Yes / Titanium alloy Ti-6Al-4V is known for both its excellent mechanical properties and its low surface hardness. This study explores a two-step process for depositing a hard nanocrystalline coating onto the surface of the Ti-alloy, followed by surface melting, which embeds hard nanoparticles into a thin surface layer of the alloy. The treated surface layer was studied using X-ray diffraction, scanning electron microscopy, and Vicker's micro-hardness testing. The results of the study show that the surface of the Ti-6Al-4V alloy can be successfully hardened by embedding nanosized Al2O3 particles into the surface using gas tungsten arc welding to melt the surface of the material. Surface melting the Ti-6Al-4V alloy with a 50A welding current produced the maximum microhardness of 701 HV0.2kg. The micro-hardness of the treated surface layer decreased with the increasing size of the nanoparticles, while the roughness of the surface increased with the increasing welding current. The heat input into the surface during the surface melting process resulted in the formation of various intermetallic compounds capable of further increasing the hardness of the Ti-6Al-4V surface.

High surface area tungsten oxynitride samples have been prepared by the temperature programmed reaction (TPR) of W0₃ with NH₃. All samples were characterized by X-ray diffraction (XRD), nitrogen physisorption, and CO chemisorption. In addition, some sample compositions were determined by elemental analysis. Samples were prepared at various heating rates (β), allowing a Redhead analysis to be carried out giving an activation energy of nitridation of 109 kJ mol⁻¹. A heating rate of 0.016 K S⁻¹ gave optimum synthesis conditions. Solid state intermediates were studied by interruption of the temperature program at various stages. No distinct suboxide phases formed along the synthesis path were found using XRD. An increase in surface area, CO uptake and nitrogen weight content, were found to occur as the reaction progressed. Reactivity experiments showed reasonable hydro deoxygenation (HDO) and hydrodenitrogenation (HDN) activities, but little hydrogenation (HYD) or hydrodesulfurization (HDS) activities. / Master of Science

Mechanical alloying, compaction by cold isostatic pressing, and pressureless sintering were used to study the potential for W â 3 wt% Ni â 1 wt% Fe to be processed into the bulk nanocrystalline form as a replacement material for depleted uranium in kinetic energy penetrators. Milling time and sintering temperature were varied from 15 to 100 hours and 1000 to 1300°C respectively. Particle size analysis and SEM showed a bimodal particle size distribution with most of the particles below 10 µm in size. XRD peak broadening analysis showed crystallite size to be reduced to below 50 nm, while peak shifting indicated a reduction in W lattice parameter due to dissolution of Ni and Fe atoms into the W BCC lattice. Post-sintering bulk characterization showed density increasing strongly with increasing sintering temperature to above 90% of theoretical density at 1200°C. Apparent activation energy for sintering decreased strongly with increasing milling time. SEM micrographs showed a bimodal grain size distribution with some areas of smaller submicron grains and others with larger grains on the order of 1 – 4 µm, likely connected to the bimodal particle size distribution from milling. XRD and SEM also showed the precipitation of two secondary phases during sintering: (Fe, Ni)6W6C incorporating carbon from the grinding media and an FCC solid solution of Ni, Fe, and W. The intermetallic carbide phase will increase strength but reduce ductility of the bulk material, which is not desirable. Micro and macrohardness testing show similar trends as density with a strong correlation with sintering temperature. / Master of Science

Wear resistant surfaces with high toughness and impact resistant properties are to be created to improve the life cycle cost of brake discs for trains. A potential solution to this industrial problem is to use an arc cladding process. This work describes the application of gas tungsten arc welding (GTAW) for a structural ceramic Metal Matrix Composite (MMC) on steel. The structure of the two ceramics examined indicates the possibility of development of a wear resistant surface, which would extend the life of the brake disc. Silicon Carbide (SiC) and Tungsten Carbide (WC) ceramics were studied to embed them in a steel matrix by an advanced GTAW method. WC particles penetrated the liquid weld pool and also partially dissolved in the steel matrix, whereas, SiC because of the physical properties never penetrated deeper into the weld pool but segregated on the surface. Successful embedding and bonding of WC led to the decision to exercise an in-depth analysis of the bonding between the WC particles and the matrix. Chemical analysis of the matrix revealed more WC dissolution as compared to particle form within the clad. It was observed that WC reinforcement particles built a strong chemical bond with the steel matrix. This was shown by electron backscatter diffraction (EBSD) analysis. The hard clad layer composed of WC reinforced steel matrix gave an matching friction coefficient to high-strength steel in cold wear conditions through Pin-on-Disc wear and friction testing. A prototype railway brake disc was created with the established GTAW parameters to find out the difficulties of producing industrial scale components.

Os objetivos deste trabalho foram: i) estudar a degradação de catalisadores do tipo Pt-M (onde M = Co e Cr) suportados em carbono após tratamento ácido e a atividade catalítica dos mesmos para a reação de redução de oxigênio; ii) avaliar o desempenho e a estabilidade de eletrocatalisadores de platina suportada em monocarbeto e dióxido de tungstênio (WC/C e WO2/C, respectivamente) para a reação de redução de oxigênio em eletrólitos ácidos. O tratamento ácido foi realizado mantendo-se uma certa quantidade do eletrocatisador em uma solução ácida (H2SO4 0,5 mol L-1) a 90ºC por 24 h. Os catalisadores Pt3Co/C e Pt3Cr/C foram caracterizados antes e após o tratamento pelas seguintes técnicas: Espectroscopia por Dispersão de Energia de Raios X (EDX), Difratometria de Raios X (DRX), Microscopia Eletrônica de Transmissão (MET), Espectroscopia de Absorção de Raios X (XAS), como também submetidos a testes eletroquímicos. Os resultados mostraram que os metais menos nobres foram lixiviados devido ao tratamento ácido e que houve variações da região do potencial de redução de óxidos. Em relação aos carbertos de tungstênio, este foram sintetizados pelo método sonoquímico e caracterizados por EDX, DRX e MET. Os resultados eletroquímicos obtidos a partir desses materiais não apresentaram atividade catalítica significante para a RRO, porém, quando se tem Pt ancorada nesse material, a reação de redução de oxigênio é catalisada, similarmente ao desempenho de Pt/C, e segue uma reação via 4 elétrons. Já os materiais formados por dióxido de tungstênio foram sintetizados pelo método de impregnação e também foram caracterizados por EDX, DRX e MET. Os dados obtidos nos testes eletroquímicos destes materiais demonstraram uma certa atividade catalítica para RRO, e que esta reação se ocorre via 2 elétrons. Já para os materiais com Pt suportada em WO2/C, a reação segue a conhecida via 4 elétrons, como no caso de Pt/C. Ao serem submetidos ao tratamento ácido, tanto os catalisadores suportados em WC/C quanto os suportados em WO2/C apresentaram maior estabilidade quando comparados ao Pt/C comercial. / The objectives of this work were: i) to study the degradation of Pt-M catalysts (where M = Co and Cr) supported on carbon after acid treatment and their catalytic activities for the oxygen reduction reaction; ii) to evaluate the performance and stability of platinum electrocatalysts based in tungsten monocarbide (WC/C) and tungsten dioxide (WO2/C) for the oxygen reduction reaction in acidic electrolytes. The acid treatment was carried out by keeping a certain amount of eletrocatalyst in an acidic solution (H2SO4 0.5 mol L-1) at 90°C for 24 h. The Pt3Co/C and Pt3Cr/C catalysts were characterized before and after treatment by the following techniques: Energy Dispersive Spectroscopy (EDS), X-Ray Diffraction (XRD), Transmission Electron Microscopy (TEM), X-Ray Absorption Spectroscopy (XAS), followed by electrochemical tests. The results showed that the non-noble metals have been leached due to the acid treatment and that there are variations in the potential region of oxide reduction. Tungsten carbides, were synthesized by a chemistry and characterized by EDS, XRD and TEM. The electrochemical results obtained for the WC/C materials showed no significant catalytic activity for the ORR, but when Pt is anchored, the oxygen reduction reaction is catalyzed, and the performance is similar to that of Pt/C, and with reaction following the 4 electrons pathways. The materials formed by tungsten dioxide were synthesized by an impregnation method, and also characterized by EDS, XRD and TEM. The data obtained in the electrochemical tests of the bare materials showed some catalytic activity for ORR, but the reaction is promoted via the 2 electrons pathways. As for the previous cases the materials formed by Pt supported on WO2/C the reaction follows the 4 electrons steps. When subjected to the acid treatment, as in the case of the catalysts supported on WC/C, the WO2/C-supported materials had higher stability when compared to the commercial Pt/C catalyst.

Porté par les préoccupations actuelles en matière de sécurité et de qualité environnementale ainsi que par les efforts de recherche entrepris dans ce domaine, le marché mondial des capteurs de gaz est en pleine expansion. Dans le contexte de la commercialisation d'un capteur de gaz, une phase d'amélioration de ses performances, et notamment de sa sensibilité et de sa stabilité, est naturellement nécessaire. Cependant, il s'avère également pertinent d'envisager d'en diminuer le coût de fabrication. Pour cela, il convient de développer une technologie utilisant d'une part des matériaux bas coût et d'autre part permettant de réduire la consommation électrique du dispositif. Dans cette optique, ce travail de thèse a porté sur la réalisation et la caractérisation d'un capteur de gaz oxyde semi-conducteur entièrement basé sur le tungstène et le trioxyde de tungstène pour la détection d'hydrogène sulfuré en milieu industriel. Le principal onjectif était de fabriquer un capteur faible coût en utilisant des techniques d'élaboration simples et des matériaux peu onéreux. Pour cela, notre travail a consisté, dans un premier temps, à développer un élément chauffant en tungstène pouvant fonctionner jusqu'à 500°C. Les procédés mis au point pour la conception de l'élément chauffant ont été utilisés dans l'élaboration des électrodes permettant de mesurer la résistance électrique du film de trioxyde de tungstène. Ensuite, nous avons travaillé sur l'optimisation du procédé de pulvérisation cathodique radio fréquence pour l'élaboration de l'élément sensible en trioxyde de tungstène. Des essais sous gaz ont montré des résultats prometteurs pour la détection d'hydrogène, de dioxyde d'azote et d'ammoniac. / Driven by current safety and environmental quality concerns and research efforts in this area, the global market for gas sensors is expanding rapidly. In the context of the marketing of a gas sensor, a phase of improvement in its performance, and in particular its sensitivity and stability, is naturally necessary. However, it is also relevant to consider reducing the cost of manufacturing. To achieve this, it is necessary to develop a technology that uses low-cost materials and reduces the device's power consumption. In this perspective, this thesis work focused on the realization and characterization of a semiconductor oxide gas sensor entirely based on tungsten and tungsten trioxide for the detection of hydrogen sulfide in an industrial environment. The main objective was to manufacturate a low-cost sensor using simple processing techniques and low-cost materials. To achieve this, our work initially consisted in developing a tungsten heating element that can operate up to 500°C. The processes developed for the conception of the heating element were used in the development of the electrodes for measuring the electrical resistance of the tungsten trioxide film. Then, we worked on the optimization of the radio frequency sputtering process for the development of the tungsten trioxide sensing element. Gas measurements have shown promising results for the detection of hydrogen sulfide, nitrogen dioxide and ammonia.

Ce travail concerne l'étude de nouvelles espèces germaniées tétravalentes et divalentes présentant un germanium dans un état de coordination non usuel.<br />Le premier chapitre est une mise au point bibliographique permettant de situer le thème de notre travail dans le cadre général de l'étude des fonctions divalentes >E14. Elle concerne plus particulièrement i) les espèces divalentes hétéroleptiques halogénées stabilisées par le ligand β-diiminate L2(Cl)Ge, ii) les dérivés germaniés porteurs de ligands de type “pince” O-chélatants. <br />Le deuxième chapitre, concerne les complexes Germanium(II)-tungstène [L2(X)Ge]nW(CO)6-n (L2 = NPhC(Me)CHC(Me)NPh ; n = 1, X = OTf ; n = 2, X = Cl). Des réactions de métathèse ion chlorure/ions peu coordinants (TfO-, BPh4-, PF6-) de ces complexes ont été envisagées pour accéder aux complexes cationiques de types [L2Ge]n+W(CO)6-n correspondants. Les structures de deux complexes germanium(II)-tungstène sont rapportées et analysées. Un équilibre entre une forme covalente et une forme ionique des dérivés à groupement triflate a été observé dans la pyridine.<br />Le troisième chapitre présente la synthèse et les études spectroscopiques (IR ; Masse ; RMN 1H, 13C, 17O) de composés du Germanium(IV) à ligand 2-méthoxybenzyle ArCH2GeHnΣn-3 (Ar = 2-(MeO)C6H4; n = 0 et 3, Σ = X, Me, Ph, OMe ; n = 1, Σ = X, Me, Mes, OMe, OTf ; n = 2, Σ = Cl). Ces études spectroscopiques, une théorique DFT et une étude RX de ArCH2GeH2OTf ont permis de démontrer que le ligand 2-méthoxybenzyle pouvait, dans la plupart des composés, adopter une géométrie permettant une interaction groupement méthoxyle et le centre germanié. Ce chapitre décrit également les synthèses de nouvelles espèces hétéroleptiques divalentes 2-(MeO)C6H4CH2Ge(Cl) et 5-(Cl)-2-(MeO)C6H3CH2Ge(Cl) et quelques aspects de leur réactivité. L'analyse structurelle d'un nouveau type de cluster – structure à un germanium(IV) hexacoordonné et neuf germanium(II) tricoordonnés – obtenu par hydrolyse lente du mélange ArCH2GeHCl2 et Et3GeOMe est également présentée.

Os objetivos deste trabalho foram: i) estudar a degradação de catalisadores do tipo Pt-M (onde M = Co e Cr) suportados em carbono após tratamento ácido e a atividade catalítica dos mesmos para a reação de redução de oxigênio; ii) avaliar o desempenho e a estabilidade de eletrocatalisadores de platina suportada em monocarbeto e dióxido de tungstênio (WC/C e WO2/C, respectivamente) para a reação de redução de oxigênio em eletrólitos ácidos. O tratamento ácido foi realizado mantendo-se uma certa quantidade do eletrocatisador em uma solução ácida (H2SO4 0,5 mol L-1) a 90ºC por 24 h. Os catalisadores Pt3Co/C e Pt3Cr/C foram caracterizados antes e após o tratamento pelas seguintes técnicas: Espectroscopia por Dispersão de Energia de Raios X (EDX), Difratometria de Raios X (DRX), Microscopia Eletrônica de Transmissão (MET), Espectroscopia de Absorção de Raios X (XAS), como também submetidos a testes eletroquímicos. Os resultados mostraram que os metais menos nobres foram lixiviados devido ao tratamento ácido e que houve variações da região do potencial de redução de óxidos. Em relação aos carbertos de tungstênio, este foram sintetizados pelo método sonoquímico e caracterizados por EDX, DRX e MET. Os resultados eletroquímicos obtidos a partir desses materiais não apresentaram atividade catalítica significante para a RRO, porém, quando se tem Pt ancorada nesse material, a reação de redução de oxigênio é catalisada, similarmente ao desempenho de Pt/C, e segue uma reação via 4 elétrons. Já os materiais formados por dióxido de tungstênio foram sintetizados pelo método de impregnação e também foram caracterizados por EDX, DRX e MET. Os dados obtidos nos testes eletroquímicos destes materiais demonstraram uma certa atividade catalítica para RRO, e que esta reação se ocorre via 2 elétrons. Já para os materiais com Pt suportada em WO2/C, a reação segue a conhecida via 4 elétrons, como no caso de Pt/C. Ao serem submetidos ao tratamento ácido, tanto os catalisadores suportados em WC/C quanto os suportados em WO2/C apresentaram maior estabilidade quando comparados ao Pt/C comercial. / The objectives of this work were: i) to study the degradation of Pt-M catalysts (where M = Co and Cr) supported on carbon after acid treatment and their catalytic activities for the oxygen reduction reaction; ii) to evaluate the performance and stability of platinum electrocatalysts based in tungsten monocarbide (WC/C) and tungsten dioxide (WO2/C) for the oxygen reduction reaction in acidic electrolytes. The acid treatment was carried out by keeping a certain amount of eletrocatalyst in an acidic solution (H2SO4 0.5 mol L-1) at 90°C for 24 h. The Pt3Co/C and Pt3Cr/C catalysts were characterized before and after treatment by the following techniques: Energy Dispersive Spectroscopy (EDS), X-Ray Diffraction (XRD), Transmission Electron Microscopy (TEM), X-Ray Absorption Spectroscopy (XAS), followed by electrochemical tests. The results showed that the non-noble metals have been leached due to the acid treatment and that there are variations in the potential region of oxide reduction. Tungsten carbides, were synthesized by a chemistry and characterized by EDS, XRD and TEM. The electrochemical results obtained for the WC/C materials showed no significant catalytic activity for the ORR, but when Pt is anchored, the oxygen reduction reaction is catalyzed, and the performance is similar to that of Pt/C, and with reaction following the 4 electrons pathways. The materials formed by tungsten dioxide were synthesized by an impregnation method, and also characterized by EDS, XRD and TEM. The data obtained in the electrochemical tests of the bare materials showed some catalytic activity for ORR, but the reaction is promoted via the 2 electrons pathways. As for the previous cases the materials formed by Pt supported on WO2/C the reaction follows the 4 electrons steps. When subjected to the acid treatment, as in the case of the catalysts supported on WC/C, the WO2/C-supported materials had higher stability when compared to the commercial Pt/C catalyst.

We performed atomistic modeling to study magnetic, mechanical, and thermal properties of materials. We executed molecular statics and dynamics simulations for this study, using density functional theory (DFT) and semi-empirical methods, such as embedded atom method (EAM) and modified embedded atom method (MEAM) potentials. In our first study, we showed that when Al atoms are substituted in barium hexaferrite, the total magnetization monotonically decreases due to the fact that Al atoms preferentially occupy the majorly contributing magnetic sites. The second study was to explore the diffusion mechanism of Ba atoms in hematite in order to study new techniques to build spherical nano-magnetic-particles. In the third study, we showed tungsten carbide growth is inhibited in the presence of vanadium carbide. In the fourth study, we showed how the mechanical and thermal properties of iron changes with vanadium doping with a newly developed MEAM interatomic potential. The physical properties of calcium were calculated in the next study, by the development of a MEAM potential which can be used for multiscale modeling. In the sixth study, the melting temperature of nanoparticles was analyzed and shown to decrease with a decrease of its size, confirming that the bulk properties of the material significantly change in its nano counterpart. Finally a portion of this research was dedicated for the simulation of sintering mechanisms of tungsten nanoparticles at different temperatures and pressures. While the first three studies were based on DFT, the last four studies focused on understanding physical phenomena using EAM/MEAMpotentials.

Ce travail s'inscrit dans les thématiques matériaux carbonés et matériaux pour l'énergie. Il s'agit d'une part de remplacer tout ou partie du platine, catalyseur de la pile à combustible basse température, par des matériaux moins coûteux et plus abondants ; et d'autre part d'optimiser l'accessibilité des sites catalytiques aux réactifs. WCl6 est imprégné en phase gazeuse en présence de dichlore sur un support dérivé du graphite expansé, avant d'être réduit/carburé afin d'obtenir des dérivés du tungstène (tungstène, carbures de tungstène). La taille et la nature des nanoparticules dépendent de la composition du gaz utilisé (H2 ou mélange H2/CH4) et de la température de réaction. En présence de H2, la réduction est complète à partir de 550°C. L'utilisation d'un mélange gazeux H2/CH4 (90/10, 85/15 ou 80/20) conduit à l'élaboration de nanoparticules de W2C et WC. L'augmentation de la température favorise le frittage des particules mais pas la carburation complète. Les tests en demi-pile effectués sur ces catalyseurs révèlent qu'ils sont peu performants. Des catalyseurs mixtes Pt-W2C sont obtenus en déposant successivement PtCl4 et WCl6. La réduction - carburation est réalisée à 900°C en présence d'un mélange H2/CH4 (85/15). Ces matériaux possèdent des performances électrocatalytiques bien supérieures à celles d'un catalyseur commercial pour un taux de platine équivalent. Ce travail concerne également la fonctionnalisation du support carboné par des groupements sulfonate. Le greffage de polystyrène sulfonate est efficace car il permet de diminuer la quantité de Nafion utilisée dans les électrodes et d'améliorer les performances catalytiques / This work is implicated in the development of carbon materials and of materials for energy applications. In the first part, we aim to totally or partially replace the platinum catalyst of the Proton Exchange Membrane Fuel Cell by less expensive and more abundant materials. In the second part, we optimize the catalytic sites accessibility for the reactants. WCl6 was impregnated on the Expanded Graphite derivated substrate by gaseous transport under chlorine pressure before being reduced and/or carburized in order to obtain tungsten derivatives (tungsten, tungsten carbides). The nature and size of the nanoparticles depend on the reducing or carburizing gas composition (H2 or H2/CH4 mixture) and the reaction temperature. Reduction is not complete until 500°C when using H2. W2C and WC mixtures are formed when using H2/CH4 mixtures (90/10, 85/15 or 80/20). The temperature increasing favours the sintering effect but not the complete carburization. All these obtained catalysts show low electrocatalytic performances when tested on a half-cell system. Platinum-tungsten hemicarbides catalysts were obtained by a successive deposition of PtCl4 and WCl6 while the reduction-carburization step was realized at 900°C under H2/CH4 mixture (85/15). These materials show higher electrocatalytic performances than a commercial platinum catalyst for an equivalent platinum ratio. The final part of this work concerns the carbon support functionnalization with sulfonate groups. Polystyrene sufonate grafting seems efficient for it helps to reduce the Nafion quantities used in the electrodes and to increase the electrocatalytic performances