Passivity breakdown of lead anode in alkaline nitrate solutions

The electrochemical and passivation behaviour of lead in NaOH solutions has been investigated by using potentiodynamic and current/time transient techniques. The E/i curves exhibit active, passive and transpassive regions prior to oxygen evolution. The active region displays one peak, AI. The passivity is due to the presence of a PbO film on the anode surface. The transpassive region exhibits two anodic peaks, AII and AIII. The influence of increasing additions of NaNO3 on the anodic features of lead in NaOH has been studied. The nitrate ions stimulate the active dissolution of lead and tend to break down the passive layer, leading to pitting corrosion. The breakdown potential decreases with an increase in the nitrate concentration and the temperature, bur increases with an increase in both the alkali concentration and the potential scan rate. The current/time transients show that the incubation time for passivity breakdown decreases with an increase in the nitrate ion concentration, the temperature and the anodic potential step. (C) 1998 Elsevier Science Ltd. All rights reserved.