Nitrogenation study of bulk Sm sub 2 (Fe,Co) sub 17 compound: comparison between two processes

The nitriding of bulk Sm sub 2 (Fe sub 0.5 Co sub 0.5 ) sub 17 compound was carried out by two different processes: fluidized bed and gaseous nitrogenation. It was investigated by x-ray diffraction and Mossbauer spectrometry. The site occupancy of iron atoms in Sm sub 2 (Fe sub 0.5 Co sub 0.5 ) sub 17 was determined, showing a full 6c site filling. The Mossbauer hyperfine parameters increase upon nitrogenation; an enhancement up to 50 kOe is noticed for the hyperfine field. Due to modifications of the sample's surface conditions, the time dependence of the nitrogen surface concentration differed according to the nitrogenation process, evidencing that the nitriding kinetics is controlled by an interfacial reaction for gaseous nitrogenation, and by diffusion for the fluidized-bed process.