A carbon-based electromagnetic shielding bulk material and its preparation and application

Abstract

This invention relates to a carbon-based electromagnetic shielding bulk material, its preparation, and its application, belonging to the technical field of electromagnetic shielding materials. This electromagnetic shielding material is prepared from porous carbon composite powder using discharge plasma sintering technology. The prepared bulk material possesses excellent mechanical, electrical, and thermal conductivity properties, and can achieve good electromagnetic shielding effectiveness across multiple wavelengths, showing broad application prospects in electromagnetic protection fields such as aerospace and civil engineering.

Description

Technical Field

[0001] This invention belongs to the field of electromagnetic shielding materials, and specifically relates to a carbon-based electromagnetic shielding bulk material and its preparation and application. Background Technology

[0002] While electromagnetic technology has brought great convenience to people's lives, it has also generated a large amount of electromagnetic radiation, causing electromagnetic pollution, affecting the normal operation of electronic equipment, harming human health, and even causing electromagnetic information leakage in severe cases. Therefore, developing highly efficient electromagnetic shielding materials is one of the most important technical means to solve the problems of electromagnetic radiation and electromagnetic pollution. On the one hand, with the rapid development of aerospace weaponry, wireless base stations, and 5G communication technology, ideal electromagnetic shielding materials should meet the characteristics of being lightweight, having strong absorption, wide bandwidth, and high thermal stability. On the other hand, for applications such as protective shells for electronic components, shielding bodies for building engineering, and protective covers for aerospace missile antennas, electromagnetic shielding structural components are also required to have excellent mechanical properties to prevent environmental forces from affecting the safety, applicability, and durability of the protective body.

[0003] Nanomaterials such as carbon nanotubes, carbon fibers, and graphene have been widely used in electromagnetic shielding due to their ultra-high conductivity, excellent mechanical properties, strong corrosion resistance, low density, ease of processing, and environmental friendliness. However, the high conductivity of carbon materials often leads to significant electromagnetic wave reflection, causing secondary pollution. Therefore, researchers typically introduce magnetic components to enhance impedance matching characteristics and improve electromagnetic wave absorption within the material. Metal-organic frameworks (MOFs) are porous materials formed by the self-assembly of organic ligands and metal ions or clusters through coordination bonds. After heat treatment, metal ions are reduced to elemental metals and uniformly distributed in the organic ligand-derived porous carbon matrix. Based on the synergistic effect of dielectric and magnetic losses, MOF-derived metal / carbon materials exhibit good electromagnetic wave absorption capabilities. However, the disordered porous carbon structure results in poor electron transport and low conductivity. Furthermore, the carbon materials mainly exist in the form of amorphous carbon with generally low graphitization, thus inhibiting their electromagnetic shielding effectiveness. For example, Zhu et al. constructed a needle-like Co3O4 / C array structure through simple high-temperature pyrolysis of ZIF-67, but the electromagnetic shielding effectiveness of this material was only 33 dB (Reference: Novel MOF-derived 3D hierarchical needle-like array architecture with excellent EMI shielding, thermal insulation and supercapacitor performance. Nanoscale. 2022.). Furthermore, in special applications such as aerospace and military, in addition to requiring high shielding effectiveness of electromagnetic shielding composite materials, there is also a demand for developing high-performance components with integrated structural functions, ultra-strong load-bearing capacity, and ultra-lightweight properties. Therefore, there is an urgent need to develop structural materials with both excellent mechanical and electromagnetic shielding effectiveness to meet the critical equipment requirements in related fields. Summary of the Invention

[0004] To address the problems of existing technologies, the technical problem to be solved by this invention is to select a metal / carbon material, wherein the carbon component provides dielectric loss and the magnetic metal provides magnetic loss, and to prepare a carbon-based electromagnetic shielding bulk material with both dielectric and magnetic losses.

[0005] The present invention discloses a carbon-based bulk material, wherein the carbon-based bulk material is obtained by spark plasma sintering using a precursor containing metal / carbon material.

[0006] The metal / carbon material is a metal / carbon derived from a crystalline porous material, wherein the crystalline porous material is a cobalt-based metal-organic framework (Co-MOF) material.

[0007] The metal / carbon material is one of metal / porous carbon or metal / carbon nanotubes (CNTs) / porous carbon.

[0008] A method for preparing a carbon-based bulk material according to the present invention includes:

[0009] (1) The metal-organic framework material was heat-treated under an inert atmosphere to obtain a metal / porous carbon material.

[0010] Alternatively, a mixture of metal-organic framework materials and melamine can be heat-treated in a mixed atmosphere to obtain metal / carbon nanotube (CNT) / porous carbon materials.

[0011] (2) Metal / porous carbon material or metal / carbon nanotube CNT / porous carbon material is subjected to spark plasma sintering treatment, and then polished to obtain carbon-based bulk material.

[0012] The preferred embodiment of the above preparation method is as follows:

[0013] In step (1), the metal-organic framework material is a cobalt-based metal-organic framework (Co-MOF) material.

[0014] The preparation method of the cobalt-based metal-organic framework (Co-MOF) material includes: dissolving 2-methylimidazole in a methanol solution containing cobalt nitrate, synthesizing crystals by solution method, centrifuging, washing, and drying; wherein the solution method reaction temperature is 20-25℃, and the reaction time is 18-24h; the centrifugation process conditions are: rotation speed 10000r / min, time 5-10min; the washing process conditions are: washing with methanol solution 3-5 times sequentially; the drying process conditions are: drying at 50-80℃ for 6-10h.

[0015] In step (1), the metal-organic framework material is subjected to heat treatment, wherein the heat treatment is performed at a heating rate of 2-5℃ / min, a calcination temperature of 600-800℃, and a holding time of 1-3h.

[0016] In step (1), the mixture of metal-organic framework material and melamine is subjected to heat treatment, wherein the heat treatment is performed at a heating rate of 2-5℃ / min, a calcination temperature of 600-900℃, and a holding time of 0.5-1.5h.

[0017] In step (1), the mixed atmosphere is methane and argon, wherein the flow rate ratio of methane to argon is 1:(0.5-2); the mixture of metal-organic framework material and melamine is wherein the mass ratio of metal-organic framework material to melamine is 1:(0.05-0.10).

[0018] The process parameters for the discharge plasma sintering treatment in step (2) are: sintering temperature 1600-2200℃, sintering pressure 60-100MPa, heating rate 90-110℃ / min, and holding time 4-10min.

[0019] Before the grinding and polishing process in step (2), the material is removed from the mold and the carbon paper is removed.

[0020] The present invention relates to the application of the carbon-based bulk material in shielding materials.

[0021] The present invention relates to the application of the carbon-based bulk material in the fields of aerospace, military defense, construction engineering, or electromagnetic protection.

[0022] Furthermore, carbon-based bulk shielding materials can be used as electromagnetic shielding devices in fields such as electromagnetic protection and aerospace.

[0023] The method of this invention can efficiently convert porous carbon into graphite bulk, which not only exhibits excellent electromagnetic shielding performance in multiple bands, but also has excellent electrical, thermal and mechanical properties. It can be used as a lightweight and efficient electromagnetic shielding structural component in aerospace, military defense or electromagnetic protection fields.

[0024] The electromagnetic shielding material of this invention is prepared using porous carbon composite powder as raw material through discharge plasma sintering technology. The resulting bulk material exhibits excellent mechanical, electrical, and thermal conductivity properties, and can achieve good electromagnetic shielding effectiveness across multiple wavelengths, showing broad application prospects in electromagnetic protection fields such as aerospace and civil engineering.

[0025] Advantages

[0026] (1) This invention combines chemical synthesis with industrial sintering technology, using spark plasma sintering to efficiently convert porous carbon into graphite. The resulting carbon-based bulk material has low density, high compactness, excellent mechanical properties, high electrical conductivity, and good thermal stability. Simultaneously, the graphitization degree of the obtained bulk material reaches up to 98%. Compared to traditional graphite preparation processes, this invention eliminates the need for external binders and repeated impregnation and calcination treatments, resulting in a shorter preparation cycle and a simpler process.

[0027] (2) The carbon-based shielding block prepared by this invention exhibits excellent electromagnetic shielding performance in the X, Ku, and K bands. T The shielding strengths reached 68.26 dB, 53.52 dB, and 32.45 dB respectively, with absorption being the dominant shielding characteristic across all three bands. Furthermore, the carbon-based bulk material exhibits excellent mechanical properties, with a flexural strength of 97 MPa and a compressive strength as high as 208 MPa, and an in-plane thermal conductivity of 248 W / m². -1 K -1 Its electrical conductivity is as high as 7311 S / cm;

[0028] (3) The carbon-based electromagnetic shielding bulk material prepared by this invention has a unique microstructure. After spark plasma sintering, the amorphous carbon forms a continuous and regular graphite conductive network, which improves the shielding effectiveness and also promotes the conductivity loss of electromagnetic waves. The strong magnetic loss caused by the synergistic magnetic metal enhances the overall impedance matching characteristics of the material, allowing electromagnetic waves to penetrate into the material. In addition, some defects in the carbon material lead to an asymmetrical distribution of charge, thus forming dipoles. At the same time, the abundant heterogeneous interfaces between C and Co exacerbate polarization relaxation loss. The coexistence of multiple loss mechanisms promotes the attenuation of electromagnetic waves inside the material, ultimately giving the prepared bulk material excellent electromagnetic shielding performance with absorption as the main component. Attached Figure Description

[0029] Figure 1 The XRD pattern of the Co-MOF obtained in Example 1;

[0030] Figure 2 These are the XRD patterns of C / Co and C / CoB obtained in Example 1;

[0031] Figure 3 This is a cross-sectional scanning electron microscope image of the bulk C / CoB prepared in Example 1;

[0032] Figure 4 This is a diagram showing the electromagnetic shielding effectiveness of the bulk C / CoB prepared in Example 1 in the X-band (8.2-12.4GHz);

[0033] Figure 5 This is a diagram showing the electromagnetic shielding effectiveness of the bulk C / CoB prepared in Example 1 in the Ku band (12.4-18GHz);

[0034] Figure 6 This is a diagram showing the electromagnetic shielding effectiveness of the bulk C / CoB prepared in Example 1 in the K-band (18-26.5GHz).

[0035] Figure 7 Here is a scanning electron microscope image of the C / CNT / Co powder obtained in Example 2;

[0036] Figure 8 This is a cross-sectional scanning electron microscope image of the bulk C / CNT / CoB prepared in Example 2;

[0037] Figure 9 This is a diagram showing the electromagnetic shielding effectiveness of the bulk C / CNT / CoB obtained in Example 2 in the K-band (18-26.5GHz).

[0038] Figure 10 This is a diagram showing the total electromagnetic shielding effectiveness of the bulk C / CoB prepared in Example 1 in the X, Ku, and K bands;

[0039] Figure 11The XRD patterns of the bulk C / CoB prepared in Comparative Example 1 and the bulk prepared in Example 1 are shown.

[0040] Figure 12 This is a cross-sectional scanning electron microscope image of the bulk C / ZnB prepared in Comparative Example 2. Detailed Implementation

[0041] The present invention will be further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Furthermore, it should be understood that after reading the teachings of this invention, those skilled in the art can make various alterations or modifications to the invention, and these equivalent forms also fall within the scope defined by the appended claims.

[0042] Example 1

[0043] (1) Weigh 8.148g of Co(NO3)3·6H2O and dissolve it in 350ml of methanol solution. Stir magnetically at 400r / min until completely dissolved, forming a light red solution. Then weigh 9.1952g of 2-methylimidazole and dissolve it in 350ml of methanol solution. Stir magnetically until dissolved. Pour the organic ligand solution into a solution containing metal ions and stir thoroughly at 22℃ for 24h to obtain a purple solution. Centrifuge to collect the product and wash it three times with methanol solution. Finally, dry it at 80℃ for 6h to obtain Co-MOF powder.

[0044] (2) Co-MOF powder was placed in a quartz crucible and pyrolyzed in a tube furnace under an argon atmosphere at a heating rate of 5℃ / min, a calcination temperature of 700℃, and a holding time of 3h to obtain Co / porous carbon powder (C / Co).

[0045] (3) Weigh 0.5g, 1.0g and 2.0g of C / Co powder and put them into high-pressure graphite molds with diameters of 10, 15 and 30mm in the order of carbon paper-sample-carbon paper. The sintering temperature is 1800℃, the sintering pressure is 80MPa, the heating rate is 100℃ / min, and the holding time is 10min. After the sintering is completed, let it cool naturally to room temperature, remove the mold, remove the carbon paper, and you will get the black block sample C / CoB.

[0046] The XRD pattern of the Co-MOF obtained in this embodiment is as follows: Figure 1 As shown, the XRD diffraction peaks of the Co-MOF prepared in the example are consistent with the XRD diffraction peaks of the simulated standard Co-MOF.

[0047] The XRD patterns of C / Co and C / CoB obtained in this embodiment are as follows: Figure 2 As shown, the test results indicate that the crystal phases mainly include Co and graphite phases.

[0048] The cross-sectional electron microscope image of the bulk C / CoB obtained in this embodiment is shown below. Figure 3 As shown in the figure, the test results indicate that the block has a smooth cross-section without obvious pores and is relatively dense overall. The density of the block was calculated to be 2.68 g / cm³ using the formula ρ = m / v. 3 The block was cut into small cubes with dimensions of 1mm x 1mm x 1mm. The compressive strength was measured at 208 MPa using a universal testing machine. The block was then cut into cuboids with dimensions of 12mm x 1mm x 1mm. The flexural strength was measured at 97 MPa using a three-point bending test. Both the flexural and compressive strength were tested three times and the average value was obtained. The electrical conductivity was measured to be 5541 S / cm (Z direction) and 7311 S / cm (XY direction) using the four-probe method. The thermal conductivity was measured to be 91 W / m² using a laser thermal conductivity meter and differential scanning calorimeter. -1 K -1 (Z direction) and 248Wm -1 K -1 (XY direction).

[0049] After demolding and polishing the bulk material prepared in this embodiment, it was cut into cuboid samples with length × width of 10.95mm × 4.5mm, 15.9mm × 8.03mm, and 22.9mm × 10.2mm, respectively, and unlimited thickness. The shielding performance of the samples in the ranges of 8.2-12.4GHz, 12.4-18GHz, and 18-26.5GHz was tested using a vector network analyzer (Keysight, N5234B). Figure 4 , 5 As shown in Figure 6, the total shielding effectiveness (SE) of the C / CoB block in the 8.2-12.4 GHz band is... T = 68.26dB, where SE A =51.35dB, SE R =16.91dB; SE in the 12.4-18GHz band T = 53.52dB, where SE A =35.47dB, SE R =18.05dB; SE in the 18-26.5GHz range T = 32.45dB, where SE A =17.61dB, SE R =14.84dB.

[0050] Example 2

[0051] The difference between this embodiment and Example 1 is that after synthesizing Co-MOF, 5 wt.% of melamine was weighed and ground to mix evenly with Co-MOF. The mixture was then placed in a quartz crucible and calcined at high temperature using a methane and argon mixture in a ratio of 1:0.5. The heating rate was 5 °C / min, the calcination temperature was 750 °C, and the holding time was 1 h, thus obtaining Co / carbon nanotube / porous carbon powder (C / CNT / Co).

[0052] Weigh 0.5g, 1.0g, and 2.0g of C / CNT / Co powder, and place them into high-pressure graphite molds with diameters of 10, 15, and 30mm in the order of carbon paper-sample-carbon paper. The sintering temperature is 1800℃, the sintering pressure is 80MPa, the heating rate is 100℃ / min, and the holding time is 10min. After sintering, allow the sample to cool naturally to room temperature, remove the mold, and remove the carbon paper to obtain the bulk sample C / CNT / CoB.

[0053] The scanning electron microscope image of the C / CNT / Co powder prepared in this embodiment is shown below. Figure 7 As shown, the test results indicate that the grown CNTs are bent and entangled, and uniformly distributed on the porous carbon surface.

[0054] The cross-sectional electron microscope image of the bulk C / CNT / CoB obtained in this embodiment is shown below. Figure 8 As shown, the test results indicate that the block cross-section is uneven and the overall structure is not dense. The density of the block, calculated using the formula ρ=m / v, is 2.26 g / cm³. 3 Lighter blocks are more widely used in military, aerospace and other fields. The block was cut into small cubes with a length × width × height of 1mm × 1mm × 1mm, and the compressive strength of the block was measured to be 92MPa through a compression test on a universal testing machine.

[0055] After demolding and polishing the bulk material prepared in this embodiment, it was cut into cuboid samples with a length × width of 10.95mm × 4.5mm and unlimited thickness. The shielding performance of the samples in the 18-26.5GHz range was tested using a vector network analyzer (Keysight, N5234B). Figure 9 As shown, the overall shielding effectiveness SE of the C / CNT / CoB block is... T = 26.24dB, where SE A =13.69dB, SE R =12.55dB.

[0056] Comparative Example 1

[0057] The difference between this comparative example and Example 1 is that after weighing C / Co powder, it was placed into a high-pressure graphite mold, and the sintering temperature was changed to 1400℃. Other sintering conditions and subsequent sample processing steps remained unchanged.

[0058] The XRD pattern of the bulk C / CoB prepared in this comparative example is as follows: Figure 11 As shown, the (002) diffraction peak of bulk C / CoB-1400 graphite sintered at 1400℃ is lower than that of bulk graphite prepared at other sintering temperatures, indicating poor graphite crystallinity. The bulk density was calculated to be 2.74 g / cm³ using ρ = m / v. 3 The block was cut into small cubes with dimensions of 1mm x 1mm x 1mm. A compression test using a universal testing machine revealed a compressive strength of 157MPa, lower than that of blocks prepared at 1800℃. Comparison demonstrates that blocks prepared below the sintering temperature of this invention do not achieve the desired effect.

[0059] Comparative Example 2

[0060] The difference between this comparative example and Example 1 is that Zn-MOF was chosen as the precursor. 16.99 g of zinc acetate was weighed and dissolved in 500 ml of N,N-dimethylformamide, and magnetically stirred at 400 rpm until completely dissolved. Then, 5.065 g of terephthalic acid and 8.5 ml of triethylamine were weighed and dissolved in 400 ml of N,N-dimethylformamide, and magnetically stirred until completely dissolved. The organic ligand solution was poured into a solution containing metal ions and stirred thoroughly at 22°C for 24 h to obtain a white solution. The product was collected by centrifugation and washed three times with methanol solution. Finally, it was dried at 60°C for 12 h to obtain Zn-MOF powder. The Zn-MOF powder was placed in a quartz crucible and pyrolyzed in a tube furnace under an argon atmosphere. The heat treatment and sintering conditions were the same as in Example 1, ultimately yielding a bulk sample C / ZnB. The cross-sectional electron micrograph of the bulk C / ZnB obtained in this comparative example is shown below. Figure 12 As shown, the test results indicate that, compared to bulk materials prepared using Co-MOF as a precursor, changing the metal type results in poorer bulk density and an uneven, bumpy cross-section. The bulk density was calculated to be 1.46 g / cm³ using the formula ρ = m / v. 3 The block was cut into small cubes with dimensions of 1mm x 1mm x 1mm. Compression tests using a universal testing machine revealed a compressive strength of only 26.24 MPa, significantly lower than that of the C / CoB block prepared using Co-MOF as a precursor. This comparison demonstrates that the type of metal in the metal-organic framework greatly influences the sample's density and mechanical properties; selecting other metals cannot achieve the desired results.

Claims

1. A method for preparing a carbon-based bulk material, comprising: (1) Under an inert atmosphere, the metal-organic framework material is heat-treated to obtain a metal / porous carbon material; Alternatively, a mixture of metal-organic framework material and melamine can be heat-treated under a mixed atmosphere to obtain metal / carbon nanotube (CNT) / porous carbon material; wherein the metal-organic framework material is a cobalt-based metal-organic framework (Co-MOF) material. (2) Metal / porous carbon material or metal / carbon nanotube CNT / porous carbon material is subjected to spark plasma sintering treatment, and then polished to obtain carbon-based bulk material; wherein the spark plasma sintering process parameters are: sintering temperature 1600-2200℃, sintering pressure 60-100 MPa, heating rate 90-110℃ / min, and holding time 4-10 min.

2. The preparation method according to claim 1, characterized in that, The preparation method of the cobalt-based metal-organic framework Co-MOF material in step (1) includes: dissolving 2-methylimidazole in a methanol solution containing cobalt nitrate, synthesizing crystals by solution method, centrifuging, washing, and drying.

3. The preparation method according to claim 1, characterized in that, In step (1), the metal-organic framework material is subjected to heat treatment, wherein the heat treatment is as follows: heating rate 2-5 ℃ / min, calcination temperature 600-800℃, and holding time 1-3 h; The mixture of the metal-organic framework material and melamine is subjected to heat treatment, wherein the heat treatment is carried out at a heating rate of 2-5 °C / min, a calcination temperature of 600-900 °C, and a holding time of 0.5-1.5 h.

4. The preparation method according to claim 1, characterized in that, In step (1), the mixed atmosphere is methane and argon, wherein the flow rate ratio of methane to argon is 1:(0.5-2); the mixture of metal-organic framework material and melamine is wherein the mass ratio of metal-organic framework material to melamine is 1:(0.05-0.10).

5. The preparation method according to claim 1, characterized in that, Before the grinding and polishing process in step (2), the material is removed from the mold and the carbon paper is removed.

6. A carbon-based bulk material prepared by the method according to any one of claims 1-5, characterized in that, The carbon-based bulk material is obtained by spark plasma sintering using a precursor containing a metal / carbon material; the metal / carbon material is one of metal / porous carbon or metal / carbon nanotubes (CNTs) / porous carbon.

7. The application of a carbon-based bulk material prepared by any one of claims 1-5 in shielding materials.

8. The application of a carbon-based bulk material prepared by any one of claims 1-5 in the fields of aerospace, military defense, construction engineering, or electromagnetic protection.

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