High-performance sintered neodymium-iron-boron magnet and preparation method

Abstract

The invention relates to the technical field of magnetic materials, in particular to a high-performance sintered neodymium-iron-boron magnet and a preparation method thereof.In order to prolong the service life of the magnet, firstly, a magnet material is limited, and the high-performance sintered neodymium-iron-boron magnet is prepared by controlling components of the magnet material and a sintering process and utilizing a gradient heating and heat preservation process; the sintered magnet has more uniform magnet crystal grain distribution, so that the magnetization of the material is more uniform; on the basis, the anticorrosive coating is modified, and the surface of the carboxylated graphene material is modified, so that a silicon element and a long carbon chain structure of an epoxy-terminated group are introduced into the graphene surface, and the corrosion resistance of the coating can be effectively improved by introducing the silicon element; the long carbon chain can effectively relieve the defect that after graphene participates in epoxy resin curing, the coating is high in brittleness and easy to peel off and separate, and the protection function of the coating can be kept for a long time.

Description

Technical Field

[0001] The present invention relates to the technical field of magnetic materials, and specifically to a high-performance sintered neodymium iron boron magnet and a preparation method thereof. Background Art

[0002] Magnetic materials are a kind of functional materials with a long history and wide applications. With the progress of industry and technology, a large number of new magnetic materials have emerged, and these materials can be roughly divided into three generations: the first generation is aluminum nickel cobalt (AlNiCo), the second generation is ferrite, and the third generation is rare earth permanent magnets; rare earth permanent magnets can be further subdivided into three stages: the first stage is SmCo5, the second stage is Sm2Co 17 ,and the third stage is Nd2Fe 14 B; Magnets have great application prospects from simple daily packaging magnets to complex fields such as new energy vehicles and wind turbines;

[0003] However, in the current common neodymium iron boron magnets during use, due to the differences in various alloy elements, there will be a large corrosion potential difference, which is extremely likely to cause the corrosion of the magnets and affect the service life and safety of the magnets. Summary of the Invention

[0004] The purpose of the present invention is to provide a high-performance sintered neodymium iron boron magnet and a preparation method thereof to solve the problems raised in the prior art.

[0005] To achieve the above purpose, the present invention provides the following technical solution: 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] Among them, by weight percentage, the ingredient composition of the neodymium iron boron magnet blank includes 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 curing of a corrosion-resistant epoxy resin coating.

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

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

[0010] S11. Mix each raw material according to the ratio, place it in a melting furnace, evacuate the air, and then fill argon gas into it until it reaches 0.05 MPa, then raise the temperature for melting. After ingot casting, place the ingot in a vacuum environment and fill hydrogen into it to perform hydrogen crushing treatment on the ingot;

[0011] S12. Re-place the hydrogenated ingot in a vacuum environment again, heat it to 300 - 400 °C, keep it warm for 1.5 - 3 h, and then complete dehydrogenation;

[0012] S13. After coarsely grinding the dehydrogenated ingot into powder, perform jet milling on it again to obtain fine ingot powder. After collecting the fine ingot powder and isostatically pressing and forming it, an ingot blank is obtained;

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

[0014] S2. Prepare a corrosion-resistant epoxy coating;

[0015] S3. Spray the corrosion-resistant epoxy coating prepared in step S2 on the surface of the neodymium iron boron magnet blank, heat it to 50 °C, keep it warm for 10 - 15 min, then heat it to 85 - 95 °C at a rate of 1 - 3 °C / min, continue to keep it warm and cure for 30 - 45 min, and then cool it to room temperature to obtain a high-performance sintered neodymium iron boron magnet.

[0016] Further, in step S2, the preparation method of the corrosion-resistant epoxy coating includes the following steps:

[0017] S21. Under the protection of a nitrogen atmosphere, disperse carboxylated graphene in dimethyl sulfoxide, ultrasonically disperse it for 45 - 90 min, then add dicyclohexylcarbodiimide to it, continue to ultrasonically disperse it for 15 - 30 min, and then uniformly drop the mixed solution into 2-azidoethylamine within 1 - 4 h. When dropping, control the temperature of the reaction system at 85 - 105 °C, continuously stir during the dropping process. After the dropping is completed, keep it warm and ultrasonically oscillate to continue the reaction for 2 - 5 h, then centrifuge to separate the precipitate, wash the precipitate with ether 2 - 5 times, and dry it to constant weight to obtain azide-modified graphene;

[0018] S22. Under the protection of a nitrogen atmosphere, disperse butynedioic acid in ether, stir and mix it evenly, then add dicyclohexylcarbodiimide to it, continue to mix for 5 - 15 min, and then drop the mixed solution into 1,3-bis(3-aminopropyl)-1,1,3,3-tetramethyldisiloxane. Heat it to 35 °C and stir and react for 1 - 2 h to remove the ether therein, then heat it to 85 - 120 °C again and stir and react for 4 - 8 h to obtain an amino-terminated silane intermediate;

[0019] S23. Disperse the amino-terminated silane intermediate in DMF. After stirring and mixing evenly, drop it into 1,1,3,3-tetramethyl-1,3-bis[3-(epoxyethylmethoxy)propyl]disiloxane. Heat the temperature to 90 - 100 °C and stir for 2 - 4 h. After rotary evaporation to remove the excess solvent and unreacted 1,1,3,3-tetramethyl-1,3-bis[3-(epoxyethylmethoxy)propyl]disiloxane monomer, add clean DMF to it again. Heat the temperature to 110 - 125 °C, add azide-modified graphene to it, and react under ultrasonic oscillation for 4 - 8 h. After centrifuging to separate the precipitate, wash the precipitate with DMF for 2 - 3 times and then dry it to constant weight to obtain modified graphene;

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

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

[0022] Further, in step S22, the mass ratio of the 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] Further, in step S23, the mass ratio of the amino-terminated silane 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] Further, in step S24, by weight, 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 part of antioxidant, and 11 - 14 parts of curing agent.

[0025] Further, 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 the magnet, the present invention first limits the magnet material itself. By controlling its components and sintering process, and using the gradient heating and heat preservation process, a more uniform magnet grain distribution is obtained in the sintered magnet, so that the magnetization of the material is more uniform;

[0028] And on this basis, the present invention also carried out a modification treatment on its anti-corrosion coating. First, the surface of the carboxylated graphene material was modified. Using 2-azidoethylamine as a modifier, the reaction between amino and carboxyl groups was utilized to introduce azide groups onto the graphene surface;

[0029] On this basis, the present invention used butynedioic acid containing alkynyl and terminal carboxyl groups as a raw material, reacted it with 1,3-bis(3-aminopropyl)-1,1,3,3-tetramethyldisiloxane containing terminal amino groups, and further reacted it with 1,1,3,3-tetramethyl-1,3-bis[3-(epoxyethylmethoxy)propyl]disiloxane containing terminal epoxy groups on this basis, thereby introducing a large amount of silicon elements, terminal epoxy groups and alkynyl groups into the reaction product; then the graphene containing azide groups was introduced into the reaction system, and the azide groups would react with the alkynyl groups, thereby introducing a long carbon chain structure of silicon elements and terminal epoxy groups onto the graphene surface. The introduction of silicon elements can effectively improve the corrosion resistance of the coating and enhance the protection of the coating; and the terminal epoxy groups can allow graphene to participate in the curing of epoxy resin together. And the present invention also considered the defect that the epoxy resin is brittle after curing. Therefore, a long carbon chain structure was introduced during the modification of graphene. The long carbon chain can effectively alleviate the defect that the coating is brittle and easy to peel off after graphene participates in the curing of epoxy resin, which is beneficial to maintaining the protection function of the coating for a long time. Detailed implementation mode

[0030] Based on the embodiments in the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative efforts fall within the scope of protection of the present invention.

[0031] In this application, in the neodymium iron boron magnet blanks prepared in Examples 1-5 and Comparative Example 5, the raw materials of each component are as 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 preparation method of a high-performance sintered neodymium iron boron magnet, comprising the following steps:

[0035] S1. Prepare a neodymium iron boron magnet blank;

[0036] S11. Mix the raw materials according to the ratio, place them in a melting furnace, evacuate and then fill argon gas into it until it reaches 0.05 MPa, then raise the temperature for melting. After ingot casting, place the ingot in a vacuum environment and fill hydrogen into it to carry out hydrogen crushing treatment on the ingot;

[0037] S12. Place the hydrogen-crushed ingot in a vacuum environment again, raise the temperature to 300-400 °C, keep it warm for 1.5-3 h, and then complete dehydrogenation;

[0038] S13. After the dehydrogenated ingot is roughly ground into powder, it is again subjected to jet milling to obtain fine ingot powder. After collecting the fine ingot powder, it is isostatically pressed and formed to obtain an ingot blank.

[0039] S14. Sinter the ingot blank, evacuate the furnace, heat it up to 430 °C at a rate of 4 °C / min, hold for 45 min, then heat it up to 850 °C at a rate of 4 °C / min again, continue to hold for 80 min, then heat it up to 1350 °C at a rate of 1.5 °C / min, hold for 100 min, cool it down at a rate of 5 °C / min to 500 °C, hold for 20 min, stop heating, and cool it in the furnace to room temperature, then polish and pickling the surface to obtain a neodymium iron boron magnet blank.

[0040] S2. Prepare a corrosion-resistant epoxy coating.

[0041] S21. Under the protection of nitrogen atmosphere by weight, disperse 1 part of carboxylated graphene in dimethyl sulfoxide, ultrasonically disperse for 90 min, then add 0.02 part of dicyclohexylcarbodiimide to it, continue to ultrasonically disperse for 30 min, then uniformly drop the mixed solution into 1.5 parts of 2-azidoethylamine within 3 h. During the dropping, control the reaction system temperature at 105 °C, continuously stir during the dropping process. After the dropping is completed, keep warm, ultrasonically oscillate and continue the reaction for 5 h, then centrifuge to separate the precipitate, wash the precipitate 5 times with ether, and dry to constant weight to obtain azide-modified graphene.

[0042] S22. Under the protection of nitrogen atmosphere, disperse 1 part of butynedioic acid in ether, stir and mix evenly, then add 0.015 part of dicyclohexylcarbodiimide to it, continue to mix for 15 min, then drop the mixed solution into 3.5 parts of 1,3-bis(3-aminopropyl)-1,1,3,3-tetramethyldisiloxane, heat up to 35 °C, stir and react for 1.5 h to remove the ether therein, then heat up to 98 °C again, stir and react for 6 h to obtain an amino-terminated silane intermediate.

[0043] S23. By weight, disperse 1 part of the amino-terminated silane intermediate in DMF, stir and mix evenly, then drop it into 1 part of 1,1,3,3-tetramethyl-1,3-bis[3-(epoxyethylmethoxy)propyl]disiloxane, heat up to 90 °C, stir and react for 3 h, then rotary evaporate to remove the excess solvent and unreacted 1,1,3,3-tetramethyl-1,3-bis[3-(epoxyethylmethoxy)propyl]disiloxane monomer, then add clean DMF to it again, heat up to 110 °C, add 0.1 part of azide-modified graphene to it, ultrasonically oscillate and react for 6 h, then centrifuge to separate the precipitate, wash the precipitate 2 times with DMF, and dry to constant weight to obtain modified graphene.

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

[0045] S3. Spray the corrosion-resistant epoxy coating prepared in step S2 on the surface of the NdFeB magnet blank, then raise the temperature to 50 °C, keep it warm for 10 min, then raise the temperature to 95 °C at a rate of 1 °C / min, continue to keep it warm and cure for 45 min, and then cool 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, the addition amount of modified graphene in step S24 is increased in this example;

[0048] S1. Prepare an NdFeB magnet blank;

[0049] S11. Mix the raw materials according to the ratio, place them in a melting furnace, evacuate, then fill it with argon gas to 0.05 MPa, raise the temperature for melting, after casting ingots, place the ingots in a vacuum environment and fill it with hydrogen to perform hydrogen crushing treatment on the ingots;

[0050] S12. Place the hydrogen-crushed ingots in a vacuum environment again, raise the temperature to 300 - 400 °C, keep it warm for 1.5 - 3 h, and complete dehydrogenation;

[0051] S13. Coarsely grind the dehydrogenated ingots into powder, then perform jet milling on them again to obtain fine ingot powder, collect the fine ingot powder, and perform isostatic pressing and molding on it to obtain an ingot blank;

[0052] S14. Sinter the ingot blank, evacuate the furnace, raise the temperature to 430 °C at a rate of 4 °C / min, keep it warm for 45 min, then raise the temperature to 850 °C at a rate of 4 °C / min again, continue to keep it warm for 80 min, then raise the temperature to 1350 °C at a rate of 1.5 °C / min again, keep it warm for 100 min, then cool at a rate of 5 °C / min to 500 °C, keep it warm for 20 min, stop heating, and cool with the furnace to room temperature, then polish and pickling the surface to obtain an NdFeB magnet blank;

[0053] S2. Prepare a corrosion-resistant epoxy coating;

[0054] S21. Under the protection of nitrogen atmosphere by weight, disperse 1 part of carboxylated graphene into dimethyl sulfoxide. After ultrasonic dispersion for 90 min, add 0.02 part of dicyclohexylcarbodiimide thereto, and continue ultrasonic dispersion for 30 min. Then, uniformly drop the mixed solution into 1.5 parts of 2-azidoethylamine within 3 h. During dropping, control the temperature of the reaction system at 105 °C, continuously stir during the dropping process. After the dropping is completed, keep the temperature, continue to react by ultrasonic oscillation for 5 h, then centrifuge to separate the precipitate, wash the precipitate with ether for 5 times, and dry to constant weight to obtain azide-modified graphene;

[0055] S22. Under the protection of nitrogen atmosphere, disperse 1 part of butynedioic acid into ether, stir and mix evenly, then add 0.015 part of dicyclohexylcarbodiimide thereto, and continue to mix for 15 min. Then, drop the mixed solution into 3.5 parts of 1,3-bis(3-aminopropyl)-1,1,3,3-tetramethyldisiloxane, raise the temperature to 35 °C, stir and react for 1.5 h to remove the ether therein. Then, raise the temperature to 98 °C again, stir and react for 6 h to obtain an amino-terminated silane intermediate;

[0056] S23. By weight, disperse 1 part of the amino-terminated silane intermediate into DMF, stir and mix evenly, then drop it into 1 part of 1,1,3,3-tetramethyl-1,3-bis[3-(epoxyethylmethoxy)propyl]disiloxane, raise the temperature to 90 °C, stir and react for 3 h. Then, rotary evaporate to remove the excess solvent and the unreacted 1,1,3,3-tetramethyl-1,3-bis[3-(epoxyethylmethoxy)propyl]disiloxane monomer. Then, add clean DMF thereto again, raise the temperature to 110 °C, add 0.1 part of azide-modified graphene thereto, react by ultrasonic oscillation for 6 h, then centrifuge to separate the precipitate, wash the precipitate with DMF for 2 times, and dry to constant weight to obtain modified graphene;

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

[0058] S3. After spraying the corrosion-resistant epoxy coating prepared in step S2 on the surface of the neodymium iron boron magnet blank, raise the temperature to 50 °C, keep the temperature for 10 min, then raise the temperature to 95 °C at a rate of 1 °C / min, continue to keep the temperature and cure for 45 min, and then cool to room temperature to obtain a high-performance sintered neodymium iron boron magnet.

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

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

[0061] S2. Prepare a corrosion-resistant epoxy coating;

[0062] S21. Under the protection of nitrogen atmosphere by weight, disperse 1 part of carboxylated graphene into dimethyl sulfoxide. After ultrasonic dispersion for 90 min, add 0.02 part of dicyclohexylcarbodiimide thereto, and continue ultrasonic dispersion for 30 min. Then, uniformly drop the mixture into 10 parts of 2-azidoethylamine within 3 h. During dropping, control the temperature of the reaction system at 105 °C, continuously stir during the dropping process. After the dropping is completed, keep warm, continue the reaction for 5 h under ultrasonic oscillation, then centrifuge to separate the precipitate, wash the precipitate 5 times with ether, and dry to constant weight to obtain azide-modified graphene;

[0063] S22. Under the protection of nitrogen atmosphere, disperse 1 part of butynedioic acid into ether, stir and mix evenly, then add 0.015 part of dicyclohexylcarbodiimide thereto, continue mixing for 15 min, and then drop the mixture into 3.5 parts of 1,3-bis(3-aminopropyl)-1,1,3,3-tetramethyldisiloxane. Raise the temperature to 35 °C, stir and react for 1.5 h to remove the ether therein, then raise the temperature to 98 °C again, stir and react for 6 h to obtain an amino-terminated silane intermediate;

[0064] S23. By weight, disperse 1 part of the amino-terminated silane intermediate into DMF, stir and mix evenly, then drop it into 1 part of 1,1,3,3-tetramethyl-1,3-bis[3-(epoxyethylmethoxy)propyl]disiloxane. Raise the temperature to 90 °C, stir and react for 3 h, then rotary evaporate to remove the excess solvent and the unreacted 1,1,3,3-tetramethyl-1,3-bis[3-(epoxyethylmethoxy)propyl]disiloxane monomer. Then, add clean DMF thereto again, raise the temperature to 110 °C, add 0.1 part of azide-modified graphene thereto, react under ultrasonic oscillation for 6 h, then centrifuge to separate the precipitate, wash the precipitate 2 times with DMF, and dry to constant weight to obtain modified graphene;

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

[0066] S3. Spray the corrosion-resistant epoxy coating prepared in step S2 on the surface of the neodymium iron boron magnet blank, then raise the temperature to 50 °C, keep warm for 10 min, then raise the temperature to 95 °C at a rate of 1 °C / min, continue to keep warm and cure for 45 min, and then cool to room temperature to obtain a high-performance sintered neodymium iron boron magnet.

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

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

[0069] S2. Prepare a corrosion-resistant epoxy coating;

[0070] S21. Under the protection of nitrogen atmosphere and by weight, disperse 1 part of carboxylated graphene in dimethyl sulfoxide. After ultrasonic dispersion for 90 min, add 0.02 part of dicyclohexylcarbodiimide thereto, and continue ultrasonic dispersion for 30 min. Then, uniformly drop the mixture into 10 parts of 2-azidoethylamine within 3 h. During the dropping, control the reaction system temperature at 105 °C, continuously stir during the dropping process. After the dropping is completed, keep the temperature, continue the reaction for 5 h with ultrasonic oscillation, then centrifuge to separate the precipitate, wash the precipitate 5 times with ether, and dry to constant weight to obtain azide-modified graphene;

[0071] S22. Under the protection of nitrogen atmosphere, disperse 1 part of butynedioic acid in ether, stir and mix evenly, then add 0.015 part of dicyclohexylcarbodiimide thereto, continue to mix for 15 min, and then drop the mixture into 4.4 parts of 1,3-bis(3-aminopropyl)-1,1,3,3-tetramethyldisiloxane. Raise the temperature to 35 °C, stir and react for 1.5 h to remove the ether therein, then raise the temperature to 98 °C again, stir and react for 6 h to obtain an amino-terminated silane intermediate;

[0072] S23. By weight, disperse 1 part of the amino-terminated silane intermediate in DMF, stir and mix evenly, then drop it into 1 part of 1,1,3,3-tetramethyl-1,3-bis[3-(epoxyethylmethoxy)propyl]disiloxane. Raise the temperature to 90 °C, stir and react for 3 h, then rotary evaporate to remove the excess solvent and the unreacted 1,1,3,3-tetramethyl-1,3-bis[3-(epoxyethylmethoxy)propyl]disiloxane monomer. Then, add clean DMF thereto again, raise the temperature to 110 °C, add 0.1 part of azide-modified graphene thereto, react with ultrasonic oscillation for 6 h, then centrifuge to separate the precipitate, wash the precipitate 2 times with DMF, and dry to constant weight to obtain modified graphene;

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

[0074] S3. After spraying the corrosion-resistant epoxy coating prepared in step S2 on the surface of the neodymium-iron-boron magnet blank, raise the temperature to 50 °C, keep the temperature for 10 min, then raise the temperature to 95 °C at a rate of 1 °C / min, continue to keep the temperature for curing for 45 min, and then cool to room temperature to obtain a high-performance sintered neodymium-iron-boron magnet.

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

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

[0077] S2. Prepare a corrosion-resistant epoxy coating;

[0078] S21. Under the protection of nitrogen atmosphere, disperse 1 part of carboxylated graphene into dimethyl sulfoxide. After ultrasonic dispersion for 90 min, add 0.02 part of dicyclohexylcarbodiimide thereto, and continue ultrasonic dispersion for 30 min. Then, uniformly drop the mixture into 10 parts of 2-azidoethylamine within 3 h. During the dropping process, control the temperature of the reaction system at 105 °C, continuously stir during the dropping process. After the dropping is completed, keep warm, continue the reaction by ultrasonic oscillation for 5 h, then centrifuge to separate the precipitate, wash the precipitate 5 times with ether, and dry to constant weight to obtain azide-modified graphene;

[0079] S22. Under the protection of nitrogen atmosphere, disperse 1 part of butynedioic acid into ether, stir and mix evenly, then add 0.015 part of dicyclohexylcarbodiimide thereto, continue to mix for 15 min, and then drop the mixture into 4.4 parts of 1,3-bis(3-aminopropyl)-1,1,3,3-tetramethyldisiloxane. Raise the temperature to 35 °C, stir and react for 1.5 h to remove the ether therein, then raise the temperature to 98 °C again, stir and react for 6 h to obtain an amino-terminated silane intermediate;

[0080] S23. By weight, disperse 1 part of the amino-terminated silane intermediate into DMF, stir and mix evenly, then drop it into 1.2 parts of 1,1,3,3-tetramethyl-1,3-bis[3-(epoxyethylmethoxy)propyl]disiloxane. Raise the temperature to 90 °C, stir and react for 3 h, then rotary evaporate to remove the excess solvent and the unreacted 1,1,3,3-tetramethyl-1,3-bis[3-(epoxyethylmethoxy)propyl]disiloxane monomer. Then, add clean DMF thereto again, raise the temperature to 110 °C, add 0.1 part of azide-modified graphene thereto, react by ultrasonic oscillation for 6 h, then centrifuge to separate the precipitate, wash the precipitate 2 times with DMF, and dry to constant weight to obtain modified graphene;

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

[0082] S3. After spraying the corrosion-resistant epoxy coating prepared in step S2 on the surface of the NdFeB magnet blank, the temperature is raised to 50 °C. After keeping the temperature for 10 min, the temperature is raised to 95 °C at a rate of 1 °C / min, and then kept for curing for 45 min. After that, it 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, modified graphene was not prepared in this comparative example;

[0085] S2. Prepare a corrosion-resistant epoxy coating;

[0086] S24. By weight, 50 parts of E51 epoxy resin, 1.5 parts of graphene, and 0.8 part of antioxidant 1010 are mixed evenly, and then 13 parts of dicyandiamide curing agent are added thereto. After continuing to mix for 5 min, a corrosion-resistant epoxy coating is obtained;

[0087] S3. After spraying the corrosion-resistant epoxy coating prepared in step S2 on the surface of the NdFeB magnet blank, the temperature is raised to 50 °C. After keeping the temperature for 10 min, the temperature is raised to 95 °C at a rate of 1 °C / min, and then kept for curing for 45 min. After that, it is cooled to room temperature to obtain a high-performance sintered NdFeB magnet.

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

[0089] The samples prepared in Examples 1-5 and Comparative Example 1 were subjected to neutral salt spray resistance detection 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 for 1 h and then cooled to room temperature. After repeating the cycle 5 times, the neutral salt spray resistance detection was carried out again;

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

[0092] Table 2

[0093]

[0094] Finally, it should be noted that the above are only the preferred embodiments of the present invention and are not used to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, for those skilled in the art, they can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements on some of the technical features. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A high performance sintered NdFeB magnet, characterized by: The high-performance sintered NdFeB magnet is composed of a NdFeB magnet blank and a corrosion-resistant epoxy coating coated on the surface of the NdFeB magnet; Wherein, the ingredients of the NdFeB magnet blank include, by 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; The corrosion-resistant epoxy coating is formed by curing the corrosion-resistant epoxy resin coating.

2. A method for preparing a high performance sintered NdFeB magnet as claimed in claim 1, characterized in that: The following steps are involved: S1. Preparation of NdFeB magnet blank; S11. The raw materials are mixed according to the ratio, placed in a smelting furnace, evacuated, filled with argon gas to 0.05MPa, heated for smelting, and after ingot casting, the ingot is placed in a vacuum environment and filled with hydrogen to perform hydrogen crushing on the ingot; S12. The ingot after hydrogen crushing is placed in a vacuum environment again, heated to 300-400°C, and kept warm for 1.5-3h to complete dehydrogenation; S13. After the dehydrogenated ingot is coarsely ground into powder, it is again subjected to jet milling to obtain ingot fine powder, the ingot fine powder is collected, and isostatically pressed to obtain an ingot body; S14. Sintering the ingot body to obtain a NdFeB magnet body; S2. Preparation of corrosion-resistant epoxy coating; S3. After spraying the corrosion-resistant epoxy coating prepared in step S2 on the surface of the NdFeB magnet blank, the temperature is raised to 50°C, kept warm for 10-15 minutes, and then the temperature is raised to 85-95°C at a rate of 1-3°C / min. After continuing to keep warm and cure for 30-45 minutes, the mixture is cooled to room temperature to obtain a high-performance sintered NdFeB magnet.

3. The method for preparing a high performance sintered NdFeB magnet according to claim 2, characterized in that: In step S2, the method for preparing the corrosion-resistant epoxy coating comprises the following steps: S21. Under nitrogen atmosphere protection, carboxylated graphene is dispersed in dimethyl sulfoxide, ultrasonically dispersed for 45-90 minutes, dicyclohexylcarbodiimide is added thereto, ultrasonically dispersed for 15-30 minutes, and the mixture is uniformly added dropwise to 2-azidoethylamine within 1-4 hours. During the addition, the temperature of the reaction system is controlled to be 85-105°C, and the mixture is continuously stirred during the addition. After the addition is completed, the mixture is kept warm and ultrasonically shaken for 2-5 hours. The precipitate is separated by centrifugation, and the precipitate is washed with ether for 2-5 times and dried to constant weight to obtain azide-modified graphene. S22. Under nitrogen atmosphere, disperse butynedioic acid in ether, stir and mix evenly, add dicyclohexylcarbodiimide, continue mixing for 5-15 minutes, add the mixture dropwise to 1,3-bis(3-aminopropyl)-1,1,3,3-tetramethyldisiloxane, heat to 35°C, stir and react for 1-2 hours to remove the ether, heat to 85-120°C again, stir and react for 4-8 hours to obtain an amino-terminated silane intermediate; S23. The terminal amino silane intermediate is dispersed in DMF, stirred and mixed evenly, and then added dropwise to 1,1,3,3-tetramethyl-1,3-bis[3-(oxiranylmethoxy)propyl]disiloxane, heated to 90-100°C, stirred and reacted for 2-4 hours, and then the excess solvent and unreacted 1,1,3,3-tetramethyl-1,3-bis[3-(oxiranylmethoxy)propyl]disiloxane monomer are removed by rotary evaporation, and then clean DMF is added thereto again, and the temperature is raised to 110-125°C, and azide-modified graphene is added thereto, and after ultrasonic vibration reaction for 4-8 hours, the precipitate is separated by centrifugation, and the precipitate is washed 2-3 times with DMF, and then dried to constant weight to obtain modified graphene; S24. After uniformly mixing the E51 epoxy resin, modified graphene and antioxidant, a curing agent is added thereto, and the mixture is mixed for 5-10 minutes to obtain a corrosion-resistant epoxy coating.

4. The method for preparing a high performance sintered NdFeB magnet according to claim 3, 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).

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

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

1.

7. The method for preparing a high performance sintered NdFeB magnet according to claim 3, characterized in that: 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.

8. The method for preparing a high performance sintered NdFeB magnet according to claim 3, characterized in that: In step S24, the antioxidant is antioxidant 1010, and the curing agent is dicyandiamide.

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