Microstructure and spatial distribution of corrosion products anodically grown on zinc in chloride solutions

- Simonkolleite-ZnO patinas are produced by electrochemical oxidation of zinc.
- Raman, XPS, XRD, FIB-SEM, SAED and STEM-EDX analyses enable to assess the spatial distribution of ZnO and simonkolleite.
- The barrier effect in cathodic polarization is probably due to nanoporous ZnO and not simonkolleite.

Zinc substrates were electrochemically oxidized in NaCl solution to produce corrosion patinas. XRD, XPS and Raman analyses enabled the identification of simonkolleite and zinc oxide as the patina constituents. FIB-SEM imaging shows that the upper part of the patinas is a network of simonkolleite nanosheets with an open microstructure that is unlikely to act as a significant barrier for corrosion processes. STEM investigations and Raman mapping measurements reveal the presence of a ca. 20-400 nm thin nanoporous ZnO-rich film below the simonkolleite and covering the zinc substrate. Under potentiostatic conditions, the reduced cathodic activity of the patina-covered zinc electrodes is assigned to this nanoporous ZnO layer.