Oxygen permeability of Fe-Ni-Cr alloys at 1100 and 1150 °C under carbon-free and carbon-containing gases

Abstract

Wagner's model of internal oxidation allows the prediction of an alloy's critical concentration of oxide forming metal required to achieve a protective oxide scale at high temperatures. The model depends on oxygen permeability in the alloy, but this parameter has not been evaluated for the Fe-Ni system, and the influence of carbon-bearing gases is unknown. Oxygen permeability measurement by internal oxidation of Fe-Ni-Cr alloys, reacted at 1100 and 1150 8C is described. Exposures in Rhines packs and flowing CO-CO2 gas mixtures serve to assess the influence of carbon on oxygen permeability at the Fe-FeO equilibrium oxygen potential. Oxygen permeability in Fe-Ni increases with iron content in a non-ideal manner in both gas environments. Higher permeability is found in carbon bearing gases for iron-rich alloys, and the size of this effect increases with temperature.