JP7291507B2 - dust core - Google Patents

Description

The present invention relates to dust cores.

The development of powder magnetic cores is actively carried out due to their high degree of freedom in shape and applicability to high-frequency bands.
In Patent Document 1, a composite magnetic material powder obtained by uniformly mixing and dispersing a crystalline magnetic material and an amorphous magnetic material is added with an organic material such as silicone-based resin, phenol-based resin, or epoxy-based resin as an insulating material. A high-frequency powder magnetic core manufactured using polymer resin and water glass is disclosed.

JP-A-2005-294458

However, the iron loss of this powder magnetic core is not necessarily sufficiently suppressed, and further suppression of the iron loss has been desired.
The present invention has been made in view of the above circumstances, and aims to further suppress iron loss, and can be implemented as the following modes.

[1] A powder magnetic core comprising soft magnetic metal particles having an average particle size of 5 μm or more and 30 μm or less and a grain boundary phase,
The grain boundary phase comprises (A) a glass containing sodium silicate as a main component and (B) a crystalline inorganic fiber,
When the cross-sectional structure of the powder magnetic core is observed in a square first field of view of 100 μm × 100 μm, on one side of the square defining the first field of view, the place where the grain boundary phase exists is the starting point of the square The grain boundary phase is formed continuously up to the side opposite to the one side, and has five or more continuous layers different from each other,
A powder magnetic core, wherein an average length of a path from the one side to the opposite side of the continuous layer is 115 μm or more.

[2] When the cross-sectional structure of the powder magnetic core is observed in a square second field of view of 50 μm × 50 µm, the area ratio of the crystalline inorganic fiber occupying the second field of view is S1, and the glass is the second field of view. The dust core according to [1], wherein the value of S1/(S1+S2) satisfies the following relational expression, where S2 is the area ratio of the field of view.
0.1≦S1/(S1+S2)≦0.3

[3] the crystalline inorganic fiber has a fiber diameter of 10 nm or more and 300 nm or less;
The dust core according to [1] or [2], wherein the crystalline inorganic fibers have an aspect ratio of 10 or more.

[4] The pressure according to any one of [1] to [3], wherein crystals containing Si are present at the interface between the surface of the crystalline inorganic fiber and the glass. powder magnetic core.

According to the above invention [1], since the crystalline inorganic fibers are present in the grain boundary phase, the resistance value of the grain boundary phase increases, and eddy current loss can be reduced.
According to the above invention [2], the eddy current loss is further reduced. Further, according to the present invention, the powder magnetic core becomes denser, and the hysteresis loss can be kept small.
According to the above invention [3], the fiber diameter of the crystalline inorganic fiber is 10 nm to 300 nm, and the aspect ratio of the crystalline inorganic fiber is 10 or more, so that resistance characteristics and heat transfer performance are improved. .
According to the above invention [4], the presence of Si-containing crystals at the interface increases the adhesion between the soft magnetic metal particles, and as a result, the resistance value of the grain boundary phase increases, and the eddy current Less loss.

It is a schematic diagram which shows a powder magnetic core. The figure on the right shows a schematic view of the cross-sectional structure of the powder magnetic core observed in the first visual field of a square of 100 μm×100 μm. It is process drawing which shows an example of the manufacturing method of a powder magnetic core.

The present invention will be described in detail below. It should be noted that, in this specification, the description using "-" for the numerical range includes the lower limit and the upper limit unless otherwise specified. For example, the description “10 to 20” includes both the lower limit “10” and the upper limit “20”. That is, "10 to 20" has the same meaning as "10 or more and 20 or less".

1. Configuration of dust core 1 As shown in the right diagram (cross-sectional view) of FIG. Become. The grain boundary phase 6 includes (A) glass containing sodium silicate as a main component and (B) crystalline inorganic fibers. The grain boundary phase 6 forms a continuous layer 21 (21A, 21B, 21C, 21D, 21E) which will be described later. In addition, hatching (parallel lines) in FIG. 1 indicates the soft magnetic metal particles 3 . Also, the dotted lines in FIG. 1 indicate the grain boundary phase 6 .
When the cross-sectional structure of the powder magnetic core 1 is observed in a square first field of view of 100 μm × 100 µm, the starting point is the place where the grain boundary phase 6 exists on one side 11 of the square defining the first field of view. The grain boundary phase 6 is formed continuously from one side 11 of the square to the opposite side 13, and has five or more continuous layers 21 different from each other. The average length of the path from one side 11 to the opposite side 13 of the continuous layer 21 is 115 μm or more.
An embodiment of the dust core 1 of the present invention will be described in detail below.

In FIG. 1, a toroidal dust core 1 is taken as an example. The shape of the dust core 1 is not particularly limited. FIG. 1 shows a cross section of a dust core 1 taken along its axial direction.

(1) Soft magnetic metal particles 3
The soft magnetic metal particles 3 are not particularly limited as long as they are soft magnetic metal particles, and can be widely used. As the soft magnetic metal particles 3, a wide range of soft magnetic pure iron particles and iron-based alloy particles can be used. As iron-based alloys, Fe--Si--Cr alloys, Fe--Si--Al alloys (sendust), Ni--Fe alloys (permalloy), Ni--Fe--Mo alloys (supermalloy), Fe-based amorphous alloys, Fe--Si Alloys, Ni--Fe alloys, Fe--Co alloys, etc. can be suitably used. Among these, Fe--Si--Cr alloys, Ni--Fe alloys (permalloy), Ni--Fe--Mo alloys (supermalloy) and Fe-based amorphous alloys are preferable from the viewpoint of magnetic permeability, coercive force and frequency characteristics.
The average particle size of the soft magnetic metal particles 3 is 5 μm or more and 30 μm or less, preferably 10 μm or more and 25 μm or less, and more preferably 15 μm or more and 22 μm or less. The average particle size of the soft magnetic metal particles 3 can be appropriately changed depending on the frequency band used. In particular, when assuming use in a high frequency band exceeding 100 kHz, the thickness is more preferably 10 μm or more and 25 μm or less. The average particle diameter of the soft magnetic metal particles 3 is obtained by calculating the equivalent circle diameter from the particle area of the powder magnetic core 1 observed by FE-SEM JSM-6330F.

The soft magnetic metal particles 3 may have a metal oxide layer (passive coating) on their surfaces. Adhesion to the grain boundary phase 6 can be improved by providing the metal oxide layer on the surface.
The metal oxide forming the metal oxide layer is not particularly limited. For example, one or more metal oxides selected from the group consisting of chromium oxide, aluminum oxide, molybdenum oxide, and tungsten oxide are preferred. In particular, the metal oxide preferably contains at least one of chromium oxide and aluminum oxide. By using these preferred metal oxides, eddy current loss is effectively suppressed.
When Fe--Si--Cr alloy particles are used as the soft magnetic metal particles 3, a metal oxide layer containing chromium oxide (Cr ₂ O ₃ ) can be easily formed. That is, a metal oxide layer is formed on the outer edges of the soft magnetic metal particles 3 by oxidizing Cr in the Fe—Si—Cr alloy.
Moreover, the thickness of the metal oxide layer is not particularly limited. The thickness can be preferably 1 nm or more and 20 nm or less. The thickness of the metal oxide layer can be measured using XPS (X-ray photoelectron spectroscopy).

(2) Grain boundary phase 6
(2.1) Structure of Grain Boundary Phase 6 The grain boundary phase 6 includes (A) glass containing sodium silicate as a main component and (B) crystalline inorganic fibers. This grain boundary phase 6 has a property of high resistance.
The component (A) glass contains sodium silicate as a main component. Here, the main component means a substance with a content (% by mass) of 50% by mass or more. The glass may include borate glass, fluorophosphate glass, phosphate glass, silicate glass, crystallized glass.
The crystalline inorganic fiber of component (B) is not particularly limited as long as it is an inorganic fiber having crystallinity. From the viewpoint of chemical stability, the inorganic fibers having crystallinity are selected from the group consisting of Al ₂ O ₃ fibers, Al ₂ O ₃ —Y ₂ O ₃ fibers, Al ₂ O ₃ —SiO ₂ fibers, and ZrO ₂ fibers. One or more selected fibers are preferably employed.
The fiber diameter of the crystalline inorganic fibers is not particularly limited. The fiber diameter of the crystalline inorganic fibers is preferably 10 nm or more and 300 nm or less, more preferably 50 nm or more and 280 nm or less, and even more preferably 100 nm or more and 220 nm or less. When the cross-sectional shape of the crystalline inorganic fiber is an irregular cross-section other than a circular cross-section, the diameter of the circumscribed circle is taken as the fiber diameter. The fiber diameter can be measured by photographing the cross section of the fiber with a scanning electron microscope.
Moreover, the aspect ratio of the crystalline inorganic fibers is not particularly limited. The aspect ratio of the crystalline inorganic fibers is preferably 10 or more, more preferably 15 or more. Although the upper limit of the aspect ratio is not particularly limited, it is usually 60.
When the fiber diameter of the crystalline inorganic fiber is 10 nm to 300 nm and the aspect ratio of the crystalline inorganic fiber is 10 or more, resistance characteristics and heat transfer performance are improved.

The content ratio of the (A) component and the (B) component in the grain boundary phase 6 is not particularly limited.
Component (A): Component (B) (mass ratio) is preferably 7:3 to 9.5:0.5. When the mass ratio is within this range, there are no grain boundary pores and the insulation is high.
Moreover, when the grain boundary phase 6 as a whole is 100 parts by mass, the total amount of the components (A) and (B) is preferably 85 parts by mass or more.
In addition, the grain boundary phase 6 can contain, for example, alumina particles, zirconia particles, crystallized glass, etc. as other components.

In the grain boundary phase 6, crystals containing Si are preferably present at the interface between the surface of the crystalline inorganic fiber and the glass. Crystals containing Si can be precipitated by adjusting the cooling gradient during heat treatment or by controlling the atmosphere.
The presence of Si-containing crystals can be confirmed by microscopic XRD, XPS, or the like. The presence of Si-containing crystals at the interface increases the adhesion between the soft magnetic metal particles 3, increases the resistance value of the grain boundary phase 6, and further reduces eddy current loss.

(2.2) First Requirement The powder magnetic core 1 of the present invention satisfies the following first requirement when the cross-sectional structure of the powder magnetic core 1 is observed in a square first field of view of 100 μm×100 μm.
The first requirement will be explained. The right diagram of FIG. 1 schematically shows a first field of view of a square of 100 μm×100 μm when observing the cross-sectional structure of the dust core 1 .
A starting point S is a place where the grain boundary phase 6 exists on one side 11 of the square defining the first field of view. From the starting point S on the side 11 of the square to the side 13 opposite to the side 11 of the square, it is found that there are five or more routes (paths) different from each other. This is the first requirement. That is, the first requirement is that there are five or more continuous layers 21 different from each other. It should be noted that when a branch point is reached on the way, the shortest route to reach the opposite side 13 is selected. As long as the number of different routes is 5 or more, there is no upper limit for the number of routes, but the normal upper limit is 30.
FIG. 1 shows five different continuous layers 21A, 21B, 21C, starting from five different starting points S1, S2, S3, S4, S5 on one side 11 and ending at different ending points E1, E2, E3, E4, E5, respectively. 21D and 21E are shown.
If this first requirement is satisfied, many continuous layers 21 are present in the dust core 1 . In the present invention, since crystalline inorganic fibers are present in the grain boundary phase 6, the resistance value of the grain boundary phase 6 increases, and eddy current loss can be reduced. Moreover, when this requirement is satisfied, the dust core 1 has good heat transfer properties. Also, the adjacent soft magnetic metal particles 3 are effectively insulated by the grain boundary phase 6, and the withstand voltage characteristics are improved. Furthermore, the continuous layer 21 of the grain boundary phase 6 binds the soft magnetic metal particles 3 together, improving the mechanical strength of the dust core 1 .
Note that the first requirement may be satisfied in at least one of a plurality of square fields of view of 100 μm×100 μm when observing the cross-sectional structure of the dust core 1 .

(2.3) Second Requirement Next, the second requirement will be described. The second requirement is that the average length of the path from one side 11 to the opposite side 13 of the continuous layer 21 is 115 μm or more.
The average length of the path of the continuous layer 21 is more preferably 120 μm or longer, and even more preferably 130 μm or longer. The upper limit of the average length of the paths of the continuous layer 21 is 150 μm.
In the example of FIG. 1, the second requirement is that the average path length of the continuous layers 21A, 21B, 21C, 21D, and 21E is 115 μm or more.
When this second requirement is satisfied, the average length of the continuous layer 21 is longer than the length of one side of the first field of view of 100 μm. That is, the continuous layer 21 meanders between the paths from the one side 11 to the opposite side 13 . When the continuous layer 21 meanders, the resistance value of the grain boundary phase 6 increases compared to when the continuous layer 21 is linear, and eddy current loss is reduced. Moreover, when this requirement is satisfied, the dust core 1 has good heat transfer properties.
The average length of the continuous layer 21 is controlled by the press pressure or the like during press molding, which will be described later. By applying a pressure of 1 GPa to 2.5 GPa at a temperature of 60° C. to 300° C., the soft magnetic metal particles 3 are intertwined to form a meandering structure.
Note that the second requirement may be satisfied in at least one of a plurality of square fields of view of 100 μm×100 μm when observing the cross-sectional structure of the dust core 1 .

(2.4) Third Requirement Next, the third requirement will be described. The dust core 1 preferably satisfies the following third requirement.
In the third requirement, the cross-sectional structure of the powder magnetic core 1 is observed in a square second field of view of 50 μm×50 μm. The third requirement is that when the area ratio of the crystalline inorganic fiber in the second field of view is S1 and the area ratio of the glass in the second field of view is S2, the value of S1/(S1+S2) is expressed by the following relational expression: It is a requirement that (1) is satisfied.

0.1≦S1/(S1+S2)≦0.3 Expression (1)

If the third requirement is satisfied, the eddy current loss suppression effect will be good. Moreover, when the third requirement is satisfied, the powder magnetic core 1 is dense, and the hysteresis loss can be kept small.
It should be noted that the third requirement may be satisfied in at least one of a plurality of 50 μm×50 μm square fields of view when observing the cross-sectional structure of the dust core 1 .

2. Method for Manufacturing Dust Core 1 The method for manufacturing the dust core 1 is not particularly limited. FIG. 2 shows an example of a method for manufacturing the dust core 1, and this manufacturing method will be described below.
(1) Preparation of Soft Magnetic Metal Powder First, a soft magnetic metal powder (soft magnetic metal particles 3) is prepared as a raw material (step S1).
(2) Heat Treatment Next, the soft magnetic metal powder is heat treated (step S2). Conditions for this heat treatment are not particularly limited. Heat treatment conditions are, for example, heat treatment temperature: 700° C. to 900° C., heating rate: 1° C. to 10° C./min, holding time: 1 minute to 120 minutes, inert atmosphere (N ₂ atmosphere, Ar atmosphere). It is preferably adopted.
(3) Binder coating Next, the soft magnetic metal powder is coated with a binder (step S3). A coating method is not particularly limited, and for example, a spray coating method, a dipping method, and a wet mixing method are preferably used. The binder is obtained by adding crystalline inorganic fibers to glass (for example, water glass) containing sodium silicate as a main component. The binder may be mixed with alumina sol, glass powder, or the like as other components. The coated soft magnetic metal powder is dried, for example, under the conditions of drying temperature: 60° C. to 150° C. and drying time: 30 minutes to 120 minutes.
(4) Molding (press molding)
In order to make the shape of the powder magnetic core 1, press molding (for example, uniaxial mold molding) is usually used (step S4). The molding pressure during press molding is preferably 1.2 GPa to 2.4 GPa, and it is better to press at a high pressure in order to obtain a high-density molded body. Also, the mold may be heated in the range of room temperature to 200° C. during press molding. Heating the mold facilitates plastic deformation of the soft magnetic metal powder, making it possible to obtain a high-density compact. On the other hand, press molding at a temperature exceeding 200° C. is not so preferable in the atmosphere because of the problem of oxidation of the soft magnetic metal powder.

(5) Heat treatment The obtained compact is heat treated (annealed) to release the strain applied during press molding (step S5). Heat treatment conditions include, for example, heat treatment temperature: 700° C. to 900° C., heating rate: 1° C./min to 10° C./min, holding time: 1 minute to 120 minutes, inert atmosphere (N ₂ atmosphere, Ar atmosphere). Conditions are preferably employed.
The heat treatment conditions are changed as appropriate depending on the type of soft magnetic metal powder used.

3. Effects of the dust core 1 of the present embodiment In the dust core 1 of the present embodiment, since the crystalline inorganic fibers are present in the grain boundary phase 6, the resistance value of the grain boundary phase 6 is increased, and eddy current loss is reduced. reduced. Moreover, in this configuration, since the heat transfer property is also good, it is effective as a countermeasure against heat generation when the dust core 1 is applied to a transformer or a motor.
Also, when the value of S1/(S1+S2) satisfies the above formula (1), the eddy current loss suppressing effect and the heat transfer effect are good. Further, according to the present invention, the powder magnetic core 1 is made dense and the hysteresis loss can be kept small.
Further, when the fiber diameter of the crystalline inorganic fiber is 10 nm to 300 nm and the aspect ratio of the crystalline inorganic fiber is 10 or more, the resistance characteristics and heat transfer performance are further improved.
In addition, when crystals containing Si are present at the interfaces, the adhesion between the soft magnetic metal particles 3 increases, and as a result, the resistance value of the grain boundary phase 6 increases, further reducing eddy current loss.

EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples.
Experimental Examples 1 to 17 are examples, and Experimental Examples 18 to 22 are comparative examples.
In the table, experimental examples are indicated using "no." Also, in the table, when "*" is added, such as "18*", it indicates that it is a comparative example.

1. Preparation of dust core (1) Experimental example 1 (no. 1)
Fe-5.5% by mass Si-4.0% by mass Cr particles (average particle size: 5 μm) produced by water atomization were used as the soft magnetic metal particles (raw material powder).
First, the soft magnetic metal powder was heat-treated. The heat treatment conditions were as follows: heat treatment temperature: 450°C, heating rate: 5.0°C/min, holding time: 15 minutes, inert atmosphere (Ar).
The soft magnetic metal particles were then coated with a coating liquid.
Specifically, a mixed slurry (coating liquid) of 1.5 g of water glass, 0.1 g of Al ₂ O ₃ crystalline inorganic fibers (fiber diameter: 350 nm, aspect ratio: 6), and 3.0 g of water was prepared. mixed with metal particles. The surplus slurry was removed so that the surfaces of the soft magnetic metal particles were covered.
Then, the coated soft magnetic metal particles were dried at 60° C. for 60 minutes.
The coated soft magnetic metal powder was then heat treated. The heat treatment conditions were heat treatment temperature: 150° C., temperature increase rate: 5° C./min, holding time: 15 minutes, inert atmosphere (N ₂ ).
Then, press molding was performed at a molding pressure of 1.8 GPa to obtain a molded body (toroidal shape (outer diameter: 8 mm, inner diameter: 4.5 mm, height: 1.5 mm). This molded body was heat treated at a temperature of 250 ° C. Heat treatment was performed at a heating rate of 5° C./min, a holding time of 15 minutes, and an inert atmosphere (Ar).

(2) Experimental Examples 2-14, 18-19 (no.2-14, 18-19)
Example 1 except that the soft magnetic metal particles and crystalline inorganic fibers shown in Table 1 were used, and the heat treatment temperature of 450 ° C. in Experimental Example 1 was changed to 800 ° C. for sendust and 500 ° C. for others. Powder magnetic cores of Experimental Examples 2-14 and 18-19 were obtained in the same manner as above.

(3) Experimental Example 15-17 (no.15-17)
Particles shown in Table 1 were used as the soft magnetic metal particles (raw material powder).
First, the soft magnetic metal powder was heat-treated. Heat treatment temperature: 800° C., heating rate: 5° C./min, holding time: 10 minutes, heat treatment was performed under the conditions of an inert atmosphere (Ar).
The soft magnetic metal particles were then coated with a coating liquid. Specifically, a mixed slurry (coating liquid) of 1.5 g of water glass, 0.1 g of the crystalline inorganic fibers of Al ₂ O ₃ listed in Table 1, and 3.0 g of water was prepared and mixed with soft magnetic metal particles. bottom. The surplus slurry was removed so that the surfaces of the soft magnetic metal particles were covered.
Then, the coated soft magnetic metal particles were dried at 60° C. for 60 minutes.
The coated soft magnetic metal powder was then heat treated. The heat treatment conditions were heat treatment temperature: 250° C., temperature increase rate: 10° C./min, holding time: 60 minutes, and 0.5% oxygen/Ar atmosphere.
Then, press molding was performed at a molding pressure of 1.8 GPa to form a molded body (toroidal shape (outer diameter: 8 mm, inner diameter: 4.5 mm, height: 1 mm). This molded body was heat treated at a temperature of 600 ° C. to 800 ° C. , Heating rate: 10 ° C./min, Holding time: 15 minutes, Cooling rate: 2 ° C./min (up to 500 ° C.), and heat treatment under the conditions of an inert atmosphere. Such a powder magnetic core was obtained.

(4) Experimental Example 20 (no.20)
Sendust particles (average particle diameter: 9 μm) produced by a water atomization method were used as the soft magnetic metal particles (raw material powder).
First, the soft magnetic metal powder was heat-treated. The heat treatment conditions were as follows: heat treatment temperature: 800° C., heating rate: 5° C./min, holding time: 15 minutes, inert atmosphere (Ar).
The soft magnetic metal particles were then coated with a coating liquid. As the coating liquid, a mixture of 3.0 g of alumina sol, 0.1 g of crystalline inorganic fibers of Al ₂ O ₃ (fiber diameter: 500 nm, aspect ratio: 6), and 3 g of water was used. Then, the coated soft magnetic metal particles were dried at 60° C. for 60 minutes.
The coated soft magnetic metal powder was then heat treated. The heat treatment conditions were heat treatment temperature: 250° C., temperature increase rate: 5° C./min, holding time: 15 minutes, inert atmosphere (N ₂ ).
Then, press molding was performed at a molding pressure of 1.8 GPa to obtain a molded body (toroidal shape (outer diameter: 8 mm, inner diameter: 4.5 mm, height: 1.5 mm). This molded body was heat-treated at a temperature of 250 ° C. Heat treatment was performed under the conditions of a temperature rate of 5° C./min, a holding time of 15 minutes, and an inert atmosphere (Ar).

(5) Experimental Example 21-22 (no.21-22)
As soft magnetic metal particles (raw material powder), sendust particles described in Table 1 produced by a water atomization method were used.
First, the soft magnetic metal powder was heat-treated. Heat treatment conditions were as follows: heat treatment temperature: 500° C., heating rate: 5° C./min, holding time: 15 minutes, inert atmosphere (Ar).
The soft magnetic metal particles were then coated with a coating liquid. As the coating liquid, a mixture of 1.5 g of water glass and 3.0 g of water was used. Then, the coated soft magnetic metal particles were dried under the conditions of 60° C. and drying time of 60 minutes.
The coated soft magnetic metal powder was then heat treated. The heat treatment conditions were as follows: heat treatment temperature: 200° C., heating rate: 5° C./min, holding time: 15 minutes, inert atmosphere (Ar).
Then, press molding was performed at a molding pressure of 1.8 GPa to obtain a molded body (toroidal shape (outer diameter: 8 mm, inner diameter: 4.5 mm, height: 1.5 mm). This molded body was heat treated at a temperature of 250 ° C. Heat treatment was carried out at a heating rate of 5° C./min, a holding time of 15 minutes, and an inert atmosphere (Ar) to obtain powder magnetic cores according to Experimental Examples 21 and 22.

2. Evaluation Method of Iron Loss Iron loss was evaluated under the following conditions using the following modified Steinmetz equation for iron loss using a measuring device (BH analyzer, manufactured by Iwasaki Tsushinki Co., Ltd., model number SY-8218).

Core conditions: outer diameter φ8 mm - inner diameter φ4.5 mm thickness 1.5 mm
Enameled wire φ0.3 15 rolls Bifilar roll

Evaluation was performed as follows.

Hysteresis loss (kW/m ³ )
"☆" ... less than 600 "◎" ... 600 or more and less than 700 "○" ... 700 or more and less than 800 "△" ... 800 or more and less than 900 "×" ... 900 or more

Eddy current loss (kW/m ³ )
"☆" ... less than 15 "◎" ... 15 or more and less than 30 "○" ... 30 or more and less than 50 "△" ... 50 or more and less than 80 "×" ... 80 or more

3. Evaluation Results Table 1 shows the evaluation results.
Experimental Example 1-17, which is an example, satisfies the following requirements (a), (b), (c), and (d).
Requirement (a): The average particle size of the soft magnetic metal particles is 5 μm or more and 30 μm or less.
Requirement (b): The grain boundary phase contains glass containing sodium silicate as a main component.
• Requirement (c): The grain boundary phase contains crystalline inorganic fibers.
Requirement (d): The grain boundary phase is formed continuously, has 5 or more continuous layers different from each other (corresponding to the first requirement of (2.2)), and the average length of the continuous layer is 115 μm This is the above (corresponding to the second requirement of (2.3)).
In contrast, Experimental Examples 18-21, which are comparative examples, do not satisfy the following requirements.
In Experimental Example 18, requirements a and d are not satisfied.
Experimental Example 19 does not satisfy the requirement a.
Experimental example 20 does not satisfy the requirement b.
Experimental Example 21 does not satisfy the requirement c.
Experimental Example 22 does not satisfy the requirement c.

Experimental Example 1-17, which is an example, had less eddy current loss than Comparative Example 18-21.
Further, among experimental examples 1-17, experimental example 6-17, which further satisfies the following requirement (e), had less eddy current loss.
Among experimental examples 6 to 17, experimental examples 11 to 17, which further satisfy the following requirements (f) and (g), had smaller hysteresis loss and eddy current loss.
Further, among Experimental Examples 11 to 17 which are examples, Experimental Examples 15 to 17, which further satisfy the following requirement (h), had less eddy current loss.

Requirement (e): The value of S1/(S1+S2) satisfies the following relational expression (corresponding to the third requirement of (2.4)).
0.1≦S1/(S1+S2)≦0.3
Requirement (f): The fiber diameter of the crystalline inorganic fiber is 10 nm or more and 300 nm or less.
Requirement (g): The aspect ratio of the crystalline inorganic fiber is 10 or more.
Requirement (h): Si-containing crystals (silicate compounds) are present at the interface between the surface of the crystalline inorganic fiber and the glass.

4. Effect of Example The powder magnetic core of this example had low hysteresis loss and low eddy current loss.

The present invention is not limited to the embodiments detailed above, and various modifications and changes are possible within the scope of the claims of the present invention.

The powder magnetic core of the present invention is particularly suitable for applications such as motor cores, transformers, choke coils, and noise absorbers.

1 ... Dust core 3 ... Soft magnetic metal particles 6 ... Grain boundary phase 11 ... One side 13 ... Opposite side 21 ... Continuous layer S (S1 to S5) ... Start point E (E1 to E5) ... End point

Claims (3)

A powder magnetic core comprising soft magnetic metal particles having an average particle size of 5 μm or more and 30 μm or less and a grain boundary phase,
The grain boundary phase comprises (A) a glass containing sodium silicate as a main component and (B) a crystalline inorganic fiber,
When the cross-sectional structure of the powder magnetic core is observed in a square first field of view of 100 μm × 100 μm, on one side of the square defining the first field of view, the place where the grain boundary phase exists is the starting point of the square The grain boundary phase is formed continuously up to the side opposite to the one side, and has five or more continuous layers different from each other,
The average length of the path from the one side to the opposite side of the continuous layer is 115 μm or more,
A powder magnetic core, wherein the soft magnetic metal particles are selected from the group consisting of Fe--Si--Cr alloy particles, sendust particles, permalloy particles, and Fe-based amorphous alloy particles. The crystalline inorganic fiber has a fiber diameter of 10 nm or more and 300 nm or less,
2. The dust core according to claim 1, wherein the crystalline inorganic fibers have an aspect ratio of 10 or more. 3. The dust core according to claim 1 , wherein crystals containing Si are present at the interface between the surface of the crystalline inorganic fiber and the glass.

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