Ultrasonic and dielectric characterization of microwave-sintered and conventionally sintered zinc oxide

Zinc oxide samples were prepared by microwave- and conventional-sintering processes using identical time-temperature profiles. Comparison of postsintering properties as a function of residual porosity over the range of 0%-35% indicated no significant difference in the ultrasonic velocity-porosity relations or the elastic moduli for the samples prepared by the two techniques. The real and imaginary parts of the permittivity of the samples processed by the two techniques were measured over a wide frequency range. In both cases, there was an increase in the measured permittivity values with decreasing porosity; however, the microwave-sintered samples had considerably higher values. Porosity levels were evaluated using bulk density measurements and scanning electron microscopy analysis. Significantly more densification was observed at intermediate temperatures for microwave sintering than for conventional sintering.