Precision microwave/resistance heating study of zirconia: Absence of microwave effect

A precision study of the microwave hybrid (2.45 GHz) and resistance heating of 3Y-TZP was undertaken during 1994-96, although these data [1-6] generally are not acquired easily. Preliminary testing involved calibration of thermocouples within the operating cavity to ensure correct temperature measurement and demonstration of microwave absorption in the absence of a susceptor. The effects of heating rate, soak time, and soak temperature were determined in terms of measurements of thermal gradient across the sample diameter, open and closed porosities, bulk density, and grain size. Comparison of these results, combined with data from other studies of rapid resistance heating for the same material, indicates that it is not necessary to invoke a microwave effect to explain the data, which show no significant differences between the two modes of heating.