Passivity of titanium: part II, the defect structure of the anodic oxide film
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The kinetic parameters of the formation of the anodic titanium oxide film on Ti in 0.5 M H2SO4 have been determined using potentiostatic polarization, electrochemical impedance spectroscopy (EIS), and the Mott-Schottky analysis (MSA). The findings are interpreted in terms of the point defect model (PDM). The oxygen vacancy is found to be the dominant point defect under all conditions studied with the metal interstitial being the minority defect. From MSA, the oxygen vacancy concentration was found to exponentially decrease from 5.03 × 1020 to 3.91 × 1019 cm−3 as the film formation voltage was increased from 2.24 to 10.24 VSHE. Using a value for the electric field strength of 1.734 × 106 V/cm, as determined by previous modeling with the PDM together with a fitted expression for the donor density and film formation potential, the oxygen vacancy diffusivity was found to be 2.6 × 10−16 cm2/s.
KeywordsTitanium Anodic oxide film Point defect structure Passivity
Investigator #2 gratefully acknowledges the partial support of this work by the FUTURE (Fundamental Understanding of Transport Under Reactor Extremes), an Energy Frontier Research Center funded by the U.S. Department of Energy (DOE), Office of Science, Basic Energy Sciences (BES) (neutron scattering studies).
This work received support from the Pennsylvania State University by the US Department of Energy through Grant No. DE-FG02-01ER15238 and by the Hyundai Motor Company.
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