A powder slurry for grain boundary diffusion of a magnet, a method of manufacturing a magnet, and a magnet manufactured thereby

Abstract

The present disclosure relates to a powder slurry for magnet grain boundary diffusion, a magnet manufacturing method and a prepared magnet, the powder slurry comprising a powder containing heavy rare earth elements, a UV monomer, a polymerization inhibitor, a photoinitiator and a dispersant; the UV monomer is a free radical curing UV monomer; the mass ratio of the powder containing heavy rare earth elements in the powder slurry is 60-80wt%, the mass ratio of the UV monomer in the powder slurry is 15-35wt%, the mass ratio of the polymerization inhibitor in the powder slurry is 0.01-0.1wt%, the mass ratio of the photoinitiator in the powder slurry is 0.5-5wt%, and the mass ratio of the dispersant in the powder slurry is 0.02-0.2wt%. The powder slurry for magnet grain boundary diffusion provided by the present disclosure does not volatilize at room temperature, can ensure the stability and controllability of the coating process, and the obtained coating uniformity is better.

Description

Technical Field

[0001] This disclosure relates to the field of rare earth permanent magnet materials, specifically to a powder slurry for magnet grain boundary diffusion, a magnet manufacturing method, and the magnet obtained therefrom. Background Technology

[0002] Neodymium iron boron (NdFeB) magnets possess excellent magnetic properties such as high remanence, high coercivity, and high energy product, leading to their widespread application in hybrid electric vehicles, wind power generation, servo motors, and energy-saving home appliances. As equipment becomes increasingly intelligent, miniaturized, and lightweight, the performance requirements for NdFeB magnets are also rising, especially in terms of high-temperature resistance. To improve magnet coercivity and operating temperature while reducing production costs, grain boundary diffusion technology has emerged and gained widespread use. The grain boundary diffusion method involves depositing a layer of heavy rare earth powder on the magnet surface using methods such as sputtering, evaporation, electrophoresis, or coating. Following heat treatment, the heavy rare earth elements diffuse into the magnet's interior, forming a magnetohardened shell at the main phase grain boundary layer to enhance coercivity. The key to this method is obtaining a uniformly thick and highly bonded heavy rare earth coating on the magnet surface.

[0003] Chinese patent document CN105144321A discloses a method for manufacturing R-Fe-B system magnets and a coating for grain boundary diffusion treatment. The method involves mixing heavy rare earth powder with organosilicon grease to form a coating, which is then applied to the magnet surface before diffusion aging. However, the coating prepared by this method remains in a paste-like state and cannot solidify before diffusion in the furnace. The coating has low adhesion to the substrate, making it easy to scrape off during operation. Furthermore, the tooling of the equipment is inadequate, resulting in incomplete coating coverage on the magnet surface. Coated products cannot be stacked together for diffusion, affecting the furnace's loading capacity and increasing costs.

[0004] Chinese patent document CN105755441B discloses a method for improving the coercivity of sintered NdFeB magnetrons by magnetron sputtering diffusion of heavy rare earth elements. The method involves degreasing and cleaning the product, ion activation, sputtering coating, and diffusion aging to prepare high coercivity magnets. The coating prepared by this method has high adhesion, but the entire process involves large investment in equipment, high energy consumption, and expensive target material processing, resulting in high final production costs, which is not conducive to mass production.

[0005] Chinese patent document CN106328367B discloses a method for preparing R-Fe-B sintered magnets. The method involves preparing a slurry from ultrafine terbium powder, organic solvent, and antioxidant, then coating it onto the surface of a neodymium iron boron magnet, followed by diffusion and aging in a vacuum furnace. However, the organic solvent in the slurry prepared by this method is easily volatilized at room temperature. After volatilization, the adhesion between the powder coating and the substrate is very low, and the powder is prone to falling off during operation, resulting in poor process control and poor product consistency. Summary of the Invention

[0006] The purpose of this disclosure is to increase the bonding force between the coating material and the magnet substrate, reduce the carbon residue in the coating material after curing during the subsequent sintering process, and further improve the coercivity of the magnet.

[0007] To achieve the above objectives, the first aspect of this disclosure provides a powder slurry for magnet grain boundary diffusion, the powder slurry comprising a powder containing heavy rare earth elements, a UV monomer, a polymerization inhibitor, a photoinitiator, and a dispersant; wherein the UV monomer is a free radical cured UV monomer;

[0008] Specifically, based on the total mass of the powder slurry, the amount of powder containing heavy rare earth elements added accounts for 60-80 wt% of the mass of the powder slurry, the amount of UV monomer added accounts for 15-35 wt% of the mass of the powder slurry, the amount of polymerization inhibitor added accounts for 0.01-0.1 wt% of the mass of the powder slurry, the amount of photoinitiator added accounts for 0.5-5 wt% of the mass of the powder slurry, and the amount of dispersant added accounts for 0.02-0.2 wt% of the mass of the powder slurry.

[0009] Optionally, the viscosity of the powder slurry is 100-5000 mPa·s.

[0010] Optionally, the UV monomer does not contain an aromatic ring in its molecular chain; preferably, the UV monomer contains an acrylate structure; more preferably, the UV monomer contains a methacrylate structure; optionally, the UV monomer is selected from at least one of pentaerythritol triacrylate, isobornyl methacrylate, pentaerythritol ethoxylate tetraacrylate, trimethylolpropane trimethacrylate, dicyclopentyl methacrylate, dipentaerythritol hexaacrylate, 3,3,5-trimethylcyclohexyl acrylate, laurate methacrylate, and polyethylene glycol dimethacrylate.

[0011] Optionally, the powder containing heavy rare earth elements has a particle size of 1–10 μm; optionally, the heavy rare earth elements in the powder are selected from at least one of Dy, Tb, and Ho; preferably, the powder containing heavy rare earth elements is selected from at least one of the fluorides, fluoride oxides, hydrides, and oxides of the heavy rare earth elements; more preferably, the powder containing heavy rare earth elements is selected from Dy2O3, Dy 1-y M y H x Tb2O3 and Tb 1-y M y H x At least one of the following, wherein M is selected from at least one of Fe, Cu, Zn and Al, x = 2 or 3, and 0 ≤ y ≤ 0.3.

[0012] Optionally, the polymerization inhibitor is selected from at least one of tert-butylcatechol, tert-butylhydroquinone, hydroquinone, and tris(N-nitroso-N-phenylhydroxylamine) aluminum salt.

[0013] Optionally, the photoinitiator is selected from at least one of benzoin dimethyl ether, 2,4,6-trimethylbenzoyl-diphenylphosphine oxide, 2-hydroxy-2-methyl-phenylacetone-1, isopropylthioxanthone, and 1-hydroxycyclohexylphenyl ketone.

[0014] Optionally, the dispersant is selected from at least one of glyceryl monooleate, polyethylene glycol oleate, and oleoyl monolaurate.

[0015] A second aspect of this disclosure provides a method for manufacturing a magnet, the method comprising:

[0016] After coating the first surface of a NdFeB substrate with a powder slurry, a first curing reaction is performed to obtain a magnet coated with a first coating; the magnet coated with the first coating is then subjected to vacuum heat treatment, grain boundary diffusion treatment, and aging treatment in sequence; or

[0017] After coating the first surface of the NdFeB substrate with the powder slurry, a first curing reaction is carried out to obtain a magnet coated with the first coating; after coating the second surface of the magnet coated with the first coating with the powder slurry, a second curing reaction is carried out to obtain a double-sided coated magnet; the double-sided coated magnet is then subjected to vacuum heat treatment, grain boundary diffusion treatment and aging treatment in sequence.

[0018] Wherein, the first surface and the second surface are selected from the upper and lower surfaces of the neodymium iron boron substrate; the powder slurry is the aforementioned powder slurry for magnet grain boundary diffusion.

[0019] Optionally, the weight gain of the double-coated magnet is 0.1% to 2% of the neodymium iron boron substrate.

[0020] Optionally, in step S1, the conditions for the first curing reaction and the second curing reaction include: irradiating the surface of the NdFeB magnet coated with powder slurry with ultraviolet light in an inert atmosphere, wherein the inert atmosphere is nitrogen or argon, and the ultraviolet light irradiation time is 1–100 s; in step S2, the conditions for the vacuum heat treatment include: a treatment temperature of 250–600 °C and a treatment time of 1–10 h; the conditions for the grain boundary diffusion treatment include: a treatment temperature of 800–1000 °C and a treatment time of 2–50 h; and the conditions for the aging treatment include: a treatment temperature of 450–600 °C and a treatment time of 1–8 h.

[0021] The third aspect of this disclosure provides a magnet prepared by the above method.

[0022] The technical solution disclosed herein has the following beneficial effects through the above-described technical solution:

[0023] 1. The powder slurry for magnet grain boundary diffusion provided in this disclosure does not volatilize at room temperature, which can ensure the stability and controllability of the coating process and the resulting coating has better uniformity.

[0024] 2. The powder slurry for magnet grain boundary diffusion provided in this disclosure is formulated with a UV adhesive system. It has a short curing time and does not require heating. Compared with conventional thermosetting, it can significantly improve production efficiency and reduce manufacturing costs, and is especially suitable for mass production. After curing, the coating has a high bonding force with the magnet substrate, which can prevent the coating from falling off during product transfer and stacking.

[0025] 3. The UV adhesive disclosed herein can be decomposed under vacuum conditions without affecting the diffusion of heavy rare earth elements into the NdFeB matrix, thereby significantly improving the coercivity of the NdFeB magnet without significantly reducing its remanence.

[0026] 4. The magnet manufacturing method disclosed herein has high utilization rate of heavy rare earth powder, convenient recycling, simple process flow, low cost, and is suitable for industrial mass production.

[0027] Other features and advantages of this disclosure will be described in detail in the following detailed description section. Detailed Implementation

[0028] The following provides a detailed description of specific embodiments of this disclosure. It should be understood that the specific embodiments described herein are for illustrative and explanatory purposes only and are not intended to limit the scope of this disclosure.

[0029] The first aspect of this disclosure provides a powder slurry for magnet grain boundary diffusion, the powder slurry comprising a powder containing heavy rare earth elements, a UV monomer, a polymerization inhibitor, a photoinitiator, and a dispersant; wherein the UV monomer is a free radical cured UV monomer;

[0030] Specifically, based on the total mass of the powder slurry, the amount of powder containing heavy rare earth elements added accounts for 60-80 wt% of the mass of the powder slurry, the amount of UV monomer added accounts for 15-35 wt% of the mass of the powder slurry, the amount of polymerization inhibitor added accounts for 0.01-0.1 wt% of the mass of the powder slurry, the amount of photoinitiator added accounts for 0.5-5 wt% of the mass of the powder slurry, and the amount of dispersant added accounts for 0.02-0.2 wt% of the mass of the powder slurry.

[0031] The inventors of this disclosure, through extensive experiments, discovered that the powder slurry prepared using the above-mentioned proportions allows for the complete removal of UV monomers, polymerization inhibitors, photoinitiators, and dispersants after polymerization and curing, leaving no carbon residue. This significantly promotes the diffusion of heavy rare earth powder into the magnet matrix and avoids the phenomenon where carbon residue hinders the diffusion of heavy rare earth powder, resulting in insignificant improvement in magnet performance after grain boundary diffusion and the inability to achieve a substantial increase in coercivity. Furthermore, when the powder slurry of this disclosure removes UV monomers, polymerization inhibitors, photoinitiators, and dispersants through polymerization and curing, the heavy rare earth powder maintains a high degree of adhesion to the matrix. Specifically, the inventors of this disclosure, through extensive experiments, found that when the temperature reaches 250-600℃, the UV monomers, polymerization inhibitors, photoinitiators, and dispersants can be completely removed, and the powder containing heavy rare earth elements adheres to the matrix surface, making it difficult for the powder containing heavy rare earth elements to fall off. The powder slurry of this disclosure has a high utilization efficiency of heavy rare earth elements.

[0032] This disclosure introduces UV curing into the field of grain boundary diffusion in magnets for the first time. The inventors have conducted numerous experiments and found that when the viscosity of the powder slurry is 100-5000 mPa·s, the coating thickness is optimal when the powder slurry is coated on the surface of the magnet, and the coercivity is significantly improved after diffusion.

[0033] In this disclosure, the free radical type UV monomer is more compatible with other components in the powder slurry, such as powders containing heavy rare earth elements, which allows the system to perform better and makes the organic system more stable during storage. Preferably, the UV monomer does not contain aromatic rings in its molecular chain; more preferably, the UV monomer contains an acrylate structure. The inventors have found through extensive experiments that the polymer formed by UV monomer containing an acrylate structure after UV curing is easily broken down into smaller molecules when subjected to high temperatures, without carbonization that would result in high carbon content and affect diffusion channels, thus improving grain boundary diffusion performance; even more preferably, the UV monomer contains a methacrylate structure.

[0034] According to this disclosure, the UV monomer may be selected from one of pentaerythritol triacrylate, trimethylolpropane trimethacrylate, dicyclopentyl methacrylate, dipentaerythritol hexaacrylate, 3,3,5-trimethylcyclohexyl acrylate, laurate methacrylate and polyethylene glycol dimethacrylate, preferably at least one of laurate methacrylate trimethylolpropane trimethacrylate and polyethylene glycol dimethacrylate.

[0035] According to this disclosure, the powder particle size of the powder containing heavy rare earth elements is preferably 1-10 μm; optionally, the heavy rare earth elements in the powder can be selected from at least one of Dy, Tb, and Ho; preferably, the powder containing heavy rare earth elements can be selected from at least one of the fluorides, fluoride oxides, hydrides, and oxides of the heavy rare earth elements; more preferably, the powder containing heavy rare earth elements is selected from Dy2O3, Dy 1-y M y H x Tb2O3 and Tb 1-y M y H x At least one of the following, wherein M is selected from at least one of Fe, Cu, Zn and Al, x = 2 or 3, and 0 ≤ y ≤ 0.3.

[0036] According to this disclosure, the polymerization inhibitor may be selected from at least one of tert-butylcatechol, tert-butylhydroquinone, hydroquinone, and tris(N-nitroso-N-phenylhydroxylamine) aluminum salt.

[0037] According to this disclosure, the photoinitiator may be selected from at least one of benzoin dimethyl ether, 2,4,6-trimethylbenzoyl-diphenylphosphine oxide, 2-hydroxy-2-methyl-phenylacetone-1, isopropylthioxanthone, and 1-hydroxycyclohexylphenyl ketone.

[0038] According to this disclosure, the dispersant may be selected from at least one of glyceryl monooleate, polyethylene glycol oleate, and oleoyl monolaurate.

[0039] The mixing methods for powders containing heavy rare earth elements, UV monomers, polymerization inhibitors, photoinitiators, and dispersants disclosed herein are well known to those skilled in the art, for example, three-roll mill mixing or ball milling can be used.

[0040] A second aspect of this disclosure provides a method for manufacturing a magnet, the method comprising:

[0041] After coating the first surface of a NdFeB substrate with a powder slurry, a first curing reaction is performed to obtain a magnet coated with a first coating; the magnet coated with the first coating is then subjected to vacuum heat treatment, grain boundary diffusion treatment, and aging treatment in sequence; or

[0042] After coating the first surface of the NdFeB substrate with the powder slurry, a first curing reaction is carried out to obtain a magnet coated with the first coating; after coating the second surface of the magnet coated with the first coating with the powder slurry, a second curing reaction is carried out to obtain a double-sided coated magnet; the double-sided coated magnet is then subjected to vacuum heat treatment, grain boundary diffusion treatment and aging treatment in sequence.

[0043] Wherein, the first surface and the second surface are selected from the upper and lower surfaces of the neodymium iron boron substrate; the powder slurry is the aforementioned powder slurry for magnet grain boundary diffusion.

[0044] In this disclosure, unless otherwise stated, directional terms such as "upper" and "lower" refer to the upper and lower surfaces of the NdFeB magnet in its normal placement state; for example, "upper surface" and "lower surface" as mentioned in this disclosure refer to the upper and lower surfaces of the NdFeB magnet in its normal placement state. Terms such as "first" and "second" in this disclosure are used to distinguish one element from another and do not indicate sequence or importance.

[0045] In this disclosure, the neodymium iron boron matrix or magnet matrix is ​​a material prepared by melting, powdering, molding, and sintering the raw materials of neodymium iron boron permanent magnet material. The raw materials for neodymium iron boron permanent magnet material are well known to those skilled in the art.

[0046] In this disclosure, the coating method of the powder slurry can be well known to those skilled in the art, including but not limited to spraying, slurry dipping, screen printing, roller coating, spin coating and other methods.

[0047] In a preferred embodiment of this disclosure, the weight gain ratio of the double-coated magnet is 0.1% to 2% of that of the neodymium iron boron magnet.

[0048] According to this disclosure, in step S1, the conditions for the first curing reaction and the second curing reaction may include: irradiating the surface of the NdFeB magnet coated with powder slurry with ultraviolet light in an inert atmosphere, wherein the inert atmosphere may be nitrogen or argon, and the ultraviolet light irradiation time may be 1 to 100 s; in step S2, the conditions for the vacuum heat treatment may include: a treatment temperature of 250 to 600°C and a treatment time of 1 to 10 h; the conditions for the grain boundary diffusion treatment may include: a treatment temperature of 800 to 1000°C and a treatment time of 2 to 50 h; the conditions for the aging treatment may include: a treatment temperature of 450 to 600°C and a treatment time of 1 to 8 h.

[0049] The third aspect of this disclosure provides a magnet prepared by the above method, the magnet having high coercivity.

[0050] The present disclosure is further illustrated by the following examples, but the present disclosure is not limited thereto. All raw materials used in the examples are commercially available.

[0051] Example 1

[0052] TbH3 powder was milled to 2.5 μm using an air jet mill to obtain the powder containing heavy rare earth elements in this embodiment. Then, the powder containing heavy rare earth elements, UV monomer, polymerization inhibitor, photoinitiator and dispersant were prepared according to the proportions shown in Table 1 and mixed thoroughly and evenly using a three-roll mill to obtain the powder slurry of this embodiment. The viscosity of the powder slurry was 700 mPa·s.

[0053] The above-mentioned powder slurry was screen-printed onto the surface of a cleaned NdFeB magnet (30*30*3mm) using a screen printing machine. The product was then placed in an argon atmosphere and irradiated with a UV lamp for 20 seconds to ensure complete curing. After curing, the product was flipped over, and the same screen printing and curing process was performed on the lower surface of the NdFeB magnet to obtain a double-sided coated magnet. The weight gain of this double-sided coated magnet compared to the uncoated magnet was 0.65%. The double-sided coated magnet was then placed in a vacuum furnace for vacuum heat treatment at 400℃ for 3 hours, diffusion at 900℃ for 8 hours, and aging treatment at 500℃ for 4 hours to obtain the diffused product. The diffused product was tested, and the results are shown in Table 2. Table 2 shows that the remanence of the diffused product decreased by only about 100 Gs, but the coercivity increased by about 10 Koe.

[0054] Table 1

[0055]

[0056] Table 2

[0057]

[0058] Example 2

[0059] First, (Dy) 0.8 Fe 0.2 H3 powder was milled to 5 μm using an air jet mill. Then, heavy rare earth powder, UV monomer, polymerization inhibitor, photoinitiator and dispersant were prepared according to the proportions shown in Table 3 below and the powder slurry was thoroughly mixed with a ball mill to obtain the powder slurry of this embodiment. The viscosity of the powder slurry was 1100 mPa·s.

[0060] The aforementioned powder slurry was screen-printed onto the surface of a cleaned NdFeB magnet (30*30*3mm) using a screen printing machine. The product was then placed in an N2 atmosphere and irradiated with a UV lamp for 50 seconds to ensure complete curing. After curing, the product was flipped over, and the same process was repeated on the other side, screen-printing and curing the powder slurry on each side. The weight gain of the double-sided powder slurry coating was 0.75%. The product was then placed in a vacuum furnace for vacuum heat treatment at 450℃ for 2 hours, followed by diffusion at 920℃ for 15 hours, and finally aging at 520℃ for 4 hours. The diffused product was tested, and the results are shown in Table 4. Table 4 shows that the remanence of the diffused product decreased by only about 90 Gs, but the coercivity increased by about 6 KOe.

[0061] Table 3

[0062]

[0063] Table 4

[0064]

[0065] Example 3

[0066] First, the mixture of Dy2O3 powder and Tb2O3 powder was milled to 1.2 μm using a high-energy ball mill. Then, the heavy rare earth powder, UV monomer, polymerization inhibitor, photoinitiator, and dispersant were prepared according to the proportions shown in Table 5 below and the powder slurry was thoroughly mixed using a three-roll mill to obtain the powder slurry of this embodiment. The viscosity of the powder slurry was 3000 mPa·s.

[0067] The aforementioned powder slurry was screen-printed onto the surface of a cleaned NdFeB magnet (30*30*3mm) using a screen printing machine. The product was then placed in an argon atmosphere and irradiated with a UV lamp for 80 seconds to ensure complete curing. After curing, the product was flipped over, and the same process was repeated on the other side, with another layer of powder slurry screen-printed and cured. The weight gain of the double-sided powder slurry coating was 0.9%. The product was then placed in a vacuum furnace for vacuum heat treatment at 350℃ for 8 hours, diffusion at 860℃ for 18 hours, and aging treatment at 485℃ for 7 hours. The diffused product was tested, and the results are shown in Table 6. Table 6 shows that the remanence of the diffused product decreased by only about 180 Gs, but the coercivity increased by about 7 Koe.

[0068] Table 5

[0069]

[0070] Table 6

[0071]

[0072] Example 4

[0073] The preparation method of the diffused NdFeB magnet in this embodiment is the same as in Example 1, except that the viscosity of the powder slurry in this embodiment is 80 mPa·s. The specific proportions of the powder slurry in this embodiment are shown in Table 7, and the test results of the diffused product are shown in Table 8. A comparison between Example 4 and Example 1 shows that when the powder slurry viscosity is reduced to 80 mPa·s, the consistency of the diffused product needs improvement. Some magnets show an increase in coercivity of only about 2 KOe, while others show an increase of 10 KOe. This indicates that if the powder slurry viscosity is too low, the coating process cannot be guaranteed to be stable and controllable, resulting in poor coating uniformity and therefore unstable improvement in magnetic properties.

[0074] Table 7

[0075]

[0076] Table 8

[0077]

[0078] Comparative Example 1

[0079] The preparation method of the diffused NdFeB magnet in this comparative example is the same as in Example 1, except that a cationic curing UV monomer is used instead of a free radical curing UV monomer. Specifically, a mixture of epoxidized triglyceride and ketene diethanolamide is used instead of a mixture of methyl laurate and pentaerythritol triacrylate. The specific proportions of the powder slurry in this comparative example are shown in Table 9, and the test results of the diffused product are shown in Table 10. As can be seen from Table 10, the remanence of the diffused product decreased by about 100 Gs, while the coercivity only increased by about 2 Koe.

[0080] A comparison of Comparative Example 1 and Example 1 shows that different UV monomers have a significant impact on the improvement of product diffusion performance. The free radical-cured UV monomer in this disclosure can be completely removed, thereby improving the diffusion channels of powders containing heavy rare earth elements and significantly increasing the coercivity of the magnet. Other UV monomers, such as cationic-cured UV monomers, affect the diffusion efficiency of the magnet and do not have a superior effect on improving the coercivity of the magnet.

[0081] Table 9

[0082]

[0083] Table 10

[0084]

[0085] The preferred embodiments of this disclosure have been described in detail above. However, this disclosure is not limited to the specific details of the above embodiments. Within the scope of the technical concept of this disclosure, various simple modifications can be made to the technical solutions of this disclosure, and these simple modifications all fall within the protection scope of this disclosure.

[0086] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any suitable manner without contradiction. In order to avoid unnecessary repetition, this disclosure will not describe the various possible combinations separately.

[0087] Furthermore, various different embodiments of this disclosure can be combined in any way, as long as they do not violate the spirit of this disclosure, they should also be regarded as the content disclosed in this disclosure.

Claims

1. A powder slurry for magnetic grain boundary diffusion, characterized in that, The powder slurry comprises powder containing heavy rare earth elements, UV monomer, polymerization inhibitor, photoinitiator, and dispersant; the UV monomer is a free radical cured UV monomer. Specifically, based on the total mass of the powder slurry, the amount of powder containing heavy rare earth elements added accounts for 60-80 wt% of the mass of the powder slurry, the amount of UV monomer added accounts for 15-35 wt% of the mass of the powder slurry, the amount of polymerization inhibitor added accounts for 0.01-0.1 wt% of the mass of the powder slurry, the amount of photoinitiator added accounts for 0.5-5 wt% of the mass of the powder slurry, and the amount of dispersant added accounts for 0.02-0.2 wt% of the mass of the powder slurry. The powder containing heavy rare earth elements is selected from at least one of the fluorides, fluoride oxides, hydrides, and oxides of the heavy rare earth elements. The UV monomer contains a methacrylate structure; The polymerization inhibitor is selected from at least one of tert-butylcatechol, tert-butylhydroquinone, hydroquinone and tris(N-nitroso-N-phenylhydroxylamine) aluminum salt; The photoinitiator is selected from at least one of benzoin dimethyl ether, 2,4,6-trimethylbenzoyl-diphenylphosphine oxide, 2-hydroxy-2-methyl-phenylacetone-1, isopropylthioxanthone, and 1-hydroxycyclohexylphenyl ketone; The dispersant is selected from at least one of glyceryl monooleate, polyethylene glycol oleate, and oleoyl monolaurate.

2. The powder slurry according to claim 1, wherein, The viscosity of the powder slurry is 100-5000 mPa·s.

3. The powder slurry according to claim 1, wherein, The UV monomer is selected from at least one of pentaerythritol triacrylate, isoborneol methacrylate, pentaerythritol tetraacrylate ethoxylate, trimethylolpropane trimethacrylate, dicyclopentyl methacrylate, dipentaerythritol hexaacrylate, 3,3,5-trimethylcyclohexyl acrylate, laurate methacrylate, and polyethylene glycol dimethacrylate.

4. The powder slurry according to claim 1, wherein, The powder containing heavy rare earth elements has a particle size of 1~10μm; The heavy rare earth elements in the powder containing heavy rare earth elements are selected from at least one of Dy, Tb and Ho.

5. The powder slurry according to claim 4, wherein, The powder containing heavy rare earth elements is selected from Dy2O3, Dy 1- y M y H x Tb2O3 and Tb 1-y M y H x At least one of the following, wherein M is selected from at least one of Fe, Cu, Zn and Al, x=2 or 3, 0≤y≤0.

3.

6. A method for manufacturing a magnet, characterized in that, The method includes: After coating the first surface of a NdFeB substrate with a powder slurry, a first curing reaction is performed to obtain a magnet coated with a first coating; the magnet coated with the first coating is then subjected to vacuum heat treatment, grain boundary diffusion treatment, and aging treatment in sequence; or After coating the first surface of the NdFeB substrate with the powder slurry, a first curing reaction is carried out to obtain a magnet coated with the first coating; after coating the second surface of the magnet coated with the first coating with the powder slurry, a second curing reaction is carried out to obtain a double-sided coated magnet; the double-sided coated magnet is then subjected to vacuum heat treatment, grain boundary diffusion treatment and aging treatment in sequence. Wherein, the first surface and the second surface are selected from the upper and lower surfaces of the NdFeB substrate; the powder slurry is the powder slurry for magnet grain boundary diffusion as described in any one of claims 1-5.

7. The magnet manufacturing method according to claim 6, wherein, The weight gain of the double-coated magnet is 0.1-2% of that of the neodymium iron boron substrate.

8. The magnet manufacturing method according to claim 6, wherein, In step S1, the conditions for the first curing reaction and the second curing reaction include: irradiating the surface of the NdFeB magnet coated with powder slurry with ultraviolet light in an inert atmosphere, wherein the inert atmosphere is nitrogen or argon, and the ultraviolet light irradiation time is 1~100s.

9. The magnet manufacturing method according to claim 6, wherein, In step S2, the conditions for vacuum heat treatment include: a treatment temperature of 250~600℃ and a treatment time of 1~10h; the conditions for grain boundary diffusion treatment include: a treatment temperature of 800~1000℃ and a treatment time of 2~50h; and the conditions for aging treatment include: a treatment temperature of 450~600℃ and a treatment time of 1~8h.

10. A magnet prepared by the magnet manufacturing method according to any one of claims 6-9.

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