Comparative investigation of the nitrogenation mechanisms of bulk intermetallic Sm2(Fe,Co)17 by two processes

The nitrogenation mechanisms of the Sm₂(Fe_0.5Co_0.5)₁₇ compound were investigated on bulk samples using X-ray diffraction and chemical analysis. Two nitrogenation processes (fluidized bed nitrogenation (FBN) and gaseous nitrogenation (GN)) were used in order to compare the different steps occurring during the treatment. The fluidized bed process leads to a constant nitrogen surface concentration after one hour treatment while the concentration increases continuously with the gaseous process. The overall bulk nitrogenation kinetics is parabolic for the fluidized bed, whereas the gaseous nitrogenation exhibits first an incubation period followed by an accelerated rate. Two different mechanisms, bulk diffusion for the FBN process and an interface reaction for the GN process, govern the nitrogenation kinetics.