BENZOTRIAZOL-COATED Sm-Fe-N-BASED MAGNETIC POWDER, AND METHOD FOR PRODUCING THE SAME

Abstract

To provide an Sm-Fe-N-based magnetic particle excellent in storage stability in atmosphere, which has no concern for iron ion generation by reacting with a constituent element Fe of the magnetic particle, and is constituted by a magnetic particle coated with a substance having a chemical structure containing no oxygen atom.SOLUTION: The above problem is solved by a benzotriazole-coated Sm-Fe-N-based magnetic powder constituted by an Sm-Fe-N-based magnetic particle whose surface is coated with benzotriazole. A mass ratio of benzotriazole occupied in the powder can be, for example, 0.2 mass% or more and 10.0 mass% or less.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to Sm-Fe-N-based magnetic powder excellent in storage stability in an air atmosphere and a method for producing the same.

Background Art

[0002] Sm 2 Fe 17 A substance obtained by introducing nitrogen into an intermetallic compound (a typical composition formula is Sm 2 Fe 17 N 3 ) is known to be a ferromagnetic material exhibiting excellent hard magnetism. In this specification, a powder of a substance obtained by introducing nitrogen into a Sm-Fe-based alloy having a stoichiometric composition of Sm 2 Fe 17 or a composition around it and being a ferromagnetic material is called "Sm-Fe-N-based magnetic powder". Sm-Fe-N-based magnetic powder is useful as a material for bonded magnets.

[0003] Sm-Fe-N-based magnetic powder usually easily oxidizes when exposed to air, and the coercive force is significantly reduced. When producing a bonded magnet using Sm-Fe-N-based magnetic powder, measures for preventing oxidation by air are required until the powder is embedded in a resin.

[0004] As a method for imparting oxidation resistance to air to Sm-Fe-N-based magnetic powder, it is known to form a phosphate film on the particle surface of the magnetic powder (for example, Patent Documents 1 to 3).

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0006] Sm-Fe-N-based magnetic powder with excellent oxidation resistance and suppressed decrease in coercive force when exposed to air, that is, excellent "storage stability" in air, is extremely useful as a magnetic material for manufacturing Sm-Fe-N-based bonded magnets because of its excellent handleability.

[0007] During the manufacture of bonded magnets, the magnetic powder particles are generally heated to about 200°C after being mixed with resin so that there is no worry about oxidation by oxidizing gases from the outside. Depending on the type of resin, the temperature may be raised to about 300°C in some cases. Also, during the use of the manufactured bonded magnet, depending on the application, it may be exposed to a temperature of several tens of degrees Celsius or higher for a long time.

[0008] In conventional Sm-Fe-N-based magnetic particles having a phosphate coating, the phosphate coating serves as a barrier layer against external oxidizing gases such as air. However, after the bonded magnet is formed, the phosphate coating or substances derived from it that have completed their role remain near the magnetic particles.

[0009] It is considered that the above phosphate is mainly composed of iron(III) phosphate formed by the reaction of phosphoric acid and Fe, which is a constituent element of the magnetic particles. The iron(III) phosphate may be reduced by Sm to form a nano-sized αFe phase during the manufacture of the bonded magnet or during the use of the bonded magnet product. The formation of the αFe phase is a factor that degrades the magnetic properties of the bonded magnet.

[0010] Also, phosphoric acid has the chemical formula H 3 PO 4As shown in [0], it is a substance containing a large amount of oxygen in the molecule. In the Sm-Fe-N bonded magnet using phosphate, there is a state where many oxygen atoms derived from phosphate exist in the vicinity of the magnetic particles. Depending on the conditions, these oxygen atoms may react with Sm of the Sm-Fe-N magnetic particles during the production of the bonded magnet or during the use of the bonded magnet product to form oxides, which can cause a decrease in magnetic properties.

[0011] An object of the present invention is to provide an Sm-Fe-N-based magnetic powder excellent in storage stability in the atmosphere, which is composed of magnetic particles coated with a substance having a chemical structure that does not generate iron ions by reacting with Fe, which is a constituent element of the magnetic particles, and does not contain oxygen atoms.

Means for Solving the Problems

[0012] The inventors have found that benzotriazole (C 6 H 5 N 3 ) is extremely effective as a coating substance for achieving the above object. Based on this finding, the following inventions are disclosed in this specification.

[0013] [1] A benzotriazole-coated Sm-Fe-N-based magnetic powder composed of Sm-Fe-N-based magnetic particles whose surfaces are coated with benzotriazole. [2] The benzotriazole-coated Sm-Fe-N-based magnetic powder according to [1] above, wherein the mass ratio of benzotriazole in the powder is 0.2% by mass or more and 10.0% by mass or less. [3] The benzotriazole-coated Sm-Fe-N-based magnetic powder according to [1] or [2] above, wherein the Sm / Fe molar ratio is 0.09 or more and 0.25 or less, and the N / Fe molar ratio excluding benzotriazole constituent atoms is 0.06 or more and 0.30 or less. [4] A method for producing a benzotriazole-coated Sm-Fe-N-based magnetic powder, comprising a coating step of mixing a powder composed of particles of an Sm-Fe-N-based magnetic material, benzotriazole, and a solvent in which benzotriazole is soluble in a non-oxidizing atmosphere to coat the surfaces of the particles of the Sm-Fe-N-based magnetic material with benzotriazole. [5] The method for producing benzotriazole-coated Sm-Fe-N-based magnetic powder according to [4] above, wherein the mass ratio of benzotriazole in the benzotriazole-coated Sm-Fe-N-based magnetic powder is 0.2% by mass or more and 10.0% by mass or less. [6] The method for producing benzotriazole-coated Sm-Fe-N-based magnetic powder according to [4] or [5] above, wherein the powder composed of particles of the Sm-Fe-N-based magnetic material has an Sm / Fe molar ratio of 0.09 or more and 0.25 or less and an N / Fe molar ratio of 0.06 or more and 0.30 or less.

Effect of the Invention

[0014] According to the present invention, an Sm-Fe-N-based magnetic powder excellent in storage stability in the air, which is composed of magnetic particles coated with benzotriazole, has been realized. Since benzotriazole does not react with Fe, which is a constituent element of magnetic particles, there is no concern about generating Fe 3+ ions. Further, since benzotriazole has a chemical structure that does not contain an oxygen atom, in an Sm-Fe-N-based bonded magnet, a decrease in magnetic properties due to oxygen in the coating layer does not occur.

Embodiments for Carrying Out the Invention

[0015] [Sm-Fe-N-based Magnetic Powder] The Sm (samarium)-Fe (iron)-N (nitrogen)-based magnetic powder of the present invention is composed of Sm-Fe-N-based magnetic particles whose surfaces are coated with benzotriazole (C 6 H 5 N 3 ).

[0016] [Particle Size] The Sm-Fe-N-based magnetic powder of the present invention exhibits excellent storage stability in the air regardless of the particle size because the powder particles are coated with benzotriazole. Considering use as a magnetic material for a bonded magnet, it is preferable that the cumulative 50% particle size D 50 in the volume-based particle size distribution by the laser diffraction / scattering method is 0.5 μm or more and 5.0 μm or less.

[0017] [Magnetic material] In the Sm-Fe-N-based magnetic powder of the present invention, the magnetic material (Sm-Fe-N-based magnetic material) is Th 2 Zn 17 type crystal structure of Sm 2 Fe 17 It is mainly composed of a magnetic phase in which N (nitrogen) atoms are introduced into the crystal lattice. It is considered that N atoms enter the interstitial positions of the Sm 2 Fe 17 crystal lattice, and the Th 2 Zn 17 type crystal structure is maintained even after the introduction of N atoms. When N atoms are introduced into Sm 2 Fe 17 , the crystal magnetic anisotropy changes from in-plane type to uniaxial type and the Curie point rises, becoming a practical magnet material. A typical composition of the Sm-Fe-N-based magnetic material with excellent magnetic properties is Sm 2 Fe 17 N 3 . It is considered that the closer the Sm / Fe molar ratio, which means the molar ratio of Sm to Fe, and the N / Fe molar ratio, which means the molar ratio of N to Fe, are to the stoichiometric composition of Sm 2 Fe 17 N 3 , the more advantageous it is in terms of magnetic properties, but it also exhibits hard magnetism in the surrounding composition range. The stoichiometric Sm / Fe molar ratio of Sm 2 Fe 17 N 3 is 0.118 and the N / Fe molar ratio is 0.176. As the Sm-Fe-N-based magnetic material of the present invention, considering that a coercive force effective as a material for bonded magnets can be stably obtained in a temperature range including room temperature, the Sm / Fe molar ratio is in the range of 0.09 or more and 0.25 or less, and the N / Fe molar ratio is preferably adjusted to a composition in the range of 0.06 or more and 0.30 or less. In addition, in the Sm-Fe-N-based magnetic material of the present invention, in addition to the Sm 2 Fe 17 phase containing N, for example, there may be mixed phases such as the SmFe 7 phase with a TbCu 7 type crystal structure, but the presence of mixed phases is allowed as long as it does not hinder the object of the present invention.

[0018] N (nitrogen) is an element contained in both the Sm-Fe-N-based magnetic material and benzotriazole. Therefore, in the benzotriazole-coated Sm-Fe-N-based magnetic powder of the present invention, it is preferable that the N / Fe molar ratio is within the above range (0.06 or more and 0.30 or less) in terms of the molar ratio excluding N which is a constituent atom of benzotriazole. The N / Fe molar ratio excluding the constituent atoms of benzotriazole can be obtained, for example, by performing a quantitative analysis of the benzotriazole contained in the benzotriazole-coated Sm-Fe-N-based magnetic powder and subtracting the N content in the benzotriazole from the N content contained in the entire powder.

[0019] [Coating with benzotriazole] According to the research of the inventors, by coating the surface of Sm-Fe-N-based magnetic particles with benzotriazole, it is possible to impart storage stability against the atmosphere to the Sm-Fe-N-based magnetic powder. In the Sm-Fe-N-based magnetic powder for bonded magnets, considering that the cumulative 50% particle size D 50 is preferably 0.5 μm or more and 5.0 μm or less as described above, it is effective to coat the surface of the Sm-Fe-N-based magnetic particles with benzotriazole so that the mass ratio of benzotriazole in the powder is 0.2 mass% or more. As a result, in the Sm-Fe-N-based magnetic powder in which the cumulative 50% particle size D 50 is adjusted to the range of 0.5 μm or more and 5.0 μm or less, it is possible to impart storage stability equivalent to or higher than that of the conventional phosphate coating. Excessive benzotriazole content is uneconomical. The mass ratio of benzotriazole in the powder is preferably set in the range of 10.0 mass% or less. A more preferable mass ratio of benzotriazole in the powder can be mentioned as the range of 0.5 mass% or more and 5.0 mass% or less.

[0020] There is no concern about the generation of iron ions due to the reaction of benzotriazole with Fe which is a constituent atom of the Sm-Fe-N-based magnetic material. Also, benzotriazole has the chemical formula C 6 H 5 N 3Since it does not contain oxygen in the molecule as represented by , it does not become an oxygen source that may oxidize the Sm-Fe-N-based magnetic material. Therefore, in the bonded magnet using the benzotriazole-coated Sm-Fe-N-based magnetic powder of the present invention, it is possible to avoid a decrease in magnetic properties that may occur due to the conventional phosphate coating.

[0021] The Sm-Fe-N-based magnetic powder according to the present invention preferably has a coercive force of 653 kA / m or more and 850 kA / m or less, more preferably 653 kA / m or more and 800 kA / m or less, when subjected to the storage stability test described later.

[0022] [Manufacturing method] In this specification, so-called bare Sm-Fe-N-based magnetic particles without a coating agent such as benzotriazole adhered thereto are particularly referred to as "particles of Sm-Fe-N-based magnetic material", and a powder composed of such bare "particles of Sm-Fe-N-based magnetic material" is referred to as "powder composed of particles of Sm-Fe-N-based magnetic material". The Sm-Fe-N-based magnetic powder of the present invention can be obtained by using a powder composed of particles of Sm-Fe-N-based magnetic material as a raw material and covering the surface of the particles of Sm-Fe-N-based magnetic material with benzotriazole by using, for example, the coating process described later.

[0023] As a manufacturing process of the powder composed of particles of Sm-Fe-N-based magnetic material as a raw material, a reduction diffusion method, a gas atomization method, etc. can be used. Among these, the process using the gas atomization method has the merit that it does not cause an environmental load due to alkaline waste liquid.

[0024] [Coating process] By a method of mixing a powder composed of particles of an Sm-Fe-N-based magnetic material serving as a raw material, benzotriazole, and a solvent in which benzotriazole is soluble in a non-oxidizing atmosphere, the surface of the particles of the Sm-Fe-N-based magnetic material can be covered with benzotriazole. As the above non-oxidizing atmosphere, for example, an inert atmosphere such as nitrogen, argon, helium, or a reducing atmosphere such as hydrogen, carbon monoxide can be applied. From the viewpoints of cost and safety, a nitrogen gas atmosphere is preferably used. As the mixing means, a pulverizing device or a mixing device such as a vibration mill, a sample mill, a Henschel mixer, a fluidized bed mixer can be used. However, it is desirable to apply a relatively mild stirring force or shorten the operation time of the device so that lattice strain is not introduced into the magnetic particles as much as possible by this mixing. Therefore, in this mixing, the purpose is not to cause new pulverization of the magnetic particles, but to coat the magnetic particles with benzotriazole and cover the surface of the magnetic particles with benzotriazole.

[0025] Benzotriazole is a solid at room temperature under atmospheric pressure. Therefore, in order to apply a uniform coating, stirring is performed together with a solvent in which benzotriazole is soluble. Examples of such a solvent include ethanol, methanol, ethylene glycol, etc.

[0026] The amount of benzotriazole to be used may be an amount such that a powder having a mass ratio of benzotriazole to the powder mass excluding the solvent component of 0.2 mass% or more and 10.0 mass% or less is obtained by this coating step. Usually, a part of the benzotriazole introduced into the apparatus adheres to the container of the pulverizing apparatus or the balls for stirring and is lost after mixing. An appropriate amount of benzotriazole to be used can be found by conducting preliminary experiments according to the apparatus used and the mixing conditions.

[0027] The amount of the solvent used may be an amount sufficient to form a coating solution of benzotriazole by mixing. For example, when ethanol is used as the solvent, it is preferable to mix in the range of 100 parts by mass or more and 500 parts by mass or less of ethanol with respect to 100 parts by mass of benzotriazole.

[0028] Regarding the mixing time, it should be a time sufficient to cover the entire surface of each magnetic particle constituting the powder with benzotriazole. When the mixing time is short, there are many portions where benzotriazole is not adhered to the surface of the particles constituting the Sm-Fe-N-based magnetic powder, and when the powder is exposed to the atmosphere, it oxidizes and a significant decrease in the coercive force is observed. Therefore, an appropriate mixing time can also be found by conducting preliminary experiments according to the apparatus used and the mixing conditions. The material temperature during mixing can be set, for example, in the range of 0°C or higher and 60°C or lower.

[0029] At the time when the coating process is completed, the solvent component remains in the Sm-Fe-N-based magnetic powder. Therefore, it is desirable to volatilize and remove the solvent component at a stage before being subjected to the manufacturing process of the bonded magnet.

Examples

[0030] The measurement of the particle size distribution of the powder, elemental analysis, measurement of the benzotriazole content, and magnetic measurement were carried out by the following methods.

[0031] (Measurement of particle size distribution) Using a laser diffraction particle size distribution measuring device (Helos / Rodos, manufactured by Sympatec), the cumulative 50% particle size D 50 in the volume-based particle size distribution was determined.

[0032] (Elemental analysis) For the elemental analysis of metals, after heating and dissolving the analysis sample with hydrochloric acid in a glove box filled with argon (Ar) gas and then diluting it to prepare a sample solution for analysis, this solution was analyzed with an ICP emission spectroscopic analyzer (Agilent720, manufactured by Agilent Technologies). Nitrogen analysis was carried out by the inert gas fusion - thermal conductivity method using an oxygen - nitrogen analyzer (manufactured by Horiba, Ltd., EMGA - 920). Carbon analysis was carried out by the infrared absorption method using a carbon - sulfur analyzer (manufactured by LECO, CS - 744).

[0033] (Measurement of benzotriazole content) A liquid chromatography - mass spectrometry apparatus (manufactured by Agilent Technologies, 6470 Triple Quad LC / MS) was used. For the preparation of the calibration curve required for quantitative analysis, a solution prepared by diluting benzotriazole (manufactured by Wako Pure Chemical Industries, special grade) with pure water to 0, 1, 2, 5, 10, 20, 50, 100 μg / L was used. As the measurement conditions for calibration curve preparation, for the mobile phase of the LC part for separating the benzotriazole component, a mixture of acetonitrile as the organic phase and a mixed aqueous solution of 10 mM ammonium acetate - 0.1% by volume acetic acid as the aqueous phase, mixed at a ratio of 1:9, was used. The separation mode was reverse - phase partition, the sample volume was 3 μL, the measurement mode was MRM, and the separated benzotriazole component was mass - analyzed in the MS part. A calibration curve was created from the set concentration and the peak intensity of the signal of the above - mentioned mass spectrometry. Next, for the analysis of the sample, 0.1 g of the sample (however, in Comparative Examples 1 and 2, 1.0 g of the sample) was dissolved in 25 mL of hydrochloric acid, and then diluted 4000 - fold with pure water. By analyzing it under the same measurement conditions as when preparing the calibration curve, the component amount of benzotriazole was calculated from the calibration curve, and the benzotriazole content in the Sm - Fe - N - based magnetic powder was calculated.

[0034] (Magnetic measurement) A sample cell filled with 20 mg of sample powder and paraffin was placed at the center of an electromagnet, and this sample cell was heated at 80 °C for 2 minutes using a hot air generator. Here, the filling amount of paraffin was set to the amount that filled the container of the sample cell with the sample powder and paraffin. Next, with the sample cell in the heated state at 80 °C, an external magnetic field of 1.0 T (tesla) was applied to the sample cell by the electromagnet for 2 minutes. Next, with the 1.0 T magnetic field applied, the sample cell was cooled to room temperature. In this way, a measurement sample with magnetic field orientation was obtained. This measurement sample was placed in a VSM (manufactured by Toei Industry Co., Ltd., VSM-5HSC) so that the direction of the applied magnetic field was parallel to the magnetic field orientation direction of the measurement sample, and the coercive force Hc was measured. The measurement conditions were a maximum applied magnetic field of 4.79 MA / m and a sweep rate of 8 kA / m·second.

[0035] [Example 1] (Synthesis of Sm-Fe-based powder by gas atomization method) As a raw material alloy, a pre-melted Sm-Fe alloy was used. As a result of elemental analysis, the Sm / Fe molar ratio of this raw material alloy was 0.14. 1000 g of this raw material was placed in a crucible made of boron nitride (BN) and melted by high-frequency induction heating in an argon (Ar) atmosphere. After the raw material alloy was completely melted, when the elapsed time from the start of heating was 30 minutes, the entire amount of the molten metal at 1550 °C was discharged from a nozzle with an inner diameter of 3.0 mm made of boron nitride (BN) into the lower gas phase space. The maximum supply pressure of the gas for discharging the molten metal was 65 kPa in terms of the differential pressure with the atmospheric gas pressure. Argon was used as the injection gas. Also, the lower gas phase space was also an argon atmosphere. All of the obtained powder (hereinafter referred to as "gas atomized powder") was recovered.

[0036] As a result of elemental analysis, the Sm / Fe molar ratio of the gas atomized powder was 0.13, which was equivalent to that of the raw material alloy. The obtained gas atomized powder was classified using a sieve with an opening of 16 μm in a glove box with a nitrogen atmosphere, and a powder (hereinafter referred to as "classified gas atomized powder") from which fine particles were removed was obtained. As a result of particle size distribution measurement, the cumulative 50% particle diameter D 50 of the classified gas atomized powder was 33.2 μm.

[0037] (Heat treatment) The gas atomized powder after the above classification was put into a rotary tube furnace, and heat treatment was carried out by holding it at 850 °C for 5 minutes while flowing argon (Ar) gas in the furnace. Then, it was cooled to a temperature near room temperature (50 °C or lower) while flowing argon gas.

[0038] (Nitriding treatment) After the temperature reached near room temperature, the flow gas flowing into the rotary tube furnace was switched from argon gas to a mixed gas composed of 35 vol% ammonia (NH 3 ) and 65 vol% hydrogen (H 2 ). Then, heating was started, and it was held at 370 °C for 60 minutes in the above mixed gas. Subsequently, while maintaining the heating, the supply of ammonia was cut off and it was exposed to a flow gas of 100% hydrogen for 60 minutes. Then, the flow gas was switched to argon gas and held at 370 °C for 60 minutes. Then, heating was stopped and it was cooled to a temperature near room temperature while flowing argon gas. Next, the flow gas flowing into the rotary tube furnace was switched from argon gas to a mixed gas composed of 35 vol% ammonia (NH 3 ) and 65 vol% hydrogen (H 2 ). Then, heating was started, and it was held at 470 °C for 60 minutes in the above mixed gas. Subsequently, while maintaining the heating, the supply of ammonia was cut off and it was exposed to a flow gas of 100% hydrogen for 60 minutes. Then, the flow gas was switched to argon gas and held at 470 °C for 60 minutes. Then, heating was stopped and it was cooled to a temperature near room temperature while flowing argon gas to obtain nitrided powder. As a result of elemental analysis, the Sm / Fe molar ratio of this nitrided powder was 0.13 and the N / Fe molar ratio was 0.16.

[0039] (Grinding) 210 g of the above nitrided powder, 2.1 g of ethanol, and 4500 g of stainless steel balls with a diameter of 1.6 mm were placed in a 1.2 L stainless steel pot filled with nitrogen gas, sealed, and subjected to a grinding treatment for 168 minutes under the conditions of an amplitude of ±2.5 mm and a vibration frequency of 29.1 Hz using a vibration mill (manufactured by Yurasu Techno Co., Ltd., YAMP-2SND). In this grinding treatment, since the particles can be crushed along the grain boundaries embrittled by the above nitriding treatment, excessive lattice strain is prevented from being introduced into the magnetic material. The sample after operation was separated from the balls in a glove box filled with nitrogen gas to obtain a powder composed of Sm-Fe-N-based magnetic material particles. As a result of the particle size distribution measurement, the cumulative 50% particle diameter D 50 was 1.7 μm. Note that the powder composed of Sm-Fe-N-based magnetic material particles was refined to such an extent that almost no brittle grain boundaries that could be broken remained during the above 168-minute grinding treatment. Therefore, even if vibration is continued under the above grinding conditions, further grinding (refinement) of the particles hardly occurs.

[0040] (Coating with benzotriazole) 200 g of the powder composed of Sm-Fe-N-based magnetic material particles obtained as described above, 6 g of benzotriazole (manufactured by Kawaguchi Chemical Industry Co., Ltd.), 8.6 g of industrial ethanol, and 4500 g of chromium steel balls with a diameter of 1.6 mm were placed in a 1.2 L stainless steel pot filled with nitrogen gas and sealed. The addition amount of benzotriazole with respect to 100 parts by mass of the powder composed of Sm-Fe-N-based magnetic material particles is 3.0 parts by mass. This stainless steel pot was set in a vibration mill (manufactured by Yurasu Techno Co., Ltd., YAMP-2SND), and operated for 5 minutes under the conditions of an amplitude of ±2.5 mm and a vibration frequency of 29.1 Hz to mix the above powder, benzotriazole, and ethanol as a solvent. The sample after operation was separated from the balls in a glove box filled with nitrogen gas to obtain a powder whose surface was covered with benzotriazole (benzotriazole-coated Sm-Fe-N-based magnetic powder). By leaving this powder in a nitrogen gas atmosphere at room temperature for 1 hour, the solvent component (ethanol) was volatilized and removed to obtain a test powder.

[0041] For the test powder obtained in this manner, elemental analysis and benzotriazole content measurement were performed by the above-described method. As a result, the mass ratio of benzotriazole in the powder, that is, the mass ratio of benzotriazole to the total mass of the magnetic material and benzotriazole was 2.2% by mass. Also, the Sm / Fe molar ratio was 0.13, and the N / Fe molar ratio excluding the benzotriazole constituent atoms was 0.17. This test powder was subjected to the following storage stability test.

[0042] (Storage Stability Test) The stainless steel tray containing the test powder was taken out from the nitrogen gas atmosphere and placed in the atmosphere at 25 °C, and atmospheric exposure was carried out for 24 hours. For the powder after the atmospheric exposure, magnetic measurement was performed by the above-described method, and the coercive force Hc was measured. As a result, the coercive force Hc of the test powder obtained in this example after 24-hour atmospheric exposure was 680 kA / m (8543 Oe). These results are shown in Table 1 together with the following examples.

[0043] [Example 2] In Example 1, a test powder was prepared under the same conditions as in Example 1, except that the coating of benzotriazole was performed by the following method using a sample mill.

[0044] (Coating of Benzotriazole) 200 g of a powder composed of Sm-Fe-N-based magnetic material particles obtained by the same procedure as in Example 1, 6 g of benzotriazole (manufactured by Kawaguchi Chemical Industry Co., Ltd.), and 8.6 g of industrial ethanol were put into a sample mill (SK-M10 manufactured by Kyoritsu Riko Co., Ltd.) in a glove box filled with nitrogen gas. The addition amount of benzotriazole with respect to 100 parts by mass of the powder composed of Sm-Fe-N-based magnetic material particles was 3.0 parts by mass. The sample mill was operated at a rotation speed of 18,000 rpm for 1 minute. By leaving this powder in a nitrogen gas atmosphere at room temperature (inside the glove box) for 1 hour, the solvent component (ethanol) was volatilized and removed to obtain a test powder.

[0045] The test powder obtained in this way was subjected to the same measurements and tests as in Example 1. As a result, the mass ratio of benzotriazole in the powder was 2.4% by mass, the Sm / Fe molar ratio was 0.13, and the N / Fe molar ratio excluding the constituent atoms of benzotriazole was 0.18. Also, the coercive force Hc after 24-hour atmospheric exposure was 705 kA / m (8856 Oe).

[0046] [Example 3] In Example 2, a test powder was prepared under the same conditions as in Example 2, except that the amount of benzotriazole charged into the sample mill was 10 g and the amount of industrial ethanol charged was 14.3 g. In this case, the addition amount of benzotriazole with respect to 100 parts by mass of the powder composed of Sm-Fe-N-based magnetic body particles is 5.0 parts by mass. The obtained test powder was subjected to the same measurements and tests as in Example 1. As a result, the mass ratio of benzotriazole in the powder was 4.3% by mass, the Sm / Fe molar ratio was 0.13, and the N / Fe molar ratio excluding the constituent atoms of benzotriazole was 0.16. Also, the coercive force Hc after 24-hour atmospheric exposure was 654 kA / m (8223 Oe).

[0047] [Example 4] In Example 2, a test powder was prepared under the same conditions as in Example 2, except that the amount of benzotriazole charged into the sample mill was 1 g and the amount of industrial ethanol charged was 1.4 g. In this case, the addition amount of benzotriazole with respect to 100 parts by mass of the powder composed of Sm-Fe-N-based magnetic body particles is 0.5 parts by mass. The obtained test powder was subjected to the same measurements and tests as in Example 1. As a result, the mass ratio of benzotriazole in the powder was 0.5% by mass, the Sm / Fe molar ratio was 0.13, and the N / Fe molar ratio excluding the constituent atoms of benzotriazole was 0.17. Also, the coercive force Hc after 24-hour atmospheric exposure was 723 kA / m (9091 Oe).

[0048] [Comparative Example 1] In Example 1, an experiment similar to Example 1 was conducted except that the coating of benzotriazole was not performed. That is, the powder composed of Sm-Fe-N-based magnetic particles after the pulverization process of Example 1 was used as the test powder. The benzotol content of this test powder was 0.01% by mass or less, the Sm / Fe molar ratio was 0.13, and the N / Fe molar ratio was 0.15. In the storage stability test, when the test powder was taken out from the nitrogen gas atmosphere into the air atmosphere, the powder temperature after 10 seconds became 245 °C, and rapid heat generation occurred. This heat generation was due to the oxidation reaction caused by the Sm-Fe-N-based magnetic particles coming into contact with oxygen in the air. The coercive force Hc after 24 hours of air exposure was very low at 147 kA / m (1853 Oe).

[0049] [Comparative Example 2] In Example 2, the test powder was prepared under the same conditions as in Example 1 except that phosphoric acid was used instead of benzodiazole. The coating of phosphoric acid was performed by the following method.

[0050] (Coating of phosphoric acid) 200 g of the powder composed of Sm-Fe-N-based magnetic particles obtained by the same procedure as in Example 1, 6 g of phosphoric acid (H 3 PO 4 ), and 8.6 g of industrial ethanol were put into a sample mill (SK-M10 manufactured by Kyoritsu Riko Co., Ltd.) in a glove box filled with nitrogen gas. The addition amount of phosphoric acid with respect to 100 parts by mass of the powder composed of Sm-Fe-N-based magnetic particles was 3.0 parts by mass. The sample mill was operated at a rotational speed of 18,000 rpm for 1 minute. This powder was placed in a nitrogen gas atmosphere at room temperature (inside the glove box) for 1 hour to volatilize and remove the solvent component (ethanol), and the test powder was obtained.

[0051] The particle surface of the test powder is considered to be covered with iron phosphate, samarium phosphate, or a composite metal salt thereof. This test powder was subjected to the same measurements and tests as in Example 1. As a result, the Sm / Fe molar ratio was 0.13 and the N / Fe molar ratio was 0.15. Also, the coercive force Hc after 24-hour air exposure was 652 kA / m (8187 Oe).

[0052] [Comparative Example 3] In Example 2, a test powder was prepared under the same conditions as in Example 2, except that the amount of benzotriazole charged into the sample mill was 0.2 g and the amount of industrial ethanol charged was 0.29 g. In this case, the addition amount of benzotriazole with respect to 100 parts by mass of the powder composed of Sm-Fe-N-based magnetic material particles is 0.1 part by mass. The obtained test powder was subjected to the same measurements and tests as in Example 1. As a result, the mass ratio of benzotriazole in the powder was 0.08% by mass, the Sm / Fe molar ratio was 0.13, and the N / Fe molar ratio excluding benzotriazole constituent atoms was 0.16. The coercive force Hc after 24-hour air exposure was 162 kA / m (2038 Oe), which was lower than that of the other examples. This decrease in coercive force is considered to be due to the oxidation of the Sm-Fe-N-based magnetic material. In this example, it is presumed that powder particles with a part of the magnetic material exposed on the surface were generated because the amount of benzotriazole used was too small. That is, in this example, it is evaluated that "a benzotriazole-coated Sm-Fe-N-based magnetic powder composed of Sm-Fe-N-based magnetic particles whose surface is covered with benzotriazole" could not be obtained.

[0053]

Table 1

[0054] As described above, it was confirmed that the method of covering the surface of Sm-Fe-N-based magnetic material particles with benzotriazole can impart storage stability against air equal to or higher than that in the case of forming a phosphate film.

Claims

1. A benzotriazole-coated Sm—Fe—N-based magnetic powder composed of Sm—Fe—N-based magnetic particles whose surfaces are covered with benzotriazole.

2. The benzotriazole-coated Sm—Fe—N-based magnetic powder according to Claim 1, wherein the mass ratio of benzotriazole in the powder is 0.2% by mass or more and 10.0% by mass or less.

3. The benzotriazole-coated Sm—Fe—N-based magnetic powder according to Claim 1, wherein the Sm / Fe molar ratio is 0.09 or more and 0.25 or less, and the N / Fe molar ratio excluding benzotriazole constituent atoms is 0.06 or more and 0.30 or less.

4. A method for producing a benzotriazole-coated Sm—Fe—N-based magnetic powder, comprising a coating step of mixing a powder composed of Sm—Fe—N-based magnetic particles, benzotriazole, and a solvent in which benzotriazole is soluble in a non-oxidizing atmosphere to cover the surfaces of the Sm—Fe—N-based magnetic particles with benzotriazole.

5. The method for producing a benzotriazole-coated Sm—Fe—N-based magnetic powder according to Claim 4, wherein the mass ratio of benzotriazole in the benzotriazole-coated Sm—Fe—N-based magnetic powder is 0.2% by mass or more and 10.0% by mass or less.

6. The method for producing a benzotriazole-coated Sm—Fe—N-based magnetic powder according to Claim 4, wherein the powder composed of Sm—Fe—N-based magnetic particles has an Sm / Fe molar ratio of 0.09 or more and 0.25 or less and an N / Fe molar ratio of 0.06 or more and 0.30 or less.

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