Preparation method of high-performance sm-(fe, m)-n magnetic powder and product thereof

Abstract

The application discloses a preparation method of high-performance Sm-(Fe, M)-N magnetic powder and a product thereof. A mixed metal solution containing a surfactant is subjected to co-precipitation to obtain a samarium-iron composite oxide, a precursor is obtained after hydrogen reduction, surface regulation treatment is performed on the precursor, then a reducing agent and a sintering inhibitor are mixed to perform reduction diffusion, and an intermediate phase is obtained through a dehydrogenation and recombination process. The intermediate phase is converted into Sm2Fe 17 N3 magnetic powder through nitriding and homogenization annealing treatment, and is subjected to a stabilization treatment in a furnace with a certain oxygen partial pressure. The magnetic powder after nitriding and stabilization is subjected to washing, magnetic separation, extraction and vacuum drying treatment. The method realizes preparation of near-spherical Sm-Fe-N magnetic powder with a submicron level without a ball milling process through multiple measures for inhibiting sintering growth during high-temperature diffusion, and has the advantages of simple process, good scalability, and important industrial application prospect, and is especially suitable for large-scale production.

Description

Technical Field

[0001] This invention belongs to the field of rare earth permanent magnet material preparation technology, and relates to a method for preparing high-performance Sm-(Fe,M)-N magnetic powder and its product. Specifically, it relates to a technique for preparing near-spherical Sm-Fe-N magnetic powder based on a co-precipitation method, and achieves particle size refinement of Sm-Fe-N magnetic powder through various measures. This method is applicable to the production of high-performance permanent magnet materials, especially in the field of Sm-Fe-N based permanent magnet materials. Background Technology

[0002] Permanent magnets play a crucial role in achieving carbon neutrality and driving the application of "clean technologies." They are core components of electric motors and generators in multiple industries, particularly in electric vehicles and wind turbines. Currently, neodymium iron boron (NdFeB) magnets are the most widely used high-performance permanent magnet material. However, with the increasing demand from practical applications, coupled with the high cost and supply risks of Nd and Dy, there is an urgent need to develop a cost-effective and high-performance alternative material to meet the growing market demand. Against this backdrop, Sm-Fe-based compounds have attracted widespread attention and have become the most promising alternative to Nd-Fe-B magnets due to their significantly lower rare earth element content, absence of heavy rare earth elements, and comparable intrinsic magnetic properties to NdFeB.

[0003] Therefore, preparing Sm-Fe-N magnetic powder with excellent magnetic properties is crucial for improving the performance of Sm-Fe-N magnets. Currently, traditional methods for preparing Sm-Fe-N powder include hydride disproportionation (HDDR), melt quenching, and mechanical alloying. However, these methods have some limitations. While mechanical alloying can prepare Sm-Fe-N magnetic powder, it also has several drawbacks. First, the powder particles tend to be too fine and irregular in shape, and internal stress and lattice defects can accumulate, affecting magnetic properties. Furthermore, nitriding efficiency is low, oxidation is a serious problem, and production costs are high. More importantly, during mechanical alloying, the alloy composition and phase composition are difficult to control precisely, which may further affect the final magnetic properties. Simultaneously, it requires sophisticated equipment and involves complex operations. While melt quenching can prepare Sm2Fe with uniform microstructure and fine grains... 17While alloys are produced, the powder typically exhibits a lamellar structure with poor flowability. This irregular lamellar powder structure can affect the material's filling density and overall properties during subsequent processing and forming, particularly limiting its application in the preparation of high-density, high-performance permanent magnets. Although the hydrogen disproportionation method (HDDR) can prepare high-performance isotropic Sm-Fe-N permanent magnet alloys, it still has some drawbacks. First, this method requires a high-pressure hydrogen environment, posing safety hazards; second, the alloy powder is prone to agglomeration during hydrogenation, affecting nitriding efficiency. Therefore, these methods face significant challenges in obtaining high-performance, near-spherical Sm-Fe-N magnetic powder. Furthermore, in practice, these methods inevitably require ball milling to refine the particle size. However, ball milling typically produces discrete particle size distributions, including nanoscale and micrometer-scale particles. More seriously, the internal stress and irregular edge defects generated during ball milling increase the demagnetizing factor and promote the formation of antimagnetic domains, thereby significantly reducing coercivity.

[0004] Therefore, exploring a simpler synthesis method that does not require ball milling to prepare submicron-sized near-spherical Sm-Fe-N powder has become crucial to solving the current problem. Studies have shown that the coercivity of Sm-Fe-N is inversely proportional to the particle size; the smaller the particle size, the greater the coercivity near the single-domain size (the single-domain size of Sm-Fe-N is 0.35 μm). The traditional chemical coprecipitation-reduction diffusion method is a simple way to directly prepare Sm-Fe-N powder, but the reduction diffusion process often leads to particle sintering and growth, resulting in a decrease in coercivity. How to inhibit sintering growth and control the powder particle size is a problem that the chemical coprecipitation-reduction diffusion method needs to solve. Summary of the Invention

[0005] The purpose of this invention is at least to address the limitations of existing Sm-Fe-N magnetic powders in terms of particle size and surface sphericity. It proposes a method for preparing high-performance Sm-(Fe,M)-N magnetic powder and its products, specifically a method for refining the particle size and improving the performance of Sm-(Fe,M)-N magnetic powder. Its core innovation lies in avoiding the use of crushing methods such as ball milling, successfully producing Sm-Fe-N magnetic powder with small particle size and high surface sphericity, especially achieving a significant breakthrough in improving coercivity. Furthermore, the near-spherical magnetic powder prepared by this invention can significantly improve the flowability and magnetic properties of injection-molded Sm-Fe-N feedstock, thereby effectively preparing injection-molded Sm-Fe-N magnets with high filling capacity and high magnetic performance. This method maintains high surface sphericity while maintaining a particle size close to a single domain, effectively solving the defects in existing technologies and providing a reliable solution for the application of high-performance magnetic powders and subsequent magnets, with broad industrial application prospects.

[0006] To achieve its intended purpose, the present invention employs the following technical solution: In a first aspect, the present invention provides Sm-(Fe,M)-N magnetic powder with a particle size of 0.5μm≤D 50 ≤2.5μm, while D 90 ≤3.5μm, and average sphericity ≥0.8; coercivity H of magnetic powder cj ≥15 KOe, maximum energy product (BH) max ≥30MGOe. The sphericity measurement here uses the sphericity factor and aspect ratio, specifically defined as: Φ=P 2 / A•V 1 / 3 (P is the surface perimeter of the particle, A is the surface area of ​​the particle, and V is the volume of the particle). The aspect ratio refers to the ratio of the maximum axial length to the minimum axial length of the particle, and the closer the aspect ratio is to 1, the better the sphericity of the particle. For the sphericity test, cold field SEM images of more than 500 particles were randomly selected, and the average value was calculated based on the sphericity of each particle. This average value was used as the average sphericity of the powder particles.

[0007] Preferably, the Sm-(Fe,M)-N powder has crystallites of Th2Zn. 17 Type crystal structure.

[0008] Secondly, the present invention provides a method for preparing high-performance Sm-(Fe,M)-N magnetic powder, comprising the following steps: Step 1, Sm2Fe 17 Alloy precursor preparation: Samarium-containing compounds and iron-containing compounds were dissolved in an aqueous solvent and stirred thoroughly to obtain a mixed salt solution. Subsequently, surfactants and precipitants were added to the mixed salt solution, and stirring was continued while maintaining the pH above 7 to ensure that all metal ions were fully precipitated. The precipitate was then collected. The precipitated product is calcined, dehydrated, and crystallized to obtain a composite metal oxide; wherein, a dispersant is added during the calcination process to inhibit particle sintering and agglomeration. The composite metal oxide was completely reduced with hydrogen at 600-750℃ to obtain Sm2Fe. 17 Alloy precursor, namely Sm2O3 / (Fe,M) composite compound; Step 2, Sm2Fe 17 Preparation of the alloy mesophase: Sm2Fe 17The alloy precursor undergoes surface conditioning treatment in air at 100-500℃, followed by thorough mixing with a reducing agent and a sintering inhibitor. It is then reduced at 700-800℃ in an argon atmosphere, and then diffused at 900-1100℃. At the same diffusion temperature, a vacuum is applied to maintain the furnace pressure between 0.001-0.10 MPa for dehydrogenation. After dehydrogenation, the furnace is purged with argon to atmospheric pressure and then recombined to obtain Sm2Fe. 17 Intermediate phase of the alloy.

[0009] The surface modulation method of this invention involves generating a thin oxide layer on the Fe surface. During reduction by a reducing agent, this oxide layer is converted into a thin-layer byproduct, thereby blocking Sm2Fe. 17 Particles come into contact with each other, thus inhibiting sintering growth. To address the issue of gases (e.g., H2) generated by the high-temperature decomposition of reducing agents (e.g., CaH2) potentially permeating into Sm2Fe... 17 The reaction leads to the formation of SmH2 and α-Fe byproducts, so a dehydrogenation and recombination process is required after reduction and diffusion.

[0010] Step 3, Sm2Fe 17 Preparation of N3 magnetic powder: Sm2Fe 17 The alloy's intermediate phase undergoes nitriding treatment, followed by annealing under an argon atmosphere to promote uniform nitrogen distribution within the particles, resulting in high-performance Sm2Fe alloy. 17 N3 magnetic powder.

[0011] Step 4, Sm2Fe 17 Stabilization treatment of N3 magnetic powder: Sm2Fe 17 The N3 magnetic powder was placed intact in the furnace, and a certain oxygen partial pressure was introduced for slow stabilization treatment to ensure that excess reducing agent was converted into oxides, while Sm2Fe... 17 A thin oxide protective film also forms on the surface of N3 magnetic powder to prevent excessive corrosion and hydrogen permeation during water washing.

[0012] Step 5, Sm2Fe 17 Post-cleaning treatment of N3 magnetic powder: The stabilized magnetic powder was then washed, magnetically separated, extracted, and vacuum dried to obtain Sm2Fe with fine particle size and excellent magnetic properties. 17 N3 magnetic powder.

[0013] Preferably, in step one, the mixed salt solution also needs to be supplemented with a metal compound containing M, wherein the molar ratio of iron ions in the iron compound to samarium ions in the samarium compound and M metal ions in the M metal compound is 1:(0.12-0.24):(0.01-0.2); M is one of La, Ce, Co, Ti, Mn, Al, Cr, and W.

[0014] Preferably, in step one, the calcination, dehydration, and crystallization treatment temperature is controlled at 500-1200℃, and the time is 1-10 hours; the amount of the dispersant added is 1-50% of the mass of the precipitate; the dispersant is a composite agent composed of one or two of organic and inorganic additives. Preferably, the organic additives include urea, ammonium bicarbonate, stearic acid, etc.; the inorganic additives include sodium chloride, potassium chloride, and potassium nitrate.

[0015] Preferably, in step one, the total mass ratio of the surfactant to the iron ions in the iron-containing compound and the samarium ions in the samarium-containing compound is 0.1-5:100, and the surfactant is at least one of polyethylene glycol, polyvinyl alcohol, polyvinylpyrrolidone, citric acid, oleic acid, oleylamine, fluorosurfactant, sodium dodecyl sulfate, hexadecyltrimethylammonium chloride, benzalkonium chloride, and hexadecylpyridine chloride.

[0016] Preferably, in step one, the molar ratio of the precipitant to the iron ions in the iron-containing compound is (1-10):(0.1-1). The amount of precipitant required should be adjusted to make the pH of the co-precipitation solution greater than 7, and the solution temperature should be maintained at 0-100℃ during the co-precipitation process. The precipitant is at least one of hydroxide ions, ammonia, oxalate ions, carbonate ions, urea, and ammonium bicarbonate.

[0017] Preferably, in step two, the reducing agent is a metal reducing agent, and its addition amount is 2-3 times the molar mass of samarium ions. Calcium hydride is the preferred reducing agent. The amount of the sintering inhibitor added is 10-50% of the reducing agent mass. Too little amount will not allow for sufficient dispersion with the composite precursor, while too much amount will coat the composite precursor, preventing calcium vapor from penetrating and affecting the reduction effect. The sintering aid is a soluble high-melting-point salt or calcium oxide, which blocks Sm2Fe. 17 The particles come into contact with each other to inhibit sintering, and can be one of NaCl, KCl, CaCl2, or CaO.

[0018] Preferably, in step two, the negative pressure dehydrogenation treatment time is 0.5-5 h, and the composite treatment time is 0.5-5 h.

[0019] Preferably, in step three, the nitriding temperature is 300-500℃, the nitriding time is 0.5-5 h, and the nitriding atmosphere is pure nitrogen or a mixture of ammonia and hydrogen, preferably a mixture of ammonia and hydrogen in a volume ratio of 1:1 to 1:5. After nitriding, the annealing treatment under an argon atmosphere is maintained at a temperature of 100-500℃ for 0.5-10 h.

[0020] Preferably, in step four, the stabilization temperature is 25-150℃, and the stabilization time is 10-72 h; during the stabilization process, the oxygen partial pressure is adjusted to 1-21% by adjusting the volume ratio of air or oxygen to argon.

[0021] Preferably, in step five, the solvent used for washing is water at 0-10℃. After repeated washing, acetic acid with a pH of 5-7 is added to remove impurities. During the extraction process, ethanol is used first, followed by a highly volatile solvent (such as acetone) to further remove residual aqueous solvent. The standard for cleanliness is that the calcium content in the magnetic powder is less than 10 ppm.

[0022] The present invention provides a method for preparing Sm-(Fe,M)-N magnetic powder with refined particle size and improved performance. This method employs multiple measures, including adding surfactants during precipitation, surface conditioning of the precursor, and adding sintering inhibitors during reduction, to refine the particle size of the Sm-Fe-N magnetic powder, thereby obtaining Sm-Fe-N magnetic powder with excellent magnetic properties. Specifically, the magnetic powder has a particle size of 0.5 μm ≤ D. 50 ≤2.5μm, while D 90 ≤3.5μm, and average sphericity ≥0.8; coercivity H of magnetic powder cj ≥15 KOe, maximum energy product (BH) max ≥30MGOe.

[0023] Compared with the prior art, the present invention has the following significant advantages: (1) Optimized precipitation conditions: By adding surfactants to the co-precipitation solution, this invention improves the nucleation, growth, and dispersion behavior of particles during precipitation, and reduces the tendency of particle agglomeration. At the same time, by precisely controlling the precipitation conditions (such as pH value, reaction temperature, precipitant concentration, precipitant type, etc.), precursor powders with narrower particle size distribution and more uniform morphology can be obtained, avoiding the problems of uneven particle size and irregular morphology commonly found in the prior art, thereby significantly improving the performance and stability of the final product.

[0024] (2) For Sm2Fe 17 The surface conditioning treatment of the alloy precursor before calcium reduction and the addition of sintering inhibitors during reduction can both inhibit particle sintering and growth during high-temperature reduction.

[0025] (3) Unlike the traditional reduction-diffusion process which uses one temperature point, this invention uses two temperature points, which realizes the reduction of samarium at low temperature and the diffusion of samarium with iron to form an alloy at high temperature. This process of first reducing at low temperature and then diffusing at high temperature can effectively suppress the loss of components caused by the volatilization of the first reduced Sm due to long-term high temperature, and at the same time can accelerate the diffusion efficiency.

[0026] (4) Effective removal of hydrogen residue and byproducts caused by the use of CaH2: This method effectively removes hydrogen residue from the reduction diffusion process and hydrogen released during washing, avoiding the negative impact of hydrogen on the purity and magnetic properties of the magnetic powder and ensuring the performance of the final powder. In particular, the negative pressure dehydrogenation step after the reduction diffusion is completed can be completed at the reduction diffusion temperature, which greatly simplifies the process and improves the controllability of the production process. The subsequent recombining step further improves the purity and performance of the magnetic powder.

[0027] (5) The magnetic powder is stabilized by adjusting the oxygen partial pressure after nitriding. This process can effectively prevent the unreacted reducing agent from reacting violently with water during the washing process. At the same time, it avoids the decrease in magnetic properties caused by hydrogen absorption during powder washing in traditional methods, thereby further improving the purity and performance of the magnetic powder.

[0028] (6) Preparation of near-spherical magnetic powder without ball milling: This invention successfully prepared near-spherical submicron Sm-Fe-N magnetic powder without ball milling using a co-precipitation method, with a particle size D 50 The nitriding uniformity is excellent within the range of 0.5-2.5 μm. This method not only prevents uneven mixing of samarium and iron raw materials but also avoids damage to the magnetic properties of Sm-Fe-N magnetic powder during traditional crushing processes, thereby producing Sm-Fe-N magnetic powder with excellent magnetic properties. Furthermore, the raw materials used in this invention are all commercially available, low-cost, and environmentally friendly, and the process is simple, feasible, and easy for large-scale production. Attached Figure Description

[0029] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments.

[0030] Figure 1 This is a process flow diagram of the high-performance samarium iron nitrogen magnetic powder prepared by co-precipitation according to the present invention.

[0031] Figure 2 SEM images of the samarium iron nitrogen magnetic powder prepared in this invention are shown, where (a) and (b) are low-magnification SEM images, and (c) and (d) are high-magnification SEM images.

[0032] Figure 3 The image shows the XRD pattern of the samarium iron nitrogen magnetic powder prepared according to the present invention. Detailed Implementation

[0033] As mentioned above, in view of the shortcomings of the prior art, the inventors of this invention, after long-term research and extensive experimentation, have proposed the technical solution of this invention, such as... Figure 1 As shown, the main steps of this technical solution include at least the following: preparation of precursor, pre-reduction + surface conditioning treatment, reduction diffusion + negative pressure dehydrogenation + recombination, nitriding treatment, stabilization treatment and post-cleaning treatment, etc., to finally obtain Sm-Fe-N product with excellent comprehensive performance.

[0034] The sphericity of the Sm-Fe-N alloy powder should be ≥0.8, and the powder particle size should satisfy 0.5 μm ≤ D. 50 ≤2.5 μm, and D 90 ≤3.5 μm.

[0035] The crystal structure of the Sm-Fe-N alloy powder grains is Th2Zn. 17 type.

[0036] The maximum magnetic energy product of the Sm-Fe-N alloy powder is preferably above 30 MGOe, and the coercivity is above 15 kOe.

[0037] The preparation method of spherical Sm-Fe-N magnetic powder for the above-mentioned high-performance permanent magnet material is described in detail, including the following steps: (1) Preparation of precursors: The precursor powder described in this invention is not strictly limited, as long as it can form an Sm-Fe alloy during the subsequent reduction and diffusion process. Preferably, the precursor powder is samarium-(iron, M)(hydride) oxide powder. More preferably, it is a samarium-iron(hydride) oxide precursor prepared by a co-precipitation method. Specifically: a samarium-containing compound and an iron-containing compound are dissolved in an aqueous solvent and stirred thoroughly to obtain a mixed salt solution; in one embodiment, a metal compound containing M is also added to the mixed salt solution. Subsequently, a surfactant and a precipitant are added to the metal ion liquid, stirring is continued, and the pH is controlled to be greater than 7 to ensure that all metal ions are fully precipitated to form a samarium-(iron, M) composite precipitate. The precipitation temperature is preferably controlled between 0-100℃. After the precipitate is formed, solid-liquid separation can be performed by filtration, centrifugation, etc., and the obtained precipitate is washed and dried to collect the precipitate product, i.e., the samarium-(iron, M)(hydride) oxide precursor. The dried precipitate can be coarsely ground by mechanical pulverizer before calcination, dehydration, and crystallization to obtain composite metal oxides. During calcination, a dispersant is added to inhibit particle sintering and agglomeration.

[0038] In one embodiment, the calcination temperature can be adjusted according to the type of metal ions and the type of precursor anions, preferably 500-1200℃, and the calcination time is preferably 1-10 h.

[0039] In one embodiment, calcination transforms the samarium-(iron, M)(hydroxide) precursor into a samarium-(iron, M)oxide precursor, providing suitable raw materials for subsequent reduction and diffusion. Since particles are prone to sintering during calcination, a dispersant can be added to the precursor powder before calcination to reduce direct contact between particles and mitigate agglomeration caused by calcination. The amount added is 1-50% of the mass of the precipitate. The dispersant can decompose or release gas during subsequent calcination, thereby increasing the porosity between particles and reducing direct contact. The dispersant can be an organic additive, an inorganic additive, or a composite additive composed of both organic and inorganic additives. Preferably, organic additives include urea, ammonium bicarbonate, stearic acid, etc.; inorganic additives include sodium chloride, potassium chloride, potassium nitrate, etc.; and composite additives can be a combination of the above two types of additives.

[0040] By controlling the stoichiometric ratio of samarium to iron, this invention employs a samarium excess design to compensate for samarium volatilization loss during reduction diffusion. Studies have shown that as the samarium compensation increases, the sphericity of the nitrided magnetic powder exhibits a trend of first increasing and then decreasing, indicating a close correlation between the samarium compensation and the sphericity of the magnetic powder. Within a certain range, appropriately increasing the samarium compensation is beneficial for improving the sphericity of the magnetic powder and further enhancing its overall magnetic properties. Therefore, this invention preferably controls the molar ratio of samarium to iron between 0.12 and 0.24:1.

[0041] The type of anion in the samarium-containing and iron-containing compounds described in this invention is not strictly limited. It can be inorganic anions such as chloride, sulfate, and nitrate, or organic anions such as alkoxides. It should be noted that the samarium-containing and iron-containing compounds in this invention are not limited to the use of corresponding salts; metallic samarium, metallic iron, or their compounds can also be used as raw materials. The compounds include oxides, hydroxides, carbonates, etc., such as samarium oxide and iron oxide. The above raw materials can be prepared into a mixed solution containing Sm ions and Fe ions by acid dissolution or other methods. The acid is preferably one or more of hydrochloric acid, sulfuric acid, and nitric acid. Water is preferably used as the solvent, but a mixed solvent system containing organic components such as ethanol and acetone can also be used as needed to adjust the solution properties and optimize the subsequent precipitation process.

[0042] In one embodiment, the precipitant is preferably hydroxide ions, ammonia, oxalate ions, carbonate ions, etc., or urea, ammonium bicarbonate, etc., which can decompose and release precipitate components under heating conditions. Preferably, the pH of the system is greater than 7 by adjusting the amount of precipitant to ensure sufficient precipitation of metal ions. The method of adding the precipitant significantly affects the particle morphology and particle size distribution. Compared with dropwise addition, single-pour addition is more conducive to the formation of a large number of crystal nuclei in a short time, thereby obtaining particles with a narrower particle size distribution and more uniform morphology. Therefore, the present invention preferably uses the pouring method to add the precipitant to obtain a more uniform and more spherical precursor powder.

[0043] In addition to precipitation reactions, iron ions and samarium ions can also form coordination compounds through coordination. In this case, iron ions and samarium ions form relatively stable complexes with ligands in the solution (such as water molecules, ammonia molecules, etc.) through coordination bonds, without immediately forming a precipitate. Such complexes can exist stably in solution and can be converted into solid precursors by evaporation, drying, etc. Therefore, in addition to samarium-(iron, M)(hydrogen) oxide precursors, the present invention can also use precursor powders prepared by other methods. Specifically, these include the following methods: (1) adding samarium salts to a suspension containing iron hydroxide particles or iron oxide particles with controlled particle size, or adding iron salts to a suspension containing samarium compound particles with controlled particle size. (2) evaporating and drying a mixed solution containing iron ions and samarium ions to obtain a solid precursor containing both iron and samarium, or adding a precipitant to form an iron hydroxide-samarium compound complex and using it as a precursor powder for samarium-iron alloys. These methods can effectively control the particle size and composition of powders, further optimize the properties of alloys, and provide suitable precursor materials for subsequent reduction and diffusion processing steps.

[0044] In one embodiment, to improve the nucleation, growth, and dispersion behavior of particles during co-precipitation and to avoid the aggregation of nano-sized particles, a surfactant can be added to the mixed salt solution before adding the precipitant. The preferred amount of surfactant added is 0.1-5:100 of the total mass of iron ions and samarium ions. The surfactant can be nonionic, anionic, or cationic. Preferably, nonionic surfactants include polyethylene glycol (PEG), polyvinyl alcohol (PVA), polyvinylpyrrolidone (PVP), citric acid stabilizer, oleic acid, and oleylamine. Anionic surfactants include fluorosurfactants (FS-50), sodium dodecyl sulfate (SDS), etc. Cationic surfactants include hexadecyltrimethylammonium chloride, benzalkonium chloride, hexadecylpyridine chloride, etc. Through the above precursor preparation process, samarium-iron oxide precursors with narrow particle size distribution and uniform morphology can be obtained, laying the foundation for the subsequent preparation of high-performance near-spherical Sm-Fe-N magnetic powder.

[0045] (2) Pre-reduction + surface conditioning treatment The composite metal oxide was completely reduced with hydrogen at 600-750℃ to obtain Sm2Fe. 17 Alloy precursor; This step is a pre-reduction treatment, preferably carried out in a hydrogen atmosphere at a temperature controlled between 600-750°C. Besides hydrogen, reducing gases such as carbon monoxide (CO) and methane (CH4) can also be used. By properly controlling the atmosphere, temperature, and time during the pre-reduction process, the composite metal oxide can be effectively reduced to Sm₂O₃ / α-Fe, i.e., Sm₂Fe. 17 The alloy precursor, this pre-reduction step helps reduce the amount of reducing agent required in the subsequent calcium reduction and diffusion process, thus improving process efficiency. The Sm2Fe obtained from the above pre-reduction... 17 The alloy precursor undergoes surface conditioning treatment at 100-500℃ in an air atmosphere to form a thin oxide layer on the particle surface. This oxide layer can be converted into a thin-layer byproduct CaO during the subsequent calcothermic reduction process, thereby reducing interparticle sintering and effectively inhibiting particle sintering and growth during high-temperature reduction diffusion.

[0046] (3) Reduction diffusion, negative pressure dehydrogenation, and recombination Samarium oxide (Sm₂O₃) has high chemical stability and is difficult to directly convert into metallic samarium through conventional hydrogen reduction. Therefore, a more powerful metal reducing agent is needed to effectively reduce Sm₂O₃. In this invention, alkali metals (such as lithium, sodium, potassium, rubidium, and cesium) or alkaline earth metals (such as magnesium, calcium, strontium, and barium) can be used as reducing agents. When heated under an inert gas atmosphere (such as argon) or vacuum conditions, the reducing agent can undergo a reduction reaction with Sm₂O₃, thereby paving the way for the subsequent formation of Sm₂Fe. 17 The intermediate alloy provides the necessary conditions. Considering the safety of experimental operations, the availability of raw materials, and the controllability of the process, this invention preferably uses metallic calcium or calcium hydride as the reducing agent. Preferably, the reducing agent is in granular or powder form, more preferably in powder form as a hydride. Powdered hydrides have a smaller particle size, making them more readily reacted with Sm₂O₃ / α-Fe, i.e., Sm₂Fe. 17 Uniform mixing of alloy precursors is beneficial for the full progress of subsequent reduction and diffusion processes and helps to suppress the formation of secondary phases such as α-Fe.

[0047] In Sm2Fe 17 In the preparation of the intermediate alloy, the reducing agent is reacted with Sm2O3 / α-Fe (i.e., Sm2Fe). 17After the alloy precursor is thoroughly mixed, a reduction-diffusion treatment is carried out under an inert gas atmosphere. Preferably, the reducing agent is calcium hydride, and its addition amount is 2-3 times the molar mass of samarium ions, followed by a reduction-diffusion reaction. The equations for the reduction-diffusion process are shown in (1) and (2): Sm2O3+3Fe+3CaH2→2Sm+3Fe+3CaO+3H2↑ (1) 2Sm + 17Fe → Sm2Fe 17 (2) In this invention, in addition to the reducing agent, a sintering inhibitor may be used if necessary to further control the particle morphology of the powder and prevent sintering. Suitable sintering inhibitors for this purpose include high-melting-point substances such as sodium chloride, potassium chloride, calcium chloride, and calcium oxide. Considering the safety of subsequent cleaning processes and experimental operations, calcium chloride is preferably used as the sintering inhibitor in this invention. The amount of sintering inhibitor added is 10-50% of the mass of the reducing agent. In specific operation, the powder to be reduced, the reducing agent, and the sintering inhibitor are mixed in proportion and poured into a custom-made iron crucible. The entire mixing process should be completed in a glove box with an oxygen content of less than 10 ppm to ensure low-oxygen conditions. Subsequently, the mixture is placed in a reactor for reduction diffusion treatment under an inert gas atmosphere. This invention preferably employs a two-step temperature process, namely, pre-reduction at 700-800℃, followed by a diffusion reaction at 900-1100℃. This stepwise heating method facilitates the reduction of Sm₂O₃ first, followed by promoting the diffusion alloying of Sm and Fe. This reduces the volatilization loss of reduced Sm under prolonged high-temperature conditions, decreases the tendency of the powder to sinter and grow under sustained high-temperature reduction conditions, and improves the Sm₂Fe alloying efficiency. 17 The formation efficiency of the intermediate alloy. The specific time can be adjusted according to the processing temperature; generally, lower temperatures require longer times, and higher temperatures require shorter times.

[0048] However, when using calcium hydride as a reducing agent as shown in equation (1), hydrogen may penetrate into the powder during the reduction process, leading to incomplete reduction or hydrogen residue in the alloy, affecting its performance. Therefore, after the reduction reaction, hydrogen must be removed from the powder by negative pressure dehydrogenation. Negative pressure can effectively promote the diffusion of hydrogen from the powder, reduce hydrogen residue, and prevent it from negatively affecting the alloy performance. This dehydrogenation process is usually carried out at a higher temperature because high temperature helps to increase the diffusion rate of hydrogen. To ensure complete removal of hydrogen, the dehydrogenation time should be controlled between 0.5 and 5 h. After the negative pressure dehydrogenation is completed, the atmospheric pressure atmosphere should be restored, and the alloy should continue to be composited and stabilized at the reduction diffusion temperature to ensure that a uniform Sm2Fe alloy is finally obtained. 17Alloying. This process, known as the recombining process of Sm-Fe alloys, is preferably carried out over a period of 0.5–5 hours. Precise control of temperature, atmosphere, and time during this process is crucial for the homogeneity and magnetic properties of the alloy, and is key to ensuring the preparation of high-quality Sm-Fe alloys.

[0049] (4) Nitriding treatment Sm2Fe 17 The alloy's intermediate phase undergoes nitriding treatment, followed by annealing under an argon atmosphere to promote uniform nitrogen distribution within the particles, resulting in high-performance Sm2Fe alloy. 17 N3 magnetic powder.

[0050] The nitriding treatment of this invention is preferably carried out in the original furnace after reduction diffusion, that is, the near-spherical Sm2Fe with relatively uniform particle size distribution obtained by reduction diffusion method. 17 The intermediate alloy remains in the original reactor without transfer; the atmosphere and temperature are directly switched for subsequent nitriding treatment. This method reduces the risk of oxidation and contamination of the intermediate alloy during transfer and improves process continuity and production efficiency. To ensure the uniformity of nitriding degree of each particle, the nitriding treatment should be carried out in a nitrogen-containing, non-oxidizing atmosphere. The nitriding atmosphere can be pure nitrogen or a mixture of ammonia and hydrogen. Preferably, the nitriding atmosphere is a mixture of ammonia and hydrogen, wherein the volume ratio of ammonia to hydrogen is preferably 1:1-1:5, more preferably 1:3. The nitriding temperature is preferably 300-500℃. When the temperature is too low, the nitriding rate is slow and the processing time is significantly prolonged; when the temperature is too high, Sm2Fe... 17 Nitrogen (N3) readily decomposes and generates impurities such as α-Fe, which is detrimental to improving magnetic properties. The nitriding time can be adjusted according to the powder particle size, charge amount, and processing temperature, preferably 0.5-5 h. After nitriding, switch to an argon atmosphere and maintain it for 0.5-10 h to promote uniform nitrogen distribution within the particles and reduce the adverse effects of residual hydrogen on subsequent performance. Through the above nitriding and homogenization treatments, Sm2Fe with a nitrogen content close to the theoretical value (3.25 wt.%) and a relatively uniform nitrogen distribution can be obtained. 17 N3 magnetic powder, which helps to improve the overall magnetic properties of the magnetic powder.

[0051] (5) Stabilization treatment Sm2Fe 17 The N3 magnetic powder was placed intact in the furnace, and a certain oxygen partial pressure was introduced for slow stabilization treatment to ensure that excess reducing agent was converted into oxides, while Sm2Fe... 17 An oxide protective film also forms on the surface of N3 magnetic powder to prevent excessive corrosion and hydrogen permeation during water washing.

[0052] After the nitriding reaction in the previous step is completed, the resulting powder contains the target product Sm2Fe. 17 In addition to N3, it may also contain byproducts such as calcium oxide, calcium nitride, and excess unreacted calcium. If the powder is directly removed and washed with water, the residual calcium will react violently with the water and release a large amount of heat, as shown in equation (3): Ca+2H2O → Ca(OH)2+H2↑ (3) The heat generated by the above reaction may cause local temperature rise in the powder and lead to changes in phase composition, thus adversely affecting the magnetic properties. Furthermore, hydrogen gas released during the water washing process may penetrate into the powder interior, causing the Sm-Fe-N lattice to expand along the c-axis, thereby affecting the magnetic properties of the magnetic powder. To mitigate the violent reaction between residual Ca and water during water washing and reduce the adverse effects of hydrogen absorption on magnetic properties, this invention includes a stabilization step after nitriding. Preferably, the powder after nitriding is subjected to slow oxidation at 25-150°C, allowing residual Ca to preferentially convert into more stable calcium oxides, thereby reducing the intensity of the reaction during subsequent water washing. The stabilization treatment can be achieved by introducing a mixture of air and an inert gas (such as argon), or a mixture of oxygen and an inert gas (such as argon). Preferably, the oxygen partial pressure in the atmosphere during the stabilization treatment is 1-21%, and the stabilization time is 10-72 h, which can be adjusted according to the powder loading, residual reducing agent content, and treatment requirements.

[0053] (6) Post-treatment of cleaning and drying The stabilized magnetic powder was then washed, magnetically separated, extracted, and vacuum dried to obtain Sm2Fe with fine particle size and excellent magnetic properties. 17 N3 magnetic powder.

[0054] The cleaning step of this invention involves removing the stabilized magnetic powder from the furnace and cleaning it with a solvent capable of dissolving calcium oxide to remove impurities. To further reduce hydrogen penetration during the water washing process, the temperature of the solvent used should be controlled at approximately 0-10°C, preferably using water. After repeated washing several times, a weak acid solution with a pH of 5-7 is added to remove calcium carbonate generated by the reaction of calcium oxide with carbon dioxide in the air, as well as some residual impurities and surface byproducts. The weak acid solution is preferably an acetic acid solution. During the cleaning process, solvents such as ethanol can also be used to remove moisture from the powder. Subsequently, a highly volatile solvent (such as acetone) is used to replace the ethanol to further remove residual solvent. After this treatment, the Ca content in the powder can be reduced to below 10 ppm. Finally, the cleaned powder should be vacuum dried at a temperature preferably room temperature to 50°C to fully remove residual solvent and maintain good particle morphology and structural integrity. The above cleaning and drying processes can further improve the purity of Sm-Fe-N magnetic powder, thus facilitating the acquisition of high-performance Sm-Fe-N magnetic powder.

[0055] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0056] Example 1: Step 1: Preparation of precursors: In this experiment, 105.04 g of ferric nitrate nonahydrate and 17.33 g of samarium nitrate hexahydrate were dissolved in 1300 mL of deionized water to obtain a mixed salt solution with an Fe ion concentration of 0.2 mol / L and a Fe to Sm ion molar ratio of 1:0.15. The solution temperature was controlled at 40℃. Polyvinylpyrrolidone (PVP) was added under stirring at a ratio of 0.2:100 of the total mass of samarium and iron ions, ensuring thorough mixing with the mixed salt solution. Subsequently, 500 mL of a 5 mol / L ammonia solution was poured into the mixed salt solution in one go, and stirring was continued for 12 h to obtain a suspension with a pH of approximately 10. The resulting suspension was allowed to stand for 12 h. The precipitate was then recovered by filtration and centrifugation. The precipitate was washed with deionized water, dehydrated with anhydrous ethanol, and then dried in an air-drying oven at 90°C for 12 hours to obtain a samarium-iron composite (hydrogen) oxide precursor. To reduce the tendency of particle sintering during subsequent calcination, 5% potassium chloride (by weight of the precursor powder) was added as a dispersant during the coarse grinding of the precursor. The coarsely ground precursor was then calcined at 900°C for 4 hours to transform it into a samarium-iron oxide precursor. Finally, a pre-reduction treatment was performed in a hydrogen atmosphere at 700°C for 7 hours to obtain Sm₂Fe for subsequent reduction and diffusion. 17 Alloy precursor (Sm2O3 / α-Fe).

[0057] Step 2, Sm2Fe 17 Preparation of the mesophase: The Sm2Fe obtained in step one 17 The alloy precursor underwent surface conditioning treatment at 300℃ for 1 h in air. Subsequently, the surface-conditioned Sm₂O₃ / α-Fe powder was thoroughly mixed with calcium hydride and calcium oxide, wherein the amount of calcium hydride added was twice the molar mass of samarium ions, and the amount of calcium oxide added was 50% of the mass of the reducing agent calcium hydride. After homogeneous mixing, the mixture was placed in an iron crucible and subjected to reduction-diffusion treatment under an argon protective atmosphere. Specifically, the mixture was first held at 800℃ for 3 h to preferentially reduce Sm₂O₃ to Sm, and then heated to 900℃ and held for 1 h to promote diffusion alloying between Sm and Fe to form Sm₂Fe. 17Mesophase. Since calcium hydride releases hydrogen gas at high temperatures, this hydrogen gas may penetrate into the powder, affecting the completeness of the reduction reaction. To address this issue, after the reduction reaction, the reaction temperature is maintained, and hydrogen gas is removed from the powder by applying negative pressure. This negative pressure dehydrogenation process accelerates the diffusion of hydrogen from the powder, reducing hydrogen residue and ensuring complete removal of hydrogen from the powder. The dehydrogenation time is 0.5 h, and the negative pressure is 0.08 MPa. After dehydrogenation, atmospheric pressure (0.1 MPa) is immediately restored, and the reduction diffusion temperature is maintained at this pressure to further promote alloy recombination and stabilization. This process, known as the Sm-Fe alloy re-recombination process, lasts for 0.5 h. Through this series of operations, a uniform Sm2Fe alloy is finally obtained. 17 Intermediate phase of the alloy.

[0058] Step 3, Sm2Fe 17 Preparation of N3 magnetic powder: The near-spherical, uniformly sized Sm2Fe2O3 particles prepared by reduction diffusion in step two... 17 The mesophase remains in the original reactor without transfer and is directly subjected to subsequent nitriding treatment. The nitriding temperature is set at 430℃, and the treatment time is 3 hours. The preferred nitriding atmosphere is a mixture of ammonia and hydrogen, with a volume ratio of ammonia to hydrogen of 1:3. Under the combined action of ammonia and hydrogen, Sm₂Fe 17 The alloy gradually transforms into Sm2Fe 17 N3 magnetic powder. After nitriding, the atmosphere was switched to argon, and the powder was annealed at 300 °C for 0.5 h to promote uniform nitrogen distribution within the particles. After the above nitriding and homogenization treatments, Sm2Fe with relatively uniform nitrogen distribution was finally obtained. 17 SEM images of N3 magnetic powder at different magnifications are as follows: Figure 2 As shown in (a)-(d), the XRD patterns are as follows: Figure 3 As shown.

[0059] Step 4, Sm2Fe 17 Stabilization treatment of N3 magnetic powder: After the nitriding in step three, Sm2Fe 17 After the N3 powder was cooled to room temperature (approximately 20°C), it underwent stabilization treatment. A mixture of argon and air was used during the stabilization process, with an argon to air flow rate ratio of 5:1 (oxygen partial pressure 3%), and the stabilization time was 12 hours.

[0060] Step 5, Sm2Fe 17 Cleaning of N3 magnetic powder: The stabilized magnetic powder from step four was removed from the furnace and repeatedly washed with ice water at approximately 0°C until the solution's pH value was close to neutral. Then, a diluted acetic acid solution with pH=7 was added to remove calcium carbonate and residual samarium-rich phase. After washing, the water in the powder was replaced with ethanol, followed by further replacement with a highly volatile organic solvent, preferably acetone. During both the washing and replacement processes, an external magnetic field was used to magnetically separate and fix the magnetic powder. The liquid was discarded and then the corresponding liquid was added again for repeated treatment. The washed powder was then placed under vacuum and dried at 25°C. After the above washing, the calcium content in the powder was less than 10 ppm. Although the powder had undergone stabilization, a small amount of hydrogen might still have penetrated into the powder during the washing process. Therefore, the washed and dried powder was further subjected to dehydrogenation treatment under a vacuum or inert gas atmosphere at 150°C for 2 hours. The magnetic properties of the magnetic powder were tested: B r =10.59 kGs, H cj =15.12 kOe, (BH) max =35.21 MGOe, sphericity 0.80, D 50 =1.06 μm.

[0061] Example 2: Step 1: Preparation of precursors: The precursor was prepared as shown in Example 1, except that 18.48 g of samarium nitrate hexahydrate was added to adjust the molar ratio of Fe ions to Sm ions to 1:0.16. The other precursor preparation conditions were the same as in Example 1.

[0062] Step 2, Sm2Fe 17 Preparation of the mesophase: Sm2Fe 17 The preparation of the intermediate phase is as shown in Example 1.

[0063] Step 3, Sm2Fe 17 Preparation of N3 magnetic powder: Sm2Fe 17 The preparation of N3 magnetic powder is as shown in Example 1.

[0064] Step 4, Sm2Fe 17 Stabilization treatment of N3 magnetic powder: Sm2Fe 17 The stabilization treatment of N3 magnetic powder is shown in Example 1.

[0065] Step 5, Sm2Fe 17 Cleaning of N3 magnetic powder: Sm2Fe 17The cleaning of N3 magnetic powder was as shown in Example 1. The magnetic properties of the magnetic powder were tested: B r =10.90 kGs, H cj =18.74 kOe, (BH) max =36.32 MGOe, sphericity 0.81, D 50 =1.08 μm.

[0066] Example 3: Step 1: Preparation of precursors: The precursor was prepared as shown in Example 1, except that 19.64 g of samarium nitrate hexahydrate was added to adjust the molar ratio of Fe ions to Sm ions to 1:0.17. The other precursor preparation conditions were the same as in Example 1.

[0067] Step 2, Sm2Fe 17 Preparation of the mesophase: Sm2Fe 17 The preparation of the intermediate phase is as shown in Example 1.

[0068] Step 3, Sm2Fe 17 Preparation of N3 magnetic powder: Sm2Fe 17 The preparation of N3 magnetic powder is as shown in Example 1.

[0069] Step 4, Sm2Fe 17 Stabilization treatment of N3 magnetic powder: Sm2Fe 17 The stabilization treatment of N3 magnetic powder is shown in Example 1.

[0070] Step 5, Sm2Fe 17 Cleaning of N3 magnetic powder: Sm2Fe 17 The cleaning of N3 magnetic powder was as shown in Example 1. The magnetic properties of the magnetic powder were tested: B r =11.32 kGs, H cj =19.76 kOe, (BH) max =37.46 MGOe, sphericity 0.83, D 50 =1.07 μm.

[0071] Example 4: Step 1: Preparation of precursors: The precursor was prepared as shown in Example 1, except that 20.80 g of samarium nitrate hexahydrate was added to adjust the molar ratio of Fe ions to Sm ions to 1:0.18. The other precursor preparation conditions were the same as in Example 1.

[0072] Step 2, Sm2Fe 17 Preparation of the mesophase: Sm2Fe 17 The preparation of the intermediate phase is as shown in Example 1.

[0073] Step 3, Sm2Fe 17 Preparation of N3 magnetic powder: Sm2Fe 17 The preparation of N3 magnetic powder is as shown in Example 1.

[0074] Step 4, Sm2Fe 17 Stabilization treatment of N3 magnetic powder: Sm2Fe 17 The stabilization treatment of N3 magnetic powder is shown in Example 1.

[0075] Step 5, Sm2Fe 17 Cleaning of N3 magnetic powder: Sm2Fe 17 The cleaning of N3 magnetic powder was as shown in Example 1. The magnetic properties of the magnetic powder were tested: B r =11.49 kGs, H cj =20.46 kOe, (BH) max =40.31 MGOe, sphericity 0.85, D 50 =1.03 μm.

[0076] Comparative Example 1: Compared with Example 4, the stabilization treatment step after nitriding was omitted. Step 1: Preparation of precursors: The preparation of the precursor is shown in Example 4.

[0077] Step 2, Sm2Fe 17 Preparation of the mesophase: Sm2Fe 17 The preparation of the intermediate phase is shown in Example 4.

[0078] Step 3, Sm2Fe 17 Preparation of N3 magnetic powder: Sm2Fe 17 The preparation of N3 magnetic powder is shown in Example 4.

[0079] Step 4, Sm2Fe 17 Stabilization treatment of N3 magnetic powder: After the nitriding in step three, Sm2Fe 17 N3 powder was taken directly from the furnace for cleaning. Step 5, Sm2Fe 17 Cleaning of N3 magnetic powder: Sm2Fe 17The cleaning of N3 magnetic powder was as shown in Example 4. The magnetic properties of the magnetic powder were tested: B r =10.01 kGs, H cj =9.56 kOe, (BH) max =24.75 MGOe, sphericity 0.80, D 50 =1.10 μm.

[0080] Comparative Example 2: Compared with Example 4, the negative pressure dehydrogenation and recombination steps after reduction diffusion were omitted. Step 1: Preparation of precursors: The preparation of the precursor is shown in Example 4.

[0081] Step 2, Sm2Fe 17 Preparation of the mesophase: The process is basically the same as in Example 4, except that after the reduction and diffusion are completed, no negative pressure dehydrogenation treatment is performed at the reaction temperature, and no subsequent recombination treatment is performed. The process proceeds directly to the next step.

[0082] Step 3, Sm2Fe 17 Preparation of N3 magnetic powder: Sm2Fe 17 The preparation of N3 magnetic powder is shown in Example 4.

[0083] Step 4, Sm2Fe 17 Stabilization treatment of N3 magnetic powder: Sm2Fe 17 The stabilization treatment of N3 magnetic powder is shown in Example 4.

[0084] Step 5, Sm2Fe 17 Cleaning of N3 magnetic powder: Sm2Fe 17 The cleaning of N3 magnetic powder was as shown in Example 4. The magnetic properties of the magnetic powder were tested: B r =9.98 kGs, H cj =10.98 kOe, (BH) max =17.90 MGOe, sphericity 0.82, D 50 =1.12 μm.

[0085] Comparative Example 3: Compared with Example 4, the steps of negative pressure dehydrogenation after reduction diffusion, recombination, and stabilization after nitriding were omitted. Step 1: Preparation of precursors: The preparation of the precursor is shown in Example 4.

[0086] Step 2, Sm2Fe 17 Preparation of the mesophase: The process is basically the same as in Example 4, except that after the reduction and diffusion are completed, no negative pressure dehydrogenation treatment is performed at the reaction temperature, and no subsequent recombination treatment is performed. The process proceeds directly to the next step.

[0087] Step 3, Sm2Fe 17 Preparation of N3 magnetic powder: Sm2Fe 17 The preparation of N3 magnetic powder is shown in Example 4.

[0088] Step 4, Sm2Fe 17 Stabilization treatment of N3 magnetic powder: After the nitriding in step three, Sm2Fe 17 N3 powder was taken directly from the furnace for cleaning. Step 5, Sm2Fe 17 Cleaning of N3 magnetic powder: Sm2Fe 17 The cleaning of N3 magnetic powder was as shown in Example 4. The magnetic properties of the magnetic powder were tested: B r =9.12 kGs, H cj =7.69 kOe, (BH) max =13.98 MGOe, sphericity 0.79, D 50 =1.16 μm.

[0089] Comparative Example 4: Compared with Example 4, the Ca reduction stage adopted a constant temperature reduction process.

[0090] Step 1: Preparation of precursors: The preparation of the precursor is shown in Example 4.

[0091] Step 2, Sm2Fe 17 Preparation of the mesophase: This step is basically the same as in Example 4, except that: the Ca reduction is carried out at a constant temperature of 900℃ for 2 hours, instead of the stepwise reduction and diffusion process of first holding at 800℃ for 3 hours to preferentially reduce Sm2O3 to Sm, and then raising the temperature to 900℃ for 1 hour for diffusion. The other steps are the same.

[0092] Step 3, Sm2Fe 17 Preparation of N3 magnetic powder: Sm2Fe 17 The preparation of N3 magnetic powder is shown in Example 4.

[0093] Step 4, Sm2Fe 17 Stabilization treatment of N3 magnetic powder: Sm2Fe 17 The stabilization treatment of N3 magnetic powder is shown in Example 4.

[0094] Step 5, Sm2Fe 17 Cleaning of N3 magnetic powder: Sm2Fe 17 The cleaning of N3 magnetic powder was as shown in Example 4. The magnetic properties of the magnetic powder were tested: B r =9.78 kGs, H cj =8.67 kOe, (BH) max =18.98 MGOe, sphericity 0.65, D 50 =2.89 μm.

[0095] Comparative Example 5: Compared with Example 4, the Ca reduction stage adopted a isothermal reduction process, and omitted the negative pressure dehydrogenation, recombination, and stabilization treatment steps after reduction diffusion and nitridation. Step 1: Preparation of precursors: The preparation of the precursor is shown in Example 4.

[0096] Step 2, Sm2Fe 17 Preparation of the mesophase: This step is basically the same as in Example 4, except that: the Ca reduction is carried out at a constant temperature of 900℃ for 2 hours, and after the reduction and diffusion are completed, no negative pressure dehydrogenation treatment is performed at the reaction temperature, nor is any subsequent recombination treatment performed, and the process proceeds directly to the next step.

[0097] Step 3, Sm2Fe 17 Preparation of N3 magnetic powder: Sm2Fe 17 The preparation of N3 magnetic powder is shown in Example 4.

[0098] Step 4, Sm2Fe 17 Stabilization treatment of N3 magnetic powder: After the nitriding in step three, Sm2Fe 17 N3 powder was taken directly from the furnace for cleaning. Step 5, Sm2Fe 17 Cleaning of N3 magnetic powder: Sm2Fe 17 The cleaning of N3 magnetic powder was as shown in Example 4. The magnetic properties of the magnetic powder were tested: B r =8.76 kGs, H cj =5.12 kOe, (BH) max =11.65 MGOe, sphericity 0.64, D 50 =2.91 μm.

[0099] Table 1: Effects of Ca reduction process, negative pressure dehydrogenation and recombination, and stabilization treatment steps on the magnetic properties of magnetic powder.

[0100]

[0101] Note: Stepwise reduction means first holding at 800℃ for 3 hours for low-temperature reduction, then raising the temperature to 900℃ and holding for 1 hour for diffusion; constant-temperature reduction means holding at 900℃ for 2 hours for reduction.

[0102] Table 1 shows the impact of Ca reduction, negative pressure dehydrogenation and recombination, and stabilization on the magnetic properties of the magnetic powder. It is evident that after stepwise reduction and diffusion, further negative pressure dehydrogenation, recombination, and stabilization significantly improve the magnetic properties. Specifically, this is reflected in the improvement of remanence (B). r The coercivity (H) increased from 8.76 kGs to 11.49 kGs. cj The energy product (BH) increases from 5.12 kOe to 20.46 kOe. max The magnetic properties increased from 11.65 MGOe to 40.31 MGOe. This demonstrates that these three steps play a crucial role in improving the magnetic properties during the co-precipitation process for preparing submicron near-spherical samarium iron nitrogen magnetic powder.

[0103] Comparative Example 6: Compared with Example 4, Sm2Fe was omitted. 17 Alloy precursor surface conditioning treatment Step 1: Preparation of precursors: The preparation of the precursor is shown in Example 4.

[0104] Step 2, Sm2Fe 17 Preparation of the mesophase: This step is basically the same as in Example 4, except that the Sm2Fe obtained in step one is not used. 17 The alloy precursor was subjected to surface conditioning treatment at 300°C for 1 h in an air atmosphere.

[0105] Step 3, Sm2Fe 17 Preparation of N3 magnetic powder: Sm2Fe 17 The preparation of N3 magnetic powder is shown in Example 4.

[0106] Step 4, Sm2Fe 17 Stabilization treatment of N3 magnetic powder: Sm2Fe 17 The stabilization treatment of N3 magnetic powder is shown in Example 4.

[0107] Step 5, Sm2Fe 17 Cleaning of N3 magnetic powder: Sm2Fe 17 The cleaning of N3 magnetic powder was as shown in Example 4. The magnetic properties of the magnetic powder were tested: B r=10.67 kGs, H cj =10.89 kOe, (BH) max =20.45 MGOe, sphericity 0.79, D 50 =2.58 μm.

[0108] Table 2: Effect of surface conditioning treatment steps on the magnetic properties of magnetic powder.

[0109]

[0110] Table 2 shows the impact of surface conditioning on the magnetic properties of magnetic powder. Surface conditioning significantly improves magnetic properties and reduces particle size. Specifically, it improves remanence (B0). r The coercivity (H) increased from 10.67 kGs to 11.49 kGs. cj The energy product (BH) increases from 10.89 kOe to 20.46 kOe. max The surface conditioning process increased from 20.45 MGOe to 40.31 MGOe. This demonstrates that the surface conditioning step plays a crucial role in enhancing the magnetic properties during the preparation of submicron near-spherical samarium iron nitrogen magnetic powder via the co-precipitation method.

[0111] Example 5: Step 1: Preparation of precursors: The precursor was prepared as shown in Example 1, except that 21.95 g of samarium nitrate hexahydrate was added to adjust the molar ratio of Fe ions to Sm ions to 1:0.19. The other precursor preparation conditions were the same as in Example 1.

[0112] Step 2, Sm2Fe 17 Preparation of the mesophase: Sm2Fe 17 The preparation of the intermediate phase is as shown in Example 1.

[0113] Step 3, Sm2Fe 17 Preparation of N3 magnetic powder: Sm2Fe 17 The preparation of N3 magnetic powder is as shown in Example 1.

[0114] Step 4, Sm2Fe 17 Stabilization treatment of N3 magnetic powder: Sm2Fe 17 The stabilization treatment of N3 magnetic powder is shown in Example 1.

[0115] Step 5, Sm2Fe 17 Cleaning of N3 magnetic powder: Sm2Fe 17The cleaning of N3 magnetic powder was as shown in Example 1. The magnetic properties of the magnetic powder were tested: B r =11.21 kGs, H cj =19.34 kOe, (BH) max =38.49 MGOe, sphericity 0.83, D 50 =1.09 μm.

[0116] Example 6: Step 1: Preparation of precursors: The precursor was prepared as shown in Example 1, except that 23.11 g of samarium nitrate hexahydrate was added to adjust the molar ratio of Fe ions to Sm ions to 1:0.20. The other precursor preparation conditions were the same as in Example 1.

[0117] Step 2, Sm2Fe 17 Preparation of the mesophase: Sm2Fe 17 The preparation of the intermediate phase is as shown in Example 1.

[0118] Step 3, Sm2Fe 17 Preparation of N3 magnetic powder: Sm2Fe 17 The preparation of N3 magnetic powder is as shown in Example 1.

[0119] Step 4, Sm2Fe 17 Stabilization treatment of N3 magnetic powder: Sm2Fe 17 The stabilization treatment of N3 magnetic powder is shown in Example 1.

[0120] Step 5, Sm2Fe 17 Cleaning of N3 magnetic powder: Sm2Fe 17 The cleaning of N3 magnetic powder was as shown in Example 1. The magnetic properties of the magnetic powder were tested: B r =11.01 kGs, H cj =18.79 kOe, (BH) max =37.12 MGOe, sphericity 0.81, D 50 =1.15 μm.

[0121] Example 7: Step 1: Preparation of precursors: The precursor was prepared as shown in Example 1, except that 24.26 g of samarium nitrate hexahydrate was added to adjust the molar ratio of Fe ions to Sm ions to 1:0.21. The other precursor preparation conditions were the same as in Example 1.

[0122] Step 2, Sm2Fe 17 Preparation of the mesophase: Sm2Fe 17 The preparation of the intermediate phase is as shown in Example 1.

[0123] Step 3, Sm2Fe 17 Preparation of N3 magnetic powder: Sm2Fe 17 The preparation of N3 magnetic powder is as shown in Example 1.

[0124] Step 4, Sm2Fe 17 Stabilization treatment of N3 magnetic powder: Sm2Fe 17 The stabilization treatment of N3 magnetic powder is shown in Example 1.

[0125] Step 5, Sm2Fe 17 Cleaning of N3 magnetic powder: Sm2Fe 17 The cleaning of N3 magnetic powder was as shown in Example 1. The magnetic properties of the magnetic powder were tested: B r =10.93 kGs, H cj =18.10 kOe, (BH) max =36.57 MGOe, sphericity 0.80, D 50 =1.26 μm.

[0126] Example 8: Step 1: Preparation of precursors: The precursor was prepared as shown in Example 1, except that 25.42 g of samarium nitrate hexahydrate was added to adjust the molar ratio of Fe ions to Sm ions to 1:0.22. The other precursor preparation conditions were the same as in Example 1.

[0127] Step 2, Sm2Fe 17 Preparation of the mesophase: Sm2Fe 17 The preparation of the intermediate phase is as shown in Example 1.

[0128] Step 3, Sm2Fe 17 Preparation of N3 magnetic powder: Sm2Fe 17 The preparation of N3 magnetic powder is as shown in Example 1.

[0129] Step 4, Sm2Fe 17 Stabilization treatment of N3 magnetic powder: Sm2Fe 17 The stabilization treatment of N3 magnetic powder is shown in Example 1.

[0130] Step 5, Sm2Fe 17 Cleaning of N3 magnetic powder: Sm2Fe 17 The cleaning of N3 magnetic powder was as shown in Example 1. The magnetic properties of the magnetic powder were tested: B r =10.10 kGs, H cj =17.69 kOe, (BH) max =34.13 MGOe, sphericity 0.80, D 50 =1.38 μm.

[0131] Table 3 Magnetic properties of magnetic powders prepared with different samarium compensation amounts

[0132] From the magnetic properties and sphericity data of magnetic powders prepared with different samarium compensation amounts in Table 2, it can be seen that the sphericity first increases and then decreases with the increase of samarium compensation amount. When the molar ratio of Fe ions to Sm ions is 1:0.18, the sphericity reaches the optimal value of 0.85. At the same time, the magnetic properties also reach the optimal level under this samarium compensation amount, specifically the remanence (B... r =11.49 kGs, coercivity (H) cj = 20.46 KOe, maximum magnetic energy product ((BH)) max = 40.31 MGOe. This led to the successful preparation of submicron-sized near-spherical Sm-Fe-N magnetic powder.

[0133] Example 9: Step 1: Preparation of precursors: The precursor was prepared as shown in Example 1, except that the amount of samarium nitrate hexahydrate in the mixed salt solution was changed to 20.80 g, and 1.31 g of chromium nitrate tetrahydrate was added as a metal compound containing M, so that the molar ratio of Fe ions to Sm ions and chromium ions was adjusted to 1:0.18:0.02. The other precursor preparation conditions were the same as in Example 1.

[0134] Step 2, Sm2Fe 17 Preparation of the mesophase: Sm2Fe 17 The preparation of the intermediate phase is as shown in Example 1.

[0135] Step 3, Sm2Fe 17 Preparation of N3 magnetic powder: Sm2Fe 17 The preparation of N3 magnetic powder is as shown in Example 1.

[0136] Step 4, Sm2Fe 17 Stabilization treatment of N3 magnetic powder: Sm2Fe17 The stabilization treatment of N3 magnetic powder is shown in Example 1.

[0137] Step 5, Sm2Fe 17 Cleaning of N3 magnetic powder: Sm2Fe 17 The cleaning of N3 magnetic powder was as shown in Example 1. The magnetic properties of the magnetic powder were tested: B r =10.89 kGs, H cj =25.69 kOe, (BH) max =36.71 MGOe, sphericity 0.84, D 50 =0.74 μm.

[0138] Table 4 Sm2Fe before and after Mn addition 17 Comparison of morphology and magnetic properties of N3 magnetic powder

[0139] As shown in Table 4, after introducing Cr, the resulting Sm2Fe 17 D of N3 magnetic powder 50 The particle size decreased from 1.03 μm to 0.74 μm, indicating that the introduction of Cr is beneficial for refining the magnetic powder particle size. With the decrease in particle size, the coercivity of the magnetic powder increased from 20.46 kOe to 25.69 kOe. Simultaneously, the introduction of the non-magnetic element Cr produces a certain magnetic dilution effect, reducing the remanence of the magnetic powder from 11.49 kGs to 10.89 kGs, and the magnetic energy product from 40.31 MGOe to 36.71 MGOe.

[0140] The above embodiments are used to illustrate and explain the present invention, and are not intended to limit the present invention. Any modifications and changes made to the present invention within the spirit and scope of the claims fall within the protection scope of the present invention.

Claims

1. A method for preparing high-performance Sm-(Fe,M)-N magnetic powder, characterized in that, The method includes the following steps: Step 1, Sm2Fe 17 Alloy precursor preparation: Samarium-containing compounds and iron-containing compounds were dissolved in an aqueous solvent and stirred thoroughly to obtain a mixed salt solution. Subsequently, surfactants and precipitants were added to the mixed salt solution, and stirring was continued while maintaining the pH above 7 to ensure that all metal ions were fully precipitated. The precipitate was then collected. The precipitated product is calcined, dehydrated, and crystallized to obtain a composite metal oxide; wherein, a dispersant is added during the calcination process to inhibit particle sintering and agglomeration. The composite metal oxide was completely reduced with hydrogen at 600-750℃ to obtain Sm2Fe. 17 Alloy precursor; Step 2, Sm2Fe 17 Preparation of the alloy mesophase: Sm2Fe 17 The alloy precursor undergoes surface conditioning treatment in air at 100-500℃, followed by thorough mixing with a reducing agent and a sintering inhibitor. It is then reduced at 700-800℃ in an argon atmosphere, and then diffused at 900-1100℃. At the same diffusion temperature, a vacuum is applied to maintain the furnace pressure between 0.001-0.10 MPa for dehydrogenation. After dehydrogenation, the furnace is purged with argon to atmospheric pressure and then recombined to obtain Sm2Fe. 17 Intermediate phase of alloy; Step 3, Sm2Fe 17 Preparation of N3 magnetic powder: Sm2Fe 17 The alloy's intermediate phase undergoes nitriding treatment, followed by annealing under an argon atmosphere to promote uniform nitrogen distribution within the particles, resulting in high-performance Sm2Fe alloy. 17 N3 magnetic powder; Step 4, Sm2Fe 17 Stabilization treatment of N3 magnetic powder: Sm2Fe 17 The N3 magnetic powder was placed intact in the furnace, and a certain oxygen partial pressure was introduced for slow stabilization treatment to ensure that excess reducing agent was converted into oxides, while Sm2Fe... 17 An oxide protective film also forms on the surface of N3 magnetic powder to prevent excessive corrosion and hydrogen permeation during water washing. Step 5, Sm2Fe 17 Cleaning of N3 magnetic powder: The stabilized magnetic powder was then washed, magnetically separated, extracted, and vacuum dried to obtain Sm2Fe with fine particle size and excellent magnetic properties. 17 N3 magnetic powder.

2. The method according to claim 1, characterized in that, The mixed salt solution mentioned in step one also needs to be added with a metal compound containing M. The molar ratio of iron ions in the iron compound to samarium ions in the samarium compound and M metal ions in the M metal compound is 1:(0.12-0.24):(0.01-0.2); M is one of La, Ce, Co, Ti, Mn, Al, Cr, and W.

3. The method according to claim 1, characterized in that, In step one, the calcination, dehydration, and crystallization treatment temperature is controlled at 500-1200℃, and the time is 1-10 h.

4. The method according to claim 1, characterized in that, In step one, the disintegrating agent is a composite agent composed of one or two of organic and inorganic additives; the surfactant is at least one of polyethylene glycol, polyvinyl alcohol, polyvinylpyrrolidone, citric acid, oleic acid, oleylamine, fluorinated surfactant, sodium dodecyl sulfate, hexadecyltrimethylammonium chloride, benzalkonium chloride, and hexadecylpyridine chloride; and the precipitant is at least one of hydroxide ions, ammonia, oxalate ions, carbonate ions, urea, and ammonium bicarbonate.

5. The method according to claim 1, characterized in that, In step one, the amount of the dispersant added is 1-50% of the mass of the precipitate; the mass ratio of the surfactant to the total mass of iron ions in the iron-containing compound and samarium ions in the samarium-containing compound is 0.1-5:100; the molar ratio of the precipitant to the iron ions in the iron-containing compound is (1-10):(0.1-1).

6. The method according to claim 1, characterized in that, In step two, the amount of reducing agent added is 2-3 times the molar mass of samarium ions; the amount of sintering inhibitor added is 10-50% of the mass of the reducing agent; the reducing agent is a metal reducing agent, and the sintering inhibitor is a soluble high-melting-point salt or calcium oxide.

7. The method according to claim 1, characterized in that, In step two, the dehydrogenation treatment time is 0.5-5 h, and the recombination treatment time is 0.5-5 h.

8. The method according to claim 1, characterized in that, In step three, the nitriding temperature is 300-500℃, the nitriding time is 0.5-5 h, and the nitriding atmosphere is pure nitrogen or a mixture of ammonia and hydrogen. After nitriding, the annealing treatment under an argon atmosphere is maintained at a temperature of 100-500℃ for 0.5-10 h.

9. The method according to claim 1, characterized in that, In step four, the stabilization temperature is 25-150℃ and the stabilization time is 10-72 h. During the stabilization process, the oxygen partial pressure is adjusted to 1-21% by adjusting the volume ratio of air or oxygen to argon.

10. A Sm-(Fe,M)-N magnetic powder, prepared by the method according to any one of claims 1-9, characterized in that: The chemical formula of the Sm-(Fe,M)-N magnetic powder is Sm2(Fe,M). 17 N3, possessing Th2Zn 17 Crystal structure of type; powder particle size ≤ 0.5μm. 50 ≤2.5μm, while D 90 ≤3.5μm, and average sphericity ≥0.8; coercivity H of magnetic powder cj ≥15 KOe, maximum energy product (BH) max ≥30MGOe.

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