Grain boundary diffusion magnet and production process thereof

Abstract

The invention discloses a grain boundary diffusion magnet and a production process thereof, and belongs to the field of neodymium-iron-boron magnets. The grain boundary diffusion magnet comprises a neodymium-iron-boron magnet and a surface coating of the neodymium-iron-boron magnet, the grain boundary diffusion magnet is prepared through a screen printing technology; the surface coating comprises the following raw materials in parts by mass: 100 parts of cerium alloy hydride, 2-4 parts of nano silicon dioxide, 1-3 parts of a dispersing agent, 0.5-2 parts of zirconium propionate and 30-45 parts of a solvent; the cerium alloy hydride includes any one of a cerium-copper alloy hydride, a cerium-aluminum alloy hydride, and a cerium-copper / aluminum alloy hydride. The cerium alloy hydride is adopted to replace heavy rare earth metal, meanwhile, other coating raw materials are matched, the effect of the cerium rare earth element is played, a heavy rare earth-free formula is achieved, a grain boundary structure is optimized, high-reducibility hydrogen can be released in the sintering process of the magnet, the magnet is protected against oxidation, the coercive force of the magnet is improved, and the service life of the magnet is prolonged. And the magnet has good consistency.

Description

Technical Field

[0001] The present invention relates to the field of neodymium iron boron magnets, and in particular to a grain boundary diffusion magnet and a production process thereof. Background Art

[0002] NdFeB permanent magnet material has a high magnetic energy product and is one of the most powerful permanent magnet materials currently available. It is widely used in electronics, electrical machinery, medical equipment, toys, packaging, hardware machinery and other fields. At the same time, the advantage of high energy density also makes NdFeB permanent magnet material play an important role in modern industry and electronic technology.

[0003] Coercivity is an important indicator for measuring the performance of magnets. The traditional method to improve the coercivity of magnets is to add heavy rare earth metals or alloys during the smelting process. However, the problem with this method is also obvious. The utilization rate of heavy rare earth elements in this process is extremely low, and the current global rare earth resources are limited. Reducing production costs and reducing the amount of heavy rare earth elements while ensuring the higher magnetic properties of NdFeB permanent magnet materials is an important direction today.

[0004] To achieve even higher-performance NdFeB permanent magnets, the grain boundary diffusion method has become a focus of attention. This method uses high temperatures to allow heavy rare earth elements to diffuse from the surface to the interior of the magnet along its grain boundaries, significantly increasing its utilization and boosting the magnet's coercivity. Screen printing, a key process in the grain boundary diffusion method, is primarily used for surface coating and patterning of magnets. Screen printing significantly reduces reliance on rare earth resources while also improving the material's coercivity and temperature stability.

[0005] Currently, the grain boundary diffusion method uses heavy rare earth elements, and heavy rare earth metal resources are very limited. In recent years, with the increase in rare earth demand, the cost of heavy rare earth metals has increased significantly. In order to alleviate the pressure on rare earth supply and reduce the excessive use of heavy rare earths, people have tried to use lower-cost, higher-content light rare earth metals as substitutes. Among them, cerium, as the most abundant metal element among all rare earth elements, is low in price. Its high reserves and low cost make it one of the preferred alternative materials. However, compared with other rare earth elements, cerium has low thermal stability. During the screen printing process, due to poor thermal stability and poor permeability, the magnetic properties of the obtained NdFeB permanent magnet material are not significantly improved. Moreover, when it is added to the printing coating, it has poor fluidity and dispersibility, is easy to fall off, and the thickness uniformity of the coating layer is poor, making it difficult to obtain NdFeB permanent magnet materials with excellent performance.

[0006] Therefore, in order to reduce dependence on heavy rare earth metals, lower production costs, and at the same time obtain a high-performance and long-life NdFeB permanent magnet material, the demand is becoming increasingly urgent. Summary of the Invention

[0007] The present invention provides a grain boundary diffusion magnet and a production process thereof, which can solve the problems of excessive reliance on heavy rare earth metals and poor performance of light rare earth metals in NdFeB permanent magnet materials in the prior art.

[0008] In a first aspect, a grain boundary diffusion magnet comprises a neodymium iron boron magnet and a surface coating of the neodymium iron boron magnet; the grain boundary diffusion magnet is prepared by screen printing technology;

[0009] The surface coating comprises the following raw materials in parts by weight:

[0010] 100 parts of cerium alloy hydride;

[0011] 2-4 parts of nano silicon dioxide;

[0012] 1 to 3 parts of dispersant;

[0013] 0.5-2 parts of zirconium propionate;

[0014] 30-45 parts of solvent;

[0015] The cerium alloy hydride includes any one of a cerium-copper alloy hydride, a cerium-aluminum alloy hydride, and a cerium-copper / aluminum alloy hydride.

[0016] Preferably, the thickness of the surface coating is 20 to 60 μm.

[0017] Preferably, the particle size of the cerium alloy hydride is 1 to 20 μm.

[0018] Preferably, the solvent includes a combination of one or more of an alcohol solvent, a ketone solvent and an ester solvent.

[0019] Preferably, the NdFeB magnet is a low coercive force NdFeB magnet.

[0020] By adopting the above technical solution, a surface coating containing cerium alloy hydride is uniformly applied to the surface of the NdFeB magnet using screen printing technology. During the preparation process, the cerium alloy hydride can enhance intergranular diffusion ability, increase diffusion depth, and optimize grain boundary structure, thereby strengthening magnetic coupling, increasing the coercive force of the magnet, and achieving good magnet consistency. In addition, during the magnet firing process, the cerium alloy hydride releases highly reducing hydrogen gas, which can reduce the oxidized components in the magnet, thereby protecting the magnet from oxidation and further improving magnet performance.

[0021] The use of cerium alloy hydride can reduce dependence on heavy rare earth metals, achieve a heavy rare earth-free formula, reduce raw material costs, and will not affect the grain boundary diffusion efficiency and the improvement of the coercive force of the magnet. After diffusing to the grain boundary of the magnet, cerium can help reconstruct the neodymium-rich phase structure, making it continuous and smooth, forming an epitaxial layer to improve magnetocrystalline anisotropy and inhibit the generation and growth of deformed nuclei.

[0022] Along with the cerium alloy hydride, zirconium propionate is added. During the magnet's sintering heat treatment, the zirconium propionate decomposes into nano-zirconium dioxide, which is evenly dispersed in the coating. This physically blocks the high-temperature aggregation of the cerium alloy hydride and inhibits its initial decomposition. It also has a certain barrier effect on oxygen diffusion, thereby reducing the oxidative deactivation of the cerium alloy hydride at high temperatures. After the cerium alloying and hydrogenation treatment, the alloy metal can help improve the long-term thermal stability of the cerium hydride, optimize the hydrogen release rate, and enhance interfacial stability. By adjusting the coating's short-term and long-term properties during the sintering process, the poor thermal stability of the cerium alloy hydride can be greatly improved, allowing the cerium to penetrate stably, forming a metallurgically bonded interfacial diffusion layer and reducing the risk of coating delamination.

[0023] Furthermore, zirconium propionate carries a positive charge after hydrolysis during dissolution, allowing it to adsorb onto the surface of cerium alloy hydride particles, preventing particle aggregation through electrostatic repulsion. The long chain structure of the propionate group also coats the particles, forming a steric barrier that physically blocks particle contact and improves the dispersibility of the cerium alloy hydride in the solvent. Furthermore, zirconium propionate helps bind the metal oxygen bonds of the magnet, thereby bonding the cerium alloy hydride and improving the bonding strength between the coating and the substrate, thus addressing the problem of hydride shedding.

[0024] Moreover, due to the high surface activity of cerium alloy hydride, it is easy to hydrolyze and release hydrogen before penetrating the grain boundary, affecting the performance of the surface coating and thus affecting the performance of the magnet. The zirconium-oxygen bond in zirconium propionate can preferably combine with the cerium in the cerium alloy hydride to form a stable bridging structure, reduce the occurrence of side reactions, and provide stability to the cerium alloy hydride.

[0025] Preferably, the cerium alloy hydride is prepared according to the following method:

[0026] The cerium and alloy metal are preheated and then smelted at 740-800°C, and then subjected to hydrogen absorption-dehydrogenation treatment in a hydrogen crushing furnace. After natural cooling, they are ball milled in a nitrogen atmosphere to obtain cerium alloy hydride.

[0027] Preferably, the molar ratio of cerium to the alloy metal is 1:(1.8-5.5); the alloy metal includes one or a combination of copper and aluminum.

[0028] More preferably, the hydrogen absorption-dehydrogenation treatment is hydrogenation at 350-400° C. and 1.5-3 MPa for 1-3 hours.

[0029] By adopting the above technical solution, copper and aluminum are selected as alloying metals of cerium alloy hydride. During the smelting process, copper atoms or aluminum atoms can be dissolved in the cerium lattice to form an alloy compound. Their doping can stabilize the structure of cerium hydride, reduce lattice distortion, inhibit phase decomposition, and optimize the structure of grain boundaries. Moreover, the addition of copper or aluminum can limit grain coarsening at high temperatures, thereby maintaining a fine-grained structure and improving the coercive force of the magnet.

[0030] Then hydrogenation treatment is carried out to obtain cerium alloy hydride. The hydrogenated rare earth alloy material can not only stabilize the cerium grain boundary diffusion process, but also produce reducing hydrogen by decomposition. It will not penetrate into the magnet and affect the magnet performance, but can also reduce the oxidized components in the magnet and protect the magnet from oxidation, thereby improving the magnetic properties of the magnet and making the magnet have good consistency.

[0031] Preferably, the particle size of the nano-silicon dioxide is 50 to 200 nm.

[0032] By adopting the above technical solution, nano-silica is also added to the surface coating. Nano-silica can help reduce the viscosity of the slurry, thereby solving the problems of poor fluidity of the cerium alloy hydride coating and poor uniformity of coating on the magnet surface. The hydrogen bond network formed after coating can also prevent sedimentation and improve distribution uniformity. At the same time, the hydroxyl groups on the surface of the nano-silica and the zirconium ions of the zirconium propionate can strengthen the electrostatic repulsion between the particles and inhibit the agglomeration of the cerium alloy hydride.

[0033] The addition of nano-silica can improve the processability of the surface coating, reduce the risk of clogging by filling the gaps between large particles in the slurry, reduce the shrinkage and interfacial stress of the coating, and avoid cracking.

[0034] The introduction of nano-silica can also improve overall performance. On the one hand, nano-silica can improve the density of the coating by filling the micropores between the cerium alloy hydride particles, thereby enhancing chemical stability. On the other hand, the polar groups on the surface of nano-silica can improve coating adhesion and reduce coating peeling. Nano-silica can also cooperate with zirconium propionate to physically block the diffusion of high-temperature oxygen, inhibit the early decomposition of cerium alloy hydride, optimize the slow release of active hydrogen, and promote the deep diffusion of cerium atoms along grain boundaries, thereby enhancing the improvement effect of rare earth elements on the magnet and increasing the coercive force of the magnet.

[0035] Preferably, the dispersant comprises one or a combination of ammonium polyacrylate and ammonium polycarboxylate.

[0036] By adopting the above technical solution, the cerium alloy hydride has high surface activity due to the presence of cerium ions, which easily leads to spontaneous agglomeration in the solvent, thus affecting the performance of the surface coating and easily causing problems such as coating cracking and uneven distribution. The addition of zirconium propionate can inhibit the agglomeration of the cerium alloy hydride to a certain extent, but the inhibitory effect is limited. To further improve the material properties, a dispersant is also added to the surface coating, and the dispersant is selected to be a compound containing carboxylate groups.

[0037] The carboxyl groups in the dispersant can regulate the charge density, further preventing the aggregation of cerium alloy hydrides through electrostatic repulsion. At the same time, the long polymer chains can stretch in the solvent, forming a physical steric hindrance that hinders the aggregation of cerium alloy hydrides. This improved dispersibility ensures that the cerium alloy hydride is evenly distributed in the coating, improving the consistency of the cerium atoms along the grain boundaries during subsequent screen printing and heat treatment, thereby increasing the coercive force of the magnet.

[0038] In addition to further improving dispersibility, the carboxyl groups contained in the dispersant can form hydrogen bonds with the surface of the magnet, thereby enhancing the bonding force between the coating and the magnet and preventing the coating from falling off.

[0039] In a second aspect, the present invention provides a process for producing a grain boundary diffusion magnet, comprising the following process steps:

[0040] S1. Clean and pretreat the surface of the NdFeB magnet;

[0041] S2. Ce alloy hydride, nano-silica, a dispersant and zirconium propionate were sequentially added to the solvent and mixed to obtain a printed coating slurry;

[0042] S3. The printed coating slurry is applied to the surface of the NdFeB magnet and printed to form a surface coating;

[0043] S4. After printing is completed, the NdFeB magnet is diffused and aged under vacuum conditions to obtain a grain boundary diffusion magnet.

[0044] By adopting the above technical solution, the NdFeB magnets are cleaned and pre-treated before screen printing to remove oil and oxide layers from the surface, ensuring a smooth surface while also ensuring good adhesion. A printed coating slurry is then evenly applied to the magnet surface, drying to form a durable surface coating. Finally, through diffusion and aging treatments, the surface coating decomposes the cerium alloy hydride. Cerium penetration improves the magnet's coercivity and magnetic properties, resulting in high-performance, long-life NdFeB magnets.

[0045] Beneficial effects of the present invention:

[0046] 1. The grain boundary diffusion magnet of the present invention includes a NdFeB magnet and a surface coating of the NdFeB magnet. The surface coating contains cerium alloy hydride, which can enhance the intergranular diffusion ability and optimize the grain boundary structure, thereby enhancing the magnetic coupling effect. During the firing process of the magnet, it can also release highly reducing hydrogen to reduce the oxidized components in the magnet, thereby protecting the magnet from oxidation, thereby improving the coercive force of the magnet and making the magnet have good consistency.

[0047] 2. In the surface coating of the grain boundary diffusion magnet of the present invention, zirconium propionate, nano-silica, and a dispersant are added along with the cerium alloy hydride. The zirconium propionate synergizes with the cerium alloy hydride to improve its thermal stability in both the short and long term, thereby adapting to magnet firing conditions and replacing heavy rare earth metals to achieve a heavy rare earth-free formulation. Furthermore, the introduction of zirconium propionate, nano-silica, and a dispersant significantly improves the dispersibility and fluidity of the cerium alloy hydride, enhancing the coating's processing properties and strengthening the bonding between the surface coating and the magnet, thereby improving the overall performance of the magnet. DETAILED DESCRIPTION

[0048] The specific embodiments of the present invention are described in detail below, but it should be understood that the protection scope of the present invention is not limited by the specific embodiments.

[0049] Preparation Example

[0050] Preparation Example 1: A cerium-copper alloy hydride was prepared according to the following method:

[0051] Cerium and copper were preheated at 250°C and then smelted at 760°C, with a molar ratio of cerium to copper being 1:5. The cerium and copper were then subjected to hydrogen absorption-dehydrogenation treatment in a hydrogen crushing furnace. The hydrogenation treatment conditions were a hydrogenation temperature of 380°C, a pressure of 3 MPa, and a time of 1 hour. After natural cooling, the cerium and copper were ball milled in a nitrogen atmosphere to obtain a cerium-copper alloy hydride.

[0052] Preparation Example 2: A cerium-aluminum alloy hydride was prepared according to the following method:

[0053] Cerium and aluminum are preheated at 300°C and then smelted at 780°C, wherein the molar ratio of cerium to copper is 1:2. Then, they are subjected to hydrogen absorption-dehydrogenation treatment in a hydrogen crushing furnace. The hydrogenation treatment conditions are hydrogenation temperature 380°C, pressure 2.5MPa and time 3h. After natural cooling, they are ball milled in a nitrogen atmosphere to obtain cerium-aluminum alloy hydride.

[0054] Preparation Example 3: A cerium-copper / aluminum alloy hydride was prepared according to the following method:

[0055] Cerium, copper and aluminum are preheated at 280°C and then smelted at 780°C, wherein the molar ratio of cerium to copper and aluminum is 1:4, wherein the molar ratio of copper to aluminum is 3:1, and then subjected to hydrogen absorption-dehydrogenation treatment in a hydrogen crushing furnace, the hydrogenation treatment conditions are hydrogenation temperature 380°C, pressure 3MPa time, 2h, natural cooling, and ball milling in a nitrogen atmosphere to obtain cerium-copper / aluminum gold hydride.

[0056] Preparation Example 4: A cerium hydride was prepared according to the following method:

[0057] Cerium is preheated at 250°C and then smelted at 750°C. It is then subjected to hydrogen absorption-dehydrogenation treatment in a hydrogen crushing furnace. The hydrogenation treatment conditions are a hydrogenation temperature of 380°C, a pressure of 2 MPa, and a time of 2 hours. After natural cooling, it is ball-milled in a nitrogen atmosphere to obtain cerium hydride.

[0058] Example

[0059] Example 1, a grain boundary diffusion magnet, is prepared according to the following process steps:

[0060] S1. Clean and pre-treat the surface of low coercivity NdFeB magnets to remove surface oil and oxide layer;

[0061] S2. 100 parts of the cerium-copper alloy hydride prepared in Preparation Example 1, 3 parts of nano-silica (average particle size of 80 nm), 2 parts of ammonium polyacrylate and 1 part of zirconium propionate were added to 40 parts of ethanol, and the mixture was uniformly mixed to obtain a printing coating slurry;

[0062] S3. The printed coating slurry is applied to the surface of the NdFeB magnet and printed to form a surface coating;

[0063] S4. After printing, the NdFeB magnet is diffused and aged under vacuum conditions to obtain a grain boundary diffused magnet. The diffusion temperature is 800°C for 6 hours, and the aging temperature is 500°C for 4 hours.

[0064] Example 2 and Example 3 are grain boundary diffusion magnets. The only difference from Example 1 is that the raw material ratio of the surface coating is adjusted, as shown in Table 1:

[0065] Table 1: Ratio of raw materials for surface coating of Example 1 to Example 3

[0066] Example 1 Example 2 Example 3 Cerium-copper alloy hydride / part 100 100 100 Nano silicon dioxide / part 3 2 4 Ammonium polyacrylate / part 2 1 3 Zirconium propionate salt / part 1 2 0.5 Ethanol / part 40 35 45

[0067] Example 4 is a grain boundary diffusion magnet, which differs from Example 1 only in that the cerium-aluminum alloy hydride prepared in Preparation Example 2 is used to replace the cerium-copper alloy hydride prepared in Preparation Example 1.

[0068] Example 5 is a grain boundary diffusion magnet, which differs from Example 1 only in that the cerium-copper alloy hydride prepared in Preparation Example 1 is replaced by an equal amount of the cerium-copper / aluminum alloy hydride prepared in Preparation Example 3.

[0069] Comparative Example

[0070] Comparative Example 1 is a grain boundary diffusion magnet, which differs from Example 1 only in that the cerium-copper alloy hydride prepared in Preparation Example 1 is replaced by an equal amount of cerium hydride prepared in Preparation Example 4.

[0071] Comparative Example 2 is a grain boundary diffusion magnet, which differs from Example 1 only in that no nano-silicon dioxide is added to the surface coating.

[0072] Comparative Example 3 is a grain boundary diffusion magnet, which is different from Example 1 only in that the added amount of zirconium propionate salt is 3 parts.

[0073] Comparative Example 4 is a grain boundary diffusion magnet, which differs from Example 1 only in that zirconium propionate salt is not added to the surface coating.

[0074] Comparative Example 5 is a grain boundary diffusion magnet, which differs from Example 1 only in that an equal amount of polyvinyl alcohol is used to replace ammonium polyacrylate.

[0075] Comparative Example 6 is a grain boundary diffusion magnet, which differs from Example 1 only in that ammonium polyacrylate is not added to the surface coating.

[0076] Performance testing

[0077] Magnetic Property Test: According to the relevant records in GB / T 3217-2013 "Magnetic Test Methods for Permanent Magnet (Hard Magnetic) Materials", the remanence (Br), intrinsic coercivity (Hcj), and maximum magnetic product energy ((BH)max) of the grain boundary diffusion magnets obtained in the Examples and Comparative Examples were tested. The test results are shown in Table 2:

[0078] Table 2 Magnetic properties test results

[0079]

[0080] According to Table 2, in combination with Example 1 and Comparative Example 1, it can be seen that the various magnetic properties of Comparative Example 1 are significantly reduced compared to Example 1. The reason is that cerium hydride is used in the surface coating of Comparative Example 1 without alloying treatment, and cerium hydride itself has poor thermal stability and high activity. During the high-temperature firing process, even though the synergistic effect of other coating compounds helps to improve stability in the early stage, in the later stage of firing, cerium hydride gradually becomes unstable, the permeability decreases, the utilization rate of rare earth metals is greatly reduced, the improvement effect on the magnet is reduced, and the coercive force decreases significantly.

[0081] Combining Example 1 and Comparative Example 2, it can be seen that the various magnetic properties of Comparative Example 2 are lower than those of Example 1. The reason is that no nano-silicon dioxide is added to the surface coating of the magnet in Comparative Example 2, and the processing performance of the surface coating is significantly affected. The fluidity of the printed coating slurry deteriorates, and the slurry coating is uneven, resulting in uneven distribution of cerium rare earth metal on the surface of the magnet, reduced improvement effect, and reduced performance of the obtained magnet.

[0082] Combining Example 1, Comparative Example 3, and Comparative Example 4, it can be seen that the various magnetic properties of Comparative Examples 3 and 4 are somewhat lower than those of Example 1. This is because the amount of zirconium propionate added in Comparative Example 3 increases. The addition of excessive zirconium propionate increases the density of flocs in the slurry, causing slurry stratification, which is not conducive to processing. In addition, the zirconium dioxide decomposed by the excessive zirconium propionate blocks the grain boundary diffusion channels of the magnet, hindering the migration of cerium atoms, resulting in a decrease in the improvement effect of rare earth metals on the magnet and a decrease in magnetic properties. No zirconium propionate was added to the surface coating of Comparative Example 4. This, on the one hand, affects the dispersibility of the cerium alloy hydride, and on the other hand, affects the thermal stability of the magnet during the initial sintering stage. The early decomposition of cerium reduces the improvement effect on the magnet and also affects the bonding force between the cerium alloy hydride and the magnet, resulting in a decrease in the performance of the resulting magnet.

[0083] Combining Example 1, Comparative Examples 5, and 6, it can be seen that the various magnetic properties of Comparative Examples 5 and 6 are somewhat lower than those of Example 1. This is because in Comparative Example 5, the dispersant used in this application is replaced by another dispersant. Since polyvinyl alcohol does not contain carboxyl groups, the dispersion of the cerium alloy hydride is poor, resulting in reduced uniformity and decreased magnet performance. In Comparative Example 6, no dispersant is added, and the cerium alloy hydride tends to aggregate in the slurry, affecting magnet performance and causing cracking and uneven distribution in the coating.

[0084] The above disclosures are only a few specific embodiments of the present invention. However, the embodiments of the present invention are not limited thereto. Any changes that can be conceived by those skilled in the art should fall within the scope of protection of the present invention.

Claims

1. A grain boundary diffusion magnet, characterized in that: It includes a NdFeB magnet and a surface coating of the NdFeB magnet; the grain boundary diffusion magnet is prepared by screen printing technology; The surface coating comprises the following raw materials in parts by mass: 100 parts of cerium alloy hydride; 2-4 parts of nano silicon dioxide; 1 to 3 parts of dispersant; 0.5-2 parts of zirconium propionate; 30-45 parts of solvent; The cerium alloy hydride includes any one of cerium-copper alloy hydride, cerium-aluminum alloy hydride and cerium-copper / aluminum alloy hydride.

2. The grain boundary diffusion magnet according to claim 1, characterized in that The thickness of the surface coating is 20 to 60 μm.

3. The grain boundary diffusion magnet according to claim 1, characterized in that The cerium alloy hydride is prepared according to the following method: The cerium and alloy metal are preheated and then smelted at 740-800°C, and then subjected to hydrogen absorption-dehydrogenation treatment in a hydrogen crushing furnace. After natural cooling, they are ball milled in a nitrogen atmosphere to obtain cerium alloy hydride.

4. The grain boundary diffusion magnet according to claim 3, characterized in that The molar ratio of the cerium to the alloy metal is 1:(1.8-5.5); the alloy metal includes one or a combination of copper and aluminum.

5. The grain boundary diffusion magnet according to claim 1, characterized in that The particle size of the cerium alloy hydride is 1 to 20 μm.

6. The grain boundary diffusion magnet according to claim 1, characterized in that The particle size of the nano silicon dioxide is 50 to 200 nm.

7. The grain boundary diffusion magnet according to claim 1, characterized in that The dispersant includes one or a combination of polyammonium acrylate and polyammonium carboxylate.

8. The grain boundary diffusion magnet according to claim 1, characterized in that The solvent includes one or more of an alcohol solvent, a ketone solvent and an ester solvent.

9. The grain boundary diffusion magnet according to claim 1, characterized in that The NdFeB magnet is a low coercive force NdFeB magnet.

10. A process for producing a grain boundary diffusion magnet according to any one of claims 1 to 9, characterized in that: The process steps include: S1. Clean and pretreat the surface of the NdFeB magnet; S2. Ce alloy hydride, nano-silica, a dispersant and zirconium propionate were sequentially added to the solvent and mixed to obtain a printed coating slurry; S3. The printed coating slurry is applied to the surface of the NdFeB magnet and printed to form a surface coating; S4. After printing is completed, the NdFeB magnet is diffused and aged under vacuum conditions to obtain a grain boundary diffusion magnet.

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