Search results for "Material chemistry"

Study of the oxidation mechanisms of Plutonium

2022

Oxidation is a key point when applied to a material such as plutonium. It is essential to understand the oxidation mechanisms in order to predict and prevent catastrophic oxidation, thus managing the reprocessing cost.The originality of this work lies in the coupling of different experimental techniques : in-situ X-ray diffraction, Photo-electron spectroscopy (XPS), FIB-SEM, Raman spectrometry and X-ray absorption (EXAFS) with numerical techniques : CALPHAD and Reverse Monte Carlo, in order to determine the oxidation mechanisms of the studied alloy : -phase stabilised PuGa 1 at%.Study of oxidation of this alloy at different temperatures and oxygen partial pressures showed the oxidation kin…

Physical, chemical and mechanical evolution of the fuel-cladding interface in irradiated PWR fuel rods

2022

During the fuel irradiation in nuclear reactor, the fuel-cladding assembly is exposed to several irradiation-induced modifications. The fuel swelling coupled with cladding creep leads to a contact between the fuel and the cladding. The oxygen transport from the UO2 fuel to the zirconium layer induces progressively the Zr-cladding oxidation. This oxidation is initially local with the formation of islets. Then, with the increasing burnup of the fuel, it conducts to a continuous layer of about 8-µm thickness, localized at the fuel-cladding interface. At high burnup, zirconia growths anchor themselves in the periphery of the fuel (which is restructured) leading to pellet/cladding interlocking. …

Perfluoroketene dithioacetals and perfluorodithiocarboxylic acid derivatives: Versatile tools for organofluorine synthesis

2007

Perfluoroketene dithioacetals are simple and versatile compounds that can be transformed into a large variety of trifluoromethyl derivatives, in particular aza- and thiaheterocycles, perhalodithiocrotonic esters, and fluorinated dithiol thiones. These unsaturated perfluorodithioesters and analogs give interesting polar cycloaddition reactions whose mechanism is strongly influenced by the fluorine substitution. This substitution plays an important role in the reactivity of saturated perfluorodithiocarboxylic acids as well. Except for the carbophilic addition of allyl Grignard reagents to perfluorocarboxamides, a domino thiophilic addition-fluoride elimination was the main reaction process. I…

Syntheses of TiO2 anatase nanocrystals with controlled size distribution. Influence of the crystallites size on the Raman spectrum and investigation …

2006

The determination of the size and the size distribution of anatase TiO2 nanopowders using Raman spectroscopy is presented. Several synthesis methods (soft chemistry, water-in-oil microemulsion, continuous hydrothermal synthesis) are used in order to control the size (from 3 to 20 nm), shape, phase and size distribution. The shift and width of the anatase Eg peak are often used to obtain the nanoparticles size. Homever, this peak is also sensitive to nonstoichiometry and others parameters. Low-frequency Raman scattering does not suffer from this problem. Size distibutions obtained by Raman spectroscopy and MET micrographs are compared. Finally, in situ Raman spectroscopy is used to study the…

Vers une approche multi-échelle et pluridisciplinaire pour l'étude et la prédiction des processus de corrosion localisée : Aspects expérimentaux et n…

2006

Habilitation à Diriger des Recherches

Synthesis of nanocrystalline NbAl3 by mechanically activated field activated pressure assisted technique

2001

Mechanical activation effect on self - sustaining combustion reaction in Mo - Si system

2001

High-temperature oxidation of Fe3Al and Fe3AlZr intermetallics

2010

International audience

Study of "alite-tricalcium silicate-gypsum"complex system

2007

International audience; The systematic study of “alite-C3A-gypsum” systems by using simultaneously the dynamic mode rheometry and the isothermal microcalorimetry made it possible to specify interactions between the different components and to quantify the effect of the mixtures on the cohesive properties of C-S-H. In the system “alite-C3A”, the presence of aluminate ions decreases both the growth rate of C-S-H and the ratio dG' /dQ which represents the increase in the elastic modulus dG' corresponding to the formation of a certain quantity of C-S-H, estimated by released heat dQ; for the great quantities of C3A, there is a positive effect of the surface developed by calcium hydroaluminates …

Hydration of alite containing alumimium

2009

International audience; The most important phase in cement is tricalcium silicate which leads during its hydration to the nucleation and growth of calcium silicate hydrate (referred to C-S-H (CaO)x-SiO2-(H2O)y). The development of this hydrate around the cement grains is responsible for the setting and hardening of cement pastes The general term for designating the tricalcium silicate in cements is alite. This name relates to all polymorphs containing various foreign ions inserted in their structure. These ions may influence the intrinsic reactivity and once released during the dissolution, they may interact also with C-S-H. The melt phase during clinkering is rich in aluminium and moreover…