JP2012204744A - Soft magnetic metal powder, method for producing the same, powder magnetic core and method for producing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a soft magnetic metal powder superior in oxidation resistance; a powder magnetic core having a high magnetic permeability and high density; and methods for producing the same.SOLUTION: The soft magnetic metal powder is obtained by containing Al powders together with carbon powders therein as a reducing agent for performing solid reduction for iron oxide powders, has an average particle diameter of 1 μm or more, is a metal powder of an Fe particle, which has a surface covered with carbon and oxide aluminum, and of which a 1.0% or more weight increase temperature measured in thermogravimetry analysis that is a method of heating the powder in air is 450°C or higher. The powder magnetic core is produced by using the soft magnetic metal powder and at lease one of an organic resin and an inorganic oxide, and has a density of 6.0 Mg/mor more.

Description

  The present invention relates to an oxidation-resistant soft magnetic metal powder having a coating formed on its surface and a method for producing the same.

  Soft magnetic ferrite and metal materials are used as magnetic core materials for choke coils, inductor elements, transformers, and the like. In recent years, electronic components are required to be small in size and to be driven with low loss even at high frequencies, and the operating current tends to increase. In order to meet these requirements, a metal material having a saturation magnetization larger than that of conventional ferrite is desired. If the saturation magnetization is large, not only can the size be reduced, but, for example, in the case of an inductor, the direct current superimposition characteristic can be maintained up to a large current region, so that a large operating current can be dealt with.

  However, since the metal material has a low electrical resistance, eddy current tends to flow and eddy current loss occurs. Since the eddy current loss is proportional to the square of the frequency, the loss increases particularly under a high-frequency magnetic field (the permeability of the real part decreases). For this reason, it was difficult to use the metal material as a bulk body. In order to solve this problem, for example, a powder magnetic core having a low core loss has been developed by molding the Fe-based alloy powder in a state of being insulated by a resin even at a high frequency of 50 kHz (Patent Document 1).

  Further, when a metal material powder is compacted and molded, stress strain remains in the metal powder, leading to deterioration of magnetic properties. That is, the coercive force increases and hysteresis loss increases. In order to reduce hysteresis loss, the molded body must be heat treated to remove stress strain. In order to avoid the problem that the resin used for insulation between powders decomposes in this heat treatment, it is reported in Patent Document 2 that water glass is used instead of resin. In addition, in order to minimize hysteresis loss, an amorphous material having a small magnetic anisotropy and a nanocrystal material obtained by miniaturizing a metal powder to a nanocrystal size have been developed.

  That is, as a soft magnetic material, in recent years, a metal material that has high magnetization, can be stably used in high frequency applications, and has low loss is desired. In order to realize this, a soft magnetic metal powder having a coating layer excellent in heat resistance is required.

JP 2006-274300 A (Table 1) JP 2004-259807 A (Table 1) JP 2009-249739 A (Examples 9 to 11) JP 2009-272615 A

  Although the magnetic metal material has higher magnetization than conventional ferrite, it has been a problem that it is easily oxidized. When applied to dust core applications, it was difficult to suppress the decrease in soft magnetic properties accompanying the deterioration of the coating layer by strain relief annealing. When applied to a magnetic core material such as a multilayer inductor, it is oxidized in the electrode firing step, making it difficult to utilize high magnetization. Therefore, a coating layer excellent in oxidation resistance in the soft magnetic metal powder constituting the magnetic core is required.

  Further, when the soft magnetic metal powder has a fine particle diameter of 1 μm or less, the density of the molded body is not sufficiently improved even by pressure molding, which causes low magnetization and magnetic permeability (Patent Document 2). ). Therefore, a soft magnetic metal powder capable of providing a high-density molded body has been required.

  An object of the present invention is to provide a soft magnetic metal powder excellent in oxidation resistance, a dust core having a high density and a high magnetic permeability, and a method for producing the same.

  As a result of earnest studies to achieve the above object, the present invention has been conceived. That is, the soft magnetic metal powder of the present invention is obtained by adding Al powder together with carbon powder as a reducing agent for solid-phase reduction of iron oxide powder, the average particle diameter is more than 1 μm, and the surface is made of carbon and aluminum oxide. The coated iron particle powder is characterized in that the temperature at which the weight increase in thermogravimetric analysis heated in the atmosphere is 1.0% or more is 450 ° C. or more.

  Furthermore, a soft magnetic metal powder having an average particle size of more than 1 μm and 20 μm or less is provided.

  Furthermore, a soft magnetic metal powder having an average particle size of 4 to 12 μm is provided.

  Since the surface of the soft magnetic metal powder is coated with carbon and aluminum oxide, the surface composition analyzed by X-ray photoelectron spectroscopy is such that Fe is less than 1 at%, C is 80 to 85 at%, and Al is 2. It is characterized by 8 to 3.4 at%. The balance is an element derived from raw materials other than Fe, C, and Al.

The method for producing a soft magnetic metal powder of the present invention comprises mixing a carbon powder and an Al powder, which are reducing agents, and an iron oxide powder,
The obtained mixed powder is subjected to heat treatment in a non-oxidizing atmosphere,
A powder having carbon and aluminum oxide in the surface composition detected by X-ray photoelectron spectroscopy and iron in the core composition is obtained.

When producing a powder magnetic core using the soft magnetic metal powder of the present invention, the density is 6.0 Mg / m ³ or more by comprising the soft magnetic metal powder and at least one of an organic resin or an inorganic oxide. The powder magnetic core which is is obtained. Thereby, high magnetization is realized.

  The powder magnetic core is characterized in that an obtained incremental magnetic permeability is 20 or more when a DC bias magnetic field generated by superimposing DC on a winding at a frequency of 100 kHz is 10 kA / m. Thereby, excellent direct current superposition characteristics can be obtained.

  The dust core is characterized in that the real part of the complex relative permeability at a frequency of 1 MHz is 20 or more. As a result, high magnetic permeability can be obtained even in the MHz band.

  The dust core can be obtained by adding an organic resin or an inorganic oxide to the obtained soft magnetic metal powder and then molding it at a pressure of 1000 MPa or 2000 MPa.

  A soft magnetic metal powder excellent in oxidation resistance, a dust core having high permeability and high density, and a method for producing them can be provided.

FIG. 1 is a graph showing DC superposition characteristics of a toroidal coil using a dust core.

Embodiments of the present invention will be described in detail.
(1) Starting material The iron oxide used as the starting material is represented by a chemical formula such as Fe ₂ O ₃ , Fe ₃ O ₄ , or FeO, but may be ferrite containing a transition metal element. The average particle size of the iron oxide powder is preferably 0.01 to less than 100 μm, more preferably less than 20 μm, and even more preferably less than 1 μm. The average particle size of the iron oxide powder greatly affects the average particle size of the finally obtained soft magnetic metal powder. When the average particle size of the iron oxide powder is less than 0.01 μm, not only the handling as a powder becomes difficult, but also the particle size of the soft magnetic metal powder after reduction becomes less than 1 μm, and the compact density is improved. It is not preferable because it does not occur. Further, it is not preferable that the average particle size of the iron oxide powder is 100 μm or more because the reduction reaction does not proceed sufficiently. The average particle size of the reduced soft magnetic metal powder is preferably more than 1 μm. If it is less than 1 μm, the density of the compact after pressing does not reach 6.0 Mg / m ³ , which is not preferable. More preferably, it is more than 1 μm and 20 μm or less. If it exceeds 20 μm, eddy current flows in the grains and eddy current loss increases, which is not preferable. More preferably, it is 4-12 micrometers. If it is this range, a molded object density can be made high enough.

  The reduced soft magnetic metal powder may be an iron-based alloy depending on the purpose. That is, an alloy such as Fe—Si, Fe—Al—Si, Fe—Ni, Fe—Co, or Fe—Si—B may be used.

(2) Reducing agent A solid powder is used as a reducing agent for reducing the iron oxide. In order to form a uniform and thin coating layer, graphite is preferable, and in order to use graphite as a coating layer, it is preferable to use a powder composed of carbon. Since graphite has a structure in which graphene sheets are laminated, it is easy to grow two-dimensionally and is suitable as a coating material. As the powder made of carbon used as the reducing agent, it is preferable to use powders of graphite, carbon black, acetylene black, various hydrocarbons and the like. However, since graphite is a conductive substance, it is preferable to ensure electrical insulation by using metal Al as a reducing agent and aluminum oxide produced as a by-product as a coating layer.

  As the reducing agent, metal Al is preferable. The melting point of metal Al is 660 ° C., which is lower than the temperature (1100 to 1400 ° C.) at which the reduction reaction described later proceeds. This is suitable for forming a covering structure. Before the reduction reaction starts, Al uniformly wets the iron oxide particles in the liquid phase state, and when the temperature is raised thereafter, the liquid phase Al reduces the iron oxide. With such a reaction mechanism, the aluminum oxide produced by the reduction reaction inevitably has a structure that covers the Fe core particles. Al compounds having a melting point exceeding 1100 ° C. are not suitable as reducing agents. Patent Document 3 (Japanese Patent Laid-Open No. 2009-249739) discloses a method in which AlN powder is added in a solid-phase reaction to dissolve Al in Fe as a core particle, but the coating layer contains aluminum oxide. Is not disclosed. Since the melting point of AlN is as high as 2200 ° C., it is not preferable as a coating material source for aluminum oxide.

  The average particle size of the solid powder serving as the reducing agent is preferably 0.01 to 10 μm. If it is less than 0.01 μm, handling becomes difficult. If it is 10 μm or more, the mixing with the iron oxide powder becomes nonuniform, and the solid phase reduction reaction becomes nonuniform, which is not preferable.

(3) Mixing conditions The iron oxide powder and the reducing agent powder are preferably mixed uniformly. In mixing these powders, a ball mill, a bead mill, a reiki machine, a mortar, a V-shaped mixer, or the like can be used.

(4) Reaction conditions It is preferable to heat-process the mixture of the said iron oxide powder and the said reducing agent powder in the range of 1100 degreeC-1400 degreeC in non-oxidizing atmosphere. Less than 1100 ° C. is not preferable because the reduction reaction becomes insufficient. Moreover, formation of a carbon coating layer will become inadequate that it is less than 1100 degreeC. When the heat treatment temperature exceeds 1400 ° C., the soft magnetic metal powder may be sintered and bulked, which is not preferable. The non-oxidizing atmosphere is an atmosphere that does not contain oxygen, and Ar, N ₂ , H ₂ , He, CO ₂ or a mixed gas thereof is preferable, and an N ₂ atmosphere is more preferable. At this time, oxygen may be mixed somewhat as an impurity, but the oxygen concentration is preferably 500 ppm or less, more preferably 100 ppm or less, and still more preferably 10 ppm or less. When the heat treatment is performed under the above preferable conditions, the iron oxide powder is uniformly reduced to produce a soft magnetic metal powder.

(5) Product purification Since the soft magnetic metal powder obtained by solid-phase reduction contains an excessive reducing agent and reaction by-products, only the ferromagnetic powder is purified and recovered by magnetic separation operation. Is preferred. It is preferable that a heat-treated powder having a predetermined mass is sufficiently dispersed in an organic solvent or water, and then only the soft magnetic metal powder is magnetically collected and purified by a permanent magnet.

(6) Particle characteristics of soft magnetic metal powder The average particle diameter of the soft magnetic metal powder thus obtained is preferably more than 1 μm. Here, the average particle diameter is a powder particle diameter when the volume integration reaches 50% of the particle size distribution measured by the laser diffraction scattering method. When the average particle size is less than 1 μm, the density of the compact after pressing does not reach 6.0 Mg / m ³ , which is not preferable. More preferably, it is more than 1 μm and 20 μm or less. If it exceeds 20 μm, eddy current flows in the grains and eddy current loss increases, which is not preferable. More preferably, it is 4-12 micrometers. If it is this range, a molded object density can be made high enough.

Moreover, the soft magnetic metal powder obtained by the said manufacturing method is the iron particle by which the surface was coat | covered with carbon and aluminum oxide. The reason why it is coated with carbon is that excess carbon was dissolved and precipitated on the reduced Fe particle surface, or carbon dioxide gas generated as a by-product of the reduction reaction caused a disproportionation reaction on the Fe particle surface. This is due to the precipitation of graphite-like carbon on the surface of the Fe particles due to, and the like. The reason for coating with aluminum oxide is that Al added as a reducing agent becomes a liquid phase during the temperature rising process, surrounds the iron oxide particles, and then the reduction reaction proceeds to coat the aluminum oxide with the Fe particles. X-ray photoelectron spectroscopy (X-ray)
When analyzed by Photoelectron Spectroscopy (XPS), Fe is preferably less than 1 at%, C is 80 to 85 at%, and Al is 2.8 to 3.4 at%. If Fe is 1 at% or more, it indicates that the portion where the metal Fe particles are exposed increases, which is not preferable because the oxidation resistance of the particles decreases. Further, if C is less than 80 at%, coating with carbon is insufficient, which is not preferable. When C is 85 at% or more, it indicates that the carbon forming the coating layer is excessive, and the volume ratio of the metal Fe particles is not preferable. If Al is less than 2.8 at%, the coating layer of aluminum oxide is insufficient and insulation between particles cannot be obtained, which is not preferable. When Al is 3.4 at%, the volume ratio of the nonmagnetic component is large, and the volume ratio of the metal Fe particles is lowered, which is not preferable.

The saturation magnetization of the soft magnetic metal powder is preferably 160 to ²⁰⁰ Am ² / kg. If it is less than 160 Am ² / kg, the content of the ferromagnetic component is low, so even if a high-density molded body is obtained, the magnetic permeability is lowered, which is not preferable. Further, if it exceeds ²⁰⁰ Am ² / kg, it is excellent as a soft magnetic material, but the coating substance is effectively insufficient, and the oxidation resistance is lowered, which is not preferable. When applied to magnetic components such as multilayer inductors, excellent oxidation resistance is required according to the manufacturing process and usage environment of the components.

  The soft magnetic metal powder exhibits excellent oxidation resistance. As a means of measuring oxidation resistance, a method of analyzing weight increment accompanying oxidation by heating in air, a method of measuring temperature change of magnetization while heating in air, a predetermined time in a constant temperature and humidity tester For example, a method of measuring the change in magnetization by leaving it alone. In particular, the weight increment accompanying oxidation is preferable because it can be analyzed with high accuracy by thermogravimetry (TG measurement). In the present invention, the temperature at which the weight increment is 1 mass% in the thermogravimetric analysis is defined and used as the “oxidation resistance temperature”. The oxidation resistance temperature of the soft magnetic iron-based powder is 450 ° C. or higher, and the oxidation resistance is excellent.

(7) Performance evaluation of powder magnetic core A binder is mixed with the soft magnetic metal powder and compression molding is performed to produce a powder magnetic core. As the binder, polyvinyl alcohol, polyvinyl butyral, epoxy resin, silicone resin, or the like is used. Further, in order to reinforce inter-particle insulation, insulating oxide fine particles such as colloidal silica and alumina fine particles may be added in addition to the binder. The amount of binder added is preferably 0.1 to 1 mass% relative to the weight of the soft magnetic metal powder. When a binder is added, the moldability is improved and an effect of insulating particles is obtained. On the other hand, since the magnetic core density is lowered, the addition amount is preferably within the above range.

  In order to sufficiently increase the density of the molded body, the pressure during molding is preferably 1000 to 2000 MPa. Patent Document 4 (Japanese Patent Laid-Open No. 2009-272615) discloses that when the molding pressure is 1000 MPa, both the permeability attenuation rate and the core loss increase, and the molding pressure is preferably 600 MPa or less. . In the magnetic powder of Patent Document 4, the substance that coats Fe particles is only carbon (conductive material). Therefore, when molded at a high pressure, the contact probability of the particles increases and the insulation of the powder magnetic core decreases, which is not preferable. Represents that. In the present invention, reference is made to the characteristics of a powder magnetic core molded at a higher 1000 to 2000 MPa, and the present invention is different from Patent Document 4.

  When a winding is applied to a molded body formed into a toroidal shape and DC superposition characteristics are measured with an LCR meter at a frequency of 100 kHz, the incremental transmission obtained when the DC bias magnetic field generated in the winding is 10 kA / m. The magnetic susceptibility is 20 or more. Here, the incremental permeability represents the permeability obtained under a magnetic field generated by passing a predetermined direct current through the winding. When the incremental magnetic permeability is less than 20, the inductance is small, which is not preferable as a soft magnetic material.

  Further, when the frequency dependence of the complex relative permeability is measured with an impedance analyzer for the toroidal shaped molded body, the real part of the complex relative permeability at a frequency of 1 MHz is 20 or more. When the magnetic permeability is less than 20, it is not suitable as a soft magnetic material. Here, the complex relative permeability represents the relative permeability measured under an alternating magnetic field in terms of a real part and an imaginary part. The real part represents a component in which the magnetic flux density follows the change of the magnetic field in the AC magnetic field (in the same phase as the magnetic field wave), and the imaginary part represents a component that cannot catch up with the change in the magnetic field (lag in phase). .

Example 1
78 g of iron oxide powder having an average particle size of 0.05 μm (Chemilite Industry: X-21), 1.7 g of aluminum powder having an average particle size of 3 μm (Soekawa Riken) and SiC powder having an average particle size of 0.01 μm (Sumitomo Osaka Cement) 3 .3 g and 17 g of carbon black powder (Mitsubishi Chemical: # 44) having an average particle size of 0.02 μm were ball mill mixed in IPA and dried to obtain a raw material mixed powder. This raw material mixed powder was heat-treated at 1400 ° C. for 2 hours in a nitrogen atmosphere, and iron oxide was solid-phase reduced to iron. In order to remove non-magnetic components from the obtained reduced powder, 5.0 g of the powder was put into 100 ml of IPA, irradiated with ultrasonic waves, and only the magnetic particles were collected with a permanent magnet and the supernatant was discarded. did. This operation was repeated until the supernatant became transparent to obtain reduced iron powder. The particle size distribution of the reduced iron powder was measured with a laser diffraction particle size distribution meter (HORIBA: LA-920). The average particle size (d50) is shown in Table 1. The saturation magnetization was measured using a vibrating sample magnetometer (RIKEN ELECTRONICS: BHV-35) with a maximum applied magnetic field of 0.8 MA / m (10 kOe). The obtained results are shown in Table 1. Moreover, TG analysis which heats the said reduced iron powder in air | atmosphere using the differential thermogravimetric analyzer (Rigaku: TAS200) was performed, and oxidation resistance was evaluated. The temperature increase rate was 10 ° C./min, and the temperature was increased to 1000 ° C. The temperature at which the mass increases by 1% is defined as “oxidation resistance temperature”, and the resulting oxidation resistance temperature is shown in Table 1.

(Example 2)
Reduced iron powder was obtained in the same manner as in Example 1 except that iron oxide powder having an average particle size of 0.6 μm (Toda Kogyo: PF3400) was used and the heat treatment temperature was 1200 ° C. Table 1 shows the average particle diameter, saturation magnetization, and oxidation resistance temperature.

(Example 3)
Reduced iron powder was obtained in the same manner as in Example 2 except that the heat treatment temperature was 1300 ° C. Table 1 shows the average particle diameter, saturation magnetization, and oxidation resistance temperature.

Example 4
Reduced iron powder was obtained in the same manner as in Example 2 except that the heat treatment temperature was 1400 ° C. Table 1 shows the average particle diameter, saturation magnetization, and oxidation resistance temperature.

(Example 5)
Reduced iron powder was obtained in the same manner as in Example 1 except that the weight of the iron oxide powder was 76.4 g and the weight of the SiC powder was 4.9 g. Table 1 shows the average particle diameter, saturation magnetization, and oxidation resistance temperature.

(Example 6)
Reduced iron powder was obtained in the same manner as in Example 4 except that the weight of the iron oxide powder was 76.4 g and the weight of the SiC powder was 4.9 g. Table 1 shows the average particle diameter, saturation magnetization, and oxidation resistance temperature.

(Comparative Example 1)
Reduced iron powder was obtained in the same manner as in Example 2 except that 70.5 g of iron oxide powder, 0 g of Al powder (no addition), 4.5 g of SiC powder, and 25 g of carbon black powder were used. Table 1 shows the average particle diameter, saturation magnetization, and oxidation resistance temperature.

(Comparative Example 2)
Reduced iron powder was obtained in the same manner as in Comparative Example 1 except that the heat treatment temperature was 1120 ° C. Table 1 shows the average particle diameter, saturation magnetization, and oxidation resistance temperature.

The oxidation resistance temperatures of Comparative Examples 1 and 2 are 406 ° C. and 397 ° C., respectively, and the oxidation resistance temperature is lower than that of Examples. From Table 1, it can be seen that the addition of Al powder improves the oxidation resistance temperature. This indicates that Al ₂ O ₃ produced from Al through the reduction reaction reinforces the coating of the iron powder.

  Table 2 shows the results of XPS analysis (ULVAC-PHI: PHI Quantera SXM) for the powders of Examples and Comparative Examples. While the Fe concentration is less than 1 at% in the examples, it is 3 at% or more in the comparative example, which indicates that the Fe particles are sufficiently covered in the examples. For this reason, the oxidation resistance temperature of the iron powder of the present invention is high.

(Example 7)
0.6 mass% of polyvinyl butyral was added to the powder of Example 1, kneaded in ethanol, dried, and sieved to an under 500 μm to obtain granulated powder. The granulated powder was compressed with a die having an outer diameter of 13.4 mm and an inner diameter of 7.7 mm with a hydraulic press at 20 ton / cm ² to produce a toroidal ring-shaped molded body having a density of 6.1 Mg / m ³ . An enameled wire having a diameter of 0.25 mm was wound around this molded body for 170 turns, and a DC superposition characteristic was measured at a frequency of 100 kHz using an LCR meter (Hewlett Packard: HP-4285A). The results are shown in FIG.

(Example 8)
A toroidal ring-shaped compact having a compact density of 6.0 Mg / m ³ was prepared in the same manner as in Example 7 except that the powder of Example 5 was used, and the DC superposition characteristics were measured. The results are shown in FIG.

Example 9
A toroidal ring-shaped compact having a compact density of 6.6 Mg / m ³ was prepared in the same manner as in Example 7 except that the powder of Example 4 was used, and the DC superposition characteristics were measured. The results are shown in FIG.

(Example 10)
A toroidal ring-shaped compact having a compact density of 6.6 Mg / m ³ was produced in the same manner as in Example 7 except that the powder of Example 6 was used, and the DC superposition characteristics were measured. The results are shown in FIG.

(Reference Example 1)
A toroidal ring-shaped molded body having a molded body density of 7.0 Mg / m ³ was prepared in the same manner as in Example 7 except that carbonyl Fe powder (BASF, SQ) having an average particle size of 3.5 μm was used. Was measured. The results are shown in FIG.

(Comparative Example 3)
Ni-Zn ferrite powder having an average particle diameter of 0.6μm (NiO: 17.7mol%, CuO : 8.8mol%, ZnO: 25.0mol%, Fe 2 O 3: 48.5mol%) is carried out except for using Molded as in Example 7. This molded body was fired at 900 ° C. for 2 hours to form a toroidal ring-shaped sintered body, and the DC superposition characteristics of the sintered body were measured. The results are shown in FIG.

(Example 11)
Using the powder of Example 2, a toroidal ring having a density of 6.3 Mg / m ^{3 was} compressed using a mold having an outer diameter of 7.2 mm and an inner diameter of 3.9 mm except that the molding pressure was 10 ton / cm ^2. A shaped compact was produced. The frequency characteristics of the magnetic permeability of this molded body were measured using an impedance analyzer (Agilent, 4291B), and the real part of the complex relative magnetic permeability at 1 MHz was 41.

(Example 12)
A toroidal ring-shaped molded body was produced and evaluated in the same manner as in Example 11 except that the powder of Example 3 was used, and a real part 23 having a complex relative permeability at 1 MHz was obtained.

(Example 13)
A toroidal ring-shaped molded body was produced and evaluated in the same manner as in Example 11 except that the powder of Example 4 was used, and a real part 21 having a complex relative permeability at 1 MHz was obtained.

(Example 14)
A toroidal ring-shaped molded body was produced and evaluated in the same manner as in Example 11 except that the powder of Example 6 was used, and a real part 23 having a complex relative permeability at 1 MHz was obtained.

(Comparative Example 4)
A toroidal ring-shaped molded body was produced and evaluated in the same manner as in Example 11 except that the powder of Comparative Example 1 was used, and a real part 13 having a complex relative permeability at 1 MHz was obtained.

(Comparative Example 5)
A toroidal ring-shaped molded body was produced and evaluated in the same manner as in Example 11 except that the powder of Comparative Example 2 was used, and a real part 13 having a complex relative permeability at 1 MHz was obtained.

From FIG. 1, the samples of Examples 8 and 9 exhibit the same permeability and direct current superposition characteristics as those of a dust core made of commercially available Fe powder. On the other hand, in the case of the ferrite sintered body sample of Comparative Example 3, when the direct current is superimposed, the permeability is remarkably reduced. The incremental permeability obtained when the magnetic field is 10 kA / m is 20 or more in each of Examples 8 and 9, but less than 5 in Comparative Example 3. This is because the magnetic flux density of the ferrite material is saturated by a low magnetic field. That is, according to the present invention, it is possible to provide a high magnetic permeability soft magnetic metal powder excellent in oxidation resistance.

Claims (10)

  It is an iron particle powder obtained by adding Al powder together with carbon powder as a reducing agent for solid-phase reduction of iron oxide powder, having an average particle diameter of more than 1 μm, and a surface coated with carbon and aluminum oxide, A soft magnetic metal powder characterized in that the temperature at which the weight increase in thermogravimetric analysis heated in the glass becomes 1.0% or more is 450 ° C or more.   2. The soft magnetic metal powder according to claim 1, having an average particle size of more than 1 μm and 20 μm or less.   The soft magnetic metal powder according to claim 1, wherein the average particle diameter is 4 to 12 μm.   The surface composition analyzed by X-ray photoelectron spectroscopy is characterized in that Fe is less than 1 at%, C is 80 to 85 at%, and Al is 2.8 to 3.4 at%. Soft magnetic metal powder. Carbon powder and Al powder, which are reducing agents, and iron oxide powder are mixed,
The obtained mixed powder is subjected to heat treatment in a non-oxidizing atmosphere,
A method for producing a soft magnetic metal powder, characterized in that a powder having carbon and aluminum oxide in the surface composition detected by X-ray photoelectron spectroscopy and iron in the core composition is obtained. The soft magnetic metal powder according to any one of claims 1 to 4 and at least one of an organic resin or an inorganic oxide,
A dust core having a density of 6.0 Mg / m ³ or more. The soft magnetic metal powder according to any one of claims 1 to 4 and at least one of an organic resin or an inorganic oxide,
A dust core having an obtained incremental magnetic permeability of 20 or more when a DC bias magnetic field generated by superimposing DC on a winding at a frequency of 100 kHz is 10 kA / m. The soft magnetic metal powder according to claim 1 and at least one of an organic resin or an inorganic oxide,
A dust core, wherein a real part of a complex relative permeability at a frequency of 1 MHz is 20 or more.   A method for producing a powder magnetic core, comprising adding an organic resin or an inorganic oxide to the soft magnetic metal powder according to any one of claims 1 to 4 and then molding the powder at a pressure of 1000 MPa to 2000 MPa. A method for producing a dust core, wherein an organic resin or an inorganic oxide is added to the soft magnetic metal powder obtained by the production method according to claim 5 and then molded at a pressure of 1000 MPa to 2000 MPa.