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The surface properties and reactivities of plasma-nitrided iron with ~'-Fe~N and e-Fe~.~N overlayers have been examined with photoelectron spectroscopy. Reactivities toward oxidation in air at room and elevated temperature, in oxygen plasma and under electrochemical conditions, have been established. Room temperature air oxidation produces mainly Fe ~+ Whose concentration increases with increasing nitrogen content in the nitride. Thermal oxidation at 500~ yields ~-Fe=O~ at the topmost surface seen by XPS, while at 125~ clear evidence for oxide decomposition with absorption of oxygen into the underlaying nitride is seen. Electrochemical passivation results exclusively in FeOOH. The thickness of this passivation layer decreases with increasing N content in the nitride. The role of nitrogen in the catalytic conversion of Fe ~ § to Fe ~ § and the mechanism of the enhanced corrosion resistance of nitrided iron is presented.

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