Passivity of Type 2205 duplex stainless steel in acetic acid/sodium acetate buffer solutions containing thiosulfate

Passivity of 2205 duplex stainless steel (DSS) with different surface pre-conditionings was investigated in thiosulfate-containing solutions using electrochemical tests, time-of-flight secondary ion mass spectrometry (ToF-SIMS) and density functional theory (DFT). While thiosulfate had no effect on air-passivated DSS in the primary passive range, it influenced fresh DSS when the air-passivated film was cathodically or mechanically removed. Surface analysis by ToF-SIMS revealed that iron sulfide was incorporated in the passive film formed on an air-passivated surface, while iron, chromium, and nickel sulfides were incorporated in the passive film formed on fresh surfaces. DFT modelling supported experimental observations.