Corrosion behaviour of zinc exposed to an extreme tropical marine atmospheric environment for 3 years

Abstract

Corrosion behaviour of Zn exposed in the coastal zone of the Nansha Islands for nearly 3 years was studied through gravimetric, and morphological observations, component analysis, and electrochemical measurements. The kinetics of the corrosion process is linear, indicating that the corrosion products have no significant protective effect on the substrate. The average corrosion rate (V _d) fluctuated with time, which was attributed to the different morphologies of corroded product film formed on the skyward and field-ward sides. Corrosion products formed on the skyward side had a three-layer structure in which Zn₅(OH)₈Cl₂·H₂O was enriched in both the outer and inner layer, NaZn₄Cl(OH)₆SO₄·6H₂O was enriched in the intermediate layer. Simultaneously, corrosion products formed on the field-ward side had a double-layer structure, in which Zn₅(OH)₈Cl₂·H₂O was concentrated in the inner layer and NaZn₄Cl(OH)₆SO₄·6H₂O was enriched in the outer layer. The degrees of corrosion on both sides at different exposure periods were also discussed.