Coating agent and coating process of rare earth permanent magnet material grain boundary diffusant

Abstract

The invention relates to a coating agent and a coating process of a rare earth permanent magnet material grain boundary diffusant, the coating agent is a phosphate-light-cured resin composite coating agent system containing branched alkyl, and the coating agent comprises 14-16 parts by mass of phosphate (preferably 2-ethylhexyl phosphate) containing branched C6-C12 alkyl, 2-4 parts by mass of epoxy resin and 1-2 parts by mass of acrylic resin. 0.01-0.05 part by mass of zinc stearate, 0.3-0.8 part by mass of nano aluminum oxide and the balance of a compound solvent of kerosene and absolute ethyl alcohol. The coating agent is used for coating the grain boundary diffusant, and a dynamic rolling and drying process is adopted, so that the problem that grain boundary diffusant powder using a light-cured resin composite coating agent system is easy to agglomerate and settle is solved, the coating effect is high, and the coated grain boundary diffusant has excellent settling resistance and oxidation resistance.

Description

Technical Field

[0001] This invention belongs to the field of surface modification technology for rare earth permanent magnet materials, specifically the field of grain boundary diffusion in rare earth permanent magnet materials. It relates to a coating agent for grain boundary diffusing agents and a process for coating grain boundary diffusing agents using this coating agent. This technology solves the problem of easy agglomeration and sedimentation of grain boundary diffusing agent powder using a photocurable resin composite coating agent system and a dynamic rolling drying process. It achieves high coating efficiency, and the coated grain boundary diffusing agent exhibits excellent anti-settling and anti-oxidation properties. Background Technology

[0002] Rare-earth permanent magnet materials are permanent magnets with extremely high magnetic energy product and coercivity, based on alloy compounds formed from rare-earth metals and transition metals and prepared through specific processes. Rare-earth elements include neodymium (Nd), praseodymium (Pr), dysprosium (Dy), and terbium (Tb). Transition metals include iron (Fe) and boron (B). Rare-earth permanent magnet materials mainly include two types of magnetic matrices: samarium cobalt (SmCo) and neodymium iron boron (NdFeB). They possess high magnetic energy product, strong remanence, and resistance to demagnetization, enabling them to generate powerful magnetic fields within a limited volume.

[0003] Traditional manufacturing processes for rare-earth permanent magnet materials require the doping of large amounts of rare-earth materials. However, global reserves of rare-earth materials are scarce and highly concentrated, consuming large amounts of expensive rare-earth resources and increasing manufacturing costs. Furthermore, the incorporation of large amounts of rare-earth elements into the main phase grains significantly reduces the remanence of the permanent magnet matrix. Under traditional manufacturing processes, high coercivity and high energy product are often mutually exclusive. Grain boundary diffusion technology uses small amounts of rare-earth elements as grain boundary diffusing agents, introducing them into the main phase grain boundaries through diffusion. This effectively improves coercivity and reduces dependence on rare-earth resources while maintaining performance.

[0004] Grain boundary diffusing agents containing rare earth elements are typically multi-element alloy powders containing one or more of neodymium (Nd), praseodymium (Pr), dysprosium (Dy), and terbium (Tb). These multi-element alloy diffusing agents can introduce Al and / or Cu to lower the melting point, improve wettability, and increase diffusion efficiency; examples include PrAlCu, PrTbCuAl, PrDyCuAl, and / or PrTbCuGa. They can also introduce Ni and / or Ga to enhance oxidation resistance and diffusion depth; examples include TbCuNi and / or PrTbAlGa. Multi-element alloy diffusing agents can improve coercivity and thermal stability in sintered permanent magnets (e.g., NdFeB and / or SmCo) without significantly reducing remanence, while simultaneously reducing the amount of rare earth elements required.

[0005] However, grain boundary diffusing agents containing rare earth elements are easily oxidized in humid or acidic / alkaline environments. Furthermore, because these agents are typically in powder form, they are prone to agglomeration and sedimentation during storage and transportation. Therefore, coating these agents is crucial. This coating not only improves their stability, oxidation resistance, and wettability during storage, transportation, and diffusion, preventing oxidation and performance degradation before high-temperature diffusion, but also promotes contact between the diffusing agent and the magnetic matrix surface during diffusion, improving diffusion uniformity and efficiency. Coating agents typically include binders and processing aids. Binders can be polymer resins, such as polyvinyl chloride, acrylic resins, polyamide resins, polyester resins, and epoxy resins. Processing aids improve the wettability of the coating agent to the magnetic powder and include coupling agents, plasticizers, and lubricants. Coupling agents include phthalate coupling agents and / or silane coupling agents. Phthalate esters can be used as plasticizers. Fatty acids, paraffin wax, and microcrystalline wax can be used as lubricants. The coating agent can also be an inorganic coating, such as an Al2O3 or ZrO2 nanofilm, which forms a protective layer through a sol-gel or spray-sintering process.

[0006] Chinese invention patent application CN108447639A discloses a rare earth magnetic powder composition, wherein the coating agent is selected from one or more of polyolefin, silicone oil, vegetable oil, and liquid paraffin, and is a liquid coating agent, and the magnetic powder is uniformly coated by grinding with a ball mill.

[0007] Chinese invention patent application CN108335815A discloses a rare earth magnetic powder composition using silane coupling agents or phthalate coupling agents as coating agents and its preparation method. The rare earth magnetic powder composition comprises 80-95 parts by weight of rare earth permanent magnet material powder, 0-5 parts by weight of additives, and 5-15 parts by weight of coating agent. The composition is dried using airflow drying or in a fluidized bed under vibration.

[0008] Chinese invention patent 201710695793.7 discloses a method for preparing an inorganic oxide-coated iron-silicon-aluminum soft magnetic powder core. The method involves adding resin, acetone, and ethanol to the magnetic powder to prepare slurry one, and adding an organosilicon surfactant, water, and ethanol to the inorganic oxide (one of nano-magnesium oxide, nano-alumina, and nano-silicon oxide) to prepare slurry two. The two slurries are then mixed, and epoxy resin is added for pressing, molding, and heat treatment.

[0009] Chinese invention patent application CN120878448A discloses a method for preparing neodymium iron boron magnets using ultrasonic-assisted screen printing and gradient temperature control. 0.8-1.8 parts by weight of nano-aluminum chloride are screen printed onto a dense preform formed by hot pressing of magnetic powder raw materials, and then a series of processes are performed to obtain the desired magnet.

[0010] In existing technologies, nano-alumina can form a dense protective layer, but it is costly and the process is complex. Coating agents for Dy and / or Tb alloys (e.g., silane / phthalate systems) typically use dry powder lamination and ultraviolet (UV) light curing technology to achieve rapid curing and prevent the sedimentation of diffused powder. However, coating agents are often hydrophobic materials, resulting in a slightly hydrophobic surface after coating. When using UV light curing systems (usually acrylic or epoxy curing systems), the slightly hydrophilic nature of the UV curing system leads to poor wettability, uneven curing, and easy aggregation and sedimentation of the coated grain boundary diffuser. Incomplete coating can also cause some of the grain boundary diffuser to come into contact with oxygen and / or water, thus rendering it ineffective.

[0011] Therefore, this invention uses a novel coating agent for grain boundary diffusers, and solves the above problems through formulation optimization and process innovation. Summary of the Invention

[0012] To address the problems and deficiencies in the prior art as described above, this invention provides a coating agent for preparing rare-earth permanent magnet materials. This coating agent, containing rare-earth elements, exhibits excellent anti-settling and anti-oxidation properties, and improves the utilization rate of the grain boundary diffuser. This invention also provides a method for coating grain boundary diffusers using this coating agent.

[0013] The grain boundary diffusing agents, rare earth alloys, alloy diffusing agents, rare earth alloy powders, powders, granules, and rare earth element-containing composite materials mentioned in this article all refer to uncoated rare earth alloy materials containing one or more rare earth elements selected from neodymium (Nd), praseodymium (Pr), dysprosium (Dy), and terbium (Tb), which can be selected from PrAlCu, PrTbCuAl, PrTbCuGa, TbCuNi, and / or PrTbAlGa, etc. Coated or uncoated rare earth alloy materials can be introduced into the surface of the main phase grain boundaries of the magnetic matrix through diffusion, effectively improving the coercivity of the magnet while ensuring strong remanence. Rare earth alloy materials coated with a coating agent become coated rare earth alloy materials.

[0014] Unless otherwise stated, all parts mentioned below are by weight, and all ratios are by weight. When referring to numerical values, the terms "between," "above," "below," "to," "from," and "not less than" include the numerical value itself.

[0015] The coating agent provided by the present invention comprises C6-C containing branches 12 14-16 parts by weight of alkyl phosphate esters; 2-4 parts by weight of epoxy resin; 1-2 parts by weight of acrylic resin; Zinc stearate 0.01-0.05 parts by weight; 0.3-0.8 parts by weight of nano-alumina; and The remaining amount of the compounded solvent; the compounded solvent is a mixture of kerosene and anhydrous ethanol.

[0016] The coating agent provided by this invention can be used to coat grain boundary diffusing agents for rare earth permanent magnet materials, such as PrAlCu, PrTbCuAl, PrDyCuAl, PrTbCuGa, TbCuNi, and / or PrTbAlGa. In a preferred embodiment, the coating agent of this invention is used to coat grain boundary diffusing agents PrAlCu, PrTbCuAl, PrDyCuAl, and / or PrTbCuGa used in NdFeB permanent magnet materials.

[0017] In this invention, the applicant discovered that, among various phosphate esters (e.g., dodecyl phosphate, octadecyl phosphate, 2-ethylhexyl phosphate), those containing branched C6-C chains are superior to straight-chain alkyl esters. 12 Alkyl phosphate esters (such as 2-ethylhexyl phosphate) are excellent and important components in the coating of grain boundary diffusion powders for rare earth permanent magnet materials. While 2-ethylhexyl phosphate (EHPA) is commonly used as an extractant for rare earth elements, it is not currently mentioned in published literature as a coating agent for grain boundary diffusion powders in rare earth permanent magnet materials. The inventors discovered that phosphate esters containing branched alkyl groups not only have good compatibility with other organic components in the coating agent, such as epoxy and acrylic resins, but also possess strong acidity due to the incomplete esterification of their functional groups (phosphate groups), making them suitable for coordination with metal particles. Therefore, they exhibit excellent wettability for grain boundary diffusers, effectively enhancing the compatibility between the diffuser and the organic phase, aiding powder dispersion, preventing sedimentation, and improving the uniformity of the grain boundary diffuser coating. They also reduce interfacial defects, preventing magnetic performance degradation caused by diffuser detachment during coating and subsequent use. The branched structure also reduces crystallization tendency, resulting in better liquid stability and more uniform powder coating. (Branched C6-C...) 12 Alkyl phosphates include, but are not limited to, EHPA (C8 branched alkyl), isooctyl phosphate (C9 branched alkyl), isononyl phosphate (C9 branched alkyl), and isodecyl phosphate (C9 branched alkyl). 10 Branched alkyl groups). Preferably, branched C8-C9 alkyl phosphates are used, and more preferably, branched C8 alkyl EHPA is used because EHPA has superior metal ion affinity. EHPA chemically bonds with rare earth alloys to form a Pr-OP passivation film, improving coating stability. EHPA coating reduces the agglomeration of grain boundary diffusing agents during mixing and molding, improving filler dispersibility, thereby enhancing the magnet's impact resistance and flexural strength. EHPA can withstand high temperatures (≤200°C). OC) It is easily decomposed and needs to be removed along with other organic binders before grain boundary diffusion. Preferably, EHPA accounts for 14-16 parts by weight of the total coating agent. If the amount of EHPA is too high, the uniformity of the coating thickness will deteriorate, and the dispersant will be wasted; if the amount of EHPA is too low, it will not provide adequate compatibility.

[0018] Epoxy resin is a conventional coating layer adhesive, typically used at 5%-30% of the grain boundary diffuser. Acrylic resin can be used to increase the hydrophilicity of the coating agent and improve powder dispersibility. The coating agent of this invention contains far less epoxy resin and acrylic resin than conventionally used. The combined use of epoxy resin and acrylic resin in the system of this invention not only enhances the adhesion of the coating layer and improves powder dispersibility, but also promotes uniform curing. Because epoxy resin and acrylic resin can themselves be used as components of a UV curing system, adding a small amount of epoxy resin and acrylic resin to the coating agent can greatly improve the compatibility between the coating agent and the UV curing resin, resulting in high curing efficiency. This coating agent can also be used as a photocuring system for the crystal diffusion process by directly adding a photoinitiator without using additional UV curing resin or with a small amount of additional UV curing resin. Considering the simplification of the process and optimization of costs, the epoxy resin in the coating agent should preferably account for 2-4 parts by mass of the total mass of the coating agent, and the acrylic resin should preferably account for 1-2 parts by mass of the total mass of the coating agent. In the preferred embodiment, the mass of epoxy resin is 1-2 times the mass of acrylic resin. In a more preferred embodiment, the mass of epoxy resin is twice the mass of acrylic resin. The total mass of epoxy resin and acrylic resin is greater than 1 / 10 and less than 1 / 2 of the mass of EHPA. The total mass of epoxy resin and acrylic resin is greater than 3% and less than 6% of the total mass of the coating agent. If the total mass of epoxy resin and acrylic resin is too high, it not only leads to the high cost of removing the organic binder at high temperatures but also hinders the control of the photocuring speed. If the total mass of epoxy resin and acrylic resin is too low, it is detrimental to the uniformity of photocuring.

[0019] The coating agent of this invention contains zinc stearate. The applicant has discovered that adding a small amount of zinc stearate to the coating agent can improve the antioxidant and dispersing properties of the grain boundary diffuser. In the prior art, the amount of zinc stearate used as a dispersant, lubricant, or interface modifier is generally not less than 0.5 parts by mass of the system, and sometimes not less than 3 parts by mass. In this invention, zinc stearate is used as an interface modifier, preferably comprising 0.01-0.05 parts by mass of the coating agent. When the amount of zinc stearate exceeds 0.05 parts by mass, or even 0.1 parts by mass or more, the coating adhesion decreases due to the hydrophobicity of the zinc stearate surface.

[0020] The coating agent of this invention also contains nano-alumina, which synergistically forms a uniform and dense protective layer. Nano-alumina has a high melting point, making it suitable for high-temperature applications, but its cost is also very high. The coating agent of this invention contains 0.3-0.8 parts by weight of nano-alumina. If the amount of nano-alumina is too low, the high-temperature resistance is not significant; if the amount of nano-alumina is too high, it is not conducive to cost control and requires a more stringent preparation process for the uniform dispersion of the nanopowder.

[0021] The coating agent of this invention further comprises a kerosene and anhydrous ethanol compound solvent, preferably kerosene and anhydrous ethanol in a 1:1 mass ratio, accounting for the remaining mass of the coating agent. The addition of the low molecular weight solvents kerosene and anhydrous ethanol reduces the viscosity of the system, serving as a dispersion medium for preparing a powder suspension, which is beneficial for the dispersion of other components of the coating agent and the dispersion of the powder, thereby achieving uniform powder coating. Kerosene is a non-polar solvent, used for the dispersion and coating of hydrophobic materials, and can isolate air, reducing the risk of oxidation of metal powders. In the subsequent wet ball milling coating process, kerosene can reduce particle agglomeration during ball milling and improve flowability. Anhydrous ethanol is a polar solvent, used for the dispersion and coating of hydrophilic materials, and can promote the formation of a uniform film of the coating agent on the particle / powder surface. Preferably, the kerosene and anhydrous ethanol compound solvent comprises not less than 60 parts by mass of the coating agent. More preferably, the kerosene and anhydrous ethanol compound solvent comprises not less than 70 parts by mass of the coating agent.

[0022] Furthermore, kerosene and anhydrous ethanol can be used as cleaning agents to remove oil from the magnet surface before grain boundary diffusion. Anhydrous ethanol can also be used as a displacement agent for kerosene to remove it, without introducing new compounds during the entire coating process. Moreover, anhydrous ethanol is highly volatile and easy to remove in post-treatment. The mixed use of kerosene and anhydrous ethanol can be used to adjust polarity and volatility, achieving both good dispersion and good post-treatment properties.

[0023] This invention also relates to a coating process for coating rare earth permanent magnet materials with grain boundary diffusing agents, the coating process comprising the following steps: S1 Solvent pretreatment; S2 wet ball milling coating; wherein the powder ratio of grain boundary diffuser to coating agent is 1:(3-5), and the coating process is carried out in an inert protective gas; S3 Ethanol replacement; S4 gradient centrifugation; S5 Dynamic Roller Drying.

[0024] Preferably, the coating process specifically includes the following steps: S1 Solvent Pretreatment: Based on the composition of the coating agent, a mixture of kerosene and anhydrous ethanol is preferred as the solvent for pretreatment of the grain boundary diffuser. The grain boundary diffuser is immersed in the kerosene-anhydrous ethanol mixture for a period of time to clean the surface of the grain boundary diffuser and displace the adsorbed oxygen on its surface. Stirring or ultrasonic mixing can be used to enhance the mixing. The immersion time is typically 20-120 minutes. The immersion time in this invention is preferably 20-60 minutes.

[0025] S2 Wet ball milling coating: The grain boundary diffusing agent and the coating agent are mixed at a mass ratio of 1:2 to 1:6 to obtain a suspension slurry of the grain boundary diffusing agent. Preferably, the mass ratio is 1:3 to 1:5, and more preferably 1:4 to 1:5, to ensure a suitable slurry viscosity and sufficient coating agent to coat the grain boundary diffusing agent without wasting excessive coating agent. Ultrasonic dispersion or ball milling is commonly used to improve powder dispersion uniformity and reduce agglomeration. This invention uses ball milling. The mixed grain boundary diffusing agent suspension slurry is ball milled under an inert gas (e.g., nitrogen or argon) protection. A planetary ball mill is preferred. The filling volume of each grinding jar is typically no more than 1 / 3 to 1 / 2 of its capacity to avoid overloading and affecting the grinding effect. ZrO2 balls can be used, and the ball-to-material ratio (ball:material) is generally between 3:1 and 10:1. Based on the material hardness and slurry viscosity, this invention preferably uses a ball-to-material ratio of 8:1 to 10:1, and more preferably 10:1. A higher ball-to-material ratio can increase the impact force, enabling high-energy or nano-grinding. The rotational speed range is 100-800 rpm, preferably 200-500 rpm, and more preferably 300-400 rpm.

[0026] S3 Ethanol replacement: Removal of kerosene from the slurry. Kerosene can be removed using different replacement agents. In a preferred embodiment of this invention, anhydrous ethanol is used as the replacement agent for kerosene, without introducing new substances. The volume ratio of anhydrous ethanol added as the replacement agent to the slurry is (2-5):1, preferably 3:1. After replacement, the anhydrous ethanol can be removed by subsequent heating or distillation drying.

[0027] S4 Gradient Centrifugation: After coating, to remove uncoated particles, the slurry is centrifuged at increased rotation speed. This invention uses gradient centrifugation, centrifuging the slurry at different speeds, for example, gradually increasing the speed for multiple centrifugations. This invention uses two or more speeds to centrifuge the slurry, with the first speed range being 800-1000 rpm and the second speed range being greater than 1000 rpm. Preferably, the second speed is greater than 1200 rpm. More preferably, the second speed is greater than 1400 rpm. The first speed is higher than the grinding speed to ensure process stability, while the second speed is a high speed to improve separation efficiency. To further improve separation efficiency, this invention preferably adds a dispersant that can selectively adsorb onto the surface of the coated powder to the slurry before centrifugation. This dispersant has good compatibility with the coating agent components on the surface of the coated powder, can adhere to the surface of the coated powder, further strengthening the steric hindrance or hydrophobic layer on the surface of the coated powder, making it more likely to form loose aggregates or remain dispersed during centrifugation; while the uncoated exposed metal surface has weak adsorption of the dispersant and will densely settle during centrifugation. The dispersant used should be compatible with the phosphate esters, epoxy resins, and acrylic resins in the coating agent of this invention. It is preferably an oil-soluble surfactant, and can be, but is not limited to, Span 80 or long-chain alkanes (such as liquid paraffin). To avoid precipitation of the coated powder, short-time centrifugation is preferred when using the first rotational speed, with a centrifugation time of 30 seconds to 30 minutes, preferably 1 minute to 10 minutes, and more preferably 2 minutes to 5 minutes. Short-time centrifugation is preferred when using the second rotational speed, with a centrifugation time of 30 seconds to 30 minutes, preferably 1 minute to 15 minutes, and more preferably 5 minutes to 10 minutes. The centrifugation process accelerates the aggregation of uncoated powder, forming dense aggregates that settle rapidly, while well-coated particles remain in the supernatant and soft precipitate. After centrifugation, the precipitate and supernatant are separated; the precipitate is rich in uncoated powder. The separated uncoated powder can be re-coated.

[0028] S5 Dynamic Rolling Drying: The slurry is subjected to vacuum dynamic rolling drying. Under a certain vacuum level, the slurry is rolled and dried at a certain temperature for a certain time to obtain the dried coated grain boundary diffusing agent. Preferably, the slurry is rolled and dried at different temperatures for a certain time under a certain vacuum level. Rolling drying can be carried out in a ball mill, and ZrO2 balls are used simultaneously to roll the coated grain boundary diffusing agent slurry during vacuum drying. Preferably, ZrO2 balls with a particle size of 1–2 mm are rolled at a low speed of 40–60 rpm. The vacuum level depends on the equipment used and the drying efficiency, and is typically between -1 MPa and -0.02 MPa, preferably between -1 MPa and -0.05 MPa, and more preferably between -0.5 MPa and -0.1 MPa. Dynamic drying can be performed at one temperature within a reasonable temperature range for a certain time, preferably at two or more different temperatures within a reasonable temperature range for a certain time. A reasonable temperature range typically refers to the temperature from room temperature to the temperature at which thermal decomposition of the coating material is avoided. The reasonable temperature range for this invention is from room temperature to 150°C. o Between C, the preferred option is from 25. o C to 100 o Between C, preferably from 40 o C to 80 o Between 40°C and 60°C. The selected different temperatures can be several increasing temperatures, several decreasing temperatures, or several arbitrary temperatures within a reasonable range. This invention preferably uses several increasing temperatures to ensure drying stability and process operability, and improve drying efficiency. It is preferable to use two or more temperatures that increase with a small temperature difference to ensure drying stability. For example, a temperature of 40°C can be selected. o Dry at C for one hour, then at 60 o Dry at C for one hour, then at 80 o Dry at C for one hour. Alternatively, you can choose to dry at 40°C. o Dry at C for one hour, then at 50 o Dry at C for half an hour, then at 60 o Dry at C for half an hour, then at 70 o Dry at C for half an hour, then at 80 o Dry at C for half an hour.

[0029] This invention is the first to use branched alkyl phosphate esters (preferably 2-ethylhexyl phosphate ester) as a key component of the coating agent for grain boundary diffusers in rare earth permanent magnet materials. The branched alkyl groups' fluidity and low crystallinity tendency, along with the acidification of the phosphate esters to enhance compatibility with organic components and grain boundary diffusers, facilitate powder dispersion. Simultaneously, this coating agent significantly reduces the amount of epoxy and acrylic resins used as adhesives, utilizing their properties as photocurable coatings to achieve "green" curing and improve curing efficiency. A very small amount of zinc stearate is added to the coating agent to adjust fluidity and dispersibility, and a small amount of nano-alumina is added to improve high-temperature resistance and optimize the dense protective layer. Kerosene and anhydrous ethanol are used as compounding solvents to simplify and optimize the coating process. The coating process of this invention optimizes various parameters by utilizing the components of the coating agent and a dynamic rolling drying process, resulting in a coated grain boundary diffuser with excellent anti-settling and anti-oxidation properties and high coating efficiency. Attached Figure Description

[0030] Figure 1 This is a SEM image of PrTbCuAl, an uncoated rare-earth permanent magnet material grain boundary diffuser. Figure 2 This is a SEM image of the rare earth permanent magnet material grain boundary diffuser PrTbCuAl after being coated with the coating agent of the present invention. Detailed Implementation

[0031] The embodiments described in this section are some, not all, embodiments of this invention, and are merely illustrative of the invention, not limiting it. Any modifications to this invention are within the scope of protection of this invention.

[0032] Example 1

[0033] Take 15 parts by weight of 2-ethylhexyl phosphate, 3 parts by weight of epoxy resin (E51), 1.5 parts by weight of acrylic resin (AR-01), 0.02 parts by weight of zinc stearate, 0.5 parts by weight of nano alumina, and 79.98 parts by weight of kerosene: anhydrous ethanol (1:1) solvent, mix them evenly, and prepare a coating agent.

[0034] PrTbCuAl powder with an average particle size of 2-8 μm was immersed in 60 mL of water. o Immerse C in a kerosene-anhydrous ethanol mixture for 30 minutes to replace adsorbed oxygen on the surface.

[0035] The treated PrTbCuAl powder and the coating agent were mixed at a mass ratio of 1:4 and ball-milled in a planetary ball mill (MITR-YXQM-1L) using ZrO2 grinding balls under nitrogen (N2) protection to obtain a slurry. The ball-to-powder ratio was 10:1, the rotation speed was 300 rpm, and the grinding time was 1.5 hours.

[0036] Subsequently, anhydrous ethanol (anhydrous ethanol: slurry volume ratio of 3:1) was added to the slurry, and the mixture was stirred for 30 minutes to remove the kerosene.

[0037] Increase the speed to 800 rpm and centrifuge the slurry for 5 minutes, then increase the speed to 1500 rpm and centrifuge the slurry for 10 minutes to remove uncoated powder.

[0038] Then, the slurry is dried: maintaining a vacuum of -0.1 MPa, first at 40... o Dry at C for one hour, then at 60°C. o Dry at C for one hour, then at 70°C. o Dry at C for half an hour, and finally at 80°C. o Drying at C for half an hour. During the drying process, ZrO2 balls are simultaneously rolled to prevent curling and agglomeration, with a ball-to-powder ratio of 1:10 and a rotation speed of 50 rpm. The resulting coated PrTbCuAl powder is obtained.

[0039] Example 2

[0040] Take 14 parts by weight of 2-ethylhexyl phosphate, 4 parts by weight of epoxy resin (E51), 2 parts by weight of acrylic resin (AR-01), 0.02 parts by weight of zinc stearate, 0.4 parts by weight of nano alumina, and 79.58 parts by weight of kerosene: anhydrous ethanol (1:1) solvent, mix them evenly, and prepare a coating agent.

[0041] PrTbCuAl powder with an average particle size of 2-8 μm was immersed in 60 mL of water. o Immerse C in a kerosene-anhydrous ethanol mixture for 30 minutes to replace adsorbed oxygen on the surface.

[0042] The treated PrTbCuAl powder was mixed with a coating agent at a mass ratio of 1:5, and ball-milled in a planetary ball mill (MITR-YXQM-1L) using ZrO2 grinding balls under nitrogen (N2) protection to obtain a slurry. The ball-to-powder ratio was 10:1, the rotation speed was 300 rpm, and the grinding time was 1.5 hours.

[0043] Subsequently, anhydrous ethanol (anhydrous ethanol: slurry volume ratio of 3:1) was added to the slurry, and the mixture was stirred for 30 minutes to remove the kerosene.

[0044] Increase the rotation speed to 800 rpm and centrifuge the slurry for 5 minutes. Then increase the rotation speed to 1400 rpm and centrifuge the slurry for 10 minutes to remove uncoated powder.

[0045] Then, the slurry is dried: maintaining a vacuum of -0.1 MPa, first at 40... o Dry at C for one hour, then at 60°C. o Dry at C for one hour, and finally at 80°C. o Drying at C for one hour. During the drying process, ZrO2 balls were simultaneously rolled to prevent curling and agglomeration, with a ball-to-powder ratio of 1:10 and a rotation speed of 50 rpm. The resulting coated PrTbCuAl powder was obtained.

[0046] Example 3

[0047] Take 16 parts by weight of 2-ethylhexyl phosphate, 4 parts by weight of epoxy resin (E51), 2 parts by weight of acrylic resin (AR-01), 0.03 parts by weight of zinc stearate, 0.6 parts by weight of nano alumina, and 77.37 parts by weight of kerosene: anhydrous ethanol (1:1) solvent, mix them evenly, and prepare a coating agent.

[0048] PrAlCu powder with an average particle size of 2-8 μm was immersed in 60 mL of water. o Immerse C in a kerosene-anhydrous ethanol mixture for 30 minutes to replace adsorbed oxygen on the surface.

[0049] The treated PrAlCu powder was mixed with a coating agent at a mass ratio of 1:4, and then ball-milled in a planetary ball mill (MITR-YXQM-1L) using ZrO2 grinding balls under nitrogen (N2) protection to obtain a slurry. The ball-to-powder ratio was 10:1, the rotation speed was 200 rpm, and the grinding time was 2 hours.

[0050] Subsequently, anhydrous ethanol (anhydrous ethanol: slurry volume ratio of 3:1) was added to the slurry, and the mixture was stirred for 30 minutes to remove the kerosene.

[0051] Increase the speed to 800 rpm and centrifuge the slurry for 5 minutes, then increase the speed to 1500 rpm and centrifuge the slurry for 10 minutes to remove uncoated powder.

[0052] Then, the slurry is dried: maintaining a vacuum of -0.1 MPa, first at 40... o Dry at C for one hour, then at 60°C. o Dry at C for one hour, and finally at 80°C. o Drying at C for one hour. During the drying process, ZrO2 balls were simultaneously rolled to prevent curling and agglomeration, with a ball-to-powder ratio of 1:10 and a rotation speed of 50 rpm. The resulting coated PrAlCu powder was obtained.

[0053] Example 4

[0054] Take 15 parts by weight of isooctyl phosphate, 2 parts by weight of epoxy resin (E51), 1 part by weight of acrylic resin (AR-01 A01), 0.04 parts by weight of zinc stearate, 0.3 parts by weight of nano alumina, and 81.66 parts by weight of kerosene: anhydrous ethanol (1:1) solvent, mix them evenly, and prepare a coating agent.

[0055] PrAlCu powder with an average particle size of 2-8 μm was immersed in 60 mL of water. o Immerse C in a kerosene-anhydrous ethanol mixture for 30 minutes to replace adsorbed oxygen on the surface.

[0056] The treated PrAlCu powder and coating agent were mixed at a mass ratio of 1:4 and ball-milled in a planetary ball mill (MITR-YXQM-1L) using ZrO2 grinding balls under nitrogen (N2) protection to obtain a slurry. The ball-to-powder ratio was 10:1, the rotation speed was 300 rpm, and the grinding time was 1.5 hours.

[0057] Subsequently, anhydrous ethanol (anhydrous ethanol: slurry volume ratio of 3:1) was added to the slurry, and the mixture was stirred for 30 minutes to remove the kerosene.

[0058] Increase the speed to 1000 rpm and centrifuge the slurry for 5 minutes, then increase the speed to 1500 rpm and centrifuge the slurry for 10 minutes to remove uncoated powder.

[0059] Then, the slurry is dried: maintaining a vacuum of -0.1 MPa, first at 40... o Dry at C for one and a half hours, then at 80 o Drying at C for one and a half hours. During the drying process, ZrO2 balls were simultaneously rolled to prevent curling and agglomeration, with a ball-to-powder ratio of 1:10 and a rotation speed of 50 rpm. The resulting coated PrAlCu powder was obtained.

[0060] Example 5

[0061] Take 14.5 parts by weight of 2-ethylhexyl phosphate, 3 parts by weight of epoxy resin (E51), 2 parts by weight of acrylic resin (AR-01), 0.05 parts by weight of zinc stearate, 0.5 parts by weight of nano alumina, and 79.95 parts by weight of kerosene: anhydrous ethanol (1:1) solvent, mix them evenly, and prepare a coating agent.

[0062] PrTbCuAl powder with an average particle size of 2-8 μm was immersed in 60 mL of water. o Immerse C in a kerosene-anhydrous ethanol mixture for 30 minutes to replace adsorbed oxygen on the surface.

[0063] The treated PrTbCuAl powder was mixed with a coating agent at a mass ratio of 1:5, and ball-milled in a planetary ball mill (MITR-YXQM-1L) using ZrO2 grinding balls under nitrogen (N2) protection to obtain a slurry. The ball-to-powder ratio was 10:1, the rotation speed was 300 rpm, and the grinding time was 1.5 hours.

[0064] Subsequently, anhydrous ethanol (anhydrous ethanol: slurry volume ratio of 3:1) was added to the slurry, and the mixture was stirred for 30 minutes to remove the kerosene.

[0065] Increase the speed to 900 rpm and centrifuge the slurry for 5 minutes, then increase the speed to 1500 rpm and centrifuge the slurry for 10 minutes to remove uncoated powder.

[0066] Then, the slurry is dried: maintaining a vacuum of -0.1 MPa, first at 40... o Dry at C for one and a half hours, then at 80 o Drying at C for one and a half hours. During the drying process, ZrO2 balls were simultaneously rolled to prevent curling and agglomeration, with a ball-to-powder ratio of 1:10 and a rotation speed of 50 rpm. The resulting coated PrTbCuAl powder was obtained.

[0067] Example 6

[0068] Take 15 parts by weight of 2-ethylhexyl phosphate, 4 parts by weight of epoxy resin (E51), 2 parts by weight of acrylic resin (AR-01), 0.01 parts by weight of zinc stearate, 0.8 parts by weight of nano alumina, and 78.19 parts by weight of kerosene: anhydrous ethanol (1:1) solvent, mix them evenly, and prepare a coating agent.

[0069] PrAlCu powder with an average particle size of 2-8 μm was immersed in 60 mL of water. o Immerse C in a kerosene-anhydrous ethanol mixture for 30 minutes to replace adsorbed oxygen on the surface.

[0070] The treated PrAlCu powder was mixed with a coating agent at a mass ratio of 1:4, and then ball-milled in a planetary ball mill (MITR-YXQM-1L) using ZrO2 grinding balls under nitrogen (N2) protection to obtain a slurry. The ball-to-powder ratio was 10:1, the rotation speed was 200 rpm, and the grinding time was 2 hours.

[0071] Subsequently, anhydrous ethanol (anhydrous ethanol: slurry volume ratio of 3:1) was added to the slurry, and the mixture was stirred for 30 minutes to remove the kerosene.

[0072] Increase the speed to 900 rpm and centrifuge the slurry for 5 minutes, then increase the speed to 1500 rpm and centrifuge the slurry for 10 minutes to remove uncoated powder.

[0073] Then, the slurry is dried: maintaining a vacuum of -0.1 MPa, first at 40... o Dry at C for one hour, then at 60°C. o Dry at C for one hour, and finally at 80°C. o Drying at C for one hour. During the drying process, ZrO2 balls were simultaneously rolled to prevent curling and agglomeration, with a ball-to-powder ratio of 1:10 and a rotation speed of 50 rpm. The resulting coated PrAlCu powder was obtained.

[0074] Comparative Example 1 Take 13 parts by weight of 2-ethylhexyl phosphate, 5 parts by weight of epoxy resin (E51), 5 parts by weight of acrylic resin (AR-01), and 77 parts by weight of kerosene: anhydrous ethanol (1:1) solvent, mix them evenly, and prepare a coating agent.

[0075] PrTbCuAl powder with an average particle size of 2-8 μm was immersed in 60 mL of water. o Immerse C in a kerosene-anhydrous ethanol mixture for 30 minutes to replace adsorbed oxygen on the surface.

[0076] The treated PrTbCuAl powder and the coating agent were mixed at a mass ratio of 1:4 and ball-milled in a planetary ball mill (MITR-YXQM-1L) using ZrO2 grinding balls under nitrogen (N2) protection to obtain a slurry. The ball-to-powder ratio was 10:1, the rotation speed was 300 rpm, and the grinding time was 1.5 hours.

[0077] Subsequently, anhydrous ethanol (anhydrous ethanol: slurry volume ratio of 3:1) was added to the slurry, and the mixture was stirred for 30 minutes to remove the kerosene.

[0078] Increase the speed to 800 rpm and centrifuge the slurry for 5 minutes, then increase the speed to 1500 rpm and centrifuge the slurry for 10 minutes to remove uncoated powder.

[0079] Then, the slurry is dried: maintaining a vacuum of -0.1 MPa, first at 40... o Dry at C for one hour, then at 60°C. o Dry at C for one hour, then at 70°C. o Dry at C for half an hour, and finally at 80°C. o Drying at C for half an hour. During the drying process, ZrO2 balls are simultaneously rolled to prevent curling and agglomeration, with a ball-to-powder ratio of 1:10 and a rotation speed of 50 rpm. The resulting coated PrTbCuAl powder is obtained.

[0080] Comparative Example 2 Take 17 parts by weight of 2-ethylhexyl phosphate, 3 parts by weight of epoxy resin (E51), 2 parts by weight of acrylic resin (AR-01), 0.06 parts by weight of zinc stearate, 0.5 parts by weight of nano alumina, and 77.44 parts by weight of kerosene: anhydrous ethanol (1:1) solvent, mix them evenly, and prepare a coating agent.

[0081] PrTbCuAl powder with an average particle size of 2-8 μm was immersed in 60 mL of water. o Immerse C in a kerosene-anhydrous ethanol mixture for 30 minutes to replace adsorbed oxygen on the surface.

[0082] The treated PrTbCuAl powder and the coating agent were mixed at a mass ratio of 1:4 and ball-milled in a planetary ball mill (MITR-YXQM-1L) using ZrO2 grinding balls under nitrogen (N2) protection to obtain a slurry. The ball-to-powder ratio was 10:1, the rotation speed was 300 rpm, and the grinding time was 1.5 hours.

[0083] Subsequently, anhydrous ethanol (anhydrous ethanol: slurry volume ratio of 3:1) was added to the slurry, and the mixture was stirred for 30 minutes to remove the kerosene.

[0084] Increase the speed to 800 rpm and centrifuge the slurry for 5 minutes, then increase the speed to 1500 rpm and centrifuge the slurry for 10 minutes to remove uncoated powder.

[0085] Then, the slurry is dried: maintaining a vacuum of -0.1 MPa, first at 40... o Dry at C for one hour, then at 60°C. o Dry at C for one hour, then at 70°C. o Dry at C for half an hour, and finally at 80°C. o Drying at C for half an hour. During the drying process, ZrO2 balls are simultaneously rolled to prevent curling and agglomeration, with a ball-to-powder ratio of 1:10 and a rotation speed of 50 rpm. The resulting coated PrTbCuAl powder is obtained.

[0086] Comparative Example 3 Take 16 parts by weight of epoxy resin (E51), 8 parts by weight of acrylic resin (AR-01), 0.03 parts by weight of zinc stearate, 0.6 parts by weight of nano alumina, and 75.37 parts by weight of kerosene: anhydrous ethanol (1:1) solvent, mix them evenly, and prepare a coating agent.

[0087] PrAlCu powder with an average particle size of 2-8 μm was immersed in 60 mL of water. o Immerse C in a kerosene-anhydrous ethanol mixture for 30 minutes to replace adsorbed oxygen on the surface.

[0088] The treated PrAlCu powder and coating agent were mixed at a mass ratio of 1:4 and ball-milled in a planetary ball mill (MITR-YXQM-1L) using ZrO2 grinding balls under nitrogen (N2) protection to obtain a slurry. The ball-to-powder ratio was 10:1, the rotation speed was 300 rpm, and the grinding time was 1.5 hours.

[0089] Subsequently, anhydrous ethanol (anhydrous ethanol: slurry volume ratio of 3:1) was added to the slurry, and the mixture was stirred for 30 minutes to remove the kerosene.

[0090] Increase the speed to 800 rpm and centrifuge the slurry for 5 minutes, then increase the speed to 1500 rpm and centrifuge the slurry for 10 minutes to remove uncoated powder.

[0091] Then, the slurry is dried: maintaining a vacuum of -0.1 MPa, first at 40... o Dry at C for one hour, then at 60°C. o Dry at C for one hour, and finally at 80°C. o Drying at C for one hour. During the drying process, ZrO2 balls were simultaneously rolled to prevent curling and agglomeration, with a ball-to-powder ratio of 1:10 and a rotation speed of 50 rpm. The resulting coated PrAlCu powder was obtained.

[0092] Comparative Example 4 Take 12 parts by weight of 2-ethylhexyl phosphate, 3 parts by weight of epoxy resin (E51), 2 parts by weight of acrylic resin (AR-01), 0.02 parts by weight of zinc stearate, 0.5 parts by weight of nano alumina, and 82.48 parts by weight of kerosene: anhydrous ethanol (1:1) solvent, mix them evenly, and prepare a coating agent.

[0093] PrTbCuAl powder with an average particle size of 2-8 μm was immersed in 60 mL of water. o Immerse C in a kerosene-anhydrous ethanol mixture for 30 minutes to replace adsorbed oxygen on the surface.

[0094] The treated PrTbCuAl powder was mixed with a coating agent at a mass ratio of 1:5, and ball-milled in a planetary ball mill (MITR-YXQM-1L) using ZrO2 grinding balls under nitrogen (N2) protection to obtain a slurry. The ball-to-powder ratio was 10:1, the rotation speed was 300 rpm, and the grinding time was 1.5 hours.

[0095] Subsequently, anhydrous ethanol (anhydrous ethanol: slurry volume ratio of 3:1) was added to the slurry, and the mixture was stirred for 30 minutes to remove the kerosene.

[0096] Increase the rotation speed to 800 rpm and centrifuge the slurry for 20 minutes to remove uncoated powder.

[0097] Then, the slurry is dried: maintaining a vacuum of -0.1 MPa, first at 40... o Dry at C for one hour, then at 60°C. o Dry at C for one hour, and finally at 80°C. o Drying at C for one hour. During the drying process, ZrO2 balls were simultaneously rolled to prevent curling and agglomeration, with a ball-to-powder ratio of 1:10 and a rotation speed of 50 rpm. The resulting coated PrTbCuAl powder was obtained.

[0098] Comparative Example 5 Take 17 parts by weight of epoxy resin (E51), 8 parts by weight of acrylic resin (AR-01), 0.8 parts by weight of nano alumina, and 74.2 parts by weight of kerosene: anhydrous ethanol (1:1) solvent, mix them evenly, and prepare a coating agent.

[0099] PrAlCu powder with an average particle size of 2-8 μm was immersed in 60 mL of water. o Immerse C in a kerosene-anhydrous ethanol mixture for 30 minutes to replace adsorbed oxygen on the surface.

[0100] The treated PrAlCu powder was mixed with a coating agent at a mass ratio of 1:3, and ball-milled in a planetary ball mill (MITR-YXQM-1L) using ZrO2 grinding balls under nitrogen (N2) protection to obtain a slurry. The ball-to-powder ratio was 10:1, the rotation speed was 300 rpm, and the grinding time was 1.5 hours.

[0101] Subsequently, anhydrous ethanol (anhydrous ethanol: slurry volume ratio of 3:1) was added to the slurry, and the mixture was stirred for 30 minutes to remove the kerosene.

[0102] Increase the speed to 800 rpm and centrifuge the slurry for 5 minutes, then increase the speed to 1500 rpm and centrifuge the slurry for 10 minutes to remove uncoated powder.

[0103] Then, the slurry is dried: maintaining a vacuum of -0.1 MPa, first at 40... o Dry at C for one hour, then at 60°C. o Dry at C for one hour, and finally at 80°C. o Drying at C for one hour. During the drying process, ZrO2 balls were simultaneously rolled to prevent curling and agglomeration, with a ball-to-powder ratio of 1:10 and a rotation speed of 50 rpm. The resulting coated PrAlCu powder was obtained.

[0104] Comparative Example 6 Take 15 parts by weight of 2-ethylhexyl phosphate, 7 parts by weight of epoxy resin (E51), 4 parts by weight of acrylic resin (AR-01), 0.01 parts by weight of zinc stearate, 0.8 parts by weight of nano alumina, and 73.19 parts by weight of kerosene: anhydrous ethanol (1:1) solvent, mix them evenly, and prepare a coating agent.

[0105] PrAlCu powder with an average particle size of 2-8 μm was immersed in 60 mL of water. o Immerse C in a kerosene-anhydrous ethanol mixture for 30 minutes to replace adsorbed oxygen on the surface.

[0106] The treated PrAlCu powder was mixed with a coating agent at a mass ratio of 1:4, and then ball-milled in a planetary ball mill (MITR-YXQM-1L) using ZrO2 grinding balls under nitrogen (N2) protection to obtain a slurry. The ball-to-powder ratio was 10:1, the rotation speed was 200 rpm, and the grinding time was 2 hours.

[0107] Subsequently, anhydrous ethanol (anhydrous ethanol: slurry volume ratio of 3:1) was added to the slurry, and the mixture was stirred for 30 minutes to remove the kerosene.

[0108] Increase the speed to 900 rpm and centrifuge the slurry for 5 minutes, then increase the speed to 1500 rpm and centrifuge the slurry for 10 minutes to remove uncoated powder.

[0109] Then, the slurry is dried: maintaining a vacuum of -0.1 MPa, first at 40... o Dry at C for one and a half hours, then at 80 o Drying at C for one and a half hours. During the drying process, ZrO2 balls were simultaneously rolled to prevent curling and agglomeration, with a ball-to-powder ratio of 1:10 and a rotation speed of 50 rpm. The resulting coated PrAlCu powder was obtained.

[0110] Testing methods

[0111] The obtained samples were subjected to the following tests to obtain the sample performance of the examples and comparative examples, as shown in Table 1.

[0112] Particle size of grain boundary diffuser before and after coating Dry powder samples, both before and after coating, were evenly sprinkled onto conductive tape on a scanning electron microscope (SEM) stage and fixed for scanning observation. Large, agglomerated particles were avoided; only relatively uniform particles, representing a significant portion of the total volume, were selected for measurement. Particle boundaries were manually marked, and the projected diameter of each particle was measured. This test is solely for observing the particle size change of the powder samples before and after coating, qualitatively indicating the dispersion and coating effect of the coating agent on the powder, and is not intended for quantitative characterization.

[0113] Settlement resistance test Take 3g of the coated dry powder sample and disperse it in 100ml of a kerosene:anhydrous ethanol (1:1) mixed solvent. Disperse the dispersion using ultrasound to obtain a uniform suspension. Transfer the suspension to a transparent graduated tube and ultrasonically disperse for 30 seconds. Record the initial liquid level height H1 and the sedimentation interface height H2 after standing for 1 hour. The sedimentation amount is calculated as H1-H2. A smaller sedimentation amount indicates stronger anti-settling performance.

[0114] Antioxidant test Take 2g of the coated dry powder sample and record the initial mass W1. Place the sample in a constant temperature and humidity chamber, maintain 85% humidity in an air atmosphere, and heat to 85°C. o Incubate at temperature C for 72 hours. Then allow to cool naturally to room temperature, weigh again, and record the mass W2. The oxidation weight gain rate is calculated as (W2-W1) / W1. The smaller the oxidation weight gain rate, the stronger the antioxidant performance.

[0115] Table 1 Sample Performance Test Results

[0116] Figure 1 and Figure 2 The images show SEM images of PrTbCuAl before and after coating. Due to the dispersing effect of the coating agent and coating process, the particle size of the PrTbCuAl particles after coating is significantly smaller than that before coating, and the number of small particles is significantly increased. This indicates that the grain boundary diffusing agent is more uniformly dispersed after coating, and the tendency to agglomerate is greatly reduced. Therefore, the coating agent of this invention exhibits excellent compatibility and dispersibility with grain boundary diffusing agents.

[0117] As can be seen from the test data in Table 1, the grain boundary diffuser coated with the coating agent of the present invention exhibits low sedimentation (<15mm) and minimal oxidative weight gain (<0.05%). The coating agent of the present invention demonstrates high coating efficiency, and the coated grain boundary diffuser exhibits excellent anti-settling and anti-oxidation properties.

Claims

1. A coating agent for a grain boundary diffuser in rare earth permanent magnet materials, characterized in that, It consists of the following components: C6-C containing branches 12 14-16 parts by weight of alkyl phosphate esters; 2-4 parts by weight of epoxy resin; 1-2 parts by weight of acrylic resin; Zinc stearate 0.01-0.05 parts by weight; 0.3-0.8 parts by weight of nano-alumina; and The remaining amount of the compounded solvent; the compounded solvent is a mixture of kerosene and anhydrous ethanol.

2. The coating agent for a grain boundary diffuser of rare earth permanent magnet material according to claim 1, characterized in that, The compound solvent is kerosene and anhydrous ethanol in a 1:1 mass ratio.

3. The coating agent for a grain boundary diffuser of a rare earth permanent magnet material according to any one of claims 1-2, characterized in that, The phosphate ester containing branched alkyl groups is 2-ethylhexyl phosphate.

4. The coating agent for a grain boundary diffuser of a rare earth permanent magnet material according to any one of claims 1-3, characterized in that, The total mass of epoxy resin and acrylic resin is greater than 10% and less than 50% of the mass of branched alkyl phosphate ester.

5. A coating process for a grain boundary diffusing agent in rare earth permanent magnet materials, characterized in that... The coating process using a coating agent comprising any one of claims 1-4 specifically includes the following steps: S1 Solvent pretreatment; S2 wet ball milling coating; wherein the powder ratio (mass ratio) of grain boundary diffuser to coating agent is 1:(3-5), and the coating process is carried out in an inert protective gas; S3 Ethanol replacement; S4 gradient centrifugation; S5 Dynamic Roller Drying.

6. The coating process for a grain boundary diffuser of a rare earth permanent magnet material according to claim 5, characterized in that... Includes the following steps: S1 Solvent pretreatment: The grain boundary diffuser was pretreated by soaking in a kerosene-ethanol mixed solvent; S2 Wet ball milling coating: The powder ratio (mass ratio) of grain boundary diffuser to coating agent is 1:(4-5), and the coating process is carried out in an inert protective gas; S3 Ethanol replacement: The volume ratio of anhydrous ethanol to slurry is (2-5):1; S4 gradient centrifugation: The slurry is centrifuged using two or more speeds, with the first speed range being 800-1000 rpm and the second speed range being greater than 1000 rpm. S5 Dynamic Roller Drying: ZrO2 balls are used for roller drying under certain vacuum and temperature gradients.

7. The coating process for a grain boundary diffuser of a rare earth permanent magnet material according to claim 6, characterized in that, In step S5, the slurry is dried by rolling with ZrO2 balls at different temperatures under a certain vacuum. The ZrO2 balls with a particle size of 1–2 mm are rolled at a low speed of 40–60 rpm.

8. The coating process for a grain boundary diffuser for rare earth permanent magnet materials according to any one of claims 5-7, characterized in that... It also includes the following steps: After step S3 and before step S4, a dispersant that can selectively adsorb onto the surface of the coated powder is added to the slurry.

9. The coating process for a grain boundary diffuser of a rare earth permanent magnet material according to any one of claims 5-8, characterized in that, In step S4, the centrifugation time for the first rotation speed is 2 to 5 minutes, and the centrifugation time for the second rotation speed is 5 to 10 minutes.

10. The coating process for a grain boundary diffuser of a rare earth permanent magnet material according to any one of claims 5-9, characterized in that, The grain boundary diffuser is a composite material containing one or more rare earth elements selected from neodymium (Nd), praseodymium (Pr), dysprosium (Dy), and terbium (Tb) and one or more non-rare earth elements selected from non-rare earth alloys copper (Cu), aluminum (Al), and gallium (Ga).

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