High-performance sintered neodymium-iron-boron magnet and method of production

Abstract

The application relates to the technical field of magnetic materials, in particular to a high-performance sintered neodymium-iron-boron magnet and a preparation method. In order to improve the service life of the magnet, the magnet material is first limited, the component and the sintering process are controlled, the gradient heating and the heat preservation process are utilized, the sintered magnet has more uniform magnet grain distribution, and the magnetization of the material is more uniform; and on the basis, the anticorrosive coating is modified, the surface of the carboxylated graphene material is modified, silicon elements and long carbon chain structures with terminal epoxy groups are introduced on the surface of the graphene, the introduction of the silicon elements can effectively improve the corrosion resistance of the coating, the long carbon chain can effectively alleviate the defect that the graphene is easy to peel off and separate after participating in the curing of the epoxy resin, and the long carbon chain is favorable for keeping the protection function of the coating for a long time.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of magnetic materials, in particular to a high-performance sintered neodymium-iron-boron magnet and a preparation method thereof. BACKGROUND

[0002] Magnetic materials are a kind of functional materials with a long history and wide application. With the progress of industry and technology, a large number of new magnetic materials have appeared. These materials can be roughly divided into three generations: the first generation is AlNiCo, the second generation is ferrite, and the third generation is rare earth permanent magnet. The rare earth permanent magnet can be further divided into three stages: the first stage is SmCo5, the second stage is Sm2Co 17 , and the third stage is Nd2Fe 14 B. From simple daily packaging magnets to complex new energy vehicles, wind turbines and other fields, magnets have great application prospects.

[0003] However, the common neodymium-iron-boron magnet has a large corrosion potential difference due to different alloy elements, which easily causes corrosion of the magnet and affects the service life and safety of the magnet. SUMMARY

[0004] The application aims to provide a high-performance sintered neodymium-iron-boron magnet and a preparation method thereof to solve the problems in the prior art.

[0005] To achieve the above-mentioned purpose, the application provides the following technical scheme: a high-performance sintered neodymium-iron-boron magnet is composed of a neodymium-iron-boron magnet blank and a corrosion-resistant epoxy coating coated on the surface of the neodymium-iron-boron magnet.

[0006] The ingredient composition of the neodymium-iron-boron magnet blank includes, in terms of weight percentage, Nd: 30-34%, B: 1.8-2.9%, Er: 9.8-12.6%, Co: 2.4-3.8%, Nb: 1.9-2.4%, Tm: 1.4-1.9%, Zr: 0.21-0.28%, and the balance is Fe.

[0007] The corrosion-resistant epoxy coating is formed after the corrosion-resistant epoxy resin coating is cured.

[0008] A preparation method of a high-performance sintered neodymium-iron-boron magnet comprises the following steps:

[0009] S1. preparing a neodymium-iron-boron magnet blank;

[0010] S11. mixing the raw materials according to the proportion, placing them in a smelting furnace, filling argon gas into the smelting furnace to 0.05 MPa after vacuumizing, heating and smelting, and then casting ingots, and placing the ingots in a vacuum environment to fill hydrogen to perform hydrogen fragmentation treatment on the ingots;

[0011] S12. Place the hydrogen-treated ingot back into a vacuum environment, heat it to 300-400℃, and hold it for 1.5-3 hours to complete the dehydrogenation process.

[0012] S13. After the dehydrogenated ingot is coarsely ground into powder, it is then subjected to air jet milling to obtain fine ingot powder. The fine ingot powder is collected and isostatically pressed into shape to obtain an ingot blank.

[0013] S14. Sinter the ingot blank to obtain a neodymium iron boron magnet blank;

[0014] S2. Preparation of corrosion-resistant epoxy coatings;

[0015] S3. After spraying the corrosion-resistant epoxy coating prepared in step S2 onto the surface of the NdFeB magnet blank, the temperature is raised to 50℃ and held for 10-15 min. Then, the temperature is raised to 85-95℃ at a rate of 1-3℃ / min and held for curing for 30-45 min. Finally, the temperature is cooled to room temperature to obtain a high-performance sintered NdFeB magnet.

[0016] Furthermore, in step S2, the method for preparing the corrosion-resistant epoxy coating includes the following steps:

[0017] S21. Under nitrogen atmosphere protection, carboxylated graphene is dispersed in dimethyl sulfoxide and ultrasonically dispersed for 45-90 min. Then, dicyclohexylcarbodiimide is added and ultrasonically dispersed for another 15-30 min. The mixture is then added dropwise to 2-azidoethylamine at a uniform rate over 1-4 h. During the addition, the reaction system temperature is controlled at 85-105℃ and the mixture is stirred continuously. After the addition is completed, the mixture is kept at the same temperature and ultrasonically vibrated for another 2-5 h. The precipitate is then separated by centrifugation and washed with diethyl ether 2-5 times. Finally, it is dried to constant weight to obtain azide-modified graphene.

[0018] S22. Under a nitrogen atmosphere, butynedioic acid is dispersed in diethyl ether and stirred until homogeneous. Then, dicyclohexylcarbodiimide is added and mixed for 5-15 min. The mixture is then added dropwise to 1,3-bis(3-aminopropyl)-1,1,3,3-tetramethyldisiloxane. The temperature is raised to 35°C and stirred for 1-2 h to remove the diethyl ether. The temperature is then raised again to 85-120°C and stirred for 4-8 h to obtain a terminal aminosilane intermediate.

[0019] S23. Disperse the terminal aminosilane intermediate in DMF, stir and mix evenly, then add it dropwise to 1,1,3,3-tetramethyl-1,3-bis[3-(epoxyethyl methoxy)propyl]disiloxane, heat to 90-100℃, stir and react for 2-4 hours, then remove excess solvent and unreacted 1,1,3,3-tetramethyl-1,3-bis[3-(epoxyethyl methoxy)propyl]disiloxane monomer by rotary evaporation, then add clean DMF again, heat to 110-125℃, add azide-modified graphene, sonicate and react for 4-8 hours, centrifuge to separate the precipitate, wash the precipitate 2-3 times with DMF, and dry to constant weight to obtain modified graphene;

[0020] S24. After mixing E51 epoxy resin, modified graphene, and antioxidant evenly, add curing agent and continue mixing for 5-10 minutes to obtain corrosion-resistant epoxy coating.

[0021] Furthermore, in step S21, the mass ratio of the carboxylated graphene, dicyclohexylcarbodiimide, and 2-azidoethylamine is 1:(0.015-0.02):(1.5-10).

[0022] Furthermore, in step S22, the mass ratio of butynedioic acid, dicyclohexylcarbodiimide, and 1,3-bis(3-aminopropyl)-1,1,3,3-tetramethyldisiloxane is 1:(0.01-0.015):(3.5-4.4).

[0023] Furthermore, in step S23, the mass ratio of the terminal aminosilane intermediate, 1,1,3,3-tetramethyl-1,3-bis[3-(epoxyethylmethoxy)propyl]disiloxane, and azide-modified graphene is 1:(1-1.2):0.1.

[0024] Furthermore, in step S24, the corrosion-resistant epoxy coating is composed of 50 parts of E51 epoxy resin, 1.5-5 parts of modified graphene, 0.4-0.9 parts of antioxidant, and 11-14 parts of curing agent by weight.

[0025] Furthermore, in step S24, the antioxidant is antioxidant 1010, and the curing agent is dicyandiamide.

[0026] Compared with the prior art, the beneficial effects of the present invention are:

[0027] In order to improve the service life of magnets, this invention first limits the magnet material itself. By controlling its composition and sintering process, and using gradient heating and heat preservation processes, the sintered magnet has a more uniform distribution of magnet grains, thereby making the magnetization of the material more uniform.

[0028] Furthermore, based on this, the present invention also modified its anti-corrosion coating. The present invention first modified the surface of the carboxyl graphene material by using 2-azidoethylamine as a modifier and utilizing the reaction between amino and carboxyl groups to introduce azide groups on the graphene surface.

[0029] Based on this, the present invention uses butynedioic acid containing alkynyl and terminal carboxyl groups as a raw material, reacting it with 1,3-bis(3-aminopropyl)-1,1,3,3-tetramethyldisiloxane containing a terminal amino group, and further reacting it with 1,1,3,3-tetramethyl-1,3-bis[3-(epoxyethylmethoxy)propyl]disiloxane containing a terminal epoxy group, thereby introducing a large amount of silicon element, terminal epoxy group, and alkynyl group into the reaction product; then, graphene containing azide groups is introduced into the reaction system, and the azide groups will... The graphene reacts with acetylene groups to introduce a long carbon chain structure of silicon and terminal epoxy groups onto the graphene surface. The introduction of silicon can effectively improve the corrosion resistance and protective properties of the coating. Furthermore, the terminal epoxy groups allow graphene to participate in the curing of epoxy resin. Considering the high brittleness of epoxy resin after curing, this invention also introduces a long carbon chain structure during the modification of graphene. The long carbon chain can effectively alleviate the defect of high brittleness and easy peeling off of the coating after graphene participates in the curing of epoxy resin, which is beneficial to maintaining the protective function of the coating for a long time. Detailed Implementation

[0030] Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0031] In this application, the raw materials of each component in the neodymium iron boron magnet blanks prepared in Examples 1-5 and Comparative Example 5 are shown in Table 1 below;

[0032] Table 1.

[0033] Nd B Er Co Nb Tm Zr Fe 32.08 2.27 10.42 2.65 2.16 1.62 0.25 balance

[0034] Example 1. A method for preparing a high-performance sintered NdFeB magnet, comprising the following steps:

[0035] S1. Preparation of neodymium iron boron magnet blanks;

[0036] S11. Mix the raw materials according to the proportion, place them in a melting furnace, evacuate the furnace, fill it with argon gas to 0.05MPa, heat up and melt, cast the ingot, place the ingot in a vacuum environment and fill it with hydrogen gas to perform hydrogen crushing treatment on the ingot.

[0037] S12. Place the hydrogen-treated ingot back into a vacuum environment, heat it to 300-400℃, and hold it for 1.5-3 hours to complete the dehydrogenation process.

[0038] S13. After the dehydrogenated ingot is coarsely ground into powder, it is then subjected to air jet milling to obtain fine ingot powder. The fine ingot powder is collected and isostatically pressed into shape to obtain an ingot blank.

[0039] S14. Sinter the ingot blank, evacuate the furnace, heat to 430℃ at a rate of 4℃ / min, hold for 45min, then heat to 850℃ at a rate of 4℃ / min again, hold for 80min, then heat to 1350℃ at a rate of 1.5℃ / min again, hold for 100min, then cool to 500℃ at a rate of 5℃ / min, hold for 20min, then stop heating, cool to room temperature with the furnace, then grind and pickle the surface to obtain the NdFeB magnet blank;

[0040] S2. Preparation of corrosion-resistant epoxy coatings;

[0041] S21. Under nitrogen atmosphere protection, 1 part by weight of carboxylated graphene was dispersed in dimethyl sulfoxide and ultrasonically dispersed for 90 min. Then, 0.02 parts of dicyclohexylcarbodiimide were added and ultrasonically dispersed for another 30 min. The mixture was then uniformly added dropwise to 1.5 parts of 2-azidoethylamine over 3 h. During the dropwise addition, the temperature of the reaction system was controlled at 105 °C and the mixture was stirred continuously. After the dropwise addition was completed, the mixture was kept at the same temperature and ultrasonically vibrated for another 5 h. The precipitate was then separated by centrifugation and washed 5 times with diethyl ether. Finally, the precipitate was dried to constant weight to obtain azide-modified graphene.

[0042] S22. Under a nitrogen atmosphere, 1 part of butynedioic acid was dispersed in diethyl ether and stirred until homogeneous. Then, 0.015 parts of dicyclohexylcarbodiimide were added and mixed for 15 min. The mixture was then added dropwise to 3.5 parts of 1,3-bis(3-aminopropyl)-1,1,3,3-tetramethyldisiloxane. The mixture was heated to 35°C and stirred for 1.5 h to remove the diethyl ether. The mixture was then heated to 98°C and stirred for 6 h to obtain a terminal aminosilane intermediate.

[0043] S23. By weight, 1 part of the terminal aminosilane intermediate was dispersed in DMF and stirred until homogeneous. Then, it was added dropwise to 1 part of 1,1,3,3-tetramethyl-1,3-bis[3-(epoxyethyl methoxy)propyl]disiloxane. The mixture was heated to 90°C and stirred for 3 hours. After removing excess solvent and unreacted 1,1,3,3-tetramethyl-1,3-bis[3-(epoxyethyl methoxy)propyl]disiloxane monomer by rotary evaporation, clean DMF was added again. The mixture was heated to 110°C and 0.1 part of azide-modified graphene was added. After ultrasonic vibration for 6 hours, the precipitate was separated by centrifugation. The precipitate was washed twice with DMF and dried to constant weight to obtain modified graphene.

[0044] S24. By weight, mix 50 parts of E51 epoxy resin, 1.5 parts of modified graphene, and 0.8 parts of antioxidant 1010 evenly, then add 13 parts of dicyandiamide curing agent and continue mixing for 5 minutes to obtain a corrosion-resistant epoxy coating.

[0045] S3. After spraying the corrosion-resistant epoxy coating prepared in step S2 onto the surface of the NdFeB magnet blank, the temperature is raised to 50℃ and held for 10 min. Then, the temperature is raised to 95℃ at a rate of 1℃ / min and held for curing for 45 min. Finally, the temperature is cooled to room temperature to obtain a high-performance sintered NdFeB magnet.

[0046] Example 2. A method for preparing a high-performance sintered NdFeB magnet, comprising the following steps:

[0047] Compared with Example 1, this example increases the amount of modified graphene added in step S24;

[0048] S1. Preparation of neodymium iron boron magnet blanks;

[0049] S11. Mix the raw materials according to the proportion, place them in a melting furnace, evacuate the furnace, fill it with argon gas to 0.05MPa, heat up and melt, cast the ingot, place the ingot in a vacuum environment and fill it with hydrogen gas to perform hydrogen crushing treatment on the ingot.

[0050] S12. Place the hydrogen-treated ingot back into a vacuum environment, heat it to 300-400℃, and hold it for 1.5-3 hours to complete the dehydrogenation process.

[0051] S13. After the dehydrogenated ingot is coarsely ground into powder, it is then subjected to air jet milling to obtain fine ingot powder. The fine ingot powder is collected and isostatically pressed into shape to obtain an ingot blank.

[0052] S14. Sinter the ingot blank, evacuate the furnace, heat to 430℃ at a rate of 4℃ / min, hold for 45min, then heat to 850℃ at a rate of 4℃ / min again, hold for 80min, then heat to 1350℃ at a rate of 1.5℃ / min again, hold for 100min, then cool to 500℃ at a rate of 5℃ / min, hold for 20min, then stop heating, cool to room temperature with the furnace, then grind and pickle the surface to obtain the NdFeB magnet blank;

[0053] S2. Preparation of corrosion-resistant epoxy coatings;

[0054] S21. Under nitrogen atmosphere protection, 1 part by weight of carboxylated graphene was dispersed in dimethyl sulfoxide and ultrasonically dispersed for 90 min. Then, 0.02 parts of dicyclohexylcarbodiimide were added and ultrasonically dispersed for another 30 min. The mixture was then uniformly added dropwise to 1.5 parts of 2-azidoethylamine over 3 h. During the dropwise addition, the temperature of the reaction system was controlled at 105 °C and the mixture was stirred continuously. After the dropwise addition was completed, the mixture was kept at the same temperature and ultrasonically vibrated for another 5 h. The precipitate was then separated by centrifugation and washed 5 times with diethyl ether. Finally, the precipitate was dried to constant weight to obtain azide-modified graphene.

[0055] S22. Under a nitrogen atmosphere, 1 part of butynedioic acid was dispersed in diethyl ether and stirred until homogeneous. Then, 0.015 parts of dicyclohexylcarbodiimide were added and mixed for 15 min. The mixture was then added dropwise to 3.5 parts of 1,3-bis(3-aminopropyl)-1,1,3,3-tetramethyldisiloxane. The mixture was heated to 35°C and stirred for 1.5 h to remove the diethyl ether. The mixture was then heated to 98°C and stirred for 6 h to obtain a terminal aminosilane intermediate.

[0056] S23. By weight, 1 part of the terminal aminosilane intermediate was dispersed in DMF and stirred until homogeneous. Then, it was added dropwise to 1 part of 1,1,3,3-tetramethyl-1,3-bis[3-(epoxyethyl methoxy)propyl]disiloxane. The mixture was heated to 90°C and stirred for 3 hours. After removing excess solvent and unreacted 1,1,3,3-tetramethyl-1,3-bis[3-(epoxyethyl methoxy)propyl]disiloxane monomer by rotary evaporation, clean DMF was added again. The mixture was heated to 110°C and 0.1 part of azide-modified graphene was added. After ultrasonic vibration for 6 hours, the precipitate was separated by centrifugation. The precipitate was washed twice with DMF and dried to constant weight to obtain modified graphene.

[0057] S24. By weight, mix 50 parts of E51 epoxy resin, 5 parts of modified graphene, and 0.8 parts of antioxidant 1010 evenly, then add 13 parts of dicyandiamide curing agent and continue mixing for 5 minutes to obtain a corrosion-resistant epoxy coating.

[0058] S3. After spraying the corrosion-resistant epoxy coating prepared in step S2 onto the surface of the NdFeB magnet blank, the temperature is raised to 50℃ and held for 10 min. Then, the temperature is raised to 95℃ at a rate of 1℃ / min and held for curing for 45 min. Finally, the temperature is cooled to room temperature to obtain a high-performance sintered NdFeB magnet.

[0059] Example 3. A method for preparing a high-performance sintered NdFeB magnet, comprising the following steps:

[0060] Compared with Example 2, this example increases the amount of 2-azidoethylamine added in step S21;

[0061] S2. Preparation of corrosion-resistant epoxy coatings;

[0062] S21. Under a nitrogen atmosphere, 1 part by weight of carboxylated graphene was dispersed in dimethyl sulfoxide and ultrasonically dispersed for 90 min. Then, 0.02 parts of dicyclohexylcarbodiimide were added and ultrasonically dispersed for another 30 min. The mixture was then added dropwise to 10 parts of 2-azidoethylamine over 3 h. During the addition, the temperature of the reaction system was controlled at 105 °C and the mixture was stirred continuously. After the addition was completed, the mixture was kept at the same temperature and ultrasonically vibrated for another 5 h. The precipitate was then separated by centrifugation and washed 5 times with diethyl ether. The precipitate was then dried to constant weight to obtain azide-modified graphene.

[0063] S22. Under a nitrogen atmosphere, 1 part of butynedioic acid was dispersed in diethyl ether and stirred until homogeneous. Then, 0.015 parts of dicyclohexylcarbodiimide were added and mixed for 15 min. The mixture was then added dropwise to 3.5 parts of 1,3-bis(3-aminopropyl)-1,1,3,3-tetramethyldisiloxane. The mixture was heated to 35°C and stirred for 1.5 h to remove the diethyl ether. The mixture was then heated to 98°C and stirred for 6 h to obtain a terminal aminosilane intermediate.

[0064] S23. By weight, 1 part of the terminal aminosilane intermediate was dispersed in DMF and stirred until homogeneous. Then, it was added dropwise to 1 part of 1,1,3,3-tetramethyl-1,3-bis[3-(epoxyethyl methoxy)propyl]disiloxane. The mixture was heated to 90°C and stirred for 3 hours. After removing excess solvent and unreacted 1,1,3,3-tetramethyl-1,3-bis[3-(epoxyethyl methoxy)propyl]disiloxane monomer by rotary evaporation, clean DMF was added again. The mixture was heated to 110°C and 0.1 part of azide-modified graphene was added. After ultrasonic vibration for 6 hours, the precipitate was separated by centrifugation. The precipitate was washed twice with DMF and dried to constant weight to obtain modified graphene.

[0065] S24. By weight, mix 50 parts of E51 epoxy resin, 5 parts of modified graphene, and 0.8 parts of antioxidant 1010 evenly, then add 13 parts of dicyandiamide curing agent and continue mixing for 5 minutes to obtain a corrosion-resistant epoxy coating.

[0066] S3. After spraying the corrosion-resistant epoxy coating prepared in step S2 onto the surface of the NdFeB magnet blank, the temperature is raised to 50℃ and held for 10 min. Then, the temperature is raised to 95℃ at a rate of 1℃ / min and held for curing for 45 min. Finally, the temperature is cooled to room temperature to obtain a high-performance sintered NdFeB magnet.

[0067] Example 4. A method for preparing a high-performance sintered NdFeB magnet, comprising the following steps:

[0068] Compared with Example 3, this example increases the amount of 1,3-bis(3-aminopropyl)-1,1,3,3-tetramethyldisiloxane added in step S22;

[0069] S2. Preparation of corrosion-resistant epoxy coatings;

[0070] S21. Under a nitrogen atmosphere, 1 part by weight of carboxylated graphene was dispersed in dimethyl sulfoxide and ultrasonically dispersed for 90 min. Then, 0.02 parts of dicyclohexylcarbodiimide were added and ultrasonically dispersed for another 30 min. The mixture was then added dropwise to 10 parts of 2-azidoethylamine over 3 h. During the addition, the temperature of the reaction system was controlled at 105 °C and the mixture was stirred continuously. After the addition was completed, the mixture was kept at the same temperature and ultrasonically vibrated for another 5 h. The precipitate was then separated by centrifugation and washed 5 times with diethyl ether. The precipitate was then dried to constant weight to obtain azide-modified graphene.

[0071] S22. Under a nitrogen atmosphere, 1 part of butynedioic acid was dispersed in diethyl ether and stirred until homogeneous. Then, 0.015 parts of dicyclohexylcarbodiimide were added and mixed for 15 min. The mixture was then added dropwise to 4.4 parts of 1,3-bis(3-aminopropyl)-1,1,3,3-tetramethyldisiloxane. The mixture was heated to 35°C and stirred for 1.5 h to remove the diethyl ether. The mixture was then heated to 98°C and stirred for 6 h to obtain a terminal aminosilane intermediate.

[0072] S23. By weight, 1 part of the terminal aminosilane intermediate was dispersed in DMF and stirred until homogeneous. Then, it was added dropwise to 1 part of 1,1,3,3-tetramethyl-1,3-bis[3-(epoxyethyl methoxy)propyl]disiloxane. The mixture was heated to 90°C and stirred for 3 hours. After removing excess solvent and unreacted 1,1,3,3-tetramethyl-1,3-bis[3-(epoxyethyl methoxy)propyl]disiloxane monomer by rotary evaporation, clean DMF was added again. The mixture was heated to 110°C and 0.1 part of azide-modified graphene was added. After ultrasonic vibration for 6 hours, the precipitate was separated by centrifugation. The precipitate was washed twice with DMF and dried to constant weight to obtain modified graphene.

[0073] S24. By weight, mix 50 parts of E51 epoxy resin, 5 parts of modified graphene, and 0.8 parts of antioxidant 1010 evenly, then add 13 parts of dicyandiamide curing agent and continue mixing for 5 minutes to obtain a corrosion-resistant epoxy coating.

[0074] S3. After spraying the corrosion-resistant epoxy coating prepared in step S2 onto the surface of the NdFeB magnet blank, the temperature is raised to 50℃ and held for 10 min. Then, the temperature is raised to 95℃ at a rate of 1℃ / min and held for curing for 45 min. Finally, the temperature is cooled to room temperature to obtain a high-performance sintered NdFeB magnet.

[0075] Example 5. A method for preparing a high-performance sintered NdFeB magnet, comprising the following steps:

[0076] Compared with Example 4, this example increases the amount of 1,1,3,3-tetramethyl-1,3-bis[3-(epoxyethylmethoxy)propyl]disiloxane added in step S23;

[0077] S2. Preparation of corrosion-resistant epoxy coatings;

[0078] S21. Under a nitrogen atmosphere, 1 part by weight of carboxylated graphene was dispersed in dimethyl sulfoxide and ultrasonically dispersed for 90 min. Then, 0.02 parts of dicyclohexylcarbodiimide were added and ultrasonically dispersed for another 30 min. The mixture was then added dropwise to 10 parts of 2-azidoethylamine over 3 h. During the addition, the temperature of the reaction system was controlled at 105 °C and the mixture was stirred continuously. After the addition was completed, the mixture was kept at the same temperature and ultrasonically vibrated for another 5 h. The precipitate was then separated by centrifugation and washed 5 times with diethyl ether. The precipitate was then dried to constant weight to obtain azide-modified graphene.

[0079] S22. Under a nitrogen atmosphere, 1 part of butynedioic acid was dispersed in diethyl ether and stirred until homogeneous. Then, 0.015 parts of dicyclohexylcarbodiimide were added and mixed for 15 min. The mixture was then added dropwise to 4.4 parts of 1,3-bis(3-aminopropyl)-1,1,3,3-tetramethyldisiloxane. The mixture was heated to 35°C and stirred for 1.5 h to remove the diethyl ether. The mixture was then heated to 98°C and stirred for 6 h to obtain a terminal aminosilane intermediate.

[0080] S23. By weight, 1 part of the terminal aminosilane intermediate was dispersed in DMF and stirred until homogeneous. Then, it was added dropwise to 1.2 parts of 1,1,3,3-tetramethyl-1,3-bis[3-(epoxyethyl methoxy)propyl]disiloxane. The mixture was heated to 90°C and stirred for 3 hours. After removing excess solvent and unreacted 1,1,3,3-tetramethyl-1,3-bis[3-(epoxyethyl methoxy)propyl]disiloxane monomer by rotary evaporation, clean DMF was added again. The mixture was heated to 110°C and 0.1 parts of azide-modified graphene were added. After ultrasonic vibration for 6 hours, the precipitate was separated by centrifugation. The precipitate was washed twice with DMF and dried to constant weight to obtain modified graphene.

[0081] S24. By weight, mix 50 parts of E51 epoxy resin, 5 parts of modified graphene, and 0.8 parts of antioxidant 1010 evenly, then add 13 parts of dicyandiamide curing agent and continue mixing for 5 minutes to obtain a corrosion-resistant epoxy coating.

[0082] S3. After spraying the corrosion-resistant epoxy coating prepared in step S2 onto the surface of the NdFeB magnet blank, the temperature is raised to 50℃ and held for 10 min. Then, the temperature is raised to 95℃ at a rate of 1℃ / min and held for curing for 45 min. Finally, the temperature is cooled to room temperature to obtain a high-performance sintered NdFeB magnet.

[0083] Comparative Example 1. A method for preparing a high-performance sintered NdFeB magnet, comprising the following steps:

[0084] Compared with Example 1, no modified graphene was prepared in this comparative example;

[0085] S2. Preparation of corrosion-resistant epoxy coatings;

[0086] S24. By weight, mix 50 parts of E51 epoxy resin, 1.5 parts of graphene, and 0.8 parts of antioxidant 1010 evenly, then add 13 parts of dicyandiamide curing agent and continue mixing for 5 minutes to obtain a corrosion-resistant epoxy coating.

[0087] S3. After spraying the corrosion-resistant epoxy coating prepared in step S2 onto the surface of the NdFeB magnet blank, the temperature is raised to 50℃ and held for 10 min. Then, the temperature is raised to 95℃ at a rate of 1℃ / min and held for curing for 45 min. Finally, the temperature is cooled to room temperature to obtain a high-performance sintered NdFeB magnet.

[0088] Testing: The magnetic properties of the samples prepared in Examples 1-5 and Comparative Example 1 were tested according to GB / T 3217;

[0089] The samples prepared in Examples 1-5 and Comparative Example 1 were tested for neutral salt spray resistance according to XBT 903-2002.

[0090] The samples prepared in Examples 1-5 and Comparative Example 1 were placed in an environment of 200°C, kept at that temperature for 1 hour, and then cooled to room temperature. This cycle was repeated 5 times, and the samples were tested again for resistance to neutral salt spray.

[0091] The test results are shown in Table 2 below;

[0092] Table 2

[0093]

[0094] Finally, it should be noted that the above descriptions are merely preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a high-performance sintered NdFeB magnet, characterized in that: Includes the following steps: S1. Preparation of NdFeB magnet blanks: S11. Mix the raw materials according to the proportion, place them in a melting furnace, evacuate the furnace, fill it with argon gas to 0.05MPa, heat up and melt, cast the ingot, place the ingot in a vacuum environment and fill it with hydrogen gas to perform hydrogen crushing treatment on the ingot. S12. Place the hydrogen-treated ingot back into a vacuum environment, heat it to 300-400℃, and hold it for 1.5-3 hours to complete the dehydrogenation process. S13. After the dehydrogenated ingot is coarsely ground into powder, it is then subjected to air jet milling to obtain fine ingot powder. The fine ingot powder is collected and isostatically pressed into shape to obtain an ingot blank. S14. Sinter the ingot blank to obtain a neodymium iron boron magnet blank; The neodymium iron boron magnet blank, by weight percentage, comprises Nd: 30-34%, B: 1.8-2.9%, Er: 9.8-12.6%, Co: 2.4-3.8%, Nb: 1.9-2.4%, Tm: 1.4-1.9%, Zr: 0.21-0.28%, with the balance being Fe; S2. Preparation of corrosion-resistant epoxy coatings: S21. Under nitrogen atmosphere protection, carboxylated graphene is dispersed in dimethyl sulfoxide and ultrasonically dispersed for 45-90 min. Then, dicyclohexylcarbodiimide is added and ultrasonically dispersed for another 15-30 min. The mixture is then added dropwise to 2-azidoethylamine at a uniform rate over 1-4 h. During the addition, the reaction system temperature is controlled at 85-105℃ and the mixture is stirred continuously. After the addition is completed, the mixture is kept at the same temperature and ultrasonically vibrated for another 2-5 h. The precipitate is then separated by centrifugation and washed with diethyl ether 2-5 times. Finally, it is dried to constant weight to obtain azide-modified graphene. S22. Under a nitrogen atmosphere, butynedioic acid is dispersed in diethyl ether and stirred until homogeneous. Then, dicyclohexylcarbodiimide is added and mixed for 5-15 min. The mixture is then added dropwise to 1,3-bis(3-aminopropyl)-1,1,3,3-tetramethyldisiloxane. The temperature is raised to 35°C and stirred for 1-2 h to remove the diethyl ether. The temperature is then raised again to 85-120°C and stirred for 4-8 h to obtain a terminal aminosilane intermediate. S23. Disperse the terminal aminosilane intermediate in DMF, stir and mix evenly, then add it dropwise to 1,1,3,3-tetramethyl-1,3-bis[3-(epoxyethyl methoxy)propyl]disiloxane, heat to 90-100℃, stir and react for 2-4 hours, then remove excess solvent and unreacted 1,1,3,3-tetramethyl-1,3-bis[3-(epoxyethyl methoxy)propyl]disiloxane monomer by rotary evaporation, then add clean DMF again, heat to 110-125℃, add azide-modified graphene, sonicate and react for 4-8 hours, centrifuge to separate the precipitate, wash the precipitate 2-3 times with DMF, and dry to constant weight to obtain modified graphene; S24. After mixing E51 epoxy resin, modified graphene, and antioxidant evenly, add curing agent and continue mixing for 5-10 minutes to obtain corrosion-resistant epoxy coating. S3. After spraying the corrosion-resistant epoxy coating prepared in step S2 onto the surface of the NdFeB magnet blank, the temperature is raised to 50℃ and held for 10-15 min. Then, the temperature is raised to 85-95℃ at a rate of 1-3℃ / min and held for curing for 30-45 min. Finally, the temperature is cooled to room temperature to obtain a high-performance sintered NdFeB magnet.

2. The method for preparing a high-performance sintered NdFeB magnet according to claim 1, characterized in that: In step S21, the mass ratio of the carboxylated graphene, dicyclohexylcarbodiimide, and 2-azidoethylamine is 1:(0.015-0.02):(1.5-10).

3. The method for preparing a high-performance sintered NdFeB magnet according to claim 1, characterized in that: In step S22, the mass ratio of butynedioic acid, dicyclohexylcarbodiimide, and 1,3-bis(3-aminopropyl)-1,1,3,3-tetramethyldisiloxane is 1:(0.01-0.015):(3.5-4.4).

4. The method for preparing a high-performance sintered NdFeB magnet according to claim 1, characterized in that: In step S23, the mass ratio of the terminal aminosilane intermediate, 1,1,3,3-tetramethyl-1,3-bis[3-(epoxyethylmethoxy)propyl]disiloxane, and azide-modified graphene is 1:(1-1.2):0.

1.

5. The method for preparing a high-performance sintered NdFeB magnet according to claim 1, characterized in that: In step S24, the corrosion-resistant epoxy coating is composed of 50 parts E51 epoxy resin, 1.5-5 parts modified graphene, 0.4-0.9 parts antioxidant, and 11-14 parts curing agent by weight.

6. The method for preparing a high-performance sintered NdFeB magnet according to claim 1, characterized in that: In step S24, the antioxidant is antioxidant 1010 and the curing agent is dicyandiamide.

Images