The scope of this thesis is the study of three Fe(III)-As(V) hydrothermal systems. The first one is the Fe(III)-AsO4-SO4 system and crystalline phases that are produced under high temperature (150-225°C); this was studied to clear up previous contradicting information on this system in relation to industrial arsenic products that are formed during the autoclave processing of arsenical sulphide gold feedstocks and asses their arsenic stability. The second system studied was Cu(II)-Fe(III)-AsO4-SO4 system at 150°C; this was investigated due to its relevance to industrial pressure leaching of copper concentrates. This system was studied in order to examine the possible effect of copper on the precipitation of scorodite. Finally, the structural and molecular examination of two members of the Ca(II)-Fe(III)-AsO4 system, namely yukonite (synthetic and natural and arseniosiderite was undertaken due to their relatively unknown nature and the potential role play in controlling arsenic release in tailings. / La portée de cette thèse comprend l'étude de trois systèmes hydrothermiques Fe(III)-As(V). Le premier système est composé de Fe(III)-AsO4-SO4 et les phases cristallines qui sont produites a haute température (150-225°C) ; celle-ci a été étudié pour élucider l'information précédente contradictoire sur ce système par rapport aux produits arsenicaux industriels qui sont formés pendant le traitement en autoclave de minerais aurifère arsenicaux sulfuré et de la stabilité des produits arsenicaux. Le deuxième système étudié était de Cu(II)-Mg(II)-Fe(III)-AsO4-SO4 à 150°C. Ce système a été étudié due a son importance dan la lixiviation industrielle du cuivre et afin d'examiner l'effet du cuivre sur la précipitation de scorodite. Finalement, l'examen structural et moléculaire de deux membres de la famille des systèmes Ca(II)-Fe(III)-AsO4 et yukonite (synthétique, naturel et arseniosiderite), ont étés observés en raison de leur nature relativement inconnue et de leur potentiel pour contrôler le dégagement d'arsenic dans les résidu

We present a study of the time evolution of the elastic properties of colloidal depletion gels. Silica colloids were suspended in NaCMC solutions and homogenized. Both the colloid volume fraction and the interaction strength (polymer concentration) were varied. The time evolution of the elastic properties of the suspensions was studied with a bulk rheometer in a double-wall Couette cell throughout the gel lifetime. The early lifetime is characterized by an elastic shear modulus that increases logarithmically with time, following which the gels experience catastrophic failure and the elastic modulus drops dramatically. As the gel collapses, various complex behaviors are seen, including a temporary stabilization against collapse, and reformation of a new gel with its own elastic properties which then follows its own trajectory to collapse. Time-lapsed images were taken of identical samples in a separate transparent cell of identical dimensions and the gel height was used to calibrate the measured shear modulus values. The visual cell also allows us to see the sample-spanning collective rearrangement involved in the collapse.

The AZ3, the most common Mg sheet alloy, is currently produced by hot rolling of the DC cast ingot. Mg wrought alloys, in general have limited formability due to hexagonal close-packed structure and preferred orientation (texture). In order to improve magnesium sheet formability, a good understanding of microstructure and texture evolution in twin-roll casting is necessary. The objectives of this research are to study the microstructural and texture evolution in twin-roll cast AZ31 Mg sheet alloy and to develop/modify alloy compositions with improved mechanical properties (weakened texture). In the first part of study, the influence of cooling rate (CR) on the casting structure of AZ31 magnesium alloy has been investigated, as a background to understand microstructural development in TRC AZ31, using different moulds to obtain slow to moderate cooling rates. It was found that grain size and secondary dendrite arm spacing (SDAS) reduces as the cooling rate increases. Moreover, it was observed that with an increase in cooling rate the fraction of second phase particles increases and the second phase particles become finer. The second part focused on the microstructure and texture study of the twin-roll cast (TRC) AZ31 (Mg-3wt.%Al-1wt.%Zn) sheet. The results indicate that TRC AZ31 exhibits a dendritic microstructure with columnar and equiaxed grains. It was noted that the amount of these second phases in the TRC alloy is greater than the conventionally cast AZ31. Recrystallization at 420 oC leads to a bimodal grain-size distribution, while a fine-grain structure is obtained after rolling and annealing. The TRC AZ31 sheet exhibits basal textures in the (i) as-received, (ii) rolled and (iii) rolled-annealed conditions. However, post-annealing of the TRC AZ31 at 420 oC produces a relatively random texture that has not been previously observed in the conventional AZ31 sheet. The texture randomization is attributed to the particle-stimulated nucleation (PSN) of new grains in the TRC structure. The preliminary evaluation of mechanical properties indicates that such annealing treatment slightly increases the ultimate tensile strength (UTS), but significantly improves elongation. In the final of part of the study, the microstructures and textures of rolled and rolled/annealed Mg-1wt.%Mn-based and Mg-1wt.%Zn-Based alloys containing different levels of Ce and Sr were examined. The Ce addition refines the as-cast and rolled/annealed grain structure of Mg-1wt.%Mn (M1) alloy. Moreover, the overall texture intensity of basal pole was weakened for rolled as well as rolled/annealed Mg-Mn-Ce alloys compared to the M1 alloy. The texture weakening was attributed to the solid solubility of Ce in Mg rather than PSN or c/a ratio alteration. The Sr addition refined the as-cast and rolled/annealed grain structure of Mg-1wt.%Mn-Sr (MJ) and Mg-1wt.%Zn (Z1) alloy. Moreover, the overall texture intensity of basal pole was weakened for rolled as well as rolled/annealed Mg-Zn-Sr (ZJ) alloys compared to the Z1 alloy. The texture weakening is attributed to the PSN of new grains with random orientations. / Le AZ3, l'alliage Mg les plus courantes de feuille, est actuellement produite par laminage à chaud de l'lingot coulé DC. Alliages de magnésium forgé, en général, ont limité en raison de la formabilité hexagonale compacte structure et l'orientation préférentielle (texture). Afin d'améliorer la formabilité feuille de magnésium, une bonne compréhension de la microstructure et l'évolution de texture dans la coulée entre cylindres est nécessaire. Les objectifs de cette recherche sont d'étudier l'évolution de la microstructure et de texture dans deux cylindres en alliage fonte AZ31 feuille de Mg et de développer / modifier des compositions d'alliages avec des propriétés mécaniques améliorées (texture affaibli). Dans la première partie de l'étude, l'influence de la vitesse de refroidissement (CR) sur la structure coulée en alliage de magnésium AZ31 des a été étudiée, comme un fond pour comprendre le développement des microstructures du TRC AZ31, en utilisant des moules différents pour obtenir lente à modérée des taux de refroidissement. On a constaté que la taille des grains et secondaire espacement des bras de dendrite (DPS) diminue à mesure que les augmentations de taux de refroidissement. Par ailleurs, il a été observé que, avec une augmentation du taux de refroidissement de la fraction de particules de seconde phase augmente et les particules de seconde phase deviennent plus fins. La seconde partie a porté sur la microstructure et la texture d'étude de la distribution à double rouleau (TRC) AZ31 (% Mg-3wt. Al-1wt.% Zn) feuille. Les résultats indiquent que la TRC AZ31 présente une microstructure dendritique avec colonnaires et de grains équiaxe. Il a été noté que le montant de ces phases secondes dans l'alliage TRC est supérieure à la AZ31 conventionnellement exprimés. Recristallisation à 420 ° C conduit à une bimodale granulométrie, alors qu'une structure à grains fins est obtenue après laminage et recuit. La feuille de TRC AZ31 expositions textures basale dans le (i) que nous avons reçues, (ii) roulé et (iii) laminé recuit conditions. Cependant, le post-recuit de l'AZ31 TRC à 420 oC produit une texture relativement aléatoire qui n'a pas été observé précédemment dans le conventionnelles AZ31 feuille. La randomisation texture est attribuée à la particule stimulée par la nucléation (PSN) de nouveaux grains dans la structure de la TRC. L'évaluation préliminaire des propriétés mécaniques indique que ces traitements de recuit augmente légèrement la résistance à la traction (UTS), mais améliore significativement l'allongement. Lors de la finale d'une partie de l'étude, les microstructures et les textures des laminés et laminé / recuits Mg-1wt.% Mn et Mg-basée 1wt.% Zn-alliages à base contenant les différents niveaux de Ce et Sr ont été examinés. L'ajout Ce affine la structure du grain de coulée et roulé / recuit de Mg-1wt.% Mn (M1) en alliage. Par ailleurs, l'intensité de la texture globale pôle basal a été affaiblie par laminé ainsi que laminé / recuits Mg-Mn-Ce alliages par rapport à l'alliage M1. L'affaiblissement texture a été attribué à la solubilité solide de Cé en Mg plutôt que PSN, ou c / une altération ratio. L'ajout de Sr raffinée que la structure des grains-coulés et laminés / recuit de Mg-1wt.% Mn-Sr (MJ) et Mg-1wt.% Zn (Z1) alliage. Par ailleurs, l'intensité de la texture globale pôle basal a été affaiblie par laminé ainsi que laminé / recuits Mg-Zn-Sr (ZJ) alliages par rapport à l'alliage Z1. L'affaiblissement texture est attribué au PSN de nouveaux grains d'orientations aléatoires.

Recently, group III-nitride nanowire heterostructures have been extensively investigated. Due to the effective lateral stress relaxation, such nanoscale heterostructures can be epitaxially grown on silicon or other foreign substrates and can exhibit drastically reduced dislocations and polarization fields, compared to their planar counterparts. This dissertation reports on the achievement of a new class of III-nitride nanoscale heterostructures, including InGaN/GaN dot-in-a-wires and nearly defect-free InN nanowires on a silicon platform. We have further developed a new generation of nanowire devices, including ultrahigh-efficiency full-color light emitting diodes (LEDs) and solar cells on a silicon platform.We have identified two major mechanisms, including poor hole transport and electron overflow, that severely limit the performance of GaN-based nanowire LEDs. With the incorporation of the special techniques of p-type modulation doping and AlGaN electron blocking layer in the dot-in-a-wire LED active region, we have demonstrated phosphor-free white-light LEDs that can exhibit, for the first time, internal quantum efficiency of > 50%, negligible efficiency droop up to ~ 2,000A/cm2, and extremely high stable emission characteristics at room temperature, which are ideally suited for future smart lighting and full-color display applications.We have also studied the epitaxial growth, fabrication and characterization of InN:Mg/i-InN/InN:Si nanowire axial structures on n-type Si(111) substrates and demonstrated the first InN nanowire solar cells. Under one-sun (AM 1.5G) illumination, the devices exhibit a short-circuit current density of ~ 14.4 mA/cm2, open circuit voltage of 0.14 V , fill factor of 34.0%, and energy conversion efficiency of 0.68%. This work opens up exciting possibilities for InGaN nanowire-based, full solar-spectrum third-generation solar cells. / Récemment, les hétérostructures à base de nitride et de groupe III ont fait l'objet de recherches intensives. Grâce à la relaxation latérale effective du stress, de telles hétérostructures d'échelle nanométrique peuvent être déposés sur du Silicium ou d'autres substrats. Celles-ci démontrent une réduction dramatique des dislocations et des champs de polarisations comparativement à leurs contreparties planes. Cette dissertation rapporte l'accomplissement d'une nouvelle classe de matériau nanométrique, soit des hétérostructures III-nitride incluant InGaN/GaN point dans fils ainsi que des nanofils d'InN presque sans défauts sur du Silicium. De plus, nous avons développé une nouvelle génération de dispositifs à base de nanofils, incluant des diodes émettrices de lumière (LEDs) à efficacité ultra haute et spectre visible complet ainsi que des cellules solaires sur une gaufre de Silicium. Nous avons identifié 2 mécanismes majeurs, incluant le faible transport des trous et le surplus d'électrons, qui limitent sérieusement la performance des LEDs à base de nanofils de GaN. Avec l'ajout de certaines techniques spéciales de modulation de type p, et une couche bloquante d'électrons faite de AlGaN dans la région active de la LED point dans fil. Par ailleurs, nous avons démontré des LEDs blanche sans phosphore qui démontrent, pour la première fois, une efficacité quantique supérieure à 50% ainsi qu'une baisse d'efficacité négligeable jusqu'à ~ 2,000A/cm2 et des caractéristiques d'émissions très hautes et stables à température pièce. Celles-ci sont donc toutes désignées pour des applications d'illumination intelligentes et des écrans pleines couleurs. La croissance par épitaxie, la fabrication et la caractérisation des nanofils d'InN:Mg/i-InN/InN:Si axiaux sur des substrats de Si(111) de type n et démontré la première cellule solaire à base d'InN. Sous l'illumination d'un soleil (AM 1.5G), les dispositifs démontrent une densité de courant de ~ 14.4 mA/cm2 en court-circuit, un voltage de circuit ouvert de 0.14V, un facteur de remplissage de 34.0% et une efficacité de conversion d'énergie de 0.68%. Ce travail ouvre des portes excitantes pour des cellules solaires plein spectre de troisième génération à base de nanofils d'InGaN.

A new process, the DIMOX$ rm sp{TM}$ Process, for making ceramic matrix and metal matrix composites was developed and commercialized by Lanxide Corporation. This technology is based on the use of a unique directed-metal oxidation process to grow ceramic matrices around pre-placed composite fillers or reinforcements. This thesis attempts to offer a good understanding of the mechanism of the process, as well as the effects of the processing parameters on the process, especially in the presence of a reinforcing material. Metal-ceramic matrix composites were grown into four different SiC powders by the directed oxidation of aluminum alloys in air at various temperatures. Microstructure, microstructural evolution, and growth kinetic studies were performed on these composites as a function of alloy compositions, processing temperature, and preform size. The results are then compared to those of composites processed without SiC-reinforcing particles. / The microstructure of the resulting composites consists of three phases: the SiC preform, a continuous $ alpha$-$ rm Al sb2O sb3$ matrix, and a network of unoxidized metal. The microstructural evolution for composites without SiC starts with an incubation period of variable length. The incubation time decreases with increase in the processing temperature and with increase in the alloy silicon content. The addition of silicon in the alloy decrease the viscosity of the melt and therefore increases the rate of metal supply to the reaction front. However increasing the magnesium content resulted only in a slight decrease of the length of the incubation period. / For composites processed with SiC particles, the growth started immediately after introducing the alloy into the hot zone of the furnace. The incubation time was very short and was not sensitive to changes in either temperatures or alloy composition. The preform does not show any evidence of degradation by the molten alloy, however the growth front tends to climb up the surface of the particles. The composite growth rate increased with decreasing in the preform particle size. / The oxidative formation of $ rm Al sb2O sb3$ matrix composites using Al-Mg and Al-Mg-Si alloys exhibits a linear type of kinetics in both the presence and absence of SiC preforms with an activation energy of 224 kJ/mol.

Due to the problems associated with conventional sintering of whisker reinforced $ rm Si sb3N sb4$ composites such as whisker bridging, reaction bonding is being studied as an alternative way to produce such composites. The major advantages of Reaction-Bonded Silicon Nitride (RBSN) over other densification methods such as hot-pressing or sintering lies in the ability to form complex final shapes without diamond machining. Negligible shrinkage of the compacts occurs during the nitridation, resulting in near-net shape RBSN components. / In the present study, the production of green compacts with homogeneous reinforcement distribution was investigated; parameters include viscosity measurements, pH adjustment and consolidation methods (isostatic pressing and slip casting). The nitridation of the Si/SiCw compacts was monitored by a microbalance system which recorded the weight gain during the reaction. Kinetics of nitridation and a study of complete nitridation were carried out. The nitridation process is very sensitive to a change in temperature-time schedule and green density whereas whisker content does not significantly influence the nitridation. A low modulus of rupture value was measured ($ sim$190MPa) due to low nitrided densities ($ sim$75%) and the presence of low density regions associated with whisker bundles.

No description available.

The main objective of this investigation was to study and improve the precipitation characteristics of Ni(OH)2 in a sulphate system at various temperatures and pHs. Solubility tests were performed by dissolving crystalline Ni(OH)2 at constant pH and temperature for various test conditions. These results were then utilised to design alternative precipitation strategies with the objective of producing clean and easily filterable nickel hydroxide. Homogeneous Ni(OH)2 precipitation was performed using NaOH solution and MgO slurry at various temperatures and pHs in pure and impure aqueous systems. Ni(OH)2 was also produced by using controlled supersaturation technique in order to improve product quality. The use of supersaturation control improved particle morphology, crystallinity, settling rates and % solids density; however, sulphate and magnesium uptake was not eliminated by this precipitation technique.

This research project aimed at the development of a PECVD process for the deposition of C60-PPPE (plasma polymerized polyethylene) NC thin films. A continuous throughput PECVD system was designed for the co-deposition of a polymer matrix and C60 particles, in effect, yielding composite thin films on 1" quartz and silicon substrates. In this process, the C 60 molecules are sublimated from their solid powder form, transported to the plasma chamber, pre-coated in-flight before being dispersed and co-deposited in the polymeric matrix. The plasma polymerization of ethane in the low pressure, radio frequency (RF) plasma was studied with a mapping of the polymer thin film growth at various deposition times. Percentage coverage of C60 films was studied at several sublimation temperatures ranging from 500-750 °C. Compositional studies of PPPE and C60 films obtained were carried out using FPA-FTIR. The surface morphology and topography of composite films was analyzed using OM and FESEM. Furthermore, samples of C60 deposited in the reactor were analyzed via TEM for possible deagglomeration and nanocoatings.

The misorientations between FCC and BCC crystals are characterized according to the common lattice correspondence relationships in terms of their parallelism conditions. Individual variants of the six models, namely the Bain, Kurdjumov-Sachs, Nishiyama-Wassermann, Pitsch, Greninger-Troiano and inverse Greninger-Troiano relations, are identified and represented in both pole figure form and in Rodrigues-Frank space with respect to various coordinate frames. In this way, the relations between the variants of these models are clarified. / The orientations of the kamacite (BCC) lamellae transformed from a single prior-taenite (FCC) grain in the Gibeon meteorite were measured by analyzing the electron backscatter diffraction patterns. The local misorientations between individual FCC and BCC crystals along their common interfaces were computed and are compared with the common lattice correspondence relationships. The orientation relations between the alpha and gamma phases in the plessite regions are also characterized. The Neumann bands (mechanical twins) and their orientation variations within individual kamacite lamellae were studied and analyzed. / A Nb-bearing TRIP steel was control rolled and a certain amount of austenite was retained through appropriate heat treatment. EBSD measurements were conducted on specimens deformed to various reductions and the textures (ODF's) of both the gamma and alpha phases were obtained from the measured data points. The orientations of the bainite formed within individual prior-austenite grains are compared to those expected from the common correspondence relationships and the average orientation of the prior-austenite grain. The crystallography of the bainite laths within a single packet is also characterized. / The orientations of the bainite formed from individual prior-austenite grains are analyzed with respect to their parent orientations. The occurrence of variant selection at the grain scale was examined using a dislocation-based model. The model considers the role of the slip systems that were active during prior deformation, as well as those of in-plane reaction, cross-slip and the partial dislocations that are linked to specific variants. In this model, the K-S and N-W correspondence relations are united through the dissociation of perfect dislocations. The variants in more than 70% of the grains examined are reasonably well predicted by this model.