Seeded growth of iron oxide onto titanate nanowires

The combination of different inorganic structures enables the preparation of multifunctional hybrid materials. The control on the formation of low dimensional nano-objects with specific morphologies and sizes is also a determinant factor to define specific properties. In this aim, the influence of the basic medium on hydrothermally prepared titanate nanowires was studied. The presence of Na+ or K+ counter ions dramatically influenced the preparation of nanoparticles or nanowires of TiO2 and titanate. In a second time, hybrid materials were prepared by the impregnation of the titanate nanowires by a solution of iron chloride followed by the addition of NaOH to induce the formation of iron oxide onto titanate nanowires by the co-precipitation method

Reactive imbibition of WC-Co substrate for PDC cutters used in oil and gas and mining drilling

International audienceCemented carbides are used in rock drilling for mining tools and wear resistant parts. These composite materials possess an excellent compromise between hardness and toughness. Nowadays, the concept of graded structure is widely studied to improve these two properties simultaneously, and so to increase the service life of drilling tools. A continuous composition gradient on several millimetres is generated in commercial WC-Co substrate for PDC cutters by using Reactive Imbibition method. The effects of this process are analysed in terms of microhardness, cobalt concentration and WC grain size. A continuous gradient of about 300HV on 8mm-height substrate is obtained in one-step by imbibition process into combination with a boron-rich coating deposed on its free surface. In part, this gradient of hardness and its shape are preserved after HPHT (high pressure-high temperature) process that is used for the diamond table deposition on the WC-Co substrate. Such gradient must significantly increase the cutter service life

Atomic-resolved depth profile of strain and cation intermixing around LaAlO 3 /SrTiO 3 interfaces

International audienceNovel behavior has been observed at the interface of LaAlO 3 /SrTiO 3 heterostructures such as two dimensional metallic conductivity, magnetic scattering and superconductivity. However, both the origins and quantification of such behavior have been complicated due to an interplay of mechanical, chemical and electronic factors. Here chemical and strain profiles near the interface of LaAlO 3 /SrTiO 3 heterostructures are correlated. Conductive and insulating samples have been processed, with thicknesses respectively above and below the commonly admitted conductivity threshold. The intermixing and structural distortions within the crystal lattice have been quantitatively measured near the interface with a depth resolution of unit cell size. A strong link between intermixing and structural distortions at such interfaces is highlighted: intermixing was more pronounced in the hetero-couple with conductive interface, whereas in-plane compressive strains extended deeper within the substrate of the hetero-couple with the insulating interface. This allows a better understanding of the interface local mechanisms leading to the conductivity

Additive manufacturing of an oxide ceramic by laser beam melting—Comparison between finite element simulation and experimental results

International audienceRecent progress in the application of Laser Beam Melting (LBM) of oxide ceramics has shown promising results. However, a deeper understanding of the process is required to master and control the track development. In this approach numerical modeling could allow higher quality, of additive manufacturing for such materials, to be achieved. The validation of an earlier developed finite element model for LBM of ceramic materials has been established through a comparison with experimental results. The model solves heat and mass transfers whilst accounting for fluid flow due to surface tension and Marangoni convection, as well as tracking the material/gas boundary. The volumetric heat source parameters used in the simulations have been calibrated with an analytical model combined with original in-situ reflectance measurements. Numerical results show good agreement with measurements of melt pool dimensions and shapes. They also provide a coherent description of the evolution of the track morphology when varying the heat source parameters. Track irregularities have also been revealed by simulations at high scanning speed and the balling effect highlighted and explained through similar simulations

Architecture et bibliothèque

En 2012, l’enssib a saisi l’opportunité de ses vingt ans pour publier dans ses Presses un ouvrage hors collection : "Architecture et bibliothèque, 20 ans de constructions", lequel proposait un tour d’horizon des questions posées par la place du bâtiment dans nos problématiques professionnelles. C’est à partir de points de vue parfois divergents, souvent complémentaires, des architectes, conservateurs de bibliothèques, élus, journaliste et programmiste, que s’ouvrait la réflexion. Dans le prolongement de cet ouvrage, et parce que la question est loin d’être épuisée, la journée « Architecture et bibliothèque » a fait entendre la parole d’architectes bâtisseurs de bibliothèques. Comment penser et bâtir ensemble la bibliothèque de demain, tel fut le fil rouge de cette journée. Afin de mieux comprendre les spécificités de la construction d’établissements publics et plus particulièrement des bibliothèques comparativement aux autres lieux de culture. Afin de s’interroger sur le statut emblématique ou non de la bibliothèque du futur, dans un univers culturel qui tend à devenir immatériel. Afin de se situer dans la cité, tant symboliquement, démocratiquement que du point de vue de l’urbanisme. Afin de repenser la place de l’usager, du lecteur, et sans doute aussi du professionnel au sein de la bibliothèque en construction. Pour toutes ces raisons, la question de l’architecture se place au coeur du métier de bibliothécaire

Impact of three different TiO2 morphologies on hydrogen evolution by methanol assisted water splitting: Nanoparticles, nanotubes and aerogels

International audienceIncreasing the activity of a photocatalyst goes through the improvement of both its absorption (light) and adsorption (reactant) properties. For a given semiconducting material, the charge carrier separation is also a very important step. Properly combining chosen phases is one option to improve this separation (example of the commercial P25) and depositing platinum on the surface of the catalyst, another one. In some cases, coupling both may nevertheless lead to a decrease of photoactivity or at least limit the potentiality of the catalyst. A third option, consisting in modifying the morphology of the photoactive phase, has shown very promising results. In this study, we have elaborated, characterized and evaluated the hydrogen evolution potentiality (through methanol assisted water splitting) of different TiO2 morphologies: nanoparticles, nanotubes and aerogels. These materials have shown different behaviours depending on both their composition and morphology. Different types of separation processes have been claimed to account for the observed different photoactivities, with more or less pronounced synergetic effects, due to: the use of Pt as a co-catalyst, the mixture of different TiO2 phases (anatase and TiO2(B) or rutile) and the specific morphology of the samples (nanotubes or aerogels). Among all the tested samples, the TiO2 aerogel supported Pt one exhibited very promising performances, three times as active as P25 supported Pt, which is already much more active than pure P25 in our testing conditions

Rapid thermal processing of CuInSe2 electroplated precursors for CuIn(S,Se)2-based thin film solar cells

International audienceDuring the elaboration of standard CISEL™cells, electroplated CuInSe2 precursors undergo a rapid thermal processing (RTP) in a sulfur-containing atmosphere to promote grain growth and enable sulfurization of the precursor. The aim of this work is to show how structural and morphological properties of the CuIn(S,Se)2-based solar cells can be modified with RTP parameters, namely temperature, heating rate, and sulfur addition. X-ray diffractograms show that the preferential (112) orientation of the electrodeposited CuInSe2 precursor is maintained after annealing but the coefficient of crystallographic texture can be modified with specific RTP parameters. It is also shown that the quantity of sulfur incorporated in the chalcopyrite lattice can be controlled and reaches almost pure CuInS2 according to the sulfur quantity used during the RTP. Another effect of the RTP annealing is to form a Mo(S,Se)2 layer which can lead to a quasi-ohmic contact between the molybdenum and the absorber. The properties of the Mo(S,Se)2 buffer layer are also studied according to the process parameters and an increase of the annealing temperature or of the sulfur concentration tends to increase the thickness of this laye