In situ study on the effects of Ni and Mo on the passive film formed on Fe–20Cr alloys by photoelectrochemical and Mott–Schottky techniques

• Published in: Journal of electroanalytical chemistry (Lausanne, Switzerland) Switzerland), 2006-05, Vol.590 (2), p.120-125
• Main Authors: Jang, HeeJin, Kwon, HyukSang
• Format: Article
• Language: English
• Subjects: Applied sciences; Corrosion; Corrosion prevention; Exact sciences and technology; Metals. Metallurgy; Mott–Schottky analysis; Passive film; Photoelectrochemistry; Semiconducting property; Stainless steel
• ISSN: 1572-6657; 1873-2569
• DOI: 10.1016/j.jelechem.2006.02.031

Effects of alloying elements (Ni and Mo) on the structure of passive film formed on Fe–20Cr alloys in pH 8.5 buffer solution were explored by analyzing the in situ electronic properties measured using the photoelectrochemical technique and Mott–Schottky analysis. The passive film formed on Fe–20Cr–10Ni was found to be mainly composed of Cr-substituted γ-Fe 2O 3 from similarities in photocurrent response for the passive films formed on the alloy and Fe–20Cr. On the other hand, the photocurrent spectra for the passive films of Fe–20Cr–15Ni–(0, 4)Mo alloys exhibited the spectral components associated with NiO and Mo oxide (MoO 2 and/or MoO 3) in addition to that induced by Cr-substituted γ-Fe 2O 3. Mott–Schottky plots for the passive films formed on Fe–20Cr–(10, 15)Ni and Fe–20Cr–15Ni–4Mo confirmed that the passive films on Fe–20Cr–(10, 15)Ni–(0, 4)Mo alloys have a base structure of Cr-substituted γ-Fe 2O 3 with variation of densities of shallow and deep donors depending on the Ni and Mo contents in the alloys. We suggest that the passive film formed on Fe–20Cr–(10, 15)Ni and Fe–20Cr–15Ni–4Mo alloys are composed of (Cr, Ni, Mo)-substituted γ-Fe 2O 3 when the concentrations of Ni and Mo are below critical values. However, NiO and Mo oxide (MoO 2 and/or MoO 3) would be precipitated in the passive films when the concentrations of Ni and Mo exceed critical values.