Effect of Cations on Protective Properties of Rust Layer Formed on Carbon Steel during Wet/Dry Cyclic Corrosion

Abstract

The present work proposed a simple approach to modify the morphology and composition of rust layers formed on carbon steel during wet/dry cyclic atmospheric corrosion, and thereby improve the protective properties of the rust layers. Rust layers were grown on carbon steel by a laboratory cyclic corrosion test. Additional immersion in sulfate solutions containing Mg²⁺, Al³⁺, Cu²⁺, or Ni²⁺ was carried out during the cyclic corrosion test to modify the rust layers. The morphology of the rust layers on carbon steel in the reference specimen that was not subjected to additional immersion showed a plate-like structure. The rust layers on the Mg²⁺ specimen consisted of plate-like and needle structures. On the other hand, the other specimens subjected to additional immersion exhibited particulate structures, although the rust layers on the Cu²⁺ specimen consisted of finer secondary particles. Rust layers on the Al³⁺ specimen and the Ni²⁺ specimen were denser compared to the other specimens. XRD revealed that the composition of the rust layer was changed by additional immersion, that is, on all the specimens subjected to the additional immersion, the growth of α-FeOOH was enhanced whereas that of Fe₃O₄ was hindered. Variations in the corrosion potential and corrosion current density obtained from potentiodynamic polarization measurements were strongly related to the morphology and composition of the rust layers.

Fig. 10 Relation between corrosion current density and α/γ^*.