Thesis (M.Sc.(Earth Sciences Practice and Management))--University of Pretoria, 2003. / Abstract in English. Includes bibliographical references.

Manufacturing processes are getting more and more complex with increasing demands of advanced and light weight engineering components, especially in aerospace industry. The global requirements on lower fuel consumption and emissions are increasing the demands in lowering weight of cast components. Ability to produce components in lower wall thickness will not only help to reduce the cost of production but also help to improve the efficiency of engineering systems resulting in lower fuel consumption and lesser environmental hazardous emissions. In order to produce thin-walled components, understanding of mechanism behind fluidity as it is effected by casting parameters is very important. Similarly, for complex components study of solidification morphology and its effects on castability is important to understand. The aim of this work was to investigate casting of thin-walled test geometries (less than 2mm) in aero-space grades of alloys. The casting trials were performed to investigate the fluidity as a function of casting parameters and filling system in thin-walled sections. Test geometries with different thickness were cast and evaluated in terms of filled area with respect to casting parameters, ı.e. casting temperature and shell preheat temperature. Different feeding systems were investigated to evaluate effects of filling mode on castability. Similarly for complex components where geometries are very organic in shape, solidification morphology effects the quality of castings. Process parameters, that effect the solidification morphology were identified and evaluated. In order to develop a relation between defect formation and process parameters, solidification behaviour was investigated using simulations and casting trials. Similarly the effect of factors that influence grain structure and flow related defects were studied. It was observed that fluidity is affected by the mode of geometry filling in investment casting process. The filling mode also have different effect on defect formation. A top-gated configuration is strongly affected by casting parameters where as a bottom-gated configuration is more stable and thus fluidity is not significantly affected by variation in casting parameters. Less porosity and flow-related defects were observed in the bottom-gated system as compared to top-gated system. In the study about casting defects as affected by process parameters, it was observed that shell thickness is important to avoid interdendritic shrinkage. It was observed that the increased shell thickness induces a steeper thermal gradient which is essential in order to minimize the width of the mushy zone. It was also observed that a slower cooling rate along with a steeper thermal gradient at the metal-mould interface not only helps to avoid shrinkage porosity but also increases fill-ability in thinner sections. The work presented here is focused on the optimization of process parameters, in order, for instance, to improve castability and reduce the casting defects in investment casting process. The work, however, does not focus on externally influencing the casting conditions or modifying the casting/manufacturing process. The future work towards PhD will be focused on externally improving the casting conditions and investigating other possible route of manufacturing for thin, complex components.

A micromorfologia é a ciência que permite estudar o solo e seus componentes em amostras indeformadas em uma escala microscópica permitindo identificar feições relacionados a sua formação e processos atuantes que podem ser aplicadas em estudos de gênese, física, mineralogia, microbiologia do solo, entre outros. Para que isso seja possível é necessário formar um material rígido o suficiente para ser laminado a partir de amostras indeformadas de solo, através do processo de impregnação de solo. No entanto, para esse procedimento são utilizados atualmente, resinas plásticas (e.g. poliéster e epóxi), e dentre elas a resina poliéster, pode ser consideradas tóxica à saúde humana devido a presença do monômero de estireno na composição, além disso há o risco de danos ao meio ambiente devido a produção de resíduos oriundos de materiais tóxicos. No Brasil, por exemplo, há poucos laboratórios que realizam o processo de impregnação de amostras de solos para análises micromorfológicas, provavelmente, devido a toxicidade dos reagentes. Diante da importância da técnica para a Ciência do Solo, torna-se fundamental buscar alternativas para a técnica de micromorfologia do solo, que sejam economicamente viáveis, e que assegurem a segurança de atividades que envolvam substâncias e produtos químicos, visando garantir a proteção da saúde, da vida e das condições normais do ambiente, contribuindo para um desenvolvimento sustentável sem comprometer a qualidade do produto final. Assim, o presente trabalho teve como objetivo eliminar ou substituir a utilização do monômero de estireno no processo de impregnação de solos por substâncias similares menos tóxicas ao manuseio e avaliar o uso de soluções de resina poliéster e soluções de resina epóxi com diferentes diluentes (estireno, acetona e álcool) no processo de impregnação de amostras de solo (argiloso, textura média e arenoso). Para isso, foram utilizadas 2 tipos de resinas: resina poliéster Arazyn 1.0#00, resina poliéster Arazyn 1.0#0.8 e resina Epóxi Epoxiglass 1504; e diferentes solventes, sendo estes: o monômero de estireno, acetona P.A e álcool etílico absoluto (99,5%). Os tratamentos foram avaliados tanto para confecção de blocos quanto na fabricação de lâminas delgadas. Além disso, avaliação da qualidade da impregnação na confecção dos blocos de solo foi feita a partir dos parâmetros: odor, cor, volume de material gasto, solubilidade do pigmento, polimerização e secagem, corte, número de reimpregnações e custos dos reagentes. Também foi verificado na qualidade final do produto, a quantidade de poros não impregnados e uma avaliação qualitativa das lâminas. Verificou-se que a resina poliéster arazyn 1.0#08 tendo a acetona como solvente apresentou resultados satisfatórios na impregnação de solos, na confecção de blocos polidos e lâminas delgadas, para ambos os tipos de solo estudados. Porém, não foi capaz de substituir totalmente o estireno, contudo promove uma redução significativa do uso do estireno devido a possibilidade de substituição por acetona. Por outro lado, o tratamento com resina epóxi apresenta grande limitação da qualidade das lâminas delgadas não sendo obtidos resultados satisfatórios no produto final. No entanto, pode ser considerado uma alternativa para trabalhos que analisam apenas blocos polidos, uma vez que apresentou resultados positivos, em todas as texturas de solo que foram impregnadas. / Micromorphology uses optical microscopy and associated techniques to study soil\'s components at the microscopic scale for undisturbed samples. This technique allows identification of features related to soil processes and formation that can be applied to soil\'s genesis, physics, mineralogy, microbiology, among others. To perform these analysis, it is commonly used rigid materials to produce thin sections from undisturbed soil samples by the soil impregnation process. However, the plastic resins (e.g., polyester resin) containing the styrene monomer is considered toxic for human health. In addition, the wastes production from toxic materials may pose environmental risks. In Brazil, for instance, there are few laboratories performing the impregnation process of soil samples for micromorphological analysis, probably because of the reagents toxicity. Thus, given the importance of micromorphology for Soil Science, it is critical to seek other alternatives for soil micromorphology analysis. These alternatives must be economically feasible, chemically safe, non-hazardous for human health, attending environmental compliances, and contributing to sustainable development without compromising the product quality. Consequently, our work aimed to eliminate or replace the use of styrene monomer in the soil impregnation process by similar substances less toxic to the handling and evaluate the use of polyester resin solutions and epoxy resin solutions with different diluents (styrene, acetone and alcohol) in the impregnation process of soil samples (clayey, medium and sandy texture). We conducted an investigation using two resins, as follows: Arazyn 1.0 # 00 polyester resin, Arazyn 1.0 polyester resin # 0.8 and Epoxy resin Epoxiglass 1504; and the following solvents: styrene monomer, acetone and absolute ethyl alcohol (99.5%). We evaluated both blocks confection and thin sections manufacture. We also assessed the impregnation quality during soil blocks preparation based on the following parameters: odor, color, amount of material spent, pigment solubility, polymerization and drying, cutting, number of reimpregnations, and reagent costs. Within the product quality we also evaluate the non-impregnated pores quantities besides a qualitative evaluation of the thin sections. We found the polyester resin Arazyn 1.0 # 08 (containing acetone as a solvent) had satisfactory results in the impregnation of soil samples for both block soils and thin sections using the three soil texture types. Even though this treatment significantly decreased the use of styrene due to the potential substitution for acetone, we were unable to completely replace the styrene. On the other hand, the epoxy resin demonstrated limitations regarding the thin section quality, so that the results were not satisfactory for the final product. The epoxy resin can be considered a good alternative for analyzing soil blocks solely, since it presented positive results for the three impregnated soil textures.

Thesis (M.Eng.)--Memorial University of Newfoundland, 2005. / Bibliography: leaves 110-113.

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

O estudo de lâminas delgadas de sílex de origem diageneticamente precoce de diversos níveis estratigráficos e localidades da Formação Assistência no Estado de São Paulo revelou pela primeira vez uma assembléia de microorganismos orgânicos delicados, excepcionalmente bem preservados neste importante marco estratigráfico e paleontológico do Neopermiano da Bacia do Paraná. Esta assembléia consiste principalmente de organismos unicelulares, dominados por cianobactérias, tanto solitárias como coloniais, sem nenhum indício de filamentos. Inclui também uma provável clorófita cocoidal, grãos de pólen e fitoclastos, além de alguns microfósseis de afinidades incertas. Estudos paleopalinológicos de resíduos orgânicos desta formação nunca detectaram os elementos delicados desta microbiota. O exame petrográfico permitiu observar não somente todos os microorganismos fósseis em três dimensões no interior da rocha, mas também a distribuição espacial original dos microorganismos e suas relações com os outros componentes da rocha. Isto facilitou a avaliação da variedade morfológica dos microfósseis resultante da degradação e permitiu inferir padrões ontogênicos de alguns dos táxons descritos. Dentre eles, foram reconhecidos 14 morfotipos, reunidos em cinco espécies (todas novas) com afinidades biológicas conhecidas (quatro espécies de cianobactérias e uma clorófita) e cinco táxons incertae sedis (dois novos). A microbiota ocorre principalmente no sílex na base da formação. Constitui massas volumosas e densas preservadas in situ interpretadas como organismos originalmente bentônicos, capazes de formar esteiras microbianas e pequenos estromatólitos. A sedimentologia aliada à ampla extensão geográfica, ao hábito, à abundância e à natureza exclusivamente unicelular dos microorganismos fósseis, alem de exemplos atuais análogos, indicam um paleoambiente aquoso raso de salinidade alta, talvez hipersalina com salinidade variável. / The study of petrographic thin sections of early diageneteic chert from diverse levels and localities of the Assistência Formation in the state of São Paulo, Brazil, revealed for the first time an exceptionally well-preserved assemblage of delicate fossil microorganisms in this important stratigraphic and paleontological Early Permian marker unit of the Paraná Basin. This assemblage consists primarily of delicate colonial and solitary unicellular microfossils, dominated by cyanobacteria, without any evidence whatsoever of filamentous microorganisms. It also includes a probable cocoidal chlorophyte, pollen grains and phytoclasts, as well as several less common microfossils of uncertain biological affinity. None of the delicate microfossils of this assemblage have ever been detected in palynological analyses of organic residues from this formation. The study of thin sections made it possible to observe not only all of the fossil microorganisms in three dimensions within the rock but also their original spatial distribution and relationships with other components of the rock. This facilitated evaluation of the morphological diversity of the fossil microorganisms and permitted inferences as to possible ontogenetic patterns. Fourteen morphotypes were recognized among the more delicate microfossils and attributed to five species (all new) of known biological affinities (four species of cyanobacterias and one chlorophyte) and five taxa of Incertae Sedis. The fossil microbiota occurs principally at the base of the formation as dense, voluminous masses interpreted as remains of an in situ benthonic microbiota of photosynthetic microorganisms capable of forming microbial mats and small stromatolites. The sedimentology, together with the widespread distribution, habit, abundance and exclusively unicellular nature of the fossil microorganisms and the paleoenvironmental implications suggested by analogous modern examples, are consistent with a shallow aquatic habitat of high and perhaps variable salinity for the microbiota.

O estudo de lâminas delgadas de sílex de origem diageneticamente precoce de diversos níveis estratigráficos e localidades da Formação Assistência no Estado de São Paulo revelou pela primeira vez uma assembléia de microorganismos orgânicos delicados, excepcionalmente bem preservados neste importante marco estratigráfico e paleontológico do Neopermiano da Bacia do Paraná. Esta assembléia consiste principalmente de organismos unicelulares, dominados por cianobactérias, tanto solitárias como coloniais, sem nenhum indício de filamentos. Inclui também uma provável clorófita cocoidal, grãos de pólen e fitoclastos, além de alguns microfósseis de afinidades incertas. Estudos paleopalinológicos de resíduos orgânicos desta formação nunca detectaram os elementos delicados desta microbiota. O exame petrográfico permitiu observar não somente todos os microorganismos fósseis em três dimensões no interior da rocha, mas também a distribuição espacial original dos microorganismos e suas relações com os outros componentes da rocha. Isto facilitou a avaliação da variedade morfológica dos microfósseis resultante da degradação e permitiu inferir padrões ontogênicos de alguns dos táxons descritos. Dentre eles, foram reconhecidos 14 morfotipos, reunidos em cinco espécies (todas novas) com afinidades biológicas conhecidas (quatro espécies de cianobactérias e uma clorófita) e cinco táxons incertae sedis (dois novos). A microbiota ocorre principalmente no sílex na base da formação. Constitui massas volumosas e densas preservadas in situ interpretadas como organismos originalmente bentônicos, capazes de formar esteiras microbianas e pequenos estromatólitos. A sedimentologia aliada à ampla extensão geográfica, ao hábito, à abundância e à natureza exclusivamente unicelular dos microorganismos fósseis, alem de exemplos atuais análogos, indicam um paleoambiente aquoso raso de salinidade alta, talvez hipersalina com salinidade variável. / The study of petrographic thin sections of early diageneteic chert from diverse levels and localities of the Assistência Formation in the state of São Paulo, Brazil, revealed for the first time an exceptionally well-preserved assemblage of delicate fossil microorganisms in this important stratigraphic and paleontological Early Permian marker unit of the Paraná Basin. This assemblage consists primarily of delicate colonial and solitary unicellular microfossils, dominated by cyanobacteria, without any evidence whatsoever of filamentous microorganisms. It also includes a probable cocoidal chlorophyte, pollen grains and phytoclasts, as well as several less common microfossils of uncertain biological affinity. None of the delicate microfossils of this assemblage have ever been detected in palynological analyses of organic residues from this formation. The study of thin sections made it possible to observe not only all of the fossil microorganisms in three dimensions within the rock but also their original spatial distribution and relationships with other components of the rock. This facilitated evaluation of the morphological diversity of the fossil microorganisms and permitted inferences as to possible ontogenetic patterns. Fourteen morphotypes were recognized among the more delicate microfossils and attributed to five species (all new) of known biological affinities (four species of cyanobacterias and one chlorophyte) and five taxa of Incertae Sedis. The fossil microbiota occurs principally at the base of the formation as dense, voluminous masses interpreted as remains of an in situ benthonic microbiota of photosynthetic microorganisms capable of forming microbial mats and small stromatolites. The sedimentology, together with the widespread distribution, habit, abundance and exclusively unicellular nature of the fossil microorganisms and the paleoenvironmental implications suggested by analogous modern examples, are consistent with a shallow aquatic habitat of high and perhaps variable salinity for the microbiota.

No description available.

Complex trace attribute analysis has been applied to 24-fold VIBROSEIS reflection data acquired on the Atlantic Coastal Plain near Charleston, S. C., to yield an expanded interpretation of a Mesozoic basin concealed beneath Coastal Plain sediments. Complex trace attributes express the seismic trace in terms of a complex variable and emphasize different components of the original seismogram. Attributes derived from synthetic seismograms of thin beds are used to interpret the patterns observed on the real data. Complex trace attributes derived from the original seismic trace complement the interpretation of a Mesozoic basin originally imaged by conventional data. The combination of single-sweep recording and use of complex trace attributes is believed to support an interpretation of a transition from basin border conglomerates into finer-grained siltstones nearer to the center of the basin. / Master of Science / incomplete_metadata

The titanium alloy, Ti-6Al-4V, is vastly studied and used in many applications because it has a transformation microstructure, which can be tailored for apt properties that are consistent up to 500°C. Compared to conventional steels, this alloy favours certain applications due to its high specific strength, hardenability, corrosion resistance, biocompatibility and weldability. Its weldability makes the alloy a good candidate for additive manufacturing (AM). Ti-6Al-4V parts are widely built by the AM process of electron beam melting (EBM). However, heat transfer remains crucial in EBM process. The high intensity localized, moving, electron beam heat source and the rapid self-cooling are critical, especially in thin parts/ sections. When thin sections are built by the EBM process, there will be microstructural variation in their build direction, which can lead to the variation of their mechanical properties. It is necessary to understand the microstructure and mechanical properties of thin sections when they are used as functional parts in various applications in aerospace, automotive, medical, etc. industries. The microstructure, tribological behaviour and mechanical properties of Ti-6Al-4V, as-built EBM thin plates were studied by means of various hardness, scratch and tensile testing. The hardness and scratch tests were performed on the thin plates to correlate the microstructural variation. In-situ micro tensile test was performed inside the scanning electron microscope (SEM), to see the sample’s deformation behaviour. Microstructural characterization revealed equiaxed grains in the transverse section and the longitudinal surface exhibited columnar grains elongated along the build direction. The size of the equiaxed grains are found to vary across the thickness of the plate. The indentation and scratch hardness also vary in correlation with the varying grain size across the plate’s thickness. The micro tensile results reveal that the tensile properties of the thin plate are comparable to that of its bulk Ti-6Al-4V counterpart.