Analysis of pit corrosion at the initial stage in sulfide solution by temporal series micrographs coupled with electrochemical techniques

摘要

Usually, pitting corrosion is investigated using electrochemical techniques. The disadvantage of this approach is the lack of information that preserves the spatial coordinates, i.e., that allows to analyze in which point of the surface the pitting corrosion process starts. This occurs because the current and potential are associated with the sum of all events occurring on the surface at a given period of time. Thus, some processes, such as the transient nature of corrosion products in sulfide solution [1] or even an estimation of the mean depth of a pit [2] cannot be investigated using only electrochemical methods. This work presents a study of the initial instants in pitting corrosion by temporal series micrographs coupled to open circuit potential (Eoc) and polarization curves (PC). The AISI 1040 steel corrosion in aqueous basic solution containing 31 × 10~(-3) mol dm~(-3) of HS- species was used how system in study. During the monitoring the Eoc were detect the induction time, the initial pit growth during the corrosion process as a function of exposition time to sulfide solution that occur before the sulfide film formation. During the PC the pit area increasing have two distinct rates in specific regions direct associate to current slope changes without any change in pit number, Figure 1. Finally, using the charge associated just a pit, it was possible to estimate his pit depth before the pit explosion.