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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. Source

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. Source

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. Source

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. Source

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. Source

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