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LD2668 .T4 1966 C34 / Master of Science

Call number: LD2668 .T4 1966 H326 / Master of Science

published_or_final_version / Mechanical Engineering / Doctoral / Doctor of Philosophy

published_or_final_version / Electrical and Electronic Engineering / Doctoral / Doctor of Philosophy

L'utilisation de dispositifs thermoélectriques à base de films minces en SiGe est envisagée dans de nombreuses applications comme la micro-génération de puissance ou le refroidissement localisé de composants microélectroniques. Le SiGe possède en effet un net avantage en terme d'integrabilite mais souffre cependant d'un déficit en terme de performances. Dans le cadre de cette thèse, nous nous sommes intéressés à la nanostructuration de ce matériau en super-réseau de boîtes quantiques (SRBQ), celle-ci devant permettre une forte augmentation de son facteur de mérite, rendue possible par une forte altération du transport thermique à l'échelle nanométrique. La réalisation, par un outil CVD de type industriel, à 750 °C, de SRBQ monocristallins lourdement dopés est présentée à partir d'analyses morphologiques (AFM), structurales (MEB, MET) et chimiques (SIMS). Des phénomènes de forts échanges Si-Ge pendant la croissance sont notamment mis en évidence et corrélés avec des mesures de conductivité thermique qui ne démontrent pas un effet significatif des boîtes sur le transport thermique. L'élaboration de structures polycristallines originales est également présentée. Enfin, la question cruciale de la détermination du facteur de mérite est abordée, notamment concernant les problèmes d'incertitudes de mesure. Une

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The experimental work described in this thesis is aimed at the elucidation of the speciation of the zinc and germanium 8-hydroxyquinoline systems. A knowledge of this speciation could aid in modelling the kinetics of solvent extraction of zinc and germanium with 7alkyl derivatives of 8-hydroxyquinoline. In this study the stability constants of the ligand 8hydroxyquinoline with the ions H+, Zn2+ and Ge4+ have been investigated by potentiometry at 25°C in a partially aqueous medium. A titration technique was used in which the hydrogen ion concentration was monitored using a glass indicating electrode. The partially aqueous medium comprised of O. 1 mol dm- 3 NaCl04 in 60% (v/v) dioxane and the concentration levels of the reagents were at least millimolar. The analysis of the potentiometric data was carried out with the aid of the computer programs HALTAFALL, ESTA and STATGRAPHICS. The results obtained for the systems involving the H+ and Zn2+ ions compare with those reported in the literature. The stability constant of a protonated species in the zinc-8-hydroxyquinoline system (ZnLH) was established for the first time. Precipitates obtained from the Zn2+ titrations were identified as zinc 8-hydroxyquinolate dihydrate. The germanium 8-hydroxyquinoline system has not been studied previously via potentiometry techniques. The complex hydrolysed species of germanium in aqueous solutions and the unusual features displayed in the formation curves increased the complexity of species selection. Although a suitable model of the species present could not be determined some evidence suggests the presence of protonated species. Hence, a prerequisite for resolving the germanium-8hydroxyquinoline system could be a more complete understanding of the hydrolysis of germanium in the partially aqueous medium used. / Thesis (M.Sc.)-University of Natal, Durban, 1991.

Germanium can be extracted from aqueous solutions by KELEX 100 dissolved in an appropriate diluent. KELEX 100 is a commercially available chelating extractant containing the active constituent 7-(4ethyl-l-methyloctyl)-8-hydroxyquinoline. Previous work in the solvent extraction of germanium with this reagent has shown that germanium is extracted most efficiently at low pH. When the germanium is present in sulphuric acid solutions at pH less than 2, the extracted complex is GeL3+HS04-,however at pH 3 to 8, the metal is extracted as GeL2(OH)2 (where HL = KELEX 100). In this work, the extraction kinetics and equilibrium extraction of germanium in the GeKELEX 100 solvent extraction system is examined by AKUFVE and shaking assemblies, which both employ rapid mixing of the organic and aqueous phases, and by a quiescent interface Lewis Cell. The AKUFVE is a Swedish designed apparatus for solvent extraction, its performance and suitability for solvent extraction studies is evaluated using the extraction experiments carried out on the GeKELEX 100 solvent extraction system. Experiments conducted using an experimental set-up with a large interfacial area to phase volume ratio reveal that the extraction of germanium occurs in two distinct kinetic regimes. The first regime occurs in the first few minutes of an extraction experiment and is fast relative to the second kinetic regime which follows this fast initial extraction period and occurs until the extraction of germanium attains the equilibrium value. In this work an extraction mechanism involving interfacial reaction of germanium and extractant is proposed to explain this kinetic behaviour. An increase in ionic strength is shown to reduce the rate of germanium extraction in the Ge-KELEX 100 solvent extraction system. Modifiers, such as organic alcohols, are shown to greatly improve extraction kinetics. / Thesis (M.Sc.)-University of Natal, Durban, 1990.