Loofah sponge-derived lightweight silicon carbide sponge shielding material and preparation method thereof

Abstract

The invention discloses a light silicon carbide sponge shielding material derived from loofah sponge and a preparation method thereof, and belongs to the field of electromagnetic shielding. The silicon carbide sponge shielding material is porous silicon carbide sponge with a three-dimensional connected network structure, the electromagnetic shielding performance of the porous silicon carbide sponge is kept stable in various severe environments, and 90% or above of electromagnetic waves can be intercepted. The preparation method of the shielding material comprises the following steps: 1, cleaning natural loofah sponge with deionized water, drying, carrying out phenolic resin solution slurry hanging treatment, and curing and forming in a vacuum hot press to obtain a cured and formed loofah sponge sample; 2, performing high-temperature carbonization treatment on the loofah sponge sample to obtain carbonized loofah sponge; and 3, carrying out reactive sintering on the carbonized loofah sponge and silicon particles in a high-vacuum or high-purity argon protection environment to obtain the porous silicon carbide sponge. Due to the hierarchical pore structure of the natural loofah sponge, the shielding material disclosed by the invention has excellent mechanical properties, good electrical conductivity and controllable heat-conducting property.

Description

Technical Field

[0001] The invention belongs to the field of electromagnetic shielding, and particularly relates to a lightweight silicon carbide sponge shielding material derived from loofah and a preparation method thereof. Background Art

[0002] Electromagnetic wave pollution is another recognized major pollution problem after air, water and solid waste pollution. Electromagnetic wave interference will not only damage other electronic devices, but also may endanger human health, such as insomnia, anxiety, headaches, etc. At present, the frequency range of electromagnetic wave applications in people's lives has gradually developed from low frequency to high frequency area (MHz~GHz). For example, the radio wave frequency used in mobile communication technology from 1G to 5G is increasing from 0.45GHz to 3.6GHz. And with the development of high-tech, the frequency of electromagnetic waves used may be higher (~26GHz or ~40GHz). Therefore, it is crucial to develop efficient electromagnetic interference protection materials. In addition, with the development of industry and technology, the application fields of materials have become more and more extensive, including outer space, polar and ocean exploration. The requirements for the environmental tolerance of materials have become more and more stringent, such as fire resistance, corrosion resistance, high temperature resistance, etc. In summary, the development of efficient electromagnetic shielding materials should not only focus on improving shielding performance, but also take into account the comprehensive performance of materials, especially the ability to resist environmental impact.

[0003] At present, among many candidate materials for electromagnetic shielding, silicon carbide is regarded as the preferred electromagnetic shielding material with environmental resistance due to its advantages of corrosion resistance, high strength and heat resistance. Silicon carbide generated under different conditions will have certain differences in crystal structure and performance. Some basic parameters of silicon carbide are sublimation temperature ~2700℃, thermal conductivity 5W / cm·K, hardness 9.5, microhardness 2840kg / mm 2 ~3320kg / mm 2 On the other hand, in addition to measuring the comprehensive performance of the material, the inherent properties of the material itself must also be taken into account. The density of silicon carbide (3.17g / cm 3 ~3.47g / cm 3 ) is higher than other non-metallic shielding materials, which does not meet the current application requirements for lightweight and high-strength materials. Whether from the perspective of material applicability in equipment or from the perspective of convenience in people's lives, lightweight materials have always been the goal pursued by people. Therefore, if silicon carbide is to be used as a material for efficient attenuation of electromagnetic waves, further optimization is needed.

[0004] Generally speaking, through good structural design, the weight of electromagnetic shielding materials can be reduced without reducing performance. Constructing a three-dimensional network structure is a good choice for the preparation of high-efficiency electromagnetic shielding materials, such as aerogels, sponges, 3D printed porous materials, etc. Compared with artificially synthesized three-dimensional network structures, the innate interwoven network of natural biomaterials has more advantages. For example, wood, bamboo, leaves, coconut shells, corn stalks, loofahs, etc. with three-dimensional porous structures. Among them, loofah is a natural network with a multi-level pore structure. It is a three-dimensional millimeter pore framework structure constructed by loofah fibers containing micro-nano pores. This natural network structure is conducive to serving as an integrated and seamless conductive path, thereby increasing the interaction frequency with the incident electromagnetic wave, which in turn helps to attenuate the incident electromagnetic wave. It not only has a multi-interface structure that is conducive to conductivity, but also exhibits good mechanical strength and lightweight properties. The density is 0.048g / cm 3 The compressive yield strength of natural loofah sponge is about 0.4MPa; the tensile strength of natural loofah fiber is about 80MPa; the density of natural loofah sponge is 0.0674±0.0093g / cm 3 . What is important is that environmentally friendly, cheap, and sustainably renewable biomaterials will be more meaningful as high-performance research and development materials to serve people's lives, which is in line with the sustainable development strategy agreed upon by people all over the world. Summary of the invention

[0005] In view of the deficiencies in the prior art, the purpose of the present invention is to provide a lightweight silicon carbide sponge shielding material derived from loofah and a preparation method thereof that is suitable for extreme environments such as fire, salt spray corrosion, acid and alkali erosion, and low-temperature freezing, so as to solve the problem of limited application of silicon carbide due to its own excessive weight, thereby solving the problem of limited application of lightweight electromagnetic shielding materials in extreme environments.

[0006] A lightweight silicon carbide sponge shielding material derived from loofah, wherein the silicon carbide sponge shielding material is a porous silicon carbide sponge with a three-dimensional interconnected network structure, with a thickness of 1.4 mm to 9.5 mm, a pore size of 3 μm to 5 mm, and a density of 0.43 g / cm 3 ~1.02g / cm 3 ;

[0007] The lightweight silicon carbide sponge shielding material derived from loofah has an electromagnetic wave frequency range of 8.2 GHz to 40 GHz, and its electromagnetic shielding performance remains stable under extreme conditions, and it can intercept more than 90% of electromagnetic waves;

[0008] The extreme conditions are fire conditions of 500°C to 1000°C, salt spray corrosion conditions of 5wt.% sodium chloride aqueous solution, acid-base corrosion conditions of first using 98wt.% sulfuric acid corrosion and then using 10mol / L sodium hydroxide aqueous solution corrosion, and low-temperature freezing conditions of -196°C.

[0009] The ratio of the electromagnetic shielding performance to the density of the lightweight silicon carbide sponge shielding material derived from loofah, i.e., the specific electromagnetic shielding effectiveness value is 24.01 dB / g·cm -3 ~47.20dB / g·cm -3 , electrical conductivity is 0.85S / m~4.07S / m, thermal conductivity is 0.114W / (m·K)~4.816W / (m·K), and mechanical properties are 0.21MPa~54.39MPa.

[0010] The preparation method of the above-mentioned lightweight silicon carbide sponge shielding material derived from loofah specifically comprises the following steps:

[0011] (1) natural loofah is cleaned with deionized water and is used as raw material for standby use after drying;

[0012] (2) drying the loofah and subjecting it to phenolic resin solution slurry treatment, and then curing and molding in a vacuum hot press to obtain a cured loofah sample;

[0013] (3) subjecting the sample obtained in step (2) to high temperature carbonization treatment to obtain carbonized loofah;

[0014] (4) The carbonized loofah and silicon particles are reacted and sintered in a high vacuum or high-purity argon protection environment to obtain a porous silicon carbide sponge.

[0015] The method for preparing the lightweight silicon carbide sponge shielding material derived from loofah also includes the following steps:

[0016] (5) During the curing and molding process of step (2), a compression height of 0 to 90% is applied to the loofah to obtain porous silicon carbide sponges of different thicknesses.

[0017] in:

[0018] In the step (1), the length of the natural loofah is 0.3m to 1.5m, and the density is 0.0633g / cm 3 ~0.1122g / cm 3 The diameter of natural loofah fiber is 0.09cm~0.47cm.

[0019] In the step (1), the temperature for drying the natural loofah is 50°C to 150°C.

[0020] In the step (2), the phenolic resin solution is prepared by mixing ethanol and phenolic resin, wherein the mass ratio of ethanol to phenolic resin is (9:1) to (2:3).

[0021] In the step (2), the curing temperature of the loofah after slurry coating is 60° C. to 150° C., and the curing time is 1 h to 17.5 h.

[0022] In the step (3), the high-temperature carbonization treatment is carried out in a mixture of hydrogen and argon or under the protection of argon, wherein the volume fraction of hydrogen is 0-10%, and the volume fraction of argon is 90%-100%; the carbonization temperature is 600°C-1000°C, and the insulation time is 1h-3h.

[0023] In the step (4), the particle size of the silicon particles is 5 μm to 1 cm, and the purity is 99% to 99.99%.

[0024] In the step (4), the high vacuum environment is 1 Pa, and the purity of the high-purity argon gas is 99.999%.

[0025] In the step (4), the sintering temperature is 1600° C. to 2000° C., and the reaction time is 1 h to 3 h.

[0026] Compared with the prior art, the present invention has the following beneficial effects:

[0027] 1. The method provided by the present invention is based on the reaction sintering technology of the three-dimensional skeleton of natural loofah and silicon carbide. The carbon-silicon reaction can generate in situ a high-efficiency electromagnetic shielding material capable of resisting extreme environments on the carbonized loofah sponge skeleton. The conversion of loofah sponge carbon into silicon carbide further improves the strength of the loofah sponge skeleton, so that the prepared porous silicon carbide inherits the multi-interface structure and light-weight characteristics of loofah.

[0028] 2. The porous lightweight silicon carbide sponge of the present invention exhibits stable electromagnetic shielding performance and adjustable thermal properties, providing a new idea for preparing high-efficiency electromagnetic shielding materials for use in extreme environments. In extreme environments such as fire, salt spray corrosion, acid and alkali erosion, and low-temperature freezing, the electromagnetic shielding performance of the porous silicon carbide sponge of the present invention remains stable, can effectively protect against electromagnetic interference, and can always intercept most electromagnetic waves.

[0029] 3. The porous silicon carbide sponge prepared by the present invention has a low density. Thanks to the multi-level pore structure of natural loofah, the material can exhibit excellent mechanical properties at low density. The three-dimensional interconnected network structure of natural loofah also provides porous silicon carbide with good electrical conductivity and controllable thermal conductivity. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1In Examples 1-6 of the present invention, the physical pictures of natural loofah, loofah after pulping treatment and the prepared porous silicon carbide sponge; wherein (a) is a physical picture of natural loofah; (b) is a physical picture of loofahs of different thicknesses after pulping treatment and curing; (c) is a physical picture of porous silicon carbide sponges of different thicknesses;

[0031] Figure 2 In Examples 1-6 of the present invention, SEM images of natural loofah, carbonized loofah and porous silicon carbide sponge and fibers thereof; wherein, (a) is a SEM image of natural loofah; (b) is a SEM image of the side of natural loofah fiber; (c) is a SEM image of the cross section of natural loofah fiber; (d) is a SEM image of carbonized loofah; (e) is a SEM image of the side of carbonized loofah fiber; (f) is a SEM image of the cross section of carbonized loofah fiber; (g) is a SEM image of porous silicon carbide sponge; (h) is a SEM image of the side of porous silicon carbide sponge fiber; (i) is a SEM image of the cross section of porous silicon carbide sponge fiber;

[0032] Figure 3 X-ray diffraction spectrum and Raman spectrum of the 2.85 mm thick porous silicon carbide sponge prepared in Example 1 of the present invention; wherein (a) is the X-ray diffraction spectrum; (b) is the Raman spectrum;

[0033] Figure 4 In Examples 1-6 of the present invention, performance analysis diagrams of porous silicon carbide sponges of different thicknesses; wherein, (a) is a conductivity comparison diagram of porous silicon carbide sponges of different thicknesses; (b) is a comparison diagram of electromagnetic shielding performance of porous silicon carbide sponges of different thicknesses in the frequency range of 8.2 GHz to 12.4 GHz; (c) is a comparison diagram of electromagnetic shielding performance of porous silicon carbide sponges of different thicknesses in the frequency range of 12 GHz to 18 GHz; (d) is a diagram showing the change law of the shielding performance of porous silicon carbide sponges with thickness changes in the frequency range of 8.2 GHz to 12.4 GHz; (e) is a diagram showing the change law of the shielding performance of porous silicon carbide sponges with thickness changes in the frequency range of 12 GHz to 18 GHz; (f) is a comparison diagram of reflection coefficients of porous silicon carbide sponges of different thicknesses in the frequency ranges of 8.2 GHz to 12.4 GHz and 12 GHz to 18 GHz;

[0034] Figure 5In Examples 1-6 of the present invention, the electromagnetic shielding performance of porous silicon carbide sponges of different thicknesses under different environments and the shielding performance comparison diagrams before and after different environmental treatments are provided, wherein (a) is a comparison diagram of the electromagnetic shielding performance of porous silicon carbide sponges of different thicknesses in the frequency range of 8.2 GHz to 12.4 GHz under a flame baking environment; (b) is a comparison diagram of the electromagnetic shielding performance of porous silicon carbide sponges of different thicknesses in the frequency range of 12 GHz to 18 GHz under a flame baking environment; (c) is a comparison diagram of the electromagnetic shielding performance of porous silicon carbide sponges of different thicknesses in the frequency range of 8.2 GHz to 12.4 GHz under the original environment and the flame baking environment; (d) is a comparison diagram of the electromagnetic shielding performance of porous silicon carbide sponges of different thicknesses in the frequency range of 8.2 GHz to 12.4 GHz under the original environment and the flame baking environment. (e) is a comparison of the electromagnetic shielding performance of porous silicon carbide sponges with different thicknesses in the frequency range of 12 GHz to 18 GHz under salt spray corrosion environment; (f) is a comparison of the electromagnetic shielding performance of porous silicon carbide sponges with different thicknesses in the frequency range of 12 GHz to 18 GHz under salt spray corrosion environment; (g) is a comparison of the electromagnetic shielding performance of porous silicon carbide sponges with different thicknesses in the frequency range of 8.2 GHz to 12.4 GHz under original environment and salt spray corrosion environment; (h) is a comparison of the electromagnetic shielding performance of porous silicon carbide sponges with different thicknesses in the frequency range of 8.2 GHz to 12.4 GHz under original environment and salt spray corrosion environment. (i) is a comparison chart of the electromagnetic shielding performance of porous silicon carbide sponges with different thicknesses in the frequency range of 8.2 GHz to 12.4 GHz under acid-base immersion conditions; (j) is a comparison chart of the electromagnetic shielding performance of porous silicon carbide sponges with different thicknesses in the frequency range of 12 GHz to 18 GHz under acid-base immersion conditions; (k) is a comparison chart of the electromagnetic shielding performance of porous silicon carbide sponges with different thicknesses in the frequency range of 8.2 GHz to 12.4 GHz under original environment and acid-base immersion conditions; (l) is a comparison chart of the electromagnetic shielding performance of porous silicon carbide sponges with different thicknesses in the frequency range of 12 GHz to 18 GHz under original environment and acid-base immersion conditions. (m) is a comparison chart of electromagnetic shielding performance of porous silicon carbide sponges with different thicknesses in the frequency range of 8.2GHz to 12.4GHz in a liquid nitrogen freezing environment; (n) is a comparison chart of electromagnetic shielding performance of porous silicon carbide sponges with different thicknesses in the frequency range of 12GHz to 18GHz in a liquid nitrogen freezing environment; (o) is a comparison chart of electromagnetic shielding performance of porous silicon carbide sponges with different thicknesses in the frequency range of 8.2GHz to 12.4GHz in a pristine environment and a liquid nitrogen freezing environment; (p) is a comparison chart of electromagnetic shielding performance of porous silicon carbide sponges with different thicknesses in the frequency range of 12GHz to 18GHz in a pristine environment and a liquid nitrogen freezing environment;

[0035] Figure 6In Example 1 of the present invention, the electromagnetic shielding performance diagrams and thermogravimetric analysis curves of a 2.85 mm thick porous silicon carbide sponge in different environments and different frequency ranges; wherein, (a) is an electromagnetic shielding performance diagram of the porous silicon carbide sponge in the frequency range of 8 GHz to 12.4 GHz at different temperatures; (b) is a thermogravimetric analysis curve of the porous silicon carbide sponge, (c) is an electromagnetic shielding performance diagram of a 2.85 mm thick porous silicon carbide sponge in the frequency range of 18 GHz to 26.5 GHz under different environments; (d) is an electromagnetic shielding performance diagram of a 2.85 mm thick porous silicon carbide sponge in the frequency range of 26.5 GHz to 40 GHz under different environments;

[0036] Figure 7 Mechanical properties diagram of porous silicon carbide sponges of different thicknesses in Examples 1-6 of the present invention;

[0037] Figure 8 Infrared images of porous silicon carbide sponges of different thicknesses under a heat source of 100° C. in Examples 1-6 of the present invention;

[0038] Fig. 9 Infrared images of porous silicon carbide sponges of different thicknesses under a 300° C. heat source in Examples 1-6 of the present invention;

[0039] Fig.10 In Comparative Example 1 of the present invention, loofah carbon powder particles and particle size volume distribution diagram; wherein, (a) is a SEM image of loofah carbon powder particles; (b) is a particle size volume distribution diagram of loofah carbon powder particles;

[0040] Fig.11 Physical pictures of solid silicon carbide of different thicknesses in Comparative Example 1 of the present invention;

[0041] Fig.12 In Comparative Example 1 of the present invention, the electromagnetic shielding performance diagrams of the solid silicon carbide shielding materials of different thicknesses are obtained; wherein (a) is a diagram of the electromagnetic shielding performance of the solid silicon carbide shielding materials of different thicknesses in the frequency range of 8 GHz to 12.4 GHz; and (b) is a comparison diagram of the shielding effectiveness values ​​of porous silicon carbide sponges of different thicknesses and solid silicon carbide shielding materials. DETAILED DESCRIPTION

[0042] Example 1

[0043] A method for preparing a lightweight silicon carbide sponge shielding material derived from loofah, specifically comprising the following steps:

[0044] (1) Select a natural loofah with a length of 1 m as the raw material of the loofah sponge, with a density of 0.0816 g / cm 3The diameter of natural loofah fiber is 0.4 cm. It is cleaned with deionized water and dried at 80°C before use as raw material.

[0045] (2) The dried loofah is treated with a phenolic resin solution, wherein the mass ratio of ethanol to phenolic resin in the phenolic resin solution is 2:3. The loofah after the slurry is cured in a vacuum hot press, and a compression force of 72% of the compression height is applied to it. The curing temperature is 150°C and the curing time is 2 hours to obtain a cured loofah sample.

[0046] (3) subjecting the sample obtained in step (2) to a high-temperature carbonization treatment under the protection of a mixture of hydrogen and argon, wherein the volume fraction of hydrogen is 5%, the volume fraction of argon is 95%, the carbonization temperature is 800° C., and the insulation time is 2 h, to obtain a carbonized loofah.

[0047] (4) The carbonized loofah was reacted and sintered with silicon particles with a particle size of 50 μm and a purity of 99.99% in a high vacuum environment of 1 Pa. The sintering temperature was 1800° C. and the reaction time was 2 h to obtain a porous silicon carbide sponge sample.

[0048] (5) The sample obtained in step (4) is cut and trimmed to obtain a porous silicon carbide sponge with a thickness of 2.85 mm and a pore size of 3 μm to 5 mm. The actual pictures of natural loofah, loofah treated with pulp and the obtained porous silicon carbide sponge are as follows: Figure 1 As shown, the SEM images of natural loofah, carbonized loofah, porous silicon carbide sponge and its fibers are shown in Figure 2 As shown in the figure, the X-ray diffraction spectrum and Raman spectrum of 2.85 mm thick porous silicon carbide sponge are shown in the figure. Figure 3 shown.

[0049] Example 2

[0050] A method for preparing a lightweight silicon carbide sponge shielding material derived from loofah, specifically comprising the following steps:

[0051] (1) Select natural loofah with a length of 0.3 m as the raw material of loofah sponge, with a density of 0.0633 g / cm 3 The diameter of natural loofah fiber is 0.09 cm. It is cleaned with deionized water and dried at 50°C for use as raw materials.

[0052] (2) The dried loofah is treated with a phenolic resin solution, wherein the mass ratio of ethanol to phenolic resin in the phenolic resin solution is 9:1. The loofah after the slurry is cured in a vacuum hot press, and a compression force of 65% of the compression height is applied to it. The curing temperature is 60°C, and the curing time is 17.5 hours to obtain a cured loofah sample.

[0053] (3) subjecting the sample obtained in step (2) to high-temperature carbonization treatment under the protection of a mixture of hydrogen and argon, wherein the volume fraction of hydrogen is 0%, the volume fraction of argon is 100%, the carbonization temperature is 600° C., and the insulation time is 3 h to obtain a carbonized loofah.

[0054] (4) The carbonized loofah was sintered with silicon particles with a particle size of 5 μm and a purity of 99% in a high-purity argon environment with a purity of 99.999%. The sintering temperature was 1600° C. and the reaction time was 3 h to obtain a porous silicon carbide sponge sample.

[0055] (5) The sample obtained in step (4) is cut and trimmed to obtain a porous silicon carbide sponge with a thickness of 3.7 mm and a pore size of 3 μm to 5 mm. The actual pictures of natural loofah, loofah treated with pulp and the obtained porous silicon carbide sponge are as follows: Figure 1 As shown, the SEM images of natural loofah, carbonized loofah, porous silicon carbide sponge and its fibers are shown in Figure 2 shown.

[0056] Example 3

[0057] A method for preparing a lightweight silicon carbide sponge shielding material derived from loofah, specifically comprising the following steps:

[0058] (1) Select natural loofah with a length of 1.5 m as the raw material of loofah sponge, with a density of 0.1122 g / cm 3 The diameter of natural loofah fiber is 0.47 cm. It is cleaned with deionized water and dried at 150°C before use as raw material.

[0059] (2) The dried loofah is treated with a phenolic resin solution, wherein the mass ratio of ethanol to phenolic resin in the phenolic resin solution is 3:2. The loofah after the slurry is cured in a vacuum hot press, and a compression force of 53% of the compression height is applied to it. The curing temperature is 135°C, and the curing time is 1 hour to obtain a cured loofah sample.

[0060] (3) subjecting the sample obtained in step (2) to a high-temperature carbonization treatment under the protection of a mixture of hydrogen and argon, wherein the volume fraction of hydrogen is 10%, the volume fraction of argon is 90%, the carbonization temperature is 1000° C., and the insulation time is 1 h, to obtain a carbonized loofah.

[0061] (4) The carbonized loofah was reacted and sintered with silicon particles with a particle size of 1 cm and a purity of 99.5% in a high vacuum environment of 1 Pa. The sintering temperature was 2000° C. and the reaction time was 1 h to obtain a porous silicon carbide sponge sample.

[0062] (5) The sample obtained in step (4) is cut and trimmed to obtain a porous silicon carbide sponge with a thickness of 4.85 mm and a pore size of 3 μm to 5 mm. The actual pictures of natural loofah, loofah treated with pulp and the obtained porous silicon carbide sponge are as follows: Figure 1 As shown, the SEM images of natural loofah, carbonized loofah, porous silicon carbide sponge and its fibers are shown in Figure 2 shown.

[0063] Example 4

[0064] A method for preparing a lightweight silicon carbide sponge shielding material derived from loofah, specifically comprising the following steps:

[0065] (1) Select natural loofah with a length of 0.8m as the raw material of loofah sponge, and the density is 0.1013g / cm 3 The diameter of natural loofah fiber is 0.2 cm. It is cleaned with deionized water and dried at 100°C before use as raw material.

[0066] (2) The dried loofah is treated with a phenolic resin solution, wherein the mass ratio of ethanol to phenolic resin in the phenolic resin solution is 1:4. The loofah after the slurry is cured in a vacuum hot press, and a compression force of 48% of the compression height is applied to it. The curing temperature is 120°C, and the curing time is 1.5 hours to obtain a cured loofah sample.

[0067] (3) subjecting the sample obtained in step (2) to high-temperature carbonization treatment under the protection of a mixture of hydrogen and argon, wherein the volume fraction of hydrogen is 1%, the volume fraction of argon is 99%, the carbonization temperature is 900° C., and the insulation time is 1.5 h to obtain a carbonized loofah.

[0068] (4) The carbonized loofah was reacted and sintered with silicon particles with a particle size of 100 μm and a purity of 99.8% in a high vacuum environment of 1 Pa at a sintering temperature of 1750° C. for a reaction time of 1.5 h to obtain a porous silicon carbide sponge sample.

[0069] (5) The sample obtained in step (4) is cut and trimmed to obtain a porous silicon carbide sponge with a thickness of 5.41 mm and a pore size of 3 μm to 5 mm. The actual pictures of natural loofah, loofah treated with pulp and the obtained porous silicon carbide sponge are as follows: Figure 1 As shown, the SEM images of natural loofah, carbonized loofah, porous silicon carbide sponge and its fibers are shown in Figure 2 shown.

[0070] Example 5

[0071] A method for preparing a lightweight silicon carbide sponge shielding material derived from loofah, specifically comprising the following steps:

[0072] (1) Select natural loofah with a length of 1.2 m as the raw material of loofah sponge, with a density of 0.0742 g / cm 3 The diameter of natural loofah fiber is 0.35 cm. It is cleaned with deionized water and dried at 120°C before use as raw material.

[0073] (2) The dried loofah is treated with a phenolic resin solution, wherein the mass ratio of ethanol to phenolic resin in the phenolic resin solution is 1:1. The loofah after the slurry is cured in a vacuum hot press, and a compression force of 27% of the compression height is applied thereto. The curing temperature is 140°C, and the curing time is 1.8 h to obtain a cured loofah sample.

[0074] (3) The sample obtained in step (2) is subjected to high-temperature carbonization treatment under the protection of a mixture of hydrogen and argon, wherein the volume fraction of hydrogen is 5%, the volume fraction of argon is 95%, the carbonization temperature is 850° C., and the insulation time is 1.6 h to obtain a carbonized loofah.

[0075] (4) The carbonized loofah was reacted and sintered with silicon particles with a particle size of 50 μm and a purity of 99.99% in a high vacuum environment of 1 Pa at a sintering temperature of 1850° C. for a reaction time of 2 h to obtain a porous silicon carbide sponge sample.

[0076] (5) The sample obtained in step (4) is cut and trimmed to obtain a porous silicon carbide sponge with a thickness of 7.56 mm and a pore size of 3 μm to 5 mm. The actual pictures of natural loofah, loofah treated with pulp and the prepared porous silicon carbide sponge are as follows: Figure 1 As shown, the SEM images of natural loofah, carbonized loofah, porous silicon carbide sponge and its fibers are shown in Figure 2 shown.

[0077] Example 6

[0078] A method for preparing a lightweight silicon carbide sponge shielding material derived from loofah, specifically comprising the following steps:

[0079] (1) Select a natural loofah with a length of 1 m as the raw material of the loofah sponge, with a density of 0.0816 g / cm 3 The diameter of natural loofah fiber is 0.41 cm. It is cleaned with deionized water and dried at 95°C before use as raw material.

[0080] (2) The dried loofah is treated with a phenolic resin solution, wherein the mass ratio of ethanol to phenolic resin in the phenolic resin solution is 2:3. The loofah after the slurry is cured in a vacuum hot press, and a compression force of 11% of the compression height is applied thereto. The curing temperature is 145°C, and the curing time is 2 h to obtain a cured loofah sample.

[0081] (3) The sample obtained in step (2) is subjected to high-temperature carbonization treatment under the protection of a mixed gas of hydrogen and argon, wherein the volume fraction of hydrogen is 0%, the volume fraction of argon is 100%, the carbonization temperature is 950° C., and the insulation time is 2 h to obtain a carbonized loofah.

[0082] (4) The carbonized loofah was reacted and sintered with silicon particles with a particle size of 50 μm and a purity of 99.99% in a high vacuum environment of 1 Pa. The sintering temperature was 1900° C. and the reaction time was 1.6 h to obtain a porous silicon carbide sponge sample.

[0083] (5) The sample obtained in step (4) is cut and trimmed to obtain a porous silicon carbide sponge with a thickness of 9.3 mm and a pore size of 3 μm to 5 mm. Figure 1 As shown, the SEM images of natural loofah, carbonized loofah, porous silicon carbide sponge and its fibers are shown in Figure 2 shown.

[0084] The porous lightweight silicon carbide sponge prepared by the present invention can protect against electromagnetic interference in extreme environments, such as fire, salt spray corrosion, acid and alkali erosion and low-temperature freezing environments, and the electromagnetic wave frequency range can reach 8.2GHz to 12.4GHz, 12GHz to 18GHz, 18GHz to 26.5GHz and 26.5GHz to 40GHz. In a variety of harsh environments, the electromagnetic shielding performance of the porous silicon carbide sponge remains stable and can always intercept more than 90% of electromagnetic waves.

[0085] Performance analysis of porous silicon carbide sponges of different thicknesses Figure 4 As shown, from Figure 4 It can be seen that the three-dimensional connected network structure provides the porous silicon carbide sponge with good electrical conductivity and electromagnetic shielding properties.

[0086] The electromagnetic shielding performance of porous silicon carbide sponges of different thicknesses under different environments and the comparison of shielding performance before and after different environmental treatments are shown in the figure below. Figure 5 The electromagnetic shielding performance diagram and thermogravimetric analysis curve of 2.85 mm thick porous silicon carbide sponge in different environments and different frequency ranges are shown in Figure 2. Figure 6 shown.

[0087] The properties of porous silicon carbide sponges of different thicknesses at room temperature are shown in Table 1. The density of the prepared sponges is 1.02 g / cm 3 , 1.0g / cm 3 , 0.97g / cm 3 , 0.52g / cm 3 , 0.46g / cm3 and 0.43g / cm 3 , at such a low density, the material can also show excellent mechanical properties, and its mechanical properties are shown in the figure Figure 7 As shown in Figure 1, this is all due to the multi-level pore structure of natural loofah. This three-dimensional interconnected network structure also provides controllable thermal conductivity for porous silicon carbide sponge. The infrared images of porous silicon carbide sponges of different thicknesses under a 100°C heat source are shown in Figure 1. Figure 8 As shown in the figure, the infrared images of porous silicon carbide sponges with different thicknesses under a heat source of 300°C are shown in the figure. Fig. 9 shown.

[0088] Table 1 Performance of porous silicon carbide sponge with different thicknesses in Example 1

[0089]

[0090]

[0091] Comparative Example 1

[0092] The main difference between Comparative Example 1 and Example 1 is that the prepared silicon carbide is solid silicon carbide. The specific scheme is as follows:

[0093] A method for preparing a solid silicon carbide shielding material specifically comprises the following steps:

[0094] (1) Select natural loofah with a length of 1 m as the raw material of carbonized loofah with a density of 0.0816 g / cm 3 The diameter of natural loofah fiber is 0.4 cm. It is cleaned with deionized water and dried at 80°C before use as raw material.

[0095] (2) The dried loofah was subjected to high-temperature carbonization treatment under the protection of a mixture of hydrogen and argon, wherein the volume fraction of hydrogen was 5%, the volume fraction of argon was 95%, the carbonization temperature was 800° C., and the insulation time was 2 hours to obtain a carbonized loofah.

[0096] (3) The carbonized loofah was subjected to high-speed ball milling at 2000 r / min for 10 h to obtain loofah carbon powder particles with a size of about 2.4 μm. The loofah carbon powder particles and particle size volume distribution are shown in FIG. Fig.10 shown.

[0097] (4) The sponge gourd carbon powder and silicon powder are uniformly mixed and compacted in a molding machine to obtain a solid silicon carbide preform.

[0098] (5) The solid silicon carbide preform was sintered in a tube furnace at a temperature of 1800°C, a high vacuum environment, and a reaction time of 2 h to obtain solid silicon carbide with thicknesses of 2.85 mm, 3.7 mm, 4.85 mm, 5.41 mm, 7.56 mm, and 9.3 mm. The actual picture is as follows Fig.11 shown.

[0099] (5) The electromagnetic shielding performance of the six solid silicon carbide shielding materials obtained in step (4) is tested. The performance of the solid silicon carbide shielding materials of different thicknesses at room temperature is shown in Table 2. The electromagnetic shielding performance diagram is shown in Fig.12 As shown in Table 1 and Table 2, it can be seen that the specific electromagnetic shielding effectiveness value (shielding effectiveness value / density) of the solid silicon carbide shielding material at room temperature is much smaller than the specific electromagnetic shielding effectiveness value of the lightweight porous silicon carbide sponge.

[0100] Table 2 Performance of solid silicon carbide shielding materials of different thicknesses in Comparative Example 1

[0101]

[0102]

[0103] Matters not covered by the present invention are known technologies.

[0104] The above embodiments are only for illustrating the technical concept and features of the present invention, and their purpose is to enable people familiar with the technology to understand the content of the present invention and implement it accordingly, and they cannot be used to limit the protection scope of the present invention. Any equivalent changes or modifications made according to the spirit of the present invention should be included in the protection scope of the present invention.

Claims

1. A lightweight silicon carbide sponge shielding material derived from loofah, characterized in that: The silicon carbide sponge shielding material is a porous silicon carbide sponge with a three-dimensional interconnected network structure, with a thickness of 1.4 mm to 9.5 mm, a pore size of 3 μm to 5 mm, and a density of 0.43 g / cm 3 ~1.02g / cm 3 ; The lightweight silicon carbide sponge shielding material derived from loofah has an electromagnetic wave frequency range of 8.2 GHz to 40 GHz, and its electromagnetic shielding performance remains stable under extreme conditions, and it can intercept more than 90% of electromagnetic waves; The extreme conditions are fire conditions of 500°C to 1000°C, salt spray corrosion conditions of 5wt.% sodium chloride aqueous solution, acid-base corrosion conditions of first using 98wt.% sulfuric acid corrosion and then using 10mol / L sodium hydroxide aqueous solution corrosion, and low-temperature freezing conditions of -196°C.

2. A lightweight silicon carbide sponge shielding material derived from loofah according to claim 1, characterized in that: The ratio of the electromagnetic shielding performance to the density of the lightweight silicon carbide sponge shielding material derived from loofah, i.e., the specific electromagnetic shielding effectiveness value is 24.01 dB / g·cm -3 ~47.20dB / g·cm -3 , electrical conductivity is 0.85S / m~4.07S / m, thermal conductivity is 0.114W / (m·K)~4.816W / (m·K), and mechanical properties are 0.21MPa~54.39MPa.

3. The method for preparing a lightweight silicon carbide sponge shielding material derived from loofah according to claim 1, characterized in that: The specific steps include: (1) natural loofah is cleaned with deionized water and is used as raw material for standby use after drying; (2) drying the luffa and subjecting it to phenolic resin solution slurry treatment, and then curing and molding in a vacuum hot press to obtain a cured luffa sample; (3) subjecting the sample obtained in step (2) to high temperature carbonization treatment to obtain carbonized loofah; (4) The carbonized loofah and silicon particles are reacted and sintered in a high vacuum or high-purity argon protection environment to obtain a porous silicon carbide sponge.

4. The method for preparing a lightweight silicon carbide sponge shielding material derived from loofah according to claim 3, characterized in that: The preparation method further comprises the following steps: (5) During the curing and molding process of step (2), a compression height of 0 to 90% is applied to the loofah to obtain porous silicon carbide sponges of different thicknesses.

5. The method for preparing a lightweight silicon carbide sponge shielding material derived from loofah according to claim 3, characterized in that: In the step (1), the length of the natural loofah is 0.3m to 1.5m, and the density is 0.0633g / cm 3 ~0.1122g / cm 3 The diameter of the natural loofah fiber is 0.09 cm to 0.47 cm; the drying temperature of the natural loofah is 50° C. to 150° C.

6. The method for preparing a lightweight silicon carbide sponge shielding material derived from loofah according to claim 3, characterized in that: In the step (2), the phenolic resin solution is prepared by mixing ethanol and phenolic resin, wherein the mass ratio of ethanol to phenolic resin is (9:1) to (2:3).

7. The method for preparing a lightweight silicon carbide sponge shielding material derived from loofah according to claim 3, characterized in that: In the step (2), the curing temperature of the loofah after slurry coating is 60° C. to 150° C., and the curing time is 1 h to 17.5 h.

8. The method for preparing a lightweight silicon carbide sponge shielding material derived from loofah according to claim 3, characterized in that: In the step (3), the high-temperature carbonization treatment is carried out in a mixture of hydrogen and argon or under the protection of argon, wherein the volume fraction of hydrogen is 0-10%, and the volume fraction of argon is 90%-100%; the carbonization temperature is 600°C-1000°C, and the insulation time is 1h-3h.

9. The method for preparing a lightweight silicon carbide sponge shielding material derived from loofah according to claim 3, characterized in that: In the step (4), the particle size of the silicon particles is 5 μm to 1 cm, and the purity is 99% to 99.99%.

10. The method for preparing a lightweight silicon carbide sponge shielding material derived from loofah according to claim 3, characterized in that: In the step (4), the high vacuum environment is 1 Pa, the purity of the high-purity argon gas is 99.999%; the sintering temperature is 1600° C. to 2000° C., and the reaction time is 1 h to 3 h.

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