Theses and Dissertations from UMD

Permanent URI for this communityhttp://hdl.handle.net/1903/2

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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    Spatial and Temporal Variability in Suspended Sediment Characteristics in the Surface Layer of the Upper Chesapeake Bay
    (2020) Barletta, Stephanie Marie; Sanford, Lawrence P; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Periodic high discharge events flush suspended sediments from the Susquehanna River and Conowingo Dam reservoir into the upper Chesapeake Bay, which extends from the mouth of the Susquehanna River to the Bay Bridge near Annapolis, MD. Sediment characteristics in the surface layer of the upper Bay and changes in these characteristics with varying river discharge and distance downstream are not well known. In order to develop an integrated understanding of surface layer sediment dynamics, several in-situ data sets were examined at the Bay head and downstream along the Bay’s center channel, providing data on the spatial and temporal variability of suspended particle characteristics including concentration, settling speed, bulk density, and size. It was found that particles are entirely disaggregated at the Dam, later aggregating to a limited extent down Bay, and that downstream characteristics are more weakly linked to Susquehanna flow at lower flows and longer distances.
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    CO-SOLVENT ASSISTED SPRAY PYROLYSIS FOR THE PREPARATION OF METAL MICROPARTILCE
    (2012) ZHONG, KAI; Ehrman, Sheryl; Chemical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Metal and bimetallic particles play an important role in catalytic, medical and electronic applications. Various techniques have been developed for the preparation of metal particles, including vaporization techniques, sonochemical, polyol method, mechanical alloying and spray pyrolysis. Compared with the other preparation techniques, the spray pyrolysis process has the advantages of easy scale up in industry, tunable particle size and controllable particle composition. Sometimes hydrogen was used in the process to promote the formation of metallic phase in a lower temperature, but it also created a potential safety problem. In order to eliminate the use of hydrogen, a cosolvent assisted ultrasonic spray pyrolysis process was developed, and ethanol (ET) and ethylene glycol (EG) are used as the cosolvent. In this study, the cosolvent assisted ultrasonic spray pyrolysis process was used for the generation of various oxide free oxide particles, and the reaction mechanism was shown. In the first part of this study, properties of ultrasonic droplet generator were investigated. Precursor solutions were atomized by a 1.7 MHz ultrasonic nebulizer. The droplet size distribution and atomization rate were measured. Relationship between droplet diameters and the physical properties were revealed by statistic tools. Bimodal droplets distribution was observed during the experiment. Then copper particles were generated by the spray pyrolysis process. Copper nitrate aqueous solution was used as the precursor and either ET or EG was used as cosolvent. Oxide free particles were generated at temperature from 400 oC to 1000 oC. It was noticed that particles morphology and formation process was strong affected by the properties of the cosolvents. In the following study, the spray pyrolysis process was successfully used for the generation of AgNi, CuNi and AgCu bi-components particles. Various particle structures were observed, and the structures were mainly determined by the thermodynamic properties of the particles components. In the last part of this dissertation, efforts mainly focused on the mechanism of AgCu particle generation. Reaction intermediates were collected. Reaction process from nitrates to pure metal and the phase separation behavior between Cu and Ag was demonstrated.