# US 2021/0241950 A1 · Iron oxide magnetic powder and manufacturing method therefor

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- Number: US 2021/0241950 A1
- Document ID: US20210241950A1
- Status: Published application
- Kind: A1
- Application number: 17/051,979
- Filed: 2019-07-17
- Published: 2021-08-05
- Earliest claimed: 2018-07-17
- Assignees: Korea Institute of Machinery & Materials
- Applicants: Korea Institute of Machinery & Materials
- Inventors: Youn Kyoung BAEK; Jung Goo LEE; Kyung Min KIM; Young Kuk KIM; Min Ji PYO
- Web page: https://patentgrep.com/patent/US20210241950A1

## CPC

- H01F 1/11: in the form of particles {(for magnetic record carriers G11B5/70626)}
- B22F 1/07: Metallic powder characterised by particles having a nanoscale microstructure (nanosized particles B22F1/054)
- B22F 9/08: by casting, e.g. through sieves or in water, by atomising or spraying (using electric discharge B22F9/14)
- C01B 33/12: Silica; Hydrates thereof, e.g. lepidoic silicic acid
- C01G 49/06: Ferric oxide [Fe2O3]
- H01F 1/0045: {Zero dimensional, e.g. nanoparticles, soft nanoparticles for medical/biological use (preparation of fullerenes in general C01B32/15)}
- H01F 1/0054: {Coated nanoparticles, e.g. nanoparticles coated with organic surfactant}
- B22F 2302/256: Silicium oxide (SiO2)
- C01P 2002/72: by d-values or two theta-values, e.g. as X-ray diagram
- C01P 2002/78: by stacking-plane distances or stacking sequences
- C01P 2004/01: depicted by an image
- C01P 2004/03: obtained by SEM
- C01P 2004/64: Nanometer sized, i.e. from 1-100 nanometer
- C01P 2006/42: Magnetic properties
- H01F: MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
- 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
- C01B: NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; {METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C}
- C01G: COMPOUNDS CONTAINING METALS NOT COVERED BY SUBCLASSES C01D OR C01F (metal hydrides {monoborane, diborane or addition complexes thereof} C01B6/00; salts of oxyacids of halogens C01B11/00; peroxides, salts or peroxyacids C01B15/00; thiosulfates, dithionites, polythionates C01B17/64; compounds containing selenium, or tellurium C01B19/00; binary compounds of nitrogen with metals C01B21/06; azides C01B21/08; {compounds containing nitrogen, other non-metals and metal C01B21/082}; metal amides C01B21/092; nitrites C01B21/50; {compounds of noble gases C01B23/0005}; phosphides C01B25/08; salts of oxyacids of phosphorus C01B25/16; carbides C01B32/90; compounds containing silicon C01B33/00; compounds containing boron C01B35/00; compounds having molecular sieve properties but not having base-exchange properties C01B37/00; compounds having molecular sieve and base-exchange properties, e.g. crystalline zeolites, C01B39/00; cyanides C01C3/08; salts of cyanamide C01C3/16; thiocyanates C01C3/20)
- C01P: INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS

## Abstract

The present invention relates to a method for producing a magnetic powder, including: preparing a precursor solution containing an iron precursor and a silica precursor; spraying the precursor solution to form iron/silica precursor droplets; drying the iron/silica precursor droplets to produce iron/silica precursor particles; and heat treating the iron/silica precursor particles to produce an iron oxide/silica composite powder in which iron oxide particles are embedded in a silica matrix. The present invention also relates to a magnetic powder produced by the method. The present invention may provide an iron oxide magnetic powder that does not use rare earth elements and a method for producing the same.

## Claims

### Claim 1

A magnetic powder, comprising:
a silica matrix; and
particles of an iron oxide embedded in the silica matrix,
wherein the particles of the iron oxide comprises particles of a hard magnetic iron oxide, and wherein the particles of the hard magnetic iron oxide are ε-Fe2O3.

### Claim 2 (depends on 1)

The magnetic powder of claim 1, wherein a proportion of the particles of the hard magnetic iron oxide in the iron oxide corresponds to 70 to 100%, a proportion of the remaining iron oxide other than the hard magnetic iron oxide in the iron oxide corresponds to 0 or greater than 0 and less than 30%, and wherein the remaining iron oxide is α-Fe2O3.

### Claim 3 (depends on 1)

The magnetic powder of claim 1, wherein a diameter of the particles of the iron oxide is 20 to 45 nm.

### Claim 4 (depends on 1)

The magnetic powder of claim 1, wherein a value of a full width at half-maximum (FWHM) of the ε-Fe2O3 is 0.36° to 0.53°.

### Claim 5 (depends on 4)

The magnetic powder of claim 4, wherein the value of the FWHM of the ε-Fe2O3 is 0.40° to 0.53°.

### Claim 6 (depends on 5)

The magnetic powder of claim 5, wherein the value of the FWHM of the ε-Fe2O3 is an FWHM of a diffraction peak with respect to a {122} plane, which is a main peak of a crystal phase of the ε-Fe2O3.

### Claim 7

A magnetic powder, comprising:
particles of an iron oxide,
wherein the particles of the iron oxide comprise particles of a hard magnetic iron oxide, and wherein the particles of the hard magnetic iron oxide are ε-Fe2O3.

### Claim 8 (depends on 7)

The magnetic powder of claim 7, wherein a proportion of the particles of the hard magnetic iron oxide in the particles of the iron oxide corresponds to 70 to 100%, a proportion of the remaining iron oxide other than the hard magnetic iron oxide in the particles of the iron oxide corresponds to 0 or greater than 0 and less than 30%, and wherein the remaining iron oxide is α-Fe2O3.

### Claim 9 (depends on 7)

The magnetic powder of claim 7, wherein a diameter of the particles of the iron oxide is 20 to 45 nm.

### Claim 10 (depends on 7)

The magnetic powder of claim 7, wherein a value of a full width at half-maximum (FWHM) of the ε-Fe2O3 is 0.36° to 0.53°.

### Claim 11 (depends on 10)

The magnetic powder of claim 10, wherein the value of the FWHM of the ε-Fe2O3 is 0.40° to 0.53°.

### Claim 12 (depends on 11)

The magnetic powder of claim 11, wherein the value of the FWHM of the ε-Fe2O3 is an FWHM of a diffraction peak with respect to a {122} plane, which is a main peak of a crystal phase of the ε-Fe2O3.

### Claim 13

A method for producing a magnetic powder, comprising:
preparing a precursor solution containing an iron precursor and a silica precursor;
spraying the precursor solution to form iron/silica precursor droplets;
drying the iron/silica precursor droplets to produce iron/silica precursor particles; and
heat treating the iron/silica precursor particles to produce an iron oxide/silica composite powder in which iron oxide particles are embedded in a silica matrix.

### Claim 14 (depends on 13)

The method of claim 13, further comprising:
producing an iron oxide powder by removing the silica matrix of the iron oxide/silica composite powder through a washing process.

### Claim 15 (depends on 13)

The method of claim 13, wherein a temperature of the heat treating is 1080 to 1210° C.

### Claim 16 (depends on 15)

The method of claim 15, wherein the temperature of the heat treating is 1080 to 1150° C.

### Claim 17 (depends on 13)

The method of claim 13, wherein a concentration of the iron precursor in the precursor solution is 15 to 60 mol % compared to 1 mol % of the silica precursor.