Passivation Behavior of Type-316L Stainless Steel in the Presence of Hydrogen Sulfide Ions Generated from a Local Anion Generating System

The passivity of type 316L stainless steel was studied in a pH 8.4 boric acid-borate buffer solution containing hydrogen sulfide ions (HS−) by using a local anion-generating system. During potentiostatic polarization of the stainless steel at a primary passive potential of 0.4 VSSE and at a secondary passive potential of 0.9 VSSE in solutions with and without HS−, the current density flowing for passive film formation was increased by the presence of HS− at both potentials, while 15 Hz impedance at 0.9 VSSE in the solution with HS− was larger than that in the solution without HS−. It was thought that the presence of HS− in the solution during film formation made the film less resistive and affected the film capacitance depending on the polarization potential. X-ray photoelectron spectroscopy (XPS) showed an increase in metal cation and oxygen anion vacancies in the passive film formed at the primary passive state in the solution containing HS−. Auger electron spectroscopy (AES) and Raman spectroscopy revealed that a sulfide layer was deposited on the stainless steel surface that was oxidized at the secondary passive state in the solution containing HS−. It is thought that application of a high potential changes the passivity of the stainless steel surface in the solution containing HS−.