Simulating Study of Atmospheric Corrosion of Galvanized Steels: Influence of Zinc Rusts on the Formation of β-FeOOH Rust Particles by Aerial Oxidation of Aqueous FeCl2 Solution

To simulate the corrosion of galvanized steel in a marine zone, steel rust of β-FeOOH particles was prepared by aerial oxidation of aqueous FeCl 2 solutions containing ZnCl 2 and zinc rusts such as ZnO and zinc hydroxychloride (Zn 5 (OH) 8 Cl 2 ·H 2 O, ZHC). The crystallinity and particle size of β-FeOOH were slightly decreased by adding the ZnC1 2 . The produced particles contained a small amount of ZnCl 2 , while the zinc rusts of ZnO and ZHC markedly impeded the crystallization and particle growth of β-FeOOH. In the presence of a large amount of zinc rusts, the formation of β-FeOOH was suppressed and γ-FeOOH and ZHC of which the particle size was larger than that of β-FeOOH were generated. The inhibitory effect on the formation of β-FeOOH was on order of ZHC ≈ ZnO ≫ ZnCl 2 . The effect of zinc rusts was ascribed to the increment of solution pH by dissolution of rust particles and adsorption of Zn(II) on a precursor of β-FeOOH particles. The adsorption of CO 2 on the products was also suppressed by the addition of ZnCl 2 and zinc rusts. These results imply that the β-FeOOH rust formed on galvanized steel in a marine environment is more compact, leading to improved corrosion resistance. However, existence of a large amount of zinc rust particles inhibits the formation of a compact rust layer and lowers the ability for corrosion resistance.