Kinetics of growth and properties of anodic antimonium oxide films

O. E. LINAREZ PÉREZ; M. LÓPEZ TEIJELO

Cancún, México.

Congreso; The 210th Meeting of The Electrochemical Society, Inc.; 2006

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 on 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 Sb in a wide range of conditions for oxide growth. Different electrolytes (phosphate, sulphate and chloride) in a wide range of pH and concentration were employed. Nature of the cation was also analysed. In addition, the morphology of the anodic films was obtained by AFM. The j/E potentiodynamic response is complex and dependent of the anion of the electrolyte. The anodic growth is explained in terms of the ?high-field? migration model and the voltammograms are simulated for this model taken into account homogeneous or preferential chemical dissolution processes coupled with the growth. The impedance spectra show an inductive response at intermediate frequencies aside from the capacitance and resistance corresponding to the dielectric properties of the film, which is associated with the accumulation of negative surface charge at the oxide/solution interface [2]. This effect is also strongly dependent on pH and cation nature.AFM images reveal that morphology of oxide films is dependent on concentration, polarization time and electrolyte. Porous films are obtained in chloride solutions.An interpretation in terms of passive electronic elements in a complex electrical equivalent circuit is given, 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.References[1] D.D. Macdonald, J. Electrochem. Soc. 139 (1992) 3434.[2] M. Bojinov, Electrochim. Acta 42 (1997) 3489.Acknowledgements: Financial support from CONICET, ANPCyT, and SECYT-UNC from Argentina is gratefully acknowledged.