Rare earth magnets and their manufacturing methods

Abstract

This disclosure provides a rare-earth magnet with improved magnetization compared to previous methods, and a method for manufacturing the same. The disclosure relates to a method for manufacturing a magnetic magnet and a rare-earth magnet obtained by this method. The method includes: preparing a mixture containing a specified magnetic powder and a modifying material powder; mixing the magnetic powder and the modifying material powder to obtain a mixed powder; compressing the mixed powder in a magnetic field to obtain a magnetically shaped body; and sintering the magnetically shaped body under pressure to obtain a sintered body. The magnetic powder comprises a first particle group and a second particle group, where d1μm represents the particle size distribution D of the first particle group. 50 And let d2μm represent the particle size distribution D of the second particle swarm. 50 The d1 and d2 satisfy the relationship 0.350≤d2 / d1≤0.500, and the ratio of the total volume of the first particle group to the total volume of the second particle group is in the range of 9:1 to 4:1.

Description

Technical Field

[0001] This disclosure relates to a method for manufacturing a rare earth magnet. More particularly, this disclosure relates to a method for manufacturing a rare earth magnet containing Sm, Fe, and N, and at least a portion comprising Th₂Zn. 17 Type crystal structure or Th2Ni 17 A magnetic phase with a crystal structure of type . Background Technology

[0002] Sm-Co and Nd-Fe-B rare earth magnets have been put into practical use as high-performance rare earth magnets, but in recent years, research has been conducted on rare earth magnets other than these.

[0003] For example, research is underway on rare-earth magnets containing Sm, Fe, and N (hereinafter sometimes referred to as "Sm-Fe-N rare-earth magnets"). Sm-Fe-N rare-earth magnets are manufactured, for example, using magnetic powders containing Sm, Fe, and N (hereinafter sometimes referred to as "SmFeN powder").

[0004] SmFeN powder contains Th2Zn 17 Type crystal structure or Th2Ni 17 The magnetic phase has a crystalline structure. It is believed that this magnetic phase is N dissolved in the Sm-Fe crystal in an interstitial form. Therefore, SmFeN powder is easily decomposed by the thermal dissociation of N. Consequently, most Sm-Fe-N rare earth magnets are manufactured by shaping SmFeN powder using resin and / or rubber.

[0005] As an alternative method for manufacturing Sm-Fe-N rare earth magnets, the manufacturing method disclosed in Patent Document 1 can be cited as an example. This manufacturing method involves mixing powder containing SmFeN powder and metallic zinc (hereinafter sometimes referred to as "metallic zinc powder"), forming the mixed powder in a magnetic field, and sintering the magnetically formed body (including liquid phase sintering).

[0006] In addition, methods for manufacturing SmFeN powder are disclosed, for example, in Patent Documents 2 and 3.

[0007] Existing technical documents

[0008] Patent Document 1: International Publication No. 2015 / 199096

[0009] Patent Document 2: Japanese Patent Application Publication No. 2017-117937

[0010] Patent Document 3: Japanese Patent Application Publication No. 2020-102606 Summary of the Invention

[0011] The sintering methods for magnetic field-formed bodies can be broadly categorized into pressureless sintering and pressure sintering. In either method, high-density rare-earth magnets (sintered bodies) are obtained by sintering the magnetic field-formed body. In pressureless sintering, since no pressure is applied to the magnetic field-formed body during sintering, a long sintering time of 6 hours or more at a high temperature above 900°C is generally required to obtain a high-density sintered body. On the other hand, in pressure sintering, because pressure is applied to the magnetic field-formed body during sintering, a high-density sintered body can generally be obtained even when sintering the magnetic field-formed body at a low temperature of 600–800°C for a short time of 0.1–5 hours.

[0012] When sintering a magnetic field-formed body of a mixture of SmFeN powder and zinc powder, pressure sintering is employed to prevent the SmFeN powder from decomposing due to heat. However, sintering is carried out at a lower temperature and for a shorter time than usual pressure sintering. Sintering is possible even at such a low temperature and in a short time because the zinc component in the zinc powder diffuses to the surface of the magnetic powder and solidifies (cures) during sintering. Thus, the zinc powder in the magnetic field-formed body functions as a binder. Furthermore, the zinc powder in the magnetic field-formed body also functions as a modifier, modifying the αFe phase on the surface of the SmFeN powder, particularly the SmFeN powder particles, and absorbing oxygen from the SmFeN powder to improve coercivity. Hereinafter, powders that simultaneously function as binders and modifiers in the manufacture of Sm-Fe-N rare-earth magnets are sometimes referred to simply as "modifier powders."

[0013] When magnetic powder is formed using resin and / or rubber, or when a mixture of magnetic powder and modified material powder is pressurized and sintered, the magnetization of the formed body (rare earth magnet) decreases accordingly with the proportion of resin and modified material that do not contribute to magnetization. On the other hand, compared to forming magnetic powder using resin and / or rubber, pressurizing and sintering a mixture of magnetic powder and modified material powder generally yields a high-density formed body (rare earth magnet), resulting in a higher magnetization. However, when the magnetic powder is SmFeN powder, even when a mixture of magnetic powder and modified material powder is pressurized and sintered, the magnetization is lower than predicted by the proportion of modified material, and the expected magnetization is not obtained.

[0014] Therefore, the present inventor has discovered the following problem: it is desirable to obtain a method for manufacturing Sm-Fe-N rare earth magnets that can further improve the magnetization intensity compared with the past.

[0015] This disclosure was made to solve the aforementioned problems. Specifically, the purpose of this disclosure is to provide a method for manufacturing Sm-Fe-N rare-earth magnets that can further improve magnetization compared to previous methods.

[0016] To achieve the above objectives, the discloser has conducted repeated and in-depth research and completed the manufacturing method of the rare earth magnets disclosed herein. The manufacturing method of the rare earth magnets disclosed herein includes the following scheme.

[0017] <1> A method for manufacturing rare earth magnets includes the following steps:

[0018] Prepare a magnetic powder containing Sm, Fe, and N, and at least a portion of which contains Th2Zn. 17 Type crystal structure or Th2Ni 17 Magnetic phases with a crystal structure of type ;

[0019] Prepare a modified material powder, wherein the modified material powder contains at least one of metallic zinc and zinc alloys.

[0020] The magnetic powder and the modified material powder are mixed to obtain a mixed powder;

[0021] The mixed powder is compressed and shaped in a magnetic field to obtain a magnetically shaped body; and

[0022] The magnetic field-formed body is pressurized and sintered to obtain a sintered body.

[0023] The magnetic powder comprises a first particle group and a second particle group.

[0024] Let d1μm represent the particle size distribution D of the first particle swarm. 50 And let d2μm represent the particle size distribution D of the second particle swarm. 50 ,

[0025] The d1 and d2 satisfy the relationship 0.350 ≤ d2 / d1 ≤ 0.500, and,

[0026] The ratio of the total volume of the first particle group to the total volume of the second particle group (total volume of the first particle group: total volume of the second particle group) is in the range of 9:1 to 4:1.

[0027] <2> according to <1> In the method for manufacturing rare earth magnets described above, d1 is 3.0 to 3.7 μm, and d2 is 1.4 to 1.8 μm.

[0028] <3> according to <1> or <2> The method for manufacturing rare earth magnets as described above, wherein the modified material powder has a D 50The thickness is 0.1–12.0 μm, and the zinc content in the modified material powder is 1–30% by mass relative to the mixed powder.

[0029] <4> according to <1> ~ <3> The method for manufacturing rare earth magnets according to any one of the claims involves compressing the mixed powder under a pressure of 10 to 1500 MPa.

[0030] <5> according to <1> ~ <4> The method for manufacturing rare earth magnets according to any one of the claims involves sintering the magnetic field forming body under pressure of 100-2000 MPa and temperature of 300-430°C for 1-30 minutes.

[0031] <6> according to <1> ~ <5> The method for manufacturing the rare earth magnet according to any one of the claims further includes the following steps:

[0032] Prior to the pressure sintering, a modified inhibition film is pre-formed on the particle surface of the second particle group; and

[0033] The sintered body is subjected to heat treatment to modify the particle surface of the first particle group.

[0034] <7> according to <6> The method for manufacturing rare earth magnets as described above, wherein the modified inhibitory coating contains phosphoric acid.

[0035] <8> according to <6> or <7> The method for manufacturing rare earth magnets described herein involves heat-treating the sintered body at 350–410°C.

[0036] <9> A rare-earth magnet is a sintered rare-earth magnet containing magnetic powder and zinc, wherein the magnetic powder contains Sm, Fe and N, and at least a portion contains Th2Zn. 17 Type crystal structure or Th2Ni 17 Magnetic phase with a crystal structure of type ,

[0037] The magnetic powder comprises a first particle group and a second particle group.

[0038] Let d1μm represent the particle size distribution D of the first particle swarm. 50 And let d2μm represent the particle size distribution D of the second particle swarm. 50 ,

[0039] The d1 and d2 satisfy the relationship 0.350 ≤ d2 / d1 ≤ 0.500, and,

[0040] The ratio of the total volume of the first particle group to the total volume of the second particle group (total volume of the first particle group: total volume of the second particle group) is in the range of 9:1 to 4:1.

[0041] According to the manufacturing method disclosed herein, by keeping the ratio of the particle size of the second particle to the particle size of the first particle group, and the ratio of the total volume of the first particle group to the total volume of the second particle group within a specified range, the density of the sintered body (rare earth magnet) can be increased. As a result, a method for manufacturing rare earth magnets that can further improve magnetization intensity compared to conventional methods can be provided. Attached Figure Description

[0042] Figure 1 This is a schematic diagram illustrating an example of the microstructure of a rare-earth magnet obtained by the manufacturing method of this disclosure.

[0043] Figure 2 This is a schematic diagram illustrating an example of the microstructure of a rare-earth magnet obtained by a conventional manufacturing method.

[0044] Figure 3 This is a schematic diagram illustrating another example of the microstructure of a rare-earth magnet obtained by a conventional manufacturing method.

[0045] Figure 4 This is a schematic diagram illustrating yet another example of the microstructure of a rare-earth magnet obtained by a conventional manufacturing method.

[0046] Figure 5 It is a coordinate graph showing the relationship between d2 / d1 and density.

[0047] Figure 6 This is a coordinate graph showing the relationship between d2 / d1 and remanence Br.

[0048] Figure 7 This shows an SEM image of the sample from Example 1.

[0049] Figure 8 This shows the SEM image of the sample from Comparative Example 3.

[0050] Figure 9 This shows the SEM image of the sample from Comparative Example 6.

[0051] Figure 10 It is a coordinate graph showing the demagnetization curve of a molded body of low coercivity powder at high temperature, and the demagnetization curve of a molded body of a mixture of low coercivity powder and high coercivity powder.

[0052] Figure 11 This is a schematic diagram illustrating an example of the microstructure of a rare-earth magnet obtained by forming a modified inhibition film on the surface of particles in the second particle group, followed by pressure sintering and heat treatment.

[0053] Figure 12 This is a schematic diagram illustrating an example of the microstructure of a rare-earth magnet obtained by pressure sintering and heat treatment after a modified inhibitory film has not been formed on the surface of the particles in the second particle group.

[0054] Explanation of reference numerals in the attached figures

[0055] 10 SmFeN powder particles (magnetic particles)

[0056] 11 First Particle Swarm

[0057] 12 Second Particle Swarm

[0058] 20 Modified Materials

[0059] 30 Modified Phases

[0060] 100 Rare earth magnets obtained by the manufacturing method of this disclosure

[0061] 200 Rare earth magnets obtained by conventional manufacturing methods Detailed Implementation

[0062] The following describes in detail the embodiments of the method for manufacturing rare earth magnets of this disclosure (hereinafter sometimes simply referred to as "the manufacturing method of this disclosure"). Furthermore, the embodiments shown below are not limited to the manufacturing method of this disclosure.

[0063] While not bound by theory, the reasons why rare earth magnets with further improved magnetization can be obtained by using the manufacturing method of this disclosure will be explained with reference to the accompanying drawings, while comparing them with conventional rare earth magnet manufacturing methods (hereinafter sometimes simply referred to as "conventional manufacturing methods").

[0064] Figure 1 This is a schematic diagram illustrating an example of the microstructure of a rare-earth magnet obtained by the manufacturing method of this disclosure. Figure 2 This is a schematic diagram illustrating an example of the microstructure of a rare-earth magnet obtained by a conventional manufacturing method. Figure 3 This is a schematic diagram illustrating another example of the microstructure of a rare-earth magnet obtained by a conventional manufacturing method. Figure 4 This is a schematic diagram illustrating yet another example of the microstructure of rare-earth magnets obtained by conventional manufacturing methods. Furthermore, Figures 1-4 The arrows in the diagram indicate the direction of magnetic orientation.

[0065] like Figure 1 As shown, in the rare earth magnet 100 obtained by the manufacturing method of this disclosure, SmFeN powder particles 10 are bonded together using a modified material 20. This is because, as described above, the modified material 20 functions as a binder. Furthermore, the surface of the SmFeN powder particles 10 is covered by the modified phase 30.

[0066] like Figure 1As shown, in the rare earth magnet 100 obtained by the manufacturing method of this disclosure, the SmFeN powder particles 10 comprise a first particle group 11 with a large particle size and a second particle group 12 with a small particle size. By having particles of the second particle group 12 present between the particles of the first particle group 11, the density of the rare earth magnet 100 can be increased, resulting in an increase in magnetization. For example... Figure 2 As shown, in one example of a rare earth magnet 200 obtained by a conventional manufacturing method, the SmFeN powder particles 10 are essentially only the first particle group 11. Therefore, the density of the rare earth magnet 200 cannot be increased, and as a result, the magnetization intensity is not improved.

[0067] In addition, such as Figure 1 As shown, the density of the rare-earth magnet 100 obtained by the manufacturing method of this disclosure can be increased when the ratio of the particle size of the second particle group 12 to the particle size of the first particle group 11 is within a specified range. For example... Figure 3 As shown, in another example of a rare-earth magnet 200 obtained by a conventional manufacturing method, the ratio of the particle size of the second particle group 12 to the particle size of the first particle group 11 is too large, resulting in a large distance between the particles in the first particle group 11. Therefore, in the rare-earth magnet 200 obtained by the conventional manufacturing method, its density cannot be increased, and as a result, the magnetization intensity is not improved.

[0068] Furthermore, in order to increase the density of the rare-earth magnet 100 obtained by the manufacturing method of this disclosure, it is necessary not only to ensure that the ratio of the particle size of the second particle group 12 to the particle size of the first particle group 11 is within a specified range, but also to ensure that the ratio of the total volume of the first particle group 11 to the total volume of the second particle group 12 is within a specified range. This is because if the particles of the second particle group 12 exist to a certain extent or more, then... Figure 1 As shown, the gaps between the particles in the first particle group 11 are fully filled, but on the other hand, if there is an excess of particles in the second particle group 12, then as... Figure 4 As shown, the gaps between the particles in the first particle group 11 widen. Moreover, due to this widening, it is impossible to increase the density of the rare-earth magnet 200 obtained by conventional manufacturing methods, resulting in no increase in magnetization.

[0069] Furthermore, compared to the large-diameter SmFeN powder particles in the first particle group 11, the small-diameter SmFeN powder particles in the second particle group 12 have a lower remanence σr. This is because the crystal structure on the particle surface deteriorates, and compared to large-diameter particles, small-diameter particles have a larger specific surface area, thus the remanence σr of small-diameter particles like those in the second particle group 12 is more prone to deterioration. If such a second particle group 12 exists in excess, it will lead to a decrease in the overall magnetization of the rare-earth magnet.

[0070] Therefore, in the manufacturing method disclosed herein, an excessive number of particles in the second particle group 12 are avoided, thereby preventing a decrease in magnetization intensity.

[0071] Although not bound by theory, as stated above, it is believed that the ratio of particle size and the ratio of total volume must be within a specified range for both the first particle group 11 and the second particle group 12 for the following reasons: The coefficient of friction of SmFeN powder particles is considered to be very high compared to magnetic powders used to manufacture Nd-Fe-B rare-earth magnets. Therefore, the flowability of SmFeN powder is poor when forming it, making it difficult to increase the filling rate of the formed body (rare-earth magnet). Furthermore, if the density increases, the magnetization increases, which can be understood from the remanence expressed by the following formula.

[0072] Remanence = Saturation magnetization × Orientation degree × (Density / True density) × Magnetic phase ratio

[0073] Next, the constituent elements of the manufacturing method of this disclosure, based on the views and other information described so far, will be explained.

[0074] Manufacturing Methods

[0075] The manufacturing method disclosed herein includes: a magnetic powder preparation step, a modified material powder preparation step, a mixing step, a magnetic field forming step, and a pressure sintering step. Optionally, it also includes a modification to inhibit film formation and a heat treatment step. Each step will be described below.

[0076] <Magnetic Powder Preparation Process>

[0077] Prepare magnetic powder (SmFeN powder). The magnetic powder (SmFeN powder) used in the manufacturing method of this disclosure contains Sm, Fe, and N, and at least a portion contains Th2Zn. 17 Type crystal structure or Th2Ni 17 There are no particular restrictions on the type of magnetic phase crystal structure. Besides the structures mentioned above, crystal structures with the TbCu7 type crystal structure can be cited as magnetic phases. Furthermore, Sm is samarium, Fe is iron, and N is nitrogen. Additionally, Th is thorium, Zn is zinc, Ni is nickel, Tb is terbium, and Cu is copper.

[0078] SmFeN powder may contain, for example, components with the formula (Sm (1-i) R i )2(Fe (1-j) Co j ) 17 N h The magnetic phase is represented by the method of manufacture disclosed herein. The rare earth magnets (hereinafter sometimes referred to as "finished products") are derived from the magnetic phase in SmFeN powder, which embodies the magnetization intensity. Furthermore, i, j, and h are molar ratios.

[0079] As a magnetic phase in SmFeN powder, R may be included, provided that it does not impair the effectiveness of the manufacturing method disclosed herein or the magnetic properties of the finished product. Such a range is represented by the value i in the above-described composition formula. i can be, for example, 0 or more, 0.10 or more, or 0.20 or more, and can be 0.50 or less, 0.40 or less, or 0.30 or less. R is one or more rare earth elements selected from Sm and Zr. In this specification, the rare earth elements are Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu. Furthermore, Zr is zirconium, Sc is scandium, Y is yttrium, La is lanthanum, Ce is cerium, Pr is praseodymium, Nd is neodymium, Pm is promethium, Sm is samarium, Eu is europium, Gd is gadolinium, Tb is terbium, Dy is dysprosium, Ho is holmium, Er is erbium, Tm is thulium, Yb is ytterbium, and Lu is lutetium.

[0080] Regarding (Sm) (1-i) R i )2(Fe (1-j) Co j ) 17 N h Typically, in Sm2(Fe (1-j) Co j ) 17 N h The Sm position is replaced by R, but it is not limited to this. For example, it can also be replaced in Sm2(Fe (1-j) Co j ) 17 N h Part of the intermittent configuration R.

[0081] As a magnetic phase in SmFeN powder, Co may also be included, provided that it does not impair the effectiveness of the manufacturing method disclosed herein or the magnetic properties of the finished product. Such a range is represented by j in the above composition formula. j can be 0 or more, 0.10 or more, or 0.20 or more, and can be 0.52 or less, 0.40 or less, or 0.30 or less.

[0082] Regarding (Sm) (1-i) R i )2(Fe (1-j) Co j ) 17 N h Typically, in (Sm (1-i) R i )2Fe 17 N h The Fe sites are replaced by Co, but this is not the only possibility. For example, it can also be found in (Sm (1-i) R i )2Fe 17 Nh It is part of the intermittent configuration Co.

[0083] The magnetic phase in SmFeN powder is formed by (SmFeN powder) (1-i) R i )2(Fe (1-j) Co j ) 17 The presence of N in interstitial form within the grains indicates that it contributes to the manifestation and enhancement of magnetic properties.

[0084] Regarding (Sm) (1-i) R i )2(Fe (1-j) Co j ) 17 N h h can be 1.5 to 4.5, typically (Sm (1-i) R i )2)(Fe (1-j) Co j ) 17 N3. h can be 1.8 or higher, 2.0 or higher, or 2.5 or higher, and can be 4.2 or lower, 4.0 or lower, or 3.5 or lower. (Sm) (1-i) R i )2(Fe (1-j) Co j ) 17 The content of N3 relative to (Sm (1-i) R i )2(Fe (1-j) Co j ) 17 N h The overall content 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, it may not be (Sm) (1-i) R i )2(Fe (1-j) Co j ) 17 N h All of them are (Sm (1-i) R i )2(Fe (1-j) Co j ) 17 N3. (Sm) (1-i) R i )2(Fe (1-j) Co j ) 17 The content of N3 relative to (Sm (1-i) R i )2(Fe (1-j) Co j ) 17 Nh The overall percentage can be below 98%, below 95%, or below 92%.

[0085] SmFeN powder, in addition to being composed of (Sm (1-i) R i )2(Fe (1-j) Co j ) 17 N h In addition to the magnetic phase indicated, other phases may be included that do not substantially impair the effectiveness of the manufacturing method of this disclosure and the magnetic properties of the product, and may contain oxygen and M. 1 And unavoidable impurity elements. From the perspective of ensuring the magnetic properties of the finished product, relative to the overall SmFeN powder, (Sm (1-i) R i )2(Fe (1-j) Co j ) 17 N h The content of the magnetic phase can also be 80% by mass or more, 85% by mass or more, or 90% by mass or more. On the other hand, relative to the overall SmFeN powder, even without excessively increasing the content of (Sm... (1-i) R i )2(Fe (1-j) Co j ) 17 N h The indicated content of the magnetic phase is also practically acceptable. Therefore, its content can be below 97% by mass, below 95% by mass, or below 93% by mass. (Sm) (1-i) R i )2(Fe (1-j) Co j ) 17 N h The remaining amount of the magnetic phase is represented by oxygen and M. 1 The content of oxygen and M. 1 Some of them may also exist in the magnetic phase as interstitial and / or substitutional types.

[0086] As for the above M 1, one or more selected from Ga, Ti, Cr, Zn, Mn, V, Mo, W, Si, Re, Cu, Al, Ca, B, Ni, and C can be cited. Unavoidable impurity elements refer to impurity elements that cannot be avoided during the manufacture of raw materials and / or magnetic powders, etc., or that cause a significant increase in manufacturing costs in order to avoid their inclusion. These elements can exist in the above magnetic phase in a substitutional and / or interstitial form, or can exist in a phase other than the above magnetic phase. Alternatively, they can also exist at the grain boundaries of these phases. Furthermore, 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.

[0087] The SmFeN powder contains a first particle group and a second particle group. The particles of the first particle group have a large particle size, and the particles of the second particle group have a small particle size. The particle sizes of the particles in the first particle group and the second particle group can be represented by a particle size distribution D 50 for each. The particle size distribution D 50 of the first particle group is represented by d1 μm, and the particle size distribution D 50 of the second particle group is represented by d2 μm. Moreover, d1 and d2 satisfy the relationship of 0.350 ≤ d2 / d1 ≤ 0.500. Due to satisfying the aforementioned relationship, it is obvious that d2 < d1, that is, the first particle group has a large particle size and the second particle group has a small particle size.

[0088] If d2 / d1 is 0.350 or more, 0.360 or more, 0.370 or more, or 0.378 or more, and is 0.500 or less, 0.490 or less, 0.486 or less, 0.480 or less, 0.470 or less, or 0.467 or less, then the particles of the second particle group effectively exist between the particles of the first particle group, the density of the compact (rare earth magnet) increases, and as a result, the magnetization intensity increases.

[0089] As long as the above relationship is satisfied, there are no particular restrictions on the particle sizes of the particles in the first particle group and the second particle group. However, in order to easily satisfy the above relationship, it is preferable that d1 and d2 are each individually in the following ranges. d1 is preferably 3.0 μm or more, 3.2 μm or more, or 3.4 μm or more, and can be 3.7 μm or less, 3.6 μm or less, or 3.5 μm or less. d2 is preferably 1.4 μm or more or 1.5 μm or more, and is preferably 1.8 μm or less, 1.7 μm or less, or 1.6 μm or less.

[0090] Furthermore, the ratio of the total volume of the first particle group to the total volume of the second particle group, i.e., (total volume of the first particle group):(total volume of the second particle group), needs to be in the range of 9:1 to 4:1. A ratio of 9:1 means, for example, that relative to the total volume of SmFeN powder, the total volume of the first particle group is 90%, and the total volume of the second particle group is 10%. Conversely, a ratio of 4:1 means, for example, that relative to the total volume of SmFeN powder, the total volume of the first particle group is 80%, and the total volume of the second particle group is 20%.

[0091] If the ratio of (total volume of the first particle group) to (total volume of the second particle group) is 9:1, or if the total volume of the second particle group is greater, then the particles of the second particle group are effectively present among the particles of the first particle group, increasing the density of the rare-earth magnets and consequently increasing the magnetization. From this perspective, the ratio of (total volume of the first particle group) to (total volume of the second particle group) is preferably 8.8:1.2 or greater, or 8.6:1.4 or greater.

[0092] If there is an excess of particles in the second particle group, the inter-particle spacing in the first particle group will actually increase. To avoid this, the ratio of (total volume of the first particle group) to (total volume of the second particle group) needs to be 4:1, or the total volume of the second particle group should be even smaller. Furthermore, the small-diameter SmFeN powder particles in the second particle group have low remanence (σr), so an excess of the second particle group leads to a decrease in the overall magnetization of the rare-earth magnet. Therefore, by preventing the inter-particle spacing in the first particle group from increasing, the density of the rare-earth magnet is suppressed, and the number of second particle groups with low σr is reduced, thereby increasing the magnetization of the rare-earth magnet. From these perspectives, the ratio of (total volume of the first particle group) to (total volume of the second particle group) is preferably 8.2:1.8 or less or 8.4:1.6 or less.

[0093] The magnetic powder, comprising a first particle group and a second particle group, is typically obtained by classifying SmFeN powder, obtained by the manufacturing method described later, into a first particle group and a second particle group, and then mixing them again. There are no particular limitations on the classification and mixing methods; known methods can be used. Examples of classification methods include sieving and air classification, and combinations thereof can also be used. Examples of mixing methods include mixing using a stirred mixer and a V-type mixer, and combinations thereof can also be used.

[0094] D of SmFeN powder 50The particle size distribution of SmFeN powder was calculated based on the following method (survey). Unless otherwise specified, the description of particle size (particle diameter) of SmFeN powder in this specification is based on the following measurement method (survey method). Furthermore, D... 50 Represents the median diameter.

[0095] Prepare a sample in which SmFeN powder is embedded in resin, grind the surface of the sample, and observe it using an optical microscope. Then, draw a straight line on the optical microscope image, and measure the length of the line segment divided by SmFeN particles (bright field). The particle size distribution of the SmFeN powder is determined from the degree distribution of the line segment lengths. The particle size distribution obtained by this method is approximately equal to that obtained by the intersection method or dry laser diffraction / scattering method.

[0096] Due to manufacturing reasons, microparticles are present in SmFeN powder. However, as long as d1 and d2 satisfy the above-mentioned relationship, there is no particular limitation on the proportion of magnetic particles (microparticles) with a particle size of 1.0 μm or less in the SmFeN powder. From the viewpoint of ensuring the mechanical strength of the molded body (rare earth magnet), the proportion of magnetic particles (microparticles) with a particle size of 1.0 μm or less in the SmFeN powder is preferably as low as possible. The proportion of microparticles relative to the total number of magnetic particles in the SmFeN powder is preferably 10.0% or less, 8.0% or less, 6.0% or less, or 4.0% or less. From the viewpoint of ease of manufacturing SmFeN powder, it is not necessary to completely eliminate microparticles; even if the lower limit of the proportion of microparticles is 1.0%, 2.0%, or 3.0%, it is not a problem in practical application.

[0097] In the manufacturing method disclosed herein, a modified material powder (described later) is mixed into SmFeN powder. Oxygen in the SmFeN powder is absorbed by the metallic zinc or zinc alloy powder in the modified material powder, thereby improving the magnetic properties, particularly the coercivity, of the molded article. The oxygen content in the SmFeN powder can be determined by considering the amount of oxygen absorbed by the modified material powder from the SmFeN powder during the manufacturing process. The oxygen content of the SmFeN powder is preferably low relative to the total SmFeN powder. The oxygen content of the SmFeN powder relative to the total SmFeN powder is preferably 2.0% by mass or less, more preferably 1.5% by mass or less, and even more preferably 1.0% by mass or less. On the other hand, drastically reducing the oxygen content in the SmFeN powder would lead to increased manufacturing costs. Therefore, the oxygen content of the SmFeN powder relative to the total SmFeN powder can be 0.1% by mass or more, 0.2% by mass or more, or 0.3% by mass or more.

[0098] There are no particular restrictions on the manufacturing method of SmFeN powder, provided that the conditions described above are met, and commercially available products can be used. Examples of methods for manufacturing SmFeN powder include: producing Sm-Fe powder from samarium oxide and iron powder using a reduction diffusion method, and then heating the powder at temperatures below 600°C in an atmosphere containing a mixture of nitrogen and hydrogen, nitrogen, and ammonia to obtain Sm-Fe-N powder. Alternatively, an example is the manufacturing of Sm-Fe alloys by a melting method, followed by nitriding the coarsely pulverized particles obtained from the alloy, and then pulverizing them until the desired particle size is achieved. Pulverization can be performed using, for example, a dry jet mill, a dry ball mill, a wet ball mill, or a wet bead mill. Combinations of these methods can also be used.

[0099] In addition to the manufacturing methods described above, SmFeN powder can also be obtained by, for example, the following manufacturing method: a pretreatment step of obtaining localized oxides by heat treatment of an oxide containing Sm and Fe in an atmosphere containing a reducing gas; a reduction step of obtaining alloy particles by heat treatment of the localized oxides in the presence of a reducing agent; and a nitriding step of obtaining nitrides by heat treatment of the alloy particles in an atmosphere containing nitrogen or ammonia at a first temperature of 400°C to 470°C and then at a second temperature of 480°C to 610°C. Especially for large alloy particles, such as those containing La, where nitriding sometimes does not fully penetrate the oxide particles, nitriding using a two-stage temperature process ensures that the interior of the oxide particles is also fully nitrided, resulting in a narrower particle size distribution and the acquisition of anisotropic SmFeN powder with high remanence.

[0100] [Oxide Preparation Process]

[0101] The oxides containing Sm and Fe used in the pretreatment process described later can be produced, for example, by mixing Sm oxide and Fe oxide, but preferably by a process of mixing a solution containing Sm and Fe with a precipitant to obtain a precipitate containing Sm and Fe (precipitation process), and a process of calcining the precipitate to obtain oxides containing Sm and Fe (oxidation process).

[0102] [Sedimentation Process]

[0103] In the precipitation process, Sm and Fe raw materials are dissolved in a strongly acidic solution to prepare a solution containing Sm and Fe. This yields Sm₂Fe₂. 17When N3 is the main phase, the molar ratio of Sm to Fe (Sm:Fe) is preferably 1.5:17 to 3.0:17, more preferably 2.0:17 to 2.5:17. Raw materials such as La, W, Co, Ti, Sc, Y, Pr, Nd, Pm, Gd, Tb, Dy, Ho, Er, Tm, and / or Lu can be added to the above solution. From the viewpoint of remanent magnetic flux density, the presence of La is preferred. From the viewpoint of coercivity and rectangularity ratio, the presence of W is preferred. From the viewpoint of temperature characteristics, the presence of Co and / or Ti is preferred.

[0104] There are no particular limitations on the use of Sm and Fe as raw materials, as long as they can dissolve in strongly acidic solutions. For example, from the viewpoint of easy availability, samarium oxide can be cited as an Sm raw material, and FeSO4 as an Fe raw material. The concentration of the solution containing Sm and Fe can be appropriately adjusted within the range where the Sm and Fe raw materials are substantially soluble in acidic solutions. From the viewpoint of solubility, sulfuric acid can be cited as an acidic solution.

[0105] An insoluble precipitate containing Sm and Fe is obtained by reacting a solution containing Sm and Fe with a precipitating agent. Here, the solution containing Sm and Fe need only be one that reacts with the precipitating agent to form a solution containing Sm and Fe. For example, the raw materials containing Sm and Fe can be prepared as separate solutions, and each solution can be added dropwise to react with the precipitating agent. Even when preparing separate solutions, the range in which each raw material is substantially soluble in acidic solutions can be appropriately adjusted. As for the precipitating agent, there is no particular limitation as long as it is a precipitating agent that reacts with a solution containing Sm and Fe in an alkaline solution to obtain a precipitate; examples include ammonia and caustic soda, with caustic soda being preferred.

[0106] From the viewpoint that the properties of the precipitate particles can be easily adjusted, the precipitation reaction is preferably carried out by separately adding a solution containing Sm and Fe and a precipitant to a solvent such as water. By appropriately controlling the supply rate of the solution containing Sm and Fe and the precipitant, the reaction temperature, the concentration of the reaction solution, and the pH value during the reaction, a precipitate with uniform distribution of constituent elements, narrow particle size distribution, and uniform powder shape can be obtained. By using such a precipitate, the magnetic properties of the SmFeN powder as the final product are improved. The reaction temperature can be 0°C or higher and 50°C or lower, preferably 35°C or higher and 45°C or lower. The concentration of the reaction solution, based on the total concentration of metal ions, is preferably 0.65 mol / L or higher and 0.85 mol / L or lower, more preferably 0.7 mol / L or higher and 0.85 mol / L or lower. The reaction pH value is preferably 5 or higher and 9 or lower, more preferably 6.5 or higher and 8 or lower.

[0107] From the viewpoint of magnetic properties, solutions containing Sm and Fe preferably also contain one or more metals selected from La, W, Co, and Ti. For example, from the viewpoint of remanent magnetic flux density, La is preferred; from the viewpoint of coercivity and rectangularity ratio, W is preferred; and from the viewpoint of temperature characteristics, Co and / or Ti is preferred. As for the La raw material, there are no particular limitations as long as it can dissolve in a strongly acidic solution; for example, La₂O₃ and LaCl₃ are examples of readily available materials. With appropriate adjustments to the range where the La, W, Co, and Ti raw materials, together with the Sm and Fe raw materials, are substantially soluble in acidic solutions, sulfuric acid is an example of an acidic solution from the viewpoint of solubility. Ammonium tungstate is an example of a W raw material; cobalt sulfate is an example of a Co raw material; and titanium sulfate is an example of a titanium raw material.

[0108] When a solution containing Sm and Fe also contains one or more metals selected from La, W, Co, and Ti, an insoluble precipitate containing Sm, Fe, and one or more metals selected from La, W, Co, and Ti is obtained. Here, the solution only needs to contain one or more metals selected from La, W, Co, and Ti when reacting with the precipitant. For example, each raw material can be prepared in a different solution and added dropwise to react with the precipitant, or it can be adjusted together with a solution containing Sm and Fe.

[0109] The powder obtained in the precipitation process is used to roughly determine the particle size, shape, and size distribution of the final SmFeN powder. When the particle size of the powder is measured using a laser diffraction wet particle size analyzer, it is preferable that the size and distribution of all powder particles fall approximately between 0.05 μm and 20 μm, and more preferably between 0.1 μm and 10 μm.

[0110] After separating the precipitate, in order to prevent the precipitate from redissolving in the residual solvent during the subsequent oxidation heat treatment process, and to prevent changes in precipitate aggregation and / or particle size distribution, powder particle size, etc., during solvent evaporation, it is preferable to desolventize the separated material. Specifically, as a desolventizing method, for example, when water is used as the solvent, drying in an oven at 70°C or higher and 200°C or lower for 5 to 12 hours can be cited.

[0111] Following the precipitation process, a step of separating and washing the resulting precipitate may be included. The washing process should be performed appropriately until the conductivity of the supernatant reaches 5 mS / m. 2 The following are steps for separating precipitates. For example, a solvent (preferably water) can be added to the obtained precipitate, and after mixing, filtration, decantation, or other methods can be used.

[0112] [Oxidation Process]

[0113] The oxidation process is a process of obtaining oxides containing Sm and Fe by calcining the precipitate formed in the precipitation process. For example, the precipitate can be converted into oxides by heat treatment. When heat treating the precipitate, it needs to be carried out in the presence of oxygen, for example, in an atmospheric atmosphere. Furthermore, since it needs to be carried out in the presence of oxygen, it is preferable that the non-metallic portion of the precipitate contains oxygen atoms.

[0114] The heat treatment temperature (hereinafter sometimes referred to as "oxidation temperature") in the oxidation process is not particularly limited, but is preferably 700°C or higher and 1300°C or lower, more preferably 900°C or higher and 1200°C or lower. Oxidation is insufficient below 700°C, and if it exceeds 1300°C, there is a tendency to fail to obtain the desired shape, average particle size, and particle size distribution of the SmFeN powder. The heat treatment time is also not particularly limited, but is preferably 1 hour or more and 3 hours or less.

[0115] The resulting oxides are oxide particles in which Sm and Fe have been fully micro-mixed within the oxide particles, reflecting the shape, particle size distribution, etc. of the precipitate.

[0116] [Pretreatment process]

[0117] The pretreatment process refers to the process of heat-treating the above-mentioned oxides containing Sm and Fe in an atmosphere containing reducing gas, thereby obtaining a partial oxide in which a portion of the oxide has been reduced.

[0118] Here, localized oxides refer to oxides in which a portion of the oxide has been reduced. The oxygen concentration of the localized oxide is not particularly limited, but is preferably 10% by mass or less, more preferably 8% by mass or less. If it exceeds 10% by mass, the heat generated during reduction with Ca in the reduction process increases, the firing temperature becomes higher, and there is a tendency to generate particles with abnormal grain growth. The oxygen concentration of the localized oxide can be determined by non-dispersive infrared absorption spectrometry (ND-IR).

[0119] The reducing gas is appropriately selected from hydrocarbon gases such as hydrogen (H2), carbon monoxide (CO), and methane (CH4), but hydrogen is preferred from a cost perspective. The gas flow rate is appropriately adjusted within a range that prevents oxide dispersion. The heat treatment temperature in the pretreatment process (hereinafter referred to as the pretreatment temperature) is preferably 300°C or higher and 950°C or lower, more preferably 400°C or higher, and even more preferably 750°C or higher. The upper limit is more preferably lower than 900°C. If the pretreatment temperature is 300°C or higher, the reduction of oxides containing Sm and Fe is carried out efficiently. In addition, if it is 950°C or lower, the grain growth and segregation of oxide particles are suppressed, and the expected particle size can be maintained. The heat treatment time is not particularly limited and can be 1 hour or more and 50 hours or less. In addition, when using hydrogen as the reducing gas, it is preferable to adjust the thickness of the oxide layer used to 20 mm or less, and then adjust the dew point in the reactor to -10°C or lower.

[0120] [Restoration Process]

[0121] The reduction process is a process of obtaining alloy particles by heat-treating the localized oxide in the presence of a reducing agent, for example, by reducing the localized oxide by contacting it with calcium melt or calcium vapor. From the viewpoint of magnetic properties, the heat treatment temperature is preferably 920°C or higher and 1200°C or lower, more preferably 950°C or higher and 1150°C or lower, and even more preferably 980°C or higher and 1100°C or lower.

[0122] The metallic calcium used as a reducing agent is in granular or powder form, preferably with a particle size of 10 mm or less. This allows for more effective suppression of agglomeration during the reduction reaction. Furthermore, the metallic calcium is preferably added in a ratio of 1.1 to 3.0 times the reaction equivalent (the stoichiometric amount required to reduce rare earth oxides, including the amount required for reduction in the case where the Fe component is in oxide form), more preferably 1.5 to 2.5 times the amount required.

[0123] In the reduction process, a disintegration accelerator may be used as needed, along with metallic calcium as a reducing agent. This disintegration accelerator is appropriately used to promote the disintegration and granulation of the product during the subsequent post-processing steps, and examples include alkaline earth metal salts such as calcium chloride and alkaline earth oxides such as calcium oxide. These disintegration accelerators are used relative to samarium oxide at a ratio of 1% to 30% by mass, preferably 5% to 30% by mass.

[0124] [Nitriding process]

[0125] The nitriding process refers to a process in which alloy particles obtained in the reduction process are heat-treated in an atmosphere containing nitrogen or ammonia at a first temperature of 400°C or higher and 470°C or lower, followed by heat treatment at a second temperature of 480°C or higher and 610°C or lower, thereby obtaining anisotropic magnetic particles. Because the granular precipitate obtained in the precipitation process is used, porous blocky alloy particles are obtained in the reduction process. Therefore, nitriding can be performed directly in a nitrogen atmosphere without pulverization, resulting in uniform nitriding. When nitriding is not performed at the first temperature but at a high temperature (the second temperature), abnormal heating occurs due to the rapid progression of nitriding, causing SmFeN decomposition and a significant decrease in magnetic properties. Furthermore, the atmosphere in the nitriding process can further delay the nitriding process; therefore, a substantially nitrogen-containing atmosphere is preferred. The term "substantially" here refers to the unavoidable presence of elements other than nitrogen due to the mixing of impurities; for example, the nitrogen content in the atmosphere is 95% or higher, preferably 97% or higher, and more preferably 99% or higher.

[0126] The first temperature in the nitriding process is 400°C or higher and 470°C or lower, preferably 410°C or higher and 450°C or lower. Below 400°C, nitriding proceeds very slowly, and above 470°C, overnitriding or decomposition can easily occur due to heat generation. The heat treatment time at the first temperature is not particularly limited, but is preferably 1 hour or higher and 40 hours or lower, more preferably 20 hours or lower. If it is less than 1 hour, nitriding may not be fully completed; if it exceeds 40 hours, productivity decreases.

[0127] The second temperature is 480°C or higher and 610°C or lower, preferably 500°C or higher and 550°C or lower. Below 480°C, nitriding may not be fully completed if the particles are large; above 610°C, overnitriding or decomposition is likely to occur. The heat treatment time at the second temperature is preferably 15 minutes or more and 5 hours or less, more preferably 30 minutes or more and 2 hours or less. If the time is less than 15 minutes, nitriding may not be fully completed; if the time exceeds 5 hours, productivity decreases.

[0128] Heat treatment at the first temperature and heat treatment at the second temperature can be carried out continuously. Heat treatment at a temperature lower than the second temperature can also be included between these heat treatments, but from a productivity point of view, continuous operation is preferred.

[0129] [Post-processing steps]

[0130] The product obtained after the nitriding process contains, in addition to magnetic particles, byproducts such as CaO and unreacted metallic calcium, which sometimes form a composite sintered mass. Immersing the product after the nitriding process in cooling water allows the CaO and metallic calcium to be separated as calcium hydroxide (Ca(OH)2) suspension. Furthermore, residual calcium hydroxide can be thoroughly removed by washing the magnetic powder with acetic acid or similar substances. When the product is immersed in water, the composite sintered mass disintegrates due to the oxidation of metallic calcium and the hydration reaction of the byproduct CaO, i.e., micronization occurs.

[0131] [Alkali Treatment Process]

[0132] Alternatively, the product obtained after the nitriding process can be added to an alkaline solution. Examples of alkaline solutions used in the alkaline treatment process include aqueous solutions of calcium hydroxide, sodium hydroxide, and ammonia. From the viewpoint of wastewater treatment and high pH values, aqueous solutions of calcium hydroxide and sodium hydroxide are preferred. Through alkaline treatment of the product, a residual Sm-rich layer containing a certain degree of oxygen functions as a protective layer, thus suppressing the increase in oxygen concentration caused by alkaline treatment.

[0133] The pH value of the alkaline solution used in the alkaline treatment process is not particularly limited, but it is preferably 9 or higher, and more preferably 10 or higher. When the pH value is less than 9, the reaction rate to form calcium hydroxide is fast, the heat generated is greater, and therefore there is a tendency for the oxygen concentration of the final SmFeN powder to be higher.

[0134] In the alkali treatment process, the SmFeN powder obtained after treatment with alkali solution can also have its moisture content reduced by methods such as decantation, as needed.

[0135] [Acid treatment process]

[0136] Following the alkali treatment step, an acid treatment step may be included. In the acid treatment step, at least a portion of the Sm-rich layer is removed, reducing the overall oxygen concentration in the SmFeN powder. Furthermore, in the manufacturing method of this embodiment, no grinding or pulverization is performed, resulting in a small average particle size and narrow particle size distribution of the SmFeN powder, and it does not contain fine powder generated by grinding or the like, thus suppressing the increase in oxygen concentration.

[0137] The acid used in the acid treatment process is not particularly limited, and examples include hydrogen chloride, nitric acid, sulfuric acid, and acetic acid. However, from the viewpoint of not leaving any impurities, hydrogen chloride and nitric acid are preferred.

[0138] The amount of acid used in the acid treatment process is preferably 3.5 parts by mass or more and 13.5 parts by mass or less per 100 parts by mass of SmFeN powder, more preferably 4 parts by mass or more and 10 parts by mass or less. If it is less than 3.5 parts by mass, oxide residues remain on the surface of the SmFeN powder, and the oxygen concentration becomes high. If it exceeds 13.5 parts by mass, it is prone to re-oxidation when exposed to the atmosphere, and the cost tends to increase due to the dissolution of SmFeN powder. By making the amount of acid 3.5 parts by mass or more and 13.5 parts by mass or less per 100 parts by mass of SmFeN powder, a rich Sm layer can be formed on the surface of the SmFeN powder to a degree that makes it difficult for re-oxidation to occur when exposed to the atmosphere after acid treatment. Therefore, SmFeN powder with low oxygen concentration, small average particle size, and narrow particle size distribution can be obtained.

[0139] In the acid treatment process, the moisture content of the SmFeN powder obtained after acid treatment can be reduced by methods such as decantation, as needed.

[0140] [Dehydration process]

[0141] Following the acid treatment step, a dehydration process is preferably included. Dehydration reduces the moisture content of the solid component before vacuum drying, suppressing oxidation during drying caused by the higher moisture content of the solid component before vacuum drying. Here, dehydration refers to the process of reducing the moisture content of the treated solid component relative to the solid component before treatment by applying pressure or centrifugal force, excluding simple decantation, filtration, and drying. The dehydration method is not particularly limited and examples include pressing and centrifugation.

[0142] The amount of water contained in the dehydrated SmFeN powder is not particularly limited, but from the viewpoint of inhibiting oxidation, it is preferably 13% by mass or less, and more preferably 10% by mass or less.

[0143] SmFeN powder obtained by acid treatment or SmFeN powder obtained by dehydration after acid treatment is preferably vacuum dried. The drying temperature is not particularly limited, but is preferably 70°C or higher, more preferably 75°C or higher. The drying time is also not particularly limited, but is preferably 1 hour or more, more preferably 3 hours or more.

[0144] <Preparation process for modified material powder>

[0145] Prepare modified material powder. The modified material powder used in the manufacturing method of this disclosure contains at least one of metallic zinc and zinc alloys. Metallic zinc refers to unalloyed zinc. The zinc component in the modified material powder binds and modifies the particles of SmFeN powder.

[0146] For SmFeN powder particles, an Fe-Zn alloy phase forms on their surface. Th₂Zn exists on the surface of the SmFeN powder particles. 17 Type and / or Th2Ni 17 In parts of the SmFeN powder with incomplete crystal structure, an α-Fe phase exists, contributing to the decrease in coercivity. This α-Fe phase combines with the zinc component of metallic zinc and / or zinc alloys to form an Fe-Zn alloy phase, suppressing the decrease in coercivity. In other words, the Fe-Zn alloy phase acts as a modifying phase. Between the particles of SmFeN powder and the particles of the modifying material powder, Fe and Zn diffuse into each other, forming the Fe-Zn alloy phase. Therefore, the SmFeN powder particles are firmly bonded together. That is, the modifying material powder acts as a binder.

[0147] If the zinc content in the modified material powder is 1% by mass or more relative to the mixed powder, a uniform Fe-Zn alloy phase (modified phase) is formed. Therefore, the coercivity is improved, and it can effectively function as a binder. From this perspective, the zinc content in the modified material powder can be 3% by mass or more, 5% by mass or more, 10% by mass or more, 15% by mass or more, or 20% by mass or more relative to the mixed powder.

[0148] On the other hand, if the zinc content in the modified material powder is 30% by mass or less relative to the mixed powder, the decrease in magnetization caused by the use of the modified material powder can be suppressed. From this point of view, the zinc content in the modified material powder can be 28% by mass or less, 26% by mass or less, 24% by mass or less, or 22% by mass or less relative to the mixed powder.

[0149] If using Zn-M 2 If M represents a zinc alloy, then 2 Elements that alloy with Zn (zinc) to achieve a melting point lower than the melting point of Zn, as well as unavoidable impurity elements, can be selected. This improves sinterability during the pressure sintering process described later. M, with a melting point lower than Zn... 2 Examples of Zn and M can be cited. 2 Elements that form eutectic alloys, etc. As such, M... 2 Typical examples include Sn, Mg, and Al, as well as combinations thereof. Sn is tin, Mg is magnesium, and Al is aluminum. Elements that lower the melting point and do not hinder the properties of the finished product can also be chosen as M. 2 In addition, unavoidable impurity elements refer to impurities in the raw materials of modified material powder that cannot be avoided, or impurity elements that would significantly increase manufacturing costs if their presence were avoided.

[0150] In Zn-M 2In the zinc alloy represented, Zn and M 2 The ratio (molar ratio) can be appropriately determined to achieve a suitable sintering temperature. M 2 The proportion (molar ratio) relative to the total zinc alloy can be, for example, 0.05 or more, 0.10 or more, or 0.20 or more, and can be less than 0.90, 0.80, 0.70, 0.60, 0.50, 0.40 or 0.30.

[0151] In addition to metallic zinc and / or zinc alloys, the modified material powder may optionally contain substances with binder and / or modifier functions, as well as other functions, provided that the effects of the present invention are not impaired. Examples of other functions include, for instance, improved corrosion resistance.

[0152] The particle size of the modified material powder is not particularly limited, but it is preferably finer than the particle size of the SmFeN powder of the first particle group, and more preferably finer than the particle size of the SmFeN powder of the second particle group. This allows the particles of the modified material powder to easily spread between the particles of the SmFeN powder. The particle size of the modified material powder is, for example, expressed in terms of D... 50 The median diameter can be 0.1 μm or more, 0.2 μm or more, 0.3 μm or more, or 0.4 μm or more, and can be 12.0 μm or less, 11.0 μm or less, 10.0 μm or less, 9.0 μm or less, 8.0 μm or less, 7.0 μm or less, 6.0 μm or less, 5.0 μm or less, 4.0 μm or less, 2.0 μm or less, 1.0 μm or less, or 0.5 μm or less. Additionally, the particle size D of the modified material powder... 50 (Median diameter) can be determined, for example, by dry laser diffraction / scattering.

[0153] If the modified material powder has a low oxygen content, it can absorb a large amount of oxygen from the SmFeN powder, which is therefore preferable. From this point of view, the oxygen content of the modified material powder is preferably 5.0% by mass or less, more preferably 3.0% by mass or less, and even more preferably 1.0% by mass or less, relative to the total modified material powder. On the other hand, drastically reducing the oxygen content of the modified material powder would lead to increased manufacturing costs. Therefore, the oxygen content of the modified material powder can be 0.1% by mass or more, 0.2% by mass or more, or 0.3% by mass or more, relative to the total modified material powder.

[0154] <Mixed Processes>

[0155] SmFeN powder and modified material powder are mixed to obtain a mixed powder. There are no particular limitations on the mixing method. Examples of mixing methods include using a mortar and pestle, a grinding wheel mixer, a stirred mixer, a mechanical blender, a V-type mixer, and a ball mill. These methods can also be combined. Furthermore, a V-type mixer is a device that consists of two cylindrical containers connected in a V-shape. By rotating the container, the powder in the container is repeatedly aggregated and separated by gravity and centrifugal force, thereby mixing the powder.

[0156] <Magnetic Field Forming Process>

[0157] The mixed powder is compressed and shaped in a magnetic field to obtain a magnetically shaped body. This allows for the imparting of orientation to the magnetically shaped body, and anisotropy to the shaped body (rare earth magnet) to increase remanence.

[0158] The magnetic field forming method can be a known method, such as compressing mixed powder into shape using a forming mold with a magnetic field generating device surrounding it. The forming pressure can be, for example, 10 MPa or more, 20 MPa or more, 30 MPa or more, 50 MPa or more, 100 MPa or more, or 150 MPa or more, and can be less than 1500 MPa, 1000 MPa or less, or 500 MPa or less. The time for applying the aforementioned forming pressure can be, for example, 0.5 minutes or more, 1 minute or more, or 3 minutes or more, and can be less than 10 minutes, 7 minutes or less, or 5 minutes or less. The applied magnetic field strength can be, for example, 500 kA / m or more, 1000 kA / m or more, 1500 kA / m or more, or 1600 kA / m or more, and can be less than 20000 kA / m, 15000 kA / m or less, 10000 A / m or less, 5000 kA / m or less, 3000 kA / m or less, or 2000 kA / m or less. Examples of methods for applying a magnetic field include applying a static magnetic field using an electromagnet and applying a pulsed magnetic field using alternating current. Furthermore, to suppress oxidation of the mixed powder, magnetic field forming is preferably performed in an inert gas atmosphere. An inert gas atmosphere includes a nitrogen atmosphere.

[0159] <Pressure sintering process>

[0160] A sintered body is obtained by pressure sintering a magnetic field formed body. The pressure sintering method is not particularly limited, and known methods can be used. Examples of pressure sintering methods include: preparing a mold with a cavity and a punch capable of sliding inside the cavity; inserting the magnetic field formed body into the cavity; and sintering the magnetic field formed body while applying pressure to it using the punch. In this method, a high-frequency induction coil is typically used to heat the mold. Alternatively, plasma discharge sintering (SPS) can also be used.

[0161] Appropriate pressure sintering conditions can be selected to sinter the magnetic field formed body while applying pressure (hereinafter sometimes referred to as "pressure sintering").

[0162] If the sintering temperature is above 300°C, the Fe on the surface of the SmFeN powder particles and the metallic zinc of the modified material powder diffuse slightly into each other in the magnetically formed body, which facilitates sintering. From this point of view, the sintering temperature can be, for example, above 310°C, above 320°C, above 340°C, or above 350°C. On the other hand, if the sintering temperature is below 430°C, the Fe on the surface of the SmFeN powder particles and the metallic zinc of the modified material powder will not diffuse excessively into each other, thus not hindering the subsequent heat treatment process, nor adversely affecting the magnetic properties of the obtained sintered body. From these points of view, the sintering temperature can be below 420°C, below 410°C, below 400°C, below 390°C, above 380°C, below 370°C, or below 360°C.

[0163] Regarding sintering pressure, any sintering pressure that can increase the density of the sintered body can be selected. Typical sintering pressures can be above 100 MPa, above 200 MPa, above 400 MPa, above 600 MPa, above 800 MPa, or above 1000 MPa, and can be below 2000 MPa, below 1800 MPa, below 1600 MPa, below 1500 MPa, below 1300 MPa, or below 1200 MPa.

[0164] The sintering time can be appropriately determined to allow the Fe on the particle surface of the SmFeN powder and the modified material powder to diffuse slightly into each other. The sintering time does not include the heating time before reaching the heat treatment temperature. The sintering time can be, for example, more than 1 minute, more than 2 minutes, or more than 3 minutes, and can be less than 30 minutes, less than 20 minutes, less than 10 minutes, or less than 5 minutes.

[0165] After the sintering time has elapsed, the sintered body is cooled, and the sintering process is complete. The faster the cooling rate, the better it suppresses oxidation of the sintered body. The cooling rate can be, for example, 0.5–200 °C / second.

[0166] Regarding the sintering atmosphere, an inert gas atmosphere, such as argon, is preferred to suppress oxidation of the magnetically formed body and the sintered body. Inert gas atmospheres include nitrogen atmospheres.

[0167] As described above, through pressure sintering, the Fe on the surface of the SmFeN powder particles and the modified material powder diffuse slightly into each other, or the diffusion of these slightly diffused portions can be arbitrarily localized to achieve modification. At this time, a modification-inhibiting film formation process and a heat treatment process are performed. The modification-inhibiting film formation process and the heat treatment process will be described below.

[0168] <Modified process to inhibit film formation>

[0169] Before pressure sintering, a modified inhibitory film is pre-formed on the surface of the second particle group. This suppresses surface modification of the second particle group. The formation of the modified inhibitory film can be done before pressure sintering, typically before mixing the SmFeN powder and the modified material powder.

[0170] Next, the reasons for suppressing particle surface modification of the second particle swarm will be explained.

[0171] Further heat treatment of the sintered body obtained by pressure sintering allows for the diffusion of Fe on the surface of the SmFeN powder particles and the modification material powder, thus improving coercivity. Details of the heat treatment process will be described later.

[0172] The SmFeN powder used in the manufacturing method of this disclosure comprises a first group of large-diameter particles and a second group of small-diameter particles. This increases the density of the sintered body, resulting in increased magnetization. If the sintered body thus obtained is heat-treated, the particles of the second group are more prone to modification due to their large specific surface area, and a portion of the magnetic phase within the particles of the second group is also modified. Thus, even with increased density of the sintered body, the magnetization will still decrease slightly. Therefore, it is preferable to form a modification inhibition film on the surface of the particles of the second group before pressure sintering to suppress surface modification of the second group of particles. This prevents the modification of a portion of the magnetic phase within the particles of the second group, thereby avoiding a slight decrease in magnetization.

[0173] As described above, the first and second particle groups are obtained by classifying SmFeN powder. In this case, the second particle group has higher coercivity than the first particle group; therefore, the second particle group can be modified unlike the first particle group. Therefore, it is appropriate to suppress the particle surface modification of the second particle group.

[0174] Furthermore, when magnetic powders with high coercivity (hereinafter sometimes referred to as "high coercivity powder") and low coercivity (hereinafter sometimes referred to as "low coercivity powder") coexist in a magnetic powder, the rectangularity of the molded body, especially at high temperatures, may sometimes decrease. This can be illustrated with the accompanying drawings below. Moreover, unless otherwise specified in this specification, regarding magnetic properties, "high temperature" refers to 100–200°C, and rectangularity is evaluated based on 10% demagnetization (Hk).

[0175] Figure 10 This is a coordinate graph showing the demagnetization curves of molded bodies made from low-coercivity powder at high temperatures, and the demagnetization curves of molded bodies made from a mixture of low-coercivity powder and high-coercivity powder. Figure 10 It can be understood that, compared with the molded body of a mixture of low-coercivity powder and high-coercivity powder, the molded body of low-coercivity magnetic powder has poor coercivity but excellent rectangularity.

[0176] As described above, the first particle group corresponds to low coercivity powder, and the second particle group corresponds to high coercivity powder. If a modified suppressive coating is formed on the second particle group, it is possible to suppress the higher coercivity of the second particle group. Therefore, the widening difference between the coercivity of the first and second particle groups can be suppressed, thereby improving rectangularity. Consequently, even when increasing the magnetization by utilizing the first and second particle groups to increase the density of the sintered body, rectangularity can still be improved, which is therefore preferable.

[0177] There are no particular limitations as long as the modified suppressing coating can suppress the interdiffusion of the magnetic phase in the particles of the second particle group and the Fe on the surface of the particles of the second particle group with the modified material powder, and does not adversely affect the magnetic properties of the rare earth magnets obtained by the manufacturing method of this disclosure. Such modified suppressing coatings typically contain phosphoric acid, but are not limited thereto.

[0178] When the modified inhibitory coating is a phosphoric acid-containing coating, the proportion of phosphoric acid in the modified inhibitory coating relative to the total modified inhibitory coating can be 40% or more by mass, 50% or more by mass, 60% or more by mass, 70% or more by mass, 80% or more by mass, or 90% or more by mass, or 100% by mass. Furthermore, when the modified inhibitory coating is a phosphoric acid-containing coating, its thickness can be 5 nm or more, 10 nm or more, 20 nm or more, 30 nm or more, 40 nm or more, or 50 nm or more, and can be less than 100 nm, less than 90 nm, less than 80 nm, less than 70 nm, or less than 60 nm.

[0179] There are no particular limitations on the method for forming a phosphoric acid-containing film for the second particle group; for example, the following methods can be cited.

[0180] By treating the particles of the second particle group with phosphoric acid, a passive film with PO bonds is formed on the surface of the particles. In the phosphoric acid treatment process, a phosphoric acid treatment agent reacts with the particles of the second particle group. Examples of phosphoric acid treatment agents include orthophosphoric acid, sodium dihydrogen phosphate, disodium hydrogen phosphate, ammonium dihydrogen phosphate, diammonium hydrogen phosphate, zinc phosphate, calcium phosphate, and other phosphate-based, hypophosphoric acid-based, hypophosphoric acid-based, pyrophosphoric acid, polyphosphoric acid, and other inorganic and organic phosphoric acids. These phosphoric acid sources are substantially dissolved in water or an organic solvent such as IPN. The particles of the second particle group are then added to a phosphoric acid bath containing reaction promoters such as nitrate ions and crystallization refiners such as V ions, Cr ions, and Mo ions, as needed, to form a passive film with PO bonds on the surface of the particles.

[0181] <Heat Treatment Process>

[0182] Before pressure sintering, a modified inhibition film is pre-formed on the particle surface of the second particle group (hereinafter sometimes simply referred to as "forming a modified inhibition film on the particle surface of the second particle group"), and then the sintered body after pressure sintering is heat-treated to modify the particle surface of the first particle group in the sintered body. This is illustrated with the accompanying drawings.

[0183] Figure 11 This is a schematic diagram illustrating an example of the microstructure of a rare earth magnet obtained by forming a modified inhibition film on the particle surface of a second particle group and then subjecting it to pressure sintering and heat treatment in the manufacturing method of this disclosure. Figure 12 This is a schematic diagram illustrating an example of the microstructure of a rare-earth magnet obtained by pressure sintering and heat treatment without forming a modified inhibition film on the surface of particles in the second particle group. Figure 11 and Figure 12 organization and Figure 1 The organizations are compared and explained.

[0184] and Figure 1 Compared to other organizations, Figure 11 and Figure 12 The organization consists of a slightly thicker modified phase 30 on the surface of particles from the first particle group 11. This is because, in order to obtain... Figure 1 The rare earth magnets with the desired structure were obtained without heat treatment of the sintered body. Figure 11 and Figure 12 The rare-earth magnets of the structure are used to heat-treat the sintered body, thereby modifying the particle surface of the first particle group 11. Since the specific surface area of ​​the particles of the first particle group 11 is small, the modification is not excessive due to heat treatment, and the modified phase 30 is only slightly thickened compared to the case without heat treatment.

[0185] and Figure 1 Compared to other organizations, Figure 11 In the organization, the thickness of the modified phase 30 on the particle surface of the second particle group 12 is approximately the same, while Figure 12 In the organization, the modified phase 30 on the particle surface of the second particle group 12 is relatively thick. This is because, in order to obtain [the desired structure]... Figure 11 The rare-earth magnets of the organization formed a modified inhibitory coating on the surface of the particles in the second particle group 12, and to obtain a coating with... Figure 12 The rare-earth magnets in the organization did not form a modified inhibitory coating on the surface of the particles in the second particle group 12. Therefore, in obtaining... Figure 11 When processing rare-earth magnets, during the heat treatment of the sintered body, the surface modification of the second particle group 12 was almost completely carried out, while the resulting rare-earth magnets exhibited... Figure 12When rare earth magnets are formed, the surface modification of the particles of the second particle group 12 is easily carried out during the heat treatment of the sintered body. Figure 11 In the organization, the rectangularity is improved because the surface modification of the second particle group 12 is suppressed. Therefore, it is preferable to form a modification suppression film on the particle surface of the second particle group 12.

[0186] Although not bound by theory, it is believed that during the heat treatment of the sintered body after pressure sintering, the modified inhibition film formed on the particle surface of the second particle group is decomposed into the elements constituting the modified inhibition film, and these elements exist in the modified phase. Therefore, it is considered that the modified phase is a phase in the Fe-Zn alloy phase containing elements from the aforementioned modified inhibition film.

[0187] The heat treatment conditions for the sintered body after pressure sintering only need to be appropriately determined to modify the surface area of ​​SmFeN powder particles, especially the surface area of ​​the first particle group. The heat treatment temperature can be, for example, above 350℃, above 360℃, above 370℃, or above 380℃, and below 410℃, below 400℃, or below 390℃. The heat treatment time can be above 6 hours, above 12 hours, or above 18 hours, and below 48 hours, below 42 hours, below 36 hours, below 30 hours, or below 24 hours.

[0188] When the sintered body after pressure sintering is heat-treated under the above heat treatment conditions, the thickness of the modified phase on the particle surface of the first particle group is, for example, about 20 to 50 nm. This is because no modified inhibition film is formed on the particle surface of the first particle group. Furthermore, when the sintered body after pressure sintering is heat-treated under the above heat treatment conditions, the thickness of the modified phase on the particle surface of the second particle group is about 20 to 50 nm when no modified inhibition film is formed, and about 1 to 20 nm when a modified inhibition film is formed.

[0189] To suppress oxidation of the sintered body, it is preferable to heat-treat the sintered body in a vacuum or in an inert gas atmosphere, including a nitrogen atmosphere. The heat treatment of the sintered body can also be performed in a forming mold for pressure sintering, immediately after pressure sintering; however, in this case, no pressure is applied to the sintered body during heat treatment. The forming mold for pressure sintering is, for example, a mold with a cavity. If the above heat treatment conditions are met, the normal magnetic phase decomposes to form an α-Fe phase, resulting in Fe and Zn not excessively diffusing into each other. In the case of heat treatment in a vacuum, the absolute pressure of the atmosphere can be 1 × 10⁻⁶. -7 Pa or above, 1×10 -6 Pa or above or 1×10 -5 Pa or higher, and can be 1×10 -2 Below Pa, 1×10-3 Pa or 1×10 -4 Below Pa.

[0190] The following describes the rare earth magnets obtained using the manufacturing method of this disclosure as described so far.

[0191] Rare Earth Magnets

[0192] The rare earth magnets obtained by the manufacturing method of this disclosure (hereinafter sometimes referred to as "the rare earth magnets of this disclosure") contain Sm, Fe and N, and at least a portion contains Th2Zn. 17 Type crystal structure or Th2Ni 17 A magnetic phase with a crystal structure. The composition of the magnetic phase is as described in the "Magnetic Powder Preparation Process".

[0193] The rare-earth magnet disclosed herein is obtained by mixing SmFeN powder with a modified material powder containing at least one of metallic zinc and zinc alloys. Therefore, the rare-earth magnet of this disclosure contains a zinc component derived from the modified material powder. Furthermore, as described above, a portion of the SmFeN powder particles and a portion of the zinc component of the modified material powder diffuse into each other to form an Fe-Zn alloy phase. In this specification, unless otherwise specified, the content of "zinc component" refers to the content (ratio) of Zn (zinc element). The zinc component of the rare-earth magnet of this disclosure is derived from metallic zinc in the modified material powder, and the zinc component content preferably ranges from 1 to 30% by mass.

[0194] Metamorphosis

[0195] In addition to the content described so far, the manufacturing method disclosed herein can be modified in various ways within the scope of the claims.

[0196] For example, some of the fine particles in the SmFeN powder can be removed before magnetic field forming. There are no particular limitations on the fine particle removal operation (fine particle removal method). Examples of fine particle removal operations (fine particle removal methods) include methods using a Cyclone (registered trademark) grading device, methods using a sieve, methods utilizing a magnetic field, and methods utilizing electrostatics. Combinations of these methods are also possible. By removing fine particles, the density of the formed body (rare earth magnet) can be further increased, and the magnetization intensity can be further improved.

[0197] [Example]

[0198] The manufacturing method of this disclosure will be described in more detail below through examples and comparative examples. Furthermore, the manufacturing method of this disclosure is not limited to the conditions used in the following examples.

[0199] Preparation of Samples

[0200] Prepare the samples for Examples 1-8 and Comparative Examples 1-7 according to the following guidelines.

[0201] <Examples 1-8 and Comparative Examples 1-5>

[0202] Dissolve 5.0 kg of FeSO4·7H2O in 2.0 kg of pure water. Then add 0.49 kg of Sm2O3, 0.74 kg of 70% sulfuric acid, and 0.035 kg of La2O3 and stir thoroughly until completely dissolved. Next, add pure water to the resulting solution to adjust the Fe concentration to 0.726 mol / L and the Sm concentration to 0.112 mol / L, thus preparing the SmFeLa sulfuric acid solution.

[0203] [Sedimentation Process]

[0204] In 20 kg of pure water maintained at 40°C, the total amount of prepared SmFeLa sulfuric acid solution was added dropwise over 70 minutes with stirring, starting from the beginning of the reaction. Simultaneously, 15% ammonia was added dropwise to adjust the pH to 7-8. This yielded a slurry containing SmFeLa hydroxide. The slurry was washed with pure water by decantation, and the hydroxide was then separated into solid and liquid components. The separated hydroxide was dried in an oven at 100°C for 10 hours.

[0205] [Oxidation Process]

[0206] The hydroxide obtained in the precipitation process was calcined at 1000°C for 1 hour in the atmosphere. After cooling, red SmFeLa oxide was obtained as the raw material powder.

[0207] [Pretreatment process]

[0208] 100g of SmFeLa oxide was placed in a steel container, with a loose layer thickness of 10mm. The container was placed in a furnace, and the pressure was reduced to 100Pa. Hydrogen gas was introduced while the temperature was raised to the pretreatment temperature of 850°C and maintained at this temperature for 15 hours. The oxygen concentration was determined by non-dispersive infrared absorption spectrometry (ND-IR) (EMGA-820 manufactured by Horiba Corporation), and the result was 5% by mass. This indicates that a black, partially reduced oxide was obtained, in which oxygen bound to Sm was not reduced, and 95% of the oxygen bound to Fe was reduced.

[0209] [Restoration Process]

[0210] 60g of the localized oxide obtained in the pretreatment process and 19.2g of metallic calcium with an average particle size of approximately 6mm were mixed and placed into a furnace. After evacuating the furnace, argon gas (Ar gas) was introduced. The temperature was raised to 1090℃ and held for 45 minutes, then cooled to obtain SmFe powder particles.

[0211] [Nitriding process]

[0212] Next, the furnace temperature was cooled to 100°C, and then vacuum was applied. Nitrogen gas was introduced while the temperature was raised to a first temperature of 430°C and maintained for 3 hours. Then, the temperature was raised to a second temperature of 500°C and maintained for 1 hour, followed by cooling to obtain a blocky product containing magnetic particles.

[0213] [Post-processing steps]

[0214] The lumpy product obtained in the nitriding process was added to 3 kg of pure water and stirred for 30 minutes. After standing, the supernatant was decanted. This process of adding, stirring, and decanting into pure water was repeated 10 times. Next, 2.5 g of 99.9% acetic acid was added and stirred for 15 minutes. After standing, the supernatant was decanted. This process of adding, stirring, and decanting into pure water was repeated twice.

[0215] [Acid treatment process]

[0216] Relative to 100 parts by weight of the powder obtained in the post-processing step, a 6% hydrochloric acid aqueous solution was added to achieve 4.3 parts by weight of hydrogen chloride, and the mixture was stirred for 1 minute. After standing, the supernatant was discharged by decantation. The addition, stirring, and decantation were repeated twice. After solid-liquid separation, the mixture was vacuum dried at 80°C for 3 hours to obtain a product with the composition Sm. 9.2 Fe 77.1 N 13.59 La 0.11 SmFeN powder.

[0217] SmFeN powder and paraffin wax were placed together in a sample container. After the paraffin wax was melted using a dryer, an orientation magnetic field of 16 kA / m was applied to align the easy magnetization axis. The sample after magnetic orientation was pulsed magnetized under a magnetizing magnetic field of 32 kA / m. The magnetic properties were measured at room temperature using a VSM (vibrating sample magnetometer) with a maximum magnetic field of 16 kA / m. The results showed that the remanence was 1.44 T and the coercivity was 750 kA / m.

[0218] The SmFeN powder obtained as described above was graded to obtain powder of a first particle group and powder of a second particle group. Then, the powder of the first particle group and the powder of the second particle group were mixed using an N-type mixer to obtain magnetic powder. The particle size distributions of the first and second particle groups are shown in Table 1. The ratio of the total volume of the first particle group to the total volume of the second particle group (total volume of the first particle group : total volume of the second particle group) is shown in Table 1-1. Table 1-1 also shows the remanence σr of the first and second particle groups.

[0219] Prepare zinc powder as a modifying material. The D of the zinc powder... 50The particle size is 0.5 μm. Furthermore, the purity of the zinc powder is 99.5% by mass.

[0220] Magnetic powder (powder from the first particle group and powder from the second particle group) was mixed with modified material powder to obtain a mixed powder. Additionally, the amount of metallic zinc mixed with the mixed powder was 5% by mass.

[0221] The mixed powder was compressed and shaped in a magnetic field to obtain a magnetically shaped body. The compression pressure was 50 MPa, and the pressure was applied for 1 minute. The applied magnetic field was 1600 kA / m. Furthermore, the compression shaping was carried out in a nitrogen atmosphere.

[0222] The magnetically shaped bodies were pressure-sintered. For the samples of Examples 1-6 and Comparative Examples 1-5, pressure sintering was performed using a high-frequency induction coil in an argon atmosphere (97000 Pa). For the samples of Examples 7-8, pressure sintering was performed using spark plasma heating (SPS) in a nitrogen atmosphere (10000 Pa). In all samples, the sintering temperature was 380°C, the sintering pressure was 1000 MPa, and the application time of the sintering pressure was 5 minutes.

[0223] <Comparative Examples 6-7>

[0224] As magnetic powder, only the powder of the first particle group was used and the powder of the second particle group was not used. Otherwise, the sample of Comparative Example 6 was prepared in the same manner as in Example 1, and the sample of Comparative Example 7 was prepared in the same manner as in Example 3.

[0225] <Example 9>

[0226] A phosphoric acid-containing coating is formed on the surface of the particles of the second particle group, and the sintered body after pressure sintering is heat-treated. Otherwise, the sample for Example 9 is prepared in the same manner as in Example 4. A phosphoric acid-containing coating is formed before mixing the SmFeN powder (powder of the first particle group and powder of the second particle group) with the modified material powder. That is, the SmFeN powder is classified into a first particle group and a second particle group, a phosphoric acid-containing coating is formed on the surface of the particles of the second particle group, and the powder of the first particle group (maintaining its classified state), the powder of the second particle group with the phosphoric acid-containing coating, and the modified material powder are mixed.

[0227] The formation of the phosphoric acid-containing film is a preparatory step prior to the phosphoric acid treatment process, consisting of a dispersion process and a surface treatment process. Details of the dispersion process, surface treatment process, and phosphoric acid treatment process are described below.

[0228] [Distributed Processes]

[0229] The second particle group consists of 5% powder by volume relative to the volume of the container used in the vibratory mill, and the medium (iron-core nylon medium, 10 mm in diameter, with a Vickers constant of 7 and a specific gravity of 7.48 g / cm³) is used. 3 The second particle group powder and media were placed in a container at a volume percentage of 60%. The mixture was dispersed in a vibratory mill under a nitrogen atmosphere for 60 minutes to obtain an intermediate powder.

[0230] [Surface treatment process]

[0231] The obtained intermediate powder was added to pure water and stirred for 1 minute. An acid solution was then added to the slurry for etching. Hydrochloric acid was used as the acid solution. While stirring, at least 50g of 5% hydrochloric acid was added per 100g of intermediate powder. Then, after confirming that the pH value reached above 3, decantation was performed until the conductivity of the slurry reached below 100μS / cm.

[0232] [Phosphoric acid treatment process]

[0233] A phosphoric acid solution was added to the obtained slurry. 1% by mass of phosphoric acid solution, calculated as PO4, was added relative to the solid content of the second particle group. The mixture was stirred for 5 minutes, and after solid-liquid separation, it was vacuum dried at 120°C for 3 hours to obtain a powder containing a phosphoric acid-coated second particle group.

[0234] The sintered bodies after pressure sintering were heat-treated under the conditions shown in Tables 2-1 and 2-2. Table 2-1 shows the remanence σr and coercivity Hc of the first and second particle groups respectively. In addition, in Table 2-1, "coating containing phosphoric acid" is denoted as "phosphate coating".

[0235] <Example 10>

[0236] No phosphoric acid-containing film was formed on the particle surface of the second particle group. Otherwise, the sample of Example 10 was prepared in the same manner as in Example 9.

[0237] "evaluate"

[0238] The density and magnetic properties of each sample were determined. The density was determined using the Archimedes method. The magnetic properties were determined using a vibrating sample magnetometer (VSM). For the samples of Example 1, Comparative Example 3, and Comparative Example 6, the cross-sections of the ground samples were examined using a scanning electron microscope (SEM) to observe the microstructure of the ground surfaces.

[0239] The evaluation results are shown in Tables 1-1 to 1-2, Tables 2-1 to 2-2, and... Figures 5-9 . Figure 5 It is a coordinate graph showing the relationship between d2 / d1 and density. Figure 6 This is a coordinate graph showing the relationship between d2 / d1 and remanence Br. Figure 7 This shows an SEM image of the sample from Example 1. Figure 8 This shows the SEM image of the sample from Comparative Example 3. Figure 9 This shows the SEM image of the sample from Comparative Example 6.

[0240]

[0241]

[0242]

[0243]

[0244] As shown in Tables 1-1 and 1-2 and Figure 5 and Figure 6 As shown, it can be understood that d1 and d2 satisfy the specified relationship, and the total volume of the first particle group: the total volume of the second particle group is within the specified range. The samples of Examples 1 to 8 have high density, and as a result, the remanence (remanent magnetization) is excellent.

[0245] On the other hand, in the samples of Comparative Examples 1 and 2, even though the total volume of the first particle group to the total volume of the second particle group was within the specified range, the density was low because d2 / d1 did not satisfy the specified relationship, resulting in low remanence. In the samples of Comparative Examples 3 to 5, although d2 / d1 satisfied the specified relationship, the density was low because the total volume of the first particle group to the total volume of the second particle group was not within the specified range, resulting in low remanence. Furthermore, in the samples of Comparative Examples 6 and 7, only the powder of the first particle group was used, and the powder of the second particle group was not used, resulting in low density and low remanence.

[0246] Furthermore, for example, the density of the sample in Example 1 is higher than that of the samples in Comparative Examples 3 and 6, which can also be seen from the SEM images of the sample in Example 1 (…). Figure 7 The dark areas (gaps) of the samples in the SEM images of Comparative Example 3 and Comparative Example 6 are smaller than those in the SEM images of the samples in Comparative Example 6. Figure 8 and Figure 9 We can understand it by looking at the darker parts of the image.

[0247] Regarding Examples 9 and 10, it can be understood that because d1 and d2 satisfy the specified relationship, and the total volume of the first particle group is within the specified range of the total volume of the second particle group, the density is high, resulting in excellent remanence. Furthermore, in Example 9, a phosphoric acid-containing film is formed on the surface of the particles in the second particle group, while in Example 10, no phosphoric acid-containing film is formed on the surface of the particles in the second particle group. Therefore, it can be understood that compared to the sample of Example 10, the sample of Example 9 has a larger Hk at 120°C and excellent rectangularity at high temperatures.

[0248] Based on the above results, the method for manufacturing rare earth magnets disclosed herein and the effects of the rare earth magnets obtained by the method can be confirmed.

Claims

1. A method for manufacturing a rare earth magnet, comprising the following steps: Prepare a magnetic powder containing Sm, Fe, and N, and at least a portion of which contains Th2Zn. 17 Type crystal structure or Th2Ni 17 Magnetic phases with a crystal structure of type ; Prepare a modified material powder, wherein the modified material powder contains at least one of metallic zinc and zinc alloys. The magnetic powder and the modified material powder are mixed to obtain a mixed powder; The mixed powder is compressed and shaped in a magnetic field to obtain a magnetically shaped body; and The magnetic field-formed body is pressurized and sintered to obtain a sintered body. The magnetic powder comprises a first particle group and a second particle group. Let d1μm represent the particle size distribution D of the first particle swarm. 50 And let d2μm represent the particle size distribution D of the second particle swarm. 50 , The d1 and d2 satisfy the relationship 0.350 ≤ d2 / d1 ≤ 0.500, and, The ratio of the total volume of the first particle swarm to the total volume of the second particle swarm, i.e., the ratio of the total volume of the first particle swarm to the total volume of the second particle swarm, is in the range of 9:1 to 4:

1. The d1 is 3.0 to 3.7 μm, and the d2 is 1.4 to 1.8 μm.

2. The method for manufacturing rare earth magnets according to claim 1, The modified material powder D 50 The thickness is 0.1–12.0 μm, and the zinc content in the modified material powder is 1–30% by mass relative to the mixed powder.

3. The method for manufacturing rare earth magnets according to claim 1 or 2, The mixed powder is compressed and shaped under a pressure of 10 to 1500 MPa.

4. The method for manufacturing rare earth magnets according to claim 1 or 2, The magnetic field formed body is subjected to pressure sintering at 100–2000 MPa and 300–430 °C for 1–30 minutes.

5. A method for manufacturing a rare earth magnet, comprising the following steps: Prepare a magnetic powder containing Sm, Fe, and N, and at least a portion of which contains Th2Zn. 17 Type crystal structure or Th2Ni 17 Magnetic phases with a crystal structure of type ; Prepare a modified material powder, wherein the modified material powder contains at least one of metallic zinc and zinc alloys. The magnetic powder and the modified material powder are mixed to obtain a mixed powder; The mixed powder is compressed and shaped in a magnetic field to obtain a magnetically shaped body; and The magnetic field-formed body is pressurized and sintered to obtain a sintered body. The magnetic powder comprises a first particle group and a second particle group. Let d1μm represent the particle size distribution D of the first particle swarm. 50 And let d2μm represent the particle size distribution D of the second particle swarm. 50 , The d1 and d2 satisfy the relationship 0.350 ≤ d2 / d1 ≤ 0.500, and, The ratio of the total volume of the first particle swarm to the total volume of the second particle swarm, i.e., the ratio of the total volume of the first particle swarm to the total volume of the second particle swarm, is in the range of 9:1 to 4:

1. The method for manufacturing the rare earth magnet also includes the following steps: Prior to the pressure sintering, a modified inhibition film is pre-formed on the particle surface of the second particle group; and The sintered body is subjected to heat treatment to modify the particle surface of the first particle group.

6. The method for manufacturing rare earth magnets according to claim 5, The d1 is 3.0 to 3.7 μm, and the d2 is 1.4 to 1.8 μm.

7. The method for manufacturing rare earth magnets according to claim 5 or 6, The modified inhibitory film contains phosphoric acid.

8. The method for manufacturing rare earth magnets according to claim 5 or 6, The sintered body is heat-treated at 350–410°C.

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