Powder surface modifier and method for improving sintered neodymium-iron-boron magnetic properties

Abstract

This invention belongs to the field of rare earth permanent magnet materials technology, and relates to a powder surface modifier and its method for improving the magnetic properties of sintered NdFeB magnets. The raw materials for preparing the powder surface modifier, by mass ratio, include: 4-10 parts of tantalum hydride, 10-20 parts of powder dispersing lubricant, 68-85 parts of organic film-forming solvent, and 1-2 parts of a strong film-forming agent. Using the powder surface modifier of this invention and its method for improving the magnetic properties of sintered NdFeB magnets, after surface modification of NdFeB magnetic powder, the magnetic properties of sintered NdFeB magnets, including Br, Hcj, and Hk / Hci, can be significantly improved, and the impurity carbon content in sintered NdFeB magnets can be significantly reduced.

Description

Technical Field

[0001] This invention belongs to the field of rare earth permanent magnet materials technology, and relates to powder surface modifiers and their methods for improving the magnetic properties of sintered NdFeB magnets. Background Technology

[0002] Sintered NdFeB magnets are a type of rare-earth permanent magnet functional material. The performance of magnets, including sintered NdFeB magnets, is primarily evaluated using two parameters: remanence (Br) and intrinsic coercivity (Hcj). Higher remanence means a stronger magnetic field strength contributed by the magnet in its working environment; higher intrinsic coercivity means a stronger resistance to demagnetization by external magnetic fields and better high-temperature thermal stability. It can be said that decades of effort in the NdFeB industry have revolved around these two parameters.

[0003] Sintered NdFeB permanent magnet materials are produced using powder metallurgy. The main production process includes: alloy smelting, casting, hydrogenation crushing, air jet milling, magnetic field orientation forming, vacuum sintering, and tempering. The purpose of the magnetic field orientation forming stage is twofold: first, to apply a magnetic force to each NdFeB powder particle using an external magnetic field, ensuring that the particle's orientation axis (c-axis) is aligned in an orderly manner along the direction of the applied magnetic field; and second, to form the magnet under appropriate molds and pressure to meet customer specifications. However, in actual production, due to the fine particle size (2-3 micrometers) and poor sphericity of the NdFeB powder, there is significant displacement resistance between the particles, making it difficult to ensure that the c-axis of all particles is strictly aligned with the direction of the applied magnetic field. Therefore, the magnetic field orientation of the pressed compact is poor, resulting in low remanence in the final sintered magnet.

[0004] Meanwhile, during the powder pressing and demolding processes, the enormous internal stress within the blank often leads to cracking and chipping of the blank, resulting in product defects. Furthermore, the rare earth elements in neodymium iron boron (Nd), praseodymium (Pr), cerium (Ce), dysprosium (Dy), and terbium (Tb) in NdFeB materials are chemically reactive, making micron-sized NdFeB powder highly susceptible to oxidation, which in turn reduces product performance.

[0005] Therefore, most NdFeB manufacturers add a small amount of organic additives to the alloy powder during production to reduce the displacement resistance between powder particles, thereby improving the orientation of the compact, reducing the internal stress of the compact, and lowering the oxygen content of the material. This additive is usually composed of fatty acid or borate ester compounds + saturated aliphatic hydrocarbon or halogenated hydrocarbon solvent + a small amount of dispersant (hereinafter referred to as "ester hydrocarbon agent"). However, this general-purpose ester-hydrocarbon agent has the following technical problems: First, the film-forming property of the solution on the surface of alloy powder particles is poor, and the "coating" effect on the particles is weak, thus limiting its effect on reducing the frictional resistance between powder particles; Second, the low-temperature volatility of the ester-hydrocarbon agent is poor, and the electronic coordination between the ester functional groups and the rare earth atoms on the surface of NdFeB powder particles is strong, which easily leads to the residual carbon impurities after thermal decomposition during the pressing and sintering of the compact (the carbon content of sintered NdFeB magnets is usually 700-1500ppm). The residual carbon atoms form a high-melting-point RC impurity phase with rare earth atoms in the intergranular space, which hinders the flow and distribution of the NdFeB-rich phase and affects the coercivity of the magnet; Third, the additive is a pure organic reagent, which has no positive effect on improving the microstructure of the material, and therefore does not make any positive contribution to the coercivity of the magnet.

[0006] To address the aforementioned issues, the sintered NdFeB industry urgently needs a new type of powder modifier to replace the currently used ester-based modifier: one that can more efficiently reduce frictional resistance between powders and achieve low carbon residue; ideally, it should also introduce a component or mechanism that can improve the microstructure of the material and effectively enhance coercivity. Summary of the Invention

[0007] The primary objective of this invention is to provide a powder surface modifier that, after surface modification of NdFeB magnetic powder, can significantly improve the magnetic properties of sintered NdFeB, including Br, Hcj, and Hk / Hci, and significantly reduce the impurity carbon content in sintered NdFeB.

[0008] To achieve this objective, in a basic implementation, the present invention provides a powder surface modifier, wherein the raw materials for preparing the powder surface modifier comprise, by mass ratio: 4-10 parts of tantalum hydride, 10-20 parts of powder dispersing lubricant, 68-85 parts of organic film-forming solvent, and 1-2 parts of potent film-forming agent.

[0009] The powder surface modifier of the present invention (which may be simply referred to as "ether tantalum agent") is mainly used for surface modification of sintered NdFeB powder, and the relevant principle is as follows: The organic film-forming solvent in the powder surface modifier of this invention is both an organic solvent and a good film-forming agent. Its main function is to promote the formation of an organic thin film on the surface of NdFeB magnetic powder particles, thereby preventing oxidation of the magnetic powder and reducing the frictional resistance of the powder. The preferred organic film-forming solvent is dipropylene glycol butyl ether.

[0010] The organic film-forming solvent is the most abundant component (68% to 85% by mass) in the powder surface modifier of this invention. Its representative component, dipropylene glycol butyl ether, is chemically very stable, with a low boiling point (222°C) and a high decomposition temperature (>250°C). It does not chemically react with the NdFeB matrix components; its surface tension is only 27.3 mN / m, thus exhibiting excellent wetting properties. Its film-forming effect is far superior to any component in traditional ester-based agents. The film-forming mechanism of dipropylene glycol butyl ether originates from its own physical properties, not from electronic coordination with the surface atoms of NdFeB particles. Therefore, it easily escapes from the NdFeB compact during vacuum low-temperature heating, resulting in less residual carbon impurities.

[0011] The powder dispersing lubricant in the powder surface modifier of this invention is both a powder dispersant and a powder lubricant, used to improve the magnetic field orientation of NdFeB powder compacts, thereby increasing the remanence (Br) of sintered NdFeB permanent magnet materials. The preferred powder dispersing lubricant is GPL102 perfluoroalkyl polyether (which has a fluorocarbon-hydrocarbon amphiphilic structure).

[0012] GPL102 perfluoroalkyl polyether is chemically very stable, with a decomposition temperature above 350℃, and can be removed at relatively low temperatures under vacuum. As an excellent powder lubricant, GPL102 perfluoroalkyl polyether can significantly reduce the frictional resistance between powder particles; even after dissolving 10-20% in dipropylene glycol butyl ether, its drag-reduction effect is still significantly better than that of ester hydrocarbon agents.

[0013] The potent film-forming agent in the powder surface modifier of the present invention is used to enhance the film-forming effect of the powder surface modifier, preferably polyvinylpyrrolidone, more preferably PVP K-90.

[0014] PVP K-90 is a potent film-forming agent used to further enhance the film-forming effect of the powder surface modifier of the present invention. Although PVP K-90 is prone to decomposition during sintering, resulting in residual carbon impurities, its addition amount accounts for only 1-2% of the total mass of the powder surface modifier of the present invention, and its upper limit of influence on the carbon content of sintered NdFeB magnets is only 40ppm, which is extremely limited.

[0015] The tantalum hydride (preferably nano-tantalum hydride with a particle size of 50-200 nm) in the powder surface modifier of this invention, after being mixed with NdFeB magnetic material powder, is uniformly and dispersedly distributed on the surface of NdFeB powder particles under the strong action of film-forming agents such as dipropylene glycol butyl ether and polyvinylpyrrolidone (PVP K-90). This nano-sized spherical ceramic solid powder acts like a ball bearing between the micron-sized NdFeB main phase particles, significantly reducing the frictional resistance between NdFeB particles, thereby effectively improving the magnetic field orientation of the compact. Particularly advantageous is that the tantalum hydride (TaH) powder undergoes in-situ dehydrogenation at 700-900℃ to form nano-tantalum. During the sintering process of the NdFeB powder compact, this nano-tantalum grain boundary phase effectively inhibits the growth of NdFeB Nd2Fe14B main phase grains, refining the grains and increasing intrinsic coercivity (Hcj).

[0016] In a preferred embodiment, the present invention provides a powder surface modifier, wherein the tantalum hydride is nano tantalum hydride with a particle size of 50-200 nm.

[0017] In a preferred embodiment, the present invention provides a powder surface modifier, wherein the powder dispersing lubricant is GPL102 perfluoroalkyl polyether.

[0018] In a preferred embodiment, the present invention provides a powder surface modifier, wherein the organic film-forming solvent is dipropylene glycol butyl ether.

[0019] In a preferred embodiment, the present invention provides a powder surface modifier, wherein the potent film-forming agent is polyvinylpyrrolidone, preferably PVP K-90.

[0020] The second objective of this invention is to provide a method for preparing the above-mentioned powder surface modifier, so as to better prepare the powder surface modifier and obtain a powder surface modifier that can significantly improve the magnetic properties of sintered NdFeB magnetic powder, including Br, Hcj and Hk / Hci, after surface modification, and significantly reduce the impurity carbon content in sintered NdFeB.

[0021] To achieve this objective, in a basic implementation, the present invention provides a method for preparing the above-mentioned powder surface modifier, wherein the preparation method involves mixing raw materials and then preparing a suspension of the powder surface modifier by means including hot bath stirring and / or ultrasonic dispersion.

[0022] In a preferred embodiment, the present invention provides a method for preparing the above-mentioned powder surface modifier, wherein: The hot bath stirring is performed at a temperature of 80-90℃, a stirring time of 30-60 minutes, and a stirring speed of 300-400 rpm; and / or The ultrasonic power of the ultrasonic wave dispersion is 0.5-2kW, the ultrasonic frequency is 20-100kHz, and the ultrasonic time is 5-10 minutes.

[0023] In a preferred embodiment, the present invention provides a method for preparing the above-mentioned powder surface modifier, wherein the preparation method includes the following steps: (1) Dissolve the high-efficiency film-forming agent in the organic film-forming solvent, stir in a water bath until a transparent homogeneous solution is obtained, and then cool to room temperature; (2) Then add the remaining raw materials, including the tantalum hydride and the powder dispersing lubricant, and stir and ultrasonically disperse to obtain a suspension of the powder surface modifier.

[0024] In a preferred embodiment, the present invention provides a method for preparing the above-mentioned powder surface modifier, wherein the preparation method includes the following steps: (1) Dissolve the high-efficiency film-forming agent (preferably PVP K-90) in the organic film-forming solvent (preferably dipropylene glycol butyl ether) and stir in a water bath at 80-90°C for 30-60 minutes until a transparent homogeneous solution is obtained; (2) Cool the above homogeneous solution to room temperature, add the powder dispersing lubricant (preferably GPL102 perfluoroalkyl polyether) and the tantalum hydride (preferably nano tantalum hydride) powder in sequence, stir and ultrasonically disperse for 5-10 minutes to form a homogeneous suspension, wherein the ultrasonic power of ultrasonic dispersion is 0.5-2kW, the ultrasonic frequency is 20-100kHz, and the stirring speed is 300-400 rpm.

[0025] A third objective of this invention is to provide a method for using the aforementioned powder surface modifier to improve the magnetic properties of sintered NdFeB, thereby significantly enhancing the magnetic properties of sintered NdFeB, including Br, Hcj, and Hk / Hci, and significantly reducing the impurity carbon content in sintered NdFeB.

[0026] To achieve this objective, in a basic implementation, the present invention provides a method for using the above-mentioned powder surface modifier to improve the magnetic properties of sintered NdFeB magnets. The method includes adding a suspension of the powder surface modifier to NdFeB magnetic powder, mixing and stirring for a period of time, and then sintering the NdFeB magnetic powder.

[0027] In a preferred embodiment, the present invention provides a method for using the above-mentioned powder surface modifier to improve the magnetic properties of sintered NdFeB magnets, wherein: The mass of the suspension of the powder surface modifier added is 0.1-0.3% of the mass of the NdFeB magnetic powder; and / or The mixing speed is 30-40 rpm, and the mixing time is 2-4 hours.

[0028] The beneficial effects of the present invention are that, by using the powder surface modifier of the present invention and the method for improving the magnetic properties of sintered NdFeB, the magnetic properties of sintered NdFeB, including Br, Hcj and Hk / Hci, can be significantly improved after surface modification of NdFeB magnetic powder, and the impurity carbon content in sintered NdFeB can be significantly reduced.

[0029] Compared to ester-based agents, the powder surface modifier of this invention can more efficiently reduce the frictional resistance between powders and significantly reduce the carbon content of sintered NdFeB magnets. Specifically, nano-TaH powder undergoes in-situ dehydrogenation at 700-900℃ to form nano-tantalum. During the sintering process of NdFeB compacts, this nano-tantalum grain boundary phase effectively inhibits the growth of the NdFeB Nd2Fe14B main phase grains, refining the grains and improving the material's microstructure. Replacing the currently used ester-based agents with the powder surface modifier of this invention can comprehensively improve the remanence, intrinsic coercivity, and squareness of the demagnetization curve of NdFeB magnets. Detailed Implementation

[0030] To better understand the technical solutions and advantages of the present invention, the present invention will be further described below through embodiments and comparative examples.

[0031] Example 1: Preparation of powder surface modifier and modification of NdFeB magnetic powder (Part 1) (1) Prepare a stainless steel reactor with a 50-liter capacity, a sealed lid, and a built-in stirrer. Fix it in a 200-liter water bath with the water bath set to 80℃. (2) Weigh out 1.2 kg of tantalum hydride nanoparticles with a particle size of 50-200 nm and a purity of 99% purchased from Beijing Xingrong Technology Co., Ltd., 3 kg of GPL102 perfluoroalkyl polyether purchased from Chemours Chemical (Shanghai) Co., Ltd., 25.5 kg of 99% dipropylene glycol butyl ether purchased from Shanghai Maclean Biochemical Technology Co., Ltd., and 0.3 kg of PVP K-90 polyvinylpyrrolidone purchased from Shanghai Maclean Biochemical Technology Co., Ltd. (3) Open the sealed cap and place the dipropylene glycol butyl ether into the reaction vessel; (4) Place PVP K-90 into the reactor, tighten the reactor sealing cover, turn on the built-in stirrer (stirring speed is 400 rpm) and stir the above solution for 30 minutes to make the solution a transparent homogeneous solution; (5) Take the reactor out of the water bath and cool it in cold water to below room temperature. Open the reactor sealing cover and put GPL102 perfluoroalkyl polyether and nano tantalum hydrogen powder into the reactor one after the other. Tighten the reactor sealing cover. (6) Apply Newmeda CG-88 coupling agent to the surface of the ultrasonic generator (Shenzhen Taiheda Technology Co., Ltd., THD-M2 type) and press it tightly against the top cover of the reactor. Turn on the reactor stirrer (stirring speed is 400 rpm), press the ultrasonic start switch, stir for 5 minutes, and stir the solid-liquid mixture in the reactor into a homogeneous suspension. The ultrasonic power is 0.5kW and the frequency is 100kHz. (7) Select 600 kg of sintered NdFeB magnet powder of grade 52H (alloy composition: Pr 5.9wt%; Nd 23.6wt%; Dy 0.2wt%; Gd 0.3wt%; B 0.93wt%; Co 0.4wt%; Cu 0.35wt%; Ga 0.25wt%; Zr 0.35wt%; Fe 67.72wt%, with an average particle size of 2.5 micrometers). Under the protection of nitrogen or inert gas, add 0.1wt% of the prepared powder surface modifier suspension to the above NdFeB powder and mix for 2 hours using an American three-dimensional mixer (speed 40 rpm). (8) The above-mentioned NdFeB powder was pressed into shape in a magnetic field. The blank size was 73×65×49mm, and the molding density was 4.0 g / cm³. 3 The magnetic field strength is 2T; (9) Place each of the above-mentioned compacts into a vacuum sintering furnace for sintering at a temperature of 1090℃ and an absolute pressure of 1×10⁻⁶. -3 -1×10 -1 Pa, heat preservation time 10 hours; (10) The sintered magnets are subjected to two-stage tempering in a vacuum sintering furnace. The tempering temperatures are 900℃ and 490℃, and the holding times are 3 hours and 6 hours, respectively. After tempering, the magnets are cooled and removed from the furnace. (11) Randomly select 10 magnetic steel samples, cut out a D10×10 mm sample cylinder from each sample, and use the NIM2000 magnetic measuring instrument of the National Institute of Metrology of China to test the magnetic properties. The average value of the 10 test results is recorded. The results are shown in Table 1. (12) Remove the outer skin of 10 samples respectively, and crush the other parts of the samples into small particles and mix them. Randomly select 3 samples and test the carbon content using the Steel Research Nake CS4600 carbon and sulfur analyzer. The average value of the 3 test results is recorded. The results are shown in Table 1.

[0032] Example 2: Preparation of powder surface modifier and modification of NdFeB magnetic powder (Part 2) (1) Prepare a stainless steel reactor with a 50-liter capacity, a sealed lid, and a built-in stirrer. Fix it in a 200-liter water bath with the water bath set to 90℃. (2) Weigh out 3 kg of nano tantalum hydride powder with a particle size of 50-200 nm and a purity of 99% purchased from Beijing Xingrong Technology Co., Ltd., 6 kg of GPL102 perfluoroalkyl polyether purchased from Chemours Chemical (Shanghai) Co., Ltd., 20.4 kg of 99% dipropylene glycol butyl ether purchased from Shanghai Maclean Biochemical Technology Co., Ltd., and 0.6 kg of PVP K-90 polyvinylpyrrolidone purchased from Shanghai Maclean Biochemical Technology Co., Ltd. (3) Open the sealed cap and place the dipropylene glycol butyl ether into the reaction vessel; (4) Place PVP K-90 into the reactor, tighten the reactor lid, turn on the built-in stirrer (stirring speed is 300 rpm) and stir the above solution for 60 minutes to make the solution a transparent homogeneous solution; (5) Take the reactor out of the water bath and cool it in cold water to below room temperature. Open the reactor sealing cover and put GPL102 perfluoroalkyl polyether and nano tantalum hydrogen powder into the reactor one after the other. Tighten the reactor sealing cover. (6) Apply Newmeda CG-88 coupling agent to the surface of the ultrasonic generator (Shenzhen Taiheda Technology Co., Ltd., THD-M2 type) and press it tightly against the top cover of the reactor. Turn on the reactor stirrer (stirring speed is 300 rpm), press the ultrasonic start switch, stir for 10 minutes, and stir the solid-liquid mixture in the reactor into a homogeneous suspension. The ultrasonic power is 2kW and the frequency is 20kHz. (7) Select 600 kg of N52 sintered NdFeB magnet powder (alloy composition: Pr 5.3wt%; Nd 21.2wt%; Ce 4wt%; B 0.95wt%; Co 0.4wt%; Cu 0.35wt%; Ga 0.1wt%; Zr 0.25wt%; Fe 67.45wt%, original powder average particle size 3.1 micrometers), add 0.3wt% of the prepared powder surface modifier suspension to the above NdFeB powder under nitrogen or inert gas protection, and mix for 4 hours using an American three-dimensional mixer (speed 30 rpm); (8) The above-mentioned NdFeB powder was pressed into shape in a magnetic field. The blank size was 88×63×52mm, and the molding density was 4.0 g / cm³. 3 The magnetic field strength is 2T; (9) Place each of the above-mentioned compacts into a vacuum sintering furnace for sintering at a temperature of 1050℃ and an absolute pressure of 1×10⁻⁶. -3 -1×10 -1 Pa, heat preservation time 5 hours; (10) The sintered magnets are subjected to two-stage tempering in a vacuum sintering furnace. The tempering temperatures are 930℃ and 630℃, and the holding times are 2 hours and 4 hours, respectively. After tempering, the magnets are cooled and removed from the furnace. (11) Randomly select 10 magnetic steel samples, cut out a D10×10 mm sample cylinder from each sample, and use the NIM2000 magnetic measuring instrument of the National Institute of Metrology of China to test the magnetic properties. The average value of the 10 test results is recorded. The results are shown in Table 1. (12) Remove the outer skin of 10 samples respectively, and crush the other parts of the samples into small particles and mix them. Randomly select 3 samples and test the carbon content using the Steel Research Nake CS4600 carbon and sulfur analyzer. The average value of the 3 test results is recorded. The results are shown in Table 1.

[0033] Comparative Example 1: Modification of NdFeB Magnetic Powder by Commercially Available Ester Hydrocarbon Agents (I) The suspension of the powder surface modifier prepared according to steps (1) to (6) of Example 1 was replaced with commercially available RF-2 type ester hydrocarbon agent (37wt% stearate, 55wt% petroleum ether, 8wt% polyacrylate dispersant, purchased from Tianjin Yuesheng Magnetoelectric Technology Co., Ltd.), and the NdFeB magnetic powder was modified and the samples were tested in the same way as in steps (7) to (12) of Example 1.

[0034] Comparative Example 2: Modification of NdFeB Magnetic Powder by Commercially Available Ester Hydrocarbon Agents (Part 2) The suspension of the powder surface modifier prepared according to steps (1) to (6) of Example 2 was replaced with a commercially available ester hydrocarbon agent (50wt% dioctyl adipate, 45wt% acetone, and 5wt% polyacrylate dispersant, purchased from Beijing Xudong Chemical Co., Ltd.), and the NdFeB magnetic powder was modified and the samples were tested in the same manner as in steps (7) to (12) of Example 2.

[0035] Table 1. Test results of carbon content and magnetic properties of sintered NdFeB permanent magnet materials.

[0036] As shown in Table 1, compared with Comparative Examples 1 and 2, the carbon content of the sintered NdFeB permanent magnet materials prepared using Examples 1 and 2 of this invention is significantly reduced, while magnetic performance parameters such as remanence (Br), intrinsic coercivity (Hcj), and squareness of the demagnetization curve (Hk / Hci) are significantly improved. This indicates that the powder surface modifier of this invention is more effective than the currently commonly used ester hydrocarbon modifiers in reducing the carbon content of sintered NdFeB permanent magnet materials and can significantly improve the overall magnetic properties of the sintered magnets, including remanence, intrinsic coercivity, and squareness of the demagnetization curve.

[0037] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of the claims and their equivalents, the invention is also intended to include these modifications and variations. The above embodiments or implementations are merely illustrative examples of the invention, and the invention can also be implemented in other specific ways or forms without departing from its gist or essential characteristics. Therefore, the described embodiments should be considered illustrative rather than limiting in any respect. The scope of the invention should be defined by the appended claims, and any changes equivalent to the intent and scope of the claims should also be included within the scope of the invention.

Claims

1. A powder surface modifier characterized by, The raw materials for preparing the powder surface modifier include, by mass ratio: 4-10 parts of tantalum hydride, 10-20 parts of powder dispersing lubricant, 68-85 parts of organic film-forming solvent, and 1-2 parts of high-efficiency film-forming agent.

2. The powder surface modifier according to claim 1, characterized by: The tantalum hydride mentioned is nano tantalum hydride with a particle size of 50-200 nm.

3. The powder surface modifier according to claim 1, characterized by: The powder dispersion lubricant is GPL102 perfluoroalkyl polyether.

4. The powder surface modifier according to claim 1, characterized by: The organic film-forming solvent is dipropylene glycol butyl ether.

5. The powder surface modifier according to claim 1, characterized in that: The high-efficiency film-forming agent is polyvinylpyrrolidone.

6. The method for preparing the powder surface modifier according to any one of claims 1-5, characterized in that: The preparation method involves mixing the raw materials and then using methods including hot bath stirring and / or ultrasonic dispersion to obtain a suspension of the powder surface modifier.

7. The preparation method according to claim 6, characterized in that: The hot bath stirring is performed at a temperature of 80-90℃, a stirring time of 30-60 minutes, and a stirring speed of 300-400 rpm; and / or The ultrasonic power of the ultrasonic wave dispersion is 0.5-2kW, the ultrasonic frequency is 20-100kHz, and the ultrasonic time is 5-10 minutes.

8. The preparation method according to claim 6, characterized in that, The preparation method includes the following steps: (1) Dissolve the high-efficiency film-forming agent in the organic film-forming solvent, stir in a water bath until a transparent homogeneous solution is obtained, and then cool to room temperature; (2) Then add the remaining raw materials, including the tantalum hydride and the powder dispersing lubricant, and stir and ultrasonically disperse to obtain a suspension of the powder surface modifier.

9. A method for improving the magnetic properties of sintered NdFeB magnets using the powder surface modifier according to any one of claims 1-5, characterized in that: The method includes adding a suspension of the powder surface modifier to NdFeB magnetic powder, mixing and stirring for a period of time, and then sintering the NdFeB magnetic powder.

10. The method according to claim 9, characterized in that: The mass of the suspension of the powder surface modifier added is 0.1-0.3% of the mass of the NdFeB magnetic powder; and / or The mixing speed is 30-40 rpm, and the mixing time is 2-4 hours.

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