The combined use of scanning vibrating electrode technique and micro-potentiometry to assess the self-repair processes in defects on “smart” coatings applied to galvanized steel

Model weldable primer coatings for galvanized steel were modified with submicron containers loaded with corrosion inhibitors. This procedure aims at introducing a new functionality in the thin coatings self-repair ability. The assessment of this property demands new protocols and new approaches, combining conventional electrochemical methods with electrochemical and analytical techniques of micrometer spatial resolution. Thus, in this work model defects were created in the coatings by using a focused ion beam (FIB). The coated samples, containing the model defects, were immersed in a NaCl 0.05 M solution and the corrosion inhibition ability was studied using the scanning vibrating electrode technique (SVET) and the scanning ion-selective electrode technique (SIET). SVET–SIET measurements were performed quasi-simultaneously. Qualitative chemical analysis was performed by SEM combined with EDS. Complementary studies were carried out by electrochemical impedance spectroscopy (EIS) to assess the effect of the containers filled with corrosion inhibitors on the barrier properties of the coatings. The electrochemical results highlight the importance of the combined use of integral and localized electrochemical techniques to extract information for a better understanding of the corrosion processes and corresponding repair of active microscopic defects formed on thin coatings containing inhibitor filled containers.

Research highlights
► Weldable primers were modified with submicron containers loaded with corrosion inhibitors.
► SVET and micro-potentiometry were used to study the corrosion inhibition ability.
► Submicron containers do not damage the barrier properties of model primers.
► Artificial defects of 50μm × 50 μm in a coating can be easily analyzed by SVET and SIET.
► Inhibiting dissolution of sacrificial Zn may result in detrimental dissolution of Fe.