Cobalt crystals of commercial purity have been grown in an electron beam zone refiner. They were tested in tension at temperatures between 150°C and -196°C. The resolved shear stress—shear strain curves are similar in form to those for the high stacking-fault energy hexagonal metals zinc, cadmium, and magnesium. There is an initial linear region for shear strains up to around 150%, with a ratio of work hardening slope to shear modulus of about 2 × 10[superscript -4].This is followed by an upturn, which is, however, smaller in magnitude for cobalt than for the other metals. Values for the critical resolved shear stress vary from 97 Kg/cm² at room temperature to approximately 170 Kg/cm² at -196°C. Two crystals of high purity cobalt were also tested, giving a critical resolved shear stress at room temperature of 65-70 Kg/cm². The Cottrell-Stokes law is not obeyed, either for temperature changes between -196°C and 18°C. or for changes in the strain rate at room temperature. An explanation in terms of dislocation theory has been put forward. Activation energies for plastic flow have been tentatively evaluated to be of the order of 35 kT. Twinning was never observed in crystals pulled at room temperature. Deformation twins produced by bending a crystal at -196°C. took two forms, very thin ones similar in appearance to Neumman bands in iron, and more usual lenticular twins. The thin twins have a {11 2̄̅̅1}habit plane. Metallographic examination of crystals pulled to large extensions and electro-polished to remove slip lines showed small needle-like markings, probably fine twins. In addition to the deformation work, certain observations have been made concerning transformation markings which supplement the work of previous investigators. It was found that secondary transformation markings are not a necessary part of the transformation, and that primary markings form on cooling as well as on heating. / Applied Science, Faculty of / Materials Engineering, Department of / Graduate

Düsseldorf, Universiẗat, Diss., 2004.

Thèse (Ph. D.)--Université Laval, 2007. / Bibliogr. Publié aussi en version électronique dans la Collection Mémoires et thèses électroniques.

Typescript, etc. / Digitized by Kansas State University Libraries

Thesis (M.Phil.)--Chinese University of Hong Kong. / Bibliography: leaves 76-79.

M. Tech. Chemical Engineering Tshwane University of Technology 2013. / The effects on cobalt electrowinning at low concentrations, varied temperature range, presence of impurities and the change in flow rate of the electrolyte on current efficiency and cathode deposition quality was investigated. The investigation was conducted in a three-electrode cell configuration, however a SEC-CCS (Symmetric Electrolysis Current-Continuous Circulating System) type was used, and forced circulation of the electrolyte as a means of agitation to help in increasing the diffusion limit current density. A 20g/L cobaltous sulphate electrolyte was prepared and electrowon using a SEC-CCS cell, 20g/L boric acid was used as a buffer for hydrogen evolution, the electrolyte was introduced from the bottom of the cell at regulated investigated flow rates of 30, 60 and 90 L/h and discharged into the pump suction end establishing a continuous circulation of the electrolyte. The temperature was regulated between investigated range 35, 55 and 75oC using immiscible heating probe. A pH meter was used to measure the pH value of the solution and pH was manipulated using 120g/L of sulphuric acid and 2M sodium hydroxide to maintain pH 4. Investigations to apprehend the effects of impurities were carried out at standard cobalt electrowinning conditions with only cobalt concentration maintained at low values to support the effort of the study. A 20 g/L cobaltous sulphate was prepared together with 120 g/L sulphuric acid, 20 g/L boric acid, and operation conditions were maintained at 450 A/m² current density, temperature of 50°C and a pH of 4. Investigated impurities considered in this study were zinc (Zn) and iron (Fe) respectively; both impurities were introduced into the cell at concentrations of 50ppm and 100ppm each. Though impurities have an effect on cobalt electrowinning, more of their effects were evident in the cobalt deposition morphology, quality and current efficiency. This rather suggests that there's opposition for the available potential, the SEC-CCS set-up proved to be optimistic. The perpetual fluid flow pattern and electrochemical reaction surface requires steady flow of fluid at moderate pressure. This will continuously supply fresh feed and consequently the rate of mass transport adequate, adversely increasing fluid flow results in decrease in current efficiency, and rather cause high energy consumption. This statement is supported by insignificant effects of the flow rate on imperative cobalt electrowinning parameters such as cathodic overpotential, cell potential, energy consumption and current efficiency. The effects of temperature changes are observed to have significant effect on current efficiency and energy consumption. The cathodic overpotentials of cobalt electrowinning decreases with an increase in temperature and the transfer coefficients rather favors high temperature operation for cobalt electrowinning, however this conditions influences reductions in the current efficiency and adversely lowers the cathode deposition quality. The positive attribute of the SEC-CCS system in the cobalt electrowinning is that it minimized pitting and peeling as hydrogen bubbles of the plate surface and this somewhat increases the quality of the metal deposit morphology, and rather has insignificant attributes to electrowinning parameters

Thesis (Ph. D.)--University of Wisconsin--Madison, 1980. / Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references.

No description available.

Investigations have been carried out for a number of cobalt deposits in Australia including three from the Mt Isa Block in Queensland, several deposits in New South Wales, and one deposit each in the Northern Territory and South Australia, with respect to the identification of cobalt-bearing mineralisation and possible modes of formation. The deposits studied cover a range of deposit and mineralisation types including hydrothermal (e.g., cobaltite, Esperanza, Queensland; arsenopyrite, Dome Rock, South Australia) and sedimentary (secondary mineralisation such as the manganese wads at Bungonia, New South Wales). Deposits that were studied previously by the author (MSc thesis) in the Mt Isa Block have been used for comparison of mineralisation and temperatures of formation. The determination of the temperatures of formation of mineralisation, in particular with respect to cobaltite and arsenopyrite, by means of the application of the FeAsSCoAsS-NiAsS ternary phase diagram and the arsenopyrite geothermometer, has helped lead to deductions concerning the modes of deposition. Other deposit features such as structural constraints and associated mineralisation aided in the formalisation of conclusions. Many of the deposits are hydrothermal in nature and contain high temperature phases including molybdenite and uraninite. The latter represent geochemical and mineralogical clues which show that many of the ores were emplaced by igneous processes associated with granites. The findings of this study suggest that despite high percentages of substituting species in arsenopyrite, derived temperatures, from the application of the binary and ternary geothermometers, are comparable. It was noted that the presence of pyrrhotite and/or löllingite to act as buffers in the system is an important constraint on the comparability of derived temperatures. Potential processing applications for the extraction of cobalt from ores are briefly discussed, with respect to the type and cobalt content of mineralisation identified. The Esperanza and the Selwyn copper-gold deposits show the greatest potential for economic cobalt recovery. / Doctor of Philosophy (PhD)

No description available.