Quantitative analysis of local fine structure on diffusion of point defects in passive film on Ti

The diffusion of point defects in passivation determines all physico-electrochemical processes in materials corrosion and protection. In this study, a multiscale quantitative methodology was developed to reveal the diffusivity of oxygen vacancies on titanium surface (similar to 5.0 nm thickness) in 1.0 M H2SO4 solution based on X-ray absorption fine structure (XAFS), combining with electrochemical impedance spectroscopy (EIS) and Mott-Schottky. EIS equivalent circuit exhibits that the high electronic field across passive film is 1.06 x 10(6)V cm(-1). Mott-Schottky space charge capacitance indicates n-type semiconducting film with the donor density of similar to 10(21) cm(-3). Three important structure parameters have been firstly proposed from XAFS theoretical calculation at Ti Kedge to quantitatively describe the point defects transport between metal/film/solution interfaces. The half-jump distance equals half Ti-Ti distance subtly changing with oxidation potentials. The coordination coefficient is defined as the probability of activation jump from Ti-O coordination. And the Debye-Waller factor of structure disorder is related to the donor density of Mott-Schottky. Overall, the diffusivity of oxygen vacancies is in the range of (1.84 -4.71) x 10(-17) cm(2) s(-1) under the electric field, which determines the interfacial equilibrium of passivation and dissolution during potentiodynamic polarization. And the activation energy for motion has a minimum of 0.89 eV at 1.5 V. This multiscale quantitative methodology predicts well the potential dependent steady-state in the corrosive system. (C) 2019 Elsevier Ltd. All rights reserved.