Self-healing coatings with multiple functionalities for the corrosion protection of metals

Lately different incorporation methods for inhibitors into organic coatings are described in literature [1,2]. Direct addition has several well-known drawbacks (incompatibility with the coating, uncontrollable inhibitor leaching, etc.). Alternatively inhibitors are accommodated in containers like Layered Double Hydroxides (LDH). In an encapsulation like this, not only the inhibitor release can be controlled and restricted depending on the pH, but also higher concentrations of insoluble substances in coatings can be achieved. In this publication a comparison of different incorporation methods for corrosion inhibitors for hot dip galvanized steel into self-healing organic coatings will be presented. Firstly the self-healing ability of an Polyesterurethaneacrylate coating containing these inhibitor recipients will be shown. Secondly their leaching out process will be studied with advanced local electrochemical methods. Scanning Vibrating Electrode Technique (SVET) allows the measurement of the electric field in solution by means of a vibrating microelectrode. As a result potential or – through calibration – ionic current density mappings can be recorded. Scanning Ion-selective Electrode Technique (SIET) is a micro-potentiometric technique which allows the local determination of individual ion concentrations. Other ions are avoided through an ion-exchange liquid in the tip of the microelectrode. With Scanning Electrochemical Microscopy (SECM) the local concentration of one selected electro-active species is monitored. By means of a redox reaction cycle between the ultra-microelectrode tip and the surface the discrimination of areas of different substrate activity is possible. All these techniques enable one to follow the leaching out process in-situ and with high spatial resolution revealing information about its mechanism.