Thesis(M.S.)--Case Western Reserve University, 2009 / Title from PDF (viewed on 2010-01-28) Department of EMC - Mechanical Engineering Includes abstract Includes bibliographical references and appendices Available online via the OhioLINK ETD Center

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An ultra-high burnup metallic inert matrix nuclear fuel concept is being characterized and evaluated by Lawrence Livermore National Laboratory based on a metal matrix fuel concept originally developed at the Bochvar Institute in Russia. The concept comprises a dispersion of uranium metal microspheres in a Zr-based alloy matrix that provides thermal bonding between the fuel particles and the cladding material. The objective of this study was to experimentally evaluate both the microstructural and thermophysical properties of Zr-Fe-Cu alloys. The experiments and analyses described were divided into three main parts, nominally based on the analysis methods used to examine the alloys. An Electron Probe Microanalyzer (EPMA) was used to characterize the metallurgical properties of the proposed matrix alloys. The groups of alloys were cast using a high temperature inert atmosphere furnace. The cast alloys showed the expected combination of phases with the exception of the ZrFe2 Laves phase which was predicted for the Zr-12Fe-15Cu1 alloy but was not detected. The Zr-12Fe-5Cu alloy consisted of a Zr solution phase dispersed in a matrix of two different intermetallic phases. The second alloy, Zr-12Fe-10Cu, did not produce a homogenous mixture and consisted of two distinct phase morphologies. The top half of the sample was Zr rich and contained Zr precipitates dispersed in a matrix of intermetallic compounds while the bottom half consisted solely of intermetallic compounds. The third alloy, Zr-12Fe-15Cu, was comprised of four different intermetallic phases three of which had the same apparent Zr_(2)(Fe,Cu) structure but had distinct phase morphologies based on the Backscatter Electron (BSE) images. Upon determining the phase morphologies of each of the fabricated alloys Differential Scanning Calorimetry (DSC) and Thermal Gravimetric Analysis (TGA) were used to measure phase transformation and melting temperatures. Little difference was observed between the as-cast and annealed samples. The transitions shifted slightly to higher temperatures and the annealed Zr-12Fe-15Cu alloy only had two transitions compared to three seen in the as-cast samples. Slight changes were observed in the melting temperatures between the as-cast and annealed alloys. Zr-12Fe-5Cu had the largest melting temperature (886.3°C) while Zr-12Fe-10Cu had the smallest melting temperature (870°C). The third alloy, Zr-12Fe-15Cu, had a melting point just below that of Zr-12Fe-5Cu at 882.7°C. Light Flash Analysis (LFA) was implemented to determine the low temperature (20-260°C) thermal diffusivity values of each alloy. The as-cast measurements were more precise than the annealed samples, most likely the result of non-ideal sample integrity prior to loading. Each of the three alloys showed a linear increase in thermal diffusivity over the temperature range. Values for Zr-12Fe-5Cu ranged from 3.54 ± 0.06 mm2/s to 4.42 ± 0.10 mm^(2)/s. The Zr-12Fe-10Cu alloy had maximum and minimum values of 4.19 ± 0.22 mm^(2)/s and 3.17 ± 0.16 mm^(2)/s, respectively. Lastly, Zr-12Fe-15Cu had the largest thermal diffusivity ranging from 3.52 ± 0.15 mm^(2)/s at 20°C to 4.64 ± 0.16 mm_(2)/s at 260°C. Overall, the data from the LFA measurements showed that the Zr-Fe-Cu alloy system had similar diffusivity values compared to other common reactor materials.

This thesis presents a framework for a microstructural model of a catalyst layer in a proton exchange membrane (PEM) fuel cell. In this study, a stochastic model that uses individual carbon, platinum and ionomer particles as building blocks to construct a catalyst layer geometry, resulting in optimal porosity and material mass ratios has been employed. The construction rule set in this design is easily variable, enabling a wide range of catalyst layer geometries to be made. The generated catalyst layers were found to exhibit many of the features found in currently poduced catalyst layers. The resulting geometries were subsequently examined on the basis of electronic percolation, mean chord length and effective diffusivity of the pore phase. Catalyst layer percolation was found to be most effected by the number of carbon see particles used and the specified porosity. The mean chord lengths of all of the catalyst layer geometries produced Knudsen numbers ranging in order of magnitude between 0.1 and 10, thus indicating that gas diffusion within the catalyst layers lies in the transition regime between bulk and Knudsen diffusion. Calculated effective diffusivities within the pore space of the model were shown to be relatively insensitive to changes in the catalyst layer composition and construction rule set other then porosity, indicating that the pore size distribution does not significantly vary when the catalyst layer mass ratios vary. / Thesis (Master, Mechanical and Materials Engineering) -- Queen's University, 2012-08-31 08:52:55.747

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Two different types of rhizomorphs were produced by A. luteobubalina in vitro conditions - aerial and submerged. They differed in growth rate, amount of mucilage, extent of peripheral hyphae, degree of pigmentation and in the structure of inner cortex. Otherwise they had a similar internal structure comprising 4 radial zones, namely, peripheral hyphae, outer cortex, inner cortex and medulla. Two membrane permeant symplastic fluorescent tracers, carboxy-DFFDA and CMAC which ultimately sequestered in vacuoles, behaved in a similar fashion in aerial and submerged rhizomorphs regardless of whether pigment was present in the outer cortical cell walls or in the extracellular material. Rhizomorphs appeared to be mostly impermeable to these probes with exception of a few fluorescent patches that potentially connected peripheral hyphae to inner cortical cells. In contrast, the apoplastic tracer HPTS which was applied to fresh material and its localisation determined in semi-thin (dry) sections following anhydrous freeze substitution appeared to be impeded by the pigmentation in cell walls and/or the extracellular material in the outer cortical zone. Structures identified as air pores arose directly from the mycelium and grew upwards into the air. A cluster of rhizomorph apices is initiated immediately beneath the air pores. As air pores elongated they differentiated into a cylindrical structure. Mature air pores became pigmented as did also the surface mycelium of the colony. The pigmented surface layer extended into the base of air pores, where it was elevated into a mound by tissue inside the base of the air pore. Beneath the pigmented surface layer there was a region of loose hyphae with extensive gas space between them. This gas space extended into the base of the air pore and was continuous with the central gas canal of rhizomorphs. Oxygen is conducted through the air pores and their associated rhizomorph gas canals into the oxygen electrode chamber with a conductivity averaging 679??68x10-12 m3s-1. The time averaged oxygen concentration data from the oxygen electrode chamber were used to compare three different air pore diffusion models. It was found that the widely used pseudo-steady-state model overestimated the oxygen conductivity. Finally, a model developed on the basis of fundamental transport equations was used to calculate oxygen diffusivities. This model gave a better comparison with the experimental data.

Thesis (Ph. D.)--University of Wisconsin, 1967. / Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references.

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A critical survey of the present state of the quantum statistical theory of thermal conductivity is given. Recently several attempts have been made to extend Kubo's treatment of electrical conduction to other irreversible transport processes in -which the interaction between the driving system and the system of interest is not precisely known. No completely satisfactory solution of the problems involved is contained in the literature. In this thesis, a detailed derivation of a Kubo-type formula for thermal conductivity is given, using essentially the concepts and methods of Nakajima and Mori, with no pretense that it settles the problem completely. Some general remarks are made on the evaluation of a Kubo-type expression, in particular, the use of Van Hove's master equations and the reduction of the usual N-particle formula to a single particle formula. An explicit calculation of thermal conductivity is made for the simple model of elastic electron scattering by randomly distributed, spherically symmetric impurities. / Science, Faculty of / Physics and Astronomy, Department of / Graduate