# US 12,110,577 B2 · Dust core

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- Number: US 12,110,577 B2
- Document ID: US12110577B2
- Status: Granted
- Kind: B2
- Application number: 17/421,201
- Filed: 2020-03-11
- Published: 2022-02-24
- Granted: 2024-10-08
- Earliest claimed: 2019-03-22
- Assignees: Niterra Co., Ltd.
- Applicants: Ngk Spark Plug Co., Ltd.
- Inventors: Hiroshi Watanabe; Satoshi Mori; Manami Fujii; Katsuya Takaoka; Hiroki Takeuchi; Hisashi Kozuka
- Web page: https://patentgrep.com/patent/US12110577B2

## CPC

- C22C 38/02: containing silicon
- B22F 1/00: Metallic powder; Treatment of metallic powder, e.g. to facilitate working or to improve properties
- B22F 1/05: Metallic powder characterised by the size or surface area of the particles
- B22F 1/052: characterised by a mixture of particles of different sizes or by the particle size distribution
- B22F 1/105: containing inorganic lubricating or binding agents, e.g. metal salts
- B22F 1/16: Metallic particles coated with a non-metal (coated with lubricating or binding agents or with organic material B22F1/10)
- C22C 38/18: containing chromium
- H01F 1/20: in the form of particles, e.g. powder (H01F1/147 takes precedence)
- H01F 1/24: the particles being insulated
- B22F 2003/248: {Thermal after-treatment}
- B22F 2301/35: Iron
- B22F 2302/253: Aluminum oxide (Al2O3)
- B22F 2304/10: Micron size particles, i.e. above 1 micrometer up to 500 micrometer
- B22F 2998/10: Processes characterised by the sequence of their steps
- C22C 2200/02: Amorphous
- C22C: ALLOYS (treatment of alloys C21D, C22F)
- B22F: WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER (making alloys by powder metallurgy C22C); APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
- H01F: MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES

## Abstract

The iron loss of a dust core is reduced. A dust core (1) includes soft magnetic metal particles (3) having an average particle size of 5 μm or more and 30 μm or less, and a particle boundary phase (6). The particle boundary phase (6) includes a polycrystalline compound containing Al (aluminum). When a sectional structure of the dust core (1) is observed, an area percentage of α-Al2O3 in the particle boundary phase (6) is 75% or less. An average thickness Ta of the particle boundary phase (6) is 10 nm or more and 300 nm or less. According to the present invention, the iron loss is reduced.

## Claims

### Claim 1

A dust core comprising soft magnetic metal particles and a particle boundary phase, the soft magnetic metal particles having an average particle size of 5 μm or more and 30 μm or less,
wherein the particle boundary phase includes a polycrystalline compound containing Al (aluminum),
when a sectional structure of the dust core is observed, an area percentage of α-Al2O3 in the particle boundary phase is 75% or less,
when the sectional structure of the dust core is observed in a first field of view of a 150 μm×150 μm square, and when, in a region where the particle boundary phase is located in an H-letter shape, two intersecting points where two vertical lines and one horizontal line that constitute the H letter intersect are connected with a straight line, and a perpendicular bisector of the straight line is drawn, a crossing width at a position where the perpendicular bisector crosses the particle boundary phase is defined as a thickness Tn of the particle boundary phase, and
when the thickness of the particle boundary phase is measured at five positions to respectively determine Tn (where n is an integer of 1 to 5), and an average thickness Ta which is an average of Tn (where n is an integer of 1 to 5) is calculated,
the average thickness Ta is 10 nm or more and 300 nm or less.

### Claim 2 (depends on 1)

The dust core according to claim 1, wherein
when a ratio of an amount of Al to an amount of oxygen in the particle boundary phase is measured, Al:O (molar ratio) is 2.0:2.5 to 2.0:2.9.

### Claim 3 (depends on 1)

The dust core according to claim 1,
wherein when the sectional structure of the dust core is observed in a second field of view of a 100 μm×100 μm square, the particle boundary phase is continuously formed from a start point at which the particle boundary phase is present on one side of the square defining the second field of view to a side opposing the one side of the square, and the dust core has five or more continuous layers that are different from each other, and
an average length of paths of the continuous layers from the one side to the opposing side is 115 μm or more.

### Claim 4 (depends on 1)

The dust core according to claim 1,
wherein when the sectional structure of the dust core is observed in a third field of view of a 100 μm×100 μm square, and an area percentage P (%) of pores in the third field of view is determined,
a difference between P1 and P2 is 3% or less,
where P1 represents a maximum value of the area percentage P, and P2 represents a minimum value of the area percentage P.

### Claim 5 (depends on 1)

The dust core according to claim 1,
wherein when the sectional structure of the dust core is observed, an area percentage S(Al) of the polycrystalline compound containing Al (aluminum) in the particle boundary phase is 85% or more and 100% or less, and
when, in the area percentage S(Al), an area percentage S(α) of α-Al2O3 is represented by A %, an area percentage S(γ) of γ-Al2O3 is represented by B %, and an area percentage S(o) of Al2O3 having another crystal structures is represented by C %, 80≤A+B≤100 (where 0≤A≤40, 40≤B≤100) and 0≤C≤20 (A+B+C=100).