Doctor of Philosophy, Case Western Reserve University, 2016, Materials Science and Engineering

Study of Anodic Oxide Films on Titanium and Titanium-Zirconium Alloys and their Potential for Capacitive Energy Storage Abstract by MIN-KYONG CHUNG Anodic oxide films were formed on titanium and titanium-zirconium alloys. They were studied for their ability to serve as dielectrics for storage of electrical energy and for their utility as anodes of electrolytic capacitors. The work comprised a study of the development of structure and electrochemical properties of TiO2 and of mixed TiO2-ZrO2 oxide films during their short-time anodic formation and during long-time repair-anodization in oxidizing electrolyte. The TiO2 anodic films evolved from an initially homogeneous amorphous state by nucleation of nanometer-sized grains and by additional recrystallization into films with islands of nm-grains and eventually with `anatase'-phase oxide nodules. They became embedded in the inner parts of the film, forming a stratified oxide layer and eventually replaced and overgrew most of the original anodic film. During this development the electrochemical parameters and the oxide-dielectrics' property changes were recorded in-situ and interpreted by electrochemical impedance spectroscopy (EIS) and by equivalent circuit (EC) modeling. The permittivity of the films increased as a result of the recrystallization. However, their leakage currents increased also and diminished their useful electric field strength. Mixed TiO2-ZrO2 films were formed by anodizing Ti-Zr alloy. They developed in similar fashion as the TiO2 films, except they remained relatively homogenous during long-time anodization because of their resistance to recrystallization. They maintained a lower leakage current and were better suited as a capacitor dielectric. Another objective was the development of a process to synthesize homogeneous anodes of Ti-Zr anode alloy with high surface enhancement. The process is based on magnesiothermic reduction of titanium and/or zirconium halides and the (open full item for complete abstract)

Committee: Gerhard Welsch Dr. (Advisor); Matthew Willard Dr. (Committee Member); Sehirlioglu Alp Dr. (Committee Member); Merat Francis Dr. (Committee Member) Subjects: Energy; Engineering; Materials Science