Electrosorption involves the application of an electrical potential between carbon electrode pairs submerged in brackish water, effectively “trapping” the ions in an electrical double layer at the solid-liquid interface. Electrosorption has significant applications in environmental engineering, including desalination of water by capacitive deionization (CDI), and in energy storage by supercapacitors. This work combines experimental and modeling studies to investigate the transport and sorption mechanisms of ions in the pores of mesoporous carbon materials that were synthesized at the Oak Ridge National Laboratory (ORNL). The main contribution of this research is examining the effects of operational parameters such as applied potential, solution temperature, ionic concentration, and valence of ions, on the electrosorption behavior of mesoporous carbon materials with the aim to improve the desalination efficiency in the CDI process. It was found that the rates of sorption by mesoporous carbon electrodes and their regeneration increased at a higher temperature and on application of a high-frequency, low-amplitude AC signal. Neutron imaging has been employed as a tool to visually observe and quantify the transport and distribution of ions within the carbon electrodes. The neutron images revealed interesting ion transport phenomena that can aid in the optimization of the CDI process. From the ion concentration profiles inside the electrodes, the effective diffusivities of gadolinium and lithium ions were obtained under various conditions of applied potential. Information on the diffusivity of ions can aid in theoretical modeling of the CDI process as well as guide strategies for the design of advanced electrode materials. In the final part of the study, the extraction of salinity gradient energy or ‘blue energy’ by mixing fluids of different salinities was assessed based on the principle of capacitive double layer expansion. Neutron imaging of blue energy recovery cycles was conducted to observe the ion transport behavior during the various steps of the cycle. The results obtained provide insights into the fundamental ion transport mechanisms during electrosorption by mesoporous carbon materials. This research has important implications for developing advanced system designs for desalination of saline water and energy storage devices.

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Na presente dissertação, foi desenvolvido um equipamento para tomografia com nêutrons que está operacional e instalado no canal de irradiação 14 do Reator Nuclear de Pesquisas IEA-R1 do IPEN-CNEN/SP. As imagens apresentadas neste trabalho, são de objetos que foram selecionados de modo a realçarem uma das principais aplicações da técnica, que é o estudo de materiais hidrogenados mesmo se envoltos por espessa camada de alguns metais. Neste equipamento, uma tomografia completa pode ser obtida em 400 s, com uma resolução espacial máxima de 205 μm. Estas características são comparáveis às dos equipamentos mais desenvolvidos em operação em outros países, e propiciam imagens com qualidade suficiente para que sejam realizadas análises tanto qualitativas quanto quantitativas dos objetos inspecionados. A implementação da técnica da tomografia com nêutrons abre a possibilidade de novas linhas de pesquisa, pois disponibiliza uma nova ferramenta para inspeção de objetos, que fornece uma visão da sua estrutura interna, que nem sempre é possível por métodos de imageamento bidimensional. / In the work reported in this dissertation, a facility for neutron tomography was developed and installed at the irradiation channel #14 of the IEA-R1 nuclear research reactor of IPEN-CNEN/SP. Several selected objects were inspected, and the obtained images demonstrate the main characteristic of the present technique that is its capability to visualize hydrogenous rich substances. In such facility, a tomography can be obtained in 400 s with a spatial resolution of 205 μm, and the obtained images have sufficient quality to allow qualitative and quantitative analysis. These characteristics are very similar to the ones of the top facilities around the world, and the quality of the provided images are sufficient to allow qualitative and quantitative analysis of the inspected object. The implementation of the neutron tomography technique opens up the possibility of new research as it provides a new tool for inspection of objects, which provides a view of its internal structure, which is not always possible for two-dimensional imaging methods.

Rich tomography is becoming increasingly popular since we have seen a substantial increase in computational power and storage. Instead of measuring one scalar for each ray, multiple measurements are needed per ray for various imaging modalities. This advancement has allowed the design of experiments and equipment which facilitate a broad spectrum of applications. We present new reconstruction results and methods for several imaging modalities including x-ray diffraction strain tomography, Photoelastic tomography and Polarimet- ric Neutron Magnetic Field Tomography (PNMFT). We begin with a survey of the Radon and x-ray transforms discussing several procedures for inversion. Furthermore we highlight the Singular Value Decomposition (SVD) of the Radon transform and consider some stability results for reconstruction in Sobolev spaces. We then move onto define the Non-Abelian Ray Transform (NART), Longitudinal Ray Transform (LRT), Transverse Ray Transform (TRT) and the Truncated Trans- verse Ray Transform (TTRT) where we highlight some results on the complete inver- sion procedure, SVD and mention stability results in Sobolev spaces. Thereafter we derive some relations between these transforms. Next we discuss the imaging modali- ties in mind and relate the transforms to their specific inverse problems, primarily being linear. Specifically, NART arises in the formulation of PNMFT where we want to im- age magnetic structures within magnetic materials with the use of polarized neutrons. After some initial numerical studies we extend the known Radon inversion presented by experimentalists, reconstructing fairly weak magnetic fields, to reconstruct PNMFT data up to phase wrapping. We can recover the strain field tomographically for a polycrystalline material using diffraction data and deduce that a certain moment of that data corresponds to the TRT. Quite naturally the whole strain tensor can be reconstructed from diffraction data measured using rotations about six axes. We develop an innovative explicit plane-by-plane filtered back-projection reconstruction algorithm for the TRT, using data from rotations about three orthogonal axes and state the reasoning why two- axis data is insufficient. For the first time we give the first published results of TRT reconstruction. To complete our discussion we present Photoelastic tomography which relates to the TTRT and implement the algorithm discussing the difficulties that arise in reconstructing data. Ultimately we return to PNMFT highlighting the nonlinear inverse problem due to phase wrapping. We propose an iterative reconstruction algorithm, namely the Modified Newton Kantarovich method (MNK) where we keep the Jacobian (Fréchet derivative) fixed at the first step. However, this is shown to fail for large angles suggesting to develop the Newton Kantarovich (NK) method where we update the Jacobian at each step of the iteration process.

Na presente dissertação, foi desenvolvido um equipamento para tomografia com nêutrons que está operacional e instalado no canal de irradiação 14 do Reator Nuclear de Pesquisas IEA-R1 do IPEN-CNEN/SP. As imagens apresentadas neste trabalho, são de objetos que foram selecionados de modo a realçarem uma das principais aplicações da técnica, que é o estudo de materiais hidrogenados mesmo se envoltos por espessa camada de alguns metais. Neste equipamento, uma tomografia completa pode ser obtida em 400 s, com uma resolução espacial máxima de 205 μm. Estas características são comparáveis às dos equipamentos mais desenvolvidos em operação em outros países, e propiciam imagens com qualidade suficiente para que sejam realizadas análises tanto qualitativas quanto quantitativas dos objetos inspecionados. A implementação da técnica da tomografia com nêutrons abre a possibilidade de novas linhas de pesquisa, pois disponibiliza uma nova ferramenta para inspeção de objetos, que fornece uma visão da sua estrutura interna, que nem sempre é possível por métodos de imageamento bidimensional. / In the work reported in this dissertation, a facility for neutron tomography was developed and installed at the irradiation channel #14 of the IEA-R1 nuclear research reactor of IPEN-CNEN/SP. Several selected objects were inspected, and the obtained images demonstrate the main characteristic of the present technique that is its capability to visualize hydrogenous rich substances. In such facility, a tomography can be obtained in 400 s with a spatial resolution of 205 μm, and the obtained images have sufficient quality to allow qualitative and quantitative analysis. These characteristics are very similar to the ones of the top facilities around the world, and the quality of the provided images are sufficient to allow qualitative and quantitative analysis of the inspected object. The implementation of the neutron tomography technique opens up the possibility of new research as it provides a new tool for inspection of objects, which provides a view of its internal structure, which is not always possible for two-dimensional imaging methods.

Le sujet de la thèse vise à développer un imageur neutron portable présentant des performances de détection compatibles avec les besoins de la recherche et de l’industrie nucléaire, notamment ceux du démantèlement. Cette thèse se décompose en trois axes principaux de recherche, précédés d’une phase de recherche bibliographique. Suite à cette dernière, l’approche de localisation retenue est l‘imagerie de neutrons rapides par encodage spatial. Les détecteurs de neutrons ont été étudiés et plusieurs choix, adaptés à cette problématique, ont été retenus pour la suite de l’étude. Le premier axe est consacré aux études sur le développement d’un détecteur de neutrons sensible à la position. Le deuxième axe est lié à la conception et au prototypage d’un imageur neutronique, se reposant sur un masque codé et un détecteur Timepix modifié par une couche de paraffine. Le dernier axe concerne le déploiement et la caractérisation expérimentale de ce prototype. / The subject of the thesis aims at developing a portable neutron imager with detection performance compatible with the needs of the nuclear research and industry, in particular those of decommissioning. This thesis is divided into three main areas of research, preceded by a bibliographic research phase. Following the latter, the localization approach adopted is spatial encoding fast neutron imaging. Neutron detectors were studied and several choices adapted to this challenge were selected for the continuation of the study. The first axis is dedicated to the studies on the development of a position-sensitive neutron detector. The second axis is related to the design and prototyping of a portable neutron imager, based on a coded aperture and a Timepix detector enhanced with a paraffin layer. The last axis concerns the deployment and experimental characterization of this prototype.

Les micropiles à combustibles sont envisagées pour remplacer ou prolonger l’autonomie des batteries dans les dispositifs nomades. Dans ce domaine, la miniaturisation très poussée a abouti à la réalisation de prototypes planaires multi-cellules d’une puissance de 3 à 5 W. La différence d’architecture par rapport aux piles à combustibles « classiques », l’absence d’auxiliaires de fonctionnement et l’utilisation direct de l’air ambiant comme réactif amènent de nouvelles problématiques au niveau de la gestion de l’eau produite. Le travail de cette thèse porte sur la caractérisation de la gestion de l’eau et l’augmentation de la durée de vie d’un système de micropiles à combustible planaire « à respiration », à température ambiante. L’impact prépondérant de la thermique a été mis en avant, au niveau des points de fonctionnement (noyage aux faibles densités de courant et assèchement aux forts courants) comme au niveau local (gradients entre cellules). Les phénomènes d’assèchement et de noyage ont été étudiés grâce à l’imagerie neutronique. Un des principaux phénomènes observé est la rétrodiffusion d’eau vers l’anode suite une condensation au niveau de la cathode, conduisant à une importante perte de puissance. Une étude de la dégradation lors de fonctionnement longue durée a permis de montrer qu’une mauvaise gestion de l’eau favorise la corrosion d’éléments métalliques, conduisant à une diminution des performances. Une solution visant à éliminer ces phénomènes a été développée et implémentée avec succès. L’intégration du microporeux développé lors de cette thèse a permis d’atteindre une dégradation de 0,1 mV/h sur 2500 h de fonctionnement à 3,5 W. / Micro fuel cells have been considered as potential substitute or complement to batteries for nomad systems, in order to enhance their autonomy. Miniaturization of these objects led to the development of multi-cells planar arrays delivering 3 to 5 W. The specificities of this design compared to the “conventionnal” fuel cell stack architecture, coupled to the removal of peripheral components and the use of ambient air as oxidant, comes along with new challenges concerning water management. This work is focused on the characterization of water management and the lifetime improvement of a planar air-breathing fuel cell array at ambient temperature. Thermal effects have been demonstrated to be of first order concerning the operating conditions (flooding at low current density and drying-out at elevated one) and the local heterogeneities (between cells). Drying-out and flooding have been investigated using neutron imaging. One of the major phenomena observed is back-diffusion linked to water condensation on the cathode side, leading to anodic water accumulation and concomitant power decrease. Investigation of the degradation during long term operation pointed out corrosion of metallic elements as the major issue involved in performance decrease. Development and successful implementation of a solution to counter these troubles led to a limited degradation of 0.1 mV/h during a 2500 h operation at 3.5 W.

Bitumen acts as a binding agent in asphalt mixtures where it binds the aggregates together. It is known for its potential to heal small cracks and recover its mechanical properties under the right conditions. Though this self-healing property is known, there is currently a lack of knowledge about the mechanisms that drive the process. To optimize the use of this material for pavement design, the healing ability should be better understood and controlled. In this work, it is investigated how neutron imaging can be used to increase the understanding of the mechanisms behind the self-healing in bitumen. As a first step, the sample size requirement set by the measurement technique was determined. In order to detect micro cracks in bitumen by using this technique, the sample must be sufficiently small to allow neutron transmission. On the other hand, too small samples would complicate the structural analysis of the material since less information would be possible to obtain. Bitumen with different dimensions were scanned with neutrons to determine the maximum sample thickness. This work was followed by evaluating the healing capability of fractured bitumen and mastic samples, by using time series neutron tomography. The studied samples had a varying combination of hydrated lime (HL) filler concentration, crack volume, and contact area between the broken pieces. The data acquired from the time series tomography scans was analyzed using a three-dimensional analysis procedure including denoising, segmentation and volume measurements. From the volumetric analysis, it appeared that the initial crack size and crack shape have a large impact on the healing rate. It was found that bitumen, mastic with 20%, and 30% filler content had a similar healing behavior for relatively small crack volumes. When increasing the content of HL in the mastic, the healing rate decreases exponentially, with a drastic decrease after reaching a filler content of about 30%. / Bitumen fungerar som bindemedel i asfaltsblandningar där det binder ihop stenaggregaten. Bitumen är känd för sin förmåga att läka små sprickor och återfå sina mekaniska egenskaper under rätt förutsättningar. Trots att den självläkande egenskapen är välkänd, råder det idag en brist på kunskap om de mekanismer som ligger bakom denna process. För att optimera användandet av bitumen för vägbeläggningar behövs en bättre förståelse kring denna läkande egenskap. I detta projekt undersöks det hur neutronavbildning kan användas för att öka förståelsen kring de mekanismer som ligger bakom den självläkande egenskapen hos bitumen. Som ett första steg bestämdes provstorlekskravet för denna analysteknik. För att möjliggöra detekteringen av små sprickor i bitumen genom att använda denna teknik måste provmaterialet vara tillräckligt tunt för att neutronerna ska kunna transmitteras genom materialet. Allt för små provstorlekar skulle, å andra sidan, försvåra analysen av materialets struktur då informationen man kan erhålla blir mer begränsad. Bitumen med olika provstorlekar skannades med neutroner för att bestämma den maximala provtjockleken. Därefter analyserades den självläkande förmågan hos brutna bitumen- och bitumenmastixprover med tidsserie neutrontomografi. Prover med olika mängder av kalciumhydroxidfiller i bitumenblandningen, olika storlek på sprickvolymen och kontaktytan mellan de brutna provdelarna studerades. Data erhållna från experimenten användes för att göra en 3-dimensionell analys som inkluderade brusreducering av bilder, segmentering och volymmätningar. Från volymanalyserna konstaterades det att den initiala sprickstorleken och sprickformen har en stor inverkan på läkningstakten. Bitumen, mastix med 20%, och 30% filler-additiv uppvisade liknande läkningsegenskaper för relativt små sprickstorlekar. Vid en ökning av mängden filler material i mastixen minskar läkningstakten exponentiellt, med en drastisk minskning när man passerar en filler-koncentration på runt 30%. / <p>QC 210303</p>

Pour les structures de génie civil avec un rôle d’étanchéité, lors d’un accident grave, la perméabilité du béton est une question clé. Les mesures de perméabilités actuelles ne permettent d'avoir que des grandeurs moyennes (structurelles) qui ne conviennent pas pour des éprouvettes hétérogènes (fissures et/ou armatures). La compréhension des détails de l'écoulement des fluides est cruciale en raison des implications sur les voies préférentielles (interface acier/béton, fissures, etc.). Le but de cette thèse est de proposer une nouvelle méthodologie et de tester un nouveau dispositif expérimental par imagerie neutronique à la ligne de faisceaux D50 à l’Institut Laue Langevin à Grenoble. Le test consiste à injecter de l’eau normale (H2O), sous haute pression, dans un échantillon de béton coulé et saturé en eau lourde (D2O), afin de suivre la progression d’un front d’eau dans le temps par différence d’atténuation entre ces deux eaux. Une campagne expérimentale a été lancée sur des éprouvettes de béton sous différentes configurations (béton sain, béton fissuré et béton avec une armature) et des mesures de perméabilité locale dans les singularités (zone fissurée, interface armature-béton, etc.) ont été faites. Les essais ont montré que les mesures classiques de perméabilité sont sous-estimées et les écoulements dans le béton sont contrôlés par les défauts. / For civil engineering structures, especially containment buildings during a severe accident, the permeability of concrete is a key issue. Current permeability measurements allow only average (structural) magnitudes, which are not suitable for heterogeneous samples (cracks and/or reinforcements). Understanding the details of fluid flow is crucial because of the implications of preferred pathways (steel/concrete interface, cracks, etc.). The aim of this thesis is to propose a new methodology, and to test a new experimental setup, using neutron imaging at the D50 beam line at the Institute Laue Langevin in Grenoble to measure flow directly. The test consists of injecting normal water (H2O) under high pressure, into a concrete sample casted and saturated with heavy water (D2O), in order to follow the evolution of a waterfront over time by difference of attenuation between these two waters. An experimental campaign was launched on concrete specimens in different configurations (proper concrete, cracked concrete and concrete with reinforcement) and measurements of local permeability in singularities (cracked zone, reinforcement-concrete interface, etc.) were done. Tests have shown that classical permeability measurements are underestimated and flows in concrete are controlled by defects.

Current environmental and energy sustainability trends have instigated considerable interest in alternative energy technologies that exhibit reduced dependence on fossil fuels. The advantages of such a direction are two-fold: reduced greenhouse gas emissions (notably CO2) and improved energy sustainability. Fuel cells are recognized as a potential technology that achieves both of these goals. However, improvements to fuel cell power density and stability must be realized to make them economically competitive with traditional, fossil-based technologies. The work in this dissertation is largely focused on the use of analytical tools for the study of transport processes in three fuel cell systems toward improvement of fuel cell performance. Polymer electrolyte membrane fuel cells (PEMFCs) are fueled by hydrogen and oxygen to generate electrical current. Microbial fuel cells (MFCs) use bacteria to degrade carbon compounds, such as those found in wastewaters, and simultaneously generate an electric current. Enzyme fuel cells (EFCs) operate similarly to PEMFCs but replace precious metal catalysts, such as platinum, with biologically-derived enzymes. The use of enzymes also allows EFCs to utilize simple carbon compounds as fuel. The operation of all three fuel cell systems involves different modes of ion and electron transport and can be affected negatively by transport limitations. Electrochemical impedance spectroscopy (EIS) was used in this work to study the distribution of transport resistances in all three fuel cell systems. The results of EIS were used to better understand the transport resistances that limited fuel cell power output. By using this technique, experimental conditions (including operating conditions, construction, and materials) were identified to develop fuel cells with greater power output and longevity. In addition to EIS, neutron imaging was employed to quantify the distribution of water in PEMFCs and EFCs. Water content is an integral aspect of providing optimal power output from both fuel cell systems. Neutron imaging contributed to developing an explanation for the loss of water observed in an operating EFC despite conditions designed to mitigate water loss. The findings of this dissertation contribute to the improvement of fuel cell technology in an effort to make these energy devices more economically viable.