Detailed resolution of microscopic depassivation events on stainless steel in chloride solution leading to pitting

Chloride Ion Interactions with Oxide-Covered Aluminum Leading to Pitting Corrosion: A Review

“…al. ; 51,70 chemo-mechanical model first proposed by Hoar; 5 and ion migration to and reaction at the oxide/metal interface suggested by many 3,5,7,10,12,14,39,51,52,70,91 and recently refined by McCafferty 13,14 are plausible theories considering the experimental results. At the present time McCafferty's stepwise model shows the most significant agreement with the overall experimental data predicting: Cl − is adsorbed and incorporated in the oxide film, moves toward the metal-oxide interface, a lower i pass with Cl − incorporation, oxide thinning prior to E pit , and the formation and rupture of blisters.…”

“…Also, the physical appearance showed the development of cracks, which would indicate stress build up. The stress build up can occur by Cl − migration and formation of Cl-Al islands at the oxide/metal interface, 51,70 Cl − migration and Al dissolution leading to hydrogen production at the oxide/metal interface, 13,14,[122][123][124][125][126] or oxide cracking caused by the presence of Cl − within the oxide film.…”

Pitting Corrosion of Metals

“…Most authorities now refer to critical concentrations of order 1M or higher in Me n+ , which for believable anodic current densities (say, less than 100 A cm -2 in the most extreme case 10 ), entails an effective diffusion length of at least 0.1-1 μm. For "perfectly" flat surfaces, this leads to the speculation that a slow blistering type of corrosion occurs under the passive film, with only molecular-sized channels for communication with the bulk solution; then this structure pops open, leading to pit growth-similar to a proposal of Mattin and Burstein, 11 and recalling earlier work by authors who referred to "salt islands" or "blisters." This critical chemistry is postulated to correspond to a thermodynamic criterion : a critical solubility of metal cations in equilibrium with the relevant oxide or hydroxide.…”

Effects of applied potential on stable pitting of 304 stainless steel

“…They demonstrated and proved that the pit stable or metastable growth is controlled by corrosion products diffusion, since the pitting current density is independent of the applied potential. As is well known, a chloride-induced pit must be either enriched in chloride, or of a lower pH, or both relative to the bulk solution, in order to sustain continuous propagation of pit [18][19][20][21]23,26]. This mechanism is also suitable for crevice corrosion [27,28].…”

“…Burstein et al [3,4,[18][19][20][21][22][23][24][25] used a tiny specimen, a microelectrode to study pit nucleation and propagation, and obtained single and separated current transients. They demonstrated and proved that the pit stable or metastable growth is controlled by corrosion products diffusion, since the pitting current density is independent of the applied potential.…”