(Georgia Institute of Technology, 2012-05-07)
Sikri, Tarun Vabhav Pratap
Stainless steels are utilized for their high toughness and resistance to general corrosion. Austenitic (300 series) stainless steels are the most popular because they are ductile and can be easily formed into desired geometries. They can also be case hardened to form alternating layers of martensitic and austenitic microstructures for applications that require high toughness and resistance to surface wear. However their usage is limited in comparison to other ferrous alloys due to higher initial costs and susceptibility to pitting and intergranular (IGC) corrosion. A microcell was developed to study these localized corrosion phenomena in microstructural regions of interest by performing polarization (spot) tests within well defined areas on metallic surfaces. Spot tests across profiles of welded 304 stainless steel confirmed that sensitization, greater acidities and higher chloride contents increase susceptibility and greater additions of chromium and nickel reduce susceptibility to localized corrosion. Spot tests across a case hardened (CSS 42L) stainless steel profile revealed that the austenitic sensitized outer layer was more susceptible to localized attack compared to the martensitic matrix. A more complete understanding of how microstructure affects these localized corrosion processes will lead to better alloy modifications, service environments and maintenance making this class of material a more sustainable alternative.
(Georgia Institute of Technology, 2012-05-07)
Fuller, Jeffrey
Fuel cells have several obstacles before they can see widespread use. Nafion, the current most successful polymer for use in polymer electrolyte fuel cells (PEMFCs) has been characterized by numerous other studies both experimental and computational. This study determines the, until now unexplored, behavior of oxygen within a Nafion system hydrated at 10 and 20wt%. The systems are equilibrated at temperatures of 353, 363, 373, and 383 Kelvin. Then the structure and transport characteristics of the system are explored using pair correlation and mean square displacement functions. As the hydration increased, the oxygen molecules became more coordinated with water resulting in a decrease in the diffusion coefficient of oxygen within the system. This has important implications in the efficiency of the fuel cell. This data furthers the pursuit of a more perfect polymer membrane for use in fuel cells.