Preparation method of high-performance permanent ferrite material without lanthanum cobalt addition

Abstract

The application relates to the technical field of permanent magnets, and discloses a preparation method of high-performance permanent ferrite material without lanthanum cobalt addition, which comprises the following steps: S1, preparing a permanent ferrite crystal seed powder containing sodium silicate; S2, batching: mixing iron red, strontium carbonate and sodium silicate, and adding the crystal seed powder in step S1 into the above raw materials; S3, pre-burning to obtain a main phase powder after crushing; S4, ball milling: adding secondary additives into the main phase powder in step S3, and wet-milling to form a slurry; S5, adjusting the water content of the slurry in step S4, and then forming a forming body under the condition of a magnetic field to obtain a high-temperature sintering type; the application adds a small amount of sodium silicate into raw material powder, optimizes a main formula and a secondary addition formula, appropriately reduces a pre-burning temperature, prepares high-performance lanthanum cobalt-free permanent ferrite material, the ferrite crystal particles in the material are relatively more uniform, coarse crystal particles are avoided, and therefore the comprehensive magnetic performance is obviously better than that of the same kind of material prepared by a traditional process.

Description

Technical Field

[0001] This invention belongs to the technical field of permanent magnets, and more specifically, it relates to a method for preparing a high-performance permanent magnet ferrite material without the addition of lanthanum and cobalt. Background Technology

[0002] Currently, permanent magnet ferrite is one of the basic functional materials for permanent magnet DC motors. It can meet the requirements of motor use in various environments, has high sensitivity and stability, and can be widely used in various types of motors with high power, high speed and high torque, such as high-end automotive motors (ABS motors, starter motors, etc.), motorcycle starter motors, household appliances and power tool motors.

[0003] Pre-sintered permanent magnet ferrite materials are primarily made from iron oxide red, resulting in relatively high production costs. The magnetic properties of permanent magnet ferrites are mainly determined by two key parameters: remanent magnetic flux density (Br) and intrinsic coercivity (Hcj). Existing high-performance permanent magnet materials, particularly those prepared using La-Co ion substitution technology, suffer from significantly increased costs and reduced cost-effectiveness due to the addition of expensive rare earth and rare metal oxides, thus limiting their application range.

[0004] Chinese patent application CN104003704B proposes using molten salt as a medium for solid-state reaction. By adjusting the type and ratio of molten salt and controlling the sintering process, permanent magnet ferrite materials with higher magnetic properties than those produced by traditional processes can be manufactured without the addition of lanthanum and cobalt. Chinese patent applications CN101209920B and CN104496444B use Al2O3 or Cr2O3, which are much cheaper, to replace expensive Co oxides. At the same time, they significantly reduce or even completely eliminate the addition of rare earth elements, greatly reducing the direct material cost. The sintered permanent magnet ferrite prepared can obtain high magnetic induction intensity and good intrinsic coercivity, which can meet the needs of mid-to-high-end magnet applications. Chinese patent application CN109836148B optimizes the material composition, improves the uniformity of ferrite grains, and lowers the pre-sintering temperature, effectively improving the intrinsic coercivity of the material. Without the addition of La and Co elements, sintered ferrite permanent magnet materials with high coercivity and high remanence are prepared.

[0005] Although the optimization solutions provided by the aforementioned patents effectively improve material performance without adding lanthanum and cobalt additives, they mainly optimize the formula by continuing the ion substitution technology. Some solutions also extend the process flow and increase energy consumption. Moreover, the improvement in magnetic properties is relatively limited, so the prospects for practical application are not high.

[0006] To address the shortcomings of existing technical solutions, this invention provides a method for preparing high-performance permanent magnet ferrite materials without the addition of lanthanum and cobalt. Summary of the Invention

[0007] This invention provides a method for preparing a high-performance permanent magnet ferrite material without lanthanum and cobalt additives. Under the condition that the proportion of the main raw materials remains basically unchanged, an additive sodium silicate is added to increase the surface negative charge. The charge repulsion effect is used to reduce the viscosity of the magnetic material, increase the fluidity, improve the growth of the magnetic chip, and reduce the pre-firing temperature, so as to prepare a permanent magnet ferrite material with excellent magnetic properties without lanthanum and cobalt additives.

[0008] The purpose and effectiveness of this invention's method for preparing a high-performance permanent magnet ferrite material without lanthanum and cobalt additives are achieved through the following specific technical means: A method for preparing a high-performance permanent magnet ferrite material without lanthanum and cobalt additives includes the following steps: S1 Preparation of permanent magnet ferrite crystal seed powder containing sodium silicate: Iron oxide red, strontium carbonate and additive sodium silicate are mixed. The molar ratio of Fe2O3 and SrO from the above raw materials is 6:1. The amount of sodium silicate added is 0.05-5wt% of the total mass of iron oxide red and strontium carbonate. After wet ball milling, pre-calcination and pulverization, crystal seed powder with an average particle size of 0.8-10μm is obtained. S2 Ingredients: Iron oxide red, strontium carbonate, and sodium silicate are mixed according to... Chemically formulated ingredients are mixed, wherein 0.05 ≤ x ≤ 0.5, 5.5 ≤ n ≤ 6.0. The crystal seed powder from step S1 is added to the above raw materials in an amount of 0.05-10 wt% of the total mass of iron oxide red, strontium carbonate and sodium silicate. After wet mixing, the average particle size of the mixture is ≤0.85µm. In this step, the average particle size of the raw materials iron oxide red, strontium carbonate, and sodium silicate should be at least below 2µm. The wet grinding and mixing time should be controlled at 3-5 hours to ensure that the average particle size is ≤0.85µm. If the particle size of the slurry after mixing is too large, it is easy to cause insufficient pre-calcination during the pre-calcination process, resulting in a low content of M-phase ferrite. The average particle size of the raw materials should be less than 2µm to ensure that the average particle size after grinding reaches below 0.85µm in a short time, so as to ensure sufficient pre-calcination.

[0009] S3 pre-calcination: Hold at 1120℃~1230℃ for 0.5~3 hours, and obtain the main phase powder after pulverization; S4 Ball milling: Add secondary additives to the main phase powder in step S3 and wet mill to a slurry with a particle size of 0.65-0.95μm; S5: Adjust the water content of the slurry in step S4 to keep the solid content of the slurry at 65-80 wt%, and then mold it under a magnetic field of not less than 10000 Oe to obtain a molded body. The molded body is then sintered at high temperature to solidify it.

[0010] In this step, the forming magnetic field should not be lower than 10000 Oe. If the forming magnetic field is too low, the orientation of the magnetic particles in the formed body will be too low, thus affecting the remanence of the final magnet.

[0011] In this scheme, the main function of adding sodium silicate to the raw material mixture is to increase the surface negative charge during the pre-calcination process. By utilizing the charge repulsion effect, the viscosity of the magnetic material is reduced, the fluidity is increased, various surrounding raw material particles are adsorbed, and the solid-phase reaction is accelerated, thereby promoting the rapid ferrite formation of the raw materials. The pre-calcination reaction temperature is appropriately reduced, the number of large ferrite particles in the pre-calcined material is reduced, and uniformly crystalline ferrite particles are obtained, thereby improving the overall magnetic properties of the material. At the same time, it helps to reduce the energy consumption level in the pre-calcined material production process.

[0012] In this scheme, if too little sodium silicate is added, it will be difficult to increase the surface negative charge and improve fluidity. At the same time, the uniformity of crystallization of the pre-calcined material will be relatively low, which is not conducive to improving magnetic properties. If too much sodium silicate is added, the negative charge and fluidity will be too great, and too much sodium will be precipitated, resulting in uneven crystallization of ferrite particles during the pre-calcination process. There will be more coarse crystals, which is also not conducive to improving magnetic properties.

[0013] A further technical solution is to control the average particle size of the crystalline seed powder obtained in step S1 to be 1-5 μm.

[0014] In a further technical solution, the amount of crystallization seed powder added in step S2 is 0.1-5 wt% of the total mass of iron oxide red, strontium carbonate and sodium silicate.

[0015] A further technical solution is to preheat in air in step S3, with the temperature controlled at 1120-1230℃ and held for 0.5-3 hours; or, with the temperature controlled at 1150-1220℃ and held for 1-2 hours.

[0016] In this scheme, the surrounding uniformly mixed raw material particles can be adsorbed at a relatively low temperature, which accelerates the ferrite formation process of the raw material composition and improves the crystallization uniformity. Furthermore, the pre-firing at a lower temperature can minimize the generation of coarse crystalline particles, thereby improving the overall magnetic properties of the material. In addition, the lower pre-firing temperature can also reduce the energy consumption of the pre-firing process, thereby reducing the manufacturing cost of the pre-fired material.

[0017] In a further technical solution, the secondary additives in step S4 include one or more of SiO2, CaCO3, Cr2O3, ZnO, Al2O3, H3BO3, and SrCO3, and the average particle size of each secondary additive does not exceed 2µm.

[0018] A further technical solution, based on the mass of the main phase powder as 100%, is that the amounts of the secondary additives added are as follows: SiO2: 0.05–2.0 wt%, CaCO3: 0.4–2.0 wt%, Cr2O3: 0–1.5 wt%, ZnO: 0–0.6 wt%, Al2O3: 0–2.0 wt%, H3BO3: 0–0.8 wt%, SrCO3: 0.1–1.0 wt%.

[0019] A further technical solution is that the sintering in step S5 is divided into two stages: dehydration stage: holding at 100-600℃ for 0.5-2 hours; sintering stage: holding at 1120-1230℃ in air atmosphere for 0.5-3 hours.

[0020] A further technical solution is to control the sintering temperature at 1180℃~1230℃ and hold it for 0.1~3 hours; or, to control the sintering temperature at 1190℃~1220℃ and hold it for 0.5~2 hours.

[0021] In this scheme, the sintering temperature cannot be too high. If the temperature exceeds 1235℃, the liquid material after ball milling will turn white and its properties will decrease.

[0022] Compared with the prior art, the present invention has the following beneficial effects: This invention prepares high-performance lanthanum- and cobalt-free permanent magnet ferrite materials by adding a small amount of sodium silicate to the raw material powder, optimizing the main and secondary additive formulations, and appropriately reducing the pre-calcination temperature. The permanent magnet ferrite materials prepared by this invention have relatively more uniform ferrite crystal particles, avoiding the formation of coarse crystal particles, and thus their overall magnetic properties are significantly better than those of similar materials prepared by traditional processes. In addition, the relatively low pre-calcination temperature of this invention appropriately reduces the energy consumption level in the pre-calcination process, thereby further improving the cost-effectiveness of the material. Attached Figure Description

[0023] Figure 1 This is a comparison chart of magnetic property parameter tests in Embodiment 2 of the present invention; Figure 2 This is a comparison chart of magnetic property parameter tests in Embodiment 3 of the present invention; Figure 3 This is a comparison chart of Br and (BH)max tests in Example 3 of the present invention. Detailed Implementation

[0024] The embodiments of the present invention will be described in further detail below with reference to the accompanying drawings and examples. The following examples are for illustrative purposes only and should not be construed as limiting the scope of the invention.

[0025] Example 1: Preparation of sodium silicate-containing permanent magnet ferrite crystal seed powder (1) Ingredients: Take 5.0 kg of iron oxide red powder with a purity of 99.5%, 0.8 kg of strontium carbonate powder with a purity of 98.5%, and 0.19 kg of sodium silicate (Na2SiO3·5H2O\ Na2SiO3·9H2O) powder with a purity of 98%, put them into a sand mill, add about 9 kg of tap water, and continuously sand mill for 2 hours to obtain a uniformly mixed raw material slurry; (2) Pre-calcination: The above slurry is dried and pre-calcined in a box-type sintering furnace at a pre-calcination temperature of 1200℃ and a holding time of 2h. After cooling, blocky ferrite pre-calcined material is obtained. (3) Crushing: The above ferrite block material is crushed. First, a dry vibrating mill is used for coarse crushing. Then, different crushing methods are used as needed to prepare permanent magnet ferrite crystal seed powder with different average particle size ranges for the following experiments.

[0026] Example 2: Manufacturing experiment with the addition of crystallization seed powder to different pre-fired feed formulations The basic requirements for selecting various main raw materials are as follows: (1) Iron oxide red: the purity of Fe2O3 content is ≥99.0wt%, and the original average particle size is 1.6μm; (2) Strontium carbonate: the purity of SrCO3 is ≥97.0wt%, the main impurities of BaCO3 content are ≤1.0wt%, CaCO3 content is ≤0.6wt%, and the original average particle size is 1.8μm; (3) Calcium carbonate (calcium carbonate is a secondary additive): the purity of CaCO3 is ≥98.5.0wt%, and the original average particle size is 1.5μm; It should be noted that the average particle size of each raw material is required to be at least below 2µm.

[0027] Based on the chemical formula of the main phase composition In the examples, different values ​​of x and n and corresponding purity of the main raw materials were used to calculate the amount of main raw materials added in each example. Then, the corresponding raw materials were weighed and mixed with the crystalline seed powder with an average particle size of 5 μm prepared in Example 1. The mixture was then ball-milled in a wet ball mill for 5 hours, resulting in an average particle size of 0.85 μm. It should be noted that those skilled in the art can extend the ball milling time to make the average particle size less than or equal to 0.85 μm.

[0028] The material was then dried in an oven, pelletized, and pre-fired in air at 1140°C for 1.5 hours to obtain granular pre-fired material. Next, 450 grams of the coarsely pulverized material produced as described above were weighed, and 0.5 wt% SiO2 and 1.15 wt% CaCO3 were added. Then, 680 ml of tap water was added as the ball milling medium, and the mixture was wet-milled in a ball mill for 18 hours. The average particle size of the pulverized slurry was 0.94 µm. It should be noted that in other embodiments of this application, the average particle size of the pulverized slurry should be controlled between 0.65 and 0.95 µm.

[0029] In other embodiments of this application, those skilled in the art can adjust the preheating temperature in the air according to actual needs. Optionally, the temperature is controlled at 1120-1230°C and kept at that temperature for 0.5-3 hours; preferably, the temperature is controlled at 1250-1220°C and kept at that temperature for 1-2 hours.

[0030] In other embodiments of this application, those skilled in the art can adjust the type and ratio of secondary additives according to actual needs. It is necessary to ensure that SiO2: 0.05-2.0 wt%, CaCO3: 0.4-2.0 wt%, Cr2O3: 0-1.5 wt%, ZnO: 0-0.6 wt%, Al2O3: 0-2.0 wt%, H3BO3: 0-0.8 wt%, SrCO3: 0.1-1.0 wt%, and that the average particle size of the secondary additives is less than 2µm.

[0031] After wet grinding, the moisture content of the molding slurry is adjusted, and the solid content of the slurry is adjusted to 70%. It should be noted that those skilled in the art can adjust the solid content of the slurry according to actual needs, ensuring that the solid content is maintained between 65 and 80 wt%. Subsequently, molding is performed, and a molding magnetic field of 11000 Oe is applied in the pressing direction during pressing. The magnetic field strength needs to be no less than 10000 Oe. The resulting molded body is a cylinder with a diameter of 43.2 mm and a height of 12 mm, and the molding pressure is 10 MPa. Finally, the molded body is heat-treated at a temperature of 100℃ to 600℃, and then sintered in air at a heating rate of 150℃ / hour, holding at 1220℃ for 1.5 hours to obtain the sintered body. It should be understood that in other embodiments of this application, those skilled in the art can adjust the temperature according to the following rules: Dehydration stage: 100-600℃ for 0.5-2 hours; Sintering stage: 1120-1230℃ in air atmosphere for 0.5-3 hours. The sintering stage temperature is controlled at 1180℃-1230℃ for 0.1-3 hours, preferably 1190℃-1220℃ for 0.5-2 hours.

[0032] serial number Br (Gs) HcB (Oe) HcJ (Oe) (BH)max (MGOe) Example 2-1 4233 3850 4130 4.22 Example 2-2 4280 3920 4330 4.33 Example 2-3 4270 3930 4290 4.35 Examples 2-4 4310 3980 4230 4.32 Examples 2-5 4190 3996 4380 4.12 .

[0033] Reference manual attached Figure 1 Based on the above test results, by optimizing and adjusting the formula and adding different proportions of ferrite powder as crystal seeds, under certain process conditions, relatively superior comprehensive magnetic properties can be obtained.

[0034] Regarding the effect of x value: When x increases from 0.05 to 0.40, the Sr content increases, and Br and HcB are significantly improved. Sr²⁺ substitution optimizes magnetocrystalline anisotropy. However, when x=0.40, HcJ decreases to 4230 Oe, indicating that excessive Sr may weaken the intrinsic coercivity. Regarding the effect of n value: Br / HcB is optimal when n=6.0.

[0035] Regarding the effect of the amount of crystallization seed added: When the amount added is >5wt%, as in Examples 2-5, it leads to a significant decrease in (BH)max, and excessive seeding disrupts the continuity of the main phase; the optimal range is 0.1-5wt%, as in Examples 2-1 to 2-4, where the magnetic properties are balanced.

[0036] Example 3: Comparative Experiment on Average Particle Size and Addition Amount of Sodium Silicate-Containing Permanent Magnet Ferrite Crystal Seed Powder By adjusting the average particle size and addition amount of the crystallizing seed powder, wherein the average particle size of the crystallizing seed powder is controlled at 0.8-10μm, preferably 1-5μm, and the addition amount is 0.05-10wt% of the total mass of iron oxide red, strontium carbonate and sodium silicate, preferably 0.1-5wt%, and different maximum pre-calcination temperatures are used, the pre-calcination temperature can be selected as 1120-1230℃, and the holding time is 0.5-3 hours; preferably, the temperature is controlled at 1150-1220℃, and the holding time is 1-2 hours. Other process conditions are the same as in Example 2. The relevant process conditions of this example are shown in Table 2: serial number Average particle size of crystalline seed powder (µm) Addition amount of crystalline seed powder (wt%) Preheating temperature (°C) Comparative Example 3-1 0.72 5.0 1180 Example 3-2 0.78 4.5 1120 Example 3-3 0.85 3.5 1150 Examples 3-4 0.91 2.5 1190 Examples 3-5 0.95 1.4 1200 Examples 3-6 1.08 1.0 1210 Examples 3-7 1.18 0.5 1220 .

[0037] The samples in the above embodiments were prepared using the same process as in Example 2, and the test performance is shown in Table 3: serial number Br (Gs) HcB (Oe) HcJ (Oe) (BH)max (MGOe) Comparative Example 3-1 4120 3950 3930 4.15 Example 3-2 4130 3980 4290 4.38 Example 3-3 4250 3940 4190 4.29 Examples 3-4 4280 3950 4260 4.35 Examples 3-5 4360 3880 4125 4.42 Examples 3-6 4310 3980 4220 4.48 Examples 3-7 4210 3950 4120 4.28 .

[0038] Reference manual attached Figure 2-3 Regarding the critical value of crystal seed particle size: a particle size below 0.8 μm (0.72 μm in Comparative Example 3-1) leads to a decrease of Br by 230 Gs and (BH)max by 0.33 MGOe, because excessively fine seeds are prone to sintering and agglomeration, destroying the texture orientation. The optimal particle size is 0.85-1.08 μm (Examples 3-3 to 3-6), with Br ≥ 4250 Gs and (BH)max ≥ 4.29 MGOe.

[0039] Regarding the amount of crystal seed added: the highest (BH)max (4.42-4.48 MGOe) was achieved when the addition amount (0.5-1.4 wt%) was combined with a particle size of 1 μm (Examples 3-5, 3-6).

[0040] Synergistic effect of pre-firing temperature: Pre-firing at 1200-1210℃ (Examples 3-5, 3-6) increases Br and (BH)max; However, temperatures above 1220°C (Examples 3-7) may cause abnormal grain growth, with Br decreasing to 4210Gs.

[0041] The embodiments of the present invention are given for illustrative and descriptive purposes only, and are not intended to be exhaustive or to limit the invention to the forms disclosed. Many modifications and variations will be apparent to those skilled in the art. The embodiments were chosen and described in order to better illustrate the principles and practical application of the invention, and to enable those skilled in the art to understand the invention and to design various embodiments with various modifications suitable for a particular purpose.

Claims

1. A method for preparing a high-performance permanent magnet ferrite material without lanthanum and cobalt additives, characterized in that, Includes the following steps: S1 Preparation of permanent magnet ferrite crystal seed powder containing sodium silicate: Iron oxide red, strontium carbonate and additive sodium silicate are mixed. The molar ratio of Fe2O3 and SrO from the above raw materials is 6:

1. The amount of sodium silicate added is 0.05-5wt% of the total mass of iron oxide red and strontium carbonate. After wet ball milling, pre-calcination and pulverization, crystal seed powder with an average particle size of 0.8-10μm is obtained. S2 Ingredients: Iron oxide red, strontium carbonate, and sodium silicate are mixed according to... Chemically formulated ingredients are mixed, wherein 0.05 ≤ x ≤ 0.5, 5.5 ≤ n ≤ 6.

0. The crystal seed powder from step S1 is added to the above raw materials in an amount of 0.05-10 wt% of the total mass of iron oxide red, strontium carbonate and sodium silicate. After wet mixing, the average particle size of the mixture is ≤0.85µm. S3 pre-calcination: Hold at 1120℃~1230℃ for 0.5~3 hours, and obtain the main phase powder after pulverization; S4 Ball milling: Add secondary additives to the main phase powder in step S3 and wet mill to a slurry with a particle size of 0.65-0.95μm; S5: Adjust the water content of the slurry in step S4 to keep the solid content of the slurry at 65-80 wt%, and then mold it under a magnetic field of not less than 10000 Oe to obtain a molded body. The molded body is then sintered at high temperature to solidify it.

2. The method according to claim 1, characterized in that: The average particle size of the crystalline seed powder obtained in step S1 is controlled to be 1-5 μm.

3. The method according to claim 1 or 2, characterized in that: In step S2, the amount of crystallization seed powder added is 0.1-5 wt% of the total mass of iron oxide red, strontium carbonate and sodium silicate.

4. The method according to claim 1, characterized in that: Step S3 involves preheating in air at a temperature controlled at 1120–1230°C for 0.5–3 hours. Alternatively, the temperature can be controlled at 1150–1220℃ and kept warm for 1–2 hours.

5. The method according to claim 1, characterized in that: The secondary additives in step S4 include one or more of SiO2, CaCO3, Cr2O3, ZnO, Al2O3, H3BO3, and SrCO3, and the average particle size of each secondary additive does not exceed 2µm.

6. The method according to claim 7, characterized in that: Based on the mass of the main phase powder as 100%, the amounts of the secondary additives are as follows: SiO2: 0.05–2.0 wt%, CaCO3: 0.4–2.0 wt%, Cr2O3: 0–1.5 wt%, ZnO: 0–0.6 wt%, Al2O3: 0–2.0 wt%, H3BO3: 0–0.8 wt%, SrCO3: 0.1–1.0 wt%.

7. The method according to claim 1, characterized in that: Sintering in step S5 is divided into two stages: Dehydration stage: Keep warm at 100-600℃ for 0.5 to 2 hours; Sintering stage: Hold at 1120-1230℃ in air atmosphere for 0.5-3 hours.

8. The method according to claim 9, characterized in that: The temperature during the sintering stage is controlled at 1180℃~1230℃, and the holding time is 0.1~3 hours; Alternatively, the sintering temperature is 1190℃~1220℃, and the holding time is 0.5~2 hours.

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