Rare earth-iron-nitrogen-based magnetic powder, compound for bonded magnet, bonded magnet, and method for producing rare earth-iron-nitrogen-based magnetic powder

Patent metadata

Field	Value
Publication number	US-11990259-B2
Application number	US-202118013072-A
Country	US
Kind code	B2
Filing date	Mar 31, 2021
Priority date	Jun 29, 2020
Publication date	May 21, 2024
Grant date	May 21, 2024

Abstract

A rare earth-iron-nitrogen-based magnetic powder according to this invention contains, as main constituent components, a rare-earth element (R), iron (Fe), and nitrogen (N). Moreover, this magnetic powder has an average particle size of 1.0-10.0 μm, and contains 22.0-30.0 mass % of a rare-earth element (R) and 2.5-4.0 mass % of nitrogen (N). Further, this magnetic powder includes: a core part having any one crystal structure among a Th 2 Zn 17 type, a Th 2 Ni 17 type, and a TbCu 7 type; and a shell layer provided on the surface of the core part and having a thickness of 1-30 nm. The shell layer contains a rare-earth element (R) and iron (Fe) so that the R/Fe atomic ratio is 0.3-5.0, and further contains 0-10 at % (exclusive of 0) of nitrogen (N). Furthermore, this magnetic powder contains compound particles composed of a rare-earth element (R) and phosphorus (P).

First claim

The invention claimed is:

1. A rare earth-iron-nitrogen-based magnetic powder comprising a rare earth element (R), iron (Fe), and nitrogen (N) as main constituents,
the magnetic powder having an average particle size of 1.0 μm or more and 10.0 μm or less and having a rare earth element (R) content of 22.0% by mass or more and 30.0% by mass or less and a nitrogen (N) content of 2.5% by mass or more and 4.0% by mass or less,
the magnetic powder comprising magnetic particles comprising: a core having a crystal structure selected from the group consisting of Th 2 Zn 17 -type, Th 2 Ni 17 -type, and TbCu 7 -type crystal structures; and a shell layer having a thickness of 1 nm or more and 30 nm or less and provided on a surface of the core,
the shell layer containing a rare earth element (R) and iron (Fe) in an atomic ratio R/Fe of 0.3 or more and 5.0 or less and having a nitrogen (N) content of more than 0 at % and 10 at % or less,
the magnetic powder further comprising particles of a compound comprising a rare earth element (R) and phosphorus (P).

2. The magnetic powder according to claim 1 , wherein
the shell layer has a two-layer structure comprising an outer layer and an inner layer,
the outer layer comprises oxygen (O) and calcium (Ca) in addition to the rare earth element (R), iron (Fe), and nitrogen (N), and
the inner layer comprises oxygen (O) in addition to the rare earth element (R), iron (Fe), and nitrogen (N) and is free of calcium (Ca).

3. The magnetic powder according to claim 2 , wherein
the shell layer has a two-layer structure comprising an outer layer and an inner layer, and
the outer layer has an atomic ratio R/Fe of A, the inner layer has an atomic ratio R/Fe of B, and B<A is satisfied.

4. The magnetic powder according to claim 1 , comprising samarium (Sm) as the rare earth element (R).

5. The magnetic powder according to claim 1 , further comprising a phosphoric acid-derived compound coating on uppermost surfaces of the magnetic particles.

6. The magnetic powder according to claim 1 , having a rate of coercive force retention of 70% or more that is calculated as the percentage ratio (H c,300 /H c ) of the coercive force (H c,300 ) of the magnetic powder measured after the magnetic powder is heated at 300° C. for 1 hour in an argon (Ar) atmosphere to the coercive force (H c ) of the magnetic powder measured before the heating.

7. A compound for forming a bonded magnet, the compound comprising: the magnetic powder according to claim 1 ; and a resin binder.

8. A bonded magnet comprising: the magnetic powder according to claim 1 ; and a resin binder.

9. A method for producing the rare earth-iron-nitrogen-based magnetic powder according to claim 1 , the method comprising:
a preparation step that comprises preparing rare earth oxide particles and rare earth-iron alloy particles having a crystal structure selected from the group consisting of Th 2 Zn 17 -type, Th 2 Ni 17 -type, and TbCu 7 -type crystal structures;
a mixing step that comprises mixing 100 parts by mass of the rare earth-iron alloy particles with 1 to 20 parts by mass of the rare earth oxide particles so as to form a raw material mixture comprising rare earth-iron alloy particles with a particle size of 15.0 μm or less and rare earth oxide particles with a particle size of 2.0 μm or less;
a reduction-diffusion treatment step that comprises adding to, and mixing with the raw material mixture, a reducing agent in an amount 1.1 to 10.0 times an equivalent of the reducing agent required to reduce an oxygen component in the raw material mixture and comprises heating the mixture of the reducing agent and the raw material mixture at a temperature in a range of 730° C. to 1,050° C. in a non-oxidizing atmosphere to produce a reduction-diffusion reaction product; and
a heating and nitriding step that comprises heating and nitriding the reduction-diffusion reaction product at a temperature in a range of 300° C. to 500° C. in a gas stream comprising nitrogen and/or ammonia to form a nitridation reaction product, wherein
one or both of the preparation step and the mixing step comprise forming a phosphoric acid-derived compound coating on the rare earth-iron alloy particles.

10. The method according to claim 9 , wherein the mixing step comprises mixing and crushing the rare earth-iron alloy particles and the rare earth oxide particles in a crushing solvent containing a phosphoric acid-based surface treatment agent to form a phosphoric acid-derived compound coating on the rare earth-iron alloy particles.

11. The method according to claim 9 , further comprising the step of subjecting the reduction-diffusion reaction product to disintegration treatment before the heating and nitriding.

12. The method according to claim 9 , further comprising a wet treatment step that comprises placing the reduction-diffusion reaction product and/or the nitridation reaction product in a washing liquid comprising water and/or a glycol to allow the reduction-diffusion reaction product and/or the nitridation reaction product to disintegrate and thus to reduce the content of a reducing agent-derived component in the reduction-diffusion reaction product and/or the nitridation reaction product.

13. The method according to claim 9 , further comprising the step of forming a phosphoric acid-derived compound coating on a surface of a product resulting from the heating and nitriding.

14. The method according to claim 9 , wherein the raw material mixture has a weight loss on heating of less than 1% by mass.

15. The method according to claim 9 , wherein heating the mixture of the reducing agent and the raw material mixture is performed for 0 to 10 hours to produce the reduction-diffusion reaction product.

16. The magnetic powder according to claim 2 , comprising samarium (Sm) as the rare earth element (R).

17. The magnetic powder according to claim 2 , further comprising a phosphoric acid-derived compound coating on uppermost surfaces of the magnetic particles.

18. The magnetic powder according to claim 2 , having a rate of coercive force retention of 70% or more that is calculated as the percentage ratio (H c,300 /H c ) of the coercive force (H c,300 ) of the magnetic powder measured after the magnetic powder is heated at 300° C. for 1 hour in an argon (Ar) atmosphere to the coercive force (H c ) of the magnetic powder measured before the heating.

19. A compound for forming a bonded magnet, the compound comprising: the magnetic powder according to claim 2 ; and a resin binder.

20. A bonded magnet comprising: the magnetic powder according to claim 2 ; and a resin binder.

Assignees

• Univ Tohoku
• Sumitomo Metal Mining Co

Inventors

• Sugimoto Satoshi
• Matsuura Masashi
• Ishikawa Takashi
• Yoneyama Yukinobu

Classifications

• H01F1/0551 Primary

  in the form of particles, e.g. rapid quenched powders or ribbon flakes · CPC title

• B22F1/05

  Metallic powder characterised by the size or surface area of the particles · CPC title

• B22F1/10

  Metallic powder containing lubricating or binding agents; Metallic powder containing organic material · CPC title

• C08K9/02

  Ingredients treated with inorganic substances · CPC title

• C22C38/001

  containing N · CPC title