SmFeN magnetic powder and preparation method thereof, magnet and motor

Abstract

The invention provides SmFeN magnetic powder and a preparation method thereof, a magnet and a motor, the SmFeN magnetic powder comprises Sm2Fe17Nx, x is more than or equal to 2.0 and less than or equal to 4.0; the proportion of the SmFeN magnetic powder with the particle size of 1-3 microns is not less than 80%; the SmFeN magnetic powder further comprises alpha-Fe, and the relative content proportion of the alpha-Fe in the SmFeN magnetic powder is not larger than 5 wt%. The SmFeN magnetic powder provided by the invention has relatively fine particle size and relatively narrow particle size distribution, the particle size is uniform and high in consistency, and the coercive force of the SmFeN magnetic powder is improved; meanwhile, the content of alpha-Fe in the SmFeN magnetic powder is low, the content of a main phase Sm2Fe17Nx is high, and the negative influence of an alpha-Fe soft magnetic phase on the SmFeN magnetic powder is reduced; therefore, the SmFeN magnetic powder has relatively high coercive force.

Description

Technical Field

[0001] The present invention belongs to the technical field of magnetic materials, and relates to a SmFeN magnetic powder, in particular to a SmFeN magnetic powder and its preparation method, magnet and motor. Background Art

[0002] The rare earth-iron-nitrogen system has a Sm2Fe 17 structure 17 N x compound with a nucleation-type coercivity generation mechanism, and the purer its main phase is, the higher the coercivity is. Currently, the commonly used preparation methods include reduction diffusion method, coprecipitation method and melt spinning method, etc. Since the reduction diffusion method uses rare earth oxides as raw materials and the process is relatively simpler than the coprecipitation method, it is used as the preferred method. However, α-Fe phase will be generated during reduction diffusion, pulverization and nitridation processes, and its proportion can even be as high as more than 10%. And the α-Fe phase is a soft magnetic phase. During the magnetization process of the magnetic powder, it will be preferentially demagnetized and has very strong magnetic conductivity, resulting in that the Sm2Fe 17 N x magnetic powder is also extremely easy to be demagnetized, seriously affecting the coercivity of the magnetic powder. Magnetic powder with low coercivity will affect the heat resistance of the magnet, resulting in the failure of the magnet at high temperature and thus being unable to be used.

[0003] When using a magnet with relatively high heat resistance in an electric motor or the like, it is necessary to further improve the coercivity of the magnetic powder. As one of the methods to improve the coercivity, the most commonly used is to refine the magnetic powder, that is, a smaller particle size. For example, when the magnetic powder is crushed to a D50 particle size of less than 1.5 μm or even less than 1 μm, the coercivity of the magnetic powder can be greatly increased to 16 kOe or even 20 kOe. However, when the particle size of the magnetic powder is further refined to less than 0.8 μm or even less than 0.6 μm, the coercivity drops sharply. The root cause is that the oxidation caused by the finer powder has offset the increase in coercivity brought by it, so the magnetic powder cannot be refined indefinitely.

[0004] CN106384638A discloses a preparation method of a high-performance anisotropic Sm-Fe-N permanent magnet. Mixing anisotropic Sm2Fe 17 N x alloy powder and a small amount of low-melting-point metal / alloy powder, or 17 N xA thin layer of low-melting-point metal / alloy film is coated on the surface of the alloy powder, and then it is oriented and compacted under a magnetic field, and then hot-pressed and sintered at a temperature of 480-520 °C to obtain a high-performance anisotropic Sm-Fe-N permanent magnet. The low-melting-point metal / alloy composition consists of R-M, R-N, R-(M,N) or N-N, with a melting point range of 300-450 °C. R is one or more of La, Ce, Pr, Nd, Gd, Tb, Dy, Ho, M is one or more of Fe, Co, Ni, and N is one or more of Cu, Al, Ga, Zn, Sn, Ag. The advantage of this invention is that it can prepare a highly dense anisotropic Sm2Fe 17 N x permanent magnet, so high permanent magnetic properties can be obtained.

[0005] CN105129860A discloses a process for preparing rare earth permanent magnet Sm2Fe 17 N x powder. Using Fe-M powder (M = one or more combinations of Hf, Zr, Co, Nb, Cr, V, Ti, Ga, B, etc.) and Sm powder as raw materials, the solid-liquid phase diffusion reaction method is used to prepare Sm2Fe 17 intermetallic compound, and then the final product Sm2Fe 17 N x is obtained through nitridation. The process steps are: (1) uniformly mixing Fe-M alloy powder and Sm powder; (2) cold-pressing the mixed raw material powder into a shape; (3) performing a solid-liquid phase diffusion reaction on the cold-pressed green body to prepare a Sm2Fe 17 single-phase block; (4) crushing and finely grinding the Sm2Fe 17 single-phase block into powder, and performing nitridation in an atmosphere containing N2 or NH3 to prepare Sm2Fe 17 N x powder. Based on this, anisotropic bonded magnets with excellent properties can be prepared. This process has simple operation, easy control of process parameters, is environmentally friendly and pollution-free, and is easy to realize large-scale production.

[0006] Currently, the publicly available SmFeN magnetic powders all have certain defects. There is a problem that the content of α-Fe phase is too high, which leads to a decrease in the coercivity of the magnetic powder, and when the magnetic powder is further refined to 0.8 μm or even below 0.6 μm to enhance the coercivity, the coercivity will drop sharply instead. Therefore, it is crucial to develop and design a new type of SmFeN magnetic powder, its preparation method, magnet and motor. Summary of the Invention

[0007] In view of the deficiencies in the prior art, the purpose of the present invention is to provide a SmFeN magnetic powder, a preparation method thereof, a magnet and an electric motor. The SmFeN magnetic powder provided by the present invention has a finer particle size and a narrower particle size distribution, with uniform particle size and high consistency, which improves the coercivity of the SmFeN magnetic powder; at the same time, the content of α-Fe in the SmFeN magnetic powder is low, and the content of the main phase Sm2Fe 17 N x is high, reducing the negative impact of the α-Fe soft magnetic phase on the SmFeN magnetic powder; therefore, the SmFeN magnetic powder has a high coercivity.

[0008] To achieve this purpose, the present invention adopts the following technical solutions:

[0009] In the first aspect, the present invention provides a SmFeN magnetic powder, the SmFeN magnetic powder includes Sm2Fe 17 N x , where 2.0 ≤ x ≤ 4.0;

[0010] The proportion of the SmFeN magnetic powder with a particle size of 1-3 μm is not less than 80%;

[0011] The SmFeN magnetic powder also includes α-Fe, and the relative content proportion of α-Fe in the SmFeN magnetic powder is not more than 5 wt%.

[0012] The particle size distribution of the magnetic powder is very important for the performance of the magnetic powder. The narrower the particle size distribution, the greater the improvement in performance. Moreover, a narrow particle size distribution is very beneficial for both bonded molding and injection molding, which can improve the powder fluidity and the performance of the final product.

[0013] The SmFeN magnetic powder provided by the present invention has a finer particle size and a narrower particle size distribution, with uniform particle size and high consistency, which improves the coercivity of the SmFeN magnetic powder; at the same time, the content of α-Fe in the SmFeN magnetic powder is low, and the content of the main phase Sm2Fe 17 N x is high, reducing the negative impact of the α-Fe soft magnetic phase on the SmFeN magnetic powder; therefore, the SmFeN magnetic powder has a high coercivity.

[0014] In the present invention, 2.0 ≤ x ≤ 4.0. The value of x can be, for example, 2.0, 2.2, 2.4, 2.6, 2.8, 3.0, 3.2, 3.4, 3.6, 3.8 or 4.0, but is not limited to the listed values. Other unlisted values within this numerical range are equally applicable.

[0015] In the SmFeN magnetic powder of the present invention, the proportion of particles with a particle size of 1-3 μm is not less than 80%, for example, it can be 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98% or 99%, but is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0016] In the SmFeN magnetic powder of the present invention, the relative content proportion of α-Fe is not more than 5 wt%, for example, it can be 5 wt%, 4.8 wt%, 4.6 wt%, 4.4 wt%, 4.2 wt%, 4 wt%, 3.8 wt%, 3.6 wt%, 3.4 wt%, 3.2 wt%, 3 wt%, 2.8 wt%, 2.6 wt%, 2.4 wt%, 2.2 wt%, 2 wt%, 1.8 wt%, 1.6 wt%, 1.4 wt%, 1.2 wt% or 1 wt%, but is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0017] Preferably, the D10 particle size of the SmFeN magnetic powder is 0.7-1 μm, for example, it can be 0.7 μm, 0.72 μm, 0.75 μm, 0.77 μm, 0.8 μm, 0.82 μm, 0.85 μm, 0.87 μm, 0.9 μm, 0.92 μm, 0.95 μm, 0.97 μm or 1 μm, but is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0018] Preferably, the D50 particle size of the SmFeN magnetic powder is 1.5-2 μm, for example, it can be 1.5 μm, 1.55 μm, 1.6 μm, 1.65 μm, 1.7 μm, 1.75 μm, 1.8 μm, 1.85 μm, 1.9 μm, 1.95 μm or 2 μm, but is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0019] Preferably, the D90 particle size of the SmFeN magnetic powder is 2.73-3.75, for example, it can be 2.73, 2.75, 2.8, 2.85, 2.9, 2.95, 3, 3.05, 3.1, 3.15, 3.2, 3.25, 3.3, 3.35, 3.4, 3.45, 3.5, 3.55, 3.6, 3.65, 3.7 or 3.75, but is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0020] Preferably, the ratio of the D90 particle size to the D10 particle size of the SmFeN magnetic powder is not greater than 4.5, for example, it can be 4.5, 4.4, 4.3, 4.2, 4.1, 4.0, 3.9, 3.8, 3.7, 3.6, 3.5, 3.4, 3.3, 3.2, 3.1 or 3.0, but is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0021] In a second aspect, the present invention provides a preparation method of the SmFeN magnetic powder described in the first aspect, and the preparation method includes:

[0022] After mixing Sm2O3, Fe powder and metallic Ca, reduction diffusion is carried out through a first heat treatment to obtain Sm2Fe 17 alloy, and then nitriding is carried out through a second heat treatment in an ammonia atmosphere. After pulverization, acid treatment is carried out with a weak acid to obtain the SmFeN magnetic powder.

[0023] In the preparation method of the present invention, when the first heat treatment is carried out, Sm2O3 is reduced to metallic Sm, and metallic Sm and Fe powder form Sm2Fe 17 alloy after a diffusion reaction.

[0024] In the present invention, a weak acid is used for acid treatment. This is because when the weak acid is added to the pulverized material after pulverization, it will preferentially react with the α-Fe phase in the pulverized material, rather than reacting with Sm2Fe 17 N x in the pulverized material; on the contrary, if a medium-strong acid is used, it will react with the Sm2Fe 17 N x magnetic powder in the slurry, and cannot play the role of reducing the α-Fe phase in the magnetic powder.

[0025] Preferably, in the mixing, the mass ratio of Sm2O3 to Fe is converted according to the molar ratio of Sm to Fe being 2:17, and the mass of Sm2O3 is in excess by at least 40%.

[0026] The purpose of the mass of Sm2O3 in the present invention being in excess by at least 40% is to reduce the α-Fe phase caused by uneven composition while ensuring the full progress of the reduction diffusion reaction.

[0027] In the present invention, the mass of Sm2O3 is in excess by at least 40%, for example, it can be 40%, 42%, 44%, 46%, 48%, 50%, 52%, 54%, 56%, 58%, 60%, 62%, 64%, 66% or 68%, but is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0028] Preferably, in the mixing, according to the full reduction of Sm2O3 to Sm and the formation of Sm2Fe with Fe17 Calculate the mass of Ca required and make the mass of Ca in excess by at least 40%.

[0029] The purpose of making the mass of Ca in excess by at least 40% in the present invention is to reduce the α-Fe phase caused by compositional non-uniformity while ensuring the full progress of the reduction-diffusion reaction.

[0030] In the present invention, the mass of Ca is in excess by at least 40%, for example, it can be 40%, 42%, 44%, 46%, 48%, 50%, 52%, 54%, 56%, 58%, 60%, 62%, 64%, 66% or 68%, but it is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0031] Preferably, the temperature of the first heat treatment is 1000 - 1200 °C and the time is 10 - 14 h.

[0032] In the present invention, the temperature of the first heat treatment is 1000 - 1200 °C, for example, it can be 1000 °C, 1020 °C, 1040 °C, 1060 °C, 1080 °C, 1100 °C, 1120 °C, 1140 °C, 1160 °C, 1180 °C or 1200 °C, but it is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0033] In the present invention, the time of the first heat treatment is 10 - 14 h, for example, it can be 10 h, 10.5 h, 11 h, 11.5 h, 12 h, 12.5 h, 13 h, 13.5 h or 14 h, but it is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0034] In the present invention, the first heat treatment is carried out at a high enough temperature and for a long enough time to conduct the reduction-diffusion reaction, so that the reaction can proceed fully, and thus Sm2Fe can be completely formed inside the grains 17 phase and reduce the remaining α-Fe phase due to insufficient reaction.

[0035] Preferably, the first heat treatment is carried out in an inert atmosphere.

[0036] Preferably, between the first heat treatment and the second heat treatment, cleaning and drying are also carried out in sequence.

[0037] In the present invention, when cleaning, the Sm2Fe alloy block after the first heat treatment 17 is put into cold water. The by-product calcium oxide in the block will react with water, causing the block to disintegrate into coarse powder, and the calcium oxide impurity phase in the magnetic powder can be removed. During cleaning, water is repeatedly added for replacement. After cleaning, the Sm2Fe 17The content of calcium oxide heterophase in the alloy is extremely low. After filtration and drying, Sm2Fe 17 coarse alloy powder is obtained.

[0038] Preferably, the cleaning liquid used for the cleaning includes water.

[0039] Preferably, the temperature of the second heat treatment is 500-600 °C, and the time is 10-14 h.

[0040] In the present invention, the temperature of the second heat treatment is 500-600 °C. For example, it can be 500 °C, 510 °C, 520 °C, 530 °C, 540 °C, 550 °C, 560 °C, 570 °C, 580 °C, 590 °C or 600 °C, but is not limited to the listed values. Other unlisted values within this numerical range are equally applicable.

[0041] In the present invention, the time of the second heat treatment is 10-14 h. For example, it can be 10 h, 10.5 h, 11 h, 11.5 h, 12 h, 12.5 h, 13 h, 13.5 h or 14 h, but is not limited to the listed values. Other unlisted values within this numerical range are equally applicable.

[0042] Preferably, the D50 particle size of the pulverized material obtained after pulverization is 1.5-2 μm. For example, it can be 1.5 μm, 1.6 μm, 1.7 μm, 1.8 μm, 1.9 μm or 2 μm, but is not limited to the listed values. Other unlisted values within this numerical range are equally applicable.

[0043] Preferably, the pulverization method includes ball milling, and the grinding balls used for the ball milling are zirconia balls.

[0044] Preferably, the ball-to-material ratio in the ball milling is 5-10. For example, it can be 5, 5.5, 6, 6.5, 7, 7.5, 8, 8.5, 9, 9.5 or 10, but is not limited to the listed values. Other unlisted values within this numerical range are equally applicable; preferably 6-8.

[0045] Preferably, a ball milling medium is added during the ball milling. The ball milling medium includes isopropyl alcohol, and the mass ratio of the material to isopropyl alcohol in the ball milling is 0.5-2. For example, it can be 0.5, 0.6, 0.8, 1, 1.2, 1.4, 1.6, 1.8 or 2, but is not limited to the listed values. Other unlisted values within this numerical range are equally applicable, and preferably 0.8-1.5

[0046] Preferably, the time of the ball milling is 3-10 h. For example, it can be 3 h, 4 h, 5 h, 6 h, 7 h, 8 h, 9 h or 10 h, but is not limited to the listed values. Other unlisted values within this numerical range are equally applicable, and preferably 5-8 h.

[0047] Preferably, the weak acid includes any one or a combination of at least two of acetic acid, citric acid, oxalic acid, boric acid, sulfurous acid, nitrous acid, or silicic acid. Typical but non-limiting combinations include the combination of acetic acid and citric acid, the combination of oxalic acid and boric acid, the combination of sulfurous acid and nitrous acid, the combination of nitrous acid and silicic acid, or the combination of acetic acid, citric acid, and oxalic acid.

[0048] Preferably, the volume concentration of the weak acid is 5 - 30%, for example, it can be 5%, 7%, 10%, 12%, 15%, 17%, 20%, 22%, 25%, 27%, or 30%, but is not limited to the listed values. Other unlisted values within this range are equally applicable.

[0049] In the present invention, the volume concentration of the weak acid is 5 - 30%. If the volume concentration is too small, the reaction will proceed slowly and the efficiency of removing the α-Fe phase will be low; if the volume concentration is too large, it will react excessively and react with Sm2Fe 17 N x and it is difficult to control.

[0050] Preferably, the pH of the weak acid is 5.5 - 6.5, for example, it can be 5.5, 5.6, 5.7, 5.8, 5.9, 6, 6.1, 6.2, 6.3, 6.4, or 6.5, but is not limited to the listed values. Other unlisted values within this range are equally applicable.

[0051] In the present invention, the pH of the weak acid is 5.5 - 6.5. If the pH value is too small, the acidity will be too strong and it will react excessively and react with Sm2Fe 17 N x and it is difficult to control; if the pH value is too large, the acidity will be too weak to react and it will be difficult to remove the α-Fe phase.

[0052] Preferably, the acid treatment includes mixing the crushed material with the weak acid to obtain a slurry.

[0053] Preferably, the mass fraction of the weak acid in the slurry is 20 - 50wt%, for example, it can be 20wt%, 25wt%, 30wt%, 35wt%, 40wt%, 45wt%, or 50wt%, but is not limited to the listed values. Other unlisted values within this range are equally applicable.

[0054] Preferably, after the acid treatment, solid-liquid separation and drying are sequentially carried out.

[0055] As a preferred technical solution of the preparation method of the present invention, the preparation method includes:

[0056] (1) Mix Sm2O3, Fe powder and metallic Ca to obtain a mixed material; in the mixing, convert the mass ratio of Sm2O3 to Fe according to the molar ratio of Sm to Fe being 2:17, and make the mass of Sm2O3 in excess by at least 40%; calculate the mass of Ca required according to reducing all Sm2O3 to Sm and reacting with Fe to form Sm2Fe 17 and make the mass of Ca in excess by at least 40%

[0057] (2) In an inert atmosphere, perform reduction diffusion on the mixed material obtained in step (1) by heat treatment at a temperature of 1000 - 1200 °C for 10 - 14 h to obtain a Sm2Fe 17 alloy;

[0058] (3) Use water to wash the Sm2Fe 17 alloy obtained in step (2) and then dry it to obtain a dried material:

[0059] (4) Perform nitridation on the dried material obtained in step (3) by heat treatment at a temperature of 500 - 600 °C for 10 - 14 h in an ammonia atmosphere to obtain a nitrided material;

[0060] (5) Ball - mill the nitrided material obtained in step (4) for 3 - 10 h to obtain a ball - milled material with a D50 particle size of 1.5 - 2 μm; the grinding balls used for the ball - milling are zirconia balls, the ball - to - material ratio is 5 - 10, and the mass ratio of the nitrided material to isopropanol is 0.5 - 2;

[0061] (6) Mix a weak acid with a volume concentration of 5 - 30% and a pH of 5.5 - 6.5 with the ball - milled material obtained in step (5) to obtain a slurry with a mass fraction of the weak acid of 20 - 50 wt%, and perform solid - liquid separation and drying on the obtained slurry in sequence to obtain the SmFeN magnetic powder described above.

[0062] In a third aspect, the present invention provides a magnet, which is prepared from the SmFeN magnetic powder described in the first aspect.

[0063] In a fourth aspect, the present invention provides an electric machine, which includes the magnet described in the third aspect.

[0064] Compared with the prior art, the present invention has the following beneficial effects:

[0065] The SmFeN magnetic powder provided by the present invention has a finer particle size and a narrower particle size distribution, with uniform particle size and high consistency, which improves the coercivity of the SmFeN magnetic powder; meanwhile, the content of α - Fe in the SmFeN magnetic powder is low, and the main phase is Sm2Fe 17 N xThe content is relatively high, reducing the negative impact of α-Fe soft magnetic phase on SmFeN magnetic powder; therefore, the SmFeN magnetic powder has a relatively high coercivity. Detailed implementation manners

[0066] The technical solution of the present invention will be further described below through specific implementation manners. Those skilled in the art should understand that the embodiments are only for helping to understand the present invention and should not be regarded as specific limitations on the present invention.

[0067] Example 1

[0068] This example provides a SmFeN magnetic powder, and the SmFeN magnetic powder includes Sm2Fe 17 N3; the proportion of the SmFeN magnetic powder with a particle size of 1-3 μm is 85%.

[0069] The preparation method of the SmFeN magnetic powder is as follows:

[0070] (1) After mixing Sm2O3, Fe powder and metallic Ca, a mixed material is obtained; in the mixing, the mass ratio of Sm2O3 to Fe is converted according to the molar ratio of Sm to Fe being 2:17, and the mass of Sm2O3 is in excess by 50%; according to completely reducing Sm2O3 to Sm and reacting with Fe to form Sm2Fe 17 to calculate the required mass of Ca, and the mass of Ca is in excess by 50%;

[0071] (2) In an argon atmosphere, the mixed material obtained in step (1) is subjected to reduction diffusion by heat treatment at a temperature of 1100 °C for 12 h to obtain Sm2Fe 17 alloy;

[0072] (3) The Sm2Fe obtained in step (2) is washed with water 17 and then dried to obtain a dried material;

[0073] (4) The dried material obtained in step (3) is nitrided by heat treatment in an ammonia atmosphere at a temperature of 550 °C for 12 h to obtain a nitrided material;

[0074] (5) The nitrided material obtained in step (4) is ball-milled for 6 h to obtain a ball-milled material with a D50 particle size of 1.8 μm; the grinding balls used for the ball-milling are zirconia balls, the ball-to-material ratio is 8, and isopropanol is added during the ball-milling, and the mass ratio of the nitrided material to isopropanol is 1.2;

[0075] (6) Acetic acid with a volume concentration of 18% and a pH of 6 is mixed with the ball-milled material obtained in step (5) to obtain a slurry with a mass fraction of acetic acid of 35 wt%, and the obtained slurry is subjected to solid-liquid separation and drying in sequence to obtain the SmFeN magnetic powder described above.

[0076] Example 2

[0077] This example provides a kind of SmFeN magnetic powder, and the SmFeN magnetic powder includes Sm2Fe 17 N2, and the proportion of the particle size of 1 - 3μm in the SmFeN magnetic powder is 95%.

[0078] The preparation method of the SmFeN magnetic powder is as follows:

[0079] (1) After mixing Sm2O3, Fe powder and metallic Ca, a mixed material is obtained; in the mixing, the mass ratio of Sm2O3 to Fe is converted according to the molar ratio of Sm to Fe being 2:17, and the mass of Sm2O3 is in excess by at least 60%; according to completely reducing Sm2O3 to Sm and reacting with Fe to form Sm2Fe 17 to calculate the required mass of Ca, and the mass of Ca is in excess by at least 60%;

[0080] (2) Under an argon atmosphere, the mixed material obtained in step (1) is subjected to reduction diffusion by heat treatment at a temperature of 1000°C for 14h to obtain Sm2Fe 17 alloy;

[0081] (3) The Sm2Fe obtained in step (2) is washed with water and then dried to obtain a dried material; 17

[0082] (4) The dried material obtained in step (3) is nitrided by heat treatment at a temperature of 600°C for 10h under an ammonia atmosphere to obtain a nitrided material;

[0083] (5) The nitrided material obtained in step (4) is ball - milled for 3h to obtain a ball - milled material with a D50 particle size of 2μm; the grinding balls used in the ball - milling are zirconia balls, the ball - to - material ratio is 10, and isopropanol is added during the ball - milling, and the mass ratio of the nitrided material to isopropanol is 0.5;

[0084] (6) Boric acid with a volume concentration of 30% and a pH of 5.5 is mixed with the ball - milled material obtained in step (5) to obtain a slurry with a mass fraction of boric acid of 20wt%, and the obtained slurry is subjected to solid - liquid separation and drying in sequence to obtain the SmFeN magnetic powder described above.

[0085] Example 3

[0086] This example provides a kind of SmFeN magnetic powder, and the SmFeN magnetic powder includes Sm2Fe 17 N4, and the proportion of the particle size of 1 - 3μm in the SmFeN magnetic powder is 80%.

[0087] The preparation method of the SmFeN magnetic powder is as follows: ​

[0088] (1) Mix Sm2O3, Fe powder and metallic Ca to obtain a mixed material; in the mixing, convert the mass ratio of Sm2O3 to Fe according to the molar ratio of Sm to Fe being 2:17, and make the mass of Sm2O3 in excess by 40%; calculate the mass of Ca required according to 17 fully reducing Sm2O3 to Sm and reacting with Fe to form Sm2Fe

[0089] (2) In an argon atmosphere, perform reduction diffusion on the mixed material obtained in step (1) by heat treatment at a temperature of 1200 °C for 10 h to obtain a Sm2Fe 17 alloy;

[0090] (3) Use water to wash and then dry the Sm2Fe 17 alloy obtained in step (2) to obtain a dried material;

[0091] (4) Nitridize the dried material obtained in step (3) by heat treatment in an ammonia atmosphere at a temperature of 500 °C for 14 h to obtain a nitrided material;

[0092] (5) Perform ball milling on the nitrided material obtained in step (4) for 10 h to obtain a ball-milled material with a D50 particle size of 1.5 μm; the grinding balls used in the ball milling are zirconia balls, the ball-to-material ratio is 5, and isopropanol is added during the ball milling, and the mass ratio of the nitrided material to isopropanol is 2;

[0093] (6) Mix sulfurous acid with a volume concentration of 5% and a pH of 6.5 with the ball-milled material obtained in step (5) to obtain a slurry with a mass fraction of sulfurous acid of 50 wt%, and perform solid-liquid separation and drying on the obtained slurry in sequence to obtain the SmFeN magnetic powder.

[0094] Example 4

[0095] This example provides a SmFeN magnetic powder, which is the same as Example 1 in all respects except that the ball-to-material ratio in step (5) of the preparation method of the SmFeN magnetic powder is 5.

[0096] Example 5

[0097] This example provides a SmFeN magnetic powder, which is the same as Example 1 in all respects except that the ball-to-material ratio in step (5) of the preparation method of the SmFeN magnetic powder is 10.

[0098] Example 6

[0099] This example provides a SmFeN magnetic powder, which is the same as Example 1 in all respects except that the mass ratio of the nitrided material to isopropanol in step (5) of the preparation method of the SmFeN magnetic powder is 0.5.

[0100] Example 7

[0101] This example provides a kind of SmFeN magnetic powder. Except that the mass ratio of the nitriding material to isopropanol in step (5) of the preparation method of the SmFeN magnetic powder is 2, the rest are the same as those in Example 1.

[0102] Example 8

[0103] This example provides a kind of SmFeN magnetic powder. Except that the ball milling time in step (5) of the preparation method of the SmFeN magnetic powder is 3 h, the rest are the same as those in Example 1.

[0104] Example 9

[0105] This example provides a kind of SmFeN magnetic powder. Except that the ball milling time in step (5) of the preparation method of the SmFeN magnetic powder is 10 h, the rest are the same as those in Example 1.

[0106] Example 10

[0107] This example provides a kind of SmFeN magnetic powder. Except that the volume concentration of acetic acid in step (6) of the preparation method of the SmFeN magnetic powder is 5%, the rest are the same as those in Example 1.

[0108] Example 11

[0109] This example provides a kind of SmFeN magnetic powder. Except that the volume concentration of acetic acid in step (6) of the preparation method of the SmFeN magnetic powder is 30%, the rest are the same as those in Example 1.

[0110] Example 12

[0111] This example provides a kind of SmFeN magnetic powder. Except that the pH of acetic acid in step (6) of the preparation method of the SmFeN magnetic powder is 5.5, the rest are the same as those in Example 1.

[0112] Example 13

[0113] This example provides a kind of SmFeN magnetic powder. Except that the pH of acetic acid in step (6) of the preparation method of the SmFeN magnetic powder is 6.5, the rest are the same as those in Example 1.

[0114] Example 14

[0115] This example provides a kind of SmFeN magnetic powder. Except that the mass fraction of acetic acid in the slurry obtained in step (6) of the preparation method of the SmFeN magnetic powder is 20 wt%, the rest are the same as those in Example 1.

[0116] Example 15

[0117] This embodiment provides a SmFeN magnetic powder, which is the same as that of Example 1 in all aspects except that the mass fraction of acetic acid in the slurry obtained in step (6) of the preparation method of the SmFeN magnetic powder is 50 wt%.

[0118] Example 16

[0119] This embodiment provides a SmFeN magnetic powder, which is the same as that of Example 1 in all aspects except that acetic acid in step (6) of the preparation method of the SmFeN magnetic powder is replaced by oxalic acid.

[0120] Example 17

[0121] This embodiment provides a SmFeN magnetic powder, which is the same as that of Example 1 in all aspects except that acetic acid in step (6) of the preparation method of the SmFeN magnetic powder is replaced by silicic acid.

[0122] Example 18

[0123] This embodiment provides a SmFeN magnetic powder, which is the same as that of Example 1 in all aspects except that the mass of Sm2O3 is in excess by 20% in step (1) of the preparation method of the SmFeN magnetic powder.

[0124] Example 19

[0125] This embodiment provides a SmFeN magnetic powder, which is the same as that of Example 1 in all aspects except that the mass of Ca is in excess by 20% in step (1) of the preparation method of the SmFeN magnetic powder.

[0126] Example 20

[0127] This embodiment provides a SmFeN magnetic powder, which is the same as that of Example 1 in all aspects except that the heat treatment temperature in step (2) of the preparation method of the SmFeN magnetic powder is 800 °C.

[0128] Example 21

[0129] This embodiment provides a SmFeN magnetic powder, which is the same as that of Example 1 in all aspects except that the heat treatment temperature in step (2) of the preparation method of the SmFeN magnetic powder is 1400 °C.

[0130] Example 22

[0131] This embodiment provides a SmFeN magnetic powder, which is the same as that of Example 1 in all aspects except that the heat treatment temperature in step (4) of the preparation method of the SmFeN magnetic powder is 300 °C.

[0132] Example 23

[0133] This embodiment provides a kind of SmFeN magnetic powder. Except that the heat treatment temperature in step (4) of the preparation method of the SmFeN magnetic powder is 800 °C, the rest are the same as those in Embodiment 1.

[0134] Example 24

[0135] This embodiment provides a kind of SmFeN magnetic powder. Except that the ball-milled material with a D50 particle size of 1 μm is obtained after ball milling in step (5) of the preparation method of the SmFeN magnetic powder, the rest are the same as those in Embodiment 1.

[0136] Example 25

[0137] This embodiment provides a kind of SmFeN magnetic powder. Except that the ball-milled material with a D50 particle size of 3 μm is obtained after ball milling in step (5) of the preparation method of the SmFeN magnetic powder, the rest are the same as those in Embodiment 1.

[0138] Example 26

[0139] This embodiment provides a kind of SmFeN magnetic powder. Except that the volume concentration of acetic acid in step (6) of the preparation method of the SmFeN magnetic powder is 2%, the rest are the same as those in Embodiment 1.

[0140] Example 27

[0141] This embodiment provides a kind of SmFeN magnetic powder. Except that the volume concentration of acetic acid in step (6) of the preparation method of the SmFeN magnetic powder is 40%, the rest are the same as those in Embodiment 1.

[0142] Example 28

[0143] This embodiment provides a kind of SmFeN magnetic powder. Except that the pH of acetic acid in step (6) of the preparation method of the SmFeN magnetic powder is 4.5, the rest are the same as those in Embodiment 1.

[0144] Example 29

[0145] This embodiment provides a kind of SmFeN magnetic powder. Except that the pH of acetic acid in step (6) of the preparation method of the SmFeN magnetic powder is 6.8, the rest are the same as those in Embodiment 1.

[0146] Comparative Example 1

[0147] This comparative example provides a kind of SmFeN magnetic powder. Except that the step of mixing acetic acid with a volume concentration of 18% and a pH of 6 with the ball-milled material obtained in step (5) to obtain a slurry with a mass fraction of acetic acid of 35 wt% in step (6) of the preparation method of the SmFeN magnetic powder is omitted, the rest are the same as those in Embodiment 1.

[0148] The D10 particle size, D50 particle size and D90 particle size of the SmFeN magnetic powder in Examples 1 to 29 and Comparative Example 1 were tested by a particle size analyzer. The ratio of D90 / D10 was obtained by dividing the D90 particle size by the D10 particle size, as shown in Table 1.

[0149] The X-ray patterns of the SmFeN magnetic powder in Examples 1 to 29 and Comparative Example 1 were tested by an X-ray diffractometer. The relative content ratio of the α-Fe phase in the SmFeN magnetic powder was obtained by dividing the intensity corresponding to the strongest peak (110) of the α-Fe phase in the XRD results by the intensity corresponding to the strongest peak (303) of the SmFeN magnetic powder and multiplying by 100% to normalize it into a percentage, as shown in Table 1.

[0150] An appropriate amount of the SmFeN magnetic powder in Examples 1 to 29 and Comparative Example 1 was taken and mixed with 5 wt% epoxy resin to prepare a standard cylinder with a diameter of 10 mm. The coercivity was tested by a coercivity tester, and the coercivity of the SmFeN magnetic powder is shown in Table 1.

[0151] Table 1

[0152]

[0153]

[0154] It can be seen from Table 1 that:

[0155] (1) The SmFeN magnetic powder provided in Examples 1 to 17 has finer particle size and narrower particle size distribution, uniform particle size and high consistency, lower content of the α-Fe soft magnetic phase, and higher coercivity.

[0156] (2) By comparing Example 1 with Examples 18 and 19, it can be seen that the excess mass of Sm2O3 and the excess mass ratio of Ca in the preparation method of SmFeN magnetic powder will affect the performance of SmFeN magnetic powder; when the excess mass ratio of Sm2O3 is low, the D10 particle size, D50 particle size and D90 particle size will become larger, D90 / D10 will become larger, the relative content ratio α-Fe / SmFeN will become larger, and the coercive force will become smaller. This is because when the Sm2O3 ratio is low, the α-Fe phase content in the magnetic powder will increase, which directly leads to a decrease in coercive force, and the α-Fe phase content will increase. When the amount of Ca increases, it will make it more difficult to grind the magnetic powder during grinding, so the particle size of the magnetic powder becomes coarser; when the mass excess ratio of Ca is low, it will cause the particle size of D10, D50 and D90 to become larger, D90 / D10 to increase, the relative content ratio α-Fe / SmFeN to increase, and the coercive force to decrease. This is because when Ca is too little, Sm2O3 cannot be completely reduced to metal Sm, resulting in residual Sm2O3 in the magnetic powder, and the Sm content of the magnetic powder is low, and the α-Fe phase content increases. The increase in the α-Fe phase content makes it more difficult to grind the magnetic powder during grinding, thereby making the particle size of the magnetic powder coarser;

[0157] (3) By comparing Example 1 with Examples 20 and 21, it can be seen that the temperature of the heat treatment in step (2) of the method for preparing SmFeN magnetic powder will affect the performance of the SmFeN magnetic powder; when the temperature of the heat treatment in step (2) is too low, the D10 particle size, D50 particle size and D90 particle size will become larger, D90 / D10 will become larger, the relative content ratio α-Fe / SmFeN will become larger, and the coercive force will become smaller. This is because when the heat treatment temperature is too low, Sm and Fe form Sm2Fe 17 The reaction is not complete, resulting in an increase in the α-Fe phase content; when the heat treatment temperature in step (2) is too high, the D10 particle size becomes larger, the D50 particle size becomes larger, and the D90 particle size becomes larger, D90 / D10 becomes larger, the relative content ratio α-Fe / SmFeN becomes larger, and the coercive force becomes smaller. This is because when the heat treatment temperature is too high, Sm volatilizes severely, resulting in a decrease in the remaining Sm available for reaction and an increase in the α-Fe phase content. The increase in the α-Fe phase content makes it more difficult to grind the magnetic powder during grinding, thereby making the magnetic powder particle size coarser;

[0158] (4) By comparing Example 1 with Examples 22 and 23, it can be seen that the temperature of the heat treatment in step (4) of the preparation method of SmFeN magnetic powder will affect the performance of the SmFeN magnetic powder; when the temperature of the heat treatment in step (4) is too low, it will cause Sm2Fe 17 Magnetic powder cannot be completely nitrided, Sm2Fe 17 N xIn it, when x ≤ 2.0, the relative content ratio of α-Fe / SmFeN increases and the coercivity decreases. This is because the magnetic powder cannot be completely nitrided, and the un-nitrided magnetic powder, like α-Fe, will cause a significant reduction in coercivity. At this time, the main phase is no longer the SmFeN phase; when the heat treatment temperature in step (4) is too high, it will cause Sm2Fe 17 N x phase to decompose into α-Fe phase and SmN, the relative content ratio of α-Fe / SmFeN increases, and the coercivity decreases. This is because Sm2Fe 17 N x phase is unstable and decomposes at too high a temperature. At this time, the main phase is no longer the SmFeN phase;

[0159] (5) By comparing Example 1 with Examples 24 and 25, it can be seen that the D50 particle size obtained after ball milling in step (5) of the preparation method of SmFeN magnetic powder will affect the performance of SmFeN magnetic powder; when the D50 particle size obtained after ball milling in step (5) is too small, it will cause the D10 particle size and the D90 particle size to become smaller, D90 / D10 to become smaller, the relative content ratio of α-Fe / SmFeN to increase, and the coercivity to decrease. This is because when the particle size of the magnetic powder is too small, the surface area of the magnetic powder increases sharply, the activity increases, and it is very easy to oxidize, generating α-Fe phase and Sm2O3, thus resulting in a decrease in coercivity; when the D50 particle size obtained after ball milling in step (5) is too large, it will cause the D10 particle size and the D90 particle size to become larger, D90 / D10 to become larger, and the relative content ratio of α-Fe / SmFeN to change little, and the coercivity to become lower. This is because the coercivity of SmFeN magnetic powder is very closely related to the particle size. Within a certain range, the coercivity increases as the particle size decreases. When the particle size is too coarse, a multi-domain structure will be formed, resulting in a decrease in coercivity;

[0160] (6) By comparing Example 1 with Examples 26 and 27, it can be seen that the volume concentration of the weak acid in step (6) of the preparation method of SmFeN magnetic powder will affect the performance of SmFeN magnetic powder; when the volume concentration of the weak acid is too low, it will cause the particle size to change not significantly, the relative content ratio of α-Fe / SmFeN to increase, and the coercivity to decrease. This is because when the volume concentration of the weak acid is too low, it cannot react completely with α-Fe in the magnetic powder, resulting in more α-Fe remaining and a decrease in coercivity; when the volume concentration of the weak acid is too high, it will cause the particle size to change little, the relative content ratio of α-Fe / SmFeN to decrease, and the coercivity to decrease. This is because when the volume concentration of the weak acid is too high, the main phase SmFeN will be over-corroded, resulting in changes in the morphology and composition of the magnetic powder, thus reducing the coercivity;

[0161] (7) It can be seen from the comparison between Example 1 and Examples 28 and 29 that the pH of the weak acid in step (6) of the preparation method of SmFeN magnetic powder will affect the performance of SmFeN magnetic powder; when the pH of the weak acid is on the low side, the acidity is too strong, which will cause the main phase SmFeN to be corroded excessively, resulting in changes in the morphology and composition of the magnetic powder and a decrease in coercivity; when the pH of the weak acid is on the high side, the acidity is too weak, which will cause incomplete reaction with α-Fe in the magnetic powder, resulting in more remaining α-Fe and a decrease in coercivity.

[0162] (8) It can be seen from the comparison between Example 1 and Comparative Example 1 that the SmFeN magnetic powder provided by the present invention has finer particle size and narrower particle size distribution, uniform particle size and high consistency, which improves the coercivity of the SmFeN magnetic powder; at the same time, the content of α-Fe in the SmFeN magnetic powder is low, and the content of the main phase Sm2Fe 17 N x is high, reducing the negative impact of the α-Fe soft magnetic phase on the SmFeN magnetic powder; therefore, the SmFeN magnetic powder has high coercivity.

[0163] The above are only specific embodiments 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 conceived by those skilled in the art within the technical scope disclosed by the present invention fall within the protection scope and the disclosure scope of the present invention.

Claims

1. A SmFeN magnetic powder, characterized in that, The SmFeN magnetic powder includes Sm2Fe 17 N x , where 2.0 ≤ x ≤ 4.0; The proportion of the SmFeN magnetic powder with a particle size of 1 - 3 μm is not less than 80%; The SmFeN magnetic powder further includes α-Fe, and the relative content ratio of α-Fe in the SmFeN magnetic powder is not more than 5 wt%.

2. The SmFeN magnetic powder according to claim 1, characterized in that, The D10 particle size of the SmFeN magnetic powder is 0.7 - 1 μm; Preferably, the D50 particle size of the SmFeN magnetic powder is 1.5 - 2 μm; Preferably, the D90 particle size of the SmFeN magnetic powder is 2.73 - 3.75; Preferably, the ratio of the D90 particle size to the D10 particle size of the SmFeN magnetic powder is not more than 4.

5.

3. A method for preparing the SmFeN magnetic powder according to claim 1 or 2, characterized in that, The preparation method includes: After mixing Sm2O3, Fe powder and metallic Ca, reduction diffusion is carried out through the first heat treatment to obtain Sm2Fe 17 alloy. Then, nitridation is carried out through the second heat treatment in an ammonia gas atmosphere. After pulverization, acid treatment is carried out with a weak acid to obtain the above-mentioned SmFeN magnetic powder.

4. The preparation method according to claim 3, characterized in that, In the mixing, the mass ratio of Sm2O3 to Fe is converted according to the molar ratio of Sm to Fe being 2:17, and the mass of Sm2O3 is in excess by at least 40%; Preferably, in the mixing, the mass of Ca required is calculated according to completely reducing Sm2O3 to Sm and reacting with Fe to form Sm2Fe 17 and the mass of Ca is in excess of at least 40%.

5. The preparation method according to claim 3 or 4, characterized in that, The temperature of the first heat treatment is 1000 - 1200 °C, and the time is 10 - 14 h; Preferably, the first heat treatment is carried out in an inert atmosphere; Preferably, between the first heat treatment and the second heat treatment, cleaning and drying are also carried out in sequence; Preferably, the cleaning liquid used for the cleaning includes water.

6. The preparation method according to any one of claims 3 to 5, characterized in that The temperature of the second heat treatment is 500 - 600 °C, and the time is 10 - 14 h; Preferably, the D50 particle size of the crushed material obtained after crushing is 1.5 - 2 μm; Preferably, the crushing method includes ball milling, and the grinding balls used for the ball milling are zirconia balls; Preferably, the ball-to-material ratio in the ball milling is 5 - 10, preferably 6 - 8; Preferably, a ball milling medium is added during the ball milling, the ball milling medium includes isopropanol, and the mass ratio of the material to isopropanol in the ball milling is 0.5 - 2, preferably 0.8 - 1.5 Preferably, the time of the ball milling is 3 - 10 h, preferably 5 - 8 h.

7. The preparation method according to any one of claims 3 to 6, characterized in that, The weak acid includes any one or a combination of at least two of acetic acid, citric acid, oxalic acid, boric acid, sulfurous acid, nitrous acid, or silicic acid; Preferably, the volume concentration of the weak acid is 5 - 30%; Preferably, the pH of the weak acid is 5.5 - 6.5; Preferably, the acid treatment includes mixing the crushed material with the weak acid to obtain a slurry; Preferably, the mass fraction of the weak acid in the slurry is 20 - 50 wt%; Preferably, after the acid treatment, solid-liquid separation and drying are also carried out in sequence.

8. The preparation method according to any one of claims 3 to 7, characterized in that, The preparation method includes: (1) After mixing Sm2O3, Fe powder and metallic Ca, a mixed material is obtained; in the mixing, the mass ratio of Sm2O3 to Fe is converted according to the molar ratio of Sm to Fe being 2:17, and the mass of Sm2O3 is in excess by at least 40%; according to completely reducing Sm2O3 to Sm and reacting with Fe to form Sm2Fe 17 to calculate the required mass of Ca, and the mass of Ca is in excess by at least 40%; (2) The mixed material obtained in step (1) is subjected to reduction diffusion by heat treatment at a temperature of 1000 - 1200 °C for 10 - 14 h in an inert atmosphere to obtain Sm2Fe 17 alloy; (3) Use water to wash the product obtained in step (2) of the Sm2Fe 17 alloy and then dry it to obtain a dried material; (4) Nitriding the dried material obtained in step (3) by heat treatment at a temperature of 500 - 600 °C and a time of 10 - 14 h in an ammonia atmosphere to obtain a nitrided material; (5) Ball milling the nitrided material obtained in step (4) for 3 - 10 h to obtain a ball-milled material with a D50 particle size of 1.5 - 2 μm; the grinding balls used for the ball milling are zirconia balls, the ball-to-material ratio is 5 - 10, and isopropanol is added during the ball milling, and the mass ratio of the nitrided material to isopropanol is 0.5 - 2; (6) Mixing a weak acid with a volume concentration of 5 - 30% and a pH of 5.5 - 6.5 with the ball-milled material obtained in step (5) to obtain a slurry with a mass fraction of the weak acid of 20 - 50 wt%, and subjecting the obtained slurry to solid-liquid separation and drying in sequence to obtain the SmFeN magnetic powder described above.

9. A magnet, characterized in that, The magnet is prepared from the SmFeN magnetic powder described in claim 1 or 2.

10. A motor, characterized in that, The motor includes the magnet described in claim 9.

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