This paper describes a high resolution optical and electrochemical study into how metallic tin acts to reduce the rate of filiform corrosion (FFC) initiation and propagation on tin and iron-tin intermetallic (Fe-Sn IM) coatings for packaging steels. The time-dependent extent of FFC was determined optically using time lapse photography and by repeated in-situ scanning using a scanning Kelvin probe (SKP) apparatus. FFC was not observed on tin coatings but was found to propagate at a significantly reduced rate on the Fe-Sn IM when compared to pure iron. A rotating disk electrode (RDE) technique was subsequently used. O_2 reduction currents were low on both pure tin and tin coatings when compared to pure iron, intermediate values being obtained for the Fe-Sn IM. It is concluded that the rate of FFC is related to the overpotential for the oxygen reduction reaction (ORR).
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