59 research outputs found
Elaboration de céramiques transparentes Er YAG (synthÚse de poudre par co-précipitation et frittage SPS)
Les cĂ©ramiques polycristallines transparentes de YAG (Yttrium Aluminium Garnet, Y3Al5O12) et de YAG dopĂ© par des lanthanides (Nd, Er, Ho, etc.) ont des propriĂ©tĂ©s optiques comparables aux monocristaux et peuvent ĂȘtre utilisĂ©es comme milieu laser solide dans les lasers solides Ă haute capacitĂ© calorifique. L utilisation de ces cĂ©ramiques polycristallines transparentes prĂ©sente de nombreux avantages comparĂ©s aux monocristaux. Ces matĂ©riaux ont une meilleure conductivitĂ© thermique et sont fabriquĂ©s Ă plus faible coĂ»t tout en prĂ©sentant des propriĂ©tĂ©s mĂ©caniques amĂ©liorĂ©es et ce, sur des piĂšces de plus grandes dimensions. De plus, il est possible d atteindre de plus forts taux de dopage avec une rĂ©partition uniforme du dopant. Le dopage du YAG par l erbium (0.25 %at.) permet une Ă©mission laser eye-safe de 1645nm. De plus, un faible taux de dopage permet d Ă©viter le phĂ©nomĂšne d upconversion lors de l effet laser.Les conditions pour obtenir la transparence sont, entre autres, l absence de dĂ©fauts, une trĂšs grande puretĂ© (>99.9%), une rĂ©partition de taille de grains homogĂšne et une densitĂ© trĂšs Ă©levĂ©e (>99.9%).Les cĂ©ramiques transparentes sont obtenues par la voie mĂ©tallurgie des poudres. La synthĂšse par voie chimique (co-prĂ©cipitation, sol-gel, voie hydrothermale ) permet la production de poudres trĂšs pures, avec une taille de particules homogĂšne et nanomĂ©trique, comparĂ©e Ă la synthĂšse par voie mĂ©canique (broyage d oxydes). Le frittage SPS (Spark Plasma Sintering) permet quant Ă lui une densification rapide, Ă plus basse tempĂ©rature, empĂȘchant ainsi une croissance excessive et anormale des grains lors de la densification. L application d un courant Ă©lectrique de forte intensitĂ© associĂ©e Ă une charge uniaxiale permet d accĂ©lerer la cinĂ©tique de frittage comparĂ© aux mĂ©thodes de frittage conventionelles.Ce travail porte sur l Ă©laboration de cĂ©ramiques polycristallines transparentes Er:YAG par la voie mĂ©tallurgie des poudres. La synthĂšse de poudre est rĂ©alisĂ©e par co-prĂ©cipitation inverse d une solution de nitrates dans l hydrogĂ©nocarbonate d ammonium. L influence des paramĂštres de synthĂšse tels que le pH, la concentration, le temps de maturation ou encore le cycle de calcination a Ă©tĂ© Ă©tudiĂ©e. AprĂšs optimisation des conditions de synthĂšse, des particules d Er:YAG pur prĂ©sentant une taille moyenne de 50nm ont Ă©tĂ© obtenues. L Ă©tude des mĂ©canismes rĂ©actionnels a Ă©tĂ© menĂ©e en associant diffĂ©rentes techniques de caractĂ©risations en tempĂ©rature telles que la spectromĂ©trie IR, la diffraction des rayons X, ainsi que des analyses thermo-gravimĂ©triques et diffĂ©rentielles. La formation de la phase YAG Ă 1050C passe par la formation d une phase intermĂ©diaire, le YAP (Yttrium Aluminium Perovskite, YAlO3) Ă 900C.Les poudres synthĂ©tisĂ©es ont ensuite Ă©tĂ© frittĂ©es par frittage flash SPS. L Ă©tude de l influence du cycle de frittage (tempĂ©rature, charge, rampe, maintien) sur la microstructure et son optimisation a Ă©tĂ© rĂ©alisĂ©e Ă partir de poudre commerciale et a permis l obtention de cĂ©ramiques transparentes de diamĂštre 30mm et d Ă©paisseur 3mm. Un changement d Ă©chelle a Ă©galement Ă©tĂ© rĂ©alisĂ© permettant la rĂ©alisation d Ă©chantillons de diamĂštre 60mm d une part, et d Ă©paisseur 6mm d autre partYttrium aluminium garnet (YAG, Y3Al5O12) transparent ceramics have attracted much attention since it can replace single crystals as host materials in solid state heat capacity lasers. These polycrystalline ceramics present improved mechanical and spectroscopic properties, as well as a better heat conductivity, lower fabrication costs for larger size materials. Furthermore, it is possible to reach higher doping concentrations as well a uniform distribution. Doping YAG with Erbium (Er:YAG) allows eye-safe emission at 1645nm. Moreover, a low doping rate (0.5%at.) enables upconversion process during laser operation. Conditions for transparency are amongst others, the absence of defects, a high purity (>99.9%), an homogeneous grain size as well as a high density (>99.9%).Transparent polycrystalline ceramics can be obtained by powder metallurgy route. Powders, synthesized by chemical reactions such as sol-gel process, co-precipitation or hydrothermal methods, present some advantages like high purity, homogeneity and nano-sized particles compared to those obtained by solid-state reactions. A recent process called Spark Plasma Sintering (SPS) is presented to be a promising technique for the densification of nanostructured materials. Indeed, high current and pressure allow sintering at lower temperatures in shorter sintering time than in regular processes. Besides, rapid heating enables to limit excessive grain growth.In this study, Er:YAG nanopowders have been synthesized by co-precipitation using nitrates as precursors and ammonium hydrogen carbonate as precipitant. The influence of precipitation parameters such as pH, concentration, aging time, or even calcination temperature, has been studied. Er:YAG nanoparticles, with an average grain size of 30nm have been successfully synthesized. The reaction mechanisms have been investigated using different techniques such as infrared spectroscopy, x-ray diffraction, thermal analyses The YAG phase is formed around 1050C passing through an intermediate phase called YAP (Yttrium Aluminium Perovskite, YAlO3) at 900C.Synthesized and commercial powders have been sintered to transparency using SPS device. Optimisation of the sintering conditions (temperature, load, heating rate, dwell time) have been realized using commercial powder. Transparent polycrystalline ceramic specimens with a 30mm diameter and 3mm thickness have been successfully obtained. A scale-up study enabled to produce samples with a diameter up to 60mm and also with 6mm thicknessDIJON-BU Doc.Ă©lectronique (212319901) / SudocSudocFranceF
Mise en Ćuvre de la Loi sur le devoir de vigilance. Rapport sur les premiers plans adoptĂ©s par les entreprises
Tracking des transferts des bactéries porteuses de résistances entre animal, homme et environnement
Design of Fe3âxO4 raspberry decorated graphene nanocomposites with high performances in lithium-ion battery
Fe3âxO4 raspberry shaped nanostructures/graphene nanocomposites were synthesized by a one-step polyol-solvothermal method to be tested as electrode materials for Li-ion battery (LIB). Indeed, Fe3âxO4 raspberry shaped nanostructures consist of original oriented aggregates of Fe3âxO4 magnetite nanocrystals, ensuring a low oxidation state of magnetite and a hollow and porous structure, which has been easily combined with graphene sheets. The resulting nanocomposite powder displays a very homogeneous spatial distribution of Fe3âxO4 nanostructures at the surface of the graphene sheets. These original nanostructures and their strong interaction with the graphene sheets resulted in very small capacity fading upon Li+ ion intercalation. Reversible capacity, as high as 660 mAh/g, makes this material promising for anode in Li-ion batteries application
SIMBIO-SYS : Scientific Cameras and Spectrometer for the BepiColombo Mission
The SIMBIO-SYS (Spectrometer and Imaging for MPO BepiColombo Integrated Observatory SYStem) is a complex instrument suite part of the scientific payload of the Mercury Planetary Orbiter for the BepiColombo mission, the last of the cornerstone missions of the European Space Agency (ESA) Horizon + science program. The SIMBIO-SYS instrument will provide all the science imaging capability of the BepiColombo MPO spacecraft. It consists of three channels: the STereo imaging Channel (STC), with a broad spectral band in the 400-950 nm range and medium spatial resolution (at best 58 m/px), that will provide Digital Terrain Model of the entire surface of the planet with an accuracy better than 80 m; the High Resolution Imaging Channel (HRIC), with broad spectral bands in the 400-900 nm range and high spatial resolution (at best 6 m/px), that will provide high-resolution images of about 20% of the surface, and the Visible and near-Infrared Hyperspectral Imaging channel (VIHI), with high spectral resolution (6 nm at finest) in the 400-2000 nm range and spatial resolution reaching 120 m/px, it will provide global coverage at 480 m/px with the spectral information, assuming the first orbit around Mercury with periherm at 480 km from the surface. SIMBIO-SYS will provide high-resolution images, the Digital Terrain Model of the entire surface, and the surface composition using a wide spectral range, as for instance detecting sulphides or material derived by sulphur and carbon oxidation, at resolutions and coverage higher than the MESSENGER mission with a full co-alignment of the three channels. All the data that will be acquired will allow to cover a wide range of scientific objectives, from the surface processes and cartography up to the internal structure, contributing to the libration experiment, and the surface-exosphere interaction. The global 3D and spectral mapping will allow to study the morphology and the composition of any surface feature. In this work, we describe the on-ground calibrations and the results obtained, providing an important overview of the instrument performances. The calibrations have been performed at channel and at system levels, utilizing specific setup in most of the cases realized for SIMBIO-SYS. In the case of the stereo camera (STC), it has been necessary to have a validation of the new stereo concept adopted, based on the push-frame. This work describes also the results of the Near-Earth Commissioning Phase performed few weeks after the Launch (20 October 2018). According to the calibration results and the first commissioning the three channels are working very well.Peer reviewe
SynthÚse et caractérisation de borures, carbures et nitrures de M (M=Hf ou Zr) à partir de mélanges de poudres à base de HfCl[indice]4 ou MO[indice]2 activés mécaniquement (essais préliminaires de frittage de poudres de HfB[indice]2)
Ce travail est consacré à l'élaboration de borures, carbures et nitrures à base de zirconium ou de hafnium à partir de poudres de chlorures et d'oxydes de ces éléments activés par mécanosynthÚse. La synthÚse des composés s'est déroulée en trois étapes: broyage, traitement thermique et lavage. Les mécanismes réactionnels intervenant à chacune de ces trois étapes ont été étudiés pour l'ensemble des mélanges. Dans le but d'obtenir des produits " purs ", aprÚs traitement thermique, les mélanges ont été lavés. Les microstructures des produits obtenus ont été caractérisées. Lorsque les borures sont synthétisés à partir de chlorures de hafnium, la morphologie des monocristaux se présente sous forme soit de grains facettés, soit de nanobùtonnets, suivant la composition du mélange initial. Les conditions nécessaires à l'obtention des nanobùtonnets ont été mises en évidence. Dans le cas particulier des borures de hafnium, une étude de leur mise en forme par pressage à chaud a été effectuée.NANCY/VANDOEUVRE-INPL (545472102) / SudocSudocFranceF
High Efficiency Toluene Gas Phase Degradation on Sulfate Promoted Titania Photocatalyst
International audienc
Synthesis of YAG nanopowder by the co-precipitation method: Influence of pH and study of the reaction mechanisms
International audienceYAG nanopowders with an average grain size of 30 nm have been successfully synthesized by the co-precipitation method using nitrates with precipitant of ammonium hydrogen carbonate. The influence of precipitation conditions such as pH, aging time and calcination temperature on the formation of secondary phases has been studied. The accurate control of pH value at every stage of precipitation process is crucial to avoid the presence of YAM (Yttrium Aluminium Monoclinic, Y4Al2O9) and yttrium oxide (Y2O3) after calcination. The reaction mechanisms have been investigated using different techniques such as infrared spectroscopy, x-ray diffraction and thermal analyses. The YAG phase is formed around 1050 degrees C passing through an intermediate phase called YAP (Yttrium Aluminium Perovskite, YAlO3). Local chemical heterogeneities are responsible for the deviation of the Y:Al ratio and the formation of YAP during heat treatment
Implementing the French Duty of Vigilance Law. When enterprises drew up their first plans
Implementing the French Duty of Vigilance Law: When entreprises drew up their first plans
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