Effect of chloride concentration and temperature on growth of 1D Pit

Diffusion-controlled pit growth of Super 13Cr stainless steel (S13Cr) was studied using a one-dimensional (1D) pit electrode in 0.1-3 M NaCl solutions at 85 A degrees C. High anodic potential was applied to dissolve 1D S13Cr electrode to a target pit depth. Removal and reprecipitation of salt film on the growing 1D pit was then performed by applying low and high anodic potential in sequence. Finally, the potential of the 1D pit was scanned downward until the pit stopped growing. Diffusion-limited current density measured during pit growth and calculated pit depth were used to determine the product of diffusion coefficient (D) and saturation concentration (C (sat)) of metal ion. Da (TM) C (sat) value decreased as bulk NaCl concentration increased. A pit dissolution model incorporating the effect of bulk NaCl concentration and temperature on D and C (sat) was developed for comparison of the results. The Da (TM) C (sat) value predicted from the pit model resulted in a good fit with the Da (TM) C (sat) value determined experimentally for different NaCl concentrations. To evaluate the effect of temperature on pit growth, Da (TM) C (sat) values obtained in different temperatures were compared. The value of Da (TM) C (sat) was found to increase at higher temperature because of higher C (sat) and larger D.