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Properties of spontaneously and electrochemically formed Ti/TiO2 layers in sodium chloride solution

In this study, TiO2 oxide layer on titanium was formed spontaneously (S) and potentiostatically in phosphate buffer solution (EC). It was shown by means of ellipsometry and atomic force microscopy, that the Ti/TiO2 surface is very flat with an average roughness of only 2.3 nm (S) and 3.4 nm (EC) and oxide layer thickness of 4.1 nm (S) and 16.1 nm (EC). The electrochemical properties and corrosion protective effectiveness were examined by means of cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and single crystal electrode (SCrE). The CV indicates the behavior of the valve metals with the anodic formation of the barrier oxide film. The semiconducting properties were studied by Mott- Schottky analysis. A preponderance of anion vacancies, which act as electron donors, over cation vacancies within the passive film formed electrochemically, was established providing n- type semiconducting behavior of the film. The obtained EIS data were modelled utilizing electrical equivalent circuit. The corrosion protection effectiveness value of 94.7 % indicates that the corrosion properties were greatly enhanced upon modification by TiO2 oxide layer. The EIS results also indicate that the oxide film on the Ti surface consists of two layers, an inner barrier layer associated with higher impedance values and responsible for corrosion protection, and an outer porous layer characterized by lower impedance values and lower compactness.

Ti/TiO2 layer ; electrochemistry ; ellipsometry ; atomic force microscopy ; cyclic voltammetry (CV) ; electrochemical impedance spectroscopy (EIS) ; single crystal electrode (SCrE)

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