Role of Halides on the Passivation of Iron in Alkaline Buffer Solutions

Abstract

Cyclic voltammetric studies were carried out on pure iron in alkaline borate and phosphate buffer solutions at pH 10.8. At higher potentials, on anodic polarization, iron forms FeB 4O7 and FeOOH in borate buffer, and FeHPO 4 in phosphate buffer which got converted to higher valency phosphates. In phosphate solutions, in presence of halides, the interfacial diffusion layer turned to be cation selective outer sublayer and an anion selective inner sublayer, and in borate solutions a precipitate layer of metal oxyhydroxide was formed, which was anion selective, and anions adsorb on this.