Corrosion behavior of field-exposed zinc in a tropical marine atmosphere

Corrosion behavior of zinc exposed to a tropical marine atmosphere for 4 years was investigated. The results showed an obvious decrease in the corrosion rate, which was attributed to the development of the protective corrosion product layer with one element of this structure being simonkolleite (Zn5Cl2[OH]8.H2O). Corrosion of zinc initiated from localized corrosion, which was characterized with some pits, grooves, grain boundaries, and crystallographic features during the initial six exposure months. As the exposure time extended, uniform corrosion occurred and the corrosion products presented a three-layer structure where Zn5Cl2(OH)8.H2O was concentrated close to the bottom, sodium zinc chlorohydroxysulfate (NaZn4Cl[OH]6SO4.6H2O) was enriched in the middle layer, while zinc hydroxycarbonates and zincite (ZnO) covered the surface.