A cerium-doped carbon-coated iron oxide composite fiber and a preparation method thereof

Abstract

This invention discloses a cerium-doped carbon-coated iron oxide composite fiber and its preparation method. The composite fiber has a core-shell structure, with the outer shell layer consisting of PAN and CeO2, and the core layer consisting of PMMA and MIL-101(Fe). The outer shell layer is used to reduce the emissivity of the composite fiber in long-wave infrared, and the core layer is used to absorb radar waves. The composite material of this invention can significantly reduce infrared emissivity, greatly broaden the effective radar absorption bandwidth, and achieve efficient synergy between radar absorption and infrared stealth functions. At the same time, the prepared Fe2O3 / FeOOH / C@CeO2-700 composite fiber has a certain degree of corrosion resistance, thus solving the problem that traditional materials are difficult to balance in terms of corrosion resistance and radar / infrared compatible stealth performance.

Description

Technical Field

[0001] This invention belongs to the field of multi-band radar-compatible infrared stealth technology, and particularly relates to a cerium-doped carbon-coated iron oxide composite fiber and its preparation method. Background Technology

[0002] As modern detection systems evolve towards multi-functionality, high precision, and networking, single radar or infrared stealth technologies are no longer sufficient to address the threats posed by multi-band detection. Corrosion-resistant radar-compatible infrared stealth materials have become a major research direction in multi-functional stealth technology. To achieve infrared stealth, reducing the target temperature is crucial. However, radar stealth requires strong absorption and low reflection of electromagnetic waves, while infrared stealth requires low absorption and high reflection of materials. Resolving this contradiction is essential for achieving radar-infrared compatible stealth. Radar stealth and infrared stealth target microwave / millimeter-wave (radar band) and infrared / thermal radiation (infrared band) detection, respectively. Their physical mechanisms belong to different electromagnetic spectrum ranges, and the fundamental difference in stealth principles constitutes the root of the contradiction. Traditional materials are difficult to optimize synergistically, specifically manifesting in three aspects of the contradiction: I. High conductivity / high dielectric loss characteristics that enhance radar absorption often exacerbate infrared emission. For example, although carbon-based materials can enhance radar loss, their high thermal conductivity accelerates surface heat transfer and intensifies infrared radiation. Although metal fillers (aluminum powder, ferrite) can improve dielectric loss, their high reflectivity and high thermal conductivity cause performance to be offset and reduced.

[0003] Second, radar absorbing materials require low surface impedance to reduce reflection, while infrared low emissivity materials usually have high dielectric constants, which leads to increased radar wave interface reflection, making it difficult to balance low radar reflection and low infrared radiation.

[0004] Third, radar stealth requires a certain thickness to achieve impedance matching, while infrared stealth requires a multi-layered heat insulation structure. The combination of the two results in excessive material thickness and weight, which limits their application in lightweight platforms.

[0005] Existing doped oxide materials exhibit high infrared emissivity, which is detrimental to infrared stealth. Furthermore, their effective radar absorption bandwidth is narrow, and their structural design makes it difficult to coordinate the control of both radar and infrared physical mechanisms, resulting in low efficiency in the synergy of dual-band stealth performance. More critically, stealth equipment often operates in harsh environments such as marine salt spray, high humidity, and industrial acid rain: traditional compatible stealth materials are susceptible to corrosion, leading to the shedding of the radar-absorbing layer and a sharp increase in infrared emissivity, making long-term stable service impossible. Therefore, developing a new type of stealth material that simultaneously possesses wide-band radar absorption, low infrared emissivity, and excellent corrosion resistance has become an urgent need for the practical application of equipment. Summary of the Invention

[0006] The purpose of this invention is to provide a cerium-doped carbon-coated iron oxide composite fiber and its preparation method, so as to obtain a multifunctional composite material compatible with radar and infrared stealth.

[0007] The present invention adopts the following technical solution: a cerium-doped carbon-coated iron oxide composite fiber, the composite fiber having a core-shell structure, the outer shell layer of the core-shell structure being PAN and CeO2, the core layer of the core-shell structure being PMMA and MIL-101(Fe), the outer shell layer being used to reduce the infrared emissivity of the composite fiber in the long-wavelength band, and the core layer being used for radar absorption.

[0008] A method for preparing cerium-doped carbon-coated iron oxide composite fibers involves using core-layer spinning solution and shell-layer spinning solution as raw materials and employing coaxial electrospinning technology to prepare a composite fiber membrane with a core-shell hierarchical structure. Then, the composite fiber membrane is pre-oxidized and then pyrolyzed at high temperature to carbonize the polymer and convert the MOF into iron oxide, ultimately obtaining inorganic / carbon-based core-shell functional fibers. The core spinning solution contains PMMA and MIL-101(Fe); The shell spinning solution contains PAN and CeO2.

[0009] The beneficial effects of this invention are: The composite material of the present invention can significantly reduce infrared emissivity, greatly broaden the effective radar absorption bandwidth, and achieve efficient synergy between radar absorption and infrared stealth functions, thereby solving the problem that traditional materials are difficult to balance in the field of radar / infrared compatible stealth. This invention designs a one-dimensional composite fiber with a "core-shell" double-layer structure, which integrates the low infrared emission function (achieved by CeO2 in the outer shell layer) with the wide-band radar wave absorption function (achieved by iron-based MOF derivatives in the core layer). This structure enables materials that are originally contradictory in electromagnetic properties to work together. The outer shell layer of this invention provides low infrared emissivity while protecting the microwave absorbing components of the core layer; when the core layer absorbs microwaves efficiently, the outer shell layer can partially block heat conduction, slow down the surface temperature rise, and the prepared composite fiber has a certain degree of corrosion resistance. Attached Figure Description

[0010] Figure 1 The reflection loss diagram of Fe2O3 / FeOOH / C@CeO2-600 prepared in Example 1 is shown. Figure 2 Infrared emissivity diagram of Fe2O3 / FeOOH / C@CeO2-600 prepared in Example 1; Figure 3 TEM images of the MIL-101(Fe) / PMMA and CeO2 / PAN precursors at 100 nm were obtained for Example 2. Figure 4SEM images of the MIL-101(Fe) / PMMA and CeO2 / PAN precursors obtained in Example 2 at 200 nm; Figure 5 The SEM image of Fe2O3 / FeOOH / C@CeO2-700 at 500 nm was obtained for Example 2; Figure 6 The X-ray diffraction pattern of Fe2O3 / FeOOH / C@CeO2-700 prepared in Example 2; Figure 7 Dielectric constant diagram of Fe2O3 / FeOOH / C@CeO2-700 prepared in Example 2; Figure 8 The reflection loss diagram of Fe2O3 / FeOOH / C@CeO2-700 prepared in Example 2 is shown. Figure 9 This is a two-dimensional mapping of the effective bandwidth of Fe2O3 / FeOOH / C@CeO2-700 obtained in Example 2; Figure 10 Infrared emissivity diagram of Fe2O3 / FeOOH / C@CeO2-700 prepared in Example 2; Figure 11 The reflection loss diagram of Fe2O3 / FeOOH / C@CeO2-800 prepared in Example 3 is shown. Figure 12 Infrared emissivity diagram of Fe2O3 / FeOOH / C@CeO2-800 prepared in Example 3; Figure 13 Corrosion potential and current parameters of Fe2O3 / FeOOH / C@CeO2 prepared in Examples 1, 2, and 3 are shown in the diagram. Figure 14 The diagram shows the open-circuit potential versus time parameters of Fe2O3 / FeOOH / C@CeO2 prepared in Examples 1, 2, and 3. Figure 15 Dielectric constant diagram of Fe2O3 / FeOOH / C@CeO2-700 (4:6) prepared in Example 4; Figure 16 The reflection loss diagram of Fe2O3 / FeOOH / C@CeO2-700 (4:6) prepared in Example 4; Figure 17 The effective bandwidth two-dimensional mapping diagram of Fe2O3 / FeOOH / C@CeO2-700 (4:6) prepared in Example 4; Figure 18 Dielectric constant diagram of Fe2O3 / FeOOH / C@CeO2-700 (5:5) prepared in Example 5; Figure 19The reflection loss diagram of Fe2O3 / FeOOH / C@CeO2-700 (5:5) prepared in Example 5; Figure 20 The effective bandwidth two-dimensional mapping diagram of Fe2O3 / FeOOH / C@CeO2-700 (5:5) prepared in Example 5 is shown. Detailed Implementation

[0011] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments.

[0012] This invention discloses a cerium-doped carbon-coated iron oxide composite fiber. The composite fiber has a core-shell structure, with the outer shell layer being PAN and CeO2, and the core layer being PMMA and MIL-101(Fe). The outer shell layer is used to reduce the emissivity of the composite fiber in the long-wave infrared, and the core layer is used for radar absorption.

[0013] This invention also discloses a cerium-doped carbon-coated iron oxide composite fiber and its preparation method: Using core-shell spinning solution and shell-shell spinning solution as raw materials, a composite fiber membrane with a core-shell hierarchical structure was prepared by coaxial electrospinning process. Then, the composite fiber membrane was pre-oxidized and then pyrolyzed at high temperature to carbonize the polymer and convert MOF into iron oxide, finally obtaining inorganic / carbon-based core-shell functional fiber. The core spinning solution contains PMMA and MIL-101(Fe); The shell spinning solution contains PAN and CeO2.

[0014] The mass ratio of PMMA to MIL-101(Fe) is 1.4:1.

[0015] The mass ratio of PAN to CeO2 is 0.6:1.

[0016] The mass ratio of MIL-101(Fe) to CeO2 is 1:1.

[0017] The flow rate ratio of the core spinning solution to the shell spinning solution is 3:1.

[0018] The parameters for the coaxial electrospinning process are: positive voltage 18 kV, negative voltage 1.2 kV, receiving distance 20 cm; continuous spinning for 6 h.

[0019] The method for obtaining the core spinning solution is as follows: PMMA and DMF are magnetically stirred in a sample bottle for 4 h until the solution becomes transparent, the temperature range is controlled at 20-30℃, and the stirring speed is 800 rpm / min. Then, dry MIL-101(Fe) powder is added, and the mixture is stirred at 800 rpm / min for 6 h within the temperature range of 20-30℃ to obtain the core spinning solution.

[0020] The method for obtaining the shell spinning solution is as follows: PAN and DMF are magnetically stirred in a sample bottle for 4 h until the solution becomes transparent, the temperature range is controlled at 20-30℃, and the mixture is stirred at a speed of 800 rpm / min. Then, dry CeO2 powder is added, and the mixture is stirred at a speed of 800 rpm / min for 6 h within the temperature range of 20-30℃ to obtain the shell spinning solution.

[0021] The outer shell layer (CeO2 / C) of the composite fiber in this invention is mainly responsible for regulating infrared emissivity to achieve low infrared emissivity; the core layer (Fe-based derivative / C) is mainly responsible for dissipating radar wave energy to achieve broadband absorption. The two work together to ultimately achieve the effect of "radar / infrared compatible stealth".

[0022] This invention directly prepares organic precursor core-shell fibers with clear interfaces by precisely controlling the formulation, flow rate, and spinning voltage (positive 16-20 kV, negative 0.8-2 kV) of the core layer solution (PMMA solution containing MIL-101(Fe)) and the shell layer solution (PAN solution containing CeO2).

[0023] This invention involves pre-oxidizing the composite fiber membrane (200-300°C) followed by high-temperature pyrolysis (600-800°C) to carbonize the polymer and convert the MOF (Metal-Oxide-Foil) into iron oxides, ultimately yielding inorganic / carbon-based core-shell functional fibers. The pre-oxidation step stabilizes the fiber morphology and prevents agglomeration; the high-temperature pyrolysis (e.g., 700°C) carbonizes the polymer and converts the MOF into active iron oxides, ultimately resulting in inorganic / carbon-based core-shell functional fibers. When the mass ratio of PAN to CeO2 is strictly controlled at 0.6:1, the amorphous carbon formed by PAN and CeO2 particles achieve optimal interfacial bonding after pre-oxidation and carbonization. At this point, the shell not only possesses good electrical conductivity (from carbon) but also extremely low infrared emissivity (from uniformly dispersed CeO2), with a measured minimum reflection loss of -54.9 dB. Conversely, if this ratio is deviated from, either the infrared emissivity will be too high (>0.5) due to insufficient CeO2, or the conductivity of the shell will drop sharply due to CeO2 agglomeration, making it impossible to form an effective conduction loss network and resulting in poor absorption performance.

[0024] In this invention, PMMA is the only viable polymer for the core spinning solution. After pyrolysis, PMMA forms a porous, loose carbon-based core structure, providing ample space for the subsequent loading of MIL-101(Fe) pyrolysis products, while preventing the core layer from becoming too dense and hindering the entry of electromagnetic waves. If other polymers are used instead, the mechanical stability of the core-shell structure cannot be maintained, or the wave absorption performance will be reduced.

[0025] The MIL-101(Fe) in this invention is the only iron-based MOF with a core layer capable of achieving broadband microwave absorption. MIL-101(Fe) possesses ultra-large pore volume and abundant metal sites. After pyrolysis, it generates nanoparticles uniformly embedded in the carbon matrix, simultaneously providing dielectric loss (carbon matrix) and magnetic loss (iron oxide), making it the core material for achieving a strong absorption of -54.9 dB. When MIL-101(Fe) is mixed with PMMA in DMF solvent, it does not agglomerate or degrade, ensuring the stability of the spinning solution.

[0026] The PAN used in this invention is the only optional polymer for shell spinning solution. The core reason is that PAN undergoes cyclization and cross-linking during the pre-oxidation stage at 200°C, forming a stable ladder structure. After pyrolysis, it can form a continuous and dense carbon shell, effectively encapsulating CeO2 and maintaining a low infrared emissivity.

[0027] In this invention, CeO2 is the only filler capable of achieving low infrared emissivity in the shell layer. CeO2 exhibits low intrinsic infrared emissivity in the 8-14μm wavelength band, and its structure remains intact after pyrolysis. It is the only metal oxide that can maintain low emissivity under high-temperature processing. If replaced with other fillers, the infrared stealth requirements cannot be met; furthermore, it has poor compatibility with PAN and is prone to agglomeration, leading to an uneven shell layer. CeO2 is the only shell filler that can simultaneously achieve a synergistic effect of ε=0.37 and -54.9dB, matching the microwave absorption function of the core layer.

[0028] Example 1 Synthesis of MIL-101(Fe): 10 mmol of ferric chloride hexahydrate and 5 mmol of terephthalic acid were mixed in 60 mL of DMF solution and stirred evenly for 35 min to obtain a mixed solution. The mixed solution was placed in a stainless steel high-pressure reactor with a 100 mL PTFE liner and placed in a forced-air drying oven at 110 °C for 20 h. After the reaction was completed, the resulting mixed solution was vacuum filtered, washed three times each with DMF and anhydrous ethanol, and then dried in an oven at 70 °C for 12 h to obtain MIL-101(Fe) powder.

[0029] Preparation of PMMA / MIL-101(Fe)@PAN / CeO2 fibers: 1.4 g of PMMA and 8 mL of DMF were magnetically stirred in a sample vial for 4 h until the solution became clear, with the temperature controlled within the range of 20-30 °C and the stirring speed at 800 rpm / min. Then, 1 g of dry MIL-101(Fe) powder was added, and the mixture was stirred for 6 h at 800 rpm / min within the temperature range of 20-30 °C to obtain the core spinning solution.

[0030] 0.6 g of PAN and 8 mL of DMF were magnetically stirred in a sample vial for 4 h until the solution became clear, with the temperature controlled within the range of 20-30℃ and the stirring speed at 800 rpm / min. Then, 1 g of dry CeO2 powder was added, and the mixture was stirred for 6 h at 800 rpm / min within the temperature range of 20-30℃ to obtain the shell spinning solution.

[0031] Preparation of core-shell composite fibers by electrospinning: The silica receiving paper was fixed to the roller receiver according to a suitable size. The core spinning solution and shell spinning solution were loaded into syringes respectively. Then, the power was turned on to carry out electrospinning synthesis. A syringe system with 21G+16G stainless steel needles (inner diameter 0.5 mm + inner diameter 1.2 mm) was used. The positive voltage was set to 18 kV and the negative voltage to 1.2 kV. The injection rate of the shell spinning solution was 0.06 mm / min, and the injection rate of the core spinning solution was 0.02 mm / min. The receiving distance was 20 cm. After continuous spinning for 6 hours, the fiber composite membrane was collected on the silica receiving paper. After spinning, the fiber composite membrane was dried under vacuum at 60℃.

[0032] Preparation of Fe2O3 / FeOOH / C@CeO2 fibers: The dried fiber composite membrane was transferred to a tube furnace and heated to 200℃ at 2℃ / min under N2 protection and held for 2 h to stabilize the fiber structure. Subsequently, the temperature was increased to 600℃ at 2℃ / min and held at a constant temperature for 2 h to obtain the composite fiber material, denoted as Fe2O3 / FeOOH / C@CeO2-600.

[0033] The Fe2O3 / FeOOH / C@CeO2-600 obtained in this embodiment was ground into powder and then uniformly mixed with paraffin wax and pressed into a ring. The mass ratio of powder to paraffin wax was 3:7, and the total weight was 0.1 g. The ring was pressed into a coaxial sample ring with an outer diameter of 7.00 mm and an inner diameter of 3.04 mm, and a thickness of 2.87 mm. This sample was used for subsequent testing.

[0034] like Figure 1 and Figure 2As shown, the Fe2O3 / FeOOH / C@CeO2-600 obtained in this embodiment was tested using a Fourier transform infrared spectrometer in the infrared wavelength range of 8-14 μm. The test results showed that the average emissivity of Fe2O3 / FeOOH / C@CeO2-600 in this band was 0.377. Subsequently, the complex permittivity and complex permeability of the sample in the 2-18 GHz band were measured using a microwave vector network analyzer. Then, the reflection loss of the simulated single-layer absorbing material was calculated using transmission line theory. Finally, it was found that the lowest reflection loss at a matching thickness of 1.99 mm was -4.6 dB, indicating no absorbing performance. During pyrolysis at 600°C, the conductivity of the carbon shell and the iron oxide core did not reach optimal matching, and the interfacial polarization effect between them was weak, further weakening the overall electromagnetic wave attenuation capability.

[0035] Example 2 The difference between this embodiment and Embodiment 1 is that: 1. The high-temperature pyrolysis temperature in the preparation of Fe2O3 / FeOOH / C@CeO2 fiber is: then the temperature is increased to 700℃ at 2℃ / min and held at a constant temperature for 2 h to obtain the composite fiber material, denoted as Fe2O3 / FeOOH / C@CeO2-700.

[0036] 2. Press into a coaxial sample ring with an outer diameter of 7.00 mm and an inner diameter of 3.04 mm, and a thickness of 2.93 mm.

[0037] The composite fiber precursors MIL-101(Fe) / PMMA and CeO2 / PAN obtained in this embodiment were observed by transmission electron microscopy, as follows: Figure 3 As shown, the fiber structure is consistent with the design, exhibiting a core-shell structure. The core of the fiber is darker in color, while the outer shell is lighter in color, which not only proves the successful preparation of the core-shell nanofibers but also confirms the good coating effect. The outer layer shows a continuous shell structure with relatively uniform thickness. CeO2 is dispersed and embedded in the PAN matrix without obvious large-sized aggregates, indicating that CeO2 has good compatibility with the PAN solution in DMF after magnetic stirring. The inner layer is a thinner core layer with a clear interface with the outer layer. The PMMA matrix encapsulates the MIL-101(Fe) particles. The precursors MIL-101(Fe) / PMMA and CeO2 / PAN in this embodiment were examined by scanning electron microscopy, and the resulting images are shown below. Figure 4As shown in the figure. Experimental results show that the overall fiber distribution is relatively uniform, with no obvious bead-like defects or agglomerated particles, indicating that the CeO2 nanoparticles are well dispersed in the PAN solution and the solution does not break down during spinning due to agglomeration. The three-dimensional network structure formed by the interwoven fibers, exhibiting an irregular orientation distribution, indicates that the viscosity of the PAN-CeO2 composite solution is moderate, the solvent evaporates uniformly during electrospinning, and the fiber-forming properties are stable. MIL-101(Fe) has good compatibility with PMMA and does not significantly damage the film-forming properties of PMMA. The smooth fiber surface indicates that the core layer solution is subjected to uniform stress during electrospinning, the inner and outer layer flow rates are well matched, and the electrospinning parameters are set reasonably. The pyrolytic fiber Fe2O3 / FeOOH / C@CeO2-700 of this embodiment was examined by scanning electron microscopy, and the resulting image is shown in the figure. Figure 5 As shown in the figure. Experimental results show that the fibers exhibit an interwoven network structure, which enhances structural stability through interfacial interactions. The outer PAN layer pyrolyzes under N2 atmosphere to generate carbon material, with CeO2 uniformly dispersed in the carbon matrix. The fiber surface may appear slightly rough due to the presence of CeO2. The inner PMMA layer retains a small amount of carbon after pyrolysis, but the MIL-101(Fe) pyrolysis generates an iron-based oxide / carbon composite material, which may fill the fiber interior or adhere to the inner wall, forming a core layer. The fibers do not show obvious agglomeration, indicating good dispersibility.

[0038] The XRD pattern of Fe2O3 / FeOOH / C@CeO2-700 obtained in this embodiment is shown below. Figure 6 As shown in the figure, the broadened shoulder peak at 2θ = 10°~30° indicates the presence of characteristic diffuse scattering of amorphous carbon, possibly due to the cyclization and dehydrogenation of the molecular chain of PAN (polyacrylonitrile) during pyrolysis in N2 at 700℃ to generate amorphous carbon. The CeO2 peak indicates that its structure was not destroyed, suggesting that CeO2 at high temperatures... 4+ The oxidation state is stable and no reduction occurs. The inner Fe layer is mainly composed of Fe2O3 and FeOOH, possibly due to trace oxidation or hydrolysis residues in the N2 atmosphere. The outer CeO2 / C layer and the inner Fe oxide / carbon layer form a core-shell fiber through electrospinning. After pyrolysis, the fiber matrix (carbon) remains continuous, while CeO2 and Fe oxides are uniformly distributed at the core-shell interface, which is beneficial for multiple scattering and loss of electromagnetic waves.

[0039] In this embodiment, the complex permittivity and complex permeability of the Fe2O3 / FeOOH / C@CeO2-700 samples were measured using a microwave vector network analyzer at 2-18 GHz. Figure 7As shown in the figure, ε' decreases from around 10 at 2 GHz to around 6 at 18 GHz, generally decreasing with increasing frequency. ε'' decreases from around 6.5 at 2 GHz to 2.8 at 18 GHz, generally decreasing monotonically with increasing frequency. However, the loss in the low-frequency band (2-6 GHz) is significantly higher than that in the high-frequency band. The decrease in ε' and ε'' may be related to the dominance of the dielectric response of the carbon matrix. The interfacial polarization of CeO2 and iron oxide contributes more at low frequencies, but with increasing frequency, electronic / ionic polarization dominates, leading to a decrease in both the real and imaginary parts.

[0040] The reflection loss of the Fe2O3 / FeOOH / C@CeO2-700 single-layer absorbing material obtained in this embodiment was calculated and simulated as follows: Figure 8 As shown in the figure, the thicknesses of the simulated single-layer absorbing material are 1.5 mm, 1.99 mm, 2.4 mm, 3.0 mm, 3.5 mm, 4.0 mm, and 4.5 mm. The figure shows that the lowest reflection loss occurs at a thickness of 1.99 mm and a frequency of 17.44 GHz. In the high-frequency range of 14-18 GHz (reflection loss <-10 dB), this is likely due to the synergistic effect of the magnetic loss of the iron-based oxide and the conductive loss of the carbon matrix, leading to enhanced relaxation and interfacial polarization, thus reducing reflection loss. The core-shell structure may create a gradient impedance; the impedance matching is optimal at a thickness of 1.99 mm, resulting in the lowest reflection loss of -54.9 dB.

[0041] The two-dimensional mapping results of Fe2O3 / FeOOH / C@CeO2-700 obtained in this embodiment at 2-18 GHz are as follows: Figure 9 As shown in the figure, the reflection loss at different frequencies and thicknesses is represented by the color depth. At a thickness of 2.4 mm, the EAB = 6.32 GHz. The low-frequency band (2-6 GHz) is lighter in color (reflection loss <-10 dB), confirming weak absorption capability. However, the color slightly darkens as the thickness increases to 3.5 mm, indicating a slight improvement in low-frequency absorption. In the mid-frequency band (6-12 GHz), the dark area significantly expands and shifts in position with thickness, indicating that thickness adjustment can optimize absorption performance at specific frequencies. The high-frequency band (12-18 GHz) exhibits broadband absorption, possibly due to the magnetic-dielectric synergistic loss (hysteresis loss + interface polarization) of the inner iron oxide layer covering this band, while the dielectric loss of the outer layer extends the bandwidth. When the thickness is less than 2 mm, the EAB is narrow (<3 GHz), only covering the high-frequency band (14-18 GHz), possibly because the absorption path is short and cannot excite the inner layer's magnetic loss. When the thickness is greater than 3.6 mm, the EAB narrows (<4 GHz), possibly because excessive thickness leads to enhanced electromagnetic wave transmission and decreased absorption efficiency.

[0042] The infrared emissivity results of Fe2O3 / FeOOH / C@CeO2-700 obtained in this embodiment are as follows: Figure 10 As shown in the figure, the average infrared emissivity within the wavelength range of 8–14 μm is 0.379, exhibiting low emissivity and wide-band uniformity. The emissivity curve is flat without significant fluctuations, indicating excellent stability of the material in infrared radiation modulation. The outer low-emissivity matrix protects the inner functional filler, reducing the erosion of iron in MIL-101(Fe) by environmental factors and maintaining long-term stable infrared modulation performance.

[0043] Example 3 The difference between this embodiment and Embodiment 1 is that: 1. The high-temperature pyrolysis temperature in the preparation of Fe2O3 / FeOOH / C@CeO2 fiber, namely: the temperature is then increased to 800℃ at 2℃ / min and held at a constant temperature for 2 h to obtain the composite fiber material, denoted as Fe2O3 / FeOOH / C@CeO2-800.

[0044] 2. Press into a coaxial sample ring with an outer diameter of 7.00 mm and an inner diameter of 3.04 mm, and a thickness of 3.05 mm.

[0045] like Figure 11 and 12 As shown, the Fe2O3 / FeOOH / C@CeO2-800 obtained in this embodiment was tested using a Fourier transform infrared spectrometer in the infrared wavelength range of 8–14 μm. The test results showed that the average emissivity of Fe2O3 / FeOOH / C@CeO2-800 in this band was 0.392. At high temperatures, CeO2 particles may agglomerate due to intensified thermal motion, losing their uniform dispersion state, resulting in an increase in infrared emissivity in local areas, but the difference is not significant compared to 700°C. Subsequently, the complex permittivity and complex permeability of the sample in the 2–18 GHz frequency band were measured using a microwave vector network analyzer. Combined with transmission line theory, the reflection loss of the simulated single-layer absorbing material was calculated. Finally, the minimum reflection loss at a matching thickness of 5.0 mm was found to be -21.14 dB. The high temperature of 800°C causes excessive graphitization of the carbon matrix, resulting in a sharp increase in conductivity. According to transmission line theory, when the input impedance of a material differs too much from its free-space impedance (377 Ω), electromagnetic waves will be strongly reflected at the material surface and cannot penetrate into the material's interior. Excessive absorption at such high temperatures may cause the core-shell structure to collapse. On the other hand, intense thermal motion may disrupt the uniform distribution of CeO2 within the shell, resulting in performance that is not as excellent as at 700℃.

[0046] The Tafel curves of test examples 1, 2, and 3 were obtained, and the corrosion current and corrosion voltage were calculated. The test results are as follows: Figure 13As shown, the larger the absolute value (the more positive) of the equilibrium potential for corrosion reaction, the weaker the tendency for active corrosion; the lower the corrosion current density, the better the corrosion resistance of the material. Fe2O3 / FeOOH / C@CeO2-700 has the lowest corrosion current density (5.595 × 10⁻⁶). −7 A / cm 2 This indicates the lowest corrosion rate and optimal corrosion resistance. At 700℃, a more stable microstructure forms, promoting the formation of a passivation film that hinders the penetration of corrosive media, resulting in the best corrosion resistance. This is because the carbon layer after pyrolysis can block the penetration and diffusion of external corrosive media into the fiber interior. Furthermore, high-temperature derived carbon-based materials themselves have a graphite-like structure, extremely low electrochemical activity, and intrinsic corrosion resistance when exposed to acidic, alkaline, and salt environments. The CeO2 lattice contains Ce... 3+ / Ce 4+ Redox pairs and oxygen vacancies can react with OH- to catalyze the formation of a dense passivation film at defects on the material surface.

[0047] Figure 14 The diagram shows the open-circuit potential versus time for Examples 1, 2, and 3. A higher OCP indicates a higher redox potential, making the material more difficult to oxidize and corrode. A higher OCP also means a weaker driving force for the corrosion reaction, slower corrosion, and a lower corresponding corrosion current. The resulting Fe2O3 / FeOOH / C@CeO2-700 exhibits the highest and most stable OCP. corr Minimal, with optimal corrosion resistance.

[0048] Example 4 The difference between this embodiment and embodiment 2 is that: The obtained Fe2O3 / FeOOH / C@CeO2-700 was ground into powder and then uniformly mixed with paraffin wax and pressed into a ring. The mass ratio of powder to paraffin wax was 4:6.

[0049] The complex permittivity of the Fe2O3 / FeOOH / C@CeO2-700 (4:6) monolayer absorbing material obtained in this embodiment was calculated by simulation as follows: Figure 15 As shown, the reflection loss is as follows Figure 16 As shown, the two-dimensional mapping diagram is as follows: Figure 17 As shown. The test method is the same as in Example 2. At a thickness of 1.87 mm, the sample reaches its strongest absorption peak of -34.2 dB at a frequency of 17.84 GHz, indicating the lowest reflection loss. The maximum EAB (reflection loss ≤ -10 dB) is reached at a thickness of 2.25 mm. Compared to Fe2O3 / FeOOH / C@CeO2-700, the lowest reflection loss is reduced by 20.7 dB, and the EAB is reduced by 0.32 GHz.

[0050] Example 5 The difference between this embodiment and embodiment 2 is that: The obtained Fe2O3 / FeOOH / C@CeO2-700 was ground into powder and then uniformly mixed with paraffin wax and pressed into a ring. The mass ratio of powder to paraffin wax was 5:5.

[0051] The complex permittivity of the Fe2O3 / FeOOH / C@CeO2-700 (5:5) monolayer absorbing material obtained in this embodiment was calculated by simulation as follows: Figure 18 As shown, the reflection loss is as follows Figure 19 As shown, the two-dimensional mapping diagram is as follows: Figure 20 As shown. The test method is the same as in Example 2. The 1.75 mm thick sample had a minimum reflection loss of -21.01 dB at 17.52 GHz. The maximum EAB of 5.76 GHz was reached at a thickness of 2.07 mm (reflection loss ≤ -10 dB). Compared with Fe2O3 / FeOOH / C@CeO2-700, the minimum reflection loss was reduced by 33.89 dB and the EAB was reduced by 0.56 GHz.

[0052] Therefore, it can be seen that the microwave absorption performance of Fe2O3 / FeOOH / C@CeO2-700 in Example 2 is significantly better than that in Examples 4 and 5. The reason is that the mixture of 30% microwave absorber and paraffin enhances charge accumulation and improves high-frequency loss; 70% paraffin maintains the porous structure and prolongs the electromagnetic wave reflection path.

[0053] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A cerium-doped carbon-coated iron oxide composite fiber, characterized in that, The composite fiber has a core-shell structure, with the outer shell layer being PAN and CeO2, and the core layer being PMMA and MIL-101(Fe). The outer shell layer is used to reduce the emissivity of the composite fiber in long-wave infrared, and the core layer is used for radar absorption.

2. A method for preparing cerium-doped carbon-coated iron oxide composite fibers, characterized in that... ； Using core-shell spinning solution and shell-shell spinning solution as raw materials, a composite fiber membrane with a core-shell hierarchical structure was prepared by coaxial electrospinning process. Then, the composite fiber membrane was pre-oxidized and then pyrolyzed at high temperature to carbonize the polymer and convert MOF into iron oxide, finally obtaining inorganic / carbon-based core-shell functional fiber. The core spinning solution contains PMMA and MIL-101(Fe); The shell spinning solution contains PAN and CeO2.

3. The method for preparing cerium-doped carbon-coated iron oxide composite fibers according to claim 1, characterized in that, in, The mass ratio of PMMA to MIL-101(Fe) is 1.4:

1.

4. The method for preparing cerium-doped carbon-coated iron oxide composite fibers according to claim 1, characterized in that, in, The mass ratio of PAN to CeO2 is 0.6:

1.

5. The method for preparing cerium-doped carbon-coated iron oxide composite fibers according to claim 1, characterized in that, in, The mass ratio of MIL-101(Fe) to CeO2 is 1:

1.

6. The method for preparing cerium-doped carbon-coated iron oxide composite fibers according to claim 1, characterized in that, The flow rate ratio of the core spinning solution to the shell spinning solution is 3:

1.

7. The method for preparing cerium-doped carbon-coated iron oxide composite fibers according to claim 1, characterized in that, The parameters for the coaxial electrospinning process are: positive voltage 18 kV, negative voltage 1.2 kV, receiving distance 20 cm; continuous spinning for 6 h.

8. The method for preparing cerium-doped carbon-coated iron oxide composite fibers according to claim 1, characterized in that, The method for obtaining the core spinning solution is as follows: PMMA and DMF are magnetically stirred in a sample bottle for 4 h until the solution becomes transparent, the temperature range is controlled at 20-30℃, and the mixture is stirred at a speed of 800 rpm / min. Then, dry MIL-101(Fe) powder is added, and the mixture is stirred at a speed of 800 rpm / min for 6 h within the temperature range of 20-30℃ to obtain the core spinning solution.

9. The method for preparing cerium-doped carbon-coated iron oxide composite fibers according to claim 1, characterized in that, The method for obtaining the shell spinning solution is as follows: PAN and DMF are magnetically stirred in a sample bottle for 4 h until the solution becomes transparent, the temperature range is controlled at 20-30℃, and the mixture is stirred at a speed of 800 rpm / min. Then, dry CeO2 powder is added, and the mixture is stirred at a speed of 800 rpm / min for 6 h within the temperature range of 20-30℃ to obtain the shell spinning solution.

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