A theoretical model is developed for the description of the compaction of granular materials exemplified by granulated ceramic powders. Its predictions compare satisfactorily to results of uniaxial compaction tests of ceramic granules of lead magnesium niobate‐lead titanate (PMN‐PT), rutile, and spray‐dried alumina. The theory uses volume‐based statistical mechanics and an activation analogy to treat, in parallel, the rearrangement of granules and their deformation. Variation of the model incorporates a distribution of barriers to deformation, which can be considered to include the effects of statistical pressure distributions within the compact. Other curve‐fitting schemes available in the literature are shown to correspond to particular cases of the theory, and a justification of the equations used in those schemes is provided on physical grounds.
Recent observations on microwave heating in ceramic materials have included saturation effects wherein the dependence of the heating rate on microwave power becomes sublinear, with a resulting decrease in efficiency relative to standard Joule heating. A model based on absorption by bivacancy rotations is shown to account for the anomalous power dependence. Rotation, by its very nature, is shown to result in an effective confinement of the dipoles and t o reproduce the sublinear effect both qualitatively and quantitatively. Explicit calculations are presented for a simple model, the results are examined in the light of observations on ferric oxide, and the rotational absorber model is compared with a translational counterpart treated earlier.
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