Nonstationary processes that occur on nonpolarizable lead surface in sulfuric acid

Abstract

The dynamics of variations in the currentless potential of a lead electrode in 2 M solution of sulfuric acid after cathode treatment by liberating hydrogen is studied. It is shown that, in the course of cathodic polarization, the liberation of hydrogen is accompanied by the formation of a film of lead sulfates due to corrosion that occurs on the metal surface. The major component of the measured potential is the voltage drop in the sulfate film. Two explanations for the simultaneous occurrence of the processes of hydrogen liberation and lead corrosion, which is impossible from the viewpoint of thermodynamics, are proposed. The first explanation is based on the electrical nonuniformity of the surface, which results from current localization at single active points (microzones), and on the absence of a protective cathodic potential at a distance from these points. The second explanation involves the voltage drop in the sulfate film, which is the component of the potential measured at the film–electrolyte interface. At the metal–film interface, the anodic polarization of the metal surface can occur, while nominally cathodic polarization takes place. Upon current interruption, the intricate processes of the growth and recrystallization of the sulfate film accompanied by the stepwise passivation of lead continue to occur. The limiting process for the corrosion system is the anodic reaction of the dissolution of lead.