The surface charge accumulation model applied to antimony oxide films

O. E. LINAREZ PÉREZ; M. LÓPEZ TEIJELO

Simposio; 10th Symposium on the passivation of metals and semi-conductors and the properties of thin oxide layers; 2011

The investigation of the processes of formation of passive films on valve metals and their characterization are of great importance from both scientific and technological point of views. On valve metals, barrier-type oxide films with low electronic conductivity grow by ionic migration and diffusion. When valve metals are anodically polarized, oxide films grow irreversibly by a field-assisted migration of ions through the film. Metals such as titanium, niobium, zirconium, tantalum and tungsten, among others, have been extensively studied in the past due to their numerous applications. In addition, studies on the kinetics of growth, stability and electronic properties of passive films on these metals have been carried out because of its importance from the point of view of corrosion. On the other hand, antimony passive behaviour has been much less studied. Recently, we have fully characterized the kinetics of anodic growth, morphology, chemical composition and stability of antimony oxide films grown in buffered phosphate electrolytes by electrochemical methods, in-situ ellipsometry, x-ray photoemission spectroscopy (XPS) and atomic force microscopy1,2. In the first stages of anodization, soluble species formation followed by formation of a highly hydrated film takes place, while at higher potentials, growth of an anisotropic anodic oxide film following a ?high-field? mechanism takes place. Oxygen evolution occurring simultaneously with oxide growth is also detected. XPS measurements indicated that anodic films are composed only by Sb2O3. Hydration as well as phosphate ions incorporation into the film was also demonstrated. Ellipsometric results indicate that anodic films dissolve in the electrolysis media. The stability of passive antimony oxide films at open circuit was also characterized and the parameters for the ?high-field? mechanism as well as dissolution current for different conditions were obtained. Regarding the electrical properties of anodic layers formed on pure antimony a certain number of investigations have been made3,4. Nevertheless, a comprehensive study of the anodic behaviour of antimony in solutions of different composition and a complete description of the electrical properties of oxide films formed by antimony anodization have not be given. In order to achieve a better understanding of the antimony/electrolyte system, electrochemical impedance data obtained for anodic films formed in different phosphate concentrations as well as grown up to distinct potentials are discussed with reference to the surface charge approach for the formation/dissolution of barrier anodic oxide films, which provides a mechanistic interpretation of the impedance spectra, and the applicability of the model for the different conditions is assessed. References 1 O.E. Linarez Pérez, M.A. Pérez, M. López Teijelo, J. Electroanal. Chem. 632 (2009) 64. 2 O.E. Linarez Pérez, M.D. Sánchez, M. López Teijelo, J. Electroanal. Chem. 645 (2010) 143-148. 3 M. Bojinov, I. Kanazirski, A. Girginov, Electrochim. Acta 41 (1996) 2695-2705 4 M. Metiko?-Huković, R. Babić, S. Brinić, J. Power Sources 157 (2006) 563-570.