Effect of Bromide Ions on the Electrochemical Behavior of Iron

The kinetics of active anodic dissolution of iron in acidic bromide solutions as well as the evolution of hydrogen have been investigated. The kinetics are analogous to those reported previously [Chin, Nobe, J. Electrochem. Soc., Vol. 119, p. 1457 (1972); Kuo, Nobe, ibid, Vol. 125, p. 853 (1978)] for iron in acidic chloride solutions. In addition to the active region, the anodic behavior in the passive and transpassive regions has been examined. The effects of Br^- on the passive behavior of Fe in 0.5M H₂SO₄ (pH 0.3) are quite similar to the effects of chloride ions, as reported previously [Nobe, Tobias, Corrosion, Vol. 20, No. 8, p. 263 (1964)]. Complete breakdown of passivity occurs at about 2mM Br^-. In neutral and acidic concentrated bromide solutions, high rate electrodissolution of Fe, which appears to be controlled by mass transfer, is obtained above 0 V vs SCE. At potentials just below this region, a black salt film completely covers the Fe surface. However, at potentials above approximately 2 V, a bright, shiny surface is observed.