A. Fattah-Alhosseini, O. Imantalab,
Volume 11, Issue 2 (6-2014)
Abstract
In this study, effect of immersion time on the electrochemical behaviour of AISI 321 stainless steel (AISI 321)
in 0.1 M H
2SO
4
solution under open circuit potential (OCP) conditions was evaluated by potentiodynamic
polarization, Mott–Schottky analysis and electrochemical impedance spectroscopy (EIS). Mott–Schottky analysis
revealed that the passive films behave as n-type and p-type semiconductors at potentials below and above the flat band
potential, respectively. Also, Mott–Schottky analysis indicated that the donor and acceptor densities are in the range
1021 cm-3 and increased with the immersion time. EIS results showed that the best equivalent circuit presents two time
constants: The high-medium frequencies time constant can be correlated with the charge transfer process and the low
frequencies time constant has been associated with the redox processes taking place in the surface film. According to
this equivalent circuit, the polarization resistance (interfacial impedance) initially increases with the immersion time
(1 to 12 h), and then it is observed to decreases. This variation is fully accordance with potentiodynamic polarization
results
