Effect of oxygen reduction on the retention of passivity by 430 stainless steel in naturally aerated dilute sulphuric acid

The role of the cathodic reaction of oxygen reduction in extending the passivity retention time (t_r) of conventional 430 stainless steel (F e-) 7Cr) in naturally aerated dilute sulphuric acid has been demonstrated. Theoretically evaluated and experimentally obtained values of t_r after passivation at a potential corresponding to the middle of the passive region of the anodic polarisation curve and experimental values of t_r after passivation at a potential within the cathodic loop region are compared. The effect of oxygen reduction on maintenance of passivity, following passivation at the potential corresponding to the middle of the passive region, is small and diminished with an increase in the passivation time. In contrast, this effect is particularly significant if the passivation potential is within the cathodic loop region. The cathodic loop region is thus proposed as a preferable region for the implementation of anodic protection in the studied system as it provides a prolonged aftereffect and, hence, enhances the reliability of protection.