Characterization of passive film on 2205 duplex stainless steel in sodium thiosulphate solution

The electrochemical behaviour of passive film formed on 2205 duplex stainless steel in 0.1 M Na2S2O3 solutions was investigated using potentiodynamic polarization, EIS, Mott–Schottky analysis and the compositions of oxide film in different passive regions were carried out by XPS. The results indicated that the impedance is dependent on the applied potential indicating the occurrence of a charge transfer reaction in a porous film. The doping densities evaluated from Mott–Schottky plots demonstrated that there existence of two donor levels in the space charge layer of the passive films. The donor density (ND1 and ND2) values are in the range of 1020–1021 cm3, and decreases exponentially with increasing film formation potential, which is in good agreement with the theoretical consequences of the PDM. The polarization curve and XPS results shows that in the passive regions the 2205 duplex stainless steel exhibits different electrochemical and semiconductor properties.