Comparative investigation of the nitrogenation mechanisms of bulk intermetallic Sm-2(Fe,Co)(17) by two processes

The nitrogenation mechanisms of the Sm-2(Fe0.5Co0.5)(17) compound were inve stigated on bulk samples using X-ray diffraction and chemical analysis. Two nitrogenation processes (fluidized bed nitrogenation (FBN) and gaseous nit rogenation (GN)) were used in order to compare the different steps occurrin g during the treatment. The fluidized bed process leads to a constant nitro gen surface concentration after one hour treatment while the concentration increases continuously with the gaseous process. The overall bulk nitrogena tion kinetics is parabolic for the fluidized bed, whereas the gaseous nitro genation exhibits first an incubation period followed by an accelerated rat e. Two different mechanisms, bulk diffusion for the FBN process and an inte rface reaction for the GN process, govern the nitrogenation kinetics. (C) 2 000 Kluwer Academic Publishers.