In Situ Studies of Sulfate Nest Formation on Iron

Initial -induced atmospheric corrosion of iron has been followed in situ by three highly surface sensitive and complementary techniques, infrared reflection absorption spectroscopy, quartz crystal microbalance, and atomic force microscopy. The resulting corrosion attack was local in nature and resembled what are called sulfate nests, frequently observed on steel naturally exposed outdoors. The conclusions drawn challenge the established model for the formation and growth of sulfate nests: alone in humid air is not a sufficient prerequisite for sulfate nest formation. Only when an oxidant such as or is added to the corrosive atmosphere, can sulfate nests be detected. The conditions and formation of sulfate nests and other forms of local corrosion attacks are discussed in view of all in situ observations generated.