A compression-isostatic sintered magnetic powder which avoids caking, a method for producing the same, and a magnet containing the same

Abstract

The application relates to the technical field of magnetic materials, in particular to a pressure anisotropy sintered magnetic powder capable of avoiding caking, a preparation method of the pressure anisotropy sintered magnetic powder and a magnet containing the pressure anisotropy sintered magnetic powder. The pressure anisotropy sintered magnetic powder is composed of UiO-66 and SmFeN, the preparation method is that high-purity samarium blocks and iron blocks are used as raw materials, alloying, crushing into powder, nitriding and mixing ball milling are carried out to obtain the pressure anisotropy sintered magnetic powder, the magnet contains the pressure anisotropy sintered magnetic powder capable of avoiding caking, and the magnet is obtained through hole breaking, blank preparation and sintering. The UiO-66 in the pressure anisotropy sintered magnetic powder provided by the application can absorb moisture, prevent liquid phase bridges from being formed between the magnetic powders, and further avoid caking between the magnetic powders.

Description

Technical Field

[0001] This invention relates to the field of magnetic materials technology, specifically to a non-agglomerated sintered magnetic powder that avoids agglomeration, its preparation method, and a magnet containing the powder. Background Technology

[0002] Permanent magnet materials are essential for the healthy and steady development of various high-tech fields. While existing NdFeB rare-earth permanent magnet materials have high magnetic properties and are widely used, they consume large amounts of rare-earth elements such as Nd, Pr, Dy, and Tb, leading to an imbalance in the use of strategic rare-earth elements and even waste. Therefore, the development of low-rare-earth or high-abundance rare-earth permanent magnet materials is a research hotspot in the field of rare-earth permanent magnet materials. Anisotropic sintered SmFeN permanent magnet materials have long attracted widespread attention due to their advantages of high Curie temperature, high cost-effectiveness, high magnetic anisotropy, and corrosion resistance. Anisotropic sintered SmFeN permanent magnet materials are obtained by preparing magnetic powder into a preform and then sintering it. However, the agglomeration of magnetic powder can cause cracks in the preform, resulting in a low molding yield and poor magnetic powder orientation. Ultimately, this leads to poor mechanical and magnetic properties of the sintered body.

[0003] Agglomeration is a common phenomenon in anisotropic sintered magnetic powders. Large-area agglomeration will affect the orientation and molding process in the subsequent anisotropic sintered magnet preparation process. Furthermore, due to the irregularity of agglomerated magnetic powder, large pores will be left in the ligands after molding. Agglomerated magnetic powder will also affect the sintering behavior of the magnet. Since the degree of sintering of magnetic powder within agglomerated magnetic powder is higher than that between agglomerated magnetic powder particles, the required sintering temperature will be increased, which can easily lead to over-burning, excessive grain enlargement, and destruction of the required nanocrystalline structure, making it difficult to obtain nanomagnets. The agglomeration is mainly caused by the water in the anisotropic sintered magnetic powder binding the magnetic powder particles together tightly through the action of hydrogen bonds and liquid phase bridges.

[0004] UiO-66, a three-dimensional porous zirconium-based MOF, is composed of 1,4-phthalic acid linkers and cationic Zr6O4(OH)4 nodes, possessing octahedral and tetrahedral cavities. It has attracted considerable attention due to its excellent thermal stability, water stability, acid stability, and ease of synthesis. Due to capillary effect, the porous channels of UiO-66 adsorb water from the environment. This invention combines UiO-66 with anisotropic sintered magnetic powder to adsorb trace amounts of moisture in the magnetic powder and prevent moisture from the air from penetrating between the magnetic powder particles, thus reducing the agglomeration behavior of the magnetic powder. To our knowledge, no relevant data has yet reported combining UiO-66 with anisotropic sintered magnetic powder to reduce the agglomeration behavior of magnetic powder. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a non-agglomerated sintered magnetic powder that avoids agglomeration, its preparation method, and a magnet containing it, with the aim of solving the problem of magnetic powder agglomeration during the preparation of non-agglomerated sintered magnets.

[0006] To solve the above problems, the technical solution of the present invention is as follows:

[0007] In a first aspect, the present invention provides a method for preparing anisotropic sintered magnetic powder that avoids agglomeration, the specific steps of which are as follows:

[0008] Alloying: Using samarium and iron blocks as raw materials, the mixture is repeatedly melted 4-6 times in a vacuum arc melting furnace to prepare alloy blocks. The alloy blocks are then heat-treated to obtain Sm2Fe. 17 alloy.

[0009] Crushing into powder: for Sm2Fe 17 The alloy was subjected to rapid melt quenching and spinning under argon protection to obtain Sm2Fe. 17 The Sm2Fe17 strip was then ball-milled into powder using a stainless steel ball mill to obtain Sm2Fe. 17 Powder.

[0010] Nitriding: Sm2Fe 17 The powder was placed in a tube furnace for nitriding to obtain SmFeN powder.

[0011] Mixed ball milling: UiO-66 and SmFeN powders are added to a stainless steel ball mill and ball milled to obtain anisotropic sintered magnetic powder that avoids agglomeration.

[0012] Preferably, in step (1), the purity of the samarium block and the iron block is above 99.9%, and the atomic ratio of Sm to Fe is 2.2-2.5:17.

[0013] Preferably, in step (1), the working current of the vacuum arc melting furnace is 130-150A, and the working atmosphere is argon.

[0014] Preferably, the heat treatment conditions in step (1) are: treatment at 1000-1100℃ for 10-16 hours.

[0015] Preferably, the belt-spinning speed in step (2) is 15-25 m / s.

[0016] Preferably, the ball milling conditions in step (2) are: ball milling at 150-180 r / min for 4-6 hours, with a ball-to-material ratio of 1:4-6.

[0017] Preferably, the nitriding conditions in step (3) are: calcination at 490-550°C for 5-8 hours in a nitrogen atmosphere.

[0018] Preferably, in step (4), the average particle size of UiO-66 is 50-100 nm and the average pore size is 0.8-1 nm.

[0019] Preferably, the mass ratio of SmFeN to UiO-66 in step (4) is 10:1-3.

[0020] Preferably, the ball milling conditions in step (4) are: ball milling at 200-240 r / min for 1-3 h, with a ball-to-material ratio of 1:4-6.

[0021] Secondly, the present invention provides anisotropic sintered magnetic powder that avoids agglomeration, wherein the anisotropic sintered magnetic powder that avoids agglomeration is prepared by the above-described preparation method.

[0022] Thirdly, the present invention provides a magnet comprising the non-agglomerated anisotropic sintered magnetic powder described in the present invention.

[0023] Preferably, the magnet is prepared by the following method:

[0024] (1) Pore breaking: The above-mentioned non-agglomerated anisotropic sintered magnetic powder is added to N,N-dimethylformamide to break the pores. The resulting mixture is filtered under vacuum and dried to obtain pore-broken anisotropic sintered magnetic powder.

[0025] (2) Preform preparation: The pore-filled, anisotropic sintered magnetic powder is oriented and pressed to obtain a preform.

[0026] (3) Sintering: The preform from step (2) is sintered once and twice in an argon atmosphere to finally obtain the magnet.

[0027] Preferably, in step (1), the mass ratio of the non-agglomerated sintered magnetic powder and N,N-dimethylformamide to avoid agglomeration is 10:50-80.

[0028] Preferably, the conditions for creating the hole in step (1) are: reflux at 150-155℃ for 24-36 hours.

[0029] Preferably, in step (2), the orientation pressing is carried out in a magnetic field with a magnetic field strength of 1.5-2T.

[0030] Preferably, the conditions for the first sintering in step (3) are: sintering at 300-400℃ for 2-4 hours; and the conditions for the second sintering are: sintering at 400-600℃ for 1-3 hours.

[0031] Compared with existing technologies, the present invention has the following advantages and beneficial effects:

[0032] This invention discloses an anisotropic sintered magnetic powder that avoids agglomeration. The anisotropic sintered magnetic powder uses high-purity samarium and iron blocks as raw materials. The raw materials are alloyed, crushed into powder, nitrided, and then ball-milled to obtain anisotropic sintered magnetic powder with a uniform mixture of SmFeN and UIO-66. The SmFeN and UIO-66 exist in a uniformly mixed state. The porous channels of UIO-66 have an adsorption effect on water in the environment, which can adsorb trace amounts of moisture in the magnetic powder and prevent moisture from the air from penetrating between the magnetic powder particles, thus reducing agglomeration.

[0033] This invention discloses a magnet comprising anisotropic sintered magnetic powder that prevents agglomeration. Using the anisotropic sintered magnetic powder prepared according to this invention as raw material, anisotropic SmFeN magnets are obtained through pore breaking, preform preparation, and sintering. The pore breaking process involves heating and refluxing with N,N-dimethylformamide to disrupt the channels of UIO-66, causing it to dissociate. The released organic monomers adhere to the surface of the magnetic powder after drying, preventing the spatial obstruction caused by the three-dimensional structure of UIO-66 from affecting subsequent pressing and orientation. This also facilitates the formation of a dense magnet after calcination. The sintering process includes two calcination steps. The first calcination primarily converts the organic matter on the surface of the magnetic powder into a carbon layer, densifying the sintered magnet. Simultaneously, the presence of the carbon layer increases the resistivity of the product and inhibits the growth of the main phase grains and the exchange coupling between grains, thereby reducing eddy current losses while minimizing magnetic performance loss. Detailed Implementation

[0034] The technical solutions in the embodiments of the present invention will be clearly and completely described below. 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 skilled in the art without creative effort are within the scope of protection of the present invention.

[0035] Example 1

[0036] Preparation of anisotropic sintered magnetic powder to avoid agglomeration

[0037] Alloying: Using samarium and iron blocks as raw materials, with an Sm to Fe atomic ratio of 2.3:17, the materials were repeatedly melted five times in a vacuum arc melting furnace at an operating current of 140A and an argon atmosphere to prepare alloy blocks. The alloy blocks were then treated at 1050℃ for 13 hours to obtain Sm2Fe. 17 alloy.

[0038] Crushing into powder: for Sm2Fe 17 The alloy was subjected to rapid melt quenching and strip spinning under argon protection at a speed of 20 m / s to obtain Sm2Fe. 17 Strip material, then Sm2Fe 17Sm2Fe was obtained by ball milling stainless steel strip at 160 r / min for 5 h with a ball-to-material ratio of 1:5. 17 Powder.

[0039] Nitriding: Sm2Fe 17 The powder was placed in a tube furnace for nitriding and calcined at 520°C for 6.5 h in a nitrogen atmosphere to obtain SmFeN powder.

[0040] Mixed ball milling: 20g UiO-66 (average particle size of 76nm, average pore size of 0.92nm) and 100g SmFeN powder were added to a stainless steel ball mill and ball milled at 220r / min for 2h with a ball-to-material ratio of 1:5 to obtain anisotropic sintered magnetic powder that avoids agglomeration.

[0041] Prepare a magnet containing the above-mentioned non-agglomerated sintered magnetic powder.

[0042] Pore ​​breaking: 10g of the above-mentioned non-caking anisotropic sintered magnetic powder was added to 70g of N,N-dimethylformamide and refluxed at 150℃ for 30h. The resulting mixture was filtered under vacuum and dried to obtain pore-breaking anisotropic sintered magnetic powder.

[0043] Preform preparation: The pore-filled, anisotropic sintered magnetic powder is oriented and pressed into a mold with a magnetic field strength of 1.8T to obtain the preform.

[0044] (3) Sintering: The preform from step (2) is sintered sequentially in an argon atmosphere at 350 °C for 3 hours, and then the temperature is raised to 500 °C for 2 hours to finally obtain the magnet.

[0045] Example 2

[0046] Preparation of anisotropic sintered magnetic powder to avoid agglomeration

[0047] Alloying: Using samarium and iron blocks as raw materials, with an Sm to Fe atomic ratio of 2.2:17, the materials were repeatedly melted four times in a vacuum arc melting furnace at an operating current of 130A and an argon atmosphere to prepare alloy blocks. The alloy blocks were then treated at 1000℃ for 10 hours to obtain Sm2Fe. 17 alloy.

[0048] Crushing into powder: for Sm2Fe 17 The alloy was subjected to rapid melt quenching and strip spinning under argon protection at a speed of 15 m / s to obtain Sm2Fe. 17 Strip material, then Sm2Fe 17 Sm2Fe was obtained by ball milling stainless steel strip at 150 r / min for 4 h with a ball-to-material ratio of 1:4-6. 17 Powder.

[0049] Nitriding: Sm2Fe 17 The powder was placed in a tube furnace for nitriding and calcined at 490°C for 5-8 hours in a nitrogen atmosphere to obtain SmFeN powder.

[0050] Mixed ball milling: 10g UiO-66 (average particle size of 52nm, average pore size of 0.93nm) and 100g SmFeN powder were added to a stainless steel ball mill and ball milled at 200r / min for 1h with a ball-to-material ratio of 1:4 to obtain anisotropic sintered magnetic powder that avoids agglomeration.

[0051] Prepare a magnet containing the above-mentioned non-agglomerated sintered magnetic powder.

[0052] Pore ​​breaking: 10g of the above-mentioned non-caking anisotropic sintered magnetic powder was added to 50g of N,N-dimethylformamide and refluxed at 150℃ for 24h. The resulting mixture was filtered under vacuum and dried to obtain pore-breaking anisotropic sintered magnetic powder.

[0053] Preform preparation: The porous, anisotropic sintered magnetic powder is oriented and pressed into a mold with a magnetic field strength of 1.5T to obtain the preform.

[0054] Sintering: The preform from step (2) is sintered sequentially in an argon atmosphere at 300°C for 2 hours, then the temperature is raised to 400°C and sintered for 1 hour to finally obtain the magnet.

[0055] Example 3

[0056] Preparation of anisotropic sintered magnetic powder to avoid agglomeration

[0057] Alloying: Using samarium and iron blocks as raw materials, with an Sm to Fe atomic ratio of 2.5:17, the materials were repeatedly melted 4-6 times in a vacuum arc melting furnace. The working current of the vacuum arc melting furnace was 150A, and the working atmosphere was argon. Alloy blocks were prepared and then treated at 1100℃ for 16 hours to obtain Sm2Fe. 17 alloy.

[0058] Crushing into powder: for Sm2Fe 17 The alloy was subjected to rapid melt quenching and strip spinning under argon protection at a speed of 25 m / s to obtain Sm2Fe. 17 Strip material, then Sm2Fe 17 Sm2Fe was obtained by ball milling stainless steel strip at 180 r / min for 6 h with a ball-to-material ratio of 1:6. 17 Powder.

[0059] Nitriding: Sm2Fe 17 The powder was placed in a tube furnace for nitriding and calcined at 550°C for 5-8 hours in a nitrogen atmosphere to obtain SmFeN powder.

[0060] Mixed ball milling: 30g UiO-66 (average particle size of 95nm, average pore size of 0.98nm) and 100g SmFeN powder were added to a stainless steel ball mill and ball milled at 200-240r / min for 3h with a ball-to-material ratio of 1:6 to obtain anisotropic sintered magnetic powder that avoids agglomeration.

[0061] Prepare a magnet containing the above-mentioned non-agglomerated sintered magnetic powder.

[0062] Pore ​​breaking: 10g of the above-mentioned non-caking anisotropic sintered magnetic powder was added to 80g of N,N-dimethylformamide and refluxed at 155℃ for 36h. The resulting mixture was filtered under vacuum and dried to obtain pore-breaking anisotropic sintered magnetic powder.

[0063] Preform preparation: The porous, anisotropic sintered magnetic powder is oriented and pressed into a mold with a magnetic field strength of 2T to obtain the preform.

[0064] Sintering: The preform from step (2) is sintered sequentially in an argon atmosphere at 400 °C for 4 hours, and then the temperature is raised to 600 °C for 3 hours to finally obtain the magnet.

[0065] Preparation of anisotropic sintered magnetic powder

[0066] Alloying: Using samarium and iron blocks as raw materials, with an Sm to Fe atomic ratio of 2.3:17, the materials were repeatedly melted five times in a vacuum arc melting furnace at an operating current of 140A and an argon atmosphere to prepare alloy blocks. The alloy blocks were then treated at 1050℃ for 13 hours to obtain Sm2Fe. 17 alloy.

[0067] Crushing into powder: for Sm2Fe 17 The alloy was subjected to rapid melt quenching and strip spinning under argon protection at a speed of 20 m / s to obtain Sm2Fe. 17 Strip material, then Sm2Fe 17 Sm2Fe was obtained by ball milling stainless steel strip at 160 r / min for 5 h with a ball-to-material ratio of 1:5. 17 Powder.

[0068] Nitriding: Sm2Fe 17 The powder was placed in a tube furnace for nitriding and calcined at 520°C for 6.5 h in a nitrogen atmosphere to obtain SmFeN powder.

[0069] Ball milling: 100g of SmFeN powder was added to a stainless steel ball mill and milled at 220r / min for 2h with a ball-to-material ratio of 1:5 to obtain anisotropic sintered magnetic powder.

[0070] Preparation of magnets containing anisotropic sintered magnetic powder

[0071] Preform preparation: The anisotropic sintered magnetic powder is oriented and pressed into a mold with a magnetic field strength of 1.8T to obtain the preform.

[0072] (2) Sintering: The preform from step (2) is sintered sequentially in an argon atmosphere at 350 °C for 3 hours, and then the temperature is raised to 500 °C for 2 hours to finally obtain the magnet.

[0073] Preparation of anisotropic sintered magnetic powder to avoid agglomeration

[0074] Alloying: Using samarium and iron blocks as raw materials, with an Sm to Fe atomic ratio of 2.3:17, the materials were repeatedly melted five times in a vacuum arc melting furnace at an operating current of 140A and an argon atmosphere to prepare alloy blocks. The alloy blocks were then treated at 1050℃ for 13 hours to obtain Sm2Fe. 17 alloy.

[0075] Crushing into powder: for Sm2Fe 17 The alloy was subjected to rapid melt quenching and strip spinning under argon protection at a speed of 20 m / s to obtain Sm2Fe. 17 Strip material, then Sm2Fe 17 Sm2Fe was obtained by ball milling stainless steel strip at 160 r / min for 5 h with a ball-to-material ratio of 1:5. 17 Powder.

[0076] Nitriding: Sm2Fe 17 The powder was placed in a tube furnace for nitriding and calcined at 520°C for 6.5 h in a nitrogen atmosphere to obtain SmFeN powder.

[0077] Mixed ball milling: 20g UiO-66 (average particle size of 76nm, average pore size of 0.92nm) and 100g SmFeN powder were added to a stainless steel ball mill and ball milled at 220r / min for 2h with a ball-to-material ratio of 1:5 to obtain anisotropic sintered magnetic powder that avoids agglomeration.

[0078] Prepare a magnet containing the above-mentioned non-agglomerated sintered magnetic powder.

[0079] Preform preparation: The anisotropic sintered magnetic powder is oriented and pressed into a mold with a magnetic field strength of 1.8T to obtain the preform.

[0080] (2) Sintering: The preform from step (2) is sintered sequentially in an argon atmosphere at 350 °C for 3 hours, and then the temperature is raised to 500 °C for 2 hours to finally obtain the magnet.

[0081] Long-term storage agglomeration experiment of magnetic powder

[0082] The magnetic powders from the above embodiments and comparative examples were stored in the same environment (temperature 25±3°C, humidity 50±10RH%), and the agglomeration of the magnetic powder was observed periodically, as shown in Table 1:

[0083] Table 1. Magnetic Powder Agglomeration Status

[0084] ;

[0085] Data analysis: As can be seen from Table 1, the non-caking anisotropic sintered magnetic powder prepared by the present invention can still maintain good dispersion and no agglomeration after 2 months. When the content of UIO-66 in the magnetic powder is reduced, a small amount of agglomeration appears after 1 month. When no UIO-66 is added, a large amount of agglomeration appears after 2 months.

[0086] Magnet performance experiment

[0087] The magnetic properties of the magnet were tested using the VSM method, and the magnet density was measured using the Archimedes displacement method.

[0088] Table 2 Magnet Technical Specifications

[0089] ;

[0090] Data analysis: Table 2 shows that the magnet prepared by the present invention has excellent magnetic properties and compactness. It can be seen from Example 1 and Comparative Example 2 that the hole-breaking step plays a crucial role in improving the magnetic properties and the overall compactness of the magnet.

[0091] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A method for preparing anisotropic sintered magnetic powder to avoid agglomeration, characterized in that, Includes the following steps: Alloying: Using samarium and iron blocks as raw materials, the mixture is repeatedly melted 4-6 times in a vacuum arc melting furnace to prepare alloy blocks. The alloy blocks are then heat-treated at 1000-1100℃ for 10-16 hours to obtain Sm2Fe. 17 alloy; Crushing into powder: for Sm2Fe 17 The alloy was subjected to rapid melt quenching and strip spinning under argon protection at a speed of 15-25 m / s to obtain Sm2Fe. 17 Strip material, then Sm2Fe 17 Sm2Fe was obtained by ball milling stainless steel strip into powder at 150-180 r / min for 4-6 hours with a ball-to-material ratio of 1:4-6. 17 Powder; (3) Nitriding: Sm2Fe 17 The powder was placed in a tube furnace for nitriding to obtain SmFeN powder; (4) Mixed ball milling: Add UiO-66 and SmFeN powder to a stainless steel ball mill and ball mill at 200-240 r / min for 1-3 h with a ball-to-material ratio of 1:4-6 to obtain anisotropic sintered magnetic powder that avoids agglomeration.

2. The method for preparing anisotropic sintered magnetic powder to avoid agglomeration according to claim 1, characterized in that, In step (1), the purity of the samarium block and the iron block is above 99.9%, and the atomic ratio of Sm to Fe is 2.2-2.5:

17.

3. The method for preparing anisotropic sintered magnetic powder to avoid agglomeration according to claim 1, characterized in that, In step (1), the working current of the vacuum arc melting furnace is 130-150A, and the working atmosphere is argon.

4. The method for preparing anisotropic sintered magnetic powder to avoid agglomeration according to claim 1, characterized in that, The nitriding conditions in step (3) are: calcination at 490-550℃ for 5-8 hours in a nitrogen atmosphere.

5. The method for preparing anisotropic sintered magnetic powder to avoid agglomeration according to claim 1, characterized in that, In step (4), the average particle size of UiO-66 is 50-100nm and the average pore size is 0.8-1nm.

6. The method for preparing anisotropic sintered magnetic powder to avoid agglomeration according to claim 1, characterized in that, In step (4), the mass ratio of SmFeN to UiO-66 is 10:1-3.

7. A type of anisotropic sintered magnetic powder that avoids agglomeration, characterized in that, The non-agglomerated anisotropic sintered magnetic powder is prepared by the preparation method according to any one of claims 1-6.

8. A magnet, characterized in that, The magnet comprises the non-agglomerated sintered magnetic powder as described in claim 7.

9. A magnet according to claim 8, characterized in that, The magnet is prepared by the following method: (1) Pore breaking: The non-agglomerated anisotropic sintered magnetic powder of claim 7 is added to N,N-dimethylformamide to break pores. The resulting mixture is filtered under vacuum and dried to obtain pore-broken anisotropic sintered magnetic powder. (2) Preform preparation: The pore-filled, anisotropic sintered magnetic powder is oriented and pressed to obtain a preform; (3) Sintering: The preform from step (2) is sintered once and twice in an argon atmosphere to finally obtain the magnet.

10. A magnet according to claim 9, characterized in that, In step (1), the mass ratio of the anisotropic sintered magnetic powder and N,N-dimethylformamide to avoid agglomeration is 10:50-80; the conditions for breaking the pores in step (1) are: reflow at 150-155℃ for 24-36h; the orientation pressing in step (2) is carried out in a magnetic field with a magnetic field strength of 1.5-2T; the conditions for the first sintering in step (3) are: sintering at 300-400℃ for 2-4h; the conditions for the second sintering are: sintering at 400-600℃ for 1-3h.