Composition of Anolyte Within Pit Anode of Austenitic Stainless Steels in Chloride Solution

Abstract

The acidity and the concentrations of metal and chloride ions in the solution within a pit were measured for some austenitic stainless steels using an artificial pit activated galvanostatically in 0.5N NaCl solution at 70 C (158 F). The pH and the chloride ion concentration changed in a range of pH -0.13 to 0.80 and 3.78 to 6.47N, respectively. The lower pH value rather than those predicted from the thermodynamical calculation seems to be explained by the effects of hydroxychloro-complexes and highly concentrated chloride solution. The critical potential and the critical anodic current density for the pit growth are discussed in relation to the chemical and electrochemical characteristics for the anolyte within a pit.