Contribution to Adsorption of Aromatic Amines on Mild Steel Surface from HCl Solutions by Impedance, UV, and Raman Spectroscopy

Generally, aromatic amines are regarded as effective inhibitors for pickling and acid cleaning of mild steel in hydrochloric acid. Most previous studies advocate the view that the inhibition is a result of adsorption of the π-electron cloud of the aromatic ring on the iron and steel surface through vacant dπ orbital of iron. Later studies indicate a possible electrostatic adsorption or chemisorption due to synergistic action between halide ion and amine molecules as responsible for inhibition. In this paper, an attempt is made to study the mechanism of adsorption by using the concept of ϕ–scale of potential as proposed by Antropov. The potential of zero charge (PZC) of mild steel is studied by two different techniques, and the mechanism of adsorption thus predicted has been found to corroborate the results of in situ Raman scattering study.