AbstractAbout 300 million tonnes of inferred Ni resource in ultramafic hosted rocks is present in 'Thompson Nickel Belt' in north central Manitoba. The processing challenges result from electrostatic interaction between pentlandite (the main Ni-mineral) and serpentine (the main gangue and one of the MgO minerals). As a contribution to meeting the challenge, the thesis examines the role of particle and bubble surface charge and the effect of fibre disintegration on flotation behavior of an ultramafic Ni ore sample. For surface charge characterization the sedimentation potential technique was used. A novel integrated device was developed to measure sedimentation potential, conductivity and pH simultaneously. Maxwell's model was used to calculate volume fraction of dispersed phase from conductivity, and zeta potential, when appropriate, was calculated from the Smoluchowski equation. The technique was validated by showing good agreement with iso-electric point for alumina, silica and bubble suspensions with electrophoresis measurements. The technique was extended to characterize mixed minerals including ultramafic ore, and bubbles in the presence of particles. The results provided some evidence of metal ion adsorption on particles and the possibility of non-hydrophobic particle attachment to bubbles. The latter was reinforced by visualization studies of a pendant bubble exposed to particle suspensions.A novel fibre disintegration strategy was devised combining both chemical (acid) and physical (grinding) treatment based on work to enhance carbon dioxide uptake by serpentine. Using HCl, subsequent conventional flotation (amyl xanthate, soda ash and MIBC) gave significantly improved results over the untreated ore. Using H2SO4, arguably the practical option led to flotation without collector due to elemental sulphur formation on pentlandite, and without frother due to high ionic strength solutions. Improved Ni grade-recovery with higher MgO mineral rejection was achieved. Structural changes in the fibres were followed using various spectroscopic techniques and a mechanism of fibre disintegration suggested. / Environ 300 millions de tonnes de ressources inférées de Ni ultramafiques hébergé est présent dans 'ceinture nickélifère de Thompson' dans le centre-nord du Manitoba. Le traitement des défis résultant de l'interaction électrostatique entre pentlandite (le principal Ni-minéraux) et la serpentine. En tant que contribution à relever le défi, la thèse examine le rôle des particules et la charge de surface des bulles et l'effet de la désintégration des fibres sur le comportement de flottaison d'un échantillon de minerai de nickel ultramafiques. Pour la caractérisation de charge de surface de la technique de sédimentation potentielle a été utilisée. Un nouveau dispositif intégré a été développé pour mesurer le potentiel de sédimentation, la conductivité et le pH simultanément. Le modèle de Maxwell a été utilisée pour calculer la fraction volumique de phase dispersée de la conductivité, et le potentiel zêta, le cas échéant, a été calculée à partir de l'équation de Smoluchowski. La technique a été validée en montrant un bon accord avec l'iso-électrique de point pour les suspensions d'alumine, de silice et de bulles avec des mesures d'électrophorèse. La technique a été étendue afin de caractériser les minéraux mélangés, y compris de minerai ultramafiques, et des bulles dans la présence de particules. Les résultats ont fourni des preuves de ion métallique adsorption sur les particules et la possibilité de l'attachement des particules non-hydrophobe à bulles. Ce dernier a été renforcée par des études de la visualisation d'une bulle Pendentif exposés à des suspensions de particules.Une stratégie nouvelle fibre de désintégration a été conçu combinant à la fois chimique (acide) et physiques (broyage) un traitement basé sur le travail pour améliorer l'absorption du dioxyde de carbone par la serpentine. En utilisant HCl, à la suite de flottation conventionnelle (amyl xanthate, la cendre de soude et de MIBC) a donné des résultats nettement améliorés au cours des minerais non traités. Utiliser H2SO4, sans doute l'option la pratique conduit à de flottaison sans collecteur due à la formation du soufre élémentaire sur la pentlandite, et sans buse due à des solutions à haute force ionique. Amélioration de qualité Ni-reprise avec le rejet supérieur de MgO de a été atteint. Les changements structurels dans les fibres ont été suivis en utilisant diverses techniques de spectroscopie et d'un mécanisme de désintégration de fibre suggéré.

In the processing of steels, various types of alloy compositions and heat treatments have been used to improve strength and ductility. Unfortunately, these methods are usually accompanied by a decrease in formability. It has been well recognized that the presence of retained austenite, in microstructures which include ferrite and bainite, can significantly strengthen the steel and improve ductility by transforming to martensite under an applied stress or strain. This is the basic principal behind the TRIP (transformation-induced plasticity) effect. / In this work, the effects of thermomechanical processing (TMP) and chemical composition on the structure and properties of C-Si-Mn TRIP steels were investigated. It was found that the addition of Nb to these steels not only increases the volume fraction of retained austenite, but also improves the total elongation and tensile properties. It was also revealed that the combination of strength and ductility is further optimised by varying the C content in the steel. For C-Si-Mn Nb-bearing TRIP steels, the bainite transformation conditions are the critical parameters in dictating the final mechanical properties. / The effects of retained austenite characteristics on the mechanical properties were examined. Although the retained austenite volume fraction is indeed a key factor in controlling the final properties, there are other parameters that must be considered, such as the morphology, particle size, solute enrichment and the mechanical stability of the retained austentite. In this work, the approach involved a systematic investigation of the effects of TMP parameters on the state of the retained austenite characteristics and finally, an evaluation of the final mechanical properties. It was revealed that, for a given ferrite/bainite structure, the tensile strength and total elongation are controlled by the volume fraction and the mechanical stability of the retained austenite. Increasing the mechanical stability of retained austenite leads to transformation at higher strains. (Abstract shortened by UMI.)

In order to deal with the negative impacts associated with disposal of used oils by thermal remediation, a study of the material under combustion-like conditions was undertaken. Two used motor oils were subjected to slow heating using a Thermogravimetric Analyzer coupled with a Fourier Transform Infrared Spectrometer. Based on the results obtained, mechanisms of the general transformation process the oil undergoes and the evolution of the solid particles were proposed. The presence of Polycyclic Aromatic Hydrocarbons (PAHs), considered hazardous, was observed and individual PAHs were identified. The results show that initial oxygen content in the oil plays a significant role in the thermal remediation process, primarily leading to smaller, more compact final residues. This may have significant implications In terms of leachability of toxic metals. The insight gained here can be utilized in further studies to understand and then possibly control, the process in practical combustion systems.

Powder metallurgy (P/M) processing has become an important technique replacing many casting applications, especially for the fabrication of refractory metals where very high melting temperatures are required. Improvement in powder production, cleanliness and characterization techniques, combined with an increased understanding of basic compaction and sintering principles and a need for metals with high strength to weight ratios has led to an increased interest in titanium powder utilization. P/M techniques for Ti-6Al-4V powder can enable the production of high quality parts at lower processing temperatures and cost. For most applications prealloyed powder produced by the hydride-dehydride process (HDH) is used, due to the lower cost of this powder as compared to Ti-6Al-4V powder produced by other methods. / General characterization of a Ti-6Al-4V HDH powder and the effects of using a zinc stearate on the green and sintered density were examined at different compaction pressures and sintering temperatures. (Abstract shortened by UMI.)

The concentration of hydrogen is one of the most important parameters in liquid aluminum processing because it is responsible for gas porosity which affects casing quality, ie. pressure tightness, mechanical properties etc. In order to gain optimum quality, the amount of hydrogen dissolved in liquid aluminum must be known prior to casting. This has led to the development of several techniques to quantify hydrogen in liquid aluminum. Among these is the Reduced Pressure Test (RPT). The RPT is simple, very inexpensive and commonly used in aluminum foundries to obtain a qualitative evaluation of the melt hydrogen level. / In this thesis the development of the RPT to a truly quantitative level is discussed. This includes redesigning of the steel mold and the application of a riser. The mold was redesigned to improve the test sensitivity while a CO$ sb2$-bonded sand riser was applied in order to eliminate volumetric shrinkage and ensure a constant volume sample. As the sample has a constant volume, either the sample weight or density can be used to quantify the hydrogen content. The simplest technique is to use the sample weight. / Several parameters that affect the test sensitivity and reproducibility were studied, such as chamber pressure, amount of inclusions, pouring temperature, and mold temperature. It was found that there are two important parameters that strongly affect the test; chamber pressure and amount of inclusions. The lower the chamber pressure the better the test sensitivity but the poorer the test reproducibility. Increasing the amount of inclusions improves the test sensitivity. / The constant volume sample can be used to predict the amount of hydrogen in the melt for various types of alloys including 319, 356, 357 and 413 within a reasonable margin of error. The error as measured by this technique was found to be in the range of $ pm$0.025-0.049 ml./100 g.Al. if the sample weight is used, and in the range of $ pm$0.025-0.047 ml./100 g,Al. if the sample density is used. / A simple mathematical model based on a mass balance approach was developed to calculate pore size and sample density. The model predicts the density accurately for various types of alloys and different melt treatments.

A new application of heat pipes is introduced. The present research deals with the development of a heat pipe for the on-line quality control of liquid aluminum silicon foundry alloys. / Thermal analysis is a technique whereby a small quantity of a melt is allowed to solidify while its cooling curve is recorded. Analysis of the cooling curve with standard mathematical algorithms allows one to determine a number of useful parameters that characterize the liquid and solid states of the material. In aluminum-silicon casting alloys thermal analysis is often used to assess the grain size and degree of eutectic modification of the alloy before pouring. / A novel probe has been developed for conducting thermal analysis of aluminum alloy melts. The probe, which resides in the melt, need not be withdrawn as it solidifies a small sample (i.e. button) at a predetermined cooling rate. Once the cooling curve results have been acquired, the probe can be instructed to remelt the frozen button and await instructions for analyzing a fresh sample. / The operating principle of this novel device is based on heat pipe technology. In simple terms, a heat pipe consists of a condenser and an evaporator which contain a relatively small quantity of working substance fluid. As heat is absorbed by the evaporator, the liquid phase of the working substance is vaporized and subsequently condensed on the condenser walls from which heat is extracted. / It has been shown that the designed probe, which is classified as a gas loaded annular thermosyphon, is completely workable in the range of conditions typically encountered in the thermal analysis of aluminum alloys. The thermal analysis results obtained with this new technique are in a good agreement with those of conventional thermal analysis. In addition, the new method is applicable to a wider range of operating conditions and is easier to use. Based on the semi-continuous nature of the new method, it does not need pre-preparation (materials, labour, pre-heating, thermocouple installation for each test, isolation of the sampling cup, etc.) to start thermal analysis. Also, from a cooling rate point of view, the system is well controllable. Moreover, it is shown that the probe is simple in construction, easy to use, and intelligent enough to provide semi-continuous thermal analysis. There are no consumable materials and moving parts. / Thermal analysis results are reported for pure aluminum, hypoeutectic aluminum silicon (356) and eutectic aluminum silicon (413) casting alloys. Agreement in the results between the new and conventional systems is shown to be excellent. Finally, a heat transfer/solidification model of the heat pipe thermal analysis probe is derived and validated.

Fluid flow and filtration phenomena associated with filtration of liquid aluminum using reticulated ceramic filters were systematically investigated. It was found that fluid flow through this type of filter could be described by Darcy's Law up to a Reynolds number of 8, and the permeability of this type of filter ranged from about $9 times10 sp{-3}$ to $4 times10 sp{-2} rm mm sp2$. / Parameters affecting filtration processes during the initial period were identified, some of which could be quantified numerically using a 2-D computational domain. According to these numerical analyses, the clean filter coefficient for this type of filter was linearly dependent on the dimensionless Stokes velocity of the suspended particles, had a $-$0.96 power dependence on the Peclet number, a $-$6.93 power dependence on the effective porosity of the filter, and exhibited only a weak dependence on the Reynolds number, in the Darcy velocity regime. / The dynamic behaviour of this type of filter was analyzed theoretically and simulated numerically using newly proposed correlations relating the filter coefficient and the pressure drop to the amount of particles captured within the filter (the specific deposit), and a model describing the morphology of captured particles. The simulated results showed that the filtration efficiency and the pressure drop increased with inlet particle concentration and filtration time; these increases were however, insignificant when the inlet particle concentration was less than 1 ppm for filtration periods of two hours, however, when the inlet concentration (initial and continued) reached 10 ppm, the change became appreciable. / Experimental data, obtained from liquid aluminum filtration tests conducted by the author in both laboratory and industrial settings, compared favourably with the numerical results.

Oxidation experiments were carried out on six different aluminum alloy compositions in order to determine the effects that silicon, strontium, and magnesium have on the oxidation behavior at temperatures between 700 and 800°C. This was determined through weight gain studies using a thermogravimetric balance, microscopic examination of sample surfaces and cross-sections, and chemical analysis of the phases formed during oxidation. / The addition of 12% silicon to aluminum promoted the formation of alpha-alumina nodules on the sample surface at 800°C by reducing the viscosity of the molten metal to allow for better feeding of fresh metal through cracks in the top oxide. Strontium was found to prevent the formation of oxide nodules in an Al-12%Si alloy through the formation of a strontium containing oxide. Similarly, in a commercial 356 alloy, strontium greatly reduced the extent of oxidation by preventing the preferential oxidation of magnesium. It is believed that the mechanism responsible for this is also through the formation of a strontium containing oxide. / Oxidation experiments conducted on an Al-3%Mg alloy revealed that magnesium preferentially oxidizes to form two oxides, firstly MgO, and secondly MgAl 2O4, which forms only from the reaction of MgO and aluminum. Weight gains for this alloy were greatly affected by the oxidizing temperature. Higher temperatures shortened the incubation time to breakaway oxidation and decreased the time required to oxidize all the magnesium from the alloy.

Along with the essential importance of the metallurgical sector, one must recognise that it is also one of the largest sources of environmental pollution. In particular, the problem of electric arc furnace (EAF) dusts is of a growing concern due to the increase in popularity of EAF steelmaking. This dust is classified as a hazardous product due to the elevated content of toxic metals (e.g., Cr). / Studies on the properties of EAF dusts are sparse. Experiments were performed in order to determine the chemical and physical characteristics of the dust. It was determined that EAF dust is constituted of randomly distributed agglomerations of homogeneously nucleated particles and entrained particles. The main elements present within the particular dust were iron and chromium, the latter due to the fact that the dust used was formed within a stainless steel mini-mill. The main phases present within the dust were Fe2O3/Fe 3O4 and Cr2O3. / Thermal remediation experiments were then carried out in a computer controlled thermogravimetric system. The parameters studied during the tests included temperature, residence time and heating rate. In addition, the behaviour of the EAF dust during remediation was studied; in terms of weight and volume loss, gas evolution, particle morphology and resulting leachability of the treated product. Furthermore, it was observed that at temperatures greater than 1200°C metal leachability decreased significantly due to a decrease in toxic metal concentration within the treated product and the formation of a resistant, dense, plate-like morphology. At 1600°C, no toxic metals leached out of the remediated EAF dust and volume reduction was significant, resulting in a product that would be safe and more economical to landfill.

The CANMET-McGill Mathematical Model has been expanded and improved to provide a more comprehensive predictive tool for simulation of temperature evolution in the hot rolling of steel. The model uses a Windows(TM)-based, user-friendly, graphical interface and the explicit finite-difference method in two dimensions to simulate the rolling of flat product. / Data input options were expanded to allow an initial temperature gradient in the steel to be rolled, the inclusion of a runout table in the calculations, specific chemical compositions and a choice of emissivity values. / A novel, chemistry-dependent thermal conductivity term was developed to account for the variation in heat conduction through the thickness of the steel and to ensure that the temperature of the entire cross-section is accurately predicted. In addition, the model now calculates a heat of transformation for phase changes from austenite to ferrite, pearlite and bainite. / An automated self-calibration module was included to facilitate the calibration of the model's predictions to empirically obtained temperature setpoints. / The model's temperature predictions were validated against both industrial and laboratory data with excellent results.