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

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 Epit shifts to positive values by increasing molybdate concentration. It is found that the increase in Epit could not be referred to the changes in DCcrit and DCsat, since these values are slightly reduced by adding Molybdate to the solution. In contrast, the active dissolution rate of the metal assessed by idiss,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 idiss,max/idiff,crit (which reflects Ecrit), and idiss,max/ilim (which reflects Esat). Therefore, increasing the Ecrit and Esat at the pit growth process is responsible for the observed raising of the Epit in presence of Molybdate.