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Anodic oxides on a beta type Nb–Ti alloy and their characterization by electrochemical impedance spectroscopy
Author(s) -
Woldemedhin Michael Teka,
Raabe Dierk,
Hassel Achim Walter
Publication year - 2010
Publication title -
physica status solidi (a)
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.532
H-Index - 104
eISSN - 1862-6319
pISSN - 1862-6300
DOI - 10.1002/pssa.200983324
Subject(s) - materials science , dielectric spectroscopy , passivation , oxide , alloy , cyclic voltammetry , analytical chemistry (journal) , electrochemistry , electrolyte , anode , dielectric , electrode , metallurgy , composite material , chemistry , optoelectronics , layer (electronics) , chromatography
Anodic oxides were grown on the surface of an electropolished (Ti–30 at% Nb) beta‐titanium (β‐Ti) alloy by cyclic voltammetry. The scan rate was 100 mV s −1 between 0 and 8 V in increments of l V in an acetate buffer of pH 6.0. Electrochemical impedance spectroscopy was carried out right after each anodic oxide growth increment to study the electronic properties of the oxide/electrolyte interface in a wide frequency range from 100 kHz to 10 MHz with an AC perturbation voltage of 10 mV. A film formation factor of 2.4 nm V −1 was found and a relative permittivity number (dielectric constant) of 42.4 was determined for the oxide film formed. Mott–Schottky analysis on a potentiostatically formed 7 nm thick oxide film was performed to assess the semiconducting properties of the mixed anodic oxide grown on the alloy. A flat band potential of −0.47 V (standard hydrogen electrode, SHE) was determined, connected to a donor density of 8.2 × 10 17 cm −3 . β‐Ti being highly isotropic in terms of mechanical properties should be superior to the stiffer α‐Ti compound. Its application, however, requires a passivation behaviour comparable or better than α‐Ti which in fact is found.