High-temperature-resistant high-performance neodymium-iron-boron permanent magnet material and preparation method thereof

Abstract

This invention discloses a high-temperature resistant, high-performance neodymium iron boron (NdFeB) permanent magnet material and its preparation method, belonging to the technical field of NdFeB permanent magnet materials. The material is prepared by mixing, melting, crushing, sintering, tempering, coating, and curing NdFeB magnetic powder, auxiliary metal, hyperbranched polyimide polymer-modified nano-zirconia, and a silane coupling agent. The invention introduces hyperbranched polyimide polymer-modified nano-zirconia into the composition, which exhibits excellent thermal stability, enabling the permanent magnet material to maintain stable magnetic and mechanical properties at high temperatures. It also demonstrates good resistance to attenuation and low thermal demagnetization. The interfacial bonding strength of the nano-zirconia is improved after modification with hyperbranched polyimide. Click chemistry enhances the interfacial compatibility between the nano-zirconia and polyimide, improving the interfacial bonding strength of the nano-zirconia on the NdFeB matrix. The three-dimensional branched structure of the hyperbranched polyimide can form physical cross-linking points within the material, enhancing its mechanical strength.

Description

Technical Field

[0001] This invention belongs to the field of neodymium iron boron permanent magnet material technology, and particularly relates to a high-temperature resistant, high-performance neodymium iron boron permanent magnet material and its preparation method. Background Technology

[0002] Neodymium iron boron (NdFeB) permanent magnets are widely used in wind power generation, new energy vehicle drive motors, precision medical devices, aerospace, and electronic information fields due to their extremely high energy product, high coercivity, and high remanence. However, traditional NdFeB magnets are prone to significant degradation of magnetic properties at high temperatures. Their Curie temperature is relatively low (typically between 310–410°C), and their coercivity drops sharply at high temperatures, severely limiting their application in high-temperature conditions.

[0003] To improve the high-temperature resistance of NdFeB materials, existing technologies typically employ alloying methods, adding heavy rare earth elements (such as Dy and Tb) to promote grain boundary diffusion and enhance the coercivity and thermal stability of the magnet. However, these elements are expensive and scarce, significantly increasing material costs. Another approach is to introduce highly stable second-phase or composite ceramic particles, such as oxides and nitrides, into the magnet to suppress grain boundary migration and magnetic domain reversal at high temperatures. However, these methods often face problems such as poor interfacial bonding and uneven dispersion, leading to inconsistencies in mechanical and magnetic properties.

[0004] Chinese patent CN120126889A discloses a ferrite / neodymium iron boron composite magnetic material using polyimide as a partial binder phase. However, the polyimide used in this patent method exhibits poor compatibility and dispersibility with both ferrite and neodymium iron boron magnetic powders, leading to interface defects and agglomeration, which affects the uniformity and stability of the material's overall performance. Especially at high temperatures, the significant difference in thermal expansion coefficients between organic and inorganic magnetic powders easily results in microcracks and further degradation of magnetic properties. Furthermore, the neodymium iron boron material in this invention is a bonded neodymium iron boron material, which exhibits inferior impact resistance, bending resistance, and shear resistance compared to sintered neodymium iron boron materials. Therefore, developing a sintered neodymium iron boron composite modified material with good interface compatibility and excellent thermal stability has become crucial for improving the high-temperature performance of neodymium iron boron permanent magnet materials. Summary of the Invention

[0005] In order to overcome the shortcomings of the prior art, this invention discloses a high-temperature resistant, high-performance neodymium iron boron permanent magnet material, which is prepared by mixing, grinding, molding, and curing neodymium iron boron magnetic powder, auxiliary metal, hyperbranched polyimide polymer-modified nano-zirconia and silane coupling agent. By introducing hyperbranched polyimide polymer-modified nano-zirconia, the overall performance of the material is significantly improved.

[0006] To achieve the above objectives, the following technical solution is adopted: On the one hand, the present invention provides a high-temperature resistant high-performance neodymium iron boron permanent magnet material, comprising the following components by mass: 90-108 parts of neodymium iron boron magnetic powder, 4-10 parts of auxiliary metal, 2.5-5 parts of hyperbranched polyimide polymer modified nano-zirconia, and 0.1-1 parts of silane coupling agent.

[0007] Furthermore, the hyperbranched polyimide polymer-modified nano-zirconia is prepared through the following steps:

[0008] S1. N'-(2-aminoethyl)-N'-(4,6-dichloro-1,3,5-triazin-2-yl)ethylenediamine and 4-vinylaniline were added to N,N-dimethylformamide, followed by triethylamine. The mixture was stirred at 60-90°C for 4-8 hours under nitrogen protection. The reaction solution was poured into deionized water, filtered, and the filter cake was washed with deionized water until neutral. The mixture was then dried under vacuum to obtain the triazinyldiamine monomer.

[0009] The reaction process of the triazine diamine monomer is as follows:

[0010] ;

[0011] The N'-(2-aminoethyl)-N'-(4,6-dichloro-1,3,5-triazin-2-yl)ethylenediamine is obtained by reacting cyanuric chloride and diethylenetriamine, and the reaction process is as follows:

[0012] ;

[0013] S2. Triazine diamine monomer and 4,4'-biphenyl ether dianhydride were added to N-methylpyrrolidone. Under nitrogen protection, the mixture was stirred at 0-5℃ for 4-6 h. Then pyridine was added, the temperature was raised to 150-180℃, and the mixture was stirred for 8-12 h. The reaction solution was poured into ethanol, filtered, and the filter cake was washed three times with ethanol under reflux. The mixture was then dried under vacuum to obtain triazine polyimide.

[0014] S3. Triazine polyimide and tris[2-(3-mercaptopropoxy)ethyl]isocyanurate were added to tetrahydrofuran, and then photoinitiator 2-hydroxy-2-methylphenylpropane-1-one was added. The mixture was irradiated with ultraviolet light at a wavelength of 365 nm at 30-50°C for 2-4 hours. After the reaction was completed, the mixture was filtered, the filter cake was washed with n-hexane, and then dried under vacuum to obtain hyperbranched polyimide.

[0015] S4. Disperse nano-zirconia in 50% ethanol solution, sonicate for 30-60 min to form a dispersion, add itaconic acid and p-toluenesulfonic acid to the dispersion, heat to 70-80℃ and reflux for 6-10 h. After the reaction is completed, centrifuge the reaction solution, wash the precipitate with ethanol, and then vacuum dry to obtain itaconic acid modified nano-zirconia.

[0016] S5. Hyperbranched polyimide, itaconic acid-modified nano-zirconia, and triethylamine were added to N,N-dimethylacetamide. Under nitrogen protection, 2-hydroxy-2-methylphenylpropane-1-one was added as a photoinitiator. The reaction was carried out at 30-50°C with ultraviolet light of wavelength 365 nm for 2-4 hours. After the reaction was completed, the reaction solution was centrifuged, the precipitate was washed with N,N-dimethylacetamide, and dried under vacuum to obtain hyperbranched polyimide polymer-modified nano-zirconia.

[0017] In the above reaction process, N'-(2-aminoethyl)-N'-(4,6-dichloro-1,3,5-triazin-2-yl)ethylenediamine containing triazine groups is first reacted with 4-vinylaniline to introduce double bonds. Then, the product is used as a diamine monomer and reacted with 4,4'-biphenyl dianhydride to obtain triazine polyimide. The triazine polyimide is then reacted with tris[2-(3-mercaptopropoxy)ethyl]isocyanurate, which has three thiol groups in its molecular structure, via a thiol-alkenyl click reaction, with the thiol group in excess, to obtain hyperbranched polyimide containing unreacted thiol groups. Itaconic acid is reacted with the hydroxyl groups on the surface of nano-zirconia to obtain modified nano-zirconia, while introducing double bonds to the surface of nano-zirconia. The obtained itaconic acid-modified nano-zirconia reacts with hyperbranched polyimide to finally obtain hyperbranched polyimide polymer-modified nano-zirconia.

[0018] Further, in step S1, the feeding ratio of N'-(2-aminoethyl)-N'-(4,6-dichloro-1,3,5-triazin-2-yl)ethylenediamine, 4-vinylaniline, triethylamine, and N,N-dimethylformamide is 10g: 5.07-6.08g: 7.12-8.90mL: 107-191mL.

[0019] Further, in step S2, the feeding ratio of triazine diamine monomer, 4,4'-biphenyl ether dianhydride, pyridine and N-methylpyrrolidone is 10g: 9.77-10.26g: 2.54-3.81mL: 153-236mL.

[0020] Further, in step S3, the feeding ratio of triazine polyimide, tris[2-(3-mercaptopropoxy)ethyl]isocyanurate, 2-hydroxy-2-methylphenylpropane-1-one and tetrahydrofuran is 10g: 5.1-8.2g: 0.067-0.145g: 90-163mL.

[0021] Furthermore, in step S4, the feeding ratio of nano-zirconia, itaconic acid, p-toluenesulfonic acid, and ethanol solution is 10g: 10-15g: 0.05-0.1g: 110-180mL.

[0022] Furthermore, in step S5, the feeding ratio of hyperbranched polyimide, itaconic acid-modified nano-zirconia, N,N-dimethylacetamide, triethylamine, and 2-hydroxy-2-methylphenylpropane-1-one is 30-50g: 10g: 340-766mL: 0.41-1.37mL: 0.2-0.6g.

[0023] Furthermore, the silane coupling agent is one of γ-aminopropyltriethoxysilane, γ-(2,3-epoxypropoxy)propyltrimethoxysilane, or methacryloyloxypropyltrimethoxysilane.

[0024] Furthermore, the auxiliary metal is composed of the following components in mass percentage: boron 0.5-1.5%, molybdenum 0.5-2%, gadolinium 1-3%, copper 0.2-1%, gallium 0.2-0.8%, cobalt 1-5%, with the remainder being neodymium.

[0025] On the other hand, the present invention also provides a method for preparing the high-temperature resistant, high-performance neodymium iron boron permanent magnet material, comprising the following steps:

[0026] (1) Weigh the neodymium iron boron magnetic powder, auxiliary metal and silane coupling agent according to the proportion, mix them and smelt them to obtain alloy ingots;

[0027] (2) The alloy ingot is crushed and powdered, and then oriented and pressed under a magnetic field strength of 1.5-2.5T;

[0028] (3) The compact is sintered under vacuum or argon protection at a temperature of 1040-1080℃ and held for 2-4 hours.

[0029] (4) The sintered magnets are subjected to two-stage tempering: the first stage tempering temperature is 800-900℃ and the holding temperature is 1-2h; the second stage tempering temperature is 500-600℃ and the holding temperature is 2-3h.

[0030] (5) The hyperbranched polyimide polymer modified nano-zirconia is dispersed in N-methylpyrrolidone to prepare a coating liquid with a solid content of 5-15% by mass and uniformly coated on the magnet surface.

[0031] (6) The magnet coated with hyperbranched polyimide polymer modified nano-zirconia is cured at 100-200℃ for 0.5-2h to obtain the permanent magnet material.

[0032] The beneficial effects of this invention are as follows: The high-temperature resistant, high-performance neodymium iron boron permanent magnet material prepared by this invention is obtained by mixing, melting, crushing, sintering, tempering, coating, and curing neodymium iron boron magnetic powder, auxiliary metal, hyperbranched polyimide polymer-modified nano-zirconia, and silane coupling agent. By introducing hyperbranched polyimide polymer-modified nano-zirconia coating onto the surface of the neodymium iron boron material, the comprehensive performance of the permanent magnet material is significantly improved.

[0033] Hyperbranched polyimide itself has excellent thermal stability. The triazine ring and isocyanurate structure contained in its molecular chain further improve the thermal decomposition temperature and oxidation resistance. The triazine ring is an aromatic heterocyclic structure with high bond energy and conjugation stability, while the isocyanurate structure has good thermal stability and chemical inertness. These structural units work together to enable the material to maintain stable magnetic and mechanical properties at high temperatures. Nano-zirconia itself is a high-temperature resistant ceramic material. After being modified by hyperbranched polyimide, its interfacial bonding strength on the permanent magnet matrix is ​​improved, which inhibits grain boundary migration and magnetic performance decay at high temperatures.

[0034] Through thiol-olefin click chemistry, unreacted thiol groups are introduced into the hyperbranched polyimide molecules, enabling them to further react with the double bonds on the itaconic acid-modified nano-zirconia surface to form chemical bonds. This enhances the interfacial compatibility between nano-zirconia and polyimide. At the same time, the carboxyl and hydroxyl groups introduced into the nano-zirconia surface during itaconic acid modification also enhance its interaction with silane coupling agents and metal surfaces, further improving the overall interfacial bonding state of the material.

[0035] The three-dimensional branched structure of hyperbranched polyimide has a large number of terminal functional groups and molecular chain entanglement capabilities, which can form physical cross-linking points on the material surface and enhance the mechanical strength of the material. The introduction of nano-zirconia acts as a reinforcing phase, improving the hardness, wear resistance and fatigue resistance of the permanent magnet material. The synergistic effect of the two significantly improves the mechanical properties and durability of the permanent magnet material, making the permanent magnet material have good resistance to attenuation and low thermal demagnetization.

[0036] In addition, the addition of auxiliary metal elements can optimize the grain boundary phase structure and magnetic domain organization of NdFeB magnets, thereby improving coercivity and Curie temperature. Attached Figure Description

[0037] Figure 1 This is a SEM image of the tensile cross-section of the neodymium iron boron permanent magnet material prepared in Example 3 of the present invention.

[0038] The accompanying drawings are provided to further illustrate the invention and form part of the specification. They are used together with the embodiments of the invention to explain the invention and do not constitute a limitation thereof. Detailed Implementation

[0039] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0040] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those familiar to those skilled in the art. Furthermore, any methods and materials similar to or equivalent to those described herein may be applied to this invention. The preferred embodiments and materials described herein are for illustrative purposes only and do not limit the scope of this application.

[0041] Unless otherwise specified, the experimental methods used in the following examples are conventional methods, and the experimental materials used in the following examples are all purchased from commercial channels.

[0042] Example 1: A high-temperature resistant, high-performance neodymium iron boron permanent magnet material, comprising the following components by mass: 90 parts neodymium iron boron magnetic powder, 4 parts auxiliary metal, 2.5 parts hyperbranched polyimide polymer-modified nano-zirconia, and 0.1 parts silane coupling agent; wherein the silane coupling agent is γ-aminopropyltriethoxysilane; the auxiliary metal is composed of the following components by mass percentage: boron 0.5%, molybdenum 0.5%, gadolinium 1%, copper 0.2%, gallium 0.2%, cobalt 1%, with the remainder being neodymium.

[0043] The hyperbranched polyimide polymer-modified nano-zirconia was prepared through the following steps:

[0044] S1. 10g of N'-(2-aminoethyl)-N'-(4,6-dichloro-1,3,5-triazin-2-yl)ethylenediamine and 5.07g of 4-vinylaniline were added to 107mL of N,N-dimethylformamide, followed by 7.12mL of triethylamine. The mixture was stirred at 60℃ for 4h under nitrogen protection. The reaction solution was poured into deionized water, filtered, and the filter cake was washed with deionized water until neutral. The mixture was then dried under vacuum to obtain the triazinyldiamine monomer.

[0045] S2. 10g of triazine diamine monomer and 9.77g of 4,4'-biphenyl ether dianhydride were added to 153mL of N-methylpyrrolidone. Under nitrogen protection, the mixture was stirred at 0℃ for 4h, and then 2.54mL of pyridine was added. The temperature was raised to 150℃ and the mixture was stirred for 8h. The reaction solution was poured into ethanol, filtered, and the filter cake was washed three times with ethanol under reflux. The mixture was then dried under vacuum to obtain triazine polyimide.

[0046] S3. 10g of triazine polyimide and 5.1g of tris[2-(3-mercaptopropoxy)ethyl]isocyanurate were added to 90mL of tetrahydrofuran, and then 0.067g of photoinitiator 2-hydroxy-2-methylphenylpropane-1-one were added. The mixture was irradiated with ultraviolet light at 365nm wavelength at 30℃ for 2h. After the reaction was completed, the mixture was filtered, the filter cake was washed with n-hexane, and then dried under vacuum to obtain hyperbranched polyimide.

[0047] S4. Disperse 10g of nano-zirconia in 110mL of 50% ethanol solution, sonicate for 30min to form a dispersion, add 10g of itaconic acid and 0.05g of p-toluenesulfonic acid to the dispersion, heat to 70℃ and reflux for 6h. After the reaction is completed, centrifuge the reaction solution, wash the precipitate with ethanol, and then vacuum dry to obtain itaconic acid modified nano-zirconia.

[0048] S5. Add 30g of hyperbranched polyimide, 10g of itaconic acid-modified nano-zirconia and 0.41mL of triethylamine to 340mL of N,N-dimethylacetamide. Under nitrogen protection, add 0.2g of photoinitiator 2-hydroxy-2-methylphenylpropane-1-one. At 30℃, irradiate with ultraviolet light at a wavelength of 365nm for 2h. After the reaction is completed, centrifuge the reaction solution, wash the precipitate with N,N-dimethylacetamide, and dry it under vacuum to obtain hyperbranched polyimide polymer-modified nano-zirconia.

[0049] The preparation method of the high-temperature resistant, high-performance neodymium iron boron permanent magnet material includes the following steps:

[0050] (1) Weigh the neodymium iron boron magnetic powder, auxiliary metal and silane coupling agent according to the proportion, mix them and smelt them to obtain alloy ingots;

[0051] (2) The alloy ingot is crushed and powdered, and then oriented and pressed under a magnetic field strength of 1.5T;

[0052] (3) The compact is sintered under vacuum or argon protection at a temperature of 1040℃ for 2 hours.

[0053] (4) The sintered magnets are subjected to two-stage tempering: the first stage tempering temperature is 800℃ and the holding time is 1h; the second stage tempering temperature is 500℃ and the holding time is 2h.

[0054] (5) The hyperbranched polyimide polymer modified nano-zirconia is dispersed in N-methylpyrrolidone to prepare a coating liquid with a solid content of 5-15% by mass and uniformly coated on the magnet surface.

[0055] (6) The magnet coated with hyperbranched polyimide polymer modified nano-zirconia was cured at 100°C for 0.5 h to obtain the permanent magnet material.

[0056] Example 2: A high-temperature resistant, high-performance neodymium iron boron permanent magnet material, comprising the following components by mass: 108 parts neodymium iron boron magnetic powder, 10 parts auxiliary metal, 5 parts hyperbranched polyimide polymer-modified nano-zirconia, and 1 part silane coupling agent; wherein the silane coupling agent is γ-(2,3-epoxypropoxy)propyltrimethoxysilane; the auxiliary metal is composed of the following components by mass percentage: boron 1.5%, molybdenum 2%, gadolinium 3%, copper 1%, gallium 0.8%, cobalt 5%, with the remainder being neodymium.

[0057] The hyperbranched polyimide polymer-modified nano-zirconia was prepared through the following steps:

[0058] S1. 10g of N'-(2-aminoethyl)-N'-(4,6-dichloro-1,3,5-triazin-2-yl)ethylenediamine and 6.08g of 4-vinylaniline were added to 191mL of N,N-dimethylformamide, followed by 8.90mL of triethylamine. The mixture was stirred at 90℃ for 8h under nitrogen protection. The reaction solution was poured into deionized water, filtered, and the filter cake was washed with deionized water until neutral. The mixture was then dried under vacuum to obtain the triazinyldiamine monomer.

[0059] S2. 10g of triazine diamine monomer and 10.26g of 4,4'-biphenyl ether dianhydride were added to 236mL of N-methylpyrrolidone. Under nitrogen protection, the mixture was stirred at 5°C for 6h. Then, 3.81mL of pyridine was added, the temperature was raised to 180°C, and the mixture was stirred for 12h. The reaction solution was poured into ethanol, filtered, and the filter cake was washed three times by reflux with ethanol. After vacuum drying, triazine polyimide was obtained.

[0060] S3. 10g of triazine polyimide and 8.2g of tris[2-(3-mercaptopropoxy)ethyl]isocyanurate were added to 163mL of tetrahydrofuran, and then 0.145g of photoinitiator 2-hydroxy-2-methylphenylpropane-1-one were added. The mixture was irradiated with ultraviolet light at 50℃ for 4h with a wavelength of 365nm. After the reaction was completed, the mixture was filtered, the filter cake was washed with n-hexane, and then dried under vacuum to obtain hyperbranched polyimide.

[0061] S4. Disperse 10g of nano-zirconia in 180mL of 50% ethanol solution, sonicate for 60min to form a dispersion, add 15g of itaconic acid and 0.1g of p-toluenesulfonic acid to the dispersion, heat to 80℃ and reflux for 10h. After the reaction is completed, centrifuge the reaction solution, wash the precipitate with ethanol, and then dry it under vacuum to obtain itaconic acid modified nano-zirconia.

[0062] S5. Add 50g of hyperbranched polyimide, 10g of itaconic acid-modified nano-zirconia and 1.37mL of triethylamine to 766mL of N,N-dimethylacetamide. Under nitrogen protection, add 0.6g of photoinitiator 2-hydroxy-2-methylphenylpropane-1-one. At 50℃, irradiate with ultraviolet light at a wavelength of 365nm for 4h. After the reaction is completed, centrifuge the reaction solution, wash the precipitate with N,N-dimethylacetamide, and dry under vacuum to obtain hyperbranched polyimide polymer-modified nano-zirconia.

[0063] The preparation method of the high-temperature resistant, high-performance neodymium iron boron permanent magnet material includes the following steps:

[0064] (1) Weigh the neodymium iron boron magnetic powder, auxiliary metal and silane coupling agent according to the proportion, mix them and smelt them to obtain alloy ingots;

[0065] (2) The alloy ingot is crushed and powdered, and then oriented and pressed under a magnetic field strength of 2.5T;

[0066] (3) The compact is sintered under vacuum or argon protection at a temperature of 1080℃ for 4 hours.

[0067] (4) The sintered magnets are subjected to two-stage tempering: the first stage tempering temperature is 900℃ and the holding time is 2h; the second stage tempering temperature is 600℃ and the holding time is 3h.

[0068] (5) The hyperbranched polyimide polymer modified nano-zirconia is dispersed in N-methylpyrrolidone to prepare a coating liquid with a solid content of 15% by mass, and uniformly coated on the magnet surface.

[0069] (6) The magnet coated with hyperbranched polyimide polymer modified nano-zirconia was cured at 200°C for 2 hours to obtain the permanent magnet material.

[0070] Example 3: A high-temperature resistant, high-performance neodymium iron boron permanent magnet material, comprising the following components by mass: 99 parts neodymium iron boron magnetic powder, 7 parts auxiliary metal, 3.8 parts hyperbranched polyimide polymer-modified nano-zirconia, and 0.5 parts silane coupling agent; wherein the silane coupling agent is methacryloxypropyltrimethoxysilane; the auxiliary metal is composed of the following components by mass percentage: boron 1.0%, molybdenum 1.2%, gadolinium 2.0%, copper 0.6%, gallium 0.5%, cobalt 3.0%, with the remainder being neodymium.

[0071] The hyperbranched polyimide polymer-modified nano-zirconia was prepared through the following steps:

[0072] S1. 10g of N'-(2-aminoethyl)-N'-(4,6-dichloro-1,3,5-triazin-2-yl)ethylenediamine and 5.5g of 4-vinylaniline were added to 150mL of N,N-dimethylformamide, followed by 8.0mL of triethylamine. The mixture was stirred at 75°C for 6 hours under nitrogen protection. The reaction solution was poured into deionized water, filtered, and the filter cake was washed with deionized water until neutral. The mixture was then dried under vacuum to obtain the triazinyldiamine monomer.

[0073] S2. 10g of triazine diamine monomer and 10.0g of 4,4'-biphenyl ether dianhydride were added to 195mL of N-methylpyrrolidone. Under nitrogen protection, the mixture was stirred at 2℃ for 5h. Then, 3.25mL of pyridine was added, the temperature was raised to 165℃, and the mixture was stirred for 10h. The reaction solution was poured into ethanol, filtered, and the filter cake was washed three times with ethanol under reflux. The mixture was then dried under vacuum to obtain triazine polyimide.

[0074] S3. 10g of triazine polyimide and 6.5g of tris[2-(3-mercaptopropoxy)ethyl]isocyanurate were added to 125mL of tetrahydrofuran, and then 0.1g of photoinitiator 2-hydroxy-2-methylphenylpropane-1-one was added. The mixture was irradiated with ultraviolet light at 40℃ for 3h with a wavelength of 365nm. After the reaction was completed, the mixture was filtered, the filter cake was washed with n-hexane, and then dried under vacuum to obtain hyperbranched polyimide.

[0075] S4. Disperse 10g of nano-zirconia in 145mL of 50% ethanol solution, sonicate for 45min to form a dispersion, add 12.5g of itaconic acid and 0.075g of p-toluenesulfonic acid to the dispersion, heat to 75℃ and reflux for 8h. After the reaction is completed, centrifuge the reaction solution, wash the precipitate with ethanol, and then vacuum dry to obtain itaconic acid modified nano-zirconia.

[0076] S5. Add 40g of hyperbranched polyimide, 10g of itaconic acid-modified nano-zirconia and 0.9mL of triethylamine to 550mL of N,N-dimethylacetamide. Under nitrogen protection, add 0.4g of photoinitiator 2-hydroxy-2-methylphenylpropane-1-one. At 40℃, irradiate with ultraviolet light with a wavelength of 365nm for 3h. After the reaction is completed, centrifuge the reaction solution, wash the precipitate with N,N-dimethylacetamide, and dry it under vacuum to obtain hyperbranched polyimide polymer-modified nano-zirconia.

[0077] The preparation method of the high-temperature resistant, high-performance neodymium iron boron permanent magnet material includes the following steps:

[0078] (1) Weigh the neodymium iron boron magnetic powder, auxiliary metal and silane coupling agent according to the proportion, mix them and smelt them to obtain alloy ingots;

[0079] (2) The alloy ingot is crushed and powdered, and then oriented and pressed under a magnetic field strength of 2.0T;

[0080] (3) The compact is sintered under vacuum or argon protection at a temperature of 1060℃ for 3 hours.

[0081] (4) The sintered magnets are subjected to two-stage tempering: the first stage tempering temperature is 850℃ and the holding time is 1.5h; the second stage tempering temperature is 550℃ and the holding time is 2.5h.

[0082] (5) The hyperbranched polyimide polymer modified nano-zirconia is dispersed in N-methylpyrrolidone to prepare a coating liquid with a solid content of 10% by mass, and uniformly coated on the magnet surface.

[0083] (6) The magnet coated with hyperbranched polyimide polymer modified nano-zirconia was cured at 150°C for 1.5 h to obtain the permanent magnet material.

[0084] Comparative Example 1: The difference between this comparative example and Example 3 is that an equal amount of unmodified polyimide and nano-zirconia is used instead of hyperbranched polyimide polymer-modified nano-zirconia. The feeding ratio of polyimide and nano-zirconia is the same as that of hyperbranched polyimide and itaconic acid-modified nano-zirconia in Example 3. The other components, component contents, and preparation process are the same as in Example 3.

[0085] Comparative Example 2: The difference between this comparative example and Example 3 is that the components only contain neodymium iron boron magnetic powder and auxiliary metals, while the other components, component contents, and preparation process are the same as in Example 3.

[0086] Comparative Example 3: The difference between this comparative example and Example 3 is that an equal amount of hyperbranched polyimide is used instead of hyperbranched polyimide polymer-modified nano-zirconia in the components. The other components, component contents, and preparation process are the same as in Example 3.

[0087] Results Analysis

[0088] According to the national standard GB / T 3217-2013 "Magnetic Test Methods for Permanent Magnet (Hard Magnetic) Materials", the remanence (Br), coercivity (Hcj), and maximum energy product (BH) of each group of materials at 20℃ were determined. max After the sample was kept at 150℃ for 1 hour, its coercivity (Hcj), remanence (Br), and maximum energy product (BH) were measured. max The remanence temperature coefficient (αBr) and coercivity temperature coefficient (βHcj) for the range of 20-150℃ are calculated using the following formulas:

[0089] Temperature coefficient of remanence: αBr=(Br t−Br0) / Br0×(T-T0)×100% (unit: % / ℃),

[0090] Temperature coefficient of coercivity: βHcj=(Hcj) t −Hcj0) / Hcj0×(T-T0)×100% (unit: % / ℃),

[0091] Where Br0 and Hcj0 are parameters at 20℃, Br t Hcj t The parameters are set to 150℃, T=150℃, T0=20℃.

[0092] The flexural strength and tensile strength of each group of materials were measured using a universal testing machine, and the hardness of each group of materials was determined using a Vickers hardness tester. The results of the above measurements are shown in Table 1.

[0093] Table 1 Comparison of Performance Test Results of NdFeB Permanent Magnet Materials

[0094]

[0095] As shown in Table 1, at 20℃, Comparative Example 1 exhibits the highest remanence and magnetic energy product because it contains no non-magnetic additives and has the highest content of magnetic materials. However, at 20℃, the coercivity of all example groups is significantly higher than that of Comparative Example 1, demonstrating the effective role of the auxiliary metal and hyperbranched polyimide polymer-modified nano-zirconia composite in enhancing intrinsic coercivity. High-temperature coercivity is a key indicator for evaluating high-temperature resistance. At 150℃, the retention rates of coercivity, remanence, and maximum magnetic energy product in the example groups are much higher than those in all comparative examples. In Comparative Example 1, due to the lack of protection, its coercivity, remanence, and maximum magnetic energy product all decrease significantly. The small absolute values ​​of the remanence temperature coefficient and coercivity temperature coefficient in each example group indicate their magnetic properties. The decay rate with increasing temperature is slow, and the thermal stability is better than that of the comparative example. In the bending strength and hardness tests, the mechanical properties of the example group are the best. The hardness and strength of the comparative example 1 are mainly due to the lack of modification effect of hyperbranched polyimide polymer modified nano-zirconia in the matrix itself. Due to poor interfacial bonding, the mechanical properties of the comparative example 2 are even lower than those of the comparative example 1. The strength of the comparative example 3 is acceptable, but the hardness is obviously insufficient. This proves the key contribution of nano-zirconia to improving the hardness and wear resistance of the material. In summary, the present invention significantly improves the coercivity, high temperature stability and mechanical properties of neodymium iron boron permanent magnet materials by the synergistic effect of hyperbranched polyimide polymer modified nano-zirconia and auxiliary metal, while reducing the room temperature magnetic properties by a small amount.

[0096] The tensile fracture surface of the sample from Example 3 was observed using a LEO 1530VP scanning electron microscope; the image is shown below. Figure 1 ,from Figure 1As can be seen, the components in the permanent magnet material are evenly dispersed and in close contact. The morphology of the magnetic powder particles is difficult to distinguish, indicating that the components of the permanent magnet material prepared by this invention are fully combined and evenly distributed, without agglomeration or stratification.

[0097] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

[0098] The present invention and its embodiments have been described above. This description is not restrictive, and the embodiments shown are only one of the embodiments of the present invention. The actual application is not limited to this. In conclusion, if those skilled in the art are inspired by this description and design similar methods and embodiments without departing from the spirit of the present invention, they should all fall within the protection scope of the present invention.

Claims

1. A high-temperature resistant, high-performance neodymium iron boron permanent magnet material, characterized in that: The composition includes the following components by weight: 90-108 parts of neodymium iron boron magnetic powder, 4-10 parts of auxiliary metal, 2.5-5 parts of hyperbranched polyimide polymer-modified nano-zirconia, and 0.1-1 parts of silane coupling agent; The hyperbranched polyimide polymer-modified nano-zirconia was prepared through the following steps: S1. N'-(2-aminoethyl)-N'-(4,6-dichloro-1,3,5-triazin-2-yl)ethylenediamine and 4-vinylaniline were added to N,N-dimethylformamide, followed by triethylamine. The mixture was stirred at 60-90°C for 4-8 hours under nitrogen protection. The reaction solution was poured into deionized water, filtered, and the filter cake was washed with deionized water until neutral. The mixture was then dried under vacuum to obtain the triazinyldiamine monomer. S2. Triazine diamine monomer and 4,4'-biphenyl ether dianhydride were added to N-methylpyrrolidone. Under nitrogen protection, the mixture was stirred at 0-5℃ for 4-6 h. Then pyridine was added, the temperature was raised to 150-180℃, and the mixture was stirred for 8-12 h. The reaction solution was poured into ethanol, filtered, and the filter cake was washed three times with ethanol under reflux. The mixture was then dried under vacuum to obtain triazine polyimide. S3. Triazine polyimide and tris[2-(3-mercaptopropoxy)ethyl]isocyanurate were added to tetrahydrofuran, and then photoinitiator 2-hydroxy-2-methylphenylpropane-1-one was added. The mixture was irradiated with ultraviolet light at a wavelength of 365 nm at 30-50°C for 2-4 hours. After the reaction was completed, the mixture was filtered, the filter cake was washed with n-hexane, and then dried under vacuum to obtain hyperbranched polyimide. S4. Disperse nano-zirconia in 50% ethanol solution, sonicate for 30-60 min to form a dispersion, add itaconic acid and p-toluenesulfonic acid to the dispersion, heat to 70-80℃ and reflux for 6-10 h. After the reaction is completed, centrifuge the reaction solution, wash the precipitate with ethanol, and then vacuum dry to obtain itaconic acid modified nano-zirconia. S5. Hyperbranched polyimide, itaconic acid-modified nano-zirconia, and triethylamine were added to N,N-dimethylacetamide. Under nitrogen protection, 2-hydroxy-2-methylphenylpropane-1-one was added as a photoinitiator. The reaction was carried out at 30-50°C with ultraviolet light of wavelength 365 nm for 2-4 hours. After the reaction was completed, the reaction solution was centrifuged, the precipitate was washed with N,N-dimethylacetamide, and dried under vacuum to obtain hyperbranched polyimide polymer-modified nano-zirconia.

2. The high-temperature resistant, high-performance NdFeB permanent magnet material according to claim 1, characterized in that: In step S1, the feeding ratio of N'-(2-aminoethyl)-N'-(4,6-dichloro-1,3,5-triazin-2-yl)ethylenediamine, 4-vinylaniline, triethylamine, and N,N-dimethylformamide is 10g: 5.07-6.08g: 7.12-8.90mL: 107-191mL.

3. The high-temperature resistant, high-performance NdFeB permanent magnet material according to claim 2, characterized in that: In step S2, the feeding ratio of triazine diamine monomer, 4,4'-biphenyl ether dianhydride, pyridine, and N-methylpyrrolidone is 10g: 9.77-10.26g: 2.54-3.81mL: 153-236mL.

4. The high-temperature resistant, high-performance neodymium iron boron permanent magnet material according to claim 3, characterized in that: In step S3, the feeding ratio of triazine polyimide, tris[2-(3-mercaptopropoxy)ethyl]isocyanurate, 2-hydroxy-2-methylphenylpropane-1-one and tetrahydrofuran is 10g: 5.1-8.2g: 0.067-0.145g: 90-163mL.

5. The high-temperature resistant, high-performance NdFeB permanent magnet material according to claim 4, characterized in that: In step S4, the feeding ratio of nano-zirconia, itaconic acid, p-toluenesulfonic acid and ethanol solution is 10g: 10-15g: 0.05-0.1g: 110-180mL.

6. The high-temperature resistant, high-performance NdFeB permanent magnet material according to claim 5, characterized in that: In step S5, the feeding ratio of hyperbranched polyimide, itaconic acid-modified nano-zirconia, N,N-dimethylacetamide, triethylamine, and 2-hydroxy-2-methylphenylpropane-1-one is 30-50g: 10g: 340-766mL: 0.41-1.37mL: 0.2-0.6g.

7. The high-temperature resistant, high-performance NdFeB permanent magnet material according to claim 6, characterized in that: The silane coupling agent is one of γ-aminopropyltriethoxysilane, γ-(2,3-epoxypropoxy)propyltrimethoxysilane, or methacryloyloxypropyltrimethoxysilane.

8. The high-temperature resistant, high-performance NdFeB permanent magnet material according to claim 7, characterized in that: The auxiliary metal is composed of the following components in mass percentage: boron 0.5-1.5%, molybdenum 0.5-2%, gadolinium 1-3%, copper 0.2-1%, gallium 0.2-0.8%, cobalt 1-5%, with the remainder being neodymium.

9. The method for preparing the high-temperature resistant, high-performance NdFeB permanent magnet material as described in any one of claims 1-8, characterized in that: Includes the following steps: (1) Weigh the neodymium iron boron magnetic powder, auxiliary metal and silane coupling agent according to the proportion, mix them and smelt them to obtain alloy ingots; (2) The alloy ingot is crushed and powdered, and then oriented and pressed under a magnetic field strength of 1.5-2.5T; (3) The compact is sintered under vacuum or argon protection at a temperature of 1040-1080℃ and held for 2-4 hours. (4) The sintered magnets are subjected to two-stage tempering: the first stage tempering temperature is 800-900℃ and the holding temperature is 1-2h; the second stage tempering temperature is 500-600℃ and the holding temperature is 2-3h. (5) The hyperbranched polyimide polymer modified nano-zirconia is dispersed in N-methylpyrrolidone to prepare a coating liquid with a solid content of 5-15% by mass and uniformly coated on the magnet surface. (6) The magnet coated with hyperbranched polyimide polymer modified nano-zirconia is cured at 100-200℃ for 0.5-2h to obtain the permanent magnet material.

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