Scanning Kelvin Probe investigations on the delamination of polymeric coatings from metallic surfaces

The corrosion behaviour of zinc- and polymer-coated steel has been investigated from a very fundamental standpoint of view in order to be able to derive the important parameters for suitable short-term corrosion tests, which are capable of simulating outdoor exposure behaviour. A very simple model system has been investigated mainly by in situ Scanning Kelvin Probe measurements and surface analysis after removal of the polymer. Both types of defect have been considered. The delamination from a defect with an intact zinc layer is due to the formation of a galvanic element. The oxygen reduction in the delaminated area leads to an alkalinization of the interface and therefore to an anodic reaction with the consequence of oxide growth. Cathodic delamination is strongly influenced by the CO2-concentration in the atmosphere. The delamination starting from a defect down to steel has shown to be a complex combination of anodic undermining and cathodic delamination, the latter one becoming more important with increasing corrosion time and therefore influencing the cathodic protection of the defect. (C) 2000 Elsevier Science S.A. All rights reserved.