Etude de la ségrégation de surface dans des alliages de substitution par la méthode de Monte Carlo. II. Applications aux systèmes binaire et ternaire

Application of the Monte Carlo simulation to the estimation of surface segregations is presented for the f.c.c. Cu-Pt system. The estimates are discussed and compared with experimental results from the literature. Then this method is applied to the ternary b.c.c. Fe-Cr-Al system. The influence on the segregation profiles of energetic parameters expressing the chemical interactions between elements is discussed.L'application de la méthode de Monte Carlo à la prévision des ségrégations de surface est présentée dans le cas du système c.f.c. Cu-Pt. Les estimations sont discutées comparativement aux résultats expérimentaux de la littérature. Cette technique de simulation est ensuite appliquée au système ternaire c.c. Fe-Cr-Al. L'influence des paramètres énergétiques traduisant les interactions chimiques sur les profils de ségrégation est discutée

Surface segregation in binary Cu-Ni and Pt-Ni alloys using Monte Carlo simulation

International audienceMonte Carlo simulation is used to calculate the surface segregation in Cu-Ni and Pt-Ni alloys. The first system is characterized by its segregating tendency with a weak size effect, the second one exhibits an ordering tendency with a strong mismatch. Introduction of an elastic energy term in the Markov chain is necessary for the Pt-Ni system whose segregating properties are dominated by competition between chemical and elastic energy contributions. Interesting information is deduced from this kind of simulation concerning the atomic distributions in the surface plane

Etude de la ségrégation superficielle dans les alliages de substitution par la méthode de Monte Carlo. I. Aspects généraux

The study of surface segregation in substitutional alloys is approached by Monte Carlo simulation. First, we study a linear open chain of two components in order to compare the results given by simulation with those given by an exact treatment. Then we discuss the surface segregation of a semi-infinite crystal of a binary alloy and, in particular, the factors responsible for the size distribution of surface clusters. Finally the choice of an energetic model is briefly discussed with respect to surface segregation.L'étude de la ségrégation de surface dans des alliages de substitution est abordée par la méthode de Monte Carlo. Dans un premier temps nous traitons le cas d'une chaîne linéaire ouverte à deux composants afin de comparer les résultats fournis par la simulation à ceux issus de traitements exacts. Le cas d'un cristal semiinfini d'un alliage binaire est ensuite abordé. Les facteurs influençant la distribution de taille des amas de surface sont analysés. De même le choix d'un modèle énergétique et ses conséquences sur la ségrégation sont rapidement discutés

Wetting properties of gas diffusion layers: Application of the Cassie-Baxter and Wenzel equations.

International audienceIn this paper, the wetting behaviours of as received and aged commercial 10% PTFE loaded gas diffusion layer were studied using the Wilhelmy plate method with liquid water temperature ranging from 5 to 60 degrees C. Comparison were made with an untreated sample and a PTFE smooth plate. These experimental results, supported by chemical and morphological surface characterizations, were discussed in the frame of the Wenzel and Cassie-Baxter regimes. For each wetting regime, surface fraction of solid, PTFE and carbon fibres and/or roughness coefficient were estimated by solving a system of Cassie-Baxter and/or Wenzel equations. The transition to one wetting regime to the other is also commented. Finally, the effects of ageing and of water temperature were studied. Ageing was found to alter the wetting behaviour of the GDL through its chemical degradation. An erosion and the crazing of the PTFE coating and an oxidation of the carbon fibres were pointed out. The decrease of the water surface tension linked to an increase of its temperature is also shown to lead to a better wetting and to an increase of the solid surface fraction value. This effect is reinforced by GDL ageing. (C) 2012 Elsevier B.V. All rights reserved

Surface charges of oxides and wettability: Application to TiO2-SiO2 composite films

International audienceThe super-hydrophilicity which can exist at the interface between oxides and aqueous solutions is able to sustain industrial and domestic applications. Several experimental results obtained on TiO2-SiO2 composite thin films via a sol-gel route have confirmed a natural and persistent super hydrophilicity under standard atmosphere. This property can be easily photo-regenerated after a long aging period in ambient atmosphere using a short UV illumination. The electrochemical double layer which classically exists between oxide surfaces and aqueous solution is unfavorable to high wettability properties of ideal flat surfaces. The present study indicates how the surface rugosity and the disjoining pressure caused by surface charges are able to explain the stability of a prewetting film. This film can withstand to vaporization in a weakly under saturated atmosphere, having a protective action despite a carbon contamination brought by standard atmosphere. (C) 2013 The Authors. Published by Elsevier B. V. All rights reserved

Characterization of wettability in gas diffusion layer in proton exchange membrane fuel cells.

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SURFACE SEGREGATIONS IN EMBRITTLED (FexNi1-x)z (PyB1-y)1-z GLASSY RIBBONS BY AUGER ELECTRON SPECTROSCOPY

Nous avons étudié par spectrométrie Auger les ségrégations à la surface de rubans amorphes bruts de trempe et recuits de composition Fe16Ni64P14B6 et (Fe½ Ni½)1-xBx. Après recuit de 2 heures à 300°C, les rubans contenant 20 et 23 % de bore sont fragilisés, le ruban à 17 % de bore restant ductile. Tous les échantillons recuits présentent une ségrégation marquée de métalloïde, sans qu'il y ait de corrélation directe entre celle-ci et la fragilisation des rubans.We have searched for a correlation between surface segregation of constituent elements and thermal embrittlement in (Fe0.5Ni0.5)1-x (ByP1-y)x glassy ribbons. Surface segregations are investigated by A.E.S. on as quenched and annealed glassy ribbons Fe16Ni64P14B6 and (Fe½ Ni½)1-xBx (x = 0.17, 0.20, 0.23). Embrittlement is observed after annealing at 573K during 2 h on all the samples except the Fe41.5Ni41.5B17. We obtain large segregation of metalloïd elements on all the annealed samples indicating, no direct correlation with the mechanical behaviour

Characterisation of wettability in gas diffusion layer in PEMFCs

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Characterisation of wettability in gas diffusion layer in proton exchange membrane fuel cells

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