A spin-on dispersant for grain boundary diffusion of cerium-doped neodymium-iron-boron magnets and methods of use

Abstract

The application discloses a spin coating dispersant for grain boundary diffusion of cerium-rich neodymium-iron-boron magnet and a use method, and belongs to the technical field of neodymium-iron-boron magnet. In view of the selection of the dispersant when rare earth elements are coated by the spin coating method in the process of the grain boundary diffusion of the cerium-rich neodymium-iron-boron magnet, the application provides a suitable spin coating dispersant, which can maximally improve the magnetism of the cerium-rich neodymium-iron-boron magnet under the premise that the magnet and the rare earth elements have the same weight, thereby reducing the total amount of the rare earth elements used in the grain boundary diffusion and reducing the cost. The spin coating dispersant is composed of polyvinyl alcohol and diacetone alcohol as a cosolvent in different mass ratios. Through reasonable compounding of the polyvinyl alcohol and the cosolvent, the surface tension of the dispersion system can be effectively reduced, the wetting capacity of the dispersant to the dispersion source can be enhanced, and the diffusion source can be uniformly dispersed in the dispersant through the steric hindrance effect, so that a stable suspension is formed, and the uniformity of the grain boundary diffusion is remarkably improved.

Description

Technical Field

[0001] This invention belongs to the field of neodymium iron boron (NdFeB) magnet technology, specifically relating to a spin-coating dispersant for grain boundary diffusion in cerium-rich NdFeB magnets and its application method. Especially in the fields of consumer electronics, electric vehicles, and home appliances, where magnetic performance requirements are moderate but cost is highly sensitive, this grain boundary diffusion modification process for cerium-rich NdFeB magnets can both improve magnet performance and effectively control costs. Background Technology

[0002] Driven by global "dual carbon" goals, strategic emerging industries such as new energy vehicles, wind power generation, and energy-saving home appliances have experienced explosive growth, directly boosting market demand for neodymium iron boron (NdFeB) rare earth permanent magnet materials. However, the production of high-performance NdFeB magnets is highly dependent on medium and heavy rare earth elements such as praseodymium and neodymium. These elements have very low reserves in nature, and long-term over-exploitation has led to increasingly tight resource supplies and volatile prices, severely restricting the sustainable development of the permanent magnet industry. In stark contrast, light rare earth elements such as lanthanum and cerium have relatively high content, but are often left idle and wasted due to a lack of suitable applications. Replacing the currently scarce praseodymium and neodymium with abundant and inexpensive cerium can not only reduce the raw material costs of permanent magnet materials but also promote the comprehensive utilization of rare earth resources, possessing significant research value and long-term strategic significance.

[0003] Cerium has a low magnetocrystalline anisotropy field, and directly replacing neodymium in large quantities would lead to a significant decrease in the coercivity of NdFeB magnets, making it difficult to meet the stability requirements of high-end equipment. Therefore, cerium resources have long been in a state of "high reserves, low utilization," remaining idle. How to achieve efficient application of cerium in NdFeB magnets through process innovation has become a key breakthrough in resolving the supply and demand contradiction of rare earth resources. Grain boundary diffusion technology, as the core process for modifying NdFeB magnets, can improve the coercivity of magnets while reducing the amount of heavy rare earth elements used, making it a key technology for preparing high-performance NdFeB magnets. However, research on grain boundary diffusion in cerium-rich NdFeB magnets, where cerium replaces NdFeB, is still in its early stages.

[0004] Spin coating offers advantages such as ease of operation, uniform coating, and strong industrial adaptability, making it a commonly used coating method in grain boundary diffusion processes. However, existing spin coating dispersants present numerous problems in the application of cerium-rich NdFeB magnets. Traditional dispersants (such as anhydrous ethanol and single polymer solutions) cannot effectively suppress the agglomeration of diffusion source (such as terbium fluoride TbF3) particles. The grain boundary structure of cerium-rich NdFeB magnets is more complex due to the introduction of cerium; uneven dispersion of the diffusion source can lead to local over- or under-diffusion, increasing the fluctuation range of magnet performance and severely affecting product consistency. Some dispersants have poor compatibility with the magnet matrix or diffusion source, resulting in side reactions during grain boundary diffusion and reducing the magnet's performance and stability. Therefore, developing a spin coating dispersant suitable for grain boundary diffusion in cerium-rich NdFeB magnets, possessing high dispersion stability, good compatibility, and adaptability, is of significant practical importance for promoting the industrial application of cerium-rich NdFeB magnets. Summary of the Invention

[0005] To address the problems of uneven dispersion, poor compatibility, and limited performance improvement in existing spin-coating dispersants for grain boundary diffusion of cerium-rich NdFeB magnets, the present invention aims to provide a spin-coating dispersant composed of polyvinyl alcohol (PVA) as a polymeric dispersant and diacetone alcohol as a cosolvent. This dispersant can maximize the improvement of the magnetic properties of cerium-rich NdFeB magnets while maintaining the same amount of magnets and rare earth elements, thereby reducing the total amount of heavy rare earth elements used for grain boundary diffusion and achieving the dual goals of resource conservation and cost optimization.

[0006] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0007] This invention provides a spin-coating dispersant for grain boundary diffusion in cerium-rich NdFeB magnets. The spin-coating dispersant is a binary composite solution composed of a high molecular weight dispersant, polyvinyl alcohol, and a co-solvent, diacetone alcohol. The polyvinyl alcohol serves as the main film-forming substance, providing a good carrier and adhesion performance for the diffusion source. The diacetone alcohol serves as a co-solvent, adjusting the solubility and evaporation rate of the solution to ensure the uniformity and stability of the coating.

[0008] Polyvinyl alcohol (PVA), a high-molecular-weight dispersant, has molecules with a certain chain length and volume. Its molecular chains contain numerous hydroxyl groups, which can adsorb onto the surface of terbium fluoride (TF) particles via hydrogen bonds, forming a steric hindrance layer that prevents the TF particles from approaching each other and agglomerating. Simultaneously, PVA's good water solubility and high viscosity can reduce the settling velocity of TF particles, improve the stability of the dispersion system, and regulate the surface tension of the dispersion system, promoting the wetting of TF by the medium and further enhancing its dispersion.

[0009] The co-solvent diacetone alcohol can partially dissolve the surface of terbium fluoride by interacting with ions or molecules. The resulting solvation layer reduces the surface energy of the particles, decreasing the attraction between them and facilitating the dispersion of terbium fluoride. Diacetone alcohol materials can also reduce the surface tension of the dispersion medium, making the terbium fluoride particles easier to wet. Simultaneously, diacetone alcohol materials can penetrate into the agglomerates of terbium fluoride particles, breaking them apart and ensuring thorough dispersion of the terbium fluoride particles in the medium.

[0010] Furthermore, the mass ratio of the polymeric dispersant polyvinyl alcohol to the cosolvent diacetone alcohol ranges from 10:1 to 1:10. By changing the ratio of the two, the viscosity, surface tension, and other physicochemical properties of the dispersant solution can be flexibly controlled to meet the requirements of different spin-coating process conditions and magnet surface conditions.

[0011] Preferably, the mass ratio of the polymeric dispersant polyvinyl alcohol to the cosolvent diacetone alcohol is 2:1 (Example 3), 1:1 (Example 4), 2:3 (Example 5), and 2:4 (Example 6).

[0012] A method for preparing a spin-coating dispersant for grain boundary diffusion of cerium-rich NdFeB magnets involves stirring and mixing a polymeric dispersant, polyvinyl alcohol, and a co-solvent, diacetone alcohol, at 100°C. After thorough dissolution and homogenization (homogenization refers to thorough stirring and mixing), a uniform and stable spin-coating dispersant is obtained.

[0013] The present invention provides a method for using a spin-coating dispersant for grain boundary diffusion in cerium-rich NdFeB magnets, comprising the following steps:

[0014] Step 1: Cut the cerium-rich NdFeB magnet into sheet-shaped substrate magnets that meet the requirements of the grain boundary diffusion process, and perform surface treatment processes such as oxide layer removal, precision polishing, acidification and cleaning on the surface of the sheet-shaped substrate magnets to ensure that the surface of the sheet-shaped substrate magnets meets the cleanliness and flatness requirements of the process.

[0015] Step 2: Add the diffusion source powder to the spin-coating dispersant and stir thoroughly to obtain the diffusion source solution;

[0016] Step 3: The diffusion source solution is uniformly dropped onto the surface of the sheet-like substrate magnet after surface treatment. The diffusion source solution is spread evenly under centrifugal force by spin coating. The solution is then dried to allow the solvent in the coating to fully evaporate. Finally, a diffusion source coating with uniform thickness and good adhesion is formed on the surface of the sheet-like substrate magnet, and the magnet to be diffused is obtained.

[0017] Step 4: Perform grain boundary diffusion heat treatment on the dried magnet to be diffused, so that the effective components in the diffusion source can diffuse fully along the grain boundary of the magnet, and finally obtain a diffused magnet with optimized performance.

[0018] Furthermore, in step 1, the surface treatment process of removing the oxide layer, precision polishing, acidification, and cleaning is performed sequentially on the substrate magnet surface. Specifically, the natural oxide layer on the substrate magnet surface is first removed by chemical etching or physical grinding. Then, the substrate magnet surface is polished to a mirror finish through multiple polishing processes. Next, it is immersed in a 3wt.% HNO3 solution for 60 seconds. Finally, ultrasonic cleaning is performed sequentially using deionized water, anhydrous ethanol, and other cleaning agents to thoroughly remove residual impurities and contaminants from the surface. This ensures that the coating has excellent wettability and adhesion.

[0019] Furthermore, in step 1, the cerium-rich NdFeB magnet is a sintered NdFeB material prepared by a dual-alloy method, wherein the weight ratio of cerium (Ce) in the total rare earth elements RE = Nd + Pr + Ce + Dy + Tb (Ce / RE) is 10% to 40%. This ratio range can be precisely controlled according to the specific performance requirements of the magnet to achieve a balance between magnet performance and cost. In step 2, the diffusion source powder is a heavy rare earth fluoride with a purity ≥99.9% and a median particle size D50 = 2±0.5μm.

[0020] Furthermore, in step 3, the diffusion source solution is uniformly spread under centrifugal force through spin coating. Specifically, this is done in steps: first, spin coating is performed at 2000 rpm for 60 seconds to initially spread the dispersion and remove excess solution; then, spin coating is performed at 900 rpm for 10 seconds, followed by drying in a 170°C drying chamber for 5 minutes. To ensure the coating thickness meets the process requirements, this coating-drying process is repeated three times. High-speed spin coating can quickly spread the suspension, initially control the basic coating thickness, and remove bubbles; low-speed spin coating allows the suspension to flow back and fill microscopic depressions, eliminating edge thickness differences and achieving uniform coverage of the entire surface. Repeated high- and low-speed spin coating ultimately allows the suspension to form a uniform thickness, few defects, strong adhesion, and high density coating on the magnet surface.

[0021] Furthermore, in step 4, the grain boundary diffusion heat treatment involves first performing a high-temperature annealing treatment, followed by a second high-temperature treatment. Specifically, this involves annealing at 1000°C for 5 hours, with the vacuum level inside the furnace strictly controlled to be no less than 10 kJ / m³. -1 The process is carried out in a low-oxygen environment to ensure that the effective components in the diffusion source receive sufficient diffusion motive force, enabling them to migrate and diffuse fully along the magnet's grain boundaries. After cooling to 550℃, a second high-temperature treatment is performed for 2 hours. This second high-temperature treatment can regulate the microstructure of the magnet, eliminate internal stress generated during diffusion, and further optimize the magnet's magnetic properties.

[0022] Furthermore, before high-temperature annealing, the magnet to be diffused is tightly wrapped with molybdenum foil. This is to effectively prevent the magnet from reacting with other components in the furnace during the high-temperature annealing process, while also reducing the volatilization of elements on the magnet surface, thus ensuring the stability and consistency of the diffusion process.

[0023] Furthermore, the relationship between the spin-coating dispersant and the diffusion source powder is controlled as follows: the mass ratio of the high molecular weight dispersant polyvinyl alcohol to the diffusion source powder in the spin-coating dispersant is controlled at 1:2. This ratio has been verified through extensive experiments, ensuring that the diffusion source has a suitable concentration in the coating, satisfying the component content required for diffusion while also guaranteeing good film-forming properties and adhesion of the coating.

[0024] Compared with the prior art, the present invention has the following advantages:

[0025] 1. Excellent dispersion effect and high diffusion uniformity: This invention effectively reduces the surface tension of the dispersion system by rationally compounding polymeric dispersants and cosolvents, enhances the wetting ability of the dispersant to the dispersion source, and through steric hindrance, makes the diffusion source uniformly dispersed in the dispersant to form a stable suspension, which significantly improves the uniformity of grain boundary diffusion.

[0026] 2. Good compatibility and no side reactions: The components in the dispersant have good compatibility with the cerium-rich NdFeB magnet matrix and diffusion source. No side reactions will occur during the grain boundary diffusion process. There are no defects such as pores and cracks at the magnet grain boundaries, and the structure is intact, which ensures the performance and stability of the magnet.

[0027] 3. Simple process and strong industrial adaptability: The equipment required for the method of this invention (spin coater, vacuum high-temperature furnace) are all existing industrial equipment, requiring no additional special equipment, thus significantly reducing equipment investment costs. Process parameters (spin coater speed, temperature, and holding time) can be precisely controlled, and the operation steps are simple, making it easy to achieve industrial production. This helps to reduce the production cost of cerium-rich NdFeB magnets and improve production efficiency. Attached Figure Description

[0028] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0029] Figure 1This is a comparison chart of magnet performance with different proportions of polyvinyl alcohol (substance A) as a polymeric dispersant and diacetone alcohol (substance B) as a cosolvent. The chart shows that the coercivity is significantly improved after grain boundary diffusion. In particular, the coercivity is significantly better when the mass ratio of A to B is 2:3 (Example 5) and 2:4 (Example 6). Combined with the comparison of their magnetic energy products, 34.05 MGOe and 33.37 MGOe, it is clear that Example 5 exhibits the best overall performance.

[0030] Figure 2 This is a comparison chart of the magnet performance prepared by the method of this invention with that of magnets prepared by traditional methods using anhydrous ethanol alone, polyvinyl alcohol alone, diacetone alcohol alone, and a mixture thereof. As shown in the chart, the magnet prepared using the dispersant of this invention exhibits significantly higher coercivity than that of a single dispersant or a gaseous mixture, fully demonstrating the synergistic effect of the combination of polyvinyl alcohol and diacetone alcohol. Detailed Implementation

[0031] To gain a deeper understanding of the present invention, the technical solutions of the present invention will be described in detail below with reference to specific embodiments. However, the present invention has multiple implementations and is not limited to the specific examples listed herein. The presentation of these examples is intended to enhance a comprehensive understanding of the disclosure of the present invention, rather than to limit the scope of protection of the present invention.

[0032] Example 1

[0033] ① Dispersant preparation: Weigh 0.50 g of polyvinyl alcohol (purity ≥93.5%, degree of alcoholysis 97.5-99 mol%, viscosity 3.5-4.5 mPa·s) and 0.05 g of diacetone alcohol (purity 99.5%) as a co-solvent and add them to a beaker, then pour in 5 mL of double-distilled water. Place the beaker in a constant temperature water bath at 100℃, start the stirring device, and stir at 800 r / min for 0.5 h until the solution is homogeneous and transparent, thus obtaining the dispersant solution.

[0034] ② Dispersion of diffusion source: Weigh 1 g of terbium fluoride powder (99.99% purity) for grain boundary diffusion in cerium-rich NdFeB magnets and add it to the above dispersant solution. Stir at 800 r / min for 20 min to uniformly disperse the diffusion source in the dispersant, and obtain a uniform diffusion source dispersion.

[0035] ③ Spin coating operation: The pretreated cerium-rich NdFeB magnet (10 mm × 10 mm × 3 mm) was fixed on the sample stage of the spin coater, and 0.5 mL of diffusion source dispersion was dropped onto the magnet surface. The spin coater speed was set to 2000 r / min, the spin coating time was 60 s, and then the spin coater was set at a low speed of 900 r / min for 10 s to uniformly coat the suspension on the magnet surface. Then it was dried in a drying oven at 170℃ for 5 min. This coating process was repeated three times to obtain a coating with a thickness of about 15 μm and a coverage of over 98%.

[0036] ④ Drying and diffusion treatment: Wrap the spin-coated magnet with 0.1 mm thick molybdenum foil, place it in a vacuum tube furnace, and evacuate to a vacuum level better than 2 × 10⁻⁶. -3 Pa is first annealed at 1000℃ for 5 hours, then cooled to 550℃ and subjected to a second high-temperature treatment for 2 hours to complete the grain boundary diffusion process of the cerium-rich NdFeB magnet.

[0037] Example 2

[0038] The grain boundary diffusion steps for the cerium-rich NdFeB magnets are essentially the same as in Example 1, except that the mass of diacetone alcohol used is changed from 0.05 g to 0.10 g, thereby changing the ratio of polyvinyl alcohol to diacetone alcohol from 10:1 to 5:1.

[0039] ① Dispersant preparation: Weigh 0.50 g of polyvinyl alcohol (purity ≥93.5%, degree of alcoholysis 97.5-99 mol%, viscosity 3.5-4.5 mPa·s) and 0.10 g of diacetone alcohol (purity 99.5%) as a co-solvent and add them to a beaker, then pour in 5 mL of double-distilled water. Place the beaker in a constant temperature water bath at 100℃, start the stirring device, and stir at 800 r / min for 0.5 h until the solution is homogeneous and transparent, thus obtaining the dispersant solution.

[0040] Example 3

[0041] The grain boundary diffusion steps for the cerium-rich NdFeB magnets are the same as in Example 1, except that the mass of diacetone alcohol used is changed from 0.05 g to 0.25 g, thereby changing the ratio of polyvinyl alcohol to diacetone alcohol from 10:1 to 2:1.

[0042] ① Dispersant preparation: Weigh 0.50 g of polyvinyl alcohol (purity ≥93.5%, degree of alcoholysis 97.5~99 mol%, viscosity 3.5-4.5 mPa.s) and 0.25 g of diacetone alcohol (purity 99.5%) into a beaker, then pour in 5 mL of double-distilled water. Place the beaker in a constant temperature water bath at 100℃, start the stirring device, and stir at 800 r / min for 0.5 h until the solution is homogeneous and transparent, thus obtaining the dispersant solution.

[0043] Example 4

[0044] The grain boundary diffusion steps for the cerium-rich NdFeB magnets are the same as in Example 1, except that the mass of diacetone alcohol used is changed from 0.05 g to 0.50 g, thereby changing the ratio of polyvinyl alcohol to diacetone alcohol from 10:1 to 1:1.

[0045] ① Dispersant preparation: Weigh 0.50 g of polyvinyl alcohol (purity ≥93.5%, degree of alcoholysis 97.5-99 mol%, viscosity 3.5-4.5 mPa·s) and 0.50 g of diacetone alcohol (purity 99.5%) as a co-solvent and add them to a beaker, then pour in 5 mL of double-distilled water. Place the beaker in a constant temperature water bath at 100℃, start the stirring device, and stir at 800 r / min for 0.5 h until the solution is homogeneous and transparent, thus obtaining the dispersant solution.

[0046] Example 5

[0047] The grain boundary diffusion steps for the cerium-rich NdFeB magnets are the same as in Example 1, except that the mass of diacetone alcohol used is changed from 0.05 g to 0.75 g, thus changing the ratio of polyvinyl alcohol to diacetone alcohol from 10:1 to 2:3.

[0048] ① Dispersant preparation: Weigh 0.50 g of polyvinyl alcohol (purity ≥93.5%, degree of alcoholysis 97.5-99 mol%, viscosity 3.5-4.5 mPa·s) and 0.75 g of diacetone alcohol (purity 99.5%) into a beaker, then pour in 5 mL of double-distilled water. Place the beaker in a constant temperature water bath at 100℃, start the stirring device, and stir at 800 r / min for 0.5 h until the solution is homogeneous and transparent, thus obtaining the dispersant solution.

[0049] Example 6

[0050] The grain boundary diffusion steps for the cerium-rich NdFeB magnets are the same as in Example 1, except that the mass of diacetone alcohol used is changed from 0.05 g to 1.00 g, thus changing the ratio of polyvinyl alcohol to diacetone alcohol from 10:1 to 1:2.

[0051] ① Dispersant preparation: Weigh 0.50 g of polyvinyl alcohol (purity ≥93.5%, degree of alcoholysis 97.5-99 mol%, viscosity 3.5-4.5 mPa·s) and 1.00 g of diacetone alcohol (purity 99.5%) as a co-solvent and add them to a beaker, then pour in 5 mL of double-distilled water. Place the beaker in a constant temperature water bath at 100℃, start the stirring device, and stir at 800 r / min for 0.5 h until the solution is homogeneous and transparent, thus obtaining the dispersant solution.

[0052] Example 7

[0053] The grain boundary diffusion steps for the cerium-rich NdFeB magnets are the same as in Example 1, except that the mass of diacetone alcohol used is changed from 0.05 g to 2.50 g, thereby changing the ratio of polyvinyl alcohol to diacetone alcohol from 10:1 to 1:5.

[0054] ① Dispersant preparation: Weigh 0.50 g of polyvinyl alcohol (purity ≥93.5%, degree of alcoholysis 97.5-99 mol%, viscosity 3.5-4.5 mPa·s) and 2.50 g of diacetone alcohol (purity 99.5%) as a co-solvent and add them to a beaker, then pour in 5 mL of double-distilled water. Place the beaker in a constant temperature water bath at 100℃, start the stirring device, and stir at 800 r / min for 0.5 h until the solution is homogeneous and transparent, thus obtaining the dispersant solution.

[0055] Example 8

[0056] The grain boundary diffusion steps for the cerium-rich NdFeB magnets are the same as in Example 1, except that the mass of diacetone alcohol used is changed from 0.05 g to 5.00 g, thereby changing the ratio of polyvinyl alcohol to diacetone alcohol from 10:1 to 1:10.

[0057] ① Dispersant preparation: Weigh 0.50 g of polyvinyl alcohol (purity ≥93.5%, degree of alcoholysis 97.5-99 mol%, viscosity 3.5-4.5 mPa.s) and 5.00 g of diacetone alcohol (purity 99.5%) as a co-solvent and add them to a beaker, then pour in 5 mL of double-distilled water. Place the beaker in a constant temperature water bath at 100℃, start the stirring device, and stir at 800 r / min for 0.5 h until the solution is homogeneous and transparent, thus obtaining the dispersant solution.

[0058] Comparative Example 1

[0059] The difference between this embodiment and Example 1 is that anhydrous ethanol is used as the dispersant alone:

[0060] ① Dispersion of diffusion source: Weigh 1 g of terbium fluoride powder for grain boundary diffusion in cerium-rich NdFeB magnets and add 50 mL of anhydrous ethanol (purity 99.7%). Stir at 800 r / min for 0.5 h at 50℃, cool and centrifuge, discard the supernatant to obtain a uniform dispersion of diffusion source.

[0061] Comparative Example 2

[0062] The difference between this embodiment and Example 1 is that polyvinyl alcohol is used as the dispersant:

[0063] ① Dispersant preparation: Weigh 0.50 g of polyvinyl alcohol (purity ≥93.5%, degree of alcoholysis 97.5-99 mol%, viscosity 3.5-4.5 mPa.s) into a beaker, and then pour in 5 mL of double-distilled water. Place the beaker in a constant temperature water bath at 100℃, start the stirring device, and stir at 800 r / min for 0.5 h to obtain a uniform dispersant solution.

[0064] Comparative Example 3

[0065] The difference between this embodiment and Example 1 is that diacetone alcohol is used as the dispersant alone:

[0066] ① Dispersant preparation: Weigh 0.75 g of the co-solvent diacetone alcohol (purity 99.5%) and add it to a beaker, then pour in 5 mL of double-distilled water. Place the beaker in a constant temperature water bath at 100 ℃, start the stirring device, and stir at 800 r / min for 0.5 h to obtain a uniform dispersant solution.

[0067] Comparative Example 4

[0068] The difference between this embodiment and Example 1 is that the dispersant used is a mixture of polyvinyl alcohol and anhydrous ethanol:

[0069] ① Dispersant preparation: A mixed solvent of polyvinyl alcohol and anhydrous ethanol was selected as the dispersant. 0.50 g of polyvinyl alcohol was weighed and added to a beaker, followed by 5 mL of double-distilled water. The beaker was placed in a 100℃ constant temperature water bath, and the stirring device was started. The mixture was stirred at 800 r / min for 0.5 h. After cooling, 50 mL of anhydrous ethanol was added, and the mixture was stirred at 800 r / min for 0.2 h at 50℃. After cooling, the mixture was centrifuged, and the supernatant was discarded to obtain a uniform diffusion source dispersion.

[0070] Comparative Example 5

[0071] The difference between this embodiment and Example 1 is that the dispersant used is a mixture of polyvinyl alcohol and 3-methoxybutanol:

[0072] ① Dispersant preparation:

[0073] A mixed solvent of polyvinyl alcohol and anhydrous ethanol was selected as the dispersant. 0.50 g of polyvinyl alcohol was weighed and added to a beaker, followed by 5 mL of double-distilled water. The beaker was placed in a 100℃ constant temperature water bath, and the stirring device was started, stirring at 800 r / min for 0.5 h. 0.5 g of 3-methoxybutanol was then added, and the mixture was stirred at 800 r / min for 0.2 h at 50℃. After cooling, the mixture was centrifuged, and the supernatant was discarded to obtain a uniform diffusion source dispersion.

[0074] Performance testing

[0075] The performance of the cerium-rich NdFeB magnets prepared in Examples 1-8 and Comparative Examples 1-5 was tested, and the test results are shown in the table below. Substance A represents the polymeric dispersant polyvinyl alcohol, and substance B represents the cosolvent diacetone alcohol.

[0076] Dispersant liquid <![CDATA[H cj (no)]]> Br (kGs) (BH)max (MGOe) <![CDATA[H cj +(BH)max]]> primitive magnet 12.18 11.87 33.49 45.67 Example 1 (0.50g A + 0.05g B) 15.42 11.48 31.40 47.94 Example 2 (0.50g A + 0.10g B) 15.66 11.67 32.45 47.22 Example 3 (0.50g A + 0.25g B) 15.33 11.65 32.90 48.23 Example 4 (0.50g A + 0.50g B) 15.78 11.70 33.05 48.83 Example 5 (0.50g A + 0.75g B) 16.37 11.78 34.05 50.42 Example 6 (0.50g A + 1.00g B) 16.49 11.69 33.37 49.86 Example 7 (0.50g A + 2.50g B) 15.51 11.76 33.37 45.97 Example 8 (0.50g A + 5.00g B) 15.62 11.78 33.51 45.94 Comparative Example 1 (50 mL anhydrous ethanol) 13.47 11.60 31.52 44.99 Comparative Example 2 (0.5g A) 14.65 11.74 31.77 46.42 Comparative Example 3 (0.75g B) 14.20 11.82 32.90 47.1 Comparative Example 4 (0.5g A + 50mL anhydrous ethanol) 13.84 11.68 32.42 46.26 Comparative Example 5 (0.5g A + 0.5g 3-methoxybutanol) 14.53 11.77 31.81 46.34

[0077] Quantitative data comparison clearly demonstrates the significant performance advantages of the dispersant and its application method of this invention. Compared to the original magnets, the main performance indicators such as coercivity and energy product of all tested magnets were significantly improved. However, the coercivity and energy product of the cerium-rich NdFeB magnets prepared using the dispersant and application method of this invention (Examples 1-8) were superior to those of magnets prepared using single dispersants and other mixed dispersants (Comparative Examples 1-5). Among them, Example 5 (polyvinyl alcohol and diacetone alcohol in a mass ratio of 2:3) exhibited the best overall performance, with a coercivity of 16.37 kOe, an increase of 34.4% compared to the original magnet, and an energy product of 34.05 MGOe, showing not only no loss but also an increase of 1.67%. This is because at this ratio, the viscosity and surface tension of the dispersion reached the optimal balance, resulting in the most uniform dispersion of terbium fluoride and more complete grain boundary diffusion. Compared to individual dispersants, the coercivity of Example 5 was 21.5% higher than that of anhydrous ethanol, 11.7% higher than that of polyvinyl alcohol, and 15.3% higher than that of diacetone alcohol, with maximum energy products 8.02%, 7.18%, and 3.50% higher, respectively. Compared to the mixed dispersants (polyvinyl alcohol + anhydrous ethanol) (Comparative Example 4) and (polyvinyl alcohol + 3-methoxybutanol) (Comparative Example 5), the coercivity of Example 5 was 18.3% and 12.7% higher, respectively, with maximum energy products 5.03% and 7.04% higher, respectively. This demonstrates that the cerium-rich NdFeB magnets prepared using the dispersant and method of this invention exhibit superior performance compared to single and other mixed dispersant systems.

[0078] Contents not described in detail in this specification are prior art known to those skilled in the art. Although illustrative specific embodiments of the invention have been described above to facilitate understanding by those skilled in the art, it should be understood that the invention is not limited to the scope of the specific embodiments. Various modifications are readily apparent to those skilled in the art as long as they fall within the spirit and scope of the invention as defined and determined by the appended claims, and all inventions utilizing the concept of this invention are protected.

Claims

1. A spin-coating dispersant for grain boundary diffusion in cerium-rich NdFeB magnets, characterized in that: The spin-coating dispersant is a binary composite solution composed of a high molecular weight dispersant, polyvinyl alcohol, and a co-solvent, diacetone alcohol. The polyvinyl alcohol serves as the main film-forming substance, providing a good carrier and adhesion performance for the diffusion source. The diacetone alcohol serves as a co-solvent, adjusting the solubility and evaporation rate of the solution to ensure the uniformity and stability of the coating. The mass ratio of the high molecular weight dispersant, polyvinyl alcohol, to the co-solvent, diacetone alcohol ranges from 10:1 to 1:

10.

2. A method for preparing a spin-coating dispersant for grain boundary diffusion in cerium-rich NdFeB magnets as described in claim 1, characterized in that, Polyvinyl alcohol, a polymeric dispersant, and diacetone alcohol, a co-solvent, were stirred and mixed at 100°C. After thorough dissolution and homogenization, a uniform and stable dispersant for spin coating was prepared.

3. A method of using the spin-coating dispersant for grain boundary diffusion in cerium-rich NdFeB magnets as described in claim 1, characterized in that, Includes the following steps: Step 1: Cut the cerium-rich NdFeB magnet into sheet-shaped substrate magnets that meet the requirements of the grain boundary diffusion process, and perform surface treatment processes such as oxide layer removal, precision polishing, acidification and cleaning on the surface of the sheet-shaped substrate magnets to ensure that the surface of the sheet-shaped substrate magnets meets the cleanliness and flatness requirements of the process. Step 2: Add the diffusion source powder to the spin-coating dispersant and stir thoroughly to obtain the diffusion source solution; Step 3: The diffusion source solution is uniformly dropped onto the surface of the sheet-like substrate magnet after surface treatment. The diffusion source solution is spread evenly under centrifugal force by spin coating. The solution is then dried to allow the solvent in the coating to fully evaporate. Finally, a diffusion source coating with uniform thickness and good adhesion is formed on the surface of the sheet-like substrate magnet, and the magnet to be diffused is obtained. Step 4: Perform grain boundary diffusion heat treatment on the dried magnet to be diffused, so that the effective components in the diffusion source can diffuse fully along the grain boundary of the magnet, and finally obtain the diffused magnet.

4. The method of using the spin-coating dispersant for grain boundary diffusion of cerium-rich NdFeB magnets according to claim 3, characterized in that, In step 1, the surface treatment process of removing the oxide layer, precision polishing, acidification and cleaning is carried out on the surface of the substrate magnet in sequence. Specifically, the natural oxide layer on the surface of the substrate magnet is first removed by chemical etching or physical grinding. Then, the surface of the substrate magnet is polished to a mirror effect through multiple polishing processes. Next, it is immersed in 3wt.% HNO3 solution for 60 seconds. Finally, it is ultrasonically cleaned with deionized water and anhydrous ethanol in sequence to thoroughly remove the impurities and contaminants remaining on the surface.

5. The method of using the spin-coating dispersant for grain boundary diffusion of cerium-rich NdFeB magnets according to claim 3, characterized in that, In step 1, the cerium-rich NdFeB magnet is a sintered NdFeB material prepared by a dual alloying method, wherein the weight percentage of cerium in the total rare earth elements RE = Nd + Pr + Ce + Dy + Tb (Ce / RE) is 10%~40%; in step 2, the diffusion source powder is a heavy rare earth fluoride with a purity ≥99.9% and a median particle size D50 = 2±0.5μm.

6. The method of using the spin-coating dispersant for grain boundary diffusion of cerium-rich NdFeB magnets according to claim 3, characterized in that, In step 3, the diffusion source solution is evenly spread under centrifugal force by spin coating. Specifically, the process is carried out in steps: first, spin coating is performed at a speed of 2000 rpm for 60 seconds to initially spread the dispersion and remove excess solution; then, spin coating is performed at a speed of 900 rpm for 10 seconds; and then the solution is placed in a drying device at 170°C for 5 minutes. To ensure that the coating thickness meets the process requirements, this process is repeated three times.

7. The method of using the spin-coating dispersant for grain boundary diffusion of cerium-rich NdFeB magnets according to claim 3, characterized in that, In step 4, the grain boundary diffusion heat treatment involves first performing a high-temperature annealing treatment, followed by a second high-temperature treatment. Specifically, the annealing treatment is carried out at 1000℃ for 5 hours, with strict control of the vacuum level inside the furnace during the annealing process to ensure that it is carried out in a low-oxygen environment. After cooling down to 550℃, a second high-temperature treatment is performed for 2 hours.

8. The method of using the spin-coating dispersant for grain boundary diffusion of cerium-rich NdFeB magnets according to claim 7, characterized in that, Before high-temperature annealing, the magnet to be diffused is tightly wrapped with molybdenum foil to prevent it from reacting with other components in the furnace during the high-temperature annealing process. This also reduces the volatilization of elements on the magnet surface, ensuring the stability and consistency of the diffusion process.

9. The method of using the spin-coating dispersant for grain boundary diffusion of cerium-rich NdFeB magnets according to claim 3, characterized in that, The control relationship between the dispersant and the diffusion source powder for spin coating is as follows: the mass ratio of the high molecular weight dispersant polyvinyl alcohol to the diffusion source powder in the spin coating dispersant is controlled to be 1:2.

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