CN114743783B - Method for reducing oxygen content of sintered NdFeB magnet - Google Patents
Method for reducing oxygen content of sintered NdFeB magnet Download PDFInfo
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- 229910001172 neodymium magnet Inorganic materials 0.000 title claims abstract description 62
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 title claims abstract description 21
- 239000001301 oxygen Substances 0.000 title claims abstract description 21
- 229910052760 oxygen Inorganic materials 0.000 title claims abstract description 21
- 238000000034 method Methods 0.000 title claims abstract description 18
- 239000006247 magnetic powder Substances 0.000 claims description 62
- QJVKUMXDEUEQLH-UHFFFAOYSA-N [B].[Fe].[Nd] Chemical compound [B].[Fe].[Nd] QJVKUMXDEUEQLH-UHFFFAOYSA-N 0.000 claims description 40
- 238000010438 heat treatment Methods 0.000 claims description 38
- 238000004321 preservation Methods 0.000 claims description 32
- 238000001816 cooling Methods 0.000 claims description 29
- 238000006243 chemical reaction Methods 0.000 claims description 27
- VPASWAQPISSKJP-UHFFFAOYSA-N ethyl prop-2-enoate;isocyanic acid Chemical compound N=C=O.CCOC(=O)C=C VPASWAQPISSKJP-UHFFFAOYSA-N 0.000 claims description 27
- 239000003999 initiator Substances 0.000 claims description 17
- 238000005245 sintering Methods 0.000 claims description 17
- LFQSCWFLJHTTHZ-UHFFFAOYSA-N Ethanol Chemical compound CCO LFQSCWFLJHTTHZ-UHFFFAOYSA-N 0.000 claims description 16
- 239000003054 catalyst Substances 0.000 claims description 16
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 claims description 15
- 238000010992 reflux Methods 0.000 claims description 14
- 238000001291 vacuum drying Methods 0.000 claims description 12
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims description 11
- 239000011261 inert gas Substances 0.000 claims description 8
- 238000010907 mechanical stirring Methods 0.000 claims description 8
- 238000005406 washing Methods 0.000 claims description 8
- 229910052757 nitrogen Inorganic materials 0.000 claims description 7
- OZAIFHULBGXAKX-UHFFFAOYSA-N 2-(2-cyanopropan-2-yldiazenyl)-2-methylpropanenitrile Chemical group N#CC(C)(C)N=NC(C)(C)C#N OZAIFHULBGXAKX-UHFFFAOYSA-N 0.000 claims description 6
- 238000003756 stirring Methods 0.000 claims description 5
- UKLDJPRMSDWDSL-UHFFFAOYSA-L [dibutyl(dodecanoyloxy)stannyl] dodecanoate Chemical compound CCCCCCCCCCCC(=O)O[Sn](CCCC)(CCCC)OC(=O)CCCCCCCCCCC UKLDJPRMSDWDSL-UHFFFAOYSA-L 0.000 claims description 4
- 239000012975 dibutyltin dilaurate Substances 0.000 claims description 4
- KSBAEPSJVUENNK-UHFFFAOYSA-L tin(ii) 2-ethylhexanoate Chemical group [Sn+2].CCCCC(CC)C([O-])=O.CCCCC(CC)C([O-])=O KSBAEPSJVUENNK-UHFFFAOYSA-L 0.000 claims description 3
- 238000001914 filtration Methods 0.000 claims description 2
- 239000000463 material Substances 0.000 abstract description 2
- 230000000052 comparative effect Effects 0.000 description 13
- PPBRXRYQALVLMV-UHFFFAOYSA-N Styrene Chemical group C=CC1=CC=CC=C1 PPBRXRYQALVLMV-UHFFFAOYSA-N 0.000 description 6
- 239000011203 carbon fibre reinforced carbon Substances 0.000 description 5
- 238000007254 oxidation reaction Methods 0.000 description 5
- 229920000642 polymer Polymers 0.000 description 5
- 238000000967 suction filtration Methods 0.000 description 5
- VVQNEPGJFQJSBK-UHFFFAOYSA-N Methyl methacrylate Chemical group COC(=O)C(C)=C VVQNEPGJFQJSBK-UHFFFAOYSA-N 0.000 description 4
- 239000011248 coating agent Substances 0.000 description 4
- 239000011247 coating layer Substances 0.000 description 4
- 238000000576 coating method Methods 0.000 description 4
- 230000000694 effects Effects 0.000 description 4
- 239000003607 modifier Substances 0.000 description 4
- 239000000178 monomer Substances 0.000 description 4
- 230000003647 oxidation Effects 0.000 description 4
- XDLMVUHYZWKMMD-UHFFFAOYSA-N 3-trimethoxysilylpropyl 2-methylprop-2-enoate Chemical group CO[Si](OC)(OC)CCCOC(=O)C(C)=C XDLMVUHYZWKMMD-UHFFFAOYSA-N 0.000 description 3
- 239000006087 Silane Coupling Agent Substances 0.000 description 3
- YXFVVABEGXRONW-UHFFFAOYSA-N Toluene Chemical compound CC1=CC=CC=C1 YXFVVABEGXRONW-UHFFFAOYSA-N 0.000 description 3
- 238000002156 mixing Methods 0.000 description 3
- 230000008569 process Effects 0.000 description 3
- 238000003860 storage Methods 0.000 description 3
- 239000000126 substance Substances 0.000 description 3
- WYURNTSHIVDZCO-UHFFFAOYSA-N Tetrahydrofuran Chemical compound C1CCOC1 WYURNTSHIVDZCO-UHFFFAOYSA-N 0.000 description 2
- 230000009471 action Effects 0.000 description 2
- NKSJNEHGWDZZQF-UHFFFAOYSA-N ethenyl(trimethoxy)silane Chemical group CO[Si](OC)(OC)C=C NKSJNEHGWDZZQF-UHFFFAOYSA-N 0.000 description 2
- 125000002887 hydroxy group Chemical group [H]O* 0.000 description 2
- 239000010410 layer Substances 0.000 description 2
- 230000004048 modification Effects 0.000 description 2
- 238000012986 modification Methods 0.000 description 2
- 238000002360 preparation method Methods 0.000 description 2
- 230000002265 prevention Effects 0.000 description 2
- 239000000047 product Substances 0.000 description 2
- UFHFLCQGNIYNRP-UHFFFAOYSA-N Hydrogen Chemical compound [H][H] UFHFLCQGNIYNRP-UHFFFAOYSA-N 0.000 description 1
- NIXOWILDQLNWCW-UHFFFAOYSA-N acrylic acid group Chemical group C(C=C)(=O)O NIXOWILDQLNWCW-UHFFFAOYSA-N 0.000 description 1
- 238000007259 addition reaction Methods 0.000 description 1
- 230000003064 anti-oxidating effect Effects 0.000 description 1
- 125000003118 aryl group Chemical group 0.000 description 1
- 230000009286 beneficial effect Effects 0.000 description 1
- 239000006227 byproduct Substances 0.000 description 1
- 239000007810 chemical reaction solvent Substances 0.000 description 1
- 239000003795 chemical substances by application Substances 0.000 description 1
- 238000005253 cladding Methods 0.000 description 1
- 229910001873 dinitrogen Inorganic materials 0.000 description 1
- 238000003487 electrochemical reaction Methods 0.000 description 1
- 238000005516 engineering process Methods 0.000 description 1
- 125000000524 functional group Chemical group 0.000 description 1
- 238000003837 high-temperature calcination Methods 0.000 description 1
- 239000001257 hydrogen Substances 0.000 description 1
- 229910052739 hydrogen Inorganic materials 0.000 description 1
- XEEYBQQBJWHFJM-UHFFFAOYSA-N iron Substances [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 description 1
- IQPQWNKOIGAROB-UHFFFAOYSA-N isocyanate group Chemical group [N-]=C=O IQPQWNKOIGAROB-UHFFFAOYSA-N 0.000 description 1
- WELLGRANCAVMDP-UHFFFAOYSA-N isocyanatoethane;prop-2-enoic acid Chemical compound CCN=C=O.OC(=O)C=C WELLGRANCAVMDP-UHFFFAOYSA-N 0.000 description 1
- 238000004519 manufacturing process Methods 0.000 description 1
- 229910052751 metal Inorganic materials 0.000 description 1
- 239000002184 metal Substances 0.000 description 1
- 239000003960 organic solvent Substances 0.000 description 1
- 239000002245 particle Substances 0.000 description 1
- 238000006116 polymerization reaction Methods 0.000 description 1
- 238000003825 pressing Methods 0.000 description 1
- 229910052761 rare earth metal Inorganic materials 0.000 description 1
- 239000000376 reactant Substances 0.000 description 1
- 230000035484 reaction time Effects 0.000 description 1
- 238000011084 recovery Methods 0.000 description 1
- 238000004904 shortening Methods 0.000 description 1
- 238000001179 sorption measurement Methods 0.000 description 1
- YLQBMQCUIZJEEH-UHFFFAOYSA-N tetrahydrofuran Natural products C=1C=COC=1 YLQBMQCUIZJEEH-UHFFFAOYSA-N 0.000 description 1
Classifications
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
- H01F41/00—Apparatus or processes specially adapted for manufacturing or assembling magnets, inductances or transformers; Apparatus or processes specially adapted for manufacturing materials characterised by their magnetic properties
- H01F41/02—Apparatus or processes specially adapted for manufacturing or assembling magnets, inductances or transformers; Apparatus or processes specially adapted for manufacturing materials characterised by their magnetic properties for manufacturing cores, coils, or magnets
- H01F41/0253—Apparatus or processes specially adapted for manufacturing or assembling magnets, inductances or transformers; Apparatus or processes specially adapted for manufacturing materials characterised by their magnetic properties for manufacturing cores, coils, or magnets for manufacturing permanent magnets
- H01F41/026—Apparatus or processes specially adapted for manufacturing or assembling magnets, inductances or transformers; Apparatus or processes specially adapted for manufacturing materials characterised by their magnetic properties for manufacturing cores, coils, or magnets for manufacturing permanent magnets protecting methods against environmental influences, e.g. oxygen, by surface treatment
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
- H01F1/00—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties
- H01F1/01—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials
- H01F1/03—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity
- H01F1/032—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity of hard-magnetic materials
- H01F1/04—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity of hard-magnetic materials metals or alloys
- H01F1/047—Alloys characterised by their composition
- H01F1/053—Alloys characterised by their composition containing rare earth metals
- H01F1/055—Alloys characterised by their composition containing rare earth metals and magnetic transition metals, e.g. SmCo5
- H01F1/057—Alloys characterised by their composition containing rare earth metals and magnetic transition metals, e.g. SmCo5 and IIIa elements, e.g. Nd2Fe14B
- H01F1/0571—Alloys characterised by their composition containing rare earth metals and magnetic transition metals, e.g. SmCo5 and IIIa elements, e.g. Nd2Fe14B in the form of particles, e.g. rapid quenched powders or ribbon flakes
- H01F1/0575—Alloys characterised by their composition containing rare earth metals and magnetic transition metals, e.g. SmCo5 and IIIa elements, e.g. Nd2Fe14B in the form of particles, e.g. rapid quenched powders or ribbon flakes pressed, sintered or bonded together
- H01F1/0577—Alloys characterised by their composition containing rare earth metals and magnetic transition metals, e.g. SmCo5 and IIIa elements, e.g. Nd2Fe14B in the form of particles, e.g. rapid quenched powders or ribbon flakes pressed, sintered or bonded together sintered
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
- H01F41/00—Apparatus or processes specially adapted for manufacturing or assembling magnets, inductances or transformers; Apparatus or processes specially adapted for manufacturing materials characterised by their magnetic properties
- H01F41/02—Apparatus or processes specially adapted for manufacturing or assembling magnets, inductances or transformers; Apparatus or processes specially adapted for manufacturing materials characterised by their magnetic properties for manufacturing cores, coils, or magnets
- H01F41/0253—Apparatus or processes specially adapted for manufacturing or assembling magnets, inductances or transformers; Apparatus or processes specially adapted for manufacturing materials characterised by their magnetic properties for manufacturing cores, coils, or magnets for manufacturing permanent magnets
- H01F41/0266—Moulding; Pressing
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- Engineering & Computer Science (AREA)
- Power Engineering (AREA)
- Manufacturing & Machinery (AREA)
- Chemical & Material Sciences (AREA)
- Crystallography & Structural Chemistry (AREA)
- Inorganic Chemistry (AREA)
- Environmental & Geological Engineering (AREA)
- Hard Magnetic Materials (AREA)
- Powder Metallurgy (AREA)
Abstract
The invention discloses a method for reducing oxygen content of a sintered neodymium-iron-boron magnet, which relates to the technical field of magnet materials.
Description
Technical field:
the invention relates to the technical field of magnet materials, in particular to a method for reducing oxygen content of a sintered NdFeB magnet.
The background technology is as follows:
The sintered NdFeB magnet has higher remanence and magnetic energy product, good dynamic recovery characteristic and high cost performance compared with other permanent magnets, and is widely applied to various fields of electronics, automobiles, computers, energy sources, medical appliances and the like. Because the rare earth element has high metal activity, the neodymium-iron-boron magnetic powder is very easy to be oxidized by electrochemical reaction with oxygen and water vapor in the air at normal temperature, thereby influencing the performance of the sintered neodymium-iron-boron magnet, and therefore, the magnetic powder needs to be subjected to anti-oxidation treatment in the production process of the sintered neodymium-iron-boron magnet. The method commonly used at present is to add a very small amount (less than or equal to 0.5 wt%) of organic matters before or after the air flow mill after hydrogen crushing, and coat the organic matters on the surface of the magnetic powder in a physical mixing mode to prevent the magnetic powder from being oxidized due to contact with oxygen and water vapor in the air, so that the oxygen content of the sintered NdFeB magnet is reduced, and the magnetic performance of the sintered NdFeB magnet is improved.
The method of adding organic matters into magnetic powder and physically mixing the organic matters can prevent oxidation in a short time, but the adsorption force between the organic matters and the magnetic powder is weak, and part of the organic matters are high in volatility, so that the organic matters are easily desorbed from the surface of the magnetic powder to lose the oxidation prevention effect, long-time storage of the magnetic powder is not facilitated, and a pressed compact cannot be exposed to air for a long time in the pressing process. Furthermore, the physical mixing mode cannot completely and densely cover the organic matters on the surfaces of all the magnetic powder due to poor fluidity of the magnetic powder, so that the oxidation prevention effect is poor.
The patent CN108231310A discloses a preparation method of modified neodymium-iron-boron magnetic powder, which comprises the steps of connecting a silane coupling agent containing carbon-carbon double bonds with the neodymium-iron-boron magnetic powder through chemical bonds, adding an acrylic unsaturated monomer and/or an aromatic unsaturated monomer to the silane coupling agent containing carbon-carbon double bonds to carry out grafting reaction, and forming a coating layer on the surface of the neodymium-iron-boron magnetic powder to obtain the modified neodymium-iron-boron magnetic powder. The patent describes the preparation principle that the silane coupling agent can react with hydroxyl (-OH) on the surface of magnetic powder and is connected with the magnetic powder through a chemical bond, so that the surface of the magnetic powder is coated with a layer of organic matters containing carbon-carbon double bond functional groups, the hydrophilicity of the magnetic powder is changed into lipophilicity, unsaturated monomers firstly react with the modifying agent on the surface of the magnetic powder through grafting of the carbon-carbon double bonds, and then the unsaturated monomers undergo polymerization reaction on the basis, and a layer of complete and compact polymer coating layer is formed on the surface of the magnetic powder. The invention aims to modify the method, and the oxygen content of the neodymium iron boron sintered body is expected to be further reduced.
The invention comprises the following steps:
The technical problem to be solved by the invention is to provide a method for reducing the oxygen content of a sintered neodymium-iron-boron magnet, which adopts isocyanate ethyl acrylate as a modifier, realizes surface coating on neodymium-iron-boron magnetic powder through chemical reaction, improves the uniformity and stability of the surface coating, and ensures the magnetic performance of the sintered neodymium-iron-boron magnet while reducing the oxygen content of the sintered neodymium-iron-boron magnet.
The technical problems to be solved by the invention are realized by adopting the following technical scheme:
a method for reducing oxygen content of a sintered neodymium-iron-boron magnet, comprising the following steps:
(1) Vacuum drying neodymium iron boron magnetic powder and a catalyst, adding the dried neodymium iron boron magnetic powder and the catalyst into isocyanate ethyl acrylate, heating and refluxing under the protection of nitrogen, mechanical stirring and ultrasonic assistance, adding an initiator, continuing the refluxing reaction, cooling after the reaction is finished, adding water, stirring, suction filtering, washing with ethanol, and vacuum drying to obtain modified neodymium iron boron magnetic powder;
(2) Carrying out magnetic field orientation profiling on the modified NdFeB magnetic powder to obtain a blank;
(3) And (3) sequentially carrying out high-temperature roasting and vacuum sintering on the blank, cooling and then carrying out heat treatment to obtain the sintered NdFeB magnet.
In the step (1), hydroxyl on the surface of the neodymium iron boron magnetic powder reacts with isocyanate groups in isocyanate ethyl acrylate molecules under the action of a catalyst, so that the isocyanate ethyl acrylate is connected with the neodymium iron boron magnetic powder through chemical bonds; under the action of an initiator, carbon-carbon double bonds in isocyanate ethyl acrylate molecules rapidly undergo polyaddition reaction to form a complete, uniform and compact polymer coating on the surface of the magnetic powder, so that the neodymium iron boron magnetic powder is protected, oxygen and water vapor in the air are isolated, and oxidation of the neodymium iron boron magnetic powder in the storage and processing processes is prevented.
In the step (1), isocyanate ethyl acrylate is taken as a reactant to participate in the reaction, and is taken as a reaction solvent, so that a large amount of organic solvent is avoided, the cost is reduced, the post-treatment operation is reduced, the reaction is quenched by adding water during the post-treatment, the redundant isocyanate ethyl acrylate reacts with water, and the byproducts can be removed by washing with ethanol.
In the step (1), nitrogen protection is used for removing interference of oxygen in air on chemical reaction, mechanical stirring and ultrasonic assistance are used for increasing the contact area of isocyanate ethyl acrylate and neodymium iron boron magnetic powder, shortening reaction time and improving reaction uniformity.
The mass ratio of the neodymium iron boron magnetic powder to the isocyanate ethyl acrylate is 100 (10-20).
The catalyst is stannous octoate or dibutyl tin dilaurate.
The dosage of the catalyst is 0.1-1% of the mass of the isocyanate ethyl acrylate.
The initiator is azobisisobutyronitrile or azobisisoheptonitrile.
The amount of the initiator is 0.05-0.5% of the mass of the isocyanate ethyl acrylate.
The magnetic field adopts a direct current pulse magnetic field, and the magnetic field pressure is 1.8-2.0T.
The high-temperature roasting temperature is 500-600 ℃, and the heat preservation time is 1-3h. The polymer coating is removed by high temperature calcination.
The vacuum sintering temperature is 1050-1150 ℃ and the heat preservation time is 2-4h.
The cooling is to naturally cool to 700-800 ℃ and then to cool to below 100 ℃ by introducing inert gas.
The heat treatment is divided into two stages, the primary heat treatment temperature is 850-950 ℃, and the heat preservation time is 1-3h; the temperature of the secondary heat treatment is 500-600 ℃, and the heat preservation time is 1-3h.
The beneficial effects of the invention are as follows: according to the invention, isocyanate ethyl acrylate is used as a modifier, and a complete, uniform and compact polymer coating layer is formed on the surface of the neodymium-iron-boron magnetic powder after addition reaction and polyaddition reaction, so that oxygen and water vapor in air are isolated through the polymer coating layer, oxidation reaction of the neodymium-iron-boron magnetic powder in the storage and processing processes is prevented, the oxygen content of the sintered neodymium-iron-boron magnetic powder is reduced, and the magnetic property of the sintered neodymium-iron-boron magnetic powder is ensured.
The specific embodiment is as follows:
The invention is further described in connection with the following embodiments in order to make the technical means, the creation features, the achievement of the purpose and the effect of the invention easy to understand.
The components of the neodymium iron boron magnetic powder in the following examples and comparative examples are 15% of Nd, 0.25% of Co, 3.2% of B, 0.2% of Cu, the balance of Fe and the average particle size of 3.5 μm.
Example 1
(1) And (3) adding 100g of neodymium iron boron magnetic powder and a catalyst into 10g of isocyanate ethyl acrylate after vacuum drying, heating and refluxing for reaction for 30min under the protection of nitrogen, under the assistance of mechanical stirring and ultrasonic waves, adding an initiator, continuing to reflux for reaction for 2h, cooling after the reaction, adding water, stirring, carrying out suction filtration, washing with ethanol, and carrying out vacuum drying to obtain the modified neodymium iron boron magnetic powder.
(2) The modified NdFeB magnetic powder is subjected to magnetic field orientation profiling, a direct current pulse magnetic field is adopted as a magnetic field, the magnetic field pressure is 1.8T, a blank is obtained,
(3) Sequentially carrying out high-temperature roasting and vacuum sintering on the blank, wherein the high-temperature roasting temperature is 500 ℃, and the heat preservation time is 2 hours; the vacuum sintering temperature is 1050 ℃, the heat preservation time is 4 hours, the heat treatment is carried out after the cooling, the cooling is that the natural cooling is carried out to 700 ℃ firstly, then inert gas is introduced to cool to 50 ℃, the heat treatment is divided into two stages, the primary heat treatment temperature is 850 ℃, and the heat preservation time is 2 hours; the second-stage heat treatment temperature is 500 ℃, and the heat preservation time is 3 hours, so that the sintered NdFeB magnet is obtained.
Wherein the catalyst is dibutyl tin dilaurate, and the dosage is 0.5% of the mass of the isocyanate ethyl acrylate; the initiator is azodiisobutyronitrile and the dosage is 0.25 percent of the mass of the isocyanate ethyl acrylate.
Example 2
(1) And (3) adding 100g of neodymium iron boron magnetic powder and a catalyst into 15g of isocyanate ethyl acrylate after vacuum drying, heating and refluxing for reaction for 30min under the protection of nitrogen, under the assistance of mechanical stirring and ultrasonic waves, adding an initiator, continuing to reflux for reaction for 2h, cooling after the reaction, adding water, stirring, carrying out suction filtration, washing with ethanol, and carrying out vacuum drying to obtain the modified neodymium iron boron magnetic powder.
(2) The modified NdFeB magnetic powder is subjected to magnetic field orientation profiling, a direct current pulse magnetic field is adopted as a magnetic field, the magnetic field pressure is 2.0T, a blank is obtained,
(3) Sequentially carrying out high-temperature roasting and vacuum sintering on the blank, wherein the high-temperature roasting temperature is 550 ℃, and the heat preservation time is 2 hours; the vacuum sintering temperature is 1150 ℃, the heat preservation time is 3 hours, the heat treatment is carried out after the cooling, the cooling is that the natural cooling is carried out to 740 ℃ firstly, then inert gas is introduced to cool to 80 ℃, the heat treatment is divided into two stages, the primary heat treatment temperature is 900 ℃, and the heat preservation time is 2 hours; the second-stage heat treatment temperature is 600 ℃, and the heat preservation time is 2 hours, so that the sintered NdFeB magnet is obtained.
Wherein the catalyst is dibutyl tin dilaurate, and the dosage is 0.5% of the mass of the isocyanate ethyl acrylate; the initiator is azodiisobutyronitrile and the dosage is 0.25 percent of the mass of the isocyanate ethyl acrylate.
Example 3
(1) And (3) vacuum drying 100g of neodymium iron boron magnetic powder and a catalyst, adding the dried neodymium iron boron magnetic powder and the catalyst into 20g of isocyanate ethyl acrylate, heating and refluxing for reaction for 30min under the protection of nitrogen gas, under the assistance of mechanical stirring and ultrasonic waves, adding an initiator, continuing to reflux for reaction for 2h, cooling after the reaction, adding water, stirring, carrying out suction filtration, washing with ethanol, and carrying out vacuum drying to obtain the modified neodymium iron boron magnetic powder.
(2) The modified NdFeB magnetic powder is subjected to magnetic field orientation profiling, a direct current pulse magnetic field is adopted as a magnetic field, the magnetic field pressure is 2.0T, a blank is obtained,
(3) Sequentially carrying out high-temperature roasting and vacuum sintering on the blank, wherein the high-temperature roasting temperature is 600 ℃, and the heat preservation time is 1.5h; the vacuum sintering temperature is 1050 ℃, the heat preservation time is 3 hours, the heat treatment is carried out after the cooling, the cooling is that the natural cooling is carried out to 710 ℃ firstly, then inert gas is introduced to cool to 60 ℃, the heat treatment is divided into two stages, the primary heat treatment temperature is 900 ℃, and the heat preservation time is 2 hours; the second-stage heat treatment temperature is 550 ℃, and the heat preservation time is 3 hours, so that the sintered NdFeB magnet is obtained.
Wherein the catalyst is stannous octoate, and the dosage is 0.5% of the mass of isocyanate ethyl acrylate; the initiator is azo-bis-isoheptanenitrile, and the dosage is 0.25 percent of the mass of the isocyanate ethyl acrylate.
Comparative example 1
The isocyanate ethyl acrylate in example 3 was replaced with methacryloxypropyl trimethoxysilane and methyl methacrylate to give comparative example 1.
(1) 100G of neodymium iron boron magnetic powder is added into 100mL of tetrahydrofuran solution of methacryloxypropyl trimethoxy silane with mass concentration of 0.5wt%, temperature is raised for reflux reaction for 30min under the protection of nitrogen and under the assistance of mechanical stirring and ultrasonic waves, then 20g of methyl methacrylate and an initiator are added, reflux reaction is continued for 2h, and after the reaction is finished, cooling, suction filtration, ethanol washing and vacuum drying are carried out, so that the modified neodymium iron boron magnetic powder is obtained.
(2) The modified NdFeB magnetic powder is subjected to magnetic field orientation profiling, a direct current pulse magnetic field is adopted as a magnetic field, the magnetic field pressure is 2.0T, a blank is obtained,
(3) Sequentially carrying out high-temperature roasting and vacuum sintering on the blank, wherein the high-temperature roasting temperature is 600 ℃, and the heat preservation time is 1.5h; the vacuum sintering temperature is 1050 ℃, the heat preservation time is 3 hours, the heat treatment is carried out after the cooling, the cooling is that the natural cooling is carried out to 710 ℃ firstly, then inert gas is introduced to cool to 60 ℃, the heat treatment is divided into two stages, the primary heat treatment temperature is 900 ℃, and the heat preservation time is 2 hours; the second-stage heat treatment temperature is 550 ℃, and the heat preservation time is 3 hours, so that the sintered NdFeB magnet is obtained.
Wherein the initiator is azo-bis-isoheptanenitrile, and the dosage is 0.25 percent of the mass of the methyl methacrylate.
Comparative example 2
The isocyanate ethyl acrylate in example 3 was replaced with vinyltrimethoxysilane and styrene to give comparative example 2.
(1) 100G of neodymium iron boron magnetic powder is added into 100mL of toluene solution of vinyl trimethoxy silane with mass concentration of 0.5wt%, temperature is raised for reflux reaction for 30min under the protection of nitrogen and under the assistance of mechanical stirring and ultrasonic waves, then 20g of styrene and an initiator are added, reflux reaction is continued for 2h, and after the reaction is finished, cooling, suction filtration, ethanol washing and vacuum drying are carried out, so that the modified neodymium iron boron magnetic powder is obtained.
(2) The modified NdFeB magnetic powder is subjected to magnetic field orientation profiling, a direct current pulse magnetic field is adopted as a magnetic field, the magnetic field pressure is 2.0T, a blank is obtained,
(3) Sequentially carrying out high-temperature roasting and vacuum sintering on the blank, wherein the high-temperature roasting temperature is 600 ℃, and the heat preservation time is 1.5h; the vacuum sintering temperature is 1050 ℃, the heat preservation time is 3 hours, the heat treatment is carried out after the cooling, the cooling is that the natural cooling is carried out to 710 ℃ firstly, then inert gas is introduced to cool to 60 ℃, the heat treatment is divided into two stages, the primary heat treatment temperature is 900 ℃, and the heat preservation time is 2 hours; the second-stage heat treatment temperature is 550 ℃, and the heat preservation time is 3 hours, so that the sintered NdFeB magnet is obtained.
Wherein the initiator is azo diisoheptonitrile, and the dosage is 0.25 percent of the mass of the styrene.
Comparative example 3
Step (1) in example 3 was deleted, i.e., neodymium iron boron magnetic powder was not subjected to cladding modification, to obtain comparative example 3.
(1) The neodymium iron boron magnetic powder is subjected to magnetic field orientation profiling, a direct current pulse magnetic field is adopted as a magnetic field, the magnetic field pressure is 2.0T, a blank is obtained,
(2) Sequentially carrying out high-temperature roasting and vacuum sintering on the blank, wherein the high-temperature roasting temperature is 600 ℃, and the heat preservation time is 1.5h; the vacuum sintering temperature is 1050 ℃, the heat preservation time is 3 hours, the heat treatment is carried out after the cooling, the cooling is that the natural cooling is carried out to 710 ℃ firstly, then inert gas is introduced to cool to 60 ℃, the heat treatment is divided into two stages, the primary heat treatment temperature is 900 ℃, and the heat preservation time is 2 hours; the second-stage heat treatment temperature is 550 ℃, and the heat preservation time is 3 hours, so that the sintered NdFeB magnet is obtained.
The modified neodymium iron boron magnetic powder prepared in the step (1) in the examples 1-3 and the comparative examples 1-2 and the neodymium iron boron magnetic powder used in the step (1) in the comparative example 3 are placed in the same air environment for 7 days before orientation profiling, and then the following corresponding orientation profiling, high-temperature roasting, vacuum sintering and heat treatment are carried out, wherein the orientation profiling adopts an open press. The magnetic properties and oxygen content of the prepared sintered NdFeB magnet were measured, and the results are shown in Table 1.
The magnetic performance of the magnet is measured by using an HS-40 type B-H loop measuring instrument, the oxygen content of the magnet is measured by using an IRO-I oxygen measuring instrument, and the magnet is tested in parallel for three times, and the average value is obtained.
TABLE 1
| Remanence (kGs) | Coercivity (kOe) | Magnetic energy product (MGOe) | Oxygen content (ppm) | |
| Example 1 | 12.53 | 16.81 | 43.70 | 502 |
| Example 2 | 12.51 | 16.82 | 43.74 | 419 |
| Example 3 | 12.50 | 16.81 | 43.72 | 345 |
| Comparative example 1 | 12.47 | 16.73 | 43.68 | 627 |
| Comparative example 2 | 12.45 | 16.78 | 43.67 | 683 |
| Comparative example 3 | 12.52 | 16.82 | 43.72 | 1268 |
As can be seen from Table 1, the use of ethyl isocyanate acrylate as the modifier in examples 1-3 of the present invention can further reduce the oxygen content of the sintered NdFeB magnet without causing a significant decrease in the magnetic properties of the sintered NdFeB magnet, relative to the use of methacryloxypropyl trimethoxysilane and methyl methacrylate as the modifier in comparative example 1.
The foregoing has shown and described the basic principles and main features of the present invention and the advantages of the present invention. It will be understood by those skilled in the art that the present invention is not limited to the embodiments described above, and that the above embodiments and descriptions are merely illustrative of the principles of the present invention, and various changes and modifications may be made without departing from the spirit and scope of the invention, which is defined in the appended claims. The scope of the invention is defined by the appended claims and equivalents thereof.
Claims (6)
1. A method for reducing oxygen content of a sintered neodymium-iron-boron magnet, comprising the following steps:
(1) Vacuum drying neodymium iron boron magnetic powder and a catalyst, adding the dried neodymium iron boron magnetic powder and the catalyst into isocyanate ethyl acrylate, heating and refluxing under the protection of nitrogen, mechanical stirring and ultrasonic assistance, adding an initiator, continuing the refluxing reaction, cooling after the reaction is finished, adding water, stirring, suction filtering, washing with ethanol, and vacuum drying to obtain modified neodymium iron boron magnetic powder;
(2) Carrying out magnetic field orientation profiling on the modified NdFeB magnetic powder to obtain a blank;
(3) Sequentially performing high-temperature roasting and vacuum sintering on the blank, cooling and performing heat treatment to obtain a sintered NdFeB magnet;
The mass ratio of the neodymium iron boron magnetic powder to the isocyanate ethyl acrylate is 100 (10-20);
the catalyst is stannous octoate or dibutyl tin dilaurate;
the initiator is azobisisobutyronitrile or azobisisoheptonitrile;
The high-temperature roasting temperature is 500-600 ℃, and the heat preservation time is 1-3h; the temperature of the vacuum sintering is 1050-1150 ℃ and the heat preservation time is 2-4h.
2. The method according to claim 1, characterized in that: the dosage of the catalyst is 0.1-1% of the mass of the isocyanate ethyl acrylate.
3. The method according to claim 1, characterized in that: the amount of the initiator is 0.05-0.5% of the mass of the isocyanate ethyl acrylate.
4. The method according to claim 1, characterized in that: the magnetic field adopts a direct current pulse magnetic field, and the magnetic field pressure is 1.8-2.0T.
5. The method according to claim 1, characterized in that: the cooling is to naturally cool to 700-800 ℃ and then to cool to below 100 ℃ by introducing inert gas.
6. The method according to claim 1, characterized in that: the heat treatment is divided into two stages, the primary heat treatment temperature is 850-950 ℃, and the heat preservation time is 1-3h; the temperature of the secondary heat treatment is 500-600 ℃, and the heat preservation time is 1-3h.
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