Electrochemical Study of Passive Oxide Film Formation on Carbon Steel and Its Interaction With H2o2

Abstract

Carbon steel corrosion is an electrochemical process associated with the dissolution of Fe ions caused by breakdown of passivated films on the metal surface. It is one of the operational and safety challenges in nuclear industry. Water radiolysis produces highly reactive species in the presence of ionizing radiation, the environment in the reactor coolant system of CANDU nuclear plant. Water radiolysis products, in particular, H₂O₂, enhance the corrosion rate of carbon steel pipes used in the CANDU heat transport system. The corrosion kinetics is complex and depends on the physical and chemical properties of the steel surface and solution pH and redox conditions. The interaction of H₂O₂ with iron oxide/hydroxide films on carbon steel was studied by electrochemical and surface analytical techniques. Iron oxide/hydroxide films were grown potentiostatically for different lengths of time at various potentials and characterized using Electrochemical Impedance Spectroscopy (EIS). The interaction of oxide films with H₂O₂ was studied mainly at room temperature (limited study at higher temperatures) by monitoring the open circuit potential (or corrosion potential, E_CORR) as a function of exposure time to H₂O₂, and by performing EIS after different reaction times. Ex-situ Raman spectroscopy was also performed to characterize some of the films.