Gas dispersion properties of flotation systems, such as: bubble size (db), gas holdup (epsilong) and gas velocity (Jg) are became increasingly relevant in the past 10 years for optimization of flotation systems. Flotation system kinetics have been related to the bubble surface area flux (Sb), which is known to be derived from gas dispersion properties (Jg, db). Modeling of flotation systems and in particular flotation kinetics requires reliable measurements of Jg and to do this, two novel sensors were developed. The sensors collect bubbles by natural buoyancy, and relate gas flow to either accumulation of the gas bubbles (discontinuous technique) or the pressure drop across an orifice (continuous technique). Fundamental flow equations were derived to relate those properties to Jg. Experiments range from laboratory scale (column of 15.24 cm diameter and 4 m high) to industrial flotation systems (up to 130 m3 flotation cells) were performed to validate the sensing principles and reliability of the sensor measurements. Over the range of Jg from 0.20 to 3.00 (cm/s) the continuous sensor accuracy ranges from –2.40 to –4.20 % and –0.90 to –1.93 % for tubes of 7.62 and 10.16 (cm) diameter respectively. Sampling tests indicate that tubes of 7.62 and 10.16 (cm) diameter gave same results for discontinuous and continuous techniques. In contrast, for tubes smaller than 7.62 (cm) a bias occurs between the two techniques, being the continuous always higher than the discontinuous, for example the difference between the on-off Jg sensor with a 0.5 (inch) diameter tube (1.27 cm) and the continuous 4 (inch) (10.16 cm) diameter tube is as high as 45 %. Analysis of the sensitivity of the relationship between sensors measurements and process parameters, for example bulk density, were performed. Both sensors were used in industrial applications to set the gas profiles across banks of flotation cells and, along with metallurgical analysis, allowed the industrial operators, to / Les propriétés des systèmes de flottation ayant rapport à la dispersion de gaz, par exemple: la taille des bulles (db), la charge gazeuse (epsilong), et la vélocité de gaz (Jg), sont devenues de plus en plus importantes les vingt dernières années dans l’optimisation de ces systèmes. Une relation a été établie entre la cinétique des systèmes de flottation et le flux superficiel des bulles (Sb), dérivée des propriétés de la dispersion de gaz Jg et db. La modélisation des systèmes de flottation et particulièrment de la cinétique requiert des mesures exactes de Jg et pour cette raison, deux nouvelles sondes ont été développées. Ces sondes recueillent les bulles par flottabilité naturelle et font le lien entre la circulation gazeuse et ou l’accumulation des bulles (technique en discontinu) ou le changement de pression à travers un orifice (technique en continu). Des équations de bases pour la circulation ont été dérivées afin de relier ces propriétés à Jg. Des expériences en laboratoire (colonne de 15.24 cm de diamètre et 4 m de hauteur) et en industrie (volumes cellulaires jusqu’à 130m3) ont été complétées afin de valider les principes de précision et de fiabilité des mesures des sondes. Pour des valeurs de Jg entre 0.20 et 3.00 (cm/s) la précision de la sonde a été variée entre –2.40 et 4.20 % et entre –0.90 et –1.93 % pour des diamètres de tubes de 7.62 et 10.16 (cm) respectivement. Des tests par prélèvement ont indiqué que les tubes avec un diamètre entre 7.62 et 10.16 (cm) ont donné les mêmes résultats pour les techniques en continu et en discontinu. Par contraste, pour les tubes de diamètre de moins de 7.62 (cm), la tendance de la sonde en continu était de donner une mesure plus élevée que celui en discontinu. Par exemple, la différence entre une sonde en discontinu avec un diamètre de 1.27 (cm) et celui en continu avec un diamètre de 10.16 (cm) peut atteindre 45%. L’analyse de la p

An electrochemical permeation cell has been used to test the influence of microstructural characteristics of metal specimens and electrochemical processing parameters on electrochemical hydrogen diffusion. The affect of intercrystalline volume, entry surface roughness, cathodic charging current density and different cold working conditions on hydrogen diffusion through polycrystalline metals was tested. Nanocrystalline specimens of pure nickel and of 80%-Nickel 20%-Iron were tested to determine the affect of intercrystalline volume on hydrogen breakthrough diffusion. Specimens of pure palladium were tested to determine the influence of entry surface roughness, cathodic charging current density, different cold working and texture conditions on hydrogen permeation. A series of permeation tests performed on nanocrystalline nickel were used to optimize the measurement conditions. Experiments performed on 80/20 Ni-Fe thin foils determined that the hydrogen breakthrough diffusion coefficient drops dramatically with increasing grain size in the range of 20--40 nanometers. Above 40 nanometers, the breakthrough diffusion coefficient reaches a steady-state level. This decrease in breakthrough diffusion coefficient is thought to be due to a decrease in intercrystalline volume. Tests performed on palladium showed that the hydrogen effective diffusion coefficient increased logarithmically with increasing cathodic charging current density. These experiments also demonstrated that the optimum charging current density for palladium is 0.1 mA/cm2. Other tests on palladium determined that the surface roughness, on the entry side of the specimens, had no influence on the effective diffusion coefficient, processing efficiency or hydrogen subsurface entry concentration. Experiments on cold rolled palladium sheets determined that cold working dramatically lowers both the hydrogen subsurface entry concentration and effective diffusion coefficient. The lowering of the effective diffusio

The Melt-Leach-Evaporation (MLE) process is under development for the extraction of valuable Group IA or IIA metals of the Periodic Table, such as lithium, calcium, magnesium and strontium. The process consists of mixing and contacting the value metal source material, which might be an ore or concentrate, with an excess of molten metal which is acting as a reductant and lixiviant. In the process, the value metal extracted from the source material is dissolved in the excess molten metallic solvent and is subsequently extracted as a vapour by vacuum distillation. The vapour is condensed and recuperated in the metallic state. / An experimental program involving eight experiments was carried out. The experimental procedure consisted in essence of melting the aluminum reductant in a crucible and adding the source material, SrCO$ sb3,$ and other reactant (Mg or Bi). (Abstract shortened by UMI.)

The design of thermomechanical processing schedules to control microstructures requires the knowledge of the austenite-to-ferrite transformation start temperature (Ar$ sb3$). Further, in curved mold continuous casting, transverse cracking occurs during the unbending procedure to straighten the solidified curved strand, and this can also strongly depend on the austenite-to-ferrite transformation. In both of these industrial processes, during deformation, the temperature usually decreases continuously. Thus, two new methods to determine the Ar$ sb3$, based on continuous cooling compression (CCC) and continuous cooling torsion (CCT), have been developed. While the latter is applicable for low and high strains, the former can be only used for low strains. / The aim of this investigation was to determine the effect of deformation in the single phase austenite and two phase austenite plus ferrite region on the transformation and dynamic transformation behaviour of austenite-to-ferrite. CCC tests were carried out on a low carbon steel and the influence of strain, strain rate, cooling rate and austenite grain size, was examined. / During the application of strain, the generated dislocations cause an increase in stored strain energy. This energy adds to the driving force for austenite-to-ferrite transformation, increasing the kinetics of this transformation, raising the Ar$ sb3$ in this way. The faster kinetics leads to a finer polygonal ferrite grain size after transformation. In contrast to the effect of increasing strain, accelerated cooling rates decrease the transformation start temperature, but can still lead to grain refinement via high nucleation rates. By increasing the cooling rate, fine acicular ferrite with a high aspect ratio could be obtained. Since, the ferrite grain size is directly related to austenite grain size, by varying austenite grain size, a wide range of ferrite grain sizes could be obtained. Finally, deforming close to the Ar$ sb3$ maximizes the strain effect on dynamically transformed ferrite.

The way in which texture development is affected by hot rolling, intercritical rolling, and warm rolling was studied in a plain carbon, a niobium microalloyed and an interstitial free steel. Three processing parameters were varied: the austenitizing temperature (1250$ sp circ$C or 1150$ sp circ$C), amount of reduction (90% or 75%) and finish rolling temperature (1020$ sp circ$C, 870$ sp circ$C, 770$ sp circ$C, 730$ sp circ$C and 630$ sp circ$C for the first two materials, and 1020$ sp circ$C, 920$ sp circ$C, 870$ sp circ$C, 820$ sp circ$C, 720$ sp circ$C and 620$ sp circ$C for the IF steel). It was found that lower reheating temperatures and larger deformations lead to more intense textures. The effect of finish rolling temperature was different for each steel. In the plain carbon, only warm rolling produced a strong texture. In the interstitial free steel, the strongest textures were again produced by rolling in the ferrite range. In the niobium microalloyed steel, the retardation of austenite recrystallization intensifies the fcc deformation texture components; thus, a fairly strong texture is inherited by the ferrite, which is in turn enhanced by further deformation. The experimental textures were compared with the transformation textures predicted by using the Kurdjumov-Sachs relationship. It was found that when most of the reduction was applied in the austenite recrystallization range, the cube texture appeared to form, which transformed preferentially into the rotated cube $ { 001 } langle110 rangle$. When the austenite remained in the pancaked state, the expected transformation products of the fcc rolling texture, i.e. the copper $ { 112 } langle111 rangle$, brass $ { 110 } langle112 rangle$, S $ { 123 } langle634 rangle$ and Goss $ { 110 } langle001 rangle,$ again appeared, with clear preferences for particular variants. The calculations indicate that the final ferrite texture formed from either recrystallized or deformed austenite is significantly modifi

Iron(III) solvent extraction removal from zinc process solutions by OPAP (octylphenyl acid phosphate) and D2EHPA (di-(2-ethylhexyl)phosphoric acid) was studied within the context of stripping with strong HCl such that a saleable waste-free iron product could be generated downstream. Operated under ambient extraction and HCl stripping conditions, 0.95 F OPAP was found to be a highly suitable extractant for the removal of iron(III) from strong synthetic ZnSO 4-H2SO4 solutions and for the preparation of concentrated iron chloride strip solutions. Its major advantages included: very low sulphate co-extraction; reasonable zinc co-extraction; very low chloride back-extraction; and sufficient iron build-up and acid balance when a 'moderate strength' HCl-FeCl2 strip feed (3.38 N HCl-58.5 g/L Fe(II)-9.7 g/L Fe(III)) was used. Certain advantages were exhibited by 1.25 F D2EHPA over 0.95 F OPAP. These included a greater relative stability in aqueous streams, slightly better Fe3+/Zn2+ selectivity, and a comparable iron(III) loading capacity (&sim;20 g/L) when operated at 50°C. However, major drawbacks with D2EHPA were identified which included significant sulphate co-extraction (approximately twenty times greater than 0.95 F OPAP) and ineffective stripping and hence poor iron build-up ( < 100 g/L) with the 'moderate strength' strip feed.

Previous use of the diffraction technique as a means of characterizing microstructure in multiphase steels has been generally limited to measurements of retained austenite. Other phases, specifically martensite, have not been examined in complex microstructures since there exists peak overlap with ferrite. This research looks at using neutron diffraction as a means to characterize martensite in a multiphase steel microstructure, thus providing a more complete characterization tool. / Three low carbon steels, comprised of a dual-phase, ferrite-martensite microstructure, were used in this study. Two diffraction methods were investigated; a direct deconvolution of the martensite peaks from the ferrite peak, and an indirect determination of martensite volume fraction from ferrite peak broadening. Lastly, mechanical properties were investigated in order to determine if a correlation exists with ferrite peak broadening. / The results indicate that the martensite phase has a prominent strain broadening effect in diffraction. The nature of this strain effect was hypothesized and a model was developed to confirm the findings. Finally, tensile testing showed that the mechanical properties were dependent on peak broadening and martensite volume fraction.

Enameling steel, used in a vast range of applications, can suffer from a surface defect resembling fish scale. In this study, the effects of several microstructural, physical and coating factors on the hydrogen diffusion in low carbon steel were investigated using an electrochemical permeation apparatus, to find out the way to prevent the surface defects on the enamel coatings. / A new mechanism explaining the formation of the surface defects on the enameling steel was proposed after summarizing the experimental results. Then, the effects of porosity, dislocation density, the surface roughness of a steel substrate, oxide passive layer and Pd coating on the hydrogen diffusion coefficient, hydrogen concentration and hydrogen flux were investigated. / The variations of hydrogen diffusion coefficient, hydrogen concentration in steel and hydrogen flux caused by all factors listed previously were calculated in order to understand the effect of these factors on hydrogen diffusion.

The existing approaches to the detection of precipitation are based on one of the following four techniques: (1) electron microscopy; (2) chemical or electrochemical extraction; (3) the measurement of electrical resistivity; and (4) the analysis of mechanical properties. These techniques can only be used at room temperature on quenched samples. However, the direct measurement of precipitation kinetics at high temperatures is also possible through analysis of the mechanical properties of the specimens. / In this work, a creep method was developed and applied to the detection of aluminum nitride precipitation in a dual phase 3% silicon steel. These steels are used in electric power applications, typically as magnetic core materials for transformers, electric motors and generators. Prior to loading, the specimens are solution treated for 20 minutes and then cooled to the test temperature. A constant stress is applied to the sample by means of a computerized MTS machine and the strain is recorded continuously during testing. Microstructural examination revealed that the austenite fraction and morphology and microstructure of the ferrite matrix are quite different depending on whether samples are directly heated or heated and then cooled to the test temperature. The resulting creep rate is sensitive to the occurrence of precipitation; thus the slope of the true strain-log (time) curve decreases immediately after initiation. The precipitation-time-temperature diagrams determined in this way are of classical C shape.

It is quite difficult to quantitatively define the ability of a material to be cold forged. The limit of the forming process is governed by a complicated interplay of such factors as material microstructure, rate of deformation, tool and workpiece geometry and the friction at the interface of the workpiece and tool. / The success of a cold forming process is primarily determined by the formability of the stock material. Consistent product quality and increase in productivity requires parts to be plastically deformed without failure. Expensive downtime, tooling damage and material waste are often the consequences of material failure during loading. A means of assessing formability is, therefore, clearly required. / A revised upset test is examined, seeking to represent the actual cold heading process and to minimize the effect of test specific factors, such as changing friction at the die-workpiece interface. It is designed to be easily used by industry, requiring minimal sample preparation and the use of a simple and reliable testing device. Preliminary tests are performed and the limitations of this test are investigated. Possibilities for future improvements are considered.