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 combination of the operating frequency, the sample shape, and its permittivity. In contrast, our studies show that on a microscopic scale, the local electric fields are disproportionately intense close to grain boundaries and rough surfaces due to strong focusing. Also, the electric field in the interparticle contact zone exhibits preferred polarization directions despite illumination by a randomly polarized wave. This can lead to a highly nonuniform energy deposition and accelerated mass transfer rates via ponderomotive diffusion and plasma generation. (C) 1999 American Institute of Physics. [S0021-8979(99)08101-3].