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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Item 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.Item 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.Item Experimental study of the partitioning of Cu, Ag, Au, Mo and W among pyrrhotite and immiscible Fe-S-O and silicate melts(2007-08-14) Mengason, Michael James; Candela, Philip A; Piccoli, Philip M; Geology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Partition coefficients have been determined for several transition metals amongst a rhyolitic silicate melt, pyrrhotite, and an immiscible Fe-S-O melt. Two sets of experiments were performed in sealed silica tubes at 1035°C-1045°C, FMQ-NNO O2, and logS2 ~1 bar, and analyzed by EMPA and LA-ICP-MS. Experiments yielded DFe-S-O/melt ±1σ(mean) for Au =300±100, Ag =120±20, Cu >200, Mo =90±10 and W =9±3, and Dpo/melt for Au =120±50, Ag =58±8, Cu >200, Mo =35±3 and W =1.2±0.6x10-3. Some preliminary data are also presented on the partitioning of Si, Ti, V, Co, Zn, Re, Th and U. Modeling predicts the loss to a daughter melt of up to 50% of the initial Au, >37% Cu, 24% Ag, 19% Mo, and 2% W when Fe-S-O melts are removed with other cumulate phases during fractionation. This would reduce the metal available to potential intrusion-related hydrothermal ore deposits.