Composite-coated soft magnetic metal powder and method for producing same

Abstract

[Problem] To provide: a composite-coated soft magnetic metal powder having exceptional green compact insulation properties, without causing any decrease in magnetic permeability, by combining a silicon oxide coating layer and a coating layer of a silicon compound that contains an organic substance; and a method for producing the same. [Solution] A composite-coated soft magnetic metal powder having exceptional green compact insulation properties without decreasing magnetic permeability can be obtained by forming, on the surface of soft magnetic metal particles containing 20 mass% or more of iron, a composite coating provided with a silicon oxide coating layer having an average thickness of 0.1-20 nm as a first layer and a silicon-containing coating layer having a structure in which silicon to which a C8-20 linear alkyl group is bonded is siloxane bonded as a second layer.

Description

Composite coated soft magnetic metal powder and its manufacturing method

[0001] The present invention relates to a composite-coated soft magnetic metal powder having good insulating properties and high magnetic permeability (μ), suitable for producing powder magnetic cores for electric and electronic components such as inductors, choke coils, transformers, reactors, and motors, and a method for producing the same.

[0002] Conventionally, dust cores using soft magnetic metal powders such as iron powder, iron-containing alloy powders, and intermetallic compound powders have been known as magnetic cores for inductors, choke coils, transformers, reactors, motors, etc. However, dust cores using such iron-containing soft magnetic metal powders have lower electrical resistivity than dust cores using ferrite powders, and are therefore manufactured by coating the surface of the soft magnetic metal powder with an insulating film, followed by compression molding and heat treatment.

[0003] Various insulating coatings have been proposed in the past. The present applicant has also disclosed, for example, in Patent Documents 1 and 2, silicon oxide-coated soft magnetic metal powders in which a silicon oxide coating layer is formed as an insulating coating layer by a so-called sol-gel method, and methods for producing the same. Patent Document 3 discloses a technique for forming an insulating layer primarily composed of an organosiloxane compound on the surface of a soft magnetic material. Patent Document 4 discloses a technique for mixing two types of soft magnetic particles with different average particle sizes to increase the packing density when forming a powder compact from a soft magnetic material. This technique also discloses a technique for coating the surface of soft magnetic particles with a small average particle size with a so-called silane coupling agent having a linear chain portion with six or more carbon atoms. Patent Document 5 discloses a composition in which a magnetic powder of an iron-based alloy having a median diameter (D50) of 1 to 500 μm is coated with one or more selected from glass, silicone resin, and coupling agents.

[0004] JP 2019-143241 A JP 2021-085065 A JP 2021-022609 A JP 2021-095629 A JP 2023-107555 A

[0005] The silicon oxide-coated soft magnetic metal powders disclosed in Patent Documents 1 and 2 have excellent insulating properties, but to further improve the insulating properties, it is necessary to increase the thickness of the silicon oxide layer, which poses the problem of reduced magnetic permeability. The insulating layer disclosed in Patent Document 3 is provided to adjust the capacitive reactance, and has poor insulating properties due to the inclusion of an organic substance in the coating layer. Like Patent Document 3, the coating layer disclosed in Patent Document 4 also has poor insulating properties due to the inclusion of an organic substance. The composition disclosed in Patent Document 5 is intended for use in injection molding and is unsuitable for use in forming a powder compact.

[0006] In view of the above problems, the present invention aims to provide a silicon oxide-coated soft magnetic metal powder that has excellent insulating properties without causing a decrease in magnetic permeability by combining a silicon oxide coating layer with a coating layer of a silicon compound containing an organic substance, and a method for producing the same.

[0007] To achieve the above object, the present specification discloses the following inventions. [1] A composite-coated soft magnetic metal powder composed of soft magnetic metal particles containing 20% ​​by mass or more of iron and having an insulating coating layer formed on the surface thereof, wherein the insulating coating layer has a multilayer structure including a first layer made of a silicon oxide coating layer with an average thickness of 0.1 nm to 20 nm, and a second layer formed on the first layer made of a silicon-containing coating layer having a structure in which silicon bonded to a linear alkyl group having 8 to 20 carbon atoms is siloxane-bonded. In this specification, the insulating coating layer having the multilayer structure is referred to as the "composite coating." [2] The composite-coated soft magnetic metal powder according to [1] above, wherein the first layer made of the silicon oxide coating layer has an average thickness of 0.5 nm to 20 nm. [3] The composite-coated soft magnetic metal powder according to [1] or [2] above, wherein the amount of the silicon-containing coating layer, which is the second layer, is 0.1 mg or more and 10 mg or less in terms of the mass of carbon contained in the second layer per unit mass (g) of the composite-coated soft magnetic metal powder. [4] The composite-coated soft magnetic metal powder according to any one of [1] to [3] above, wherein the atomic ratio of carbon to silicon (C / Si) measured by X-ray photoelectron spectroscopy (XPS) is 1.5 or more and 10 or less. [5] The composite-coated soft magnetic metal powder according to any one of [1] to [4] above, wherein the iron concentration measured by X-ray photoelectron spectroscopy (XPS) is less than 0.5 atomic %. [6] The composite-coated soft magnetic metal powder according to any one of [1] to [5] above, wherein the cumulative 50% particle diameter D50 on a volume basis, obtained by laser diffraction particle size distribution measurement, is 0.1 μm or more and 50 μm or less.

[0008] [7] A method for producing a composite-coated soft magnetic metal powder comprising soft magnetic metal particles containing 20% ​​by mass or more of iron and having an insulating coating layer formed on the surface thereof, the method comprising: a slurry preparation step of dispersing the soft magnetic metal powder containing 20% ​​by mass or more of iron, the soft magnetic metal powder having a silicon oxide coating layer with an average thickness of 0.1 nm to 20 nm formed on the surface thereof, in a mixed solvent of water and an organic solvent to obtain a slurry; a silane coupling agent addition step of adding and mixing a monoalkyltrialkoxysilane having a linear alkyl group of 8 to 20 carbon atoms and a hydrolysis catalyst for the monoalkyltrialkoxysilane to the slurry to form a coating layer of a hydrolysis product of the monoalkyltrialkoxysilane on the surface of the soft magnetic metal powder; and an aging step of dehydrating and condensing the coating layer of the hydrolysis product of the monoalkyltrialkoxysilane. [8] The method for producing a composite-coated soft magnetic metal powder according to [7] above, wherein the silicon oxide coating layer has an average thickness of 0.5 nm to 20 nm. [9] The method for producing a composite-coated soft magnetic metal powder according to [7] above, wherein the slurry preparation step includes the steps of: mixing a soft magnetic metal powder composed of soft magnetic metal particles containing 20% ​​by mass or more of iron with a tetraalkoxysilane in a mixed solvent of water and an organic solvent containing 1% by mass or more and 40% by mass or less of water to obtain a slurry in which the soft magnetic metal powder is dispersed; and mixing a hydrolysis catalyst for the tetraalkoxysilane with the slurry to form a silicon oxide coating layer having an average thickness of 0.1 nm or more and 20 nm or less on the surface of the soft magnetic metal powder.

[10] The method for producing a composite-coated soft magnetic metal powder according to [9] above, wherein the silicon oxide coating layer forming step forms a silicon oxide coating layer having an average thickness of 0.5 nm or more and 20 nm or less.

[11] The method for producing a composite-coated soft magnetic metal powder according to any of [7] to

[10] above, wherein the hydrolysis catalyst for the monoalkyltrialkoxysilane is ammonia.

[0009] By using the manufacturing method of the present invention, it has become possible to manufacture composite-coated soft magnetic metal powder that has excellent insulating properties and magnetic permeability when compacted.

[0010] [Soft Magnetic Metal Powder] In the present invention, a soft magnetic metal powder composed of soft magnetic metal particles containing 20% ​​by mass or more of iron is used as a starting material. Specific examples of the soft magnetic metal containing 20% ​​by mass or more of iron include Fe-Si alloys, Fe-Si-Cr alloys, Fe-Al-Si alloys (Sendust), and Fe-Ni alloys (Ni mass 30 to 80% by mass) having a permalloy composition. The soft magnetic metal may contain elements such as Mo, Co, Cu, Nb, B, and C as needed. Furthermore, the crystal structure of the soft magnetic metal particles may be crystalline or amorphous.

[0011] Hereinafter, in this specification, unless otherwise specified, "soft magnetic metal containing 20% ​​by mass or more of iron" will be simply referred to as "soft magnetic metal." In the present invention, the magnetic properties of the soft magnetic metal powder are not particularly specified, but a powder with a low coercive force (Hc) and a high saturation magnetization (σs) is preferred. The lower the Hc, the better, and 3.98 kA / m (approximately 50 (Oe)) or less is preferable. If the Hc exceeds 3.98 kA / m, the energy loss when reversing the magnetic field becomes large, which may be disadvantageous for magnetic core applications.

[0012] Also, the higher the σs, the better. ２ / kg (100 emu / g) or more is preferred. ２ If the density is less than 1 / kg, a large amount of magnetic powder is required, which inevitably increases the size of the magnetic core.

[0013] In the present invention, the average particle size of the primary particles of the soft magnetic metal powder is not particularly specified. However, conventionally, the average particle size of the primary particles has been in the range of 0.10 μm to 50.0 μm, and soft magnetic metal powder having an average particle size of any primary particle within this range can be used depending on the purpose.

[0014] [Silicon oxide coating layer] In the present invention, first, a silicon oxide-coated soft magnetic metal powder is prepared in which a silicon oxide coating layer with an average thickness of 0.5 nm to 20 nm is formed as a first insulating layer on the surface of the soft magnetic metal particles. The silicon oxide-coated soft magnetic metal powder can be produced by a wet method using silicon alkoxide as described in Patent Document 1 or Patent Document 2, but it is also possible to use powder produced by a known dry coating method such as sputtering. The coating method using silicon alkoxide is generally called a sol-gel method, and is superior in terms of mass productivity compared to the dry method described above.

[0015] When tetraalkoxysilane is used as the silicon alkoxide and the tetraalkoxysilane is hydrolyzed, some or all of the alkoxy groups are replaced with hydroxyl groups (OH groups), resulting in a silanol derivative. When the silanol derivative that has coated the surface of the soft magnetic metal powder undergoes dehydration condensation, the coating layer takes on a polysiloxane structure, and when the polysiloxane structure is further heated, silica (SiO ２ ) becomes.

[0016] In the present invention, when the sol-gel method is used, the coating of the polysiloxane structure in which some of the alkoxy groups of the tetraalkoxysilane remain, to the silica coating, are collectively referred to as the silicon oxide coating.

[0017] As the tetraalkoxysilane, for example, tetramethoxysilane, tetraethoxysilane, tetrapropoxysilane, etc. can be used, but it is preferable to use tetraethoxysilane because it has good wettability to the soft magnetic metal powder and can form a uniform coating layer.

[0018] [Thickness of Silicon Oxide Coating Layer] The average thickness of the silicon oxide coating layer is preferably 0.5 nm or more and 20 nm or less, and more preferably 1 nm or more and 10 nm or less. If the thickness is less than 0.5 nm, many defects will be present in the coating layer, making it difficult to ensure insulation. On the other hand, if the thickness exceeds 20 nm, although the insulation will be improved, the green density of the soft magnetic metal powder will decrease, which is undesirable as it will deteriorate the magnetic properties. The average thickness of the silicon oxide coating layer can be measured by a dissolution method. Details of the measurement method will be described later.

[0019] [Silicon-containing coating layer] The greatest technical feature of the present invention is that a second insulating layer having a structure in which silicon bonded by a linear alkyl group having a carbon number of 8 to 20 is siloxane-bonded on the surface of soft magnetic metal particles on which a silicon oxide coating layer is formed as the first insulating layer. In this specification, the insulating layer containing silicon bonded by the linear alkyl group is referred to as a silicon-containing coating layer.

[0020] The reason why the formation of the silicon-containing coating layer as the second insulating layer improves the insulating properties of the composite-coated soft magnetic metal powder compact is currently unclear, but the inventors speculate as follows: The silicon oxide coating layer, which is the first insulating layer, has extremely high resistivity, but is hard, and it is thought that the resistivity decreases due to reasons such as cracks occurring in the coating layer when the compact is produced by compression molding. In contrast, the silicon-containing coating layer contains organic substances, which gives it flexibility and is thought to prevent cracks from occurring within the silicon oxide coating layer during compression molding. Furthermore, the silicon-containing coating layer has lubricity, which may improve the sliding properties between silicon oxide-coated soft magnetic particles during compression molding, thereby improving the packing density of the composite-coated soft magnetic metal powder compact.

[0021] The silicon-containing coating layer can be obtained by adding a monoalkyltrialkoxysilane having a linear alkyl group having from 8 to 20 carbon atoms to a slurry in which the silicon oxide-coated soft magnetic metal powder is dispersed in water or a mixed solution of water and an organic solvent, hydrolyzing the monoalkyltrialkoxysilane, coating the surface of the soft magnetic metal particles on which the silicon oxide coating layer has been formed with the hydrolysis product, and then dehydrating and condensing the coating layer of the hydrolysis product. The dehydration and condensation converts the hydrolysis product into an organopolysiloxane in which silicon is bonded via siloxane bonds.

[0022] Monoalkyltrialkoxysilanes are substances commonly known as silane coupling agents. Silane coupling agents are a general term for silicon compounds having both inorganic and organic reactive sites. Examples of monoalkyltrialkoxysilanes that can be used include octyltrimethoxysilane, octyltriethoxysilane, nonyltrimethoxysilane, decyltrimethoxysilane, undecyltrimethoxysilane, dodecyltrimethoxysilane, tetradecyltrimethoxysilane, hexadecyltrimethoxysilane, and octadecyltrimethoxysilane, in which a linear alkyl group having 8 to 20 carbon atoms is bonded to silicon. Compounds having 7 or fewer carbon atoms are not preferred because the improvement in lubricity and the increase in volume resistivity are insufficient. Silane coupling agents having 21 or more carbon atoms are not generally manufactured and are difficult to obtain, making them undesirable.

[0023] As described above, in the present invention, the monoalkyltrialkoxysilane is not used as a coupling agent, but is used to obtain a coating layer that contains an organic substance as a constituent and has flexibility or lubricity.

[0024] [Amount of silicon-containing coating layer] The amount of silicon-containing coating layer of the second layer is evaluated by the mass of carbon contained in the silicon-containing coating layer per unit mass (g) of the composite-coated soft magnetic metal powder. The amount of silicon-containing coating layer is preferably 0.1 mg or more and 10 mg or less of carbon per unit mass. If the mass of carbon contained in the silicon-containing coating layer is 0.1 mg or more, it is advantageous for sufficiently covering the entire first coating layer and obtaining an excellent effect of improving lubricity. Furthermore, if the mass of carbon contained in the silicon-containing coating layer exceeds 10 mg, the coating layer becomes excessive, which is uneconomical as it does not contribute to improving volume resistivity, and is undesirable from the viewpoint of a significant decrease in magnetic permeability due to an increase in non-magnetic components.

[0025] [C / Si of Silicon-Containing Coating Layer] In the present invention, the C content of the silicon-containing coating layer of the second layer is evaluated by the carbon-to-silicon atomic ratio (C / Si) obtained by measuring the composite-coated soft magnetic metal powder by X-ray photoelectron spectroscopy (XPS). XPS is a surface analysis method in which a solid surface is irradiated with soft X-rays as an excitation source in an ultra-high vacuum and the photoelectrons emitted from the solid surface are analyzed by spectroscopy. XPS is a surface analysis method in which a solid surface is irradiated with soft X-rays as an excitation source and the photoelectrons emitted from the solid surface are analyzed by spectroscopy. In XPS, the incident X-rays penetrate to a considerable depth (approximately 1 to 10 μm) from the solid surface, but the escape depth of the excited photoelectrons is an extremely small value of several nanometers or less. Therefore, the XPS measurement results reflect the composition of the surface portion of the silicon-containing coating layer of the second layer. In the present invention, since ion sputtering is not performed during XPS measurement, the measured amount of C is C contained in the silicon-containing coating layer of the second layer, and therefore the C / Si can be used as an index of the C content in the silicon-containing coating layer of the second layer.

[0026] The carbon to silicon atomic ratio (C / Si) measured by XPS is preferably 1.5 or more and 10 or less. A C / Si of 1.5 or more is advantageous in that the entire first coating layer is sufficiently coated and excellent lubricity is obtained. On the other hand, a C / Si ratio of more than 10 is undesirable from the viewpoint that the coating layer becomes excessive, which does not contribute to improving volume resistivity and is uneconomical, and that the magnetic permeability decreases significantly due to an increase in non-magnetic components.

[0027] [Evaluation of Defects in the Composite Coating Layer] When the composite-coated soft magnetic metal powder obtained by the present invention is measured by XPS, a spectrum of metallic iron (referred to as Fe(M)) may be observed. However, this iron spectrum originates from soft magnetic metal particles containing 20% ​​by mass or more of iron. As described above, the escape depth of photoelectrons emitted from the solid surface in XPS measurement is an extremely small value of several nanometers or less. In the composite-coated soft magnetic metal powder of the present invention, if defects exist in the composite coating layer, exposing the base soft magnetic metal, or if a composite coating is formed but has a thickness thinner than the escape depth, the photoelectron spectrum of the constituent components of the soft magnetic metal is detected. Therefore, the iron concentration detected by XPS measurement can be used as an indicator of the amount of defects present in the composite coating layer. In the present invention, the iron concentration measured by XPS is preferably less than 0.5 atomic %.

[0028] [Volume-based cumulative 50% particle diameter] In the present invention, the volume-based cumulative 50% particle diameter D50 of the composite-coated soft magnetic metal powder obtained by a laser diffraction particle size distribution measurement method is preferably 0.1 μm or more and 50 μm or less. A particle size smaller than 0.1 μm may result in a strong cohesive force, reduced compressibility, and a reduced volume fraction of the soft magnetic particles. A particle size greater than 50 μm may result in an increased eddy current within the particle, reducing the magnetic permeability at high frequencies.

[0029] [Slurry Preparation Step] In the manufacturing method of the present invention, first, a slurry is prepared by dispersing silicon oxide-coated soft magnetic metal powder composed of soft magnetic metal particles containing 20 mass% or more of iron, the soft magnetic metal particles having a silicon oxide coating layer formed on the surface thereof with an average coating layer thickness of 0.5 nm to 20 nm, in water or a mixed solvent of water and an organic solvent. As described above, the manufacturing methods described in Patent Documents 1 and 2 may be used as a manufacturing method for the silicon oxide-coated soft magnetic metal powder. Examples of methods for manufacturing silicon oxide-coated soft magnetic metal powder include the following methods.

[0030] The slurry preparation step in the manufacturing method of the present invention can be exemplified by a step of mixing a soft magnetic metal powder containing 20% ​​by mass or more of iron and tetraalkoxysilane in a mixed solvent of water and an organic solvent containing 1% by mass or more and 40% by mass or less of water to obtain a slurry in which the soft magnetic metal powder is dispersed, and a step of mixing a hydrolysis catalyst for the tetraalkoxysilane with the slurry in which the soft magnetic metal powder is dispersed to form a silicon oxide coating layer with an average film thickness of 0.5 nm or more and 20 nm or less on the surface of the soft magnetic metal particles. However, the slurry preparation step in the manufacturing method of the present invention is not limited to the above examples.

[0031] [Silane Coupling Agent Addition Step] A monoalkyltrialkoxysilane having a linear alkyl group of 8 to 20 carbon atoms and a hydrolysis catalyst for the monoalkyltrialkoxysilane are added to and mixed with the slurry containing the soft magnetic metal powder having the silicon oxide coating layer obtained in the above step, thereby causing a hydrolysis reaction of the monoalkyltrialkoxysilane, and coating the surface of the soft magnetic metal powder having the silicon oxide coating layer with the hydrolysis product of the monoalkyltrialkoxysilane. As the monoalkyltrialkoxysilane, octyltrimethoxysilane, nonyltrimethoxysilane, octyltriethoxysilane, decyltrimethoxysilane, undecyltrimethoxysilane, dodecyltrimethoxysilane, tetradecyltrimethoxysilane, hexadecyltrimethoxysilane, octadecyltrimethoxysilane, etc. can be used, but it is preferable to use octyltriethoxysilane, decyltrimethoxysilane, dodecyltrimethoxysilane, or hexadecyltrimethoxysilane, which are easily available raw materials.

[0032] As the hydrolysis catalyst for the monoalkyltrialkoxysilane, alkali catalysts such as alkali metal hydroxides, amines, and ammonia can be used. However, it is preferable to use ammonia because it is less likely to leave impurities in the silicon oxide coating layer and is easily available.

[0033] [Aging step] The slurry containing the soft magnetic metal powder having a silicon oxide coating layer coated with the hydrolysis product of monoalkyltrialkoxysilane by the hydrolysis reaction is maintained at a temperature of 20°C or higher and 80°C or lower for 5 to 240 minutes to dehydrate and condense the hydrolysis product of monoalkyltrialkoxysilane, thereby converting the coating layer made of the hydrolysis product into a second silicon-containing coating layer having a structure in which silicon bonded to a linear alkyl group having from 8 to 20 carbon atoms is siloxane-bonded.

[0034] The slurry containing the soft magnetic metal powder having a silicon oxide coating coated with the hydrolysis product of monoalkyltrialkoxysilane obtained by the above process is maintained at a temperature range of 20°C to 80°C for 5 to 240 minutes to dehydrate and condense the hydrolysis product of monoalkyltrialkoxysilane. By the dehydration and condensation, the coating of the hydrolysis product of monoalkyltrialkoxysilane is converted into a second silicon-containing coating layer having a structure in which silicon bonded to a linear alkyl group having from 8 to 20 carbon atoms is siloxane-bonded.

[0035] [Solid-liquid separation and drying] The composite-coated soft magnetic metal powder is recovered from the slurry containing the composite-coated soft magnetic metal powder obtained by the series of steps described above using a known solid-liquid separation means. Known solid-liquid separation means such as filtration, centrifugation, and decantation can be used as the solid-liquid separation means. A flocculant may be added during solid-liquid separation. The recovered composite-coated soft magnetic metal powder is preferably dried in air, an inert gas atmosphere such as nitrogen or argon, or in vacuum at a temperature of 80°C to 150°C.

[0036] In the examples and comparative examples of the present invention, the following measurement methods were employed. [Silicon content] The silicon content of powder was analyzed by a dissolution method as follows. First, hydrochloric acid and perchloric acid were added to a powder sample (raw material powder, silicon oxide-coated soft magnetic metal powder, or composite-coated soft magnetic metal powder) to cause thermal decomposition, and the sample was heated until white smoke of perchloric acid was generated. The sample was then heated to dryness. After cooling, water and hydrochloric acid were added and the mixture was heated to dissolve soluble salts. Next, the insoluble residue was filtered using filter paper, and the residue together with the filter paper was transferred to a crucible, dried, and incinerated. After cooling, the crucible was weighed. A small amount of sulfuric acid and hydrofluoric acid was added, and the mixture was heated to dryness and then ignited. After cooling, the crucible was weighed. The second weighed value was subtracted from the first weighed value, and the weight difference was used as the SiO ２ The Si content in the powder sample was calculated from the calculated value.

[0037] [Average Film Thickness of Silicon Oxide Coating Layer] When the difference between the Si content of the silicon oxide coated soft magnetic metal powder measured by the above method and the Si content of the raw material powder is defined as D (mass %), the mass proportion P (mass %) of the silicon oxide coating layer is determined by the ratio of the Si atomic weight to the SiO ２ It is calculated from the molecular weight using the following formula: P = D x SiO ２ Molecular weight / Si atomic weight = D x 60.08 / 28.09 The density of the silicon oxide coating layer is d (g / cm ３ ), the BET specific surface area of ​​the raw material powder (core particle) is S (m ２ / g), the average thickness Ts (nm) of the silicon oxide coating layer is expressed by the following formula: Ts = 10 × P / (d × S) where d is 2.65 (g / cm ３ ) can be used. The number 10 on the right side is a unit conversion factor. If the silicon content of the raw material powder is unknown, the silicon oxide coating of the silicon oxide-coated soft magnetic gold powder can be dissolved by alkaline etching or the like, and the silicon content of the obtained raw material powder can be measured by a dissolution method or the like.

[0038] It was confirmed that the average film thickness of the silicon oxide coating layer calculated by the above method was in good agreement with the results of transmission electron microscope (TEM) observation of the cross section of the silicon oxide-coated soft magnetic metal powder prepared by the ion milling method.

[0039] [Carbon Content] The carbon content of the raw material powder or composite coated soft magnetic powder was measured using a carbon / sulfur analyzer (EMIA-22V manufactured by Horiba Ltd.).

[0040] [Carbon content in silicon-containing coating layer] The carbon content in the silicon-containing coating layer can be calculated from the difference in the measured carbon values ​​between the raw material powder and the composite-coated soft magnetic powder. If the carbon content of the raw material powder is unknown, it can be determined by oxidizing and removing the carbon in the silicon-containing coating of the composite-coated soft magnetic metal powder with an oxidizing agent, and measuring the carbon content of the resulting silicon oxide-coated soft magnetic metal powder.

[0041] [XPS Measurement] XPS measurement was performed using a PHI5000 VersaProbe III manufactured by ULVAC-PHI, Inc. The analysis area was φ100 μm, the X-ray source was an Al tube, the X-ray source output was 25 W, and the analysis angle was 45°. In the obtained photoelectron spectrum, Si was in the 2p orbital, C was in the 1s orbital, N was in the 1s orbital, and Fe was in the 2p orbital. ３／２ orbital, Ni is 2p ３／２ The mole fractions of Si, C, N, Fe, and Ni were calculated using the orbital spectrum and the relative sensitivity coefficients of each photoelectron spectrum by a computer built into the instrument. ３／２ The orbital was used. The Shirley method was used for background processing. Sputter etching was not performed, and the photoelectron spectrum of the outermost surface of the particles was measured. As described above, the C content of the silicon-containing coating layer was evaluated by the atomic ratio of carbon to silicon (C / Si). Ion sputtering was not performed.

[0042] [Particle size distribution] Using a laser diffraction particle size distribution analyzer (HELOS particle size distribution analyzer manufactured by SYMPATEC; HELOS & RODOS (airflow dispersion module)), the volume-based cumulative 10% particle diameter (D10), cumulative 25% particle diameter (D25), cumulative 50% particle diameter (D50), cumulative 75% particle diameter (D75), cumulative 90% particle diameter (D90), and cumulative 99% particle diameter (D99) were determined at a dispersion pressure of 5 bar (0.5 MPa).

[0043] [BET Specific Surface Area] The BET specific surface area was measured using a Macsorb manufactured by Mountec Co., Ltd., by flowing nitrogen gas into the measuring device at 105°C for 20 minutes to degas the sample, and then by flowing a mixed gas of nitrogen and helium (N ２ The measurement was carried out by the BET single-point method while flowing a mixture of 30% by volume of NaCl and 70% by volume of He.

[0044] [Volume Resistivity of Compacted Powder] The volume resistivity of the silicon oxide-coated soft magnetic metal powder was measured using a powder resistance measurement unit (MCP-PD600) manufactured by Nitto Seiko Analytech Co., Ltd., a high-resistivity resistivity meter Hiresta UX (MCP-HT800) manufactured by Nitto Seiko Analytech Co., Ltd., and high-resistivity powder measurement system software manufactured by Nitto Seiko Analytech Co., Ltd. A load of 20 kN was applied to a powder sample having a mass of 4 g in an insulator cylinder having an inner diameter of 20 mm to prepare a disk-shaped compacted powder sample having a diameter of 20 mm, and the volume resistivity was measured by the double ring electrode method with a load of 20 kN applied to the compacted powder sample.

[0045] In the case of the raw material powder, the volume resistivity of the same compressed powder sample as above was measured by the four-terminal method while a load of 20 kN was applied, using MCP-PD600, a low-resistance resistivity meter Loresta GXII (MCP-T710) manufactured by Nitto Seiko Analytech Co., Ltd., and low-resistance powder measurement system software manufactured by Nitto Seiko Analytech Co., Ltd.

[0046] Hereinafter, the volume resistivity of the powder compact measured under a load of 20 kN will be simply referred to as the "volume resistivity of the powder compact." In the present invention, the volume resistivity of the powder compact after the coating treatment is 10 １１ A value of Ω·cm or more was judged to be good.

[0047] [Measurement of Magnetic Permeability (μ') of Compacted Powder] Soft magnetic metal powder, liquid epoxy resin, and methyl ethyl ketone were weighed in a mass ratio of 16:1:12 before coating, after silicon oxide coating, or after composite coating. These were then kneaded using a planetary centrifugal mixer (ARE-250, manufactured by THINKY Corporation) to obtain a composite powder of soft magnetic metal powder and epoxy resin. 1.65 g of this composite powder was placed in a doughnut-shaped container and a load of 36.3 kN was applied using a hand press to obtain a toroidal-shaped compact with an outer diameter of 14 mm and an inner diameter of 9 mm. This compact was then heat-treated in a nitrogen atmosphere at 150°C for 1 hour and cured to obtain a toroidal core. The real part μ' of the complex relative magnetic permeability of this toroidal core was measured at 100 kHz and 20 mT using a B-H analyzer (SY-8218, manufactured by Iwasaki Electric Co., Ltd.).

[0048] Hereinafter, μ′ of the powder compact obtained by applying a load of 36.3 kN will be simply referred to as “magnetic permeability of the powder compact.” In the present invention, a powder compact whose magnetic permeability was reduced by 20% or less due to the coating treatment was judged to be good.

[0049] [Comparative Example 1] As the raw material powder (core particles), Fe-3.5 mass % Si-4.5 mass % Cr soft magnetic metal powder (BET specific surface area: 0.68 m ２ / g, D50: 3.1 μm). The volume resistivity of a compact of this raw material powder was 5.5×10 ２ The electrical conductivity was Ω·cm and the magnetic permeability was 18.3.

[0050] The slurry preparation step consisted of the following three steps, which were carried out in succession, following the example described in Patent Document 2.

[0051] 306 g of pure water and 1650 g of isopropyl alcohol (IPA) were charged into a 5000 mL reaction vessel at room temperature and mixed using a stirring blade to prepare a mixed solvent. 5550 g of the raw material powder was added to the mixed solvent, the liquid temperature was adjusted to 40°C, and the mixture was stirred at 380 rpm for 5 minutes to obtain a slurry (mixing step S1).

[0052] 34.9 g of tetraethoxysilane (TEOS: special grade reagent, manufactured by Wako Pure Chemical Industries, Ltd.) dispensed into a small beaker was added all at once to the slurry obtained in the above mixing step S1. The TEOS adhering to the small beaker was washed off with 200 g of IPA, which was then added to the slurry. After the TEOS addition, the temperature of the slurry was maintained at 40°C and stirring was continued for 5 minutes to allow the hydrolysis product of TEOS to react with the surfaces of the raw material powder particles. (Alkoxide Addition Step S2)

[0053] Thereafter, 239 g of 25% by mass ammonia water, a TEOS hydrolysis catalyst, was continuously added to the slurry obtained in the alkoxide addition step S2 at a rate of 2.6 g / min. Ten minutes after the start of the ammonia water addition, the pump was operated to send the slurry to a high-pressure homogenizer (LAB1000, manufactured by SMT Co., Ltd.) at a rate of 450 g / min. Simultaneously with the sending, the high-pressure homogenizer was set to a pressure of 15 MPa (150 bar) to carry out a dispersion treatment. The slurry after the dispersion treatment was set to return to the 5000 mL reaction vessel. This series of treatments (slurry withdrawal → dispersion treatment → slurry return circulation operation) was continued while the ammonia water was continuously added.

[0054] After the addition of aqueous ammonia was completed, the mixture was held for 60 minutes while stirring and dispersing, forming a silicon oxide coating layer on the surface of the soft magnetic metal powder. The temperature of the slurry was maintained at 40°C until this point. After holding for 60 minutes, 10 g of the slurry was sampled and subjected to solid-liquid separation using a Nutsche suction filtration device, and the filtrate was recovered. Si content of the recovered filtrate was analyzed using an inductively coupled plasma (ICP) optical emission spectrometer (720 ICP-OES, manufactured by Agilent Technologies Inc.), and it was found to be less than the detection limit of 10 ppm. It was confirmed that no TEOS remained in the liquid, and the hydrolysis reaction of the added TEOS had been completed. Since no TEOS remained in the filtrate, the average film thickness of the silicon oxide coating layer of the silicon oxide-coated soft magnetic metal powder of this comparative example was calculated to be 1 nm using the above-mentioned calculation method. (Hydrolysis Catalyst Addition Step S3)

[0055] The volume resistivity of the green compact obtained by compacting the silicon oxide-coated soft magnetic metal powder according to this comparative example at 64 MPa was 3.4×10 ６ The volume resistivity and magnetic permeability of the compact of the silicon oxide-coated soft magnetic metal powder according to this comparative example are shown in Table 1. Note that the volume resistivity is determined using a 10 １１ Ω cm or more: 〇, 10 ８ Ω・cm or more 10 １１ Less than Ω cm: △, 10 ８Less than Ω·cm is indicated by × (same in Tables 2 and 3).

[0056] Example 1: 306 g of pure water and 1650 g of isopropyl alcohol (IPA) were added to a 5000 mL reaction vessel at room temperature and mixed using a stirring blade to prepare a mixed solvent. 5550 g of silicon oxide-coated soft magnetic metal powder with a silicon oxide coating layer having an average thickness of 1 nm, obtained using the same procedure as in Comparative Example 1, was added to the mixed solvent and stirred at 380 rpm for 5 minutes to obtain a slurry. As a silane coupling agent addition step, 37.2 g of hexadecyltrimethoxysilane (HDTMS: H1376 manufactured by Tokyo Chemical Industry Co., Ltd., linear alkyl group having 16 carbon atoms) dispensed into a small beaker was added all at once to the resulting slurry. HDTMS adhering to the small beaker was washed off with 200 g of IPA and added to the slurry. After the HDTMS addition, 120 g of 25% by weight ammonia water was added all at once as a hydrolysis catalyst. After the addition of aqueous ammonia, the temperature of the slurry was maintained at 40°C for 120 minutes under stirring, so that the surfaces of the silicon oxide-coated soft magnetic metal powder were coated with the hydrolysis product of HDTMS and the coating layer of the hydrolysis product was dehydrated and condensed. During this time, the pH of the slurry was 11.

[0057] The slurry obtained in the silane coupling agent addition step was subjected to solid-liquid separation using a Nutsche suction filtration apparatus to recover the solids. The recovered solids were dried in a nitrogen atmosphere at 100°C for 12 hours to obtain the composite-coated soft magnetic metal powder according to this example. Since no Si was detected in Si analysis using an inductively coupled plasma (ICP) optical emission spectrometer (720 ICP-OES manufactured by Agilent Technologies Inc.) and no HDTMS remained in the filtrate, the mass of carbon in the silicon-containing second coating layer per unit mass (g) of the composite-coated soft magnetic metal powder according to this example was calculated to be 3.7 mg using the above calculation method.

[0058] When the composite coated soft magnetic metal powder according to this example was subjected to XPS measurement, the carbon to silicon atomic ratio C / Si was 2.2 and the iron concentration was 0.2 atomic %. In addition, the volume resistivity of the green compact obtained by compression molding the composite coated soft magnetic metal powder according to this example was 6.1 × 10 １１ The magnetic permeability is 19.0 Ω·cm, and the volume resistivity is 10 ５ The increase was about 100%. From these results, it can be seen that the composite coated soft magnetic metal powder obtained by the manufacturing method of the present invention has excellent insulating properties for the compact. Table 1 also shows the volume resistivity, magnetic permeability, and the percentage decrease in magnetic permeability of the composite coated soft magnetic metal powder according to this example. Table 1 also shows the C / Si value and iron concentration of the composite coated soft magnetic metal powder obtained by XPS measurement.

[0059] [Example 2] A composite-coated soft magnetic metal powder according to Example 2 was obtained in the same manner as in Example 1, except that the amount of TEOS added to the slurry was 87.3 g. The average film thickness of the silicon oxide coating layer of the composite-coated soft magnetic metal powder according to this example was calculated to be 2.5 nm using the calculation method described above. The volume resistivity of a compact of the composite-coated soft magnetic metal powder according to this example was 1.0 x 10 １２ The volume resistivity of the compact increased with an increase in the average film thickness of the silicon oxide coating layer. Table 1 also shows the volume resistivity, magnetic permeability, and percentage decrease in magnetic permeability of the composite-coated soft magnetic metal powder according to this example, as well as the C / Si value and iron concentration of the composite-coated soft magnetic metal powder obtained by XPS measurement.

[0060] [Comparative Examples 2, 3 and 15] Silicon oxide-coated soft magnetic metal powders were obtained in the same procedure as Comparative Example 1, except that the amount of TEOS added to the slurry in the alkoxide addition step was 174.5 g in Comparative Example 2, 349 g in Comparative Example 3, and 10.5 g in Comparative Example 15. In these cases, the average thickness of the silicon oxide coating layer was 5 nm in Comparative Example 2, 10 nm in Comparative Example 3, and 0.3 nm in Comparative Example 15. The volume resistivities of the compacts of the silicon oxide-coated soft magnetic metal powders according to these comparative examples were 5.0×10 for Comparative Example 2, 5.0×10 for Comparative Example 3, and 5.0×10 for Comparative Example 15. ８ Ω cm, and Comparative Example 3 is 7.9 × 10８ Ω cm, and Comparative Example 15 is 1.4 × 10 ６ Ω cm. Comparing these results with those of Example 1, it can be seen that forming a silicon-containing coating layer to form a multi-layer structure of the coating layer is more effective in improving the volume resistivity of the compact than increasing the average film thickness of the silicon oxide coating layer. Table 1 also shows the volume resistivity, magnetic permeability, and rate of change in magnetic permeability of the compacts of the silicon oxide-coated soft magnetic metal powders according to these comparative examples.

[0061] [Examples 3 and 13] A composite-coated soft magnetic metal powder according to Example 3 was obtained using the same procedure as Example 1, except that a slurry in which silicon oxide-coated soft magnetic metal powder having a silicon oxide coating layer with an average thickness of 5 nm, obtained using the same procedure as Comparative Example 2, was dispersed, was used. Furthermore, a composite-coated soft magnetic metal powder according to Example 13 was obtained using the same procedure as Example 1, except that a slurry in which silicon oxide-coated soft magnetic metal powder having a silicon oxide coating layer with an average thickness of 0.3 nm, obtained using the same procedure as Comparative Example 15, was dispersed, was used. The volume resistivity of a compact of the composite-coated soft magnetic metal powder according to Example 3 was 8.7 x 10 １２ Ω cm, and the volume resistivity of the compact of the composite-coated soft magnetic metal powder according to Example 13 was 4.9 × 10 １１ Table 1 also shows the volume resistivity, magnetic permeability, and rate of change in magnetic permeability of the compacts of the composite coated soft magnetic metal powders of Examples 3 and 13, as well as the C / Si value and iron concentration of the composite coated soft magnetic metal powders obtained by XPS measurement.

[0062] [Examples 4 and 5] Composite-coated soft magnetic metal powders were obtained using the same procedure as in Example 3, except that in the silane coupling agent addition step, 25.2 g of dodecyltrimethoxysilane (DDTMS: D3383 manufactured by Tokyo Chemical Industry Co., Ltd., linear alkyl group having 12 carbon atoms) was added in Example 4, and 25.2 g of octyltrimethoxysilane (OTMS: T2875 manufactured by Tokyo Chemical Industry Co., Ltd., linear alkyl group having 8 carbon atoms) was added in Example 5 instead of HDTMS. In these cases, the mass of carbon in the silicon-containing coating layer contained per unit mass (g) of the composite-coated soft magnetic metal powder was calculated to be 2.8 mg for Example 4 and 1.9 mg for Example 5. The volume resistivities of the compacts of the composite-coated soft magnetic metal powders according to these examples were 1.0 x 10 for Example 4 and 1.0 x 10 for Example 5, respectively. １２ Ω cm, and Example 5 is 4.8 × 10 １１ Ω cm. Furthermore, when XPS measurement was performed on the composite coated soft magnetic metal powders according to these examples, the carbon to silicon atomic ratio C / Si was 2.1 for Example 4 and 1.5 for Example 5. Table 1 shows the volume resistivity, magnetic permeability, and rate of change in magnetic permeability of the compacts of the composite coated soft magnetic metal powders according to these examples, as well as the C / Si value and iron concentration of the composite coated soft magnetic metal powders obtained by XPS measurement.

[0063] [Comparative Examples 4 and 5] Composite-coated soft magnetic metal powders were obtained using the same procedure as in Example 3, except that in the silane coupling agent addition step, instead of HDTMS, 14.6 g of methyltrimethoxysilane (MTMS: M0660 manufactured by Tokyo Chemical Industry Co., Ltd., linear alkyl group having one carbon atom) was added in Comparative Example 4, and 24.3 g of phenylethyltrimethoxysilane (PhETMS: T3542 manufactured by Tokyo Chemical Industry Co., Ltd.) was added in Comparative Example 5. In these cases, the mass of carbon in the silicon-containing coating layer contained per unit mass (g) of the composite-coated soft magnetic metal powder was calculated to be 0.2 mg in Comparative Example 4 and 1.9 mg in Comparative Example 5. The volume resistivities of the green compacts obtained by compression-molding the composite-coated soft magnetic metal powders according to these comparative examples were 5.7 x 10 for Comparative Example 4 and 5. ９ Ω cm, and Comparative Example 5 is 1.0 × 10 １０Ω cm, both of which were lower than those of Example 3. Furthermore, when XPS measurement was performed on the composite coated soft magnetic metal powders according to these comparative examples, the carbon to silicon atomic ratio C / Si was 0.2 for Comparative Example 4 and 1.2 for Comparative Example 5. Table 1 also shows the volume resistivity, magnetic permeability, and rate of change in magnetic permeability of the compacts of the composite coated soft magnetic metal powders according to these comparative examples, as well as the C / Si value and iron concentration of the composite coated soft magnetic metal powders obtained by XPS measurement.

[0064] [Comparative Examples 6 and 7] In the alkoxide addition step, 34.9 g of TEOS and 37.2 g of HDTMS were added simultaneously to the slurry in Comparative Example 6, and 185 g of HDTMS was added in Comparative Example 7. The same procedure as in Comparative Example 1 was used to form only a silicon-containing coating layer on the surface of the raw soft magnetic metal powder. In this case, the mass of carbon in the silicon-containing coating layer contained per unit mass (g) of the composite-coated soft magnetic metal powder was calculated to be 3.7 mg in Comparative Example 6 and 18 mg in Comparative Example 7. The volume resistivities of the compacts of the soft magnetic metal powders coated with the silicon-containing coating layers according to these comparative examples were 9.0 x 10 for Comparative Example 6 and 9.0 x 10 for Comparative Example 7. ９ Ω cm, and Comparative Example 7 was 2.1 × 10 ８ The volume resistivity, magnetic permeability, and rate of change in magnetic permeability of the compacts of the soft magnetic metal powders coated with the silicon-containing coating layers according to the comparative examples are shown in Table 1.

[0065] [Example 6] As the raw material powder (core particles), Fe-Si-Cr-B-C amorphous alloy soft magnetic metal powder (BET specific surface area: 0.08 m) was used. ２ / g, D50: 26.0 μm), the amount of TEOS added to the slurry in the alkoxide addition step was 20.4 g, and 3.9 g of HDTMS was added in the silane coupling agent addition step. The composite coated soft magnetic metal powder of this example was obtained using the same procedure as in Example 3, except that the mass of carbon in the silicon-containing coating layer contained per unit mass (g) of the composite coated soft magnetic metal powder in this example was calculated to be 0.4 mg. The volume resistivity of a compact of this raw material powder was 1.8 × 10 －２The volume resistivity of the compact of the composite coated soft magnetic metal powder according to this example was 2.1×10 １２ The value was Ω·cm.

[0066] [Examples 7 and 8] Composite-coated soft magnetic metal powders according to the present examples were obtained using the same procedure as in Example 6, except that the amount of TEOS added in the slurry preparation step was 40.8 g in Example 7 and 61.2 g in Example 8. The mass of carbon in the silicon-containing coating layer contained per unit mass (g) of the composite-coated soft magnetic metal powder in Examples 7 and 8 was calculated to be 0.4 mg in both cases. In these cases, the average thicknesses of the silicon oxide layer in the first layer were calculated to be 10 nm and 15 nm, respectively. The volume resistivities of the green compacts obtained by compression-molding the composite-coated soft magnetic metal powders according to these examples were 7.2 x 10 for Example 7 and 7.2 x 10 for Example 8. １１ Ω cm, and Example 8 is 8.5 × 10 １１ The value was Ω·cm.

[0067] [Example 9] A composite-coated soft magnetic metal powder was obtained using the same procedure as in Example 6, except that DDTMS was used instead of HDTMS in the silane coupling agent addition step. The mass of carbon in the silicon-containing coating layer contained per unit mass (g) of the composite-coated soft magnetic metal powder in this example was calculated to be 0.3 mg. The volume resistivity of the compacted powder of the composite-coated soft magnetic metal powder according to this example was 1.1 x 10 １１ Table 2 shows the volume resistivity, magnetic permeability, and rate of change in magnetic permeability of the composite coated soft magnetic metal powders according to Examples 6 to 9, as well as the C / Si value and iron concentration of the composite coated soft magnetic metal powders obtained by XPS measurement.

[0068] [Comparative Example 8] A silicon-containing coated soft magnetic metal powder according to this comparative example was obtained in the same manner as in Comparative Example 1, except that the same soft magnetic metal powder as in Example 6 was used as the raw material powder (core particles). The volume resistivity of the silicon-containing coated soft magnetic metal powder compact according to this comparative example was 1.6 × 10 －１ The value was low.

[0069] Comparative Example 9 A composite-coated soft magnetic metal powder was obtained in the same manner as in Example 6, except that MTMS was used instead of HDTMS in the silane coupling agent addition step. The volume resistivity of the compact of the composite-coated soft magnetic metal powder according to this comparative example was 7.1 × 10 －２ Ω·cm, which was an extremely low value.

[0070] Comparative Example 10: Using the same soft magnetic metal powder as in Example 6 as the raw material powder (core particles), and setting the amount of TEOS added in the slurry preparation step to 61.2 g, the same as in Example 8, a silicon oxide-coated soft magnetic metal powder was obtained. The volume resistivity of the compact of the silicon oxide-coated soft magnetic metal powder according to this comparative example was 3.1 × 10 ０ The value was Ω·cm.

[0071] [Comparative Example 11] A silicon oxide-coated soft magnetic metal powder was obtained by adding 122.4 g of TEOS in the slurry preparation step, which was twice that of Comparative Example 11. In this case, the average thickness of the silicon oxide coating layer was calculated to be 30 nm. The volume resistivity of the compact of the silicon oxide-coated soft magnetic metal powder according to this comparative example was 4.7 × 10 ８ Table 2 also shows the volume resistivity, magnetic permeability, and rate of change in magnetic permeability of the compacts of the soft magnetic metal powders subjected to each coating treatment according to Comparative Examples 8 to 11.

[0072] [Example 10] Carbonyl iron powder (BET specific surface area: 0.94 m) was used as the raw material powder (core particles). ２ A composite coated soft magnetic metal powder according to this example was obtained using a silicon-containing coating layer containing 143.0 g of TEOS in the slurry preparation step and 46.0 g of HDTMS in the silane coupling agent addition step, using a silicon-containing coating layer containing 4.6 mg of silicon oxide per unit mass (g) of the composite coated soft magnetic metal powder in this example. The average thickness of the silicon oxide coating layer was calculated to be 3 nm. The volume resistivity of a compact of this raw material powder was 7.2 x 10 －３ The volume resistivity of the compact of the composite coated soft magnetic metal powder according to this example was 5.0×10 １１ The electrical resistance was Ω·cm and the magnetic permeability was 9.3.

[0073] [Example 11] A composite coated soft magnetic metal powder according to this example was obtained using the same procedure as in Example 10, except that the amount of TEOS added in the slurry preparation step was 238.3 g. The mass of carbon in the silicon-containing coating layer contained per unit mass (g) of the composite coated soft magnetic metal powder according to this example was calculated to be 4.6 mg. The volume resistivity of a compact of the composite coated soft magnetic metal powder according to this example was 1.0 x 10 １３ The electrical resistance was Ω·cm and the magnetic permeability was 8.4.

[0074] [Comparative Examples 12 and 13] Silicon oxide-coated soft magnetic metal powders were obtained using the same soft magnetic metal powder as in Example 10 as the raw material powder (core particles), with the amount of TEOS added in the slurry preparation step being 238.3 g in Comparative Example 12, the same as in Example 11, and 476.7 g in Comparative Example 13, twice that of Example 11. The volume resistivity and magnetic permeability of the compacts of the silicon oxide-coated soft magnetic metal powders according to these comparative examples were 2.5 × 10 for Comparative Example 12 and 2.5 × 10 for Comparative Example 13, respectively. ６ Ω cm and 8.1, and Comparative Example 13 was 1.0 × 10 ９ Table 3 also shows the volume resistivity, magnetic permeability, and rate of change in magnetic permeability of the compacts of the soft magnetic metal powders subjected to each coating treatment in Examples 10 and 11 and Comparative Examples 12 and 13.

[0075] [Example 12] As the raw material powder (core particles), Fe-50Ni soft magnetic metal powder (BET specific surface area: 1.17 m) was used. ２ / g, D50: 0.6 μm), the amount of TEOS added in the slurry preparation step was 119.1 g, and 57.4 g of HDTMS was added in the silane coupling agent addition step. The composite coated soft magnetic metal powder of this example was obtained using the same procedure as in Example 1, except that the mass of carbon in the silicon-containing coating layer contained per unit mass (g) of the composite coated soft magnetic metal powder in this example was calculated to be 5.7 mg. In this case, the average thickness of the silicon oxide coating layer was calculated to be 2 nm. The volume resistivity of a compact of this raw material powder was 1.5 × 10 ４ The volume resistivity of the compact of the composite coated soft magnetic metal powder according to this example was 1.0×10１３ The electrical resistance was Ω·cm and the magnetic permeability was 9.5.

[0076] Comparative Example 14: Using the same soft magnetic metal powder as in Example 12 as the raw material powder (core particles), and increasing the amount of TEOS added in the slurry preparation step to 297.7 g, which is 2.5 times that of Example 12, a silicon oxide-coated soft magnetic metal powder was obtained. The volume resistivity of the compact of the silicon oxide-coated soft magnetic metal powder according to this comparative example was 2.5×10 ８ The volume resistivity, magnetic permeability, and rate of change in magnetic permeability of the compacts of the soft magnetic metal powders subjected to each coating treatment according to Example 12 and Comparative Example 14 are also shown in Table 3.

[0077]

[0078]

[0079]

[0080] From the above results, in Comparative Examples 1, 2, and 3, in which only the silicon oxide coating layer was formed and no silicon-containing coating layer was formed, even if the thickness of the silicon oxide coating layer was increased to 10 nm, the volume resistivity of the green compact was 10 ９ In Comparative Examples 4 and 5, the number of carbon atoms in the linear chain was less than 8, or the number of carbon atoms in the alkyl group was 8 or more but the number of carbon atoms in the linear chain was less than 8, so the volume resistivity of the green compact was 10 ９ In Comparative Example 6, the first and second layers were formed simultaneously, so the alkyl groups on the surface were small, and the lubricating effect was reduced to 10 ９ In Comparative Example 7, the first layer that ensures the insulation resistance is not present, and the insulation is maintained by the trace amount of silicon contained in the second layer. ９The volume resistivity remained below Ω cm. In the cases of Examples 1 to 5, in which both a silicon oxide coating layer and a silicon-containing coating layer were formed in combination, all of the green compacts exhibited excellent volume resistivities, which is thought to be because, as described above, the presence of the silicon-containing layer prevented the silicon oxide coating layer from being destroyed during compression molding. The results of Examples 6 to 12 also demonstrate that the effects of the present invention can be obtained regardless of the composition and particle size of the raw material powder.

Claims

1. A composite-coated soft magnetic metal powder consisting of soft magnetic metal particles containing 20% ​​by mass or more of iron and having an insulating coating layer formed on the surface thereof, wherein the insulating coating layer has a multi-layer structure including a first layer consisting of a silicon oxide coating layer having an average thickness of 0.1 nm to 20 nm, and a second layer formed on the first layer consisting of a silicon-containing coating layer having a siloxane bond structure in which silicon bonded to a linear alkyl group having 8 to 20 carbon atoms is bonded.

2. The composite-coated soft magnetic metal powder according to claim 1, wherein the first layer made of the silicon oxide coating layer has an average film thickness of 0.5 nm or more and 20 nm or less.

3. The composite-coated soft magnetic metal powder according to claim 1, wherein the amount of the silicon-containing coating layer, which is the second layer, is 0.1 mg or more and 10 mg or less in terms of the mass of carbon contained in the second layer per unit mass (g) of the composite-coated soft magnetic metal powder.

4. The composite-coated soft magnetic metal powder according to claim 1, wherein the atomic ratio of carbon to silicon (C / Si) measured by X-ray photoelectron spectroscopy (XPS) is 1.5 or more and 10 or less.

5. The composite-coated soft magnetic metal powder according to claim 1, wherein the iron concentration measured by X-ray photoelectron spectroscopy (XPS) is less than 0.5 atomic %.

6. The composite-coated soft magnetic metal powder according to claim 1, wherein the volume-based cumulative 50% particle diameter D50 obtained by a laser diffraction particle size distribution measurement method is 0.1 μm or more and 50 μm or less.

7. A method for producing composite-coated soft magnetic metal powder composed of soft magnetic metal particles containing 20% ​​by mass or more of iron and having an insulating coating layer formed on the surface thereof, the method comprising: a slurry preparation step of dispersing soft magnetic metal powder containing 20% ​​by mass or more of iron, the soft magnetic metal powder having a silicon oxide coating layer with an average thickness of 0.1 nm to 20 nm formed on the surface thereof, in a mixed solvent of water and an organic solvent to obtain a slurry; a silane coupling agent addition step of adding and mixing a monoalkyltrialkoxysilane having a linear alkyl group of 8 to 20 carbon atoms and a hydrolysis catalyst for the monoalkyltrialkoxysilane to the slurry, thereby forming a coating layer of a hydrolysis product of the monoalkyltrialkoxysilane on the surface of the soft magnetic metal powder; and an aging step of dehydrating and condensing the coating layer of the hydrolysis product of the monoalkyltrialkoxysilane.

8. The method for producing composite-coated soft magnetic metal powder according to claim 7, wherein the silicon oxide coating layer has an average film thickness of 0.5 nm or more and 20 nm or less.

9. A method for producing a composite-coated soft magnetic metal powder according to claim 7, wherein the slurry preparation step comprises the steps of: mixing a soft magnetic metal powder composed of soft magnetic metal particles containing 20% ​​by mass or more of iron with tetraalkoxysilane in a mixed solvent of water and an organic solvent containing 1% by mass or more and 40% by mass or less of water to obtain a slurry in which the soft magnetic metal powder is dispersed; and mixing a hydrolysis catalyst for tetraalkoxysilane with the slurry to form a silicon oxide coating layer having an average film thickness of 0.1 nm or more and 20 nm or less on the surface of the soft magnetic metal powder.

10. The method for producing composite-coated soft magnetic metal powder according to claim 9, wherein in the step of forming the silicon oxide coating layer, a silicon oxide coating layer having an average film thickness of 0.5 nm or more and 20 nm or less is formed.

11. The method for producing composite-coated soft magnetic metal powder according to claim 7, wherein the catalyst for hydrolysis of the monoalkyltrialkoxysilane is ammonia.

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