Anodic degradation of Zn-Ni coatings in moderately alkaline NaCl solution

Carbon steel samples covered with initially crack-free zinc-nickel coatings were polarized with a small anodic overpotential in moderately alkaline NaCl solution. Along with zinc dissolution, the coatings developed a mud-crack pattern due to tensile stress release, allowing the electrolyte to access the underlying steel surface. Simonkolleite grew on both the zinc-nickel coating and the steel substrate. The resulting current density, that was first strongly anodic, switched to small cathodic values when the coating surface was almost fully covered by a compact simonkolleite layer. (c) 2021 Elsevier B.V. All rights reserved.

Automated summary

In moderately alkaline NaCl solution, carbon steel samples with crack-free zinc-nickel coatings were polarized with a small anodic overpotential, leading to the development of a mud-crack pattern on the coatings and the growth of simonkolleite. The resulting current density switched from strongly anodic to small cathodic values as the coating surface was almost fully covered by a compact simonkolleite layer.