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We studied the high temperature decomposition mechanism for the [Fe.sub.17][Sm.sub.2][N.sub.3] phase using several different experimental techniques, as thermomagnetic and thermogravimetric analyses. Our results show that the decomposition occurs in a two step scheme. In the first reaction we have the formation of SmN and a solid solution of nitrogen in iron. In the second step, this solid solution degases, and we observe the evolution of nitrogen over a broad temperature range.

X-ray diffraction patterns and diffusion profile microbe measurements of partially nitrided samples were obtained for the Fe(sub 17)Nd(sub 2) phase. X-ray diffraction patterns arose due to the projection of pure and nitrided patterns, with mutual stresses causing displacement and widening of lines between the phases. Nitrogenation during the Fe(sub 17)Nd(sub 2) phase precipitated an entire nitrided phase from a nitrogen-free phase.

The nitrogen diffusion patterns on several RE2Fe17 intermetallic compounds are studied. The nitriding process was done in both slabs and powder samples, which were characterized and analyzed thermomagnetically and metallographically. The diffusion process occurs by both mechanisms: shell-core model and along preferential paths. A broadening caused by stress or by dilution was detected in pure phase transition.

The effects of different contents of nitrogen in both Pr2Fe17 and Nd2Fe17 and of cobalt in both Nd2Fe17 and Nd2Fe17N2 center dot 2 are investigated by means of Mossbauer spectroscopy (MS) and thermal magnetic analysis (TMA). The results confirm that either nitrogen or cobalt increases the hyperfine field (Bhf) as well as the Curie temperature (Tc) of the material. The hyperfine parameters for nominal contents of nitrogen above y = 1.5 are the same as those observed in fully nitrided samples. Our data also reveal that the combination of both N and Co produces an additional increase of Tc. The same behaviour is observed in Bhf of Nd2(Fe1-xCox)17N2 center dot 2 in the range 0 < x < 0.1. After a restricted maximum at x approximately equal to 0.02-0.05, Bhf decreases with increasing x.