Effect of Fluoride Ion on the Pitting Corrosion of Type 304 Stainless Steel in Neutral NaCl Solution

Abstract

Effect of fluoride ions on the pitting behavior of type 304 stainless steel has been studied in neutral chloride solutions at 303K. It has been confirmed by means of potentiodynamic polarization measurements that fluoride ions inhibit the chloride ion-induced pitting corrosion and promote the uniform dissolution of the steel. A linear relationship was found to exist between the logarithm of the minimum F^- concentration required to inhibit pitting and the logarithm of the Cl^- concentration. For a given F^- concentration, the critical Cl^- concentration required to induce pitting is given by the following equation:
log[Cl^-]=1.36log[F^-]-0.08 [molarity]
This equation suggests that there are Cl^-and F^-ions competitively adsorb on the surface, which can be described by Freundlich's adsorption isotherm.