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University of Pennsylvania

Diffusion

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Cation Kinetics And Electric Field Effect In Zirconia, Yanhao Dong Jan 2017

Cation Kinetics And Electric Field Effect In Zirconia, Yanhao Dong

Publicly Accessible Penn Dissertations

Cation diffusion controls mass transport and microstructural evolution in zirconia above 1200 oC. In past research, its experimentally measured activation energy of 5 eV cannot be reproduced by computer simulation, which gives >10 eV and a cation vacancy mechanism implicating enhanced diffusion in oxidizing atmosphere, contradicting experimental evidence. This thesis was undertaken to answer these questions and to explore new ground in cation kinetics.

To help search for low-energy configurations in zirconia alloys, we employed crystal chemistry to boost sampling efficiency, by >1,000 times, and obtained plausible “ground states” to launch ab-initio calculations for cation defects and migration. The ...


Dynamics In Polymer Nanocomposites Containing Fixed And Mobile Nanoparticles, Chia-Chun Lin Jan 2015

Dynamics In Polymer Nanocomposites Containing Fixed And Mobile Nanoparticles, Chia-Chun Lin

Publicly Accessible Penn Dissertations

This dissertation describes experimental studies on the dynamics of polymer nanocomposites (PNC), namely, center-of-mass (COM) polymer diffusion in PNCs, and COM nanoparticle (NP) diffusion in polymer melts. Elastic recoil detection (ERD) is used for polymer diffusion studies and Rutherford backscattering (RBS) is used for NP diffusion studies. Diffusion of the tracer polymer, deuterated poly(methyl methacrylate) (dPMMA) is slowed down in a PMMA matrix filled with hydroxyl-capped spherical silica nanoparticles. A confinement parameter, ID/2Rg, where ID is interparticle distance and 2Rg is probe size is defined to account for the NP crowding effect. For highly crowded region where ID ...