Production method of anisotropic rare earth magnet powder

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 600° C. under a hydrogen atmosphere;
• b) heating the hydride product of step (a) up to a temperature in the range of from 760° to 860° C. under a hydrogen gas atmosphere of from 0.2 to 0.6 atm to react it further with hydrogen and cause a phase transformation (decomposition of the hydride to an RH2 phase, an Fe phase and an Fe2B phase), the phase transformation reaction proceeding at a relative reaction rate Vr1 of from 05 to 0.80, wherein:
• Vr1=1/0.576·[{(PH2)½−0.39}/0.61]·exp (−Ea/RT)×10−9
• Wherein:
• 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 products of step (b) under a hydrogen gas pressure of from 0.1 to 0.001 atm and thus reacting said products with hydrogen and causing a reverse phase transformation (changing from the three decomposed phases to R2Fe14BHx by desorption), the reverse phase transformation reaction proceeding at a relative reaction rate Vr2 of from 0.10 to 0.95, wherein:
• Vr2=[1/0.576·{0.39−(PH2)½}/0.38]·exp (−Ea/RT)×10−9
• and ii) a second stage comprising desorbing hydrogen from the R2Fel4BHx until the hydrogen pressure is less than 10−2 torr.

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 as starting material, to produce a hydride R2Fe14BHx (x:
• atomic ratio of hydrogen), by reacting the RFeB based alloy with hydrogen at a temperature of less than 600° C. under a hydrogen atmosphere less than 1.0 atm necessary for hydrogenation;
• b) further hydrogenating the hydride product from step (a) to produce a mixture of an RH2 phase, an Fe phase and an Fe2B phase and to make crystallographic orientation of the Fe2B phase consistent with that of R2Fe14BHx by effecting a phase transformation with heating said hydride up to a phase transformation temperature in the range of from 760° to 860° C. under a hydrogen atmosphere of from 0.2 to 0.6 atm at a relative phase transformation speed with a relative reaction rate Vrl within the range of from 0.05 to 0.80, wherein:
• Vr1=[1/0.576·{(PH2)½−0.39}/0.61]·exp (−Ea/RT)×10−9
• Wherein:
• PH2:
• hydrogen gas pressure (Pa)
• Ea:
• activation energy of alloy (J/molK)
• R:
• Gas constant
• T:
• Absolute temperature (K);
• and
• c) effecting desorption, including i) a first stage comprising effecting a reverse phase transformation of the mixture by desorbing hydrogen from the RH2 while controlling relative phase transformation speed so that a relative reaction rate Vr2 has a value of from 0.10 to 0.95 at a temperature in the range of from 760° to 860° C. under a hydrogen atmosphere of from 0.1 to 0.001 atm, and producing a fine grained recombined hydride R2Fe14BHx having a crystallographic orientation consistent with that of the Fe2B phase, wherein:
• Vr2=[1/0.576·{0.39−(PH2)½}/0.38]·exp (−Ea/RT)×10−9
• and ii) a second stage comprising desorbing hydrogen from the recombined hydride R2Fe14BHx until hydrogen pressure becomes less than 10−2 torr to produce the fine grained R2Fe14BHx phase.

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), up to 20 at % of Co 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 600° C. under a hydrogen atmosphere;
• b) heating the product of step (a) up to a temperature in the range of from 760° to 800° 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=1/0.576·[{PH2−0.39}/0.61]·exp (−Ea/RT)×10−9
• Wherein:
• PH2:
• hydrogen gas pressure (Pa)
• Ea:
• activation energy of allow (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 phas4e transformation in which a relative reaction rate Vr2 has a value of from 0.10 to 0.95, wherein:
• Vr2=[1/0.576·{0.39−(PH2)½/0.38}·exp (−Ea/RT)×10−9
• and (ii) a second stage comprising desorbing hydrogen from the RFeB based alloy produced from the first stage until the hydrogen pressure is less than 10−2 torr.