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Various geotechnical-related energy applications, such as geothermal piles, subject soils to temperature changes. Recorded temperature variations around thermo-active infrastructure and within the active layer of the permafrost reveal the cyclic and transient nature of these temperature changes. Previous studies on the thermo-mechanical behavior of soils did not consider the effect of the temperature change rate on such behavior. Since it is widely accepted nowadays that soil behavior is rate-dependent, evaluating soil behavior under more realistic, transient temperature changes is crucial. In this dissertation, a method to calibrate triaxial cells used to expose soil samples to transient thermal loads is developed. This calibration is critical to ensure reliable thermally induced pore water pressure measurements and estimates of thermally induced volumetric strains of tested specimens. Then, thermally induced water flow and pore pressure generation under partial drainage conditions are formulated to account for the effect of temperature change rate on the thermal consolidation of cohesive soils. The formulation is performed by coupling Darcy's law for water flow in porous media with existing relations estimating thermally induced fully-drained volumetric strains. The resulting partial differential equation—the thermal consolidation theory—is solved and validated against experimental results that used the calibration from the first task. Using this newly developed theory, it was found that temperature-dependent properties of the pore water and the soil's hydraulic conductivity have a significant role in thermal consolidation. Lastly, a microstructural analysis is performed to assess the evolution of the microstructure of a normally consolidated clay under a full thermal cycle consisting of a freezing (F), thawing (T), heating (H), and cooling (C) thermal path. This microstructural investigation aims to explain the observed macroscale responses of cohesive soils under such a thermal path. After each step along the considered thermal path, the microstructure evolution was assessed using measurements of the specific surface area and pore size distribution. In the end, the variations of specific surface areas and pore size distributions were used to explain the macro-scale thermo-mechanical behavior of cohesive soils. / Doctor of Philosophy / Temperature can impact the properties of the soil, such as strength and stiffness. Besides the alterations in the strength, temperature change can cause volume change in the ground. In cold regions such as Alaska, the soil is frozen all year (i.e., permafrost) or experiences freezing-thawing cycles throughout the year. Freezing strengthens the soil but causes expansion of its volume, destroying infrastructures, including roads, runways, and buildings. Also, geothermal energy applications that utilize the ground as a heat exchanger medium may increase or decrease the surrounding soil temperature. Increasing the ground temperature changes the strength of the soil and also causes settlements. Climate change is also aggravating the situation. The temperature rises due to climate change alters the temperature pattern worldwide. Furthermore, global warming exposes frozen grounds to longer thawing stages at higher temperatures, deteriorating the permafrost. Consequently, such thermal cycles make cold regions' infrastructures susceptible to damage. Measurements of the temperature variations in the ground show that they are cyclic in nature, with different rates, maximums, and minimums. Therefore, it is essential to study the thermal behavior of soils under cyclic thermal loads. For this purpose, a new method for accurately measuring soils' response to more realistic temperature changes is developed in this dissertation. Then a model is developed to predict thermally induced volume changes and water pressures that account for the rate of temperature change. The model is then used for a sensitivity analysis to study the most important parameters controlling the deformation induced by temperature changes. It was found that variations of pore water properties with temperature and the ability of the soil to retain or drain water are the two most critical parameters that control thermally induced deformation in soils. Finally, the microstructure evolution of cohesive soils with temperature is also investigated to explain the observed alterations in soil behavior with temperature. This microstructural assessment suggests that the microstructure of soils reacts to temperature by changing the pore size distribution, shape, and number of pores.

After the invention of the high-efficiency blue light-emitting diode (LED) at the end of the twentieth century, a new generation of light-emitting devices based on III-nitrides emerged, showcasing the capabilities of this semiconductor family. Despite the current limitations in the fabrication of III-nitrides, their optical and electronic properties still place them as some of the most promising semiconductors to continue the development of optoelectronic devices. To take full advantage of the versatility offered by these materials, the fabrication of novel III-nitride-based devices demands rigorous control of all of its stages. From the initial deposition of the materials, which involves controlling the composition and size of often complex heterostructures, up to the microfabrication processing used to create a final device, any deficiency occurring will negatively impact the performance of the device. Most of the time, these deficiencies reflect in microscopic defects, hindering their detection and identification of their origin. Without such knowledge, the deficiencies cannot be fixed, stalling the improvement of the device fabrication process and, consequently, its performance. This dissertation presents a variety of methodological approaches to characterize, from a microstructural point of view, different properties of novel III-nitride-based heterostructures and devices. The characterizations include studying the structure, interface, composition, and crystalline defects of different heterostructures and evaluating the microfabrication quality of microscopic LEDs. The results of the different characterizations contributed to developing novel LED and photocatalytic devices, for example, a single-quantum-well InGaN-based red LED with a high color purity, a monolithic phosphor-free white LED, microscopic green LEDs with a size smaller than 5×5 μm$^2$, and metal oxide/GaN-based photocatalysts with improved resilience to photocorrosion. The analyses and results presented in this dissertation strongly relied on the analytical capabilities offered by transmission electron microscopy, which proved to be a convenient and versatile tool for the characterization of many aspects related to the fabrication of III-nitride-based optoelectronic devices.

No / The performance of cement-based materials can be controlled and tailored by adjusting the characteristics of reinforced nano inclusions. Therefore, the lateral size effect of graphene on the nano/micro-structures of ultra-high performance concrete (UHPC) was explored, and then the mechanical properties were investigated to analyze the structure–property correlation of composites in this paper. The test results show that due to nucleation site effect and the formation of core–shell elements, incorporating graphene with lateral size of > 50 µm improves the polymerization degree and mean molecule chain length of C-S-H gel by 242.6% and 56.3%, respectively. Meanwhile, the porosity and average pore volume of composites is reduced by 41.4% and 43.4%. Furthermore, graphene can effectively inhibit the initiation and propagation of cracks by crack-bridging, crack-deflection, pinning and being pulled-out effect, and the wrinkling characteristic is conductive to the enhancement of pinning effect. These improvements on nano- and micro- structures result in that the compressive strength, compressive toughness and three-point bending modulus of UHPC are increased by 43.5%, 95.7% and 39.1%, respectively, when graphene with lateral size of > 50 µm and dosage of 0.5% is added. Compared to graphene with lateral size of > 50 µm, graphene with average lateral size of 10 µm has less folds and larger effective size, then reducing the distance between core–shell elements. Hence, the addition of graphene with average lateral size of 10 µm leads to 21.1% reduction for Ca(OH)2 crystal orientation index, as well as 30.0% increase for three-point bending strength. It can be, therefore, concluded that the lateral size of graphene obviously influences the nano/micro-structures of UHPC, thus leading to the significantly different reinforcing effects of graphene on mechanical behaviors of UHPC.

The study aimed at investigating the chemical composition and microstructure of raw iron ore from the deposits in Muko area (south-western Uganda). The quality of this iron ore was evaluated to establish its suitability to serve as a raw material for iron production. Samples were taken from the six hills of Muko ore deposits and tests carried out to establish their composition and properties. X-ray diffraction and scanning electron microscopy were employed in the investigation and chemical analysis performed to determine the compounds constituting the ore. The quality of this ore was compared to generalized world market standards and ores from other nations. It was found that Muko ore is a rich hematite grade with Fe content above 65%. It has little gangue (&lt;6% SiO2 and 3-4% Al2O3) and low contents of the deleterious elements (P ~ 0.02% and S &lt; 0.006%), which correspond to acceptable levels for commercial iron ores. / <p>QC 20130531</p> / Sustainable Technology Development in the Lake Victoria Region

Os objetivos deste trabalho foram: a) realizar a análise microestrutural de cerâmicas odontológicas e relacioná-la aos valores de resistência à flexão obtidos, b) avaliar o efeito de dois tipos de envelhecimento (ciclagem mecânica e ciclagem em autoclave) sobre a resistência à flexão desses materiais e c) avaliar se a configuração do espécime (discos versus barras) é capaz de alterar o efeito da ciclagem mecânica sobre a resistência à flexão. Cinco materiais foram utilizados: zircônia tetragonal policristalina estabilizada por ítrio (YZ), alumina policristalina (AL), alumina infiltrada por vidro/reforçada por zircônia (ICZ) e duas porcelanas (VM7 e VM9). Espécimes em forma de barra (2 x 4 x 16 mm) e disco (12 mm x 2 mm) foram confeccionados conforme as recomendações dos fabricantes. A densidade foi determinada pelo método de Arquimedes, as constantes elásticas foram determinadas pelo método do pulso-eco ultrassônico. Microscopia óptica e eletrônica de varredura foram utilizadas para determinar a fração e tamanho médio de poros e partículas e a análise de EDS para a realização de análise química dos microconstituintes. O efeito do envelhecimento por ciclagem mecânica (YZ, AL e ICZ: 80 N por 105 ciclos e VM7 e VM9: 45 N por 104 ciclos, a 2 Hz) ou por ciclagem em autoclave a 134°C, pressão de 2,2 kgf/cm2 durante 5h, foi avaliado nos espécimes em forma de barra e comparados com um grupo controle, não ciclado. O efeito do envelhecimento por ciclagem mecânica foi comparado entre os espécimes em forma de barra e disco para as porcelanas estudadas. Houve diferenças significativas entre os valores de resistência em função do material, causadas pelas diferenças em sua microestrutura, sendo que as porcelanas apresentam baixos valores de resistência (VM7: 69,4 MPa e VM9: 64,7 MPa), enquanto que a AL e a ICZ apresentaram valores intermediários (462,8 MPa e 408,6 MPa, respectivamente) e a YZ apresentou o maior valor de resistência à flexão (869 MPa). Após a ciclagem mecânica, somente o material AL apresentou redução estatisticamente significativa da resistência à flexão (389,2 MPa). A ciclagem em autoclave não resultou em degradação significativa da resistência de nenhum dos materiais testados. A configuração do espécime (barra ou disco) não alterou o efeito da ciclagem mecânica sobre a resistência das porcelanas testadas (nenhum material apresentou queda da resistência após ciclagem). Entretanto, nos espécimes em forma de disco a resistência à flexão da VM7 foi significativamente maior que a da VM9 (69,6 MPa e 57,6 MPa, respectivamente), enquanto que nos espécimes em forma de barra não houve diferença estatística entre os valores de resistência das duas porcelanas (VM7: 61,1 MPa e VM9: 68,8 MPa). / The aims of this study were: to perform a microestrutural analysis of dental ceramics and correlate the results with the flexural strength obtained; to evaluate two aging process (mechanical cycling and autoclave cycling) on the flexural strength of the materials and to evaluate the specimen configuration (bar or disc) on the flexural strength of mechanical cycling aged specimens. The five ceramics tested were: yttria-stabilized zirconia (YZ), polycrystalline alumina (AL), glass-infiltrated alumina/zirconia reinforced (ICZ) and two dental porcelains (VM7 and VM9). Bars (2 x 4 x 16 mm) and discs (12 mm x 2 mm) were produced according to the manufactures instructions. Density was obtained by Arquimedes method and the elastics constants were obtained by ultrasonic pulse-echo method. Optical and Scanning Electron Microscope were used to determine the fraction and size of both pores and particles while the chemical composition was obtained by EDS. Aging effect on flexural strength after mechanical or autoclave cycling was evaluated on bar specimens and compared to a control group, which was not cycled. The specimen configurations (bars or discs) were compared after mechanical cycling for porcelains. Microestrutural differences between material resulted on flexural strength values statistically different, porcelains presented lower values of flexural strength (VM7: 69,4 MPa and VM9: 64,7 MPa), while AL and ICZ presented intermediate flexural strength (462,8 MPa and 408,6 MPa, respectively) and YZ presented the highest flexural strength (869 MPa). Only AL presented a significant lower flexural strength after mechanical cycling (389,2 MPa). Autoclave cycling did not influence the flexural strength of the studied materials. Also, the specimen configuration did not influence the flexural strength values before or after mechanical cycling. It should be noted that disc specimens of VM7 presented significantly higher flexural strength values than VM9 (69,6 MPa and 57,6 MPa, respectively), however for bar specimens no statistical difference was noted between the mean strength of both porcelains (VM7: 61,1 MPa and VM9: 68,8 MPa).

Os objetivos deste trabalho foram: a) realizar a análise microestrutural de cerâmicas odontológicas e relacioná-la aos valores de resistência à flexão obtidos, b) avaliar o efeito de dois tipos de envelhecimento (ciclagem mecânica e ciclagem em autoclave) sobre a resistência à flexão desses materiais e c) avaliar se a configuração do espécime (discos versus barras) é capaz de alterar o efeito da ciclagem mecânica sobre a resistência à flexão. Cinco materiais foram utilizados: zircônia tetragonal policristalina estabilizada por ítrio (YZ), alumina policristalina (AL), alumina infiltrada por vidro/reforçada por zircônia (ICZ) e duas porcelanas (VM7 e VM9). Espécimes em forma de barra (2 x 4 x 16 mm) e disco (12 mm x 2 mm) foram confeccionados conforme as recomendações dos fabricantes. A densidade foi determinada pelo método de Arquimedes, as constantes elásticas foram determinadas pelo método do pulso-eco ultrassônico. Microscopia óptica e eletrônica de varredura foram utilizadas para determinar a fração e tamanho médio de poros e partículas e a análise de EDS para a realização de análise química dos microconstituintes. O efeito do envelhecimento por ciclagem mecânica (YZ, AL e ICZ: 80 N por 105 ciclos e VM7 e VM9: 45 N por 104 ciclos, a 2 Hz) ou por ciclagem em autoclave a 134°C, pressão de 2,2 kgf/cm2 durante 5h, foi avaliado nos espécimes em forma de barra e comparados com um grupo controle, não ciclado. O efeito do envelhecimento por ciclagem mecânica foi comparado entre os espécimes em forma de barra e disco para as porcelanas estudadas. Houve diferenças significativas entre os valores de resistência em função do material, causadas pelas diferenças em sua microestrutura, sendo que as porcelanas apresentam baixos valores de resistência (VM7: 69,4 MPa e VM9: 64,7 MPa), enquanto que a AL e a ICZ apresentaram valores intermediários (462,8 MPa e 408,6 MPa, respectivamente) e a YZ apresentou o maior valor de resistência à flexão (869 MPa). Após a ciclagem mecânica, somente o material AL apresentou redução estatisticamente significativa da resistência à flexão (389,2 MPa). A ciclagem em autoclave não resultou em degradação significativa da resistência de nenhum dos materiais testados. A configuração do espécime (barra ou disco) não alterou o efeito da ciclagem mecânica sobre a resistência das porcelanas testadas (nenhum material apresentou queda da resistência após ciclagem). Entretanto, nos espécimes em forma de disco a resistência à flexão da VM7 foi significativamente maior que a da VM9 (69,6 MPa e 57,6 MPa, respectivamente), enquanto que nos espécimes em forma de barra não houve diferença estatística entre os valores de resistência das duas porcelanas (VM7: 61,1 MPa e VM9: 68,8 MPa). / The aims of this study were: to perform a microestrutural analysis of dental ceramics and correlate the results with the flexural strength obtained; to evaluate two aging process (mechanical cycling and autoclave cycling) on the flexural strength of the materials and to evaluate the specimen configuration (bar or disc) on the flexural strength of mechanical cycling aged specimens. The five ceramics tested were: yttria-stabilized zirconia (YZ), polycrystalline alumina (AL), glass-infiltrated alumina/zirconia reinforced (ICZ) and two dental porcelains (VM7 and VM9). Bars (2 x 4 x 16 mm) and discs (12 mm x 2 mm) were produced according to the manufactures instructions. Density was obtained by Arquimedes method and the elastics constants were obtained by ultrasonic pulse-echo method. Optical and Scanning Electron Microscope were used to determine the fraction and size of both pores and particles while the chemical composition was obtained by EDS. Aging effect on flexural strength after mechanical or autoclave cycling was evaluated on bar specimens and compared to a control group, which was not cycled. The specimen configurations (bars or discs) were compared after mechanical cycling for porcelains. Microestrutural differences between material resulted on flexural strength values statistically different, porcelains presented lower values of flexural strength (VM7: 69,4 MPa and VM9: 64,7 MPa), while AL and ICZ presented intermediate flexural strength (462,8 MPa and 408,6 MPa, respectively) and YZ presented the highest flexural strength (869 MPa). Only AL presented a significant lower flexural strength after mechanical cycling (389,2 MPa). Autoclave cycling did not influence the flexural strength of the studied materials. Also, the specimen configuration did not influence the flexural strength values before or after mechanical cycling. It should be noted that disc specimens of VM7 presented significantly higher flexural strength values than VM9 (69,6 MPa and 57,6 MPa, respectively), however for bar specimens no statistical difference was noted between the mean strength of both porcelains (VM7: 61,1 MPa and VM9: 68,8 MPa).

Yes / Titanium alloys are known for their excellent corrosion resistance; however, low surface hardness results in poor wear resistance, which limits its potential application. This study employs a novel two-step process to embed a hard Ni coating containing a mixture of nanosized particles (Al2O3 and TiO2) into the surface of the Ti-6Al-4V alloy using an electric arc produced during the inert tungsten gas welding process. The surface of the sample was evaluated using Vickers Microhardness, Scanning electron microscopy, Energy dispersive spectroscopy and pin-on-plate wear testing. Microstructural analysis showed that impregnating the titanium surface with Ni/(Al2O3 and TiO2) nanomaterials resulted in the formation of a hard martensitic structure to a depth of approximately 2 mm below the surface. The changes observed are driven by modification of the surface chemistry and the presence of nickel, causing grain size reduction, solid solution strengthening and dispersion strengthening of the treated layer by the nanoparticles. The hardness of the treated layer increased by more than 180% when 40 nm Al2O3 and 30 nm TiO2 particles were embedded into the surface. Similarly, the wear resistance of the treated surface improved by 100%.

No description available.