THE DISPROPORTIONATION OF ND2FE14B UNDER HYDROGEN IN ND-FE-B ALLOYS

The kinetics of the disproportionation reaction, in which the Nd2Fe14B phase forms Fe, Nd-hydride, and Fe2B under hydrogen, have been investigated by thermopiezic analysis. These studies have shown that the disproportionation temperature is dependent upon grain size, and is considerably lower for Nd-Fe-B alloys with submicron grain sizes, when compared with the cast 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 Nd2Fe14B phase in the alloy, can be related to the temperature range over which the reaction occurs and to the amount of Fe and Fe2B that forms as a result of the disproportionation reaction. The latter can be monitored by measuring the magnetization of the disproportionated material.