Effect of Atmospheric Oxygen on the Electrode Potential and Corrosion Inhibition of Steel in Acid Solutions

Abstract

The resting potential of a steel electrode in an acid electrolyte is usually displaced by the addition of a pickling inhibitor. The positive or negative direction of the displacement has been taken as a criterion of the anodic or cathodic nature of the inhibition. The present work shows that at low levels of inhibition the diffusion of atmospheric oxygen into the electrolyte has only a small effect on the resting potentials, but much larger effects are obtained as the inhibition increases above∼80%. The resting potential measured under such conditions can therefore be a misleading criterion of the relative proportion of anodic or cathodic inhibition.

Parallel results were obtained from experiments on the rate of corrosion. The effect of atmospheric oxygen was small at low levels of inhibition, but above ∼90% inhibition exposure to the atmosphere more than doubled the rate of corrosion.