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National audience; Information about the aggregation state of fine particles is an important element for process control, product quality monitoring and fundamental understanding in many cases of industrial slurries. When aggregates are small or fragile objects, their withdrawal is difficult and off-line characterization may be a source of error. This work deals with the application of different in line methods to the characterization of silica aggregate size and morphology. These methods are based on turbidimetry. One of them consists of the analysis of the turbidity fluctuations and is operated on a commercial instrument. The other one uses the aggregate settling velocity which is determined by turbidimetry too, however with a home-made apparatus. This work gives us the opportunity to define morphological models for small aggregates and to calculate their drag coefficient. Thanks to these models, the aggregate morphological characteristics and the number of their constituting particles can be derived from the experimental results. Agreement between the different methods is examined and discussed.

National audience; Nous présentons des résultats expérimentaux concernant les capacités de stockage du méthane sur des charbons actifs à haute pression. Les expériences portent sur les possibilités d'augmenter les capacités de stockage par l'intermédiaire de la formation d'hydrates de méthane. Les courbes de stockage et de déstockage en fonction de la pression ont été tracées pour des pressions variant de 0 à 80 bar. La caractérisation structurale des charbons utilisés a permis de mettre en avant l'influence de la distribution de taille des pores. Les capacités de stockage obtenues sont fonction de la quantité d'eau utilisée, et peuvent être augmentées jusqu'à 30% par rapport aux capacités de stockage du charbon sec.

National audience; The two phase fluids have promising application in refrigeration thanks to their large cooling capacity and their storage ability. However, the lack of information on their properties makes the selection of a proper fluid uneasy. An experimental set-up inspired from the scrapped surface heat exchanger technology is presented in this paper. It was developed both to generate and to characterise slurries in a rheological point of view. The large range of temperature envisaged here allows enlarging the field of application of the technology to cooler temperatures (freezer applications) and to positive ones (air conditioning systems). The principle of the viscosity measurements is described on solutions of ethyl alcohol; a hydrate is also presented as an example of compound showing a dissociation temperature in the range concerned by air conditioning applications.

National audience; Dans un but d'optimisation du procédé de granulation sèche de poudres, une presse à rouleaux instrumentée a été développée. Une première campagne d'essais a permis de visualiser le profil des contraintes à la surface des rouleaux en fonction de l'angle de rotation, ainsi que l'allure des différents paramètres (couple, effort, entrefer) au cours de l'essai.

National audience; Ce travail présente l'étude cinétique de la réduction de l'octooxyde d'uranium par l'ammoniac en dioxyde d'uranium. Cette réduction a été suivie par thermogravimétrie, elle se déroule en deux étapes : La formation d'un oxyde sous-stoechiométrique U3O8-x, puis la réduction de U3O8-x en UO2. L'influence des paramètres physico-chimiques (pressions partielles, température) a été étudiée. Quelles que soient les conditions de température et de pression partielle de gaz, la perte de masse finale est inférieure à la perte de masse théorique. Des analyses chimiques sur l'oxyde final et des expériences de diffraction des rayons X ont permis de démontrer que cet écart est dû à l'insertion d'azote dans le solide. L'étude cinétique a ensuite été abordée.

National audience; We present here the main results of an experimental study of aggregation which was performed on two silica granular samples: one is naturally hydrophilic; the other has been made hydrophobic by superficial grafting of hydrophobic groups. Aggregation is studied in water-ethanol mixtures of variable compositions and followed by in situ turbidimetry at different stirring rates. The aggregation behaviors of the two samples are quite different. Aggregates of hydrophilic particles are small and fragile whereas aggregates of hydrophobic particles are large and particularly solid. Interpretation of these differences is presented; it is based on several elements: modeling of hydrophobic interaction and of aggregate morphology, modeling of the aggregate optical properties and determination of the aggregation and fragmentation rates. Essential modification introduced by non-wetting consists of the formation of gas bridges around contact points between particles in aggregates.

National audience; La réalisation d'éléments sensibles de capteurs de gaz par la technologie sérigraphie apparaît être une solution qui répond au cahier des charges: faibles coûts, production de masse avec bonne reproductibilité et stabilité des capteurs. De plus, les technologies micro-électroniques sont de plus en plus utilisées pour la fabrication de micro-capteurs ce qui permet une diminution des puissances de chauffage et une miniaturisation des capteurs dans l'objectif de produire des dispositifs multi-capteurs. L'objectif de cette étude est d'optimiser les compositions des encres de sérigraphie et les paramètres de dépôt de couches SnO2 sur des substrats de type wafer de silicium pour améliorer les performances électriques des capteurs (conductance et stabilité) et les propriétés d'adhésion entre les couches de SnO2 et les substrats.

National audience; Dans les conduites pétrolières sous-marines ou dans celles de gaz, la formation de bouchons d'hydrates de gaz est un problème majeur. Pour les éliminer après leur formation, on peut avoir recours à un procédé de dépressurisation symétrique, c'est-à-dire des deux cotés du bouchon. Le but de ce travail est d'étudier la cinétique de dissociation afin d'estimer les durées de dissociation à mettre en oeuvre sur plate-forme pétrolière. Ce modèle est confronté aux données expérimentales présentes dans la littérature. Ce modèle intègre la porosité du bouchon, la structure des hydrates ainsi que la géométrie de la conduite. Nous présentons également un dispositif nous permettant d'obtenir les données expérimentales complémentaires. Ce dispositif est un réacteur de 10 litres composé d'une cellule de 15 cm de hauteur et de 7 cm de diamètre pouvant fonctionner à 30 MPa. Il nous permet d'accéder aux données manquantes de la littérature : diffusivité thermique et perméabilité hydraulique en fonction de la porosité des bouchons.

The control of inclusion elimination is getting more and more important to obtain clean steel. This paper presents a methodology under development for predicting cluster growth and elimination in ladle - RH system. The first key point is to express the collision efficiency, which is very specific for alumina cluster due to the non-wetting fluid. Second, a description of the two-phase flow in the system is necessary. In our calculations with Fluent CFD package and Lagrangian approach for bubbles, bubble growth is implemented, which improves the predictions. Using global reactor decomposition makes possible the prediction of the time evolution of cluster distribution. Important effect of fractal dimension is demonstrated.

A dynamic physically based model has been developed to unravel the complex relationships between the overall Solid Oxide Cells (SOCs) response and the reaction mechanisms taking place in the electrodes. This numerical tool combines modules for different length-scales from the electrode microstructure up to the single repeat unit. First, models have been developed to emulate digital twins of electrode microstructures made of the classical SOCs materials [1]. The microstructural properties of the active layers and the current collectors are then computed on the synthetic volumes and used as inputs in the electrochemical models. The microscale models for the active layers take into account the mass and the charge transport phenomena for the solid and gas phases. For each electrode, the proposed reaction mechanism is split in a sequence of elementary steps with different pathways that can be activated depending on the polarization [2, 3]. The electrode models are finally coupled with a macroscopic description including the cell geometry and the design of the gas channels [4]. This model allows computing the cell polarization curves, the overpotentials and the EIS together with the distribution of the local current density and gas composition in the single repeat unit. This multiscale model has been used to study a typical cell made of the classical SOCs materials: the electrolyte was in Yttria Stabilized Zirconia (YSZ) whereas the hydrogen and oxygen electrodes were respectively composed by a cermet of Nickel and YSZ (Ni-YSZ) and a composite of Lanthanum doped Strontium Cobaltite Ferrite and Ceria doped Gadolinium Oxide (LSCF-CGO). For this cell, the representativeness of the electrodes synthetic microstructures have been checked on reconstructions obtained by tomographic techniques. It has been shown that the synthetic electrodes reproduce accurately the real microstructures. Moreover, the models at the electrode level have been carefully validated on polarizations curves and Electrochemical Impedance Spectra (EIS) measured on symmetrical cells using a three-electrode setup. It is worth noting that the electrodes of the tested symmetrical cells were manufactured using the same materials and composition than the complete cell. Finally, a specific attention has been paid in this work to validate the approach with an original experimental setup allowing the measurement of the local current densities on the full cell without electrode segmentation. This setup is composed of nine symmetrical-spaced pins that perform the measurement of local polarization curves from the inlet to the cell outlet. A campaign of tests has been carried out in fuel cell and electrolysis mode with different temperatures and flow rates. A good agreement has been found between the experimental and simulated data. It has been shown that the model is able to reproduce the evolution of the local polarization curves with a higher current density at the cell inlet. Furthermore, the simulated EIS for the cell have been found to be consistent with the experimental ones. The fully validated model has been used to analyze the cell operation in electrolysis and fuel cell mode. The reaction pathways associated to the elementary steps in the active layers have been discussed depending on the position within the electrodes and the polarizations. This model will then be used to implement the degradation laws such as the Ni agglomeration and compute the loss of cell performances and the remaining useful lifetime [5]. Moreover, the model could be applied to interpret the evolution of the EIS upon operation. [1] H. Moussaoui, J. Laurencin, Y. Gavet, G. Delette, M. Hubert, P. Cloetens, T. Le Bihan, J. Debayle, Stochastic geometrical modeling of solid oxide cells electrodes validated on 3D reconstructions, Computational Materials Science. 143 (2018) 262-276. [2] F. Monaco, E. Effori, M. Hubert, E. Siebert, G. Geneste, B. Morel, E. Djurado, D. Montinaro, J. Laurencin, Electrode Kinetics of Porous Ni-3YSZ Cermet Operated in Fuel Cell and Electrolysis Modes for Solid Oxide Cell Application. Under review. [3] E. Effori, J. Laurencin, E. Da Rosa Silva, M. Hubert, T. David, M. Petitjean, L. Dessemond, E. Siebert, An elementary kinetic model for the LSCF and LSCF-CGO electrodes for solid oxide cells: impact of oxygen partial pressure and degradation on the electrode response. Under review. [4] J. Laurencin, D. Kane, G. Delette, J. Deseure, F. Lefebvre-Joud, Modelling of solid oxide steam electrolyser: Impact of the operating conditions on hydrogen production. Journal of Power Sources. 196 (2011) 2080-2093. [5] M. Hubert, J. Laurencin, P. Cloetens, B. Morel, D. Montinaro, F. Lefebvre-Joud, Impact of Nickel agglomeration on Solid Oxide Cell operated in fuel cell and electrolysis modes. Journal of Power Sources. 397 (2018) 240-251. Figure 1

International audience; The metals oxidation kinetics controlled by the diffusion of charged species (ions, vacancy, etc.) has been theoretically treated since the thirties. Some authors, such as Hauffe and Wagner, propose that the gas-oxide interface is electrically negative with respect to the metal-oxide one and that the potential difference between two interfaces is one of the driving forces in oxidation. In this context, the application of an external electric field, which increases or decreases this potential difference, must act as an accelerator or a retarder of the system’s reactivity. However, in the literature the results of effect of an electric field are very different and there is no agreement on its dependence on the nature of the material, the temperature and the oxidizing atmosphere. This work concerns the study of the physico-chemical behavior of a zirconium alloy (Zicaloy-4) during its exposure to high temperature under oxygen and the influence of an external voltage. In this respect, thermogravimetric experiments at 850°C with the application in situ of an electric field were carried out. The general objective is to model the diffusion of charged species in the oxidation process under the influence of an electric field, taking into account chemical and electric potential as driving forces. The results show that a constant voltage (10 Volt) improves mass gain in 20% of the sample pretreated at high temperature under helium. The voltage-free oxidation kinetics exhibit a parabolic regime up to 4 hours in isothermal stage. In contrast, oxidation with electrical potential shows mixed behavior. Optical microscopy reveals that the thickness of the ZrO2 layer is globally greater on the oxidized sample under electrical field. In addition, the negatively polarized face is more oxidized according to theory.

Bench-walls are evolutionary wall shapes found in many karstic ducts. Their different thickness and width indicate a hydraulic understanding in a network of fractures evolved towards the building of horizontal or vertical drains in the limestone mass., Les banquettes-limites sont des formes d'évolution pariétale présentes dans de nombreux conduits karstiques. De différentes largeurs et épaisseurs, elles indiquent une dynamique hydraulique au sein d'un maillage de fractures qui évolue vers l'édification de drains horizontaux ou verticaux dans la masse calcaire. Jusqu'à présent, seuls les phénomènes hydrodynamiques intervenant dans leur élaboration ont été étudiés selon des contextes de spéléogenèse en milieu épinoyé à noyé suite à une élévation du niveau de base local ou régional, d'asséchement progressif dans le conduit, de l'altération incompléte par dissolution voire de corrosion sous remplissage des argiles déposées par aggradation sédimentaire. (Zupan-Hajna, 2003) ; (Nehme et al., 2009) ; (Jaillet et al., 2011,) ; (Dandurand et al., 2011). Si le flux hydraulique est évoqué comme agent de façonnement, il n'en est pas de même du contenant, ici la roche encaissante, substrat au développement de ces morphologies particulières. Les analyses géochimiques réalisées dans les parties concaves et convexes des parois induisant des banquettes- limites montrent une hétérogéneité dans les séries calcaires rgoniennes de leurs composants chimiques, de leurs textures, et de leurs ciments et cémentations de dépôt. Ces ensembles hétéropiques des séquences du Barremo-Aptien ont contribué de manière passive à la constitution des banquettes-limites. Un protocole de caractérisation géochimique par spectroscopie ICP-AES a été mis en place pour mesurer la concentration en éléments majeurs, mineurs et traces sur des échantillons calcaires du Barrémien supérieur et Aptien inférieur prélevés au niveau des différents reliefs pariétaux en cavité. Cette approche s'inspire de l'étude menée dans la même région sur les sédiments du Crétacé supérieur et de l'Eocène (Jolivet et al., 2020). Des échantillons de roche ont été prélevés sur six sites et ont ensuite été polis afin de déterminer leur structure de dépôt d'après le tableau de classification de Dunham (1962). Les sites de prélèvement se trouvent d'une part en Ardèche en rive gauche des gorges et d'autre part sur le plateau de Méjannes le Clap dans le Gard.

This effort focuses on morphology of cyclopentane hydrates formed from pure and saline water. Different brine solutions of Na2SO4, NaCl, NaCl-MgCl2, or NaCl-KCl-MgCl2 are considered at different concentrations and subcoolings. Especially, a small close reactor cell was used under a microscope with neither agitation nor seeds. Results show that the CPH crystals morphology is approximately comparable at the same subcooling, while the size of the individual crystals drops significantly with increasing of subcooling, regardless the type of salts and their concentrations.