Effect of anions on formation of ferrite coatings on carbon steel by hydrothermal method

Abstract

The major concerns in Primary Heat Transport circuits of water cooled nuclear power plants are corrosion of structural materials and radiation field buildup on out-of-core surfaces due to accumulation of activated corrosion products. To address these concerns, hot conditioning and metal ion passivation are employed, which lead to the formation of protective magnetite coating on structural alloys like carbon steel. In this study, investigations were undertaken to modify the magnetite/ferrite films hydrothermally in the presence of zinc (Zn2+) and nickel (Ni2+) ions by using different salts of these ions containing anions such as acetate, nitrate and sulphate. Mixed ferrite coatings containing Zn2+ and Ni2+ ions were developed on carbon steel in lithiated water in presence of these anions at 250 °C by hydrothermal method and subsequently characterized by grazing incidence-X-ray diffraction for phase identification and scanning electron microscopy for surface morphology. The effects of these anions were studied by comparing the corrosion resistance properties of ferrite coated carbon steel specimens. The corrosion properties were studied in lithium hydroxide medium at ambient temperature by electrochemical techniques and the results of the investigation are discussed in this paper.