Dynamic High-Temperature Monitoring of Microwave Energy Absorption and Heating of Materials with Ultrafast In Situ Synchrotron X-Ray Tomographic Microscopy and Powder Diffraction Techniques

Abstract

In-situ time- and temperature-resolved synchrotron radiation techniques like ultrafast synchrotron X-ray tomographic microscopy and powder diffraction are unique tools for the dynamic characterization of materials processing by microwave heating. The absorption of microwave energy is typically a very fast process, with heating rates of the order of hundreds of degrees per second being no exception. The microwave energy absorption efficiency changes significantly with increasing temperature. Another unique feature of microwave heating is the intrinsic dielectric and/or magnetic selectivity, which often translates into the preferential deposition of microwave field energy only into specific specimen regions. For inhomogeneous materials in particular, complex patterns for the dynamic electromagnetic and temperature field distributions can be expected thus making the use of 3D monitoring methods not only meaningful but also necessary. We report on our recent progress with the in-situ characterization of microwave heating of metallic, ceramic and composite materials at very high heating rates. Experimental methods with subsecond temporal resolution, in particular high-temperature time-resolved X-ray scattering and time-resolved X-ray microtomography using synchrotron radiation, are discussed. Examples include microwave-assisted structural phase transitions and sintering in Al-alloys, foaming of construction materials, microwave processing of ceramics and composites.