Photo-induced processes on ZnO and its possible impact on cathodic delamination of organic coatings on galvanised steel

Abstract

The influence of sunlight on cathodic delamination of polymer-coated, galvanised steel is considered regarding the semiconductor properties of zinc passive layers. Zinc and galvanised steel were studied potentiostatically in O2-rich, moderate alkaline electrolyte under UV-, violet and green light. Currents increased instantaneously, intensity- and wavelength-dependant according to the photoeffect. After electrolyte preconditioning of galvanised, pre-treated and coated (6 µm) steel, light positively shifted the open-circuit-potentials (ocp). Mechanistic considerations are provided using Mott-Schottky-plots and Chopped Linear Sweep Voltammetry (CLSV). Under certain conditions, oxygen reduction reaction (ORR) intensification is found and should be considered in future studies of paint adhesion on zinc.