Degradation behavior of protective rust layer in chloride solution

摘要

The degradation of protective rust layer onweathering steels was investigated by electrochemical method inchloride solutions. The samples used were weathering steels whichhad been exposed in rural atmosphere for about 35 years.Electrode potential changes were measured in some chloridesolutions for the samples with protective rust layer. The restpotential shifted from original 200 to 300 mV vs. SSE to lessnoble and fairly constant values after 48 to 72 hours immersion.The constant potential gave less noble values with increasingchloride ion concentration. From the results of corrosionmonitoring and visual observation, it is concluded that thedecrease in rest potential is attributed the increased number ofactive sites for anodic dissolution. The alloying elements such asCr, P and Cu are concentrated in rust layer at correspondingportions where active dissolution occurred on metal/rust interface.It is not observed that chloride permeation under high chloride ionconcentration environments is inhibited by the presence of these elements.