Made available in DSpace on 2014-10-09T12:32:10Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T13:57:55Z (GMT). No. of bitstreams: 0 / Dissertacao (Mestrado) / IPEN/D / Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP

Made available in DSpace on 2014-10-09T12:36:26Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T13:59:27Z (GMT). No. of bitstreams: 1 03872.pdf: 3194792 bytes, checksum: c608bc82f2dd8dcd16cb89209d801adc (MD5) / Dissertacao (Mestrado) / IPEN/D / Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP

Made available in DSpace on 2014-10-09T12:48:21Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:07:03Z (GMT). No. of bitstreams: 1 09313.pdf: 17480162 bytes, checksum: 68e2e858c1f33e3137e90b76bd5cbc99 (MD5) / Tese (Doutoramento) / IPEN/T / Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP

Made available in DSpace on 2014-10-09T12:32:54Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:08:46Z (GMT). No. of bitstreams: 0 / Dissertacao (Mestrado) / IPEN/D / Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP

Made available in DSpace on 2014-10-09T12:37:17Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:09:07Z (GMT). No. of bitstreams: 1 02044.pdf: 6648951 bytes, checksum: 98f65fdf18484fade28803cf88a3e67d (MD5) / Dissertacao (Mestrado) / IPEN/D / Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP

Thesis (MTech: Chemical Engineering))--Cape Peninsula University of Technology, 2012 / The microbial ferrous-iron oxidation process plays a significant role in bioleaching, providing ferric-iron (Fe3+) − a strong oxidising agent for the dissolution of most sulphide minerals. An extensive literature review has shown that several studies have been carried out on microbial ferrous-iron oxidation, mostly in stirred tank reactors and in conditions close to optimum. However, limited studies have been carried out on this subject in the context of heap bioleach situation. Despite the fact a packed column system may be used to represent heap bioleaching, most of the studies on microbial ferrous-iron oxidation in such systems were carried out under flooded/fluidised conditions which do not adequately represent solution flow dynamics in a heap system. The microbial ferrous-iron oxidation kinetics of Leptospirillum ferriphilum were studied at substrate loading rates of 0.17 – 0.5 g.L-1h -1 (dilution rates 0.033 – 0.1 h-1). The study was conducted in a packed column with a view to investigating the kinetics in a system which simulates the solution flow dynamics of a typical heap bioleach operation. Glass marbles, 15 mm in diameter, were used as reactor packing. The microbial oxidation kinetics were investigated in a continuous mode at the desired loading rates. The pH of the bioreactor was maintained at pH 1.45 ± 0.05 and the aeration at 15 mL.s-1. Both Monod and Hansford models were used to describe the biooxidation kinetics.

Parmi les matériaux fonctionnels, les oxydes à structure pérovskite présentent une très grande variété de propriétés, de très nombreux dispositifs avancés les utilisent donc comme éléments actifs. On compte au nombre de ces propriétés l'antiferroélectricité, caractérisée à l'échelle atomique par un agencement antiparallèle de dipôles électriques. Le zirconate de plomb, PbZrO3, est considéré comme l'archétype de l'antiferroélectrique à structure pérovskite. Malgré sa découverte il y a plus de 80 ans, la physique présidant sa relation structure-Propriété reste incomprise. Cette étude de doctorat vise donc à étudier la structure de PbZrO3 sous diverses sollicitations, notamment de température, champ électrique, et pression hydrostatique, les propriétés électriques de ses différentes phases ainsi qu'à proposer des modèles permettant d'expliquer leur relation. L'accent sera mis en particulier sur la phase dite “intermédiaire” et qui présente des propriétés ferroélectriques. La compréhension acquise au cours de cette étude permet de proposer des dispositifs innovants à base de matériau antiferroélectrique. / Among functional materials, oxides with a perovskite structure exhibit a large variety of properties which make them an active material of choice in a wide range of advanced devices. Antiferroelectricity is one such property and is characterized at the atomic scale by an antiparallel pattern of electrical dipoles. Lead zirconate (PbZrO3) is considered as the archetype of antiferroelectric perovskites. Despite its discovery more than 80 years ago, the physics presiding over the relationship between its structure and its properties remain to be established. This thesis aims to study the structure of lead zirconate under various conditions (temperature, electric field, hydrostatic pressure), the electrical properties of its phases, as well as to propose models explaining their relationship. This study has a particular focus on the so-Called “intermediate” phase which exhibits ferroelectric properties. The knowledge acquired during this study enables the proposal of innovative devices based on antiferroelectrics.

Philosophiae Doctor - PhD / This project is aimed at fabricating a smart material. Zinc oxide and vanadium dioxide have received a great deal of attention in recent years because they are used in various applications. ZnO semiconductor in particular has a potential application in optoelectronic devices such as light emitting diodes (LED), sensors and in photovoltaic cell industry as a transparent electrode. VO2 also has found application in smart windows, solar technology and infrared smart devices. Hence the need to synthesis or fabricate a new smart material using VO2 and an active ZnO based nano-composites family in which ZnO matrix will be hosting thermally active VO2 nano-crystals is the basis of this study. Since VO2 behave as an MIT Mott’s type oxides and exhibits a thermally driven semiconductor-metal phase transition at about 68 oC and as a direct result ZnO:VO2 nano-composites would exhibit a reversible and modulated optical transmission in the infra-red (IR) while maintaining a constant optical transmission in the UV-Vis range. The synthesis is possible by pulsed laser deposition and ion implantation. Synthesis by pulsed laser deposition will involve thin films multilayer fabrication. ZnO buffer layer thin film will be deposited on the glass and ZnO single crystals and subsequent layer of VO2 and ZnO will be deposited on the substrate. X-ray diffraction (XRD) reveals that the series of ZnO thin films deposited by Pulsed Laser Deposition (PLD) on glass substrates has the hexagonal wurtzite structure with a c-axis preferential orientation. In addition the XRD results registered for VO2 samples indicate that all thin films exhibits a monoclinic VO2 (M) phase. UV-Vis NIR measurements of multilayered structures showed the optical tunability at the near-IR region and an enhanced transparency (>30 %) at the visible range.

Made available in DSpace on 2014-10-09T12:40:58Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T13:56:39Z (GMT). No. of bitstreams: 1 03973.pdf: 4389182 bytes, checksum: b10987cb9b3ec2a2bd2d1083fded1bfc (MD5) / Dissertacao (Mestrado) / IPEN/D / Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP

Made available in DSpace on 2014-10-09T12:32:10Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T13:57:55Z (GMT). No. of bitstreams: 0 / Foram fabricadas amostras de placas combustíveis contendo núcleos de cermets U3O8-Al com concentrações de U3O8 variando de 10 a 90% em peso (3,4 a 55,5% em volume). Amostras contendo núcleos com 58% em peso de U3O8, foram fabricadas a partir de compactados com densidades variando de 75 a 95% da densidade teórica. É discutida a influência da concentração de U3O8 e da porosidade do compactado de partida sobre a porosidade e uniformidade da espessura do núcleo obtido. Os núcleos U3O8-Al foram submetidos a ensaios de corrosão por água deionizada nas temperaturas 30, 50, 70 e 90°C, onde os núcleos foram expostos através de um defeito artificial produzido no revestimento. Os resultados obtidos mostram que a corrosão dos núcleos é acompanhada pela liberação de hidrogênio. O volume total de hidrogênio liberado (V) e o tempo transcorrido até que seja observado o início da liberação de hidrogênio (tempo de incubação ti, são dependentes da porosidade do núcleo e da temperatura absoluta (T), podendo ser descritos pelas equações: V = K1 eα1 P - K2 T eα2 P e ti = eK1 + K2 P + K3 / T + K4 P / T onde P é a fração volumétrica de vazios (porosidade) e K1, K2, K3,K4, α1 e α2 são constantes. É proposto e discutido um mecanismo para o processo de corrosão de núcleos U3O8-Al. O revestimento das amostras de placas combustíveis foi submetido a ensaios de corrosão sob condições similares às encontradas no reator IEA-R1 operando às potências de 2 MW, 5 MW e 10 MW. Foi verificado o efeito da presença de heterogeneidades superficiais e de um tratamento de limpeza química sobre o comportamento da corrosão do revestimento. Os resultados obtidos mostram que a corrosão é regulada pela dissolução/erosão da camada de óxido formada e segue lei linear para as três condições de testes e que a presença de heterogeneidades superficiais ou o tratamento de limpeza química não alteram significativamente a corrosão do revestimento para tempos de exposição de até 20 dias. Estão apresentadas as velocidades de corrosão e as espessuras das camadas de óxido observadas nos três ensaios efetuados. Não foi observado ataque localizado significativo. / Dissertacao (Mestrado) / IPEN/D / Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP