The delamination of polymeric coatings from steel. Part 1: Calibration of the Kelvinprobe and basic delamination mechanism

Abstract

In the first part of this study are presented the theory and the experimental techniques which are necessary to investigate the delamination of model coatings on steel. It is shown that the electrochemical reactions taking place at the substrate/electrolyte and substrate/polymer interfaces are responsible for delamination. Due to the fact that the electrochemical reactions are accompanied by changes in the corrosion potential, it is possible to identify and follow the delamination by measuring the corrosion potential as a function of time and local position. Furthermore, it is demonstrated that the Volta-potential difference between a reference metal and the model polymer surface is determined by the corrosion potential, whereas the influence of the Donnan-potential is small and constant. By combining several experimental techniques, like the Scanning Kelvinprobe, Auger electron spectroscopy and mechanical de-adhesion tests, the delamination process is studied in detail and a model is presented, which is based on the existence of a galvanic element at the substrate/polymer interface. The uncoated iron is the local anode, where the iron dissolution predominates, whereas the delaminated part represents the local cathode and, within this area, only the oxygen reduction takes place. The second and third part of this paper deal with an experimental verification of this model.