Modelling mesoporous alumina microstructure with 3D random models of platelets

International audienceThis work focuses on a mesoporous material made of nanometric alumina "platelets" of unknown shape. We develop a 3D random microstructure to model the porous material , based on 2D Transmission Electron Microscopy (TEM) images, without prior knowledge on the spatial distribution of alumina inside the material. The TEM images , acquired on samples with thickness 300 nm, a scale much larger than the platelets's size, are too blurry and noisy to allow one to distinguish platelets or platelets aggregates individually. In a first step, the TEM images correlation function and integral range are estimated. The presence of long-range fluctuations, due to the TEM inhomogeneous detection , is detected and corrected by filtering. The corrected correlation function is used as a morphological descriptor for the model. After testing a Boolean model of platelets, a two-scales model of microstructure is introduced to replicate the statistical dispersion of platelets observed on TEM images. Accordingly a set of two-scales Boolean models with varying physically-admissible platelets shapes is proposed. Upon optimization, the model takes into account the dispersion of platelets in the microstructure as observed on TEM images. Comparing it to X-ray diffraction and nitrogen porosimetry data, the model is found to be in good agreement with the material in terms of specific surface area

TORTUOSIMETRIC OPERATOR FOR COMPLEX POROUS MEDIA CHARACTERIZATION

Geometric tortuosity is one of the foremost topological characteristics of porous media. Despite the various definitions in the literature, to our knowledge, they are all linked to an arbitrary propagation direction. This article proposes a novel topological descriptor, named M-tortuosity, by giving a more straightforward definition, describing the data regardless of physicochemical processes. M-tortuosity, based on the concept of geometric tortuosity, is a scalable descriptor, meaning that information of several dimensions (scalar, histograms, 3D maps) is available. It is applicable on complex disconnected structures without any arbitrary definition of entry and exit. Topological information can be represented by aggregation into a unique scalar descriptor for classification purposes. It is extended by iterative erosions to take into account porous structure narrowness, especially bottleneck effects. This new descriptor, called M-tortuosity-by-iterative-erosions, describes tortuosity of the porous part as seen by a spherical particle of given size walking along the network. Boolean models are used to simulate different porous media structures in order to test the proposed characterization

Apport de la simulation dans l'optimisation de l'analyse quantitative par microsonde électronique de catalyseurs hétérogènes

Electron Probe Micro Analysis (EPMA) is frequently used to measure the local concentration of active elements in heterogeneous catalysts. However, when classical procedures are used, a significant deficit is observed both in local total concentration and mean total concentrations. A Monte Carlo program simulating measured intensities (characteristic lines and continuous background) has been written using PENELOPE routines. We have included in this program models taking into account the different physical phenomena likely to lead to the observed signal loss (insulating properties, roughness, porosity, energy loss at interfaces). Simulation results have shown that an important roughness (Ra>200nm) was the only parameter apt to lead to a significant total signal loss. This led us to inquire into another origin to explain the signal loss observed on mesoporous samples. Measurements conducted on a mesoporous alumina confirmed that measuring aluminum, oxygen and carbon leads to a correct total of concentrations. Signal loss is thus explained by the contamination of the sample during its preparation, the components of the embedding resin diffusing into the porosity and reacting with the reactive surface of the catalyst support. In the case of macroporous catalysts, local roughness effect is very important. The simulations have shown the efficiency of the Peak to Background method to correct these local roughness effects. Measurements conducted on reforming and hydrotreating catalysts have led to a correct total concentration and confirmed the contribution of the Peak to Background method to achieve local quantitative measurement.La microanalyse quantitative par sonde électronique est fréquemment utilisée pour mesurer la teneur locale en éléments actifs des catalyseurs hétérogènes. Toutefois, en utilisant les procédures habituelles, un déficit significatif dans le bilan local et le bilan moyen des concentrations est observé. Un programme Monte Carlo simulant les intensités mesurées en microanalyse X (raies caractéristiques et fond continu) a été écrit à l'aide des routines de PENELOPE. Nous avons inclus dans ce programme des modèles prenant en compte les différents phénomènes physiques susceptibles d'expliquer le déficit observé (caractère isolant de l'échantillon, rugosité, porosité, pertes d'énergie spécifiques aux interfaces). Les résultats de simulation ont montré que seule une rugosité importante (Ra>200 nm) pouvait conduire à un déficit de signal global significatif. Ceci nous a amené à rechercher une autre cause pour expliquer le déficit observé sur les catalyseurs mésoporeux. Des mesures sur une alumine mésoporeuse ont confirmé qu'en dosant l'aluminium, l'oxygène et le carbone un bilan des concentrations correct était obtenu. Le déficit est alors expliqué par la contamination importante de l'échantillon durant sa préparation, les composants des résines d'enrobage diffusant dans la porosité et réagissant avec la surface très réactive des supports de catalyseurs. Dans le cas de catalyseurs macroporeux, l'effet local de la rugosité est très important. Les simulations ont montré l'efficacité de la méthode Pic/Fond pour corriger ces effets locaux de rugosité. Les mesures réalisées sur des catalyseurs de reformage et d'hydrotraitement ont conduit à un bilan des concentrations correct et confirmé l'apport de la méthode Pic/Fond pour tendre vers une mesure quantitative locale

Apport de la simulation dans l'optimisation de l'analyse quantitative par microsonde électronique de catalyseurs hétérogènes

MONTPELLIER-BU Sciences (341722106) / SudocSudocFranceF

Small-angle X-ray scattering intensity of multiscale models of spheres

International audienceThe different approaches found in literature to compute small angle X-ray scattering intensities of stochastic Boolean models from their analytical formulations or their numerical realizations are reviewed. The advantages and drawbacks of the methods for the interpretation of small angle X-ray scattering curves are investigated. Examples of multiscale models built from union and intersection of Boolean models of spheres and from Gamma or log-normal radius distribution are given. The scattered intensity computed from projections of realizations of such models are compared with the intensity computed from their analytical covariance. It appears that computation from projection induces strong finite size effect with a relative variance constant and equal to 0.5. Comparison of scattering intensities of an intersection of Boolean model and the corresponding Cox model shows only subtle differences

Enhanced EDX images by fusion of multimodal SEM images using pansharpening techniques

International audienceThe goal of this paper is to explore the potential interest of image fusion in the context of multimodal scanning electron microscope (SEM) imaging. In particular, we aim at merging the backscattered electron images that usually have a high spatial resolution but do not provide enough discriminative information to physically classify the nature of the sample, with energy-dispersive X-ray spectroscopy (EDX) images that have dis-criminative information but a lower spatial resolution. The produced images are named enhanced EDX. To achieve this goal, we have compared the results obtained with classical pansharpening techniques for image fusion with an original approach tailored for multimodal SEM fusion of information. Quantitative assessment is obtained by means of two SEM images and a simulated dataset produced by a software based on PENELOPE

Sparse Stereo Disparity Map Densification using Hierarchical Image Segmentation

International audienceWe describe a novel method for propagating disparity values using hierarchical segmentation by waterfall and robust regression models. High confidence disparity values obtained by state of the art stereo matching algorithms are interpolated using a coarse to fine approach. We start from a coarse segmentation of the image and try to fit each region’s disparities using robust regression models. If the fit is not satisfying, the process is repeated on a finer region’s segmentation. Erroneous values in the initial sparse disparity maps are generally excluded, as we use robust regressions algorithms and left-right consistency checks. Final disparity maps are therefore not only denser but can also be more accurate. The proposed method is general and independent from the sparse disparity map generation: it can therefore be used as a post-processing step for any stereo-matching algorithm

A morphological approach for texture detection, application to SEM stereo reconstruction

International audienc