Carbon / carbon composite material surface lightweight porous heat emission coating and preparation method thereof

Abstract

The invention discloses a carbon / carbon composite material surface lightweight porous heat emission coating and a preparation method thereof, and belongs to the field of infrared radiation. Comprising the following steps: uniformly spraying porous carbon powder slurry containing silica sol to the surface of a carbon / carbon composite material matrix, and drying; the porous carbon powder slurry contains silica sol; repeatedly spraying and drying until the porous carbon powder slurry uniformly covers the surface of the matrix to obtain a slurry layer attached to the surface of the carbon / carbon composite material matrix; curing the slurry layer to obtain a pre-coating layer; pyrolytic carbon is deposited on the surface of the carbon / carbon composite material with the pre-coating layer through a CVD method, the high-binding-force infrared radiation coating is prepared, natural gas serves as a carbon source when the pyrolytic carbon is deposited, and argon serves as protective gas when the pyrolytic carbon is deposited; a porous skeleton carbon material is selected as a coating raw material, silica sol is used as a binder, the light coating with the high infrared emissivity larger than 0.93 is prepared through a simple preparation technology, and the excellent infrared radiation performance is obtained.

Description

Technical Field

[0001] The present invention relates to the field of infrared radiation technology, and in particular to a lightweight porous thermal emission coating on the surface of a carbon / carbon composite material and a preparation method thereof. Background Art

[0002] During the round trip between the Earth and space, reusable spacecraft (such as the space shuttle) experience aerodynamic heat transfer between the surface and the atmosphere, which causes local areas to heat up rapidly. In addition, the temperature difference between day and night in space is too large, and the spacecraft frequently experiences extreme temperatures and local overheating, which may not only damage the performance of the spacecraft, but also shorten its service life. Therefore, the development of spacecraft materials that still have excellent performance in high-temperature environments has become a core research direction in this field. Carbon / carbon composite materials have low density, excellent mechanical properties and good high-temperature resistance, and have been widely used in the aerospace field. However, carbon / carbon composite materials have low porosity and limited surface radiation heat dissipation capacity. In the high-temperature environment of space, they are prone to thermal damage and performance degradation due to heat accumulation. Therefore, it is necessary to prepare a coating on its surface that can effectively increase heat output to minimize its surface temperature rise and improve its comprehensive performance. Therefore, the research and development of thermal emission coatings on the surface of carbon / carbon composite materials has become an important research direction.

[0003] Current research on infrared radiation materials primarily focuses on porous polymer films, such as polyvinylidene fluoride (PVDF). These materials achieve excellent infrared properties by leveraging micro- and nano-pores left behind by evaporation of the solution, resulting in superior infrared radiation performance. However, the preparation process for porous polymer films is cumbersome, lacks reproducibility, and poses challenges for large-scale production. Furthermore, excessively small nanopores can easily restrict the material's thermal emission pathways, hindering heat dissipation. Alternatively, some studies have employed inorganic fillers (such as transition metal silicides and quartz fibers) to create coatings using slurry impregnation followed by sintering, achieving thermal emission coefficients as high as 0.9. However, the thermal expansion coefficients of these materials differ significantly from those of carbon / carbon composites, making them susceptible to cracking and shedding at high temperatures due to thermal expansion. Furthermore, these materials are generally heavy, and the infrared radiation performance of the coatings is closely related to coating thickness. Consequently, these materials struggle to meet the aerospace industry's pursuit of lightweight and high-efficiency coatings.

[0004] In summary, the preparation of lightweight porous and high-efficiency thermal emission coatings with appropriate pore size and excellent performance on the surface of carbon / carbon composites has become a hot topic that needs to be studied urgently. Summary of the Invention

[0005] In order to solve the above problems, the present application provides a preparation method of a light-weight porous thermal emission coating on the surface of carbon / carbon composite material. A porous carbon with a skeleton structure and a binder are used to prepare a slurry in a set proportion and deionized water. The slurry is sprayed on the surface of the carbon / carbon composite material by an air compression spraying process to obtain a thermal emission coating with strong adhesion after depositing pyrolytic carbon. A high-infrared-emissivity light-weight coating with an infrared emissivity greater than 0.93 is prepared by a simple preparation process, and excellent infrared radiation performance and strong adhesion are obtained.

[0006] In order to achieve the above purpose, the technical scheme adopted by the present application is as follows: a light-weight porous thermal emission coating on the surface of carbon / carbon composite material and a preparation method, comprising the following steps: The porous carbon powder slurry containing silica sol is uniformly sprayed on the surface of the carbon / carbon composite material substrate and dried; The spraying and drying are repeated until the porous carbon powder slurry uniformly covers the surface of the substrate, and a slurry layer attached to the surface of the carbon / carbon composite material substrate is obtained; The slurry layer is solidified to obtain a pre-coating layer; Pyrolytic carbon is deposited on the surface of the carbon / carbon composite material with the pre-coating layer by a CVD method to obtain an infrared radiation coating with strong adhesion. The carbon source is natural gas and the protective gas is argon during the deposition of the pyrolytic carbon.

[0007] Further, the composition of the porous carbon powder slurry is as follows in terms of mass fraction: 6-10 parts of porous carbon, 0.8-1.2 parts of dispersant, 1-3 parts of silica sol, and 15-20 parts of deionized water.

[0008] Further, the dispersant is sodium dodecyl benzene sulfonate, polyvinyl pyrrolidone or ammonium polyacrylate.

[0009] Further, the porous carbon powder is carbonized from phenolic resin, and the pore size is 200 nm-5 μm.

[0010] Further, during the preparation of the porous carbon powder slurry, the porous carbon powder is added to the dispersant solution in multiple times and is dispersed by ultrasonic. When the porous carbon powder is added to the dispersant solution, the solution needs to be uniformly dispersed before the next addition.

[0011] Further, after the porous carbon powder slurry is dried, the number of repeated spraying is 1-4 times.

[0012] Further, the solidification temperature is 200℃, and the solidification time is 2-3 h.

[0013] Further, the deposition temperature of the pyrolytic carbon is 1020-1070℃, and the deposition time is 15-35 min.

[0014] Furthermore, the gas flow ratio of natural gas to argon during the deposition of pyrolytic carbon is 1:1-4.

[0015] The present invention can also provide a lightweight porous thermal emission coating on the surface of a carbon / carbon composite material, which is obtained by adopting the preparation method described above.

[0016] Compared with the prior art, the present invention has the following beneficial effects: The present invention provides a method for preparing a lightweight porous thermal emissive coating on the surface of a carbon / carbon composite material. The method uses porous carbon with a skeleton structure having an ultra-high specific surface area as a raw material, and uses silica sol as a binder. The silica sol is used as a binder to solidify the porous carbon skeleton, thereby improving the initial bonding strength between the pre-coating layer and the substrate. Then, a CVD method is used to deposit pyrolytic carbon on the surface of the carbon / carbon composite material to prepare a coating with strong bonding and excellent infrared radiation performance. The pyrolytic carbon fills the gaps in the porous carbon skeleton to form a mechanical interlocking structure, thereby improving the bonding strength between the coating and the substrate. The high infrared emissivity of the pyrolytic carbon itself directly enhances the thermal radiation efficiency. Specifically, the following are embodied: (1) The coating has excellent infrared radiation performance, with an average infrared emissivity of greater than 0.93 in the 1-22 μm band; (2) The porous carbon and the carbon / carbon composite matrix are both carbonaceous materials, with similar thermal expansion coefficients, so the coating is not easy to fall off, and the coating surface density is low, thereby achieving the goal of "lightweight"; (3) The coating preparation process is simple and easy to achieve large-scale preparation.

[0017] Furthermore, by spraying multiple times to stack thin layers, the thickness difference of a single spray is reduced, making the coating more uniform.

[0018] Furthermore, the high carbon content ensures that the main body of the coating is a porous carbon skeleton, and the lightweight property comes from the pore structure; silica sol provides adhesion, balancing strength and porosity; sodium dodecylbenzene sulfonate (ionic) or polyvinyl pyrrolidone / ammonium polyacrylate (polymer) stabilizes the slurry through electrostatic repulsion or steric hindrance, respectively, to prevent porous carbon agglomeration; stepwise addition and ultrasonic dispersion: avoid particle agglomeration, ensure slurry fluidity, and provide a basis for spraying uniformity.

[0019] Furthermore, the pore size of the porous carbon is 0.2μm-5μm: the large pore structure is conducive to the infiltration and filling of pyrolytic carbon during the CVD process, enhancing the density of the coating; the nanoscale pores may increase the surface roughness and increase the thermal radiation surface area.

[0020] Furthermore, the controllable carbonization process of phenolic resin carbonized porous carbon ensures the chemical purity of the porous carbon and prevents impurities from affecting high-temperature performance.

[0021] Furthermore, the silica sol dehydrates and condenses to form a Si-O-Si network, which fixes the porous carbon skeleton, prevents the pre-coating from cracking or falling off during the subsequent CVD high-temperature process, and avoids oxidation damage to the carbon / carbon matrix during the pre-curing stage.

[0022] Furthermore, the CVD deposition temperature is 1020-1070°C, matching the temperature resistance of the carbon / carbon matrix while ensuring that natural gas is pyrolyzed to generate pyrolytic carbon.

[0023] Furthermore, argon dilutes the carbon source and controls the pyrolytic carbon deposition rate. Too high a carbon source concentration may lead to too fast deposition and pore blockage; too slow a concentration may affect the bonding strength. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 is a low-magnification SEM image of the infrared radiation coating prepared in Example 1.

[0025] Figure 2 This is a high-magnification SEM image of the infrared radiation coating prepared in Example 1.

[0026] Figure 3 is the XRD pattern of the infrared radiation coating prepared in Example 1. DETAILED DESCRIPTION

[0027] The technical solution of the present invention will be described clearly and completely below. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. All other embodiments derived by persons of ordinary skill in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0028] In the present invention, unless otherwise specified, all the embodiments and preferred implementation methods mentioned herein can be combined with each other to form a new technical solution.

[0029] In the present invention, unless otherwise specified, all technical features and preferred features mentioned herein can be combined with each other to form a new technical solution.

[0030] The present invention provides a method for preparing a lightweight porous thermal emissive coating on the surface of a carbon / carbon composite material, comprising the following steps: (1) dissolving a dispersant in deionized water containing silica sol and stirring uniformly to obtain a dispersant solution; wherein the dispersant is polyvinyl pyrrolidone, sodium dodecylbenzene sulfonate or ammonium polyacrylate; (2) adding porous carbon powder to the dispersant solution obtained in step (1) in batches and uniformly dispersing the powder by ultrasonication; wherein the porous carbon powder is obtained by carbonizing a self-made phenolic resin and has a pore size of 200 nm to 5 μm; each time the porous carbon powder is added to the solution, it is necessary to wait for the solution to be uniformly dispersed before adding the next powder; in the specific implementation process, preferably, the slurry composition is as follows, calculated by weight: 6 to 10 parts of porous carbon, 0.8 to 1.2 parts of dispersant, 1 to 3 parts of silica sol, and 15 to 20 parts of deionized water; (3) using an air compressor to evenly spray the slurry described in step (2) onto the surface of the carbon / carbon composite material, repeat the spraying after drying, and then solidify to obtain a pre-coating layer; wherein the number of repeated spraying after drying is 1 to 4 times; the curing temperature is 200° C., and the curing time is 2 to 3 hours; (4) Depositing pyrolytic carbon on a surface of a carbon / carbon composite material having a pre-coating layer by a CVD method to produce an infrared radiation coating. The pyrolytic carbon deposition temperature is 1020-1070°C, and the deposition time is 15-35 minutes. The carbon source for the pyrolytic carbon deposition is natural gas, and the shielding gas is argon. The gas flow ratio of natural gas to argon during the pyrolytic carbon deposition is 1:1-4.

[0031] Specific examples of the present invention are given below, which are only intended to further illustrate the present invention in detail and are not intended to limit the present invention.

[0032] Example 1 A method for preparing a lightweight porous thermal emissive coating on the surface of a carbon / carbon composite material, the preparation method is as follows: (1) Select porous carbon with a pore size of 1 μm, add 0.8 parts of sodium dodecylbenzenesulfonate and 2.5 parts of silica sol to 20 parts of deionized water, and stir for 20 minutes to obtain a solution for use; (2) adding porous carbon powder to the above solution in batches, 2 parts each time, for a total of 10 times, and preparing a slurry after ultrasonic dispersion; (3) Using an air compressor, spray the slurry evenly onto the surface of the carbon / carbon composite material. Repeat the spraying four times after the surface is dry. After drying, place it at 200°C for 2 hours to cure. (4) Using the chemical vapor deposition process, pyrolytic carbon was deposited on the carbon / carbon composite material with a pre-coated surface at 1070°C and a natural gas to argon gas flow ratio of 1:4 for 15 minutes, so that the coating had good bonding strength with the surface of the carbon / carbon composite material.

[0033] The average infrared emissivity of the prepared coating in the 1~22μm band is 0.97. After depositing the pyrolytic carbon coating, the average infrared emissivity in the 1~22μm band is 0.95.

[0034] Example 2 A method for preparing a lightweight porous thermal emissive coating on the surface of a carbon / carbon composite material, the preparation method is as follows: (1) Select porous carbon with a pore size of 3 μm, add 1.2 parts of ammonium polyacrylate and 2 parts of silica sol to 18 parts of deionized water, and stir for 20 minutes to obtain a solution for use; (2) adding the porous carbon powder to the above solution in portions, 2 parts each time, for a total of 6 times, and preparing a slurry after ultrasonic dispersion; (3) Using an air compressor, spray the slurry evenly onto the surface of the carbon / carbon composite material. Repeat the spraying twice after the surface is dry. After drying, place it at 200°C for 2.5 hours to cure. (4) Using the chemical vapor deposition process, pyrolytic carbon was deposited on the carbon / carbon composite material with a pre-coated surface at 1050°C and a natural gas to argon gas flow ratio of 1:1 for 30 minutes, so that the coating had good bonding strength with the surface of the carbon / carbon composite material.

[0035] The average infrared emissivity of the prepared coating in the 1~22μm band is 0.96. After depositing the pyrolytic carbon coating, the average infrared emissivity in the 1~22μm band is 0.93.

[0036] Example 3 A method for preparing a lightweight porous thermal emissive coating on the surface of a carbon / carbon composite material, the preparation method is as follows: (1) Select porous carbon with a pore size of 5 μm, add 1 part of sodium dodecylbenzenesulfonate and 3 parts of silica sol to 15 parts of deionized water, and stir for 20 minutes to obtain a solution for use; (2) adding the porous carbon powder to the above solution in portions, 2 parts each time, for a total of 6 times, and preparing a slurry after ultrasonic dispersion; (3) Using an air compressor, spray the slurry evenly onto the surface of the carbon / carbon composite material. Repeat the spraying three times after the surface is dry. After drying, place it at 200°C for 3 hours to cure. (4) Using the chemical vapor deposition process, pyrolytic carbon was deposited on the carbon / carbon composite material with a pre-coated surface at 1020°C and a natural gas to argon gas flow ratio of 1:3 for 15 minutes, so that the coating had good bonding strength with the surface of the carbon / carbon composite material.

[0037] The average infrared emissivity of the prepared coating in the 1~22μm band is 0.95. After depositing the pyrolytic carbon coating, the average infrared emissivity in the 1~22μm band is 0.93.

[0038] Example 4 A method for preparing a lightweight porous thermal emissive coating on the surface of a carbon / carbon composite material, the preparation method is as follows: (1) Select porous carbon with a pore size of 2 μm, add 0.8 parts of polyvinyl pyrrolidone and 1.5 parts of silica sol to 15 parts of deionized water, and stir for 20 minutes to obtain a solution for use; (2) adding porous carbon powder to the above solution in portions, 2 parts each time, for a total of 8 times, and preparing a slurry after ultrasonic dispersion; (3) Using an air compressor, spray the slurry evenly onto the surface of the carbon / carbon composite material. Repeat the spraying four times after the surface is dry. After drying, place it at 200°C for 3 hours to cure. (4) Using the chemical vapor deposition process, pyrolytic carbon was deposited on the carbon / carbon composite material with a pre-coated surface at 1070°C and a natural gas to argon gas flow ratio of 1:2 for 35 minutes, so that the coating had good bonding strength with the surface of the carbon / carbon composite material.

[0039] The average infrared emissivity of the prepared coating in the 1~22μm band is 0.97. After depositing the pyrolytic carbon coating, the average infrared emissivity in the 1~22μm band is 0.93.

[0040] Example 5 A method for preparing a lightweight porous thermal emissive coating on the surface of a carbon / carbon composite material, the preparation method is as follows: (1) Select porous carbon with a pore size of 200 nm, add 0.8 parts of polyvinyl pyrrolidone and 1 part of silica sol to 15 parts of deionized water, and stir for 20 minutes to obtain a solution for use; (2) adding porous carbon powder to the above solution in portions, 2 parts each time, for a total of 8 times, and preparing a slurry after ultrasonic dispersion; (3) Using an air compressor, spray the slurry evenly onto the surface of the carbon / carbon composite material. Repeat the spraying twice after the surface is dry. After drying, place the mixture at 200°C for 2.5 hours. (4) Using the chemical vapor deposition process, pyrolytic carbon was deposited on the carbon / carbon composite material with a pre-coated surface at 1060°C and a natural gas to argon gas flow ratio of 1:2.5 for 30 minutes, so that the coating had good bonding strength with the surface of the carbon / carbon composite material.

[0041] The average infrared emissivity of the prepared coating in the 1~22μm band is 0.97. After depositing the pyrolytic carbon coating, the average infrared emissivity in the 1~22μm band is 0.93.

[0042] Comparative Example 1 A method for preparing a lightweight porous thermal emissive coating on the surface of a carbon / carbon composite material, the preparation method is as follows: (1) Select porous carbon with a pore size of 100 nm, add 1.2 parts of sodium dodecylbenzenesulfonate and 1.5 parts of silica sol to 15 parts of deionized water, and stir for 20 minutes to obtain a solution for use; (2) adding porous carbon powder to the above solution in portions, 2 parts each time, for a total of 10 parts, and uniformly dispersing by ultrasonication to obtain a slurry; (3) using air compressor, the slurry is uniformly sprayed to the surface of carbon / carbon composite material, and after the surface is dried, the spraying is repeated 4 times; after drying, it is placed at 200℃ for curing for 3h; (4) using chemical vapor deposition process, the carbon / carbon composite material with pre-coating on the surface is deposited with pyrolytic carbon at 1070℃ under the condition that the flow ratio of natural gas to argon gas is 4:1, and the deposition time is 20min, so that the coating has good bonding force with the surface of carbon / carbon composite material.

[0043] The average infrared emissivity of the prepared coating in the wavelength band of 1-22μm is 0.93, and after the pyrolytic carbon coating is deposited, the average infrared emissivity in the wavelength band of 1-22μm is 0.88.

[0044] Comparative Example 2 The preparation method of the light and porous thermal emission coating on the surface of carbon / carbon composite material is as follows: (1) porous carbon with a pore size of 2μm is selected, 0.8 parts of sodium dodecyl benzene sulfonate and 1.5 parts of silica sol are added to 15 parts of deionized water, and stirring is carried out for 20min to obtain a solution for use; (2) the porous carbon powder is added to the above solution in several times, 2 parts each time, a total of 2 parts, and after ultrasonic dispersion, a slurry is prepared; (3) using air compressor, the slurry is uniformly sprayed to the surface of carbon / carbon composite material, and after the surface is dried, the spraying is repeated 2 times; after drying, it is placed at 200℃ for curing for 3h; (4) using chemical vapor deposition process, the carbon / carbon composite material with pre-coating on the surface is deposited with pyrolytic carbon at 1070℃ under the condition that the flow ratio of natural gas to argon gas is 1:4, and the deposition time is 15min, so that the coating has good bonding force with the surface of carbon / carbon composite material.

[0045] The average infrared emissivity of the prepared coating in the wavelength band of 1-22μm is 0.91, and after the pyrolytic carbon coating is deposited, the average infrared emissivity in the wavelength band of 1-22μm is 0.89.

[0046] Reference Figure 1 and Figure 2In Example 1, the pore size of the porous carbon powder is appropriate, which is conducive to the external propagation of thermal emission, and the deposition of pyrolytic carbon does not cause large-scale sealing, the emissivity does not decrease much, and remains stable. In Comparative Example 1, the pore size of the porous carbon selected is too small. At the nanoscale, too small a pore size will limit the scattering path of thermal emission, thereby reducing the emissivity. In addition, in the process of depositing pyrolytic carbon, due to the small pore size and fast sealing, it is very easy to cause excessive sealing, resulting in a rapid decrease in emissivity, making it difficult to achieve the ideal infrared radiation effect. In Comparative Example 2, due to the low proportion of porous carbon in the slurry and the low number of spraying times, the coating thickness is thinner and the material emissivity is significantly reduced. Therefore, controlling the appropriate coating thickness is more conducive to obtaining excellent infrared radiation effects. refer to Figure 3 The strongest peak of the XRD diffraction pattern of the homemade porous carbon powder is consistent with that of graphite (PDF#41-1487), and no impurity peak appears.

[0047] In summary, the present invention provides a method for preparing a lightweight porous thermal emissive coating on the surface of a carbon / carbon composite material. The core innovation of the present invention lies in overcoming the compatibility problem of high emissivity and strong interface bonding of traditional coatings through the coordinated optimization of the material system and process design. In the specific implementation process, ultra-high specific surface area porous carbon with a three-dimensional interpenetrating network structure is selected as the radiation functional phase, and the composite morphology of its nano-scale pores and micron-scale skeleton is utilized to significantly enhance the surface roughness and light wave scattering effect of the coating; at the same time, silica sol is used as an inorganic binder to form Si-OC chemical bonds between the porous carbon particles through a sol-gel reaction to construct a stable three-dimensional load-bearing framework. Further, a pyrolytic carbon transition layer is gradiently deposited on the surface of the carbon / carbon matrix through chemical vapor deposition (CVD) technology to achieve cross-dimensional bonding of the coating-substrate interface from the nanoscale to the microscale, wherein the crystal structure matching of the pyrolytic carbon and the matrix carbonaceous material significantly reduces the interfacial thermal stress. This technical solution presents three major synergistic advantages: (1) Based on the multi-level pore structure of the porous carbon skeleton and the graphite-like microcrystalline structure formed by CVD modification, a continuous radiation spectrum band is formed in the wide spectral range of 1~22μm, and the average infrared emissivity exceeds 0.93; (2) By constructing a gradient interface system of "porous carbon / silica sol-CVD pyrolytic carbon-matrix", the thermal expansion coefficient of the coating is less different from that of the matrix. Combined with the lightweight porous structure design, the dual needs of weight reduction and thermal shock resistance of aerospace components are achieved; (3) The process path combining sol impregnation and CVD deposition is adopted to avoid the complex high-temperature sintering process, shorten the preparation cycle of a single product, and accurately control the process parameters.

[0048] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the above embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing a lightweight porous thermal emissive coating on the surface of a carbon / carbon composite material, characterized in that: The following steps are involved: The porous carbon powder slurry containing silica sol is evenly sprayed onto the surface of the carbon / carbon composite material matrix and dried; Repeat the spraying and drying until the porous carbon powder slurry evenly covers the substrate surface, thereby obtaining a slurry layer attached to the surface of the carbon / carbon composite material substrate; The slurry layer is cured to obtain a pre-coat layer; The CVD method is used to deposit pyrolytic carbon on the surface of a carbon / carbon composite material with a pre-coating layer to obtain a strong-bonding infrared radiation coating. When depositing the pyrolytic carbon, the carbon source is natural gas and the protective gas is argon.

2. The method for preparing a lightweight porous thermal emissive coating on the surface of a carbon / carbon composite material according to claim 1, characterized in that: The porous carbon powder slurry has the following components in parts by mass: 6-10 parts of porous carbon, 0.8-1.2 parts of dispersant, 1-3 parts of silica sol, and 15-20 parts of deionized water.

3. The method for preparing a lightweight porous thermal emissive coating on the surface of a carbon / carbon composite material according to claim 2, characterized in that: The dispersant is sodium dodecylbenzenesulfonate, polyvinyl pyrrolidone or ammonium polyacrylate.

4. The method for preparing a lightweight porous thermal emissive coating on a carbon / carbon composite material surface according to claim 2, characterized in that: Porous carbon powder is carbonized from phenolic resin, and its pore size is 200nm~5μm.

5. The method for preparing a lightweight porous thermal emissive coating on the surface of a carbon / carbon composite material according to claim 2, characterized in that: When preparing porous carbon powder slurry, the porous carbon powder is added to the dispersant solution several times and ultrasonically dispersed. When adding the porous carbon powder to the dispersant solution, it is necessary to wait until the solution is evenly dispersed before adding the next time.

6. The method for preparing a lightweight porous thermal emissive coating on the surface of a carbon / carbon composite material according to claim 1, characterized in that: After the porous carbon powder slurry is dry, repeat the spraying 1 to 4 times.

7. The method for preparing a lightweight porous thermal emissive coating on the surface of a carbon / carbon composite material according to claim 1, characterized in that: The curing temperature is 200° C. and the curing time is 2 to 3 hours.

8. The method for preparing a lightweight porous thermal emissive coating on the surface of a carbon / carbon composite material according to claim 1, characterized in that: The temperature for depositing pyrolytic carbon is 1020~1070℃, and the deposition time is 15~35min.

9. The method for preparing a lightweight porous thermal emissive coating on the surface of a carbon / carbon composite material according to claim 1, characterized in that: The gas flow ratio of natural gas to argon during the deposition of pyrolytic carbon is 1:1-4.

10. A lightweight porous thermal emission coating on the surface of a carbon / carbon composite material, characterized in that: The method is as described in any one of claims 1 to 9.

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