High-coercivity samarium-iron-nitrogen magnetic powder and preparation method thereof

Abstract

The invention discloses high-coercivity samarium-iron-nitrogen magnetic powder and a preparation method thereof. The high-coercivity samarium-iron-nitrogen magnetic powder has anisotropy, and the particle size of the magnetic powder is micron-sized. The preparation method of the high-coercivity samarium-iron-nitrogen magnetic powder comprises the following steps: preparing an organic combined grinding agent containing a solvent, a surfactant and a coupling agent in proportion, and mixing the organic combined grinding agent with samarium-iron-nitrogen raw material powder to obtain a mixed material; grinding the mixed material to obtain ground slurry; and carrying out ultrasonic dispersion on the grinding slurry, and carrying out particle screening and drying to obtain the high-coercivity samarium-iron-nitrogen magnetic powder. The obtained micron magnetic powder has the obviously improved coercive force level, and the coercive force level can be equivalent to the coercive force level of submicron samarium-iron-nitrogen magnetic powder; requirements on preparation equipment are low, and the process is simple.

Description

Technical Field

[0001] The present invention belongs to the technical field of high-performance magnetic powder, and particularly relates to a high coercivity samarium iron nitride magnetic powder and a preparation method thereof. Background Art

[0002] The rapid development of green energy technologies such as electric vehicles, wind power generation, and energy-saving furniture has brought a booming development space to the high-performance permanent magnet market, and at the same time, it has also brought a large number of urgent demands for high-performance and high-temperature magnets. Traditional neodymium iron boron magnets are currently the most magnetic magnetic materials, but due to the large consumption of praseodymium-neodymium rare earth resources and the need to add expensive Dy / Tb heavy rare earths for high-temperature applications, the neodymium iron boron magnet market faces severe cost problems. Therefore, the development of the fourth-generation permanent magnet materials without praseodymium-neodymium rare earth elements has attracted much attention in the field of magnetic materials. Among the candidate materials for many fourth-generation permanent magnet materials, samarium iron nitride rare earth permanent magnet materials are considered to be the first choice, not only because the magnetic potential of samarium iron nitride materials can be comparable to that of neodymium iron boron, but also because the temperature resistance and corrosion resistance of samarium iron nitride materials are better than those of neodymium iron boron.

[0003] Obtaining high-performance magnetic powder, especially obtaining high coercivity anisotropic magnetic powder, is an important prerequisite for the development of high-performance samarium iron nitride bulk materials. At present, the powder metallurgy method and the reduction diffusion method are the main preparation methods for obtaining anisotropic samarium iron nitride magnetic powder. However, whether it is the powder metallurgy method or the reduction diffusion method, there are huge challenges in obtaining high coercivity samarium iron nitride magnetic powder. The coercivity of commercial samarium iron nitride magnetic powder is difficult to exceed 11.0 kOe, and the corresponding magnetic powder particle size is mostly 1-3 microns.

[0004] Theory and practice show that the coercivity of samarium iron nitride magnetic powder has a very obvious size effect. According to the magnetic single domain theory, when the size of samarium iron nitride magnetic powder is greater than the single domain critical size of 0.35 microns, the coercivity of the magnetic powder will increase with the decrease of the particle size and reach the highest at the single domain critical size of 0.35 microns. Many practical studies have also confirmed the existence of this size effect. Based on this, refining the particle size of magnetic powder has become the core strategy for improving anisotropic samarium iron nitride magnetic powder for many years, and it is also the primary concern in the samarium iron nitride research field to improve the coercivity of magnetic powder.

[0005] Regarding the development work to obtain high coercivity by refining the size of magnetic powder particles, many progresses have been made so far. However, it also faces many drawbacks such as poor process friendliness or low process efficiency caused by the preparation of small particle sizes. For example, Jingwu Zheng et al. successfully prepared submicron samarium iron nitride magnetic powder by spray-assisted chemical reduction diffusion method. At a particle size of 0.616 μm, a high coercivity of 14.7 kOe was obtained (the magnetic powder is a near-spherical compact structure). However, due to the addition of special spray equipment, this method has high equipment requirements and high danger due to the repeated use of hydrogen. At the same time, since this preparation method is actually a kind of reduction diffusion method, it also fails to avoid the drawbacks commonly existing in the conventional reduction diffusion method, such as many preparation processes, complex process, and strict process control. Patent CN 114898960 A uses co-precipitation-assisted chemical diffusion reduction method to successfully reduce the samarium iron nitride magnetic powder to submicron size, and the coercivity of the magnetic powder is 11.7 - 14.3 kOe (the magnetic powder is a near-spherical compact structure). Although this method avoids the requirement of special equipment and has significantly improved process safety, the drawbacks commonly existing in the conventional reduction diffusion method, such as many preparation processes, complex process, and strict process control, still exist. Another example is that X.B. Ma et al. successfully prepared submicron flaky samarium iron nitride magnetic powder by wet ball milling-assisted powder metallurgy method (the submicron is the in-plane size of the magnetic powder sheet, the thickness size of the magnetic powder sheet is less than 100 nm, and the magnetic powder sheet is a compact structure), and obtained a high coercivity of 13.0 kOe. Although this method avoids the drawbacks such as special equipment, high danger, many processes, complex process, and strict process control, the process efficiency is relatively low (the ball milling process time is 720 min), and the too fine thickness of the submicron magnetic powder leads to room for improvement in the increase of the coercivity of the obtained magnetic powder.

[0006] In addition, although many development works have confirmed the effectiveness of refining the size of magnetic powder particles in improving the coercivity of samarium iron nitride magnetic powder, from the application perspective, during the process of processing magnetic powder into magnets, too fine particles are prone to cause powder oxidation, reduce the magnetism of the magnetic powder, increase the risk of magnetic powder ignition, and the smaller the particle size, the higher the difficulty of magnetic field orientation, which in turn easily leads to poor magnet performance due to difficult orientation. Therefore, from the actual application of magnetic powder, the more ideal particle size is micron size. Recently, Yuping Li et al. obtained high coercivity micron samarium iron nitride magnetic powder and micron samarium iron silicon nitride magnetic powder by reduction diffusion method. Although the coercivity of the samarium iron silicon nitride magnetic powder is 12.72 - 14.92 kOe, the coercivity of the samarium iron nitride magnetic powder is only 12.17 kOe. The coercivity level has been improved compared with commercial magnetic powder, but it is significantly lower than the common submicron size level. And since this magnetic powder is also obtained by reduction diffusion method, it also has the drawbacks of the reduction diffusion method itself, such as many preparation processes, complex process, and strict process control.

[0007] Therefore, how to obtain micron-sized samarium iron nitride magnetic powder with high coercivity, so that the magnetic powder has high coercivity at the micron size, especially high coercivity equivalent to that of submicron-sized magnetic powder, has become an important difficulty faced in the field of anisotropic samarium iron nitride magnetic powder. Summary of the Invention

[0008] To overcome the problem in the prior art that micron-sized samarium iron nitride magnetic powder with high coercivity cannot be obtained, the purpose of the present invention is to provide a high coercivity samarium iron nitride magnetic powder and its preparation method, to solve the technical problem that the high coercivity of conventional anisotropic samarium iron nitride magnetic powder depends on submicron refinement size, and it is difficult to obtain high coercivity at the micron size, especially difficult to obtain high coercivity equivalent to that of submicron-sized magnetic powder at the micron size, which has important application significance.

[0009] To achieve the above purpose, the technical solution adopted by the present invention is as follows:

[0010] A high coercivity samarium iron nitride magnetic powder, the high coercivity samarium iron nitride magnetic powder has anisotropy, and the particle size of the magnetic powder is micron-sized.

[0011] Further, the particle size of the high coercivity samarium iron nitride magnetic powder is 2 - 10 microns, and the coercivity of the magnetic powder ≥ 13.48 kOe.

[0012] Further, the particle size of the high coercivity samarium iron nitride magnetic powder is 2 - 5 microns, and the coercivity of the magnetic powder ≥ 14.0 kOe.

[0013] Further, the interior of the high coercivity samarium iron nitride magnetic powder is a compact structure, and the surface of the magnetic powder is an uneven structure including several protrusions and pits.

[0014] Further, in the uneven structure including several protrusions and pits, the pits are formed by the gaps between the protrusions, and there is an adhesion structure between the protrusions or between the protrusion and the surface. Through the adhesion structure, the protrusions and the internal compact structure form an integral particle; the shape of the pits is irregular, and the size is mostly from nano-size to submicron-size.

[0015] Further, the particle size of the magnetic powder is the particle size of dispersed single magnetic powder, not the particle size of agglomerated magnetic powder.

[0016] Further, the coercivity of the magnetic powder is the coercivity measured along the parallel direction of the magnetic field after the magnetic powder is oriented, and the coercivity of the magnetic powder is preferably ≥ 14.5 kOe.

[0017] A preparation method of a high coercivity samarium iron nitride magnetic powder, comprising the following steps:

[0018] Prepare an organic combined abrasive containing a solvent, a surfactant and a coupling agent in proportion, mix the organic combined abrasive with the samarium iron nitride raw material magnetic powder to obtain a mixed material;

[0019] Grind the mixed materials to obtain a ground slurry;

[0020] Perform ultrasonic dispersion on the ground slurry, and after particle screening and drying, obtain high coercivity samarium iron nitride magnetic powder.

[0021] Furthermore, the grinding is carried out under anaerobic conditions

[0022] Furthermore, the anaerobic condition is a condition where the oxygen content is lower than 0.1%;

[0023] More preferably, the anaerobic condition is a condition where the oxygen content is lower than 0.01%;

[0024] Furthermore, the anaerobic condition includes but is not limited to one of anaerobic conditions such as argon, nitrogen, helium, ammonia, etc., or a mixed condition thereof;

[0025] Furthermore, in the preparation method, all steps are carried out under anaerobic conditions;

[0026] Furthermore, the samarium iron nitride raw material magnetic powder is a powder metallurgy raw material magnetic powder with a particle size not exceeding 200 microns; the coupling agent is a silane coupling agent.

[0027] More preferably, the particle size of the samarium iron nitride raw material magnetic powder does not exceed 100 microns;

[0028] Furthermore, the solvent is n-hexane, or a mixture of n-hexane and other non-polar solvents (such as ethyl oleate, ethyl acetate, n-pentane, gasoline, etc.); the surfactant is oleic acid, oleylamine, palmitic acid, stearic acid, linoleic acid, arachidic acid or behenic acid; the coupling agent is KH550, KH560 or KH570.

[0029] Furthermore, the mass ratio of the solvent, surfactant, and coupling agent is (10 - 200):(0.5 - 200):(0 - 10); the mass ratio of the organic combined abrasive to the samarium iron nitride raw material magnetic powder is 30:100 - 400:100; for the grinding, the ball-to-material ratio is 1:1 - 25:1, and the grinding time is 20 - 360 min; for the particle screening, sedimentation screening or air flow screening is used to screen particles with a particle size of 1 - 10 microns.

[0030] Furthermore, the mass ratio of the solvent, surfactant, and coupling agent is (30 - 70):(1 - 10):(0.2 - 2); for the grinding, the ball-to-material ratio is 3:1 - 15:1, and the grinding time is 30 - 150 min.

[0031] More preferably, the mass ratio of the solvent, surfactant, and coupling agent is (40 - 60):(1 - 5):(0.1 - 1).

[0032] Further, the mass ratio of the abrasive to the samarium iron nitride raw material magnetic powder is 40:100 - 100:100.

[0033] Further, the equipment used for grinding includes but is not limited to a vibrating ball mill, a planetary ball mill, and a three-dimensional vibrating ball mill.

[0034] Further, during ultrasonic dispersion, the ultrasonic power is > 200 W and the time is > 1 min, preferably greater than 5 min.

[0035] More preferably, ultrasonic dispersion is carried out in an ultrasonic medium with the addition of a surfactant (such as sodium alkyl sulfonate or sodium fatty alcohol polyether sulfate) and a foaming agent.

[0036] Further, when using the air flow particle size screening method for screening, the mesh size of the sieve device is 1 - 10 microns, preferably 2 - 5 microns.

[0037] Further, a multi-stage sieve device is used for particle screening.

[0038] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0039] The present invention starts from regulating the internal structure of samarium iron nitride micron magnetic powder and forming magnetic domain pinning inside the particles. By using the combined conditions of a solvent, a surfactant, and a coupling agent, the ball milling energy of the samarium iron nitride raw material magnetic powder is regulated. When the grinding balls collide with the magnetic powder, it does not mainly cause the overall fragmentation of the particles, but inputs energy into the particles to trigger the generation of internal structures inside the particles, that is: most of the ball milling energy does not break the micron-sized large particles into multiple sub-micron-sized small particles, but effectively transfers to the inside of the micron-sized particles and triggers internal structure changes such as the formation of new grain boundaries, the change of lattice width, and the generation of lattice defects inside the particles. These internal structures will introduce magnetic pinning during the reverse magnetic domain movement, and thus the micron magnetic powder obtains high coercivity relying on the magnetic pinning effect rather than the size effect of the sub-micron magnetic powder.

[0040] The present invention solves the technical problem that the high coercivity of conventional anisotropic samarium iron nitride magnetic powder depends on sub-micron refinement size, and it is difficult to obtain high coercivity at the micron size, especially difficult to obtain high coercivity equivalent to that of the sub-micron size at the micron size. Compared with the conventional samarium iron nitride micron magnetic powder obtained by the prior art, the micron magnetic powder obtained by the present invention has a significantly improved coercivity level, and the coercivity level can be equivalent to that of the high coercivity level of the sub-micron samarium iron nitride magnetic powder. Compared with the sub-micron magnetic powder obtained by the prior art, the coercivity level of the present invention is equivalent to it, but the requirements for the preparation equipment are low and the process is simple. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 It is the SEM diagram of the magnetic powder obtained in Example 1 of the present invention;

[0042] Figure 2 This is the SEM image of the magnetic powder obtained in Example 2 of the present invention;

[0043] Figure 3 This is the XRD pattern of the magnetic powder obtained in Example 2 of the present invention;

[0044] Figure 4 This is the magnetization curve of the magnetic powder obtained in Example 2 of the present invention;

[0045] Figure 5 This is the demagnetization curve of the magnetic powder obtained in Example 2 of the present invention. Detailed implementation manners

[0046] To facilitate the understanding of the present invention, the present invention will be described more comprehensively below with reference to the relevant drawings. The preferred embodiments of the present invention are shown in the drawings. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein. On the contrary, these embodiments are provided to make the disclosure of the present invention more thorough and comprehensive.

[0047] A preparation method of a high coercivity samarium iron nitride magnetic powder of the present invention includes the following steps:

[0048] (1) Prepare an organic combined abrasive containing a solvent, a surfactant, and a coupling agent in proportion, mix the organic combined abrasive with the samarium iron nitride raw material magnetic powder to obtain a mixed material;

[0049] (2) Select grinding balls, mix and seal them with the mixed material in proportion, and then place them on a grinding device for grinding to obtain a grinding slurry; The grinding device includes but is not limited to a vibrating ball mill, a planetary ball mill, or a three-dimensional vibrating ball mill.

[0050] (3) Take out the grinding slurry, perform ultrasonic dispersion, and after particle screening and powder drying, obtain the target high coercivity samarium iron nitride magnetic powder with a micron size.

[0051] Among them, the samarium iron nitride raw material magnetic powder is a samarium iron nitride coarse powder prepared by a conventional powder metallurgy method, and its average particle size does not exceed 200 microns.

[0052] The organic combined abrasive includes:

[0053] Solvent: n-hexane, or a mixture of n-hexane and other non-polar solvents (such as ethyl oleate, ethyl acetate, n-pentane, gasoline, etc.); The surfactant includes but is not limited to oleic acid, oleylamine, palmitic acid, stearic acid, linoleic acid, arachidic acid, or behenic acid;

[0054] The coupling agent includes but is not limited to KH550, KH560, or KH570;

[0055] The mass ratio of the solvent, surfactant, and coupling agent is (10 - 200):(0.5 - 200):(0 - 10), preferably (30 - 70):(1 - 10):(0.2 - 2);

[0056] More preferably, the mass ratio of the solvent, surfactant, and coupling agent is (40 - 60):(1 - 5):(0.1 - 1).

[0057] The mass ratio of the organic combined abrasive to the samarium iron nitride raw material magnetic powder is 30:100 - 400:100, preferably 40:100 - 100:100.

[0058] During the grinding, the ball - to - material ratio is 1:1 - 25:1, preferably 3:1 - 15:1; the grinding time is 20 - 360 min, preferably 30 - 150 min; more preferably, the grinding time is 45 - 90 min.

[0059] For the particle size screening, sedimentation screening method or air - flow screening method is used to screen particles with a particle size of 1 - 10 microns.

[0060] When using the air - flow particle size screening method for screening, the mesh size of the screen device is 1 - 10 microns, preferably 2 - 5 microns.

[0061] Furthermore, a multi - stage screen device is preferably used.

[0062] The high - coercivity samarium iron nitride magnetic powder prepared by the present invention has anisotropy, the magnetic powder particle size is in the micron range, with a particle size of 1 - 10 microns, preferably 2 - 5 microns.

[0063] The coercivity of the magnetic powder is the coercivity measured along the direction parallel to the magnetic field after the magnetic powder is oriented, and the coercivity of the magnetic powder ≥ 13.48 kOe; preferably, the coercivity of the magnetic powder is preferably ≥ 14.0 kOe, more preferably ≥ 14.5 kOe;

[0064] The particle size of the magnetic powder is the particle size of dispersed single magnetic powder, not the particle size of agglomerated magnetic powder.

[0065] The surface and the interior of the magnetic powder have different structures. The interior is a conventional compact structure, and the surface is an uneven structure containing many protrusions and pits.

[0066] The uneven structure containing many protrusions and pits further includes that the pits are formed by the gaps between the protrusions, and there is an adhesion structure between the protrusions or between the protrusions and the surface. Through the adhesion structure, an integral particle is formed between the protrusions and the interior compact structure.

[0067] The shape of the pits is irregular, and the size is mostly in the range from nanometer size to sub - micron size.

[0068] The hard magnetic phase component of the magnetic powder is Sm2(Fe, T) 17 N 3±δ , where the T element includes but is not limited to saturation magnetization increasing and coercivity increasing elements such as Cu, Mn, V, Co, etc.;

[0069] For the magnetic powder, the mass percentages of its main elements are as follows:

[0070] Rare earth metal element Sm: 22.0 - 28.0%;

[0071] Non-rare earth metal elements Fe, T: 70.0 - 74.6%;

[0072] Non-metal element N: 2.8 - 3.5%.

[0073] Surfactants and coupling agents not only play an important role in regulating the mechanical behavior of powder fragmentation, but also have the advantages of maintaining the crystal structure of the powder and reducing powder oxidation. Surfactants and coupling agents are first the molecular bridges connecting polar powders and non-polar solvents. Both play an important role in regulating the mechanical behavior of powder fragmentation because after they are dissolved in the solvent, they can not only cause changes in the solution viscosity and thus change the impact kinetic energy of the grinding balls, but also form an effective barrier between the magnetic powders and between the magnetic powders and the grinding balls. This barrier will further weaken the actual impact energy received by the magnetic powders, and finally when the grinding balls collide with the magnetic powders in the present invention, it does not dominate particle fragmentation, but inputs into the particles to cause the generation of internal particle structures.

[0074] At the same time, there are also differences between surfactants and coupling agents in terms of their combined functions with the solvent and their effects on the magnetism of magnetic powders. Surfactants have a single-chain structure and coupling agents have a multi-chain structure. Therefore, relatively speaking, surfactants move faster in the solvent and are more likely to be preferentially adsorbed between newly formed fracture surfaces. Thus, in terms of preferentially promoting the further expansion of fracture cracks and preferentially determining the morphology of large particles after surface fragmentation, the role of surfactants is more obvious than that of coupling agents. However, surfactants have a single-point adsorption with magnetic powders, and there are often intervals between adsorption points, so the antioxidant effect on magnetic powders is not ideal. For coupling agents, the multi-chain structure determines that one molecule can form multiple adsorption points with magnetic powders. Although the moving speed is not as fast as that of surfactants, the adsorption point density with magnetic powders can far exceed that of surfactants and can form continuous and tight adsorption. Therefore, coupling agents have more advantages in enhancing the antioxidant ability of magnetic powders and promoting the acquisition of high coercivity of magnetic powders.

[0075] The following are specific examples.

[0076] Example 1

[0077] (1) Prepare an organic-inorganic homogeneous composite abrasive by mixing n-hexane, oleic acid, and KH550 silane coupling agent in a mass ratio of 52:2:2. Then, mix the composite abrasive with the powder metallurgy samarium-iron-nitrogen raw material magnetic powder in a mass ratio of 56:100 to obtain a mixed material.

[0078] (2) Select stainless steel grinding balls and mix them with the mixed material in a ball-to-material ratio of 10:1, seal them, and then place them on a vibrating ball mill for grinding. After ball milling for 90 minutes, a ground slurry is obtained.

[0079] (3) Take out the ground slurry, perform ultrasonic dispersion, screen out large particles by sedimentation, and dry the powder to obtain the target micron-sized high coercivity samarium-iron-nitrogen magnetic powder.

[0080] See Figure 1 , observe the morphology of the magnetic powder obtained in this example by scanning electron microscopy (SEM), and obtain magnetic powder with a size of 2 - 5 microns. Its surface and interior have different structures. The interior is a conventional compact structure, and the surface is an uneven structure with many protrusions and pits. Perform structural detection on the obtained magnetic powder using an X-ray diffractometer (XRD). The diffraction peak of the target magnetic powder shows broadening and left shift compared to the micron magnetic powder before treatment, indicating that the internal structure of the magnetic powder obtained in this example has changed, including grain size refinement (new grain boundaries are formed within the grains) and lattice expansion compared to the magnetic powder before the process treatment. Seal the obtained magnetic powder with epoxy resin, orient and cure it under a 3T magnetic field, magnetize it under a magnetic field of ≥6T after curing, and then measure the magnetization behavior and macroscopic magnetic properties of the magnetic powder using a vibrating sample magnetometer (VSM). The initial magnetization curve of the magnetic powder shows a concave behavior (corresponding to enhanced pinning effect) compared to the magnetic powder before treatment, and the coercivity of the magnetic powder is 14.39 kOe.

[0081] Example 2

[0082] (1) Prepare an organic composite abrasive by mixing n-hexane, oleic acid, and KH550 silane coupling agent in a mass ratio of 52:2:0.5. Then, mix the composite abrasive with the powder metallurgy samarium-iron-nitrogen raw material magnetic powder in a mass ratio of 54.5:100 to obtain a mixed material.

[0083] (2) Select stainless steel grinding balls and mix them with the mixed material in a ball-to-material ratio of 10:1, seal them, and then place them on a vibrating ball mill for grinding. After ball milling for 90 minutes, a ground slurry is obtained.

[0084] (3) Take out the ground slurry, perform ultrasonic dispersion, screen the particles by air flow, and dry the powder to obtain the target samarium-iron-nitrogen magnetic powder.

[0085] The SEM morphology of the magnetic powder obtained in this example was observed, and it was found that most of the magnetic powder was 2 - 5 microns in size, with different structures on its surface and inside. The inside was a conventional compact structure, and the surface was an uneven structure with many protrusions and pits (as shown in Figure 2 ); The structure of the obtained magnetic powder was detected by XRD. The diffraction peaks of the magnetic powder showed broadening and left shift compared with the magnetic powder before treatment (corresponding to grain refinement and lattice expansion, as shown in Figure 3 ), indicating that the internal structure of the magnetic powder obtained in this example had changed compared with the magnetic powder before treatment, including grain size refinement (new grain boundaries formed within the grains) and lattice expansion; The obtained magnetic powder was sealed with epoxy resin, oriented and cured in a 3T magnetic field, magnetized in a magnetic field of ≥6T after curing, and then the magnetization behavior and macroscopic magnetic properties of the magnetic powder were measured using a vibrating sample magnetometer (VSM). The magnetization curve of the magnetic powder showed a concave-down behavior compared with the magnetic powder before treatment (as shown in Figure 4 , corresponding to enhanced pinning effect), and the coercivity of the magnetic powder was 15.0 kOe (as shown in Figure 5 ).

[0086] Example 3

[0087] (1) According to the mass ratio of 52:2:0.5, n - hexane, oleic acid, and KH550 silane coupling agent were formulated into an organic combined abrasive, and then the combined abrasive was mixed with the powder metallurgy samarium - iron - nitrogen raw magnetic powder according to the mass ratio of 54.5:100 to obtain a mixed material;

[0088] (2) Stainless steel grinding balls were selected and mixed with the mixed material according to the ball - to - material ratio of 10:1, sealed, and then placed on a vibrating ball mill for grinding. After ball milling for 120 min, a grinding slurry was obtained;

[0089] (3) The grinding slurry was taken out, ultrasonically dispersed, and after sedimentation, screening of particles, and drying of the powder, the target micron - sized high - coercivity samarium - iron - nitrogen magnetic powder was obtained.

[0090] The SEM morphology of the magnetic powder obtained in this example was observed, and it was found that most of the magnetic powder was 1 - 5 microns in size, with different structures on its surface and inside. The inside was a conventional compact structure, and the surface was an uneven structure with many protrusions and pits; The structure of the obtained magnetic powder was detected by XRD. The diffraction peaks of the magnetic powder showed broadening and left shift compared with the magnetic powder before treatment, indicating that the internal structure of the magnetic powder obtained in this example had changed compared with the magnetic powder before the process treatment, including grain size refinement, formation of new grain boundaries, and lattice expansion; The obtained magnetic powder was sealed with epoxy resin, oriented and cured in a 3T magnetic field, magnetized in a magnetic field of ≥6T after curing, and then the magnetization behavior and macroscopic magnetic properties of the magnetic powder were measured using VSM. The magnetization curve of the magnetic powder showed a concave - down behavior and enhanced pinning effect compared with the magnetic powder before treatment, and the coercivity of the magnetic powder was 14.45 kOe.

[0091] Example 4

[0092] (1) According to the mass ratio of 52:100:0.5, n-hexane, oleic acid, and KH550 silane coupling agent were formulated into an organic combined abrasive, and then the combined abrasive and the powder metallurgy samarium iron nitride raw material magnetic powder were mixed according to the mass ratio of 152.5:100 to obtain a mixed material;

[0093] (2) Select stainless steel grinding balls, mix and seal them with the mixed material according to the ball-to-material ratio of 10:1, and then place them on a vibrating ball mill for grinding. After ball milling for 90 min, a grinding slurry was obtained;

[0094] (3) Take out the grinding slurry, perform ultrasonic dispersion, and after sedimentation screening of large particles and powder drying, the target micron-sized high coercivity samarium iron nitride magnetic powder was obtained.

[0095] The SEM morphology of the magnetic powder obtained in this example was observed, and most of the magnetic powder was 2 - 5 microns in size. Its surface and interior had different structures. The interior was a conventional compact structure, and the surface was an uneven structure containing many protrusions and pits; the structure of the obtained magnetic powder was detected by XRD, and the diffraction peaks of the magnetic powder showed broadening and left shift compared with the magnetic powder before treatment, indicating that the magnetic powder obtained in this example had internal structure changes such as grain size refinement, new grain boundary formation, and lattice expansion compared with the magnetic powder before the process treatment; the obtained magnetic powder was sealed with epoxy resin, oriented and cured under a 3T magnetic field, magnetized under a magnetic field of ≥6T after curing, and then the magnetization behavior and macroscopic magnetic properties of the magnetic powder were measured by VSM. The magnetization curve of the magnetic powder showed a concave behavior and enhanced pinning effect compared with the magnetic powder before treatment, and the coercivity of the magnetic powder was 13.56 kOe.

[0096] Example 5

[0097] (1) According to the mass ratio of 52:2:0.5, n-hexane, oleic acid, and KH550 silane coupling agent were formulated into an organic combined abrasive, and then the combined abrasive and the powder metallurgy samarium iron nitride raw material magnetic powder were mixed according to the mass ratio of 54.5:100 to obtain a mixed material;

[0098] (2) Select stainless steel grinding balls, mix and seal them with the mixed material according to the ball-to-material ratio of 10:1, and then place them on a vibrating ball mill for grinding. After ball milling for 30 min, a grinding slurry was obtained;

[0099] (3) Take out the grinding slurry, perform ultrasonic dispersion, and after screening the particles by air flow and powder drying, the target samarium iron nitride magnetic powder was obtained.

[0100] The SEM morphology of the magnetic powder obtained in this example was observed. It was found that most of the magnetic powder had a size of 2 - 10 μm, and its surface and interior had different structures. The interior was a conventional compact structure, while the surface was an uneven structure with many protrusions and pits. The structure of the obtained magnetic powder was detected by XRD. The diffraction peaks of the obtained magnetic powder showed broadening and left shift compared with those of the magnetic powder before treatment, indicating that the obtained magnetic powder in this example had internal structure changes such as grain size refinement, formation of new grain boundaries, and lattice expansion compared with the magnetic powder before the process treatment. The obtained magnetic powder was sealed with epoxy resin, oriented and cured under a 3T magnetic field, magnetized under a magnetic field of ≥6T after curing, and then the magnetization behavior and macroscopic magnetic properties of the magnetic powder were measured by VSM. It was found that the magnetization curve of the obtained magnetic powder showed a concave behavior and enhanced pinning effect compared with that of the magnetic powder before treatment, and the coercivity of the obtained magnetic powder was 13.48 kOe.

[0101] Example 6

[0102] (1) According to the mass ratio of 100:50:0.5, n - hexane, oleic acid, and KH550 silane coupling agent were formulated into an organic combined abrasive, and then the combined abrasive and the powder metallurgy samarium - iron - nitrogen raw material magnetic powder were mixed according to the mass ratio of 54.5:100 to obtain a mixed material.

[0103] (2) Stainless steel grinding balls were selected and mixed with the mixed material according to the ball - to - material ratio of 10:1, sealed, and then placed on a vibration ball mill for grinding. After 90 minutes of ball milling, a grinding slurry was obtained.

[0104] (3) The grinding slurry was taken out, ultrasonically dispersed, and after sieving large particles and drying the powder by sedimentation particle size, the target micron - sized high - coercivity samarium - iron - nitrogen magnetic powder was obtained.

[0105] The SEM morphology of the magnetic powder obtained in this example was observed. It was found that most of the magnetic powder had a size of 2 - 5 μm, and its surface and interior had different structures. The interior was a conventional compact structure, while the surface was an uneven structure with many protrusions and pits. The structure of the obtained magnetic powder was detected by XRD. The diffraction peaks of the obtained magnetic powder showed broadening and left shift compared with those of the magnetic powder before treatment, indicating that the obtained magnetic powder in this example had internal structure changes such as grain size refinement, formation of new grain boundaries, and lattice expansion compared with the magnetic powder before the process treatment. The obtained magnetic powder was sealed with epoxy resin, oriented and cured under a 3T magnetic field, magnetized under a magnetic field of ≥6T after curing, and then the magnetization behavior and macroscopic magnetic properties of the magnetic powder were measured by VSM. It was found that the magnetization curve of the obtained magnetic powder showed a concave behavior and enhanced pinning effect compared with that of the magnetic powder before treatment, and the coercivity of the obtained magnetic powder was 13.86 kOe.

[0106] Comparative Example 1

[0107] The magnetic powder was prepared according to the method disclosed by X.B. Ma et al. The specific steps are as follows:

[0108] (1) Weigh the raw samarium-iron-nitrogen magnetic powder to be processed. Then, using heptane as the solvent, add oleic acid with a mass ratio of 100% to the magnetic powder and 5% of KH550 silane coupling agent for mixing to obtain a mixed material.

[0109] (2) Select stainless steel grinding balls and mix them with the mixed material in a ball-to-material ratio of 30:1, seal them, and then place them on a vibrating ball mill for grinding. After ball milling for 720 minutes, a ground slurry is obtained.

[0110] (3) Take out the ground slurry, perform ultrasonic dispersion, and after sedimentation particle size screening and powder drying, magnetic powder is obtained.

[0111] For the magnetic powder obtained in this comparative example, SEM morphology observation was carried out. The obtained magnetic powder has a submicron particle size (three-dimensional submicron flake powder, mostly submicron in-plane and nanometer in thickness), and both the interior and surface of the particles have a conventional compact structure (the particle surface is no longer an uneven structure with many protrusions and pits); for the obtained magnetic powder, XRD was used for structure detection. The diffraction peaks of the magnetic powder showed broadening compared to those of the magnetic powder before treatment, but there was no left shift, indicating that there is no internal structure change of lattice expansion in this comparative example; for the obtained magnetic powder, epoxy resin was used for sample sealing, and it was oriented and cured under a 3T magnetic field. After curing, it was magnetized under a magnetic field of ≥6T, and then VSM was used to measure the macroscopic magnetic properties. The coercivity of the magnetic powder was obtained as 12.30 kOe.

[0112] Comparative Example 2

[0113] Replace the n-hexane solvent in the examples of the present invention with a conventional n-heptane solvent. The specific steps are as follows:

[0114] (1) Prepare an organic combined grinding agent by mixing n-heptane, oleic acid, and KH550 silane coupling agent in a mass ratio of 52:2:0.5. Then, mix the combined grinding agent with the powder metallurgy samarium-iron-nitrogen raw material magnetic powder in a mass ratio of 54.5:100 to obtain a mixed material.

[0115] (2) Select stainless steel grinding balls and mix them with the mixed material in a ball-to-material ratio of 10:1, seal them, and then place them on a vibrating ball mill for grinding. After ball milling for 30 minutes, a ground slurry is obtained.

[0116] (3) Take out the ground slurry, perform ultrasonic dispersion, and after sedimentation particle size screening and powder drying, magnetic powder is obtained.

[0117] The SEM morphology of the magnetic powder obtained in this comparative example was observed, and the magnetic powder was found to be irregular sub-micron powder with a particle size of 0.1 - 0.8 μm, and both the interior and surface of the particles had a conventional compact structure (the particle surface was no longer an uneven structure with many protrusions and pits); the XRD was used to detect the structure of the obtained magnetic powder, and the diffraction peaks of the magnetic powder showed broadening compared with those of the magnetic powder before treatment, but no left shift was observed, indicating that there was no internal structure change such as lattice expansion in this comparative example; the obtained magnetic powder was sealed with epoxy resin, oriented and cured under a 3T magnetic field, magnetized under a magnetic field of ≥6T after curing, and then the macroscopic magnetic properties were measured using VSM, and the coercivity of the magnetic powder was obtained as 12.52 kOe.

[0118] The results of SEM observation and VSM detection of the samarium iron nitride powders prepared in the above Examples 1 - 6 and Comparative Examples 1 - 2 are summarized in Table 1 as follows.

[0119] Table 1 Summary of SEM observation and VSM detection results of samarium iron nitride magnetic powders obtained in Examples 1 - 6 and Comparative Examples 1 - 2

[0120] Example Particle size Whether the surface is flat Coercivity of magnetic powder / kOe Example 1 Micron Not flat, with many protrusions and pits 14.39 Example 2 Micron Not flat, with many protrusions and pits 15.00 Example 3 Micron Not flat, with many protrusions and pits 14.45 Example 4 Micron Not flat, with many protrusions and pits 13.56 Example 5 Micron Not flat, with many protrusions and pits 13.48 Example 6 Micron Not flat, with many protrusions and pits 13.86 Comparative example 1 Sub-micron Flat 12.30 Comparative example 2 Sub-micron Flat 12.52

[0121] Through Examples 1 - 6 and Comparative Examples 1 - 2, it can be found that by the above technical solutions of the present invention, micron-sized high-coercivity samarium iron nitride magnetic powder can be effectively obtained. Compared with the samarium iron nitride micron magnetic powder obtained by the prior art, the micron magnetic powder obtained by the present invention has a significantly improved coercivity level, and the coercivity level can be comparable to that of the sub-micron samarium iron nitride magnetic powder. Compared with the sub-micron magnetic powder obtained by the prior art, the coercivity level of the present invention is comparable to it, but the requirements for the preparation equipment are low, the process is simple, and at the same time, the magnetic repeatability of the magnetic powder is high. Combining the above advantages with the strong antioxidant property of the micron magnetic powder, the magnetic powder obtained by the present invention is very suitable for large-scale applications.

[0122] Example 7

[0123] (1) According to the mass ratio of 30:1:0.2, n-hexane, oleylamine, and KH550 silane coupling agent were formulated into an organic combined abrasive, and then the combined abrasive was mixed with the powder metallurgy samarium iron nitride raw material magnetic powder according to the mass ratio of 30:100 to obtain a mixed material;

[0124] (2) Stainless steel grinding balls were selected and mixed with the mixed material according to a ball-to-material ratio of 1:1, sealed, and then placed on a three-dimensional vibration ball mill for grinding under anaerobic conditions. After ball milling for 360 min, a grinding slurry was obtained;

[0125] (3) The grinding slurry was taken out, ultrasonically dispersed, and particles with a particle size of 1 - 10 μm were screened by sedimentation, and after drying, micron-sized high-coercivity samarium iron nitride magnetic powder was obtained.

[0126] Example 8

[0127] (1) Prepare an organic combined abrasive by mixing n - hexane, palmitic acid, and KH560 silane coupling agent in a mass ratio of 70:5:2. Then, mix the combined abrasive with the powder metallurgy samarium - iron - nitrogen raw material magnetic powder in a mass ratio of 77:100 to obtain a mixed material.

[0128] (2) Select stainless - steel grinding balls, mix them with the mixed material in a ball - to - material ratio of 25:1, seal the mixture, and then place it on a planetary ball mill for grinding. After ball - milling for 20 min, a ground slurry is obtained.

[0129] (3) Take out the ground slurry, perform ultrasonic dispersion, screen out large particles and powders through sedimentation particle size, and then dry them to obtain micron - sized high - coercivity samarium - iron - nitrogen magnetic powder.

[0130] Example 9

[0131] (1) Prepare an organic combined abrasive by mixing n - hexane, stearic acid, and KH570 silane coupling agent in a mass ratio of 40:10:0.1. Then, mix the combined abrasive with the powder metallurgy samarium - iron - nitrogen raw material magnetic powder in a mass ratio of 50:100 to obtain a mixed material.

[0132] (2) Select stainless - steel grinding balls, mix them with the mixed material in a ball - to - material ratio of 3:1, seal the mixture, and then place it on a vibrating ball mill for grinding under nitrogen. After ball - milling for 60 min, a ground slurry is obtained.

[0133] (3) Take out the ground slurry, perform ultrasonic dispersion, screen out particles with a size of 1 - 10 microns through sedimentation particle size, and then dry them to obtain micron - sized high - coercivity samarium - iron - nitrogen magnetic powder.

[0134] Example 10

[0135] (1) Prepare an organic combined abrasive by mixing n - hexane, linoleic acid, and KH560 silane coupling agent in a mass ratio of 60:7:1. Then, mix the combined abrasive with the powder metallurgy samarium - iron - nitrogen raw material magnetic powder in a mass ratio of 68:100 to obtain a mixed material.

[0136] (2) Select stainless - steel grinding balls, mix them with the mixed material in a ball - to - material ratio of 15:1, seal the mixture, and then place it on a vibrating ball mill for grinding. After ball - milling for 100 min, a ground slurry is obtained.

[0137] (3) Take out the ground slurry, perform ultrasonic dispersion for 10 min, screen out particles with a size of 1 - 10 microns through sedimentation particle size, and then dry them to obtain micron - sized high - coercivity samarium - iron - nitrogen magnetic powder.

[0138] Example 11

[0139] (1) Prepare an organic combined abrasive by mixing hexane, arachidic acid, and KH570 silane coupling agent in a mass ratio of 200:200:10. Then, mix the combined abrasive with the powder metallurgy samarium iron nitride raw material magnetic powder in a mass ratio of 400:100 to obtain a mixed material.

[0140] (2) Select stainless steel grinding balls and mix and seal them with the mixed material in a ball-to-material ratio of 20:1. Then, place them on a vibration ball mill for grinding. After ball milling for 150 minutes, a ground slurry is obtained.

[0141] (3) Take out the ground slurry, perform ultrasonic dispersion, add a surfactant (sodium alkyl sulfonate) in the ultrasonic medium, screen particles with a particle size of 1 - 10 microns by sedimentation, and dry to obtain micron-sized high coercivity samarium iron nitride magnetic powder.

[0142] Example 12

[0143] (1) Prepare an organic combined abrasive by mixing hexane, behenic acid, and KH550 silane coupling agent in a mass ratio of 10:150:5. Then, mix the combined abrasive with the powder metallurgy samarium iron nitride raw material magnetic powder in a mass ratio of 60:100 to obtain a mixed material.

[0144] (2) Select stainless steel grinding balls and mix and seal them with the mixed material in a ball-to-material ratio of 25:1. Then, place them on a vibratory ball mill for grinding. After ball milling for 90 minutes, a ground slurry is obtained.

[0145] (3) Take out the ground slurry, perform ultrasonic dispersion, screen particles with a particle size of 1 - 10 microns by air flow screening method, and dry to obtain micron-sized high coercivity samarium iron nitride magnetic powder.

[0146] Example 13

[0147] (1) Prepare an organic combined abrasive by mixing hexane, oleic acid, and KH550 silane coupling agent in a mass ratio of 40:100:1.7. Then, mix the combined abrasive with the powder metallurgy samarium iron nitride raw material magnetic powder in a mass ratio of 200:100 to obtain a mixed material.

[0148] (2) Select stainless steel grinding balls and mix and seal them with the mixed material in a ball-to-material ratio of 7:1. Then, place them on a vibration ball mill for grinding. After ball milling for 45 minutes, a ground slurry is obtained.

[0149] (3) Take out the ground slurry, perform ultrasonic dispersion (add sodium fatty alcohol polyether sulfate in the ultrasonic medium), screen particles with a particle size of 2 - 5 microns by a multi-stage screen device, and dry to obtain micron-sized high coercivity samarium iron nitride magnetic powder.

[0150] Example 14

[0151] (1) Under nitrogen protection, according to a mass ratio of 200:0.5, n-hexane, n-pentane and oleic acid are formulated into an organic combined abrasive, and then the combined abrasive and the powder metallurgy samarium iron nitride raw material magnetic powder are mixed according to a mass ratio of 40:80:100 to obtain a mixed material;

[0152] (2) Select stainless steel grinding balls, and mix and seal them with the mixed material according to a ball-to-material ratio of 8:1, and then place them on a vibrating ball mill for grinding. After ball milling for 70 minutes, a grinding slurry is obtained;

[0153] (3) Take out the grinding slurry, perform ultrasonic dispersion at 300 W for 8 minutes, screen particles with a mesh size of 2 - 5 microns through a sieve device with a mesh size of 2 - 5 microns, and dry to obtain micron-sized high coercivity samarium iron nitride magnetic powder.

[0154] Example 15

[0155] (1) Under anaerobic conditions, according to a mass ratio of 100:200:10, n-hexane, ethyl oleate and oleic acid are formulated into an organic combined abrasive, and then the combined abrasive and the powder metallurgy samarium iron nitride raw material magnetic powder are mixed according to a mass ratio of 100:100:100 to obtain a mixed material;

[0156] (2) Select stainless steel grinding balls, and mix and seal them with the mixed material according to a ball-to-material ratio of 5:1, and then place them on a vibrating ball mill for grinding. After ball milling for 30 minutes, a grinding slurry is obtained;

[0157] (3) Take out the grinding slurry, perform ultrasonic dispersion at 230 W for 6 minutes, screen particles with a mesh size of 1 - 10 microns through a sieve device with a mesh size of 1 - 10 microns, and dry to obtain micron-sized high coercivity samarium iron nitride magnetic powder.

[0158] The examples in the present invention can produce micron-sized high coercivity samarium iron nitride magnetic powder.

[0159] It should be understood that the above examples are only for illustrating the technical concept and characteristics of the present invention, and the purpose is to enable those skilled in the art to understand the content of the present invention and implement it accordingly. It cannot be used to limit the protection scope of the present invention. Any equivalent changes or modifications made according to the spirit and essence of the present invention should be covered within the protection scope of the present invention.

[0160] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the technical field to which the present invention belongs. The terms used in the specification of the present invention are only for the purpose of describing specific embodiments, and are not intended to limit the present invention. The term "and / or" used herein includes any and all combinations of one or more of the related listed items.

Claims

1. A high coercivity samarium-iron-nitrogen magnetic powder, characterized in that, The high coercivity samarium iron nitride magnetic powder is anisotropic, and the particle size of the magnetic powder is in the micron range.

2. The high coercivity samarium iron nitride magnetic powder according to claim 1, characterized in that, The particle size of the high coercivity samarium iron nitride magnetic powder is 1 - 10 microns, and the coercivity of the magnetic powder is ≥ 13.48 kOe.

3. The high coercivity samarium iron nitride magnetic powder according to claim 1, wherein The interior of the high coercivity samarium iron nitride magnetic powder is a compact structure, and the surface of the magnetic powder is an uneven structure containing a number of protrusions and pits.

4. The high coercivity samarium iron nitride magnetic powder according to claim 3, characterized in that, In the uneven structure containing a number of protrusions and pits, the pits are formed by the gaps between the protrusions, and there is an adhesion structure between the protrusions or between the protrusions and the surface. Through the adhesion structure, the protrusions and the internal compact structure form an integral particle; the shape of the pits is irregular, and the size ranges from nanoscale to sub - micron scale.

5. A method for preparing high coercivity samarium iron nitride magnetic powder, characterized in that, It includes the following steps: Prepare an organic combined abrasive containing a solvent, a surfactant and a coupling agent in proportion, and mix the organic combined abrasive with the samarium iron nitride raw material magnetic powder to obtain a mixed material. Grind the mixed material to obtain a grinding slurry. Perform ultrasonic dispersion on the grinding slurry, and after particle screening and drying, obtain the high coercivity samarium iron nitride magnetic powder.

6. The preparation method of the high coercivity samarium iron nitride magnetic powder according to claim 5, characterized in that, The samarium iron nitride raw material magnetic powder is a powder metallurgy raw material magnetic powder with a particle size not exceeding 200 microns; the coupling agent is a silane coupling agent.

7. The preparation method of the high coercivity samarium iron nitride magnetic powder according to claim 5, characterized in that, The solvent is n - hexane; the surfactants are oleic acid, oleylamine, palmitic acid, stearic acid, linoleic acid, arachidic acid or behenic acid; the coupling agents are KH550, KH560 or KH570.

8. The preparation method of the high coercivity samarium iron nitride magnetic powder according to claim 5, characterized in that, The mass ratio of the organic combined abrasive to the samarium iron nitride raw material magnetic powder is 30:100 - 400:

100.

9. The preparation method of the high coercivity samarium iron nitride magnetic powder according to claim 5, characterized in that, The mass ratio of the solvent, the surfactant and the coupling agent is (10 - 200):(0.5 - 200):(0 - 10); during the grinding, the ball - to - material ratio is 1:1 - 25:1, and the grinding time is 20 - 360 min; for the particle screening, sedimentation screening method or air flow screening method is used to screen particles with a particle size of 1 - 10 microns.

10. The preparation method of the high coercivity samarium iron nitride magnetic powder according to claim 5, characterized in that, The mass ratio of the solvent, the surfactant and the coupling agent is (30 - 70):(1 - 10):(0.2 - 2); during the grinding, the ball - to - material ratio is 3:1 - 15:1, and the grinding time is 30 - 150 min.

Images