# US 12,112,884 B2 · Method for improving corrosion resistance of neodymium-iron-boron materials by low-temperature oxidation and/or nitridation treatment

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- Number: US 12,112,884 B2
- Document ID: US12112884B2
- Status: Granted
- Kind: B2
- Application number: 17/711,551
- Filed: 2022-04-01
- Published: 2023-09-07
- Granted: 2024-10-08
- Earliest claimed: 2022-03-02
- Assignees: Zhejiang University
- Applicants: Zhejiang University
- Inventors: Mi Yan; Jiaying Jin; Wang Chen; Chen Wu
- Web page: https://patentgrep.com/patent/US12112884B2

## CPC

- H01F 41/026: {protecting methods against environmental influences, e.g. oxygen, by surface treatment (magnetic particles with skin H01F1/061, H01F1/09, H01F1/24, H01F1/33 and G11B5/706)}
- C21D 8/1255: {with diffusion of elements, e.g. decarburising, nitriding}
- H01F 1/057: and IIIa elements, e.g. Nd2Fe14B
- H01F 1/0577: {sintered}
- Y02E 10/72: Wind turbines with rotation axis in wind direction
- H01F: MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
- C21D: MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING (surface treatment of metallic material involving at least one process provided for in class C23 and at least one process covered by this subclass C23F17/00; unidirectional solidification of eutectic materials or unidirectional demixing of eutectoid materials C30B)
- Y02E: REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION

## Abstract

A method for improving the corrosion resistance of NdFeB materials is provided. The method includes in-situ growing a layer of oxide, nitride, or oxynitride on the surface of NdFeB magnet correspondingly by performing at least one of an oxidation treatment and a nitridation treatment at low temperature in a range of 200˜400° C., thereby significantly improving the corrosion resistance of the magnet. The method is simple to operate, low-cost, green, safe, and efficient. Depending on the parameters of the low-temperature oxidation and/or nitridation treatment, the thickness of the oxide, nitride, or oxynitride layer is adjustable from 10 nm to 100 μm, which can improve the corrosion resistance of the magnet while maintaining excellent magnetic properties. Moreover, the thin surface layer is in-situ grown on the NdFeB substrate, which is strong and stable over a long service period and can be applied for mass production.

## Claims

### Claim 1

A method for improving corrosion resistance of neodymium-iron-boron (NdFeB) materials, consisting of:
in-situ growing at least one selected from a group consisting of an oxide layer, a nitride layer and an oxynitride layer on a surface of a NdFeB magnet by correspondingly performing at least one of oxidation treatment and nitridation treatment of the NdFeB magnet;
wherein the “performing at least one of the oxidation treatment and the nitridation treatment” consists of:
providing the NdFeB magnet in a tube furnace or an atmosphere furnace;
vacuumizing to 10−2-10−4 pascals (Pa) in the tube furnace or the atmosphere furnace;
introducing at least one selected a group consisting of oxygen (O2), nitrogen (N2), ammonia gas (NH3) and water vapor with a flow rate in a range of 200-5000 milliliters per minute (mL/min) into the tube furnace or the atmosphere furnace; and
controlling a temperature of the at least one of the oxidation treatment and the nitridation treatment in a range of 300-350 degrees Celsius (° C.) for 0.5-24 hours;
wherein the oxide layer consists of an oxide of one or more elements from the NdFeB magnet; the nitride layer consists of a nitride of one or more elements from the NdFeB magnet; and the oxynitride layer consists of an oxynitride of one or more elements from the NdFeB magnet.

### Claim 2 (depends on 1)

The method according to claim 1, wherein a thickness of the at least one selected from the group consisting of the oxide, the nitride and the oxynitride layer is adjustable in a range from 10 nanometers (nm) to 100 micrometers (μm).

### Claim 3 (depends on 1)

The method according to claim 1, wherein components of the NdFeB magnet, in atomic percent, are (REaRE′1-a)x(FebM1-b)100-x-y-zM′yBz,
where RE is neodymium (Nd) or a mixture of neodymium (Nd) and at least one of lanthanide elements except lanthanum (La), cerium (Ce) and yttrium (Y); RE′ is at least one selected from a group consisting of La, Ce and Y; Fe is iron; M is one or two of cobalt (Co) and nickel (Ni); M′ is at least one selected from a group consisting of niobium (Nb), zirconium (Zr), tantalum (Ta), vanadium (V), aluminum (Al), copper (Cu), gallium (Ga), titanium (Ti), chromium (Cr), molybdenum (Mo), manganese (Mn), silver (Ag), gold (Au), lead (Pb) and silicon (Si); B is boron; and a, b, x, y, and z respectively satisfy conditions comprising: 0.55≤a≤1, 0.8≤b≤1, 12≤x≤18, 0≤y≤2, and 5.5≤z≤6.5.