Paper about x-ray microwave calorimetry in Thermochimica Acta

A new paper entitled “Microwave calorimetry using X-rays” has just been published in the scientific journal Thermochimica Acta. The paper describes some recent experimental results of the Electromagnetic Wave Processing Group of the Swiss Federal Laboratories for Materials Testing and Research – EMPA- in collaboration with the Microwave Area of the Institute ITACA.

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.

The paper is published on line and it is available in the website of Thermochimica Acta.

For more information about the experiments described in the paper, please contact directly with the authors.

Paper about microwave synthesis in Thermochimica Acta

A new paper entitled “Reactive synthesis of Ti–Al intermetallics during microwave heating in an E-field maximum” has recently been published in the scientific journal Thermochimica Acta. This work describes some experiments carried out by the Electromagnetic Wave Processing Group of the Swiss Federal Laboratories for Materials Testing and Research – EMPA- in collaboration with the Microwave Area of the Institute ITACA.

The experiments deal about the time-resolved X-ray diffraction synchrotron radiation technique used in combination with E-field microwave heating to study in situ the kinetics of intermetallic phase formation in the Ti–Al system.

The reaction of Ti with Al is triggered by the melting and spreading of Al onto the surface of Ti particles. The tetragonal TiAl3phase is the primary reaction product, formed by instantaneous nucleation at the interface between the unreacted Ti cores and the Al melt. The growth of TiAl3 layers is diffusion-controlled.

These preliminary results demonstrate that microwave heating can readily be used to rapidly synthesise intermetallic phases from high-purity elemental powders constituents.

The paper is published on line and can be found in the website of Thermochimica Acta.

For more information about the experiments described in the paper, please contact directly with the authors.

SLS Measurements

Researchers of the Swiss Federal Laboratories for Materials Testing and Research – EMPA – lead by Dr. Sebastien Vaucher in collaboration with researchers of the Microwave Division of the research institute ITACA are performing since 2006 time-resolved experiments pioneering in situ microwave heating experiments at the Suisse Light Source, Materials Science Beamline (SLS-MS).

The Swiss Light Source (SLS) at the Paul Scherrer Institut (PSI) is a third-generation synchrotron light source. In the design of SLS a high priority was given to the items quality (high brightness), flexibility (wide wavelength spectrum) and stability (very stable temperature conditions) for the primary electron beam and the secondary photon beams. With an energy of 2.4 GeV, it provides photon beams of high brightness for research in materials science, biology and chemistry. The SLS is the Swiss National Source, open for international research groups as well. It offers unique research opportunities to academic research teams as well as industrial research groups.

The fast frame rate of the MYTHEN detector enables experiments to be carried out in which the structural and microstructural evolution of solids under microwave application can be accurately followed in near-to-real time, while monitoring the microwave heating processes and eventually fine tuning the microwave application for processing for a broad variety of materials. The high-temperature time-resolved powder diffraction experiments provide a detailed set of informations on the phase transformation sequence(s) and kinetics during the exposure of the materials to microwaves.

The picture below shows the facilities of SLS and the microwave equipment of the measurements

In addition, 3D microtomography is a modern powerful instrument to observe the morphology of conventional or microwave sintered parts. Synchrotron-based X-ray tomographic experiments are performed at the TOMCAT beamline of the Swiss Light Source to investigate the inner structure of metal-diamond composites manufactured by liquid metal infiltration. The access to the cross-sections of bulk sintered materials offers a deeper insight into the interface reactions taking place during microwave heating.

This opens new possibilities for the evaluation of microwave effects at the interface between the dissimilar constituents of composite materials and supports the improvement of the microwave heating powder processing route towards sintered parts with high uniformity and improved thermal contact at the metal-diamond interfaces.

An excellent example of these measurements is the efficient microwave-assisted carbothermal reduction of magnetite Fe3O4 to iron, a process of high interest for the steel industry. A transient iron oxide phase was found which intermediates the transition from magnetite, Fe3O4, to wüstite, FeO. The kinetics of this phase transformation provides a deeper understanding of volumetric heating by microwaves.

Some of these measurements have been published in the following scientific journals.

  • Nicula R, Ishizaki K, Stir M, Catala,Civera J,M, Vaucher S , “Microwave energy absorption driven by dynamic structural and magnetization states in Fe85B15 metallic glass ribbons”, APPLIED PHYSICS LETTERS 95, 174104 (2009)
  • Nicula R, Stir M, Ishizaki K, Catala,Civera J,M, Vaucher S, “Nanocrystallization of amorphous alloys using microwaves: in situ timeresolved synchrotron radiation studies”, JOURNAL OF PHYSICS: CONFERENCE SERIES 144, 012109 (2009)
  • Nicula R, Stir M, Ishizaki K, Catala,civera JM, Vaucher S , “Rapid nanocrystallization of softmagnetic amorphous alloys using microwave induction heating”, SCRIPTA MATERIALIA 60, 120 (2009)