UMD Theses and Dissertations

Permanent URI for this collectionhttp://hdl.handle.net/1903/3

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 given thesis/dissertation in DRUM.

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Now showing 1 - 6 of 6
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    Sulfur Management to Enhance Yield and Protein Quality of Grain Legumes
    (2020) Rushovich, Dana Alison; Weil, Raymond; Environmental Science and Technology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Sulfur (S) is an essential macronutrient and a key component in essential amino acids, methionine and cysteine (MET+CYS) that are the building blocks of protein. For a number of reasons, including difficulties in analysis for S, soil testing and fertility management has largely ignored this essential plant macronutrient. Trials were carried out over three years to evaluate the role of S fertility on the yield, seed S content, S yield and seed MET+CYS content of three types of grain legumes: double crop soybeans (Glycine Max), full season soybeans, and common dry beans (Phaseolus vulgaris). Sulfur fertility management significantly increased yield, seed S content, S yield, and seed MET+CYS content on low S soils. Additionally, four soil extractions were evaluated as potential methods to improve S fertility recommendations. Calcium phosphate extractions more accurately identified sites that had a yield or seed s content response to applied S compared to Mehlich 3 and Calcium Chloride.
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    EVALUATION AND IMPROVEMENT OF MECHANICAL AND CHEMICAL RESILIENCE OF INTERMEDIATE-TEMPERATURE SOLID OXIDE FUEL CELL ANODES
    (2017) Hays, Thomas; Wachsman, Eric D; Material Science and Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Solid oxide fuel cells are in the process of reaching maturity as an energy generation technology, but a number of technical challenges exist, namely mechanical and chemical resilience, that hinder the realization of their full potential and widespread deployment. As more research and development work has been performed on intermediate temperature SOFCs based on gadolinium doped ceria, there persists a number of gaps in the understanding of the behavior of these devices. The mechanical properties of component material and SOFC structures in non-ambient conditions, the nature and degree of damage caused by sulfurized hydrocarbon fuels, and the potential for leveraging produced thermal energy are not satisfactorily characterized for GDC-based SOFCs. Mechanical testing of porous GDC and anode supported SOFC coupons from room temperature to 650°C was performed in air and reducing conditions using a test system designed and built for this application. Spherical porosity was determined to result in the higher strength compared to other pore geometries and a positive linear dependence between temperature and strength was determined for SOFC coupons. Additionally, placing the electrolyte layer in compressive stress resulted in higher strengths. Standard SOFCs were operated while exposed to hydrogen and methane containing ppm level hydrogen sulfide concentration. An infiltration technique was used to deposit a fine layer of GDC on the inner surfaces of some cell anodes, and the results of sulfur expose was compared between infiltrated and unmodified cells. GDC infiltration allowed cells to operate stably for hundreds of hours on sulfurized fuel while unmodified cells were fatally damaged in less than two days. A primary and a resulting secondary degradation mechanism were identified and associated with sulfur and carbon respectively through surface analysis. A novel technique for measuring thermal power output of small-scale SOFCs operating on a variety of fuels was developed and used to evaluate electrical and thermal outputs while operating on simulated anaerobic digester biogas. These findings were used to propose a multi-utility generation system centered on a nominal 10 kW SOFC unit fed by anaerobic digesters and capable of producing clean water and electricity for 50 individuals through direct contact membrane distillation driven by captured waste heat from the SOFC.
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    Assessing the Oxidative History of Miller Range Martian Meteorites
    (2016) Dottin III, James Wosley; Farquhar, James; Geology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Miller Range (MIL) Martian meteorites are oxidized nakhlites. Early studies attribute their oxidation to reduction-oxidation reactions involving assimilated sulfate. I utilize the sulfur isotope and major element composition of the MIL pairs to assess their oxidative history. MIL sulfides display an average sulfur isotope composition that is different from Nakhla sulfate and sulfide. The sulfur isotope differences produce a mixing array between juvenile sulfur and mass-independent sulfur signatures, indicating assimilation of anomalous sulfur into the melt. I estimate an fO2 of QFM (+3.5 ± 0.4) and a sulfur content of 360 ppm ± 12 – 1300 ppm ± 50. With these results, I test the hypothesis of sulfate assimilation through models of charge balance, isotope mixing, and degassing of sulfur bearing compounds. I conclude that sulfate assimilation was significant in the oxidation of the MIL pairs but, additional oxidants were assimilated.
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    COPPER CORROSION IN THE FLOWERS OF SULFER TEST ENVIRONMENT
    (2015) Mahadeo, Dinesh Michael; Pecht, Michael G; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Sulfur, present in the environment in the form of sulfur dioxide and hydrogen sulfide, can produce failure in electronics. In particular, copper, which is used extensively in electronic products, is subject to corrosion in the presence of sulfur. This thesis examines the corrosion of copper under the Flowers of Sulfur (FoS) test at varying temperatures and durations. The FoS test setup, described in ASTM B809, was initially designed to evaluate surface finish porosity, but this setup may have boarder application. To expand the applicability of the FoS test, it is important to characterize the test environment. To this end, a systematic study of copper corrosion was conducted through weight gain measurements of copper coupons that were subjected to FoS test environments. From the test results, a model was developed that correlates copper sulfide thickness to temperature and time under the FoS test. This model can be used to determine test conditions given a target field environment.
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    Spring Seedbed Characteristics after Winterkilled Cover Crops
    (2013) Lounsbury, Natalie; Weil, Raymond R; Environmental Science and Technology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Tillage is the common practice for seedbed preparation prior to early spring vegetables. To investigate the possibility of eliminating the need for spring tillage through the use of cover crops, spring seedbed characteristics after winterkilled cover crops forage radish (Raphanus sativus L.) and oat (Avena sativa L.) were monitored prior to and during growth of no-till and rototilled plantings of spinach (Spinacia oleracea var. Tyee) over four site years in Maryland's Coastal Plain and Piedmont regions. Results indicate that forage radish can facilitate no-till planting of spring vegetables in the mid-Atlantic without herbicides or fertilizer. Forage radish increases soil nitrate and sulfate in early spring and is best suited as a cover crop before the earliest planted main crops.
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    The Effect of CO2 on Copper Partitioning in Sulfur- Free and Sulfur-Bearing Felsic Melt-Vapor-Brine Assemblages
    (2012) Tattitch, Brian Christopher; Candela, Philip; Piccoli, Philip; Geology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Analysis of fluid inclusions from porphyry copper deposits (PCD) reveals that magmatic vapor and/or brine are vital for the removal of copper from arc magmas and its transport to the site of ore formation. Experiments in melt-vapor-brine systems allow for investigating the partitioning of copper between silicate melts and volatile phases under magmatic conditions. The presence of CO2 affects both the pressure of vapor saturation and the composition of exsolving volatile phases. However, PCD are primarily sulfide ore deposits, and the role of sulfur must also be examined as part of magmatic-hydrothermal experiments. Therefore, the partitioning of copper in CO2 ± S-bearing experiments was examined in an attempt to provide insights into copper partitioning and the generation of PCD. I present the results from experiments performed at 800 °C and 100 MPa in CO2-bearing melt-vapor-brine systems with XCO2 = 0.10 and 0.38. The compositions of vapor and brine inclusions and run-product glasses were used to determine the compositions of the magmatic phases. The partitioning of copper between brine and vapor (DCu b/v ±2σ) increases from 25(±6) to 100 (±30) for sulfur-free experiments and increases from 11(±3) to 95(±23) for sulfur-bearing experiments as XCO2 is increased from 0.10 to 0.38. The partitioning of copper between vapor and melt (DCu v/m ±2σ) decreases from 9.6(±3.3) (sulfur-free, HCl-bearing), 18(±8) (sulfur-bearing, HCl-free), and 30(±11) (sulfur-bearing, HCl-bearing) at XCO2 = 0.10, to 2(±0.8)(HCl-free) at XCO2 = 0.38, sulfur-free or sulfur-bearing. These data demonstrate that copper partitioning in sulfur-free, CO2-bearing systems is controlled by the changes in the salinity of the vapor and brine corresponding to changes in XCO2. Sulfur-bearing experiments demonstrate that magmatic vapors are enriched in copper in the presence of sulfur at low XCO2. However, the enrichment of copper in the magmatic vapor is suppressed for sulfur-bearing systems at high XCO2. The MVPart model presented by Candela and Piccoli (1998) was modified to incorporate CO2 to predict trends in efficiency of removal of copper into exsolving CO2-bearing magmatic volatile phases. The CO2-MVPart model predicts two to three times lower efficiency for CO2-rich (XCO2 = 0.38) magmatic volatile phases compared to low-CO2 (XCO2 ≤ 0.10) systems.