Effects of EDTA on the electronic properties of passive film on Fe–20Cr in pH 8.5 buffer solution

Effects of EDTA (ethylene diammine tetraacetic acid) on the electronic properties of passive film formed on Fe–20Cr alloy in pH 8.5 buffer solution were examined by the photo-electrochemical and impedance techniques to elucidate the structure and composition of passive film on the alloy. XPS composition profile in depth for the passive film revealed that Cr content in the outermost layer of the passive film was higher for the passive film formed in the solution containing EDTA than that in solution without EDTA, due presumably to the selective dissolution of Fe oxide by EDTA. In spite of the selective dissolution of Fe oxide in the outer layer of the passive film, the photocurrent spectra and the Mott–Schottky plots for the passive film formed on Fe–20Cr in EDTA containing solution were very close to those in EDTA-free solution, which strongly supports that the passive film on Fe–20Cr in pH 8.5 buffer solution is a single layered Cr-substituted γ-Fe2O3 oxide rather than a duplex layered oxide composed of inner Cr oxide and outer Fe oxide.