Characterization of the corrosion products formed on zinc in archipelagic subtropical environments

The atmospheric corrosion of zinc samples exposed at 25 test sites with different climatic and pollution conditions was investigated during a two-year exposure program carried out in three of the Canary Islands (Spain) as to cover the typical range of subtropical environmental conditions. The composition and distribution of the corrosion products of zinc were analyzed qualitatively by X-ray diffraction (XRD). Simonkolleite (Zn5(OH)8Cl2) and hydrozincite (Zn4CO3(OH)6·H2O) were the corrosion products more frequently observed, revealing that chloride and carbon dioxide are the most aggressive pollutants present in the atmosphere. Sulphate-containing species, namely Zinc oxysulfate (Zn3O(SO4)2), Zinc hydroxysulfate (Zn4SO4(OH)6), Zinc diamminehydroxynitrate (Zn5(OH)8(NO3)2·2NH3) and zinc chlorohydroxysulfate (NaZn4Cl(OH)6SO4·6H2O), were also found though in smaller amounts