Ultralow-oxygen high-stability samarium-cobalt permanent magnet ultrafine powder, preparation method thereof and samarium-cobalt permanent magnet

Abstract

The invention discloses ultra-low-oxygen high-stability samarium-cobalt permanent magnet ultrafine powder, a preparation method thereof and a samarium-cobalt permanent magnet, and belongs to the technical field of permanent magnet materials.The preparation method comprises the steps that samarium-cobalt permanent magnet coarse powder is put into a sanding powder tank which has ultra-low water and oxygen content and is protected by inert gas, and then a dispersing agent and an organic solvent are added to be stirred and mixed to be uniform; and then introducing the samarium cobalt coarse powder in the powder into sanding equipment to obtain the samarium cobalt powder. The particle size of the samarium-cobalt permanent magnet material ultrafine powder can be stably kept at about 1 mu m, the oxygen content is within 10 ppm, the problem that the ultrafine powder is prone to oxidation, prone to combustion and difficult to transfer is solved by means of a sand grinding process in a vacuum glove box, and the particle size of the samarium-cobalt permanent magnet material is greatly reduced by means of a double-tank circulating sand grinding process. The acquisition rate of the samarium-cobalt permanent magnet material ultrafine powder and the uniform stability of the granularity of the ultrafine powder are improved; by adopting the ultrafine powder, a heterogeneous samarium-cobalt magnet with high mechanical property and low anisotropy can be prepared, so that the application range of the samarium-cobalt ultrafine powder is widened.

Description

Technical Field

[0001] The present invention relates to the technical field of permanent magnet materials, and particularly to an ultra-low oxygen and high-stability samarium cobalt permanent magnet ultrafine powder, a preparation method thereof, and a samarium cobalt permanent magnet prepared therefrom. Background Art

[0002] Samarium cobalt ultrafine powder is an important rare earth functional material, having advantages such as high magnetic energy product, good thermal stability, and corrosion resistance. The particle size of traditional samarium cobalt magnet powder is generally in the range of 3 - 5 μm. It is found through investigation that samarium cobalt permanent magnet ultrafine powder (<2 μm) has not been widely used because the preparation process and application technology of samarium cobalt permanent magnet ultrafine powder are not yet mature. However, some micro-devices with high performance requirements currently need ultrafine powder for preparation, so the application of ultrafine powder has broad application prospects in the future.

[0003] Currently, traditional rare earth permanent magnet powder preparation often uses jet mills and ball mills to prepare fine powder. Using the jet mill process, large quantities of rare earth permanent magnet powder can be prepared, but the powder particle size remains in the range of 3 - 5 μm, and at the same time, about 10% of the ultrafine powder with finer particle size (particle size in the range of 1.5 - 2.5) will be produced. These ultrafine powders have problems such as small quantity and high oxygen content, and are not suitable for special process preparation.

[0004] Currently, ball milling is commonly used to prepare ultrafine powder. Although the ball milling process can effectively reduce the particle size of the powder, since the particle size distribution of the ultrafine powder obtained by this process is relatively wide and the quantity obtained each time is small, it is only applied to the laboratory research stage. In addition, the current ball milling process also has the following disadvantages: the risk of oxidation of magnetic powder is relatively high, resulting in great instability and narrowness in the application of ultrafine powder.

[0005] Therefore, how to prepare samarium cobalt permanent magnet ultrafine powder with uniform particle size and ultra-low oxygen content, and its wide application prospect field have become technical problems to be overcome currently. Summary of the Invention

[0006] One of the purposes of the present invention is to provide a preparation method of an ultra-low oxygen and high-stability samarium cobalt permanent magnet ultrafine powder to solve the above problems.

[0007] To achieve the above purpose, the technical solution adopted by the present invention is as follows: A preparation method of an ultra-low oxygen and high-stability samarium cobalt permanent magnet ultrafine powder, comprising the following steps: Step 1: Put the samarium cobalt permanent magnet coarse powder into a sand milling powder tank with ultra-low water and oxygen content and protected by inert gas; Step 2: Then, a dispersant is added at 0.5-1.5% of the mass of the coarse powder. The purpose of adding the dispersant is to prevent cold welding agglomeration and coarsening of the ultrafine powder. If the addition amount of the dispersant is too small, it cannot achieve the effect of dispersing the ultrafine powder particles, and if it is too much, it is easy to cause oxidation of the ultrafine powder during the subsequent heat treatment process. Step 3: Then, an organic solvent is added and stirred evenly. The purpose of adding the solvent is to enable the dispersant to better wrap the ultrafine powder and make the powder enter the subsequent sand mill more evenly. Step 4: The samarium-cobalt coarse powder in the powder tank (the coarse powder is first placed in the powder tank and then transported to the sand mill through a pipeline using an organic solvent to collide and break with the grinding balls) is introduced into the sand grinding equipment, and ultrafine powder is prepared through different processes (sand grinding time).

[0008] As a preferred technical solution, in Step 1, the coarse powder is placed in the sand grinding powder tank through a vacuum glove box. The water and oxygen content in the vacuum glove box is less than 10 ppm, the inert gas is argon, and the purity of the argon is ≥99.99%. The purpose of using the vacuum glove box is to provide an ultra-low oxygen environment for the powder transportation to prevent oxidation of the ultrafine powder during the transportation process.

[0009] As a preferred technical solution, in Step 2, the dispersant is selected from at least one of oleylamine, oleic acid, and kerosene, and the addition amount of the dispersant is 1% of the mass of the coarse powder.

[0010] As a preferred technical solution, in Step 3, the organic solvent is selected from at least one of n-heptane, petroleum ether, ethanol, and water, and the addition amount of the organic solvent is 2-3 times the volume of the coarse powder.

[0011] As a preferred technical solution, in Step 4, the sand grinding equipment includes two independent vacuum glove boxes. At least one powder tank is arranged in one of the vacuum glove boxes, a stirrer is arranged in the powder tank, a sand grinding chamber is arranged in the other vacuum glove box, and the outlet and inlet of the powder tank are respectively communicated with the sand grinding chamber through a powder fluid inlet and outlet pipeline.

[0012] More preferably, two powder tanks are provided, namely powder tank A and powder tank B, to form a double-tank circulation system.

[0013] When single-tank circulation is selected, the coarse powder material enters the grinding chamber of the sand mill from tank A (B) through a pipeline. After being ground, the powder material returns to tank A (B), and the coarse powder is repeatedly ground in this way. One of the disadvantages is that some coarse powder materials are prone to staying in the pipeline all the time, resulting in insufficient grinding of the powder material, and then leading to very poor and unstable particle size uniformity of the final obtained powder material. For double-tank circulation, the coarse powder material goes from tank A to the grinding chamber, and after being ground, it enters tank B. After all the powder material in tank A has been ground and entered tank B, it goes in the reverse direction, and the powder material in tank B is ground and then enters tank A, and repeated grinding is carried out in this way. The double-tank circulation system can fully make the powder material pass through the grinding chamber, achieving a very good grinding effect. Finally, the particle size of the ultrafine powder is relatively fine, about 1 μm, and the uniformity and stability of the powder material are relatively good, which can also be seen from Figure 3 the particle size test result diagram of

[0014] More preferably, the sand mill includes a grinding chamber box body, a grinding cylinder and a support frame. Considering that the grinding cylinder has a certain weight during the disassembly and assembly process, in order to reduce the labor intensity of the operator, an auxiliary support frame for the grinding cylinder is designed. The purpose of this setting is to facilitate the disassembly and assembly of the grinding cylinder in the glove box, and always ensure that the sand mill equipment operates and runs under low oxygen.

[0015] The innovations of the above-mentioned sand mill equipment include: placing the powder tank and the grinding chamber in the glove box, which helps to ensure the low-oxygen process during the operation of the sand mill and the process of powder material entering and leaving. At the same time, the newly added stirrer can promote the full mixing of the powder material with the dispersant and the organic solvent, which helps the powder material to evenly enter the grinding chamber and improves the grinding efficiency.

[0016] As a preferred technical solution, in step 4, the grinding media balls of the sand mill are zirconia balls, the diameter range of the grinding media balls is 0.6 - 0.8 mm, the rotation speed of the sand mill is 1800 - 2500 r / min, the grinding time is 1 - 100 h, and more preferably 10 - 100 h.

[0017] Preferably, in an ultra-low oxygen environment, the samarium-cobalt coarse powder in the sanded powder tank is transported to the sand mill through a pipeline. Pipeline transportation can adopt existing technologies. The traditional role of adding the organic solution mentioned above is to make the powder material in a fluid state, promote the powder material to enter the grinding chamber, and at the same time avoid blockage of the powder material in the pipeline.

[0018] The principle of sand grinding is to rotate the coarse powder and the grinding balls at a high speed together. Through the shearing force of the hard grinding balls, the coarse powder is broken. The broken powder material realizes the full refinement of the powder material through the circulation process between the storage tank and the grinding chamber, and finally obtains the ultrafine powder.

[0019] The grinding time and the sand grinding cycle times of the coarse powder affect the particle size and the uniformity and stability of the ultrafine powder. Therefore, appropriate grinding time and powder material circulation process can change the characteristics of the ultrafine powder.

[0020] The particle size of the samarium-cobalt permanent magnet ultrafine powder obtained by the novel sand grinding equipment of the present invention can be uniformly and stably around 1 μm, and the oxygen content is below 10 ppm.

[0021] The second object of the present invention is to provide an ultra-low oxygen and high-stability samarium-cobalt permanent magnet ultrafine powder prepared by the above preparation method.

[0022] The third object of the present invention is to provide a samarium-cobalt permanent magnet with a heterogeneous structure prepared from the ultra-low oxygen and high-stability samarium-cobalt permanent magnet ultrafine powder prepared by the above preparation method. The preparation method of the samarium-cobalt permanent magnet with a heterogeneous structure is to add the ultra-low oxygen and high-stability samarium-cobalt permanent magnet ultrafine powder to the traditional samarium-cobalt permanent magnet coarse powder with a particle size of 3-5 μm.

[0023] As a preferred technical solution, the specific preparation method of the samarium-cobalt permanent magnet with a heterogeneous structure is as follows: Step S1: Add the ultra-low oxygen and high-stability samarium-cobalt permanent magnet ultrafine powder to the traditional samarium-cobalt permanent magnet coarse powder with a particle size of 3-5 μm to obtain a heterogeneous samarium-cobalt permanent magnet powder; Step S2: Put the heterogeneous samarium-cobalt permanent magnet powder obtained in Step S1 into a rubber mold for shaping, and cover it completely with plastic wrap to obtain a shaped samarium-cobalt magnet; Step S3: Magnetize and cold isostatically press the shaped samarium-cobalt magnet obtained in Step S3 to obtain a green body; Step S4: Sinter, solutionize and age the green body obtained in Step S3 to finally obtain a samarium-cobalt permanent magnet with a heterogeneous structure.

[0024] As a preferred technical solution, in Step S1, the ultra-low oxygen and high-stability samarium-cobalt permanent magnet ultrafine powder is added according to 5-30% of the total mass of the powder; Preferably, in Step S2, the ratio of the outer diameter to the inner diameter of the rubber mold is 1:3; Preferably, in Step S3, the magnetization magnetic field strength is 1000-1500 V, and the pressure of the cold isostatic pressing is 200-250 MPa.

[0025] Compared with the prior art, the advantages of the present invention are as follows: (1) The present invention uses a sand grinding powder preparation process to prepare ultrafine powder of samarium-cobalt permanent magnet materials. The particle size can be stably maintained at about 1 μm, and the oxygen content is within 10 ppm. Compared with the conventional ball milling process and the existing sand grinding process, the particle size of the ultrafine powder is more stable and uniform, and the oxygen content is lower; (2) The present invention uses a sand grinding powder preparation process in a vacuum glove box, which not only solves the problems of easy oxidation, easy combustion and difficult transportation of ultrafine powder, but also preferably improves the yield of the ultrafine powder of samarium-cobalt permanent magnet materials and the uniform stability of the particle size of the ultrafine powder through a double-tank circulating sand grinding process; (3) Using the ultrafine powder of the present invention, a heterogeneous samarium cobalt magnet with high mechanical properties and low anisotropy was successfully prepared, broadening the application of samarium cobalt ultrafine powder. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 is the overall structure diagram of the sand milling equipment of the present invention; Figure 2 is the front view of the sand milling chamber before improvement and Figure 1 the comparison of the front views of the sand milling chambers in; Figure 3 is the particle size test chart of double-tank grinding for 30 h in Example 2 of the present invention; Figure 4 is the particle size test chart of single-tank grinding for 40 h in Comparative Example 3 of the present invention; In the figure: 1, stirrer; 2, vacuum glove box; 3, powder tank A; 4, powder tank B; 5, control valve; 6, sand milling chamber; 61, sand milling chamber box body; 62, sand milling cylinder; 63, support frame; 7, feed pipe; 8, discharge pipe. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0027] The present invention will be further described below in conjunction with embodiments.

[0028] In the following embodiments, the structure of the sand milling equipment used is as follows: As Figure 1 shown, it includes two independent vacuum glove boxes 2, and two powder tanks are arranged in one of the vacuum glove boxes 2, namely powder tank A 3 and powder tank B 4. A stirrer 1 is arranged in each of the powder tanks A 3 and B 4. A sand milling chamber 6 is arranged in the other vacuum glove box 2. The lower ends of the powder tanks A 3 and B 4 are communicated with the sand milling chamber 6 through a feed pipe 7, and the upper ends of the powder tanks A 3 and B 4 are communicated with the sand milling chamber 6 through a discharge pipe 8; Among them, the sand milling chamber 6 is as Figure 2 shown, including a sand milling chamber box body 61, a sand milling cylinder 62 is arranged in the sand milling chamber box body 61, and a support frame 63 for supporting the sand milling cylinder 62 is also arranged; The coarse powder enters the sand milling chamber 6 from the feed pipe 7 at the bottom of the powder tank A 3. After sand milling, it enters the powder tank B 4 through the discharge pipe 8. After all the powder in the powder tank A 3 has been sand milled and entered the powder tank B 4, sand milling is carried out in the reverse direction, that is, the powder in the powder tank B 4 enters the powder tank A 3 after passing through the bottom feed pipe 7 and the sand milling chamber 6, so as to carry out repeated sand milling. The control valve 5 at the pipeline interface can determine the flow mode of the powder.

[0029] Example 1

[0030] An ultra-low oxygen and highly stable samarium cobalt permanent magnet ultra-fine powder, and its preparation method has the following steps: Step 1: Put 3 kg of coarse samarium cobalt permanent magnet powder (particle size 4 - 5 μm) into a glove box, and conduct three cycles of argon gas cleaning on the coarse powder to ensure an ultra-low oxygen environment in the coarse powder; put the coarse powder after argon gas cleaning into a storage tank; Step 2: Add 30 g of oleylamine to the storage tank; Step 3: Then add 1000 ml of n-heptane and stir evenly; The stirring is carried out in a powder tank using an automatic stirring head. Because after stirring evenly, the coarse samarium cobalt powder can form a stable fluid state with organic solvents, etc., which is better for sand grinding and crushing refinement in the sand grinding chamber; The working principle is that in the tank barrel, the powder, dispersant, and organic solvent are fully stirred evenly, which helps the powder to be sand ground in the sand mill; if not stirred evenly, it is easy to cause problems such as sand mill blockage and uneven powder sand grinding; Step 4: Introduce the coarse samarium cobalt powder in the powder into a sand mill, and sand grind it for 10 h using a double-tank circulation system; the media balls of the sand mill are zirconia balls with a diameter of 0.6 mm, and the rotation speed of the sand mill is 1800 r / min; obtain an ultra-low oxygen and highly stable samarium cobalt permanent magnet ultra-fine powder with a particle size of 2.55 μm.

[0031] Use the above-mentioned ultra-low oxygen and highly stable samarium cobalt permanent magnet ultra-fine powder to prepare a heterogeneous structure samarium cobalt permanent magnet. The specific steps are as follows: Step S1: Mix 40 g of the above-prepared samarium cobalt permanent magnet ultra-fine powder into 360 g of traditional samarium cobalt powder (particle size 3 - 5 μm) according to a ratio of 10 wt%, and mix in a mixer for 8 h to obtain a heterogeneous samarium cobalt permanent magnet powder with uniform mixing of coarse powder and ultra-fine powder; Step S2: Put the heterogeneous samarium cobalt permanent magnet powder into a rubber mold for shaping, and after covering it completely with plastic wrap, seal it with a vacuum packaging bag to obtain a shaped samarium cobalt magnet; Step S3: Saturate the shaped samarium cobalt magnet with magnetic charge and perform cold isostatic pressing under a pressure of 250 MPa to obtain a green compact; Step S4: Put the green compact into a sintering furnace with a glove box, after filling argon to make the oxygen content in the operating environment lower than 10 ppm, use the glove box to remove the vacuum packaging of the green compact, and put the sample into the sintering furnace. First, evacuate for 1 h to make the vacuum degree in the sintering furnace reach 5×10 -3Start heating at below Pa, then raise the temperature from room temperature to 360 °C at a rate of 3 °C / min, hold for 4 h to fully volatilize the organic matter in the green body; then raise the temperature to 1210 °C at a rate of 5 °C / min, sinter and hold for 1 h, and introduce 0.6 argon when the temperature reaches 1210 °C. After sintering, cool to 1190 °C at a rate of 1 °C / min for solution treatment for 4 h, and finally air-cool to room temperature; for aging treatment, raise the temperature from room temperature to 810 °C at a rate of 8 °C / min, hold for 24 h, and then cool to 400 °C at a rate of 2 °C / min and hold for 10 h; finally, a heterogeneous structure magnet with high mechanical properties is obtained.

[0032] Example 2

[0033] A method for preparing ultra-low oxygen and high-stability samarium cobalt permanent magnet ultra-fine powder, except for step 4, using a double-tank circulation system for sanding for 20 h, the rest is the same as in Example 1; the resulting ultra-low oxygen and high-stability samarium cobalt permanent magnet ultra-fine powder has a particle size of 1.32 μm.

[0034] Example 3

[0035] A method for preparing ultra-low oxygen and high-stability samarium cobalt permanent magnet ultra-fine powder, except for step 4, using a double-tank circulation system for sanding for 30 h, the rest is the same as in Example 1; the resulting ultra-low oxygen and high-stability samarium cobalt permanent magnet ultra-fine powder has a particle size of 1.31 μm.

[0036] Example 4

[0037] A method for preparing ultra-low oxygen and high-stability samarium cobalt permanent magnet ultra-fine powder, except for step 4, using a double-tank circulation system for sanding for 40 h, the rest is the same as in Example 1. The resulting ultra-low oxygen and high-stability samarium cobalt permanent magnet ultra-fine powder has a particle size of 1.32 μm.

[0038] Comparative Example 1 A method for preparing ultra-low oxygen and high-stability samarium cobalt permanent magnet ultra-fine powder, except for step 4, using a single-tank system for sanding for 20 h, the rest is the same as in Example 1. The resulting ultra-low oxygen and high-stability samarium cobalt permanent magnet ultra-fine powder has a particle size of 1.99 μm.

[0039] Comparative Example 2 A method for preparing ultra-low oxygen and high-stability samarium cobalt permanent magnet ultra-fine powder, except for step 4, using a single-tank system for sanding for 30 h, the rest is the same as in Example 1. The resulting ultra-low oxygen and high-stability samarium cobalt permanent magnet ultra-fine powder has a particle size of 1.54 μm.

[0040] Comparative Example 3 A method for preparing ultra-low oxygen and high-stability samarium cobalt permanent magnet ultra-fine powder, except for step 4, using a single-tank system for sanding for 40 h, the rest is the same as in Example 1. The resulting ultra-low oxygen and high-stability samarium cobalt permanent magnet ultra-fine powder has a particle size of 1.43 μm.

[0041] Comparative Example 4 Preparation method of ultra-low oxygen and high-stability samarium cobalt permanent magnet ultrafine powder. Except in step 4 where it is milled in a single-tank system for 50 hours, the rest is the same as in Example 1. As a result, the particle size of the obtained ultra-low oxygen and high-stability samarium cobalt permanent magnet ultrafine powder is 1.55 μm.

[0042] From the comparison of Examples 1 - 4, it can be seen that the double-tank circulating grinding cannot play the role of refining the powder material with the extension of time. This shows that the particle size of the powder material will not decrease with the extension of the grinding time. However, by observing the particle size test data (such as Figure 3 ), it is found that the uniformity of the particle size distribution of the powder material obtained by double-tank circulating grinding is better. This shows that using double-tank grinding can promote all the powder materials to enter the grinding mill to participate in the grinding process, which is beneficial to improving the grinding efficiency of the powder material.

[0043] From Comparative Examples 1 - 4, it can be seen that with the extension of the single-tank grinding time, the particle size of the powder material has a tendency to grow. This is because after the powder material is ground for a long time, the specific surface area of the ultrafine powder increases, and the ability of the dispersant to wrap the powder material decreases, resulting in the aggregation and growth of fine particles. Therefore, long-term single-tank circulating grinding cannot effectively reduce the particle size of the powder material. In addition, the powder material ground by single-tank circulating grinding has an uneven distribution of thick and thin (as shown in Figure 4 ), making the application of the ultrafine powder unstable.

[0044] The application method of the ultra-low oxygen and high-stability samarium cobalt ultrafine powder obtained in the present invention is to add the obtained ultra-low oxygen and high-stability samarium cobalt ultrafine powder (taking the one prepared in Example 3 as an example) to the samarium cobalt coarse powder with a traditional particle size (4 - 5 μm) to form a heterogeneous structure samarium cobalt material with different particle sizes.

[0045] Use a universal testing machine to conduct a three-point bending test on it to obtain the flexural mechanical properties of the material. According to the national standard (GB / T31967.2 - 2015) Test methods for physical properties of rare earth permanent magnet materials - Part 2: Determination of flexural strength. The dimensions of the specimen are h×b×l as 5×6×20 (l>17) respectively. Since the samarium cobalt permanent magnet material has large mechanical anisotropy, when the magnetization direction is along the three directions of 5×6×20, there are large performance differences in the flexural properties. This phenomenon is also a major problem of the current samarium cobalt permanent magnet material, mainly affecting subsequent processing and restricting the application of the samarium cobalt material. From the specific mechanical data in Table 1 below, it can be seen that after applying the ultra-low oxygen and high-stability ultrafine powder of the present invention, the flexural performance of the samarium cobalt permanent magnet has been greatly improved, and at the same time, the difference in mechanical properties in each direction has been reduced.

[0046] Table 1 Properties of different samarium cobalt materials , Through the improvement of the sand mill equipment and the regulation of the sanding process, the present invention achieves ultra-low oxygen content and uniform stability of the ultra-fine powder of samarium cobalt permanent magnet materials. The present invention also promotes the stable preparation, transportation and storage of ultra-fine samarium cobalt powder, and expands the usage methods of the ultra-fine powder. Adding ultra-low oxygen ultra-fine samarium cobalt powder to normal samarium cobalt powder can promote the formation of a special heterogeneous structure in the samarium cobalt magnet, while stabilizing the magnetic properties, it can also significantly and stably improve the mechanical properties of samarium cobalt.

[0047] The above are only the preferred embodiments of the present invention, and are not intended to limit the present invention. Any modifications, equivalent replacements, and improvements made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A method for preparing ultra-low oxygen high-stability samarium cobalt permanent magnet ultrafine powder, characterized in that: The steps include: Step 1, placing the coarse powder of samarium cobalt permanent magnet into a sand milling jar with ultra-low water and oxygen content and protected by inert gas; Step 2, adding a dispersant according to 0.5-1.5% of the mass of the coarse powder; Step 3, adding organic solvent and stirring to mix; Step 4: introduce the coarse samarium cobalt powder in the powder tank into a sand mill to prepare ultrafine powder.

2. The preparation method according to claim 1, characterized in that: In step 1, the coarse powder is placed in a sand milling tank through a vacuum glove box, the water and oxygen content in the vacuum glove box is less than 10 ppm, the inert gas is argon, and the purity of the argon is ≥99.99%.

3. The preparation method according to claim 1, characterized in that: In step 2, the dispersant is selected from at least one of oleylamine, oleic acid, and kerosene, and the amount of the dispersant added is 1% of the mass of the coarse powder.

4. The preparation method according to claim 1, characterized in that: In step 3, the organic solvent is selected from at least one of n-heptane, petroleum ether, ethanol and water, and the amount of the organic solvent added is 2 to 3 times the volume of the coarse powder.

5. The preparation method according to claim 1, characterized in that: In step 4, the sand grinding equipment includes two independent vacuum glove boxes, one of which is provided with at least one powder tank, and a stirrer is provided in the powder tank, and a sand grinding chamber is provided in the other vacuum glove box, and the outlet and inlet of the powder tank are connected to the sand grinding chamber through powder fluid inlet and outlet pipes respectively.

6. The preparation method according to claim 1, characterized in that: In step 4, the medium balls of the sand mill are zirconia balls, the diameter of the medium balls ranges from 0.6 to 0.8 mm, the rotation speed of the sand mill is 1800 to 2500 r / min, and the sand milling time is 1 to 100 h.

7. Ultra-low oxygen and highly stable samarium cobalt permanent magnet ultrafine powder prepared by the preparation method according to any one of claims 1 to 6.

8. A samarium cobalt permanent magnet with a heterogeneous structure prepared by using the ultra-low oxygen high-stability samarium cobalt permanent magnet ultrafine powder prepared by the preparation method of any one of claims 1 to 6, characterized in that: The method for preparing the heterogeneous structured samarium cobalt permanent magnet is to add the ultra-low oxygen high-stability samarium cobalt permanent magnet ultrafine powder to a conventional samarium cobalt permanent magnet coarse powder with a particle size of 3-5 μm.

9. The samarium cobalt permanent magnet with a heterogeneous structure according to claim 8, characterized in that: The specific preparation method of the samarium cobalt permanent magnet with heterogeneous structure is: Step S1: adding the ultra-low oxygen high-stability samarium cobalt permanent magnet ultrafine powder to a conventional samarium cobalt permanent magnet coarse powder with a particle size of 3-5 μm to obtain a heterogeneous samarium cobalt permanent magnet powder; Step S2: placing the heterogeneous samarium-cobalt permanent magnet powder obtained in step S1 into a rubber mold for shaping, and fully covering it with a plastic wrap to obtain a shaped samarium-cobalt magnet; Step S3: magnetizing and cold isostatically pressing the shaped samarium cobalt magnet obtained in step S3 to obtain a green body; Step S4: sintering, solid solutionizing and aging the green body obtained in step S3 to finally obtain a samarium cobalt permanent magnet with a heterogeneous structure.

10. The samarium cobalt permanent magnet with a heterogeneous structure according to claim 9, characterized in that: In step S1, the ultra-low oxygen high-stability samarium cobalt permanent magnet ultrafine powder is added according to 5-30% of the total mass of the powder; Preferably, in step S2, the ratio of the outer diameter to the inner diameter of the rubber mold is 1:3; Preferably, in step S3, the magnetizing magnetic field is 1000-1500 V, and the cold isostatic pressing pressure is 200-250 MPa.

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