Pitting corrosion of lead in sodium carbonate solutions containing NO3-ions

Pitting corrosion of Pb in Na2CO3 solutions (pH = 10.8) containing NaNO3 as a pitting corrosion agent has been studied using potentiodynamic anodic polarization, cyclic voltammetry and chronoamperometry techniques, complemented with scanning electron microscopy (SEM) examinations of the electrode surface. In the absence of NO3-, the anodic voltammetric response exhibits three anodic peaks prior to oxygen evolution. The first anodic peak A(1) corresponds to the formation of PbCO3 layer and soluble Pb2+ species in solution. The second anodic peak A(2) is due to the formation of PbO beneath the carbonate layer. Peak A(2) is followed by a wide passive region which extends up to the appearance of the third anodic peak A(3). The later is related to the formation of PbO2. Addition of NO3- to the carbonate solution stimulates the anodic dissolution through peaks A(1) and A(2) and breaks down the dual passive layer prior to peak A(3). The breakdown potential decreases with an increase in nitrate concentration, temperature and electrode rotation rate, but increases with an increase in carbonate concentration and potential scan rate. Successive cycling leads to a progressive increase in breakdown potential. The current/time transients show that the incubation time for passivity breakdown decreases with increasing the applied anodic potential, nitrate concentration and temperature. (C) 2004 Published by Elsevier Ltd.