Concentration of Cl^- and pH Changes within Crevice for Type 304 Stainless Steel in NaCl/NaF Solution

Abstract

Concentrating behavior of hydrogen and chloride ion in the anolyte during electrolysis for type 304 stainless steel was studied using the cell separated with a glass filter in various concentrations of NaCl/NaF mixed solution.
In NaCl solutions, charge passed during electrolysis, Q was in the linear relationship with pH decreasing, while two-stages in concentrating process with slow and then fast rate were observed for Cl^-. Decreasing pH of the anolyte was mainly dependent on the increasing of Cl^- concentration.
NaCl/NaF mixed solutions, the rate of decreasing pH and increasing Cl^- concentration in the anolyte during electrolysis decreased with increasing NaF concentration in constant concentrations of NaCl solution.
The results suggest that fluoride ions act as a inhibitor to chloride ions-induced crevice corrosion for stainless steel.