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High fossil fuel consumption in transportation and industry results in an increase of the emission of green-house gases. To preserve clean air, new strategies are required. The main intention is to decrease the amount of CO2 emission by using lean-burn engines while increasing the combustion efficiency and decreasing the fuel consumption. However, the lean-burn engines have high air-to-fuel ratio which complicates the reduction of the oxides of nitrogen, NOx . The emission of these highly noxious pollutants, NOx , breeds both environmental and health problems. Thus, new catalytic strategies have been steadily developed. One of these strategies is the NOx storage and reduction (NSR) catalysts. Since the reduction of the NOx under excess oxygen condition is very difficult, the NSR catalysts store the NOx until the end of the lean phase that is subsequently alternated with the rich-fuel phase during which the trapped NOx is released and reduced. To develop NSR technology, different storage materials, the coverage of these metals/metal-oxides, support materials, precious metals, temperature, etc. have been widely investigated. In this thesis, the (100) surface of BaO with dopants (K, Na, Ca and La), (100) and (110) surfaces of Li2O, Na2O and K2O are investigated as storage materials. In addition, alkali metal (Li, Na and K) loaded (001) surface of TiO2 (titania) anatase is investigated as a support material for the NOx storage and reduction catalysts. The main aim is to increase the sulfur resistance. The introduction of the dopants on the BaO (100) surface has increased the stability of the NO2 . The combination of local lattice strain and different oxidation state, which is obtained by the La doped BaO (100) surface, benefit both NO2 adsorption performance and sulfur tolerance. The binding energies of NO2 adsorption configurations over the alkali metal oxide (100) and (110) surfaces were higher than the binding energies of SO2 adsorption configurations. The stability of all of NO2 adsorption geometries on the alkali metal-loaded TiO2 (001) surface were higher than the stability of SO2 adsorption geometries. Increasing basicity enhanced the adsorption of NO2 molecule.

Made available in DSpace on 2017-07-21T20:42:41Z (GMT). No. of bitstreams: 1 Graciela Aparecida Santos Silva.pdf: 4725206 bytes, checksum: 1b5275fc3c55802f9ed0465ffbc48d75 (MD5) Previous issue date: 2013-02-22 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / The purpose of this work was the synthesis of nanoscaled BaO-Al2O3-MnO2 system and its characterization. The nanoparticulate system was prepared by mixing salts of Ba, Al and Mn in a chamber of low temperature, lyophilizing the solutions of their salts, and followed by calcination in the temperature range from 230 °C to 1190° C.This synthesis was compared with two other systems, prepared using a chemical mixture of oxides, with a particle size of conventional size and also with the phase of nanoscale oxides, followed by calcination in the same temperature conditions. The colorimetric properties of ceramic powders were evaluated by UV-visible spectroscopy and coordinates CIE-L a b and characterized by X-ray diffraction, Xray fluorescence, simultaneous thermal analyisis, scanning electron microscopy and laser scattering technique. This nanoscaled synthesis provides a possible application in the production on ceramic pigments because the resulting powder showed different color in comparison to the other systems. The nanoparticulate system showed the advantage of needing lower calcination temperatures, and, at 1135ºC,showed a different color that was not presented by powders synthetized by other methods. / A proposta deste trabalho consiste na síntese em nanoescala do sistema BaO-Al2O3-MnO2, bem como sua caracterização. O sistema nanoparticulado foi preparado misturando sais de Ba, Al e Mn em câmara de baixa temperatura, liofilizando-se assim as soluções dos respectivos sais, seguidos de calcinação na faixa de temperatura de 230 °C a 1190 °C. Comparou-se esta síntese com duas metodologias, preparadas através de uma mistura química de óxidos, com tamanho de partícula convencional e também com tamanho de fase dos óxidos em nanoescala, seguidas de calcinação nas mesmas condições de temperatura. Os pós cerâmicos foram avaliadas por espectroscopia no UV-visível e coordenadas CIE-L a b e caracterizado por difração raios X, fluorescência de raios X, termogravimetria e análise termodiferencial simultânea, microscopia eletrônica de varredura e espectroscopia de fotocorrelação. Essa síntese por nanoescala traz a possível aplicação na produção de pigmentos cerâmicos, pois trouxe alterações colorimétricas diferentes comparando com os outros sistemas. Esse método teve vantagem, pois trouxe temperaturas de calcinação mais baixa, e em 1135 ºC, o sistema nanoparticulado apresentou uma coloração que não foi observado para os outros métodos de síntese.

Made available in DSpace on 2014-12-17T14:57:52Z (GMT). No. of bitstreams: 1 DanielJHC_TESE.pdf: 5059546 bytes, checksum: d026fcca3b608eb8f8318d620f8e0f29 (MD5) Previous issue date: 2012-02-23 / In this work, it is proposed the study of the effect of barium oxide acting as synthetic flow in the behavior of masses for stoneware from the use of raw materials found in the deposits of minerals of the Rio Grande do Norte that it makes use of a great natural potential for the industrialization of the product. The porcelanato is a sophisticated product with excellent final properties being applied as ceramic coating in buildings of high standard of engineering. The raw materials selected for the development of the study had been two types of argilas, two types of feldspatos, dolomita, talco, barium carbonate and silica, being characterized by X-ray fluorescence, X-ray diffraction, granulometric analysis, dilatometric analysis and thermal analysis. Thus, it is intended to define four formulations using the cited raw materials that will be processed, conformed and sintered in the temperatures of 1150 ?C, 1175 ?C, 1200 ?C, 1225 ?C e 1250 ?C. From the physical characterizations, chemical and morphologic of the formed formulations, the effect of barium oxide is determined in the physical and mechanical properties of the studied system carrying water absorption tests, linear retraction, apparent porosity, apparent specific mass, compacting curve, flexural strength and microstructural analysis by XRD and SEM. After analyzing the results, indicated that barium oxide acts as a flux of high temperature and as the ordering of structure, where the embedded glass phase has the nucleating effect phase potassium silico-aluminum reacting with free silica which together with the high content of potassium concentrated form a new crystalline phase called microcline. The masses studied with the addition of barium oxide present physical-mechanical properties highly satisfactory in reduced firing temperatures, which implies a saving in energy given off in the production and increased productivity / Neste trabalho, prop?e-se o estudo do efeito do ?xido de b?rio atuando como fluxo sint?tico no comportamento de massas para porcelanato a partir da utiliza??o de mat?rias-primas encontradas no estado do Rio Grande do Norte que disp?e de um grande potencial natural para industrializa??o do produto. O porcelanato ? um produto com excelentes propriedades finais, sendo aplicado como revestimento cer?mico em diversos empreendimentos da constru??o civil. As mat?rias-primas selecionadas para o desenvolvimento do estudo foram dois tipos de argilas, dois tipos de feldspatos, dolomita, talco, carbonato de b?rio e s?lica, sendo caracterizadas por an?lises de fluoresc?ncia de raios X, difra??o de raios X, an?lise granulom?trica e an?lises t?rmicas. Assim sendo, procede-se o processamento, conforma??o e sinteriza??o de quatro formula??es utilizando as mat?rias-primas citadas nas temperaturas de 1150 ?C, 1175 ?C, 1200 ?C, 1225 ?C e 1250 ?C. A partir das caracteriza??es f?sicas, qu?micas e morfol?gicas das formula??es, determina-se o efeito do ?xido de b?rio nas propriedades f?sicas e mec?nicas do sistema estudado realizando ensaios de absor??o de ?gua, retra??o linear, porosidade aparente, massa espec?fica aparente, curva de compacta??o, tens?o de ruptura a flex?o, difra??o de raios X e microscopia eletr?nica de varredura com a microan?lise por EDS. Ap?s a an?lise dos resultados, verifica-se que o ?xido de b?rio atua como fundente de alta temperatura e como ordenador de estrutura, onde incorporado ? fase v?trea, possui efeito nucleante da fase sil?cio-alum?nio-pot?ssio reagindo com a s?lica livre que juntamente com o alto teor de pot?ssio concentrado forma uma nova fase cristalina denominada microcl?nio. As massas estudadas com o acr?scimo do ?xido de b?rio apresentam propriedades f?sico-mec?nicas extremamente satisfat?rias em temperaturas de queima reduzidas, o que implica em uma economia na energia desprendida para a produ??o e aumento de produtividade / 2020-01-01

This thesis reports on the elemental growth of oxide thin films including TiO_x, BaO_x and Ba_xTi_yO_z by Ti/Ba deposition and oxidation. The films were grown on two different substrates, Au(111) and SrTiO₃(001), and studied using a variety of surface characterisation techniques. On the reconstructed Au(111) surface, three different TiO_x structures were obtained with increasing Ti amounts deposited: a (2 × 2) Ti₂O₃ honeycomb structure, a pinwheel structure that is the result of a Moiré pattern, and a triangular island TiO_1.30 structure. The structures arise from raised Ti coverages and have increased Ti densities. Although Ba deposited on the reconstructed Au(111) has a weak interaction with the substrate, the BaO_x thin films can grow epitaxially and lift the Au(111) reconstruction. Two well-ordered phases, a (6 × 6) and a (2√3 × 2√3) BaO_x structure, were obtained which may have octopolar-based surface structures. For Ba & Ti deposition on Au(111), a locally ordered (5 × 5) BaxTiyOz structure was observed in the sub-monolayer regime. What is more interesting is the possible formation of a BaO-TiO surface alloy with short-range ordering achieved by Ba deposition on the (2 × 2) Ti₂O₃-templated Au(111) surface. This is the first time that surface-alloying has been observed for oxides. When Ti is deposited onto the SrTiO₃(001) surface, it is incorporated into the substrate by forming a variety of Ti-rich SrTiO₃ surface reconstructions, such as c(4 × 2), (6 × 2), (9 × 2) and (√5 ×√5)-R26.6°. Ti deposition provides a completely different route to obtaining these reconstructions at much lower anneal temperatures than the previously reported preparation procedures involving sputtering and annealing the SrTiO₃ sample. Anatase islands with (1 × 3) and (1 × 5) periodicities were also formed by increasing the Ti deposition amount and post-annealing. Reconstructed SrTiO₃ substrate surface has a lattice that differs from the bulk crystal and affects the epitaxial growth of BaO, however, a locally ordered BaO_x structure was observed on the sputtered substrate with a growth temperature of 300 °C. Depositing Ba & Ti on SrTiO₃(001) results in the formation of BaO_x clusters and the Ti incorporation into the substrate, forming the familiar Ti-rich SrTiO₃ surface reconstructions.

Portland clinker is thanks to its large-scale production a continuously studied topic. Clinker, or Portland cement, is used for construction purposes, or for insulation and special applications. One of these special applications could be shielding of different types of radiation by making use of the content of barium ions. The present master’s thesis examines the influence of barium oxide on the formation and properties of Portland clinker, which could be, by incorporation of barium ions into the system, used as a binder for buildings resistant to various types of radiation. Barium sulfate and barium carbonate were added to the raw meal in order to prepare clinkers with different content of barium oxide. The effect of barium on the formation of clinker phases was studied (by XRD – Rietveld analysis and by the microscopic point integration), as well as the effects on the variations of temperature of the phase formation (TG-DTA) and the rate of alite formation under isothermal conditions. Furthermore, the ability of barium to become a part of clinker minerals was studied by SEM with EDS, and the solubility of barium phases by ICP-OES. The hydration of clinker minerals containing barium was studied by isothermal calorimetry.

No / A new dual-log spiral geometry is proposed for microstrip resonators, offering substantial advantages in performance and size reduction at subgigahertz frequencies when realized in superconducting materials. The spiral is logarithmic in line spacing and width such that the width of the spiral line increases smoothly with the increase of the current density, reaching its maximum where the current density is maximum (in its center for ¿/2 resonators). Preliminary results of such a logarithmic ten-turn (2 × 5 turns) spiral, realized with double-sided YBCO thin film, showed a Q.-factor seven times higher than that of a single ten-turn uniform spiral made of YBCO thin film and 64 times higher than a copper counterpart. The insertion loss of the YBCO dual log-spiral has a high degree of independence of the input power in comparison with a uniform Archimedian spiral, increasing by only 2.5% for a 30-dBm increase of the input power, compared with nearly 31% for the uniform spiral. A simple approximate method, developed for prediction of the resonant frequency of the new resonators, shows a good agreement with the test results.