JP7156226B2 - Method for manufacturing rare earth magnet - Google Patents

Description

The present disclosure relates to a method for manufacturing rare earth magnets. In particular, the present disclosure relates to a method for producing a samarium-iron-nitrogen rare earth magnet.

As high-performance rare earth magnets, samarium-cobalt rare earth magnets and neodymium-iron-boron rare earth magnets have been put into practical use, but in recent years, rare earth magnets other than these have been investigated.

For example, samarium-iron-nitrogen rare earth magnets are being studied. A samarium-iron-nitrogen rare earth magnet is manufactured using magnetic powder containing samarium, iron and nitrogen (hereinafter sometimes referred to as "samarium-iron-nitrogen magnetic powder").

The samarium-iron-nitrogen based magnetic powder contains a magnetic phase having either a Th ₂ Zn ₁₇ -type or a Th ₂ Ni ₁₇ -type crystal structure. This magnetic phase is considered to be an interstitial solid solution of nitrogen in samarium-iron crystals. Therefore, the samarium-iron-nitrogen based magnetic powder is likely to decompose due to the separation of N by heat. For this reason, samarium-iron-nitrogen rare earth magnets are often produced by molding samarium-iron-nitrogen magnetic powder using resin and/or rubber.

As a method for manufacturing a samarium-iron-nitrogen rare earth magnet other than the above, there is a manufacturing method disclosed in Patent Document 1, for example. In this manufacturing method, samarium-iron-nitrogen based magnetic powder and powder containing metallic zinc are mixed, the mixed powder is compacted in a magnetic field, and the magnetic compact is sintered (including liquid phase sintering). .

WO2015/199096

When samarium-iron-nitrogen magnetic powder (hereinafter sometimes referred to as "magnetic powder") and powder containing metallic zinc (hereinafter sometimes referred to as "metallic zinc powder") are sintered, metallic zinc powder The zinc component inside diffuses into the surface of the magnetic powder in a solid or liquid phase and is sintered (solidified). Thus, metallic zinc powder has a function as a binder. The metallic zinc powder also functions as a modifier that modifies the αFe phase in the magnetic powder and absorbs oxygen in the magnetic powder to improve the coercive force. Powders that function as both a binder and a modifier include metallic zinc powders as well as zinc alloy powders. Hereinafter, the powder containing at least one of metallic zinc powder and zinc alloy powder may be referred to as "modifying material powder".

However, when magnetic powder and metallic zinc powder are simply mixed in sintering, as in the conventional method, many magnetic powder particles do not come into contact with the modifying material, so the above modification is not sufficient. The present inventors have found the problem that the improvement is not sufficient.

The present disclosure has been made to solve the above problems. That is, an object of the present disclosure is to provide a method for producing a samarium-iron-nitrogen rare earth magnet capable of further improving the coercive force compared to conventional methods.

In order to achieve the above object, the present inventors have made intensive studies and completed a method for producing a rare earth magnet according to the present disclosure. A method for manufacturing a rare earth magnet of the present disclosure includes the following aspects.
<1> Modifier powder containing at least one of metallic zinc powder and zinc alloy powder and samarium-iron-nitrogen magnetic powder are mixed and sintered to obtain a density of 5.0 to 7.2 g/ obtaining a sintered body of cm ³ and storing the sintered body inside a container;
heating the sintered body while decompressing the inside of the container to generate zinc vapor from at least one of metallic zinc powder and zinc alloy powder in the sintered body;
Depositing a zinc component on the particle surfaces of the magnetic powder in the sintered body by at least either injecting an inert gas into the interior of the vessel or cooling the interior of the vessel;
A method for producing a rare earth magnet, comprising:

According to the present disclosure, zinc vapor is generated inside the sintered body, and the sintered body has a predetermined density. For powder particles, the zinc component of the modifier can be deposited on the surface of the particles. As a result, it is possible to provide a method for producing a samarium-iron-nitrogen rare earth magnet capable of further improving the coercive force compared to conventional methods.

FIG. 1 is a schematic diagram showing a state in which mixed powder of magnetic powder and modifier powder is stored in a cavity of a sintering mold. FIG. 2 is a schematic diagram showing a state in which the sintered body is stored in the cavity of the sintering mold. FIG. 3 is a schematic diagram showing a state in which the sintered compact is heated while the pressure inside the cavity of the sintering mold is reduced. FIG. 4 is a schematic diagram showing a state in which the zinc component is deposited on the particle surfaces of the magnetic powder from the state of FIG. FIG. 5 is an explanatory view schematically showing a state when a sintered body having a predetermined density is heated in a decompression vessel. FIG. 6 is an explanatory diagram schematically showing a state when a sintered body having a density of less than a predetermined value is heated in a decompression vessel. FIG. 7 is an explanatory diagram schematically showing a state when a sintered body having a density exceeding a predetermined value is heated in a decompression vessel. FIG. 8 is a vapor pressure curve of zinc. FIG. 9 is a schematic diagram showing a state in which magnetic powder and modifier powder are mixed. FIG. 10 is a schematic diagram showing a state in which a modified film is formed on the particle surface of magnetic powder by a conventional method for producing a rare earth magnet. FIG. 11 is a schematic diagram showing a state in which a modified film is uniformly formed on the surface of magnetic powder particles.

Hereinafter, embodiments of the method for producing a rare earth magnet of the present disclosure will be described in detail. It should be noted that the embodiments shown below do not limit the method of manufacturing the rare earth magnet of the present disclosure.

The reason why the magnetic powder is not sufficiently modified with the modifier powder in the conventional method for manufacturing rare earth magnets will be described with reference to the drawings.

FIG. 9 is a schematic diagram showing a state in which magnetic powder and modifier powder are mixed. FIG. 10 is a schematic diagram showing a state in which a modified film is formed on the particle surface of magnetic powder by a conventional method for producing a rare earth magnet.

Even if the magnetic powder 10 and the modifier powder 20 are mixed, the particles of each powder are not completely and uniformly mixed as shown in FIG. Further, since the modifier powder 20 is softer than the magnetic powder 10, the particles of the modifier powder 20 are sandwiched between the particles of the magnetic powder 10 during mixing, and the particles of the modifier powder 20 are deformed. I have something to do. At that time, the deformed modifier adheres to the surfaces of the particles of the magnetic powder 10 . However, in that case, the modifier does not adhere to each particle of the magnetic powder 10 . In addition, particles of the modifier powder 20 may aggregate during mixing.

In the conventional rare earth magnet manufacturing method, the magnetic powder 10 and the modifier powder 20 are heated (sintered) in the state described above. Therefore, as shown in FIG. 10, there are particles of the magnetic powder 10 that have the modified coating 22 formed on their surfaces, while there are particles of the magnetic powder 10 that do not have the modified coating 22 formed on their surfaces. . Further, among the particles of the magnetic powder 10 having the modified coating 22 formed on the surface, there are many particles (not shown) having the modified coating 22 formed only on a part of the surface. Further, the modifier powder 20 that aggregates during mixing becomes lumps 24 as shown in FIG. The lumps 24 hardly contribute to modifying the magnetic powder 10 .

In order to improve the coercive force by modifying the αFe phase in the magnetic powder and absorbing oxygen in the magnetic powder, it is desirable to form the modified coating 22 as uniformly as possible on each particle of the magnetic powder 10 . be However, in the conventional method for manufacturing rare earth magnets, the desired coercive force was not obtained because the modified film 22 was formed as shown in FIG.

The present inventors have found the following regarding the formation of the modified coating 22 .

After heating the inside of the container containing the magnetic powder 10 and the modifying material powder 20 while reducing the pressure to generate zinc vapor, an inert gas is injected into the container or the inside of the reduced pressure container is cooled. A zinc component can be deposited on the particle surfaces of the powder 10 to form a uniform modified coating 22 . Here, "uniform" does not mean that there are particles with the modified coating 22 formed on the surface and particles without the modified coating 22 formed on the surface, as shown in FIG. As shown in FIG. 11, it means that the modified coating 22 is substantially formed on the surface of each particle. Also, in each particle, it means that the modified coating 22 is formed not only on part of the particle surface, but substantially on the entire surface of the particle.

Although not bound by theory, even if the mixture of the magnetic powder 10 and the modifier powder 20 is not uniform, if the mixed powder is heated in a decompression container to generate zinc vapor from the modifier powder 20, magnetic Through the gaps between the particles of the powder 10, the zinc vapor spreads uniformly over the entire magnetic powder 10. In this state, when at least one of injecting an inert gas into the inside of the container and cooling the inside of the container is performed, the zinc vapor uniformly spread over the entire magnetic powder 10 is condensed, and the magnetic powder 10 is A zinc component is uniformly deposited on the surface of each particle of , forming a modified coating 22 . As a result, a coated magnetic powder 28 having a uniform modified coating 22 as shown in FIG. 11 is obtained. In order to obtain the coated magnetic powder 28 as shown in FIG. 11, a sintered body of mixed powder of the magnetic powder 10 and the modifier powder 20 having a predetermined density is prepared in advance, and the sintered body is placed in a container. The present inventors have found that the sintered body may be heated while the pressure inside the container is reduced. In the following description, "the sintered compact is stored in a container, and the sintered compact is heated while the pressure inside the container is reduced" means "heating the sintered compact in the reduced-pressure container". be.

Although not bound by theory, the reason why a uniform coated magnetic powder can be obtained in a sintered body by using a sintered body having a predetermined density will be described with reference to the drawings. FIG. 5 is an explanatory view schematically showing a state when a sintered body having a predetermined density is heated in a decompression vessel. FIG. 6 is an explanatory diagram schematically showing a state when a sintered body having a density of less than a predetermined value is heated in a decompression vessel. FIG. 7 is an explanatory diagram schematically showing a state when a sintered body having a density exceeding a predetermined value is heated in a decompression vessel.

When the sintered body 30 has a predetermined density, the sintered body 30 has a predetermined air permeability. When the sintered body 30 having a predetermined air permeability is heated in a decompression container, a differential pressure is generated between the inside and outside of the sintered body 30 . Due to this pressure difference, as indicated by the arrows in FIG. Although zinc vapor spreads throughout the interior of the sintered body 30, very little zinc vapor is discharged outside the sintered body 30. Therefore, when the zinc vapor remaining inside the sintered body 30 is condensed by injecting an inert gas into the interior of the decompression vessel or by cooling the interior of the vessel, uniform reformation as shown in FIG. A coated magnetic powder 28 having a fine coating 22 is obtained.

If the sintered body 30 has a density less than the predetermined value, the sintered body 30 has excessive air permeability. When the sintered body 30 having excessive air permeability is heated in a vacuum container, most of the zinc vapor generated from the modifier powder 20 is discharged to the outside of the sintered body 30 as indicated by the arrows in FIG. be. As a result, the modified film 22 is hardly formed on the surface of the magnetic powder 10, and the modification of the magnetic powder does not progress.

If the sintered body 30 has a density exceeding a predetermined value, the spacing between the particles of the magnetic powder 10 is very narrow, and as indicated by the arrow in FIG. The movement range is limited and the zinc vapor does not spread throughout the interior of the sintered body 30 . In addition, since the air permeability of the sintered body 30 is also very low, the reduced pressure does not act on the inside of the sintered body 30, so that the zinc vapor is difficult to move inside the sintered body 30. Therefore, inside the sintered body 30, there is a large difference in concentration of zinc vapor depending on the part. As a result, even if the vapor of zinc inside the sintered body 30 is condensed by injecting an inert gas into the interior of the decompression vessel or by cooling the interior of the vessel, the coating magnetism having the uniform modified coating 22 can be obtained. No powder 28 is obtained.

Constituent elements of the method for manufacturing a rare earth magnet according to the present disclosure, which have been completed based on the knowledge and the like described so far, will be described below.

<<Method for producing rare earth magnet>>
A method of manufacturing a rare earth magnet of the present disclosure includes a sintered body forming step, a zinc vapor generation step, and a zinc component deposition step. Each step will be described below.

<Sintered body forming process>
A modifier powder containing at least one of metallic zinc powder and zinc alloy powder is mixed with samarium-iron-nitrogen based magnetic powder to obtain a mixed powder. This mixed powder is sintered to obtain a sintered body having a density of 5.0 to 7.2 g/cm ³ . Then, the sintered body is stored inside the container. "Modifier powder containing at least one of metallic zinc powder and zinc alloy powder" and "samarium-iron-nitrogen-based magnetic powder" are sometimes referred to as "modifier powder" and "magnetic powder", respectively. This is as described above.

As long as a desired zinc vapor pressure can be obtained in the zinc vapor generation step described later, the container for storing the sintered body is not particularly limited. For example, the cavity of the sintering mold used to form the sintered body may be used as the container.

FIG. 1 is a schematic diagram showing a state in which mixed powder of magnetic powder and modifier powder is stored in a cavity of a sintering mold. The sintering mold 40 has a punch 50 and a die 60 . The die 60 has a cavity 65 and the punch 50 slides inside the cavity 65 . A vacuum pump (not shown) is connected to the cavity 65 so that the pressure inside the cavity 65 can be reduced. The pressure reduction in the cavity 65 will be described in the "zinc vapor generation step".

As shown in FIG. 1, mixed powder of magnetic powder 10 and modifier powder 20 is stored in cavity 65 of sintering mold 40 . When the mixed powder is stored in the cavity 65 of the sintering mold 40, a mold different from the sintering mold 40 is prepared, and the magnetic powder 10 and the modifier powder are produced using the mold. The mixed powder of 20 may be compression-molded in advance to obtain a compact, and the compact may be stored in the cavity 65 . Alternatively, a powder compact may be obtained by compression-molding the mixed powder using the sintering mold 40 . When a green compact is obtained using the sintering mold 40, the mixed powder is compression-molded by moving the punch 50 in the direction indicated by the white arrow in FIG.

The pressure when the mixed powder is compression-molded to obtain a green compact may be appropriately determined in consideration of the particle size of the magnetic powder 10 and modifier powder 20, the density of the green compact, and the like. The pressure for obtaining the compact may be, for example, 20 MPa or higher, 50 MPa or higher, 100 MPa or higher, or 150 MPa or higher, and may be 400 MPa or lower, 350 MPa or lower, 300 MPa or lower, 250 MPa or lower, or 200 MPa or lower.

Compression molding of the mixed powder may be performed in a magnetic field to obtain a magnetic compact of the mixed powder. As a result, anisotropy can be imparted to the rare earth magnet (hereinafter sometimes referred to as “result”) obtained by the method for producing a rare earth magnet of the present disclosure, and remanent magnetization can be improved.

The method of compression molding in a magnetic field may be a conventional method such as a method of compression molding the mixed powder using a molding die having a magnetic field generator installed around it. The magnitude of the applied magnetic field may be 300 kA/m or more, 500 kA/m or more, 1000 kA/m, or 1500 kA/m or more, and may be 4000 kA/m or less, 3000 kA/m or less, 2500 kA/m, or 2000 kA/m. may be: As a method of applying a magnetic field, there are a method of applying a static magnetic field using an electromagnet, a method of applying a pulse magnetic field using an alternating current, and the like.

A mold used for compression molding of the mixed powder (including compression molding in a magnetic field) may be used in common with the sintering mold 40 shown in FIG. 1, for example. When compression molding in a magnetic field is shared with the sintering mold 40, the punch 50 and the die 60 are made of a material that can easily apply a magnetic field in the cavity 65 and can withstand high temperature and high pressure during sintering. preferably made of Materials for the punch 50 and the die 60 include, for example, tungsten carbide cemented carbide and/or Inconel. A combination of these may also be used.

The magnetic powder and modifier powder may be mixed and then stored inside the mold used for compaction, or they may be stored inside the mold used for compaction without being mixed. good too. When the magnetic powder and the modifier powder are stored in the mold used for compaction without being mixed with each other, the storage operation mixes the magnetic powder and the modifier powder.

When the magnetic powder and the modifying material powder are mixed and stored in the mold used for compaction, the mixing method is not particularly limited. Mixing methods include methods using a mortar, Nobilta (registered trademark), Muller wheel mixer, agitator mixer, Mechanofusion, V-type mixer, ball mill, and the like. You may combine these methods. In addition, the V-type mixer has a container in which two cylindrical containers are connected in a V shape, and by rotating the container, the powder in the container is repeatedly aggregated and separated by gravity and centrifugal force, and mixed. It is a device that

Next, sintering of the powder compact will be described. As shown in FIG. 1, the sintering may be performed by storing the mixed powder of the magnetic powder 10 and the modifying material powder 20 as it is in the cavity 65 of the sintering mold 40. The mixed powder may be compression molded and the green compact may be stored in the cavity 65 and sintered. As mentioned above, compaction of mixed powders may be performed in a magnetic field.

An example of the sintering method will be described with reference to FIG. A die 60 having a cavity 65 and a punch 50 slidable inside the cavity 65 are prepared. Then, the green compact is stored in the cavity 65 and is sintered while applying pressure to the green compact by the punch 50 .

Although the punch 50 shown in FIG. 1 has a cylindrical shape and the cavity 65 of the die 60 has a cylindrical shape, the shape of the punch 50 and the cavity 65 can be varied according to the shape of the product.

A pressure device (not shown) is connected to the punch 50, and by moving the punch 50 in the axial direction (in the direction of the white arrow in FIG. 1) inside the cavity 65, pressure is applied to the powder compact. Although two punches 50 are provided in the embodiment shown in FIG. 1, both may be moved, or either one may be moved. Examples of pressurizing devices include hydraulic cylinders, pneumatic cylinders, electric servo cylinders, and combinations thereof. In addition, at least one of the punch 50 and the die 60 is provided with a heater (not shown) inside or on its outer periphery, or at least one of the punch 50 and the die 60 can be inserted into a heating furnace. . Typically, for example, a heater or heating furnace is installed around the die 60 .

The form of the punch 50 and the die 60 is not limited to the form shown in FIG. In the embodiment shown in FIG. 1, the die 60 is provided with a through-hole and the through-hole is used as the cavity 65, but this is not restrictive. For example, the die 60 may be provided with a closed bottom cavity 65 and a punch 50 on the opposite side of the bottom.

The sintering conditions may be appropriately determined so that the density of the sintered body is 5.0 to 7.2 g/cm ³ . As the sintering method, either solid-phase diffusion, in which the magnetic powder and the modifier powder mutually diffuse in the solid phase, or liquid-phase sintering, in which the magnetic powder in the solid phase and the modifier powder in the liquid phase diffuse. can also be adopted. In order to form a uniform modified coating, it is preferable to deposit as much zinc component as possible on the particle surfaces of the magnetic powder by the zinc generating step and the zinc component depositing step, which will be described later. For this reason, solid-phase diffusion is preferable because it is preferable that reforming does not proceed during sintering of the green compact of the mixed powder. When the modifier powder has a melting point of T ° C., the sintering temperature may be, for example, (T-50) ° C. or higher, (T-45) ° C. or higher, or (T-40) ° C. or higher, and T °C or lower, (T-5) °C or lower, (T-10) °C or lower, (T-15) °C or lower, (T-20) °C or lower, or (T-30) °C or lower.

When the modifier powder mainly contains metallic zinc powder, since the melting point of metallic zinc is 420° C., the sintering temperature is, for example, 370° C. or higher, 375° C. or higher, or 380° C. or higher. Well, it may be 420° C. or less, 415° C. or less, 410° C. or less, 405° C. or less, 400° C. or less, or 390° C. or less. When the modifier powder mainly contains Zn _0.95 Al _0.05 alloy (Zn: 95 atomic %, Al: 5 atomic %) powder, the melting point of Zn _0.95 Al _0.05 alloy is 400 °C, the sintering temperature may be, for example, 350°C or higher, 355°C or higher, or 360°C or higher, 400°C or lower, 395°C or lower, 390°C or lower, 385°C or lower, 380°C or lower, or It may be 370° C. or lower. Note that “mainly” means that the content of the relevant powder is 70% by mass or more, 80% by mass or more, 90% by mass or more, or 95% by mass or more with respect to the entire modifier powder 20, and 100% by mass % or less, 99 mass % or less, 98 mass % or less, 97 mass % or less, 96 mass % or less, or 95 mass % or less.

Regarding the sintering temperature, when the modifier powder mainly contains both the metallic zinc powder and the zinc alloy powder, the lower of the melting point of the metallic zinc powder and the zinc alloy powder is applied as the above-mentioned T. . For example, when the modifier powder contains both the metallic zinc powder and the _{Zn0.95Al0.05 alloy powder as hot water, T is the melting point of the Zn0.95Al0.05 alloy ,} that is, 400 ℃ apply. When there are multiple types of zinc alloy powder, T is the lowest melting point among the melting points of the metal zinc alloy powder and the multiple types of zinc alloy powder. By doing so, it is possible to retain the aspect of solid-phase sintering while part of the modifier powder is melted during sintering. Note that "mainly containing both metallic zinc powder and zinc alloy powder" means that the total content of metallic zinc powder and zinc alloy powder is 70% by mass or more, 80% by mass or more, relative to the entire modifier powder, 90% by mass or more, or 95% by mass or more, and 100% by mass or less, 99% by mass or less, 98% by mass or less, 97% by mass or less, 96% by mass, or 95% by mass or less. When there are multiple types of zinc alloy powder, the total content of the metal zinc alloy powder and multiple types of zinc alloy powder is 70% by mass or more, 80% by mass or more, and 90% by mass with respect to the entire modifier powder. or 95% by mass or more, and 100% by mass or less, 99% by mass or less, 98% by mass or less, 97% by mass or less, 96% by mass or less, or 95% by mass or less.

The sintering pressure and sintering time are appropriately adjusted so that the density of the sintered body is 5.0 to 7.2 g/cm ³ in consideration of the particle size and compounding amount of the magnetic powder and modifier powder. You just have to decide. The sintering pressure may be, for example, 500 MPa or higher, 700 MPa or higher, 900 MPa or higher, 1100 MPa or higher, 1300 MPa or higher, or 1500 MPa or higher. Below, it may be 1900 MPa or less, or 1700 MPa or less. The sintering time may be, for example, 10 seconds or more, 100 seconds or more, 500 seconds or more, 1000 seconds or more, 1500 seconds or more, 1800 seconds or more, 2000 seconds or more, 2500 seconds or more, 3600 seconds or more, and 3200 seconds or more. 3000 seconds or less, 2800 seconds or less, or 2700 seconds or less.

By sintering the powder compact under the above sintering conditions, a sintered compact having a density of 5.0 to 7.2 g/cm ³ is obtained. As described above, a density of 5.0 g/cm ³ or more is advantageous in preventing zinc vapor from being discharged from the inside of the sintered body to the outside. From this point of view, the density is preferably 5.5 g/cm ³ or higher, more preferably 6.0 g/cm ³ or higher, and even more preferably 6.5 g/cm ³ or higher. On the other hand, if the density is 7.2 g/cm ³ or less, it is advantageous for zinc vapor to spread inside the sintered body. From this point of view, the density is preferably 7.0 g/cm ³ or less, more preferably 6.8 g/cm ³ or less.

From the viewpoint of preventing oxidation of the powder compact and the sintered compact, sintering is preferably performed in an inert gas atmosphere. The inert gas atmosphere also includes a nitrogen gas atmosphere.

The sintered body obtained as described above is stored inside a container. The container is not particularly limited as long as it does not interfere with the zinc vapor generation step and the zinc component deposition step, which will be described later, and the cavity 65 of the sintering mold 40 shown in FIG. 1 may be used as the container. The entire sintering mold 40 may be stored in a separately prepared container. Alternatively, the sintered body may be removed from the sintering mold and stored in a separately prepared container.

Next, the magnetic powder and modifier powder will be described.

<Magnetic powder>
The magnetic powder used in the method for producing a rare earth magnet of the present disclosure should contain Sm, Fe, and N. Such a magnetic powder typically contains a magnetic phase having a crystal structure of either Th ₂ Zn ₁₇ type or Th ₂ Ni ₁₇ type at least in part. As the crystal structure of the magnetic phase, in addition to the structures described above, a phase having a TbCu ₇ -type crystal structure and the like can be mentioned. Here, Sm is samarium, Fe is iron, and N is nitrogen. Also, Th is thorium, Zn is zinc, Ni is nickel, Tb is terbium, and Cu is copper.

The magnetic powder may contain, for example, a magnetic phase represented by the composition formula (Sm _(1-i) R _i ) ₂ (Fe _(1-j) Co _j ) ₁₇ N _h . A rare earth magnet obtained by the manufacturing method of the present disclosure (hereinafter sometimes referred to as "product") develops magnetic properties due to the magnetic phase in the magnetic powder. Note that i, j, and h are molar ratios.

The magnetic phase in the magnetic powder may contain R as long as it does not impair the effects of the production method of the present disclosure and the magnetic properties of the product. Such a range is represented by i in the above compositional formula. i may be, for example, 0 or more, 0.10 or more, or 0.20 or more, and may be 0.50 or less, 0.40 or less, or 0.30 or less. R is one or more selected from rare earth elements other than Sm, Y and Zr. As used herein, rare earth elements are Sc, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu. Y is yttrium, Zr is zirconium, Sc is scandium, La is lanthanum, Ce is cerium, Pr is praseodymium, Nd is neodymium, Pm is promethium, Sm is samarium, Eu is eurobium, Gd is gadolinium, Tb is terbium, Dy is dysprosium, Ho is holmium, Er is erbium, Tm is thulium, Yb is ytterbium, and Lu is ruthenium.

For ( _{Sm (1-i) R i} ) ₂ (Fe _{( 1-j) Co j ) 17} N _h , typically Although R is substituted at the position, it is not limited to this. For example, Sm ₂ (Fe _(1−j) Co _j ) ₁₇ N _h may be interstitially arranged with a portion of R.

The magnetic phase in the magnetic powder may contain Co to the extent that it does not impair the effects of the manufacturing method of the present disclosure and the magnetic properties of the product. Such a range is represented by j in the above compositional formula. j may be 0 or more, 0.10 or more, or 0.20 or more, and may be 0.52 or less, 0.40 or less, or 0.30 or less.

For (Sm _(1-i) R _i ) ₂ (Fe _(1-j) Co _j ) ₁₇ N _h , typically the Fe content of (Sm _(1-i) R _i ) ₂ Fe ₁₇ N _h Although Co is substituted at the position, it is not limited to this. For example, (Sm _(1−i) R _i ) ₂ Fe ₁₇ N _h may be partially interstitially arranged with Co.

_{The magnetic phase} in the _{magnetic powder} has the magnetic _properties Contribute to the expression and improvement of

For (Sm _(1−i) R _i ) ₂ (Fe _(1−j) Co _j ) ₁₇ N _h , h can range from 1.5 to 4.5, but typically (Sm _{(1 -i)} R _i ) ₂ (Fe _(1−j) Co _j ) ₁₇ N ₃ ; h may be 1.8 or more, 2.0 or more, or 2.5 or more, and may be 4.2 or less, 4.0 or less, or 3.5 or less. (Sm _{(1-i) R i ) 2 (} Fe _{( 1 - j ) Co j ) 17} N The content of is preferably 70% by mass or more, more preferably 80% by mass or more, and even more preferably 90% by mass. On the other hand, all of (Sm _(1-i) R _i ) ₂ (Fe _(1-j) Co _j ) ₁₇ N _h are (Sm _(1-i) R _i ) ₂ (Fe _(1-j) Co _j ) It _does not have to be _17N3 . (Sm _{(1-i) R i ) 2 (} Fe _{( 1 - j ) Co j ) 17} N may be 99% by mass or less, 98% by mass or less, or 97% by mass or less.

In addition to the magnetic phase represented by (Sm _(1-i) R _i ) ₂ (Fe _(1-j) Co _j ) ₁₇ N _h , the magnetic powder has the effects of the production method of the present disclosure and the magnetic properties of the product. Oxygen, M1, and unavoidable impurity elements may be contained within ^a range that does not substantially impair the characteristics. From the viewpoint of ensuring the magnetic properties of the product, the content of the magnetic phase represented by (Sm _(1-i) R _i ) ₂ (Fe _(1-j) Co _j ) ₁₇ N _h with respect to the entire magnetic powder may be 80% by weight or more, 85% by weight or more, or 90% by weight or more. On the other hand, even if the content of the magnetic phase represented by (Sm _(1-i) R _i ) ₂ (Fe _(1-j) Co _j ) ₁₇ N _h is not excessively increased with respect to the entire magnetic powder, There is no practical problem. Therefore, the content may be 99% by mass or less, 98% by mass or less, or 97% by mass or less. The remainder of the magnetic phase represented by (Sm _(1−i) R _i ) ₂ (Fe _(1−j) Co _j ) ₁₇ N _h is the content of oxygen and M ¹ . ^A portion of M1 may also be present in the magnetic phase in an interstitial and/or substitutional form.

The above-mentioned M1 includes at ^{least one} selected from Ga, Ti, Cr, Zn, Mn, V, Mo, W, Si, Re, Cu, Al, Ca, B, Ni, and C. An unavoidable impurity element is an impurity element whose inclusion is unavoidable in the production of raw materials and/or magnetic powders, or whose avoidance causes a significant increase in manufacturing costs. Say. These elements may exist in the magnetic phase described above in a substitutional and/or interstitial type, or may exist in a phase other than the magnetic phase described above. Alternatively, it may exist at the grain boundaries of these phases. Ga is gallium, Ti is titanium, Cr is chromium, Zn is zinc, Mn is manganese, V is vanadium, Mo is molybdenum, W is tungsten, Si is silicon, Re is rhenium, Cu is copper, Al is aluminum, Ca is calcium, B is boron, Ni is nickel, and C is carbon.

The particle size of the magnetic powder is not particularly limited as long as the resulting product has desired magnetic properties and does not interfere with the effects of the method for producing a rare earth magnet of the present disclosure, such as movement of zinc vapor. The particle size of the magnetic powder may be _D50 , for example, greater than 1 μm, 2 μm or more, 3 μm or more, 4 μm or more, 5 μm or more, 6 μm or more, 7 μm or more, 8 μm or more, or 9 μm or more, 20 μm or less, or 19 μm. 18 μm or less, 17 μm or less, 16 μm or less, 15 μm or less, 14 μm or less, 13 μm or less, 12 μm or less, 11 μm or less, or 10 μm or less. In addition, _D50 means a median diameter. Also, the _D50 of the magnetic powder is measured by, for example, a dry laser diffraction/scattering method.

In the method for producing a rare earth magnet of the present disclosure, magnetic powder is modified with modifier powder. Oxygen in the magnetic powder can be absorbed by the metallic zinc or zinc alloy powder in the modifier powder to improve the magnetic properties, particularly the coercive force, of the product. The oxygen content in the magnetic powder may be determined by considering the amount of oxygen absorbed by the modifier powder in the magnetic powder during the manufacturing process. The oxygen content of the magnetic powder is preferably as low as possible with respect to the magnetic powder as a whole. The oxygen content of the magnetic powder is preferably 2.00% by mass or less, more preferably 1.34% by mass or less, and even more preferably 1.05% by mass or less with respect to the entire magnetic powder. On the other hand, extremely reducing the oxygen content in the magnetic powder results in an increase in manufacturing costs. Therefore, the oxygen content of the magnetic powder may be 0.1% by mass or more, 0.2% by mass or more, or 0.3% by mass or more with respect to the entire magnetic powder.

There are no particular restrictions on the production method of the magnetic powder as long as it satisfies the requirements described above, and commercially available products may be used. As a method for producing magnetic powder, for example, Sm--Fe alloy powder is produced from samarium oxide and iron powder by a reduction diffusion method, and heated to 600° C. or less in an atmosphere such as a mixed gas of nitrogen and hydrogen, nitrogen gas, and ammonia gas. and heat treatment to obtain Sm--Fe--N powder. Alternatively, for example, a method of producing an Sm—Fe alloy by a melting method, coarsely pulverizing the alloy, nitriding the coarsely pulverized grains obtained, and further pulverizing it to a desired particle size can be used. For pulverization, for example, a dry jet mill, a dry ball mill, a wet ball mill, a wet bead mill, or the like can be used. Moreover, you may use these in combination.

<Modifying material powder>
The modifier powder used in the method for producing a rare earth magnet of the present disclosure contains at least one of zinc metal and zinc alloy.

Metallic zinc means unalloyed zinc. The purity of metallic zinc may be 95.0 wt% or higher, 98.0 wt% or higher, 99.0 wt% or higher, or 99.9 wt% or higher. The metal surface lead powder may be produced by the hydrogen plasma reaction method (HRMR method).

When a zinc alloy is represented by Zn- ^M2 , ^M2 is preferably an element that alloys with Zn (zinc) to lower the melting start temperature of the zinc alloy below the melting point of Zn and an unavoidable impurity element. . Examples of ^M2 that lowers the melting start temperature of the zinc alloy below the melting point of Zn include elements that form a eutectic alloy with Zn and ^M2 . Such ^M2 typically includes Sn, Mg, and Al, combinations thereof, and the like. Sn is tin, Mg is magnesium, and Al is aluminum. An element that does not impair the melting point lowering effect of these elements and the properties of the product can also be selected as ^M2 . In addition, unavoidable impurity elements are impurities contained in the raw materials of the modifier powder, which cannot be avoided, or which lead to a significant increase in manufacturing costs in order to avoid them. That's what I mean.

In the zinc alloy represented by Zn—M ² , the ratio (molar ratio) of Zn and M ² may be appropriately determined so that the sintering temperature and the heating temperature of the sintered body are appropriate. ^The ratio (molar ratio) of M2 to the entire zinc alloy may be, for example, 0.02 or more, 0.05 or more, 0.10 or more, or 0.20 or more, and 0.90 or less, 0.80 or less , 0.70 or less, 0.60 or less, 0.50 or less, 0.40 or less, or 0.30 or less.

The particle size of the modifier powder is not particularly limited, but it is preferably smaller than the particle size of the magnetic powder. The particle size of the modifier powder is D ₅₀ (median diameter), and may be, for example, more than 0.1 μm, 0.5 μm or more, 1 μm or more, or 2 μm or more, and 12 μm or less, 11 μm or less, 10 μm or less, or 9 μm. 8 μm or less, 7 μm or less, 6 μm or less, 5 μm or less, or 4 μm or less. Also, the particle size of the modifier powder is measured by, for example, a dry laser diffraction/scattering method.

If the modifier powder has a low oxygen content, it is preferable because a large amount of oxygen in the magnetic powder can be absorbed. From this point of view, the oxygen content of the modifier powder is preferably 5.0% by mass or less, more preferably 3.0% by mass, and even more preferably 1.0% by mass or less, relative to the entire modifier powder. preferable. On the other hand, extremely reducing the oxygen content of the modifier powder results in an increase in manufacturing cost. Therefore, the content of oxygen in the modifier powder may be 0.1% by mass or more, 0.2% by mass or more, or 0.3% by mass or more with respect to the entire modifier powder.

As described above, the modifier powder functions as both a binder and a modifier. However, since the modifier powder does not contribute to the magnetization of the product, if the modifier powder is mixed in an excessive amount, the magnetization of the product decreases. From the viewpoint of ensuring the functions as a binder and a modifier powder, the zinc component of the modifier powder is 1% by mass or more, 3% by mass or more, and 6% by mass with respect to the total of the magnetic powder and the modifier powder. The modifier powder may be mixed so as to have a content of 9% by mass or more. From the viewpoint of suppressing a decrease in the magnetization of the product, the modifier powder is mixed so that the zinc component is 20% by mass or less, 18% by mass or less, or 16% by mass or less with respect to the entire mixed powder. you can The zinc component means the amount of zinc in the modifier powder. For example, when the modifier powder contains both metallic zinc and a zinc alloy, the amount of zinc in the metallic zinc and zinc It is the total amount of zinc in the alloy.

<Zinc vapor generation process>
While reducing the pressure inside the container, the sintered body is heated to generate zinc vapor from at least one of the metallic zinc powder and the zinc alloy powder in the sintered body.

The zinc vapor generation step will be described with reference to the drawings. FIG. 2 is a schematic diagram showing a state in which the sintered body is stored in the cavity of the sintering mold. FIG. 3 is a schematic diagram showing a state in which the sintered compact is heated while the pressure inside the cavity of the sintering mold is reduced. Here, for example, zinc vapor generation when the cavity 65 of the sintering mold 40 is used as a container as shown in FIGS. 2 and 3 will be described, but the present invention is not limited to this. As described above, the entire sintering mold 40 may be stored in a separately prepared container. Alternatively, the sintered body 30 may be removed from the sintering mold 40 and stored in a separately prepared container.

When the sintering mold 40 is used in the zinc vapor generation step, a vacuum pump (not shown) or the like is connected to the cavity 65 to reduce the pressure inside the cavity 65 . A heater or the like provided in the sintering mold 40 can be used to heat the sintered body 30 .

When the sintering mold 40 is not used in the zinc vapor generation step, the pressure inside the container is reduced by connecting, for example, a vacuum pump or the like to a separately prepared container or the like. Then, for example, the sintered body 30 in the container is heated by a heater or the like provided in the container. Examples of such a container include a vacuum heating furnace.

When the sintering mold 40 is used in the zinc vapor generation process, the sintered body 30 is stored in the cavity 65 of the sintering mold 40 as shown in FIG. Since the inside of the cavity 65 is used as a container, pressure is not applied in the sliding direction of the punch 50 . The sintered body 30 contains mixed powder particles, that is, particles of the magnetic powder 10 and the modifier powder 20 . Then, in the state shown in FIG. 2, the sintered body 30 is heated while reducing the pressure in the cavity 65 so that the magnetic powder 10 does not melt and zinc vapor is generated from the modifier powder 20 . At this time, as shown in FIG. 3, the space between the particles of the magnetic powder 10 is filled with zinc vapor 26 inside the sintered body 30 . Therefore, it is assumed that the particles of the modifier powder 20 are uniformly distributed inside the sintered body 30 in the state shown in FIG. Even without it, if the zinc vapor 26 is generated, the zinc vapor 26 spreads uniformly among the particles of the magnetic powder 10 . As a result, the modified coating 22 is uniformly deposited on the particle surfaces of the magnetic powder 10 in the zinc deposition step, which will be described later.

From the viewpoint of uniform distribution of the zinc vapor 26 between the particles of the magnetic powder 10, the metallic zinc and/or zinc alloy of the modifier powder 20 is preferably sublimated. Sublimation means that a solid (solid phase) becomes a gas (gas phase) without passing through a liquid (liquid phase). Zinc vapor 26 (gas) can move more freely between particles of magnetic powder 10 than zinc melt (liquid). Therefore, although not bound by theory, it is believed that the zinc vapor 26 is more likely to spread among the particles of the magnetic powder 10 when the zinc vapor 26 is formed without going through the zinc melt (liquid).

FIG. 8 is a vapor pressure curve of zinc. In FIG. 8, the solid curve indicates the vapor pressure curve of zinc. The lower part of the vapor pressure curve indicates that zinc is a gas, or gas and liquid. The upper part of the vapor pressure curve indicates that zinc is solid or liquid. Regarding the upper side of the vapor pressure curve, with the melting point of zinc (420° C.) as a boundary, the low temperature side indicates that zinc is solid, and the high temperature side indicates that zinc is liquid. When generating the zinc vapor 26, it is preferable to heat the sintered body 30 in a reduced pressure atmosphere in which zinc sublimates based on the vapor pressure curve. Even if zinc does not sublimate, it is preferable to heat the sintered body 30 in a reduced-pressure atmosphere in which the molten zinc is rapidly vaporized. When the modifier powder 20 in the sintered body 30 contains a zinc alloy, the degree of pressure reduction and the heating temperature can be appropriately determined based on the vapor pressure curve of the zinc alloy or according to the vapor pressure curve of zinc. good.

When the melting point of the modifier powder 20 is T ° C., the heating temperature of the sintered body 30 is, for example, (T-40) ° C. or higher, (T-30) ° C. or higher, (T-20) ° C. or higher, ( T-10) ° C. or higher, T ° C. or higher, (T + 10) ° C. or higher, (T + 20) ° C. or higher, or (T + 30) ° C. or higher, (T + 80) ° C. or lower, (T + 70) ° C. or lower, (T + 60) ° C. Below, it may be (T+50)° C. or less, or (T+40)° C. or less. The pressure in the container when heating the sintered body 30 at such a temperature (excluding the partial pressure of zinc vapor and the vapor of the element alloyed with zinc) is, for example, 1 × 10 ^-6 MPa or more, 1×10 ⁻⁵ MPa or more, 1×10 ⁻⁴ MPa or more, 1×10 ⁻³ MPa or more, 1×10 ⁻² MPa or more, 1×10 ⁻¹ MPa or more, or 1×10 ⁰ MPa or more It may be 1×10 ³ MPa or less, 1×10 ² MPa or less, or 1×10 Pa or less.

When the modifier powder 20 in the sintered body 30 mainly contains metallic zinc powder, the heating temperature of the sintered body 30 is, for example, 380° C. or higher, 390° C. or higher, 400° C. or higher, or 410° C. or higher. , 420°C or higher, 430°C or higher, 440°C or higher, or 450°C or higher, and may be 500°C or lower, 490°C or lower, 480°C or lower, 470°C or lower, or 460°C or lower. Further, the pressure in the container (excluding the partial pressure of zinc vapor) when heating the sintered body 30 at such a temperature is, for example, 1×10 ⁻⁶ MPa or more, 1×10 ⁻⁵ MPa or more, It may be 1×10 ⁻⁴ MPa or more, 1×10 ⁻³ MPa or more, 1×10 ⁻² MPa or more, 1×10 ⁻¹ MPa or more, or 1×10 ⁰ MPa or more, and 1×10 ³ MPa or less. , 1×10 ² MPa or less, or 1×10 Pa or less. It should be noted that modifying material powder 20 "mainly" contains metallic zinc powder means that the content of metallic zinc powder is, for example, 70% by mass or more, 80% by mass or more, 90% by mass or more, relative to the entire modifier powder 20. % by mass or more, or 95% by mass or more, and 100% by mass or less, 99% by mass or less, 98% by mass or less, 97% by mass or less, 96% by mass, or 95% by mass or less.

When the modifier powder 20 in the sintered body 30 mainly contains the Zn _0.95 Al _0.05 alloy powder, the heating temperature of the sintered body 30 is, for example, 360° C. or higher, 370° C. or higher, 380°C or higher, 390°C or higher, 400°C or higher, 410°C or higher, 420°C or higher, or 430°C or higher; It's okay. In addition, the pressure in the container when heating the sintered body 30 at such a temperature (excluding the partial pressures of zinc vapor and aluminum vapor) is, for example, 1×10 ⁻⁶ MPa or more, 1×10 ⁻⁵ MPa or more, 1×10 ⁻⁴ MPa or more, 1×10 ⁻³ MPa or more, 1×10 ⁻² MPa or more, 1×10 ⁻¹ MPa or more, or 1×10 ⁰ MPa or more, and 1×10 It may be ³ MPa or less, 1×10 ² MPa or less, or 1×10 Pa or less. Note that the modifying material powder 20 “mainly” contains the Zn _0.95 Al _0.05 alloy powder means that the content of the Zn _0.95 Al _0.05 alloy powder is , 70% by mass or more, 80% by mass or more, 90% by mass or more, or 95% by mass or more, and 100% by mass or less, 99% by mass or less, 98% by mass or less, 97% by mass or less, 96% by mass, or 95% by mass % or less.

Regarding the heating temperature of the sintered body, when the modifying material powder mainly contains both the metallic zinc powder and the zinc alloy powder, the above-mentioned T is the lower of the melting point of the metallic zinc powder and the zinc alloy powder. to adopt. For example, when the modifier powder mainly contains both the metallic zinc powder and the Zn _0.95 Al _0.05 alloy powder, T is the melting point of the Zn _0.95 Al _0.05 alloy, that is, 400 ° C. apply. When there are multiple types of zinc alloy powder, T is the lowest melting point among the melting points of the metal zinc alloy powder and the multiple types of zinc alloy powder. By doing so, the metallic zinc and/or zinc alloy in the sintered body sublimes during heating of the sintered body, or evaporates immediately after melting. Note that "mainly containing both metallic zinc powder and zinc alloy powder" means that the total content of metallic zinc powder and zinc alloy powder is 70% by mass or more, 80% by mass or more, relative to the entire modifier powder, 90% by mass or more, or 95% by mass or more, and 100% by mass or less, 99% by mass or less, 98% by mass or less, 97% by mass or less, 96% by mass, or 95% by mass or less. When there are multiple types of zinc alloy powder, the total content of the metal zinc alloy powder and multiple types of zinc alloy powder is 70% by mass or more, 80% by mass or more, and 90% by mass with respect to the entire modifier powder. or 95% by mass or more, and 100% by mass or less, 99% by mass or less, 98% by mass or less, 97% by mass or less, 96% by mass or less, or 95% by mass or less.

The heating time of the sintered body 30 may be appropriately determined in consideration of the mass of the sintered body 30, the particle size of the magnetic powder 10 and the modifier powder 20 in the sintered body 30, and the like. The heating time of the sintered body 30 may be, for example, 10 minutes or more, 50 minutes or more, 100 minutes or more, 200 minutes or more, or 300 minutes or more, and may be 1000 minutes or less, 800 minutes or less, 600 minutes or less, or It may be 400 minutes or less.

<Zinc component deposition process>
An inert gas is injected into the container in which the zinc vapor 26 is generated to deposit the zinc component on the particle surfaces of the magnetic powder 10 in the sintered body 30 . Alternatively, the inside of the container in which the zinc vapor 26 is generated is cooled to deposit the zinc component on the particle surfaces of the magnetic powder 10 in the sintered body 30 . At least one of the injection of the inert gas into the interior of the container and the cooling of the interior of the container may be performed. Note that the inert gas includes nitrogen gas.

The zinc component deposition step will be further described with reference to the drawings. Here, as shown in FIGS. 3 and 4, a case where a sintering mold 40 is used as a container will be described, but the container is not limited to this. That is, the container is not particularly limited as long as it can generate zinc vapor in the zinc vapor generation step described above and can condense zinc vapor in the zinc component deposition step. Since the inside of the cavity 65 of the sintering mold 40 is used as a container, pressure is not applied in the sliding direction of the punch 50 .

As shown in FIG. 3, the sintered body 30 stored in the cavity 65 of the sintering mold 40 is heated while the cavity 65 is decompressed to obtain particles of the magnetic powder 10. The gap is filled with zinc vapor 26 .

FIG. 4 is a schematic diagram showing a state in which the zinc component is deposited on the particle surfaces of the magnetic powder from the state of FIG. As shown in FIG. 3 , a zinc component is deposited on the surface of the magnetic powder 10 particles filled with zinc vapor 26 from the zinc vapor 26 to form the modified coating 22 . As a result, a uniform coated magnetic powder 28 can be obtained inside the sintered body 30, as shown in FIG.

Deposition of the zinc component can be performed by injecting inert gas into the interior of the container or by cooling the interior of the container. This will be explained using the vapor pressure curve of zinc shown in FIG. Assuming that the state shown in FIG. 3 is point A in FIG. 8, the zinc component can be deposited by, for example, pressurizing (repressurizing) to point B in FIG. 8 or cooling to point C in FIG. Just do it. Pressurization (repressurization) and cooling may be combined.

As a method of pressurizing (repressurizing) the container containing the magnetic powder 10 and the zinc vapor 26, for example, in the embodiment shown in FIG. a method of injecting an inert gas into the The inert gas is used as the pressurizing medium to prevent the sintered body 30 and the coated magnetic powder 28 from being oxidized.

When injecting an inert gas into the container to deposit the zinc component, the pressure inside the container after injecting the inert gas and the speed at which this pressure is reached are determined by the fact that the zinc vapor is in the liquid phase. It is more preferable to determine these pressures and velocities so that the deposition takes place in a timely manner. This makes the modified coating 22 formed on the particle surface of the magnetic powder 10 more uniform. Even if the zinc vapor deposits through the liquid phase, it is preferable to determine the pressure and speed so that the modified coating 22 forms immediately from the liquid phase.

The pressure inside the container after injecting the inert gas (the pressure at point B in FIG. 8) may be, for example, 1×10 ⁴ Pa or higher or 1×10 ⁵ Pa or higher. Alternatively, an inert gas may be injected into the container to bring the pressure inside the container to, for example, equal to atmospheric pressure. Also, the speed at which such a pressure is reached is preferably faster, and may be, for example, 1000 Pa/sec or more, 10000 Pa/sec or more, or 100000 Pa/sec or more.

As a method for rapidly cooling the inside of the container containing the magnetic powder 10 and zinc vapor, for example, in the embodiment shown in FIG. etc. A method of cooling the inside of the cavity 65 includes a method of cooling at least one of the punch 50 and the die to cool the inside of the cavity 65 . Alternatively, a cooling pipe or the like may be arranged in the cavity 65 and a cooling medium may be introduced into the cooling pipe.

When the inside of the container is cooled to deposit the zinc component, it is more preferable to cool the inside of the container so that the zinc vapor deposits without passing through the liquid phase. This makes the modified coating 22 formed on the particle surface of the magnetic powder 10 more uniform. Even when the zinc vapor deposits through the liquid phase, cooling the inside of the container as fast as possible contributes to uniformity of the modified coating.

If the temperature inside the container when zinc vapor is present in the container is Tr ° C., the temperature inside the container is, for example, (Tr-30) ° C. or lower, (Tr-50) ° C. or lower, (Tr-80 ) ° C. or lower, (tR-100) ° C. or lower, (Tr-150) ° C. or lower, (Tr-200) ° C. or lower, (Tr-230) ° C. or lower, or (Tr-250) ° C. or lower. .

A faster cooling rate is preferable, and the cooling rate may be, for example, 1° C./second or more, 10° C./second or more, or 100° C./second or more.

Simultaneously with the deposition of the modified film 22, the modification progresses and contributes to the improvement of the coercive force. The sintered body 30 that has been reformed in this way can be used as a rare earth magnet.

<deformation>
Various modifications can be made to the method for producing a rare earth magnet of the present disclosure within the scope of the claims. For example, after depositing the modified coating 22 on the surfaces of the particles of the magnetic powder 10 in the sintered body 30, the sintered body 30 may be solid phase sintered and/or liquid sintered. As a result, the density of the sintered body 30 is improved, which contributes to the improvement of saturation magnetization, and the reformation proceeds further, contributing to the improvement of coercive force.

EXAMPLES Hereinafter, the method for producing a rare earth magnet of the present disclosure will be described more specifically with reference to examples and comparative examples. The method for producing a rare earth magnet of the present disclosure is not limited to the conditions used in the examples below.

《Preparation of sample》
Samples of rare earth magnets were prepared as follows.

<Examples 1 to 5 and Comparative Examples 1 to 2>
Samarium-iron-nitrogen based magnetic powder was prepared as the magnetic powder. The magnetic powder contained _93.0 % by _mass of _Sm2Fe17N3 . The particle size of the magnetic powder was as shown in Table 1.

Metal zinc powder and Zn _0.95 Al _0.05 alloy powder were prepared as modifier powders. The particle size of the metallic zinc powder was _D50 of 0.5 μm and the purity of the metallic zinc powder was 99.4% by weight. The particle size of the Zn _0.95 Al _0.05 alloy powder was 0.4 μm in D ₅₀ and the purity of the Zn _0.95 Al _0.05 alloy powder was 98.5 mass %.

A mixed powder was obtained by mixing the magnetic powder and the modifier powder using a V-shaped mixer. Table 1 shows the amount of metallic zinc relative to the total amount of magnetic powder and modifier powder.

A green compact was obtained by compression-molding the mixed powder in a magnetic field using a magnetic field molding die having the same structure as the sintering die 40 shown in FIG. The compression molding pressure was 50 MPa. The applied magnetic field was 1600 kA/m. The green compact was put into the sintering mold 40 shown in FIG. 1 and sintered. The sintering temperature, sintering pressure, and sintering time are as shown in Table 1, and the density of the sintered body 30 was adjusted by changing the sintering time. Sintering was performed in an argon gas atmosphere, and the atmospheric pressure (argon gas partial pressure) was 97000Pa.

The sintered body 30 is stored in the sintering mold 40 shown in FIGS. 2 to 4, zinc vapor is generated, and the zinc component is deposited on the particle surfaces of the magnetic powder 10 in the sintered body 30, A rare earth magnet was obtained. Various conditions were as shown in Table 1.

"evaluation"
Density and magnetic properties were measured for the samples of Examples 1-5 and Comparative Examples 1-2. Measurements were made at room temperature. The density was measured before and after deposition of the modified coating 22 by the Archimedes method. Magnetic properties were measured using a vibrating sample magnetometer (VSM).

Table 1 shows the results.

From Table 1, it was confirmed that the samples of Examples 1 to 5, in which the density of the sintered body 30 was within the predetermined range, had improved coercive force.

From these results, the effect of the method for producing a rare earth magnet according to the present disclosure could be confirmed.

REFERENCE SIGNS LIST 10 magnetic powder 20 modifier powder 22 modified coating 24 mass 26 zinc vapor 28 coated magnetic powder 30 sintered compact 40 sintering mold 50 punch 60 die 65 cavity

Claims (1)

Modifier powder containing at least one of metallic zinc powder and zinc alloy powder and samarium-iron-nitrogen magnetic powder are mixed and sintered to obtain a density of 5.0 to 7.2 g/cm ³ . Obtaining a sintered body and storing the sintered body inside a container;
heating the sintered body while decompressing the inside of the container to generate zinc vapor from at least one of metallic zinc powder and zinc alloy powder in the sintered body;
Depositing a zinc component on the particle surfaces of the magnetic powder in the sintered body by at least either injecting an inert gas into the interior of the vessel or cooling the interior of the vessel;
A method for producing a rare earth magnet, comprising:

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