Rare earth magnet and method for manufacturing the same

Abstract

To provide a rare earth magnet capable of improving magnetization further more than the prior arts, and a production method thereof.SOLUTION: The present invention relates to a production method of a rare earth magnet including: preparing a predetermined magnetic powder and a modified material powder; obtaining a mixed powder by mixing the magnetic powder and the modified material powder; obtaining a magnetic field molded body by performing compression molding of the mixed powder in a magnetic field; and obtaining a sintered body by performing pressure sintering of the magnetic field molded body. The magnetic powder contains a first particle group and a second particle group. Particle size distribution D50 of the first particle group is expressed as d1 μm, and particle size distribution D50 of the second particle size is expressed as d2 μm. The d1 and the d2 satisfy a relation of 0.350≤d2 / d1≤0.500, and a ratio of a total volume of the first particle group and a total volume of the second particle volume ranges from 9:1 to 4:1. The present invention also relates to a rare earth magnet obtained by the production method.SELECTED DRAWING: Figure 6

Description

Technical Field

[0001] The present disclosure relates to a method for manufacturing a rare earth magnet. In particular, the present disclosure relates to a method for manufacturing a rare earth magnet containing Sm, Fe, and N, and having a magnetic phase having a crystal structure of at least one of the Th2Zn 17 type and Th2Ni 17 type.

Background Art

[0002] As high-performance rare earth magnets, Sm-Co-based rare earth magnets and Nd-Fe-B-based rare earth magnets have been put into practical use. In recent years, rare earth magnets other than these have been studied.

[0003] For example, rare earth magnets containing Sm, Fe, and N (hereinafter sometimes referred to as "Sm-Fe-N-based rare earth magnets") have been studied. The Sm-Fe-N-based rare earth magnet is manufactured, for example, using magnetic powder containing Sm, Fe, and N (hereinafter sometimes referred to as "SmFeN powder").

[0004] SmFeN powder includes a magnetic phase having a crystal structure of at least one of the Th2Zn 17 type and Th2Ni 17 type. This magnetic phase is considered to be a solid solution in which N penetrates into the Sm-Fe crystal. Therefore, SmFeN powder is likely to be decomposed by the separation of N due to heat. For this reason, Sm-Fe-N-based rare earth magnets are often manufactured by molding SmFeN powder using resin and / or rubber.

[0005] As another manufacturing method of Sm-Fe-N-based rare earth magnets, for example, the manufacturing method disclosed in Patent Document 1 can be mentioned. This manufacturing method mixes SmFeN powder and powder containing metallic zinc (hereinafter sometimes referred to as "metallic zinc powder"), molds the mixed powder in a magnetic field, and sinters (including liquid phase sintering) the magnetic field molded body.

[0006] Also, the manufacturing method of SmFeN powder is disclosed in Patent Documents 2 and 3, for example.

Prior Art Documents

Patent Documents

[0007]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0008] The sintering methods of magnetic field formed bodies are roughly classified into a non-pressure sintering method and a pressure sintering method. In any of the sintering methods, by sintering the magnetic field formed body, a high-density rare earth magnet (sintered body) can be obtained. In the non-pressure sintering method, since no pressure is applied to the magnetic field formed body during sintering, in order to obtain a high-density sintered body, it is common to sinter the magnetic field formed body at a high temperature of 900 °C or higher for a long time of 6 hours or more. On the other hand, in the pressure sintering method, since pressure is applied to the magnetic field formed body during sintering, it is common to obtain a high-density sintered body even if the magnetic field formed body is sintered at a low temperature of 600 to 800 °C for a short time of 0.1 to 5 hours.

[0009] When sintering a magnetic field-formed body of a mixed powder of SmFeN powder and metallic zinc powder, in order to avoid the decomposition of the SmFeN powder due to heat, pressure sintering is adopted, but sintering is carried out at a temperature lower than the sintering temperature of normal pressure sintering and in a shorter time. The reason why sintering is possible even at such a low temperature and in a short time is that the zinc component in the metallic zinc powder diffuses to the surface of the magnetic powder during sintering and sinters (solidifies). Thus, the metallic zinc powder in the magnetic field-formed body has a function as a binder. Further, the metallic zinc powder in the magnetic field-formed body also has a function as a modifier that modifies the αFe phase on the surface of the SmFeN powder particles, especially the SmFeN powder, and absorbs oxygen in the SmFeN powder to improve the coercivity. Hereinafter, a powder that is used in the production of Sm-Fe-N-based rare earth magnets and has both a function as a binder and a function as a modifier may be simply referred to as a "modifier powder".

[0010] When forming magnetic powder using resin and / or rubber, etc., and when pressure-sintering a mixed powder of magnetic powder and modifier powder, in either case, the magnetization of the formed body (rare earth magnet) decreases by the content ratio of the resin and the modifier that do not contribute to magnetization. On the other hand, compared with the case of forming magnetic powder using resin and / or rubber, etc., when pressure-sintering a mixed powder of magnetic powder and modifier powder, generally, a high-density formed body (rare earth magnet) can be obtained, and as a result, it is easy to obtain high magnetization. However, when the magnetic powder is SmFeN powder, even when pressure-sintering a mixed powder of magnetic powder and modifier powder, the magnetization may decrease more than predicted from the content ratio of the modifier, and the desired magnetization may not be obtained.

[0011] From these facts, the inventors have found the problem that a method for manufacturing Sm-Fe-N-based rare earth magnets that can further improve magnetization compared to the prior art is desired.

[0012] The present disclosure has been made to solve the above problems. That is, an object of the present disclosure is to provide a method for manufacturing Sm-Fe-N-based rare earth magnets that can further improve magnetization compared to the prior art.

Means for Solving the Problems

[0013] In order to achieve the above object, the inventors of the present invention have conducted intensive studies and completed a method for manufacturing a rare earth magnet of the present disclosure. The method for manufacturing a rare earth magnet of the present disclosure includes the following aspects. 〈1〉 Containing Sm, Fe, and N, at least a part of which is Th2Zn 17 type and Th2Ni 17 Preparing magnetic powder having a magnetic phase having any one of the crystal structures of the type, and Preparing a modifier powder containing at least one of metallic zinc and zinc alloys, Mixing the magnetic powder and the modifier powder to obtain a mixed powder, Compression molding the mixed powder in a magnetic field to obtain a magnetic field molded body, and Pressurizing and sintering the magnetic field molded body to obtain a sintered body, including, The magnetic powder includes a first particle group and a second particle group, The particle size distribution D of the first particle group 50 is represented by d1 μm, and the particle size distribution D of the second particle group 50 is represented by d2 μm, The d1 and the d2 satisfy the relationship of 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 (total volume of the first particle group: total volume of the second particle group) is in the range of 9:1 to 4:1. Method for manufacturing a rare earth magnet. 〈2〉 The d1 is 3.0 to 3.7 μm, and the d2 is 1.4 to 1.8 μm. The method for manufacturing a rare earth magnet according to item 〈1〉. 〈3〉 The D of the modifier powder 50 is 0.1 to 12.0 μm, and the content ratio of the zinc component in the modifier powder is 1 to 30% by mass with respect to the mixed powder. The method for manufacturing a rare earth magnet according to item 〈1〉 or 〈2〉. 〈4〉 Compression molding the mixed powder at a pressure of 10 to 1500 MPa. The method for manufacturing a rare earth magnet according to any one of items 〈1〉 to 〈3〉. <5> The method for manufacturing a rare earth magnet according to any one of <1> to <4>, wherein the magnetic field forming body is pressure-sintered at a pressure of 100 to 2000 MPa and a temperature of 300 to 430 °C for 1 to 30 minutes. <6> Before the pressure sintering, forming a modification suppression film on the particle surface of the second particle group in advance, and heat-treating the sintered body to advance the modification of the particle surface of the first particle group. The method for manufacturing a rare earth magnet according to any one of <1> to <5>, further comprising the above steps. <7> The method for manufacturing a rare earth magnet according to <6>, wherein the modification suppression film contains phosphoric acid. <8> The method for manufacturing a rare earth magnet according to <6> or <7>, wherein the sintered body is heat-treated at 350 to 410 °C. <9> A rare earth magnet of a sintered body containing Sm, Fe, and N, and having a magnetic phase with at least a part having a crystal structure of either Th2Zn 17 type and Th2Ni 17 type, and containing a zinc component, wherein the magnetic powder includes a first particle group and a second particle group, the particle size distribution D 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, 50 the d1 and the d2 satisfy the relationship of 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 (the total volume of the first particle group: the total volume of the second particle group) is in the range of 9:1 to 4:1. A rare earth magnet. [Advantages of the Invention]

[0014] According to the manufacturing method of the present disclosure, by setting the ratio of the particle size of the second particles 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 predetermined range, the density of the sintered body (rare earth magnet) can be improved. As a result, it is possible to provide a method for manufacturing a rare earth magnet capable of further improving magnetization compared to the prior art.

Brief Description of the Drawings

[0015]

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Embodiments for Carrying Out the Invention

[0016] Hereinafter, embodiments of the manufacturing method of the rare earth magnet of the present disclosure (hereinafter, sometimes simply referred to as "the manufacturing method of the present disclosure") will be described in detail. Note that the embodiments shown below do not limit the manufacturing method of the present disclosure.

[0017] Although not bound by theory, the reason why a rare earth magnet with further improved magnetization can be obtained by the manufacturing method of the present disclosure will be described with reference to the drawings while comparing it with the conventional manufacturing method of rare earth magnets (hereinafter sometimes simply referred to as "conventional manufacturing method").

[0018] FIG. 1 is a schematic diagram showing an example of the structure of a rare earth magnet obtained by the manufacturing method of the present disclosure. FIG. 2 is a schematic diagram showing an example of the structure of a rare earth magnet obtained by the conventional manufacturing method. FIG. 3 is a schematic diagram showing another example of the structure of a rare earth magnet obtained by the conventional manufacturing method. FIG. 4 is a schematic diagram showing still another example of the structure of a rare earth magnet obtained by the conventional manufacturing method. The arrows in FIGS. 1 to 4 indicate the magnetic orientation direction.

[0019] As shown in FIG. 1, in the rare earth magnet 100 obtained by the manufacturing method of the present disclosure, SmFeN powder particles 10 are bonded by a modifier 20. This is because, as described above, the modifier 20 has a function as a binder. And the surface of the SmFeN powder particles 10 is coated with a modified phase 30.

[0020] As shown in FIG. 1, in the rare earth magnet 100 obtained by the manufacturing method of the present disclosure, the SmFeN powder particles 10 include a first particle group 11 having a large particle size and a second particle group 12 having a small particle size. By the presence of each particle of the second particle group 12 between each particle of the first particle group 11, the density of the rare earth magnet 100 can be increased, and as a result, the magnetization is improved. For example, as shown in FIG. 2, in an example of the rare earth magnet 200 obtained by the conventional manufacturing method, since the SmFeN powder particles 10 are substantially only the first particle group 11, the density of the rare earth magnet 200 cannot be increased, and as a result, the magnetization is not improved.

[0021] Also, as shown in FIG. 1, the density of the rare earth magnet 100 obtained by the manufacturing method of the present 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 predetermined range. For example, as shown in FIG. 3, in another example of the rare earth magnet 200 obtained by the conventional manufacturing method, since 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, the distance between the particles of the first particle group 11 becomes large. Therefore, in the rare earth magnet 200 obtained by the conventional manufacturing method, its density cannot be increased, and as a result, the magnetization is not improved.

[0022] In addition, in order to increase the density of the rare earth magnet 100 obtained by the manufacturing method of the present disclosure, not only 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 predetermined range, but also the ratio of the total volume of the first particle group 11 to the total volume of the second particle group 12 needs to be within a predetermined range. This is because when the particles of the second particle group 12 exist to a certain extent or more, as shown in FIG. 1, the gaps between the particles of the first particle group 11 are sufficiently filled, while when the particles of the second particle group 12 exist excessively, as shown in FIG. 4, the gaps between the particles of the first particle group 11 expand. And due to this expansion, the density of the rare earth magnet 200 obtained by the conventional manufacturing method cannot be increased, and as a result, the magnetization is not improved.

[0023] Also, compared with the large particle size SmFeN powder particles such as the first particle group 11, the small particle size SmFeN powder particles such as the second particle group 12 have a small particle remanent magnetization σr. This is because the crystal structure of the particle surface is deteriorated, and the small particle size particles have a larger specific surface area compared with the large particle size particles. Therefore, the small particle size particles such as the second particle group 12 are likely to have their particle remanent magnetization σr deteriorated. When such an excessive amount of the second particle group 12 exists, it leads to a decrease in the magnetization of the entire rare earth magnet.

[0024] From these facts, in the manufacturing method of the present disclosure, the excessive presence of the particles of the second particle group 12 is avoided to avoid a decrease in magnetization.

[0025] Although not restricted by theory, as described above, for the particles of each of the first particle group 11 and the second particle group 12, it is considered that the reason why both the particle size ratio and the total volume ratio need to be within a predetermined range is as follows. The friction coefficient of SmFeN powder particles is extremely large compared to magnetic powders and the like used in the production of Nd-Fe-B-based rare earth magnets. Therefore, when molding SmFeN powder, it is considered that this is due to the fact that its fluidity is not good and it is difficult to increase the filling rate of the molded body (rare earth magnet). Note that the fact that magnetization increases as density increases can be understood from the fact that the residual magnetization can be expressed by the following equation. Residual magnetization = saturation magnetization × orientation degree × (density / true density) × magnetic phase ratio

[0026] Next, the constituent requirements of the manufacturing method of the present disclosure, which have been completed based on the findings described so far, will be described.

[0027] 《Manufacturing Method》 The manufacturing method of the present disclosure includes a magnetic powder preparation step, a modifier powder preparation step, a mixing step, a magnetic field molding step, and a pressure sintering step. Optionally, it also includes a modification suppression film formation step and a heat treatment step. Hereinafter, each step will be described.

[0028] 〈Magnetic Powder Preparation Step〉 Prepare magnetic powder (SmFeN powder). The magnetic powder (SmFeN powder) used in the manufacturing method of the present disclosure contains Sm, Fe, and N, and at least a part thereof is Th2Zn 17 type and Th2Ni 17 There is no particular limitation as long as it has a magnetic phase having any of the crystal structures. Examples of the crystal structure of the magnetic phase include phases having a TbCu7-type crystal structure in addition to the aforementioned structures. Note that Sm is samarium, Fe is iron, and N is nitrogen. Also, Th is thorium, Zn is zinc, Ni is nickel, Tb is terbium, and Cu is copper.

[0029] In the SmFeN powder, for example, the composition formula (Sm (1-i) R i )2(Fe (1-j) Co j ) 17 Nh It may contain a magnetic phase represented by the following. The rare earth magnet obtained by the production method of the present disclosure (hereinafter sometimes referred to as "product") exhibits magnetization derived from the magnetic phase in the SmFeN powder. Here, i, j, and h are molar ratios.

[0030] The magnetic phase in the SmFeN powder may contain R as long as it does not inhibit the effects of the production method of the present disclosure and the magnetic properties of the product. Such a range is represented by i in the above composition formula. i may be, for example, 0 or more, 0.10 or more, or 0.20 or more, and may be 0.50 or less, 0.40 or less, or 0.30 or less. R is one or more selected from rare earth elements other than Sm 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. Here, 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.

[0031] (Sm (1-i) R i )2(Fe (1-j) Co j ) 17 N h Typically, for (Sm (1-j) Co j ) 17 N h R substitutes for Sm at the Sm position, but it is not limited to this. For example, in Sm2(Fe (1-j) Co j ) 17 N h a part of R may be arranged in an intrusion type.

[0032] The magnetic phase in the SmFeN powder may contain Co as long as it does not inhibit the effects of the manufacturing method of the present disclosure and the magnetic properties of the product. Such a range is represented by j in the above composition formula. j may be 0 or more, 0.10 or more, or 0.20 or more, and may be 0.52 or less, 0.40 or less, or 0.30 or less.

[0033] (Sm (1-i) R i )2(Fe (1-j) Co j ) 17 N h Regarding (Sm (1-i) R i )2Fe 17 N h Typically, Co substitutes for Fe at the Fe position, but it is not limited to this. For example, in (Sm (1-i) R i )2Fe 17 N h Some of the invading Co may be arranged.

[0034] The magnetic phase in the SmFeN powder is contributed to the manifestation and improvement of magnetic properties by the presence of N in an invading type in the crystal grains represented by (Sm (1-i) R i )2(Fe (1-j) Co j ) 17

[0035] (Sm (1-i) R i )2(Fe (1-j) Co j ) 17 N h Regarding (Sm (1-i) R i )2(Fe (1-j) Co j ) 17 N3, h can take values from 1.5 to 4.5. Typically, it is (Sm (1-i) R i )2(Fe (1-j) Co j )17 N h For the whole (Sm (1-i) R i )2(Fe (1-j) Co j ) 17 The content of N3 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, (Sm (1-i) R i )2(Fe (1-j) Co j ) 17 N h Not all of them need to be (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 N h For the whole (Sm (1-i) R i )2(Fe (1-j) Co j ) 17 The content of N3 may be 98% by mass or less, 95% by mass or less, or 92% by mass or less.

[0036] In addition to the magnetic phase represented by SmFeN powder, (Sm (1-i) R i )2(Fe (1-j) Co j ) 17 N h It may contain oxygen and M 1 as well as inevitable impurity elements, as long as the effects of the manufacturing method of the present disclosure and the magnetic properties of the product are not substantially inhibited. From the viewpoint of ensuring the magnetic properties of the product, for the whole SmFeN powder, (Sm (1-i) R i )2(Fe (1-j) Co j ) 17 N h The content of the magnetic phase represented by may be 80% by mass or more, 85% by mass or more, or 90% by mass or more. On the other hand, for the whole SmFeN powder, (Sm (1-i) R i)2(Fe (1-j) Co j ) 17 N h Even if the content of the magnetic phase represented by is not excessively high, there are no practical problems. Therefore, the content may be 97% by mass or less, 95% by mass or less, or 93% by mass or less. (Sm (1-i) R i )2(Fe (1-j) Co j ) 17 N h The remainder of the magnetic phase represented by becomes the content of oxygen and M 1 . Also, a part of oxygen and M 1 may be of the interstitial and / or substitutional type and may be present in the magnetic phase.

[0037] As the above-mentioned 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 mentioned. Unavoidable impurity elements refer to impurity elements that cannot be avoided during the production of raw materials and / or magnetic powder, or that would cause a significant increase in production costs to avoid. These elements may be present in the above-mentioned magnetic phase in the substitutional and / or interstitial type, may be present in a phase other than the above-mentioned magnetic phase, or may be present at the grain boundaries of these phases. Note that 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.

[0038] 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 size of each particle of the first particle group and the second particle group can be represented by the particle size distribution D 50 . The particle size distribution D 50 of the first particle group is represented by d1 μm, and the particle size distribution D 50It is represented by d2 μm. And d1 and d2 satisfy the relationship of 0.350 ≦ d2 / d1 ≦ 0.500. From satisfying the above 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.

[0039] If d2 / d1 is 0.350 or more, 0.360 or more, 0.370 or more, or 0.378 or more, and 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 particles of the second particle group advantageously exist between the particles of the first particle group, the density of the molded body (rare earth magnet) increases, and as a result, the magnetization is improved.

[0040] As long as the above relationship is satisfied, the particle sizes of the particles of each of the first particle group and the second particle group are not particularly limited. However, in order to easily satisfy the above relationship, it is preferable that each of d1 and d2 is independently in the following ranges. d1 is preferably 3.0 μm or more, 3.2 μm or more, or 3.4 μm or more, and may 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 preferably 1.8 μm or less, 1.7 μm or less, or 1.6 μm or less.

[0041] Also, the ratio of the total volume of the first particle group to the total volume of the second particle group, that is, (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. (Total volume of the first particle group):(total volume of the second particle group) being 9:1 means that, for example, the total volume of the first particle group is 90% and the total volume of the second particle group is 10% with respect to the total volume of the SmFeN powder. Also, (total volume of the first particle group):(total volume of the second particle group) being 4:1 means that, for example, the total volume of the first particle group is 80% and the total volume of the second particle group is 20% with respect to the total volume of the SmFeN powder.

[0042] If (total volume of the first particle group):(total volume of the second particle group) is 9:1 or the total volume of the second particle group is more than that, each particle of the second particle group is advantageously present between each particle of the first particle group, increasing the density of the rare earth magnet, and as a result, the magnetization is improved. From this perspective, (total volume of the first particle group):(total volume of the second particle group) is preferably 8.8:1.2 or more or 8.6:1.4 or more.

[0043] When the particles of the second particle group are present in excess, the gaps between each particle of the first particle group conversely expand. To avoid this, (total volume of the first particle group):(total volume of the second particle group) should be 4:1 or the total volume of the second particle group should be less than that. Also, since the remanent magnetization σr of the particles of the small particle size SmFeN powder such as the second particle group is small, if the second particle group is present in excess, it will lead to a decrease in the magnetization of the entire rare earth magnet. For these reasons, by avoiding the expansion of the intervals between each particle of the first particle group, suppressing the decrease in the density of the rare earth magnet, and reducing the number of the second particle group with a small σr, the magnetization of the rare earth magnet is improved. From these perspectives, (total volume of the first particle group):(total volume of the second particle group) is preferably 8.2:1.8 or less or 8.4:1.6 or less.

[0044] The magnetic powder containing the first particle group and the second particle group is typically obtained by classifying the SmFeN powder obtained by the manufacturing method described later into the first particle group and the second particle group and then mixing them again. There are no particular restrictions on the classification and mixing methods, and well-known methods may be used. Examples of the classification method include sieve classification and air classification, etc., and these may be combined. Examples of the mixing method include a method of mixing using an agitator type mixer and a V-type mixer, etc., and these may be combined.

[0045] D of the SmFeN powder 50 is calculated from the particle size distribution of the SmFeN powder, and the particle size distribution of the SmFeN powder is measured (investigated) by the following method. In this specification, unless otherwise specified, the description regarding the size (particle size) of the particles of the SmFeN powder is based on the following measurement method (investigation method). Note that D50 means the median diameter.

[0046] Prepare a sample in which SmFeN powder is resin-embedded, polish the surface of the sample, and observe it with an optical microscope. Then, draw a straight line on the optical microscope image, measure the length of the line segment separated by SmFeN particles (bright field), and determine the particle size distribution of the SmFeN powder from the frequency distribution of the line segment lengths. The particle size distribution obtained by this method is almost equal to the particle size distribution obtained by the intersection method or the dry laser diffraction / scattering method.

[0047] In SmFeN powder, there are fine particles due to manufacturing convenience and the like. However, as long as d1 and d2 satisfy the above relationships, there is no particular limitation on the proportion of magnetic particles (fine particles) having a particle size of 1.0 μm or less in the SmFeN powder. From the viewpoint of ensuring the mechanical strength of the compact (rare earth magnet), it is preferably as low as possible. With respect to the total number of magnetic particles in the SmFeN powder, the proportion of fine particles is preferably 10.0% or less, 8.0% or less, 6.0% or less, or 4.0% or less. From the viewpoint of manufacturing convenience of the SmFeN powder, etc., the fine particles do not have to be completely absent, and even if the lower limit of the proportion of the fine particles is 1.0%, 2.0%, or 3.0%, there is no practical problem.

[0048] In the manufacturing method of the present disclosure, a modifying material powder described below is mixed with the SmFeN powder. Oxygen in the SmFeN powder is absorbed by the metallic zinc or zinc alloy powder in the modifying material powder, whereby the magnetic properties of the molded body, particularly the coercive force, can be improved. The oxygen content in the SmFeN powder may be determined in consideration of the amount of oxygen in the SmFeN powder absorbed by the modifying material powder during the manufacturing process. It is preferable that the oxygen content of the SmFeN powder is low with respect to the entire SmFeN powder. The oxygen content of the 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 with respect to the entire SmFeN powder. On the other hand, extremely reducing the oxygen content in the SmFeN powder leads to an increase in manufacturing cost. Therefore, the oxygen content of the SmFeN powder may be 0.1% by mass or more, 0.2% by mass or more, or 0.3% by mass or more with respect to the entire SmFeN powder.

[0049] The manufacturing method of the SmFeN powder is not particularly limited as long as it satisfies what has been described so far, and commercially available products may be used. Examples of the manufacturing method of the SmFeN powder include, for example, a method of manufacturing Sm-Fe powder from samarium oxide and iron powder by a reduction diffusion method, and performing a heat treatment at 600 °C or lower in an atmosphere such as a mixed gas of nitrogen and hydrogen, nitrogen gas, and ammonia gas to obtain Sm-Fe-N powder. Alternatively, for example, a method of manufacturing a Sm-Fe alloy by a melting method, nitriding the coarsely pulverized particles obtained by coarsely pulverizing the alloy, and further pulverizing it until it reaches a desired particle size may be mentioned. For pulverization, for example, a dry jet mill, a dry ball mill, a wet ball mill, or a wet bead mill can be used. These may be used in combination.

[0050] In addition to the aforementioned manufacturing method, the SmFeN powder can be obtained, for example, by subjecting an oxide containing Sm and Fe to a heat treatment in an atmosphere containing a reducing gas to obtain a pre-treatment step of obtaining a partial oxide, subjecting the partial oxide to a heat treatment in the presence of a reducing agent to obtain an alloy particle reduction step, and subjecting the alloy particle to a heat treatment at a first temperature of 400 °C or higher and 470 °C or lower in an atmosphere containing nitrogen or ammonia, and then subjecting it to a heat treatment at a second temperature of 480 °C or higher and 610 °C or lower to obtain a nitride nitriding step. Particularly for alloy particles with a large particle size, such as alloy particles containing La, nitridation may not proceed sufficiently inside the oxide particles. However, when nitriding at two-stage temperatures, the inside of the oxide particles is also sufficiently nitrided, resulting in a narrow particle size distribution and an anisotropic SmFeN powder with high residual magnetization can be obtained.

[0051] [Oxide preparation step] The oxide containing Sm and Fe used in the pre-treatment step described below may be prepared, for example, by mixing Sm oxide and Fe oxide. However, it is preferably produced by mixing a solution containing Sm and Fe with a precipitating agent to obtain a precipitate containing Sm and Fe (precipitation step), and firing the precipitate to obtain an oxide containing Sm and Fe (oxidation step).

[0052] [Precipitation step] In the precipitation step, a solution containing Sm and Fe is prepared by dissolving Sm raw material and Fe raw material in a strongly acidic solution. When obtaining Sm2Fe 17 N3 as the main phase, the molar ratio of Sm and Fe (Sm:Fe) is preferably 1.5:17 to 3.0:17, and 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 may be added to the above-mentioned solution. In terms of the residual magnetic flux density, it is preferably contained La. In terms of the coercive force and squareness ratio, it is preferably contained W. In terms of the temperature characteristics, it is preferably contained Co and / or Ti.

[0053] The Sm raw material and the Fe raw material are not limited as long as they can be dissolved in a strongly acidic solution. For example, from the perspective of easy availability, samarium oxide can be used as the Sm raw material, and FeSO4 can be used as the Fe raw material. The concentration of the solution containing Sm and Fe can be appropriately adjusted within the range where the Sm raw material and the Fe raw material are substantially dissolved in the acidic solution. Examples of the acidic solution include sulfuric acid in terms of solubility.

[0054] By reacting the solution containing Sm and Fe with a precipitant, an insoluble precipitate containing Sm and Fe is obtained. Here, the solution containing Sm and Fe only needs to be a solution containing Sm and Fe during the reaction with the precipitant. For example, the raw materials containing Sm and Fe can be prepared as separate solutions, and each solution can be dropped to react with the precipitant. Even when prepared as separate solutions, appropriate adjustment is made within the range where each raw material is substantially dissolved in the acidic solution. The precipitant is not limited as long as it reacts with the solution containing Sm and Fe in an alkaline solution to obtain a precipitate, and examples include aqueous ammonia and caustic soda, and caustic soda is preferred.

[0055] From the point that the properties of the precipitate particles can be easily adjusted, the precipitation reaction preferably uses a method of dropping the solution containing Sm and Fe and the precipitant into a solvent such as water respectively. By appropriately controlling the supply rate of the solution containing Sm and Fe and the precipitant, the reaction temperature, the reaction solution concentration, the pH during the reaction, etc., a precipitate with a homogeneous distribution of constituent elements, a narrow particle size distribution, and a regular powder shape can be obtained. By using such a precipitate, the magnetic properties of the final product, SmFeN powder, are improved. The reaction temperature can be 0°C or higher and 50°C or lower, and preferably 35°C or higher and 45°C or lower. The reaction solution concentration is preferably 0.65 mol / L or higher and 0.85 mol / L or lower as the total concentration of metal ions, and more preferably 0.7 mol / L or higher and 0.85 mol / L or lower. The reaction pH is preferably 5 or higher and 9 or lower, and more preferably 6.5 or higher and 8 or lower.

[0056] The solution containing Sm and Fe preferably contains at least one metal selected from the group consisting of La, W, Co, and Ti in terms of magnetic properties. For example, in terms of residual magnetic flux density, it is preferable to contain La, in terms of coercive force and squareness ratio, it is preferable to contain W, and in terms of temperature characteristics, it is preferable to contain Co and / or Ti. The La raw material is not limited as long as it can be dissolved in a strongly acidic solution. For example, in terms of availability, La2O3, LaCl3, etc. can be mentioned. Together with the Sm raw material and Fe raw material, the La raw material, W raw material, Co raw material, and Ti raw material are appropriately adjusted within the range where they are substantially dissolved in the acidic solution. As the acidic solution, sulfuric acid can be mentioned in terms of solubility. As the W raw material, ammonium tungstate can be mentioned, as the Co raw material, cobalt sulfate can be mentioned, and as the titanium raw material, titanium sulfate can be mentioned.

[0057] When the solution containing Sm and Fe further contains at least one metal selected from the group consisting of La, W, Co, and Ti, an insoluble precipitate containing Sm, Fe, and at least one selected from the group consisting of La, W, Co, and Ti is obtained. Here, the solution only needs to contain at least one selected from the group consisting of La, W, Co, and Ti during the reaction with the precipitating agent. For example, each raw material can be prepared as a separate solution, and each solution can be dropped to react with the precipitating agent, or it can be adjusted together with the solution containing Sm and Fe.

[0058] The powder particle size, powder shape, and particle size distribution of the finally obtained SmFeN powder are approximately determined by the powder obtained in the precipitation step. When the particle size of the obtained powder is measured by a laser diffraction wet particle size distribution analyzer, it is preferable that the entire powder falls within a size and distribution range of 0.05 μm or more and 20 μm or less, preferably 0.1 μm or more and 10 μm or less.

[0059] After separating the precipitate, in order to suppress the redissolution of the precipitate in the remaining solvent during the heat treatment of the subsequent oxidation process, the aggregation of the precipitate when the solvent evaporates, and the changes in the particle size distribution, powder particle diameter, etc., it is preferable to remove the solvent from the separated material. Specifically, as a method for removing the solvent, for example, when water is used as the solvent, a method of drying in an oven at 70°C or higher and 200°C or lower for 5 hours or longer and 12 hours or shorter can be mentioned.

[0060] After the precipitation step, a step of separating and washing the obtained precipitate may be included. The washing step is appropriately performed until the conductivity of the supernatant solution becomes 5 mS / m 2 or less. As a method for separating the precipitate, for example, after adding a solvent (preferably water) to the obtained precipitate and mixing, a filtration method, a decantation method, etc. can be used.

[0061] [Oxidation process] The oxidation process is a process of obtaining an oxide containing Sm and Fe by firing the precipitate formed in the precipitation process. For example, the precipitate can be converted into an oxide by heat treatment. When heat-treating the precipitate, it is necessary to perform it in the presence of oxygen. For example, it can be performed in an air atmosphere. Also, since it is necessary to be performed in the presence of oxygen, it is preferable that the non-metallic part in the precipitate contains oxygen atoms.

[0062] The heat treatment temperature in the oxidation process (hereinafter sometimes referred to as "oxidation temperature") is not particularly limited, but is preferably 700°C or higher and 1300°C or lower, and more preferably 900°C or higher and 1200°C or lower. If it is less than 700°C, the oxidation will be insufficient, and if it exceeds 1300°C, the shape, average particle diameter, and particle size distribution of the target SmFeN powder tend not to be obtained. The heat treatment time is also not particularly limited, but is preferably 1 hour or longer and 3 hours or shorter.

[0063] The obtained oxide is an oxide particle in which the microscopic mixing of Sm and Fe is sufficiently achieved within the oxide particle, and the shape, particle size distribution, etc. of the precipitate are reflected.

[0064] [Pretreatment process] The pretreatment step is a step of obtaining a partial oxide in which a part of the oxide is reduced by heat-treating the above-described oxide containing Sm and Fe in an atmosphere containing a reducing gas.

[0065] Here, the partial oxide refers to an oxide in which a part of the oxide is reduced. The oxygen concentration of the partial oxide is not particularly limited, but is preferably 10% by mass or less, and more preferably 8% by mass or less. When it exceeds 10% by mass, the exothermic reduction with Ca becomes large in the reduction step, and there is a tendency for abnormal particle growth to occur due to an increase in the firing temperature. Here, the oxygen concentration of the partial oxide can be measured by the non-dispersive infrared absorption method (ND-IR).

[0066] The reducing gas is appropriately selected from hydrocarbon gases such as hydrogen (H2), carbon monoxide (CO), and methane (CH4). In terms of cost, hydrogen gas is preferable, and the gas flow rate is appropriately adjusted within a range where the oxide does not scatter. The heat treatment temperature in the pretreatment step (hereinafter, 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 less than 900°C. When the pretreatment temperature is 300°C or higher, the reduction of the oxide containing Sm and Fe proceeds efficiently. When it is 950°C or lower, the growth and segregation of oxide particles are suppressed, and a desired particle diameter can be maintained. The heat treatment time is not particularly limited, but can be 1 hour or more and 50 hours or less. When hydrogen is used as the reducing gas, it is preferable to adjust the thickness of the oxide layer to be used to 20 mm or less and further adjust the dew point in the reaction furnace to -10°C or lower.

[0067] [Reduction Step] The reduction step is a step of obtaining alloy particles by heat-treating the partial oxide in the presence of a reducing agent. For example, the reduction is carried out by bringing the partial oxide into contact with a calcium melt or calcium vapor. 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 from the viewpoint of magnetic properties.

[0068] The metal calcium, which is a reducing agent, is used in granular or powdered form, and its particle size is preferably 10 mm or less. This can more effectively suppress aggregation during the reduction reaction. Also, the metal calcium is preferably added in a proportion of 1.1 to 3.0 times the reaction equivalent (the stoichiometric amount required to reduce the rare earth oxide, including the amount required to reduce the Fe component if it is in the form of an oxide), and more preferably 1.5 to 2.5 times the amount.

[0069] In the reduction step, a disintegration accelerator can be used as needed together with the metal calcium, which is a reducing agent. This disintegration accelerator is appropriately used to promote the disintegration and granulation of the product during the post-treatment step described later, and examples thereof include alkaline earth metal salts such as calcium chloride and alkaline earth oxides such as calcium oxide. These disintegration accelerators are used in a proportion of 1% by mass or more and 30% by mass or less, preferably 5% by mass or more and 30% by mass or less, per samarium oxide.

[0070] [Nitriding Step] The nitriding process is a process of obtaining anisotropic magnetic particles by heat-treating the alloy particles obtained in the reduction process at a first temperature of 400°C or higher and 470°C or lower in an atmosphere containing nitrogen or ammonia, and then heat-treating at a second temperature of 480°C or higher and 610°C or lower for nitriding treatment. Since the particulate precipitate obtained in the above precipitation process is used, porous massive alloy particles are obtained in the reduction process. As a result, heat treatment can be immediately performed in a nitrogen atmosphere for nitriding without performing a pulverization treatment, so that nitriding can be performed uniformly. If heat treatment is performed at a high temperature of the second temperature without nitriding at the first temperature, abnormal heat generation may occur due to rapid progress of nitriding, SmFeN may decompose, and the magnetic properties may be greatly reduced. Further, since the atmosphere in the nitriding process can slow down the progress of nitriding, it is preferably substantially under a nitrogen-containing atmosphere. The term "substantially" as used herein is used in consideration of the inevitable inclusion of elements other than nitrogen due to contamination with impurities or the like. For example, the ratio of nitrogen in the atmosphere is 95% or more, preferably 97% or more, and more preferably 99% or more.

[0071] The first temperature in the nitriding process is 400°C or higher and 470°C or lower, but preferably 410°C or higher and 450°C or lower. If it is less than 400°C, the progress of nitriding is very slow, and if it exceeds 470°C, over-nitriding or decomposition is likely to occur due to heat generation. The heat treatment time at the first temperature is not particularly limited, but is preferably 1 hour or more and 40 hours or less, and more preferably 20 hours or less. If it is less than 1 hour, nitriding may not proceed sufficiently, and if it exceeds 40 hours, productivity decreases.

[0072] The second temperature is 480°C or higher and 610°C or lower, but preferably 500°C or higher and 550°C or lower. If it is less than 480°C, nitriding may not proceed sufficiently if the particles are large, and if it exceeds 610°C, over-nitriding 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, and more preferably 30 minutes or more and 2 hours or less. If it is less than 15 minutes, nitriding may not proceed sufficiently, and if it exceeds 5 hours, productivity decreases.

[0073] The heat treatment at the first temperature and the heat treatment at the second temperature may be performed continuously. During these heat treatments, a heat treatment at a temperature lower than the second temperature may be included, but from the viewpoint of productivity, it is preferably performed continuously.

[0074] [Post-treatment process] The product obtained after the nitriding process contains, in addition to magnetic particles, by-produced CaO, unreacted metallic calcium, etc., and may be in a sintered lump state in which these are combined. The product obtained after the nitriding process can be put into cooling water to separate CaO and metallic calcium as a calcium hydroxide (Ca(OH)2) suspension. Further, the remaining calcium hydroxide may be sufficiently removed by washing the magnetic powder with acetic acid or the like. When the product is put into water, the disintegration, i.e., pulverization, of the combined sintered lump-like reaction product proceeds due to the oxidation of metallic calcium by water and the hydration reaction of by-produced CaO.

[0075] [Alkali treatment process] The product obtained after the nitriding process may be put into an alkali solution. Examples of the alkali solution used in the alkali treatment process include an aqueous calcium hydroxide solution, an aqueous sodium hydroxide solution, an aqueous ammonia solution, etc. Among them, from the viewpoints of wastewater treatment and high pH, an aqueous calcium hydroxide solution and an aqueous sodium hydroxide solution are preferable. Due to the alkali treatment of the product, an Sm-rich layer containing a certain amount of oxygen remains and functions as a protective layer, thus suppressing an increase in the oxygen concentration due to the alkali treatment.

[0076] The pH of the alkali solution used in the alkali treatment process is not particularly limited, but is preferably 9 or more, more preferably 10 or more. If the pH is less than 9, the reaction rate when becoming calcium hydroxide is fast and the heat generation becomes large, so the oxygen concentration of the finally obtained SmFeN powder tends to be high.

[0077] In the alkali treatment process, the SmFeN powder obtained after treatment with the alkali solution can also reduce moisture by methods such as decantation if necessary.

[0078] [Acid treatment step] After the alkali treatment step, an acid treatment step of further treating with an acid may be included. In the acid treatment step, at least a part of the aforementioned Sm-rich layer is removed to reduce the oxygen concentration in the entire SmFeN powder. Also, in the manufacturing method according to an embodiment of the present invention, since pulverization or the like is not performed, the average particle size of the SmFeN powder is small, the particle size distribution is narrow, and there is no fine powder generated by pulverization or the like, so it is possible to suppress an increase in the oxygen concentration.

[0079] The acid used in the acid treatment step is not particularly limited, and examples include hydrogen chloride, nitric acid, sulfuric acid, acetic acid, etc. Among them, hydrogen chloride and nitric acid are preferable in that no impurities remain.

[0080] The amount of the acid used in the acid treatment step is preferably 3.5 parts by mass or more and 13.5 parts by mass or less, more preferably 4 parts by mass or more and 10 parts by mass or less, based on 100 parts by mass of the SmFeN powder. If it is less than 3.5 parts by mass, the oxide on the surface of the SmFeN powder remains and the oxygen concentration becomes high. If it exceeds 13.5 parts by mass, reoxidation tends to occur when exposed to the atmosphere, and since the SmFeN powder is dissolved, the cost also tends to increase. By setting the amount of the acid to 3.5 parts by mass or more and 13.5 parts by mass or less based on 100 parts by mass of the SmFeN powder, a Sm-rich layer oxidized to such an extent that reoxidation hardly occurs when exposed to the atmosphere after the acid treatment can cover the surface of the SmFeN powder, so that a SmFeN powder with a low oxygen concentration, a small average particle size, and a narrow particle size distribution can be obtained.

[0081] In the acid treatment step, the SmFeN powder obtained after treatment with an acid can also reduce moisture by methods such as decantation if necessary.

[0082] [Dehydration step] After the acid treatment step, it is preferable to include a dehydration treatment step. By the dehydration treatment, the moisture in the solid content before vacuum drying can be reduced, and the progress of oxidation during drying caused by the solid content before vacuum drying containing more moisture can be suppressed. Here, the dehydration treatment means a treatment that reduces the moisture value contained in the solid content after treatment with respect to the solid content before treatment by applying pressure or centrifugal force, and does not include mere decantation, filtration, or drying. The dehydration treatment method is not particularly limited, and examples include pressing and centrifugation.

[0083] The amount of moisture contained in the SmFeN powder after the dehydration treatment is not particularly limited, but is preferably 13% by mass or less, more preferably 10% by mass or less, from the viewpoint of suppressing the progress of oxidation.

[0084] The SmFeN powder obtained by the acid treatment or the SmFeN powder obtained by the dehydration treatment after the 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 longer, more preferably 3 hours or longer.

[0085] 〈Modifier powder preparation step〉 Prepare the modifier powder. The modifier powder used in the production method of the present disclosure contains at least one of metallic zinc and zinc alloy. Metallic zinc means zinc that is not alloyed. The zinc component in the modifier powder binds and modifies the particles of the SmFeN powder.

[0086] In the SmFeN powder particles, an Fe-Zn alloy phase is formed on the surface. On the surface of the particles of the SmFeN powder, Th2Zn 17 type and / or Th2Ni 17There are parts with an incomplete crystal structure such as a certain type, and an α-Fe phase exists in those parts, which causes a decrease in the coercive force. This α-Fe phase forms a Fe-Zn alloy phase with the zinc component of the metallic zinc and / or zinc alloy, suppressing the decrease in the coercive force. That is, the Fe-Zn alloy phase acts as a modifying phase. Between the particles of the SmFeN powder and the particles of the modifying material powder, Fe and Zn diffuse into each other, forming a Fe-Zn alloy phase. Therefore, the SmFeN powder particles can be firmly bonded. That is, the modifying material powder functions as a binder.

[0087] If the content ratio of the zinc component in the modifying material powder is 1% by mass or more with respect to the mixed powder, a homogeneous Fe-Zn alloy phase (modifying phase) is formed, so the coercive force is improved, and the function as a binder can also be advantageously exerted. From this perspective, the content ratio of metallic zinc in the modifying material powder may 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 with respect to the mixed powder.

[0088] On the other hand, if the content ratio of the zinc component in the modifying material powder is 30% by mass or less with respect to the mixed powder, the decrease in magnetization due to the use of the modifying material powder can be suppressed. From this perspective, the content ratio of the zinc component in the modifying material powder may be 28% by mass or less, 26% by mass or less, 24% by mass or less, or 22% by mass or less with respect to the mixed powder.

[0089] The zinc alloy is represented by Zn-M 2 , and M 2 may be selected from elements that alloy with Zn (zinc) to lower the melting start temperature of the zinc alloy below the melting point of Zn and inevitable impurity elements. Thereby, the sinterability is improved in the pressure sintering process described later. As M 2 that lowers the melting point of Zn, elements that form a eutectic alloy with Zn and M 2 etc. can be mentioned. Such M 2Examples include Sn, Mg, Al, and combinations thereof. Sn is tin, Mg is magnesium, and Al is aluminum. Regarding the melting point lowering effect of these elements and elements that do not inhibit the properties of the product, M 2 can be selected. In addition, inevitable impurity elements refer to impurity elements such as impurities contained in the raw materials of the modifier powder, whose inclusion cannot be avoided, or whose avoidance would cause a significant increase in manufacturing costs.

[0090] Zn-M 2 In the zinc alloy represented by, the ratios (molar ratios) of Zn and M 2 may be appropriately determined so that the sintering temperature is appropriate. The ratio (molar ratio) of M 2 to the entire zinc alloy may be, for example, 0.05 or more, 0.10 or more, or 0.20 or more, and may be 0.90 or less, 0.80 or less, 0.70 or less, 0.60 or less, 0.50 or less, 0.40 or less, or 0.30 or less.

[0091] In addition to metallic zinc and / or zinc alloy, the modifier powder may optionally contain substances having a binder function and / or a modifying function and other functions, as long as the effects of the present invention are not impaired. Examples of other functions include a function of improving corrosion resistance.

[0092] The particle size of the modifier powder is not particularly limited, but it is preferably finer than the particle size of the SmFeN powder in the first particle group, and more preferably finer than the particle size of the SmFeN powder in the second particle group. Thereby, the particles of the modifier powder can easily spread between the particles of the SmFeN powder. The particle size of the modifier powder is, for example, D 50 (median diameter), and may be 0.1 μm or more, 0.2 μm or more, 0.3 μm or more, or 0.4 μm or more, and may 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. Also, the particle size D 50(Median diameter) is measured, for example, by the dry laser diffraction / scattering method.

[0093] When the oxygen content of the modifier powder is low, it is preferable because it can absorb a large amount of oxygen in the SmFeN powder. From this perspective, the oxygen content of the modifier 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, based on the total amount of the modifier powder. On the other hand, extremely reducing the oxygen content of the modifier powder leads to an increase in manufacturing cost. Therefore, the oxygen content of the modifier powder may be 0.1% by mass or more, 0.2% by mass or more, or 0.3% by mass or more, based on the total amount of the modifier powder.

[0094] 〈Mixing step〉 The SmFeN powder and the modifier powder are mixed to obtain a mixed powder. There is no particular limitation on the mixing method. Examples of the mixing method include a method of mixing using a mortar, a muller wheel type mixer, an agitator type mixer, mechanofusion, a V-type mixer, and a ball mill. These methods may be combined. Note that a V-type mixer is a device equipped with a container in which two cylindrical containers are connected in a V shape, and by rotating the container, the powder in the container is repeatedly aggregated and separated by gravity and centrifugal force and mixed.

[0095] 〈Magnetic field forming step〉 The mixed powder is compression-molded in a magnetic field to obtain a magnetic field formed body. Thereby, orientation can be imparted to the magnetic field formed body, anisotropy can be imparted to the formed body (rare earth magnet), and the residual magnetization can be improved.

[0096] The magnetic field forming method may be a well-known method such as a method of compression molding a mixed powder using a mold with a magnetic field generating device installed around it. The molding pressure may 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 may be 1500 MPa or less, 1000 MPa or less, or 500 MPa or less. The time for applying the aforementioned molding pressure may be, for example, 0.5 minutes or more, 1 minute or more, or 3 minutes or more, and may be 10 minutes or less, 7 minutes or less, or 5 minutes or less. The magnitude of the applied magnetic field may 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 may be 20000 kA / m or less, 15000 kA / m or less, 10000 kA / m or less, 5000 kA / m or less, 3000 kA / m or less, or 2000 kA / m or less. Examples of the method of applying the magnetic field include a method of applying a static magnetic field using an electromagnet and a method of applying a pulsed magnetic field using alternating current. Further, in order to suppress oxidation of the mixed powder, it is preferable that the magnetic field forming is performed in an inert gas atmosphere. The inert gas atmosphere includes a nitrogen gas atmosphere.

[0097] 〈Pressure Sintering Process〉 The magnetic field formed body is pressure sintered to obtain a sintered body. The method of pressure sintering is not particularly limited, and a well-known method can be applied. Examples of the pressure sintering method include preparing a die having a cavity and a punch slidable inside the cavity, inserting the magnetic field formed body inside the cavity, and sintering the magnetic field formed body while applying pressure to it with the punch. In the case of this method, typically, the die is heated using a high-frequency induction coil. Alternatively, a spark plasma sintering (SPS) method may be used.

[0098] The pressure sintering conditions may be appropriately selected so that the magnetic field formed body can be sintered (hereinafter sometimes referred to as "pressure sintered") while applying pressure to the magnetic field formed body.

[0099] If the sintering temperature is 300°C or higher, in the magnetic field-formed body, Fe on the particle surface of the SmFeN powder and metallic zinc of the modifier powder slightly interdiffuse, contributing to sintering. From this perspective, the sintering temperature may be, for example, 310°C or higher, 320°C or higher, 340°C or higher, or 350°C or higher. On the other hand, if the sintering temperature is 430°C or lower, Fe on the particle surface of the SmFeN powder and metallic zinc of the modifier powder do not excessively interdiffuse, and it does not cause any problems in the heat treatment process described later or have an adverse effect on the magnetic properties of the obtained sintered body. From these perspectives, the sintering temperature may be 420°C or lower, 410°C or lower, 400°C or lower, 390°C or lower, 380°C or lower, 370°C or lower, or 360°C or lower.

[0100] Regarding the sintering pressure, a sintering pressure that can increase the density of the sintered body may be appropriately selected. The sintering pressure may typically be 100 MPa or higher, 200 MPa or higher, 400 MPa or higher, 600 MPa or higher, 800 MPa or higher, or 1000 MPa or higher, and may be 2000 MPa or lower, 1800 MPa or lower, 1600 MPa or lower, 1500 MPa or lower, 1300 MPa or lower, or 1200 MPa or lower.

[0101] The sintering time may be appropriately determined so that Fe on the particle surface of the SmFeN powder and the modifier powder slightly interdiffuse. The sintering time does not include the temperature rising time until the heat treatment temperature is reached. The sintering time may be, for example, 1 minute or longer, 2 minutes or longer, or 3 minutes or longer, and may be 30 minutes or shorter, 20 minutes or shorter, 10 minutes or shorter, or 5 minutes or shorter.

[0102] After the sintering time has elapsed, the sintered body is cooled to complete the sintering. A faster cooling rate can suppress oxidation of the sintered body, etc. The cooling rate may be, for example, 0.5 to 200°C / second.

[0103] Regarding the sintering atmosphere, an inert gas atmosphere such as an argon gas atmosphere is preferable in order to suppress oxidation of the magnetic field-formed body and the sintered body. The inert gas atmosphere includes a nitrogen gas atmosphere.

[0104] As described above, by pressure sintering, Fe on the surface of SmFeN powder particles and the modifier powder slightly interdiffuse with each other. Optionally, a part of the slight interdiffusion part may be advanced to advance the modification. In that case, a modification suppression film formation step and a heat treatment step are performed. Hereinafter, the modification suppression film formation step and the heat treatment step will be described.

[0105] 〈Modification Suppression Film Formation Step〉 Before pressure sintering, a modification suppression film is formed on the surface of the particles of the second particle group in advance. Thereby, the modification of the surface of the particles of the second particle group can be suppressed. The formation of the modification suppression film may be before pressure sintering, and typically, it is before the mixing of the SmFeN powder and the modifier powder.

[0106] Next, the reason for suppressing the modification of the surface of the particles of the second particle group will be described.

[0107] By further heat-treating the sintered body obtained by pressure sintering, the interdiffusion between Fe on the surface of the SmFeN powder particles and the modifier powder proceeds, the modification proceeds, and it contributes to the improvement of the coercive force. Details of the heat treatment step will be described later.

[0108] The SmFeN powder used in the manufacturing method of the present disclosure includes a first particle group having a large particle size and a second particle group having a small particle size. Thereby, the density of the sintered body is improved, and as a result, the magnetization is improved. When the sintered body thus obtained is heat-treated, since the particles of the second particle group have a large specific surface area, the modification easily proceeds, and a part of the magnetic phase in the particles of the second particle group may also be modified. Then, even if the density of the sintered body is improved, the magnetization may decrease to some extent. Therefore, it is preferable to form a modification suppression film on the surface of the particles of the second particle group in advance before pressure sintering to suppress the modification of the surface of the particles of the second particle group. Thereby, it is possible to avoid that a part of the magnetic phase in the particles of the second particle group is also modified, and as a result, it is possible to avoid a slight decrease in magnetization.

[0109] As described above, the first particle group and the second particle group are obtained by classifying SmFeN powder. At this time, compared with the first particle group, since the second particle group has a high coercive force, the second particle group does not need to be modified as much as the first particle group. Therefore, it is advantageous to suppress the modification of the particle surface of the second particle group.

[0110] In addition, when a magnetic powder having a high coercive force (hereinafter sometimes referred to as "high coercive force powder") and a magnetic powder having a low coercive force (hereinafter sometimes referred to as "low coercive force powder") coexist in the magnetic powder, the rectangularity of a molded body of such a magnetic powder, particularly the rectangularity at high temperature, may decrease. This can be explained as follows with reference to the drawings. In this specification, unless otherwise specified, regarding magnetic properties, "high temperature" means 100 to 200 °C, and the rectangularity is evaluated by Hk at 10% demagnetization.

[0111] FIG. 10 is a graph showing the demagnetization curve of a molded body of a low coercive force powder and the demagnetization curve of a molded body of a mixed powder of a low coercive force powder and a high coercive force powder at high temperature. It can be understood from FIG. 10 that compared with the molded body of the mixed powder of the low coercive force powder and the high coercive force powder, the molded body of the low coercive force powder is inferior in coercive force but excellent in rectangularity.

[0112] As described above, the first particle group corresponds to the low coercive force powder, and the second particle group corresponds to the high coercive force powder. When a modification-inhibiting film is formed on the second particle group, it is possible to suppress the second particle group from having an even higher coercive force. From this, it is possible to suppress the difference in coercive force between the first particle group and the second particle group from expanding, and to improve the rectangularity. As a result, by improving the density of the sintered body with the first particle group and the second particle group, even when the magnetization is improved, the rectangularity can be improved, which is more preferable.

[0113] The modification-inhibiting film is not particularly limited as long as it can suppress the mutual diffusion between the magnetic phase in the particles of the second particle group and Fe on the particle surface of the second particle group and the modifier powder, and does not adversely affect the magnetic properties of the rare earth magnet obtained by the production method of the present disclosure. Such a modification-inhibiting film typically contains, but is not limited to, phosphoric acid.

[0114] When the modification-inhibiting film is a film containing phosphoric acid, the phosphoric acid content ratio in the modification-inhibiting film may be 40% by mass or more, 50% by mass or more, 60% by mass or more, 70% by mass or more, 80% by mass or more, or 90% by mass or more, or even 100% by mass, based on the entire modification-inhibiting film. Also, when the modification-inhibiting film is a film containing phosphoric acid, its thickness may 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 may be 100 nm or less, 90 nm or less, 80 nm or less, 70 nm or less, or 60 nm or less.

[0115] There is no particular limitation on the method for forming a film containing phosphoric acid on the second particle group. For example, the following methods can be mentioned.

[0116] By subjecting the particles of the second particle group to phosphoric acid treatment, a passive film having a P-O bond is formed on the particle surface of the second particle group. In the phosphoric acid treatment step, the phosphoric acid treatment agent is reacted with the particles of the second particle group. Examples of the phosphoric acid treatment agent include phosphate-based such as orthophosphoric acid, sodium dihydrogen phosphate, disodium hydrogen phosphate, ammonium dihydrogen phosphate, diammonium hydrogen phosphate, zinc phosphate, calcium phosphate, hypophosphorous acid-based, hypophosphite-based, inorganic phosphoric acids such as pyrophosphoric acid and polyphosphoric acid-based, and organic phosphoric acids. These phosphoric acid sources are basically dissolved in water or an organic solvent such as IPN, and the particles of the second particle group are put into a phosphoric acid bath added with a reaction accelerator such as nitrate ions and a crystal refinement agent such as V ions, Cr ions, and Mo ions as necessary to form a passive film having a P-O bond on the particle surface of the second particle group.

[0117] 〈Heat treatment step〉 Before pressure sintering, if a modification suppression film is formed in advance on the particle surfaces of the second particle group (hereinafter, sometimes simply referred to as "forming a modification suppression film on the particle surfaces of the second particle group"), the sintered body after pressure sintering is heat-treated to promote the modification of the particle surfaces of the first particle group in the sintered body. This will be described with reference to the drawings.

[0118] FIG. 11 is a schematic diagram showing an example of the structure of a rare earth magnet obtained by forming a modification suppression film on the particle surfaces of the second particle group, followed by pressure sintering and heat treatment in the manufacturing method of the present disclosure. FIG. 12 is a schematic diagram showing an example of the structure of a rare earth magnet obtained by not forming a modification suppression film on the particle surfaces of the second particle group, followed by pressure sintering and heat treatment. The structures of FIGS. 11 and 12 will be described while comparing them with the structure of FIG. 1.

[0119] Compared with the structure of FIG. 1, in both the structures of FIGS. 11 and 12, the modified phase 30 on the particle surfaces of the first particle group 11 is slightly thicker. This is because, to obtain a rare earth magnet having the structure of FIG. 1, the sintered body is not heat-treated, whereas to obtain a rare earth magnet having the structures of FIGS. 11 and 12, the sintered body is heat-treated, and due to this heat treatment, the modification of the particle surfaces of the first particle group 11 has progressed. Since the particles of the first particle group 11 have a relatively small specific surface area, the modification does not progress excessively due to the heat treatment, and compared with the case where there is no heat treatment, the modified phase 30 only becomes slightly thicker.

[0120] Compared with the structure of FIG. 1, in the structure of FIG. 11, the thickness of the modified phase 30 on the particle surface of the second particle group 12 is substantially the same, while in the structure of FIG. 12, the modified phase 30 on the particle surface of the second particle group 12 is thick. This is because in order to obtain the rare earth magnet having the structure of FIG. 11, a modification suppression film is formed on the particle surface of the second particle group 12, while in order to obtain the rare earth magnet having the structure of FIG. 12, a modification suppression film is not formed on the particle surface of the second particle group 12. As a result, when obtaining the rare earth magnet having the structure of FIG. 11, during the heat treatment of the sintered body, the modification of the particle surface of the second particle group 12 hardly proceeds, whereas when obtaining the rare earth magnet having the structure of FIG. 12, during the heat treatment of the sintered body, the modification of the particle surface of the second particle group 12 easily proceeds. In the structure of FIG. 11, since the progress of the modification of the particle surface of the second particle group 12 is suppressed, the squareness is improved. Therefore, it is preferable to form a modification suppression film on the particle surface of the second particle group 12.

[0121] Although not bound by theory, during the heat treatment of the sintered body after pressure sintering, the modification suppression film formed on the particle surface of the second particle group is decomposed into the elements constituting the modification suppression film, and these elements are considered to be present in the modified phase. From this, it is considered that the modified phase is a phase in which elements derived from the above-described modification suppression film are present in the Fe-Zn alloy phase.

[0122] The heat treatment conditions of the sintered body after pressure sintering may be appropriately determined so as to be capable of modifying the surface of the SmFeN powder particles, particularly the surface of the first particle group. The heat treatment temperature may be, for example, 350 ° C or higher, 360 ° C or higher, 370 ° C or higher, or 380 ° C or higher, and may be 410 ° C or lower, 400 ° C or lower, or 390 ° C or lower. The heat treatment time may be 6 hours or longer, 12 hours or longer, or 18 hours or longer, and may be 48 hours or shorter, 42 hours or shorter, 36 hours or shorter, 30 hours or shorter, or 24 hours or shorter.

[0123] Under the above heat treatment conditions, when the sintered body after pressure sintering is heat treated, 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 modification suppression film is formed on the particle surface of the first particle group. Further, under the above heat treatment conditions, when the sintered body after pressure sintering is heat treated, the thickness of the modified phase on the particle surface of the second particle group is about 20 to 50 nm when no modification suppression film is formed, and about 1 to 20 nm when a modification suppression film is formed.

[0124] To suppress oxidation of the sintered body, it is preferable to heat treat the sintered body in a vacuum or an inert gas atmosphere. The inert gas atmosphere includes a nitrogen gas atmosphere. The heat treatment of the sintered body may be carried out in the molding die used for pressure sintering following pressure sintering. In that case, however, no pressure is applied to the sintered body during the heat treatment. The molding die used for pressure sintering is, for example, a die having a cavity. If the above-described heat treatment conditions are satisfied, the normal magnetic phase decomposes to generate an α-Fe phase, and as a result of the generation, Fe and Zn do not diffuse excessively with each other. When the heat treatment is carried out in a vacuum, the absolute pressure of the atmosphere is 1×10 -7 Pa or more, 1×10 -6 Pa or more, or 1×10 -5 Pa or more, and may be 1×10 -2 Pa or less, 1×10 -3 Pa or less, or 1×10 -4 Pa or less.

[0125] The rare earth magnet obtained by the manufacturing method of the present disclosure described so far will be described below.

[0126] 《Rare Earth Magnet》 The rare earth magnet obtained by the manufacturing method of the present disclosure (hereinafter sometimes referred to as "the rare earth magnet of the present disclosure") contains Sm, Fe, and N, and at least a part thereof has a magnetic phase having a crystal structure of either the Th2Zn 17 type and the Th2Ni 17 type. The composition and the like of the magnetic phase are as described in "〈Magnetic Powder Preparation Step〉".

[0127] The rare earth magnet of the present disclosure is obtained using a mixed powder of SmFeN powder and a modifier powder containing at least one of metallic zinc and a zinc alloy. Therefore, the rare earth magnet of the present disclosure contains a zinc component derived from the modifier powder. And as described above, a part of the particles of the SmFeN powder and a part of the zinc component of the modifier powder diffuse into each other to form an Fe-Zn alloy phase. In this specification, unless otherwise specified, the content of the "zinc component" means the content (content ratio) of Zn (zinc element). The zinc component of the rare earth magnet of the present disclosure is derived from the metallic zinc of the modifier powder, and the content range of the zinc component is preferably 1 to 30% by mass.

[0128] 《Modification》 In addition to what has been described so far, the manufacturing method of the present disclosure can be variously modified within the scope of the content described in the claims.

[0129] For example, a part of the fine particles in the SmFeN powder may be removed in advance before magnetic field forming. There is no particular limitation on the fine particle removal operation (fine particle removal method). Examples of the fine particle removal operation (fine particle removal method) include a method using a cyclone (registered trademark) classifier, a method using a sieve, a method using a magnetic field, and a method using static electricity. Combinations of these may also be used. By removing the fine particles, the density of the compact (rare earth magnet) can be further increased, and the magnetization can be further increased.

Examples

[0130] Hereinafter, the manufacturing method of the present disclosure will be described more specifically with reference to Examples and Comparative Examples. Note that the manufacturing method of the present disclosure is not limited to the conditions used in the following examples.

[0131] 《Preparation of Samples》 Samples of Examples 1 to 8 and Comparative Examples 1 to 7 were prepared as follows.

[0132] 〈Examples 1 to 8 and Comparative Examples 1 to 5〉 2.0 kg of pure water was mixed and dissolved with 5.0 kg of FeSO4·7H2O. Further, 0.49 kg of Sm2O3, 0.74 kg of 70% sulfuric acid, and 0.035 kg of La2O3 were added and stirred well to be completely dissolved. Next, pure water was added to the obtained solution and adjusted to finally have an Fe concentration of 0.726 mol / L and a Sm concentration of 0.112 mol / L to obtain a SmFeLa sulfuric acid solution.

[0133] [Precipitation process] The entire amount of the prepared SmFeLa sulfuric acid solution was added dropwise with stirring over 70 minutes from the start of the reaction into 20 kg of pure water maintained at a temperature of 40°C. At the same time, 15% ammonia solution was added dropwise to adjust the pH to 7 - 8. Thereby, a slurry containing SmFeLa hydroxide was obtained. The obtained slurry was washed with pure water by decantation and then the hydroxide was subjected to solid-liquid separation. The separated hydroxide was dried in an oven at 100°C for 10 hours.

[0134] [Oxidation process] The hydroxide obtained in the precipitation process was calcined at 1000°C in the air for 1 hour. After cooling, a red SmFeLa oxide was obtained as a raw material powder.

[0135] [Pretreatment process] 100 g of SmFeLa oxide was placed in a steel container to have a bulk thickness of 10 mm. The container was placed in a furnace and evacuated to 100 Pa, and then heated to a pretreatment temperature of 850°C while introducing hydrogen gas and held for 15 hours. When the oxygen concentration was measured by non-dispersive infrared absorption method (ND-IR) (EMGA-820 manufactured by Horiba, Ltd.), it was 5 mass%. Thus, it was found that the oxygen bound to Sm was not reduced, and among the oxygen bound to Fe, 95% was reduced to obtain a black partial oxide.

[0136] [Reduction process] 60 g of the partial oxide obtained in the pretreatment process and 19.2 g of metallic calcium with an average particle diameter of about 6 mm were mixed and placed in a furnace. After evacuating the furnace, argon gas (Ar gas) was introduced. It was heated to 1090°C and held for 45 minutes, and then cooled to obtain SmFe powder particles.

[0137] [Nitriding process] Subsequently, the temperature inside the furnace was cooled to 100°C, and then the furnace was evacuated and heated to a first temperature of 430°C while introducing nitrogen gas, and held for 3 hours.Then, the temperature was raised to a second temperature of 500°C, and held for 1 hour, and then cooled to obtain a mass product containing magnetic particles.

[0138] [Post-processing process] The aggregated product obtained in the nitriding step was poured into 3 kg of pure water and stirred for 30 minutes. After standing, the supernatant was drained by decantation. The process of pouring into pure water, stirring and decantation was repeated 10 times. Next, 2.5 g of 99.9% acetic acid was poured into the product and stirred for 15 minutes. After standing, the supernatant was drained by decantation. The process of pouring into pure water, stirring and decantation was repeated twice.

[0139] [Acid treatment process] A 6% aqueous hydrochloric acid solution was added to 100 parts by mass of the powder obtained in the post-treatment step so that the hydrogen chloride content was 4.3 parts by mass, and the mixture was stirred for 1 minute. After being allowed to stand, the supernatant was drained by decantation. The process of pouring into pure water, stirring, and decantation was repeated twice. After solid-liquid separation, the mixture was vacuum-dried at 80°C for 3 hours to obtain Sm. 9.2 Fe 77.1 N 13.59 La 0.11 A SmFeN powder having the following composition was obtained.

[0140] The SmFeN powder was packed into a sample container together with paraffin wax, and the paraffin wax was melted in a dryer, after which the easy axis of magnetization was aligned in an orientation magnetic field of 16 kA / m. This magnetically oriented sample was pulse-magnetized in a magnetizing magnetic field of 32 kA / m, and the magnetic properties were measured at room temperature using a VSM (vibrating sample magnetometer) with a maximum magnetic field of 16 kA / m, revealing a residual magnetization of 1.44 T and a coercive force of 750 kA / m.

[0141] The SmFeN powder obtained as described above was classified to obtain a powder of the first particle group and a powder of the 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 a magnetic powder. The particle size distributions of the first particle group and the second particle group were as 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) was as shown in Table 1-1. Table 1-1 also shows the particle residual magnetization σr of the first particle group and the second particle group respectively.

[0142] As a modifier powder, metallic zinc powder was prepared. The D 50 of the metallic zinc powder was 0.5 μm. Also, the purity of the metallic zinc powder was 99.5 mass%.

[0143] The magnetic powder (powder of the first particle group and powder of the second particle group) and the modifier powder were mixed to obtain a mixed powder. Also, the mixing amount of metallic zinc with respect to the entire mixed powder was 5 mass%.

[0144] The mixed powder was compression-molded in a magnetic field to obtain a magnetic field-formed body. The pressure for compression molding was 50 MPa. The application time of this pressure was 1 minute. The applied magnetic field was 1600 kA / m. Also, the compression molding was performed in a nitrogen atmosphere.

[0145] The magnetic field-formed body was pressure-sintered. For the samples of Examples 1 to 6 and Comparative Examples 1 to 5, pressure-sintering was performed in an argon gas atmosphere (97000 Pa) using a high-frequency induction coil. For the samples of Examples 7 to 8, pressure-sintering was performed in a nitrogen gas atmosphere (10000 Pa) using spark plasma sintering (SPS method). In any of the samples, the sintering temperature was 380 °C, the sintering pressure was 1000 MPa, and the application time of the sintering pressure was 5 minutes.

[0146] 〈Comparative Examples 6 to 7〉 As magnetic powders, samples of Comparative Example 6 were prepared in the same manner as in Example 1 and samples of Comparative Example 7 were prepared in the same manner as in Example 3, except that only the powder of the first particle group was used and the powder of the second particle group was not used.

[0147] <Example 9> A sample of Example 9 was prepared in the same manner as in Example 4, except that a film containing phosphoric acid was formed on the particle surface of the second particle group and the sintered body after pressure sintering was heat-treated. The formation of the film containing phosphoric acid was carried out before mixing the SmFeN powder (the powder of the first particle group and the powder of the second particle group) and the modifier powder. That is, the SmFeN powder was classified into the first particle group and the second particle group, a film containing phosphoric acid was formed on the particle surface of the second particle group, and the powder of the first particle group as it was classified, the powder of the second particle group on which the film containing phosphoric acid was formed, and the modifier powder were mixed.

[0148] Before the phosphoric acid treatment step, as a preparation step, a dispersion step and a surface treatment step were carried out for the formation of the film containing phosphoric acid. The details of the dispersion step, the surface treatment step, and the phosphoric acid treatment step are as follows.

[0149] [Dispersion step] The powder of the second particle group and the media were put into a container so that the powder of the second particle group was 5% by volume and the media (iron core nylon media, diameter 10 mm, Vickers constant of the coated part nylon 7, specific gravity 7.48 g / cm3) was 60% by volume with respect to the volume of the container used for the vibration mill. The powder of the second particle group and the media were dispersed for 60 minutes under a nitrogen atmosphere by a vibration mill to obtain intermediate powder.

[0150] [Surface treatment step] The obtained intermediate powder was put into pure water and stirred for 1 minute. An acid solution was added to this slurry for etching. As the acid solution, a hydrochloric acid solution was used. While stirring, 50 g or more of 5% hydrochloric acid was added to 100 g of the intermediate powder. Then, it was confirmed that the pH became 3 or more, and decantation was carried out until the electric conductivity of the slurry became 100 μS / cm or less.

[0151] [Phosphoric acid treatment step] A phosphoric acid solution was added to the obtained slurry. The phosphoric acid solution was introduced in an amount of 1% by mass as PO4 with respect to the solid content of the particles of the second particle group. Stirring was carried out for 5 minutes, followed by solid-liquid separation, and then vacuum drying was carried out at 120 °C for 3 hours to obtain the powder of the second particle group on which a film containing phosphoric acid was formed.

[0152] The sintered body after pressure sintering was heat-treated under the conditions shown in Tables 2-1 and 2-2. In Table 2-1, the particle residual magnetization σ r and the particle coercive force Hc of each of the first particle group and the second particle group were also noted. In Table 2-1, the "coating containing phosphoric acid" was denoted as "phosphate coating".

[0153] 〈Example 10〉 A sample of Example 10 was prepared in the same manner as in Example 9, except that a coating containing phosphoric acid was not formed on the particle surface of the second particle group.

[0154] 《Evaluation》 For each sample, the density and magnetic properties were measured. The density was measured by the Archimedes method. The magnetic properties were measured using a vibrating sample magnetometer (VSM). For the samples of Example 1, Comparative Example 3, and Comparative Example 6, the cross-section of the sample was polished, and the polished surface was observed for its microstructure using a scanning electron microscope (SEM).

[0155] The evaluation results are shown in Tables 1-1 to 1-2, Tables 2-1 to 2-2, and Figures 5 to 9. Figure 5 is a graph showing the relationship between d2 / d1 and the density. Figure 6 is a graph showing the relationship between d2 / d1 and the residual magnetization Br. Figure 7 shows the SEM image of the sample of Example 1. Figure 8 shows the SEM image of the sample of Comparative Example 3. Figure 9 shows the SEM image of the sample of Comparative Example 6.

[0156]

Table 1-1

[0157]

Table 1-2

[0158]

Table 2-1

[0159]

Table 2-2

[0160] As shown in Table 1-1, Table 1-2, Figure 5 and Figure 6, it can be understood that for the samples of Examples 1 to 8 where d1 and d2 satisfy a predetermined relationship and the total volume of the first particle group: the total volume of the second particle group is within a predetermined range, the density is high, and as a result, the residual magnetization is excellent.

[0161] On the other hand, in the samples of Comparative Example 1 and Comparative Example 2, even though the total volume of the first particle group: the total volume of the second particle group is within a predetermined range, since d2 / d1 does not satisfy the predetermined relationship, the density is low, and as a result, the residual magnetization is low. In the samples of Comparative Examples 3 to 5, although d2 / d1 satisfies the predetermined relationship, since the total volume of the first particle group: the total volume of the second particle group is not within the predetermined range, the density is low, and as a result, the residual magnetization is low. Also, in the samples of Comparative Examples 6 and 7, since only the powder of the first particle group was used and the powder of the second particle group was not used, the density is low, and as a result, the residual magnetization is low.

[0162] Also, for example, the fact that the density of the sample of Example 1 is higher than the densities of the samples of Comparative Example 3 and Comparative Example 6 can also be understood from the fact that the dark portions (voids) in the SEM image (Figure 7) of the sample of Example 1 are fewer than the dark portions in the SEM images (Figure 8 and Figure 9) of the samples of Comparative Example 3 and Comparative Example 6.

[0163] Regarding Example 9 and Example 10, since d1 and d2 satisfy a predetermined relationship and the total volume of the first particle group: the total volume of the second particle group is within a predetermined range, it can be understood that the density is high, and as a result, the residual magnetization is excellent. Also, in Example 9, a film containing phosphoric acid was formed on the particle surface of the second particle group, while in Example 10, a film containing phosphoric acid was not formed on the particle surface of the second particle group. Therefore, it can be understood that the sample of Example 9 has a larger Hk at 120°C and is excellent in squareness at high temperatures compared to the sample of Example 10.

[0164] From the above results, the manufacturing method of the rare earth magnet of the present disclosure and the effects of the rare earth magnet obtained thereby could be confirmed.

Explanation of reference numerals

[0165] 10 SmFeN powder particles (magnetic particles) 11 First particle group 12 Second particle group 20 Modifying material 30 Modified phase 100 Rare earth magnet obtained by the manufacturing method of the present disclosure 200 Rare earth magnet obtained by the conventional manufacturing method

Claims

1. Prepare a magnetic powder containing Sm, Fe, and N, at least a part of which is Th ２ Zn １７ type and Th ２ Ni １７ and having a magnetic phase with any one of the crystal structures of type, and Prepare a modifier powder containing at least one of metallic zinc and zinc alloy, Mix the magnetic powder and the modifier powder to obtain a mixed powder, Compression-mold the mixed powder in a magnetic field to obtain a magnetic field-formed body, and Sinter the magnetic field-formed body under pressure to obtain a sintered body, including, The magnetic powder includes a first particle group and a second particle group, The particle size distribution D of the first particle group ５０ is represented by d １ μm, and the particle size distribution D of the second particle group ５０ is represented by d ２ μm, The d １ and the d ２ satisfy the relationship of 0.350 ≦ d ２ / d １ ≦ 0.500, The ratio of the total volume of the first particle group to the total volume of the second particle group (the total volume of the first particle group: the total volume of the second particle group) 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, A method for manufacturing a rare earth magnet.

2. The D of the modifier powder ５０ is 0.1 to 12.0 μm, and the content ratio of the zinc component in the modifier powder is 1 to 30% by mass with respect to the mixed powder. The method for manufacturing a rare earth magnet according to claim 1.

3. Compression-mold the mixed powder at a pressure of 10 to 1500 MPa. The method for manufacturing a rare earth magnet according to claim 1 or 2.

4. The method for producing a rare earth magnet according to any one of claims 1 to 3, wherein the magnetic field forming body is pressure-sintered at a pressure of 100 to 2000 MPa and a temperature of 300 to 430 °C for 1 to 30 minutes.

5. Preparing a magnetic powder containing Sm, Fe, and N and having a magnetic phase with at least a part having a crystal structure of either Th2Zn17 type or Th2Ni17 type, preparing a modifier powder containing at least one of metallic zinc and a zinc alloy, mixing the magnetic powder and the modifier powder to obtain a mixed powder, compression-molding the mixed powder in a magnetic field to obtain a magnetic field forming body, and pressure-sintering the magnetic field forming body to obtain a sintered body, including wherein the magnetic powder includes a first particle group and a second particle group, the particle size distribution D50 of the first particle group is represented by d1 μm, and the particle size distribution D50 of the second particle group is represented by d2 μm, the d1 and the d2 satisfy the relationship of 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 (the total volume of the first particle group: the total volume of the second particle group) is in the range of 9:1 to 4:1, and it is a method for producing a rare earth magnet, before the pressure-sintering, forming a modification suppression film on the particle surface of the second particle group in advance, and, heat-treating the sintered body to advance the modification of the particle surface of the first particle group, further including

6. The method for producing a rare earth magnet according to claim 5, wherein the d1 is 3.0 to 3.7 μm and the d2 is 1.4 to 1.8 μm.

7. The method for producing a rare earth magnet according to claim 5 or 6, wherein the modification suppression film contains phosphoric acid.

8. The method for manufacturing a rare earth magnet according to any one of claims 5 to 7, wherein the sintered compact is heat-treated at 350 to 410 °C.

Images