The Kinetics and Mechanism of Atmospheric Corrosion Occurring on Tin and Iron-Tin Intermetallic Coated Steels

This paper describes a systematic study into the initiation and propagation of cathodic delamination on pure iron, pure tin and industrially important tin and iron-tin intermetallic (FeSn and FeSn 2 ) coatings for packaging steels, as a function of coating weight. Cathodic disbondment rates for an organic lacquer overcoat applied to the various metallic coatings are determined using an in-situ scanning Kelvin probe technique. Cathodic disbondment was not observed on pure tin and was found to propagate at reduced rates on the FeSn and FeSn 2 intermetallic coatings, relative to pure iron. An explanation of these findings is given in terms of electrocatalytic activity of various metallic surfaces for the cathodic oxygen reduction reaction. It is shown that the relative susceptibility of Fe, Sn, FeSn and FeSn 2 to cathodic disbondment increases with decreasing cathodic overpotential and is independent of metallic coating weight.