Thesis (M. S.)--Mechanical Engineering, Georgia Institute of Technology, 2009. / Committee Chair: Qu, Jianmin; Committee Member: Kohl,Paul A.; Committee Member: Liu, Meilin; Committee Member: McDowell, David L.; Committee Member: Zhu, Ting.

Thesis (Ph. D.)--University of Texas at Austin, 2006. / Vita. Includes bibliographical references.

Thesis (Ph. D.)--West Virginia University, 2005. / Title from document title page. Document formatted into pages; contains xii, 148 p. : ill. (some col.). Includes abstract. Includes bibliographical references (p. 119-124).

Thesis (M.S.)--Montana State University--Bozeman, 2005. / Typescript. Chairperson, Graduate Committee: Max Deibert. Includes bibliographical references (leaves 56-58).

Thesis (M.S.)--Montana State University--Bozeman, 2005. / Typescript. Chairperson, Graduate Committee: Vic A. Cundy. Includes bibliographical references (leaf 80).

Thesis (Ph. D.)--University of Texas at Austin, 2007. / Vita. Includes bibliographical references.

Thesis (M.S.)--West Virginia University, 2007. / Title from document title page. Document formatted into pages; contains vii, 92 p. : ill. (some col.). Includes abstract. Includes bibliographical references (p. 89-92).

The MgO:TiO2 :ZrO2 ternary system was investigated as a possible novel anode material in a solid oxide fuel cell. Titanium-substituted yttria-stabilised zirconias have the necessary electrical conductivity properties for a ZrO2 -based fluorite electrode but problems have been encountered such as a decrease in unit-cell size upon reduction leading to mechanical failure. By incorporating magnesium into the titanium-stabilised zirconia structure, it was thought that the cubic-fluorite structure might be stabilised. A phase diagram study was made of the MgO:TiO2 : ZrO2 ternary system at 1500°C. Upon researching the literature phase diagram of the MgO:TiO2 :ZrO2 system, it was found that the authors had not studied the single-phase region in the ZrO2 -rich area extensively and did not use a consistent temperature for their analysis of samples. This has meant that the phase diagram has had to be reinvestigated. The results obtained at 1500°C are in disagreement with the previously published phase diagram. A large area bounded by single-phase cubic-fluorite was detected; however the central region of this domain contained both tetragonal and cubic-fluorite domains. This implies that for the central region of this phase area that the cubic- fluorite phase is not stable at 1500°C. Selected stabilised cubic-fluorite samples with ~ 10 atom% Mg were annealed at l000°C after preparation at 1500°C and it was found that due to the presence of other phases present at 1000°C, that the cubic-fluorite phase is thermodynamically unstable at lower temperatures. DTA analysis revealed that as the titanium content in the cubic-fluorite solid-solution increased, the phase transition from tetragonal phase (+ MgO) to cubic-fluorite phase decreased. These results were used to provide a basis for a temperature phase diagram showing the likely phase transitions that occur at a particular temperature range. The activation energy for conduction increased and ionic conductivity decreased with increasing titanium content in the solid solution, due to the effects of local distortions created by the smaller ionic radius of titanium when compared to zirconium.

The main concerns of air travel are the operating costs of general aviation aircraft. Hybrid-electric system design provides a great opportunity for future aircraft models to be environmentally friendly. The Hybrid-electric power propulsion system experienced a growing interest driven by determined targets. Electric technologies have proven promising success to achieve a successful result in the near- and long-term. Combining fuel cells and batteries, this technology can enable a significant reduction in fuel consumption, noise, and emissions. Different types of fuel cells and batteries are proposed and discussed during this work. The Cessna C-172 is a candidate to test the combination of the most promising fuel cells and batteries for a hybridization or complete electrification strategy.

Solid oxide fuel cells (SOFCs) represent a much cleaner and more efficient method for harnessing fossil fuel energy than conventional combustion; however, the challenge with making SOFCs mainstream lies in reducing operating costs and staving off their rapid degradation. High cathode polarization remains a bottleneck for lowering operation temperature. On the anode side, supplying SOFCs with hydrocarbon-based fuels poses many problems for systems using state-of-the-art material specifications such as composites of Ni and yttria-stabilized zirconia (YSZ). Various novel materials and surface modifications have been found to mitigate these problems, but more information towards a more profound understanding the role of these materials is desired. In this work, advanced Raman spectroscopic techniques were applied toward this end. Raman spectroscopy was used for the tracking of the evolution of water, carbon, sulfur, and oxygen species as well as new phases at SOFC electrode surfaces following or during exposure to various temperatures, atmospheres, and electrochemical stimuli. This information, coupled with performance data and other characterizations, would help to clarify the mechanisms of anode contamination reactions and oxygen reduction reactions. Knowledge gained from this work would also help to connect electrode modifications with performance enhancement and poisoning tolerance, offering insights vital to design of better electrodes. In addition, lack of adequate Raman signal from certain species, which is one of Raman spectroscopy’s limitations, was addressed. Surface enhanced Raman scattering (SERS) techniques were used in both in situ and ex situ analyses to increase signal yield from gas species and phases that are found only in trace amounts on electrode surfaces. Finally, a more practical thrust of this work was the application of this study methodology and the knowledge gained from it to cells with NASA's bielectrode supported cell (BSC) architecture. These types of cells also offer great prospects for superior specific power density due to their low weight. Ultimately, the goal of this thrust was progress towards achieving optimum performance of SOFCs operating under hydrocarbon fuels.