Thermodynamic basis of antagonistic effects of oxygen and sulphur on corrosion of passivating metals

Highlights: • Correlation between the enthalpies of adsorption of O (S) on metals and the enthalpies of formation of the metal oxides (sulfides). • Plot of enthalpies of S adsorption versus enthalpies of O adsorptionto classify metals according to their capacity to adsorb rather O or S. • Using this plot, the resistance of metals and alloys to S-induced corrosion can be predicted. A thermodynamic basis is used to explain why some metals are prone to develop a resistant passivation layer whereas some are subject to S-induced corrosion. We revisit the correlations between formation enthalpies of adsorbed (2D) and bulk (3D) compounds, both for the M–O and the M–S systems. Then we plot S adsorption enthalpy versus O adsorption enthalpy. This plot allows us to classify the various metals according to their capacity to adsorb rather O or S. Applied to corrosion science and engineering, this work should help predicting the resistance of metals and alloys to corrosion induced by environmental sulphur.