High-temperature low-loss mnzn ferrite material and preparation method thereof

Abstract

This invention relates to the field of MnZn ferrite materials, and in particular to a high-temperature, low-loss MnZn ferrite material and its preparation method. The material comprises a main component and auxiliary components. The main component is Fe2O3, ZnO, and MnO. The auxiliary components include Nb2O5, ZrO2, TiO2, Co2O3, and at least one of CaCO3, SiO2, CuO, and Bi2O3. Simultaneously, a novel auxiliary component, BaTiO3, with a positive temperature coefficient of resistivity, is added. The Curie temperature of BaTiO3 is 80–120 °C, and its surface is coated with a nanoscale Al2O3 insulating layer to prevent the Ti⁴⁺ valence state change of BaTiO3 in the equilibrium oxygen partial pressure sintering atmosphere of MnZn ferrite. The MnZn ferrite material prepared by this method exhibits low-loss characteristics at high temperatures (150–160 °C).

Description

Technical Field

[0001] This patented invention belongs to the field of advanced preparation and application of high-performance power ferrite soft magnetic materials, and relates to a high-temperature low-loss MnZn ferrite material and its preparation method. Background Technology

[0002] The losses in manganese-zinc power ferrites increase sharply at high temperatures, primarily because the increased temperature leads to a higher Fe²⁺ ion concentration, intensifying hopping conduction between Fe²⁺ and Fe³⁺ electrons, decreasing the material resistivity, and significantly increasing eddy current losses. Traditional methods involve adding CaO, SiO₂ to form high-resistivity grain boundaries or doping with high-valence ions to suppress Fe²⁺ formation. However, these methods passively increase the matrix resistivity, and their effectiveness often diminishes at high temperatures (>100℃) and they cannot actively respond to temperature changes. Positive temperature coefficient (PTC) ceramics (such as BaTiO₃-based ceramics) exhibit a sharp increase in resistivity by several orders of magnitude near the Curie temperature. If such materials could be introduced into ferrites in a controllable manner, it is hoped that the overall effective resistivity of the composite material could be "actively increased" at high temperatures, thereby directly suppressing eddy current losses.

[0003] Patent CN 112979301 A discloses a "High-Frequency, High-Temperature, Low-Loss MnZn Power Ferrite Material and its Preparation Method," whose main components include Fe2O3: 53.5–56.5 mol%, MnO: 32.5–35.5 mol%, and ZnO: 9.0–12.0 mol%; the additives include 0.01–0.06 wt% BaTiO3 and 0.1–0.3 wt% CaCu3Ti4O3. 12 MnZn power ferrites prepared by combined doping using the high resistance characteristics of BTO and CCTO are applied at frequencies in the MHz range.

[0004] Patent CN 108530050A discloses a "Wide-Temperature, Low-Loss, High-Impedance MnZn Soft Magnetic Ferrite Material and Preparation Method," whose main materials include Fe2O3: 52.0–55.0 mol%, ZnO: 9.5–12.5 mol%, and the remainder being MnO. Additives include CaO, Nb2O5, Co2O3, HfO2, and Bi2O3, as well as 0.001–0.05 wt% nano-BaTiO3. It still utilizes the high resistivity of BTO, increasing the contact between nano-BTO powder and the particulate material to increase the grain boundary resistivity of the MnZn ferrite. Data shows that only a maximum temperature of 120℃ was tested, and the performance at 100kHz and 200mT was 321 kW / m. 3 .

[0005] Patent CN 114685153 B discloses "Wide-temperature and wide-frequency MnZn power ferrite material and preparation method", the main components of which include 51.5-53.0 mol% Fe2O3 and 10.0-12.0 mol% ZnO, with the remainder being MnO; the additives include 0.02-0.08 wt% CaCO3, 0.01-0.05 wt% Nb2O5, 0.01-0.05 wt% ZrO2, 0.3-0.5 wt% Co2O3, 0.01-0.02 wt% NiO and 0.001-0.012 wt% BTO-based PTC dielectric ceramic powder. It utilizes the PTC effect of BTO to improve loss over a wide temperature range of 25-140℃ and a wide frequency range of 100-300kHz. Data shows that under test conditions of 100 kHz and 200 mT, the loss at 140℃ gradually decreases to 498 kW / m² with increasing BTO content. 3 .

[0006] In summary, BTO-based dielectric materials exhibiting the PTC effect, when applied to MnZn ferrite, optimize high-temperature performance at different frequencies. However, according to patents CN 103058651 A ("A Modified Barium Titanate-Based Lead-Free Positive Temperature Coefficient Resistor Material and Its Preparation Method") and CN 101445365 A ("A Barium Titanate-Based Positive Temperature Coefficient Resistor Material and Its Preparation Method"), the sintering conditions of BTO are carried out in an atmospheric atmosphere, which is incompatible with the sintering atmosphere of ferrite. Furthermore, its composition (such as Ti...) 4 (⁺) In the reducing sintering atmosphere of ferrites, they are easily reduced to a low valence state, which in turn becomes a donor impurity and worsens the resistivity. Therefore, direct doping may not be able to fully realize its characteristics. Therefore, this invention develops a high-temperature, low-loss MnZn ferrite material and its preparation method. Summary of the Invention

[0007] The present invention aims to overcome the above-mentioned technical obstacles and provide a novel MnZn ferrite composite material and its preparation method.

[0008] This method introduces BTO ceramic particles as functional impurities by surface insulating coating, thereby stabilizing them during the sintering process of the ferrite matrix. It also utilizes the positive temperature coefficient of resistance to specifically improve the resistivity and loss performance of ferrite at high temperatures. The core of this invention's technical solution lies in: (1) utilizing the exponential increase in resistivity of BTO ceramics above the Curie temperature (preferably doped BTO with a Curie temperature adjusted between 80℃ and 120℃) as a grain boundary resistance layer to optimize the high-temperature loss of MnZn ferrite; (2) employing an insulating coating technique to modify the surface of BTO, achieving an insulating-coated structure of particles; (3) using a segmented ball milling process to break down the main component particles and ensure the auxiliary components are evenly distributed, while avoiding damage to the surface structure of the surface-coated BaTiO3 during sand milling; (4) sintering is carried out under a segmented controlled oxygen partial pressure atmosphere, as per the standard MnZn ferrite specifications. In the high-temperature, low-oxygen stage, the insulating shell effectively prevents the external reducing atmosphere from contacting the internal BTO particles, maintaining the Ti... 4 The ⁺ valence state is stable, preventing it from reverting to donor-type Ti³⁺, which would worsen resistivity.

[0009] Specifically, the technical solution provided by this invention is as follows:

[0010] A high-temperature, low-loss MnZn ferrite material and its preparation method, comprising the following steps:

[0011] Step 1: Preparation of surface-coated BaTiO3 powder:

[0012] Submicron-sized barium titanate powder with a Curie temperature of 80–120 °C was ultrasonically dispersed in a 0.2 mol / L dilute nitric acid solution, followed by centrifugation and washing with deionized water until neutral, and then substituted three times with anhydrous ethanol. Finally, it was dispersed in anhydrous isopropanol for later use. Under drying and stirring conditions, the above-treated BTO suspension was added dropwise to an anhydrous isopropanol solution containing aluminum isopropoxide (concentration of 0.1–0.3 mol / L) and acetylacetone chelating agent (molar ratio of 0.6:1 to aluminum). The mixture was heated to 70 °C, and water for hydrolysis was slowly added dropwise under constant stirring, controlling the pH of the reaction system, and the reaction was continued for 6 hours. After the reaction, the precursor powder was obtained after aging, repeated centrifugation and washing with anhydrous ethanol, and vacuum drying. The powder was then heat-treated in air: heated to 600 °C at a rate of 1–3 °C / min and held for 2–3 hours. After cooling, continuous and dense amorphous Al2O3 insulating layer coated particles are obtained.

[0013] Step 2: Preparation of MnZn pre-calcined material:

[0014] The main components Fe2O3, ZnO, and MnO were proportioned according to the measured values ​​of each component. A uniform slurry was obtained through a single ball milling process using a wet mixing technique. After drying and pulverizing, the slurry was pre-fired at 800-900℃ in an air atmosphere, and cooled with the furnace. The resulting product was a pre-fired MnZn ferrite material with an active spinel structure.

[0015] Step 3, Segmented ball milling:

[0016] Add the designed amount of auxiliary components to the pre-calcined material prepared in step (2), add deionized water at a mass ratio of 1:1 to raw material, and perform the first stage of secondary wet ball milling for 20-30 min; then add the surface-coated BaTiO3 auxiliary components, and perform the second stage of low-speed ball milling for 10-20 min, and obtain powder after drying.

[0017] Step 4, Granulation and Compression:

[0018] The granules obtained in step (3) with 12-15% PVA were granulated and sieved, and then baked at 120℃ for 9-10 minutes to obtain granules with uniform size and good flowability. They were then bidirectionally pressed into 25×15×7.5mm green rings using a 16-ton press.

[0019] Step 5, Sintering:

[0020] The green ring pressed in step (4) is placed into a bell furnace for sintering. The sintering temperature is 1200~1300℃ and the holding time is 3~6h. The sintering atmosphere is under balanced oxygen partial pressure.

[0021] Preferably, in step 1, the water used for hydrolysis consists of deionized water, ethanol, and dilute nitric acid, and the hydrolysis ratio r (the ratio of deionized water to metal alkoxide) is controlled within the range of 2 to 4, the pH value is controlled within the range of 3.5 to 4.5, and the thickness of the continuous and dense amorphous Al2O3 insulating layer formed is 20 to 50 nm.

[0022] Preferably, in step 3, the auxiliary components include surface-coated BTO, Nb2O5, ZrO2, TiO2, and Co2O3, and also include a flux, wherein the flux is at least one of CaCO3, SiO2, CuO, and Bi2O3;

[0023] Furthermore, as a preferred embodiment, based on the total weight of the main components Fe2O3, ZnO, and MnO as 100%, the amount of auxiliary components added is as follows: surface-coated BTO: 0.025~0.10wt%, Nb2O5: 0.015~0.035wt%, ZrO2: 0.01~0.02wt%, TiO2: 0.12~0.30wt%, Co2O3: 0.10~0.20wt%, and CaCO3: 0.03~0.05wt%.

[0024] Preferably, in step 3, the segmented ball milling process is divided into two stages. The first stage has a ball milling speed of 300 rpm and a ball milling particle size D. 50 The particle size was controlled within the range of 1.3~1.6μm, and the ball milling speed in the second stage was 100rpm; the final powder D after two stages of ball milling 50 : 1.2~1.5μm;

[0025] Preferably, in step 4, the powder is sieved through 60-mesh and 120-mesh sieves to remove large and small particles, improve the size uniformity, flowability, and bulk density of the powder, and control the density of the pressed green ring to 2.9~3.1 g / cm³. 3 ;

[0026] Preferably, in step 5, the sintering holding temperature is 1200~1300℃, which is much higher than the sintering temperature of the surface-coated BTO, and the equilibrium oxygen partial pressure O2 is controlled at 3.5~4.2 vol during the holding stage.

[0027] A high-temperature, low-loss MnZn ferrite material is obtained by the aforementioned coated PTC doped high-temperature, low-loss MnZn ferrite material and its preparation method.

[0028] The beneficial effects of this invention are:

[0029] (1) A method for preparing high-temperature, low-loss, and high-permeability MnZn ferrite materials is provided. Barium titanate-based materials with a positive temperature coefficient are doped into MnZn ferrite as grain boundary impurities. On the one hand, utilizing the positive temperature coefficient characteristic that the resistivity of BTO ceramics increases with increasing temperature, the grain boundary resistance formed by BTO gradually increases as the temperature rises, effectively hindering electron transitions at high temperatures and reducing high-temperature eddy current losses. On the other hand, by insulating the surface of BTO, the contradiction between the BTO grain boundary layer and the MnZn ferrite ceramic in the sintering process is resolved: by introducing an insulating layer, the harmful chemical reactions between the BTO grain boundary layer and the ferrite matrix during high-temperature sintering (especially Ti) are effectively blocked. 4 The reduction of ⁺ allows two materials with drastically different requirements for sintering atmosphere to be successfully combined.

[0030] (2) A MnZn ferrite material with high temperature and low loss characteristics is provided. At 100kHz & 200mT, the Pcv at 150℃ is 345kW / m. 3 Pcv at 160℃: 383kW / m 3 . Attached Figure Description

[0032] Figure 1 This is a SEM image of MnZn ferrite. Figure 1 (a) is a cross-sectional view of BTO with 0.075 wt% surface coating; Figure 1 (b) is a cross-sectional structure diagram of 0.075wt% BTO doped with BTO; the black solid circles in the figure represent abnormally grown grains. Detailed Implementation

[0033] The technical solution of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0034] Step 1: Preparation of surface-coated BTO powder:

[0035] Submicron-sized doped barium titanate powder with a Curie temperature of 120℃ was ultrasonically dispersed in a 0.2 mol / L dilute nitric acid solution, followed by centrifugation and washing with deionized water until neutral, and then substituted three times with anhydrous ethanol. Finally, it was dispersed in anhydrous isopropanol for later use. Under drying and stirring conditions, the above-treated BTO suspension was added dropwise to an anhydrous isopropanol solution containing aluminum isopropoxide (0.1 mol / L) and acetylacetone chelating agent (molar ratio of aluminum to acetylacetone 0.6:1). The mixture was heated to 70℃, and under constant stirring, water for hydrolysis (composed of water, anhydrous ethanol, and dilute nitric acid, with a molar ratio of deionized water to aluminum isopropoxide of 3:1 and a volume ratio of anhydrous ethanol to water of 2:1) was slowly added dropwise. The pH of the reaction system was controlled at 4.5 ± 0.3, and the reaction was continued for 6 hours. After the reaction was completed, the precursor powder was obtained after aging, repeated centrifugation and washing with anhydrous ethanol, and vacuum drying. The powder was heat-treated in air: the temperature was increased to 600℃ at a rate of 2℃ / min and held for 2 hours. After cooling, continuous and dense amorphous Al2O3 insulating layer coated particles were obtained.

[0036] Step 2: Preparation of MnZn pre-calcined material:

[0037] The ingredients were prepared according to the metered proportions of 53.07 mol% Fe2O3, 8.74 mol% ZnO and 38.19 mol% MnO. After one wet ball milling (300 rpm, 10 min), a uniform slurry was obtained. After drying and pulverizing, it was pre-calcined at 850℃ for 2 h in an air atmosphere. The slurry was cooled with the furnace. After the reaction, a pre-calcined MnZn ferrite material with an active spinel structure was obtained.

[0038] Step 3, Segmented ball milling:

[0039] The designed-measured auxiliary components were added to the pre-calcined material prepared in step (2): Nb2O5: 0.025wt%, ZrO2: 0.02wt%, TiO2: 0.25wt%, Co2O3: 0.15wt%, and CaCO3: 0.04wt%. Deionized water was added at a mass ratio of 1:1 to the raw material, and the first stage of wet ball milling was performed for 20 min at 300 rpm. Subsequently, BTO@Al2O3 of different mass percentages as shown in Table 1 was added in Examples 2-5. The second stage of low-speed ball milling was performed for 15 min at 100 rpm, and the dry powder was obtained after drying in a drying oven at 120℃ for 4 h. As a comparison, Example 1* did not add BTO or surface-coated BTO, and in order to maintain the consistency of the ball milling particle size, Example 1* also adopted the segmented ball milling process. Examples 6*-9* added the same mass percentage of uncoated BTO as Examples 2-5 to study the effect of insulation coating on high-temperature loss. In addition, Example 10* uses a conventional ball milling process, directly adding all auxiliary components to the pre-calcined material and wet ball milling at 300 rpm for 25 min to maintain the same particle size distribution as Examples 1-9.

[0040] Table 1. Amount of auxiliary ingredients added in different embodiments and comparative examples

[0041] Note: Numbered with * indicates comparative examples, i.e., 2~5 are examples, and 1*, 6*~10* are comparative examples.

[0042] Step 4, Granulation and Compression:

[0043] The powder obtained in step 3 was crushed and sieved, then 15% PVA was added for granulation. The granules were passed through 60-mesh and 120-mesh sieves to remove large and small particles. After drying at 120℃ for 9.5 minutes, uniformly sized and free-flowing granules were obtained. These granules were then bidirectionally pressed into 25×15×7.5mm green rings using a 16-ton press, with a green density of 3.0 g / cm³. 3 .

[0044] Step 5, Sintering:

[0045] The pressed green ring obtained in step 4 was placed into a bell furnace for sintering. The sintering temperature was 1250℃ and the holding time was 3h. Sintering was carried out under balanced oxygen partial pressure and the oxygen content in the holding section was 4.0 vol.

[0046] Electromagnetic performance testing:

[0047] The sample rings prepared according to the above steps were tested for power consumption Pcv, saturation flux density Bs, and initial permeability μi using a SY8218 instrument from Iwasaki Corporation, Japan. The test conditions were as follows: Pcv was tested at 100 kHz and 200 mT; Bs was tested at 1 kHz and 1194 A / m. The performance is recorded in Table 2 below:

[0048] Table 2. Properties of MnZn ferrite materials obtained in different embodiments and comparative examples:

[0049] Note: Numbered with * indicates comparative examples, i.e., 2~5 are examples, and 1*, 6*~10* are comparative examples.

[0050] The test data in the table above shows that:

[0051] In Examples 2-5, when MnZn ferrite was doped with 0.025wt%~0.010wt% and coated with BTO, the high-temperature loss at 140~160℃ was optimized compared to Comparative Example 1*. The optimal high-temperature loss was achieved when the doping concentration was 0.075wt%, with a loss of 345kW / m² at 150℃. 3 Compared to Example 1*, it is 7.2% improved, with a power loss of 383 kW / m at 160°C. 3 It is 9.5% better than Example 1*.

[0052] Compared with Examples 6*~9*, BTO without insulation coating was used as an auxiliary component to optimize high-temperature loss. Data shows that when the doping concentration is low (0.025wt%), the high-temperature loss is slightly improved, but it is still higher than the loss in Example 2. As the concentration increases, the loss gradually deteriorates.

[0053] Comparative Example 10*, which has the same auxiliary components as Example 4 (0.075 wt% surface-coated BTO), did not employ segmented ball milling. Its wear performance was not optimized.

[0054] In summary, based on the analysis of the embodiments and comparative examples, it can be seen that the combination of the insulating-coated BTO auxiliary component and the new ball milling process optimizes the high-temperature loss of MnZn ferrite. In the above MnZn ferrite preparation process, the insulating-coated BTO does not participate in the phase growth process of MnZn ferrite during sintering, gradually segregating to the grain boundaries to form a high-resistivity grain boundary layer. Furthermore, due to the positive temperature coefficient of BTO itself, the resistivity of the grain boundary layer gradually increases as the temperature rises, suppressing electron transitions at high temperatures and thus reducing eddy current losses. While BTO without surface insulating coating also possesses this characteristic, during the equilibrium oxygen partial pressure sintering process of MnZn ferrite, the lack of a surface insulating protective layer results in higher Ti... 4+ Reduced to a lower valence state, it becomes a donor impurity, worsening resistivity and leading to increased losses. Simultaneously, due to changes in the phase structure of BTO, abnormal grain growth occurs in the MnZn ferrite, such as... Figure 1 As shown in (b), the loss performance is further deteriorated, illustrating the crucial role of the Al2O3 insulating coating. Simultaneously, the new process (segmented ball milling) avoids the destructive effects on the structure of the insulating-coated BTO caused by traditional ball milling. The loss performance of Comparative Example 10* demonstrates that the high-speed ball milling process damages the structure of the insulating-coated BTO, resulting in partial exposure of BTO. The deterioration in loss performance is the best proof of this.

[0055] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a high-temperature, low-loss MnZn ferrite material, characterized in that, Includes the following steps: Step 1: Preparation of BaTiO3 powder with Al2O3 coating: A continuous and dense amorphous Al2O3 insulating layer is coated on the surface of submicron-sized doped barium titanate (BTO) powder using the sol-gel surface coating technology to form coated particulate powder. Step 2: Preparation of MnZn pre-calcined material: The material is prepared according to the composition of 52.5~53.5 mol% Fe2O3, 7.9~8.9 mol% ZnO, and the remainder is MnO. After one ball milling and mixing, the pre-calcined material is MnZn ferrite pre-calcined material with active spinel structure. Step 3, Segmented Ball Milling: Mix the MnZn ferrite pre-calcined material with an equal mass of deionized water and perform segmented ball milling. Add auxiliary components for the first stage of ball milling to obtain powder with a D50 of 1.3~1.6μm. The auxiliary components in the first stage include Nb2O5, ZrO2, TiO2, Co2O3, and at least one of CaCO3, SiO2, CuO, and Bi2O3. Then add surface-coated BaTiO3 powder for the second stage of ball milling to obtain powder with a D50 of 1.2~1.5μm. Step 4, Granulation and pressing: PVA is added to the obtained powder for granulation to obtain granules with uniform size and good flowability. After pressing, green body is obtained. Step 5, Sintering: The obtained green blank is sintered to obtain high-temperature, low-loss, high-permeability MnZn ferrite material.

2. The method for preparing a high-temperature, low-loss MnZn ferrite material as described in claim 1, characterized in that, In step 1, the Curie temperature of the selected BaTiO3 is 80~120℃, and the thickness of the continuous and dense amorphous Al2O3 insulating layer is 20~50nm.

3. The method for preparing a high-temperature, low-loss MnZn ferrite material as described in claim 1, characterized in that, In step 2, the pre-firing atmosphere is air, and the pre-firing temperature is 800~900℃.

4. The method for preparing a high-temperature, low-loss MnZn ferrite material as described in claim 1, characterized in that, In step 3, the secondary ball milling adopts a segmented ball milling process. The first segment has a ball milling speed of 300 rpm and a ball milling time of 20-30 min. The second segment adds surface-coated BaTiO3 auxiliary components, with a ball milling speed of 100 rpm and a ball milling time of 10-20 min.

5. The method for preparing a high-temperature, low-loss MnZn ferrite material as described in claim 1, characterized in that, In step 3, the final particle size D50 of the segmented ball milling is controlled at 1.2~1.5μm.

6. The method for preparing a high-temperature, low-loss MnZn ferrite material as described in claim 1, characterized in that, In step 3, the content of auxiliary components, calculated based on the total weight percentage of Fe2O3, ZnO, and MnO, is as follows: surface-coated BaTiO3: 0.025~0.1wt%, Nb2O5: 0.015~0.035wt%, ZrO2: 0.01~0.02wt%, TiO2: 0.12~0.30wt%, Co2O3: 0.10~0.20wt%, and CaCO3: 0.03~0.05wt%.

7. The method for preparing a high-temperature, low-loss MnZn ferrite material as described in claim 1, characterized in that, In step 4, the amount of PVA added is 12-15%. After granulation, the particles are sieved through 60-mesh and 120-mesh screens to remove large and small particles, and then baked in a 120℃ oven for 9-10 minutes.

8. The method for preparing a high-temperature, low-loss MnZn ferrite material as described in claim 1, characterized in that, In step 4, a 16-ton press is used to bidirectionally compress the granular material into green rings measuring 25×15×7.5mm, with a density of 2.9~3.1g / cm³. 3 .

9. The method for preparing a high-temperature, low-loss MnZn ferrite material as described in claim 1, characterized in that, In step 5, sintering is carried out in a bell furnace under balanced oxygen partial pressure. The sintering holding temperature is 1200~1300℃ and the holding time is 3~6h. The balanced oxygen partial pressure O2 is 3.5~4.2 vol during the holding stage.

10. A high-temperature, low-loss MnZn ferrite material, characterized in that, It was prepared using the preparation method of a high-temperature, low-loss MnZn ferrite material as described in any one of claims 1-9.

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