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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

Electron paramagnetic resonance (EPR) and Mössbauer spectroscopy were used to examine the distribution of iron in mitochondria from Saccharomyces cerevisiae. These organelles were packed into EPR and Mössbauer cuvettes, affording spectra with unprecedented signal/noise ratios. EPR spectra of as-isolated intact mitochondria exhibited fourteen distinct signals, some of which were assigned according to previously reported g-values obtained using isolated proteins. Signals from adventitious manganese (II) and iron (III) were largely removed when mitochondria were isolated in buffers supplemented with the metal chelators EDTA or EGTA. Signals were simulated and intensities were quantified to afford spin concentrations and estimates of the concentration of EPR-active species in mitochondria. The effects of treating samples with chemical modifiers were examined. Packed samples were analyzed for protein and metal content, affording averaged values of 50 mg/mL [protein], 590 µM [Fe], 340 µM [Cu], and 17 µM [Mn]. 57Fe-enriched intact mitochondria isolated in the presence of metal chelators exhibited Mössbauer spectra dominated by three components. Approximately 60% of the 57Fe in the sample gave rise to a quadrupole doublet, most of which was diamagnetic. The parameters of this doublet are typical of S = 0 [4Fe-4S]2+ clusters and S = 0 ferrous heme groups. Spectra of samples reduced with dithionite, pH 8.5, suggested that at least half of this doublet arose from [4Fe-4S]2+ clusters. The second major component exhibited in the Mössbauer spectra arose from high-spin ferrous ions (10%-30%). The third major component (15%) came from iron exhibiting magnetic hyperfine interactions and is likely reflected in the Fe-containing species observed by EPR. The results presented here suggest that mitochondria contain ~ 600 µM of Fe overall, ~ 200 – 400 µM organized as [4Fe-4S]2+ clusters, with about 25 µM due to the [4Fe-4S]2+ cluster of aconitase. Approximately 60 µM – 200 µM of the Fe in mitochondria is high-spin ferrous ions, ~ 40 µM as the Rieske S = 1/2 [2Fe-2S]+ cluster of cytochrome bc1, and ~20 µM as the S = 1/2 [2Fe-2S]+ cluster of succinate dehydrogenase. The high-spin ferric hemes of the a3:CuB site of cytochrome oxidase and cytochrome c peroxidase each account for ~ 4 µM of Fe.

Electron paramagnetic resonance (EPR) and Mössbauer spectroscopy were used to examine the distribution of iron in mitochondria from Saccharomyces cerevisiae. These organelles were packed into EPR and Mössbauer cuvettes, affording spectra with unprecedented signal/noise ratios. EPR spectra of as-isolated intact mitochondria exhibited fourteen distinct signals, some of which were assigned according to previously reported g-values obtained using isolated proteins. Signals from adventitious manganese (II) and iron (III) were largely removed when mitochondria were isolated in buffers supplemented with the metal chelators EDTA or EGTA. Signals were simulated and intensities were quantified to afford spin concentrations and estimates of the concentration of EPR-active species in mitochondria. The effects of treating samples with chemical modifiers were examined. Packed samples were analyzed for protein and metal content, affording averaged values of 50 mg/mL [protein], 590 µM [Fe], 340 µM [Cu], and 17 µM [Mn]. 57Fe-enriched intact mitochondria isolated in the presence of metal chelators exhibited Mössbauer spectra dominated by three components. Approximately 60% of the 57Fe in the sample gave rise to a quadrupole doublet, most of which was diamagnetic. The parameters of this doublet are typical of S = 0 [4Fe-4S]2+ clusters and S = 0 ferrous heme groups. Spectra of samples reduced with dithionite, pH 8.5, suggested that at least half of this doublet arose from [4Fe-4S]2+ clusters. The second major component exhibited in the Mössbauer spectra arose from high-spin ferrous ions (10%-30%). The third major component (15%) came from iron exhibiting magnetic hyperfine interactions and is likely reflected in the Fe-containing species observed by EPR. The results presented here suggest that mitochondria contain ~ 600 µM of Fe overall, ~ 200 – 400 µM organized as [4Fe-4S]2+ clusters, with about 25 µM due to the [4Fe-4S]2+ cluster of aconitase. Approximately 60 µM – 200 µM of the Fe in mitochondria is high-spin ferrous ions, ~ 40 µM as the Rieske S = 1/2 [2Fe-2S]+ cluster of cytochrome bc1, and ~20 µM as the S = 1/2 [2Fe-2S]+ cluster of succinate dehydrogenase. The high-spin ferric hemes of the a3:CuB site of cytochrome oxidase and cytochrome c peroxidase each account for ~ 4 µM of Fe.

Mossbauer Spectroscopy has been used to investigate the site of Fe inclusions in a suite of synthetic diamonds (de Beers MDAS). Information on the hyperfine magnetic fields and electric field gradients at Fe sites in the diamond grains were obtained from Mossbauer Spectroscopy of diamond grains ranging in size from 25 to 250 um. The Fe inclusions in these samples resulted from the synthesis of the diamond grains in which Fe was used as a catalytic solvent. The Mossbauer measurements were carried at room temperature with a constant acceleration spectrometer operating in transmission geometry. The samples with the largest grain size of 180-250 um gave a well defined six component magnetically split spectrum, similar to the Zeeman split sextet obtained for natural iron. As the grain sizes decreased the intensity of the magnetically split components became greatly reduced and a strong paramagnetic component appeared. At grain sizes 105-45 um the spectra are dominated by a central single line with some evidence of an asymmetric doublet. For the finest grain size 38-25 um, the reappearance of the six magnetic hyperfine splitting components together with the strong central single paramagnetic component was observed. The change in the Mossbauer patterns observed with decreasing grain size suggest that a rapid phase transition of the Fe inclusions from ferromagnetic to superparamagnetic takes place. The analysis of Mossbauer spectra yielded a value of the hyperfine magnetic field of Bhf = -32.4(4) T and an electric field gradient in the range of Vzz = 1.4(4) 1.8( 7) X 10'8 V.cm- 2 at the site of the probe s7Fe nucleus. These values compare favourably with other measurements. / Thesis (M.Sc.)-University of Durban-Westville, 1992.

Software for Moessbauer spectroscopy has been developed for use on the Apple computer. This software is capable of collecting and fitting Moessbauer data when the Apple computer is interfaced with the ND2200 series multichannel analyzer. The software was tested in a study of the feasibility of using Moessbauer spectroscopy to study glass. Results indicate that iron in brown commercial glass and the volcanic glasses behaves similarly. This study concludes that Moessbauer spectroscopy is a promising method for the study of natural and archeological glasses and quality control in the manufacture of commercial glass. / Department of Physics and Astronomy

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