X-ray reflectivity, diffraction and grazing incidence small angle X-ray scattering as complementary methods in the microstructural study of sol–gel zirconia thin films

X-ray reflectometry, X-ray diffraction and grazing incidence small angle X-ray scattering have been complementary used to fully characterize zirconia (ZrO2) thin films obtained by the sol–gel route. The films were synthesized on various sapphire (Al2O3), silicon (Si) and glass mirrorpolished wafers by a dip-coating process in a zirconia precursor sol. Versus the synthesis parameters as alkoxide sol concentration, withdrawal speed and annealing temperature, the microstructure of the layer is managed and its different microstructural parameters such as thickness, mass density, crystalline phase, grain size and spatial arrangement have been determined. The as prepared layers are amorphous. During a thermal treatment at low temperature (<1000 -C), the layers thickness decreases while their mass density increases. Simultaneously the zirconia precursor crystallises in the zirconia tetragonal form and the coating is made of randomly oriented nanocrystals which self organise in a dense close-packed microstructure. At low temperature, this microstructural evolution is similar whatever the substrate. Moreover, the layer evolves as the corresponding bulk xerogel showing that the presence of the interface does not modify the thermal microstructure evolution of the layer which is controlled by a normal grain growth leading to relatively dense nanocrystalline thin films

Molecular Dynamics approach of sol–gel transition: Comparison with experiments

A new aggregation model by a Molecular Dynamics approach at constant temperature was compared with experimental results on a zirconia precursor gelling process. The evolution of the distribution of the experimental scattered intensities (small angle X-ray scattering curves), during gelling, was compared with the results of our Molecular Dynamics method, via the computation of structure factors of the numerical structure for different times:a very good agreement was found. Our numerical model allows one to understand the evolution as a function of time of the size and quantity of matter corresponding to the upper limit of the fractal domain

Paramètres de composition des mélanges de particules de chènevotte pour l'élaboration de béton de chanvre

National audienceThis study is located in a green building approach axed on the eco-materials and innovative construction complexes for building insulation and sustainable development. The shive (a co-product of hemp) may be one of the first used plants for this purpose. To determine the concrete mix with vegetable fibers, three levels of milling were applied to the same shives and these fractions were analyzed in terms of size and packing densities. Two methods are used to characterize the particle size: sieve analysis and image analysis. Grain size analysis by sieving gives only a partial description of the distribution. Image analysis completes the grain size distribution and its parameters (Féret diameter, throbbing, etc.) are useful in optimizing plant skeleton. Packing densities (on individual shive and on a series of mixture) bring new elements to understand the relationship controlling the granular stack of vegetable fibers.L'étude se place dans une démarche d'éco-construction avec pour principal axe la conception d'éco-matériau et de complexes constructifs innovants destinés à l'isolation des bâtiments de basse consommation (BBC) notamment. La chènevotte issue du chanvre est un co-produit de plus en plus appréciée pour cet usage. Afin d'établir la composition de bétons incorporant ces fibres végétales, trois niveaux de broyage ont été appliqués sur une même chènevotte, et ces fractions ont été analysées du point de vue de la morphologie et de la compacité des particules. Deux méthodes sont employées pour la caractérisation granulométrique : l'analyse par tamisage et l'analyse d'images. Compte tenu de l'élancement élevé de la plupart des fibres, le tamisage ne donne qu'une description partielle de la distribution granulaire. L'analyse d'images complète l'identification, et ses paramètres (diamètre de Féret, élancement, etc.) sont utiles à l'optimisation du squelette végétal, sous l'aspect de sa compacité notamment. Des mesures de compacité individuelles et des mesures complémentaires sur des mélanges apportent des éléments nouveaux pour comprendre les relations contrôlant l'empilement granulaire des fibres végétales

Conformally equivariant quantization: Existence and uniqueness

We prove the existence and the uniqueness of a conformally equivariant symbol calculus and quantization on any conformally flat pseudo-Riemannian manifold (M,\rg). In other words, we establish a canonical isomorphism between the spaces of polynomials on $T^*M$ and of differential operators on tensor densities over $M$, both viewed as modules over the Lie algebra \so(p+1,q+1) where $p+q=\dim(M)$. This quantization exists for generic values of the weights of the tensor densities and compute the critical values of the weights yielding obstructions to the existence of such an isomorphism. In the particular case of half-densities, we obtain a conformally invariant star-product.Comment: LaTeX document, 32 pages; improved versio

Inter- and Intragranular Stress Determination with Kossel Microdiffraction in a Scanning Electron Microscope

A Kossel microdiffraction experimental set up is under development inside a Scanning Electron Microscope (SEM) in order to determine the crystallographic orientation as well as the inter- and intragranular strains and stresses on the micron scale, using a one cubic micrometer spot. The experimental Kossel line patterns are obtained by way of a CCD camera and are then fully indexed using a home-made simulation program. The so-determined orientation is compared with Electron Back-Scattered Diffraction (EBSD) results, and in-situ tests are performed inside the SEM using a tensile/compressive machine. The aim is to verify a 50MPa stress sensitivity for this technique and to take advantage from this microscope environment to associate microstructure observations (slip lines, particle decohesion, crack initiation) with determined stress analyses

Investigation of passive and active silica-tin oxide nanostructured optical fibers fabricated by " inverse dip-coating " and " powder in tube " method based on the chemical sol-gel process and laser emission

International audienceThis paper presents a study of original nanostructured optical fibers based on the SiO 2-SnO 2-(Yb 3+) system. Two different processes have been developed and compared: the sol-gel chemical method associated to the " inverse dip-coating " (IDC) and the " powder in tube " (PIT) process. The microstructural and optical properties of the fibers are studied according to the concentration of SnO 2. X-Ray Diffraction as well as Transmission Electron Microscopy studies show that SnO 2 crystallizes into the cassiterite phase as nanoparticles with a diameter ranging from 4 to 50 nm as a function of tin oxide concentration. A comparative study highlights a better conservation of SnO 2 into the fiber core with the PIT approach according to the refractive index profile and X-Ray analysis measurement. The attenuation evaluated by the classic cutback method gives respectively values higher than 3 dB/m and 0.2 dB/m in the visible (VIS) and infrared (IR) range for the PIT fiber whereas background losses reach 0.5 dB/m in the VIS range for IDC fibers. The introduction of ytterbium ions into the core of PIT fibers, directly in the first chemical step, leads to a laser emission (between 1050 and 1100 nm) according to the fiber length under 850 nm wavelength pumping. Luminescence studies have demonstrated the influence of the tin oxide nanostructure on the rare earth optical properties especially by the modification of the absorption (850 to 1000 nm) and emission (950 to 1100 nm) by discretization of the bands, as well as on the IR emission lifetime evaluated to 10 µs

Assessment of the suitability of gravel wash mud as raw material for the synthesis of an alkali-activated binder

Gravel wash mud (GWM), a waste product from gravel mining was dried and processed into a fine powder to be activated by different concentrations of sodium hydroxide (NaOH) solutions for the synthesis of an alkali-activated binder. The GWM powders were thermally treated at five different calcination temperatures 550, 650, 750, 850 and 950°C. The characterisation of the raw material comprises the particle size distribution (PSD) by laser granulometry, the chemical and mineralogical composition by X-ray fluorescence and X-ray diffraction analysis respectively, and simultaneous thermal analysis. The performance of the alkali-activated binders was examined using compression strength tests and the microstructure was observed using scanning electron microscopy (SEM). The GWM was classified as an aluminosilicate raw material with kaolinite and illite as main clay minerals. Furthermore, a mean particle size around 6.50μm was determined for the uncalcined and calcined GWM powders. The SEM images of the developed binders showed the formation of a compact microstructure, however, relatively low strengths were achieved. This preliminary study highlights an example of an aluminosilicate prime material, which shows very promising chemical and mineralogical characteristics, but its suitability for alkaline activation without further additives was not confirmed as far as performance-based criteria are considered

PPERFORMANCE EVALUATION OF TWO MIPS FOR THE SPE-LC-UV DETERMINATION OF p-[18F]MPPF IN PLASMA

FP6 STRP 516984 MI-lab-on-chi

Image-derived input function in dynamic human PET/CT: methodology and validation with 11C-acetate and 18F-fluorothioheptadecanoic acid in muscle and 18F-fluorodeoxyglucose in brain

International audienc