Crack-microstructure interactions occurring during the flaw introduction process were studied in a model brittle composite, a cordierite glass-ceramic. Microstructural effects associated with the repropagation of the introduced flaws under the imposition of a mechanical load were also examined. Two general types of crystallized microstructures were investigated for samples heat-treated from the original glass: a fine structure composed of a uniform precipitation of very small (< 0.1 µm) crystallites, and a coarser structure characterized by crystallites, and a coarser structure characterized by crystallites ~ 1-2 µm in diameter dispersed within a much finer-grained (< 0.1 µm) crystalline matrix. Surface damage was simulated by the Vicker's microhardness technique, with indentations being made over a wide load range to duplicate varying degrees of severity in the contact events. Direct measurement of the indentation flaws was made by calibrated scanning electron microscopy. Fracture toughness values were determined by direct calculation from the indentation parameters. The repropagation of the indentation flaws was investigated by strength tests performed in biaxial flexure. The results indicated that flaw introduction, as well as strength, fracture toughness, and the magnitude of strength loss sustained from surface damage, were all significantly affected by crack interactions with the crystallites in the glass-ceramic samples. The crack-crystallite interactions were extensive in the coarse microstructure samples. Crack pinning by the dispersed phase crystallites occurred at flaw sizes approximately equal to the mean free path distance between the dispersions, while at larger flaw sizes, crack deflection around the dispersed crystallites took place. Crack-microstructure interactions were absent in these same samples at flaw sizes less than the mean free path distance, and were not observed at all in the original glass or in samples heat-treated to yield only the fine microstructure. In the coarse microstructure samples, the size of flaws introduced by surface contact was found to be limited by the crack pinning interaction, thus confirming the basic concept of the dispersion-strengthening model for brittle composites. A substantial toughening effect in these same samples was realized from the crack deflection. Fracture toughness for the coarse microstructure samples exhibited a crack size-dependency, with toughness values corresponding to that of the matrix measured at small flaw sizes, and to that of the composite, at larger flaw sizes. The phenomenon was not present in either the original glass or in the fine microstructure samples. The crack-crystallite interactions occurring in the coarse microstructure samples greatly improved mechanical performance. The combination of decreased flaw size from crack pinning and increased fracture toughness from crack deflection resulted in strength values which were superior to those of the original glass. The crack size dependent fracture toughness enhanced the ability of the coarse microstructure samples to avoid potential strength losses following surface contact. / Ph. D.

В результате проведенных исследований подобраны и исследованы отечественные сырьевые материалы, рассчитан и разработан состав массы прекурсора и синтезирован композитный материал для производства кордиеритовой керамики. Разработаны составы масс для производства кордиеритовой керамики различными способами формования: шликерным литьем, пластическим и полусухим формованием. Проведенные исследования показывают возможность получения кордиеритовой керамики на основе сырья отечественных месторождений с высоким содержанием α-кордиерита. / As a result of the conducted research, domestic raw materials were selected and studied, the composition of the precursor mass was calculated and developed, and a composite material for the production of cordierite ceramics was synthesized. Mass compositions for the production of cordierite ceramics by various molding methods have been developed: by slip casting, plastic and semi-dry molding. The results of investigation show the possibility of obtaining cordierite ceramics based on the raw materials of domestic deposits with a high content of α-cordierite.

Разработаны составы масс для производства керамических кордиеритовых субстратов различными способами формования: полусухим и пластическим формованием. Проведенные исследования показывают возможность получения кордиеритовой керамики на основе сырья отечественных месторождений с высоким содержанием кордиерита. / Mass compositions to produce ceramic cordierite substrates by various molding methods have been developed: semi-dry and plastic molding. The conducted studies show the possibility of obtaining cordierite ceramics based on raw materials from domestic deposits with a high content of cordierite.

16 samples of increasing metamorphic grade from the Ballachulish Igneous Complex and Aureole, located in the west of Scotland, were studied in order to analyze the sulfide mineralogy and to what extent they were affected by contact metamorphism. The samples were collected from two lithologies, the Creran Succession and the Ballachulish Slate lithology, as well as from the igneous complex. The sulfides of main interest in the samples are pyrite and pyrrhotite. At the onset of contact metamorphism, pyrite disappears while pyrrhotite gets more abundant as metamorphic grade increases. Pyrrhotite also undergoes multiple changes such as 1) elongation and thinning of the grains, 2) development of 120° grain-boundaries, 3) development of pyrite-zones within the pyrrhotite and 4) the decomposition of pyrrhotite and alignment of pyrite along its grain-boundaries at high temperature. The elongation of the grains occurs in both the Creran Succession and the Ballachulish Slate. The rest of the textures, however, can only be found in the Creran Succession. The two lithologies differ by the high graphite content in the Ballachulish Slate. The elongated grains as well as the pyrite inclusions in the pyrrhotite both are strong evidence of recrystallization. The absence of pyrite in the Ballachulish Slate was most probably caused by the buffering properties of the graphite-rich fluid in these rocks, causing more reducing conditions. There is evidence against a heavy, pervasive fluid flow through the aureole. However, the inner contact zone seems to have been affected by a more pronounced fluid flow. This could have been caused by the metamorphic fluid working in conjunction with fluids released from the intrusion. Regarding the mobility of S in the aureole, no strong evidence could be found, other than the decomposition of pyrrhotite grain-boundaries in the high-grade metamorphic samples.

The following investigations have been carried out in this thesis 1)Cordierite is already well known for its low thermal expansion behaviour. Chemical substitutions at various octahedral and tetrahedral sites have been done and their thermal expansion characteristics have been studied Synthesis of cordierite in more reactive environment provided by AlF3 used as sintering aid has been attempted 2) Diffuse ferroelectric phase transition of lead based perovskite materials leads to low expansion region. Solid solutions of lead iron niobate with lead titanate is investigated to increase the structural distortion and see it this low expansion region can be extended to wider temperature Preparation of materials with higher tetragonal distortion In PbTi03- BlFeO3 system is undertaken to study the thermal expansion anisotropy. 3) Composites between lead iron niobate(+(x) and lead titanate (-(x below Tc) has been undertaken to prepare low expansion hulk over a wide temperature range 4) Acoustic emission has been employed as a tool to detect the microcracking in solid solutions between PFN1-x, PTx, and PT1-x, ,BFx, It is hoped to understand relation between magnitude of lattice distortion transition temperature and microcracking in ceramics of the class of materials.

The diploma thesis focuses on new possibilities to reduce raw materials costs in production of heat-resistant cordierite ceramics. Cordierite is very often used as furnace wagon lining and for production of blazing utilities for its high resistance against temperature changes. The thesis gives complete overview of cordierite material. It includes description of different production technologies for form-pieces preparation, raw materials for their production and their applications. The goal of performed laboratory measuring in an experimental part was to verify and prove a possibility of reducing raw-material costs in production of cordierite ceramics by using cheaper preferably secondary raw materials.

The present work aimed at designing a thermally efficient microreactor system coupling methanol steam reforming with methanol combustion for autothermal hydrogen production. A preliminary study was performed by analyzing three prototype reactor configurations to identify the optimal radial distribution pattern upon enhancing the reactor self-insulation. The annular heat integration pattern of Architecture C showed superior performance in providing efficient heat retention to the system with a 50 - 150 degrees C decrease in maximum external-surface temperature. Detailed work was performed using Architecture C configuration to optimize the catalyst placement in the microreactor network, and optimize reforming and combustion flows, using no third coolant line. The optimized combustion and reforming catalyst configuration prevented the hot-spot migration from the reactor midpoint and enabled stable reactor operation at all process flowrates studied. Best results were obtained at high reforming flowrates (1800 sccm) with an increase in combustion flowrate (300 sccm) with the net H2 yield of 53% and thermal efficiency of >80% from methanol with minimal insulation to the heatintegrated microchannel network. The use of the third bank of channels for recuperative heat exchange by four different reactor configurations was explored to further enhance the reactor performance; the maximum overall hydrogen yield was increased to 58% by preheating the reforming stream in the outer 16 heat retention channels. An initial 3-D COMSOL model of the 25-channeled heat-exchanger microreactor was developed to predict the reactor hotspot shape, location, optimum process flowrates and substrate thermal conductivity. This study indicated that low thermal conductivity materials (e.g. ceramics, glass) provides enhanced efficiencies than high conductivity materials (e.g. silicon, stainless steel), by maintaining substantial thermal gradients in the system through minimization of axial heat conduction. Final summary of the study included the determination of system energy density; a gravimetric energy density of 169.34 Wh/kg and a volumetric energy density of 506.02 Wh/l were achieved from brass architectures for 10 hrs operation, which is higher than the energy density of Li-Ion batteries (120 Wh/kg and 350 Wh/l). Overall, this research successfully established the optimal process flowrates and reactor design to enhance the potential of a thermally-efficient heat-exchanger microchannel network for autothermal hydrogen production in portable applications.

Mémoire (M.Sc.T)-- Université du Québec à Chicoutimi 1986. / "Mémoire présenté en vue de l'obtention du diplôme de M.Sc.A. (sciences de la terre)" CaQCU Document électronique également accessible en format PDF. CaQCU

The life cycle analysis compares the environmental impacts of catalytic converters and the effects of not using these devices. To environmentally evaluate the catalytic converter, the emissions during extraction, processing, use of the product are considered. All relevant materials and energy supplies are evaluated for the catalytic converter. The goal of this life cycle is to compare the pollutants of a car with and without a catalytic converter. Pollutants examined are carbon monoxide (CO), carbon dioxide (CO2), hydrocarbons (HC), and nitrogen oxides (NOx). The main finding is that even considering materials and processing, a catalytic converter decreases the CO, HC and NOx pollutant emissions. The CO2 emissions are increased with a catalytic converter, but this increase is small relative to the overall CO2 emissions. The majority of catalytic converter pollutants are caused by the use phase, not extraction or processing. The life cycle analysis indicates that a catalytic converter decreases damage to human health by almost half, and the ecosystem quality damage is decreased by more than half. There is no damage to resources without a converter, as there are no materials or energy required; the damages with a converter are so small that they are not a significant factor. Overall, catalytic converters can be seen as worthwhile environmental products when considering short term effects like human health effects of smog, which are their design intent. If broader environmental perspectives that include climate change are considered, then the benefits depend on the weighting of these different environmental impacts. / Master of Science

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