Corrosion potential oscillations of nickel-containing stainless steel in concentrated sulphuric acid: II Mechanism and kinetic modelling

In the current work, the mechanism for oscillations in mixed potential of UNS S30403 Stainless steel in concentrated sulphuric acid is refined to clarify the importance of the stability limit of nickel sulphide in relation to the passivation potential of the steel. It is rationalized that the oscillation of the corrosion potential can occur spontaneously only when the nickel sulphide stability limit lies within a specific potential range above the passivation potential of the steel and below the tangent for re-activation. Two possible kinetic models are proposed and contrasted to illustrate which better explains the potential-time behaviour for depassivation.