Gasification fine ash residual carbon supported ZnFe2O4 nanospheres composite material and its preparation method

Abstract

The invention discloses a composite material of ZnFe2O4 nano microspheres loaded on residual carbon of coal gasification fine ash and a preparation method thereof. In the composite material, the ZnFe2O4 nano microspheres are disorderly adhered to the surface of the residual carbon of coal gasification fine ash, and one end of the flaky structure of part of the residual carbon of coal gasification fine ash is inserted into the ZnFe2O4 nano microspheres. The preparation method of the composite material comprises the following steps: S1: Preparation of residual carbon of coal gasification fine ash; S2: Adding the residual carbon of coal gasification fine ash in S1 into ethylene glycol and carrying out ultrasonic treatment for dispersion; S3: Adding zinc salt and iron salt into the mixed solution in S2, stirring and mixing evenly, then continuing to add polyethylene glycol 4000 and anhydrous sodium acetate, and stirring and mixing evenly; S4: Placing the mixed solution in S3 into a reaction kettle for reaction, and after the reaction, washing and drying to obtain an ultra-thin wave-absorbing material. The wave-absorbing material prepared by the invention has excellent electromagnetic wave absorption performance, and realizes the resource recycling of solid waste in coal gasification technology.

Description

Technical Field

[0001] The present invention relates to the technical field of microwave absorption materials, and particularly to a composite material of ZnFe2O4 nanospheres loaded on residual carbon of fine ash from coal gasification and a preparation method thereof. Background Art

[0002] With the rapid development of electronic information industry equipment such as mobile cellular networks, high-speed processors, broadband radars, and satellite communications, the resulting electromagnetic pollution and electromagnetic interference pose potential risks to human health, the operation of electronic devices, and information security. To solve electromagnetic pollution and interference, the development of microwave absorption materials with low density, thin thickness, wide frequency band, and strong absorption has gradually become a research hotspot.

[0003] The progress of modern coal gasification technology has recently become a key part of efficient utilization and clean coal technology. However, a large amount of slag is generated during the coal gasification process. The problem of the discharge of coal gasification slag is becoming increasingly serious. Coal gasification slag can be divided into fine slag (FS) and coarse slag. Coarse slag is generally used for building materials, while FS is very limited in terms of resource reuse due to its rich carbon content (20%-60%). On the one hand, the stacking or landfill of FS will occupy a large amount of land and cause metal pollution to the soil and water bodies. On the other hand, due to the rich residual carbon and specific surface area of FS, it can have high value. The high temperature and reducing atmosphere during the coal gasification process may lead to the graphitization of residual carbon (RC), so residual carbon (RC) can be used as a potential microwave absorption carbon material.

[0004] Pure carbon materials are not suitable as absorption materials because of their poor impedance matching characteristics. Therefore, researchers combine carbon and ferrite materials to meet the conditions of impedance and attenuation loss and enhance the microwave absorption performance. The main purpose of the present invention is to prepare a new composite material using residual carbon (RC) as a raw material. Summary of the Invention

[0005] Based on the technical problems existing in the background art, the present invention proposes a composite material of ZnFe2O4 nanospheres loaded on residual carbon of fine ash from coal gasification and a preparation method thereof. This microwave absorption material has excellent EMWA performance and realizes the resource reuse of solid waste in coal gasification technology.

[0006] In the composite material of ZnFe2O4 nanospheres loaded on residual carbon of fine ash from coal gasification proposed by the present invention, the ZnFe2O4 nanospheres are disorderly adhered to the surface of the residual carbon of fine ash from coal gasification, and one end of a part of the flaky structure of the residual carbon of fine ash from coal gasification is inserted into the ZnFe2O4 nanospheres.

[0007] The preparation method of the above-mentioned composite material of ZnFe2O4 nanospheres loaded on residual carbon of fine ash from coal gasification proposed by the present invention comprises the following method steps:

[0008] S1: Preparation of fine ash residual carbon from coal gasification;

[0009] S2: Add the fine ash residual carbon from coal gasification in S1 into ethylene glycol and perform ultrasonic treatment for dispersion;

[0010] S3: Add zinc salt and iron salt into the mixed solution in S2, stir and mix evenly, then continue to add polyethylene glycol 4000 and anhydrous sodium acetate, and stir and mix evenly;

[0011] S4: Place the mixed solution in S3 into a reaction kettle for reaction, and after the reaction, wash and dry to obtain an ultrathin microwave absorbing material.

[0012] Preferably, the fine ash residual carbon from coal gasification in S1 is prepared by a two-step acid leaching method.

[0013] Preferably, the mass molar ratio of the fine ash residual carbon from coal gasification, zinc salt, iron salt, polyethylene glycol 4000 and anhydrous sodium acetate is 1g: 2-6 mmol: 4-12 mmol: 1-3g: 4-8g.

[0014] Preferably, the power of the ultrasonic treatment in S2 is 400-800W, and the ultrasonic treatment time is 20-40min.

[0015] Preferably, the zinc salt in S2 is one or more of zinc chloride and its hydrates, zinc nitrate and its hydrates, zinc sulfate and its hydrates.

[0016] Preferably, the iron salt in S2 is one or more of iron chloride and its hydrates, iron nitrate and its hydrates, iron sulfate and its hydrates.

[0017] Preferably, the reaction temperature in S4 is 190-210 °C and the reaction time is 8-12h.

[0018] Preferably, in S4, the product is washed with deionized water and anhydrous ethanol respectively, and the washed product is dried at 50-70 °C for 10-14h.

[0019] Application of the above-mentioned fine ash residual carbon from coal gasification supported ZnFe2O4 nano-microsphere composite material in the microwave absorbing material proposed by the present invention.

[0020] Advantageous technical effects of the present invention:

[0021] The ZnFe2O4 / residual carbon (ZFO / RC) nano-composite material of the present invention is prepared by a one-step hydrothermal synthesis method with ZnFe2O4 microspheres modifying residual carbon, and the preparation method is simple. The ZFO / RC composite material has excellent EMWA performance, and the minimum reflection loss (RL) at 13.04 GHz min) was -46.33 dB, and the maximum effective absorption bandwidth (EAB, RL ≤ -10 dB) reached 2.96 GHz (11.76 - 14.72 GHz) at a thickness of 1.48 mm. CST simulations show that the ZFO / RC composite has excellent microwave absorption ability in the actual field of radar stealth. Therefore, this composite material is a wave-absorbing material with ultra-thin EMWA ability and application prospects, and can be used to promote the resource recycling of solid waste in coal gasification technology. Description of the Drawings

[0022] Figure 1 In (a) are the XRD patterns of RC and ZFO / RC, (b) are the FT-IR spectra of RC and ZFO / RC, and (c - d) are the hysteresis loops of the ZFO / RC composite;

[0023] Figure 2 In (a - c), (d - f), (g - i) are the SEM images of ZFO / RC - 1, ZFO / RC - 2, ZFO / RC - 3 respectively; (j) is the EDX mapping of ZFO / RC - 3;

[0024] Figure 3 In (a - c), (d - f), (g - i) are the TEM and HRTEM images of ZFO / RC - 1, ZFO / RC - 2, ZFO / RC - 3 respectively; (j) is the elemental mapping of ZFO / RC - 3;

[0025] Figure 4 is the XPS spectrum of ZFO / RC - 3; (a) total spectrum, (b) C 1s, (c) O 1s, (d) Fe 2p, (e) Zn 2p.

[0026] Figure 5 In (a - b), (c - d), (e - f) are the reflection loss curves and 3D diagrams of the composites of ZFO / RC - 1, ZFO / RC - 2, ZFO / RC - 3 respectively;

[0027] Figure 6 are the electromagnetic parameters of the composite at 6.0 - 18.0 GHz; (a) ε′, (b) ε″, (c) μ′, (d) μ″, (e) tanδ ε , (f) tanδ μ ;

[0028] Figure 7 In (a - c) are the Cole - Cole curves of ZFO / RC - 1, ZFO / RC - 2, ZFO / RC - 3 respectively; (d - f) are the C0, α, |Zin / Z0| curves of the composite;

[0029] Figure 8CTS simulation diagrams of the samples; (a) PEC model, (b) PEC model coated with ZFO / RC-3, (c) RCS curve diagrams of PEC and PEC coated with ZFO / RC-3. Detailed implementation manners

[0030] In the present invention, the crystal structure was tested by an X-ray diffractometer (XRD, LabX XRD-6000, Shimadzu, Japan) within a scattering range (2θ) of 15° - 80°. The composite materials were tested by using Fourier transform infrared spectroscopy (FT-IR) Nicoleti S5 (Seymour, USA). They were tested at room temperature with a vibrating sample magnetometer (VSM, PPMS-9, from Quantum Design, USA) at ±3 T / MH. The surface morphology, microstructure and elemental distribution of the samples were observed by using a field emission scanning electron microscope (FEI Sirion 2000, FEI Company, Netherlands) and a high-resolution transmission electron microscope (JEOL-2010, JEOL Ltd., Japan). The X-ray photoelectron spectroscopy (XPS) instrument was Thermo Fisher Scientific Inc. ESCALAB MK, USA, which was used to analyze the surface chemical state of the ZFO / RC composite materials. The electromagnetic parameters of the ZFO / RC composite materials were obtained by a vector network analyzer (AV 3629D, CETC 41st institute, China) in the range of 2.0 - 18.0 GHz. Before the test, 40 wt% of the ZFO / RC hybrid material and 60 wt% of paraffin were uniformly mixed. The ZFO / RC-paraffin composite material was made into the shape of a cylindrical mold with an inner diameter of 3.04 mm and an outer diameter of 7.00 mm.

[0031] Example 1

[0032] The preparation method of the above-mentioned coal gasification fine ash residual carbon loaded ZnFe2O4 nano-microsphere composite material proposed by the present invention is as follows:

[0033] S1: The coal gasification fine ash residual carbon (RC) was obtained by a two-step acid leaching method. The specific method refers to Example 1 in CN114181663A;

[0034] S2: 0.6 g of the coal gasification fine ash residual carbon in S1 was added to 50 ml of ethylene glycol and ultrasonicated for 20 min at 400 W for dispersion;

[0035] S3: 1.5 mmol of ZnCl2 and 3 mmol of FeCl3·6H2O were added to the mixed solution in S2. After vigorously stirring for 15 min, 1.0 g of polyethylene glycol 4000 and 3.6 g of anhydrous sodium acetate were further added, and the mixture was stirred at 50 °C for 1 h;

[0036] S4: Place the mixed solution of S3 in a reaction kettle, react at 190 °C for 8 h, wash the reaction product with deionized water and absolute ethanol, and dry the washed product at 50 °C for 10 h to obtain an ultrathin microwave absorption material, denoted as ZFO / RC-1.

[0037] Example 2

[0038] The preparation method of the above-mentioned coal gasification fine ash residual carbon supported ZnFe2O4 nanospheres composite material proposed by the present invention is as follows:

[0039] S1: Prepare coal gasification fine ash residual carbon (RC) by a two-step acid leaching method, and the specific method refers to Example 1 in CN114181663A;

[0040] S2: Add 0.6 g of coal gasification fine ash residual carbon in S1 to 50 ml of ethylene glycol and ultrasonically disperse it for 30 min at 600 W;

[0041] S3: Add 2.5 mmol of ZnCl2 and 5 mmol of FeCl3·6H2O to the mixed solution of S2, stir vigorously for 15 min, then continue to add 1.0 g of polyethylene glycol 4000 and 3.6 g of anhydrous sodium acetate, and stir at 50 °C for 1 h;

[0042] S4: Place the mixed solution of S3 in a reaction kettle, react at 200 °C for 10 h, wash the reaction product with deionized water and absolute ethanol, and dry the washed product at 60 °C for 12 h to obtain an ultrathin microwave absorption material, denoted as ZFO / RC-2.

[0043] Example 3

[0044] The preparation method of the above-mentioned coal gasification fine ash residual carbon supported ZnFe2O4 nanospheres composite material proposed by the present invention is as follows:

[0045] S1: Prepare coal gasification fine ash residual carbon (RC) by a two-step acid leaching method, and the specific method refers to Example 1 in CN114181663A;

[0046] S2: Add 0.6 g of coal gasification fine ash residual carbon in S1 to 50 ml of ethylene glycol and ultrasonically disperse it for 40 min at 800 W;

[0047] S3: Add 3.5 mmol of ZnCl2 and 7 mmol of FeCl3·6H2O to the mixed solution of S2, stir vigorously for 15 min, then continue to add 1.0 g of polyethylene glycol 4000 and 3.6 g of anhydrous sodium acetate, and stir at 50 °C for 1 h;

[0048] S4: Place the mixed solution of S3 in a reaction kettle and react at 210 °C for 12 h. After the reaction, the product is washed with deionized water and absolute ethanol, and the washed product is dried at 70 °C for 14 h to obtain an ultrathin microwave absorption material, denoted as ZFO / RC-3.

[0049] To study the crystal structures of RC and ZFO / RC composites, Figure 1 (a) shows the XRD pattern. Eight distinct characteristic peaks at 2θ = 18.1°, 29.9°, 35.2°, 42.8°, 53.1°, 56.6°, 62.2°, and 73.5° are consistent with the (111), (220), (311), (400), (422), (511), (440), and (533) crystal planes of ZnFe2O4, respectively, indicating the successful preparation of zinc ferrite in the ZFO / RC composite. In addition, two diffraction peaks at 2θ = 25.8° and 43.5° belong to the (002) and (100) crystal planes of graphite, indicating an increase in the degree of graphitization of carbon after gasification. Specifically, the intensity of the (002) plane decreases, and the (100) plane disappears with the increase in the content of ZnFe2O4 microspheres. As Figure 1 (b) shows, the functional groups of RC and ZFO / RC composites were detected by FT-IR spectroscopy. The characteristic peaks at 570 and 440 cm -1 of the three ZFO / RC composites can be attributed to the stretching vibrations of Fe-O and Zn-O bands, indicating the successful preparation of ZnFe2O4 nanospheres. The characteristic peaks at 1620 cm -1 and 1140 cm -1 correspond to the stretching vibrations of C=C in the benzene ring and C-O of the alkoxy group in RC. In addition, the absorption peak at 2930 cm -1 may be attributed to the vibration of C-H, while 3440 cm -1 corresponds to the -OH bond.

[0050] Figure 1 (c-d) The magnetic properties of the ZFO / RC composites were detected by VSM. As Figure 1 (c) shows, the saturation magnetization (Ms) values of ZFO / RC-1, ZFO / RC-2, and ZFO / RC-3 are 22.73, 28.45, and 39.34 emu / g, respectively. Ms is related to the content of ZnFe2O4 nanospheres. Therefore, the addition of ZFO results in a higher saturation magnetization value. In addition, as Figure 1 (d) shows, the coercivity values (Hc) are approximately 5.4, 26.5, and 25.1 Oe. The coercivity value is affected by various factors, such as particle surface effect, steric hindrance effect, coupling effect, etc. The hysteresis loop indicates that the ZFO / RC composites have magnetic loss.

[0051] The microstructure, surface morphology, and elemental distribution of the ZFO / RC composite were investigated by SEM and TEM ( Figure 2 and Figure 3 ). Figure 2 (a-i) shows that ZFO adheres to the surface of RC in a disordered manner, with a regular microsphere structure. As the mass fractions of iron and zinc elements increase in the experiment, the ZnFe2O4 nano-microspheres gradually increase in the synthesized ZFO / RC composite. In addition, Figure 2 (c, f, i) shows that the diameters of the ZnFe2O4 nano-microspheres are approximately 200, 300, and 400 nm, respectively. From Figure 2 (e, h) and Figure 3 (e), it can be seen that some RC flake structures are inserted into the ZFO nano-microspheres, forming a special heterogeneous interface, which enhances the interfacial polarization and thus is beneficial to enhancing the microwave absorption performance. As Figure 3 (c, f, i) shows, the HRTEM images indicate that the lattice distance of 0.249 nm is consistent with the (311) crystal plane of ZnFe2O4. In addition, the residual carbon with a crystal plane distance of 0.34 nm is consistent with the (002) crystal plane of graphite carbon, which is consistent with the results obtained by X-ray diffraction. Figure 2 (j) and Figure 3 (j) show the elemental distributions of C, O, Fe, and Zn in the ZFO / RC-3 hybrid material. In summary, the unique multi-structured ZFO / RC composite was successfully prepared.

[0052] The ZFO / RC-3 composite was subjected to XPS testing. As Figure 4 (a) shows, ZFO / RC-3 has carbon, oxygen, iron, and zinc elements, which is consistent with the EDX spectrum. In Figure 4 (b), the C1s spectrum of ZFO / RC-3 is divided into five peaks at 284.75, 285.60, 285.65, 288.85, and 291.00 eV, which correspond to C═C, C-O, C-OH, O═C-OH, and π-π, respectively. In particular, the π-π vibration effect in the aromatic functional group may lead to the appearance of a special peak at 291.00 eV. From Figure 4 (c), the O 1s spectrum is divided into three prominent peaks at 530.59, 532.10, and 533.32 eV, which confirm the existence of lattice oxygen, surface adsorbed oxygen, and oxygen-containing groups, respectively. The spectrum of Fe 2p is shown in Figure 4 (d). The characteristic peaks of Fe 2p3 / 2 at 711.39 and 713.62 eV indicate that Fe 3+ occupies the tetrahedral and octahedral sites in ZnFe2O4, respectively. In addition, the peak of Fe 2p1 / 2 is at 725.52 eV, while the satellite peaks at 719.52 and 733.18 eV further describe Fe3+ The situation. As Figure 4 (e) shows, the spectrum of Zn 2p presents two strong characteristic peaks, belonging to Zn 2p1 / 2 and Zn 2p3 / 2, located at 1045.14 and 1022.04 eV respectively.

[0053] To evaluate the EMWA performance of the materials, the RL values of the ZFO / RC composites with different ZnFe2O4 nanosphere contents can be calculated. The reflection loss deduced from the dielectric constant and magnetic permeability is calculated using the following formulas (1) and (2):

[0054]

[0055]

[0056] where Z0 is the impedance of free space; c, f, and d represent the speed of light, frequency, and the thickness of the ZFO / RC composite respectively. ε γ (ε γ = ε′ - jε″) represents the complex dielectric constant, and μ γ (μ γ = μ′ - jμ″) represents the complex magnetic permeability.

[0057] Figure 5 For the typical reflection loss curve and 3D plot of RL of the ZFO / RC composite to explore the influence of the ZnFe2O4 nanoparticle content on the electromagnetic attenuation ability of the prepared composite. As Figure 5 (a, c) shows, the minimum reflection loss (RL min ) values of ZFO / RC-1 and ZFO / RC-2 are only -13.36 dB (1.0 mm) and -17.33 dB (1.5 mm). It is worth noting that the RL min value of the ZFO / RC-3 composite reaches an outstanding absorption intensity of -46.33 dB (1.48 mm) at 13.04 GHz, and the maximum EAB is 2.96 GHz with an ultra-thin matching thickness of 1.48 mm. The EMWA performance of the ZFO / RC-3 composite is better than that of ZFO / RC-1 and ZFO / RC-2. Therefore, the content of ZnFe2O4 nanospheres has a great influence on the EMWA ability of this ultra-thin carbon residue-based ZFO / RC wave-absorbing material.

[0058] As the ZFO content increases, ε′ and ε″ gradually decrease, as Figure 6(as shown in (a, b)). The ε′ is distributed between 14.24 - 25.28, showing a downward trend throughout the measurement range, exhibiting a frequency dispersion behavior that is beneficial for microwave energy attenuation. ZFO / RC-3 has a suitable ε′ value, enabling microwaves to penetrate into the absorber under favorable conditions. The interfacial polarization generated at the ZFO-RC interface and the numerous defects on the surface of RC may lead to differences in the complex permittivity of the ZFO / RC composite material. The μ′ and μ″ of the permeability are in the ranges of 0.90 - 1.09 and -0.05 - 0.19 respectively, as Figure 6 (c, d), indicating the existence of multiple resonances. With the increase in the addition amount of ZnFe2O4, the magnetic properties of the ZFO / RC composite material are improved and various magnetic loss mechanisms are generated. To further analyze the loss mechanism, tanδ is calculated based on the obtained electromagnetic parameters ε = ε″ / ε′ and tanδ μ = μ″ / μ′. It is worth noting that in Figure 6 (e, f), the ZFO / RC composite material exhibits a higher tanδ ε value than the tanδ μ value, indicating that dielectric loss is the main mechanism for the attenuation of electromagnetic wave energy.

[0059] The relaxation process contributes to dielectric loss and can be described by the Cole-Cole semicircle in the microwave frequency range. The correlation between ε' and ε” can be expressed as follows:

[0060]

[0061] where ε s represents the static dielectric constant, ε ∞ represents the optical frequency dielectric constant, f is the frequency of the microwave, and τ is the time of polarization relaxation. Therefore, ε' and ε” can be expressed as follows:

[0062]

[0063]

[0064] According to formulas (4) and (5), the relationship between ε' and ε” can be deduced as follows:

[0065]

[0066] As Figure 7As shown in (a-c), the Cole-Cole curves of the ZFO / RC hybrid materials. The Debye relaxation process is beneficial to improving the EMWA ability of the absorber. The interfacial polarization of ZFO-RC may lead to the dielectric loss of the ZFO / RC nanocomposites. According to previous studies, natural resonance and eddy current loss are the main reasons for the magnetic loss in magnetoelectric cooperative MAMs. Equations (7) and (8) show that the eddy current loss is related to the diameter d and the conductivity σ. If C0 is a constant, then the magnetic loss is only generated by the eddy current loss.

[0067]

[0068] C0 = μ″(μ′) -2 f -1 (8)

[0069] In Figure 7 (d), the value of C0 shows a downward trend, indicating that natural resonance is the reason for the magnetic loss of the ZFO / RC composite material, rather than eddy current loss. To evaluate the microwave dissipation ability, the attenuation coefficient (α) is defined as follows:

[0070]

[0071] Figure 7 (e) shows that in the range of 6.0 - 18.0 GHz, the α value of ZFO / RC-1 is higher than that of ZFO / RC-2 and ZFO / RC-3. However, the α value of ZFO / RC-3 shows the best EMWA ability. Therefore, the microwave absorption characteristics of ZFO / RC depend to a large extent on the content of ZnFe2O4. In addition, the absorbing material needs to have an ideal impedance match, which is crucial for electromagnetic waves to enter the interior of the absorber. Figure 7 (f) shows the |Z in / Z0|~f graph at 1.48 mm. The |Z in / Z0| value of ZFO / RC-3 is approximately 1. However, the values of ZFO / RC-1 and ZFO / RC-2 are less than 0.6 and 0.8 respectively, which means that the ZFO / RC-3 composite material has a better impedance match than ZFO / RC-1 and ZFO / RC-2. The ZFO / RC-3 composite material exhibits excellent EMWA ability, and due to the balance between the complex permittivity and permeability, its impedance matching is better than that of other composite materials.

[0072] The remarkable EMWA properties of the ZFO / RC hybrid materials are mainly due to the presence of these factors. First, the residual carbon can change the dielectric parameters, which is beneficial to achieving proper impedance matching of the obtained composite materials. Second, the presence of a large number of defects and various oxygen-containing functional groups can lead to dipole polarization and defect polarization on the surface of the RC, such as -OH, thereby further attenuating the incident microwave energy. Third, many ZnFe2O4 nanoparticles are modified on the surface of the RC, which can result in a heterogeneous interface between the ZnFe2O4 microspheres and the RC. Fourth, according to Cao's electron hopping theory, electromagnetic energy can be absorbed by electrons, and the electrons migrate and jump to the residual carbon lamellae, thus promoting the transfer of electromagnetic wave energy into heat energy. Fifth, the microwave energy can be dissipated through multiple reflections of the incident wave between the nearby RC sheets. Finally, the ferromagnetic ZnFe2O4 microspheres provide natural resonance and eddy current loss for the synthesized composite materials, which can further attenuate the incident wave. Table 1 shows the comparison of the EMWA properties of the ZnFe2O4 / RC composite materials with similar magnetic carbon-based composite materials, indicating that the ultrathin ZFO / RC exhibits excellent RL ability. All in all, the ZFO / RC nanocomposite materials show ultrathin EMWA properties.

[0073] Table 1 Comparison of the EMWA properties of the composite materials

[0074] Sample Thickness(mm) <![CDATA[RL min (dB)]]> EAB(RL≤-10dB) Refs. <![CDATA[ZnFe2O4 / polyaniline / graphene]]> 3.29 -58.00 3.91 [1] <![CDATA[ZnFe2O4@C]]> 2.00 -51.38 4.10 [2] <![CDATA[RGO / MWCNTs / ZnFe2O4]]> 1.00 -22.20 2.30 [3] <![CDATA[ZnFe2O4@ZnO@rGO]]> 2.00 -35.20 3.70 [4] <![CDATA[ZnFe2O4@PANI-rGO]]> 2.10 -49.99 4.32 [5 <![CDATA[ZnFe2O4@graphene@TiO2]]> 2.50 -55.60 3.80 [6] <![CDATA[yolk-shellZnFe2O4@C]]> 1.40 -37.10 3.80 [7] <![CDATA[ZnFe2O4@C / MWCNTs]]> 2.50 -40.65 0.97 [8] <![CDATA[ZnFe2O4 / RC]]> 1.48 -46.33 2.96 This application

[0075] Where:

[0076] [1] Qiao, Y., Xiao, J.P., Jia, Q., et al. Preparation and microwave absorption properties of ZnFe2O4 / polyaniline / graphene oxide composite[J]. Results Phys, 2019, 13.

[0077] [2] Huang, Y., Xing, W.J., Fan, J.L., et al. Preparation and microwave absorption properties of the hollow ZnFe2O4@C composites with core-shell structure[J]. J Magn Magn Mater, 2020, 502.

[0078] [3]Shu, R.W., Zhang, G.Y., Zhang, J.B., et al. Fabrication of reduced graphene oxide / multi-walled carbon nanotubes / zinc ferrite hybrid composites as high-performance microwave absorbers[J]. J Alloy Compd, 2018, 736: 1 - 11.

[0079] [4]Li, F., Zhuang, L., Zhan, W.W., et al. Desirable microwave absorption performance of ZnFe2O4@ZnO@rGO nanocomposites based on controllable permittivity and permeability[J]. Ceram Int, 2020, 46(13): 21744 - 51.

[0080] [5]Zhao, X.X., Huang, Y., Yan, J., et al. Excellent electromagnetic wave absorption properties of the ternary composite ZnFe2O4@PANI - rGO optimized by introducing covalent bonds[J]. Composites Science and Technology, 2021, 210.

[0081] [6]Wang, Y., Zhu, H.Y., Chen, Y.B., et al. Design of hollow ZnFe2O4 microspheres@graphene decorated with TiO2 nanosheets as a high - performance low frequency absorber[J]. Mater Chem Phys, 2017, 202: 184 - 9.

[0082] [7]Li, H.Q., Hou, Y.H., Li, L.C. Tunable design of yolk-shell ZnFe2O4@C composites for enhancing electromagnetic wave absorption[J]. Powder Technol, 2021, 378: 216-26.

[0083] [8]Tang, Y.T., Yin, P.F., Zhang, L.M., et al. Novel carbon encapsulated zinc ferrite / MWCNTs composite: preparation and low-frequency microwave absorption investigation[J]. Ceram Int, 2020, 46(18): 28250-61.

[0084] The RCS plays an important role in manufacturing stealth aircraft to avoid being detected by radar inspection systems. To evaluate the practical application of ZFO / RC in the far field, the CST Studio Suite 2020 software was used to obtain the RCS value. The preset model (180 mm × 180 mm) was established by PEC (0.5 mm) and ZFO / RC composite material (1.48 mm) at 13.00 GHz. The RCS value can be calculated as follows.

[0085] σ (dBm 2 ) = 10 log((4πS / λ 2 ) |E s / E i |) 2 (10)

[0086] where σ represents the RCS value; λ represents the wavelength of the electromagnetic wave; S represents the area of the plate; E s and E i correspond to the electric field strengths of the scattered wave and the incident wave, respectively. Figure 8 Shows the RCS value curves and three-dimensional intensity images of the PEC and the PEC sample coated with ZFO / RC-3 from -90° to 90°. The maximum RCS value shown by the PEC coated with ZFO / RC-3 is around -15 dBm 2 , which is significantly lower than that of the pure PEC model, thus indicating that ZFO / RC-3 can reduce the radar scattering intensity of the PEC sheet and has excellent microwave attenuation ability at all incident wave angles. The ZFO / RC composite material can be used as a promising wave-absorbing material for practical applications.

[0087] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. Preparation method of zinc ferrite nanospheres composite material loaded with fine ash residual carbon of coal gasification, characterized in that The ZnFe₂O₄ nano-microspheres adhere to the surface of the fine ash residual carbon of coal gasification disorderly, and one end of the flaky structure of some fine ash residual carbon of coal gasification is inserted into the ZnFe₂O₄ nano-microspheres; The preparation method of the composite material is as follows: S1: Preparation of fine ash residual carbon of coal gasification; S2: Add the fine ash residual carbon of coal gasification in S1 into ethylene glycol and disperse it by ultrasonic treatment; S3: Add zinc salt and iron salt into the mixed solution in S2, stir and mix evenly, then continue to add polyethylene glycol 4000 and anhydrous sodium acetate, and stir and mix evenly; S4: Place the mixed solution in S3 in a reaction kettle for reaction, and after the reaction, wash and dry to obtain the ultra-thin microwave absorbing material.

2. The preparation method of the gasification fine ash residual carbon supported ZnFe2O4 nano-microsphere composite material according to claim 1, characterized in that, The fine ash residual carbon of coal gasification in S1 is prepared by a two-step acid leaching method.

3. The preparation method of the coal gasification fine ash residual carbon supported ZnFe2O4 nano microsphere composite material according to claim 1, characterized in that, The mass molar ratio of the fine ash residual carbon of coal gasification, zinc salt, iron salt, polyethylene glycol 4000 and anhydrous sodium acetate is 1g: 2-6 mmol: 4-12 mmol: 1-3g: 4-8g.

4. The preparation method of the gasification fine ash residual carbon supported ZnFe2O4 nano-microsphere composite material according to claim 1, characterized in that, The power of the ultrasonic treatment in S2 is 400-800W, and the ultrasonic treatment time is 20-40min.

5. The preparation method of the coal gasification fine ash residual carbon supported ZnFe2O4 nanosphere composite material according to claim 1, characterized in that, The zinc salt in S2 is one or several of zinc chloride and its hydrates, zinc nitrate and its hydrates, zinc sulfate and its hydrates.

6. The preparation method of the coal gasification fine ash residual carbon supported ZnFe2O4 nano-microsphere composite material according to claim 1, characterized in that, The iron salt in S2 is one or several of ferric chloride and its hydrates, ferric nitrate and its hydrates, ferric sulfate and its hydrates.

7. The preparation method of the gasification fine ash residual carbon supported ZnFe2O4 nano-microsphere composite material according to claim 1, characterized in that, The reaction temperature in S4 is 190-210 °C, and the reaction time is 8-12h.

8. The preparation method of the gasification fine ash residual carbon supported ZnFe2O4 nanospherical composite material according to claim 1, characterized in that, In S4, the product is washed with deionized water and anhydrous ethanol respectively, and the washed product is dried at 50-70 °C for 10-14h.

9. A composite material of zinc ferrite nanospheres loaded on fine ash residual carbon of coal gasification, characterized in that, Prepared by the preparation method according to any one of claims 1-8.

10. Application of the composite material of fine ash residual carbon of coal gasification loaded with ZnFe₂O₄ nano-microspheres in a microwave absorbing material as claimed in claim 9.

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