Kinetics of growth and properties of anodic oxide films on "valve" metals.

O. E. LINAREZ PÉREZ; M. LÓPEZ TEIJELO

Thessaloniki, Greece

Congreso; 55th Annual Meeting of the International Society of Electrochemistry; 2004

The anodic film growth on metals is a major problem in electrochemistry, both from the fundamental and practical point of view. Despite considerable work has been carried out, no universally accepted model in the case of the "valve" metals has been devised to explain the mechanism of anodic oxide growth.On typical valve metals the growth has been described in terms of the high field model (HFM) as proposed by Verwey and Cabrera and Mott, the point defect model (PDM) developed by Macdonald [1] and more recently by the model proposed by Bojinov [2] which is based in a surface charge approach. Nevertheless, in most cases the films are considered homogeneous in thickness and the effect of the formation of pores and/or pits has not been considered in detail.In this paper, galvanostatic and potentiodynamic methods were combined with electrochemical impedance spectroscopy (EIS) measurements as well as the ellipsometric response in order to study the electrochemical behaviour of some valve metals (mainly Sb and Bi) in different electrolytes and in the presence of aggressive anions (Cl-) in a wide range of conditions for oxide growth. In addition, the morphology of the anodic films was obtained by AFM images.An interpretation in terms of passive electronic elements in a complex electrical equivalent circuit and the significance of the elements is assigned. For the interpretation of the results, the values for the oxide thickness obtained by ellipsometry as well as the morphologic and structural characteristics of the porous films are employed in order to discuss the physical model of the overall interface.[1] D.D.Macdonald, J.Electrochem.Soc., 139, 3434 (1992).[2] M. Bojinov, Electrochim. Acta 42, 3489 (1997).Acknowledgements: We thank CONICET, SECYT-UNC, Agencia Córdoba Ciencia S.E. and ANPCyT for their financial support.