The importance of aluminum nitride (AlN) stems from its application in microelectronics as a substrate material due to its high thermal conductivity, high electrical resistance, mechanical strength and hardness, thermal durability and chemical stability. Yttria (Y2O3) is the best additive for AlN sintering, which undergoes densification through a liquid phase mechanism. The surface oxide, Al2O3, reacts with the oxide additive, Y2O3, to form a Y-Al-O-N liquid that promotes particle rearrangement and densification. Construction of the phase relations in this multicomponent system is becoming essential for further development of AlN. / Binary diagrams of A2O3-Y2O3, AlN-Al2O3, and AlN-Y2O3 were thermodynamically modeled in this work. The obtained Gibbs free energies of the components, stoichiometric phases and solution parameters were used for the calculation of the isothermal sections and liquidus surface of the AlN-Al2O 3-Y2O3 system. Phase evolutions, melting and solidifications in the Al2O3-Y2O3 phase diagram were investigated using x-ray diffraction and in situ high temperature neutron diffractometry. The phase diagram of AlN-Y2O 3 system was established and verified experimentally. The predicted ternary phase diagram for AlN-Al2O3-Y2O 3 was also verified experimentally using in situ high temperature neutron diffractometry and it has been constructed for the first time in this work. / A self-consistent thermodynamic database including all the phases in the AlN-Al2O3-Y2O3 system was developed during the course of this project. This database was used to explain the experimental results of AlN sintering. It has been found that the samples with high densities had lower liquid formation temperatures, and low thermal conductivity was related to the residual Al2O3 and high YAP (Al2O3.Y2O3) content.

During sintering, $ rm Si sb3N sb4$ transforms through a liquid phase from the metastable $ alpha$ phase to the stable $ beta$ phase. In this work, $ rm Y sb2O sb3, Al sb2O sb3$ and AlN were added as liquid-forming additives, which react with surface SiO$ sb2$ on the $ rm Si sb3N sb4$ particles. The mechanism of pressureless sintering $ rm Si sb3N sb4$ with these additives was a combination of particle rearrangement, solution-precipitation and elimination of closed porosity. The rate of densification and $ alpha$-$ beta$ phase transformation were strongly influenced by the amount and viscosity of liquid phase. The kinetics suggested that the rate of densification increased with $ rm Al sb2O sb3$ content, since the higher viscosity of the liquid provided more capillary pressure. On the other hand, the rate of transformation was improved by a higher $ rm Y sb2O sb3$ content, because of the increased rate of solution and diffusion in the low viscosity liquid environment. In addition, AlN decreased the rates of both densification and transformation, due to its low solubility in the liquid phase. / A morphology analysis was carried out on the samples sintered in the range 1600$ sp circ$C to 1900$ sp circ$C and at 1850$ sp circ$C for various soaking times. The coarsening process of the $ beta$ grains occurred with increasing temperature. Moreover, the $ beta$ grain aspect ratio and size distribution also increased with prolonged sintering. The formation of $ beta$ phase indeed improved the mechanical properties of the materials, however, excessive grain growth led to microcracking, which decreased the strength. The best values were obtained at 1850$ sp circ$C for one hour and corresponded with 98% theoretical density and 100% $ beta$ structure. At higher temperature, the strength decreased, due to decomposition of the $ rm Si sb3N sb4.$

This investigation considers the influence of manufacturing on a composite material's resistance to delamination. Mixed-mode toughness data was measured for a five harness satin (5HS) carbon/epoxy manufactured by resin transfer moulding (RTM). The effect of fibre volume fraction on both initiation and propagation fracture toughness was also determined. Fibre volume fractions of 57% and 66% were considered under Mode I (interlaminar tension), Mode II (interlaminar shear) and Mixed-Mode I-II loading of 25%, 50% and 75%. Flat rectangular plates, from which specimens were obtained, were manufactured by RTM. Double cantilever beam (DCB) specimens were used for Mode I and Mixed-Mode I-II, following ASTM standards D5528 and D6671. End-notched flexure (ENF) specimens were used for Mode II. Initiation toughness therefore increased as the contribution of Mode II towards Mixed-Mode I-II delamination growth increased. Important toughening mechanisms were observed in all cases, which resulted in propagation fracture toughness being at least 200% higher than initiation fracture toughness. The dominant mechanism responsible for fracture work was the energy dissipated in creating and translating the crack tip damage zone across a non-planar path. The increase in fibre volume fraction decreased initiation fracture toughness at all mixed-mode ratios, and increased propagation fracture toughness at high Mode I contributions towards Mixed-Mode I-II delamination growth. Increasing the fibre volume fraction had no effect on propagation fracture toughness at a Mixed-Mode ratio of 75%. Additionally, the Virtual Crack Closure Technique (VCCT) implemented in Abaqus® was evaluated as an analysis tool to model the initiation and growth of delaminations in composites. Two finite element models of DCB specimen were built (2D and 3D). The material's delamination behavior was governed by the mixed-mode fracture data measured experimen / Ce projet visait à étudier l'influence du procédé de fabrication sur la capacité d'un matériau composite à résister au délaminage. Les données en mode mixte ont été mesurées pour un composite avec une résine d'époxy et un tissu de carbone d'armure satin à cinq harnais (5HS carbon/epoxy), fabriqué à l'aide du moulage par transfert de résine (RTM). L'effet du pourcentage volumique de fibre sur la ténacité à la rupture, à l'initiation et à la propagation, a également été déterminé. Des pourcentages volumiques de 57% et 66% ont été considérés en Mode I (tension interlaminaire), en Mode II (cisaillement interlaminaire) et en Mode-mixte I-II à 25%, 50% et 75%. Des plaques rectangulaires ont été fabriquées par RTM, desquelles tous les échantillons ont été découpés. Des échantillons en double poutre encastrée (DCB) ont été utilisés pour les essais en Mode I et en Mode-mixte, selon les standards ASTM D5528 et D6671. Des échantillons de type end-notched flexure (ENF) ont été utilisés pour les essais en Mode II. La ténacité à l'initiation de la rupture a donc augmenté lorsque la contribution du Mode II a été augmentée lors des essais en Mode-mixte. Des mécanismes de renforcement ont été observés dans tous les cas, faisant en sorte que la ténacité à la propagation de la rupture était au moins 200% plus élevée que la ténacité à l'initiation de la rupture. Le principal mécanisme responsable du travail de rupture était la dissipation d'énergie associée à l'avancement de la fissure le long d'un chemin non-planaire. Ceci est caractéristique des composites tissés. L'augmentation du pourcentage volumique de fibre a fait diminuer la ténacité à l'initiation de la rupture dans tout les cas, et a également fait augmenter la ténacité à la propagation de la rupture lorsque la contribution du Mode I en Mode-mixte était élevée. L'augmentation du t

In recent years the magnesium application in automobile sector has been increasing. Recent research and development studies of magnesium and its alloys have focused on weight reduction, energy saving and limiting environmental impact. In this regard researchers have identified incorporating certain key alloying elements like Al, Zn, Si, Pb, Ge, Bi, Sb, Sr, etc. to the magnesium alloys.These alloying elements are seen as potential elements for novel magnesium alloy design with superior structural properties to the existing alloys used for automotive applications. The continued developments in CALPHAD (Chapter 2) assessment of alloys (and other materials) brought about the development of thermodynamic databases. These databases contain the Gibbs free enegy description of all the phases present in a system with respect to temperature and composition. With the use of Gibbs energy minimization software such as FactSage one can have access to these databases to calculate the amounts and compositions of all phases at equilibrium at any temperature and composition in multicomponent alloys, the amount of phases appearing during equilibrium or non-equilibrium cooling can be calculated too. Such thermodynamic databases are prepared by critical evaluation, modeling, and optimization. In a thermodynamic ''optimization'' adjustable model parameters are calculated using, simultaneously, all available thermodynamic and phase-equilibrium data in order to obtain one set of model equations as functions of temperature and composition. Thermodynamic data, such as activities, can aid in the evaluation of the phase diagrams, and information on phase equilibria can be used to deduce thermodynamic properties. Thus, it is frequently possible to resolve discrepancies in the available data. From the model equations, all of the thermodynamic properties and phase diagrams can be back-calculated, and interpolations and extrapolations / Ces dernières années, l'usage du magnésium dans le secteur de l'automobile a été en croissant. Les études récentes en recherche et développement du magnésium et de ses alliages se sont surtout concentrées sur la réduction de poids, l'économie d'énergie et la limitation des impacts environnementaux. À cet égard, les chercheurs ont identifié certains éléments clés comme Al, Zn, Si, Pb, Ge, Bi, Sr, etc. qui peuvent être incorporés aux alliages de magnésium. Ces éléments sont perçus comme de première importance dans le design de nouveaux alliages de magnésium ayant des propriétés structurales supérieures comparés aux alliages présentement existants dans l'industrie automobile.Les améliorations continues dans la modélisation des alliages (et autres matériaux) par la technique CALPHAD a conduit au développement de banques de données thermodynamiques. Ces banques de données contiennent la description de l'énergie libre de Gibbs pour toutes les phases présentes dans le système par rapport à la température et la composition. En utilisant des logiciels de minimisation de l'énergie libre de Gibbs tel que FactSage, il est possible d'avoir accès à ces banques de données pour calculer les quantités et les compositions de toutes les phases à l'équilibre à n'importe quelles température et composition dans des alliages à plusieurs composants ou encore pour calculer la quantité des phases à l'équilibre ou non durant le refroidissement.De telles banques de données thermodynamiques sont conçues grâce à des évaluations critiques, des modélisations et des optimisations. Lors d'une optimisation thermodynamique, les paramètres ajustables du modèle sont calculés en utilisant simultanément toutes les données thermodynamiques et du diagramme de phases afin d'obtenir un ensemble d'équations du modèle en fonction de la température et de la composition. Les donnée

The process of superplastic forming in 7475 aluminum alloy was analyzed using orientation imaging microscopy (OIM), x-ray diffraction and scanning electron microscopy (SEM). These techniques were used to determine the effect of the superplastic forming on texture, grain boundary character distribution (GBCD), grain size, residual stress and microstructure at different stages of the deformation of specimens deformed in tension. Results indicate that a microstructure is transformed mainly by the grain boundary sliding process that is responsible for rapid randomization of texture. There is also much evidence for crystallographic slip occurring in conjunction with grain boundary sliding. Accommodation of superplastic flow is linked to increased dislocations density in the lattice. At a threshold level, the dislocation density reaches certain saturation level and the nucleation of voids starts. At this threshold strain, the deformation mechanism is altered and superplastic flow proceeds, however, cavities continue to be produced and coalesce due to the grain boundary sliding process. A precipitate free zone is observed during deformation. This zone is more plastic and presents an orientational difference when compared to the grain interior. It is theorized that this precipitate free zone aids in the accommodation of GBS and plays a role in the cavitation process. The Kernel average misorientation function of OIM was used to indicate the level of strain within the grains to explain the formation of cavities.

In niobium (Nb) microalloyed steels one of the strengthening mechanisms is precipitation of Nb(C, N). Precipitation in austenite has been studied and applied for many decades, but its precipitation in ferrite has been paid less attention. Some of the findings are somewhat contradictory. / Due to environmental and resource saving consideration in recent years, more and more scrap has been recycled and re-used. Thus, tramp elements inevitably exist in steel such as Cu, Sn, Ni and so on. These elements may influence properties of steels at some extent although they are very little in content. / The X80 steel examined in this thesis contains up to 0.09%wt. Nb, as well as 0.4% Cu, both of which can potentially precipitate in ferrite. However, most research has shown that Cu levels below 0.5% in steel do not precipitate out under normal processing conditions. / In the present work, this X80 steel was processed by a variety of thermomechanical treatments. The as hot deformed mechanical properties were tested and microstructures were characterized by field emission gun scanning electron microscopy (FEG-SEM). At low aging temperatures, simulating the coiling stage in steel hot rolling, many fine Cu precipitates were observed in ferrite compared to a few relatively large Nb containing precipitates. These results were rationalized, and the consequences were discussed.

Recent interest in hydrogen as an energy source has resulted in development of new technologies such as non-thermal plasma processing of natural gas. We report the development of a process yielding hydrogen from natural gas that generates no green house gases and thus meets the Kyoto accord targets. / In this process, natural gas is treated in a dielectric barrier discharge (DBD) yielding hydrogen and solid carbon according to the following reaction: CH4 (g) → 2H2 (g) + C (s). The direct cracking of the hydrocarbon is possible if the natural gas is injected in the plasma zone, created by the presence of a dielectric ceramic material. / It was found that the dielectric material plays an important role on plasma intensity. The change in ceramic properties affects the parameters of the discharge. It was discovered that the number of micro-discharges increased when a ceramic with a higher dielectric constant was used. Furthermore, the ceramic relative permittivity or dielectric constant has a direct influence on the hydrogen yield. / However, the challenge is that when using a commercial high dielectric ceramic as barrier they tend to break in the plasma environment. In the attempt of improving the process efficiency medium permittivity dielectric ceramics (9 < K' <166) were fabricated and successfully tested in the discharge reactor. A broad variety of ceramics (from low to high permittivity) were tested and the results suggested that the CH4 conversion using high dielectric constant barrier is much higher than using conventional barrier material such as A12O3.

Frothers are surface-active agents used in flotation to decrease bubble size and promote froth stability. The common frothers are alcohols and polyglycols. One means to classify frothers is by the extent of bubble size reduction. Bubble size measurement is labour-intensive and this thesis explores the use of gas holdup as a surrogate for bubble size. / Nine frothers with different chemical structures were tested in a bubble column equipped with instrumentation to measure bubble size and gas holdup. A correlation between frother structure and gas holdup is observed: for alcohols, gas holdup increases with hydrocarbon chain length and whether branched or straight chain does not seem to matter; and for polyglycols, gas holdup increases with number of propoxy groups. The ranking of the frother on the basis of gas holdup is the same as that given by other methods. The assumed unique relationship between gas holdup and bubble size is examined. For a given frother the relationship appears to hold. Evidence is presented that the continued increase in gas holdup at high frother concentration is correlated with a continued decrease in bubble size. When comparing frothers, however, it is shown that for equal gas holdup bubble size can be quite different. The effect is discussed in terms of bubble velocity in the swarm.

The overview of the history of quantitative x-ray microanalysis shows the efficiency of the use of standards to achieve the most reliable quantification. State-of-the-art cold field emission gun scanning electron microscopes offer excellent resolution but lack a sufficient level of beam current stability essential for reliable quantitative microanalysis. The purpose of this work is to develop a new method for quantitative x-ray microanalysis adapted to unstable beam current conditions. / In the Cliff and Lorimer method, which was developed for the analytical transmission electron microscope, the composition was calculated from the ratio of the characteristic x-ray intensities of two elements in the same spectrum. In this work, this ratio method is applied to bulk specimens in a scanning electron microscope (SEM). In order to reduce the amplitude of error propagation, the proposed ratio for SEM quantitative microanalysis is the intensity of a x-ray divided by the sum of intensities of one or more characteristic lines of each of tire elements found in the specimen. Moreover, the calculated x-ray intensities are corrected for the effects of absorption, fluorescence and Coster-Kronig yields, and other physical factors normally considered in microbeam analysis. Uncertainties in physical parameters and models, clue to the lack of exhaustive measurements as well as their scattering, revealed by a disaggrement between the measured and calculated ratios, are minimized by the use of a calibration factor inserted into the ratio. This calibration factor is determined using a standard for a given element. It can be used as often as needed and allows for the correction of uncertainties in the x-ray detector efficiency. In order to quantify the specimen, the measured experimental ratio is compared to a simulated ratio with the appropriate calibration factor. The composition is interpolated from the theoretical ratio curves. Two methods of calculation of emitted x-ray intensity are proposed, by analytical calculations using the Pouchou and Pichoir model or by an in-house developed Monte Carlo simulation program. Two sets of National Bureau of Standards (NBS) microanalysis standard reference materials, AuCu (SRM 482) and AuAg (SRM 481), are used to validate this method. / The comparison of calculated composition with the nominal one underlines the need for a beam-energy-dependent calibration factor, particularly because of ionization cross-section uncertainties. The use of high energy characteristic x-ray lines (above 5 keV) permits accuracy around 3% with a beam-energy-dependent calibration factor. The effects of beam energy, ionization cross-section models, mass-absorption coefficients and x-ray generation methods are compensated by the appropriate calibration factor. The change of the family of characteristic lines affects the accuracy. Finally, as in any quantitative microanalysis, the use of a filter to extract the characteristic intensity causes errors for low energy peaks. The analysis of the effect of calibration factors and mass-absorption coefficient enhances the need for refining the x-ray generation and emission parameters. / The error propagation is less important than if using the classical Cliff and Lorimer method in a SEM. However, the use of appropriate calibration factors and pair of lines offers promising accuracy in almost any conditions. This method is independent of the beam current, which is the purpose of this work. Despite many uncertainties of physical parameters, this method offers an efficient and reliable alternative to quantitative x-ray microanalysis with any electron microscope. Although developed for a binary material, the method can be extended to heterogeneous, rough, multiple-component materials, inasmuch as it can be simulated with a Monte Carlo program or any other method that computes characteristic x-ray lines intensities.

Comminution is a process used in mineral processing for the size reduction of mined material, to permit effective handling, separation and recovery. The equipment used is kinetically complex, with very high-energy impacts and high forces, leading to great amounts of abrasive wear. It is desired to develop a better understanding of these processes, to both measure them and increase comminution while reducing wear. The Steel Wheel Abrasion Test is a laboratory technique used to generate controlled, abrasive three-body wear. By altering the applied force, rotational speed of the wheel and abrasive agent used in the SWAT, the wear behaviour of a material can be quantified. High-stress wear, which occurs when abrasive material is degraded during the test, can replicate the processes occurring in comminution systems. This work has found that abrasive wear will increase with increasing input energy into the tribological interaction. This wear can be linked to the energy input into the system, through the measurement of applied forces, wheel rotational speed and generated torque. This results in the development of a specific abrasion energy, EAS, which provide an energy metric for the abrasion process. Furthermore, the breakage induced in the abrasive particles can also be quantified and evaluated, generating a comminution metric, the specific comminution energy, ECS. These indices can then be linked, to develop an understanding of systems where comminution and abrasion occur concurrently. / La communition est un procédé utilisé dans l'industrie minéralurgique pour la réduction de taille d'un minerai, afin de permettre le transport, la séparation, la récupération et l'extraction de ce matériel. L'équipement utilisé pour cette tâche est complexe, soumis à des forces élevées et des impacts violents, ce qui génère une quantité importante d'usure. Une plus grande connaissance des processus de comminution et d'usure est nécessaire pour pouvoir évaluer leur amplitude, dans le but de favoriser la comminution tout en minimisant l'usure. Le test d'abrasion par roue d'acier (SWAT) est une technique de laboratoire utilisée pour générer de l'usure abrasive à trois composantes. En contrôlant la force appliquée, la vitesse de rotation de la roue et l'agent abrasif employé lors du test SWAT, il est possible d'évaluer la réponse d'une surface à l'abrasion. L'usure de haut stress, générée dans les systèmes où les agents abrasifs sont fracturés, peut répliquer les procédés présents dans l'équipement de communition. Ce projet a trouvé que l'usure abrasive augmente avec une augmentation de l'énergie investie dans l'interaction tribologique. Cette usure peut être liée à l'énergie du système, en mesurant les forces appliquées, la vitesse de rotation de la roue et la torsion générée. Ces valeurs peuvent être utilisées pour calculer une valeur spécifique d'énergie d'abrasion, EAS, qui agit comme indice pour le procédé d'abrasion. De plus, la fragmentation créée dans les particules abrasives peut être évaluée, pour générer un indice de communition, ECS, l'énergie spécifique de communition. Ces deux indices peuvent être liés, pour rejoindre les procédés de communition et d'abrasion.