Mise en place de l'extraction liquide-liquide en microsystèmes établir des écoulements segmentés à façon pour optimiser le transfert de masse

National audienceLiquid-liquid extraction is commonly used for radiochemical analysis. When miniaturized, it can benefitfrom the advantages of microfluidic tools i.e. possible coupling, precise control of the interfacial areabetween the aqueous and organic phases, and contact time. A first study, dedicated to liquid-liquidextraction with parallel flows of europium diluted in nitric acid by the N,N′-dimethyl-N,N′-dibutyltetradecylmalonic diamide [1, 2], allowed us to highlight the limitations of parallel flows for aslow chemical system. One way to optimize yields of extraction of the kinetically slow systems is toincrease the specific interfacial area. For this reason, segmented flows formation and characteristicswere investigated, as a function of the physicochemical properties of a biphasic system, flow rates andthe dimensions of a focalized flux junction. In the following, two multiphase models of the droplets sizecorresponding to the transition and dripping regimes were validated and will be used for theoptimization of the specific interfacial area.L’extraction liquide-liquide est couramment utilisée pour les analyses radiochimiques. Miniaturisée,elle peut bénéficier des avantages des outils microfluidiques qui sont la possibilité de réaliser descouplages, le contrôle précis de l’aire interfaciale entre les phases aqueuse et organique en présence,et des temps de contact. Une première étude, dédiée à l’extraction liquide-liquide en flux parallèlesd’europium en milieu nitrique par le N,N’-dimethyl N,N’-dibutyl tetradecylmalonamide [1, 2], a permisde mettre en évidence les limitations des flux parallèles pour un système chimique lent. Une façond’optimiser les rendements d’extraction des systèmes cinétiquement lents est de mettre en œuvre desécoulements permettant d’augmenter l’aire interfaciale spécifique. C’est pourquoi nous étudions laformation d’écoulements segmentés à façon en fonction des propriétés physico-chimiques d’un systèmechimique biphasique, des débits et des dimensions d’une jonction en flux focalisé. L’utilisation de deuxmodèles de calcul des tailles de gouttes en régimes d’écoulements transitoire

Microsystèmes d'extraction par solvant pour l'analyse radiochimique

National audienceL’analyse des radionucléides dans les solutions de combustibles irradiés ou dans les déchets de haute ou moyenne activité implique l’enchaînement de plusieurs opérations de séparation/purification avant la mesure par spectroscopies nucléaires ou ICP-MS. Ces étapes sont sources de déchets et d’exposition aux radiations, et implique l’utilisation de volumes non négligeables de réactifs chimiques ou de solvants. Résoudre ce problème passe par la miniaturisation des outils d’analyse et le développement de laboratoires sur puce dédiés aux analyses liées au domaine nucléaire. La micro extraction liquide-liquide ($\mu$-ELL) a été développée pour des applications d’analyse de radionucléides dans des effluents radioactifs

Liquid-liquid extraction of two radiochemical systems at micro-scale predict and achieve segmented flow to optimize mass transfer

International audienceOne of the most important separation techniques in radiochemical procedures is solvent extraction. In the last decade, a growing interest in its use in microsystems with multiphase micro-flows has emerged because such systems allow a good control of the interface area between aqueous and organic phases as well as of the contact time of the two phases.A previous study was devoted to the micro-extraction in parallel flows of uranium in chloride media by Aliquat 336 and europium in nitric acid by the N,N'-dimethyl N,N'-dibutyl tetradecylmalonamide. While in the first case an optimal extraction yield could be obtained, slower reaction kinetics prevented the second chemical system extraction from being complete. A way to improve mass transfer for slow systems is to increase the specific interfacial area. We therefore investigated liquid-liquid extraction for the same chemical systems by implementing segmented flows. Both the internal circulation stimulated within droplets by their passage along micro-channels and the increase in the interfacial area are responsible for a large enhancement in the interfacial mass transfer and reaction rate. Therefore, an improvement in liquid-liquid extraction yield could be expected. Based on previous works from Van Steijn and Xu, a numerical model was developed to accurately predict the characteristics of droplet production at a T-junction (volumes, frequency, spacing, and specific interfacial area) for the two aforementioned chemical systems. Using parameters screening, the respective influence of liquids viscosities, dimensional parameters and flow rates was evidenced. This numerical model was verified experimentally by generating on-chip segmented flows, and offered ways of improvement in both operating parameters and chip design. Finally, phase separation was obtained using selective membrane, and radionuclides micro-extractions were performed. Micro-extraction yields were compared to conventional batch extraction

Prediction of the formation of segmented flow in microsystems for radiochemical liquid-liquid extraction

International audienceOne of the most important separation techniques in radiochemical procedures is solvent extraction. It involves concentrated acids and corrosive solvents that require microsystems built with robust materials. In the last decade, a growing interest in its use in microsystems has emerged because such systems allow a good control of both the interface area between aqueous and organic phases, and the contact time of the two phases. After a study of parallel flow [1], our goal is to understand and compare the formation of segmented flow for T, flow focusing, and co-flow junctions, and to predict the optimal design in order to enhance solvent extraction

Développement d'un microsystème de micro liquide à interfaces stabilisées par patterning hydrophobe/hydrophile résistant pour l'analyse des radionucléides

National audienceLa fonctionnalisation des microcanaux par un patterning hydrophile/hydrophobe constitue une solution technique originale, pouvant faciliter la mise en oeuvre des écoulements parallèles en microsystèmes. En effet, lorsque les deux phases ont des viscosités trop différentes, la modification de surface d'une partie du microcanal pour la rendre hydrophile (la phase aqueuse s’écoule de façon confinée dans la partie rendue hydrophile) permet d'augmenter les temps de contacts des deux phases et donc d’améliorer le transfert de matière. Dans le cas ou les deux phases ont des viscosités proches, la modification de surface d'une partie du microcanal permet de stabiliser les écoulements et donc d'augmenter le domaine d'utilisation du microsystème (on a accès a un plus grand nombre de couples de débits aqueux et organiques). Ce sont les tests de modification de surface réalisés et leur résistance a l'acide et aux solvants qui seront présentés

CATALYCITY AND AGEING STUDY OF SPACE SHUTTLE MATERIAL: REGENERATION OF THEIR ORIGINAL CATALYTIC PROPERTIES

The heating of the space vehicle during the re-entry phase and the oxidation of the material surface leads to the loss of protective properties. The atmospheric re-entry conditions are recreated with a non equilibrium low pressure RF plasma and the relative oxygen atom concentration is measured by Actinometric Optical Spectroscopy. Silicon carbide targets polluted with metallic species show different degrees of reactivity than SiC alone [1]. In this work a systematic study of SiC oxidation at high temperature (1100K) has been performed in order to determine kinetic and the oxidation mechanisms. Also the role of chromium oxide as a diffusion barrier into the bulk is examined [2]. In order to determine the oxidation mechanisms the isotopic oxygen O-2(18) has been used, in targets with different deposition layers at different times ranging from 10 to 30 min and die formation of CO, CO2 and SiO, during the ablation has been followed by mass spectrometry analysis. Surface oxidation and Oxygen diffusion in the material bulk was measured by Scanning Electron Microscopy (SEM), X-ray Photoelectron Spectroscopy (XPS) [3], secondary ion mass spectroscopy (SIMS). Besides the recombination of oxygen atoms, the ablation of the material and the diffusion of oxygen coining from the gas phase in the bulk of this material have been pointed out. The results show that at 1300K the kinetic of oxidation is faster than at 1000K. In this range of temperatures chromium oxide remains stable and limits the diffusion of oxygen