The effect of chloride and sulfate anions on the iron dissolution rate in neutral and nearly neutral media

Analysis of results of steady-state potentiostatic measurements on iron in the neutral and nearly neutral borate solutions is complicated by the fact that the metal is in the state of active-passive transition near the free-corrosion potential. This difficulty is overcome using the method of neural network simulation. The study of the behavior of neural-network model shows that chloride and sulfate ions can promote or inhibit iron dissolution depending on their concentration and the pH value of solution. The ambiguous effect of anions is explained by the fact that, when they are adsorbed at the metal, they prevent its cations from passing to the solution, and, entering into the metal-water adsorption complexes, they assist the decomposition of complexes thus promoting the dissolution. Sulfate ions, compared with chloride ions, are, probably more adsorption-active with respect both to iron and to water adsorbed on it.