Metal treatment – Process of modifying or maintaining internal physical... – Magnetic materials
Reexamination Certificate
1999-04-12
2001-12-11
Jenkins, Daniel J. (Department: 1742)
Metal treatment
Process of modifying or maintaining internal physical...
Magnetic materials
C148S513000, C427S216000, C427S217000, C419S020000, C419S035000
Reexamination Certificate
active
06328817
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a bonded permanent magnet material used in a motor, a speaker, an actuator or the like and directs to an exchange spring magnet having a composite structure of a hard magnetic phase represented by Sm
2
Fe
17
N
x
and a soft magnetic phase of Fe or Fe—Co alloy or the like in the same texture, and it also relates to a novel powder for permanent magnet with well-balanced high magnetization and high coercive force, a method for producing the powder and an anisotropic permanent magnet made by the powder.
BACKGROUND ART
An exchange spring magnet behaves as a single hard magnetic material because of strong exchange bonding force between both phases described above and, at the same time, it exhibits such a specific behavior that magnetization reversibly springs back to a change of an external magnetic field in the second quadrant of a demagnetization curve. Recently, an optimum use of the effect has attracted special interest.
A suggested method of allowing a soft magnetic phase to exist in an alloy for magnet is roughly divided into two ways. The method belonging to the first division is a method of causing the soft magnetic phase separation as a result of p precipitation from a molten alloy with a controlled composition on solidification during cooling or the following heat treatment after cooling, and includes various methods, for example, a method described in Unexamined Patent Publication No. Hei 5-135928 wherein a Nd—Fe—B alloy containing excess Fe is molten, solidified and heat-treated to obtain a micro-crystal aggregate of a Fe
3
B phase (soft magnetic phase) and a Nd
2
Fe
14
B phase (hard magnetic layer), or a method described in Unexamined Patent Publication No. Hei 6-330252 wherein a Sm—Fe—N alloy containing excess Fe is molten, solidified and heat-treated, thereby allowing to make a Fe phase (soft magnetic phase) and a Sm
2
Fe
17
N
x
phase (hard magnetic layer) coexist as a crystal having a grain size of not more than 0.5 &mgr;m, respectively. However, these alloys obtained by these methods can be used only as an isotropic magnet alloy and have such disadvantages that there is a limitation in characteristics for novel use in future and that expensive and large-scale equipment for melting and quenching solidification of the alloy are required.
The method belonging to the second division is a method of using needle-like iron powder as a base material and changing the surface portion into a hard magnetic phase by using a chemical treatment and a heat treatment. Unexamined Patent Publication No. Hei 7-272913 discloses a raw material for permanent magnet, comprising needle-like iron powder, an aluminum phosphate coating layer, a rare earth diffusion layer or a rare earth-iron-boron diffusion layer or a rare earth-boron-nitrogen diffusion layer, and an aluminum phosphate coating layer, said layers being provided in order on the surface of the needle-like iron powder, and also discloses a method for producing the raw material, which comprises the steps of heating FeOOH (Goethite) needle-like grains under the state of being coated with aluminum phosphate in a hydrogen atmosphere to 300-500° C., thereby reducing FeOOH to Fe (needle-like iron powder); heating to 650-1000° C. in an argon atmosphere under the presence of rare earth or rare earth and boron, thereby diffusing rare earth, or rare earth and boron on the surface of the aluminum phosphate-coated needle-like iron powder; heating to 500-300° C. in a nitrogen atmosphere, thereby diffusing nitrogen on the surface layer; and heating to 300-500° C in an argon atmosphere, thereby coating with aluminum phosphate again. According to this method, magnetic characteristics are improved by the oxidizing inhibition effect due to double coating of aluminum phosphate and the action as a magnetic domain wall thereof, but stable excellent magnetic characteristics can not be obtained. This reason is as follows. That is, during the evaporation and diffusion of Sm, aluminum phosphate is decomposed and reduced by a strong reducing force of Sm and Al is incorporated into the iron powder, whereas, Sm is oxidized and the hard magnetic phase of the Sm—Fe—N alloy is not easily formed, resulting in deterioration of magnetic characteristics.
More particularly, the present invention relates to an improvement in exchange spring magnet by using the method belonging to the second division, and an object of the present invention is to provide a powder for permanent magnet having stable excellent magnetic characteristics by homogeneously diffusing and forming a hard magnetic layer on the surface of needle-like Fe fine particles, a method for producing the powder, and an anisotropic permanent magnet made by the powder.
DISCLOSURE OF INVENTION
To attain the object described above, the powder for permanent magnet according to the present invention, comprises needle-like fine particles of Fe or Fe—Co alloy as a base material, a hard magnetic layer containing Fe, Sm and N provided on the surface of said needle-like fine particles, and a separation layer of an oxide of rare earth element provided outside said hard magnetic layer. By having such a separation layer, the respective needle-like fine particles are separated and adhesion between the needle-like fine particles and grain growth are inhibited, thereby inhibiting a reduction in aspect ratio. As a result, a permanent magnet having excellent shape anisotropy can be obtained.
Furthermore, the powder for permanent magnet of the present invention comprises a sintered body powder having a particle diameter of 10 to 100 &mgr;m, said sintered body powder comprising needle-like fine particles of Fe or Fe—Co alloy as a base material, a hard magnetic layer containing Fe, Sm and N provided on the surface of said needle-like fine particles, and a separation layer of an oxide of rare earth element provided outside said hard magnetic layer. By using such a separation layer, bonding of iron phases is inhibited on sintering, thereby making it possible to obtain a well-dispersed high-density sintered body.
Furthermore, when the separation layer is coated with one or more metals of Zn, Sn and Pb, an intermetallic compound is formed between Sm and these low-melting point metals, thereby markedly improving a coercive force.
In the present invention, a first invention provides a powder for permanent magnet, comprising needle-like fine particles of Fe or Fe—Co alloy as a base material, a hard magnetic layer containing Fe, Sm and N provided on the surface of said needle-like fine particles, and a separation layer of an oxide of rare earth element provided outside said hard magnetic layer. As the rare earth elements, one or more rare earth elements of Nd, La, Ce, Pr, Sm and Y can be used.
Furthermore, a second invention provides a powder for permanent magnet, comprising a sintered body powder having a particle diameter of 10 to 100 &mgr;m, said sintered body powder comprising needle-like fine particles of Fe or Fe—Co alloy as a base material, a hard magnetic layer containing Fe, Sm and N provided on the surface of said needle-like fine particles, and a separation layer of an oxide of a rare earth element provided outside said hard magnetic layer.
In the first invention, a third invention provides a powder for permanent magnet wherein a separation layer is coated with one or more metals of Zn, Sn and Pb.
To produce the powder for permanent magnet described above, a fourth invention provides a method for producing a powder for permanent magnet, which comprises coating the surface of needle-like Fe fine particles or needle-like Fe—Co alloy fine particles, said fine particles having a major axis of 0.1 to 3 &mgr;m and a minor axis of 0.03 to 0.4 &mgr;m, with a hydroxide of rare earth element by using wet deposition method; subjecting the fine particles to filtration and drying; heat- treating the dried fine particles in an atmosphere of a hydrogen gas or an inert gas, or a mixture thereof; coating the resultant needle-like Fe fine particles or needle-like Fe—Co alloy fine particles
Jenkins Daniel J.
Marshall Gerstein & Borun
Santoku Metal Industry Co. Ltd.
LandOfFree
Powder for permanent magnet, method for its production and... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Powder for permanent magnet, method for its production and..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Powder for permanent magnet, method for its production and... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2571352