The continuous heating to fracture test (CHF) developed at McGill was used to study the effect of decarburization on the incipient melting temperature. In the CHF test, a sample was deformed at a constant true strain rate, while its temperature is increased at a constant rate. This test allows the incipient melting temperature to be determined using a single test, instead of the several required by isothermal tensile testing. An isothermal decarburization step, to create a decarburized layer at the surface of the sample, was added prior to the CHF test. / Analysis of the true stress vs temperature curves obtained by CHF testing allows the incipient melting temperature to be determined. Optical metallography was used to determine the effect of decarburization time on the observed depth of decarburization. The heat transfer characteristics of induction heating were studied, since this heating technique is known to create a significant temperature gradient at the surface of the piece being heated. Since the decarburized layer is in the high temperature zone, and also has a higher melting point due to its lower carbon content, it plays an important role in the melting process. / A phenomenological model was derived to describe the melting process. It allows for both the temperature gradient due to induction heating and the melting point gradient due to decarburization. The hypothesis is advanced that melting takes place at the position, within the sample, where the temperature profile crosses the incipient melting temperature gradient. From this study, it appears that decarburization acts so as to limit the risk of hot shortness on a workpiece being forged at high temperatures. This is because decarburization raises the IMT, and in this way widens the temperature window of optimum workability.

Formation of Pb and Ca precipitates on a silica surface in the presence of sulphate and carbonate under neutral to alkaline condition is studied using zeta potential measurements, Scanning Electron Microscopy (SEM), and X-Ray Photoelectron Spectroscopy (XPS). The effect of carbonate on displacing sulphate is discussed. / In the Pb/sulphate system, precipitates of predominantly Pb-oxide/hydroxide formed on the silica surface. In the Pb/carbonate system, the precipitates were predominantly Pb-carbonate/hydroxy carbonate. Precipitates in both the Pb/SO$ sb4$ and Pb/CO$ sb3$ systems were dispersed by addition of sufficient carbonate, the silica surface eventually becoming free of precipitates. This dispersion was considered to be due to: a high negative surface charge density on both lead carbonate and silica; nucleation being promoted at high concentrations of carbonate, resulting in small precipitates; and increased solubility at high carbonate concentrations. / In the Ca system, calcium sulphate precipitates did not form on the silica particles while calcium carbonate precipitates did. The precipitates were not removed by increasing carbonate concentration. The difference from the Pb system is attributed to a low negative surface charge density on calcium carbonate compared to lead carbonate, leading to less dispersing conditions, and the higher solubility of calcium sulphate compared to lead sulphate.

The onset of a 'late' rotating vortex over an off-centre drain nozzle at 2/3 radius was studied in an 1160-mm diameter tank. It was found that using a sloped bottom ladle could be beneficial in terms of steel yield, provided the exit nozzle is located 'centrically'. / Miner modification of the nozzle (skewed nozzle) to impart a radial component of velocity to the spinning vortex core was found to be effective in making AMEPA system sensitive to early slag entrainment phenomena by diverting the core away from the central vertical axis of the nozzle. / A 0.75 scale water model was constructed to simulate the flow of liquid steel through a ladle shroud in the presence of gas infiltration. It was found that the ladle shroud slag detector could be temporarily 'blinded' by gas bubbles or permanently blinded by a standing submerged gas jet.

Variant selection rules are described that predict the austenite-to-mariensite transformation textures of an Fe-30% Ni alloy. The occurrence of variant selection is explained in detail using the crystal plasticity model of Bishop and Hill and the Kurdjumov-Sachs transformation relationship. A correlation is established between the slip systems of the former and the rotation axes of the latter. The selection criteria are based on a combination of slip activity, that is, active slip systems defined in terms of positive shears, and permissible dislocation reactions. Thus some of the variants selected are associated with slip systems that are active, while the remainder are accounted for by the in-plane reaction of active dislocations to form inactive or unstressed dislocations. The variant selection criteria are tested against two strain paths; plane strain rolling and axisymmetric compression. Extensive studies were conducted on the former strain path and revealed excellent agreement between the measured and predicted transformation textures. A more detailed analysis is still required for the axisymmetric compression strain path, although, the results obtained indicate that the variant selection model does indeed generate a transformation texture that is consistent with the experimental one.

A full-scale physical model of a delta-shaped, four-strand tundish was constructed at McGill University to find optimal operating conditions for the tundish. The objective of this work was to determine how best to increase steel production rates by 14% over current tundish operating conditions, these being 12 tons/min with four 15.0 mm outlet nozzles for a 500 mm depth of liquid steel while maintaining steel quality levels. Two options were suggested: the normal head option uses 16.0 mm outlet nozzles and maintains the 500 mm tundish level, while the high head option uses 14.8 mm outlet nozzles and raises the depth of liquid steel within the tundish to 800 mm. The important effects of flow control devices on the hydrodynamic performance of the tundish were also tested, using two different types of flow modifiers: Impact Pad and Turbo-Stop. For a proper comparison between the two options, three aspects were investigated; vortex formation phenomena during tundish draining between ladle changes, Residence Time Distribution (RTD), and Inclusion Separation Ratios (ISR). Inclusion removal rates were studied experimentally with the aid of the aqueous" Liquid Metal Cleanliness Analyzer (LiMCA) system. Particle Image Velocimetry (PIV) was used to visualize the actual instantaneous, or momentary, flows, thereby providing the data needed for time averaged velocity fields and turbulent kinetic energies. A mathematical model based on METFLO was developed to simulate these tundish operations numerically. The Renormalization Group turbulence model (RNG) as well as the standard high Reynolds number k-s turbulence model (STD) was implemented in order to simulate the turbulent flows within the tundish. The validity of METFLO was confirmed by PIV measurements and the numerical predictions of the RTD, and RRI matched the results of physical modelling.

In this study a technique--that almost completely eliminates shrinkage microporosity--has been developed which uses small additions of strontium together with risers and chills to produce porosity-free AZ91C (Mg/Al/Zn) magnesium casting alloy castings. With the optimum level of Sr addition (0.01% to 0.02% Sr), shrinkage microporosity was removed from the casting and concentrated in the riser. The castings were already grain-refined by carbon inoculation. The effect of strontium is explained by a further reduction in the grain size of the castings from 250$ mu$m to 120$ mu$m. This effect produces a much denser casting due to increased mass feeding. In addition, a slow grain growth rate, caused by Sr addition, may keep the liquid intergranular-channel radius large during the final stages of solidification, and results in improved intergranular feeding. Another effect of strontium addition may possibly be attributed to a decrease in the surface tension and viscosity of the liquid AZ91C alloy, which in turn increases capillary feeding of the liquid metal. (Abstract shortened by UMI.)

Iron and silicon are the major impurities in the 1000 series of wrought aluminum alloys. As the aluminum is recycled, it picks up more and more of these impurities which cannot economically be refined out of the aluminum. When the concentration of these impurities reaches a certain limit (maximum limit in 1000 series is 1 weight percent (Fe+Si)), the aluminum must be downgraded. The Fe and Si form brittle intermetallic phases in these alloys. The two main phases are the plate-like $ beta$-AlFeSi (Al$ sb5$FeSi) and $ alpha$-AlFeSi (Al$ sb8$Fe$ sb2$Si) which has a Chinese Script morphology. The mechanical properties of these alloys are believed to depend largely on the nature of these intermetallics. / In the first part of this study, the conditions at which the intermetallics form, along with the ability of strontium to modify them were investigated. The second part consisted of determining how the morphology of the Al-Fe-Si phases affects the mechanical properties of the worked product. It was found that the formation of the Chinese Script morphology is promoted with increasing cooling rates, Fe/Si ratios and additions of strontium. However, the relative amount of Chinese Script was found to decrease with increasing (Fe+Si) levels. Tensile testing and formability testing (Erichsen ball punch deformation test) revealed that the presence of a Chinese Script morphology of Al-Fe-Si intermetallics (as opposed to the plate-like morphology) imparts no significant beneficial effect on the formability of the final rolled sheet.

The solution chemistry and statistical modelling of the O$ sb2$-CaCl$ sb2$-HCl leaching of a high-grade arseniferrous uranium ore (Key Lake, N. Saskatchewan) were studied with the objective of optimizing the co-extraction of uranium and radium. To this end, two types of experiments were carried out: (a) those designed to study arsenic speciation under simulated U-leaching conditions, with the use of model arsenide minerals, namely niccolite (NiAs), rammelsbergite (NiAs$ sb2$) and gersdorffite (NiAsS); and (b) statistically designed tests involving actual leaching of samples of the Key Lake ore. / Niccolite and rammelsbergite were found to yield H$ sb3$AsO$ sb3$ in solution as oppossed to gersdorffite, which was found to yield H$ sb3$AsO$ sb4$. H$ sb3$AsO$ sb3$ was found to be metastable in the Fe$ sb2$(SO$ sb4) sb3$ leaching system, while in the FeCl$ sb3$ and pressure (O$ sb2$) leaching systems, further oxidation to H$ sb3$AsO$ sb4$ was observed to take place at relatively slow rates. A mechanism has been advanced to account for the latter slow oxidation of H$ sb3$AsO$ sb3$ to H$ sb3$AsO$ sb4$. Finally, it was concluded that the formation of As(III)/As(V) in oxidative acid leaching is independent of the prevailing suspension redox potential which, in turn, renders impractical the possible stabilization of As(III) via potential control. / The solubility of RaSO$ sb4$ in HCl-MeCl$ sb{ rm x}$ leaching media was quantitatively established by employing the "reduced activity coefficient" method. The estimated solubility profiles clearly demonstrated the effectiveness of CaCl$ sb2$ in solubilizing radium as oppossed to other monochloride salt additions. / Finally, optimization of the co-extraction of U and Ra was attained with the use of a computer-aided response surface methodology. An incomplete three-level, four-variable factorial design (Box-Behnken) was applied in the region: 0.33 kg/L $ leq$ d$ sb{ rm s}$ $ leq$ 0.99 kg/L; 0.5N $ leq$ (HCl) $ sb{ rm o}$ $ leq$ 1.5 N; 1.5 M $ leq$ (CaCl$ sb2 rbrack sb{ rm o}$ $ leq$ 3.5 M; and 2 hrs $ leq$ Time$ leq$ 6 hrs. Temperature and oxygen pressure were kept constant at 68$ sp circ$C and 510 kPa (75 psi), respectively. Uranium and radium were found to dissolve simultaneously and rapidly (99% co-extraction in 2 hrs). Effective reduction of radioactivity levels from 10,000 pCi/g Ra$ sp{226}$ down to 160 pCi/g has been achieved in a single-stage batch process, thus making possible the production of environmentally innocuous tailings.

Nickel constitutes the major impurity encountered during copper electrorefining (Cu ER) operations. Continuous nickel build-up in the electrolyte is controlled by withdrawing a fraction of solution from the tankhouse and separate nickel as crude NiSO4.2H2O via Evaporative Crystallisation . The energy required to evaporate water is high, increasing thus the operation costs; moreover, the product thus obtained is of poor quality in terms of purity and crystal size. / As part of an ongoing research project launched at McGill University, the Solvent Displacement Crystallisation (SDC) technique is investigated as an attractive alternative to the conventional method. SDC involves the addition of low-boiling point, watermiscible organic solvents (MOs) to aqueous solutions to cause salt precipitation based on the "salting out" effect. The crystals are separated by filtration whereas the solvent is subsequently recovered for reuse by low-temperature distillation. / The present work describes the successful application of SDC method to the precipitation of NiSO4.6H2O from Cu ER spent electrolytes. Tests have been performed on synthetic and industrial electrolytes (courtesy of Canadian Copper Refineries), using Isopropanol as precipitant. By maintaining a low supersaturation (i.e. controlled addition of the solvent to the electrolyte) and heterogeneous crystallisation conditions (use of seed/product recycling), crystal growth is favoured while impurity uptake/contamination is minimised.

This research investigates the possibility of recovering the metallic content of the dust generated by stainless steelmaking operations in the Electric Arc Furnace (EAF) at ATLAS Stainless Steels by recycling it to the EAF. The physical and chemical properties of the dust were determined. The pelletization of dust-carbon fines was optimized in order to obtain strong pellets capable of carbothermic self-reduction. The high temperature behavior of dust-carbon pellets was investigated in a Thermogravimetric Analyzer (TGA) coupled with a Fourier-Transform Infrared Spectrometer (FTIR). The mechanisms involved in metal recovery were identified. The feasibility of direct recycling was verified by testing pellets in a scaled-down simulation of the EAF process. As a result of this research practical recommendations concerning the application of the direct recycling process at ATLAS were formulated.