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

Abstract

To provide composite coated soft magnetic metal powder in which the insulating property of a green compact is excellent without causing the reduction of magnetic permeability by combining a silicon oxide coating layer and a coating layer of a silicon compound containing an organic substance, and to provide a method for producing the same.SOLUTION: By forming a composite coating in which a silicon oxide coating layer having an average film thickness of 0.1 nm or more and 20 nm or less is provided as a first layer and a silicon-containing coating layer having a structure in which a linear alkyl group having 8 or more and 20 or less carbon atoms is bonded by a siloxane bond is provided as a second layer on the surfaces of soft magnetic metal particles containing 20 mass% or more of iron, it is possible to obtain a composite-coated soft magnetic metal powder having excellent insulating properties of a green compact without decreasing the permeability.SELECTED DRAWING: None

Description

[Technical Field]

[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. [Background technology]

[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, and the present applicant has also disclosed, for example, in Patent Documents 1 and 2, silicon oxide-coated soft magnetic metal powder in which a silicon oxide coating layer is formed as an insulating coating layer by a so-called sol-gel method, and a method for producing the same. Patent Document 3 discloses a technique for forming an insulating layer made mainly 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 in order to increase the packing density when forming a powder compact from a soft magnetic material. This technique involves coating the surfaces 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 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. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 2019-143241 [Patent Document 2] Patent Publication No. 2021-085065 [Patent Document 3] Patent Publication No. 2021-022609 [Patent Document 4] Patent Publication No. 2021-095629 [Patent Document 5] Japanese Patent Publication No. 2023-107555 Summary of the Invention [Problem to be solved by the invention]

[0005] The silicon oxide-coated soft magnetic metal powders disclosed in Patent Documents 1 and 2 have excellent insulating properties, but in order to further improve the insulating properties, it is necessary to increase the thickness of the silicon oxide layer, which poses the problem of a decrease in magnetic permeability. The insulating layer disclosed in Patent Document 3 was provided to adjust the capacitive reactance, and had poor insulating properties because it contained an organic substance in the coating layer.Like Patent Document 3, the coating layer disclosed in Patent Document 4 also had poor insulating properties because it contained an organic substance. The composition disclosed in Patent Document 5 is intended for use in injection molding, and is not suitable for use in forming a green 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. [Means for solving the problem]

[0007] In order to achieve the above object, the present specification discloses the following invention. [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 multilayer 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 consisting of a silicon-containing coating layer formed on the first layer and 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 above-described multi-layer structure is referred to as a "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 film thickness of 0.5 nm or more and 20 nm or less. [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 the above [1] to [4], 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 the above [1] to [5], 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.

[0008] [7] A method for producing 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, 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 or more and 20 nm or less 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 a monoalkyltrialkoxysilane having a linear alkyl group having from 8 to 20 carbon atoms and a hydrolysis catalyst for the monoalkyltrialkoxysilane to the slurry and mixing them to form a coating layer of a hydrolysis product of the monoalkyltrialkoxysilane on the surface of the soft magnetic metal powder; an aging step of dehydrating and condensing the coating layer of the hydrolysis product of the monoalkyltrialkoxysilane; A method for producing a composite coated soft magnetic metal powder having the above-mentioned features. [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 film thickness of 0.5 nm or more and 20 nm or less. [9] The slurry preparation step A step of mixing a soft magnetic metal powder constituted by 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; a step of mixing a tetraalkoxysilane hydrolysis catalyst 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; The method for producing the composite coated soft magnetic metal powder according to [7] above, which comprises:

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

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

[10] , wherein the hydrolysis catalyst for the monoalkyltrialkoxysilane is ammonia. [Effects of the Invention]

[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. DETAILED DESCRIPTION OF THE INVENTION

[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) that are permalloy compositions. The soft magnetic metals may contain elements such as Mo, Co, Cu, Nb, B, and C as needed. 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 preferable. 2 If the amount 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 or more and 50.0 μm or less, 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, silicon oxide-coated soft magnetic metal powder is prepared by forming a silicon oxide coating layer with an average thickness of 0.5 nm to 20 nm 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), forming a silanol derivative. When the silanol derivative that coats 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, it becomes silica (SiO2).

[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, deteriorating the magnetic properties, which is not preferable. 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 to 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 to 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 is 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 a siloxane bond.

[0022] Monoalkyltrialkoxysilanes are commonly known as silane coupling agents. Silane coupling agents are a general term for silicon compounds that have both inorganic and organic reactive sites. Examples of monoalkyltrialkoxysilanes that can be used include octyltrimethoxysilane, octyltriethoxysilane, nonyltrimethoxysilane, decyltrimethoxysilane, undecyltrimethoxysilane, dodecyltrimethoxysilane, tetradecyltrimethoxysilane, hexadecyltrimethoxysilane, and octadecyltrimethoxysilane, which are compounds in which a linear alkyl group having 8 to 20 carbon atoms is bonded to silicon. Compounds with 7 or fewer carbon atoms are not preferred because they provide insufficient improvement in lubricity and an insufficient increase in volume resistivity. Silane coupling agents with 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 attached] The amount of carbon in the silicon-containing coating layer of the second layer is evaluated by the mass of carbon in the silicon-containing coating layer per unit mass (g) of the composite-coated soft magnetic metal powder. The amount of carbon in the silicon-containing coating layer is preferably 0.1 mg or more and 10 mg or less per unit mass. When the mass of carbon in the silicon-containing coating layer is 0.1 mg or more, the entire first coating layer is sufficiently coated, which is advantageous for achieving excellent lubricity improvement. Furthermore, when the mass of carbon in the silicon-containing coating layer exceeds 10 mg, the coating layer becomes excessive, which is uneconomical because 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 second silicon-containing coating layer is evaluated by the atomic ratio of carbon to silicon (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 ultrahigh 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 a considerable depth (approximately 1 to 10 μm) from the solid surface, but the escape depth of the excited photoelectrons is extremely small, at several nm 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 C amount is the C contained in the silicon-containing coating layer of the second layer. Therefore, the C / Si ratio can be used as an indicator of the C content of 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 for sufficiently covering the entire first coating layer and obtaining an excellent effect of improving lubricity. On the other hand, a C / Si ratio of more than 10 is undesirable from the viewpoints that the coating layer becomes excessive, which is uneconomical because it does not contribute to improving volume resistivity, and also significantly reduces magnetic permeability due to an increase in non-magnetic components.

[0027] [Evaluation of defects in composite coating layers] 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% ​​or more by mass of iron. As described above, the escape depth of photoelectrons emitted from a 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 underlying soft magnetic metal, or if a composite coating is formed but has a thickness less 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 size] In the present invention, the composite-coated soft magnetic metal powder preferably has a volume-based cumulative 50% particle diameter D50 obtained by a laser diffraction particle size distribution measurement method of 0.1 μm or more and 50 μm or less. A particle diameter smaller than 0.1 μm may result in a strong cohesion force, reduced compressibility, and a reduced volume fraction of soft magnetic particles. A particle diameter greater than 50 μm may result in increased eddy currents within the particles, reducing magnetic permeability at high frequencies.

[0029] [Slurry preparation process] 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 method of the silicon oxide-coated soft magnetic metal powder may be based on the manufacturing methods described in Patent Document 1 or Patent Document 2. Examples of the manufacturing method of the silicon oxide-coated soft magnetic metal powder include the following method.

[0030] The slurry preparation step of 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 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 example.

[0031] [Silane coupling agent addition process] 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 obtained by the above process, in which the soft magnetic metal powder having the silicon oxide coating layer formed thereon is dispersed, thereby inducing a hydrolysis reaction of the monoalkyltrialkoxysilane, and the surface of the soft magnetic metal powder having the silicon oxide coating layer formed thereon is coated 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 process] 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 range of 20°C or higher and 80°C or lower for 5 to 240 minutes, and the hydrolysis product of monoalkyltrialkoxysilane is dehydrated and condensed, thereby converting the coating layer made of the hydrolysis product into a second silicon-containing coating layer having a siloxane-bonded structure in which silicon bonded to a linear alkyl group having 8 to 20 carbon atoms is 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. The dehydration and condensation converts the coating of the hydrolysis product of monoalkyltrialkoxysilane 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 above-mentioned series of steps using a known solid-liquid separation means. As the solid-liquid separation means, known solid-liquid separation means such as filtration, centrifugation, decantation, etc. can be used. During solid-liquid separation, a flocculant may be added. The recovered composite-coated soft magnetic metal powder is preferably dried in an air atmosphere, an inert gas atmosphere such as nitrogen or argon, or in a vacuum at a temperature of 80° C. or higher and 150° C. or lower.

[0036] In the examples and comparative examples of the present invention, the following measurement methods were employed. [Silicon content] The silicon content of the powder was analyzed by the dissolution method as follows. First, hydrochloric acid and perchloric acid were added to the powder sample (raw powder, silicon oxide-coated soft magnetic metal powder, or composite-coated soft magnetic metal powder) to thermally decompose it. The mixture was heated until white smoke from perchloric acid was generated. The mixture was then heated to dryness. After cooling, water and hydrochloric acid were added and the mixture was heated to dissolve the soluble salts. The insoluble residue was then filtered using filter paper, and the residue, along with the filter paper, was transferred to a crucible, dried, and incinerated. After cooling, the crucible and the mixture were weighed. A small amount of sulfuric acid and hydrofluoric acid were added, and the mixture was heated to dryness and then ignited. After cooling, the crucible and the mixture were weighed. The second weighing value was then subtracted from the first, and the weight difference was calculated as SiO2. The Si content in the powder sample was then determined from this value.

[0037] [Average thickness of silicon oxide coating layer] If 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 D (mass%), the mass proportion P (mass%) of the silicon oxide coating layer is calculated from the Si atomic weight and the SiO molecular weight using the following formula. P=D×SiO2 molecular weight / Si atomic weight=D×60.08 / 28.09 The density of the silicon oxide coating layer is d (g / cm 3 ), and the BET specific surface area of ​​the raw material powder (core particle) is S (m 2 / g), the average film thickness Ts (nm) of the silicon oxide coating layer is expressed by the following formula: Ts = 10 × P / (d × S) Here, the value of 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, it can be determined by dissolving the silicon oxide coating of the silicon oxide-coated soft magnetic gold powder using alkaline etching or the like, and measuring the silicon content of the obtained raw material powder using 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 silicon oxide-coated soft magnetic metal powder prepared by ion milling.

[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] [Amount of carbon in silicon-containing coating layer] The carbon content in the silicon-containing coating layer can be calculated from the difference in the carbon measurement 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 then measuring the carbon content of the resulting silicon oxide-coated soft magnetic metal powder.

[0041] [XPS measurement] The XPS measurements were performed using a PHI5000 VersaProbeIII manufactured by ULVAC-PHI. 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°. The photoelectron spectrum obtained showed that 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. No sputter etching was performed, and the photoelectron spectrum was measured on the outermost surface of the particle. As described above, the C content of the silicon-containing coating layer was evaluated based on the atomic ratio of carbon to silicon (C / Si), without ion sputtering.

[0042] [Particle size distribution] Using a laser diffraction particle size distribution analyzer (SYMPATEC's HELOS particle size distribution analyzer; HELOS & RODOS (airflow dispersion module)), the volume-based cumulative 10% particle size (D10), cumulative 25% particle size (D25), cumulative 50% particle size (D50), cumulative 75% particle size (D75), cumulative 90% particle size (D90), and cumulative 99% particle size (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 by the BET single-point method using a Macsorb made by Mountech Co., Ltd., by flowing nitrogen gas into the measuring device at 105°C for 20 minutes to degas it, and then flowing a mixed gas of nitrogen and helium (N: 30 vol%, He: 70 vol%).

[0044] [Volume resistivity of powder compact] 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-resistance resistivity meter Hiresta UX (MCP-HT800) manufactured by Nitto Seiko Analytech Co., Ltd., and high-resistance powder measurement system software manufactured by Nitto Seiko Analytech Co., Ltd. A load of 20 kN was applied to a 4 g powder sample within an insulator cylinder with an inner diameter of 20 mm to produce a disk-shaped compressed powder sample with 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 compressed powder sample.

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

[0047] [Measuring the magnetic permeability (μ') of powder compacts] Soft magnetic metal powder, liquid epoxy resin, and methyl ethyl ketone were weighed in a mass ratio of 16:1:12 before and after the silicon oxide coating or composite coating process. These were then kneaded using a planetary centrifugal mixer (THINKY Corporation: ARE-250) 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 green compact with an outer diameter of 14 mm and an inner diameter of 9 mm. This green compact was then heat-treated in a nitrogen atmosphere at 150°C for 1 hour to harden it, yielding a toroidal core. The real part μ' of the complex relative permeability of this toroidal core was measured at 100 kHz and 20 mT using a BH analyzer (Iwasaki Electric Co., Ltd.: SY-8218).

[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 deemed to be good. [Example]

[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) was used. 2 The volume resistivity of the 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: This slurry preparation step was carried out in accordance with the example described in Patent Document 2.

[0051] 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 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. TEOS adhering to the small beaker was washed off with 200 g of IPA and 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 surface of the raw material powder particles. (Alkoxide Addition Step S2)

[0053] Subsequently, 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 started, and the slurry was sent to a high-pressure homogenizer (LAB1000, manufactured by SMT Corporation) at a rate of 450 g / min. Simultaneously with the liquid transfer, 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 stirred and dispersed for 60 minutes to form 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 60 minutes of stirring, 10 g of the slurry was collected and subjected to solid-liquid separation using a Nutsche suction filtration device to recover the filtrate. Si content in the recovered filtrate was analyzed using an inductively coupled plasma (ICP) optical emission spectrometer (720 ICP-OES, manufactured by Agilent Technologies Inc.). The result was that the Si content was below the detection limit of 10 ppm, indicating that no TEOS remained in the liquid and that 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 electrical conductivity was Ω·cm and the magnetic permeability was 17.9. Table 1 shows the volume resistivity and magnetic permeability of the compact of the silicon oxide-coated soft magnetic metal powder according to this comparative example. 11 Ω·cm or more: 〇, 10 8 Ω cm or more 10 11 Less than Ω·cm is △, 108 Values ​​below Ω·cm are indicated by × (same as in Tables 2 and 3).

[0056] [Example 1] A 5000 mL reaction vessel was charged with 306 g of pure water and 1650 g of isopropyl alcohol (IPA) 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. Any 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 filter 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 of this example. Si analysis using an inductively coupled plasma (ICP) optical emission spectrometer (720 ICP-OES, manufactured by Agilent Technologies Inc.) did not detect Si, and no HDTMS remained in the filtrate. Therefore, the mass of carbon in the silicon-containing second coating layer per unit mass (g) of the composite-coated soft magnetic metal powder of 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 %. The volume resistivity of the green compact obtained by compacting 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 results show that the composite coated soft magnetic metal powder obtained by the manufacturing method of the present invention has excellent insulating properties for the compact. The volume resistivity, magnetic permeability, and permeability reduction rate of the composite coated soft magnetic metal powder according to this example are shown in Table 1. 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 of this example was calculated to be 2.5 nm using the above-mentioned calculation method. The volume resistivity of the compact of the composite-coated soft magnetic metal powder of this example was 1.0 × 10 12 The volume resistivity of the compact increased with increasing average thickness of the silicon oxide coating layer. Table 1 also shows the volume resistivity, magnetic permeability, and permeability reduction rate 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 using the same procedure as in 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 7.9×10 8 Ω·cm, and Comparative Example 15 is 1.4×10 6 Comparing these results with those of Example 1, it is clear that forming a silicon-containing coating layer to form a multi-layered coating layer is more effective in improving the volume resistivity of the powder compact than increasing the average 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 in Example 1, except that a slurry containing a dispersed silicon oxide-coated soft magnetic metal powder having a silicon oxide coating layer with an average thickness of 5 nm, which was obtained using the same procedure as in Comparative Example 2, was used. Furthermore, a composite-coated soft magnetic metal powder according to Example 13 was obtained using the same procedure as in Example 1, except that a slurry containing a dispersed silicon oxide-coated soft magnetic metal powder having a silicon oxide coating layer with an average thickness of 0.3 nm, which was obtained using the same procedure as in Comparative Example 15, was used. The volume resistivity of a compact of the composite-coated soft magnetic metal powder according to Example 3 was 8.7 × 10 12 Ω·cm, and the volume resistivity of the compact of the composite-coated soft magnetic metal powder of Example 13 was 4.9×10 11 The resistance was Ω·cm. 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, instead of HDTMS, 25.2 g of dodecyltrimethoxysilane (DDTMS: D3383 manufactured by Tokyo Chemical Industry Co., Ltd., linear alkyl group carbon number: 12) was added in Example 4, and 25.2 g of octyltrimethoxysilane (OTMS: T2875 manufactured by Tokyo Chemical Industry Co., Ltd., linear alkyl group carbon number: 8) was added in 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 2.8 mg in Example 4 and 1.9 mg in Example 5, respectively. The volume resistivity of the compacts of the composite coated soft magnetic metal powders according to these examples was 1.0 × 10 for Example 4. 12 Ω cm, Example 5 is 4.8 × 10 11 Furthermore, when XPS measurement was performed on the composite coated soft magnetic metal powders according to these examples, the atomic ratio of carbon to silicon, C / Si, was 2.1 for Example 4 and 1.5 for 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 of 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 carbon number: 1) 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, respectively. 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 × 10 for Comparative Example 4 and 5.7 × 10 for Comparative Example 5. 9Ω·cm, and Comparative Example 5 is 1.0×10 10 Ω·cm, both of which were lower than those of Example 3. Furthermore, when XPS measurement was performed on the composite coated soft magnetic metal powder according to this comparative example, the atomic ratio of carbon to silicon, 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, only a silicon-containing coating layer was formed on the surface of the raw material soft magnetic metal powder using the same procedure as in Comparative Example 1, except that 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. 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 3.7 mg in Comparative Example 6 and 18 mg in Comparative Example 7, respectively. The volume resistivities of the compacts of the soft magnetic metal powders coated with the silicon-containing coating layer according to these comparative examples were 9.0×10 for Comparative Example 6 and 9.0×10 for Comparative Example 7. 9 Ω·cm, and Comparative Example 7 was 2.1×10 8 Ω·cm, and it is clear that a high volume resistivity cannot be obtained unless a silicon oxide coating layer is formed as the first layer. Table 1 also shows the volume resistivity, magnetic permeability, and rate of change in magnetic permeability of the compacts of the soft magnetic metal powder coated with the silicon-containing coating layer according to these comparative examples.

[0065] [Example 6] The raw material powder (core particles) was Fe-Si-Cr-BC amorphous alloy soft magnetic metal powder (BET specific surface area: 0.08 m 2A composite coated soft magnetic metal powder according to this example was obtained using the same procedure as in Example 3, except that a silicon-containing coating layer containing 20.4 g of TEOS was added to the slurry in the alkoxide addition step, and 3.9 g of HDTMS was added 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 0.4 mg. The volume resistivity of a compact of this raw material powder was 1.8 x 10 -2 The electrical conductivity was Ω·cm and the magnetic permeability was 17.7. The volume resistivity of the compact of the composite coated soft magnetic metal powder according to this example was 2.1 × 10 12 The resistance 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 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 first silicon oxide 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 × 10 for Example 7 and 7.2 × 10 for Example 8. 11 Ω cm, Example 8 is 8.5 × 10 11 The resistance 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 × 10 11 The resistance was Ω·cm. 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] The 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 Ω·cm, which was a low value.

[0069] Comparative Example 9 A composite-coated soft magnetic metal powder was obtained using the same procedure 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] The same soft magnetic metal powder as in Example 6 was used as the raw material powder (core particles), and the amount of TEOS added in the slurry preparation step was 61.2 g, the same as in Example 8, to obtain a silicon oxide-coated soft magnetic metal powder. 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 resistance was Ω·cm.

[0071] [Comparative Example 11] The amount of TEOS added in the slurry preparation step was 122.4 g, which was twice that of Comparative Example 11, to obtain a silicon oxide-coated soft magnetic metal powder. 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 The resistance was Ω·cm. 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 particle). 2 The composite coated soft magnetic metal powder of this example was obtained using the same procedure as in Example 1, except that 143.0 g of TEOS was added in the slurry preparation step, and 46.0 g of HDTMS was added 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 of this example was calculated to be 4.6 mg. In this case, 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 × 10 -3 The electrical conductivity was Ω·cm and the magnetic permeability was 9.9. 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 conductivity 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 in this example was calculated to be 4.6 mg. The volume resistivity of the compact of the composite coated soft magnetic metal powder according to this example was 1.0 × 10 13 The electrical conductivity was Ω·cm and the magnetic permeability was 8.4.

[0074] [Comparative Examples 12 and 13] The same soft magnetic metal powder as in Example 10 was used as the raw material powder (core particles), and the amount of TEOS added in the slurry preparation process was 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, to obtain silicon oxide-coated soft magnetic metal powder. 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. 6 Ω·cm and 8.1, and Comparative Example 13 was 1.0×10 9The resistivity was 7.5 Ω·cm. 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 the 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 The composite coated soft magnetic metal powder of this example was obtained using the same procedure as in Example 1, except that 119.1 g of TEOS was added in the slurry preparation step, and 57.4 g of HDTMS was added 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 of 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 x 10 4 The electrical conductivity was Ω·cm and the magnetic permeability was 11.7. The volume resistivity of the compact of the composite coated soft magnetic metal powder according to this example was 1.0 × 10 13 The electrical conductivity was Ω·cm and the magnetic permeability was 9.5.

[0076] [Comparative Example 14] The same soft magnetic metal powder as in Example 12 was used as the raw material powder (core particles), and the amount of TEOS added in the slurry preparation step was set to 297.7 g, 2.5 times that of Example 12, to obtain a silicon oxide-coated soft magnetic metal powder. 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 electrical conductivity was Ω·cm and the magnetic permeability was 7.7. 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 the coating treatments in Example 12 and Comparative Example 14.

[0077] [Table 1]

[0078] [Table 2]

[0079] [Table 3]

[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 It was less than Ω·cm. 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 The resistance remained at about Ω·cm. 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. 9 The volume resistivity remained at about Ω·cm. 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. 9 The volume resistivity remained below Ω·cm. In 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 compacts exhibited excellent volume resistivity. This is thought to be because, as described above, the presence of the silicon-containing layer prevented the silicon oxide coating layer from being damaged during compression molding. Furthermore, the results of Examples 6 to 12 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 is comprised 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 having an average thickness of 0.1 nm or more and 20 nm or less, and a second layer made of a silicon-containing coating layer formed on the first layer and having a structure in which silicon bonded to a linear alkyl group having 8 to 20 carbon atoms is siloxane-bonded.

2. 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. 2. 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. 2. The composite-coated soft magnetic metal powder according to claim 1, wherein the carbon to silicon atomic ratio (C / Si) measured by X-ray photoelectron spectroscopy (XPS) is 1.5 or more and 10 or less.

5. 2. 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. 2. 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 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, comprising: a slurry preparation step of dispersing soft magnetic metal powder containing 20 mass% or more of iron, the soft magnetic metal powder having a silicon oxide coating layer with an average thickness of 0.1 nm or more and 20 nm or less 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 a monoalkyltrialkoxysilane having a linear alkyl group having from 8 to 20 carbon atoms and a hydrolysis catalyst for the monoalkyltrialkoxysilane to the slurry and mixing them to form a coating layer of a hydrolysis product of the monoalkyltrialkoxysilane on the surface of the soft magnetic metal powder; an aging step of dehydrating and condensing the coating layer of the hydrolysis product of the monoalkyltrialkoxysilane; A method for producing a composite coated soft magnetic metal powder having the above-mentioned features.

8. 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. The slurry preparation step comprises: A step of mixing a soft magnetic metal powder constituted by soft magnetic metal particles containing 20% ​​by mass or more of iron with a mixed solvent of water and an organic solvent containing 1% by mass or more and 40% by mass or less of water, and tetraalkoxysilane to obtain a slurry in which the soft magnetic metal powder is dispersed; a step of mixing a tetraalkoxysilane hydrolysis catalyst 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; The method for producing a composite-coated soft magnetic metal powder according to claim 7, comprising:

10. The method for producing a 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 thickness of 0.5 nm or more and 20 nm or less is formed.

11. 8. 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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