Effect of fluoride ion on the crevice corrosion for type 304 stainless steel in neutral NaCl solution

The effect of fluoride ion on crevice corrosion for FPM/matal of type 304 stainless steel was studied in terms of critical potential, Vcrev, in neutral NaCl/NaF mixed solutions at 303 K. 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] = α log[NaF] + β [molarity] This equation suggests that Cl- and F- competitively adsorbed on the metal surface, which can be described by Freundlich adsorption isotherm.