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School of Chemistry, Faculty of Science, University of Witwatersrand, Johannesburg, South Africa Johannesburg, 2016 / The synthesis of pure layered clay minerals has to be evaluated at low temperatures, pressures and short reaction times to scale up to commercial processes. However, it has been discovered that under such reaction conditions, reactions experience considerable difficulties. Such difficulties include low yields of products that occur with associated other minerals, and long reaction times. Thus, the synthesis of synthetic clay minerals is commonly approached by the hydrothermal technique, which involves the crystallization of substances at high vapour pressures and temperatures. However, the employment of the hydrothermal technique is time- and water consuming, thus, the need for an energy-saving and reaction accelerating process method. In the work presented here particular interest is paid to the synthetic layered clay mineral pyrophyllite, which is used as a pressure transmitting medium in the making of synthetic diamond. As opposed to the hydrothermal technique, this work adopts the synthetic method resin gel for the synthesis of these layered materials. Preliminary results by Loren Purcell have shown that the resin-gel synthesis method has been able to make apparently layered materials that appear to have a thermal gravimetric profile that indicates a gradual mass loss of both surface and structural water. The work presented here reproduces these results and further explores other Si\Al ratio’s, silica and alumina precursors for the synthesis of pyrophyllite-like materials and the different heating methods of the gels. Transmission electron microscopy (TEM) shows that irrespective of the synthesis conditions sheet-like or platy crystals are formed. Scanning electron microscopy (SEM) confirms on the TEM observations and shows that the surface texture of the crystals has a compact appearance. Thermal gravimetric analysis (TGA) of the materials confirms on previous observations from preliminary results, materials indicate both adsorbed surface and interlayer water. Powder Xray diffraction (PXRD) is inconclusive of the determination of phase pure pyrophyllite. Furthermore, Brunauer-Emmett-Teller (BET) reveals that the materials are mesoporous solids and the materials were also characterised by DSC, Raman and HRTEM. / MT2016

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The objective of this study was to determine the effects of processing on sodium - potassium and calcium - phosphorus ratios in tuna canned in oil and in water, peanut butter, white and whole wheat flours. Mineral levels were determined by atomic absorption spectrophotometry in food samples at various stages in the production of these finished products. The average sodium - potassium ratios of the tuna samples were: 1.37 raw, 1.24 precooked, 1.87 canned in oil and 1.61 canned in water. Processing did not significantly effect sodium and potassium ratios in canned tuna. The average calcium - phosphorus ratios of the tuna samples were: 0.034 raw, 0.024 precooked, 0.034 canned in oil and 0.065 canned in water. The ratio of the canned in water meat was significantly effected by processing. The average sodium - potassium ratios of the peanut samples were: 0.034 raw, 0.043 roasted, 0.031 blanched and 0.781 peanut butter. The ratio of peanut butter was significantly greater than the ratios of the other peanut samples. The average calcium - phosphorus ratios of the peanut samples were: 0.148 raw, 0.121 roasted, 0.141 blanched and 0.128 peanut butter. These ratios were not significantly effected by processing. The average sodium - potassium ratio was 0.16 in white flours, 0.84 in whole wheat flour and 0.89 in the kernel. The average calcium - phosphorus ratio was 0.14 in white flours, 0.07 in whole wheat flour and 0.07 in the kernel. The ratios of the kernel and whole wheat flour were not significantly different. Processing significantly effected the ratios of the white flour. The preferred concentration of sodium chloride and a 1:1 sodium - potassium chloride mixture in white and whole wheat breads was also studied. Bread samples were made with 1.0%, 0.75% and 0.5% levels of both salt treatments. They were evaluated by an untrained flavor panel for overall desirability with a nine point hedonic scale. The judges preferred a sodium chloride white bread with a 7.0 sodium - potassium ratio, and a sodium chloride whole wheat bread with a 3.29 ratio. These ratios were both lower than those found in commercial products. White and whole wheat breads made with 0.75% sodium chloride were as acceptable as breads made with 1.0% 1:1 sodium - potassium chloride mixture. The sodium - potassium ratio of the salt mixture white bread was 1.20 and the ratio of the whole wheat bread was 0.91. The addition of salt to finished products for flavor had an effect on the sodium - potassium ratio of the foods studied. Also, reducing the amount of added salt to commercial breads and replacing some sodium chloride with potassium chloride were acceptable means of lowering the sodium - potassium ratios of white and whole wheat breads. / Graduation date: 1982

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Thesis (Ph. D.)--University of Texas at Austin, 2000. / Vita. Includes bibliographical references (leaves 219-237). Available also in a digital version from Dissertation Abstracts.

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