![]() This leads to the formation of a concentration gradient in the boundary layer at the cathode, with enrichment of NaF and depletion of AlF 3 at the interface. It is caused by the fact that the sodium ion is the carrier of current, while aluminum is being deposited. This effect is related to the cathodic concentration overvoltage which is mass transfer controlled. Read more Navigate Downĭuring electrolysis, the content of sodium increases with increasing cathodic current density. ![]() It should be noted that the mobilized passive surface and corrosion kinetics may moreover develop over time should the dioxygen consumption kinetics be higher than the rate at which it is renewed. In the event that a corrosion site is initiated in an area difficult for the dioxygen to access, the mobilized passive surface will be delocalized to areas where O 2 is available. Where there is an abundance of dioxygen present around the initiated anodic site, the mobilized passive surface is immediately adjacent, which implies minor ohmic drops between active and passive sites and a high corrosion rate. The dioxygen availability therefore constitutes another factor affecting the mobilized passive surface for the cathodic reaction and consequently the corrosion kinetics. This phenomenon is typically encountered in partially-immersed structures for which the dissolved-dioxygen concentration is low in the immersed part and high in the emerged part. For a color version of the figure, see In actual structures, the existence of dioxygen concentration gradients thus generates potential gradients in the absence of corrosion. Effect of dioxygen availability on the polarization curve of a passive steel. The value of the cathodic current saturation is defined as the cathodic limiting current i lim.įigure 1.25. In the case of a limited amount of dioxygen, the cathodic curve loses its exponential nature beyond a certain level of polarization and saturation of the cathodic current is observed. This availability is conditioned in particular by the dioxygen’s ability to diffuse through the cement matrix. In practice, the dissolved dioxygen is not always available in large amounts in the interstitial solution in contact with the steel. Previous discussions regarding the establishment of the equilibrium of a corrosion system implicitly assumed there to be an unlimited amount of dioxygen available for the cathodic reaction. Physically, the cathodic current corresponds to the amount of dioxygen reduced by time unit (or alternatively of hydroxyl ions formed by time unit), at the steel-concrete interface. Fabrice Deby, in Corrosion and its Consequences for Reinforced Concrete Structures, 2018 1.3.2.4.3 Dioxygen availability at the cathodeĬathodic reaction naturally plays an important role in the establishment of the equilibrium of a corrosion system (uniform or localized).
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |