Samarium-iron-nitrogen material as well as preparation method and application thereof

Abstract

The invention provides a samarium-iron-nitrogen material and a preparation method and application thereof, and the preparation method comprises the following steps: preparing a samarium-iron alloy block, and then preparing the samarium-iron alloy block into samarium-iron alloy powder; the samarium-iron alloy powder is sequentially subjected to hydrogenation, disproportionation, dehydrogenation and recombination, and pretreated samarium-iron alloy powder is obtained; the pretreated samarium-iron alloy powder is subjected to gradient nitridation, and nitrided powder is obtained; and finally, mixing the nitrided powder with a coating agent to obtain the samarium-iron-nitrogen material. According to the preparation method, the Sm-Fe alloy is treated through the hydrogenation-disproportionation-dehydrogenation-recombination process, a rapid channel is provided for nitrogen diffusion, introduction of nitrogen is promoted through the gradient nitriding process, the stability of the samarium-iron-nitrogen material is improved through coating, and the samarium-iron-nitrogen material high in nitrogen content, excellent in magnetic performance and high in stability is obtained.

Description

Technical Field

[0001] The present invention belongs to the technical field of magnetic materials and relates to a samarium iron nitrogen material and a preparation method and application thereof. Background Art

[0002] SmFeN permanent magnets, with their high Curie temperature, excellent temperature and chemical properties, and low price, are the most promising permanent magnet materials after neodymium iron boron (NdFeB). They are a material with the potential to surpass NdFeB in performance. In terms of physical and chemical properties, SmFeN exhibits high corrosion resistance, oxidation resistance, and high-temperature resistance, making it valuable and promising for applications in various extreme environments, particularly in the automotive, consumer electronics, and aerospace industries. Furthermore, samarium and iron raw materials are abundant and inexpensive, offering significant cost advantages over NdFeB. Therefore, SmFeN, a material with significant application value, has broad applications in magnetic materials, electronic materials, and other fields. Currently, the main methods for preparing SmFeN include solid-phase and sol-gel methods. However, these methods suffer from complex processes and low product purity.

[0003] In the prior art, the performance of samarium iron nitride materials is improved by coating or rapid quenching methods. For example, CN105702407A discloses a method for preparing a magnetic ceramic-coated SmFeN permanent magnet material. Ferrous chloride, butyl titanate and other substances are mixed, heated in a water bath, and concentrated to obtain a ceramic intermediate gel. Then, samarium powder and iron powder are mixed and smelted, annealed, and ball-milled into metal powder. The metal powder is then coated with the ceramic intermediate gel with magnetic surface and composite fired to obtain a magnetic ceramic-coated SmFeN permanent magnet material. Although the obtained SmFeN powder is stable and not easily oxidized, the ceramic coating inevitably reduces the plasticity and toughness of the material, making it difficult to use.

[0004] For example, CN114008728A discloses a method for preparing a SmFeN-based magnetic material. The raw metals are Sm, Fe, Go, Zr, and Ti. Samarium-iron alloy powder is obtained by melt rapid quenching, and then heat treated at 460°C for 8 hours in a nitrogen atmosphere to obtain SmFeN powder. However, the process is complex, the production cost is high, and the resulting powder is relatively active and easily oxidized, affecting performance.

[0005] Among the methods for preparing rare earth permanent magnet alloys, rapid quenching, powder metallurgy and hydrogen crushing are complex processes, long cycles, high energy consumption and difficult industrial production. The obtained powder material has a disordered structure. In addition to the SmFeN phase, the powder also contains many impurities. The nitrogen content of traditional Sm-Fe-N materials (x≈3) is limited by the Sm2Fe 17Due to the thermodynamic stability of the phase, it is difficult for nitrogen atoms to penetrate into the crystal lattice, and traditional powder production requires ball milling. During the ball milling process, the material will release a lot of heat, and the powder will be easily oxidized or even burn, which is not conducive to subsequent drying and use.

[0006] Based on the above research, it is necessary to provide a method for preparing a samarium iron nitrogen material, which can prepare a samarium iron nitrogen material with high nitrogen content, excellent performance and high stability. Summary of the Invention

[0007] The object of the present invention is to provide a samarium iron nitrogen material and a preparation method and application thereof, and in particular to a samarium iron nitrogen material with a high nitrogen content and a preparation method and application thereof. The preparation method treats an Sm-Fe alloy through a hydrogenation-disproportionation-dehydrogenation-recombination process, provides a fast channel for nitrogen diffusion, promotes the introduction of nitrogen through a gradient nitridation process, and improves the stability of the samarium iron nitrogen material through coating, thereby obtaining a samarium iron nitrogen material with a high nitrogen content, excellent magnetic properties and high stability.

[0008] In order to achieve the purpose of the invention, the present invention adopts the following technical solutions:

[0009] In a first aspect, the present invention provides a method for preparing a samarium iron nitrogen material, the preparation method comprising the following steps:

[0010] (1) preparing a samarium-iron alloy block, and then preparing the samarium-iron alloy block into a samarium-iron alloy powder;

[0011] (2) sequentially hydrogenating, disproportionating, dehydrogenating, and recombining the samarium-iron alloy powder of step (1) to obtain pretreated samarium-iron alloy powder;

[0012] (3) performing gradient nitriding on the pretreated samarium-iron alloy powder in step (2) to obtain a nitrided powder;

[0013] The gradient nitriding includes pre-nitriding, main nitriding and quenching performed in sequence, wherein the temperature of the main nitriding is higher than the temperature of the pre-nitriding;

[0014] (4) Mixing the nitrided powder in step (3) with a coating agent to obtain the samarium iron nitrogen material.

[0015] Since the nitrogen content of traditional Sm-Fe-N materials is limited to Sm2Fe 17Thermodynamic stability of the phase makes it difficult for nitrogen atoms to penetrate into the crystal lattice. The present invention utilizes hydrogenation-disproportionation-dehydrogenation-recombination to pretreat the samarium-iron alloy, and then performs a nitriding reaction, which can effectively improve the degree of nitriding and improve the magnetic properties; specifically, hydrogenation ensures that the samarium-iron alloy is fully hydrogenated into SmH2+Fe, disproportionation promotes Fe phase nano-sizing (target grain size <100nm), and then removes free hydrogen. The final recombination stage promotes the decomposition of SmH2 into Sm vapor, which is then compounded with the Fe phase to form a samarium-iron alloy, so that the alloy powder obtains a nanocrystalline structure (grain size <100nm) and a high-density grain boundary, providing a fast channel for nitrogen diffusion. Therefore, the hydrogenation-disproportionation-dehydrogenation-recombination process for treating Sm-Fe alloy can It can provide a fast channel for nitrogen diffusion; after pretreatment, the present invention adopts a gradient nitriding process, first performs low-temperature pre-nitriding to make nitrogen atoms preferentially occupy grain boundary positions (x≈1.5), then performs medium-temperature main nitriding to promote nitrogen diffusion into the interior of the lattice (x≥3.8), and finally performs rapid cooling to lock the position of nitrogen atoms; after nitriding, the present invention coats the nitrided powder to form a dense protective film, which not only ensures the performance of the material, but also ensures the safety of the production process, preventing ball milling heat from generating oxidation or even combustion of the powder. Therefore, the present invention obtains a samarium iron nitrogen material with high nitrogen content, excellent magnetic properties and high stability through multi-step coordination.

[0016] The present invention performs surface activation treatment before nitriding, that is, Ar plasma etching is performed on the Sm-Fe alloy powder before nitriding to remove the surface oxide layer and expose active Fe sites.

[0017] Preferably, the method for preparing the samarium-iron alloy block in step (1) comprises: mixing and smelting a samarium source and an iron source to obtain the samarium-iron alloy block.

[0018] Preferably, the mass ratio of the samarium source to the iron source is (0.70:1-0.90):1, for example, it can be 0.70:1, 0.725:1, 0.75:1, 0.775:1, 0.8:1, 0.825:1, 0.85:1, 0.875:1 or 0.90:1, but is not limited to the listed values. Other unlisted values ​​within the numerical range are also applicable, preferably (0.8:1-0.86):1.

[0019] Since samarium will volatilize during alloy production, the present invention preferably adds more samarium than the formula amount, but it should not be added too much to avoid affecting the magnetic properties of the material. The mass ratio of the samarium source to the iron source is preferably within an appropriate range.

[0020] Specifically, when preparing the samarium-iron alloy according to the present invention, the amount of samarium oxide input is increased when preparing the raw materials, and the mass of samarium oxide added per mole of samarium-iron alloy is 15.036g-30.072g, for example, it can be 15.036g, 20g, 25g or 30.072g, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0021] Preferably, the samarium source comprises samarium oxide, and the iron source comprises reduced iron powder.

[0022] Preferably, calcium particles are added when the samarium source and the iron source are mixed and smelted.

[0023] Preferably, the method of preparing samarium-iron alloy blocks into samarium-iron alloy powder in step (1) comprises: crushing and jet milling the samarium-iron alloy blocks.

[0024] Preferably, the particles are crushed to an average particle size of 1 to 5 mm, for example, 1 mm, 2 mm, 3 mm, 4 mm or 5 mm, but are not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0025] Preferably, the rotation speed of the air flow mill is 100 to 400 r / min, for example, 100 r / min, 200 r / min, 300 r / min or 400 r / min, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0026] When preparing samarium-iron alloy powder in the present invention, the rotation speed of the jet mill will affect the initial particle size of the powder, thereby affecting the magnetic properties and ultimately affecting the nitrogen content of the SmFeN powder.

[0027] Preferably, the medium of the jet mill is nitrogen with a purity of ≥99.9%, for example, 99.91%, 99.93%, 99.95%, 99.97% or 99.99%, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0028] Preferably, the average particle size of the samarium-iron alloy powder in step (1) is 10 to 50 μm, for example, 10 μm, 20 μm, 30 μm, 40 μm or 50 μm, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0029] Preferably, the hydrogenation temperature in step (2) is 400-500°C, for example, 400°C, 425°C, 450°C, 475°C or 500°C, and the time is 1-2h, for example, 1h, 1.25h, 1.5h, 1.75h or 2h, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0030] Preferably, the hydrogen pressure of the hydrogenation in step (2) is 0.1-1 MPa, for example, 0.1 MPa, 0.3 MPa, 0.5 MPa, 0.7 MPa or 1 MPa, and the hydrogen purity is ≥99.999%, for example, 99.999%, 99.9991%, 99.9995% or 99.9999%, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0031] During hydrogenation, the present invention uses high-purity hydrogen of ≥99.999% to avoid oxidation caused by O2 / H2O impurities.

[0032] Preferably, the temperature of the disproportionation in step (2) is 700-800°C (lower than the melting point of Sm), for example, 700°C, 725°C, 750°C, 775°C or 800°C, and the time is 1-2h, for example, 1h, 1.5h or 2h, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0033] Preferably, the hydrogen pressure during the disproportionation in step (2) is the same as the hydrogen pressure during the hydrogenation.

[0034] Preferably, the dehydrogenation and recombination in step (2) include: first dehydrogenating at a first temperature (300-400°C) in a vacuum or inert atmosphere (to avoid material pulverization caused by too rapid dehydrogenation), and then heating to a second temperature (600-700°C) for recombination.

[0035] Preferably, the dehydrogenation temperature in step (2) is 300-400°C, for example, 300°C, 325°C, 350°C, 375°C or 400°C, and the dehydrogenation time is 1-3h, for example, 1h, 1.5h, 2h, 2.5h or 3h, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0036] Preferably, the temperature of the recombination in step (2) is 600-700°C, for example, 600°C, 625°C, 650°C, 675°C or 700°C, and the time is 1-3h, for example, 1h, 1.5h, 2h, 2.5h or 3h, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0037] Before the gradient nitriding of the pretreated samarium-iron alloy powder in step (2) of the present invention, titanium metal powder is added to the pretreated samarium-iron alloy powder and mixed evenly before nitriding.

[0038] Preferably, the temperature of the pre-nitriding in step (3) is 200-300°C, for example, it can be 200°C, 225°C, 250°C, 275°C or 300°C, and the time is 1-3h, for example, it can be 1h, 1.5h, 2h, 2.5h or 3h, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0039] Preferably, the pre-nitridation atmosphere in step (3) comprises ammonia and hydrogen.

[0040] Preferably, the temperature of the main nitriding in step (3) is 400-450°C, for example, it can be 400°C, 410°C, 420°C, 430°C, 440°C or 450°C, and the time is 1-3h, for example, it can be 1h, 1.5h, 2h, 2.5h or 3h, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0041] Preferably, the main nitriding in step (3) is carried out under pressure.

[0042] Preferably, during the main nitriding in step (3), the pressure is 0.5-1 MPa in a N2 atmosphere, for example, 0.5 MPa, 0.7 MPa, 0.9 MPa or 1 MPa, with pulsed pressurization (increasing the pressure by 0.2 MPa every 10 minutes);

[0043] Preferably, the cooling rate of the quenching in step (3) is ≥50°C / min (quenching to room temperature), for example, it can be 52°C / min, 54°C / min, 56°C / min, 58°C / min or 60°C / min, but is not limited to the listed values. Other values ​​not listed within the numerical range are also applicable.

[0044] Preferably, the amount of nitrided powder used in the mixing in step (4) is n, 100g≤n≤2000g, for example, it can be 100g, 250g, 500g, 750g, 1000g, 1250g, 1500g, 1750g or 2000g, but is not limited to the listed values. Other unlisted values ​​within the numerical range are also applicable, preferably 500g≤n≤1000g.

[0045] Preferably, the mixing method in step (4) includes ball milling.

[0046] Preferably, the frequency of the ball milling is 1 to 5 Hz, for example, 1 Hz, 2 Hz, 3 Hz, 4 Hz or 5 Hz, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0047] The frequency of ball milling after nitriding in the present invention will affect the particle size of the powder, and ultimately affect the performance of the product.

[0048] Preferably, the ball milling time is 1 to 20 hours, for example, 1 hour, 5 hours, 10 hours, 15 hours or 20 hours, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0049] Preferably, the coating agent in step (4) includes sodium polymetaphosphate and / or sodium polyacrylate.

[0050] Preferably, the addition amount of the sodium polymetaphosphate is 1 to 5 wt% of the nitrided powder, for example, it can be 1 wt%, 2 wt%, 3 wt%, 4 wt% or 5 wt%, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0051] Preferably, the addition amount of the sodium polyacrylate is 0.5-1wt% of the nitrided powder, for example, it can be 0.5wt%, 0.6wt%, 0.7wt%, 0.8wt%, 0.9wt% or 1wt%, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0052] Preferably, after the mixing in step (4), the mixture is dried, and the dried powder is collected, filled with nitrogen, and stored at room temperature and pressure for future use.

[0053] In a second aspect, the present invention provides a samarium iron nitrogen material, which is prepared by the preparation method described in the first aspect.

[0054] Preferably, the nitrogen content in the samarium iron nitrogen material is above 2.9wt%, for example, it can be 2.9wt%, 3.0wt%, 3.1wt%, 3.2wt%, 3.3wt%, 3.4wt%, 3.5wt%, 3.6wt%, 3.7wt%, 3.8wt%, 3.9wt% or 4wt%, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0055] In a third aspect, the present invention provides an application of the samarium iron nitride material as described in the second aspect, wherein the application includes use in the field of magnetic materials or electronic materials.

[0056] Compared with the prior art, the present invention has the following beneficial effects:

[0057] The present invention firstly utilizes hydrogenation-disproportionation-dehydrogenation-recombination to pretreat the samarium iron alloy, so that the alloy powder obtains a nanocrystalline structure (grain size <100nm) and high-density grain boundaries, providing a fast channel for nitrogen diffusion; after the pretreatment, the present invention adopts a gradient nitriding process, firstly performs low-temperature pre-nitriding to make nitrogen atoms preferentially occupy grain boundary positions (x≈1.5), then performs medium-temperature main nitriding to promote nitrogen diffusion into the interior of the crystal lattice (x≥3.8), and finally performs rapid cooling to lock the positions of nitrogen atoms; after nitriding, the present invention coats the nitrided powder to form a dense protective film, which not only ensures the performance of the material but also ensures the safety of the production process and prevents heat generated by ball milling from causing oxidation or even combustion of the powder. Therefore, the present invention obtains a samarium iron nitrogen material with high nitrogen content, excellent magnetic properties and high stability through multi-step coordination. DETAILED DESCRIPTION

[0058] The technical solution of the present invention is further described below by way of specific embodiments. It should be understood by those skilled in the art that the embodiments are merely to help understand the present invention and should not be regarded as specific limitations of the present invention.

[0059] Example 1

[0060] This embodiment provides a method for preparing a samarium iron nitrogen material, the preparation method comprising the following steps:

[0061] (1) 360 g of samarium oxide, 430 g of reduced iron powder, and 180 g of pure calcium particles were sintered in a sintering furnace at 750° C. in vacuum, kept warm for 3 h, and then heated to 1050° C. and kept warm for 4.5 h to obtain a samarium-iron alloy;

[0062] Wherein, the mass ratio of the samarium oxide to the reduced iron powder is 0.84:1;

[0063] (2) Taking several lumps of samarium-iron alloy, crushing them in a crusher to obtain particles, feeding the obtained particles into a jet mill at a speed of 200 r / min, using 99.9% pure nitrogen as the medium, to obtain an alloy powder with an average particle size of 10 μm;

[0064] (3) placing the alloy powder in a reaction furnace and subjecting the alloy powder to a hydrogenation-disproportionation-dehydrogenation-recombination process;

[0065] The hydrogenation conditions were: 400°C, 1 MPa hydrogen pressure, and holding for 1 hour;

[0066] The disproportionation conditions were as follows: heating to 700°C, maintaining hydrogen pressure, and holding for 1.5 hours;

[0067] The dehydrogenation-recombination conditions are: staged heating in argon: first stage: 300°C to remove free hydrogen, holding time for 2 hours; second stage: 600°C for 2 hours, to promote the decomposition of SmH2 into Sm vapor, which then recombine with Fe to form samarium-iron alloy;

[0068] (4) Add 36 g of titanium metal powder to the powder obtained in step (3) and mix well;

[0069] (5) Place the sample in a nitriding furnace for gradient nitriding. The first step is low-temperature pre-nitriding: introduce NH3 / H2 mixed gas (volume ratio 3:1) at 200°C for 2 hours; the second step is medium-temperature main nitriding: pulse pressurization (0.2 MPa every 10 minutes) in a 0.5 MPa N2 atmosphere at 400°C for 3 hours; the third step is rapid cooling: after nitriding, quench to room temperature at a rate of 50°C / min to lock the position of nitrogen atoms;

[0070] (6) 100 g of the SmFeN powder obtained in step (5) was poured into a ball mill equipped with 8 kg steel balls. An appropriate amount of alcohol was added so that the alcohol liquid level was 2 cm higher than the steel balls. Then, sodium polymetaphosphate and sodium polyacrylate were added. The amounts of sodium polymetaphosphate and sodium polyacrylate added were 1% and 0.5% of the mass of the SmFeN powder, respectively. The mixture was ball milled at a frequency of 4 Hz for 12 hours to refine the SmFeN powder.

[0071] (7) After the ball milling is completed, the water and the slurry are separated, and the container containing the slurry is placed in a vacuum drying oven and the temperature is set to 75° C. to obtain the samarium iron nitrogen material.

[0072] Example 2

[0073] This embodiment provides a method for preparing a samarium iron nitrogen material, the preparation method comprising the following steps:

[0074] (1) 344 g of samarium oxide, 430 g of reduced iron powder, and 180 g of pure calcium particles were sintered in a sintering furnace at 750° C. in vacuum, kept at this temperature for 3 h, and then heated to 1050° C. and kept at this temperature for 4.5 h to obtain a samarium-iron alloy;

[0075] Wherein, the mass ratio of the samarium oxide to the reduced iron powder is 0.80:1;

[0076] (2) Taking several lumps of samarium-iron alloy, crushing them in a crusher to obtain particles, feeding the obtained particles into a jet mill at a speed of 100 r / min, using 99.9% pure nitrogen as the medium, to obtain an alloy powder with an average particle size of 20 μm;

[0077] (3) placing the alloy powder in a reaction furnace and subjecting the alloy powder to a hydrogenation-disproportionation-dehydrogenation-recombination process;

[0078] The hydrogenation conditions were: 450°C, 0.5 MPa hydrogen pressure, and holding temperature for 1 hour;

[0079] The disproportionation conditions were as follows: heating to 750°C, maintaining hydrogen pressure, and holding for 1.5 hours;

[0080] The dehydrogenation-recombination conditions are as follows: staged heating in argon: first stage: 350°C to remove free hydrogen, holding time for 2 hours; second stage: 700°C for 2 hours, to promote the decomposition of SmH2 into Sm vapor, which then recombine with Fe to form samarium-iron alloy;

[0081] (4) Add 36 g of titanium metal powder to the powder obtained in step (3) and mix well;

[0082] (5) Place the sample in a nitriding furnace for gradient nitriding. The first step is low-temperature pre-nitriding: introduce NH3 / H2 mixed gas (volume ratio 3:1) at 250°C for 2 hours; the second step is medium-temperature main nitriding: pulse pressurization (0.2 MPa every 10 minutes) at 450°C in a 1MPa N2 atmosphere for 3 hours; the third step is rapid cooling: after nitriding, quench to room temperature at a rate of 55°C / min to lock the position of nitrogen atoms;

[0083] (6) 100 g of the SmFeN powder obtained in step (5) was poured into a ball mill equipped with 8 kg steel balls. An appropriate amount of alcohol was added so that the alcohol liquid level was 2 cm higher than the steel balls. Then, sodium polymetaphosphate and sodium polyacrylate were added. The addition amounts of sodium polymetaphosphate and sodium polyacrylate were 3% and 0.7% of the mass of the SmFeN powder, respectively. The mixture was ball milled at a frequency of 5 Hz for 2 hours to refine the SmFeN powder.

[0084] (7) After the ball milling is completed, the water and the slurry are separated, and the container containing the slurry is placed in a vacuum drying oven and the temperature is set to 75° C. to obtain the samarium iron nitrogen material.

[0085] Example 3

[0086] This embodiment provides a method for preparing a samarium iron nitrogen material, the preparation method comprising the following steps:

[0087] (1) 370 g of samarium oxide, 430 g of reduced iron powder, and 180 g of pure calcium particles were sintered in a sintering furnace at 750° C. in vacuum, kept at this temperature for 3 h, and then heated to 1050° C. and kept at this temperature for 4.5 h to obtain a samarium-iron alloy;

[0088] Wherein, the mass ratio of the samarium oxide to the reduced iron powder is 0.86:1;

[0089] (2) Taking several lumps of samarium-iron alloy, crushing them in a crusher to obtain particles, feeding the obtained particles into a jet mill at a speed of 400 r / min, using 99.9% pure nitrogen as the medium, to obtain an alloy powder with an average particle size of 10 μm;

[0090] (3) placing the alloy powder in a reaction furnace and subjecting the alloy powder to a hydrogenation-disproportionation-dehydrogenation-recombination process;

[0091] The hydrogenation conditions were: 500°C, 0.1 MPa hydrogen pressure, and holding temperature for 2 hours;

[0092] The disproportionation conditions were as follows: heating to 800°C, maintaining hydrogen pressure, and holding for 1.5 hours;

[0093] The dehydrogenation-recombination conditions are as follows: staged heating in argon: first stage: 400°C to remove free hydrogen, holding time for 2 hours; second stage: 700°C to hold time for 2 hours, to promote the decomposition of SmH2 into Sm vapor, which then recombine with Fe to form samarium-iron alloy;

[0094] (4) Add 36 g of titanium metal powder to the powder obtained in step (3) and mix well;

[0095] (5) Place the sample in a nitriding furnace for gradient nitriding. The first step is low-temperature pre-nitriding: introduce NH3 / H2 mixed gas (volume ratio 3:1) at 300°C for 2 hours; the second step is medium-temperature main nitriding: pulse pressurization (0.2 MPa every 10 minutes) in a 1MPa N2 atmosphere at 450°C for 3 hours; the third step is rapid cooling: after nitriding, quench to room temperature at a rate of 50°C / min to lock the position of nitrogen atoms;

[0096] (6) 100 g of the SmFeN powder obtained in step (5) was poured into a ball mill equipped with 8 kg steel balls. An appropriate amount of alcohol was added so that the alcohol liquid level was 2 cm higher than the steel balls. Then, sodium polymetaphosphate and sodium polyacrylate were added. The addition amounts of sodium polymetaphosphate and sodium polyacrylate were 5% and 1% of the mass of the SmFeN powder, respectively. The SmFeN powder was refined by ball milling at a frequency of 1 Hz for 20 hours.

[0097] (7) After the ball milling is completed, the water and the slurry are separated, and the container containing the slurry is placed in a vacuum drying oven and the temperature is set to 75° C. to obtain the samarium iron nitrogen material.

[0098] Example 4

[0099] This embodiment provides a method for preparing a samarium iron nitrogen material. The preparation method is the same as that of Example 1, except that in step (1), 300 g of samarium oxide is taken and the mass ratio of the samarium oxide to the reduced iron powder is 0.7:1.

[0100] Example 5

[0101] This embodiment provides a method for preparing a samarium iron nitrogen material. The preparation method is the same as that of Example 1, except that in step (1), 387 g of samarium oxide is taken and the mass ratio of the samarium oxide to the reduced iron powder is 0.9:1.

[0102] Example 6

[0103] This embodiment provides a method for preparing a samarium iron nitrogen material. The preparation method is the same as that of Example 1, except that the rotation speed of the air flow mill in step (2) is 80 r / min to adapt the average particle size of the obtained alloy powder.

[0104] Example 7

[0105] This embodiment provides a method for preparing a samarium iron nitrogen material. The preparation method is the same as that of Example 1, except that the rotation speed of the air flow mill in step (2) is 600 r / min to adapt the average particle size of the obtained alloy powder.

[0106] Example 8

[0107] This embodiment provides a method for preparing a samarium iron nitrogen material. The preparation method is the same as that of Example 1 except that the frequency of the ball milling in step (6) is 0.5 Hz.

[0108] Example 9

[0109] This embodiment provides a method for preparing a samarium iron nitrogen material. The preparation method is the same as that of Example 1 except that the frequency of the ball milling in step (6) is 7 Hz.

[0110] Comparative Example 1

[0111] This comparative example provides a method for preparing a samarium iron nitrogen material. The preparation method is the same as Example 1 except that the gradient nitriding in step (5) is not performed, but nitriding is performed at 500° C. under normal pressure for 10 h.

[0112] Comparative Example 2

[0113] This comparative example provides a method for preparing a samarium iron nitrogen material. The preparation method is the same as Example 1 except that step (3) is not performed.

[0114] Comparative Example 3

[0115] This comparative example provides a method for preparing a samarium iron nitrogen material. The preparation method is the same as Example 1 except that the low-temperature pre-nitriding step (5) is not performed.

[0116] Comparative Example 4

[0117] This comparative example provides a method for preparing a samarium iron nitrogen material. The preparation method is the same as Example 1 except that the medium-temperature main nitriding step described in step (5) is not performed.

[0118] The samarium iron nitride materials obtained in the above examples and comparative examples were tested for oxygen content, nitrogen content, D50, SEM electron microscopy, and intrinsic coercivity. The oxygen content was used to characterize the degree of oxidation, the nitrogen content was used to characterize the nitriding effect of the SmFeN powder itself, D50 was used to characterize the powder particle size after ball milling, the average thickness of the coating layer was obtained by SEM electron microscopy, and the intrinsic coercivity was used to characterize the magnetic powder performance after ball milling.

[0119] The test results are shown in Table 1:

[0120] Table 1

[0121]

[0122] From Table 1 above, we can see that:

[0123] (1) The SmFeN powder obtained by the method provided in Example 1 of the present invention has an oxygen content of 1.46%, a nitrogen content of 3.92%, a powder particle size D50 of 1.92 μm, and a low degree of oxidation of the powder. Due to a certain degree of coating during the preparation process, no explosion occurred. The intrinsic coercive force of the SmFeN powder is 18.05 Koe, which shows that the preparation method of the present invention ensures the activity and magnetic properties of the product and can be used for the preparation of high-nitrogen-content samarium iron nitrogen magnetic powder. At the same time, by comparing Example 1 with Examples 4-5, it can be seen that the ratio of raw materials in different proportions will affect the nitrogen content and magnetic properties of the product. The reason is that samarium will volatilize during the production of the alloy, but too much samarium will also reduce the magnetic properties.

[0124] (2) A comparison of Example 1 with Examples 6-7 shows that, given a constant steel ball mass and milled powder mass, the jet mill speed affects the initial particle size of the powder before milling, thereby affecting the magnetic properties and the nitrogen content of the final SmFeN powder. A comparison of Example 1 with Examples 8-9 shows that, given a constant jet mill speed, steel ball mass, powder mass, and additives, the milling frequency also affects the powder particle size, ultimately leading to reduced powder performance.

[0125] (3) From the comparison between Example 1 and Comparative Example 1, it can be seen that the traditional nitriding method has a low degree of nitriding, which ultimately leads to reduced powder performance. From the comparison between Example 1 and Comparative Example 2, it can be seen that the powder treated by the hydrogenation-disproportionation-dehydrogenation-recombination process can effectively improve the nitriding degree of the powder in the subsequent nitriding process, thereby reflecting the gain of the fine structure treatment produced by the hydrogenation-disproportionation-dehydrogenation-recombination process on nitrogen diffusion; from Example 1 and Comparative Examples 3-4, it can be seen that the gradient nitriding of the present invention includes pre-nitriding, main nitriding and quenching carried out in sequence. Pre-nitriding allows nitrogen atoms to preferentially occupy the grain boundary position, and main nitriding promotes the diffusion of nitrogen into the interior of the lattice. The lack of pre-nitriding or main nitriding will affect the nitrogen content and magnetic properties in the samarium iron nitrogen.

[0126] The above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention fall within the protection scope and disclosure scope of the present invention.

Claims

1. A method for preparing a samarium iron nitrogen material, characterized in that: The preparation method comprises the following steps: (1) preparing a samarium-iron alloy block, and then preparing the samarium-iron alloy block into a samarium-iron alloy powder; (2) sequentially hydrogenating, disproportionating, dehydrogenating, and recombining the samarium-iron alloy powder of step (1) to obtain pretreated samarium-iron alloy powder; (3) performing gradient nitriding on the pretreated samarium-iron alloy powder in step (2) to obtain a nitrided powder; The gradient nitriding includes pre-nitriding, main nitriding and quenching performed in sequence, wherein the temperature of the main nitriding is higher than the temperature of the pre-nitriding; (4) Mixing the nitrided powder in step (3) with a coating agent to obtain the samarium iron nitrogen material.

2. The preparation method according to claim 1, characterized in that The method for preparing the samarium-iron alloy block in step (1) comprises: mixing and smelting a samarium source and an iron source to obtain the samarium-iron alloy block; Preferably, the mass ratio of the samarium source to the iron source is (0.70:1-0.90):1, preferably (0.8:1-0.86):1; Preferably, the samarium source comprises samarium oxide, and the iron source comprises reduced iron powder.

3. The preparation method according to claim 1 or 2, characterized in that The method for preparing samarium-iron alloy blocks into samarium-iron alloy powder in step (1) comprises: crushing and jet milling the samarium-iron alloy blocks; Preferably, the crushing is performed to particles with an average particle size of 1 to 5 mm; Preferably, the rotation speed of the jet mill is 100-400 r / min; Preferably, the medium of the jet mill is nitrogen with a purity of ≥99.9%; Preferably, the average particle size of the samarium-iron alloy powder in step (1) is 10 to 50 μm.

4. The preparation method according to any one of claims 1 to 3, characterized in that The hydrogenation temperature in step (2) is 400-500° C. and the time is 1-2 h; Preferably, the hydrogen pressure of the hydrogenation in step (2) is 0.1-1 MPa, and the hydrogen purity is ≥99.999%.

5. The preparation method according to any one of claims 1 to 4, characterized in that The disproportionation temperature in step (2) is 700-800° C. and the time is 1-2 h; Preferably, the hydrogen pressure during the disproportionation in step (2) is the same as the hydrogen pressure during the hydrogenation; Preferably, the dehydrogenation and recombination in step (2) comprises: first dehydrogenating at a first temperature in a vacuum or inert atmosphere, and then heating to a second temperature for recombination; Preferably, the dehydrogenation temperature in step (2) is 300-400° C. and the time is 1-3 h; Preferably, the temperature of the recombination in step (2) is 600-700° C. and the time is 1-3 h.

6. The preparation method according to any one of claims 1 to 5, characterized in that The pre-nitriding temperature in step (3) is 200-300° C. and the time is 1-3 hours; Preferably, the pre-nitriding atmosphere in step (3) comprises ammonia and hydrogen; Preferably, the temperature of the main nitriding in step (3) is 400-450° C. and the time is 1-3 hours; Preferably, the main nitriding in step (3) is carried out under pressure; Preferably, the main nitriding in step (3) is carried out in a N2 atmosphere with a pressure of 0.5-1 MPa under pulsed pressure; Preferably, the cooling rate of the quenching in step (3) is ≥50°C / min.

7. The preparation method according to any one of claims 1 to 6, characterized in that The mixing method in step (4) includes ball milling; Preferably, the frequency of the ball milling is 1 to 5 Hz; Preferably, the ball milling time is 1 to 20 hours; Preferably, the coating agent in step (4) comprises sodium polymetaphosphate and / or sodium polyacrylate; Preferably, the amount of sodium polymetaphosphate added is 1 to 5 wt% of the nitrided powder; Preferably, the addition amount of the sodium polyacrylate is 0.5-1 wt % of the nitrided powder.

8. A samarium iron nitrogen material, characterized in that The samarium iron nitrogen material is prepared by the preparation method according to any one of claims 1 to 7.

9. The samarium iron nitrogen material according to claim 8, characterized in that The nitrogen content in the samarium iron nitrogen material is above 2.9 wt%.

10. Use of the samarium iron nitrogen material according to claim 8 or 9, characterized in that: The applications include use in the fields of magnetic materials or electronic materials.

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