Verification of passivity condition of carbon steel under cathodic protection through in-situ spectroscopy

Cathodic protection (CP) is a consolidated technique involving the circulation of a cathodic current (iprot) from an anode to a structure. This causes the electrode alkalisation depending on iprot and on the kinetics of the diffusive motion of ions, influencing the surface state of the metal. In this paper, the surface condition of carbon steel under CP has been studied through in-situ Raman spectroscopy and atomic force microscopy (AFM), combined with electrochemical impedance spectroscopy (EIS), for a protection potential (Eprot) of 1.1 V/CSE (Cu/CuSO4). Results show that depending on alkalisation, Fe3O4 converts to other ferric species like γ-Fe2O3 and α-FeOOH.