The effect of Si on the kinetics of Nb(C,N) precipitation was investigated by using fractional softening measurements. Compression specimens, with diameters of 7.6 mm and lengths of 11.4 mm, were prepared from four Nb microalloyed steels containing a range of Si concentrations from 0.01 wt% to 0.41 wt%. The stress relaxation method was used in the beginning of this work, but the majority of the experimental results were derived from double-hit compression tests, with a strain of 0.3 applied to represent each pass at a strain rate of 0.1/sec. A solution heat treatment was applied immediately prior to each test. / It was found that the rate of Nb(C,N) precipitation in hot deformed austenite increases with Si concentration. This phenomenon is attributed to the increases in both the Nb diffusivity and the activities of C and N that result from Si addition. Based on the Dutta and Sellars model, an expression for the effect of strain rate on the precipitation start time has been proposed. The present experimental results can then be extrapolated to mill conditions.

The aim of this work was to develop a viable solvent-extraction based system for the separation of rhodium (Rh) from aqueous chloride solutions. Ultimately, two different systems were developed. Kelex 100, a commercially available derivative of 8-hydroxyquinoline, was used as the extractant reagent in both of these systems. One of the systems involved the supported liquid membrane (SLM) extraction of Rh. In this system a very thin microporous "Gore-Tex" polymer sheet, impregnated with an organic solution of Kelex 100, served as the SLM. The other system involved the conversion of the chlorocomplexes of Rh to bromocomplexes prior to their solvent extraction with Kelex 100. / The results of the lab-scale experiments using a SLM of Kelex 100 having a surface area of 44 cm2 are reported. The optimum conditions for Rh permeation were found as a feed solution of 2.5 M HCl and a strip solution of 0.1 M HCl. The SLM was quite stable at the optimum conditions with no sign of organic loss or membrane deterioration after 72 hours of operation. It was determined that the HCl activity gradient across the membrane acts as the driving force that "pumps" the non-aquated Rh chlorocomplexes against their concentration gradient. The mechanism of Rh permeation was the ion-pair formation between the protonated Kelex 100 and RhCl6 3- complexes. The rate of Rh permeation was in the order of 10-6 mol.m-2.s-1. The mechanism of HCl and H2O permeation, which were co-extracted along with Rh chlorocomplexes, were found to be the hydration of protons at the low feed acid region and the formation of microemulsions at the high feed acid region. The permeated acid and water were separated from the SLM receiving phase by contacting the latter phase with an organic solution of trioctylamine (TOA). The chlorocomplexes of Rh(III) and acid are readily extracted to the TOA organic phase and subsequently subjected to differential stripping with a concentrated solution of Cl- and a mild NaOH solution, respectively. By interfacing the TOA solvent extraction with the SLM of Kelex 100 highly concentrated solutions of Rh (at least 10 times the initial concentration) and raffinates essentially free of rhodium were produced. / The UV-Visible investigations revealed that the bromocomplexes of Rh undergo aquation to a much lesser extent than that of the chlorocomplexes. The chlorocomplexes of Rh were converted to bromocomplexes by precipitating first the Na(NH4)2Rh(NO2)6 salt and subsequently dissolving that in an HBr solution. The newly formed bromocomplexes of Rh(III) responded very favorably to extraction with Kelex 100. Relatively high distribution coefficients, about 20, and very steep extraction isotherms were generated. The freshly loaded Kelex 100 organic was efficiently stripped upon contact with a strip solution of 6--8 M HCl and a contact time of 10--12 hours. The developed system shows high promise from a practical implementation point of view.

The kinetics of calcium and sodium removal at 730$ sp circ$C by chlorination from commercial purity (99.7% Al) and aluminum-1wt% magnesium alloys has been investigated. The contribution of chlorine containing gas bubbles, of intermediate reaction products generated by the chlorination process, as well as evaporation through the melt surface, to the removal of calcium and/or sodium has been documented quantitatively. Experimental parameters investigated were chlorine concentration in the gas bubbles and gas flow rate. The measurement of frequency of bubble formation at the tip of the gas bubbling nozzle enabled the surface areas of the bubbles to be estimated which in turn enabled melt phase mass transfer coefficients for the bubbles to be calculated. / It was demonstrated that the removal of calcium and sodium followed first order reaction kinetics with respect to calcium and sodium concentrations. The removal of the above mentioned elements was represented well by a kinetic model in which mass transfer of sodium and calcium in melt phase was rate limiting. / In the case of the magnesium containing alloys, the MgCl$ sb2$ salt phase that was generated during chlorination was found to have a profound effect on the removal of calcium and sodium. The contribution of the salt phase to the removal of these elements was calculated to reach as high as 60%. In commercial purity aluminum, however, while the major contribution to the removal of calcium was from the chlorine containing gas bubbles, the major contribution to the removal of sodium was calculated to be evaporation of sodium through the melt surface.

Flotation of sphalerite with xanthate in the presence of iron ions has been studied as a function of pH. Sphalerite floated readily at pH 8-11 in the presence of ferrous ions, but not in the presence of ferric ions. The Fe$ sp{2+}$ ion concentration, pH and oxygen concentration were shown to be factors in controlling flotation. Electrokinetic measurements indicated that the surface charge increased in the presence of Fe$ sp{2+}$ ions and oxygen, and decreased upon adding xanthate and in the presence of Fe$ sp{2+}$ ions with the absence of oxygen. / As a prelude to surface analysis to try to identify the species responsible for the sphalerite flotation, bulk precipitates formed from iron salt and xanthate solutions under various conditions were obtained and analysed. Analysis techniques included ultraviolet spectroscopy, infrared spectroscopy, x-ray diffraction and Mossbauer spectroscopy. / It was tentatively concluded that the bulk precipitates contained three ferric components: two hydroxy xanthates, Fe(OH)$ sb2$X and Fe(OH)X$ sb2$ and an iron oxide, FeO$ sb{ rm x}.$ / Iron xanthate precipitates prepared over the pH range 6-12 showed a flotation response and electrokinetic behaviour similar to those of Fe$ sp{2+}$/xanthate-treated sphalerite. / An ex situ X-ray photoelectron spectroscopic (XPS), ex situ infrared (DRIFTS) and in situ infrared (ATR) investigation of the interaction of sphalerite with ferrous, ferric and xanthate ions at pH 10 was undertaken. The formation of the hydrophobic surface species was found to involve initial adsorption of Fe$ sp{2+},$ followed by oxidation to Fe$ sp{3+}$ and subsequent reaction with xanthate. There was no significant incorporation of Fe$ sp{3+}.$ / A three-step reaction mechanism is proposed to account for Fe$ sp{2+}$ ion activation of sphalerite: (i) adsorption of Fe(OH)$ sp+,$ (ii) oxidation to Fe(OH)$ sp{2+}$ on the surface, (iii) reaction with xanthate to form Fe(OH)$ sb2$X or Fe(OH)X$ sb2.$

Zinc-based electrogalvanized coatings have attracted increasing interest from the automobile industry and steelmakers because of their excellent corrosion resistance and good mechanical properties. The coating properties are closely related to the microstructure of deposit. Among them, texture is a key factor which influences the coating properties. This study demonstrates the microstructure and corrosion behaviors of the electrodeposited zinc, zinc-iron, and zinc-nickel coatings on steel sheet deposited at different current density, pH and coating thicknesses. The evolution of the coating microstructure--texture, surface morphology, interplanar spacings, microstress, alloy content, and phase composition--is investigated in various deposition conditions. This work also demonstrates the influence of the coating microstructure upon corrosion behavior. In addition, the early stage of deposition behavior is observed in order to demonstrate the growth mechanism of deposits. / The surface morphology and texture of coatings are investigated using AFM (Atomic Force Microscope), SEM and x-ray diffractometers. Corrosion behaviors are analyzed by the Tafel extrapolation method from the potentiodynamic polarization curves as well as by the electrochemical noise tests. / It is found that the zinc based coatings show a significant variation in texture with the change of deposition parameters. The present work suggests that the transformation of texture is closely related to the evolution of coating morphology and the change of alloy content in the deposit as well as phase composition. This work also demonstrates that there is a correlation between morphology and the texture of coatings. The morphology of hexagonal platelets represents the basal $ {0001 }$ fiber texture. The morphology of hexagonal ridges represents the pyramidal non-fiber texture and the morphology of triangular-based pyramids represents the pyramidal $ {$101X$ }$ fiber texture. From the corrosion test, it is found that the texture of coatings strongly influences corrosion resistance. The coatings with strong $ {0001 }$ texture have better corrosion resistance than the coatings with weak $ {0001 }$ texture or a $ {$101X$ }$ fiber texture component. The influence of alloy content and phase composition upon corrosion behavior is also discussed. Consequently, it is proposed how to optimize the deposition process to obtain the desirable texture, morphology and alloy content of the deposit for better corrosion resistance.

The aim of this work is to offer a quantitative assessment as to what extent the texture and the microstructure influence the cold headability of steel wires. / For this, a set of cold drawn low carbon steel wires/AISI 1030 were prepared. The samples were drawn, without heat treatment, in between passes of up to 78% reduction in area (RA) in 5 passes. The deformed samples were then heat treated according to various schedules. / Texture development was studied at a given thickness, by measuring the (110), (200) and (211) pole figures by X-ray diffraction; furthermore, the results were represented and using the Orientation Distribution Function (ODF). A strong $ langle$110$ rangle$ texture was found. / Using special dies, compression tests were made in order to obtain information on such mechanical properties as the yield strength and the homogeneous strain energy. / Multiple regression analysis was made in order to correlate the aspect ratio, the grain size, the Taylor factor and the maximum ODF intensity against the yield strength and the homogeneous strain energy.

Al-Si-Mg alloys containing 7% silicon are the most widely used aluminum foundry alloys owing to their good mechanical properties and excellent castability. Nevertheless, design engineers traditionally apply a design casting factor when designing cast components to ensure that proper strength will be obtained in spite of the recent emergence of techniques of control of the molten alloy quality on which depend, afterwards, the mechanical properties of the castings. / In this study, the feasibility of using electrical conductivity to non-destructively predict secondary dendrite arm spacing was investigated on both as-cast and heat treated alloys. In the as-cast condition, conductivity decreases linearly with increasing DAS from 30 $ mu$m, while, below 30 $ mu$m, conductivity readings are influenced by alloying elements retained in solid solution due to the fast solid state cooling rates. Conductivity changes with DAS are more important when the silicon morphology is finer i.e. the alloy modified. After heat treatment, the DAS-conductivity relationships become linear as a result of the homogenisation of the aluminum matrix, but the slopes of the lines are small and the accuracy of DAS determination does not extend below 15 $ mu$m. Conductivity is also greatly influenced by the degree of precipitation achieved during artificial aging so that the determination of DAS by conductivity measurement is best used after quenching (T4 condition).

Cold headability is the ability of a cylindrical metallic specimen to be shaped at high strain rate into the head of a bolt, screw or other cold-formed part without cracking. This property is material dependent and can be influenced by many factors such as chemical composition, surface condition, and microstructure. This project focuses on the effect of microstructure upon the cold headability of a medium carbon steel (1036M). Six different microstructures were produced by various heat treatment conditions. Drop Weight Tower (DWT) tests, developed at McGill in 2000 by Dr. N. Nickoletopoulos, were used on samples of these materials. Visual inspection, metallographic and SEM analysis were performed to identify cracks on the surface of tested samples, and trace their cause. The axial and circumferential strains of tested samples were measured and the strains at which cracks first occurred were used to assess the cold headability. This research further indicates that DWT testing is a valid method for evaluating the cold headability of metallic materials and that the cold headability is particularly sensitive to the microstructure of a material.

Al-7%Si-0.3Mg (A356) foundry alloy is strontium modified and heat treated in order to obtain optimum mechanical properties. To date, the role that strontium modification plays in the precipitation process during the heat treatment is not well understood. The objective of the present work is to obtain a better understanding of the effect that strontium modification and heat treatment parameters exert on the properties of heat-treated Al-7%Si-0.3Mg alloy. The investigation consisted of a systematic measurement of the electrical conductivity and matrix microhardness of heat-treated coupons under different process conditions. Tensile properties were also measured and a transmission electron microscopy study of critical samples was done. The results obtained in this work indicate that the heat treatment of this alloy can be optimized. Solution heat treatment and artificial aging can be reduced and natural aging manipulated. The use of a continuous heating artificial aging is proposed. During the heat treatment of the A356 alloy under certain conditions not only does the precipitation of the Mg2Si occur, but also that of silicon. It was found that strontium modification does not influence the precipitation kinetics of the Mg2Si, but it does retard the precipitation of the silicon out of the matrix.

High quality aluminum castings must contain a minimum of defects. Currently, melt treatments, including degassing and liquid metal filtering, are used to this end. Reducing hydrogen pick-up and the formation of inclusions is a more efficient way of dealing with defect control, however, the configuration of most current casting processes make prevention difficult. / This thesis proposes a new process which involves submerging a mold in the molten metal. Process improvements include the elimination of liquid metal pouring and transferring, the reduction of melt temperatures and the availability of hot liquid to feed shrinkage. / A prototype device was constructed using high temperature heat pipes to provide cooling. Excellent mold filling was attainable after optimizing the preheat temperature, the melt temperature and the submerging velocity of the mold. The process also provided directional solidification with a flat solid/liquid interface. After considering the characteristics of the prototype, an improved device is proposed.