Powder pretreatment process for preparing magnet

Abstract

The invention relates to the field of magnet material treatment, and discloses a powder pretreatment process for preparing magnets, which comprises the following steps: S1, carrying out plasma surface activation pretreatment on the surface of alloy powder; s2, a solvent is added into a double-layer jacket reaction kettle, stirring is started, a coating material is slowly added, and an ultrasonic-assisted system is started; s3, pretreatment in a reaction kettle; s4, starting a spiral feeding system, continuously introducing nitrogen to maintain an inert environment, starting and continuously operating an electrostatic elimination device, and carrying out multi-field synergistic mixed coating; s5, microwave-assisted drying; s6, recovering the coating material; s7, powder post-treatment; according to the powder pretreatment process for preparing the magnet, coating treatment on the alloy powder can be achieved, the problem that the final magnetic performance is affected due to the fact that the powder makes contact with air and is prone to oxidation is solved, the binding force of a coating material and the powder is high, and the powder dispersion uniformity is good.

Description

Technical Field

[0001] The present invention relates to the field of magnet material processing, and more particularly to a powder pre-treatment process for preparing magnets. Background Art

[0002] There are many alloys used to make magnets, such as neodymium iron boron, samarium cobalt iron, iron silicon, iron silicon chromium, and iron silicon aluminum. The current process for making magnets is to first prepare the alloy powder, then press it into shape according to the required shape, and then sinter, machine, and magnetize it to produce the desired magnet.

[0003] After alloy powder is prepared, it needs to be treated to prevent contact with air and oxidation. The current treatment process generally uses inert gas protection, chemical coating or surface passivation. These existing treatment processes are not effective in preventing oxidation and nitriding. Summary of the Invention

[0004] In order to solve the above technical problems, the present invention provides a powder pretreatment process for preparing magnets.

[0005] The present invention provides a powder pretreatment process for preparing magnets, comprising the following steps: S1: Plasma surface activation pretreatment is performed on the surface of the alloy powder.

[0006] S2: Add heat transfer oil to the double-layer jacketed reactor, set the first stage temperature to 40-50°C, start stirring and slowly add the coating material, turn on the ultrasonic auxiliary system, raise the temperature to 60-70°C and mix thoroughly.

[0007] Preferably, the coating material is one or more of wax, oil, and solvent.

[0008] Solvents include: Alkanes: n-hexane, n-heptane.

[0009] Oil includes: kerosene, diesel, gasoline, and mineral oil.

[0010] Waxes include: paraffin wax, carnauba wax, Fischer-Tropsch wax, and polyethylene wax.

[0011] S3: reactor pretreatment; The reactor was evacuated to -0.08 MPa, and high-purity nitrogen was introduced for replacement 3-5 times to maintain a slightly positive pressure (0.02-0.05 MPa). The electric field gradient system was started and the electrode voltage was adjusted.

[0012] S4: Start the spiral feeding system, control the feeding rate to 0.5-1kg / min, continuously introduce nitrogen to maintain an inert environment, start and continuously operate the static elimination device, and perform multi-field synergistic mixing and coating.

[0013] Preferably, the multi-field synergistic hybrid coating is specifically as follows: starting the acoustic field-magnetic field system on the reactor, with a magnetic field intensity of 0.1-0.5T, a frequency of 50-100Hz, an acoustic field power of 200-400W, and a frequency of 15-25kHz; The electric field gradient system controls the electric field strength from 0.5 to 2 kV / cm and dynamically adjusts the electric field direction, changing it every 5 minutes. And inject supercritical fluid into the reactor: inject supercritical CO2, control the pressure at 7.5-10MPa, maintain the temperature at 35-45℃, and last for 15-20 minutes.

[0014] S5: microwave-assisted drying; Start the directional microwave system (2.45GHz) with a power of 200-500W and adjust the power in stages.

[0015] S6: Recycling of coating materials; The vacuum system (-0.095 MPa) was turned on, and the coating material was recovered by graded condensation (three levels: 15°C, 5°C, and -5°C). The recovered coating material was filtered and purified online, and the vacuum extraction rate was controlled.

[0016] S7: powder post-processing; The mixture was slowly cooled to room temperature, vacuumed to remove all residual coating materials, and the powder was taken out under nitrogen protection and sealed.

[0017] Preferably, in step S1, the alloy powder is placed in a vacuum reaction chamber, evacuated to 50-100 Pa, high-purity argon gas is introduced, and the plasma generator is activated, with the power set at 300-500 W, and the plasma discharge is maintained for 3-5 minutes. During the plasma bombardment process, the powder surface is gradually cleaned and a nanoscale rough structure is formed. The treated powder has a higher surface activity, which is beneficial for the subsequent coating reaction. This method can significantly improve the bonding strength between the powder and the coating material and reduce powder flaking during subsequent processing.

[0018] Preferably, in step S2, heat transfer oil is introduced into the double-jacketed reactor, the temperature is controlled at 40-50°C with a temperature control accuracy of ±1°C, stirring is started at a speed of 200-300 rpm, and the temperature is maintained for 5-10 minutes to reach a stable temperature.

[0019] Preferably, in step S2, the coating material is slowly added according to the metered amount at a rate of 0.5-1 kg / min, while continuous stirring is maintained and the dissolution state is observed.

[0020] Preferably, in step S2, the frequency of the ultrasonic auxiliary system is set to 20-40kHz, and the power density is 0.3-0.5W / cm 3, intermittent ultrasound, working for 15 minutes and stopping for 5 minutes, the total processing time is 30-45 minutes.

[0021] Preferably, in step S2, the heat transfer oil is heated to 60-70°C at a heating rate of 2-3°C / min, and maintained at this temperature for 15-20 minutes to ensure thorough mixing.

[0022] Preferably, in step S3, the reactor is first closed, the vacuum system is started, and the vacuum pressure is evacuated to -0.08 MPa, maintained for 10 minutes, and then nitrogen is introduced for replacement 3-5 times, each time for 5 minutes.

[0023] Preferably: the acoustic field-magnetic field system includes an electromagnet arranged in the reactor and an ultrasonic transducer arranged on the reactor; The electromagnet generates a magnetic field of 0.1-0.5T and a frequency controlled at 50-100Hz, which can effectively act on micron-sized powders. The acoustic power of the ultrasonic transducer is 200-400W, and the sound wave frequency is controlled at 15-25kHz, which matches the magnetic field frequency. The synergistic effect of the acoustic and magnetic fields can significantly improve the dispersion of the powder.

[0024] Preferably, the electric field gradient system includes an annular electrode array arranged on the wall of the reactor. The electric field strength of the annular electrode array is controlled at 0.5-2 kV / cm. By dynamically adjusting the electrode voltage, the direction of the electric field is changed every 5 minutes. The electric field force and the acoustic magnetic field work together to align the powder particles.

[0025] Dynamically adjusting the electric field direction prevents powder aggregation under a single electric field orientation. Changing the electric field direction every five minutes allows the charged powder particles to redisperse and align under the action of the changing electric field force. Magnetic powders align along the magnetic field in a magnetic field, and the synergistic effect of the electric field gradient and the acoustic field maintains powder orientation while preventing agglomeration, ultimately forming a uniform and ordered microstructure that improves the magnet's magnetic properties.

[0026] The beneficial effects of the present invention are as follows: the powder pretreatment process for preparing magnets proposed in the present invention can realize coating treatment of alloy powder, avoiding the problem that the powder is easily oxidized when in contact with air, which affects the final magnetic properties. The coating material has a strong bonding force with the powder, and the powder is well dispersed.

[0027] Through multi-field coupling, a unique ordered microstructure is formed: the synergy of acoustic and magnetic fields significantly improves powder dispersibility. The electric field gradient and supercritical fluid work together to achieve nanoscale coating uniformity, significantly enhancing magnetic properties.

[0028] Significantly improved coating adhesion and oxidation resistance: Plasma pretreatment increases powder surface activity. The optimized coating has excellent adhesion and is less likely to fall off during subsequent processing. It also improves oxidation resistance. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 is a screenshot of Table 1 in Example 2 of the present invention; Figure 2 is a screenshot of Table 2 in Example 3 of the present invention; Figure 3 This is a screenshot of Table 3 in Example 4 of the present invention; Figure 4 is a screenshot of Table 4 in Example 5 of the present invention; Figure 5 is a screenshot of Table 5 in Example 6 of the present invention; Figure 6 This is a screenshot of Table 6 in Example 7 of the present invention. DETAILED DESCRIPTION

[0030] The subject matter described herein will now be discussed with reference to exemplary embodiments. It should be understood that these embodiments are discussed solely to enable those skilled in the art to better understand and implement the subject matter described herein, and that the functions and arrangements of the elements discussed may be varied without departing from the scope of this specification. Various examples may omit, substitute, or add various processes or components as needed. In addition, features described with respect to some examples may also be combined in other examples.

[0031] Example 1 In this embodiment, a powder pretreatment process for preparing magnets is proposed, comprising the following steps: S1: Plasma surface activation pretreatment of the alloy powder surface; Specifically: The alloy powder is loaded into a vacuum reaction chamber and evacuated to 50Pa, 80Pa, or 100Pa. In the present embodiment, the pressure is evacuated to 80Pa. Then, high-purity argon gas is introduced, and the plasma generator is started. The power is set at 300W, 400W, or 500W. In the present embodiment, the power is set at 400W. The plasma discharge is maintained for 3 minutes, 4 minutes, or 5 minutes. In the present embodiment, the plasma discharge is maintained for 3 minutes.

[0032] S2: Add heat transfer oil to the double-jacketed reactor, set the first stage temperature to 40°C, 45°C, or 50°C, start stirring and slowly add the coating material, turn on the ultrasonic auxiliary system, raise the temperature to 60°C, 65°C, or 70°C for thorough mixing; Specifically, heat transfer oil is introduced into the double-jacketed reactor, the temperature is controlled at 40°C, 45°C or 50°C, and in this embodiment, the temperature is controlled at 45°C with a temperature control accuracy of ±1°C, stirring is started, the speed is 200 rpm, 250 rpm or 300 rpm, and in this embodiment, the speed is 250 rpm, and the temperature is maintained for 5, 7 or 10 minutes to reach a stable temperature, and in this embodiment, the temperature is maintained for 5 minutes; Slowly add the coating material according to the metered amount at a rate of 0.5 kg / min, 0.7 kg / min, or 1 kg / min. In this embodiment, the rate is 0.7 kg / min. Keep stirring and observe the dissolution state. The frequency of the ultrasonic auxiliary system is set to 20kHz, 30kHz or 40kHz. In this embodiment, the frequency is set to 30kHz and the power density is 0.3W / cm 3 or 0.4W / cm 3 or 0.5W / cm 3 In this embodiment, the power density is 0.5W / cm 3 , intermittent ultrasound, working for 15 minutes and stopping for 5 minutes, the total treatment time is 30 or 40 or 45 minutes, and the total treatment time in this embodiment is 40 minutes; The heat transfer oil is heated to 60°C, 65°C or 70°C. In this embodiment, the heat transfer oil is heated to 65°C at a heating rate of 2°C / min, 2.5°C / min or 3°C / min. In this embodiment, the heating rate is 2.5°C / min. The temperature is maintained for 15 minutes, 18 minutes or 20 minutes. In this embodiment, the temperature is maintained for 18 minutes to ensure sufficient mixing.

[0033] The coating material is one or more of wax, oil, and solvent. In this embodiment, the coating material is a mixture of wax, oil, and solvent.

[0034] The solvent includes alkanes; in this embodiment, the alkanes are n-hexane and n-heptane.

[0035] Oil includes: kerosene, diesel, gasoline, and mineral oil.

[0036] Waxes include: paraffin wax, carnauba wax, Fischer-Tropsch wax, and polyethylene wax.

[0037] S3: reactor pretreatment; First, the reactor was closed and the vacuum system was started. The reactor was evacuated to -0.08 MPa and maintained for 10 minutes. High-purity nitrogen was introduced for replacement 3, 4, or 5 times. In this embodiment, high-purity nitrogen was introduced for replacement 4 times, each time for 5 minutes, maintaining a slightly positive pressure (0.02-0.05 MPa). The electric field gradient system was started and the electrode voltage was adjusted.

[0038] S4: Start the spiral feeding system and control the feeding rate to 0.5 kg / min, 0.75 kg / min or 1 kg / min. In this embodiment, the feeding rate is controlled to 0.75 kg / min. Nitrogen is continuously introduced to maintain an inert environment. The static elimination device is started and continuously operated for multi-field synergistic mixing and coating.

[0039] The multi-field synergistic hybrid coating is specifically as follows: starting the acoustic field-magnetic field system on the reactor, with a magnetic field intensity of 0.1T, 0.3T, or 0.5T, and in this embodiment, the magnetic field intensity is 0.3T, a frequency of 50Hz, 75Hz, or 100Hz, and in this embodiment, the frequency is 75Hz, an acoustic field power of 200W, 300W, or 400W, and in this embodiment, the acoustic field power is 300W, and a frequency of 15kHz, 20kHz, or 25kHz, and in this embodiment, the frequency is 20kHz; The electric field gradient system controls the electric field strength to 0.5 kV / cm, 1 kV / cm, or 2 kV / cm. In this embodiment, the electric field strength is 1 kV / cm. The electric field direction is dynamically adjusted, changing the electric field direction every 5 minutes. And inject supercritical fluid into the reactor: inject supercritical CO2, the pressure is controlled at 7.5MPa or 9MPa or 10MPa, and in this embodiment the pressure is controlled at 9MPa; the temperature is maintained at 35°C or 40°C or 45°C, and in this embodiment the temperature is maintained at 40°C; the duration is 15 minutes or 18 minutes or 20 minutes, and in this embodiment the duration is 18 minutes.

[0040] in: The acoustic field-magnetic field system includes an electromagnet arranged in the reactor and an ultrasonic transducer arranged on the reactor; The electromagnet generates a magnetic field of 0.1T, 0.3T, or 0.5T, and in this embodiment, the magnetic field strength is 0.3T; the frequency is controlled at 50Hz, 75Hz, or 100Hz, and in this embodiment, the frequency is 75Hz, which can effectively act on micron-sized powders; the sound power of the ultrasonic transducer is 200W, 300W, or 400W, and in this embodiment, the sound field power is 300W; the sound wave frequency is controlled at 5kHz, 20kHz, or 25kHz, and in this embodiment, the frequency is 20kHz, which matches the magnetic field frequency. The synergistic effect of the acoustic and magnetic fields can significantly improve the dispersibility of the powder.

[0041] The electric field gradient system includes a ring electrode array arranged on the wall of the reactor. The electric field strength of the ring electrode array is controlled at 0.5kV / cm, 1kV / cm, or 2kV / cm. In this embodiment, the electric field strength is 1kV / cm. By dynamically adjusting the electrode voltage, the direction of the electric field is changed every 5 minutes. The electric field force works together with the acoustic magnetic field to align the powder particles.

[0042] S5: microwave-assisted drying; Start the directional microwave system (2.45GHz) with a power of 200-500W, and adjust the power in stages; S6: Recycling of coating materials; The vacuum system (-0.095 MPa) was turned on, and the recovery was carried out by graded condensation (three levels: 15°C, 5°C, and -5°C). The recovered solvent was filtered and purified online, and the vacuum extraction rate was controlled.

[0043] S7: powder post-processing; The mixture was slowly cooled to room temperature, vacuumed to remove all residual coating materials, and the powder was taken out under nitrogen protection and sealed.

[0044] Example 2 This example is used to study the effect of acoustic magnetic field synergy on powder dispersibility Experimental content: 1. Sample preparation: Take equal amounts (500g) of NdFeB powder and divide them into four groups. The coating material is a mixture of wax, oil, and solvent in a ratio of 1:1:1. The coating material usage is 2% of the powder mass. Group A: no field treatment; Group B: sound field processing only (20kHz, 300W); Group C: magnetic field treatment only (0.3 T, 75 Hz); Group D: Acousto-magnetic field coordinated processing (parameters are the same as in Example 1).

[0045] 2. Processing conditions: Processing time: 20 minutes; Temperature: The first stage temperature is 45°C, start stirring and slowly add the coating material, turn on the ultrasonic auxiliary system, and then raise the temperature to 65°C; Nitrogen protection; Stirring speed: 250rpm.

[0046] 3. Test method: Laser particle size analysis; Calculation of agglomeration coefficient.

[0047] 4. Experimental results: See attached Figure 1 Table 1 in .

[0048] 5. Result analysis: The D50 value of group D was the lowest, indicating that the synergistic treatment of the acoustic and magnetic fields was the most effective. The aggregation coefficient = (D90-D10) / D50, with group D having the lowest value, indicates the most uniform dispersion.

[0049] Example 3 This example is used to study the synergistic effect of electric field gradient and supercritical fluid on coating uniformity.

[0050] Experimental content: 1. Sample preparation: 500 g of the NdFeB alloy powder treated in step S1 of Example 1 were divided into four groups; Group A: conventional covering; Group B: electric field gradient treatment (1 kV / cm); Group C: supercritical CO2 treatment (8.5MPa, 40℃); Group D: Electric field + supercritical synergistic treatment.

[0051] 2. Processing conditions: The coating material is paraffin wax, and the amount is 2% of the mass of NdFeB powder; Processing time: 15 minutes; The direction of the electric field changes every 5 minutes.

[0052] 3. Test method: Observe the coating thickness; Coverage calculation.

[0053] 4. Experimental results: See attached Figure 2 Table 2 in .

[0054] 5. Result analysis: The coating layer of group D was the thinnest and most uniform, with the smallest standard deviation; the coverage rate was significantly improved, reaching 98.5%.

[0055] Example 4 This study was used to investigate the effect of microstructure on magnetic properties.

[0056] Experimental content: 1. Sample preparation: The four groups of samples that had undergone different coating treatments in Example 3 were pressed into φ10×10 mm samples using an axial press with a pressure of 200 MPa and a holding time of 10 minutes.

[0057] Sintering temperature: 1080℃.

[0058] Holding time: 2h.

[0059] 2. Test method: VSM tests magnetic properties; XRD analysis of grain orientation; Coercivity test.

[0060] 3. Experimental results: See attached Figure 3 Table 3 in .

[0061] 4. Result analysis: The magnetic properties of samples in group D were comprehensively improved, with the degree of orientation increasing by 11 percentage points and the coercive force increasing by 21.6%.

[0062] Example 5 This example is used to study the effect of plasma treatment on the surface activity of powders.

[0063] Experimental content: 1. Sample preparation: Take 500g of NdFeB powder and divide it into 4 groups; Group A: untreated; Group B: plasma treatment (60 Pa, 350 W, 3 min); Group C: plasma treatment (60 Pa, 350 W, 5 min); Group D: plasma treatment (60Pa, 350W, 7min).

[0064] 2. Test method: XPS analysis of surface chemical state; Contact angle test; AFM surface morphology analysis; Surface energy calculation.

[0065] 3. Experimental results: See attached Figure 4 Table 4 in .

[0066] 4. Result analysis: The optimal treatment time is 5 minutes, and the effect of extending the treatment time is not obvious; the surface energy is significantly improved, which is beneficial for subsequent coating; the surface roughness is increased, providing more binding sites.

[0067] Example 6 This embodiment is used to test the bonding strength of the coating layer.

[0068] Experimental content: 1. Sample preparation: The four groups of samples in Example 5 were treated with the complete coating process from S2 to S7 in Example 1, wherein the coating material was paraffin wax in an amount of 2% of the powder mass; Coating temperature: The first stage temperature is 45°C, start stirring and slowly add the coating material, turn on the ultrasonic auxiliary system, and then raise the temperature to 65°C; Processing time: 20 minutes.

[0069] 2. Test method: Ultrasonic peel test (40kHz, 500W); Thermal cycle test (25-80℃, 100 times); Mechanical wear test.

[0070] 3. Experimental results: See attached Figure 5 Table 5 in .

[0071] 4. Result analysis: After plasma treatment, the stripping rate is significantly reduced; the coating stability is optimal under 5 minutes of treatment time; and the mechanical wear resistance is significantly improved.

[0072] Example 7 This example is used to evaluate the antioxidant properties of the sample that has been coated according to Example 6.

[0073] Experimental content: 1. Accelerated oxidation test: Place the sample in an 80°C / 85%RH environment; Test time: 0h, 24h, 48h, 72h; Sampling and analysis were performed every 12 hours.

[0074] 2. Test method: TG-DTA thermal analysis; XRD phase analysis; Magnetic property decay measurement.

[0075] 3. Experimental results: See attached Figure 6 Table 6 in .

[0076] 4. Results Analysis The oxidation rate of the treated sample was significantly reduced, and the oxidation weight gain after 72 hours was only 23.7% of that of the untreated sample, and the magnetic property degradation was effectively inhibited.

[0077] The above describes an embodiment of the present invention, but this embodiment is not limited to the above-mentioned specific implementation methods. The above-mentioned specific implementation methods are merely illustrative and not restrictive. Ordinary technicians in this field can also make many forms based on the inspiration of this embodiment, all of which are protected by this embodiment.

Claims

1. A powder pretreatment process for preparing magnets, characterized in that: The steps include: S1: Plasma surface activation pretreatment of the alloy powder surface; S2: Add heat transfer oil to the double-jacketed reactor, set the first stage temperature to 40-50°C, start stirring and slowly add the coating material, turn on the ultrasonic auxiliary system, raise the temperature to 60-70°C and mix thoroughly; S3: reactor pretreatment; The reactor was evacuated to -0.08 MPa, and high-purity nitrogen was introduced for replacement 3-5 times to maintain a slightly positive pressure. The electric field gradient system was started and the electrode voltage was adjusted. S4: Start the spiral feeding system, control the feeding rate to 0.5-1kg / min, continuously introduce nitrogen to maintain an inert environment, start and continuously operate the static elimination device, and perform multi-field synergistic mixing and coating; S5: microwave-assisted drying; Start the directional microwave system with a power of 200-500W and adjust the power in stages; S6: Recycling of coating materials; Start the vacuum system, perform graded condensation to recover the coating material, perform online filtration and purification of the recovered coating material, and control the vacuum extraction rate; S7: powder post-processing; The mixture was slowly cooled to room temperature, vacuumed to remove all residual coating materials, and the powder was taken out under nitrogen protection and sealed.

2. A powder pretreatment process for preparing magnets according to claim 1, characterized in that: In step S1, the alloy powder is loaded into a vacuum reaction chamber, evacuated to 50-100 Pa, high-purity argon gas is introduced, the plasma generator is started, the power is set at 300-500 W, and the plasma discharge is maintained for 3-5 minutes.

3. A powder pretreatment process for preparing magnets according to claim 1, characterized in that: The coating material is one or more of wax, oil and solvent.

4. A powder pretreatment process for preparing magnets according to claim 1, characterized in that: In step S2, heat transfer oil is introduced into the double-jacketed reactor, the temperature is controlled at 40-50°C with a temperature control accuracy of ±1°C, stirring is started, the rotation speed is 200-300 rpm, and the temperature is maintained for 5-10 minutes to reach a stable temperature.

5. A powder pretreatment process for preparing magnets according to claim 4, characterized in that: In step S2, the frequency of the ultrasonic auxiliary system is set to 20-40kHz and the power density is 0.3-0.5W / cm 3 , intermittent ultrasound, working for 15 minutes and stopping for 5 minutes, the total processing time is 30-45 minutes.

6. A powder pretreatment process for preparing magnets according to claim 5, characterized in that: In step S2, the heat transfer oil is heated to 60-70°C at a heating rate of 2-3°C / min and maintained at this temperature for 15-20 minutes to ensure thorough mixing.

7. A powder pretreatment process for preparing magnets according to claim 1, characterized in that: In step S3, the reactor is first closed, the vacuum system is started, and the vacuum pressure is evacuated to -0.08 MPa, maintained for 10 minutes, and then nitrogen is introduced for replacement 3-5 times, each time for 5 minutes.

8. A powder pretreatment process for preparing magnets according to claim 7, characterized in that: In step S4, the multi-field synergistic hybrid coating is specifically as follows: starting the acoustic field-magnetic field system on the reactor, with a magnetic field intensity of 0.1-0.5T, a frequency of 50-100Hz, an acoustic field power of 200-400W, and a frequency of 15-25kHz; The electric field gradient system controls the electric field strength from 0.5 to 2 kV / cm and dynamically adjusts the electric field direction, changing it every 5 minutes. And inject supercritical fluid into the reactor: inject supercritical CO2, control the pressure at 7.5-10MPa, maintain the temperature at 35-45℃, and last for 15-20 minutes.

9. A powder pretreatment process for preparing magnets according to claim 8, characterized in that: The acoustic field-magnetic field system includes an electromagnet arranged in the reactor and an ultrasonic transducer arranged on the reactor; The electromagnet generates a magnetic field of 0.1-0.5T and a frequency controlled at 50-100Hz, which can effectively act on micron-sized powders. The acoustic power of the ultrasonic transducer is 200-400W, and the sound wave frequency is controlled at 15-25kHz, which matches the magnetic field frequency. The synergistic effect of the acoustic and magnetic fields can significantly improve the dispersion of the powder.

10. A powder pretreatment process for preparing magnets according to claim 8, characterized in that: The electric field gradient system includes a ring electrode array set on the wall of the reactor. The electric field strength of the ring electrode array is controlled at 0.5-2kV / cm. By dynamically adjusting the electrode voltage, the direction of the electric field is changed every 5 minutes. The electric field force and the acoustic magnetic field work together to align the powder particles.

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