Date of Graduation
Statler College of Engineering and Mineral Resources
Mechanical and Aerospace Engineering
Ever J Barbero
The need for energy nowadays is causing a heated debate in our society. One way to increase the energy sustainability is to harvest waste energy from current processes. For example, industrial processes, home heating and automotive exhaust, all generate copious amounts of heat that is usually wasted. In the diesel powered automobiles, up to 65% of the chemical fuel is lost as waste heat that is mostly rejected through the cooling radiator and exhaust systems with the temperature normally exceeding 600 °C. Thermoelectric materials have the ability of converting wasted heat and temperature difference into electricity. Thermoelectric materials need to possess high energy conversion efficiency (Figure of merit (ZT)) to be viable for thermoelectric devices. Current available high performance thermoelectric materials are mostly heavy metal based materials and they are not suitable for operating at high temperatures due to oxidation, decomposition, vaporization, and harmful environmental impact.;This thesis is focused on the investigation of the oxide thermoelectric materials of Ca3Co4O9 for harvesting the waste heat, such as those from the diesel powered vehicles, at high temperatures in the air. Layered Calcium Cobalt Oxide Ca3Co4O 9 is a promising thermoelectric material for TE devices with a reported energy conversion efficiency ZT=0.83 at 700 °C for single crystal. This performance of single crystal Ca3Co4O9 is outstanding, but, producing single crystals is expensive, and not realistic for practical large scale applications. A more practical production process from the economic perspective, is the development of polycrystalline Ca 3Co4O9. Current Ca3Co4O 9 polycrystalline ceramics have low performance, achieving ZT of ∼0.10-0.20. This thesis details the multiscale microstructure engineering performed on polycrystal Ca3Co4O9 to improve its thermoelectric performance. The first part describes the approach of cation stoichiometric substitution of Ca or Co to increase the phonon scattering and improve the thermoelectric properties. The second part reports the effect of minute amount of Cation non-stoichiometric addition on the microstructure of the polycrystal Ca3Co4O9 samples and their electrical and thermal transport properties. The final part reports a novel approach to introduce metallic nano-inclusions to Ca3Co4O9 to improve the electrical conductivity of polycrystal Ca3Co4O 9.
Calvillo-Gonzalez, Paulo Sergio, "Tuning the Thermoelectric Performance of Complex Oxides through Multiscale Microstructure Engineering" (2014). Graduate Theses, Dissertations, and Problem Reports. 5302.