A thin adhesive film, located between two bonded adherents, is capable of localizing the energy of elastic waves in the form of an interface wave. Under study are the phase velocity and transmission losses of the interface wave which were measured during the entire course of polymerization of the adhesive. It is shown that the phase velocity of the interface wave and the effective shear modulus of the interface film, calculated from the velocity data, are related to the strength of the adhesive bonds. The general transmission loss factor, which is a function of the relaxation maximum of losses arising during the course of polymerization of the adhesive, is another parameter correlated with the strength. The shear strength of the joint was determined on a special specimen in the form of a lap joint, which was also used for acoustic measurements.

Temperature gradients that develop in ceramic materials during microwave heating are known to be strongly dependent on the applied microwave frequency. To gain a better understanding of this dependence, identical samples of ZnO powder compacts were microwave heated at three distinct widely separated frequencies of 2.45, 30, and 83 GHz and the core and surface temperatures were simultaneously monitored. At 2.45 GHz, the approximately uniform “volumetric” heating tends to raise the temperature of the sample as a whole, but the interior becomes hotter than the exterior because of heat loss from the surface. At 30 and 83 GHz, this interior to exterior temperature difference was found to be reversed, especially for high heating rates. This reversal resulted from increased energy deposition close to the sample's surface associated with reduced skin depth. A model for solving Maxwell's equations was incorporated into a newly developed two‐dimensional (2‐D) heat transport simulation code. The numerical simulations are in agreement with the experimental results. Simultaneous application of two or more widely separated frequencies is expected to allow electronic tailoring of the temperature profile during sintering.

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.