Effect of sulphide ions on corrosion behaviour of iron in alkaline solutions

Abstract

Potential time curves are constructed for Fe electrodes in aerated NaOH solutions devoid of, and containing, increasing concentrations of S^2- ions. In sulphide free solutions, the steady state potentials are reached from negative values indicating oxide film thickening. Lower concentrations of S^2- ions enhance oxide film thickening and the potential moves more in the noble direction. Increasing the S^2- ion content causes the potential to fluctuate in the active and noble directions during a time span, which depends on the S^2- ion content. The steady state potential of the iron varies linearly with both the concentration of S^2- and pH of solution. A mechanism is proposed for the formation of FeS involving a two electron transfer process.