Ti-6Al-4V, known for high strength-to-weight ratio and good resistance to corrosion, has been widely used in aerospace, biomedical, and high-performance sports applications. A wide range of physical and mechanical properties of Ti-6Al-4V can be achieved by varying the microstructures via deformation and recrystallization processes. The aim of this thesis is to establish a microstructure-sensitive fatigue analysis approach that can be applied in engineering applications such as fretting fatigue to permit explicit assessment of the influence of microstructure. In this thesis, crystal plasticity constitutive relations are developed to model the cyclic deformation -TiAl has beenabehavior of Ti-6Al-4V. The development of the slip bands within widely reported and has been found to play an important role in deformation and fatigue behaviors of Ti-6Al-4V. The shear enhanced model is used to simulate the formation and evolution of slip bands triggered by planar slip under static or quasi-static loading at room temperature. Fatigue Indicator Parameters (FIPs) are introduced to reflect driving force for the different crack formation mechanisms in Ti-6Al-4V. The cyclic stress-strain behavior and fretting fatigue sensitivity to microstructure and loading parameters in dual phase Ti-6Al-4V are investigated.

Catalysis is an important field of study in chemical engineering and chemistry due to its application in a vast number of chemical transformations. Traditionally, catalysts have been developed as homogeneous molecular species or as heterogeneous insoluble materials. While homogeneous catalysts are typically very active and selective, they are difficult to recover. Conversely, heterogeneous catalysts are easy to recover and reuse, but they generally are less selective. To address these issues, the immobilization of homogeneous catalyst analogs onto solid supports has been a subject of research for the past few decades. Nonetheless, the effects of immobilization are still not completely predictable, and so continued effort is required to develop new immobilized catalysts as well as to develop a better understanding of how different parameters affect catalytic behavior. This dissertation presents the synthesis, characterization, and evaluation of new immobilized catalysts for different applications. First, a solid base catalyst supported on silica was developed and studied in the synthesis of cyclic carbonates from epoxides and carbon dioxide. Next, polymer and silica supported vanadium Schiff base catalysts were developed and evaluated for use in the oxidative kinetic resolution of alpha-hydroxy esters, an enantioselective reaction. Lastly, salen catalyst analogs with amine reactive functional groups were synthesized and characterized for grafting onto aminosilicas with different degrees of amine group isolation. The grafted catalysts were then tested to determine how catalyst spacing on the surface affects their behavior. Throughout the presentation of these results, comparisons are made amongst the new supported catalysts and relevant existing catalysts to discern general trends which could be applied to a wider range of immobilized catalysts. Finally, research opportunities for further improvements in these areas are suggested.

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / Impedance Spectroscopy has been performed at the metal-semiconductor transition of vanadium dioxide thin films. The samples have been deposited by reactive magnetron sputtering onto heated glass substrates. The crystallographic properties and morphology of the samples have been established by X-ray diffraction. By the spectra measured between 30 and 100 celsius degrees, the volume fractions of the monoclinic and tetragonal phases were quantified. The real and imaginary parts of the electrical impedance have been measured in VO2 thin films as function of the frequency (100 kHz to 1GHz) and temperature (30ºC to 90ºC). For fixed frequencies larger than 100 MHz, the hysteresis presented by the real part of the impedance when the critical temperature is surpassed became inverted. Below the semiconductor/metal transition, the Argand plots can be well reproduced assuming a Debye-like system with one relaxation time. After the beginning of the transition this approach fails, and at least two relaxation times are needed. We attribute one of them to the intrinsic processes taken place in the material, and the other to extrinsic properties like grain boundaries. / Foi realizada uma análise, por espectroscopia de impedância, das propriedades de filmes finos de dióxido de vanádio. As amostras foram depositadas por magnetron sputtering sobre substratos de vidro aquecidos em atmosfera reativa de argônio e oxigênio. Características cristalográficas e morfológicas dos filmes foram estabelecidas por difração de RX. Através de medidas de espectros de difração em temperaturas compreendidas entre 30 e 100 graus Celsius, foram quantificadas as frações volumétricas das fases monoclínica e tetragonal. As partes real e imaginária da impedância elétrica foram medidas em filmes policristalinos de VO2 tanto em função da frequência (100 KHz a 1 GHz) quanto da temperatura (30 ºC a 90ºC). Para frequências fixas maiores que 100 MHz, o ciclo de histerese apresentado pela parte real da impedância é suprimido e invertido quando a temperatura da amostra ultrapassa a temperatura crítica. Abaixo da transição semicondutor/metal, os diagramas de Argand podem ser bem reproduzidos assumindo-se um sistema, tipo Debye, com um único tempo de relaxação. Após o início da transição, este aproximação falha e são necessários pelo menos 2 tempos de relaxação. Um destes tempos de relaxação foi atribuído a processos intrínsecos que ocorrem no material e o outro a propriedades extrínsecas, como fronteiras de grãos.

A comparison between a traditional fixed high voltage direct current energy transmission system and a mobile transmission system utilizing vanadium redox flow batteries has been conducted in this degree work.  The purpose of this comparison was to evaluate if a mobile energy transmission system could be competitive in terms of energy efficiency and cost-effectiveness for use in offshore wind power applications. A literary study was made to fully grasp the various technologies and to create empirical ground of which cost estimation methods and energy calculations could be derived. A specific scenario was designed to compare the two transmission systems with the same conditions. To perform the comparison, a model was designed and simulated in MATLAB. The results from the model showed that the flow battery system fell behind in energy efficiency with a total energy loss of 33.3 % compared to the 11.7 % of the traditional system, future efficiency estimations landed it at a more competitive 17.5 %. The techno-economic results proved that a mobile flow battery system would be up to nine times more expensive in comparison to a traditional transmission system, with the best-case scenario resulting in it being roughly two times more expensive. The main cause of this was found out to be the expensive energy subsystem, specifically the electrolyte, used in the flow battery system. Several environmental risks arise when using a flow battery system with this electrolyte as well which could harm marine life severely. In conclusion; with further development and cost reductions, a case could be made for the advantages of a truly mobile energy transmission system. Specifically, in terms of the pure flexibility and mobility of the system, allowing it to circumvent certain complications. The mobility of the system gives the possibility of selling energy where the spot prices are at their highest, providing a higher revenue potential compared to a traditional fixed system. As for now though, it is simply too expensive to be a viable solution.

Made available in DSpace on 2014-06-11T19:22:54Z (GMT). No. of bitstreams: 0 Previous issue date: 2011-05-03Bitstream added on 2014-06-13T19:49:15Z : No. of bitstreams: 1 paula_as_me_sjrp.pdf: 3130641 bytes, checksum: 88335016faa035282519ac1dcb6b41b9 (MD5) / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / Como em qualquer método de imagem utilizado em medicina, foi desenvolvido para a ressonância magnética por imagem (MRI) um agente de contraste que pudesse realçar apenas as lesões e não os tecidos normais, possibilitando desta maneira não apenas a localização do tecido afetado, mas propiciando também um diagnóstico mais preciso e diferenciado. Os agentes de contraste geralmente utilizados em MRI afetam seletivamente os tempos de relaxamento T1 dos diferentes tecidos, embora os tempos de T2 podem também ser alterados pela introdução desses agentes. Este trabalho caracteriza-se pela busca de novos compostos micro ou mesoporosos que possam ser utilizados como agentes de contraste para MRI. A principal diferença entre os compostos estudados e os quelatos de gadolínio empregados atualmente em MRI está na usa composição química e estado físico. Estes novos compostos são zeólitos, cuja principal característica é sua estrutura altamente cristalina formada por canais e cavidades bem definidas, canais e cavidades onde ocorre a imobilização de íons metálicos. As sínteses destes novos materiais microporosos foram realizadas utilizando-se templates orgânicos derivados da decahidroquinolina, 2,6 dimetil piperidina, 3,5 dimetil piperidina e espartênio. Antes de serem utilizados em diferentes condições de química sol-gel os novos templates sintetizados foram caracterizados por ressonância magnética nuclear ( 13 C e 1 H), espectrometria de massa e por difração de raios-X de monocristais. Os novos materiais microporosos foram sintetizados em diferentes condições de química sol- gel e os principais produtos obtidos foram novos vanadiosilicatos. Os novos materiais microporosos foram caracterizados pelas técnicas de difração de raios-X, ressonância magnética do estado sólido dos núcleos 29 Si, 51 V e 13 C, microscopia eletrônica de varredura, espalhamento Raman... / As in any other imaging method used in modern medicine, Magnetic Resonance Imaging (MRI) requires a contrast media. The contrast media can enhance the contrast of the damage tissue in comparison to the normal ones, facilitating the location of the damage area and providing information for a precise diagnosis. Most of the contrast media commonly used in MRI, affect the relaxation time T1 of the different tissues, and in some case also the relaxation time T2. The main goal of this work was the searching for new microporous or mesoporous materials that could replace the traditional contrast media based on chelates of gadolinium. These microporous materials, different form the chelates of gadolinium, are made up by well defined system of nanoporous and nanochanels where the metal are located. In order to synthesized these new microporous materials, a new family of structure directing agents (SDAs) derivatives of decahydroquinolinium; 2,6 dimethyl piperidine; 3,5 dimethyl piperidine and (S)-Sparteinium were synthesized. The as made new templates were fully characterized by 13 C, 1 H-NMR, ES- Mass Spectrometry, and single crystal X-Ray diffraction. Different sol gel chemistry conditions were studied and explored throughout this study using the new SDAs, however the most out sanding results were obtained for vanadosilicates. The new vanadosilicates were fully characterized by 13 C, 29 Si and 51 V NMR-MAS (Nuclear Magnetic Resonance-Magic Angle Spinning), Scanning electronic microscopy (SEM), Raman scattering and Thermogravimetric analysis (TGA). Some of the vanadosilicates synthesized with SDAs (1, 2, 3, 5, 7, 8, 9, 10, 11) were found to be isomorphous to the Titanosilicate ETS-10 and to the Vanadosilicate AM-6, which open up the possibility of their use as catalyst for shape selectivity oxidative calalysis. Althoug, Vanadosilicates prepared with N-Etil-Sparteinium are stil under... (Complete abstract click electronic access below)

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A utilização de novas rotas de síntese de materiais nanoestruturados tem levado à obtenção de materiais apresentando novas propriedades e aplicações. O presente trabalho teve como principal objetivo realizar a síntese e a caracterização de nanopartículas de óxido de vanádio obtidas pelo método da decomposição de peróxido utilizando o tratamento hidrotermal. Por meio do controle do tempo e da temperatura de síntese, foi possível obter nanoestruturas de pentóxido de vanádio com diferentes fases cristalinas e morfologias. Os resultados de espectroscopia Raman e difração de raios X (DRX) mostraram que o tratamento hidrotermal da solução em temperaturas de até 180oC, durante 2 horas, leva à formação da fase V2O5nH2O monoclínica, apresentando uma orientação preferencial na direção 00l. A partir desta temperatura, o material obtido passou a ter a fase ortorrômbica perdendo sua orientação preferencial. Através das medidas de termogravimetria (TG) foi observado que, dependendo da condição de síntese, as amostras apresentam diferentes quantidades de moléculas de água (H2O) intercaladas em sua estrutura. Imagens de microscopia eletrônica mostraram que as nanoestruturas obtidas podem possuir a forma de fitas, fios ou bastões. Utilizando a técnica de espectroscopia de absorção de raios X (XAS), foi possível verificar a presença de íons de V4+ nas amostras de fase monoclínica, o que não foi observado naquelas que possuem estrutura ortorrômbica. Pela técnica de XAS também foi possível constatar que as amostras de estrutura ortorrômbica possuem menor grau de desordem ao redor do átomo de vanádio. O estudo do mecanismo de crescimento da nanoestrutura de V2O5nH2O mostrou que ocorre um crescimento lateral, o qual pode ser descrito pelo mecanismo denominado Coalescência Orientada ou Oriented attachment (OA). Finalmente, através da decomposição do peróxido de vanádio, foi possível obter compostos vanadatos contendo cátions de Na+ em sua estrutura. / The use of new routes for nanostructured materials synthesis has lead to materials with new properties and applications. This PhD project aimed to realize the synthesis and the characterization of vanadium pentoxide nanoparticles obtained by peroxide decomposition using the hydrothermal treatment. By controlling synthesis time and temperature it was possible to achieve vanadium pentoxide nanoparticles with different crystalline phases and orphologies. The results of Raman spectroscopy and X-ray diffraction (XRD) showed that the hydrothermal treatment of the solution at temperatures up to 180oC for two hours leads to formation of the V2O5nH2O monoclinic phase with a preferential orientation on 00l direction. From this temperature on the material obtained began to present the orthorhombic phase misleading its preferential orientation. Through thermogravimetry (TG) measurements it was seen that depending on the synthesis condition the samples contains different amounts of water molecules (H2O) interleaved in their structure. Images of transmission electron microscopy (TEM) showed that the V2O5nH2O compound could have different morphologies such as ribbons, wires and rods. From X-Ray Absorption spectroscopy (XAS) measurements, it was observed the presence of V4+ ions in the monoclinic phase samples, which was not observed on orthorhombic structure samples. Through the XAS technique was also observed that the orthorhombic structure samples have a lower degree of disorder around the vanadium atom. Regarding the growth mechanism of these nanostructures, it was possible to verify that has been a wide growth which can be explained by the mechanism denominated Oriented Attachment (OA). Finally, through vanadium peroxide decomposition vanadates compounds containing Na+ cation in its structure were carried out.

Medidas de atenuação ultrassônica e constante elástica em ligas de Cr-V, utilizando técnicas de pulso eco foram realizadas e as transições na temperatura de Neel, TN, estudadas. Um modelo teórico é proposto para descrever os comportamentos da atenuação e constante elástica perto da transição em TN. De acordo com o modelo proposto a adição de vanádio diminui drasticamente o coeficiente de difusão, modificando a natureza da transição. Foram utilizadas amostras de cromo contendo 0,2%V; 0,5%V; 0,67%V; 1,0%V e 1,5%V. A partir da dependência aproximadamente linear de TN com a concentração de vanádio conclui-se que 3,3% V corresponderá à TN= 0K. O efeito do campo magnético até 4,5T revelou-se insuficientemente para a obtenção de monodomínio magnético e não causa nenhuma variação mensurável em TN / Measurements of ultrasonic attenuation and elastic Constant in Cr-V alloys, using pulse echo techniques were realized and the transitions at the Neel temperature, TN, were studied. We propose a theoretical model which describe the behavior of the ultrasonic attenuation and elastic Constant near the transition in TN. According to the theoretical model the addition of Vanadium to chromium, drastically diminishes the diffusion coefficient thus changing the nature of the transition. It was used samples of chromium containing 0,2%V; 0,5%V; 0,67%V; 1,0%V and 1,5%V. From the approximately linear dependence of TN with the vanadium concentration it was concluded that 3,3%V corresponds to TN= 0. The effect of magnetic fields up to 4,5T was insufficient to produce single-Q samples, and did not cause any mensurable variation in TN

Made available in DSpace on 2014-10-09T12:44:55Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:01:00Z (GMT). No. of bitstreams: 1 07019.pdf: 8194512 bytes, checksum: 2e06aca4af1ce7ca845478381a7195b2 (MD5) / Tese (Doutoramento) / IPEN/T / Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP