High-stability magnetic core material and preparation method thereof

Abstract

The invention provides a high-stability magnetic core material and a preparation method thereof, and belongs to the technical field of ferrite materials.The preparation method comprises the following steps that raw materials are subjected to primary ball milling and then mixed, and mixed powder is obtained; pressing the mixed powder into a material block, and presintering to obtain MnZn ferrite; the preparation method comprises the following steps: grinding MnZn ferrite to obtain MnZn ferrite powder, and loading nano SiO2 and nano MgO on the surface of the MnZn ferrite powder to obtain coated MnZn ferrite powder; mixing the MnZn coated ferrite powder with Bi2O3, Ta2O5 and SnO2, and carrying out secondary ball milling, so as to obtain doped ferrite powder; mixing and granulating the doped ferrite powder and an adhesive, and pressing into a green body; and sintering the green body to obtain the MnZn ferrite magnetic core material. Volume mutation of the magnetic core material under thermal shock can be counteracted, and the magnetic core material is prevented from cracking after being subjected to thermal shock.

Description

Technical Field

[0001] The present invention relates to the technical field of ferrite materials, and in particular to a high-stability magnetic core material and a preparation method thereof. Background Art

[0002] With the rapid development of cloud computing, big data, artificial intelligence, and other fields, network servers are increasingly demanding high-performance magnetic core materials. The high-temperature, high-frequency, and high-load operating environments of network servers place increasing demands on the performance and stability of magnetic core materials. Existing magnetic core materials have low strength, and when subjected to thermal shock, they can cause internal cracks due to sudden volume changes, leading to network server failures. Summary of the Invention

[0003] In view of the technical problems existing in the background technology, the present application provides a high-stability magnetic core material and a preparation method thereof, aiming to solve the technical problems of low strength and poor thermal shock resistance of existing magnetic core materials.

[0004] In a first aspect, an embodiment of the present application provides a method for preparing a high-stability magnetic core material, comprising the following steps:

[0005] Fe2O3, Mn3O4 and ZnO are used as raw materials, ball-milled once and then mixed to obtain a mixed powder;

[0006] The mixed powder is pressed into blocks and pre-fired in a nitrogen atmosphere to obtain spinel-structured MnZn ferrite;

[0007] After crushing the MnZn ferrite, a MnZn ferrite powder is obtained, and nano-SiO2 and nano-MgO are loaded on the surface of the MnZn ferrite powder to obtain coated MnZn ferrite powder;

[0008] The coated MnZn ferrite powder is mixed with Bi2O3, Ta2O5 and SnO2 and then ball-milled twice to obtain doped ferrite powder;

[0009] The doped ferrite powder is mixed with a binder, granulated, and then pressed into a green body;

[0010] The green body is sintered to obtain a MnZn ferrite core material.

[0011] In some embodiments, the step of loading nano-SiO2 and nano-MgO on the surface of the MnZn ferrite powder comprises: Dispersing MgCl2·6H2O and TEOS in water to obtain a mixed solution; The MnZn ferrite powder is dispersed in the mixed liquid, into which (NH4)2CO3 solution is added dropwise, stirred for reaction, filtered, and calcined to obtain the coated MnZn ferrite powder.

[0012] In some embodiments, the mass ratio of MgCl2·6H2O to TEOS in the mixed solution is (2-5):1; The concentration of (NH4)2CO3 solution is 1 mol / L, the molar ratio of (NH4)2CO3 to MgCl2·6H2O is 1:1, and the dropping rate of (NH4)2CO3 solution is 3~15mL / min.

[0013] In some embodiments, the stirring reaction temperature is 60-80°C and the reaction time is 2-3h; The calcination temperature is 600~700℃ and the calcination time is 2~3h.

[0014] In some embodiments, the main crystalline phase raw materials include Fe2O3, Mn3O4 and ZnO in a molar ratio of 1: (0.23-0.27): (0.2-0.3) based on molar parts.

[0015] In some embodiments, the mass percentages of SiO2, MgO, Bi2O3, Ta2O5, and SnO2 in the MnZn ferrite powder are SiO2 0.05%~0.1%, MgO 0.1%~0.5%, Bi2O3 2%~4%, Ta2O5 0.02%~0.04%, and SnO2 0.1%~0.2%, respectively.

[0016] In some embodiments, the pre-firing temperature is 800-900° C., and the pre-firing time is 2-3 hours.

[0017] In some embodiments, the particle size of the doped ferrite powder after secondary ball milling is 0.5-2 μm.

[0018] In some embodiments, the sintering process includes the following steps: Heating stage: 25℃~600℃, heating rate 1℃ / min, keeping at 600℃ for 1h, 600℃~900℃, heating rate 2.5℃ / min, 900℃~1250℃, heating rate 2.5℃ / min, using balanced oxygen partial pressure; Sintering stage: hold at 1250℃ for 15min, 1250℃~1150℃, cooling rate 3℃ / min, hold at 1150℃ for 3h, oxygen partial pressure PO2=0.20atm; Cooling stage: 1150℃~900℃, cooling rate 3℃ / min, 900℃~room temperature, cooling with the furnace, using balanced oxygen partial pressure.

[0019] In a second aspect, an embodiment of the present application provides a magnetic core material with high stability, which is produced using the above method.

[0020] Different from the existing technical solutions, the beneficial effects of this application include:

[0021] 1. The present invention coats the surface of MnZn ferrite powder with nano-SiO2 and nano-MgO. After sintering, SiO2 can refine the MnZn ferrite grains and thicken the grain boundaries of the MnZn ferrite core material. The thicker grain boundaries serve as a buffer against thermal shock effects. In addition, SiO2 has a low expansion coefficient, which can offset the sudden volume change of the core material under thermal shock and prevent the core material from cracking after thermal shock.

[0022] An excessively thick grain boundary layer can reduce the thermal conductivity of the core material. A core with too low a magnetic thermal conductivity can exacerbate thermal stress at the grain boundaries at high temperatures, leading to a deterioration in the loss-temperature characteristics and reduced stability at high temperatures. MgO improves the thermal conductivity of the grain boundary phase, thereby increasing the thermal conductivity of the core material and ensuring high performance at high temperatures.

[0023] 2. In the MnZn ferrite core material prepared by the present invention, the SiO2 addition amount is 0.05%~0.1%. The higher SiO2 addition amount can ensure the formation of a thicker grain boundary layer outside the MnZn ferrite grains, thereby improving the strength of the core material. The sol-gel method is used to evenly load SiO2 on the outside of the MnZn ferrite powder, which can make the SiO2 evenly distributed and avoid the uneven resistivity distribution caused by the uneven generation of the grain boundary layer.

[0024] A higher amount of SiO2 added will lead to uneven grain growth and increase the porosity of the magnetic core material. In the present invention, MgO and MgO are loaded on the outside of the MnZn ferrite powder. 2+ Can partially replace Mn 2+ or Zn 2+ By adjusting the grain distortion and inhibiting abnormal grain growth through the difference in ionic radius, SiO2 and MgO work synergistically to produce a magnetic core material with high strength, good thermal conductivity, low porosity, and uniform grains.

[0025] 3. Both Ta2O5 and SnO2 can promote uniform grain growth and reduce the porosity of the core material, thereby improving the thermal conductivity and strength of the core material. High-temperature sintering will cause Zn evaporation, resulting in component segregation and the formation of a high-loss second phase. Adding Bi2O3 can reduce the sintering temperature, inhibit Zn volatilization, and avoid degradation of the MnZn ferrite structure.

[0026] The above description is only an overview of the technical solution of the present application. In order to more clearly understand the technical means of the present application, it can be implemented in accordance with the contents of the specification. In order to make the above and other purposes, features and advantages of the present application more obvious and easy to understand, the specific implementation methods of the present application are listed below. DETAILED DESCRIPTION

[0027] The following embodiments of the technical solution of the present application are described in detail. The following embodiments are only used to more clearly illustrate the technical solution of the present application and are therefore only used as examples and are not intended to limit the scope of protection of the present application.

[0028] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which this application belongs; the terms used herein are only for the purpose of describing specific embodiments and are not intended to limit this application; the terms "including" and "having" and any variations thereof in the description and claims of this application are intended to cover non-exclusive inclusions.

[0029] Some specific examples are listed below. It should be noted that the examples described below are exemplary and are only used to explain the present application, and should not be construed as limiting the present application. Where specific techniques or conditions are not specified in the examples, the techniques or conditions described in the literature in this area or the product specifications are used. Reagents or instruments used without manufacturer's indication are all commercially available conventional products.

[0030] 1. Preparation method

[0031] Example 1

[0032] The preparation method of coated MnZn ferrite powder comprises the following steps:

[0033] The main crystal phase raw materials Fe2O3, Mn3O4 and ZnO are ball-milled once, the atomic ratio of Fe, Mn and Zn is 1:0.8:0.2, zirconium balls are used as ball milling media, the mass ratio of raw materials, zirconium balls and water is 1:3:1.5, the ball milling time is 3h, the ball milling speed is 240r / min, and the particle size of the mixed powder obtained after the first ball milling is 2μm, thereby obtaining a mixed powder.

[0034] The mixed powder and the binder polyvinyl alcohol are mixed evenly and granulated, and then pressed into blocks, which are pre-fired in a N2 atmosphere at a pre-fired temperature of 800°C and a pre-fired time of 3 hours to obtain spinel-structured MnZn ferrite.

[0035] The MnZn ferrite is crushed to obtain MnZn ferrite powder, and the average particle size of the MnZn ferrite powder is 3 μm.

[0036] Take 500 mL of 10 mmol / L MgCl2·6H2O solution, disperse 0.5 g of TEOS in the MgCl2·6H2O solution to obtain a mixed solution; disperse 100 g of MnZn ferrite powder in the mixed solution, add (NH4)2CO3 solution dropwise, stir to react, filter, and calcine to obtain coated MnZn ferrite powder.

[0037] The coated MnZn ferrite powder was crushed and mixed with a doping crystal phase raw material and then subjected to secondary ball milling. The doping crystal phase raw materials included Bi2O3, Ta2O5 and SnO2, and the mass percentages of the doping crystal phase were Bi2O32%, Ta2O50.04% and SnO20.1%, respectively. The secondary ball milling used zirconium balls as the ball milling medium. The high-speed ball milling was carried out for 8 hours under a nitrogen atmosphere at a ball milling speed of 450 r / min. The average particle size of the doped ferrite powder obtained after the secondary ball milling was 2 μm, thereby obtaining a doped ferrite powder.

[0038] The doped ferrite powder is mixed with a binder and granulated, and then pressed into a green body with a pressing pressure of 7 MPa and a holding time of 10 seconds.

[0039] The green body is sintered to obtain a MnZn ferrite material.

[0040] The sintering process includes the following steps:

[0041] Heating stage: 25℃~600℃, heating rate 1℃ / min, keeping at 600℃ for 1h, 600℃~900℃, heating rate 2.5℃ / min, 900℃~1250℃, heating rate 2.5℃ / min, using balanced oxygen partial pressure; Sintering stage: hold at 1250℃ for 15min, 1250℃~1150℃, cooling rate 3℃ / min, hold at 1150℃ for 3h, oxygen partial pressure PO2=0.20atm; Cooling stage: 1150℃~900℃, cooling rate 3℃ / min, 900℃~room temperature, cooling with the furnace, using balanced oxygen partial pressure.

[0042] Example 2

[0043] The difference between Example 2 and Example 1 is that the main crystalline phase raw materials Fe2O3, Mn3O4 and ZnO are ball-milled and mixed once, and the atomic ratio of Fe, Mn and Zn is 2:0.7:0.3.

[0044] The coated MnZn ferrite powder is crushed and mixed with doped crystal phase raw materials and then ball milled for the second time. The doped crystal phase raw materials include Bi2O3, Ta2O5 and SnO2, and the mass percentages of the doped crystal phase are Bi2O34%, Ta2O50.02% and SnO20.2% respectively.

[0045] The other steps are the same as those in Example 1.

[0046] Comparative Example 1 The difference between Comparative Example 1 and Example 1 is that in Comparative Example 1, nano-MgO and nano-SiO2 are not coated, and MgO and SiO2 are mixed with the main crystalline phase raw material during the secondary ball milling process, with the mass percentages of MgO and SiO2 in the main crystalline phase being 0.2% and 0.1%, respectively.

[0047] Comparative Example 2 The difference between Comparative Example 2 and Example 1 is that the MnZn ferrite powder coated in Comparative Example 2 is only coated with nano-SiO2, and MgO is mixed with the main crystal phase raw material during the secondary ball milling process, with the mass percentage of MgO in the main crystal phase being 0.2%.

[0048] Comparative Example 3 The difference between Comparative Example 3 and Example 1 is that in Comparative Example 3, the coated MnZn ferrite powder is only coated with nano-MgO, and SiO2 is mixed with the main crystal phase raw material during the secondary ball milling process, with the mass percentage of SiO2 in the main crystal phase being 0.1%.

[0049] Comparative Example 4 The difference between Comparative Example 4 and Example 1 is that in Comparative Example 4, the coated MnZn ferrite powder is only coated with nano-SiO2, and no MgO is added to the MnZn ferrite core material.

[0050] Comparative Example 5 The difference between Comparative Example 5 and Example 1 is that in Comparative Example 5, the coated MnZn ferrite powder is only coated with nano-MgO, and no SiO2 is added to the MnZn ferrite core material.

[0051] Comparative Example 6 The difference between Comparative Example 6 and Example 1 is that SiO2 and MgO are not added in the preparation of the MnZn ferrite core material in Comparative Example 6.

[0052] 2. Test Method

[0053] 1. Bending strength test method: MnZn ferrite core material is made into a magnetic strip sample with a size of 2mm×4mm×30mm, and a universal testing machine is used to test the three-point bending strength of the magnetic strip.

[0054] 2. Thermal shock resistance test method: MnZn ferrite core material is made into φ17×8mm 2 Place the ring sample in a 400℃ molten tin furnace, immerse the ring sample completely in the tin surface for 1~2s, and check whether there are cracks on the sample surface to judge the thermal shock resistance of the sample.

[0055] 3. Density detection method: Archimedes method.

[0056] 4. Thermal conductivity detection method: steady-state heat flow method.

[0057] 5. Unit volume loss test method: Use BH analyzer for testing, the test conditions are 100℃, 3 MHz, B m =30 mT.

[0058] 3. Analysis of test results of various embodiments and comparative examples

[0059] The bending strength, thermal shock resistance and thermal conductivity of the MnZn ferrite core materials prepared in the examples and comparative examples were tested. The test results are shown in Table 1 below.

[0060] Table 1 Performance test results of the MnZn ferrite core materials prepared in various embodiments and comparative examples serial number Bending strength / MPa Thermal shock resistance <![CDATA[Density / g·cm -3 > <![CDATA[Thermal conductivity / W·(m·K) -1 > <![CDATA[Loss per unit volume / kW·m -3 > Example 1 85.6 No cracks 5.02 11.5 698 Example 2 84.7 No cracks 4.98 11.3 712 Comparative Example 1 72.1 Cracks 3.96 8.6 1623 Comparative Example 2 83.5 No cracks 4.78 9.8 1125 Comparative Example 3 78.8 Cracks 4.42 10.3 1358 Comparative Example 4 81.2 No cracks 4.35 8.3 1254 Comparative Example 5 75.6 Cracks 4.88 10.5 951 Comparative Example 6 65.4 Cracks 4.16 9.2 1149

[0061] The MnZn ferrite core material prepared in Examples 1 to 2 of the present application has good bending strength and thermal shock resistance, and a high density, indicating that the porosity in the core material is low and the thermal conductivity is high, which can reduce the temperature rise of the device and improve the stability of the core at high temperatures. It has low unit volume loss under high temperature and high frequency conditions and is suitable for high temperature and high frequency application scenarios.

[0062] In Comparative Example 1, direct doping with SiO2 and MgO results in a high SiO2 addition, leading to uneven grain size distribution, abnormal grain growth, increased porosity, and reduced density. Furthermore, uneven grain boundary growth leads to the accumulation of impurities at the grain boundaries, which in turn affects the thermal shock resistance and eddy current loss per unit volume of the magnetic core material. In Examples 1 and 2 of the present invention, SiO2 and MgO are first loaded onto MnZn ferrite powder, resulting in a uniform distribution of SiO2 and MgO, thus forming uniform grain boundaries and improving the bending strength and thermal shock resistance of the magnetic core material.

[0063] In Comparative Example 2, MgO was not coated on the outside of the MnZn ferrite powder, resulting in a slight decrease in the thermal conductivity of the core material and an increase in the unit volume loss, indicating that the simultaneous and uniform loading of MgO and SiO2 is conducive to MgO playing its role in regulating thermal conductivity.

[0064] In Comparative Example 3, SiO2 was not coated on the outside of the MnZn ferrite powder, resulting in a significant decrease in bending strength and thermal shock resistance, indicating that SiO2 cannot be evenly distributed by grinding alone.

[0065] In Comparative Example 4, the MnZn ferrite powder is only coated with nano-SiO2, and no MgO is added to the MnZn ferrite core material, so the thermal conductivity is greatly reduced.

[0066] In Comparative Example 5, the MnZn ferrite powder is only coated with nano-MgO, and no SiO2 is added to the MnZn ferrite core material. The bending strength of the core material is greatly reduced, and the thermal shock resistance is reduced, indicating that SiO2 can make the core have better toughness.

[0067] In Comparative Example 6, MgO and SiO2 were not added, and the bending strength and thermal shock resistance decreased, the density decreased, the porosity increased, the thermal conductivity decreased, and the unit volume loss increased, indicating that the synergistic effect of MgO and SiO2 can make the magnetic core have better performance.

[0068] It should be noted that the present application is not limited to the above-mentioned embodiments. The above-mentioned embodiments are merely examples, and any embodiments having substantially the same structure and effect as the technical concept within the scope of the present application are all included in the technical scope of the present application. In addition, without departing from the scope of the present application, any other embodiments that can be conceived by those skilled in the art and that combine some of the constituent elements in the embodiments are also included in the scope of the present application.

Claims

1. A method for preparing a high-stability magnetic core material, characterized in that: The steps include: Fe2O3, Mn3O4 and ZnO are used as raw materials, ball-milled once and then mixed to obtain a mixed powder; Pressing the mixed powder into blocks, and pre-sintering in a N2 atmosphere to obtain spinel-structured MnZn ferrite; The MnZn ferrite is crushed to obtain MnZn ferrite powder, and nano-SiO2 and nano-MgO are loaded on the surface of the MnZn ferrite powder to obtain coated MnZn ferrite powder; The coated MnZn ferrite powder is mixed with Bi2O3, Ta2O5 and SnO2 and then ball-milled for a second time to obtain doped ferrite powder; The doped ferrite powder is mixed with a binder, granulated, and then pressed into a green body; The green body is sintered to obtain a MnZn ferrite core material.

2. The method for preparing a magnetic core material with high stability according to claim 1, characterized in that: Loading nano-SiO2 and nano-MgO on the surface of the MnZn ferrite powder comprises the following steps: MgCl2·6H2O and TEOS are dispersed in water to obtain a mixed solution; The MnZn ferrite powder is dispersed in the mixed liquid, and (NH4)2CO3 solution is added dropwise thereto. The mixture is stirred for reaction, filtered, and calcined to obtain the coated MnZn ferrite powder.

3. The method for preparing a magnetic core material with high stability according to claim 2, characterized in that: The mass ratio of MgCl2·6H2O to TEOS in the mixed solution is (2-5):1; The concentration of the (NH4)2CO3 solution is 1 mol / L, the molar ratio of (NH4)2CO3 to MgCl2·6H2O is 1:1, and the dropping rate of the (NH4)2CO3 solution is 3-15 mL / min.

4. The method for preparing a magnetic core material with high stability according to claim 2, characterized in that: The stirring reaction temperature is 60-80°C and the reaction time is 2-3h; The calcination temperature is 600-700° C., and the calcination time is 2-3 hours.

5. The method for preparing a magnetic core material with high stability according to claim 1, characterized in that: In terms of molar ratio, the main crystalline phase raw materials include Fe2O3, Mn3O4 and ZnO, and the molar ratio thereof is 1: (0.23~0.27): (0.2~0.3).

6. The method for preparing a magnetic core material with high stability according to claim 1, characterized in that: The mass percentages of SiO2, MgO, Bi2O3, Ta2O5 and SnO2 in the MnZn ferrite powder are SiO2 0.05%-0.1%, MgO 0.1%-0.5%, Bi2O3 2%-4%, Ta2O5 0.02%-0.04% and SnO2 0.1%-0.2%, respectively.

7. The method for preparing a magnetic core material with high stability according to claim 1, characterized in that: The pre-firing temperature is 800-900° C., and the pre-firing time is 2-3 hours.

8. The method for preparing a magnetic core material with high stability according to claim 1, characterized in that: The particle size of the doped ferrite powder after the secondary ball milling is 0.5-2 μm.

9. The method for preparing a magnetic core material with high stability according to claim 1, characterized in that: The sintering process comprises the following steps: Heating stage: 25℃~600℃, heating rate 1℃ / min, keeping at 600℃ for 1h, 600℃~900℃, heating rate 2.5℃ / min, 900℃~1250℃, heating rate 2.5℃ / min, using balanced oxygen partial pressure; Sintering stage: hold at 1250℃ for 15min, 1250℃~1150℃, cooling rate 3℃ / min, hold at 1150℃ for 3h, oxygen partial pressure PO2=0.20atm; Cooling stage: 1150℃~900℃, cooling rate 3℃ / min, 900℃~room temperature, cooling with the furnace, using balanced oxygen partial pressure.

10. A high-stability magnetic core material, characterized in that: The method is as described in any one of claims 1 to 9.