O presente trabalho de mestrado teve como meta realizar um estudo do comportamento do cobre particulado em ensaios tribológicos do tipo pino contra disco. O cobre é atualmente utilizado em até 15% em massa das pastilhas de freios automotivos e tal utilização é responsável pela emissão de até 70% do cobre particulado presente no ar. Devido ao caráter carcinogênico do cobre, se faz necessária sua substituição. Foram realizados ensaios tribológicos pino disco com adição de diferentes meios interfaciais. Foram utilizados pares tribológicos aço/aço, em ensaios a seco de pino contra disco com adição de meio interfacial nanoparticulado de óxido de ferro, grafite e de cobre metálico em diferentes granulometrias (400 m, 20 m e 50 nm). Após os ensaios, amostras das superfícies de pinos e discos para cada uma das adições de cobre, bem como para a condição sem adição de meio interfacial, foram caracterizadas utilizando técnicas de microscopia eletrônica de varredura, de forma a entender o comportamento das partículas de cobre e sua contribuição para o coeficiente de atrito. As adições de cobre obtiveram os maiores coeficientes de atrito, e entre elas os coeficientes de atrito foram mais altos durante todos os ensaios para a adição de 50 nm, seguido de 20 m e 400 m. A análise das superfícies tribológicas em MEV mostrou heterogeneidade das superfícies ensaiadas em relação à presença de debris oxidados e camadas compactas. Observou-se a presença de cobre apenas nas superfícies ensaiadas com adição dos cobres de 50 nm e 20 m. A presença de um filme óxido compacto e contínuo foi observada apenas nas superfícies tribológicas ensaiadas sem adição de meio interfacial e com adição de cobre a 400 m. / The purpose of this work was to investigate the behaviour of particulate copper in pin on discs tribotests. Copper is present in up to 15% in mass of brake pads composition, and it is responsible for the emission of up to 70% of the particulate copper present in airborne emissions. Due to its carcinogenic character, its replacement is considered necessary. Pin on discs tribotests were performed with the addition of different interfacial medias. The tribopair used was steel/steel, in dry sliding condition with the addition of nanoparticulated magnetite, graphite, and metallic copper in different granulometries (400 m, 20 m and 50 nm). After the tribotests, samples of both pin and disc surfaces for each of the copper additions, as well as a the condition with no interfacial media addition, were characterized using scanning electronic microscope techniques, in order to understand the behaviour of copper particles and their contribution to the friction coefficient. The three copper additions presented the highest friction coefficients among all additions; the highest friction coefficient was obtained by the smallest granulometry, 50 nm, followed by 20 m and 400 m. The analysis of the tribosurfaces using SEM showed the surface heterogeneity regarding the presence of oxide debris and compact layers. The presence of copper was only observed for the additions of the copper powders of 50 nm and 20 m. The presence of an oxide continuous and compact film was only observed for the tribosurfaces with no interfacial media addition and the addition of the copper with 400 m.

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Particle accelerators are a leading tool for frontier science. Pushing that frontier further demands more machines with higher performance, and more of a very expensive technology: superconducting radio-frequency (SRF) acceleration. From a materials perspective this means reducing residual surface resistance or raising the operating temperature (currently ~2 K) of SRF cavities. Both are pursued by materials modification: nitrogen doping/infusion in the first instance and coating with Nb3Sn in the second. Materials characterization is key to achieving understanding and directing RandD. However, very little has been done. This present work aims to fill the knowledge gap and to provide needed, validated tools to the accelerator science community. In this connection, SIMS, XPS and EBSD have proven especially valuable and represent the majority of discussion in this dissertation. / Doctor of Philosophy / Particle accelerators are a powerful tool that helps us expand our knowledge of science and how the universe works. Pushing that knowledge further requires us to use more and more powerful particle accelerators. Particle accelerators are based on a very expensive technology: superconducting radio-frequency (SRF) cavities. These cavities are hollow tubes made from niobium and shaped in such a way as to cause electromagnetic waves to form. These waves are what are used to accelerate particles. The energy input and loss of energy as heat are massive resulting in millions of dollars a year in electric bills at particle accelerator facilities. In order to build bigger and more powerful particle accelerates they most be more efficient or they become prohibitively expensive. In this dissertation I look at several next generation materials used in building particle accelerators. In particular I describe and go into detail about how to characterize these materials. In other words, how we determine the materials properties and how those properties affect the performance.

No description available.

No description available.

Introduction of nanocarbons, such as graphene and carbon nanotubes, to metal matrices, may enhance the electrical and thermal transport, mechanical properties and some other properties of the composite materials. However, uniform distribution of the nanocarbon phase in the matrix material and manufacturing the composites in large scale can be challenging using traditional mixing methods. In this study, a facile method to fabricate metal-nanocarbon composites was developed. Firstly, copper (Cu)-polydopamine (PDA) composite was fabricated by coating Cu powders with the bioinspired PDA polymer, which was then converted to a graphite-like structure during the subsequent sintering. In terms of the properties, compared to the pure Cu sample, the Cu-PDA composite showed increased electrical and thermal conductivity, higher microindentation hardness, and enhanced wear resistance. These findings suggest the inclusion of nanocarbon phase converted from PDA can simultaneously improve the electrical, thermal, and mechanical properties of sintered Cu materials. Effect of sintering temperature and coating time (carbon content) on the microstructure and properties of the composites were discussed. Secondly, aluminum (Al)-copper nanoparticles (CuNP)-PDA composite was fabricated with a new method, to improve the sintering behavior of Al for serving as feedstock materials of additive manufacturing (AM). CuNPs were synthesized by directly reducing Cu ions in the aqueous solution. With the assistance of the PDA coating, the CuNPs can be better attached to the Al powder surfaces. The composite samples showed better sintering behavior by exhibiting higher electrical conductivities and mechanical properties, which may be due to local nanosized alloying phases generation after sintering. These findings illustrated that the composite powders could be a good candidate feedstock material for AM. The structural characterizations of the metal nanocarbon powders and the composites were performed with SEM, TEM, XRD and Raman spectroscopy. With the help of these techniques, the formation of the targeted structures in the composite was studied, including graphite-like structures of cPDA and nano alloying phases in Al-CuNP-PDA composites. Apart from the composite materials fabrication, a novel and facile manufacturing method based on metal powders was also developed. In this study, a new type of Cu- binder paste was formed, which not only can be utilized with direct ink/paste printing but also can be casted into a soft silicone rubber mold. Three-dimensional (3D) metal parts can then be subsequently obtained after sintering. Comparing to other additive manufacturing methods that involve high energy laser or electron beams, this new approach does not require expensive facilities, and it is less time-consuming. Moreover, the silicone rubber molds can be easily removed and reused. In summary, the composite powders fabricated in this study can be utilized as feedstock materials for additive manufacturing of metals and alloys. The new soft-mold casting could be used as an alternative method to manufacture 3D metal components. Therefore, the materials and the processing methods developed in the current study could have broad applications in various metal industries. / Mechanical Engineering

This dissertation presents new solutions for turbine engines in need of wireless temperature sensors at temperatures up to 1300oC. Two important goals have been achieved in this dissertation. First, a novel method for precisely characterizing the dielectric properties of high temperature ceramic materials at high temperatures is presented for microwave frequencies. This technique is based on a high-quality (Q)-factor dielectrically-loaded cavity resonator, which allows for accurate characterization of both dielectric constant and loss tangent of the material. The dielectric properties of Silicon Carbonitride (SiCN) and Silicoboron Carbonitride (SiBCN) ceramics, developed at UCF Advanced Materials Processing and Analysis Center (AMPC) are characterized from 25 to 1300oC. It is observed that the dielectric constant and loss tangent of SiCN and SiBCN materials increase monotonously with temperature. This temperature dependency provides the valuable basis for development of wireless passive temperature sensors for high-temperature applications. Second, wireless temperature sensors are designed based on the aforementioned hightemperature ceramic materials. The dielectric constant of high-temperature ceramics increases monotonically with temperature and as a result changes the resonant frequency of the resonator. Therefore, the temperature can be extracted by measuring the change of the resonant frequency of the resonator. In order for the resonator to operate wirelessly, antennas need to be included in the design. Three different types of sensors, corresponding to different antenna configurations, are designed and the prototypes are fabricated and tested. All of the sensors successfully perform at temperatures over 1000oC. These wireless passive sensor designs will significantly benefit turbine engines in need of sensors operating at harsh environments

Nitride-based semiconductor materials make it possible to fabricate optoelectronic devices that operate in the whole electromagnetic range, since the band gaps of these compounds can be modified by doping. Among these materials, the sp2-hybridized boron nitride has properties that make it a potential candidate for integration in devices operating in the short-wavelength limit, under harsh environment conditions, due to the strength of the B-N bond.  Nevertheless, this binary compound has been the less studied material among the nitrides, due to the lack of complete control on the growth process. This thesis is focused on the study of the optical properties of sp2-hybridized boron nitride grown by hot-wall chemical vapor deposition (CVD) method, at the Department of Physics, Chemistry and Biology, at Linköping University, Sweden. The samples received for this study were grown on c-plane aluminum nitride as the buffer layer, which in turn was grown by nitridation on c- plane oriented sapphire, as the substrate material. The first objective of the research presented in this thesis was the development of a suitable ellipsometry model in a spectral region ranging from the infrared to the ultraviolet zones of the electromagnetic spectrum, with the aim of obtaining in the process optical properties such as the index of refraction, the energy of the fundamental electronic interband transition, the frequencies for the optical vibrational modes of the crystal lattice, as well as their broadenings, and the numerical values of the dielectric constants; and on the other hand, structural parameters such as the layers thicknesses, and examine the possibility of the presence of roughness or porosity on the boron nitride layer, which may affect the optical properties, by incorporating their effects into the model. The determination of these parameters, and their relation with the growth process, is important for the future adequate design of heterostructure-based devices that incorporate this material. In particular, emphasis has been put on the modeling of the polar lattice resonance contributions, with the TO- LO model, by using infrared spectroscopic ellipsometry as the characterization technique to study the phonon behavior, in the aforementioned spectral region, of the boron nitride. On the other hand, spectroscopic ellipsometry in the visible-ultraviolet spectral range was used to study the behavior of the material, by combining a Cauchy model, including an Urbach tail for the absorption edge, and a Lorentz oscillator in order to account for the absorption in the material in the UV zone. This first step on the research project was carried out at Linköping University.  The second objective in the research project was to carry out additional studies on the samples received, in order to complement the information provided by the ellipsometry model and to improve the model itself, provided that it was possible. The characterization techniques used were X-ray diffraction, which made it possible to confirm that in fact boron nitride was present in the samples studied, and made it possible to verify the crystalline quality of the aforementioned samples, and in turn relate it to the quality of the ellipsometry spectra previously obtained; the Raman spectroscopy made it possible to further verify and compare the crystalline qualities of the samples received, as well as to obtain the frequency for the Raman active B-N stretching vibration in the basal plane, and to compare this value with that corresponding to the bulk sp2-boron nitride; scanning electron microscopy made it possible to observe the rough surface morphologies of the samples and thus relate them to some of the conclusions derived from the ellipsometry model; and finally cathodoluminescence measurements carried out at low temperature (4 K) allowed to obtain a broad band emission, on all the samples studied, which could be related to native defects inside the boron nitride layers, i.e., boron vacancies. Nevertheless, no trace of a free carrier recombination was observed. Considering that the hexagonal-boron nitride is nowadays considered to be a direct band gap semiconductor, it may be indirectly concluded, in principle, that the dominant phase present in the samples studied was the rhombohedral polytype. Moreover, it can be tentatively concluded that the lack of an observable interband recombination may be due to the indirect band gap nature of the rhombohedral phase of the boron nitride. Spectroscopic ellipsometry does not give a definite answer regarding this issue either, because the samples analyzed were crystalline by nature, thus not being possible to use mathematical expressions for the dielectric function models that incorporate the band gap value as a fitting parameter. Therefore, the nature of the band gap emission in the rhombohedral phase of the boron nitride is still an open research question. On the other hand, luminescent emissions originating from radiative excitonic recombinations were not observed in the cathodoluminescence spectra. This second step of the project was carried out at the Leroy Eyring Center for Solid State Science at Arizona State University.

Os estudos focando a otimização do reforço dos tubos de concreto para obras de saneamento são importantes por estes componentes estarem vinculados a grandes necessidades sociais que ainda atingem o Brasil e outros países em desenvolvimento bem como pelo fato destes componentes serem produzidos em série, o que gera economia de escala. Neste sentido, a utilização de fibras como reforço dos tubos trás consigo um grande número de vantagens aplicativas e de desempenho. A tendência internacional de busca por um consenso no dimensionamento e controle do concreto reforçado com fibras (CRF) como material estrutural está sendo direcionada para o fib Model Code 2010. Geralmente, para a caracterização do CRF são utilizados os ensaios de flexão de vigas. Porém, a moldagem desses corpos de prova para o controle do CRF dos tubos apresentou resultados inadequados em estudos anteriores. A definição do reforço ótimo de tubos de CRF através da tentativa e erro no ensaio de compressão diametral do componente deve ser evitada pelos elevados gastos (financeiros, de material e tempo) associados a esta metodologia. O projeto deve ser atingido através de modelos confiáveis que possam otimizar o reforço através da previsão adequada do desempenho do componente. Da mesma forma, deve-se obter procedimentos de controle do material que sejam concatenados com os procedimentos de controle do produto. Neste sentido, esta tese propõe uma metodologia para a caracterização e controle do comportamento mecânico do CRF para a produção de tubos, que permita modelar o comportamento do componente no ensaio de compressão diametral e verificar sua adequação a uma aplicação estrutural. O estudo foi dividido em três fases principais. Na primeira houve a avaliação de um método de ensaio alternativo ao de flexão de prismas para o controle do CRF. Na segunda fase experimental houve a incorporação de modificações no método de ensaio de compressão diametral do componente de modo a aproximá-lo à filosofia do fib Model Code 2010. Nesta etapa foram avaliados tubos com reforço de fibras de aço, macrofibras poliméricas e vergalhões para comprovar a pertinência da nova metodologia de ensaio. Na terceira fase do estudo foi realizada uma simulação numérica para previsão de comportamento dos componentes ensaiados utilizando os parâmetros do material caracterizados através do método de ensaio alternativo validado na primeira fase. Os resultados obtidos na modelagem foram comparados com o resultado experimental do ensaio do componente de modo a validar a metodologia proposta. Os resultados demonstraram a adequação do ensaio Barcelona para a caracterização e controle do comportamento mecânico do CRF destinado à produção de tubos. Essa caracterização poderá subsidiar simulações numéricas do comportamento do componente no ensaio de compressão diametral. Com isto, ábacos de projeto de tubos de concreto reforçados com diferentes tipos de fibras poderão ser desenvolvidos, identificando as classes resistentes que serão atendidas dependendo do diâmetro do tubo e do teor de fibras empregados. Esta tese aponta também para a necessidade de uma revisão na normalização vigente, estabelecendo critérios relacionados ao comportamento pós-fissuração que avaliem o estado limite de serviço e o estado limite último. Isto permitirá uma avaliação homogênea do tipo de reforço e tornará mais adequada a comparação entre distintos tipos de reforço (fibras ou convencional). / The international trend for a consensus about the design and control of fibre reinforced concrete (FRC) as a structural material is based on the fib Model Code 2010. Generally, in order to characterize the FRC, bending tests are used. However, the moulding of these control test specimens of the FRC pipes is not quite simple as has been shown by previous studies. The design of FRC pipes through trial and error in the component-crushing test should be avoided. This test shall be limited to the acceptance control or final validation of a new component, designed through reliable models that optimize the reinforcement and the component performance. These models should allow both design and prediction of the component behaviour related to the quality control. In that sense, this thesis proposes a methodology for characterizing and controlling the mechanical behaviour of FRC for the production of pipes. This study allows modelling the component behaviour in crushing test and verifying their suitability for structural application. The methodology considered consisted in three main topics: evaluation of an alternative method of FRC control test; modification of the procedure of the crushing test method in order to approach the fib Model Code 2010 philosophy, and prediction the mechanical behaviour of the components comparing numerical simulation results with experiments results. In this last topic, the characterization of the materials performance by the alternative test method was considered. The results indicated that the Barcelona test is suitable in order to characterize and control the mechanical behaviour of the FRC used for the production of pipes. This characterization is able to support numerical simulations of the component behaviour in crushing test. It allows the development of design tables identifying the pipes resistant classes considering a variety of parameters such as types and contents of fibres and pipes diameters. This thesis also points out the need for a review of the current standards, establishing parameters related to the post-cracking behaviour to assess the serviceability limit state and the ultimate limit state. This allows a homogeneous evaluation of the reinforcement type and makes it more suited to comparing different types of reinforcement (fibre or conventional).

No presente trabalho, investigamos algumas propriedades e aplicações para imagens de diferença de polarização (PDI\'s) propondo dois sistemas de aquisição destas imagens como alternativas à arquitetura proposta por Tyo (1996). O primeiro sistema aqui abordado faz uso de duas câmeras e dois polarizadores para a obtenção de PDI\'s. A redundância, em termos de elementos de aquisição de imagens, visa suprir uma deficiência do sistema supracitado, qual seja a sua impossibilidade de operar em tempo real. O segundo projeto propõe a utilização de filtros polarizadores baseados em implementações de estruturas Fabry-Perot utilizando-se filmes finos birrefringentes de TiOx, como elemento principal de um dispositivo que possa ser produzido na forma de um microssistema integrado de aquisição de imagens completamente compatível com as tecnologias de produção CMOS disponíveis hoje em dia. Dadas as possibilidades envolvendo esse último projeto, definimos como objetivo principal deste trabalho a obtenção de filtros polarizadores baseados em tecnologia de filmes finos birrefringentes, que foram obtidos por deposição física num equipamento de Sputtering DC. Na etapa de análise dos dados, foram feitas caracterizações ópticas (espectrofotometria) e RBS tanto dos filtros finais quanto dos filmes de TiOx, que foram ensaiados previamente para a extração de parâmetros necessários para o projeto dos filtros de interferência. Conclui-se o trabalho comprovando a possibilidade de se obter filtros polarizadores que possam ser utilizados em sistemas integrados de aquisição de imagens, mas ressalva-se que o equipamento de Sputtering DC empregado não é o ideal para essa aplicação, sugerindo-se o uso de equipamentos capazes de monitorar espessura e índices de refração durante o processo de deposição dos filmes (um exemplo seria um sistema de deposição por e-beam acoplado a um elipsômetro de transmitância) / In the present work, it was investigated some properties and applications for polarization-difference images (PDI\'s), what led us to the proposition of two acquisition systems for such images as alternatives to the architecture proposed by Tyo (1996). The first system here discussed uses two cameras and two polarizers in the attainment of PDI\'s. The image elements redundancy is supposed to overcome a deficiency of the above-mentioned system that is its inability to operate in real time. The second project proposes the use of polarizing filters based on Fabry-Perot structures obtained with birefringent thin films of TiOx. Such filters are the key elements in a device that can be implemented as an integrated microsystem, fully compatible with the CMOS production technologies, available nowadays. Given the possibilities associated with this last project, it was defined as the main goal of this work, the attainment of polarizing filters based on birefringent thin films technology, physically deposited by a DC Sputtering equipment. During the phase of data analysis, it was carried out optical characterizations (spectrofotometry) as well as RBS analysis, both for the filters itself and for the TiOx films, that were previously investigated in order to determine the required parameters for the design of the interference filters. This work is concluded by proving the possibility of using polarizing filters in integrated image acquisition systems, but a remark ismade stating that the employed equipment is not the ideal one for such applications and it is suggested the use of deposition set up capable to monitor thickness and refractive indexes during the run (an example would be an e-beam equipment connected to a transmittance ellipsometer).