# US 12,183,495 B2 · Magnetoplumbite-type hexagonal ferrite and method for producing radio wave absorber

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- Number: US 12,183,495 B2
- Document ID: US12183495B2
- Status: Granted
- Kind: B2
- Application number: 17/176,279
- Filed: 2021-02-16
- Published: 2021-06-03
- Granted: 2024-12-31
- Earliest claimed: 2018-08-28
- Assignees: FUJIFILM Corporation
- Applicants: FUJIFILM Corporation
- Inventors: Hirokazu Hashimoto
- Web page: https://patentgrep.com/patent/US12183495B2

## CPC

- H01F 1/348: {Hexaferrites with decreased hardness or anisotropy, i.e. with increased permeability in the microwave (GHz) range, e.g. having a hexagonal crystallographic structure}
- H01F 1/37: in a bonding agent
- H05K 9/0075: {Magnetic shielding materials}
- H01F: MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
- H05K: PRINTED CIRCUITS; CASINGS OR CONSTRUCTIONAL DETAILS OF ELECTRIC APPARATUS; MANUFACTURE OF ASSEMBLAGES OF ELECTRICAL COMPONENTS

## Abstract

A method for producing a powder of a magnetoplumbite-type hexagonal ferrite which is an aggregate of particles of a compound represented by Formula (1), the method including: a step A of adjusting a pH of an aqueous solution containing a Fe salt, an Al salt, and at least one metal element salt selected from the group consisting of a Sr salt, a Ba salt, a Ca salt, and a Pb salt to exceed 8.0, thereby obtaining a reaction product; a step B of drying the reaction product obtained in the step A, thereby obtaining a dried product; and a step C of firing the dried product obtained in Step B, thereby obtaining a fired product, and application. In Formula (1), A represents at least one metal element selected from the group consisting of Sr, Ba, Ca, and Pb, and x satisfies 1.5≤x≤8.0. AFe(12-x)AlxO19 Formula (1)

## Claims

### Claim 1

A method for producing a powder of a magnetoplumbite-type hexagonal ferrite which is an aggregate of particles of a compound represented by Formula (1), the method comprising:
a step A of adjusting a pH of an aqueous solution containing a Fe salt, an Al salt, and at least one metal element salt selected from the group consisting of a Sr salt, a Ba salt, a Ca salt, and a Pb salt to exceed 8.0, thereby obtaining a reaction product;
a step B of drying the reaction product obtained in the step A, thereby obtaining a dried product; and
a step C of firing the dried product obtained in Step B, thereby obtaining a fired product,
AFe(12-x)AlxO19 Formula (1)
in Formula (1), A represents at least one metal element selected from the group consisting of Sr, Ba, Ca, and Pb, and x satisfies 1.5≤x≤8.0,
wherein, in the step A, a liquid temperature of the aqueous solution is 15° C. to 40° C.

### Claim 2 (depends on 1)

The method for producing a powder of a magnetoplumbite-type hexagonal ferrite according to claim 1,
wherein the at least one metal element salt is selected from the group consisting of a Sr salt, a Ba salt, and a Ca salt.

### Claim 3 (depends on 1)

The method for producing a powder of a magnetoplumbite-type hexagonal ferrite according to claim 1,
wherein the at least one metal element salt includes a Sr salt.

### Claim 4 (depends on 1)

The method for producing a powder of a magnetoplumbite-type hexagonal ferrite according to claim 1,
wherein, in the step A, the pH of the aqueous solution is adjusted to be 9.5 or more to obtain the reaction product.

### Claim 5 (depends on 1)

The method for producing a powder of a magnetoplumbite-type hexagonal ferrite according to claim 1,
wherein, in the step A, the pH of the aqueous solution is adjusted to be 9.0 or more to obtain the reaction product.

### Claim 6 (depends on 1)

The method for producing a powder of a magnetoplumbite-type hexagonal ferrite according to claim 1,
wherein x in Formula (1) satisfies 1.5≤x≤3.0.

### Claim 7 (depends on 1)

A method for producing a radio wave absorber, the method comprising:
a step I of obtaining a powder of a magnetoplumbite-type hexagonal ferrite by the method for producing a powder of a magnetoplumbite-type hexagonal ferrite according to claim 1; and
a step II of forming a molded body using a composition for a radio wave absorber containing the powder of the magnetoplumbite-type hexagonal ferrite obtained in the step I, and a binder.