A theoretical and experimental study is presented of texture evolution in hcp zirconium deformed at high temperatures. It is shown that, within the temperature range in which nuclear components are fabricated, the development of crystallographic texture is controlled by the simultaneous activation of $ langle$a$ rangle$ and $ langle$c + a$ rangle$ slip. This is demonstrated by experiments on Zr-2.5 Nb and unalloyed Zr deformed along three of the four elementary strain paths: axisymmetric elongation and compression and pure shear. Further experimental work on the axisymmetric deformation of unalloyed Zr and Zr-20 Nb shows that the influence of the bcc $ beta$-Zr phase present in Zr-2.5 Nb at the temperatures of interest is not due to the formation of crystallographic textures in this phase. / Texture evolution modelling was implemented for the case of polycrystalline hcp metals by making use of the duality principle between the generalized Taylor and Bishop-Hill theories of polycrystal plasticity and with the help of linear programming. The high temperature experimental textures for the three elementary strain paths mentioned above were successfully predicted using the relaxed constraint theory. It is shown that, for the cases of pure shear and compression, the so-called pancake version of this approach gives a better approximation to the observed textures than the full constraint calculations. For axisymmetric elongation, the curling version of the relaxed constraint model gives the best results. / By the analysis of slip activity maps, it is shown that the limitations of the full constraint model reside in the high activity level for $ langle$c + a$ rangle$ slip associated with this approach. When the relaxed constraint model is applied, the activity level of $ langle$c + a$ rangle$ slip is considerably reduced, leading to much better agreement of the predicted textures with the experimental results. The full constraint model is also applied to simulate texture evolution in $ alpha$-Zr deformed in simple shear at room temperature. It is demonstrated that the level of agreement is at least as good as that obtained when full constraint calculations were carried out. Finally, a high temperature texture rosette is proposed for prediction of the textures developed during tube forming operations for Zr alloy nuclear components. (Abstract shortened with permission of author.)

The digestion (dehydration and dissolving), in a molten salt containing MgCl2, of partially hydrated MgCl2 in the form of 'prills' was visually observed. The 'prills' were prepared by Magnola Metallurgie Inc. Pictures of the digestion are presented and two types of bubbling behaviours were observed. / It was concluded that the digestion process occurred in two steps: (1) dehydration/hydrolysis of prills in the solid state and (2) dissolution of the dehydrated products. Each step was accompanied by a distinctive bubbling behaviour as the gas products of the step were evolved. / The type of bubbling behaviour associated with the first step was termed 'Primary Bubbling' and was due to the release of the waters of hydration, hereinafter termed dehydration. The second type of bubbling behaviour observed was termed 'Secondary Bubbling' and was due to the decomposition of dissolved oxide in the molten salt according to the reaction: MgOHCldiss→MgOs+HCl g / The solubility of the dissolved oxide was seen to be a function of temperature and MgCl2 activity in the melt. Analysis of the gas evolved during Secondary Bubbling revealed a gas composition of about 51 vol.% HCl and 49 vol.% H2O, indicating that dissolved oxide was also being chlorinated by the reaction: MgOHCldiss →MgCl2l+HO g / Injection of Ar decomposed the dissolved oxide by offsetting the first reaction above to the left and injection of HCl chlorinated solid MgO by the reaction: MgOs+2H Clg→MgCl2l +H2Og / Surprisingly, it was found the HCl atmosphere in the freeboard of the reactor had no significant effect to suppress the hydrolysis reaction occurring during dehydration.

The purpose of the present work was to remove selectively manganese from a neutral leach zinc-rich solution at 80ºC using the gas mixture of sulphur dioxide (SO2) and oxygen (O2) as oxidizing agent. In order to determine the optimum conditions for manganese removal using SO 2/O2, several semi-batch experiments were performed, where the effects of pH, ORP, SO2/O2 ratio, mixing intensity, etc. were investigated. Results of these tests showed that SO2/O 2 was a fast and effective oxidant for removing manganese down to ppm level provided that the appropriate reactor design, agitation and SO 2/O2 ratio were employed. In an attempt to improve the precipitate's characteristics, e.g. crystallinity and solid/liquid separation, a new technique called Step-Wise Oxidative Precipitation (S.W.O.P) was investigated using a two-reactor continuous circuit employing pH and ORP control and precipitate recycling. These tests revealed that a birnessite-like phase with general formula (Na0.7Ca0.3)Mn7O14·2.8H 2O was produced with co-precipitation of a significant amount of zinc apparently via substitution. The applied technique (S.W.O.P combined with recycling) proved effective in producing dense particles but not on lowering zinc losses. The biggest advantage of this novel oxidation technique was the total elimination of scaling. (Abstract shortened by UMI.)

The aggregation behaviour of sphalerite suspension and the role of zinc and magnesium ions are investigated. Aggregation is monitored by suspension analysis (turbidity) and optical microscopy and, in particular, a conductivity-settling technique. To probe the mechanisms, electrophoretic mobility (zeta potential) measurements and field emission scanning electron microscopy (FE-SEM) imaging are used. / In the case of sphalerite alone, for samples from a variety of sources, aggregation occurred at pH 8--10, well above the range in iso-electric point (pH 2--6). The aggregation is attributed to the presence of Zn(OH) 2, the dominant species over this pH range. To test whether zinc hydrolysis products promote aggregation silica and chalcopyrite suspensions were doped with Zn2+ ions; aggregation over the same pH range was found. This observation is similar to that of Healy and Jellet (1967) for zinc oxide, ZnO. They suggested aggregation was due to release of Zn2+ ions to form Zn(OH)2 which polymerizes and flocculates the particles. The same mechanism is proposed for sphalerite. / Aggregation due to magnesium ions was determined using the settling rate of sphalerite and silica suspensions (individually) as a function of Mg 2+ concentration, pH and suspension density (%v/v solids). Aggregation at pH > 10 was found for both minerals corresponding to magnesium hydroxide. However, the mineral's response to the three variables suggests the mechanism for each is different. The proposed mechanism of aggregation by Mg(OH) 2 for sphalerite is chemical bridging and for silica, electrostatic bridging. Electrostatic bridging is revealed by aggregation passing through a maximum as a function of both coagulant concentration and pH. For sphalerite, while there is a maximum with [Mg2+] (Mg2+ concentration) there is none with pH (after allowing for the self-aggregation of sphalerite). Further, electrostatic bridging requires surface patches of the bridging material (Mg(OH)2) and the FE-SEM images showed no such evidence. The interpretation for silica aggregating with Mg2+ follows that proposed by Krishnan and Iwasaki (1986). The pH, [Mg2+] and solid concentration effects are compatible with electrostatic bridging, as is the morphology as hydroxide patches were identified by FE-SEM. / In certain cases the conductivity-settling data suggested the particles were more conductive than the liquid. The conductivity-settling technique was adapted to measure the electrical conductivity of particles dispersed in water. The conductivity was estimated at the iso-conductivity point where the solution and the particles have the same conductivity. The technique was tested on chalcocite, chalcopyrite, galena, pyrite and sphalerite. The order of mineral conductivity followed that of their electrochemical rest potential, as expected. It is observed that the adsorption of xanthate significantly reduced the conductivity of chalcopyrite and copper activation increased the conductivity of sphalerite but treatment with lead had no effect.

Crystallisation, one of the oldest unit operations, is of major economic importance in the hydrometallurgical industry for the separation and/or production of inorganic metal compounds in the form of good quality crystals, both in terms of purity and size. However, industrial crystallisation techniques usually have high energy requirements (e.g. evaporative crystallisation) and the residual solutions are often extremely corrosive, resulting in elevated operating and maintenance costs. Additionally, the majority of industrial crystallisation methods do not render to the appropriate supersaturation control, therefore the produced salts are agglomerates of fine crystallites with heavy solution entrainment and contamination. / In this work, the Solvent Displacement Crystallisation (SDC) technique is investigated as an attractive alternative to the conventional crystallisation methods. SDC involves the addition of low-boiling point, water-miscible 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 was initiated with the main objective to develop a solid scientific understanding of the SDC process and propose specific applications to hydrometallurgical systems of practical interest. / Criteria for the selection of organic solvents with suitable physical and chemical properties have been established and various compounds screened to determine their amenability to SDC; 2-propanol was selected as an effective salting out agent to cause precipitation of most metallic sulphates of practical interest from acidic solutions and opted for use in further studies. Differences in crystallisation behaviour among the various metal sulphates were attributed to differences in hydration energy (the energy required for a hydrated ion to be separated from its bound water). / None of the tested metal chlorides could be successfully separated from HCl-H2O system with 2-propanol. This was explained in terms of enhanced metal chlorides solubilities in non-aqueous solvents relative to water by formation of chloro-complexes of larger stability constants. The preferential formation of chloro-complexes in mixed aqueous and organic solvents is the result of the almost linear drastic increase in the activity of Cl - with mole fraction organic. / Successful examples of using the SDC method in conjunction with an industrial process involve precipitation of NiSO4·6H2O from copper electrorefining spent electrolytes, residual sulphate removal as gypsum (CaSO4·2H2O) in chloride leaching processes and ZnO separation/NaOH regeneration in the system Na2ZnO2, - NaOH - H2O. 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.

Several mineral flotation plants utilize process water with high soluble salt content. The processing of soluble minerals, the use of recycle streams, sea or well water give rise to this situation. It is unclear as to the overall effect on flotation response though there does seem to be evidence of bubble size reduction, increased froth stability and reduced reagent dosage. The present work aims to quantify the effects of salts commonly present in process water on gas dispersion (bubble size and gas holdup) and froth properties (solid and liquid overflow rates) and to compare to a typical frother, MIBC (methyl isobutyl carbinol). Three sets of experiments were run: 2-phase, 3-phase using talc and 3-phase using ore. All tests were run in a laboratory column. The salts examined in the 2-phase tests were NaCl, CaCl₂, Na₂SO₄, Na₂S₂O₃ and Al₂(SO₄)₃. Tests were conducted to determine the effects of salt type and concentration on gas holdup, bubble size distribution and foaming. The salts containing multivalent ions had a greater impact than did the monovalent ions, in keeping with the literature. A relationship between gas holdup and ionic strength was established. The effects of NaCl and MIBC on frothing and on solid and liquid overflow rates in 3-phase tests using 1%w/w talc were investigated. The results showed increased frothing and overflow rates upon the addition of NaCl, comparable to adding MIBC. Three-phase tests using ore (Falconbridge's Brunswick Mine) explored the effect of NaCl concentration. The results show reduction in bubble size and increased gas holdup in salt solutions comparable to those in the 2-phase tests. For each case, the concentration of MIBC giving equivalent gas holdup and frothing as the salt systems was determined. Proposed mechanisms for coalescence inhibition and froth stability in salt solutions are briefly reviewed in light of the current findings.

Zirconium alloys pickup hydrogen, during reactor operation. When the hydrogen content exceeds the solubility limit, the hydrides are formed. These hydrides have deleterious influence on the mechanical properties of the material. Therefore, it is important to improve our understanding of hydride morphology and behavior at different conditions approximating nuclear reactor environments. Initial analysis was done on the hydrided, cold-worked and stress-relieved (CWSR) Zircaloy-4 sheet-samples. The hydrides have been identified as δ-ZrH1.5 phase. They were located within the grains and along the grain boundaries, but the grain boundary hydrides appeared to be dominant. The preferential orientation relationship of (0001)α-Zr//(111)δ-ZrH1.5 was observed between hydrides and the matrix at all locations. The changes in hydrogen concentration had no effect on the crystallographic orientation relationship of the hydrides. Subsequently, the hydride behavior under hoop stress has been studied in detail. A range of hoop stresses were applied to the Zircaloy-4 cladding tube in a high pressure hydrogen gas furnace at a temperature of 350ºC and a pressure of 20 MPa. Optical micrographs of the samples showed an increase in the number of hydrides oriented along radial direction at higher hoop stresses. Apart from radial hydrides, the hydrides which were inclined at an angle to circumferential and radial directions were also observed. Interestingly, the hydrides which were oriented perpendicular to the circumferential direction followed a {10 1}α-Zr//{111}δ-ZrH1.5. relationship with the matrix grains. Habit planes of {10 1}, {10 7}, {10 3}, {10 0} were observed for the hydrides which were inclined at an angle to the circumferential direction. This study helps in understanding the complex behavior of radial hydrides. An attempt has been made to understand the superior resistance to corrosion and substantially lower hydrogen pickup of the Zr-1Nb alloy when compared with Zircaloy-4. Thus, Zircaloy-4, Zr-2.5Nb and Zr-1Nb (E110) alloys were hydrided in a high pressure hydrogen gas furnace. The hydrides in Zr-1Nb (E110) were short and thick, without any preferential orientation with respect to the sample reference direction. Heavy {10 2} twins were observed in the Zr-1Nb alloys, which were not seen in the Zircaloy-4 and Zr-2.5Nb alloys. Almost 50 % of hydrides in the Zr-1Nb (E110) alloy showed a new crystallographic relation of (0001)α-Zr//{100}δ-ZrH1.5. This new orientation relationship in the Zr-1Nb alloy is attributed to the presence of twin boundaries. In addition, the microstructural changes at the weld zone and its effects on the hydride behavior have been studied. The weld zone shows predominantly basket-weave structures, with very few colonies of parallel plate structures. Variant selection for α-phase formation inside prior β-grains was identified at the weld center. As we move from the weld center to the as-received zone, the variant selection is found to be less probable. At the weld zone, a complete random orientation of hydrides was observed. Moreover, the δ-hydride platelets at the weld zone were always found to be growing perpendicular to the α-colonies, which had a misorientation of 60º, and followed a (0001)α-Zr//{111}δ-ZrH1.5 orientation relationship with the zirconium matrix. A proposed description of the complex distribution of hydrides and alloy microstructures, at the weld and heat affected zones, will contribute to a better understanding of the mechanisms of fuel cladding failure in various types of nuclear reactors. / Les alliages de zirconium ramassent de l'hydrogène, au cours de l'opération de réacteur. Lorsque la teneur d'hydrogène dépasse la limite de solubilité, les hydrures sont formés. Ces hydrures ont un effet néfaste sur les propriétés mécaniques du matériel. Par conséquent, il est important d'améliorer notre compréhension de la morphologie des hydrures et leur comportement sur les conditions différentes rapprochant des environnements de réacteur nucléaire. L'analyse initiale a été faite sur les hydrided hydrures, travaillés à froid et soulagés de contraintes du Zircaloy-4 (CWSR) feuille-échantillons. Les hydrures ont été identifiés comme phase δ-ZrH1.5. Ils sont trouvés dans les grains et le long des frontières de grains, mais les hydrures de limite de grain semblaient être dominants. La relation d'orientation préférentielle de (0001)α-Zr// (111)δ-ZrH1.5 a été observée entre hydrures et la matrice à tous les endroits. Les variations de concentration de l'hydrogène n'ont eu aucun effet sur la relation de l'orientation cristallographique des hydrures. Par la suite, le comportement d'hydrure sous hoop stress a été étudié en détail. Une plage de hoop stress a été appliquée au tube de revêtement du Zircaloy-4 dans un four à gaz à haute pression d'hydrogène à une température de 350ºC et sous une pression de 20 MPa. La microscopie optique des échantillons ont montré une augmentation du nombre des hydrures orientés le long de la direction radiale à des données de hoop stress plus élevées. Hormis les hydrures radiaux, les hydrures qui étaient enclins à un angle de circonférence et radiales des instructions ont aussi été observés. Fait intéressant, les hydrures qui étaient orientés perpendiculairement à la direction de circonférence suivent la relation de {10 1}α-Zr//{111}δ-ZrH1.5 avec les grains de la matrice. Les plans d'habitude de {10 1}, {10 7}, {10 3}, {10 0} ont été observés pour l'hydrure qui étaient enclins à un angle avec la direction de la circonférence. Cette étude permet de comprendre le comportement complexe des hydrures radiaux. Une tentative à comprendre la résistance à la corrosion et à baisser substantiellement la ramasse de l'hydrogène de l'alliage Zr-1Nb comparativement à Zircaloy-4. Ainsi, Zircaloy-4, Zr-2.5Nb et alliages Zr-1Nb (E110) ont été hydrudés dans un four à gaz à haute pression de l'hydrogène. Les hydrures dans le Zr-1Nb (E110) étaient courts et épais, avec aucune orientation préférentielle par rapport à la direction des échantillons de référence. Des jumeaux lourds {10 2} ont été observés dans les alliages de Zr-1Nb, qui n'étaient pas considérés dans la Zircaloy-4 et Zr-alliages 2.5Nb. Près de 50 % des hydrures dans l'alliage Zr-1Nb (E110) ont montrés une nouvelle relation cristallographique de (0001)α-Zr//{100}δ-ZrH1.5 Cette nouvelle relation d'orientation dans l'alliage Zr-1Nb est attribuée à la présence des limites des jumeaux. En outre, les changements des microstructures à la zone de soudure et ses effets sur le comportement d'hydrure ont été étudiés. La zone de soudure montre surtout des structures nattées, avec très peu de colonies ayant des structures de plaques parallèles. La sélection variante pour la formation de α-phase à l'intérieur de grains de β préalables a été identifiée au centre de la soudure. Alors que nous déplaçons du centre de soudure à la zone reçu, la sélection de la variante est jugée moins probable. Dans la zone de soudure, une orientation aléatoire complète des hydrures a été observée. En outre, les plaquettes δ-hydrure dans la zone de soudure ont toujours été croissante perpendiculaire aux α-colonies, qui avaient une différence angulaire de 60º et qui suivent une (0001)α-Zr//{111}δ-ZrH1.5 relation d'orientation avec la matrice de zirconium.

A novel method has been developed to prepare magnetic carriers for metal ion removal from dilute solutions. In this work, magnetic carriers were prepared by coating an organic surfactant on magnetic particles. The coating was deposited by molecular self-assembly. Two coatings were tested, using two similar bolaamphiphiles* of different chain lengths, HS-(CH2)11-COOH and HS-(CH 2)15-COOH. The magnetic particles were nanosized maghemite (gamma-Fe2O3). / The surfactants were synthesized and characterized. Magnetic carriers were prepared, characterized, and tested for metal ion loading. Molecular orientation, density, and stability of the surfactant coatings were characterized by diffuse reflectance infrared Fourier-transform spectroscopy (DRIFTS), x-ray photoelectron spectroscopy (XPS), wetting tests, and leaching tests. The coatings, resulting from the chemisorption of the surfactants on maghemite through carboxylate bonding, were found to be dense, well-packed, and resistant to acid and base attack. / The potential use of coated particles for metal ion removal was assessed with Cu and Ag solutions. The metal ion uptake by the carriers was characterized by atomic adsorption and MRS. The influence of pH and metal concentration on adsorption was studied. Metal ion uptake was found to be dependent on pH, and was not significantly different for both types of coated carriers and for bare maghemite. The maximum loading capacity was low, at approximately 6 mg Cu/g particles for Cu. The similarity in loading for coated and bare particles needs further clarification. / *Bolaamphiphiles are surfactants with a functional group at each end.

Five slightly different IF 409 ferritic stainless steels were investigated by means of continuous cooling compression (CCC) testing. These compression test were performed at a constant strain rate of $1.8 times10 rm sp{-4}s sp{-1}$ over a 600$ sp circ$C temperature range (i.c. from 1200$ sp circ$C- 600$ sp circ$C) at four different cooling rates (0.25, 0.5. 1.0 and 2.0$ sp circ$C/sec). The reheating temperature and time were varied and the effect of this on precipitation is discussed. / The analysis of the CCC test results, and the optical microscopy observations, indicated that neither solute drag nor phase transformation is responsible for the deviations observed in these flow curves. TEM bright field images were used to verify the presence of precipitates, and to calculate the strengthening influence of these particles on the flow curve. It is shown that, in the niobium bearing materials, the precipitation of carbonitrides is responsible for the increase in flow stress. Conversely, in the titanium bearing materials, the titanium carbonitride precipitates were determined to have no effect on the flow stress. / It was discovered that increasing the solution temperature and time resulted in the occurrence of precipitation at higher temperatures, and that these precipitates were coarsened to a greater extent. Also, when the holding temperature and/or the holding time was decreased, the amount of niobium put into solution decreased, which led to precipitation starting at lower temperatures. / A method was developed for determining the precipitation start and finish temperatures from the CCC results. These temperatures were converted to precipitation start and finish times for each of the four cooling rates. This revealed that the precipitation start and finish times increase with decreasing cooling rate in both the 0.2% Nb and 0.1% Nb + 0.1% Ti stainless steels. Finally, a continuous cooling precipitation diagram was constructed for the two niobium bearing materials using these start and finish times.

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.