Ferrite neodymium iron boron composite magnetic material and preparation method thereof

Abstract

The invention relates to the technical field of magnetic materials, in particular to a ferrite neodymium iron boron composite magnetic material and a preparation method thereof. The ferrite neodymium iron boron composite magnetic material comprises the following raw materials in parts by weight: 20-30 parts of ferrite magnetic powder, 40-50 parts of neodymium iron boron magnetic powder, 5-10 parts of silicon dioxide, 2-5 parts of carbon nanotubes, 0.5-1 part of polyethylene and 0.5-2 parts of polyimide. The high-temperature-resistant and corrosion-resistant permanent magnet has high magnet performance and also has high-temperature-resistant performance and corrosion-resistant performance.

Description

Technical Field

[0001] The present invention relates to the technical field of magnetic materials, and particularly to a ferrite neodymium iron boron composite magnetic material and a preparation method thereof. Background Art

[0002] Neodymium iron boron magnetic materials are known as the "magnetic king" due to their excellent magnetic properties. Neodymium iron boron magnetic materials are alloys of neodymium, iron oxide, etc., also known as magnet steels. Neodymium iron boron has extremely high magnetic energy product and coercivity, and the advantage of high energy density enables neodymium iron boron permanent magnetic materials to be widely used in modern industry and electronic technology, thus making it possible to miniaturize, lighten, and thin devices such as instruments, electroacoustic motors, magnetic separation and magnetization. The advantages of neodymium iron boron are high cost performance and good mechanical properties; the disadvantages are low Curie temperature point, poor temperature characteristics, and easy to powder and corrode. It must be improved by adjusting its chemical composition and adopting surface treatment methods to meet the requirements of practical applications. Ferrite is a ferromagnetic metal oxide. In terms of electrical properties, the resistivity of ferrite is much larger than that of metal and alloy magnetic materials, and it also has higher dielectric properties. The magnetic properties of ferrite also show higher magnetic permeability at high frequencies. Therefore, ferrite has become a widely used non-metallic magnetic material in the field of high-frequency weak electricity. Due to the low magnetic energy stored per unit volume of ferrite and the low saturation magnetization intensity, its application in low-frequency strong electricity and high-power fields requiring higher magnetic energy density is limited.

[0003] In the prior art, by compounding ferrite and neodymium iron boron magnetic powder, a high-cost-performance ferrite neodymium iron boron magnetic material is prepared. However, the magnetic energy product, high-temperature resistance and corrosion resistance of the ferrite neodymium iron boron magnetic material prepared by the prior art are poor. Summary of the Invention

[0004] Aiming at the deficiencies of the above prior art, the purpose of the present invention is to provide a ferrite neodymium iron boron composite magnetic material which has high magnetic properties while having high-temperature resistance and corrosion resistance.

[0005] The above technical purpose of the present invention is achieved by the following technical solutions: A ferrite neodymium iron boron composite magnetic material, which comprises the following raw materials in parts by weight: 20-30 parts of ferrite magnetic powder, 40-50 parts of neodymium iron boron magnetic powder, 5-10 parts of silicon dioxide, 2-5 parts of carbon nanotubes, 0.5-1 part of polyethylene, and 0.5-2 parts of polyimide.

[0006] By precisely controlling the ratio of ferrite magnetic powder (20 - 30 parts) to neodymium iron boron magnetic powder (40 - 50 parts) and adding carbon nanotubes (2 - 5 parts), the present invention can effectively enhance the magnetic flux density and coercivity inside the material, thereby significantly improving the magnetic energy product of the final product. The high electrical conductivity and mechanical strength of carbon nanotubes contribute to the formation of a more efficient magnetic circuit, further optimizing the magnetic properties. Adding polyimide (0.5 - 2 parts) as an adhesive makes the prepared magnetic material have a stable structure. Polyimide can also be used as a heat-resistant additive. Utilizing its excellent thermal stability, without sacrificing other properties, it greatly improves the high-temperature resistance of the composite material. Polyimide can maintain good mechanical strength and dimensional stability under high-temperature conditions, making this composite magnetic material suitable for application environments within a wider temperature range. The combined use of silica (5 - 10 parts) and polyethylene (0.5 - 1 part) not only helps to fill and seal the micropores on the material surface, reducing the intrusion path of external corrosive media, but also provides an additional protective layer, thus effectively enhancing the corrosion resistance of the composite material. This makes the magnetic material have better durability in humid or corrosive environments.

[0007] In summary, the ferrite neodymium iron boron composite magnetic material of the present invention, by reasonably selecting and proportioning each component, overcomes the problems of insufficient magnetic energy product, high-temperature resistance, and corrosion resistance in the prior art, achieves the goals of high performance and low cost, and has important industrial application value.

[0008] Among them, the particle size of the ferrite magnetic powder is 200 - 300 nm. The smaller particle size of the ferrite magnetic powder helps to increase the specific surface area inside the material, thereby improving the magnetic permeability and coercivity of the magnetic material. This helps to enhance the overall magnetic energy product of the final composite material. The nanoscale particle size can be more evenly dispersed in the composite material, reducing the agglomeration phenomenon, making the internal structure of the material more uniform, and being beneficial to improving the mechanical strength and stability of the material.

[0009] Among them, the particle size of the neodymium iron boron magnetic powder is 500 - 1000 nm. Selecting an appropriately larger particle size of the neodymium iron boron magnetic powder (compared with the ferrite magnetic powder) can maintain good mechanical processing performance while ensuring a sufficiently high remanence and maximum magnetic energy product. This is because although too small a particle size can increase the surface activity, it may also cause the material to become too fragile. The appropriate particle size helps to form an efficient magnetic flux path, ensuring the effective conduction of the magnetic field, which is crucial for improving the magnetic properties of the composite material.

[0010] Among them, the particle size of the silica is 20 - 50 nm. Nanoscale silica particles can effectively fill the micro-pores in the material, providing a dense protective layer, thus significantly enhancing the corrosion resistance of the composite material. This tiny particle size allows it to better cover the surface of the substrate, reducing the intrusion path of the corrosive medium. Adding an appropriate amount of silica with a small particle size can also play a toughening role, improving the hardness and wear resistance of the composite material through the dispersion strengthening mechanism, while not overly affecting the flexibility of the material. Silica itself has good high-temperature resistance, and its nanoscale form can further enhance the stability and durability of the composite material at high temperatures.

[0011] In summary, by precisely controlling the particle sizes of the ferrite magnetic powder, neodymium iron boron magnetic powder, and silica, the magnetic properties, mechanical properties, corrosion resistance, and heat resistance of the composite magnetic material can be effectively improved, achieving the best balance between high performance and cost-effectiveness.

[0012] The second object of the present invention is to provide a preparation method of the above-mentioned ferrite neodymium iron boron composite magnetic material, which includes the following preparation steps:

[0013] Step 1: Mix polyethylene, carbon nanotubes, and silica, and perform ball milling for 2 - 3 h to obtain mixture A;

[0014] Step 2: Mix mixture A with ferrite magnetic powder, neodymium iron boron magnetic powder, and polyimide, first stir, and then perform ball milling to obtain mixture B;

[0015] Step 3: Perform vibration treatment on mixture B to obtain mixed powder;

[0016] Step 4: Place the mixed powder under the protection of an inert gas, orient and shape it in a magnetic field, and then perform static pressure forming to obtain a magnet blank;

[0017] Step 5: Sinter the magnet blank in an oxygen atmosphere, and then naturally cool it to obtain the ferrite neodymium iron boron composite magnetic material.

[0018] By initially mixing polyethylene, carbon nanotubes, and silica and performing ball milling for 2 - 3 hours, the present invention helps to achieve a good dispersion state among these components, especially effectively dispersing carbon nanotubes and preventing their agglomeration, thus providing a uniform base material for subsequent steps. The ball milling process not only realizes physical refinement but also promotes the surface interaction between different materials, increasing the contact area between components and being beneficial to improving the interfacial bonding strength between phases in the final composite material.

[0019] After adding ferrite magnetic powder, neodymium iron boron magnetic powder and polyimide to the mixture A, stirring and ball milling are carried out again to ensure that all raw materials can be more evenly distributed, which can guarantee the consistency of the internal structure and magnetic properties of the composite material. Step two helps to form a tighter and more uniform microstructure, making the final product have better mechanical strength, thermal stability and magnetic properties.

[0020] Step three can help remove tiny impurities and air bubbles in the mixed powder through vibration treatment, make the powder more dense, reduce defects in the finished product, and improve the overall density of the material. During the vibration process, the powders in different particle size ranges collide and squeeze with each other, and small particle substances enter the gaps between large particles, forming a magnetic material with higher density, reducing the voids between the prepared materials, which is beneficial to improving the corrosion resistance and high-temperature resistance of the magnetic material. The mixed powder after vibration treatment is more likely to form a high-quality shape during the subsequent pressing process, improving the dimensional accuracy and appearance quality of the product.

[0021] Orienting and shaping the mixed powder under the protection of inert gas and in a magnetic field can make the magnetic particles align along the magnetic field direction, greatly improving the remanence and maximum magnetic energy product of the composite material, and significantly enhancing its magnetic properties. Using an inert gas (such as argon) for protection can prevent the magnetic material from being oxidized during the forming process and maintain its original characteristics and properties.

[0022] Sintering in an oxygen atmosphere can promote necessary chemical reactions or vitrification transitions of certain components (such as polyimide or silica), thereby enhancing the structural stability of the composite material and its high-temperature resistance, corrosion resistance and other characteristics. By controlling the sintering temperature and time, the grain size and distribution of magnetic particles can be precisely regulated, and then the magnetic properties of the material can be optimized. Natural cooling helps to reduce the internal stress caused by rapid cooling and ensure the quality of the finished product.

[0023] In summary, this preparation method effectively overcomes the problems of low magnetic energy product, poor high-temperature resistance and corrosion resistance in the existing technology, and manufactures a high-performance ferrite neodymium iron boron composite magnetic material, which is suitable for a wider range of application scenarios.

[0024] Among them, in step one, the ball milling speed is 300 - 500 rpm, and the ball-to-material ratio is 1 - 10:1.

[0025] In the first step of the present invention, by selecting a ball milling speed of 300 - 500 rpm, it is possible to ensure effective pulverization and mixing while avoiding excessive wear and unnecessary energy consumption caused by too high a speed. This medium - range speed helps to maintain an appropriate collision frequency and impact force, promoting the uniform dispersion among polyethylene, carbon nanotubes, and silica. An appropriate ball milling speed can help achieve a finer particle size distribution and contribute to breaking up agglomerates, especially for materials like carbon nanotubes that are prone to agglomeration, facilitating their better dispersion in the matrix and thus enhancing the overall performance of the final composite material.

[0026] In summary, adopting a ball milling speed of 300 - 500 rpm and a ball - to - material ratio of 1 - 10:1 in the first step can effectively optimize the energy utilization efficiency during the preparation process, reduce unnecessary losses, and significantly improve the comprehensive performance of the final neodymium - iron - boron ferrite composite magnetic material, including but not limited to magnetic properties, mechanical strength, and durability.

[0027] Among them, in the second step, the stirring speed is 200 - 300 rpm and the stirring time is 1 - 2 h; and / or, in the second step, the ball milling speed is 300 - 600 rpm, the ball - to - material ratio is 7 - 10:1, and the ball milling time is 2 - 3 h.

[0028] The present invention uses a stirring speed of 200 - 300 rpm to ensure the preliminary uniform mixing between mixture A, ferrite magnetic powder, neodymium - iron - boron magnetic powder, and polyimide. Stirring within this speed range can provide sufficient shear force to break up possible agglomerates, especially for nanoscale materials (such as silica and carbon nanotubes), facilitating their uniform distribution in the composite system.

[0029] The stirring speed (200 - 300 rpm) of the present invention can prevent mechanical damage to polyimide or magnetic powder, while ensuring sufficient mixing time (1 - 2 hours), enabling all components to be in full contact and interact with each other for a long time, promoting a better dispersion effect during the subsequent ball milling process. By appropriate stirring speed and time, the interfacial bonding between different components can be enhanced, laying a foundation for the subsequent formation of a composite material with a good internal structure, thereby improving the performance of the final product.

[0030] Selecting a ball milling speed of 300 - 600 rpm and a ball - to - material ratio of 7 - 10:1 can ensure effective pulverization and refinement while ensuring that all raw materials are fully ground and mixed. After 2 - 3 hours of ball milling treatment, a denser and more uniform microstructure can be obtained, which is beneficial to improving the mechanical strength and magnetic properties of the composite material. Especially for materials containing multiple different characteristics (such as magnetic powder and polymer), good dispersion and a tight structure are the basis for achieving high performance.

[0031] In summary, the jointly acting stirring speed, stirring time, and ball milling conditions set in Step 2 can effectively optimize the mixing quality among the components, improve the overall performance of the composite material, including but not limited to enhancing its magnetic properties, mechanical strength, durability, and chemical stability, etc., while also taking into account the requirements of production efficiency and cost control.

[0032] Among them, in Step 3, the vibration frequency is 300 - 500 Hz, and the vibration lasts for 1 - 2 h.

[0033] Among them, in Step 4, the magnetic field strength is 1 - 3 T, and the pressure for static pressure forming is 600 - 700 MPa.

[0034] Among them, in Step 5, the sintering temperature is 900 - 1000 °C.

[0035] The beneficial effects of the present invention are as follows:

[0036] The ferrite neodymium iron boron composite magnetic material of the present invention, by reasonably selecting and proportioning each component, overcomes the problems of insufficient magnetic energy product, high temperature resistance, and corrosion resistance in the prior art, realizes the goal of high performance and low cost, and has important industrial application value. Specific Embodiments

[0037] In order to make the technical problems, technical solutions, and beneficial effects to be solved by the present invention more clear and understandable, the present invention will be further described in detail below in conjunction with embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0038] Example 1

[0039] A preparation method of a ferrite neodymium iron boron composite magnetic material, which includes the following preparation steps:

[0040] Step 1: By weight, 0.5 part of low-density polyethylene, 2 parts of carbon nanotubes, and 5 parts of silicon dioxide are mixed, and ball milled for 2 h at 300 rpm with a ball-to-material ratio of 1:1 to obtain mixture A; among them, the particle size of silicon dioxide is 50 nm.

[0041] Step 2: Mixture A is mixed with 20 parts of ferrite magnetic powder, 40 parts of neodymium iron boron magnetic powder, and 0.5 part of polyimide adhesive. First, stir at a stirring speed of 200 rpm for 1 h, and then ball mill at a ball mill speed of 300 rpm with a ball-to-material ratio of 7:1 for 2 h to obtain mixture B; among them, the particle size of ferrite magnetic powder is 300 nm, and the particle size of neodymium iron boron magnetic powder is 1000 nm.

[0042] Step 3: Vibration treatment is performed on mixture B with a vibration frequency of 300 Hz for 2 h to obtain mixed powder;

[0043] Step 4: Under the protection of an inert gas, place the mixed powder in a magnetic field with a magnetic field strength of 1 T for orientation and shaping, and then perform static pressure forming. The pressure of the static pressure forming is 600 MPa to obtain a magnet blank.

[0044] Step 5: Sinter the magnet blank in an oxygen atmosphere at a sintering temperature of 900 °C, and then naturally cool it to obtain the ferrite neodymium iron boron composite magnetic material.

[0045] Example 2

[0046] A preparation method of a ferrite neodymium iron boron composite magnetic material, which includes the following preparation steps:

[0047] Step 1: By weight, mix 0.75 parts of low-density polyethylene, 3.5 parts of carbon nanotubes, and 7.5 parts of silicon dioxide, and perform ball milling treatment for 2.5 h at 400 rpm with a ball-to-material ratio of 5:1 to obtain mixture A; among them, the particle size of the silicon dioxide is 35 nm.

[0048] Step 2: Mix mixture A with 25 parts of ferrite magnetic powder, 45 parts of neodymium iron boron magnetic powder, and 1.2 parts of polyimide adhesive. First, stir at a stirring speed of 250 rpm for 1.5 h, and then perform ball milling at a ball milling speed of 450 rpm with a ball-to-material ratio of 8.5:1 for 2.5 h to obtain mixture B; among them, the particle size of the ferrite magnetic powder is 250 nm, and the particle size of the neodymium iron boron magnetic powder is 750 nm.

[0049] Step 3: Perform vibration treatment on mixture B at a vibration frequency of 400 Hz for 1.5 h to obtain the mixed powder.

[0050] Step 4: Under the protection of an inert gas, place the mixed powder in a magnetic field with a magnetic field strength of 2 T for orientation and shaping, and then perform static pressure forming. The pressure of the static pressure forming is 650 MPa to obtain a magnet blank.

[0051] Step 5: Sinter the magnet blank in an oxygen atmosphere at a sintering temperature of 950 °C, and then naturally cool it to obtain the ferrite neodymium iron boron composite magnetic material.

[0052] Example 3

[0053] A preparation method of a ferrite neodymium iron boron composite magnetic material, which includes the following preparation steps:

[0054] Step 1: By weight, mix 1 part of low-density polyethylene, 5 parts of carbon nanotubes, and 10 parts of silicon dioxide, and perform ball milling treatment for 3 h at 500 rpm with a ball-to-material ratio of 10:1 to obtain mixture A; among them, the particle size of the silicon dioxide is 20 nm.

[0055] Step 2: Mix mixture A with 30 parts of ferrite magnetic powder, 50 parts of neodymium iron boron magnetic powder, and 2 parts of polyimide adhesive. First, stir at a speed of 300 rpm for 2 hours, and then perform ball milling at a rotational speed of 600 rpm with a ball-to-material ratio of 10:1 for 3 hours to obtain mixture B. Among them, the particle size of the ferrite magnetic powder is 200 nm, and the particle size of the neodymium iron boron magnetic powder is 500 nm.

[0056] Step 3: Subject mixture B to vibration treatment at a vibration frequency of 500 Hz for 2 hours to obtain mixed powder.

[0057] Step 4: Under the protection of an inert gas, place the mixed powder in a magnetic field with a magnetic field strength of 3 T for orientation and shaping, and then perform static pressure molding at a pressure of 700 MPa to obtain a magnet blank.

[0058] Step 5: Sinter the magnet blank in an oxygen atmosphere at a sintering temperature of 1000 °C, and then naturally cool it to obtain a ferrite neodymium iron boron composite magnetic material.

[0059] Comparative Example 1

[0060] The difference between Comparative Example 1 and Example 2 is that polyethylene was not added in Comparative Example 1, and the other preparation steps are the same as those in Example 2.

[0061] The differences between Comparative Examples 2 - 7 and Example 2 are that the particle sizes of silica, ferrite magnetic powder, and neodymium iron boron magnetic powder in Comparative Examples 2 - 7 are different from those in Example 2, and the other preparation steps are the same as those in Example 2. The powder particle sizes in Example 2 and Comparative Examples 2 - 7 are shown in Table 1.

[0062] Group Silica (nm) Ferrite magnetic powder (nm) NdFeB magnetic powder (nm) Example 2 35 250 750 Comparative Example 2 10 250 750 Comparative Example 3 60 250 750 Comparative Example 4 35 150 750 Comparative Example 5 35 350 750 Comparative Example 6 35 250 450 Comparative Example 7 35 250 1100

[0063] Comparative Example 8

[0064] The difference between Comparative Example 8 and Example 2 is that Comparative Example 8 does not include Step 3, that is, subjecting mixture B to vibration treatment at a vibration frequency of 300 - 500 Hz for 1 - 2 hours to obtain mixed powder. The other preparation steps of Comparative Example 8 are the same as those in Example 2 and will not be elaborated here.

[0065] Performance Test

[0066] Make the ferrite neodymium iron boron composite magnetic materials prepared in Examples 1 - 3 and Comparative Examples 1 - 8 into cylindrical magnets with a height of Φ250 mm × 25 mm, and conduct tests on the maximum magnetic energy product in accordance with GB / T13560 - 2017. The high-temperature resistance performance test is carried out by Kebiao Testing, and the corrosion resistance performance test is the corrosion rate caused by placing the test piece in concentrated sulfuric acid mist for the same time. The results are shown in Table 2:

[0067] Table 2:

[0068]

[0069] Table 1:

[0070]

[0071] It can be seen from the above test results that the ferrite neodymium iron boron composite magnetic material of the present invention has a high magnetic energy product, good high temperature resistance and corrosion resistance. By comparing Example 2 with Comparative Example 1, it can be seen that the addition of polyethylene can improve the magnetic energy product, high temperature resistance and corrosion resistance of the magnetic material. By comparing Example 2 with Comparative Examples 2-7, it can be seen that the selection of the particle size ranges of the silica, ferrite magnetic powder and neodymium iron boron magnetic powder of the present invention has a synergistic effect, and the magnetic energy product, high temperature resistance and corrosion resistance of the magnetic material can be effectively improved by selecting specific powder particle sizes. By comparing Example 2 with Comparative Example 8, it can be seen that the preparation method of the present invention, by vibrating the mixture of materials after mixing, is beneficial to improving the magnetic energy product, high temperature resistance and corrosion resistance of the magnetic material of the present invention.

[0072] The above embodiments are only explanations of the present invention, and they are not limitations of the present invention. Those skilled in the art can make modifications to these embodiments without creative contributions according to needs after reading this specification, but as long as they are within the scope of the claims of the present invention, they are protected by the patent law.

Claims

1. A ferrite neodymium iron boron composite magnetic material, characterized in that: The invention comprises the following raw materials in parts by weight: 20-30 parts of ferrite magnetic powder, 40-50 parts of neodymium iron boron magnetic powder, 5-10 parts of silicon dioxide, 2-5 parts of carbon nanotubes, 0.5-1 parts of polyethylene and 0.5-2 parts of polyimide.

2. The ferrite NdFeB composite magnetic material according to claim 1, characterized in that: The particle size of the ferrite magnetic powder is 200-300nm.

3. The ferrite NdFeB composite magnetic material according to claim 2, characterized in that: The particle size of the NdFeB magnetic powder is 500-1000nm.

4. The ferrite NdFeB composite magnetic material according to claim 3, characterized in that: The particle size of the silicon dioxide is 20-50 nm.

5. A method for preparing a ferrite NdFeB composite magnetic material according to any one of claims 1 to 4, characterized in that: The method comprises the following preparation steps: Step 1: Mix polyethylene, carbon nanotubes and silicon dioxide, and ball-mill for 2-3 hours to obtain a mixture A; Step 2: Mix the mixture A with ferrite magnetic powder, NdFeB magnetic powder and polyimide, stir them first, and then ball mill them to obtain a mixture B; Step 3, vibrating the mixture B to obtain a mixed powder; Step 4: Place the mixed powder in a magnetic field under the protection of an inert gas for orientation and shaping, and then statically press to obtain a magnet embryo; Step 5: Sintering the magnet embryo in an oxygen atmosphere, and then naturally cooling it to obtain a ferrite NdFeB composite magnetic material.

6. The method for preparing a ferrite NdFeB composite magnetic material according to claim 5, characterized in that: In step 1, the ball milling speed is 300-500 rpm, and the ball-to-material ratio is 1-10:

1.

7. The method for preparing a ferrite NdFeB composite magnetic material according to claim 5, characterized in that: In step 2, the stirring speed is 200-300 rpm, and the stirring is for 1-2 hours; and / or, in step 2, the ball milling speed is 300-600 rpm, the ball-to-material ratio is 7-10:1, and the ball milling is for 2-3 hours.

8. The method for preparing a ferrite NdFeB composite magnetic material according to claim 5, characterized in that: In step three, the vibration frequency is 300-500 Hz, and the vibration time is 1-2 hours.

9. The method for preparing a ferrite NdFeB composite magnetic material according to claim 5, characterized in that: In step 4, the magnetic field strength is 1-3T, and the static pressing pressure is 600-700MPa.

10. The method for preparing a ferrite NdFeB composite magnetic material according to claim 5, characterized in that: In step five, the sintering temperature is 900-1000°C.

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