In-situ Observation of Chloride Ion in Iron Pit

Abstract

Pitting corrosion of pure iron in borate buffer solution was studied by in-situ technics using chloride isotope ³⁶Cl. Relationships between chloride ion concentration and current density in pit during pitting corrosion was discussed. Some results are summarized as follows.
(1) Pits growth process is divided into two steps by the variation of chloride ion concentration and pitting current with time.
The first step: chloride ion concentration on a pit surface (γ_p) increases linearly with time while the current density (i_p) stays constant.
The second step: γ_p stays at a constant, on the other hand, i_p decreases gradually with time.
(2) Both of γ_p and i_p increase with external electrode potential.
(3) Also γ_p and i_p increase with a logarithmic low of the chloride ion concentration in a bulk solution.