Composition of Corrosion Product Formed on Iron in Selenious Acid Solution

Abstract

The corrosion product formed on iron in a selenious acid solution was studied by combining immersion tests and instrumental analyses such as ESCA, IMMA, electron microscopy and FT-IR spectroscopy. The product formed after exposure for a short period (2∼5min) was mostly FeSeO₃·nH₂O with a small amount of Fe₃O₄ or γ-FeOOH. On the other hand, after exposure for a long time (20hr), the product was iron selenite hydrate only. The corrosion product formed at room temperature (25°C) consisted of dark-green spherical small crystallites, while that formed at a relatively high temperature (60°C) consisted of dark-pinkish well-developed crystals with needle-shape. These two corrosion products had essentially the same composition. The outermost part of the product contained a small amount of impurities and adsorbed contaminants such as H, B, C, Na, Mg, Al, Si, K, Ca and Cu. These contaminants are probably not significant constituents of the corrosion product.