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Cerbelaud M.,University of Nantes | Lestriez B.,University of Nantes | Guyomard D.,University of Nantes | Videcoq A.,Limoges National Superior School of Industrial Ceramics | Ferrando R.,CNR Institute of Materials for Electronics and Magnetism

Dilute aqueous suspensions of silicon nanoparticles and sodium carboxymethylcellulose salt (CMC) are studied experimentally and numerically by Brownian dynamics simulations. The study focuses on the adsorption of CMC on silicon and on the aggregation state as a function of the suspension composition. To perform simulations, a coarse-grained model has first been developed for the CMC molecules. Then, this model has been applied to study numerically the behavior of suspensions of silicon and CMC. Simulation parameters have been fixed on the basis of experimental characterizations. Results of Brownian dynamics simulations performed with our model are found in qualitative good agreement with experiments and allow a good description of the main features of the experimental behavior. © 2012 American Chemical Society. Source

Gaalova J.,Czech Institute of Chemical Process Fundamentals | Barbier J.,University of Poitiers | Rossignol S.,Limoges National Superior School of Industrial Ceramics
Journal of Hazardous Materials

This study was a comparison between Ru-catalysts and similar, previously investigated, Pt-catalysts. In this paper, ruthenium catalysts for catalytic wet air oxidation are prepared, characterized and tested. Both catalysts were supported on commercial CeO2 as well as mixed oxide Zr0.1(Ce0.75Pr0.25)0.9O2. The catalysts were characterized by measuring the oxygen storage capacities (OSC), BET, XRD, FTIR and chemisorption of hydrogen. In addition, the effect of sintering (treatments under H2) was compared with both of the catalysts. The comparison of the results showed that initial intrinsic activity of ruthenium is not significantly influenced by the type of the support, which is contrast to platinum. Furthermore, the particle size of Ru had an important effect on CWAO activity: the higher the particle size, the better the activity. This was different with Pt-catalysts, where the optimal particle size was smaller, having about 15% of metal dispersion. © 2010 Elsevier B.V. Source

Cerbelaud M.,University of Genoa | Ferrando R.,University of Genoa | Videcoq A.,Limoges National Superior School of Industrial Ceramics
Journal of Chemical Physics

The influence of dilution on the aggregation process of suspensions composed of two kinds of oxide particles (alumina positively charged particles d1 =400 nm and silica negatively charged particles d2 =250 nm) has been studied by computer simulations. Two kinds of simulations have been performed: Brownian dynamics simulations to study the aggregation process and its kinetics and global minimization searches to find the most stable configurations of aggregates. We show that the rate of dilution has a strong influence on the structure and on the shape of aggregates in Brownian dynamics simulations. By confronting these aggregates with the stable aggregates found by global minimization, we demonstrate that they are metastable and their shape is explained by the competition between the kinetics of aggregate coalescence and the kinetics of aggregate reorganization into more stable configurations. © 2010 American Institute of Physics. Source

Martias C.,Limoges National Superior School of Industrial Ceramics | Joliff Y.,University of Toulon | Favotto C.,University of Toulon
Composites Part B: Engineering

This work presents thermomechanical experiments whose results have led to a new formulation of composite panels for building construction. This panel has the advantage to be lightweight and 2 h firebreak. Plaster, under the β-hemihydrate form, is used as a matrix and mineral products (vermiculite, mica, glass fibers) are added as lightweight additives, mechanical reinforcement and thermal insulator. The both effects of the particles size distribution of plaster, and of the amounts of additives, on the mechanical properties are investigated at room temperature. Three approaches are proposed and compared: experimental, analytical and numerical to quantify the impact of additives on the mechanical properties. Thus, the results obtained, including porosity, density and mechanical property, permit to retain a formulation of composite. This formulation is tested under ISO 834 fire conditions to validate its use as passive protection in building construction. © 2014 Elsevier Ltd. All rights reserved. Source

Lebreton F.,CEA Marcoule Nuclear Site | Lebreton F.,Limoges National Superior School of Industrial Ceramics | Belin R.C.,French Atomic Energy Commission | Prieur D.,CEA Marcoule Nuclear Site | And 2 more authors.
Inorganic Chemistry

In order to reduce the nuclear waste inventory and radiotoxicity, U 1-xAm xO 2±δ materials are promising fuels for heterogeneous transmutation. In this context, they are generally fabricated from UO 2+δ and AmO 2-δ dioxide powders. In the subsequent solid solution, americium is assumed to be trivalent whereas uranium exhibits a mixed-valence (+IV/+V) state. However, no formation mechanisms were ever evidenced and, more particularly, it was not possible to know whether the reduction of Am(IV) to Am(III) occurs before the solid-solution formation, or only once it is established. In this study, we used high-temperature X-ray diffraction on a UO 2±δ/AmO 2-δ (15 mol%) mixture to observe in situ the formation of the U 1-xAm xO 2±δ solid solution. We show that UO 2+δ is, at relatively low temperature (<700 K), oxidized to U 4O 9-δ, which is likely to be caused by oxygen release from the simultaneous AmO 2-δ reduction to cubic Am 2O 3±δ. Cubic Am 2O 3+δ then transforms to hexagonal Am 2O 3 at 1300 K. Thus, the initial Am(IV) is fully reduced to Am(III) before the solid solution starts forming at 1740 K. The UO 2 fluorite phase vanishes after 4 h at 1970 K, indicating that the formation of the solid solution is completed, which proves that this solid solution is formed after the complete reduction of Am(IV) to Am(III). © 2012 American Chemical Society. Source

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