Electrochemical stability of the metal/paint interface: A combined Impedance Spectroscopy and Scanning Kelvin Probe study

摘要

Paints and organic coatings are applied on metallic substrates to protect them from environmental deterioration and for aesthetic reasons. The coatings used these days range from simple single layer to very complex coating systems. With respect to the coating functionality the uptake of water is an important factor for the long term stability of coatings, e.g. the corrosive attack of the underlying metallic substrate. Organic coatings are often analysed by means of Electrochemical Impedance Spectroscopy (EIS). The final purpose of the EIS characterisation of protecting organic coatings is to obtain information about the system properties such as the presence of defects, reactivity of the interface, adhesion and barrier properties to water. Many EIS studies correlate the data with accelerated corrosion tests such as the neutral salt spray test or use aggressive conditions like varied / elevated temperatures for the prediction of service time of coating systems. The transport of hydrated ions along a coating/metal substrate interface is verifiable in humid air when a coating defect is covered with an electrolyte. The process of cathodic delamination is usually dominant on iron, steel and zinc substrates in such environments and can be monitored by a Scanning Kelvin Probe (SKP), which is a suited method for non-destructive measurements of electrode potentials at buried coating/metal interfaces.