| This research seeks (i) to use a single-mode microwave cavity to process ceramics and ceramic based composites, (ii) to study the conditions or parameters needed to successfully apply the microwaves to processing of materials, and (iii) to study the interactions between materials and microwaves.; In sintering studies, alumina ceramics and alumina matrix 10wt% zirconia composites were microwave-heated between 1500{dollar}spcirc{dollar}C and 1600{dollar}spcirc{dollar}C giving a density of about 96% up to nearly 100% of theoretical without 'thermal runaway' or cracking. The density, hardness, and toughness for individually- and batch-processed specimens were relatively uniform with respect to the cavity mode and specimens' location inside the insulation called 'casket' during microwave heating. For example, the mean and standard deviation of the hardness was 16.19 GPa {dollar}pm{dollar} 0.58 GPa for a total of 24 alumina specimens microwave-heated in batches of 6 specimens each. This corresponds to a coefficient of variation of only 0.036.; Microwave power was successfully utilized to burn out organic binder from ceramic powder compacts without cracking the specimens and without using any insulation material to enclose the specimens. The extent of binder burn-out significantly depended on material composition due to the dielectric properties of each material. For example, Al{dollar}sb2{dollar}O{dollar}sb3{dollar}/10wt% SiC burned out the binder more successfully than either monolithic alumina or alumina containing 10wt% zirconia.; In a joining study, ceramic materials and glass ceramics were successfully joined using a spin-on material interlayer under ambient or low externally applied pressures. Notches of submillimeter dimension were made in the specimens prior to joining. During the joining process the notch dimensions changed by no more than a few percent.; In addition, this study revealed that compared to conventional heating, microwave heating has remarkable effects in crack healing. For alumina specimens with initial Vickers cracks about 350{dollar}mu{dollar}m long, the cracks were nearly completely healed by microwave heating at 1742K, while conventional heating healed the identical cracks by only about 40% to 50% of the initial crack length.; In microwave hybrid heating utilizing a casket, the casket plays an important role. The measured steady-state inner wall casket temperature, T{dollar}sb{lcub}rm i{rcub}{dollar}, varied from about 1100{dollar}spcirc{dollar}C to 1500{dollar}spcirc{dollar}C depending on the casket geometry at 600 Watts input power. In addition, for a microwave input power of 200 Watts to 700 Watts, T{dollar}sb{lcub}rm i{rcub}{dollar} ranged from 740{dollar}spcirc{dollar}C to 1574{dollar}spcirc{dollar}C depending on a combination of casket geometry and microwave power. Based on the experimental data, a simple model equation was developed to describe T{dollar}sb{lcub}rm i{rcub}{dollar} in terms of the casket geometry and the microwave power level. A least-squares fitting indicated that the model equation well described the experimental data obtained in this study. The R{dollar}sp2{dollar}, coefficient of determination value was 0.954 for all 144 data used for fitting without grouping the data. |
