The disproportionation of Nd/sub 2/Fe/sub 14/B under hydrogen in Nd-Fe-B alloys

The kinetics of the disproportionation reaction in which the Nd/sub 2/Fe/sub 14/B phase forms Fe, Nd-hydride, and Fe/sub 2/B under hydrogen has been investigated by thermopiezic analysis. These studies have shown that the disproportionation temperature is dependent on grain size, and is considerably lower for Nd-Fe-B alloys with submicron grain sizes when compared with the case material. Thus, melt-spun material disproportionates at a temperature about 300 degrees C below that of cast alloy (at a heating rate of 1 degrees C/min). In addition, the amount of Nd/sub 2/Fe/sub 14/B phase in the alloy can be related to the temperature range over which the reaction occurs and to the amount of Fe and Fe/sub 2/B that forms as a result of the disproportionation reaction. The latter can be monitored by measuring the magnetization of the disproportionated material.<
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