597 resultados para Óxidos de cério
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Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)
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Pós-graduação em Química - IBILCE
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Pós-graduação em Química - IQ
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Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)
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Pós-graduação em Química - IQ
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Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)
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Pós-graduação em Química - IQ
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Silver containing heavy metal oxide glasses and glass ceramics of the system WO3-SbPO4-PbO-AgCl with different AgCl contents have been prepared and their thermal, structural and optical properties characterized. Glass ceramics containing metallic silver nanoparticles have been prepared by annealing glass samples at temperatures above the glass transition and analyzed by transmission electron microscopy and energy dispersive X-ray microanalysis. The presence of the metallic clusters has been also confirmed by the observation of a surface plasmon resonimce band in the visible range. Cyclic voltammetric measurements indicated the presence of metallic silver into the glasses, even before to perform the thermal treatment.
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L'elaborato descrive la realizzazione di una piattaforma e software relativo, per testare i componenti di una ruota di momento.
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This thesis tries to interpret the origin and evolution of karst-like forms present in Arabia Terra, a region of Mars that develops in the equatorial zone of the planet. The work has been carried out specifically in the craters Crommelin (4o 91’ N-10o 51’ E), 12000088 (3o 48’ N-1o 30’ E), NE 12000088 (4° 20’ N-2° 50’ E), C "2" (3° 54’ N-1° W), and in their surrounding areas. These craters contain layered deposits characterized by a high albedo and on which erosion is very pronounced. The area containing the craters is a plateau that has the same characteristics of albedo and texture. The preliminary morphological study has made use of instrumentation such as the Mars Reconnaissance Orbiter (MRO), in particular HiRISE images (High Resolution Imaging Science Experiment), CTX (Context Camera) and CRISM (Compact Reconnaissance Imaging Spectrometers for Mars). A regional geomorphological map has been drawn up containing the main morphotypes, and detailed geomorphological maps were prepared for different karst-like morphologies. The analysis of spectral data collected from CRISM instrumentation has allowed to identify the footprint of sulphate minerals in the external area. Data were collected for morphometric negative forms (karst-like) and positive forms (mud volcanoes, dikes and pingos). For the analysis of the relief forms DTMs (Digital Terrain Models) produced by the union of stereographic CTX couples or HiRISE were used. From the analysis of high-resolution images morphological footprints similar to periglacial environments have been identified, including the presence of patterned ground and polygonal cracks found all over the area of investigation, and relief structures similar to pingos present in the crater C "2". These observations allow us to imagine a geological past with a cold climate at the equator able to freeze the few fluids present in the Martian arid terrain. The development of karst-like landforms, on the other hand, can be attributed to a subsequent improval of the weather conditions that led to a normal climate regime for the equatorial areas, resulting in the degradation of the permafrost. The melt waters have thus allowed the partial dissolution of the sulphate layers. The karst-like forms look rather fresh suggesting them to be not that old.
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Este trabajo tiene como objeto caracterizar las capas de óxido formadas en el acero AISI 316L en función de la deformación del material y de su contenido en Cr a distintas temperaturas. Este acero se utiliza en los internos de las vasijas de los reactores nucleares de agua ligera, y un mejor conocimiento de su proceso de oxidación puede suponer un avance en el desarrollo de los reactores de cuarta generación. Para ello se realizaron ensayos termogravimétricos y se analizaron los resultados con técnicas de microscopía óptica y electrónica, espectrometría y difracción de rayos X. Los resultados obtenidos muestran la similitud en morfología y composición elemental de los óxidos formados en muestras de este acero con distintos grados de deformación y contenido en Cr y las diferencias resultantes en cuanto a la ganancia de masa. Abstract The object of this work is to characterize the oxide layers formed in AISI 316L steel based on the material deformation and its Cr content at various temperatures. This kind of steel is used in the inside elements of the light water nuclear reactor vessels and further knowledge in the oxidation process could mean a greater development in fourth generation reactors. Thermogravimetric tests were undertaken for this purpose, leading to the results analysis with the use of optical and electronic microscopic techniques as well as spectrometry and X–ray diffraction. The obtained results show the resemblance in the morphology and elemental composition of the oxides formed in samples of this steel with different deformation and Cr content degrees. The results also showed differences in the mass gain.
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Pie de imp. consta en col
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Resumen: Descripción: escena donde la hija abraza a su madre, al fondo una mujer presencia la reconciliación