Effect of Dissolved Chlorine on the Pitting Behavior of 304L Stainless Steel in a 0.5 N NaCl Solution.

摘要

Electrochemical experiments were performed on a 304L stainless steel alloy in a 0.5 N Sodium Chloride solution as a function of chlorine content (0-180 mg/1). Experiments performed included a measurement of the corrosion potential as a function of time, the determination of the breakdown potential, and of the repassivation potential, utilizing cyclic polarization curves; and the use of a scratching electrode technique to measure the kinetic aspects of the breakdown of passivity. The addition of chlorine to a solution of pH5 in the concentration range of 20-60 ppm chlorine resulted in a significant shift in the corrosion potential in the noble direction. At higher concentrations of chlorine the corrosion potential shifts back toward that observed without chlorine additions. Chlorine also results in a monotonic shift in the breakdown potential, suggesting that the passive film is rendered more stable against the initiation of localized corrosion. However, the repassivation potential exhibits a minimum in the chlorine concentration range where the corrosion potential exhibits a maximum. This data suggests that the rate of propagation of localized corrosion should be maximized in this chlorine regime (20-60 mg.1). When scratching electrode experiments are performed, the number of pits is minimized but the size of the pits is maximized. Keywords: Diffusion; Liquid phases; Solids; Films. (AW)