Preparation method of samarium-iron-nitrogen composite material and modification process

Abstract

The application relates to the technical field of rare earth permanent magnet materials, and discloses a preparation method and a modification process of a samarium iron-nitrogen composite material. The preparation method comprises the following steps: taking raw materials according to a proportioning ratio, wherein the raw materials comprise samarium iron-nitrogen magnetic powder, resin powder, an antioxidant and a lubricant; uniformly mixing the raw materials to obtain a mixture, feeding the mixture into a parallel double-screw extruder to perform high-temperature extrusion granulation, cooling and shaping, blowing and drying by means of an air knife, and cutting to obtain composite material granules; the modification process comprises the following steps: adding samarium iron-nitrogen main phase powder into anhydrous ethanol and oleic acid to perform wet grinding, continuously adding phosphoric acid aqueous solution and a coupling agent in a non-stop state to continue grinding, discharging, filtering and vacuum drying. The application is coupled by grinding and crushing and chemical coating modification, a passivation layer and a modification layer are continuously constructed on the surface of the magnetic powder, and the oxidation resistance of the samarium iron-nitrogen magnetic powder and the interfacial compatibility with the resin are improved.

Description

Technical Field

[0001] This invention relates to the field of rare earth permanent magnet materials technology, specifically to a method for preparing samarium iron nitrogen composite materials and a modification process. Background Technology

[0002] Samarium iron nitrogen (SFIN) magnetic powder is a rare earth permanent magnet material. SFIN composite material is a bonded magnet material prepared by mixing SFIN magnetic powder with resin powder, followed by extrusion granulation and injection molding. SFIN composite material combines the magnetic properties of SFIN magnetic powder with the molding and processing capabilities of resin matrix.

[0003] The current process for preparing samarium iron nitrogen composite materials is divided into two stages: magnetic powder preparation and composite granulation. The operation process is to refine the samarium iron nitrogen main phase alloy into samarium iron nitrogen magnetic powder through ball milling, then mix the samarium iron nitrogen magnetic powder with resin powder, feed it into a twin-screw extruder for high-temperature melt blending, and then cool and shape the material in a water tank and cut it into pellets to obtain samarium iron nitrogen composite material granules.

[0004] Because unmodified samarium iron nitride (SFIN) magnetic powder has high chemical reactivity of iron and high surface energy, existing preparation processes have certain shortcomings. During the high-temperature mixing and granulation stage of a twin-screw extruder, SFIN magnetic powder is prone to irreversible oxidation, leading to damage to its crystal structure and attenuation of the magnetic properties of the composite material. The significant difference in interfacial polarity between the inorganic SFIN magnetic powder and the organic resin matrix results in uneven dispersion of the powder in the molten resin, leading to significant particle agglomeration. This agglomeration creates micropores and localized stress concentration within the SFIN composite material, ultimately resulting in poor melt flowability and reduced mechanical strength of the injection-molded parts. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a method for preparing samarium iron nitrogen composite materials and a modification process, aiming to solve the problems of samarium iron nitrogen magnetic powder being prone to oxidation during high-temperature mixing, leading to attenuation of magnetic properties, and the poor interfacial compatibility between samarium iron nitrogen magnetic powder and resin matrix, resulting in poor material processing fluidity and reduced mechanical strength.

[0006] To achieve the above objectives, the present invention provides the following technical solution:

[0007] In a first aspect, the present invention provides a method for preparing a samarium-iron-nitrogen composite material, which adopts the following technical solution:

[0008] A method for preparing a samarium iron nitrogen composite material includes the following steps:

[0009] Weigh out the samarium iron nitrogen magnetic powder, resin powder, antioxidant, and lubricant according to the specified ratio;

[0010] The samarium iron nitrogen magnetic powder, the resin powder, the antioxidant, and the lubricant are put into a high-speed mixer and mixed evenly to obtain a mixture.

[0011] The mixture is fed into a parallel twin-screw extruder for high-temperature extrusion granulation, and the mixture is melt-extruded to form extruded strips.

[0012] The extruded strip is fed into a constant temperature water bath for cooling and shaping, the surface moisture is dried by an air knife, and it is cut by a pelletizer to obtain samarium iron nitrogen composite material granules.

[0013] By adopting the above technical solution, the high-temperature melting and high-shear action of the parallel twin-screw extruder facilitates the wetting and coating of the modified magnetic powder particles with the molten resin matrix. Water cooling, shaping, and pelletizing further help to produce composite material granules with a more uniform distribution of components, which is beneficial for subsequent injection molding processes.

[0014] Preferably, the raw materials are weighed in the following mass percentages: 79.0%-94.6% of the samarium iron nitrogen magnetic powder, 5.0%-20.0% of the resin powder, 0.2%-0.5% of the antioxidant, and 0.2%-0.5% of the lubricant. The resin powder is selected from one of polyphenylene sulfide resin powder and polyamide 12 resin powder; the antioxidant is antioxidant 1010; and the lubricant is lubricant EBS.

[0015] By employing the above technical solutions, polyphenylene sulfide resin exhibits properties such as high temperature resistance, dimensional stability, and chemical corrosion resistance, making it suitable for preparing heat-resistant magnets; polyamide 12 resin possesses good toughness and processability. Antioxidant 1010 can capture free radicals generated during hot working, helping to mitigate the thermo-oxidative degradation of the resin matrix. Lubricant EBS helps reduce internal friction of the melt and external friction between the material and the mechanical surface, improving processing fluidity. The composite of all components possesses good magnetic properties and mechanical strength.

[0016] Preferably, the precursor particles of the samarium iron nitrogen magnetic powder before modification are made by uniformly mixing 27%-31% Sm2O3 powder and 69%-73% Fe powder by mass, and adding 12%-18% metallic Ca particles relative to the total mass of Sm2O3 and Fe. The mixture is placed in an alumina crucible and heated to 1100-1200℃ under argon protection for 2-5 hours. After furnace cooling, the mixture is crushed to a particle size of 0.5mm-2mm to obtain the precursor particles. These precursor particles are then placed in a reactor equipped with an online pH meter, and deionized water is added for stirring and washing. When the pH of the slurry system drops to 8.5-9.5, washing is immediately stopped, and the mixture is centrifuged and dried in a vacuum drying oven at 50-80℃ to obtain a slightly alkaline samarium iron alloy powder with trace amounts of Ca(OH)2 adhering to its surface.

[0017] By employing the above-mentioned technical solution, alloy powder is prepared using a reduction-diffusion method. By controlling the final pH value during the washing process to 8.5-9.5, trace amounts of Ca(OH)₂ are retained on the surface of the alloy powder. These trace alkaline substances react with phosphoric acid during subsequent phosphoric acid coating treatment to form a composite precipitate of calcium phosphate and iron phosphate. Compared to a single iron phosphate film, the composite phosphate film is relatively dense and has better adhesion to the magnetic powder surface, thus contributing to improved passivation performance.

[0018] Preferably, the samarium iron nitrogen main phase powder is prepared by the following process: the slightly alkaline samarium iron alloy powder with trace amounts of Ca(OH)2 adhering to its surface is mixed evenly with 1.0%-3.0% by mass of one of NaN3 powder and calcium cyanamide powder and loaded into a multifunctional atmosphere rotary kiln with a magnetic fluid seal. The kiln is evacuated to a gauge pressure of -0.05MPa to -0.09MPa and heated to 360-430℃ and held for 1.5-2 hours. Then, high-purity nitrogen is introduced to an absolute pressure of 0.3-0.8MPa and heated to 470-520℃ and held for 2-3 hours. The kiln is then cooled to obtain the samarium iron nitrogen main phase powder.

[0019] By employing the above technical solution, NaN3 or calcium cyanamide is used as the solid nitrogen source, and a double nitriding treatment is performed in conjunction with high-purity nitrogen gas. When the temperature is raised to 360-430℃, the solid nitrogen source undergoes thermal decomposition, directly releasing highly active nitrogen atoms between alloy powder particles. Subsequently, under high-pressure nitrogen gas, the temperature is raised to 470-520℃, where gaseous nitrogen molecules and nitrogen atoms generated from solid-phase decomposition diffuse synergistically into the crystal lattice of the main phase alloy, which is beneficial for improving nitriding efficiency and helps to obtain samarium iron nitrogen main phase powder with a relatively complete phase structure.

[0020] Preferably, the process of mixing the feed into the high-speed mixer to achieve uniform mixing specifically involves:

[0021] Mix at room temperature at a speed of 800 r / min for 30-60 minutes; the main speed of the parallel twin-screw extruder is set to 8-15 r / min.

[0022] Preferably, when the resin powder is polyphenylene sulfide resin powder, the barrel temperature profile of the parallel twin-screw extruder is set sequentially from the feeding section to the die head to 280℃, 290℃, 300℃, 310℃, 310℃, and 300℃; when the resin powder is polyamide 12 resin powder, the barrel temperature profile of the parallel twin-screw extruder is set sequentially from the feeding section to the die head to 185℃, 195℃, 210℃, 220℃, 220℃, and 210℃.

[0023] By adopting the above technical solution, specific barrel temperature profiles are set for different matrix resins, exhibiting a stepped distribution from the feeding section to the die head. This temperature profile helps the resin to be better plasticized before entering the mixing zone, while also reducing the risk of resin degradation or magnetic powder oxidation caused by excessively high temperatures at the die head. Combined with a specific main unit rotation speed to generate appropriate shear force, this helps improve the dispersion effect and reduces damage to the magnetic powder caused by overheating due to shear friction.

[0024] Secondly, the present invention provides a process for modifying samarium iron nitrogen composite materials, comprising the following steps:

[0025] Samarium iron nitrogen main phase powder is put into a wet ball mill with a temperature control jacket. Anhydrous ethanol and oleic acid accounting for 1.0%-3.0% of the magnetic powder mass are added at a liquid-solid ratio of 1:1. The jacket water temperature is controlled to maintain the system at 35-45℃, and the mixture is ground at 400-700 r / min for 30-60 minutes.

[0026] Add a phosphoric acid aqueous solution with a mass concentration of 85% at 0.5%-1.5% of the magnetic powder mass dropwise without stopping the machine, and continue grinding for 1-2 hours at 75-85℃.

[0027] Add 0.5%-2.0% of one of KH-550 silane coupling agents and KH-560 coupling agents by weight of the magnetic powder and continue grinding for 20-40 minutes. Filter the discharged material and vacuum dry it at 60-90°C to obtain the modified samarium iron nitrogen magnetic powder.

[0028] By adopting the above technical solution, this invention couples grinding and pulverization with chemical coating modification to achieve multiple composite modifications on the surface of samarium iron nitrogen magnetic powder. The specific reaction process and mechanism are as follows:

[0029] In the first stage, preliminary dispersion and grinding are carried out using oleic acid at a low temperature of 35-45℃. Oleic acid molecules contain long-chain hydrophobic C-H bonds and polar carboxyl groups. The polar carboxyl groups can be adsorbed on the surface of samarium iron nitrogen magnetic powder. The long-chain C-H bonds are arranged outward, reducing the surface energy of the magnetic powder and helping to reduce particle agglomeration, thus providing a more uniform reaction interface for subsequent coating. At the same time, the low temperature helps to reduce the probability of oxidation of the newly formed active surfaces generated during mechanical grinding.

[0030] In the second stage, the temperature is raised to 75-85℃ using a temperature-controlled jacket to provide the activation energy required for the reaction, and an aqueous phosphoric acid solution is added dropwise to continue grinding. The phosphoric acid reacts chemically with trace oxides or adhering alkaline substances on the surface of the magnetic powder, forming a relatively stable phosphate inorganic passivation film in situ on the magnetic powder surface. This passivation film can block the penetration of oxygen and moisture into the magnetic powder, helping to improve its antioxidant and high-temperature resistance properties.

[0031] In the third stage, a coupling agent is added dropwise and the grinding process continues for 20-40 minutes. The groups generated after the coupling agent is hydrolyzed undergo a condensation reaction with the hydroxyl groups remaining on the phosphate coating layer or the surface of the magnetic powder, forming chemical bonds. The other end of the coupling agent has an organophilic group, which can physically entangle or chemically react with the macromolecular chains when mixed with the resin matrix in the subsequent process, which is beneficial to improving the interfacial compatibility between inorganic magnetic powder and organic resin.

[0032] The above-described wet ball milling process is carried out continuously in the same equipment. By adjusting the temperature and controlling the grinding time, each step achieves the in-situ continuous construction of the oleic acid dispersion layer, phosphate passivation layer, and coupling agent modification layer. This helps reduce the possibility of secondary oxidation of intermediate products exposed to air, helps maintain the relative integrity of the coating layer, and helps improve the uniformity of powder modification and production efficiency.

[0033] This invention provides a method for preparing samarium iron nitrogen composite materials and a modification process. It has the following beneficial effects:

[0034] 1. This invention constructs a hydrophobic interface, a phosphate inorganic passivation film, and an organic modification layer sequentially on the surface of samarium iron nitrogen magnetic powder through the continuous dripping and grinding of oleic acid, phosphoric acid aqueous solution, and coupling agent. This blocks the penetration of oxygen and moisture into the magnetic powder, improving the oxidation resistance and high temperature resistance of the magnetic powder. At the same time, the organic-loving groups at the end of the coupling agent improve the interfacial compatibility between the inorganic magnetic powder and the organic resin matrix, enabling the magnetic powder to be uniformly dispersed in the composite material and ensuring the mechanical strength of the final injection-molded magnet.

[0035] 2. This invention uses a reduction diffusion method to prepare alloy powder and strictly controls the pH value during the washing stage to retain trace amounts of calcium hydroxide on the powder surface. In the subsequent phosphoric acid coating step, trace amounts of alkaline substances react with phosphoric acid to generate a composite precipitate of calcium phosphate and iron phosphate. Compared with a single iron phosphate layer, this composite phosphate film structure is more compact and has stronger adhesion to the magnetic powder surface, further improving the passivation effect of the magnetic powder surface.

[0036] 3. This invention couples mechanical grinding and pulverization with chemical surface coating processes, continuously completing dispersion, passivation, and coupling modification in the same temperature-controlled wet ball mill. This avoids secondary oxidation of the modified intermediate products when exposed to air, ensuring the integrity of the chemical coating layer. At the same time, it reduces material transfer steps, simplifies the process flow, and improves the production efficiency of magnetic powder modification. Attached Figure Description

[0037] Figure 1 This is a comparison chart of the overall nitrogen content of the main phase powder and the core nitrogen content under different processes in embodiments of the present invention.

[0038] Figure 2 This is a graph showing the relationship between the powder suspension rate of magnetic powder and the standing time under different surface modification processes in this embodiment of the invention.

[0039] Figure 3 This is a graph showing the relationship between the oxidation weight gain rate of magnetic powder under different surface modification processes and high-temperature aging time in an embodiment of the present invention.

[0040] Figure 4 This is a comparison chart showing the irreversible flux loss rate of bonded magnets prepared under different processes in embodiments of the present invention as a function of high-temperature aging time. Detailed Implementation

[0041] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. 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.

[0042] Preparation Examples 1-4:

[0043] Preparation Example 1:

[0044] This preparation example provides a method for preparing samarium iron nitrogen magnetic powder, including the following steps:

[0045] Weigh out 29% Sm2O3 powder and 71% Fe powder by mass percentage, mix them evenly, add 15% of metallic Ca particles relative to the total mass of Sm2O3 and Fe, put them into an alumina crucible, and react at a constant temperature of 1150℃ for 3 hours under argon protection at a rate of 8℃ / min. After cooling in the furnace, crush them to a particle size of 0.5mm-2mm to obtain precursor particles.

[0046] The precursor particles were put into a reactor equipped with an online pH meter, and deionized water was added for stirring and washing. When the pH value of the slurry system dropped to 9.0, washing was stopped immediately and centrifuged. The mixture was then dried in a vacuum drying oven at 60°C to obtain a slightly alkaline samarium-iron alloy powder with trace amounts of Ca(OH)2 on its surface.

[0047] The slightly alkaline alloy powder was mixed evenly with 2.0% NaN3 powder and loaded into a multi-functional atmosphere rotary kiln with a magnetic fluid seal. The rotation speed was set to 2 r / min, the vacuum was evacuated to -0.07 MPa, and the temperature was raised to 400℃ and held for 2 hours.

[0048] Then, high-purity nitrogen gas was introduced to an absolute pressure of 0.5 MPa, the rotation speed was adjusted to 6 r / min, the temperature was raised to 500℃ and held for 2.5 hours, and then cooled to obtain samarium iron nitrogen main phase powder.

[0049] The main phase powder was put into a wet ball mill with a temperature-controlled jacket. Anhydrous ethanol and 2.0% oleic acid by weight of the magnetic powder were added at a liquid-solid ratio of 1:1. The jacket water temperature was controlled to maintain the system at 40℃, and the mixture was ground at 500 r / min for 45 minutes.

[0050] While maintaining continuous operation, add 1.0% (by weight of magnetic powder) of an aqueous phosphoric acid solution (85% by mass concentration) dropwise, heat to 80°C, and continue grinding for 1.5 hours. Finally, add 1.0% (by weight of magnetic powder) of KH-550 silane coupling agent and continue grinding for 30 minutes. Filter the material and vacuum dry it at 80°C to obtain samarium iron nitrogen magnetic powder.

[0051] Preparation Example 2:

[0052] This preparation example provides a method for preparing samarium iron nitrogen magnetic powder, including the following steps:

[0053] Weigh out 27% Sm2O3 powder and 73% Fe powder by mass percentage, mix them evenly, add 12% of metallic Ca particles relative to the total mass of Sm2O3 and Fe, put them into an alumina crucible, heat to 1100℃ under argon protection and react at a constant temperature for 2 hours, cool with the furnace and crush to a particle size of 0.5mm-2mm to obtain precursor particles.

[0054] The precursor particles were put into a reactor equipped with an online pH meter, and deionized water was added for stirring and washing. When the pH value of the slurry system dropped to 8.5, washing was stopped immediately and centrifuged. The mixture was then dried in a vacuum drying oven at 50°C to obtain a slightly alkaline samarium iron alloy powder with trace amounts of Ca(OH)2 on its surface.

[0055] The slightly alkaline alloy powder was mixed evenly with 1.0% NaN3 powder and loaded into a multi-functional atmosphere rotary kiln with a magnetic fluid seal. The rotation speed was set to 1 r / min, the vacuum was evacuated to -0.05 MPa, and the temperature was raised to 360℃ and held for 1.5 hours.

[0056] Then, high-purity nitrogen gas was introduced to an absolute pressure of 0.3 MPa, the rotation speed was adjusted to 5 r / min, the temperature was raised to 470℃ and held for 2 hours, and then cooled to obtain samarium iron nitrogen main phase powder.

[0057] The main phase powder was put into a wet ball mill with a temperature-controlled jacket. Anhydrous ethanol and oleic acid accounting for 1.0% of the magnetic powder mass were added at a liquid-to-solid ratio of 1:1. The jacket water temperature was controlled to maintain the system at 35℃, and the mixture was ground at 400 r / min for 20 minutes.

[0058] Add 0.5% (85% by mass) of phosphoric acid aqueous solution (by mass of magnetic powder) dropwise without stopping the machine, and heat to 75°C and continue grinding for 1 hour.

[0059] Finally, add 0.5% KH-550 silane coupling agent by weight of the magnetic powder and continue grinding for 20 minutes. Filter the material and vacuum dry it at 60°C to obtain samarium iron nitrogen magnetic powder.

[0060] Preparation Example 3:

[0061] This preparation example provides a method for preparing samarium iron nitrogen magnetic powder, including the following steps:

[0062] Weigh out 31% Sm2O3 powder and 69% Fe powder by mass percentage, mix them evenly, add 18% of metallic Ca particles relative to the total mass of Sm2O3 and Fe, put them into an alumina crucible, heat to 1200℃ under argon protection and react at a constant temperature for 5 hours, cool with the furnace and crush to a particle size of 0.5mm-2mm to obtain precursor particles.

[0063] The precursor particles were put into a reactor equipped with an online pH meter, and deionized water was added for stirring and washing. When the pH value of the slurry system dropped to 9.5, washing was stopped immediately and centrifuged. The mixture was then dried in a vacuum drying oven at 80°C to obtain a slightly alkaline samarium iron alloy powder with trace amounts of Ca(OH)2 on its surface.

[0064] The slightly alkaline alloy powder was mixed evenly with 3.0% NaN3 powder and loaded into a multifunctional atmosphere rotary kiln with a magnetic fluid seal. The rotation speed was set to 3 r / min, the vacuum was evacuated to -0.09 MPa, and the temperature was raised to 430℃ and held for 2 hours.

[0065] Then, high-purity nitrogen gas was introduced to an absolute pressure of 0.8 MPa, the rotation speed was adjusted to 8 r / min, the temperature was raised to 520℃ and held for 3 hours, and then cooled to obtain samarium iron nitrogen main phase powder.

[0066] The main phase powder was put into a wet ball mill with a temperature-controlled jacket. Anhydrous ethanol and oleic acid accounting for 3.0% of the magnetic powder mass were added at a liquid-to-solid ratio of 1:1. The jacket water temperature was controlled to maintain the system at 45℃, and the mixture was ground at 700 r / min for 60 minutes.

[0067] Add 1.5% (85% by mass) of phosphoric acid aqueous solution (by mass of magnetic powder) dropwise without stopping the machine, and heat to 85°C and continue grinding for 2 hours.

[0068] Finally, add 2.0% KH-550 silane coupling agent by weight of the magnetic powder and continue grinding for 40 minutes. Filter the material and vacuum dry it at 90°C to obtain samarium iron nitrogen magnetic powder.

[0069] Preparation Example 4:

[0070] This preparation example provides a method for preparing samarium iron nitrogen magnetic powder, including the following steps: weigh 29% Sm2O3 powder and 71% Fe powder by mass percentage, mix them evenly, add 15% of metallic Ca particles relative to the total mass of Sm2O3 and Fe, put them into a corundum crucible, heat to 1150℃ at 8℃ / min under argon protection and react at a constant temperature for 3 hours, cool with the furnace and crush to a particle size of 0.5mm-2mm to obtain precursor particles.

[0071] The precursor particles were put into a reactor equipped with an online pH meter, and deionized water was added for stirring and washing. When the pH value of the slurry system dropped to 9.0, washing was stopped immediately and centrifuged. The mixture was then dried in a vacuum drying oven at 60°C to obtain a slightly alkaline samarium-iron alloy powder with trace amounts of Ca(OH)2 on its surface.

[0072] The slightly alkaline alloy powder was mixed evenly with 2.0% calcium cyanamide (CaCN2) powder and loaded into a multi-functional atmosphere rotary kiln with a magnetic fluid seal. The rotation speed was set to 2 r / min, the vacuum was evacuated to -0.07 MPa, and the temperature was raised to 400℃ and held for 2 hours.

[0073] High-purity nitrogen was then introduced to an absolute pressure of 0.5 MPa, the rotation speed was adjusted to 6 r / min, and the temperature was raised to 500℃ and held for 2.5 hours. After cooling, samarium iron nitrogen main phase powder was obtained. This main phase powder was put into a wet ball mill with a temperature-controlled jacket, and anhydrous ethanol and oleic acid (2.0% of the magnetic powder mass) were added at a liquid-to-solid ratio of 1:1. The jacket water temperature was controlled to maintain the system at 40℃, and the milling was carried out at 500 r / min for 45 minutes.

[0074] Add 1.0% (85% by mass) of phosphoric acid aqueous solution (by mass of magnetic powder) dropwise without stopping the machine, heat to 80°C and continue grinding for 1.5 hours.

[0075] Finally, add 1.0% KH-560 coupling agent by weight of the magnetic powder and continue grinding for 30 minutes. Filter the material and vacuum dry it at 80°C to obtain samarium iron nitrogen magnetic powder.

[0076] Examples 1-4:

[0077] Example 1:

[0078] This embodiment provides a method for preparing a samarium-iron-nitrogen composite material, including the following steps:

[0079] Weigh out 89.4% of the samarium iron nitrogen magnetic powder obtained from Preparation Example 1, 10.0% of the polyphenylene sulfide (PPS) resin powder, 0.3% of the antioxidant 1010 and 0.3% of the lubricant EBS (N,N'-ethylene bis-stearamide) by mass percentage.

[0080] The above materials are put into a high-speed mixer and mixed at 800 r / min for 45 minutes at room temperature.

[0081] The uniformly mixed material is fed into a parallel twin-screw extruder for high-temperature extrusion granulation. The barrel temperature profile of the twin-screw extruder is set sequentially from the feeding section to the die head as 280℃, 290℃, 300℃, 310℃, 310℃, and 300℃, and the main extruder speed is set to 12 r / min.

[0082] After the material is melted at high temperature and blended and extruded under high shear, the extruded strip enters a constant temperature water bath to cool and solidify. The surface moisture is dried by an air knife and then cut by a pelletizer to obtain samarium iron nitrogen composite material granules.

[0083] Example 2:

[0084] This embodiment provides a method for preparing a samarium-iron-nitrogen composite material, including the following steps:

[0085] Weigh out 94.6% of the samarium iron nitrogen magnetic powder obtained from Preparation Example 2, 5.0% of the polyphenylene sulfide (PPS) resin powder, 0.2% of the antioxidant 1010 and 0.2% of the lubricant EBS by mass percentage.

[0086] The above materials are put into a high-speed mixer and mixed at 800 r / min for 30 minutes at room temperature.

[0087] The uniformly mixed material is fed into a parallel twin-screw extruder for high-temperature extrusion granulation. The barrel temperature profile of the twin-screw extruder is set sequentially from the feeding section to the die head as 280℃, 290℃, 300℃, 310℃, 310℃, and 300℃, and the main extruder speed is set to 8 r / min.

[0088] After the material is melted at high temperature and blended and extruded under high shear, the extruded strip enters a constant temperature water bath to cool and solidify. The surface moisture is dried by an air knife and then cut by a pelletizer to obtain samarium iron nitrogen composite material granules.

[0089] Example 3:

[0090] This embodiment provides a method for preparing a samarium-iron-nitrogen composite material, including the following steps:

[0091] Weigh out 79.0% of the samarium iron nitrogen magnetic powder obtained from Preparation Example 3, 20.0% of the polyphenylene sulfide (PPS) resin powder, 0.5% of the antioxidant 1010 and 0.5% of the lubricant EBS by mass percentage.

[0092] The above materials are put into a high-speed mixer and mixed at 800 r / min for 60 minutes at room temperature.

[0093] The uniformly mixed material is fed into a parallel twin-screw extruder for high-temperature extrusion granulation. The barrel temperature profile of the twin-screw extruder is set sequentially from the feeding section to the die head as 280℃, 290℃, 300℃, 310℃, 310℃, and 300℃, and the main extruder speed is set to 15 r / min.

[0094] After the material is melted at high temperature and blended and extruded under high shear, the extruded strip enters a constant temperature water bath to cool and solidify. The surface moisture is dried by an air knife and then cut by a pelletizer to obtain samarium iron nitrogen composite material granules.

[0095] Example 4:

[0096] This embodiment provides a method for preparing a samarium-iron-nitrogen composite material, including the following steps:

[0097] Weigh out 89.4% of the samarium iron nitrogen magnetic powder obtained from Preparation Example 1, 10.0% of polyamide 12 (PA12) resin powder, 0.3% of antioxidant 1010 and 0.3% of lubricant EBS by mass percentage.

[0098] The above materials are put into a high-speed mixer and mixed at 800 r / min for 45 minutes at room temperature.

[0099] The uniformly mixed material is fed into a parallel twin-screw extruder for high-temperature extrusion granulation. The barrel temperature profile of the twin-screw extruder is set sequentially from the feeding section to the die head as 185℃, 195℃, 210℃, 220℃, 220℃, and 210℃, and the main extruder speed is set to 12 r / min.

[0100] After the mixture is melt-extruded, the extruded strip enters a constant temperature water bath for cooling and shaping. The surface moisture is dried by an air knife, and the strip is cut by a pelletizer to obtain samarium iron nitrogen composite material granules.

[0101] Comparative Examples 1-4:

[0102] Comparative Example 1:

[0103] Compared with Example 1, the differences are as follows: in the precursor washing stage, the slurry system is washed to pH=7.0 neutral; in the nitriding stage, constant pressure nitriding at atmospheric pressure (0.1MPa) is used throughout; in the powder modification stage, oleic acid and phosphoric acid aqueous solution are not added, only 1.0% KH-550 is added for conventional grinding, and the rest are the same.

[0104] Comparative Example 2:

[0105] Compared with Example 1, the difference is that in the precursor washing stage, the amount of deionized water is increased and the washing time is extended. The slurry system is washed until the pH=7.0 neutral, then the washing is stopped and centrifuged to completely remove the calcium residue on the surface. All other aspects are the same.

[0106] Comparative Example 3:

[0107] Compared with Example 1, the difference is that during the nitriding stage, the rotary kiln containing the material is heated to 450°C and held at that temperature for 4.5 hours. During this period, nitrogen gas is introduced into the kiln throughout and maintained at atmospheric pressure (0.1MPa). Negative pressure vacuum induction and positive pressure deep expansion nitrogen operation are not performed. All other operations are the same.

[0108] Comparative Example 4:

[0109] Compared with Example 1, the difference is that in the wet ball milling modification stage, 2.0% oleic acid and 1.0% phosphoric acid aqueous solution by mass of magnetic powder are added to the ball mill at room temperature at one time, and the temperature is directly raised to 80°C for continuous grinding for 2 hours. The step-time operation of low temperature followed by high temperature is not performed. All other steps are the same.

[0110] Test Examples 1-4:

[0111] Test Example 1:

[0112] 200 grams of the main phase powder from Preparation Example 1, Preparation Example 2, Preparation Example 3, and Comparative Examples 1 and 3 after the nitriding stage were weighed out respectively. Each group of main phase powder was divided into two equal parts, which were labeled as the original sample group and the etching group respectively.

[0113] The pulse heating inert gas melting combined with thermal conductivity method was used. The original sample powder was placed in a graphite crucible and heated to melt. The overall nitrogen mass fraction of the powder was determined using an oxygen and nitrogen analyzer, and the average data of multiple parallel tests was recorded as the overall mass fraction parameter.

[0114] The etched powder was placed in a 0.12 mol / L dilute hydrochloric acid solution, the system temperature was kept constant at 25℃, and the mixture was slowly stirred at 150 r / min for 22 minutes to allow the surface material of the powder to undergo controllable weak acid exfoliation.

[0115] When the mass loss of powder in the reaction system reaches 14% to 16% of the initial mass, a large amount of deionized water is immediately added to dilute and terminate the etching reaction. The remaining core powder is separated by vacuum filtration and then vacuum dried at 60°C for 12 hours.

[0116] Using the same instruments and calibration parameters as the original sample group, the dried core powder was independently tested to obtain the mass fraction of dissolved nitrogen in its core region.

[0117] Table 1. Test data of nitrogen mass fraction in Preparation Examples 1 to 3 and comparative examples

[0118] Sample source Overall nitrogen mass fraction (%) Nitrogen mass fraction (%) in the heart Preparation Example 1 3.47 3.39 Preparation Example 2 3.21 3.14 Preparation Example 3 3.68 3.55 Comparative Example 1 2.94 1.62 Comparative Example 3 3.05 1.87

[0119] Conclusions and Analysis:

[0120] According to Table 1 and Figure 1 The data from Preparation Examples 1, 2, and 3 show a high degree of consistency in the overall nitrogen content and the nitrogen content in the core of the main phase powders, with the mass fraction difference before and after etching generally remaining within 0.13%. Conventional constant-pressure nitriding processes often face technical bottlenecks in industrial production due to impeded deep mass transfer. When nitrogen molecules contact the surface of precursor particles at atmospheric pressure, the surface alloy rapidly undergoes a nitriding reaction accompanied by volume expansion of the crystal lattice. This localized expansion caused by phase transformation squeezes and closes the original micropores inside the powder from the outside in, making it difficult for subsequent reacting gases to overcome physical resistance and continue to diffuse into the core. The test data from Comparative Examples 1 and 3 directly reflect this physical limitation phenomenon; the nitrogen mass fraction in the core shows a significant decrease compared to the overall value, with a decrease exceeding 38%, revealing a large number of unreacted, nitrogen-depleted soft magnetic regions inside the particles.

[0121] The introduction of dynamic pressure swing nitriding bypasses the gas-phase diffusion barrier caused by surface densification. In the vacuum negative pressure induction stage, residual gas in the precursor micropores is forcibly extracted, opening up the capillary transport network extending to the particle core. In the positive pressure deep diffusion stage, the absolute pressure gradient forces nitrogen gas in a high-concentration state to enter the deep layer of the powder along the pre-cleaned pores, directly reaching the interior of the particles for in-situ reaction under pressure difference. This sequential gas pressure operation delays the premature closure of surface pores, providing a continuous thermodynamic driving force for the solid solution of nitrogen atoms in the deep alloy lattice. The etching results of the prepared examples confirm that the nitriding degree in the core region has reached a level similar to that of the surface layer. The homogenization of the overall composition eliminates the local demagnetization nucleation sites caused by the residue of soft magnetic phase at the microscopic physical mechanism, providing a basic material guarantee for the subsequent composite material to maintain stable intrinsic coercivity.

[0122] Test Example 2:

[0123] 15.0 grams of the samarium iron nitrogen magnetic powder finally prepared in Preparation Example 1, Preparation Example 2, Preparation Example 3, and Comparative Example 1 and Comparative Example 4 were weighed out respectively as samples for surface polarity reversal test.

[0124] Each group of test samples was poured into a 500 ml transparent beaker containing 300 ml of deionized water. The mechanical stirrer was started and the mixture was dispersed at a speed of 400 r / min for 10 minutes to ensure that the powder was fully mixed in the aqueous medium.

[0125] Turn off the mechanical stirrer and place the beaker on a vibration-free test bench. At test points where the settling time reaches 10 minutes, 30 minutes, and 60 minutes, carefully collect the suspended magnetic powder floating on the liquid surface using a skimmer.

[0126] The collected suspended magnetic powder was transferred to a constant-weight petri dish and then dried in a vacuum drying oven at 80°C until its mass no longer changed.

[0127] The mass of dried powder collected at each time point was weighed using a high-precision analytical balance, and the percentage of the powder collected at each time point was calculated to obtain the powder suspension rate data that characterizes the surface oleophilic properties at the corresponding time point.

[0128] Table 2. Powder suspension rate test data of Preparation Examples 1 to 3 and Comparative Examples as a function of standing time

[0129] Sample source 10-minute static suspension rate (%) 30-minute static suspension rate (%) Suspension rate after 60 minutes of settling (%) Preparation Example 1 99.82 99.63 99.41 Preparation Example 2 99.37 98.92 98.75 Preparation Example 3 99.54 99.31 99.13 Comparative Example 1 25.68 15.34 12.31 Comparative Example 4 78.41 73.18 68.57

[0130] Conclusions and Analysis:

[0131] From Table 2 and Figure 2The data distribution shows that the modified magnetic powders prepared in Examples 1 to 3 exhibit significant suspension stability in the aqueous medium. Even after standing for 60 minutes, their powder suspension rate remained stable at over 98.7%. This macroscopic anti-settling physical phenomenon directly proves that the powder surface has changed from its original high-energy hydrophilic state to a low-surface-energy oleophilic state. Traditional wet grinding often relies solely on silane coupling agents for direct coating. As shown in the test results of Comparative Example 1, due to the lack of a dense organic binding layer on the powder surface, the interfacial polarity reversal is incomplete, and most high-density particles quickly overcome the surface tension of water and settle to the bottom within a short time. In contrast, this invention utilizes the slightly alkaline residue on the precursor surface as a trigger point for the chemical reaction, promoting the preferential in-situ saponification of oleic acid at the inorganic interface, forming a coating layer with hydrophobic properties.

[0132] The timing of reagent addition has a decisive impact on the final powder coating state. Comparative Example 4, which used a mixture of oleic acid and phosphoric acid aqueous solution added simultaneously at room temperature, achieved an initial suspension rate of barely 78.41%, but this rate showed a significant and continuous decline with increasing standing time, eventually dropping to 68.57%. The mixed reagents underwent competitive physical adsorption and even side reactions at room temperature, disrupting the orderly reaction sequence of powder particle deagglomeration followed by coating. This resulted in numerous dense defects in the in-situ grown inorganic and organic coating layers, and the exposed polar hydrophilic sites caused powder agglomeration in water and accelerated sedimentation.

[0133] The preparation group strictly adhered to the sequential operation logic of step-temperature variation. The phosphoric acid aqueous solution was introduced at a specific high-temperature reaction stage, not only completely replacing calcium ions in the system to form an insoluble polybasic calcium phosphate barrier layer, but also further locking the hydrophobic long-chain alkyl groups on the surface through multi-site chemical bonding. This microscopic encapsulation mechanism helps avoid the generation of free coating agents, ensuring that each powder particle surface is endowed with a uniform and robust oleophilic barrier. This lays a reliable physicochemical foundation for subsequent efficient wetting of the resin matrix without dead zones and for the uniform transfer of interfacial stress within the composite material.

[0134] Test Example 3:

[0135] 20.0 grams of the samarium iron nitrogen magnetic powder finally prepared in Preparation Example 1, Preparation Example 2, Preparation Example 3, Comparative Example 1 and Comparative Example 4 were weighed out respectively as samples for high-temperature antioxidant performance testing.

[0136] Each group of test samples was spread evenly in a pre-weighed, dry alumina crucible to ensure that the powder spread thickness was uniform (controlled at about 2 mm) in order to eliminate the interference of the stacking effect on gas diffusion.

[0137] The alumina crucible containing the sample was transferred into a high-temperature aging test chamber with forced convection. The chamber was set to a constant temperature of 150°C in an air atmosphere for continuous high-temperature accelerated oxidation exposure.

[0138] At test nodes where the aging exposure time reached 100 hours, 300 hours, and 500 hours, the crucible was removed and quickly placed in a vacuum desiccator containing desiccant to cool to room temperature.

[0139] The total mass of the sample after cooling at each time point was weighed using a high-precision analytical balance with an accuracy of 0.1 mg, and the percentage increase in mass relative to the initial input mass was calculated to obtain the oxidation weight gain rate data characterizing the antioxidant capacity of the powder at the corresponding time point.

[0140] Table 3. Test data on the oxidative weight gain of powders in Preparation Examples 1 to 3 and the comparative examples as a function of aging time.

[0141] Sample source Weight gain rate after 100 hours of oxidation (%) Weight gain rate after 300 hours of oxidation (%) Weight gain rate after 500 hours of oxidation (%) Preparation Example 1 0.12 0.21 0.31 Preparation Example 3 0.15 0.25 0.38 Preparation Example 2 0.18 0.32 0.48 Comparative Example 4 0.52 1.15 1.88 Comparative Example 1 0.85 1.76 2.94

[0142] Conclusions and Analysis:

[0143] Observation Table 3 and Figure 3 The data distribution clearly shows that the modified magnetic powders prepared in Examples 1 to 3 exhibited excellent thermodynamic stability in a harsh aerobic environment at 150°C. With prolonged exposure time, the oxidative weight gain rate increased slowly, and even after 500 hours of high-temperature aging, the weight gain rate was still strictly controlled below 0.48%. Due to the poor intrinsic thermal stability of samarium iron nitrogen materials, they readily undergo irreversible oxidation reactions with oxygen at high temperatures, generating a non-magnetic phase. In Comparative Example 1, the powder coated solely with a traditional silane coupling agent lacked a dense, non-porous physical barrier layer on its surface, allowing oxygen molecules to easily penetrate the thin organic layer and reach the powder surface, resulting in an oxidative weight gain rate of 2.94% after 500 hours. This indicates that its microscopic magnetic domain structure had been severely damaged.

[0144] The test data of Comparative Example 4 also revealed a fatal flaw caused by incorrect reagent addition timing. Due to the competitive adsorption of oleic acid and phosphoric acid at room temperature, the density of the coating layer was compromised. This coating structure, containing microscopic pores and phase boundary defects, was prone to localized cracking under high-temperature thermal stress, resulting in a 500-hour weight gain of only 1.88%, which failed to meet the standards for stringent industrial applications. In contrast, the preparation group strictly controlled the temperature gradient and timing to grow a bilayer inorganic-organic composite protective layer on the magnetic powder surface in situ. This layer consisted of an inner layer of polyphosphate calcium salt and an outer layer of hydrophobic alkyl chains of calcium soap. This structure not only achieved a complete polarity reversal at room temperature but also exhibited physical isolation at high temperatures. The dense inorganic phosphate undercoat cut off the lattice diffusion channels of oxygen atoms, while the tightly interlocked organic long chains of the outer layer buffered the interfacial stress caused by thermal expansion and contraction. The synergistic effect of both inhibited the high-temperature oxidation reaction from the source, extending the weather resistance and magnetic performance retention of the samarium iron nitrogen magnetic powder throughout its service life.

[0145] Figure 3 This is a graph showing the relationship between the oxidation weight gain rate of magnetic powder under different surface modification processes of the present invention and the change of high temperature aging time. The graph distinguishes the differences in high temperature oxidation behavior of Preparation Example 1, Preparation Example 2, Preparation Example 3 and Comparative Example 1 and Comparative Example 4 in air atmosphere by different gray line types.

[0146] Test Example 4:

[0147] Appropriate amounts of the samarium iron nitrogen magnetic powders finally prepared in Preparation Example 1, Preparation Example 2, Preparation Example 3, Comparative Example 1, and Comparative Example 4 were weighed and mixed uniformly with epoxy resin in a mixer at a mass ratio of 97.5:2.5 to granulate.

[0148] The granulated mixture is placed in a mold and pressed into a cylindrical anisotropic bonded magnet (10mm x 10mm) under a 1.5T orientation magnetic field and a molding pressure of 800MPa. It is then cured at 150℃ for 2 hours.

[0149] The cylindrical sample was saturated with magnetizer under a pulsed magnetic field greater than 4.5T, and then its initial open-circuit magnetic flux was accurately measured at room temperature (25℃) using a fluxmeter.

[0150] The test samples were moved into a high-temperature aging test chamber set at 120°C and subjected to continuous heat exposure in the air environment.

[0151] The samples were removed at 100 hours, 300 hours and 500 hours of aging time, and allowed to cool and recover fully at room temperature for 2 hours before their open-circuit magnetic flux was measured again.

[0152] The irreversible magnetic flux loss rate of the sample at each time point is calculated using the following formula: the difference in magnetic flux loss obtained by subtracting the open-circuit magnetic flux after aging from the initial open-circuit magnetic flux is divided by the initial open-circuit magnetic flux, and finally multiplied by 100% to convert it into a percentage, which is used to evaluate the thermal demagnetization dysreactivity of the magnet under actual service conditions.

[0153] Table 4. Irreversible flux loss rate test data of Preparation Examples 1 to 3 and Comparative Examples as a function of aging time

[0154] Sample source Irreversible flux loss rate over 100 hours (%) Irreversible flux loss rate over 300 hours (%) Irreversible flux loss rate over 500 hours (%) Preparation Example 1 1.2 1.8 2.5 Preparation Example 3 1.5 2.4 3.2 Preparation Example 2 1.9 3.1 4.1 Comparative Example 4 3.5 6.2 8.5 Comparative Example 1 4.8 8.5 12.4

[0155] Conclusions and Analysis:

[0156] Observation Table 4 and Figure 4 The data confirms that the prepared examples (1 to 3) exhibited significant high-temperature resistance to environmental interference and resistance to demagnetization after being prepared into bonded magnets. After a long and rigorous aging process at 120°C for 500 hours, the irreversible flux loss rate of prepared example 1 was only 2.5%, and even prepared example 2, with slightly inferior formulation parameters, was stably controlled within 4.1%.

[0157] The superior macroscopic electromagnetic properties are the ultimate manifestation of the advantages of the microscopic mechanism in the preceding tests. Combining the uniform nitrided structure of Test Example 1 and the anti-oxidation experiment of Test Example 3, it can be seen that in Comparative Examples 1 and 4, due to the presence of a nitrogen-depleted soft magnetic phase in the core of the powder or physical defects in the surface coating layer, high-temperature air easily penetrates the resin gaps and reacts with the exposed magnetic powder surface, leading to the decomposition of the main phase and irreversible collapse of coercivity. As reflected in the data in Table 4, after 500 hours of aging, the magnetic flux loss rate of Comparative Example 1 increased significantly, reaching 12.4%, which cannot meet the requirements of practical engineering applications. In contrast, the double-layer composite protective layer constructed on the surface of the prepared examples through a stepped temperature change sequence not only endows the powder with good resin compatibility (Test Example 2), but also forms an anti-oxidation protective layer inside the bonded magnet, locking nitrogen atoms in the deep lattice, which helps to suppress magnetic domain flipping caused by thermal fluctuations, thereby ensuring the irreversible magnetic flux stability of the magnetic powder under extreme working conditions.

Claims

1. A method for preparing a samarium-iron-nitrogen composite material, characterized in that, Includes the following steps: Weigh out the samarium iron nitrogen magnetic powder, resin powder, antioxidant, and lubricant according to the specified ratio; The samarium iron nitrogen magnetic powder, the resin powder, the antioxidant, and the lubricant are put into a high-speed mixer and mixed evenly to obtain a mixture. The mixture is fed into a parallel twin-screw extruder for high-temperature extrusion granulation, and the mixture is melt-extruded to form extruded strips. The extruded strip is fed into a constant temperature water bath for cooling and shaping, the surface moisture is dried by an air knife, and it is cut by a pelletizer to obtain samarium iron nitrogen composite material granules.

2. The preparation method according to claim 1, characterized in that, The raw materials are weighed according to the following mass percentages: 79.0%-94.6% of the samarium iron nitrogen magnetic powder, 5.0%-20.0% of the resin powder, 0.2%-0.5% of the antioxidant, and 0.2%-0.5% of the lubricant.

3. The preparation method according to claim 2, characterized in that, The resin powder is selected from one of polyphenylene sulfide resin powder and polyamide 12 resin powder; the antioxidant is antioxidant 1010; and the lubricant is lubricant EBS.

4. The preparation method according to claim 1, characterized in that, The precursor particles of the samarium iron nitrogen magnetic powder before modification are made by uniformly mixing 27%-31% Sm2O3 powder and 69%-73% Fe powder by mass percentage, and adding 12%-18% of metallic Ca particles relative to the total mass of Sm2O3 and Fe. The mixture is placed in an alumina crucible and heated to 1100-1200℃ under argon protection for 2-5 hours. After furnace cooling, the mixture is crushed to a particle size of 0.5mm-2mm to obtain the precursor particles.

5. The preparation method according to claim 4, characterized in that, The precursor particles were put into a reactor equipped with an online pH meter, and deionized water was added for stirring and washing. When the pH value of the slurry system dropped to 8.5-9.5, washing was stopped immediately and centrifuged. The mixture was then dried in a vacuum drying oven at 50-80℃ to obtain a slightly alkaline samarium iron alloy powder with trace amounts of Ca(OH)2 on its surface.

6. The preparation method according to claim 5, characterized in that, The samarium-iron-nitrogen main phase powder is prepared by the following process: The slightly alkaline samarium iron alloy powder with trace amounts of Ca(OH)2 on its surface is mixed evenly with 1.0%-3.0% by mass of one of the following: NaN3 powder and calcium cyanamide powder. The mixture is then loaded into a multifunctional rotary kiln with a magnetic fluid seal, evacuated to a gauge pressure of -0.05MPa to -0.09MPa, and heated to 360-430℃ and held for 1.5-2 hours. Then, high-purity nitrogen gas is introduced to an absolute pressure of 0.3-0.8 MPa, the temperature is raised to 470-520℃ and held for 2-3 hours, and then cooled to obtain the samarium iron nitrogen main phase powder.

7. The preparation method according to claim 1, characterized in that, The process of mixing the feed into the high-speed mixer until uniform is achieved is specifically as follows: Mix at room temperature at a speed of 800 r / min for 30-60 minutes; The main motor speed of the parallel twin-screw extruder is set to 8-15 r / min.

8. The preparation method according to claim 3, characterized in that, When the resin powder is polyphenylene sulfide resin powder, the barrel temperature profile of the parallel twin-screw extruder is set sequentially from the feeding section to the die head as 280℃, 290℃, 300℃, 310℃, 310℃, and 300℃.

9. The preparation method according to claim 3, characterized in that, When the resin powder is polyamide 12 resin powder, the barrel temperature profile of the parallel twin-screw extruder is set sequentially from the feeding section to the die head as 185℃, 195℃, 210℃, 220℃, 220℃, 210℃.

10. A modification process for samarium iron nitrogen composite materials, characterized in that, Includes the following steps: Samarium iron nitrogen main phase powder is put into a wet ball mill with a temperature control jacket. Anhydrous ethanol and oleic acid accounting for 1.0%-3.0% of the magnetic powder mass are added at a liquid-solid ratio of 1:

1. The jacket water temperature is controlled to maintain the system at 35-45℃, and the mixture is ground at 400-700 r / min for 30-60 minutes. Add a phosphoric acid aqueous solution with a mass concentration of 85% at 0.5%-1.5% of the magnetic powder mass dropwise without stopping the machine, and continue grinding for 1-2 hours at 75-85℃. Add 0.5%-2.0% of one of KH-550 silane coupling agents and KH-560 coupling agents by weight of the magnetic powder and continue grinding for 20-40 minutes. Filter the discharged material and vacuum dry it at 60-90°C to obtain the modified samarium iron nitrogen magnetic powder.

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