The Plasma and Electrical Contact group has the instruments to study chemical processes and problems associated with electrical contacts. It is also a long-time user of the Instruments, large facilities such as the European Synchrotron Radiation Facility (ESRF), the Synchrotron Soleil, neutron sources in France and England, the Mersen High Current Laboratory in Grenoble and the heavy ion storage rings in Denmark and Sweden.
Electric contacts
The "Electric Contacts" team is an expert in the study of the degradation of electrical contacts used in switches, in the automotive and aeronautical industries. The influence of arcing and mechanical stress on contact wear brings together fields such as metallurgy, magnetism, friction, mechanical properties of materials, plasma spectroscopy and ignition of electric cables.
The images, presented above with magnifications from x1'500 to x20'000, in false colors, were taken by scanning electron microscopy and colorized by deep learning. They show the surface of a silver electrode and the consequences of an electric arc, a plasma at several thousand kelvin, on this originally flat surface. The surface is very disturbed and covered with particles of different sizes. These particles are produced by the solidification of silver microdroplets, due to the ejection, via the buoyancy, of silver in liquid phase, at the level of the arc feet.
Recent publications:
Effects of arc during mechanical bounces on contact material for different power supply frequencies, A. Ramzi, E. Carvou, A. Schach, Proceeding of the 30th International Conference on Electric Contacts, 7-11 June 2021, Switzerland, pp. 52-59.
Study of vibration transfer in automotive connectors for understanding of fretting corrosion damage, M. Mavuni, E. Carvou, G. Lalet, Proceeding of the 30th International Conference on Electric Contacts, 7-11 June 2021, Switzerland, pp. 178-185.
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Nanoparticle formation in flames
This work is based on the use of Small Angle X-Ray Scattering (SAXS) to measure the size distribution of soot particles formed in hydrocarbon flames and how this distribution can be modified by additives. Experiments are performed at the ESRF in Grenoble. The group is a pioneer in this research that allows soot formation to be followed in-situ, in real time in laboratory scale flames.
Demonstration of the Onset of Soot Particle Aggregation and Growth in an Ethylene Flame by Small Angle X-Ray Scattering, J. B. A. Mitchell, S. di Stasio, J.L. LeGarrec, A.I. Florescu-Mitchell, T. Narayanan and M. Sztucki, Journal of Applied Physics 105, 124904 (2009).
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Nanoparticle formation in plasmas
Having demonstrated that SAXS can be used in dilute gaseous environments such as flames, we have applied the method to investigating nanoparticles created in microwave air plasmas and most recently in laser ablation plumes and electrical arcs. This is a non-intrusive method and yields information on nanoparticle condensation phenomena under extremes of temperature. Experiments are performed at the ESRF and Synchrotron Soleil in collaboration with researchers from the University of Tel Aviv in Israel, The University of Bourgogne and Schneider Electric.
Evidence for nanoparticles in microwave-generated fireballs observed by synchrotron X-ray scattering, J.B.A. Mitchell, J.L. LeGarrec, M. Sztucki, T. Nayaranan, V. Dikhtyar and E. Jerby, Phys. Rev. Lett. 100, 065001 (2008).
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Synchrotron radiation study of free nanoparticles
This work performed in collaboration with scientists from Synchrotron Soleil, the CEA, IRSN and the University of Rouen involves injecting pre-prepared nanoparticles into a vacuum apparatus via an aerodynamic lens and performing x-ray photoelectron and mass spectrometric studies on these particles as they are exposed to tuneable soft x-ray radiation. Amongst the goals of the project is to examine slow oxidation phenomena and to characterise soot particle chemistry. In future experiments, SAXS will be applied to these experiments to tie down the size of the particles exiting the lens, prior to irradiation.
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