Measurement of the loss probability of nitrogen atoms at 823 K on iron nitride ε-Fe2N1−x

The loss probability of nitrogen atoms on iron nitride ε-Fe2N1−x is measured at 823 K. Pure iron tubes of different sections are nitrided by a post-discharge process. For treatment times between 15 and 120 min, nitrided substrates have an ε-Fe2N1−x layer, in contact with the gas phase, overlying a layer of γ′-Fe4N above the α-Fe diffusion layer. To explain the layers growth in the experimental conditions described herein, which can be estimated by thickness measurements by optical micrographs of the treated substrates, only constant flux density conditions can be retained. With this boundary condition, by the mean of a model solving the coupled transport equations, determination of the loss probability of nitrogen atoms on the ε-Fe2N1−x is possible. It requires that the rate limiting step corresponds to both surface reaction and gas phase diffusion limitations. At 823 K, this loss probability is 10−2±10%.