Rare earth magnet and method for producing the same

Abstract

To provide a Sm-Fe-N based rare earth magnet which is more difficult in demagnetization in comparison to existing one especially at a high temperature under such an environment that an external magnetic field is applied, and a manufacturing method thereof.SOLUTION: Disclosed are a method for manufacturing a rare earth magnet, and a rare earth magnet that can be obtained by the method. The method comprises the steps of: preparing SmFeN magnetic powder; preparing powder of a modifier containing a zinc component; obtaining a powder mixture by mixing the SmFeN magnetic powder and the modifier powder; obtaining a magnetically-shaped compact by a compression shaping method of the powder mixture in a magnetic field; obtaining a sintered compact by pressure sintering the magnetically-shaped compact; and performing a heat treatment of the sintered compact. In the method, D50 of the magnetic powder is 1.50 μm or more and 3.00 μm or less; the content of the zinc component in the modifier powder is 6 mass% or more and 30 mass% or less; and the temperature of the heat treatment is 350°C or above and 410°C or below.SELECTED DRAWING: Figure 5

Description

Technical Field

[0001] The present disclosure relates to rare earth magnets and methods for manufacturing the same. In particular, the present disclosure relates to rare earth magnets containing Sm, Fe, and N, at least a part of which has a crystal structure of either the Th2Zn 17 type and Th2Ni 17 type, and methods for manufacturing the same.

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, however, 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 magnets are manufactured, for example, using magnetic powder containing Sm, Fe, and N (hereinafter sometimes referred to as "SmFeN powder").

[0004] SmFeN powder has a magnetic phase having a crystal structure of either the Th2Zn 17 type and Th2Ni 17 type. This magnetic phase is considered to be a solid solution in which N has invaded the Sm-Fe crystal. Therefore, SmFeN powder is liable 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 other manufacturing methods for 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. Further, Patent Document 2 discloses a method for manufacturing a rare earth magnet in which SmFeN powder coated with a zinc component on the surface is molded in a magnetic field and the magnetic field molded body is sintered.

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

Prior Art Documents

Patent Documents

[0007]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Summary of the Invention

Problems to be Solved by the Invention

[0008] Sintering methods for magnetic field-formed bodies are roughly classified into a non-pressure sintering method and a pressure sintering method. In any sintering method, 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 generally possible 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 decomposition of the SmFeN powder due to heat, pressure sintering is employed, but sintering is performed 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 then sinters (solidifies). In this way, the metallic zinc powder in the magnetic field-formed body has a function as a binder. In addition, the metallic zinc powder in the magnetic field-formed body also has a function as a modifier that modifies the α-Fe phase in 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 the function as a binder and the function as a modifier may be referred to as a "modifying material powder".

[0010] When a permanent magnet such as an Sm-Fe-N-based rare earth magnet is used in a motor, the permanent magnet is placed in an external magnetic field environment that changes periodically. Therefore, the permanent magnet is affected by the external magnetic field. This will be described with reference to the drawings.

[0011] FIG. 1 is an explanatory diagram schematically showing the demagnetization curve of an ideal permanent magnet. B r is the residual magnetic flux density, and H c indicates the coercivity. In the external magnetic field environment within the range indicated by the "motor operating region" in FIG. 1 (the range of the broken line in FIG. 1), the permanent magnet in the motor is used. In the motor operating region, it is affected by the magnetic field from the stator. In an ideal permanent magnet, in the motor operating region, the magnetization does not decrease due to the external magnetic field. However, in an actual permanent magnet, in the motor operating region, the magnetization decreases due to the external magnetic field.

[0012] FIG. 2 is an explanatory diagram schematically showing the demagnetization curves of Sm-Fe-N-based rare earth magnets and Nd-Fe-B-based rare earth magnets. The broken line indicates the motor operating region. As shown in FIG. 2, compared with the Nd-Fe-B-based rare earth magnet, in the Sm-Fe-N-based rare earth magnet, the coercivity (H c) is large, but in the motor operating region, the decrease in magnetization (demagnetization) due to an external magnetic field is large. When the decrease in magnetization (demagnetization) due to an external magnetic field is large in the motor operating region, the current control on the stator side of the motor becomes complicated, and the load on the inverter connected to the motor increases. To relieve the load on the inverter, an inverter with a large capacity is required, which impairs economic efficiency. This is particularly noticeable when the motor operates at high power and the permanent magnets in the motor become hot. In this specification, unless otherwise specified, regarding magnetic properties, "high temperature" means 100 to 200 °C.

[0013] From these facts, the inventors have found the problem that there is a demand for an Sm-Fe-N-based rare earth magnet that is more difficult to demagnetize than conventional ones and a method for manufacturing the same, particularly at high temperatures, in the motor operating region.

[0014] The present disclosure has been made to solve the above problems. That is, an object of the present disclosure is to provide an Sm-Fe-N-based rare earth magnet that is more difficult to demagnetize than conventional ones and a method for manufacturing the same, particularly at high temperatures, in an environment where an external magnetic field is applied.

Means for Solving the Problems

[0015] The inventors have intensively studied to achieve the above object and completed the rare earth magnet and the method for manufacturing the same of the present disclosure. The rare earth magnet and the method for manufacturing the same of the present disclosure include the following aspects. 〈1〉Preparing magnetic powder 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, 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-formed body, Pressure-sintering the magnetic field-formed body to obtain a sintered body, and Heat-treating the sintered body. including D of the magnetic powder 50 is 1.50 μm or more and 3.00 μm or less, the content ratio of the zinc component in the modifier powder is 6% by mass or more and 30% by mass or less with respect to the mixed powder, and the heat treatment is performed at 350 °C or more and 410 °C or less, Method for manufacturing a rare earth magnet. <2> In the magnetic powder, the ratio of magnetic powder particles having a particle size of 1.00 μm or less is 1.50% or less with respect to the total number of magnetic powder particles of the magnetic powder, and the content ratio of the zinc component in the modifier powder is 6% by mass or more and 10% by mass or less with respect to the mixed powder. The method for manufacturing a rare earth magnet according to item <1>. <3> Heat-treat until an Fe-Zn alloy phase is formed on 90% or more of the particle surfaces of the magnetic powder in the sintered body. The method for manufacturing a rare earth magnet according to item <1> or <2>. <4> The heat treatment is performed at 350 °C or more and 400 °C or less. The method for manufacturing a rare earth magnet according to any one of items <1> to <3>. <5> The heat treatment is performed over 3 hours or more and 40 hours or less. The method for manufacturing a rare earth magnet according to any one of items <1> to <4>. <6> The magnetic field compact is pressure-sintered 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 1 minute or more and 30 minutes or less. The method for manufacturing a rare earth magnet according to any one of items <1> to <5>. <7> A rare earth magnet in which the magnetic powder is sintered together with a modifier powder containing at least one of metallic zinc and zinc alloy, the magnetic powder contains Sm, Fe, and N, at least a part of the magnetic powder is Th2Zn 17 type and Th2Ni 17 has a crystal structure of either type, the rare earth magnet contains 6% by mass or more and 30% by mass or less of a zinc component, D of the magnetic powder 50 is 1.50 μm or more and 3.00 μm or less, and On more than 90% of the surface of the magnetic powder, an Fe-Zn alloy phase is formed. Rare earth magnet.

Advantages of the Invention

[0016] According to the present disclosure, by heat-treating a sintered body using magnetic powder having a predetermined particle size D 50 at a predetermined temperature, it is possible to provide an Sm-Fe-N-based rare earth magnet that is less likely to be demagnetized than conventional ones and a method for manufacturing the same in an environment where an external magnetic field is applied.

Brief Description of the Drawings

[0017]

Figure 1

Figure 2

Figure 3A

Figure 3B

Figure 4

Figure 5

Figure 6

Figure 7

Modes for Carrying Out the Invention

[0018] Hereinafter, embodiments of the rare earth magnet and the method for manufacturing the same according to the present disclosure will be described in detail. Note that the embodiments shown below do not limit the rare earth magnet and the method for manufacturing the same according to the present disclosure.

[0019] The reason why the rare earth magnet of the present disclosure is less likely to be demagnetized than before will be described with reference to the drawings together with its manufacturing method.

[0020] The rare earth magnet of the present disclosure is obtained by sintering a mixed powder of SmFeN powder and modifier powder. If many of the SmFeN powder particles used have a single magnetic domain, a decrease in demagnetization can be suppressed. When the SmFeN powder particles have multiple magnetic domains, magnetic walls exist between the magnetic domains. When the SmFeN powder particles have multiple magnetic domains, the resulting rare earth magnet is more likely to be demagnetized. Therefore, the magnetic powder particles are made to have a particle size equal to or less than a predetermined value so that many of the magnetic powder particles have a single magnetic domain.

[0021] Also, the surface of the SmFeN powder particles is likely to become a starting point for magnetization reversal due to the presence of the α-Fe phase that did not contribute to the formation of the magnetic phase. In order to suppress this, it is useful to modify the surface of the magnetic powder particles. FIG. 3A is an explanatory diagram schematically showing SmFeN powder particles having a sufficient modification phase formed on the surface. FIG. 3B is an explanatory diagram schematically showing SmFeN powder particles having no sufficient modification phase formed on the surface.

[0022] As shown in FIGS. 3A and 3B, the modification phase 20 is formed on the surface of the SmFeN powder particles 10. The modification phase 20 is an Fe-Zn alloy phase formed by alloying the α-Fe phase present on the surface of the SmFeN powder particles 10 with Zn of the modifier. Since the α-Fe phase is a soft magnetic phase while the Fe-Zn alloy phase is a non-magnetic phase, it is possible to avoid becoming a starting point for magnetization reversal, and as a result, demagnetization can be suppressed.

[0023] As shown in Fig. 3A, when a 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 at a predetermined coverage rate or more, demagnetization can be sufficiently suppressed. On the other hand, as shown in Fig. 3B, when the modified phase 20 is not 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 only at less than a predetermined coverage rate, demagnetization cannot be sufficiently suppressed. This is because, as shown in Fig. 3B, voids 22 exist in a part of the modified phase 20, and at the part of the voids 22, the surface of the SmFeN powder particles 10 remains unmodified and is exposed.

[0024] The modified phase 20 as shown in Fig. 3A can be obtained by heat-treating a sintered body of a mixed powder of SmFeN powder and modifier powder under predetermined conditions.

[0025] Next, the constituent requirements of the rare earth magnet and its manufacturing method of the present disclosure, which have been completed based on the findings described so far, will be described.

[0026] 《Manufacturing Method of Rare Earth Magnet》 The manufacturing method of the rare earth magnet of the present disclosure (hereinafter, may be simply referred to as "the manufacturing method of the present disclosure") includes a magnetic powder preparation step, a modifier powder preparation step, a mixing step, a magnetic field forming step, a pressure sintering step, and a heat treatment step. Hereinafter, each step will be described.

[0027] 〈Magnetic Powder Preparation Step〉 Prepare a 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 of the type. Examples of the crystal structure of the magnetic phase include a phase having a TbCu7-type crystal structure in addition to the above-described structures. Here, Sm is samarium, Fe is iron, and N is nitrogen. Also, Th is thorium, Zn is zinc, Ni is nickel, Tb is terbium, and Cu is copper.

[0028] In the SmFeN powder, for example, the magnetic phase represented by the composition formula (Sm (1-i) R i )2(Fe (1-j) Co j ) 17 N h may be contained. The rare earth magnet obtained by the manufacturing method of the present disclosure (hereinafter sometimes referred to as "product") exhibits magnetization due to the magnetic phase in the SmFeN powder. Here, i, j, and h are molar ratios.

[0029] In the magnetic phase in the SmFeN powder, R may be contained within a range that 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 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.

[0030] (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 is not limited to this. For example, in Sm2(Fe (1-j) Co j ) 17 N h a part of R may be disposed in an intrusion type.

[0031] In the magnetic phase of the SmFeN powder, Co may be contained as long as it does not inhibit the effects of the manufacturing method of the present disclosure and the magnetic properties of the resulting product. Such a range is represented by j in the above compositional formula. j may be 0 or more, 0.10 or more, or 0.20 or more, and may be 0.52 or less, 0.50 or less, 0.40 or less, or 0.30 or less.

[0032] (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 Part of the invasive Co may be arranged.

[0033] The magnetic phase in the SmFeN powder contributes to the manifestation and improvement of magnetic properties by the invasive presence of N in the crystal grains represented by (Sm (1-i) R i )2(Fe (1-j) Co j ) 17 .

[0034] (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) Ri )2(Fe (1-j) Co j ) 17 N h The content of (Sm (1-i) R i )2(Fe (1-j) Co j ) 17 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 does not necessarily have 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 The content of (Sm (1-i) R i )2(Fe (1-j) Co j ) 17 N3 may be 98% by mass or less, 95% by mass or less, or 92% by mass or less.

[0035] In addition to the magnetic phase represented by SmFeN powder, (Sm (1-i) R i )2(Fe (1-j) Co j ) 17 N h 1 (1-i) and inevitable impurity elements may be contained as long as they do not substantially inhibit the effects of the manufacturing method of the present disclosure and the magnetic properties of the resulting product. From the viewpoint of ensuring the magnetic properties of the resulting product, with respect to the entire SmFeN powder, (Sm (1-i) R i )2(Fe (1-j) Co j ) 17 N hThe 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, with respect to the entire 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 is no practical problem. 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 is the content of oxygen and M 1 . Also, a part of oxygen and M 1 may be present in the magnetic phase in an interstitial and / or substitutional form.

[0036] Examples of the above-mentioned M 1 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 impurity elements that cannot be avoided during the production of raw materials and / or magnetic powders, or that would cause a significant increase in production costs to avoid. These elements may be present in the above-mentioned magnetic phase in a substitutional and / or interstitial form, or may be present in a phase other than the above-mentioned magnetic phase. Alternatively, they 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.

[0037] If the D 50 of the SmFeN powder is 3.00 μm or less, most of the SmFeN powder particles have a single magnetic domain. From this perspective, the D 50may 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, for the convenience of manufacturing magnetic powder particles having a single magnetic domain, D of the SmFeN powder 50 is 1.50 μm or more, 1.60 μm or more, 1.70 μm or more, 1.80 μm or more, 1.90 μm or more, or 2.00 μm or more.

[0038] D of the SmFeN powder 50 is calculated from the particle size distribution of the SmFeN powder. Also, 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 diameter) of the particles of the SmFeN powder is based on the following measurement method (investigation method). Note that D 50 means the median diameter.

[0039] Prepare a sample in which the SmFeN powder is embedded in resin, 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 where the straight line is separated by SmFeN particles (bright field), and obtain 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.

[0040] Fine powder particles may be present in the SmFeN powder due to manufacturing convenience or the like. In this specification, unless otherwise specified, "fine powder particles" means magnetic powder particles having a particle diameter of 1.0 μm or less. D of the SmFeN powder 50As long as the above-described range is satisfied, there is no particular limitation on the ratio of magnetic powder 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 preferable that the ratio of magnetic powder particles (fine particles) having a particle size of 1.0 μm or less in the SmFeN powder be as low as possible. With respect to the total number of all magnetic powder particles in the SmFeN powder, the ratio of the fine particles 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 convenience in the production of the SmFeN powder and the like, the fine particles do not have to be completely absent, and even if the lower limit of the ratio of the fine particles is 0.50%, 1.00%, or 1.20%, there are no practical problems.

[0041] In the production method of the present disclosure, a modifier powder described later is mixed with the SmFeN powder. Oxygen in the SmFeN powder can be absorbed by the metallic zinc and / or zinc alloy powder in the modifier powder, thereby improving the magnetic properties, particularly the coercive force, of the product. The oxygen content in the SmFeN powder may be determined in consideration of the amount of oxygen in the SmFeN powder absorbed by the modifier powder during the steps of the production method of the present disclosure. It is preferable that the oxygen content of the SmFeN powder be low with respect to the entire SmFeN powder. The oxygen content of the SmFeN powder is preferably 2.0 mass% or less, more preferably 1.5 mass% or less, and even more preferably 1.0 mass% or less with respect to the entire SmFeN powder. On the other hand, extremely reducing the oxygen content in the SmFeN powder causes an increase in production cost. For this reason, the oxygen content of the SmFeN powder may be 0.1 mass% or more, 0.2 mass% or more, or 0.3 mass% or more with respect to the entire SmFeN powder.

[0042] If the SmFeN powder satisfies what has been described so far, there is no particular limitation on its manufacturing method, and commercially available products may be used. As a manufacturing method of SmFeN powder, for example, Sm-Fe powder is manufactured from samarium oxide and iron powder by a reduction diffusion method, and heat treatment is performed 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. Or, for example, a method of manufacturing an 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 can 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.

[0043] In addition to the above-described manufacturing method, SmFeN powder can be obtained, for example, by a manufacturing method including a pretreatment step of obtaining partial oxides by heat-treating an oxide containing Sm and Fe in a reducing gas-containing atmosphere, a step of obtaining alloy particles by heat-treating the partial oxides in the presence of a reducing agent, and a step of heat-treating the alloy particles in a nitrogen- or ammonia-containing atmosphere at a first temperature of 400 °C or higher and 470 °C or lower, and then heat-treating at a second temperature of 480 °C or higher and 610 °C or lower to obtain nitrides. Particularly for alloy particles with a large particle size, for example, alloy particles containing La, nitridation may not proceed sufficiently inside the oxide particles. However, when nitriding is performed at two-stage temperatures, the inside of the oxide particles is also sufficiently nitrided, and SmFeN powder with a narrow particle size distribution and high residual magnetization anisotropy can be obtained.

[0044] [Oxide Preparation Step] The oxide containing Sm and Fe used in the pretreatment step described later may be prepared, for example, by mixing Sm oxide and Fe oxide. However, it is preferably manufactured by a step of mixing a solution containing Sm and Fe with a precipitating agent to obtain a precipitate containing Sm and Fe (precipitation step), and a step of firing the precipitate to obtain an oxide containing Sm and Fe (oxidation step).

[0045] [Precipitation Step] In the precipitation process, Sm raw material and Fe raw material are dissolved in a strongly acidic solution to prepare a solution containing Sm and Fe. When obtaining Sm2Fe 17 N3 as the magnetic phase, the molar ratio of Sm and 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 may be added to the above-mentioned solution. 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. In terms of temperature characteristics, it is preferable to contain Co and / or Ti.

[0046] The Sm raw material and Fe raw material are not limited as long as they can be dissolved in a strongly acidic solution. For example, in terms of 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 Fe raw material are substantially dissolved in the acidic solution. Examples of the acidic solution include sulfuric acid in terms of solubility.

[0047] By reacting the 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 a solution containing Sm and Fe during the reaction with the precipitating agent. 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 precipitating agent. Even when prepared as separate solutions, it is appropriately adjusted within the range where each raw material is substantially dissolved in the acidic solution. The precipitating agent 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.

[0048] The precipitation reaction is preferably carried out by dropping a solution containing Sm and Fe and a precipitant into a solvent such as water, respectively, because the properties of the precipitate particles can be easily adjusted. By appropriately controlling the supply rates 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.

[0049] The solution containing Sm and Fe preferably further contains at least one metal selected from the group consisting of La, W, Co, and Ti in terms of magnetic properties. For example, it is preferable to contain La in terms of residual magnetic flux density, it is preferable to contain W in terms of coercive force and squareness ratio, and it is preferable to contain Co and / or Ti in terms of temperature characteristics. 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 the Fe raw material, the La raw material, the W raw material, the Co raw material, and the Ti raw material are appropriately adjusted within the range where they are substantially dissolved in an 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, titania sulfate can be mentioned.

[0050] When the solution containing Sm and Fe further contains one or more metals selected from the group consisting of La, W, Co, and Ti, an insoluble precipitate containing Sm, Fe, and one or more selected from the group consisting of La, W, Co, and Ti is obtained. Here, the solution only needs to contain one or more selected from the group consisting of La, W, Co, and Ti during the reaction with the precipitant. For example, each raw material can be prepared as a separate solution, and each solution can be dropped and reacted with the precipitant, or it can be prepared together with the solution containing Sm and Fe.

[0051] 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 has a size and distribution that substantially fall within the range of 0.05 μm or more and 20 μm or less, preferably 0.1 μm or more and 10 μm or less.

[0052] After separating the precipitate, in order to suppress the precipitate from redissolving in the remaining solvent during the heat treatment of the subsequent oxidation step, the precipitate from aggregating when the solvent evaporates, or the particle size distribution, powder particle size, etc. from changing, it is preferable to desolvate the separated material. As a method for desolvating, specifically, 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 more and 12 hours or less can be mentioned.

[0053] 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.

[0054] [Oxidation Step] The oxidation step is a step of obtaining an oxide containing Sm and Fe by firing the precipitate formed in the precipitation step. For example, the precipitate can be converted into an oxide by heat treatment. When heat-treating the precipitate, it is necessary to carry out the treatment in the presence of oxygen. For example, it can be carried out in an air atmosphere. Also, since it is necessary to carry out the treatment in the presence of oxygen, it is preferable that the non-metallic portion of the precipitate contains oxygen atoms.

[0055] The heat treatment temperature in the oxidation step (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 not particularly limited either, but is preferably 1 hour or longer and 3 hours or shorter.

[0056] The obtained oxide is an oxide particle in which microscopic mixing of Sm and Fe is sufficiently achieved within the oxide particles, and the shape, particle size distribution, etc. of the precipitate are reflected.

[0057] [Pretreatment step] The pretreatment step is a step of obtaining a partially reduced oxide in which a part of the oxide is reduced by heat-treating the above-mentioned oxide containing Sm and Fe in an atmosphere containing a reducing gas.

[0058] Here, the partially reduced oxide refers to an oxide in which a part of the oxide is reduced. The oxygen concentration of the partially reduced oxide is not particularly limited, but is preferably 10% by mass or less, and more preferably 8% by mass or less. If it exceeds 10% by mass, the exothermic reduction with Ca in the reduction step becomes large, and there is a tendency for particles with abnormal grain growth to be formed due to the increase in the firing temperature. Here, the oxygen concentration of the partially reduced oxide can be measured by the non-dispersive infrared absorption method (ND-IR).

[0059] 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 preferred. The flow rate of the gas is appropriately adjusted within a range where the oxide does not scatter. The heat treatment temperature in the pretreatment step (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. When the pretreatment temperature is 300°C or higher, the reduction of the oxide containing Sm and Fe proceeds efficiently. Also, when it is 950°C or lower, the growth and segregation of oxide particles are suppressed, and the desired particle size 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.

[0060] [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.

[0061] The metal calcium as the reducing agent is used in a granular or powdered form, and its particle size is preferably 10 mm or less. Thereby, aggregation during the reduction reaction can be more effectively suppressed. 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 this when the Fe component is in the form of an oxide), and more preferably 1.5 to 2.5 times the amount.

[0062] In the reduction process, a disintegration accelerator can be used as needed together with metallic calcium as the reducing agent. This disintegration accelerator is appropriately used to promote the disintegration and granulation of the product during the post-treatment process described later. Examples thereof include alkaline earth metal salts such as calcium chloride and alkaline earth metal 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.

[0063] [Nitriding process] The nitriding process is a process of obtaining anisotropic magnetic powder 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 performing a nitriding treatment by heat-treating at a second temperature of 480°C or higher and 610°C or lower. Since the particulate precipitate obtained in the above precipitation process is used, porous massive alloy particles are obtained in the reduction process. Thereby, since heat treatment can be immediately performed in a nitrogen atmosphere for nitriding without performing a pulverization treatment, 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 the rapid progress of nitriding, SmFeN may decompose, and the magnetic properties may be significantly 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. Here, the term "substantially" is used in consideration of the inevitable inclusion of elements other than nitrogen due to the mixing of impurities or the like. For example, the proportion of nitrogen in the atmosphere is 95% or more, preferably 97% or more, and more preferably 99% or more.

[0064] 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.

[0065] The second temperature is 480°C or higher and 610°C or lower, preferably 500°C or higher and 550°C or lower. If it is less than 480°C, nitridation may not proceed sufficiently when the particles are large, and if it exceeds 610°C, over-nitridation or decomposition is likely to occur. The heat treatment time at the second temperature is preferably 15 minutes or longer and 5 hours or shorter, more preferably 30 minutes or longer and 2 hours or shorter. If it is less than 15 minutes, nitridation may not proceed sufficiently, and if it exceeds 5 hours, productivity decreases.

[0066] The heat treatment at the first temperature and the heat treatment at the second temperature may be carried out continuously. Between 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 carried out continuously.

[0067] [Post-treatment process] The product obtained after the nitridation process contains, in addition to the magnetic powder 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 nitridation 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.

[0068] [Alkali treatment process] The product obtained after the nitridation 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 preferred. Due to the alkali treatment of the product, a 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.

[0069] The pH of the alkaline solution used in the alkaline treatment step 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 calcium hydroxide is formed is fast and the heat generation is large, so the oxygen concentration of the finally obtained SmFeN powder tends to be high.

[0070] In the alkaline treatment step, the SmFeN powder obtained after treatment with the alkaline solution can also reduce moisture by methods such as decantation if necessary.

[0071] [Acid treatment step] After the alkaline 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. Further, in the manufacturing method according to the 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 since it does not contain fine powder generated by pulverization or the like, it is possible to suppress an increase in the oxygen concentration.

[0072] The acid used in the acid treatment step is not particularly limited, and examples thereof include hydrogen chloride, nitric acid, sulfuric acid, acetic acid, and the like. Among them, hydrogen chloride and nitric acid are preferable in that no impurities remain.

[0073] 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 with respect to 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 easily occurs 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 with respect to 100 parts by mass of the SmFeN powder, it is possible to cover the surface of the SmFeN powder with a Sm-rich layer oxidized to such an extent that reoxidation hardly occurs when exposed to the atmosphere after acid treatment. Therefore, an SmFeN powder having a low oxygen concentration, a small average particle size, and a narrow particle size distribution can be obtained.

[0074] 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.

[0075] [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.

[0076] 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.

[0077] The SmFeN powder obtained by acid treatment or the SmFeN powder obtained by dehydration treatment after acid treatment is preferably vacuum dried. The drying temperature is not particularly limited, but is preferably 70 °C or higher, more preferably 75 °C or higher. The drying time is also not particularly limited, but is preferably 1 hour or longer, more preferably 3 hours or longer.

[0078] The SmFeN powder prepared by the methods described so far is classified to adjust the D 50 of the SmFeN powder. As the classification method, well-known methods can be used. Examples of the classification method include the use of sieves, gravity classification, inertial classification, and centrifugal classification.

[0079] 〈Modifier powder preparation step〉 Prepare a modified material powder. The modified material powder used in the manufacturing method of the present disclosure contains at least one of metallic zinc and zinc alloys. Metallic zinc means zinc that is not alloyed. The zinc component in the modified material powder modifies and binds the particles of SmFeN powder. Also, when the SmFeN powder particles contain fine particles, the fine particles are rendered harmless with respect to magnetic properties.

[0080] Mainly, in the heat treatment step described later, the zinc component of the modified material powder diffuses on the surface of the SmFeN powder particles to form an Fe-Zn alloy phase. "Mainly" means that although the diffusion also occurs in the sintering step preceding the heat treatment step, most of the diffusion occurs in the heat treatment step. On the surface of the SmFeN powder particles, there are parts where the crystal structures such as the Th2Zn 17 type and / or Th2Ni 17 type are not complete, and an α-Fe phase exists in those parts, which causes demagnetization. In the heat treatment step, this α-Fe phase forms an Fe-Zn alloy phase with the zinc component of the modified material powder to suppress demagnetization. That is, Fe and Zn diffuse mutually between the SmFeN powder particles and the modified material powder particles to form an Fe-Zn alloy phase. Also, the modified material powder can strongly bond the SmFeN powder particles to each other. That is, the modified material powder also functions as a binder.

[0081] Fine particles may exist in the SmFeN powder, but even in such a case, by heat-treating the sintered body, a fine Fe-Zn alloy phase derived from the fine particles becomes hardly recognizable. The reason is considered to be as follows. In the fine particles of the SmFeN powder, an Fe-Zn alloy phase is formed not only on the particle surface but also almost throughout the particle. This is because in the fine particles, the proportion of parts where the crystal structures such as the Th2Zn 17 type and / or Th2Ni 17 type are not complete is large. And much of the Fe-Zn alloy phase derived from the fine particles is integrated with the Fe-Zn alloy phase formed on the surface of the SmFeN particles (particles other than the fine particles) having a relatively large particle size.

[0082] If the content ratio of the zinc component in the modifying material powder is 6% by mass or more, 7% by mass or more, or 8% by mass or more with respect to the mixed powder, as shown in FIG. 3A, most of the surface of the SmFeN powder particles is covered with a modified phase, and demagnetization can be suppressed. That is, an Fe-Zn alloy phase as a modified phase is formed in a film shape on the surface of the SmFeN powder particles.

[0083] 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, a decrease in magnetization due to the use of the modifying material powder can be suppressed. From this viewpoint, the content ratio of the zinc component in the modifying material powder may be 25% by mass or less, 20% by mass or less, 15% by mass or less, or 10% by mass or less with respect to the mixed powder.

[0084] In the manufacturing method of the present disclosure, since the SmFeN powder having D within the above-described range is used, even with a relatively small amount of the modifying material powder, after heat-treating the sintered body, as shown in FIG. 3A, most of the surface of the SmFeN powder particles can be covered with the modified phase. From this viewpoint, the content ratio of the zinc component in the modifying material powder may be 10% by mass or less, less than 10% by mass, or 9% by mass or less with respect to the mixed powder. 50 When the zinc alloy is represented by Zn-M

[0085] 2 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 step described later. Examples of M that lowers the melting point below that of Zn 2 include elements that form a eutectic alloy with Zn and M 2 Typical examples of such M 2 include Sn, Mg, and Al and combinations thereof. Sn is tin, Mg is magnesium, and Al is aluminum. Regarding the melting point lowering action by these elements and elements that do not inhibit the characteristics of the product, M 2 ​It can be selected as such. Also, inevitable impurity elements refer to impurity elements such as those contained in the raw materials of the modifier powder, which cannot be avoided in terms of their inclusion, or which would cause a significant increase in manufacturing costs to avoid.

[0086] Zn-M 2 In the zinc alloy represented by, Zn and M 2 The ratio (molar ratio) may be appropriately determined so that the sintering temperature is appropriate. The ratio (molar ratio) of M to the entire zinc alloy 2 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.

[0087] In addition to metallic zinc and / or zinc alloy, the modifier powder may optionally contain a substance 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.

[0088] The particle size of the modifier powder is not particularly limited, but it is preferably finer than the particle size of the SmFeN powder. Thereby, the particles of the modifier powder can easily spread among the particles of the SmFeN powder. The particle size of the modifier powder is, for example, D 50 (Median diameter) may be 0.1 μm or more, 0.5 μm or more, or 1.0 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, or 2.0 μm or less. Also, the particle size D of the modifier powder 50 (Median diameter) is measured, for example, by the dry laser diffraction / scattering method.

[0089] When the oxygen content of the modifying material 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 modifying 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, based on the total amount of the modifying material powder. On the other hand, extremely reducing the oxygen content of the modifying material powder leads to an increase in production cost. Therefore, the oxygen content of the modifying material 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 modifying material powder.

[0090] 〈Mixing step〉 The SmFeN powder and the modifying material 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, mechanical fusion, a V-type mixer, and a ball mill. These methods may be combined. The 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.

[0091] 〈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 product (rare earth magnet), and the residual magnetization can be improved.

[0092] 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.

[0093] 〈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, the spark plasma sintering (SPS) method may be used.

[0094] The pressure sintering conditions may be appropriately selected so that the magnetic field formed body can be sintered while pressure is applied to the magnetic field formed body (hereinafter, sometimes referred to as "pressure sintering").

[0095] 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 the zinc component of the modifier powder slightly interdiffuse, contributing to sintering. The interdiffusion may be solid-phase diffusion or liquid-phase diffusion. 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 the zinc component of the modifier powder do not interdiffuse excessively, and it will not cause any hindrance to the subsequent heat treatment process 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.

[0096] 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, 500 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.

[0097] The sintering time may be appropriately determined so that Fe on the particle surface of the SmFeN powder and the zinc component of 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.

[0098] After the sintering time has elapsed, the sintered body is cooled to end the sintering. A faster cooling rate can suppress oxidation of the sintered body, etc. The cooling rate may be, for example, 0.5 - 200°C / second.

[0099] Regarding the sintering atmosphere, an inert gas atmosphere is preferred in order to suppress the oxidation of the magnetic field-formed body and the sintered body. The inert gas atmosphere includes an argon gas atmosphere and a nitrogen gas atmosphere. Alternatively, sintering may be performed in a vacuum.

[0100] 〈Heat Treatment Step〉 The sintered body is heat-treated. As a result, an Fe-Zn alloy phase is formed in a film shape on the surface of the SmFeN powder particles, and the particles of the SmFeN powder and the particles of the modifier powder are more firmly bonded together (hereinafter, this may be referred to as "solidifying" or "solidification"). At the same time, the modification is promoted. And by this modification, demagnetization can be suppressed. Further, when the SmFeN powder contains fine particles, an Fe-Zn alloy phase is formed in almost the entire fine particles, and most of the Fe-Zn alloy phase is integrated with the film-shaped Fe-Zn alloy phase formed on the surface of particles having a relatively large particle size (particles other than fine particles).

[0101] If the heat treatment temperature is 350 °C or higher, a modified phase 20 as shown in Fig. 3A can be obtained. From this viewpoint, the heat treatment temperature x °C may be 360 °C or higher, 370 °C or higher, or 380 °C or higher.

[0102] On the other hand, if the heat treatment temperature is 410 °C or lower, Fe and Zn do not diffuse excessively with each other. However, although solidification, modification, and detoxification of fine particles can be achieved at a heat treatment temperature of 410 °C, since kinks occur, the heat treatment temperature is preferably 400 °C or lower or 390 °C or lower. Note that kink means that the magnetization rapidly decreases with respect to a slight decrease in the magnetic field in a region other than the region showing the coercive force of the magnetization-magnetic field curve (M-H curve).

[0103] There is no particular limitation on the heat treatment time, but the heat treatment time may be determined using the following formulas (1) and (2) with the heat treatment temperature being x °C and the heat treatment time being y hours. y ≧ -0.32x + 136 ··· Formula (1) 350 ≦ x ≦ 410 ··· Formula (2)

[0104] The above formulas (1) and (2) have been confirmed by experiments, and specifically show that the higher the heat treatment temperature, the shorter the heat treatment time with respect to solidification and the formation of the modified phase 20 as shown in FIG. 3A.

[0105] Regarding the formation of the modified phase 20 as shown in FIG. 3A, it is ideal to perform heat treatment until the entire particle surface of the SmFeN powder is covered with the modified phase 20, that is, until 100% of the particle surface of the SmFeN powder is covered with the modified phase 20 (coating rate 100%). However, if heat treatment is performed until 90% or more, 92% or more, 94% or more, 96% or more, or 98% or more of the particle surface of the SmFeN powder is covered with the modified phase 20, it is substantially equivalent to covering the entire particle surface of the SmFeN powder with the modified phase 20. The method for measuring the coating rate will be described in "Rare Earth Magnets".

[0106] From the viewpoint of improving the coating rate of the modified phase 20 as much as possible, in the above formula (1), y≧-0.32x + 137 is more preferable, y≧-0.32x + 140 is even more preferable, and y≧-0.32x + 145 is even more preferable.

[0107] As described above, the modified phase 20 shown in FIG. 3A is formed by alloying the α-Fe phase present on the surface of the SmFeN powder particles and the zinc component in the modifier powder. To form the modified phase 20, the heat treatment time may typically be 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 the α-Fe phase present on the surface of the SmFeN powder particles is limited, and the depth to which the zinc component in the modifier powder diffuses into the SmFeN powder particles is also limited. Therefore, even if heat treatment is performed for an excessively long time, the formation of the modified phase 20 saturates. 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.

[0108] 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 performed in the mold used for pressure sintering. However, in that case, no pressure is applied to the sintered body during the heat treatment. 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 into each other.

[0109] The rare earth magnet obtained by the manufacturing method of the present disclosure described so far will be described below.

[0110] 《Rare Earth Magnet》 As described above, the rare earth magnet of the present disclosure is obtained by sintering SmFeN powder together with a modifier powder containing at least one of metallic zinc and zinc alloy. The SmFeN powder contains Sm, Fe, and N, and at least a part thereof has a magnetic phase having a crystal structure of either Th2Zn 17 type and Th2Ni 17 type. The composition etc. of the magnetic phase are as described in "《Manufacturing Method of Rare Earth Magnet》".

[0111] Since the rare earth magnet of the present disclosure is obtained by sintering SmFeN powder together with a modifier powder containing at least one of metallic zinc and zinc alloy, the content ratio of the zinc component in the rare earth magnet of the present disclosure is substantially equal to the content ratio of the zinc component in the modifier powder with respect to the mixed powder. Further, since the modification phase formed on the surface of the SmFeN powder particles is thin, the D 50 of the SmFeN powder in the rare earth magnet of the present disclosure is substantially equal to the D 50 of the SmFeN powder before sintering. These specific numerical ranges etc. are as described in "《Manufacturing Method of Rare Earth Magnet》".

[0112] In the rare earth magnet of the present disclosure, a modified phase is formed on the surface of the SmFeN powder particles, and the modified phase is an Fe-Zn alloy phase. The modified phase covers 90% or more, 92% or more, 94% or more, 96% or more, or 98% or more of the surface of the SmFeN powder particles. Such a modified phase can suppress demagnetization.

[0113] The coverage rate is measured (investigated) by the following method. In this specification, unless otherwise specified, the description regarding the coverage rate is based on the following measurement method (investigation method).

[0114] The cross-section of the sintered body after heat treatment is polished, and the polished surface is subjected to component analysis (surface analysis) for each of Fe and Zn to obtain an Fe mapping image and a Zn mapping image. The Fe mapping image and the Zn mapping image are superimposed to obtain an integrated mapping image. In the integrated mapping image, the region of the SmFeN powder particles is identified, and the outer peripheral length L of the SmFeN powder particles is measured. In the integrated mapping image, among the outer peripheries of the SmFeN powder particles, the length L of the portion sandwiched between the Fe detection region and the Zn detection region c and the length L of the portion sandwiched between the Fe detection region and the non-detection region g are measured. The non-detection region means a region where neither Fe nor Zn is detected. Then, the coverage rate (%) is calculated from the following formula (3). Coverage rate (%) = L c / (L c + L g ) × 100 ··· Formula (3)

[0115] In the above formula (3), (L c + L g ) means the total peripheral length of the surface of the SmFeN powder particles in the cross-section, and L c means the covered length of the SmFeN powder particle surface.

[0116] 《Modification》 In addition to what has been described so far, the rare earth magnets and their manufacturing methods of the present disclosure can be variously modified within the scope of the content described in the claims.

[0117] For example, when the magnetic powder contains fine particles, as long as D of the magnetic powder satisfies the above-described range before magnetic field forming, a part or all of the fine particles may be removed in advance. 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 molded body (rare earth magnet) can be further increased, and the magnetization can be further increased. 50

Examples

Examples

[0118] Hereinafter, the rare earth magnets and their manufacturing methods of the present disclosure will be described more specifically with reference to Examples and Comparative Examples. Note that the rare earth magnets and their manufacturing methods of the present disclosure are not limited to the conditions used in the following examples.

[0119] 《Preparation of Samples》 Samples of Examples 1 to 4 and Comparative Examples 1 to 3 were prepared as follows.

[0120] 5.0 kg of FeSO4·7H2O was mixed and dissolved in 2.0 kg of pure water. 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 finally, the Fe concentration was adjusted to 0.726 mol / L and the Sm concentration was adjusted to 0.112 mol / L to obtain a SmFeLa sulfuric acid solution.

[0121] [Precipitation Step] The entire amount of the prepared SmFeLa sulfate solution was dropped into 20 kg of pure water kept at a temperature of 40°C for 70 minutes from the start of the reaction while stirring, and at the same time, 15% ammonia solution was dropped to adjust the pH to 7-8. This resulted in a slurry containing SmFeLa hydroxide. The obtained slurry was washed with pure water by decantation, and the hydroxide was separated into solid and liquid. The separated hydroxide was dried in an oven at 100°C for 10 hours.

[0122] [Oxidation process] The hydroxide obtained in the precipitation process was calcined in air at 1000°C for 1 hour. After cooling, red SmFeLa oxide was obtained as raw powder.

[0123] [Pretreatment process] 100 g of SmFeLa oxide was placed in a steel container so that the bulk thickness was 10 mm. The container was placed in a furnace and the pressure was reduced to 100 Pa. Then, the container was heated to the pretreatment temperature of 850°C while introducing hydrogen gas, and was maintained for 15 hours. The oxygen concentration was measured by non-dispersive infrared absorption (ND-IR) (EMGA-820 manufactured by Horiba, Ltd.) and found to be 5 mass%. This revealed that the oxygen bonded to Sm was not reduced, and 95% of the oxygen bonded to Fe was reduced, resulting in a black partial oxide.

[0124] [Reduction process] 60 g of the partial oxide obtained in the pretreatment process and 19.2 g of metallic calcium with an average particle size of about 6 mm were mixed and placed in a furnace. After evacuating the furnace, argon gas (Ar gas) was introduced. The temperature was raised to 1090°C and held for 45 minutes, and then cooled to obtain SmFe powder particles.

[0125] [Nitriding process] Subsequently, the temperature inside the furnace was cooled to 100°C, and then the furnace was evacuated to a vacuum, and while introducing nitrogen gas, the temperature was raised to a first temperature of 430°C 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 lump-shaped product containing magnetic powder particles.

[0126] [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.

[0127] [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.

[0128] 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.

[0129] The SmFeN powder obtained as described above was classified, and the D 50 The particle size distribution of the SmFeN powder after classification was adjusted to 2.00 μm, 3.00 μm, 3.08 μm, and 3.70 μm. Figure 4 is a graph showing the particle size distribution of the SmFeN powder after classification. Classification was performed using a semi-free vortex classifier (A-20 manufactured by Nisshin Engineering Co., Ltd.). 50It is shown in Table 1-1. In Table 1-1, the ratio of SmFeN powder particles (fine particles) having a particle size of 1.00 μm or less for each sample is also shown. The ratio of SmFeN powder particles (fine particles) having a particle size of 1.00 μm or less is the ratio with respect to the total number of SmFeN powder particles.

[0130] As the modifying material 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%.

[0131] The SmFeN powder and the modifying material powder were mixed to obtain a mixed powder. The zinc component content ratio with respect to the entire mixed powder, that is, the mixing amount of the modifying material powder, was as shown in Table 1-1.

[0132] The mixed powder was compression-molded in a magnetic field to obtain a magnetic field molded body. The pressure of the 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.

[0133] The magnetic field molded body was pressure-sintered. Using a high-frequency induction coil, pressure sintering was performed in an argon gas atmosphere (97000 Pa). The sintering temperature was 380 °C, the sintering pressure was 500 MPa, and the application time of the sintering pressure was 5 minutes.

[0134] The sintered body was heat-treated in vacuum (10 -2 Pa). The heat treatment temperature was 380 °C, and the heat treatment time was 24 hours.

[0135] 《Evaluation》 For each sample, the coating rate and magnetic properties were measured. The magnetic properties were measured using a vibrating sample magnetometer (VSM) at room temperature and 120 °C. Demagnetization was evaluated by the magnetic field H r when the residual magnetization B k decreased from 10% magnetization at 120 °C.

[0136] The evaluation results are shown in Tables 1-1 to 1-2 and Figures 5 to 7. In Table 1-2, the residual magnetization and coercive force are the measurement results at room temperature. Figure 5 is a graph showing the demagnetization curves of the samples of Example 1 and Comparative Example 1. Figure 6 is an integrated mapping image of the sample of Example 1. Figure 7 is an integrated mapping image of the sample of Comparative Example 1. In Figures 6 and 7, the darkest part indicates voids.

[0137]

Table 1-1

[0138]

Table 1-2

[0139] From Tables 1-1 and 1-2, in the samples of all examples, H at 120 °C k is 700 kA / m or more, and it can be understood that the rare earth magnet obtained by the manufacturing method of the present disclosure (the rare earth magnet of the present disclosure) can suppress demagnetization.

[0140] On the other hand, in the sample of Comparative Example 1, since the content ratio of the zinc component in the modifier powder is low, the coating rate is low, and as a result, demagnetization cannot be suppressed. In the samples of Comparative Example 2 and Comparative Example 3, although the coating rate is high, demagnetization cannot be suppressed. This is considered to be because, since D of the SmFeN powder particles 50 is large, the SmFeN powder particles have a large number of magnetic domains, and as a result, many magnetic domain walls that cause deterioration of magnetic properties are present in the SmFeN powder particles.

[0141] Also, from Figure 5, it can be understood that, compared with the sample of Comparative Example 1, the sample of Example 1 has a slightly lower residual magnetization (magnetization when the magnetic field is 0), but the demagnetization is gentle. And from Figures 6 and 7, it can be understood that, compared with the sample of Comparative Example 1, the sample of Example 1 has a smaller area of the darkest part, that is, fewer voids, and a higher coating rate of the modified phase of the SmFeN powder particles.

[0142] From the above results, the effects of the rare earth magnet and the method for producing the same according to the present disclosure could be confirmed.

Description of Reference Numerals

[0143] 10 SmFeN powder particles 20 Modified phase 22 Void

Claims

【Claim 1】 Containing Sm, Fe, and N, at least a part of which is Th ２ Zn １７ type and Th ２ Ni １７ Preparing a magnetic powder having a magnetic phase with any one of the crystal structures of the type and Th 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; Pressing and sintering the magnetic field molded body 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 1 minute or more and 30 minutes or less to obtain a sintered body; and Heat-treating the sintered body; including The D of the magnetic powder ５０ is 1.50 μm or more and 3.00 μm or less, in the magnetic powder, the proportion of magnetic powder particles having a particle size of 1.00 μm or less is 1.50% or less with respect to the total number of magnetic powder particles in the magnetic powder; the content ratio of the zinc component in the modifier powder is 6% by mass or more and 10% by mass or less with respect to the mixed powder; the oxygen content of the modifier powder is 5.0% by mass or less; regarding the conditions of the heat treatment, when the temperature and time are x °C and y hours, respectively, y ≥ -0.32x + 136 and 350 ≤ x ≤ 400 are satisfied, the heat treatment is carried out at 350 °C or more and 400 °C or less for 3 hours or more and 40 hours or less, and by the heat treatment, an Fe-Zn alloy phase is formed on 90% or more of the particle surface of the magnetic powder particles, A method for manufacturing a rare earth magnet.

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