WO2012132783A1 - 複合軟磁性粉末及びその製造方法、並びにそれを用いた圧粉磁心 - Google Patents
複合軟磁性粉末及びその製造方法、並びにそれを用いた圧粉磁心 Download PDFInfo
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- WO2012132783A1 WO2012132783A1 PCT/JP2012/055657 JP2012055657W WO2012132783A1 WO 2012132783 A1 WO2012132783 A1 WO 2012132783A1 JP 2012055657 W JP2012055657 W JP 2012055657W WO 2012132783 A1 WO2012132783 A1 WO 2012132783A1
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C29/00—Alloys based on carbides, oxides, nitrides, borides, or silicides, e.g. cermets, or other metal compounds, e.g. oxynitrides, sulfides
- C22C29/16—Alloys based on carbides, oxides, nitrides, borides, or silicides, e.g. cermets, or other metal compounds, e.g. oxynitrides, sulfides based on nitrides
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- B—PERFORMING OPERATIONS; TRANSPORTING
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- B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
- B22F1/00—Metallic powder; Treatment of metallic powder, e.g. to facilitate working or to improve properties
- B22F1/16—Metallic particles coated with a non-metal
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
- H01F1/00—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties
- H01F1/01—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
- H01F1/00—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties
- H01F1/01—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials
- H01F1/03—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity
- H01F1/12—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity of soft-magnetic materials
- H01F1/14—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity of soft-magnetic materials metals or alloys
- H01F1/20—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity of soft-magnetic materials metals or alloys in the form of particles, e.g. powder
- H01F1/22—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity of soft-magnetic materials metals or alloys in the form of particles, e.g. powder pressed, sintered, or bound together
- H01F1/24—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity of soft-magnetic materials metals or alloys in the form of particles, e.g. powder pressed, sintered, or bound together the particles being insulated
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
- H01F41/00—Apparatus or processes specially adapted for manufacturing or assembling magnets, inductances or transformers; Apparatus or processes specially adapted for manufacturing materials characterised by their magnetic properties
- H01F41/005—Impregnating or encapsulating
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
- H01F41/00—Apparatus or processes specially adapted for manufacturing or assembling magnets, inductances or transformers; Apparatus or processes specially adapted for manufacturing materials characterised by their magnetic properties
- H01F41/02—Apparatus or processes specially adapted for manufacturing or assembling magnets, inductances or transformers; Apparatus or processes specially adapted for manufacturing materials characterised by their magnetic properties for manufacturing cores, coils, or magnets
- H01F41/0206—Manufacturing of magnetic cores by mechanical means
- H01F41/0246—Manufacturing of magnetic circuits by moulding or by pressing powder
Definitions
- the present invention relates to a composite soft magnetic powder having a coating layer mainly composed of boron nitride, a method for producing the same, and a dust core using the same.
- Japanese Patent Application Laid-Open No. 2004-259807 is for a powder magnetic core mainly composed of metal particles having an average particle diameter of 0.001 to 1 ⁇ m obtained by reducing a metal oxide, and the surface of the metal particles being coated with carbon or boron nitride.
- a magnetic powder is disclosed.
- this magnetic powder has a small average particle diameter of 0.001 to 1 ⁇ m, the volume ratio of the insulating coating is relatively large, and the density is as small as less than 6.0 Mg / m 3 . Therefore, high magnetic permeability and high saturation magnetization cannot be obtained with a dust core made of this magnetic powder.
- JP 2010-236021 discloses that a pure iron powder having an oxide layer on its surface is coated with a solution containing boron or a boron compound, and a soft magnetic powder is compression-molded, and the resulting molded body is heated to 500 in a nitrogen gas atmosphere.
- a method of manufacturing a dust core in which a film made of boron or a boron compound is converted into a film made of boron nitride by heat treatment at 0 ° C., and then distortion is removed by raising the heat treatment temperature to 1000 ° C.
- the coating layer is easily peeled off during compression molding, and insulation between pure iron particles is insufficient.
- the loss of the dust core obtained by this method is large.
- boron or a boron compound is nitrided after compression molding, but the volume of the coating layer increases due to nitriding, and the space factor of the magnetic component decreases. In addition, nitriding by-products and unreacted components cannot be removed. As a result, the density of the dust core obtained by this method is low, and the magnetic permeability is also low.
- Fe 4 N powder and B powder are mixed at a weight ratio of 1: 1 and in a nitrogen gas atmosphere. It is disclosed that nanoparticles comprising Fe core particles and a hexagonal boron nitride (h-BN) coating layer can be obtained by heat treatment at 1000 ° C. Fe nanocapsules coated with BN layer are mainly produced when Fe nanoparticles are smaller than 20 nm, and bamboo-structured BN nanotubes holding Fe nanoparticles are produced when Fe nanoparticles are larger than 100 nm. It is described.
- h-BN hexagonal boron nitride
- an object of the present invention is to provide a composite soft magnetic powder having a high density and high saturation magnetization and good lubricity, a method for producing the same, and a composite soft magnetic powder having a high magnetic permeability and excellent DC superposition characteristics. It is to provide a lossy dust core.
- the composite soft magnetic powder of the present invention comprises a soft magnetic iron-based core particle having an average particle diameter of 2 to 100 ⁇ m and a layer mainly composed of boron nitride covering at least a part of the surface of the soft magnetic iron-based core particle.
- the coating layer is made of boron nitride microcrystal grains having an average crystal grain size of 3 to 15 nm with different crystal axis orientations, and has a polycrystal having an average thickness of 6.6% or less of the average grain size of the soft magnetic iron-based core particles. It is a body layer.
- the soft magnetic iron-based particles are preferably made of pure iron or an alloy containing iron as a main component.
- the ratio of Fe on the outermost surface of the composite soft magnetic powder is preferably 12 atomic% or less.
- the core particles are preferably entirely covered with a layer mainly composed of boron nitride, but may be partially covered. In the former case, of course, the proportion of Fe on the outermost surface is 0 atomic%. In the latter case, if the ratio of Fe on the outermost surface of the composite soft magnetic powder is 12 atomic% or less, the coating layer functions sufficiently as an insulating coating in the dust core, and eddy current loss can be suppressed.
- the “ratio of Fe on the outermost surface” means the ratio of iron to the total of boron, nitrogen, oxygen, and iron on the outermost surface, and iron is not limited to pure iron, but all Fe in a compound (eg, oxide) state. including.
- the volume ratio of iron is preferably 70% or more. If the thickness and covering state of the coating layer mainly composed of boron nitride are configured as described above, the ratio of the soft magnetic iron-based core particles can be increased, and high magnetic permeability and high magnetization can be obtained.
- the above composite soft magnetic powder is produced by mixing (1) iron nitride powder having an average particle diameter of 2 to 100 ⁇ m and boron powder having an average particle diameter of 0.1 to 10 ⁇ m, and (2) the obtained mixed powder in a nitrogen atmosphere. And (3) non-magnetic components are removed by heat treatment at a temperature of 600 to 850 ° C.
- the atomic ratio between the iron nitride powder and the boron powder is preferably B / Fe ⁇ 0.03.
- the heat treatment temperature is preferably 650 to 800 ° C, more preferably 700 to 800 ° C.
- the dust core of the present invention is characterized by comprising the above composite soft magnetic powder.
- a dust core according to a preferred embodiment of the present invention has a density of 5-7 Mg / m 3 and a core loss of 528 kW / m 3 or less (measured at a frequency of 50 kHz and an excitation magnetic flux density of 50 mT),
- the rate of change of the core loss with respect to the density [(kW / m 3 ) / (Mg / m 3 )] is ⁇ 96 or more.
- the core loss is preferably 260 kW / m 3 or less, more preferably 220 kW / m 3 or less.
- the change rate of the core loss is preferably ⁇ 75 or more, more preferably ⁇ 70 or more.
- boron nitride has a solid lubricating function, a high-density powder magnetic core can be obtained while suppressing distortion due to molding. Since the distortion is small, the hysteresis loss can be suppressed, and the change rate with respect to the density of the core loss becomes small.
- the composite soft magnetic powder of the present invention consisting of soft magnetic iron-based core particles having a boron nitride coating layer has high density and high saturation magnetization and good lubricity. Therefore, it has high density and high permeability by compression molding. A dust core having excellent direct current superposition characteristics and low loss can be obtained.
- FIG. 2 is a TEM photograph showing a cross section of the composite soft magnetic powder of Example 1.
- FIG. 3 is a TEM photograph showing a cross section of a coating layer of the composite soft magnetic powder of Example 1.
- FIG. 2 (a) is a schematic diagram showing the crystal structure of the coating layer of soot.
- 4 is a graph showing the relationship between the incremental relative permeability of the dust cores of Example 1 and Comparative Example 1 and the DC bias magnetic field.
- 6 is a graph showing the relationship between the incremental relative permeability of the dust cores of Example 2 and Comparative Example 2 and the DC bias magnetic field.
- 6 is a graph showing the relationship between the incremental relative permeability of the dust cores of Examples 1, 4, and 5 and Comparative Examples 5 and 6 and the DC bias magnetic field.
- 6 is a graph showing the relationship between the volume ratio of iron and the heat treatment temperature in the composite soft magnetic powders of Examples 1, 4, and 5 and Comparative Examples 5 and 6.
- 6 is a graph showing the relationship between the coercive force of the dust cores of Examples 1, 4, and 5 and Comparative Examples 5 and 6 and the heat treatment temperature.
- 6 is a graph showing the relationship between the loss of dust cores of Examples 1, 4, and 5 and Comparative Examples 5 and 6 and the heat treatment temperature.
- 6 is a TEM photograph showing a cross section of a composite soft magnetic powder core particle of Comparative Example 5.
- 6 is a graph showing the relationship between the incremental relative permeability of the dust cores of Examples 6 to 8 and the DC bias magnetic field.
- 6 is a graph showing the relationship between the loss and density of dust cores of Examples 9 to 11 and Comparative Examples 8 to 10.
- 6 is a graph showing the relationship between the XRD strength of the composite soft magnetic powder obtained in Example 12 and the heat treatment temperature.
- 10 is a graph showing the relationship between the XRD chart of the composite soft magnetic powder obtained in Comparative Example 11 and the heat treatment temperature.
- 4 is a TEM photograph (magnification: 1,000,000 times) of a boron nitride coating layer of the composite soft magnetic powder obtained in Comparative Example 12.
- FIG. 15 is a schematic diagram of the boron nitride coating layer of FIG.
- Soft magnetic iron-based core particles are preferably made of pure iron or an iron-based alloy. Pure iron is optimal for obtaining high saturation magnetization, but an Fe—Si alloy containing 1% by mass or more of Si is preferable in order to reduce loss. However, when the Si content increases, there is a problem that the core particles are difficult to be plastically deformed and the moldability to the dust core is reduced. For this reason, the upper limit of the Si content is preferably 8% by mass. A more preferable Si content is 2 to 7% by mass. Ni and / or Al may be contained in addition to Si. For example, a Fe—Si—Al alloy or a Fe—Ni alloy can be used.
- the volume ratio of pure iron or iron alloy constituting the soft magnetic iron-based core particles is preferably 70% or more.
- pure iron or iron alloy may be simply referred to as “iron”.
- iron When the volume ratio of iron is less than 70%, sufficient magnetic permeability cannot be obtained when a dust core is formed.
- a more preferred volume ratio is 80 to 95%.
- the volume ratio exceeds 95%, the boron nitride coating layer is too thin, and sufficient insulation cannot be obtained in the dust core.
- the volume ratio VR of iron is obtained from the saturation magnetization value Bs of the composite soft magnetic powder measured by a vibrating sample magnetometer (VSM) by applying a magnetic field of 10 kOe by the following equation.
- Bs / Bs1 V1 ⁇ ⁇ 1 / (V1 ⁇ ⁇ 1 + V2 ⁇ ⁇ 2)
- VR [V1 / (V1 + V2)] x 100 (%)
- the average particle size D of the composite soft magnetic powder is 2 to 100 ⁇ m.
- the average particle diameter D is represented by d50 measured using a laser diffraction / scattering particle size distribution measuring apparatus.
- the average particle size of the composite soft magnetic powder is preferably 2 to 80 ⁇ m, more preferably 2 to 50 ⁇ m, and most preferably 2 to 40 ⁇ m.
- Cv is preferably 30 to 70%, more preferably 40 to 60%.
- Cv ( ⁇ / D) ⁇ 100 (%) (where ⁇ is the standard deviation of the particle size distribution of the composite soft magnetic powder, and D is the average particle size of the composite soft magnetic powder).
- the coating layer is a polycrystalline body made of boron nitride microcrystal grains having an average crystal grain size of 3 to 15 nm having different crystal axis orientations, it exhibits excellent lubricity during molding. As a result, the coating layer can follow the deformation of the core particles during compression molding, and the insulation in the dust core is sufficiently maintained. If the average grain size is less than 3 nm, the lubricating effect of the coating layer is not sufficient. On the other hand, when the average crystal grain size exceeds 15 nm, the effect of polycrystal is reduced, and the coating layer may be destroyed during compression molding.
- the average crystal grain size is preferably 3 to 12 nm.
- the average crystal grain size of boron nitride microcrystal grains is measured by measuring the size of microcrystal grains traversed by a plurality of line segments in an arbitrary direction and a direction perpendicular thereto in the cross-sectional TEM photograph of the coating layer. Obtained by averaging for grains.
- the average number of microcrystals is 20 or more.
- the average thickness T A of the coating layer is 6.6% or less, preferably 0.5 to 6.6%, more preferably 1 to 6.5% of the average particle diameter D A of the soft magnetic iron-based core particles.
- T A exceeds 6.6% of D A
- the volume ratio of the soft magnetic iron-based core particles decreases, and the saturation magnetization of the composite soft magnetic powder decreases.
- T A is less than 0.5% of D A
- the dust core does not have sufficient insulation.
- the coating layer does not completely cover the core particles, but the boron nitride coating layer is actually uneven and has an uncoated portion.
- the coverage by the boron nitride layer is represented by the ratio of Fe on the outermost surface.
- the ratio of Fe on the outermost surface is preferably 12 atomic% or less. If the proportion of Fe on the outermost surface is more than 12%, the proportion of exposed portions not covered with boron nitride is too large, and a sufficient insulating effect cannot be obtained.
- the proportion of Fe on the outermost surface is determined by X-ray photoelectron spectroscopy (XPS).
- the elemental composition of the outermost surface of the sample is analyzed by irradiating the sample with monochromatic X-rays in an ultra-high vacuum using the XPS method and measuring the energy of the emitted photoelectrons. Specifically, boron, nitrogen, oxygen and iron are quantitatively analyzed by narrow spectrum measurement, and the ratio of Fe on the outermost surface is obtained. Since the XPS analysis depth is 5 nm, “outermost surface” means the surface area up to a depth of 5 nm.
- Raw material powder (a) Iron nitride powder Fe 4 N is suitable as the iron nitride powder, but Fe 3 N, Fe 2 N, or a mixture thereof may be used.
- the iron nitride powder contains unavoidable impurities such as carbon and oxygen, but the carbon content is preferably 0.02% by mass or less, and more preferably 0.007% by mass or less.
- the average particle size of the iron nitride powder may be substantially the same as the average particle size of the composite soft magnetic powder, preferably 2 to 100 ⁇ m, more preferably 2 to 50 ⁇ m, and most preferably 10 to 40 ⁇ m.
- the iron nitride powder becomes soft magnetic iron core particles by mixing and heat-treating with boron powder described later.
- Boron powder has an average particle size of 0.1 to 10 ⁇ m.
- the average particle size is less than 0.1 ⁇ m, the boron powder tends to agglomerate and is difficult to mix with the iron nitride powder.
- the average particle size exceeds 10 ⁇ m, it is necessary to use a grinding medium for sufficient mixing with the iron nitride powder, which may cause impurities to be mixed from the grinding medium.
- the average particle size of the boron powder is preferably 0.5 to 10 ⁇ m, more preferably 0.5 to 5 ⁇ m.
- the B / Fe atomic ratio is preferably 0.8 ⁇ B / Fe ⁇ 0.03.
- the B / Fe atomic ratio exceeds 0.8, excess boron that does not contribute to the formation of the coating layer is used, and the manufacturing cost increases.
- the B / Fe atomic ratio is less than 0.03, there is too little boron powder present between the core particles, and the growth of crystal grains is promoted by sintering of the core particles, and the desired magnetic core characteristics cannot be obtained.
- the atomic ratio of B / Fe is more preferably 0.8 ⁇ B / Fe ⁇ 0.1, further preferably 0.8 ⁇ B / Fe ⁇ 0.125, and most preferably 0.8 ⁇ B / Fe ⁇ 0.25.
- the obtained mixed powder is heat treated at a temperature of 600 to 850 ° C in a nitrogen atmosphere.
- the heat treatment is preferably performed, for example, in an alumina crucible in an electric furnace.
- a composite soft magnetic powder having a coating layer mainly composed of boron nitride on the outer periphery of the soft magnetic iron-based core particles is synthesized.
- the nitrogen atmosphere is preferably nitrogen gas alone, but may be a mixed gas of nitrogen and an inert gas such as Ar or He or ammonia.
- the heat treatment temperature exceeds 850 ° C., not only the coating layer mainly composed of boron nitride is too thick, but also enters into the core particles and decreases the volume ratio of iron, thereby reducing the soft magnetic properties of the composite soft magnetic powder.
- the temperature is lower than 600 ° C., a coating layer mainly composed of boron nitride is not formed, and when iron nitride is used as a raw material, the composite soft magnetic has iron particles as a core because iron is not generated because the decomposition temperature is lower than iron nitride.
- the powder cannot be synthesized.
- a preferable heat treatment temperature is 650 to 800 ° C.
- the time for maintaining the temperature at 600 to 850 ° C. is preferably 0.5 to 50 hours, more preferably 1 to 10 hours, and most preferably 1.5 to 5 hours.
- the powder after heat treatment is put into an organic solvent such as isopropyl alcohol (IPA), dispersed by ultrasonic irradiation, and then collected by a magnetic separation method using a permanent magnet to collect only soft magnetic iron-based particles. Purify and remove non-magnetic components.
- IPA isopropyl alcohol
- a binder is added to the composite soft magnetic powder and granulated.
- the binder it is preferable to use polyvinyl butyral (PVB), polyvinyl alcohol (PVA), acrylic emulsion, colloidal silica, or the like.
- a powder magnetic core is manufactured by compression-molding the obtained granulated powder with a press using a mold.
- the compression molding pressure can be set as appropriate, but is preferably 500 to 2000 MPa, for example.
- FIG. 1 is a TEM photograph of a cross section of the composite soft magnetic powder. It was confirmed that the iron-based core particles had a surface portion that was not covered with the boron nitride layer, and the surface of the core particles was not completely covered.
- the coating layer is mainly composed of boron nitride, but also contains boron oxide, and the ratio of Fe (partial oxide) on the outermost surface is 6.7 atomic%. It was. From the TEM photograph of the cross section of the composite soft magnetic powder and the analysis result of the surface composition by XPS, it is considered that the proportion of Fe on the outermost surface corresponds to the proportion of the uncoated surface portion. From the TEM photograph in FIG.
- FIG. 2 (a) showing an enlarged view of the boron nitride coating layer, it was found that the boron nitride layer was a polycrystal composed of boron nitride microcrystal grains having different crystal axis (C axis) orientations.
- FIG. 2 (b) schematically shows polycrystalline boron nitride coating layers having different C-axis orientations. In FIG. 2 (b), the arrow indicates the C-axis orientation of each crystal.
- the average crystal grain size determined from boron nitride microcrystal grains crossing any two line segments of the same length orthogonal to each other was 4 nm.
- the saturation magnetization (maximum magnetization when the applied magnetic field was 10 kOe) of the composite soft magnetic powder measured by VSM was 205 emu / g.
- T A / D A obtained from the volume ratio of iron was 3.8%.
- a transformer core or the like is required to have high DC superposition characteristics, but the DC superposition characteristics of a dust core can be expressed by an incremental relative permeability. Therefore, the incremental relative permeability of the dust core was measured by the following method. First, the dust core was put in a resin case, and a 0.7 mm diameter enameled copper wire was wound for 20 turns, and the inductance was measured with an LCR meter at a frequency of 100 kHz. The incremental relative permeability was calculated by the following formula (1).
- Fig. 3 shows the relationship between the incremental relative permeability and the DC bias magnetic field.
- Comparative Example 1 Granulated by adding PVB / ethanol solution to commercial iron powder (BAQ SQ) with an average particle size of 3.5 ⁇ m, saturation magnetization of 204 emu / g, and Fe ratio of 24.6 atomic% on the outermost surface.
- a toroidal ring-shaped dust core having an outer diameter of 13.4 mm, an inner diameter of 7.7 mm, and a thickness of 4 mm was produced by compression molding at a pressure of 1470 MPa with a press, and evaluated under the same conditions as in Example 1.
- the density of the dust core was 6.9 Mg / m 3
- the coercive force was 19.9 Oe
- the loss was 176 kW / m 3 .
- Fig. 3 shows the relationship between the incremental relative permeability and the DC bias magnetic field.
- the average particle diameter of the composite soft magnetic powder is 30 ⁇ m
- the saturation magnetization is 196 emu / g
- the volume ratio of iron is 71%
- the ratio of Fe on the outermost surface is 6.0 atomic%
- the boron nitride coating layer was made of polycrystals having different C-axis orientations.
- the average thickness T A of the boron nitride coating layer calculated from the saturation magnetization was 1.6 ⁇ m, and T A / D A determined from the volume ratio of iron was 6.0%.
- Toroidal compact powder with outer diameter of 13.4 mm, inner diameter of 7.7 mm and thickness of 4 mm by adding PVB / ethanol solution to the composite soft magnetic powder and granulating it with a hydraulic press at a pressure of 1960 MPa A magnetic core was manufactured and evaluated under the same conditions as in Example 1. As a result, the density of the dust core was 6.8 Mg / m 3 , the coercive force was 15.5 Oe, and the loss was 284 kW / m 3 .
- Fig. 4 shows the relationship between the incremental relative permeability and the DC bias magnetic field.
- Comparative Example 2 Granulation by adding PVB / ethanol solution to commercially available iron powder (manufactured by Kojundo Chemical Co., Ltd.) with an average particle size of 36 ⁇ m, saturation magnetization of 198 emu / g, and the ratio of Fe on the outermost surface of 23.7 atomic% Then, a toroidal ring-shaped dust core having an outer diameter of 13.4 mm, an inner diameter of 7.7 mm, and a thickness of 4 mm was manufactured by compression molding at a pressure of 1960 MPa with a hydraulic press, and evaluated under the same conditions as in Example 1.
- Fig. 4 shows the relationship between the incremental relative permeability and the DC bias magnetic field.
- the average particle diameter of the composite soft magnetic powder is 85 ⁇ m
- the saturation magnetization is 198 emu / g
- the volume ratio of iron is 73%
- the ratio of Fe on the outermost surface is 11.5 atomic%
- the boron nitride coating layer was made of polycrystals having different C-axis orientations.
- the average thickness T A of the boron nitride coating layer was calculated from the saturation magnetization is 4.1 .mu.m, the T A / D A calculated from the volume ratio of iron was 4.9%.
- Toroidal compact powder with outer diameter of 13.4 mm, inner diameter of 7.7 mm and thickness of 4 mm by adding PVB / ethanol solution to the composite soft magnetic powder and granulating it with a hydraulic press at a pressure of 1960 MPa A magnetic core was manufactured and evaluated under the same conditions as in Example 1. As a result, the density of the dust core was 7.1 Mg / m 3 , the coercive force was 18.2 Oe, and the loss was 528 kW / m 3 .
- Comparative Example 3 A commercial iron powder with an average particle diameter of 90 ⁇ m, saturation magnetization of 199 emu / g, and Fe ratio of 24.1 atomic% on the outermost surface is granulated by adding a PVB / ethanol solution at a pressure of 1960 MPa with a hydraulic press.
- a toroidal ring-shaped dust core having an outer diameter of 13.4 mm, an inner diameter of 7.7 mm, and a thickness of 4 mm was produced by compression molding and evaluated under the same conditions as in Example 1. As a result, the density of the dust core was 7.0 Mg / m 3 , the coercive force was 27.0 Oe, and the loss was 667 kW / m 3 .
- Table 1 shows the average particle diameter, B / Fe atomic ratio, and heat treatment temperature of the iron nitride powder and boron powder, the average particle diameter of the composite soft magnetic powder, the volume ratio of iron, the ratio of Fe on the outermost surface, and the saturation magnetization,
- the average particle diameter D A of the core particles is shown in Table 2
- the average thickness T A and the average crystal grain size of the coating layer, and T A / D A are shown in Table 3
- the density, coercive force and The loss is shown in Table 4
- the surface composition and chemical state of the composite soft magnetic powder are shown in Table 5.
- the dust core made of the composite soft magnetic powder of the present invention having a Fe ratio of 12 atomic% or less on the outermost surface is made of a comparative iron powder having no coating layer. It has a higher density than the dust core. This is considered to be an effect of lubricity of the boron nitride coating layer. Therefore, the dust core of the present invention has a higher magnetic permeability than the dust core of the comparative example, excellent direct current superposition characteristics, and low loss. In addition, since the value of a loss changes with powder particle diameters, the comparison of loss was performed between powder magnetic cores made of powders having the same particle diameter.
- the average particle diameter of the composite soft magnetic powder is 4.3 ⁇ m
- the saturation magnetization is 205 emu / g
- the volume ratio of iron is 81%
- the ratio of Fe on the outermost surface is 11.7 atomic%
- boron nitride The average crystal grain size was 3 nm.
- the boron nitride coating layer was made of polycrystals having different C-axis orientations.
- the average thickness T A of the boron nitride coating layer calculated from the saturation magnetization was 0.15 ⁇ m, and T A / D A determined from the volume ratio of iron was 3.8%.
- FIG. 5 shows the relationship between the incremental relative permeability and the DC bias magnetic field.
- the average particle size of the composite soft magnetic powder is 4.3 ⁇ m
- the saturation magnetization is 204 emu / g
- the volume ratio of iron is 80%
- the ratio of Fe on the outermost surface is 5.0 atomic%
- boron nitride The average grain size was 8 nm.
- the boron nitride coating layer was made of polycrystals having different C-axis orientations.
- the average thickness T A of the boron nitride coating layer calculated from the saturation magnetization was 0.16 ⁇ m, and T A / D A calculated from the volume ratio of iron was 4.0%.
- FIG. 5 shows the relationship between the incremental relative permeability and the DC bias magnetic field.
- FIG. 9 is a TEM photograph of a cross section of the composite soft magnetic powder. As is apparent from FIG. 9, since the heat treatment temperature was too high at 900 ° C., a boron nitride coating layer that was thicker than necessary was formed.
- FIG. 5 shows the relationship between the incremental relative permeability and the DC bias magnetic field.
- the average thickness T A of the boron nitride coating layer was 0.40 ⁇ m, and T A / D A obtained from the volume ratio of iron was 9.5%. Since the heat treatment temperature was too high at 1000 ° C., an unnecessarily thick boron nitride coating layer was formed.
- FIG. 5 shows the relationship between the incremental relative permeability and the DC bias magnetic field.
- the average particle diameter of iron nitride powder and boron powder, B / Fe atomic ratio, and heat treatment temperature are shown in Table 6, the average particle diameter of composite soft magnetic powder, the volume ratio of iron, the ratio of Fe on the outermost surface and the saturation magnetization,
- the average particle diameter D A of the core particles is shown in Table 7
- the average thickness T A and the average crystal grain size of the coating layer, and T A / D A are shown in Table 8
- the density, coercive force and The loss is shown in Table 9, and the surface composition and chemical state of the composite soft magnetic powder are shown in Table 10.
- Fig. 6 shows the relationship between the iron volume ratio and the heat treatment temperature in the composite soft magnetic powder
- Fig. 7 shows the relationship between the coercive force of the dust core and the heat treatment temperature
- the loss of the dust core and the heat treatment temperature Is shown in FIG.
- the boron nitride coating layer in the composite soft magnetic powder of Comparative Example 5 was not only thick at a maximum of 300 nm, but also partially penetrated into the core particles. Therefore, the volume ratio of iron was smaller than that in Example 1, and the saturation magnetization of the obtained dust core was small.
- the boron nitride coating layer was destroyed during compression molding, and the function as an insulating layer could not be sufficiently exhibited.
- a dust core having a coercive force of less than 24 ⁇ Oe can be obtained.
- the coercive force is less than 24 Oe, the loss of the dust core is small. From this, it can be seen that when the composite soft magnetic powder synthesized within the heat treatment temperature range of the present invention is used, a dust core having high permeability, excellent DC superposition characteristics, and low loss can be obtained.
- FIG. 10 shows the relationship between the incremental relative permeability and the DC bias magnetic field.
- FIG. 10 shows the relationship between the incremental relative permeability and the DC bias magnetic field.
- FIG. 10 shows the relationship between the incremental relative permeability and the DC bias magnetic field.
- Example 9 A dust core was prepared and evaluated in the same manner as in Example 1 except that the compression molding pressure was 1030 MPa. Table 15 shows the density and loss of the dust core.
- Example 10 A dust core was prepared and evaluated in the same manner as in Example 1 except that the compression molding pressure was 520 MPa. Table 15 shows the density and loss of the dust core.
- Example 11 A dust core was prepared and evaluated in the same manner as in Example 1 except that the compression molding pressure was 310 MPa. Table 15 shows the density and loss of the dust core.
- Comparative Example 8 A dust core was prepared and evaluated in the same manner as in Comparative Example 1 except that the compression molding pressure was 1030 MPa. Table 15 shows the density and loss of the dust core.
- Comparative Example 9 A dust core was prepared and evaluated in the same manner as in Comparative Example 1 except that the compression molding pressure was 520 MPa. Table 15 shows the density and loss of the dust core.
- Comparative Example 10 A dust core was prepared and evaluated in the same manner as in Comparative Example 1 except that the compression molding pressure was 310 MPa. Table 15 shows the density and loss of the dust core.
- FIG. 11 shows the relationship between the density and loss of the dust core.
- the straight line shown in FIG. 11 is obtained by the least square method.
- the loss of the dust core of the example was smaller than that of the dust core of the comparative example. This tendency was remarkable when the density was low (low molding pressure).
- the loss of the comparative example is 308 kW / m 3
- the loss of the example is as small as 214 kW / m 3 .
- FIG. 12 shows the relationship between the XRD strength of the composite soft magnetic powder and the heat treatment temperature. As is clear from FIG.
- Fe 4 N was observed in the composite soft magnetic powder heat-treated at a low temperature of 500 ° C. or lower, but no Fe—B compound was observed, and the composite heat-treated at a high temperature of 600 ° C. or higher. In the soft magnetic powder, not only Fe 4 N but also Fe—B compounds were not observed. This means that Fe 4 N was completely decomposed into bcc-Fe without being converted into Fe—B compounds. As described above, in the method of the present invention using iron nitride powder as a starting material, a boron nitride coating layer is formed on the surface of iron nitride particles without producing an Fe—B compound.
- a boron nitride coating layer was formed on the composite soft magnetic powder obtained by heat treatment at 700 ° C. and 800 ° C.
- the average thickness of the boron nitride coating layer in the case of heat treatment at 700 ° C. and 800 ° C. was 3.8% and 4.0% of the particle size of the core particles, respectively.
- the average thickness of the boron nitride coating layer is more than 6.6% of the particle diameter of the core particles, and the space factor is low when a dust core is used. there were.
- the heat treatment temperature was 1300 ° C., a thicker boron nitride coating layer was formed.
- the heat treatment temperature is preferably 600 to 850 ° C.
- the heat treatment temperature is preferably 600 to 850 ° C.
- Comparative Example 11 50% by mass of ⁇ -Fe 2 O 3 powder with an average particle size of 0.03 ⁇ m and 50% by mass of boron powder with an average particle size of 30 ⁇ m were mixed in a V-type mixer for 10 minutes, then placed in an alumina boat and placed in the furnace In a nitrogen stream with a flow rate of 2 L / min, the temperature is increased from room temperature at a rate of 3 ° C / min, heat-treated at 500 ° C, 750 ° C, 950 ° C and 1500 ° C for 15 minutes, and magnetic separation in IPA The nonmagnetic content was removed by the above to obtain a composite soft magnetic powder. X-ray diffraction measurement was performed on each composite soft magnetic powder and the raw material before the heat treatment. FIG.
- FIG. 13 shows the XRD measurement results.
- FeB, Fe 2 B and FeB 49 were detected in the composite soft magnetic powder heat-treated at 750 ° C. and 950 ° C., but in the composite soft magnetic powder heat-treated at 1500 ° C. -B was not detected, and boron nitride was detected. From this, it can be seen that when iron oxide powder and boron powder are used as starting materials, boron nitride is formed after the Fe-B compound is once formed, which is different from the reaction step of the present invention.
- Comparative Example 12 A composite soft magnetic powder was produced in the same manner as in Comparative Example 11 except that heat treatment was performed at 1100 ° C. for 2 hours.
- FIG. 14 is a TEM photograph (magnification: 1 million times) of the boron nitride coating layer of the composite soft magnetic powder
- FIG. 15 is a schematic diagram thereof.
- the boron nitride coating layer was composed of a multilayered film crystal having C-axis orientations substantially aligned in the radial direction, and was different from the polycrystalline boron nitride coating layer of the present invention consisting of microcrystalline grains having different C-axis orientations.
- FIG. 15 a striped crystal lattice was observed in the layered boron nitride coating layer of Comparative Example 12.
- the lattice plane 2 was laminated almost in parallel along the surface of the iron-based core particle 1.
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Abstract
Description
(1) 軟磁性鉄系コア粒子
軟磁性鉄系コア粒子は純鉄又は鉄を主成分とする合金からなるのが好ましい。高い飽和磁化を得るためには純鉄が最適であるが、損失を低減するためにはSiを1質量%以上含有するFe-Si合金が好ましい。ただし、Siの含有量が多くなるとコア粒子が塑性変形しにくくなり、圧粉磁心への成形性が低下するという問題がある。このため、Siの含有量の上限は8質量%が好ましい。より好ましいSiの含有量は2~7質量%である。Si以外にNi及び/又はAlを含有しても良く、例えばFe-Si-Al合金、Fe-Ni合金を用いることができる。
Bs/Bs1=V1×ρ1/(V1×ρ1+V2×ρ2)
VR=[V1/(V1+V2)]×100(%)
Bs:複合軟磁性粉末の飽和磁化
Bs1:鉄の飽和磁化
V1:鉄の体積
V2:窒化ホウ素の体積
ρ1:鉄の密度
ρ2:窒化ホウ素の密度
複合軟磁性粉末の平均粒径Dは2~100μmである。平均粒径Dはレーザー回折/散乱式粒径分布測定装置を用いて測定したd50により表す。平均粒径が2μm未満であると、絶縁性被覆層を施した複合軟磁性粉末における鉄の体積比率が低すぎて複合軟磁性粉末の飽和磁化が小さいだけでなく、複合軟磁性粉末の流動性が低くて圧縮成形時の取扱いが困難である。一方、平均粒径が100μmを超えると、中高周波数域での渦電流損失を十分抑制することができない。複合軟磁性粉末の平均粒径は好ましくは2~80μmであり、より好ましくは2~50μmであり、最も好ましくは2~40μmである。
被覆層は結晶軸方位の異なる平均結晶粒径3~15 nmの窒化ホウ素微結晶粒からなる多結晶体であるので、成形時に優れた潤滑性を発揮する。これにより、圧縮成形時のコア粒子の変形に被覆層も追随でき、圧粉磁心における絶縁性が十分に保たれる。平均結晶粒径が3 nm未満では被覆層による潤滑効果が十分でない。一方、平均結晶粒径が15 nm超では多結晶の効果が薄れ、圧縮成形時に被覆層が破壊するおそれがある。平均結晶粒径は好ましくは3~12 nmである。窒化ホウ素微結晶粒の平均結晶粒径は、被覆層の断面TEM写真において任意の方向及びそれに直交する方向の複数の線分の各々が横切る微結晶粒の大きさを計測し、全体の微結晶粒について平均することにより求める。平均する微結晶の数は20個以上とする。
本発明の複合軟磁性粉末において、被覆層はコア粒子を完全に覆っている訳ではなく、実際は窒化ホウ素被覆層は不均一であり、未被覆部分がある。窒化ホウ素層による被覆率は最表面におけるFeの割合で表される。本発明の複合軟磁性粉末においては、最表面におけるFeの割合は12原子%以下であるのが好ましい。最表面におけるFeの割合が12%超であると、窒化ホウ素に被覆されていない露出部分の割合が多すぎ、十分な絶縁効果が得られない。最表面におけるFeの割合はX線光電子分光分析法(X-ray Photoelectron Spectroscopy:XPS)より求める。XPS法により超高真空中で試料に単色X線を照射し、放出される光電子のエネルギーを測定することにより、試料の最表面の元素組成を分析する。具体的には、ナロースペクトル測定によりホウ素、窒素、酸素及び鉄の定量分析を行い、最表面におけるFeの割合を求める。XPS分析深さは5 nmであるので、「最表面」は5 nmの深さまでの表面領域を意味する。
(1) 原料粉末
(a) 窒化鉄粉末
窒化鉄粉末としてはFe4Nが好適であるが、Fe3N、Fe2N、又はこれらの混合物でも良い。窒化鉄粉末には炭素、酸素等の不可避的不純物も含まれるが、炭素の含有量は0.02質量%以下が好ましく、0.007質量%以下がより好ましい。窒化鉄粉末の平均粒径は複合軟磁性粉末の平均粒径とほぼ同じで良く、好ましくは2~100μmであり、より好ましくは2~50μmであり、最も好ましくは10~40μmである。窒化鉄粉末は、後述するホウ素粉末と混合して熱処理することにより、軟磁性鉄コア粒子となる。
ホウ素粉末は0.1~10μmの平均粒径を有する。平均粒径が0.1μm未満であると、ホウ素粉末は凝集する傾向があり、窒化鉄粉末との混合が困難である。一方、平均粒径が10μmを超えると、窒化鉄粉末と十分に混合するために粉砕媒体を用いることが必要になり、粉砕媒体から不純物の混入を招くおそれがある。ホウ素粉末の平均粒径は好ましくは0.5~10μmであり、より好ましくは0.5~5μmである。
窒化鉄粉末とホウ素粉末とをB/Fe原子比が0.03以上となるように配合し、乳鉢、V型混合機、ライカイ機、ボールミル、ビーズミル、回転式ミキサ等により混合するのが好ましい。B/Feの原子比については、0.8≧B/Fe≧0.03が好ましい。B/Fe原子比が0.8を超えると被覆層の形成に寄与しない過剰のホウ素を用いることになり、製造コストが高くなる。一方、B/Fe原子比が0.03未満の場合、コア粒子間に存在するホウ素粉末が少なすぎ、コア粒子同士の焼結により結晶粒の成長が促進され、所望の磁心特性が得られない。B/Feの原子比はより好ましくは0.8≧B/Fe≧0.1であり、さらに好ましくは0.8≧B/Fe≧0.125であり、最も好ましくは0.8≧B/Fe≧0.25である。
得られた混合粉を窒素雰囲気中において600~850℃の温度で熱処理する。熱処理は、例えば電気炉内のアルミナ製るつぼ中で行うのが好ましい。この熱処理により、軟磁性鉄系コア粒子の外周に窒化ホウ素を主体とする被覆層を有する複合軟磁性粉末が合成される。窒素雰囲気は窒素ガス単独が好ましいが、窒素とAr、He等の不活性ガス又はアンモニアとの混合ガスでも良い。熱処理温度が850℃超では窒化ホウ素を主体とする被覆層が厚過ぎるだけでなく、コア粒子内に進入し、鉄の体積比率を低下させて複合軟磁性粉末の軟磁気特性を低下させる。一方、600℃未満では窒化ホウ素を主体とする被覆層が形成されず、窒化鉄を原料とした場合は、窒化鉄の分解温度より低いため鉄が生成せず鉄粒子をコアとする複合軟磁性粉末を合成できない。好ましい熱処理温度は650~800℃である。600~850℃の温度に保持する時間(熱処理時間)は0.5~50時間が好ましく、1~10時間がより好ましく、1.5~5時間が最も好ましい。
熱処理後の粉末をイソプロピルアルコール(IPA)等の有機溶媒に投入し、超音波照射により分散させた後、永久磁石で軟磁性鉄系コア粒子のみを捕集する磁気分離法により精製し、非磁性成分を除去する。
複合軟磁性粉末にバインダを添加して造粒する。バインダとしては、ポリビニルブチラール(PVB)、ポリビニルアルコール(PVA)、アクリルエマルジョン、コロイダルシリカ等を用いるのが好ましい。得られた造粒粉を金型によるプレスで圧縮成形することにより圧粉磁心を製造する。圧縮成形の圧力は適宜設定できるが、例えば500~2000 MPaが好ましい。
(1) 複合軟磁性粉末の製造及び測定
平均粒径4.4μmの窒化鉄粉末(Fe/N原子比=4:1)と平均粒径0.7μmのホウ素粉末を0.6のB/Fe原子比で混合した後、窒素雰囲気中において700℃で2時間熱処理し、IPA中での磁気分離により非磁性分を除去し、平均粒径4.3μmの複合軟磁性粉末を得た。図1は複合軟磁性粉末の断面のTEM写真である。鉄系コア粒子には窒化ホウ素層で被覆されていない表面部分があり、コア粒子の表面が完全に被覆されている訳ではないことが確認された。
複合軟磁性粉末にPVB/エタノール溶液を添加して造粒し、油圧プレスで1470 MPaの圧力で圧縮成形することにより外径13.4 mm、内径7.7 mm及び厚さ4 mmのトロイダルリング状の圧粉磁心を製造した。圧粉磁心の質量及び寸法から密度を求めた。圧粉磁心の保磁力はVSMにより測定した。その結果、圧粉磁心の密度は7.0 Mg/m3であり、保磁力は11.1 Oeであった。
L=μ0μrΔN2Ae/le・・・(1)
L:インダクタンス[H]、
μ0:真空の透磁率=4π×10-7 [H/m]、
μrΔ:増分比透磁率、
N:巻数、
Ae:有効断面積[m2]、
le:有効磁路長[m]。
平均粒径が3.5μm、飽和磁化が204 emu/g、及び最表面におけるFeの割合が24.6原子%の市販の鉄粉末(BASF製SQ)にPVB/エタノール溶液を添加して造粒し、油圧プレスで1470 MPaの圧力で圧縮成形することにより外径13.4 mm、内径7.7 mm及び厚さ4 mmのトロイダルリング状の圧粉磁心を製造し、実施例1と同じ条件で評価した。その結果、圧粉磁心の密度は6.9 Mg/m3であり、保磁力は19.9 Oeであり、損失は176 kW/m3であった。増分比透磁率と直流バイアス磁界との関係を図3に示す。
平均粒径47μmの窒化鉄粉末(Fe/N原子比=4:1)と平均粒径0.7μmのホウ素粉末を0.6のB/Fe原子比で混合し、窒素雰囲気中において800℃で2時間熱処理し、IPA中での磁気分離により非磁性分を除去し、複合軟磁性粉末を得た。複合軟磁性粉末の平均粒径は30μmであり、飽和磁化は196 emu/gであり、鉄の体積比率は71%であり、最表面におけるFeの割合は6.0原子%、窒化ホウ素の平均結晶粒径は12 nmであった。TEM写真観察の結果、窒化ホウ素被覆層はC軸方位の異なる多結晶からなることが分った。飽和磁化から算出した窒化ホウ素被覆層の平均厚さTAは1.6μmであり、鉄の体積比率から求めたTA/DAは6.0%であった。
平均粒径が36μm、飽和磁化が198 emu/g、最表面におけるFeの割合が23.7原子%の市販の鉄粉末(株式会社高純度化学研究所製)にPVB/エタノール溶液を添加して造粒し、油圧プレスで1960 MPaの圧力で圧縮成形することにより外径13.4 mm、内径7.7 mm及び厚さ4 mmのトロイダルリング状の圧粉磁心を製造し、実施例1と同じ条件で評価した。その結果、圧粉磁心の密度は6.5 Mg/m3であり、保磁力は30.5 Oeであり、損失は550 kW/m3であった。増分比透磁率と直流バイアス磁界との関係を図4に示す。
平均粒径90μmの窒化鉄粉末(Fe/N原子比=4:1)と平均粒径0.7μmのホウ素粉末を0.6のB/Fe原子比で混合し、窒素雰囲気中において800℃で2時間熱処理し、IPA中での磁気分離により非磁性分を除去し、複合軟磁性粉末を得た。複合軟磁性粉末の平均粒径は85μmであり、飽和磁化は198 emu/gであり、鉄の体積比率は73%であり、最表面におけるFeの割合は11.5原子%、窒化ホウ素の平均結晶粒径は10 nmであった。TEM写真観察の結果、窒化ホウ素被覆層はC軸方位の異なる多結晶からなることが分った。飽和磁化から算出した窒化ホウ素被覆層の平均厚さTAは4.1μmであり、鉄の体積比率から求めたTA/DAは4.9%であった。
平均粒径が90μm、飽和磁化が199 emu/g、最表面におけるFeの割合が24.1原子%の市販の鉄粉末にPVB/エタノール溶液を添加して造粒し、油圧プレスで1960 MPaの圧力で圧縮成形することにより外径13.4 mm、内径7.7 mm及び厚さ4 mmのトロイダルリング状の圧粉磁心を製造し、実施例1と同じ条件で評価した。その結果、圧粉磁心の密度は7.0 Mg/m3であり、保磁力は27.0 Oeであり、損失は667 kW/m3であった。
平均粒径4.4μmの窒化鉄粉末(Fe/N原子比=4:1)と平均粒径0.7μmのホウ素粉末を0.6のB/Fe原子比で混合し、窒素雰囲気中において500℃で2時間熱処理し、IPA中での磁気分離により非磁性分を除去した。しかし、熱処理温度が500℃と低すぎたので、原料の窒化鉄粉末はほとんど変化なく、鉄粒子をコアとする複合軟磁性粉末は得られなかった。
平均粒径4.4μmの窒化鉄粉末(Fe/N原子比=4:1)と平均粒径0.7μmのホウ素粉末を0.6のB/Fe原子比で混合し、窒素雰囲気中において600℃で2時間熱処理し、IPA中での磁気分離により非磁性分を除去し、複合軟磁性粉末を得た。複合軟磁性粉末の平均粒径は4.3μmであり、飽和磁化は205 emu/gであり、鉄の体積比率は81%であり、最表面におけるFeの割合は11.7原子%であり、窒化ホウ素の平均結晶粒径は3 nmであった。TEM写真観察の結果、窒化ホウ素被覆層はC軸方位の異なる多結晶からなることが分った。飽和磁化から算出した窒化ホウ素被覆層の平均厚さTAは0.15μmであり、鉄の体積比率から求めたTA/DAは3.8%であった。
平均粒径4.4μmの窒化鉄粉末(Fe/N原子比=4:1)と平均粒径0.7μmのホウ素粉末を0.6のB/Fe原子比で混合し、窒素雰囲気中において800℃で2時間熱処理し、IPA中での磁気分離により非磁性分を除去し、複合軟磁性粉末を得た。複合軟磁性粉末の平均粒径は4.3μmであり、飽和磁化は204 emu/gであり、鉄の体積比率は80%であり、最表面におけるFeの割合は5.0原子%であり、窒化ホウ素の平均結晶粒径は8 nmであった。TEM写真観察の結果、窒化ホウ素被覆層はC軸方位の異なる多結晶からなることが分った。飽和磁化から算出した窒化ホウ素被覆層の平均厚さTAは0.16μmであり、鉄の体積比率から求めたTA/DAは4.0%であった。
平均粒径4.4μmの窒化鉄粉末(Fe/N原子比=4:1)と平均粒径0.7μmのホウ素粉末を0.6のB/Fe原子比で混合し、窒素雰囲気中において900℃で2時間熱処理し、IPA中での磁気分離により非磁性分を除去し、複合軟磁性粉末を得た。複合軟磁性粉末の平均粒径は4.6μmであり、飽和磁化は194 emu/gであり、鉄の体積比率は69%であり、最表面におけるFeの割合は1.1原子%であり、窒化ホウ素の平均結晶粒径は16 nmであった。窒化ホウ素被覆層の平均厚さTAは0.28μmであり、鉄の体積比率から求めたTA/DAは6.9%であった。図9は複合軟磁性粉末の断面のTEM写真である。図9から明らかなように、熱処理温度が900℃と高すぎたので必要以上に厚い窒化ホウ素被覆層が形成された。
平均粒径4.4μmの窒化鉄粉末(Fe/N原子比=4:1)と平均粒径0.7μmのホウ素粉末を0.6のB/Fe原子比で混合し、窒素雰囲気中において1000℃で2時間熱処理し、IPA中での磁気分離により非磁性分を除去し、複合軟磁性粉末を得た。複合軟磁性粉末の平均粒径は5.0μmであり、飽和磁化は182 emu/gであり、鉄の体積比率は58%であり、窒化ホウ素の平均結晶粒径は20 nmであった。窒化ホウ素被覆層の平均厚さTAは0.40μmであり、鉄の体積比率から求めたTA/DAは9.5%であった。熱処理温度が1000℃と高すぎたので必要以上に厚い窒化ホウ素被覆層が形成された。
平均粒径4.4μmの窒化鉄粉末(Fe/N原子比=4:1)と平均粒径0.7μmのホウ素粉末を0.25のB/Fe原子比で混合し、窒素雰囲気中において700℃で2時間熱処理し、IPA中での磁気分離により非磁性分を除去し、複合軟磁性粉末を得た。最表面におけるFeの割合は6.0原子%であった。TEM写真観察の結果、窒化ホウ素被覆層はC軸方位の異なる多結晶からなることが分った。
平均粒径4.4μmの窒化鉄粉末(Fe/N原子比=4:1)と平均粒径0.7μmのホウ素粉末を0.125のB/Fe原子比で混合し、窒素雰囲気中において700℃で2時間熱処理し、IPA中での磁気分離により非磁性分を除去し、複合軟磁性粉末を得た。最表面におけるFeの割合は5.3原子%であった。TEM写真観察の結果、窒化ホウ素被覆層はC軸方位の異なる多結晶からなることが分った。
平均粒径4.4μmの窒化鉄粉末(Fe/N原子比=4:1)と平均粒径0.7μmのホウ素粉末を0.05のB/Fe原子比で混合し、窒素雰囲気中において700℃で2時間熱処理し、IPA中での磁気分離により非磁性分を除去し、複合軟磁性粉末を得た。最表面におけるFeの割合は6.4原子%であった。TEM写真観察の結果、窒化ホウ素被覆層はC軸方位の異なる多結晶からなることが分った。
平均粒径4.4μmの窒化鉄粉末(Fe/N原子比=4:1)と平均粒径0.7μmのホウ素粉末を0.025のB/Fe原子比で混合し、窒素雰囲気中において700℃で2時間熱処理したところ、鉄粉末が焼結して硬い塊状になり、複合軟磁性粉末が得られなかった。
圧縮成形圧力を1030 MPaとした以外実施例1と同様にして圧粉磁心を作製し、評価した。圧粉磁心の密度及び損失を表15に示す。
圧縮成形圧力を520 MPaとした以外実施例1と同様にして圧粉磁心を作製し、評価した。圧粉磁心の密度及び損失を表15に示す。
圧縮成形圧力を310 MPaとした以外実施例1と同様にして圧粉磁心を作製し、評価した。圧粉磁心の密度及び損失を表15に示す。
圧縮成形圧力を1030 MPaとした以外比較例1と同様にして圧粉磁心を作製し、評価した。圧粉磁心の密度及び損失を表15に示す。
圧縮成形圧力を520 MPaとした以外比較例1と同様にして圧粉磁心を作製し、評価した。圧粉磁心の密度及び損失を表15に示す。
圧縮成形圧力を310 MPaとした以外比較例1と同様にして圧粉磁心を作製し、評価した。圧粉磁心の密度及び損失を表15に示す。
平均粒径4.4μmの窒化鉄粉末(Fe/N原子比=4:1)90質量%と平均粒径0.7μmのホウ素粉末10質量%とを混合した後、窒素雰囲気中において400℃、500℃、600℃、700℃、800℃、900℃、1000℃及び1300℃の各温度で2時間熱処理し、IPA中での磁気分離により非磁性分を除去し、複合軟磁性粉末を得た。複合軟磁性粉末のXRD強度と熱処理温度との関係を図12に示す。図12から明らかなように、500℃以下の低温で熱処理した複合軟磁性粉末にはFe4Nが認められたが、Fe-B化合物は認められず、また600℃以上の高温で熱処理した複合軟磁性粉末にはFe4Nだけでなく、Fe-B化合物も認められなかった。これは、Fe4NがFe-B化合物に転化することなくbcc-Feに完全に分解したことを意味する。このように、窒化鉄粉末を出発原料とする本発明の方法では、窒化鉄粒子の表面にFe-B化合物が生成されずに窒化ホウ素被覆層が形成される。
平均粒径0.03μmのα-Fe2O3粉末50質量%と平均粒径30μmのホウ素粉末50質量%とをV型混合機中で10分間混合した後、アルミナ製ボートに入れ、炉の中で流量2 L/分の窒素気流中で室温から3℃/分の速度で昇温し、500℃、750℃、950℃及び1500℃の各温度で15分間熱処理し、IPA中での磁気分離により非磁性分を除去し、複合軟磁性粉末を得た。各複合軟磁性粉末及びその熱処理前の原料に対して、X線回折測定を行なった。図13はXRDの測定結果を示す。図13から明らかなように、750℃及び950℃で熱処理してなる複合軟磁性粉末ではFeB、Fe2B及びFeB49が検出されたが、1500℃で熱処理してなる複合軟磁性粉末ではFe-Bが検出されず、窒化ホウ素が検出された。これから、酸化鉄粉末とホウ素粉末を出発原料とする場合、一旦Fe-B化合物が形成された後で窒化ホウ素が形成され、本発明の反応工程と異なることが分る。
1100℃で2時間熱処理した以外は比較例11と同じ方法で複合軟磁性粉末を製造した。図14は複合軟磁性粉末の窒化ホウ素被覆層のTEM写真(倍率:100万倍)であり、図15はその模式図である。窒化ホウ素被覆層はC軸方位が半径方向にほぼ揃った多層の膜状結晶からなり、C軸方位の異なる微結晶粒からなる本発明の多結晶窒化ホウ素被覆層と異なっていた。図15から明らかなように、比較例12の層状の窒化ホウ素被覆層には縞模様の結晶格子が認められた。格子面2は、鉄系コア粒子1の表面に沿ってほぼ並行に積層されていた。
Claims (11)
- 平均粒径2~100μmの軟磁性鉄系コア粒子と、前記軟磁性鉄系コア粒子の表面の少なくとも一部を被覆する窒化ホウ素を主体とする層とからなる複合軟磁性粉末であって、
前記被覆層は結晶軸方位の異なる平均結晶粒径3~15 nmの窒化ホウ素微結晶粒からなり、前記軟磁性鉄系コア粒子の平均粒径の6.6%以下の平均厚さを有する多結晶体層であることを特徴とする複合軟磁性粉末。 - 請求項1に記載の複合軟磁性粉末において、前記軟磁性鉄系コア粒子が純鉄又は鉄を主成分とする合金からなることを特徴とする複合軟磁性粉末。
- 請求項1又は2に記載の複合軟磁性粉末において、最表面におけるFeの割合が12原子%以下であることを特徴とする複合軟磁性粉末。
- 請求項1~3のいずれかに記載の複合軟磁性粉末において、純鉄又は鉄合金の体積比率が70%以上であることを特徴とする複合軟磁性粉末。
- 請求項1~4のいずれかに記載の複合軟磁性粉末を製造する方法において、(1) 平均粒径2~100μmの窒化鉄粉末と平均粒径0.1~10μmのホウ素粉末とを混合し、(2) 得られた混合粉を窒素雰囲気中において600~850℃の温度で熱処理し、(3) 非磁性成分を除去することを特徴とする方法。
- 請求項5に記載の複合軟磁性粉末の製造方法において、前記窒化鉄粉末と前記ホウ素粉末との原子比がB/Fe≧0.03であることを特徴とする方法。
- 請求項5又は6に記載の複合軟磁性粉末の製造方法において、熱処理温度を650~800℃とすることを特徴とする方法。
- 請求項7に記載の複合軟磁性粉末の製造方法において、熱処理温度を700~800℃とすることを特徴とする方法。
- 複合軟磁性粉末からなる圧粉磁心であって、前記複合軟磁性粉末は平均粒径2~100μmの軟磁性鉄系コア粒子と、前記軟磁性鉄系コア粒子の表面の少なくとも一部を被覆する窒化ホウ素を主体とする層とからなり、前記被覆層は結晶軸方位の異なる平均結晶粒径3~15 nmの窒化ホウ素微結晶粒からなり、前記軟磁性鉄系コア粒子の平均粒径の6.6%以下の平均厚さを有する多結晶体層であることを特徴とする圧粉磁心。
- 請求項9に記載の圧粉磁心において、前記軟磁性鉄系コア粒子が純鉄又は鉄を主成分とする合金からなることを特徴とする圧粉磁心。
- 請求項9又は10に記載の圧粉磁心において、5~7 Mg/m3の密度を有し、50 kHzの周波数及び50 mTの励磁磁束密度で測定したコアロスが528 kW/m3以下であり、密度に対する前記コアロスの変化率[(kW/m3)/(Mg/m3)]が-96以上であることを特徴とする圧粉磁心。
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JP2005200286A (ja) | 2004-01-19 | 2005-07-28 | Hitachi Metals Ltd | 窒化ほう素クラスターの製造方法、および窒化ほう素微小体 |
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JP4684461B2 (ja) * | 2000-04-28 | 2011-05-18 | パナソニック株式会社 | 磁性素子の製造方法 |
JP4277284B2 (ja) * | 2002-05-24 | 2009-06-10 | 日立金属株式会社 | 微小体の製造方法および微小体 |
JP2004253697A (ja) * | 2003-02-21 | 2004-09-09 | Hitachi Metals Ltd | 永久磁石材料及び永久磁石 |
JP4560784B2 (ja) * | 2004-02-24 | 2010-10-13 | 日立金属株式会社 | 金属微粒子およびその製造方法ならびに磁気ビーズ |
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JP2004124248A (ja) * | 2002-05-24 | 2004-04-22 | Hitachi Metals Ltd | 金属超微粒子とその製造方法、微小体の製造方法、および微小体 |
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Cited By (6)
Publication number | Priority date | Publication date | Assignee | Title |
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JP2014192454A (ja) * | 2013-03-28 | 2014-10-06 | Hitachi Metals Ltd | 複合被覆軟磁性金属粉末の製造方法および複合被覆軟磁性金属粉末、並びにこれを用いた圧粉磁心 |
JP2016184641A (ja) * | 2015-03-26 | 2016-10-20 | Tdk株式会社 | 軟磁性金属圧粉コア、及び、リアクトルまたはインダクタ |
WO2017086146A1 (ja) * | 2015-11-17 | 2017-05-26 | アルプス電気株式会社 | 磁性粉末の製造方法 |
JPWO2017086146A1 (ja) * | 2015-11-17 | 2018-09-13 | アルプス電気株式会社 | 磁性粉末の製造方法 |
JP2018182203A (ja) * | 2017-04-19 | 2018-11-15 | 株式会社村田製作所 | コイル部品 |
CN113543908A (zh) * | 2019-03-22 | 2021-10-22 | 日本特殊陶业株式会社 | 压粉磁芯 |
Also Published As
Publication number | Publication date |
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JPWO2012132783A1 (ja) | 2014-07-28 |
CN103339694A (zh) | 2013-10-02 |
EP2696356A4 (en) | 2014-12-24 |
EP2696356A1 (en) | 2014-02-12 |
US20130277601A1 (en) | 2013-10-24 |
WO2012131872A1 (ja) | 2012-10-04 |
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