INVESTIGATIONS OF NONLINEAR PROCESSES BY TRANSIENTS - KINETICS OF DISSOLUTION OF INHIBITOR LAYERS ON COPPER

The dissolution of inhibitor layers of AHT (3-amino-5-heptyl-1,2,4-triazole) on copper wires in 0.5 M H2SO4 was studied by potentiostatic current and capacity transients in a time range from 10 mus to 1000 s. The potential dependent transients show three characteristic regions corresponding to different transfer controlled processes. For short periods an almost constant current of inhibited corrosion through a metastable inhibitor layer is observed. In the second region the dissolution of this layer causes a strong increase in copper corrosion, which was taken as a direct measure of the desorption process. The electrode capacity, C, increases correspondingly. The dissolution itself is not accompanied by a notable charge transfer and, hence, cannot directly be monitored. The last region is dominated by an almost constant active copper dissolution current. The layer dissolution in the second region starts with an inhomogeneous nucleation process. Initially, holes are generated stochastically in the AHT layer and form nuclei of corrosion pits on the copper surface. Based on this model the complete transients can be calculated.