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

Abstract

The application 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 following steps: preparing a rare earth-iron-copper alloy rapid solidification sheet through rapid solidification smelting, obtaining a rare earth-rich alloy through one-time annealing, obtaining a fast-quenching ribbon with nanoscale grains through fast-quenching treatment, carrying out secondary annealing to make the main phase grains grow to 1-5 microns and form a rare earth-Cu-rich grain boundary phase, then realizing crystal breaking through hydrogen explosion technology, then carrying out nitriding treatment, and finally obtaining the high-performance anisotropic rare earth iron-nitrogen magnetic powder with an average particle size of 1-5 microns through fine grinding.

Description

Technical Field

[0001] This application belongs to the field of rare earth magnetic material preparation, specifically relating to a method for preparing high-performance anisotropic rare earth iron-nitrogen magnetic powder. Background Technology

[0002] Rare earth iron nitride magnetic powder (such as RFe) 12 N and R2Fe 17 Nitrogen oxides (N3, where R represents rare earth elements) are a class of high-performance rare earth permanent magnet materials. Research and development of high-performance rare earth iron nitride magnetic powders are of great significance for promoting the miniaturization and high-performance of micromotors. In particular, anisotropic rare earth iron nitride magnetic powders have become a research hotspot in this field because their maximum theoretical magnetic energy product can be four times that of isotropic counterparts. Related research shows that anisotropic RFe... 12 N and R2Fe 17 The coercivity mechanism of N3-type rare-earth iron nitride magnetic powder is mainly controlled by nucleation. To obtain magnetic powder with high magnetic energy product, the powder needs to be anisotropic, single-crystal particle type, and RFe... 12 N and R2Fe 17 The size of N3 type rare earth iron nitride particles or grains must be strictly controlled between 1 and 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 rapid solidification and other smelting techniques. This process typically requires high-temperature, long-duration annealing to obtain high-purity RFe. 12 N and R2Fe 17 N3 type alloy, but this high-temperature, long-term annealing treatment will cause the initial RFe 12 N and R2Fe 17 In N3-type rapid-solidifying flakes or smelted alloys, grains ranging from a few micrometers in size grow to tens of micrometers. According to the formation mechanism of coercivity in anisotropic rare-earth iron nitride magnetic powder, to prepare high-performance anisotropic rare-earth iron nitride magnetic powder, the coarse grains (tens of micrometers) after annealing must be nitrided, followed by a certain crushing technique to break them through the grains to below 5 μm. However, anisotropic rare-earth iron nitride magnetic powder obtained by this method has sharp points and numerous defects, which result in low coercivity and magnetic energy product. Although existing technologies use rapid quenching processes to prepare nanocrystalline samarium iron nitride magnetic powder, the resulting fine grains are randomly oriented, meaning the obtained powder is isotropic samarium iron nitride magnetic powder.

[0004] In summary, existing technologies have many shortcomings in preparing high-performance anisotropic rare-earth iron nitride magnetic powders, making it difficult to meet the needs of practical applications. Therefore, there is an urgent need for a new preparation method that can effectively overcome the deficiencies of existing technologies and produce high-performance anisotropic rare-earth iron nitride magnetic powders with a size of 1–5 μm, few surface defects, and a near-spherical particle morphology. Summary of the Invention

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

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

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

[0008] S1, rare earth-iron-copper alloy quick-solidification sheets are prepared by quick-solidification smelting;

[0009] S2, anneal the quick-setting sheet described in S1 once to obtain a rare earth-iron-copper alloy rich in rare earth elements;

[0010] S3, rapid quenching treatment of the rare earth-rich rare earth-iron-copper alloy described in S2 to obtain a rapid quenching band with an average grain size of nanometers.

[0011] S4, secondary annealing of the rapid quenching zone described in S3, yields a main phase grain of Sm2Fe. 17 or NdFe 12 A fast-quenching zone with a main phase grain size of 1-5 μm and rich in rare earth-Cu grain boundary phases;

[0012] S5, hydrogen explosion crushing of the rapidly quenched strip after secondary annealing of S4 to obtain intergranular fragmented particles;

[0013] S6, nitriding treatment is performed on the particles after S5 hydrogen explosion crushing;

[0014] S7, the particles after S6 nitriding treatment are finely ground and crushed to obtain anisotropic rare earth iron nitrogen magnetic powder with an average particle size of 1-5 μm.

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

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

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

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

[0019] Furthermore, the specific conditions for the secondary annealing in S4 are: annealing temperature of 800–850℃, vacuum degree ≤3×10⁻³ Pa, and annealing time of 1–3 hours; preferably, the microstructure of the rapid quenching zone after secondary annealing consists of Sm₂Fe with a grain size of 1–5 μm. 17 or NdFe 12 The microstructure consists of a main phase grain and a grain boundary phase rich in Sm-Cu or Nd-Cu. This microstructure makes the magnetic powder more magnetic and provides conditions for subsequent hydrogen explosion crushing to be intergranular crushing. More preferably, the grain size of the main phase grain is 3 to 4 μm.

[0020] Furthermore, the specific steps of the S5 hydrogen explosion crushing are as follows: heating the rapid quenching strip to 200-300°C and holding it for 2 hours under hydrogen conditions of 0.05-2 atm; preferably, the specific steps of the S5 hydrogen explosion crushing are as follows: heating the rapid quenching strip to 250°C under hydrogen conditions of 1 atm; through hydrogen explosion crushing, intergranular crushed particles are obtained, avoiding the sharp points or other defects formed by traditional transgranular crushing, thereby improving the final magnetic properties.

[0021] Further, the nitriding temperature in S6 is 400-600℃, and the nitriding time is 4-15 hours; preferably, the process before nitriding includes coarse crushing, that is, crushing the particles after hydrogen explosion to particles with a particle size of 20-150μm; more preferably, the coarse crushing process is to crush the particles after hydrogen explosion to particles with a particle size of 100μm.

[0022] Furthermore, the fine grinding in S7 can be selected from either air jet milling or ball milling; preferably, when ball milling is used, the ball-to-material ratio is 10:1.

[0023] The method for preparing high-performance anisotropic rare-earth iron-nitrogen magnetic powder provided by the embodiments of this application has at least the following beneficial effects:

[0024] This application precisely controls the main phase grain size to 1-5 μm by adding a specific amount of Cu in the composition design and combining rapid quenching and two annealing processes. At the same time, it forms a grain boundary phase rich in rare earth-Cu, so that the subsequent hydrogen explosion crushing is mainly intergranular crushing. Compared with traditional transgranular crushing, intergranular crushing basically avoids the generation of sharp points and other defects, thereby significantly improving the magnetic properties of the final magnetic powder.

[0025] Through the synergistic effect of each step, this application finally prepares anisotropic rare earth iron-nitrogen magnetic powder with a particle size of 1-5 μm, few surface defects, and a near-spherical morphology. This magnetic powder has high remanence, coercivity, and magnetic energy product, which can meet the stringent requirements of miniaturization and high performance of micromotors for magnetic materials and has significant advantages in practical applications. Attached Figure Description

[0026] Figure 1 The image shown is a scanning electron microscope (SEM) image of the rapidly quenched strip obtained after secondary annealing in Example 1.

[0027] Figure 2 The image shows a scanning electron microscope (SEM) image of the anisotropic magnetic powder obtained in Example 1.

[0028] Figure 3 The magnetic property curves of the anisotropic magnetic powder prepared in Example 1 are shown. Detailed Implementation

[0029] The present application will now be further described based on preferred embodiments and with reference to the accompanying drawings.

[0030] Example 1

[0031] (1) Rapid solidification smelting: Weigh high-purity iron, samarium, and copper, and smelt them according to the chemical atomic ratio Sm 2.1 Fe 16.9 Cu 0.1 The raw materials were batched according to the corresponding burn-off amount, and then placed in a rapid solidification furnace for melting. A chemical atomic ratio of Sm was prepared under a wheel speed of 4 m / s. 2.1 Fe 16.9 Cu 0.1 Quick-setting tablets;

[0032] (2) First annealing treatment: The quick-setting sheets obtained in step (1) are placed in an annealing furnace and annealed for 24 hours at 1050℃ and a vacuum degree ≤3×10-3Pa to obtain samarium-rich Sm 2.1 Fe 16.9 Cu 0.1 Quick-setting tablets;

[0033] (3) Rapid quenching treatment: The rapidly solidified wafers after annealing in step (2) are placed in a rapid quenching device and subjected to rapid quenching treatment at a wheel speed of 30 m / s to obtain Sm with an average grain size of 100 nm. 2.1 Fe 16.9 Cu 0.1 Rapid quenching belt;

[0034] (4) Secondary annealing treatment: The rapidly quenched strip obtained in step (3) is annealed at 800℃ and under a vacuum degree ≤3×10-3Pa for 2 hours. Figure 1 The image shows a scanning electron microscope (SEM) image of the rapidly quenched zone after annealing. It can be seen from the image that Sm2Fe was obtained. 17 The main phase grains are about 2.5 μm and the fast quenching zone is rich in Sm-Cu grain boundary phase;

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

[0036] (6) Nitriding treatment: The particles obtained from the hydrogen explosion 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℃ for 15 hours to obtain Sm 2.1 Fe 16.9 Cu 0.1 N3;

[0037] (7) Fine grinding and crushing: Under the condition of a ball-to-material ratio of 10:1, a ball mill is used to grind the Sm after nitriding in step (6). 2.1 Fe 16.9 Cu 0.1 N3 particles were ball-milled to an average particle size of 2.5 micrometers to obtain high-performance anisotropic magnetic powder, the scanning electron microscope image of which is shown below. Figure 2 As shown.

[0038] Magnetic property testing:

[0039] The anisotropic magnetic powder, adhesive, and hardener obtained in Example 1 are uniformly mixed in a mass ratio of 2:3:1. Specifically, the powder and adhesive can be mixed first, and then the mixed colloid and hardener can be mixed evenly. The uniformly mixed colloid is placed into a cylindrical hole in a special alignment plate (such as non-magnetic PVC material), and a baffle is used to cover the back of the hole to prevent the colloid from leaking. A magnetic field of 1.5T is applied to the alignment plate using an electromagnet for more than 1 hour, and the mixed colloid is allowed to solidify. The solidified alignment column is removed from the alignment plate to complete the preparation of the magnetic alignment sample for magnetic property measurement.

[0040] The remanence, coercivity, and magnetic energy product of the magnetically oriented sample from Example 1 were measured using a vibrating sample magnetometer. Figure 3 The magnetic properties curves of the magnetic powder are 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) Weigh out high-purity iron, neodymium, and copper according to the chemical atomic ratio Nd 1.1 Fe 11.9 Cu 0.1 The raw materials were batched according to the corresponding burn-off amount, and then placed in a rapid solidification furnace for melting. Under a wheel speed of 3 m / s, Nd2O3 with a chemical atomic ratio of 1000 Nd2O3 was prepared. 1.1 Fe 11.9 Cu 0.1 Quick-setting tablets;

[0043] (2) The rapid-setting sheet obtained in step (1) is placed in an annealing furnace and annealed for 48 hours at 1050℃ and a vacuum degree ≤3×10-3Pa to obtain Nd2-rich Nd2. 1.1 Fe 11.9 Cu 0.1 Quick-setting tablets;

[0044] (3) The rapidly solidified sheet after annealing in step (2) is placed in a rapid quenching equipment and subjected to rapid quenching at a wheel speed of 40 m / s to obtain Nd with an average grain size of 100 nm. 1.1 Fe 11.9 Cu 0.1 Rapid quenching belt;

[0045] (4) The rapidly quenched strip obtained in step (3) is annealed at 820℃ and under a vacuum degree ≤3×10-3Pa for 2 hours to obtain NdFe. 12 The fast quenching zone has a main phase grain size of about 4 μm and is rich in Nd-Cu grain boundary phase;

[0046] (5) Place the quenched strip after the second annealing in step (4) into a reaction vessel filled with 1 atm of hydrogen gas, heat it to 250°C and maintain it for 2 hours to perform hydrogen explosion crushing on the quenched strip. During this process, the quenched strip absorbs hydrogen gas and expands. Due to the different degrees of hydrogen absorption and expansion between the main phase and the grain boundary phase, internal stress is generated, thereby achieving intergranular crushing and finally obtaining intergranular crushed Nd. 1.1 Fe 11.9 Cu 0.1 Particles;

[0047] (6) The particles obtained from the hydrogen explosion 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 550℃ for 5 hours to obtain Nd. 1.1 Fe 11.9 Cu 0.1 N;

[0048] (7) Under the condition of a ball-to-material ratio of 10:1, the Nd nitrided in step (6) is processed by a ball mill. 1.1 Fe 11.9 Cu 0.1 N particles were ball-milled to an average particle size of 4 micrometers to obtain high-performance anisotropic Nd2. 1.1 Fe 11.9 Cu 0.1 N magnetic powder.

[0049] The anisotropic Nd2 of Example 2 was tested according to the detection method in Example 1. 1.1 Fe 11.9 Cu 0.1 The magnetic orientation of N magnetic powder was determined, and the Nd obtained in Example 2 was analyzed using a vibrating sample magnetometer. 1.1 Fe 11.9 Cu 0.1 The remanence, coercivity, and energy product of the N magnetic powder were measured, and the results were: remanence Mr = 120 emu / g, coercivity iHc = 5300 Oe, and energy product (BH)max = 20 MGOe.

[0050] Example 3

[0051] (1) Weigh out high-purity iron, neodymium, and copper according to the chemical atomic ratio Nd 1.1 Fe 11.94 Cu 0.06 The raw materials were batched according to the corresponding burn-off amount, and then placed in a rapid solidification furnace for melting. Under a wheel speed of 5 m / s, Nd2O3 with a chemical atomic ratio of 0.5% was obtained. 1.1 Fe 11.94 Cu 0.06 Quick-setting tablets;

[0052] (2) The rapid-setting sheet obtained in step (1) is placed in an annealing furnace and annealed for 24 hours at 1080℃ and a vacuum degree ≤3×10-3Pa to obtain Nd2-rich Nd2. 1.1 Fe 11.94 Cu 0.06 Quick-setting tablets;

[0053] (3) The rapidly solidified sheet after annealing in step (2) is placed in a rapid quenching equipment and subjected to rapid quenching at a wheel speed of 45 m / s to obtain Nd with an average grain size of 100 nm. 1.1 Fe 11.94 Cu 0.06 Rapid quenching belt;

[0054] (4) The rapidly quenched strip obtained in step (3) is subjected to a vacuum of ≤3×10 at 800℃. -3 Annealing at Pa for 1.5 hours yielded NdFe. 12 The fast quenching zone has a main phase grain size of about 2μm and is rich in Nd-Cu grain boundary phase;

[0055] (5) Place the quenched strip after the second annealing in step (4) into a reaction vessel filled with 1 atm of hydrogen gas, heat it to 250°C and maintain it for 2 hours to perform hydrogen explosion crushing on the quenched strip. During this process, the quenched strip absorbs hydrogen gas and expands. Due to the different degrees of hydrogen absorption and expansion between the main phase and the grain boundary phase, internal stress is generated, thereby achieving intergranular crushing and finally obtaining intergranular crushed Nd. 1.1 Fe 11.94 Cu 0.06 Particles;

[0056] (6) The particles obtained from the hydrogen explosion 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 560℃ for 4 hours 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, the Nd nitrided in step (6) is processed by a ball mill. 1.1 Fe 11.94 Cu 0.06 N particles were ball-milled to an average particle size of 2 micrometers to obtain high-performance anisotropic Nd2 particles. 1.1 Fe 11.94 Cu 0.06 N magnetic powder.

[0058] The anisotropic Nd2O3 of Example 3 was tested according to the detection method in Example 1. 1.1 Fe 11.94 Cu 0.06 The magnetic orientation of N magnetic powder was determined, and the Nd obtained in Example 3 was analyzed using a vibrating sample magnetometer.1.1 Fe 11.94 Cu 0.06 The remanence, coercivity, and energy product of the N magnetic powder were measured, and the results were: remanence Mr = 122 emu / g, coercivity iHc = 5000 Oe, and energy product (BH)max = 21 MGOe.

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

Claims

1. A method for preparing high-performance anisotropic rare-earth iron-nitrogen magnetic powder, characterized in that, Specifically, the following steps are included: S1, rare earth-iron-copper alloy quick-solidification sheets are prepared by quick-solidification smelting; S2, annealing the rapid solidification sheet described in S1 once to obtain a rare earth-rich rare earth-iron-copper alloy; The specific conditions for the first annealing in S2 are: annealing temperature 1000~1100℃, vacuum degree ≤3×10 -3 Pa, annealing time is 24~48 hours; S3, rapid quenching of the rare earth-rich rare earth-iron-copper alloy described in S2 to obtain a rapid quenching band with an average grain size of nanometers. S4, the rapid quenching zone described in the secondary annealing treatment S3, yields a rapid quenching zone with a main phase grain size of 1~5μm and rich in rare earth-Cu grain boundary phase; The specific conditions for the secondary annealing in S4 are: annealing temperature 800~850℃, vacuum degree ≤3×10 -3 Pa, annealing time is 1~3 hours; S5, hydrogen explosion crushing of the rapidly quenched strip after secondary annealing of S4 to obtain intergranular fragmented particles; S6, nitriding treatment is performed on the particles after S5 hydrogen explosion crushing; S7, the particles after S6 nitriding are finely ground and crushed to obtain anisotropic rare earth iron nitrogen magnetic powder with an average particle size of 1~5μm. The rare earth element in the rare earth-iron-copper alloy is Sm. 2.1 Fe 17-x Cu x or Nd 1.1 Fe 12-x Cu x And 0.05≤x≤0.

1.

2. The method for preparing high-performance anisotropic rare earth iron-nitrogen magnetic powder according to claim 1, characterized in that, The main phase grains are Sm2Fe. 17 or NdFe 12 .

3. The method for preparing high-performance anisotropic rare earth iron-nitrogen magnetic powder according to claim 1, characterized in that, The wheel speed for the S1 medium-speed solidification smelting is 2~5m / s.

4. The method for preparing high-performance anisotropic rare earth iron-nitrogen magnetic powder according to claim 1, characterized in that, The average grain size of the rapid quenching band obtained in S3 is 100~200nm; And / or, the wheel speed in the rapid quenching process in S3 is 30~50m / s.

5. The method for preparing high-performance anisotropic rare earth iron-nitrogen magnetic powder according to claim 1, characterized in that, The specific steps of hydrogen explosion crushing in S5 are as follows: under hydrogen conditions of 0.05~2 atm, the rapid quenching strip is heated to 200-300℃ and held for 2 hours.

6. The method for preparing high-performance anisotropic rare earth iron-nitrogen magnetic powder according to claim 1, characterized in that, The nitriding temperature in S6 is 400~600℃, and the nitriding time is 4~15 hours.

7. The method for preparing high-performance anisotropic rare earth iron-nitrogen magnetic powder according to claim 6, characterized in that, The S6 nitriding process also includes coarse crushing, which involves crushing the hydrogen-exploded particles into particles with a diameter of 20~150μm.

8. The method for preparing high-performance anisotropic rare earth iron-nitrogen magnetic powder according to claim 1, characterized in that, The fine grinding process in S7 is selected from either air jet milling or ball milling.

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