Progress in understanding the dielectric properties of heterogeneous materials results in an increasing diversity of applications. Today’s computational electromagnetics (CEM) offers the capability to model simple materials routinely even on personal computers. However accounting for the random stucture of nanocomposites remains a challenge that requires the help of emerging multiscale methods to incorporate microscopic information The effect of packing, grain size, porosity as well as surfaces and interfaces playing a crucial role in a variety of polarization processes, the interaction with MW cannot be accounted for by simple rules of mixtures. CE remains tied to the fundamental question about the effective medium approaches for characterizing nanoscale materials. Our research allows quantifying the evolution of each crystalline phases of a nanocomposite under microwave irradiation as well as the microwave field influence on the effective dielectric properties. Detailed correlations between history of strain, composition, temperature, and final physical and mechanical properties of the material become possible.

Our research on microwave analytics and in-situ microwave heating instrumentation includes the development of technical solutions for time-resolved process monitoring, volumetric temperature measurements, real-time monitoring of phase formation, grain-growth, sintering and of structural phase transitions.
Dedicated microwave applicators for broad band dielectric characterisation of nanostructured materials from room- to high-temperature are developed in collaboration with the Polytechnical University of Valencia (Spain) and the CNRS – University of Lille (France).

Time-resolved X-ray diffraction
Heating rates of tens of degrees per second or higher are not unusual in microwave heating. The use of high energy synchrotron radiation and of fast X-ray detectors is required for in situ microwave heating X-ray powder diffraction studies.
Pioneering in situ microwave heating experiments using synchrotron radiation are performed since late 2006 at the Swiss Light Source on various powder specimens. We follow the evolution of constituent phases in different nanomaterials with sub-second time resolution. The high-temperature time-resolved powder diffraction experiments provide information on chemical reactions, phase transformation sequences, microstructural evolution and kinetics during the exposure of the materials to microwaves. The in situ TRXRD synchrotron radiation experiments are performed at the Materials Science beamline MS X04SA at the SLS.

Stir, M., Ishizaki, K., Vaucher, S. and Nicula, R. Mechanism and kinetics of the reduction of magnetite to iron during heating in a microwave E-field maximum. J. Appl. Phys. 105, Article number 124901 (4 pp.) (2009). DOI:10.1063/1.3148264

Vaucher, S., Stir, M., Ishizaki, K., Catala-Civera, J.-M. & Nicula, R. Reactive synthesis of Ti-Al intermetallics during microwave heating in an E-field maximum. Thermochimica Acta 522 (2011) pp 151-154. DOI:10.1016/j.tca.2010.11.026