Graphite felt heat shield and preparation method thereof

Abstract

The invention discloses a graphite felt heat insulation screen and a preparation method thereof, belongs to the technical field of heat insulation material processing, and is used for solving the technical problem that the heat insulation and high-temperature oxidation resistance of a graphite felt heat insulation screen in the prior art need to be further improved. After the fiber cloth is dried, redundant sol is drained off, then the fiber cloth is flatly laid and stacked layer by layer, five-layer stacked fiber cloth is formed, and standing and aging are conducted for 16-18 h. By constructing a high-porosity fiber skeleton, optimizing interface wetting, introducing a multi-component ceramic-carbon composite system and assisting supercritical shape preserving and reductive graphitization treatment, the heat insulation performance of the graphite felt heat insulation screen is effectively improved, the oxidation resistance of the graphite felt heat insulation screen is improved, and the service life of the graphite felt heat insulation screen is prolonged. Therefore, the graphite felt heat insulation screen has stable heat insulation performance at high temperature.

Description

Technical Field

[0001] This invention relates to the field of thermal insulation material processing technology, specifically to a graphite felt thermal insulation screen and its preparation method. Background Technology

[0002] With the rapid development of aerospace, high-temperature equipment, energy batteries, metallurgical industry and high-end thermal equipment, increasingly higher requirements are being placed on the thermal insulation performance, oxidation resistance and structural stability of thermal insulation materials under high-temperature environments. Especially under extreme service conditions above 1000℃, thermal insulation materials not only need to have ultra-low thermal conductivity, but also need to maintain stable structure and performance without deterioration under long-term thermal oxidation to meet the needs of high reliability applications.

[0003] Currently, graphite felt, as a porous lightweight material composed of carbon fiber or graphite fiber, is widely used in vacuum furnaces, high-temperature furnaces, spacecraft thermal protection, and new energy thermal management systems due to its advantages such as low density, high temperature resistance, thermal shock resistance, and low thermal conductivity. However, traditional graphite felt is prone to rapid oxidation and ablation in air or oxygen-containing environments when the temperature exceeds 600-800℃, leading to rapid loss of material mass, structural collapse, and a sharp decline in thermal insulation performance. This severely limits its high-temperature application in non-inert atmospheres. Furthermore, conventional graphite felt is mostly prepared using conventional fiber spreading and carbonization processes, and the pore structure mainly relies on the random stacking of fibers. During subsequent high-temperature heat treatment or use, it is prone to sintering densification or local collapse, resulting in a significant increase in thermal conductivity and making it difficult to maintain a stable thermal insulation effect over a long period of time.

[0004] To address this technical deficiency, a solution is proposed. Summary of the Invention

[0005] The purpose of this invention is to provide a graphite felt heat insulation screen and its preparation method, which solves the technical problem that the heat insulation and high-temperature oxidation resistance of graphite felt heat insulation screens in the prior art need to be further improved.

[0006] The objective of this invention can be achieved through the following technical solution: a method for preparing a graphite felt heat insulation screen, comprising the following steps: S1. Mix tetraethyl orthosilicate, trimethoxyborane, aluminum chloride, yttrium chloride, anhydrous ethanol and purified water until the system is dissolved. Add polydimethylsiloxane to the reaction system, increase the stirring speed, and mix evenly for 10-15 minutes. Add phenolic epoxy resin solution to the reaction system and stir to disperse for 2-3 minutes to obtain a mixed sol. S2. After soaking the activated fiber membrane in the mixed sol for 10-15 seconds, the excess sol is drained off. Then, the membrane is laid flat and stacked layer by layer to form five layers of stacked fiber cloth. The membrane is left to age for 16-18 hours and then processed to obtain the graphite felt precursor. The activated fiber membrane is obtained by activating the porous spun membrane with an activation solution. S3. The graphite felt precursor is calcined to prepare a graphite felt heat insulation screen.

[0007] Furthermore, in step S1, the ratio of the amounts of tetraethyl orthosilicate, trimethoxyborane, aluminum chloride, yttrium chloride, anhydrous ethanol, purified water, polydimethylsiloxane, and phenolic epoxy resin solution is 12-15g:2-3g:4-5g:0.8-1.2g:50mL:8mL:8-9g:14mL, and the phenolic epoxy resin solution is composed of phenolic epoxy resin and anhydrous ethanol at a ratio of 1g:1mL.

[0008] Furthermore, in step S2, the post-processing includes: after static aging, immersing it in anhydrous ethanol at room temperature, replacing the anhydrous ethanol every 12 hours, and after replacing the anhydrous ethanol three times, placing it in a supercritical drying device, setting the temperature to 260-270℃ and the pressure to 9-9.6MPa, and maintaining the temperature and pressure for 2-3 hours to remove the anhydrous ethanol, thereby obtaining the graphite felt precursor.

[0009] Furthermore, the method for preparing the activated fiber membrane is as follows: the porous spun membrane is completely immersed in an activation solution at a temperature of 65-75℃, kept at the temperature for 120-160 minutes, and then post-treated to obtain the activated fiber membrane.

[0010] According to claim 3, a method for preparing a graphite felt heat insulation screen is characterized in that the activation solution is composed of 4-6 mol / L nitric acid solution and 25-28 wt% hydrogen peroxide in a volume ratio of 8:3, and the post-treatment includes: after the reaction is completed, the temperature of the reaction system is lowered to room temperature, the fiber cloth is taken out from the activation solution, washed with purified water until neutral, and then transferred to a drying oven at a temperature of 70-80℃ and dried to constant weight to obtain an activated fiber membrane.

[0011] Furthermore, the porous spun membrane is obtained by the following steps: A1. Mix and stir polyacrylonitrile, polyethylene glycol and N,N-dimethylformamide until dissolved to obtain a spinning solution; A2. Using spinning solution as raw material, after electrospinning, the fiber membrane obtained by electrospinning is taken out from the aluminum foil, cut, and a rectangular electrospun membrane with a thickness of 2-3 mm is prepared. A3. Place the electrospun membrane in purified water at a temperature of 60-70℃ and soak for 10-12 hours. Then, perform post-treatment to obtain a porous spun membrane.

[0012] Furthermore, in step A1, the ratio of polyacrylonitrile, polyethylene glycol, and N,N-dimethylformamide is 5g:1.1-1.3g:50mL.

[0013] Furthermore, in step A2, during the electrospinning process, a roller covered with aluminum foil is used as a receiver, the receiver distance is set to 18-20cm, the spinning voltage is 18-22kV, the diameter of the spinning needle is 0.8-1mm, and the feeding rate of a single spinning needle is 18-20μL / min.

[0014] Furthermore, in step A3, the post-processing includes: after soaking, removing it from the purified water, draining it, transferring it to an oven at a temperature of 70-80℃, and drying it to a constant weight to obtain a porous spun membrane.

[0015] Furthermore, in step S3, the calcination operation includes: placing the graphite felt precursor in a tube furnace protected by a mixed gas atmosphere, heating the tube furnace to 1200-1300℃ at a rate of 5-8℃ / min, holding the temperature for 40-60min, then heating it to 2200-2500℃ at a rate of 3-5℃ / min, holding the temperature for 90-120min, and then naturally cooling it to room temperature to obtain the graphite felt heat insulation screen.

[0016] Furthermore, the mixed gas is composed of argon and carbon monoxide in a volume ratio of 20:1-2.

[0017] The present invention also proposes a graphite felt heat insulation screen, which is prepared by the above-mentioned method for preparing a graphite felt heat insulation screen.

[0018] The present invention has the following beneficial effects: This invention involves electrospinning a compound of polyacrylonitrile and polyethylene glycol, followed by hot water washing to dissolve the polyethylene glycol, forming a highly interconnected microporous structure within the fiber and between fibers. This results in a fiber membrane exhibiting high porosity, multi-scale pore sizes, and highly tortuous heat flow channels on a macroscopic scale. Subsequently, strong oxidation activation not only introduces polar groups such as carboxyl and hydroxyl groups onto the fiber surface, increasing the interfacial bonding with the sol, but also further improves the fiber roughness through slight etching, allowing the sol to fully wet and uniformly adhere, and forming a slightly stabilized structure on the fiber surface. This avoids melt shrinkage during heating, significantly enhancing the stability of the skeleton morphology. As a result, the material can maintain its interconnected pore structure even under subsequent supercritical drying and high-temperature graphitization conditions, laying the structural foundation for maintaining low thermal conductivity across the entire temperature range. This invention also employs tetraethyl orthosilicate, trimethoxyborane, aluminum chloride, and yttrium chloride to construct a multi-component inorganic network containing silicon, boron, aluminum, and yttrium, and introduces polydimethylsiloxane and phenolic epoxy resin as sources of carbon phase for SiOC ceramics and high carbon residue. After hydrolysis, polycondensation, and subsequent graphitization treatment, a borosilicate / aluminoborosilicate glass film with a certain viscosity is formed on the surface of the material in a high-temperature oxidizing atmosphere. The boron element endows the glass phase with good fluidity and self-healing ability, which can seal surface microcracks and pores. Aluminum and yttrium enhance the high-temperature viscosity and stability of the glass phase, inhibiting overall sintering densification. This glass film effectively blocks oxygen from penetrating into the interior, thereby protecting the internal graphite structure and improving its anti-oxidation and thermal insulation properties. Polydimethylsiloxane is transformed into SiOC and free carbon phases during carbonization and graphitization, while phenolic resin provides a high carbon residue, which together with polyacrylonitrile graphitized fibers form a multi-scale graphitized skeleton. This makes the solid phase path continuous but highly tortuous, and the interfacial thermal resistance huge, thereby reducing the thermal conductivity. This invention also ensures the integrity and shape preservation of the composite sol-gel network through supercritical drying, avoiding structural shrinkage caused by capillary forces. Under an atmosphere of argon and carbon monoxide, the polyacrylonitrile fiber and phenolic carbon phase are highly graphitized, forming a graphite-based framework with structural strength. Simultaneously, polydimethylsiloxane decomposes to generate SiOC ceramics and locally free carbon, further increasing the number and complexity of interfaces in the composite framework. The ceramic phase exists in a dispersed neck-like form, connecting the carbon phase in a "point-like" manner, providing necessary mechanical support while avoiding the formation of large-area dense thermal channels, ensuring that the thermal insulation performance remains at a low and stable level even after long-term thermal oxidation. Detailed Implementation

[0019] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0020] In this application, the effective component content of polyacrylonitrile is 99%, the average molecular weight is 85,000, and it is selected from commercially available products of Wuhan Xinyang Ruihe Chemical Technology Co., Ltd. In this application, the polyethylene glycol is PEG-2000, with an effective ingredient content of 99%, and is selected from commercially available products of Shandong Kunbo Biotechnology Co., Ltd. In this application, the phenolic epoxy resin is model F-51, which is selected from commercially available products of Jining Fangyu Chemical Co., Ltd. In this application, polydimethylsiloxane is a dihydroxy silicone oil with an effective ingredient content of 98% and a hydroxyl content of 8.5%, selected from commercially available products of Hubei Langbowan Biomedical Co., Ltd. Example

[0021] This embodiment provides a method for preparing a graphite felt heat insulation screen, specifically including the following steps: Step 1: Preparation of porous spun membrane Polyacrylonitrile, polyethylene glycol and N,N-dimethylformamide were added to a reaction flask at a ratio of 5g:1.1g:50mL and stirred. The temperature of the reaction flask was raised to 80℃ and stirred until the system dissolved. The temperature of the reaction flask was then lowered to room temperature to obtain the spinning solution. Using spinning solution as raw material, after electrospinning, a roller covered with aluminum foil is used as a receiver. The receiver distance is set to 18cm, the spinning voltage is 18kV, the diameter of the spinning needle is 0.8mm, and several spinning needles are set in parallel and fixed. The feed rate of a single spinning needle is set to 18μL / min. Electrospinning is then carried out. After the electrospinning is completed, the fiber membrane obtained by electrospinning is taken out from the aluminum foil, cut, and a rectangular electrospinned membrane with a thickness of 2mm is prepared. The electrospun membrane was placed in purified water at 60℃ and soaked for 10 hours. Then it was taken out of the purified water and drained. After draining, it was transferred to an oven at 70℃ and dried to constant weight to obtain a porous spun membrane.

[0022] In the reaction, polyethylene glycol is used as a pore-forming agent. After electrospinning the spinning solution, it is dissolved by hot water immersion. The porous spun membrane skeleton with high porosity, multi-scale pore size and highly interconnected tortuous channels is constructed by utilizing the phase separation and sacrificial phase dissolution mechanism. This not only significantly reduces the effective solid volume fraction and the continuity of the heat conduction path of the material, laying the structural foundation for the graphite felt heat shield to maintain an ultra-low thermal conductivity in the whole temperature range, but also provides sufficient interfaces and channels for subsequent activation treatment and deep wetting of composite sol. Thus, it can still maintain a stable porous structure and excellent heat insulation performance under high temperature oxidation conditions.

[0023] Step 2: Preparation of activated fiber membrane Mix 4 mol / L nitric acid solution and 25 wt% hydrogen peroxide at a volume ratio of 8:3 to obtain an activation solution; The porous spun membrane was completely immersed in an activation solution at 65°C and kept at that temperature for 120 minutes. The fiber cloth was then removed from the activation solution, and the spun membrane was washed with purified water until neutral. It was then transferred to a drying oven at 70°C and dried to constant weight to obtain the activated fiber membrane.

[0024] In the reaction, the -CN on the surface of the porous spun membrane can be gradually converted into active groups such as amide, carboxyl, and hydroxyl groups by a high-temperature acidic oxidant, which makes it more wettable with the sol (silanol, aluminum alcohol, boron alcohol, phenolic, PDMS end groups). Nitric acid is a strong oxidant that can selectively attack the amorphous regions of polyacrylonitrile fibers to form micro-etching, thereby increasing the surface roughness of the material and significantly enhancing the wetting, adsorption, and chemical bonding of the mixed sol on the fibers, promoting the subsequent formation of a uniform and continuous organic-inorganic composite gel network. The large number of interfaces established by oxidation activation further improves the interfacial thermal resistance and enhances the adhesion and self-healing ability of the glass phase at high temperatures, thus giving the final graphite felt heat insulation screen excellent high-temperature structural stability and ultra-low thermal conductivity.

[0025] Step 3: Prepare the mixed sol Phenolic epoxy resin and anhydrous ethanol were mixed evenly at a ratio of 1g:1mL to obtain a phenolic epoxy resin solution. Weigh out 120g of tetraethyl orthosilicate, 20g of trimethoxyborane, 40g of aluminum chloride, 8g of yttrium chloride, 500mL of anhydrous ethanol, and 80mL of purified water and add them to a reaction flask. Stir until the system is dissolved. Add 80g of polydimethylsiloxane to the reaction flask, increase the stirring speed to 1000rpm, and stir for 10min. Add 140mL of phenolic epoxy resin solution to the reaction flask and stir to disperse for 2min to obtain a mixed sol.

[0026] In the reaction, a multi-component inorganic sol network containing various bonds such as Si-O-Si / BO-Si / Al-O-Si / YO-Si is constructed through hydrolysis-condensation. Polydimethylsiloxane is added to the sol, and the terminal hydroxyl groups of polydimethylsiloxane can undergo condensation association with Si-OH groups in the sol, forming a homogeneous mixed sol under high-speed stirring. The phenolic epoxy resin cross-links and cures with the carboxyl and hydroxyl groups in the sol through hydrogen bonding and van der Waals interactions. The Si, B, Al, and Y multi-component inorganic network transforms into borosilicate, aluminoborosilicate, and Y-doped borosilicate glass phases in a high-temperature oxidizing environment, forming a continuous or quasi-continuous glass film on the material surface, preventing oxygen penetration and thus protecting the internal graphite structure. Polydimethylsiloxane and phenolic resin form an organic-inorganic hybrid sol, which is transformed into a multi-scale composite framework of graphite carbon, SiOC ceramics, and borosilicate / aluminoborosilicate glass during subsequent drying and high-temperature calcination. This creates a microscopic structure with dense interfaces, tortuous paths, and a self-healing protective film, thereby improving the material's thermal insulation performance and excellent oxidation resistance.

[0027] Step 4: Preparation of graphite felt precursor After immersing the activated fiber membrane in the mixed sol for 10 seconds, excess sol was drained off. The membrane was then laid flat and stacked layer by layer, with an overlap of 3 mm between adjacent activated fiber membranes in the same layer. When laying the upper activated fiber membrane, its body covered the overlap seam between the lower activated fiber membranes, forming a five-layer stacked fiber cloth. After static aging for 16 hours, the membrane was immersed in anhydrous ethanol. At room temperature, the anhydrous ethanol was replaced every 12 hours. After three replacements of anhydrous ethanol, the membrane was placed in a supercritical drying device with a temperature of 260℃ and a pressure of 9MPa for 2 hours. The anhydrous ethanol was then removed to obtain the graphite felt precursor.

[0028] In the reaction, a continuous and uniform organic-inorganic hybrid gel network is constructed on the surface and inside the pores of the activated fiber membrane through sol impregnation, overlapping and stacking, gel aging, ethanol replacement and supercritical drying processes. The network is intact and retains its shape under conditions without capillary force damage, thereby forming a graphite felt precursor with high porosity, high specific surface area and multi-scale interconnected pore structure. In the subsequent high-temperature graphitization, the precursor can be transformed into a dispersed support framework composed of graphite carbon, SiOC ceramics and multi-component borosilicate glass, which provides the necessary mechanical strength, avoids the formation of dense thermal conductive channels, and forms a continuous self-healing protective film in an oxidizing environment, thereby improving the thermal insulation performance and high-temperature oxidation resistance of the material.

[0029] Step 5: Prepare graphite felt heat insulation screen Argon and carbon monoxide were mixed at a volume ratio of 20:1 to obtain a mixed gas. The graphite felt precursor was placed in a tube furnace under mixed gas atmosphere protection. The tube furnace was heated to 1200℃ at a rate of 5℃ / min and held for 40min. Then, it was heated to 2200℃ at a rate of 3℃ / min and held for 90min. The furnace was then allowed to cool naturally to room temperature to obtain the graphite felt heat insulation screen.

[0030] In the reaction, the graphite felt precursor obtained by supercritical drying is subjected to staged heating and calcination in a mixed atmosphere of argon and carbon monoxide. This process achieves deep carbonization and high graphitization of the fiber matrix and phenolic resin, SiOC ceramization of polydimethylsiloxane, and glass network rearrangement of multi-component oxides derived from tetraethyl orthosilicate, trimethoxyboron, alkylaluminum chloride, and yttrium chloride. The reducing CO atmosphere removes residual active oxygen in the system, inhibits oxidative damage to the carbon skeleton during heating, and promotes the orderly growth of graphite grains. On the other hand, it avoids excessive densification of the multi-component oxides at high temperatures, thereby maintaining the high porosity and multi-scale pore structure of the gel skeleton. After this process, a multiphase composite framework is formed inside the material, consisting of a highly graphitized carbon skeleton, a diffusely distributed SiOC ceramic, and a glass phase characterized by silicon-boron-aluminum-yttrium. The ceramic and glass phases provide point support and passivation for the carbon phase in the form of dispersed necks, which not only ensures the necessary mechanical strength of the material but also avoids the formation of large-area dense thermal conductive channels. During subsequent oxidation service, a self-healing adhesive glass protective film is generated on the surface, which effectively blocks oxygen from penetrating into the interior and improves the material's thermal insulation performance and high-temperature oxidation resistance. Example

[0031] This embodiment provides a method for preparing a graphite felt heat insulation screen, specifically including the following steps: Step 1: Preparation of porous spun membrane Polyacrylonitrile, polyethylene glycol and N,N-dimethylformamide were added to a reaction flask at a ratio of 5g:1.2g:50mL and stirred. The temperature of the reaction flask was raised to 85℃ and stirred until the system dissolved. The temperature of the reaction flask was then lowered to room temperature to obtain the spinning solution. Using spinning solution as raw material, after electrospinning, a roller covered with aluminum foil is used as a receiver. The receiver distance is set to 19 cm, the spinning voltage is 20 kV, the diameter of the spinning needle is 0.9 mm, and several spinning needles are set in parallel and fixed. The feed rate of a single spinning needle is set to 19 μL / min. Electrospinning is then carried out. After the electrospinning is completed, the fiber membrane obtained by electrospinning is taken out from the aluminum foil, cut, and a rectangular electrospinned membrane with a thickness of 2.5 mm is prepared. The electrospun membrane was placed in purified water at 65°C and soaked for 1 hour. Then it was removed from the purified water and drained. After draining, it was transferred to an oven at 75°C and dried to constant weight to obtain a porous spun membrane.

[0032] Step 2: Preparation of activated fiber membrane Mix 5 mol / L nitric acid solution and 27 wt% hydrogen peroxide at a volume ratio of 8:3 to obtain an activation solution; The porous spun membrane was completely immersed in an activation solution at 70°C and kept at that temperature for 140 minutes. The fiber cloth was then removed from the activation solution, and the spun membrane was washed with purified water until neutral. It was then transferred to a drying oven at 75°C and dried to constant weight to obtain the activated fiber membrane.

[0033] Step 3: Prepare the mixed sol Phenolic epoxy resin and anhydrous ethanol were mixed evenly at a ratio of 1g:1mL to obtain a phenolic epoxy resin solution. Weigh out 135g of tetraethyl orthosilicate, 25g of trimethoxyborane, 45g of aluminum chloride, 10g of yttrium chloride, 500mL of anhydrous ethanol and 80mL of purified water and add them to a reaction flask. Stir until the system is dissolved. Add 85g of polydimethylsiloxane to the reaction flask, increase the stirring speed to 1100rpm, and stir for 13min. Add 140mL of phenolic epoxy resin solution to the reaction flask and stir to disperse for 2.5min to obtain a mixed sol.

[0034] Step 4: Preparation of graphite felt precursor After immersing the activated fiber membrane in the mixed sol for 13 seconds, excess sol was drained off. The membrane was then laid flat and stacked layer by layer, with an overlap of 4 mm between adjacent activated fiber membranes in the same layer. When laying the upper activated fiber membrane, its body covered the overlap seam between the lower activated fiber membranes, forming a five-layer stacked fiber cloth. After static aging for 17 hours, the membrane was immersed in anhydrous ethanol. At room temperature, the anhydrous ethanol was replaced every 12 hours. After three replacements of anhydrous ethanol, the membrane was placed in a supercritical drying device at a temperature of 265℃ and a pressure of 9.3 MPa for 2.5 hours. The anhydrous ethanol was then removed to obtain the graphite felt precursor.

[0035] Step 5: Prepare graphite felt heat insulation screen Argon and carbon monoxide were mixed at a volume ratio of 20:1.5 to obtain a mixed gas. The graphite felt precursor was placed in a tube furnace under mixed gas atmosphere protection. The tube furnace was heated to 1250℃ at a rate of 6.5℃ / min and held for 50 min. Then, it was heated to 2350℃ at a rate of 4℃ / min and held for 105 min. The furnace was then allowed to cool naturally to room temperature to obtain the graphite felt heat insulation screen. Example

[0036] This embodiment provides a method for preparing a graphite felt heat insulation screen, specifically including the following steps: Step 1: Preparation of porous spun membrane Polyacrylonitrile, polyethylene glycol and N,N-dimethylformamide were added to a reaction flask at a ratio of 5g:1.3g:50mL and stirred. The temperature of the reaction flask was raised to 90℃ and stirred until the system dissolved. The temperature of the reaction flask was then lowered to room temperature to obtain the spinning solution. Using spinning solution as raw material, after electrospinning, a roller covered with aluminum foil is used as a receiver. The receiver distance is set to 20cm, the spinning voltage is 22kV, the diameter of the spinning needle is 1mm, and several spinning needles are set in parallel and fixed. The feed rate of a single spinning needle is set to 20μL / min. Electrospinning is then carried out. After the electrospinning is completed, the fiber membrane obtained by electrospinning is taken out from the aluminum foil, cut, and a rectangular electrospinned membrane with a thickness of 3mm is prepared. The electrospun membrane was placed in purified water at 70℃ and soaked for 12 hours. Then it was taken out of the purified water and drained. After draining, it was transferred to an oven at 80℃ and dried to constant weight to obtain a porous spun membrane.

[0037] Step 2: Preparation of activated fiber membrane Mix 6 mol / L nitric acid solution and 28 wt% hydrogen peroxide at a volume ratio of 8:3 to obtain an activation solution; The porous spun membrane was completely immersed in an activation solution at 75°C and kept at that temperature for 160 minutes. The fiber cloth was then removed from the activation solution and washed with purified water until neutral. The membrane was then transferred to a drying oven at 80°C and dried to constant weight to obtain the activated fiber membrane.

[0038] Step 3: Prepare the mixed sol Phenolic epoxy resin and anhydrous ethanol were mixed evenly at a ratio of 1g:1mL to obtain a phenolic epoxy resin solution. Weigh out 150g of tetraethyl orthosilicate, 30g of trimethoxyborane, 50g of aluminum chloride, 12g of yttrium chloride, 500mL of anhydrous ethanol, and 80mL of purified water and add them to a reaction flask. Stir until the system is dissolved. Add 90g of polydimethylsiloxane to the reaction flask, increase the stirring speed to 1200rpm, and stir for 15min. Add 140mL of phenolic epoxy resin solution to the reaction flask and stir for 3min to obtain a mixed sol.

[0039] Step 4: Preparation of graphite felt precursor After immersing the activated fiber membrane in the mixed sol for 15 seconds, excess sol was drained off. The membrane was then laid flat and stacked layer by layer, with an overlap of 5 mm between adjacent activated fiber membranes in the same layer. When laying the upper activated fiber membrane, its body covered the overlap seam between the lower activated fiber membranes, forming a five-layer stacked fiber cloth. After static aging for 18 hours, the membrane was immersed in anhydrous ethanol. At room temperature, the anhydrous ethanol was replaced every 12 hours. After three replacements of anhydrous ethanol, the membrane was placed in a supercritical drying device with a temperature of 270℃ and a pressure of 9.6 MPa for 3 hours. The anhydrous ethanol was then removed to obtain the graphite felt precursor.

[0040] Step 5: Prepare graphite felt heat insulation screen Argon and carbon monoxide were mixed at a volume ratio of 20:2 to obtain a mixed gas. The graphite felt precursor was placed in a tube furnace under mixed gas atmosphere protection. The tube furnace was heated to 1300℃ at a rate of 8℃ / min and held for 60min. Then, it was heated to 2500℃ at a rate of 5℃ / min and held for 120min. The furnace was then allowed to cool naturally to room temperature to obtain the graphite felt heat insulation screen.

[0041] Comparative Example 1 The difference between this comparative example and Example 3 is that polyethylene glycol was not added in step 1.

[0042] Comparative Example 2 The difference between this comparative example and Example 3 is that step 2 is omitted, and the porous spun membrane prepared in step 1 is used instead of the activated fiber membrane in step 4.

[0043] Comparative Example 3 The difference between this comparative example and Example 3 is that polydimethylsiloxane was not added in step 3.

[0044] Comparative Example 4 The difference between this comparative example and Example 3 is that carbon monoxide was not added to the mixed gas in step 5.

[0045] Performance testing: The graphite felt heat insulation screen samples prepared in Examples 1-3 and Comparative Examples 1-4 were thermally oxidized for 100 h at temperatures of 200℃, 500℃, 800℃, 1000℃, and 1200℃, respectively, and the thermal conductivity of the samples was measured. The thermal conductivity of the samples was determined in accordance with the standard GB / T 5990-2021 "Test methods for thermal conductivity, specific heat capacity and thermal diffusivity of refractory materials (hot wire method)". The specific test data are shown in Table 1 below.

[0046] Table 1 - Performance Test Data of Samples

[0047] Data Analysis: Comparative analysis of the data in Table 1 shows that the thermal conductivity of the graphite felt heat insulation screen sample prepared in this invention reaches 0.050-0.052 W / (m·K) after thermal oxidation at 200℃ for 100 h; 0.058-0.061 W / (m·K) after thermal oxidation at 500℃ for 100 h; 0.082-0.085 W / (m·K) after thermal oxidation at 800℃ for 100 h; and 0.102-0.1 W / (m·K) after thermal oxidation at 1000℃ for 100 h. The thermal conductivity reached 0.129-0.132 W / (m·K) after thermal oxidation at 1200℃ for 100 h. All performance test data were better than those of the comparative example. This indicates that the present invention, by constructing a high-porosity fiber skeleton, optimizing interface wetting, introducing a multi-component ceramic-carbon composite system, and supplementing it with supercritical conformal and reducing graphitization treatment, not only effectively improved the thermal insulation performance of the graphite felt heat insulation screen, but also improved its oxidation resistance, so that the graphite felt heat insulation screen exhibits stable thermal insulation performance at high temperatures.

[0048] The preferred embodiments of the present invention disclosed above are merely illustrative of the invention. These preferred embodiments do not exhaustively describe all details, nor do they limit the invention to specific implementations. Clearly, many modifications and variations can be made based on the content of this specification. This specification selects and specifically describes these embodiments to better explain the principles and practical applications of the invention, thereby enabling those skilled in the art to better understand and utilize the invention. The invention is limited only by the claims and their full scope and equivalents.

Claims

1. A method for preparing a graphite felt heat insulation screen, characterized in that, Includes the following steps: S1. Mix tetraethyl orthosilicate, trimethoxyborane, aluminum chloride, yttrium chloride, anhydrous ethanol and purified water until the system is dissolved. Add polydimethylsiloxane to the reaction system, increase the stirring speed, and mix evenly for 10-15 minutes. Add phenolic epoxy resin solution to the reaction system and stir to disperse for 2-3 minutes to obtain a mixed sol. S2. After soaking the activated fiber membrane in the mixed sol for 10-15 seconds, the excess sol is drained off. Then, the membrane is laid flat and stacked layer by layer to form five layers of stacked fiber cloth. The membrane is left to age for 16-18 hours and then processed to obtain the graphite felt precursor. The activated fiber membrane is obtained by activating the porous spun membrane with an activation solution. S3. The graphite felt precursor is calcined to prepare a graphite felt heat insulation screen.

2. The method for preparing a graphite felt heat insulation screen according to claim 1, characterized in that, In step S1, the ratio of tetraethyl orthosilicate, trimethoxyborane, aluminum chloride, yttrium chloride, anhydrous ethanol, purified water, polydimethylsiloxane, and phenolic epoxy resin solution is 12-15g:2-3g:4-5g:0.8-1.2g:50mL:8mL:8-9g:14mL, and the phenolic epoxy resin solution is composed of phenolic epoxy resin and anhydrous ethanol at a ratio of 1g:1mL. In step S2, the post-treatment includes: after static aging, immersing it in anhydrous ethanol at room temperature, replacing the anhydrous ethanol every 12 hours, and after three replacements, placing it in a supercritical drying device, setting the temperature to 260-270℃ and the pressure to 9-9.6MPa, and maintaining the temperature and pressure for 2-3 hours to remove the anhydrous ethanol, thereby obtaining the graphite felt precursor.

3. The method for preparing a graphite felt heat insulation screen according to claim 1, characterized in that, The method for preparing activated fiber membrane is as follows: the porous spun membrane is completely immersed in an activation solution at a temperature of 65-75℃, kept at the temperature for 120-160 minutes, and then post-treated to obtain activated fiber membrane.

4. The method for preparing a graphite felt heat insulation screen according to claim 3, characterized in that, The activation solution is composed of 4-6 mol / L nitric acid solution and 25-28 wt% hydrogen peroxide in a volume ratio of 8:

3. The post-treatment includes: after the reaction is completed, the temperature of the reaction system is reduced to room temperature, the fiber cloth is taken out from the activation solution, washed with purified water until neutral, and then transferred to a drying oven at a temperature of 70-80℃ and dried to constant weight to obtain the activated fiber membrane.

5. The method for preparing a graphite felt heat insulation screen according to claim 1, characterized in that, Porous spun membranes are obtained by the following steps: A1. Mix and stir polyacrylonitrile, polyethylene glycol and N,N-dimethylformamide until dissolved to obtain a spinning solution; A2. Using spinning solution as raw material, after electrospinning, the fiber membrane obtained by electrospinning is taken out from the aluminum foil, cut, and a rectangular electrospun membrane with a thickness of 2-3 mm is prepared. A3. Place the electrospun membrane in purified water at a temperature of 60-70℃ and soak for 10-12 hours. Then, perform post-treatment to obtain a porous spun membrane.

6. The method for preparing a graphite felt heat insulation screen according to claim 5, characterized in that, In step A1, the ratio of polyacrylonitrile, polyethylene glycol, and N,N-dimethylformamide is 5g:1.1-1.3g:50mL; in step A2, during the electrospinning process, a roller covered with aluminum foil is used as a receiver, the receiver distance is set to 18-20cm, the spinning voltage is 18-22kV, the diameter of the spinning needle is 0.8-1mm, and the feed rate of a single spinning needle is 18-20μL / min; in step A3, the post-treatment includes: after soaking, removing it from the purified water, draining it, transferring it to an oven at a temperature of 70-80℃, and drying it to constant weight to obtain a porous spun membrane.

7. The method for preparing a graphite felt heat insulation screen according to claim 1, characterized in that, In step S3, the calcination operation includes: placing the graphite felt precursor in a tube furnace protected by a mixed gas atmosphere, heating the tube furnace to 1200-1300℃ at a rate of 5-8℃ / min, holding the temperature for 40-60min, then heating it to 2200-2500℃ at a rate of 3-5℃ / min, holding the temperature for 90-120min, and then naturally cooling it to room temperature to obtain the graphite felt heat insulation screen.

8. The method for preparing a graphite felt heat insulation screen according to claim 7, characterized in that, The mixed gas consists of argon and carbon monoxide in a volume ratio of 20:1-2.

9. A graphite felt heat insulation screen, characterized in that, The graphite felt heat insulation screen is prepared using the preparation method of a graphite felt heat insulation screen as described in any one of claims 1-8.

Images