Center Europeen Of La Ceramique

Limoges, France

Center Europeen Of La Ceramique

Limoges, France
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Tomilov A.,Center Europeen Of La Ceramique | Videcoq A.,Center Europeen Of La Ceramique | Cerbelaud M.,University of Nantes | Piechowiak M.A.,Center Europeen Of La Ceramique | And 5 more authors.
Journal of Physical Chemistry B | Year: 2013

Numerical simulations constitute a precious tool for understanding the role of key parameters influencing the colloidal arrangement in suspensions, which is crucial for many applications. The present paper investigates numerically the role of hydrodynamic interactions on the aggregation processes in colloidal suspensions. Three simulation techniques are used: Brownian dynamics without hydrodynamic interactions, Brownian dynamics including some of the hydrodynamic interactions, using the Yamakawa-Rotne-Prager tensor, and stochastic rotation dynamics coupled with molecular dynamics. A system of monodisperse colloids strongly interacting through a generalized Lennard-Jones potential is studied for a colloid volume fraction ranging from 2.5 to 20%. Interestingly, effects of the hydrodynamic interactions are shown in the details of the aggregation processes. It is observed that the hydrodynamic interactions slow down the aggregation kinetics in the initial nucleation stage, while they speed up the next cluster coalescence stage. It is shown that the latter is due to an enhanced cluster diffusion in the simulations including hydrodynamic interactions. The higher the colloid volume fraction, the more pronounced the effects on the aggregation kinetics. It is also observed that hydrodynamic interactions slow down the reorganization kinetics. It turns out that the Brownian dynamics technique using the Yamakawa-Rotne-Prager tensor tends to overestimate the effects on cluster diffusion and cluster reorganization, even if it can be a method of choice for very dilute suspensions. © 2013 American Chemical Society.

Lignie A.,Charles Gerhardt Institute | Zhou W.,CNRS Charles Coulomb Laboratory | Armand P.,Charles Gerhardt Institute | Ruffle B.,CNRS Charles Coulomb Laboratory | And 6 more authors.
ChemPhysChem | Year: 2014

From high-precision Brillouin spectroscopy measurements, six elastic constants (C11, C33, C44, C66, C12, and C14) of a flux-grown GeO2 single crystal with the α-quartz-like structure are obtained in the 298-1273 K temperature range. High-temperature powder X-ray diffraction data is collected to determine the temperature dependence of the lattice parameters and the volume thermal expansion coefficients. The temperature dependence of the mass density, ρ, is evaluated and used to estimate the thermal dependence of its refractive indices (ordinary and extraordinary), according to the Lorentz-Lorenz equation. The extraction of the ambient piezoelectric stress contribution, e11, from the C′11-C11 difference gives, for the piezoelectric strain coefficient d11, a value of 5.7(2) pC N-1, which is more than twice that of α-quartz. As the quartz structure of α-GeO2 remains stable until melting, piezoelectric activity is observed until 1273 K. The temperature dependence of six elastic constants of a α-GeO2 flux-grown single crystal is identified within the temperature range 298-1273 K. The extraction of the ambient piezoelectric stress contribution results in a α-GeO2 piezoelectric strain coefficient that is more than twice that of α-quartz, confirming the potential of this phase as a piezoelectric material. Copyright © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Piechowiak M.A.,Center Europeen Of La Ceramique | Videcoq A.,Center Europeen Of La Ceramique | Ferrando R.,University of Genoa | Bochicchio D.,University of Genoa | And 2 more authors.
Physical Chemistry Chemical Physics | Year: 2012

Aggregation kinetics and gel formation in aqueous suspensions that undergo heteroaggregation are studied by means of Brownian dynamics simulations. The simulated system, described in a previous paper [M. A. Piechowiak, A. Videcoq, F. Rossignol, C. Pagnoux, C. Carrion, M. Cerbelaud, R. Ferrando, Langmuir, 2010, 26(15), 12540-12547.], is constituted of two kinds of synthesized, almost equally sized colloids: silica particles that are negatively charged and alumina-coated silica particles that are positively charged. The interactions between colloids are modeled by the DLVO potential. Several compositions are analyzed, from silica-rich to alumina-rich cases. The particle volume fraction φ is varied in the range 6-12%. The study of the aggregation kinetics allows us to clarify the effect of those variations on the clustering process. Gelation is analyzed by detection of spanning clusters in each x-, y-, z-direction of the cubic simulation box. Percolating networks start to be observed from φ = 7%, a low value of the volume fraction close to the solid volume fraction experimentally measured in sediments of those suspensions. © 2012 the Owner Societies.

Hubert M.,French National Center for Scientific Research | Delaizir G.,Center Europeen Of La Ceramique | Monnier J.,CNRS East Paris Institute of Chemistry and Materials Science | Godart C.,CNRS East Paris Institute of Chemistry and Materials Science | And 3 more authors.
Optics Express | Year: 2011

An innovative way to produce chalcogenide glasses and glass-ceramics for infrared devices is reported. This new method of synthesis at low temperature combining ball-milling and sintering by SPS (Spark Plasma Sintering) is a technological breakthrough to produce efficient infrared chalcogenide glasses and glass-ceramics. This technique will offer the possibility to strongly decrease the cost of infrared devices and to produce new chalcogenide glasses. It will also permit to increase the potential of some glass compositions by allowing their shaping at desired dimensions. © 2011 Optical Society of America.

Suasmoro S.,CNRS Heterogeneous Materials Study Group | Khalfi M.F.,University Djilali Liabes | Khalfi A.,University Djilali Liabes | Trolliard G.,Center Europeen Of La Ceramique | And 2 more authors.
Ceramics International | Year: 2012

The value of critical current density at 77 K in "zero" applied field (Jc) characterizing the superconducting state for YBa 2Cu3O7-δ ceramics is closely related to the microstructure. The interrelationships between the microstructural factors such as pore volume fraction, oxygen content, average grain size, are complex. However, these factors also influence the normal state resistivity measured at room temperature (ρ300). We demonstrate how the current carrying cross section influences Jc and ρ300 in a similar way. Data, reported for two classes of YBa2Cu3O7-δ: small grain porous ceramics and larger-grain denser ceramics, reveal an approximate linear relation between ρ300 K and Jc. Extrapolation of this relation to a fully dense small grain YBa 2Cu3O7-δ ceramic yields values of ρ300 = 0.4 mΩ cm and Jc = 103 A cm-2. © 2011 Published by Elsevier Ltd and Techna Group S.r.l.

Piechowiak M.A.,Center Europeen Of La Ceramique | Videcoq A.,Center Europeen Of La Ceramique | Rossignol F.,Center Europeen Of La Ceramique | Pagnoux C.,Center Europeen Of La Ceramique | And 3 more authors.
Langmuir | Year: 2010

Fluorescent silica and alumina-like spherical particles with almost equal sizes are synthesized. Dilute aqueous suspensions are prepared with various ratios of those colloidal particles that exhibit opposite surface charges. These suspensions undergo heteroaggregation for a wide range of compositions. The structure of the formed aggregates is analyzed by means of confocal microscopy. The experimental results are compared to those of Brownian dynamics simulations in which the interactions between colloids are modeled by the DLVO potential. Good agreement between experiments and simulations is obtained. © 2010 American Chemical Society.

Bourret J.,Center Europeen Of La Ceramique | Michot A.,Center Europeen Of La Ceramique | Tessier-Doyen N.,Center Europeen Of La Ceramique | Nait-Ali B.,Center Europeen Of La Ceramique | And 5 more authors.
Journal of the American Ceramic Society | Year: 2014

A clay-based material exhibiting high pore volume fraction and low thermal conductivity suitable for thermal insulation is described. Starting with a commercial clay containing >75% kaolinite, foams were made by mixing in water and methyl cellulose as a surfactant then beating. After drying at 70°C, the pore volume fraction >94% remains almost constant for treatments up to 1150°C. In contrast, the phases constituting the solid skeleton evolve strongly with removal of surfactant, dehydroxylation of kaolinite, and formation of mullite. The latter leads to greater mechanical strength but also an increase in thermal conductivity. Thermal treatment of the kaolin foam at 1100°C yields a suitable compromise between low thermal conductivity of 0.054 W.(m.K)-1 at room temperature with a compressive yield stress of 0.04 MPa. The radiation component in the effective thermal conductivity is <10% at 20°C increasing to >50% at 500°C. © 2014 The American Ceramic Society.

Seifi S.,Center Europeen Of La Ceramique | Seifi S.,CNRS Poitiers Institute of Chemistry: Materials and Natural Resources | Diatta-Dieme M.T.,University of Ziguinchor | Diatta-Dieme M.T.,Center Europeen Of La Ceramique | And 4 more authors.
Construction and Building Materials | Year: 2016

Kaolinite-urea complexes were prepared with kaolinite from KGa-1 kaolin by two techniques, mixing and ball-milling at room temperature in water. The intercalation degree was found to be 72% and 69% respectively. Urea-intercalated kaolinite has potential applications in industry, since it change most of the chemical and thermal behaviors. Particularly, ion intercalation into kaolinite structure changes the amount of reactive acidic and basic sites on the internal and external surfaces. In this study XRD patterns and infrared spectroscopy of kaolinite-urea complexes confirm the intercalation of urea into kaolinite by the expansion of the basal spacing of kaolinite from 0.715 nm to 1.069 nm. The expansion of kaolinite is due to entering urea into interlayers that confirms the occurrence of hydrogen bonding between urea and kaolinite. Thermal analyses (TG, DSC and thermodilatometry) evidence changes in transformation temperatures of intercalated kaolinite. The sintering densification is shifted to lower temperature and kaolinite-urea complexes can be used in new ceramics for building with lower CO2 specific emission. © 2016 Elsevier Ltd. All rights reserved.

Fukuda K.,Nagoya Institute of Technology | Asaka T.,Nagoya Institute of Technology | Hamaguchi R.,Nagoya Institute of Technology | Suzuki T.,Nagoya Institute of Technology | And 7 more authors.
Chemistry of Materials | Year: 2011

We have successfully synthesized the highly c-axis-oriented polycrystals of apatite-type lanthanum silicate by the reactive diffusion technique. When the La 2SiO 5/La 2Si 2O 7 diffusion couples were isothermally heated at 1773-1873 K for 5-100 h, the apatite polycrystals were readily produced in the form of a layer at the interfacial boundaries. The annealed couples were characterized using optical microscopy, micro-Raman spectroscopy, X-ray diffractometry, and electron probe microanalysis. The product layers were composed of the highly c-axis-oriented prismatic crystallites, with their elongation directions being almost parallel to the diffusion direction. The formation of the apatite layer was controlled by volume diffusion, the overall reaction of which is described by (10 + 6x)La 2SiO 5 + (4-3x)La 2Si 2O 7 → 3La 9.33+2x(SiO 4) 6O 2+3x (0.01 ≤ x ≤ 0.13). The apatite layer formed at 1873 K was characterized by the steady decrease of the x-value along the diffusion direction from 0.13 at the La 2SiO 5/apatite interface to 0.01 at the apatite/La 2Si 2O 7 interface. We have also prepared sandwich-type La 2Si 2O 7/La 2SiO 5/La 2Si 2O 7 diffusion couples and heated them at 1873 K for 100 h. The annealed couple was mechanically processed, and the thin-plate electrolyte consisting of the highly c-axis-oriented polycrystal was obtained. The oxide-ion conductivity was determined from the impedance spectroscopy data at 573-973 K, which steadily increased from 2.4 × 10 -3 S/cm to 2.39 × 10 -2 S/cm with increasing temperature. The empirical activation energy of conduction was 0.35 eV, which compares well with the calculated migration energy of 0.32 eV in a previous study. © 2011 American Chemical Society.

Fukuda K.,Nagoya Institute of Technology | Asaka T.,Nagoya Institute of Technology | Okino M.,Nagoya Institute of Technology | Berghout A.,Center Europeen Of La Ceramique | And 4 more authors.
Solid State Ionics | Year: 2012

The anisotropy of oxide-ion conduction was clarified for the apatite-type La 9.33 + 2x(SiO 4) 6O 2 + 3x (0.01 ≤ x ≤ 0.13). We synthesized the polycrystalline materials of apatite by the isothermal heating of the sandwich-type La 2Si 2O 7/La 2SiO 5/La 2Si 2O 7 diffusion couples at 1873 K for 100 h. The resulting polycrystals were subsequently characterized using optical microscopy, X-ray diffractometry and impedance spectroscopy. The individual c-axes of the crystallites were appreciably aligned along the diffusion direction, while their a-axes were, around the common c-axis direction, oriented randomly. We obtained the impedance spectroscopy data of the polycrystalline electrolyte, the planar electrodes of which were parallel to the common c-axis. Thus, the obtained bulk conductivity (σ̄ bulk ∥ c) corresponds to the average value of those perpendicular to the c-axis, which steadily increased from 1.6 × 10 - 5 to 3.8 × 10 - 4 S/cm with increasing temperature from 623 to 848 K. The bulk conductivity parallel to the c-axis (σ bulk ⊥ c) that was determined in a previous study was, when compared at the same temperature, necessarily higher than the corresponding σ̄ bulk ∥ c value; the magnitude of anisotropy (σ bulk ⊥ c / σ̄ bulk ∥ c) steadily decreased with increasing temperature from 2.1 × 10 2 at 623 K to 4.5 × 10 1 at 823 K. The activation energy of σ̄ bulk ∥ c was 0.71 eV, which is almost twice that of σ bulk ⊥ c (0.35 eV). © 2012 Elsevier B.V. All rights reserved.

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