CoFe2O4 / coal gasification residue composite material, preparation method and application

Abstract

The application discloses a CoFe2O4 / coal gasification residual carbon composite material, a preparation method and application, and steps of the preparation method are as follows: S1: dissolving coal gasification residual carbon in ethylene glycol; S2: adding a cobalt source and an iron source into the mixed solution in S1, and then entering anhydrous sodium acetate to react after mixing; S3: after the reaction is completed, washing and drying are performed, and the CoFe2O4 / coal gasification residual carbon composite material is obtained. The CFO / RC composite material is successfully synthesized by using a simple hydrothermal method. The existence of different functional groups and defects in the residual carbon enhances mutual coupling, interface polarization and dipole polarization; in addition, loading CoFe2O4 on the irregular surface of the carbon material can promote multiple scattering and reflection of incident electromagnetic waves, and a new practical preparation scheme is provided for developing a microwave absorption material.

Description

Technical Field

[0001] This invention relates to the field of composite material technology, and in particular to CoFe2O4 / coal gasification residue composite material, its preparation method and application. Background Technology

[0002] With the rapid development of civilian communication methods, the frequency of microwave utilization in daily life is constantly increasing. Microwaves (EMWs) are widely used in wireless communication, healthcare, scientific research, and other fields. While higher communication frequencies make information exchange faster and more convenient, they also bring increasingly serious problems of electromagnetic interference and electromagnetic pollution. The radiation generated by microwaves can interfere with surrounding instruments and affect human health. Prolonged exposure to high-frequency microwave radiation can cause polar molecules in body fluids to oscillate at high frequencies, leading to energy consumption and body heating, thus adversely affecting human health. The World Health Organization (WHO) has listed electromagnetic pollution as the fourth largest environmental pollutant of the 21st century. To reduce harmful electromagnetic radiation or interference, advanced microwave absorbing materials (MAMs) have become indispensable.

[0003] Coal gasification is the leading technology in the coal chemical industry, and as one of the main ways to cleanly utilize coal, this technology has developed rapidly. However, the emission of gasification slag is increasing year by year. Currently, the cumulative stockpile of gasification slag in my country has reached hundreds of millions of tons, becoming a key factor restricting the development of the coal chemical industry. Coal gasification fine slag (CGFS) accounts for 30%-70% of the total gasification slag, and its main components are carbon and inorganic matter, possessing dual attributes as both fuel and raw material. However, CGFS has a high degree of graphitization of residual carbon, with some carbon encapsulated in the slag, and poor reactivity of inorganic components, making CGFS difficult to utilize effectively. Currently, less than 30% of CGFS is treated through landfill and incineration, while the rest is stockpiled on open ground, occupying a large area and having a low utilization rate. High moisture content also limits its transportation and reuse through combustion or energy recovery. CGFS is in powder form, characterized by high residual carbon (RC) content, high moisture content, and rich pore structure. When the gasifier is running at full load, the RC content in the gasification fine slag can reach as high as 60%. Resin-converted carbon (RC) mainly exists in the form of irregular particles with a highly developed pore structure, exhibiting a high degree of order, and some disordered carbon undergoes graphitization. Although RC possesses certain microwave absorption properties, it cannot meet the requirements of new microwave absorbing materials, such as light weight, wide absorption bandwidth, thin thickness, and strong absorption. Therefore, how to adjust the performance of RC to meet the requirements of new microwave absorbing materials is a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0004] Based on the technical problems existing in the background technology, this invention proposes a CoFe2O4 / coal gasification residue composite material, its preparation method and application. The prepared composite material has stronger microwave absorption capability.

[0005] The preparation method of CoFe2O4 / coal gasification residue composite material proposed in this invention includes the following steps:

[0006] S1: Dissolve the residual carbon from coal gasification in ethylene glycol;

[0007] S2: Add cobalt source and iron source to the mixture of S1, mix, and then add anhydrous sodium acetate to react;

[0008] S3: After the reaction is complete, the CoFe2O4 / coal gasification residue composite material is obtained by washing and drying.

[0009] Preferably, the molar ratio of coal gasification residue, anhydrous sodium acetate, cobalt source, and iron source is 1g:4-8g:8-25mmol:16-50mmol.

[0010] Preferably, the cobalt source is one of cobalt chloride and its hydrate, cobalt sulfate and its hydrate, cobalt nitrate and its hydrate, cobalt acetate and its hydrate, and cobalt oxalate and its hydrate.

[0011] Preferably, the iron source is one of ferric chloride and its hydrate, ferric sulfate and its hydrate, ferric nitrate and its hydrate, ferric acetate and its hydrate, and ferric oxalate and its hydrate.

[0012] Preferably, the reaction temperature in S2 is 180-220℃, and the reaction time is 5-15h.

[0013] Preferably, the drying temperature in S3 is 40-80℃, and the time is 8-16h.

[0014] The CoFe2O4 / coal gasification residue composite material prepared by the above method proposed in this invention.

[0015] The present invention relates to the application of the CoFe2O4 / coal gasification residue composite material in microwave absorbing materials.

[0016] Beneficial technical effects of the present invention:

[0017] This invention successfully synthesized CFO / RC composite materials using a simple hydrothermal method. The presence of different functional groups and defects in the residual carbon enhances mutual coupling, interfacial polarization, and dipole polarization. Furthermore, loading CoFe2O4 onto the irregular surface of the carbon material promotes multiple scattering and reflection of incident electromagnetic waves. Notably, the prepared CFO / RC-2 composite material exhibits a high RL (reflectance ratio) at a thickness of 2.44 mm. minThe EAB is -44dB, while CFO / RC-3 has an EAB of 4.16GHz at a thickness of 1.18 mm. This invention provides a new and practical preparation scheme for the development of microwave absorbing materials. Attached Figure Description

[0018] Figure 1 The XRD patterns of (a) RC and CFO / RC composite materials, (b) FT-IR patterns of RC and CFO / RC composite materials, and (c, d) VSM patterns of CFO / RC composite materials proposed in this invention are shown.

[0019] Figure 2 SEM images of the CFO / RC composite material proposed in this invention: (ac)CFO / RC-1, (df)CFO / RC-2, (gi)CFO / RC-3;

[0020] Figure 3 The images are TEM images of the CFO / RC composite material proposed in this invention: (a, b) CFO / RC-1, (c, d) CFO / RC-2, (e, f) CFO / RC-3, and (g) EDX mapping images of CFO / RC-2.

[0021] Figure 4 The full spectrum of CFO / RC-2 proposed in this invention is (a) C 1s, (b) O 1s, (c) Fe 2p, and (d) Co 2p.

[0022] Figure 5 The corresponding relationships between different thicknesses, frequencies, and reflection losses proposed in this invention are: (ac)CFO / RC-1, (df)CFO / RC-2, and (gi)CFO / RC-3;

[0023] Figure 6 The (a)ε′, (b)ε″, (c)μ′, (d)μ″, and (e)tanδ of the CFO / RC proposed in this invention ε 、(f)tanδ μ curve;

[0024] Figure 7 The Cole-Cole semicircles (a) CFO / RC-1, (b) CFO / RC-2, (c) CFO / RC-3 and CFO / RC composite materials proposed in this invention have (d) CO and (e) α.

[0025] Figure 8 The |Z proposed in this invention in / Z0|Curves (a) CFO / RC-1, (b) CFO / RC-2, (c) CFO / RC-3;

[0026] Figure 9The present invention provides (a) a PEC and an RCS curve overlaid on the PEC with CFO / RC-2, and (b) a PEC and a model overlaid on the PEC with CFO / RC-2.

[0027] Figure 10 This invention presents the microwave absorption mechanism of the CFO / RC composite material. Detailed Implementation

[0028] The present invention will be further explained below with reference to specific embodiments.

[0029] The coal gasification fine slag of this invention is collected from the gasifier and the particle size of the coal gasification fine slag is ground to 2 μm using a ball milling method. Similar to previous studies, the RC is prepared by a two-step acidification method using coal gasification fine slag. The coal gasification fine slag is used as raw material, mixed, stirred, and filtered with hydrofluoric acid solution in a container. The filtered solid is washed with water until neutral and then dried. The dried solid is mixed, stirred, and filtered with hydrochloric acid solution in a container, and the filtered solid is washed with water until neutral and then dried to obtain the coal gasification fine slag residue RC.

[0030] The ferric chloride hexahydrate (FeCl3·6H2O, AR), cobalt chloride (CoCl2·6H2O, AR), anhydrous sodium acetate (NaAc, AR) and ethylene glycol (EG, AR) of this invention were purchased from Sinopharm Chemical Reagent Co., Ltd.

[0031] Example 1

[0032] First, 0.3 g of RC was dissolved in 40 mL of EG, and then sonicated for 30 minutes. 2.5 mmol of CoCl₂·6H₂O and 5.0 mmol of FeCl₃·6H₂O were uniformly distributed in the RC and EG mixture. After vigorous stirring for 15 minutes, 1.8 g of NaAc was added to the mixture. The solution was then stirred at 50 °C for 1 hour, transferred to a Teflon-lined stainless steel autoclave (100 mL), and maintained at 200 °C for 10 hours. Subsequently, the product was washed with deionized water and anhydrous ethanol, and dried at 60 °C for 12 hours. The resulting CoFe₂O₄ / coal gasification residue (CFO / RC) composite material was labeled CFO / RC-1.

[0033] Example 2

[0034] First, 0.3 g of RC was dissolved in 40 mL of EG, and then sonicated for 30 minutes. 5.0 mmol of CoCl₂·6H₂O and 10.0 mmol of FeCl₃·6H₂O were uniformly distributed in the RC and EG mixture. After vigorous stirring for 15 minutes, 1.8 g of NaAc was added to the mixture. The solution was then stirred at 50 °C for 1 hour, transferred to a Teflon-lined stainless steel autoclave (100 mL), and maintained at 200 °C for 10 hours. Subsequently, the product was washed with deionized water and anhydrous ethanol, and dried at 60 °C for 12 hours. The resulting CoFe₂O₄ / coal gasification residue (CFO / RC) composite material was labeled CFO / RC-2.

[0035] Example 3

[0036] First, 0.3 g of RC was dissolved in 40 mL of EG, and then sonicated for 30 minutes. 7.5 mmol of CoCl₂·6H₂O and 15.0 mmol of FeCl₃·6H₂O were uniformly distributed in the RC and EG mixture. After vigorous stirring for 15 minutes, 1.8 g of NaAc was added to the mixture. The solution was then stirred at 50 °C for 1 hour, transferred to a Teflon-lined stainless steel autoclave (100 mL), and maintained at 200 °C for 10 hours. Subsequently, the product was washed with deionized water and anhydrous ethanol, and dried at 60 °C for 12 hours. The resulting CoFe₂O₄ / coal gasification residue (CFO / RC) composite material was labeled CFO / RC-3.

[0037] Figure 1 (a) X-ray diffraction (XRD) patterns are shown to elucidate the crystal structures of the CFO / RC composite and pure RC. The XRD peaks observed at 2θ = 18.1°, 29.9°, 35.2°, 42.8°, 53.1°, 56.6°, 62.2°, and 73.5° correspond to the (111), (220), (311), (400), (422), (511), (440), and (533) crystal planes of CFO, respectively. This correspondence verifies the successful synthesis of cobalt ferrite in the CFO / RC composite. Furthermore, two peaks were found at 2θ = 25.8° and 43.5°, aligning with the (002) and (100) crystal planes of graphite, respectively; this indicates an increased degree of graphitization of carbon after gasification. Notably, the intensity of the (002) peak decreases and the (100) peak disappears after the introduction of CFO nanospheres. Figure 1 (b) shows the Fourier transform infrared spectrum of the CoFe2O4 / RC composite material. The values ​​at 591 and 417 cm⁻¹ are... -1 The vibrational peaks observed at [location missing] confirm the formation of CoFe₂O₄ nanoparticles in octahedral and tetrahedral spinels. Furthermore, vibrational peaks were observed at 1630 and 3430 cm⁻¹. -1The absorption peaks at 1100 cm⁻¹ can be attributed to the benzene ring and -OH, respectively. -1 The absorption peak at that point may originate from CO, CO, and CC, which has also been found in RC and CFO / RC composites. Figure 1 (c, d) illustrate the magnetic parameters of the CFO / RC composite materials, which were determined using VSM. The saturation magnetization (Ms) is affected by the RC content. The measured Ms values ​​for CFO / RC-1, CFO / RC-2, and CFO / RC-3 were 48.0, 48.6, and 38.4 emu / g, respectively. Furthermore, the coercivity (Hc) values ​​varied among the samples, with Hc values ​​of 379.3, 604.7, and 664.9 Oe for CFO / RC-1, CFO / RC-2, and CFO / RC-3, respectively. The observed hysteresis loops indicate that the magnetic loss behavior of the CFO / RC samples can be tuned by adjusting the metal ion content.

[0038] like Figure 2 and Figure 3 As shown, a comprehensive analysis of the microstructure and elemental distribution inside the CFO / RC composite material was conducted using SEM and TEM. Figure 2 (ai) shows that CFO nanospheres are randomly attached to the RC surface, forming a uniform nanosphere structure. It is noteworthy that... Figure 2 (e, h) and Figure 3 (e) reveals the presence of specific RC sheets that establish connections between CFO nanospheres, ultimately forming diverse heterogeneous interfaces. This interconnection enhances interfacial polarization, thereby improving microwave absorption efficiency. Figure 3 The high-resolution TEM (HRTEM) image shown in (df) verifies the 0.25 nm lattice spacing, consistent with the (311) crystal plane of CFO. Furthermore, through... Figure 3 (g) We can also understand the spatial distribution of C, O, Fe, and Co elements in the CFO / RC-2 composite material. In summary, we have successfully prepared a unique CFO / RC composite material characterized by a multi-structural configuration.

[0039] To analyze the chemical composition of CoFe2O4 / RC, we performed XPS analysis. Figure 4 (a) shows the full spectrum confirming the presence of C, O, Fe, and Co elements in the CFO / RC composite material. Figure 4 In (b), the C1s spectrum of the composite material showed five peaks at 284.7, 285.5, 286.7, 288.8 and 291.2 eV, which correspond to C=C, CO, C-OH, O=C-OH and π-π bonds, respectively. Figure 4(c) shows the O1s spectrum, with three peaks at 530.5, 532.3 and 534.1 eV, representing lattice oxygen, surface-absorbed oxygen and oxygen-containing groups, respectively. Figure 4 The Fe 2p spectrum in (d) shows peaks at 711.0, 713.5, and 724.8 eV, corresponding to Fe 2p peaks, respectively. 3 / 2 and Fe 2p 1 / 2 The results indicate the valence state distribution of Fe in CoFe₂O₄. The appearance of satellite peaks at 718.6 and 731.8 eV further confirms the presence of Fe in the composite material. 3+ .like Figure 4 As shown in (e), Co 2p 3 / 2 and Co 2p 1 / 2 These peaks are consistent with those at 781.5 and 796.6 eV, respectively. Additionally, two satellite peaks are observed at approximately 787.1 and 803.8 eV, indicating the presence of Co in CFO / RC-2. 2+ .

[0040] Transmission line theory helps to quantify microwave absorption through reflection loss. The calculation process includes the free-space intrinsic impedance (Z0) and the input impedance (Z). in It can be described as follows:

[0041]

[0042]

[0043]

[0044] In the formula, f represents the electromagnetic frequency of the interference pattern, c represents the speed of light, d represents the thickness of the absorber, and μ r , ε r μ0 and ε0 represent the electromagnetic induction intensity and dielectric constant of the absorber and free space, respectively. When the RL value of the absorber is below -10 dB, it indicates that more than 90% of the energy in the incident wave is converted into heat energy by the absorbing medium. Therefore, when evaluating the microwave absorption characteristics of materials, the frequency band with RL values ​​below -10 dB is usually referred to as EAB.

[0045] Based on previous research, with a thickness of 4.8 mm, the RL of RC minReaching -52.3dB at 5.04GHz indicates that pure RC can only achieve excellent absorption and a narrow effective bandwidth with greater thickness, which is why we improved the RC by adding ferrite materials. This phenomenon is caused by the relatively high dielectric constant of the RC itself, which reduces impedance matching and affects electromagnetic wave loss. However, by introducing magnetic CoFe2O4, the spatial structure of the composite material becomes more diverse, and the microwave absorption capability is significantly improved. Figure 5 The variation of RL with frequency is shown for CFO / RC composites of different thicknesses. For example... Figure 5 As shown in (d), the ideal RL of CFO / RC-2 min The thicknesses are 2.44 mm and 1.5 mm, respectively, and at frequencies of 7.76 GHz and 13.44 GHz, they are approximately -43.99 dB and 25.33 dB, respectively. For example... Figure 5 As shown in (a), the EAB of the composite was also significantly improved, with the maximum EAB of CFO / RC-1 reaching 3.84 GHz (14.16–18.00 GHz). Furthermore, as... Figure 5 As shown in (g), the maximum EAB of the CFO / RC-3 is 4.16 GHz (13.84-18.00 GHz). From Figure 5 As shown in (c, f, e), the peak position of RL shifts from low frequency to high frequency as the thickness decreases, which provides feasibility for applying the material to different wavebands. Experimental results show that there is a strong synergistic effect among the various components, with CoFe2O4 significantly improving the microwave absorption characteristics of the composite material.

[0046] The absorption properties of MAM are affected by ε r and μ r The influence of electromagnetic fields. Typically, the real parts of the complex permittivity (ε') and complex permeability (μ') are related to the polarization and absorption of the material by the applied magnetic field. On the other hand, the imaginary parts of the complex permeability (μ") and complex permittivity (ε") characterize the power loss resulting from the recombination of magnetic and electric dipole moments under the influence of electromagnetic fields in the MAM, and they are related to the material's ability to absorb electrical and electromagnetic energy. Figure 6 The values ​​of ε′, ε′, μ′, μ′, and tanδ for CFO / RC-1, CFO / RC-2, and CFO / RC-3 are shown. ε and tanδ μ The research results show that, for example Figure 6 As shown in (a), within the measurement range of 2-18 GHz, ε' of CFO / RC-1 to CFO / RC-3 steadily decreases from 13.97 to 10.89, from 18.79 to 13.83, and from 26.85 to 15.83, exhibiting a strong dielectric dispersion effect. The variation pattern of ε” is basically similar to that of ε'. Figure 6(b) The ε' of CFO / RC-3 drops significantly from 11.91 to 6.70, while CFO / RC-1 and CFO / RC-2 remain essentially linear in the 2-18 GHz range. The low ε' value of CFO / RC-1 and the high ε' value of CFO / RC-3 may be detrimental to impedance matching characteristics. The ε' value of CFO / RC-2 falls between that of CFO / RC-1 and CFO / RC-3, and its dielectric constant is suitable for microwave entry into the absorber. The significant increase in ε' of CFO / RC-2 near 8 GHz is likely due to defects and interfaces in the CoFe2O4 and RC composite material, leading to more relaxation and polarization, further increasing dielectric loss. The composite permeability of the CFO / RC samples is as follows: Figure 6 As shown in (c, d). Figure 6 As shown in (c), μ' of CFO / RC-1 and CFO / RC-2 decreases in the 2-18 GHz range, while μ' of CFO / RC-3 increases at 14 GHz. The μ' and μ" values ​​of CFO / RC-1 and CFO / RC-2 are higher than those of CFO / RC-3. Generally, there is a certain proportional relationship between the composite permeability and Ms strength of the composite material. That is, the higher the Ms value of the CFO / RC-1 and CFO / RC-2 composite materials, the higher the magnetic permeability. The μ" of the three samples first increases, then increases in the 2-18 GHz range, and shows significant fluctuations in the 6-12 GHz range. The main causes of magnetic loss usually include natural resonance, domain wall resonance, and hysteresis. However, hysteresis loss can be ignored in the presence of a weak magnetic field, while domain wall resonance mainly exists in the megahertz frequency range. On the other hand, natural resonance occurs at a lower frequency compared to exchange resonance. In the results given, the resonance peak is mainly attributed to natural resonance. Figure 6 tanδ shown in (e, f) ε and tanδ μ The trends are the same as those of ε” and μ”, respectively. It is worth noting that, compared to tanδ… μ In comparison, the dielectric loss and magnetic loss tangent of the CFO / RC composite material are significantly higher. ε The value is higher, indicating that dielectric loss is the main mechanism of electromagnetic microwave absorption.

[0047] In fact, the loss module in a MAM includes dielectric loss and magnetic loss. Magnetic loss is mainly affected by several mechanisms, including eddy current loss, hysteresis loss, domain wall resonance, and natural resonance. On the other hand, dielectric loss mainly arises from polarization relaxation processes, such as interfacial polarization, electronic polarization, or ionic polarization. For MAMs, Debye theory provides an analysis of the complex permittivity. According to Debye theory, the behavior of the permittivity can be described using standard Cole-Cole semicircles. Each semicircle corresponds to a Debye polarization phase transition, indicating the Debye polarization relaxation process. By analyzing the characteristics of the semicircles, information about the complex permittivity and underlying polarization mechanisms can be obtained.

[0048]

[0049] ε' and ε” can be derived from the above formula:

[0050]

[0051]

[0052] The correlation between ε' and ε” can be described as follows:

[0053]

[0054] In the given equation, ε s It is the steady-state dielectric constant, ε ∞ τ represents the dielectric constant when the frequency approaches infinity, and τ is the relaxation time. Figure 7 (ac) describes the relationship between ε' and ε” in the CFO / RC composites. Several identifiable semicircles were observed in CFO / RC-1 and CFO / RC-2, indicating the presence of a Debye polarization phase transition. Notably, the CFO / RC-2 composite exhibits strong microwave absorption properties and a pronounced Debye relaxation process.

[0055] To gain a deeper understanding of the magnetic loss mechanism, the domain wall resonance and eddy current losses can be derived from C0 determined in equations (8) and (9):

[0056]

[0057]

[0058] When the C0 value tends to be constant, eddy current loss becomes the main factor in magnetic loss. However, as Figure 7 As shown in (d), the CFO / RC composite material is not constant in the 2-18 GHz range. This indicates that eddy current loss is not the main magnetic loss mechanism of the CFO / RC series samples.

[0059] The following section focuses on impedance matching and attenuation constant, which are key factors affecting the absorption capability of electromagnetic waves. The attenuation coefficient plays a crucial role in describing the attenuation of electromagnetic waves in the absorber and can be characterized by the following formula:

[0060] like Figure 7 As shown in (e), the attenuation coefficient of the CFO / RC composite material ranges from 15.24 to 318.30. The attenuation coefficient is mainly affected by the Ms and Hc of the composite material. The dielectric properties of RC are the main reason why the relative content of RC in CFO / RC significantly changes the attenuation coefficient. It can change the dielectric constant and permeability to an appropriate range, thereby optimizing the impedance matching characteristics of the absorbing material. In addition, compared with the other two groups of samples, the CFO / RC-3 composite material has the largest value across the entire frequency range, but its electromagnetic wave absorption performance is not ideal, indicating that the electromagnetic wave absorption capability of the material depends not only on the attenuation constant.

[0061] Absorbing materials require ideal impedance matching, which is crucial for electromagnetic waves to enter the absorber. Figure 8 The results in (ac) show the impedance matching of CFO / RC samples with three different thicknesses. |Z of CFO / RC-1 in The / Z0| value is significantly greater than 1, while the |Z0| value of CFO / RC-3 is much greater than 1. in The / Z0| value is significantly less than 1. In contrast, only CFO / RC-2 shows a |Z0| value under more thickness conditions. in The / Z0| value is closer to 1. This indicates that the CFO / RC-2 composite material has better impedance matching, exhibits excellent microwave absorption capability, and achieves a good balance between RC and CFO, thus balancing the complex permittivity and permeability better than other composite materials.

[0062] Based on previous research results, Figure 10 The mechanism by which CFO / RC composites possess excellent microwave absorption properties is explained. First, the irregularly shaped RC particles loaded with regular spherical CoFe2O4 particles form a unique three-dimensional spatial structure, enhancing impedance matching. This structure promotes multiple scattering and reflection of incident microwaves, thereby improving energy dissipation efficiency. Second, the presence of residual carbon in the composite provides good conductivity. Free electrons within the conductive channels undergo transitions and transfers, converting electromagnetic waves into thermal energy dissipation. Third, the residual carbon possesses various functional groups and defects, enhancing interfacial polarization and dipole polarization. This further reduces the microwave incident rate in the complex structure. Finally, the synergistic effect of magnetic loss contributes to the effective attenuation of electromagnetic waves. In summary, the combination of these mechanisms in CFO / RC composites endows them with effective microwave absorption capabilities.

[0063] Radar cross section (RCS) plays a crucial role in designing stealth aircraft to evade radar surveillance systems. To evaluate the practical utility of CFO / RC in the far-field scenario, a predefined model (180 mm × 180 mm) was built in CST simulation, consisting of a perfect electrical conductor (PEC) coating (0.5 mm) and CFO / RC material (2.44 mm) covering 8.00 GHz. Figure 9 Three-dimensional intensity images and RCS value curves from -90° to 90° are shown for PEC and PEC coated with CFO / RC-2. Notably, the PEC coated with CFO / RC-2 exhibits an RCS of approximately -10 dBm. 2 The maximum RCS value was observed, which was significantly lower than that of the PEC plate. This observation indicates that CFO / RC-2 possesses strong microwave attenuation capabilities, reducing radar scattering intensity from all angles of the incident wave. Therefore, CFO / RC composite materials have broad development prospects as microwave absorbing materials in practical applications.

Claims

1. A method for preparing CoFe2O4 / coal gasification residue composite material, characterized in that, The steps are as follows: S1: Dissolve coal gasification residue in ethylene glycol; S2: Add cobalt source and iron source to the mixture of S1, mix, and then add anhydrous sodium acetate to react; S3: After the reaction is complete, the CoFe2O4 / coal gasification residue composite material is obtained by washing and drying. The mass molar ratio of coal gasification residue, anhydrous sodium acetate, cobalt source and iron source is 1g:4-8g:8-25mmol:16-50mmol; The reaction in S2 is carried out at a temperature of 180-220℃ for 5-15 hours. The drying temperature in S3 is 40-80℃, and the time is 8-16 hours. Coal gasification residue is obtained by the following method: fine coal gasification slag is collected from the gasifier and the particle size of the fine coal gasification slag is ground to 2 μm by ball milling; the fine coal gasification slag after ball milling is prepared by a two-step acidification method, which involves mixing, stirring and filtering it with hydrofluoric acid solution in a container; the solid obtained by filtration is washed with water until neutral and then dried; the dried solid is mixed with hydrochloric acid solution in a container, stirred and filtered, and the solid obtained by filtration is washed with water until neutral and then dried to obtain coal gasification residue.

2. The preparation method of the CoFe2O4 / coal gasification residue composite material according to claim 1, characterized in that, The cobalt source is one of cobalt chloride and its hydrate, cobalt sulfate and its hydrate, cobalt nitrate and its hydrate, cobalt acetate and its hydrate, and cobalt oxalate and its hydrate.

3. The preparation method of the CoFe2O4 / coal gasification residue composite material according to claim 1, characterized in that, The iron source is one of ferric chloride and its hydrate, ferric sulfate and its hydrate, ferric nitrate and its hydrate, ferric acetate and its hydrate, and ferric oxalate and its hydrate.

4. The CoFe2O4 / coal gasification residue composite material prepared by the method according to any one of claims 1-3.

5. The application of the CoFe2O4 / coal gasification residue composite material as described in claim 4 in microwave absorbing materials.

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