# US 10,504,640 B2 · Iron nitride materials and magnets including iron nitride materials

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- Number: US 10,504,640 B2
- Document ID: US10504640B2
- Status: Granted
- Kind: B2
- Application number: 14/900,944
- Filed: 2014-06-24
- Published: 2016-05-19
- Granted: 2019-12-10
- Earliest claimed: 2013-06-27
- Assignees: Regents of the University of Minnesota
- Applicants: Regents of the University of Minnesota; Jian-Ping Wang; Yanfeng Jiang
- Inventors: Jian-Ping Wang; Yanfeng Jiang
- Web page: https://patentgrep.com/patent/US10504640B2

## CPC

- H01F 1/047: Alloys characterised by their composition
- B22F 9/04: starting from solid material, e.g. by crushing, grinding or milling ({C22C1/1084 takes precedence}; crushing, grinding or milling, in general, see the relevant subclasses, e.g. B02C)
- C22C 38/00: Ferrous alloys, e.g. steel alloys (cast-iron alloys C22C37/00)
- C22C 38/001: {containing N}
- H01F 1/086: {sintered}
- H01F 41/0266: {Moulding; Pressing (H01F41/0273 takes precedence; hard magnetic particles H01F1/06, H01F1/11)}
- B22F 2998/10: Processes characterised by the sequence of their steps
- B22F 2999/00: Aspects linked to processes or compositions used in powder metallurgy
- C22C 2202/02: Magnetic
- 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
- C22C: ALLOYS (treatment of alloys C21D, C22F)

## Abstract

The disclosure describes magnetic materials including iron nitride, bulk permanent magnets including iron nitride, techniques for forming magnetic materials including iron nitride, and techniques for forming bulk permanent magnets including iron nitride.

## Claims

### Claim 1

A method comprising:
heating a mixture including iron and nitrogen to form a molten iron nitride-containing material and thereby forming the molten iron nitride-containing material; and
casting, quenching, and pressing the molten iron nitride-containing material to form a workpiece including at least one Fe8N phase domain.

### Claim 2 (depends on 1)

The method of claim 1, wherein casting, quenching, and pressing comprises continuously casting, quenching, and pressing the molten iron nitride-containing material to form a workpiece having a dimension that is longer than other dimensions of the workpiece.

### Claim 3 (depends on 1)

The method of claim 1, further comprising:
milling, in a bin of a rolling mode milling apparatus, a stirring mode milling apparatus, or a vibration mode milling apparatus, an iron-containing raw material in the presence of a nitrogen source to generate a powder including iron nitride, and
wherein heating the mixture including iron and nitrogen comprises heating the powder including iron nitride.

### Claim 4 (depends on 3)

The method of claim 3, wherein the nitrogen source comprises at least one of ammonium nitrate, an amide-containing material, or a hydrazine-containing material.

### Claim 5 (depends on 4)

The method of claim 4, wherein the at least one of the amide-containing or hydrazine-containing material comprises at least one of a liquid amide, a solution containing an amide, a hydrazine, or a solution containing hydrazine.

### Claim 6 (depends on 4)

The method of claim 4, wherein the at least one of the amide-containing or hydrazine-containing material comprises at least one of carbamide, methanamide, benzamide, or acetamide.

### Claim 7 (depends on 3)

The method of claim 3, wherein the iron-containing raw material comprises substantially pure iron.

### Claim 8 (depends on 3)

The method of claim 3, further comprising adding a catalyst to the iron-containing raw material.

### Claim 9 (depends on 8)

The method of claim 8, wherein the catalyst comprises at least one of nickel or cobalt.

### Claim 10 (depends on 3)

The method of claim 3, wherein the iron-containing raw material comprises a powder with an average diameter of less than about 100 μm.

### Claim 11 (depends on 3)

The method of claim 3, wherein the powder including iron nitride comprises at least one of FeN, Fe2N, Fe3N, Fe4N, Fe2N6, Fe8N, Fe16N2, or FeNx, wherein x is in the range of from about 0.05 to about 0.5.

### Claim 12 (depends on 3)

The method of claim 3, further comprising milling an iron precursor to form the iron-containing raw material.

### Claim 13 (depends on 12)

The method of claim 12, wherein the iron precursor comprises at least one of Fe, FeCl3, Fe2O3, or Fe3O4.

### Claim 14 (depends on 12)

The method of claim 12, wherein milling the iron precursor to form the iron-containing raw material comprises milling the iron precursor in the presence of at least one of Ca, Al, or Na under conditions sufficient to cause an oxidation reaction between the at least one of Ca, Al, or Na and oxygen present in the iron precursor.

### Claim 15 (depends on 3)

The method of claim 3, further comprising melting spinning an iron precursor to form the iron-containing raw material.

### Claim 16 (depends on 15)

The method of claim 15, wherein melting spinning the iron precursor comprises:
forming molten iron precursor;
cold rolling the molten iron precursor to form a brittle ribbon of material;
heat treating the brittle ribbon of material; and
shattering the brittle ribbon of material to form the iron-containing raw material.

### Claim 17 (depends on 1)

The method of claim 1, wherein a dimension of the workpiece including at least one Fe8N phase domain is less than about 50 millimeters in at least one axis.

### Claim 18 (depends on 1)

The method of claim 1, wherein the molten iron nitride-containing material includes an iron atom-to-nitrogen atom ratio of about 8:1.

### Claim 19 (depends on 1)

The method of claim 1, wherein the molten iron-nitride containing material includes at least one ferromagnetic or nonmagnetic dopant.

### Claim 20 (depends on 19)

The method of claim 19, wherein the at least one ferromagnetic or nonmagnetic dopant comprises at least one of Sc, Ti, V, Cr, Mn, Co, Ni, Cu, Zn, Zr, Nb, Mo, Ru, Rh, Pd, Ag, Cd, Pt, Au, Sm, C, Pb, W, Ga, Y, Mg, Hf, or Ta.

### Claim 21 (depends on 19)

The method of claim 19, wherein the molten iron-nitride containing material comprises less than about 10 atomic percent of the at least one ferromagnetic or nonmagnetic dopant.

### Claim 22 (depends on 1)

The method of claim 1, wherein the molten iron-nitride containing material further comprises at least one phase stabilizer.

### Claim 23 (depends on 22)

The method of claim 22, wherein the at least one phase stabilizer comprises at least one of B, Al, C, Si, P, O, Co, Cr, Mn, or S.

### Claim 24 (depends on 22)

The method of claim 22, wherein the molten iron-nitride containing material comprises between about 0.1 atomic percent and about 15 atomic percent of the at least one phase stabilizer.

### Claim 25 (depends on 1)

The method of claim 1, wherein heating the mixture including iron and nitrogen to form the molten iron nitride-containing material comprises heating the mixture at a temperature greater than about 1500° C.

### Claim 26 (depends on 1)

The method of claim 1, wherein continuously casting, quenching, and pressing the molten iron nitride-containing material comprises casting the molten iron nitride-containing material at a temperature in the range of from about 650° C. to about 1200° C.

### Claim 27 (depends on 1)

The method of claim 1, wherein continuously casting, quenching, and pressing the molten iron nitride-containing material comprises quenching the iron nitride-containing material to a temperature above about 650° C.

### Claim 28 (depends on 1)

The method of claim 1, wherein continuously casting, quenching, and pressing the molten iron nitride-containing material comprises pressing the iron nitride-containing material at a temperature below about 250° C. and a pressure in the range of from about 5 tons to about 50 tons.

### Claim 29 (depends on 1)

The method of claim 1, further comprising straining and post-annealing the workpiece including at least one Fe8N phase domain to form a workpiece including at least one Fe16N2 phase domain.

### Claim 30 (depends on 29)

The method of claim 29, wherein straining and post-annealing the workpiece including at least one Fe8N phase domain reduces the dimension of the workpiece.

### Claim 31 (depends on 30)

The method of claim 30, wherein the dimension of the workpiece including at least one Fe16N2 phase domain in the at least one axis following straining and post-annealing is less than about 0.1 mm.

### Claim 32 (depends on 29)

The method of claim 29, wherein, after straining and post-annealing, the workpiece consists essentially of a single Fe16N2 phase domain.

### Claim 33 (depends on 29)

The method of claim 29, wherein straining the workpiece including at least one Fe8N phase domain comprises exerting a tensile strain on the workpiece in the range of from about 0.3% to about 12%.

### Claim 34 (depends on 33)

The method of claim 33, wherein the tensile strain is applied in a direction substantially parallel to at least one <001> crystal axis in the workpiece including at least one Fe8N phase domain.

### Claim 35 (depends on 29)

The method of claim 29, wherein post-annealing the workpiece including at least one Fe8N phase domain comprises heating the workpiece including at least one Fe8N phase domain to a temperature in the range of from about 100° C. to about 250° C.

### Claim 36 (depends on 29)

The method of claim 29, wherein the workpiece including at least one Fe16N2 phase domain is characterized as being magnetically anisotropic.

### Claim 37 (depends on 36)

The method of claim 36, wherein the energy product, coercivity and saturation magnetization of the workpiece including at least one Fe16N2 phase domain are different at different orientations.

### Claim 38 (depends on 1)

The method of claim 1, further comprising forming the mixture including iron and nitrogen by exposing an iron-containing material to a urea diffusion process.

### Claim 39 (depends on 1)

The method of claim 1, wherein the workpiece including at least one Fe8N phase domain comprises at least one of a fiber, a wire, a filament, a cable, a film, a thick film, a foil, a ribbon, or a sheet.