The aim of this thesis was to examine materials using high resolution X-ray diffraction techniques. Initial work involved the synthesis of various metal phosphates to investigate their suitability for charge density work. Many of these were discovered to be of insufficient quality for further study. Much of the phosphate synthesis work performed at the moment utilises an ionic liquid both as a solvent and structure directing agent which dictates the topology of the structure due to its size and charge density. As such the ionic liquid 1-ethyl-3-methylimidazolium hexafluorophosphate used in the synthesis process was examined with high resolution X-ray diffraction as it was possible to produce large pure crystals which could be examined further. A high resolution data set was also collected from the metal organic framework SIMOF-1 which produced a preliminary multipole model however further data collections are required to improve the quality of the model. A multi-technique investigation involving X-ray diffraction, solid state NMR and first principles calculations was carried out on the aluminophosphate material AlPO₄-15. A synchrotron X-ray single crystal diffraction study was carried out on the same sample as that used in solid state NMR studies. The model from the single crystal study, together with a model from a literature high resolution study of the same material, were used as starting points for the first-principles calculations of the NMR parameters. This enabled the ³¹P and ²⁷Al NMR spectra to be unambiguously assigned and all the NMR parameters calculated agreed well with the experimental spectra even without relaxing the X-ray derived structural models. Highlighting that as long as a good data set has been collected in the first place the atomic positions would not change too drastically. Other aspects of this thesis involved investigations into other ionothermally prepared systems such as the use of different phosphonate sources to provide functionality to the materials. This work resulted in some interesting findings such as the ionic liquid breaking down and being incorporated into the framework via the metal. Many of the structures produced were of a layered nature however a molecular structure was also synthesised which is unlike the vast majority of hydrothermally prepared phosphonates, which are layered. The negligible vapour pressure provided by the ionic liquid has enabled synthesis reactions to be investigated with glass vessels on an energy dispersive beam line. This work highlighted how it is possible to study the synthesis process in-situ and compare microwave assisted reactions against a conventional heating method, the results indicate that two different types of reactions are occurring resulting in different intermediates which is due to the way the reagents are heated. The microwave assisted reactions also result in larger purer crystals which highlights the importance of the method in materials synthesis. The use of a specially designed environmental gas cell was used to investigate the adsorption properties of the metal organic framework CPO-27-Co in-situ. Using the cell it was possible to locate sulfur dioxide physisorbed and chemisorbed sites with in the framework which could be removed by the application of a vacuum and heat. It was also possible to locate the chemisorbed sites for nitric oxide within the metal organic framework however due to the low scattering factor and disorder from the gas it was not possible to locate the physisorbed sites.

published_or_final_version / Chemistry / Doctoral / Doctor of Philosophy

The specific goal of the investigation was the measurement, as a function of temperature, of the self-diffusion coefficients of Pb210 and Cl36 in PbCl2-KCl compositions in the region of the first compound, and to calculate from these data the activation energy necessary for the diffusion of these ions.

The original purpose of this investigation was to attempt to apply the coulostatic method directly to a molten salt system. The inability to duplicate the reported capacity data for this system resulted in an investigation of the probable cause of this discrepancy between the data obtained by these different methods (14, 15).

In recognition of the shortcomings inherent to the operating temperature ranges of current fuel cell systems, namely the“temperature gap" between 200C and 600C, an effort to develop an intermediate-temperature molten-salt electrolyte fuel cell (IT-MSFC) was undertaken. In this type of fuel cell, the molten salt electrolyte is supported on a porous support, in a planar or other geometry similar to that used in existing fuel cell technologies, such as phosphoric acid fuel cell (PAFC) and molten carbonate fuel cells (MCFC). Such a fuel cell using a molten hydroxide electrolyte and Pt/C catalyst was constructed and tested using hydrogen and oxygen as fuel. The performance was comparable to that which has been obtained from PEM fuel cells at the low end of the voltage range, reaching 950ma/cm2 at 0.4 V in the highest performing test. Performance was superior to PEM fuel cells at the high end of the voltage range, due to the more favorable kinetics at the higher temperatures, with an open circuit voltage (OCV) of 1.0 V with a linear performance curve between 1.0 V and 0.6 V, which is characteristic of fuel cells with low kinetic overpotentials. Longevity of the fuel cell was very poor, however a number of experiments were undertaken to improve it, enabling extension of operating life from 5 minutes to 30 minutes, which is still far too low for practical use. The key problem was identified as electrolyte retention by the support matrix and possible degradation of the gas diffusion layer and catalyst. Experiments were also conducted using methanol vapor as fuel, and it was found to provide performance close to that recorded with pure hydrogen. Experiments were also conducted using several alternative molten salts, including nitrate and chloride eutectics. Combinations of nitrates with hydroxides added to act as a charge carrier produced a working fuel cell, however performance was greatly reduced. Though preliminary, the work described herein demonstrates the great potential of IT-MSFC, and outlines the work needed to make this type of fuel cell practical.

Thesis (Ph. D.)--University of Hong Kong, 2002. / Includes bibliographical references.

The mycotoxin, fumonisin B1 is produced by the mould Fusarium moniliforme, a common contaminant of maize and maize products. Small doses (mg/kg) of ingested fumonisin B1 have been shown to cause diseases and even death in animals, including non-human primates. Thus highly sensitive methods have been employed to detect fumonisin B1 presence in foods, feeds and in animals. This study comprised two parts.The initial part focused on establishing reliable extraction, purification and quantitation of fumonisin B1 using high-performance liquid chromatography (HPLC) on culture extracts. The second part was to analyse sera of Black African women with pre-eclampsia for the presence of fumonisin B1 using HPLC. Maize patty cultures and broth cultures were inoculated with Fusarium moniliforme PPRI 1059 and incubated. Fumonisin B1 was extracted and purified by centrifugation strong anion exchange chromatography (SAX). Eluents from SAX cartridges were analysed using Thin-layer chromatography (TLC) and fluorescence HPLC after o-phythadialdehyde (OPA) derivatisation. Fumonisin B1 standards on HPLC gave a retention time of 7.5 minutes using methanol/0.1 M sodium dihydrogen phosphate (68 + 32, pH 3.3) as mobile phase and a 25 cm C8 column. Patty cultures produced the highest yields of fumonisin B1. In the case of serum samples, a double-blind study was carried out using women attending the obstetric clinic at a large city teaching hospital. The population comprised normal, pre-eclamptic and eclamptic women. On HPLC analysis a significantly higher mean concentration of fumonisin B1 concentration was found in the eclamptic group (P<0,005) as compared to the other two groups.Thus fumonisin B1 may have a role to play in eclampsia for which the aetiology is still unknown. / Thesis (M.Med.Sc.)-University of Natal, 1999.

Thesis (Ph. D.)--University of Missouri-Columbia, 2004. / Typescript. Vita. Includes bibliographical references (leaves 118-122). Also available on the Internet.

Thesis (Ph. D.)--University of Missouri-Columbia, 2004. / Typescript. Vita. Includes bibliographical references (leaves 118-122). Also available on the Internet.

No description available.