Theses and Dissertations at Montana State University (MSU)
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Item Stabilization of metallic catalyst microstructures against high-temperature thermal coarsening(Montana State University - Bozeman, College of Engineering, 2016) Driscoll, David Robert; Chairperson, Graduate Committee: Stephen W. Sofie; Clay D. Hunt, Julie E. Muretta and Stephen W. Sofie were co-authors of the article, 'Thermally stabilized nickel electro-catalyst introduced by infiltration for high temprature electrochemical energy conversion' in the journal 'Transactions of the Electrochemical Society' which is contained within this thesis.; Cameron H. Law and Stephen W. Sofie were co-authors of the article, 'Design and synthesis of metallic nanoparticle-ceramic support interfaces for enhancing thermal stability' in the journal 'Ceramic transactions' which is contained within this thesis.; Stephen W. Sofie was a co-author of the article, 'Stabilization of nano-scale metallic microstructure against thermal coarsening' in the journal 'Ceramic transactions' which is contained within this thesis.; Melissa D. McIntyre, Martha M. Welander, Stephen W. Sofie and Robert A. Walker were co-authors of the article, 'Enhancement of high temperature metallic catalysts : aluminum titanate in the nickel-zirconia system' in the journal 'Applied catalysis A: general' which is contained within this thesis.; Thesis contains two articles of which David Robert Driscoll is not the main author.; Melissa D. McIntyre, Martha M. Welander, Daniel E. Perea, Robert A. Walker and Stephen W. Sofie were co-authors of the article, 'Aluminum oxide processed as a beneficial additive in SOFC anodes' submitted to the journal 'Journal of the electrochemical society' which is contained within this thesis.; Clay D. Hunt, Daniel E. Perea, and Stephen W. Sofie were co-authors of the article, 'Diffusion caging : thermodynamic arrest of Ostwald ripening' submitted to the journal 'Advanced Materials' which is contained within this thesis.The size and shape of metal particulate at high temperature is dictated by surface energy. In systems containing very small metal particles, smaller particles shrink and disappear as they grow into larger particles in a process referred to as coarsening. Coarsening causes irreversible degradation in a number of important systems including automotive catalytic converters and solid oxide fuel cells (SOFC) through a loss of catalyst (metal) surface area. This phenomenon is exemplified by nickel metal catalyst that is supported on ytrria-stabilized zirconia (YSZ) which represents a materials system critical to the function of SOFCs. It has been demonstrated that additions of aluminum titanate (ALT) to the Ni-YSZ system with subsequent thermal treatment can act to stabilize the geometry of Ni on YSZ. In demonstration SOFCs, ALT has increased the time required for the first 10% of degradation by a factor of 115. This work has sought to elucidate the mechanisms by which ALT imparts increased stability. The work contained here demonstrates that ALT easily decomposes to Al 2O 3 and TiO 2. During thermal treatment, the alumina reacts with NiO to form nickel aluminate and the titania interacts with the YSZ where it can form Zr 5Ti 7O 24 -- a mixed ion electron conducting phase. In this way, the Al and Ti components of ALT have been determined to act independently where alumina appears to be dominant in microstructural stabilization. During cell operation, the nickel aluminate decomposes to nickel metal decorated with alumina nano-particulate. This geometry forms the basis of 'diffusion caging' as a stabilization mechanism which is the subject of Chapter 8. The role of titania appears to be less important except when processing occurs in a way that facilitates formation of the MIEC phase. However, Ni-YSZ cermets have also shown a strength enhancement when doped with ALT. This strength enhancement is likely due to the influence of titania (Chapter 7). Future work has the potential to extend concepts discussed here to a number of high temperature catalytic systems.