Electrocapillary Action of Corrosion Inhibitors

Abstract

Indelli and Pancaldi¹ and I² have compared some characteristic phenomena occurring at the interface of a dropping mercury microelectrode and electrolyte solutions with phenomena encountered in corrosion inhibition². It was found² that the effectiveness of numerous corrosion inhibitors is reflected in their ability to suppress various polarographic maxima (abnormal current peaks in the current-voltage curves of the mercury microelectrode). In particular, it was shown that the order of relative inhibiting effectiveness of a number of amine inhibitors (for the iron – sulphuric acid system) is the same as that of their effectiveness in suppressing certain polarographic maxima. These amines (both aliphatic and aromatic) were most effective in suppressing maxima corresponding to the negative branch of the electrocapillary curve at which mercury is negatively charged with respect to the solution. This is consistent with Mann's³ conclusion that amines inhibit the corrosion of iron in sulphuric acid by becoming adsorbed on the cathodic areas of this metal. It was thus demonstrated that significant similarities exist between the processes involved in polarographic maxima and their suppression, on one hand, and in metallic corrosion and its inhibition, on the other⁴. Campbell⁵ has also employed polarographic techniques in detecting corrosion inhibitors.