THE ANODIC BEHAVIOR OF HOT-GALVANIZED ZINC LAYER IN ALKALINE-SOLUTION

Abstract

The anodic behaviour of a hot-galvanized zinc layer characterized by three spangle sectors has been studied in comparison with pure bulk zinc in KOH solution using potentiodynamic polarization and impedance methods. The hot-galvanized zinc layer showed a higher anodic dissolution current than the pure bulk zinc over all potential ranges, due largely to the alloying elements, Al and Pb. Also, the pure bulk zinc gave no notable anodic current peak in the passivation potential range, whereas the spangle specimen gave a marked anodic current peak in the potential range -0.75 to -0.65 V(SCE) due to hydrogen adsorbed/absorbed on spangles. From the variation of impedance spectra with exposure time at an applied anodic potential of -1.0 V(SCE), it is suggested that the passivation process on the pure bulk zinc readily attains a steady state, whereas it is disturbed on the spangle specimen by the adsorbed/absorbed hydrogen, thus proceeding in an unstable manner.