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Thesis (Ph. D.)--University of Wisconsin, 1965. / Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliography.

This work has shown that nitrogen dioxide will selectively remove uranium hexafluoride from a mixture containing the hexafluorides of uranium, molybdenum and tungsten via the formation of nitrylium hexafluorouranate(V). The production of lower uranium fluorides and elemental sulphur or sulphur fluorides from many of the attempted preparations of uranium(VI) thiofluorides was predicted from a thermodynamic study of the stabilities of MC1nF6-n (M = U, Mo, W; n = 1-5), MOnF6-2n' MSnF6-2n (M = U, Mo, W; n = 1 or 2) with respect to decomposition and disproportionation. Sorption of the liquid hexafluorides on various potential sorbents was investigated. Encouraging results were obtained for cryolite. Salts such as ARuF6 (A = K, Rb, NH4) were synthesised by direct interactions between AF and RuF5 in AHF. These reactions were found to require the presence of a polar solvent. It was found that ruthenium pentafluoride in liquid uranium hexafluoride could be removed by the Introduction of trace quantities of water.

Attempts have been made to synthesise thio-fluoride species of tantalum, osmium and iridium. The reaction of tantalum thiotrichloride and tri- bromide with an excess of anhydrous HF yields [SH3]+ [Ta2F11]-. When anhydrous HF is added to a solution of TaSX3 (X =C1 or Br) in aceto- nitrile an oil is formed which contains =NH and ENH+. The thermal reactions of the hexafluorides of osmium and iridium with zinc and boron sulphides yield the adducts SF4.MF5 (M=Os or Ir). Infra-red and X-ray powder diffraction studies indicate that they have contributions to the bonding from the ionic formulations [SF3]+ [MF6]-. The reaction of MF6 with antimony sulphide in anhydrous HF gives only lower oxidation-state fluorides. The reaction of the alkali metal fluorides with tungsten thiotetra-fluoride in anhydrous HF has yielded the first examples of solids containing [W2S2F9]- and [WSF5]-, viz. M+[W2S2F9]- (M=Li, Na, K, Rb or Cs) and M+[WSF5]- (M=Rb or Cs). Nitrosyl fluoride reacts rapidly with tungsten thiotetrafluoride to yield [NO]+ [WOF5]-, [NO]2+ [WF8]2- and sulphuryl fluoride. However, a low-temperature n.m.r. study has shown that the reaction initially yields [W2S2F9]- and [WSF5]-. Tungsten oxidetetrafluoride reacts with an excess of sulphur tetra-fluoride to give [SF3]+ [W2O2F9]-. X-ray powder diffraction, infra-red and n.m.r. studies have shown that fluorine bridging between [SF3]+ and [W2O2F9]- in the solid state or in solution in sulphur dioxide is minimal. The reaction between tungsten thiotetrafluoride and sulphur tetrafluoride yields only tungsten hexafluoride and sulphur. Xenon difluoride reacts violently with tungsten thiotetrafluoride in the solid state to yield tungsten hexafluoride, xenon and fluorides of sulphur. When the reaction is conducted in sulphuryl chloride fluoride at low-temperature a red-brown solution is formed. This has been shown to consist of tungsten hexafluoride and the radical cation, S8+. by n.m.r. and e.s.r. spectroscopy. The standard enthalpy of formation of tungsten thiotetrafluoride has been determined by hydrolysis in alkaline media.

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Philosophiae Doctor - PhD / Search for an ideal scaffold for guided tissue/bone (GTR/GBR) regeneration continues as till now none of the commercially available GTR/GBR membrane fulfils the desired criteria. Currently, a variety of new materials and techniques have been investigated all over the world to improve the properties of GTR/GBR membranes. In the recent past three dimensional bioactive scaffolds composed of natural polymers have gained enormous popularity as potential future GTR/GBR devices. Electrospinning has emerged as one of the relatively simple, cost effective and efficient technique to fabricate three dimensional nanofibrous scaffolds in the field of tissue engineering. The rationale of this project is to investigate the natural polymers based bioactive nanofibrous scaffolds for GTR/GBR applications in the field of Periodontology.

Thesis (Ph. D.)--University of Wisconsin, 1966. / Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliography.

A study of the reactions between molybdenum and tungsten disilicide (MoSi2 and WSi2) with anhydrous hydrogen fluoride and fluorine was carried out to investigate the chemical behaviour of the materials. These two compounds were used as alternatives that resemble the chemical behaviour of uranium silicide (U3Si2). An extensive literature survey of U3Si2 processing techniques is included, which guided the process selection for this work. The thermogravimetric results of a study into the dry fluorination of molybdenum and tungsten disicilides using both anhydrous hydrogen fluoride and dilute fluorine gas as fluorinating agents are reported. For both solids the observed reactions with fluorine follow the thermodynamically predicted routes, in which the formation of the volatile metal hexafluorides, along with gaseous silicon tetrafluoride was observed. The disilicides get fully converted at roughly 300 to 400 °C respectively. The expected products for the reactions of both solids with hydrogen fluoride are solid tungsten metal, solid molybdenum metal, hydrogen gas, and gaseous silicon tetrafluoride. The metal fluorides (WF4 and MoF3) were not obtained because they form at low temperatures only. Therefore the metals of molybdenum and tungsten were obtained as final products respectively from both reactions; and were verified with the aid of XRF and XRD analyses. Mass-transfer phenomena are shown to play a role in the reactions between hydrogen fluoride and both disilicides, preventing unrestrained complete fluorination of the two solids. Kinetic parameters are reported and the rate limiting mechanisms identified. Copyright / Dissertation (MSc)--University of Pretoria, 2012. / Chemical Engineering / unrestricted

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Background: Studies of assessing dietary fluoride intake in children have employed different dietary methods mainly “2-day duplicate” and “3-day food diary” methods. However, none of these methods have been validated or standardised. Main aims: The main aims of the current study were to develop a better understanding of strengths and weaknesses of dietary assessment methods “2-day duplicate plate” and “3-day food diary” by comparing dietary fluoride intake estimated by each method and evaluate the validity of the two methods for estimating dietary fluoride intake in young children. Methods: Sixty one healthy 4-6 year old children living in fluoridated area of the north-east of England since birth were recruited via 10 primary schools. Dietary information was collected using “2-day duplicate plate” and “3-day food diary” methods. Two 24-h urine samples and two samples of post brushing expectorate (a mixture of saliva, toothpaste and water used to rinse after brushing) from each child. Completeness of 24-h urine samples was checked using urinary excretion of creatinine and urinary flow rate. Validity of the two dietary assessment methods was checked by measuring urinary excretion of nitrogen and potassium as independent validity checks. Total daily fluoride intake from diet and toothpaste ingestion and urinary fluoride excretion was determined for each child. Results: All participated children completed all aspects of the study. According to the validity criteria, dietary data of 58 (95%) children, when collected by the 3-day food diary, were considered valid. However, when the dietary data were collected by the 2-day duplicate plate method, the data for 46 (75%) children were viewed as valid. Mean total dietary fluoride intake was 0.533 mg/d by the 3-day food diary method and 0.583 mg/d by the 2-day duplicate plate method. No statistically significant difference in total dietary fluoride intake was observed between the two methods. The mean difference in estimated dietary fluoride intake by the two dietary assessment methods was -0.050 mg/d with 95% limits of agreement of -0.501 to + 0.401 mg/d. Conclusion: Either the 3-day food diary or the 2-day duplicate plate method can be used when investigating mean total daily dietary fluoride intake of a population. However the methods cannot be used interchangeably at the individual level.