The use of modern electrochemical methods in the development of corrosion protective coatings

Abstract

The industrial corrosion research in the past used descriptive methods for the development of corrosion protective coatings. The legal demand of environmentally friendly coatings and customer demand of high-performance coatings requires the understanding of corrosion effects and the protection against these with organic protective layers. Therefore, actual developments of corrosion protective coatings use modern electrochemical methods for a mechanistic understanding of corrosion processes and there protection. This approach promotes a better description of the interaction between a coating and the corrosion mechanism of the substrate, the development of new coatings with known protection mechanism and additionally actual corrosion protective concepts could be optimized. With the Scanning Kelvin Probe (SKP) the corrosion rate at different geometries and conditions of an E-coated sample has been measured, showing an increased corrosion rate up to seven times higher if the electrolyte layer is very thin. Furthermore, simulated disturbances of pre-treated surfaces have been carried out by a local deposition with mineral oils. By means of SKP measurements, their effect on the pre-treatment layer and on a consecutively applied E-coat were discussed. It was shown that these simulated disturbances could be detected from changes in the Volta potential and that they correlate with noise effects on the coating. Utilizing electrochemical impedance spectroscopy (EIS), an easy way will be presented to measure the “network density” as an indicator of the performance of the corrosion protection by a coating in dependence of its curing temperature, thickness, etc. Finally a new “fast corrosion test” has been developed which measures the delaminated area with EIS after a certain fast climate chamber test. This test correlates quite well with the standard climate chamber test, whereas the expenditure of time could be reduced to 4 days instead of 10–12 weeks.