Nitrogenation of R2Fe17 compounds: R=rare earth

The reaction between nitrogen gas and the series of R2Fe17 intermetallic compounds is studied by thermopiezic analysis on micron-size powders. Nitrogen diffusion in the range 300–550 °C can be represented by an activated interstitial diffusion process D=D0e−Em/kT with D0=1.95×10−10 m2 s−1 and an activation energy Em=0.81 eV. This stage of the nitrogenation reaction leads to the formation of R2Fe17N3−δ nitrides which have structures related to those of the parent compounds. Heating above about 800 °C leads to complete disproportionation of the compounds into a mixture of rare-earth nitride and iron.