Corrosion Performance of AISI-309 Exposed to Molten Salts V₂O₅-Na₂SO₄at 700°C Applying EIS andRpElectrochemical Techniques

Abstract

The corrosion performance of AISI-309 exposed 5 days to molten salts 50 mol% V2O5-50 mol% Na2SO4at 700°C is reported in this paper. Such evaluation was made using three electrochemical techniques: potentiodynamic polarization curve (PC), electrochemical impedance spectroscopy (EIS), and linear polarization resistance (Rp). FromPC, the Tafel slopes,Icorr, andEcorrwere obtained. From Nyquist and Bode plots, it was possible to determine two different stages; the first one showed just one loop, which indicated the initial formation of Cr2O3layer over the metallic surface; after that, the dissolution of Cr2O3formed a porous layer, which became part of the corrosion products; at the same time a NiO layer combined with sulfur was forming, which was suggested as the second stage, represented by two capacitive loops. EIS plots were in agreement with the physical characterization made from SEM and EDS analyses. Fitting of EIS experimental data allowed us to propose two electrical circuits, being in concordance with the corrosion stages. Parameters obtained from the simulation of EIS data are also reported. From the results, it was stated that AISI-309 suffered intergranular corrosion due to the presence of sulfur, which diffused to the metallic surface through a porous Cr2O3layer.

Intergranular corrosion: Comparison between experiments and cellular automata

“…For example, the determination of the pitting potential denes the sensitivity to this type of corrosion [10], double loop electrochemical potentiokinetic reaction tests inquire about the degree of sensitization of the SS [11], electrochemical impedance spectroscopy experiments give information on the limiting corrosion processes [12]. Among those, linear voltammetry is often performed in the case of IGC to investigate whether the SS remains passive (where the SS dissolves slowly and uniformly) or it is polarized in its transpassive state (where IGC occurs) in its chemical environment (see Figure 1) [13,14].…”

Use of Electrochemical Impedance Spectroscopy for the Evaluation of Performance of PEM Fuel Cells Based on Carbon Cloth Gas Diffusion Electrodes

“…In order to overcome this issue, electrochemical impedance spectroscopy (EIS) has to be carried out together with polarization curve measurements. EIS is a well-established technique for a complete analysis of electrochemical device behavior, but it has also been used in other fields of applied sciences in order to evaluate, for instance, the corrosion behavior of stainless steel [21] and different metallic alloys [22,23] at various operating conditions and in different media and even for biomedical applications [24].…”