Preparation method of manganese zinc ferrite core with ultrahigh magnetic saturation

Abstract

The invention relates to the technical field of oxide magnetic material manufacturing, and discloses a preparation method of an ultrahigh magnetic saturation manganese zinc ferrite magnetic core, and the preparation method comprises the following steps: S1, weighing raw materials in parts by mass; s2, mixing and calcining the rare earth oxide and ferric oxide; s3, mixing the rare earth doped precursor with manganese oxide and zinc oxide; s4, coating the main component mixed powder by a sol-gel method; s5, performing microwave irradiation activation on the coated powder, and synchronously applying a pulsed magnetic field to induce orientation; s6, performing compression molding on the activated powder, and then performing staged sintering; and S7, annealing and cooling the sintered green body to obtain the magnetic core. By adopting innovative processes such as calcination treatment of rare earth oxide and ferric oxide, coating by a sol-gel method, microwave irradiation activation and pulsed magnetic field induced orientation, the magnetic saturation intensity and consistency of the magnetic core are remarkably improved, and the problem of non-uniform doping of rare earth in the prior art is solved.

Description

Technical Field

[0001] The invention relates to the technical field of oxide magnetic material manufacturing, in particular to a method for preparing an ultra-high magnetic saturation manganese-zinc ferrite core. Background Art

[0002] Manganese-zinc ferrite, due to its high magnetic permeability, low loss, and excellent frequency characteristics, has been widely used in magnetic and electronic fields such as high-frequency transformers, inductors, and EMI anti-interference components. Its performance stability and magnetic saturation strength are primarily dependent on the coordinated control of its microscopic crystal structure, magnetic ion distribution, and sintering process.

[0003] The current mainstream methods for preparing manganese-zinc ferrite mostly use traditional processes such as co-precipitation and ceramic sintering. These processes typically directly mix the raw materials, ball-mill, dry, and then sinter at high temperature to form a polycrystalline magnetic core. However, this process has the following technical bottlenecks:

[0004] First, while rare earth element doping can improve magnetic properties, the simple and crude mixing method leads to low doping efficiency and insufficient solid solution of the doping elements in the crystal lattice, which in turn affects the improvement of magnetic permeability and magnetic saturation strength. In particular, during high-temperature sintering, rare earth oxides easily form a second phase agglomeration, causing grain distortion and increased hysteresis losses.

[0005] Secondly, the diffusion behavior of magnetic ions during the sintering process is difficult to precisely control, resulting in uneven grain size distribution and insufficient orientation in the final product, which affects the overall magnetic stability and consistency of the core.

[0006] In addition, during the entire sintering process, most existing methods use a single thermal field, the magnetic orientation process is limited by the spontaneous growth mechanism of grains, and the ability to control magnetic anisotropy is limited, which also limits the preparation of high-performance magnetic cores.

[0007] Furthermore, the high-temperature sintering process presents issues such as uneven zinc volatilization and oxidation, leading to segregation of magnetic components and inconsistent shrinkage in the finished product. Although some processes utilize a protective atmosphere, achieving a good balance between enhancing magnetic properties and ensuring structural stability remains difficult.

[0008] Therefore, the present invention proposes a method for preparing an ultra-high magnetic saturation manganese-zinc ferrite core to solve the deficiencies of the prior art. Summary of the Invention

[0009] In view of the shortcomings of the existing technology, the present invention provides a method for preparing an ultra-high magnetic saturation manganese-zinc ferrite core, which solves the problems of uneven rare earth doping, unstable magnetic ion distribution, and volatilization and oxidation during the sintering process in the existing technology.

[0010] To achieve the above objectives, the present invention is implemented through the following technical solutions: A method for preparing an ultra-high magnetic saturation manganese-zinc ferrite core, comprising the following steps:

[0011] S1. Weigh the raw materials in parts by mass, the raw materials comprising 50-54 parts of ferric oxide, 22-26 parts of manganese oxide, 20-24 parts of zinc oxide, and 1.5-2.5 parts of rare earth oxides;

[0012] S2. The rare earth oxide is mixed with ferric oxide and calcined to obtain a rare earth-doped precursor;

[0013] S3. The rare earth-doped precursor is mixed with manganese oxide and zinc oxide to obtain a main component mixed powder;

[0014] S4. The main component of the mixed powder is sol-gel coated to form a coated powder;

[0015] S5. The coated powder is activated by microwave irradiation and simultaneously applied with a pulsed magnetic field to induce orientation to obtain an activated powder;

[0016] S6. The activated powder is compression molded and sintered in stages, wherein the staged sintering comprises a first stage microwave sintering and a second stage reducing atmosphere sintering to obtain a sintered green body;

[0017] S7. Annealing and cooling the sintered green body to obtain the magnetic core.

[0018] Preferably, the calcination temperature in step S2 is 600-650° C., the calcination time is 1.5-2.5 hours, and the molar ratio of rare earth oxide to ferric oxide is 1:2-1:4.

[0019] Preferably, the step of mixing the rare earth doped precursor with manganese oxide and zinc oxide to obtain a main component mixed powder comprises:

[0020] The rare earth doping precursor is mixed with manganese oxide and zinc oxide in proportion, and the mixture is placed in a ball mill and ball milled using ethanol as a dispersion medium;

[0021] The ball milling time in the ball mill is 4-8 hours, and the ball-to-material mass ratio is 5:1;

[0022] After ball milling, the mixture is dried and sieved to obtain the main component mixed powder.

[0023] Preferably, the step of coating the main component mixed powder by a sol-gel method to form coated powder comprises:

[0024] Mixing ethyl orthosilicate and ethanol in a mass ratio of 1:3-1:5, adding an acidic catalyst and hydrolyzing for 6-10 hours to obtain a silica sol;

[0025] Aluminum isopropoxide and ethanol are mixed in a mass ratio of 1:4-1:6, and hydrolyzed for 4-8 hours to obtain aluminum oxide sol;

[0026] The silica sol and the alumina sol are mixed in a mass ratio of 2:1-4:1, and the main component mixed powder is added, and ultrasonic dispersion is performed for 20-40 minutes;

[0027] After dispersion, the powder is dried at 80-100° C. for 2-4 hours to form a coating layer with a thickness of 30-50 nm to obtain coated powder.

[0028] Preferably, the step of activating the coated powder by microwave irradiation and simultaneously applying a pulsed magnetic field to induce orientation to obtain the activated powder comprises:

[0029] The coated powder is placed in a microwave reaction chamber and irradiated at a frequency of 2.40-2.50 GHz under a nitrogen atmosphere, with a microwave power of 700-900 W and an irradiation time of 10-15 minutes;

[0030] A pulsed magnetic field is applied synchronously with a magnetic field strength of 0.5-1.0 T, a pulse frequency of 5-15 Hz, and a magnetic field direction that forms an angle of 30-60° with the polarization direction of the microwave electric field;

[0031] After irradiation, activated powder with lattice orientation is obtained.

[0032] Preferably, the step of compression molding the activated powder comprises:

[0033] Filling the activated powder into a mold pre-coated with a zinc stearate release agent, and press-molding at a pressure of 120-180 MPa;

[0034] After holding the pressure for 3-7 minutes, demould to obtain a green body;

[0035] The mold temperature is 25-60°C.

[0036] Preferably, the endpoint temperature of the first stage microwave sintering is 900-950°C, and the heating rate is 15-25°C / min;

[0037] The reducing atmosphere in the second stage is a mixed gas of carbon monoxide and hydrogen.

[0038] Preferably, the initial mass ratio of carbon monoxide to hydrogen is 1:4-1:6, and the hydrogen flow rate increases by 3-7% every 10 minutes.

[0039] Preferably, the step of annealing and cooling the sintered green body to obtain the magnetic core comprises:

[0040] Placing the sintered green body in a hydrogen atmosphere, heating it to 500-700°C at a rate of 5-10°C / min, and keeping the temperature for 1-3 hours;

[0041] After annealing, cool to 150-200°C at a rate of 1-5°C / min in the furnace;

[0042] The magnetic core is obtained by air cooling in the range of 150-200° C. to room temperature.

[0043] The present invention provides a method for preparing an ultra-high magnetic saturation manganese-zinc ferrite core. It has the following beneficial effects:

[0044] 1. This invention pre-calcines rare earth oxides and ferric oxide to form a stable doping structure, shortening the subsequent reaction path and ensuring more uniform crystal growth. This improves the magnetic saturation strength and consistency of the core. Traditional processes often directly mix rare earths into the base powder, resulting in low doping efficiency and unstable grain distribution. This invention effectively solves this randomness problem.

[0045] 2. This invention utilizes a microwave-synchronized pulsed magnetic field activation process, applying a short-duration external field to the magnetic particles, which promotes the pre-alignment of the magnetic moment directions, ultimately achieving a highly oriented magnetic core structure. This process is not currently available in the field of manganese-zinc ferrites. Conventional single-heating methods are unable to achieve this pre-orientation effect and can easily lead to divergence of magnetic properties. This invention addresses this gap.

[0046] 3. Sol-gel composite coating forms a stable nanoshell, stabilizing the powder surface before high-temperature sintering, preventing component volatilization and impurity diffusion, and making magnetic properties no longer dependent on over-sintering. Compared to conventional dry-mix coating or mechanical coating, this solution is more sophisticated and reliable, and does not require an additional heating step, reducing process sensitivity.

[0047] 4. This invention utilizes a staged sintering process combined with an atmosphere control strategy to achieve both improved sintering efficiency and quality. The first stage uses microwave heating for rapid densification, while the second stage uses a reducing atmosphere to homogenize the structure, significantly enhancing the magnetic properties of the finished core. Conventional single-stage sintering is prone to uneven burn-through or excessive oxidation, resulting in reduced magnetic properties. This invention addresses this "struggle to achieve both" in sintering. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] Figure 1 It is a flow chart of the preparation method of the present invention. DETAILED DESCRIPTION

[0049] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the drawings in the present specification. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0050] In order to better understand the present invention, the above contents are described in detail below in conjunction with specific embodiments.

[0051] Please see the attached Figure 1 A method for preparing an ultra-high magnetic saturation manganese-zinc ferrite core comprises the following steps:

[0052] S1. Weigh the raw materials in parts by mass, the raw materials comprising 50-54 parts of ferric oxide, 22-26 parts of manganese oxide, 20-24 parts of zinc oxide, and 1.5-2.5 parts of rare earth oxides;

[0053] The raw materials are weighed according to mass proportions, and the raw materials include 50-54 parts of ferric oxide, 22-26 parts of manganese oxide, 20-24 parts of zinc oxide, and 1.5-2.5 parts of rare earth oxide.

[0054] This component design is based on the spinel crystal structure of the ferrite core, in which iron oxide is the primary source of magnetic properties. Manganese oxide is used to adjust the crystal's magnetic anisotropy, thereby reducing coercivity. Zinc oxide replaces iron ions in octahedral positions in the crystal lattice, increasing magnetic permeability and effectively reducing eddy current losses at high frequencies. Rare earth oxides (such as lanthanum oxide or yttrium oxide) can be enriched at grain boundaries during the sintering process, forming a stable structure and inhibiting abnormal grain growth, thereby improving the consistency of magnetic properties and magnetic saturation strength.

[0055] S2. The rare earth oxide is mixed with ferric oxide and calcined to obtain a rare earth-doped precursor;

[0056] The rare earth oxide is mixed with ferric oxide, the calcination temperature is controlled at 600-650° C., the calcination time is 1.5-2.5 hours, and the molar ratio of the rare earth oxide to ferric oxide is 1:2-1:4, to obtain a rare earth doped precursor.

[0057] Rare earth elements (such as lanthanum in lanthanum oxide) react with ferric oxide in a solid phase reaction at medium temperature to form a rare earth iron composite oxide with a stable crystal structure. This structure has good thermal stability and can act as a crystal nucleus to participate in subsequent reaction processes, helping to improve the crystal orientation consistency of the material. At the same time, the introduction of rare earth elements at this stage helps to inhibit abnormal grain growth during the subsequent sintering process, refine the grain size, and enhance the uniformity of the structure, thereby improving the magnetic stability and magnetic saturation strength of the core.

[0058] S3. The rare earth-doped precursor is mixed with manganese oxide and zinc oxide to obtain a main component mixed powder;

[0059] The rare earth doping precursor is mixed with manganese oxide and zinc oxide in proportion, ethanol is added as a dispersion medium, and ball milled in a ball mill for 4-8 hours with a ball-to-material mass ratio of 5:1; after ball milling, the mixture is dried and sieved to obtain a main component mixed powder.

[0060] Ball milling promotes uniform mixing of powders through mechanical force, ensuring full contact between different components at the microscopic scale. This increases the specific surface area, facilitating uniformity in subsequent coating and sintering processes. Ethanol, as a polar solvent, helps prevent particle agglomeration and improves dispersion efficiency. The drying and sieving processes further control particle size distribution and enhance compactness during compaction.

[0061] S4. The main component of the mixed powder is sol-gel coated to form a coated powder;

[0062] TEOS and ethanol are mixed in a mass ratio of 1:3-1:5, and an acidic catalyst is added for hydrolysis for 6-10 hours to obtain a silica sol; aluminum isopropoxide and ethanol are mixed in a mass ratio of 1:4-1:6, and hydrolyzed for 4-8 hours to obtain an aluminum oxide sol; the two sols are then mixed in a mass ratio of 2:1-4:1, and ultrasonically dispersed with a main component mixed powder for 20-40 minutes, followed by drying at 80-100°C for 2-4 hours to form a coating layer with a thickness of 30-50 nanometers to obtain a coated powder.

[0063] This step utilizes a sol-gel method to form a uniform, dense silica-aluminum oxide composite coating in situ on the powder surface. The silica layer exhibits excellent thermal stability and airtightness, effectively inhibiting the volatilization of zinc oxide during sintering, thereby maintaining the chemical stability of the core components. Aluminum oxide participates in grain boundary reactions at high temperatures, promoting uniform grain growth and improving overall sintering density. Furthermore, this composite coating inhibits intense redox reactions between powders, stabilizes the grain boundary structure, and enhances the core's microstructural integrity and magnetic performance consistency.

[0064] S5. The coated powder is activated by microwave irradiation and simultaneously applied with a pulsed magnetic field to induce orientation to obtain an activated powder;

[0065] The coated powder is placed in a microwave reaction chamber and irradiated at a frequency of 2.40-2.50 GHz under a nitrogen atmosphere, with a microwave power of 700-900 W and an irradiation time of 10-15 minutes. At the same time, a pulsed magnetic field is applied with a magnetic field strength of 0.5-1.0 Tesla and a pulse frequency of 5-15 Hz. The direction of the magnetic field forms an angle of 30-60° with the polarization direction of the microwave electric field. After the irradiation, an activated powder with lattice orientation is obtained.

[0066] Microwave heating is an efficient non-contact energy transfer method that can use electromagnetic waves to selectively act on the surface of powders, causing them to quickly produce a thermal excitation effect, thereby forming a short-term high-energy activation layer on the surface of the particles. This excitation layer provides favorable conditions for the migration, reaction and bonding of ions in the subsequent molding and sintering processes. At the same time, the simultaneous application of a pulsed magnetic field during the irradiation process can effectively induce the magnetic elements in the powder to be oriented in a specific direction in the crystal lattice. Through this external field synergistic effect, the preliminary regulation of magnetic anisotropy can be achieved at the powder level, laying the foundation for the subsequent overall magnetic performance directionality of the magnetic core material, and significantly improving the magnetic saturation intensity and magnetic response consistency.

[0067] S6. The activated powder is compression molded and sintered in stages, wherein the staged sintering comprises a first stage microwave sintering and a second stage reducing atmosphere sintering to obtain a sintered green body;

[0068] The activated powder is filled into a mold pre-coated with zinc stearate release agent and pressed under a pressure of 120-180 MPa. The mold is then demolded after holding the pressure for 3-7 minutes. The mold temperature is controlled at 25-60°C. This is followed by staged sintering. The first stage utilizes microwave sintering, with the final temperature controlled at 900-950°C and a heating rate of 15-25°C / minute. The second stage utilizes a reducing atmosphere, using a mixture of carbon monoxide and hydrogen with an initial mass ratio of 1:4-1:6. The hydrogen flow rate is increased by 3-7% every 10 minutes, ultimately resulting in a sintered body. Precisely controlling the temperature and pressure conditions during the compression molding stage significantly increases the green body's density and reduces porosity, effectively minimizing the risk of shrinkage deformation and cracking during subsequent sintering and ensuring dimensional stability.

[0069] The first stage of microwave sintering utilizes a non-traditional heating method, characterized by rapid and uniform temperature rise, which enables synchronous grain growth, suppresses microcracks and localized stress concentrations caused by temperature gradients, and improves microstructural uniformity. The second stage introduces a reducing atmosphere for protective sintering, which not only inhibits metal oxidation but also effectively regulates the concentration and distribution of oxygen vacancies in the powder, preventing the uncontrolled reduction of some magnetic elements. This enhances the material's structural density and magnetic stability while improving soft magnetic properties.

[0070] S7. Annealing and cooling the sintered green body to obtain the magnetic core.

[0071] The sintered green body is placed in a hydrogen atmosphere, heated to 500-700°C at a rate of 5-10°C / min, and kept warm for 1-3 hours; after annealing, it is furnace-cooled to 150-200°C at a rate of 1-5°C / min, and then air-cooled to room temperature within this temperature range to finally obtain the magnetic core.

[0072] The annealing process, by providing a mild and controllable heat treatment environment, can effectively release residual stress within the material and repair lattice distortion and defects caused by the sintering process, thereby improving the material's microstructure. Hydrogen, as a typical reducing atmosphere, can effectively prevent re-oxidation on the surface of the core while promoting further stabilization of the grain boundary structure. During the process of slowly cooling to 150-200°C with the furnace, the temperature difference is small, which helps to avoid microcracks in the grains due to sudden changes in thermal stress, thereby maintaining the overall structural integrity of the core. Air cooling in the 150-200°C range is conducive to the rapid solidification of the ideal crystal structure formed after annealing, preventing the precipitation of impurity phases, and ultimately obtaining a core material with high magnetic saturation, high stability and excellent consistency.

[0073] Example 1:

[0074] Step 1-Weigh the raw materials (by mass):

[0075] 52 parts of ferric oxide, 24 parts of manganese oxide, 22 parts of zinc oxide, and 2 parts of rare earth oxide (lanthanum oxide).

[0076] Step 2-Precursor preparation:

[0077] Lanthanum oxide and ferric oxide were mixed in a molar ratio of 1:3;

[0078] Place in a muffle furnace and calcine at 600℃ for 2 hours;

[0079] After natural cooling, the mixture is ground to a particle size of ≤5 μm to obtain a rare earth doping precursor.

[0080] Step 3 - Principal Component Mixture:

[0081] Add the precursor, manganese oxide and zinc oxide into a ball mill;

[0082] Zirconia balls were added at a ball-to-material ratio of 5:1, and ethanol was used as the dispersion medium;

[0083] Ball milling for 6 hours at 200 rpm;

[0084] The slurry was dried at 80°C and passed through a 200-mesh sieve to obtain a main component mixed powder.

[0085] Step 4-Sol coating:

[0086] Silica sol: TEOS and ethanol were mixed in a volume ratio of 1:4, and 0.1 mol / L hydrochloric acid was added and hydrolyzed for 8 hours;

[0087] Aluminum oxide sol: aluminum isopropoxide and ethanol are mixed in a volume ratio of 1:5 and hydrolyzed for 5 hours;

[0088] The two sols were mixed in a volume ratio of 3:1 and the main component powder was added;

[0089] Ultrasonic dispersion was performed for 30 minutes and drying was performed at 80°C for 2 hours to form a coating layer with a thickness of about 40 nm.

[0090] Step 5 - Microwave Magnetic Field Activation:

[0091] The coated powder is spread flat on a quartz tray and placed in a microwave reaction chamber;

[0092] Under nitrogen atmosphere, irradiation was performed at a frequency of 2.45 GHz and a power of 800 W for 12 minutes;

[0093] A 0.8T pulsed magnetic field with a pulse frequency of 10 Hz was applied synchronously, and the direction of the magnetic field formed an angle of 45° with the microwave electric field.

[0094] Step 6 - Molding:

[0095] Pre-coat the inner wall of the mold with zinc stearate release agent and preheat to 40°C;

[0096] After powder filling, pressurize at 150MPa and maintain pressure for 5 minutes;

[0097] De-mould slowly to obtain a density ≥3.2g / cm 3 of the green body.

[0098] Step 7 - Staged sintering:

[0099] The first stage (microwave sintering):

[0100] Under nitrogen protection, the temperature was raised to 930°C at a rate of 20°C / min;

[0101] Keep warm for 15 minutes;

[0102] The second stage (reductive sintering):

[0103] Switch to a CO:H2=1:5 (volume ratio) mixed gas;

[0104] The hydrogen flow rate was increased by 5% every 10 minutes, and the total sintering time was 1.5 hours.

[0105] Step 8- Annealing and cooling:

[0106] The sintered green body was placed in a tube furnace, heated to 500°C at 5°C / min under a hydrogen atmosphere, and kept at this temperature for 2 hours;

[0107] Cool down to 180℃ at a rate of 2℃ / min;

[0108] After being taken out, the magnetic core was obtained by air cooling to room temperature.

[0109] Example 2:

[0110] Step 1-Weigh the raw materials (by mass):

[0111] 53 parts of ferric oxide, 23 parts of manganese oxide, 21 parts of zinc oxide, and 1.5 parts of rare earth oxide (yttrium oxide).

[0112] Step 2-Precursor preparation:

[0113] Yttrium oxide and ferric oxide are mixed in a molar ratio of 1:2;

[0114] Place in a muffle furnace and calcine at 650℃ for 1.5 hours;

[0115] After natural cooling, the mixture is ground to a particle size of ≤5 μm to obtain a rare earth doping precursor.

[0116] Step 3 - Principal Component Mixture:

[0117] Add the precursor, manganese oxide and zinc oxide into a ball mill;

[0118] Zirconia balls were added at a ball-to-material ratio of 5:1, and ethanol was used as the dispersion medium;

[0119] Ball milling for 8 hours at 200 rpm;

[0120] The slurry was dried at 90°C and passed through a 200-mesh sieve to obtain a main component mixed powder.

[0121] Step 4-Sol coating:

[0122] Silica sol: TEOS and ethanol were mixed in a volume ratio of 1:3, and 0.1 mol / L hydrochloric acid was added and hydrolyzed for 9 hours;

[0123] Aluminum oxide sol: aluminum isopropoxide and ethanol are mixed in a volume ratio of 1:6 and hydrolyzed for 6 hours;

[0124] The two sols were mixed in a volume ratio of 4:1 and the main component powder was added;

[0125] Ultrasonic dispersion was performed for 35 minutes and drying was performed at 90°C for 3 hours to form a coating layer with a thickness of about 45 nm.

[0126] Step 5 - Microwave Magnetic Field Activation:

[0127] The coated powder is spread flat on a quartz tray and placed in a microwave reaction chamber;

[0128] Under nitrogen atmosphere, irradiation was carried out at a frequency of 2.45 GHz and a power of 900 W for 10 minutes;

[0129] A 0.9T pulsed magnetic field was applied synchronously with a pulse frequency of 15 Hz, and the direction of the magnetic field formed an angle of 60° with the microwave electric field.

[0130] Step 6 - Molding:

[0131] Pre-coat the inner wall of the mold with zinc stearate release agent and preheat to 30°C;

[0132] After powder filling, pressurize at 180 MPa and maintain pressure for 3 minutes;

[0133] De-mould slowly to obtain a density ≥3.2g / cm 3 of the green body.

[0134] Step 7 - Staged sintering:

[0135] The first stage (microwave sintering):

[0136] Under nitrogen protection, the temperature was raised to 950°C at a rate of 25°C / min;

[0137] Keep warm for 15 minutes;

[0138] The second stage (reductive sintering):

[0139] Switch to a CO:H2=1:6 (volume ratio) mixed gas;

[0140] The hydrogen flow rate was increased by 7% every 10 minutes, and the total sintering time was 1.5 hours.

[0141] Step 8- Annealing and cooling:

[0142] The sintered green body was placed in a tube furnace, heated to 600°C at 5°C / min under hydrogen atmosphere, and kept at this temperature for 3 hours;

[0143] Cool down to 150℃ at a rate of 5℃ / min;

[0144] After being taken out, the magnetic core was obtained by air cooling to room temperature.

[0145] Example 3

[0146] Step 1-Weigh the raw materials (by mass):

[0147] 50 parts of ferric oxide, 26 parts of manganese oxide, 23 parts of zinc oxide, and 2.2 parts of rare earth oxide (lanthanum oxide).

[0148] Step 2-Precursor preparation:

[0149] Lanthanum oxide and ferric oxide were mixed in a molar ratio of 1:4;

[0150] Place in a muffle furnace and calcine at 625℃ for 2.5 hours;

[0151] After natural cooling, the mixture is ground to a particle size of ≤5 μm to obtain a rare earth doping precursor.

[0152] Step 3 - Principal Component Mixture:

[0153] Add the precursor, manganese oxide and zinc oxide into a ball mill;

[0154] Zirconia balls were added at a ball-to-material ratio of 5:1, and ethanol was used as the dispersion medium;

[0155] Ball milling for 4 hours at 200 rpm;

[0156] The slurry was dried at 80°C and passed through a 200-mesh sieve to obtain a main component mixed powder.

[0157] Step 4-Sol coating:

[0158] Silica sol: TEOS and ethanol were mixed in a volume ratio of 1:5, and 0.1 mol / L hydrochloric acid was added and hydrolyzed for 6 hours;

[0159] Aluminum oxide sol: aluminum isopropoxide and ethanol are mixed in a volume ratio of 1:4 and hydrolyzed for 4 hours;

[0160] The two sols were mixed in a volume ratio of 2:1 and the main component powder was added;

[0161] Ultrasonic dispersion was performed for 20 minutes and drying was performed at 80°C for 4 hours to form a coating layer with a thickness of about 35 nm.

[0162] Step 5 - Microwave Magnetic Field Activation:

[0163] The coated powder is spread flat on a quartz tray and placed in a microwave reaction chamber;

[0164] Under nitrogen atmosphere, irradiation was performed at a frequency of 2.45 GHz and a power of 700 W for 15 minutes;

[0165] A 0.5T pulsed magnetic field was applied synchronously with a pulse frequency of 5 Hz, and the direction of the magnetic field formed an angle of 30° with the microwave electric field.

[0166] Step 6 - Molding:

[0167] Pre-coat the inner wall of the mold with zinc stearate release agent and preheat to 55°C;

[0168] After powder filling, pressurize at 140 MPa and maintain pressure for 6 minutes;

[0169] De-mould slowly to obtain a density ≥3.2g / cm3 of the green body.

[0170] Step 7 - Staged sintering:

[0171] The first stage (microwave sintering):

[0172] Under nitrogen protection, the temperature was raised to 900°C at a rate of 15°C / min;

[0173] Keep warm for 15 minutes;

[0174] The second stage (reductive sintering):

[0175] Switch to CO:H2=1:4 (volume ratio) mixed gas;

[0176] The hydrogen flow rate was increased by 3% every 10 minutes, and the total sintering time was 1.5 hours.

[0177] Step 8- Annealing and cooling:

[0178] The sintered green body was placed in a tube furnace, heated to 550°C at 5°C / min under hydrogen atmosphere, and kept at this temperature for 1 hour;

[0179] Cool down to 200℃ at a rate of 1℃ / min;

[0180] After being taken out, the magnetic core was obtained by air cooling to room temperature.

[0181] Example 4

[0182] Step 1-Weigh the raw materials (by mass):

[0183] 54 parts of ferric oxide, 22 parts of manganese oxide, 20 parts of zinc oxide, and 2.5 parts of rare earth oxide (yttrium oxide).

[0184] Step 2-Precursor preparation:

[0185] Yttrium oxide and ferric oxide were mixed in a molar ratio of 1:3.5;

[0186] Place in a muffle furnace and calcine at 630℃ for 1.8 hours;

[0187] After natural cooling, the mixture is ground to a particle size of ≤5 μm to obtain a rare earth doping precursor.

[0188] Step 3 - Principal Component Mixture:

[0189] Add the precursor, manganese oxide and zinc oxide into a ball mill;

[0190] Zirconia balls were added at a ball-to-material ratio of 5:1, and ethanol was used as the dispersion medium;

[0191] Ball milling for 5 hours at 200 rpm;

[0192] The slurry was dried at 100°C and passed through a 200-mesh sieve to obtain a main component mixed powder.

[0193] Step 4-Sol coating:

[0194] Silica sol: TEOS and ethanol were mixed in a volume ratio of 1:4, and 0.1 mol / L hydrochloric acid was added and hydrolyzed for 8 hours;

[0195] Aluminum oxide sol: aluminum isopropoxide and ethanol are mixed in a volume ratio of 1:6 and hydrolyzed for 6 hours;

[0196] The two sols were mixed in a volume ratio of 3.5:1 and the main component powder was added;

[0197] Ultrasonic dispersion was performed for 40 minutes and drying was performed at 100°C for 2 hours to form a coating layer with a thickness of about 50 nm.

[0198] Step 5 - Microwave Magnetic Field Activation:

[0199] The coated powder is spread flat on a quartz tray and placed in a microwave reaction chamber;

[0200] Under nitrogen atmosphere, irradiation was performed at 2.45 GHz frequency and 800 W power for 13 minutes;

[0201] A 1.0 T pulsed magnetic field was applied synchronously with a pulse frequency of 13 Hz, and the direction of the magnetic field formed an angle of 35° with the microwave electric field.

[0202] Step 6 - Molding:

[0203] Pre-coat the inner wall of the mold with zinc stearate release agent and preheat to room temperature (25°C);

[0204] After powder filling, pressurize at 160 MPa and maintain pressure for 4 minutes;

[0205] De-mould slowly to obtain a density ≥3.2g / cm 3 of the green body.

[0206] Step 7 - Staged sintering:

[0207] The first stage (microwave sintering):

[0208] Under nitrogen protection, the temperature was raised to 945°C at a rate of 22°C / min;

[0209] Keep warm for 15 minutes;

[0210] The second stage (reductive sintering):

[0211] Switch to a CO:H2=1:6 (volume ratio) mixed gas;

[0212] The hydrogen flow rate was increased by 6% every 10 minutes, and the total sintering time was 1.5 hours.

[0213] Step 8- Annealing and cooling:

[0214] The sintered green body was placed in a tube furnace, heated to 700 °C at 5 °C / min under hydrogen atmosphere, and kept at this temperature for 3 h;

[0215] Cool down to 170℃ at a rate of 3℃ / min;

[0216] After being taken out, the magnetic core was obtained by air cooling to room temperature.

[0217] Example 5

[0218] Step 1-Weigh the raw materials (by mass):

[0219] 51 parts of ferric oxide, 25 parts of manganese oxide, 24 parts of zinc oxide, and 1.8 parts of rare earth oxide (lanthanum oxide).

[0220] Step 2-Precursor preparation:

[0221] Lanthanum oxide and ferric oxide were mixed in a molar ratio of 1:2;

[0222] Place in a muffle furnace and calcine at 600℃ for 2 hours;

[0223] After natural cooling, the mixture is ground to a particle size of ≤5 μm to obtain a rare earth doping precursor.

[0224] Step 3 - Principal Component Mixture:

[0225] Add the precursor, manganese oxide and zinc oxide into a ball mill;

[0226] Zirconia balls were added at a ball-to-material ratio of 5:1, and ethanol was used as the dispersion medium;

[0227] Ball milling for 7 hours at 200 rpm;

[0228] The slurry was dried at 90°C and passed through a 200-mesh sieve to obtain a main component mixed powder.

[0229] Step 4-Sol coating:

[0230] Silica sol: TEOS and ethanol were mixed in a volume ratio of 1:3, and 0.1 mol / L hydrochloric acid was added and hydrolyzed for 10 hours;

[0231] Aluminum oxide sol: aluminum isopropoxide and ethanol are mixed in a volume ratio of 1:5 and hydrolyzed for 7 hours;

[0232] The two sols were mixed in a volume ratio of 4:1 and the main component powder was added;

[0233] Ultrasonic dispersion was performed for 30 minutes and drying was performed at 90°C for 3 hours to form a coating layer with a thickness of about 38 nm.

[0234] Step 5 - Microwave Magnetic Field Activation:

[0235] The coated powder is spread flat on a quartz tray and placed in a microwave reaction chamber;

[0236] Under nitrogen atmosphere, irradiation was performed at a frequency of 2.45 GHz and a power of 850 W for 11 minutes;

[0237] A 0.6T pulsed magnetic field with a pulse frequency of 8 Hz was applied synchronously, and the direction of the magnetic field formed an angle of 50° with the microwave electric field.

[0238] Step 6 - Molding:

[0239] Pre-coat the inner wall of the mold with zinc stearate release agent and preheat to 45°C;

[0240] After powder filling, pressurize at 125MPa and maintain pressure for 6 minutes;

[0241] De-mould slowly to obtain a density ≥3.2g / cm 3 of the green body.

[0242] Step 7 - Staged sintering:

[0243] The first stage (microwave sintering):

[0244] Under nitrogen protection, the temperature was raised to 910°C at a rate of 18°C / min;

[0245] Keep warm for 15 minutes;

[0246] The second stage (reductive sintering):

[0247] Switch to a CO:H2=1:5 (volume ratio) mixed gas;

[0248] The hydrogen flow rate was increased by 4% every 10 minutes, and the total sintering time was 1.5 hours.

[0249] Step 8- Annealing and cooling:

[0250] The sintered green body was placed in a tube furnace, heated to 580°C at 5°C / min under hydrogen atmosphere, and kept at this temperature for 2 hours;

[0251] Cool down to 200℃ at a rate of 4℃ / min;

[0252] After being taken out, the magnetic core was obtained by air cooling to room temperature.

[0253] Comparative Example 1:

[0254] Compared with Example 1, no rare earth oxide (lanthanum oxide) was added, and the precursor calcination step was not performed. Other preparation methods and formulas were the same.

[0255] Comparative Example 2:

[0256] Compared with Example 2, only microwave irradiation was used (the pulsed magnetic field was canceled), and the microwave frequency was set to 2.2 GHz. Other preparation methods and formulas were the same.

[0257] Comparative Example 3:

[0258] Compared with Example 3, the staged sintering is eliminated and the steel is sintered to 900° C. in an air atmosphere at one time. Other preparation methods and formulas are the same.

[0259] Experiment 1 (Effect of rare earth doping on magnetic saturation intensity):

[0260] Sample preparation:

[0261] Magnetic cores (numbered S1-S5) were prepared according to the formulation and preparation process of Example 1;

[0262] Magnetic cores (numbered C1-C5) were prepared according to the formulation and preparation process of Comparative Example 1.

[0263] Test equipment and conditions:

[0264] Vibrating sample magnetometer (VSM, LakeShore 7404), calibration error <±1.5%;

[0265] The magnetic performance parameters are only obtained through hysteresis loop testing.

[0266] Each sample (S1-S5, C1-C5) was tested three times with a 30-minute interval between each test to eliminate the influence of equipment temperature drift. The average value was obtained after eliminating outliers.

[0267] Experimental steps:

[0268] Sample fixation: glue the magnetic core to the quartz rod with non-magnetic glue to ensure there is no stress in the vertical direction;

[0269] Magnetic field loading: linearly increase from 0 kA / m to 1500 kA / m (rate 50 kA / m / s), and record the magnetization curve;

[0270] Data acquisition: only two core parameters, saturation magnetization (Bs) and coercive force (Hc), are recorded;

[0271] Environmental control: The laboratory temperature is maintained at 25±1℃, without additional atmosphere protection.

[0272] The experimental data are shown in Table 1:

[0273] Table 1: Comparison of magnetic properties of rare earth doped and undoped cores

[0274]

[0275] The magnetic saturation intensity shows a clear trend towards grouping. The overall distribution of the Example samples is concentrated, with Bs values remaining around 510 mT with minimal fluctuation, demonstrating good stability. S3 and S4, in particular, reach 521 and 518 mT, respectively, demonstrating reliable magnetic performance. However, the comparative example samples exhibit a wide range of values, with the lowest value being only 379 mT, a significant decrease compared to the Example samples, indicating a certain degree of uncertainty and unstable performance.

[0276] Coercivity also exhibits differentiated characteristics. The Hc values of the rare-earth-doped group are concentrated between 13 and 16 A / m, with a manageable range of variation. The control group exhibits a more chaotic distribution, with some samples exceeding 30 A / m, including C3, which reaches as high as 34.2 A / m, indicating severe restriction of magnetic domain motion and a slowed magnetic response. Some samples, such as C5, exhibit significant hysteresis during testing, with a delay of up to 15ms, reflecting a more complex internal state.

[0277] Overall, rare earth doping significantly increases magnetic saturation strength and reduces magnetic property fluctuations. While some initial jitter or minor errors may exist in individual tests, the consistency and repeatability between samples clearly demonstrate that the doped group exhibits superior magnetic response and more predictable performance.

[0278] Experiment 2 (Effect of composite field sintering method on magnetic properties):

[0279] Sample preparation:

[0280] Magnetic cores (numbered A1-A5) were prepared according to the formulation and preparation process of Example 2;

[0281] Magnetic cores (numbered B1-B5) were prepared according to the formulation and preparation process of Comparative Example 2.

[0282] Test equipment and methods:

[0283] Equipment: Vibrating sample magnetometer (VSM, LakeShore 7404);

[0284] Parameter extraction: only saturation magnetization (Bs) and coercive force (Hc) are collected;

[0285] Testing frequency: Each sample was tested three times with an interval of 30 minutes, and the average value was taken after eliminating the deviation value;

[0286] Test environment: room temperature (25±1℃), without external protective atmosphere.

[0287] Steps:

[0288] Sample fixation: The magnetic core is fixed to the quartz rod, firmly bonded and kept free of mechanical stress;

[0289] Magnetic field loading: linear sweep 0–1500 kA / m, rate 50 kA / m / s;

[0290] Data recording: export hysteresis loop and read Bs and Hc indicators.

[0291] The experimental data are shown in Table 2:

[0292] Table 2: Performance comparison of composite field and single microwave sintered magnetic cores

[0293]

[0294] As shown in Table 2, the core samples from the composite field sintering group (A1–A5) exhibited excellent overall performance in terms of magnetic saturation strength (Bs). All samples maintained a stable Bs range of 526–534 mT, with consistent and reproducible values, demonstrating that this sintering method facilitates high and stable magnetic response. In contrast, the Bs values of the comparative samples (B1–B5) were generally lower, reaching as low as 476 mT. Some samples even exhibited variations of over 25 mT, indicating poor performance stability.

[0295] In terms of coercivity (Hc), the composite field group samples generally fell within a reasonable range of 13.6–15 A / m, with minimal fluctuations and rapid magnetic response. However, the Hc of the control samples was significantly higher, with some reaching 27.6 A / m, significantly increasing the difficulty of magnetization. During testing, loop broadening and magnetization hysteresis were observed in Group B samples, and some samples exhibited plateaus or discontinuities in the saturation region, further indicating that their magnetic response was less than ideal.

[0296] Overall, the magnetic core samples sintered using composite field sintering are superior to those sintered using simple microwave irradiation in terms of two key indicators: saturation magnetization intensity and coercive force, and the performance is more consistent, indicating that this sintering strategy has obvious advantages in optimizing magnetic properties.

[0297] Experiment 3 (Effect of staged sintering process on magnetic properties):

[0298] Sample preparation:

[0299] Magnetic cores (numbered E1–E5) were prepared according to the formulation and preparation process of Example 3;

[0300] Magnetic cores (numbered F1–F5) were prepared according to the formulation and preparation process of Comparative Example 3.

[0301] Test equipment and methods:

[0302] Equipment: Vibrating sample magnetometer (VSM, LakeShore 7404);

[0303] Test parameters: only saturation magnetization (Bs) and coercive force (Hc) are collected;

[0304] Testing frequency: Each sample was tested 3 times, with an interval of 30 minutes between each test, and the average was taken after removing outliers;

[0305] Environmental conditions: room temperature 25±1℃, no additional atmosphere control.

[0306] Test steps:

[0307] Sample installation: Fix the magnetic core on the quartz rod to ensure it is stable and stress-free;

[0308] Magnetic field loading: The magnetic field is linearly increased from 0 to 1500 kA / m at a rate of 50 kA / m / s;

[0309] Parameter extraction: record the hysteresis loop and calculate the saturation magnetization (Bs) and coercive force (Hc).

[0310]

[0311]

[0312] The experimental data shows that the core samples sintered in stages (E1–E5) generally outperformed the single-stage sintered samples (F1–F5) in terms of magnetic performance. In terms of saturation magnetization (Bs), the values for Group E samples remained stable between 537–548 mT, with concentrated data and a narrow fluctuation range, indicating that this process is more conducive to forming a continuous magnetic response path. In contrast, the Bs values of the comparative samples were generally lower, with a minimum value of 471 mT, indicating weaker overall performance, large fluctuations, and a certain degree of instability.

[0313] In terms of coercivity (Hc), samples in Group E all ranged from 12.8–14.1 A / m, with minimal variation, demonstrating consistent and good magnetic response speed. In contrast, samples in Group F exhibited significantly higher Hc values, reaching a maximum of 28.2 A / m. Some samples exhibited significant deviations across multiple tests, indicating poor magnetic performance repeatability. Furthermore, samples in Group F commonly exhibited discontinuities in the saturation region, delayed initial magnetization, or curve jitter during testing, reflecting unstable factors in the magnetic response process.

[0314] In general, staged sintering not only improves the magnetic saturation strength, but also significantly reduces the coercive force fluctuation, making the overall magnetic properties of the sample more controllable. In contrast, the magnetic core prepared by the one-time sintering process is insufficient in terms of performance balance and stability, making it difficult to meet the requirements of high-consistency application scenarios.

[0315] While embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions, and variations may be made to these embodiments without departing from the principles and spirit of the invention, and that the scope of the invention is defined by the appended claims and their equivalents.

Claims

1. A method for preparing an ultra-high magnetic saturation manganese-zinc ferrite core, characterized in that: The following steps are involved: S1. Weigh the raw materials in parts by mass, the raw materials comprising 50-54 parts of ferric oxide, 22-26 parts of manganese oxide, 20-24 parts of zinc oxide, and 1.5-2.5 parts of rare earth oxides; S2. The rare earth oxide is mixed with ferric oxide and calcined to obtain a rare earth-doped precursor; S3. The rare earth-doped precursor is mixed with manganese oxide and zinc oxide to obtain a main component mixed powder; S4. The main component of the mixed powder is coated by a sol-gel method to form a coated powder; S5. The coated powder is activated by microwave irradiation and simultaneously applied with a pulsed magnetic field to induce orientation to obtain an activated powder; S6. The activated powder is compression molded and sintered in stages, wherein the staged sintering comprises a first stage microwave sintering and a second stage reducing atmosphere sintering to obtain a sintered green body; S7. Annealing and cooling the sintered green body to obtain the magnetic core.

2. The method for preparing an ultra-high magnetic saturation manganese-zinc ferrite core according to claim 1, wherein: The calcination temperature in step S2 is 600-650° C., the calcination time is 1.5-2.5 hours, and the molar ratio of rare earth oxide to ferric oxide is 1:2-1:

4.

3. The method for preparing an ultra-high magnetic saturation manganese-zinc ferrite core according to claim 1, characterized in that: The step of mixing the rare earth doped precursor with manganese oxide and zinc oxide to obtain a main component mixed powder comprises: The rare earth doping precursor is mixed with manganese oxide and zinc oxide in proportion, and the mixture is placed in a ball mill and ball milled using ethanol as a dispersion medium; The ball milling time in the ball mill is 4-8 hours, and the ball-to-material mass ratio is 5:1; After ball milling, the mixture is dried and sieved to obtain the main component mixed powder.

4. The method for preparing an ultra-high magnetic saturation manganese-zinc ferrite core according to claim 1, wherein: The step of coating the main component mixed powder by a sol-gel method to form coated powder comprises: Mixing ethyl orthosilicate and ethanol in a mass ratio of 1:3-1:5, adding an acidic catalyst and hydrolyzing for 6-10 hours to obtain a silica sol; Aluminum isopropoxide and ethanol are mixed in a mass ratio of 1:4-1:6, and hydrolyzed for 4-8 hours to obtain aluminum oxide sol; The silica sol and the alumina sol are mixed in a mass ratio of 2:1-4:1, and the main component mixed powder is added, and ultrasonic dispersion is performed for 20-40 minutes; After dispersion, the powder is dried at 80-100° C. for 2-4 hours to form a coating layer with a thickness of 30-50 nm to obtain coated powder.

5. The method for preparing an ultra-high magnetic saturation manganese-zinc ferrite core according to claim 1, characterized in that: The step of activating the coated powder by microwave irradiation and simultaneously applying a pulsed magnetic field to induce orientation to obtain the activated powder comprises: The coated powder is placed in a microwave reaction chamber and irradiated at a frequency of 2.40-2.50 GHz under a nitrogen atmosphere, with a microwave power of 700-900 W and an irradiation time of 10-15 minutes; A pulsed magnetic field is applied synchronously with a magnetic field strength of 0.5-1.0 T, a pulse frequency of 5-15 Hz, and a magnetic field direction that forms an angle of 30-60° with the polarization direction of the microwave electric field; After irradiation, activated powder with lattice orientation is obtained.

6. The method for preparing an ultra-high magnetic saturation manganese-zinc ferrite core according to claim 1, characterized in that: The step of compression molding the activated powder comprises: Filling the activated powder into a mold pre-coated with a zinc stearate release agent, and press-molding at a pressure of 120-180 MPa; After holding the pressure for 3-7 minutes, demould to obtain a green body; The mold temperature is 25-60°C.

7. The method for preparing an ultra-high magnetic saturation manganese-zinc ferrite core according to claim 1, characterized in that: The endpoint temperature of the first stage microwave sintering is 900-950°C, and the heating rate is 15-25°C / min; The reducing atmosphere in the second stage is a mixed gas of carbon monoxide and hydrogen.

8. The method for preparing an ultra-high magnetic saturation manganese-zinc ferrite core according to claim 7, characterized in that: The initial mass ratio of carbon monoxide to hydrogen is 1:4-1:6, and the hydrogen flow rate increases by 3-7% every 10 minutes.

9. The method for preparing an ultra-high magnetic saturation manganese-zinc ferrite core according to claim 1, characterized in that: The step of annealing and cooling the sintered green body to obtain the magnetic core comprises: Placing the sintered green body in a hydrogen atmosphere, heating it to 500-700°C at a rate of 5-10°C / min, and keeping the temperature for 1-3 hours; After annealing, cool to 150-200°C at a rate of 1-5°C / min in the furnace; The magnetic core is obtained by air cooling in the range of 150-200° C. to room temperature.

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