Neodymium-iron-boron regenerated magnet and preparation method thereof

Abstract

The invention discloses a neodymium-iron-boron regenerated magnet and a preparation method thereof, and belongs to the technical field of neodymium-iron-boron permanent magnet materials, and the preparation method comprises the following steps: S1, crushing washed and deoiled neodymium-iron-boron waste containing a metal coating into waste particles, then adding the waste particles into an acidic BMIC-AlCl3 ionic liquid, and carrying out microwave treatment under ultrasonic stirring so as to obtain a neodymium-iron-boron regenerated magnet; after filtering, wet screening, washing and vacuum drying, coating-free neodymium iron boron particles are obtained; s2, performing hydrogen decrepitation on the plating-free neodymium iron boron particles to obtain regenerated neodymium iron boron powder, and mixing the regenerated neodymium iron boron powder with dispersing agent powder under argon protection to obtain mixed powder; s3, the mixed powder is subjected to magnetic field orientation profiling, sintering, gradient diffusion and aging treatment in sequence under nitrogen protection, and after cooling, the neodymium iron boron regenerated magnet is obtained; the neodymium-iron-boron regenerated magnet prepared by the method has excellent comprehensive magnetic performance, and the problem that the magnetic performance of an existing regenerated neodymium-iron-boron magnet is low is solved.

Description

Technical Field

[0001] This invention belongs to the field of neodymium iron boron permanent magnet technology, specifically relating to a neodymium iron boron regenerated magnet and its preparation method. Background Technology

[0002] The manufacturing and use of sintered NdFeB permanent magnet materials often generate a large amount of waste, such as cutting and machining waste and magnets from scrapped motors. To avoid wasting raw materials and improve the effective utilization of rare earth resources, recycling waste NdFeB materials to manufacture recycled NdFeB magnets is of great significance.

[0003] Currently, the common method for recycling NdFeB magnet waste is to clean and remove impurities, then crush the waste into NdFeB magnet waste powder. This powder is then mixed with virgin NdFeB magnet powder, re-pressed, and sintered to obtain recycled NdFeB magnets. However, most NdFeB magnet waste contains metal plating (such as nickel, zinc, or aluminum plating). Directly mixing NdFeB magnet waste powder containing metal plating with virgin NdFeB magnet powder will reduce the magnetic properties of the recycled NdFeB magnets. Furthermore, using acid washing to remove the metal plating not only corrodes the NdFeB matrix but also increases the oxygen content, resulting in lower magnetic properties of the recycled NdFeB magnets.

[0004] Therefore, how to recycle and process NdFeB waste containing metal coatings and use it to prepare NdFeB regenerated magnets with high magnetic properties is a technical problem that needs to be solved. Summary of the Invention

[0005] The purpose of this invention is to provide a neodymium iron boron regenerated magnet and its preparation method, so as to solve the problems in the background art.

[0006] The objective of this invention can be achieved through the following technical solutions: A method for preparing a neodymium iron boron regenerated magnet includes the following steps: Step S1: The waste NdFeB containing metal coating after washing and degreasing is mechanically crushed to obtain waste particles with an average particle size of 3-5 mm. The waste particles are added to acidic BMIC-AlCl3 (1-butyl-3-methylimidazolium chloride-aluminum trichloride) ionic liquid. The acidic BMIC-AlCl3 ionic liquid without waste particles is microwave-treated under ultrasonic stirring. After filtration, wet screening, washing and vacuum drying, uncoated NdFeB particles are obtained. Step S2: The uncoated NdFeB particles are subjected to hydrogen crushing to obtain regenerated NdFeB powder with an average particle size of 3μm. Dispersant powder is added to the regenerated NdFeB powder and mixed evenly under argon protection to obtain mixed powder. Step S3: The mixed powder is magnetically oriented and pressed under nitrogen protection to obtain a pressed blank. Then, the pressed blank is sintered in a vacuum environment to obtain a sintered magnet. The sintered magnet is then subjected to gradient diffusion treatment and aging treatment under nitrogen protection. After cooling to room temperature, a neodymium iron boron regenerated magnet is obtained.

[0007] Furthermore, the molar ratio of 1-butyl-3-methylimidazolium chloride and aluminum trichloride in the acidic BMIC-AlCl3 ionic liquid is 1:2, at which point the acidic BMIC-AlCl3 ionic liquid can selectively dissolve the metal coating.

[0008] Furthermore, the microwave treatment frequency in step S1 is 2.4 GHz, the microwave treatment power is 800 W, and the microwave treatment time is 10-15 min. Microwave treatment can not only rapidly heat the ionic liquid to 200-250 °C, but also generate thermal stress between the metal coating and the NdFeB substrate by utilizing the difference in thermal expansion coefficients between the metal coating and the NdFeB substrate. Moreover, microwaves can penetrate the pores of the coating, causing the residual moisture in the pores to vaporize and form high-pressure microbubbles. Under the combined action of thermal stress and microbubble bursting, the metal coating is peeled off from the surface of the NdFeB substrate and disintegrates into fine coating particles.

[0009] Furthermore, the filter element used for filtration in step S1 has a pore size of 0.5 μm; the liquid used for wet sieving is ethanol, and the sieve mesh size is 2-3 mm.

[0010] Further, the amount of the dispersant powder used in step S2 is 3-5% of the mass of the recycled NdFeB powder; the dispersant powder is composed of terbium aluminum copper alloy powder with an average particle size of 2μm and cerium dioxide nanoparticles with an average particle size of 50nm mixed in a mass ratio of 20:1. Furthermore, the composition of the terbium-aluminum-copper alloy powder by weight percentage is: terbium 70%, aluminum 20%, and copper 10%.

[0011] Furthermore, the sintering temperature in step S3 is 1080°C, and the sintering time is 4 hours.

[0012] Further, the gradient diffusion treatment in step S3 is as follows: first, keep at 800℃ for 3 hours, and then cool down to 600℃ at a cooling rate of 10℃ / min and keep at that temperature for 1.5 hours.

[0013] Furthermore, the aging treatment in step S3 is performed at a temperature of 480-500℃ for 1 hour; after aging treatment, the internal stress of the magnet can be eliminated, and the demagnetizing domain nucleation field can be optimized.

[0014] A neodymium iron boron regenerated magnet is prepared by the above preparation method.

[0015] Beneficial effects: This invention first crushes NdFeB waste containing metal coatings into relatively large particles of 3-5 mm. Then, under ultrasonic stirring, microwave treatment combined with acidic BMIC-AlCl3 ionic liquid works synergistically to peel off and disintegrate the metal coating from the waste particles into smaller particles, with some of the metal coating dissolving in the acidic BMIC-AlCl3 ionic liquid. After filtration, the large NdFeB matrix particles and the small metal coating particles are separated from the acidic BMIC-AlCl3 ionic liquid. Finally, wet sieving in ethanol is used to efficiently separate the large NdFeB matrix particles and the small metal coating particles, thus obtaining uncoated NdFeB particles. Compared to traditional acid washing processes, the used ionic liquid can be recycled through electrolysis, effectively avoiding wastewater discharge and reducing NdFeB matrix loss and oxidation. This invention optimizes the microstructure of regenerated magnets through the synergistic effect of diffusing agent powder and gradient diffusion treatment, significantly improving the magnetic properties of NdFeB regenerated magnets. During holding at 800℃, Tb rapidly diffuses into the NdFeB main phase, partially replacing Nd sites to form a solid solution, enhancing the magnetocrystalline anisotropy of the main phase and laying the foundation for high coercivity. A thin and continuous grain boundary phase is formed in the aluminum-copper alloy, blocking magnetic exchange coupling between main phase grains. During slow cooling to 600℃, Tb precipitates from the supersaturated solid solution, forming a nanoscale dispersed phase along the grain boundaries, constructing a core-shell structure. The core maintains high remanence, while the shell provides high coercivity. Cerium dioxide nanopowder pins grain boundaries to inhibit abnormal grain growth and simultaneously captures oxygen impurities in the grain boundaries, suppressing Tb oxidation, resulting in NdFeB regenerated magnets with superior overall magnetic properties. Detailed Implementation

[0016] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0017] Example 1 This embodiment provides a neodymium iron boron regenerated magnet, which is prepared by the following method: Step S1: The NdFeB waste containing metal coating after washing and degreasing is mechanically crushed to obtain waste particles with an average particle size of 3 mm. The waste particles are added to an acidic BMIC-AlCl3 ionic liquid with a molar ratio of 1-butyl-3-methylimidazolium chloride and aluminum trichloride of 1:2. Under ultrasonic stirring, the acidic BMIC-AlCl3 ionic liquid without waste particles is microwaved at a frequency of 2.4 GHz and a power of 800 W for 10 min. After filtration through a filter with a pore size of 0.5 μm, wet screening is performed in ethanol using a 2 mm pore size sieve. After washing and vacuum drying, uncoated NdFeB particles are obtained. Step S2: The uncoated NdFeB particles are subjected to hydrogen annealing to obtain recycled NdFeB powder with an average particle size of 3 μm. 3 wt% of dispersant powder is added to the recycled NdFeB powder. The dispersant powder is composed of terbium aluminum copper alloy powder (Tb) with an average particle size of 2 μm. 70 Al 20 Cu 10 The mixture of cerium dioxide nanoparticles with an average particle size of 50 nm and cerium dioxide nanoparticles at a mass ratio of 20:1 was prepared and mixed evenly under argon protection to obtain a mixed powder. Step S3: The mixed powder is magnetically oriented and pressed under nitrogen protection to obtain a pressed blank. The pressed blank is then sintered in a vacuum environment at 1080℃ for 4 hours to obtain a sintered magnet. Under nitrogen protection, the sintered magnet is subjected to gradient diffusion treatment: first, it is held at 800℃ for 3 hours, then cooled to 600℃ at a cooling rate of 10℃ / min and held for 1.5 hours, and finally aged at 480℃ for 1 hour. After cooling to room temperature, a neodymium iron boron regenerated magnet is obtained.

[0018] Example 2 This embodiment provides a neodymium iron boron regenerated magnet, which is prepared by the following method: Step S1: The NdFeB waste containing metal coating after washing and degreasing is mechanically crushed to obtain waste particles with an average particle size of 4 mm. The waste particles are added to an acidic BMIC-AlCl3 ionic liquid with a molar ratio of 1-butyl-3-methylimidazolium chloride and aluminum trichloride of 1:2. Under ultrasonic stirring, the acidic BMIC-AlCl3 ionic liquid without waste particles is microwaved at a frequency of 2.4 GHz and a power of 800 W for 13 min. After filtration through a filter with a pore size of 0.5 μm, wet screening in ethanol using a 3 mm pore size sieve, washing, and vacuum drying, uncoated NdFeB particles are obtained. Step S2: The uncoated NdFeB particles are subjected to hydrogen annealing to obtain recycled NdFeB powder with an average particle size of 3 μm. 4 wt% of dispersant powder is added to the recycled NdFeB powder. The dispersant powder is composed of terbium aluminum copper alloy powder (Tb) with an average particle size of 2 μm. 70 Al 20Cu 10 The mixture of cerium dioxide nanoparticles with an average particle size of 50 nm and cerium dioxide nanoparticles at a mass ratio of 20:1 was prepared and mixed evenly under argon protection to obtain a mixed powder. Step S3: The mixed powder is magnetically oriented and pressed under nitrogen protection to obtain a pressed blank. The pressed blank is then sintered in a vacuum environment at 1080℃ for 4 hours to obtain a sintered magnet. Under nitrogen protection, the sintered magnet is subjected to gradient diffusion treatment: first, it is held at 800℃ for 3 hours, then cooled to 600℃ at a cooling rate of 10℃ / min and held for 1.5 hours, and finally aged at 490℃ for 1 hour. After cooling to room temperature, a neodymium iron boron regenerated magnet is obtained.

[0019] Example 3 This embodiment provides a neodymium iron boron regenerated magnet, which is prepared by the following method: Step S1: The NdFeB waste containing metal coating after washing and degreasing is mechanically crushed to obtain waste particles with an average particle size of 5 mm. The waste particles are added to an acidic BMIC-AlCl3 ionic liquid with a molar ratio of 1-butyl-3-methylimidazolium chloride and aluminum trichloride of 1:2. Under ultrasonic stirring, the acidic BMIC-AlCl3 ionic liquid without waste particles is microwaved at a frequency of 2.4 GHz and a power of 800 W for 15 min. After filtration through a filter with a pore size of 0.5 μm, wet screening is performed in ethanol using a 3 mm pore size sieve. After washing and vacuum drying, uncoated NdFeB particles are obtained. Step S2: The uncoated NdFeB particles are subjected to hydrogen pulverization to obtain recycled NdFeB powder with an average particle size of 3 μm. 5 wt% of dispersant powder is added to the recycled NdFeB powder. The dispersant powder is composed of terbium aluminum copper alloy powder (Tb) with an average particle size of 2 μm. 70 Al 20 Cu 10 The mixture of cerium dioxide nanoparticles with an average particle size of 50 nm and cerium dioxide nanoparticles at a mass ratio of 20:1 was prepared and mixed evenly under argon protection to obtain a mixed powder. Step S3: The mixed powder is magnetically oriented and pressed under nitrogen protection to obtain a pressed blank. The pressed blank is then sintered in a vacuum environment at 1080℃ for 4 hours to obtain a sintered magnet. Under nitrogen protection, the sintered magnet is subjected to gradient diffusion treatment: first, it is held at 800℃ for 3 hours, then cooled to 600℃ at a cooling rate of 10℃ / min and held for 1.5 hours, and finally aged at 500℃ for 1 hour. After cooling to room temperature, a neodymium iron boron regenerated magnet is obtained.

[0020] Comparative Example 1 The difference between this comparative example and Example 3 is that, in step S1, an equal amount of nitric acid solution with a pH of 2 was used to replace the acidic BMIC-AlCl3 ionic liquid, and the treatment time was the same. All other raw materials and steps were the same.

[0021] Comparative Example 2 The difference between this comparative example and Example 3 is that microwave treatment is not performed in step S1. Instead, the waste particles are added to the acidic BMIC-AlCl3 ionic liquid and ultrasonically stirred for the same amount of time. All other raw materials and steps are the same.

[0022] Comparative Example 3 The difference between this comparative example and Example 3 is that the sintered magnet was subjected to diffusion treatment at 800°C for 5 hours in step S3, while the other raw materials and steps are the same.

[0023] The performance of the neodymium iron boron regenerated magnets prepared in Examples 1-3 and Comparative Examples 1-3 was tested. The magnetic properties of the neodymium iron boron regenerated magnets were tested according to GB / T 3217-2013 standard, and the results are shown in Table 1. Table 1 project Example 1 Example 2 Example 3 Comparative Example 1 Comparative Example 2 Comparative Example 3 Remanence Br / kGs 13.1 13.3 13.5 12.1 12.6 12.9 Coercivity Hcj / kOe 17.8 18.3 18.8 14.5 15.2 17.4 <![CDATA[Maximum magnetic energy product (BH) max / MGOe]]> 44.3 45.1 45.9 36.8 37.5 40.1 As can be seen from the data in Table 1, the neodymium iron boron regenerated magnets prepared in Examples 1-3 have Br > 13 kGs, Hcj > 17.5 kOe, and (BH) max With a molecular weight >44 MGOe, it exhibits superior magnetic properties; Comparative Example 1 uses nitric acid solution instead of acidic ionic liquid, which causes corrosion of the waste NdFeB substrate, increases oxygen content, and leaves metal coating residue, resulting in a significant decrease in the magnetic properties of the regenerated magnet; Comparative Example 2 does not use microwave treatment, resulting in a large amount of metal coating residue, which leads to a significant decrease in magnetic properties; Comparative Example 3 uses isothermal diffusion treatment, which causes Tb over-diffusion to form an anomalous core-shell, resulting in the regenerated magnet's performance being inferior to that of gradient diffusion treatment.

[0024] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.

[0025] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a neodymium iron boron regenerated magnet, characterized in that, Includes the following steps: Step S1: The NdFeB waste containing metal coating after washing and degreasing is mechanically crushed to obtain waste particles with an average particle size of 3-5 mm. The waste particles are added to acidic BMIC-AlCl3 ionic liquid. The acidic BMIC-AlCl3 ionic liquid without waste particles is microwave-treated under ultrasonic stirring. After filtration, wet screening, washing and vacuum drying, uncoated NdFeB particles are obtained. Step S2: The uncoated NdFeB particles are subjected to hydrogen crushing to obtain regenerated NdFeB powder with an average particle size of 3μm. Dispersant powder is added to the regenerated NdFeB powder and mixed evenly under argon protection to obtain mixed powder. Step S3: The mixed powder is magnetically oriented and pressed under nitrogen protection to obtain a pressed blank. Then, the pressed blank is sintered in a vacuum environment to obtain a sintered magnet. The sintered magnet is then subjected to gradient diffusion treatment and aging treatment under nitrogen protection. After cooling to room temperature, a neodymium iron boron regenerated magnet is obtained.

2. The method for preparing a neodymium iron boron regenerated magnet according to claim 1, characterized in that, The molar ratio of 1-butyl-3-methylimidazolium chloride to aluminum trichloride in the acidic BMIC-AlCl3 ionic liquid is 1:

2.

3. The method for preparing a neodymium iron boron regenerated magnet according to claim 1, characterized in that, The microwave processing frequency is 2.4 GHz, the microwave processing power is 800 W, and the microwave processing time is 10-15 min.

4. The method for preparing a neodymium iron boron regenerated magnet according to claim 1, characterized in that, The filter element used for filtration has a pore size of 0.5 μm; the liquid used for wet sieving is ethanol, and the sieve mesh size is 2-3 mm.

5. The method for preparing a neodymium iron boron regenerated magnet according to claim 1, characterized in that, The amount of the dispersant powder is 3-5% of the mass of the recycled NdFeB powder; the dispersant powder is composed of terbium aluminum copper alloy powder with an average particle size of 2μm and cerium dioxide nanoparticles with an average particle size of 50nm mixed at a mass ratio of 20:

1.

6. The method for preparing a neodymium iron boron regenerated magnet according to claim 5, characterized in that, The composition of the terbium-aluminum-copper alloy powder by weight percentage is: terbium 70%, aluminum 20%, and copper 10%.

7. The method for preparing a neodymium iron boron regenerated magnet according to claim 1, characterized in that, The sintering temperature is 1080℃ and the sintering time is 4 hours.

8. The method for preparing a neodymium iron boron regenerated magnet according to claim 1, characterized in that, The gradient diffusion process is as follows: first, the temperature is kept at 800℃ for 3 hours, and then the temperature is lowered to 600℃ at a rate of 10℃ / min and kept at that temperature for 1.5 hours.

9. The method for preparing a neodymium iron boron regenerated magnet according to claim 1, characterized in that, The aging treatment temperature is 480-500℃, and the aging treatment time is 1 hour.

10. A neodymium iron boron regenerated magnet, characterized in that, Prepared by the method according to any one of claims 1-9.