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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2005 - 200912010 - 20171

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    Growth and Stabilization of Ag and Ni Nanoclusters within a Polymer Matrix Via Aerosol Spray Pyrolysis
    (2017) Romano, Michelangelo; Zachariah, Michael R; Material Science and Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Metal nanoclusters exhibiting enhanced properties are inherently unstable​ ​because of their high specific surface area. This work investigates how the​ ​undesirable agglomeration of these nanostructures can be circumvented by​ ​incorporating them into a polymer matrix. Using aerosol spray pyrolysis (ASP), Ag​ ​and Ni nanoclusters less than 20 nm in diameter have been synthesized by growing​ ​and trapping them within polyvinylpyrrolidone (PVP), polyethylene glycol (PEG),​ ​and polyethylene oxide (PEO). Experimental process variables including the polymer​ ​system’s molecular weight, the temperature of the tube furnace reactor, the carrier gas​ ​flow rate, and the metal salt concentration within the ASP precursor solution have​ ​been studied to understand which parameters govern nanocluster formation and​ ​growth. Having analyzed the correlations that exist between these parameters and the​ ​size distribution of the Ag and Ni nanoclusters, a qualitative model is proposed that​ ​identifies which primary mechanisms underlie the formation of metal nanoclusters​ ​within a polymer matrix.
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    Patterned Nickel Anode Stability in SOFC Environments with H2, CO and CH4 Fuel Feeds
    (2005-07-28) Becker, Benjamin; Jackson, Gregory S; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Single cell solid oxide fuel cells supported on single crystal YSZ electrolytes with patterned Ni anodes fabricated through sputter deposition and photolithographic techniques and with porous LSM/YSZ cermet cathodes were tested electrochemically to assess the stability of the Ni anodes in SOFC environments. Anode stability and electrochemical performance for H2, CO and CH4 electrochemical oxidation were characterized at cell temperatures between 750 ºC and 800 ºC under humidified (PH20/Pfuel = 0.05) conditions. Changes in performance of anodes polarized by typical working fuel cell overpotentials (100 - 200 mV) were compared to anodes kept at open circuit conditions. An increase in surface roughness was much greater for the polarized anodes than those kept under open circuit conditions. Electrochemical impedance spectroscopy and sweep voltammetry, over 10 continuous hours of testing, consistently showed constant performance for the polarized anodes and a drop in performance for the open circuit anodes.