Evaluating the Critical Chemistry for Repassivation at the Corroding Surface Using Mass Transport Model-Based Artificial Pit Experiments

Abstract

One-dimensional mass transport model calculations were utilized to design experiments with stainless steel artificial pit electrodes to determine the critical concentration of cations at the corroding surface representing the transition between stable pitting and repassivation. Rapid polarization scans following salt film precipitation and consequent open circuit dilution to different surface concentrations permitted the evaluation of kinetics at various degrees of saturation. These experiments showed a distinct change in kinetics as the surface concentration decreased, thus identifying the critical pit chemistry for the onset of repassivation. Chemical modeling of oxide precipitation from solution permitted the investigation of oxide nucleation across varying surface concentration as a function of pH as the cause of repassivation. This analysis enabled the estimation of the pH at which the first oxide would precipitate in the critical pit solution chemistry, which when combined with cation hydrolysis calculations, resulted in the evaluation of the critical pH at the transition between pit stability and repassivation. A mixed potential theory-based analysis of these results was utilized to provide mechanistic support to the quantitative framework describing critical factors for pitting stability and repassivation.

Amphilic Water‐Lean Carbon Capture Solvent Wetting Behavior through Decomposition by Stainless‐Steel Interfaces

“…It has been reported that surface oxides and hydroxides of Fe, Cr, and Mo atoms are abundant on the surface of 316 L stainless steel becoming more and more prominent at pH levels greater than 9. [35] We surmise that these oxides and hydroxides are likely providing the H and O atoms required to produce the observed "hydrolysis" degradation in the highly basic 1-IPADM-2-BOL.…”

Numerical Investigation of Critical Electrochemical Factors for Localized Corrosion using a Multi-species Reactive Transport Model

“…We consider three types of electrode reactions happening during the experiment: anodic metal dissolution, internal and external cathodic reactions [41]. Anodic dissolution and the internal cathodic reaction occur on the corroding surface of the 316L stainless steel wire, which is directly exposed to sodium chloride solution.…”

“…The simplest of mechanistic models consider mass transport of solute species (e.g., metal or hydrogen ions) in the solution environment based on the Fick's law of diffusion [36]. Therefore, the 1-D Fickian diffusion model has been widely used to simulate the evolution of the chemistry inside the 1-D pit [37][38][39][40][41][42]. Srinivasan et al used this model to evaluate the effect of the external hemispherical boundary layer on the cation flux inside the pit [40] and to demonstrate the dilution of cations near the corroding surface when repassivation happens [41,42].…”

“…Therefore, the 1-D Fickian diffusion model has been widely used to simulate the evolution of the chemistry inside the 1-D pit [37][38][39][40][41][42]. Srinivasan et al used this model to evaluate the effect of the external hemispherical boundary layer on the cation flux inside the pit [40] and to demonstrate the dilution of cations near the corroding surface when repassivation happens [41,42]. Jun et al applied the similar model to analyze the effects of chloride concentration and temperature on 1-D pit growth [39].…”

Accessing the full spectrum of corrosion behaviour of tempered type 420 stainless steel

“…[26,27] The metastable pit growth often results in pits with lacy covers, which are able to maintain a high concentration of Cl − and a lowpH electrolyte within occluded pit cavities. [28,29] Stable pit growth is associated with a critical electrochemical potential (E pit ) or a critical pitting temperature, [30,31] and stable pits generally have a larger pit volume, with the pit depth acting as the diffusion barrier. [32,33] Bipolar electrochemistry has now become accessible for corrosion testing and screening, featuring a noncontact experimental setup, by in parallel being able to observe the full corrosion response during one single experiment.…”