M. Ito et al., EFFECT OF MILLING ATMOSPHERE ON THE PREPARATION OF SM2FE17NX POWDER BY MECHANICAL GRINDING (REPRINTED FROM J JAPAN INST METALS, VOL 60, PG 427, 1996), Materials transactions, JIM, 37(11), 1996, pp. 1704-1709
The preparation of Sm2Fe17Nx permanent magnet powders has been tried b
y mechanical grinding (MG) for a short time without crystallization he
at treatment which was usually needed to obtain a Th2Zn17 structure in
the conventional method by MG or MA. MG was carried out in three kind
s of atmospheres; i.e., Ar, N-2 and NH3 gas. Untreated and hydrogenate
d Sm2.5Fe17 alloy powders were used as the starting materials. The (Y-
Fe precipitation was detected in the powder after MG for over 14.4 ks.
The grain size of powder obtained by MG for 10.8 ks was around 10 nm
which was much finer than the single magnetic domain size of about 300
nm. The existence of hydrogen promoted not only the nitriding of powd
ers but the oxidation. The hydrogenated powder after MG in NH3 and nit
riding had a high oxygen content of about 13000 ppm. This oxidation pr
evented the absorption of nitrogen during the nitriding process. The u
ntreated powders after MG in NH3, however, were nitrided efficiently u
p to 38000 ppm at a low temperature of 623 K, and the oxygen content w
as about 7000 ppm. The maximum coercivity of 0.93 MA . m(-1) (11.7 kOe
) was obtained with the untreated powder after MG in NH3 and nitriding
at 623 K for 10.8 ks in N-2.