A permanent magnet ferrite powder, its preparation method and its application

Abstract

This invention relates to a permanent magnet ferrite powder, its preparation method, and its application. The method includes the following steps: mixing an iron source with strontium carbonate raw material, followed by mixing, pre-calcination, and crushing to obtain the permanent magnet ferrite powder; the strontium carbonate raw material meets the following characteristics: a SrCO3 mass percentage of 95.0-97.5%; a SiO2 mass percentage of 0.5-2.5%; an average particle size of 3-8 μm; and the strontium carbonate particles have a spindle-shaped, olive-shaped, or spherical macroscopic morphology, with the ratio c / a of the particle's axial length c to its diagonal spacing a being less than 3. This method uses specific coarse-grained strontium carbonate raw material with high silica content, solving the technical problems of uneven raw material mixing and abnormal grain growth during sintering.

Description

Technical Field

[0001] This invention relates to the field of magnetic materials technology, and in particular to a permanent magnet ferrite powder, its preparation method, and its application. Background Technology

[0002] Traditional permanent magnet ferrite production technology requires that the purity of strontium carbonate must reach above 97% (SrCO3) (CN101989479B), and the average particle size must be below 2μm (such as CN 108285348 B, CN102924069A, etc.), or even higher, with a purity of above 98% (such as CN 112321292 A) in order for the comprehensive performance M value (remanence Br + intrinsic coercivity Hcj / 3) of the prepared permanent magnet ferrite magnet to reach the ideal range. Although existing technologies also suggest that 96.5% SrCO3 can be used to prepare permanent magnet ferrites, for example, CN 103626486 B discloses a strontium-calcium ferrite pre-sintered material and its preparation method. This invention provides a strontium-calcium ferrite pre-sintered material prepared from iron oxide (Fe2O3) and strontium carbonate as raw materials, and calcium carbonate, silicon dioxide, and activated alumina as additives; wherein the molar ratio of iron oxide to strontium carbonate is n=5.7~6.3. The raw material iron oxide contains TFe≥68.0%, Fe2O3≥98.0%, and SiO2<0.3%; the raw material strontium carbonate contains SrCO3>96.0%. However, its purpose is to lower the pre-calcination temperature, therefore it mainly focuses on secondary additives. Given the requirement of SiO2 < 0.3%, the total SrCO3 and BaO3 content of strontium carbonate must be high. While it doesn't specify the average particle size of strontium carbonate, based on common production technology knowledge, it can be assumed that the implicit production condition of an average particle size of strontium carbonate below 2μm still needs to be met. This is because traditional production technology considers that in actual production, low-purity, high-average-particle-size strontium carbonate is difficult to achieve the performance level of products made from high-quality strontium carbonate (i.e., strontium carbonate with a SrCO3 mass percentage higher than 97.5% and an average particle size less than 2μm) as raw material. Furthermore, SiO2 ≥ 0.5%, especially SiO2 ≥ 1%, is considered to have a disastrous impact on performance.

[0003] During our research and development process, our team discovered that most existing high-quality strontium carbonate has a needle-like or fine columnar morphology with an average particle size below 2 μm and a large specific surface area. Due to the high end stress, the needle-like or fine columnar morphology exhibits good activity during high-temperature solid-state reactions. However, during production, we occasionally encountered issues such as locally coarse crystal points on the cross-section of the pre-sintered spheres, affecting the final performance. This is likely because the needle-like or fine columnar morphology has poor flowability, easily forming clusters that are difficult to disperse, leading to overly active local solid-state reactions and abnormal grain growth, thus negating the advantages of high purity. Average particle size detection can easily reflect the clustering state. When the average particle size exceeds 1.5 μm, the performance of the resulting permanent magnet ferrite powder decreases significantly with increasing average strontium carbonate particle size, especially the intrinsic coercivity. This is why the average particle size of strontium carbonate is traditionally considered to be below 2 μm in permanent magnet ferrite production. Conversely, the difficulty in dispersing strontium carbonate with needle-like or fine columnar morphology may lead to high purity requirements during the production of permanent magnet ferrites. The total content of SrCO3 and BaO3 needs to reach above 98.5%, and SrCO3 needs to be above 97.5% to ensure the high performance and stability of the product.

[0004] Furthermore, as an important basic industrial raw material, strontium carbonate is undergoing industrial reform, leading to increasingly fierce competition in the procurement of high-purity, high-quality strontium carbonate. The permanent magnet ferrite industry is a major consumer of strontium carbonate. In order to broaden raw material channels, while ensuring that the magnetic properties meet current standards, it is necessary to develop a technology for preparing permanent magnet ferrites using coarse-grained strontium carbonate (purity above 95%, average particle size relaxed to above 2μm). Summary of the Invention

[0005] The purpose of this invention is to provide a method for preparing permanent magnet ferrite powder. This method uses strontium carbonate raw materials with specific coarse particles and high silica content, which solves the technical problems of uneven mixing of raw materials and abnormal grain growth during sintering.

[0006] The technical solution adopted by this invention to solve its technical problem is:

[0007] A method for preparing permanent magnet ferrite powder, the method comprising the following steps: mixing an iron source with strontium carbonate raw material, and obtaining the permanent magnet ferrite powder by mixing, pre-calcining and crushing; wherein the strontium carbonate raw material satisfies a combination of the following characteristics: (a) the mass percentage of SrCO3 is 95.0-97.5%; (b) the mass percentage of SiO2 is 0.5-2.5%; (c) the average particle size is 3-8 μm; and (d) the particles of the strontium carbonate raw material have a spindle-shaped, olive-shaped or spherical morphology.

[0008] In their production practice, the inventors discovered that even coarse-grained strontium carbonate (i.e., 95-97.5% SrCO3 by mass and an average particle size of 3-8 μm) with spindle-shaped, olive-shaped, or spherical morphologies can still produce high-performance permanent magnet ferrites. The reason for this is likely that these morphological characteristics improve the flowability of strontium carbonate, leading to more uniform mixing, better grain growth consistency, and more uniform crystal points on the cross-section of the pre-calcined material after sintering, thus improving overall performance. Although some individual grain agglomeration may occur, the small c / a ratio makes them less prone to interweaving, and the agglomerates are easily broken up during production.

[0009] During the research and development process, the inventors also discovered that when using the aforementioned coarse-grained strontium carbonate, the fluidity of the mixture significantly improved. During pre-calcination, the final temperature range was wider than that of higher-quality strontium carbonate, meaning that higher intrinsic coercivity could be obtained at lower temperatures, or higher remanence at higher temperatures. The permanent magnet ferrite powder obtained from this strontium carbonate raw material, as coarse powder, requires secondary batching in the later stages, followed by wet or dry pressing to obtain permanent magnet ferrite devices. The wider final temperature range indicates that the product performance can meet more diverse needs. During pre-calcination, the uniform crystallization of the spherical material cross-section indicates good uniformity of the high-temperature solid-phase reaction and good consistency in grain size, further proving the uniformity of the mixture.

[0010] This invention exhibits a high tolerance for SiO2 content in strontium carbonate raw materials, unlike existing technologies which require SiO2 mass percentages to be below 0.3% or 0.6%. Industrial strontium carbonate is primarily composed of elements such as strontium, barium, sulfur, calcium, and silicon. After the solid-state reaction, silicon is the main impurity affecting the performance of ferrite magnets; therefore, existing technologies often strictly control silicon content to achieve stable quality. However, in production practice, the inventors have found that even with a high silicon content (up to 1.88%), the coarse-grained strontium carbonate used does not damage remanence, and the performance of the resulting product still meets existing technological standards. This is likely because the coarse-grained strontium carbonate with this morphological characteristic is easier to disperse uniformly, resulting in a more uniform distribution of silicon at grain boundaries, while also limiting abnormal grain growth, which is beneficial for improving intrinsic properties.

[0011] Preferably, the molar ratio of the iron source to the strontium carbonate raw material, calculated as iron oxide and strontium carbonate, is n(Fe2O3):n(SrCO3) = 5.5-6.2.

[0012] Preferably, the particle size distribution D of the strontium carbonate raw material is... 50 The range is 3.5-10.0 μm.

[0013] Preferably, the ratio of the axial length c of the strontium carbonate raw material particles to the diagonal spacing a is less than 3.

[0014] Preferably, the average particle size of the strontium carbonate raw material is 4-7 μm.

[0015] Preferably, the pre-firing temperature is 1250-1340℃.

[0016] Preferably, the mixture is a dry ball milling mixture. After dry ball milling, the material is densified and pelletized, and then pre-fired. The pre-fired temperature is 1250-1320℃.

[0017] Preferably, the mixture is a wet ball milling mixture. After wet ball milling, the material is dehydrated and then pre-fired. The pre-fired temperature is 1250-1340℃.

[0018] The main purpose of dry ball milling and wet ball milling is to break up agglomerates, make the mixture uniform, and enable the iron source to contact the coarse strontium carbonate particles at the microscale, thereby increasing the reaction contact area. Although the mixing process is not significantly different from existing technologies, the mixing effect differs due to the completely different state of strontium carbonate.

[0019] Preferably, the iron source is iron oxide; the microstructure of the strontium carbonate raw material particles is spindle-shaped, consisting of an approximately hexagonal main body and conical portions at both ends of the main body.

[0020] Preferably, in the batching step, 0.01-0.6% silica is added, based on a total mass of 100% iron source and strontium carbonate. Similar to existing technologies, performance and shrinkage ratio can still be controlled by adding silica during the batching process.

[0021] A permanent magnet ferrite powder is prepared by the method described in this invention.

[0022] The application of the permanent magnet ferrite powder described in this invention in the preparation of sintered permanent magnet ferrite.

[0023] The beneficial effects of this invention are:

[0024] Existing technologies generally believe that fine-particle raw materials are necessary to ensure reactivity. However, the agglomeration of fine particles actually leads to abnormal grain growth, limiting the improvement of coercivity. This invention takes the opposite approach, using coarse-particle strontium carbonate with a specific morphology to fundamentally improve the uniformity of powder mixing, effectively suppressing abnormal grain growth during sintering. This results in a fine and uniformly distributed microstructure, thereby significantly improving the intrinsic coercivity (Hcj) of the product and breaking through the performance bottleneck of existing technologies.

[0025] This invention fundamentally solves the technical problems of uneven raw material mixing and abnormal grain growth during sintering. The invention creatively uses coarse-grained strontium carbonate with an average particle size of 3-8 μm and an axial length to diagonal spacing ratio (c / a) of less than 3. Its excellent dispersibility and flowability effectively avoid the problems associated with traditional ultrafine needle-like powders (such as...). Figure 3 (As shown) This addresses the agglomeration problem that easily occurs during dry or wet mixing, ensuring the uniformity of the microstructure of the pre-sintered material and the final sintered magnet.

[0026] Because the raw materials are mixed more uniformly and the reaction is more stable and controllable, the sensitivity of this invention to process parameters such as sintering temperature and holding time is significantly reduced. This means that in large-scale industrial production, even if the process parameters fluctuate to some extent, the product performance can remain highly stable, thereby improving product consistency and yield, and reducing scrap losses. Attached Figure Description

[0027] Figure 1 This is a scanning electron microscope (SEM) image of the strontium carbonate raw material used in Example 1 of the present invention;

[0028] Figure 2 yes Figure 1 The diagram shows a particle morphology model of strontium carbonate raw material. In the diagram, c is the axial length of the particle, which is the distance between the vertices of the two hexagonal pyramids, and a is the diagonal spacing between the bases of the hexagonal prism of the particle.

[0029] Figure 3 This is a scanning electron microscope (SEM) image of the conventional needle-shaped strontium carbonate raw material used in Comparative Example 1;

[0030] Figure 4 This is a comparison chart of the particle size distribution of the strontium carbonate raw material used in Example 1 and the strontium carbonate raw material used in Comparative Example 1. Detailed Implementation

[0031] The technical solution of the present invention will be further described in detail below through specific embodiments. It should be understood that the implementation of the present invention is not limited to the following embodiments, and any modifications and / or alterations made to the present invention will fall within the protection scope of the present invention.

[0032] In this invention, unless otherwise specified, all parts and percentages are by weight, and the equipment and raw materials used are commercially available or commonly used in the art. Unless otherwise specified, the methods in the following embodiments are conventional methods in the art.

[0033] Unless otherwise specified, the reagents used in the following examples can be purchased from a regular biochemical reagent store.

[0034] The technical specifications of the iron oxide used in the examples and comparative examples are shown in Table 1.

[0035] Table 1 Technical Indicators of Iron Red

[0036] Element Na2O MgO Al2O3 SiO2 [P4O6] SO3 Cl Content 0.025 0.015 0.076 0.092 0.015 0.007 0.142 Element CaO TiO2 Cr2O3 MnO Fe2O3 NiO Other Content 0.076 0.014 0.012 0.437 99.016 0.035 Balance

[0037] In the following embodiments, the average particle size (D) 50 The particle size was measured using a German Helos | RODOS laser particle size analyzer, in accordance with GB / T 19077.1-2024 Particle Size Analysis by Laser Diffraction.

[0038] Example 1

[0039] A method for preparing permanent magnet ferrite powder from coarse-particle strontium carbonate, the specific steps of which are as follows:

[0040] Iron oxide red and coarse strontium carbonate were mixed at a molar ratio of 5.81: strontium carbonate to iron oxide. 0.1% silica (by total mass of iron oxide red and strontium carbonate) was added. The mixture was then dry-milled for 15 minutes using a plow mill, followed by compaction for 30 minutes. The mixture was then pelletized and fed into a rotary kiln for pre-firing at 1310℃ for 2 hours. After cooling, the pellets were crushed and passed through a 50-mesh sieve to obtain permanent magnet ferrite powder.

[0041] The coarse-grained strontium carbonate has a SrCO3 mass percentage of 97%, a SiO2 mass percentage of 1.88%, an average particle size of 4.10 μm, and a c / a ratio of less than 3. Due to the presence of strontium carbonate particles of different sizes in the field of view, the c / a value cannot be determined as a specific value.

[0042] Microscopic (SEM) images and morphological model diagrams of coarse strontium carbonate particles are shown below. Figure 1 , Figure 2 As shown. According to Figure 1 It can be seen that the strontium carbonate raw material exhibits a spindle-shaped or olive-shaped morphology when observed under a scanning electron microscope, and its average particle size (D) is... 50 The particle size is 4-7 μm, and the ratio (c / a) of the axial length (c) of the particles to the diagonal spacing (a) is less than 3. The microstructural characteristics of the strontium carbonate raw materials in Examples 2-8 below all meet this condition.

[0043] The performance results of the prepared permanent magnet ferrite powder Hcj are shown in Table 2.

[0044] Example 2

[0045] A method for preparing permanent magnet ferrite powder from coarse-particle strontium carbonate, the specific steps of which are as follows:

[0046] Iron oxide red and coarse strontium carbonate were mixed at a molar ratio of 5.92 (iron oxide:strontium carbonate). Silica was added at a total mass of 0.2% (iron oxide red and strontium carbonate). The mixture was then dry-milled for 15 minutes using a plow mill, followed by ball milling for 30 minutes to densify the mixture. The resulting pellets were then fed into a rotary kiln for pre-firing at 1320℃ for 2 hours. After cooling, the pellets were crushed and passed through a 50-mesh sieve to obtain permanent magnet ferrite powder.

[0047] The coarse-grained strontium carbonate has a SrCO3 mass percentage of 97%, a SiO2 mass percentage of 1.52%, an average particle size of 4.98 μm, and a c / a ratio of less than 3.

[0048] Example 3

[0049] A method for preparing permanent magnet ferrite powder from coarse-particle strontium carbonate, the specific steps of which are as follows:

[0050] Iron oxide red and coarse strontium carbonate were mixed with silica in a molar ratio of 5.81 (iron oxide:strontium carbonate) using a plow mill for 15 minutes, followed by dry ball milling for 45 minutes to densify the mixture. The mixture was then pelletized and fed into a rotary kiln for pre-firing at 1310℃ for 2 hours. After cooling, the mixture was crushed and passed through a 50-mesh sieve to obtain permanent magnet ferrite powder.

[0051] The coarse-particle strontium carbonate has a SrCO3 mass percentage of 95.3%, a SiO2 mass percentage of 2.46%, an average particle size of 5.28 μm, and a c / a ratio of less than 3.

[0052] Example 4

[0053] A method for preparing permanent magnet ferrite powder from coarse-particle strontium carbonate, the specific steps of which are as follows:

[0054] Iron oxide red and coarse strontium carbonate were mixed at a molar ratio of 5.72 (iron oxide:strontium carbonate). Silica was added at a total mass of 0.1% (iron oxide red and strontium carbonate). The mixture was then dry-milled for 15 minutes using a plow mill, followed by ball milling for 60 minutes to densify the mixture. The resulting pellets were then fed into a rotary kiln and pre-fired at 1310℃ for 2 hours. After cooling, the pellets were crushed and passed through a 50-mesh sieve to obtain permanent magnet ferrite powder.

[0055] The coarse-particle strontium carbonate has a SrCO3 mass percentage of 96%, a SiO2 mass percentage of 1.88%, an average particle size of 5.33 μm, and a c / a ratio of less than 3.

[0056] Example 5

[0057] A method for preparing permanent magnet ferrite powder from coarse-particle strontium carbonate, the specific steps of which are as follows:

[0058] Iron oxide red and coarse strontium carbonate were mixed at a molar ratio of 5.81: strontium carbonate to iron oxide. 0.1% silica (by total mass of iron oxide red and strontium carbonate) was added. The mixture was then dry-milled for 15 minutes using a plow mill, followed by compaction for 30 minutes. The mixture was then pelletized and fed into a rotary kiln for pre-firing at 1310℃ for 2 hours. After cooling, the pellets were crushed and passed through a 50-mesh sieve to obtain permanent magnet ferrite powder.

[0059] The coarse-grained strontium carbonate has a SrCO3 mass percentage of 97.3%, a SiO2 mass percentage of 0.63%, an average particle size of 3.17 μm, and a c / a ratio of less than 3.

[0060] Example 6

[0061] A method for preparing permanent magnet ferrite powder from coarse-particle strontium carbonate, the specific steps of which are as follows:

[0062] Iron oxide red and coarse strontium carbonate were mixed at a molar ratio of 5.81: strontium carbonate to iron oxide, with an additional 0.1% of the total mass of iron oxide red and strontium carbonate added. After slurrying, the mixture was wet-milled and centrifuged to obtain a cake with a moisture content of 22%. The cake was then fed into a rotary kiln and pre-fired at 1330℃ for 2 hours. After cooling, crushing, and passing through a 50-mesh sieve, permanent magnet ferrite powder was obtained.

[0063] The coarse-grained strontium carbonate has a SrCO3 mass percentage of 97%, a SiO2 mass percentage of 1.88%, an average particle size of 5.28 μm, and a c / a ratio of less than 3.

[0064] Example 7

[0065] A method for preparing permanent magnet ferrite powder from coarse-particle strontium carbonate, the specific steps of which are as follows:

[0066] Iron oxide red and coarse strontium carbonate were mixed at a molar ratio of 5.81 (iron oxide:strontium carbonate). Silica was added at a total mass of 0.1% (iron oxide red and strontium carbonate). The mixture was then dry-milled for 15 minutes using a plow mill, followed by compaction for 30 minutes, pelletizing, and then pre-fired in a rotary kiln at 1250℃ for 2 hours. After cooling, the mixture was crushed and passed through a 50-mesh sieve to obtain permanent magnet ferrite powder.

[0067] The coarse-grained strontium carbonate has a SrCO3 mass percentage of 97%, a SiO2 mass percentage of 1.88%, an average particle size of 7.68 μm, and a c / a ratio of less than 3.

[0068] Example 8

[0069] A method for preparing permanent magnet ferrite powder from coarse-particle strontium carbonate, the specific steps of which are as follows:

[0070] Iron oxide red and coarse strontium carbonate were mixed at a molar ratio of 6.1: 6.1. Silica was added at a total mass of 0.1% of iron oxide red and strontium carbonate. The mixture was then dry-milled for 15 minutes using a plow mill, followed by compaction for 30 minutes, pelletizing, and then pre-fired in a rotary kiln at 1260℃ for 2 hours. After cooling, the mixture was crushed and passed through a 50-mesh sieve to obtain permanent magnet ferrite powder.

[0071] The coarse-grained strontium carbonate has a SrCO3 mass percentage of 97%, a SiO2 mass percentage of 1.88%, an average particle size of 6.20 μm, and a c / a ratio of less than 3.

[0072] Comparative Example 1

[0073] A method for using permanent magnet ferrite powder (existing technology) includes the following steps:

[0074] Iron oxide red and high-quality strontium carbonate were mixed at a molar ratio of 5.81: strontium carbonate to iron oxide. 0.1% silica (by total mass of iron oxide red and strontium carbonate) was added. The mixture was then dry-milled for 15 minutes using a plow mill, followed by ball milling for 60 minutes to densify the mixture. The mixture was then pelletized and fed into a rotary kiln for pre-firing at 1310℃ for 2 hours. After cooling, the pellets were crushed and passed through a 50-mesh sieve to obtain permanent magnet ferrite powder.

[0075] The high-quality strontium carbonate has a SrCO3 mass percentage of 97.5%, a SiO2 mass percentage of 0.28%, and an average particle size of 1.33 μm.

[0076] High-quality strontium carbonate has a needle-like or fine columnar morphology, see Figure 3 As shown, the c / a ratio is much greater than 3, so the observed morphology is needle-like or fine columnar, and there are abnormal bright spots on the cross-section of the pre-fired spherical material.

[0077] A comparison of the particle size distribution of the strontium carbonate raw material used in Example 1 and Comparative Example 1 is shown in the figure. Figure 4 As can be seen from the figure, the peak of the particle size distribution curve of the raw material used in Comparative Example 1, representing the prior art, is located in the fine particle range of approximately 1-2 μm. 50 The median diameter (D) is approximately 1.33 μm. In contrast, the peak value of the particle size distribution curve of the raw material used in Example 1 of this invention shifts significantly to the right to the coarse particle range of approximately 5-6 μm. 50 The value is approximately 5.28 μm. This strongly demonstrates that, in terms of raw material selection, this invention breaks through the industry's technical prejudice that fine-particle strontium carbonate with a particle size of less than 2 μm must be used, and creatively selects coarse-particle raw materials with an average particle size in the range of 4-7 μm, which are generally considered by those skilled in the art to be unfavorable for preparing high-performance products.

[0078] As can be seen from the performance data in Table 2, it is precisely this coarse-particle raw material, which has been rejected by the prior art, that, under the synergistic effect of the specific morphology (c / a<3) and composition characteristics (high SiO2 content) defined by this invention, has solved the fundamental problems in the prior art, such as uneven mixing and abnormal grain growth caused by the easy agglomeration of fine particles. As a result, it has obtained unexpectedly superior magnetic properties (especially intrinsic coercivity Hcj) and a wider process window.

[0079] Comparative Example 2

[0080] The difference from Example 1 is that high-quality strontium carbonate was used, and the dry ball milling and densification time was 30 minutes.

[0081] A method for producing permanent magnet ferrite powder, the specific steps of which are as follows:

[0082] Iron oxide red and coarse strontium carbonate were mixed at a molar ratio of 5.81: strontium carbonate to iron oxide. 0.1% silica (by total mass of iron oxide red and strontium carbonate) was added. The mixture was then dry-milled for 15 minutes using a plow mill, followed by compaction for 30 minutes. The mixture was then pelletized and fed into a rotary kiln for pre-firing at 1310℃ for 2 hours. After cooling, the pellets were crushed and passed through a 50-mesh sieve to obtain permanent magnet ferrite powder.

[0083] The high-quality strontium carbonate has a SrCO3 mass percentage of 97.5%, a SiO2 mass percentage of 0.28%, and an average particle size of 1.33 μm.

[0084] High-quality strontium carbonate has a needle-like or fine columnar morphology.

[0085] Comparative Example 3

[0086] The difference from Example 1 is that strontium carbonate with a needle-like or fine columnar morphology, containing 96.5% SrCO3 by mass, and 0.59% SiO2 by mass, with an average particle size of 1.21 μm, was selected.

[0087] A method for producing permanent magnet ferrite powder, the specific steps of which are as follows:

[0088] Iron oxide red and strontium carbonate were mixed at a molar ratio of 5.81: strontium carbonate to iron oxide, and 0.1% silica (by total mass of iron oxide red and strontium carbonate) was added. The mixture was then mixed by a plow mill for 15 minutes, followed by dry ball milling for 60 minutes to form pellets. The pellets were then fed into a rotary kiln and pre-fired at 1310℃ for 2 hours. After cooling, the pellets were crushed and passed through a 50-mesh sieve to obtain permanent magnet ferrite powder.

[0089] Strontium carbonate with a needle-like or fine columnar morphology, containing 96.5% SrCO3 by mass and 0.59% SiO2 by mass, with an average particle size of 1.21 μm, was selected.

[0090] Comparative Example 4

[0091] The difference from Example 1 is that strontium carbonate with a needle-like or fine columnar morphology, containing 97.8% SrCO3 by mass, and 0.26% SiO2 by mass, with an average particle size of 2.28 μm, was selected.

[0092] A method for producing permanent magnet ferrite powder, the specific steps of which are as follows:

[0093] Iron oxide red and coarse strontium carbonate were mixed at a molar ratio of 5.81: strontium carbonate to iron oxide. 0.1% silica (by total mass of iron oxide red and strontium carbonate) was added. The mixture was then dry-milled for 15 minutes using a plow mill, followed by compaction for 30 minutes. The mixture was then pelletized and fed into a rotary kiln for pre-firing at 1310℃ for 2 hours. After cooling, the pellets were crushed and passed through a 50-mesh sieve to obtain permanent magnet ferrite powder.

[0094] Strontium carbonate with a needle-like or fine columnar morphology, containing 97.8% SrCO3 by mass, 0.26% SiO2 by mass, and an average particle size of 2.28 μm was selected.

[0095] Comparative Example 5

[0096] The difference from Example 1 is that high-quality strontium carbonate was used for pre-calcination at 1320°C:

[0097] A method for producing permanent magnet ferrite powder, the specific steps of which are as follows:

[0098] Iron oxide red and high-quality strontium carbonate were mixed at a molar ratio of 5.81: strontium carbonate to iron oxide. 0.1% silica (by total mass of iron oxide red and strontium carbonate) was added. The mixture was then dry-milled for 15 minutes using a plow mill, followed by ball milling for 60 minutes to densify the mixture. The mixture was then pelletized and fed into a rotary kiln for pre-firing at 1320℃ for 2 hours. After cooling, the pellets were crushed and passed through a 50-mesh sieve to obtain permanent magnet ferrite powder.

[0099] The high-quality strontium carbonate has a SrCO3 mass percentage of 97.5%, a SiO2 mass percentage of 0.28%, and an average particle size of 1.33 μm.

[0100] High-quality strontium carbonate has a needle-like or fine columnar morphology.

[0101] Comparative Example 6

[0102] The difference from Example 1 is that high-quality strontium carbonate was used for pre-calcination at 1250°C.

[0103] A method for producing permanent magnet ferrite powder, the specific steps of which are as follows:

[0104] Iron oxide red and high-quality strontium carbonate were mixed at a molar ratio of 5.81: strontium carbonate to iron oxide. 0.1% silica (by total mass of iron oxide red and strontium carbonate) was added. The mixture was then dry-milled for 15 minutes using a plow mill, followed by ball milling for 60 minutes to densify the mixture. The mixture was then pelletized and fed into a rotary kiln for pre-firing at 1250℃ for 2 hours. After cooling, the pellets were crushed and passed through a 50-mesh sieve to obtain permanent magnet ferrite powder.

[0105] The high-quality strontium carbonate has a SrCO3 mass percentage of 97.5%, a SiO2 mass percentage of 0.28%, and an average particle size of 1.33 μm.

[0106] High-quality strontium carbonate has a needle-like or fine columnar morphology.

[0107] Performance testing:

[0108] Average particle size: The average particle size was measured using an average particle size analyzer, with 3.7g of strontium carbonate, 5g of iron oxide red, and 5g of permanent magnet ferrite powder weighed.

[0109] BH Magnetic Tester: Weigh 1 kg of the magnetic powder prepared in the examples and comparative examples, add 1.2% CaCO3, 0.25% SiO2, and 0.15% H3BO3 by weight of the magnetic powder, add water and ball mill until the average particle size is 0.7±0.02μm, then dehydrate to obtain a cake, press the cake at 8000Gs and 35t molding pressure for 10s to obtain a 35mm diameter round cake, sinter at 1250℃, then polish the surface and measure the magnetic properties. Under this formulation system, the performance targets are: Br ≥4150 Gs, Hcb ≥2850 Oe, Hcj ≥2900, BHmax ≥3.80MGOe, M value ≥5180, shrinkage ratio 1.145±0.015, Hk / Hcj ≥95.5%.

[0110] The detection performance is shown in Table 2.

[0111] Table 2. Performance test results of magnetic powders prepared in the examples and comparative examples.

[0112] Group No. Br (Gs) Hcb (Oe) Hcj (Oe) BHmax (MGOe) Hk / Hcj (%) M value Average particle size (pm) Shrinkage ratio Example 1 4197 3147 3208 4.22 96.63 5266 0.7 1.154 Example 2 4193 3140 3199 4.24 96.78 5259 0.7 1.155 Example 3 4176 3008 3252 4.18 95.95 5213 0.71 1.159 Example 4 4180 3006 3064 4.20 96.31 5201 0.71 1.153 Example 5 4208 2957 2956 4.20 95.99 5194 0.68 1.152 Example 6 4201 2948 3002 4.23 95.81 5202 0.68 1.156 Example 7 4199 3088 3135 4.25 96.69 5244 0.68 1.157 Example 8 4193 3076 3130 4.23 96.54 5236 0.68 1.157 Comparative Example 1 4191 2920 3006 4.21 95.4 5193 0.69 1.153 Comparative Example 2 4171 2929 2965 4.19 950 5159 0.71 1.154 Comparative Example 3 4142 2936 2998 4.10 95.6 5141 0.70 1.152 Comparative Example 4 4179 2778 2839 4.20 95.2 5125 0.70 1.155 Comparative Example 5 4203 2806 2853 4.27 96.21 5154 0.71 1.154 Comparative Example 6 4124 3050 3105 4.08 96.32 5159 0.70 1.155

[0113] Traditional permanent magnet ferrite production technology is based on the understanding that high-purity (SrCO3>97.5%) and fine-particle (average particle size<2μm) strontium carbonate must be used. Figure 3 It is evident that this high-quality strontium carbonate typically exhibits a needle-like or fine columnar morphology with a c / a ratio much greater than 3. Although it has high activity, it is extremely prone to uneven mixing due to end stress and clustering effects, which in turn leads to abnormal grain growth during the pre-calcination process, ultimately restricting the uniformity and stability of the magnet's performance. It is also quite sensitive to the pre-calcination process conditions.

[0114] This invention utilizes coarse-grained strontium carbonate with a specific morphology, exhibiting an SrCO3 content of 95-97.5%, a SiO2 tolerance of 0.5-2.5%, and an average particle size range of 3-8 μm. A key characteristic is its particle morphology with a c / a ratio less than 3. This morphology significantly improves the flowability of the raw material, enabling it to achieve far greater uniform dispersion than needle-shaped materials during mixing. This uniform contact at the microscale ensures that subsequent solid-phase reactions proceed smoothly and consistently, effectively suppressing localized overreaction and abnormal grain growth, thus laying the foundation for obtaining excellent magnetic properties.

[0115] The data from the examples fully demonstrate this advantage. Example 1 meets or even exceeds the key magnetic performance parameters of Comparative Example 1, which represents the prior art standard, especially with a significantly higher intrinsic coercivity Hcj, indicating that the magnetic powder prepared by this invention has stronger demagnetization resistance. More importantly, compared to Comparative Example 1, which requires a densification time of up to 60 minutes to ensure performance, Example 1 only requires 30 minutes to achieve superior results. This directly proves the advantages of improved mixing efficiency and simplified process brought about by the new raw material morphology.

[0116] Another significant advantage of this invention is the broadening of the process window and the improvement of product stability. This is particularly evident when comparing performance at different pre-calcination temperatures. Comparative Examples 5 and 6 show that when using conventional needle-shaped strontium carbonate, fluctuations in the pre-calcination temperature directly lead to severe oscillations in magnetic properties: at low temperatures (Comparative Example 6), the remanence Br is severely damaged, while at high temperatures (Comparative Example 5), the coercivity Hcj and Hcb deteriorate significantly. This necessitates frequent temperature monitoring during production, a common problem in actual production. In contrast, Examples 1, 7, and 8 of this invention maintain all magnetic properties within the standard range over a wide temperature range from 1250°C to 1320°C, with overall performance far exceeding the lower limit, demonstrating better process adaptability and stability. This wide temperature range characteristic means that it is easier to control and obtain consistently high-performance products in actual production, reducing production difficulty and scrap rate. Furthermore, the spherical materials calcined in Examples 1-8 have smooth and uniform cross-sections, while Comparative Examples 2-5 show local bright spots, and Comparative Example 6 is generally darker, which corresponds to the performance test results.

[0117] In summary, this invention is not a simple substitution of raw materials, but rather solves the problem of uneven mixing caused by the poor flowability of traditional raw materials by introducing coarse-grained strontium carbonate with a specific morphology. While achieving excellent magnetic properties, it also broadens the range of raw material selection and significantly improves product stability.

Claims

1. A method for producing permanent ferrite magnetic powder, characterized by comprising the steps of: 50 ​ The iron source is compounded with the strontium carbonate raw material, and the permanent magnet ferrite magnetic powder is prepared by mixing, pre-sintering and crushing; the strontium carbonate raw material satisfies the following combination of characteristics: (a) the mass percentage of SrCO3 is 95.0-97.5%; (b) the mass percentage of SiO2 is 0.5-2.5%; (c) an average particle size of 3-8 μm, a particle size distribution D 50 3.5-10.0 μm; and (d) the particles of the strontium carbonate raw material have a spindle, olive or quasi-spherical morphology, and the ratio c / a of the axial length c to the diagonal spacing a of the particles is less than 3.

2. The production method according to claim 1, characterized by, The compounding molar ratio of the iron source to the strontium carbonate raw material, calculated based on iron oxide and strontium carbonate, is n(Fe2O3):n(SrCO3) = 5.5-6.

2.

3. The preparation method according to claim 1, characterized in that, The average particle size of the particles of the strontium carbonate raw material is 4-7 μm.

4. The method of claim 1, wherein, The pre-sintering temperature is 1250-1340℃.

5. The preparation method according to claim 1, characterized in that, The mixing is dry ball-milling mixing, after dry ball-milling mixing, the material is densified and balling, and then pre-sintering; the pre-sintering temperature is 1250-1320℃.

6. The method of claim 1, wherein, The mixing is wet ball-milling mixing, after wet ball-milling mixing, the material is dehydrated, and then pre-sintering; the pre-sintering temperature is 1250-1340℃.

7. The preparation method according to claim 1, characterized in that, The iron source is iron red; the microstructure profile of the particles of the strontium carbonate raw material presents a spindle shape composed of a main trunk part approximately in hexagonal shape and tapered parts located at both ends of the main trunk.

8. The method according to any one of claims 1-7, characterized in that, In the compounding step, 0.01-0.6% of silicon dioxide is additionally added, based on the total mass of the iron source and the strontium carbonate being 100%.

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