Preparation method of high-power high-temperature-stability M-type strontium ferrite

Abstract

A high-power, high-temperature-stability M-type strontium ferrite belongs to the field of ferrite material preparation technology. The ferrite comprises a main formulation of SrCO3, La2O3, CaCO3, MnO, SnO2, Fe2O3, and Co2O3, and additives composed of CaCO3, SiO2, H3BO3, and La2O3. This invention introduces Sn-Mn ions for co-substitution, thereby constructing a Sn... 4+ -Mn 2+ The charge balance mechanism effectively suppressed the Fe ionization induced by the introduction of high-valence ions. 3+ To Fe 2+ Price change behavior, effective compensation after replacement due to the introduction of non-magnetic Sn 4+ This results in a loss of lattice magnetic moment. Simultaneously, through a stepped pre-sintering and sintering process, a CoFe2O4 hard magnetic spinel phase is induced to precipitate in the M-type strontium ferrite main phase. The negative coercivity temperature coefficient of the CoFe2O4 phase complements the inherent positive temperature coefficient of the matrix.

Description

Technical Field

[0001] This invention belongs to the field of ferrite material preparation technology, and specifically relates to a method for preparing high-power, high-temperature-stability M-type strontium ferrite material for micro-motors in new energy vehicles. Background Technology

[0002] The new energy vehicle industry has experienced explosive growth. As a core component of new energy drive systems, the performance of permanent magnet motors directly determines the power output, energy efficiency, and driving range of the entire vehicle. Although rare earth permanent magnet NdFeB materials have excellent performance, their availability is limited by strategic reserves of rare earth resources and cost fluctuations. M-type strontium ferrite, with its good magnetic properties and significant cost advantages, has become an important alternative for permanent magnet materials in micro-motors. High-performance micro-motors place stringent requirements on power density and miniaturization, necessitating permanent magnets with high power density, reflected in material properties as high remanent magnetic induction intensity (B). r High coercivity H c and high energy product (BH) max High B r It can directly enhance the air gap magnetic flux, thereby improving the transient torque and power density of the motor; high H c This endows the motor with extremely strong demagnetization resistance, ensuring its safe operation under peak current and overload conditions; while high (BH) max This forms the physical basis for achieving high-efficiency and lightweight design of motors. However, compared with traditional industrial applications, new energy vehicles face more stringent and complex operating environments. Because vehicles need to adapt to extreme temperatures ranging from the extremely low temperatures of high-latitude regions to the extreme temperatures of summer heat exposure or high-load motor operation, micro-motors must maintain stable operation over a wide temperature range. Given the inherently high temperature coefficient of SrM ferrite, its magnetic properties can fluctuate nonlinearly over this wide temperature range. This can easily cause a surge in magnetic flux at low temperatures, leading to controller saturation, and at high temperatures, it can cause irreversible demagnetization due to a decrease in coercivity. These problems seriously threaten the efficiency and output stability of the motor, becoming a key technical bottleneck restricting its application in high-end automotive motors. Therefore, in-depth research on the temperature stability of SrM ferrite over a wide temperature range has significant engineering application value and practical significance for developing high-performance ferrite materials suitable for the operating conditions of new energy vehicles.

[0003] In the prior art, some progress has been made in the research on the wide-temperature stability of M-type strontium ferrite. For example, patent CN101106001A discloses a low-temperature coefficient permanent magnet ferrite material and its manufacturing method, whose performance index is: remanent magnetic induction intensity B r =420 mT, magnetic coercivity H cb =310.8kA / m, intrinsic coercivity H cj ≥333.1 kA / m, maximum energy product (BH)max ≥34.1kJ / m 3 The remanence temperature coefficient α = -0.14% / K and the coercivity temperature coefficient β = 0.15% / K. However, the room-temperature magnetic properties of this technology are relatively limited, making it difficult to meet the requirements of applications with higher magnetic performance.

[0004] In pursuit of higher room-temperature magnetic properties, current technologies mainly focus on achieving B through La-Co plasma substitution. r With H cj Synergistic enhancement. For example, patent CN119751040A discloses a method for preparing high-performance ferrite, the disclosed performance index of which is remanent magnetic induction intensity B. r ≥420mT, magnetic coercivity H cb ≥320 kA / m, intrinsic coercivity H cj ≥375 kA / m, maximum energy product (BH) max ≥30kJ / m 3 Temperature coefficients α and β were not reported. The high-performance permanent magnet ferrite disclosed by Shanghai Longci Technology Co., Ltd. has the following performance indicators: B r =430~440mT,H cb =316.4~326.5kA / m, H cj =332.2~383.6 kA / m, (BH) max =36.24~37.44kJ / m 3 Temperature coefficients α and β were not reported. Tang Shaochun et al. from Nanjing University disclosed a high-performance permanent magnet ferrite preparation technology. This technology, through optimization of the ion substitution formula and preparation process, successfully prepared ferrite magnets with performance indicators comparable to the TDK-FB6B grade. Its disclosed main magnetic performance indicators reach: B r ≥430mT, magnetic coercivity H cb ≥310.4kA / m, intrinsic coercivity H cj ≥326.3 kA / m, maximum energy product (BH) max ≥33.4kJ / m 3 Although the aforementioned prior art achieves high remanence and coercivity at room temperature, none of its disclosures address the optimization of the remanence temperature coefficient α and the coercivity temperature coefficient β. Furthermore, in practical applications, such highly doped, high-performance ferrites often come with the risk of temperature coefficient degradation. Therefore, the aforementioned prior art struggles to simultaneously achieve high remanence and coercivity at room temperature. r -H c Temperature stability under high temperature and wide temperature range conditions is no longer sufficient to meet the requirements of micro motors and auxiliary systems for new energy vehicles for constant magnetic performance output of magnets under wide temperature range, large temperature difference, and harsh operating conditions. Summary of the Invention

[0005] The purpose of this invention is to address the problems existing in the prior art by proposing a method for preparing high-power, high-temperature-stability M-type strontium ferrite.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0007] A high-power, high-temperature-stability M-type strontium ferrite comprises a main formulation and additives, wherein the main formulation comprises: 3.2~8.2 mol% SrCO3, 2.4~5.3 mol% La2O3, 0.8~2.4 mol% CaCO3, 0.7~2.2 mol% MnO, 0.9~3.6 mol% SnO2, 78.2~85.3 mol% Fe2O3, and 1.3~3.6 mol% Co2O3;

[0008] The additives, in percentage of the main formulation, include: 0.2~2.2 wt% CaCO3, 0.3~1.4 wt% SiO2, 0.2~1.2 wt% H3BO3, and 0.5~2.1 wt% La2O3.

[0009] A method for preparing high-power, high-temperature-stability M-type strontium ferrite includes the following steps:

[0010] Step 1. Using SrCO3, La2O3, CaCO3, MnO, SnO2, Fe2O3, and Co2O3 as raw materials, weigh them according to the following ratio: 3.2~8.2 mol% SrCO3, 2.4~5.3 mol% La2O3, 0.8~2.4 mol% CaCO3, 0.7~2.2 mol% MnO, 0.9~3.6 mol% SnO2, 78.2~85.3 mol% Fe2O3, and 1.3~3.6 mol% Co2O3, to obtain a mixture.

[0011] Step 2. The mixture obtained in Step 1 is ball-milled for 10-14 hours to obtain primary ball-milled material;

[0012] Step 3. After drying the primary ball milling material obtained in Step 2, sieve it through a 20-40 mesh screen to obtain sieved material;

[0013] Step 4. Perform step-by-step pre-firing on the sieved material obtained in Step 3. First, hold the material at 850~950℃ for 0.5~1.5h, then raise the temperature to 1200~1300℃ and hold for 0.5~1.5h. After the pre-firing is completed, cool the material with the furnace to obtain the pre-fired material.

[0014] Step 5. Add additives to the pre-calcined powder obtained in Step 4 to obtain a mixture; the additives, according to the weight percentage of the pre-calcined powder, include: 0.2~2.2 wt% CaCO3, 0.3~1.4 wt% SiO2, 0.2~1.2 wt% H3BO3, and 0.5~2.1 wt% La2O3;

[0015] Step 6. The mixture obtained in Step 5 is ball-milled a second time for 18-22 hours in a ball mill, and the particle size of the powder is controlled between 0.5 and 0.9 μm to obtain the secondary ball-milled material;

[0016] Step 7. The secondary ball milling material obtained in Step 6 is dehydrated using filter paper and gauze, and the moisture content is controlled between 15% and 30%. Then, it is pressed into shape under a magnetic field forming press with a forming magnetic field strength of 1.2 to 1.8T and a forming pressure of 80 to 120MPa to obtain a shaped blank.

[0017] Step 8. The shaped blank obtained in Step 7 is placed in a sintering furnace and held at 900~1000℃ for 0.2~1.0h, then heated to 1100~1200℃ and held for 0.2~1.0h; after sintering, it is cooled to room temperature with the furnace to obtain the M-type strontium ferrite.

[0018] Furthermore, the M-type strontium ferrite obtained in step 8 contains a CoFe2O4 hard magnetic spinel phase, which is located at the main phase grain boundaries and within the grains. The volume fraction of the CoFe2O4 hard magnetic spinel phase accounts for 15.8%-28.6% of the total phase.

[0019] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0020] 1. Achieved synergistic improvement in magnetic properties and temperature stability: This invention, based on the traditional La-Co high-performance system, additionally introduces Sn-Mn ions for co-substitution. Among the many types of M-type ferrites, due to Sr... 2+ The smaller radius leads to a significantly enhanced lattice contraction in Sn. 4+ The site-preferred occupancy of the 4f2 sites allows for effective compensation of the temperature characteristics of the magnetocrystalline anisotropic field even at relatively low doping levels. Simultaneously, the use of equimolar ratios of Mn... 2+ Replace, by constructing Sn 4+ -Mn 2 + The charge balance mechanism effectively suppressed the Fe ionization induced by the introduction of high-valence ions. 3+ To Fe 2+ The variable valence behavior, after replacing the 12k bits, effectively compensated for the introduction of non-magnetic Sn. 4+This results in a loss of lattice magnetic moment. The aforementioned synergistic effect allows this invention to improve the temperature coefficient while avoiding a significant decrease in saturation magnetization and remanence, successfully overcoming the technical bottleneck of the difficulty in achieving both high temperature stability and high magnetic performance in traditional doping processes.

[0021] 2. An adaptive temperature compensation mechanism based on second-phase regulation was constructed: By designing a matched stepped pre-sintering and sintering process, an appropriate amount of CoFe2O4 hard magnetic spinel phase was induced to precipitate in situ within the M-type strontium ferrite main phase. The negative coercivity temperature coefficient of the CoFe2O4 phase was utilized to create a complementary effect with the inherent positive temperature coefficient of the matrix.

[0022] In this process, the temperature coefficient control is closely related to the volume fraction of the second phase CoFe2O4. If the precipitation of the second phase is insufficient, it is difficult to achieve an effective compensation effect; excessive precipitation will lead to abnormal growth of the second phase and coarsening of the main phase grains, weakening the magnetic domain pinning effect and reducing magnetic properties. Therefore, this invention precisely adjusts the holding time of the stepped pre-sintering process to 0.5~1.5h and the holding time of the stepped sintering process to 0.2~1.0h to control the ion segregation and desolvation process in the M-type strontium ferrite lattice, thereby inducing the in-situ precipitation of CoFe2O4 with a volume fraction of approximately 15.8%-28.6% of the total phase composition at the main phase grain boundaries and within the grains. In a wide temperature range environment, the two magnetic phases achieve mutual positive and negative compensation of the coercivity change trend with temperature. This multiphase synergistic mechanism effectively reduces the fluctuation of material coercivity with ambient temperature, significantly improves the material's anti-demagnetization ability and magnetic flux stability at extreme temperatures, and fundamentally overcomes the inherent defects of single M-type ferrite that is easy to demagnetize at low temperatures and has low remanence at high temperatures, thus meeting the application requirements of new energy vehicles in harsh environments with large temperature differences. Attached Figure Description

[0023] Figure 1 SEM image of the M-type strontium ferrite prepared in Comparative Example 1 of this invention;

[0024] Figure 2 The image shows a SEM image of the M-type strontium ferrite prepared in Comparative Example 2 of this invention.

[0025] Figure 3 SEM image of the M-type strontium ferrite prepared in Comparative Example 3 of this invention;

[0026] Figure 4 SEM image of the M-type strontium ferrite prepared in the embodiment of the present invention. Detailed Implementation

[0027] To make the objectives, technical solutions, and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the embodiments and accompanying drawings.

[0028] Comparative Example 1

[0029] A method for preparing M-type strontium ferrite includes the following steps:

[0030] Step 1: Using SrCO3, La2O3, CaCO3, Fe2O3, and Co2O3 as raw materials, weigh them according to the following ratio: 3.2~8.2 mol% SrCO3, 2.4~5.3 mol% La2O3, 0.8~2.4 mol% CaCO3, 0.7~2.2 mol% MnO, 0.9~3.6 mol% SnO2, 78.2~85.3 mol% Fe2O3, and 1.3~3.6 mol% Co2O3, to obtain a mixture.

[0031] Step 2: The mixture obtained in Step 1 is ball-milled for 10 hours to obtain primary ball-milled material;

[0032] Step 3: After drying the primary ball milling material obtained in Step 2, sieve it through a 20-40 mesh screen to obtain sieved material;

[0033] Step 4: Pre-fire the sieved material obtained in Step 3 at a temperature of 1280℃ for 2 hours. After pre-firing, cool down the furnace to obtain the pre-fired material.

[0034] Step 5: Add additives to the pre-calcined material obtained in Step 4. The additives, calculated by weight percentage as oxides, are: 0.2~2.2 wt% CaCO3, 0.3~1.4 wt% SiO2, 0.2~1.2 wt% H3BO3, and 0.5~2.1 wt% La2O3, to obtain a mixture.

[0035] Step 6: The mixture obtained in Step 5 is ball-milled a second time for 20 hours in a ball mill, and the particle size of the powder is controlled between 0.5 and 0.9 μm to obtain the secondary ball-milled material;

[0036] Step 7: Dehydrate the secondary ball milling material obtained in Step 6 using filter paper and gauze, controlling the moisture content to be between 15% and 30%. Then, press it into shape under a magnetic field forming press with a forming magnetic field strength of 1.2 to 1.8T and a forming pressure of 80 to 120MPa to obtain a shaped blank.

[0037] Step 8: Place the shaped blank obtained in Step 7 into a sintering furnace and sinter it at a temperature of 1180°C for 1 hour. Cool it to room temperature with the furnace to obtain the M-type strontium ferrite.

[0038] Figure 1 The image shows a SEM image of the M-type strontium ferrite material prepared in Comparative Example 1. This sample exhibits typical and unique M-type hexagonal ferrite microstructure characteristics.

[0039] Comparative Example 2

[0040] A method for preparing M-type strontium ferrite includes the following steps:

[0041] Step 1: Using SrCO3, La2O3, CaCO3, MnO, SnO2, Fe2O3, and Co2O3 as raw materials, weigh them according to the following ratio: 3.2~8.2 mol% SrCO3, 2.4~5.3 mol% La2O3, 0.8~2.4 mol% CaCO3, 0.7~2.2 mol% MnO, 0.9~3.6 mol% SnO2, 78.2~85.3 mol% Fe2O3, and 1.3~3.6 mol% Co2O3, to obtain a mixture.

[0042] Step 2: The mixture obtained in Step 1 is ball-milled for 10-14 hours to obtain primary ball-milled material;

[0043] Step 3: After drying the primary ball milling material obtained in Step 2, sieve it through a 20-40 mesh screen to obtain sieved material;

[0044] Step 4: Pre-fire the sieved material obtained in Step 3 at a temperature of 1280℃ for 2 hours. After pre-firing, cool down the furnace to obtain the pre-fired material.

[0045] Step 5: Add additives to the pre-calcined powder obtained in Step 4. The additives, calculated by weight percentage as oxides, are: 0.2~2.2 wt% CaCO3, 0.3~1.4 wt% SiO2, 0.2~1.2 wt% H3BO3, and 0.5~2.1 wt% La2O3, to obtain a mixture.

[0046] Step 6: The mixture obtained in Step 5 is ball-milled a second time for 20 hours in a ball mill, and the particle size of the powder is controlled between 0.5 and 0.9 μm to obtain the secondary ball-milled material;

[0047] Step 7: Dehydrate the secondary ball milling material obtained in Step 6 using filter paper and gauze, controlling the moisture content to be between 15% and 30%. Then, press it into shape under a magnetic field forming press with a forming magnetic field strength of 1.2 to 1.8T and a forming pressure of 80 to 120MPa to obtain a shaped blank.

[0048] Step 8: The shaped blank obtained in Step 7 is placed in a sintering furnace and sintered at 1180°C for 1 hour. After sintering, it is cooled to room temperature with the furnace to obtain the M-type strontium ferrite.

[0049] Figure 2SEM images of M-type strontium ferrite were prepared for Comparative Example 2. The obtained samples exhibited a typical hexagonal lamellar structure with good crystallinity, low porosity, and good density.

[0050] Comparative Example 3

[0051] A method for preparing M-type strontium ferrite includes the following steps:

[0052] Step 1: Using SrCO3, La2O3, CaCO3, Fe2O3, and Co2O3 as raw materials, weigh them according to the following ratio: 3.2~8.2 mol% SrCO3, 2.4~5.3 mol% La2O3, 0.8~2.4 mol% CaCO3, 78.2~85.3 mol% Fe2O3, and 1.3~3.6 mol% Co2O3, to obtain a mixture.

[0053] Step 2: The mixture obtained in Step 1 is ball-milled for 10-14 hours to obtain primary ball-milled material;

[0054] Step 3: After drying the primary ball milling material obtained in Step 2, sieve it through a 20-40 mesh screen to obtain sieved material;

[0055] Step 4: Perform stepped pre-firing on the sieved material obtained in Step 3, holding at 850~950℃ for 0.5~1.5h, then raising the temperature to 1200~1300℃ and holding for 0.5~1.5h. After pre-firing, cool down with the furnace to obtain pre-fired material;

[0056] Step 5: Add additives to the pre-calcined material obtained in Step 4. The additives, calculated by weight percentage as oxides, are: 0.2~2.2 wt% CaCO3, 0.3~1.4 wt% SiO2, 0.2~1.2 wt% H3BO3, and 0.5~2.1 wt% La2O3, to obtain a mixture.

[0057] Step 6: The mixture obtained in Step 5 is ball-milled a second time for 18-22 hours in a ball mill, and the particle size of the powder is controlled between 0.5 and 0.9 μm to obtain the secondary ball-milled material;

[0058] Step 7: Dehydrate the secondary ball milling material obtained in Step 6 using filter paper and gauze, controlling the moisture content to be between 15% and 30%. Then, press it into shape under a magnetic field forming press with a forming magnetic field strength of 1.2 to 1.8T and a forming pressure of 80 to 120MPa to obtain a shaped blank.

[0059] Step 8: The shaped blank obtained in Step 7 is placed in a sintering furnace and held at 900~1000℃ for 0.2~1.0h, then heated to 1100~1200℃ and held for 0.2~1.0h. After sintering, it is cooled to room temperature with the furnace to obtain the M-type strontium ferrite.

[0060] Figure 3 The image shows the SEM image of the M-type strontium ferrite prepared in Comparative Example 3, compared with... Figure 1 Unlike the uniform single-phase structure, Figure 3 The microstructural features of the coexistence of multiple phases can be clearly observed.

[0061] Example

[0062] A method for preparing a high-power, high-temperature-stability M-type strontium ferrite material includes the following steps:

[0063] Step 1: Using SrCO3, La2O3, CaCO3, MnO, SnO2, Fe2O3, and Co2O3 as raw materials, weigh them according to the following ratio: 3.2~8.2 mol% SrCO3, 2.4~5.3 mol% La2O3, 0.8~2.4 mol% CaCO3, 0.7~2.2 mol% MnO, 0.9~3.6 mol% SnO2, 78.2~85.3 mol% Fe2O3, and 1.3~3.6 mol% Co2O3, to obtain a mixture.

[0064] Step 2: The mixture obtained in Step 1 is ball-milled for 10-14 hours to obtain primary ball-milled material;

[0065] Step 3: After drying the primary ball milling material obtained in Step 2, sieve it through a 20-40 mesh screen to obtain sieved material;

[0066] Step 4: Perform stepped pre-firing on the sieved material obtained in Step 3, holding at 850~950℃ for 0.5~1.5h, then raising the temperature to 1200~1300℃ and holding for 0.5~1.5h. After pre-firing, cool down with the furnace to obtain pre-fired material;

[0067] Step 5: Add additives to the pre-calcined powder obtained in Step 4. The additives, calculated by weight percentage as oxides, are: 0.2~2.2 wt% CaCO3, 0.3~1.4 wt% SiO2, 0.2~1.2 wt% H3BO3, and 0.5~2.1 wt% La2O3, to obtain a mixture.

[0068] Step 6: The mixture obtained in Step 5 is ball-milled a second time for 18-22 hours in a ball mill, and the particle size of the powder is controlled between 0.5 and 0.9 μm to obtain the secondary ball-milled material;

[0069] Step 7: Dehydrate the secondary ball milling material obtained in Step 6 using filter paper and gauze, controlling the moisture content to be between 15% and 30%. Then, press it into shape under a magnetic field forming press with a forming magnetic field strength of 1.2 to 1.8T and a forming pressure of 80 to 120MPa to obtain a shaped blank.

[0070] Step 8: The shaped blank obtained in Step 7 is placed in a sintering furnace and held at 900~1000℃ for 0.2~1.0h, then heated to 1100~1200℃ and held for 0.2~1.0h. After sintering, it is cooled to room temperature with the furnace to obtain the M-type strontium ferrite.

[0071] Figure 4 The SEM image of the M-type strontium ferrite material prepared for the example is the same as that of the gradient sintering process in Comparative Example 3. The second phase particles can be observed to be uniformly dispersed at the grain boundaries of the large hexagonal main phase grains. The sample has low porosity and good density.

[0072] The difference between the examples and Comparative Example 1 is that, on the one hand, Sn-Mn ion substitution was not used in the main formulation of Comparative Example 1, so it does not have the ability to selectively control the occupancy of lattice sites and compensate for magnetic moments, making it difficult to achieve a synergistic improvement in magnetic properties and temperature stability; on the other hand, the step-by-step pre-firing and sintering process was not used, so it was impossible to construct an adaptive temperature compensation mechanism based on complex phase coupling, thus making it difficult to obtain an ideal low temperature coefficient.

[0073] The difference between the embodiment and Comparative Example 2 is that Comparative Example 2 did not use a stepped pre-firing and sintering process, and therefore could not obtain a low temperature coefficient through an adaptive temperature compensation mechanism.

[0074] The difference between the examples and Comparative Example 3 is that the main formulation of Comparative Example 3 did not introduce Sn-Mn ion substitution, making it difficult to achieve a synergistic improvement in magnetic properties and temperature stability.

[0075] Table 1. Magnetic properties and temperature coefficient test results of each comparative example and embodiment within the range of 25-120°C.

[0076] project <![CDATA[B r (mT)]]> <![CDATA[H cb (kA / m)]]> <![CDATA[H cj (kA / m)]]> <![CDATA[(BH) max (kJ / m 3 )]]> α(% / K) β(% / K) Comparative Example 1 422 302 361 32.2 -0.25 0.28 Comparative Example 2 434 314 372 35.4 -0.22 0.24 Comparative Example 3 427 310 368 34.8 -0.20 0.14 Example 438 316 377 36.3 -0.17 0.09

[0077] Table 1 lists the performance data of Examples 1-3 and the Comparative Example in terms of magnetic properties, remanence temperature coefficient α, and coercivity temperature coefficient β. Comparative Example 1 was prepared using a conventional single La-Co ion substitution strategy, with a remanence temperature coefficient of -0.25% / K and a coercivity temperature coefficient of 0.28% / K. Due to the inherent physical properties of the single magnetic phase system and the strong temperature dependence of Co ion contribution to the anisotropic field, the ferrite material prepared using the traditional La-Co substitution strategy exhibits high temperature sensitivity. This performance level results in large magnetic flux fluctuations over a wide temperature range, making it difficult to meet the stringent requirements for magnetic performance stability under complex environmental temperature differences in micromotors used in new energy vehicles.

[0078] Thanks to the Sn-Mn ion substitution process, the examples demonstrated significantly better temperature stability than Comparative Example 1 while maintaining magnetic properties. This is attributed to the synergistic regulation mechanism of the Sn-Mn ion pairs: on the one hand, Sn... 4+ Preferentially occupying specific sites in the crystal lattice effectively reduces the sensitivity of the magnetocrystalline anisotropy field to ambient temperature, thereby reducing the rate of change of coercivity with temperature. On the other hand, Mn 2+ Effective compensation was achieved by utilizing its high spin magnetic moment, improving thermal stability without sacrificing saturation magnetization and room-temperature coercivity. Furthermore, by designing a matched stepped pre-sintering and sintering process, a suitable amount of spinel-type CoFe2O4 second phase was precipitated in situ within the SrM main phase matrix. Its negative coercivity temperature coefficient characteristics complemented the main phase, thus achieving effective compensation and optimization of the overall temperature coefficient of the material. Attributable to the intrinsic modulation of the Sn-Mn ion lattice and the extrinsic compensation of the second phase, compared to Comparative Example 1, this embodiment successfully balanced excellent room-temperature magnetic properties with superior wide-temperature stability.

[0079] The embodiments described above are merely illustrative of specific implementations of the present invention, and while the descriptions are detailed, they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the scope of protection of the present invention.

Claims

1. A high-power, high-temperature-stability M-type strontium ferrite, characterized in that, It includes the main formulation and additives, wherein the main formulation includes: 3.2~8.2 mol% SrCO3, 2.4~5.3 mol% La2O3, 0.8~2.4 mol% CaCO3, 0.7~2.2 mol% MnO, 0.9~3.6 mol% SnO2, 78.2~85.3 mol% Fe2O3, and 1.3~3.6 mol% Co2O3; The additives constitute the following percentages of the main formulation: 0.2~2.2 wt% CaCO3, 0.3~1.4 wt% SiO2, 0.2~1.2 wt% H3BO3, and 0.5~2.1 wt% La2O3.

2. A method for preparing high-power, high-temperature-stability M-type strontium ferrite, characterized in that, Includes the following steps: Step 1. Using SrCO3, La2O3, CaCO3, MnO, SnO2, Fe2O3, and Co2O3 as raw materials, weigh them according to the following ratio: 3.2~8.2 mol% SrCO3, 2.4~5.3 mol% La2O3, 0.8~2.4 mol% CaCO3, 0.7~2.2 mol% MnO, 0.9~3.6 mol% SnO2, 78.2~85.3 mol% Fe2O3, and 1.3~3.6 mol% Co2O3, to obtain a mixture. Step 2. The mixture obtained in Step 1 is ball-milled once to obtain primary ball-milled material; Step 3. After drying the primary ball milling material obtained in Step 2, sieve it to obtain sieved material; Step 4. Perform step-by-step pre-firing on the sieved material obtained in Step 3. First, hold the material at 850~950℃ for 0.5~1.5h, then raise the temperature to 1200~1300℃ and hold for 0.5~1.5h. After the pre-firing is completed, cool the material with the furnace to obtain the pre-fired material. Step 5. Add additives to the pre-calcined material obtained in Step 4 to obtain a mixture; the additives, according to the weight percentage of the pre-calcined material, include: 0.2~2.2 wt% CaCO3, 0.3~1.4 wt% SiO2, 0.2~1.2 wt% H3BO3, and 0.5~2.1 wt% La2O3; Step 6. The mixture obtained in Step 5 is ball-milled a second time in a ball mill to obtain secondary ball-milled material; Step 7. Dehydrate and press the secondary ball milling material obtained in Step 6 to obtain a shaped blank; Step 8. The shaped blank obtained in Step 7 is placed in a sintering furnace and held at 900~1000℃ for 0.2~1.0h, then heated to 1100~1200℃ and held for 0.2~1.0h; after sintering, it is cooled to room temperature with the furnace to obtain the M-type strontium ferrite.

3. The method for preparing high-power, high-temperature-stability M-type strontium ferrite according to claim 2, characterized in that, The ball milling time in step 2 is 10-14 h; the ball milling time in step 6 is 18-22 h, and the particle size of the powder is controlled between 0.5 and 0.9 μm.

4. The method for preparing high-power, high-temperature-stability M-type strontium ferrite according to claim 2, characterized in that, In step 7, the secondary ball milling material obtained in step 6 is dehydrated using filter paper and gauze, and the moisture content is controlled between 15% and 30%. Then, it is pressed into shape under a magnetic field forming press with a forming magnetic field strength of 1.2 to 1.8T and a forming pressure of 80 to 120MPa to obtain a shaped blank.

5. The method for preparing high-power, high-temperature-stability M-type strontium ferrite according to claim 2, characterized in that, The M-type strontium ferrite obtained in step 8 contains the CoFe2O4 hard magnetic spinel phase.

6. The method for preparing high-power, high-temperature-stability M-type strontium ferrite according to claim 5, characterized in that, The CoFe2O4 hard magnetic spinel phase is located at the grain boundaries and within the main phase, and its volume fraction accounts for 15.8%-28.6% of the total phase.

Images