Kaoutar Naji

Most of the lines of the French railway network are divided into segments equipped with “tracks circuits”. They are used for both the train position detection and the signals control required for the traffic safety and are separated by Insulated Rail Joints (IRJ) which consist in end-to-end track sections separated by an insulating gap generally made of polymer and are maintained rigid by bolted side fishplates. Due to the nature of IRJ materials and rail steel creep, the usually employed IRJs constitute weak points regarding mechanical and electrical properties which lead to maintenance interventions or traffic malfunctions. The current study aims to design and to characterize innovative and reliable IRJs constituted of three parts. A middle part, which ensures the electrical insulation, is surrounded by two graded parts providing a progressive evolution of the mechanical properties between the insulating part and the rail...

The advanced knowledge of the nature of the point defects (type of charge carriers, their concentrations,…) in uranium oxide presents a great interest for both manufacturing phases but also for understanding the behaviour of these oxides under irradiation and during mechanical or thermal loads to which they are subjected. The measurement of the electrical properties provides an indirect way to characterise the nature of these defects. Uranium oxide has several valence states. The conditions for moving from a valence to another one depend upon the redox potential of the environment. This oxide can be found in several forms depending on the chemical composition and thus on the oxygen content in the gas phase with which it’s in equilibrium. In this work, a device called ADELAIDE was used. It enables both the in-situ characterisation of the electrical properties of the samples, the control of the oxygen partial pressure and temperature. Particularly, the control of the oxygen partial pressure may be achieved when using equilibrium between hydrogen, oxygen and water vapor. Depending on the partial pressures aimed, a different equilibrium between carbon dioxide, oxygen and carbon monoxide can be used. This internship was concerned by: - Bibliographic study describing uranium dioxide, its crystallographic structure, thermodynamic and electrical properties. - Presentation of the experimental device and the theoretical expression of the oxygen partial pressure for both equilibriums mentioned above. - Realisation of electrical conductivity measurements of different samples of uranium dioxide. A qualification of the measuring conductivity was achieved as well as a study of the effects of the presence of an aliovalent doping on these properties.