Anodic Dissolution of Iron in Acidic Sulfate Electrolytes: I . Formation and Growth of a Porous Salt Film

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Abstract
High rate anodic dissolution of iron in a sulfuric acid electrolyte causes the solution near the electrode surface to become supersaturated in ferrous sulfate. Ferrous sulfate crystals precipitate on the electrode surface when the surface concentration exceeds a critical value. This critical value is about 1.8 times greater than the saturation concentration of ferrous sulfate. Continued precipitation results in the growth of a porous ferrous sulfate film on the surface. A mathematical model describing the initial formation and subsequent growth of this salt film is developed for a rotating disk geometry. A perturbation analysis serves as the foundation of this model. The salt film thickness is nearly proportional to the square root of time shortly after the initial precipitation. The film growth rate falls off sharply in time following this initial period because of depletion of ferrous ions from the solution adjacent to the electrode surface.
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