Mechanism of Corrosion of Low-Carbon Steel in 1 M Solutions of Hydrochloric Acid Saturated with Oxygen

Potentiometry and voltammetry with a rotating disk electrode are used to study the corrosion of St3 low-carbon steel in 1 M HCl containing dissolved molecular oxygen from the mass loss of metal samples in a static and dynamic aggressive environment. It is shown that molecular oxygen in the acid solution and the transition from the static to dynamic state of an aggressive medium accelerates the corrosion of steel. The corrosion of steel in this environment includes the anodic ionization of steel in the kinetic region and two partial cathodic reactions: the evolution of hydrogen and the reduction of dissolved molecular oxygen, characterized by kinetic and diffusion controls, respectively. Modeling the effect the hydrodynamic mode of the motion of a corrosive medium has on the rate of the cathodic reduction of molecular O-2 on low-carbon steel using the Levich equation and comparing the results to experimental data suggests with high probability that in the flow of a corrosive medium it mainly proceeds according to the scheme O-2 + 2H(+) + 2e = H2O2. The values of the true kinetic currents of the cathodic reaction are estimated for a steel disk electrode in 1 M HCl that is freely aerated with air and forcibly aerated with gaseous O-2. The effective coefficient of diffusion of dissolved molecular O-2 in 1 M HCl is established.