Patent ID: 6444052
Filing Date: 2002-09-03
Classification: B22F,C22C,H01F

Abstract:
A method of producing an anisotropic magnet powder comprising the following sequential steps:a) hydrogenating an RFeB based alloy, comprising from 11 to 15 at % of a rare earth element (R), from 5.5 to 8.0 at % of boron (B), iron (Fe) and unavoidable impurity, to produce a hydride R2Fe14BHx (x: atomic ratio of hydrogen), by reacting the RFeB based alloy with hydrogen at a temperature of less than 600Â° C. under a hydrogen atmosphere; b) heating the product of step (a) up to a temperature in the range of from 760Â° to 860Â° C. under a hydrogen gas atmosphere of from 0.2 to 0.6 atm to effect phase transformation at a relative reaction rate Vr1, having a value of from 0.05 to 0.80, wherein: Vr1=1/0.576Â·[{(PH2)Â½âˆ’0.39}/0.61]Â·exp (âˆ’Ea/RT)Ã—10âˆ’9 â€ƒWherein PH2: hydrogen gas pressure (Pa) Ea: activation energy of alloy (J/molK) R: Gas constant T: Absolute temperature (K) c) effecting desorption including (i) a first stage comprising heating the product of step (b) under a hydrogen gas pressure of from 0.1 to 0.001 atm to react said product with hydrogen at a relative speed range of a reverse phase transformation in which a relative reaction rate Vr2 has a value of from 0.10 to 0.95, wherein: Vr2=[1/0.576Â·{0.39âˆ’(PH2)Â½/0.38}Â·exp (âˆ’Ea/RT)Ã—10âˆ’9 â€ƒand ii) a second stage comprising desorbing hydrogen from the RFeB based alloy produced from the first stage until the hydrogen pressure is less than 10âˆ’2 torr.