Iron tetranitrogen / zirconium dioxide / carbon composite nanofiber material and preparation method and application thereof

Abstract

The application discloses a kind of iron tetranitrogen / zirconium dioxide / carbon composite nanofiber materials and preparation method and application thereof, belong to electromagnetic wave absorbing material technical field.The preparation method of the present application includes the following steps: iron salt, zirconium salt and polymer carbon source are dispersed in solvent to carry out electrostatic spinning, and obtain nanofiber precursor;The nanofiber precursor is pre-oxidized, and high-temperature carbonization reaction is carried out to obtain iron oxide / zirconium dioxide / carbon composite nanofiber material;The iron oxide / zirconium dioxide / carbon composite nanofiber material is nitriding in ammonia, and is obtained.The synthesis method of the present application is simple, no other by-products are generated in heat treatment process, the prepared iron tetranitrogen / zirconium dioxide / carbon composite nanofiber material is uniform in diameter, narrow in diameter distribution, and has excellent electromagnetic wave absorbing performance.

Description

Technical Field

[0001] This invention relates to the field of electromagnetic wave absorbing materials technology, and in particular to a ferro-nitrogen / zirconium dioxide / carbon composite nanofiber material, its preparation method, and its application. Background Technology

[0002] The information disclosed in the background section of this invention is intended only to enhance the understanding of the overall background of the invention and is not necessarily to be construed as an admission or in any way implying that such information constitutes prior art known to those skilled in the art.

[0003] The increasingly serious problem of electromagnetic pollution can interfere with the operation of precision instruments and threaten human life. Therefore, the development of electromagnetic wave absorbing materials with high strength and wide bandwidth absorption has become one of the hot topics in the scientific community. For example, patent CN 113652769 B (authorization announcement date: August 22, 2023) discloses the preparation of Fe3C / C fiber composite microwave absorber and its application in microwave absorption. Among many materials, transition metal nitrides have become one of the candidate materials for the next generation of electromagnetic wave absorption, following metal oxides, sulfides, and carbides, due to their high conductivity, excellent chemical stability, and corrosion resistance. Among them, iron tetranitrogen (ITN) has attracted widespread attention from scholars due to its excellent electromagnetic properties, mechanical properties, and oxidation resistance. In particular, compared with materials such as Fe2O3 or Fe3C, ITN can exert multiple loss mechanisms due to its higher electrical conductivity and magnetic permeability, and has the potential to become a high-quality electromagnetic wave absorber.

[0004] Precise atomic ratios and suitable nitriding temperatures are key factors in ensuring the synthesis of pure iron in the tetranitrogen phase. Traditional direct nitriding methods are extremely demanding, making it impossible to achieve controllable preparation of nitrides. Using a programmed temperature rise method in an ammonia atmosphere for nitriding, controlling the ammonia decomposition rate by adjusting temperature and gas flow rate, and thus regulating the ratio of iron atoms to active nitrogen atoms, is a highly reasonable approach. For example, patent CN 111704115 A (publication date: 2020.09.25) discloses the preparation of pure-phase Fe4N by calcining α-Fe2O3 obtained through a hydrothermal reaction under ammonia. However, pure-phase Fe4N has limited electromagnetic wave absorption performance; its extremely high conductivity leads to severe impedance mismatch, limiting its application in higher-end fields. Rational design and combination of material components to form multi-component composite materials, utilizing synergistic effects to leverage the advantages of each component, is an effective method to improve the performance of microwave absorbing materials. How to prepare Fe4N composite materials with strong loss capacity and a wide effective absorption bandwidth is an urgent problem to be solved. Summary of the Invention

[0005] In view of this, the present invention provides a Fe4N / zirconia / carbon composite nanofiber material, its preparation method and application, which solves the problems of weak loss capacity and narrow effective absorption bandwidth of pure phase Fe4N.

[0006] In a first aspect, the present invention provides a method for preparing iron tetranitrogen / zirconium dioxide / carbon composite nanofibers, comprising the following steps:

[0007] Iron salts, zirconium salts and polymer carbon sources were dispersed in a solvent and electrospun to obtain nanofiber precursors.

[0008] The nanofiber precursor was subjected to pre-oxidation and high-temperature carbonization to obtain a magnetite / zirconia / carbon composite nanofiber material.

[0009] The iron(II) oxide / zirconia / carbon composite nanofiber material is obtained by nitriding in ammonia gas.

[0010] Preferably, the solvent is a mixture of N,N-dimethylformamide and glacial acetic acid, wherein the volume ratio of N,N-dimethylformamide to glacial acetic acid is (10-30):1.

[0011] Preferably, the iron salt is ferric acetylacetone or ferric nitrate;

[0012] Alternatively, the zirconium salt is zirconium n-butoxide or zirconium acetylacetonate;

[0013] Alternatively, the carbon source of the polymer may be polyvinylpyrrolidone or polyacrylonitrile.

[0014] Preferably, the ratio of the iron salt, zirconium salt, polymer carbon source and solvent is (0.2-2)g:(0.5-2)g:(0.5-5)g:(5-20)mL.

[0015] Preferably, the pre-oxidation is carried out in an air atmosphere at a temperature of 120–250°C for a time of 80–400 min.

[0016] Preferably, the high-temperature carbonization reaction is carried out at a temperature of 500–1000°C, a heating rate of 1–5°C / min, and a reaction time of 1–5 h.

[0017] Preferably, the nitriding reaction is carried out at a temperature of 400–700°C, a heating rate of 1–6°C / min, and a reaction time of 1–4 h.

[0018] Secondly, the present invention provides a ferronitrogen / zirconium dioxide / carbon composite nanofiber material obtained by the above preparation method.

[0019] Thirdly, the present invention provides the application of the above-mentioned iron tetranitrogen / zirconium dioxide / carbon composite nanofiber material in the field of electromagnetic wave absorption.

[0020] Fourthly, the present invention provides a microwave absorbing material, including the above-mentioned iron tetranitrogen / zirconium dioxide / carbon composite nanofiber material.

[0021] Compared with the prior art, the present invention has achieved the following beneficial effects:

[0022] (1) The synthesis method of the present invention is simple, requiring only one electrospinning, one high-temperature carbonization reaction and one nitriding reaction to obtain the final product. The prepared iron tetranitrogen / zirconia / carbon composite nanofiber material has a uniform diameter and narrow diameter distribution, and no other by-products are generated during the heat treatment process.

[0023] (2) In the iron-tetranitrogen / zirconium dioxide / carbon composite nanofiber material prepared by the present invention, Fe4N has high saturation magnetization and high conductivity, excellent oxidation resistance and stable mechanical properties, which improves the magnetic and electrical conductivity of the material and enhances magnetic loss and electrical conductivity loss; ZrO2 is a low-loss transparent material that can allow electromagnetic waves to enter the material smoothly without reflection, which helps to tune the electromagnetic parameters of the material and optimize impedance matching; carbon has advantages such as low density, large reserves, strong chemical stability and strong corrosion resistance, and can be used as a good skeleton material; the presence of fiber structure can cause multiple scattering of electromagnetic waves inside the material, and at the same time help energy transfer and promote the consumption of electromagnetic energy; therefore, the iron-tetranitrogen / zirconium dioxide / carbon composite nanofiber material of the present invention exerts excellent electromagnetic wave absorption performance through the synergistic effect of each substance and structure, has strong loss capacity and wide effective absorption bandwidth, and is expected to be widely used in the preparation of electromagnetic wave absorbing materials. Attached Figure Description

[0024] The accompanying drawings, which form part of this specification, are used to provide a further understanding of the invention. The illustrative embodiments and descriptions of the invention are used to explain the invention and do not constitute an undue limitation thereof. Obviously, those skilled in the art can obtain other drawings based on these drawings without any inventive effort.

[0025] Figure 1 This is the XRD pattern of the iron tetranitrogen / zirconium dioxide / carbon composite nanofibers prepared in Example 1 of this invention;

[0026] Figure 2 a is a SEM image of the iron(II) oxide / zirconia / carbon composite nanofiber precursor of Example 1 of the present invention; Figure 2 b is a SEM image of the iron(II) oxide / zirconia / carbon composite nanofibers of Example 1 of the present invention; Figure 2 c is a SEM image of the iron tetranitrogen / zirconium dioxide / carbon composite nanofibers of Example 1 of the present invention; Figure 2d is a TEM image of the iron tetranitrogen / zirconium dioxide / carbon composite nanofibers of Example 1 of the present invention;

[0027] Figure 3 This is the XRD pattern of the iron-nitrogen / carbon composite nanofibers prepared in Comparative Example 1 of this invention;

[0028] Figure 4 This is a SEM image of the iron-nitrogen / carbon composite nanofibers prepared in Comparative Example 1 of this invention.

[0029] Figure 5 This is the XRD pattern of the zirconium dioxide / carbon composite nanofibers prepared in Comparative Example 2 of this invention;

[0030] Figure 6 This is a SEM image of the zirconium dioxide / carbon composite nanofibers prepared in Comparative Example 2 of this invention.

[0031] Figure 7 The composite microwave absorbing material prepared from the iron tetranitrogen / zirconium dioxide / carbon composite nanofibers obtained in Example 1 of this invention includes: (a) real part diagram of dielectric constant; (b) imaginary part diagram of dielectric constant; (c) tangent diagram of dielectric loss; and (d) Cole-Cole diagram.

[0032] Figure 8 The composite microwave absorbing material prepared from the iron-nitrogen / zirconium dioxide / carbon composite nanofibers obtained in Example 1 of this invention includes: (a) real part diagram of magnetic permeability; (b) imaginary part diagram of dielectric constant; and (c) tangent diagram of magnetic loss.

[0033] Figure 9 The composite microwave absorbing material prepared from the iron tetranitrogen / zirconium dioxide / carbon composite nanofibers obtained in Example 1 of this invention includes: (a) attenuation coefficient diagram; (b) impedance matching diagram;

[0034] Figure 10 The composite microwave absorbing material prepared from the iron-tetranitrogen / zirconium dioxide / carbon composite nanofibers obtained in Example 1 of this invention is shown in: (a) a three-dimensional reflection loss diagram; (b) Figure 10 a corresponds to the two-dimensional reflection loss projection diagram;

[0035] Figure 11 The composite microwave absorbing material prepared from iron-nitrogen / carbon composite nanofibers in Comparative Example 1 of this invention includes: (a) attenuation coefficient diagram; (b) impedance matching diagram;

[0036] Figure 12 The composite microwave absorbing material prepared from iron-tetranitrogen / carbon composite nanofibers in Comparative Example 1 of this invention is shown in: (a) a three-dimensional reflection loss diagram; (b) Figure 12 a corresponds to the two-dimensional reflection loss projection diagram;

[0037] Figure 13The composite microwave absorbing material prepared from zirconium dioxide / carbon composite nanofibers in Comparative Example 2 of this invention is shown in: (a) attenuation coefficient diagram; (b) impedance matching diagram.

[0038] Figure 14 The composite microwave absorbing material prepared from zirconium dioxide / carbon composite nanofibers in Comparative Example 2 of this invention is shown in: (a) a three-dimensional reflection loss diagram; (b) Figure 14 The corresponding two-dimensional reflection loss projection diagram. Detailed Implementation

[0039] It should be noted that the following detailed descriptions are exemplary and intended to provide further illustration of the invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0040] This invention provides a method for preparing iron tetranitrogen / zirconium dioxide / carbon composite nanofibers, comprising the following steps:

[0041] Iron salts, zirconium salts and polymer carbon sources were dispersed in a solvent and electrospun to obtain nanofiber precursors.

[0042] The nanofiber precursor was subjected to pre-oxidation and high-temperature carbonization to obtain a magnetite / zirconia / carbon composite nanofiber material.

[0043] The iron(II) oxide / zirconia / carbon composite nanofiber material is obtained by nitriding in ammonia gas.

[0044] The present invention can obtain the final product through one electrospinning, one high-temperature carbonization reaction and one nitriding reaction. The prepared iron tetranitrogen / zirconium dioxide / carbon composite nanofiber material has a uniform diameter and narrow diameter distribution, and no other by-products are generated during the heat treatment process.

[0045] The solvent of this invention is a mixture of N,N-dimethylformamide and glacial acetic acid, wherein the volume ratio of N,N-dimethylformamide to glacial acetic acid is (10-30):1. During the subsequent electrospinning process, the addition of a small amount of glacial acetic acid can effectively prevent the hydrolysis of zirconium salts. N,N-dimethylformamide decomposes into a small amount of dimethylamine, making the polymer carbon source more easily deprotonated, thus facilitating its combination with iron and zirconium ions to form metal clusters.

[0046] In this invention, the iron salt is preferably ferric acetylacetonate or ferric nitrate, the zirconium salt is preferably zirconium n-butoxide or zirconium acetylacetonate, and the polymer carbon source is polyvinylpyrrolidone or polyacrylonitrile. Iron ions, zirconium ions, and the polymer carbon source self-assemble through coordination bonds to form metal clusters, which then recombine to form precursors for iron(III) oxide, zirconium dioxide, and carbon composite nanofibers. The polymer carbon source can increase the viscosity of the solution and regulate the binding rate between the metal clusters / ions and the polymer carbon source in the solution, thus contributing to the formation of the fiber structure.

[0047] The preferred ratio of iron salt, zirconium salt, polymer carbon source, and solvent in this invention is (0.2–2) g : (0.5–2) g : (0.5–5) g : (5–20) mL; more preferably, it is (0.8–1.2) g : (1–1.5) g : (1–2) g : (8–15) mL. The above addition ratio is beneficial to the formation of nanofiber precursors.

[0048] This invention does not impose special limitations on the electrospinning process; nanofibers can be prepared using electrospinning methods commonly used in the field. Preferably, the voltage for electrospinning is 8–20 kV, and the distance between the syringe needle and the receiving plate is 10–25 cm; more preferably, the voltage is 10–18 kV, and the distance between the syringe needle and the receiving plate is 12–20 cm.

[0049] In this invention, pre-oxidation is carried out in an air atmosphere; for example, the nanofiber precursor can be placed in a conventional oven. The preferred pre-oxidation temperature is 120–250°C, and the preferred time is 80–400 min; more preferably, the pre-oxidation temperature is 150–200°C, and the time is 100–200 min; most preferably, the pre-oxidation temperature is 180°C, and the time is 120 min. During the pre-oxidation process, some solvents evaporate, and elements such as hydrogen, nitrogen, iron, and zirconium undergo preliminary oxidation, which helps to reduce the thermal shrinkage rate of the fiber and ensure the morphological stability of the fiber after subsequent carbonization.

[0050] In this invention, the high-temperature carbonization reaction is carried out at a temperature of 500–1000°C, a heating rate of 1–5°C / min, and a reaction time of 1–5 h. More preferably, the high-temperature carbonization reaction is carried out at a temperature of 600–800°C, a heating rate of 1.5–2.5°C / min, and a reaction time of 1.5–3.0 h; most preferably, the high-temperature carbonization reaction is carried out at a temperature of 700°C, a heating rate of 2°C / min, and a reaction time of 2 h. The high-temperature carbonization reaction of this invention is carried out under a nitrogen or argon atmosphere. During this process, the carbonaceous material (polymer carbon source) is continuously heated, the degree of graphitization gradually increases, iron ions combine with oxygen under high-temperature conditions to form Fe3O4, and zirconium ions combine with oxygen under high-temperature conditions to form ZrO2.

[0051] The nitriding reaction of the present invention is carried out at a temperature of 400–700°C, a heating rate of 1–6°C / min, and a reaction time of 1–4 h. More preferably, the nitriding reaction is carried out at a temperature of 500–600°C, a heating rate of 2–5°C / min, and a reaction time of 1.5–3 h; most preferably, the nitriding reaction is carried out at a temperature of 520°C, a heating rate of 4°C / min, and a reaction time of 2 h. During the above nitriding reaction, Fe3O4 reacts with ammonia to generate Fe4N.

[0052] This invention also provides a Fe4N / ZrO2 / carbon composite nanofiber material obtained by the above preparation method. The composite nanofiber material of this invention contains Fe, Zr, O, N, and C elements, wherein Fe and N elements exist in the form of Fe4N, Zr and O elements exist in the form of ZrO2, and C element exists in the form of a composite of amorphous carbon and graphitized carbon.

[0053] This invention also provides the application of the above-mentioned iron tetranitrogen / zirconium dioxide / carbon composite nanofiber material in the field of electromagnetic wave absorption.

[0054] In the iron-tetranitrogen / zirconium dioxide / carbon composite nanofiber material of this invention, Fe4N possesses high saturation magnetization and high electrical conductivity, excellent oxidation resistance, and stable mechanical properties, thereby improving the material's magnetic and electrical conductivity and enhancing magnetic and electrical losses. ZrO2 is a low-loss transparent material that allows electromagnetic waves to smoothly enter the material without reflection, helping to tune the material's electromagnetic parameters and optimize impedance matching. Carbonaceous materials have advantages such as low density, large reserves, chemical stability, and strong corrosion resistance, making them excellent scaffold materials. The presence of the fiber structure allows for multiple scattering of electromagnetic waves within the material, while also facilitating energy transfer and promoting electromagnetic energy dissipation. Therefore, the iron-tetranitrogen / zirconium dioxide / carbon composite nanofiber material of this invention can be applied in the field of electromagnetic wave absorption.

[0055] The present invention also provides a microwave absorbing material, including the above-mentioned iron tetranitrogen / zirconium dioxide / carbon composite nanofiber material.

[0056] The microwave absorbing material of this invention is prepared by mixing a tetranitrogen iron / zirconium dioxide / carbon composite nanofiber material with paraffin wax. This invention does not impose any particular limitation on the mixing method; for example, it can be mixed by heating and stirring. The mixing temperature is preferably 40–60°C to make the paraffin wax fluid, thereby ensuring that the tetranitrogen iron / zirconium dioxide / carbon composite nanofiber material is uniformly distributed in the paraffin wax. The mass ratio of the tetranitrogen iron / zirconium dioxide / carbon composite nanofiber material to paraffin wax is preferably 1:1–3, more preferably 1:1.5.

[0057] The microwave absorbing material prepared by this invention can achieve a reflection loss of -63.7dB for electromagnetic waves at high frequencies (12.5GHz), with a matching thickness of only 3.3mm and an effective absorption bandwidth of up to 7.0GHz at 2.7mm. It has high microwave absorption performance and has wide application value.

[0058] The technical solution of the present invention will be further described below with reference to specific embodiments.

[0059] Example 1

[0060] This embodiment provides a method for preparing iron tetranitrogen / zirconium dioxide / carbon composite nanofibers, the specific steps of which are as follows:

[0061] (1) Dissolve 0.9 g of ferric acetylacetone (2.5 mmol), 1.2 g of zirconium n-butoxide (80% purity, 2.5 mmol), and 1.4 g of polyvinylpyrrolidone in a mixed solvent of 10 mL of N,N-dimethylformamide and 0.5 mL of glacial acetic acid. After stirring evenly, transfer the solution into a syringe for electrospinning. The voltage is 14 kV, and the distance between the syringe needle and the receiving plate is 15 cm. After electrospinning, a nanofiber precursor sample is obtained.

[0062] (2) The obtained nanofiber precursor sample was placed in an oven at 180℃ for 120 min to pre-oxidize and obtain the iron oxide / zirconia / carbon composite nanofiber precursor; then 0.1 g of the iron oxide / zirconia / carbon composite nanofiber precursor sample was transferred to a tube furnace and heated to 700℃ at a heating rate of 2℃ / min under a nitrogen atmosphere and held for 2 h. After natural cooling to room temperature, the iron oxide / zirconia / carbon composite nanofiber was obtained.

[0063] (3) Take 0.1g of iron(II) oxide / zirconia / carbon composite nanofibers and transfer them to a nitriding furnace. In an ammonia atmosphere, heat the nanofibers to 520℃ at a heating rate of 4℃ / min and keep them at that temperature for 2 hours. Then, let them cool naturally to room temperature to obtain iron(II) oxide / zirconia / carbon composite nanofibers.

[0064] Figure 1 The image shows the X-ray diffraction (XRD) pattern of the iron tetranitrogen / zirconium dioxide / carbon composite nanofibers prepared in Example 1, which confirms that the prepared material contains iron tetranitrogen, zirconium dioxide, and carbon.

[0065] Figure 2 Image a is a scanning electron microscope (SEM) image of the iron(II) oxide / zirconia / carbon composite nanofiber precursor obtained after the pre-oxidation step in step (2) of Example 1. It can be seen that the fibers are uniform in size, with a diameter of approximately 150 nm. Figure 2As shown in b, the size of the iron(III) oxide / zirconia / carbon composite nanofibers after the high-temperature carbonization reaction is not significantly different from that of its precursor, with a diameter of approximately 150 nm. Fe3O4 nanoparticles are clearly visible on the surface, and the particle distribution is uniform. Figure 2 As can be seen in step (3), the size of the iron-nitrogen / zirconium dioxide / carbon composite nanofibers prepared in step (3) is not much different from that of the iron-nitrogen / zirconium dioxide / carbon composite nanofibers. The diameter of the fibers is maintained at about 150 nm. At the same time, Fe4N nanoparticles can be observed on the surface, and their size and distribution are very uniform. Figure 2 Image d is a transmission electron microscope (TEM) image of the iron-tetranitrogen / zirconium dioxide / carbon composite nanofibers obtained in Example 1. It can be clearly observed that Fe4N and ZrO2 with a size of about 35 nm are distributed inside the fiber as even smaller grains.

[0066] Example 2

[0067] This embodiment provides a method for preparing iron tetranitrogen / zirconium dioxide / carbon composite nanofibers, the specific steps of which are as follows:

[0068] (1) Dissolve 0.9 g of ferric nitrate nonahydrate (2.2 mmol), 1.2 g of zirconium acetylacetonate (2.5 mmol), and 1.4 g of polyacrylonitrile in a mixture of 10 mL of N,N-dimethylformamide and 0.5 mL of glacial acetic acid. After stirring evenly, transfer the solution to a syringe for electrospinning. The voltage is 18 kV, and the distance between the syringe needle and the receiving plate is 15 cm. After electrospinning, a nanofiber precursor sample is obtained.

[0069] (2) The obtained nanofiber precursor sample was placed in a 200℃ oven for pre-oxidation for 150 min to obtain iron oxide / zirconia / carbon composite nanofiber precursor; then 0.1 g of iron oxide / zirconia / carbon composite nanofiber precursor sample was transferred to a tube furnace, heated to 700℃ in a nitrogen atmosphere at a heating rate of 2℃ / min and held for 2 h, and then naturally cooled to room temperature to obtain iron oxide / zirconia / carbon composite nanofiber.

[0070] (3) Take 0.1g of iron(II) oxide / zirconia / carbon composite nanofibers and transfer them to a nitriding furnace. In an ammonia atmosphere, heat the nanofibers to 520℃ at a heating rate of 4℃ / min and keep them at that temperature for 2 hours. Then, let them cool naturally to room temperature to obtain iron(II) oxide / zirconia / carbon composite nanofibers.

[0071] Example 3

[0072] This embodiment provides a method for preparing iron tetranitrogen / zirconium dioxide / carbon composite nanofibers, the specific steps of which are as follows:

[0073] (1) Dissolve 1.2 g of ferric acetylacetone (3.4 mmol), 1.5 g of zirconium acetylacetone (3.1 mmol), and 2 g of polyvinylpyrrolidone in a mixture of 15 mL of N,N-dimethylformamide and 0.8 mL of glacial acetic acid. After stirring evenly, transfer the solution into a syringe for electrospinning. The voltage is 18 kV, and the distance between the syringe needle and the receiving plate is 15 cm. After electrospinning, a nanofiber precursor sample is obtained.

[0074] (2) The obtained nanofiber precursor sample was placed in an oven at 180℃ for 150 min to pre-oxidize and obtain the iron oxide / zirconia / carbon composite nanofiber precursor; then 0.1 g of the iron oxide / zirconia / carbon composite nanofiber precursor sample was transferred to a tube furnace and heated to 650℃ at a heating rate of 2℃ / min in a nitrogen atmosphere and held for 3 h. After natural cooling to room temperature, the iron oxide / zirconia / carbon composite nanofiber was obtained.

[0075] (3) Take 0.1g of iron(II) oxide / zirconia / carbon composite nanofibers and transfer them to a nitriding furnace. In an ammonia atmosphere, heat the nanofibers to 580℃ at a heating rate of 5℃ / min and keep them at that temperature for 2 hours. Then, let them cool naturally to room temperature to obtain iron(II) oxide / zirconia / carbon composite nanofibers.

[0076] Comparative Example 1

[0077] The difference from Example 1 is that the amount of iron acetylacetone was increased to 1.8 g (5 mmol), the amount of zirconium n-butoxide was reduced to 0, and the rest remained unchanged. Iron tetranitrogen / carbon composite nanofibers were finally prepared.

[0078] Figure 3 The image shows the XRD pattern of the iron-tetranitrogen / carbon composite nanofibers prepared in Comparative Example 1, confirming that the material phases are iron-tetranitrogen and carbon.

[0079] Figure 4 The SEM image of the iron-nitrogen / carbon composite nanofibers prepared in Comparative Example 1 shows that the morphology of the product remains fibrous when the amount of iron salt and zirconium salt added is changed. This indicates that changing the ratio of metal salts will not destroy the regular morphology of the product and will still allow the product to form a nanofiber structure.

[0080] Comparative Example 2

[0081] The difference from Example 1 is that the amount of iron acetylacetone was reduced to 0 g, the amount of zirconium n-butoxide was increased to 2.4 g (80% purity, 5 mmol), and the rest remained unchanged. Zirconium dioxide / carbon composite nanofibers were finally prepared.

[0082] Figure 5The XRD pattern of the zirconium dioxide / carbon composite nanofibers prepared in Comparative Example 2 confirms that the material phases are zirconium dioxide and carbon.

[0083] Figure 6 The SEM image of the zirconium dioxide / carbon composite nanofibers prepared in Comparative Example 2 shows that the morphology of the product remains fibrous when the amount of iron salt and zirconium salt added is changed. This indicates that changing the ratio of metal salts will not destroy the regular morphology of the product and will still allow the product to form a nanofiber structure.

[0084] Experimental Example

[0085] The iron tetranitrogen / zirconia / carbon composite nanofibers of Example 1, the iron tetranitrogen / carbon composite nanofibers of Comparative Example 1, and the zirconia / carbon composite nanofibers of Comparative Example 2 were mixed with paraffin at 50°C at a mass ratio of 1:1.5. After cooling, composite microwave absorbing materials were obtained. Electromagnetic parameters were tested using an Agilent Technologies E8363A electromagnetic wave vector network analyzer, and the microwave absorption performance of the materials was calculated based on the electromagnetic parameters.

[0086] Figure 7 a is the real part diagram of the dielectric constant of the composite microwave absorbing material prepared by the iron tetranitrogen / zirconium dioxide / carbon composite nanofibers obtained in Example 1. The average real part of the dielectric constant of the composite microwave absorbing material can be calculated to be 4.89. Figure 7 b is the imaginary part diagram of the dielectric constant. The average imaginary part of the dielectric constant of the composite absorbing material can be calculated to be 3.32. It is observed that the imaginary part of the dielectric constant decreases with the increase of frequency, which is caused by the dispersion effect, proving that the composite absorbing material has good conductivity. Figure 7 c is the dielectric loss tangent diagram. The average dielectric loss tangent of this composite absorbing material can be calculated to be 0.65, indicating that it has strong dielectric loss capability. Figure 7 d is the Cole-Cole diagram, in which multiple downward-facing semicircles are observed, indicating various types of polarization relaxation behavior in the front material. At the same time, the right end of the curve has a long, upward-curving arc, proving that the material has excellent electrical conductivity loss capability.

[0087] Figure 8 a is the real part diagram of the magnetic permeability of the composite microwave absorbing material prepared by the iron-nitrogen / zirconium dioxide / carbon composite nanofibers obtained in Example 1. The real part of the average dielectric constant of the composite microwave absorbing material can be calculated to be 1.04. Figure 8 b is the imaginary part diagram of the dielectric constant, from which the average imaginary part of the dielectric constant of the composite absorbing material can be calculated to be 0.05; Figure 8 c is the magnetic loss tangent diagram. The average magnetic loss tangent of this composite absorbing material can be calculated to be 0.05, indicating that it has strong magnetic loss capability.

[0088] Figure 9 a is the attenuation coefficient diagram of the composite microwave absorbing material prepared by the iron tetranitrogen / zirconium dioxide / carbon composite nanofibers obtained in Example 1. It can be calculated that the average attenuation coefficient of the material is 165.69, which has excellent comprehensive loss capability. Figure 9 b is the impedance matching diagram. It can be seen that at a frequency of 8-14GHz, the impedance matching value of the material is around 1, which has excellent impedance matching performance. Electromagnetic waves can enter the electromagnetic wave interior without being reflected, and are thus attenuated by the material's super loss capability.

[0089] Figure 10 a is a three-dimensional reflection loss diagram of the composite microwave absorbing material prepared by the iron tetranitrogen / zirconium dioxide / carbon composite nanofibers obtained in Example 1. When the frequency is 12.5 GHz, the absorption effect of electromagnetic waves is the best, and the minimum reflection loss value reaches -63.7 dB. Figure 10 b is Figure 10 The corresponding two-dimensional reflection loss projection diagram shows that at a thickness of 2.7 mm, the effective absorption bandwidth is as high as 7.0 GHz.

[0090] Figure 11 Figure a shows the attenuation coefficient of the composite microwave absorbing material prepared from iron-nitrogen / carbon composite nanofibers in Comparative Example 1. The average attenuation coefficient of this composite microwave absorbing material can be calculated to be 148.37, which shows excellent comprehensive loss capability. Figure 11 b is the impedance matching diagram. It can be seen that the impedance matching value of the composite absorbing material is far from 1, and the impedance mismatch is serious. Most electromagnetic waves are blocked outside the material and cannot enter the material. Therefore, the loss capacity cannot be utilized and the electromagnetic wave absorption performance is poor.

[0091] Figure 12 a is a three-dimensional reflection loss diagram of the composite microwave absorbing material prepared by iron-nitrogen / carbon composite nanofibers in Comparative Example 1. When the frequency is 16.4 GHz, the absorption effect of electromagnetic waves is the best, and the minimum reflection loss value reaches -21.8 dB. Figure 12 b is Figure 12 The corresponding two-dimensional reflection loss projection diagram shows that at a thickness of 1.7 mm, the effective absorption bandwidth is only 5.5 GHz. Its minimum reflection loss value and effective absorption bandwidth are both inferior to those of Example 1, indicating poor absorption performance.

[0092] Figure 13 Figure a shows the attenuation coefficient of the composite microwave absorbing material prepared by zirconium dioxide / carbon composite nanofibers in Comparative Example 2. It can be calculated that the average attenuation coefficient of the composite microwave absorbing material is 3.88, which indicates poor overall loss capability. Figure 13b is the impedance matching diagram. It can be seen that across most frequency bands, the material's impedance matching value is far from 1, indicating a severe impedance mismatch. Most electromagnetic waves are blocked outside the material and cannot penetrate its interior. Combined with... Figure 13 The material has poor loss capacity and very poor wave absorption performance.

[0093] Figure 14 a is a three-dimensional reflection loss diagram of the composite microwave absorbing material prepared by zirconium dioxide / carbon composite nanofibers in Comparative Example 2. The minimum reflection loss value of the material is only -1.5dB. Figure 14 b is Figure 14 The corresponding two-dimensional reflection loss projection diagram shows that the effective absorption bandwidth cannot be observed in the diagram. Its minimum reflection loss value and effective absorption bandwidth are far inferior to those of Example 1, indicating poor absorption performance.

[0094] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing Fe4N / zirconium dioxide / carbon composite nanofiber material, characterized in that, Includes the following steps: Iron salt, zirconium salt, and polymer carbon source are dispersed in a solvent and electrospun to obtain nanofiber precursors; the solvent is a mixture of N,N-dimethylformamide and glacial acetic acid, the iron salt is ferric acetylacetonate or ferric nitrate, the zirconium salt is zirconium n-butoxide or zirconium acetylacetonate, and the polymer carbon source is polyvinylpyrrolidone or polyacrylonitrile. The nanofiber precursor was subjected to pre-oxidation and high-temperature carbonization to obtain a magnetite / zirconia / carbon composite nanofiber material. The iron(II) oxide / zirconia / carbon composite nanofiber material is obtained by nitriding in ammonia gas.

2. The preparation method according to claim 1, characterized in that, In the solvent, the volume ratio of N,N-dimethylformamide to glacial acetic acid is (10~30):

1.

3. The preparation method according to claim 1, characterized in that, The ratio of the iron salt, zirconium salt, polymer carbon source and solvent is (0.2~2)g:(0.5~2)g:(0.5~5)g:(5~20)mL.

4. The preparation method according to claim 1, characterized in that, The pre-oxidation is carried out in an air atmosphere at a temperature of 120~250℃ for 80~400 min.

5. The preparation method according to claim 1, characterized in that, The high-temperature carbonization reaction is carried out at a temperature of 500~1000℃, a heating rate of 1~5℃ / min, and a reaction time of 1~5 h.

6. The preparation method according to claim 1, characterized in that, The nitriding reaction is carried out at a temperature of 400~700℃, a heating rate of 1~6℃ / min, and a reaction time of 1~4 h.

7. The Fe4N / zirconium dioxide / carbon composite nanofiber material obtained by the preparation method according to any one of claims 1 to 6.

8. The application of the Fe4N / zirconium dioxide / carbon composite nanofiber material as described in claim 7 in the field of electromagnetic wave absorption.

9. A microwave absorbing material, characterized in that, Including the Fe4N / zirconium dioxide / carbon composite nanofiber material as described in claim 7.

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