Preparation method of high-performance anisotropic rare earth iron nitrogen magnetic powder

Abstract

The invention discloses a preparation method of high-performance anisotropic rare earth iron nitrogen magnetic powder, and belongs to the field of rare earth magnetic material preparation.The method comprises the steps that a rare earth-iron-copper alloy rapid hardening sheet is prepared through rapid hardening smelting, a rare earth-rich alloy is obtained through primary annealing, rapid quenching treatment is conducted to obtain a rapid quenching belt of nanoscale grains, and the rapid quenching belt of the nanoscale grains is subjected to secondary annealing treatment to obtain the high-performance anisotropic rare earth iron nitrogen magnetic powder. The preparation method comprises the following steps: performing primary annealing on main phase grains, performing secondary annealing to enable the main phase grains to grow to 1-5 microns and form a grain boundary phase rich in rare earth-Cu, performing intergranular crushing by utilizing a hydrogen explosion technology, performing nitridation treatment, and finally performing fine grinding and crushing to obtain the high-performance anisotropic rare earth iron nitrogen magnetic powder with the average grain size of 1-5 microns.

Description

Technical Field

[0001] This application belongs to the field of rare earth magnetic material preparation, and particularly relates to a method for preparing high-performance anisotropic rare earth iron nitride magnetic powder. Background Art

[0002] Rare earth iron nitride magnetic powder (such as RFe 12 N and R2Fe 17 N3, where R is a rare earth element) is a type of rare earth permanent magnetic material with high performance. Research and development of high-performance rare earth iron nitride magnetic powder are of great significance for promoting the miniaturization and high-performance process of micro and special motors. In particular, anisotropic rare earth iron nitride magnetic powder has become a research hotspot in this field because its maximum theoretical magnetic energy product can reach 4 times that of isotropic magnetic powder of the same kind. Related research shows that the coercivity mechanism of anisotropic RFe 12 N and R2Fe 17 N3-type rare earth iron nitride magnetic powder is mainly controlled by nucleation. To obtain magnetic powder with high magnetic energy product, the magnetic powder needs to be single-crystal grain-type anisotropic magnetic powder, and the size of RFe 12 N and R2Fe 17 N3-type rare earth iron nitride particles or grains must be strictly controlled between 1 - 5 μm.

[0003] However, in the prior art, anisotropic RFe 12 N and R2Fe 17 N3-type rare earth iron nitride magnetic powder is mainly prepared by smelting technologies such as rapid solidification. Using this technology for preparation usually requires high-temperature and long-time annealing treatment to obtain RFe with high single-phase property 12 N and R2Fe 17 N3-type alloy. However, this high-temperature and long-time annealing treatment will cause the several-micron-sized grains in the initial RFe 12 N and R2Fe 17 N3-type rapid solidification sheet or smelted alloy to grow to dozens of microns. According to the formation mechanism of the coercivity of anisotropic rare earth iron nitride magnetic powder, to prepare high-performance anisotropic rare earth iron nitride magnetic powder, the coarsened grains up to dozens of microns after annealing must be nitrided, and then a certain crushing technology is adopted to make them transgranularly crushed to less than 5 μm. However, the anisotropic rare earth iron nitride magnetic powder obtained by the transgranular crushing method has tips and many defects, and these defects will cause the coercivity and magnetic energy product of the material to be not high. Although there is prior art using the rapid quenching process to prepare nanocrystalline samarium iron nitride magnetic powder, the fine grains obtained are randomly oriented, that is, isotropic samarium iron nitride magnetic powder is obtained.

[0004] In summary, there are many deficiencies in the prior art in the preparation of high-performance anisotropic rare earth iron nitride magnetic powder, making it difficult to meet the requirements of practical applications. Therefore, there is an urgent need for a new preparation method that can effectively overcome the defects of the prior art and prepare high-performance anisotropic rare earth iron nitride magnetic powder with a size of 1-5 μm, few surface defects on the particles, and a near-spherical particle morphology. Summary of the Invention

[0005] The purpose of this application is to provide a preparation method for high-performance anisotropic rare earth iron nitride magnetic powder, to solve the problems existing in the above prior art, and to prepare high-performance anisotropic rare earth iron nitride magnetic powder with a size of about 1-5 μm.

[0006] The embodiments of this application can be realized through the following technical solutions:

[0007] A preparation method for high-performance anisotropic rare earth iron nitride magnetic powder specifically includes the following steps:

[0008] S1, preparing a rapid-solidification sheet of rare earth-iron-copper alloy by rapid-solidification melting;

[0009] S2, performing a first annealing treatment on the rapid-solidification sheet in S1 to obtain a rare earth-iron-copper alloy rich in rare earth;

[0010] S3, performing a rapid quenching treatment on the rare earth-iron-copper alloy rich in rare earth in S2 to obtain a rapid-quenching ribbon with an average grain size in the nanometer range;

[0011] S4, performing a second annealing treatment on the rapid-quenching ribbon in S3 to obtain a rapid-quenching ribbon with main phase grains of Sm2Fe 17 or NdFe 12 , main phase grain size of 1-5 μm, and rich in rare earth-Cu grain boundary phase;

[0012] S5, performing a hydrogen explosion fragmentation on the rapid-quenching ribbon after the second annealing in S4 to obtain particles fragmented along the grain boundaries;

[0013] S6, performing a nitriding treatment on the particles after the hydrogen explosion fragmentation in S5;

[0014] S7, performing a fine grinding and fragmentation on the particles after the nitriding treatment in S6 to obtain anisotropic rare earth iron nitride magnetic powder with an average particle size of 1-5 μm;

[0015] Among them, the rare earth element in the rare earth-iron-copper alloy is selected from any one of samarium and neodymium, and the atomic ratio of the copper element is in the range of 0.05-0.1.

[0016] Furthermore, the wheel speed of the rapid-solidification melting in S1 (i.e., the rotation speed of the copper roll in the rapid-solidification equipment) is 2-5 m / s; in some specific embodiments, the rare earth-iron-copper alloy is Sm 2.1 Fe 17-xCu x or Nd 1.1 Fe 12-x Cu x , wherein 0.05 ≤ x ≤ 0.1; preferably, high-purity iron, samarium or neodymium, and copper are used as raw materials for rapid solidification melting.

[0017] Furthermore, the specific conditions for the first annealing in S2 are: the annealing temperature is 1000 - 1100 °C, the vacuum degree ≤ 3×10-3 Pa, and the annealing time is 24 - 48 hours.

[0018] Furthermore, the wheel speed during the rapid quenching process in S3 is 30 - 50 m / s; the average grain size of the finally obtained rapidly quenched ribbon is 100 - 200 nm.

[0019] Furthermore, the specific conditions for the second annealing in S4 are: the annealing temperature is 800 - 850 °C, the vacuum degree ≤ 3×10-3 Pa, and the annealing time is 1 - 3 hours; preferably, the microstructure of the rapidly quenched ribbon after the second annealing consists of main phase grains with a grain size of 1 - 5 μm of Sm2Fe 17 or NdFe 12 and grain boundary phases rich in Sm-Cu or Nd-Cu. This microstructure makes the magnetic powder more excellent in magnetic performance on the one hand, and provides conditions for subsequent hydrogen explosion fragmentation to be intergranular fragmentation on the other hand; more preferably, the grain size of the main phase grains is 3 - 4 μm.

[0020] Furthermore, the specific steps of the hydrogen explosion fragmentation in S5 are to heat the rapidly quenched ribbon to 200 - 300 °C and hold for 2 hours under 0.05 - 2 atm hydrogen conditions; preferably, the specific steps of the hydrogen explosion fragmentation in S5 are to heat the rapidly quenched ribbon to 250 °C under 1 atm hydrogen conditions; through hydrogen explosion fragmentation, particles with intergranular fragmentation are obtained, avoiding tips or other defects formed by traditional transgranular fragmentation, thereby improving the final magnetic properties.

[0021] Furthermore, the nitriding temperature in S6 is 400 - 600 °C, and the nitriding time is 4 - 15 hours; preferably, coarse crushing treatment is also included before nitriding, that is, the particles after hydrogen explosion fragmentation are crushed into particles with a particle size of 20 - 150 μm; more preferably, the coarse crushing treatment is to crush the particles after hydrogen explosion fragmentation into particles with a particle size of 100 μm.

[0022] Furthermore, the fine grinding and crushing in S7 can be selected from any one of jet mill crushing or ball mill crushing; preferably, when ball mill crushing is used, the ball-to-material ratio is 10:1.

[0023] The preparation method of a high-performance anisotropic rare earth iron nitride magnetic powder provided by the embodiments of the present application has at least the following beneficial effects:

[0024] In this application, by adding a specific amount of Cu in the composition design and combining the rapid quenching process with two annealing processes, the grain size of the main phase is precisely controlled to be 1 - 5 μm, and at the same time, a grain boundary phase rich in rare earth - Cu is formed, so that the subsequent hydrogen explosion fragmentation is mainly intergranular fragmentation. Compared with the traditional transgranular fragmentation, intergranular fragmentation basically avoids the generation of tips and other defects, thereby significantly improving the magnetic properties of the final magnetic powder;

[0025] Through the synergistic effect of each step, anisotropic rare earth iron nitride magnetic powder with a particle size of 1 - 5 μm, few surface defects and a morphology close to spherical is finally prepared. This magnetic powder has high remanence, coercivity and magnetic energy product, can meet the stringent requirements of miniaturization and high performance of micro - special motors for magnetic materials, and has significant advantages in practical applications. Description of the Drawings

[0026] Figure 1 It is a scanning electron microscope image of the rapidly quenched strip obtained after the secondary annealing treatment in Example 1;

[0027] Figure 2 It is a scanning electron microscope image of the anisotropic magnetic powder finally obtained in Example 1;

[0028] Figure 3 It is the magnetic property curve of the anisotropic magnetic powder prepared in Example 1. Detailed Embodiments

[0029] Hereinafter, this application will be further described based on the preferred embodiments with reference to the drawings.

[0030] Example 1

[0031] (1) Rapid solidification melting: Weigh high - purity iron, samarium and copper, and prepare the ingredients according to the chemical atomic ratio of Sm 2.1 Fe 16.9 Cu 0.1 and the corresponding burn - loss amount. Put the prepared raw materials into a rapid solidification furnace for melting, and prepare a rapidly quenched sheet with a chemical atomic ratio of Sm 2.1 Fe 16.9 Cu 0.1 under the condition of a wheel speed of 4 m / s;

[0032] (2) First annealing treatment: Put the rapidly quenched sheet prepared in step (1) into an annealing furnace, and anneal it for 24 hours at 1050 °C and a vacuum degree ≤ 3×10 - 3 Pa to obtain a rapidly quenched sheet of Sm - rich Sm 2.1 Fe 16.9 Cu 0.1 ;

[0033] (3) Rapid quenching treatment: The rapidly solidified sheet annealed in step (2) is placed in a rapid quenching device and subjected to rapid quenching treatment under the condition of a wheel speed of 30 m / s to obtain a rapidly quenched ribbon with an average grain size of 100 nm of Sm 2.1 Fe 16.9 Cu 0.1 rapidly quenched ribbon;

[0034] (4) Secondary annealing treatment: The rapidly quenched ribbon obtained in step (3) is annealed at 800 °C under a vacuum degree ≤ 3×10-3 Pa for 2 hours, Figure 1 The scanning electron microscope image of the rapidly quenched ribbon after annealing is shown. It can be seen from the figure that a rapidly quenched ribbon with main phase grains of about 2.5 μm and rich in Sm-Cu grain boundary phase is obtained; 17 main phase grains are about 2.5 μm or so and rich in Sm-Cu grain boundary phase;

[0035] (5) Hydrogen explosion fragmentation: The rapidly quenched ribbon after secondary annealing in step (4) is placed in a reaction vessel filled with 1 atm of hydrogen, heated to 250 °C and maintained for 2 hours to carry out hydrogen explosion fragmentation on the rapidly quenched ribbon. During this process, the rapidly quenched ribbon absorbs hydrogen and expands. Due to the different degrees of hydrogen absorption expansion of the main phase and the grain boundary phase, internal stress is generated, thereby realizing intergranular fragmentation, and finally obtaining intergranular fragmented Sm 2.1 Fe 16.9 Cu 0.1 particles;

[0036] (6) Nitriding treatment: The particles after hydrogen explosion fragmentation in step (5) are first coarsely crushed to about 100 μm, and then placed in a nitriding furnace and nitrided at a nitriding temperature of 420 °C for 15 hours to obtain Sm 2.1 Fe 16.9 Cu 0.1 N3;

[0037] (7) Fine grinding and fragmentation: Under the condition of a ball-to-material ratio of 10:1, a ball mill is used to ball-mill and fragment the Sm 2.1 Fe 16.9 Cu 0.1 N3 particles to an average particle size of 2.5 microns to obtain high-performance anisotropic magnetic powder, and its scanning electron microscope image is as shown in Figure 2 shown.

[0038] Magnetic property detection:

[0039] The anisotropic magnetic powder, glue, and hardener obtained in Example 1 were uniformly mixed at a mass ratio of 2:3:1. Specifically, during mixing, the powder and glue can be mixed first, and then the mixed colloid and hardener can be mixed evenly; the uniformly mixed new colloid is placed in the cylindrical holes of a special orientation plate (such as a non-magnetic PVC material), and the back of the hole is blocked with a baffle to prevent the colloid from leaking; a magnetic field of 1.5 T is applied to the orientation plate using an electromagnet for about 1 hour or more, and wait for the mixed colloid to solidify; the solidified orientation column is taken out of the orientation plate to complete the preparation of the magnetically oriented sample for magnetic property measurement.

[0040] The remanence, coercivity, and magnetic energy product of the sample after magnetic orientation in Example 1 were measured using a vibrating sample magnetometer. Figure 3 The magnetic property curve of the magnetic powder is shown, and the results are: remanence Mr = 133 emu / g, coercivity iHc = 12000 Oe, and magnetic energy product (BH)max = 32 MGOe.

[0041] Example 2

[0042] (1) High-purity iron, neodymium, and copper were weighed and proportioned according to the chemical atomic ratio Nd 1.1 Fe 11.9 Cu 0.1 and the corresponding burn-off amount. The prepared raw materials were placed in a rapid solidification furnace for melting, and a rapid solidification sheet with a chemical atomic ratio of Nd 1.1 Fe 11.9 Cu 0.1 was prepared under the condition of a wheel speed of 3 m / s.

[0043] (2) The rapid solidification sheet prepared in step (1) was placed in an annealing furnace and annealed at 1050 °C under a vacuum degree ≤ 3×10-3 Pa for 48 hours to obtain a rapid solidification sheet of Nd 1.1 Fe 11.9 Cu 0.1 rich in neodymium.

[0044] (3) The rapid solidification sheet annealed in step (2) was placed in a rapid quenching device and subjected to rapid quenching treatment at a wheel speed of 40 m / s to obtain a rapid quenching ribbon of Nd 1.1 Fe 11.9 Cu 0.1 with an average grain size of 100 nm.

[0045] (4) The rapid quenching ribbon obtained in step (3) was annealed at 820 °C under a vacuum degree ≤ 3×10-3 Pa for 2 hours to obtain a rapid quenching ribbon with a main phase grain of NdFe 12 about 4 μm and rich in Nd-Cu grain boundary phase.

[0046] (5) Put the rapidly quenched strip after secondary annealing in step (4) into a reaction vessel filled with hydrogen at 1 atm, heat it to 250 °C and hold for 2 hours to carry out hydrogen explosion fragmentation on the rapidly quenched strip. During this process, the rapidly quenched strip absorbs hydrogen and expands. Due to the different degrees of hydrogen absorption expansion of the main phase and the grain boundary phase, internal stress is generated, thereby realizing intergranular fragmentation, and finally obtaining intergranular fragmented Nd 1.1 Fe 11.9 Cu 0.1 particles;

[0047] (6) First, roughly crush the particles after hydrogen explosion fragmentation in step (5) to about 100 μm, and then put them into a nitriding furnace. Nitride them for 5 hours under the condition that the nitriding temperature is 550 °C to obtain Nd 1.1 Fe 11.9 Cu 0.1 N;

[0048] (7) Under the condition that the ball-to-material ratio is 10:1, use a ball mill to ball-mill and crush the Nd 1.1 Fe 11.9 Cu 0.1 N particles until the average particle size of the particles is 4 μm to obtain high-performance anisotropic Nd 1.1 Fe 11.9 Cu 0.1 N magnetic powder.

[0049] Complete the magnetic orientation of the anisotropic Nd 1.1 Fe 11.9 Cu 0.1 N magnetic powder in Example 2 according to the detection method in Example 1, and use a vibrating sample magnetometer to measure the remanence, coercivity and magnetic energy product of the Nd 1.1 Fe 11.9 Cu 0.1 N magnetic powder obtained in Example 2. The results are: remanence Mr = 120 emu / g, coercivity iHc = 5300 Oe, magnetic energy product (BH)max = 20 MGOe.

[0050] Example 3

[0051] (1) Weigh high-purity iron, neodymium and copper, and proportion the ingredients according to the chemical atomic ratio Nd 1.1 Fe 11.94 Cu 0.06 and the corresponding burn-off amount. Place the prepared raw materials in a rapid solidification furnace for melting, and prepare a rapid solidification sheet with a chemical atomic ratio of Nd 1.1 Fe 11.94 Cu 0.06 under the condition that the wheel speed is 5 m / s;

[0052] (2) Put the rapidly solidified sheet prepared in step (1) into an annealing furnace and anneal it for 24 hours under the conditions of 1080 °C and a vacuum degree ≤ 3×10-3 Pa to obtain a rapidly solidified sheet rich in neodymium Nd 1.1 Fe 11.94 Cu 0.06 ;

[0053] (3) Put the rapidly solidified sheet annealed in step (2) into a rapid quenching device and perform rapid quenching treatment under the condition of a wheel speed of 45 m / s to obtain a rapidly quenched ribbon with an average grain size of 100 nm Nd 1.1 Fe 11.94 Cu 0.06 ;

[0054] (4) Anneal the rapidly quenched ribbon obtained in step (3) for 1.5 hours under the conditions of 800 °C and a vacuum degree ≤ 3×10 -3 Pa to obtain a rapidly quenched ribbon with a main phase grain of about 2 μm and rich in Nd-Cu grain boundary phase; 12 ;

[0055] (5) Put the rapidly quenched ribbon after secondary annealing in step (4) into a reaction vessel filled with hydrogen at 1 atm, heat it to 250 °C and keep it for 2 hours to perform hydrogen explosion fragmentation on the rapidly quenched ribbon. During this process, the rapidly quenched ribbon absorbs hydrogen and expands. Due to the different degrees of hydrogen absorption expansion of the main phase and the grain boundary phase, internal stress is generated, thus realizing intergranular fragmentation, and finally obtaining intergranular fragmented Nd 1.1 Fe 11.94 Cu 0.06 particles;

[0056] (6) First, coarsely fragment the particles after hydrogen explosion fragmentation in step (5) to about 100 μm, and then put them into a nitriding furnace and nitride them for 4 hours under the condition of a nitriding temperature of 560 °C to obtain Nd 1.1 Fe 11.94 Cu 0.06 N;

[0057] (7) Under the condition of a ball-to-material ratio of 10:1, use a ball mill to ball-mill and fragment the Nd 1.1 Fe 11.94 Cu 0.06 N particles until the average particle size is 2 microns to obtain high-performance anisotropic Nd 1.1 Fe 11.94 Cu 0.06 N magnetic powder.

[0058] Complete the magnetic orientation of the anisotropic Nd 1.1 Fe 11.94 Cu 0.06 N magnetic powder in Example 3 according to the detection method in Example 1, and use a vibrating sample magnetometer to measure the Nd obtained in Example 31.1 Fe 11.94 Cu 0.06 The remanence, coercivity and maximum energy product of the N magnetic powder were measured, and the results were: remanence Mr = 122 emu / g, coercivity iHc = 5000 Oe, and maximum energy product (BH)max = 21 MGOe.

[0059] The specific embodiments of the present application have been introduced in detail above. For those skilled in the art of this technology, without departing from the principle of the present application, several improvements and modifications can still be made to the present application, and these improvements and modifications also fall within the protection scope of the claims of the present application.

Claims

1. A method for preparing a high-performance anisotropic rare earth iron nitride magnetic powder, characterized in that, Specifically, it includes the following steps: S1. Prepare a rapid solidification sheet of rare earth-iron-copper alloy by rapid solidification melting; S2. Anneal the rapid solidification sheet in S1 once to obtain a rare earth-iron-copper alloy rich in rare earth; S3. Perform rapid quenching treatment on the rare earth-rich rare earth-iron-copper alloy in S2 to obtain a rapidly quenched ribbon with an average grain size in the nanometer range; S4. Anneal the rapidly quenched ribbon in S3 twice to obtain a rapidly quenched ribbon with a primary phase grain size of 1 - 5 μm and rich in rare earth-Cu grain boundary phase; S5. Perform hydrogen explosion fragmentation on the rapidly quenched ribbon after the second annealing in S4 to obtain intergranularly fragmented particles; S6. Perform nitriding treatment on the particles after hydrogen explosion fragmentation in S5; S7. Perform fine grinding and fragmentation on the particles after nitriding treatment in S6 to obtain anisotropic rare earth iron nitride magnetic powder with an average particle size of 1 - 5 μm; Among them, the rare earth element in the rare earth-iron-copper alloy is selected from any one of samarium and neodymium, and the atomic ratio of the copper element is in the range of 0.05 - 0.

1.

2. The preparation method of a high-performance anisotropic rare earth iron nitride magnetic powder according to claim 1, wherein, The main phase grains are Sm2Fe 17 or NdFe 12 .

3. The preparation method of a high-performance anisotropic rare earth iron nitride magnetic powder according to claim 1, wherein, The wheel speed of the rapid solidification melting in S1 is 2 - 5 m / s.

4. The preparation method of a high-performance anisotropic rare earth iron nitride magnetic powder according to claim 1, wherein, The specific conditions for the first annealing in S2 are: the annealing temperature is 1000 - 1100 °C, the vacuum degree ≤ 3×10-3 Pa, and the annealing time is 24 - 48 hours.

5. The preparation method of a high-performance anisotropic rare earth iron nitride magnetic powder according to claim 1, wherein, The average grain size of the rapidly quenched ribbon obtained in S3 is 100 - 200 nm; And / or, the wheel speed during the rapid quenching process in S3 is 30 - 50 m / s.

6. The preparation method of a high-performance anisotropic rare earth iron nitride magnetic powder according to claim 1, wherein, The specific conditions for the second annealing in S4 are: the annealing temperature is 800 - 850 °C, the vacuum degree ≤ 3×10-3 Pa, and the annealing time is 1 - 3 hours.

7. The preparation method of a high-performance anisotropic rare earth iron nitride magnetic powder according to claim 1, wherein, The specific steps of the hydrogen explosion fragmentation in S5 are to heat the rapidly quenched ribbon to 200 - 300 °C and hold for 2 hours under the condition of 0.05 - 2 atm hydrogen.

8. The preparation method of a high-performance anisotropic rare earth iron nitride magnetic powder according to claim 1, wherein, The nitriding temperature in S6 is 400 - 600 °C, and the nitriding time is 4 - 15 hours.

9. The preparation method of a high-performance anisotropic rare earth iron nitride magnetic powder according to claim 8, wherein, Before the nitriding in S6, it also includes coarse fragmentation treatment, that is, fragmenting the particles after hydrogen explosion fragmentation into particles with a particle size of 20 - 150 μm.

10. The preparation method of a high-performance anisotropic rare earth iron nitride magnetic powder according to claim 1, wherein, The fine grinding and crushing of the S7 can be selected from any one of jet mill crushing or ball mill crushing.

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