Y. González-García

In Situ Scanning Electrochemical Microscopy (SECM) Detection of Metal Dissolution during Zinc Corrosion by Means of Mercury Sphere‐Cap Microelectrode Tips

This work presents a scanning electrochemical microscopy (SECM)-based in situ corrosion probing methodology that is capable of monitoring the release of zinc species in corrosion processes. It is based on the use of Hg-coated Pt microelectrodes as SECM tips, which offer a wider negative potential range than bare platinum or other noble-metal tips. This allows for the reduction of zinc ions at the tip to be investigated with low interference from hydrogen evolution and oxygen reduction from aqueous solutions. The processes involved in the corrosion of zinc during its immersion in chloride-containing solutions were successfully monitored by scanning the SECM tip, set at an adequate potential, across the sample either in one direction or in the X-Y plane parallel to its surface. In this way, it was possible to detect the anodic and cathodic sites at which the dissolution of zinc and the reduction of oxygen occurred, respectively. Additionally, cyclic voltammetry (CV) or constant potential measurements were used to monitor the release of zinc species collected at the tip during an SECM scan.

Coil-coated steel: corrosion resistance and adhesion as a function of the composition of the intermediate galvanic layer

The corrosion behaviour of coil-coated steel (CCS) sheets with different intermediate zinc-based coatings was examined by electrochemical impedance spectroscopy (EIS). Corrosion tests were performed in a 0.5 M NaCl aqueous solution in contact with the air, at ambient temperature. The results of pull-off adhesion test are also presented. The impedance data show that the improvement in the protective behaviour of the composite system is connected with the higher resistance values for the samples in which aluminium was added to the galvanized layer, and the best results are shown by CCS with aluzinc (Zn-55Al). These effects have been related to differences in the adhesion of the organic coating to the underlying metal substrate, as determined from both non-exposed samples and samples exposed to the electrolyte solution.