Affordable Access

Publisher Website

The corrosion and passivation of iron in the presence of halide ions in aqueous solution

Authors
Journal
Corrosion Science
0010-938X
Publisher
Elsevier
Publication Date
Volume
19
Issue
11
Identifiers
DOI: 10.1016/s0010-938x(79)80113-4

Abstract

Abstract The anodic dissolution behaviour of iron in halide solutions has been studied with both stationary and rotating electrodes. With stationary electrodes active dissolution kinetics are observed, whereas with rotation a pronounced active/passive transition occurs. A distinct pitting potential ( E c ) was noted in each solution, the value of E c increasing in the order I>Br>Cl>F. Halide ion concentration and electrode velocity did not have any effect on the value of E c , indicating that the kinetics of pit initiation are independent of mass-transfer effects. During anodic dissolution at potentials more regative than E c , an inhibiting effect was noted, the degree of which depended on the atomic radius of the anion. A model is suggested which involves three electrode reactions of iron with the electrolyte: (1) Active dissolution involving the well-known FeOH + (ads) rate-determining step. (2) Above the passivation potential, increased reaction of the metal surface with hydroxyl ions causes passivation due to the enhanced access of OH − to the surface and accelerated removal of solvated protons caused by rotation and a thinning of the diffusion layer. (3) At the pitting potential, direct reaction of the metal with electro-adsorbed halide ions produces pit initiation and growth by a complex ion formation reaction not possible at lower electrode potentials.

There are no comments yet on this publication. Be the first to share your thoughts.