Electrochemical and impedance characterization of passive films on niobium in alkaline and acidic solutions

Dragica B. Camovska, Martin Lj. Arsov, Toma P. Grcev

Abstract


In this work electrochemical characterization of the anodic passive films formed on Nb in alkaline (0.1 – 5 M KOH) and acidic solution (H2SO4) was carried out by cyclic voltammetry and electrochemical impedance spectroscopy (EIS). Potentiodynamic measurements yielded a classical electrochemical passivation curve for both alkaline (KOH) and acidic (H2SO4) solution. In addition EIS-measurements were performed at several potentials in order to characterize the Nb/solution, and/or Nb/Nb2O5 / solution interfaces. The impedance behaviour of the passive films on Nb can be adequately described with a simple EEC; Rel in series with a parallel circuit CPE (Q)Rct(ox). The calculate values of the passive oxide (Nb2O5) films resistivity ranged between 1011–1010 Ω cm with relative dielectric constant ( εf ≈ 14) for KOH-solutions and approx. 2⋅1012 Ω cm for 1 M H2SO4, indicating that the Nb-passive films, generated in acidic solutions, are better corrosion protectors then those formed in alkaline solutions.


Keywords


passive films; niobium; cyclic voltammetry; electrochemical impedance spectroscopy

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DOI: http://dx.doi.org/10.20450/mjcce.2007.263

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Copyright (c) 2016 Dragica B. Camovska, Martin Lj. Arsov, Toma P. Grcev

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