ULTRASONIC AND DIELECTRIC CHARACTERIZATION OF MICROWAVE-SINTERED AND CONVENTIONALLY SINTERED ZINC-OXIDE

Zinc oxide samples were prepared by microwave- and conventional-sinter ing 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 prep ared by the two techniques. The real and imaginary parts of the permit tivity of the samples processed by the two techniques were measured ov er a wide frequency range, In both cases, there was an increase in the measured permittivity values with decreasing porosity; however, the m icron;ave-sintered samples had considerably higher values. Porosity le vels were evaluated using bulk density measurements and scanning elect ron microscopy analysis. Significantly more densification was observed at intermediate temperatures for microwave sintering than for convent ional sintering.