Oxide/hydroxide films on tin. II: Characterization of the anodic growth in alkaline solutions

The anodic growth of oxide/hydroxide films formed on tin in borate solutions (pH 8.9) has been studied. At potentials more positive than −0.2 V (SHE), oxide film growth occurs by an activation-controlled ionic condition under the influence of a high electric field across the film according to an exponential law as on valve metals. Optical properties of the anodic oxide films have been obtained by “in situ” ellipsometry. Tin oxide/hydroxide films are practically transparent and highly hydrated. Electrical properties of tin oxide layers have been obtained by electrochemical impedance spectroscopy. Impedance spectra are explained in terms of a simple physical model assuming that oxide layer behaves as an inhomogeneous single-layer film.