FORMATION OF NAZN4CL(OH)6SO4.6H2O IN A MARINE ATMOSPHERE

Recent investigations of zinc samples exposed in atmospheric field and laboratory exposure conditions have provided evidence of two newly di scovered zinc chlorohydroxosulfates as corrosion products. In order to obtain a better understanding, detailed studies have been undertaken to characterize the formation and growth of both zinc chlorohydroxosul fates. One of them is observed mainly in marine environments, the othe r mainly in industrial environments, and the present study aims at des cribing the formation of sodium zinc chlorohydroxosulfate, NaZn4Cl(OH) 6SO4.6H2O, in a marine atmosphere. A field exposure program has been p erformed with emphasis on short exposure periods and detailed characte rization of initially formed layers of corrosion products by means of a multianalytical approach. A reaction sequence is identified which is consistent with all methods used. It involves the consecutive formati on of three structurally related phases, namely zinc hydroxycarbonate as the initial phase, zinc hydroxychloride as the intermediate phase a nd sodium zinc chlorohydroxosulfate as the final phase.