Influence of the Chemical Composition and Electronic Structure of Passive Films Grown on 316L SS on Their Transient Electrochemical Behavior

Abstract

Modifications of the passive film formed on 316L stainless steel (SS) in acidic media were performed under dc or ac polarization. The effects of these ageing treatments on the chemical composition and the electronic structure of the passive film were studied. Chemical analysis with angle resolved X-ray photoelectron spectroscopy revealed that ageing induces a net enrichment in chromium oxide in the inner part of the passive film and an increase of the thickness of the inner oxide. Semiconducting behavior of the passive films was revealed by a Mott-Schottky analysis. The passive film was considered as a dielectric with different trapping levels lying in the bandgap. The observed n- or p-type semiconductivity can be assumed to be the result of the ionization of these trap levels under polarization. The most important modification of the electronic structure observed after ageing was a net decrease of the density of acceptor levels, which is associated with a less disordered inner chromium oxide. In the light of these results, the effect of ageing on the transient electrical coupling of the passive film with an active surface was investigated in free potential conditions. The capacitive response revealed by the potential and current transients was related to the localized states in the bandgap of the passive film. The current transient during the potential drop was related to the repassivation of the active surface. At the same time, electrons from the active site are transiently stored in the capacity formed by trap levels in the inner oxide of the passive film before being consumed by the cathodic reaction. The kinetics of the overall process should be limited by the heights of the potential barriers at the different interfaces and by the energy level of the acceptor-type traps. © 2004 The Electrochemical Society. All rights reserved.

Physicochemical Characterization of Passive Films and Corrosion Layers by Differential Admittance and Photocurrent Spectroscopy

“…Both these values are larger than the oxide film thickness usually reported for passive iron (3 ~ 5 nm), nickel (2 ~ 3 nm), chromium and stainless steels (2 ~ 3 nm) in different solutions before the onset of the transpassive region, [51][52][53][54][55][56] so that the hypothesis of SC space charge width much lesser than the thickness of SC could be untenable and the electrical equivalent circuit of the junction should be modified by adding a further capacitance in parallel with the C SC term which accounts for the metal contribution to the total stored charge. 57 On the other hand donor or acceptor concentration larger than 10 20 ~ 10 21 cm -3 for passive films on iron, nickel and stainless steel have been reported [58][59][60][61][62][63][64][65][66] and up to 10 22 cm -3 in some chromium carbon steel. 67 At such high level of donor or acceptor concentration the applicability of classical M-S theory to the study of a degenerate (or strong impurity metal 68 ) semiconductor/electrolyte interface is open to serious doubts.…”

UV illumination on the atmospheric corrosion of Q450 weathering steel depositing with NH4Cl

“…Based on MottSchottky theory, [28] the capacitance of the Helmholtz layer (C H ) can be neglected. [29] The capacitances of n-type semiconductors were given by Eq. (1),…”

Pasividad en solución de fosfato de aceros inoxidables solidificados unidireccionalmente

“…El análisis de MottSchottky (Figura 7) indica un comportamiento lineal con una pendiente característica de óxidos semiconductor tipo n en el rango de potenciales entre -0,45 V a 0,10 V. Los defectos puntuales dentro de la película pasivante pueden ser especies metálicas intersticiales o vacancias de oxígeno, o ambas. Una segunda pendiente puede ser atribuida a una distribución no homogénea de dopaje en los semiconductores, a la presencia de estados de interfaciales o a un segundo estado donor o a una distribución de estados donores sobre el bandgap [14,15]. El valor de potencial de banda plana, E bp , es aproximadamente igual a -0,45 V, para todas las muestras.…”