Iron-deficient co2z-type ferrite, method for preparing the same, and use thereof

Abstract

The application belongs to the technical field of electronic ceramics, and particularly relates to a Co2Z-type ferrite with iron deficiency and a preparation method and application thereof. The Co2Z-type ferrite with iron deficiency comprises a ferrite base material and a sintering aid. The ferrite base material is composed of 2.9BaOxReO2CoO10.6Fe2O3. ReO is a dopant, wherein Re is an ion with a radius equal to that of Ba 2+ near but not equal cations; the sintering aid comprises an aid for promoting sintering and an aid for limiting grain growth in the sintering process; and x is 0.08-0.1. The application realizes uniform coating of the base material particles by utilizing the hydroxyl functional groups existing on the surface of the base phase powder after water quenching of a salt solution and the good film-forming property of a composite sol, so as to realize optimization of the magnetic properties of the material and reduce the electrical loss of the material at high frequencies. The obtained Co2Z-type ferrite with iron deficiency has low loss and high cutoff frequency at super-high frequencies at a relatively low sintering temperature.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of electronic ceramics, and particularly relates to a Co2Z type ferrite with iron deficiency, a preparation method and application thereof. BACKGROUND

[0002] At present, the commonly used soft magnetic ferrite materials in industry mainly include spinel structure ferrite (mainly nickel-zinc, manganese-zinc ferrite) and planar hexagonal ferrite (Co2Z, Co2Y ferrite) and the like. The highest use frequency of the nickel-zinc, manganese-zinc ferrite with spinel structure is limited by the crystal structure. For example, the nickel-zinc ferrite will have a significant performance deterioration due to the skin effect and eddy current loss caused by electromagnetic induction when the frequency is higher than 100 MHz; the nickel-copper-zinc ferrite will have a sharp increase in hysteresis loss and a significant decrease in quality factor when the frequency is higher than 300 MHz, and thus is not suitable for manufacturing antennas and related devices with higher frequency.

[0003] The frequency range applied by the 5G technology is approximately 450MHz-6.0GHz for the receiving and transmitting ends. The hexagonal ferrite has a high magnetic crystal anisotropy and a theoretical resonance frequency of up to 3.4GHz, and the Z type hexagonal ferrite material has high initial permeability, high cutoff frequency and good stability, and thus becomes an important candidate magnetic material for the application of super-high frequency antenna devices.

[0004] A Chinese patent with the application number CN201310275973.1 and the name of "ferrite-based composite magnetic antenna substrate material and preparation method thereof" discloses a ferrite-based composite magnetic antenna substrate material and a preparation method thereof. The substrate material is composed of 85-90% of main phase material and 15-10% of auxiliary phase material. The main phase material is Co2Z type hexagonal ferrite with a formula of Ba 3-x Sr x Co2Fe 24-y O 41Wherein x is in the range of 0-1.5, y is in the range of 0-4; the auxiliary phase material is a polyimide resin. The magnetic medium composite substrate material provided by the application has a magnetic permeability of about 2.5-4.5 and a dielectric constant of 7-9 in the 300MHz-3GHz frequency band; the magnetic loss tangent in the 300MHz-1GHz frequency band can be lower than 0.01; the magnetic loss tangent in the 1GHz-3GHz frequency band can be lower than 0.05; the dielectric loss tangent in the 300MHz-3GHz frequency band can be lower than 0.005; at the same time, the miniaturization factor is higher, and it also has a certain flexibility, and the mechanical impact resistance is better than that of conventional ceramic substrate materials. Not only helps to reduce the weight and volume of the antenna, but also helps to improve the bandwidth of the microstrip antenna and suppress the generation of surface waves. But the target material of the patent is a composite magnetic substrate (ferrite and resin composite material) with polyimide resin as the adhesive, which is a ferrite-based composite magnetic medium antenna substrate material obtained by curing at 280-300℃ with resin as the adhesive. The use environment temperature and service life of this kind of composite substrate material are limited to a certain extent; and after the polyimide (dielectric constant is about 2.8, magnetic permeability is 1) and the prepared Co2Z type ferrite are compounded in proportion, the magnetic permeability of the composite material can be adjusted to 2.5-4.5, the dielectric constant can be adjusted to about 7-9, and the composite material has high magnetic loss in the 1GHz-3GHz frequency band and high dielectric loss tangent in the 300MHz-3GHz frequency range.

[0005] The Chinese invention patent with application number CN202010172783.7 and the name of "a high-flexibility magnetic medium composite substrate material and its preparation method and application" discloses a high-flexibility magnetic medium composite substrate material and its preparation method and application, wherein the high-flexibility magnetic medium composite substrate material is composed of a main phase material and an auxiliary phase material in a mass percentage of 1:0.5-1.5, the main phase material is a hexagonal crystal system ferrite with an initial magnetic permeability greater than 15 and a cutoff frequency greater than 1GHz, and the formula of the hexagonal crystal system ferrite is (Ba 0.5+y Sr 0.5-y )3Co 1.6+x Zn 0.4-x Fe 23 O 41, where the value range of x is -0.1-0.1, the value range of y is -0.2-0.2, the auxiliary phase material is polydimethylsiloxane (PDMS); the dopant is WO3, and the doping amount is 0.1-0.3wt%. This material is a very good magnetic dielectric substrate material with high flexibility, which is suitable for inorganic / organic composite flexible magnetic dielectric substrate materials for 300MHz-5GHz microstrip antenna applications. However, the patent ultimately uses polydimethylsiloxane as an adhesive and cures it at 100°C to obtain a ferrite-based composite magnetic dielectric antenna substrate material. The prepared composite material has a dielectric constant of 5.8 and a magnetic permeability of 2.78 at 1GHz; the dielectric loss is 0.0095, and the magnetic loss is 0.13 (Example 1); the dielectric constant is low and the loss is large.

[0006] The invention patent application number CN201580041623.6, entitled "Co2Z type ferrite composite material for ultra-high frequency antennas", discloses a ferrite composition containing Ba, Co and Ir and having a Z-type hexagonal ferrite phase and a Y-type hexagonal ferrite phase. The ferrite composition has the following formula: Ba3Co (2+x) Ir x Fe (24-2x) O 41 , wherein x = 0.05-0.20. The composition has equal or substantially equal magnetic permeability and dielectric constant, while maintaining low magnetic loss factor and dielectric loss factor. The composition is suitable for ultra-high frequency applications such as high frequency and microwave antennas. However, this patent pre-synthesizes Z-type ferrite with two crystal forms (Z-type and Y-type) by directly mixing several oxides involved in the main phase and doping phase, such as BaCO3, Co3O4, Fe2O3 and IrO2 (doping phase) at one time; resulting in a lower dielectric constant and greater loss.

[0007] The invention patent application number CN201680013105.8, entitled “Mo-doped Co2Z-type ferrite composite material for ultra-high frequency” discloses a Co2Z hexagonal ferrite composition comprising one or both of barium and strontium and molybdenum, wherein the Co2Z hexagonal ferrite composition has the formula (Ba2Sr (3-Z) )Co (2+X) Mo x Fe (y-2x) O 41, wherein x=0.01 to 0.20; y=20 to 24; and z=0 to 3. The composition can exhibit high magnetic permeability and equal or substantially equal values ​​of magnetic permeability and permittivity, while maintaining low magnetic loss tangent and dielectric loss tangent and loss factor. The composition is suitable for high frequency applications, such as ultra-high frequency and microwave antennas and other devices. However, this patent directly mixes several oxides involved in the main phase and the doping phase, such as BaCO3, SrCO3, Co3O4, Fe2O3 and MoO2 (doping phase) at one time, resulting in a lower dielectric constant and a larger loss.

[0008] The Chinese invention patent application number CN201910237811.6, titled "A Miniaturized Array Antenna Based on M-Type Barium Ferrite Material," discloses a miniaturized array antenna based on M-type barium ferrite material, belonging to the field of antenna substrate material technology. The substrate material of the array antenna is M-type barium ferrite substituted with lanthanum (La) and cobalt (Co), with a formula of BaFe (12-5x) (LaCo) 3x O 19 , where 0<x≤0.12. The invention can improve the relative magnetic permeability of M-type barium ferrite by the position of lanthanum and cobalt in M-type barium ferrite and the size of the ionic magnetic moment. (12-5x) (LaCo) 3x O 19 ) formula can reduce the relative dielectric constant of M-type barium ferrite.

[0009] However, this patent directly mixes several oxides and carbonates involved in the main phase and doping phase, such as BaCO3, Co2O3, Fe2O3 and La2O3, at one time, performs pre-synthesis first, and then prepares M-type barium ferrite by ball milling the pre-synthesized powder and Bi2O3 sintering aid, granulating and forming, and then sintering. The dielectric loss and magnetic loss are too high.

[0010] The literature (Xiang Chengcheng. Preparation and Characterization of Co2Z Ferrite Materials for Antenna Miniaturization [D]. Master's Thesis of Huazhong University of Science and Technology, 2011.01) proposed to take Co2Z hexagonal ferrite as the research object, and studied the influence of factors such as iron deficiency formula, preparation process parameters, and Sr doping on the material phase structure, micromorphology, and electromagnetic properties. The study showed that under the optimized process conditions of first grinding time 2.5h, pre-sintering temperature 1240℃ / 2.5h, second grinding time 3h, and sintering temperature 1050℃ / 3.5h, the electromagnetic properties of Co2Z hexagonal ferrite were significantly improved; with the increase of iron deficiency, the magnetic permeability of the sample first increased and then decreased. When the iron deficiency y=10.4, the relative magnetic permeability at 1GHz reached a maximum value of approximately 7, and the saturation magnetization intensity M sAs the amount of iron deficiency increases, the coercive force decreases first and then increases slightly. As the amount of Sr substitution increases, the magnetic permeability of the sample increases first and then decreases. For the sample with Sr doping amount x = 0.3, at a frequency of 1 GHz, μ' r Reach 7.5, μ' r The saturation magnetization Ms increases with the increase of the substitution amount, while the coercive force first decreases slightly and then increases with the increase of the substitution amount. When the substitution amount x = 0.4 and x = 0.8, the coercive force reaches a minimum of 68.11Oe and a maximum of 176.59Oe, respectively.

[0011] However, this patent directly mixes several oxides and carbonates involved in the main phase and doping phase, such as BaCO3, Co3O4, Fe2O3, and SrCO3, at one time, performs pre-synthesis first, and then prepares M-type barium ferrite by ball milling the pre-synthesized powder and Bi2O3 sintering aid, granulating and forming, and then sintering; the dielectric loss and magnetic loss are too high.

[0012] The literature (Chen Hui. Research on magnetic substrate materials used in mobile phone communication antennas [D]. Master's thesis of University of Electronic Science and Technology of China, 2018.06) studied the relevant theories of two different crystal structures of hexagonal ferrite, Z-type and Y-type. First, the iron deficiency degree of Z-type hexagonal ferrite material, Sr 2+ Substitution, sintering aid addition, preparation process conditions and Cr 3+ The effects of doping amount on the phase structure, microstructure and electromagnetic properties of the material were studied. The results showed that the degree of iron deficiency, Sr 2+ Substitution, sintering aid addition, preparation process conditions and Cr 3+ The doping amount has a significant effect on the magnetic permeability and permeability cutoff frequency of the material. 0.7 Sr 0.3 O·2CoO·10.8Fe2O3, sintering aid addition amount is 3wt%, sintering temperature is 1000℃, electromagnetic parameters can be prepared: μ r '~4.6, μ r ”~0.19,ε r '~5.5, ε r ”~0.01(1.5GHz) and μ r '~4.6, μ r '~0.36, ε r '~5.37, ε r ”~0.012(1.8GHz) material, the magnetic permeability of Z-type hexagonal ferrite material varies with Cr 3+ The cutoff frequency decreases with the increase of Cr doping amount. 3+The increase of doping amount shifts to high frequency; In addition, the phase structure and electromagnetic parameter characteristics of Y-type hexagonal ferrite materials were preliminarily studied. At different sintering temperatures, the performance of the material was almost not affected. Within a certain frequency range, the electromagnetic parameters remained basically stable. Finally, μ r '~2, μ r ”~0.11,ε r '~9.53, ε r ”~0.03(0.5-4GHz) materials.

[0013] However, this prior art also directly mixes several oxides and carbonates involved in the main phase and the doping phase, such as BaCO3, Co3O4, Fe2O3, and SrCO3, at one time, performs pre-synthesis, and then prepares M-type barium ferrite by ball milling the pre-synthesized powder and Bi2O3 sintering aid, granulating and forming, and then sintering; the dielectric loss and magnetic loss are too high.

[0014] Literature (Jing Yulan, Su Hua, Tang Xiaoli, Xia Qi. Study on the influence of H3BO3 doping on Co2Z-based magneto-dielectric antenna substrate materials [J]. Piezoelectrics and Acousto-Optics, 2014, 36(2): 187-189, 193) In order to develop magneto-dielectric substrate materials suitable for the miniaturization of 915MHz RFID antennas, the solid phase reaction sintering method was used to study the effect of H3BO3 doping on (Ba 0.5 Sr 0.5 )3Co2Fe 24 O 41 The study investigated the influence of H3BO3 doping on the micromorphology and magnetic-dielectric properties of ferrites. The study found that H3BO3 doping significantly promotes the low-temperature sintering phase formation of Co2Z ferrite. Furthermore, H3BO3 doping also helps inhibit grain growth in Co2Z ferrites. With increasing H3BO3 doping levels, the magnetic permeability of the material system decreases continuously, while the dielectric constant first increases and then decreases. When the mass fraction of H3BO3 doping is 4%, the material system achieves a comprehensive magnetic-dielectric performance of 2.45, a dielectric constant of 10.41, a magnetic loss tangent of 0.057, and a dielectric loss tangent of 0.005 at 915 MHz.

[0015] However, in the prior art, H3BO3 is mainly used as a dopant to reduce the sintering temperature of Co2Z ferrite (the actual sintering temperature is 900°C), and the essence is that H3BO3 is used as a dopant precursor. During the sintering process, H3BO3 decomposes to generate B2O3 (the decomposition temperature range is about 170-500°C), and B2O3 can dissolve alkaline metal oxides such as BaO and SrO to generate glassy borate and metaborate, which are located at the grain boundaries and promote sintering. These products are amorphous, so no glass phase is observed in the XRD results in the prior art; the B element only enters the part of the ferrite that forms a glass phase, and there is no doping in the low Co2Z ferrite that does not form a glass phase, resulting in obvious composition inhomogeneity in the ferrite material (glass phase part and grain part), and also leading to unsatisfactory magnetic properties.

[0016] A low-loss high-frequency magnetic material and a preparation method thereof are disclosed in Chinese Patent Application No. CN202110549706.3, entitled "A low-loss high-frequency magnetic material and a preparation method thereof". The magnetic material belongs to the field of electronic materials. The magnetic material is Ba3Co2Fe 24-x-y Pr x Sm y O 41 Hexagonal ferrite; x = 0.05-0.30, y = 0.01-0.10. The low-loss high-frequency magnetic material is prepared by a sol-gel method, achieving low loss and high-frequency magnetic properties. In the frequency range of 1MHz-1.8GHz, it has low loss and near-equal magnetic properties (its permeability and dielectric constant are both around 5-15, and the magnetic loss coefficient and dielectric loss coefficient in the frequency range are both lower than 0.005). When used as an antenna substrate, the low-loss high-frequency magnetic material can well realize the miniaturization and high frequency of the antenna, and is conducive to improving the transmission efficiency of the microstrip antenna and reducing the transmission loss of the antenna, providing a new material for the design of high-frequency and integrated small-size wireless communication devices. However, the main raw materials of this patent are nitrate, citric acid, ammonia water, etc., and the sol-gel method combined with self-propagating is used to prepare the pre-synthesized powder, which has the problems of high cost and difficulty in large-scale production. In the patent, the similar sites (Me1-Me10) of the trivalent ion Fe 3+ in the Co2Z ferrite are replaced by doping, which involves changes in the molecular magnetic moment, which will have a significant adverse effect on the macroscopic magnetic properties of the ferrite, i.e., increasing the permeability will lead to a decrease in other magnetic properties, and vice versa.

[0017] The Chinese invention patent with application number CN202111091418.4 and titled "A Co2Z type ferrite material, its preparation method and use" provides a Co2Z type ferrite material, its preparation method and use. The preparation method comprises the following steps: (1) using electrodialysis to treat the Y type mixed solution and the M type mixed solution respectively to obtain a Y type cation mixed solution and an M type cation mixed solution; (2) mixing the Y type cation mixed solution and the M type cation mixed solution with ammonium bicarbonate respectively, and drying to obtain a Y type ferrite precursor and an M type ferrite precursor; (3) pressing the Y type ferrite precursor, the M type ferrite precursor and the binder into a shape, pre-sintering once, and sintering twice to obtain a Co2Z type ferrite material; the substituted metal ions include Ba 2+ and / or Sr 2+ . This invention uses electrodialysis to prepare a Co2Z type ferrite material with uniform mixing, small particle size, few impurities and high performance, which is suitable for ultra-high frequency magnetic devices, reduces the sintering temperature, and saves the preparation process. However, the main raw material of this patent is nitrate, and a nitrate solution is prepared. The solution is electrodialyzed, and then ammonium bicarbonate is added and stirred, and dried to obtain two precursors respectively. The precursors are mixed in proportion, and then high-temperature pre-synthesis is carried out to prepare pre-synthesized Y+M type ferrite powder. There are problems such as high cost, complex process, and difficulty in large-scale production. The sintering process of the patent takes advantage of the relatively small size of the pre-synthesized powder, does not add sintering aids, and directly sinters at high temperature (sintering at 1150°C and keeping warm for 4 hours) to prepare sintered ferrite, which has high energy consumption.

[0018] The Chinese invention patent application number CN202110527759.5, entitled "A method for preparing a Co2Z type ferrite sintered sheet", discloses a method for preparing a Co2Z type ferrite sintered sheet, comprising the following steps: 1) preparing the sintered sheet according to Ba x Sr 3- x Co2Fe y O 41 The invention provides a method for preparing Co2Z type ferrite sintered sheets, which has the advantages of simple process and convenient operation. The obtained ferrite sintered sheets have good magnetic properties, can meet the application requirements at high frequencies, and have broad market prospects. However, the ultimate goal of the patent is to use pre-synthesized ferrite powder as the main raw material, prepare ferrite substrates by tape casting method, with low magnetic permeability and a cutoff frequency of only about 2.1GHz.

[0019] The application number is CN202110500939.4, and the title is “A textured Z-type Ba 0.52 Sr 2.48 Co2Fe 24 O 41 The Chinese invention patent "Method for preparing hexagonal ferrite" discloses a textured Z-type Ba 0.52 Sr 2.48 Co2Fe 24 O 41 The preparation method of hexagonal ferrite comprises the following steps: uniformly mixing, grinding, and tableting barium carbonate, strontium carbonate, cobalt oxide, and iron oxide raw materials in a certain stoichiometric ratio, and then calcining them in a box furnace at high temperature to synthesize phase A; placing phase A in a tube furnace and annealing it in a flowing oxygen atmosphere to obtain sample B; grinding sample B into powder, taking a certain amount of the powder and dispersing it in a premix of polyvinyl alcohol and deionized water to prepare a slurry, and then transferring the slurry into an alloy mold. After being treated under magnetic field conditions for a period of time, pressure is applied to the slurry to form a green blank sample C; removing the magnetic field, taking out sample C, and sintering it in a box furnace at high temperature to obtain textured Ba. 0.52 Sr 2.48 Co2Fe 24 O 41 The textured Ba prepared by the invention 0.52 Sr 2.48 Co2Fe 24 O 41 When used in single-phase multiferroic materials, this material offers significant advantages, including high magnetoelectric coupling temperature and strong coupling strength. However, this patent requires a period of magnetization to achieve oriented alignment of the powder, followed by the formation of a green billet and subsequent high-temperature sintering. This process is complex, requires high equipment requirements, and is difficult to scale up for mass production. Summary of the Invention

[0020] The purpose of the present invention is to provide an iron-deficient Co2Z type ferrite with low loss and high cutoff frequency at ultra-high frequency, a preparation method and its application in 5G mobile phone antennas.

[0021] To achieve the above object, the technical solution adopted by the present invention is as follows:

[0022] An iron-deficient Co2Z type ferrite comprises a ferrite base material and a sintering aid, wherein the ferrite base material is composed of 2.9BaO·xReO·2CoO·10.6Fe2O3; ReO is a dopant, wherein Re is an ion radius equal to Ba 2+ Close but not equal cations; sintering aids include aids that promote sintering and aids that limit grain growth during sintering; x is 0.08-0.1.

[0023] In a preferred embodiment, considering a small amount of doping and in order not to affect the crystal structure of the original material, the ion radius of Re is 0.0945-0.1755 nm.

[0024] In a preferred embodiment, Re is Sr 2+ , Ca 2+ and Mg 2+ One or more of .

[0025] The ionic radius of these species is similar to that of Ba 2+ It is closer and easier to enter the lattice of hexagonal ferrite base material, and is closer to Ba 2+ There are certain differences in the ionic radius, which easily leads to structural distortion.

[0026] In a preferred embodiment, Re is Sr 2+ , Ca 2+ One or both of .

[0027] Ba 2+ The ionic radius is 0.135nm and the electronegativity is 0.89; Ca 2+ The ionic radius is 0.099nm and the electronegativity is 1.00; Sr 2+ The ionic radius of ferrite is 0.113nm and the electronegativity is 0.95, which can easily enter the lattice of hexagonal ferrite matrix and easily cause structural distortion.

[0028] Because Ba 2+ The position in the hexagonal ferrite is fixed. The present invention mainly introduces the doping ions into the Ba 2 + Similar positions are used to achieve microstructural distortion and electronegativity changes, thereby regulating the corresponding properties of sintered ferrite.

[0029] Mg 2+ The ionic radius is 0.065nm and the electronegativity is 1.31. The ionic radius is too small, so the effect is relatively poor.

[0030] In a preferred embodiment, the sintering-promoting additive is Bi2O3, Nb2O5 or V2O5.

[0031] The melting point of Bi2O3 is 817℃, the melting point of Nb2O5 is 1485℃±5℃, and the melting point of V2O5 is 690℃. Considering that the melting point of Nb2O5 is higher and V2O5 may be toxic, Bi2O3 is often used as a sintering aid.

[0032] In a preferred embodiment, the additive for limiting grain growth during sintering is SiO2, MgO or Al2O3.

[0033] SiO2, MgO and Al2O3 are common additives that can be used to limit grain growth during the sintering process.

[0034] Based on the same inventive concept, the present invention also claims a method for preparing the iron-deficient Co2Z type ferrite by low temperature sintering, comprising the following steps:

[0035] S1. Drying, ball-milling, and sintering barium oxide, cobalt oxide, and iron oxide to obtain a powder; adding the powder to a dopant solution and quenching the mixture with a salt solution to obtain a ferrite base material;

[0036] S2. Add an alcohol solvent to the auxiliary agent precursor that limits grain growth during the sintering process, stir and dissolve, and then add a mixed solvent of acid and water to react to obtain sol A; add an auxiliary agent precursor that promotes sintering to sol A, stir evenly, and then stand and seal for 200-280 hours to obtain a composite sol;

[0037] S3, mixing the ferrite base material and the composite sol, performing ball milling, drying, and heat treatment to obtain a composite powder having a core-shell structure;

[0038] S4, after ball milling the composite powder, adding a binder and continuing ball milling to obtain a slurry; spray granulating the slurry, and compression molding to obtain a green body; drying and sintering the green body to obtain the iron-deficient Co2Z type ferrite.

[0039] In a preferred embodiment, the barium oxide, cobalt oxide and iron oxide are all micron-sized.

[0040] In a preferred embodiment, the particle size D50 of the barium oxide, cobalt oxide and iron oxide is 0.5-2.0 μm.

[0041] If the particle size of the oxide raw material is too large, the temperature required for synthesizing the Co2Z type ferrite-based phase powder will be high, the time will be long, and impurities will be easily generated; if the particle size of the oxide raw material is too small, on the one hand, the powder price will be high, and on the other hand, the ball milling mixing process will not be easy to mix evenly, resulting in the presence of impurities in the synthesized Co2Z type ferrite-based phase powder.

[0042] In a preferred embodiment, the molar ratio of barium oxide, cobalt oxide and iron oxide is 2.5-3.5:1-3:10-11.

[0043] If the molar ratio of barium oxide, cobalt oxide or iron oxide is too large, the pre-synthesized powder will be a mixed phase, including Co2Z ferrite and excess barium oxide, cobalt oxide or iron oxide oxide; thus, the phase will be uneven, affecting the performance.

[0044] If the molar ratio of barium oxide, cobalt oxide or iron oxide is too small, the powder after pre-synthesis is in a mixed phase, leading to uneven phase and affecting performance. For example, if barium oxide is too little, Co2Z ferrite and CoFe2O4 oxide may be generated.

[0045] In one preferred embodiment, the temperature of drying in step S1 is 60-90°C, and the time is 20-30h.

[0046] In one preferred embodiment, the medium for ball milling in step S1 is ethanol or water, and corundum balls, zirconium oxide or agate are used as grinding balls. The ball milling time is 4-8h, and the rotation speed of the ball mill is 200-600r / min. -1 .

[0047] Deionized water can also be used as a ball milling medium. Ethanol as a ball milling medium, the powder after drying of the obtained slurry is relatively loose, because the chemical polarity of ethanol is relatively small; and deionized water as a ball milling medium, the obtained powder is easy to agglomerate, which is not conducive to the subsequent process, therefore, ethanol is preferred.

[0048] From the price point of view, the grinding ball is best with corundum ball.

[0049] Experiments show that if the ball milling time is too short, the several oxides cannot be mixed uniformly; and if the time is too long, the production efficiency is reduced.

[0050] If the rotation speed of the ball mill is too slow, the several oxides cannot be mixed uniformly; and if the rotation speed is too fast, the energy consumption is high, the equipment wears out greatly, and the grinding dust generated by the ball mill tank and the grinding ball increases, leading to an increase in the impurity content in the raw material, and finally leading to a decrease in the performance of the ferrite.

[0051] In one preferred embodiment, the mass ratio of material:ball:medium in the ball milling process in step S1 is 1:1-2:1-2.

[0052] In the ball milling process,

[0053] 1 Material effect: too much material, the several oxides in the raw material cannot be mixed uniformly; too little material, the slurry obtained per batch is too little, and the production efficiency is reduced;

[0054] 2 The effect of medium is just the opposite of material: too much medium, that is, too much water or ethanol, the yield per batch is reduced, and the solid content of the slurry is low, affecting the effect of spray granulation;

[0055] Too little medium is equivalent to too much material, and the several oxides in the raw material cannot be mixed uniformly.

[0056] 3 The effect of grinding ball: too many grinding balls, on the one hand, will lead to an increase in grinding dust, and on the other hand, the yield per batch is too small, and the production efficiency is reduced; too few grinding balls, and the several oxides in the raw material cannot be mixed uniformly.

[0057] In a preferred embodiment, the sintering in step S1 is: 3-7°C·min -1 The heating rate is raised to 800-1500℃ and then kept at this temperature for 0.5-8h; then the temperature is raised to 1-3℃·min -1 The cooling rate is reduced to 300-800℃ and then kept warm for 0.2-4h.

[0058] During the sintering process in step S1, the heating rate has an impact: if the heating rate is too slow, production efficiency will be affected and energy consumption will be increased; if the heating rate is too high, there will be a significant temperature difference between the surface and the interior of the evenly mixed oxide powder pile in the furnace. Because the thermal conductivity coefficients of the oxide raw materials and the pre-synthesized ferrite powder are relatively low, it is easy for the pre-synthesized ferrite on the surface to be slightly sintered, while the oxide raw materials inside have not yet completely reacted, which ultimately leads to impurities in the pre-synthesized powder.

[0059] Influence of holding temperature: If the holding temperature is too low, the mixed oxides cannot react completely to form ferrite; if the holding temperature is too high, the generated ferrite powder will undergo a certain degree of sintering, which is not conducive to the next step of water quenching / ball milling mixing.

[0060] The effect of holding time is similar to that of temperature: a shorter holding time is similar to a lower temperature; a longer holding time is similar to a higher temperature.

[0061] In a preferred embodiment, the sintering temperature in step S1 is 1050-1350° C., and the holding time is 1-4 hours; after cooling to 400-800° C., the temperature is kept for 0.4-2 hours.

[0062] In a preferred embodiment, the salt solution quenching in step S1 refers to: adding the powder into the dopant solution, stirring, standing, washing, and secondary drying.

[0063] In a preferred embodiment, the dopant solution in step S1 is a nitrate solution of the dopant.

[0064] In a preferred embodiment, the concentration of the dopant nitrate in the dopant solution is 0.05-1.5 mol·L -1 , preferably 0.25-0.5 mol·L -1 .

[0065] In the present invention, the goal of salt solution quenching is to diffuse a certain amount of ions into the Co2Z ferrite lattice to regulate its magnetic properties. Therefore, when the salt solution concentration is too low, under the same salt solution quenching conditions, too few ions enter the ferrite lattice, and the desired effect cannot be achieved.

[0066] However, if the concentration is too high, experimental results show that the total amount of ions diffusing into the ferrite lattice does not increase significantly. Instead, it causes waste of inorganic salts and increases the workload of the next centrifugal washing step. This is because under the set salt solution water quenching conditions, the diffusion energy is constant and mainly depends on the temperature of the powder and the number of ions in the salt solution that come into contact with the powder.

[0067] In a preferred embodiment, the temperature of the salt solution water quenching in step S1 is 300-800°C, preferably 600-800°C.

[0068] In a preferred embodiment, in the salt solution water quenching in step S1, the ratio of the dopant nitrate solution to the powder is 10-200 ml solution / 1 g powder, preferably 50-150 ml solution / 1 g powder.

[0069] The ratio of the dopant nitrate solution to the powder is too high, which means that the volume of the salt solution is large and the material is small. Because after water quenching, the powder needs to be separated from the salt solution by centrifugation and washing for the next step. Too much salt solution will lead to a large workload for the separation operation and also cause waste.

[0070] The ratio of the dopant nitrate solution to the powder is too low, which means that the volume of the salt solution is small and the material is large. Because water quenching is actually pouring high-temperature ferrite powder into the salt solution, the heat exchange will cause the water temperature of the salt solution to rise. If the amount of water is too little, it may cause the water to boil or vaporize and splash out, which will pose certain safety hazards in the operation. At the same time, the goal of water quenching - to break the powder by using the temperature difference - cannot be achieved.

[0071] In a preferred embodiment, the standing time is 12-48 hours.

[0072] In a preferred embodiment, the washing is centrifugal washing with water for 3-5 times.

[0073] In a preferred embodiment, the secondary drying temperature is 60-90° C. and the time is 20-30 hours.

[0074] In a preferred embodiment, the molar ratio of the auxiliary agent precursor for limiting grain growth during the sintering process to the ferrite base material in step S2 is 0.05-1.50:1, preferably 0.10-1.00:1.

[0075] The auxiliary agent precursor that limits the grain growth during the sintering process is converted into SiO2 after heat treatment. SiO2 itself does not have magnetism. If too much is added, the material density will decrease at the same sintering temperature and the overall magnetic properties will decrease; if too little is added, it will not be able to effectively prevent the grain growth during the sintering process, and will also lead to a significant increase in material loss.

[0076] In a preferred embodiment, the molar ratio of the sintering-promoting auxiliary agent precursor to the ferrite base material in step S2 is 0.01-0.20:1, preferably 0.02-0.10:1.

[0077] The sintering aid precursor is converted into Bi2O3 after heat treatment. If too much is added, the Co2Z ferrite will easily experience abnormal grain growth during the sintering process, resulting in a significant increase in material loss; if too little is added, sintering will become difficult. At the same sintering temperature, the density of the obtained Co2Z ferrite material will decrease, and the overall magnetic properties of the material will decrease.

[0078] In a preferred embodiment, the alcohol solvent is ethanol, propanol or isopropanol.

[0079] Taking cost into consideration, ethanol is preferred.

[0080] In a preferred embodiment, the acid is hydrochloric acid or nitric acid.

[0081] In a preferred embodiment, the volume ratio of the auxiliary agent precursor for limiting grain growth during sintering, alcohol solvent, deionized water, and acid is y:300:(2500-y):200; 1260>y>6.3.

[0082] The influence of the amount of additive precursor added: If there is too much additive precursor, the concentration of the obtained sol is too high, the viscosity is high, and the stability is reduced. Too high viscosity is not conducive to the coating of the sol on the powder surface, and the reduced stability is not conducive to the storage of the sol; if there is too little additive precursor, the concentration of the obtained sol is too low, which is not conducive to the sol forming a film layer of a certain thickness on the powder surface, and the effect of limiting the grain growth during the sintering process is not obvious;

[0083] The influence of the amount of alcohol solvent added: If the alcohol solvent is too little, the additive precursor (TEOS) cannot be fully dissolved. When the acid and water solvents are added dropwise in the next step, the sol is prone to white precipitation, and the uniformity and stability of the sol are reduced. If the alcohol solvent is too much, when the sol is coated on the surface of the ferrite powder, the boiling point of the alcohol is significantly lower than that of water during the drying process, and it evaporates too quickly, which can easily cause the film layer to crack.

[0084] The influence of water addition: Too much water will lead to too low sol concentration, which has the same effect as too much alcohol solvent. In addition, too much water will also lead to too low acid concentration (because the acid concentration and the added volume are fixed), which is not conducive to promoting the hydrolysis of the additive precursor (TEOS), thereby reducing the film-forming effect of the sol. Too little water will lead to too high sol concentration, which has the same effect as too much additive precursor.

[0085] The influence of the amount of acid added: If too little acid is added, the effect is similar to that of too much water; if too much acid is added, the pH of the sol will decrease, the hydrolysis of the additive precursor (TEOS) will be accelerated, the viscosity of the sol will increase, and the stability will decrease.

[0086] In a preferred embodiment, the molar concentration of the auxiliary agent precursor that limits grain growth during sintering is 0.01-2.00 mol·L -1 .

[0087] In a preferred embodiment, 630>y>12.6.

[0088] In a preferred embodiment, the molar concentration of the auxiliary agent precursor that limits grain growth during sintering is 0.02-1.00 mol·L -1 .

[0089] In a preferred embodiment, in the composite sol, Bi 3+ The molar concentration is 1.50-15.0×10 - 3 mol L -1 , preferably 4.00-10.0×10 -3 mol L -1 .

[0090] In a preferred embodiment, the ratio of the ferrite base material to the composite sol in step S3 is: 0.5-5 ml sol / 1 g powder, preferably 1.0-4.0 ml solution / 1 g powder.

[0091] If the ratio is too large, it means that the amount of sintering aid and inhibitor added is too much at the same time. First of all, sintering aid and inhibitor are both non-magnetic materials. If they are added in excessive amounts, the overall magnetic properties of the ferrite material will decrease after sintering.

[0092] If the ratio is too small, it means that the amount of sintering aid and inhibitor added is too small at the same time, which will cause the density of ferrite to decrease significantly after sintering, and thus the magnetic properties will decrease.

[0093] In a preferred embodiment, the ball milling in step S3 uses corundum balls as grinding balls, the ball milling time is 4-8 hours, and the ball mill speed is 200-600 rpm. -1.

[0094] In a preferred embodiment, the heating rate of the heat treatment process in step S3 is 0.2-4°C·min -1 The heat treatment temperature is 200-800℃ and the sintering time is 0.2-4h.

[0095] The heat treatment process is essentially the process by which the dried gel shrinks and forms an oxide network. A certain amount of Si-OH, Al-OR (organic functional groups), and Bi-OH functional groups still exist in the dried xerogel; after heat treatment, a network structure such as Si-O-Si-O-, Si-O-Bi-O-, or Bi-O-Bi- is formed. The xerogel coated on the particle surface has a certain thickness. When the heating rate is too fast, the surface of the gel first dehydrates or dealcoholizes and shrinks, forming a dense network, while the interior of the gel has not yet completed these reactions and will continue to dehydrate or dealcoholize. Because the surface layer is dense, the water or alcohol inside cannot escape quickly and remains within the film layer. As the temperature rises, the volume of the vapor formed by water and alcohol will rapidly increase, ultimately causing the gel film layer to rupture. However, if the heating rate is too slow, production efficiency is low and energy consumption is high.

[0096] If the holding time is too short, the dehydration / dealcoholization reaction of the gel cannot be completed completely, and these reactions will be completed in the next ferrite sintering process (because the sintering process temperature is higher), and the water or alcohol produced by the reaction will escape from the inside of the block material in the form of vapor, causing the ferrite to crack and the magnetic properties to deteriorate; if the holding time is too long, the production efficiency is low and the energy consumption is high.

[0097] The heat treatment temperature is determined by thermogravimetry. If the temperature is too low, the dehydration / dealcoholization reaction of the gel after drying cannot be carried out thoroughly, and the result is similar to that of a short holding time. If the temperature is too high, the ferrite powder may stick together due to the initial sintering, which is not conducive to the uniform mixing with the binder in the next ball milling process.

[0098] In a preferred embodiment, the heating rate of sintering in step S3 is 0.5-2°C·min -1 , the sintering temperature is 300-700℃, and the sintering time is 0.5-2h.

[0099] In a preferred embodiment, the ball milling medium in step S4 is water, and corundum balls are used as grinding balls; and the mass ratio of material, balls and water during the ball milling process is 1:2:1-2.

[0100] In a preferred embodiment, the binder in step S4 is a polyvinyl alcohol aqueous solution, a carboxymethyl cellulose aqueous solution or a dextrin aqueous solution.

[0101] In a preferred embodiment, the concentration of the binder in step S4 is 8-12 wt %.

[0102] If the binder concentration is too low, a large amount of binder aqueous solution will need to be added to ensure that the amount of PVA added reaches a certain value in order to obtain a green body (the unsintered sample after the granulated powder is molded) with a certain strength. This is because the green body needs to be dried after molding before sintering, which will cause water to evaporate and lead to a higher porosity in the green body. As a result, under the same sintering process, the resulting ferrite has a lower bulk density and unsatisfactory magnetic properties.

[0103] If the concentration of the binder is too high, its viscosity will be high, and it will not be easy to mix it with the ferrite powder during the ball milling process. The distribution of the binder in the granulated powder will be uneven, and the green body after molding will have obvious defects. For example, the powder without binder cannot be molded or has low strength. It will also lead to uneven density of the ferrite after sintering, reduced performance, and poor batch stability.

[0104] In a preferred embodiment, the amount of the binder added in step S4 is 5-15 wt % of the mass of the material to be ground.

[0105] If the amount of binder added is too little, the green body will have low strength and density, which will make it easy to break. In addition, the density of the ferrite after sintering will be poor and the magnetic properties will be low.

[0106] If too much binder is added, the moisture content in the green body will be high, and the content of organic PVA will also be high. As a result, the density of the green body after drying will be low. At the same time, PVA will decompose or be oxidized during the debinding process. Both of these factors will lead to low density and poor magnetic properties of the ferrite after sintering.

[0107] In a preferred embodiment, the ball milling time in step S4 is 0.5-6.0 hours, and the ball mill speed is 50-400 rpm. -1 .

[0108] In a preferred embodiment, the ball milling time in step S4 is 1-5 hours, and the ball mill speed is 100-300 rpm. -1 .

[0109] Spray granulation and compression molding are relatively mature existing technologies.

[0110] In a preferred embodiment, the spray granulation process is as follows: the solid content of the slurry is 40-55wt%, and the binder content is 0.5-1.0wt%; during the spray granulation process, the hot air temperature at the dryer inlet is 350-400°C, and the outlet temperature is 90-110°C.

[0111] In a preferred embodiment, the compression molding process is as follows: the granulated powder is placed in a mold of a desired diameter, and the mold is formed using a pressure of 60-80 MPa and maintained at the pressure for 1 minute.

[0112] In a preferred embodiment, the green body in step S4 is dried at a temperature of 60-90° C. for 20-30 hours.

[0113] In a preferred embodiment, the heating rate of sintering in step S4 is 1-6°C·min -1 , sintering temperature is: 600-1300℃, and sintering time is 1-8h.

[0114] Influence of sintering temperature: If the temperature is too low, sintering cannot be performed and the density of ferrite is poor; if the temperature is too high, ferrite will experience abnormal grain growth and surface decomposition. These factors will lead to lower magnetic properties of ferrite after sintering.

[0115] Influence of heating rate: If the heating rate is too fast, the trace moisture in the green body and the gaseous products produced by the decomposition or oxidation of PVA in the binder removal process cannot be discharged in time, which will cause cracks or even cracks in the block, making it waste and unusable. If the heating rate is too fast, it is not a problem in principle, but it will lead to reduced production efficiency and increased energy consumption.

[0116] Influence of holding time: If the holding time is too short, the sintering densification process will not be thorough, resulting in low density and unsatisfactory magnetic properties of the ferrite after sintering. If the holding time is too long, the ferrite grains will grow abnormally and a small amount of surface ferrite will decompose, which will lead to a decrease in ferrite performance. It will also lead to increased energy consumption and reduced production efficiency.

[0117] In a preferred embodiment, the heating rate of sintering in step S4 is 1.5-4.5°C·min -1 , sintering temperature is: 800-1200℃, and sintering time is 2-6h.

[0118] Based on the same inventive concept, the present invention also claims to protect the application of the iron-deficient Co2Z type ferrite in the preparation of substrate materials for mobile phone antennas, which is particularly suitable for the high frequency and miniaturization requirements of 5G mobile phone antennas.

[0119] The present invention is further explained below:

[0120] The present invention reduces the magnetic loss of the material at high frequencies by designing an iron-deficient formula of the base phase powder;

[0121] By quenching the base phase powder with Re2+ salt solution, first, the particle size can be refined and the sintering activity of the base phase powder can be improved. Second, the alkaline earth metal ions Re2+ with a smaller radius enter the lattice of the surface layer of the base phase powder, forming a special structure with "distorted outer layer structure and complete inner layer lattice", which reduces the magnetic permeability of the powder and increases its cutoff frequency. Third, abundant hydroxyl-containing functional groups are generated on the surface of the powder, which improves the uniformity of the composite film wrapping around the base phase powder.

[0122] Using Re 2+ High electronegativity (electron acceptor) increases the grain resistance of the base material and reduces the electrical loss of the material at high frequencies;

[0123] The base phase powder after salt solution water quenching is coated with Bi2O3-SiO2 composite sol to improve the uniformity of ferrite grains after sintering and reduce the sintering temperature;

[0124] The hydroxyl functional groups on the surface of the base phase powder after water quenching with salt solution and the good film-forming property of the composite sol are utilized to achieve uniform coating of the base material particles. The low melting point of Bi2O3 can promote sintering and reduce the sintering temperature of the material. The high melting point of SiO2 can limit the growth of the base material grains during the sintering process, and effectively control the grain size and uniformity of the ferrite material after sintering, thereby optimizing the magnetic properties of the material. The SiO2 layer also reduces the grain boundary resistivity of the material, ultimately reducing the material's electrical loss at high frequencies.

[0125] The iron-deficient Co2Z-type ferrite obtained by the present invention has low loss and high cutoff frequency at ultra-high frequency at a relatively low sintering temperature, can be used as a substrate material for mobile phone antennas, and is suitable for the high-frequency and miniaturization requirements of 5G mobile phone antennas.

[0126] From a theoretical point of view, as long as the expected goals can be achieved, it is natural to hope that the amount of oxide sintering aids and grain growth inhibitors added directly in other literature and patents is as small as possible, because both additives are non-magnetic materials and the sintering process is mainly located at the grain boundaries. Therefore, as long as they are added, from the perspective of composition, they will have a negative impact on the overall performance of the ferrite after sintering.

[0127] Based on this, when the addition amount is fixed, it is hoped that the sintering aid and grain growth inhibitor can be evenly dispersed in the base phase powder through ball milling. In this way, the two additives can maximize their effectiveness during the sintering process, thereby improving the magnetic properties of the sintered ferrite. However, in reality, when the two additives are added in the form of particles, at a certain addition amount, they cannot be evenly mixed with the base phase powder, resulting in a decrease in the performance of the ferrite material after sintering. Therefore, in practice, this problem is often solved by increasing the addition amount of both.

[0128] In the present invention, it is proposed to add the two additives in the form of a sol. Since the sol is a liquid phase, the uniformity of the mixing of the two additives with the base phase powder can be greatly improved during the ball milling mixing process of the sol and the base phase powder. Then, through heat treatment, the TEOS and Bi-N in the sol are converted into two additives, SiO2 and Bi2O3.

[0129] The specific effects of the salt solution water quenching in the present invention are as follows: the hydroxyl functional groups existing on the surface of the base phase powder after the salt solution water quenching and the good film-forming property of the composite sol are utilized to achieve uniform coating of the base material particles, wherein the low melting point of Bi2O3 can promote sintering and reduce the sintering temperature of the material; the high melting point of SiO2 can limit the growth of the base material grains during the sintering process, thereby achieving effective control of the grain size and uniformity of the ferrite material after sintering, thereby achieving optimization of the material's magnetic properties; the SiO2 layer simultaneously reduces the grain boundary resistivity of the material, ultimately reducing the material's electrical loss at high frequencies.

[0130] The principle of salt solution water quenching-sol coating is explained as follows: The core of salt solution water quenching is to pour the base phase powder at high temperature directly into the salt solution. First, the temperature difference between the surface and the interior of the particles is used to utilize the thermal expansion and contraction phenomenon to achieve powder crushing, that is, powder particle size refinement; second, at high temperature, the powder surface can undergo certain chemical reactions with the water in the salt solution, generating a large number of hydroxyl functional groups on the surface of the powder particles, such as Ba-OH / Co-OH / Fe-OH, etc. In the next step of sol stirring and ball milling, these hydroxyl functional groups on the powder surface can combine with similar functional groups in the sol through hydrogen bonds, thereby improving the binding between the sol and the particle surface, and then improving the uniformity of the sol coating of the particles. That is, through the form of sol, combined with the hydroxyl functional groups generated by salt solution water quenching, the small amount of non-magnetic components (Bi2O3 and SiO2) added to the powder particles can be uniformly coated, thereby effectively realizing the independent function of each component.

[0131] The beneficial effects of the present invention are:

[0132] 1. Reduce the magnetic loss of the material at high frequency through the iron-deficient formula design of the base material;

[0133] 2. Re-processing the base phase powder 2+ Salt solution quenching, first, can refine the particle size and improve the sintering activity of the base phase powder; second, the alkaline earth metal ions with smaller radius Re 2+ It enters the crystal lattice of the base phase powder surface, forming a special structure of "distorted outer layer structure and complete inner layer lattice", reducing the magnetic permeability of the powder and increasing its cutoff frequency; thirdly, it produces abundant hydroxyl-containing functional groups on the powder surface, improving the uniformity of the composite film wrapping the base phase powder;

[0134] 3. Use Re 2+High electronegativity (electron acceptor) improves the grain resistance of the base material, and reduces the electrical loss of the material at high frequency;

[0135] 4 The base phase powder after water quenching of the salt solution is wrapped with a composite sol, which improves the uniformity of the ferrite crystal grains after sintering and reduces the sintering temperature;

[0136] Compared with the direct addition of oxide sintering aids and grain growth inhibitors adopted in other documents and patents, the method of the present application is realized by adopting a liquid phase method, i.e. sol immersion combined with heat treatment, and has the advantages of small addition amount, easy realization of uniform distribution of the aids in the base phase powder, etc. BRIEF DESCRIPTION OF DRAWINGS

[0137] Figure 1 XRD patterns of the sintered materials obtained in Examples 1, 2 and 3 and Comparative Example 4;

[0138] Figure 2 Particle size distribution curves of the base phase powders obtained by water quenching of the salt solution in Example 1 and pure water in Comparative Example 4;

[0139] Figure 3 Scanning electron microscope photos of the base phase powders obtained by water quenching of the salt solution in Example 1 and pure water in Comparative Example 4;

[0140] Figure 4 SEM photos and EDS patterns of the sintered materials in Example 1;

[0141] Figure 5 SEM photos and EDS patterns of the sintered materials in Comparative Example 4;

[0142] Figure 6 Real part curves of the magnetic permeability of the sintered ferrite materials obtained in Examples 1, 2 and 3 and Comparative Example 4;

[0143] Figure 7 Real part curves of the dielectric constant of the sintered ferrite materials obtained in Examples 1, 2 and 3 and Comparative Example 4; DETAILED DESCRIPTION

[0144] The technical solutions of the present application will be further illustrated below through specific examples. Those skilled in the art should understand that the examples are only used to help understand the present application and should not be regarded as specific limitations on the present application.

[0145] Example 1

[0146] (1) Drying and weighing of the powders: μm-BaO, μm-CoO and μm-Fe2O3 powders were dried at 80°C for 24h, and then μm-BaO 445g, μm-CoO 150g and μm-Fe2O3 1692g were weighed respectively for standby;

[0147] (2) Preparation of alkaline earth metal salt solution: Dissolve a certain amount of Ca(NO3)2·4H2O in water in the corresponding ratio of 70.85g Ca(NO3)2·4H2O to 1000g water to obtain about 0.3mol L -1 Ca 2+ Ionic aqueous solution;

[0148] (3) Preparation of composite sol: SiO2 sol was prepared according to the ratio of HCl:H2O:TEOS:C2H5OH of 200:2468.5:31.5:300 (volume ratio) as follows: 200 ml HCl (1.0 mol L -1 ) and 2468.5 ml H2O mixed evenly - marked as solution A; 31.5 ml TEOS and 300 ml C2H5OH mixed evenly, marked as solution B; solution B was added dropwise to solution A under stirring at a rate of 50 mL·h -1 After the addition is complete, stir for 1 hour to obtain SiO2 sol; then add 12.50g Bi(NO3)3·5H2O to the sol, stir and dissolve, continue stirring the composite sol at room temperature for 24 hours, and then seal to obtain a stable composite sol, in which Bi 3+ The concentration is about 8.59×10 -3 mol L -1 The concentration of TEOS is about 0.05 mol L -1 ;

[0149] (4) Synthesis of base phase powder and salt solution quenching: Weighed μm-BaO, μm-CoO and μm-Fe2O3 powders were added to a corundum ball mill, with ethanol as the medium and corundum balls as the grinding balls. The ratio of powder: ball: ethanol was 1:2:2 (mass ratio), the ball milling time was 4 h, and the ball mill speed was 400 rpm. -1 The slurry was dried at 80℃ for 24h and then heated in a box furnace at 5℃·min -1 After heating to 1250℃ and holding for 2.5h, an iron-deficient Co2Z-type ferrite matrix powder with a composition of 2.9BaO·2CoO·10.6Fe2O3 was obtained; the matrix powder was then heated to 2℃·min -1 The cooling rate was reduced to 700℃ and kept at this temperature for 0.5h. The powder was taken out and poured directly into a certain volume of alkaline earth metal nitrate solution at 25℃ (the ratio of salt solution to base phase powder was 100ml solution: 1g powder). -1The suspension was stirred for 2 hours and then allowed to stand for 24 hours. The supernatant was removed and the precipitate was washed three times by centrifugation with H2O. The resulting powder was dried at 80°C for 24 hours to obtain a 2.9BaO·x1(CaO)·2CoO·10.6Fe2O3-based phase powder with fine particle size, rich surface hydroxyl functional groups, and "distorted outer layer structure and complete inner layer lattice".

[0150] (5) Preparation of core-shell structure composite powder: a certain amount of base phase powder quenched with salt solution was poured into a certain volume of Bi2O3-SiO2 composite sol at 25°C (the ratio of base phase powder to composite sol was: 1g powder: 2ml sol), and the mixture was stirred at 300 rpm. -1 The suspension was stirred at a speed of 1.0 h, and then the suspension was transferred to a ball mill, and ball milled for 6 h with corundum balls as grinding balls at a ball mill speed of 400 rpm. -1 The slurry was then dried at 80°C under stirring and then heated to 1.0°C·min -1 The temperature was raised to 600°C and kept for 1.0h to obtain a composite powder of Bi2O3-SiO2 film coated with a base phase fine powder after salt solution water quenching;

[0151] (6) Ball milling and sintering of composite powder: The composite powder was added to a corundum ball mill, with water as the ball milling medium and corundum balls as the grinding balls. The material: ball: water ratio was 1:2:2 (mass ratio). A PVA aqueous solution containing 10 wt% of the total mass of the powder was added and the powder was ball milled for 4.0 h at a ball mill speed of 300 rpm. -1 The slurry after ball milling was spray granulated and molded to obtain a green body; the green body was dried at 80℃ for 24h and then heated at 2.0℃·mim -1 The temperature was raised to 1000°C and kept at this temperature for 3.0 hours to obtain the target material.

[0152] Example 2

[0153] (1) Drying and weighing of powders: Dry the three powders of μm-BaO, μm-CoO and μm-Fe2O3 at 80℃ for 24h, and then weigh 445g of μm-BaO, 150g of μm-CoO and 1692g of μm-Fe2O3 respectively for use;

[0154] (2) Preparation of alkaline earth metal salt solution: Dissolve a certain amount of Ca(NO3)2·4H2O in water in the corresponding ratio of 63.49 g Sr(NO3)2:1000 g water to obtain about 0.3 mol L -1 Sr 2+ Ionic aqueous solution;

[0155] (3) Preparation of composite sol: SiO2 sol was prepared according to the ratio of HCl:H2O:TEOS:C2H5OH of 200:2468.5:31.5:300 (volume ratio) as follows: 200 ml HCl (1.0 mol L -1 ) and 2468.5 ml H2O mixed evenly - marked as solution A; 31.5 ml TEOS and 300 ml C2H5OH mixed evenly, marked as solution B; solution B was added dropwise to solution A under stirring at a rate of 50 mL·h -1 After the addition is complete, stir for 1 hour to obtain SiO2 sol; then add 12.50g Bi(NO3)3·5H2O to the sol, stir and dissolve, continue stirring the composite sol at room temperature for 24 hours, and then seal to obtain a stable composite sol, in which Bi 3+ The concentration is about 8.59×10 -3 mol L -1 The concentration of TEOS is about 0.05 mol L -1 ;

[0156] (4) Synthesis of base phase powder and salt solution quenching: Weighed μm-BaO, μm-CoO and μm-Fe2O3 powders were added to a corundum ball mill, with ethanol as the medium and corundum balls as the grinding balls. The ratio of powder: ball: ethanol was 1:2:2 (mass ratio), the ball milling time was 4 h, and the ball mill speed was 400 rpm. -1 The slurry was dried at 80℃ for 24h and then heated in a box furnace at 5℃·min -1 After heating to 1250℃ and holding for 2.5h, an iron-deficient Co2Z-type ferrite matrix powder with a composition of 2.9BaO·2CoO·10.6Fe2O3 was obtained; the matrix powder was then heated to 2℃·min -1 The cooling rate was reduced to 700℃ and kept at this temperature for 0.5h. The powder was taken out and poured directly into a certain volume of alkaline earth metal nitrate solution at 25℃ (the ratio of salt solution to base phase powder was 100ml solution: 1g powder). -1 The suspension was stirred for 2 hours and then allowed to stand for 24 hours. The supernatant was removed and the precipitate was washed three times by centrifugation with H2O. The resulting powder was dried at 80°C for 24 hours to obtain a 2.9BaO·x2(SrO)·2CoO·10.6Fe2O3-based phase powder with fine particle size, rich surface hydroxyl functional groups, and "distorted outer layer structure and complete inner layer lattice".

[0157] (5) Preparation of core-shell structure composite powder: a certain amount of base phase powder quenched with salt solution was poured into a certain volume of Bi2O3-SiO2 composite sol at 25°C (the ratio of base phase powder to composite sol was: 1g powder: 2ml sol), and the mixture was stirred at 300 rpm. -1 The suspension was stirred at a speed of 1.0 h, and then the suspension was transferred to a ball mill, and ball milled for 6 h with corundum balls as grinding balls at a ball mill speed of 400 rpm. -1 The slurry was then dried at 80°C under stirring and then heated to 1.0°C·min -1 The temperature was raised to 600°C and kept for 1.0h to obtain a composite powder of Bi2O3-SiO2 film coated with a base phase fine powder after water quenching with a salt solution;

[0158] (6) Ball milling and sintering of composite powder: The composite powder was added to a corundum ball mill, with water as the ball milling medium and corundum balls as the grinding balls. The material: ball: water ratio was 1:2:2 (mass ratio). A PVA aqueous solution containing 10 wt% of the total mass of the powder was added and the powder was ball milled for 4.0 h at a ball mill speed of 300 rpm. -1 The slurry after ball milling was spray granulated and molded to obtain a green body; the green body was dried at 80℃ for 24h and then heated at 2.0℃·mim -1 The temperature was raised to 1000°C and kept for 3.0 hours to obtain the target material.

[0159] Example 3

[0160] (1) Drying and weighing of powders: Dry the three powders of μm-BaO, μm-CoO and μm-Fe2O3 at 80℃ for 24h, and then weigh 445g of μm-BaO, 150g of μm-CoO and 1692g of μm-Fe2O3 respectively for use;

[0161] (2) Preparation of alkaline earth metal salt solution: Dissolve a certain amount of Ca(NO3)2·4H2O in water in the corresponding ratio of 76.92g Mg(NO3)2·6H2O:1000g water to obtain about 0.3mol L -1 Mg 2+ Ionic aqueous solution;

[0162] (3) Preparation of composite sol: SiO2 sol was prepared according to the ratio of HCl:H2O:TEOS:C2H5OH of 200:2468.5:31.5:300 (volume ratio) as follows: 200 ml HCl (1.0 mol L -1) and 2468.5 ml H2O mixed evenly - marked as solution A; 31.5 ml TEOS and 300 ml C2H5OH mixed evenly, marked as solution B; solution B was added dropwise to solution A under stirring at a rate of 50 mL·h -1 After the addition is complete, stir for 1 hour to obtain SiO2 sol; then add 12.50g Bi(NO3)3·5H2O to the sol, stir and dissolve, continue stirring the composite sol at room temperature for 24 hours, and then seal to obtain a stable composite sol, in which Bi 3+ The concentration is about 8.59×10 -3 mol L -1 The concentration of TEOS is about 0.05 mol L -1 ;

[0163] (4) Synthesis of base phase powder and salt solution quenching: Weighed μm-BaO, μm-CoO and μm-Fe2O3 powders were added to a corundum ball mill, with ethanol as the medium and corundum balls as the grinding balls. The ratio of powder: ball: ethanol was 1:2:2 (mass ratio), the ball milling time was 4 h, and the ball mill speed was 400 rpm. -1 The slurry was dried at 80℃ for 24h and then heated in a box furnace at 5℃·min -1 After heating to 1250℃ and holding for 2.5h, an iron-deficient Co2Z-type ferrite matrix powder with a composition of 2.9BaO·2CoO·10.6Fe2O3 was obtained; the matrix powder was then heated to 2℃·min -1 The cooling rate was reduced to 700℃ and kept at this temperature for 0.5h. The powder was taken out and poured directly into a certain volume of alkaline earth metal nitrate solution at 25℃ (the ratio of salt solution to base phase powder was 100ml solution: 1g powder). -1 The suspension was stirred for 2 hours and then allowed to stand for 24 hours. The supernatant was removed and the precipitate was washed three times by centrifugation with H2O. The resulting powder was dried at 80°C for 24 hours to obtain a 2.9BaO·x3(MgO)·2CoO·10.6Fe2O3-based phase powder with fine particle size, rich surface hydroxyl functional groups, and "distorted outer layer structure and complete inner layer lattice".

[0164] (5) Preparation of core-shell structure composite powder: a certain amount of base phase powder quenched with salt solution was poured into a certain volume of Bi2O3-SiO2 composite sol at 25°C (the ratio of base phase powder to composite sol was: 1g powder: 2ml sol), and the mixture was stirred at 300 rpm. -1 The suspension was stirred at a speed of 1.0 h, and then the suspension was transferred to a ball mill, and ball milled for 6 h with corundum balls as grinding balls at a ball mill speed of 400 rpm. -1The slurry was then dried at 80°C under stirring and then heated to 1.0°C·min -1 The temperature was raised to 600°C and kept for 1.0h to obtain a composite powder of Bi2O3-SiO2 film coated with a base phase fine powder after water quenching with a salt solution;

[0165] (6) Ball milling and sintering of composite powder: The composite powder was added to a corundum ball mill, with water as the ball milling medium and corundum balls as the grinding balls. The material: ball: water ratio was 1:2:2 (mass ratio). A PVA aqueous solution containing 10 wt% of the total mass of the powder was added and the powder was ball milled for 4.0 h at a ball mill speed of 300 rpm. -1 The slurry after ball milling was spray granulated and molded to obtain a green body; the green body was dried at 80℃ for 24h and then heated at 2.0℃·mim -1 The temperature was raised to 1000°C and kept for 3.0 hours to obtain the target material.

[0166] Comparative Example 1: Reducing Ca 2+ The concentration of ions is 0.15 mol L -1 (Originally 0.30 mol L -1 )

[0167] (1) Drying and weighing of powders: Dry the three powders of μm-BaO, μm-CoO and μm-Fe2O3 at 80℃ for 24h, and then weigh 445g of μm-BaO, 150g of μm-CoO and 1692g of μm-Fe2O3 respectively for use;

[0168] (2) Preparation of alkaline earth metal salt solution: Dissolve a certain amount of Ca(NO3)2·4H2O in water at a ratio of 35.42 g Ca(NO3)2·4H2O to 1000 g water to obtain about 0.15 mol L -1 Ca 2+ Ionic aqueous solution;

[0169] (3) Preparation of composite sol: SiO2 sol was prepared according to the ratio of HCl:H2O:TEOS:C2H5OH of 200:2468.5:31.5:300 (volume ratio) as follows: 200 ml HCl (1.0 mol L -1 ) and 2468.5 ml H2O mixed evenly - marked as solution A; 31.5 ml TEOS and 300 ml C2H5OH mixed evenly, marked as solution B; solution B was added dropwise to solution A under stirring at a rate of 50 mL·h -1After the addition is complete, stir for 1 hour to obtain SiO2 sol; then add 12.50g Bi(NO3)3·5H2O to the sol, stir and dissolve, continue stirring the composite sol at room temperature for 24 hours, and then seal to obtain a stable composite sol, in which Bi 3+ The concentration is about 8.59×10 -3 mol L -1 The concentration of TEOS is about 0.05 mol L -1 ;

[0170] (4) Synthesis of base phase powder and salt solution quenching: Weighed μm-BaO, μm-CoO and μm-Fe2O3 powders were added to a corundum ball mill, with ethanol as the medium and corundum balls as the grinding balls. The ratio of powder: ball: ethanol was 1:2:2 (mass ratio), the ball milling time was 4 h, and the ball mill speed was 400 rpm. -1 The slurry was dried at 80℃ for 24h and then heated in a box furnace at 5℃·min -1 After heating to 1250℃ and holding for 2.5h, an iron-deficient Co2Z-type ferrite matrix powder with a composition of 2.9BaO·2CoO·10.6Fe2O3 was obtained; the matrix powder was then heated to 2℃·min -1 The cooling rate was reduced to 700℃ and kept at this temperature for 0.5h. The powder was taken out and poured directly into a certain volume of alkaline earth metal nitrate solution at 25℃ (the ratio of salt solution to base phase powder was 100ml solution: 1g powder). -1 The suspension was stirred for 2 hours and then allowed to stand for 24 hours. The supernatant was removed and the precipitate was washed three times by centrifugation with H2O. The resulting powder was dried at 80°C for 24 hours to obtain a 2.9BaO·x4(CaO)·2CoO·10.6Fe2O3-based phase powder with fine particle size, rich surface hydroxyl functional groups, and "distorted outer layer structure and complete inner layer lattice".

[0171] (5) Preparation of core-shell structure composite powder: a certain amount of base phase powder quenched with salt solution was poured into a certain volume of Bi2O3-SiO2 composite sol at 25°C (the ratio of base phase powder to composite sol was: 1g powder: 2ml sol), and the mixture was stirred at 300 rpm. -1 The suspension was stirred at a speed of 1.0 h, and then the suspension was transferred to a ball mill, and ball milled for 6 h with corundum balls as grinding balls at a ball mill speed of 400 rpm. -1 The slurry was then dried at 80°C under stirring and then heated to 1.0°C·min -1 The temperature was raised to 600°C and kept for 1.0h to obtain a composite powder of Bi2O3-SiO2 film coated with a base phase fine powder after water quenching with a salt solution;

[0172] (6) Ball milling and sintering of composite powder: The composite powder was added to a corundum ball mill, with water as the ball milling medium and corundum balls as the grinding balls. The material: ball: water ratio was 1:2:2 (mass ratio). A PVA aqueous solution containing 10 wt% of the total mass of the powder was added and the powder was ball milled for 4.0 h at a ball mill speed of 300 rpm. -1 The slurry after ball milling was spray granulated and molded to obtain a green body; the green body was dried at 80℃ for 24h and then heated at 2.0℃·mim -1 The temperature was raised to 1000°C and kept at this temperature for 3.0 hours to obtain the target material.

[0173] Comparative Example 2: Adding Ca 2+ The concentration of ions is 0.60 mol L -1 (Originally 0.30 mol L -1 )

[0174] (1) Drying and weighing of powders: Dry the three powders of μm-BaO, μm-CoO and μm-Fe2O3 at 80℃ for 24h, and then weigh 445g of μm-BaO, 150g of μm-CoO and 1692g of μm-Fe2O3 respectively for use;

[0175] (2) Preparation of alkaline earth metal salt solution: According to the ratio of 141.69g Ca(NO3)2·4H2O:1000g water, a certain amount of Ca(NO3)2·4H2O was dissolved in water in the corresponding proportion to obtain about 0.6mol L -1 Ca 2+ Ionic aqueous solution;

[0176] (3) Preparation of composite sol: SiO2 sol was prepared according to the ratio of HCl:H2O:TEOS:C2H5OH of 200:2468.5:31.5:300 (volume ratio) as follows: 200 ml HCl (1.0 mol L -1 ) and 2468.5 ml H2O mixed evenly - marked as solution A; 31.5 ml TEOS and 300 ml C2H5OH mixed evenly, marked as solution B; solution B was added dropwise to solution A under stirring at a rate of 50 mL·h -1 After the addition is complete, stir for 1 hour to obtain SiO2 sol; then add 12.50g Bi(NO3)3·5H2O to the sol, stir and dissolve, continue stirring the composite sol at room temperature for 24 hours, and then seal to obtain a stable composite sol, in which Bi 3+ The concentration is about 8.59×10 -3 mol L -1 The concentration of TEOS is about 0.05 mol L -1 ;

[0177] (4) Synthesis of base phase powder and salt solution quenching: Weighed μm-BaO, μm-CoO and μm-Fe2O3 powders were added to a corundum ball mill, with ethanol as the medium and corundum balls as the grinding balls. The ratio of powder: ball: ethanol was 1:2:2 (mass ratio), the ball milling time was 4 h, and the ball mill speed was 400 rpm. -1 The slurry was dried at 80℃ for 24h and then heated in a box furnace at 5℃·min -1 After heating to 1250℃ and holding for 2.5h, an iron-deficient Co2Z-type ferrite matrix powder with a composition of 2.9BaO·2CoO·10.6Fe2O3 was obtained; the matrix powder was then heated to 2℃·min -1 The cooling rate was reduced to 700℃ and kept at this temperature for 0.5h. The powder was taken out and poured directly into a certain volume of alkaline earth metal nitrate solution at 25℃ (the ratio of salt solution to base phase powder was 100ml solution: 1g powder). -1 The suspension was stirred for 2 hours and then allowed to stand for 24 hours. The supernatant was removed and the precipitate was washed three times by centrifugation with H2O. The resulting powder was dried at 80°C for 24 hours to obtain a 2.9BaO·x5(CaO)·2CoO·10.6Fe2O3-based phase powder with fine particle size, rich surface hydroxyl functional groups, and "distorted outer layer structure and complete inner layer lattice".

[0178] (5) Preparation of core-shell structure composite powder: a certain amount of base phase powder quenched with salt solution was poured into a certain volume of Bi2O3-SiO2 composite sol at 25°C (the ratio of base phase powder to composite sol was: 1g powder: 2ml sol), and the mixture was stirred at 300 rpm. -1 The suspension was stirred at a speed of 1.0 h, and then the suspension was transferred to a ball mill, and ball milled for 6 h with corundum balls as grinding balls at a ball mill speed of 400 rpm. -1 The slurry was then dried at 80°C under stirring and then heated to 1.0°C·min -1 The temperature was raised to 600°C and kept for 1.0h to obtain a composite powder of Bi2O3-SiO2 film coated with a base phase fine powder after salt solution water quenching;

[0179] (6) Ball milling and sintering of composite powder: The composite powder was added to a corundum ball mill, with water as the ball milling medium and corundum balls as the grinding balls. The material: ball: water ratio was 1:2:2 (mass ratio). A PVA aqueous solution containing 10 wt% of the total mass of the powder was added and the powder was ball milled for 4.0 h at a ball mill speed of 300 rpm. -1 The slurry after ball milling was spray granulated and molded to obtain a green body; the green body was dried at 80℃ for 24h and then heated at 2.0℃·mim -1 The temperature was raised to 1000°C and kept at this temperature for 3.0 hours to obtain the target material.

[0180] Comparative Example 3: Lowering the brine quenching temperature to 500°C (originally 700°C)

[0181] (1) Drying and weighing of powders: Dry the three powders of μm-BaO, μm-CoO and μm-Fe2O3 at 80℃ for 24h, and then weigh 445g of μm-BaO, 150g of μm-CoO and 1692g of μm-Fe2O3 respectively for use;

[0182] (2) Preparation of alkaline earth metal salt solution: Dissolve a certain amount of Ca(NO3)2·4H2O in water in the corresponding ratio of 70.85g Ca(NO3)2·4H2O to 1000g water to obtain about 0.3mol L -1 Ca 2+ Ionic aqueous solution;

[0183] (3) Preparation of composite sol: SiO2 sol was prepared according to the ratio of HCl:H2O:TEOS:C2H5OH of 200:2468.5:31.5:300 (volume ratio) as follows: 200 ml HCl (1.0 mol L -1 ) and 2468.5 ml H2O mixed evenly - marked as solution A; 31.5 ml TEOS and 300 ml C2H5OH mixed evenly, marked as solution B; solution B was added dropwise to solution A under stirring at a rate of 50 mL·h -1 After the addition is complete, stir for 1 hour to obtain SiO2 sol; then add 12.50g Bi(NO3)3·5H2O to the sol, stir and dissolve, continue stirring the composite sol at room temperature for 24 hours, and then seal to obtain a stable composite sol, in which Bi 3+ The concentration is about 8.59×10 -3 mol L -1 The concentration of TEOS is about 0.05 mol L -1 ;

[0184] (4) Synthesis of base phase powder and salt solution quenching: Weighed μm-BaO, μm-CoO and μm-Fe2O3 powders were added to a corundum ball mill, with ethanol as the medium and corundum balls as the grinding balls. The ratio of powder: ball: ethanol was 1:2:2 (mass ratio), the ball milling time was 4 h, and the ball mill speed was 400 rpm. -1 The slurry was dried at 80℃ for 24h and then heated in a box furnace at 5℃·min -1After heating to 1250℃ and holding for 2.5h, an iron-deficient Co2Z-type ferrite matrix powder with a composition of 2.9BaO·2CoO·10.6Fe2O3 was obtained; the matrix powder was then heated to 2℃·min -1 The cooling rate was reduced to 500℃ and kept at this temperature for 0.5h. The powder was taken out and poured directly into a certain volume of alkaline earth metal nitrate solution at 25℃ (the ratio of salt solution to base phase powder was 100ml solution: 1g powder). -1 The suspension was stirred for 2 hours and then allowed to stand for 24 hours. The supernatant was removed and the precipitate was washed three times by centrifugation with H2O. The resulting powder was dried at 80°C for 24 hours to obtain a 2.9BaO·x6(CaO)·2CoO·10.6Fe2O3-based phase powder with fine particle size, rich surface hydroxyl functional groups, and "distorted outer layer structure and complete inner layer lattice".

[0185] (5) Preparation of core-shell structure composite powder: a certain amount of base phase powder quenched with salt solution was poured into a certain volume of Bi2O3-SiO2 composite sol at 25°C (the ratio of base phase powder to composite sol was: 1g powder: 2ml sol), and the mixture was stirred at 300 rpm. -1 The suspension was stirred at a speed of 1.0 h, and then the suspension was transferred to a ball mill, and ball milled for 6 h with corundum balls as grinding balls at a ball mill speed of 400 rpm. -1 The slurry was then dried at 80°C under stirring and then heated to 1.0°C·min -1 The temperature was raised to 600°C and kept for 1.0h to obtain a composite powder of Bi2O3-SiO2 film coated with a base phase fine powder after salt solution water quenching;

[0186] (6) Ball milling and sintering of composite powder: The composite powder was added to a corundum ball mill, with water as the ball milling medium and corundum balls as the grinding balls. The material: ball: water ratio was 1:2:2 (mass ratio). A PVA aqueous solution containing 10 wt% of the total mass of the powder was added and the powder was ball milled for 4.0 h at a ball mill speed of 300 rpm. -1 The slurry after ball milling was spray granulated and molded to obtain a green body; the green body was dried at 80℃ for 24h and then heated at 2.0℃·mim -1 The temperature was raised to 1000°C and kept at this temperature for 3.0 hours to obtain the target material.

[0187] The compositions of the powders obtained after quenching the salt solutions of Examples 1-3 and Comparative Examples 1-3 were analyzed, and the analysis results are shown in Table 1.

[0188] Table 1 Composition analysis results of the powders obtained after quenching with salt solution in Examples 1-3 and Comparative Examples 1-3

[0189]

[0190] As can be seen from the table, different salt solution compositions and concentrations all have a certain impact on the composition of the base phase powder obtained after water quenching. The higher the concentration and the higher the water quenching temperature, the greater the concentration of alkaline earth metal ions entering the ferrite lattice.

[0191] Comparative Example 4: water quenching, no salt solution;

[0192] (1) Drying and weighing of powders: Dry the three powders of μm-BaO, μm-CoO and μm-Fe2O3 at 80℃ for 24h, and then weigh 445g of μm-BaO, 150g of μm-CoO and 1692g of μm-Fe2O3 respectively for use;

[0193] (2) Preparation of composite sol: SiO2 sol was prepared according to the ratio of HCl:H2O:TEOS:C2H5OH of 200:2468.5:31.5:300 (volume ratio) as follows: 200 ml HCl (1.0 mol L -1 ) and 2468.5 ml H2O mixed evenly - marked as solution A; 31.5 ml TEOS and 300 ml C2H5OH mixed evenly, marked as solution B; solution B was added dropwise to solution A under stirring at a rate of 50 mL·h -1 After the addition is complete, stir for 1 hour to obtain SiO2 sol; then add 12.50g Bi(NO3)3·5H2O to the sol, stir and dissolve, continue stirring the composite sol at room temperature for 24 hours, and then seal to obtain a stable composite sol, in which Bi 3+ The concentration is about 8.59×10 -3 mol L -1 The concentration of TEOS is about 0.05 mol L -1 ;

[0194] (3) Synthesis and water quenching of base phase powder: Weighed μm-BaO, μm-CoO and μm-Fe2O3 powders were added to a corundum ball mill, using ethanol as the medium and corundum balls as the grinding balls. The ratio of powder: ball: ethanol was 1:2:2 (mass ratio), the ball milling time was 4 h, and the ball mill speed was 400 rpm. -1 The slurry was dried at 80℃ for 24h and then heated in a box furnace at 5℃·min -1 After heating to 1250℃ and holding for 2.5h, an iron-deficient Co2Z-type ferrite matrix powder with a composition of 2.9BaO·2CoO·10.6Fe2O3 was obtained; the matrix powder was then heated to 2℃·min -1The cooling rate was reduced to 700℃ and kept at this temperature for 0.5h. The powder was taken out and poured directly into a certain volume of water at 25℃ (the ratio of water to base phase powder was 100ml water: 1g powder). -1 The suspension was stirred for 2 hours and then allowed to stand for 24 hours. The supernatant was removed and the precipitate was washed three times by centrifugation with H2O. The resulting powder was dried at 80°C for 24 hours to obtain a 2.9BaO·2CoO·10.6Fe2O3-based phase powder with fine particle size, rich surface hydroxyl functional groups, and "distorted outer layer structure and complete inner layer lattice".

[0195] (4) Preparation of core-shell structure composite powder: a certain amount of base phase powder quenched with salt solution was poured into a certain volume of Bi2O3-SiO2 composite sol at 25°C (the ratio of base phase powder to composite sol was: 1g powder: 2ml sol), and the mixture was stirred at 300 rpm. -1 The suspension was stirred at a speed of 1.0 h, and then the suspension was transferred to a ball mill, and ball milled for 6 h with corundum balls as grinding balls at a ball mill speed of 400 rpm. -1 The slurry was then dried at 80°C under stirring and then heated to 1.0°C·min -1 The temperature was raised to 600°C and kept for 1.0h to obtain a composite powder of Bi2O3-SiO2 film coated with a base phase fine powder after water quenching with a salt solution;

[0196] (6) Ball milling and sintering of composite powder: The composite powder was added to a corundum ball mill, with water as the ball milling medium and corundum balls as the grinding balls. The material: ball: water ratio was 1:2:2 (mass ratio). A PVA aqueous solution containing 10 wt% of the total mass of the powder was added and the powder was ball milled for 4.0 h at a ball mill speed of 300 rpm. -1 The slurry after ball milling was spray granulated and molded to obtain a green body; the green body was dried at 80℃ for 24h and then heated at 2.0℃·mim -1 The temperature was raised to 1000°C and kept for 3.0 hours to obtain the target material.

[0197] The XRD patterns of the sintered materials obtained in Examples 1, 2, 3 and Comparative Example 4 are shown in the following table. Figure 1 As shown in the figure, it can be seen that the main phase of the obtained powder is hexagonal Co2Z type ferrite, and the alkaline earth metal ions entering the ferrite lattice due to water quenching with salt solution do not change the original crystal structure of the ferrite.

[0198] The particle size distribution curves of the base phase powder obtained by quenching with salt solution in Example 1 and the base phase powder obtained by quenching with pure water in Comparative Example 4 are shown in Figure 2. Figure 2 As shown in the figure, the particle size of the two powders is not much different, with D50 being 1.30 and 1.35 μm respectively.

[0199] Scanning electron microscope images of the base phase powder obtained by quenching with salt solution in Example 1 and the base phase powder obtained by quenching with pure water in Comparative Example 4 were taken. Figure 3 As shown, a is Example 1, and b is Comparative Example 4. As can be seen from the figure, there is no obvious difference in the particle size of the two powders.

[0200] However, salt solution quenching will migrate alkaline earth metal ions into the ferrite lattice, thereby regulating its properties, while water quenching does not have this function.

[0201] Figure 4 and Figure 5 The SEM images and EDS spectra (polished fracture) of the sintered materials of Example 1 and Comparative Example 4 are respectively. Figure 4 , (a) is the SEM image of Example 1, (a1) the surface distribution of Ba elements in Figure a, (a2) the surface distribution of Co elements in Figure a, and (a3) ​​the surface distribution of Fe elements in Figure a; Figure 5 (b) SEM image of comparative example 4, (b1) Ba element surface distribution in Figure b, (b2) Co element surface distribution in Figure b, (b3) Fe element surface distribution in Figure b, (b4) Bi element surface distribution in Figure b, (b5) Si element surface distribution in Figure b. It can be seen from the figure that the alkaline earth metal ions Ca2+ that enter the ferrite lattice are quenched by water. 2+ ( Figure 4 -a4), as well as the sintering aid Bi2O3 introduced into the ferrite through the sol and the SiO2 as a grain growth inhibitor during the sintering process, are uniformly distributed in the ferrite after sintering.

[0202] The magnetic permeability of the sintered ferrite materials obtained in Examples 1, 2 and 3 and Comparative Example 4 was tested and the results were as follows: Figure 6 The dielectric constants of the sintered ferrite materials obtained in Examples 1, 2, and 3 and Comparative Example 4 were tested and the results were as follows: Figure 7 shown.

[0203] Comparative Example 5: No Si

[0204] (1) Drying and weighing of powders: Dry the three powders of μm-BaO, μm-CoO and μm-Fe2O3 at 80℃ for 24h, and then weigh 445g of μm-BaO, 150g of μm-CoO and 1692g of μm-Fe2O3 respectively for use;

[0205] (2) Preparation of alkaline earth metal salt solution: Dissolve a certain amount of Ca(NO3)2·4H2O in water in the corresponding ratio of 70.85g Ca(NO3)2·4H2O to 1000g water to obtain about 0.3mol L -1 Ca 2+ Ionic aqueous solution;

[0206] (3)Bi 3+ Preparation of solution: Add 12.50g Bi(NO3)3·5H2O into 3000ml water, stir to dissolve and seal to obtain Bi 3+ The concentration is about 8.59×10 -3 mol L -1 aqueous solution;

[0207] (4) Synthesis of base phase powder and salt solution quenching: Weighed μm-BaO, μm-CoO and μm-Fe2O3 powders were added to a corundum ball mill, with ethanol as the medium and corundum balls as the grinding balls. The ratio of powder: ball: ethanol was 1:2:2 (mass ratio), the ball milling time was 4 h, and the ball mill speed was 400 rpm. -1 The slurry was dried at 80℃ for 24h and then heated in a box furnace at 5℃·min -1 After heating to 1250℃ and holding for 2.5h, an iron-deficient Co2Z-type ferrite matrix powder with a composition of 2.9BaO·2CoO·10.6Fe2O3 was obtained; the matrix powder was then heated to 2℃·min -1 The cooling rate was reduced to 700℃ and kept at this temperature for 0.5h. The powder was taken out and poured directly into a certain volume of alkaline earth metal nitrate solution at 25℃ (the ratio of salt solution to base phase powder was 100ml solution: 1g powder). -1 The suspension was stirred for 2 hours and then allowed to stand for 24 hours. The supernatant was removed and the precipitate was washed three times by centrifugation with H2O. The resulting powder was dried at 80°C for 24 hours to obtain a 2.9BaO·x1(CaO)·2CoO·10.6Fe2O3-based phase powder with fine particle size, rich surface hydroxyl functional groups, and "distorted outer layer structure and complete inner layer lattice".

[0208] (5) Preparation of composite powder: Pour a certain amount of base phase powder quenched with salt solution into a certain volume of Bi 3+ The solution (the ratio of base phase powder to composite sol is: 1g powder: 2ml solution) was stirred at 300 rpm. -1 The suspension was stirred at a speed of 1.0 h, and then the suspension was transferred to a ball mill, and ball milled for 6 h with corundum balls as grinding balls at a ball mill speed of 400 rpm. -1 The slurry was then dried at 80°C under stirring and then heated to 1.0°C·min -1 The temperature was raised to 600°C and kept at this temperature for 1.0h to obtain a composite powder of base phase fine powder after water quenching with a salt solution containing Bi2O3 sintering aid;

[0209] (6) Ball milling and sintering of composite powder: The composite powder was added to a corundum ball mill, with water as the ball milling medium and corundum balls as the grinding balls. The material: ball: water ratio was 1:2:2 (mass ratio). A PVA aqueous solution containing 10 wt% of the total mass of the powder was added and the powder was ball milled for 4.0 h at a ball mill speed of 300 rpm. -1 The slurry after ball milling was spray granulated and molded to obtain a green body; the green body was dried at 80℃ for 24h and then heated at 2.0℃·mim -1 The temperature was raised to 1000°C and kept for 3.0 hours to obtain the target material.

[0210] Comparative Example 6: No Bi

[0211] (1) Drying and weighing of powders: Dry the three powders of μm-BaO, μm-CoO and μm-Fe2O3 at 80℃ for 24h, and then weigh 445g of μm-BaO, 150g of μm-CoO and 1692g of μm-Fe2O3 respectively for use;

[0212] (2) Preparation of alkaline earth metal salt solution: Dissolve a certain amount of Ca(NO3)2·4H2O in water in the corresponding ratio of 70.85g Ca(NO3)2·4H2O to 1000g water to obtain about 0.3mol L -1 Ca 2+ Ionic aqueous solution;

[0213] (3) Preparation of SiO2 sol: SiO2 sol was prepared according to the ratio of HCl:H2O:TEOS:C2H5OH of 200:2468.5:31.5:300 (volume ratio) as follows: 200 ml HCl (1.0 mol L -1 ) and 2468.5 ml H2O mixed evenly - marked as solution A; 31.5 ml TEOS and 300 ml C2H5OH mixed evenly, marked as solution B; solution B was added dropwise to solution A under stirring at a rate of 50 mL·h -1 After the addition was complete, the mixture was stirred for 1 h and sealed to obtain SiO2 sol, in which the concentration of TEOS was about 0.05 mol L -1 ;

[0214] (4) Synthesis of base phase powder and salt solution quenching: Weighed μm-BaO, μm-CoO and μm-Fe2O3 powders were added to a corundum ball mill, with ethanol as the medium and corundum balls as the grinding balls. The ratio of powder: ball: ethanol was 1:2:2 (mass ratio), the ball milling time was 4 h, and the ball mill speed was 400 rpm. -1 The slurry was dried at 80℃ for 24h and then heated in a box furnace at 5℃·min -1After heating to 1250℃ and holding for 2.5h, an iron-deficient Co2Z-type ferrite matrix powder with a composition of 2.9BaO·2CoO·10.6Fe2O3 was obtained; the matrix powder was then heated to 2℃·min -1 The cooling rate was reduced to 700℃ and kept at this temperature for 0.5h. The powder was taken out and poured directly into a certain volume of alkaline earth metal nitrate solution at 25℃ (the ratio of salt solution to base phase powder was 100ml solution: 1g powder). -1 The suspension was stirred for 2 hours and then allowed to stand for 24 hours. The supernatant was removed and the precipitate was washed three times by centrifugation with H2O. The resulting powder was dried at 80°C for 24 hours to obtain a 2.9BaO·x1(CaO)·2CoO·10.6Fe2O3-based phase powder with fine particle size, rich surface hydroxyl functional groups, and "distorted outer layer structure and complete inner layer lattice".

[0215] (5) Preparation of core-shell structure composite powder: a certain amount of base phase powder quenched with salt solution was poured into a certain volume of SiO2 sol at 25°C (the ratio of base phase powder to sol was: 1g powder: 2ml sol), and the mixture was stirred at 300 rpm. -1 The suspension was stirred at a speed of 1.0 h, and then the suspension was transferred to a ball mill, and the ball mill was used as a corundum ball for 6 h at a speed of 400 rpm. -1 The slurry was then dried at 80°C under stirring and then heated to 1.0°C·min -1 The temperature was raised to 600°C and kept for 1.0h to obtain a composite powder of SiO2 film-coated base phase fine powder after salt solution water quenching;

[0216] (6) Ball milling and sintering of composite powder: The composite powder was added to a corundum ball mill, with water as the ball milling medium and corundum balls as the grinding balls. The material: ball: water ratio was 1:2:2 (mass ratio). A PVA aqueous solution containing 10 wt% of the total mass of the powder was added and the powder was ball milled for 4.0 h at a ball mill speed of 300 rpm. -1 The slurry after ball milling was spray granulated and molded to obtain a green body; the green body was dried at 80℃ for 24h and then heated at 2.0℃·mim -1 The temperature was raised to 1000°C and kept at this temperature for 3.0 hours to obtain the target material.

[0217] Comparative Example 7: Direct synthesis of doped powder without water quenching, composite sol coating powder

[0218] (1) Drying and weighing of powders: Dry the four powders of μm-BaO, μm-CoO, μm-Fe2O3 and μm-CaCO3 at 80°C for 24 h, and then weigh 445 g of μm-BaO, 150 g of μm-CoO, 1692 g of μm-Fe2O3 and 9.5 g of μm-CaCO3 for later use;

[0219] (2) Preparation of the composite sol: SiO2 sol was prepared according to the ratio of HCl:H2O:TEOS:C2H5OH as 200:2468.5:31.5:300 (volume ratio) as follows: 200 ml of HCl (1.0 mol L -1 ) was mixed with 2468.5 ml of H2O at room temperature to form solution A; 31.5 ml of TEOS and 300 ml of C2H5OH were mixed to form solution B; solution B was added dropwise into solution A under stirring at a rate of 50 mL h -1 , and after the addition was completed, the mixture was stirred for 1 h to obtain SiO2 sol; then 12.50 g of Bi(NO3)3 5H2O was added into the sol, and after stirring and dissolving, the composite sol was continuously stirred at room temperature for 24 h, and then sealed to obtain a stable composite sol, wherein the concentration of Bi 3+ was about 8.59 x 10 -3 mol L -1 , and the concentration of TEOS was about 0.05 mol L -1 ;

[0220] (3) Synthesis of base phase powder: the weighed μm-BaO, μm-CoO, μm-Fe2O3 and μm-CaCO3 powders were added into a corundum ball mill tank, and ethanol was used as medium, wherein the ratio of powder:ball:ethanol was 1:2:2 (mass ratio), the ball milling time was 4 h, and the rotation speed of the ball mill was 400 r / min -1 ; the slurry was dried at 80°C for 24 h, and then was heated in a box furnace at a rate of 5°C / min -1 to 1250°C, and then was kept at 1250°C for 2.5 h, and then was cooled at a rate of 2°C / min -1 to 600°C, and then was cooled in the furnace to obtain base phase powder with a composition of 2.9BaO 0.095(CaO) 2CoO 10.6Fe2O3;

[0221] (4) Preparation of core-shell structure composite powder: a certain amount of base phase powder was poured into a certain volume of Bi2O3-SiO2 composite sol at 25°C (the ratio of base phase powder to composite sol was 1 g of powder:2 ml of sol), and the suspension was stirred at a speed of 300 r / min -1 for 1.0 h, and then the suspension was transferred into a ball mill tank, and corundum balls were used as grinding balls, and the ball milling was performed for 6 h at a rotation speed of 400 r / min -1 ; then the slurry was dried at 80°C under stirring, and then was heated at a rate of 1.0°C / min -1 to 600°C, and then was kept at 600°C for 1.0 h to obtain composite powder of base phase fine powder coated with Bi2O3-SiO2 film;

[0222] (5) Ball milling and sintering of composite powder: The composite powder was added to a corundum ball mill, with water as the ball milling medium and corundum balls as the grinding balls. The material: ball: water ratio was 1:2:2 (mass ratio). A PVA aqueous solution containing 10 wt% of the total mass of the powder was added and the powder was ball milled for 4.0 h at a ball mill speed of 300 rpm. -1 The slurry after ball milling was spray granulated and molded to obtain a green body; the green body was dried at 80℃ for 24h and then heated at 2.0℃·mim -1 The temperature was raised to 1000°C and kept for 3.0 hours to obtain the target material.

[0223] Comparative Example 8: Direct synthesis of doped powder without water quenching, sintering aids and inhibitors are directly added using oxides

[0224] (1) Drying and weighing of powders: Dry six kinds of powders, namely, μm-BaO, μm-CoO, μm-Fe2O3, μm-CaCO3, μm-Bi2O3, and μm-SiO2, at 80°C for 24 h, and then weigh 445 g of μm-BaO, 150 g of μm-CoO, 1692 g of μm-Fe2O3, and 9.5 g of μm-CaCO3 for later use;

[0225] (2) Synthesis of base phase powder: Weighed μm-BaO, μm-CoO, μm-Fe2O3 and μm-CaCO3 powders were added to a corundum ball mill, using ethanol as the medium and corundum balls as the grinding balls. The ratio of powder: ball: ethanol was 1:2:2 (mass ratio), the ball milling time was 4 h, and the ball mill speed was 400 rpm. -1 The slurry was dried at 80℃ for 24h and then heated in a box furnace at 5℃·min -1 After heating to 1250℃ and keeping it for 2.5h, the temperature was then increased to 2℃·min. -1 After the cooling rate is reduced to 600℃, the powder is cooled in the furnace to obtain a base phase powder with a composition of 2.9BaO·0.095(CaO)·2CoO·10.6Fe2O3;

[0226] (3) A certain amount of base phase powder, μm-Bi2O3 (sintering aid) and μm-SiO2 (grain growth inhibitor) were added to a corundum ball mill. The ratio of base phase: Bi2O3: SiO2 was 100:0.5:0.7 (mass ratio). Corundum balls were used as milling balls, ethanol was used as the medium, and the ratio of powder: ball: ethanol was 1:2:2 (mass ratio). The milling time was 4 h and the ball mill speed was 400 rpm. -1 , drying the slurry at 80°C for 24h to obtain a composite powder with sintering aid Bi2O3 and grain growth inhibitor SiO2 added;

[0227] (4) Ball milling and sintering of composite powder: The composite powder was added to a corundum ball mill, with water as the ball milling medium and corundum balls as the grinding balls. The material: ball: water ratio was 1:2:2 (mass ratio). A PVA aqueous solution containing 10 wt% of the total mass of the powder was added and the powder was ball milled for 4.0 h at a speed of 300 rpm. -1 The slurry after ball milling was spray granulated and molded to obtain a green body; the green body was dried at 80℃ for 24h and then heated at 2.0℃·mim -1 The temperature was raised to 1000°C and kept for 3.0 hours to obtain the target material.

[0228] The data of the embodiments and comparative examples are summarized in Table 2.

[0229] Table 2 Main performance parameters of ferrite materials after sintering obtained in different embodiments and comparative examples

[0230]

[0231] *Performance parameters at 1GHz

[0232] It can be seen that the corresponding magnetic properties and loss data are significantly lower than those reported in the current literature.

[0233] The results show:

[0234] Ba 2+ , ionic radius: 0.135nm, electronegativity: 0.89; Ca 2+ Ionic radius: 0.099nm, electronegativity: 1.00); Sr 2+ Ionic radius: 0.113nm, electronegativity: 0.95; Mg 2+ Ionic radius: 0.065nm, electronegativity: 1.31.

[0235] Combining the electronegativity of the three alkaline earth ions and their content in the ferrite lattice (see Table 1) and Table 2, and comparing Examples 1, 2, and 3, it can be seen that with the change in the electronegativity of the doped ions and the amount entering the ferrite lattice, the dielectric loss tangent and the magnetic loss tangent both gradually increase; under similar compositions, the greater the number of doped ions and the greater the structural distortion, the smaller the magnetic permeability and the smaller the magnetic loss at high frequency; the higher the content of the doped ions, the greater the electronegativity and the higher the dielectric constant, the smaller the electrical loss at high frequency.

[0236] Comparing Example 1 with Comparative Examples 1 and 2, it can be seen that the Ca 2+ The higher the content, the greater the structural distortion of the ferrite, resulting in a gradual decrease in the dielectric loss and magnetic loss of the ferrite. 2+ The amount of Ca entering the lattice is too much (0.105 in Comparative Example 2, higher than 0.095 in Example 1), and some Ca 2+It may enter other lattice gaps, resulting in an increase in the real part of the magnetic permeability and the real part of the dielectric constant, as well as the dielectric loss and magnetic loss.

[0237] Comparing Example 1 and Comparative Example 3, similar to Example 1 and Comparative Example 1, due to the decrease in the temperature of the salt water quenching, the Ca2+ that enters the ferrite lattice 2+ When the content is relatively low (Comparative Example 3, 0.035), the corresponding real part of the magnetic permeability and the real part of the dielectric constant, the dielectric loss tangent and the magnetic loss tangent all increase significantly.

[0238] Comparing Example 1 with Comparative Example 4, Comparative Example 4 has no doped ions, and its real part of magnetic permeability and real part of dielectric constant are both relatively high, which also leads to a significant increase in its dielectric loss tangent and magnetic loss tangent.

[0239] Comparing Example 1 and Comparative Example 5, Comparative Example 5 does not contain a grain growth inhibitor, so the grains in the ferrite will grow abnormally after sintering, and its magnetic permeability and real part of the dielectric constant will also increase significantly, resulting in a significant increase in its dielectric loss tangent and magnetic loss tangent.

[0240] Comparing Example 1 with Comparative Example 6, without the sintering aid, the density of the sintered ferrite decreases, and the magnetic loss and electric loss increase significantly.

[0241] Comparison of Example 1 and Comparative Example 7 shows that the pre-synthesized Co2Z ferrite powder (Comparative Example 7) prepared by introducing the dopant by initial mixing rather than by water quenching with a salt solution has the same composition as the pre-synthesized powder of Example 1. However, due to the lack of powder size refinement caused by water quenching and the special structure of "distorted outer layer structure and complete inner layer lattice" formed by water quenching with a salt solution, the main magnetic properties of the ferrite obtained in Comparative Example 7 after sintering are significantly reduced.

[0242] Comparing the effects of Example 1 and Comparative Example 8, it can be seen that the composition of the pre-synthesized ferrite powder is the same in both, but in Example 1, the sintering aid and the grain growth inhibitor are introduced by means of a composite sol, and the ratio is base material: Bi2O3: SiO2 equal to 100:0.4:0.6 (mass ratio), and in Example 8, the sintering aid and the grain growth inhibitor are introduced by means of an oxide, and the ratio is base material: Bi2O3: SiO2 equal to 100:0.5:0.7 (mass ratio). The results show that the magnetic properties of the sintered ferrite obtained in Example 1 are significantly better than those in Comparative Example 8, which shows that the introduction of the auxiliary agent by means of a composite sol has the advantage of achieving uniform distribution of the auxiliary agent in the base phase powder under the premise of less addition, thereby obtaining the advantage of a sintered ferrite with excellent magnetic properties. In summary, the iron-deficient Co2Z type ferrite obtained by the present invention has low loss and high cut-off frequency at ultra-high frequency at a lower sintering temperature, can be used as a substrate material for mobile phone antennas, and is suitable for the requirements of high frequency and miniaturization of 5G mobile phone antennas.

[0243] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as within the scope of protection of the present invention.

Claims

1. An iron-deficient Co2Z type ferrite, characterized in that It includes a ferrite base material and a sintering aid, wherein the ferrite base material is composed of 2.9 BaO· x ReO·2CoO·10.6Fe2O3; ReO is a dopant, where Re is the same ionic radius as Ba 2+ Close but not equal cations; the ionic radius of Re is 0.0945-0.1755 nm; sintering aids include those that promote sintering and those that limit grain growth during sintering; x is 0.08-0.1; Re is Sr 2+ , Ca 2+ One or more of the following; The method for preparing the iron-deficient Co2Z type ferrite comprises the following steps: S1. Drying, ball-milling, and sintering barium oxide, cobalt oxide, and iron oxide to obtain a powder; adding the powder to a dopant solution and quenching the mixture with a salt solution to obtain a ferrite base material; S2. Add an alcohol solvent to the auxiliary agent precursor that limits grain growth during the sintering process, stir and dissolve, and then add a mixed solvent of acid and water to react to obtain sol A; add an auxiliary agent precursor that promotes sintering to sol A, stir evenly, and then stand and seal for 200-280 hours to obtain a composite sol; S3, mixing the ferrite base material and the composite sol, performing ball milling, drying, and heat treatment to obtain a composite powder having a core-shell structure; S4, after ball milling the composite powder, adding a binder and continuing ball milling to obtain a slurry; spray granulating the slurry, and compression molding to obtain a green body; drying and sintering the green body to obtain the iron-deficient Co2Z type ferrite.

2. The iron-deficient Co2Z type ferrite according to claim 1, characterized in that The auxiliary agent for promoting sintering is Bi2O3, Nb2O5 or V2O5; the auxiliary agent for limiting grain growth during sintering is SiO2, MgO or Al2O3.

3. The iron-deficient Co2Z type ferrite according to claim 1, characterized in that The barium oxide, cobalt oxide and iron oxide are all micron-sized.

4. The iron-deficient Co2Z type ferrite according to claim 1, characterized in that The particle size D50 of the barium oxide, cobalt oxide and iron oxide is 0.5-2.0 μm.

5. The iron-deficient Co2Z type ferrite according to claim 1, characterized in that The ball milling medium in step S1 is ethanol or water, the ball milling time is 4-8 h, and the ball mill speed is 200-600 rpm. -1 During the ball milling process, the mass ratio of material: ball: medium is 1:1-2:1-2; the sintering in step S1 is: 3-7 ℃·mim -1 The heating rate is raised to 800-1500℃ and then kept at this temperature for 0.5-8 h; then the temperature is raised to 1-3℃·min -1 The cooling rate is reduced to 300-800℃ and then kept warm for 0.2-4 h.

6. The iron-deficient Co2Z type ferrite according to claim 1, characterized in that The salt solution quenching in step S1 includes: adding the powder to the dopant solution, stirring, standing, washing, and secondary drying; the dopant solution in step S1 is a nitrate solution of the dopant; the temperature of the salt solution quenching is 300-800°C; and the ratio of the nitrate solution of the dopant to the powder is 10-200 ml of solution per 1 g of powder.

7. The iron-deficient Co2Z type ferrite according to claim 1, characterized in that The molar ratio of the auxiliary agent precursor for limiting the grain growth during the sintering process to the ferrite base material in step S2 is 0.05-1.50:1; in the composite sol, Bi 3+ The molar concentration is 1.50-15.0×10 -3 mol L -1 The heating rate of the heat treatment process in step S3 is 0.2-4°C min -1 The heat treatment temperature is 200-800 ° C, the sintering time is 0.2-4 h; the sintering heating rate in step S4 is 1-6 ° C·mim -1 , sintering temperature is: 600-1300℃, and sintering time is 1-8 h.

8. Use of the iron-deficient Co2Z type ferrite according to any one of claims 1 to 7 in preparing a substrate material for a mobile phone antenna.

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