<div>Thin films with selective spectral properties have great potential for use in applications such as solar thermal absorbers, selective thermal emitters, thermal barrier coatings, and thermophotovoltaics. Understanding the dependence of their optical properties with temperature is crucial for practical applications. Relatively less-used films with high thermal stability, high refractive index, and infrared transparency, such as cerium oxide CeO2 and magnesium oxide (MgO) have not been studied extensively for high-temperature applications. In this paper, CeO2, MgO, and several multilayer samples containing these compounds will be studied their change of optical properties with increasing temperature across the visible and infrared spectrum. In this work, I introduce Spectroscopic Ellipsometry (SE) to analyze dielectric constants of films and measure its thickness at multiple incident angles in visible and near-Infrared (IR) wavelengths both at room temperature and elevated temperatures. Using ellipsometry, several single and multilayer thin films (CeO2 and other transparent materials-based) have been measured their dielectric constants and thickness at room temperature and high temperature up to 500°C using thermal control stages called INSTEC. The change of their optical properties with temperatures has been characterized using theoretical modelling. Fitting their optical properties have been observed by changing thickness of each layer and calculating the corresponding Cauchy parameters in transparent material. Finally, FTIR measurements will be used to further characterize direct emission of these films at higher temperatures. This will be performed at room temperature and high temperature up to 1400 °C.</div>

Thermal Barrier Coatings have been used for decades to impose a thermal gradient between the hot combustion gases and the underlying superalloy substrate in engine turbine blades. Yttria Stabilized Zirconia (YSZ) is an industry standard high temperature ceramic for turbine applications. The protective coating is adhered to the substrate using a nickel based alloy bond coat. Through exposure to high temperature, a Thermally Grown Oxide (TGO) layer develops at the bond coat-YSZ interface. Large residual stresses develop in these layers due to thermal expansion mismatch that occurs during cool down from high temperature spraying and cyclic operating conditions. Despite their standard use, much is to be determined as to how these residual stresses are linked to the various failure modes. This study developed techniques to monitor the strain and stress in these internal layers during thermal gradient and mechanical conditions representing operating conditions. The thermal gradient is applied across the coating thickness of the tubular samples from infrared heating of the outer coating and forced air internal cooling of the substrate. While thermal and mechanical loading conditions are applied, 2-dimensional diffraction measurements are taken using the high-energy Synchrotron X-Rays and analyzed to provide high-resolution depth-resolved strain. This study will include fatigue comparisons through use of samples, which are both 'as-coated' as well as aged to various stages in a TBC lifespan. Studies reveal that variations in thermal gradients and mechanical loads create corresponding trends in depth resolved strains with the largest effects displayed at or near the bond coat/TBC interface. Single cycles as well as experiments targeting thermal gradient and mechanical effects were conducted to capture these trends. Inelastic behavior such as creep was observed and quantified for the different layers at high temperatures. From these studies more accurate lifespan predictions, material behaviors, and causes of failure modes can be determined. The work further develops measurement and analysis techniques for diffraction measurements in internal layers on a coated tubular sample which can be used by various industries to analyze similar geometries with different applications.

Advanced aerospace materials require extensive testing and characterization to anticipate and ensure their integrity under hostile environments. Characterization methods utilizing synchrotron X-Ray diffraction and spectroscopy can decrease the time required to determine an emerging material's readiness for application through intrinsic information on the material response and failure mechanisms. In this study, thermal barrier coating samples applicable to turbine blades of jet engines were studied using Raman and Photoluminescence spectroscopy as well as Synchrotron X-ray diffraction while Kevlar based fiber composites applicable to ballistic resistant armor were studied using Raman spectroscopy to investigate the mechanical state and corresponding damage and failure mechanisms. Piezospectroscopic studies on the stress state of the thermally grown oxide (TGO) within the thermal barrier coatings, on a hollow cylindrical specimen, provided results that indicate variations within the TGO. Comparison of measured photo-luminescence spectra of the specimen before and after long duration thermal aging showcases the development of the system and the initiation of micro-damage. Raman spectroscopy performed on Kevlar ballistic composites with nano-scale additives, presented insight into the additives' role in load transfer and damage propagation through a comparison of the shift in optical spectra to that of the pristine fibers. The results presented herein utilize changes in the measured emission from these non-destructive testing techniques to link the phenomena with material response. Techniques to optimize imaging and spectral collection are addressed as well. The findings will advance the use of the techniques in the development of aerospace materials, providing a more complete understanding of land and aircraft turbine blade coatings, and fiber composite response to complex loading.

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Thermal barrier coatings (TBCs) are advanced material systems used in the hot sections of gas turbines. The TBCs are designed to provide insulation against hot gases by a ceramic top coat and to provide oxidation and corrosion resistance by a metallic bond coat. As the operating environment is harsh and complex, the TBC often requires stricter material properties. Failure of TBCs can limit the longevity of the turbine severely. In this study, failure caused by erosion has been the main focus. The erosion behaviour of TBCs processed by atmospheric plasma spay (APS), electron beam physical vapour deposition (EB-PVD), and plasma spray physical vapour deposition (PS-PVD) has been studied by an experimental investigation and a literature study. The erosion performance of different TBCs was studied by conducting erosion tests under 90° and 15° alumina particle impact (50 μm) and measuring the weight loss and thickness loss of the ceramic top coat. Variables affecting the erosion behaviour were studied by means of scanning electron microscopy (SEM), investigating the microstructure, the erosion damage, porosity content, and column density. Hardness tests were also conducted to investigate a potential correlation between hardness and erosion performance. It was evident that the 8YSZ top coat processed by EB-PVD had higher erosion resistance than APS, which in turn had higher erosion resistance than PS-PVD. Their microstructures are significantly different, resulting in different erosion failure mechanisms. APS TBCs have a splat-on-splat lamellar microstructure, and the failure mechanismsare ploughing of furrows, splat boundary failure, and tunneling via pores. In contrast, EB-PVD TBCs have columnar microstructure and fail by near-surface cracking. The investigated PS-PVD TBC had a feathery columnar microstructure, containing many large grain boundaries and flaws, making grain boundary failure the governing mechanism. The APS and EB-PVD TBCs impacted at a 90° angle had significantly higher erosion rates than those eroded at 15°, which also was reported in literature. However, the opposite was observed for the PS-PVD TBCs. The level of porosity and hardness of the TBC top coat was found to affect the erosion rate, even though no evident correlations could be observed in this study. No factor alone was found to dictate the erosion behaviour of the investigated TBCs. Based on the literature study and findings in the experimental study, a TBC with good erosion performance has, in general, low porosity, few defects, high hardness and high fracture toughness. Specifically for APS TBCs, good splat bonding is favourable and for EB-PVD and PS-PVD it recommended to have high column density, columns orthogonal to the substrate, and low gap width between the columns.

The aerospace industry strives to develop new methods of refining gas turbine engines by increasing power and thermal efficiencies while simultaneously reducing cost. Turbine engines operate under high temperatures and therefore thermal barrier coatings (TBCs) composed of yttria-stabilized zirconia (YSZ) play an important role in improving the performance of the components that make up the engine. Failure of the TBC could lead to catastrophic events, thus requiring consistent and accurate characterization for supplier qualification and production quality assurance. However, due to porosity and the anisotropic behavior of the coating and variability in processing of TBCs, consistent characterization has proven to be extremely challenging. One of the reoccurring issues is the inconsistency in measuring percent porosity, which stems from the difficulty in distinguishing filled pores from damaged, unfilled voids. Sample preparation of TBCs involves sectioning, mounting, grinding, polishing, and characterization. Eliminating variability in characterization begins with mounting which is a critical step to protect the surface integrity and edge retention of the coating during grinding and polishing. The curing kinetics of a slow cure two part epoxy was investigated and the TBC samples were mounted and cured at heating rates of 2, 5, and 10°C/min to 55°C and 70°C. Grinding and polishing procedures simulated industry practices followed by characterization with optical microscopy. Results showed that heating rates of 2°C/min to 55°C and 70°C have the best impregnation properties while uncontrolled or high heating rates of 10°C/min had an increase in the amount of pullouts and lack of infiltration from the epoxy. The curing kinetics of the epoxy needs to be controlled to eliminate the ambiguity of filled and unfilled pores. / Master of Science

Os objetivos deste trabalho foram relacionar o atendimento das necessidades humanas dos funcionários com os indicadores de qualidade do leite, avaliar o conhecimento técnico tanto dos ordenhadores quanto dos proprietários e gerentes, observar as práticas realizadas na ordenha, relacionando-as com os indicadores de qualidade do leite e verificar a adoção de ferramentas da gestão administrativa de explorações leiteiras, segundo o sistema MDA, da Clínica do Leite - ESALQ/USP. Para atingir estes objetivos, 74 propriedades leiteiras localizadas nos Estados de São Paulo, Minas Gerais e Rio de Janeiro participaram deste projeto. Estas propriedades foram divididas em dois grupos, a partir da média de contagem bacteriana total (CBT) apresentada, sendo o grupo com alta CBT com média superior a 200.000 ufc/ml e o grupo com baixa CBT, com média inferior a 50.000 ufc/ml. Foram realizadas visitas a estas propriedades, com duração de meio dia, sendo que estas constituíram no acompanhamento da rotina de ordenha, aplicação de questionários com os ordenhadores sobre questões relacionadas ao atendimento das necessidades humanas, segundo Maslow e conhecimentos técnicos e aplicação de questionários com os proprietários ou gerentes sobre aspectos relacionados ao gerenciamento das propriedades, segundo o sistema MDA. Os dados foram analisados por estatística descritiva e também pela metodologia de árvores de regressão, relacionando as questões com a CBT e contagem de células somáticas (CCS). A média de CBT das propriedades com alta CBT foi de 330.113 ufc/ml (± 143.865 ufc/ml) e das com baixa CBT foi 49.126 ufc/ml (± 36.704 ufc/ml). Já para CCS, as médias foram: 908.473 céls/ml (± 463.992 céls/ml) para propriedades com alta CBT e 605.728 céls/ml (± 282.885 céls/ml) para propriedades com baixa CBT. Tanto os funcionários quanto proprietários ou gerentes de ambos os grupos apresentaram conhecimento satisfatório sobre a rotina de ordenha, mas uma pequena porcentagem dos grupos conhecia os conceitos relacionados à qualidade do leite. No entanto, os conhecimentos sobre mastite foram maiores para os funcionários e proprietários ou gerentes das propriedades com baixa CBT. Com relação ao atendimento das necessidades humanas, todas as necessidades tenderam a ser mais bem atendidas para os funcionários das propriedades com baixa CBT, com exceção das necessidades fisiológicas. O mesmo perfil pode ser observado para o gerenciamento administrativo das propriedades com baixa CBT, sendo que a adoção das ferramentas de gestão, como política básica, gestão da rotina, procedimentos operacionais e recursos humanos, tendeu a ser maior nestas propriedades. Além disso, os procedimentos recomendados da rotina de ordenha foram mais e melhor conduzidos pelas propriedades com baixa CBT, assim como a limpeza dos equipamentos. Desta forma, pode-se observar que os aspectos relacionados ao conhecimento técnico, comprometimento dos funcionários, conseguido através do atendimento das necessidades humanas, adoção de ferramentas de gestão administrativa e a ordenha estão interferindo na qualidade do leite produzido. Apesar das propriedades com baixa CBT terem apresentado resultados melhores nestas áreas, há a possibilidade de melhorar ainda mais a qualidade do produto, através do investimento em todas as áreas relacionadas neste projeto. / The purposes of this work were to relate satisfaction of employees\' human needs with milk quality indicators, to evaluate technical knowledge of milkers and producers or managers, to observe milking practices conducted, relating them to milk quality indicators and to verify adoption of dairy farms management tools, according to MDA system, of Clínica do Leite - ESALQ/USP. In order to achieving these goals, 74 dairy farms located in states of São Paulo, Minas Gerais and Rio de Janeiro participated of this work. These dairy farms were divided in two groups, from total bacterial count (TBC) average, being the group with high TBC with average greater than 200,000 cfu/ml and the group with low TBC with average minor than 50,000 cfu/ml. Visits to these farms were accomplished during half day, being these constituted of milking routine observation, application of questionnaires to milkers about satisfaction of human needs, according to Maslow and technical knowledge and application of questionnaire to producers or managers about aspects related to farms management, according to MDA system. Statistical analyses were performed by descriptive statistics and also by regression trees methodology, relating questions with TBC and somatic cell count (SCC). The TBC average of dairy farms with high TBC was 330,113 cfu/ml (± 143,865 cfu/ml), and of those with low TBC was 49,126 cfu/ml (± 36,704 cfu/ml). The averages of SCC were: 908,473 cells/ml (± 463,992 cells/ml) to dairy farms with high TBC and 605,728 cells/ml (± 282,885 cells/ml) to dairy farms with low TBC. Both groups of milkers and producers or managers showed a satisfactory knowledge about milking routine, but a little percentage of both groups knew the concepts related to milk quality. Nevertheless, knowledge about mastitis was greater to milkers and producers or managers of dairy farms with low TBC. Regarding human needs satisfaction, all needs tended to be more satisfied to milkers of dairy farms with low TBC, except for physiological needs. The same scenario was observed to administrative management of dairy farms with low TBC, being the adoption of management tools, like basic policy, routine management, operational protocols and human resource, tended to be greater at these farms. Besides, milking routine recommended practices were more and better conducted by dairy farms with low TBC, just like equipment cleaning. In this way, it can be observed that aspects related to technical knowledge, employees commitment, achieved through satisfaction of human needs, adoption of administrative management tools and milking were interfering at milk quality. Despite dairy farms with low TBC showed better results at these areas, there is a possibility to improve the product quality, through investment in all related areas of these work.

Thermal barrier coatings (TBC) are used in the hot sections of gas turbine engine in order to insulate the substrate at high temperature. Molten salt infiltration retards the durability of TBCs. The current standard material, i.e. 8YSZ is susceptible to molten salt infiltration. Therefore, alternate TBC materials are desirable. In addition to material composition, the TBC microstructure plays an important role in mitigating molten salt infiltration. Therefore, in this work, three different TBC variations were investigated. The first variation was a columnar microstructured 48YSZ TBC processed by SPS (48YSZ-SPS). The second variation was a columnar microstructured 8YSZ TBC processed by SPS (8YSZ-SPS), and the third variation was a lamellar microstructured 8YSZ TBC deposited by APS (8YSZ-APS). The as-sprayed TBC specimens were characterized by SEM/EDS, porosity analysis and XRD measurements. Later, the TBC specimens were exposed to hot corrosion test and their interaction with the molten salts were investigated using SEM (EDS and XRD). It was shown that an increase in stabilizer content (yttria content) in zirconia (in the case of 48YSZ) leads to an improved hot corrosion resistance due to the adequate amount of yttria content, which restricts the molten salt infiltration by forming needle like YVO4 phase. In terms of microstructure comparison, the infiltration behavior was similar for columnar microstructured 8YSZ and lamellar microstructured 8YSZ-APS as the molten salts infiltrated the coatings completely compared to the 48YSZ TBC. Furthermore, it seems that the molten salt infiltrates the TBC through globular pores, delamination cracks and splat boundaries in the case of APS-TBCs whereas the column gaps favor easier infiltration of molten salts in the case of columnar microstructured SPS processed TBCs.