Sand casting is the most widely used casting process for both ferrous and non-ferrous alloys; however, the process is marred by large grain size structures and long solidification times. The coarser microstructure has a negative effect on the mechanical properties of the cast components and the long processing time affects the overall productivity of the process. The research reported herein addresses these problems for aluminum sand castings by enhancing the rate of heat extraction from the casting by replacing air, which is typically present in the pores of the sand mold and has a relatively low thermal conductivity by helium which has a thermal conductivity that is at least five times that of air in the temperature range of interest. The effect of (1) the flow rate of helium, (2) the way in which it is introduced into the mold, and (3) the mold design on (a) the average grain size, (b) the secondary dendrite arm spacing, and (c) the room temperature tensile properties of castings is investigated and compared to their counterparts produced in a typical sand casting process. In addition, a cost analysis of the helium-assisted sand casting process is performed and an optimum set of parameters are identified. It is found that when the helium-assisted sand casting process is performed with close to the optimum parameters it produces castings that exhibit a 22 percent increase in ultimate tensile strength and a 34 percent increase in yield strength with no significant loss of ductility, no degradation in the quality of the as-cast surfaces, and no significant increase in the overall cost.

Digitized by Kansas Correctional Industries

The development of the conductivity coefficients is reviewed for both highly degenerate metals, having an energy dependent relaxation time, and semiconductors, obeying Boltzmann statistics and having a relaxation time varying as the energy to the λ power.

Orientador: Darcy Hiroe Fujii Kanda / Coorientador: Haroldo Naoyuki Nagashima / Banca: Fernando Rogerio de Paula / Banca: Roberto Mendonça Faria / Resumo: Neste trabalho, estudamos os processos de condução envolvidos na condutividade elétrica de nanocompósitos de polianilina com óxido de índio e estanho (PANI/ITO) e de poliuretano com negro de fumo (PU/NF), a partir da aplicação de um modelo estatístico de rede de resistores e da análise da condutividade dc próximo ao limiar de percolação. O modelo estatístico foi desenvolvido em linguagem Fortran 90 para gerar a estrutura morfológica desses nanocompósitos e calcular a condutividade elétrica alternada pela aplicação de uma técnica de matriz de transferência. O modelo levou em consideração a estrutura desordenada da PANI não dopada, a formação de segmentos moles e duros no PU e a distribuição aleatória de nanopartículas e agregados de ITO e NF em suas respectivas matrizes. A impedância entre dois sítios vizinhos da matriz polimérica, tanto para PANI quanto para PU, foi calculada pelo modelo de Dyre, enquanto que a impedância entre dois sítios vizinhos que compõem a fase condutora de ambos nanocompósitos foi calculada pelo modelo de Drude. Foram realizadas medidas de espectroscopia de impedância e de condutividade dc para ambos os compósitos, com diferentes concentrações da fase condutora. Os objetivos foram analisar os processos de condução, determinar o limiar de percolação e os expoentes críticos da condutividade. De acordo com os resultados das simulações e dos resultados experimentais, o processo de condução entre dois sítios da matriz polimérica obedece ao modelo de distribuição aleatória de barreiras de energia livre de Dyre (RFEB), ao passo que a condução nos domínios condutores é descrita pelo modelo de Drude. A análise das medidas de condutividade dc realizadas abaixo do limiar de percolação de ambos os compósitos indica que o processo de condução... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: In this paper, we study the conducting processes involved in electrical conductivity of polyaniline/indium tin oxide nanocomposites (PANI/ITO) and polyurethane/carbon black nanocomposites (PU/CB), from the application of a statistical model of network resistors and the analysis of the dc conductivity near the percolation threshold. The statistical model was developed in Fortran 90 to generate the morphological structure of these nanocomposites and calculate the alternating electrical conductivity by applying a transfer matrix technique. The model took into account the disordered structure of undoped PANI, the formation of soft and hard segments in PU and random distribution of nanoparticles and aggregates of ITO and NF in their respective matrix. The impedance between two neighboring sites of the polymeric matrix, for both PANI and PU, was calculated by the model of Dyre, while the impedance between two neighboring sites from conductive phase was calculated by the Drude model. Were measured impedance spectroscopy and dc conductivity for both composites, with different concentrations of the phase conductor. The objectives were to analyze the processes of conduction, determine the percolation threshold and critical exponents of conductivity. According to the simulations and experimental results, the conduction process, between two sites of the polymeric matrix, is in agreement with random free energy barriers model proposed by Dyre (RFEB), while the conduction in the conductive phase is described by the Drude model. The analysis of the dc conductivity measurements obtained below the percolation threshold on both the composites indicates that the process of conduction occurs via hopping between sites of the polymeric matrix. In the region of percolation, both the hopping and tunneling can contribute to the conduction process. However, for samples with concentrations... (Complete abstract click electronic access below) / Mestre

The electrical conductivity of the pyromagmas from the Northeast Crater of Mount Etna, Sicily was measured over the temperature range 1032°C to 1071°C and over the frequency range 1 kHz to 400 kHz. Measurements were made using a four-terminal Wenner array in conjunction with a Wavetek Model 110B portable signal generator and Hewlett Packard Model 731 portable electronic voltmeters. The electrical conductivity is of the order of 0.4 mhos/m with less than 20% dispersion over the frequency range. Over the 40 degree temperature interval the temperature coefficient of resistance corresponds to an activation energy of 1.5 ± 0.5 eV. The value for the electrical conductivity of the gas-charged pyromagma is related to values determined in the laboratory for gas-free melts of lava and for glasses and slags of similar chemical composition. An original design of semi-expendable graphite-molybdenum electrode contributed greatly to the reliability of the measurements. A chromatographic analysis of the vent gases, and a silicate analysis, a modal analysis and a normal analysis of the lavas are included for completeness. Finally, as an aid to future electromagnetic probing activity, an analysis and estimate are made of the variation of electrical conductivity of pyromagma with depth in a volcanic conduit. / Graduation date: 1970

The objective of this project was to design a prototype field air permeameter that can be used to track changes in the hydraulic conductivity within soil covers with time. The evolution of soil structure in reclamation soil covers at the Syncrude Canada Ltd. oilsands mine is currently being studied. The Guelph permeameter is currently used to measure hydraulic conductivity, but gathering the data is a very time consuming task due to the relatively low hydraulic conductivity of the cover materials. The use of a faster, more efficient method would increase the capabilities for tracking changes in hydraulic conductivity of reclamation soil covers with time. <p>Three air permeameter design options were evaluated. One design was chosen and a prototype was built. Preliminary field trials were conducted at the Syncrude Canada Ltd. oilsands mine in August 2005. Air permeability measurements were taken on various soil cover treatments and slope positions. Improvements to the air permeameter were implemented in 2006, and additional data gathered. Guelph permeameter testing was carried out alongside the air permeameter in both field seasons. The air permeameter and Guelph permeameter were also tested under controlled laboratory conditions and compared to standard constant head column tests. <p>Results include correlations of air and water permeability for various materials and soil structures. Using dry uniform sand in a laboratory setting, the full scale air permeameter provided permeability values within 21% of a standard constant head column test. Testing of the air and Guelph permeameters on a cover constructed of peat-mineral mix over tailings sand revealed a difference of approximately one order of magnitude in permeability values. A difference of approximately two orders of magnitude existed between permeability values measured with the air and Guelph permeameters on till/secondary soil covers. <p>Further investigation into the difference between values of permeability measured with both methods is necessary. If successful, the air permeameter could prove to be a viable alternative to the Guelph permeameter for use in long-term monitoring of soil covers used in mine reclamation or waste containment. A more efficient air permeability method would allow a greater number of measurements to be made in a shorter time and could be used to track temporal as well as spatial variability in hydraulic conductivity.

This M.A.Sc. work focuses on the development of a sensor to operate at industrially relevant conditions, directly in autoclaves, to generate accurate online free acidity estimates. The main goal is to obtain accurate (within 5% from titrated) free acid estimates at leach temperature while compensating for various metals in solution at high solid loadings. The electrodeless conductivity sensor and calibration technique that were developed in previous work have been improved upon for operation in slurry systems. The sensor operates at temperature on the basis of induction currents and is suitable for very concentrated solutions containing solid dispersions. Three systems have been investigated: limonitic feeds, limonite-saprolite blends, and a converter slag feed. Up to 40 wt.% solids were tested with investigation carried out from 25°C to 260°C. High quality estimates of acidity were produced for all systems studied, with the average difference between measured and titrated acidities being within 5%.

This M.A.Sc. work focuses on the development of a sensor to operate at industrially relevant conditions, directly in autoclaves, to generate accurate online free acidity estimates. The main goal is to obtain accurate (within 5% from titrated) free acid estimates at leach temperature while compensating for various metals in solution at high solid loadings. The electrodeless conductivity sensor and calibration technique that were developed in previous work have been improved upon for operation in slurry systems. The sensor operates at temperature on the basis of induction currents and is suitable for very concentrated solutions containing solid dispersions. Three systems have been investigated: limonitic feeds, limonite-saprolite blends, and a converter slag feed. Up to 40 wt.% solids were tested with investigation carried out from 25°C to 260°C. High quality estimates of acidity were produced for all systems studied, with the average difference between measured and titrated acidities being within 5%.

The objective of this project was to design a prototype field air permeameter that can be used to track changes in the hydraulic conductivity within soil covers with time. The evolution of soil structure in reclamation soil covers at the Syncrude Canada Ltd. oilsands mine is currently being studied. The Guelph permeameter is currently used to measure hydraulic conductivity, but gathering the data is a very time consuming task due to the relatively low hydraulic conductivity of the cover materials. The use of a faster, more efficient method would increase the capabilities for tracking changes in hydraulic conductivity of reclamation soil covers with time. <p>Three air permeameter design options were evaluated. One design was chosen and a prototype was built. Preliminary field trials were conducted at the Syncrude Canada Ltd. oilsands mine in August 2005. Air permeability measurements were taken on various soil cover treatments and slope positions. Improvements to the air permeameter were implemented in 2006, and additional data gathered. Guelph permeameter testing was carried out alongside the air permeameter in both field seasons. The air permeameter and Guelph permeameter were also tested under controlled laboratory conditions and compared to standard constant head column tests. <p>Results include correlations of air and water permeability for various materials and soil structures. Using dry uniform sand in a laboratory setting, the full scale air permeameter provided permeability values within 21% of a standard constant head column test. Testing of the air and Guelph permeameters on a cover constructed of peat-mineral mix over tailings sand revealed a difference of approximately one order of magnitude in permeability values. A difference of approximately two orders of magnitude existed between permeability values measured with the air and Guelph permeameters on till/secondary soil covers. <p>Further investigation into the difference between values of permeability measured with both methods is necessary. If successful, the air permeameter could prove to be a viable alternative to the Guelph permeameter for use in long-term monitoring of soil covers used in mine reclamation or waste containment. A more efficient air permeability method would allow a greater number of measurements to be made in a shorter time and could be used to track temporal as well as spatial variability in hydraulic conductivity.

Thermal transport in nanowires and nanotubes has attached much attention due to their use in various functional devices and their use as a model system for low dimensional transport phenomena. The precise control of the crystal structure, defects, characteristic size, and electronic properties of nanowires has allowed for fundamental studies of phonon and electron transport in a variety of nanoscale systems. The thermal conductivity in nanostructured materials can vary greatly compared to bulk values owing to classical and quantum size effects. In this work, two model systems for investigating fundamental phonon transport were investigated for potential use in thermoelectric and thermal management applications. The thermoelectric properties of twin defect indium arsenide nanowires and the thermal conductivity of polythiophene nanofibers with improved polymer chain crystallinity were measured with a microfabricated measurement device. The effects of twin planes on reducing the mean free path of phonons in indium arsenide and the effects of improved chain alignment in increasing the thermal conductivity in polymer fibers is discussed. / text