Strontium ferrite and preparation method thereof

Abstract

The invention discloses a preparation method of strontium ferrite and the strontium ferrite and belongs to the technical field of permanent magnet materials, and the preparation method of the strontium ferrite is characterized by comprising the following preparation steps: S1, raw material preparation: mixing 80-88 parts by weight of ferric oxide, 6.5-8.5 parts by weight of strontium carbonate and 0.5-0.9 part by weight of calcium carbonate powder to obtain a mixture A; s2, performing primary wet ball milling on the mixture A to obtain mixture A slurry; s3, drying the slurry of the mixture A obtained in the step S2, pre-sintering, and crushing to obtain pre-sintered powder; s4, mixing 0.8-1.5 parts by weight of cobaltosic oxide, 3-4 parts by weight of lanthanum oxide, 0.2-0.6 part by weight of silicon dioxide and 2-6 parts by weight of a dispersing agent with the pre-sintered material powder, and performing secondary wet ball milling to obtain slurry of a mixture B; and S5, drying the slurry of the mixture B, pressing into a blank, and sintering to obtain the strontium ferrite at the sintering temperature of 1175-1205 DEG C, and keeping the temperature for 4-6 hours, thereby achieving the effect of improving the magnetic performance of the strontium ferrite.

Description

Technical Field

[0001] The invention relates to the technical field of permanent magnetic materials, and in particular to a preparation method of strontium ferrite and the strontium ferrite. Background Art

[0002] Permanent magnetic materials are widely used in the fields of automobiles, computers, information communications, aerospace, and electrical manufacturing. In an era when the global manufacturing industry is increasingly developed, permanent ferrite, as one of the permanent magnetic materials, has become the most widely used permanent magnetic material due to its abundant raw material sources, simple production conditions, controllable processes, and strong anti-corrosion properties of the product. It has occupied a dominant position in production and application.

[0003] As a type of permanent magnet, strontium ferrite has a stable hexagonal magnetoplumbite (M-type) structure, high coercive force, magnetic energy product and resistivity, and can be used in high-frequency occasions. In addition, the raw materials of strontium ferrite are cheap, widely available, and have a simple manufacturing process, making them suitable for mass production. The existing production process of permanent magnet strontium ferrite includes pre-sintering material production and magnetic parts production. Pre-sintering is one of the important processes in the production of permanent magnet ferrite by the oxide method, and plays an important role in the quality of the product. The purpose of pre-sintering is to keep the mixture at a certain temperature for several hours, so that a preliminary solid-phase reaction occurs between the particles of the mixture to generate some ferrite. Its role is mainly reflected in reducing the unevenness of chemical activity, reducing the shrinkage rate of sintered products, and increasing the sintering density and ease of forming of the product. Some low-melting sintering aids will be added during the pre-sintering process to achieve the effect of sintering at a lower sintering temperature, but the magnetic properties of the strontium ferrite obtained are still poor, which is difficult to meet market demand. Summary of the invention

[0004] In order to improve the magnetic properties of strontium ferrite, the present invention provides a preparation method of strontium ferrite and the strontium ferrite.

[0005] The first aspect of the present invention is to provide a method for preparing strontium ferrite, which adopts the following technical scheme: A method for preparing strontium ferrite comprises the following steps: S1. Raw material preparation: by weight, 80-88 parts of ferric oxide, 6.5-8.5 parts of strontium carbonate, and 0.5-0.9 parts of calcium carbonate powder are mixed to obtain a mixture A; S2, wet ball milling the mixture A to obtain a mixture A slurry; S3, drying the mixture A slurry obtained in step S2, pre-sintering it, and then crushing it to obtain pre-sintered powder; S4, 0.8-1.5 parts by weight of cobalt trioxide, 3-4 parts by weight of lanthanum oxide, 0.2-0.6 parts by weight of silicon dioxide, 2-6 parts by weight of a dispersant and the pre-sintered powder are mixed and then subjected to secondary wet ball milling to obtain a mixture B slurry; S5. Dry the mixture B slurry, press it into green compacts, and then sinter it to obtain strontium ferrite. The sintering temperature is 1175-1205° C. and the temperature is kept for 4-6 hours.

[0006] By adopting the above technical scheme, the addition of additives such as calcium carbonate and silicon dioxide can reduce the sintering temperature, promote solid phase reaction, increase the remanence of ferrite, shorten the production cycle, and achieve the purpose of saving energy; and as a dispersant in the secondary ball milling process, the remanence and orientation degree of the permanent magnet ferrite can be improved during pressing; distributed at the grain boundaries, excessive growth of grains during the sintering process can be controlled, and the coercive force of the permanent magnet ferrite can be improved.

[0007] Specifically, calcium carbonate is in a molten state at a relatively low temperature, which can realize a liquid phase reaction that promotes the reaction rate, promotes the density of the magnet, shortens the production cycle, and reduces the sintering cost. A small amount of calcium ions produced during the sintering process of calcium carbonate will replace strontium ions, and most of the calcium ions will act as a sintering aid to promote the solid phase reaction and promote the densification of ferrite, thereby increasing the remanence. Since the radius of calcium ions and strontium ions is similar, excess calcium ions will form impurities with strontium ions, lanthanum ions, etc. in the original components, which is not conducive to improving the magnetic properties. Excessive calcium ions will cause excessive and uneven grain growth.

[0008] The role of silica additives is: silica has a high melting point, and the reaction of silica and ferric oxide will generate low-melting-point iron silicate, which greatly reduces the sintering temperature and achieves the purpose of lowering the solid-phase reaction temperature, thereby increasing the density of the magnet. Iron silicate will inhibit the growth of grains, thereby obtaining a higher coercive force. However, excessive addition of silica will reduce the density and remanence of the material.

[0009] Lanthanum ions partially replace strontium in strontium ferrite, which can stabilize the crystal structure and significantly improve the magnetic properties of strontium ferrite. Therefore, the combined use of various additives in the present application can effectively improve the magnetic properties of ferrite.

[0010] The increase in sintering temperature is beneficial to the growth of grains. During the solid-phase sintering process, as the grains grow and densify, the grain size will become larger. Although this increases the remanence of the material, it reduces the coercive force of the material. In order to simultaneously increase the remanence and coercive force, it is necessary to ensure that the grains remain uniform and small while densifying. Additives such as cobalt tetroxide, lanthanum oxide, and silicon dioxide are added as sintering aids during the secondary ball milling to achieve liquid phase sintering. The sintering aid forms a liquid phase at high temperature, which can not only promote the sintering reaction process, but also adhere to the surface of the grains to hinder grain growth, thereby achieving uniform, fine, and dense growth of the grains. Therefore, when the sintering temperature is limited to the range of 1175-1205°C in this application, the coercive force and remanence of the ferrite can be effectively guaranteed.

[0011] Preferably, the step S4 further comprises 0.1-0.2 parts by weight of aluminum oxide.

[0012] By adopting the above technical solution, the radii of aluminum ions and iron ions are very close. Adding aluminum oxide will increase the magnetocrystalline anisotropy field of the magnet. At the same time, aluminum oxide will diffuse between the grain boundaries and have the effect of refining the grains. Therefore, such additives will greatly increase the coercive force of the magnet, but the addition of excessive aluminum oxide will reduce the remanence of the magnet.

[0013] Preferably, the cobalt tetroxide comprises 1-1.3 parts by weight and the silicon dioxide comprises 0.35-0.5 parts by weight.

[0014] Preferably, the average particle size of the suspended particles in the mixture A slurry is 1.0-1.5 μm.

[0015] Preferably, the average particle size of the suspended particles in the mixture B slurry is 0.65-0.75 μm.

[0016] Preferably, in step S3, the pre-sintering process is carried out at a temperature of 1260-1340° C. for 1-1.5 hours.

[0017] By adopting the above technical solution, the pre-sintering setting enables sufficient ferritization and reduces the deformation degree of the final product. At the same time, pre-sintering reduces the volume of the crystal, and the gas can be discharged during this process. No gas escape is required during the secondary sintering, thereby improving the densification and mechanical strength of the final ferrite, thereby reducing the deformation degree of the product.

[0018] Preferably, the heating rate in step S5 is 2.5-4.5°C / min.

[0019] Preferably, the dispersant is one or both of isobutylene-maleic anhydride copolymer and sorbitol.

[0020] Preferably, the weight ratio of the isobutylene-maleic anhydride copolymer to sorbitol is 1:(1-1.5).

[0021] By adopting the above technical solution, the dispersant is composed of isobutylene-maleic anhydride copolymer and sorbitol, which effectively improves the dispersion of magnetic grains, makes the distribution of magnetic grains more uniform, and helps to improve the magnetic properties of ferrite.

[0022] The second aspect of the present invention is to provide strontium ferrite obtained by the above-mentioned method for preparing strontium ferrite.

[0023] In summary, the present invention has the following beneficial effects: 1. The addition of calcium carbonate and silicon dioxide as additives in the present application reduces the sintering temperature and promotes the solid phase reaction. The addition of cobalt oxide and lanthanum oxide can improve the remanence of ferrite. Calcium carbonate, silicon dioxide, cobalt oxide and lanthanum oxide are used as dispersants in the secondary ball milling process, which can improve the remanence and orientation of the permanent magnet ferrite during pressing. They are distributed at the grain boundaries, control the excessive growth of grains during the sintering process, improve the coercive force of the permanent magnet ferrite, and ensure the magnetic properties of the strontium ferrite.

[0024] 2. The combination of pre-sintering and sintering in the present application improves the magnetic properties and mechanical strength of the final ferrite. The improvement in mechanical strength can effectively reduce the degree of deformation of the strontium ferrite product. DETAILED DESCRIPTION

[0025] The present invention is further described in detail below with reference to the embodiments.

[0026] A method for preparing strontium ferrite comprises the following steps: S1. Raw material preparation: by weight, 80-88 parts of ferric oxide, 6.5-8.5 parts of strontium carbonate, and 0.5-0.9 parts of calcium carbonate powder are mixed to obtain a mixture A; S2, wet ball milling the mixture A to obtain a mixture A slurry; S3, drying the mixture A slurry obtained in step S2, pre-sintering it, and then crushing it to obtain pre-sintered powder; S4, 0.8-1.5 parts by weight of cobalt trioxide, 3-4 parts by weight of lanthanum oxide, 0.2-0.6 parts by weight of silicon dioxide, 2-6 parts by weight of a dispersant and the pre-sintered powder are mixed and then subjected to secondary wet ball milling to obtain a mixture B slurry; S5. Dry the mixture B slurry, press it into green compacts, and then sinter it to obtain strontium ferrite. The sintering temperature is 1175-1205° C. and the temperature is kept for 4-6 hours.

[0027] Preferably, the step S4 further comprises 0.1-0.2 parts by weight of aluminum oxide.

[0028] Preferably, the cobalt tetroxide comprises 1-1.3 parts by weight and the silicon dioxide comprises 0.35-0.5 parts by weight.

[0029] Preferably, the average particle size of the suspended particles in the mixture A slurry is 1.0-1.5 μm.

[0030] Preferably, the average particle size of the suspended particles in the mixture B slurry is 0.65-0.75 μm.

[0031] Preferably, in step S3, the pre-sintering process is carried out at a temperature of 1260-1340° C. for 1-1.5 hours.

[0032] Preferably, the heating rate in step S5 is 2.5-4.5°C / min.

[0033] Preferably, the dispersant is one or both of isobutylene-maleic anhydride copolymer and sorbitol.

[0034] Preferably, the weight ratio of the isobutylene-maleic anhydride copolymer to sorbitol is 1:(1-1.5).

[0035] Example 1 A method for preparing strontium ferrite comprises the following steps: S1. Raw material preparation: 80 kg of ferric oxide, 6.5 kg of strontium carbonate and 0.5 kg of calcium carbonate powder are mixed to obtain a mixture A; S2, wet ball milling the mixture A until the average particle size of the suspended particles in the mixture A slurry is 1.0 μm, then stopping the ball milling to obtain the mixture A slurry; S3, drying the mixture A slurry obtained in step S2 and then pre-sintering it, wherein the pre-sintering process is to keep the mixture A slurry at 1260° C. for 1.5 hours and then crush it to obtain pre-sintered powder; S4, 0.8 kg of cobalt tetraoxide, 3 kg of lanthanum oxide, 0.2 kg of silicon dioxide, 2 kg of dispersant sorbitol and the pre-burned powder are mixed and then subjected to secondary wet ball milling until the average particle size of the suspended particles in the mixture B slurry is 0.65 μm, and then the wet milling is stopped to obtain the mixture B slurry; S5. Dry the mixture B slurry, press it into green compacts, and then sinter it to obtain strontium ferrite. Raise the temperature to 1175° C. at a rate of 2.5° C. / min and keep it at that temperature for 6 hours.

[0036] Example 2 A method for preparing strontium ferrite comprises the following steps: S1. Raw material preparation: 84 kg of ferric oxide, 7.5 kg of strontium carbonate and 0.7 kg of calcium carbonate powder were mixed to obtain a mixture A; S2, wet ball milling the mixture A until the average particle size of the suspended particles in the mixture A slurry is 1.0 μm, then stopping the ball milling to obtain the mixture A slurry; S3, drying the mixture A slurry obtained in step S2 and then pre-sintering it, wherein the pre-sintering process is to keep the mixture A slurry at 1300° C. for 1.5 hours and then crush it to obtain pre-sintered powder; S4, 0.8 kg of cobalt tetraoxide, 3 kg of lanthanum oxide, 0.2 kg of silicon dioxide, 2 kg of dispersant sorbitol and the pre-calcined powder are mixed and then subjected to secondary wet ball milling until the average particle size of the suspended particles in the mixture B slurry is 0.65 μm, and then the wet milling is stopped to obtain a mixture B slurry; S5. Dry the mixture B slurry, press it into green compacts, and then sinter it to obtain strontium ferrite. Raise the temperature to 1175° C. at a rate of 2.5° C. / min and keep it at that temperature for 6 hours.

[0037] Example 3 A method for preparing strontium ferrite comprises the following steps: S1. Raw material preparation: 88 kg of ferric oxide, 8.5 kg of strontium carbonate and 0.9 kg of calcium carbonate powder are mixed to obtain a mixture A; S2, wet ball milling the mixture A until the average particle size of the suspended particles in the mixture A slurry is 1.0 μm, then stopping the ball milling to obtain the mixture A slurry; S3, drying the mixture A slurry obtained in step S2 and then pre-sintering it, wherein the pre-sintering process is to keep the mixture A slurry at 1340° C. for 1 hour and then crush it to obtain pre-sintered powder; S4, 0.8 kg of cobalt tetraoxide, 3 kg of lanthanum oxide, 0.2 kg of silicon dioxide, 2 kg of dispersant sorbitol and the pre-calcined powder are mixed and then subjected to secondary wet ball milling until the average particle size of the suspended particles in the mixture B slurry is 0.65 μm, and then the wet milling is stopped to obtain a mixture B slurry; S5. Dry the mixture B slurry, press it into green compacts, and then sinter it to obtain strontium ferrite. Raise the temperature to 1175° C. at a rate of 2.5° C. / min and keep it at that temperature for 6 hours.

[0038] Example 4 A method for preparing strontium ferrite comprises the following steps: S1. Raw material preparation: 84 kg of ferric oxide, 7.5 kg of strontium carbonate and 0.7 kg of calcium carbonate powder were mixed to obtain a mixture A; S2, wet ball milling the mixture A until the average particle size of the suspended particles in the mixture A slurry is 1.0 μm, then stopping the ball milling to obtain the mixture A slurry; S3, drying the mixture A slurry obtained in step S2 and then pre-sintering it, wherein the pre-sintering process is to keep the mixture A slurry at 1300° C. for 1.5 hours and then crush it to obtain pre-sintered powder; S4, 1 kg of cobalt tetraoxide, 3.5 kg of lanthanum oxide, 0.35 kg of silicon dioxide, 4 kg of isobutylene-maleic anhydride copolymer as a dispersant and the pre-sintered powder are mixed and then subjected to secondary wet ball milling until the average particle size of the suspended particles in the mixture B slurry is 0.65 μm, and then the wet milling is stopped to obtain a mixture B slurry; S5. Dry the mixture B slurry, press it into green compacts, and then sinter it to obtain strontium ferrite. Raise the temperature to 1175° C. at a rate of 2.5° C. / min and keep it at that temperature for 6 hours.

[0039] Example 5 A method for preparing strontium ferrite comprises the following steps: S1. Raw material preparation: 84 kg of ferric oxide, 7.5 kg of strontium carbonate and 0.7 kg of calcium carbonate powder were mixed to obtain a mixture A; S2, wet ball milling the mixture A until the average particle size of the suspended particles in the mixture A slurry is 1.0 μm, then stopping the ball milling to obtain the mixture A slurry; S3, drying the mixture A slurry obtained in step S2 and then pre-sintering it, wherein the pre-sintering process is to keep the mixture A slurry at 1300° C. for 1.5 hours and then crush it to obtain pre-sintered powder; S4, 1.3 kg of cobalt tetraoxide, 3.5 kg of lanthanum oxide, 0.5 kg of silicon dioxide, 5 kg of isobutylene-maleic anhydride copolymer as a dispersant and the pre-sintered powder are mixed and then subjected to secondary wet ball milling until the average particle size of the suspended particles in the mixture B slurry is 0.65 μm, and then the wet milling is stopped to obtain a mixture B slurry; S5. Dry the mixture B slurry, press it into green compacts, and then sinter it to obtain strontium ferrite. Raise the temperature to 1175° C. at a rate of 2.5° C. / min and keep it at that temperature for 6 hours.

[0040] Example 6 A method for preparing strontium ferrite comprises the following steps: S1. Raw material preparation: 84 kg of ferric oxide, 7.5 kg of strontium carbonate and 0.7 kg of calcium carbonate powder were mixed to obtain a mixture A; S2, wet ball milling the mixture A until the average particle size of the suspended particles in the mixture A slurry is 1.0 μm, then stopping the ball milling to obtain the mixture A slurry; S3, drying the mixture A slurry obtained in step S2 and then pre-sintering it, wherein the pre-sintering process is to keep the mixture A slurry at 1300° C. for 1.5 hours and then crush it to obtain pre-sintered powder; S4, 1.5 kg of cobalt tetraoxide, 4 kg of lanthanum oxide, 0.6 kg of silicon dioxide, 6 kg of isobutylene-maleic anhydride copolymer as a dispersant and the pre-sintered powder are mixed and then subjected to secondary wet ball milling until the average particle size of the suspended particles in the mixture B slurry is 0.65 μm, and then the wet milling is stopped to obtain a mixture B slurry; S5. Dry the mixture B slurry, press it into green compacts, and then sinter it to obtain strontium ferrite. Raise the temperature to 1175° C. at a rate of 2.5° C. / min and keep it at that temperature for 6 hours.

[0041] Example 7 A method for preparing strontium ferrite is different from that of Example 5 in that 0.1 kg of aluminum oxide is further added in step S4, and the rest is the same as that of Example 5.

[0042] Example 8 A method for preparing strontium ferrite is different from that of Example 5 in that 0.2 kg of aluminum oxide is further added in step S4, and the rest is the same as that of Example 5.

[0043] Example 9 A method for preparing strontium ferrite is different from that of Example 8 in that, in the wet ball milling of step S2, the ball milling is stopped until the average particle size of the suspended particles in the mixture A slurry is 1.3 μm to obtain the mixture A slurry, and the rest is the same as that of Example 8.

[0044] Example 10 A method for preparing strontium ferrite is different from Example 8 in that, in the wet ball milling of step S2, the ball milling is stopped until the average particle size of the suspended particles in the mixture A slurry is 1.5 μm to obtain the mixture A slurry, and the rest is the same as Example 8.

[0045] Embodiment 11 A method for preparing strontium ferrite, which is different from that of Example 8 in that, in the wet ball milling of step S2, the ball milling is stopped until the average particle size of the suspended particles in the mixture A slurry is 1.3 μm to obtain the mixture A slurry, and in step S4, the secondary wet ball milling is performed until the average particle size of the suspended particles in the mixture B slurry is 0.70 μm, and then the wet milling is stopped to obtain the mixture B slurry. The rest is the same as Example 8.

[0046] Comparative Example 11 A method for preparing strontium ferrite, which is different from Example 11 in that the secondary wet ball milling in step S4 is stopped until the average particle size of the suspended particles in the mixture B slurry is 0.60 μm to obtain the mixture B slurry, and the rest is the same as Example 11.

[0047] Example 12 A method for preparing strontium ferrite, which is different from that of Example 8 in that, in the wet ball milling of step S2, the ball milling is stopped until the average particle size of the suspended particles in the mixture A slurry is 1.3 μm to obtain the mixture A slurry, and in step S4, the secondary wet ball milling is performed until the average particle size of the suspended particles in the mixture B slurry is 0.75 μm, and then the wet grinding is stopped to obtain the mixture B slurry. The rest is the same as Example 8.

[0048] Comparative Example 12 A method for preparing strontium ferrite, which is different from Example 12 in that the secondary wet ball milling in step S4 is performed until the average particle size of the suspended particles in the mixture B slurry is 0.80 μm, then the wet milling is stopped to obtain the mixture B slurry, and the rest is the same as Example 12.

[0049] Embodiment 13 A method for preparing strontium ferrite, which is different from Example 11 in that the pre-sintering process is to keep the temperature at 680°C for 1 hour, then increase the temperature to 950°C, keep the temperature for 1.5 hours, and then crush to obtain pre-sintered powder. The rest is the same as Example 11.

[0050] Embodiment 14 A method for preparing strontium ferrite, which is different from Example 11 in that the heating rate in step S5 is different, specifically, the temperature is increased to 1175°C at a rate of 4.5°C / min and kept warm for 6 hours.

[0051] Embodiment 15 A method for preparing strontium ferrite, which is different from Example 11 in that the heating rate in step S5 is different, specifically, the temperature is increased to 1175°C at a rate of 5.5°C / min and kept warm for 6 hours.

[0052] Example 16 A method for preparing strontium ferrite, which is different from Example 11 in that the sintering temperature is 1205° C. and the sintering time is 4 hours.

[0053] Embodiment 17 A method for preparing strontium ferrite, which is different from Example 11 in that the sintering temperature is 1220° C. and the sintering time is 4 hours.

[0054] Embodiment 18 A method for preparing strontium ferrite, which is different from Example 11 in that, when the total amount of the dispersant is 5 kg, the dispersant includes isobutylene-maleic anhydride copolymer and sorbitol in a weight ratio of 1:1.

[0055] Embodiment 19 A method for preparing strontium ferrite, which is different from Example 11 in that, when the total amount of the dispersant is 5 kg, the dispersant includes isobutylene-maleic anhydride copolymer and sorbitol in a weight ratio of 1:1.5.

[0056] Embodiment 20 A method for preparing strontium ferrite, which is different from Example 18 in that, when the total amount of the dispersant is 5 kg, the dispersant includes isobutylene-maleic anhydride copolymer and calcium gluconate in a weight ratio of 1:1.

[0057] Comparative Example 1 A method for preparing strontium ferrite, which is different from Example 5 in that there is no pre-sintering process, specifically: S1, raw material preparation: 84 kg of ferric oxide, 7.5 kg of strontium carbonate, 0.7 kg of calcium carbonate powder, 1.3 kg of cobalt tetraoxide, 3.5 kg of lanthanum oxide, 0.5 kg of silicon dioxide, and 5 kg of dispersant isobutylene-maleic anhydride copolymer are mixed to obtain a mixture; S2, wet-milling the mixture until the average particle size of the suspended particles in the mixture slurry is 0.65 μm, then stopping the wet-milling to obtain a mixture slurry; S3. Dry the mixture slurry, press it into green compacts, and then sinter it to obtain strontium ferrite. Raise the temperature to 1175°C at a rate of 2.5°C / min and keep it at that temperature for 6 hours.

[0058] Comparative Example 2 A method for preparing strontium ferrite is different from that of Example 5 in that cobalt tetroxide is not included in step S4, and the rest is the same as that of Example 5.

[0059] Comparative Example 3 A method for preparing strontium ferrite is different from that of Example 5 in that there is no silicon dioxide in step S4, and the rest is the same as that of Example 5.

[0060] Comparative Example 4 A method for preparing strontium ferrite is different from that of Example 5 in that no lanthanum oxide is included in step S4, and the rest is the same as that of Example 5.

[0061] Comparative Example 5 A method for preparing strontium ferrite is different from that of Example 5 in that the content of calcium carbonate powder in step S1 is 1.1 kg, and the rest is the same as that of Example 5.

[0062] Comparative Example 6 A method for preparing strontium ferrite, which is different from Example 5 in that the content of cobalt tetroxide in step S4 is 1.8 kg, the content of lanthanum oxide is 4.3 kg, and the content of silicon dioxide powder is 0.8 kg, and the rest are the same as Example 5.

[0063] Comparative Example 7 A method for preparing strontium ferrite, which is different from Example 5 in that the content of cobalt tetroxide in step S4 is 0.6 kg, the content of lanthanum oxide is 2.5 kg, and the content of silicon dioxide powder is 0.1 kg, and the rest are the same as Example 5.

[0064] Performance Testing The remanence (Br), intrinsic coercive force (Hcj), magnetic energy product (BH) and density of the strontium ferrite obtained in the above examples and comparative examples were tested. The test results are shown in Table 1.

[0065] Table 1 Magnetic properties test results of strontium ferrite

[0066] From the table above we can see that: The remanence of the strontium ferrite obtained in Examples 1-3 of the present application is greater than or equal to 4426Gs, the intrinsic coercivity is higher than 4690Oe, and the magnetic energy product is higher than 4.6MGOe. It can be seen that the strontium ferrite obtained in Examples 1-3 of the present application has good magnetic properties.

[0067] Compared with Example 2, when the contents of ferric oxide, strontium carbonate and calcium carbonate remain unchanged, as the contents of cobalt tetroxide, lanthanum oxide, silicon dioxide and dispersant increase, the remanence, intrinsic coercivity and magnetic energy product of the strontium ferrite obtained in Example 4-6 are higher than the remanence, intrinsic coercivity and magnetic energy product in Example 2. It can be seen that as the contents of cobalt tetroxide, lanthanum oxide and silicon dioxide increase, the magnetic properties of strontium ferrite can be further improved. However, when the contents of cobalt tetroxide, lanthanum oxide, silicon dioxide and dispersant reach the content limits in Example 6, the magnetic properties of strontium ferrite no longer increase. It can be seen that when the contents of cobalt tetroxide, lanthanum oxide, silicon dioxide and dispersant are within the range specified in the present application, the magnetic properties of strontium ferrite can be effectively guaranteed.

[0068] Compared with Example 5, the addition of aluminum oxide in Examples 7-8 further improves the remanence, intrinsic coercivity and magnetic energy product of strontium ferrite. It can be seen that the combination of aluminum oxide with cobalt oxide, lanthanum oxide and silicon dioxide can effectively improve the magnetic properties of strontium ferrite.

[0069] Compared with Example 8, Examples 9-12, the average particle size of the suspended particles in the mixture A slurry and the average particle size of the suspended particles in the mixture B slurry also have a certain influence on the magnetic properties of the strontium ferrite, especially the average particle size of the suspended particles in the mixture B slurry. It can be seen from Comparative Example 11 and Comparative Example 12 that when the average particle size of the suspended particles in the mixture B slurry is lower than or higher than the average particle size specified in the present application, the magnetic properties of the strontium ferrite in Comparative Example 11 and Comparative Example 12 are reduced. It can be seen that the particle size of the suspended particles in the mixture B slurry has a significant effect on the magnetic properties of the strontium ferrite.

[0070] Compared with Example 11, Examples 14-15 can ensure the magnetic properties of strontium ferrite when the heating rate during sintering is within the range of 4.5°C / min. However, when the heating rate exceeds 4.5°C / min, it can be seen from Example 15 that the magnetic properties of the strontium ferrite are reduced compared with Example 14.

[0071] Compared with Example 11, as the sintering temperature increases, the magnetic properties of the strontium ferrite obtained in Example 16 are improved compared with Example 11, but when the sintering temperature exceeds 1205°C, the magnetic properties of the strontium ferrite obtained in Example 17 are reduced. It can be seen that when the sintering temperature is limited to between 1175-1205°C in the present application, the magnetic properties of the strontium ferrite can be effectively improved.

[0072] Compared with Example 11, when the dispersant is a mixture of isobutylene-maleic anhydride copolymer and sorbitol, the magnetic properties of the strontium ferrite obtained in Examples 18-19 are improved compared with those in Example 11. It can be seen that the combined use of the two dispersants makes the magnetic particles more evenly dispersed and the particle size distribution after grinding more uniform, which is beneficial to improving the magnetic properties of the strontium ferrite.

[0073] Compared with Example 18, after replacing sorbitol with an equal amount of calcium gluconate, the magnetic properties of the strontium ferrite obtained in Example 20 are lower than those in Example 18. It can be seen that the combined use of isobutylene-maleic anhydride copolymer and sorbitol can effectively ensure the magnetic properties of strontium ferrite.

[0074] Compared with Example 5, when there is no sintering process and each raw material is ground once, the magnetic properties of the strontium ferrite obtained in Comparative Example 1 are significantly lower than those in Example 5. It can be seen that the pre-sintering setting in the present application can effectively improve the magnetic properties of strontium ferrite.

[0075] Compared with Example 5, when cobalt tetraoxide, silicon dioxide or lanthanum oxide is absent in step S4, the magnetic properties of the strontium ferrite obtained in Comparative Examples 2-4 are all reduced. It can be seen that the addition of these three additives effectively improves the magnetic properties of strontium ferrite.

[0076] Compared with Example 5, when the content of calcium carbonate or the content of cobalt tetroxide, silicon dioxide, and lanthanum oxide is not within the range specified in the present application, the magnetic properties of the strontium ferrite obtained in Comparative Examples 5-7 are all lower than those in Example 5. It can be seen that the content of calcium carbonate, cobalt tetroxide, silicon dioxide, and lanthanum oxide has a direct effect on the magnetic properties of strontium ferrite.

[0077] The embodiments of this specific implementation method are all preferred embodiments of the present invention, and are not intended to limit the protection scope of the present invention. Therefore, any equivalent changes made based on the structure, shape, and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for preparing strontium ferrite, characterized in that: The method comprises the following preparation steps: S1. Raw material preparation: by weight, 80-88 parts of ferric oxide, 6.5-8.5 parts of strontium carbonate, and 0.5-0.9 parts of calcium carbonate powder are mixed to obtain a mixture A; S2, wet ball milling the mixture A to obtain a mixture A slurry; S3, drying the mixture A slurry obtained in step S2, pre-sintering it, and then crushing it to obtain pre-sintered powder; S4, 0.8-1.5 parts by weight of cobalt trioxide, 3-4 parts by weight of lanthanum oxide, 0.2-0.6 parts by weight of silicon dioxide, 2-6 parts by weight of a dispersant and the pre-sintered powder are mixed and then subjected to secondary wet ball milling to obtain a mixture B slurry; S5. Dry the mixture B slurry, press it into green compacts, and then sinter it to obtain strontium ferrite. The sintering temperature is 1175-1205° C. and the temperature is kept for 4-6 hours.

2. The method for preparing strontium ferrite according to claim 1, characterized in that: The step S4 further comprises 0.1-0.2 parts by weight of aluminum oxide.

3. The method for preparing strontium ferrite according to claim 1, characterized in that: The cobalt tetroxide is 1-1.3 parts by weight and the silicon dioxide is 0.35-0.5 parts by weight.

4. The method for preparing strontium ferrite according to claim 1, characterized in that: The average particle size of the suspended particles in the mixture A slurry is 1.0-1.5 μm.

5. The method for preparing strontium ferrite according to claim 1, characterized in that: The average particle size of the suspended particles in the mixture B slurry is 0.65-0.75 μm.

6. The method for preparing strontium ferrite according to claim 1, characterized in that: In step S3, the pre-sintering process is to keep the temperature at 1260-1340° C. for 1-1.5 hours.

7. The method for preparing strontium ferrite according to claim 1, characterized in that: The heating rate in step S5 is 2.5-4.5°C / min.

8. The method for preparing strontium ferrite according to claim 1, characterized in that: The dispersant is one or both of isobutylene-maleic anhydride copolymer and sorbitol.

9. The method for preparing strontium ferrite according to claim 8, characterized in that: The weight ratio of the isobutylene-maleic anhydride copolymer to sorbitol is 1:(1-1.5).

10. Strontium ferrite obtained by the method for preparing strontium ferrite according to any one of claims 1 to 9.

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