Atualmente o ramo industrial tem voltado grande parte de suas atenções para situações ambientais. Um dos grandes problemas mundiais encontra-se no uso de cromo hexavalente, prejudicial à saúde humana, além de contaminar leitos e rios por ser solúvel em água e a fosfatização que é responsável pela eutrofização das águas. Novos processos sustentáveis têm sido estudados para reduzir os impactos ambientais causados por esses tratamentos, dentre os quais podemos citar os revestimentos chamados de nanocerâmicos, por formarem camadas nanoestruturadas de óxido de zircônio na superfície do substrato. Vários parâmetros influenciam na formação da camada (substrato, pH, concentração, tempo). O trabalho teve como objetivo o estudo da influência dos parâmetros no desempenho contra a corrosão do revestimento formado por camadas de conversão obtidas a base de ácido hexafluorzircônio em aço galvanizado. O comportamento eletroquímico foi analisado através dos ensaios de potencial de circuito aberto, espectroscopia de impedância eletroquímica e polarização potenciodinâmica. Também foram realizados ensaios de avaliação anticorrosiva com adição de um revestimento final (tinta comercial) sobre a camada de conversão para avaliar o comportamento como revestimento. A partir dos ensaios realizados chega-se a parâmetros que foram considerados ideais e com melhor desempenho. Com isso obtém-se um pré-tratamento capaz de fazer frente a processos convencionais de cromatização e fosfatização. / Currently, the industrial sector has turned much of their attention to environmental situations. One of the great global problems is the use of hexavalent chromium, harmful to human health and pollute rivers and beds being soluble in water and phosphate which is responsible for water eutrophication. New sustainable processes have been studied to reduce the environmental impacts caused by these treatments, among which we can mention the nanoceramic coatings called for forming nanostructured layers of zirconium oxide on the substrate surface. Several parameters influence the layer formation (substrate, pH, concentration, time). The work aims to study the influence of parameters on the performance against corrosion coating formed by conversion layers obtained acid based hexafluorzirconic on galvanized steel. The electrochemical behavior was analyzed through the trials of open circuit potential data, electrochemical impedance spectroscopy and polarization. Also evaluation trials were performed with addition of an anti-corrosive top coat (commercial ink) on the layer of conversion coating painted as to evaluate the corrosion resistance. From the tests to parameters that were considered ideal and best performance. Thus is obtained a pretreatment able to cope with the conventional processes chromate and phosphate.

Please read the abstract in the section 00front of this document / Dissertation (MSc (Chemistry))--University of Pretoria, 2003. / Chemistry / unrestricted

No description available.

The nanoparticles of zirconium oxide, sulfated and phosphated zirconia were used to modify a Nafion membrane in order to improve its water retention, thermal stability, proton conductivity and methanol permeability so that it can be used at higher temperatures in fuel cell. These modified Nafion nanocomposite membrane with inorganic nanoparticles have been designed to run at operating temperatures between 120 oC and 140 oC because higher temperature operation reduces the impact of carbon monoxide poisoning, allows attainment of high power density and reduces cathode flooding as water is produced as vapor. The inorganic nanoparticles were incorporated within the Nafion matrix by recast, ion exchange and impregnation methods. The membrane properties were determined by ion exchange capacity (IEC), water uptake, methanol permeability and proton conductivity. The characterization of the inorganic nanoparticles within the nanocomposite membranes was determined by X-Ray diffraction (XRD), Brunau-Emmett-Teller (BET) surface area and Fourier transform infrared spectroscopy (FTIR) for structural properties. Thermal gravimetric analysis (TGA) and Differential scanning calorimetry (DSC) were used to determine the thermal properties, and the morphological properties were probed by Transmission electron microscopy (TEM) and Scanning electron microscopy (SEM). Pristine ZrO2, sulfated and phosphated ZrO2 nanoparticles were synthesized successfully. The particle sizes ranged from 30 nm to 10 nm respectively. The resulted particles were incorporated to a Nafion membrane with good dispersity. The conductivity of the nanocomposite membrane were around 0.1037 S/cm at 25 oC with a higher water uptake of 42 %. These results were confirmed by the highest IEC value of 1.42 meg.g-1 of Nafion/ S-ZrO2 nanocomposites membrane. These high IEC value may due to the incorporation of superacid S-ZrO2 nanoparticles which increased the membrane acid property for providing new strong acid site. / Chemical Engineering / M. Tech. (Chemical Engineering)

This work was produced as part of a multidisciplinary study of the corrosion of zirconium alloys undertaken by a consortium of universities working in the MUZIC program; Oxford, Manchester and The Open University. The objective of the project as a whole was to further the understanding of the mechanisms of the breakaway oxidation process and to characterise these corrosion processes within a number of fuel rod cladding materials. This thesis describes laser 3D atom probe characterisation of the nano-scale chemical redistribution of oxygen and other solutes that occurs at the metal-oxide interface during corrosion, and a large body of technique development that was required to achieve this goal. The development of the metal-oxide interface of ZIRLO, a Zr-Nb-Sn-Fe-O alloy, is followed by generating 3D atomic scale reconstructions at four different stages of corrosion. The formation of a sub-oxide ZrO layer is seen during pre-transition oxide development. The ZrO interfacial layer is consumed by the rapid formation of oxide after the breakaway transition. After transition the chemistry of the interface is similar to the early pre-transition case, although an oxygen-saturated layer of metal adjacent to the interface formed during corrosion remains. The ZrO interfacial layer (Zr-ZrO-ZrO₂) and the region of oxygen-saturated material ahead of the metal-oxide interface alter the distribution of minor alloying additions such as niobium and iron. The ZrO layer increases the acceptance of niobium into the oxide, which is otherwise seen to be rejected at the Zr-ZrO2 interface along with iron. Niobium is seen to precipitate out of solution as nano-scale particles near the interface after around 100 days of corrosion. This is not seen in the bulk metal matrix of the corroded material due to the absence of other factors driving the process: the stress at the interface and a very high oxygen concentration in the metal ahead of the interface. The nano-scale niobium particles are found to be of a meta-stable composition. Iron is seen to redistribute in the corroded material and can be correlated with the local oxygen concentration. Similarities are seen in the behaviour of solutes within pre-transition ZIRLO and Zircaloy-4 (Zr-Sn-Fe-O). In both cases no redistribution of tin is seen at the metal-oxide interface. A Zr-Nb-Ti alloy with very poor corrosion resistance was also analysed in this way, and the similarities and differences with chemically-similar ZIRLO are discussed. The segregation of solutes to grain boundaries and solute clustering within the matrix are also examined before and after corrosion.

L’oxyde de zirconium est un matériau prometteur pour le stockage des actinides en formation géologique profonde. Pour la sureté de stockage, la stabilité de ces matrices dans les milieux géologiques doit être examinée. Une connaissance approfondie de la solubilité des phases solides de confinement des déchets radioactifs s’avère donc nécessaire. La solubilité de ZrO2 est très faible aux pH neutres (<10-8M), et augmente aux pH acides et alcalins. Cependant, les valeurs de solubilités publiées varient de plus de 6 ordres de grandeurs. L’objectif de ces travaux de thèse est de comprendre les processus ayant lieu, à l’équilibre, à l’interface ZrO2/solution et d’étudier la réactivité de surface de ce matériau en contact avec des solutions aqueuses. La solubilité de ZrO2 monoclinique et cubique a été explorée en approchant l’équilibre depuis les conditions de sous-saturation. Un protocole expérimental robuste a été développé permettant de mesurer, au plus précis possible, les très faibles concentrations de zirconium en solution (limite de quantification [Zr] ~10-11M). Les phases solides ont été caractérisées par BET, XRD, SAXS,HR-TEM and STEM-HAADF avant et après l’atteinte de l’équilibre afin d’étudier la réactivité de surface des matériaux mis en contact avec les solutions aqueuses. En vue de comprendre les mécanismes se déroulant à l’interface aussi bien que la faible solubilité dans les milieux aqueux, l’hydrolyse des liaisons Zr-O-Zr par les molécules d’eau a été étudiée par la méthode DFT en utilisant le code VASP. Cette étude nous a permis de proposer un mécanisme de dissolution dont l’étape limitante, aux pH neutres, est la difficulté de former un complexe activé à l’interface ZrO2/solution. / Zirconium dioxide is a promising ceramic for the specific immobilization of actinides in a geological disposal vault. An appropriate knowledge of the solubility controlling solid phases confining radioactive waste is necessary if one wants to assess the stability of ZrO2 in a disposal environmental conditions. The solubility of zirconium oxide is very low at neutral pH (<10-8M), but increases at highly acidic and alkaline pH. Solubility values may differ by more than 6 orders of magnitude at a given pH, indicating high uncertainties. The objective of this work is to understand processes governing the equilibrium between zirconium oxide and water, and to study the surface reactivity of the material in contact with aqueous solutions. The solubility of monoclinic and of cubic ZrO2 in aqueous solutions were investigated, approaching equilibrium from under-saturated conditions.The low solubility of zirconia makes its measurement a challenging task. A reliable experimental procedure was developed to measure low concentrations of zirconium (limit of quantitation[Zr] ~10-11M). In order to examine the surface reactivity, solid phases were further characterized by BET, XRD, SAXS, HR-TEM and STEM-HAADFbefore and after reaching equilibrium. In order to understand the reaction mechanism taking place at the zirconia/water interface as well as the low solubility in aqueous phase, hydrolysis of Zr-O-Zr bonds by a single and multiple water molecule were studied using the periodic DFT code, with Vienna ab initio simulation package (VASP). This study led to the proposal of a dissolution mechanism whose limiting step, in the neutral pH range, is the difficulty of formation of an activated complex.

Metal oxide thin films serve as critical components in many modern technologies, including microelectronic devices. Industrial state-of-the-art production utilizes vapor-phase techniques to make high-quality (dense, smooth, uniform) thin film materials. However, vapor-phase techniques require large energy inputs and expensive equipment and precursors. Solution-phase routes to metal oxides have attracted great interest as cost-effective alternatives to vapor-phase methods and also offer the potential of large-area coverage, facile control of metal composition, and low-temperature processing. Solution deposition has previously been dominated by sol-gel routes, which utilize organic ligands, additives, and/or solvents. However, sol-gel films are often porous and contain residual carbon impurities, which can negatively impact device properties. All-inorganic aqueous routes produce dense, ultrasmooth films without carbon impurities, but the mechanisms involved in converting aqueous precursors to metal oxides are virtually unexplored. Understanding these mechanisms and the parameters that influence them is critical for widespread use of aqueous approaches to prepare microelectronic components. Additionally, understanding (and controlling) density and composition inhomogeneities is important for optimizing electronic properties. An overview of deposition approaches and the challenges facing aqueous routes are presented in Chapter I. A summary of thin film characterization techniques central to this work is given in Chapter II. This dissertation contributes to the field of solution-phase deposition by focusing on three areas. First, an all-inorganic aqueous route to high-κ metal oxide dielectrics is developed for two ternary systems. Chapters III and IV detail the film formation chemistry and film properties of lanthanum zirconium oxide (LZO) and zirconium aluminum oxide (ZAO), respectively. The functionality of these dielectrics as device components is also demonstrated. Second, the impact of steam annealing on the evolution of aqueous-derived films is reported. Chapter V demonstrates that steam annealing lowers processing temperatures by effectively reducing residual counterion content, improving film stability with respect to water absorption, and enhancing dielectric properties of LZO films. Third, density and composition inhomogeneities in aqueous-derived films are investigated. Chapters VI and VII examine density inhomogeneities in single- and multi-metal component thin films, respectively, and show that these density inhomogeneities are related to inhomogeneous metal component distributions. This dissertation includes previously published coauthored material.

Orientador: Renata Marques de Melo Marinho / Coorientador: Tiago Moreira Bastos Campos / Banca: Alexandre Luiz Souto Borges / Banca: Eliandra de Sousa Trichês / Resumo: Com o avanço da ciência e processamento de materiais, a zircônia odontológica deixou de ser um material opaco para apresentar certa translucidez, possibilitando a confecção de peças ultrafinas. Sabe-se que a água em contato com a superfície das zircônias convencionais acarreta na transformação de fase T-M e subsequente decréscimo de resistência, mas esses efeitos nas zircônias translúcidas ainda não foram explorados. Para avaliar, mapear e caracterizar os efeitos da cinética de envelhecimento acelerado em zircônias de alta translucidez, foram cortados 39 blocos de Y-TZP (VITA YZ, VITA HT, InCoris TZI) para cada zircônia comercial, onde posteriormente foram sinterizados (1530 ºC, 2h) e atribuídos a 13 grupos com 3 amostras cada: Um controle e 12 envelhecidos hidrotermicamente a 134 ºC com pressão constante de 2 bars por 6, 10, 14, 18, 22, 26, 30, 40, 60, 80, 100 e 140 horas. A análise em DRX foi utilizada para quantificar a transformação de fase da zircônia (tetragonal-monoclínica) em diferentes profundidades do material ao se trocar o ânodo do tubo irradiador (Cr, Co e Cu). Uma curva cinética de envelhecimento foi feita para cada profundidade para as 3 zircônias comerciais. Para avaliar os efeitos do envelhecimento hidrotermal nas propriedades mecânicas, 270 discos de Y-TZP foram cortados, 90 para cada tipo, sinterizados e atribuídos a 3 grupos: C-Controle; E1- envelhecido até 26h e E2- envelhecido até 140 horas. Os discos foram testados em uma máquina de teste universal (EMI... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: To evaluate, map and characterize the effects of the accelerated aging kinetics of high translucency zirconias, this study was split into 2 parts: One part evaluating the superficial changes after in vitro hydrothermal aging and the second part aiming the effects of this aging on the mechanical properties of those ceramics. 117 Y-TZP (VITA YZ, VITA HT, InCoris TZI) blocks were cut, 39 for each commercial zirconia, sintered (1530 ºC, 2h) and assigned to 13 groups with 3 samples each: One being a control, aging-free group, and 12 groups that were prematurely aged hydrothermally at 134 ºC and constant pressure of 2 bars through 6, 10, 14, 18, 22, 26, 30, 40, 60, 80, 100 and 140 hours. XRD was used to quantify the amount of zirconia phase transformation (tetragonalmonoclinic) on different depths of the material by swapping the anode tube (Cr, Co, and Cu). An aging kinetic curve was made for each depth for the 3 commercial zirconias. To evaluate the effects of the hydrothermal aging on the mechanical properties, Y-TZP blocks were rounded to a cilindrical shape. 270 discs were cut, 90 for each kind, sintered as mentioned above and assigned to 3 groups: C-Control; E1- Aged through 26h and E2- Aged through 140h. Disks were then tested in a universal testing machine (EMIC) under a load of 1000 kg till fracture of the specimen and the surface was evaluated under SEM. The aging kinetics curves work similarly for all the YTZP used in this study, characterized by phase transformation asce... (Complete abstract click electronic access below) / Mestre

Revestimentos de máquinas e equipamentos industriais sofrem desgastes consideráveis por abrasão, impacto e ataque químico, o que torna necessária frequente parada de produção para ações de manutenção. Esta situação motiva o desenvolvimento de materiais de maior resistência a estas solicitações. A adição de óxidos de zircônio e cério em compostos à base de alumina tem demonstrado a capacidade de aumentar as propriedades mecânicas deste tipo de cerâmica, tornando estes materiais promissores candidatos ao uso em maquinário industrial. Neste contexto, o objetivo deste trabalho foi o estudo da influência da adição de diferentes teores, 25, 30 e 35% de zircônia parcialmente estabilizada com 14% de céria (ZPEC) em compósitos à base de alumina. Para obtenção destes compostos, óxido de alumínio, óxido de cério e óxido de zircônio foram misturados em moinho de bolas e conformados por prensagem isostática a frio, seguido de secagem e sinterização entre 1300 e 1600°C. As propriedades físicas, químicas e mecânicas dos materiais após a sinterização foram avaliadas por ensaios porosidade aparente, densidade relativa, retração linear de queima, dureza Vickers, resistência à flexão em 4 pontos e ao choque térmico, e tenacidade à fratura (KIc). Os materiais investigados apresentaram densificação na faixa de 94,3% a 95,75% da densidade teórica para a temperatura de sinterização de 1600°C, e estes valores aumentaram com aumento do teor de ZPEC. Estes compósitos apresentaram uma melhora de 23% na resistência à flexão em comparação coma alumina pura. / Machinery and industrial equipment coatings suffer considerable damage from abrasion, impact and chemical attack, which makes it necessary to stop frequent maintenance actions. This situation motivates the development of materials of greater resistance to these requests. The insertion of zirconium oxide and cerium oxide in alumina-based compound has shown the ability to increase the mechanical properties of this type of technical ceramics. In this context, the objective of this work is the study of the influence of zirconium oxide and cerium oxide content (25 to 35%) in alumina-based composite. For these compounds, aluminum oxide, cerium oxide and zirconium oxide were mixed in ball mill and then, conformed by isostatic pressing. After, passed through a drying process and were the 1300, 1500 and 1600°C sintering. The mechanical properties of the materials after sintering were evaluated by mechanical resistance tests, Vickers hardness, KIc, thermal shock, linear shrinkage and porosity. The investigated materials showed densification in the range of 94.3 % to 95.75% of the theoretical density at sintering temperature of 1600 ° C and these values increased with the increase of ZPEC content. These composites can reach 23% of flexural strength greater than that of pure alumina, and with a tendency to increase this improvement with the percentage increase of ZPEC in alumina.

Chen Fei. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2005. / Includes bibliographical references (leaves 86-92). / Abstracts in English and Chinese. / Acknowledgements --- p.i / List of publications --- p.ii / Abstract (In English) --- p.iii / Abstract (In Chinese) --- p.v / Table of contents --- p.vii / List of figures --- p.x / List of tables --- p.xiv / Chapter Chapter I --- Introduction --- p.1 / Chapter Chapter II --- Sol-gel channel waveguides --- p.6 / Chapter 2.1 --- General sol-gel process --- p.6 / Chapter 2.2 --- Dye-doped sol-gel zirconia and zirconia-ORMOSIL materials --- p.10 / Chapter 2.3 --- Fabrication of sol-gel channel waveguides --- p.15 / Chapter 2.3.1 --- General process of the photolithographic technique --- p.15 / Chapter 2.3.2 --- Channels in glass substrates by using photolithographic wet etching technique --- p.19 / Chapter 2.3.3 --- Channels in fused silica substrates by using photolithographic dry etching technique (Inductive-coupled plasma etching) --- p.24 / Chapter Chapter III --- Coupled-wave theory and experimental setup of distributed feedback channel waveguide lasers --- p.27 / Chapter 3.1 --- Coupled-wave theory of distributed feedback lasers --- p.27 / Chapter 3.2 --- Experimental setup --- p.33 / Chapter Chapter IV --- One-dimensional and two-dimensional optical waveguide analysis --- p.37 / Chapter 4.1 --- 1-D planar waveguide analysis --- p.37 / Chapter 4.2 --- 2-D channel waveguide analysis using the Marcatili method --- p.39 / Chapter 4.2.1 --- The Eypq modes: Polarization in the y direction --- p.42 / Chapter 4.2.2 --- The Eypq modes: Polarization in the x direction --- p.46 / Chapter 4.3 --- 2-D channel waveguide analysis using the effective index method --- p.48 / Chapter Chapter V --- Distributed feedback channel waveguide lasers tunable in the visible --- p.50 / Chapter 5.1 --- Rhodamine 6G-doped zirconia planar and channel waveguides --- p.51 / Chapter 5.2 --- Results and discussion --- p.56 / Chapter 5.3 --- Summary --- p.66 / Chapter Chapter VI --- Near infrared distributed feedback channel waveguide lasers --- p.68 / Chapter 6.1 --- LDS dye-doped zirconia-ORMOSIL planar and channel waveguides --- p.68 / Chapter 6.2 --- Results and discussion --- p.72 / Chapter 6.3 --- Summary --- p.80 / Chapter Chapter VII --- Summary --- p.81 / References --- p.86