Passivity of AISI ۳۱۶L stainless steel as a function of nitric concentration

In this study, electrochemical behaviour of passive films formed on AISI ۳۱۶L stainless steel (AISI ۳۱۶L) in three acidic solutions concentrations (۰.۳, ۰.۶, and ۰.۹M HNO۳) under open circuit potential conditions were evaluated by potentiodynamic polarization, Mott–Schottky analysis and electrochemical impedance spectroscopy (EIS) techniques. The potentiodynamic polarization results showed that the corrosion potentials of AISI ۳۱۶L shift towards positive direction with increase in solution concentration. Also, these results reveal that the corrosion rate of AISI ۳۱۶L is enhanced in solutions with higher nitric content. Mott–Schottky analysis revealed that passive films behave as p-type and n-type semiconductors at potentials below and above the flat band potential, respectively. Also, Mott–Schottky analysis indicated that the donor and acceptor densities increased with solution concentration. EIS data showed that the equivalent circuit Rs((RctQdl)(RfQf)) by two time constants is applicable. Also, EIS results reveal that the charge transfer resistance and passive film resistance decrease with solution concentration.

Keywords:

EIS , p-type semiconductor , n-type semiconductor , Mott–Schottky