Preparation method of auxiliary alloy powder with nanometer particle size

Abstract

The invention discloses a preparation method of auxiliary alloy powder with nano particle size, which comprises the following steps: (1) dissolving naphthalene and lithium into an organic solvent, and reacting in a stirring state to obtain a reducing agent naphthalene lithium; (2) dissolving a rare earth metal salt or a metal salt into an organic solvent, then mixing with the reducing agent, and stirring until the reaction is complete; and (3) precipitates are collected through high-speed centrifugation, by-products are removed through cleaning, finally, vacuum drying is conducted, and the nanometer auxiliary alloy powder is obtained. According to the method, the process is simple and efficient, the high-purity auxiliary alloy powder with the nanometer particle size can be prepared, the auxiliary alloy powder is applied to the grain boundary adding technology of the neodymium-iron-boron magnet, the main phase alloy can be evenly coated with the nanometer powder, good fluidity is achieved, and therefore the utilization rate of the rare earth material is increased. According to the modified magnetic powder, the coercive force of the sintered neodymium-iron-boron magnet is enhanced, and meanwhile, the squareness and the residual magnetism rate of the magnet are improved, so that the stability and the high-temperature resistance of the magnet are improved.

Description

Technical Field

[0001] This invention belongs to the field of rare earth nanomaterial preparation technology, specifically a method for preparing auxiliary alloy powder with nano-sized particles, which is used to improve the coercivity of magnetic materials at low cost. Background Technology

[0002] Sintered neodymium iron boron (NdFeB) magnets possess excellent magnetic properties, making them the most widely used permanent magnet material in the world. Sintered NdFeB rare-earth permanent magnets are widely used in new energy industries such as hybrid vehicles and wind power generation, and the market demand for ultra-high coercivity magnets is becoming increasingly urgent. There are four common processes for improving the coercivity of sintered NdFeB magnets: melting alloying, grain refinement, grain boundary diffusion, and grain boundary addition.

[0003] Grain boundary addition is a method to improve the performance of sintered magnets by mixing neodymium iron boron magnetic powder with auxiliary alloy powder in a certain proportion, followed by pressing, sintering, and heat treatment. It can significantly improve the coercivity of a magnet while slightly reducing its remanence. Grain boundary addition requires less heavy rare earth element and is not limited by magnet size, making it more suitable for industrial sintering of blank magnets. This method has two main advantages: First, during sintering, the heavy rare earth-rich components of the auxiliary alloy can be uniformly and diffusely distributed on the surface of the main phase grains, forming a thick shell. This shell reduces excess liquid phase, increases the volume fraction of the main phase, and reduces the intrusion of other elements, thereby improving the coercivity of the magnet. Simultaneously, other additive elements such as Al, Cu, Ga, and Co in the auxiliary alloy can effectively improve the boundary structure and grain boundary phase characteristics of the magnet, such as wettability and surface tension. Secondly, by controlling the sintering temperature and time, heavy rare earth elements are prevented from entering the main phase, ensuring that the grain boundary phase maintains a high anisotropic field. This not only reduces the probability of heavy rare earth elements and iron in the main phase undergoing ferrimagnetic coupling, but also prevents the remanence of the magnet from decreasing significantly.

[0004] However, large-particle-size auxiliary alloy powders cannot uniformly coat the main phase alloy particles, resulting in insufficient magnetic powder flowability and low orientation during molding. Furthermore, adding a large proportion of such auxiliary alloy powders leads to a decrease in the remanence and squareness of the magnet, and the addition of larger-sized auxiliary alloys easily introduces large amounts of impurity elements such as oxygen, nitrogen, and carbon, thereby reducing the magnet's performance. Summary of the Invention

[0005] Based on the above, the purpose of this invention is to provide a low-cost and high-efficiency method for preparing nano-sized auxiliary alloy powders for use in magnet grain boundary addition technology, providing technical support for improving the coercivity of NdFeB magnets.

[0006] To achieve its purpose, the present invention adopts the following technical solution: The present invention provides a method for preparing auxiliary alloy powder with nanoparticle size, comprising the following steps: (1) Preparation of reducing agent: Naphthalene and lithium are dissolved in an organic solvent and reacted under stirring to obtain the reducing agent naphthalene lithium; (2) Dissolve rare earth metal salts or metal salts in an organic solvent, and then mix them with the reducing agent in step (1) and stir until the reaction is complete; (3) After the reaction in step (2) is completed, the precipitate is collected under high-speed centrifugation at 6000-12000 r / min, and the byproducts are washed away. Finally, the nano-auxiliary alloy powder is obtained by vacuum drying.

[0007] As a further preferred embodiment of the technical solution of the present invention, in step (1), the molar ratio of naphthalene to lithium is 0.05:1-2:1.

[0008] Furthermore, in step (1), the stirring speed is 500-1000 r / min and the stirring time is 12-48 h.

[0009] Further, in step (1), the organic solvent is tetrahydrofuran or toluene.

[0010] Furthermore, in step (2), the rare earth metal salt is any one of praseodymium chloride, neodymium chloride, dysprosium chloride, or terbium chloride.

[0011] Further, in step (2), the metal salt is any one of aluminum chloride, copper chloride, gallium chloride, cobalt chloride, or tin chloride.

[0012] Further, in step (2), the molar mass ratio of the reducing agent to the metal salt is 1.1:1-1.5:1.

[0013] Furthermore, the organic solvent in step (2) is the same as the organic solvent in step (1).

[0014] Furthermore, in step (2), the stirring speed is 500-1000 r / min and the stirring time is 1-6 h.

[0015] Furthermore, in step (3), the reagents used to clean and remove byproducts are tetrahydrofuran and toluene.

[0016] The beneficial effects of this invention are as follows: The method of this invention is simple and efficient, and can prepare high-purity auxiliary alloy powder with nano-sized particles. This auxiliary alloy powder is used in the grain boundary addition technology of NdFeB magnets. The nanoparticles can uniformly coat the main phase alloy and have good fluidity, thereby improving the utilization rate of rare earth materials. This modified magnetic powder not only enhances the coercivity of the resulting sintered NdFeB magnets, but also helps to improve the squareness and remanence of the magnets, thereby improving the stability and high-temperature resistance of the magnets. Attached Figure Description

[0017] Figure 1 Transmission electron microscopy image of Al nanoparticles prepared in Example 1 of this invention; Figure 2 This is a transmission electron micrograph of the Co nanoparticles prepared in Example 2 of the present invention; Figure 3 Transmission electron microscopy image of Pr nanoparticles prepared in Example 3 of this invention; Figure 4 This is a scanning electron microscope image of the sintered NdFeB magnet prepared in Experimental Example 1 of the present invention; Figure 5 This is a comparison diagram of the demagnetization curves of the magnets obtained in Experimental Example 1 and Comparative Example 1 of the present invention. Detailed Implementation

[0018] The preparation method of the present invention will be described below through specific embodiments to enable those skilled in the art to understand the present invention. However, it should be understood that the present invention is not limited to the scope of the specific embodiments. For those skilled in the art, as long as various changes are within the spirit and scope of the present invention as defined and determined by the claims, these changes are obvious. All inventions utilizing the concept of the present invention are within the scope of protection.

[0019] Example 1 This embodiment provides a method for preparing auxiliary alloy powder with nano-sized particles, comprising the following steps: (1) Preparation of reducing agent: 2 mmol of naphthalene and 2 mmol of lithium were dissolved in 10 mL of tetrahydrofuran and stirred at 1000 r / min for 12 h to obtain the reducing agent naphthalene lithium; (2) Add 0.5 mmol of aluminum chloride to 25 mL of tetrahydrofuran and stir at 1000 r / min for 24 h until completely dissolved. Then mix it with naphthalene lithium (the molar mass ratio of naphthalene lithium to aluminum chloride is 1.3:1) in step (1) and stir at 1000 r / min for 6 h until the reaction is complete. (3) After the reaction in step (2) is completed, centrifuge at 8000 r / min for 3 min, collect the precipitate, add 30 mL of tetrahydrofuran to the precipitate, centrifuge and wash at 8000 r / min for 3 min, repeat the washing twice, and take the precipitate; add 30 mL of toluene to the precipitate, centrifuge and wash at 8000 r / min for 3 min, repeat the washing once, and take the precipitate. Vacuum dry the precipitate at 70℃ for 2 h to obtain the final product Al nano-alloy powder. Its transmission electron microscopy image ( Figure 1 The results show that the prepared Al nanoparticles have an approximately spherical morphology, a size distribution between 2 and 5 nm, and are uniformly dispersed. This demonstrates that this method can successfully prepare high-purity auxiliary alloy powders with uniform particle size distribution.

[0020] Example 2 This embodiment provides a method for preparing auxiliary alloy powder with nano-sized particles, comprising the following steps: (1) Preparation of reducing agent: 2 mmol of naphthalene and 1 mmol of lithium were dissolved in 10 mL of toluene and stirred at 1000 r / min for 48 h to obtain the reducing agent naphthalene lithium; (2) Add 0.3 mmol of cobalt chloride to 25 mL of toluene and stir at 1000 r / min for 24 h until completely dissolved. Then mix it with lithium naphthalene (the molar mass ratio of lithium naphthalene to cobalt chloride is 1.5:1) in step (1) and stir at 1000 r / min for 5 h until the reaction is complete. (3) After the reaction in step (2) is completed, centrifuge at 10000 r / min for 3 min, collect the precipitate, add 30 mL of tetrahydrofuran to the precipitate, centrifuge and wash at 10000 r / min for 3 min, repeat the washing twice, and take the precipitate; add 30 mL of toluene to the precipitate, centrifuge and wash at 10000 r / min for 3 min, repeat the washing once, and take the precipitate. Vacuum dry the precipitate at 70℃ for 2 h to obtain the final product Co nano-alloy powder. Its transmission electron microscopy image ( Figure 2 The results show that the prepared Co nanoparticles have an approximately spherical morphology, a size distribution between 2 and 5 nm, and are uniformly dispersed. This demonstrates that this method can successfully prepare high-purity auxiliary alloy powders with uniform particle size distribution.

[0021] Example 3 (1) Preparation of reducing agent: 0.05 mmol of naphthalene and 1 mmol of lithium were dissolved in 10 mL of tetrahydrofuran and stirred at 1000 r / min for 24 h to obtain the reducing agent naphthalene lithium; (2) Add 0.3 mmol of praseodymium chloride to 25 mL of tetrahydrofuran and stir at 800 r / min for 24 h until completely dissolved. Then mix it with lithium naphthalene (the molar mass ratio of lithium naphthalene to praseodymium chloride is 1.1:1) from step (1) and stir at 1000 r / min for 5 h until the reaction is complete. (3) After the reaction in step (2) is completed, centrifuge at 12000 r / min for 3 min, collect the precipitate, add 30 mL of tetrahydrofuran to the precipitate, centrifuge and wash at 12000 r / min for 3 min, repeat the washing twice, and take the precipitate; add 30 mL of toluene to the precipitate, centrifuge and wash at 12000 r / min for 3 min, repeat the washing once, and take the precipitate. Vacuum dry the precipitate at 70℃ for 2 h to obtain the final product Pr nano-alloy powder. Its transmission electron microscopy image ( Figure 3 The results show that the prepared Pr nanoparticles have an approximately spherical morphology, a size distribution between 2 and 5 nm, and are uniformly dispersed. This demonstrates that this method can successfully prepare high-purity auxiliary alloy powders with uniform particle size distribution.

[0022] Experimental Example 1 To verify that the nano-sized auxiliary alloy powder prepared in this invention can enhance the coercivity of sintered NdFeB magnets, the auxiliary alloy powder prepared in Example 1 was mixed with the main alloy magnetic powder to obtain modified magnetic powder. The specific implementation steps are as follows: (1) Preparation of main alloy powder: using Nd2Fe 14 The main phase is a type B compound, and the main alloy micron powder is obtained through a smelting process, a hydrogen crushing process, and an air jet milling process. The raw material element composition of the main alloy powder is as follows: Nd 30 wt%, Fe 69 wt%, and B 69 wt%.

[0023] The smelting process, hydrogen crushing process, and air jet milling process are all known in the art. The smelting process includes melting and rapidly solidifying the main phase raw material to obtain the main alloy sheet. To prevent oxidation of the main phase raw material and the alloy sheet obtained therefrom, the smelting is carried out in a vacuum or inert atmosphere.

[0024] Furthermore, the smelting process employs a rapid solidification casting process, in which the smelted main phase raw material is rapidly cooled and solidified, and then cast into main alloy sheets at a smelting temperature of 1400℃.

[0025] Furthermore, the hydrogen crushing process includes the following steps: first, the main alloy sheet absorbs hydrogen; the reaction between the main alloy sheet and hydrogen gas induces volume expansion of the alloy sheet's crystal lattice, causing the main alloy sheet to break; then, it is heated to remove hydrogen, obtaining the initial magnetic powder of the main alloy. The hydrogen pressure used during hydrogen crushing is 0.05 MPa, and the heating and dehydrogenation temperature is 500℃.

[0026] (2) Preparation of modified magnetic powder: Add auxiliary alloy powder to the main alloy micron powder, with a mass ratio of auxiliary alloy powder to main alloy powder of 0.8:99.2, and then shear and mix in a high-efficiency shear mixer for 45 min to obtain modified magnetic powder.

[0027] (3) Preparation of sintered NdFeB magnets: Modified magnetic powder was pressed in a magnetic field to obtain a blank with a density of 4.25 g / cm³. 3 The green body is placed in a vacuum sintering furnace at a vacuum degree of 10. -3 Sintering was started at Pa, and pre-sintered at 385℃ for 1 h; then sintered at 1084℃ for 4 h. After sintering, the magnet was cooled to room temperature by blowing air to obtain the sintered magnet. The sintered magnet was aged at 920℃ for 1.5 h, then aged at 490℃ for 3 h, and then rapidly cooled to room temperature to obtain the sintered NdFeB magnet. Figure 4 The surface morphology and EDS distribution of the sintered NdFeB magnets are shown in the figure. The auxiliary alloy powder is uniformly distributed within the sintered NdFeB magnets. Elemental analysis confirms that it forms a continuous and uniform coating on the surface of the main phase alloy particles.

[0028] Comparative Example 1 The procedure is the same as in Experiment 1, except that no auxiliary alloy powder is added.

[0029] Comparison of the demagnetization curves of the magnets prepared in Experimental Example 1 and Comparative Example 1: Figure 5 As shown in the figure, this curve directly reflects the permanent magnet's ability to resist demagnetization and the stability of its magnetic properties.

[0030] analyze Figure 5 The results show that the overall performance of the magnet in Experimental Example 1 is significantly better than that in Comparative Example 1. Specifically: 1. Higher remanence: When the external magnetic field is zero, the magnetic induction intensity of Experimental Example 1 is higher, indicating that it can retain stronger magnetism. 2. Greater coercivity: The intercept of the curve on the horizontal axis of Experimental Example 1 is more negative, indicating that it has a stronger ability to resist external reverse magnetic fields and is more difficult to demagnetize. 3. Excellent squareness and magnetic energy product: The demagnetization curve of Experimental Example 1 is closer to an ideal rectangle, and the area enclosed by its curve is larger, indicating that it has a higher maximum magnetic energy product, that is, the magnet has a stronger ability to store magnetic energy. In summary, Figure 5 The results clearly demonstrate that by optimizing the addition of auxiliary alloys (Experimental Example 1), a permanent magnet material with high magnetic properties, high stability, and excellent comprehensive performance was successfully prepared.

Claims

1. A method for preparing a nano-sized auxiliary alloy powder, characterized in that, Includes the following steps: (1) Preparation of reducing agent: Naphthalene and lithium are dissolved in an organic solvent and reacted under stirring to obtain the reducing agent naphthalene lithium; (2) Dissolve rare earth metal salts or metal salts in an organic solvent, and then mix them with the reducing agent in step (1) and stir until the reaction is complete; (3) After the reaction in step (2) is completed, the precipitate is collected under high-speed centrifugation at 6000-12000 r / min, and the byproducts are washed away. Finally, the nano-auxiliary alloy powder is obtained by vacuum drying.

2. The method for preparing a nano-sized auxiliary alloy powder according to claim 1, characterized in that, In step (1), the molar ratio of naphthalene to lithium is 0.05:1-2:

1.

3. The method for preparing a nano-sized auxiliary alloy powder according to claim 2, characterized in that, In step (1), the stirring speed is 500-1000 r / min and the stirring time is 12-48 h.

4. The method for preparing a nano-sized auxiliary alloy powder according to claim 3, characterized in that, In step (1), the organic solvent is tetrahydrofuran or toluene.

5. The method for preparing a nano-sized auxiliary alloy powder according to claim 4, characterized in that, In step (2), the rare earth metal salt is any one of praseodymium chloride, neodymium chloride, dysprosium chloride, or terbium chloride.

6. The method for preparing a nano-sized auxiliary alloy powder according to claim 4, characterized in that, In step (2), the metal salt is any one of aluminum chloride, copper chloride, gallium chloride, cobalt chloride or tin chloride.

7. The method for preparing a nano-sized auxiliary alloy powder according to claim 1, characterized in that, In step (2), the molar mass ratio of the reducing agent to the metal salt is 1.1:1-1.5:

1.

8. A method for preparing a nano-sized auxiliary alloy powder according to any one of claims 1-7, characterized in that, The organic solvent in step (2) is the same as the organic solvent in step (1).

9. A method for preparing a nano-sized auxiliary alloy powder according to any one of claims 1-7, characterized in that, In step (2), the stirring speed is 500-1000 r / min and the stirring time is 1-6 h.

10. A method for preparing a nano-sized auxiliary alloy powder according to any one of claims 1-7, characterized in that, In step (3), the reagents used to clean and remove byproducts are tetrahydrofuran and toluene.

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