No description available.

No description available.

Corrosion is an unstoppable process that occurs spontaneously in many areas of industry, specially, oil and gas industries. Therefore, the need of developing protective coating to lower the cost of corrosion is very consistent. Among different methods, electrodeposition has been a popular method since it offer many advantages such as low cost, ability to control the surface and thickness of the coating, ability to perform at low temperature and pressure, and very convenience. Ceramic nanoparticles have been widely incorporated into metal coating and used as a protective layer to improve both corrosion and hardness properties. Diazonium synthesis was used to modify cerium oxide nanoparticles by grafting with ferrocene for use in nickel nanocomposite coating. Citric acid and citrate salt were used as stabilizing ligands for yttrium oxide and praseodymium oxide nanoparticles in nickel plating solution to prevent the formation of hydroxide, thus, higher amount of nanoparticles was able to incorporate into nanocomposite coatings. These fabricated coatings were evaluate for the corrosion and mechanical properties using many different instruments and electrochemical techniques. As modified cerium oxide, stabilized yttrium oxide or praseodymium oxide added into nickel coatings. The results showed an increase in hardness and corrosion resistance leading to the overall improvement compare to pure nickel coating.

A class of novel nickel cobalt oxide hollow nanosponges were synthesized through a sodium borohydride reduction strategy. Due to their porous and hollow nanostructures, and synergetic effects between their components, the optimized nickel cobalt oxide nanosponges exhibited excellent catalytic activity towards oxygen evolution reaction.

Hot section components of land-based gas turbines are subject to extremely harsh, high temperature environments and require the use of advanced materials. Directionally solidified Ni-base superalloys are often chosen as materials for these hot section components due to their excellent creep resistance and fatigue properties at high temperatures. These blades undergo complex thermomechanical loading conditions throughout their service life, and the influences of blade geometry and variable operation can make life prediction difficult. Accurate predictions of material response under thermomechanical loading conditions is essential for life prediction of these components. Complex crystal viscoplasticity models are often used to capture the behavior of Ni-base superalloys. While accurate, these models are computationally expensive and are not suitable for all phases of design. This work involves the calibration of a previously developed reduced-order, macroscale transversely isotropic viscoplasticity model to a directionally solidified Ni-base superalloy. The unified model is capable of capturing isothermal and thermomechanical responses in addition to secondary creep behavior. An extreme reduced order microstructure-sensitive constitutive model is also developed using an artificial neural network to provide a rapid first-order approximation of material response under various temperatures, rates of loading, and material orientation from the axis of solidification.

No description available.

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

Le nickel est connu pour son utilisation dans la préparation d’alliages réputés peu sensibles à la contamination bactérienne, très utilisés dans les secteurs agro-alimentaires et médicaux. Cependant, les bactéries apparaissent capables d’adhérer même à ce type de matériau et de le coloniser sous forme de biofilms. Les biofilms sont des communautés de micro-organismes, adhérant entre eux et à une surface, grâce à la sécrétion d’une matrice adhésive offrant une protection contre la dessiccation, les défenses de l’hôte et un grand nombre d’agents antimicrobiens. Ces biofilms manifestent des propriétés de multirésistances aux biocides qui causent des problèmes sanitaires majeurs dans les installations hospitalières et industrielles. D’importantes modifications de l’expression génétique accompagnent la vie en biofilm et induisent des caractères spécifiques dont des résistances accrues aux biocides et la production de facteurs de virulence. Parmi ces derniers, les curli, qui sont un composé protéique majeur de la matrice extracellulaire chez les bactéries Escherichia coli et Salmonella spp., jouent un rôle clé dans la formation de biofilms sur surfaces inertes et biologiques. Ce travail a consisté à explorer la contribution de la vie en biofilm à la survie des bactéries Escherichia coli K-12 productrices de curli en présence de nickel. Pour cela, l’effet physiologique d’ions solubles de nickel sur la survie des bactéries a été testé sur des supports inertes en polystyrène ou en acier. Nous avons montré que des concentrations sub-inhibitrices de nickel induisent une augmentation de l’épaisseur et de la densité du biofilm. Cet effet ne dépend pas des modifications physico-chimiques de la surface cellulaire par le nickel, ni de l’activité de la seule pompe d’efflux à nickel connue d’E. coli, RcnA. Par contre, le nickel à faible concentration induit l’expression des curli, ainsi que leur production. C’est donc via l’activation transcriptionnelle des gènes codant les curli que l’augmentation du biofilm par le nickel se produit. Ce travail s’est également appliqué à rechercher la nature du relais gouvernant la mise en place des curli en réponse à la présence de nickel. Aucun des régulateurs principaux de l’expression des curli ne joue un rôle décisif. Nos résultats nous conduisent à suggérer que l’effet du nickel repose sur un phénomène global de réponse au stress oxydant dont le mécanisme reste à déterminer. / Nickel is known for its use in alloy preparation, which is renowned for not being very sensitive to bacterial contamination, and thus widely used in the food-processing and medical sectors. However, bacteria appeared to be able to adhere even on this type of material, and to colonize it in the form of biofilms. Biofilms are microorganisms’ communities, adherent between themselves and to a surface, thanks to the secretion of an adhesive matrix, which offers them protection against desiccation, host defences and a great number of antimicrobial agents. Biofilms express biocidal multiresistance properties, which causes major sanitary problems in hospitals and industries. Biofilm life comes with important modifications in the genetic expression, which induces specific characteristics like increased biocides resistances and virulence factors production. In the latter, curli are a major proteic component of the extracellular matrix in the bacteria Escherichia coli and Salmonella spp., and curli play a key role in biofilm formation on inert and biologic surfaces. This work had consisted of the exploration of the biofilm life-style contribution in the survival of E. coli K-12 bacteria that produces curli in the presence of nickel. In that aim, physiological effect of soluble ions of nickel on the bacterial survival has been tested on inert supports such as polystyrene and stainless steel. We have shown that sub-inhibitory concentrations of nickel induce an increase in the biofilm thickness and density. This effect does not rely on physicochemical modifications on the bacterial surface, nor on RcnA activity, which is the only known efflux pump dedicated to nickel in E. coli. On the other hand, low concentrations of nickel induce curli expression and their production. Hence, the nickel-induced biofilm increase occurs through transcriptional activation of curli genes. This work also tried to find the nature of the relay that governs curli setting up in response to the presence of nickel. None of the curli principal regulators seem to be implicated in this curli production increase. Thus, our results suggest that nickel effect lies on a more global response phenomenon like oxidative stress, but the involved mechanism needs to be determined.

L’objectif de cette étude est de préparer des catalyseurs bimétalliques Ni-X/SiO2, de les caractériser, et de comparer leur activité en hydrogénation du styrène en éthylbenzène,ainsi que leur sélectivité en hydrogénation de la double liaison oléfinique du styrène, par rapport à l’hydrogénation du noyau benzénique. L’élément X est greffé de manière contrôlée sur le nickel, et est choisi selon son électronégativité, soit inférieure (Zr), soit égale (Sn), soit supérieure (Au) à celle du nickel, dans le but d’étudier les effets géométriques et/ou électroniques qu'il pourrait induire. Parmi les échantillons préparés, le catalyseur Ni-Au/SiO2s’est révélé presque aussi actif que le catalyseur non dopé et nettement plus sélectif dans l’hydrogénation du styrène en éthylbenzène. / The aim of the present study is to prepare silica-supported Ni-X bimetallic catalysts, tocharacterize them, and to compare their catalytic activity in the hydrogenation of styrene, as well as their selectivity in the hydrogenation of the styrene’s olefinic double bond instead of the hydrogenation of the aromatic ring. The element X is grafted in a controlled way on the supported nickel particles, and is chosen according to its electronegativity, which is eitherlower (Zr), or equivalent (Sn), or higher (Au) than the electronegativity of Ni, in order to study the geometrical and/or electronic effects due to the doping of Nickel. Among the prepared samples, the Ni-Au/SiO2 catalyst has exhibited high activity and high selectivity in the hydrogenation of styrene into ethylbenzene, which makes the doping of Ni by Au apromising alternative for PyGas selective hydrogenation catalysts.

Cette étude concerne la formation d'hydrogène par le procédé de vaporeformage et la production de gaz de synthèse par le procédé de reformage à sec, au moyen de catalyseurs tout en augmentant la résistance à la formation de coke. Sept oxydes mixtes NiₓMg₆₋ₓAl₂ 800 (0 ≤ x ≤ 6) ont été obtenus, en passant par la voie hydrotalcite suivie d'une calcination à 800°C. L'espèce active dans les deux réactions étudiées est le nickel métallique. Une partie de ces oxydes a été imprégnée par 0,5 % en masse de ruthénium et recalcinée à 800°C, puisque le ruthénium améliore la réductibilité des espèces oxydes de nickel. Dans le procédé de vaporeformage et en abscence de ruthénium, le prétraitement réducteur est une étape nécessaire pour activer le catalyseur. L'ajout du ruthénium améliore l'activité catalytique, la sélectivité et la résistance à la formation de coke des oxydes étudiés et ceci en abscence de prétraitement réducteur avant test. Une interaction ruthénium-nickel serait à l'origine de ces bonnes performances catalytiques. Le catalyseur Ru/Ni₆Al₂ 800 800 présente les meilleures performances catalytiques, parmi les systèmes étudiés, puisqu'il assure une meilleure interaction Ru-Ni. / This study is related to the formation of hydrogen by the steam reforming process and the production of synthesis gas by the dry reforming process, using catalysts, leading to increased resistance to coke formation. Seven mixed oxides NiₓMg₆₋ₓAl₂ 800 (0 ≤ x ≤ 6) were obtained, by hydrotalcite route followed by calcination at 800°C. Metallic nickel is the active species in both studied reactions. Some of these oxides have been impregnated with 0.5 wt % of ruthenium and recalcined at 800°C. In steam reforming test and in absence of ruthenium, the reducing pretreatment step is necessary to activate the catalyst. Ruthenium addition improves the catalytic activity, selectivity and the resistance to coke formation, with no reducing step prior to the test. An interaction between nickel and ruthenium is in origin of these good catalytic performances since ruthenium improves the reductibility of nickel species. The catalyst Ru/Ni₆Al₂ 800 800 presents the best catalytic performances among the studied systems, because it presents a better Ru-Ni interaction.