A method for controlling sintered strontium ferrite materials

Abstract

This invention relates to a method for controlling the particle size distribution of sintered strontium ferrite materials. The method includes: first, adjusting the type and ratio of additives according to the D50 particle size of the strontium ferrite pre-sintered powder and the performance requirements of the strontium ferrite material; ball milling the strontium ferrite pre-sintered powder, additives, and dispersant until the target D50 particle size is achieved to obtain a mixed slurry; then, dehydrating the mixed slurry, sequentially performing orientation wet pressing and drying to obtain a green body; subsequently, sintering the green body, controlling the heating rate to reach the sintering temperature and holding it at that temperature, followed by cooling to obtain the strontium ferrite material. The method provided by this invention combines the particle size characteristics of the pre-sintered powder, the selection of additives, and the control of the ball milling and sintering processes to control the preparation of high-performance sintered strontium ferrite materials.

Description

Technical Field

[0001] This invention relates to the field of magnetic material preparation technology, specifically to a method for controlling sintered strontium ferrite materials. Background Technology

[0002] Ferrite permanent magnets belong to the second generation of permanent magnet materials. They are characterized by high resistivity, good temperature stability, and strong resistance to environmental stress. Furthermore, their abundant raw material sources, low cost, and suitability for mass production make them key electronic materials for components such as micro-motors in electroacoustic devices, high-power industrial motors, new energy vehicles, intelligent machinery, and unmanned power systems. Although the maximum energy product of ferrite magnets (strontium ferrite) is only 1 / 10 that of rare earth magnets (sintered NdFeB permanent magnets), the uneven distribution of rare earth metal resources, the scarcity of certain heavy rare earth metals, the instability of the rare earth supply chain, and the potential negative environmental impacts of rare earth mining make the search for and development of more environmentally friendly and lower-cost sintered ferrite permanent magnet alternatives particularly urgent. The demand for high-end strontium ferrite materials will continue to increase.

[0003] Currently, efforts to improve the performance of strontium ferrite materials mainly focus on two key aspects: optimization of magnetic powder performance and enhancement of magnet performance. Magnetic powder performance can be optimized by doping the raw materials with rare earth ions to replace some elements, and by adding dispersants to modify the powder surface. Magnet performance can be improved by using appropriate additives and modifying the sintering process. During sintering, additives accumulate at grain boundaries, playing a dual role of fluxing and inhibiting grain growth. This not only refines the grains and increases the magnet density but also significantly improves the material's microstructure, which is beneficial for increasing the proportion of single-domain particles and improving rectangularity.

[0004] For example, the existing study "Influence of SiO2 and CaO additions on the microstructure and magnetic properties of sintered Sr-hexaferrite. Journal of the European Ceramic Society, 25(9), 1681-1688" discloses that adding SiO2 and CaO (or CaCO3) before sintering strontium ferrite can react at low temperatures to form a calcium silicate phase. However, if strontium ferrite with excess SrO is sintered at a eutectic temperature above 1210℃, the liquid phase will react with the calcium silicate formed by CaO and SiO2. The final composition of the liquid phase will determine the grain growth rate of the ferrite, affecting the grain size and magnet density, and further affecting the magnetic properties. In addition, some studies have shown that the addition of additives can only improve one aspect of the magnetic properties of the magnet, but often causes a decrease in another aspect of the magnetic properties, which has obvious limitations. Furthermore, the failure to combine the analysis of additive usage, front-end ball milling process, and back-end sintering process may lead to formulation conflicts when selecting additives. The lack of quantitative analysis of the impact of additive content and ratio on magnets may result in a situation where a single magnetic powder requires repeated testing and sintering to produce a magnet that meets the requirements.

[0005] Therefore, it is necessary to develop a fully monitorable preparation process from magnetic powder to magnet, which matches the characteristics of magnetic powder, the selection of additives, and the ball milling and sintering processes, to quickly prepare magnetic powder into magnets with customized properties, thereby improving production efficiency and reducing production costs. Summary of the Invention

[0006] To address the above problems, the present invention aims to provide a method for controlling the sintering of strontium ferrite materials. Compared with the prior art, the method provided by the present invention combines the particle size characteristics of the pre-sintered powder, the selection of additives, and the control of ball milling and sintering processes, which can control the preparation of high-performance sintered strontium ferrite materials.

[0007] To achieve this objective, the present invention adopts the following technical solution:

[0008] This invention provides a method for controlling the sintering of strontium ferrite materials, the method comprising the following steps:

[0009] (1) Based on the D50 particle size of the strontium ferrite pre-sintered powder and the performance requirements of the strontium ferrite material, the type and ratio of additives are adjusted, and the strontium ferrite pre-sintered powder, additives and dispersant are ball-milled to reach the target D50 particle size to obtain a mixed slurry.

[0010] (2) The mixed slurry obtained in step (2) is dehydrated, and then oriented wet pressing and drying are performed in sequence to obtain a green body;

[0011] (3) The green blank obtained in step (2) is subjected to sintering treatment. During the sintering treatment, the heating rate is controlled to reach the sintering temperature and held at that temperature, and then cooled to obtain strontium ferrite material.

[0012] In this invention, the type and ratio of additives are controlled based on the D50 particle size and other characteristics of the strontium ferrite pre-sintered powder, as well as the ball milling and sintering processes are adjusted. The magnetic properties of ferrite materials are closely related to their slurry particle size. This invention can improve the dispersibility of the slurry and appropriately reduce the magnetic powder particle size, thus achieving a higher grain orientation. Furthermore, by controlling the type of additives and adjusting the sintering process, the orientation and density of the ferrite material can be further improved. Moreover, by controlling the type of additives, different ferrite materials with specific performance requirements can be prepared based on a single magnetic powder pre-sintered powder, meeting the needs of different application scenarios.

[0013] Preferably, the additives in step (1) include silicon dioxide and calcium carbonate.

[0014] Preferably, the additive further includes bismuth oxide and / or aluminum oxide.

[0015] In this invention, the additive silicon dioxide is generally nanoscale, while calcium carbonate, bismuth oxide, aluminum oxide, etc. are generally micrometer-scale, and all are industrial-grade. The particle size of the micrometer-scale additives generally meets the requirements of D50 = 0.5-2.5 μm and D90 / D10 < 5.

[0016] Preferably, when the D50 particle size of the strontium ferrite pre-sintered powder is <1μm, the mass of silicon dioxide accounts for 0.5-0.6% of the mass of the strontium ferrite pre-sintered powder, for example, it can be 0.5%, 0.52%, 0.54%, 0.56%, 0.58% or 0.6%, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0017] Preferably, when the D50 particle size of the strontium ferrite pre-sintered powder is 1-3 μm, the mass of silicon dioxide accounts for 0.4-0.5% of the mass of the strontium ferrite pre-sintered powder, for example, it can be 0.4%, 0.42%, 0.44%, 0.46%, 0.48% or 0.5%, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0018] Preferably, when the D50 particle size of the strontium ferrite pre-sintered powder is >3μm, the mass of silicon dioxide accounts for 0.2-0.4% of the mass of the strontium ferrite pre-sintered powder, for example, it can be 0.2%, 0.22%, 0.24%, 0.26%, 0.28%, 0.3%, 0.32%, 0.34%, 0.36%, 0.38% or 0.4%, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0019] In this invention, the amount of silica added in the additive is controlled according to the D50 particle size of the strontium ferrite pre-sintered powder. This invention preferably adopts the correspondence between the aforementioned D50 particle size range and the mass percentage of silica because, during the sintering process, the silicate liquid phase, with silica as a network forming agent, is the main factor controlling sintering. Too high or too low a content will affect the structure and properties of the sintered body. Too high a content can easily cause abnormal grain growth, leading to a decrease in coercivity; too low a content can easily result in incomplete sintering and insufficient density of the sintered body. Therefore, this invention controls the addition of silica according to the D50 particle size range. Different D50 particle size ranges reflect the specific surface area of ​​the pre-sintered powder; the larger the particle size, the smaller the specific surface area, the less silicate liquid phase is required, and the less silica content in the formulation. Therefore, this invention can accurately predict and control the amount of silica used, thereby meeting the performance requirements of strontium ferrite materials.

[0020] Preferably, the strontium ferrite pre-burned powder in step (1) is pure M-phase strontium ferrite.

[0021] Preferably, the chemical formula of the strontium ferrite pre-sintered powder is SrFe. x O 19 The value of X is 11-12, for example, it can be 11, 11.2, 11.4, 11.6, 11.8 or 12, but it is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0022] Preferably, the dispersant comprises calcium gluconate and / or sodium carboxymethyl cellulose.

[0023] Preferably, the mass of the dispersant accounts for 0.3-0.5% of the mass of the strontium ferrite pre-calcined powder, for example, it can be 0.3%, 0.32%, 0.34%, 0.36%, 0.38%, 0.40%, 0.42%, 0.44%, 0.46%, 0.48% or 0.5%, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0024] Preferably, a solvent is also added during the ball milling process.

[0025] Preferably, the solvent includes water.

[0026] Preferably, the solid-liquid ratio of the slurry mixture in the ball mill is 1:(1.5-2.5), for example, it can be 1:1.5, 1:1.6, 1:1.7, 1:1.8, 1:1.9, 1:2, 1:2.1, 1:2.2, 1:2.3, 1:2.4 or 1:2.5, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0027] Preferably, the grinding balls used in the ball mill include stainless steel balls.

[0028] Preferably, the diameter of the grinding balls used in the ball mill is 2-5 mm, for example, 2 mm, 3 mm, 4 mm or 5 mm, but not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0029] Preferably, the mass ratio of strontium ferrite pre-calcined powder to grinding balls in the ball mill is 1:(10-20), for example, it can be 1:10, 1:12, 1:14, 1:16, 1:18 or 1:20, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0030] Preferably, the water content in the mixture slurry during dehydration in step (2) is 30-50% by mass, for example, it can be 30%, 32%, 34%, 36%, 38%, 40%, 42%, 44%, 46%, 48% or 50%, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0031] Preferably, the orientation wet pressing pressure is 4.5-6.5 MPa, for example, it can be 4.5 MPa, 4.6 MPa, 4.8 MPa, 5 MPa, 5.2 MPa, 5.4 MPa, 5.6 MPa, 5.8 MPa, 6 MPa, 6.2 MPa, 6.4 MPa or 6.5 MPa, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0032] Preferably, the holding time for the orientation wet pressing is 30-60s, for example, it can be 30s, 35s, 40s, 45s, 50s, 55s or 60s, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0033] Preferably, the maximum orientation magnetic induction intensity of the orientation wet pressing is 0.5-1.5T, for example, it can be 0.5T, 0.6T, 0.8T, 1T, 1.2T, 1.4T or 1.5T, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0034] Preferably, the drying temperature is 60-90℃, for example, it can be 60℃, 62℃, 64℃, 66℃, 68℃, 70℃, 72℃, 74℃, 76℃, 78℃, 80℃, 82℃, 84℃, 86℃, 88℃ or 90℃, but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0035] Preferably, the drying time is 2-4 hours, for example, it can be 2 hours, 2.2 hours, 2.4 hours, 2.6 hours, 2.8 hours, 3 hours, 3.2 hours, 3.4 hours, 3.6 hours, 3.8 hours or 4 hours, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0036] Preferably, the sintering temperature in step (3) is 1150-1250℃, for example, it can be 1150℃, 1160℃, 1170℃, 1180℃, 1190℃, 1200℃, 1210℃, 1220℃, 1230℃, 1240℃ or 1250℃, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0037] Preferably, the heat preservation time is 10-60 minutes, for example, it can be 10 minutes, 20 minutes, 30 minutes, 40 minutes, 50 minutes or 60 minutes, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0038] Preferably, the heating process includes: first heating to 800°C at a first heating rate, and then heating to the sintering temperature at a second heating rate.

[0039] Preferably, the first heating rate is ≤5℃ / min, for example, it can be 5℃ / min, 4℃ / min, 3℃ / min, 2℃ / min or 1℃ / min, but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0040] Preferably, the second heating rate is ≤10℃ / min, for example, it can be 10℃ / min, 8℃ / min, 6℃ / min, 5℃ / min, 4℃ / min, 3℃ / min, 2℃ / min or 1℃ / min, but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0041] Preferably, the strontium ferrite material is classified according to remanence and coercivity, including a first ferrite material, a second ferrite material, a third ferrite material, and a fourth ferrite material.

[0042] Preferably, the properties of the first ferrite material satisfy the following: remanence Br is 4150-4250 Gs, for example, it can be 4150 Gs, 4160 Gs, 4170 Gs, 4180 Gs, 4190 Gs, 4200 Gs, 4210 Gs, 4220 Gs, 4230 Gs, 4240 Gs or 4250 Gs, but is not limited to the listed values, and other unlisted values ​​within the range are also applicable; coercivity Hcj is 3400-3700 Oe, for example, it can be The values ​​can be 3400 Oe, 3450 Oe, 3500 Oe, 3550 Oe, 3600 Oe, 3650 Oe, or 3700 Oe, but are not limited to the listed values; other unlisted values ​​within the range also apply. The maximum magnetic energy product BH is 4.1-4.3 MGOe, for example, it can be 4.1 MGOe, 4.2 MGOe, or 4.3 MGOe, but is not limited to the listed values; other unlisted values ​​within the range also apply. The bulk density is ≥5.0 g / cm³. 3 For example, it could be 5.0 g / cm³. 3 5.1g / cm 3 5.2g / cm 3 5.3g / cm 3 5.4g / cm 3 Or 5.5g / cm 3 However, this does not limit the listed values; other unlisted values ​​within the range are also applicable.

[0043] Preferably, the second ferrite material has the following properties: remanence Br is 4050-4150 Gs, for example, it can be 4050 Gs, 4060 Gs, 4070 Gs, 4080 Gs, 4090 Gs, 4100 Gs, 4110 Gs, 4120 Gs, 4130 Gs, 4140 Gs or 4150 Gs, but is not limited to the listed values, and other unlisted values ​​within the range are also applicable; coercivity Hcj is 4200-4400 Ω. Oe, for example, can be 4200Oe, 4250Oe, 4300Oe, 4350Oe, or 4400Oe, but is not limited to the listed values; other unlisted values ​​within the range also apply; the maximum magnetic energy product BH is 4.0-4.2 MGOe, for example, can be 4.0 MGOe, 4.1 MGOe, or 4.2 MGOe, but is not limited to the listed values; other unlisted values ​​within the range also apply; bulk density ≥ 4.95 g / cm³ 3 For example, it could be 4.95 g / cm³ 3 4.96 g / cm 3 4.97g / cm 3 4.98g / cm 3 4.99g / cm 3Or 5.00g / cm 3 However, this does not limit the listed values; other unlisted values ​​within the range are also applicable.

[0044] Preferably, the third ferrite material has the following properties: remanence Br is 4000-4100 Gs, for example, it can be 4000 Gs, 4010 Gs, 4020 Gs, 4030 Gs, 4040 Gs, 4050 Gs, 4060 Gs, 4070 Gs, 4080 Gs, 4090 Gs or 4100 Gs, but is not limited to the listed values, and other unlisted values ​​within the range are also applicable; coercivity Hcj is 4300-4500 Oe, for example, it can be 43 00 Oe, 4350 Oe, 4400 Oe, 4450 Oe, or 4500 Oe, but not limited to the listed values; other unlisted values ​​within the range also apply; the maximum magnetic energy product BH is 3.9-4.1 MGOe, for example, it can be 3.90 MGOe, 3.95 MGOe, 4.00 MGOe, 4.05 MGOe, or 4.10 MGOe, but not limited to the listed values; other unlisted values ​​within the range also apply; bulk density ≥ 4.90 g / cm³. 3 For example, it could be 4.90 g / cm³ 3 4.95g / cm 3 4.96 g / cm 3 4.97g / cm 3 4.98g / cm 3 4.99g / cm 3 Or 5.00g / cm 3 However, this does not limit the listed values; other unlisted values ​​within the range are also applicable.

[0045] Preferably, the fourth ferrite material has the following properties: remanence Br is 3850-3950 Gs, for example, it can be 3850 Gs, 3860 Gs, 3870 Gs, 3880 Gs, 3890 Gs, 3900 Gs, 3910 Gs, 3920 Gs, 3930 Gs, 3940 Gs or 3950 Gs, but is not limited to the listed values, and other unlisted values ​​within the range are also applicable; coercivity Hcj is 4600-4700 Oe, for example... For example, the values ​​could be 4600 Oe, 4620 Oe, 4640 Oe, 4680 Oe, or 4700 Oe, but are not limited to the listed values; other unlisted values ​​within the range also apply. The maximum magnetic energy product BH is 3.7-4.0 MGOe, for example, it could be 3.7 MGOe, 3.8 MGOe, 3.9 MGOe, or 4.0 MGOe, but are not limited to the listed values; other unlisted values ​​within the range also apply. The bulk density is ≥4.88 g / cm³. 3For example, it could be 4.88 g / cm³ 3 4.90 g / cm 3 4.95g / cm 3 4.96 g / cm 3 4.97g / cm 3 4.98g / cm 3 4.99g / cm 3 Or 5.00g / cm 3 However, this does not limit the listed values; other unlisted values ​​within the range are also applicable.

[0046] In this invention, based on remanence and coercivity, the first ferrite material generally represents a high remanence magnet, the second ferrite material generally represents a high remanence and high coercivity magnet, the third ferrite material generally represents a high coercivity magnet, and the fourth ferrite material generally represents an ultra-high coercivity magnet. The remanence and coercivity ranges corresponding to each type of magnet are as described above.

[0047] Preferably, when the strontium ferrite material is the first ferrite material, the D50 particle size of the strontium ferrite pre-sintered powder is ≥2μm, for example, it can be 2μm, 3μm, 4μm, 5μm or 6μm, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0048] Preferably, when the strontium ferrite material is a first ferrite material, the molar ratio of calcium carbonate to silicon dioxide in the additive is (1.8-2.5):1, for example, it can be 1.8:1, 1.9:1, 2:1, 2.1:1, 2.2:1, 2.3:1, 2.4:1 or 2.5:1, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0049] Preferably, when the strontium ferrite material is the first ferrite material, the mass percentage of bismuth oxide in the additive to the mass of the strontium ferrite pre-calcined powder is ≤1%, for example, it can be 1%, 0.9%, 0.8%, 0.6% or 0.5%, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0050] Preferably, when the strontium ferrite material is the first ferrite material, the rotation speed of the ball mill is 50-100 rpm, for example, it can be 50 rpm, 60 rpm, 70 rpm, 80 rpm, 90 rpm or 100 rpm, but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0051] Preferably, when the strontium ferrite material is a first ferrite material, the ball milling time is 8-20 hours, for example, it can be 8 hours, 10 hours, 12 hours, 14 hours, 16 hours, 18 hours or 20 hours, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0052] Preferably, when the strontium ferrite material is a first ferrite material, the particle size of the ball milling to the target D50 is 0.7-0.9 μm, for example, it can be 0.7 μm, 0.75 μm, 0.8 μm, 0.85 μm or 0.9 μm, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0053] Preferably, when the strontium ferrite material is a first ferrite material, the sintering temperature is 1200-1250℃, for example, it can be 1200℃, 1210℃, 1220℃, 1230℃, 1240℃ or 1250℃, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0054] Preferably, when the strontium ferrite material is a second ferrite material, the D50 particle size of the strontium ferrite pre-sintered powder is 1-3 μm, for example, it can be 1 μm, 1.2 μm, 1.4 μm, 1.6 μm, 1.8 μm, 2 μm, 2.2 μm, 2.4 μm, 2.6 μm, 2.8 μm or 3 μm, but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0055] Preferably, when the strontium ferrite material is a second ferrite material, the molar ratio of calcium carbonate to silicon dioxide in the additive is (1.5-1.8):1, for example, it can be 1.5:1, 1.6:1, 1.7:1 or 1.8:1, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0056] Preferably, when the strontium ferrite material is a second ferrite material, the rotation speed of the ball mill is 50-150 rpm, for example, it can be 50 rpm, 60 rpm, 70 rpm, 80 rpm, 90 rpm, 100 rpm, 110 rpm, 120 rpm, 130 rpm, 140 rpm or 150 rpm, but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0057] Preferably, when the strontium ferrite material is a second ferrite material, the ball milling time is 12-24 hours, for example, it can be 12 hours, 14 hours, 16 hours, 18 hours, 20 hours, 22 hours or 24 hours, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0058] Preferably, when the strontium ferrite material is a second ferrite material, the particle size of the ball milling to the target D50 is 0.65-0.9 μm, for example, it can be 0.65 μm, 0.70 μm, 0.75 μm, 0.80 μm, 0.85 μm or 0.90 μm, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0059] Preferably, when the strontium ferrite material is a second ferrite material, the sintering temperature is 1180-1220℃, for example, it can be 1180℃, 1190℃, 1200℃, 1210℃ or 1220℃, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0060] Preferably, when the strontium ferrite material is a third ferrite material, the D50 particle size of the strontium ferrite pre-sintered powder is 1-3 μm, for example, it can be 1 μm, 1.2 μm, 1.4 μm, 1.6 μm, 1.8 μm, 2 μm, 2.2 μm, 2.4 μm, 2.6 μm, 2.8 μm or 3 μm, but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0061] Preferably, when the strontium ferrite material is a third ferrite material, the molar ratio of calcium carbonate to silicon dioxide in the additive is (1.2-1.5):1, for example, it can be 1.2:1, 1.3:1, 1.4:1 or 1.5:1, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0062] Preferably, when the strontium ferrite material is a third ferrite material, the rotation speed of the ball mill is 100-200 rpm, for example, it can be 100 rpm, 110 rpm, 120 rpm, 130 rpm, 140 rpm, 150 rpm, 160 rpm, 170 rpm, 180 rpm, 190 rpm or 200 rpm, but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0063] Preferably, when the strontium ferrite material is a third ferrite material, the ball milling time is 16-36 hours, for example, it can be 16 hours, 18 hours, 20 hours, 22 hours, 24 hours, 26 hours, 28 hours, 30 hours, 32 hours, 34 hours or 36 hours, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0064] Preferably, when the strontium ferrite material is a third ferrite material, the particle size of the ball milling to the target D50 is 0.6-0.8 μm, for example, it can be 0.6 μm, 0.65 μm, 0.7 μm, 0.75 μm or 0.8 μm, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0065] Preferably, when the strontium ferrite material is a third ferrite material, the sintering temperature is 1150-1200℃, for example, it can be 1150℃, 1160℃, 1170℃, 1180℃, 1190℃ or 1200℃, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0066] Preferably, when the strontium ferrite material is a fourth ferrite material, the D50 particle size of the strontium ferrite pre-sintered powder is ≤3μm, for example, it can be 3μm, 2.8μm, 2.6μm, 2.4μm, 2.2μm, 2μm, 1.8μm, 1.6μm, 1.4μm, 1.2μm or 1μm, but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0067] Preferably, when the strontium ferrite material is a fourth ferrite material, the molar ratio of calcium carbonate to silicon dioxide in the additive is (1.2-1.5):1, for example, it can be 1.2:1, 1.3:1, 1.4:1 or 1.5:1, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0068] Preferably, when the strontium ferrite material is a fourth ferrite material, the percentage of alumina in the additive to the mass of the strontium ferrite pre-calcined powder is ≤1.5%, for example, it can be 1.5%, 1.4%, 1.3%, 1.2%, 1.1% or 1%, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0069] Preferably, when the strontium ferrite material is a fourth ferrite material, the rotation speed of the ball mill is 100-200 rpm, for example, it can be 100 rpm, 110 rpm, 120 rpm, 130 rpm, 140 rpm, 150 rpm, 160 rpm, 170 rpm, 180 rpm, 190 rpm or 200 rpm, but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0070] Preferably, when the strontium ferrite material is a fourth ferrite material, the ball milling time is 16-36 hours, for example, it can be 16 hours, 18 hours, 20 hours, 22 hours, 24 hours, 26 hours, 28 hours, 30 hours, 32 hours, 34 hours or 36 hours, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0071] Preferably, when the strontium ferrite material is a fourth ferrite material, the particle size of the ball milling to the target D50 is 0.6-0.8 μm, for example, it can be 0.6 μm, 0.65 μm, 0.7 μm, 0.75 μm or 0.8 μm, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0072] Preferably, when the strontium ferrite material is a fourth ferrite material, the sintering temperature is 1150-1200℃, for example, it can be 1150℃, 1160℃, 1170℃, 1180℃, 1190℃ or 1200℃, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0073] In this invention, based on the performance requirements of the strontium ferrite material—namely, the performance requirements for preparing the first, second, third, and fourth ferrite materials—the above-mentioned scheme is preferably used to control the molar ratio of calcium carbonate and silicon dioxide, as well as whether to add bismuth oxide, aluminum oxide, etc. This is because the molar ratio of calcium carbonate and silicon dioxide in the additives affects the composition of the silicate formed during sintering. Silicate liquid phases with different compositions have different viscosities at high temperatures and also have different effects on grain growth orientation. Therefore, by controlling the molar ratio of calcium carbonate and silicon dioxide, this invention can further control the viscosity of the silicate liquid phase and its influence on grain growth, thereby meeting the performance requirements of the strontium ferrite material. Furthermore, bismuth oxide and aluminum oxide can alter the properties of the ferrite through high-temperature doping, thereby further preparing the strontium ferrite material with the desired performance requirements.

[0074] In this invention, the ball milling speed and time are adjusted according to the performance requirements of the strontium ferrite material, thereby optimally controlling the ball milling to the D50 particle size endpoint. The first to fourth ferrite materials correspond to different target D50 particle size ranges because powders of different particle sizes have different sintering activities. Samples with smaller particle sizes have higher sintering activities and are more likely to obtain dense sintered bodies under the same sintering conditions. Furthermore, the grain size and orientation after sintering directly determine the magnet performance; smaller grain sizes lead to greater coercivity, and samples with better grain orientation consistency have better remanence. Therefore, this invention can further regulate the performance of the strontium ferrite material by controlling the D50 particle size after ball milling. In addition, before the end of ball milling, a small amount of slurry is dried to test whether the size of the powder after ball milling meets the target requirements. If the requirements are met, the powder is discharged; otherwise, ball milling continues.

[0075] In this invention, the sintering heating rate and sintering temperature are controlled according to the performance requirements of the strontium ferrite material and the additive formulation. The first to fourth ferrite materials each correspond to different sintering temperature ranges because different ferrite materials use different additive formulations. These different additive formulations result in different silicate liquid phase compositions at high temperatures, leading to variations in viscosity and the grain growth process during sintering, as well as different degrees of sintering promotion. Specifically, at the same sintering temperature, this can result in different sintering densities and differences in grain size and orientation within the sintered body. Therefore, this invention preferably sets different sintering temperature ranges for different additive formulations, enabling the control of sintering density, grain size, and orientation to achieve the desired magnetic properties.

[0076] In this invention, the heating rate is controlled within a specific range because, in the later stages of magnet sintering, the heating rate has a significant impact on the mass transfer and growth mode of the grains. A faster heating rate helps to avoid abnormal grain growth and is suitable for obtaining magnets with smaller grain sizes and higher density at higher temperatures. A slower heating rate is conducive to the fusion growth between grains and is suitable for obtaining magnets with larger grain sizes and higher density at lower temperatures. Thus, by optimizing the range of heating rates, this invention can further regulate the properties of ferrite materials.

[0077] Compared with the prior art, the present invention has the following beneficial effects:

[0078] (1) The method provided by the present invention can match the characteristics of magnetic powder, the selection of additives, ball milling and sintering processes, and can achieve quantitative control of magnet performance. It can quickly produce customized magnets that meet specific performance requirements, avoiding the need for repeated testing of additives and sintering processes when using a single magnetic powder, thereby significantly improving production efficiency and reducing production costs.

[0079] (2) The method provided by the present invention can prepare a first ferrite material with high remanence, a second material with high remanence and high coercivity, a third ferrite material with high coercivity and a fourth ferrite material with ultra-high coercivity, to meet the needs of different fields. Attached Figure Description

[0080] Figure 1 This is a flowchart of the method described in Embodiment 1 of the present invention;

[0081] Figure 2 This is a demagnetization curve of the strontium ferrite material described in Embodiment 1 of the present invention;

[0082] Figure 3 This is a demagnetization curve of the strontium ferrite material described in Embodiment 2 of the present invention;

[0083] Figure 4 This is a demagnetization curve of the strontium ferrite material described in Embodiment 3 of the present invention;

[0084] Figure 5 This is a demagnetization curve of the strontium ferrite material described in Embodiment 4 of the present invention;

[0085] Figure 6 This is a demagnetization curve of the strontium ferrite material described in Embodiment 5 of the present invention;

[0086] Figure 7 This is a demagnetization curve of the strontium ferrite material described in Embodiment 6 of the present invention. Detailed Implementation

[0087] The technical solution of the present invention will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention and should not be construed as limiting the invention in any way.

[0088] In the following examples, the D50 particle size of strontium ferrite pre-sintered powder was tested using the SYMPATEC GmbH HELOS & RODOS dry method.

[0089] The particle size distribution of the oxide powder in the following examples was tested using ISO 24235-2007, "Fine ceramics (advanced ceramics, advanced industrial ceramics) - Determination of particle size distribution of ceramic powders by laser diffraction".

[0090] Example 1

[0091] This embodiment provides a method for controlling the sintering of strontium ferrite materials, such as... Figure 1 As shown, the method includes the following steps:

[0092] (1) Select strontium ferrite pre-sintered powder, specifically pure M-phase strontium ferrite with the chemical formula SrFe. x O 19Where X is 12, and the D50 particle size is 2.5-3.0 μm, based on the D50 particle size of the strontium ferrite pre-sintered powder and the performance requirements of the strontium ferrite material (taking the first ferrite material as the target product), the additives are set as calcium carbonate and silicon dioxide. The mass of silicon dioxide accounts for 0.5% of the mass of the strontium ferrite pre-sintered powder, and the molar ratio of calcium carbonate to silicon dioxide is 2:1. The strontium ferrite pre-sintered powder, additives, and dispersant are added... The mixture was placed in a ball mill jar containing 500g of pre-calcined material, 2.5g of dispersant (calcium gluconate), 8kg of 5mm stainless steel grinding balls, and 1.02kg of water as a ball milling solvent. The solid-liquid ratio of the mixture in the ball mill was 1:2, the mass ratio of strontium ferrite pre-calcined material powder to grinding balls was 1:16, the ball milling speed was 100rpm, and the time was 18h. The mixture was milled until the target D50 particle size was 0.85μm to obtain the mixed slurry.

[0093] (2) The slurry obtained in step (2) is dehydrated until the mass percentage of water in the slurry is 35%. Then it is put into a cylindrical mold with a diameter of 25 mm for orientation wet pressing. The forming pressure is 6.0 MPa, the holding time is 30 s, the maximum orientation magnetic induction intensity is 1.5 T, and then it is dried at 60°C for 4 h to obtain a green body.

[0094] (3) The green blank obtained in step (2) is subjected to sintering treatment. In the sintering treatment, the temperature is first raised to 800°C at a heating rate of 5°C / min, then raised to 1210°C at a heating rate of 5°C / min and held for 30 min, and then cooled to obtain strontium ferrite material.

[0095] Example 2

[0096] This embodiment provides a method for controlling the sintering of strontium ferrite materials, the method comprising the following steps:

[0097] (1) Select strontium ferrite pre-sintered powder, specifically pure M-phase strontium ferrite with the chemical formula SrFe. x O 19Where X is 11.6, and D50 particle size is 2.0-2.5μm, based on the D50 particle size of the strontium ferrite pre-sintered powder and the performance requirements of the strontium ferrite material (with the second ferrite material as the target product), the additives are set as calcium carbonate and silicon dioxide. The mass of silicon dioxide accounts for 0.45% of the mass of the strontium ferrite pre-sintered powder, and the molar ratio of calcium carbonate to silicon dioxide is 1.8:1. The strontium ferrite pre-sintered powder, additives, and dispersion are then mixed. The agent was added to the ball mill jar, including 500g of pre-calcined material, 2.5g of dispersant (calcium gluconate), 8kg of 3mm stainless steel grinding balls, and 0.81kg of ball milling solvent water. The solid-liquid ratio of the mixed slurry in the ball mill was 1:1.6, the mass ratio of strontium ferrite pre-calcined material powder to grinding balls was 1:16, the ball milling speed was 80rpm, the time was 16h, and the ball milling was carried out until the target D50 particle size was 0.75μm to obtain the mixed slurry.

[0098] (2) The slurry obtained in step (2) is dehydrated until the water content in the slurry is 40% by mass. Then it is put into a cylindrical mold with a diameter of 25 mm for orientation wet pressing. The forming pressure is 5.5 MPa, the holding time is 30 s, the maximum orientation magnetic induction intensity is 1.0 T, and then it is dried at 60°C for 4 h to obtain a green body.

[0099] (3) The green blank obtained in step (2) is subjected to sintering treatment. In the sintering treatment, the temperature is first raised to 800°C at a heating rate of 5°C / min, then raised to 1180°C at a heating rate of 5°C / min and held for 30 min, and then cooled to obtain strontium ferrite material.

[0100] Example 3

[0101] This embodiment provides a method for controlling the sintering of strontium ferrite materials, the method comprising the following steps:

[0102] (1) Select strontium ferrite pre-sintered powder, specifically pure M-phase strontium ferrite with the chemical formula SrFe. x O 19Where X is 12, and the D50 particle size is 2.5-3.0 μm, based on the D50 particle size of the strontium ferrite pre-sintered powder and the performance requirements of the strontium ferrite material (taking the first ferrite material as the target product), the additives are set as calcium carbonate, silicon dioxide, and bismuth oxide. The mass of silicon dioxide accounts for 0.5% of the mass of the strontium ferrite pre-sintered powder, the molar ratio of calcium carbonate to silicon dioxide is 2:1, and the mass of bismuth oxide accounts for 0.5% of the mass of the strontium ferrite pre-sintered powder. The pre-calcined ferrite powder, additives, and dispersant were added to a ball mill jar, with 500g of pre-calcined ferrite and 2.5g of dispersant (sodium carboxymethyl cellulose). 5mm stainless steel grinding balls with a mass of 6kg were used, and 1kg of water was added as a ball milling solvent. The solid-liquid ratio of the mixture in the ball mill was 1:1.9, the mass ratio of strontium ferrite pre-calcined ferrite powder to grinding balls was 1:12, the ball milling speed was 100rpm, and the time was 18h. The mixture was ball milled until the target D50 particle size was 0.85μm to obtain the mixed slurry.

[0103] (2) The slurry obtained in step (2) is dehydrated until the mass percentage of water in the slurry is 35%. Then it is put into a cylindrical mold with a diameter of 25 mm for orientation wet pressing. The forming pressure is 6.0 MPa, the holding time is 30 s, the maximum orientation magnetic induction intensity is 1.5 T, and then it is dried at 60°C for 4 h to obtain a green body.

[0104] (3) The green blank obtained in step (2) is subjected to sintering treatment. In the sintering treatment, the temperature is first raised to 800°C at a heating rate of 5°C / min, then raised to 1220°C at a heating rate of 5°C / min and held for 30 min, and then cooled to obtain strontium ferrite material.

[0105] Example 4

[0106] This embodiment provides a method for controlling the sintering of strontium ferrite materials, the method comprising the following steps:

[0107] (1) Select strontium ferrite pre-sintered powder, specifically pure M-phase strontium ferrite with the chemical formula SrFe. x O 19Where X is 11.8, and D50 particle size is 2.0-2.5 μm, based on the D50 particle size of the strontium ferrite pre-sintered powder and the performance requirements of the strontium ferrite material (with the second ferrite material as the target product), the additives are set as calcium carbonate and silicon dioxide. The mass of silicon dioxide accounts for 0.45% of the mass of the strontium ferrite pre-sintered powder, and the molar ratio of calcium carbonate to silicon dioxide is 1.5:1. The strontium ferrite pre-sintered powder, additives, and dispersion are then mixed. The agent was added to the ball mill jar, including 500g of pre-calcined material, 2g of dispersant (calcium gluconate), 10kg of 3mm stainless steel grinding balls, and 0.76kg of ball milling solvent water. The solid-liquid ratio of the mixed slurry in the ball mill was 1:1.5, the mass ratio of strontium ferrite pre-calcined material powder to grinding balls was 1:20, the ball milling speed was 80rpm, the time was 20h, and the ball milling was carried out until the target D50 particle size was 0.72μm to obtain the mixed slurry.

[0108] (2) The slurry obtained in step (2) is dehydrated until the water content in the slurry is 40% by mass. Then it is put into a cylindrical mold with a diameter of 25 mm for orientation wet pressing. The forming pressure is 5.5 MPa, the holding time is 30 s, the maximum orientation magnetic induction intensity is 1.0 T, and then it is dried at 60°C for 4 h to obtain a green body.

[0109] (3) The green blank obtained in step (2) is subjected to sintering treatment. In the sintering treatment, the temperature is first raised to 800°C at a heating rate of 5°C / min, then raised to 1190°C at a heating rate of 5°C / min and held for 60 min, and then cooled to obtain strontium ferrite material.

[0110] Example 5

[0111] This embodiment provides a method for controlling the sintering of strontium ferrite materials, the method comprising the following steps:

[0112] (1) Select strontium ferrite pre-sintered powder, specifically pure M-phase strontium ferrite with the chemical formula SrFe. x O 19Where X is 11.8, and D50 particle size is 2.0-2.5 μm, based on the D50 particle size of the strontium ferrite pre-sintered powder and the performance requirements of the strontium ferrite material (taking the fourth ferrite material as the target product), the additives are set as calcium carbonate, silicon dioxide, and alumina. The mass of silicon dioxide accounts for 0.4% of the mass of the strontium ferrite pre-sintered powder, the molar ratio of calcium carbonate to silicon dioxide is 1.5:1, and the mass of alumina accounts for 0.65% of the mass of the strontium ferrite pre-sintered powder. Oxide pre-calcined powder, additives, and dispersants were added to a ball mill jar, with 500g of pre-calcined powder and 2.5g of dispersant (sodium carboxymethyl cellulose). 2mm stainless steel grinding balls with a mass of 8kg were used, and 1.27kg of water was added as a ball milling solvent. The solid-liquid ratio of the mixed slurry in the ball mill was 1:2.5, and the mass ratio of strontium ferrite pre-calcined powder to grinding balls was 1:16. The ball milling speed was 100rpm, and the time was 20h. The ball milling was carried out until the target D50 particle size was 0.72μm, and the mixed slurry was obtained.

[0113] (2) The slurry obtained in step (2) is dehydrated until the water content in the slurry is 40% by mass. Then it is put into a cylindrical mold with a diameter of 25 mm for orientation wet pressing. The forming pressure is 5.5 MPa, the holding time is 30 s, the maximum orientation magnetic induction intensity is 1.0 T, and then it is dried at 60°C for 4 h to obtain a green body.

[0114] (3) The green blank obtained in step (2) is subjected to sintering treatment. In the sintering treatment, the temperature is first raised to 800°C at a heating rate of 5°C / min, then raised to 1200°C at a heating rate of 10°C / min and held for 30 min, and then cooled to obtain strontium ferrite material.

[0115] Example 6

[0116] This embodiment provides a method for controlling the sintering of strontium ferrite materials, the method comprising the following steps:

[0117] (1) Select strontium ferrite pre-sintered powder, specifically pure M-phase strontium ferrite with the chemical formula SrFe. x O 19Where X is 11.8, and D50 particle size is 2.0-2.5 μm, based on the D50 particle size of the strontium ferrite pre-sintered powder and the performance requirements of the strontium ferrite material (with the third ferrite material as the target product), the additives are set as calcium carbonate and silicon dioxide. The mass of silicon dioxide accounts for 0.4% of the mass of the strontium ferrite pre-sintered powder, and the molar ratio of calcium carbonate to silicon dioxide is 1.5:1. The strontium ferrite pre-sintered powder, additives, and dispersant are added... The mixture was placed in a ball mill jar containing 500g of pre-calcined material, 2.5g of dispersant (calcium gluconate), 10kg of 2mm stainless steel grinding balls, and 0.81kg of water as a ball milling solvent. The solid-liquid ratio of the mixture in the ball mill was 1:1.6, the mass ratio of strontium ferrite pre-calcined material powder to grinding balls was 1:20, the ball milling speed was 150rpm, and the time was 20h. The mixture was milled until the target D50 particle size was 0.65μm to obtain the mixed slurry.

[0118] (2) The slurry obtained in step (2) is dehydrated until the water content in the slurry is 30% by mass. Then it is put into a cylindrical mold with a diameter of 25 mm for orientation wet pressing. The forming pressure is 6.5 MPa, the holding time is 60 s, the maximum orientation magnetic induction intensity is 1.0 T, and then it is dried at 60°C for 4 h to obtain a green body.

[0119] (3) The green blank obtained in step (2) is subjected to sintering treatment. In the sintering treatment, the temperature is first raised to 800°C at a heating rate of 5°C / min, then raised to 1200°C at a heating rate of 10°C / min and held for 30 min, and then cooled to obtain strontium ferrite material.

[0120] Example 7

[0121] This embodiment provides a method for controlling sintered strontium ferrite materials. The only difference from Embodiment 1 is that the D50 particle size of the strontium ferrite pre-sintered powder in the preparation of the first ferrite material is 3-3.5 μm, and the mass of silicon dioxide accounts for 0.4% of the mass of the strontium ferrite pre-sintered powder.

[0122] Example 8

[0123] This embodiment provides a method for controlling sintered strontium ferrite materials. The only difference from Embodiment 1 is that the D50 particle size of the strontium ferrite pre-sintered powder in the preparation of the first ferrite material is 3.5-4 μm, and the mass of silicon dioxide accounts for 0.2% of the mass of the strontium ferrite pre-sintered powder.

[0124] Example 9

[0125] This embodiment provides a method for controlling sintered strontium ferrite materials. The only difference from Example 5 is that the D50 particle size of the strontium ferrite pre-sintered powder in the preparation of the fourth ferrite material is 0.5-1μm, and the mass of silicon dioxide accounts for 0.5% of the mass of the strontium ferrite pre-sintered powder.

[0126] Example 10

[0127] This embodiment provides a method for controlling sintered strontium ferrite materials. The only difference from Example 5 is that the D50 particle size of the strontium ferrite pre-sintered powder in the preparation of the fourth ferrite material is 0.5-1μm, and the mass of silicon dioxide accounts for 0.6% of the mass of the strontium ferrite pre-sintered powder.

[0128] Example 11

[0129] This embodiment provides a method for controlling the sintering of strontium ferrite materials. The only difference from Embodiment 1 is that the mass of silicon dioxide in the preparation of the first ferrite material accounts for 0.3% of the mass of the strontium ferrite pre-sintered powder.

[0130] Example 12

[0131] This embodiment provides a method for controlling the sintering of strontium ferrite materials. The only difference from Embodiment 1 is that the mass of silicon dioxide in the preparation of the first ferrite material accounts for 0.6% of the mass of the strontium ferrite pre-sintered powder.

[0132] Example 13

[0133] This embodiment provides a method for controlling sintered strontium ferrite materials. The only difference from Example 1 is that the first ferrite material is prepared by ball milling until the target D50 particle size is 0.6 μm.

[0134] Example 14

[0135] This embodiment provides a method for controlling sintered strontium ferrite materials. The only difference from Example 1 is that the first ferrite material is prepared by ball milling until the target D50 particle size is 1.0 μm.

[0136] Example 15

[0137] This embodiment provides a method for controlling the sintering of strontium ferrite materials. The only difference from Embodiment 1 is that the sintering temperature in the preparation of the first ferrite material is 1190°C.

[0138] Example 16

[0139] This embodiment provides a method for controlling the sintering of strontium ferrite materials. The only difference from Embodiment 1 is that the sintering temperature in the preparation of the first ferrite material is 1260°C.

[0140] Example 17

[0141] This embodiment provides a method for controlling sintered strontium ferrite materials. The only difference from Example 1 is that the molar ratio of calcium carbonate to silicon dioxide in the preparation of the first ferrite material is 1.5:1.

[0142] Example 18

[0143] This embodiment provides a method for controlling sintered strontium ferrite materials. The only difference from Example 1 is that the molar ratio of calcium carbonate to silicon dioxide in the preparation of the first ferrite material is 3.0:1.

[0144] Example 19

[0145] This embodiment provides a method for controlling sintered strontium ferrite materials. The only difference from Example 2 is that the second ferrite material is prepared by ball milling until the target D50 particle size is 0.6 μm.

[0146] Example 20

[0147] This embodiment provides a method for controlling sintered strontium ferrite materials. The only difference from Example 2 is that the second ferrite material is prepared by ball milling until the target D50 particle size is 0.95 μm.

[0148] Example 21

[0149] This embodiment provides a method for controlling the sintering of strontium ferrite materials. The only difference from Embodiment 2 is that the sintering temperature in the preparation of the second ferrite material is 1150°C.

[0150] Example 22

[0151] This embodiment provides a method for controlling the sintering of strontium ferrite materials. The only difference from Embodiment 2 is that the sintering temperature in the preparation of the second ferrite material is 1250°C.

[0152] Example 23

[0153] This embodiment provides a method for controlling sintered strontium ferrite materials. The only difference from Example 2 is that the molar ratio of calcium carbonate to silicon dioxide in the preparation of the second ferrite material is 1.0:1.

[0154] Example 24

[0155] This embodiment provides a method for controlling sintered strontium ferrite materials. The only difference from Example 2 is that the molar ratio of calcium carbonate to silicon dioxide in the preparation of the second ferrite material is 2.0:1.

[0156] Example 25

[0157] This embodiment provides a method for controlling the sintering of strontium ferrite materials. The only difference from Embodiment 6 is that the sintering temperature in the preparation of the third ferrite material is 1140°C.

[0158] Example 26

[0159] This embodiment provides a method for controlling the sintering of strontium ferrite materials. The only difference from Example 6 is that the sintering temperature in the preparation of the third ferrite material is 1220°C.

[0160] Example 27

[0161] This embodiment provides a method for controlling sintered strontium ferrite materials. The only difference from Example 6 is that the molar ratio of calcium carbonate to silicon dioxide in the preparation of the third ferrite material is 1:1.

[0162] Example 28

[0163] This embodiment provides a method for controlling sintered strontium ferrite materials. The only difference from Example 6 is that the molar ratio of calcium carbonate to silicon dioxide in the preparation of the third ferrite material is 1.8:1.

[0164] Example 29

[0165] This embodiment provides a method for controlling the sintering of strontium ferrite materials. The only difference from Embodiment 5 is that the sintering temperature in the preparation of the fourth ferrite material is 1130°C.

[0166] Example 30

[0167] This embodiment provides a method for controlling the sintering of strontium ferrite materials. The only difference from Embodiment 5 is that the sintering temperature in the preparation of the fourth ferrite material is 1230°C.

[0168] Example 31

[0169] This embodiment provides a method for controlling sintered strontium ferrite materials. The only difference from Example 5 is that the molar ratio of calcium carbonate to silicon dioxide in the preparation of the fourth ferrite material is 1:1.

[0170] Example 32

[0171] This embodiment provides a method for controlling sintered strontium ferrite materials. The only difference from Example 5 is that the molar ratio of calcium carbonate to silicon dioxide in the preparation of the fourth ferrite material is 2:1.

[0172] Taking Examples 1-6 as examples, the demagnetization curves of the obtained strontium ferrite materials are as follows: Figure 2-7 As shown, from Figure 2-7It can be seen that the methods provided in Examples 1-6 can produce products with the required performance, and the demagnetization curve has a high squareness and the magnetic energy product of the product is large.

[0173] The magnetic properties of the ferrite materials in the above embodiments were tested in accordance with GB / T 3217-2013 "Magnetic Test Methods for Permanent Magnet (Hard Magnet) Materials"; the magnetic properties were tested using a LE-AMH 500 permanent magnet material BH instrument (double coil method), as shown in Table 1.

[0174] Referring to GB / T 4472-2011 "Determination of Density and Relative Density of Chemical Products", the bulk density of the ferrite material in the above embodiments was tested, as shown in Table 1.

[0175] Table 1

[0176]

[0177]

[0178]

[0179] The following points can be observed from the data in Table 1:

[0180] (1) As can be seen from the data of Examples 1-6, the methods provided in Examples 1 and 3 can prepare the first ferrite material, the methods provided in Examples 2 and 4 can prepare the second ferrite material, the method provided in Example 5 can prepare the fourth ferrite material, and the method provided in Example 6 can prepare the third ferrite material, and can meet the performance requirements.

[0181] (2) As can be seen from the data of Examples 1 and 7-8, Examples 5 and 19-20, the present invention preferably controls the amount of silica added in the additive according to the D50 particle size of the strontium ferrite pre-sintered powder. As can be seen from the data of Examples 1 and 11-12, the present invention further controls the amount of silica added by controlling the percentage of silica mass in the strontium ferrite pre-sintered powder mass, which can further avoid the influence of excessively high or low silica content on the performance of ferrite materials, thereby obtaining ferrite materials that meet the performance requirements.

[0182] (3) It can be seen from the data of Examples 1 and 13-14, Examples 2 and 19-20 that the D50 particle size after ball milling in Examples 13-14 and 19-20 is not within the preferred control range of the present invention, and it is impossible to prepare ferrite materials that meet the performance requirements. It can be seen that the present invention can further regulate the sintering activity of the powder by preferredly controlling the D50 particle size range after ball milling, thereby obtaining ferrite materials that meet the performance requirements.

[0183] (4) It can be seen from the data of Examples 1 and 15-16, Examples 2 and 21-22, Examples 6 and 25-26, Examples 5 and 29-30 that the sintering temperature in Examples 15-16, 21-22, 25-26 and 29-30 is not within the preferred control range of the present invention, and ferrite materials that meet the performance requirements cannot be prepared. It can be seen that the present invention can further regulate the grain growth process by preferredly controlling the sintering temperature, thereby obtaining ferrite materials that meet the performance requirements.

[0184] (5) As can be seen from the data of Examples 1 and 17-18, Examples 2 and 23-24, Examples 6 and 27-28, Examples 5 and 31-32, the molar ratio of calcium carbonate to silicon dioxide in Examples 17-18, 23-24, 27-28 and 31-32 is not within the preferred control range of the present invention, and ferrite materials that meet the performance requirements cannot be prepared. It can be seen that the present invention can further regulate the composition of silicates formed during sintering by preferredly controlling the molar ratio of calcium carbonate to silicon dioxide. The silicate liquid phases with different compositions have different viscosities at high temperatures and have different effects on the grains, thereby obtaining ferrite materials that meet the performance requirements.

[0185] In summary, the method provided by this invention can adapt the characteristics of magnetic powder, the selection of additives, ball milling and sintering processes, and can achieve quantitative control of magnet performance. It can quickly produce customized magnets that meet specific performance requirements, avoiding the need for repeated testing of additives and sintering processes when using a single magnetic powder, thereby significantly improving production efficiency and reducing production costs.

[0186] The applicant declares that the above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. A method for controlling the sintering of strontium ferrite materials, characterized in that, The method includes the following steps: (1) Based on the D50 particle size of the strontium ferrite pre-sintered powder and the performance requirements of the strontium ferrite material, the type and ratio of additives are adjusted, and the strontium ferrite pre-sintered powder, additives and dispersant are ball-milled to reach the target D50 particle size to obtain a mixed slurry. (2) The mixed slurry obtained in step (1) is dehydrated, and then oriented wet pressing and drying are performed in sequence to obtain a green body; (3) The green blank obtained in step (2) is subjected to sintering treatment. During the sintering treatment, the heating rate is controlled until the sintering temperature is reached and the temperature is held. Then the blank is cooled to obtain strontium ferrite material. The additives mentioned in step (1) include silicon dioxide and calcium carbonate; When the D50 particle size of the strontium ferrite pre-sintered powder is <1μm, 1-3μm, and >3μm, the mass of silicon dioxide accounts for 0.5-0.6%, 0.4-0.5%, and 0.2-0.4% of the mass of the strontium ferrite pre-sintered powder, respectively. The strontium ferrite materials are classified according to their remanence and coercivity, including a first ferrite material, a second ferrite material, a third ferrite material, and a fourth ferrite material; When the strontium ferrite materials are respectively the first ferrite material, the second ferrite material, the third ferrite material, and the fourth ferrite material, the molar ratio of calcium carbonate and silicon dioxide in the additives are (1.8-2.5):1, (1.6-1.8):1, (1.2-1.5):1, and (1.2-1.5):1, respectively; The D50 particle sizes of the pre-sintered powders of the first ferrite material, the second ferrite material, the third ferrite material, and the fourth ferrite material are ≥2μm, 1-3μm, 1-3μm, and ≤3μm, respectively. The target D50 particle sizes after ball milling are 0.7-0.9μm, 0.7-0.75μm, 0.6-0.65μm, and 0.6-0.8μm, respectively. The sintering temperatures are 1200-1250℃, 1180-1190℃, 1200℃, and 1150-1200℃, respectively. The additives in the fourth ferrite material also include alumina, wherein the mass percentage of alumina in the additive is 0.65%-1.5% of the mass of the strontium ferrite pre-sintered powder.

2. The method according to claim 1, characterized in that, The additives in the first ferrite material also include bismuth oxide.

3. The method according to claim 1, characterized in that, The strontium ferrite pre-burned powder in step (1) is pure M-phase strontium ferrite.

4. The method according to claim 1, characterized in that, The chemical formula of the strontium ferrite pre-sintered powder is SrFe. x O 19 , where X takes values ​​from 11 to 12.

5. The method according to claim 1, characterized in that, The dispersant includes calcium gluconate and / or sodium carboxymethyl cellulose.

6. The method according to claim 1, characterized in that, The mass of the dispersant accounts for 0.3-0.5% of the mass of the strontium ferrite pre-sintered powder.

7. The method according to claim 1, characterized in that, A solvent is also added during the ball milling process.

8. The method according to claim 7, characterized in that, The solvent includes water.

9. The method according to claim 7, characterized in that, The solid-liquid ratio of the slurry mixture in the ball mill is 1:(1.5-2.5).

10. The method according to claim 1, characterized in that, The grinding balls used in the ball mill include stainless steel balls.

11. The method according to claim 1, characterized in that, The diameter of the grinding balls used in the ball mill is 2-5 mm.

12. The method according to claim 1, characterized in that, The mass ratio of strontium ferrite pre-calcined powder to grinding balls in the ball mill is 1:(10-20).

13. The method according to claim 1, characterized in that, In step (2), the water content in the mixed slurry is dehydrated to 30-50% by mass.

14. The method according to claim 1, characterized in that, The pressure for the orientation wet pressing is 4.5-6.5 MPa.

15. The method according to claim 1, characterized in that, The holding time for the orientation wet pressing is 30-60 seconds.

16. The method according to claim 1, characterized in that, The maximum orientation magnetic induction intensity of the orientation wet pressing is 0.5-1.5T.

17. The method according to claim 1, characterized in that, The drying temperature is 60-90℃.

18. The method according to claim 1, characterized in that, The drying time is 2-4 hours.

19. The method according to claim 1, characterized in that, The heat preservation time is 10-60 minutes.

20. The method according to claim 1, characterized in that, The heating process includes: first heating to 800°C at a first heating rate, and then heating to the sintering temperature at a second heating rate.

21. The method according to claim 20, characterized in that, The first heating rate is ≤5℃ / min.

22. The method according to claim 20, characterized in that, The second heating rate is ≤10℃ / min.

23. The method according to claim 1, characterized in that, The first ferrite material meets the following performance requirements: remanence Br = 4150-4250 Gs, coercivity Hcj = 3400-3700 Oe, maximum energy product BH = 4.1-4.3 MGOe, and bulk density ≥ 5.0 g / cm³. 3 .

24. The method according to claim 1, characterized in that, The second ferrite material meets the following performance requirements: remanence Br = 4110-4150 Gs, coercivity Hcj = 4200-4350 Oe, maximum energy product BH = 4.1-4.2 MGOe, and bulk density ≥ 4.95 g / cm³. 3 .

25. The method according to claim 1, characterized in that, The third ferrite material meets the following performance requirements: remanence Br = 4000-4060 Gs, coercivity Hcj = 4400-4500 Oe, maximum energy product BH = 3.9-4.0 MGOe, and bulk density ≥ 4.90 g / cm³. 3 .

26. The method according to claim 1, characterized in that, The fourth ferrite material meets the following performance requirements: remanence Br = 3850-3950 Gs, coercivity Hcj = 4600-4700 Oe, maximum energy product BH = 3.7-4.0 MGOe, and bulk density ≥ 4.88 g / cm³. 3 .

27. The method according to claim 2, characterized in that, When the strontium ferrite material is the first ferrite material, the mass percentage of bismuth oxide in the additive is ≤1% of the mass of the strontium ferrite pre-calcined powder.

28. The method according to claim 1, characterized in that, When the strontium ferrite material is the first ferrite material, the ball mill rotation speed is 50-100 rpm.

29. The method according to claim 1, characterized in that, When the strontium ferrite material is the first ferrite material, the ball milling time is 8-20 hours.

30. The method according to claim 1, characterized in that, When the strontium ferrite material is a second ferrite material, the ball mill rotation speed is 50-150 rpm.

31. The method according to claim 1, characterized in that, When the strontium ferrite material is a second ferrite material, the ball milling time is 12-24 hours.

32. The method according to claim 1, characterized in that, When the strontium ferrite material is a third ferrite material, the ball mill rotation speed is 100-200 rpm.

33. The method according to claim 1, characterized in that, When the strontium ferrite material is a third ferrite material, the ball milling time is 16-36 hours.

34. The method according to claim 1, characterized in that, When the strontium ferrite material is a fourth ferrite material, the ball milling speed is 100-200 rpm.

35. The method according to claim 1, characterized in that, When the strontium ferrite material is a fourth ferrite material, the ball milling time is 16-36 hours.

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