No description available.

No description available.

No description available.

No description available.

D.Sc. / Please refer to full text to view abstract

This dissertation presents studies of both anodic and cathodic electrodeposition of thin films, and their applications as supercapacitors and electrocatalysts for polysulfide reduction and oxidation.

A dissertation submitted to the Faculty of Science, University of the Witwatersrand, Johannesburg, in fulfilment of requirements for the degree of Master of Science. May 2016. / Tungsten carbide cobalt (WC-Co) cemented carbides are widely used for cutting, drilling, machining and as wear resistant materials due to the combination of high hardness and fracture toughness. In this work, we report on as-milled and as-sintered WC-10Co-20Fe samples which were ball milled for 15 hrs and sintered using liquid phase sintering (LPS). These samples were investigated by Vickers hardness test, microstructural analysis, X-ray diffraction (XRD), transmission Mössbauer spectroscopy (TMS) and conversion electron Mössbauer spectroscopy (CEMS) techniques. A mean hardness value of 1160 ± 42 HV was obtained for WC-10Co sample while a value of 776 ± 35 HV was determined for the WC-10Co-20Fe using the Vickers hardness tester. The lower hardness value for WC-10Co-20Fe is attributed to the high volume of the binders (10% Co and 20 %Fe) incorporated in the sample. The microstructural analysis of the as-sintered WC-10Co and WC-10Co-20Fe samples reveals that the light regions represent the WC phases and the dark regions signify the presence of the Co and CoFe phases in the as-sintered WC-10Co and WC-10Co-20Fe samples, respectively. The energy dispersive spectroscopy (EDS) of the as-sintered samples shows the presence of the starting powders used (WC, Co and Fe) and some Cr contamination resulting from either the production process or the starting powders. / GR 2016

This research project is a preliminary investigation of the effect of SiC abrasive breakdown on the wear rate of a WC-12wt%Co mining alloy. Wear tests were carried out on a two body-sliding wear apparatus under (a) “Ideal” (replacing the SiC paper periodically to ensure continual exposure to fresh abrasives), (b) “No debris” (removing the wear debris periodically) and (c) “With debris” (retaining the wear debris for the entire wear test) wear conditions. The WC-12wt%Co specimens and SiC abrasive grits were examined before and after the wear tests using optical, stereo and electron microscopy. As wear progressed, the SiC abrasives blunted thereby increasing the abrasive/specimen contact area, resulting in a reduction in the WC-12wt%Co wear rate. Wear debris clogging the interstices between the abrasive grits caused a further reduction in the WC-12wt%Co wear rate by adding to the abrasive/specimen contact area already created by blunting. Increasing the applied load resulted in an increase in the WC-12wt%Co wear rate under “Ideal” wear conditions. Under the remaining wear conditions, the increased load resulted in a faster deterioration of the SiC grits. The dominant wear mechanisms under all conditions are characterized by hard abrasive wear that caused extensive grooving, Co binder extrusion and cracking and fragmentation of WC grains.

A thesis submitted in fulfilment of the requirements for the degree of Doctor of Philosophy in the Department of Chemical Engineering, University of the Witwatersrand. / This work was undertaken to study the growth rate of APT crystals and hence obtain some information on the nucleation rate [Abbreviated Abstract. Open document to view full version] / AC2017

Thesis (M.S.)--University of Missouri-Columbia, 2006. / The entire dissertation/thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file (which also appears in the research.pdf); a non-technical general description, or public abstract, appears in the public.pdf file. Title from title screen of research.pdf file viewed on (February 26, 2007) Includes bibliographical references.