Sm-Fe-N-based magnetic powder with good magnetic field orientation and method for producing the same

Abstract

The present invention provides an Sm-Fe-N-based magnetic powder that exhibits good magnetic field orientation and excellent SFD reduction effects after magnetic field orientation treatment. [Solution] A powder consisting of particles mainly composed of Sm, Fe, and N, wherein the molar ratio of Sm to Fe (Sm / Fe) is 0.09 or more and 0.25 or less, and the molar ratio of N to Fe (N / Fe) is 0.06 or more and 0.30 or less, and the cumulative 50% particle size in the volume-based particle size distribution by laser diffraction-scattering method D 50 The size is between 0.5 μm and 5.0 μm, and the Th2Zn is determined by Rietveld analysis in the X-ray diffraction pattern using Co-Kα rays. 17 A Sm-Fe-N magnetic powder having a March coefficient of 0.90 or higher on the (220) plane of the type crystal structure.

Description

[Technical Field]

[0001] The present invention relates to an Sm-Fe-N-based magnetic powder with good magnetic field orientation, in which the particles are easily rotated by a magnetic field, and to a method for producing the same. [Background technology]

[0002] Sm2Fe 17 A substance in which nitrogen has been introduced into an intermetallic compound (a typical chemical formula is Sm2Fe) 17 N3) is known to be a ferromagnetic material exhibiting excellent hard magnetism. In this specification, Sm2Fe 17 A powder of a ferromagnetic material obtained by introducing nitrogen into an Sm-Fe alloy at or near its stoichiometric composition is called "Sm-Fe-N magnetic powder." Sm-Fe-N magnetic powder is useful as a material for bonded magnets and sintered magnets.

[0003] Regarding Sm-Fe-N magnetic powders, various studies have been conducted on particle shape and particle size distribution to improve magnetic properties when used in bonded magnets and sintered magnets. For example, Patent Document 1 discloses a technology for producing anisotropic Sm-Fe-N magnetic powder with low oxygen concentration, small average particle diameter, and narrow particle size distribution by reduction-diffusion. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2020-102606 [Overview of the Initiative] [Problems that the invention aims to solve]

[0005] In the manufacturing process of bonded magnets and sintered magnets, a "magnetic field orientation" treatment is performed on magnetic powder by applying a magnetic field to align the magnetization direction of the particles as much as possible. In this specification, the powder characteristic that indicates how easily the magnetization direction of powder particles aligns in a certain direction when a magnetic field is applied, i.e., how easily it is magnetic field oriented, is called "magnetic field orientation property." Good magnetic field orientation property means that the powder has the property of being easily oriented by a magnetic field. SFD (Switching field distribution) is an index that can be used to know the degree of particle orientation (i.e., how well the magnetization direction is aligned) in powder that has undergone magnetic field orientation treatment. SFD is sometimes called "coercivity distribution" or "reversing field distribution." The SFD of magnetic powder is the half-width of the differential curve of the magnetic hysteresis curve (MH curve) = coercivity H c It is defined as the value obtained by dividing by [a certain factor]. In powders with good magnetic field orientation, the SFD after magnetic field orientation treatment becomes small, resulting in high magnetic properties when bonded magnets or sintered magnets are constructed.

[0006] While conventional Sm-Fe-N magnetic powders have been known to incorporate improvements in particle size distribution and particle size, such as those described in Patent Document 1, there was still room for improvement regarding magnetic field orientation. The present invention aims to provide an Sm-Fe-N magnetic powder that exhibits good magnetic field orientation and excellent SFD reduction effects after magnetic field orientation treatment. [Means for solving the problem]

[0007] The above objective is achieved by the following invention. [1] A powder having a composition in which particles mainly composed of Sm, Fe, and N have a molar ratio of Sm to Fe (Sm / Fe) of 0.09 or more and 0.25 or less, and a molar ratio of N to Fe (N / Fe) of 0.06 or more and 0.30 or less, and the cumulative 50% particle size in the volume-based particle size distribution by laser diffraction-scattering method D 50 The size is between 0.5 μm and 5.0 μm, and the Th2Zn is determined by Rietveld analysis in the X-ray diffraction pattern using Co-Kα rays. 17 A Sm-Fe-N magnetic powder having a March coefficient of 0.90 or higher on the (220) plane of the type crystal structure.

[0008] The Sm-Fe-N-based magnetic powder of [1] above can be manufactured, for example, by the following method. [2] A gas atomization step of obtaining a powder of a Sm-Fe-based alloy having a Sm / Fe molar ratio of 0.09 or more and 0.25 or less by a gas atomization method, After heating and holding the powder obtained in the gas atomization step at a temperature of 250°C or more and 500°C or less in a hydrogen gas atmosphere, and then heating it at a temperature of 900°C or more and 1200°C or less, a heat treatment step of coarsening the crystal grains of the particles of the powder, A pulverization step of pulverizing the powder of the Sm-Fe-based alloy whose crystal grains have been coarsened by the heat treatment step, thereby making the particles of the powder finer by fracture including intragranular fracture, A nitriding step of introducing nitrogen into the particles of the powder by heating and holding the powder of the Sm-Fe-based alloy made finer by the pulverization step in a non-oxidizing gas atmosphere containing a nitrogen compound or nitrogen at a temperature range of 500°C or less, A method for producing a Sm-Fe-N-based magnetic powder, comprising: [3] A surface treatment step of forming a fatty acid film on the particle surface of the powder after the nitriding step, The method for producing a Sm-Fe-N-based magnetic powder according to [2] above, further comprising:

Advantages of the Invention

[0009] According to the present invention, a Sm-Fe-N-based magnetic powder having good magnetic field orientation and excellent in the effect of reducing SFD after magnetic field orientation treatment has been realized. This Sm-Fe-N-based magnetic powder can contribute to the high performance of bonded magnets and sintered magnets using the Sm-Fe-N-based magnetic powder due to its good magnetic field orientation.

Brief Description of the Drawings

[0010] [Figure 1] A diagram schematically showing the configuration of the gas atomization apparatus used in the examples. [Figure 2] A diagram schematically showing the cross-sectional structure near the bottom of the crucible of the gas atomization apparatus used in the examples. [Figure 3] Graph showing the relationship between the March coefficient of the (220) plane and the SFD after magnetic field orientation for the Sm-Fe-N-based magnetic powder obtained in the examples and comparative examples.

Mode for Carrying Out the Invention

[0011] [Composition of Powder] In the present invention, a powder composed of particles mainly containing Sm (samarium), Fe (iron), and N (nitrogen), and having a composition in which the molar ratio Sm / Fe of Sm to Fe is 0.09 or more and 0.25 or less, and the molar ratio N / Fe of N to Fe is 0.06 or more and 0.30 or less is targeted. "Particles mainly containing Sm, Fe, and N" means particles in which the top three elements in the order of the content of the elements contained in the particles in terms of mass ratio are occupied by the three elements Sm, Fe, and N.

[0012] The magnetic phase in the Sm-Fe-N-based magnetic powder is mainly a magnetic phase in which N (nitrogen) atoms are introduced into the crystal lattice of Sm2Fe with a Th2Zn 17 type crystal structure. It is considered that N atoms enter the interstitial positions of the Sm2Fe 17 crystal lattice, and the Th2Zn 17 type crystal structure is maintained even after the introduction of N atoms. When N atoms are introduced into Sm2Fe 17 the crystal magnetic anisotropy changes from in-plane type to uniaxial type and the Curie point rises, becoming a practical magnet material. As is well known, a typical composition of Sm-Fe-N-based magnetic powder with excellent magnetic properties is Sm2Fe 17 N3. The Sm / Fe molar ratio in the Sm2Fe 17 N3 composition is 0.118, and the N / Fe molar ratio is 0.176. In Sm2Fe 17 N3 composition, the Sm / Fe molar ratio is 0.118 and the N / Fe molar ratio is 0.176. When N atoms are introduced into Sm2Fe 17While composition closer to the stoichiometric composition of N3 is considered advantageous in terms of magnetic properties, hard magnetism is also observed in surrounding compositional ranges. This invention focuses on Sm-Fe-N magnetic powders with a compositional range of Sm / Fe molar ratio between 0.09 and 0.25, and N / Fe molar ratio between 0.06 and 0.30, considering the achievement of good hard magnetism. A more preferable range for the Sm / Fe molar ratio is 0.10 to 0.20, and a more preferable range for the N / Fe molar ratio is 0.11 to 0.27. Note that the Sm-Fe-N magnetic powder targeted by this invention includes Sm2Fe containing N. 17 In addition to the specified phase, other phases such as the SmFe7 phase with a TbCu7-type crystal structure may also be present. However, the presence of these other phases is acceptable as long as they do not hinder the objectives of the present invention.

[0013] [Particle size distribution of powders] Considering the need to achieve excellent magnetic properties as an aggregate of Sm-Fe-N magnetic particles, such as bonded magnets, this invention provides a volume-based particle size distribution of Sm-Fe-N magnetic powder measured by laser diffraction and scattering, specifically the cumulative 50% particle size D. 50 The particle size is specified as 0.5 μm or more and 5.0 μm or less.

[0014] [March coefficient] The closer the March coefficient, determined by Rietveld analysis from the X-ray diffraction pattern of a metal powder sample, is to 1, the more random the distribution of crystal orientations of the particles constituting the powder sample is considered to be during X-ray diffraction measurement. Generally, when a powder sample is loaded to a predetermined thickness into the sample holder of an X-ray diffractometer without any external forces other than gravity acting on the particles, the March coefficient tends to be less than 1 in powders composed of flat crystal particles, as the proportion of the crystal thickness direction oriented in the depth direction of the sample holder increases. The inventors have found that this March coefficient can be used as an indicator to determine the magnetic field orientation of magnetic particles.

[0015] In the case of Sm-Fe-N magnetic powders, Th2Zn is determined by Rietveld analysis of the X-ray diffraction pattern using Co-Kα rays. 17It is preferable to use the March coefficient of the (220) plane of the type crystal structure. 17 In a type crystal structure, the a-axis and b-axis of the unit cell are equivalent, so analyzing the orientation distribution of the (110) plane allows for a higher accuracy in determining whether the crystal orientation is biased or random. The (220) plane is used as the peak that appears in the X-ray diffraction pattern. After various studies, it was found that Sm-Fe-N magnetic powders with a March coefficient of 0.90 or higher on the (220) plane tend to undergo smooth particle rotation when subjected to magnetic field orientation treatment, resulting in a lower SFD after magnetic field orientation treatment. The aforementioned March coefficient is preferably between 0.90 and 1.30, and more preferably between 0.90 and 1.20.

[0016] [Magnetic Field Orientation SFD] It is preferable that the Sm-Fe-N-based magnetic powder has an SFD (magnetic field orientation SFD) of 0.70 or less after the magnetic field orientation treatment described later, and it is even more preferable that it has an SFD of 0.65 or less.

[0017] [Manufacturing Process] A preferred manufacturing process for obtaining the aforementioned Sm-Fe-N magnetic powder with good magnetic field orientation is "gas atomization → heat treatment → pulverization → nitriding treatment".

[0018] [Gas atomization] Gas atomization is a powder formation method in which molten metal discharged into a gas phase space is rapidly blown with gas to break it down into fine liquid phase particles, and these liquid phase particles are rapidly cooled and solidified while in flight in the gas phase space. As metal raw materials for generating the molten metal to be used in gas atomization, pre-melted Sm-Fe-based master alloys with known compositions, metallic Sm, metallic Fe, etc., can be used. (Sm2Fe) 17 The stoichiometric Sm / Fe molar ratio is 0.118. The composition of the molten metal is Sm2Fe 17It is desirable to adjust the composition to a value relatively close to the stoichiometric composition, specifically, to a Sm / Fe molar ratio in the range of 0.09 to 0.25. The inclusion of metal elements other than Sm and Fe is permissible as long as it does not impair the required properties of the final magnetic powder, but the total content of Sm and Fe in the molten metal is preferably 95.0% by mass or more, and more preferably 98.0% by mass or more. It is desirable to produce the molten metal in an inert gas atmosphere excluding nitrogen or in a vacuum.

[0019] Molten metal, maintained at a predetermined temperature and thoroughly homogenized, is discharged from a nozzle into the gas phase space, and a cooling gas is forcefully blown onto the molten metal immediately after discharge. This causes the molten metal to become fine liquid phase particles that fly through the gas phase space and solidify. The molten metal temperature during discharge should be set within the range of 1400 to 1900°C. The particle size can be controlled by the atomization conditions, but if necessary, the gas atomized powder may be graded using a sieve or the like to adjust the particle size before being used in subsequent processes. Considering that the gas atomized powder will be ground into fine particles with an average particle diameter of a few μm or less in subsequent processes, the particle size of the gas atomized powder should be such that the cumulative 50% particle size D is measured in the volume-based particle size distribution by laser diffraction and scattering method. 50 For example, it is preferable that the particle size be 70.0 μm or less, more preferably 50.0 μm or less, and even more preferably 25.0 μm or less. There is no particular limit to the lower limit of the particle size of the gas atomizing powder, however, as described above D 50 However, since it is currently very difficult to industrially synthesize particles smaller than 5.0 μm, the above D 50 The particle size should be adjusted to a range of 5.0 μm or larger, or it may be controlled to a range of 10.0 μm or larger.

[0020] In the gas atomization process, it is desirable that the pressurizing gas used to discharge the molten metal, the propellant gas sprayed onto the molten metal, and the atmospheric gas in the gas phase space through which the liquid phase particles fly are all inert gases excluding nitrogen. If these gases contain nitrogen, the gas atomized powder will be incompletely nitrided, making it difficult to achieve highly uniform nitriding in subsequent nitriding processes.

[0021] [Heat treatment] The grain size of gas-atomized powder of Sm-Fe alloy (hereinafter sometimes referred to as "Sm-Fe gas-atomized powder") is coarsened by heat treatment at high temperatures. At this time, it is preferable to perform a hydrogen treatment before raising the temperature, which involves heating and holding the powder at a temperature of 250°C to 500°C in a hydrogen gas atmosphere. The holding time at this temperature can be, for example, 1 to 60 minutes. Performing the hydrogen treatment at this stage makes it easier to obtain a powder with a March coefficient close to 1 through the subsequent grinding process. After the hydrogen treatment, heating to 900°C or higher coarses the grains to a size where the average grain size in the equivalent circle diameter of the particle cross-section is, for example, about 3 to 15 μm. This grain coarsening makes it easier for intra-grain fracture to occur during subsequent grinding, making it easier to obtain a fine Sm-Fe alloy powder with a high proportion of particles consisting of single grains. Heating to 930°C or higher is more preferable. Since excessive heating is uneconomical, the heating temperature is preferably set within a range of 1200°C or less, and may be controlled within a range of 1100°C or less, or even 1000°C or less. The holding time in the temperature range of 900°C to 1200°C can be, for example, 10 seconds to 10 minutes, or it may be set within a range of 30 seconds to 5 minutes. The heating atmosphere should preferably be an inert gas atmosphere excluding nitrogen, or a vacuum.

[0022] In Sm-Fe gas atomization powders, it is possible that a Sm-Fe metallic phase with a TbCu7-type crystal structure may be formed depending on the conditions. The TbCu7-type Sm-Fe metallic phase is Th2Zn 17 Compared to the mold, the anisotropic magnetic field after nitriding is small and it is difficult to obtain high coercivity, so it is desirable that the amount of Sm-Fe-based metallic phase in the TbCu7 type be as small as possible. Upon heating to the above temperature range, the crystalline phase of the TbCu7 type becomes Th2Zn 17 Because it transforms the structure, this heat treatment is also effective in homogenizing the microstructure.

[0023] [Crush] When a powder of Sm-Fe alloy, whose grains have been coarsened by the above heat treatment, is subjected to mechanical grinding, individual particles fracture not only at grain boundaries (intergranular fracture) but also within grains (intragranular fracture). When the powder particles are refined by this "fracture including intragranular fracture," a fine Sm-Fe alloy powder with a high proportion of particles consisting of single grains can be obtained. Suitable grinding means for this invention include, for example, wet ball mills and jet mills.

[0024] From the perspective of fragmenting particles by fracture including intragranular fracture, the particle size after grinding is the cumulative 50% particle size D in the volume-based particle size distribution measured by laser diffraction and scattering. 50 It is preferable to adjust the particle size to be 5.0 μm or less, and more preferably to be 3.0 μm or less. Excessive refinement may increase crystal lattice strain due to the application of excessive external force, potentially adversely affecting the magnetic properties. Typically, the above particle size D 50 It is preferable to grind the material to a size of 0.5 μm or larger, but grinding to a size of 1.0 μm or larger is also acceptable. Furthermore, the particle size distribution may be optimized by classifying the powder obtained by grinding and removing coarse particles, or, if necessary, excessively small fine particles.

[0025] [nitriding treatment] Next, a nitriding treatment is performed to obtain Sm-Fe-N magnetic powder. The nitriding treatment can be carried out by heating and holding the finely ground Sm-Fe alloy powder in a nitrogen compound or a nitrogen-containing non-oxidizing gas atmosphere. If the heating temperature is too high, Sm2Fe 17 Sm2Fe crystal with nitrogen atoms embedded within it 17Because the N3-based structure becomes unstable, nitriding becomes difficult. It is desirable to keep the heating temperature for nitriding below 500°C. At very low temperatures, nitriding takes a long time to proceed, which is disadvantageous for uniformly diffusing nitrogen atoms into the interior of the particles. Heating at 300°C or higher is effective. For the atmospheric gas of the nitriding treatment, a reducing atmosphere consisting of a mixture of ammonia (NH3) and hydrogen (H2) is practical. For example, the mixing ratio of ammonia to hydrogen, NH3:H2, can be in the range of 10:90 to 60:40. Other atmospheric gases that can be used for nitriding treatment include a mixture of hydrogen, ammonia, and nitrogen (N2), a mixture of hydrogen, ammonia, and argon (Ar), ammonia alone, a mixture of ammonia and nitrogen, a mixture of ammonia and argon, nitrogen gas, and a mixture of nitrogen and hydrogen, and these are used to create a non-oxidizing atmosphere. The optimal time for nitriding treatment varies somewhat depending on the average particle size of the powder, the composition of the atmospheric gas, and the temperature, but typically, an optimal time can be found within the range of 15 to 240 minutes when the N / Fe molar ratio falls within the predetermined range mentioned above. After nitriding, classification may be performed to adjust the particle size distribution to an appropriate level for the intended application.

[0026] As described above, Sm-Fe-N magnetic powder can be obtained, but it is preferable to control the oxygen concentration of the atmosphere to which the powder is exposed throughout all processes from the gas atomization step to the nitriding step to 10 ppm or less.

[0027] [Surface treatment] To impart storage stability and improve handling of Sm-Fe-N magnetic powder after nitriding, it is effective to apply a surface treatment to form a fatty acid film on the particle surface of the powder after the nitriding process. Specifically, a method can be employed in which the nitrided Sm-Fe-N magnetic powder and one or more fatty acids having 12 to 20 carbon atoms per molecule are mixed in a non-oxidizing atmosphere. Examples of such fatty acids include lauric acid, myristic acid, palmitic acid, stearic acid, oleic acid, linoleic acid, linolenic acid, dihomo-γ-linolenic acid, arachidonic acid, and eicosapentaenoic acid. As the non-oxidizing atmosphere, for example, an inert atmosphere such as nitrogen, argon, or helium, or a reducing atmosphere such as hydrogen or carbon monoxide can be applied. From the viewpoint of cost and safety, a nitrogen gas atmosphere is preferably used. As a mixing means, grinding or mixing equipment such as a vibrating mill, sample mill, Henschel mixer, or fluidized bed mixer can be used.

[0028] Such a fatty acid coating prevents external oxygen from reacting with the Sm-Fe-N magnetic phase due to steric hindrance by the fatty acid molecules. Therefore, Sm-Fe-N magnetic powders treated with fatty acids can be exposed to ambient air at room temperature during handling until they are delivered to the manufacturing process of bonded magnets or sintered magnets. [Examples]

[0029] In each of the following examples, elemental analysis, particle size distribution measurement, magnetic measurement, and X-ray diffraction measurement of the powder were performed using the following methods.

[0030] (Elemental analysis) The analysis of metallic elements was performed by heating and dissolving the sample in hydrochloric acid in a glove box filled with argon (Ar) gas, then diluting it to prepare an analytical sample solution, which was then analyzed using an ICP emission spectrometer (Agilent 720, manufactured by Agilent Technologies). Nitrogen analysis was performed using an oxygen-nitrogen analyzer (Horiba EMGA-920) by the inert gas fusion-thermal conductivity method.

[0031] (Measurement of particle size distribution of powders) A laser diffraction particle size distribution analyzer (Sympatec, Helos / Rodos) was used to determine the cumulative 50% particle size D of the volume-based particle size distribution. 50 They sought it.

[0032] (Magnetic measurement of powders) A sample cell containing 20 mg of sample powder and paraffin was placed in the center of an electromagnet, and the sample cell was heated to 80°C for 2 minutes using a hot air generator. The amount of paraffin used was such that the sample powder and paraffin filled the container of the sample cell. Next, while the sample cell was still heated at 80°C, an external magnetic field of 1.0 T (Tesla) was applied to the sample cell by the electromagnet for 2 minutes. Then, while the 1.0 T magnetic field was still applied, the sample cell was cooled to room temperature. In this way, a measurement sample oriented in a magnetic field was obtained. This measurement sample was placed in a VSM (VSM-5HSC, manufactured by Toei Kogyo Co., Ltd.) so that the direction of the applied magnetic field was parallel to the magnetic field orientation direction of the measurement sample, and the coercivity H c The coercivity H was measured. The measurement conditions were a maximum applied magnetic field of 4.79 MA / m and a sweep speed of 8 kA / m·sec. The width at half maximum of the differential curve of the obtained magnetization curve was defined as the coercivity H. c The SFD, determined by division, was calculated using the software attached to the device. The SFD after this magnetic field orientation processing is called the "magnetic field orientation SFD". With a few exceptions, the same SFD (Surface Field Diameter) was calculated for powders before magnetic field orientation. This SFD before magnetic field orientation treatment is called "unoriented SFD."

[0033] (X-ray diffraction measurement) For the powder sample, the X-ray diffraction pattern was measured using Co-Kα radiation at a tube voltage of 45kV and a tube current of 40mA. The Th2Zn X-ray diffraction pattern was then analyzed. 17The March coefficients for the diffraction peaks of the (220) plane of the type crystal structure were determined. Specifically, the X-ray diffraction patterns obtained above were evaluated using Rietveld analysis based on ICSD (Inorganic Crystal Structure Database) No. 192366: Samarium Iron Nitride (2 / 17 / 3) with integrated powder X-ray analysis software (Rigaku Corporation, PDXL2), and the March coefficients were determined. The orientation hkl of the selective orientation was set to 110.

[0034] [Example 1] (Synthesis of Sm-Fe-based powders by gas atomization method) Figure 1 schematically shows the configuration of the gas atomization apparatus used in this example. Inside the chamber, there are two independent spaces, upper and lower, which can be evacuated by a vacuum exhaust device 10. These spaces can be made into gas phase spaces with a predetermined gas atmosphere by introducing gas from atmospheric gas supply sources 11a and 11b. The upper space contains a crucible 1, in which the raw material is melted by induction heating with a high-frequency coil 4 to form molten metal 5. A molten metal discharge nozzle member 2 is attached to the bottom of the crucible 1 to discharge the molten metal 5 into the lower gas phase space. The molten metal flow path is blocked by pressing the stopper 3 against the molten metal discharge nozzle member 2 until the molten metal 5 is discharged. After the molten metal 5 is sufficiently homogenized and a predetermined temperature is obtained, the gas supply device 13 for molten metal discharge supplies gas at a predetermined pressure to the surface of the molten metal in the crucible 1, and the stopper 3 is raised to discharge the molten metal 5 from the tip of the molten metal discharge nozzle member 2 into the lower gas phase space. The lower gas phase space is equipped with a gas injection nozzle 6 for blowing gas onto the discharged molten metal 5. Before discharge begins, gas is supplied from the gas supply device 12 to the gas injection nozzle 6, and the gas is injected from the gas injection nozzle 6 at a high pressure. By applying this strong jet of injected gas to the molten metal 5, fine particles of the molten metal 5 are formed, and these fine particles are rapidly cooled and solidified. The solidified metal particles 7 accumulate at the bottom of the lower gas phase space.

[0035] Figure 2 schematically shows an example of the cross-sectional structure near the bottom of the crucible of a gas atomizing device. The molten metal discharge nozzle member 2 attached to the bottom of the crucible 1 has a discharge port 21, which is the opening at the tip of the nozzle, and a stopper contact surface 22. The stopper 3 is movable in the vertical direction and has the function of blocking the flow path of the nozzle by contacting the stopper contact surface 22 of the molten metal discharge nozzle member 2, and opening the flow path of the nozzle by moving away from the stopper contact surface 22 when molten metal is discharged. In this example, the entire crucible 1 is made of CaO-containing ZrO2, the entire molten metal discharge nozzle member 2 is made of CaO-containing ZrO2, and at least the portion of the stopper 3 that is immersed in the molten metal 5 is made of thermoalloy. The inner diameter of the nozzle of the molten metal discharge nozzle member 2 is 3.0 mm.

[0036] Sm metal and Sm-Fe alloy were used as raw materials. Sm metal and Sm-Fe alloy were mixed so that the Sm / Fe molar ratio was 0.17. 999.5g of this raw material was placed in a crucible and melted by high-frequency induction heating in an Ar atmosphere. After the raw material alloy was completely molten, at 48 minutes from the start of heating, the entire amount of molten metal at 1650°C was discharged from the nozzle into the lower gas phase space. The maximum supply pressure of the molten metal discharge gas was set to a differential pressure of 57kPa compared to the atmospheric gas pressure. Ar was used as the ejection gas. The lower gas phase space was also maintained as an Ar atmosphere. The generated powder was collected, and coarse particles were removed using a 500μm mesh sieve in a glove box under a nitrogen atmosphere. Gas atomized powder was obtained in this way. Elemental analysis of the gas atomized powder revealed a Sm / Fe molar ratio of 0.15. Furthermore, the cumulative 50% particle size D of the volume-based particle size distribution of the gas atomized powder, obtained by laser diffraction and scattering analysis, was also determined. 50 It was 43.7 μm.

[0037] (Heat treatment) An electrically heated tubular furnace filled with nitrogen gas was used as the heat treatment furnace. The above-mentioned Sm-Fe gas atomized powder was placed in a sealed container filled with nitrogen gas and transferred into the glove box, and then charged into the tubular furnace without exposure to the atmosphere. First, hydrogen treatment was performed by flowing hydrogen gas through the tubular furnace and raising the temperature from room temperature to 300°C at a rate of 10°C / min, and then holding it at 300°C for 30 minutes. After that, the temperature was raised from 300°C to 990°C at a rate of 10°C / min while flowing argon gas, and then held at 990°C for 10 minutes, and then cooled to below 50°C while flowing argon gas to obtain the heat-treated powder.

[0038] (Crush) The obtained heat-treated powder was placed in an airtight container filled with nitrogen gas and transferred from the tubular furnace to another glove box filled with nitrogen gas. Inside this glove box, 500 g of heat-treated powder, 11.25 kg of 1.6 mm diameter stainless steel balls, and 7.5 mL of isopropyl alcohol as a lubricant were placed in a 3000 mL stainless steel mill pot and sealed. Next, the mill pot containing the heat-treated powder was placed in a vibratory mill (YAMP-6SND, manufactured by Eurastechno Co., Ltd.), and grinding was performed with an amplitude of ±2.5 mm, a vibration frequency of 60 Hz, and an operating time of 168 minutes. Then, the contents of the mill pot were passed through a sieve to remove the stainless steel balls on the sieve, and the powder that passed through the sieve was collected. The above loading and collection of the mill pot and sieving operations were performed inside a glove box under a nitrogen atmosphere.

[0039] (nitriding treatment) The pulverized powder obtained as described above was transferred to an electrically heated tubular furnace under a nitrogen atmosphere. A mixed gas consisting of 35% ammonia (NH3) gas and 65% hydrogen (H2) gas was then flowed into the tubular furnace to replace the gas inside. Subsequently, while flowing the mixed gas, the temperature was raised to 390°C at a rate of 10°C / min and held at 390°C for 300 minutes to perform the nitriding treatment. Next, the gas flowing into the tubular furnace was changed to hydrogen (H2) gas and held at 390°C for another 130 minutes. After that, the gas flowing into the tubular furnace was changed to argon gas and held at 390°C for 90 minutes. After that, heating was stopped and the furnace was cooled to near room temperature while flowing argon gas to obtain nitrided powder.

[0040] (Surface treatment) In a nitrogen gas-atmosphere glove box, 100 g of the nitrided powder (Sm-Fe-N magnetic powder) obtained as described above and 5 g of stearic acid were placed in a sample mill (Kyōritsu Rikou, SK-M10) and mixed at 9000 rpm for 120 seconds to coat the surface of the magnetic particles with fatty acids. The amount of fatty acid added per 100 parts by mass of nitrided powder was 5 parts by mass. In this manner, the Sm-Fe-N magnetic powder used as the test powder in this example was obtained.

[0041] (Powder properties) The properties of the obtained Sm-Fe-N magnetic powder (test powder) were investigated using the method described above. X-ray diffraction measurements revealed that the test powder is Th2Zn. 17 It was confirmed that it possesses a type crystal structure. The March coefficient of the (220) plane of the powder sample in this example was 0.91. The cumulative 50% particle size D of this test powder, obtained by laser diffraction and scattering method, shows the volume-based particle size distribution. 50 It was 1.7 μm. Compositional analysis revealed that the test powder in this example had an Sm / Fe molar ratio of 0.15 and an N / Fe molar ratio of 0.18. Magnetic measurement results showed that the magnetic field orientation SFD of the powder sample in this example was 0.62. The results are shown in Table 1 (the same applies to each of the following examples).

[0042] In addition, the unoriented SFD (Surface Field Diameter) of the test powder used in this example was also measured before the magnetic field orientation treatment. The unoriented SFD was 1.00. The ratio of magnetic field-oriented SFD to unoriented SFD is 0.62 / 1.00 = 0.62, indicating that the SFD is significantly reduced by the magnetic field orientation treatment. This suggests that the powder used in this example has a property that makes it easy for the particle orientation to align (easily rotate).

[0043] [Example 2] In the grinding process of Example 1, the mill pot capacity was changed to 1200 mL, the grinding conditions were changed to 200 g of heat-treated powder, 4.5 kg of 3.2 mm diameter stainless steel balls, a vibratory mill (YAMP-2SND, manufactured by Euras Techno Co., Ltd.), and an operating time of 84 minutes. In the nitriding process, a mixed gas with a composition of 35 volume% ammonia (NH3) gas and 65 volume% hydrogen (H2) gas was flowed through the furnace while it was held at 300°C for 60 minutes, and the gas flowing through the tubular furnace was changed to hydrogen (H2) gas. Sm-Fe-N magnetic powder was obtained in the same manner as in Example 1, except that the mixture was then heated at 300°C for another 100 minutes, the gas flowing through the tubular furnace was changed to argon gas and heated at 300°C for 90 minutes, and in the surface treatment step, 3 g of powder consisting of Sm-Fe-N magnetic particles (raw material powder) and 0.09 g of stearic acid were placed in a 70 mL mixer with a stainless steel propeller and mixed at 25,000 rpm for 60 seconds. The obtained Sm-Fe-N magnetic powder was used as the test powder, and the above-mentioned properties were evaluated.

[0044] X-ray diffraction measurements revealed that the test powder is Th2Zn. 17 It was confirmed that it possesses a type crystal structure. The March coefficient of the (220) plane of the powder sample in this example was 1.08. The cumulative 50% particle size D of this test powder, obtained by laser diffraction and scattering method, shows the volume-based particle size distribution. 50 It was 2.7 μm. Compositional analysis revealed that the powder used in this example had an Sm / Fe molar ratio of 0.15 and an N / Fe molar ratio of 0.19. Magnetic measurement results showed that the magnetic field orientation SFD of the powder sample in this example was 0.62.

[0045] In addition, the unoriented SFD of the test powder in this example was also measured before the magnetic field orientation treatment, similar to Example 1. The unoriented SFD was 2.15. The ratio of magnetic field-oriented SFD to unoriented SFD is 0.62 / 2.15 ≈ 0.29, indicating that the SFD is significantly reduced by the magnetic field orientation treatment. This suggests that the powder used in this example has a property that makes it easy for the particle orientation to align (easily rotate).

[0046] [Comparative Example 1] In this example, the above-mentioned properties were evaluated using Sm-Fe-N magnetic powder synthesized by a known method utilizing reduction-diffusion as the test powder. Specifically, the Sm-Fe-N magnetic powder, which was the test powder, was obtained through a process that included obtaining a composite hydroxide of Sm-Fe by neutralization reaction, obtaining a composite oxide of Sm-Fe by heat treatment, obtaining a partial oxide with a reducing gas, a reduction process by reduction-diffusion method, a nitriding process, a washing process to remove by-products derived from the reducing agent, and a surface treatment process to protect the particle surface with a phosphoric acid compound.

[0047] X-ray diffraction measurements revealed that the test powder is Th2Zn. 17 It was confirmed that it possesses a type crystal structure. The March coefficient of the (220) plane of the powder sample in this example was 0.66. The cumulative 50% particle size D of this test powder, obtained by laser diffraction and scattering method, shows the volume-based particle size distribution. 50 It was 2.7 μm. Compositional analysis revealed that the test powder in this example had an Sm / Fe molar ratio of 0.12 and an N / Fe molar ratio of 0.17. Magnetic measurement results showed that the magnetic field orientation SFD of the powder sample in this example was 0.79.

[0048] In addition, the unoriented SFD of the test powder in this example was also measured before the magnetic field orientation treatment, similar to Example 1. The unoriented SFD was 1.06. The ratio of magnetic field-oriented SFD to unoriented SFD was 0.79 / 1.06 ≈ 0.75, indicating that the decrease in SFD due to the magnetic field orientation treatment was less than in Examples 1 and 2. This suggests that the powder used in this example has properties that make it less likely for the particles to align (less likely to rotate) compared to those in the examples.

[0049] [Comparative Example 2] In this example, the above-mentioned properties were evaluated using Sm-Fe-N magnetic powder synthesized by a known method utilizing reduction-diffusion as the test powder. Specifically, the Sm-Fe-N magnetic powder, which was the test powder, was obtained through a process of mixing Sm raw material, Fe raw material, and reducing agent, a reduction process by reduction-diffusion method, a nitriding process, a washing process to remove by-products derived from the reducing agent, and a grinding process to refine the particles and protect the particle surface with a phosphate compound.

[0050] X-ray diffraction measurements revealed that the test powder is Th2Zn. 17 It was confirmed that it possesses a type crystal structure. The March coefficient of the (220) plane of the powder sample in this example was 0.86. The cumulative 50% particle size D of this test powder, obtained by laser diffraction and scattering method, shows the volume-based particle size distribution. 50 It was 2.1 μm. Compositional analysis revealed that the test powder in this example had an Sm / Fe molar ratio of 0.12 and an N / Fe molar ratio of 0.17. Magnetic measurement results showed that the magnetic field orientation SFD of the powder sample in this example was 0.74.

[0051] [Table 1]

[0052] Figure 3 shows the relationship between the March coefficient of the (220) plane and the SFD after magnetic field orientation for the Sm-Fe-N magnetic powders (tested powders) obtained in each example. The Sm-Fe-N magnetic powder of the example obtained by a predetermined manufacturing process using the gas atomization method exhibits a higher March coefficient of 0.90 or more for the (220) plane compared to the comparative example Sm-Fe-N magnetic powder obtained by a known manufacturing process using the reduction-diffusion method, indicating a decrease in SFD after magnetic field orientation. [Explanation of Symbols]

[0053] 1 crucible 2. Molten metal discharge nozzle component 3 Stopper 4. High-frequency coil 5. Molten metal 6 Gas injection nozzle 7. Solidified metal particles 10 Vacuum exhaust system 11a, 11b Atmosphere gas supply source 12. Injection gas supply device 13. Gas supply device for molten metal discharge 21 Discharge port 22 Stopper contact surface

Claims

1. A powder consisting mainly of particles composed of Sm, Fe, and N, wherein the molar ratio of Sm to Fe (Sm / Fe) is 0.09 or more and 0.25 or less, and the molar ratio of N to Fe (N / Fe) is 0.06 or more and 0.30 or less, and the cumulative 50% particle size D in the volume-based particle size distribution measured by laser diffraction and scattering method. ５０ The thickness is between 0.5 μm and 5.0 μm, and the Th obtained by Rietveld analysis in the X-ray diffraction pattern using Co-Kα rays is ２ Zn １７ A Sm-Fe-N magnetic powder having a March coefficient of 0.90 or higher on the (220) plane of the type crystal structure.

2. A gas atomization process to obtain powder of an Sm-Fe alloy having an Sm / Fe molar ratio of 0.09 or more and 0.25 or less by gas atomization, A heat treatment step is performed in which the powder obtained in the gas atomization step is heated and held in a hydrogen gas atmosphere at a temperature of 250°C to 500°C, and then heated to a temperature of 900°C to 1200°C to coarse the crystalline grains of the powder particles. A grinding step is performed to pulverize the powder of the Sm-Fe alloy whose crystal grains have been coarsened by the heat treatment step, thereby refining the powder particles by fracture including intra-grain fracture, A nitriding step is performed in which nitrogen is introduced into the particles of the Sm-Fe alloy powder, which has been finely ground by the aforementioned grinding step, by heating and holding it in a nitrogen compound or a non-oxidizing gas atmosphere containing nitrogen at a temperature range of 500°C or less. A method for producing Sm-Fe-N-based magnetic powder having the following characteristics.

3. A surface treatment step in which a fatty acid film is formed on the particle surface of the powder after the nitriding step, A method for producing an Sm-Fe-N-based magnetic powder according to claim 2, further comprising the above.

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