Characterization of thermal oxide films formed on a duplex stainless steel by means of confocal-Raman microscopy and electrochemical techniques

In this work oxide films have been developed on the surface of a duplex stainless steel (UNS 1.4462) using high temperature confocal microscopy to follow their growth. The characteristics of these oxide films have been analyzed by means of weight-gain measurements, Raman microscopy and electrochemical techniques, namely potentiodynamic polarization curves and electrochemical impedance spectroscopy. The results show an increase in the amount of oxides (particularly γ-Fe₂O₃ and Fe₃O₄) with temperature. Regarding the electrochemical properties of these films, the corrosion resistance of the film tends to be lower with the heat treatment temperature, probably due to a more porous and heterogeneous scale. Mott-Schottky plots show the n-type semiconductive behavior of the films with donor densities that decrease with the enhancement of the temperature.