A mechanism for the formation of annealed compact oxide layers at the interface between anodic titania nanotube arrays and Ti foil |
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Authors: | Chien-Chon Chen Wen C Say Sheng-Jen Hsieh and Eric Wei-Guang Diau |
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Institution: | (1) Department of Applied Chemistry and Institute of Molecular Science, National Chiao Tung University, Hsinchu, 30010, Taiwan;(2) Department of Energy and Resources, National United University, Miaoli, 36003, Taiwan;(3) Department of Materials & Mineral Resources Engineering, National Taipei University of Technology, Taipei, 10643, Taiwan;(4) Department of Engineering Technology and Department of Mechanical Engineering, Texas A&M University, College Station, TX 77843-3367, USA |
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Abstract: | We propose a mechanism for the growth of crystalline anodic titanium-oxide (ATO) nanochannel arrays based on thermodynamic
considerations and structural imperfections. Both amorphous and crystalline ATO films were obtained from the anodization of
a titanium foil. Amorphous ATO nanotubes have a single-layer form, which makes them inefficient for use in photo-catalytic
and solar-cell applications. Annealed ATO nanotubes are considered non-stoichiometric if the effect of oxygen partial pressure
on the composition is significant. The driving force behind growing crystalline ATO nanotubes is the drawing of oxygen from
the atmosphere to the oxygen site, which consequently decreases the concentration of oxygen vacancies in the anatase phase.
The small ionization energies of titanium ions produce the stoichiometric defects. A diagram showing Gibbs energy and Kroger–Vink
notation to indicate the strong influence of the non-stoichiometric ATO structure is deduced. |
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Keywords: | PACS" target="_blank">PACS 61 46 Fg 64 70 Nd 61 50 Ah |
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