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As a candidate for dynamic electric contacts, Nano-twinned copper has intrinsic conductivity and enhanced fretting resistance. To better understand its general mechanical behavior, we conduct molecular dynamics simulation studies to investigate responses of nano-twinned copper to stress and to one-directional and two-directional sliding processes, in comparison with single crystal and nano-grained model systems. Obtained results suggest that the twin boundary blocks dislocation movement more effectively and the degree of emitting dislocations under stress is considerably lower than that of grain boundary. The inverse H-P relation only occurring in nano-grained materials does not necessarily result from grain boundary sliding. Under sliding conditions, dislocations are easier to be generated in the single crystal system. During the two-directional sliding process, Bauschinger effect is observed in the single crystal and nano-twinned systems, while the situation is opposite for the nano-grained system. The nano-twinned Cu shows the least dislocation accumulation during two-directional sliding. / Materials Engineering

X-ray diffraction topography, using both conventional and synchrotron sources, has been employd t reveal, to a resoltuoon of 1um, internal structural imperfections in diamonds from Brazil. Many of these diamonds were found to be twinned; and X-ray studies have been made of twinned diamonds from Brazil and elsewhere, in order to elucidate the mechanisms of twinning in diamond. Numerous X-ray topographs have been taken of contact twins (mcles), interpenetrant cubes and mulitple twins. The well collimated beam of synchrotron radiation at the SERV Daresbury Laboratory has proved most useful in revealing, in the forward reflexion Laue photographers, small twinned regions of diamons: the presence of which would have been mised by conventioanl methods.

The effect of annealing conditions on the microstructure evolution of CVD nickel was investigated systematically in the present study by differential scanning calorimetry, optical microscopy and transmission electron microscopy (TEM), upon both ex-situ and in-situ annealing. TEM observation revealed the as-deposited CVD nickel possessed a bi-modal grain structure, with large columnar grains embedded in nanocrystalline matrix. Ultrafine and nano growth twins were present as well as multiply twinned grains with five-fold symmetry. Microstructure observation upon annealing showed that grain growth did not occur until annealing at 400ºC. Detwinning was observed at 400ºC and higher temperatures. The ultrafine and nano twins tended to transform into dislocation cell structures and this phenomenon was driven by the excess free energy associated with the high density of grown-in twin boundaries. The five-fold twinned grains were found to be thermally stable up to 600ºC. The hardness was observed to decrease with increasing annealing temperature.

The effect of annealing conditions on the microstructure evolution of CVD nickel was investigated systematically in the present study by differential scanning calorimetry, optical microscopy and transmission electron microscopy (TEM), upon both ex-situ and in-situ annealing. TEM observation revealed the as-deposited CVD nickel possessed a bi-modal grain structure, with large columnar grains embedded in nanocrystalline matrix. Ultrafine and nano growth twins were present as well as multiply twinned grains with five-fold symmetry. Microstructure observation upon annealing showed that grain growth did not occur until annealing at 400ºC. Detwinning was observed at 400ºC and higher temperatures. The ultrafine and nano twins tended to transform into dislocation cell structures and this phenomenon was driven by the excess free energy associated with the high density of grown-in twin boundaries. The five-fold twinned grains were found to be thermally stable up to 600ºC. The hardness was observed to decrease with increasing annealing temperature.

This thesis research investigates the surface properties and performances of gold nanoparticles, microarc oxidation coating, and epitaxial nano-twinned copper film. The research aims to understand the critical behavior of material surfaces in order to facilitate design and development of new materials for tribological applications. The research will focus on improving of the gun barrel performances. Experimental approaches will be used for combining analysis with basic thermal energy transfer principles. Results obtained here will be used for developing new materials to be used in facilitating gun barrels. Experimental approach includes scanning calorimetry-thremogravimetric analysis, tribological testing, and potentiodynamic polarization. The fundamental understanding obtained here will be beneficial for the gun barrel design, manufacturing, and military technologies followed by the results of experiments with different three types of materials. The results of this research showed that the coatings with microarc oxidation and nano-twinned structure improved wear resistance from the tribological examinations and size of AuNPs affected their thermal behaviors measured by differential scanning calorimetry and thermogravimetric analysis method.

Abstract: Oil pollution and spills cause serious damage to marine ecosystems and coastal environments. Currently, oily waters recuperated form a spill must be shipped onshore for treatment. This limits the volume of water that can be treated during a spill. There is a need to develop technologies to treat oily waters below 15 ppm (parts per million) at the site of the spill. Synthetic membrane technologies are widely used in water treatment and purification. They can offer an on-site solution to contaminated oily water treatment in oil production and spills. The suitability of a membrane for use in this application is determined by the type of material used in its fabrication. Compared to polymeric membranes, inorganic membranes are inert to microbiological degradation, offer high chemical and thermal resistance, and can easily be backflushed and cleaned once fouled. However, inorganic membranes consisting of metal oxides are heavier and more expensive than polymeric membranes, due to their bulky and brittle ceramic support layers. This limits their application when the overall weight of a process unit is of concern. A newly developed 2D/3D material, named twinned alumina nanosheets (TAN), has recently been used to make dynamic membranes. The nanoplatelets forming TAN have a length of 4 µm, a width of 1 µm, and a thickness of 100 nm. They have a very high permeability, a 0.2 µm-pore size and a porosity up to 88% due to their low nanosheet volume. These unique characteristics make TAN a very promising material to form membrane selective layers. However, they must be supported on a very open layer in order to take advantage of their high porosity. In this work, a composite membrane was produced with a selective layer of 2D/3D alumina nanoplatelets deposited onto stainless steel meshes and ceramic supports. The structure of the TAN in the selective layer was reinforced with binders. The main objective of this work was to verify the adhesion of the TANs onto the support. The crystallization of TAN was optimized to obtain an open 2D/3D structure. This structure was then deposited on a stainless-steel mesh. The mesh was pretreated by electrochemical etching to achieve a re-entrant surface. The mesh was immersed in an etching solution and placed parallel to a conductive graphite plate under a constant electric potential of 5V for 4 min. Aqueous solutions of silica sol and colloidal silver were tested as binding agents. They were deposited on the mesh with TAN and sintered for 4 hrs. Experiments were performed on testing stainless steel meshes with different opening sizes and comparing different calcination temperatures. The best sintering temperature was 800°C for a mesh with an opening size of 35µm. The synthesized membrane was challenged with a suspension of 10 ppm bentonite clay at a constant pressure of 100 mbar. The integral structure of a TAN membrane produced with a 2.5wt% silica binder was maintained after backflushing. The 2.5wt% silica membrane had a high flux and the particle filtration process for this membrane was modelled as pore constriction and intermediate blocking, indicating that backflushing provided the deep cleaning of pores. According to the SEM images, the 2.5wt% silica membrane preserved the integral structure of the TAN, while the pores tended to fill with silica at higher silica concentrations. The effective pore size of the 2.5wt% silica membrane was estimated to be the smallest, which is approximately 0.53 μm. The 7.5wt% silica membrane had half the permeate flux of the other membranes, because of the high concentration of binder filling the pores of the TAN selective layer. The SiO 2 binder had a positive effect in reinforcing the TAN particles. The flux of the membrane did not increase after backflushing indicating that the selective layer of the membrane was securely bound to the stainless steel mesh. The membrane exhibited flux decline between backflushings indicating that particles were retained on its surface. SEM images taken after the filtration showed that this membrane completely released bentonite particles form its pores. Tests were also performed with a membrane having two TAN coatings on the wire mesh. This reduced the flux but did not improve the retention of fine particles. Colloidal silver was found to be a poor binding agent as particles were released particles from its selective layer. Silica was a highly successful binding agent while colloidal silver was not. TAN was also successfully deposited onto ceramic supports. It was also retained on top of the membrane after backflushing. The results of this work demonstrate that TANs reinforced and bound with silica are a promising type of material to form membrane selective layers. These layers have an open pore structure with a three-dimensional channel connectivity on both stainless steel and ceramic supports. The selective layer was successfully bound to the stainless steel supports. If the pore size of this membrane were to be reduced, it would meet the requirements for use at the site of an oil spill to treat contaminated waters as it does not need the heavier supports found in traditional ceramic membranes. Résumé: La pollution et les déversements d'hydrocarbures causent de graves dommages aux écosystèmes marins et aux environnements côtiers. À l'heure actuelle, les eaux huileuses récupérées d'un déversement doivent être expédiées à terre pour leur décontamination. Ceci limite le volume d’eau contaminé qui peut être traité. Il est nécessaire de développer des technologies permettant de traiter les eaux huileuses en dessous de 15 ppm (parties par million) sur le site du déversement. Les technologies membranaires sont largement utilisées dans le traitement et la purification de l'eau. La possibilité de se servir d’une membrane dans cette application est déterminée par les matériaux utilisés dans sa fabrication. Comparées aux membranes polymères, les membranes inorganiques sont inertes vis-à-vis de la dégradation microbiologique, offrent une résistance chimique et thermique élevée et peuvent facilement être rincées et nettoyées une fois encrassées. Cependant, les membranes inorganiques constituées d'oxydes métalliques sont plus lourdes et plus coûteuses que les membranes polymères, en raison de leurs couches de support en céramique volumineuses et cassantes. Cela limite leur application lorsque le poids total d'une unité de traitement est préoccupant. Un matériau 2D/3D récemment développé, appelé TAN (Twinned Alumina Nanosheets), a récemment été utilisé dans la formation de membranes dynamiques. Les nano-plaquettes formant les TAN ont une longueur de 4 µm, une largeur de 1 µm et une épaisseur de 100 nm. Ils ont une très haute perméabilité, une taille de pores de 0,2 µm et une porosité allant jusqu'à 88% en raison du faible volume des nanofeuilles. Ces caractéristiques uniques font du TAN un matériau très prometteur pour la formation de couches sélectives de membranes. Cependant, ils doivent être déposes sur une couche très ouverte afin de tirer parti de leur grande porosité. Au cours de ce travail, une membrane composite a été réalisée avec une couche sélective de nanoplaques d’alumine 2D / 3D (TAN) déposées sur deux types de supports; des mailles en acier inoxydable et des supports en céramique. La structure du TAN dans la couche sélective a été renforcée avec des liants. L'objectif principal de ce travail était de vérifier l'adhérence des TAN sur le support. La cristallisation des TAN a été optimisée pour obtenir une structure 2D/3D ouverte. Cette structure a ensuite été déposée sur un treillis en acier inoxydable. Les mailles ont été prétraitées pour obtenir une surface réentrante. Le maillage a été immergé dans une solution de gravure et placé parallèlement à une plaque de graphite conductrice sous un potentiel électrique constant de 5 V pendant 4 min. Des solutions aqueuses de sol de silice et d’argent colloïdal ont été testées en tant que liants. Ils ont été déposés sur la maille et frittés pendant 4 heures. Des expériences ont été effectuées sur des mailles en acier inoxydable avec différentes tailles d’ouverture et températures de calcination. La meilleure température de frittage était de 800 ° C pour un treillis ayant une taille d'ouverture de 35 µm. La membrane synthétisée a été mise à l’essai avec une suspension de 10 ppm d'argile bentonite à une pression constante de 100 mbar. La structure intégrale de la membrane couche de TAN produite avec un liant à 2,5wt% de silice a été maintenue après les tests de perméabilité. La structure 3D poreuse a tendance à se remplir de silice à des concentrations de silice supérieures à 2,5wt%. La taille effective des pores de la membrane produite avec 2,5wt% de liant de silice a été estimée à 0,53 µm. Le flux de la membrane n'a pas augmenté après le rinçage, indiquant que la couche sélective de la membrane était liée de manière sûre au maillage en acier inoxydable. La membrane présentait un déclin de flux entre les rinçages indiquant que des particules étaient retenues à sa surface. Les images au microscope à balayage prises après la filtration ont montré que cette membrane libère complètement les particules de bentonite de ses pores. Des essais ont également été réalisés avec une membrane comportant deux revêtements TAN sur le treillis métallique. Cela réduit le flux mais n'améliore pas la rétention des particules fines. L'argent colloïdal s'est avéré être un agent de liaison médiocre car des particules sont libérées de sa couche sélective. La silice était un liant très efficace, contrairement à l'argent colloïdal. Le TAN a également été déposé avec succès sur des supports en céramique. Il est également resté sur la membrane après le rinçage à contre-courant. Les résultats de ce travail démontrent que les TAN renforcés avec un liant de silice sont un type de matériau prometteur pour former des couches sélectives, avec des structures à pores ouverts possédant une connectivité de canal tridimensionnelle, sur des supports en acier inoxydable et en céramique. La couche sélective a été liée avec succès au support en acier inoxydable. Si la taille des pores de cette membrane devait être réduite, elle pourrait être utilisée sur le site d'un déversement d'hydrocarbures pour traiter les eaux contaminées car elle ne nécessite pas les supports plus lourds que l'on trouve dans les membranes de céramique traditionnelles.

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