No description available.

Cette thèse vise à étudier le comportement multiéchelle (nano-, micro- et macroscopique) des composites, basé sur une étude fine utilisant les techniques les plus modernes pour comprendre les interfaces et les quantifier. Deux séries de renforts sur une échelle micrométrique, des fibres de carbone (CF) et des matériaux à base de graphène ont été utilisées ici. Pour améliorer l'interaction entre les nanorenforts et la matrice polymère, deux voies principales ont été utilisées dans cette thèse : l'oxydation des renforts et la greffe de nanotubes de carbone sur leur surface.L'étude en elle-même a été menée à une échelle microscopique pour étudier la résistance interfaciale entre une fibre de carbone (CF) et la matrice époxy, avec des essais de traction effectués in situ dans la chambre d'un microscope à double colonne MEB-FIB (microscope électronique à balayage couplé à un faisceau d'ions focalisé). Le faisceau d'ions a été utilisé pour découper une éprouvette de traction du composite contenant à la fois de l'époxy et de la CF. Le champ de tractiona été appliqué via le nanomanipulateur et l'essai a été observé via les deux colonnes ionique et électronique (sous deux angles de vue différents) et a permis d'estimer le champ de déformation, et donc la résistance interfaciale au moment de la rupture. Une expérience similaire a été menée sur un composite où les renforts sont des nanoplaquettes de graphène.Enfin, l'étude en microscopie électronique en transmission de la région de l'interface entre l'époxy et les renforts a révélé la présence d'une interphase et a permis de mesurer son épaisseur et donner une indication de sa nature. À cette fin, une analyse EELS (spectroscopie par pertes d'énergie des électrons) a été effectuée, permettant de mesurer la densité de l'échantillon très localement (taille de sonde de l'ordre du dixième de nanomètre) en travers ou parallèlement à l'interface. Un scénario sur les modes de liaison chimique entre les deux milieux en fonction du traitement de surface utilisé permet d'expliquer la nature des interphases observées. / This thesis aims to investigate the multiscale (nano-, micro-, and macro-scopic) behavior of the composites based on a fine investigation using the most modern techniques, to understand the interfaces and to quantify them. Two series of reinforcements on a micrometer scale, carbon fibers (CFs) and graphene-based materials, were studied here. To improve the interactions between these nanofillers and the surrounding polymer matrix, two major routes were used in this thesis: the oxidation of the fillers and the grafting of carbon nanotubes on their surface.The study itself was conducted on a microscopic scale on the interfacial strength between CFs and the epoxy matrix, with tensile tests carried out in-situ in the chamber of a double-column FIB-SEM microscope (scanning electron microscope coupled to a focused ion beam). The ion beam was used to mill a thin bond-shaped tensile specimen of composite containing both an epoxy and a CF part. Thetensile stress field was applied using the nanomanipulator and the test was observed both via the ionic and the electronic columns (with two different angles of view) to estimate the strain field, hence the interfacial strength when the failure is observed. A similar experiment was led on a composite with GNPs.Finally, the transmission electron microscopy (TEM) study of the interface region between the epoxy and the graphene-based nanofillers revealed the existence of an interphase and allowed to measure its thickness and give an indication of its nature. For this purpose, an EELS (electron energy-loss spectroscopy) analysis was carried out, making it possible to measure the density of the sample very locally (probe size of the order of a tenth of a nanometer) across or parallelly to an interface. A scenario on the chemical bonding modes between the two media as a function of the surface treatment used makes it possible to explain the nature of the observed interphases.

The main objective of this dissertation is to quantify petrophysical properties of conventional and unconventional reservoirs using a mechanistic approach. Unconventional transport mechanisms are described from the pore to the reservoir scale to examine their effects on macroscopic petrophysical properties in hydrocarbon-bearing organic shale. Petrophysical properties at the pore level are quantified with a new finite-difference method. A geometrical approximation is invoked to describe the interstitial space of grid-based images of porous media. Subsequently, a generalized Laplace equation is derived and solved numerically to calculate fluid pressure and velocity distributions in the interstitial space. The resulting macroscopic permeability values are within 6% of results obtained with the Lattice-Boltzmann method after performing grid refinements. The finite-difference method is on average six times faster than the Lattice-Boltzmann method. In the next step, slip flow and Knudsen diffusion are added to the pore-scale method to take into account unconventional flow mechanisms in hydrocarbon-bearing shale. The effect of these mechanisms is appraised with a pore-scale image of Eagle Ford shale as well as with several grain packs. It is shown that neglecting slip flow in samples with pore-throat sizes in the nanometer range could result in errors as high as 2000% when estimating permeability in unconventional reservoirs. A new fluid percolation model is proposed for hydrocarbon-bearing shale. Electrical conductivity is quantified in the presence of kerogen, clay, hydrocarbon, water, and the Stern-diffuse layer in grain packs as well as in the Eagle Ford shale pore-scale image. The pore-scale model enables a critical study of the [delta]LogR evaluation method commonly used with gas-bearing shale to assess kerogen concentration. A parallel conductor model is introduced based on Archie's equation for water conductivity in pores and a parallel conductive path for the Stern-diffuse layer. Additionally, a non-destructive core analysis method is proposed for estimating input parameters of the parallel conductor model in shale formations. A modified reservoir model of single-phase, compressible fluid is also developed to take into account the following unconventional transport mechanisms: (a) slip flow and Knudsen diffusion enhancement in apparent permeability, (b) Langmuir desorption as a source of gas generation at kerogen surfaces, and (c) the diffusion mechanism in kerogen as a gas supply to adsorbed layers. The model includes an iterative verification method of surface mass balance to ensure real-time desorption-adsorption equilibrium with gas production. Gas desorption from kerogen surfaces and gas diffusion in kerogen are the main mechanisms responsible for higher-than-expected production velocities commonly observed in shale-gas reservoirs. Slip flow and Knudsen diffusion marginally enhance production rates by increasing permeability during production. / text

[pt] A caracterização tridimensional tem sido mais utilizada na área da ciência dos materiais devido à necessidade de melhor compreensão e resultados mais precisos acerca da microestrutura dos materiais, que não são completamente revelados pelas técnicas tradicionais de microscopia bidimensional. No presente trabalho dois tipos de técnicas de caracterização 3D foram utilizadas: MicroTC - Microtomografia de Raios-X (com tomógrafos de bancada e baseados em fonte síncrotron) e FIB-SEM (feixe de íons focalizados acoplados a um MEV). Estas técnicas foram aplicadas a um sistema específico: descontinuidades em metal de solda subaquática molhada. Estas descontinuidades (poros, trincas e inclusões) apresentam tamanhos típicos variando de nanômetros a dezenas de micrômetros. Além disso, apresentam formas, distribuição espacial e orientação bastante variada e complexa. Assim, esta tese apresenta o desenvolvimento de metodologia de aquisição, processamento, análise e visualização 3D de poros, trincas e inclusões em solda subaquática molhada, a partir de imagens obtidas por MicroTC e FIB-SEM. As técnicas de aquisição foram otimizadas para os diferentes tipos de descontinuidades. Rotinas especializadas de processamento e análise de imagens foram criadas, sempre que possível utilizando um ambiente de software livre (FIJI/ImageJ). Diversas medidas foram automaticamente obtidas: número de objetos, volume, fração volumétrica, área superficial, diâmetro de Feret, espessura, esfericidade e compacidade. Além disso, a construção de imagens 3D permitiu observar a forma e a distribuição espacial das descontinuidades presentes. Visando avaliar a sensibilidade para detecção de trincas por MicroTC, um corpo de prova com seção variável foi submetido a um ensaio de tração, de forma que as diferentes seções sofressem diferentes valores de tensão. Foi verificada uma correlação positiva entre o valor de tensão e o número, comprimento e espessura das trincas detectadas. Este experimento também revelou o impacto da resolução espacial e do ruído sobre a possibilidade de detectar as trincas de forma acurada. / [en] 3D characterization is growing quickly in materials science due to the demands of better microstructural characterization, which cannot be fully achieved with the traditional 2D microscopy techniques. In this work, two types of 3D characterization techniques were employed: MicroCT – microcomputed x-ray tomography (with both bench top and synchrotron sources) and FIB-SEM (focused ion beam coupled to SEM). These techniques were applied to a specific system: discontinuities in underwater wet welds. These discontinuities (pores, cracks and inclusions) range in size from nanometers to tens of microns. Moreover, they present complex and varied shapes, spatial distribution and orientation. Thus, this thesis presents the development of methodology for the acquisition, processing, analysis and visualization of pores, cracks and inclusions in underwater wet welds, from images obtained by MicroCT and FIB-SEM. The acquisition techniques and conditions were optimized for the different kinds of discontinuities. Specialized routines for image processing and analysis were developed, employing a free software environment whenever possible (FIJI/ImageJ). Several measurements were automatically obtained: number of objects, volume, volume fraction, surface area, feret diameter, thickness, sphericity and compacity. Moreover, the rendering of 3D images allowed the observation of the shape and spatial distribution of the discontinuities in the weld metal. To evaluate the detection sensitivity of cracks by MicroCT, a specimen with varied cross-sections was submitted to a tensile test, so that the different sections were submitted to to different stress values. A positive correlation was observed between the stress value and the number, length and thickness of the detected cracks. This experiment also showed the influence of spatial resolution and noise upon the possibility of detecting cracks accurately.

L'objectif de la thèse présentée ici est l'optimisation de matériaux carbonésnanoporeux au moyen de la “conception de matériaux virtuels”. En ce qui concerne cette échelle de travail (~ 10nm), la Nanotomographie FIB-SEM est la seule technique d'imagerie donnant accès à une information sur la géométrie tridimensionnelle. Cependant, pour l'optimisation du comportement, l'espace des pores doit être reconstruit à partir des données tirées des images obtenues. Jusqu'à présent ce problème n'était pas résolu. Pour pouvoir le maîtriser, on a développé une simulation d'images FIB-SEM. Les images FIB-SEM simulées peuvent être utilisées pour la vérification et la validation des algorithmes de segmentation. En utilisant les données d'image simulées, un nouvel algorithme pour la reconstruction de l'espace des pores à partir des données FIB-SEM a été développé.Deux études de cas avec des carbones nanoporeux utilisés pour le stockage d'énergie sont présentées, en utilisant les nouvelles techniques pour la caractérisation et l'optimisation des électrodes Li-ion de type EDLC'S (« electric double-layer capacitors », soit supercondensateurs). L'espace des pores reconstruit est modélisé géométriquement à l'aide de la géométrie stochastique. Enfin, on a simulé les propriétés électriques des matériaux enutilisant des structures modélisées et simulées. / The aim of the work presented here is to optimize nanoporous carbon materials by means of 'virtual material design'. On this length scale (~ 10nm) Focused Ion Beam – Scanning Electron Microscopy Nanotomography (FIB-SEM) is the only imaging technique providing three dimensional geometric information. Yet, for the optimization, the pore space of the materials must be reconstructed from the resulting image data, which was a generally unsolved problem so far.To overcome this problem, a simulation method for FIB-SEM images was developed. The resulting synthetic FIB-SEM images could then be used to test and validate segmentation algorithms. Using simulated image data, a new algorithm for the morphological segmentation of the highly porous structures from FIB-SEM data was developed, enabling the reconstruction of the three dimensional pore space from FIB-SEM images.Two case studies with nanoporous carbons used for energy storage are presented, using the new techniques for the characterization and optimization of electrodes of Li-ion batteries and electric double layer capacitors (EDLC's), respectively. The reconstructed pore space is modeled geometrically by means of stochastic geometry. Finally, the electrical properties of the materials were simulated using both imaged real and modeled structures.

Kyoto University (京都大学) / 0048 / 新制・課程博士 / 博士(工学) / 甲第17561号 / 工博第3720号 / 新制||工||1567(附属図書館) / 30327 / 京都大学大学院工学研究科航空宇宙工学専攻 / (主査)教授 吉田 英生, 教授 江口 浩一, 准教授 鈴木 基史 / 学位規則第4条第1項該当

The formation of conversion coatings based on Ce, trivalent Cr and Ti/Zr is triggered by the local pH increase at cathodic IM sites of the aluminium alloy microstructure. The pH gradient is created over the cathodic intermetallic (IM) sites of the microstructure and its intensity is influenced by their activity which depends on their chemical composition, their size, and spatial distribution. Furthermore, the pre-treatment applied also affects the surface reactivity. The role of each of the microstructural features on the increased pH gradient and the subsequent triggering of local conversion coating deposition remains to be understood. To address the knowledge gap, model cast Al-Si-Fe and Al-Si-Cu-Fe alloys have been designed. Cerium based conversion coating treatment with standard parameters is applied to investigate the microstructure’s influence. Furthermore, four different surface pre-treatments’ effect on the topographical and electrochemical properties have been investigated by localized techniques and have been correlated with deposition experiment observations to prove surface reactivity. In this study, it was found that the four surface pre-treatments – polishing, NaOH, NaOH-HNO3, NaOH-H2SO4 activate the surface of alloys containing Fe-rich IM and Cu-rich IM differently. The surface pre-treatment NaOH-HNO3 was found most detrimental to the surface reactivity as the pre-treatment resulted in passivation of the IM and a drastic reduction in its volta potential. The best pre-treatment for the alloy Al-Si-Fe was found to be one with NaOH etching. In the case of Al-Si-Cu-Fe alloy, pre-treatments where a pickling step (with either H2SO4 or HNO3) was applied followed a NaOH etching step, the surface of the IM was activated more than other pre-treatments due to selective Al dealloying and Cu-redeposition. The extent of Cu-redeposition was observed to be the most when surfaces were pickled with HNO3 solution and with the NaOH- HNO3 pre-treatment, fastest deposition kinetics were observed. In the cast Al-Si-Cu-Fe alloy, the localized deposits were preferentially observed to form on only strong cathodic Cu-rich IM. The size (surface area) of the Cu-rich IM correlated linearly with the lateral deposition area as well as z-direction spread. It was found that the pH gradient resulting from the oxygen reduction reaction near an IM is very local and does not affect pH gradients of a neighbouring Cu-rich IM. The size did not have a profound impact on the extent of deposition occurring on a Cu-rich IM, but it was found that big Cu-rich IM activated faster for deposition reaction than small Cu-rich IM. When the progression of deposition on both coarse and fine microstructure cast Al-Si-Cu-Fe was quantitatively monitored at increasing conversion coating times 0.5h, 1h and 2h, it was observed that big Cu-rich IM in the coarse alloy triggered deposition faster than small Cu-rich IM. Deposition mechanism on Fe-rich IM was found to be composition specific. In the cast of big Fe-rich β-Al5FeSi IM, localized deposition initiated at the border on the IM and is explained based on Si content in the composition of the IM, which has very high resistivity. In another Fe-rich IM, although of a much smaller size, which had lower Si content and was richer in Fe, a localized deposition was observed on the entire IM. / Bildning av omvandlingsbeläggningar baserade på Ce, trivalent Cr och Ti/Zr initieras av lokalt förhöjd pH vid katodiska intermetalliska platser I aluminiumlegeringens mikrostruktur. Utbredningen av den starka pH-gradientens uppkomst över katodiska intermetalliska (IM) platser av mikrostrukturen påverkas av dess aktivitet som i sin tur beror på dess kemiska sammansättning, storlek, och rumslig fördelning. Ytans reaktivitet påverkas dessutom av dess förbehandling. Rollen av mikrostrukturens egenskaper på den förhöjda pH-gradienten och efterföljande initiering av lokal omvandlingsbeläggning återstår att förstå. För att komplettera detta kunskapsgap har Al-Si-Fe och Al-Si-Cu-Fe modellgjutlegeringar utformats. Cerium-baserade behandlingar för omvandlingsbeläggning med standardparametrar tillämpas för undersökning av mikrostrukturens påverkan. Effekten av fyra olika ytförbehandlingar på topografiska och elektrokemiska egenskaper har dessutom undersökts med lokaliserade metoder och har korrelerats med observationer vid depositionsexperient för att bevisa ytreaktivitet. I denna studie har det visats att de fyra ytförbehandlingarna – polering, NaOH, NaOH-HNO3, NaOH-H2SO4 – aktiverar ytan hos legeringar innehållande Fe-rika intermetaller och Cu-rika intermetaller på olika vis. Ytförbehandlingen med NaOH-HNO3 visades vara skadligast för ytans reaktivitet eftersom förbehandlingen resulterade i passivering av IM och en drastisk sänkning av dess volta-potential. Den bästa förbehandlingen för Al-Si-Fe-legeringen visades vara med NaOH-etsning. I Al-Si-Cu-Fe-legeringens fall, var förbehandling där ett betningssteg (antingen med H2SO4 eller HNO3) tillämpades följt av etsning med NaOH, aktiverades ytan av IM mer än med andra förbehandlingar på grund av selektiv korrosion av Al och Cu-återdeposition. Utbredningen av Cu-återdeposition observerades vara störst när ytor var betade med HNO3-lösning och depositionens kinetik var som hastigast vid förbehandling med NaOH-HNO3. I den gjutna Al-Si-Cu-Fe-legeringen observerades lokaliserade depositionerna att bildas endast på starkt katodiska Cu-rika IM. Storleken (ytarea) på de Cu-rika IM korrelerade linjärt med den laterala depositionsytan samt med spridning i z-riktning. Det visade sig att pH-gradienten som uppkom via syrereduktionsreaktionen nära IM är väldigt lokal och påverkar ej pH-gradienter vid närliggande Cu-rik IM. Storleken hade ingen anmärkningsvärd verkan på utbredningen av deposition på Cu-rik IM, men stora Cu-rika IM visade sig aktiveras snabbare för depositionsreaktion än små Cu-rika IM. När depositionens framfart över grov och fin mikrostruktur i gjuten Al-Si-Cu-Fe följdes kvantitativt vid ökande omvandlingsbeläggningstid 0,5h; 1h och 2h, så observerades att stora Cu-rika IM i den grova legeringen påbörjade depositionen snabbare än små Cu-rika IM. Depositionsmekanismen på Fe-rika IM visades vara specifik för sammansättning. I gjutgodset med stora Fe-rika β-Al5FeSi IM visades lokaliserad deposition initieras vid gränsen av IM vilket förklaras baserat på Si-halt i IM sammansättning, som har väldigt hög resistivitet. I en annan Fe-rik IM, dock av mycket mindre storlek, som hade lägre Si-halt och rikare med Fe, en lokaliserad deposition var observerad över hela IM.

Ce travail a porté sur la caractérisation et la quantification en 3D de la répartition de charges de différents types (nanoparticules, nanotubes, etc.) dans des matrices polymères. Nous nous focalisons sur les techniques de tomographie en microscopie électronique. Une approche multiple en tomographie électronique a été réalisée : la tomographie en FIB/MEB (faisceau d’ions focalisé/microscope électronique à balayage), la tomographie en MEB et la tomographie en MET (microscope électronique en transmission). Les nanocomposites polymère sont généralement élaborés aux fins d’améliorer les propriétés physiques (mécanique, électrique, etc.) du matériau polymère constituant la matrice, grâce à une addition contrôlée de charges nanométriques. La caractérisation de tels matériaux, et l’établissement de corrélations précises entre la microstructure et les propriétés d’usage, requièrent une approche tri-dimensionnelle. En raison de la taille nanométrique des charges, la microscopie électronique est incontournable. Deux systèmes de nanocomposite polymère ont été étudiés par une approche multiple de tomographie électronique : P(BuA-stat-S)/MWNTs (copolymère statistique poly (styrène-co-acrylate de butyl) renforcé par des nanotubes de carbone multi-parois), et P(BuA-stat-MMA)/SiO2 (copolymère statistique poly(butyl acrylate-co-methyl methacrylate) renforcé par des nanoparticules de silice). Par combinaison de divers techniques, la caractérisation et la quantification des nanocharges ont été possibles. En particulier, la taille, la fraction volumique et la distribution des charges ont été mesurées. Cette étude a ainsi fourni des informations en 3D qui contribuent à mieux comprendre les propriétés des nanocomposites. Une attention particulière a été portée aux artefacts et causes d’erreur possibles durant l’étape de traitement 3D. Nous avons également essayé de comparer les différentes techniques utilisées du point de vue de leurs avantages et inconvénients respectifs, en dégageant des possibilités d’amélioration future. / This work is focused on the characterization and quantification of the 3D distribution of different types of fillers (nanoparticles, nanotubes, etc.) in polymer matrices. We have essentially used tomography techniques in electron microscopy. Multiple approaches to electron tomography were performed: FIB-SEM (focused ion beam/scanning electron microscope) tomography, SEM tomography and TEM (transmission electron microscope) tomography. Polymer nanocomposites are basically synthesized in order to improve the physical properties (mechanical, electric, etc.) of the pure polymer constituting the matrix, by a controlled addition of fillers at the nanoscale. The characterization of such materials and the establishment of accurate correlations between the microstructure and the modified properties require a three-dimensional approach. According to the nanometric size of the fillers, electron microscopy techniques are needed. Two systems of polymer nanocomposites have been studied by multiple electron tomography approaches: P(BuA-stat-S)/MWNTs (statistical copolymer poly(styrene-co-butyl acrylate) reinforced by multi-walled carbon nanotubes) and P(BuA-stat-MMA)/SiO2 (statistical copolymer poly(butyl acrylate-co-methyl methacrylate) reinforced by silica nanoparticles). By combining various techniques, the characterization and the quantification of nanofillers were possible. In particular, statistics about size, distribution and volume fraction of the fillers were measured. This study has then provided 3D information, which contributes to a better understanding of properties of the nanocomposites. Attention has been paid to analyze carefully original data, and artifacts and causes of errors or inaccuracy were considered in the 3D treatments. We also attempted to compare benefits and drawbacks of all techniques employed in this study, and perspectives for future improvements have been proposed.

L’objectif principal de ce travail est d’optimise la tomographie par coupe sériée dans un microscope ‘FIB’, en utilisant soit l’imagerie électronique du microscope à balayage (tomographie FIB-MEB), soit la diffraction des électrons rétrodiffusés (tomographie dite EBSD 3D). Dans les 2 cas, des couches successives de l’objet d’étude sont abrasées à l’aide du faisceau ionique, et les images MEB ou EBSD ainsi acquises séquentiellement sont utilisées pour reconstruire le volume du matériau. A cause de différentes sources de perturbation incontrôlées, des dérives sont généralement présentes durant l'acquisition en tomographie FIB-MEB. Nous avons ainsi développé une procédure in situ de correction des dérives afin de garder automatiquement la zone d'intérêt (ROI) dans le champ de vue. Afin de reconstruction le volume exploré, un alignement post-mortem aussi précis que possible est requis. Les méthodes actuelles utilisant la corrélation-croisée, pour robuste que soit cette technique numérique, présente de sévères limitations car il est difficile, sinon parfois impossible de se fier à une référence absolue. Ceci a été démontré par des expériences spécifiques ; nous proposons ainsi 2 méthodes alternatives qui permettent un bon alignement. Concernant la tomographie EBSD 3D, les difficultés techniques liées au pilotage de la sonde ionique pour l'abrasion précise et au repositionnement géométrique correct de l’échantillon entre les positions d'abrasion et d’EBSD conduisent à une limitation importante de la résolution spatiale avec les systèmes commerciaux (environ 50 nm)3. L’EBSD 3D souffre par ailleurs de limites théoriques (grand volume d'interaction électrons-solide et effets d'abrasion. Une nouvelle approche, qui couple l'imagerie MEB de bonne résolution en basse tension, et la cartographie d'orientation cristalline en EBSD avec des tensions élevées de MEB est proposée. Elle a nécessité le développement de scripts informatiques permettant de piloter à la fois les opérations d’abrasion par FIB et l’acquisition des images MEB et des cartes EBSD. L’intérêt et la faisabilité de notre approche est démontrée sur un cas concret (superalliage de nickel). En dernier lieu, s’agissant de cartographie d’orientation cristalline, une méthode alternative à l’EBSD a été testée, qui repose sur l’influence des effets de canalisation (ions ou électrons) sur les contrastes en imagerie d’électrons secondaires. Cette méthode corrèle à des simulations la variation d’intensité de chaque grain dans une série d’images expérimentales obtenues en inclinant et/ou tournant l’échantillon sous le faisceau primaire. Là encore, la méthode est testée sur un cas réel (polycritsal de TiN) et montre, par comparaison avec une cartographie EBSD, une désorientation maximale d'environ 4° pour les angles d’Euler. Les perspectives d’application de cette approche, potentiellement beaucoup plus rapide que l’EBSD, sont évoquées. / The aim of current work is to optimize the serial-sectioning based tomography in a dual-beam focused ion beam (FIB) microscope, either by imaging in scanning electron microscopy (so-called FIB-SEM tomography), or by electron backscatter diffraction (so-called 3D-EBSD tomography). In both two cases, successive layers of studying object are eroded with the help of ion beam, and sequentially acquired SEM or EBSD images are utilized to reconstruct material volume. Because of different uncontrolled disruptions, drifts are generally presented during the acquisition of FIB-SEM tomography. We have developed thus a live drift correction procedure to keep automatically the region of interest (ROI) in the field of view. For the reconstruction of investigated volume, a highly precise post-mortem alignment is desired. Current methods using the cross-correlation, expected to be robust as this digital technique, show severe limitations as it is difficult, even impossible sometimes to trust an absolute reference. This has been demonstrated by specially-prepared experiments; we suggest therefore two alternative methods, which allow good-quality alignment and lie respectively on obtaining the surface topography by a stereoscopic approach, independent of the acquisition of FIB-SEM tomography, and realisation of a crossed ‘hole’ thanks to the ion beam. As for 3D-EBSD tomography, technical problems, linked to the driving the ion beam for accurate machining and correct geometrical repositioning of the sample between milling and EBSD position, lead to an important limitation of spatial resolution in commercial softwares (~ 50 nm)3. Moreover, 3D EBSD suffers from theoretical limits (large electron-solid interaction volume for EBSD and FIB milling effects), and seems so fastidious because of very long time to implement. A new approach, coupling SEM imaging of good resolution (a few nanometres for X and Y directions) at low SEM voltage and crystal orientation mapping with EBSD at high SEM voltage, is proposed. This method requested the development of computer scripts, which allow to drive the milling of FIB, the acquisition of SEM images and EBSD maps. The interest and feasibility of our approaches are demonstrated by a concrete case (nickel super-alloy). Finally, as regards crystal orientation mapping, an alternative way to EBSD has been tested; which works on the influence of channelling effects (ions or electrons) on the imaging contrast of secondary electrons. This new method correlates the simulations with the intensity variation of each grain within an experimental image series obtained by tilting and/or rotating the sample under the primary beam. This routine is applied again on a real case (polycrystal TiN), and shows a max misorientation of about 4° for Euler angles, compared to an EBSD map. The application perspectives of this approach, potentially faster than EBSD, are also evoked.

The aim of this work was to study the separate effect of fission fragment damage on the structural integrity and matrix dissolution of uranium dioxide in water. Radiation damage similar to fission damage was created by irradiating bulk undoped and doped ‘SIMFUEL’ disks of UO2, undoped bulk CeO2 and thin films of UO2 and CeO2 with high energy Xe and U ions. The UO2 thin films, with thicknesses in the range of 90 – 150 nm, were deposited onto (001), (110) and (111) orientations of single crystal LSAT (Al10La3O51Sr14Ta7) and YSZ (Yttria-Stabilised Zirconia) substrates. The CeO2 thin films were deposited onto single crystal silicon (001) substrates. Part of the bulk UO2 and CeO2 samples, the thin films of UO2 on the LSAT substrates and the thin films of CeO2 were irradiated with 92 MeV 129Xe23+ ions to a fluence of 4.8 × 1015 ions/cm2 to simulate the damage produced by fission fragments in uranium dioxide nuclear fuel. Part of the bulk UO2 and CeO2 samples and the thin films of UO2 on the YSZ substrates were irradiated with 110 MeV 238U31+ ions to a fluence of 5 × 1010, 5 × 1011 and 5 × 1012 ions/cm2 to study the accumulation of the damage induced. The irradiated and unirradiated samples were studied using scanning electron microscopy (SEM), focused ion beam (FIB), atomic force microscopy (AFM), energy dispersive X-ray (EDX) spectroscopy, electron probe microanalysis (EPMA), X-ray diffraction (XRD), electron backscatter diffraction (EBSD), secondary ion mass spectrometry (SIMS) and X-ray photoelectron spectroscopy (XPS) techniques to characterise the as-produced samples and assess the effects of the ion irradiations. Dissolution experiments were conducted to assess the effect of the Xe ion irradiation on the dissolution of the thin film UO2 samples on the LSAT substrates and the bulk and thin film CeO2 samples. The solutions obtained from the leaching of the irradiated and unirradiated samples were analysed using inductively coupled plasma mass spectrometry (ICP-MS). XRD studies of the bulk UO2 samples showed that the ion irradiations resulted in an increased lattice parameter, microstrain and decreased crystallite size, as expected. The irradiated UO2 thin films on the LSAT substrates underwent significant microstructural and crystallographic rearrangements. It was shown that by irradiating thin films of UO2 with high energy, high fluence ions, it is possible to produce a structure that is similar to a thin slice through the high burn-up structure. It is expected that the ion irradiation induced chemical mixing of the UO2 films with the substrate elements (La, Sr, Al, Ta). As a result, a material similar to a doped SIMFUEL with induced radiation damage was produced.