Evaluation of ultrasonically determined elasticity-porosity relations in zinc oxide

Ultrasonically determined elastic moduli in ZnO samples sintered to various densities were evaluated using both an empirical model and the Mori-Tanaka effective field theory. Both approaches have been successfully used to model the modulus-porosity relations in several material systems. In the present investigation, application of the empirical model predicted elastic moduli which deviated significantly from the experimental results. The deviation was attributed to the porosity dependence of Poisson's ratio which was neglected in this model. When this dependence was accounted for empirically, the fit to the experimental data was improved dramatically. Analysis of the data in the context of the Mori-Tanaka model indicates that the porosity shape changes significantly during the sintering process. This analysis may provide a convenient way to quantitatively compare such changes for ceramic materials prepared by different processing techniques, such as by conventional and microwave sintering.