The Effect of Amines on the Electrode Potential of Mild Steel in Tap Water and Acid Solutions

Abstract

Potentials of SAE 1020 steel were measured in and tap water, each with added amines. The steady state potential was found to be a function of the nature and concentration of the amine additives. The effect could not be completely reversed in all cases when the metal was placed in amine‐free solutions. Anodic and cathodic polarization measurements in the presence of the amines showed that both anodic and cathodic areas were affected by the inhibitor. Decomposition potential curves for those systems pointed to the same conclusion.The data are discussed in terms of a generalized theory of corrosion inhibition. It is postulated that the measured changes are due to adsorption of the polar compounds on the metal surface. The lack of complete reversibility is attributed to the heterogeneity of the surface giving rise to a variety of adsorption energies. Inhibition at the anodic areas is considered to be due to an actual reduction in tendency for the iron ions to go into solution due to a displacement of electrons from the metal toward the positively charged particle rather than toward the cathodic areas within the metal. The amines may act as inhibitors at the cathodic areas by virtue of diffusion effects, increased resistance, and overvoltage.