Microwave calorimetry using X-rays

An alternative approach for microwave calorimetry is proposed which relies on the synchrotron radiation powder diffraction technique as well as on the Grüneisen formalism for the analysis of thermal expansion. Cobalt was selected as suitable magnetic material for the present evaluation of the method. First results are reported concerning the calorimetric assessment of the HCP (hexagonal close-packed) to FCC (face centered cubic) transition of cobalt from in situ time-resolved X-ray diffraction experiments performed during magnetic (H-field) microwave heating. The X-ray calorimetry method yields specific heat capacity estimations that compare well with results from conventional differential scanning calorimetry measurements. In the presence of the 2.45 GHz microwave H-field, an 'anomalous' behaviour of the heat capacity across the structural phase transition is detected, which can be correlated with the magnetic spin reorientation transition of cobalt in the same temperature range. © 2011 Elsevier B.V. All rights reserved.We kindly acknowledge the help of Fabia Gozzo, Antonio Cervellino and the team at the MS X04SA beamline at the Swiss Light Source. This work was jointly supported by the Swiss National Science Foundation (SNSF) and by the German Science Foundation (DFG), Project "Calorimetry of phase transitions in ultrafast conventional and electromagnetic heating", SNSF Grant 20PA21-129123 and DFG Grant SCHI331/21-1.Nicula, R.; Stir, M.; Wurm, A.; Catalá Civera, JM.; Ishizaki, K.; Vaucher, S.; Zhuravlev, E.... (2011). Microwave calorimetry using X-rays. Thermochimica Acta. 526(1):137-142. https://doi.org/10.1016/j.tca.2011.09.007S137142526