The Electrochemical Behavior of AISI ۳۲۱ Stainless Steel in Alkaline Media

In this paper, the electrochemical behaviour of passive films formed on AISI ۳۲۱ stainless steel (AISI ۳۲۱) immersed in ۰.۱ M NaOH + ۰.۱ M KOH solution was evaluated by different electrochemical techniques. For this purpose, passive films were formed at open circuit potential for ۱ to ۱۲ hours and then electrochemical measurements were done. The polarization curves suggested that AISI ۳۲۱ showed excellent passive behaviour in ۰.۱ M NaOH + ۰.۱ M KOH solution. Mott–Schottky analysis indicated that the accepted densities were in the range of ۱۰۲۱ cm-۳ and decreased with immersion time. Electrochemical impedance spectroscopy (EIS) results showed that the best electrical equivalent circuit presented two time constants: The high-medium frequencies time constant could be correlated with the charge transfer process and the low frequencies time constant was associated with redox processes taking place in the surface film. Also, EIS results showed that polarization resistance was increased with formation time from ۱ until ۱۲ hours, due to the thickening of passive film.

Keywords:

Stainless steel , Passive film , Mott–Schottky , EIS