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

Abstract

The invention discloses a high-temperature-resistant high-performance neodymium-iron-boron permanent magnet material and a preparation method thereof, and belongs to the technical field of neodymium-iron-boron permanent magnet materials. The material is prepared from neodymium iron boron magnetic powder, auxiliary metal, hyperbranched polyimide polymer modified nano zirconium oxide and a silane coupling agent through mixing, smelting, crushing, sintering, tempering, coating and curing. The hyperbranched polyimide polymer modified nano-zirconia is introduced into the components, so that the permanent magnet material has excellent thermal stability, the permanent magnet material can still keep stable magnetic performance and mechanical performance at high temperature, the attenuation resistance is good, the thermal demagnetization is low, and the interface bonding strength is improved after the nano-zirconia is modified by hyperbranched polyimide. The interfacial compatibility between the nano zirconium oxide and the polyimide is enhanced through click chemical reaction, and the interfacial bonding strength of the nano zirconium oxide on a neodymium iron boron matrix is improved. The three-dimensional branched structure of the hyperbranched polyimide can form physical crosslinking points in the material, so that the mechanical strength of the material is enhanced.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of neodymium-iron-boron permanent magnetic materials, and particularly relates to a high-temperature-resistant high-performance neodymium-iron-boron permanent magnetic material and a preparation method thereof. BACKGROUND

[0002] Neodymium-iron-boron permanent magnetic materials are widely used in the fields of wind power generation, new energy vehicle driving motor, precision medical instruments, aerospace and electronic information, etc. due to their extremely high magnetic energy product, high coercivity and high residual magnetic density. However, the traditional neodymium-iron-boron magnet is prone to significant attenuation of magnetic properties under high-temperature environment, and has a low Curie temperature (usually between 310-410°C), and the coercivity sharply decreases at high temperature, which seriously limits its application under high-temperature working conditions.

[0003] In order to improve the high-temperature resistance of neodymium-iron-boron materials, the existing technology usually adopts an alloying method, which adds heavy rare earth elements (such as Dy and Tb) for grain boundary diffusion to improve the coercivity and thermal stability of the magnet, but such elements are expensive and scarce in resources, which greatly increases the cost of the material. Another approach is to introduce a second phase or composite ceramic particles, such as oxides and nitrides, into the magnet to inhibit grain boundary migration and magnetic domain reversal at high temperature, but such methods often face problems such as poor interface bonding, uneven dispersion, etc., leading to inconsistency of mechanical and magnetic properties.

[0004] The invention patent with the publication number CN120126889A proposes a ferrite / neodymium-iron-boron composite magnetic material, which uses polyimide as part of the binder phase. However, the polyimide used in the method of this patent has poor compatibility and dispersibility with ferrite magnetic powder and neodymium-iron-boron magnetic powder, and is prone to interface defects and agglomeration, affecting the uniformity and stability of the overall performance of the material. Especially under high-temperature conditions, the difference in thermal expansion coefficient between organic matter and inorganic magnetic powder is significant, which easily leads to micro-cracks and further degradation of magnetic properties. In addition, the neodymium-iron-boron material in this invention is a bonded neodymium-iron-boron material, which has disadvantages in impact resistance, bending resistance and shear resistance compared with 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 a key to improving the high-temperature performance of neodymium-iron-boron permanent magnetic materials. SUMMARY

[0005] In view of the above situation, in order to overcome the defects of the prior art, the application discloses a high-temperature-resistant high-performance neodymium-iron-boron permanent magnetic material, which is prepared by mixing, grinding, molding, curing and other steps from neodymium-iron-boron magnetic powder, auxiliary metal, hyperbranched polyimide polymer modified nano zirconium oxide and silane coupling agent. By introducing hyperbranched polyimide polymer modified nano zirconium oxide, the comprehensive performance of the material is significantly improved.

[0006] In order to achieve the above object, the following technical scheme is adopted: on the one hand, the application provides a high-temperature-resistant high-performance neodymium-iron-boron permanent magnet material, which comprises the following components in parts by mass: neodymium-iron-boron magnetic powder 90-108 parts, auxiliary metal 4-10 parts, hyperbranched polyimide polymer modified nano zirconium oxide 2.5-5 parts, and silane coupling agent 0.1-1 part.

[0007] Further, the hyperbranched polyimide polymer modified nano zirconium oxide is prepared by the following steps: S1. N'-(2-aminoethyl)-N'-(4,6-dichloro-1,3,5-triazin-2-yl) ethylenediamine and 4-vinylaniline are added to N,N-dimethylformamide, and triethylamine is added, and stirring reaction is carried out at 60-90 DEG C under nitrogen protection for 4-8 h, the reaction liquid is poured into deionized water, filtration is carried out, the filter cake is washed to neutral with deionized water, and vacuum drying is carried out to obtain triazine-based diamine monomer; The reaction process of the triazine-based diamine monomer is as follows: ; The N'-(2-aminoethyl)-N'-(4,6-dichloro-1,3,5-triazin-2-yl) ethylenediamine is obtained by the reaction of cyanuric chloride and diethylenetriamine, and the reaction process is as follows: ; S2. The triazine-based diamine monomer and 4,4'-diphenyl ether dianhydride are added to N-methylpyrrolidone, pyridine is added after stirring reaction at 0-5 DEG C under nitrogen protection for 4-6 h, and the temperature is increased to 150-180 DEG C, and stirring reaction is carried out for 8-12 h, the reaction liquid is poured into ethanol, filtration is carried out, the filter cake is washed with ethanol reflux for 3 times, and vacuum drying is carried out to obtain triazine-based polyimide; S3. The triazine-based polyimide and tris[2-(3-mercapto propoxy) ethyl] isocyanurate are added to tetrahydrofuran, and a photoinitiator 2-hydroxy-2-methylphenylpropane-1-ketone is added, and the reaction is carried out under the irradiation of ultraviolet light with a wavelength of 365 nm at 30-50 DEG C for 2-4 h, and after the reaction is completed, filtration is carried out, the filter cake is washed with n-hexane, and then vacuum drying is carried out to obtain hyperbranched polyimide; S4. Nano zirconium oxide is dispersed in 50% ethanol solution, ultrasonic treatment is carried out for 30-60 min to form a dispersion liquid, itaconic acid and p-toluenesulfonic acid are added to the dispersion liquid, the temperature is increased to 70-80 DEG C to reflux for 6-10 h, after the reaction is completed, the reaction liquid is centrifuged and separated, the precipitate is washed with ethanol, and then vacuum drying is carried out to obtain itaconic acid modified nano zirconium oxide; S5. The hyperbranched polyimide, itaconic acid modified nano zirconium oxide and triethylamine are added into N,N-dimethylacetamide, under the protection of nitrogen, a photoinitiator 2-hydroxy-2-methylphenylpropane-1-ketone is added, and the reaction is irradiated with ultraviolet light with a wavelength of 365 nm at 30-50 °C for 2-4 h. After the reaction is completed, the reaction solution is centrifuged and separated, the precipitate is washed with N,N-dimethylacetamide, and vacuum drying is performed to obtain hyperbranched polyimide polymer modified nano zirconium oxide.

[0008] In the above reaction process, first, N'-(2-aminoethyl)-N'-(4,6-dichloro-1,3,5-triazin-2-yl)ethylenediamine containing a triazine group is reacted with 4-vinylaniline to introduce a double bond, then the product is used as a diamine monomer, and reacted with 4,4'-diphenyl ether dianhydride to obtain a triazine-based polyimide. The triazine-based polyimide is reacted with tri[2-(3-mercaptopropoxy)ethyl]isocyanurate having three mercapto groups in the molecular structure through a thiol-alkenyl click reaction, and the mercapto group is controlled to be in excess to obtain a hyperbranched polyimide containing unreacted mercapto groups. Itaconic acid is reacted with the hydroxyl groups on the surface of nano zirconium oxide to obtain modified nano zirconium oxide, and at the same time, a double bond is introduced onto the surface of nano zirconium oxide. The obtained itaconic acid modified nano zirconium oxide is reacted with the hyperbranched polyimide to finally obtain hyperbranched polyimide polymer modified nano zirconium oxide.

[0009] Further, in the 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 10 g: 5.07-6.08 g: 7.12-8.90 mL: 107-191 mL.

[0010] Further, in the step S2, the feeding ratio of triazine-based diamine monomer, 4,4'-diphenyl ether dianhydride, pyridine and N-methylpyrrolidone is 10 g: 9.77-10.26 g: 2.54-3.81 mL: 153-236 mL.

[0011] Further, in the step S3, the feeding ratio of triazine-based polyimide, tri[2-(3-mercaptopropoxy)ethyl]isocyanurate, 2-hydroxy-2-methylphenylpropane-1-ketone and tetrahydrofuran is 10 g: 5.1-8.2 g: 0.067-0.145 g: 90-163 mL.

[0012] Further, in the step S4, the feeding ratio of nano zirconium oxide, itaconic acid, p-toluenesulfonic acid and ethanol solution is 10 g: 10-15 g: 0.05-0.1 g: 110-180 mL.

[0013] Further, the feeding ratio of hyperbranched polyimide, itaconic acid modified nano zirconium oxide, N,N-dimethylacetamide, triethylamine and 2-hydroxy-2-methylphenylpropane-1-ketone in step S5 is 30-50 g: 10 g: 340-766 mL: 0.41-1.37 mL: 0.2-0.6 g.

[0014] Further, the silane coupling agent is one of gamma-aminopropyl triethoxysilane, gamma-(2,3-epoxypropoxy) propyl trimethoxysilane or methacryloyloxy propyl trimethoxysilane.

[0015] Further, the auxiliary metal is composed of the following components by 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%, and the rest is neodymium.

[0016] In another aspect, the application also provides a preparation method of the high-temperature-resistant high-performance neodymium-iron-boron permanent magnet material, comprising the following steps: (1) weighing the neodymium-iron-boron magnetic powder, auxiliary metal and silane coupling agent according to the proportion, mixing and then melting to obtain an alloy ingot; (2) crushing the alloy ingot into powder and performing orientation molding under the condition of a magnetic field strength of 1.5-2.5 T; (3) sintering the compact under vacuum or argon protection, the sintering temperature is 1040-1080℃, and the holding time is 2-4 h; (4) performing two-stage tempering treatment on the sintered magnet: the first-stage tempering temperature is 800-900℃, and the holding time is 1-2 h; the second-stage tempering temperature is 500-600℃, and the holding time is 2-3 h; (5) dispersing the hyperbranched polyimide polymer modified nano zirconium oxide in N-methyl pyrrolidone to prepare a coating liquid with a solid content of 5-15% by mass fraction, and uniformly coating the surface of the magnet; (6) curing the magnet coated with the hyperbranched polyimide polymer modified nano zirconium oxide at 100-200℃ for 0.5-2 h to obtain the permanent magnet material.

[0017] The high-temperature-resistant high-performance neodymium-iron-boron permanent magnet material prepared by the application is prepared by mixing, melting, crushing, sintering, tempering, coating and curing of neodymium-iron-boron magnetic powder, auxiliary metal, hyperbranched polyimide polymer modified nano zirconium oxide and silane coupling agent, and the hyperbranched polyimide polymer modified nano zirconium oxide is coated on the surface of the neodymium-iron-boron material, which significantly improves the comprehensive performance of the permanent magnet material.

[0018] The hyperbranched polyimide itself has excellent thermal stability, the triazine ring and isocyanurate structure contained in the molecular chain further improve the thermal decomposition temperature and the oxidation resistance, the triazine ring is an aromatic heterocyclic structure, has high bond energy and conjugate stability, and the isocyanurate structure has good thermal stability and chemical inertness, the structure units jointly act, so that the material can still maintain stable magnetic properties and mechanical properties at high temperature, the nano zirconium oxide itself is a high-temperature-resistant ceramic material, after being modified by the hyperbranched polyimide, the interface bonding strength of the nano zirconium oxide on the permanent magnet material matrix is improved, and the grain boundary migration and magnetic performance attenuation at high temperature are inhibited.

[0019] By means of a thiol-alkenyl click chemical reaction, unreacted thiol groups are introduced into the hyperbranched polyimide molecules, so that the thiol groups can further react with the double bonds on the surface of the itaconic acid modified nano zirconium oxide to form chemical bonds, and the interfacial compatibility between the nano zirconium oxide and the polyimide is enhanced, and meanwhile, the carboxyl and hydroxyl groups introduced on the surface of the nano zirconium oxide during the itaconic acid modification process also enhance the interaction between the nano zirconium oxide and the silane coupling agent and the metal surface, and further improve the interface bonding state of the overall material.

[0020] The three-dimensional branched structure of the hyperbranched polyimide has more terminal functional groups and molecular chain entanglement ability, can form physical crosslinking points on the material surface, and enhances the mechanical strength of the material, and the introduction of the nano zirconium oxide plays a reinforcing phase role, improves the hardness, wear resistance and fatigue resistance of the permanent magnet material, and the synergistic effect of the two significantly improves the mechanical properties and durability of the permanent magnet material, so that the permanent magnet material has good anti-decay ability and low thermal demagnetization.

[0021] In addition, the addition of the auxiliary metal element can also optimize the grain boundary phase structure and magnetic domain organization of the neodymium-iron-boron magnet, so as to improve the coercive force and Curie temperature. BRIEF DESCRIPTION OF DRAWINGS

[0022] Figure 1 The SEM image of the tensile fracture surface of the neodymium-iron-boron permanent magnet material prepared in example 3 of the present application.

[0023] The accompanying drawings are used to provide a further understanding of the present application, and constitute a part of the specification, and are used to explain the present application together with the embodiments of the present application, and do not constitute a limitation on the present application. DETAILED DESCRIPTION

[0024] The technical solutions in the embodiments of the present application are described below clearly and completely, obviously, the described embodiments are only part of the embodiments of the present application, not all the embodiments, based on the embodiments in the present application, all other embodiments obtained by the person skilled in the art without creative labor belong to the protection scope of the present application.

[0025] Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. Also, any method and material similar or equivalent to those described herein can be used in the practice of the present application. The preferred methods and materials are described herein, by way of example only, and without limitation, as encompassed within the scope of the present application.

[0026] The experimental methods in the following examples are all conventional methods unless otherwise specified. The experimental materials used in the following examples are all commercially available unless otherwise specified.

[0027] Example 1: A high-temperature-resistant high-performance neodymium-iron-boron permanent magnet material, comprising the following components by mass fraction: neodymium-iron-boron magnetic powder 90 parts, auxiliary metal 4 parts, hyperbranched polyimide polymer modified nano zirconium oxide 2.5 parts, silane coupling agent 0.1 part; the silane coupling agent is γ-aminopropyl triethoxysilane; 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%, and the rest is neodymium.

[0028] The hyperbranched polyimide polymer modified nano zirconium oxide is prepared by the following steps: S1. 10g of N'-(2-aminoethyl)-N'-(4,6-dichloro-1,3,5-triazin-2-yl)ethylenediamine and 5.07g of 4-vinylaniline are added to 107mL of N,N-dimethylformamide, then 7.12mL of triethylamine is added, and the reaction is stirred at 60°C under nitrogen protection for 4h. The reaction solution is poured into deionized water, filtered, and the filter cake is washed with deionized water until neutral, and then vacuum dried to obtain a triazine-based diamine monomer; S2. 10g of the triazine-based diamine monomer and 9.77g of 4,4'-biphenyl ether dianhydride are added to 153mL of N-methylpyrrolidone, and the reaction is stirred at 0°C under nitrogen protection for 4h, then 2.54mL of pyridine is added, and the reaction is stirred at 150°C for 8h. The reaction solution is poured into ethanol, filtered, and the filter cake is refluxed with ethanol for 3 times, and then vacuum dried to obtain a triazine-based polyimide; S3. 10g of the triazine-based polyimide and 5.1g of tris[2-(3-mercaptopropoxy)ethyl]isocyanurate are added to 90mL of tetrahydrofuran, then 0.067g of a photoinitiator 2-hydroxy-2-methylphenylpropane-1-ketone is added, and the reaction is irradiated with ultraviolet light of wavelength 365nm at 30°C for 2h. After the reaction is completed, the reaction solution is filtered, the filter cake is washed with n-hexane, and then vacuum dried to obtain a hyperbranched polyimide; S4. 10 g of nano-zirconium oxide was dispersed in 110 mL of 50% ethanol solution, and ultrasonic treatment was performed for 30 min to form a dispersion liquid. 10 g of itaconic acid and 0.05 g of p-toluenesulfonic acid were added to the dispersion liquid, and the reaction was performed at 70°C under reflux for 6 h. After the reaction was completed, the reaction liquid was centrifuged and separated, the precipitate was washed with ethanol, and then vacuum drying was performed to obtain itaconic acid-modified nano-zirconium oxide; S5. 30 g of hyperbranched polyimide, 10 g of itaconic acid-modified nano-zirconium oxide, and 0.41 mL of triethylamine were added to 340 mL of N,N-dimethylacetamide. Under nitrogen protection, 0.2 g of a photoinitiator 2-hydroxy-2-methylphenylpropane-1-ketone was added, and the reaction was performed at 30°C under irradiation of ultraviolet light with a wavelength of 365 nm for 2 h. After the reaction was completed, the reaction liquid was centrifuged and separated, the precipitate was washed with N,N-dimethylacetamide, and then vacuum drying was performed to obtain hyperbranched polyimide polymer-modified nano-zirconium oxide.

[0029] The preparation method of the high-temperature-resistant high-performance neodymium-iron-boron permanent magnet material comprises the following steps: (1) The neodymium-iron-boron magnetic powder, the auxiliary metal, and the silane coupling agent are weighed according to the proportion, mixed, and then subjected to melting to obtain an alloy ingot; (2) The alloy ingot is crushed into powder, and the powder is subjected to orientation molding under the condition that the magnetic field strength is 1.5T; (3) The compact is subjected to sintering under vacuum or argon protection, the sintering temperature is 1040°C, and the temperature is maintained for 2h; (4) The magnet after sintering is subjected to two-stage tempering treatment: the first-stage tempering temperature is 800°C, the temperature is maintained for 1h; and the second-stage tempering temperature is 500°C, the temperature is maintained for 2h; (5) The hyperbranched polyimide polymer-modified nano-zirconium oxide is dispersed in N-methylpyrrolidone to prepare a coating liquid with a solid content of 5-15% by mass fraction, and the coating liquid is uniformly coated on the surface of the magnet; (6) The magnet coated with the hyperbranched polyimide polymer-modified nano-zirconium oxide is solidified at 100°C for 0.5h to obtain the permanent magnet material.

[0030] Example 2: A high-temperature-resistant high-performance neodymium-iron-boron permanent magnet material comprises the following components in parts by mass: 108 parts of neodymium-iron-boron magnetic powder, 10 parts of auxiliary metal, 5 parts of hyperbranched polyimide polymer-modified nano-zirconium oxide, and 1 part of silane coupling agent; the silane coupling agent is γ-(2,3-epoxypropoxy) propyl trimethoxysilane; the auxiliary metal is composed of the following components in percentage by mass: 1.5% of boron, 2% of molybdenum, 3% of gadolinium, 1% of copper, 0.8% of gallium, 5% of cobalt, and the rest is neodymium.

[0031] The hyperbranched polyimide polymer-modified nano-zirconium oxide is prepared by the following steps: S1. 10 g of N'-(2-aminoethyl)-N'-(4,6-dichloro-1,3,5-triazin-2-yl)ethylenediamine and 6.08 g of 4-vinylaniline were added to 191 mL of N,N-dimethylformamide, and 8.90 mL of triethylamine was added, and the reaction was stirred at 90°C for 8 h under nitrogen protection. The reaction solution was poured into deionized water, filtered, and the filter cake was washed with deionized water until neutral, and then vacuum dried to obtain a triazine-based diamine monomer; S2. 10 g of the triazine-based diamine monomer and 10.26 g of 4,4'-biphenyl ether dianhydride were added to 236 mL of N-methylpyrrolidone, and after stirring at 5°C for 6 h under nitrogen protection, 3.81 mL of pyridine was added, and the temperature was raised to 180°C, and the reaction was stirred for 12 h. The reaction solution was poured into ethanol, filtered, and the filter cake was washed with refluxing ethanol three times, and then vacuum dried to obtain a triazine-based polyimide; S3. 10 g of the triazine-based polyimide and 8.2 g of tris[2-(3-mercaptopropoxy)ethyl]isocyanurate were added to 163 mL of tetrahydrofuran, and 0.145 g of a photoinitiator 2-hydroxy-2-methylphenylpropan-1-one was added, and the reaction was irradiated with ultraviolet light of wavelength 365 nm at 50°C for 4 h. After the reaction was completed, the reaction solution was filtered, the filter cake was washed with n-hexane, and then vacuum dried to obtain a hyperbranched polyimide; S4. 10 g of nano zirconium oxide was dispersed in 180 mL of 50% ethanol solution, and ultrasonic treatment was performed for 60 min to form a dispersion liquid. 15 g of itaconic acid and 0.1 g of p-toluenesulfonic acid were added to the dispersion liquid, and the temperature was raised to 80°C to reflux for 10 h. After the reaction was completed, the reaction solution was centrifuged and separated, the precipitate was washed with ethanol, and then vacuum dried to obtain itaconic acid modified nano zirconium oxide; S5. 50 g of the hyperbranched polyimide, 10 g of the itaconic acid modified nano zirconium oxide, and 1.37 mL of triethylamine were added to 766 mL of N,N-dimethylacetamide, and 0.6 g of a photoinitiator 2-hydroxy-2-methylphenylpropan-1-one was added under nitrogen protection, and the reaction was irradiated with ultraviolet light of wavelength 365 nm at 50°C for 4 h. After the reaction was completed, the reaction solution was centrifuged and separated, the precipitate was washed with N,N-dimethylacetamide, and then vacuum dried to obtain a hyperbranched polyimide polymer modified nano zirconium oxide.

[0032] The preparation method of the high-temperature-resistant high-performance neodymium-iron-boron permanent magnet material comprises the following steps: (1) The neodymium-iron-boron magnetic powder, the auxiliary metal, and the silane coupling agent are weighed according to the proportion, mixed, and then subjected to melting to obtain an alloy ingot; (2) The alloy ingot is crushed into powder, and the powder is subjected to orientation molding under the condition that the magnetic field strength is 2.5T; (3) The compact is sintered under vacuum or argon protection, and the sintering temperature is 1080°C, and the holding time is 4h; (4) the sintered magnet is subjected to two-stage tempering treatment: 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; (5) the hyperbranched polyimide polymer modified nano zirconium oxide is dispersed in N-methyl pyrrolidone to prepare a coating liquid with a solid content of 15% by mass fraction, and is uniformly coated on the surface of the magnet; (6) the magnet coated with the hyperbranched polyimide polymer modified nano zirconium oxide is cured at 200℃ for 2h to obtain the permanent magnet material.

[0033] Example 3: A high-temperature-resistant high-performance neodymium-iron-boron permanent magnet material, comprising the following components by mass fraction: neodymium-iron-boron magnetic powder 99 parts, auxiliary metal 7 parts, hyperbranched polyimide polymer modified nano zirconium oxide 3.8 parts, silane coupling agent 0.5 parts; the silane coupling agent is methacryloyloxypropyl trimethoxysilane; 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%, and the rest is neodymium.

[0034] The hyperbranched polyimide polymer modified nano zirconium oxide is prepared by the following steps: S1. 10g N'-(2-aminoethyl)-N'-(4,6-dichloro-1,3,5-triazin-2-yl)ethylenediamine and 5.5g 4-vinylaniline are added to 150mL N,N-dimethylformamide, then 8.0mL triethylamine is added, and the reaction is stirred at 75℃ for 6h under nitrogen protection. The reaction liquid is poured into deionized water, filtered, and the filter cake is washed with deionized water until neutral, and then vacuum dried to obtain a triazine-based diamine monomer; S2. 10g triazine-based diamine monomer and 10.0g 4,4'-diphenyl ether dianhydride are added to 195mL N-methyl pyrrolidone, and the reaction is stirred at 2℃ for 5h under nitrogen protection, then 3.25mL pyridine is added, and the reaction is stirred at 165℃ for 10h. The reaction liquid is poured into ethanol, filtered, and the filter cake is washed with refluxing ethanol for 3 times, and then vacuum dried to obtain a triazine-based polyimide; S3. 10g triazine-based polyimide and 6.5g tris[2-(3-mercaptopropoxy)ethyl]isocyanurate are added to 125mL tetrahydrofuran, then 0.1g photoinitiator 2-hydroxy-2-methylphenylpropane-1-ketone is added, and the reaction is irradiated with ultraviolet light of wavelength 365nm at 40℃ for 3h. After the reaction is completed, the reaction liquid is filtered, the filter cake is washed with n-hexane, and then vacuum dried to obtain a hyperbranched polyimide; S4. 10 g of nano-zirconium oxide was dispersed in 145 mL of 50% ethanol solution, and ultrasonic treatment was performed for 45 min to form a dispersion liquid. 12.5 g of itaconic acid and 0.075 g of p-toluenesulfonic acid were added to the dispersion liquid, and the reaction was performed at 75°C under reflux for 8 h. After the reaction was completed, the reaction liquid was centrifuged and separated, the precipitate was washed with ethanol, and then vacuum drying was performed to obtain itaconic acid-modified nano-zirconium oxide; S5. 40 g of hyperbranched polyimide, 10 g of itaconic acid-modified nano-zirconium oxide, and 0.9 mL of triethylamine were added to 550 mL of N,N-dimethylacetamide. Under nitrogen protection, 0.4 g of a photoinitiator 2-hydroxy-2-methylphenylpropane-1-ketone was added, and the reaction was performed at 40°C under irradiation of ultraviolet light with a wavelength of 365 nm for 3 h. After the reaction was completed, the reaction liquid was centrifuged and separated, the precipitate was washed with N,N-dimethylacetamide, and then vacuum drying was performed to obtain hyperbranched polyimide polymer-modified nano-zirconium oxide.

[0035] The preparation method of the high-temperature-resistant high-performance neodymium-iron-boron permanent magnet material comprises the following steps: (1) The neodymium-iron-boron magnetic powder, the auxiliary metal, and the silane coupling agent are weighed according to the proportion, mixed, and then subjected to smelting to obtain an alloy ingot; (2) The alloy ingot is crushed into powder, and the powder is subjected to orientation molding under the condition that the magnetic field strength is 2.0T; (3) The compact is subjected to sintering under vacuum or argon protection, the sintering temperature is 1060°C, and the temperature is maintained for 3h; (4) The magnet after sintering is subjected to two-stage tempering treatment: the first-stage tempering temperature is 850°C, the temperature is maintained for 1.5h; and the second-stage tempering temperature is 550°C, the temperature is maintained for 2.5h; (5) The hyperbranched polyimide polymer-modified nano-zirconium oxide is dispersed in N-methylpyrrolidone to prepare a coating liquid with a solid content of 10% by mass fraction, and the coating liquid is uniformly coated on the surface of the magnet; (6) The magnet coated with the hyperbranched polyimide polymer-modified nano-zirconium oxide is solidified at 150°C for 1.5h to obtain the permanent magnet material.

[0036] Comparative Example 1: The difference between this comparative example and Example 3 is that the same amount of unmodified polyimide and nano-zirconium dioxide are used instead of the hyperbranched polyimide polymer-modified nano-zirconium oxide, the feeding ratio of the polyimide and the nano-zirconium dioxide is the same as the feeding ratio of the hyperbranched polyimide and the itaconic acid-modified nano-zirconium oxide in Example 3, and the other components, component contents, and preparation processes are the same as those in Example 3.

[0037] Comparative Example 2: The difference between this comparative example and Example 3 is that only the neodymium-iron-boron magnetic powder and the auxiliary metal are contained in the components, and the other components, component contents, and preparation processes are the same as those in Example 3.

[0038] Comparative Example 3: The difference between this comparative example and Example 3 is that the same amount of hyperbranched polyimide is used instead of hyperbranched polyimide polymer to modify nano zirconium oxide in the components, and the rest of the components, component content, and preparation process are the same as Example 3.

[0039] Result analysis According to the national standard GB / T 3217-2013 "Permanent magnet (hard magnet) material magnetic test method", the remanence (Br), coercivity (Hcj) and maximum magnetic energy product (BH max ) of each group of materials at 20℃ were determined. After the sample was kept at 150℃ for 1h, the coercivity (Hcj), remanence (Br) and maximum magnetic energy product (BH max ) were measured, and the remanence temperature coefficient (αBr) and coercivity temperature coefficient (βHcj) of 20-150℃ were calculated. The calculation formula is as follows: Reamanence temperature coefficient: αBr=(Br t −Br0) / Br0×(T-T0)×100%(unit: % / ℃), Coercivity temperature coefficient: βHcj=(Hcj t −Hcj0) / Hcj0×(T-T0)×100%(unit: % / ℃), Wherein, Br0, Hcj0 is the parameter at 20℃, Br t , Hcj t is the parameter at 150℃, T=150℃, T0=20℃.

[0040] The bending strength and tensile strength of each group of materials were measured by universal material testing machine, and the hardness of each group of materials was determined by Vickers hardness tester. The above determination results are shown in Table 1.

[0041] Table 1: Comparison of neodymium iron boron permanent magnet material performance test results

[0042] It can be seen from the data in Table 1 that at 20°C, the remanence and magnetic energy product of Comparative Example 1 are the highest because it does not contain any non-magnetic additive phase and has the highest content of magnetic material. However, at 20°C, the coercivity of all embodiment groups is significantly higher than that of Comparative Example 1, proving the effective effect of the composite addition of auxiliary metal and hyperbranched polyimide polymer modified nano-zirconia on improving the intrinsic coercivity. High-temperature coercivity is a key indicator for measuring high-temperature resistance. At 150°C, the retention rates of the coercivity, remanence and maximum magnetic energy product of the embodiment group are much higher than those of all comparative examples. Due to the lack of protection in Comparative Example 1, its coercivity, remanence and maximum magnetic energy product are significantly reduced. The absolute values ​​of the remanence temperature coefficient and coercivity temperature coefficient of each embodiment group are small, indicating that its magnetic properties The attenuation amplitude is slow with increasing temperature, and the thermal stability is better than that of the comparative example; in the bending strength and hardness tests: the mechanical properties of the embodiment group are the best, the hardness and strength of comparative example 1 mainly come from the lack of the modification effect of the matrix itself by the hyperbranched polyimide polymer modified nano-zirconia, the mechanical properties of comparative example 2 are even lower than those of comparative example 1 due to poor interface bonding, the strength of comparative example 3 is acceptable, but the hardness is obviously insufficient, which 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 coercive force, high temperature stability and mechanical properties of neodymium iron boron permanent magnet materials through the synergistic effect of hyperbranched polyimide polymer modified nano-zirconia and auxiliary metal, while reducing a small amount of room temperature magnetic properties.

[0043] The tensile fracture surface of the sample of Example 3 was observed by LEO 1530VP scanning electron microscope. Figure 1 ,from Figure 1 It can be seen from the figure that the components in the permanent magnetic material are evenly dispersed and in close contact, and the morphology of the magnetic powder particles is difficult to distinguish, indicating that the components of the permanent magnetic material prepared by the present invention are fully combined and evenly distributed without agglomeration or stratification.

[0044] While embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions, and variations may be made to these embodiments without departing from the principles and spirit of the invention, and that the scope of the invention is defined by the appended claims and their equivalents.

[0045] The present invention and its embodiments are described above. Such description is not restrictive. The embodiment shown in the embodiment is only one embodiment of the present invention, and actual application is not limited thereto. In short, if a person skilled in the art is inspired by the above, and does not deviate from the purpose of the invention, without creatively designing methods and embodiments similar to the technical solution, they shall fall within the scope of protection of the present invention.

Claims

1. A high-temperature resistant, high-performance NdFeB permanent magnet material, characterized by: The invention comprises the following components in parts 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 zirconium oxide, and 0.1-1 part of silane coupling agent; The hyperbranched polyimide polymer modified nano zirconium oxide is prepared by the following steps: S1. Add N'-(2-aminoethyl)-N'-(4,6-dichloro-1,3,5-triazin-2-yl)ethylenediamine and 4-vinylaniline to N,N-dimethylformamide, then add triethylamine. Under nitrogen protection, stir and react at 60-90°C for 4-8 hours. Pour the reaction solution into deionized water, filter, wash the filter cake with deionized water until neutral, and vacuum dry to obtain a triazine diamine monomer. S2. Add triazine diamine monomer and 4,4'-biphenyl ether dianhydride to N-methylpyrrolidone, stir and react at 0-5°C for 4-6 hours under nitrogen protection, then add pyridine, raise the temperature to 150-180°C, stir and react for 8-12 hours, pour the reaction solution into ethanol, filter, wash the filter cake with ethanol reflux three times, and vacuum dry to obtain triazine polyimide; S3. triazine-based polyimide and tris[2-(3-mercaptopropoxy)ethyl]isocyanurate were added to tetrahydrofuran, and then a photoinitiator 2-hydroxy-2-methylphenylpropane-1-one was added. The reaction was carried out at 30-50°C with ultraviolet light of 365 nm for 2-4 hours. After the reaction was completed, the filter cake was washed with n-hexane and then dried in vacuo to obtain a hyperbranched polyimide. S4. The nano-zirconia was dispersed in a 50% ethanol solution and ultrasonically treated for 30-60 min to form a dispersion. Itaconic acid and p-toluenesulfonic acid were added to the dispersion and the temperature was raised to 70-80 ° C and refluxed for 6-10 h. After the reaction, the reaction solution was centrifuged, the precipitate was washed with ethanol, and then vacuum dried 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, a photoinitiator 2-hydroxy-2-methylphenylpropane-1-one was added. The reaction was carried out at 30-50°C under ultraviolet light with a wavelength of 365 nm for 2-4 hours. After the reaction was completed, the reaction solution was centrifuged and the precipitate was washed with N,N-dimethylacetamide. The hyperbranched polyimide polymer-modified nano-zirconia was obtained by vacuum drying.

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-triazine-2-yl)ethylenediamine, 4-vinylaniline, triethylamine, and N,N-dimethylformamide is 10 g: 5.07-6.08 g: 7.12-8.90 mL: 107-191 mL.

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

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

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-zirconium oxide, itaconic acid, p-toluenesulfonic acid and ethanol solution is 10 g: 10-15 g: 0.05-0.1 g: 110-180 mL.

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-zirconium oxide, N,N-dimethylacetamide, triethylamine and 2-hydroxy-2-methylphenylpropane-1-one is 30-50 g:10 g:340-766 mL:0.41-1.37 mL:0.2-0.6 g.

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-epoxypropyloxy)propyltrimethoxysilane or methacryloxypropyltrimethoxysilane.

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 percentage by mass: 0.5-1.5% boron, 0.5-2% molybdenum, 1-3% gadolinium, 0.2-1% copper, 0.2-0.8% gallium, 1-5% cobalt, and the rest is neodymium.

9. The method for preparing a high-temperature resistant, high-performance NdFeB permanent magnet material according to any one of claims 1 to 8, characterized in that: The following steps are involved: (1) NdFeB magnetic powder, auxiliary metal and silane coupling agent are weighed according to the proportion, mixed and smelted to obtain an alloy ingot; (2) crushing the alloy ingot into powder and subjecting it to orientation pressing under a magnetic field strength of 1.5-2.5T; (3) Sintering the compact under vacuum or argon protection at a temperature of 1040-1080°C for 2-4 hours; (4) The sintered magnet is subjected to two-stage tempering treatment: the first stage tempering temperature is 800-900℃, and the heat preservation time is 1-2h; the second stage tempering temperature is 500-600℃, and the heat preservation time is 2-3h; (5) dispersing the hyperbranched polyimide polymer modified nano-zirconia in N-methylpyrrolidone to prepare a coating liquid with a solid content of 5-15% by mass, and uniformly coating the surface of the magnet; (6) Curing the magnet coated with the hyperbranched polyimide polymer modified nano-zirconia at 100-200° C. for 0.5-2 h to obtain the permanent magnetic material.

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