# US 7,608,153 B2 · Rare earth magnet and method therefor

> Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt

- Number: US 7,608,153 B2
- Document ID: US7608153B2
- Status: Granted
- Kind: B2
- Application number: 11/017,010
- Filed: 2004-12-21
- Published: 2005-06-23
- Granted: 2009-10-27
- Earliest claimed: 2003-12-22
- Assignees: Nissan Motor Co., Ltd.
- Applicants: Takae Ono, legal representative
- Inventors: Tetsurou Tayu; Hideaki Ono; Yoshio Kawashita; Makoto Kano; Munekatsu Shimada
- Web page: https://patentgrep.com/patent/US7608153B2

## CPC

- H01F 1/0576: {pressed, e.g. hot working}
- H01F 1/08: pressed, sintered, or bound together
- H02K 1/02: characterised by the magnetic material
- H02K 1/2781: Magnets shaped to vary the mechanical air gap between the magnets and the stator
- H01F: MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
- H02K: DYNAMO-ELECTRIC MACHINES (dynamo-electric relays H01H53/00; conversion of DC or AC input power into surge output power {H03K3/53})

## Abstract

A rare earth magnet includes rare earth magnet particles; and amorphous and/or crystalline terbium oxide present at the boundary of the rare earth magnet particles and represented by the formula: TbOn, wherein 1.5<n≦2. The rare earth magnet prevents decrease eddy current effectively.

## Claims

### Claim 1

A rare earth magnet, comprising:
rare earth magnet particles; and
amorphous and/or crystalline terbium oxide present at a boundary of the rare earth magnet particles and represented by the formula: TbOn, wherein 1.5 <n≦2;
wherein said rare earth magnet particles are connected by said terbium oxide, and wherein individual rare earth magnet particles comprise a cluster of fine crystal grains;
wherein the terbium oxide is contained in an amount of 1 to 10 wt % based on a weight of the rare earth magnet.

### Claim 2 (depends on 1)

A rare earth magnet according to claim 1, which is obtained by hotforming magnet powder to produce a rare earth magnet having terbium oxide bound to whole of or a part of the surface of the rare earth magnet particles.

### Claim 3 (depends on 2)

A rare earth magnet according to claim 2, wherein the terbium oxide bound to the surface of the rare earth magnet particles is obtained by hydrolyzing terbium alkoxide placed on the surface of the rare earth magnet particles.

### Claim 4 (depends on 1)

A rare earth magnet according to claim 1, wherein an average diameter of the rare earth magnet particles is from 1 to 500 μm.

### Claim 5 (depends on 1)

A rare earth magnet according to claim 1, wherein the rare earth magnet is a Nd—Fe—B type magnet.

### Claim 6 (depends on 1)

A rare earth magnet according to claim 1, wherein the rare earth magnet is an anisotropic magnet.

### Claim 7

A method for producing a rare earth magnet, comprising:
a coating process of covering whole of or a part of a surface of rare earth magnet powder with terbium alkoxide by applying a liquid including the terbium alkoxide to the surface of the rare earth magnet powder under a dry atmosphere;
a hydrolysis process of hydrolyzing the terbium alkoxide at the surface of the rare earth magnet powder to obtain a first intermediate magnetic powder;
a heating process of heat-treating the first intermediate magnetic powder under a vacuum atmosphere or an inert gas atmosphere to obtain a second intermediate magnetic powder;
a filling process of filling the second intermediate magnetic powder into a mold; and
a molding process of molding the second intermediate magnetic powder filled in the mold to produce a rare earth magnet comprising rare earth magnet particles and amorphous and/or crystalline terbium oxide present at a boundary of the rare earth magnet particles represented by the formula: TbOn, wherein 1.5 <n≦2;
wherein said rare earth magnet particles are connected by said terbium oxide, and at least one rare earth magnetic particle comprises a cluster of fine crystal grains;
wherein the terbium oxide is contained in an amount of 1 to 10 wt % based on a weight of the rare earth magnet.

### Claim 8 (depends on 7)

A method for producing the rare earth magnet according to claim 7, wherein the hydrolysis process is a process of hydrolyzing the terbium alkoxide at the surface of the rare earth magnet powder by exposing the rare earth magnet powder covered with the terbium alkoxide to water-containing gas to obtain the first intermediate magnetic powder.

### Claim 9 (depends on 7)

A method for producing the rare earth magnet according to claim 7, wherein the rare earth magnet powder is an anisotropic magnet powder, and which further comprises between the heating process and the molding process a premolding process of premolding the rare earth magnet powder while subjecting the rare earth magnet powder to magnetic field orientation.

### Claim 10 (depends on 1)

A motor comprising the rare earth magnet of claim 1.

### Claim 11 (depends on 1)

The rare earth magnet according to claim 1, wherein said rare earth magnet particles are produced from an anisotropic rare earth magnet powder by use of an HDDR method or by use of hot deformation.

### Claim 12 (depends on 1)

The rare earth magnet according to claim 1, wherein a grain size of said crystal grains is not more than 500 nm.

### Claim 13 (depends on 1)

The rare earth magnet of claim 1, wherein the rare earth magnet exhibits an electrical resistivity within a range from 22.0 μΩm to 82.0 μΩm.

### Claim 14 (depends on 13)

The rare earth magnet of claim 13, wherein the rare earth magnet further exhibits a coercive force of 0.91 to 0.96 MA/m.