Sm-fe-n-based magnet powder, sm-fe-n-based sintered magnet, and production method therefor

Abstract

Provided are Sm-Fe-N-based magnetic powder having high squareness, a Sm-Fe-N-based sintered magnet, and methods for producing the Sm-Fe-N-based magnetic powder and Sm-Fe-N-based sintered magnet. The Sm-Fe-N-based magnetic powder: contains particles containing samarium, iron, and nitrogen, and does not contain particles of an oxide of samarium having a particle diameter of 0.1 μm or more; or the number ratio of particles of an oxide of samarium having a particle diameter of 0.1 μm or more is 10% or less, and does not contain copper or contains 5 ppm or less of copper.

Description

Sm-Fe-N magnetic powder, Sm-Fe-N sintered magnet, and manufacturing method thereof

[0001] The present invention relates to an Sm-Fe-N magnetic powder, an Sm-Fe-N sintered magnet, and methods for producing the same.

[0002] Sm—Fe—N magnets are representative of rare earth-transition metal-nitrogen magnets, and have a high anisotropy field and saturation magnetization. Furthermore, their Curie temperature is relatively higher than other rare earth-transition metal-nitrogen magnets, making them excellent in heat resistance. Sm—Fe—N magnets are among the best magnets.

[0003] Sm—Fe—N magnetic powder is used as the raw material for Sm—Fe—N magnets. An alloy of Sm and Fe is produced, for example, by a reduction-diffusion method using calcium (Ca). Patent Document 1 discloses a method in which Sm—Fe oxide powder and metallic Ca are mixed in a blender, followed by pressing and heating.

[0004] Japanese Patent Application Laid-Open No. 2013-245357

[0005] Available metallic Ca inevitably contains trace amounts of metal elements other than Ca. In the method of mixing metallic Ca with a material containing Sm and Fe, as in Patent Document 1, the above metal elements also enter the resulting Sm—Fe alloy. Contamination in the Sm—Fe alloy reduces the magnetic properties (typically, squareness) of the Sm—Fe—N magnetic powder.

[0006] An object of the present disclosure is to provide an Sm—Fe—N based magnetic powder and an Sm—Fe—N based sintered magnet having high squareness, as well as methods for producing the same.

[0007] According to one aspect of the present disclosure, there is provided an Sm—Fe—N based magnetic powder comprising particles containing samarium, iron, and nitrogen, wherein the powder does not contain samarium oxide particles having a particle size of 0.1 μm or more, or the proportion of samarium oxide particles having a particle size of 0.1 μm or more is 10% or less, and the powder does not contain copper, or contains copper in an amount of 5 ppm or less.

[0008] According to another aspect of the present disclosure, there is provided an Sm—Fe—N sintered magnet comprising a sintered body of a material containing the above-mentioned Sm—Fe—N magnetic powder.

[0009] According to another aspect of the present disclosure, there is provided a method for producing an Sm—Fe—N system magnetic powder, comprising: obtaining an Sm—Fe alloy powder from a precursor powder of an Sm—Fe alloy by a reduction-diffusion method using calcium; nitriding the Sm—Fe alloy powder to obtain an Sm—Fe—N system precursor powder; and washing the Sm—Fe—N system precursor powder with water to obtain an Sm—Fe—N system magnetic powder, wherein in the reduction-diffusion method, calcium vapor is brought into contact with the precursor powder of the Sm—Fe alloy.

[0010] According to another aspect of the present disclosure, there is provided a method for producing an Sm—Fe—N sintered magnet, comprising: obtaining an Sm—Fe alloy powder from a precursor powder of an Sm—Fe alloy by a reduction-diffusion method using calcium; nitriding the Sm—Fe alloy powder to obtain an Sm—Fe—N precursor powder; washing the Sm—Fe—N precursor powder with water to obtain an Sm—Fe—N magnetic powder; and pressure-sintering the Sm—Fe—N magnetic powder, wherein in the reduction-diffusion method, calcium vapor is brought into contact with the precursor powder of the Sm—Fe alloy.

[0011] According to the present disclosure, it is possible to provide an Sm—Fe—N based magnetic powder and an Sm—Fe—N based sintered magnet having high squareness, as well as methods for producing the same.

[0012] 1 is a flowchart showing a method for manufacturing a magnetic powder according to the first embodiment of the present disclosure, and FIG. 2 is a flowchart showing a method for manufacturing a sintered magnet according to the first embodiment of the present disclosure.

[0013] Hereinafter, the Sm—Fe—N magnetic powder and Sm—Fe—N sintered magnet according to the embodiments of the present disclosure will be described in detail together with their manufacturing methods, but the present disclosure is not limited to these embodiments.

[0014] [Embodiment] (Sm—Fe—N based magnetic powder) The Sm—Fe—N based magnetic powder of this embodiment (hereinafter may be simply referred to as magnetic powder) contains particles (hereinafter may be referred to as main phase particles) containing samarium (Sm), iron (Fe), and nitrogen (N). The main phase particles are crystalline particles.

[0015] The main phase grains form the main phase of the magnet. The main phase grains can have any composition consisting of Sm, Fe, and N. The crystal structure of the main phase grains can be, for example, Th. ２ Zn １７ Type, Th ２ Ni １７ Type, ThMn １２ Type: TbCu ７ The crystal structure of the main phase grains is not limited to this, and may be any crystal structure consisting of Sm, Fe, and N. A typical crystal structure of the main phase grains is Sm ２ Fe １７ N ３ It is a structure.

[0016] The magnetic powder does not contain Sm oxide particles with a diameter of 0.1 μm or more, or the number ratio of Sm oxide particles with a diameter of 0.1 μm or more is 10% or less. Sm oxide particles with a diameter of 0.1 μm or more are usually not contained in magnetic powders that have undergone a reduction-diffusion method using Ca. Magnetic powders with a number ratio of Sm oxide particles with a diameter of 0.1 μm or more exceeding 10% can be considered to have not undergone a reduction-diffusion method using Ca. The magnetic powder of this embodiment is manufactured by a method that uses a reduction-diffusion method using Ca. Sm oxide particles with a diameter of less than 0.1 μm can be contained in magnetic powders that have undergone a reduction-diffusion method using Ca. Sm is a metal that is easily oxidized, and Sm oxide particles with a diameter of less than 0.1 μm can be formed, for example, by subsequent oxidation of the magnetic powder.

[0017] The reduction-diffusion method is a method for producing alloys, and involves chemical processes of reduction and diffusion. In the reduction-diffusion method, for example, a reducing agent (typically Ca) is added to a mixture of a transition metal powder such as Fe and an oxide of a rare earth element, and the mixture is heated. This reduces the oxide, causing a diffusion reaction between the rare earth element and the transition metal, resulting in an alloy.

[0018] The number ratio of Sm oxide particles may be 7.0% or less, or may be 3.0% or less.

[0019] The number ratio of Sm oxide particles can be calculated from the cross section of the magnetic powder as follows. First, the magnetic powder is fixed with any appropriate resin (e.g., epoxy resin). Next, the resin is polished to expose the cross section of the magnetic powder. The cross section of the magnetic powder is observed with a scanning electron microscope (SEM-EDS) equipped with an energy dispersive X-ray spectroscopy (EDS) device. The observation field is set to an area in which at least 30 particles can be seen in their entirety. The observation field is, for example, 50 μm × 50 μm. From within the observation field, 30 particles whose entire cross sections can be confirmed are selected, and Sm oxide particles are identified from among these. Sm oxide particles are particles that do not contain Fe atoms. Sm oxide particles contain many oxygen atoms. Sm oxide particles and main phase grains can be distinguished, for example, by the Fe atomic weight and oxygen atomic weight.

[0020] The cross-sectional areas of all identified Sm oxide particles are measured. The diameter of a circle (equivalent circle) having the same area as the measured cross-sectional area is regarded as the particle size of the Sm oxide particle, and the number of Sm oxide particles with a particle size of 0.1 μm or more is determined. The number of Sm oxide particles with a particle size of 0.1 μm or more divided by the total number of particles observed (30) is the number ratio of Sm oxide particles.

[0021] The particles refer to primary particles, and the particle size calculated above is the particle size of the primary particles.

[0022] The Sm oxide is typically Sm ２ O ３ and SmO.

[0023] The magnetic powder does not contain copper (Cu) or contains Cu at 5 ppm or less. This indicates low contamination. One cause of contamination is trace amounts of metal elements contained in the Ca-containing material (typically, metallic Ca) used in the reduction-diffusion method. Metallic Ca usually contains 30 ppm or more of Cu. Although the magnetic powder of this embodiment is produced through a reduction-diffusion method using metallic Ca, the Cu content is low. This is thought to result in high squareness.

[0024] The Cu content may be 4.9 ppm or less, 4.8 ppm or less, or 4.5 ppm or less.

[0025] The Cu content can be measured by inductively coupled plasma mass spectrometry (ICP-MS).

[0026] Squareness is evaluated by the squareness ratio Hk / Hcj. The squareness ratio Hk / Hcj is the ratio of the coercive force Hcj to the magnitude of the reverse magnetic field Hk at which the remanence Br is 90% in the J-H demagnetization curve. The closer the squareness ratio Hk / Hcj is to 1, the higher the squareness. High squareness means that when a reverse magnetic field is applied to the magnetic powder, gradual demagnetization is less likely to occur until the reverse magnetic field becomes equal to the coercive force Hcj. High squareness indicates excellent performance as a magnetic material. The coercive force Hcj is a physical quantity that indicates the magnitude of the magnetic field in the opposite direction required to demagnetize a material magnetized in a certain direction.

[0027] The demagnetization curve can be measured using a vibrating sample magnetometer (VSM). ｃ and residual magnetic flux density Br can be evaluated.

[0028] The squareness ratio Hk / Hcj of the magnetic powder of this embodiment is, for example, 22% or more, or 24% or more.

[0029] The magnetic powder also contains a small amount of calcium (Ca). A small Ca content improves the remanence Br. The magnetic powder contains no Ca or 0.1% by mass or less of Ca. The Ca content may be 0.08% by mass or less, 0.065% by mass or less, or 0.055% by mass or less.

[0030] The content of Ca element can be measured by inductively coupled plasma atomic emission spectrometry (ICP-AES).

[0031] The magnetic powder contains no oxygen or 0.8% by mass or less of oxygen. Having an oxygen content of 0.8% by mass or less means that the formation of a film containing oxides and / or hydroxides (hereinafter sometimes simply referred to as an "oxide film") on the surface of the magnetic powder is suppressed. Therefore, decomposition of the main phase by the oxide film is suppressed during the sintering process, resulting in a sintered magnet with higher coercivity. The oxygen content of the magnetic powder may be 0.70% by mass or less, 0.30% by mass or less, or 0.10% by mass or less.

[0032] The oxygen content can be measured by inert gas fusion-non-dispersive infrared absorption (NDIR).

[0033] The average particle size of the magnetic powder is 0.5 μm or more and 5 μm or less. The average particle size of the magnetic powder may be 4.0 μm or less, 3.5 μm or less, or 3.0 μm or less, in order to further increase the coercive force of the resulting magnet. The average particle size of the magnetic powder may be 1.0 μm or more, in order to suppress superparamagnetism. A small average particle size also contributes to improved squareness.

[0034] The "average particle size" of a powder refers to the particle size (D50) at the point where the cumulative value reaches 50% on a cumulative curve obtained by calculating the particle size distribution on a volume basis and setting the total volume to 100%. The average particle size can be measured using a laser diffraction / scattering particle size / particle size distribution measuring device or a scanning electron microscope.

[0035] The magnetic powder contains main phase grains and may contain Sm oxide particles. The proportion of Sm oxide particles with a particle size of 0.1 μm or more is small, and Sm oxide particles with a particle size of less than 0.1 μm have little effect on the measurement of the average particle size. The average particle size of the magnetic powder can be regarded as the average particle size of the main phase grains.

[0036] The coercive force Hcj of the magnetic powder may be 800 kA / m or more, 850 kA / m or more, or 900 kA / m or more.

[0037] The saturation magnetization Js due to the mass magnetic susceptibility of the magnetic powder is 120 A m ３ / kg or more, and 130 A m ３ / kg or more.

[0038] (Sm—Fe—N based sintered magnet) The Sm—Fe—N based sintered magnet is obtained by sintering (firing) a magnetic material containing the above-mentioned magnetic powder at a high temperature. The Sm—Fe—N based sintered magnet includes a sintered body of a magnetic material containing the above-mentioned magnetic powder. In the present disclosure, a sintered magnet refers to a magnet obtained by sintering a magnetic material at a high temperature.

[0039] Because the magnetic powder has a low Cu content, the resulting sintered magnet has high squareness. The squareness ratio Hk / Hcj of the sintered magnet is, for example, 22% or more, 24% or more, 28% or more, or 30% or more.

[0040] The magnetic material may consist essentially of Sm—Fe—N magnetic powder, but may also contain one or more other materials, such as a magnetic powder consisting of a rare earth element other than Sm, Fe, and N, or a magnetic powder consisting of a rare earth element including Sm, a transition metal element other than Fe, and N. Examples of rare earth elements other than Sm include lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), and ytterbium (Yb). Examples of transition metal elements other than Fe include cobalt (Co), chromium (Cr), titanium (Ti), Zr (zirconia), niobium (Nb), and tungsten (W). The Sm—Fe—N sintered magnet of this embodiment may contain trace elements that are inevitably mixed in, such as carbon (C), silicon (Si), aluminum (Al), nickel (Ni), and manganese (Mn).

[0041] The coercive force Hcj of the sintered magnet may be 650 kA / m or more, 700 kA / m or more, or 750 kA / m or more.

[0042] The saturation magnetization Js due to the mass magnetic susceptibility of the sintered magnet is 120 A m ３ / kg or more, and 130 A m ３ / kg or more.

[0043] (Method for Manufacturing Sm—Fe—N Magnetic Powder) Sm—Fe—N magnetic powder can be manufactured by a method comprising the steps of obtaining Sm—Fe alloy powder from a precursor powder of an Sm—Fe alloy by a reduction-diffusion method using calcium, nitriding the Sm—Fe alloy powder to obtain an Sm—Fe—N precursor powder, and washing the Sm—Fe—N precursor powder with water to obtain the Sm—Fe—N magnetic powder. In the reduction-diffusion method, calcium vapor is brought into contact with the precursor powder of the Sm—Fe alloy. FIG. 1 is a flowchart showing the method for manufacturing a sintered magnet in embodiment 1.

[0044] (Method for Manufacturing Sm—Fe—N Sintered Magnet) An Sm—Fe—N sintered magnet can be manufactured by a method comprising the steps of obtaining an Sm—Fe alloy powder from an Sm—Fe alloy precursor powder by a reduction-diffusion method using calcium, nitriding the Sm—Fe alloy powder to obtain an Sm—Fe—N precursor powder, washing the Sm—Fe—N precursor powder with water to obtain an Sm—Fe—N magnetic powder, and pressure-sintering the Sm—Fe—N magnetic powder. In the reduction-diffusion method, calcium vapor is brought into contact with the Sm—Fe alloy precursor powder. FIG. 2 is a flowchart showing the method for manufacturing a sintered magnet according to the first embodiment.

[0045] All manufacturing processes for the magnetic powder and sintered magnet are carried out in an atmosphere with a low oxygen concentration of 2 ppm or less by volume, which may be 1 ppm or less, or 0.5 ppm or less.

[0046] All of the above steps are carried out, for example, in a glove box purged with an inert gas (one or a mixture of two or more gases such as nitrogen, argon, and helium), preferably in a glove box connected to a gas circulation type oxygen and moisture purifier.

[0047] Other steps performed after the nitriding treatment and before the pressure firing (for example, (5) orientation and magnetization, which will be described later) are also performed in the above-mentioned low-oxygen concentration atmosphere.

[0048] However, for material handling purposes, it is permissible to place the Sm--Fe--N magnetic powder in an air atmosphere while immersed in an organic solvent capable of preventing oxidation between the time of washing and the time of pressure firing.

[0049] The reduction-diffusion method is carried out by bringing Ca vapor into contact with the precursor powder of the Sm—Fe alloy in a heating furnace, whereby a reduction reaction and alloying occur.

[0050] According to the above method, the amounts of Ca and Cu contained in the magnetic powder are reduced. When the saturated vapor pressure of Ca is reached in the heating furnace, metallic Ca does not appear to evaporate until it is consumed by the reduction reaction (until the air pressure in the heating furnace drops). In other words, the above method is thought to suppress excessive contact between metallic Ca and Sm compounds, thereby reducing the contamination of the magnetic powder with Ca and Cu. Unreacted Ca vapor, for example, solidifies and adheres to the inner wall of the heating furnace, preventing it from being mixed into the container containing the precursor powder. Because Cu has a low vapor pressure, theoretically, Cu does not migrate to the sample powder in methods using Ca vapor.

[0051] In the conventional method of mixing powders, more metallic Ca than necessary is usually used to efficiently induce the reduction reaction. As a result, there is a large amount of excess metallic Ca, and a large amount of unreacted Ca remains in the alloy powder. In addition, other metal elements (typically Cu) contained in the metallic Ca are likely to be mixed into the alloy powder.

[0052] Residual Ca and by-products (e.g., CaO) in the alloy powder are usually removed by washing with water after nitriding. Washing with water can increase the oxygen content of the precursor powder and degrade the magnetic properties of the resulting magnetic powder. According to this embodiment, since there is little Ca remaining in the alloy powder, the washing time and frequency can be shortened. Therefore, the oxygen content of the magnetic powder can also be reduced. The Ca contained in the magnetic powder is mainly unreacted Ca that remains without being removed. Cu cannot be removed by washing with water.

[0053] (1) Preparation of Alloy Powder (S11) In this embodiment, an alloy powder containing Sm and Fe (Sm—Fe alloy) is prepared by a reduction diffusion method using its precursor powder.

[0054] In the Sm—Fe alloy powder, the amount of Sm relative to the total amount of Sm and Fe may be, for example, 9 atm % or more and 14 atm % or less, and the average particle size of the alloy powder may be, for example, 1 μm or more and 50 μm or less.

[0055] Examples of precursor powders for Sm—Fe alloys include a mixed powder of Sm compound powder, iron powder, and iron oxide powder, Sm—Fe-based oxide powder, and Sm—Fe-based hydroxide powder. The precursor powder is prepared, for example, by a coprecipitation method. The precursor powder may be pre-reduced in a reducing atmosphere. The pre-reducing step is performed, for example, by heating the precursor powder to 400° C. or higher in a hydrogen atmosphere.

[0056] The reduction-diffusion method is carried out by bringing Ca vapor into contact with a precursor powder of an Sm—Fe alloy in a heating furnace. Specifically, the precursor powder of the Sm—Fe alloy and metallic Ca are placed in a heating furnace so as not to come into contact with each other (for example, by storing them in separate containers). The heating furnace is then heated in an inert gas atmosphere to generate Ca vapor.

[0057] The Sm compound contained in the precursor powder is reduced by Ca and reacts with Fe to obtain Sm—Fe alloy powder. The heating time may be, for example, 1 hour or more and 10 hours or less.

[0058] (2) Crushing, Pulverization, and Classification: Prior to the nitriding treatment and washing, the Sm—Fe alloy may be crushed or pulverized, and then classified as necessary. Fine powder is removed from the crushed powder by classification. Crushing, pulverization, and classification are carried out under conditions such that the average particle size of the resulting Sm—Fe—N magnetic powder is 0.5 μm or more and 5 μm or less.

[0059] Crushing or grinding can be carried out using, but is not limited to, an agate mortar, a jet mill (airflow grinding type, etc.), a ball mill, etc. Examples of airflow grinding type jet mills include, but are not limited to, the MC44 manufactured by Micromachinazione. Classification can be carried out using, but is not limited to, an airflow classifier, etc.

[0060] (3) Nitriding (S12) Nitriding is typically performed by heat treatment in a nitrogen atmosphere or a mixed atmosphere of ammonia and hydrogen, thereby incorporating nitrogen into the crystals of the alloy powder to obtain a Sm—Fe—N precursor powder.

[0061] When nitrogen gas is used, the partial pressure of nitrogen may be 10 kPa or more and 100 kPa or less, and the heating time may be 5 hours or more and 30 hours or less. When a mixed gas of ammonia and hydrogen is used, the partial pressure of ammonia may be 20 kPa or more and 40 kPa or less, and the heating time may be 10 minutes or more and 50 minutes or less, when the total pressure of the mixed gas is 0.1 MPa.

[0062] In the nitriding treatment, the heating temperature is preferably 350° C. or higher and 500° C. or lower, more preferably 400° C. or higher and 500° C. or lower. By using this heating temperature, it is possible to prevent decomposition into SmN and Fe, which may occur when the nitriding reaction is carried out at a higher temperature, and it is possible to allow the reaction to proceed more sufficiently compared to when the nitriding reaction is carried out at a lower temperature.

[0063] The nitriding treatment can typically be carried out under atmospheric pressure, for example, at a pressure of 900 hPa or more and 1,100 hPa or less, more preferably 950 hPa or more and 1,050 hPa or less.

[0064] (4) Washing (S13) The Sm—Fe—N precursor powder is washed with water. By-products (CaO, unreacted Ca, etc.) contained in the Sm—Fe—N precursor powder can be physically removed by washing. By-products can also be removed by chemical reaction with water. For example, Ca reacts with water to become calcium hydroxide, which dissolves in water.

[0065] The washing is carried out, for example, by putting the Sm—Fe—N precursor powder into water and stirring it, and then stopping the stirring to remove the resulting precipitate and drying it to obtain the Sm—Fe—N magnetic powder.

[0066] Washing may be performed multiple times. For example, the Sm—Fe—N precursor powder is placed in water, stirred, and then allowed to stand, the supernatant liquid is removed, and new water is added. The above-described procedure may then be repeated a desired number of times. The stirring time may be 1 minute or more and 30 minutes or less. The number of repetitions may be 2 to 10 times.

[0067] Between such washings, the magnetic powder may be washed with acetic acid or hydrochloric acid, etc. This will further remove any remaining Ca.

[0068] Drying can be performed by evacuation. The degree of vacuum may be, for example, -95 kPa or less. The treatment time may be, for example, 1 hour or more and 10 hours or less. The inside of the vacuum device is maintained in a low-oxygen atmosphere, and may be at a vacuum of, for example, 5 Pa or less, or may be filled with an inert gas atmosphere, or an inert gas may be flowed in under reduced pressure.

[0069] (5) Filling: The resulting material containing the Sm—Fe—N magnetic powder is filled into a mold. (3) After the nitriding treatment (S12), the process up to at least this filling step is carried out in an atmosphere with a low oxygen concentration, where the volumetric oxygen concentration is 2 ppm or less. The mold used may have any shape, and for example, a cylindrical mold can be used, but is not limited thereto.

[0070] (6) Magnetic Field Compaction Before pressure sintering, the magnetic material may be compacted in a magnetic field. Magnetic field compaction is a process of compacting a magnetic material while applying a magnetic field. For magnetic field compaction, for example, a powder press equipped with a magnetic field generator is used. By compacting in a magnetic field, the easy magnetization axis of the Sm—Fe—N magnetic powder is aligned, resulting in higher magnetic properties.

[0071] The conditions for the magnetic field molding are not particularly limited. The magnetic field to be applied may be, for example, a static magnetic field of 1 T or more (or even 2 T or more), or a pulsed magnetic field. The magnetic field molding may be performed on a magnetic material filled in a mold.

[0072] (7) Pressure Sintering (S14) The material containing the Sm—Fe—N magnetic powder packed into the mold is pressure sintered. This produces a Sm—Fe—N sintered magnet. The treatment (e.g., pressure sintering) after the Sm—Fe—N magnetic powder is packed into the mold may be performed while the Sm—Fe—N magnetic powder is immersed in an organic solvent capable of preventing oxidation.

[0073] Any pressure sintering method, including electric pressure sintering, can be used for the pressure sintering. Pressure sintering may be performed, for example, by hot pressing or electric sintering. Hot pressing is a common sintering method in which heating is performed while applying pressure in an inert atmosphere such as Ar. Electric sintering is a method in which a certain pressure is applied to a mold and an electric current is applied while maintaining this pressure. The interior of the pulse electric sintering machine is maintained in a vacuum of, for example, 5 Pa or less. The applied pressure may be higher than atmospheric pressure and may be a pressure capable of forming a sintered magnet, for example, in the range of 100 MPa to 2000 MPa. Electric sintering is performed, for example, at a temperature of 400°C to 600°C for a time of 30 seconds to 10 minutes.

[0074] Although the embodiments of the present disclosure have been described in detail above, the present disclosure is not limited to these. The above embodiments can be modified in design without departing from the spirit and scope of the present disclosure.

[0075] In the above-described embodiment, the magnetic powder and sintered magnet are produced in a low-oxygen atmosphere with a volumetric oxygen concentration of 2 ppm or less, but the oxygen concentration is not limited to this and may be, for example, 10 ppm or less.

[0076] In the above-described embodiment, the first container having an opening for containing the Sm—Fe alloy precursor powder and the second container for containing the Ca-containing compound are arranged so that the opening of the first container is located below the opening of the second container, but this is not limiting. The positional relationship between the first container and the second container is not particularly limited, and the opening of the first container may be located above the opening of the second container, or the openings of the first container and the second container may be located on approximately the same plane.

[0077] In the above-described embodiment, metallic Ca is used as the Ca-containing substance, but the Ca-containing substance is not limited to this. ２ Examples include:

[0078] In the above-described embodiment, a sintered magnet is manufactured, but the present invention is not limited to this. The magnetic powder of the above-described embodiment can be used to manufacture a bonded magnet.

[0079] Hereinafter, the present disclosure will be described in more detail with reference to examples. However, the present disclosure is not limited to the following examples, and it is of course possible to carry out the present disclosure by making appropriate modifications within the scope applicable to the above and below-described aims, and all such modifications are included in the technical scope of the present disclosure.

[0080] Example 1 (i) Preparation of Alloy Powder by Reduction-Diffusion Method 0.5 g of a mixed powder (alloy precursor powder) of samarium oxide powder and iron powder and 1.14 g of metallic Ca (Cu content: 33 ppm) with an average particle size of 2 mm were placed in separate containers and placed in a heating furnace. Each container was positioned so that the opening of the container containing the alloy precursor powder was closer to the bottom of the heating furnace than the opening of the container containing metallic Ca. After evacuating the heating furnace, argon gas was introduced. The temperature was raised to 950°C and maintained for 5 hours to prepare a Sm—Fe alloy.

[0081] (ii) Crushing The obtained Sm-Fe alloy was crushed in an agate mortar to obtain Sm-Fe alloy powder having an average particle size of 4.83 μm.

[0082] (iii) Nitriding Treatment The obtained Sm-Fe alloy powder was heat treated at 475° C. for 23 hours in a nitrogen atmosphere to obtain a Sm-Fe-N based precursor powder.

[0083] (iv) Washing: The obtained Sm—Fe—N-based precursor powder was poured into washing water and stirred for 10 minutes. After leaving it to stand, the supernatant was drained by decantation. This process was repeated three times. After solid-liquid separation, the powder was vacuum dried for one hour to obtain a magnetic powder.

[0084] (v) Filling: 0.2 g of the magnetic powder obtained was immersed in heptane to prepare a slurry, which was then filled into a cemented carbide mold.

[0085] (vi) Pressure sintering: The mold was placed in a pulse current sintering machine equipped with a servo-controlled press mechanism. Next, a pressure of 1500 MPa was applied to the sintered magnet in an Ar atmosphere maintained at 20 Pa. While maintaining this pressure, the magnet was subjected to current sintering at 400°C for 2 minutes, yielding a sintered magnet.

[0086] In Example 1, the processes from (ii) crushing to (v) filling were carried out in a glove box (substituted with nitrogen) connected to a gas circulation type oxygen and moisture purifier. The oxygen concentration in the glove box was set to 1 ppm or less. The sample was moved between each device so as not to be exposed to the atmosphere. (vi) Pressurized firing was carried out in an Ar atmosphere.

[0087] Comparative Example 1 A sintered magnet was obtained in the same manner as in Example 1, except that 3.25 g of a mixed powder of samarium oxide powder and iron powder was mixed with 0.48 g of metallic calcium having an average particle size of 2 mm, and the mixture was placed in the same container and placed in a heating furnace.

[0088] [Evaluation] (Cu Content) The Cu content of the Sm—Fe—N magnetic powder was measured using inductively coupled plasma mass spectrometry (ICP-MS).

[0089] (Ca Content) The Ca content of the Sm-Fe-N magnetic powder was measured using inductively coupled plasma atomic emission spectroscopy (ICP-AES).

[0090] (Number Proportion of Sm Oxide Particles) The cross section of the magnetic powder was observed by SEM-EDS, and the number proportion of Sm oxide particles with a particle size of 0.1 μm or more among 30 particles selected arbitrarily within the observation field was calculated as described above.

[0091] (Oxygen Content) The oxygen content of the Sm-Fe-N magnetic powder was measured by inert gas fusion-non-dispersive infrared absorption method (NDIR method).

[0092] (Average Particle Size) The average particle size (D50) of the Sm-Fe-N magnetic powder was measured using a laser diffraction particle size distribution measuring device (MT3000 manufactured by Microtrac Bell).

[0093] (Magnetic Properties) The magnetic properties (coercive force, mass magnetic susceptibility, and squareness ratio) of the Sm-Fe-N magnetic powder and sintered magnet were measured using a vibrating sample magnetometer (VSM).

[0094]

[0095] The Sm—Fe—N based sintered magnets of the present disclosure can be used in a wide range of applications in the field of various motors, such as in-vehicle accessory motors and main motors for electric vehicles (EVs) and hybrid electric vehicles (HEVs), and more specifically, in oil pump motors, electric power steering motors, and EV / HEV drive motors.

[0096] This application claims priority based on Japanese Patent Application No. 2024-150909, filed on September 2, 2024, the entire contents of which are incorporated herein by reference.

Claims

1. A Sm-Fe-N magnetic powder containing particles containing samarium, iron, and nitrogen, which does not contain samarium oxide particles with a particle size of 0.1 μm or more, or the number ratio of samarium oxide particles with a particle size of 0.1 μm or more is 10% or less, and which does not contain copper or contains copper at 5 ppm or less.

2. The Sm-Fe-N magnetic powder according to claim 1, which does not contain calcium or contains calcium in an amount of 0.1 mass % or less.

3. The Sm-Fe-N magnetic powder according to claim 1 or 2, which does not contain oxygen or contains oxygen in an amount of 0.8 mass % or less.

4. The Sm-Fe-N magnetic powder according to any one of claims 1 to 3, having an average particle size of 0.5 μm or more and 5 μm or less.

5. Ratio of Squareness H ｋ / H ｃｊ The Sm—Fe—N based magnetic powder according to any one of claims 1 to 4, wherein the content of Sm—Fe—N is 22% or more.

6. A Sm-Fe-N sintered magnet comprising a sintered body of a material containing the Sm-Fe-N magnetic powder according to any one of claims 1 to 5.

7. Ratio of Squareness H ｋ / H ｃｊ The Sm—Fe—N sintered magnet according to claim 6, wherein the content of Sm—Fe—N is 24% or more.

8. A method for producing Sm-Fe-N magnetic powder, comprising: obtaining Sm-Fe alloy powder from Sm-Fe alloy precursor powder by a reduction-diffusion method using calcium; nitriding the Sm-Fe alloy powder to obtain Sm-Fe-N precursor powder; and washing the Sm-Fe-N precursor powder with water to obtain Sm-Fe-N magnetic powder, wherein the reduction-diffusion method involves bringing calcium vapor into contact with the Sm-Fe alloy precursor powder.

9. A method for producing a Sm-Fe-N sintered magnet, comprising: obtaining Sm-Fe alloy powder from a precursor powder of an Sm-Fe alloy by a reduction-diffusion method using calcium; nitriding the Sm-Fe alloy powder to obtain a Sm-Fe-N precursor powder; washing the Sm-Fe-N precursor powder with water to obtain a Sm-Fe-N magnetic powder; and pressure-sintering the Sm-Fe-N magnetic powder, wherein the reduction-diffusion method involves bringing calcium vapor into contact with the precursor powder of the Sm-Fe alloy.

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