Effect of dissolved oxygen on the corrosion behavior of 304 SS in 0.1 N nitric acid containing chloride

• Published in: Materials research express 2018-04, Vol.5 (4), p.46526
• Main Authors: Khobragade, Nilay N, Bansod, Ankur V, Patil, Awanikumar P
• Format: Article
• Language: English
• Subjects: 304 SS; chloride; deareation; nitric acid; potentiodynamic polarization
• ISSN: 2053-1591; 2053-1591
• DOI: 10.1088/2053-1591/aab8de

A study was undertaken in several selected mixed nitric acid/chloride ( NO 3 − Cl − ratio) electrolytes with the nitric acid concentration of 0.1 N and chloride concentration of 0, 10, 100, 1000 and 10 000 ppm. Electrochemical tests like potentiodynamic polarization test, electrochemical impedance spectroscopy (EIS) and Mott-Schottky analysis (M-S) were carried out when the electrolytes were in deaerated condition and were in open to air (OTA) condition, and the effect of dissolved oxygen was evaluated on the corrosion behavior of 304 SS. It was found that at a critical NO 3 − Cl − ratio, a passive state is attained at the earliest in OTA condition. Also, the passive film resistance showed higher values in OTA condition than in deaerated condition exhibiting the effect of dissolved oxygen. The results of EIS results confirmed the results obtained by potentiodynamic polarization wherein the low passive current densities were obtained in OTA condition. Mott-Schottky analysis revealed the lowest defect densities in 100 ppm Cl− solution in OTA condition and in 10 ppm Cl− solution in deaerated condition indicating less defective films formed in these solutions. XPS analysis showed that the film was bilayer in nature in confirmation with M-S analysis. The results were discussed with point defect model (PDM) and by competitive surface adsorption.