3. Electronic Theses and Dissertations (ETDs) - All submissions
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Item Carbothermic reduction of alumina into a metallic solvent phase(1998) Caizergues, DerekExperiments have been conducted at around 17000C to determine the whether carbothermic reduction of alumina is possible at these temperatures. Total pressure of the system was reduced to around 30 kPa and various metallic solvents such as copper, nickel, iron and tin were used to dissolve the metallic aluminium produced. The use of a solvent (and hence decreasing the activity of metallic aluminium) and a lower pressure are thermodynamic requirements to increase the extent of reduction under a given set of conditions. This enables the use of lower temperatures than are required under atmospheric conditions. The highest recovery of aluminium was achieved with the nickel solvent decreasing in order from iron, copper and tin. This ranking was also in accord with the extent of deviation from ideality in the respective binary solutions of these solvents with aluminiur, The nickel-aluminium system displays the largest negative deviation from ideality whereas the till, aluminium system showed a positive deviation. The rate and extent of the reduction was found to be highly dependent on temperature and pressure. The pseudo first order reaction rate was found to be the primary order for the reduction of aluminium in all the solvents used. It is also suggested that the reduction rate was controlled primarily by chemical reaction rate father than by transport processes. This is due to the extreme sensitivity of the rate and extent of the reaction to temperature.Item Hardness and penetration of gutta percha when exposed to two endodontic solvents(2015-04-21) Patel, EbrahimPurpose: Endodontic retreatment requires the removal of the obturation material from the root canal system. Gutta percha (GP), the most commonly employed obturation material, requires mechanical instrumentation coupled with a chemical adjunct to facilitate its removal. Xylene and Eucalyptus oil are recommended as endodontic solvents due to their dissolving capacity of GP. This study sought to test the changes in the hardness and penetrability of three types of GP (Conventional, Thermafil® and Guttacore™) when exposed to these solvents, utilizing distilled water as a control. Method and materials: Textural analysis was performed to determine the hardness by testing for rigidity, and the penetrability by testing for deformation energy and resilience. These properties were tested on 81 GP cones prior to, and following solvent exposure. For each outcome variable, results were tabulated by group. Between-group differences were assessed by means of a General Linear Model, with the outcome variable as the dependent variable and the solvent, GP type and solvent-GP type interaction as the independent variables. Results: A significant decrease in rigidity and deformation energy was observed across all groups. Resilience was observed to decrease with the thermoplastic GP, Thermafil and Guttacore, but increased with conventional GP. Thermoplastic GP was more amenable to a reduction in hardness and penetration when compared with Conventional GP. A greater reduction in the hardness of Thermafil was observed with Eucalyptus oil. Conventional GP was susceptible to a significant reduction in hardness with both solvents, however its penetrability may be reduced following exposure to Xylene. Guttacore was significantly altered by both solvents. Conclusions: Considering the toxicity profile of Xylene, and the biocompatibility and antimicrobial effects of Eucalyptol, Eucalyptus oil is recommended for use during endodontic retreatment.