Electrochemical Behavior of the Passive Films Formed on Alloy 22 (UNS N06022) in Acidic Solutions.

Passive behavior and semiconducting properties of alloy 22 in sulfuric and nitric acidic solutions were studied. Corrosion current density was measured from potentiodynamic polarization plots, defect density was drawn from Mott-Schottky analysis, and finally polarization resistance and passive film thickness were estimated by electrochemical impedance spectroscopy. Potentiodynamic polarization curves suggested that alloy 22 showed excellent passive behavior in both nitric and sulfuric solutions. Mott-Schottky analysis revealed that the passive films formed on alloy 22 in both acidic solutions behave as n-type and p-type semiconductors. Also, this analysis indicated that the donor and acceptor densities are in the range 10 cm and increased with solution concentration. In conclusion, electrochemical impedance spectroscopy and Mott-Schottky analysis revealed that dilute nitric and sulfuric acidic solutions offer better conditions of the passive film formation on alloy 22 with higher protection behavior than concentrated nitric and sulfuric solutions, due to the growth of a much thicker and less defective films. [ABSTRACT FROM AUTHOR]