Lost iron and iron converted into rust in steels submitted to dry–wet corrosion process

Abstract

During the electrochemical corrosion of iron and steel not all the iron removed from the steel forms later part of the iron phases that remain stick to the surface. Here we report numerical data that demonstrates that the conversion of iron into adherent rust is not always equal to one, at least for steels submitted to chloride ions in dry–wet cyclical processes. For that purpose, the adherent (AR) and non-adherent rusts (NAR) formed on weathering and carbon steels exposed to these tests were weighted and fully characterized using different techniques. We have found that 2–38% of the corroded iron is lost, while 3–18% is converted into NAR. The NAR for both steels are composed of lepidocrocite, goethite, hematite, and traces of akaganeite, independent of the investigated exposure times and chloride concentrations. The AR was composed of lepidocrocite, spinel phase, goethite and akaganeite. Comparison of these results with those obtained in total immersion tests is also addressed.