Rare-earth oxides used in oxide dispersion strengthening are known to provide excellent strength and deformability over ordinary dispersion strengthening. It has been suggested that this may be due to the development of molybdate compounds instead of pure dispersed oxide particles. These alloys are produced by dispersing particles of certain rare-earth oxides in a molybdenum matrix and forming the mixture into a composite ingot. During the high-temperature consolidation process, the oxides are converted into rare-earth molybdates. With subsequent processing, these molybdate phases undergo deformation to form high-surface-area ribbons that serve to inhibit dislocation movement, thus improving the mechanical properties of the molybdenum matrix. It is still unknown what specific compounds, phases, and crystal structures provide these metal-oxides with their high strength and deformability. Because the molybdate phases are formed at high temperatures and low oxygen partial pressures, little is also known of the high-temperature phase equilibria of the REO-Mo systems under these conditions. The primary goal of this study was to deifine phase equilibria on systems of Mo with rare-earth oxides. The project aimed to identify compounds, phases, and specific oxidation states of molybdenum at various processing conditions. Systems of LaO1.5-MoOx, YO1.5-MoOx, and ZrO2- MoOx were investigated at temperatures of 1000??nd 1200??and O2 partial pressures ranging from 10-4 Pa to 10-13 Pa. Samples were prepared using powder starting materials of Mo and rare-earth oxides were combined in stoichiometric ratios. The samples were then electrically heated in a ceramic tube furnace in which the oxygen partial pressure was controlled by means of a combined flow of H2 and CO2 gas. Characterization was performed using x-ray diffraction, with published powder diffraction files for phase identification.

Die polymere Komponente in reaktiven Zement-in-Polymer (c/p) Dispersionen hat einen entscheidenden Einfluss auf die Bildung der Mikrostruktur von c/p beschichteten Rovings in Beton. Elektronenmikroskopische Untersuchungen zeigen für den gut wasserlöslichen Poly(vinylalkohol) Ca(OH)2- Ablagerungen an der Grenzfläche, während für das hydrophobe Poly(vinylacetat) ein Gefüge aus teilhydratisiertem Klinker gefunden wird. Durch eine zeitliche Verfolgung der Wasseraufnahme mittels kernmagnetischer Resonanzspektroskopie konnte dies auf Unterschiede im Quellungsverhalten als Resultat der unterschiedlichen chemischen Struktur und Reaktivität gegenüber Alkalien zurückgeführt werden.

Dispersion has been shown to degrade miscibility in miscible displacements by lowering the concentration of the injected solute at the displacement fronts. Dispersion can also improve oil recovery by increasing sweep efficiency. Either way, dispersion is an important factor in understanding miscible displacement performance. Conventionally, dispersion is measured in the laboratory by fitting the solution of one-dimensional convection-dispersion equation (CDE) to the effluent concentration from a core flood. However dispersion is anisotropic and mixing occurs in both longitudinal and transverse directions. This dissertation uses the analytical solution of the two-dimensional CDE to simultaneously determine longitudinal and transverse dispersion. The two-dimensional analytical solution for an instantaneous finite volume source is used to investigate anisotropic mixing in miscible displacements. We conclude that transverse mixing becomes significant with large a concentration gradient in the transverse direction and significant local variation in flow directions owing to heterogeneity. We also utilized simulation models similar to Blackwell's (1962) experiments to determine transverse dispersion. This model coupled with the analytical solution for two-dimensional CDE for continuous injection source is used to determine longitudinal and transverse dispersivity for the flow medium. The validated model is used to investigate the effect of heterogeneity and other first contact miscible (FCM) scaling groups on dispersion. We derive the dimensionless scaling groups that affect FCM displacements and determine their impact on dispersion. Experimental design is used to determine the impact and interactions of significant scaling groups and generate a response surface function for dispersion based on the scaling groups. The level of heterogeneity is found to most significantly impact longitudinal dispersion, while transverse dispersion is most significantly impacted by the dispersion number. Finally, a mathematical procedure is developed to use the estimated dispersivities to determine a-priori the maximum grid-block size to maintain an equivalent level of dispersion between fine-scale and upscaled coarse models. Non-uniform coarsening schemes is recommended and validated for reservoir models with sets of different permeability distributions. Comparable sweep and recovery are observed when the procedure was extended to multi-contact miscible (MCM) displacements. / text

A cross-section averaged Advection-Dispersion equation (ADE) model was developed to simulate the transport of fertilizer in furrow irrigation. The advection and dispersion processes were solved separately by implementing the method of the characteristics with cubic spline interpolation (and natural boundary condition) and weighted finite difference scheme respectively. A zero-flux boundary condition during advance and an advective gradient at the downstream end of an open furrow were established. Local pseudo-steady state was assumed in order to apply Fischer's longitudinal dispersion equation under non-uniform and unsteady furrow flow conditions. Also, several parameters were used to evaluate the ADE model and fertigation performance.A field tracer experiment in two types of downstream-end furrow and two treatments was conducted and described. Infiltration and roughness parameters were calibrated by implementing a volume balance approach. The calibrated parameters were used as input data to run the surface irrigation model (SRFR). The roughness coefficient was 0.045 for wheel and 0.055 for non-wheel furrow treatment for bare soil. The root mean square error (RMSE) comparing the computed and observed infiltrated volume was in the range of 0.09-0.38 m3. The close match between simulated and observed data indicates an acceptable calibration. Pulses of fertilizer injected at the head end of four furrows each having unique management characteristics were simulated satisfactorily during the entire duration of the irrigation event. The constant value of the longitudinal dispersion coefficient was 1 m2 min-1 and yielded an acceptable space-time evolution of the pulses of tracer injected. Similar results for the dispersion coefficient were obtained with Fischer's equation in non-uniform and unsteady stream flow conditions in the furrow. An evaluation of several fertigation strategies for furrow systems indicated that fertigation by pulses could help reduce leaching and runoff losses in surface irrigation systems.

Mémoire numérisé par la Division de la gestion de documents et des archives de l'Université de Montréal

The goal of this research is to develop new approaches for the improvement of the properties of polymer carbon nanotube composites by effectively aligning and dispersing the CNT's in the polymer matrix. Specifically, this researched explored at how to mediate the problem of carbon nanotube insolubility in a matrix material. This was accomplished by assessing the effects of three different dispersing agents and two different alignment methods on the final composite properties. In previous research, the dispersing agents were found to either adequately disperse the carbon nanotubes or improve the mechanical properties of the composite material.4-6 Thus, comparing the three dispersing agents in different matrix materials and different processing methods can lead to a new understanding of interfacial interactions within the different composite materials. This understanding can then lead to the creation of more effective carbon nanotube composites that both adequately disperse the carbon nanotubes and improve the mechanical properties.

In traffic safety analysis, a large number of distributions have been proposed to analyze motor vehicle crashes. Among those distributions, the traditional Poisson and Negative Binomial (NB) distributions have been the most commonly used. Although the Poisson and NB models possess desirable statistical properties, their application on modeling motor vehicle crashes are associated with limitations. In practice, traffic crash data are often over-dispersed. On rare occasions, they have shown to be under-dispersed. The over-dispersed and under-dispersed data can lead to the inconsistent standard errors of parameter estimates using the traditional Poisson distribution. Although the NB has been found to be able to model over-dispersed data, it cannot handle under-dispersed data. Among those distributions proposed to handle over-dispersed and under-dispersed datasets, the Conway-Maxwell-Poisson (COM-Poisson) and double Poisson (DP) distributions are particularly noteworthy. The DP distribution and its generalized linear model (GLM) framework has seldom been investigated and applied since its first introduction 25 years ago. The objectives of this study are to: 1) examine the applicability of the DP distribution and its regression model for analyzing crash data characterized by over- and under-dispersion, and 2) compare the performances of the DP distribution and DP GLM with those of the COM-Poisson distribution and COM-Poisson GLM in terms of goodness-of-fit (GOF) and theoretical soundness. All the DP GLMs in this study were developed based on the approximate probability mass function (PMF) of the DP distribution. Based on the simulated data, it was found that the COM-Poisson distribution performed better than the DP distribution for all nine mean-dispersion scenarios and that the DP distribution worked better for high mean scenarios independent of the type of dispersion. Using two over-dispersed empirical datasets, the results demonstrated that the DP GLM fitted the over-dispersed data almost the same as the NB model and COM-Poisson GLM. With the use of the under-dispersed empirical crash data, it was found that the overall performance of the DP GLM was much better than that of the COM-Poisson GLM in handling the under-dispersed crash data. Furthermore, it was found that the mathematics to manipulate the DP GLM was much easier than for the COM-Poisson GLM and that the DP GLM always gave smaller standard errors for the estimated coefficients.

Les émissions d’ammoniac (NH3) atmosphérique sont impliquées dans un certain nombre d’impacts environnementaux allant de la pollution d’écosystèmes terrestres et aquatiques sensibles, à la dégration de la qualité de l’air. L’application de la modélisation inverse de la dispersion, couplée à des mesures de concentrations atmosphériques, est potentiellement le seul type de méthodologie capable de quantifier les émissions d’NH3 à partir de n’importe quel type de source. Cependant, il existe plusieurs techniques et options de mesure et de modélisation, susceptibles d’être optimisées pour des sources spécifiques. Le cas particulier du NH3 dans le contexte de la modélisation inverse présente des défis majeurs métrologiques et de modélisation, liés à la nature réactive de la molécule.Cette thèse présente six expérimentations réalisées dans trois pays, dans lesquelles les émissions d’NH3 ont été quantifiées à partir de sources multiples couvrant une large gamme d’échelles et de niveaux de complexité des systèmes étudiés. Dans chaque cas, la méthode de modélisation inverse de la dispersion est adaptée à la nature spécifique de la source et aux incertitudes sur la mesure et la modélisation, prenant en compte les processus de dépôt local. Les expérimentations ont été menées avec un focus sur l’évaluation méthodologique, comparant des techniques innovantes avec des méthodes alternatives plus classiques.En dernière analyse, ce travail élargit le champ d’application de la méthode d’inversion appliquée au NH3 à l’échelle du paysage, contribuant à l’analyse intégrée des flux et bilans / Emissions of ammonia (NH3) to the atmosphere have been implicated in a web of harmful environmental impacts, from pollution of sensitive terrestrial and aquatic ecosystems to worsening of urban air quality. The application of atmospheric measurements and inverse dispersion modelling may be unique in providing a singular methodology which can quantify emissions of NH3 to the atmosphere from almost any source. However, there are various measurement and modelling techniques and options which may be implemented within the inverse dispersion method, which can be optimised for specific sources. The special case of NH3 in the context of inverse dispersion presents a number of measurement and modelling challenges, all related to the reactive nature of the molecule.This thesis features six experiments carried out in three countries, in which NH3 emissions were quantified from multiple sources across a broad range of scales and system complexities. In each case the inverse dispersion method was adapted to the specific nature of the source being investigated and the uncertainties of NH3 measurement and modelling, where local deposition must be considered. The experiments were undertaken with an emphasis on methodological evaluation, in which novel techniques were developed and alternative methods are compared.This thesis ultimately expands the scope of the inverse dispersion method applied for NH3 to the landscape scale, connecting with integrated nitrogen assessments which may bring forth new understanding into cascade of reactive nitrogen to the environment.

L'intérêt croissant pour l'intensification des procédés a conduit à l'avènement d'un nombre conséquent de nouvelles technologies. Le projet ANR PROCIP qui a financé cette thèse a pour but de développer un logiciel d’aide à la décision pour aider l’utilisateur industriel dans son choix de technologie optimale pour une application donnée. La méthodologie globale de discrimination des technologies vis-à-vis d’un système réactif est basée sur l’utilisation d’une base de données technologique et sur le calcul de critères de choix. Elle nécessite une bonne connaissance du comportement hydrodynamique des appareils et de leurs performances en termes de transfert de chaleur et de matière. Dans cet objectif, les travaux présentés ici portent notamment sur l’étude du comportement hydrodynamique de milli-réacteurs échangeurs industriels. Des méthodologies expérimentales et numériques de caractérisation ont été mises au point. Elles ont permis d’obtenir des corrélations pour l’estimation des pertes de charge, des coefficients de dispersion axiale et des temps de mélange pour plusieurs milli-réacteurs en fonction des conditions opératoires et de la géométrie des appareils. En outre, une nouvelle méthode numérique est proposée pour la détermination des coefficients de dispersion axiale et des temps de mélange. Elle est appliquée pour prédire l’effet de l’extrapolation des caractéristiques géométriques des appareils sur ces propriétés. Dans une dernière partie, l’impact de la dispersion axiale sur le taux de conversion et la sélectivité de différents schémas de synthèses chimiques est discuté. / The interest for process intensification has leaded to the emergence of a wide panel of new technologies. The aim of the ANR PROCIP collaborative project which has funded this work is to develop a new software program including a methodology for process choice focused on intensified technologies. The global methodology of discrimination between the different technologies with respect to a given reactive system is based on the use of an equipment database and on the evaluation of criterion of choice. This methodology implies a good knowledge of the hydrodynamics of the different reactors and their mass and thermal transfer performances. The purpose of the present work is to develop experimental and numerical methodologies for the hydrodynamic characterization of different industrial milli-heat-exchangers reactors. Pressure drop, mixing time and axial dispersion coefficient correlations are given as function of the operating conditions and the geometrical parameters of the reactors. In particular, a new numerical method using CFD computation for the determination of axial dispersion coefficients and mixing times is presented. This method is used to predict the effect of the scale-up of the geometrical characteristics of an intensified reactor on its hydrodynamic performances. Finally, the impact of axial dispersion on the conversion rate and the selectivity for different chemical synthesis schemes is discussed

La production d'eau chaude via des capteurs solaires photothermiques est une technique en expansion qui permettra de limiter l'utilisation des sources conventionnelles d’énergie (combustibles fossiles, nucléaire…). Le cuivre noir (CuO) s’avère être un matériau possédant des propriétés optiques sélectives intéressantes pour cette application. Ainsi, son utilisation au sein d’un absorbeur sous forme d’un matériau « tandem » est une solution envisagée. Le défi que nous avons tenté de relever au cours de ce travail, a été de réaliser ce type de matériau par dépôt électrophorétique (EPD) de nanoparticules de CuO déposé sur un substrat métallique de type wafer de silicium recouvert de platine ou d’or. Ce substrat « modèle » a été utilisé dans un premier temps, car il facilite la mise en œuvre de techniques de caractérisation telles que l’analyse par diffraction X en incidence rasante (GIXRD) ou l’analyse en coupe par microscopie électronique à balayage. Pour ce faire, la stabilisation de la suspension colloïdale de CuO, qui est une condition sine qua non pour la réalisation d’un dépôt électrophorétique, a été étudiée dans un solvant organique tel que l'isopropanol par ajout de Mg(NO3)2, ainsi que dans l’eau en utilisant du polyethylenimine comme dispersant. Ces deux adjuvants agissent comme des agents stabilisants et apportent aux nanoparticules une charge positive ce qui permet la réalisation d'un EPD cathodique. Afin d’optimiser la formulation des suspensions, la stabilité colloïdale en fonction de la teneur en stabilisant a été étudiée avant tout dépôt, par diffusion dynamique de la lumière (DLS) couplée à la vélocimétrie laser à effet Doppler.Différents revêtements contenant du CuO ont été obtenus en faisant varier les paramètres classiques de l’EPD (temps de dépôt, champ électrique, concentration en nanoparticules) pour pouvoir contrôler l'épaisseur finale et la morphologie. Par conséquent, la sélectivité optique et le rendement du tandem résultants peuvent être optimisés en jouant sur l’ensemble de ces paramètres. Des dépôts homogènes ont été obtenus pour [CuO] =5x10-4 g/cm3 pour les deux milieux. Les meilleures conditions sont 50 V.cm-1// 30mn pour la suspension d'IPA et 2 V.cm-1 // 120 mn pour la suspension en milieu aqueux. La composition et l'épaisseur des dépôts sont analysées par GIXRD, et par microscopie électronique (SEM-EDS). Pour les conditions optimisées, les matériaux tandem obtenus à partir de la suspension d'IPA+CuO possèdent une densité de 1.69 g/cm3 avec une grande rugosité. Au contraire, des surfaces homogènes et régulières sont obtenues en milieu aqueux et les dépôts présentent une densité beaucoup plus élevée d’environ 5.7 g/cm3.L’absorptance (α) et l’émittance (ԑ) ont été calculées à partir des spectres de réflectance de l'UV-VIS-NIR et de l’Infrarouge lointain, respectivement. L'efficacité (ƞ) du revêtement tandem obtenu en milieu aqueux est comprise entre 0.8-0.87 tandis qu’elle est seulement de 0.7 dans l’IPA. De plus, la faisabilité de l’EPD sur d’autres substrats métalliques plus conventionnels en vue d’une application (acier, aluminium, cuivre) a été explorée. L'efficacité des dépôts a pu être améliorée par des post-traitements de deux types. D’une part, en pyrolysant à 400°C sous atmosphère inerte le polymère (PEI) incorporé dans le revêtement. Le carbone résiduel obtenu à l’issue de cette pyrolyse a permis d’augmenter l’absorbance. D’autre part, en déposant sur la surface des revêtements une couche de nanoparticules de SiO2 qui joue le rôle de couche anti-réflexion et permet également de protéger la surface. Les deux voies ont été réalisées avec succès et le rendement le plus élevé obtenu pour ces revêtements est de 0.9. / The production of hot water by using efficient photothermal solar collectors is growing in importance to limit the use of fossil fuels. Black copper (CuO) has proved to be one of the viable solar-selective coatings owing to its nearly intrinsic properties. The formation of a tandem absorber based on CuO thin film deposited onto a highly IR reflecting metallic substrate is processed by electrophoretic deposition (EPD).In this way, the stabilization of a CuO colloidal suspension is studied previously by adding Mg(NO3)2 in isopropanol (IPA) or polyethylenimine (PEI) in water suspension. Both acts as positively charging agents and allow the realisation of a cathodic EPD. The colloidal stability as a function of the stabilizing agent content is studied prior to EPD, by dynamic light scattering (DLS) coupled with laser doppler velocimetry.CuO tandem absorbers are obtained by varying different EPD parameters to control the final thickness and also the morphology. Consequently, the optical selectivity of the tandem material is tuned and optimized. The deposition yield is compared relative to the different applied voltage range, deposition time and nanoparticle concentrations. Homogeneous deposits are obtained for [CuO]=5x10-4 g/cm3 from both suspensions. The optimum applied voltage is found to be 50 V.cm-1 for IPA suspension and 2 V.cm-1 for H2O suspension, for deposition times of 30 mins and 120 mins, respectively. The composition and the thickness of the coatings are analysed by Grazing Incidence X-ray diffraction (GIXRD), scanning electron microscopy (SEM) and the density is obtained from energy-dispersive X-ray spectroscopy (EDX). For the previously mentioned optimized conditions, CuO tandem absorbers derived from IPA suspension possess a density of 1.69 g/cm3 with high surface roughness. In contrast, homogeneous and regular surfaces is obtained from water suspensions having a higher density of 5.7 g/cm3.Moreover, absorptance (α) and emittance (ԑ) are calculated from the reflectance spectra of the UV-Vis-NIR and the Fourier transform InfraRed (FTIR) spectroscopy, respectively. α and ԑ were combined to determine the efficiency (ƞ) of the tandem material. Tandems obtained from water suspension has ƞ=0.8 -0.87 while from IPA ƞ=0.7. Besides, the applicability of this EPD is checked by performing other deposit of CuO on metallic substrates of different types.CuO tandems obtained from water suspensions are clearly more prominent to be used as solar selective tandem absorbers due to the high calculated ƞ value reported. The efficiency of such selective tandem absorbers was further enhanced by carbonization (pyrolysis under inert atmosphere) of the polymer (PEI) embedded in the coating. Otherwise, a thin film of SiO2 nanoparticles was deposited at the surface of the selective tandem absorbers to protect them. Both routes were successfully processed and proved to raise ƞ to 0.9.