AN INVESTIGATION OF THE RELATIVE ROLES OF KINETICS AND TRANSPORT IN CATHODIC INHIBITION

As part of a fundamental study of the mechanism of corrosion inhibitio n in neutral solutions, the kinetics of the cathodic processes in the absence and presence of an inhibitor have been investigated This has b een done by taking the simple inhibition process of Zn(OH)2 formation on an inert surface by reaction between Zn2+ ions in solution and OH- ions cathodically generated on the surface and treating it as an EC me chanism. A mathematical treatment shows that the half-wave potential w ill shift to more positive values in the presence of inhibitor ions, a nd that the extent of the shift will be dependent on the relative rate s of loss of OH- ions by kinetic reaction and by diffusional transport away from the electrode. Results obtained for a renewable electrode s urface, in the form of a mercury drop, show that for the Zn(OH)2 inhib itor system, homogeneous kinetics are much faster than mass transport. Various features of the model system are considered and discussed.