Aspects of the electrochemical behaviour of iron and mild steel

The corrosion of ferrous materials is briefly reviewed. The theory and practice of the impedance methods currently used in the investigation of electrochemical corrosion reactions are described in some detail. Special reference is made to the differentia~ capacitance bridge technique. Using these methods the corrosion of both iron and mild steel in lM sodium perchlorate under neutral pH conditions has been investigated. The effect of ions encountered in natural waters has also been explored, by addition to the base electrolyte. The work then examineS. the influence of a simple ortho-phosphate compound as an inhibitor of the corrosion reactions. Confirmatory evidence is g1ven to support the view that the point of zero charge on 1ron and mild steel is not attainable at neutral pH. The effect of alloying materials in mild steel 1S discussed. The results of investigations with ortho-phosphate in the base electrolyte, containing added natural water constituents, are consistent with the repair of a protective film at the electrode.