A hollow fibrous barium ferrite and its preparation method

Abstract

This invention discloses a method for preparing a hollow fibrous barium ferrite, specifically in the field of composite materials. The method comprises three steps: First, polyvinylpyrrolidone is dissolved in a polar solvent and stirred until completely dissolved. A soluble barium salt, a soluble iron salt, and citric acid are then added in proportion to prepare a spinning precursor sol. Second, the spinning precursor sol is extruded through an injection device, with an air source flow at the outlet to blow the sol into filaments, which are then collected to obtain a barium ferrite precursor fiber sponge. Third, the barium ferrite precursor fiber sponge is heated and sintered until fully sintered, and then naturally cooled to obtain the hollow fibrous barium ferrite. The hollow barium ferrite synthesized by this invention achieves adjustable grain configuration and macroscopic hollow structure. Its impedance matching performance and electromagnetic wave attenuation characteristics are good, making it suitable for applications in high-density perpendicular magnetic recording materials, microwave devices, and microwave absorbing materials.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of composite materials, in particular to a hollow fibrous barium ferrite and a preparation method thereof. BACKGROUND

[0002] In recent years, with the development of modern electromagnetic technology, advanced electronic communication technology and intelligent sensor devices have developed rapidly, and the potential harm of the emitted electromagnetic waves has become increasingly prominent. Therefore, the research on electromagnetic wave absorbing materials has become the focus in the field of material science. In order to meet the multi-frequency band requirements of wave absorbing materials, a three-dimensional porous network structure of wave absorbing materials is established, and the synergistic effect of dielectric loss and magnetic loss is used to realize the maximum attenuation of electromagnetic wave radiation.

[0003] Among them, the magnetic wave absorbing agent barium ferrite (BaFe12O19) has high Curie temperature, magnetic saturation strength and coercive force, and large uniaxial magnetic crystal anisotropy. It is stable in physical and chemical properties, has relatively good impedance matching with electromagnetic waves, and is widely studied. Although the surface magnetic particle modification and multi-dimensional wave absorbing structure design greatly improve the electromagnetic absorption capacity of the wave absorbing system, the introduction of non-magnetic conductive fillers and single magnetic particles makes these wave absorbing systems exhibit dielectric loss-based absorption characteristics. Due to the lack of optimization of the intrinsic properties and structure of the magnetic material, the particle size of the magnetic material prepared by the traditional method is too large, the coercive force is small, and it is difficult to produce significant magnetic loss capacity.

[0004] The prior art Chinese patent: a preparation method of barium ferrite / carbon nanotube / poly-3-methyl thiophene composite wave-absorbing material (publication number: CN102964571B) discloses that barium ferrite is prepared by using Ba(NO3)2·6H2O and Fe(NO3)3·9H2O as raw materials by adopting a sol-gel self-propagating combustion method, and then the barium ferrite / carbon nanotube / poly-3-methyl thiophene composite wave-absorbing material is prepared by using the barium ferrite, 20-30 nm multi-walled carbon nanotubes and 3-methyl thiophene monomers as raw materials by adopting an in-situ polymerization method. The method needs three steps for preparation, the process is complicated, and the simple blending and grinding method cannot realize the adjustment of the crystal structure and the macrostructure, and it is difficult to ensure the structural stability of the composite material. The Chinese patent: a barium ferrite-Al2O3 porous SiC loaded polyaniline wave-absorbing coating and a preparation method thereof (publication number: CN112048239A) discloses that a plurality of intermediates are prepared through multiple calcination steps, including: porous nano-SiC hollow microsphere preparation, SiC hollow microsphere loaded nano-Al2O3 preparation, lanthanum-doped barium ferrite-SiC hollow microsphere loaded nano-Al2O3 preparation and modified barium ferrite-Al2O3-SiC composite material preparation, finally realizing the barium ferrite-Al2O3 porous SiC loaded polyaniline wave-absorbing coating, and the preparation process is quite complicated. Although the multi-step preparation method realizes the design of the macrostructure of the composite material, the addition of the conductive polymer makes the system present a wave-absorbing mechanism mainly based on dielectric loss, and the magnetic loss mechanism cannot be deeply explored. The document (J. Magn. Magn. Mater. 2016, 412, 55-62) discloses a research on preparation of low-coercivity barium ferrite hollow fibers by a coaxial electrospinning method, which uses sesame oil as a core layer precursor solution and Ba(NO3)2 and Fe(NO3)3·9H2O as outer layer precursor solutions, to prepare fibers with a core-shell structure by coaxial spinning, and to obtain a hollow fiber structure by removing the core layer after calcination. However, from the observation of the micro-morphology of the fibers, the hollow structure does not appear and the hollow structure is uneven, so that the magnetic properties of the barium ferrite (BaFe 12 O 19 ) hollow fiber are difficult to utilize the advantages of the structure to fully play the characteristics of the multi-magnetic-domain ferrite. SUMMARY

[0005] The purpose of the present application is to provide a hollow fiber-like barium ferrite with a simple preparation method and optimized crystal structure and macrostructure, and a preparation method thereof. The size and dimension of the barium ferrite (BaFe 12 O 19 ) magnetic particles are designed, including the crystal configuration and the macrostructure, so as to change the lattice parameters, introduce special magnetic domain structure and new loss mechanism, realize the effective play of the magnetic loss capacity and the effective attenuation of the electromagnetic wave, and meet the effect of "thin, light, wide and strong" of the wave-absorbing system.

[0006] In order to achieve the above-mentioned purposes, the present application provides the following technical solutions.

[0007] A preparation method of hollow fibrous barium ferrite, comprising the following steps:

[0008] S1: adding 10%-25% of polyvinyl pyrrolidone into a polar solvent, stirring for 4-6h until the polyvinyl pyrrolidone is completely dissolved, and then adding soluble barium salt, soluble iron salt and citric acid in a molar ratio of Ba 2+ : Fe 3+ : 1:10-14:12-18 to obtain a spinning precursor sol, wherein the content of the polyvinyl pyrrolidone is about 8%-10%, and the stirring is performed for 3-6h until complete dissolution;

[0009] S2: loading the sol into an injection device, wherein the liquid outlet diameter of the injection device is 0.1-2mm, the extrusion rate of the spinning precursor sol is 0.01-0.1ml / min, and an air source flow with a pressure of 0.1-0.3MPa is applied at the liquid outlet, and the spinning precursor fiber sponge is collected to obtain a barium ferrite precursor fiber sponge;

[0010] S3: drying the barium ferrite precursor fiber sponge at 75-85℃ for 0.5-1.5h, heating to 500-1100℃ at a heating rate of 5-15℃ / min and maintaining for 3-6h, and naturally cooling to obtain the hollow fibrous barium ferrite.

[0011] Polyvinyl pyrrolidone (PVP) is a non-ionic high molecular compound, which is dissolved in a polar solution, and then soluble barium salt, soluble iron salt and citric acid are added to prepare a sol. The sol is extruded from the tip of an injection device, and a barium ferrite precursor fiber sponge is collected by an air flow spinning method. The air flow spinning method refers to: under the action of an air source flow with a certain pressure, air flow spinning is performed, and by adjusting the air source pressure, the injection speed and the distance of the receiving device, the barium ferrite (BaFe 12 O 19 ) precursor fiber sponge is adjusted and collected. The hollow fibrous barium ferrite is obtained by heating with a heating device.

[0012] Preferably, the molar ratio of Ba 2+ , Fe 3+ and citric acid is 1:12:15.

[0013] By adjusting the component ratio of raw materials, the efficiency of the barium ferrite is higher, and the residual unreacted impurity components are less.

[0014] Preferably, the polyvinylpyrrolidone (PVP) in step S1 includes one or more of K88-96, K30.

[0015] PVP is a spinning aid, has good adhesion, has the effects of compatibilization and coagulation, PVP with different molecular weights has different solubility, which is conducive to the adjustment of hollow structure, wherein: polyvinylpyrrolidone (PVP K88-96) is a white to light brown yellow free-flowing amorphous powder, no peculiar smell, widely used as thickening agent, emulsifier, lubricant and clarifying agent, also as a complex of disinfectant PVP-I; polyvinylpyrrolidone (PVP K30) is a white powder, has a slight odor, has strong hygroscopicity, is easily soluble in water, ethanol, diethyl ether and other organic solvents, has very strong complex adsorption capacity.

[0016] Preferably, the polar solvent in step S1 includes one or more of N,N-dimethylformamide (DMF), tetrahydrofuran, dimethylformamide, dimethylacetamide, N-methyl pyrrolidone and ethanol.

[0017] N,N-dimethylformamide (DMF), tetrahydrofuran, dimethylformamide, dimethylacetamide, N-methyl pyrrolidone and ethanol have good solubility and better volatility, which is conducive to the formation of spinning fibers.

[0018] Preferably, the soluble barium salt in step S1 is one or more of barium nitrate and barium chloride.

[0019] Preferably, the soluble barium salt in step S1 is barium nitrate.

[0020] Barium nitrate has good solubility, and the reaction conversion rate of the precursor is high.

[0021] Preferably, the soluble iron salt in step S1 is one or more of ferric nitrate, ferric carbonate and ferrous carbonate.

[0022] Preferably, the soluble iron salt in step S1 is ferric nitrate.

[0023] Ferric nitrate has good corrosion resistance, diffusivity and reactivity.

[0024] Preferably, the environmental temperature in step S2 is 20-30℃, the relative humidity is 50%-60%, and the spinning collection distance is 25-35cm.

[0025] The appropriate temperature and humidity are conducive to the formation of spinning, and the position of the collection device is adjusted constantly during the process to avoid the influence of air flow on the accumulation of spinning fibers, so as to obtain barium ferrite (BaFe 12 O 19 ) precursor fiber sponge with good morphology.

[0026] Preferably, the injection device in step S2 is a syringe.

[0027] The syringe can simply and quickly control the extrusion rate of the spinning precursor sol.

[0028] Preferably, the heating device in step S3 is a muffle furnace.

[0029] The muffle furnace has the advantages of strong stability, good heat preservation effect, high safety, etc., and through it, the barium ferrite (BaFe 12 O 19 ) precursor fiber sponge can be heated and burned, which can effectively ensure the yield of the hollow fibrous barium ferrite.

[0030] Preferably, the heating process in step S3 needs to open the air inlet of the muffle furnace.

[0031] During the heating process, the air inlet can introduce air into the heating equipment to ensure that the barium ferrite (BaFe 12 O 19 ) precursor fiber sponge is fully sintered, and finally the hollow fibrous barium ferrite is obtained.

[0032] A hollow fibrous barium ferrite prepared by the above method.

[0033] The hollow fibrous barium ferrite can effectively regulate the intrinsic properties of magnetic materials, has good impedance matching performance and electromagnetic wave attenuation characteristics of the wave absorption system, and can realize effective play of magnetic loss ability and effective attenuation of electromagnetic waves.

[0034] Compared with the prior art, the beneficial effects of the present application are:

[0035] 1. The synthesis process of the present application is simple, the synthesis time is short, it is green and environmentally friendly, the production cost is low, and mass production can be easily realized.

[0036] 2. The hollow fibrous barium ferrite (BaFe 12 O 19 ) synthesized by the present application realizes the adjustment of the grain configuration and the macroscopic hollow structure under the action of airflow spinning shear and muffle furnace heating and burning, reassigns its lattice parameters, introduces special magnetic domain structure and new loss mechanism, has good impedance matching performance and electromagnetic wave attenuation characteristics of the wave absorption system, and can be used in the fields of high-density perpendicular magnetic recording materials, microwave devices, wave absorption materials, etc. BRIEF DESCRIPTION OF DRAWINGS

[0037] Figure 1 is a schematic diagram of the nanostructure of the hollow fibrous barium ferrite (BaFe 12 O 19 ) of the present application (wherein A is a side view and B is an elevation view).

[0038] Figure 2 Hysteresis loop diagram of the hollow fibrous barium ferrite (BaFe 12 O 19 ) nanostructure. 12 O 19 ) nanostructure. 12 O 19 ) nanostructure.

[0039] Figure 3 Hysteresis loop diagram of the hollow fibrous barium ferrite (BaFe 12 O 19 ) nanostructure.

[0040] Figure 4 Wave-absorbing performance diagram of the magnetic wave-absorbing agent of the hollow fibrous barium ferrite (BaFe 12 O 19 ) nanostructure. DETAILED DESCRIPTION

[0041] The present application will be further described in conjunction with test examples and specific embodiments. However, it should not be understood that the scope of the above-mentioned subject matter of the present application is limited to the following examples, and any technology realized based on the content of the present application falls within the scope of the present application.

[0042] Example 1

[0043] As Figures 1-4 , 0.6 g of polyvinylpyrrolidone (PVP K88-96) was dissolved in 4.6 g of N,N-dimethylformamide (DMF). After stirring for 5 h until the PVP was completely dissolved. Then, 0.367 g of barium nitrate, 0.563 g of iron nitrate and 0.72 g of citric acid were added to the above solution, and stirred for 5 h until completely dissolved to obtain a spinning precursor sol.

[0044] Then, the spinning precursor sol was sucked into a syringe with a needle caliber of 1 mm, and the spinning precursor sol was extruded from the syringe at a constant injection rate of 0.03 ml / min, while an air source flow with a pressure of 0.1 MPa was applied at the injection needle port, and the room temperature was controlled at 20-30 ℃ and the relative humidity was controlled at 50%-60%, and the electrospinning was carried out to obtain a barium ferrite precursor fiber sponge.

[0045] During the spinning, the position of the collecting device was constantly adjusted so that the collection distance was always 30 cm, and a barium ferrite (BaFe12 O 19 ) precursor fiber sponge.

[0046] After the spinning is finished, the barium ferrite (BaFe 12 O 19 ) precursor fiber sponge is placed in a vacuum oven at 80°C for 1h. Then it is transferred to a muffle furnace, and heated to 900°C at a rate of 10°C / min in air atmosphere and kept for 5h, and then cooled with the furnace to obtain hollow fiber-like barium ferrite.

[0047] The obtained hollow fiber-like barium ferrite (BaFe 12 O 19 ) is mixed with polyethylene wax in a certain proportion, and then cut into a circular ring with an inner diameter of 3mm and an outer diameter of 7mm. The wave absorption performance of the composite material is obtained by a vector network analyzer. The final obtained magnetic wave absorber has good magnetic performance, with a saturation magnetization of 62emu / g and a coercive force of 5.2kOe; the minimum reflection loss of the wave absorption performance is−27.3dB, and the widest effective absorption bandwidth is 1.5GHz.

[0048] Example 2

[0049] As Figures 3-4 , 0.6g of polyvinylpyrrolidone (PVP K88-96) is dissolved in 4.6g of N,N-dimethylformamide (DMF). After stirring for 5h, the PVP is completely dissolved. Then, 0.367g of barium nitrate, 0.563g of iron nitrate and 0.72g of citric acid are added to the above solution, and stirred for 5h until completely dissolved to obtain a spinning precursor sol.

[0050] Then, the spinning precursor sol is sucked into a syringe with a needle caliber of 1mm, and the spinning precursor sol is extruded from the syringe at a constant injection rate of 0.03ml / min, while an air source airflow with a pressure of 0.1MPa is applied at the injection needle port. The room temperature is controlled at 20-30°C, and the relative humidity is controlled at 50%-60%, and the electrospinning is carried out to obtain a barium ferrite precursor fiber sponge.

[0051] During the spinning, the position of the collection device is constantly adjusted so that the collection distance is always 30cm, and a barium ferrite (BaFe 12 O 19 ) precursor fiber sponge with good morphology is obtained.

[0052] After the spinning is finished, the barium ferrite (BaFe 12 O 19The precursor fiber sponge was placed in a vacuum oven at 80 °C for 1 h. Then it was transferred to a muffle furnace, and heated to 500 °C at a rate of 10 °C / min in air atmosphere and kept for 5 h, and then cooled with the furnace to obtain hollow fibrous barium ferrite.

[0053] The obtained hollow fibrous barium ferrite (BaFe 12 O 19 ) was mixed with polyethylene wax in a certain proportion, and then cut into a ring with an inner diameter of 3 mm and an outer diameter of 7 mm. The wave absorption performance of the composite material was obtained by a vector network analyzer. The minimum reflection loss of the finally obtained magnetic wave absorber was -6.2 dB, and the widest effective absorption bandwidth was 0 GHz.

[0054] Example 3

[0055] As Figures 3-4 , 0.6 g of polyvinylpyrrolidone (PVP K88-96) was dissolved in 4.6 g of N,N-dimethylformamide (DMF). After stirring for 5 h, the PVP was completely dissolved. Then, 0.367 g of barium nitrate, 0.563 g of iron nitrate, and 0.72 g of citric acid were added to the above solution, and stirred for 5 h until completely dissolved to obtain a spinning precursor sol.

[0056] Then, the spinning precursor sol was sucked into a syringe with a needle caliber of 1 mm, and the spinning precursor sol was extruded from the syringe at a constant injection rate of 0.03 ml / min, while an air source flow with a pressure of 0.1 MPa was applied at the injection needle port. The room temperature was controlled at 20-30 °C, and the relative humidity was controlled at 50%-60%, and air flow spinning was carried out to obtain barium ferrite precursor fiber sponge.

[0057] During spinning, the position of the collection device was constantly adjusted so that the collection distance was always 30 cm, and barium ferrite (BaFe 12 O 19 ) precursor fiber sponge with good morphology was obtained.

[0058] After spinning was completed, the barium ferrite (BaFe 12 O 19 ) precursor fiber sponge was placed in a vacuum oven at 80 °C for 1 h. Then it was transferred to a muffle furnace, and heated to 700 °C at a rate of 10 °C / min in air atmosphere and kept for 5 h, and then cooled with the furnace to obtain hollow fibrous barium ferrite.

[0059] The hollow fiber-like barium ferrite obtained is mixed with polyethylene wax in a certain proportion, and then cut into a ring with an inner diameter of 3 mm and an outer diameter of 7 mm. The wave absorption performance of the composite material is obtained by a vector network analyzer. The minimum reflection loss of the finally obtained magnetic wave absorber is-8.2 dB, and the widest effective absorption bandwidth is 0 GHz.

[0060] Example 4

[0061] As Figures 3-4 , 0.6 g of polyvinylpyrrolidone (PVP K88-96) is dissolved in 4.6 g of N,N-dimethylformamide (DMF). After stirring for 5 h, the PVP is completely dissolved. Then, 0.367 g of barium nitrate, 0.563 g of iron nitrate, and 0.72 g of citric acid are added to the above solution, and stirred for 5 h until completely dissolved to obtain a spinning precursor sol.

[0062] Then, the spinning precursor sol is sucked into a syringe with a needle caliber of 1 mm, and the spinning precursor sol is extruded from the syringe at a constant injection rate of 0.03 ml / min, while an air source airflow with a pressure of 0.1 MPa is applied at the injection needle port. The room temperature is controlled at 20-30 ℃, and the relative humidity is 50%-60%, and the electrospinning is carried out to obtain a barium ferrite precursor fiber sponge.

[0063] During the spinning, the position of the collection device is constantly adjusted so that the collection distance is always 30 cm, and a barium ferrite (BaFe 12 O 19 ) precursor fiber sponge with good morphology is obtained.

[0064] After the spinning is completed, the barium ferrite (BaFe 12 O 19 ) precursor fiber sponge is placed in a vacuum oven at 80 ℃ for 1 h. Then it is transferred to a muffle furnace, and heated to 1100 ℃ at a rate of 10 ℃ / min in an air atmosphere and kept for 5 h, and then cooled with the furnace to obtain a hollow fiber-like barium ferrite.

[0065] The hollow fiber-like barium ferrite obtained is mixed with polyethylene wax in a certain proportion, and then cut into a ring with an inner diameter of 3 mm and an outer diameter of 7 mm. The wave absorption performance of the composite material is obtained by a vector network analyzer. The minimum reflection loss of the finally obtained magnetic wave absorber is-8.2 dB, and the widest effective absorption bandwidth is 0 GHz.

[0066] Comparative Example

[0067] 0.6 g of polyvinylpyrrolidone (PVP K88-96) was dissolved in 4.6 g of N,N-dimethylformamide (DMF). After stirring for 5 h until the PVP was completely dissolved. Then 0.367 g of barium nitrate, 0.563 g of iron nitrate and 0.72 g of citric acid were added to the above solution, stirred for 5 h until completely dissolved, to obtain a spinning precursor sol.

[0068] The obtained spinning precursor sol was placed in a vacuum oven at 80℃ for 1 h. Then it was ignited in air to make it undergo a self-propagating combustion reaction, to obtain fluffy coral-like black-brown powder. Then it was transferred to a muffle furnace, heated to 900℃ at a rate of 10 ℃ / min in air and kept for 5 h, and then cooled with the furnace, to obtain barium ferrite. The final obtained magnetic wave absorber has a minimum reflection loss of -8.9 dB and the widest effective absorption bandwidth of 0 GHz.

[0069] Through the analysis of Example 1 and Comparative Example, compared with the single structure of barium ferrite crystal structure obtained by self-propagating combustion method, the hollow fiber-like barium ferrite magnetic wave absorber treated at 900℃ has an optimized crystal structure and macrostructure, which reassigns its lattice parameters, introduces special magnetic domain structure and new magnetic loss mechanism. In the constructed wave absorption system, due to the hollow structure and three-dimensional porous network structure, it is beneficial to maximize the electromagnetic wave incidence and effective absorption, so as to realize the optimization of foam impedance matching performance and its attenuation characteristics, and meet the effect of "thin, light, wide and strong" of the wave absorption material.

[0070] The above only describes the preferred embodiments of the present application and should not be used to limit the present application. Any modification, equivalent replacement and improvement made within the spirit and principle of the present application should be included in the protection scope of the present application.

Claims

1. A method for producing a hollow fiber-shaped barium ferrite, characterized by, The method comprises the following steps: S1: add 10-25% polyvinylpyrrolidone to a polar solvent, stir for 4-6h until the polyvinylpyrrolidone is completely dissolved, then add soluble barium salt, soluble iron salt and citric acid in a molar ratio of 1:10-14:12-18 to a content of 8-10% polyvinylpyrrolidone, stir for 3-6h until completely dissolved to obtain a spinning precursor sol; 2+ : Fe 3+ : soluble barium salt, soluble iron salt and citric acid in a molar ratio of 1:10-14:12-18 to a content of 8-10% polyvinylpyrrolidone, stir for 3-6h until completely dissolved to obtain a spinning precursor sol; S2: loading the spinning precursor sol into an injection device, the outlet diameter of the injection device is 0.1-2 mm, the extrusion rate of the spinning precursor sol is 0.01-0.1 ml / min, the injection device is a syringe used to control the extrusion rate of the spinning precursor sol; an air source flow with a pressure of 0.1-0.3 MPa is applied at the outlet, and the spinning precursor sol is collected to obtain a barium ferrite precursor fiber sponge; the ambient temperature is 20-30°C, the relative humidity is 50%-60%, and the spinning collection distance is 25-35 cm; S3: drying the barium ferrite precursor fiber sponge at 75-85°C for 0.5-1.5 h, heating to 500-1100°C at a heating rate of 5-15°C / min and maintaining for 3-6 h, using a muffle furnace, opening the air inlet of the muffle furnace during the heating process, and introducing air into the heating device to ensure that the barium ferrite precursor fiber sponge is fully sintered; and naturally cooling to obtain the hollow fiber-like barium ferrite.

2. The method of producing a hollow fiber-shaped barium ferrite according to claim 1, characterized by, The polyvinylpyrrolidone in step S1 comprises one or more of K88-96 and K30.

3. The method for preparing hollow fibrous barium ferrite as described in claim 1, characterized in that, The polar solvent in step S1 comprises one or more of N,N-dimethylformamide, tetrahydrofuran, dimethylformamide, dimethylacetamide, N-methylpyrrolidone, and ethanol.

4. The method for preparing hollow fibrous barium ferrite as described in claim 1, characterized in that, The soluble barium salt in step S1 is one or more of barium nitrate and barium chloride.

5. The method for preparing hollow fibrous barium ferrite as described in claim 1, characterized in that, The soluble iron salt in step S1 is one or more of iron nitrate, iron carbonate, and ferrous carbonate.

6. The method for preparing hollow fibrous barium ferrite as described in claim 1, characterized in that, The injection device in step S2 is a syringe.

7. A hollow fiber-like barium ferrite prepared by the method of any one of claims 1-6.

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