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

Abstract

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 21 cm −3 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.

The effect of surface modification on the corrosion protection ability of the passive films of sensitized UNS S31803 duplex stainless steel

“…The defect densities (donor and acceptor states in n-type and p-type semiconductors, respectively) can be determined using Mott-Schottky analysis [30,31]. In spite of the fact that there are so many research works regarding the study of the effect of variables like electrolyte concentration, its pH value and polarisation parameters on the semiconducting properties of the passive layers formed on the surfaces of various types of stainless steels [25][26][27][32][33][34][35][36][37], there is not enough data representing the influence of sensitisation heat treatment, surface roughness and the number of cycles in repetitive CV method (that was used to passivate the specimens) on the properties of the passive films. So, the purpose of the present study is to investigate the effect of such processing parameters on the properties of the resulting passive layer formed on the surface of UNS S31803 DSS using different electrochemical techniques.…”