Made available in DSpace on 2014-06-12T23:14:05Z (GMT). No. of bitstreams: 2 arquivo4313_1.pdf: 4415707 bytes, checksum: 77682bd2005ccebe78c5e5cf87c30582 (MD5) license.txt: 1748 bytes, checksum: 8a4605be74aa9ea9d79846c1fba20a33 (MD5) Previous issue date: 2008 / Conselho Nacional de Desenvolvimento Científico e Tecnológico / Na elaboração de materiais nanoestruturados, a anodização do alumínio para obtenção de membranas de alumina anódica auto-organizadas tem se revelado ferramenta útil. Elas apresentam elevado grau de ordenamento que se configuram em arranjo de células hexagonais, com poros centrais e individualizados, não interconectados. Este trabalho propôs-se empregar as membranas como parte de um compósito nanoestruturado com vistas ao seu emprego como matriz para imobilização de proteínas. As membranas foram sintetizadas pela anodização de fitas de alumínio de alta pureza, verificando-se que para sua obtenção com alto padrão de organização era necessário um controle rígido do acabamento superficial do alumínio e da temperatura de anodização. O polimento eletroquímico, em uma mistura de ácido perclórico/etanol, foi superior ao químico em relação ao desbastamento da superfície, dando um aspecto espelhado à fita de alumínio (eletrodo). Filmes com bom ordenamento foram obtidos empregando-se eletrodos polidos eletroquimicamente e anodizados a baixas temperaturas. Nanocompósitos de membranas de alumina anódica com polianilina (PANI) e polietilenimina (PEI) foram sintetizados e a eles foram covalentemente imobilizadas duas enzimas importantes biotecnologicamente: peroxidase e tripsina. O compósito com PANI foi obtido tratando-se a membrana com permanganato de potássio, com vistas a depositar o dióxido de manganês sobre sua superfície, que serviu como agente oxidante na polimerização da anilina sobre a superfície da membrana. Ao microscópio eletrônico de varredura observou-se que a síntese deste polímero não obstruiu os poros da membrana. Peroxidase foi imobilizada ao compósito via glutaraldeído. O derivado da imobilização manteve suas propriedades catalíticas e apresentou-se razoavelmente estável ao reuso, bem como quando ensaiado em um sistema em fluxo. Outra funcionalização da membrana foi realizada com PEI, polímero altamente catiônico contendo aminas primárias, secundárias e terciárias, bastante utilizado na imobilização de proteínas devido às suas propriedades hidrofílicas e de fisissorção. Este processo foi conseguido fazendo-se passar pelos poros da membrana uma solução de PEI e em seguida tratando-se a mesma com glutaraldeído. Avaliou-se a porosidade do compósito resultante através de micrografias eletrônicas de varredura e observou-se que a grande maioria dos poros havia sido bloqueada pela presença do polímero e este formou uma camada sobre a superfície da membrana. O compósito alumina anódica/PEI fixou a tripsina de forma que ela permaneceu cataliticamente ativa. Também se apresentou estável ao uso em fluxo e em batelada. Observou-se que quanto maior o diâmetro do poro maiofoi a atividade enzimática encontrada da tripsina. Também foi constatado que a membrana sem funcionalização fixou a tripsina, contudo a lixiviação da mesma foi evidente, demonstrando a importância do polímero para uma imobilização efetiva desta proteína

Anodisation is a surface treatment process, commonly used to form a protective oxide coating on the surface of metals like aluminium. Anodised coatings, being grown out of the base metal have excellent interface strength but are porous and brittle. Porosity of the coating reduces the hardness and the brittle nature of the oxide induces cracking. In practice, the pores are typically filled with organic dye and sealed. Under certain controlled electrochemical conditions, anodisation results in a highly ordered hexagonal porous structure in pure aluminium. In this work, we explore the possibility of using this ordered porous alumina to form a novel metal nanocomposite as a tribological coating. By optimizing the nonporous structure and tuning the electrodeposition process, we uniformly filled the ordered pores with copper. We have measured the hardness of the resulting ordered and aligned nanocomposite. We explore the possibility of using this composite coating for tribological applications by carrying out some preliminary reciprocating wear test. Ordered porous alumina layer is formed by a two-step anodisation process. By optimizing the anodisation conditions, we control the thickness of the coating and the pore size. The interface of the porous structure and aluminium substrate is defined by a non-conducting dense barrier oxide layer. However, to deposit metal into the pores, a conducting path should be established through the barrier layer. One possibility is to etch out the bottom of the pores at the cost of the interface strength and losing out on the main advantage of anodised coatings. To be able to fill metal without this sacrifice, we utilised the dendritic structure in the barrier layer formed by a step-wise reduction of voltage towards the end of anodisation process. Optimisation of this dendritic structure led to uniform deposition of metal into pores, achieved by pulsed electrodeposition. In pulse lectrodeposition, a positive pulse is applied to remove accumulated charge near to the bottom of pores, followed by a negative pulse to deposit metal and a delay to allow diffusion of ions. By optimising the pulse shape and duration, we have achieved uniform growth of metal into pores. Further, monitoring the deposition current helped us to identify and control different phases of growth of the nanowire. The properties of the porous alumina and the nanocomposite were measured by nanoindentation. The deformation characteristics were obtained by observing the indents in a FE-SEM. We find that dendritic modification of interface has very little effect on the hardness of the porous alumina layer. We also found that the porous alumina deformed either by compaction or by forming circumferential and radial cracks. When copper is filled in the nano pores, the hardness increased by 50% and no circumferential cracks were found up to the load of 10 mN for a film thickness of about 1 µm. Coefficient of friction of the coating reciprocated against steel in dry condition is found to be around 0.4. Minimal wear was observed from the SEM images of wear track. In summary, a novel nanocomposite coating with ordered porous alumina as matrix embedded with aligned metal nano rods has been developed. This was achieved by optimally modifying the barrier layer without sacrificing the interfacial strength. Uniform coating has been achieved over an area of 10 mm x 10 mm. The coating is found to have high hardness and high wear resistance.

Kyoto University (京都大学) / 0048 / 新制・課程博士 / 博士(工学) / 甲第15393号 / 工博第3272号 / 新制||工||1493(附属図書館) / 27871 / 京都大学大学院工学研究科物質エネルギー化学専攻 / (主査)教授 井上 正志, 教授 江口 浩一, 教授 大江 浩一 / 学位規則第4条第1項該当

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Ceramic-metal matrix composites produced by powder metallurgy provide a solution in engineering applications where materials with high wear resistance are required. In the mining industry, the wear of materials is a crucial and widely recognized industrial problem as over 50 % of components fail as a result of wear damage. Increasing the wear resistance of these components will contribute to a reduction in maintenance and thereby increase efficiency. In this present research, SS316L-50wt.% Al2O3 composites were fabricated using the powder metallurgy route. The effects of the powder metallurgy processing parameters were studied. The produced cermet composites were characterized with respect to microstructure, density, hardness and toughness. Furthermore, the wear behavior of the composites was studied using pin-on-disc testing under dry sliding conditions. The produced test results were used to improve existing wear models, particularly the Wayne’s model. The highest hardness of 1085.2 HV, the highest density of 94.7 % and the lowest wear rate of 0.00397 mm3/m were obtained at a milling speed of 720 rpm, a compaction pressure of 794.4 MPa and sintering at 1400 °C in an argon atmosphere. Compared to commercial SS316 and fabricated SS316L, the composites had 7.4 times and 11 times lower wear rate, respectively. However, it is shown that using better densification methods such as hot isostatic pressing (HIP) or hot pressing can further substantial enhanced densification and improve of the composites wear resistance. Similar to its effects of the strength and the toughness, the remaining porosity was found to substantially affect the wear resistance of the sintered composites. Therefore, the porosity was used to correct the abrasion parameter in the first step of wear model improvement. The porosity represented a further consideration of the microstructure in addition to the reinforcement particle size introduced earlier by Wayne. In a second model improvement step, the test conditions were introduced in the wear resistance calculation. This model allowed the prediction of corrected wear resistance values that are characteristic of the individual test materials and are widely independent of wear test conditions. The coefficient of correlation of the model was 0.91 with respect to Wayne's data and wear test results from this study, and was 0.66 after generalization to a large range of wear data measured on multiple materials tested under varying test conditions. This opens a potential avenue for a model-based assessment of the wear resistance of novel materials as well as changes that can be expected under different wear conditions.

Orientador: Maria Helena Robert / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecanica / Made available in DSpace on 2018-07-18T06:05:22Z (GMT). No. of bitstreams: 1 Carvalho_BereniceRomano_M.pdf: 9365120 bytes, checksum: f4eb25f45bea30ae943e90ba06eaf104 (MD5) Previous issue date: 1992 / Resumo: O objetivo geral do presente estudo foi analisar comparativamente modificações estruturais que ocorrem em tratamentos térmicos objetivando a homogeneização na liga AI-5,7%Cu e na mesma liga reforçada com 30% em volume de fibras de alumina. Os materiais utilizados foram tratados em diferentes condições de temperaturas (480- e 510-C) e tempos (1, 5 e 10 horas). Suas microestruturas e perfis de distribuição do elemento cobre foram analisadas no estado "oomo fundido" e ap6s os tratamentos. Para melhor caracterização das microestruturas foi utilizado ataque metalográfico para coloração da microssegregação do cobre. Observou-se estrutura não tipicamente dendr1tica, com a presença de eutéticos junto às fibras do reforço no comp6sito como fundido. Dos resultados dos tratamentos térmicos efetuados, observou-se quase completa homogeneização na matriz ap6s tratamento a 510óC por 5 horas. No comp6sito, observou-se precipitação de CUAI em estágios iniciais de tratamento, além do agrupamento do eutético originado, na solidificação. Estas diferenças podem ser atribu1das aos reduzidos espaços inter-fibras existentes no compósito, que atuam como barreira à difusão do soluto / Abstract: This thesis describes a comparat ive analysis of the structural alterations which occur following thermic treatment of material containing AI-5.7% CU bonds, in some cases reinforced with 30% in volume of alumina fibers, with the aim of producing more a homogenous distribution of the CU. The materiaIs used were exposed to different temperatures (480' and 510'C) for various time intervals (1, 5 and 10 hours). Their microstructures and copper distribuition profiles were analized in the original material and after heat treatment. To better characterize the microstructures, metallographic attack for the coloration of copper microsegregation was employed. such analysis demonstrated the preserice of non-typical dendritic structures with the occurrence of eutectics alongside the reforcing fibres in the non-treated material. Thermic treatment resulted in.almost complete homogeneity in the matrix after 5 hours at 510'C. In the composite, apart from the eutectic groupings originating from solidification,CUAI 2 precipitation was 'also observed in the initial stages of treatment. These differences maybe ttributed to the reduced inter-fiber spaces present in the composite and which act as barriers to solute diffusion / Mestrado / Mestre em Engenharia Mecânica

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The vapour-phase reaction of 2-methy-tetrhydropyran and 2-ethyltetralydropyran with aniline over an activated alumina catalyst has been studied. The product, in each case, consisted of a mature of an N-aryl-piperidine, an N-arylpyrrolidine formed by ring contraction, and two N-alkelnylanilines formed by ring opening. The structures of the nitrogen heterocyclic compounds were established by independent syntheses involving the reaction of the appro­priate dibromoalkane with aniline. The N-alkenylanilines were characterised by hydrogenation to known N-alkylanilines and by identification of the osonolysis products. / Thesis / Master of Science (MSc)