In Situ Infrared Reflection Absorption Spectroscopy Studies of Confined Zinc Surfaces Exposed under Periodic Wet-Dry Conditions

An experimental setup for in situ infrared reflection absorption spectroscopy (IRAS) studies of atmospheric corrosion of confined metal surfaces is described. Information about the drying process of confined metal surfaces and the chemical composition and growth rate of the corrosion products in the confinement was obtained during exposure to periodic wet-dry conditions. The drying process and the formation of corrosion products during periodic wet-dry conditions with different CO 2 concentrations was studied. The decrease of the water bands from the water on the zinc surface was followed and the drying time of the confinement was approximately 6-8 h. The formation of corrosion products during the drying period was followed with in situ IRAS. The corrosion product formed under these conditions was mainly composed of ZnO with a smaller amount of Zn 5 ( OH ) 8 Cl 2 ⋅ H 2 O with <5 ppm CO 2 concentration in the air. When the CO 2 concentration was ⩾350 ppm, Zn 5 ( OH ) 6 ( CO 3 ) 2 and Zn 5 ( OH ) 8 Cl 2 ⋅ H 2 O were the dominant species in the corrosion product. With increasing CO 2 concentration the amount of chloride precipitated as Zn 5 ( OH ) 8 Cl 2 ⋅ H 2 O increased. This can be explained by the neutralization of the surface electrolyte by CO 2 resulting in the precipitation of insoluble Zn 5 ( OH ) 8 Cl 2 ⋅ H 2 O and Zn 5 ( OH ) 6 ( CO 3 ) 2 .