Modeling and Predicting Reduction Reaction Kinetics for a Stainless-Steel in NaCl Solutions

Abstract

A method for analyzing cathodic polarization curves on stainless steels is described and a framework for predicting the cathodic polarization response for UNS S13800 is developed, including a model for the diffusivity of dissolved oxygen as a function of chloride concentration and temperature. The cathodic polarization behavior of UNS S13800 in NaCl solutions, ranging from dilute to saturated, and across a range of temperature values was studied using potentiodynamic polarization, electrochemical impedance spectroscopy (EIS), and X-ray photoelectron spectroscopy (XPS). Analysis of the data indicated that the concentration of the solutions affected the ability of the oxide to catalyze reduction reactions. Dilute-to-low concentration solutions exhibited different Tafel slopes in the ORR-activation region while middle-to-high concentration solutions exhibited a single Tafel slope. The XPS and EIS results show a slightly thicker oxide formed in the low chloride concentration solutions over the course of the 18 hour open circuit duration along with a higher concentration of Fe3+ species.. The EIS data also showed the oxide formed in the low chloride solution had a higher charge-transfer resistance while the oxide formed in the high chloride solution had a higher oxide resistance.