Broadband high T c Highly magnetically soft Mn-Zn ferrite and method of making

Abstract

Broadband high T c High-conductivity manganese-zinc ferrite and preparation method, belong to ferrite material preparation technical field. High specific surface area raw material is adopted, contact area of powder in ball milling process is increased, reaction activity is improved, and sintering temperature is reduced; MnZn ferrite main formula adopts iron-rich zinc-deficient system, superexchange interaction is enhanced, and material Curie temperature is realized; secondary ball milling introduces combined additives, sintering process grain growth mechanism is regulated by means of fluxing and crystal resistance dual effects, Co2O3 is used to compensate MnZn ferrite magnetic crystal anisotropy constant, and initial magnetic permeability is improved; CaSiO3 is introduced, and is enriched in grain boundary in the sintering process, grain boundary resistivity is improved, and magnetic permeability frequency characteristic is improved; in the sintering process, oxygen partial pressure is accurately controlled in the holding and cooling stages, Fe 2+ Ion generation amount is influenced, sample resistivity is improved, and suitable sintering temperature and holding time are beneficial to grain growth and material densification.

Description

Technical Field

[0001] This invention belongs to the field of ferrite material preparation technology, specifically relating to a broadband MnZn ferrite material with high Curie temperature and high magnetic permeability and its preparation method. Background Technology

[0002] Since the nation proposed accelerating the cultivation and development of strategic emerging industries, my country's strategic emerging industries have generally shown a sustained and rapid growth trend, achieving remarkable results. In various fields such as communications, electronics, instrumentation, military, medical, automotive, new energy, and industrial control, filters are required in control circuits to cut off and attenuate interference signals, thereby reducing noise and suppressing electromagnetic interference. This plays a crucial role in the stability of electronic products. Common-mode filter inductors are an indispensable key component. With the modern electronics industry developing towards miniaturization, high frequency, and high reliability, the miniaturization of filter inductors is also urgently needed.

[0003] The industry's development has placed higher demands on high-permeability MnZn ferrite, a key material used in filter inductors, as it directly affects inductor performance. Compared to other soft magnetic materials, MnZn ferrite's advantage lies in its relatively high permeability. This allows for higher inductance with the same device geometry and number of turns, resulting in higher impedance values ​​and enhanced filtering effects, as well as facilitating device miniaturization. However, simply pursuing high permeability is no longer sufficient for future development requirements. High Curie temperature, a wide operating temperature range, and high saturation magnetic flux density must also be considered to meet the needs of various device applications. Furthermore, the material must be designed to resist interference and possess certain EMI characteristics, i.e., permeability frequency stability. Therefore, a high cutoff frequency and excellent permeability frequency characteristics are also essential.

[0004] For wideband high T cThe research on high cutoff frequency and high conductivity MnZn ferrite materials, disclosed in Chinese Patent Publication No. CN111056830 A, entitled "Wide-temperature, wide-frequency, high-impedance, high-permeability manganese-zinc ferrite and its preparation method," describes functional components, calculated by their respective oxides, as including 56.0–60.0 mol% Fe2O3 and equimolar percentages of MnO and ZnO. The auxiliary components account for 5–10% of the total mass of the functional components. These auxiliary components include TiO2, NiO, MoO3, SiO2, and Bi2O3. Utilizing high specific surface area raw materials and an optimized oxide ceramic preparation method, this method achieves high impedance and inductance stability while maintaining relatively high initial permeability and Curie temperature, and also possesses excellent resistance to temperature changes, thus broadening its applicable operating conditions. The embodiment described herein has an initial magnetic permeability of 11800 (1.0 kHz, 0.3 V, 23 ± 3 °C), a Curie temperature of 133 °C, a saturation magnetic induction of 410 mT (H = 1194 A / m, 25 °C), and a density of 4.75 g / cm³. 3 Meanwhile, its impedance is significantly improved, and its permeability stability is good over a wide temperature range, resulting in well-rounded performance. Unfortunately, its Curie temperature and saturation magnetic induction are both relatively low.

[0005] Chinese Patent Publication No. CN 112723873 A discloses a broadband, high-impedance, high-permeability MnZn soft magnetic ferrite and its preparation method. The main components include 52.5–53.9 mol% Fe₂O₃, 21.3%–23.30 mol% ZnO, and the remainder being MnO. Additives include: nano-CaCO₃: 400 ppm–1000 ppm, nano-Bi₂O₃: 100 ppm–600 ppm, nano-Nb₂O₅: 100 ppm–350 ppm, nano-SiO₂: 20 ppm–150 ppm, and nano-MoO₃: 100 ppm–500 ppm. By utilizing suitable main components and nano-additives, and employing a combination of bead milling and oxygen-enriched sintering processes, a MnZn ferrite with broadband, high permeability, and high impedance was prepared. Under conditions of 8 mV and 10 kHz, the permeability μ₀… i ≥15000; Permeability μ at 200kHz i ≥10000; Permeability μ at 500kHz i With an impedance coefficient ≥5000, it has a significant advantage and superior overall performance. However, its Curie temperature is low, only 130℃, which greatly limits its application scenarios.

[0006] Chinese Patent Publication No. CN 115745592 A discloses "A wideband high T c "High-Permeability Manganese-Zinc Ferrite Materials and Their Preparation Methods" describes materials composed of FeFe2O4, MnFe2O4, ZnFe2O4, and Li.0.5 Fe 0.5 A composite ferrite material formed by solid solution treatment of four single ferrites in Fe2O4, with the percentage contents of the four single ferrites denoted as α, β, γ, and θ, respectively, wherein 5.390% ≤ α ≤ 7.70%, 35.20% ≤ γ ≤ 38.14%, and 0.39% ≤ θ ≤ 1.56%, and α + β + γ + θ = 1. It introduces Li into the original main component. 0.5 Fe 0.5 Fe₂O₄ significantly increased the Curie temperature and also affected the position of the second peak in the permeability-temperature curve, thus adjusting the temperature curve accordingly. Regarding additives, CaMoO₄ and LiCoO₂ were selected in combination with traditional additives, significantly improving bandwidth and temperature characteristics. Finally, the initial permeability μ of MnZn ferrite was obtained. i =10000±10% (25℃, 10KHz, B<0.25mT), and the initial permeability μ is within a wide frequency range of 10KHz to 300KHz. i It has an ≥9000 rating and excellent overall performance, but its Curie temperature is only 165℃.

[0007] The University of Electronic Science and Technology of China (UESTC) has announced a high-permeability MnZn ferrite (Tao W, Dengfeng J, Chao W, et al. Ferrite materials with high saturation magnetic induction intensity and high permeability for magnetic field energy harvesting: Magnetization mechanism and Brillouin function temperature characteristics[J]. Journal of Alloys and Compounds, 2023, 933.). It has successfully prepared a ferrite with a permeability of μ... i =10000±10%, Curie temperature T c MnZn ferrite with a temperature ≥155℃ was studied, and its magnetization mechanism and Brillouin function temperature characteristics were investigated. However, at higher frequencies, the permeability of this material decreases significantly, resulting in poor permeability frequency characteristics, making it difficult to meet the requirements for wideband applications.

[0008] In summary, based on existing patents and research findings, for soft magnetic ferrites, the Snoek limit limits the cutoff frequency of MnZn ferrites to achieve high initial permeability, inevitably leading to a low cutoff frequency and consequently deterioration in broadband characteristics, which significantly restricts their applications. From a microstructural perspective, high-permeability MnZn ferrites have larger grains, thinner grain boundaries, and fewer impurities, resulting in poor permeability-frequency characteristics. Developing novel formulation systems that simultaneously achieve high permeability and high Curie temperature, and improving permeability-frequency characteristics and increasing the cutoff frequency with minimal impact on permeability, are current research hotspots with profound practical significance. Summary of the Invention

[0009] The purpose of this invention is to address the problem that current MnZn soft magnetic ferrite materials used in common-mode filter inductors cannot simultaneously achieve high permeability, high cutoff frequency, high Curie temperature, and high saturation magnetic flux density, and to provide a wideband high T... c High cutoff frequency, high conductivity MnZn ferrite material and its preparation method. The broadband high T... c High cutoff frequency, high conductivity MnZn ferrite material with initial permeability μ i =10000±10% (25℃, 10KHz, B<0.25mT), and permeability μ in a wide frequency range of 10KHz~300KHz. i ≥9000, cutoff frequency f r ≥500KHz, with Curie temperature T c ≥190℃, saturation magnetic induction intensity B s ≥510mT (25℃, 1KHz, H=1194A / m). Compared with existing similar products, the MnZn ferrite material provided by this invention has more comprehensive and superior overall performance, filling a gap in related research.

[0010] From the perspective of the properties of high-permeability MnZn ferrite materials, the Curie temperature is an intrinsic characteristic of MnZn ferrite, determined by the main formulation. A common approach to increasing the Curie temperature of MnZn ferrite is to reduce the ZnO content and increase the Fe2O3 content in the main formulation to regulate the superexchange interaction in the spinel lattice, ensuring a higher Curie temperature for MnZn ferrite. Simultaneously, from the perspective of improving frequency characteristics, a lower ZnO content is also required. In summary, to achieve a wideband high-T... cThe preparation of high-cutoff-frequency, high-conductivity MnZn ferrite materials employs an iron-rich, low-zinc system, addressing shortcomings in existing formulations and establishing a novel master formulation. However, the decrease in ZnO content inevitably leads to a corresponding decrease in the material's initial permeability, thereby reducing the overall performance of the MnZn ferrite, which contradicts our initial design intent. Therefore, how to compensate for the decrease in permeability caused by the lack of ZnO content under the new master formulation system, while maintaining a relatively high initial permeability in the MnZn ferrite, warrants in-depth investigation.

[0011] This invention focuses on high permeability and high Curie temperature, particularly on the formulation and microstructure of MnZn ferrite, establishing a novel main formulation system while meeting basic electromagnetic properties. Based on this, achieving high permeability, high cutoff frequency, and wide-bandwidth characteristics further depends on the combined effects of factors such as the material's magnetocrystalline anisotropy constant, magnetostriction coefficient, grain size, grain boundary characteristics, microstructure, and sintering density. This requires a combination of appropriate additive systems and adjustments to the preparation process. For high permeability, it is necessary to increase the grain size of MnZn ferrite and maintain a uniform microstructure, while simultaneously controlling the magnetocrystalline anisotropy number K1 to approach zero, and ensuring high sintering density and low porosity. For high cutoff frequency and good permeability frequency characteristics, it is necessary to refine the grains, increase grain boundary resistance, increase grain boundary thickness, and improve grain boundary characteristics. For high saturation magnetic induction, given a basically determined chemical composition, it is also necessary to maximize the density of the sintered body.

[0012] Based on the above comprehensive considerations, we first considered using a combination of two additives with both crystal-inhibiting and crystal-promoting effects to regulate the grain growth mechanism during sintering and achieve the optimal grain size. Specifically, a low-melting-point Bi₂O₃ additive is introduced to flux the mixture, maintaining the larger grains required for high permeability while improving the microscopic uniformity of the material; an appropriate amount of Nb₂O₅ additive is introduced to refine the grains, promoting densification of the sample during sintering while improving grain and grain boundary characteristics; furthermore, a highly anisotropic Co₂O₃ additive is introduced, as it easily enters the spinel sublattice and can regulate the ion distribution state, thereby adjusting the magnetocrystalline anisotropy constant, thus helping to improve the initial permeability of the material. Most importantly, this invention introduces CaSiO₃ into the additive system. For power-type MnZn ferrites, CaO is generally used to increase resistivity and reduce losses; for high-frequency MnZn power ferrites applied in the MHz band, SiO₂ is sometimes added. For high-permeability MnZn ferrites, the grains are relatively large and the grain boundaries are thin, making them more susceptible to the effects of doping. Therefore, it is generally believed in the industry that the introduction of Si-containing impurities into the composition should be avoided to prevent the resulting sharp deterioration of the microstructure. However, it should also be noted that high-resistivity additives often enrich the grain boundaries during sintering, increasing the grain boundary thickness and causing a significant increase in grain boundary resistance, which helps improve the frequency stability of magnetic permeability. This is crucial for high-permeability MnZn ferrites and must be utilized. CaCO3 is considered a commonly used high-resistivity material, but experimental results show that its effect on improving the frequency characteristics of magnetic permeability is not significant enough. SiO2 has extremely high resistivity, but it significantly damages the microstructure of the material, which greatly reduces the overall magnetic properties of the material, making it counterproductive. This invention takes into account the above considerations, aiming to improve the frequency characteristics of magnetic permeability using high-resistivity materials while minimizing the negative impacts. Therefore, a novel additive, CaSiO3, is considered, which has a stronger improving effect than CaCO3 and lower negative impacts. At the same time, by adapting the process to compensate for the possible decrease in magnetic properties of the material, it is helpful to obtain the target product with comprehensive performance.

[0013] Regarding the sintering process, the basic flow is as described above, employing a two-stage reduction sintering technique. The key focus is on controlling the sintering temperature and oxygen partial pressure during the holding and cooling stages. During the holding stage, because CaSiO3 has a certain crystal-promoting effect, the temperature needs to be reduced accordingly to avoid abnormal grain growth and adhesion. Simultaneously, the holding time is adjusted to regulate the solid-state reaction, ultimately achieving a large and uniform grain distribution, which is crucial for excellent overall performance. Regarding the oxygen partial pressure during the holding stage, in the first stage, the sintering oxygen partial pressure is maintained at 21%, while in the second stage, it is reduced to 12%. This is to promote the shift of the redox reaction at the end of grain growth to control Fe... 2+The total content. This invention also optimizes the control of oxygen partial pressure during the cooling stage. Its core advantage in reduction sintering technology lies in two aspects: firstly, a suitable oxygen partial pressure curve helps expel pores from the sintered body, promoting material densification and increasing macroscopic density; secondly, it can further control the balance of the redox reaction, resulting in a final product containing more Fe. 2+ These anisotropic ions can compensate for the negative magnetocrystalline anisotropy constant K1 of MnZn ferrite, making it approach 0, which helps to improve the initial permeability.

[0014] Based on the above, this invention starts with the MnZn ferrite formulation system and designs a ZnO and Fe2O3 formulation range that meets the Curie temperature requirements, thereby establishing a high Curie temperature MnZn ferrite main formulation system. Subsequently, a multi-effect additive system is introduced to improve the overall electromagnetic properties of the MnZn ferrite. Furthermore, this invention also provides an optimized preparation process and sintering curves.

[0015] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0016] A wideband high T c A high-conductivity manganese-zinc ferrite comprises a main formulation and additives. The main formulation comprises 51.8–54.0 mol% Fe₂O₃ and 16.5%–18.0 mol% ZnO, with the remainder being MnO. Based on the mass of the pre-calcined material obtained after pre-calcination, the additives comprise 0.01–0.02 wt% Co₂O₃, 0.01–0.02 wt% Nb₂O₅, 0.03–0.05 wt% Bi₂O₃, 0.02–0.04 wt% MoO₃, and 0.01–0.03 wt% CaSiO₃.

[0017] A wideband high T c A method for preparing high-conductivity manganese-zinc ferrite includes the following steps:

[0018] Step 1, Ingredients:

[0019] Using Fe2O3, ZnO and MnO as raw materials, the raw materials were calculated and weighed according to the main formula of "51.8-54.0 mol% Fe2O3 and 16.5-18.0 mol% ZnO, with the remainder being MnO".

[0020] Step 2, First ball milling:

[0021] The raw material weighed in step 1 is ball-milled once in a planetary ball mill for 1 to 2 hours to obtain primary ball milled material.

[0022] Step 3, Preheating:

[0023] After drying and sieving the primary ball milling material obtained in step 2, it is pre-calcined in air for 3-4 hours.

[0024] Step 4, Doping:

[0025] Using the mass of the pre-burned material obtained in step 3 as a benchmark, add "0.01-0.02 wt% Co2O3, 0.01-0.02 wt% Nb2O5, 0.03-0.05 wt% Bi2O3, 0.02-0.04 wt% MoO3 and 0.01-0.03 wt% CaSiO3" as additives to the pre-burned material;

[0026] Step 5, Secondary ball milling:

[0027] The mixed powder obtained in step 4 is loaded into a planetary ball mill for secondary ball milling for 2-4 hours, and the particle size is controlled and then dried.

[0028] Step 6, Granulation and Molding:

[0029] 10-15 wt% PVA binder is added to the secondary ball milling material obtained in step 5 by weight ratio, mixed and granulated, and then pressed on a press to obtain a green part of the target shape.

[0030] Step 7, Sintering:

[0031] The green blank obtained in step 6 is placed in a tube furnace for staged sintering to obtain the manganese-zinc ferrite; wherein the staged sintering process is as follows:

[0032] The first stage: heating from 50℃ to 500-600℃, with an oxygen partial pressure of 21% and a heating rate of 1-2℃ / min. This stage is the stage for enhancing the debinding process.

[0033] Second stage: Continue heating to 700-850℃, oxygen partial pressure is 21%, heating rate is 1.5-2.5℃ / min, this stage is the standard debinding stage;

[0034] The third stage: continue heating to the sintering temperature of 1300-1450℃, with an oxygen partial pressure of 21% and a heating rate of 1.5-2.5℃ / min. This stage is the sintering stage.

[0035] Fourth stage: Maintain the sintering temperature at 1300-1450℃ for 6-8 hours, with the oxygen partial pressure maintained at 21% for the first 5-6 hours and at 12% for the last 2-3 hours. This stage is the holding stage.

[0036] Fifth stage: The temperature is lowered from the sintering temperature to 1300℃, and the oxygen partial pressure gradually decreases to 5%; then the temperature is further lowered to 1100-1300℃, and the oxygen partial pressure gradually decreases to 1%; the temperature is further lowered to 950-1100℃, and the oxygen partial pressure gradually decreases to 0.1%; the temperature is further lowered to 850℃, and the oxygen partial pressure is in a pure nitrogen atmosphere, and the temperature is lowered to 50℃ in a pure nitrogen atmosphere; the cooling rate is 1.5-2.5℃ / min, and this stage is the cooling stage.

[0037] Furthermore, in step 2, the ball milling speed is 230-260 r / min; in step 3, the pre-firing temperature is 800-900℃, and the pre-firing time is 3-4 hours; in step 5, the ball milling speed is 240-270 r / min.

[0038] This invention provides a wideband high T c High-cutoff-frequency, high-conductivity MnZn ferrite materials utilize high-specific-surface-area raw materials to increase the powder contact area during ball milling, which is beneficial for improving reactivity and lowering the sintering temperature. For the main MnZn ferrite formulation, an iron-rich, zinc-deficient system is adopted to enhance superexchange, which is conducive to achieving the Curie temperature of the material. Secondary ball milling introduces combined additives, leveraging the dual effects of fluxing and crystal inhibiting to regulate the grain growth mechanism during sintering. Co₂O₃ is used to compensate for the magnetocrystalline anisotropy constant of MnZn ferrite, thereby increasing the initial permeability. The introduction of CaSiO₃ enriches it at grain boundaries during sintering, increasing grain boundary resistivity and improving the permeability-frequency characteristics. During sintering, precise control of oxygen partial pressure during the holding and cooling stages affects the Fe content. 2+ The amount of ions generated increased the resistivity of the sample, while appropriate sintering temperature and holding time were beneficial to grain growth and material densification.

[0039] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0040] 1. The wideband high T provided by this invention c High cutoff frequency, high conductivity MnZn ferrite material, initial permeability μ i =10000±10% (25℃, 10KHz, B<0.25mT), and permeability μ in a wide frequency range of 10KHz~300KHz. i ≥9000, cutoff frequency f r ≥500KHz, with Curie temperature T c ≥190℃, saturation magnetic induction intensity B s ≥510mT (25℃, 1KHz, 1194A / m). It can meet the requirements of new common-mode filter inductors and other electronic components for materials with high initial permeability, high cutoff frequency, high Curie temperature and high saturation magnetic induction intensity, and its overall performance is superior to current products.

[0041] 2. The wideband high T provided by this invention c High cutoff frequency and high conductivity MnZn ferrite materials can be developed by doping with an appropriate amount of CaSiO3 additives to regulate the grain growth mechanism during the sintering process, improve grain boundary properties, and increase grain boundary resistivity. This significantly improves the frequency stability of MnZn ferrite permeability while maintaining a relatively high initial permeability, thus expanding its application potential to higher and wider frequency bands.

[0042] 3. The segmented heat preservation sintering technology adopted in this invention has reference value. At the same time, the process adopted saves production costs, improves product yield, and lays a good foundation for the subsequent industrialization of materials. Attached Figure Description

[0043] Figure 1 SEM microstructure images of MnZn ferrites prepared in Comparative Example 1(a), Example 1(b) and Example 4(c);

[0044] Figure 2 The curves showing the initial permeability of MnZn ferrites prepared in Comparative Example 1, Example 1, and Example 4 as a function of temperature are shown.

[0045] Figure 3 The magnetic spectrum curves of the MnZn ferrites prepared in Comparative Example 1, Example 1 and Example 4 are shown.

[0046] Figure 4 The resistivity variation diagrams are shown for the MnZn ferrites prepared in Comparative Example 1, Example 1, and Example 4.

[0047] Figure 5 Impedance characteristic diagrams of MnZn ferrites prepared in Comparative Example 1, Comparative Example 2, Example 1 and Example 4;

[0048] Figure 6 The graph shows the variation of the specific loss coefficient of the MnZn ferrite prepared in Comparative Example 1, Example 1, and Example 4. Detailed Implementation

[0049] To enable those skilled in the art to better understand the technical solution of the present invention, a more detailed description will be provided through specific implementations, but the scope of protection of the present invention is not limited to these embodiments.

[0050] Unless otherwise specified, the experimental or testing methods described in the following embodiments are conventional methods, and the materials and reagents described are obtained from conventional commercial channels.

[0051] The wideband high T provided by this invention c A method for preparing high cutoff frequency and high conductivity MnZn ferrite materials, comprising the following steps for preparing samples of Examples 1-4 and Comparative Examples 1-3:

[0052] Step 1, Ingredients:

[0053] Using Fe2O3, ZnO and MnO as raw materials, the main raw materials for Examples 1-4 and Comparative Examples 1-3 were weighed according to the formulations in the table below;

[0054]

[0055] Step 2, First ball milling:

[0056] The raw material weighed in step 1 is ball-milled once in a planetary ball mill. The ball milling media is bearing steel balls, and the ball milling time is 1.5 hours to obtain primary ball milling material.

[0057] Step 3, Preheating:

[0058] The ball milling material obtained in step 2 was dried, sieved, and placed in a furnace for pre-calcination at 830°C in air atmosphere for 4 hours to obtain pre-calcined material.

[0059] Step 4, Doping:

[0060] Using the mass of the pre-sintered material obtained in step 3 as a benchmark, additives were added to the pre-sintered material, and the doping amounts are shown in the table below:

[0061]

[0062] It is worth noting that in Comparative Examples 2 and 3, the CaSiO3 additive was replaced with CaCO3;

[0063] Step 5: Secondary ball milling;

[0064] The mixed powder obtained in step 4 was loaded into a planetary ball mill for secondary ball milling for 2 hours, and the particle size was controlled and then dried.

[0065] Step 6, Granulation and Molding:

[0066] 10 wt% PVA binder was added to the secondary ball milling material obtained in step 5 by weight ratio, mixed and granulated, and then pressed on a press to obtain a green part of the target shape.

[0067] Step 7, Sintering:

[0068] The green blank obtained in step 6 is placed in a tube furnace for staged sintering to obtain the manganese-zinc ferrite; wherein the staged sintering process is as follows:

[0069] The first stage: heating from 50℃ to 600℃, with an oxygen partial pressure of 21% and a heating rate of 1-2℃ / min. This stage is the stage for enhancing the debinding process.

[0070] Second stage: Continue heating to 830℃, oxygen partial pressure is 21%, heating rate is 1.5~2.5℃ / min, this stage is the standard debinding stage;

[0071] The third stage: continue heating to the sintering temperature of 1420℃, with an oxygen partial pressure of 21% and a heating rate of 1.5~2.5℃ / min. This stage is the sintering stage.

[0072] Fourth stage: Maintain the sintering temperature constant and hold for 8 hours, with the oxygen partial pressure maintained at 21% for the first 6 hours and at 12% for the last 2 hours. This stage is the holding stage.

[0073] Fifth stage: The temperature is lowered from the sintering temperature to 1300℃, and the oxygen partial pressure gradually decreases to 5%; then the temperature is further lowered to 1100-1300℃, and the oxygen partial pressure gradually decreases to 1%; the temperature is further lowered to 950℃-1100℃, and the oxygen partial pressure gradually decreases to 0.1%; the temperature is further lowered to 850℃, and the oxygen partial pressure is in a pure nitrogen atmosphere, and the temperature is lowered to 50℃ in a pure nitrogen atmosphere; the cooling rate is 1.5-2.5℃ / min, and this stage is the cooling stage.

[0074] After winding the MnZn ferrite samples prepared in Examples 1-4 and Comparative Examples 1-3, the inductance L of the samples was measured using a Tonghui TH2826 precision LCR meter. The voltage across the samples was adjusted appropriately to ensure that B < 0.25mT. The initial permeability μ of the samples was then calculated using a formula. i The test conditions were a frequency f = 10 kHz, a typical voltage of 10 mV, and a test temperature controlled by a high-low temperature oven. The permeability-temperature characteristic curve was obtained using the temperature-controlled oven. The sample magnetic spectrum curve was also obtained using a Tonghui TH2826 precision LCR meter. By setting a large number of continuous frequency test points, the real and imaginary parts of the complex permeability at different test frequencies were obtained, and the data were calculated and plotted. The basic magnetic properties were measured using an Iwasaki SY-8218B-H analyzer to determine the saturation magnetic induction intensity B. s Test conditions: frequency f = 1 kHz, field H = 1194 A / m, temperature T = 25℃.

[0075] The permeability and basic electromagnetic properties of Examples 1-4 and Comparative Examples 1-3 at different test frequencies are shown in the table below. The test conditions are as described above, and the test temperature is 25°C.

[0076]

[0077] As shown in the table above, changes in the main formulation have a relatively small impact on the broadband characteristics of the material, but a significant impact on the initial permeability and Curie temperature. The introduction of CaSiO3 significantly improves the frequency characteristics of permeability within a certain range, while the initial permeability decreases slightly. Furthermore, CaSiO3 exhibits a more pronounced effect than CaCO3.

[0078] As shown in the table above, the saturation magnetic induction intensity of the material does not change significantly when the main formulation remains relatively unchanged. The cutoff frequency increases significantly with increasing CaSiO3 and CaCO3 content. Meanwhile, the Curie temperature of the material is greatly affected by ZnO; therefore, controlling the ZnO content is crucial for high-permeability MnZn ferrites. High-resistivity additives play a key role in controlling the frequency stability of the permeability.

[0079] Figure 1 The figures show the SEM microstructures of MnZn ferrites prepared in Comparative Example 1(a), Example 1(b), and Example 4(c). As can be seen from the figures, the addition of an appropriate amount of CaSiO3 makes the grain growth and distribution more uniform, while reducing the porosity and increasing the density, which is beneficial to improving the permeability and saturation magnetization. Figure 2 The graph shows the initial permeability of MnZn ferrites prepared in Comparative Example 1, Example 1, and Example 4 as a function of temperature. As can be seen from the graph, the introduction of CaSiO3 additive does not affect the Curie temperature of MnZn ferrite. Figure 3 The magnetic spectrum curves of the MnZn ferrites prepared in Comparative Example 1, Example 1 and Example 4 are shown in the figure. As can be seen from the figure, with the increase of CaSiO3 addition, the trend of the real permeability decreasing with the increase of frequency is slowed down, the cutoff frequency is increased, and the permeability frequency characteristics are improved. Figure 4 The resistivity variation graphs are for MnZn ferrites prepared in Comparative Example 1, Example 1, and Example 4. As can be seen from the graphs, the resistivity of the material increases monotonically with the increase of CaSiO3 content. Figure 5 The impedance characteristics of MnZn ferrites prepared in Comparative Example 1, Comparative Example 2, Example 1 and Example 4 are shown in the figure. As can be seen from the figure, with the increase of the amount of CaSiO3 and CaCO3 added, the grain boundary resistivity of the high-conductivity MnZn ferrite increases significantly, and at the same amount of addition, CaSiO3 increases the resistivity more than CaCO3. Figure 6 The graph shows the variation of the specific loss coefficient of the MnZn ferrite prepared in Comparative Example 1, Example 1 and Example 4; as can be seen from the graph, doping with CaSiO3 is beneficial to reducing the specific loss coefficient.

Claims

1. A wideband high-T c The method for preparing high-conductivity manganese-zinc ferrite is characterized by, Includes the following steps: Step 1, Ingredients: Using Fe2O3, ZnO and MnO as raw materials, calculate and weigh the raw materials according to the main formula of "51.8~54.0 mol% Fe2O3 and 16.5%~18.0 mol% ZnO, with the remainder being MnO". Step 2, First ball milling: The raw material weighed in step 1 is ball-milled once for 1-2 hours to obtain primary ball-milled material. Step 3, Preheating: After drying and sieving the primary ball milling material obtained in step 2, it is pre-calcined in air for 3-4 hours. Step 4, Doping: Using the mass of the pre-burned material obtained in step 3 as a benchmark, add "0.01~0.02wt% Co2O3, 0.01~0.02wt% Nb2O5, 0.03~0.05wt% Bi2O3, 0.02~0.04wt% MoO3 and 0.01~0.03wt% CaSiO3" as additives to the pre-burned material; Step 5: Secondary ball milling; The mixed powder obtained in step 4 is subjected to a second ball milling for 2-4 hours. Step 6, Granulation and Molding: PVA binder is added to the secondary ball milling material obtained in step 5, and after mixing and granulation, it is pressed on a press to obtain a green part; Step 7, Sintering: The green blank obtained in step 6 is sintered in stages, and then cooled to obtain the manganese-zinc ferrite; wherein the staged sintering process is as follows: First stage: Increase the temperature from 50℃ to 500~600℃, with an oxygen partial pressure of 21%; Second stage: Continue to raise the temperature to 700~850℃, with an oxygen partial pressure of 21%; Third stage: Continue to raise the temperature to the sintering temperature of 1300~1450℃, with an oxygen partial pressure of 21%; Fourth stage: Keep the sintering temperature constant and hold for 6-8 hours, with the oxygen partial pressure maintained at 21% for the first 5-6 hours and at 12% for the last 2-3 hours.

2. The wideband high-T according to claim 1 c The method for preparing high-conductivity manganese-zinc ferrite is characterized by, In step 7, the cooling process is as follows: the temperature is lowered from the sintering temperature to 1300℃, and the oxygen partial pressure gradually decreases to 5%; then the temperature is further lowered to 1100~1300℃, and the oxygen partial pressure gradually decreases to 1%; the temperature is further lowered to 950~1100℃, and the oxygen partial pressure gradually decreases to 0.1%; the temperature is further lowered to 850℃, and the oxygen partial pressure is in a pure nitrogen atmosphere, and the temperature is lowered to 50℃ in a pure nitrogen atmosphere.

3. The wideband high-T according to claim 1 c The method for preparing high-conductivity manganese-zinc ferrite is characterized by, In step 2, the ball mill speed is 230~260 r / min.

4. The wideband high-T according to claim 1 c The method for preparing high-conductivity manganese-zinc ferrite is characterized by, In step 3, the preheating temperature is 800~900℃.

5. The wideband high-T according to claim 1 c The method for preparing high-conductivity manganese-zinc ferrite is characterized by, In step 5, the ball mill speed is 240~270 r / min.

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