Compression powder core

Abstract

To decrease the loss of a powder-compact magnetic core.SOLUTION: The powder-compact magnetic core 10 hereof comprises insulation coating soft-magnetic metal powder 1 including soft-magnetic metal particles 2 having an average equivalent circle diameter 10-100 μm, and an insulation layer 3 formed on a surface of each soft-magnetic metal particle 2. In the powder-compact magnetic core 10, the insulation layer 3 contains oxide of at least one element selected from a group consisting of Al, Zr and Si. Supposing that a total area of the powder-compact magnetic core 10 is 100% in observation on a section of the powder-compact magnetic core 10 in a view field of 500 μm×500 μm, the percentage of an area that the insulation layer 3 accounts is 4% or more and 9% or less. The difference between the soft-magnetic metal particle 2 and the insulation layer 3 in thermal expansion coefficient is 3.0×10-6 / K or less.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present disclosure relates to a compressed powder core.

Background Art

[0002] Patent Document 1 discloses soft magnetic metal powder having particles composed of a soft magnetic metal part and a coating part covering the soft magnetic metal part. The coating part contains an oxide of Si and has a first coating part containing an amorphous part and a second coating part containing a crystal.

[0003] Patent Documents 2 and 3 describe insulated coated soft magnetic metal powder using zirconium oxide. Patent Document 4 describes soft magnetic powder in which the oxygen value per unit specific surface area is within a predetermined range. Patent Document 5 describes a compressed powder core using particles in which an insulating film of a metal oxide is formed on the surface of metal magnetic particles.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Patent Document 5

Summary of the Invention

Problems to be Solved by the Invention

[0005] In a compressed powder core, loss reduction is achieved by coating soft magnetic metal particles with an insulating layer. However, the fact is that the components of the insulating layer easily diffuse into the soft magnetic metal, which has an adverse effect on the characteristics of the soft magnetic metal particles. The present disclosure has been made in view of the above circumstances, and aims to reduce the loss of the compressed powder magnetic core. The present disclosure can be realized in the following forms.

Means for Solving the Problems

[0006] 〔1〕A compressed powder magnetic core containing insulated coated soft magnetic metal powder including soft magnetic metal particles with an average equivalent circle diameter of 10 μm to 100 μm and an insulating layer formed on the surface of the soft magnetic metal particles, The insulating layer contains an oxide of at least one element selected from the group consisting of Al, Zr, and Si, When the cross-section of the compressed powder magnetic core is observed in a field of view of 500 μm × 500 μm and the area of the entire compressed powder magnetic core is taken as 100%, the ratio of the area occupied by the insulating layer is 4% or more and 9% or less, The difference between the thermal expansion coefficient of the soft magnetic metal particles and the thermal expansion coefficient of the insulating layer is 3.0×10 -6 / K or less, a compressed powder magnetic core.

Effects of the Invention

[0007] According to the present disclosure, the loss of the insulated coated soft magnetic metal powder can be reduced.

Brief Description of the Drawings

[0008]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Modes for Carrying Out the Invention

[0009] Here, desirable examples of the present disclosure are shown. 〔2〕The compacted powder magnetic core, wherein an average equivalent circle diameter of particles constituting the insulating layer is 20 nm to 50 nm.

[0010] 〔3〕The compacted powder magnetic core, wherein among the soft magnetic metal particles, particles having an equivalent circle diameter of 50 μm to 100 μm are specified particles, cross-sections of 10 or more different specified particles are subjected to crystal orientation analysis, and when the number of regions separated by an orientation difference of 5° or more is measured for each of the specified particles, an average value of the number of regions measured for each of the specified particles is 9 or less.

[0011] 〔4〕The insulating layer contains an oxide of at least one element of Al or Zr, a half-value width of the strongest peak derived from the insulating layer measured by XRD is 0.80° or less, and a thickness of a diffusion layer in which at least one element of Al or Zr diffuses on a surface layer of the soft magnetic metal particles is 50 nm or less. The compacted powder magnetic core.

[0012] Hereinafter, the present disclosure will be described in detail. In this specification, for a description using "~" for a numerical range, unless otherwise specified, it includes a lower limit value and an upper limit value. For example, in the description of "10~20", both the lower limit value "10" and the upper limit value "20" are included. That is, "10~20" has the same meaning as "10 or more and 20 or less".

[0013] 1. Compacted powder magnetic core 10 The compacted powder magnetic core 10 is a compacted powder magnetic core 10 including an insulated coated soft magnetic metal powder 1 including soft magnetic metal particles 2 having an average equivalent circle diameter of 10 μm to 100 μm and an insulating layer 3 formed on a surface of the soft magnetic metal particles 2. The insulating layer 3 contains an oxide of at least one element selected from the group consisting of Al, Zr, and Si. When a cross-section of the compacted powder magnetic core 10 is observed in a field of view of 500 μm × 500 μm and the entire area of the compacted powder magnetic core 10 is taken as 100%, a ratio of an area occupied by the insulating layer 3 is 4% or more and 9% or less. A difference between a thermal expansion coefficient of the soft magnetic metal particles 2 and a thermal expansion coefficient of the insulating layer 3 is 3.0×10 -6 / K or less.

[0014] (1) Soft magnetic metal particles 2 The soft magnetic metal particles 2 are not particularly limited as long as they are soft magnetic metal particles and can be widely used. As the soft magnetic metal particles 2, particles of pure iron that are soft magnetic and particles of iron-based alloys can be widely used. As the iron-based alloys, Fe-Si alloys, Fe-Si-Cr alloys, Fe-Si-Al alloys (Sendust), Ni-Fe alloys (Permalloy), Ni-Fe-Mo alloys (Supermalloy), Fe-based amorphous alloys, Fe-Co alloys, etc. can be preferably used. Among these, Fe-Si alloys, Fe-Si-Cr alloys, Fe-Si-Al alloys (Sendust), Ni-Fe alloys (Permalloy), and Ni-Fe-Mo alloys (Supermalloy) are preferable from the viewpoints of magnetic permeability, coercive force, and frequency characteristics. When using an Fe-Si alloy, for example, an alloy having a composition of Si: 0.1 mass% to 10 mass%, and the balance: Fe and unavoidable impurities can be used. When using an Fe-Si-Cr alloy, for example, an alloy having a composition of Si: 0.1 mass% to 10 mass%, Cr: 10 mass% to 20 mass%, and the balance: Fe and unavoidable impurities can be used. The average equivalent circle diameter of the soft magnetic metal particles 2 is 10 μm or more and 100 μm or less, preferably 25 μm or more and 100 μm or less, and more preferably 50 μm or more and 100 μm or less. The average equivalent circle diameter of the soft magnetic metal particles 2 can be appropriately changed depending on the frequency band used. Particularly when assuming use in a high frequency band exceeding 100 kHz, it is more preferably 10 μm or more and 25 μm or less. Incidentally, the average equivalent circle diameter of the soft magnetic metal particles 2 can be determined by observing the cross-section of the compacted powder core 10 (see Fig. 1). Specifically, the equivalent circle diameter of the area is calculated from the particle area observed by FE-SEM of the cross-section of the compacted powder core 10, and this is taken as the average equivalent circle diameter. More specifically, the average equivalent circle diameter is determined as follows. Focus on a plurality of soft magnetic metal particles 2 that can be observed without chipping in a predetermined observation field of view (for example, 200 μm × 200 μm). Calculate the diameter (equivalent circle diameter of the area) of an ideal circle (true circle) having an area equal to the area (projection area) of each particle image of the soft magnetic metal particles 2 as the equivalent circle diameter of each particle. Then, the average equivalent circle diameter is determined by calculating the arithmetic mean of the equivalent circle diameters of each particle. The equivalent circle diameter of each particle and the average equivalent circle diameter can be determined using general image analysis software.

[0015] (2) Insulating layer 3 As described above, the insulating layer 3 contains an oxide of at least one element selected from the group consisting of Al, Zr, and Si (hereinafter also referred to as a specific element). Examples of the oxide of Al (aluminum) include γ-Al2O3 and α-Al2O3. Examples of the oxide of Zr (zirconium) include monoclinic ZrO2, tetragonal ZrO2, and cubic ZrO2. Examples of the oxide of Si (silicon) include quartz and cristobalite. Further, the oxide may be a composite oxide containing a specific element, or may be a mixture of the above oxides. Examples of such composite oxides include MgO-Al2O3 composite oxide, Y2O3-ZrO2 composite oxide, and CaO-ZrO2 composite oxide. Examples of such mixtures include ZrO2-SiO2 mixture, Al2O3-SiO2 mixture, ZrO2-Al2O3 mixture, and Al2O3-SiO2-MgO mixture. When using a ZrO2-SiO2 mixture, for example, a mixture of SiO2: 1 mass% to 45 mass% and the balance ZrO2 and unavoidable impurities can be used. When using an Al2O3 - SiO2 mixture, for example, a mixture of SiO2: 1 mass% - 45 mass%, the balance: Al2O3 and inevitable impurities can be used. When using a ZrO2 - Al2O3 mixture, for example, a mixture of Al2O3: 1 mass% - 30 mass%, the balance: ZrO2 and inevitable impurities can be used. When using an Al2O3 - SiO2 - MgO mixture, for example, a mixture of SiO2: 1 mass% - 45 mass%, MgO: 1 mass% - 10 mass%, the balance: Al2O3 and inevitable impurities can be used. Note that the composition of the insulating layer 3 can be analyzed by EPMA (Electron Probe Micro Analyser).

[0016] (3) Requirements regarding the ratio of the area occupied by the insulating layer 3 For the compacted powder core 10, when observing the cross - section of the compacted powder core 10 in a field of view of 500μm×500μm and taking the total area of the compacted powder core 10 as 100%, the ratio of the area occupied by the insulating layer 3 is 4% or more and 9% or less. The ratio of the area occupied by the insulating layer 3 is more preferably 5% or more and 7% or less. When the ratio of the area occupied by the insulating layer 3 is within a predetermined range, the balance between the hysteresis loss and the eddy current loss is improved. That is, if the ratio of the area occupied by the insulating layer 3 is too large, the hysteresis loss becomes large, and if it is too small, the eddy current loss becomes large. The ratio of the area occupied by the insulating layer 3 can be calculated by image analysis through observation by EPMA on a cross - section processed by CP (Cross - section Polisher). Note that the area of the pores 6 is not included in the area occupied by the insulating layer 3. In FIG. 1, among the pores 6, the pores 6 existing between the soft magnetic metal particles 2 and the insulating layer 3 are distinguished as pores 6A. Note that the ratio of the area occupied by the insulating layer 3 can be controlled by adjusting the blending amounts of the raw materials of the soft magnetic metal particles 2 and the insulating layer 3.

[0017] (4) Requirements regarding the difference between the thermal expansion coefficient of the soft magnetic metal particles 2 and the thermal expansion coefficient of the insulating layer 3 The difference between the coefficient of thermal expansion of the soft magnetic metal particles 2 and the coefficient of thermal expansion of the insulating layer 3 in the compressed powder core 10 is 3.0×10 -6 / K or less. The difference between the coefficient of thermal expansion of the soft magnetic metal particles 2 and the coefficient of thermal expansion of the insulating layer 3 is more preferably 2.8×10 -6 / K or less, and even more preferably 2.5×10 -6 / K or less. If the difference between the coefficient of thermal expansion of the soft magnetic metal particles 2 and the coefficient of thermal expansion of the insulating layer 3 is equal to or less than a predetermined value, the performance degradation after thermal cycling assuming the actual use environment can be reduced. Note that the difference between the coefficient of thermal expansion of the soft magnetic metal particles 2 and the coefficient of thermal expansion of the insulating layer 3 is expressed as an absolute value and is 0 or more.

[0018] The difference between the coefficient of thermal expansion of the soft magnetic metal particles 2 and the coefficient of thermal expansion of the insulating layer 3 can be obtained as follows. A single sample of the soft magnetic metal particles 2 is prepared by press molding without applying an insulating coating to the soft magnetic metal particles 2. When there is no single powder of the soft magnetic metal particles 2, the composition of the single substance of the soft magnetic metal is obtained from the sample of the insulated soft magnetic metal powder 1, and a single sample of this composition is prepared. The soft magnetic metal particles 2 are coated with the insulating layer 3 and press molded to prepare the compressed powder core 10. In accordance with JIS R 1618, the thermal expansion amounts of the single sample of the soft magnetic metal particles 2 and the compressed powder core 10 in the range of 25°C to 100°C are measured. Let the thermal expansion amount measured for the single sample be A and the thermal expansion amount measured for the compressed powder core 10 be B. The rate of change of A with respect to the temperature change in the range of 25°C to 100°C is calculated as the coefficient of thermal expansion of the soft magnetic metal particles 2. The value obtained by the following formula (1) is regarded as the thermal expansion amount C of the insulating layer 3. C = B - A ··(1) The rate of change of C with respect to the temperature change in the range of 25°C to 100°C is calculated as the coefficient of thermal expansion of the insulating layer 3. From the calculated coefficient of thermal expansion of the soft magnetic metal particles 2 and the coefficient of thermal expansion of the insulating layer 3, the difference between the coefficient of thermal expansion of the soft magnetic metal particles 2 and the coefficient of thermal expansion of the insulating layer 3 is obtained. Incidentally, the coefficient of thermal expansion of the soft magnetic metal particles 2 and the coefficient of thermal expansion of the insulating layer 3 can be controlled by appropriately designing the combination of the composition of the soft magnetic metal particles 2 and the composition of the insulating layer 3.

[0019] The combination of the composition of the soft magnetic metal particles 2 and the composition of the insulating layer 3 is not particularly limited. From the viewpoint of reducing the difference in the coefficient of thermal expansion, the preferred combination of the composition of the soft magnetic metal particles 2 and the composition of the insulating layer 3 is as follows. In addition, the combination of the composition of the soft magnetic metal particles and the composition of the insulating layer described in the examples can also be adopted. A combination in which the soft magnetic metal particles 2 are Fe-3.0 mass% Si and the insulating layer 3 is ZrO2 A combination in which the soft magnetic metal particles 2 are Fe-6.5 mass% Si and the insulating layer 3 is Al2O3-20 mass% SiO2-5 mass% MgO A combination in which the soft magnetic metal particles 2 are pure iron (100% Fe) and the insulating layer 3 is ZrO2

[0020] (5) Speculative reasons for suppressing the loss of the compacted powder core 10 The inventors of the present invention have intensively studied to suppress the loss (iron loss) of the compacted powder core 10. As a result, in the compacted powder core 10 obtained by adjusting the blending and composition of the soft magnetic metal particles 2 and the insulating layer 3, it has been found that the desired effect can be achieved when the following requirements are met. That is, the ratio of the area occupied by the insulating layer 3 is 4% or more and 9% or less, and the difference between the coefficient of thermal expansion of the soft magnetic metal particles 2 and the coefficient of thermal expansion of the insulating layer 3 is 3.0×10 -6 / K or less, and an unexpected fact that the loss of the compacted powder core 10 can be suppressed has been discovered. The present invention has been made based on this finding. In addition, when the above requirements are met, the effect of reducing the performance degradation after thermal cycling assuming the actual use environment is also achieved.

[0021] (6) Requirements regarding the average equivalent circle diameter of the particles constituting the insulating layer 3 When the insulating layer 3 is observed with a TEM (transmission electron microscope), the particles constituting the insulating layer 3 are confirmed. At least a part of these particles is formed by the crystals of the above oxides. The average equivalent circle diameter of the particles constituting the insulating layer 3 is not particularly limited. The average equivalent circle diameter of the particles constituting the insulating layer 3 is preferably 20 nm to 50 nm, more preferably 25 nm to 45 nm, and even more preferably 28 nm to 42 nm. When it is within such a range, the adhesion to the soft magnetic metal particles 2 is improved, and the resistance at the grain boundaries can reduce the eddy current loss, thereby reducing the loss. Incidentally, the average equivalent circle diameter of the particles constituting the insulating layer 3 can be determined by observing the cross-section of the compacted powder core 10. Specifically, the equivalent circle diameter of the area is calculated from the particle area observed by TEM of the cross-section of the compacted powder core 10 and used as the average equivalent circle diameter. More specifically, the average equivalent circle diameter is determined as follows. In five observation fields of 300 nm × 300 nm squares, attention is paid to a plurality of particles that can be observed without chipping. The diameter (equivalent circle diameter of the area) of an ideal circle (true circle) having an area equal to the area (projection area) of each particle image is calculated as the equivalent circle diameter of each particle. Then, the average equivalent circle diameter is obtained by arithmetically averaging the equivalent circle diameters of each particle. The equivalent circle diameter of each particle and the average equivalent circle diameter can be obtained using general image analysis software.

[0022] (7) Requirements regarding crystal orientation In the insulating-coated soft magnetic metal powder 1, particles having an equivalent circle diameter of 50 μm to 100 μm among the soft magnetic metal particles 2 are defined as specific particles. When the cross-sections of 10 or more different specific particles are subjected to crystal orientation analysis and the number of regions separated by an orientation difference of 5° or more is measured for each specific particle, the average value of the number of regions measured for each specific particle is preferably 9 or less. The average value of the number of regions measured for specific particles is preferably 8 or less, and more preferably 7 or less. The average value of the number of regions measured for specific particles can be an index representing the degree of crystal segmentation in the soft magnetic metal particles. When the average value of the number of regions measured for specific particles is below a predetermined value, the increase in hysteresis loss is suppressed, and accordingly the loss is also reduced. Incidentally, the lower limit of the average value of the number of regions measured for specific particles only needs to be 1 or more, and is usually 2 or more. Incidentally, the number of regions in specific particles can be specified by the electron backscatter diffraction (EBSD) method. The EBSD measurement is performed, for example, under the following conditions. ·Accelerating voltage: 10.00 kV ·Sample tilt (angle): 70.00° ·Collection speed: 109.15 Hz Based on the crystal orientation map obtained by EBSD measurement, measurement points with an orientation difference of 5° or more between adjacent measurement points are defined as grain boundaries, and the number of regions surrounded by the grain boundaries is counted. However, among the regions surrounded by the grain boundaries, regions with an equivalent circle diameter of 3 μm or less are excluded from the counting. The reason for excluding regions with an equivalent circle diameter of 3 μm or less is to eliminate errors in EBSD measurement caused by noise or the like.

[0023] (8) Requirements regarding the full width at half maximum of the strongest peak derived from the insulating layer 3 For the insulated coated soft magnetic metal powder 1, it is preferable that the full width at half maximum of the strongest peak derived from the insulating layer 3 measured by XRD is 0.80° or less. The fact that the full width at half maximum of the strongest peak derived from the insulating layer 3 is below a predetermined value can be an indicator of the high crystallinity of the oxide contained in the insulating layer 3. The full width at half maximum of this strongest peak may be 0.72° or less, or may be 0.66° or less. The lower limit of the full width at half maximum of the strongest peak is not particularly limited, but is usually 0.40° or more. The full width at half maximum of the strongest peak derived from the insulating layer 3 can be controlled by adjusting the composition of the insulating layer 3 and the heat treatment conditions in the manufacturing method described later.

[0024] The full width at half maximum of the strongest peak derived from the insulating layer 3 can be determined by XRD measurement of the compacted magnetic core 10 containing the insulated coated soft magnetic metal powder 1. The XRD measurement is performed, for example, under the following conditions. ·Equipment: Rigaku SmartLab ·X-ray: CuKα1 ·Tube voltage: 40 kV ·Tube current: 30 mA ·Scanning speed: 5° / min ·Sampling width: 0.02° ·Measurement range (2θ): 10° to 80° ·Incident slit: 1 / 2° ·Receiving slit 1: 15.000 mm · Light-receiving slit 2: 20.000 mm In the diffraction pattern of the compacted magnetic core 10 obtained by XRD measurement, excluding the peaks derived from the soft magnetic metal particles 2, the measurement cell, etc., a peak derived from the insulating layer 3 is obtained. When there is one peak derived from the insulating layer 3, that peak is specified as the strongest peak. When there are multiple peaks derived from the insulating layer 3, the peak with the highest intensity among the multiple peaks is specified as the strongest peak. For example, in the insulating layer 3 containing ZrO2, when two types of peaks of monoclicic ZrO2 and tetragonal ZrO2 are detected, only the peak with the higher intensity (for example, tetragonal ZrO2) is specified as the strongest peak.

[0025] Examples of the crystal phase showing the strongest peak derived from the insulating layer 3 include crystal phases selected from the group consisting of monoclinic ZrO2, tetragonal ZrO2, cubic ZrO2, γ-Al2O3, and SiO2 (quartz). In these crystal phases, examples of the strongest peak are as follows. Among these, the strongest peak is preferably a peak of either monoclinic ZrO2, tetragonal ZrO2, cubic ZrO2, or γ-Al2O3. · Monoclinic ZrO2 PDF card number: 01-080-0966 (hkl) of the strongest peak: (-1, 1, 1) d value of the strongest peak: 3.15 · Tetragonal ZrO2 PDF card number: 01-073-1441 (hkl) of the strongest peak: (0, 1, 1) d value of the strongest peak: 3.00 · Cubic ZrO2 PDF card number: 01-080-4012 (hkl) of the strongest peak: (1, 1, 1) d value of the strongest peak: 2.97 · γ-Al2O3 PDF card number: 00-010-0173 (hkl) of the strongest peak: (4, 4, 0) d value of the strongest peak: 1.40 ·SiO2 (quartz) PDF card number: 00-033-1161 (hkl) of the strongest peak: (1, 0, 1) d value of the strongest peak: 3.34

[0026] (9) Requirements regarding the thickness of the diffusion layers 5A and 5B When the insulating layer 3 contains an oxide of at least one of the elements Al or Zr, the thickness of the diffusion layers 5A and 5B in which at least one of the elements Al or Zr has diffused in the surface layer of the soft magnetic metal particles 2 is preferably 50 nm or less. The diffusion layers 5A and 5B can be formed by diffusion of at least one of the elements Al or Zr into the soft magnetic metal particles 2 by heat treatment or the like. That is, the diffusion layers 5A and 5B can be formed at the site where the soft magnetic metal particles 2 and the insulating layer 3 are in close contact. The diffusion layers 5A and 5B may be formed over the entire surface layer of the soft magnetic metal particles 2, or may be partially formed on the surface layer of the soft magnetic metal particles 2. These diffusion layers 5A and 5B may not be formed (thickness is 0 nm). The thickness of the diffusion layers 5A and 5B can be controlled by adjusting the heating rate and the like in a predetermined temperature range in the manufacturing method described later.

[0027] Whether the thickness of the diffusion layers 5A and 5B is 50 nm or less is determined by TEM-EDS (energy dispersive X-ray spectrometer) measurement of the compact magnetic core 10. Specifically, the compact magnetic core 10 is processed into a thin film sample 11 with a thickness of 100 nm by a FIB (focused ion beam) apparatus, and TEM-EDS measurement is performed. The TEM-EDS measurement is performed under conditions corresponding to a predetermined resolution (for example, Φ10 nm). As an example of such measurement conditions, a beam diameter of Φ0.24 nm, an acceleration voltage of 200 keV, and an irradiation current of 30 μA are shown.

[0028] The thin-film sample 11 will be described. As shown in Fig. 2, the thin-film sample 11 is processed such that the cross-section of the insulating layer 3 appears on the FIB observation surface S1 and the TEM observation surface S2. The TEM observation surface S2 of the thin-film sample 11 is set as the XY plane, and the FIB observation surface S1 is set as the XZ plane. On the FIB observation surface S1, the boundary lines between the insulating layer 3 and the soft magnetic metal particles 2A and 2B appear. The inclination of both boundary lines is 10 nm or less in the horizontal (X-axis direction) with respect to 100 nm in the vertical (Z-axis direction). In Fig. 2, it shows that the inclination of the right boundary line is within a predetermined range, and the inclination of the left boundary line is also within the predetermined range. The TEM-EDS observation is performed at a position 600 nm from the FIB observation surface S1 on the TEM observation surface S2. In this way, due to the inclination of the insulating layer 3 with respect to the Z-axis, it is possible to suppress the insulating layer 3 components existing inside the thin-film sample 11 from being detected as the diffusion layers 5A and 5B. Note that in Fig. 2, the illustration of the diffusion layers 5A and 5B is omitted.

[0029] When the element contained in the insulating layer 3 is Zr, the determination of whether the diffusion layers 5A and 5B are 50 nm or less is performed by the following procedure. Hereinafter, it will be described with reference to Figs. 3 and 4. [1] Obtain a TEM observation image on the TEM observation surface S2 and perform line analysis on the measurement line ML that crosses the insulating layer 3 at a position 600 nm from the FIB observation surface S1. [2] Draw two lines L1 and L2 perpendicular to the measurement line ML from the intersection points of the measurement line ML and the boundary lines between the soft magnetic metal particles 2A, 2B and the insulating layer 3. The line L1 is located on the left side of the insulating layer 3, and the line L2 is located on the right side of the insulating layer 3. [3] Calculate the average value of all the points of the Zr concentration obtained by line analysis within the measurement range inside the two lines L1 and L2. This average value is defined as the 100% line of the Zr concentration. [4] Calculate the average value of all the points of the Zr concentration obtained by line analysis within the measurement range from 500 nm to the left of the line L1 and from 500 nm to the right of the line L2. This average value is defined as the base (0%) line of the Zr concentration. [5]Based on the base (0%) line of the Zr concentration and the 100% line of the Zr concentration, calculate the 10% line of the Zr concentration. Determine the outermost points P1 and P2 among the intersection points of the 10% line of the Zr concentration and the graph of the Zr concentration. [6]Calculate the distance between point P1 and line L1. From the TEM observation image, determine the angle θ1 (0° < θ1 ≤ 90°) between the boundary line of the soft magnetic metal particle 2A and the insulating layer 3 and the measurement line ML. Calculate the thickness T1 of the diffusion layer 5A based on the following formula. The thickness T1 of the diffusion layer 5A = the distance between point P1 and line L1 × sinθ1 Calculate the distance between point P2 and line L2. From the TEM observation image, determine the angle θ2 (0° < θ2 ≤ 90°) between the boundary line of the soft magnetic metal particle 2B and the insulating layer 3 and the measurement line ML. Calculate the thickness T2 of the diffusion layer 5B based on the following formula. The thickness T2 of the diffusion layer 5B = the distance between point P2 and line L2 × sinθ2 [7]When the thickness T1 of the diffusion layer 5A is 50 nm or less and the thickness T2 of the diffusion layer 5B is 50 nm or less, determine that "the thickness of the diffusion layer is 50 nm or less" (see Fig. 3). When at least one of the thickness T1 of the diffusion layer 5A and the thickness T2 of the diffusion layer 5B is greater than 50 nm, determine that "the thickness of the diffusion layer is greater than 50 nm" (see Fig. 4). Note that the thicknesses T1 and T2 of the diffusion layers 5A and 5B may be 0 nm. That is, the diffusion layers 5A and 5B may not be detected.

[0030] For the insulated coated soft magnetic metal powder 1, it is sufficient if it is determined that "the thickness of the diffusion layer is 50 nm or less" by line analysis at one location in at least one soft magnetic metal particle 2. It is desirable that for one soft magnetic metal particle 2, line analysis is performed at three different locations and it is determined that "the thickness of the diffusion layer is 50 nm or less" in all cases. Further, it is more desirable that for the insulated coated soft magnetic metal powder 1, line analysis is performed on a plurality of thin sheet samples 11 obtained from different positions in the compacted magnetic core 10 and it is determined that "the thickness of the diffusion layer is 50 nm or less" in all cases. The number of the plurality of thin sheet samples 11 is preferably 3 or more, more preferably 5 or more, and even more preferably 10 or more.

[0031] Even when the element contained in the insulating layer 3 is Al, the Al concentration may be measured and the determination may be made in the same procedure. When both Al and Zr are contained in the insulating layer 3, the determination may be made for Al and Zr in the same procedure, and it is only necessary to confirm that all elements satisfy the requirements. Note that even when the insulating film contains oxides of elements other than Al and Zr (for example, oxides of Si), the thickness of the diffusion layer is defined as the thickness defined by the Zr concentration or the Al concentration, and the concentrations of elements other than Al and Zr are not considered.

[0032] 2. Method for manufacturing the compacted powder magnetic core 10 The method for manufacturing the compacted powder magnetic core 10 is not particularly limited. An example will be described below. (1) Preparation of the insulated soft magnetic metal powder 1 A suspension containing soft magnetic metal powder, particles of an oxide of a specific element, and a small amount of an organic component is mixed and dried. The obtained dried powder is heat-treated to obtain the insulated soft magnetic metal powder 1. The conditions of this heat treatment are not particularly limited. As the heat treatment conditions, for example, the heat treatment temperature: 600°C to 1200°C, and the conditions of an inert atmosphere (N2 atmosphere, Ar atmosphere) are preferably employed. (2) Molding (press molding) The insulated soft magnetic metal powder 1 is put into a mold and press-molded at a molding pressure of 1.0 to 1.7 GPa to obtain a molded body. (3) Heat treatment (annealing) The obtained molded body is heat-treated (annealed) to obtain the compacted powder magnetic core 10. As the heat treatment conditions, for example, the heat treatment temperature: 600°C to 1200°C, the heating rate at 350°C to 600°C: 3°C / min or more, the holding time: 10 minutes to 120 minutes, and the conditions of an inert atmosphere (N2 atmosphere, Ar atmosphere) are preferably employed. Note that the heat treatment conditions are appropriately changed depending on the types of the soft magnetic metal powder and the oxide used.

Example

[0033] Hereinafter, the present invention will be described more specifically by way of examples.

[0034] 1. Fabrication of Compressed Powder Core (1) Examples 1 to 13 As the soft magnetic metal particles (raw material powder), various particles having the types and average equivalent circle diameters described in Table 1 were used. In Table 1, each description represents the following particles. Fe: Particles of pure iron Fe-3.5Si: Fe-3.5 mass% Si particles produced by the gas atomization method Fe-Ni: Permalloy particles Fe-Si-Cr: Fe-3.5 mass% Si-1.5 mass% Cr particles produced by the water atomization method Fe-Si-Al: Sendust particles Fe-Ni-Mo: Supermalloy particles Fe-Si: Fe-5.0 mass% Si particles produced by the gas atomization method

[0035] Next, a suspension containing oxide particles of the types described in Table 1, a small amount of organic components, and a solvent was mixed with the soft magnetic metal particles, dried, and heat-treated. The concentration of the oxide particles in the suspension was set to 0.1 to 2 mass% with respect to the entire suspension. The amount of the suspension mixed with the soft magnetic metal particles was set such that the total amount of the contained oxide particles was 6% by volume with respect to the soft magnetic metal particles. The heat treatment (first heat treatment) was carried out under the conditions of a heat treatment temperature of 600°C to 1200°C in nitrogen. The heat treatment was performed for the purpose of removing the organic components in the insulating layer and promoting the crystallization of the oxide. In this way, the insulated coated soft magnetic metal powders of Examples 1 to 13 were obtained. In Table 1, each description represents the following oxide particles. Al: Al2O3 particles Si: SiO2 particles Zr: ZrO2 particles Zr-Si: ZrO2-20 mass% SiO2 particles Al-Si: Al2O3-20 mass% SiO2 particles Zr-Al: ZrO2-10 mass% Al2O3 particles

[0036] The obtained insulated-coated soft magnetic metal powder was put into a mold and press-molded at a molding pressure of 1.0 to 1.7 GPa to obtain a press-molded body with a diameter of 10 mm. This molded body was heat-treated (second heat treatment). The heat treatment was carried out under the conditions of a heat treatment temperature of 600 to 1200 °C, a heating rate in the range of 350 to 600 °C of less than 3 °C / min, and in nitrogen. In this way, the compacted powder cores of Examples 1 to 13 were obtained.

[0037] (2) Examples 14 to 20 The heat treatment temperature of the heat treatment (second heat treatment) was 600 to 1200 °C, and the heating rate in the range of 350 to 600 °C was 3 °C / min to 10 °C / min. Otherwise, in the same manner as in Examples 1 to 13, insulated-coated soft magnetic metal powder and a compacted powder core were obtained. By performing heat treatment at a temperature higher than conventional ones, the crystallinity of the insulating layer was controlled. Furthermore, by increasing the heating rate in a predetermined temperature range, it was controlled to quickly obtain an insulating layer with high crystallinity. As a result, it was possible to shorten the temperature range until an insulating layer with high crystallinity was formed, and it was presumed that diffusion of at least one of the elements Al or Zr constituting the insulating layer into the soft magnetic metal particles was suppressed.

[0038] (3) Comparative Examples 1 and 2 For the soft magnetic metal particles (raw material powder), various particles having the types and average equivalent circle diameters described in Table 1 were used. Otherwise, in the same manner as in Examples 1 to 13, insulated-coated soft magnetic metal powder and a compacted powder core were obtained.

[0039] (4) Comparative Example 3 A suspension containing no oxide particles of specific elements was used. Otherwise, in the same manner as in Examples 1 to 13, insulated-coated soft magnetic metal powder and a compacted powder core were obtained.

[0040] (5) Comparative Examples 4 and 5 The heat treatment temperature of the heat treatment (second heat treatment) was 600 to 1200 °C, and the heating rate in the range of 350 to 600 °C was 2.5 °C / min. Otherwise, in the same manner as in Examples 1 to 13, insulated-coated soft magnetic metal powder and a compacted powder core were obtained.

[0041] Table 1 summarizes the properties of the soft magnetic metal particles and the insulating layers of each example and comparative example. The column of "crystal orientation" shows the average value of the number of regions measured for specific particles, measured by the method described in the embodiment. The column of "half-width" shows the half-width of the strongest peak derived from the insulating layer, measured by the method described in the embodiment. The column of "thickness of diffusion layer" describes the thickness of the larger diffusion layer among the "thickness T1 of diffusion layer 5A" and "thickness T2 of diffusion layer 5B" calculated by the method described in the embodiment. For Example 2 and Comparative Example 3, since at least one element of Al or Zr is not detected, it is described as "-". In addition, Fig. 5 shows the graphs of the Zr concentration and O concentration in the compacted magnetic core of Example 3. The column of "equivalent average circle diameter" of the insulating layer shows the equivalent average circle diameter of the particles constituting the insulating layer, measured by the method described in the embodiment. The column of "occupied area" shows the ratio of the area occupied by the insulating layer, measured by the method described in the embodiment.

[0042]

Table 1

[0043] 2. Loss evaluation method Based on a compacted magnetic core (hereinafter referred to as a single-metal compacted magnetic core) made by only press-forming soft magnetic metal particles (median diameter D 50 : 40 μm) without performing heat treatment after molding, the hysteresis loss and eddy current loss of the compacted magnetic cores of each example and comparative example were determined under the following conditions. · Number of turns: primary: 20 turns, secondary: 40 turns · Applied magnetic field: 0.1 T, frequency: 30 kHz to 50 kHz

[0044] The evaluation was carried out as follows. Hysteresis loss D: 95% or more of the hysteresis loss of the single-metal compacted magnetic core C: 80% or more and less than 95% of the hysteresis loss of the single-metal compacted magnetic core B: More than 70% and less than 80% of the hysteresis loss of the single metal compacted powder core A: Less than 70% of the hysteresis loss of the single metal compacted powder core Note that "D" is considered to be at the same level as the hysteresis loss of the single metal compacted powder core or greater than the hysteresis loss of the single metal compacted powder core.

[0045] Eddy current loss D: 90% or more of the eddy current loss of the single metal compacted powder core C: 80% or more and less than 90% of the eddy current loss of the single metal compacted powder core B: 60% or more and less than 80% of the eddy current loss of the single metal compacted powder core A: Less than 60% of the eddy current loss of the single metal compacted powder core Note that "D" is considered to be the case where the eddy current loss of the single metal compacted powder core is not clearly improved.

[0046] 3. Evaluation results The evaluation results are shown in Table 1. Examples 1 to 20 satisfy the following requirements (a), (b), (c), and (d). · Requirement (a): It is provided with soft magnetic metal particles having an average equivalent circle diameter of 10 μm to 100 μm. · Requirement (b): The insulating layer contains an oxide of at least one element selected from the group consisting of Al, Zr, and Si. · Requirement (c): The proportion of the area occupied by the insulating layer is 4% or more and 9% or less. · Requirement (d): The difference between the thermal expansion coefficient of the soft magnetic metal particles and the thermal expansion coefficient of the insulating layer is 3.0×10 -6 / K or less.

[0047] In contrast, Comparative Examples 1 to 5 do not satisfy the following requirements. In Comparative Examples 1 and 2, requirement (a) is not satisfied. In Comparative Example 3, requirement (b) is not satisfied. In Comparative Examples 4 and 5, requirements (c) and (d) are not satisfied.

[0048] Examples 1 to 20 had the hysteresis loss and overcurrent loss suppressed in a well-balanced manner as compared with Comparative Examples 1 to 5. Further, Examples 1 to 20 had a small degradation in performance after thermal cycling. Among Examples 1 to 20, Experimental Examples 6 to 20 that further satisfied the following requirement (e) had less hysteresis loss. Among Examples 1 to 20, Experimental Examples 11 to 20 that further satisfied the following requirement (f) had less hysteresis loss and eddy current loss. Among Examples 1 to 20, Experimental Examples 14 to 20 that further satisfied the following requirement (g) had less eddy current loss. · Requirement (e): The average equivalent circle diameter of the particles constituting the insulating layer is 20 nm to 50 nm. · Requirement (f): The average value of the number of regions measured with specific particles is 9 or less. · Requirement (g): The insulating layer contains an oxide of at least one of the elements Al or Zr, the half-value width of the strongest peak derived from the insulating layer measured by XRD is 0.80° or less, and the thickness of the diffusion layer in which at least one of the elements Al or Zr diffused in the surface layer of the soft magnetic metal particles is 50 nm or less.

[0049] 4. Effects of the Examples The dust core of this example had both low hysteresis loss and low overcurrent loss.

[0050] The present invention is not limited to the embodiments described in detail above, and various modifications or changes are possible within the scope shown in the claims of the present invention.

Industrial Applicability

[0051] The dust core of the present invention is particularly preferably used in applications such as motor cores, transformers, choke coils, and noise absorbers.

Explanation of Signs

[0052] 1... Insulation-coated soft magnetic metal powder 2, 2A, 2B... Soft magnetic metal particles 3... Insulating layer 5A, 5B... Diffusion layer 6,6A … air holes 10 … compacted powder core

Claims

1. A powder compact magnetic core containing insulated-coated soft magnetic metal powder comprising soft magnetic metal particles having an average equivalent circle diameter of 10 μm to 100 μm and an insulating layer formed on the surface of the soft magnetic metal particles, The insulating layer contains an oxide of at least one element selected from the group consisting of Al, Zr, and Si, When the cross-section of the powder compact magnetic core is observed in a field of view of 500 μm × 500 μm and the area of the entire powder compact magnetic core is taken as 100%, the ratio of the area occupied by the insulating layer is 4% or more and 9% or less, The difference between the coefficient of thermal expansion of the soft magnetic metal particles and the coefficient of thermal expansion of the insulating layer is 3.0×10 －６ / K or less, the powder compact magnetic core.

2. The powder compact magnetic core according to claim 1, wherein the average equivalent circle diameter of the particles constituting the insulating layer is 20 nm to 50 nm.

3. Among the soft magnetic metal particles, particles having an equivalent circle diameter of 50 μm to 100 μm are specified particles. When the cross-sections of 10 or more different specified particles are subjected to crystal orientation analysis and the number of regions separated by an azimuth difference of 5° or more is measured for each of the specified particles, the average value of the number of regions measured for each of the specified particles is 9 or less. The powder compact magnetic core according to claim 1 or claim 2.

4. The insulating layer contains an oxide of at least one of Al and Zr, The half-value width of the strongest peak derived from the insulating layer measured by XRD is 0.80° or less, The powder compact magnetic core according to any one of claims 1 to 3, wherein the thickness of the diffusion layer in which at least one of the elements of Al or Zr diffuses in the surface layer of the soft magnetic metal particles is 50 nm or less.

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