An electrochemical and surface analytical study of the formation of nanoporous oxides on niobium

Bogdan Tzvetkov (1) , Martin Bojinov (1) , Assen Girginov (1) , Nadine Pébère (2)

1 University of Chemical Technology and Metallurgy [Sophia]
2 CIRIMAT - Centre interuniversitaire de recherche et d'ingenierie des matériaux

In the present paper, the anodization of Nb in mixed sulphate + fluoride electrolytes resulting in the formation of a nanoporous oxide film has been studied. Chronoamperometry and electrochemical impedance spectroscopy have been employed to characterise in situ the kinetics of the oxidation process. In addition, the evolution of the layer structure and morphology has been followed by ex situ scanning electron microscopy. Particularly, local electrochemical impedance spectroscopy has been used to discern between the mesoscopic 2D and 3D distributions of time constants at the electrode surface. The similarity between local and global impedance spectra during anodic oxidation of Nb demonstrates the presence of an inherent 3D distribution of the high-frequency time constant, which is interpreted as in-depth variation of the steady state conductivity of the passive film. The experimental and calculational results are discussed in relation to the micro- and nanoscopic structure of the formed oxide.

Mots clés: Anodic oxidation; Porous oxide; Local electrochemical; impedance spectroscopy; 2D and 3D distributions

Domaines: Matériaux

Bogdan Tzvetkov, Martin Bojinov, Assen Girginov, Nadine Pébère. An electrochemical and surface analytical study of the formation of nanoporous oxides on niobium. Electrochimica Acta, 2007, vol. 52, pp. 7724-7731. ⟨10.1016/j.electacta.2006.12.034⟩. ⟨hal-00806031⟩