Nonstationary processes that occur on nonpolarizable lead surface in sulfuric acid

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.     

The effect of hydrogen treatment of lead surface on its electrochemical behavior

The effect of the hydrogen treatment of a Pb/PbSO₄ electrode on the electrochemical behavior of a film of lead sulfate in a 2M H₂SO₄ solution is studied using the method of galvanostatic cycling. After the treatment, a lead sulfate film with a high resistance of ΔE/i ≈ 80 Ohm cm2 is found to appear on the lead surface. The increased resistance of the film can be attributed to the complete consumption of the hydrogen ions in the cathode reaction; it significantly decreases due to the ions’ diffusion from the solution. During the cycling (the first pulse is the hydrogen treatment, the second is the anodic formation of PbSO₄), the state of the surface of the electrode is not stabilized; it is rather modified according to the irregular periodic law. The nature of the change depends on the value of the potential, which switches the anodic pulse, as well as on the mode of the hydrogen treatment. The relaxation process of the currentless electrode potential after the hydrogen treatment shows the dynamics of the film growth with an abrupt increase in its resistance during the crystallization of a supersaturated solution in the pores.     

Mechanism of Inhibition of Corrosion of Steel in the Presence of Sulfate-Reducing Bacteria

We consider the electrochemical and microbiological aspects of microbe-induced corrosion of low-carbon steels caused by sulfate-reducing bacteria and its inhibition by organic surfactants. We propose relations that take into account the influence of the main products of the vital activity of sulfate-reducing bacteria (H₂S and HS^–) on the cathodic and anodic reactions of the corrosion process. The evaluation of the adsorption properties of organic surfactants and analysis of their influence on the kinetics of oxidation-reduction reactions enable one to develop high-performance inhibitors of microbe-induced corrosion of steels in aqueous aggressive media containing sulfate-reducing bacteria.