阅读说明：本技术 一种纳米晶永磁材料及其制备方法 (Nanocrystalline permanent magnet material and preparation method thereof ) 是由 李玉平 孙永阳 李军华 孔佳元 于 2020-05-22 设计创作，主要内容包括：本发明提供了一种纳米晶永磁材料及其制备方法。所述纳米晶永磁材料的化学式为R<Sub>x</Sub>T<Sub>y</Sub>I<Sub>z</Sub>,其中R元素为稀土金属且R元素包括Sm,T元素为过渡金属且T元素包括Fe,I元素非金属元素且I元素包括N；所述纳米晶永磁材料的平均晶粒尺寸在50nm以下。所述制备方法包括：1)将配方量的R元素源和T元素源混合并煅烧；2)将煅烧产物破碎后用氢气进行一次还原；3)将一次还原产物与金属还原剂以及隔离剂混合,在保护性气氛中进行二次还原；4)将二次还原产物在氢气中反应,得反应粉末；5)抽真空热处理,并进行渗氮,得到纳米晶永磁材料。本发明提高了纳米晶永磁材料的磁性能,使之更适合磁性元器件小型化及轻型化需求。(The invention provides a nanocrystalline permanent magnetic material and a preparation method thereof. The chemical formula of the nanocrystalline permanent magnetic material is R x T y I z Wherein R is a rare earth metal and R comprises Sm, T is a transition metal and T comprises Fe, I is a non-metal element and I comprises N; the average grain size of the nanocrystalline permanent magnetic material is below 50 nm. The preparation method comprises the following steps: 1) mixing and calcining the R element source and the T element source in the formula amount; 2) calcining the productCarrying out primary reduction by using hydrogen after crushing; 3) mixing the primary reduction product with a metal reducing agent and a separant, and carrying out secondary reduction in a protective atmosphere; 4) reacting the secondary reduction product in hydrogen to obtain reaction powder; 5) and (4) carrying out vacuum heat treatment and nitriding to obtain the nanocrystalline permanent magnet material. The invention improves the magnetic performance of the nanocrystalline permanent magnetic material, and is more suitable for the requirements of miniaturization and lightening of magnetic components.)

1. The nanocrystalline permanent magnetic material is characterized in that the chemical formula of the nanocrystalline permanent magnetic material is R_xT_yI_zWherein R is a rare earth metal and R comprises Sm, T is a transition metal and T comprises Fe, I is a non-metal element and I comprises N; x, y and z are the atomic contents of the R element, the T element and the I element respectively; the average grain size of the nanocrystalline permanent magnetic material is below 50 nm.

2. The nanocrystalline permanent magnetic material according to claim 1, wherein the nanocrystalline permanent magnetic material has a particle diameter D50 of 600nm or less;

preferably, the R element further includes any one or a combination of at least two of Nd, Pr, La, Ce, Gd, Tb, Ho, Dy, or Tb;

preferably, in the R element, the atomic number percentage of Sm is more than 90%;

preferably, the T element also comprises any one or a combination of at least two of Co, Ti, V, Cr, Mn or Ni;

preferably, in the T element, the atomic number percentage of Fe is more than 92%;

preferably, in the element I, the atomic number percentage of N is more than 85%;

preferably, in the element I, the atomic number percentage of H is less than 10%;

preferably, in the element I, the atomic number percentage of O is less than 12%.

3. The nanocrystalline permanent magnetic material according to claim 1 or 2, characterized in that in the chemical formula of the nanocrystalline permanent magnetic material, y/x is more than or equal to 8 and less than or equal to 12.5;

preferably, in the chemical formula of the nanocrystalline permanent magnetic material, z/x is more than or equal to 1.4 and less than or equal to 2.0.

4. A method of producing a nanocrystalline permanent magnetic material according to any one of claims 1-3, characterized in that the method comprises the steps of:

(1) mixing and calcining the R element source and the T element source in the formula amount to obtain a calcined product; the R element source comprises a Sm source and the T element source comprises a Fe source;

(2) crushing the calcined product in the step (1), and then carrying out primary reduction by using hydrogen to obtain a primary reduction product;

(3) mixing the primary reduction product obtained in the step (2) with a metal reducing agent and a separant, and carrying out secondary reduction in a protective atmosphere to obtain a secondary reduction product;

(4) reacting the secondary reduction product obtained in the step (3) in hydrogen to obtain reaction powder;

(5) and (4) carrying out heat treatment on the reaction powder in the step (4) under the condition of vacuum pumping, and adding nitrogen-containing gas for nitriding to obtain the nanocrystalline permanent magnet material.

5. The production method according to claim 4, wherein the R element source and the T element source in the step (1) are both oxides;

preferably, the chemical formula of the R element source in the step (1) is R₂O₃；

Preferably, the R element source in step (1) comprises Sm₂O₃；

Preferably, the R element source of step (1) further comprises Nd₂O₃、Ce₂O₃、La₂O₃、Pr₂O₃、Gd₂O₃、Tb₂O₃、Ho₂O₃、Dy₂O₃Or Tb₂O₃Any one or a combination of at least two of;

preferably, the chemical formula of the T element source in the step (1) is T₂O₃；

Preferably, the T element source of step (1) comprises Fe₂O₃；

Preferably, the T element source in the step (1) further comprises Co₂O₃、Ti₂O₃、Cr₂O₃、Ni₂O₃、V₂O₃Or Mn₂O₃Any one or a combination of at least two of;

preferably, the mixing method in step (1) is ball milling;

preferably, the ball milling medium of the ball milling is water;

preferably, the mass ratio of the ball-milled balls to the ball-milled materials to the ball-milling medium is 15 (0.9-1.1) to (0.9-1.1);

preferably, the mixing time of the step (1) is 4-6 h;

preferably, the calcination of step (1) is carried out in air;

preferably, the temperature of the calcination in the step (1) is 1050-;

preferably, the calcination time of the step (1) is 1.5-2.5 h.

6. The production method according to claim 4 or 5, wherein the crushing of step (2) comprises coarse crushing and ball milling;

preferably, the ball milling medium for ball milling crushing is water;

preferably, the mass ratio of the ball, the material and the ball milling medium of the ball milling crushing is 15 (0.9-1.1) to (0.9-1.1);

preferably, the particle size D50 of the crushed product obtained after the crushing in the step (2) is 0.8-1.2 μm;

preferably, the flow rate of the hydrogen in the step (2) is 13-17L/min;

preferably, the temperature of the primary reduction in the step (2) is 840-860 ℃;

preferably, the time for the primary reduction in the step (2) is 9-11 h.

7. The production method according to any one of claims 4 to 6, wherein the metal reducing agent of step (3) includes Ca;

preferably, in the step (3), the mass of the metal reducing agent is 16-24% of the mass of the primary reduction product;

preferably, the release agent of step (3) comprises CaO;

preferably, in the step (3), the mass of the separant is 26-34% of the mass of the primary reduction product;

preferably, the protective atmosphere in step (3) comprises any one of an argon atmosphere, a helium atmosphere or a neon atmosphere or a combination of at least two of the same;

preferably, the temperature of the secondary reduction in the step (3) is 900-1100 ℃;

preferably, the time for the secondary reduction in the step (3) is 5 to 7 hours.

8. The method according to any one of claims 4 to 7, wherein in the step (4), the secondary reduction product is washed and dried before being reacted in hydrogen;

preferably, the washing method comprises soaking in water and washing for more than 2 times;

preferably, the washing reduces Ca in the secondary reduction product²⁺Washing to below 0.2% by mass;

preferably, the drying is performed under vacuum;

preferably, the pressure of the hydrogen in the step (4) is 0.8-1 MPa;

preferably, the method for carrying out the reaction in the step (4) is dry ball milling;

preferably, the ball-to-material ratio of the dry ball milling is (14-16): 1;

preferably, the reaction time of the step (4) is 9-11 h;

preferably, the temperature for carrying out the reaction in step (4) is 15-35 ℃.

9. The method according to any one of claims 4-8, wherein the temperature of the heat treatment in step (5) is 640-660 ℃;

preferably, the time of the heat treatment in the step (5) is 0.4-0.6 h;

preferably, the nitriding temperature in the step (5) is 450-510 ℃;

preferably, the nitriding time of the step (5) is 4-7 h;

preferably, the nitrogen-containing gas of step (5) comprises nitrogen and/or ammonia.

10. The method according to any one of claims 4 to 9, characterized in that it comprises the steps of:

(1) carrying out wet ball milling and mixing on the R element source and the T element source with the formula amount by taking water as a medium for 4-6h, and calcining in air at the temperature of 1050-; the R element source comprises a Sm source and the T element source comprises a Fe source; the R element source and the T element source are both oxides;

(2) after the calcination product in the step (1) is subjected to coarse crushing and ball milling crushing, carrying out primary reduction on the obtained crushed product with the D50 of 0.8-1.2 mu m for 9-11h by using hydrogen with the flow rate of 13-17L/min at the temperature of 840-860 ℃ to obtain a primary reduction product;

(3) mixing the primary reduction product in the step (2) with a metal reducing agent and a separant, and carrying out secondary reduction for 5-7h at the temperature of 900-1100 ℃ in a protective atmosphere to obtain a secondary reduction product;

wherein the metal reducing agent comprises Ca, and the mass of the metal reducing agent is 16-24% of that of the primary reduction product; the separant comprises CaO, and the mass of the separant is 26-34% of that of the primary reduction product;

(4) soaking and cleaning the secondary reduction product obtained in the step (3) in water for more than 2 times, drying under the vacuum condition, and reacting for 9-11h in hydrogen with the pressure of 0.8-1MPa by adopting a dry ball milling method, wherein the ball-to-material ratio of the dry ball milling is (14-16):1, so as to obtain reaction powder;

(5) and (3) carrying out heat treatment on the reaction powder in the step (4) at the temperature of 640-.

Technical Field

The invention belongs to the technical field of magnetic materials, relates to a permanent magnetic material and a preparation method thereof, and particularly relates to a nanocrystalline permanent magnetic material and a preparation method thereof.

Background

The permanent magnetic material is a magnetic material which can still retain stronger magnetism after being magnetized by an external magnetic field and the external magnetic field is removed. Permanent magnet materials are widely used in various aspects of human life, such as: the production, development and application degree of the communication, computer, energy, instrument, traffic and other fields is one of the marks for measuring the economic development degree of modern countries.

The permanent magnet material with the highest magnetic performance is a rare earth neodymium iron boron permanent magnet material at present, wherein the maximum magnetic energy product of the sintered neodymium iron boron permanent magnet material exceeds 56MGOe, and the miniaturization and light-weight of devices are facilitated, so that the permanent magnet material is widely applied to the fields of wind power generation, new energy automobiles, elevators and the like in recent years. In addition, in order to prepare a magnet product with a complex shape, the bonded neodymium iron boron magnetic powder is invented. The magnetic powder can be mixed with binder (such as epoxy resin, nylon, PPS), and then molded or injection molded into bonded NdFeB magnets of various shapes. The magnet is widely applied to various micro-special motors and sensors at present. However, the neodymium iron boron material has the disadvantage of poor high temperature resistance, and the application of the neodymium iron boron material in the high temperature field is severely limited. The coercive force of the neodymium iron boron material can be improved by adding the heavy rare earth dysprosium or terbium, and the high-temperature property of the neodymium iron boron material is improved. However, dysprosium and terbium are scarce resources and are expensive, so that neodymium iron boron is very expensive.

Compared with the neodymium iron boron permanent magnet material, the samarium-iron-nitrogen permanent magnet material HAs higher Curie temperature (Tc is 750K), higher anisotropy field (HA is 12MA/m) and similar saturation magnetization (Bs is 1.56T). Moreover, the rare earth content of the samarium-iron-nitrogen permanent magnet material is lower than that of the neodymium-iron-boron permanent magnet material, so that precious rare earth resources are saved. In 1996, Nippon Sumitomo Metal mine corporation proposed the production of Sm-Fe-N alloy powder (CN1093311C) by reduction diffusion and its use in the production of bonded magnets. Subsequently, Nissan chemical industries, Inc., in 1998, disclosed a method for producing Sm-Fe-N alloy powder having a high sphericity and a method for producing the same (CN100513015C), and proposed a method for producing Sm-Fe-N alloy powder having a high magnetic property by a method comprising first hydrogen reduction and then secondary reduction and diffusion using calcium. The method can prepare the Sm-Fe-N magnetic powder with excellent performance. However, due to the limitation of the process, Sm-Fe-N magnetic powder with nano-scale grains cannot be prepared by adopting a method of nitriding after reduction diffusion.

Thereafter, CN108701518A, CN105355354A, CN106312077A, etc. also disclose various new methods for preparing Sm-Fe-N magnetic powder, and further optimize the preparation process and performance of the material. However, the grain size of the Sm-Fe-N magnetic powder prepared by the method is still relatively large, so that the magnetic performance of the material is not fully exerted.

Disclosure of Invention

Aiming at the defects in the prior art, the invention aims to provide a nanocrystalline permanent magnetic material and a preparation method thereof.

In order to achieve the purpose, the invention adopts the following technical scheme:

in a first aspect, the present invention provides a nanocrystalline permanent magnetic material having a chemical formula of R_xT_yI_zWherein R is a rare earth metal and R comprises Sm, T is a transition metal and T comprises Fe, I is a non-metal element and I comprises N; x, y and z are the atomic contents of the R element, the T element and the I element respectively; the average grain size of the nanocrystalline permanent magnetic material is below 50 nm.

The average grain size of the nanocrystalline permanent magnet material provided by the invention is less than 50nm, such as 49nm, 48nm, 47nm, 46nm, 45nm, 44nm, 43nm, 42nm, 41nm or 40 nm.

The nanocrystalline permanent magnet material provided by the invention has very fine crystal grains, so that more N atoms can be absorbed to enter into atomic gaps, and the material has more excellent magnetic performance. In addition, the exchange coupling effect between the nano crystal grains ensures that the material still has higher residual magnetism under the condition of no orientation, so that the nano crystal magnetic powder can not apply an orientation magnetic field in the forming process, thereby greatly simplifying the forming process and improving the production efficiency.

The following is a preferred technical solution of the present invention, but not a limitation to the technical solution provided by the present invention, and the technical objects and advantageous effects of the present invention can be better achieved and achieved by the following preferred technical solution.

In a preferred embodiment of the present invention, the particle diameter D50 of the nanocrystalline permanent magnetic material is less than or equal to 600nm, for example, 580nm, 560nm, 540nm, 520nm, 510nm, or 500 nm. The lower particle size also helps to improve the magnetic properties of the product.

Preferably, the R element further includes any one or a combination of at least two of Nd, Pr, La, Ce, Gd, Tb, Ho, Dy, or Tb.

In the R element, the atomic number percentage of Sm is more than 90%, for example 90%, 91%, 92%, 93%, 94%, 95%, 97%, 99% or 100%.

Preferably, the T element further includes any one or a combination of at least two of Co, Ti, V, Cr, Mn, or Ni.

Preferably, the atomic number percentage of Fe in the T element is 92% or more, for example, 92%, 93%, 94%, 95%, 96%, 98%, 100%, or the like.

The I element also includes H and/or O. H and O do not have a promoting effect on the product of the invention, but may reduce the performance, but inevitably there will be traces of H and/or O in the product.

Generally speaking, in the nanocrystalline permanent magnetic material provided by the invention, the element I only consists of an element N, an element H and an element O.

Preferably, in the element I, the atomic number percentage of N is 85% or more, for example, 85%, 90%, 95%, 100%, or the like.

Preferably, in the element I, the atomic number percentage of H is less than 10%, such as 10%, 9%, 7%, 5%, 2%, and the like. The presence of hydrogen atoms is not favorable for improving the coercivity of the material, so the content of hydrogen atoms should be reduced as much as possible.

Preferably, the atomic number percentage of O in the I element is 12% or less, for example, 12%, 10%, 9%, 8%, 7%, 6%, 5%, 4%, 3%, 2%, 1%, or the like. Although many protection measures are adopted, in each process, the material is inevitably contacted with a very small amount of oxygen, and the fine magnetic powder in the invention is very easy to be oxidized due to fine particles, so that the residual magnetism and the coercive force of the material are reduced, and the content of oxygen atoms is reduced as much as possible.

As a preferable technical scheme of the invention, in the chemical formula of the nanocrystalline permanent magnetic material, y/x is more than or equal to 8 and less than or equal to 12.5, for example, y/x is 8, 9, 10, 11, 12 or 12.5, and the like.

Preferably, the chemical formula of the nanocrystalline permanent magnetic material is 1.4 ≦ z/x ≦ 2.0, such as z/x of 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2.0, and the like.

In a second aspect, the present invention provides a method for preparing a nanocrystalline permanent magnetic material according to the first aspect, the method comprising the steps of:

(1) mixing and calcining the R element source and the T element source in the formula amount to obtain a calcined product; the R element source comprises a Sm source and the T element source comprises a Fe source;

(2) crushing the calcined product in the step (1), and then carrying out primary reduction by using hydrogen to obtain a primary reduction product;

(3) mixing the primary reduction product obtained in the step (2) with a metal reducing agent and a separant for secondary reduction to obtain a secondary reduction product;

(4) reacting the secondary reduction product obtained in the step (3) in hydrogen to obtain reaction powder;

(5) and (4) carrying out heat treatment on the reaction powder in the step (4) under the condition of vacuum pumping, and adding nitrogen-containing gas for nitriding to obtain the nanocrystalline permanent magnet material.

In the preparation method provided by the invention, the R element source and the T element source in the step (1) need to enable the R element and the T element to meet the proportion requirement defined by the first aspect.

In the preparation method provided by the invention, the mixing in the step (1) can form a uniform mixture, and the mixture is calcined to generate solid phase diffusion of R atoms and T atoms to form R_xT_yO_3(x+y)/₂An oxide. The oxide is broken and reduced for the first time in the step (2) and reduced for the second time in the step (3), oxygen atoms are all deprived, and R is formed_xT_yAnd (3) alloying powder.

In the present invention, R_xT_yAfter the alloy powder is subjected to the step (4), R with very fine grains (5-10nm) can be formed_xH_zAnd a phase T. This is because when the reaction is carried out in hydrogen, the rare earth-transition metal alloy reacts with hydrogen as follows:

2R_xT_y+zH₂＝2R_xH_z+yT

moreover, when the reaction is carried out under milder temperature conditions (e.g., room temperature), the newly formed R_xH_zThe growth driving force of the phase and the T phase is very small, so that the crystal grain size is only about 5-8 nm.

In step (5), the alloy is heat treated in vacuum, and the material is dehydrogenated to regenerate R_xT_yPhase (1):

2R_xH_z+yT＝2R_xT_y+zH₂

during the vacuum heat treatment, the crystal grains of the alloy are slightly longer, about 30-40 nm. The alloy powder is subjected to nitriding treatment in the step (5) to form final R_xT_yI_zNanocrystalline magnetic powder.

Since the production method of the present invention includes a step of reaction in hydrogen gas, part of hydrogen atoms enter the crystal lattice of the powder. Although most of the hydrogen atoms are desorbed from the powder after the vacuum heat treatment of step (5), some hydrogen atoms remain in the crystal lattice.

Despite many protective measures, the material inevitably comes into contact with very small amounts of oxygen during the various processes.

As a preferable technical scheme of the invention, the R element source and the T element source in the step (1) are both oxides.

Preferably, the chemical formula of the R element source in the step (1) is R₂O₃。

Preferably, the R element source in step (1) comprises Sm₂O₃。

Preferably, the R element source of step (1) further comprises Nd₂O₃、Ce₂O₃、La₂O₃、Pr₂O₃、Gd₂O₃、Tb₂O₃、Ho₂O₃、Dy₂O₃Or Tb₂O₃Any one or a combination of at least two of them.

Preferably, the chemical formula of the T element source in the step (1) is T₂O₃。

Preferably, the T element source of step (1) comprises Fe₂O₃。

Preferably, the T element source in the step (1) further comprises Co₂O₃、Ti₂O₃、Cr₂O₃、Ni₂O₃、V₂O₃Or Mn₂O₃Any one or a combination of at least two of them.

Preferably, the mixing method in step (1) is ball milling.

Preferably, the ball milling medium of the ball mill is water.

Preferably, the mass ratio of the ball, the material and the ball milling medium for ball milling is 15 (0.9-1.1) to (0.9-1.1), such as 15:0.9:0.9, 15:1:1, 15:0.9:1.1 or 15:1.1:1.1, etc.

Preferably, the mixing time in step (1) is 4-6h, such as 4h, 4.5h, 5h, 5.5h or 6h, etc.

Preferably, the calcination of step (1) is carried out in air.

Preferably, the temperature of the calcination in step (1) is 1050-. In the invention, if the calcining temperature in the step (1) is too high, the energy consumption is too high, and the crystal grains of the material grow excessively, so that the material cannot achieve ideal performance; if the calcining temperature in the step (1) is too low, the magnetic material structure cannot be formed, and the magnetic property of the material is too low or has no permanent magnetic property.

Preferably, the calcination in step (1) is carried out for 1.5-2.5h, such as 1.5h, 1.7h, 2.0h, 2.3h or 2.5h, etc.

As a preferable technical scheme of the invention, the crushing in the step (2) comprises coarse crushing and ball milling crushing;

preferably, the ball milling medium for ball milling is water.

Preferably, the mass ratio of the ball, the material and the ball milling medium for ball milling is 15 (0.9-1.1) to (0.9-1.1), such as 15:0.9:0.9, 15:1:1, 15:0.9:1.1 or 15:1.1:1.1, etc.

Preferably, the particle size D50 of the crushed product obtained after the crushing in step (2) is 0.8-1.2 μm, such as 0.8 μm, 0.9 μm, 1 μm, 1.1 μm or 1.2 μm.

Preferably, the flow rate of the hydrogen in the step (2) is 13-17L/min.

Preferably, the temperature of the primary reduction in step (2) is 840-860 ℃, such as 840 ℃, 845 ℃, 850 ℃, 855 ℃ or 860 ℃ and the like.

Preferably, the time for the primary reduction in step (2) is 9-11h, such as 9h, 9.5h, 10h, 10.5h or 11 h.

In a preferred embodiment of the present invention, the metal reducing agent in step (3) comprises Ca. In the present invention, the metal reducing agent functions to melt and form vapor at high temperature to further reduce the material.

Preferably, in step (3), the mass of the metal reducing agent is 16-24% of the mass of the primary reduction product, such as 16%, 17%, 18%, 19%, 20%, 21%, 22%, 23%, 24%, or the like.

Preferably, the release agent in step (3) comprises CaO, and in the present invention, the release agent is used for releasing the powder to prevent R_xT_yThe alloy powder is diffused and grown in a liquid metal reducing agent.

Preferably, in step (3), the mass of the separating agent is 26-34% of the mass of the primary reduction product, such as 26%, 27%, 28%, 29%, 30%, 31%, 32%, 33%, 34%, etc.

Preferably, the protective atmosphere in step (3) includes any one of an argon atmosphere, a helium atmosphere, or a neon atmosphere, or a combination of at least two thereof. In the invention, the protective atmosphere in the step (3) cannot be a nitrogen atmosphere, because the nitrogen may cause side reactions to occur, which may adversely affect the preparation of the nanocrystalline permanent magnetic material.

Preferably, the temperature of the secondary reduction in step (3) is 900-.

Preferably, the time for the secondary reduction in the step (3) is 5 to 7 hours.

In the step (4), the secondary reduction product is washed and dried before being reacted in hydrogen.

Preferably, the washing method comprises soaking in water and washing more than 2 times. I.e., soaked and washed multiple times.

Preferably, the washing reduces Ca in the secondary reduction product²⁺The content is washed to 0.2% or less, for example, 0.2%, 0.19%, 0.18%, 0.17%, 0.16%, or 0.15% by mass.

Preferably, the drying is performed under vacuum.

Preferably, the pressure of the hydrogen in step (4) is 0.8 to 1MPa, such as 0.8MPa, 0.85MPa, 0.9MPa, 0.95MPa or 1MPa, etc.

Preferably, the method for carrying out the reaction in step (4) is dry ball milling.

Preferably, the dry ball milling has a ball to material ratio of (14-16):1, such as 14:1, 14.5:1, 15:1, 15.5:1, or 16:1, etc.

Preferably, the reaction of step (4) is carried out for 9-11h, such as 9h, 9.5h, 10h, 10.5h or 11 h.

Preferably, the reaction of step (4) is carried out at a temperature of 15 to 35 ℃, i.e. at room temperature.

As a preferable embodiment of the present invention, the temperature of the heat treatment in the step (5) is 640-660 ℃, for example, 640 ℃, 645 ℃, 650 ℃, 655 ℃ or 660 ℃.

Preferably, the time of the heat treatment in the step (5) is 0.4-0.6h, such as 0.4h, 0.45h, 0.5h, 0.55h or 0.6 h.

Preferably, the nitriding temperature in step (5) is 450-510 ℃, such as 450 ℃, 460 ℃, 470 ℃, 480 ℃, 490 ℃, 500 ℃ or 510 ℃ and the like. In the invention, if the nitriding temperature is too high, the magnetic phase is decomposed, and the permanent magnetic property is not realized; if the nitriding temperature is too low, the nitrogen content of the material cannot fall within the range of the invention, and the permanent magnetic property is low.

Preferably, the nitriding time in step (5) is 4-7h, such as 4h, 5h, 5.5h, 6h, 6.5h or 7h, etc.

Preferably, the nitrogen-containing gas of step (5) comprises nitrogen and/or ammonia.

As a further preferable technical scheme of the preparation method of the invention, the preparation method comprises the following steps:

(1) carrying out wet ball milling and mixing on the R element source and the T element source with the formula amount by taking water as a medium for 4-6h, and calcining in air at the temperature of 1050-; the R element source comprises a Sm source and the T element source comprises a Fe source; the R element source and the T element source are both oxides;

(2) after the calcination product in the step (1) is subjected to coarse crushing and ball milling crushing, carrying out primary reduction on the obtained crushed product with the D50 of 0.8-1.2 mu m for 9-11h by using hydrogen with the flow rate of 13-17L/min at the temperature of 840-860 ℃ to obtain a primary reduction product;

(3) mixing the primary reduction product in the step (2) with a metal reducing agent and a separant, and carrying out secondary reduction for 5-7h at the temperature of 900-1100 ℃ in a protective atmosphere to obtain a secondary reduction product;

wherein the metal reducing agent comprises Ca, and the mass of the metal reducing agent is 16-24% of that of the primary reduction product; the separant comprises CaO, and the mass of the separant is 26-34% of that of the primary reduction product;

(4) soaking and cleaning the secondary reduction product obtained in the step (3) in water for more than 2 times, drying under the vacuum condition, and reacting for 9-11h in hydrogen with the pressure of 0.8-1MPa by adopting a dry ball milling method, wherein the ball-to-material ratio of the dry ball milling is (14-16):1, so as to obtain reaction powder;

(5) and (3) carrying out heat treatment on the reaction powder in the step (4) at the temperature of 640-.

Compared with the prior art, the invention has the following beneficial effects:

(1) the nanocrystalline permanent magnet material provided by the invention has very fine crystal grains, so that more N atoms can be absorbed to enter into atomic gaps, and the material has more excellent magnetic performance. In addition, exchange coupling between the nano-crystalline grains enables the material to have high remanence under the condition that orientation is not needed. The nanocrystalline permanent magnetic material improves the magnetic performance of the material by improving the components and the microstructure of the material, so that the nanocrystalline permanent magnetic material is more suitable for the miniaturization and light development of magnetic components. The magnet remanence of the nanocrystalline permanent magnet material provided by the invention is more than 4570Gs, the coercive force is more than 12568Oe, and the magnetic energy product is more than 4.53 MGOe.

(2) The preparation method provided by the invention ensures that the grain size and the particle size of the obtained nanocrystalline permanent magnetic material are small enough, ensures the product performance, is simple, and is beneficial to industrialized large-scale production.

Detailed Description

The technical solution of the present invention is further illustrated by the following specific examples. It should be understood by those skilled in the art that the examples are only for the understanding of the present invention and should not be construed as the specific limitations of the present invention.

In the present invention, all the equipment, materials and the like are commercially available or commonly used in the industry, if not specified. The methods in the following examples are conventional in the art unless otherwise specified.