Zeolite membranes have great potential in gas separation applications because of their unique selective properties. The main challenge is in synthesizing defect-free zeolite membranes. In this study, we synthesized silicalite-1 zeolite membranes on ceramic supports composed of Al2O3 and TiO2 using the pore-plugging method. We investigated the effect of the fill-level in the autoclave during the synthesis on the membrane performance. In particular, we were interested in determining the conditions at which the defects' contribution to the total transport is minimized. We adopted and further developed the approach proposed by Carter (2019) to quantify the permeance contribution through defects. Comparing the membrane performance before and after calcination, we proposed several modifications to the original analysis of Carter (2019). Knowing the defect transport contribution, we determined the corrected diffusivity, an intrinsic property of zeolite crystals at a given temperature, of several adsorbed gases on silicalite-1 crystals. The defect's contribution decreased as the autoclave fill-level increased from 94 to 98%. A further increase in the autoclave fill-level introduced more defects and caused the autoclave lid to rupture. Despite the differences in the membranes' performance arising from the autoclave fill-level, the corrected diffusivities of CO2, CH4, and N2 in silicalite-1 showed minimal variation from membrane to membrane. This proves the validity of the proposed characterization method. Moreover, the reported corrected diffusivities are comparable to the literature's values, found using other characterization methods. However, none of the previously used methods is as simple and straightforward as the one we further developed in this study.

<p>The pore-size dependence of liquid diffusivity in mesopores has been a controversial topic. It is especially meaningful in dye-sensitized solar cells (DSSCs) because the triiodide ion diffusivity is closely related to the cell performance. By applying electrochemical measurements, the pore-size dependence of ion diffusivity in DSSCs was investigated based on TiO₂ thin films of variable pore diameters. The alternation of pore-size was achieved by the epitaxial growth of TiO₂ after TiCl₄ post-treatments. From the trend of normalized diffusivities, the respective valid regimes of pore-size dependent and independent diffusion were determined, which were separated by the transition point located at 5-7 nm. In addition, my results have showed that the DSSC fabrication processes, e.g., dye loading, TiCl₄ post-treatment will not lead to the transition of diffusion behaviors. Furthermore, the unexpected drop of diffusivity after one TiCl₄ treatment is attributed to the involvement of surface diffusion in untreated TiO₂ matrix.</p> / Master of Applied Science (MASc)

Dans ce travail, nous avons étudié l’adsorption dissociative de l’hydrogène sur Pd(111) ainsi que la diffusion d’un atome de l’hydrogène sur ce même surface. A l’aide de la théorie de la fonctionnelle de la densité, nous avons mené une étude systématique de l’effet du recouvrement en surface sur l’énergétique de la dissociation de H2 sur une surface de Pd(111) couverte par des atomes de l’hydrogène. Un résultat surprenant que nous avons trouvé est que les atomes adsorbés ont non seulement un effet de poison mais peuvent aussi promouvoir la dissociation de H2 s’ils sont adsorbés sur des sites loin de la molécule d’hydrogène qui dissocie. En ce qui concerne la diffusion d’un atome d’ hydrogène sur Pd(111), nous avons déterminé le coefficient de diffusion par des simulations de dynamique moléculaire en utilisant la formule d’Einstein à différente température de la surface, Ts=500K, 300K and 250K. Une méthode de la dynamique moléculaire accélérée a été développée afin d’étudier la diffusion à bases températures. Dans notre approche, l’accélération se fait moyennant l’augmentation de l’énergie cinétique de l’atome qui diffuse suivant une distribution Maxwell-Boltzmann qui correspond à une température plus élevée et la correction de l’échelle de temps d’une façon consistante. Pour tester la validité de notre approche, nous avons effectué des simulations pour la diffusion d’un atome d’hydrogène sur Pd(111) à Ts=300K and Ts=100K. Les résultats obtenus par la méthode accélérée est en bon accord avec ceux de la simulation standard. Par la méthode accélérée, l’échelle de temps peut être étendu à l’ordre de micro-secondes. / In this thesis, we studied dissociative adsorption of hydrogen on Pd(111) with particular attention paid to the surface coverage effect and the diffusion of a hydrogen adatom on Pd(111). With the help of DFT calculations, we carried out a systematic investigation of the effect of H-adatoms on the dissociation energetics of H2 on H-covered Pd(111) surfaces at various coverages. A quite surprising finding is that the H-adatoms do not only have a poisoning effect but can also promote H2 dissociation when they are adsorbed on sites which are sufficiently far from the dissociating H2 molecule. The macroscopic diffusion coefficient of an H-adatom on Pd(111) is determined from molecular dynamics simulations with the help of Einstein formula for different surface temperatures, i.e., Ts=500K, 300K and 250K. An accelerated molecular dynamics method was developed in order to study the diffusion at low surface temperatures. In our approach, the acceleration is achieved by increasing the kinetic energy of the diffusing atom according to the Maxwell-Boltzmann distribution at a higher temperature and correcting the time scale in a consistent way. For testing the validity of our method, we performed simulations for the diffusion of H adatom on Pd(111) surface at T=300K and T=100K. The diffusion coefficient obtained from the accelerated MD method is in agreement with that obtained from the direct MD and TST methods. And the physical time scale can be extended to the order of microseconds.

Le milieu interstellaire (MIS) est la matière presente dans l'espace au sein des galaxies.Cette matière est composée de gaz et de grains de poussière. Jusqu'à présent, les radioastronomes principalement ont identifié plus de 170 molécules différentes dans le MIS.La présence de la plupart de ces molécules est expliquée à travers des réactions dans la phase gazeuse, mais la synthèse de beaucoup de ces molécules (comme H2, H2O, CO2) nécessite l'intervention d'uncatalyseur, donc des réactions dans la phase solide, sur la surface des grains de poussière. Les objectifs de cette thèse sont de comprendre quels sont les processus physico-chimiques qui ont lieu (par exemple, la diffusion et désorption) sur la surface des grains de poussière interstellaire et comment ils conduisent à la synthèse de molécules de plus en plus complexes.En particulier, l'objet de ma thèse est d'étudier:- le rôle de la diffusion des atomes d'oxygène (noté « O ») et les processus d'oxydation dans la formation des glaces interstellaires;- le couplage thermique et non thermique entre la phase gaz et la phase solide.L'astrochimie ne tendait à considérer que la diffusion des atomes d'hydrogène et les réactions d'hydrogénation, ignorant souvent le rôle de l'oxygénation ainsi que l'importance des processus d'adsorption et de désorption, d'où mes recherches approfondies sur ces thématiques.Évidemment, une meilleure connaissance de ces processus physico-chimiques et des réactions de surface aiderait les astronomes à comprendre la formation des glaces interstellaires, l'augmentation de la complexité moléculaire, et l'équilibre entre le gaz et la phase solide.Pour répondre à ces questions, de nombreuses expériences ont été réalisées avec le dispositif FORMOLISM, situé à l'Université de Cergy-Pontoise dans le cadre du LERMA (Observatoire de Paris). Via deux jets de particules avec un pompage différentiel, les atomes et les molécules sont déposés sur un échantillon froid (> 6,5 K) dans une chambre ultravide. Les produits des réactions sont ensuite sondés en utilisant la spectroscopie de masse et la spectroscopie infrarouge.Pour simuler différents environnements astrophysiques, la physique-chimie de l'état solide a été étudiée dans différentes conditions expérimentales:- La morphologie de substrat (glace d'eau amorphe soit poreuse, soit compacte, glace d'eau cristalline, silicate amorphe ou graphite)- Les espèces déposées et leur rapport relatif- La couverture des espèces déposées, de 0,1 à 2 monocouches- La température du substrat, de 6,5 à 60 K.En ce qui concerne les processus d'oxydation, les résultats montrent que l'O est très réactif avec de nombreuses espèces ; la diffusion des atomes d'O semble être beaucoup plus rapide que prévu et peut se produire par effet tunnel à des températures aussi basses que 6,5 K. Nous avons comparé les valeurs expérimentales des coefficients de diffusion et constaté que les taux de diffusion sur chaque surface, basés sur les résultats de la modélisation, étaient considérablement plus élevés que ceux prévus pour les atomes lourds tels que l'O. Nos résultats montrent que les atomes O peuvent rencontrer tous les partenaires disponibles de réaction à un taux plus rapide que le taux d'accrétion. En particulier, dans les nuages interstellaires très denses, le rapport O/H est tel que O devient l'un des partenaires réactifs dominants avec H. Ceci a un impact sur la formation de certaines espèces et sur l'abondance relative des produits formés.En ce qui concerne les processus de couplage solide-gaz (c'est à dire, l'adsorption, désorption thermique, désorption chimique), les résultats montrent que chaque processus est influencé d'une manière différente par le substrat (glace d'eau, de silicate ou graphite). Enfin, nous fournissons une liste utile des énergies de liaison de plusieurs espèces et de l'efficacité de désorption chimique des différentes réactions sur ces substrats. / The interstellar medium is the matter that exists in the space between the star systems in a galaxy. It is composed of gas and elongated tiny dust grains. To date, plenty of molecules (> 170) are known to exist in the interstellar medium. The presence of most of them can be understood in terms of gas phase reactions but the synthesis of some key species (H2, H2O, CO2) need the intervention of solid-state reactions on dust grains surface. The aims of this thesis are to understand what are the relevant physical-chemical processes (i.e., diffusion and desorption) occurring on the surface of interstellar dust grains and how these processes influence synthesis of more and more complex molecules. In particular, the focus of my thesis is the investigation of:1) the role of O-atom diffusion and the oxidation processes in the formation of interstellar ices;2) the thermal and non-thermal processes coupling gas and solid phase.The reasons of these investigations lie on the realization that, up to now, only hydrogen diffusion and hydrogenation reactions are commonly considered in solid astrochemistry and the role of oxygenation as well as the importance of adsorption and desorption processes are often disregarded.Evidently, a better knowledge of such physical-chemical processes and, in general, of the solid state physical-chemistry could help astronomers to understand the formation of interstellar ices, the increase on molecular complexity, and the equilibrium between gas and solid phase.To answer these questions, many experiments have been performed with the FORMOLISM set-up, i.e., FORmation of MOLecules in the ISM, located in the Universitè de Cergy Pontoise, Observatoire de Paris. Via two triply differentially pumped beams, atoms and molecules were aimed at a cold (>6.5 K) sample held in a Ultra high vacuum chamber. The products were probed using Mass spectroscopy and Reflexion Absorption Infrared Spectroscopy.To simulate different astrophysical environments, the solid state physical-chemistry has been studied in different experimental conditions:-The substrate morphology (Amorphous water ice, porous (p) and compact (np), crystalline (c) ice, amorphous silicate, and graphite)-The species deposited and their relative ratio-The coverage of deposited species, from 0.1 to 2 ML-The substrate temperature, from 6.5 to 60 KConcerning oxidation processes and O-atom reactivity, the results show that oxygen is very reactive with many species (i.e., H, CO, NO, H2CO, HCOOH); O diffusion appears to be much faster than previously expected and can occur via quantum mechanical tunnelling at temperatures as low as 6.5 K. We compared the experimental values of the diffusion coefficients and found that the rates of diffusion on each surface, based on modelling results, were considerably higher than those expected for heavy atoms such as oxygen. Our findings show that O atoms can scan any available reaction partners (e.g., either another H atom, if available, or a surface radical like O, OH, CO) at a faster rate than that of accretion. In particular, in very dense interstellar clouds, the O/H ratio is such that O becomes one of the dominant reactive partners together with H. This has an impact on the chemistry occurring at the surface of dust grains as either the formation of some species may be enhanced, or at least the relative abundances of the final products will be affected. An important example of how O-atom mobility can modulate the abundances of key species of ices in the ISM is the case of the H2O/CO2 ratio via the CO+O and H2CO+O pathways.Concerning gas-solid coupling processes (i.e., adsorption, sticking, thermal desorption, chemical desorption), the results show that each processes is influenced in a different way by the substrate (i.e., water ice, silicate or graphite). Moreover, we provide a useful list of binding energies of several species and chemical desorption efficiency for different reactions on different subst

La perméabilisation des cellules à l’aide d’impulsions électriques intenses, appelée électroperméabilisation, est un phénomène biologique impliqué dans des thérapies anticancéreuses récentes. Elle permet, par exemple, d’améliorer l’efficacité d’une chimiothérapie en diminuant les effets secondaires, d’effectuer des transferts de gènes, ou encore de procéder à l’ablation de tumeurs. Les mécanismes de l’électroperméabilisation restent cependant encore méconnus, et l’hypothèse majoritairement admise par la communauté de formation de pores à la surface des membranes cellulaires est en contradiction avec certains résultats expérimentaux.Le travail de modélisation proposé dans cette thèse est basé sur une approche différente des modèles d’électroporation existants. Au lieu de proposer des lois sur les propriétés des membranes à partir d’hypothèses à l’échelle moléculaire, nous établissons des lois ad hoc pour les décrire, en se basant uniquement sur les informations expérimentales disponibles. Aussi, afin de rester au plus prèsde ces dernières et faciliter la phase de calibration à venir, nous avons ajouté un modèle de transport et de diffusion de molécules dans la cellule. Une autre spécificité de notre modèle est que nous faisons la distinction entre l’état conducteur et l’état perméable des membranes.Des méthodes numériques spécifiques ainsi qu’un code en 3D et parallèle en C++ ont été écrits et validés pour résoudre les équations aux dérivées partielles de ces différents modèles. Nous validons le travail de modélisation en montrant que les simulations reproduisent qualitativement les comportements observés in vitro. / Cell permeabilization by intense electric pulses, called electropermeabilization, is a biological phenomenon involved in recent anticancer therapies. It allows, for example, to increase the efficacy of chemotherapies still reducing their side effects, to improve gene transfer, or to proceed tumor ablation. However, mechanisms of electropermeabilization are not clearly explained yet, and the mostly adopted hypothesis of the formation of pores at the membrane surface is in contradiction with several experimental results.This thesis modeling work is based on a different approach than existing electroporation models. Instead of deriving equations on membranes properties from hypothesis at the molecular scale, we prefer to write ad hoc laws to describe them, based on available experimental data only. Moreover, to be as close as possible to these data, and to ease the forthcoming work of parameter calibration, we added to our model equations of transport and diffusion of molecules in the cell. Another important feature of our model is that we differentiate the conductive state of membranes from their permeable state.Numerical methods, as well as a 3D parallel C++ code were written and validated in order to solve the partial differential equations of our models. The modeling work was validated by showing qualitative match between our simulations and the behaviours that are observed in vitro

New methods, based on tracer gas measurements and isotopicanalysis can be used to evaluate the moisture properties ofbuilding materials and provide the means for forensic analysisof the origins and history of excessive water in buildings, theimmediate practical consequences of which will be the abilityto improve the moisture performance of constructions. It is shown, in theory and through measurements how thewater vapour permeability of porous building materials can witha good degree of accuracy be estimated with tracer gasmeasurements that provide an efficient alternative to the cupmethod. Complementary measurements may be carried out in orderto evaluate the contribution of surface diffusion and theeventual enhancing effects of moisture content on the diffusioncoefficient. The Random Hopping Model is used to illustrate howthe surface diffusion coefficient depends on the amountadsorbed and the activation energy of migration that can beevaluated from the sorption isotherms. It is explained how the abundance ratios of two of the mostordinary isotopes of hydrogen and oxygen in water can be usedto determine its history. These isotopes are stable and givethe water a distinct signature that can be used to reveal itssource as shown in a case study. In a contrary manner themeasured isotopic separation can be used to determine therelevance of different transport processes and reactions. It isof central importance that not only does the magnitude ofisotopic separation for the reactions vary for deuterium andoxygen-18 but even the ratio thereof. One of the challenges hasbeen to construct an experimental method for retrieving samplesof water for comparison. Furthermore this thesis includes an evaluation of a new typeof a light weight construction with loose-fill cellulose fibre,in which the conventional polyethylene vapour barrier has beenreplaced with polypropylene fabric. With a verified model ithas been investigated how the construction would perform fordifferent internal moisture loads and reference climate fromthe literature. The results suggest that this type ofconstruction is not to be recommended. KEYWORDS:tracer gas, water vapour permeability,diffusion, surface diffusion, isotopic analysis, deuterium,oxygen-18, fractionation, vapour barrier, transient numericalmodelling of diffusion. / QC 20100611

Within the general context of solid-state sintering process, this work presents a numerical modeling approach, at the particle scale, of ceramic particle packing consolidation. Typically, the sintering process triggers several mass transport paths that are thermally activated. Among those diffusion paths, the most important ones are: surface diffusion, grain boundary diffusion and volume diffusion. Including this physics into a high-performance computing framework would permit to gain precious insights about the driving mechanisms. The aim of the present work is to develop a model and a numerical strategy able to integrate the different diffusion mechanisms into continuum mechanics framework. In the cases of surface diffusion and volume diffusion, the mass flux is calculated as a function of the surface curvature Laplacian and the hydrostatic pressure gradient, respectively. The physical model describing these two transport mechanisms is first presented within the framework of continuum mechanics. Then the numerical strategy developed for the simulation of the sintering of many particles is detailed. This strategy is based on a discretization of the problem by using a finite element approach coupled with a Level-Set method used to describe the particles free surface. This versatile strategy allows us to perform simulations involving a relatively large number of particles. Furthermore, a mesh adaptation technique allows the particles surface description to be improved, while the number of mesh elements is kept reasonable. Several 3D simulations, performed in a parallel computing framework, show the changes occurring in the structure of 3D granular stacks.

No description available.

Helium-3 surface spin echo spectroscopy (HeSE) has been used to measure the diffusive dynamics of adsorbates on close-packed metal surfaces, namely hydrogen on Cu(111), Pd(111) and Ru(0001), carbon and oxygen on Ru(0001), and oxygen on Cu(111). Chapter 2 reviews the HeSE technique and describes the relevant dynamical models and statistical methods used to interpret data in later chapters. The performance of the ionizing detector is analysed, with a focus on the signal-to-noise ratio. In Chapter 3 expressions for the classical intermediate scattering function (ISF) are introduced for open and closed systems. The effects of corrugation and surface-perpendicular motion on the amplitude of different components in the ISF are modelled analytically and compared with simulation. The exact ISF for a particle on a flat surface, obeying the Generalized Langevin Equation with exponential memory friction, is calculated analytically. In Chapter 4 the analytical ISF is calculated for quantum Brownian motion and for coherent tunneling dynamics in a tight binding system. The bounce method for calculating quantum mechanical hopping rates in dissipative systems is applied to model diffusion of hydrogen on Ru(0001). Chapter 5 presents the first HeSE measurements of carbon and oxygen diffusion. C/Ru(0001) diffusion is assigned to a small carbon cluster. The jump rate has an activation energy $E_{A}=292\pm7\,$meV in the temperature range $550\,\textrm{K}\leq T \leq 1300\,$K. Oxygen diffusion is significantly slower. By comparison of literature data with the new HeSE results, the activation energy for oxygen diffusion at low coverage is estimated as $650\pm10$meV. Oxygen measurements at high coverage $\theta\approx0.22\,$ML are consistent with strong mutual O-O interactions. Surface diffusion is also observed after exposing Cu(111) to oxygen. Chapter 6 presents low-coverage measurements of protium (H) and deuterium (D) diffusion on Ru(0001), Pd(111) and Cu(111). In the quantum activated regime there is evidence for multiple jumps in all three systems, suggesting a low dynamical friction. The measurements on Ru(0001) indicate that the deep tunneling rate is much slower for D than for H.

This thesis is dedicated to the exploration of fluid phases confined in nanoporous materials using Nuclear Magnetic Resonance (NMR) techniques, with an aim to benefit catalysis research. Included in this report are studies of pure fluids and their mixtures, confined in titania and silica catalyst supports. These investigations are conducted at industrially-relevant, high-temperature (≥ 180 °C) and high-pressure conditions (up to 13 bar), made possible by a pilot-scale chemical reactor unit, designed to operate inside the strong magnetic fields of an NMR spectrometer. NMR spectroscopy, relaxation and pulsed field gradient (PFG) diffusion experiments were performed on each of the systems discussed in this report. Cyclohexane was initially studied inside a porous titania catalyst support at 188 °C and various pressures up to 13 bar. The adsorption and desorption processes of the cyclohexane were observed, revealing a number of previously unobserved phenomena. In addition to an overall, averaged diffusion coefficient, a slow diffusion coefficient was observed within the PFG NMR data attributable to surface diffusive processes occurring within the material. Additionally, T1 relaxation studies were found to provide experimental evidence for the differing configurations of adsorbed layers on the adsorption and desorption branch of the isotherm. Cyclohexane was subsequently studied alongside fluorobenzene in a series of silica catalyst supports of 6 nm, 10 nm and 20 nm pore size. In doing this, it was hoped that the multiple phenomena observed in the titania experiments might be deconvoluted, allowing a greater level of insight. The diffusivities of the fluids were found to differ significantly between the materials, and greater evidence was found of the slow-diffusing surface phase in each of the materials. Additionally, concentrations of cyclohexane and fluorobenzene in the gas and adsorbed layers inside the pore space were calculated via the results of the PFG NMR experiments, providing a map of confined phase behaviour. Competitive adsorption effects were found to become more significant, the smaller the pore size of the material. The results of the cyclohexane and fluorobenzene in silica studies were modelled, using approaches available in the literature, which were found to give varying levels of prediction. The data set acquired in this thesis was found to provide a useful standard, against which current and future models of confined phase behaviour might be verified.