A core-shell type Sm-Fe-N alloy and a method for manufacturing the same

Abstract

This invention discloses a core-shell Sm-Fe-N alloy and its preparation method, wherein the core of the core-shell Sm-Fe-N alloy is Sm2Fe. 17 N b The outer shell is Sm 2( Fe a M 1‑a ) 17 N b M is selected from at least one of Mn, Co, Cr, or Ti, where 0.5 ≤ a ≤ 0.95 and 2.5 ≤ b ≤ 3.5. This invention first prepares Sm₂Fe using physical or chemical methods. 17 The alloy is a mixture of M-O or Sm2Fe with a surface coating of M-O. 17 The alloy is further reduced and diffused to form Sm2Fe 17 A thin Sm-Fe-M layer is formed on the alloy surface, followed by nitriding. This invention yields a high-heat-resistant and high-oxidation-resistant samarium-iron-nitrogen core-shell alloy through surface modification. By introducing metallic M into the outer shell layer, it overcomes the problem of reduced saturation magnetization caused by overall doping with metallic M, and also improves the Sm2Fe... 17 Magnetic properties of N3 at high temperatures.

Description

Technical Field

[0001] This invention relates to the field of permanent magnet materials, and in particular to a core-shell type Sm-Fe-N alloy and its preparation method, specifically a core-shell type near-spherical samarium iron alloy with Sm-Fe-N as the core and Sm-Fe-MN as the shell. Background Technology

[0002] Rare earth permanent magnets are important functional materials due to their excellent comprehensive magnetic properties, and are now widely used in many fields such as home appliances, transportation energy, military equipment, communications, medical, and automation. Samarium iron nitrogen (Samarium ferronitrogen) materials have intrinsic properties such as higher magnetic anisotropy and Curie temperature than neodymium iron boron (NdFeB). It is a new type of rare earth permanent magnet without Dy, and has high magnetic energy product and high thermal stability (≤300℃), making it an ideal magnetic material for permanent magnet synchronous motors in new energy vehicles.

[0003] Currently used Sm2Fe 17 N3 remains limited to bonded magnets because it irreversibly thermally decomposes into α-Fe and Sm-N at temperatures above 450°C. Although Sm2Fe has a particle size of less than 3 μm... 17 N3-based Sm-Fe-N micro powder exhibits high coercivity at room temperature, but the coercivity decreases due to surface oxidation after heating at 150~200℃.

[0004] Since 1990 Sm2Fe 17 N x Since the discovery of interstitial compounds by Coey et al., researchers have successively prepared Sm2Fe using various methods such as melt quenching, reduction diffusion, powder metallurgy, hydrogen disproportionation, and mechanical alloying. 17N3 powder. Preparing permanent magnets with ideal microstructures solely through process control is extremely difficult; additive elements play a crucial role in material preparation. The effects of additive elements such as Co, Cr, Nb, Zr, Mn, Ti, V, and Si on the magnetic properties of magnetic materials have been extensively studied. These additive elements influence grain size, amorphous formation ability, and magnetocrystalline exchange coupling to varying degrees, further improving the thermal stability and corrosion resistance of magnetic materials by enhancing grain magnetocrystalline anisotropy. However, these methods all employ bulk doping, distributing the doped elements throughout the powder. While improving performance, this reduces saturation magnetization, posing certain adverse effects. For example, CN114255947A discloses an Sm-Fe-N magnetic material and its manufacturing method, which improves saturation magnetization while reducing Sm usage, or suppresses the reduction in saturation magnetization to a practically acceptable range. However, to eliminate the reduction in saturation magnetization caused by element doping, multiple metal elements are introduced again, increasing the preparation difficulty and time cost. Patent CN105355354A discloses a samarium iron nitrogen-based anisotropic rare earth permanent magnet powder and its preparation method. The magnetic powder, through elemental doping, helps to eliminate defects in the 2:17 type main phase grains, reduce reverse domain nucleation points, and decouple. However, this method is simply elemental doping, which has certain adverse effects and limitations on performance improvement. Summary of the Invention

[0005] To address the issue of reduced coercivity of Sm-Fe-N magnetic powder due to surface oxidation after heating at 150-200℃, this invention proposes a core-shell structured rare earth alloy powder and its preparation method. By controlling the distribution of doping elements through surface modification, near-spherical core-shell Sm-Fe-N core and Sm-Fe-MN shell-type fine Sm-Fe alloy powder is obtained. This fully utilizes the advantages of local element doping and overcomes the problem of reduced saturation magnetization caused by overall doping.

[0006] In a first aspect, the present invention provides a core-shell Sm-Fe-N alloy, wherein the core is Sm2Fe. 17 N b The outer shell is Sm 2( Fe a M 1-a ) 17 N b M is selected from at least one of Mn, Co, Cr or Ti, 0.5≤a≤0.95, 2.5≤b≤3.5, and b is preferably 3.0.

[0007] Preferably, the core-shell Sm-Fe-N alloy has an average particle size of 1.0-4.0 micrometers and an outer shell thickness of 10-500 nm.

[0008] Secondly, the present invention provides a method for preparing a core-shell Sm-Fe-N alloy, the specific steps of which are as follows:

[0009] First, prepare Sm2Fe 17 Using the alloy as the matrix, Sm2Fe is then... 17 Sm2Fe alloys are obtained through physical or chemical methods. 17 A mixture of alloy and metal oxide MO or Sm2Fe with a surface coating of metal oxide MO 17 Alloy; then the above Sm2Fe 17 A mixture of alloy and metal oxide MO or Sm2Fe with a surface coating of metal oxide MO 17 Further reduction and diffusion of the alloy led to the formation of Sm2Fe 17 A thin Sm-Fe-M layer is formed on the alloy surface, and then further nitrided to obtain Sm2Fe. 17 N b For the core, Sm 2( Fe a M 1-a ) 17 N b It is a core-shell type Sm-Fe-N alloy with a shell.

[0010] As a preferred option, Sm2Fe 17 Alloys can be prepared by alloy spinning, chemical coprecipitation-reduction, or ultrasonic spray thermal decomposition-reduction.

[0011] As a preferred option, prepare Sm2Fe 17 A mixture of alloy and metal oxide MO or Sm2Fe with a surface coating of metal oxide MO 17 The physical or chemical methods used to alloy alloys include at least mechanical mixing or solution soaking;

[0012] The mechanical mixing can be direct mechanical mixing;

[0013] The solution soaking specifically involves Sm2Fe 17 Alloy powder is immersed in a soluble nitrate solution containing M ions, and the solution is evaporated to dryness with constant stirring. Then, it is dehydrated and decomposed at 100-400℃ to produce Sm2Fe. 17 The alloy powder is coated with a layer of metal oxide MO.

[0014] Preferably, the mixture is further reduced and diffused to allow Sm2Fe 17 The formation of an Sm-Fe-M thin layer on the surface of alloy powder refers to the application of Sm2Fe 17 Sm2Fe alloy powder mixed with metal oxide MO powder or with a surface coated with a layer of metal oxide MO17 The alloy powder undergoes a reduction treatment. During the reduction process, the metal oxide MO is reduced to elemental metal M. In this process, elemental metal M generates Sm-Fe-M through an adsorption-diffusion process at the reduction temperature, realizing the formation of Sm-Fe2Fe. 17 A certain thickness of Sm-Fe-M outer shell layer is formed on the surface of the alloy particles.

[0015] Preferably, the nitriding specifically involves nitriding core-shell structured particles containing M. Under a reducing atmosphere, nitrogen atoms diffuse into the core and outer shell layers of the core-shell structured particles through adsorption and diffusion as interstitial atoms. After nitriding, a series of processing steps are performed, including cleaning with organic alcohol to remove reduction byproducts, magnetic separation, centrifugation, and vacuum drying, to obtain Sm2Fe. 17 N b For the core, Sm 2( Fe a M 1-a ) 17 N b The powder is a core-shell type fine powder. More preferably, the nitriding treatment has a nitriding time of 0.5~4h, a nitriding temperature of 350~500℃, a nitrogen source of NH3, a reducing atmosphere of H2, and a gas flow rate of 0.2~0.8 L / min.

[0016] Preferably, the metal M includes at least one of Mn, Co, Cr, and Ti, and the metal oxide MO includes at least one of MnO, MnO2, Mn3O4, Mn2O3, CoO, Cr2O3, CrO, and TiO2. In order to achieve uniform dispersion, the average particle size of the metal oxide MO is required to be less than 20 micrometers.

[0017] As a preferred method, based on the principle of metal diffusion, by controlling Sm2Fe 17 The mixing ratio or control of alloy powder with specific metal oxide MO powder is used for impregnation of Sm2Fe. 17 The concentration of soluble nitrate solution containing M ions in alloy powder can achieve Sm 2( Fe a M 1-a ) 17 N b The thickness of the outer shell layer is controlled to be 10~500nm.

[0018] Preferably, the reduction process of samarium iron composite oxide and the reduction process of metal oxide MO can be carried out by first reducing with hydrogen and then reducing with an active metal, or by direct reduction with an active metal. The active metal includes one of calcium, sodium, and potassium. The reduction temperature is 800~1000℃, and the reduction time is 0.5~2.5h.

[0019] Compared with the prior art, the present invention has the following advantages:

[0020] (1) This invention proposes to use Sm2Fe 17 Alloy powder is used as the matrix, and then it is mechanically mixed with metal oxide MO or surface coated with MO by immersion in a soluble nitrate solution containing M ions. Then, through reduction-diffusion-nitridation, a core-shell fine powder with Sm-Fe-N as the core and Sm-Fe-MN as the shell is obtained, so that an anti-oxidation layer is formed on the surface of the samarium iron nitrogen powder, which slows down the oxidation rate of the powder in the air.

[0021] (2) The present invention relates to a core-shell structure Sm2Fe 17 N x Introducing additional metal element M into the thin outer shell of the powder not only overcomes the problem of reduced saturation magnetization caused by overall doping with metal element M, but also improves the Sm2Fe 17 N x Magnetic properties at high temperatures. Attached Figure Description

[0022] Figure 1 (a): EDS image of the rare earth alloy product with a core-shell structure after nitriding of core-shell fine powder in Example 3.

[0023] Figure 1 (b)-(e): These are map diagrams showing the positional distribution of four elements (samarium, iron, manganese, and nitrogen) in the rare earth alloy product with a core-shell structure after nitriding of core-shell fine powder in Example 3, where b is nitrogen, c is iron, d is manganese, and e is samarium.

[0024] Figure 2 Sm2Fe 17 Alloy powder formation with Sm2Fe 17 For the core, Sm2 (Fe, Mn) 17 Schematic diagrams of two routes for preparing core-shell type fine powder. Detailed Implementation

[0025] As mentioned above, in view of the shortcomings of the prior art, the inventors of this invention, through long-term research and extensive practice, have proposed the technical solution of this invention, the main basis of which includes at least the following:

[0026] (1) Under the action of excess reducing agent, Sm2Fe 17 Using alloy powder as a matrix, a high-temperature reduction-diffusion reaction is carried out on the product coated with metal oxide MO through direct mechanical mixing or solution immersion. This allows for the realization of Sm2Fe 17 A certain thickness of Sm-Fe-M outer shell layer is formed on the particle surface. By controlling the amount of metal oxide (MO) used during mixing or coating, it is possible to ensure that M only remains in the outer shell layer and does not diffuse throughout the powder.

[0027] (2) For the core-shell structure Sm2Fe 17 The particles undergo nitriding treatment, where nitrogen atoms diffuse into the core and outer shell of the core-shell structured particles via adsorption and diffusion as interstitial atoms, thereby obtaining Sm2Fe 17 N b For the core, Sm 2( Fe a M 1-a ) 17 N b This core-shell powder, with its nitrogen-doped core-shell structure, overcomes the problem of reduced saturation magnetization caused by the addition of the metal element M during overall doping. Furthermore, because Sm... 2( Fe a M 1-a ) 17 N b The presence of the outer shell layer improves the high-temperature oxidation resistance and high-temperature magnetic properties of the magnetic powder.

[0028] 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.

[0029] This invention provides a method for preparing a core-shell Sm-Fe-N alloy, the specific steps of which are as follows:

[0030] Sm2Fe is first prepared by alloy spinning, chemical co-precipitation-reduction, or ultrasonic spray thermal decomposition-reduction. 17 Using the alloy as the matrix, Sm2Fe is then... 17 Sm2Fe alloys are obtained through physical or chemical methods. 17 A mixture of alloy and metal oxide MO or Sm2Fe with a surface coating of metal oxide MO 17 Alloy; then the above Sm2Fe 17 A mixture of alloy and metal oxide MO or Sm2Fe with a surface coating of metal oxide MO 17 Further reduction and diffusion of the alloy led to the formation of Sm2Fe 17 A thin Sm-Fe-M layer is formed on the alloy surface, and then further nitrided to obtain Sm2Fe. 17 N b For the core, Sm 2( Fe a M 1-a ) 17 N b It is a core-shell type Sm-Fe-N alloy with a shell.

[0031] The alloy casting method involves melting pure samarium and pure iron metals in a molar ratio of (2~3):17 under an argon atmosphere, and then casting the molten alloy onto a high-speed rotating copper roller using a rapid quenching furnace to obtain Sm2Fe. 17 The alloy strips are then crushed mechanically or by ball milling to obtain Sm2Fe. 17 alloy powder.

[0032] The chemical coprecipitation method involves mixing water-soluble iron salts or water-soluble samarium salts, then adding a soluble alkali dropwise to coprecipitate iron ions and samarium ions. The coprecipitate obtained by centrifugation and filtration is then dehydrated and dried at 100-300℃ to obtain samarium-iron composite oxide.

[0033] The ultrasonic spray pyrolysis method involves ultrasonically atomizing a precursor solution composed of water-soluble samarium salt and water-soluble iron salt, then using air as the carrier gas to deliver it into a three-stage temperature-controlled tubular furnace. Through solvent evaporation, thermal decomposition, and densification processes, samarium-iron composite oxide is ultimately formed. The three-stage temperature control within the tubular furnace is as follows: the first stage is controlled at 100~400℃ for evaporation and dehydration; the second stage is controlled at 500~1000℃ for thermal decomposition; and the third stage is controlled at 1000~1200℃ for high-temperature densification. The carrier gas flow rate within the tubular furnace is controlled at 5~30 L / min.

[0034] Both the samarium iron composite oxides obtained by chemical coprecipitation and ultrasonic spray pyrolysis need to be reduced to obtain Sm2Fe. 17 alloy powder.

[0035] The water-soluble samarium salts mentioned in the chemical coprecipitation method and the ultrasonic spray thermal decomposition method are trivalent water-soluble samarium salts, specifically at least one of samarium chloride, samarium nitrate, and samarium sulfate. The water-soluble iron salts are trivalent water-soluble iron salts, specifically at least one of ferric chloride, ferric nitrate, and ferric sulfate. The molar ratio of the water-soluble samarium salts to the water-soluble iron salts is 0.2 to 1 times higher than the molar ratio of samarium to iron in core-shell rare earth alloy powders.

[0036] In this embodiment of the invention, Sm2Fe was prepared. 17 A mixture of alloy and metal oxide MO or Sm2Fe with a surface coating of metal oxide MO 17 The physical or chemical methods used to alloy alloys include at least mechanical mixing or solution soaking;

[0037] The mechanical mixing can be direct mechanical mixing;

[0038] The solution soaking specifically involves Sm2Fe 17 Alloy powder is immersed in a soluble nitrate solution containing M ions, and the solution is evaporated to dryness with constant stirring. Then, it is dehydrated and decomposed at 100-400℃ to produce Sm2Fe. 17The alloy powder is coated with a layer of metal oxide MO.

[0039] The mixture is further reduced and diffused, causing Sm2Fe 17 The formation of an Sm-Fe-M thin layer on the surface of alloy powder refers to the application of Sm2Fe 17 Sm2Fe alloy powder mixed with metal oxide MO powder or with a surface coated with a layer of metal oxide MO 17 The alloy powder undergoes a reduction treatment. During the reduction process, the metal oxide MO is reduced to elemental metal M. In this process, elemental metal M generates Sm-Fe-M through an adsorption-diffusion process at the reduction temperature, realizing the formation of Sm-Fe2Fe. 17 A certain thickness of Sm-Fe-M outer shell layer is formed on the surface of the alloy particles.

[0040] In this embodiment of the invention, the nitriding specifically involves nitriding core-shell structured particles containing M. Under a reducing atmosphere, nitrogen atoms diffuse into the core and outer shell layers of the core-shell structured particles through adsorption-diffusion as interstitial atoms. After nitriding, a series of processing steps are performed, including organic alcohol washing to remove reduction byproducts, magnetic separation, centrifugation, and vacuum drying, to obtain Sm2Fe. 17 N b For the core, Sm 2( Fe a M 1-a ) 17 N b The powder is a core-shell type fine powder. The nitriding treatment has a nitriding time of 0.5~4h, a nitriding temperature of 350~500℃, a nitrogen source of NH3, a reducing atmosphere of H2, and a gas flow rate of 0.2~0.8 L / min.

[0041] In this embodiment of the invention, the metal M includes at least one of Mn, Co, Cr, and Ti, and the metal oxide MO includes at least one of MnO, MnO2, Mn3O4, Mn2O3, CoO, Cr2O3, CrO, and TiO2. In order to achieve uniform dispersion, the average particle size of the metal oxide MO is required to be less than 20 micrometers.

[0042] In this embodiment of the invention, based on the principle of metal diffusion, Sm2Fe is controlled... 17 The mixing ratio or control of alloy powder with specific metal oxide MO powder is used for impregnation of Sm2Fe. 17 The concentration of soluble nitrate solution containing M ions in alloy powder can achieve Sm 2( Fe a M 1-a ) 17 N b The thickness of the outer shell layer is controlled to be 10~500nm.

[0043] In this embodiment of the invention, the reduction process of samarium iron composite oxide and the reduction process of metal oxide MO can be carried out by first reducing with hydrogen and then reducing with an active metal, or by directly reducing with an active metal. The active metal includes one of calcium, sodium, and potassium. The reduction temperature is 800~1000℃, and the reduction time is 0.5~2.5h. The amount of active metal used during the reduction process is controlled to be excessive, 1.5~3.5 times the theoretically calculated value.

[0044] The technical solution of the present invention will be further explained and described below with reference to several preferred embodiments, but the experimental conditions and setting parameters therein should not be regarded as limitations on the basic technical solution of the present invention. Furthermore, the scope of protection of the present invention is not limited to the following embodiments.

[0045] Example 1

[0046] Weigh out 6.25g of pure samarium and 16.19g of pure iron and place them into the crucible of the electric arc melting furnace, then evacuate to a vacuum of 5×10⁻⁶. -3 Argon gas was introduced as a protective gas during melting. A 150A arc current was used for 60 seconds, repeated four times to ensure uniform composition. After melting, the surface of the ingot alloy was polished to remove the oxide scale, and then it was broken into small pieces. A vacuum induction melting furnace was used. The broken alloy pieces were placed in a quartz tube with nozzles for induction heating. After the alloy melt in the quartz tube melted and boiled, pressure casting was performed. The alloy melt was rapidly cooled and ejected by high-speed rotating rollers at a speed of 15 m / s to obtain alloy strips. The obtained alloy strips were placed in a stainless steel jar and ball-milled at 300 r / min for 4 hours. The mass ratio of large to small agate beads used for ball milling was 1:3, and the mass ratio of agate beads to powder was 20:1. Hexane was used as the carrier liquid. Before ball milling, argon gas was introduced into the milling jar as a protective gas to prevent oxidation. After ball milling, hexane and agate beads were separated in a glove box using the principle of magnetic separation. The separated Sm2Fe 17 The alloy powder was placed in a vacuum drying oven with a suction pressure ≤0.7 MPa and dried for 10 hours.

[0047] See Figure 2 Weigh out 5g of Sm2Fe 17Alloy powder and 0.5g Cr2O3 powder were mixed evenly in a mortar. 1g Ca granules were added and placed in a crucible. The mixture was reacted at 900℃ for 1 hour under a flowing Ar atmosphere for reduction diffusion. After cooling, the mixture was reacted at 380℃ for 1 hour under a flowing mixed NH3-H2 atmosphere. After the reaction, the product was poured into a mortar, and an appropriate amount of ethylene glycol was added. The mixture was rubbed and washed for 0.5 hours. Then, the washing liquid was discarded using the principle of magnetic separation. The product was then repeatedly washed with ethylene glycol solution, while being sonicated, until no obvious bubbles were generated. Finally, it was rubbed three times with anhydrous ethanol to facilitate drying. The cleaned product was placed in a vacuum drying oven with a pressure ≤0.7 MPa and dried for 10 hours.

[0048] The metal element content of the product was determined by XRF, the nitrogen content by an oxygen-nitrogen analyzer, the product morphology by SEM, and the product particle size by a laser particle size analyzer, confirming the presence of Sm2Fe in the core. 17 N 2.6 The outer shell is Sm 2( Fe 0.6 Cr 0.4 ) 17 N 2.6 Samarium iron nitrogen magnetic powder with an average particle size of 2.4 micrometers was tested for magnetic properties at room temperature and 200℃ using a vibrating sample magnetometer (VSM). Oxidation weight gain analysis was performed by heating in air at 250℃. The results are shown in Table 1.

[0049] Example 2

[0050] Take 70.7 ml of 0.2 mol / L SmCl3 solution and 429.3 ml of 0.2 mol / L FeCl3 solution. Heat the mixed solution to 60°C using a heating mantle while stirring. After the mixed solution stabilizes at 60°C for a short time, add a 1 mol / L NH4HCO3 solution dropwise to the mixed solution at a constant pressure dropping funnel until the pH of the solution reaches 10. Continue stirring for 30 min to ensure uniform mixing of the substances in the flask. Allow the mixture to stand for 12 h to allow complete reaction. Centrifuge, wash, dry, and calcine at 300°C for 4 h to finally obtain the samarium iron composite oxide precursor.

[0051] Samarium iron composite oxide precursor powder was placed in a tube furnace and reduced with hydrogen at 600℃ for 1 h to obtain a mixture of α-Fe and Sm2O3. 10 g of the hydrogen-reduced sample was uniformly mixed with 0.4 g of Ca particles and placed in a crucible. The crucible was then placed in a tube furnace and reduced and diffused at 950℃ for 2 h under a flowing Ar atmosphere to obtain Sm2Fe. 17 Alloy powder.

[0052] See Figure 2 10g Sm2Fe 17Alloy powder was placed in a beaker with 1g of a 50% (w / w) Mn(NO3)2 aqueous solution, 10ml of ethanol was added, and the mixture was heated to 20°C with constant stirring until the solution evaporated to dryness. The dried powder was then placed in a tube furnace and calcined at 400°C for 4 hours under an argon atmosphere to remove excess moisture and decompose manganese nitrate into oxides that coated Sm2Fe. 17 The alloy powder surface was treated, and then 1g of Ca particles were placed in a crucible and reacted at 900℃ for 3 hours under a flowing Ar atmosphere for reduction diffusion. After cooling, the mixture was reacted at 400℃ for 1.5 hours under a flowing mixed NH3-H2 atmosphere. After the reaction, the product was poured into a mortar, and an appropriate amount of ethylene glycol was added. The mixture was rubbed and washed for 0.5 hours, and then the washing liquid was discarded using the principle of magnetic separation. The product was then repeatedly washed with ethylene glycol solution, while being sonicated, until no obvious bubbles were generated. Then, it was rubbed three times with anhydrous ethanol to facilitate drying. The cleaned product was placed in a vacuum drying oven with a pressure ≤0.7 MPa and dried for 10 hours.

[0053] The metal content of the product was detected by XRF, the nitrogen content was measured by an oxygen and nitrogen analyzer, and the morphology of the product was analyzed by SEM (see [reference]). Figure 1 The particle size of the product was measured using a laser particle size analyzer, confirming the presence of Sm2Fe in the core. 17 N 3.2 The outer shell is Sm2(Fe) 0.65 Mn 0.35 ) 17 N 3.2 Samarium iron nitrogen magnetic powder with an average particle size of 2.1 micrometers was tested for magnetic properties at room temperature and 200°C using a vibrating sample magnetometer (VSM). Oxidation weight gain analysis was performed by heating the powder in air at 250°C. The results are shown in Table 1.

[0054] Example 3

[0055] Mix 150 mL of 0.2 mol / L SmCl3 solution and 850 mL of 0.2 mol / L FeCl3 solution and pour the mixture into an ultrasonic atomizing device. Heat the inlet section of the tube furnace to 300°C, the center section to 800°C, and the tail section to 1000°C. Then turn on the atomizing device. Use an air compressor to introduce air and set the gas flow rate to 10 L / min using a gas flow meter. The carrier gas will transport the atomized water mist into the tube furnace. Continue until the solution reaction is complete, then turn off the atomizing device. After the furnace temperature has cooled to room temperature, turn it off again and collect the spray decomposition products in the collector at the tail of the tube.

[0056] 1.5g of the collected oxide powder was weighed and placed in a tube furnace. The mixture was reacted at 700℃ for 1 hour under a flowing H2-N2 atmosphere to obtain Fe2O3-SmFeO3 composite oxide powder. 1g of the pre-reduction product was weighed, and 0.3g of metallic Ca particles were added. The mixture was placed in a crucible and then pushed into a tube furnace. The mixture was reacted at 900℃ for 1 hour under a flowing Ar atmosphere to obtain the reduction product Sm2Fe. 17 Alloy powder.

[0057] See Figure 2 Weigh 0.5g of the reduction product Sm2Fe 17 Alloy powder was mixed evenly with 0.015g Mn3O4 in a mortar and placed in a crucible. The mixture was then reacted at 900℃ for 1h under a flowing Ar atmosphere for reduction treatment. The reduced product Sm-Fe-Mn was placed in a porcelain boat and pushed into a tube furnace. The mixture was then reacted at 400℃ for 1h under a flowing mixed NH3-H2 atmosphere.

[0058] After the reaction, the product in the crucible was poured into a mortar, and an appropriate amount of ethylene glycol was added. The mixture was ground and washed for 0.5 hours. Then, a magnet was placed under the mortar, and the washing liquid was poured off using the principle of magnetic separation. The product was then repeatedly washed with ethylene glycol solution, while being sonicated, until no obvious bubbles were generated. Finally, it was washed three times with anhydrous ethanol to facilitate drying. The cleaned product was placed in a vacuum drying oven with a pressure ≤0.7 MPa and dried for 10 hours.

[0059] The metal element content of the product was determined by XRF, the nitrogen content by an oxygen-nitrogen analyzer, the product morphology by SEM, and the product particle size by a laser particle size analyzer, confirming the presence of Sm2Fe in the core. 17 N3, with an outer shell of Sm2(Fe) 0.85 Mn 0.15 ) 17 The samarium iron nitrogen magnetic powder of N3 has an average particle size of 2.3 micrometers. The magnetic properties of the magnetic powder were tested at room temperature and 200°C using a vibrating sample magnetometer (VSM). The powder was also heated in air at 250°C for oxidation weight gain analysis. The results are shown in Table 1.

[0060] Example 3: EDS diagram of the core-shell rare earth alloy product after nitriding of core-shell fine powder is shown below. Figure 1 (a). Example 3: The positional distribution (Map) of nitrogen, iron, manganese, and samarium in the core-shell structured rare earth alloy product after core-shell fine powder nitriding is shown in the figure. Figure 1 (b)-(e).

[0061] Example 4

[0062] Weigh out 6.75g of pure samarium and 15.15g of pure iron and place them into the crucible of the electric arc melting furnace, then evacuate to a vacuum of 5×10⁻⁶. -3Argon gas was introduced as a protective gas during melting. A 150A arc current was used for 60 seconds, repeated four times to ensure uniform composition. After melting, the surface of the ingot alloy was polished to remove the oxide scale, and then it was broken into small pieces. A vacuum induction melting furnace was used. The broken alloy pieces were placed in a quartz tube with nozzles for induction heating. After the alloy melt in the quartz tube melted and boiled, pressure casting was performed. The alloy melt was rapidly cooled and ejected by high-speed rotating rollers at a speed of 15 m / s to obtain alloy strips. The obtained alloy strips were placed in a stainless steel jar and ball-milled at 300 r / min for 4 hours. The mass ratio of large to small agate beads used for ball milling was 1:3, and the mass ratio of agate beads to powder was 20:1. Hexane was used as the carrier liquid. Before ball milling, argon gas was introduced into the milling jar as a protective gas to prevent oxidation. After ball milling, hexane and agate beads were separated in a glove box using the principle of magnetic separation. The separated Sm2Fe 17 The alloy powder was placed in a vacuum drying oven with a suction pressure ≤0.7 MPa and dried for 10 hours.

[0063] 10g Sm2Fe 17 Alloy powder was placed in a beaker with 4g of a 50% (w / w) Co(NO3)2 aqueous solution, 10ml of ethanol was added, and the mixture was heated to 20°C with constant stirring until the solution evaporated to dryness. The evaporated powder was then placed in a tube furnace and calcined at 400°C for 4 hours under an argon atmosphere to remove excess moisture and decompose cobalt nitrate into oxides that coated Sm2Fe. 17 The alloy powder surface was treated, and then 1g of Ca particles were placed in a crucible and reacted at 900℃ for 3h under a flowing Ar atmosphere for reduction diffusion. After cooling, the mixture was reacted at 360℃ for 1.5h under a flowing mixed NH3-H2 atmosphere. After the reaction, the product was poured into a mortar, and an appropriate amount of ethylene glycol was added. The mixture was rubbed and washed for 0.5h, and then the washing liquid was discarded using the principle of magnetic separation. The product was then repeatedly washed with ethylene glycol solution, while being sonicated, until no obvious bubbles were generated. Then, it was rubbed three times with anhydrous ethanol to facilitate drying. The cleaned product was placed in a vacuum drying oven with a pressure ≤0.7Mpa and dried for 10h.

[0064] The metal content of the product was detected by XRF, the nitrogen content was measured by an oxygen and nitrogen analyzer, and the morphology of the product was analyzed by SEM (see [reference]). Figure 1 The particle size of the product was measured using a laser particle size analyzer, confirming the presence of Sm2Fe in the core. 17 N 2.6 The outer shell is Sm2(Fe) 0.52 Co 0.48 ) 17 N 2.6Samarium iron nitrogen magnetic powder with an average particle size of 1.8 micrometers was tested for magnetic properties at room temperature and 200°C using a vibrating sample magnetometer (VSM). Oxidation weight gain analysis was performed by heating the powder in air at 250°C. The results are shown in Table 1.

[0065] Example 5

[0066] Take 70.7 ml of 0.2 mol / L SmCl3 solution and 429.3 ml of 0.2 mol / L FeCl3 solution. Heat the mixed solution to 60°C using a heating mantle while stirring. After the mixed solution stabilizes at 60°C for a short time, add a 1 mol / L NH4HCO3 solution dropwise to the mixed solution at a constant pressure dropping funnel until the pH of the solution reaches 10. Continue stirring for 30 min to ensure uniform mixing of the substances in the flask. Allow the mixture to stand for 12 h to allow complete reaction. Centrifuge, wash, dry, and calcine at 300°C for 4 h to finally obtain the samarium iron composite oxide precursor.

[0067] Samarium iron composite oxide precursor powder was placed in a tube furnace and reduced with hydrogen at 600℃ for 1 h to obtain a mixture of α-Fe and Sm2O3. 10 g of the hydrogen-reduced sample was uniformly mixed with 0.4 g of Ca particles and placed in a crucible. The crucible was then placed in a tube furnace and reduced and diffused at 950℃ for 2 h under a flowing Ar atmosphere to obtain Sm2Fe. 17 Alloy powder.

[0068] Weigh out 5g of Sm2Fe 17 Alloy powder and 0.1g TiO2 powder were mixed evenly in a mortar. 1g Ca granules were added and placed in a crucible. The mixture was reacted at 950℃ for 2.0h under a flowing Ar atmosphere for reduction diffusion. After cooling, the mixture was reacted at 450℃ for 2.0h under a flowing mixed NH3-H2 atmosphere. After the reaction, the product was poured into a mortar, and an appropriate amount of ethylene glycol was added. The mixture was rubbed and washed for 0.5h. Then, the washing liquid was discarded using the principle of magnetic separation. The product was then repeatedly washed with ethylene glycol solution, while being sonicated, until no obvious bubbles were generated. Finally, it was rubbed three times with anhydrous ethanol to facilitate drying. The cleaned product was placed in a vacuum drying oven with a pressure ≤0.7MPa and dried for 10h.

[0069] The metal element content of the product was determined by XRF, the nitrogen content by an oxygen-nitrogen analyzer, the product morphology by SEM, and the product particle size by a laser particle size analyzer, confirming the presence of Sm2Fe in the core. 17 N 3.4 The outer shell is Sm 2( Fe 0.94 Ti 0.06 ) 17 N 3.4Samarium iron nitrogen magnetic powder with an average particle size of 2.8 micrometers was tested for magnetic properties at room temperature and 200°C using a vibrating sample magnetometer (VSM). Oxidation weight gain analysis was performed by heating the powder in air at 250°C. The results are shown in Table 1.

[0070] Control group 1

[0071] Fe2O3-SmFeO3 composite oxide powder was obtained using the same method as in Example 3.

[0072] Weigh 1.5g of Fe2O3-SmFeO3 composite oxide powder and mix it evenly with 0.025g of Mn3O4 in a mortar. Then, add 0.35g of metallic Ca particles and place them into an iron crucible, which is then pushed into a high-temperature reactor. React at 900℃ for 1 hour under a flowing Ar atmosphere. Place the reduced product in a porcelain boat and push it into a tube furnace. React at 400℃ for 1 hour under a flowing mixed NH3-H2 atmosphere.

[0073] After the reaction, the product in the crucible was poured into a mortar, and an appropriate amount of ethylene glycol was added. The mixture was ground and washed for 0.5 hours. Then, a magnet was placed under the mortar, and the washing liquid was poured off using the principle of magnetic separation. The product was then repeatedly washed with ethylene glycol solution, while being sonicated, until no obvious bubbles were generated. Finally, it was washed three times with anhydrous ethanol to facilitate drying. The cleaned product was placed in a vacuum drying oven with a pressure ≤0.7 MPa and dried for 10 hours.

[0074] The metal element content of the product was determined by XRF, the nitrogen content by an oxygen-nitrogen analyzer, the product morphology by SEM, and the product particle size by a laser particle size analyzer, confirming the presence of Sm2(Fe). 0.75 Mn 0.25 ) 17 The N3 samarium iron nitrogen magnetic powder has manganese dispersed throughout the powder. The average particle size of the powder is 2.4 micrometers. The magnetic properties of the magnetic powder were tested at room temperature and 200°C using a vibrating sample magnetometer (VSM). The powder was also heated in air at 250°C for oxidation weight gain analysis. The results are shown in Table 1.

[0075] Control group 2

[0076] In Example 3, the amount of Mn3O4 added was 0g, while other experimental conditions remained unchanged.

[0077] The metal element content of the product was determined by XRF, the nitrogen content by an oxygen-nitrogen analyzer, the product morphology by SEM, and the product particle size by a laser particle size analyzer, confirming the presence of Sm2Fe. 17 Samarium iron nitrogen magnetic powder of N3, with an average particle size of 2.4 micrometers, was tested for magnetic properties at room temperature and 200°C using a vibrating sample magnetometer (VSM). Oxidation weight gain analysis was performed by heating in air at 250°C. The results are shown in Table 1.

[0078] Control group 3

[0079] Take 70.7 ml of 0.2 mol / L SmCl3 solution, 429.3 ml of 0.2 mol / L FeCl3 solution, and 14 ml of 0.2 mol / L Mn(NO3)2 solution. Then perform precipitation, reduction, and nitriding as described in Example 2, but the reduction product is not soaked in Mn(NO3)2 solution again.

[0080] The metal element content of the product was determined by XRF, the nitrogen content by an oxygen-nitrogen analyzer, the product morphology by SEM, and the product particle size by a laser particle size analyzer, confirming the presence of Sm2(Fe). 0.63 Mn 0.37 ) 17 N 3.1 Samarium iron nitrogen magnetic powder, with manganese dispersed throughout the powder, has an average particle size of 2.5 micrometers. The magnetic properties of the magnetic powder were tested at room temperature and 200°C using a vibrating sample magnetometer (VSM), and oxidation weight gain analysis was performed by heating in air at 250°C. The results are shown in Table 1.

[0081] The final products of Examples 1-5 and Control Groups 1-3 were analyzed for powder phase composition using X-ray diffraction (XRD) and their relationship with Sm2Fe was determined. 17 The diffraction peaks of the N3 alloy crystals were consistent, and no diffraction peaks were found for α-Fe or other alloys. Table 1 shows that Sm2Fe prepared by different methods... 17 Both direct mixing with MO or solution immersion in alloy powders to form MO can yield core-shell samarium iron nitrogen (SMR) magnetic powder, exhibiting excellent high-temperature oxidation resistance and magnetic properties. Compared to the Mn-doped Example 3, the control group 2 (without Mn) showed a smaller decrease in magnetic properties after heating at 200°C and a lower weight gain at 250°C, indicating superior high-temperature oxidation resistance and magnetic properties with Mn doping. However, in control group 1, directly mixing Fe2O3-SmFeO3 composite oxide powder with Mn3O4 powder followed by reduction failed to form core-shell SMR magnetic powder, resulting in Mn being incorporated into the powder. While high-temperature oxidation resistance remained acceptable, the remanence and maximum energy product at room temperature were significantly lower than in Example 3. Control group 3, which involved co-precipitating Mn(NO3)2 in SmCl3 and FeCl3 solutions followed by reduction nitriding, also failed to form core-shell SMR magnetic powder, showing a significant decrease in remanence and maximum energy product at room temperature compared to Example 2.

[0082] Table 1. Performance comparison of the final product powders from Examples 1-5 and Control Groups 1-3

[0083]

Claims

1. An Sm-Fe-N alloy with a core-shell structure, characterized in that, The core-shell structure has a core of Sm2Fe. 17 N b The outer shell is Sm2(Fe) a M 1-a ) 17 N b M is selected from at least one of Co, Cr or Ti, 0.5≤a≤0.95, 2.5≤b≤3.5; The alloy is prepared by a method comprising the following steps: forming a thin Sm-Fe-M layer on the surface of Sm2Fe. 17 The alloy is subjected to nitriding treatment, which is carried out directly after the reduction-diffusion reaction.

2. The Sm-Fe-N alloy according to claim 1, characterized in that, The average particle size of the Sm-Fe-N alloy is 1.0-4.0 micrometers.

3. The Sm-Fe-N alloy according to claim 1 or 2, characterized in that, The outer shell layer thickness is 10~500nm.

4. A method for preparing the Sm-Fe-N alloy according to any one of claims 1-3, characterized in that, The method specifically involves Sm2Fe 17 Using alloys as the parent material, Sm2Fe is obtained through physical or chemical methods. 17 A mixture of alloy and metal oxide MO or Sm2Fe with a surface coating of metal oxide MO 17 Alloy; then the above Sm2Fe 17 A mixture of alloy and metal oxide MO or Sm2Fe with a surface coating of metal oxide MO 17 Further reduction and diffusion of the alloy led to the formation of Sm2Fe 17 A thin Sm-Fe-M layer is formed on the alloy surface, and then further nitrided to obtain Sm2Fe. 17 N b For the core, Sm2(Fe a M 1-a ) 17 N b It is a core-shell type Sm-Fe-N alloy with a shell.

5. The method according to claim 4, characterized in that, The Sm2Fe 17 The alloys are prepared by alloy spinning, chemical coprecipitation-reduction, or ultrasonic spray thermal decomposition-reduction.

6. The method according to claim 4, characterized in that, Preparation of Sm2Fe 17 A mixture of alloy and metal oxide MO or Sm2Fe with a surface coating of metal oxide MO 17 The physical or chemical methods for alloying include at least mechanical mixing or solution soaking.

7. The method according to claim 6, characterized in that, The solution soaking specifically involves Sm2Fe 17 Alloy powder is immersed in a soluble nitrate solution containing M ions, and the solution is evaporated to dryness with constant stirring. Then, it is dehydrated and decomposed at 100-400℃ to produce Sm2Fe. 17 The alloy powder is coated with a layer of metal oxide MO.

8. The method according to claim 4, characterized in that, The reduction diffusion process employs either hydrogen reduction followed by active metal reduction, or direct active metal reduction; the active metal includes one of calcium, sodium, and potassium; the reduction temperature is 800~1000℃, and the reduction time is 0.5~2.5h.

9. The method according to claim 4, characterized in that, The nitriding specifically involves nitriding the core-shell structured particles containing M. Under a reducing atmosphere, nitrogen atoms diffuse into the core and outer shell of the core-shell structured particles through adsorption and diffusion as interstitial atoms. The nitriding time is 0.5~4h, the nitriding temperature is 350~500℃, the nitrogen source is NH3, the reducing atmosphere is H2, and the gas flow rate is 0.2~0.8 L / min.

10. The method according to claim 4, characterized in that, Metal oxides (MOs) include at least one of CoO, Cr2O3, CrO, and TiO2, with an average particle size of less than 20 micrometers.

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