Instantaneous impedance evaluation of dissolution of AISI 304 stainless steel during intergranular corrosion

Purpose - The purpose of this paper is to focus on diversification between electrical parameters determined on the basis of instantaneous impedance measurements within the activation and reactivation scan of dissolution of sensitized AISI 304 stainless steel during a proceeding intergranular corrosion process. Design/methodology/approach - The investigations were carried out by means of dynamic electrochemical impedance spectroscopy (DEIS). DEIS measurements were conducted "on-line" while the samples were polarized in agreement with a measurement procedure presented in the ASTM G108-94 standard, in order to guarantee conditions equivalent with the DL-EPR tests performed on AISI 304 stainless steel. Findings - Performed researches revealed the advantages of the DEIS technique over standard double-loop electrochemical potentiokinetic reactivation (DL-EPR) tests in the field of intergranular corrosion investigations. Application of the DEIS technique made it possible to trace instantaneous changes in the examined system's impedance versus potential during the intergranular corrosion process. The form of recorded DEIS spectra and obtained distribution of measurement frequencies within the reactivation potential range were equivalent to those obtained for pure iron dissolution in sulfuric acid medium. As a result, instantaneous changes of electrical double layer capacitance and charge transfer resistance as a function of potential have been obtained in the range of activation and reactivation scans. Originality/value - The paper provides information regarding diversification between the electrical double layer capacitance and the charge transfer resistance determined for sensitized AISI 304 stainless steel with respect to polarization conditions during the standard DL-EPR test, which were obtained in order to evaluate the susceptibility to intergranular corrosion.