Degradation Behavior of Protective Rust Layer in Chloride Solution

摘要

The degradation of a protective rust layer on weathering steels was investigated using an electrochemical method in chloride solutions. The samples used were weathering steels which had been exposed in a rural atmosphere for about 35 years. Electrode potential changes were measured in some chloride solutions for the samples with a protective rust layer. The rest potential shifted from original 200 to 300 mV vs. SSE to less noble and fairly constant values after 48 to 72 hours immersion. The constant potential gave less noble values with increasing chloride ion concentration. From the results of corrosion monitoring and visual observation, it was concluded that the decrease in rest potential is attributed the increased number of active sites for anodic dissolution. The alloying elements such as Cr, P and Cu are concentrated in the rust layer at corresponding portions where active dissolution occurred on metal/rust interface. It was not observed that chloride permeation under high chloride ion concentration environments is inhibited by the presence of these elements.