Theses and Dissertations from UMD
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New submissions to the thesis/dissertation collections are added automatically as they are received from the Graduate School. Currently, the Graduate School deposits all theses and dissertations from a given semester after the official graduation date. This means that there may be up to a 4 month delay in the appearance of a give thesis/dissertation in DRUM
More information is available at Theses and Dissertations at University of Maryland Libraries.
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Item Metals and Metallic Alloys for Energy Harvesting and Storage(2018) Gong, Chen; Leite, Marina S; Material Science and Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Metals have been widely used for harvesting and storing energy in devices such as superabsorbers and Li-ion batteries. However, incorporating metals into a wider range of energy applications is severely limited by their intrinsic optical and electrochemical properties. Therefore, in this thesis, we provide a new class of metallic materials by forming binary mixtures of Ag, Au, Cu, and Al with novel physical properties for photonics, and a comprehensive understanding of the fundamental electrochemistry in Al and Si anode all-solid-state batteries for energy storage. The first part of my thesis focuses on developing metallic alloys with a tunable optical response. We realize a new family of metallic materials by alloying Ag, Au, and Cu with on-demand dielectric functions, which can be used in superabsorbers and hot carrier devices. We design and fabricate alloyed nanostructures with engineered optical response and spatially resolve the electric field distribution at the nanoscale by utilizing near-field scanning optical microscopy, which can potentially enhance the performance of optoelectronic devices. To understand the physical origin of the optical response of the alloys, we measure the valence band spectra and calculate the band structures of Ag-Au alloys, providing direct evidence that the change in the electronic bands is responsible for its optical property. Further, we obtain a photonic device with superior performance using metallic alloys. Specifically, an Al-Cu/Si bilayer superabsorber is reached in a lithography-free manner with maximum absorption > 99%, which can be used for energy harvesting. The second part of my thesis highlights the importance of understanding the reactions and ion distribution in energy storage devices. We inspect how the Al electrode surface changes upon cycling and directly map the Li distribution in 3-dimensions within all-solid-state batteries by implementing time-of-flight secondary ion mass spectroscopy. This research indicates that undesired chemical reactions, including the formation of an insulating layer on the Al anode surface and the trapping of Li ions at the interfaces, hinder the cycling performance of the devices. Overall, our results will contribute to the design of energy storage devices with enhanced electrochemical performance.Item Microencapsulated Phase Change Materials for Energy Storage and Thermal Management(2014) Cao, Fangyu; Yang, Bao; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The continuous increase of greenhouse gas emission, the climb in fuel prices, and the limited natural resources drive human beings to utilize energy more effectively. Changes are required in energy storage and thermal management systems, particularly through the advanced technologies and systems of thermal energy storage and heat dissipation. Phase change materials (PCMs) have received considerable attention for these applications. As a novel technology to utilize PCMs, microencapsulated phase change materials (microPCMs) have drawn great interest due to their high heat capacity and easy manipulating and operating, and thus are potentially applicable in various industries. This dissertation provides results of a systematic investigation on the design, synthesis, characterization, and applications of microPCMs. With either solid-solid PCM or liquid-solid PCM as the core material, microPCMs have been synthesized with wet-chemical methods using colloidal solutions as the reaction media. To begin with, the thermophysical properties of colloidal systems were investigated, especially the change of thermal conductivity with the concentration of surfactant. Two types of microPCMs were then synthesized using emulsion techniques, and the synthesis parameters were manipulated to enhance the thermophysical properties of the microPCMs and suppress the supercooling of encapsulated PCMs. To enhance their thermal conductivity, microPCMs with large latent heat capacity and suppressed supercooling were coated with a metal layer. The as-synthesized phase changeable and thermal conductive microPCMs were applied in a heat transfer fluid to enhance the heat transfer performance. This work was focused on the following aspects. The first aspect is the thermophysical properties of colloidal solutions, such as thermal conductivity, at low surfactant concentrations around the critical micelle concentration (CMC). The second aspect is the synthesis of microPCMs in the colloidal systems with solid-solid PCM neopentyl glycol and liquid-solid PCM n-octadecane as the core material. The third aspect is the enhancement of thermophysical properties (e.g., heat capacity, supercooling,) of the microPCMs, which was achieved by manipulating the parameters of the environment of chemical synthesis. The fourth aspect is the elevation of the thermophysical properties of the microPCMs, such as thermal conductivity, after the microPCMs were produced. The fifth and final aspect is the applications of the as-produced microPCMs, e.g., to enhance the heat transfer in bulk solid materials for latent heat storage and heat transfer fluids for heat dissipation with the aid of microPCMs, with or without coating with thermal conductive silver layer.