Microfocusing and polarization effects in spherical neck ceramic microstructures during microwave processing

During microwave sintering of compacted ceramic powders, the electric field distribution within the ceramic body on a macroscale is determined by a co mbination of the operating frequency, the sample shape, and its permittivit y. In contrast, our studies show that on a microscopic scale, the local ele ctric fields are disproportionately intense close to grain boundaries and r ough surfaces due to strong focusing. Also, the electric field in the inter particle contact zone exhibits preferred polarization directions despite il lumination by a randomly polarized wave. This can lead to a highly nonunifo rm energy deposition and accelerated mass transfer rates via ponderomotive diffusion and plasma generation. (C) 1999 American Institute of Physics. [S 0021-8979(99)08101-3].