Evaluation of Repassivation Behavior of Pits on Stainless Steel with Potential Response Method

Abstract

A new method has been proposed for evaluation of repassivation behavior of pits formed on stainless steel. The conventional cyclic polarization technique is less effective for detailed examination of repassivation because of difficulty of controlling the extent of growth of pits in spite of the fact that repassivation potential varies with the depth of pits. According to the new method, a specimen is exposed in the iron (III) chloride solution for predetermined duration to cause pits with desired maximum depth and then subjected to potential control.
After the designed control of potential, the specimen was released for open circuit condition to follow the potential. The potential response well reflected if pits repassivated during the potential-controlled period. This method is effective for the detailed study of repassivation behavior of pits since it enables determination of repassivation condition as a function of potential, time and pit depth. This technique was applied to study the effect of agitation of a solution or ultrasonic irradiation on the repassivation behavior of pits. The result showed that repassivation kinetic of pits was not influenced by such physical stimulation.