Ellipsometric study of dissolution of anodic WO3 films in aqueous solutions. 2. Reaction mechanism.
The present work demonstrates that the dissolution of anodic WO3 can be described in terms of general mechanisms already used to account for the physicochemical processes involved in the dissolution of oxides of other metals. The chemical dissolution of anodic WO3 films is characterized by in situ ellipsometry, which has proven to be a suitable technique for studying the processes taking place.(1) The capability of ellipsometry for distinguishing between thickness decrease and hydration and generation of porosity/roughness helps to analyze the thickness range within which reliable kinetic information can be obtained. The dissolution rate law found for anodic WO3 does not depend on the oxide thickness. The dissolution of anodic WO3 films includes hydration and roughening, besides thickness decrease, and is kinetically controlled by the OH- concentration at the oxide/electrolyte interface. Apart from OH-, the specific nature of electrolyte anions seems to play no kinetic role, except in promoting porosity/roughness.
Pérez
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Facultad de Ciencias Químicas, INFIQC-Departamento de Fisicoquímica, Universidad Nacional de Córdoba, Haya de la Torre y Medina Allende, Ciudad Universitaria, 5000 Córdoba, Argentina. mperez@fisquim.fcq.unc.edu.ar
López Teijelo
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