Use of Differential Capacitance Measurements To Predict the Inhibitive Behavior of Organic Nitrogen Compounds

Abstract

Abstract Using an impedance bridge, capacitance measurements were made between a pool of mercury as an anode and a dropping mercury cathode. Differential capacitance measurements derived from a series of tests at 22 to 165 C (72 to 330 F) of organic inhibitors diluted with lease condensate or diesel fuel and in a 0.1 M NaCl O4 electrolyte were used to rate probable effectiveness of typical long chain diamine salt, long chain naphthenic acid and a substituted imidazoline salt. Results indicate that inhibitive action is to some degree controlled by freedom of movement of the inhibitor molecule in the solution and at the surface of the metal and that actual adsorption on the metal surface depends on its polarization. Dipolar molecules that are normally adsorbed with positive end of the dipole to the metal will tend to be adsorbed on the cathodic side of the electro-capillary maximum; those with the negative end toward metal will be most strongly adsorbed on the anodic side. There is a lower concentration limit below which inhibitor effectiveness will diminish.