A. James Clark School of Engineering
Permanent URI for this communityhttp://hdl.handle.net/1903/1654
The collections in this community comprise faculty research works, as well as graduate theses and dissertations.
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Item TUNING THE STRUCTURE AND CHEMISTRY OF SOLID OXIDE FUEL CELL ELECTRODES FOR HIGH PERFORMANCE AND STABLE OPERATION(2021) Horlick, Samuel; Wachsman, Eric D; Chemical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Their reliability, fuel-flexibility, and high specific power make solid oxide fuel cells (SOFCs) promising next-generation power conversion devices. These advantages are theoretically attainable, but current material and structural limitations on the electrodes restrict the true potential of SOFCs on a cell level. Furthermore, ceramic processing challenges hinder the large-scale implementation of SOFCs. Here, SOFC electrodes are redesigned to develop the device closer to its theoretical potential. First, a fundamental investigation into the nature of exsolution materials provides a platform for controlling electrocatalyst properties such as: particle size, population, composition, and contact angle on host. Next, this knowledge is used to design a stable and active anode for the first ever exsolution-anode-supported SOFC and the practical limitations of this approach are identified to lead future research routes. In parallel to this study, a new method for synthesizing cheap, effective catalysts is developed to enable long-term SOFC operation with hydrocarbon fuel without sacrificing performance. Additionally, a systematic study identifies oxygen diffusion as the rate limiting step in the high current regime, and when this limitation is removed with improved system and electrode design, world-class power densities are achieved. Finally, a methodical investigation into ceramic processing of full-scale (5x5cm) SOFCs uncovers that cell flatness can be improved by optimizing green-tape compositions, sintering time/rate/temperatures, and top plate selection. Likewise, electrolyte quality depends on the top plate used in sintering and a light-weight YSZ-coated top plate gives the best balance between flatness and electrolyte quality.Item EFFECT OF GLASS JOINS ON PERFORMANCE OF LAYERED DENTAL CERAMIC SYSTEMS(2008) Saied, Mey; Lloyd, Isabel K; Lawn, Brian R; Material Science and Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Layered structures can be used to address the competing needs of systems like dental crown restorations where the exterior needs to be aesthetic and the interior needs to be strong and fatigue resistant. Dental crowns typically have an aesthetic porcelain veneer layered on a strong, fatigue resistant ceramic or metallic core. In current restorations, even when the core is shaped by a computer-aided design and manufacturing (CAD/CAM) or solid-freeform fabrication processes, the veneer is applied in sequential layers. This process is labor intensive, time consuming and may not optimize the long-term performance properties of the veneer layer. If the core and veneer layers were to be independently fabricated and then joined, their individual and the veneer-core system performance could be optimized. Some groups have explored the possibility of joining with filled epoxies, which is easier, but may not be long-lasting. In this project we explore the possibility of using more durable glassy joins. Dense, thermal-expansion-matched (to the core and veneer glass) joins can be fired at temperatures far enough below the melting and/or slumping temperatures to join veneers to cores without degradation. In this study, we design and fabricate joining glasses for bonding porcelain veneers to ceramic cores, specifically to dental aluminas and zirconias. We study the chemical bonding and mechanical integrity of the resulting layers. Finally, we assess the effects of glass joins on performance of layered dental ceramic systems.