Browsing by Subject "Alloying"

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    The role of initial particle size and alloying of Pt nanocatalysts on the degradation of proton exchange membrane fuel cells
    (2013-12) Yu, Kang (Ph. D. in materials science and engineering); Ferreira, Paulo J. (Paulo Jorge)
    This thesis discusses the effect of initial particle size and alloying of Pt nanocatalysts on the degradation of Proton Exchange Membrane Fuel Cells (PEMFC). Platinum nanocatalysts with initial particle sizes of 2.2nm, 3.2nm, 5.0nm, 6.7nm and 11.3nm were studied, before and after potential cycling. The two smallest initial particle sizes show significant degradation, while the remainder of the samples show negligible degradation after 10,000 cycles. Among the possible degradation mechanisms operating, the results show that dissolution and re-precipitation is insignificant among all the samples. On the other hand, modified electrochemical Ostwald ripening (MEOR) is the main cause for particle growth and degradation of the Pt nanocatalysts. Moreover, MEOR could also assist the coalescence of particles. Thus, controlling the Pt dissolution rate is the key factor to prevent degradation. In the case of Pt₃Co nanocatalysts, both MEOR as well as dissolution & reprecipitation play an irrelevant role in degradation. However, particle migration and coalescence seems to be more severe in Pt₃Co nanoparticles than for Pt nanoparticles.
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    Selective Laser Sintering of Nylon 12-PEEK Blends Formed by Cryogenic Mechanical Alloying
    (2000) Schultz, Jeffrey P.; Martin, Julie P.; Kander, Ronald G.; Suchicital, Carlos T.A.
    Cryogenic mechanical alloying (CMA) has been shown to be an effective means for producing composite powders with co-continuous phases throughout each particle. Consolidation of these composite particles via SLS presents the possibility of forming parts with a co-continuous microstructure. In this work the effects of milling time and PEEK volume fraction on the microstructure and mechanical properties of laser sintered Nylon 12-PEEK blends is studied. In both blends, the PEEK phase is incorporated to increase mechanical strength, stiffness and heat deflection temperature. Transmission electron microscopy and scanning electron microscopy is utilized to investigate the microstructure of the CMA powder and laser sintered parts.