusion in higher temperature oxide ceramics and glasses. Future work will explore the role of this phenomenon in grain boundary diffusion and sintering during microwave processing of ceramics.