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Formation Mechanism and Thermoelectric Energy Conversion of Titanium Dioxide Nanotube Based Multi-Component Materials and Structures

Su, Lusheng
http://rave.ohiolink.edu/etdc/view?acc_num=toledo1370793126

Abstract Details

2013, Doctor of Philosophy in Engineering, University of Toledo, College of Engineering.
This research focused on the formation mechanism of TiO2 nanotubes on pure Ti foil and the development and improvement in performance of thermoelectric multi-components. For the formation mechanism, based on our experiments and observations, oxygen formed on the anode determines the final dimension of the TiO2 nanotubes. The length of the TiO2 nanotubes achieved was 15 µm in the electrolyte containing ethylene glycol and water (98:2 vol. %) + 0.3 wt. % NH4F for 24 hours. Bent anode was employed to show that there were no nanotubes formed on the bent part. Different anodization times were used to examine the action of fluorine ions. We also used different types of Ti foils, cold rolled and hot-rolled, to evaluate the effect of preprocess condition on the oxygen formation at their surfaces. Electrochemically and chemically treated Ti foils with exposed grain boundaries were used to reveal that the nanotubes grow along the grains of the Ti substrate. Finally, a dissolution model was established to calculate the dissolved TiO2 mass. The primary strategy to improve the performance of thermoelectric materials was employing low-dimensional materials to reduce the lattice thermal conductivity as described by the Wiedemann-Franz law. Rattling structures, point defects, vacancies and multi-components were used to efficiently scatter phonons within or between the unit cell crystals. And complex crystalline structures were used to decouple the electrical conductivity and thermal conductivity to achieve this goal. Based on such considerations, we developed TiO2 nanotubes/polyaniline, TiO2 nanotubes/Te-Bi-Pb nanoparticles and TiO2 nanotubes/CoO coaxial nanocables. Firstly, TiO2 nanotubes/polyaniline (PANI) multi-components were synthesized. The experiments of how the time, voltage, concentration of F- ions and concentration of H3PO4 were associated with the formation of TiO2 nanotubes were conducted. The formation of polyaniline was confirmed by both Raman Spectroscopy and FTIR. The results showed that the optimum conditions for the formation of well aligned TiO2 nanotubes are at 20 V for 60 minutes in the electrolyte containing 0.2 M fluorine ions. The TiO2 nanotubes with the wall thickness of 20 nm and length of 3 µm were obtained in the electrolyte containing 0.2 M F-. Nanotubes with wall thickness of 10 nm and length of 600 nm formed in the solution containing 0.1 M F-. The highest absolute value of the Seebeck coefficient obtained was 123.75 µV/K. The measurement was performed at 30°C. The Seebeck coefficients of TiO2 nanotubes and TiO2 nanotubes/polyaniline multi-components were investigated. Secondly, Te-Bi-Pb nanoparticles were grown on the surface of the TiO2 nanotubes via electrochemical method. The purpose of the nanoparticles was to further enhance the performance of the thermoelectricity, specifically in our case, to increase the Seebeck coefficient. From the results obtained, the best Seebeck coefficient for pure TiO2 nanotubes was around -90 µV/K; while the best Seebeck coefficient for TiO2 nanotubes covered with scattered Te-Bi-Pb nanoparticles was about -155 µV/K. This significant improvement could be explained by the quantum confinement in such a peculiar nanostructure. Lastly, TiO2 nanotubes and TiO2-CoO coaxial nanocables were prepared by liquid phase deposition into the pores of anodic aluminum oxide (AAO) templates to form TiO2 nanotubes and TiO2-CoO coaxial nanocables. Morphological studies of the TiO2 nanotubes and TiO2-CoO coaxial nanocables were performed using scanning electron microscopy (SEM), and transmission electron microscopy (TEM). Elemental analysis of the composites was conducted by energy dispersive X-ray (EDX) spectroscopy. In addition, the Seebeck coefficients of the composites were measured. It was found that the highest absolute value of Seebeck coefficient was 393 µV/K for the TiO2 nanotube-filled AAO. The TiO2-CoO coaxial nanocable-filled AAO had the slightly lower value of 300 µV/K. Both composites showed n-type behavior.
Yong X. Gan, Dr. (Advisor)
Maria Coleman, Dr. (Committee Member)
Matthew Franchetti, Dr. (Committee Member)
Joseph Lawrence, Dr. (Committee Member)
Arunan Nadarajah, Dr. (Committee Member)
185 p.
Energy; Engineering; Materials Science
Thermoelectricity; Formation mechanism; TiO2 nanotube; Nanoparticle; Nanocable; PANI; Seebeck coefficient

Recommended Citations

Citations

  • Su, L. (2013). Formation Mechanism and Thermoelectric Energy Conversion of Titanium Dioxide Nanotube Based Multi-Component Materials and Structures [Doctoral dissertation, University of Toledo]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=toledo1370793126

    APA Style (7th edition)

  • Su, Lusheng. Formation Mechanism and Thermoelectric Energy Conversion of Titanium Dioxide Nanotube Based Multi-Component Materials and Structures. 2013. University of Toledo, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=toledo1370793126.

    MLA Style (8th edition)

  • Su, Lusheng. "Formation Mechanism and Thermoelectric Energy Conversion of Titanium Dioxide Nanotube Based Multi-Component Materials and Structures." Doctoral dissertation, University of Toledo, 2013. http://rave.ohiolink.edu/etdc/view?acc_num=toledo1370793126

    Chicago Manual of Style (17th edition)

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This open access ETD is published by University of Toledo and OhioLINK.