Effect of Molybdate on the Stability of Pit Growth in Duplex Stainless Steel 2205

Abstract

In the present study, the criteria of pit stabilization and salt formation have been investigated for DSS 2205 using the lead-in-pencil electrode in order to explore the contribution of molybdate in stable pit growth. Results show that the E pit shifts to positive values with increasing molybdate concentration. It is found that the increase in E pit could not be explained by the changes in DC crit and DC sat, since these values are slightly reduced by adding molybdate to the solution. In contrast, the active dissolution rate of the metal assessed by i diss,max is hindered in the presence of molybdate ions. Therefore, it is proposed that the mechanism for the inhibitory influence of molybdate can be attributed to an increment in the intersection point of i diss,max/i diff,crit (which reflects E crit), and i diss,max/i lim (which reflects E sat). Therefore, increasing the E crit and E sat at the pit growth process is responsible for the observed raising of the E pit in presence of molybdate.