Low-temperature sintering ni-zn magnetic core material and preparation method thereof

Abstract

The application relates to the field of magnetic core materials, and particularly discloses a low-temperature sintering NiZn magnetic core material and a preparation method thereof. The low-temperature sintering NiZn magnetic core material comprises the following raw materials in percentage by mass: NiO 10-20%, ZnO 20-35%, Fe2O3 45-55%, and a sintering aid 2-5%, wherein the sintering aid comprises at least two of Bi2O3, V2O5 and MnO. By optimizing the component proportion of each raw material and the sintering aid, the application realizes low-temperature sintering below 950 DEG C, can reduce energy consumption by more than 30% compared with the traditional process which needs to be sintered above 1200 DEG C, and solves the problems of easy decline of magnetic performance, insufficient sintering density and increased loss caused by low-temperature sintering, so that the prepared magnetic core material has low loss, a density greater than or equal to 94%, and a magnetic permeability greater than or equal to 85 (1MHz), meets the demand of high-frequency electronic devices, and has high compatibility with low-temperature packaging materials.

Description

Technical Field

[0001] This application relates to the field of magnetic core materials, and more specifically, to a low-temperature sintered NiZn magnetic core material and its preparation method. Background Technology

[0002] Currently, NiZn ferrite cores are widely used in high-frequency electronic devices such as switching power supplies, filters, and communication equipment due to their excellent high-frequency magnetic properties. However, the sintering temperature of traditional NiZn core materials is usually above 1200℃ during the manufacturing process. This not only leads to huge energy consumption in the production process and significantly increases manufacturing costs, but also places stringent requirements on the high-temperature resistance of production equipment, shortening its service life.

[0003] As electronic devices become increasingly miniaturized and integrated, more and more electronic components are being connected or packaged using low-melting-point materials (such as certain solders and encapsulating resins). The traditional high-temperature sintering process for NiZn magnetic cores can cause these low-melting-point auxiliary components to melt, deform, or degrade in performance, severely restricting the compatibility of magnetic cores with advanced packaging technologies. However, when magnetic core materials are sintered at temperatures below 1000℃, problems such as easy degradation of magnetic properties, insufficient sintering density, and increased losses arise. Summary of the Invention

[0004] To address the issues of decreased magnetic properties, insufficient sintering density, and increased losses when magnetic core materials are sintered at temperatures below 1000°C, this application provides a low-temperature sintered NiZn magnetic core material and its preparation method.

[0005] Firstly, the low-temperature sintered NiZn magnetic core material provided in this application adopts the following technical solution:

[0006] A low-temperature sintered NiZn magnetic core material comprises the following raw materials in weight percentages: NiO 10-20%, ZnO 20-35%, Fe2O 33 45-55%, sintering aids 2-5%,

[0007] The sintering aids include at least two of Bi2O3, V2O5, and MnO.

[0008] By adopting the above technical solution, Fe2O3 provides Fe 3+ NiO is the main source of magnetic moment; NiO provides Ni 2 + enhances magnetocrystalline anisotropy to improve permeability; ZnO provides Zn 2+This reduces the temperature coefficient of magnetic permeability and optimizes high-frequency stability. At this ratio, the spinel phase formation is strongly driven, and ion diffusion and site occupancy can be completed at low temperatures. When at least two of Bi2O3, V2O5, and MnO are combined, a eutectic can be formed, which is a low-viscosity liquid phase at low-temperature sintering temperatures. This liquid phase fills the gaps between powder particles through capillary action, promoting the growth of particle sintering necks and achieving low-temperature densification. The addition of sintering aids controlled at 2-5% balances the contradiction between "liquid phase promoting densification" and "excessive aids leading to the formation of a glassy phase (reducing magnetic properties)".

[0009] This application achieves low-temperature sintering below 950℃ by optimizing the composition ratio of each raw material and sintering aid. Compared with the traditional process that requires sintering above 1200℃, it can reduce energy consumption by more than 30%. At the same time, it solves the problems of easy decline in magnetic properties, insufficient sintering density, and increased loss caused by low-temperature sintering. The resulting magnetic core material has low loss, density ≥94%, and permeability ≥85 (1MHz), which meets the requirements of high-frequency electronic devices. It also has high compatibility with low-temperature packaging materials.

[0010] Preferably, the sintering aid comprises a mixture of Bi2O3, V2O5, and MnO.

[0011] By adopting the above technical solution, Bi2O3 and V2O5 preferentially form a eutectic, providing an initial liquid phase and promoting initial particle bonding; MnO and Bi2O3 further form a Bi2O3-MnO eutectic, widening the liquid phase temperature range, enhancing liquid phase fluidity, and promoting low-temperature densification, even achieving sufficient densification within thick-walled blanks; Mn 2+ It can partially replace Ni in the spinel phase 2 +(A site) inhibits abnormal grain growth and avoids increased magnetic loss due to coarse grains. The three additives work synergistically in the above raw material ratio to effectively reduce the sintering temperature, increase the density of the magnetic core material, improve magnetic permeability, and reduce loss.

[0012] Preferably, the Bi2O3 accounts for 1-3% of the total mass fraction of the raw materials, the V2O5 accounts for 0.5-1.2% of the total mass fraction of the raw materials, and the MnO accounts for 0.5-0.8% of the total mass fraction of the raw materials.

[0013] By adopting the above technical solution and controlling the specific proportions of sintering aids, using Bi₂O₃ as the main liquid phase provider, V₂O₅ to assist in lowering the eutectic temperature, and MnO to enhance liquid phase fluidity, research and experiments have shown that if Bi₂O₃ is too low, the amount of liquid phase is insufficient, leading to a decrease in density; if it is too high, excessive glass phase forms at grain boundaries, hindering the movement of magnetic domain walls and reducing magnetic permeability. V₂O₅ can inhibit Fe 3+ →Fe 2+ The reduction, but excessive amounts will lead to V 5+ Fe replacement 3+This introduces lattice defects and increases losses. Excess MnO (>0.7%) leads to Mn... 2+ Oversubstitution of Ni 2 The addition of these three factors increases the magnetocrystalline anisotropy constant (K1) and decreases the permeability. The synergistic effect of these factors achieves "sufficient liquid phase - stable magnetic moment".

[0014] Secondly, this application provides a method for preparing low-temperature sintered NiZn magnetic core material, employing the following technical solution:

[0015] A method for preparing low-temperature sintered NiZn magnetic core material includes the following steps:

[0016] Mixing: NiO, ZnO, Fe2O3 and sintering aids are mixed evenly to obtain mixed raw materials;

[0017] Ball milling: The mixed raw materials are ball milled to obtain precursor powder with a D50 of 0.8-1.2 μm;

[0018] Pretreatment: The precursor powder is kept at 570-620℃ for 1-2 hours, cooled, and then evenly sprayed with binder. After granulation, it is pressed into shape to obtain a green body.

[0019] Pre-sintering: The green billet is pre-sintered at a temperature of 700-750℃, cooled in the furnace, and then extruded to reduce the diameter of the billet by 0.3-0.6mm to obtain the pressed billet;

[0020] Sintering: The pressed blank is sintered at 880-950℃ under oxygen-enriched air for 1.5-2.5 hours, cooled in the furnace, and then ground to obtain the finished magnetic core.

[0021] By adopting the above technical solution, the raw materials are mixed and then ball-milled to refine the powder particle size, thereby increasing the contact area between particles, shortening the ion diffusion distance, and improving the low-temperature sintering activity. The precursor powder is first preheated to remove organic matter and residues and to impart a certain level of activity. Then, a binder is sprayed to uniformly coat the powder particles, forming an effective bond and increasing the green body density. During the pre-sintering process, the binder decomposes and volatilizes, forming a rigid skeleton. Extrusion plastic deformation reduces the porosity of the green body, facilitating the formation of a dense magnetic core material during sintering. Simultaneously, oxygen-rich conditions can inhibit Fe... 3+ The reduction stabilizes the spinel lattice and improves the overall performance of the magnetic core material.

[0022] Preferably, the adhesive comprises 4-8 wt% starch, 1-3 wt% glycerol, and the balance being water.

[0023] By adopting the above technical solution, starch gelatinizes to form a colloid, and hydroxyl groups form hydrogen bonds with metal oxides on the powder surface, providing basic bonding strength; glycerol acts as a plasticizer, intercalating between starch molecular chains to reduce intermolecular forces, improve the flexibility of the starch film, and reduce cracking caused by stress concentration during molding; water acts as a dispersion medium to ensure that starch and glycerol are mixed evenly, and after gelatinization, a uniform colloid is formed, which coats the powder particles to ensure granulation uniformity.

[0024] Preferably, in the pretreatment step, the amount of adhesive sprayed is 5-10% of the mass of the precursor powder.

[0025] By adopting the above technical solution, the amount of adhesive sprayed is optimized, the fluidity of the particles during granulation is improved, the density uniformity during pressing is improved, and there are no pores caused by excessive gas during subsequent decomposition.

[0026] Preferably, in the pre-sintering step, the extrusion pressure is 100-200 MPa.

[0027] By adopting the above technical solution, the extrusion pressure is optimized to allow the pre-sintered green body to undergo plastic deformation, and with the corresponding deformation, it can effectively fill the pores without introducing excessive stress, and shrink uniformly during subsequent sintering.

[0028] Preferably, the oxygen content in the sintering step is 10-15%.

[0029] In summary, this application has the following beneficial effects:

[0030] This application achieves low-temperature sintering of NiZn magnetic cores through a comprehensive design that integrates raw material proportioning, additive synergy, and process optimization. It controls the liquid phase behavior by adjusting the ternary ratio of sintering additives, refines the powder and improves densification efficiency through extrusion processes, and stabilizes magnetic properties in an oxygen-rich atmosphere. This results in magnetic core materials with high density, good permeability, and low loss, which are suitable for applications in 5G communications, new energy, and other fields. Detailed Implementation

[0031] The embodiments of the present invention will be described in detail below with reference to the examples. However, those skilled in the art will understand that the following examples are only for illustrating the present invention and should not be regarded as limiting the scope of the present invention. Specific conditions not specified in the examples shall be carried out according to conventional conditions or conditions recommended by the manufacturer. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0032] Example

[0033] Example 1

[0034] A low-temperature sintered NiZn magnetic core material comprises the following raw materials in weight percentages: NiO 20%, ZnO 20%, Fe2O3 55%, and sintering aid 5%, wherein the sintering aid is Bi2O3 3% and V2O5 2%.

[0035] A method for preparing low-temperature sintered NiZn magnetic core materials includes the following steps:

[0036] Mixing: NiO, ZnO, Fe2O3 and sintering aids are mixed evenly to obtain mixed raw materials;

[0037] Ball milling: The mixed raw materials were ball milled to obtain precursor powder with a D50 of 1.2 μm;

[0038] Pretreatment: The precursor powder is kept at 570℃ for 1 hour, cooled, and then uniformly sprayed with binder. After granulation, it is pressed into a green body. The binder includes 4 wt% starch, 1 wt% glycerol, and the balance is water. The amount of binder sprayed is 10% of the mass of the precursor powder. Pre-sintering: The green body is pre-sintered at 700℃, cooled in the furnace, and then extruded under a pressure of 100 MPa to reduce the diameter of the green body by 0.3 mm to obtain a pressed green body.

[0039] Sintering: The pressed blank is sintered at 950℃ in oxygen-enriched air with an oxygen content of 10% for 2.5 hours, cooled in the furnace, and then ground to obtain the finished magnetic core.

[0040] Example 2

[0041] A low-temperature sintered NiZn magnetic core material comprises the following raw materials in weight percentages: NiO 15%, ZnO 35%, Fe2O3 48%, sintering aid 2%, wherein the sintering aid is V2O5 1.2% and MnO 0.8%.

[0042] A method for preparing low-temperature sintered NiZn magnetic core materials includes the following steps:

[0043] Mixing: NiO, ZnO, Fe2O3 and sintering aids are mixed evenly to obtain mixed raw materials;

[0044] Ball milling: The mixed raw materials are ball milled to obtain precursor powder with a D50 of 0.8 μm;

[0045] Pretreatment: The precursor powder is kept at 620℃ for 1 hour, cooled, and then uniformly sprayed with binder. After granulation, it is pressed into a green body. The binder includes 8 wt% starch, 3 wt% glycerol, and the balance water. The amount of binder sprayed is 5% of the mass of the precursor powder. Pre-sintering: The green body is pre-sintered at 750℃, cooled in the furnace, and then extruded under a pressure of 200 MPa to reduce the diameter of the green body by 0.6 mm to obtain a pressed green body.

[0046] Sintering: The pressed blank is sintered at 900℃ in oxygen-enriched air with an oxygen content of 15% for 1.5 hours, cooled in the furnace, and then ground to obtain the finished magnetic core.

[0047] Example 3

[0048] The difference from Example 1 is that the low-temperature sintered NiZn magnetic core material includes the following raw materials by mass percentage: NiO 12.7%, ZnO 31.2%, Fe2O3 52.1%, sintering aid 4%, and the sintering aids are Bi2O3 2% and V2O5 2%; the preparation method is the same as in Example 1.

[0049] Example 4

[0050] The difference from Example 3 is that the sintering aids include 2.3% Bi2O3, 1% V2O5, and 0.7% MnO; the rest are the same as in Example 4.

[0051] Example 5

[0052] The difference from Example 4 lies in the preparation method of the low-temperature sintered NiZn magnetic core material, which includes the following steps:

[0053] Mixing: NiO, ZnO, Fe2O3 and sintering aids are mixed evenly to obtain mixed raw materials;

[0054] Ball milling: The mixed raw materials are ball milled to obtain precursor powder with a D50 of 1 μm;

[0055] Pretreatment: The precursor powder is kept at 600℃ for 1.6h, cooled and then evenly sprayed with binder. After granulation, it is pressed into a green body. Pre-sintering: The green body is pre-sintered at 730℃, cooled in the furnace and then extruded under a pressure of 140MPa to reduce the diameter of the blank by 0.45mm to obtain a pressed blank.

[0056] Sintering: The pressed blank is sintered at 930℃ in oxygen-enriched air with an oxygen content of 12% for 2 hours, cooled in the furnace, and then ground to obtain the finished magnetic core;

[0057] Everything else is the same as in Example 4.

[0058] Example 6

[0059] The difference from Example 5 is that the adhesive includes 6.5 wt% starch, 2.3 wt% glycerol and the balance water; the amount of adhesive sprayed is 7% of the precursor powder mass; the rest are the same as in Example 5.

[0060] Example 7

[0061] The difference from Example 5 is that the adhesive includes 3 wt% starch, 1 wt% glycerol and the balance water; the amount of adhesive sprayed is 13% of the mass of the precursor powder; the rest are the same as in Example 5.

[0062] Comparative Example

[0063] Comparative Example 1

[0064] The difference from Example 6 is that the low-temperature sintered NiZn magnetic core material includes the following raw materials by mass percentage: 28% NiO, 14% ZnO, 54% Fe2O3, 4% sintering aid, and the sintering aid is 52% V2O and 52% V2O; its preparation method is the same as that of Example 6.

[0065] Comparative Example 2

[0066] The difference from Example 6 is that the sintering aid is Bi2O3, which accounts for 7% of the raw material by mass; the rest are the same as in Example 6.

[0067] Comparative Example 3

[0068] The difference from Example 6 lies in the preparation method of the low-temperature sintered NiZn magnetic core material, which includes:

[0069] Mixing: NiO, ZnO, Fe2O3 and sintering aids are mixed evenly to obtain mixed raw materials;

[0070] Ball milling: The mixed raw materials are ball milled to obtain precursor powder with a D50 of 2μm;

[0071] Pretreatment: Spray 8wt% starch solution evenly onto the surface of the precursor powder, granulate, and then press to obtain a green body;

[0072] The rest is the same as in Example 6.

[0073] Comparative Example 4

[0074] The difference from Example 6 is that the pre-sintering step is omitted; otherwise, it is the same as Example 6.

[0075] Performance testing

[0076] The magnetic core materials prepared in Examples 1-7 and Comparative Examples 1-4 were subjected to density measurement using the Archimedes displacement method according to GB / T25995-2010 "Method for Determination of Density of Magnetic Materials". According to GB / T13888-2019 "Method for Measurement of Dimensions and Properties of Ferrite Cores", the magnetic core material was wound into a 10-turn coil using an impedance analyzer (Agilent E4990A) and placed in a constant temperature environment of 25°C. The test frequency was 1MHz, and the relative permeability was read under no-load conditions. According to GB / T13888-2019 "Method for Measurement of Dimensions and Properties of Ferrite Cores", the loss of the magnetic core was tested using a BH analyzer (IWATSUSY-8232) with a test frequency of 1MHz, a magnetic flux density of 20mT, and an ambient temperature of 25°C. All the above results are recorded in Table 1.

[0077] Table 1

[0078] Density (%) Magnetic permeability (1MHz) <![CDATA[Magnetic loss (kW / m 3 )]]> Example 1 95.2 87 180 Example 2 94.4 85 195 Example 3 95.5 88 171 Example 4 96.0 90 168 Example 5 96.5 92 163 Example 6 97.0 93 154 Example 7 94.8 86 171 Comparative Example 1 92.5 70 330 Comparative Example 2 90.0 77 290 Comparative Example 3 88.5 75 300 Comparative Example 4 86.0 71 320

[0079] Examples 1-6, by optimizing the raw material ratio, ternary sintering aids, and process parameters, yielded magnetic core materials with a density ≥94%, excellent magnetic permeability, and low magnetic loss. This demonstrates the synergistic effect of the "raw material ratio-aids-process" on improving low-temperature sintering performance. However, Example 7, compared to Example 6, suffered from insufficient starch content in the binder and excessive spraying, resulting in uneven granulation, increased porosity in the green body, decreased density, and poor magnetic permeability. This verifies that the binder ratio and dosage also require strict control.

[0080] As can be seen from Example 6 and Comparative Example 1, and in conjunction with Table 1, in Comparative Example 1, there was an excess of NiO and an insufficient amount of ZnO, which deviated from the stoichiometric ratio of the spinel phase. During the preparation process, spinel distortion occurred, resulting in magnetic moment disorder, a sharp drop in magnetic permeability, and a significant increase in loss.

[0081] As can be seen from Example 6 and Comparative Example 2, and in conjunction with Table 1, in Comparative Example 2, a single sintering aid (Bi2O37%) was used in excess, resulting in enrichment of the grain boundary glass phase, poor density, and decreased magnetic permeability.

[0082] As can be seen from Example 6 and Comparative Example 3, and in conjunction with Table 1: In Comparative Example 3, the ball milling particle size was coarse (D50 = 2 μm) and the binder was sprayed directly. The binder decomposed prematurely, resulting in low green compact density, which in turn led to low density of the final magnetic core material and deterioration of magnetic properties.

[0083] By comparing Example 6 and Comparative Example 4 with Table 1, it can be seen that: in Comparative Example 4, the pre-sintering step was omitted, the green body did not form a rigid skeleton, the porosity after extrusion was high (density as low as 86.0%), the grains grew abnormally, and the magnetic loss increased significantly.

[0084] This specific embodiment is merely an explanation of this application and is not intended to limit it. After reading this specification, those skilled in the art can make modifications to this embodiment without contributing any inventive step, but such modifications are protected by patent law as long as they fall within the scope of the claims of this application.

Claims

1. A method for preparing a low-temperature sintered NiZn magnetic core material, characterized in that, Includes the following steps: Mixing: Mix 10-20wt% NiO, 20-35wt% ZnO, 45-55wt% Fe2O3 and 2-5wt% sintering aid evenly to obtain a mixed raw material. The sintering aid is a mixture of Bi2O3, V2O5 and MnO, wherein Bi2O3 accounts for 1-3% of the total mass fraction of the raw material, V2O5 accounts for 0.5-1.2% of the total mass fraction of the raw material, and MnO accounts for 0.5-0.8% of the total mass fraction of the raw material. Ball milling: The mixed raw materials are ball milled to obtain precursor powder with a D50 of 0.8-1.2 μm; Pretreatment: The precursor powder is kept at 570-620℃ for 1-2 hours. After cooling, a binder is sprayed evenly. The binder includes 4-8wt% starch, 1-3wt% glycerol and the balance water. The amount of binder sprayed is 5-10% of the mass of the precursor powder. After granulation, it is pressed into shape to obtain a green body. Pre-sintering: The green billet is pre-sintered at a temperature of 700-750℃, cooled in the furnace, and then extruded under a pressure of 100-200MPa to reduce the diameter of the billet by 0.3-0.6mm, thus obtaining the pressed billet; Sintering: The pressed blank is sintered at 900-950℃ in oxygen-enriched air with an oxygen content of 10-15% for 1.5-2.5h, and then cooled in the furnace to obtain the low-temperature sintered NiZn magnetic core material.