Fe@C Composite Fibers with Controllable Ferromagnetic Properties, Preparation Method Thereof, and Applications

Abstract

Fe@C Composite Fibers with Controllable Ferromagnetic Properties, Preparation Method and Application Thereof. The present invention belongs to the technical field of nano-wave absorbing materials. The purpose of the present invention is to solve the technical problems of low absorption efficiency and narrow effective absorption bandwidth of existing ferromagnetic metal absorbers. The present invention first prepares an FeOOH precursor by a liquid-phase precipitation method, then prepares an FeOOH@C composite fiber by a solvothermal method, and finally prepares an Fe@C composite fiber by hydrogen thermal annealing. The Fe@C composite fiber is composed of Fe fibers and amorphous carbon, and the amorphous carbon is coated on the outer surface of the Fe fibers. The shell layer of the core-shell structure is amorphous carbon, and the magnetic core is Fe fibers. The preparation method of the present invention has strong controllability and good reproducibility. The obtained Fe@C composite fiber can realize the synergistic control of ferromagnetic / dielectric loss, and has good temperature and corrosion resistance, which can meet the requirements of stealth structure design in harsh environments and also has a load-bearing function at the same time.

Description

Technical Field

[0001] The present invention belongs to the technical field of nano-wave absorbing materials, and particularly relates to an Fe@C composite fiber with controllable ferromagnetic properties, a preparation method thereof, and an application thereof. Background Art

[0002] Electromagnetic wave absorbing materials are the material basis for radar stealth and electromagnetic pollution prevention, and their electromagnetic properties have an important impact on the electromagnetic radiation control efficiency. Ferromagnetic metals have good ferromagnetic loss and dielectric loss properties due to their high saturation magnetization intensity, high magnetic permeability, and adjustable conductivity. They are electromagnetic absorbers with the most excellent comprehensive performance, and their electromagnetic properties can be regulated within a certain range.

[0003] Compared with traditional ferromagnetic particles, one-dimensional ferromagnetic absorbers have a certain aspect ratio, and their axial dielectric constant and magnetic permeability are both greater than the radial dielectric constant and magnetic permeability. The orientation distribution of one-dimensional absorbers in the matrix will also affect the spectral characteristics of the wave-absorbing material, further improving its ferromagnetic loss and dielectric loss, and thus broadening its effective absorption bandwidth. In recent years, the preparation and electromagnetic property research of one-dimensional ferromagnetic absorbers have received the favor of researchers. However, traditional one-dimensional ferromagnetic absorbers have poor stability and it is difficult to achieve component structure control at the coating scale, so the potential of the absorbers is difficult to play. In order to meet the requirements of broadband, lightweight, and high-efficiency absorption, it is necessary to comprehensively use the ideas of nanometerization and compounding to explore the performance of ferromagnetic metal absorbers. Therefore, the design and preparation of one-dimensional ferromagnetic metal absorbers with both load-bearing and electromagnetic absorption functions have become a research hotspot in the field. Summary of the Invention

[0004] The purpose of the present invention is to solve the technical problems of low absorption efficiency and narrow effective absorption bandwidth of existing ferromagnetic metal absorbers, and to provide an Fe@C composite fiber with controllable ferromagnetic properties, a preparation method thereof, and an application thereof.

[0005] The purpose of the present invention is achieved by the following technical solutions:

[0006] One of the purposes of the present invention is to provide a preparation method of an Fe@C composite fiber with controllable ferromagnetic properties. The preparation method is carried out according to the following steps:

[0007] S1: Ultrasonically disperse FeSO4·7H2O and ZnSO4·7H2O in deionized water to obtain a mixed solution, then add it to a NaOH solution, stir and mix, add deionized water for dilution, then continue to stir for 24 h. After the reaction is completed, wash and vacuum dry to obtain an FeOOH precursor.

[0008] S2: Dissolve the FeOOH precursor and PVP (polyvinylpyrrolidone) in deionized water, and then stir magnetically to obtain a modified FeOOH precursor.

[0009] S3: Dispersing the modified FeOOH precursor and glucose in deionized water, stirring and mixing, and then performing a hydrothermal reaction in a reactor. After the reaction is completed, the mixture is cooled to room temperature, and the product is washed and dried to obtain FeOOH@C composite fibers;

[0010] S4: The FeOOH@C composite fiber is placed in a tubular furnace and hydrogen-annealed at 600-700° C. in a reducing atmosphere to obtain a Fe@C composite fiber with controllable ferromagnetic properties.

[0011] It is further defined that the mass ratio of FeSO4·7H2O to ZnSO4·7H2O and deionized water in the mixed solution described in S1 is (3.91-4.09):(0.91-1.19):(19.55-20.45).

[0012] It is further defined that the mass ratio of NaOH to deionized water in the NaOH solution described in S1 is (0.171-0.186):(0.938-1.0625).

[0013] It is further defined that the mass ratio of FeSO4·7H2O to NaOH in S1 is 1:(3.35-3.625).

[0014] It is further defined that after stirring and mixing in S1 for 30 minutes, deionized water is added for dilution.

[0015] It is further defined that the amount of deionized water used in each 100 mL dilution of the solution in S1 is 29.2-37.5 mL.

[0016] It is further defined that the mass ratio of FeOOH precursor to PVP in S2 is 0.1:(0.45-0.55).

[0017] It is further defined that the mass ratio of PVP to deionized water in S2 is (0.225-0.275):(9-11).

[0018] Further, S2 was magnetically stirred for 5-7 h.

[0019] It was further defined that the mass ratio of the modified FeOOH precursor and glucose in S3 was 0.079:(0.085-0.095).

[0020] It is further defined that the mass ratio of glucose to deionized water in S3 is (0.028-0.032):(9-11).

[0021] It is further defined that the hydrothermal reaction temperature in S3 is 170-190°C and the time is 2.5-3.5 h.

[0022] Further limitation: In S4, the reducing atmosphere is 5 vol% H2 and 95 vol% Ar.

[0023] Further limitation: In S4, the hydrogen thermal annealing time is 2 - 4 h, and the heating rate is 1.5 - 2.5 °C / min.

[0024] The second object of the present invention is to provide a Fe@C composite fiber with controllable ferromagnetic properties prepared by the above method. The composite fiber is composed of Fe fibers and amorphous carbon, and the amorphous carbon coats the outer surface of the Fe fibers.

[0025] Further limitation: The diameter of the composite fiber is 15 - 35 nm, and the length is 150 - 300 nm.

[0026] The third object of the present invention is to provide an application of a Fe@C composite fiber with controllable ferromagnetic properties prepared by the above method. The Fe@C composite fiber with controllable ferromagnetic properties is used to prepare a low-thickness broadband electromagnetic wave absorbing component.

[0027] Further limitation: The minimum value of RL of the low-thickness broadband electromagnetic wave absorbing component is -69.78 dB when the thickness is 1.39 mm.

[0028] The remarkable effects of the present invention compared with the prior art:

[0029] The present invention first prepares a FeOOH precursor by the liquid-phase precipitation method, then prepares a FeOOH@C composite fiber by the solvothermal method, and finally prepares a Fe@C composite fiber by hydrogen thermal annealing. The Fe@C composite fiber is composed of Fe fibers and amorphous carbon, and the amorphous carbon coats the outer surface of the Fe fibers. The shell layer of the core-shell structure is amorphous carbon, and the magnetic core is Fe fibers. The specific advantages are as follows:

[0030] (1) The preparation method of the present invention has strong controllability and good reproducibility. The prepared FeOOH precursors have uniform aspect ratios and good dispersibility.

[0031] (2) The C layer is added as a dielectric layer, enhancing the dielectric loss characteristics of the one-dimensional ferromagnetic absorber. The emergence of the core-shell structure increases the surface / interface, providing more active sites for multiple reflections / scattering of incident electromagnetic waves. At the same time, the presence of the C layer maintains the shape of the ferromagnetic fibers, ensuring that the ferromagnetic absorber has high shape anisotropy and a large specific surface area, which is conducive to enhancing the strong electron / phonon scattering effect generated by the periodic interface of the material and improving the microwave absorption efficiency of the composite material.

[0032] (3) By regulating the hydrogen thermal annealing temperature, the present invention controls the conversion degree from FeOOH precursor to Fe nanoparticles to control the ferromagnetic loss characteristics of the one-dimensional ferromagnetic absorbent. Meanwhile, the protective effect of the surface C layer significantly improves the oxidation and corrosion resistance of the material; further, the conduction network generated by the overlapping of fibers, and the C layer coats the ferromagnetic fibers, destroying the conduction network and suppressing the adverse effects of the eddy current effect.

[0033] (4) The Fe@C composite fiber of the present invention can achieve the coordinated control of ferromagnetic / dielectric loss, and has good temperature and corrosion resistance, which can meet the requirements of stealth structure design in harsh environments and also has a load-bearing function. Description of the Drawings

[0034] Figure 1 is the XRD image of FeOOH in the embodiment of the present invention, the Fe@C obtained in the embodiment and the Fe2O3@C composite fiber obtained in the comparative example;

[0035] Figure 2a is the SEM image of FeOOH in the embodiment of the present invention;

[0036] Figure 2b is the SEM image of the FeOOH@C composite fiber in the embodiment of the present invention;

[0037] Figure 2c is the SEM image of the Fe2O3@C composite fiber obtained in the comparative example;

[0038] Figure 2d is the SEM image of the Fe@C composite fiber obtained in the embodiment of the present invention;

[0039] Figure 3 is the electromagnetic wave absorption characteristic image of FeOOH in the embodiment, the Fe@C obtained in the embodiment and the Fe2O3@C composite fiber obtained in the comparative example. Specific Embodiments

[0040] In order to make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0041] The experimental methods used in the following embodiments are all conventional methods unless otherwise specified. The materials, reagents, methods and instruments used are all conventional materials, reagents, methods and instruments in the art, and those skilled in the art can obtain them through commercial channels without special instructions.

[0042] As used in the following embodiments, the terms "comprising", "including", "having", "containing" or any other variation thereof are intended to cover non-exclusive inclusion. For example, a composition, step, method, article or apparatus that comprises the listed elements is not necessarily limited to those elements, but may include other elements not expressly listed or elements inherent to such composition, step, method, article or apparatus.

[0043] When an equivalent, concentration, or other value or parameter is expressed as a range, a preferred range, or a range defined by a series of upper preferred values and lower preferred values, this should be understood to specifically disclose all ranges formed by any pairing of any upper range limit or preferred value with any lower range limit or preferred value, whether or not the ranges are separately disclosed. For example, when the range "1 to 5" is disclosed, the described range should be interpreted to include the ranges "1 to 4", "1 to 3", "1 to 2", "1 to 2 and 4 to 5", "1 to 3 and 5", etc. When a numerical range is described herein, unless otherwise stated, the range is intended to include its end values and all integers and fractions within the range. In the specification and claims of this application, range limitations may be combined and / or interchanged, and if not otherwise stated, these ranges include all sub-ranges subsumed therein.

[0044] The indefinite articles "a" and "an" before an element or component of the present invention do not limit the quantity requirement (i.e., the number of occurrences) of the element or component. Therefore, "a" or "an" should be interpreted to include one or at least one, and the singular form of an element or component also includes the plural form, unless the quantity clearly refers only to the singular form.

[0045] As used herein, "an embodiment" or "embodiments" of the present invention refer to specific features, structures, or characteristics that may be included in at least one implementation of the present invention. The phrase "in an embodiment" that appears in different places in this specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment that is mutually exclusive with other embodiments.

[0046] Examples:

[0047] The preparation method of the Fe@C composite fiber with controllable ferromagnetic properties in this embodiment is carried out according to the following steps:

[0048] S1. Preparation of FeOOH precursor:

[0049] First, at 40 °C, 14.5 g of NaOH is dissolved in 85 mL of deionized water to obtain a NaOH solution;

[0050] Then, 4.09 g of FeSO4·7H2O and 1.19 g of ZnSO4·7H2O were ultrasonically dispersed in 20.45 mL of deionized water to obtain a mixed solution, which was added to the NaOH solution. After stirring and mixing for 30 min, 40 mL of deionized water was added for dilution, and then stirring continued for 24 h. After the reaction ended, it was washed and vacuum dried to obtain the FeOOH precursor;

[0051] Preparation of S2, modified FeOOH precursor:

[0052] 0.1 g of the FeOOH precursor and 0.55 g of PVP were dissolved in 18 mL of deionized water, and then magnetically stirred for 6 h to obtain the modified FeOOH precursor;

[0053] Preparation of S3, FeOOH@C composite fiber:

[0054] 0.079 g of the modified FeOOH precursor and 0.095 g of glucose were dispersed in 33 mL of deionized water, stirred and mixed for 30 min, then transferred to a reaction kettle with a polytetrafluoroethylene lining and carried out at 180 °C for hydrothermal reaction for 3 h. After the reaction ended and cooled to room temperature, the product was washed and dried to obtain the FeOOH@C composite fiber;

[0055] Preparation of S4, Fe@C composite fiber:

[0056] The FeOOH@C composite fiber was placed in a tubular furnace. In a reducing atmosphere composed of 5 vol% H2 and 95 vol% Ar, it was first heated to 650 °C at a heating rate of 2.5 °C / min, and then hydrogen heat annealing was carried out at 650 °C for 3.5 h to obtain the Fe@C composite fiber with controllable ferromagnetic properties.

[0057] Comparative example:

[0058] The preparation method of the composite fiber in this example was carried out according to the following steps:

[0059] Preparation of S1, FeOOH precursor:

[0060] First, at 40 °C, 13.5 g of NaOH was dissolved in 75 mL of deionized water to obtain the NaOH solution;

[0061] Then, 3.91 g of FeSO4·7H2O and 0.91 g of ZnSO4·7H2O were ultrasonically dispersed in 19.55 mL of deionized water to obtain a mixed solution, which was added to the NaOH solution. After stirring and mixing for 30 min, 40 mL of deionized water was added for dilution, and then stirring continued for 24 h. After the reaction ended, it was washed and vacuum dried to obtain the FeOOH precursor;

[0062] S2. Preparation of modified FeOOH precursor:

[0063] Dissolve 0.1 g of FeOOH precursor and 0.45 g of PVP in 18 mL of deionized water, and then magnetically stir for 6 h to obtain the modified FeOOH precursor;

[0064] S3. Preparation of FeOOH@C composite fiber:

[0065] Disperse 0.079 g of the modified FeOOH precursor and 0.085 g of glucose in 27 mL of deionized water, stir and mix for 30 min, then transfer it to a reaction kettle with a polytetrafluoroethylene lining for hydrothermal reaction at 180 °C for 3 h. After the reaction is completed and cooled to room temperature, the product is washed and dried to obtain FeOOH@C composite fiber;

[0066] S4. Preparation of composite fiber:

[0067] Place the FeOOH@C composite fiber in a tubular furnace. In a reducing atmosphere composed of 5 vol% H2 and 95 vol% Ar, first heat it to 350 °C at a heating rate of 1.5 °C / min, and then perform hydrogen thermal annealing at 350 °C for 3.5 h to obtain Fe2O3@C composite fiber.

[0068] Figure 1 XRD images of FeOOH in the examples, Fe@C obtained in the examples, and Fe2O3@C composite fiber obtained in the comparative example. From Figure 1 It can be seen that when the hydrogen thermal annealing temperature reaches 350 °C, FeOOH is converted to Fe2O3 (JCPDS#33-0664); when the temperature is further increased to 650 °C, FeOOH is completely converted to Fe (JCPDS#06-0696).

[0069] Figure 2a -d are SEM images of FeOOH and FeOOH@C in the examples, Fe@C obtained in the examples, and Fe2O3@C composite fiber obtained in the comparative example. From Figure 2aIt can be seen that the diameter of the FeOOH precursor is 10 - 26 nm, the length is 430 - 570 nm, the aspect ratio is about 15:1, and the fiber size of the FeOOH precursor is uniform. After hydrogen thermal annealing, the diameter of the Fe@C composite fiber obtained in the embodiment of the present invention is 15 - 35 nm, the length is 150 - 300 nm, and its aspect ratio is about 10:1. It can be understood from the SEM images that the FeOOH, FeOOH@C, and the product Fe@C composite fiber in the embodiment of the present invention have good dispersibility and uniform particle size distribution. At the same time, due to the presence of amorphous carbon, the Fe fibers do not bend or sinter after annealing at 650 °C.

[0070] Figure 3 are the electromagnetic wave absorption characteristic images of FeOOH in the embodiment, Fe@C obtained in the embodiment, and Fe2O3@C composite fiber obtained in the comparative example. From Figure 3 It can be seen that FeOOH has almost no absorption in the range of 2 - 18 GHz. For the Fe2O3@C composite fiber obtained in the comparative example, when the thickness is 2.81 mm, the minimum RL value is -8.68 dB, and the maximum effective absorption bandwidth (< -5 GHz) is 5.73 GHz (10.71 - 16.44 GHz). For the Fe@C composite fiber, when the thickness is 1.39 mm, the minimum RL value reaches -69.78 dB, and the maximum effective absorption bandwidths of < -10 GHz and < -5 GHz are 4.71 GHz (10.61 - 15.31 GHz) and 9 GHz (9 - 18 GHz), respectively. By controlling the annealing temperature, a higher saturation magnetization intensity is obtained, and thus better microwave absorption performance is achieved. It can be seen that coating Fe fibers with C not only generates multiple interface polarizations, but also the one-dimensional structure uniformly dispersed in the matrix can form a three-dimensional network structure through cross-linking with each other, further extending the propagation path of the incident electromagnetic wave through multiple internal reflections and scattering, resulting in more dissipation of electromagnetic wave energy, which is beneficial to microwave absorption performance.

[0071] As mentioned above, the above are only the preferred specific embodiments of the present invention. These specific embodiments are all different implementation manners based on the overall concept of the present invention, and the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention should be covered by the protection scope of the present invention. Therefore, the protection scope of the present invention should be subject to the protection scope of the claims.

Claims

1. A preparation method of Fe@C composite fibers with controllable ferromagnetic properties, characterized in that, Proceed as follows: S1: Ultrasonically disperse FeSO4·7H2O and ZnSO4·7H2O in deionized water to obtain a mixed solution, then add it to NaOH solution, stir and mix, add deionized water for dilution, and then continue stirring for 24 h. After the reaction is completed, wash and vacuum dry to obtain the FeOOH precursor; S2: Dissolve the FeOOH precursor and PVP in deionized water, and then stir magnetically to obtain the modified FeOOH precursor; S3: Disperse the modified FeOOH precursor and glucose in deionized water, stir and mix, and then carry out a hydrothermal reaction in a reaction kettle. After the reaction is completed, cool to room temperature. After washing and drying the product, obtain the FeOOH@C composite fiber; S4: Place the FeOOH@C composite fiber in a tubular furnace, and carry out hydrogen thermal annealing at 600 - 700 °C in a reducing atmosphere to obtain the Fe@C composite fiber with controllable ferromagnetic properties.

2. The method according to claim 1, wherein In S1, the mass ratio of FeSO4·7H2O, ZnSO4·7H2O and deionized water in the mixed solution is (3.91 - 4.09):(0.91 - 1.19):(19.55 - 20.45), the mass ratio of NaOH and deionized water in the NaOH solution is (0.171 - 0.186):(0.938 - 1.0625), and the mass ratio of FeSO4·7H2O to NaOH is 1:(3.35 - 3.625).

3. The method according to claim 1, characterized in that In S1, add deionized water for dilution after stirring and mixing for 30 min. The amount of deionized water used for each 100 mL of diluted solution is 29.2 - 37.5 mL.

4. The method according to claim 1, wherein In S2, the mass ratio of the FeOOH precursor to PVP is 0.1:(0.45 - 0.55), the mass ratio of PVP to deionized water is (0.225 - 0.275):(9 - 11), and stir magnetically for 5 - 7 h.

5. The method according to claim 1, wherein In S3, the mass ratio of the modified FeOOH precursor to glucose is 0.079:(0.085 - 0.095), the mass ratio of glucose to deionized water is (0.028 - 0.032):(9 - 11), the hydrothermal reaction temperature is 170 - 190 °C, and the time is 2.5 - 3.5 h.

6. The method according to claim 1, characterized in that In S4, the reducing atmosphere is 5 vol% H2 and 95 vol% Ar, the hydrogen thermal annealing time is 2 - 4 h, and the heating rate is 1.5 - 2.5 °C / min.

7. The Fe@C composite fiber with controllable ferromagnetic properties prepared by the method according to any one of claims 1-6, characterized in that, It is composed of Fe fibers and amorphous carbon, and the amorphous carbon coats the outer surface of the Fe fibers.

8. The Fe@C composite fiber with controllable ferromagnetic properties according to claim 7, characterized in that, The diameter of the composite fiber is 15 - 35 nm, and the length is 150 - 300 nm.

9. Use of the Fe@C composite fiber with controllable ferromagnetic properties prepared by the method according to any one of claims 1-6, characterized in that, It is used for preparing a low-thickness broadband electromagnetic wave absorption component.

10. The application according to claim 9, wherein, The minimum value of RL of the electromagnetic wave absorption component is -69.78 dB when the thickness is 1.39 mm.

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