Study of the transition from oxidation to nitriding in a single N2-H2-O2 post-discharge

The nitriding (understood here as the reduction of native oxide present on iron samples followed by the diffusion of nitrogen in the solid) or the oxidation of a 25-μm-thick iron foil is performed in a N2-0.5 vol.% H2-0.012 vol.% O2 post-discharge by simply varying the temperature from 673 up to 773 K. The ɛ-Fe2N1−x phase is obtained at 773 K whereas the Fe3O4 phase is clearly identified at 673 K. At 723 K, either an oxide or a nitride phase is synthesized, depending on the leakage in the reactor. The measurement of the intensity of the first positive system of nitrogen indicates that the time evolution of this signal could be correlated with the growth of the oxide layer at low temperature and with the nitrogen uptake by solid diffusion at high temperature.