Iron-deficient Co2Z ferrite as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of electronic ceramics, and particularly relates to an iron-deficient Co2Z ferrite as well as a preparation method and application thereof. The iron-deficient Co2Z type ferrite comprises a ferrite base material and a sintering aid, wherein the ferrite base material is composed of 2.9 BaO * xReO * 2CoO * 10.6 Fe2O3; reO is a dopant, and Re is a cation of which the ion radius is close to but not equal to that of Ba < 2 + >; the sintering aid comprises an aid for promoting sintering and an aid for limiting grain growth in the sintering process; and x is in a range of 0.08 to 0.1. According to the invention, by utilizing hydroxyl-containing functional groups existing on the surface of the base phase powder subjected to water quenching of the salt solution and good film-forming property of the composite sol, uniform coating of base material particles is realized, so that optimization of magnetic performance of the material is realized, and electrical loss of the material under high frequency is reduced. The obtained iron-deficient Co2Z type ferrite has low loss and high cut-off frequency under ultrahigh frequency at a relatively low sintering temperature.

Description

Technical Field

[0001] The invention belongs to the technical field of electronic ceramics, and in particular relates to an iron-deficient Co2Z type ferrite and a preparation method and application thereof. Background Art

[0002] At present, the commonly used soft ferrite materials in industry mainly include: spinel ferrite (mainly nickel-zinc and manganese-zinc ferrites) and planar hexagonal ferrites (Co2Z, Co2Y ferrites), etc. Among them, the highest operating frequency of nickel-zinc and manganese-zinc ferrites with spinel structure is limited by the crystal structure. For example, the skin effect and eddy current loss caused by electromagnetic induction will cause the performance of nickel-zinc ferrite to deteriorate significantly in the frequency band above 100MHz; the hysteresis loss of nickel-copper-zinc ferrite increases sharply in the frequency band above 300MHz, and the quality factor is significantly reduced, so it is not suitable for manufacturing antennas and related devices with higher frequencies.

[0003] The frequency band used by 5G technology is roughly 450MHz-6.0GHz for receiving and transmitting ends. Hexagonal ferrite has high magnetocrystalline anisotropy and a theoretical resonance frequency of up to 3.4GHz. Z-type hexagonal ferrite material, in particular, has become an important candidate magnetic material for ultra-high frequency band antenna devices due to its high initial magnetic permeability, high cutoff frequency and good stability.

[0004] The Chinese invention patent with application number CN201310275973.1 and titled "A ferrite-based composite magnetic dielectric antenna substrate material and its preparation method" discloses a ferrite-based composite magnetic dielectric antenna substrate material and its preparation method. The substrate material is composed of 85-90% by mass of the main phase material and 15-10% by mass of the auxiliary phase material. The main phase material is Co2Z hexagonal ferrite, and its formula molecular formula is Ba 3-x Sr x Co2Fe 24-y O 41, where x is in the range of 0-1.5, and y is in the range of 0-4; the auxiliary phase material is polyimide resin. The magnetic dielectric composite substrate material provided by the invention has a magnetic permeability of about 2.5-4.5 and a dielectric constant of 7-9 in the 300MHz-3 GHz frequency band; the magnetic loss tangent in the 300MHz-1 GHz 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 high, and it also has a certain degree of flexibility, and its mechanical impact resistance is better than that of conventional ceramic substrate materials. It not only helps to reduce the weight and volume of the antenna, but also helps to increase the bandwidth of the microstrip antenna and suppress the generation of surface waves. However, the target material of the patent is a composite magnetic substrate (a composite material of ferrite and resin) with polyimide resin as an adhesive, which is a ferrite-based composite magnetic dielectric antenna substrate material obtained by curing at 280-300°C with resin as an adhesive. The ambient temperature and life of this type of composite substrate material are subject to certain restrictions; and after the composite material is compounded in proportion with the magnetic permeability of the prepared Co2Z type ferrite, the magnetic permeability of the composite material can be adjusted to 2.5-4.5, and the dielectric constant can be adjusted to about 7-9. The composite material has high magnetic loss in the 1GHz-3GHz frequency band and high dielectric loss tangent in the frequency range of 300MHz-3GHz.

[0005] The Chinese invention patent with application number CN202010172783.7 and titled “A high-flexibility magnetic dielectric composite substrate material, preparation method and application thereof” discloses a high-flexibility magnetic dielectric composite substrate material, preparation method and application thereof, wherein the high-flexibility magnetic dielectric composite substrate material is composited by a main phase material and an auxiliary phase material in a mass percentage of 1:0.5-1.5, and the main phase material is a hexagonal ferrite with an initial magnetic permeability greater than 15 and a cutoff frequency greater than 1 GHz. The formula molecular formula of the hexagonal ferrite is (Ba 0.5+y Sr 0.5-y )3Co 1.6+x Zn 0.4-x Fe 23 O 41, wherein 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 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 at 1GHz and a magnetic permeability of 2.78; 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 with application number CN201580041623.6 and titled "Co2Z-type ferrite composite material for ultra-high frequency antenna" 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, the 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 the 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 with application number CN201680013105.8 and titled “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 a 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, the patent directly mixes several oxides involved in the main phase and the doping phase at one time, such as BaCO3, SrCO3, Co3O4, Fe2O3 and MoO2 (doping phase), resulting in a lower dielectric constant and a larger loss.

[0008] The Chinese invention patent with application number CN201910237811.6 and titled "A miniaturized array antenna based on M-type barium ferrite material" discloses a miniaturized array antenna based on M-type barium ferrite material, which belongs to the technical field of antenna substrate materials. The substrate material of the array antenna is M-type barium ferrite substituted with lanthanum (La) and cobalt (Co), and the formula is 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 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 the doping phase, such as BaCO3, Co2O3, Fe2O3 and La2O3, at one time, performs pre-synthesis, and prepares M-type barium ferrite by ball milling the pre-synthesized powder and Bi2O3 sintering aid, granulating and then sintering. The dielectric loss and magnetic loss are too high.

[0010] The literature (Xiang Chengcheng. Preparation and Characteristic Research 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, Sr doping on the material phase structure, microstructure, and electromagnetic properties. The study shows 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 are significantly improved; with the increase of iron deficiency, the magnetic permeability of the sample first increases and then decreases. When the iron deficiency y=10.4, the relative magnetic permeability at 1GHz has 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 Lower than 0.4; 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 value of 68.11Oe and a maximum value of 176.59Oe, respectively.

[0011] However, this patent directly mixes several oxides and carbonates involved in the main phase and the doping phase, such as BaCO3, Co3O4, Fe2O3, and Sr CO3, at one time, performs pre-synthesis first, and prepares M-type barium ferrite by ball milling the pre-synthesized powder and Bi2O3 sintering aid, granulating and then sintering; the dielectric loss and magnetic loss are too high.

[0012] The literature (Chen Hui. Research on magnetic substrate materials for 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 morphology 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 material's magnetic permeability and magnetic permeability cutoff frequency. 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 cut-off frequency decreases with the increase of Cr 3+The doping amount increases and the material moves to high frequency. In addition, the physical structure and electromagnetic parameter characteristics of Y-type hexagonal ferrite materials are preliminarily studied. At different sintering temperatures, the performance of the material is almost not affected. Within a certain frequency range, the electromagnetic parameters basically remain stable. Finally, μ r '~2, μ r ”~0.11, ε r '~9.53, ε r ” ~ 0.03 (0.5-4GHz) materials.

[0013] However, the 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 prepares M-type barium ferrite by ball milling the pre-synthesized powder and Bi2O3 sintering aid, granulating 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 antenna applications, 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 influence of H3BO3 doping on the microstructure and magnetic properties of ferrite. Through research, it was found that H3BO3 doping can well promote the low-temperature sintering phase of Co2Z ferrite. At the same time, H3BO3 doping is also beneficial to inhibit the grain growth of Co2Z ferrite. With the increase of H3BO3 doping, the magnetic permeability of the material system continues to decrease, while the dielectric constant first increases and then decreases. When the mass fraction of doped H3BO3 is 4%, the material system can obtain a comprehensive magnetic dielectric property of 2.45 permeability, 10.41 dielectric constant, 0.057 magnetic loss tangent, and 0.005 dielectric loss tangent at 915MHz.

[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). In essence, H3BO3 is a precursor with a dopant. During the sintering process, H3BO3 decomposes to form B2O3 (the decomposition temperature range is about 170-500°C). B2O3 can dissolve alkaline metal oxides such as BaO and SrO to form glassy borates and metaborates, which are located at the grain boundaries and promote sintering. These products are amorphous, so no glass phase is observed in the XRD results of the prior art; the B element only enters part of the ferrite that forms the glass phase, while there is no doping in the low Co2Z ferrite that does not form the glass phase, resulting in obvious composition unevenness inside the ferrite material (glass phase part and grain part), which also leads to its unsatisfactory magnetic properties.

[0016] The Chinese invention patent with application number CN202110549706.3 and titled “A low-loss high-frequency magnetic dielectric material and its preparation method” discloses a low-loss high-frequency magnetic dielectric material, which belongs to the field of electronic materials. The magnetic dielectric 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 dielectric material of the invention is prepared by the sol-gel method, achieving low-loss and high-frequency magnetic dielectric properties, and has low-loss and nearly equal magnetic dielectric properties in the frequency range of 1MHz-1.8GHz (its magnetic permeability and dielectric constant are both around 5-15, and the magnetic loss coefficient and dielectric loss coefficient in the frequency band are both lower than 0.005); when the low-loss high-frequency magnetic dielectric material is used as an antenna substrate, it 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 new materials for the design of high-frequency and integrated small-size wireless communication equipment. However, the main raw materials of this patent are nitrates, citric acid, ammonia water, etc., and the sol-gel method combined with self-propagation is used to prepare the pre-synthesized powder, which has the problems of high cost and difficulty in large-scale production; the patent specifies the trivalent ion Fe in Co2Z ferrite. 3+ Doping replacement of similar sites (Me1~Me10) involves changes in the molecular magnetic moment, which will have a significant adverse effect on the macroscopic magnetic properties of ferrites, that is, increasing or decreasing the magnetic 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, preparation method and use thereof" provides a Co2Z type ferrite material, preparation method and use thereof. 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 mold, pre-sintering once, and sintering twice to obtain a Co2Z type ferrite material; the substituted metal ions include Ba 2+ and / or Sr 2+ . The 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; and the sintering process of the patent takes advantage of the relatively fine pre-synthesized powder, does not add sintering aids, and directly sintered at high temperature (sintered at 1150°C, kept warm for 4h) to prepare sintered ferrite, which has high energy consumption.

[0018] The Chinese invention patent application number is CN202110527759.5, entitled "A method for preparing a Co2Z type ferrite sintered sheet", which 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 barium source, strontium source, cobalt source and iron source are mixed in a proportion, ball-milled for the first time, sintered for the first time, and then ball-milled for the second time to obtain a powder; wherein, 1≤x≤2; 21.6≤y≤24; 2) the powder obtained in step 1) is mixed with a binder, ball-milled for the third time, and the obtained material is tape-cast to obtain a green body; 3) the green body obtained in step 2) is sintered for the second time. 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, and the magnetic permeability is close, and the cut-off frequency is 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 placing the raw materials in a box furnace for high-temperature calcination to synthesize phase A; placing phase A in a tube furnace for annealing treatment 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 premixed liquid of polyvinyl alcohol and deionized water to prepare a slurry, and then transferring the slurry to an alloy mold, and after being treated under a magnetic field for a period of time, applying pressure to the slurry for molding treatment to obtain a green blank sample C; removing the magnetic field, taking out sample C, and placing it in a box furnace for high-temperature sintering treatment to obtain a 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 the material is used for single-phase multiferroic materials, it has the significant advantages of high magnetoelectric coupling temperature and high coupling strength. However, the patent requires magnetization treatment for a period of time to achieve directional arrangement of the powder, and then obtain the green billet, and the green billet is sintered at high temperature. The operation process is complicated, the equipment requirements are high, and it is difficult to mass produce. Summary of the invention

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

[0021] To achieve the above purpose, 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 similar 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 matrix, and Ba 2+ There are certain differences in the ionic radius, which can easily cause structural distortion.

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

[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. These two can easily enter the lattice of hexagonal ferrite matrix and easily produce structural distortion.

[0028] Because Ba 2+ The position in the hexagonal ferrite is fixed. The present invention mainly introduces doping ions into the Ba 2 + Similar positions are used to achieve microstructural distortion and electronegativity change, 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 aid 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 Nb2O5 has a higher melting point and V2O5 may have certain toxicity, 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 powder; adding the powder to a dopant solution and quenching with a salt solution to obtain a ferrite base material;

[0036] S2, adding an alcohol solvent to the auxiliary agent precursor that limits the grain growth during the sintering process, stirring and dissolving, adding a mixed solvent of acid and water, and reacting to obtain a sol A; adding an auxiliary agent precursor that promotes sintering to the sol A, stirring evenly, and standing and sealing for 200-280 hours to obtain a composite sol;

[0037] S3, mixing the ferrite base material and the composite sol, and then ball milling, drying, and heat treating to obtain a composite powder with 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 pressing it 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 micrometer-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 and time required for synthesizing the Co2Z ferrite-based phase powder will be high, 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 impurities in the synthesized Co2Z 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 is a mixed phase, including Co2Z ferrite and excess barium oxide, cobalt oxide or iron oxide oxide; thus, the phase is uneven, affecting the performance.

[0044] If the molar ratio of barium oxide, cobalt oxide or iron oxide is too small, the pre-synthesized powder will be a mixed phase, resulting in uneven phases and affecting performance. For example, if there is too little barium oxide, oxides such as Co2Z ferrite and CoFe2O4 may be generated.

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

[0046] In a preferred embodiment, the medium for ball milling in step S1 is ethanol or water, corundum balls, zirconia balls or agate balls are used as grinding balls, the ball milling time is 4-8 hours, and the ball mill speed is 200-600 rpm. -1 .

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

[0048] Considering the price, corundum balls are the best grinding balls.

[0049] Experiments show that if the ball milling time is too short, several oxides are not easy to mix evenly; if the time is too long, the production efficiency is reduced.

[0050] If the speed of the ball mill is too slow, it is not easy to mix several oxides; if the speed is too fast, the energy consumption is high, the equipment is worn out, and the grinding chips generated by the ball mill and grinding balls increase, resulting in an increase in the impurity content in the raw materials, which ultimately leads to a decrease in the performance of the ferrite.

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

[0052] During ball milling,

[0053] 1. Influence of materials: If there are too many materials, the several oxides in the raw materials cannot be mixed evenly; if there are too few materials, the slurry obtained in each batch is too small, and the production efficiency is reduced;

[0054] 2. The influence of the medium is just the opposite of that of the material: too much medium, that is, too much water or ethanol, the output of each batch decreases, and the solid content of the slurry is low, which affects the effect of spray granulation;

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

[0056] 3. The influence of grinding balls: Too many grinding balls will, on the one hand, lead to an increase in grinding chips, and on the other hand, the output of each batch will be too small, and the production efficiency will decrease; too few grinding balls will make it difficult to mix the several oxides in the raw materials.

[0057] In a preferred embodiment, the sintering in step S1 is: 3-7°C·mim -1 The heating rate is increased to 800-1500℃ and then kept at this temperature for 0.5-8h; then heated at 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 an obvious temperature difference between the surface and the interior of the evenly mixed oxide powder pile in the furnace. Because the thermal conductivity of the oxide raw material 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 material inside has 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 water quenching / ball milling mixing in the next step.

[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 1-4h; after cooling to 400-800°C, the temperature is kept for 0.4-2h.

[0062] In a preferred embodiment, the salt solution quenching in step S1 refers to: adding the powder into the dopant solution for 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 water quenching is to diffuse a certain amount of ions into the lattice of Co2Z ferrite to regulate its magnetic properties. Based on this, when the salt solution concentration is too low, under the same salt solution water quenching conditions, too few ions enter the ferrite lattice and the expected goal cannot be achieved;

[0066] If the concentration is too high, the experimental results show that the total amount of ions diffused into the ferrite lattice does not increase significantly, but will cause a waste of inorganic salts and increase the workload of the next centrifugal washing. This is because under the set salt solution water quenching conditions, the diffusion energy is certain, which mainly depends on the temperature of the powder and the number of ions in contact with the powder in the salt solution.

[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 nitrate solution of the dopant to the powder is 10-200 ml solution / 1 g powder, preferably 50-150 ml solution / 1 g powder.

[0069] The ratio of the nitrate solution of the doping agent 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 centrifugal washing for the next operation. Too much salt solution will lead to too much workload for 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. There are certain safety hazards in the operation, and the goal of water quenching - using the temperature difference to break up the powder - 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 is carried out at a temperature of 60-90° C. and for a time of 20-30 hours.

[0074] In a preferred embodiment, 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, preferably 0.10-1.00:1.

[0075] The additive precursor that limits the grain growth during the sintering process is converted into SiO2 after heat treatment. SiO2 itself does not have magnetic properties. If too much is added, the density of the material 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 the material loss will also increase significantly.

[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 be 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] Considering the cost, ethanol is preferred.

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

[0081] In one 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 surface of the powder, 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 surface of the powder, and the grain growth restriction during the sintering process is not obvious;

[0083] Effect 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 in the next step, white precipitation is likely to appear in the sol, 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 in the drying process is significantly lower than that of water, and the alcohol evaporates too quickly, which is likely to cause the film layer to crack.

[0084] Effect of water addition: Too much water will lead to too low sol concentration, which is similar to the effect of 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 is similar to the effect of too much additive precursor.

[0085] 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 accelerate, 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 the grain growth during sintering is 0.01-2.00 mol·L -1 .

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

[0088] In a preferred embodiment, the molar concentration of the auxiliary agent precursor that limits the 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 too much, 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, resulting in a significant decrease in the density of the ferrite after sintering, and thus a decrease in magnetic properties.

[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 of shrinking the dried gel to form an oxide network. There are still a certain amount of Si-OH, Al-OR (organic functional group), Bi-OH and other functional groups in the dried dry gel; after heat treatment, a network structure such as Si-O-Si-O- or Si-O-Bi-O- or Bi-O-Bi- is formed. The dry gel coated on the surface of the particles has a certain thickness. When the heating rate is too fast, the surface of the gel first dehydrates or dealcoholizes and shrinks to form a dense network, while the inside of the gel has not completed these reactions and will continue to dehydrate or dealcoholize. Because the surface is dense, the water or alcohol inside cannot escape quickly and remains inside the film layer. After the temperature rises, the volume of the vapor formed by water and alcohol will increase rapidly, and finally the gel film layer will rupture; the heating rate is too slow, but the production efficiency is low and the 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 step of ferrite sintering (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 decrease; if the holding time is too long, the production efficiency is low and the energy consumption is high.

[0097] The temperature of heat treatment 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 insulation time. If the temperature is too high, the ferrite powder may stick together due to 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; during the ball milling process, the mass ratio of material, balls and water 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 concentration of the binder is too low, in order to obtain a green body with a certain strength (after the granulated powder is molded, the unsintered sample is called a green body), a large amount of binder aqueous solution needs to be added to ensure that the amount of PVA added reaches a certain value. Because the green body needs to be dried after molding before sintering, drying will cause water to volatilize, resulting in a higher porosity of the green body. In this way, under the same sintering process, the bulk density of the ferrite obtained after sintering is low and the magnetic properties are not ideal.

[0103] If the concentration of the binder is too high, its viscosity will be high, and it will not be easy to mix 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 the binder cannot be molded or has low strength. It will also cause the density of the ferrite after sintering to be uneven, the performance will be reduced, and the batch stability will be very poor.

[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 strength and density of the formed body are low, which is not only easy to break, but also the density of the ferrite after sintering is poor and the magnetic properties are 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. Therefore, 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. These two factors will lead to low density and poor magnetic properties of 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 one 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 for 1 minute.

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

[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, the ferrite will have abnormal grain growth and decomposition on the surface; 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 gas phase products produced by the decomposition or oxidation of PVA in the debinding section 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 a decrease in production efficiency and an increase in energy consumption.

[0116] Influence of holding time: If the holding time is too short, the sintering densification process will not be thorough, the density of the ferrite after sintering will be low, and the magnetic properties will not be ideal; if the holding time is too long, the ferrite grains will grow abnormally and the surface ferrite will decompose a small amount, which will lead to the decline of ferrite performance. At the same time, 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·mim -1 , the sintering temperature is: 800-1200℃, and the 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 frequency 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 of "distorted outer layer structure and complete inner layer lattice", reducing the magnetic permeability of the powder and increasing its cutoff frequency; third, rich hydroxyl-containing functional groups are generated on the surface of the powder, improving the uniformity of the composite film wrapping 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] Bi2O3-SiO2 composite sol is used to wrap the base phase powder after salt solution water quenching 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 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 electrical loss of the material at high frequencies.

[0125] 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 relatively low 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.

[0126] From a theoretical point of view, as long as the expected goals can be achieved, the directly added oxide sintering aids and grain growth inhibitors used in other documents and patents naturally hope that the amount of the two additives added is as small as possible, because both additives are non-magnetic materials, and the sintering process is mainly located at the grain boundary. 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 certain, it is hoped that the sintering aid and grain growth inhibitor can be evenly dispersed in the base phase powder through ball milling, so that during the sintering process, the two additives can play their role to the maximum extent, thereby improving the magnetic properties of the ferrite after sintering. But in fact, when the two additives are added in the form of particles, at a certain addition amount, they cannot be mixed evenly with the base phase powder, resulting in a decrease in the performance of the ferrite material after sintering. For this reason, in practice, this problem is often solved by increasing the addition amount of the two.

[0128] In the present invention, it is proposed to add two additives in the form of 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 can be 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-containing functional groups 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, and effectively control the grain size and uniformity of the ferrite material after sintering, thereby optimizing the magnetic properties of the material, and the SiO2 layer simultaneously reduces the grain boundary resistivity of the material, ultimately reducing the electrical loss of the material 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 the crushing of the powder, that is, the refinement of the powder particle size; second, at high temperature, the surface of the powder can undergo a certain chemical reaction with the water in the salt solution, and a large number of hydroxyl functional groups, such as Ba-OH / Co-OH / Fe-OH, are generated on the surface of the powder particles. In the next step of sol stirring and ball milling, these hydroxyl functional groups on the surface of the powder can be combined with similar functional groups in the sol through hydrogen bonds, thereby improving the binding property of the sol with 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 by designing the iron-deficient formula of the base material;

[0133] 2. Re 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 Re with a smaller radius 2+ Enter the lattice of the surface layer of the base phase powder to form a special structure of "distorted outer layer structure and complete inner layer lattice", which reduces the magnetic permeability of the powder and increases its cutoff frequency; thirdly, it produces abundant hydroxyl-containing functional groups on the surface of the powder to improve the uniformity of the composite film wrapping the base phase powder;

[0134] 3. Use 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;

[0135] 4. Use composite sol to wrap the base phase powder after salt solution water quenching to improve the uniformity of ferrite grains after sintering and reduce the sintering temperature;

[0136] Compared with the method adopted in other documents and patents to directly add oxide sintering aids and grain growth inhibitors by liquid phase method - i.e. sol impregnation - combined with heat treatment, the present invention has the advantages of small addition amount and easy to achieve uniform distribution of the aids in the base phase powder. BRIEF DESCRIPTION OF THE DRAWINGS

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

[0138] Figure 2 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;

[0139] Figure 3 The scanning electron microscope photos 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;

[0140] Figure 4 The SEM image and EDS spectrum of the sintered material of Example 1;

[0141] Figure 5 The SEM image and EDS spectrum of the sintered material of Comparative Example 4;

[0142] Figure 6 The 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 is the real part curve of the dielectric constant of the sintered ferrite material obtained in Examples 1, 2 and 3 and Comparative Example 4; DETAILED DESCRIPTION

[0144] The technical scheme of the present invention is further illustrated by specific examples below. Those skilled in the art should understand that the examples are only to help understand the present invention and should not be regarded as specific limitations of the present invention.

[0145] Example 1

[0146] (1) Drying and weighing of powders: Dry the three powders of μm-BaO, μm-CoO and μm-Fe2O3 at 80°C for 24 h, and then weigh 445 g of μm-BaO, 150 g of μm-CoO and 1692 g of μm-Fe2O3 for later use;

[0147] (2) Preparation of alkaline earth metal salt solution: Dissolve a certain amount of Ca(NO3)2·4H2O in water in a corresponding ratio of 70.85 g Ca(NO3)2·4H2O to 1000 g water to obtain about 0.3 mol 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 2468.5ml H2O mixed evenly - marked as solution A; 31.5ml TEOS and 300ml C2H5OH mixed evenly, marked as solution B; under stirring, solution B was added dropwise to solution A at a rate of 50mL·h -1 After the addition was completed, the mixture was stirred for 1 hour to obtain SiO2 sol; 12.50 g Bi(NO3)3·5H2O was then added to the sol, and after stirring and dissolving, the composite sol was further stirred at room temperature for 24 hours, and then sealed to obtain a stable composite sol, in which Bi 3+ 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 °C for 24 h and then heated in a box furnace at 5 °C·min -1 After the temperature was raised to 1250°C and kept at this temperature for 2.5 hours, an iron-deficient Co2Z-type ferrite matrix powder having a composition of 2.9BaO·2CoO·10.6Fe2O3 was obtained; the matrix powder was then heated to 2°C·min -1 The cooling rate was reduced to 700℃ and kept at this temperature for 0.5h. The powder was taken out and directly poured 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, then allowed to stand for 24 hours, the supernatant was removed, the precipitate was washed three times by centrifugation with H2O, and the obtained 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: 1 g powder: 2 ml 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 into a ball mill, and the ball mill was performed for 6 h with corundum balls as grinding balls at a speed of 400 rpm. -1 The slurry was then dried at 80°C under stirring and then heated to 1.0°C·mim -1 The temperature was raised to 600°C and kept for 1.0h to obtain a composite powder of Bi2O3-SiO2 film-coated 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). PVA aqueous solution containing 10 wt% of the total mass of the powder was added and ball milled for 4.0 h at a ball mill speed of 300 rpm. -1 The ball milled slurry is spray granulated and molded to obtain a green body; the green body is 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°C for 24 h, and then weigh 445 g of μm-BaO, 150 g of μm-CoO and 1692 g of μm-Fe2O3 for later use;

[0154] (2) Preparation of alkaline earth metal salt solution: Dissolve a certain amount of Ca(NO3)2·4H2O in water in a 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 2468.5ml H2O mixed evenly - marked as solution A; 31.5ml TEOS and 300ml C2H5OH mixed evenly, marked as solution B; under stirring, solution B was added dropwise to solution A at a rate of 50mL·h -1 After the addition was completed, the mixture was stirred for 1 hour to obtain SiO2 sol; 12.50 g Bi(NO3)3·5H2O was then added to the sol, and after stirring and dissolving, the composite sol was further stirred at room temperature for 24 hours, and then sealed to obtain a stable composite sol, in which Bi 3+ 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 °C for 24 h and then heated in a box furnace at 5 °C·min -1 After the temperature was raised to 1250°C and kept at this temperature for 2.5 hours, an iron-deficient Co2Z-type ferrite matrix powder having a composition of 2.9BaO·2CoO·10.6Fe2O3 was obtained; the matrix powder was then heated to 2°C·min -1 The cooling rate was reduced to 700℃ and kept at this temperature for 0.5h. The powder was taken out and directly poured 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, then allowed to stand for 24 hours, the supernatant was removed, the precipitate was washed three times by centrifugation with H2O, and the obtained 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: 1 g powder: 2 ml 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 into a ball mill, and the ball mill was performed for 6 h with corundum balls as grinding balls at a speed of 400 rpm. -1 The slurry was then dried at 80°C under stirring and then heated to 1.0°C·mim -1 The temperature was raised to 600°C and kept for 1.0h to obtain a composite powder of Bi2O3-SiO2 film-coated base phase fine powder after salt solution water quenching;

[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). PVA aqueous solution containing 10 wt% of the total mass of the powder was added and ball milled for 4.0 h at a ball mill speed of 300 rpm. -1 The ball milled slurry is spray granulated and molded to obtain a green body; the green body is 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.

[0159] Example 3

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

[0161] (2) Preparation of alkaline earth metal salt solution: Dissolve a certain amount of Ca(NO3)2·4H2O in water in a corresponding ratio of 76.92 g Mg(NO3)2·6H2O to 1000 g water to obtain about 0.3 mol 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 2468.5ml H2O mixed evenly - marked as solution A; 31.5ml TEOS and 300ml C2H5OH mixed evenly, marked as solution B; under stirring, solution B was added dropwise to solution A at a rate of 50mL·h -1 After the addition was completed, the mixture was stirred for 1 hour to obtain SiO2 sol; 12.50 g Bi(NO3)3·5H2O was then added to the sol, and after stirring and dissolving, the composite sol was further stirred at room temperature for 24 hours, and then sealed to obtain a stable composite sol, in which Bi 3+ 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 °C for 24 h and then heated in a box furnace at 5 °C·min -1 After the temperature was raised to 1250°C and kept at this temperature for 2.5 hours, an iron-deficient Co2Z-type ferrite matrix powder having a composition of 2.9BaO·2CoO·10.6Fe2O3 was obtained; the matrix powder was then heated to 2°C·min -1 The cooling rate was reduced to 700℃ and kept at this temperature for 0.5h. The powder was taken out and directly poured 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, then allowed to stand for 24 hours, the supernatant was removed, the precipitate was washed three times by centrifugation with H2O, and the obtained 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: 1 g powder: 2 ml 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 into a ball mill, and the ball mill was performed for 6 h with corundum balls as grinding balls at a speed of 400 rpm. -1The slurry was then dried at 80°C under stirring and then heated to 1.0°C·mim -1 The temperature was raised to 600°C and kept for 1.0h to obtain a composite powder of Bi2O3-SiO2 film-coated base phase fine powder after salt solution water quenching;

[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). PVA aqueous solution containing 10 wt% of the total mass of the powder was added and ball milled for 4.0 h at a ball mill speed of 300 rpm. -1 The ball milled slurry is spray granulated and molded to obtain a green body; the green body is 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.

[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°C for 24 h, and then weigh 445 g of μm-BaO, 150 g of μm-CoO and 1692 g of μm-Fe2O3 for later use;

[0168] (2) Preparation of alkaline earth metal salt solution: Dissolve a certain amount of Ca(NO3)2·4H2O in water in a corresponding 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 2468.5ml H2O mixed evenly - marked as solution A; 31.5ml TEOS and 300ml C2H5OH mixed evenly, marked as solution B; under stirring, solution B was added dropwise to solution A at a rate of 50mL·h -1After the addition was completed, the mixture was stirred for 1 hour to obtain SiO2 sol; 12.50 g Bi(NO3)3·5H2O was then added to the sol, and after stirring and dissolving, the composite sol was further stirred at room temperature for 24 hours, and then sealed to obtain a stable composite sol, in which Bi 3+ 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 °C for 24 h and then heated in a box furnace at 5 °C·min -1 After the temperature was raised to 1250°C and kept at this temperature for 2.5 hours, an iron-deficient Co2Z-type ferrite matrix powder having a composition of 2.9BaO·2CoO·10.6Fe2O3 was obtained; the matrix powder was then heated to 2°C·min -1 The cooling rate was reduced to 700℃ and kept at this temperature for 0.5h. The powder was taken out and directly poured 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, then allowed to stand for 24 hours, the supernatant was removed, the precipitate was washed three times by centrifugation with H2O, and the obtained 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: 1 g powder: 2 ml 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 into a ball mill, and the ball mill was performed for 6 h with corundum balls as grinding balls at a speed of 400 rpm. -1 The slurry was then dried at 80°C under stirring and then heated to 1.0°C·mim -1 The temperature was raised to 600°C and kept for 1.0h to obtain a composite powder of Bi2O3-SiO2 film-coated base phase fine powder after salt solution water quenching;

[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). PVA aqueous solution containing 10 wt% of the total mass of the powder was added and ball milled for 4.0 h at a ball mill speed of 300 rpm. -1 The ball milled slurry is spray granulated and molded to obtain a green body; the green body is 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°C for 24 h, and then weigh 445 g of μm-BaO, 150 g of μm-CoO and 1692 g of μm-Fe2O3 for later use;

[0175] (2) Preparation of alkaline earth metal salt solution: Dissolve a certain amount of Ca(NO3)2·4H2O in water in a corresponding ratio of 141.69 g Ca(NO3)2·4H2O to 1000 g water to obtain about 0.6 mol 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 2468.5ml H2O mixed evenly - marked as solution A; 31.5ml TEOS and 300ml C2H5OH mixed evenly, marked as solution B; under stirring, solution B was added dropwise to solution A at a rate of 50mL·h -1 After the addition was completed, the mixture was stirred for 1 hour to obtain SiO2 sol; 12.50 g Bi(NO3)3·5H2O was then added to the sol, and after stirring and dissolving, the composite sol was further stirred at room temperature for 24 hours, and then sealed to obtain a stable composite sol, in which Bi 3+ 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 °C for 24 h and then heated in a box furnace at 5 °C·min -1 After the temperature was raised to 1250°C and kept at this temperature for 2.5 hours, an iron-deficient Co2Z-type ferrite matrix powder having a composition of 2.9BaO·2CoO·10.6Fe2O3 was obtained; the matrix powder was then heated to 2°C·min -1 The cooling rate was reduced to 700℃ and kept at this temperature for 0.5h. The powder was taken out and directly poured 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, then allowed to stand for 24 hours, the supernatant was removed, the precipitate was washed three times by centrifugation with H2O, and the obtained 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: 1 g powder: 2 ml 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 into a ball mill, and the ball mill was performed for 6 h with corundum balls as grinding balls at a speed of 400 rpm. -1 The slurry was then dried at 80°C under stirring and then heated to 1.0°C·mim -1 The temperature was raised to 600°C and kept for 1.0h to obtain a composite powder of Bi2O3-SiO2 film-coated 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). PVA aqueous solution containing 10 wt% of the total mass of the powder was added and ball milled for 4.0 h at a ball mill speed of 300 rpm. -1 The ball milled slurry is spray granulated and molded to obtain a green body; the green body is 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: Lower 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°C for 24 h, and then weigh 445 g of μm-BaO, 150 g of μm-CoO and 1692 g of μm-Fe2O3 for later use;

[0182] (2) Preparation of alkaline earth metal salt solution: Dissolve a certain amount of Ca(NO3)2·4H2O in water in a corresponding ratio of 70.85 g Ca(NO3)2·4H2O to 1000 g water to obtain about 0.3 mol 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 2468.5ml H2O mixed evenly - marked as solution A; 31.5ml TEOS and 300ml C2H5OH mixed evenly, marked as solution B; under stirring, solution B was added dropwise to solution A at a rate of 50mL·h -1 After the addition was completed, the mixture was stirred for 1 hour to obtain SiO2 sol; 12.50 g Bi(NO3)3·5H2O was then added to the sol, and after stirring and dissolving, the composite sol was further stirred at room temperature for 24 hours, and then sealed to obtain a stable composite sol, in which Bi 3+ 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 °C for 24 h and then heated in a box furnace at 5 °C·min -1After the temperature was raised to 1250°C and kept at this temperature for 2.5 hours, an iron-deficient Co2Z-type ferrite matrix powder having a composition of 2.9BaO·2CoO·10.6Fe2O3 was obtained; the matrix powder was then heated to 2°C·min -1 The cooling rate was reduced to 500℃ and kept at this temperature for 0.5h. The powder was taken out and directly poured 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, then allowed to stand for 24 hours, the supernatant was removed, the precipitate was washed three times by centrifugation with H2O, and the obtained 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: 1 g powder: 2 ml 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 into a ball mill, and the ball mill was performed for 6 h with corundum balls as grinding balls at a speed of 400 rpm. -1 The slurry was then dried at 80°C under stirring and then heated to 1.0°C·mim -1 The temperature was raised to 600°C and kept for 1.0h to obtain a composite powder of Bi2O3-SiO2 film-coated 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). PVA aqueous solution containing 10 wt% of the total mass of the powder was added and ball milled for 4.0 h at a ball mill speed of 300 rpm. -1 The ball milled slurry is spray granulated and molded to obtain a green body; the green body is 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 with salt solutions of Examples 1-3 and Comparative Examples 1-3 were analyzed. 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 have a certain influence on the composition of the base phase powder obtained after water quenching of the salt solution. 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°C for 24 h, and then weigh 445 g of μm-BaO, 150 g of μm-CoO and 1692 g of μm-Fe2O3 for later 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 2468.5ml H2O mixed evenly - marked as solution A; 31.5ml TEOS and 300ml C2H5OH mixed evenly, marked as solution B; under stirring, solution B was added dropwise to solution A at a rate of 50mL·h -1 After the addition was completed, the mixture was stirred for 1 hour to obtain SiO2 sol; 12.50 g Bi(NO3)3·5H2O was then added to the sol, and after stirring and dissolving, the composite sol was further stirred at room temperature for 24 hours, and then sealed to obtain a stable composite sol, in which Bi 3+ 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 into 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 °C for 24 h and then heated in a box furnace at 5 °C·min -1 After the temperature was raised to 1250°C and kept at this temperature for 2.5 hours, an iron-deficient Co2Z-type ferrite matrix powder having a composition of 2.9BaO·2CoO·10.6Fe2O3 was obtained; the matrix powder was then heated to 2°C·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, then allowed to stand for 24 hours, the supernatant was removed, the precipitate was washed three times by centrifugation with H2O, and the obtained 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: 1 g powder: 2 ml 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 into a ball mill, and the ball mill was performed for 6 h with corundum balls as grinding balls at a speed of 400 rpm. -1 The slurry was then dried at 80°C under stirring and then heated to 1.0°C·mim -1 The temperature was raised to 600°C and kept for 1.0h to obtain a composite powder of Bi2O3-SiO2 film-coated base phase fine powder after salt solution water quenching;

[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). PVA aqueous solution containing 10 wt% of the total mass of the powder was added and ball milled for 4.0 h at a ball mill speed of 300 rpm. -1 The ball milled slurry is spray granulated and molded to obtain a green body; the green body is 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.

[0197] The sintered materials obtained in Examples 1, 2 and 3 and Comparative Example 4 were subjected to XRD pattern analysis. The results are as follows: Figure 1 As shown in the figure, it can be seen that the main phase of the obtained powder is hexagonal Co2Z ferrite, and the alkaline earth metal ions entering the ferrite lattice due to the water quenching of the 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 FIG. Figure 2 As shown in the figure, it can be seen that the particle size of the two powders is not much different, and D50 is 1.30 and 1.35 μm respectively.

[0199] Scanning electron microscope photographs were taken 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. Figure 3 As shown, a is Example 1, and b is Comparative Example 4. It can be seen from the figure that 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 element in Figure a, (a2) the surface distribution of Co element in Figure a, (a3) ​​the surface distribution of Fe element 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 after water quenching 2+ ( Figure 4 -a4), as well as the sintering aid Bi2O3 introduced into the ferrite through the sol and the SiO2 which is a grain growth inhibitor during the sintering process, are evenly 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°C for 24 h, and then weigh 445 g of μm-BaO, 150 g of μm-CoO and 1692 g of μm-Fe2O3 for later use;

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

[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 °C for 24 h and then heated in a box furnace at 5 °C·min -1 After the temperature was raised to 1250°C and kept at this temperature for 2.5 hours, an iron-deficient Co2Z-type ferrite matrix powder having a composition of 2.9BaO·2CoO·10.6Fe2O3 was obtained; the matrix powder was then heated to 2°C·min -1 The cooling rate was reduced to 700℃ and kept at this temperature for 0.5h. The powder was taken out and directly poured 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, then allowed to stand for 24 hours, the supernatant was removed, the precipitate was washed three times by centrifugation with H2O, and the obtained 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 heated at 300 rpm. -1 The suspension was stirred at a speed of 1.0 h, and then the suspension was transferred into a ball mill, and the ball mill was performed for 6 h with corundum balls as grinding balls at a speed of 400 rpm. -1 The slurry was then dried at 80°C under stirring and then heated to 1.0°C·mim -1 The temperature was raised to 600°C and kept for 1.0h to obtain a composite powder of base phase fine powder after water quenching with a salt solution containing a 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). PVA aqueous solution containing 10 wt% of the total mass of the powder was added and ball milled for 4.0 h at a ball mill speed of 300 rpm. -1 The ball milled slurry is spray granulated and molded to obtain a green body; the green body is 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.

[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°C for 24 h, and then weigh 445 g of μm-BaO, 150 g of μm-CoO and 1692 g of μm-Fe2O3 for later use;

[0212] (2) Preparation of alkaline earth metal salt solution: Dissolve a certain amount of Ca(NO3)2·4H2O in water in a corresponding ratio of 70.85 g Ca(NO3)2·4H2O to 1000 g water to obtain about 0.3 mol 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 2468.5ml H2O mixed evenly - marked as solution A; 31.5ml TEOS and 300ml C2H5OH mixed evenly, marked as solution B; under stirring, solution B was added dropwise to solution A at a rate of 50mL·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 °C for 24 h and then heated in a box furnace at 5 °C·min -1After the temperature was raised to 1250°C and kept at this temperature for 2.5 hours, an iron-deficient Co2Z-type ferrite matrix powder having a composition of 2.9BaO·2CoO·10.6Fe2O3 was obtained; the matrix powder was then heated to 2°C·min -1 The cooling rate was reduced to 700℃ and kept at this temperature for 0.5h. The powder was taken out and directly poured 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, then allowed to stand for 24 hours, the supernatant was removed, the precipitate was washed three times by centrifugation with H2O, and the obtained 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 performed for 6 h with corundum balls as grinding balls at a speed of 400 rpm. -1 The slurry was then dried at 80°C under stirring and then heated to 1.0°C·mim -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). PVA aqueous solution containing 10 wt% of the total mass of the powder was added and ball milled for 4.0 h at a ball mill speed of 300 rpm. -1 The ball milled slurry is spray granulated and molded to obtain a green body; the green body is 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 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 2468.5ml H2O mixed evenly - marked as solution A; 31.5ml TEOS and 300ml C2H5OH mixed evenly, marked as solution B; under stirring, solution B was added dropwise to solution A at a rate of 50mL·h -1 After the addition was completed, the mixture was stirred for 1 hour to obtain SiO2 sol; 12.50 g Bi(NO3)3·5H2O was then added to the sol, and after stirring and dissolving, the composite sol was further stirred at room temperature for 24 hours, and then sealed to obtain a stable composite sol, in which Bi 3+ Concentration is about 8.59×10 -3 mol L -1 The concentration of TEOS is about 0.05 mol L -1 ;

[0220] (3) Synthesis of base phase powder: Weighed μm-BaO, μm-CoO, μm-Fe2O3 and μm-CaCO3 powders were added into 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 °C for 24 h and then heated in a box furnace at 5 °C·min -1 After heating to 1250℃, keep the temperature for 2.5h, then heat at 2℃·min -1 After the cooling rate is reduced to 600°C, 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;

[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 powder: 2 ml 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 performed for 6 h with corundum balls as grinding balls at a speed of 400 rpm. -1 The slurry was then dried at 80°C under stirring and then heated to 1.0°C·mim -1 The temperature was raised to 600°C and kept for 1.0h to obtain a composite powder of Bi2O3-SiO2 film wrapped with base phase fine powder;

[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). PVA aqueous solution containing 10 wt% of the total mass of the powder was added and ball milled for 4.0 h at a ball mill speed of 300 rpm. -1 The ball milled slurry is spray granulated and molded to obtain a green body; the green body is 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.

[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 into 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 °C for 24 h and then heated in a box furnace at 5 °C·min -1 After heating to 1250℃, keep the temperature for 2.5h, then heat at 2℃·min -1 After the cooling rate is reduced to 600°C, 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 into a corundum ball mill, the ratio of base: Bi2O3: SiO2 was 100:0.5:0.7 (mass ratio), corundum balls were used as grinding balls, ethanol was used as the medium, and 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 , 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). PVA aqueous solution containing 10 wt% of the total mass of the powder was added and ball milled for 4.0 h at a ball mill speed of 300 rpm. -1 The ball milled slurry is spray granulated and molded to obtain a green body; the green body is 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.

[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 amount of doped ions and the greater the structural distortion, the smaller the magnetic permeability and the smaller the magnetic loss at high frequencies; the higher the content of doped ions, the greater the electronegativity and the higher the dielectric constant, the smaller the electrical loss at high frequencies.

[0236] Comparison of Example 1 with Comparative Examples 1 and 2 shows that the Ca 2+ The higher the content of Ca, 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 large (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, the dielectric loss and the 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 with Comparative Example 5, Comparative Example 5 does not contain a grain growth inhibitor, so abnormal grain growth will occur in the ferrite 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] Comparative Example 1 and Comparative Example 6, without the sintering aid, the density of the sintered ferrite decreases, and the magnetic loss and the electric loss increase significantly.

[0241] By comparing Example 1 and Comparative Example 7, it can be seen that the dopant is introduced by first mixing rather than by quenching with a salt solution, and the prepared pre-synthesized Co2Z ferrite powder (Comparative Example 7) has the same composition as the pre-synthesized powder of Example 1. Due to the lack of the powder size refinement caused by the water quenching and the special structure of "distorted outer layer structure and complete inner layer lattice" formed by the salt solution water quenching, the main magnetic properties of the ferrite obtained in Comparative Example 7 after sintering are significantly reduced;

[0242] By comparing the effects of Example 1 and Comparative Example 8, it can be seen that the composition of the pre-synthesized ferrite powder in both is the same, but the sintering aid and the grain growth inhibitor in Example 1 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 the sintering aid and the grain growth inhibitor in Example 8 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 relatively low sintering temperature, and 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 principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. An iron-deficient Co 2 Z-type ferrite, It is characterized in that It includes a ferrite base material and a sintering aid, wherein the ferrite base material is composed of 2.9BaO·xReO·2CoO·10.6Fe 2 O 3 ; ReO is a dopant, where Re is the ionic radius and Ba 2+ Close but not equal cations; the ionic radius of Re is 0.0945-0.1755nm; the sintering aids include aids that promote sintering and aids that limit grain growth during sintering; x is 0.08-0.

1.

2. The iron-deficient Co according to claim 1 2 Z-type ferrite, It is characterized in that Re is Sr 2+ , Ca 2+ and Mg 2+ One or more of the .

3. The iron-deficient Co according to claim 1 2 Z-type ferrite, It is characterized in that The sintering aid is Bi 2 O 3 , Nb 2 O 5 or V 2 O 5 The additive for limiting the grain growth during sintering is SiO 2 , MgO or Al 2 O 3 .

4. The iron-deficient Co according to any one of claims 1 to 3 2 Preparation method of Z-type ferrite, It is characterized in that The following steps are involved: S1, drying, ball-milling and sintering barium oxide, cobalt oxide and iron oxide to obtain powder; adding the powder to a dopant solution and quenching with a salt solution to obtain a ferrite base material; S2, adding an alcohol solvent to the auxiliary agent precursor that limits the grain growth during the sintering process, stirring and dissolving, adding a mixed solvent of acid and water, and reacting to obtain A sol; adding an auxiliary agent precursor that promotes sintering to A sol, stirring evenly, After standing and sealing for 200-280 hours, a composite sol is obtained; S3, mixing the ferrite base material and the composite sol, and then ball milling, drying, and heat treating to obtain a composite powder with a core-shell structure; S4, after ball-milling the composite powder, adding a binder and continuing ball-milling to obtain a slurry; spraying the slurry into granules and pressing the slurry into a green body; drying and sintering the green body to obtain the iron-deficient Co 2 Z-type ferrite.

5. The preparation method according to claim 4, It is characterized in that The barium oxide, cobalt oxide and iron oxide are all micrometer-sized; Preferably, the particle size D50 of the barium oxide, cobalt oxide and iron oxide is 0.5-2.0 μm.

6. The preparation method according to claim 4, It is characterized in that The molar ratio of the barium oxide, the cobalt oxide and the iron oxide is 2.5-3.5:1-3:10-11.

7. The preparation method according to claim 4, It is characterized in that The medium for ball milling in step S1 is ethanol or water. The ball milling time is 4-8h, 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: at 3-7℃·mim -1 The heating rate is increased to 800-1500℃ and then kept at this temperature for 0.5-8h; then heated at 1-3℃·min -1 The cooling rate is reduced to 300-800℃ and then kept warm for 0.2-4h.

8. The preparation method according to claim 4, It is characterized in that The salt solution quenching in step S1 refers to: adding powder to the dopant solution for 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, preferably 400-800°C; the ratio of the nitrate solution of the dopant to the powder is 10-200ml solution / 1g powder, preferably 50-150ml solution / 1g powder.

9. The preparation method according to claim 4, It is 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; preferably 0.10-1.00:1; preferably, 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 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, and the sintering time is 0.2-4h; the sintering heating rate in step S4 is 1-6°C·mim -1 , sintering temperature is: 600-1300℃, and sintering time is 1-8h.

10. The iron-deficient Co according to any one of claims 1 to 3 2 Application of Z-type ferrite in the preparation of substrate materials for mobile phone antennas.

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