Rare earth magnet and method of manufacturing the same

Abstract

The present invention relates to a rare earth magnet and a method for manufacturing the same. Provided is a Sm-Fe-N-based rare earth magnet which is less likely to demagnetize than ever before under an environment where an external magnetic field is applied, particularly at high temperatures, and a method for manufacturing the same. The method for manufacturing the rare earth magnet of the present disclosure includes: preparing a SmFeN magnetic powder; preparing a modifying material powder containing a zinc component; mixing the SmFeN magnetic powder and the modifying material powder to obtain a mixed powder; compression molding the mixed powder in a magnetic field to obtain a magnetic field molded body; pressure sintering the magnetic field molded body to obtain a sintered body; and subjecting the sintered body to heat treatment. The D 50 of the magnetic powder is 1.50 μm or more and 3.00 μm or less, the content ratio of the zinc component in the modifying material powder is 6 mass% or more and 30 mass% or less, and the heat treatment temperature is 350°C or more and 410°C or less.

Description

Technical Field

[0001] This disclosure relates to rare earth magnets and methods for manufacturing the same. In particular, this disclosure relates to magnets containing Sm, Fe, and N, possessing at least a portion of Th₂Zn. 17 Type and Th2Ni 17 Rare earth magnets of any type of magnetic phase with a crystal structure and their manufacturing methods. Background Technology

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

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

[0004] SmFeN powder possesses Th2Zn 17 Type and Th2Ni 17 The magnetic phase refers to any crystal structure of the Sm-Fe type. Regarding this magnetic phase, it is believed that N is dissolved in the Sm-Fe crystal in an intrusive form. Therefore, in SmFeN powder, N easily decomposes and deviates due to heat. Consequently, Sm-Fe-N rare earth magnets are often manufactured by molding SmFeN powder using resin and / or rubber.

[0005] As another method for manufacturing Sm-Fe-N rare-earth magnets, the method disclosed in Patent Document 1 can be cited as an example. This method involves mixing SmFeN powder with zinc-containing powder (hereinafter sometimes referred to as "zinc powder"), forming the mixed powder in a magnetic field, and sintering the magnetic field-formed body (including liquid-phase sintering). Furthermore, Patent Document 2 discloses a method for manufacturing a rare-earth magnet in which SmFeN powder with a zinc coating is formed in a magnetic field, and the magnetic field-formed body is sintered.

[0006] Methods for manufacturing SmFeN powder are disclosed, for example, in Patent Documents 3 and 4.

[0007] Existing technical documents

[0008] Patent documents

[0009] Patent Document 1: International Publication No. 2015 / 199096

[0010] Patent Document 2: Japanese Patent Application Publication No. 2020-161704

[0011] Patent Document 3: Japanese Patent Application Publication No. 2017-117937

[0012] Patent Document 4: Japanese Patent Application Publication No. 2020-102606 Summary of the Invention

[0013] The problem that the invention aims to solve

[0014] The sintering methods for magnetic field-formed bodies generally fall into two categories: pressureless sintering and pressure sintering. In both methods, high-density rare-earth magnets (sintered bodies) are obtained by sintering the magnetic field-formed body. In pressureless sintering, since no pressure is applied to the magnetic field-formed body during sintering, a high-temperature sintering time of 6 hours or more at temperatures above 900°C is generally required to obtain a high-density sintered body. On the other hand, in pressure sintering, because pressure is applied to the magnetic field-formed body during sintering, high-density sintered bodies can generally be obtained even when sintering at a low temperature of 600–800°C for a short time of 0.1–5 hours.

[0015] When sintering a magnetic field-formed body of a mixture of SmFeN powder and zinc powder, pressure sintering is employed to prevent the SmFeN powder from decomposing due to heat. However, sintering is carried out at a lower temperature and for a shorter time compared to typical pressure sintering. Even at this low temperature and short time, sintering is possible because the zinc component in the zinc powder diffuses onto the surface of the magnetic powder during sintering, thus solidifying (curing). In this way, the zinc powder in the magnetic field-formed body functions as a binder. Furthermore, the zinc powder in the magnetic field-formed body also functions as a modifier, modifying the α-Fe phase in the SmFeN powder and absorbing oxygen from the SmFeN powder to improve coercivity. Hereinafter, powders that function as both binders and modifiers, used in the manufacture of Sm-Fe-N rare-earth magnets, are sometimes referred to as "modifier powders."

[0016] When permanent magnets, such as Sm-Fe-N rare-earth magnets, are used in motors, they are placed in a periodically changing external magnetic field environment. Therefore, the permanent magnets are affected by the external magnetic field. This will be illustrated with the accompanying drawings.

[0017] Figure 1 This is an illustrative diagram schematically showing the demagnetization curve of an ideal permanent magnet. (B) r H represents the residual magnetic flux density. c Indicates coercivity. In Figure 1 The range shown in the "motor operating area" ( Figure 1In an external magnetic field environment (within the dashed line area), a permanent magnet is used in a motor. Within the motor's operating region, it is affected by the magnetic field from the stator. For an ideal permanent magnet, magnetization does not decrease due to the external magnetic field within the motor's operating region. However, in practical permanent magnets, magnetization decreases due to the external magnetic field within the motor's operating region.

[0018] Figure 2 This is a schematic diagram illustrating the demagnetization curves of Sm-Fe-N and Nd-Fe-B rare-earth magnets. The dashed line represents the motor's operating area. Figure 2 As shown, compared with Nd-Fe-B rare earth magnets, the coercivity (H) in Sm-Fe-N rare earth magnets is higher. c While the magnetization is large in the motor's operating region, the demagnetization relative to the external magnetic field is also large. In the motor's operating region, if the demagnetization relative to the external magnetic field is large, the current control on the motor's stator side becomes complex, increasing the load on the inverter connected to the motor. To alleviate the inverter load, a larger capacity inverter is required, which compromises economic efficiency. This is particularly noticeable when the motor operates at high output and the permanent magnets inside the motor reach high temperatures. It should be noted that, unless otherwise specified, in this specification, "high temperature" regarding magnetic characteristics refers to 100–200°C.

[0019] Based on the above, the inventors have discovered the following problem: it is desirable to have a Sm-Fe-N rare earth magnet that is less prone to demagnetization in the motor operating area, especially at high temperatures, and a method for manufacturing the same.

[0020] This disclosure was made to solve the aforementioned problems. Specifically, the purpose of this disclosure is to provide a Sm-Fe-N rare earth magnet that is less prone to demagnetization than before, especially at high temperatures, under an applied external magnetic field.

[0021] Methods for solving problems

[0022] To achieve the above objectives, the inventors conducted repeated and in-depth research, and completed the rare earth magnet and its manufacturing method disclosed herein. The rare earth magnet and its manufacturing method disclosed herein include the following aspects.

[0023] <1> A method for manufacturing rare earth magnets, comprising:

[0024] Prepare a Zn containing Sm, Fe, and N, with at least a portion possessing Th2Zn 17 Type and Th2Ni 17 Magnetic powder of any magnetic phase with a crystal structure in the type;

[0025] Prepare a modified material powder containing at least one of metallic zinc and zinc alloys;

[0026] The magnetic powder and the modified material powder are mixed to obtain a mixed powder;

[0027] The mixed powder is compressed and shaped in a magnetic field to obtain a magnetically shaped body;

[0028] The magnetic field-formed body is subjected to pressure sintering to obtain a sintered body; and

[0029] The sintered body is subjected to heat treatment.

[0030] Wherein, the magnetic powder D 50 The size is between 1.50 μm and 3.00 μm.

[0031] The zinc content in the modified material powder is 6% by mass or more and 30% by mass or less, relative to the mixed powder.

[0032] The heat treatment is carried out at a temperature above 350°C and below 410°C.

[0033] <2> according to <1> The method for manufacturing rare earth magnets according to the present invention, wherein, in the magnetic powder, the proportion of magnetic powder particles with a particle size of 1.00 μm or less relative to the total number of magnetic powder particles in the magnetic powder is 1.50% or less, and the content of zinc component in the modified material powder is 6% by mass or more and 10% by mass or less relative to the mixed powder.

[0034] <3> according to <1> or <2> The method for manufacturing rare earth magnets according to the present invention includes heat treatment until more than 90% of the surface area of ​​the magnetic powder particles in the sintered body forms an Fe-Zn alloy phase.

[0035] <4> according to <1> ~ <3> The method for manufacturing a rare earth magnet according to any one of the claims, wherein the heat treatment is performed at a temperature above 350°C and below 400°C.

[0036] <5> according to <1> ~ <4> The method for manufacturing a rare earth magnet according to any one of the claims, wherein the heat treatment is performed for a period of 3 hours or more but less than 40 hours.

[0037] <6> according to <1> ~ <5> The method for manufacturing a rare earth magnet according to any one of the claims, wherein the magnetic field shaped body is subjected to pressure sintering at a pressure of 200 MPa or more and 1500 MPa or less and a temperature of 300°C or more and 400°C or less for a period of 1 minute or more and 30 minutes or less.

[0038] <7> Rare earth magnets are rare earth magnets made by sintering magnetic powder together with modified material powder containing at least one of metallic zinc and zinc alloys.

[0039] The magnetic powder contains Sm, Fe and N.

[0040] At least a portion of the magnetic powder has Th2Zn. 17 Type and Th2Ni 17 Any crystal structure in the type,

[0041] The rare earth magnet contains more than 6% by mass and less than 30% by mass of zinc.

[0042] The magnetic powder D 50 It is between 1.50 μm and 3.00 μm, and

[0043] More than 90% of the surface of the magnetic powder is covered by an Fe-Zn alloy phase.

[0044] Invention Effects

[0045] According to this disclosure, by applying a particle with a specified particle size D at a specified temperature... 50 Heat treatment of sintered magnetic powders can provide Sm-Fe-N rare earth magnets that are less prone to demagnetization than before under an applied external magnetic field, as well as a method for their manufacture. Attached Figure Description

[0046] Figure 1 This is an illustrative diagram schematically showing the demagnetization curve of an ideal permanent magnet.

[0047] Figure 2 This is an illustrative diagram schematically showing the demagnetization curves of Sm-Fe-N rare earth magnets and Nd-Fe-B rare earth magnets.

[0048] Figure 3A This is an illustrative diagram schematically showing SmFeN powder particles with a sufficiently modified phase formed on their surface.

[0049] Figure 3B This is an illustrative diagram schematically showing SmFeN particles on the surface where the modified phase has not formed sufficiently.

[0050] Figure 4 This is a coordinate graph showing the particle size distribution of the graded SmFeN powder.

[0051] Figure 5 This is a coordinate graph showing the demagnetization curves of the samples of Example 1 and Comparative Example 1.

[0052] Figure 6 This is a composite mapping image of the sample from Example 1.

[0053] Figure 7 This is a composite mapping image of the sample from Comparative Example 1.

[0054] Explanation of reference numerals in the attached figures

[0055] 10SmFeN powder particles

[0056] 20 modified phases

[0057] 22 gaps Detailed Implementation

[0058] The following details the embodiments of the rare earth magnet and its manufacturing method disclosed herein. Furthermore, the embodiments shown below do not limit the rare earth magnet and its manufacturing method disclosed herein.

[0059] The reason why the rare earth magnets disclosed herein are less prone to demagnetization compared to those of the past is explained using the accompanying drawings in conjunction with their manufacturing method.

[0060] The rare-earth magnet disclosed herein is obtained by sintering a mixture of SmFeN powder and modified material powder. If the majority of the SmFeN powder particles used have single magnetic domains, the reduction in demagnetization can be suppressed. If the SmFeN powder particles have multiple magnetic domains, domain walls exist between the domains. Because the SmFeN powder particles have multiple magnetic domains, the resulting rare-earth magnet is prone to demagnetization. Therefore, the magnetic powder particles are made to a specified particle size such that the majority of the magnetic powder particles have single magnetic domains.

[0061] Furthermore, the surface of SmFeN powder particles contains an α-Fe phase that does not contribute to the formation of the magnetic phase, thus making it a potential starting point for magnetization reversal. Modifying the surface of the magnetic powder particles is useful in suppressing this phenomenon. Figure 3A This is an illustrative diagram schematically showing SmFeN powder particles with a sufficiently modified phase formed on their surface. Figure 3B This is an illustrative diagram schematically showing SmFeN powder particles whose surface has not formed a sufficiently modified phase.

[0062] like Figure 3A and 3B As shown, modified phase 20 is formed on the surface of SmFeN powder particles 10. Modified phase 20 is an Fe-Zn alloy phase formed by alloying the α-Fe phase present on the surface of SmFeN powder particles 10 with the Zn of the modified material. The α-Fe phase is a soft magnetic phase, while the Fe-Zn alloy phase is a non-magnetic phase, thus avoiding becoming the starting point of magnetization reversal, and consequently suppressing demagnetization.

[0063] like Figure 3A As shown, if the modified phase 20 is sufficiently formed on the surface of the SmFeN powder particles 10, and the modified phase 20 covers the surface of the SmFeN powder particles 10 with a specified coverage ratio or higher, demagnetization can be sufficiently suppressed. On the other hand, as Figure 3BAs shown, if the modified phase 20 is not sufficiently formed on the surface of the SmFeN powder particles 10, and the modified phase 20 only covers the surface of the SmFeN powder particles 10 with a coverage rate less than specified, demagnetization cannot be sufficiently suppressed. This is because, as... Figure 3B As shown, voids 22 exist in a portion of the modified phase 20, and in the portion of voids 22, the surface of the SmFeN powder particles 10 is exposed without modification.

[0064] Figure 3A The modified phase 20 shown is obtained by heat-treating a sintered body of a mixture of SmFeN powder and modified material powder under specified conditions.

[0065] The following describes the essential technical features of the rare earth magnet and its manufacturing method disclosed herein, based on the insights and other factors described above.

[0066] Manufacturing Methods of Rare Earth Magnets

[0067] The method for manufacturing rare earth magnets disclosed herein (hereinafter sometimes referred to as "the manufacturing method of this disclosure") includes a magnetic powder preparation step, a modified material powder preparation step, a mixing step, a magnetic field forming step, a pressure sintering step, and a heat treatment step. Each step is described below.

[0068] <Magnetic Powder Preparation Process>

[0069] Prepare magnetic powder (SmFeN powder). The magnetic powder (SmFeN powder) used in the manufacturing method of this disclosure only needs to contain Sm, Fe and N, and have at least a portion of Th2Zn. 17 Type and Th2Ni 17 There are no particular restrictions on the type of magnetic phase, which can have any of the crystal structures described above. In addition to the structures mentioned above, other crystal structures of the TbCu7 type can also be cited as magnetic phases. It should be noted that Sm is samarium, Fe is iron, and N is nitrogen. Furthermore, Th is thorium, Zn is zinc, Ni is nickel, Tb is terbium, and Cu is copper.

[0070] SmFeN powder may contain, for example, components with the formula (Sm... (1-i) R i )2(Fe (1-j) Co j ) 17 N h The magnetic phase is indicated. Rare earth magnets (hereinafter sometimes referred to as "products") obtained using the manufacturing method of this disclosure exhibit magnetization due to the magnetic phase in the SmFeN powder. It should be noted that i, j, and h are molar ratios.

[0071] In the magnetic phase of SmFeN powder, R may be present within a range that does not impede the effectiveness of the manufacturing method disclosed herein and the magnetic properties of the product. Such a range is represented by the value i in the above-described compositional formula. i can be, for example, 0 or more, 0.10 or more, or 0.20 or more, or 0.50 or less, 0.40 or less, or 0.30 or less. R is one or more rare earth elements selected from Sm and Zr. In this specification, the rare earth elements are Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu. Furthermore, Zr stands for zirconium, Sc for scandium, Y for yttrium, La for lanthanum, Ce for cerium, Pr for praseodymium, Nd for neodymium, Pm for promethium, Sm for samarium, Eu for europium, Gd for gadolinium, Tb for terbium, Dy for dysprosium, Ho for holmium, Er for erbium, Tm for thulium, Yb for ytterbium, and Lu for ruthenium.

[0072] For (Sm) (1-i) R i )2(Fe (1-j) Co j ) 17 N h Typically, R substitutes for Sm2(Fe). (1-j) Co j ) 17 N h The location of Sm, but not limited to it. For example, a portion of R can be in Sm2(Fe (1-j) Co j ) 17 N h An intrusive configuration between China and Israel.

[0073] In the magnetic phase of the SmFeN powder, Co may be present within a range that does not impede the effectiveness of the manufacturing method disclosed herein or the magnetic properties of the product. Such a range is represented by j in the above composition formula. j can be 0 or more, 0.10 or more, or 0.20 or more, and can be 0.52 or less, 0.50 or less, 0.40 or less, or 0.30 or less.

[0074] For (Sm) (1-i) R i )2(Fe (1-j) Co j ) 17 N h Typically, Co substitutes for (Sm) (1-i) R i )2Fe 17 N h The location of Fe, but not limited to. For example, a portion of Co can be found in (Sm (1-i) R i )2Fe 17 N hAn intrusive configuration between China and Israel.

[0075] Regarding the magnetic phase in SmFeN powder, N exists in an intrusive manner in the form of (SmFeN powder). (1-i) R i )2(Fe (1-j) Co j ) 17 This is reflected in the grains, which helps to manifest and enhance magnetic properties.

[0076] For (Sm) (1-i) R i )2(Fe (1-j) Co j ) 17 N h h can be taken as 1.5 to 4.5, typically (Sm (1-i) R i )2(Fe (1-j) Co j ) 17 N3. h can be 1.8 or higher, 2.0 or higher, or 2.5 or higher, or it can be below 4.2, below 4.0 or below 3.5. (Sm (1-i) R i )2(Fe (1-j) Co j ) 17 N3 relative to (Sm) (1-i) R i )2(Fe (1-j) Co j ) 17 N h The overall content is preferably 70% by mass or more, more preferably 80% by mass or more, and even more preferably 90% by mass or more. On the other hand, (Sm (1-i) R i )2(Fe (1-j) Co j ) 17 N h It doesn't have to be all (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 N3 relative to (Sm) (1-i) R i )2(Fe (1-j) Co j ) 17 N hThe overall content can be below 98% by mass, below 95% by mass, or below 92% by mass.

[0077] SmFeN powder, in addition to being composed of (Sm (1-i) R i )2(Fe (1-j) Co j ) 17 N h In addition to the magnetic phase indicated, oxygen and M may be present within a range that does not substantially impair the effectiveness of the manufacturing method of this disclosure or the magnetic properties of the product. 1 And unavoidable impurity elements. From the viewpoint of ensuring the magnetic properties of the product, relative to the overall SmFeN powder, (Sm (1-i) R i )2(Fe (1-j) Co j ) 17 N h The content of the magnetic phase can be 80% by mass or more, 85% by mass or more, or 90% by mass or more. On the other hand, relative to the SmFeN powder as a whole, even without using (Sm... (1-i) R i )2(Fe (1-j) Co j ) 17 N h The indicated magnetic phase content is too high, but there are no practical problems. Therefore, its content can be below 97% by mass, below 95% by mass, or below 93% by mass. (Sm) (1-i) R i )2(Fe (1-j) Co j ) 17 N h The magnetic phase balance is represented by oxygen and M. 1 The content of oxygen and M. 1 A portion of it may exist in the magnetic phase in an intrusive and / or substitutional manner.

[0078] As for the above M 1Examples of unavoidable impurity elements include one or more selected from Ga, Ti, Cr, Zn, Mn, V, Mo, W, Si, Re, Cu, Al, Ca, B, Ni, and C. Unavoidable impurity elements refer to those elements that cannot be avoided during the production of raw materials and / or magnetic powders, or whose presence would significantly increase manufacturing costs if avoided. These elements may exist in the aforementioned magnetic phases in a substitutional and / or intrusive manner, or in phases other than the aforementioned magnetic phases. Alternatively, they may exist at the grain boundaries of these phases. It should be noted that Ga represents gallium, Ti represents titanium, Cr represents chromium, Zn represents zinc, Mn represents manganese, V represents vanadium, Mo represents molybdenum, W represents tungsten, Si represents silicon, Re represents rhenium, Cu represents copper, Al represents aluminum, Ca represents calcium, B represents boron, Ni represents nickel, and C represents carbon.

[0079] If the D of SmFeN powder 50 If the particle size is below 3.00 μm, then most SmFeN powder particles possess single magnetic domains. From this perspective, the Di of SmFeN powder... 50 The micrometer size can be 2.90 μm or less, 2.80 μm or less, 2.70 μm or less, 2.60 μm or less, 2.50 μm or less, 2.40 μm or less, 2.30 μm or less, 2.20 μm or less, or 2.10 μm or less. On the other hand, in terms of facilitating the manufacture of magnetic powder particles with single magnetic domains, SmFeN powder has a D... 50 The size is 1.50μm or larger, 1.60μm or larger, 1.70μm or larger, 1.80μm or larger, 1.90μm or larger, or 2.00μm or larger.

[0080] D of SmFeN powder 50 The particle size distribution of SmFeN powder was calculated. Furthermore, the particle size distribution of SmFeN powder was determined (researched) using the following method. In this specification, unless otherwise specified, the description of the particle size (particle diameter) of SmFeN powder is based on the following determination method (research method). It should be noted that D... 50 This indicates the median diameter.

[0081] A sample of SmFeN powder that had been resin-filled was prepared, and its surface was ground and observed using an optical microscope. Then, a straight line was drawn on the optical microscope image, and the lengths of the line segments divided by SmFeN particles (bright field) were measured. The particle size distribution of the SmFeN powder was determined based on the frequency distribution of the line segment lengths. The particle size distribution obtained by this method is approximately equal to that obtained using the intersection method or dry laser diffraction-scattering method.

[0082] In SmFeN powder, microparticles may sometimes be present due to manufacturing reasons, etc. In this specification, unless otherwise specified, "microparticles" refers to magnetic powder particles with a particle size of 1.0 μm or less. As long as the D of the SmFeN powder... 50 If the above range is met, there is no particular limitation on the proportion of magnetic powder particles (microparticles) with a particle size of 1.0 μm or less in the SmFeN powder. From the viewpoint of ensuring the mechanical strength of the molded body (rare earth magnet), the proportion of magnetic powder particles (microparticles) with a particle size of 1.0 μm or less in the SmFeN powder is preferably as low as possible. The proportion of microparticles relative to the total number of magnetic powder particles in the SmFeN powder is preferably 15.00% or less, 13.40% or less, 10.00% or less, 8.00% or less, 6.00% or less, 4.00% or less, 3.00% or less, 2.50% or less, 2.00% or less, 1.50% or less, 1.43% or less, or 1.40% or less. From the viewpoint of ease of manufacturing SmFeN powder, microparticles are not necessarily completely absent; even if the lower limit of the proportion of microparticles is 0.50%, 1.00%, or 1.20%, it is not a problem in practical application.

[0083] In the manufacturing method of this disclosure, the modified material powder described later is mixed into SmFeN powder. Oxygen in the SmFeN powder is absorbed by the zinc and / or zinc alloy powder in the modified material powder, thereby improving the magnetic properties of the product, particularly the coercivity. Regarding the oxygen content in the SmFeN powder, the amount of oxygen absorbed by the modified material powder from the SmFeN powder can be considered in the steps of the manufacturing method of this disclosure. A low oxygen content in the SmFeN powder relative to the overall SmFeN powder is preferable. The oxygen content of the SmFeN powder relative to the overall SmFeN powder is preferably 2.0% by mass or less, more preferably 1.5% by mass or less, and even more preferably 1.0% by mass or less. On the other hand, drastically reducing the oxygen content in the SmFeN powder leads to an increase in manufacturing costs. Therefore, the oxygen content of the SmFeN powder relative to the overall SmFeN powder can be 0.1% by mass or more, 0.2% by mass or more, or 0.3% by mass or more.

[0084] As long as the above-described conditions are met, there are no particular restrictions on the manufacturing method of SmFeN powder, and commercially available products can be used. Examples of manufacturing methods for SmFeN powder include producing Sm-Fe powder from samarium oxide and iron powder via a reduction diffusion method, followed by heating at temperatures below 600°C in an atmosphere containing a mixture of nitrogen and hydrogen, nitrogen, and ammonia to obtain Sm-Fe-N powder. Alternatively, examples include manufacturing Sm-Fe alloys using a melting method, coarsely pulverizing the alloy to obtain coarse particles, nitriding the coarse particles, and further pulverizing them to the desired particle size. For pulverization, methods such as dry jet milling, dry ball milling, wet ball milling, or wet bead milling can be used. Combinations of these methods can also be used.

[0085] In addition to the manufacturing methods described above, SmFeN powder can also be obtained, for example, by the following manufacturing method: a pretreatment step of heat-treating an oxide containing Sm and Fe in an atmosphere containing a reducing gas to obtain a partial oxide; a step of heat-treating the partial oxide in the presence of a reducing agent to obtain alloy particles; and a step of heat-treating the alloy particles in an atmosphere containing nitrogen or ammonia at a first temperature of 400°C to 470°C, followed by heat-treating at a second temperature of 480°C to 610°C to obtain a nitride. Especially for large-particle alloy particles, such as those containing La, nitriding sometimes does not fully penetrate the interior of the oxide particles. If nitriding is performed at both stages of temperature, the interior of the oxide particles is also fully nitrided, resulting in anisotropic SmFeN powder with a narrow particle size distribution and high remanent magnetization.

[0086] [Oxide Preparation Process]

[0087] The oxides containing Sm and Fe used in the pretreatment process described later can be produced, for example, by mixing Sm oxides and Fe oxides, but it is preferred to manufacture them by a process of mixing a solution containing Sm and Fe with a precipitant to obtain a precipitate containing Sm and Fe (precipitation process) and calcining the precipitate to obtain oxides containing Sm and Fe (oxidation process).

[0088] [Sedimentation Process]

[0089] In the precipitation process, Sm and Fe raw materials are dissolved in a strongly acidic solution to prepare a solution containing Sm and Fe. This process yields Sm₂Fe₂. 17When N3 is the magnetic phase, the molar ratio of Sm to Fe (Sm:Fe) is preferably 1.5:17 to 3.0:17, more preferably 2.0:17 to 2.5:17. Raw materials such as La, W, Co, Ti, Sc, Y, Pr, Nd, Pm, Gd, Tb, Dy, Ho, Er, Tm, and / or Lu can be added to the above solution. From the viewpoint of remanent magnetic flux density, the presence of La is preferred. From the perspective of coercivity and rectangularity ratio, the presence of W is preferred. From the perspective of temperature characteristics, the presence of Co and / or Ti is preferred.

[0090] There are no limitations on the type of raw material used for Sm and Fe, as long as it can dissolve in a strongly acidic solution. For example, considering ease of availability, samarium oxide can be listed as a raw material for Sm, and FeSO4 can be listed as a raw material for Fe. The concentration of the solution containing Sm and Fe can be appropriately adjusted within the range where the Sm and Fe raw materials are substantially soluble in acidic solutions. Sulfuric acid can be cited as an example of an acidic solution, considering its solubility.

[0091] By reacting a solution containing Sm and Fe with a precipitating agent, an insoluble precipitate containing Sm and Fe is obtained. Here, the solution containing Sm and Fe only needs to be able to react with the precipitating agent to become a solution containing Sm and Fe. For example, the raw materials containing Sm and Fe can be prepared as separate solutions, and each solution is added dropwise to react with the precipitating agent. When preparing separate solutions, the solution should be adjusted appropriately within the range where each raw material is substantially soluble in an acidic solution. As for the precipitating agent, there are no limitations as long as it is an alkaline solution that reacts with the solution containing Sm and Fe to obtain a precipitate; examples include ammonia and caustic soda, with caustic soda being preferred.

[0092] From the perspective of easily adjusting the particle properties of the precipitate, the precipitation reaction is preferably carried out by separately adding a solution containing Sm and Fe and a precipitant to a solvent such as water. By appropriately controlling the supply rate of the solution containing Sm and Fe and the precipitant, the reaction temperature, the concentration of the reaction solution, and the pH during the reaction, a precipitate with uniform distribution of constituent elements, narrow particle size distribution, and uniform powder shape can be obtained. By using such a precipitate, the magnetic properties of the SmFeN powder as the final product are improved. The reaction temperature can be 0°C or higher and 50°C or lower, preferably 35°C or higher and 45°C or lower. The concentration of the reaction solution, based on the total concentration of metal ions, is preferably 0.65 mol / L or higher and 0.85 mol / L or lower, more preferably 0.7 mol / L or higher and 0.85 mol / L or lower. The reaction pH is preferably 5 or higher and 9 or lower, more preferably 6.5 or higher and 8 or lower.

[0093] From a magnetic property perspective, it is preferable that the solution containing Sm and Fe also contains one or more metals selected from La, W, Co, and Ti. For example, from the perspective of remanent magnetic flux density, La is preferred; from the perspective of coercivity and rectangularity ratio, W is preferred; and from the perspective of temperature characteristics, Co and / or Ti are preferred. As for the La raw material, there are no limitations as long as it can dissolve in a strongly acidic solution; for example, La₂O₃ and LaCl₃ are examples of readily available materials. Along with the Sm and Fe raw materials, appropriate adjustments are made within the range where the La, W, Co, and Ti raw materials are substantially soluble in acidic solutions. Sulfuric acid is an example of an acidic solution, considering solubility. Ammonium tungstate is an example of a W raw material; cobalt sulfate is an example of a Co raw material; and titanium oxysulfate is an example of a titanium raw material.

[0094] When a solution containing Sm and Fe also contains one or more metals selected from La, W, Co, and Ti, an insoluble precipitate containing Sm, Fe, and one or more metals selected from La, W, Co, and Ti is obtained. Here, the solution only needs to contain one or more metals selected from La, W, Co, and Ti when reacting with the precipitant. For example, each raw material can be prepared as a separate solution, and each solution can be added dropwise to react with the precipitant, or it can be prepared together with a solution containing Sm and Fe.

[0095] The final SmFeN powder particle size, shape, and particle size distribution are largely determined by the powder obtained in the precipitation process. When the particle size of the powder is measured using a laser diffraction wet particle size analyzer, it is preferable that all the powder falls within the range of approximately 0.05 μm to 20 μm, and more preferably 0.1 μm to 10 μm.

[0096] After separating the precipitate, in order to prevent the precipitate from redissolving in the residual solvent during the subsequent heat treatment of the oxidation process, and to prevent the precipitate from agglomerating or changing in particle size distribution or powder particle size during solvent evaporation, it is preferable to desolventize the separated material. Specifically, as a desolventizing method, if water is used as the solvent, a method of drying in an oven at 70°C or higher and 200°C for 5 to 12 hours can be cited.

[0097] Following the precipitation process, a step of separating and washing the resulting precipitate may be included. The washing process may be performed appropriately until the conductivity of the supernatant solution reaches 5 mS / m. 2 The following are steps for separating precipitates. For example, a solvent (preferably water) can be added to the obtained precipitate and mixed, followed by filtration, decantation, or other methods.

[0098] [Oxidation Process]

[0099] The oxidation process is a process of obtaining oxides containing Sm and Fe by calcining the precipitate formed in the precipitation process. For example, the precipitate can be converted into oxides by heat treatment. When heat treating the precipitate, it needs to be carried out in the presence of oxygen, for example, in an atmospheric atmosphere. In addition, since it needs to be carried out in the presence of oxygen, it is preferable that the non-metallic portion of the precipitate contains oxygen atoms.

[0100] There is no particular limitation on the heat treatment temperature (hereinafter sometimes referred to as "oxidation temperature") in the oxidation process, but it is preferably 700°C or higher and 1300°C or lower, more preferably 900°C or higher and 1200°C or lower. Oxidation becomes incomplete below 700°C, and above 1300°C, there is a tendency to fail to obtain the desired shape, average particle size, and particle size distribution of the SmFeN powder. There is also no particular limitation on the heat treatment time, but it is preferably 1 hour or more and 3 hours or less.

[0101] The resulting oxides are oxide particles that reflect the thorough microscopic mixing of Sm and Fe within the oxide particles, as well as the shape and particle size distribution of the precipitate.

[0102] [Pre-treatment process]

[0103] The pretreatment process involves heat-treating the aforementioned oxides containing Sm and Fe in an atmosphere containing a reducing gas to obtain a partially reduced oxide.

[0104] Here, "partial oxide" refers to an oxide in which a portion of the oxide has been reduced. The oxygen concentration of the partial oxide is not particularly limited, but is preferably 10% by mass or less, more preferably 8% by mass or less. If it exceeds 10% by mass, the heat of reduction with Ca during the reduction process increases, the firing temperature rises, and there is a tendency to produce particles that have undergone abnormal particle growth. The oxygen concentration of the partial oxide can be determined using non-dispersive infrared absorption spectrometry (ND-IR).

[0105] The reducing gas is appropriately selected from hydrocarbon gases such as hydrogen (H2), carbon monoxide (CO), and methane (CH4). From a cost perspective, hydrogen is preferred, and the gas flow rate is adjusted appropriately within a range that prevents oxide dispersion. The heat treatment temperature in the pretreatment process (hereinafter sometimes referred to as the "pretreatment temperature") is preferably 300°C or higher and 950°C or lower, more preferably 400°C or higher, and even more preferably 750°C or higher. The upper limit is more preferably less than 900°C. If the pretreatment temperature is 300°C or higher, the reduction of oxides containing Sm and Fe is carried out effectively. Furthermore, if it is 950°C or lower, the growth and segregation of oxide particles can be suppressed, and the desired particle size can be maintained. There is no particular limitation on the heat treatment time; it can be set to 1 hour or more and 50 hours or less. Additionally, when using hydrogen as the reducing gas, it is preferable to adjust the thickness of the oxide layer used to 20 mm or less, thereby adjusting the dew point in the reactor to -10°C or lower.

[0106] [Restoration Process]

[0107] The reduction process is a process of obtaining alloy particles by heat-treating the aforementioned partial oxides in the presence of a reducing agent, for example, by contacting the partial oxides with calcium melt or calcium vapor. From the perspective of magnetic properties, the heat treatment temperature is preferably 920°C or higher and 1200°C or lower, more preferably 950°C or higher and 1150°C or lower, and even more preferably 980°C or higher and 1100°C or lower.

[0108] The metallic calcium used as a reducing agent is in granular or powder form, preferably with a particle size of 10 mm or less. This allows for more effective suppression of aggregation during the reduction reaction. Furthermore, the metallic calcium is preferably added in a ratio of 1.1 to 3.0 times the reaction equivalent (the stoichiometric amount required to reduce rare earth oxides, including the amount required to reduce them in the case of Fe components in oxide form), more preferably 1.5 to 2.5 times the amount required.

[0109] In the reduction process, a disintegration accelerator can be used as needed, along with metallic calcium as a reducing agent. This disintegration accelerator is a substance appropriately used in the subsequent post-processing steps to promote the disintegration and granulation of the product; examples include alkaline earth metal salts such as calcium chloride and alkaline earth oxides such as calcium oxide. These disintegration accelerators are used at a ratio of 1% to 30% by mass per unit of samarium oxide, preferably 5% to 30% by mass per unit.

[0110] [Nitriding process]

[0111] The so-called nitriding process involves heat-treating the alloy particles obtained in the reduction process at a first temperature of 400°C to 470°C in a nitrogen- or ammonia-containing atmosphere, followed by a second heat treatment at 480°C to 610°C, thereby obtaining anisotropic magnetic powder particles. Because the particulate precipitate obtained in the precipitation process is used, porous, blocky alloy particles are obtained in the reduction process. Therefore, nitriding can be performed directly in a nitrogen atmosphere without pulverization, resulting in uniform nitriding. If nitriding is performed at a high temperature (second temperature) instead of the first temperature, nitriding proceeds rapidly, sometimes causing abnormal heating, SmFeN decomposition, and a significant decrease in magnetic properties. Furthermore, since nitriding can be performed more slowly, the atmosphere in the nitriding process is preferably essentially nitrogen-containing. The term "basically" as used here refers to the unavoidable presence of elements other than nitrogen due to the mixing of impurities, for example, the proportion of nitrogen in the atmosphere is 95% or more, preferably 97% or more, and more preferably 99% or more.

[0112] The initial temperature in the nitriding process is above 400°C and below 470°C, preferably above 410°C and below 450°C. Below 400°C, nitriding proceeds very slowly; above 470°C, overnitriding or decomposition can easily occur due to heat generation. The heat treatment time at the initial temperature is not particularly limited, but is preferably above 1 hour and below 40 hours, more preferably below 20 hours. If it is less than 1 hour, nitriding may not be fully completed; if it exceeds 40 hours, productivity decreases.

[0113] The second temperature is 480°C or higher and 610°C or lower, preferably 500°C or higher and 550°C or lower. If the temperature is below 480°C, nitriding may not be sufficient if the particles are large; if the temperature exceeds 610°C, overnitriding or decomposition is likely to occur. The heat treatment time at the second temperature is preferably 15 minutes or more and 5 hours or less, more preferably 30 minutes or more and 2 hours or less. If the treatment time is less than 15 minutes, nitriding may not be sufficient; if the treatment time exceeds 5 hours, productivity will decrease.

[0114] Heat treatment at the first temperature and heat treatment at the second temperature can be carried out continuously, and heat treatment at a temperature lower than the second temperature can also be included between these heat treatments. From a productivity point of view, it is preferable to carry them out continuously.

[0115] [Post-processing steps]

[0116] The product obtained after the nitriding process contains, in addition to magnetic powder particles, byproduct CaO and unreacted metallic calcium, sometimes forming a composite sintered mass. The product obtained after the nitriding process can be placed in cooling water to separate the CaO and metallic calcium as calcium hydroxide (Ca(OH)2) suspension. Furthermore, residual calcium hydroxide can be thoroughly removed by washing the magnetic powder with acetic acid or similar substances. When the product is placed in water, the composite sintered mass of the reaction product disintegrates through the oxidation of metallic calcium due to water and the hydration reaction of the byproduct CaO, i.e., micronization.

[0117] [Alkali Treatment Process]

[0118] Alternatively, the product obtained after the nitriding process can be added to an alkaline solution. Examples of alkaline solutions used in the alkaline treatment process include aqueous solutions of calcium hydroxide, sodium hydroxide, and ammonia. Among these, aqueous solutions of calcium hydroxide and sodium hydroxide are preferred for wastewater treatment and high pH conditions. Through alkaline treatment of the product, a residual oxygen-rich Sm layer, which to some extent functions as a protective layer, is retained, thus suppressing the increase in oxygen concentration caused by alkaline treatment.

[0119] There is no particular limitation on the pH of the alkaline solution used in the alkaline treatment process, but it is preferably 9 or higher, and more preferably 10 or higher. If the pH is less than 9, the reaction rate when forming calcium hydroxide is fast, the heat generation is increased, and therefore the oxygen concentration of the final SmFeN powder tends to be higher.

[0120] In the alkali treatment process, for the SmFeN powder obtained after treatment with alkali solution, the moisture content can also be reduced by methods such as decantation, as needed.

[0121] [Acid treatment process]

[0122] Following the alkali treatment step, an acid treatment step may be included. In the acid treatment step, at least a portion of the aforementioned Sm-rich layer is removed, reducing the overall oxygen concentration in the SmFeN powder. Furthermore, in the manufacturing method of this embodiment, since pulverization is not performed, the average particle size of the SmFeN powder is small, the particle size distribution is narrow, and it does not contain microparticles generated by pulverization, thus suppressing the increase in oxygen concentration.

[0123] There are no particular limitations on the acids used in the acid treatment process; examples include hydrogen chloride, nitric acid, sulfuric acid, and acetic acid. However, hydrogen chloride and nitric acid are preferred from the perspective of leaving no impurities.

[0124] Regarding the amount of acid used in the acid treatment process, it is preferably 3.5 parts by mass or more and 13.5 parts by mass or less relative to 100 parts by mass of SmFeN powder, more preferably 4 parts by mass or more and 10 parts by mass or less. Below 3.5 parts by mass, oxide residues remain on the surface of the SmFeN powder, increasing the oxygen concentration. Above 13.5 parts by mass, re-oxidation easily occurs upon exposure to the atmosphere. Furthermore, dissolving the SmFeN powder tends to increase costs. By ensuring that the amount of acid is 3.5 parts by mass or more and 13.5 parts by mass or less relative to 100 parts by mass of SmFeN powder, a rich Sm layer can be formed on the surface of the SmFeN powder to a degree that prevents re-oxidation upon exposure to the atmosphere after acid treatment, thereby obtaining SmFeN powder with low oxygen concentration, small average particle size, and narrow particle size distribution.

[0125] In the acid treatment process, for the SmFeN powder obtained after acid treatment, the moisture content can also be reduced by methods such as decantation, as needed.

[0126] [Dehydration process]

[0127] Following the acid treatment step, a dehydration process is preferred. Dehydration reduces the moisture content of the solid component before vacuum drying, inhibiting oxidation during drying caused by higher moisture content in the solid component before vacuum drying. Here, dehydration refers to the process of reducing the moisture content of the solid component after treatment relative to the solid component before treatment by applying pressure or centrifugal force, and does not include simple decantation, filtration, or drying. There are no particular limitations on the dehydration method; examples include pressing and centrifugation.

[0128] There is no particular limitation on the amount of water contained in the dehydrated SmFeN powder, but from the viewpoint of inhibiting oxidation, it is preferably 13% by mass or less, and more preferably 10% by mass or less.

[0129] For SmFeN powder obtained by acid treatment or SmFeN powder obtained by dehydration after acid treatment, vacuum drying is preferred. There is no particular limitation on the drying temperature, but 70°C or higher is preferred, and 75°C or higher is more preferred. There is also no particular limitation on the drying time, but 1 hour or more is preferred, and 3 hours or more is more preferred.

[0130] The SmFeN powder prepared using the methods described above was classified, and the D of the SmFeN powder was adjusted. 50 The classification method can use well-known methods. Examples of classification methods include the use of sieves, gravity classification, inertial classification, and centrifugal classification.

[0131] <Preparation process for modified material powder>

[0132] Prepare modified material powder. The modified material powder used in the manufacturing method of this disclosure contains at least one of metallic zinc and zinc alloys. Metallic zinc refers to unalloyed zinc. The zinc component in the modified material powder is used to modify and bond the particles of SmFeN powder. Furthermore, in the case where the SmFeN powder particles contain microparticles, the microparticles are rendered harmless regarding magnetic properties.

[0133] The zinc component of the modified material powder diffuses onto the surface of the SmFeN powder particles, forming an Fe-Zn alloy phase, primarily during the heat treatment process described later. "Primarily" indicates that this diffusion also occurs during the sintering process prior to heat treatment, but the majority of the diffusion occurs during the heat treatment process. Th₂Zn is present on the surface of the SmFeN powder particles. 17 Type and / or Th2Ni 17 In parts with incomplete crystal structures, such as those of the SmFeN type, the presence of an α-Fe phase contributes to demagnetization. During the heat treatment process, this α-Fe phase combines with the zinc component of the modified material powder to form an Fe-Zn alloy phase, thus suppressing demagnetization. Specifically, Fe and Zn interdiffusion occurs between SmFeN powder particles and modified material powder particles, forming an Fe-Zn alloy phase. Furthermore, the modified material powder effectively bonds the SmFeN powder particles together. In other words, the modified material powder also functions as a binder.

[0134] In SmFeN powder, micro-particles are sometimes present. Even in these cases, the fine Fe-Zn alloy phase derived from the micro-particles cannot be largely identified through heat treatment of the sintered body. The reasoning is as follows: The micro-particles in SmFeN powder form the Fe-Zn alloy phase not only on their particle surface but also over the entire particle. This is because Th₂Zn… 17 Type and / or Th2Ni 17 The proportion of incomplete crystal structures, such as the micro-particles, is large. Moreover, the Fe-Zn alloy phase from the micro-particles is mostly integrated with the Fe-Zn alloy phase formed on the surface of larger SmFeN particles (particles other than micro-particles).

[0135] If the zinc content in the modified material powder is 6% or more, 7% or more, or 8% or more by mass relative to the mixed powder, then... Figure 3A As shown, most of the surface of the SmFeN powder particles is covered by the modified phase, which can suppress demagnetization. That is, the Fe-Zn alloy phase, as the modified phase, forms a film on the surface of the SmFeN powder particles.

[0136] On the other hand, if the zinc content in the modified material powder is 30% by mass or less relative to the mixed powder, the decrease in magnetization caused by the use of the modified material powder can be suppressed. From this point of view, the zinc content in the modified material powder can be 25% by mass or less, 20% by mass or less, 15% by mass or less, or 10% by mass or less relative to the mixed powder.

[0137] Furthermore, in the manufacturing method disclosed herein, since D with the aforementioned range is used... 50 SmFeN powder, therefore even a relatively small amount of modified material powder, after heat treatment of the sintered body, such as Figure 3A As shown, a large portion of the surface of SmFeN powder particles can also be coated with a modified phase. From this perspective, the zinc content in the modified material powder can be less than 10% by mass, less than 10% by mass, or less than 9% by mass, relative to the mixed powder.

[0138] Using Zn-M 2 When referring to zinc alloys, M 2 Elements that alloy with Zn (zinc), causing the melting start temperature of the zinc alloy to be lower than the melting point of Zn, and unavoidable impurity elements can be selected. This improves sinterability in the pressure sintering process described later. M is used to specify the element that causes the melting start temperature to be lower than the melting point of Zn. 2 Examples of Zn and M can be given. 2 Elements that form eutectic alloys, etc. As such, M... 2 Typical examples include Sn, Mg, and Al, as well as combinations thereof. Sn is tin, Mg is magnesium, and Al is aluminum. For elements that do not hinder the lowering of the melting point of these elements or the characteristics of the products, M can also be chosen. 2 In addition, the so-called unavoidable impurity elements refer to impurities contained in the raw materials of the modified material powder that cannot be avoided or that would lead to a significant increase in manufacturing costs.

[0139] In Zn-M 2 In the zinc alloys represented, Zn and M can be appropriately determined. 2 The ratio (molar ratio) is determined to achieve an appropriate sintering temperature. M 2 The molar ratio relative to the overall zinc alloy can be, for example, 0.05 or more, 0.10 or more, or 0.20 or more, or 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.

[0140] The modified material powder may contain any substances with binder and / or modifier functions and other functions, other than metallic zinc and / or zinc alloys, provided that the effects of the present invention are not impaired. Examples of other functions include, for instance, improved corrosion resistance.

[0141] There are no particular restrictions on the particle size of the modified material powder, but it is preferably finer than that of the SmFeN powder. This allows the particles of the modified material powder to easily spread between the particles of the SmFeN powder. The particle size of the modified material powder is, for example, expressed in terms of D... 50 The median diameter can be 0.1 μm or more, 0.5 μm or more, or 1.0 μm or more, or less than 12.0 μm, 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, or 2.0 μm or less. Additionally, the particle size D of the modified material powder... 50 (Median diameter) can be determined, for example, by dry laser diffraction-scattering.

[0142] If the modified material powder has a low oxygen content, it can absorb a large amount of oxygen from the SmFeN powder, which is preferable. From this point of view, the oxygen content of the modified material powder relative to the whole modified material powder is preferably 5.0% by mass or less, more preferably 3.0% by mass or less, and even more preferably 1.0% by mass or less. On the other hand, drastically reducing the oxygen content of the modified material powder will lead to an increase in manufacturing costs. Therefore, the oxygen content of the modified material powder relative to the whole modified material powder can be 0.1% by mass or more, 0.2% by mass or more, or 0.3% by mass or more.

[0143] <Mixed Process>

[0144] SmFeN powder and modified material powder are mixed to obtain a mixed powder. There are no particular limitations on the mixing method. Examples of mixing methods include using a mortar and pestle, a muller wheel mixer, a stirrer mixer, a mechanical fusion machine, a V-type mixer, and a ball mill. These methods can be combined. It should be noted that a V-type mixer is a device that uses two cylindrical containers connected in a V-shape, rotating which repeatedly gathers and separates the powder within the containers using gravity and centrifugal force to achieve mixing.

[0145] <Magnetic field forming process>

[0146] The mixed powder is compressed and shaped in a magnetic field to obtain a magnetically shaped body. This allows for the imparting of orientation to the magnetically shaped body, anisotropy to the product (rare earth magnet), and improvement of remanent magnetization.

[0147] The magnetic field forming method can be a known method such as using a molding die with a magnetic field generating device surrounding it, or compressing a mixed powder. The forming pressure can be, for example, 10 MPa or more, 20 MPa or more, 30 MPa or more, 50 MPa or more, 100 MPa or more, or 150 MPa or more, or 1500 MPa or less, 1000 MPa or less, or 500 MPa or less. The time for applying the above forming pressure can be, for example, 0.5 minutes or more, 1 minute or more, or 3 minutes or more, or 10 minutes or less, 7 minutes or less, or 5 minutes or less. The magnitude of the applied magnetic field can be, for example, 500 kA / m or more, 1000 kA / m or more, 1500 kA / m or more, or 1600 kA / m or more, or 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 less than 2000 kA / m. Methods for applying a magnetic field include applying a static magnetic field using an electromagnet and applying a pulsed magnetic field using alternating current. Furthermore, to suppress oxidation of the mixed powder, magnetic field forming is preferably performed in a non-reactive gas atmosphere. A non-reactive gas atmosphere includes a nitrogen atmosphere.

[0148] <Pressure sintering process>

[0149] The magnetic field-formed body is subjected to pressure sintering to obtain a sintered body. The pressure sintering method is not particularly limited, and known methods can be used. Examples of pressure sintering methods include: preparing a mold with a cavity and a punch capable of sliding inside the cavity; inserting the magnetic field-formed body inside the cavity; applying pressure to the magnetic field-formed body with the punch; and simultaneously sintering the magnetic field-formed body. In this case, typically, a high-frequency induction coil is used to heat the mold. Alternatively, plasma discharge sintering (SPS) can also be used.

[0150] Appropriate pressure sintering conditions can be selected so that pressure can be applied to the magnetic field molded body while sintering it (hereinafter sometimes referred to as "pressure sintering").

[0151] If the sintering temperature is above 300°C, the Fe on the surface of the SmFeN powder particles and the zinc component of the modified material powder slightly interdiffused in the magnetically formed body, which facilitates sintering. This interdiffusion can be solid-phase diffusion or liquid-phase diffusion. From this perspective, the sintering temperature can be, for example, above 310°C, above 320°C, above 340°C, or above 350°C. On the other hand, if the sintering temperature is below 430°C, the Fe on the surface of the SmFeN powder particles and the zinc component of the modified material powder do not excessively interdiffused, thus not hindering the subsequent heat treatment process, nor adversely affecting the magnetic properties of the resulting sintered body. From these perspectives, the sintering temperature can be below 420°C, below 410°C, below 400°C, below 390°C, below 380°C, below 370°C, or below 360°C.

[0152] Regarding the sintering pressure, an appropriate sintering pressure that can increase the density of the sintered body can be selected. Typical sintering pressures can be above 100 MPa, above 200 MPa, above 400 MPa, above 500 MPa, above 600 MPa, above 800 MPa, or above 1000 MPa; and below 2000 MPa, below 1800 MPa, below 1600 MPa, below 1500 MPa, below 1300 MPa, or below 1200 MPa.

[0153] The sintering time can be appropriately determined so that the Fe on the particle surface of the SmFeN powder and the zinc component of the modified material powder slightly interdiffused. The sintering time does not include the heating time until the heat treatment temperature is reached. The sintering time can be, for example, more than 1 minute, more than 2 minutes, or more than 3 minutes, or less than 30 minutes, less than 20 minutes, less than 10 minutes, or less than 5 minutes.

[0154] After the sintering time has elapsed, the sintered body is cooled to complete the sintering process. The faster the cooling rate, the more it suppresses oxidation of the sintered body. The cooling rate can be, for example, 0.5–200 °C / second.

[0155] For the sintering atmosphere, an inert gas atmosphere is preferred to suppress oxidation of the magnetically formed and sintered body. Inert gas atmospheres include argon and nitrogen atmospheres. Alternatively, sintering can also be performed in a vacuum.

[0156] <Heat Treatment Process>

[0157] The sintered body is heat-treated. This forms a Fe-Zn alloy phase as a coating on the surface of the SmFeN powder particles, strengthening the bond between the SmFeN powder particles and the modified material powder particles (hereinafter sometimes referred to as "curing") while promoting modification. Furthermore, this modification suppresses demagnetization. Additionally, when the SmFeN powder contains microparticles, a Fe-Zn alloy phase is formed on the approximate entirety of these microparticles, largely integrated with the coating Fe-Zn alloy phase formed on the surface of larger particles (particles other than microparticles).

[0158] If the heat treatment temperature is above 350℃, then the following can be obtained: Figure 3A The modified phase 20 is shown. From this point of view, the heat treatment temperature x℃ can be above 360℃, above 370℃, or above 380℃.

[0159] On the other hand, if the heat treatment temperature is below 410°C, Fe and Zn do not excessively interdiffusion. However, although solidification, modification, and the detoxification of microparticles can be achieved at a heat treatment temperature of 410°C, the heat treatment temperature is preferably below 400°C or 390°C due to the occurrence of a knick. It should be noted that a knick refers to a sharp decrease in magnetization relative to a slight decrease in the magnetic field in a region outside the region representing coercivity on the magnetization-magnetic field curve (MH curve).

[0160] There is no particular restriction on the heat treatment time. The heat treatment temperature can be set to x℃ and the heat treatment time to y hours. The heat treatment time can be determined using the following formulas (1) and (2).

[0161] y≥-0.32x+136…Equation (1)

[0162] 350≤x≤410…Equation (2)

[0163] Equations (1) and (2) above are formulas confirmed through experiments, regarding curing and such Figure 3A The formation of the modified phase 20 shown specifically illustrates that the higher the heat treatment temperature, the shorter the heat treatment time.

[0164] Regarding Figure 3AIdeally, the formation of the modified phase 20 shown is achieved through heat treatment until the entire surface of the SmFeN powder particles is covered by the modified phase 20, i.e., 100% coverage of the SmFeN powder particle surface (100% coverage). However, if heat treatment is performed until 90%, 92%, 94%, 96%, or 98% or more of the SmFeN powder particle surface is covered by the modified phase 20, it is essentially equivalent to the complete coverage of the SmFeN powder particle surface by the modified phase 20. The method for determining the coverage rate is explained in "Rare Earth Magnets".

[0165] From the viewpoint of maximizing the coverage of the modified phase 20, the above formula (1) is more preferably y≥-0.32x+137, more preferably y≥-0.32x+140, and even more preferably y≥-0.32x+145.

[0166] As mentioned above, Figure 3A The modified phase 20 shown is formed by alloying the α-Fe phase present on the surface of SmFeN powder particles with the zinc component in the modified material powder. To form the modified phase 20, the heat treatment time is typically 3 hours or more, 4 hours or more, 5 hours or more, 8 hours or more, 10 hours or more, 12 hours or more, 15 hours or more, 17 hours or more, or 20 hours or more. On the other hand, the amount of α-Fe phase present on the surface of SmFeN powder particles is limited, and the diffusion depth of the zinc component in the modified material powder into the SmFeN powder particles is also limited. Therefore, even with excessively long heat treatment times, the formation of the modified phase 20 will saturate. From this viewpoint, the heat treatment time y (hours) is preferably 40 hours or less, 35 hours or less, 30 hours or less, 25 hours or less, or 24 hours or less.

[0167] To suppress oxidation of the sintered body, it is preferable to heat treat the sintered body in a vacuum or in an inert gas atmosphere, including a nitrogen atmosphere. The heat treatment of the sintered body can be carried out in a mold used in pressure sintering; however, in this case, no pressure is applied to the sintered body during heat treatment. As long as the above heat treatment conditions are met, normal magnetic phase decomposition to form the α-Fe phase will not occur, resulting in excessive interdiffusion of Fe and Zn.

[0168] The following describes the rare earth magnets obtained by the manufacturing method of this disclosure as described above.

[0169] Rare Earth Magnets

[0170] As described above, the rare-earth magnet of this disclosure is made by sintering SmFeN powder together with a modified material powder containing at least one of metallic zinc and zinc alloys. The SmFeN powder contains Sm, Fe, and N, and has at least a portion of Th2Zn.17 Type and Th2Ni 17 A magnetic phase of any crystal structure in the type. The composition of the magnetic phase is as described in "Methods for Manufacturing Rare Earth Magnets".

[0171] Regarding the rare-earth magnets of this disclosure, since SmFeN powder is sintered together with a modifying material powder containing at least one of metallic zinc and zinc alloys, the zinc content of the rare-earth magnets of this disclosure is substantially equal to the zinc content in the modifying material powder relative to the mixed powder. Furthermore, since the modified phase formed on the surface of the SmFeN powder particles is thin, the Di of the SmFeN powder in the rare-earth magnets of this disclosure is... 50 D with SmFeN powder before sintering 50 They are essentially equal. These specific numerical ranges are as described in "The Manufacturing Method of Rare Earth Magnets".

[0172] In the rare-earth magnet disclosed herein, a modified phase, which is an Fe-Zn alloy phase, is formed on the surface of SmFeN powder particles. The modified phase covers 90%, 92%, 94%, 96%, or 98% or more of the surface of the SmFeN powder particles. This modified phase helps to suppress demagnetization.

[0173] Coverage is determined (studied) using the following methods. Unless otherwise specified, all statements regarding coverage in this specification are based on the following determination methods (study methods).

[0174] The cross-section of the heat-treated sintered body was ground, and compositional analysis (surface analysis) was performed on the ground surface for Fe and Zn respectively, obtaining Fe mapping images (Fe surface scan images) and Zn mapping images (Zn surface scan images). The Fe and Zn mapping images were then superimposed to obtain a composite mapping image (composite surface scan image). In the composite mapping image, the regions of SmFeN powder particles were identified, and the peripheral length L of the SmFeN powder particles was measured. In the composite mapping image, the length L of the portion of the SmFeN powder particle's periphery that is sandwiched between the Fe and Zn detection regions was also measured. c And the length L of the portion sandwiched between the Fe detection region and the non-detection region. g The non-detection area refers to the area where neither Fe nor Zn is detected. Then, the coverage rate (%) is calculated according to the following formula (3).

[0175] Coverage rate (%) = L c / (L c +L g )×100···Equation (3)

[0176] In the above equation (3), (L c+L g ) means the total perimeter of the surface of the SmFeN powder particles at the cross-section, L c This means the coating length on the surface of SmFeN powder particles.

[0177] Metamorphosis

[0178] In addition to the above description, the rare earth magnets and their manufacturing methods disclosed herein can be modified in various ways within the scope of the contents described in the patent claims.

[0179] For example, when the magnetic powder contains microparticles, before magnetic field forming, as long as the D of the magnetic powder is... 50 If the above conditions are met, some or all of the fine powder particles can be removed beforehand. There are no particular limitations on the fine powder particle removal operation (fine powder particle removal method). Examples of fine powder removal operations (fine powder removal methods) include methods using a cyclone separator (registered trademark), methods using sieves, methods utilizing magnetic fields, and methods utilizing electrostatics. Combinations of these methods are also possible. By removing fine powder particles, the density of the molded body (rare earth magnet) can be further increased, and the magnetization can be further enhanced.

[0180] Example

[0181] The rare-earth magnets and their manufacturing methods of the present disclosure are described in more detail below through examples and comparative examples. Furthermore, the rare-earth magnets and their manufacturing methods of the present disclosure are not limited to the conditions used in the following examples.

[0182] Sample Preparation

[0183] Prepare the samples for Examples 1-4 and Comparative Examples 1-3 according to the following guidelines.

[0184] Dissolve 5.0 kg of FeSO4·7H2O in 2.0 kg of pure water. Then add 0.49 kg of Sm2O3, 0.74 kg of 70% sulfuric acid, and 0.035 kg of La2O3, and stir thoroughly until completely dissolved. Next, add pure water to the resulting solution to adjust the Fe concentration to 0.726 mol / L and the Sm concentration to 0.112 mol / L, thus preparing an SmFeLa sulfuric acid solution.

[0185] [Sedimentation Process]

[0186] The entire volume of the prepared SmFeLa sulfuric acid solution was added dropwise over 70 minutes with stirring, starting at 20 kg of pure water maintained at 40°C, while simultaneously adding 15% ammonia solution to adjust the pH to 7-8. This yielded a slurry containing SmFeLa hydroxide. The slurry was washed with pure water by decantation to separate the hydroxide from the liquid. The separated hydroxide was then dried in an oven at 100°C for 10 hours.

[0187] [Oxidation Process]

[0188] The hydroxide obtained in the precipitation process was calcined at 1000°C in the atmosphere for 1 hour. After cooling, it was used as a raw material powder to obtain red SmFeLa oxide.

[0189] [Pre-treatment process]

[0190] 100g of SmFeLa oxide was packed into a steel container with a porosity of 10mm. The container was placed in a furnace, and the pressure was reduced to 100Pa. Hydrogen gas was introduced while the temperature was raised to 850°C (the pretreatment temperature), and maintained at this temperature for 15 hours. The oxygen concentration was determined using non-dispersive infrared absorption spectrometry (ND-IR) (EMGA-820 manufactured by Horiba Corporation), and the result was 5% by mass. Therefore, a black partial oxide was obtained, in which oxygen bound to Sm was not reduced, and 95% of the oxygen bound to Fe was reduced.

[0191] [Restoration Process]

[0192] 60g of the partial oxide obtained in the pretreatment process and 19.2g of metallic calcium with an average particle size of about 6mm were mixed and placed in a furnace. After evacuating the furnace, argon gas was introduced. The temperature was raised to 1090℃ and held for 45 minutes, then cooled to obtain SmFe powder particles.

[0193] [Nitriding process]

[0194] Next, after cooling the furnace temperature to 100°C, vacuum exhaust (evacuation) was performed, and nitrogen gas was introduced while the temperature was raised to the first temperature of 430°C and maintained for 3 hours. Then, the temperature was raised to the second temperature of 500°C and maintained for 1 hour, followed by cooling to obtain a blocky product containing magnetic powder particles.

[0195] [Post-processing steps]

[0196] The lumpy product obtained in the nitriding process was added to 3 kg of pure water and stirred for 30 minutes. After standing, the supernatant was decanted. This process of adding, stirring, and decanting into pure water was repeated 10 times. Next, 2.5 g of 99.9% acetic acid was added and stirred for 15 minutes. After standing, the supernatant was decanted. This process of adding, stirring, and decanting into pure water was repeated twice.

[0197] [Acid treatment process]

[0198] To 100 parts by weight of the powder obtained in the post-processing step, add 6% hydrochloric acid aqueous solution to make hydrogen chloride 4.3 parts by weight, and stir for 1 minute. After standing, drain the supernatant by decantation. Repeat the addition, stirring, and decantation process twice with pure water. After solid-liquid separation, vacuum dry at 80°C for 3 hours to obtain Sm 9.2 Fe 77.1 N 13.59 La 0.11 The composition is SmFeN powder.

[0199] SmFeN powder was filled into a sample container along with paraffin wax. After melting the paraffin wax with a blower, the sample was aligned with its easily magnetized axis under an orientation magnetic field of 16 kA / m. The magnetically oriented sample was then pulsed magnetized with a magnetizing magnetic field of 32 kA / m. The magnetic properties were measured at room temperature using a VSM (vibrating sample magnetometer) with a maximum magnetic field of 16 kA / m. The results showed a remanent magnetization of 1.44 T and a coercivity of 750 kA / m.

[0200] The SmFeN powder obtained as described above was classified to determine the D of the SmFeN powder. 50 Adjusted to 2.00μm, 3.00μm, 3.08μm and 3.70μm. Figure 4 This is a coordinate graph showing the particle size distribution of the classified SmFeN powder. Classification was performed using a semi-free vortex classifier (Nisshin Engineering Co., Ltd. A-20). The D values ​​of each sample... 50 As shown in Table 1-1. Additionally, Table 1-1 also records the proportion of SmFeN powder particles (microparticles) with a particle size of 1.00 μm or less for each sample. The proportion of SmFeN powder particles (microparticles) with a particle size of 1.00 μm or less is relative to the total number of SmFeN powder particles.

[0201] Zinc powder was prepared as a modified material powder. The D of the zinc powder... 50 The particle size is 0.5 μm. Furthermore, the purity of the zinc powder is 99.5% by mass.

[0202] SmFeN powder and modified material powder were mixed to obtain a mixed powder. The zinc content ratio relative to the total mixed powder, i.e., the amount of modified material powder mixed, is shown in Table 1-1.

[0203] The mixed powder was compressed and molded in a magnetic field to obtain a magnetically molded body. The compression molding pressure was 50 MPa, and the pressure was applied for 1 minute. The applied magnetic field was 1600 kA / m. Furthermore, the compression molding was carried out in a nitrogen atmosphere.

[0204] The magnetic field-formed body was subjected to pressure sintering. High-frequency induction coils were used for pressure sintering in an argon atmosphere (97000 Pa). The sintering temperature was 380℃, the sintering pressure was 500 MPa, and the pressure was applied for 5 minutes.

[0205] The sintered body is placed in a vacuum (10) -2 The heat treatment was carried out at 380℃ for 24 hours.

[0206] "evaluate"

[0207] For each specimen, the coating percentage and magnetic properties were determined. Magnetic properties were measured using a vibrating specimen magnetometer (VSM) at room temperature and 120°C. Regarding demagnetization, the residual magnetization B was measured at 120°C. r The magnetic field H at the beginning of reducing magnetization by 10% k To conduct an evaluation.

[0208] The evaluation results are shown in Tables 1-1 to 1-2 and... Figures 5-7 In Table 1-2, the remanent magnetization and coercivity are the results measured at room temperature. Figure 5 This is a coordinate graph showing the demagnetization curves of the samples of Example 1 and Comparative Example 1. Figure 6 This is a composite mapping image of the sample from Example 1. Figure 7 This is a composite mapping image of the sample from Comparative Example 1. Figure 6 and Figure 7 In the middle, the darkest part represents the gap.

[0209] Table 1-1

[0210]

[0211] Table 1-2

[0212]

[0213] As can be understood from Tables 1-1 and 1-2, in all the samples of the embodiments, H at 120°C k With a strength of 700 kA / m or higher, the rare earth magnets (rare earth magnets of this disclosure) obtained by the manufacturing method of this disclosure can suppress demagnetization.

[0214] On the other hand, in the sample of Comparative Example 1, the coating rate was low due to the low proportion of zinc in the modified material powder, resulting in the inability to suppress demagnetization. In the samples of Comparative Examples 2 and 3, although the coating rate was high, demagnetization could not be suppressed. This is believed to be because the D of the SmFeN powder particles... 50 Because of its large size, SmFeN powder particles have multiple magnetic domains, resulting in a large number of domain walls in SmFeN powder particles that lead to the deterioration of magnetic properties.

[0215] In addition, by Figure 5 It is understandable that, compared to the sample of Comparative Example 1, the sample of Example 1, although having slightly lower remanent magnetization (magnetization when the magnetic field is 0), demagnetized more slowly. Furthermore, from... Figure 6 and Figure 7 It is understandable that, compared with the sample of Comparative Example 1, the sample of Example 1 has fewer darkest areas, i.e. fewer voids, and a higher coverage of the modified phase of SmFeN powder particles.

[0216] The above results confirm the effectiveness of the rare earth magnet and its manufacturing method disclosed herein.

Claims

1. A method for manufacturing rare earth magnets, comprising: Prepare a Zn containing Sm, Fe, and N, with at least a portion possessing Th2Zn 17 Type and Th2Ni 17 Magnetic powder of any magnetic phase with a crystal structure in the type; Prepare a modified material powder containing at least one of metallic zinc and zinc alloys; The magnetic powder and the modified material powder are mixed to obtain a mixed powder; The mixed powder is compressed and shaped in a magnetic field to obtain a magnetically shaped body; The magnetic field-formed body is subjected to pressure sintering at a pressure of 200 MPa to 1500 MPa and a temperature of 300°C to 400°C for a duration of 1 minute to 30 minutes to obtain a sintered body; and The sintered body is subjected to heat treatment. Wherein, the magnetic powder D 50 The size is between 1.50 μm and 3.00 μm. In the magnetic powder, the proportion of magnetic powder particles with a particle size of 1.00 μm or less relative to the total number of magnetic powder particles is 1.50% or less. The zinc content in the modified material powder is 6% by mass or more and 10% by mass or less, relative to the mixed powder. The oxygen content of the modified material powder is below 5.0% by mass. Regarding the conditions for the heat treatment, when the temperature is set to x℃ and the time to y hours, the following conditions are met: y≥-0.32x+136 and 350≤x≤400， The heat treatment is carried out at a temperature above 350°C and below 400°C for a duration of 3 to 40 hours. Through the heat treatment, an Fe-Zn alloy phase is formed on more than 90% of the surface of the magnetic powder particles.

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