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

Abstract

The effect of fluoride ion on crevice corrosion for FPM/matal of type 304 stainless steel was studied in terms of critical potential, V_crev, in neutral NaCl/NaF mixed solutions at 303K. It was found that fluoride ion has inhibitive effect to the chloride ion-induced crevice corrosion. Linear relationships were found to exist between the logarithm of the minimum F^- concentration required to inhibit crevice corrosion and the logarithm of Cl^- concentration at constant potentials. For a given F^- concentration, the minimum Cl^- concentration required to induce crevice corrosion is given by the following equation:
log[NaCl]=αlog[NaF]+β [molarity]
This equation suggests that Cl^- and F^- competitively adsorbed on the metal surface, which can be described by Freundlich adsorption isotherm.