3. Electronic Theses and Dissertations (ETDs) - All submissions
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Item Investigating the corrosion resistance of copper-ruthenium coatings(2018) Zaba, WinnieCopper has been widely used, and its increased application in different industries resulted in high demands. With more applications, it has increased the need to improve the mechanical, and corrosion properties to improve its life span during operation. Pure copper has been used in many aqueous environments (e.g. pipe lines, storage tanks, and electro-winning) because of its good conductivity and corrosion resistivity. However, when it is exposed to harsh environmental conditions with high acidity it experiences corrosion. This research focuses on these corrosion characteristics. Appropriate surface chemistry is very important in many of the copper applications. Surface engineering techniques have been applied to improve the corrosion property of many materials like stainless steel, but only a few scientific investigations and developments have been done on copper. This development has been carried out by introducing ruthenium to the copper surface to improve the corrosion resistance and serviceability of copper in general. The ruthenium was added to the copper surface using thermal spray coating high velocity oxygen fuel spray coating, cold spray coating, spark plasma sintering, and electroplating. One should note that the nature of the surface coating and arrangement of the powder particles determines the overall protection that can be achieved/induced. For the different coatings and alloys, ruthenium was added in 0.5, 1, and 2 weight percent. This research found that in many cases, the corrosion resistance increased with increase in ruthenium content. The HVOF and SPS experienced the same trend. The CSC coating did not achieve any corrosion resistance improvement when compared to as-received copper. The electroplating of a copper substrate successfully decreased the corrosion rate in sulphuric acid at 65°C. The electroplated powders had contaminations that affected the corrosion characteristics of the coating and the alloy. Other properties of the material were also affected after the ruthenium addition. These also include the hardness of the materials which was increased with the increase in ruthenium content. The research limitations encountered was the shortage of equipment to perform other tests like the scratch adhesion test which would have validated the adhesion property of the coatings.Item Galvanic interactions between minerals during dissolution(1994) Holmes, Paul RichardA quantitative description of galvanic interactions between sulphide minerals based on thermodynamic and kinetic parameters has been developed. The basis for quantitative description involves conducting a voltage balance over the galvanic couple. The contributions to the voltage balance include the galvanic couple cell emf, kinetic descriptions of the anodic and cathodic half reactions, the voltage characteristics 'of mineral-mineral contacts and solution voltage losses. The rates of the anodic and cathodic half' reactions were modelled by the Butler-Volmer equation and ti1ediffusion equation. A potentiostat was used to vary the voltages losses across mineral-mineral contacts. TIle galvanic couples were constructed. as rotating ring disc electrodes and hence electrolyte voltage losses were negligible. Three galvanic couples, copper-platinum, copper-pyrite and galena-pyrite, were electrochemically characterised under different conditions of ferric concentration, electrode rotation rate and temperature. The effect of illumination on the anodic dissolution of galena was investigated. The electrochemical model is in good agreement with experimentally measured galvanic currents. Galvanic interaction is a dynamic function and various models are developed which account for dynamic behaviour in galvanic cells.