Soft magnetic material and method for manufacturing the same

Abstract

To provide a soft magnetic material and a method for manufacturing the soft magnetic material, the material having a small average particle diameter, high roundness, and a low degree of necking, thereby achieving low iron loss.SOLUTION: The method for manufacturing a soft magnetic material includes: a spray-drying step of spray-drying a slurry containing Fe and X, X being at least one element selected from Ti, Mn, Ni, Co, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Cu, Zn, and Si, to obtain granules having an average particle diameter of 20 μm to 200 μm; and a heat-treatment step of heat-treating the granules in a reducing gas at 800°C to 1200°C to obtain a heat-treated material.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present disclosure relates to soft magnetic materials and methods for making the same. [Background technology]

[0002] Soft magnetic materials are known as magnetic core materials for electric devices such as motors and transformers (see Patent Documents 1 and 2). In particular, there is a demand for soft magnetic powders with excellent high-frequency characteristics, for example, for the development of axial motors at high frequencies of 2 kHz or higher. Conventional soft magnetic powders have a problem in that, in magnetic bodies made from the soft magnetic powders, i.e., magnetic compacts, eddy currents are generated throughout the component due to conduction between particles, resulting in high iron loss. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] International Publication No. 2017 / 164376 [Patent Document 2] International Publication No. 2018 / 155608 Summary of the Invention [Problem to be solved by the invention]

[0004] An object of the present disclosure is to provide a soft magnetic material having a small average grain size, a high degree of circularity, and a small degree of necking, and therefore a small core loss, and a method for producing the same. [Means for solving the problem]

[0005] A method for producing a soft magnetic material according to one embodiment of the present disclosure includes a spray-drying step of spray-drying a slurry containing Fe and X (X is one or more elements selected from Ti, Mn, Ni, Co, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Cu, Zn, and Si) to obtain granulated material having an average particle size of 20 μm or more and 200 μm or less, and a heat-treatment step of heat-treating the granulated material in a reducing gas at 800° C. or more and 1200° C. or less to obtain a heat-treated material.

[0006] A soft magnetic material according to one embodiment of the present disclosure has a first phase and a second phase having crystals with a bcc structure containing Fe and X (X is one or more elements selected from Ti, Mn, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Cu, Zn, and Si), and for one element of X contained in both phases, the content of the element in the second phase is at least 2 times but not more than 10 times the content of the element in the first phase. 5 The average circularity is 0.55 or more, and the average particle size is 160 μm or less.

[0007] Furthermore, a soft magnetic material according to an embodiment of the present disclosure has a first phase and a second phase having crystals with a bcc structure containing Fe and X (X is one or more transition metals selected from Ni and Co), and for one element of X contained in both phases, the content of the element in the second phase is more than 1 time and less than 10 times the content of the element in the first phase. 5 The average circularity is 0.55 or more, and the average particle size is 160 μm or less. [Effects of the Invention]

[0008] The present disclosure provides a soft magnetic material with a small average particle size, high circularity, and low necking, and a manufacturing method thereof, which allows the production of a magnetic material with low iron loss even at high frequencies. In particular, the present disclosure relates to a metallic soft magnetic material, such as an Fe-X soft magnetic material, which has high magnetization, magnetic flux density, and magnetic permeability. [Brief explanation of the drawings]

[0009] [Figure 1A] 1 shows an SEM (scanning electron microscope) image of the magnetic powder produced in Example 4. [Figure 1B] 1 shows an SEM image of the magnetic powder produced in Example 4 and the Ni concentration at each point quantified by EDX (energy dispersive X-ray fluorescence analysis). [Figure 1C] 1 shows an SEM image of the magnetic powder produced in Example 4 and the Mn concentration at each point quantified by EDX. [Figure 2]1 shows an XRD (X-ray diffraction) pattern of the magnetic powder produced in Example 4. [Figure 3A] 1 shows an SEM image of the magnetic powder produced in Example 7. [Figure 3B] 1 shows an SEM image of the magnetic powder produced in Example 7 and the Ni concentration at each point quantified by EDX. [Figure 3C] 1 shows an SEM image of the magnetic powder produced in Example 7 and the Mn concentration at each point quantified by EDX. [Figure 4] 1 shows an XRD pattern of the magnetic powder produced in Example 7. [Figure 5A] 1 shows a STEM (scanning transmission electron microscope)-HAADF (annular dark field) image and a STEM-EDX mapping image of a cross section of the magnetic powder produced in Example 7. [Figure 5B] The Ni and Mn concentration profiles are shown along the lines in FIG. 5A. DETAILED DESCRIPTION OF THE INVENTION

[0010] Embodiments of the present disclosure are described in detail below. However, the embodiments described below are examples for embodying the technical ideas of the present disclosure, and the present disclosure is not limited to the following. In this specification, the term "process" includes not only an independent process, but also a process that cannot be clearly distinguished from other processes, as long as the intended purpose of the process is achieved. Furthermore, a numerical range indicated using "to" indicates a range that includes the numerical values ​​before and after "to" as the minimum and maximum values, respectively.

[0011] <<Method of manufacturing soft magnetic materials>> The method for producing a soft magnetic material of this embodiment is characterized by including a spray-drying step of spray-drying a slurry containing Fe and X (X is one or more elements selected from Ti, Mn, Ni, Co, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Cu, Zn, and Si) to obtain granules having an average particle size of 20 μm or more and 200 μm or less, and a heat-treatment step of heat-treating the granules in a reducing gas at 800° C. or more and 1200° C. or less to obtain a heat-treated product.

[0012] The metallic soft magnetic material, which is the Fe-X soft magnetic material of this embodiment, can also be obtained by reducing granules or granules with adjusted particle size by a method of removing unnecessary components in the liquid and drying the slurry containing Mn-Ni-ferrite, which is the raw material before reduction, without spray drying, as in Patent Documents 1 or 2, or by a method of classifying the slurry in addition to the above, as in the examples of this embodiment. Here, the spray drying method of this embodiment will be described in detail.

[0013] <Spray drying process> Spray drying is performed by spraying a raw material slurry, such as a Mn-Ni ferrite slurry, in a shower-like manner and then drying the sprayed slurry by blowing hot air onto it, thereby obtaining a granulated product. Spray drying can be performed using a spray drying device equipped with an atomizer disk, including a rotary disk, a pin-type disk, or a Coanda disk, or a two-fluid, three-fluid, or four-fluid nozzle. The spray medium is primarily water, and may contain known organic substances, inorganic substances, organometallic substances, etc., such as solvents, dispersants, and flocculants. The spray drying conditions, device, etc. can be appropriately selected from known techniques. Typically, the device has one or more nozzles or disks for introducing the raw material slurry and one or more nozzles for airflow. The raw material slurry is dispersed in the drying chamber of the spray device, and the liquid phase is quickly removed from the raw material slurry to obtain the desired granulated product. The flow rate supplied to each disk or nozzle and the flow rate ratio between each disk or nozzle can also be appropriately set. The temperature of the drying chamber may be set appropriately depending on the content of the raw slurry, the rate of removal of the liquid phase, etc., but is preferably 80°C or higher and 150°C or lower, more preferably 101°C or higher and 130°C or lower.

[0014] The concentration of the raw slurry (such as Mn-Ni-ferrite slurry) (mass of raw slurry / (mass of raw slurry+mass of spray medium)) may be 3% by mass or more and 50% by mass or less, and preferably 13% by mass or more and 45% by mass or less.

[0015] The average particle size of the granules obtained by spray drying is 20 μm to 200 μm, preferably 40 μm to 150 μm. If it is less than 20 μm, the particle size will be small, 16 μm or less, after heat treatment, resulting in large hysteresis loss. If it exceeds 200 μm, the particle size will be large, 160 μm or more, after heat treatment, resulting in large intragranular eddy current loss. In either case, iron loss will increase, which is undesirable.

[0016] <Slurry preparation process> The slurry used in the spray drying process is, for example, A slurry preparation process in which a basic pH adjusting solution is added dropwise to a stirring vessel having stirring blades while stirring together with an acidic solution containing Fe and X (X is one or more elements selected from Ti, Mn, Ni, Co, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Cu, Zn, and Si) to generate ferrite nanoparticles and obtain a slurry, wherein the dropping time T (s) is T≧375000VD 2 / 3 (where V(m 3 ) indicates the volume of the stirring vessel, and D (m) indicates the diameter of the stirring blade. The slurry can be produced by a slurry production process that satisfies the above.

[0017] The raw material slurry (Mn-Ni ferrite slurry) can be prepared by known methods (e.g., Japanese Patent No. 7055417 (Patent Document 3)) using an aqueous solution (reaction solution) of, for example, MnSO4·5H2O (manganese(II) sulfate pentahydrate), NiSO4·6H2O (nickel(II) sulfate hexahydrate), or FeSO4·7H2O (iron(II) sulfate heptahydrate) and a basic (preferably greater than 7 and less than 16) pH adjuster such as aqueous sodium hydroxide solution. An appropriate amount (preferably greater than 0% and less than 50% of the total reaction solution) of the reaction solution, previously adjusted to an acidic range (preferably greater than -1 and less than 7), is placed in a reaction vessel (also referred to herein as the reaction field). The reaction vessel is then mechanically stirred at room temperature with an appropriate power and rotation speed. The pH of the reaction field solution is gradually changed from acidic to basic, producing ferrite nanoparticles in the reaction field. During this process, divalent Fe ions are oxidized using an oxidizing agent, such as oxygen in the air, to form oxides with mixed divalent and trivalent valences, producing the desired raw material slurry. The stirring blades used may be vertical. Using a vertical stirring blade allows for efficient introduction of oxygen from the air into the reaction site. By reducing the drip rate of the reaction solution and pH adjuster to a level that prevents excessive oxidation of the reaction solution, it is possible to obtain a raw material slurry with reduced by-products, such as oxides, hydroxides, and oxyhydroxides, that are different from ferrite. This tends to improve the magnetic properties of the final Fe-X soft magnetic material. To prevent excessive oxidation, it is important to reduce the stirring speed and the number of rotations of the stirring blades, modify the shape of the stirring blades, slow down or stop the introduction of oxygen or air by bubbling, or the dripping of oxidizing agents such as sodium nitrite aqueous solution. After taking these measures, it is important to set a sufficiently long drip time. The drip time, T (s), is determined by the volume of the stirring vessel, V (m 3 ), where the diameter of the stirring blade is D (m), T≧375000VD 2 / 3On the other hand, Jun Nishitsuji, Ryoya Okazaki, Satoshi Abe, Jun Akamatsu, Nobuyoshi Imaoka, Michiya Kume, Yoshinaka Kawakami, Hiroyuki Hosokawa, and Kimihiro Ozaki, IEEE TRANSACTIONS ON MAGNETICS, VOL. 59, NO. 11 (2023) P. 2000706 (Non-Patent Document 1), states that P V is 0.2kW / m, the same as in Patent Document 1. 3 In this study, V = 0.050 and D = 0.220, and therefore a dropping time of 116 minutes or more is preferable, but air bubbling is used to accelerate oxidation, and the dropping is completed in 15 minutes. As a result, oxyhydroxides such as goethite are observed, as shown in Figure 3 of Non-Patent Document 1. In contrast, in the present invention, the air bubbling similar to that in Non-Patent Document 1 is stopped, and the intake of atmospheric oxygen, which serves as an oxidant, is limited to the stirring action of the vertical blades, and the dropping time is set to 120 minutes, thereby enabling the production of a high-purity raw material slurry free of by-products such as goethite.

[0018] <Heat treatment process> The heat treatment is performed by heat-treating the resulting granules in a reducing gas, yielding a heat-treated product. The reducing gas can be appropriately selected from hydrogen (H), hydrogen nitride gases such as ammonia (NH) and hydrazine (NH-NH), carbon monoxide (CO), and hydrocarbon gases such as methane (CH), with hydrogen gas being preferred from a cost perspective. The gas flow rate is appropriately adjusted within a range that does not cause oxides to escape. The heat treatment temperature is between 800°C and 1200°C, but is preferably between 900°C and 1150°C, which exceeds the α-γ transition temperature, and is cost-effective because the reactor can be made of Hastelloy or Inconel. A heat treatment temperature of 800°C or higher allows efficient reduction of the granules. A heat treatment temperature of 1200°C or lower suppresses particle growth of the granules, allowing the desired particle size to be maintained. The heat treatment time is preferably between 1 minute and 14,400 minutes, and more preferably between 10 minutes and 1,440 minutes. If the heat treatment time is less than 1 minute, the heat treatment step in the present disclosure is an endothermic reaction and the required temperature cannot be reached, resulting in insufficient reduction reaction.If the heat treatment time exceeds 14,400 minutes, particles that undergo unacceptable grain growth begin to appear.

[0019] <Gradual oxidation process> Immediately after the heat treatment, a gradual oxidation treatment is preferably performed in an atmosphere containing an inert gas to achieve an oxygen partial pressure lower than that of the atmosphere. Gradual oxidation oxidizes and passivates the surface of the heat-treated powder (providing a surface oxide layer such as wüstite or ferrite), thereby preventing spontaneous combustion or combustion due to rapid oxidation during exposure to the atmosphere. The atmosphere can be appropriately selected from inert gases such as nitrogen, rare gases such as argon, oxygen, or the atmosphere. A combination of argon and oxygen is preferred to prevent deterioration of the magnetic material's properties. The gradual oxidation temperature is preferably between room temperature and 500°C. Temperatures above 500°C result in excessive passivation of the magnetic powder surface, resulting in a deterioration of the magnetic powder's properties. The gradual oxidation time is preferably between 1 minute and 14,400 minutes. A gradual oxidation time of less than 1 minute results in insufficient surface passivation, potentially leading to fire upon removal. A gradual oxidation time of longer than 14,400 minutes results in excessive passivation, resulting in a deterioration of the magnetic powder's properties. The oxygen partial pressure is preferably 0.01% or more and less than 21%, more preferably 0.1% or more and less than 4%. If the oxygen partial pressure is less than 0.01%, the surface will not be sufficiently passivated, which may result in fire when the material is removed, while if it is 21% or more, sudden oxidation may result in spontaneous combustion or combustion.

[0020] There is also a gradual oxidation method in which the reactor is first evacuated and then gradually opened at room temperature to increase the oxygen concentration, preventing sudden exposure to the atmosphere.

[0021] <Soft magnetic material> Soft magnetic materials are materials with low coercive force and high saturation magnetic flux density. Unlike oxide soft magnetic materials such as ferrite, which have low saturation magnetic flux density, soft magnetic materials are Fe-X alloys containing Fe and X (X is one or more elements selected from Ti, Mn, Ni, Co, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Cu, Zn, and Si), which have excellent heat resistance, core loss, and magnetic permeability. Furthermore, coating, as described below, can further improve the electrical resistance of the magnetic material, further reduce loss, and improve magnetization and magnetic permeability.

[0022] The Fe-X alloy preferably comprises a first phase containing Fe and X, and a second phase containing Fe and X, the X content of which is greater than that of the first phase on an atomic basis. Here, the X content is the X content (atomic %) when the sum of Fe and X is taken as 100 atomic %. The X content of the second phase is 1.1 to 10 times the X content of the first phase. 5 Less than 10 times is preferable, and more than 2 times is preferable. 5 It is more preferable that the ratio of the X content is equal to or less than 100 times. Here, the ratio of the X content is calculated based on the content of the same element contained in both phases. By setting the X content of the second phase within the above range, it is possible to achieve both low coercivity and high magnetization, making it suitable as a soft magnetic material with excellent high-frequency characteristics.

[0023] When X is Ti or Mn, the content of X in the second phase is not less than 2 times the content of X in the first phase, but not more than 10 times the content of X in the first phase. 5 When X is one of Zr, Hf, V, Nb, Ta, Cr, Mo, W, Cu, Zn, and Si, the content of X in the second phase is preferably 1.5 times or more and 10 times or less. 5 When X is Ni or Co, the content of X in the second phase is preferably more than 1 time, and more preferably 1.1 times or more and 10 times or less. 5 The ratio is preferably 1.2 times or less, and may be 1.2 times or more, 1.3 times or more, or 1.4 times or more. Here, the ratio of X content is calculated based on the content of the same single element contained in both phases. By setting the ratio within this range, it is possible to achieve both low coercivity and high saturation magnetization, for example, a soft magnetic material with a coercivity of 80 A / m or less and a saturation magnetization of 0.3 T or more can be obtained. Use of such a soft magnetic material can achieve lower loss in high-frequency applications. Due to a disproportionation reaction during heat treatment, Fe-X alloys can have a structure in which nanoscale X composition fluctuations exist and nanoscale first and second phases are ferromagnetically bonded. This structure is thought to result in low coercivity and high saturation magnetization. Fe-X alloys can be produced by known methods, such as those described in WO2017 / 164376 and WO2018 / 155608.

[0024] The first and second phases of the Fe-X alloy have bcc crystal structures containing Fe and X, which can improve magnetization. The bcc crystallite size of the first and second phases of the Fe-X alloy is preferably 1 nm or more and less than 100 nm. The Fe-X alloy can contain additional components other than the X component. In this case, the content of the X component is preferably greater than the content of the other additional components. The content of the additional components in the first and second phases is the content (atomic %) of the additional component when the sum of the X component and Fe, including the additional components, in the first and second phases is taken as 100 atomic %. This allows for both low coercivity and improved magnetization.

[0025] Among Fe-X alloys, those in which X is Mn (referred to as "Fe-X(X=Mn)"), those in which X is Ni (referred to as "Fe-X(X=Ni)"), and those in which X is Mn and Ni (referred to as "Fe-X(X=Mn,Ni)") are preferred. Ni and Mn may be the main components of X. When X is Mn or Ni, it may contain smaller amounts of other components, but it is more preferable that X consists essentially of these components. Here, "consisting essentially of these components" means that the content of other metal components is less than 1 mass%. Fe-X (X=Mn) tends to have higher electrical resistance and heat resistance than Fe powder (pure iron). This is thought to be due to the presence of an X-enriched phase. As predicted by the Slater-Pauling curve, Fe-X (X=Ni) exhibits high magnetization when the Ni content is greater than 0 and less than 12 atomic %. Fe-X (X=Mn, Ni) combines the advantages of both Fe-X (X=Mn) and Fe-X (X=Ni). That is, it can increase electrical resistance, reduce eddy current loss, and improve heat resistance and magnetization.

[0026] The soft magnetic material obtained by heat treatment is preferably in the form of powder, since it is easy to mold a powder magnetic core of any shape into a compact stator such as an axial motor core. 50The particle size can be, for example, 1 μm to 5 mm, preferably 5 μm to 1 mm, more preferably 10 μm to 500 μm, even more preferably 160 μm or less, and even more preferably 130 μm or less. This range suppresses coercive force and distortion during annealing. Furthermore, when used as a stator core for a motor used in next-generation mobility (including flying cars) and drones operating at 2 kHz or higher, it is preferable because it provides a good balance between coercive force, which contributes to hysteresis loss, and eddy current loss, which depends on the particle size. When used as an inductor or transformer for a non-insulated or isolated DC-DC converter used in next-generation mobility operating at 5 kHz to 10 kHz or lower, the particle size is preferably 60 μm to 80 μm. When used as an inductor or transformer for an AC-DC converter used in a small adapter operating at 50 kHz to 120 kHz or lower, the particle size is preferably 16 μm to 26 μm. In the case of high-voltage transformers, pulse transformers, and pulse inductors of 50,000 V or less, when driven at 2 kHz or more and 100 kHz or less, the average particle size D is preferably 18 μm or more and 130 μm or less. 50 is the particle size at which the integrated value of the particle size distribution based on the volume of the magnetic powder corresponds to 50%, as determined by a dry laser diffraction particle size distribution analyzer.

[0027] To remove impurities and oxide films from the surface of the magnetic material, a washing step is preferably performed in which the magnetic material is washed with an acidic aqueous solution. Examples of acid compounds used for washing include inorganic and organic acids. Examples of inorganic acids include sulfuric acid, hydrochloric acid, nitric acid, phosphoric acid, boric acid, and hydrofluoric acid, while examples of organic acids include acetic acid, formic acid, oxalic acid, tartaric acid, and citric acid. The pH during washing is preferably less than pH 7, more preferably less than pH 3. The washing time is preferably between 1 minute and 600 minutes. It is preferable to stir the aqueous solution during washing.

[0028] <Classification process> It is preferable to include a classification step after the heat treatment step, in which the soft magnetic material obtained in the heat treatment step is classified to obtain a classified product. By classification, a soft magnetic material with a desired average particle size can be obtained. There are no particular restrictions on the classification method, and well-known methods may be used, such as sieve classification, vibration classification, hydraulic classification, and air classification. In other words, a classification method based on any principle, such as gravity field classification, inertial field classification, or centrifugal field classification, may be selected.

[0029] <Coating process> It is preferable to include a coating step in which the soft magnetic material obtained by the heat treatment step or classification step is coated with a silicon compound, a phosphorus compound, a magnesium compound, an aluminum compound, or the like. Among these, it is preferable to include a phosphorus compound coating step. One of the reasons for this preference is as follows: a fine and moderately soft substance such as a phosphorus compound, which is not as hard as ferrite or transition metal oxides, but not too soft like resin, coats the Fe-X alloy powder or is present between the particles, which has the advantage of not deteriorating the inherent properties of the soft magnetic powder, such as magnetic permeability.

[0030] In the coating step, for example, an aqueous solution containing a phosphate compound and a rare earth compound is preferably mixed with a magnetic material, which is a soft magnetic material, to form a coating containing a phosphorus compound containing a rare earth metal element on the surface of the soft magnetic material. The coating step causes a reaction between the metal component contained in the magnetic material and the phosphorus component contained in the phosphate compound, forming a coating. The coating may be a coating containing a phosphorus compound containing a rare earth metal element, or a coating containing a rare earth phosphate. Depending on the combination of elements contained in the coating and the atmosphere during heating after coating formation, heating after the formation of a coating containing a rare earth phosphate may result in a coating containing a phosphorus compound other than phosphate.

[0031] Examples of the phosphoric acid compound contained in the aqueous solution include phosphate-based compounds such as orthophosphoric acid, sodium dihydrogen phosphate, sodium monohydrogen phosphate, ammonium dihydrogen phosphate, ammonium monohydrogen phosphate, zinc phosphate, and calcium phosphate, inorganic phosphoric acids such as hypophosphorous acid, hypophosphite, pyrophosphoric acid, and polyphosphoric acid, and organic phosphoric acids and salts thereof. These compounds may be used alone or in combination of two or more.

[0032] The content of the phosphate compound in the aqueous solution is preferably 0.0001% by mass to 50% by mass, more preferably 0.001% by mass to 10% by mass, calculated as PO. Within these ranges, the phosphate compound tends to have high solubility in water and high storage stability.

[0033] During the coating process, the rare earth metal elements derived from the rare earth compound contained in the aqueous solution adhere to the magnetic material. The amount of rare earth compound contained in the aqueous solution is preferably 0.0001% by mass or more, more preferably 0.01% by mass or more, and even more preferably 0.1% by mass or more, relative to the coated magnetic material. A rare earth metal element content of 0.0001% by mass or more in the coated magnetic material tends to stabilize the coating weight, a content of 0.01% by mass or more tends to further reduce loss, and a content of 0.1% by mass or more tends to further improve heat resistance. The upper limit of the rare earth metal element content in the coated magnetic material can be 50% by mass or less, preferably 10% by mass or less. By keeping the rare earth metal element content in the coated magnetic material at 50% by mass or less, the magnetic permeability of the coated magnetic material can be suppressed, thereby suppressing deterioration of its properties. The rare earth metal element precipitates on the surface of the magnetic material as a phosphorus compound containing the rare earth metal element or a phosphate containing a rare earth element.

[0034] Because rare earth metal elements tend to have a small Gibbs energy change (ΔG) in the oxidation reaction in the temperature range (approximately 400°C to 700°C) when heating coated magnetic materials, using rare earth compounds in the coating process allows for the production of coated magnetic materials with excellent heat resistance. Table 1 shows the Gibbs energy change in the oxidation reaction of rare earth oxides at 600°C.

[0035] [Table 1]

[0036] The rare earth compound contains a rare earth metal element. Ce, Nd, Sm, La, Dy, Y, or Pr is preferred, with Ce, Nd, Sm, La, or Dy being more preferred, Ce, Sm, La, or Dy being even more preferred, and Sm or Dy being particularly preferred. The rare earth compound is preferably a compound that generates rare earth ions in an aqueous solution, such as a rare earth oxide, rare earth hydroxide, rare earth chloride, rare earth sulfate, rare earth nitrate, or rare earth acetate, with rare earth chloride being more preferred. Specific examples of preferred rare earth compounds include chlorides of one or more rare earth elements selected from the group consisting of Ce, Nd, Sm, La, and Dy. These compounds may be used alone or in combination. Because rare earth chlorides tend to be easily soluble, the use of rare earth chlorides makes it easier to obtain the aqueous solution used in the coating process.

[0037] In the aqueous solution containing a phosphoric acid compound and a rare earth compound, the content of the rare earth compound is preferably 0.001% by mass to 10% by mass, more preferably 0.01% by mass to 5% by mass, in which case the rare earth compound tends to have high solubility in water and high storage stability.

[0038] The reaction time for forming a coating on the surface of the magnetic material is preferably 1 minute or more and 600 minutes or less, and more preferably 5 minutes or more and 120 minutes or less.

[0039] Examples of reaction solvents for the coating step include water and mixed solvents of water and hydrophilic organic solvents. When these solvents are used, phosphate salts with smaller particle sizes are precipitated compared to when hydrophobic organic solvents are used, resulting in the formation of a dense coating. Among these, water is preferred. When a mixed solvent of water and hydrophilic organic solvent is used, examples of the hydrophilic organic solvent include ethanol, methanol, 2-propanol, acetone, and 2-butanone. The content of the hydrophilic organic solvent in the mixed solvent is preferably 0.1% by mass or more and 80% by mass or less, more preferably 1% by mass or more and 50% by mass or less.

[0040] During the coating process, the pH of the aqueous solution may increase as phosphoric acid derived from the phosphate compound adheres to the magnetic material. In this case, the pH of the aqueous solution may be adjusted by adding an inorganic or organic acid. When adjusting the pH, the pH range can be greater than 0 and less than 7, preferably 1 to 4.5, more preferably 1.6 to 3.9, and even more preferably 2 to 3. By adjusting the pH to 1 or greater, the precipitation rate of the phosphorus compound containing a rare earth metal element can be slowed compared to a pH below 1, making it easier to control the thickness of the coating. At a pH of 7 or greater, the amount of phosphate precipitation decreases, resulting in insufficient coating and increased loss. Therefore, a pH of less than 7 is preferable. By adjusting the pH to 4.5 or less, the phosphate precipitation rate can be kept at a moderate level. Inorganic acids include sulfuric acid, hydrochloric acid, nitric acid, phosphoric acid, boric acid, and hydrofluoric acid. Organic acids include acetic acid, formic acid, oxalic acid, tartaric acid, and citric acid. While inorganic acids are preferred from the perspective of wastewater treatment, organic acids can be used in combination depending on the purpose. A mixture of inorganic and organic acids may be used. To adjust the pH, inorganic or organic acids may be added as needed during the coating process so that the pH falls within the above range. Since the pH rises rapidly in the early stages of the coating process, it is preferable to shorten the intervals at which inorganic or organic acids are added for pH control.

[0041] In the coating process, the content of the magnetic material in the mixture of the aqueous solution containing the phosphate compound and the rare earth compound and the magnetic material can be 0.0001% by mass to 70% by mass, and preferably 0.01% by mass to 10% by mass. Within these ranges, the thickness of the coating tends to be stable.

[0042] For the purpose of improving the water resistance and corrosion resistance of the coating and the magnetic properties of the magnetic powder, oxoacid salts such as molybdate, tungstate, vanadate, and chromate, oxidizing agents such as sodium nitrate and sodium nitrite, and chelating agents such as EDTA may be further added. When the aqueous solution contains an oxoacid salt, its concentration is preferably 0.0001% by mass to 10% by mass, and more preferably 0.01% by mass to 1% by mass. When the aqueous solution contains an oxidizing agent, its concentration is preferably 0.0001% by mass to 10% by mass, and more preferably 0.01% by mass to 1% by mass. When the aqueous solution contains a chelating ...

[0043] In the coating process, the order of mixing the components is not important as long as the aqueous solution containing the phosphate compound and the rare earth compound can be mixed with the soft magnetic magnetic material. In the coating process, it is preferable to first mix the aqueous solution containing the rare earth compound with the magnetic material, and then mix the phosphate compound. Mixing the aqueous solution containing the rare earth compound with the magnetic material in advance makes it easier for the rare earth compound to adhere or bond to the surface of the magnetic material, thereby increasing the amount of the coating containing the phosphorus compound. When mixing the aqueous solution containing the rare earth compound with the magnetic material in advance, the mixture can be mixed and then stirred at a pH of preferably 2 to 12, more preferably 4 to 10, and even more preferably 5 to 8, for at least 1 minute, and then the aqueous solution containing the phosphate compound can be added.

[0044] The coating step may be performed only once, or may be performed two or more times. By performing the coating step two or more times, a thick coating containing a phosphorus compound containing a rare earth metal element can be formed on the surface of the magnetic material. The upper limit of the number of coating steps can be, for example, 10 or less, or may be 5 or less. The number of coating steps may be two.

[0045] When the coating step is performed two or more times, the magnetic material may be purified between the coating steps. The magnetic material on which the coating has been formed can be purified, for example, by heating at a temperature of 100°C to 800°C, filtering, or the like.

[0046] When the coating step is performed two or more times, it is preferable that the aqueous solution in the n-th coating step is obtained by adding a rare earth compound to the aqueous solution in the (n-1)-th coating step. In this case, the n-th coating step can be performed without purifying the magnetic material after the (n-1)-th coating step. n is an integer of 2 or more, but when the coating step is performed k times, n is preferably any integer between 2 and k. When n is any integer between 2 and k, the aqueous solution obtained by adding a rare earth compound to the aqueous solution in the coating step is used in all coating steps from the second step onwards.

[0047] The type of rare earth compound added to the aqueous solution in the n-th coating step may be the same as or different from the rare earth compound contained in the aqueous solution in the (n-1)-th coating step.

[0048] The concentration of the rare earth compound added to the aqueous solution in the n-th coating step may be determined appropriately depending on the reaction time of the (n-1)th coating step and the type of rare earth compound. The concentration of the rare earth compound added to the aqueous solution in the n-th coating step is preferably 0.01 to 50 times, more preferably 0.1 to 10 times, the content of the rare earth compound in the aqueous solution in the (n-1)th coating step. Within these ranges, unevenness in the thickness of the coating film can be reduced.

[0049] When the coating process is performed two or more times, the pH of the mixture obtained by mixing the aqueous solution and the magnetic material in the m-th coating process is preferably lower than the pH of the mixture obtained by mixing the aqueous solution and the magnetic material in the (m-1)th coating process, with the difference being preferably 0.1 or more, more preferably 1 or more. Note that the reaction between the phosphate compound and the magnetic material may reduce the amount of free phosphoric acid in the aqueous solution, causing the pH of the mixture of the aqueous solution and the magnetic material to increase. If the pH fluctuates during the reaction, the pH of the mixture obtained by mixing the aqueous solution and the magnetic material in the (m-1)th coating process refers to the pH at the end of the (m-1)th coating process. When the pH of the mixture obtained by mixing the aqueous solution and the magnetic material in the m-th coating process is lower than that in the (m-1)th coating process, the efficiency of forming a coating containing a phosphorus compound on the magnetic material can be improved.

[0050] Although m is an integer of 2 or greater, if the coating process is performed k times, m may be any integer between 2 and k inclusive. When m is any integer between 2 and k inclusive, in all coating processes from the second onwards, an aqueous solution with a lower pH than the mixed solution obtained by mixing the aqueous solution and magnetic material in the previous coating process is used. Alternatively, when k is 3 or greater, the pH in the first coating process and the pH in the second coating process may be different, and the pH in the third and subsequent coating processes may be adjusted to be in the same pH range as in the second coating process.

[0051] In the m-th coating step, the pH of the aqueous solution may be adjusted by adding an inorganic or organic acid. When adjusting the pH, the pH range can be greater than 0 and less than 7, preferably 1 to 4.5, more preferably 1.6 to 3.9, and even more preferably 2 to 3. By adjusting the pH to 1 or greater, the precipitation rate of the phosphorus compound containing a rare earth metal element can be reduced compared to a pH below 1, making it easier to control the thickness of the coating formed. A pH of less than 7 is preferable because a pH of 7 or greater reduces the amount of phosphate precipitation, resulting in insufficient coating and increased loss. By adjusting the pH to 4.5 or less, the phosphate precipitation rate can be kept at a reasonable level. The acid to be added can be inorganic or organic. Inorganic acids include sulfuric acid, hydrochloric acid, nitric acid, phosphoric acid, boric acid, and hydrofluoric acid. Organic acids include acetic acid, formic acid, oxalic acid, tartaric acid, and citric acid. While inorganic acids are preferred from the perspective of wastewater treatment, organic acids can be used in combination depending on the purpose. A mixture of inorganic and organic acids may also be used. To adjust the pH, an inorganic or organic acid may be added as needed during the coating process so that the pH falls within the above range. Since the pH rises rapidly in the early stages of the coating process, it is preferable to shorten the intervals at which inorganic or organic acids are added for pH control.

[0052] The pH can be adjusted to a range of 1 to 4.5 by adding an inorganic or organic acid to the aqueous solution for at least 1 minute, preferably for at least 30 minutes to reduce areas where the coating is thin. Because the pH rises rapidly in the initial stage of pH maintenance, it is preferable to add the inorganic or organic acid for pH control at short intervals. As coating progresses, the pH fluctuations gradually slow down, and the intervals between additions of the inorganic or organic acid become longer, allowing the reaction endpoint to be determined.

[0053] The n-th coating step may also serve as the m-th coating step, that is, the pH may be adjusted in the n-th coating step as the m-th coating step.

[0054] After the coating step, coating may be performed using an aqueous solution containing a phosphate compound and a compound of a non-rare earth metal element. In this case, the method for producing a coated magnetic material preferably includes a first coating step, and a second coating step after the first coating step, in which the aqueous solution containing the phosphate compound and a compound of a non-rare earth metal element is mixed with the magnetic material to form a coating containing phosphate and the non-rare earth metal element on the surface of the magnetic material. By performing the second coating step, the amount of the coating containing phosphorus formed on the surface of the magnetic material can be increased. Furthermore, by performing the second coating step, the rare earth metal element can be biased toward the side of the coating closest to the magnetic material.

[0055] The type and concentration of the phosphate compound in the aqueous solution used in the second coating step are the same as those described for the coating step. The non-rare earth metal element may be any element other than a rare earth metal element, including metal elements other than rare earth metal elements and metalloid elements. Metal elements other than rare earth metal elements include alkali metal elements such as Li, Na, K, Rb, and Cs; alkaline earth metal elements such as Ca, Sr, and Ba; transition metal elements such as Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Mn, Fe, Ru, Co, Ni, Pd, Pt, Cu, Ag, and Au; and typical elements such as Zn, Cd, and Al. Metalloid elements include B, Al, Si, and Ge. Among these, metal elements are preferred, and in order to obtain a coated magnetic material with excellent heat resistance, metal elements whose Gibbs energy change (ΔG) in the oxidation reaction is -300 kJ / mol O2 or less in the temperature range when the coated magnetic material is heated (approximately 400°C to approximately 700°C) are more preferred, with transition metals being even more preferred, and Cr, W, Mn, Mo, Nb, and V being particularly preferred. Table 2 shows the Gibbs energy change in the oxidation reaction of metal oxides other than rare earths at 600°C.

[0056] [Table 2]

[0057] Examples of compounds of non-rare earth metal elements include oxoacids, heteroacids, chlorides, hydroxides, nitrides, oxides, borides, fluorides, nitrates, phosphates, sulfates, and silicates of non-rare earth metal elements, with oxoacids being preferred. The oxoacid may be a polyacid. Among these, metal oxoacid compounds are preferred, transition metal oxoacid compounds are more preferred, and oxoacid compounds of Cr, W, Mn, Mo, Nb, and V are even more preferred. The above-listed compounds of non-rare earth metal elements may be used alone or in combination of two or more.

[0058] The content of the compound of the non-rare earth metal element in the aqueous solution used in the second coating step is preferably 0.001% by mass or more and 10% by mass or less, and more preferably 0.01% by mass or more and 5% by mass or less.

[0059] In the second coating step, the reaction time for forming a coating on the surface of the magnetic material is preferably 1 minute or more and 10 hours or less, and more preferably 5 minutes or more and 120 minutes or less.

[0060] In the second coating step, it is preferable to adjust the pH by adding an inorganic or organic acid to the aqueous solution. The pH range for adjusting the pH can be greater than 0 and less than 7, preferably greater than 1 and less than 4.5, more preferably greater than 1.6 and less than 3.9, and even more preferably greater than 2 and less than 3. By adjusting the pH to 1 or greater, the phosphate deposition rate can be slowed compared to a pH below 1, making it easier to control the thickness of the coating formed. A pH of 7 or greater tends to reduce the amount of phosphate deposition, resulting in insufficient coating and increased loss, so a pH below 7 is preferable. By adjusting the pH to 4.5 or less, the phosphate deposition rate can be kept at a moderate level. The acid to be added can be inorganic or organic. Examples of inorganic acids include sulfuric acid, hydrochloric acid, nitric acid, phosphoric acid, boric acid, and hydrofluoric acid. Examples of organic acids include acetic acid, formic acid, oxalic acid, tartaric acid, and citric acid. While inorganic acids are preferred for wastewater treatment, organic acids can be used in combination depending on the purpose. A mixture of inorganic and organic acids can also be used. To adjust the pH, an inorganic or organic acid may be added as needed during the coating process so that the pH falls within the above range. Since the pH rises rapidly in the early stages of the coating process, it is preferable to shorten the intervals at which inorganic or organic acids are added for pH control.

[0061] The pH can be adjusted to a range of 1 to 4.5 by adding an inorganic or organic acid to the aqueous solution for at least 1 minute, preferably for at least 30 minutes to reduce areas where the coating is thin. Because the pH rises rapidly in the initial stage of pH maintenance, it is preferable to add the inorganic or organic acid for pH control at short intervals. As coating progresses, the pH fluctuations gradually slow down, and the intervals between additions of the inorganic or organic acid become longer, allowing the reaction endpoint to be determined.

[0062] After the coating step and, if necessary, the second coating step described above, the coated magnetic material may be purified. In the purification step of the coated magnetic material, liquid components can be removed, for example, by heating at 100°C to 500°C, filtration through a filter, ceramic membrane filtration, suction filtration, centrifugation, or the like.

[0063] Furthermore, a coating fixation step may be performed after the coating step and, if necessary, the second coating step described above. In the coating fixation step, the purified coated magnetic material is treated at high temperature to bake the phosphorus onto the magnetic material. The temperature condition for the high-temperature treatment is preferably 50°C or higher and 500°C or lower, more preferably 100°C or higher and 300°C or lower. The time for the high-temperature treatment is preferably 1 minute or higher and 6000 minutes or lower, more preferably 10 minutes or higher and 600 minutes or lower.

[0064] <<Soft magnetic materials>> The soft magnetic material of this embodiment has a first phase and a second phase having crystals with a bcc structure containing Fe and X (X is one or more elements selected from Ti, Mn, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Cu, Zn, and Si), and for one element of X contained in both phases, the content of the element in the second phase is 2 times or more and 10 times or more the content of the element in the first phase. 5 The average circularity is 0.55 or more, and the average particle size is 160 μm or less.

[0065] The soft magnetic material of this embodiment has a first phase and a second phase having a crystal with a bcc structure containing Fe and X (X is one or more transition metals selected from Ni and Co), and for one element of X contained in both phases, the content of the element in the second phase is more than 1 time and less than 10 times the content of the element in the first phase. 5 The average circularity is 0.55 or more, and the average particle size is 160 μm or less.

[0066] The soft magnetic material of this embodiment can be produced, for example, by the method for producing the soft magnetic material of this embodiment described above. The composition of the soft magnetic material, the ratio of the contents of one element of X contained in both phases, the average particle size, etc. are the same as those described above for the soft magnetic material obtained by heat treatment. X is preferably Mn and / or Ni.

[0067] The average circularity of the soft magnetic material is 0.55 or more, preferably 0.6 or more, more preferably 0.65 or more, or 0.70 or more. The upper limit of circularity is 1. The closer the circularity is to 1, the more preferable it is because the contact between powder particles becomes closer to point contact and the smaller the inter-particle eddy current loss. The proportion of particles with a circularity of 0.8 or more may be 30 mass% or more, preferably 40 mass% or more, and more preferably 50 mass% or more. Circularity is an index that represents the circularity of the particle outline shape, and the closer it is to a circle, the closer it is to 1. Here, circularity can be calculated from the cross-sectional area S of the particle and its perimeter L using the following formula: Circularity = 4πS / L 2

[0068] The average necking degree of a soft magnetic material with an average particle size of 160 μm or less may be 4 or less, preferably 3 or less, and more preferably 2 or less. When there is no necking, the average particle size and projected particle size are equal, and the variance of the particle size distribution is very small, the necking degree will be a value very close to 1. The necking degree is an index that indicates the degree of particle aggregation; if there is no connection and / or contact between the individual powder particles due to aggregation, the value will be close to 1. If all the powder particles are connected and / or contacted due to aggregation, the value will be virtually infinite in terms of discussing high-frequency characteristics, but in reality it will take on a finite value that is much larger than 4.

[0069] The degree of necking was determined by a dry laser diffraction particle size distribution analyzer. 50 In an SEM photograph of a "sufficiently representative portion" of the entire powder particles, when observing an image of the aggregate of powder particles projected onto a plane perpendicular to the photographing direction, the number average particle size of the portion that can be recognized as a particle is d 50 It can be calculated using the following formula using the projected particle diameter. Note that a "sufficiently representative portion" must be a number that can be considered "representative," meaning that the investigation must cover at least 30 powder particles. Necking degree = D 50 / d 50

[0070] In this disclosure, the necking degree is defined for an aggregate of powder particles with an average particle size of 160 μm or less. This means that powder particles with an average particle size of 160 μm or less are prone to necking due to agglomeration. In this case, for example, an aggregate of particles with a necking degree of 4 or less can be easily coated to produce a compact with reduced interparticle eddy current loss. Even if the compact is formed without a coating treatment, the electrical connection between the particles is relaxed, and in this case, the interparticle eddy current loss is comparatively reduced, resulting in excellent iron loss. On the other hand, in the case of an aggregate of particles with an average particle size exceeding 160 μm, even if the equation for the necking degree is applied to this aggregate and a value such as 4 is obtained, even if the interparticle eddy current loss is indeed reduced, the intraparticle eddy current loss remains large, resulting in an inability to exhibit excellent iron loss.

[0071] The degree of necking increases not only when the particle size of the primary particles is small, but also when the soft magnetic powder particles are bonded together due to aggregation and sintering caused by the heat treatment conditions of the raw material granules. The degree of necking is also greatly affected by the particle shape and surface condition, and tends to increase when the particle shape has many flat surfaces.

[0072] For soft magnetic materials, the span is an index that represents the particle size distribution and is defined as follows: Span = (D 90 -D 10 ) / D 50 The value of D 50 When the circularity is 160 μm or less and the circularity is high, a smaller span is preferable from the viewpoint of reducing iron loss. The span may be 1 or less, 0.5 or less, or 0.4 or less.

[0073] The standard deviation of the particle size distribution is D 50 For particles with the same D, it is preferable that the standard deviation is small from the viewpoint of reducing iron loss. 50 When the standard deviation of the particle size distribution is 160 μm or less, the standard deviation of the particle size distribution may preferably be 80 μm or less, more preferably 50 μm or less, and even more preferably 30 μm or less.

[0074] D 50 Magnetic materials with a particle size of 16 μm or more, a narrow particle size distribution (small span of particle size distribution, small standard deviation), and little necking have a small coordination number between particles, which reduces the probability of magnetic powder particles bonding together, and both inter- and intra-particle eddy currents tend to be small, resulting in low loss. In particular, pulse transformers and other devices that need to avoid insulation breakdown do not require a high filling rate, so a narrow particle size distribution is an effective application. 50 Even if the particle size is small, the particle size distribution is wide and 50 When the volume fraction of larger particles increases, D 50 This is not desirable because the eddy current loss at the target frequency determined by D 50 If the volume fraction of smaller particles is large, the particles will come into contact with each other more frequently, which is undesirable because it will cause significant eddy current loss between particles and hysteresis loss at the target frequency.

[0075] <<Coated soft magnetic material>> The coated soft magnetic material of this embodiment comprises a soft magnetic material and a silicon compound coating containing a silicon-containing compound (including silica or silicate) and / or a phosphorus compound coating containing a rare earth metal element, phosphorus, and oxygen, formed on the surface of the soft magnetic material. The coating may contain a phosphorus compound containing a rare earth metal element, and the phosphorus compound may be a phosphate. The coating may also contain an oxide that does not contain a rare earth metal element, in which case the phosphorus compound containing the rare earth metal element does not have to be a phosphate. Examples of rare earth metal elements include Ce, Nd, Sm, La, Dy, Y, and Pr, with Ce, Nd, Sm, La, and Dy being preferred. The coated soft magnetic material is not limited to a completely coated soft magnetic material, but may also be a partially coated soft magnetic material. Here, the coating method for the silicon-containing compound will be described. For example, known methods include a method in which a polysilazane compound is introduced onto the powder surface and thermally decomposed in the atmosphere to remove the ammonia component to form a silica film, and a method in which a silicone resin is introduced onto the powder interface and thermally decomposed to remove the organic component to form a silica interface.

[0076] The average particle size of the coated soft magnetic material is as described for the soft magnetic material. The thickness of the coating containing rare earth metal elements, phosphorus, and oxygen is preferably 2 nm to 10 μm, more preferably 5 nm to 500 nm, from the viewpoint of the insulating properties and heat resistance of the coated magnetic material. The thickness of the coating can be measured by performing compositional analysis on a cross section of the coated magnetic material using EDX line analysis.

[0077] It is preferable that oxygen is present in a greater amount than phosphorus in the coating. In this case, there is at least a portion of the coating in the thickness direction where oxygen is present in a greater amount than phosphorus. The portion of the coating in the thickness direction where oxygen is present in a greater amount than phosphorus is preferably 10% or more, more preferably 50% or more, and even more preferably the entire area. The oxygen content is preferably more than 1 time that of phosphorus, and can be 2 times or more, or even 3 times or more. The upper limit of the oxygen content can be, for example, 10 times or less that of phosphorus.

[0078] In addition to rare earth metal elements, phosphorus, and oxygen, the coating may also contain non-rare earth metal elements other than phosphorus and oxygen. Non-rare earth metal elements other than phosphorus and oxygen include metal elements other than rare earth metal elements, metalloid elements, H, C, N, O, F, P, S, Cl, Br, and I. Metal elements other than rare earth metal elements include alkali metal elements such as Li, Na, K, Rb, and Cs; alkaline earth metal elements such as Ca, Sr, and Ba; transition metal elements such as Fe, Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Mn, Ru, Co, Ni, Pd, Pt, Cu, Ag, and Au; and zinc group elements such as Zn, Cd, and Al, as well as typical elements including earth metals. Metalloid elements include B, Al, Si, and Ge. Among these, metal elements are preferred, and in order to obtain a coated magnetic material with excellent heat resistance, metal elements whose Gibbs energy change (ΔG) in the oxidation reaction is -300 kJ / mol O2 or less in the temperature range when the coated magnetic material is heated (approximately 400°C or higher and approximately 700°C or lower) are more preferred, with transition metals being even more preferred, and Cr, W, Mn, Mo, Nb, and V being particularly preferred. These elements contained in the coating may be derived from the magnetic material to be coated, or may be elements that were present during the coating formation reaction.

[0079] When the coating contains non-rare earth metal elements other than phosphorus and oxygen, the content of the non-rare earth metal elements and the rare earth metal elements in the coating preferably reaches a maximum value for the non-rare earth metal elements and then a maximum value for the rare earth metal elements in the direction from the surface of the coating toward the magnetic material. This tends to improve insulation. When the thickness of the coating is T, the distance between the position showing the maximum value for the non-rare earth metal elements and the position showing the maximum value for the rare earth metal elements in the direction from the surface of the coating toward the magnetic material is preferably 0.001 × T or more and 0.99 × T or less, and more preferably 0.1 × T or more and 0.9 × T or less. Within the range of 0.1 × T or more and 0.9 × T or less, insulation tends to be further improved.

[0080] The content of the non-rare earth metal element preferably reaches a maximum value and then decreases in the direction from the surface of the coating toward the magnetic material, and then begins to increase. Such a distribution tends to improve the heat resistance of the coating. When forming the coating, the coating process is performed two or more times, and in the second or subsequent coating processes, an inorganic acid is added to the aqueous solution to adjust the pH to 1 or more and 4.5 or less, thereby forming a coating so that the content of the non-rare earth metal element exhibits this distribution. The minimum value before the content of the non-rare earth metal element reaches a maximum value, decreases, and then begins to increase is preferably 0.9 times or less, more preferably 0.5 times or less, of the maximum value. The lower limit of the minimum value can be 0.001 times or more of the maximum value.

[0081] In the coating, each of the above elements may be present in either a crystalline or amorphous form. The concentration (atomic %) of each element in the coating can be measured by performing a composition analysis of the coated magnetic material using EDX line analysis. The presence of a microcrystalline phosphate compound or composite oxide in the coating increases mechanical strength and improves heat resistance.

[0082] As the soft magnetic material contained in the coated magnetic material, those described above in relation to the method for producing the coated magnetic material can be used.

[0083] The content of rare earth metal elements in the coated magnetic material is preferably 0.0001% by mass or more, more preferably 0.01% by mass or more, and even more preferably 0.1% by mass or more. A content of 0.0001% by mass or more tends to withstand high-temperature heat treatment, a content of 0.01% by mass or more tends to withstand even higher-temperature heat treatment, and a content of 0.1% by mass or more tends to provide improved insulation. The upper limit of the rare earth metal element content can be 50% by mass or less, preferably 10% by mass or less. By keeping the content of rare earth metal elements in the coated magnetic material at 50% by mass or less, it is possible to suppress a decrease in the magnetic permeability of the coated magnetic material and thus suppress deterioration of its properties. The content of rare earth metal elements in the coated magnetic material is measured using inductively coupled plasma atomic emission spectroscopy (ICP-AES).

[0084] The phosphorus content in the coated magnetic material is preferably 0.0001% by mass to 15% by mass, more preferably 0.001% by mass to 5% by mass. Within this range, heat resistance tends to improve. The phosphorus content in the coated magnetic material is measured using ICP-AES.

[0085] The compact of the soft magnetic material of this embodiment can be produced from the soft magnetic material of the present disclosure by the method described below.

[0086] The anisotropic particle size (R a ) may be 95 μm or less, preferably 90 μm or less, and more preferably 80 μm or less. R a =(4S / π) 0.5 / A Here, S represents the area of ​​one of the grains constituting the compact, and A represents the aspect ratio of that grain. The smaller the average anisotropic grain size, the smaller the intragranular eddy current loss and the more magnetically isotropic the compact can be. The lower limit is not particularly limited, but as in this example, 2When only particles of 30 or more are measured, the average anisotropic grain size tends to be 8 μm or more. The average anisotropic grain size is the number average value of the anisotropic grain size in the cross section of the compact, and the measured value R for 30 or more particles a It is preferable that the average value of

[0087] Iron loss W of compacts containing coated magnetic material 10 / 2k The iron loss W may be 300 W / kg or less, preferably 280 W / kg or less, and more preferably 200 W / kg or less. The lower limit of the iron loss W may be 20 W / kg or more. The hysteresis loss W of the coated magnetic material h The hysteresis loss W can be 180 W / kg or less, preferably 150 W / kg or less, and more preferably 130 W / kg or less. h The lower limit of the eddy current loss W of the coated magnetic material may be 19 W / kg or more. e The eddy current loss W can be 220 W / kg or less, preferably 120 W / kg or less, and more preferably 45 W / kg or less. e The lower limit of the loss may be 1 W / kg or more. max = 1T, the value measured at a frequency of 2kHz.

[0088] Also, B max =0.5T, iron loss W measured at a frequency of 5kHz 5 / 5k The iron loss W can be 400 W / kg or less, preferably 300 W / kg or less, and more preferably 150 W / kg or less. The lower limit of the iron loss W may be 25 W / kg or more. Under this condition, the hysteresis loss W of the coated magnetic material h The hysteresis loss W can be 150 W / kg or less, preferably 140 W / kg or less, and more preferably 110 W / kg or less. h The lower limit of the eddy current loss W of the coated magnetic material may be 24 W / kg or more. e The eddy current loss W can be set to 200 W / kg or less, preferably 165 W / kg or less, and more preferably 50 W / kg or less. e The lower limit may be 1 W / kg or more.

[0089] B max =0.5T, iron loss W measured at a frequency of 10kHz 5 / 10k The iron loss W can be 1000 W / kg or less, preferably 950 W / kg or less, and more preferably 400 W / kg or less. The lower limit of the iron loss W may be 50 W / kg or more. Under this condition, the hysteresis loss W of the coated magnetic material h The hysteresis loss W can be 300 W / kg or less, preferably 280 W / kg or less, and more preferably 220 W / kg or less. h The lower limit of the eddy current loss W of the coated magnetic material may be 48 W / kg or more. e The eddy current loss W can be set to 700 W / kg or less, preferably 650 W / kg or less, and more preferably 180 W / kg or less. e The lower limit may be 1 W / kg or more.

[0090] The compact containing the coated magnetic material has a magnetic flux density (B 100 ) may be 1.1 T or more, 1.2 T or more, 1.3 T or more, 1.4 T or more, preferably 1.5 T or more.

[0091] In this embodiment, the compact that has undergone the heating process can be set to such a numerical range. The heating temperature in the heating process can be, for example, 600°C. A compact in which losses such as iron loss W are within these numerical ranges may not contain resin and glass. When a coated magnetic material, rather than a compact, has undergone the heating process, the iron loss W and hysteresis loss W measured for the coated magnetic material can be set to such a range. h , eddy current loss W e may be in the ranges mentioned above.

[0092] <Method of manufacturing molded body> The soft magnetic material obtained by the method for producing a soft magnetic material of this embodiment can be heated and molded (heating step) to produce a molded body.

[0093] The heating temperature is preferably 100°C or higher and 1200°C or lower. The heating step can be performed to remove distortion caused by pressure or to partially react the coating of the coated magnetic material to obtain an integrated molded body. To remove distortion caused by pressure, the heating temperature is preferably 300°C or higher and 1000°C or lower, and more preferably 400°C or higher and 700°C or lower. The coated magnetic material obtained by coating the soft magnetic material has a coating with excellent thermal stability, so loss of the coating is suppressed even after the heating step. The heating temperature may be 500°C or higher. In this case, it is preferable that the molded body does not contain resin or glass. This is because deterioration of resin and glass tends to be significant at temperatures above 500°C. The heating step time is preferably 1 minute or higher and 6000 minutes or lower, and more preferably 10 minutes or higher and 600 minutes or lower. The heating step may be performed in a nitrogen atmosphere or in air. The heating step is preferably performed in an inert atmosphere such as an argon atmosphere or vacuum. If heating is performed in a nitrogen atmosphere, the magnetic material may be nitrided, resulting in a deterioration in its properties, so the heating step is preferably performed in an inert atmosphere other than a nitrogen atmosphere.

[0094] It is preferable to include a step of pressurizing the coated magnetic material to obtain a pressure-molded product before heating. In this case, the heating step is a step of heating the pressure-molded product obtained in the step of obtaining a pressure-molded product. A process such as a hot press method or HIP (hot isostatic press) in which heating is performed while applying pressure may also be used.

[0095] The pressure conditions are preferably 0.01 GPa or more and 10 GPa or less, and more preferably 0.5 GPa or more and 5 GPa or less. A pressure-molded product of the desired shape can be obtained by filling a mold with the coated magnetic material and then applying pressure. When using a mold, a lubricant, as described below, may be applied to the inner wall of the mold cavity before filling with the coated magnetic material. Applying a lubricant to the inner wall of the mold cavity can improve the releasability of the pressure-molded product from the mold.

[0096] When pressurizing, the coated magnetic material may be pressed alone. When pressurizing, the coated magnetic material may be mixed with a binder, lubricant, etc., and then pressed. Examples of binders include thermosetting resins such as epoxy resin, urethane resin, phenolic resin, methacrylic resin, acrylic resin, and silicone resin, and thermoplastic resins such as polyamide resin and thermoplastic silicone resin. The amount of binder used is preferably 0.01 to 1000 parts by mass, more preferably 1 to 50 parts by mass, per 100 parts by mass of the coated magnetic material. When the amount of binder used is within the above range, a molded product with excellent mechanical strength and low losses such as iron loss can be obtained.

[0097] Lubricants that can be used include metal soaps such as zinc stearate, calcium stearate, and lithium stearate, amines or amides such as 1,2-bis(stearoylamino)ethane, long-chain hydrocarbons such as wax, silicone oil, and fluorine-containing compounds. The amount of lubricant used is preferably 0.00001 to 10 parts by mass, and more preferably 0.01 to 5 parts by mass, per 100 parts by mass of the coated magnetic material. When the amount of lubricant used is within the above range, the releasability of the pressure-molded product from the mold cavity can be improved.

[0098] The packing ratio of the compact obtained by the above manufacturing method can be 10% or more and 100% or less, and preferably 80% or more and 100% or less. The packing ratio here refers to the ratio (percentage) of the compact density to the true density. The ratio (percentage) of the volume of the coated magnetic material to the volume of the compact obtained in this embodiment can be 40% or more and 100% or less, and preferably 80% or more and 100% or less. The ratio of the area of ​​the coated magnetic material to the area of ​​the compact in a cross section of a portion of the compact may be considered to be the ratio of the volume of the coated magnetic material to the volume of the compact.

[0099] The compact obtained by the above manufacturing method is an aggregate of coated magnetic materials with a coating that has excellent thermal stability, so the coating is maintained even after the heating process, suppressing losses such as iron loss. After the heating process, the coatings of individual coated magnetic materials may partially react and fuse with those of adjacent coated magnetic materials, forming an integrated structure while maintaining the insulating state between the magnetic materials. The compact can be obtained from the coated magnetic material without using a binder such as resin or glass. Resin may induce eddy currents when carbonized during heat treatment. Glass may also deteriorate during heat treatment. For this reason, when using binders such as resin or glass, it is preferable to heat the compact at a relatively low temperature. By producing a compact that does not contain resin or glass, it is possible to suppress an increase in loss even when heated at a relatively high temperature, for example, above 500°C. Furthermore, heating at a relatively high temperature can more effectively remove distortion caused by pressure. Furthermore, the use of the above-mentioned lubricant in combination increases the density of the compact, chemically bonds adjacent coated magnetic materials, and improves mechanical strength.

[0100] <<Applications>> The compact can be used in a variety of applications as a powder magnetic core with reduced iron loss. For example, it can be applied to transformers, coils, heads, inductors, reactors, cores (magnetic cores), yokes, various actuators, etc. The compact can also be used as a soft magnetic part to be incorporated into various motors such as motors for rotating machines and linear motors. Examples of motors for rotating machines include voice coil motors, induction motors, reactance motors, and axial motors. It is particularly effective as a stator core for axial motors that operate at 2 kHz or higher.

[0101] The soft magnetic material of the present disclosure and the molded article made from the soft magnetic material are highly effective when applied not only to axial motors but also to high-frequency, high-rotation devices, systems, and equipment of 2 kHz or more.

[0102] The inventors have thoroughly investigated the relationship between the operating frequency f (kHz) of the equipment to which the magnetic material is applied and the average particle size at which iron loss is excellent, and have found that, when the average particle size of the magnetic material of the present disclosure is r, the following relationship exists: r=184×f -0.5 Therefore, when applied to equipment with a frequency of f (kHz), the average particle size is 184f -0.5 The soft magnetic material of the present disclosure having a particle diameter of 1 μm is a magnetic material in which core loss, particularly intragranular eddy current loss, is suppressed. When f=2, r=130, when f=5, r=80, and when f=10, r=60.

[0103] The present disclosure includes the following aspects. (Section 1) a spray drying step of spray-drying a slurry containing Fe and X (X is one or more elements selected from Ti, Mn, Ni, Co, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Cu, Zn, and Si) to obtain granules having an average particle size of 20 μm or more and 200 μm or less; and a heat treatment step of heat-treating the granulated material in a reducing gas at 800°C or higher and 1200°C or lower to obtain a heat-treated material; A method for producing a soft magnetic material, comprising: (Section 2) Furthermore, a slurry preparation step is provided in which a basic pH adjusting solution is dropped into a stirring vessel having stirring blades while stirring together with an acidic solution containing Fe and X (X is one or more elements selected from Ti, Mn, Ni, Co, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Cu, Zn, and Si) to generate ferrite nanoparticles and obtain a slurry, wherein the dropping time T (s) is T≧375000VD 2 / 3 (where V(m 3 ) indicates the volume of the stirring vessel, and D (m) indicates the diameter of the stirring blade. Item 2. A method for producing a soft magnetic material according to item 1, comprising the step of preparing a slurry that satisfies the above. (Section 3) Item 3. The method for producing a soft magnetic material according to item 1 or 2, further comprising a classification step of classifying the heat-treated product to obtain a classified product. (Section 4) Item 4. The method for producing a soft magnetic material according to Item 3, further comprising a coating step of mixing the classified material with an aqueous solution containing a phosphate compound and a rare earth compound to form a coating film containing a phosphorus compound containing a rare earth metal element on the surface of the classified material. (Section 5) The alloy has a first phase and a second phase each having a crystal with a bcc structure containing Fe and X (X being one or more elements selected from Ti, Mn, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Cu, Zn, and Si), With respect to one element of X contained in both phases, the content of the element in the second phase is 2 times or more to 10 times or more the content of the element in the first phase. 5 It is less than double, A soft magnetic material with an average circularity of 0.55 or more and an average particle size of 160 μm or less. (Section 6) Item 6. The soft magnetic material according to item 5, wherein X contains Mn. (Section 7) The first and second phases have crystals with a bcc structure containing Fe and X (X is one or more transition metals selected from Ni and Co), With respect to one element of X contained in both phases, the content of the element in the second phase is more than 1 time and less than 10 times the content of the element in the first phase. 5 It is less than double, A soft magnetic material with an average circularity of 0.55 or more and an average particle size of 160 μm or less. (Section 8) 8. The soft magnetic material according to any one of items 5 to 7, having an average particle size of 130 μm or less. (Section 9) Item 9. The soft magnetic material according to any one of items 5 to 8, which has a necking degree of 4 or less. (Section 10) 10. The soft magnetic material according to any one of items 5 to 9, wherein the ratio of particles having a circularity of 0.8 or more is 30% or more by number. (Section 11) 11. The soft magnetic material according to any one of items 5 to 10, wherein the average circularity is 0.6 or more. (Section 12) A soft magnetic material used at frequencies f (kHz) of 2 kHz or more, with an average particle size of 184f -0.5 A soft magnetic material according to any one of items 5 to 11, having a particle size of 0.1 μm or less. (Section 13) 13. A soft magnetic material according to any one of items 5 to 12, coated with a silicon compound or a phosphate compound. (Section 14) A soft magnetic material compact produced from the soft magnetic material according to any one of items 5 to 12 or the material according to item 13, wherein the average anisotropic grain size of the soft magnetic material determined from a cross-sectional image of the compact is 90 μm or less. (Section 15) A stator core of an axial motor that uses the soft magnetic material according to any one of items 5 to 12 or the material according to item 13 and that operates at 2 kHz or higher. [Example]

[0104] Examples will be described below. Unless otherwise specified, "%" is by mass.

[0105] Comparative Example 1 An aqueous solution (pH 3.5) was prepared using MnSO4·5H2O (manganese(II) sulfate pentahydrate), NiSO4·6H2O (nickel(II) sulfate hexahydrate), and FeSO4·7H2O (iron(II) sulfate heptahydrate) as raw materials, with the atomic concentration ratio of Fe, Ni, and Mn being 97.9:2.0:0.1. A portion of the aqueous solution with a sulfate concentration of 0.84 mol / L was poured into a stirring vessel (stirring layer volume V = 0.051 m) equipped with a stirring blade. 3 ), and the diameter of the stirring blade (D = 0.220 (m)). The remaining aqueous solution and a pH adjuster (pH 15.2) containing NaOH aqueous solution were added dropwise to the stirring bed while stirring to obtain Mn-Ni-ferrite slurry. At this time, the power per unit volume P V to 0.2kW / m 3The dropping time was 120 minutes. The resulting slurry was suction filtered and dried with hot air at 50°C to obtain Mn-Ni-ferrite granules. The XRD pattern of the granules indicated that a nearly single-phase Mn-Ni-ferrite was obtained. The resulting granules were classified to particle sizes of 63 to 125 μm. The classified granules were heated to 300°C at a rate of 10°C / min in a hydrogen atmosphere, held for 30 minutes, then heated to 450°C at a rate of 10°C / min, held for 30 minutes, then heated to 750°C at a rate of 10°C / min, then heated to 950°C at a rate of 5°C / min, and finally to 1050°C at a rate of 5°C / min. Heat treatment was then performed in a hydrogen atmosphere for 75 minutes. After this, the temperature was rapidly lowered to room temperature, and gradual oxidation was performed for 30 minutes in an argon atmosphere with an oxygen partial pressure of 3% by volume to obtain soft magnetic powder. The resulting soft magnetic powder was crushed using a cutter mill and classified using a sieve. The powder remaining on the sieve with 150 μm openings was used as the Fe—Ni—Mn soft magnetic powder of Comparative Example 1. 50 The obtained Fe—Ni—Mn powder was coated with a silicon compound by a known method of mixing a polysilazane compound with an organic solvent and heating the mixture, thereby obtaining a silicon compound-coated soft magnetic material of Comparative Example 1.

[0106] Example 1 The same procedure as in Comparative Example 1 was carried out except that the material that passed through the 150 μm sieve and remained on the 100 μm sieve was used as the Fe—Ni—Mn soft magnetic powder. 50 The powder thus obtained was coated with a silicon compound in the same manner as in Comparative Example 1, thereby obtaining a coated soft magnetic material of Example 1.

[0107] Example 2 The same procedure as in Comparative Example 1 was carried out except that the material that passed through the 100 μm sieve and remained on the 53 μm sieve was used as the obtained Fe—Ni—Mn soft magnetic powder. 50 The powder thus obtained was coated with a silicon compound in the same manner as in Comparative Example 1, thereby obtaining a coated soft magnetic material of Example 2.

[0108] Example 3 The same procedure as in Comparative Example 1 was carried out except that the Fe—Ni—Mn soft magnetic powder passed through a sieve with a mesh size of 53 μm was used. 50 The powder thus obtained was coated with a silicon compound in the same manner as in Comparative Example 1, thereby obtaining a coated soft magnetic material of Example 3.

[0109] Example 4 A Mn-Ni-ferrite slurry was obtained in the same manner as in Comparative Example 1. The solute concentration of the slurry was concentrated to 12% or more, and the slurry was spray-dried at 100°C with an atomizer rotation speed of 6,000 rpm to obtain Mn-Ni-ferrite granules. The granules were heated to 300°C at 10°C / min in a hydrogen atmosphere, held for 30 minutes, then heated to 450°C at 10°C / min and held for 30 minutes, then heated to 750°C at 10°C / min, then heated to 950°C at 5°C / min, and finally to 1,050°C at 5°C / min. The mixture was then heat-treated in a hydrogen atmosphere for 75 minutes. The mixture was then rapidly cooled to room temperature and slowly oxidized in an argon atmosphere with an oxygen partial pressure of 3% by volume for 30 minutes to obtain soft magnetic powder. The obtained soft magnetic powder was crushed with a cutter mill, and the powder that passed through a sieve with 150 μm openings was used, and the powder that remained on a sieve with 100 μm openings was used. 50 was 154 μm.

[0110] The SEM image of the Fe-Ni-Mn soft magnetic powder from above is shown in Figure 1A, the SEM-EDX results for Ni in the range are shown in Figure 1B, the SEM-EDX results for Mn in Figure 1C, and the XRD pattern in Figure 2. In the SEM-EDX, the atomic concentrations of Fe, Ni, and Mn were calculated so that the total was 100%. In Figure 1B, the Ni content in the first phase (0.94 at%) was calculated to be more than 10 times that of the first phase (0.94 at%). 5 a second phase (a phase having a Ni content of 1.46 to 2.13 at%) having a Ni content of 1.1 times or less, and a second phase (a phase having a Ni content of 1.1 to 10 at%) having a Ni content of 1.1 times or more, and a second phase (a phase having a Ni content of 1.46 to 2.13 at%) having a Ni content of 1.1 times or less, and a second phase (a phase having a Ni content of 1.1 to 5It was confirmed that there was a second phase (1.46 to 2.13 at%) with a Ni content less than twice that of the first phase (0.06 at%). 5 It was confirmed that there was a second phase (0.12 to 0.25 at%) with a Mn content of 0.12 to 0.25 times or less. Furthermore, it was confirmed from Figure 2 that this soft magnetic powder has a bcc structure. In other words, it was found that the first and second phases when X of this soft magnetic powder is Ni, and the first and second phases when X is Mn, all of these phases have a bcc structure.

[0111] Thereafter, in the same manner as in Comparative Example 1, the obtained Fe—Ni—Mn soft magnetic powder was coated with a silicon compound to obtain a coated soft magnetic material of Example 4.

[0112] Example 5 The same procedure as in Example 4 was carried out, except that the material that passed through the 100 μm sieve and remained on the 53 μm sieve was used. 50 The thickness was 99 μm. By coating with a silicon compound in the same manner as in Comparative Example 1, a coated soft magnetic material of Example 5 was obtained.

[0113] Example 6 The same procedure as in Example 4 was carried out except that the powder that had been classified using a sieve with 53 μm openings was used. 50 The thickness was 53 μm, and the coated soft magnetic material of Example 6 was obtained by coating with a silicon compound in the same manner as in Comparative Example 1.

[0114] Comparative Example 2 The slurry was adjusted so that the atomic concentration ratio of Fe, Ni, and Mn was 95.9:4.0:0.1, and the powder that passed through a sieve with a mesh size of 300 μm was used as the Fe-Ni-Mn soft magnetic powder. The powder was coated with a phosphorus compound in the following steps in the same manner as in Comparative Example 1. (i) Cleaning of soft magnetic materials 50 g of the soft magnetic material was added to an aqueous solution adjusted to pH 1.1 or less with dilute hydrochloric acid, and stirred for 10 minutes to remove surface oxide films and contaminants. (ii) Coating process An aqueous solution of samarium chloride (8% by mass relative to the soft magnetic material) was added to the washed soft magnetic material and stirred for 15 minutes. Next, an aqueous solution of sodium molybdate (2.9% by mass relative to the soft magnetic material) and an aqueous phosphoric acid solution (pH 2) containing orthophosphoric acid and sodium dihydrogen phosphate (4% by mass relative to the soft magnetic material) were added and stirred for 7 minutes. The final concentrations of each component were 16.6% by mass of the soft magnetic material, 0.001% by mass of samarium chloride, and 0.01% by mass of the phosphate compound (PO4 equivalent). The pH of the treatment bath rose from 3 to 5. (iii) pH adjustment process An aqueous solution containing samarium chloride in an amount of 8% by mass relative to the coated magnetic material was added, and the reaction mixture was stirred for 30 minutes while controlling the pH to a range of 2.5±0.1 by adding 6% by mass of hydrochloric acid from time to time. (iv) Drying and baking The coated magnetic material after the pH adjustment step was dried by heating at 100°C for 4 hours in a vacuum, and then heated at 200°C for 4 hours to bake the coating.

[0115] Example 7 A soft magnetic powder was obtained in the same manner as in Example 4, except that the atomic concentration ratio of Fe, Ni, and Mn in the slurry was 95.9:4.0:0.1 and the solute concentration of the Mn-Ni-ferrite slurry was 25%. The obtained soft magnetic powder was crushed using a cutter mill and then classified using a sieve with an opening of 53 μm. The D of the obtained Fe-Ni-Mn soft magnetic powder 50 was 51.9 μm.

[0116] The SEM image of the Fe-Ni-Mn soft magnetic powder from above and the SEM-EDX results for Ni and Mn in the range are shown in Figures 3A to 3C, and the XRD pattern is shown in Figure 4. In the SEM-EDX, the atomic concentrations of Fe, Ni, and Mn were calculated to be 100% in total, as in Example 2. Figure 3B shows that the Ni content in the first phase (2.79 at%) is more than 10 times that of the first phase. 5 a second phase (2.97 to 3.94 at%) having a Ni content of 1.1 times or less, and a second phase (2.97 to 3.94 at%) having a Ni content of 1.1 times or more and 10 times or less; 5 It was confirmed that there was a second phase (3.26 to 3.94 at%) with a Ni content less than twice that of the first phase (0.01 at%). Furthermore, Fig. 3C shows that the Mn content in the first phase (0.01 at%) was more than twice that of the first phase (10 at%). 5 It was confirmed that there was a second phase (a phase of 0.06 to 0.19 at%) with a Mn content of 0.06 to 0.19 times or less. Furthermore, it was confirmed from Fig. 4 that this soft magnetic powder has a bcc structure. That is, it was found that the first and second phases when X of this soft magnetic powder is Ni, and the first and second phases when X is Mn, all of these phases have a bcc structure.

[0117] The elemental concentration distribution in the powder cross section was measured after thinning the sample using a focused ion beam (FIB). It was then measured using a STEM (FEI, model number Talos F200X; accelerating voltage 200 kV) and an attached STEM-EDX (system: FEI, model number SuperX; detector: Bruker SDD detector). The measurement results are shown in Figures 5A and 5B. In the obtained EDX mapping image, the average Ni and Mn intensities for each pixel (2.84 nm × 2.84 nm) were converted to the Ni and Mn concentrations of the powder obtained by ICP-AES (Ni 4 atomic % and Mn 0.1 atomic %, respectively), and a line profile was created to determine the continuous change in atomic concentration. Figure 5B shows that there is a first phase with a Ni content of 2.5 at% (minimum) and a second phase with a Ni content of 5.5 at% (maximum), and that the Ni content of this second phase is more than 1 time, and even 1.1 times, the Ni content of the first phase. Figure 5B also shows that there is a first phase with a Mn content of 0.01 at% (minimum) and a second phase with a Mn content of 0.18 at% (maximum), and that the Mn content of this second phase is more than twice the Mn content of the first phase.

[0118] Thereafter, this Fe—Ni—Mn soft magnetic powder was coated with a phosphorus compound in the same manner as in Comparative Example 2, to obtain a coated soft magnetic material of Example 7.

[0119] The Fe—Ni—Mn soft magnetic powders produced in the examples and comparative examples were evaluated by the following methods. The evaluation results are shown in Tables 3 to 5.

[0120] <Average particle size> The average particle size (D50), D10, D90 and standard deviation of the soft magnetic powder were measured using a laser diffraction particle size distribution measuring device (HELOS&RODOS manufactured by Japan Laser Co., Ltd.).

[0121] <Circularity> The magnetic material was dispersed and hardened in an epoxy resin or similar, and the particle cross-section was exposed by polishing, after which it was imaged using an electron microscope. Image processing software was used to determine the average circularity (C50) and the percentage of magnetic particles with a circularity of 0.8 or more (P80) based on the number of particles, limiting the images to particles with a diameter of 5 μm or more (this was done to prevent erroneous measurements due to contamination, etc.).

[0122] <Projected particle size, necking degree> After dispersing the magnetic material on carbon tape, an image was taken with an electron microscope. For the obtained particle image, the circle-equivalent particle diameter of the part recognized as being separated into the inside and outside by a continuous line segment was calculated for the number of particles that "sufficiently represent the powder group." The number average was then used to determine the projected particle diameter (d 50 Next, the volume average particle diameter (D 50 ) and compare this value with the above d 50 The necking degree was calculated from the above (necking degree = volume average particle diameter / projected particle diameter).

[0123] <Hysteresis loss, eddy current loss, iron loss, magnetic flux density at 10,000 A / m> The coated magnetic material was placed in a mold with an inner diameter of 10 mm and an outer diameter of 14 mm, and compacted under a pressure of 980 MPa. The compact was then heated at 600°C for 1 hour in an Ar atmosphere to produce a toroidal compact. These compacts were wound with 50 turns of copper wire on the primary side and 50 turns on the secondary side to form evaluation samples. These evaluation samples were used to measure the W 10 / 2k (Iron loss (W / kg) at 2kHz, 1T), W 5 / 5k (Iron loss (W / kg) at 5kHz and 0.5T), W 5 / 10k The iron loss was evaluated using the two-frequency method (iron loss (W / kg) at 10 kHz and 0.5 T). At the same time, the iron loss value was measured at 10 Hz to 100 Hz with a magnetic flux density of 1 T, and at 400 to 800 Hz with a magnetic flux density of 0.5 T, and the hysteresis loss (W h10 / 2k , W h5 / 5k , Wh5 / 10k (W / kg)) and eddy current loss (W e10 / 2k , W e5 / 5k , W e5 / 10k (W / kg) was calculated.

[0124] In addition, using these evaluation samples, the magnetic flux density (B 100 (T)) was evaluated.

[0125] <Average anisotropic particle size> The coated magnetic material was placed in a mold with an outer diameter of 5.5 mm and molded under a pressure of 980 MPa. The molded body was then heated at 600°C for 1 hour in an Ar atmosphere to produce a disk-shaped molded body. These molded bodies were impregnated with epoxy resin and polished to a mirror surface, after which the cross section of the molded body was photographed with an electron microscope. From the obtained cross-sectional image, it was possible to determine the 50 μm 2 The particle diameter and aspect ratio were calculated from the cross section of the particles that make up the compact, and R a was calculated and the average value was calculated.

[0126] [Table 3]

[0127] [Table 4]

[0128] [Table 5]

[0129] [Table 6]

[0130] The smaller the particle size, the smaller the eddy current loss under all conditions, and as a result, the smaller the iron loss. 5 / 5k It was found that the iron loss was reduced compared to Comparative Example 1, in which the average particle size was 300 μm, with a power of 230 W / kg or less.

[0131] The span ((D90-D10) / D50) of the soft magnetic powders of Examples 1 to 7 was all 0.4 or less, and the standard deviation σ was all 50 μm or less. It was found that the proportion of large particles that generate intragranular eddy currents was small, which reduced eddy current loss and, as a result, reduced iron loss.

[0132] It was found that the soft magnetic materials produced in Examples 4 to 6 by spray drying had a higher circularity than Examples 1 to 3 with similar particle sizes, and a necking degree closer to 1, which resulted in smaller eddy current loss and, as a result, smaller iron loss. Furthermore, the soft magnetic materials of Examples 4 to 6 have a ratio of particles with a circularity of 0.8 or more of 30% or more, which is also the basis for their extremely excellent high-frequency characteristics.

[0133] The soft magnetic powders of Examples 2, 3, and 5 to 7 are Fe-X soft magnetic materials with particle sizes of 130 μm or less, and are particularly effective as stator cores for axial motors used in next-generation mobility systems operating at 2 kHz or higher. The soft magnetic powders of Examples 6 and 7 are Fe-X soft magnetic materials with particle sizes of 60 μm or less, and are particularly effective as stator cores for axial motors used in next-generation mobility systems operating at 5 kHz or higher, as well as in inductors or transformers for non-insulated or insulated DC-DC converters used in next-generation mobility systems operating at 5 kHz to 10 kHz.

[0134] The compacts of the soft magnetic powders of Examples 1 to 7 were R aThe particle size is 90 μm or less, and the particles are small in diameter and have a small aspect ratio, which reduces eddy current loss and provides magnetic isotropy, making it particularly effective for applications such as the stator core of an axial motor with a three-dimensional magnetic circuit, and the inductors and transformers of a DC-DC converter.

Claims

1. a spray drying step of spray-drying a slurry containing Fe and X (X is one or more elements selected from Ti, Mn, Ni, Co, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Cu, Zn, and Si) to obtain granulated material having an average particle size of 20 μm to 200 μm; and a heat treatment step of heat-treating the granulated material in a reducing gas at 800°C or higher and 1200°C or lower to obtain a heat-treated material; A method for producing a soft magnetic material, comprising:

2. Further, a slurry preparation step is provided in which a basic pH adjusting solution is dropped into a stirring tank having stirring blades while stirring together with an acidic solution containing Fe and X (X is one or more elements selected from Ti, Mn, Ni, Co, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Cu, Zn, and Si) to generate ferrite nanoparticles and obtain a slurry, wherein the dropping time T (s) is T≧375000VD ２／３ (where V(m ３ ) indicates the volume of the stirring vessel, and D (m) indicates the diameter of the stirring blade.

2. The method for producing a soft magnetic material according to claim 1, further comprising the step of preparing a slurry that satisfies the above.

3. 3. The method for producing a soft magnetic material according to claim 1, further comprising a step of classifying the heat-treated product to obtain a classified product.

4. 4. The method for producing a soft magnetic material according to claim 3, further comprising a coating step of mixing the classified material with an aqueous solution containing a phosphate compound and a rare earth compound to form a coating containing a phosphorus compound with a rare earth metal element on the surface of the classified material.

5. The alloy has a first phase and a second phase having a crystal with a bcc structure containing Fe and X (X is one or more elements selected from Ti, Mn, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Cu, Zn, and Si), With respect to one element of X contained in both phases, the content of the element in the second phase is 2 times or more to 10 times or more the content of the element in the first phase. ５ It is less than double, A soft magnetic material having an average circularity of 0.55 or more and an average particle size of 160 μm or less.

6. The soft magnetic material according to claim 5 , wherein X comprises Mn.

7. The alloy has a first phase and a second phase having a crystal with a bcc structure containing Fe and X (X is one or more transition metals selected from Ni and Co), With respect to one element of X contained in both phases, the content of the element in the second phase is more than 1 time and less than 10 times the content of the element in the first phase. ５ It is less than double, A soft magnetic material having an average circularity of 0.55 or more and an average particle size of 160 μm or less.

8. 8. The soft magnetic material according to claim 5, wherein the average particle size is 130 μm or less.

9. 8. The soft magnetic material according to claim 5, wherein the necking degree is 4 or less.

10. 8. The soft magnetic material according to claim 5, wherein the proportion of particles having a circularity of 0.8 or more is 30% or more by number.

11. 8. The soft magnetic material according to claim 5, wherein the average circularity is 0.6 or more.

12. A soft magnetic material used at a frequency f (kHz) of 2 kHz or more, having an average particle size of 184f －０．５ The soft magnetic material according to any one of claims 5 to 7, wherein the thickness is 0.1 μm or less.

13. A material obtained by coating the soft magnetic material according to any one of claims 5 to 7 with a silicon compound or a phosphate compound.

14. A soft magnetic material compact produced from the soft magnetic material according to any one of claims 5 to 7, wherein the average anisotropic grain size of the soft magnetic material determined from a cross-sectional image of the compact is 90 μm or less.

15. A stator core of an axial motor that operates at 2 kHz or more, using the soft magnetic material according to any one of claims 5 to 7.

Images