Assesment of Nickel-Based Alloy Passive Film Stability Through Thermodynamic Modeling

Alloy 22 exhibits highly corrosion resistant behaviour in various aggressive environments.  This corrosion resistance property of the metals is attributed to stability of the protective passive oxide film present on its surface.  The passive film acts as a barrier between the metal surface and corrosive salt solutions present in the environment.  It is hypothesized if the passive film constituents dissolve in the salt solution, the passive film will be no longer be available to protect the metal surface, which should result in high general corrosion rates of the metal in a environment.  The objective of this paper is to explore the stability of the Alloy 22 passive film by calculating the solubility of passive film constituents in various salt compositions and at different temperatures.  The predicted solubility results are compared with the general corrosion rate data. It is found that the marked increase in solubilities of passive film constituents correlates well with marked increases in general corrosion rate.