Cemhti

Orléans, France
Orléans, France
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Valensi F.,University of Orléans | Pellerin N.,CEMHTI | Pellerin N.,University of Orléans | Pellerin S.,University of Orléans | And 2 more authors.
High Temperature Material Processes | Year: 2010

The shielding gas used in the welding process has a strong influence on the metal transfer characteristics. When the gas is chemically active the physicochemical properties of the electrodes can be strongly altered which can increase or decrease arc stability. In order to get a better control over the process it is essential to understand how the electrodes are affected. As the electrode extremities are molten they can easily adsorb gases from the shielding gas, which can affect their microstructure. CO2 is one of the most commonly used active shielding gases. It is then interesting to know if the liquid metal at the extremity of the electrode can adsorbed the carbon it supplies, as it has strong influence on steel mechanical properties. Besides, various phases can form during metal cooling, depending on its concentration. It is then possible to get information on the carbon content by studying the ratio between phases. In order to show a possible enrichment, only the relative spatial evolution can be studied and no accurate phase identification is needed. Cross sections of the samples have been studied, using mainly optic microscopy. The two main phase ratio have been calculated after processing the obtained images. The results show a higher ratio of the phase associated to the highest carbon content close to the sample periphery, which support the hypothesis of carbon adsorption by the molten metal.


Bazin D.,University Paris - Sud | Andre G.,French Atomic Energy Commission | Weil R.,University Paris - Sud | Matzen G.,CEMHTI | And 4 more authors.
Urology | Year: 2012

Objective: Bacterial imprints are always observed on highly carbonated apatite kidney stones but not struvite kidney stones. Struvite and carbonated apatite stones with a high CO 3 2/PO 4 3 rate are believed to develop from infections, but their structural differences at the mesoscopic scale lack explanation. Methods: We investigated 17 urinary calculi composed mainly of struvite or carbonated apatite by Fourier transform infrared, scanning electron microscopy, and powder neutron diffraction techniques. Results: Carbonated apatite but not struvite stones showed bacterial imprints. If the same stone contained both carbonated apatite and struvite components, bacterial imprints were observed on the carbonated apatite but not the struvite part. Moreover, neutron powder diffraction experiments revealed the crystal size of struvite stones were larger than that of carbonated apatite stones (250 ± 50 vs 50 nm). Conclusion: Bacterial imprints may appear more easily on kidney stones with small nanocrystals, such as carbonated apatite than with large nanocrystals, such as struvite. This approach may help identify bacteria contributing to stone formation, perhaps with negative results of urine culture. © 2012 Elsevier Inc. All Rights Reserved.


Loyan A.V.,National Aerospace University - Kharkiv Aviation Institute | Koshelev N.N.,National Aerospace University - Kharkiv Aviation Institute | Maksymenko T.A.,National Aerospace University - Kharkiv Aviation Institute | Leufroy A.,University of Orléans | And 9 more authors.
Romanian Reports of Physics | Year: 2011

In first, we present the performances of the lower power Hall effect thruster SPT-20M7 manufactured by KhAI (Ukraine). In second, we show that the ion energy distribution function in the plasma plume, and recorded by two Retarded Potential Analyser (KhAI and GREMI), exhibits two populations. In third, we indicate the chemical and microstructural changes of the insulated ceramics of the thruster.


Plevacova K.,CEA Cadarache Center | Journeau C.,CEA Cadarache Center | Piluso P.,CEA Cadarache Center | Zhdanov V.,National Nuclear Center | And 2 more authors.
Journal of Nuclear Materials | Year: 2011

Since the TMI and Chernobyl accidents the risk of nuclear severe accident is intensively studied for existing and future reactors. In case of a core melt-down accident in a nuclear reactor, a complex melt, called corium, forms. To be able to perform experiments with prototypic corium materials at high temperature, a coating which resists to different corium melts related to Generation I and II Water Reactors and Generation IV sodium fast reactor was researched in our experimental platforms both in IAE NNC in Kazakhstan and in CEA in France. Zirconium carbide was selected as protective coating for graphite crucibles used in our induction furnaces: VCG-135 and VITI. The method of coating application, called reactive wetting, was developed. Zirconium carbide revealed to resist well to the (U x, Zr y)O 2-z water reactor corium. It has also the advantage not to bring new elements to this chemical system. The coating was then tested with sodium fast reactor corium melts containing steel or absorbers. Undesirable interactions were observed between the coating and these materials, leading to the carburization of the corium ingots. Concerning the resistance of the coating to oxide melts without ZrO 2, the zirconium carbide coating keeps its role of protective barrier with UO 2-Al 2O 3 below 2000 °C but does not resist to a UO 2-Eu 2O 3 mixture. © 2011 Elsevier B.V. All rights reserved.


Plevacova K.,CEA Cadarache Center | Journeau C.,CEA Cadarache Center | Piluso P.,CEA Cadarache Center | Poirier J.,CEMHTI
Ceramics International | Year: 2014

In the frame of the Generation IV Sodium Fast Reactor (SFR) safety studies, a core catcher with a sacrificial material could be placed at the bottom of the nuclear reactor. Its role is to dilute the (U, Pu)O2 molten fuel in case of a hypothetical core meltdown accident. A Al2O 3-HfO2 ceramic is a candidate for the sacrificial material. To understand how the molten fuel would mix with this sacrificial material, the UO2-Al2O3-HfO2 system was investigated at CEA Cadarache PLINIUS corium platform. The eutectic position of the UO2-Al2O3-HfO2 was determined: the eutectic temperature is 1728±22 C (2001±22 K) and the eutectic composition is 30 wt% UO2-35 wt% Al2O 3-35 wt% HfO2. Then, the pseudo-binary UO2-(50 wt% Al2O3-50 wt% HfO2) phase diagram has been proposed. © 2013 Elsevier Ltd and Techna Group S.r.l.


De Bilbao E.,Prisme Institute | Blond E.,Prisme Institute | Michel C.,Albi-Carmaux School of Engineering | Cutard T.,Albi-Carmaux School of Engineering | And 2 more authors.
InterCeram: International Ceramic Review | Year: 2010

This paper proposes a new method to determine the Young's modulus by means of high temperature bending test. Considering that the global behaviour of the experimental device and the sample is purely elastic during the unload phase and by exploiting that the effects of the indentation under the contact are lower at the beginning of the unloading, it is proposed to deduce the Young's modulus from the slope of the unloading curve. It can be shown that the Young's modulus for different silicon carbide (SiC) based refractory materials obtained by using this method is in good agreement with results of others tests such as tensile test or ultrasonic measurement.


Borodin O.,U.S. Army | Price D.L.,CEMHTI | Aoun B.,Argonne National Laboratory | Gonzalez M.A.,Laue Langevin Institute | And 6 more authors.
Physical Chemistry Chemical Physics | Year: 2016

The influence of water on the structure of a prototype ionic liquid (IL) 1-octyl-3-methylimidazolium tetrafluoroborate (C8mimBF4) is examined in the IL-rich regime using high-energy X-ray diffraction (HEXRD) and molecular dynamics (MD) simulations. A many-body polarizable force field APPLE&P was developed for C8mimBF4-water mixture. It predicts structure factors of pure IL and IL-water mixture in excellent agreement with the HEXRD experiments. The MD results provide detailed insights into the structural changes from the partial structure factors, 2-D projections of the simulation box and 3-D distribution functions. Water partitioning with IL and its competition with BF4 - for complexing the imidazolium rings was examined. The added water molecules occupy a diffuse coordination shell around the imidazolium ring but are not present around the alkyl tail. The strong coordination of the fluorine atoms of the BF4 - anions to the imidazolium ring is not significantly changed by the addition of water. A complementary packing of water and imidazolium around BF4 - was found. These results are consistent with the very small differences in the average structure between the pure IL and the mixture. © the Owner Societies 2016.


Leboeuf V.,Cemhti | Blondeau J.-P.,Cemhti | De Sousa Meneses D.,Cemhti | Veron O.,Cemhti
Journal of Non-Crystalline Solids | Year: 2013

The aim of this work is to obtain information on structural modification of glass during potassium ionic exchange for mechanical reinforcement. These modifications are evaluated by two characterization methods; scanning electronic microscopy and Fourier transform infrared spectroscopy. The SEM study gives the potassium concentration pro file, allows the kinetics of ionic exchange to be observed and gives access to the interdiffusion coefficient with a good concordance between theoretical and experimental concentration profiles. We have verified that the exchange is done between Na+ and K+ ions. We have coupled this SEM result to infrared spectroscopy measurements in middle and far infrared ranges and have proved that infrared spectroscopy allows the access of the structural evolution of glass near the surface after chemical tempering. The evolution of the stretching vibration of Qn modes, between 850 and 1250 cm-1, shows a depolymerization of the silica network. The Gaussian positions of Qn modes evolve with the exchange time and prove that there is an increase in the rigidity of the silica network due to a compression state. © 2013 Published by Elsevier B.V.

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