Sm-Fe-N-based magnets

Abstract

To provide an Sm-Fe-N system magnet which is highly dense and has significantly suppressed reduction in coercive force compared to the state of Sm-Fe-N system powder.SOLUTION: An Sm-Fe-N system magnet includes Sm-Fe-N particles and an interparticle metal phase present between the Sm-Fe-N particles, the Sm-Fe-N system particles have an average particle diameter of less than 2.0 μm, and the number of particles having an aspect ratio of 2.0 or more is 10% or less, and the interparticle metal phase includes Fe3Zn10 phase and a granular α-Fe phase, and the proportion of the Fe3Zn10 phase in the intergranular metal phase is 80% or more in area ratio.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to Sm-Fe-N-based magnets.

Background Art

[0002] Sm-Fe-N-based magnets are expected to be high-performance magnets because they have a high Curie temperature of 477 °C, a small temperature change in magnetic properties, and a high anisotropy magnetic field of 20.6 MA / m, which is the theoretical limit value of coercivity.

[0003] Patent Document 1 describes a method for producing fine Sm-Fe-N-based powder by subjecting a precursor powder of Sm-Fe alloy to reduction diffusion to form alloy powder and then nitriding it.

[0004] Here, in order to produce a high-performance magnet from magnetic powder with high coercivity, it is necessary to sinter the Sm-Fe-N-based powder.

[0005] However, when the Sm-Fe-N-based powder is sintered at a high temperature, there is a problem that the magnetic properties deteriorate. In particular, due to the sintering treatment, the coercivity of the Sm-Fe-N-based magnet greatly decreases.

[0006] Also, Patent Document 2 proposes suppressing a decrease in the coercivity of a magnet obtained after sintering by coating the surface of the Sm-Fe-N-based powder with a secondary phase containing a metal such as zirconium.

Prior Art Documents

Patent Documents

[0007]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0008] Generally, Sm-Fe-N-based magnets are manufactured by sintering Sm-Fe-N-based powder under pressure. However, when sintering Sm-Fe-N-based magnets under pressure conditions, there is a problem that the coercivity of the magnet significantly decreases compared to the coercivity in the powder state, and it is difficult to obtain a Sm-Fe-N-based magnet that achieves both denseness and coercivity.

[0009] The present invention has been made in view of such a background, and an object of the present invention is to provide a Sm-Fe-N-based magnet having high denseness and significantly suppressed decrease in coercivity compared to the state of Sm-Fe-N-based powder.

Means for Solving the Problems

[0010] In the present invention, a Sm-Fe-N-based magnet, Sm-Fe-N-based particles, and an inter-particle metal phase existing between the Sm-Fe-N-based particles, and having the Sm-Fe-N-based particles have an average particle diameter of less than 2.0 μm, and the number of Sm-Fe-N-based particles having an aspect ratio of 2.0 or more is 10% or less, the inter-particle metal phase contains Fe 3 Zn 10 phases and granular α-Fe phases, the ratio of the Fe 3 Zn 10 phase in the inter-particle metal phase is 80% or more in terms of area ratio, and a Sm-Fe-N-based magnet is provided.

Effects of the Invention

[0011] In the present invention, it is possible to provide a Sm-Fe-N-based magnet having high denseness and significantly suppressed decrease in coercivity compared to the state of Sm-Fe-N-based powder.

Brief Description of the Drawings

[0012]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

MODE FOR CARRYING OUT THE INVENTION

[0013] Hereinafter, one embodiment of the present invention will be described.

[0014] As described above, when sintering a Sm-Fe-N type powder in a pressurized state, it has been recognized that the coercive force of the magnet significantly decreases compared to the coercive force in the powder.

[0015] Therefore, it is necessary to sinter a Sm-Fe-N type magnet with a Sm-Fe-N type powder in an unpressurized state. However, with such a manufacturing method, it is difficult to obtain a sufficiently dense Sm-Fe-N type magnet.

[0016] In contrast, in one embodiment of the present invention, as will be described in detail hereinafter, it is possible to provide an Sm-Fe-N-based magnet having high tightness and significantly suppressing a decrease in coercive force as compared with the state of Sm-Fe-N-based powder.

[0017] That is, In one embodiment of the present invention, an Sm-Fe-N-based magnet, Sm-Fe-N-based particles, and an interparticle metal phase existing between the Sm-Fe-N-based particles, having, wherein the Sm-Fe-N-based particles have an average particle diameter of less than 2.0 μm, and the number of Sm-Fe-N-based particles having an aspect ratio of 2.0 or more is 10% or less, and the interparticle metal phase contains 3 Fe 10 Zn phases and granular α-Fe phases, and the ratio of the 3 Fe 10 Zn

[0018] phase in the interparticle metal phase is 80% or more in terms of area ratio, there is provided an Sm-Fe-N-based magnet.

[0019] Here, in the present application, the area ratio of each phase in the interparticle metal phase is an average value obtained by image analysis of a cross-sectional photograph. Specifically, Sm-Fe-N-based particles, an interparticle metal phase, an oxide phase, voids, etc. are identified by a backscattered electron image of a scanning electron microscope (FE-SEM) of a cross-section of an exposed sample or an energy-dispersive X-ray spectroscopy (EDS) mapping image, and the area ratio of the target phase is obtained by image analysis. The area ratio is obtained by averaging the area ratios obtained from each of 20 cross-sectional photographs of a field of view containing 20 or more Sm-Fe-N-based particles.

[0020] In the Sm-Fe-N-based magnet according to one embodiment of the present invention, an interparticle metal phase is disposed between the Sm-Fe-N-based particles. This interparticle metal phase has an Fe 3 Zn 10 phase of 80% or more in terms of area ratio and granular α-Fe phases.Generally, when granular α-Fe exists on the surface of Sm-Fe-N-based particles, when a magnetic field is applied to the Sm-Fe-N-based particles, the magnetization of the Sm-Fe-N-based particles is reversed by this α-Fe, and the coercivity of the magnet decreases.

[0021] However, in one embodiment of the present invention, the granular α-Fe phase is not on the surface of the Sm-Fe-N-based particles but is arranged in the interparticle metal phase. That is, the granular α-Fe phase does not adjoin the Sm-Fe-N-based particles and occupies most of the interparticle metal phase with Fe 3 Zn 10 being in contact with the Sm-Fe-N-based particles through the phase.

[0022] In such a form, it becomes difficult for the magnetization to reverse due to the α-Fe phase. Also, for this reason, even when a magnet is manufactured by pressure-sintering Sm-Fe-N-based particles, a decrease in coercivity can be significantly suppressed.

[0023] Also, the Sm-Fe-N-based magnet according to one embodiment of the present invention can be manufactured by subjecting Sm-Fe-N-based particles to a pressure-sintering process. For this reason, in one embodiment of the present invention, a sufficiently dense Sm-Fe-N-based magnet can be manufactured.

[0024] (Sm-Fe-N-based magnet according to one embodiment of the present invention) Hereinafter, with reference to the drawings, one embodiment of the present invention will be described in more detail.

[0025] FIG. 1 schematically shows an example of a partial cross-section of an Sm-Fe-N-based magnet (hereinafter referred to as the "first magnet") 100 according to one embodiment of the present invention.

[0026] As shown in FIG. 1, the first magnet 100 has a plurality of Sm-Fe-N-based particles 110 that are mutually bonded.

[0027] Also, the first magnet 100 has an interparticle metal phase 120 formed between the Sm-Fe-N-based particles 110.

[0028] The inter-particle metal phase 120 mainly contains Fe 3 Zn 10 phase 130 and the granular α-Fe phase 140 existing in the Fe 3 Zn 10 phase 130.

[0029] In the inter-particle metal phase 120, Fe 3 Zn 10 The proportion (area ratio) occupied by phase 130 is 80% or more. On the other hand, in the inter-particle metal phase 120, the area ratio of the granular α-Fe phase 140 is, for example, 10% or less.

[0030] In the inter-particle metal phase 120, the granular α-Fe phase 140 is 3 Zn 10 covered by phase 130. Therefore, due to the above-mentioned effect, in the first magnet 100, by disposing such an inter-particle metal phase 120 between the Sm-Fe-N-based particles 110, a decrease in coercive force can be significantly suppressed.

[0031] Moreover, since the first magnet 100 having such a configuration can be manufactured by pressure sintering Sm-Fe-N-based powder, it has significantly high density.

[0032] For example, the first magnet 100 may have a residual magnetic flux density of 4.8 kG or more.

[0033] (Details of each part in the Sm-Fe-N-based magnet according to an embodiment of the present invention) Next, each part included in the Sm-Fe-N-based magnet according to an embodiment of the present invention will be described in more detail.

[0034] Here, each part included in the Sm-Fe-N-based magnet according to an embodiment of the present invention will be described by taking the above-mentioned first magnet 100 as an example. Therefore, when representing each part, the reference numerals shown in FIG. 1 are used.

[0035] (Sm-Fe-N-based particles 110) The Sm-Fe-N-based particles 110 are particles containing samarium, iron, and nitrogen.

[0036] The Sm-Fe-N-based particles 110 may have other additional elements. The additional element may be at least one selected from the group consisting of rare earth elements (excluding samarium) such as neodymium and praseodymium, and cobalt.

[0037] Note that the total content of the additional element is preferably less than 30 at% from the viewpoints of the anisotropy magnetic field and magnetization.

[0038] The average particle diameter of the Sm-Fe-N-based particles 110 is preferably less than 2.0 μm. When the average particle diameter of the Sm-Fe-N-based particles 110 is less than 2.0 μm, the coercivity of the Sm-Fe-N-based magnet becomes higher.

[0039] In the magnet according to an embodiment of the present invention, the ratio of the Sm-Fe-N-based particles 110 having an aspect ratio of 2.0 or more is preferably 10% or less, and more preferably 8% or less. When the ratio of the Sm-Fe-N-based particles 110 having an aspect ratio of 2.0 or more is 10% or less, the coercivity of the magnet according to an embodiment of the present invention becomes higher. Further, the average particle diameter of the Sm-Fe-N-based particles 110 is preferably larger than 0.1 μm. When the average particle diameter of the Sm-Fe-N-based particles 110 is 0.1 μm or less, it becomes difficult to suppress the oxidation of the Sm-Fe-N-based particles, and heterophases are likely to occur in the magnet according to an embodiment of the present invention.

[0040] The amount of oxygen contained in the Sm-Fe-N-based particles 110 is, for example, 1 wt% or less. When the oxygen content increases, heterophases are likely to occur in the magnet according to an embodiment of the present invention.

[0041] (Inter-particle metal phase 120) As described above, Fe contained in the inter-particle metal phase 120 3 Zn 10 The area ratio of the phase 130 is 80% or more. Fe 3 Zn 10The area ratio of phase 130 is preferably 82% or more.

[0042] On the other hand, the area ratio of the granular α-Fe phase 140 contained in the interparticle metal phase 120 is, for example, 10% or less, preferably 5% or less.

[0043] The average particle diameter of the α-Fe phase 140 is, for example, in the range of 5 nm or more and 500 nm or less, preferably in the range of 30 nm or more and 300 nm or less.

[0044] In the present application, the average particle diameter of the granular α-Fe phase 140 means the average of the measured values of 30 particles.

[0045] The interparticle metal phase 120 is a phase in which the content rate of metal elements such as iron (Fe) and zinc (Zn) excluding rare earth elements, oxygen, carbon, nitrogen, etc. is 80 at% or more. Further, in the first magnet 100, in addition to the Sm-Fe-N-based particles 110 and the interparticle metal phase 120, another phase such as an oxide, a nitride, and / or a carbide may be included.

[0046] (Other features) In the Sm-Fe-N-based magnet according to one embodiment of the present invention, a coating layer may be formed on at least a part of the surface of the Sm-Fe-N-based particles 110.

[0047] The coating layer is mainly composed of an Sm-Fe-Zn phase. The content of Zn in the coating layer is, for example, in the range of 1 at% or more and 20 at% or less, preferably in the range of 5 at% or more and 15 at% or less.

[0048] Further, the coating layer may have a thickness in the range of, for example, 1 nm or more and 100 nm or less, preferably in the range of 20 nm or more and 50 nm or less. In the present application, the "thickness of the coating layer" means the average of the measured values obtained for 20 Sm-Fe-N-based particles 110.

[0049] Note that the coating layer does not necessarily have to be disposed over the entire surface of the Sm-Fe-N-based particles 110. That is, the coating layer may be intermittently or locally disposed on a part of the surface of the Sm-Fe-N-based particles 110.

[0050] The amount of Zn contained in the Sm-Fe-N-based magnet according to one embodiment of the present invention is, for example, in the range of 1 wt% to 20 wt%.

[0051] Also, the amount of oxygen contained in the Sm-Fe-N-based magnet according to one embodiment of the present invention is, for example, less than 1 wt%, and preferably less than 0.8 wt%.

[0052] (Method for manufacturing an Sm-Fe-N-based magnet according to one embodiment of the present invention) Next, with reference to FIG. 2, the method for manufacturing an Sm-Fe-N-based magnet according to one embodiment of the present invention will be described in more detail.

[0053] FIG. 2 schematically shows an example of the flow of a method for manufacturing an Sm-Fe-N-based magnet according to one embodiment of the present invention (hereinafter referred to as the "first method").

[0054] As shown in FIG. 2, the first method includes a step of preparing an Sm-Fe-N-based magnet powder (step S110), a step of mixing Zn powder with the magnet powder to prepare a mixed powder (step S120), a step of molding the mixed powder to obtain a molded body (step S130), a step of pressure-sintering the molded body (step S140), and

[0055] Hereinafter, each step will be described.

[0056] (Step S110) First, an Sm-Fe-N-based magnet powder is prepared.

[0057] The method for manufacturing the magnet powder is not particularly limited.

[0058] Hereinafter, an example of a method for manufacturing magnet powder will be described with reference to FIG. 3.

[0059] FIG. 3 schematically shows the flow of a method for manufacturing Sm-Fe-N-based magnet powder.

[0060] As shown in FIG. 3, this method for manufacturing magnet powder includes a step (S10) of producing a precursor powder of a samarium-iron (Sm-Fe) alloy, a step (S20) of reducing and diffusing the precursor powder in an inert gas atmosphere to produce Sm-Fe alloy powder, a step (S30) of nitriding the Sm-Fe alloy powder to produce Sm-Fe-N alloy powder, a step (S40) of washing the Sm-Fe-N alloy powder, and has.

[0061] Hereinafter, each step will be briefly described.

[0062] (Step S10) First, a precursor powder of a Sm-Fe alloy is produced.

[0063] The precursor powder may be, for example, Sm-Fe-based oxide powder or Sm-Fe-based hydroxide powder. Hereinafter, Sm-Fe-based oxide powder and Sm-Fe-based hydroxide powder are also collectively referred to as Sm-Fe-based (hydro)oxide powder.

[0064] The precursor powder may be produced, for example, by a coprecipitation method. In this method, first, a precipitating agent such as an alkali is added to a solution containing a samarium salt and an iron salt to precipitate, and then the precipitate is recovered by filtration, centrifugation, etc. Next, after washing and drying the precipitate, the precipitate is pulverized to obtain Sm-Fe-based (hydro)oxide powder.

[0065] Note that when the Sm-Fe-N-based magnet powder contains metallic iron, its magnetic properties deteriorate. Therefore, when producing the precursor powder, it is preferable to add samarium in an amount in excess of the stoichiometric ratio.

[0066] The counter ions in the samarium salt and iron salt may be inorganic ions such as chloride ions, sulfate ions, nitrate ions, etc., or organic ions such as alkoxides.

[0067] As the solvent contained in the solution containing the samarium salt and iron salt, water can be used, but an organic solvent such as ethanol may also be used.

[0068] As the alkali, hydroxides of alkali metals and alkaline earth metals, and ammonia can be used. Further, a compound that decomposes by an external action such as heat of urea or the like and exhibits an action as a precipitating agent may be used.

[0069] The obtained precursor powder may then be handled in an environment where the atmosphere is blocked, such as a glove box, until the Sm-Fe-N-based magnet powder is manufactured. When using an inert gas atmosphere, the oxygen concentration is preferably 1 ppm or less.

[0070] The obtained precursor powder is preferably pre-reduced in a reducing atmosphere. Thereby, the amount of calcium used in the subsequent reduction diffusion step (step S20) can be reduced, and the generation of coarse Sm-Fe-based alloy particles can be suppressed.

[0071] The pre-reduction of the precursor powder may be carried out, for example, by heating the precursor powder to 400 °C or higher in a hydrogen atmosphere. The treatment temperature is preferably in the range of 500 °C to 800 °C. When pre-reduction is carried out in this temperature range, a powder of Sm-Fe-based alloy with uniform particle size can be obtained.

[0072] (Step S20) Next, the precursor powder is subjected to a reduction diffusion treatment in an inert gas atmosphere.

[0073] As a method for reduction diffusion of the precursor powder, for example, the precursor powder is mixed with calcium (Ca) or calcium hydride (CaH 2After mixing with (), methods such as heating to a temperature above the melting point of Ca (about 842 °C) can be mentioned.

[0074] During this treatment, Sm reduced by Ca diffuses in the Ca melt and reacts with Fe, thereby forming Sm-Fe alloy powder.

[0075] There is a correlation between the temperature of the reduction diffusion treatment and the particle size of the Sm-Fe alloy powder. The higher the temperature of the reduction diffusion, the larger the particle size of the Sm-Fe alloy powder.

[0076] The average particle size of the Sm-Fe alloy powder is preferably less than 2.0 μm. When the average particle size of the Sm-Fe alloy powder is less than 2.0 μm, the coercivity of the magnet becomes even higher. The average particle size of the Sm-Fe alloy powder is more preferably greater than 0.1 μm and less than 2.0 μm.

[0077] In order to obtain Sm-Fe alloy powder with uniform particle size, it is preferable to perform reduction diffusion treatment on the precursor powder at 850 °C to 1050 °C for about 1 minute to 2 hours in an inert gas atmosphere.

[0078] As the reduction diffusion progresses in the precursor, crystallization progresses and Sm-Fe alloy powder is formed. In the obtained Sm-Fe alloy powder, a Sm-rich phase is formed on at least a part of the surface of each particle.

[0079] In the Sm-Fe alloy powder, the proportion of particles with an aspect ratio of 2.0 or more is preferably 10% or less, and more preferably 8% or less. When the proportion of particles with an aspect ratio of 2.0 or more is 10% or less, the coercivity of the magnet powder becomes even higher.

[0080] The residual oxygen content in the Sm-Fe alloy powder obtained after step S20 is preferably less than 1.0 wt%. When the residual oxygen content of the Sm-Fe alloy powder is less than 1.0 wt%, the coercivity of the magnet becomes even higher.

[0081] (Step S30) Next, the obtained Sm-Fe-based alloy powder is nitrided.

[0082] Examples of the method for nitriding the Sm-Fe-based alloy powder include heat-treating the Sm-Fe-based alloy powder at 300°C to 500°C in an atmosphere such as ammonia, a mixed gas of ammonia and hydrogen, nitrogen, or a mixed gas of nitrogen and hydrogen.

[0083] When ammonia is used, it is possible to nitride the Sm-Fe-based alloy powder in a short time. However, the nitrogen content in the Sm-Fe-N-based magnet powder may become higher than the optimum value. In this case, after nitriding the Sm-Fe-based alloy powder, it is preferable to anneal it in hydrogen. Thereby, excess nitrogen can be discharged from the crystal lattice.

[0084] By the nitriding treatment, Sm-Fe-N-based alloy powder is formed.

[0085] The composition of the particles contained in the Sm-Fe-N-based alloy powder is preferably Sm 2 Fe 17 N 3 in this case.

[0086] For example, in an ammonia-hydrogen mixed atmosphere, the Sm-Fe-based alloy powder is heat-treated at 350°C to 450°C for 10 minutes to 2 hours, and then annealed at 350°C to 450°C for 30 minutes to 2 hours in a hydrogen atmosphere. Thereby, the nitrogen content in the Sm-Fe-N-based magnet powder can be optimized.

[0087] (Step S40) Next, the Sm-Fe-N-based alloy powder formed in Step S30 is washed.

[0088] The Sm-Fe-N-based alloy powder formed in Step S30 contains a calcium compound. The washing treatment is carried out to remove such a calcium compound.

[0089] The cleaning treatment is carried out using a cleaning liquid such as water and / or alcohol. Alternatively, the cleaning liquid may be an acid such as sulfuric acid amide. Alternatively, after cleaning the Sm-Fe-N based alloy powder with water and / or alcohol, cleaning may be further performed using sulfuric acid amide. The temperature of the cleaning liquid is not particularly limited, but it is preferable to select a temperature at which the solubility of CaO and Ca(OH) 2 is high. For example, when the cleaning liquid is water, it is preferably from 0°C to room temperature.

[0090] Note that the cleaning process may be carried out before the nitriding treatment.

[0091] The cleaned Sm-Fe-N based alloy powder is preferably dried thereafter.

[0092] The drying temperature is not particularly limited, but it is preferably from room temperature to 100°C. By setting the drying temperature to 100°C or lower, oxidation of the Sm-Fe-N based alloy powder can be suppressed.

[0093] Also, a dehydrogenation treatment may be carried out on the Sm-Fe-N based alloy powder. By the dehydrogenation treatment, hydrogen that has penetrated between the crystal lattices during the cleaning treatment can be removed.

[0094] The method of the dehydrogenation treatment is not particularly limited. For example, the dehydrogenation treatment may be carried out by heating the Sm-Fe-N based alloy powder under vacuum or in an inert gas atmosphere. For example, the dehydrogenation treatment may be carried out by heat-treating the Sm-Fe-N based alloy powder at 150°C to 250°C for 1 hour under a vacuum atmosphere.

[0095] By the above steps, the Sm-Fe-N based alloy powder can be produced. The residual oxygen amount in the alloy powder is less than 1 wt%.

[0096] Note that the average particle diameter of the obtained Sm-Fe-N based alloy powder is preferably larger than 0.1 μm and less than 2.0 μm.

[0097] The residual oxygen content is preferably 1.0 wt% or less, and more preferably less than 0.8 wt%.

[0098] (Step S120) Next, Zn powder is mixed with the Sm-Fe-N-based magnet powder produced by the aforementioned method to prepare a mixed powder.

[0099] The average particle diameter of the Zn powder is, for example, in the range of 5 μm to 100 μm. In particular, the average particle diameter of the Zn powder is preferably larger than that of the Sm-Fe-N-based magnet powder.

[0100] The mixing amount of the Zn powder is not particularly limited, but for example, it may be in a ratio of 1 wt% or more and 20 wt% or less with respect to the entire mixed powder.

[0101] The method for mixing the Sm-Fe-N-based magnet powder and the Zn powder is not particularly limited, but it is preferable to mix them so that no physical damage occurs on the surface of each particle of the Sm-Fe-N-based magnet powder. For example, it is preferable to avoid methods such as mixing by a ball mill and crushing.

[0102] (Step S130) Next, the mixed powder is molded to form a molded body.

[0103] The molding is preferably carried out in a magnetic field application environment such as a static magnetic field. When molding in a static magnetic field, a molded body in which the easy magnetization axis of the magnet particles is oriented along the static magnetic field can be obtained, and an anisotropic magnet can be obtained after sintering.

[0104] For example, a molded body is obtained by applying a static magnetic field to the mixed powder in a mold and pressing the mixed powder with the mold.

[0105] The pressure exerted by the mold on the mixed powder may be, for example, 10 MPa or more and 3000 MPa or less. For uniform diffusion of Zn, the pressure is preferably 500 MPa or less.

[0106] The strength of the magnetic field applied to the mixed powder may be 400 kA / m or more and 3000 kA / m or less.

[0107] (Step S140) Next, the compact is sintered under a pressure state.

[0108] By the sintering treatment, the Zn particles contained in the compact dissolve. The dissolved Zn spreads so as to cover the Sm-Fe-N based magnet powder during the sintering process, and finally, a magnet having the above-described form can be manufactured.

[0109] The pressure sintering treatment may be carried out, for example, by a spark plasma method, a hot press method, or a resistance pressure sintering method. Among these, the resistance pressure sintering method, which can achieve low heat load sintering by high-speed heating and short-time sintering, is preferable.

[0110] The sintering conditions may be appropriately set according to the composition of the magnet to be manufactured, the average particle diameter of the powder contained, and the like.

[0111] The sintering process may have a temperature rising process and a temperature holding process following the temperature rising process, or may have only the temperature rising process.

[0112] The temperature reached in the temperature rising process may be, for example, 420°C or more and 600°C or less.

[0113] The heating rate in the temperature rising process may be, for example, 5°C / min or more and 100°C / min or less.

[0114] The sintering time in the temperature holding process is, for example, 5 hours or less, and may be 0 hours.

[0115] The heating method of the compact is not particularly limited. The compact may be sintered by resistance heating, electric current heating, or high-frequency heating.

[0116] The compact may be pressurized, for example, while being placed in a mold.

[0117] The pressing pressure is, for example, in the range of 1 GPa to 2 GPa, preferably in the range of 1.2 GPa to 1.5 GPa.

[0118] Note that the application of pressure may start from room temperature. Alternatively, the application of pressure may start after the temperature of the compact reaches near the melting point of Zn (for example, around 420 °C).

[0119] The atmosphere for the sintering treatment is, for example, a nitrogen atmosphere, an argon atmosphere, or a vacuum (reduced pressure atmosphere). The oxygen concentration and the moisture concentration in the atmosphere are preferably 1 ppm or less, respectively, and more preferably 0.5 ppm or less, respectively. Note that these concentrations are in mole fraction.

[0120] After the sintering treatment, the sintered body may be cooled. The cooling rate of the sintered body may be, for example, 5 °C / min or more and 100 °C / min or less.

[0121] By the above steps, an Sm-Fe-N-based magnet having the above-described characteristics can be manufactured.

Examples

[0122] Hereinafter, examples of the present invention will be described. In the following description, Examples 1 to 4 are examples, and Examples 11 to 12 are comparative examples.

[0123] (Example 1) An Sm-Fe-N-based magnet was manufactured by the following method.

[0124] (Preparation of mixed powder) First, a mixed powder was prepared by the following method.

[0125] (Preparation of Sm-Fe-(hydro)oxide powder) 64.64 g of iron(III) nitrate nonahydrate and 12.93 g of samarium(III) nitrate hexahydrate were dissolved in 800 ml of water. After stirring, 120 ml of a 2 mol / L potassium hydroxide aqueous solution was added dropwise. Then, the mixture was stirred overnight at room temperature to prepare a suspension. Next, the suspension was filtered, and the filtrate was washed. After that, it was dried overnight at 120 °C in an air atmosphere using a hot air oven. Next, the filtrate was coarsely pulverized with a blade mill and then finely pulverized in ethanol using a rotary mill with stainless steel balls. Next, the filtrate finely pulverized in ethanol was centrifuged and then dried under vacuum to produce Sm-Fe-(hydr)oxide powder.

[0126] (Pre-reduction) The Sm-Fe-(hydr)oxide powder was pre-reduced by heat treatment at 600 °C for 6 hours in a hydrogen atmosphere to produce a powder (referred to as powder A).

[0127] (Reductive diffusion) 5.0 g of powder A and 2.5 g of calcium powder were placed in an iron crucible and subjected to reductive diffusion by heating at 900 °C for 1 hour to produce a powder (referred to as powder B).

[0128] (Nitriding) After cooling powder B to room temperature, it was heated to 380 °C in a hydrogen atmosphere. Next, it was heated to 420 °C in an ammonia-hydrogen mixed atmosphere with a volume ratio of 1:2 and held for 1 hour to nitride powder B.

[0129] Next, it was annealed at 420 °C for 1 hour in a hydrogen atmosphere and then annealed at 420 °C for 0.5 hour in an argon atmosphere to optimize the nitrogen content in the powder. As a result, powder C was obtained.

[0130] (Washing) Powder C was washed 5 times with pure water. After adding washed powder C and an aqueous amidosulfuric acid solution to adjust the pH to 5 and holding for 15 minutes, the calcium compound was removed. Next, powder C was washed with pure water to remove amidosulfuric acid. As a result, powder D was obtained.

[0131] (Vacuum drying) After replacing the water remaining in Powder D with 2-propanol, it was dried under vacuum at room temperature.

[0132] The vacuum-dried Powder D was dehydrogenated at 200 °C for 3 hours under vacuum.

[0133] Note that the processes after pre-reduction were carried out in a glove box under an argon atmosphere without exposure to the atmosphere.

[0134] Through the above processes, Sm-Fe-N-based magnet powder (hereinafter referred to as "Powder E") was obtained.

[0135] (Evaluation of Powder E) At this stage, various evaluations of the obtained Powder E were carried out.

[0136] (Evaluation of Coercivity) The coercivity of Powder E was measured using the following method.

[0137] First, after mixing Powder E and a thermoplastic resin, it was oriented in a magnetic field of 20 kOe to prepare a sample for measuring the powder coercivity. Next, using a vibrating sample magnetometer (VSM), the coercivity of the sample for measuring the powder coercivity was measured. The measurement temperature was 27 °C, and the maximum applied magnetic field was 90 kOe.

[0138] As a result of the measurement, the coercivity of the sample for measuring the powder coercivity was 32.2 kOe.

[0139] (Measurement of Average Particle Size) Powder E and a thermosetting epoxy resin were kneaded and thermally cured. Then, by irradiating with a focused ion beam (FIB) for etching, the cross-section was exposed to prepare a sample.

[0140] Using a field emission scanning electron microscope (FE-SEM), the cross-section of the sample was observed, and contour lines were drawn for more than 200 randomly extracted particles.

[0141] The contour line corresponds to the surface of the particle and / or the surface of the contacting particles. However, the contacting particles can be distinguished by FE-SEM backscattered electron images or energy-dispersive X-ray spectroscopy (EDS) mapping.

[0142] Next, the diameter of a circle with the same area as the region surrounded by the contour line is defined as the particle diameter of the particle. By volume-weighted averaging the particle diameters of these particles, the average particle diameter of Powder E was calculated.

[0143] The average particle diameter of Powder E was 1.4 μm.

[0144] (Preparation of Mixed Powder) Next, Powder E (i.e., Sm-Fe-N-based magnet powder) and Zn powder were slowly mixed by a V-type mixer to prepare a mixed powder.

[0145] The addition amount of Zn powder was 10 wt% based on the whole mixed powder. The average particle diameter of Zn powder is 6 μm to 9 μm.

[0146] The prepared mixed powder is referred to as "Mixed Powder 1".

[0147] (Fabrication of Magnet) Next, Mixed Powder 1 was molded by the following method, and the obtained molded body was sintered to fabricate a magnet.

[0148] The molding pressure was 200 MPa.

[0149] The pressure of the molded body during the sintering process was 1200 MPa. Note that the pressure application was carried out from room temperature. The sintering temperature of the molded body was 470 °C, and the sintering time was 5 minutes.

[0150] Thereby, a sintered magnet was obtained. The obtained sintered magnet is referred to as "Magnet 1".

[0151] (Example 2) A sintered magnet was produced in the same manner as in Example 1. However, in this Example 2, the application of pressure during the sintering process started when the temperature of the green compact reached 470°C. Other manufacturing conditions were the same as in the case of Example 1.

[0152] The obtained sintered magnet is referred to as "Magnet 2".

[0153] (Example 3) A sintered magnet was produced in the same manner as in Example 2. However, in this Example 3, the addition amount of Zn powder in the mixed powder was 5 wt%. Other manufacturing conditions were the same as in the case of Example 2.

[0154] The obtained sintered magnet is referred to as "Magnet 3".

[0155] (Example 4) A sintered magnet was produced in the same manner as in Example 2. However, in this Example 4, the addition amount of Zn powder in the mixed powder was 20 wt%. Other manufacturing conditions were the same as in the case of Example 2.

[0156] The obtained sintered magnet is referred to as "Magnet 4".

[0157] (Example 11) A sintered magnet was produced in the same manner as in Example 1. However, in this Example 11, Zn powder was not added to Powder E, and Powder E was directly formed and sintered to produce a magnet.

[0158] The obtained sintered magnet is referred to as "Magnet 11".

[0159] (Example 12) A sintered magnet was produced in the same manner as in Example 2. However, in this Example 12, during the preparation of the mixed powder, Powder E and Zn powder were dispersed and mixed using a ball mill device. Other manufacturing conditions were the same as in the case of Example 2.

[0160] The obtained sintered magnet is referred to as "Magnet 12".

[0161] Table 1 below summarizes the manufacturing conditions of each magnet.

[0162]

Table 1

[0163] (Shape Evaluation of Sm-Fe-N Based Particles) For each magnet, the average particle diameter of the Sm-Fe-N based particles contained therein was measured. Also, the aspect ratio of the Sm-Fe-N based particles was evaluated.

[0164] The average particle diameter of the Sm-Fe-N based particles was measured in the same manner as in the case of measuring the average particle diameter of the aforementioned Particle E, except that the cross-section was exposed by irradiating the cut magnet with a focused ion beam (FIB) and performing etching to prepare a sample.

[0165] Also, the aspect ratio was evaluated as follows.

[0166] For each particle, a quadrilateral that circumscribes the contour line and has the minimum area was defined. The aspect ratio of each particle was calculated by dividing the length of the long side of the obtained quadrilateral by the length of the short side. Furthermore, the ratio of particles having an aspect ratio of 2 or more was evaluated.

[0167] (Evaluation of Inter-Particle Metal Phase) For each magnet, the inter-particle metal phase formed between the Sm-Fe-N based particles was evaluated.

[0168] Fig. 4 shows the mapping results of Zn, Fe, and Sm obtained by energy dispersive X-ray spectroscopy (EDS) analysis of the cross-section of Magnet 2.

[0169] From Fig. 4, it can be seen that there is a region in the inter-particle metal phase that does not contain Sm but contains both Zn and Fe. Also, it can be seen that granular Fe components are dispersed in the inter-particle metal phase.

[0170] Figure 5 shows the electron diffraction image of the interparticle metal phase part of the cross-section of magnet 2. Figure 6 shows the TEM image of the analysis location. Further, Figure 7 shows the EDS mapping result of Zn in the region shown in Figure 6.

[0171] In Figure 6, the locations indicated by marks "*1" and "*2" respectively correspond to the diffraction images "(1)" and "(2)" in Figure 5. Also, from the comparison between Figure 7 and Figure 6, it can be seen that the locations represented by marks "*1" and "*2" in Figure 6 are both Zn-rich regions in the interparticle metal phase.

[0172] From Figure 4, in the interparticle metal phase, the Zn-rich region is composed of Fe 3 Zn 10 phase as can be seen.

[0173] In the interparticle metal phase, the area ratios occupied by the Fe 3 Zn 10 phase and the granular α-Fe phase were evaluated by image analysis. As described above, the results obtained from 20 cross-sectional photographs of the field of view containing 20 or more Sm-Fe-N-based particles were averaged to obtain the area ratio.

[0174] (Evaluation of the surface of Sm-Fe-N-based particles) Twenty Sm-Fe-N-based particles were selected, and the thickness of the coating layer (Sm-Fe-Zn phase) formed on the surface of each particle was measured. These measurement results were averaged to obtain the average thickness of the coating layer.

[0175] Also, in the 20 selected Sm-Fe-N-based particles, the amount of Zn contained in the coating layer was determined by EDS. These measurement results were averaged to obtain the average value of the amount of Zn contained in the coating layer.

[0176] (Measurement of the amount of Zn in the magnet) The amount of Zn contained in the entire magnet was evaluated by the high-frequency inductively coupled plasma (ICP) emission analysis method.

[0177] (Measurement of Residual Oxygen Content in Magnet) For each magnet, the residual oxygen content was evaluated by the inert gas fusion-non-dispersive infrared absorption method.

[0178] (Evaluation of Coercive Force and Residual Flux Density) The coercive force of each magnet was measured using a vibrating sample magnetometer (VSM). The measurement temperature was 27 °C and the maximum applied magnetic field was 90 kOe.

[0179] Also, using the same apparatus, the residual flux density in each magnet was measured.

[0180] The evaluation results for each magnet are summarized in Table 2 below.

[0181] [Table 2] As shown in Table 2, in Magnets 1 to 3, an inter-particle metal phase was formed in all cases, and it was found that the inter-particle metal phase contained an Fe 3 Zn 10 phase and a granular α-Fe phase. The area ratio of the Fe 3 Zn 10 phase in the inter-particle metal phase was 82% or more in all cases, and the area ratio of the granular α-Fe phase was 9% or less in all cases.

[0182] On the other hand, in Magnet 12, although an inter-particle metal phase was formed, the area ratio of the Fe 3 Zn 10 phase contained therein was 55%.

[0183] In Magnets 11 and 12, the coercive force was at most 19.1 kOe, which was significantly lower than the coercive force of Powder E, which was 32.2 kOe.

[0184] On the other hand, in Magnets 1 to 3, the coercive force was 20.5 kOe or more in all cases, indicating that the decrease in coercive force was significantly suppressed. Also, the residual flux density was 4.8 kG or more in all cases, confirming that relatively dense magnets were formed.

Explanation of Symbols

[0185] 100 Sm-Fe-N-based magnet 110 Sm-Fe-N-based particles 120 Inter-particle metal phase 130 Fe 3 Zn 10 Phase 140 Granular α-Fe phase

Claims

1. An Sm-Fe-N-based magnet, comprising: Sm-Fe-N-based particles; and an inter-particle metal phase existing between the Sm-Fe-N-based particles, wherein the Sm-Fe-N-based particles have an average particle diameter of less than 2.0 μm, and the number of Sm-Fe-N-based particles having an aspect ratio of 2.0 or more is 10% or less, and The inter-particle metal phase contains Fe ３ Zn １０ phase and granular α-Fe phase, and The Fe in the inter-particle metal phase ３ Zn １０ The proportion of the phase is 80% or more in terms of area ratio, the oxygen content is less than 1.0 wt%.

2. The Sm-Fe-N-based magnet according to claim 1, wherein the ratio of the α-Fe phase in the inter-particle metal phase is 10% or less in terms of area ratio.

3. A Sm-Fe-Zn-based coating layer is formed on at least a part of the surface of the Sm-Fe-N-based particles, and the Zn content in the coating layer is in the range of 1 at% or more and 20 at% or less.

4. The Sm-Fe-N-based magnet according to claim 3, wherein the coating layer has an average thickness of 1 nm or more and 100 nm or less.

5. The Sm-Fe-N-based magnet according to any one of claims 1 to 4, wherein the Zn content contained in the Sm-Fe-N-based magnet is 1 wt% or more and 20 wt% or less.

Images