Microwave-Enhanced Solid State Reactions in Ionic Crystalline Solids

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The primary goal of this research project is to isolate and characterize a microwave-field-enhancement effect on ionic transport in ionic ceramics. The investigation will emphasize experiments to establish whether this microwave driving force is a dominant mechanism responsible for enhanced solid state diffusion and of interface chemical reactions. Measurements will made using halide salts, a 14 GHz microwave source, and a nonresonant waveguide applicator. Theoretical analyses will be conducted in collaboration with researchers from the Institute of Applied Physics, Russian Academy of Science (Nizhny Novgorod). Design of the experiments, the experimental applicator, and experimental operation will be completed in collaboration with a researcher from Rockwell International. Two sets of experiments are planned: (1) measurements of microwave effects on grain boundary diffusion of K+ ions into NaCl and Na+ ions into KCl, and (2) measurements of microwave effects on interface-limited solid-state reaction rates for (pseudo) binary compound formation. In both cases, th e reactions will be compared for microwave-irradiated and microwave-free samples as a function of sample temperature, microwave field strength, and electric field polarization. In addition, the PIs plan experimental studies of temperature distributions within microwave-heated ceramic specimen. This will address questions of accurate thermometry in microwave heating/materials processing and whether reports of enhanced reactions in microwave-heated glasses and ceramics can be (at least partially) explained by core-to surface temperature differentials of up to several hundred degrees Celsius. Specifically, the PIs will characterize internal temperature gradients due to inverted temperature profiles through the experimental examination of solid-state compound formation in microwave-heated oxide particulate composites in which the two component oxide phases in the starting compact react to form one or two quasi binary compounds. The results will be compared to predictions based on heat transport and microwave absorption modeling in oxide particulate composites.