L’émergence de nouveaux matériaux structurés à l’échelle nanométrique, aux propriétés contrôlées, a ouvert de nouvelles perspectives vis-à-vis des matériaux qui nous entourent. C’est notamment le cas des métaux et de leurs alliages et il est crucial d’établir le lien entre leurs propriétés structurales et leurs propriétés chimique et physique pour en permettre une utilisation optimale. Cette thèse s’inscrit dans ce contexte et porte sur la synthèse et la caractérisation en microscopie électronique en transmission de nanoparticules d’alliage bimétallique Au-Cu. En s’appuyant sur le diagramme de phase décrit à l’échelle macroscopique, nous nous sommes particulièrement intéressés aux nanoparticules de compositions nominales Au3Cu, AuCu et AuCu3. Le premier axe de ce travail consiste en l’élaboration de nanoparticules d’alliage Au-Cu. Deux voies de synthèse sont explorées : la voie chimique reposant sur le procédé polyol et la voie physique par ablation par laser pulsé. Le premier mode d’élaboration permet l’obtention de nanoparticules parfaitement cubiques dont la composition est systématiquement riche en Au. Les nanoparticules produites par voie physique présentent en revanche une composition maitrisée et modifiable. D’un point de vue structural, un recuit de ces dernières particules mène à leur mise en ordre chimique et à l’observation de structures L10 et L12. Cependant, nous montrons que cette transition de phase est bloquée dans les nanostructures présentant des défauts structuraux. Enfin, l’évolution du paramètre de maille des nanoparticules synthétisées selon ces deux voies de synthèse, en fonction de leur composition, a été établie et suit exactement la loi de Vegard décrite pour le matériau massif.Dans un second temps, nous avons observé des nanoparticules obtenues par voie physique en microscopie électronique en transmission environnementale, c’est-à-dire dans des conditions proches des environnements d’utilisation habituellement appliqués en catalyse. Les expériences menées en température révèlent que le mécanisme de dissolution de nanoparticules d’Au et d’alliage Au-Cu portées à haute température se fait en deux étapes : il y a fusion des nanoparticules suivi de leur évaporation pour des tailles de nanoparticules centrées autour de 10 nm. Les expériences réalisées en couplant le chauffage des nanoparticules au passage d’un gaz (H2 ou O2), en flux et dans des conditions de pression bien supérieures à celles accessibles jusqu’à maintenant, ont permis d’étudier leur comportement thermodynamique en condition oxydantes et réductrices. Nous avons notamment montré que des cycles d’oxydo-réduction de nanoparticules de taille moyenne supérieure à 20 nm conduisent à un effet Kirkendall menant, de manière réversible, à la formation de nanoparticules creuses (doughnut). Cette thèse interdisciplinaire constitue travail pionnier dans la compréhension du système d’alliage bimétallique Au-Cu à l’échelle nanoscopique / The emergence of new materials, structured at the nanoscale, with controlled properties, has opened new prospects regarding materials around us. In particular for metals and alloys, it seems crucial to connect their structural properties to their chemical and physical properties in order to optimise their use.Within this context, this thesis is focused on the synthesis and the characterisation of Au-Cu bimetallic alloy nanoparticles by transmission electron microscopy. On the basis of the bulk phase diagram, we especially studied particles with nominal compositions Au3Cu, AuCu et AuCu3.The first part of this work is dedicated to the synthesis of nanoparticles in two different ways. The chemical way is based on the polyol process and leads to nanoparticles exhibiting a cubic shape, and a systematically rich Au content. On the other hand, nanoparticles obtained by Pulsed Laser Deposition (PLD), a physical method of synthesis, display a well-controlled and tuneable composition. From a structural point of view, the annealing of the particles leads to chemical order and the stabilisation of L10 and L12 structures. However, we reveal that this phase transition is blocked in nanostructures with crystal defects. Moreover, we establish the evolution of the lattice parameter of the particles as a function of the composition and we demonstrate that, as in the bulk case, it is in agreement with Vegard’s law.In the second part, the nanoparticles synthesised via the physical method are studied using environmental transmission electron microscopy, i.e. in conditions close to those usually applied in catalytic reactors. Experiments performed at high temperature highlight that the dissolution of Au and Au-Cu nanoparticles occurs in a two-step process: fusion occurs first and is followed by evaporation for nanoparticles with a mean diameter of 10 nm.Coupling heating with gas flow (H2 or O2) in higher pressure condition than those usually reached allows us to study the thermodynamic behaviour of the nanoparticles in oxidative or reductive conditions. Most Notably, we show that oxidation-reduction cycles performed on nanoparticles with a diameter larger than 20 nm leads to a Kirkendall effect and the reversible formation of hollow particles (doughnuts).This cross-disciplinary thesis is a pioneering work towards understanding the bimetallic Au-Cu alloy system at atomic scale

Ce travail de thèse est dédié à l’étude théorique de l’effet de l'environnement sur les nano-catalyseurs AuCu. Ainsi dans le cadre de la théorie de la fonctionnelle de la densité (DFT), la stabilité du système bimétallique AuCu, modélisé sous forme de surfaces semi-infinies, de nanoparticules libres et de nanoparticules supportées, a été examinée en présence et en absence de gaz réactif. Du point de vue thermodynamique, et sous conditions de vide, la ségrégation de l’or en surface est favorisée, en partie grâce à sa plus faible énergie de surface comparée à celle du cuivre. En revanche, en présence de molécules de gaz (CO, NO ou O2), les résultats montrent une ségrégation inversée, du cuivre vers la surface et de l’or vers le volume. Ces résultats confirment et expliquent les observations expérimentales et permettent aussi de prédire la localisation du cuivre à la surface de l’alliage en présence de chaque environnement gazeux. Sur les surfaces, l’étude énergétique de l’anisotropie de ségrégation (c'est-à-dire la force de ségrégation pour chaque type de terminaison de la surface) montre une ségrégation préférentielle de Cu vers la surface (110) en présence de gaz. L’analyse de la structure électronique issue des calculs de la densité d’état et des distributions de charges met en évidence des caractères très différents pour les molécules de gaz et donc des effets différents sur l’alliage AuCu, à savoir un caractère local pour CO, semi-local pour NO et complètement singulier dans le cas de O2.Sous forme de nanoparticule (cuboctaèdre de 38 atomes), l’étude de l’évolution de la stabilité de AuCu en fonction de la teneur en Au et pour différents types d’alliages (cœur-coquille, alliage régulier, peau-cœur) a été effectuée grâce aux calculs de l’énergie de surface. Les résultats révèlent l’existence d’une relation linéaire entre la composition chimique et la stabilité de AuCu. En outre, à partir d’une teneur en Au de 20%, les nano-alliages bimétalliques AuCu se révèlent plus stables que les composantes Au et Cu pures. En présence de gaz, un modèle thermodynamique qui prend en compte l’adsorption des molécules de CO a été développé pour prédire le diagramme de stabilité en fonction de la température et de la pression de CO. Les résultats montrent l’instabilité des nanoparticules de Cu sous pression de gaz et prédisent une composition critique en Au (15%) à partir de laquelle l’alliage AuCu devient stable sous gaz réactif. Ces résultats sont en parfait accord avec des résultats expérimentaux récemment publiés.Enfin, l'effet du support oxyde a été soigneusement étudié en considérant l’interaction des nanoparticules AuCu sur la surface de TiO2(100) anatase. L’analyse des composantes énergétiques (énergies de dépôt, énergies d’interaction, etc ..), des effets géométriques (déformations de la nanoparticule et du support) et des propriétés électroniques (transferts de charges) ainsi que l’étude de la réactivité ont permis de comprendre le comportement de l’alliage supporté et d’évaluer l’effet du support anatase, pas du tout le même en fonction de la structure et de l’ordre chimique de la nanoparticule considérée. / This thesis is devoted to the theoretical description of the effect of the environment on AuCu nanocatalysts. In the framework of density functional theory (DFT), the stability of the AuCu bimetallic system, modeled as semi-infinite surfaces, free nanoparticles and supported nanoparticles, was studied in the presence and in the absence of reactive gas. From a thermodynamic point of view, and under vacuum conditions, the segregation of gold at the surface is favored, which is due, in part, to its lower surface energy compared to that of copper. However, in the presence of gas molecules (CO, NO or O2), the results show an inverted segregation, of copper towards the surface and of gold towards the bulk. These results confirm and explain the experimental observations and also make it possible to predict the localization of the copper on the surface of the alloy in the presence of gas environment.Over the AuCu surfaces, the energetic study of segregation anisotropy (i.e. the segregation forces versus surface terminations) shows preferential segregation of Cu toward the (110) surface, in the presence of gas. The analyses of the electronic structure from the calculation of density of states and charge distributions reveal very different characters of gas molecules and therefore different effects on the AuCu alloy, namely a local character for CO, semi-local for NO and a completely different behavior for the case of O2.In the form of nanosized particle (truncated cuboctahedron of 38 atoms), the AuCu stability as a function of Au content and for different alloy types (core-shell, regular alloy, skin-heart) was investigated by considering surface energy calculations. The results reveal the existence of a linear relationship between the chemical composition and the stability of AuCu. In addition, for Au content equal and beyond 20%, the AuCu bimetallic nano-alloys are found to be more stable than the pure Au and Cu components. In the presence of gas, a thermodynamic model that takes into account the adsorption of CO molecules was developed to predict the stability diagram as a function of temperature and CO pressure. The results show the instability of Cu nanoparticles under gas pressure and predict a critical composition in Au of about 15% from which the AuCu nanoalloys become stable. These results are in full agreement with recent experimental reports.Finally, the effect of the oxide support has been carefully investigated by considering the adsorption of AuCu nanoparticles over TiO2 (100) anatase surface. The analysis of energetic components (deposition and interaction energies etc.), geometric effects (nanoparticle and support deformations) and electronic properties (charge transfers) as well as the study of the reactivity, made it possible to understand the behavior of the supported nanoalloys and to evaluate the effect of the anatase support; not at all the same depending on the structure and the chemical order of the considered nanoparticle.

Investigations on size dependent phase stability and transformations in isolated nanoparticles have gained momentum in recent times. Size dependent phase stability generates size specific particle microstructure which consequently yields size specific functionality. One important prerequisite for conducting studies on nanoparticles is their synthesis. A substantial amount of research effort has therefore been focused on devising methodologies for synthesizing nanoparticles with controlled shapes and sizes. The present thesis deals with both these two aspects: (a) synthesis of nanoparticles and (b) phase transformations in nanoparticles. The system chosen in this study is AuCu intermetallic nanoparticles. The choice of AuCu nanoparticle was due to the fact that the literature contains abundance of structural and thermodynamic data on Au–Cu system which makes it a model system for investigating size dependence of phase transformations. With respect to synthesis, the present thesis provides methodologies for synthesizing alloyed Au–Cu nanoparticles of different sizes, Au–Cu nano-chain network structures and uniform Au–Cu2S hybrid nanoparticles. For every type, results are obtained from a detailed investigation of their formation mechanisms which are also presented in the thesis. With respect to phase transformation, the thesis presents results on the size dependence of fcc to L10 transformation onset in Au–Cu nanoparticles under isothermal annealing conditions. The present thesis is divided into eight chapters. A summary of results and key conclusions of work presented in each chapter are as follows. The ‘introduction’ chapter (chapter I) describes the organization of the thesis. Chapter II (literature study) presents a review of the research work reported in the literature on the various methodologies used for synthesizing Au–Cu based nanoparticles of different shapes and sizes and on ordering transformation in AuCu nanoparticles. The chapter also presents a brief discussion on the reaction variables that control the process of nucleation and growth of the nanoparticles in solution. Chapter III titled ‘experimental details and instrumentation’ describes the synthesis procedures that were used for producing various nanoparticles in the present work. The chapter also briefly describes the various characterization techniques that were used to investigate the nanoparticles. The fourth chapter titled ‘synthesis and mechanistic study of different sizes of AuCu nanoparticles’ provides two different methodologies for synthesis, referred as ‘two-stage process’ and ‘two-step process’ that have been used for producing alloyed AuCu nanoparticles of different sizes (5, 7, 10, 14, 17, 25 nm). The ‘two-stage’ process involved sequential reduction of Au and Cu precursors in a one pot synthesis process. Whereas, the ‘two-step’ process involved a two-pot synthesis in which separately synthesized Au nanoparticles were coated with Cu to generate alloyed AuCu nanoparticles. In the two-stage synthesis process it was observed that by changing the total surfactant-to-metal precursor molar ratio, sizes of the alloyed AuCu nanoparticles can be varied. ‘Total surfactants’ here include equal molar amounts of oleic acid and oleylamine surfactants. Interestingly, it was observed that there exists a limitation with respect to the minimum nanoparticle size that can be achieved by using the two-stage process. The minimum AuCu nanoparticle size achieved using the two-stage synthesis process was 14 nm. Mechanism of formation of AuCu nanoparticles in the two-stage synthesis process was investigated to find out the reason for this size limitation and also to determine how the synthesis process can be engineered to synthesize alloyed AuCu nanoparticles with smaller (<14nm) sizes. Studies to evaluate mechanism of synthesis were conducted by investigating phase and size of nanoparticles present in the reaction mixture extracted at various stages of the synthesis process. Their studies revealed that (a) the nanoparticle formation mechanism in the two-stage synthesis process involves initial formation of Au nanoparticles followed by a heterogeneous nucleation and diffusion of Cu atoms into these Au rich seeds to form Au–Cu intermetallic nanoparticles and (b) by increasing the relative molar amount of the oleylamine surfactant, size of the initial Au seed nanoparticles can be further reduced from the minimum size that can be achieved in the case when equal molar amounts of oleylamine and oleic acid surfactants are used. The information obtained from the mechanistic study was then utilized to design the two-step synthesis process. In the two-step process, Au nanoparticles were synthesized in a reaction mixture containing only the oleylamine surfactant. Use of only oleylamine resulted in production of pure Au nanoparticles with sizes that were well below 10 nm. These Au nanoparticles were washed and dispersed in a solution containing Cu precursor. Introduction of a reducing agent into this reaction mixture led to the heterogeneous nucleation of Cu onto the Au seed particles and their subsequent diffusion into them to form alloyed AuCu nanoparticles with sizes of ~5, 7 and 10 nm. The study present in this chapter essentially signified that the surfactants used in the reaction mixture not only prevent nanoparticles from agglomerating in the final dispersion but also control their nucleation and growth and therefore can be used as a tool to tune nanoparticle sizes. The fifth chapter titled ‘size dependent onset of FCC-to-L10 transformations in AuCu alloy nanoparticles’ illustrates the effect of AuCu nanoparticle size on the onset of ordering under isothermal annealing conditions. Nanoparticles in this study were annealed in-situ in a transmission electron microscope. Samples were prepared by drop drying a highly dilute dispersion of as-synthesized nanoparticles onto an electron transparent TEM grid. Nanoparticles sitting on the TEM grid were well separated from each other to minimize particle sintering during the annealing operation. It was however observed that during the isothermal annealing, particle coarsening due to atomic diffusion was appreciable for 5 nm particles but negligible for 7 and 10 nm particles. Therefore for this study only 7 nm and 10 nm sized particles were considered. Onset of ordering was determined from the time when first sign of the diffraction spot, corresponding to the ordered phase, appears in the selected area electron diffraction pattern from a region containing large number of AuCu nanoparticles. Through a series of isothermal experiments it was observed that the time for onset of ordering increased with decrease in size of the nanoparticles. It is speculated that the delay in onset of ordering may be due to the fact that with a decrease in nanoparticle size the probability of a nanoparticle containing a fluctuation that shall generate a thermodynamically stable nuclei of the ordered phase decreases. A sharp interface between the ordered and the disordered phase inside the particle was also observed which suggested that the ordering transformation in as-synthesized fcc AuCu nanoparticles is a first order transformation. The sixth chapter titled ‘synthesis and characterization of Au1-xCux–Cu2S hybrid nanostructures: morphology control by reaction engineering’ provides a modified polyol method based synthesis strategy for producing uniform Au–Cu2S hybrid nanoparticles. Detailed compositional and structural characterization revealed that the hybrid nanoparticles are composed of cube shaped Au-rich, Au–Cu solid solution phase and hemispherical shaped Cu2S phase. Interestingly, the hemispherical Cu2S phase was attached to only one facet of the cube shaped phase. A study on the formation mechanism of hybrid nanoparticles was also conducted by characterizing specimens extracted from the reaction mixture at different stages of the synthesis process. The study revealed that the mechanism of formation of hybrid nanoparticles involved initial formation of isolated cube shaped pure Au nanoparticles and Cu–thiolate complex with a sheet morphology. With increase in time at 180°C, the Cu–thiolate complex decomposed and one part of the Cu atoms that were produced from the decomposition were utilized in forming the spherical Cu2S and other part diffused into the Au nanoparticles to form Au–Cu solid solution phase. The chapter also presents a study on the effect of dodecanethiol (DDT) on achieving the hemisphere-on-cube hybrid morphology. In this study it is illustrated that an optimum concentration of dodecanethiol is required both for achieving size and morphological uniformity of the participating phases and for their attachment to form a hybrid nanoparticle. The seventh chapter titled ‘synthesis of Au–Cu nano-chains network and effect of temperature on morphological evolution’ provides methodology for synthesizing fcc Au– Cu nano-chain network structures using polyvinylprrolidone (PVP) surfactant. It was observed that with increase in the molar amount of PVP in the reaction mixture, morphology of the as-synthesized product gradually changed from isolated nanoparticles to branched nano-chain like. The nano-chains contained twins which indicated an absence of continuous growth and possibility of growth by oriented attachment of initially formed Au–Cu nanoparticles. Both in-situ and ex-situ annealing of the nano-chains led to their decomposition into isolated nanoparticles of varying sizes. Annealing also caused fcc-to¬L10 phase transformation. Investigation of the wave length of perturbation leading to breaking of a nano-chain into particles indicated that the surface energy anisotropy affects the splitting of nano-chain network structure into nano-sized particles. The thesis ends with a last chapter where we have presented possible future extension of current work.

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L’activité catalytique de l’or en réaction d’oxydation préférentielle du CO (PROX) dépend de plusieurs facteurs tels que la nature du support, l’ajout de promoteurs, la taille des particules ou la nature du prétraitement. L’objectif de cette thèse a donc été de clarifier l’influence de ces paramètres sur cette réaction en utilisant des catalyseurs à base d’or modifiés. Dans une 1ère partie, nous avons étudié un système à base d’or supporté sur des oxydes Ce-Fe préparés par co-imprégnation ou imprégnations successives en faisant varier le rapport Ce/Fe. Le dopage de la cérine par le fer conduit à la formation d’une solution solide qui améliore l’activité en PROX en raison d’une mobilité d’oxygène accrue. Dans une 2ème partie, nous avons évalué une série de supports (Al2O3, CeO2 et Ce2Zr2O7) pour optimiser le dépôt de Au, Cu ou Au-Cu. La combinaison Au-Cu/CeO2 s’est révélée être la meilleure en PROX. Nous avons donc étudié l’influence du rapport Au/Cu (1/3, 1/1 ou 3/1) ainsi que l’influence du pré-traitement (calcination ou réduction) sur ce système. Les catalyseurs ont été systématiquement caractérisés par des méthodes physico-chimiques (BET, DRX, MET, XPS, RTP, FTIR). Les performances catalytiques du système Au-Cu/CeO2 dépendent fortement de la taille des particules, de l’état chimique de l’or déterminé par XPS, de l’interaction Au-support et de la distribution de surface des 2 métaux. Une étude cinétique corrélée à de l’infrarouge à transformée de Fourier a permis d’établir un mécanisme de réaction d’oxydation de CO dans le lequel CO adsorbé réagit avec O2 adsorbé pour conduire à la formation de CO2. / The catalytic activity of gold for CO preferential oxidation in rich hydrogen (PROX) is generally influenced by various parameters such as the nature of support, the addition of a promoter, the particle size or the pre-treatment. Therefore, the objectives of this work were to clarify the influence of these parameters on a series of modified gold catalysts in PROX reaction. In a 1rst part, we have studied a system based on Au supported on Ce-Fe oxides prepared by co-precipitation or impregnation with various Ce/Fe ratios. The doping of CeO2 by iron led to the formation of a solid solution which improved the PROX activity due to an increase of the oxygen mobility. In a 2nd part, a series of supports (Al2O3, CeO2, and Ce2Zr2O7) was evaluated in order to load Au, Cu or Au-Cu. The combination of Au-Cu/CeO2 was shown to be the best system. The influence of Au/Cu (1/3, 1/1 or 3/1) ratio was therefore undertaken along with the effect of the pre-treatment (calcination or reduction). The catalysts have been systematically characterized by physico-chemical techniques (BET, XRD, TEM, XPS, TPR, FTIR). The kinetics of PROX reaction and CO oxidation mechanism on Au-Cu/CeO2 were explored and correlated with an FTIR study. The catalytic performances of these catalysts are strongly dependent upon the particle size of the metal, the chemical state of gold, the gold-support interaction and the surface distribution of Au and Cu. We have proposed a CO oxidation mechanism in which adsorbed CO reacts with adsorbed O2 to produce CO2.

Submitted by Cleide Dantas (cleidedantas@ufpa.br) on 2014-04-08T17:15:22Z No. of bitstreams: 2 license_rdf: 23898 bytes, checksum: e363e809996cf46ada20da1accfcd9c7 (MD5) Dissertacao_EfeitoAdicoesNi.pdf: 5757867 bytes, checksum: 8a77abd3b782bdae2352df421372bf23 (MD5) / Approved for entry into archive by Ana Rosa Silva (arosa@ufpa.br) on 2014-09-01T15:39:57Z (GMT) No. of bitstreams: 2 license_rdf: 23898 bytes, checksum: e363e809996cf46ada20da1accfcd9c7 (MD5) Dissertacao_EfeitoAdicoesNi.pdf: 5757867 bytes, checksum: 8a77abd3b782bdae2352df421372bf23 (MD5) / Made available in DSpace on 2014-09-01T15:39:57Z (GMT). No. of bitstreams: 2 license_rdf: 23898 bytes, checksum: e363e809996cf46ada20da1accfcd9c7 (MD5) Dissertacao_EfeitoAdicoesNi.pdf: 5757867 bytes, checksum: 8a77abd3b782bdae2352df421372bf23 (MD5) Previous issue date: 2013 / CAPES - Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / Este trabalho estudou a influência dos teores dos solutos Mg e Ni na modificação das propriedades térmicas, elétricas e mecânicas de uma liga Al-Cu-Fe para aplicação como condutor de energia elétrica. Para a realização do presente estudo, as ligas foram obtidas por fundição unidirecional horizontal, a partir da base do alumínio de pureza comercial com adição dos teores 0,05%p Cu e [0,24 a 0,28]%p Fe. Tal base foi modificada em uma primeira etapa com teores de 0,45, 0,60 e 0,80%p Mg. As ligas obtidas com estes teores tiveram suas propriedades estudadas para que se selecionasse um teor de Mg para posterior adição de Ni à liga. O estudo destas propriedades na primeira etapa passou pela análise das propriedades térmicas: velocidade de solidificação (VL) e taxa de resfriamento (Ṫ). A caracterização elétrica estudou a propriedade condutividade elétrica (φ) e o levantamento das propriedades mecânicas: limite de resistência à tração (σ) e microdureza Vickers (HV). A liga com adição de Ni passou por tratamentos térmicos de envelhecimento, por 1, 4 e 8h. Estas amostras foram analisadas em um microscópio eletrônico de varredura - MEV pelos sinais de elétrons retroespalhados – ERE e espectroscopia de energia dispersiva – EDS. Como resultados do estudo, encontrou-se que adições de Mg influenciaram significativamente a viscosidade das ligas, elevando as velocidades de solidificação nos instantes finais. Os ensaios de microdureza das amostras envelhecidas mostraram que houve um acréscimo significativo de dureza na quarta hora de envelhecimento, da mesma forma que as análises de EDS mostraram que a concentração de Ni também elevou-se nesta condição de tratamento. / This work studied the influence of Mg and Ni solute content on the modification of the thermal, electrical and mechanical properties of an Al-Cu-Fe alloy for application as an electrical conductor. To realize the present study, the alloys were obtained by unidirectional horizontal casting, starting from the commercial pure aluminum with the addition of 0.05wt% Cu and [0.24 to 0.28]wt% Fe content. This basis was modified on a first stage with 0.45, 0.60 and 0.80wt% of Mg content. The alloys obtained with these contents had its properties studied for the selection of a Mg content for further Ni addition at the alloy. The study of these properties on the first stage passed through the analysis of the thermal properties: growth rate (VL) and cooling rate (Ṫ). The electrical characterization studied the electrical conductivity property (φ) and the following mechanical properties were determined: ultimate tensile strength (σ) and Vickers microhardness (HV). The alloy which has Ni additions passed through ageing heat treatments of 1, 4 and 8 hours. These samples were analyzed in a scanning electron microscope – SEM by the electrons backscattered – EBS and energy dispersive spectroscopy – EDS signals. As a result of the research, it was found that Mg additions had significantly influenced the alloys viscosity, increasing its growth rates at the final moments of the solidification. The microhardness tests for the aged samples showed that they suffered a significant gain of hardness at the fourth hour of ageing, also, the EDS analysis showed that Ni content increased at the same treating conditions.

Gold-based catalysts can be replaced with platinum group catalysts in catalytic automotive exhaust aftertreatment if their thermal stability and durability issues can be resolved. Hence, one of the potential markets for gold catalysis is the automotive after treatment market, our interest is to synthesize a gold-based catalyst which has practical applications in automotive industry specifically for diesel-methane dual fuel low-temperature combustion strategy where the exhaust temperature is varying from ~ 200 to400° C. Our research focused on synthesizing a bimetallic gold-copper catalyst which is not only highly active for CO oxidation reaction but also sinter-resistant at temperatures normally observed at LTC engine exhaust. The Au-Cu@SiO2 catalyst exhibited excellent efficacy for CO oxidation with >95% conversion to CO2 achieved at 300 °C. While the presence of Cu enhanced CO conversion at low to intermediate temperatures (50-300 °C), silica encapsulation of the Au-Cu nanocomposites facilitated for remarkable stability of the catalyst. Moreover, the catalyst exhibited remarkable stability at high reaction temperatures which could be attributed to the SiO2 encapsulation of nanoparticles. The activity and stability of Au-Cu@SiO2 catalyst are suitable for its application in automotive after treatment devices, especially in low-temperature combustion engine exhaust.

.L'objectif de cette étude était, en premier lieu, de mettre en place en Thaïlande un testd'adhésion par traction-écaillage sur une machine de traction classique (test" macroscopique "), de le comparer au test " microscopique " Grenoblois fonctionnant dansla chambre du MEB et de l'utiliser pour évaluer l'adhérence des calamines de process sur desaciers industriels. Deux paramètres ont été étudiés, la vitesse de déformation et la teneur desaciers en silicium. Il apparaît que l'écaillage des calamines au cours du test augmente quandaugmente la vitesse de déformation. Une vitesse de déformation élevée entraîne unedéformation au premier écaillage plus faible, donc une adhérence mesurée plus faible. Ceteffet est lié aux phénomènes de relaxation. On a pu alors montrer que la présence d'oxyde(s)contenant Si, situé(s) à l'interface avec le métal, augmentait l'adhérence. Les étudesd'oxydation dans la vapeur d'eau qui ont aussi été réalisées ont révélé que la présence desilicium réduisait la vitesse d'oxydation. En augmentant la teneur en Si, les couches defayalite et de wüstite s'épaississent ; par contre, les couches externes s'amincissent. Pour lesaciers contenant du cuivre, la vitesse d'oxydation est réduite quand la teneur en Cu estaugmentée. De la même façon, les couches internes sont plus épaisses et on observe uneaugmentation du nombre de précipités de Cu quand la teneur en cet élément augmente.

.L’objectif de cette étude était, en premier lieu, de mettre en place en Thaïlande un testd’adhésion par traction-écaillage sur une machine de traction classique (test« macroscopique »), de le comparer au test « microscopique » Grenoblois fonctionnant dansla chambre du MEB et de l’utiliser pour évaluer l’adhérence des calamines de process sur desaciers industriels. Deux paramètres ont été étudiés, la vitesse de déformation et la teneur desaciers en silicium. Il apparaît que l’écaillage des calamines au cours du test augmente quandaugmente la vitesse de déformation. Une vitesse de déformation élevée entraîne unedéformation au premier écaillage plus faible, donc une adhérence mesurée plus faible. Ceteffet est lié aux phénomènes de relaxation. On a pu alors montrer que la présence d’oxyde(s)contenant Si, situé(s) à l’interface avec le métal, augmentait l’adhérence. Les étudesd’oxydation dans la vapeur d’eau qui ont aussi été réalisées ont révélé que la présence desilicium réduisait la vitesse d’oxydation. En augmentant la teneur en Si, les couches defayalite et de wüstite s’épaississent ; par contre, les couches externes s’amincissent. Pour lesaciers contenant du cuivre, la vitesse d’oxydation est réduite quand la teneur en Cu estaugmentée. De la même façon, les couches internes sont plus épaisses et on observe uneaugmentation du nombre de précipités de Cu quand la teneur en cet élément augmente. / The purpose of this study was first to develop in Thailand a “macroscopic” adhesion testusing a conventional tensile machine, to compare it to the micro-tensile test used in Grenobleand sitting in the SEM chamber, and to use it for measuring adhesion of scales grown duringprocessing on industrial steels. Parameters affecting the test, i.e. strain rate and Si content ofsteels were investigated. The results showed that spallation of scales during strainingincreased with increasing tensile strain rate. A higher strain rate resulted in lower straininitiating the first spallation and lower mechanical adhesion of scales, which could beexplained by a relaxation effect. Oxide containing Si existed at the steel-scale interface andpromoted adhesion of scales. Oxidation studies were also performed, and the behaviour inwater vapour of steels with different contents of Si and Cu was investigated. Increasing Sicontent tended to decrease oxidation rate. It also resulted in the thickening of the wüstite andfayalite layers which formed by internal oxidation. When Si in steel increased, theintermediate (FeO + Fe3O4) and outermost (Fe2O3 sitting on Fe3O4) layers formed by externaloxidation were thinner. For Cu containing steel, increasing Cu content tended to decrease theoxidation rate. It also decreased the innermost and intermediate layers and resulted in moreCu precipitates along steel-scale interface.