A highly stable magnetic core material and its preparation method

Abstract

This application provides a highly stable magnetic core material and its preparation method, belonging to the field of ferrite material technology. The method includes the following steps: raw materials are ball-milled and mixed to obtain a mixed powder; the mixed powder is pressed into blocks and pre-fired to obtain MnZn ferrite; the MnZn ferrite is crushed to obtain MnZn ferrite powder; nano-SiO2 and nano-MgO are loaded onto 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 a second time to obtain doped ferrite powder; the doped ferrite powder is mixed with a binder, granulated, and then pressed into a blank; the blank is sintered to obtain the MnZn ferrite magnetic core material. This application can offset the volume change of the magnetic core material under thermal shock, avoiding cracking of the magnetic core material after thermal shock.

Description

Technical Field

[0001] This invention relates to the field of ferrite materials technology, specifically to a highly stable magnetic core material and its preparation method. Background Technology

[0002] With the rapid development of cloud computing, big data, artificial intelligence, and other fields, the demand for high-performance magnetic core materials for network servers is increasing. Network servers operate under high temperature, high frequency, and high load conditions, which continuously raises the requirements for the performance and stability of magnetic core materials. Existing magnetic core materials have relatively low strength, and under thermal shock, internal volume changes may cause microcracks, leading to network server failure. Summary of the Invention

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

[0004] In a first aspect, embodiments of this application provide a method for preparing a highly stable magnetic core material, comprising the following steps:

[0005] Fe2O3, Mn3O4 and ZnO were ball-milled and then mixed to obtain a mixed powder.

[0006] The mixed powder was pressed into blocks and pre-fired in a N2 atmosphere to obtain spinel-structured MnZn ferrite.

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

[0008] The coated MnZn ferrite powder was 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 blank is sintered to obtain MnZn ferrite core material.

[0011] In some embodiments, the step of loading nano-SiO2 and nano-MgO onto the surface of MnZn ferrite powder includes:

[0012] MgCl2·6H2O and TEOS were dispersed in water to obtain a mixed solution;

[0013] MnZn ferrite powder was dispersed in a mixed solution, and (NH4)2CO3 solution was added dropwise. After stirring, reacting, filtering, and calcining, coated MnZn ferrite powder was obtained.

[0014] In some embodiments, the mass ratio of MgCl2·6H2O to TEOS in the mixture is (2~5):1;

[0015] 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.

[0016] In some embodiments, the stirring reaction temperature is 60~80℃, and the reaction time is 2~3h;

[0017] The calcination temperature is 600~700℃, and the calcination time is 2~3h.

[0018] In some embodiments, the main crystalline phase raw materials include Fe2O3, Mn3O4 and ZnO in molar parts, with a molar ratio of 1:(0.23~0.27):(0.2~0.3).

[0019] In some embodiments, the mass percentages of SiO2, MgO, Bi2O3, Ta2O5, and SnO2 in the MnZn ferrite powder are 0.05%~0.1% for SiO2, 0.1%~0.5% for MgO, 2%~4% for Bi2O3, 0.02%~0.04% for Ta2O5, and 0.1%~0.2% for SnO2.

[0020] In some embodiments, the pre-firing temperature is 800~900℃ and the pre-firing time is 2~3h.

[0021] In some embodiments, the particle size of the ferrite powder after secondary ball milling is 0.5~2μm.

[0022] In some embodiments, the sintering process includes the following steps:

[0023] Heating phase: 25℃~600℃, heating rate 1℃ / min, hold at 600℃ for 1h, 600℃~900℃, heating rate 2.5℃ / min, 900℃~1250℃, heating rate 2.5℃ / min, using balanced oxygen partial pressure;

[0024] Sintering stage: Hold at 1250℃ for 15 min, cool at 1250℃~1150℃ at a rate of 3℃ / min, hold at 1150℃ for 3 h, oxygen partial pressure PO2=0.20atm;

[0025] Cooling stage: 1150℃~900℃, cooling rate 3℃ / min, 900℃~room temperature, cooling with the furnace, using balanced oxygen partial pressure.

[0026] Secondly, embodiments of this application provide a highly stable magnetic core material, which is prepared using the above-described method.

[0027] The advantages of this application, which differ from existing technical solutions, include:

[0028] 1. In this invention, nano-SiO2 and nano-MgO are coated on the surface of MnZn ferrite powder. After sintering, SiO2 can refine the grains of MnZn ferrite and thicken the grain boundaries of MnZn ferrite core material. The thicker grain boundaries act as a buffer against thermal shock. In addition, SiO2 has a low coefficient of thermal expansion, which can offset the volume change of the core material under thermal shock and prevent the core material from cracking after thermal shock.

[0029] Excessive grain boundary layer thickness reduces the thermal conductivity of the magnetic core material. Conversely, excessively low magnetic thermal conductivity exacerbates thermal stress at the grain boundaries under high-temperature conditions, leading to deterioration of loss temperature characteristics and reduced stability of the core material at high temperatures. MgO can improve the thermal conductivity of the grain boundary phase, thereby increasing the thermal conductivity of the core material and ensuring its high performance at high temperatures.

[0030] 2. In the MnZn ferrite core material prepared by this invention, the SiO2 content is 0.05%~0.1%. The higher SiO2 content can ensure that a thicker grain boundary layer is formed outside the MnZn ferrite grains, thereby improving the strength of the core material. The sol-gel method is used to uniformly load SiO2 on the outside of the MnZn ferrite powder, which can make the SiO2 distribution uniform and avoid the uneven resistivity distribution caused by the uneven formation of the grain boundary layer.

[0031] A higher SiO2 content can lead to uneven grain growth and increased porosity of the magnetic core material. This invention also loads MgO and MgO onto the MnZn ferrite powder. 2+ It can partially replace Mn 2+ or Zn 2+ By adjusting the difference in ionic radius, grain distortion can be controlled, and abnormal grain growth can be suppressed. The synergistic effect of SiO2 and MgO can produce magnetic core materials with high strength, good thermal conductivity, low porosity, and uniform grain size.

[0032] 3. Both Ta2O5 and SnO2 can promote uniform grain growth and reduce the porosity of the magnetic core material, thereby improving thermal conductivity and the strength of the magnetic core material. High-temperature sintering can cause Zn evaporation, leading to component segregation and the formation of a high-loss second phase. Adding Bi2O3 can lower the sintering temperature, inhibit Zn volatilization, and prevent the degradation of the MnZn ferrite structure.

[0033] The above description is only an overview of the technical solution of this application. In order to better understand the technical means of this application and to implement it in accordance with the contents of the specification, and to make the above and other objects, features and advantages of this application more obvious and understandable, the following are specific embodiments of this application. Detailed Implementation

[0034] The embodiments of the technical solution of this application will be described in detail below. The following embodiments are only used to illustrate the technical solution of this application more clearly, and are therefore only examples, and should not be used to limit the scope of protection of this application.

[0035] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains; the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the application; the terms “comprising” and “having”, and any variations thereof, in the specification and claims of this application are intended to cover non-exclusive inclusion.

[0036] The following are some specific embodiments. It should be noted that the embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they shall be performed in accordance with the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments whose manufacturers are not specified are all conventional products that can be obtained commercially.

[0037] I. Preparation Method

[0038] Example 1

[0039] The preparation method of MnZn coated ferrite powder includes the following steps:

[0040] The main crystalline phase raw materials Fe2O3, Mn3O4 and ZnO were mixed by ball milling once. The atomic ratio of Fe, Mn and Zn was 1:0.8:0.2. Zirconium balls were used as the ball milling medium for the first ball milling. The mass ratio of raw materials, zirconium balls and water was 1:3:1.5. The ball milling time was 3 hours and the ball milling speed was 240 r / min. The particle size of the mixed powder obtained after the first ball milling was 2 μm.

[0041] After the mixed powder and the binder polyvinyl alcohol are mixed evenly and granulated, the mixture is pressed into blocks and pre-fired in a N2 atmosphere at a temperature of 800℃ for 3 hours to obtain spinel-structured MnZn ferrite.

[0042] After crushing MnZn ferrite, MnZn ferrite powder is obtained with an average particle size of 3μm.

[0043] Take 500 mL of 10 mmol / L MgCl2·6H2O solution, disperse 0.5 g TEOS in the MgCl2·6H2O solution to obtain a mixed solution; disperse 100 g MnZn ferrite powder in the mixed solution, add (NH4)2CO3 solution dropwise, stir to react, filter, and calcine to obtain coated MnZn ferrite powder.

[0044] After crushing the MnZn ferrite powder, it was mixed with the doped crystalline phase raw materials and then subjected to secondary ball milling. The doped crystalline phase raw materials included Bi2O3, Ta2O5 and SnO2, which accounted for 2% of the main crystalline phase by mass, 0.04% of Bi2O3, 0.04% of Ta2O5 and 0.1% of SnO2, respectively. Zirconium balls were used as the ball milling medium for the secondary ball milling. The ball milling was carried out at high speed for 8 hours under a N2 atmosphere and the ball milling speed was 450 r / min. The average particle size of the doped ferrite powder obtained after the secondary ball milling was 2 μm.

[0045] The doped ferrite powder was mixed with a binder, granulated, and then pressed into a blank. The pressing pressure was 7 MPa and the holding time was 10 s.

[0046] The blank is sintered to obtain MnZn ferrite material.

[0047] The sintering process includes the following steps:

[0048] Heating phase: 25℃~600℃, heating rate 1℃ / min, hold at 600℃ for 1h, 600℃~900℃, heating rate 2.5℃ / min, 900℃~1250℃, heating rate 2.5℃ / min, using balanced oxygen partial pressure;

[0049] Sintering stage: Hold at 1250℃ for 15 min, cool at 1250℃~1150℃ at a rate of 3℃ / min, hold at 1150℃ for 3 h, oxygen partial pressure PO2=0.20atm;

[0050] Cooling stage: 1150℃~900℃, cooling rate 3℃ / min, 900℃~room temperature, cooling with the furnace, using balanced oxygen partial pressure.

[0051] Example 2

[0052] 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.

[0053] After the coated MnZn ferrite powder was crushed, it was mixed with the doped crystalline phase raw materials and then subjected to secondary ball milling. The doped crystalline phase raw materials included Bi2O3, Ta2O5 and SnO2, and their mass percentages of the main crystalline phases were 4% Bi2O3, 0.02% Ta2O5 and 0.2% SnO2, respectively.

[0054] The other steps are the same as in Example 1.

[0055] Comparative Example 1

[0056] The difference between Comparative Example 1 and Example 1 is that Comparative Example 1 does not have nano-MgO and nano-SiO2 coated. Instead, MgO and SiO2 are mixed with the main crystalline phase raw materials during a secondary ball milling process, accounting for 0.2% and 0.1% of the main crystalline phase by mass, respectively.

[0057] Comparative Example 2

[0058] The difference between Comparative Example 2 and Example 1 is that the MnZn ferrite powder in Comparative Example 2 is coated with only nano-SiO2, and MgO is mixed with the main crystalline phase raw material during the secondary ball milling process, accounting for 0.2% of the mass of the main crystalline phase.

[0059] Comparative Example 3

[0060] The difference between Comparative Example 3 and Example 1 is that the MnZn ferrite powder coated in Comparative Example 3 is coated with only nano-MgO, and SiO2 is mixed with the main crystalline phase raw material during the secondary ball milling process, accounting for 0.1% of the mass of the main crystalline phase SiO2.

[0061] Comparative Example 4

[0062] The difference between Comparative Example 4 and Example 1 is that the MnZn ferrite powder in Comparative Example 4 is coated with only nano-SiO2, and no MgO is added to the MnZn ferrite core material.

[0063] Comparative Example 5

[0064] The difference between Comparative Example 5 and Example 1 is that the MnZn ferrite powder in Comparative Example 5 is coated with only nano-MgO, and no SiO2 is added to the MnZn ferrite core material.

[0065] Comparative Example 6

[0066] The difference between Comparative Example 6 and Example 1 is that SiO2 and MgO were not added in the preparation of the MnZn ferrite core material in Comparative Example 6.

[0067] II. Testing Methods

[0068] 1. Bending strength test method: The MnZn ferrite core material is made into a magnetic strip sample with a size of 2mm×4mm×30mm. The three-point bending strength of the magnetic strip is tested using a universal testing machine.

[0069] 2. Thermal shock resistance test method: MnZn ferrite core material is made into a φ17×8mm core. 2 The ring-shaped sample was placed in a 400°C tin melting furnace, and the ring-shaped sample was completely immersed in the tin surface for 1-2 seconds. The thermal shock resistance of the sample was judged by checking whether there were cracks on the sample surface.

[0070] 3. Density detection method: Archimedes method.

[0071] 4. Thermal conductivity testing method: steady-state heat flow method.

[0072] 5. Unit volume loss detection method: Detection was performed using a BH analyzer under the following conditions: 100℃, 3 MHz, B... m =30 mT.

[0073] III. Analysis of Test Results for Each Embodiment and Comparative Example

[0074] The bending strength, thermal shock resistance and thermal conductivity of the MnZn ferrite core materials prepared in each embodiment and comparative example were tested, and the test results are shown in Table 1 below.

[0075] Table 1. Performance test results of MnZn ferrite core materials prepared in each embodiment and comparative example.

[0076] 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

[0077] The MnZn ferrite core materials prepared in Examples 1-2 of this application have good bending strength and thermal shock resistance, and high density, indicating that the core material has low porosity and high thermal conductivity, which can reduce the temperature rise of the device, improve the stability of the core at high temperature, and have low unit volume loss under high temperature and high frequency conditions, making it suitable for high temperature and high frequency application scenarios.

[0078] In Comparative Example 1, SiO2 and MgO were directly doped. The high amount of SiO2 added led to uneven grain size distribution, abnormal grain growth, and increased porosity, resulting in decreased density. Uneven grain boundary growth and impurity accumulation at the grain boundaries also negatively impacted the thermal shock resistance and eddy current loss per unit volume of the magnetic core material. In Examples 1 and 2 of this invention, SiO2 and MgO were first loaded onto MnZn ferrite powder, allowing for a uniform distribution of SiO2 and MgO, thereby generating uniform grain boundaries and improving the bending strength and thermal shock resistance of the magnetic core material.

[0079] In Comparative Example 2, the absence of MgO coating on the MnZn ferrite powder resulted in a slight decrease in the thermal conductivity of the magnetic core material and an increase in the unit volume loss. This indicates that the simultaneous and uniform loading of MgO and SiO2 is beneficial for MgO to play its role in regulating thermal conductivity.

[0080] In Comparative Example 3, SiO2 was not coated on the outside of the MnZn ferrite powder, which resulted in a significant reduction in flexural strength and thermal shock resistance, indicating that grinding alone cannot make SiO2 evenly distributed.

[0081] In Comparative Example 4, the MnZn ferrite powder was only coated with nano-SiO2, and no MgO was added to the MnZn ferrite core material, resulting in a significant reduction in thermal conductivity.

[0082] In Comparative Example 5, the MnZn ferrite powder was only coated with nano-MgO. No SiO2 was added to the MnZn ferrite core material. The bending strength of the core material decreased significantly and the thermal shock resistance was reduced, indicating that SiO2 can give the core better toughness.

[0083] In Comparative Example 6, without the addition of MgO and SiO2, 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 give the magnetic core better performance.

[0084] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.

Claims

1. A method for preparing a highly stable magnetic core material, characterized in that, Includes the following steps: Fe2O3, Mn3O4 and ZnO were ball-milled and then mixed to obtain a mixed powder. The mixed powder was pressed into blocks and pre-fired in a N2 atmosphere to obtain spinel-structured MnZn ferrite. After crushing the MnZn ferrite, MnZn ferrite powder is obtained. Nano-SiO2 and nano-MgO are loaded onto the surface of the MnZn ferrite powder to obtain coated MnZn ferrite powder. Loading nano-SiO2 and nano-MgO onto the surface of the MnZn ferrite powder includes the following steps: MgCl2·6H2O and TEOS were dispersed in water to obtain a mixed solution; The MnZn ferrite powder was dispersed in a mixed solution, and (NH4)2CO3 solution was added dropwise. After stirring, reacting, filtering, and calcining, coated MnZn ferrite powder was obtained. The mass percentages of SiO2 and MgO in the MnZn ferrite powder were 0.05%~0.1% for SiO2 and 0.1%~0.5% for MgO. The stirring reaction temperature is 60-80℃, and the reaction time is 2-3 hours. The calcination temperature is 600-700℃, and the calcination time is 2-3 hours. The coated MnZn ferrite powder was mixed with Bi2O3, Ta2O5 and SnO2 and then ball-milled twice to obtain doped ferrite powder. The doped ferrite powder is mixed with a binder, granulated, and then pressed into a green body. The blank is sintered to obtain MnZn ferrite core material.

2. The method for preparing the high-stability magnetic core material according to claim 1, characterized in that, The mass ratio of MgCl2·6H2O to TEOS in the mixture 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.

3. The method for preparing the high-stability magnetic core material according to claim 1, characterized in that, The main crystalline phase raw materials include Fe2O3, Mn3O4 and ZnO, with the atomic ratio of Fe, Mn and Zn being 2:0.7:0.

3.

4. The method for preparing the high-stability magnetic core material according to claim 1, characterized in that, The mass percentages of Bi2O3, Ta2O5, and SnO2 in the MnZn ferrite powder are 2%~4% for Bi2O3, 0.02%~0.04% for Ta2O5, and 0.1%~0.2% for SnO2.

5. The method for preparing the high-stability magnetic core material according to claim 1, characterized in that, The pre-firing temperature is 800~900℃, and the pre-firing time is 2~3h.

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

7. The method for preparing the high-stability magnetic core material according to claim 1, characterized in that, The sintering process includes the following steps: Heating phase: 25℃~600℃, heating rate 1℃ / min, hold 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 15 min, cool at 1250℃~1150℃ at a rate of 3℃ / min, hold at 1150℃ for 3 h, 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.

8. A highly stable magnetic core material, characterized in that, It is prepared by any one of the preparation methods described in claims 1 to 7.