A high-temperature resistant carbon fiber electric heating felt and its preparation method and application

Abstract

The present invention belongs to the technical field of electric heating materials, and relates to a high-temperature resistant carbon fiber electric heating felt, and its preparation method and application. The preparation process of the high-temperature resistant carbon fiber electric heating felt is as follows: by impregnating the carbon fiber felt with an inorganic nanopowder composite emulsion and performing high-temperature heat treatment, a nano lining layer is formed on the surface of the carbon fiber; then a silicon oxide-aluminum oxide-titanium oxide composite sol is prepared, and the silanized composite powder is dispersed into the sol, and finally, the nanoparticles in the sol are self-assembled on the surface of the carbon fiber lining layer and densified by heat treatment to form a dense composite coating on the surface of the carbon fiber. Compared with the prior art, the carbon fiber electric heating felt of the present invention has excellent high-temperature antioxidant properties. While maintaining the original light weight, flexibility, stable conductive properties and high emissivity, the upper limit of the electric heating application temperature is increased to 600°C, significantly expanding its application range in the electric heating field.

Description

Technical Field

[0001] The present invention belongs to the technical field of electric heating materials, and in particular relates to a high-temperature resistant carbon fiber electric heating felt and a preparation method and application thereof. Background Art

[0002] As a high-performance fiber material, carbon fiber has been widely used in numerous fields due to its advantages, such as light weight, flexibility, high-temperature resistance, and high tensile strength. In recent years, it has been discovered that the application of carbon fiber in the manufacture of electric heating elements can fully utilize its outstanding performance advantages, showing broad application prospects in the field of electric heating. Compared with traditional metal heating elements, carbon fiber electric heating elements can improve the electric-to-heat conversion efficiency by over 20%, significantly improving energy utilization efficiency. Furthermore, carbon fiber has excellent infrared radiation properties, with an infrared emissivity of 0.8-0.95, which effectively emits infrared electromagnetic waves. In low-temperature civilian applications such as electric blankets and physical therapy devices, it can provide gentle and comfortable radiant heat to the human body. In industrial production, the high infrared emissivity means that carbon fiber electric heating elements can transfer more heat to the workpiece or the environment in the form of radiation. Compared with heat transfer through conduction and convection, this radiant heating method is more efficient and uniform, making it very beneficial for high-temperature processes requiring precise temperature control. Furthermore, carbon fiber electric heating elements have the advantages of fast response time, which can quickly convert electrical energy into heat energy, achieve rapid temperature rise, significantly shorten heating time, and improve production and application efficiency.

[0003] However, the initial oxidation temperature of carbon fiber is around 400°C. When the temperature exceeds 500°C, a violent oxidation reaction will occur, causing its mechanical strength and electrical conductivity to drop sharply, severely limiting the operating temperature range of the carbon fiber electric heating element, making it unable to work stably in a high-temperature aerobic environment. In order to solve this problem, researchers have developed carbon fiber electric heating tubes, which isolate oxygen by placing the carbon fiber heating element in a vacuum or a quartz tube filled with inert gas. Although this method ensures that the carbon fiber electric heating element can generate heat stably under high temperature conditions, the presence of the quartz tube not only hinders heat transfer, but also sacrifices the advantages of carbon fiber itself, such as lightness and flexibility, limiting its application scenarios. Therefore, it is of great significance and practical value to develop a carbon fiber electric heating element that can work in a high-temperature aerobic environment while retaining the characteristics of lightness and flexibility and without adding additional thermal resistance.

[0004] Patent CN105645962B provides a method for preparing a high-temperature resistant, oxidation-resistant, and thermally conductive carbon fiber / silicon carbide composite material: immersing a carbon fiber fabric in an Fe(NO3)3 solution and drying it; placing the catalyst-loaded carbon fiber fabric in a tube furnace; introducing Ar and H2; then introducing a carbon source to obtain a carbon fiber fabric with carbon nanotubes after growth; stacking 4-8 layers of carbon fiber fabric and immersing them in a xylene solution of polycarbosilane; after immersing them under negative pressure, removing the carbon fiber fabric stack and drying it to form a block; oxidizing it in a muffle furnace for 1-2 hours; placing the block in a tube furnace, introducing Ar and heating it to 1200°C, and then cooling it to obtain a high-temperature resistant, oxidation-resistant, and thermally conductive carbon fiber / silicon carbide composite material. However, the conductivity and flexibility of the composite material obtained in this patent are both reduced to varying degrees compared to the original carbon fiber fabric. Patent CN115262218B provides a method for preparing high-temperature resistant and oxidation-resistant carbon fibers, including the process steps of carbon fiber surface treatment, atomic layer deposition of an antioxidant layer, and high-temperature oxygen-free annealing, to obtain carbon fibers with a high-temperature resistant and oxidation-resistant film deposited on the surface. The high-temperature resistant and oxidation-resistant film on the surface of the carbon fibers is compounded with different components and structurally designed. By preferentially depositing silicon atoms, a silicon carbide interface layer is formed between the carbon fibers and the antioxidant film, and the bonding force between the two is enhanced by chemical bonds; silicon oxide layers and aluminum oxide layers are alternately deposited, and the number of aluminum oxide deposition layers varies periodically, forming a denser, void-free membrane structure, thereby improving the high-temperature resistance and oxidation resistance of the carbon fibers; and the thickness of the antioxidant film layer is at the nanometer and micrometer level, ensuring the softness of the carbon fibers. However, the dense coating of this patent hinders the conduction of electrons between fibers, reducing the electrical conductivity. Summary of the Invention

[0005] The purpose of the present invention is to overcome the problems existing in the above-mentioned prior art and to provide a high-temperature resistant carbon fiber electric heating felt and its preparation method and application. The carbon fiber electric heating felt has excellent high-temperature resistance while ensuring light weight, flexibility, good conductivity and high emissivity.

[0006] The purpose of the present invention can be achieved by the following technical solutions:

[0007] The present invention provides a method for preparing a high-temperature resistant carbon fiber electric heating felt, comprising the following steps:

[0008] S1, mixing silicon oxide, titanium oxide, silicon carbide, and titanium carbide nanopowders in a mass ratio of (0.5-2): (0.5-2): (0.5-2): (0.5-2) to obtain a mixed nanopowder, then adding water, a coupling agent, a thickener, and a dispersant, and shearing and stirring to obtain a nanocomposite emulsion,

[0009] In step S1, the mass ratio of water to mixed nanopowder is 1:1 to 3:1, the mass of the coupling agent is 1 to 5% of the total mass of the water and mixed nanopowder, the mass of the thickener is 5 to 15% of the total mass of the water and mixed nanopowder, and the mass of the dispersant is 1 to 3% of the total mass of the water and mixed nanopowder;

[0010] S2, Preparation of Carbon Fiber Felt Nanocomposite Lining Layer:

[0011] S2-1, immersing the carbon fiber felt in concentrated nitric acid at 75° C. for oxidation activation for 3 to 8 hours, washing with water, and then drying to obtain an activated carbon fiber felt;

[0012] S2-2, immersing the activated carbon fiber felt obtained in step S2-1 into the nanocomposite emulsion obtained in step S1, heating to 50-60° C., and ultrasonically treating for 30 minutes at an ultrasonic power of 50-100 W and a frequency of 20-60 kHz;

[0013] S2-3, taking out the carbon fiber felt treated in step S2-2, drying it at 60-80°C for 1-3 hours, and then performing a heat treatment. The heat treatment conditions are: nitrogen atmosphere, heating rate of 3-5°C / min, heating to 1300-1600°C, keeping the temperature for 2-3 hours, and cooling naturally;

[0014] S2-4, heating the carbon fiber felt treated in step S2-3 to 50-60° C., and ultrasonically cleaning the felt for 0.5-3 hours at an ultrasonic power of 80-120 W and a frequency of 30-80 kHz to obtain a carbon fiber felt with a nanocomposite lining layer coated on the fiber surface;

[0015] S3, silanization treatment of the carbon fiber felt: immersing the carbon fiber felt with the nanocomposite liner coated on the fiber surface obtained in step S2-4 in water, and then adding a coupling agent with a mass of 1-3% of the mass of water and an organic silane with a mass of 1-3% of the mass of water, stirring thoroughly, and then standing for 20-30 hours. The mixture is taken out and dried to obtain a carbon fiber felt with a silanized fiber surface;

[0016] S4, silanization treatment of the emissivity-enhancing powder: fully stir water, emissivity-enhancing powder, coupling agent, and organosilane in a mass ratio of 100:(5-15):(1-3):(1-3), let stand for 20-30 hours, take out, and dry to obtain a silanized emissivity-enhancing powder;

[0017] S5, silanization treatment of the conductive enhancing powder: fully stir water, conductive enhancing powder, coupling agent, and organosilane in a mass ratio of 100:(5-15):(1-3):(1-3), let stand for 20-30 hours, take out, and dry to obtain silanized conductive enhancing powder;

[0018] S6, preparation of silicon oxide-aluminum oxide-titania composite sol:

[0019] S6-1, uniformly mixing a silicon oxide precursor, an aluminum oxide precursor, and a titanium oxide precursor in a molar ratio of (2-3): (1-1.5): (1-1.5), then adding anhydrous ethanol in a ratio of anhydrous ethanol volume to the total volume of the precursors = (2:1) to (3:1), and mixing thoroughly to obtain a precursor mixed solution;

[0020] S6-2, slowly adding water dropwise to the precursor mixed solution prepared in step S6-1 while stirring, wherein the molar ratio of the total amount of precursor to the added water is 3:1 to 4:1;

[0021] S6-3, adjusting the pH of the solution obtained in step S6-2 to 5-6 with glacial acetic acid, aging at room temperature to 60° C. for 20-30 hours to obtain a silicon oxide-aluminum oxide-titania composite sol;

[0022] S7, outer coating self-assembly step:

[0023] S7-1, dispersing the silanized emissivity enhancing powder obtained in step S4 and the silanized conductivity enhancing powder obtained in step S5 in the silica-alumina-titania composite sol obtained in step S6-3, wherein the mass ratio of the silanized emissivity enhancing powder, the silanized conductivity enhancing powder, and the silica-alumina-titania composite sol is (2-5):1:(3-10). After thorough stirring, the carbon fiber felt with silanized fiber surface obtained in step S3 is added thereto, and the mixture is reacted for 1-3 days under slow stirring.

[0024] S7-2, during the reaction process, 5 g of a 3-5 wt.% aqueous solution of an alkali metal carbonate was added dropwise every 6-8 hours. After the reaction, the pH of the reaction system was adjusted to 8-12 with 5-20 wt.% aqueous ammonia. The carbon fiber felt was then taken out, rinsed 1-2 times with anhydrous ethanol, and dried at 60-80° C. for 2 hours to obtain a carbon fiber felt with a surface self-assembled outer layer coating.

[0025] S8, densification of the self-assembled outer coating: heat-treat the carbon fiber felt with the surface self-assembled outer coating obtained in step S7-2 under the following conditions: nitrogen atmosphere, heating to 800-1200°C at 3-10°C / min, keeping warm for 1-3h, and naturally cooling to obtain a high-temperature resistant carbon fiber electric heating felt with a double-layer coating on the fiber surface.

[0026] Furthermore, in step S1, the particle size of the silicon oxide, titanium oxide, silicon carbide, and titanium carbide nanopowders is in the range of 20 nm to 80 nm.

[0027] The silicon oxide, titanium oxide, silicon carbide and titanium carbide nanopowders are ball-milled to obtain mixed nanopowders. The ball milling speed is 200 r / min to 500 r / min and the ball milling time is 0.5 h to 3 h.

[0028] The coupling agent is selected from at least one of KH550, KH560 or KH570,

[0029] The thickener is selected from at least one of sodium carboxymethyl cellulose, polyacrylic acid or sodium alginate,

[0030] The dispersant is selected from at least one of polyacrylamide and sodium lauryl sulfate,

[0031] The shear stirring has a rotation speed of 600 r / min to 1500 r / min and a time of 0.5 h to 1 h.

[0032] Furthermore, in step S2-1, the carbon fiber felt is selected from at least one of polyacrylonitrile-based carbon fiber felt, asphalt-based carbon fiber felt or viscose-based carbon fiber felt, and the thickness of the carbon fiber felt is 0.2 to 50 mm.

[0033] Furthermore, in steps S3, S4, and S5, the coupling agent is selected from at least one of KH550, KH560, and KH570, and the organosilane is selected from at least one of ethyl orthosilicate and methyl orthosilicate.

[0034] Furthermore, in step S4, the emissivity enhancing powder is selected from at least one of silicon carbide and aluminum oxide.

[0035] Furthermore, in step S5, the conductive reinforcing powder is selected from at least one of titanium carbide and zirconium boride.

[0036] Furthermore, in step S6-1, the silicon oxide precursor is selected from at least one of ethyl silicate or methyl silicate, the aluminum oxide precursor is aluminum isopropoxide, and the titanium oxide precursor is selected from at least one of titanium tetrachloride or tetrabutyl titanate.

[0037] Furthermore, in step S7-2, the alkali metal carbonate aqueous solution is selected from at least one of a lithium carbonate aqueous solution, a sodium carbonate aqueous solution or a potassium carbonate aqueous solution.

[0038] On the other hand, the present invention also provides a high-temperature resistant carbon fiber electric heating felt prepared by the above preparation method.

[0039] In a third aspect, the present invention also provides for the application of the high-temperature-resistant carbon fiber electric heating felt prepared above in the field of electric heating. The resulting carbon fiber electric heating felt, with enhanced high-temperature resistance based on a double-layer coating, maintains its original lightweight, flexible, stable electrical conductivity, and high emissivity while achieving an initial oxidation temperature >650°C, raising the upper temperature limit for electric heating applications to 600°C. This significantly expands its application range in the electric heating field and can be applied to electric heating applications with a temperature limit of approximately 600°C, such as industrial heating, special material processing, and high-temperature experimental equipment. It has excellent application prospects and economic benefits.

[0040] Compared with the prior art, the present invention has the following beneficial effects:

[0041] (1) Resistant to high-temperature oxidation and suitable for high-temperature electric heating applications: The present invention provides a high-temperature resistant carbon fiber electric heating felt that can withstand high temperatures of 600°C. Its carbon fibers are not oxidized and are stably conductive. This is because the surface of the carbon fiber has been subjected to high-temperature heat treatment and is pre-coated with a layer of nano-lining layer. The nano-lining layer forms strong Si-C bonds and Ti-C bonds with the carbon fiber surface, changing the originally smooth and inert carbon fiber surface into a rough and active nano-lining, which is conducive to the uniform adhesion of the subsequent coating; at the same time, the subsequent long-term impregnation process allows nanoparticles such as silicon carbide, aluminum oxide, titanium carbide, and zirconium boride to be uniformly self-assembled on the carbon fiber surface coated with the nano-lining, which not only ensures the uniform coating of the coating, but also avoids the generation of excess sol bonding between the fibers. In addition, the periodic addition of an alkali metal carbonate aqueous solution can introduce alkali metal elements into the coating as a flux, allowing the nano-coating to densify during the subsequent heat treatment process. In summary, the modification of the nano-liner, the promotion of the self-assembly process, and the introduction of alkali metal elements enable the outer coating to evenly cover the surface of each carbon fiber and densely isolate oxygen, providing a structural basis for the use of carbon fiber electric heating felt at high temperatures of 600°C.

[0042] (2) High emissivity and good conductivity: The present invention provides a high-temperature resistant carbon fiber electric heating felt, which is characterized in that nanoparticles such as silicon carbide, aluminum oxide, titanium carbide, and zirconium boride in the mixed sol are self-assembled on the surface of the carbon fiber to form an outer coating, and the unique properties of these nanoparticles are fully utilized to effectively ensure the overall conductivity and radiation characteristics of the carbon fiber electric heating felt. First, silicon carbide and aluminum oxide with high infrared radiation emissivity are selected as emissivity enhancement powders to weaken the negative impact of the dense coating itself on the infrared emissivity of the carbon fiber felt; then, conductive nanopowders such as titanium carbide and zirconium boride are added as conductive enhancement powders to construct a conductive network in the dense coating, ensuring the overall high conductivity of the carbon fiber electric heating felt. In addition, silanization treatment is performed on the surface of the nanoparticles and the carbon fiber to improve the interface bonding between them, so that the nanoparticles can form a uniform and stable self-assembled nanocoating on the surface of the carbon fiber. Finally, the densification of the coating provides good coating and fixation for the emissivity enhancement powder and the conductivity enhancement powder. The synergistic effect of these mechanisms enables the carbon fiber electric heating felt to maintain stable electrical conductivity and high emissivity under the coverage of dense coating.

[0043] (3) Lightweight and flexible: The present invention provides a carbon fiber electric heating felt with enhanced high temperature resistance based on a double-layer coating, which retains the lightness and flexibility of the original carbon fiber electric heating felt after being coated. First, in the preparation process, inorganic powders below 100nm are mainly used. Through the self-assembly process, nanoparticles can be evenly and stably attached to the surface of the carbon fiber, avoiding local excessive aggregation or accumulation. The thickness of the coating can be effectively controlled, and the thickest position does not exceed 0.5 microns. This thinner coating structure will not have a significant impact on the intrinsic lightness and flexibility of the carbon fiber electric heating felt. In addition, during the composite sol reaction process, by periodically adding an alkali metal carbonate aqueous solution, the pH value of the coating can be adjusted, promoting the condensation reaction of the oxide gel, further optimizing the density and continuity of the coating, and ensuring the uniformity of the coating. In summary, by finely controlling the size and dispersion of the nanoparticles and optimizing the thickness and uniformity of the coating, the carbon fiber electric heating felt can maintain its original lightness and flexibility while meeting the requirements of use in high temperature environments. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Figure 1 Thermogravimetric test results of different carbon fiber electric heating felt samples;

[0045] Figure 2 The weight loss rate of different carbon fiber electric heating felt samples when kept at 600℃ for 10 minutes;

[0046] Figure 3 This is a SEM photo of the nanocomposite lining layer of the high-temperature resistant carbon fiber electric heating felt sample of Example 1 of the present invention;

[0047] Figure 4 This is an SEM photo of a double-layer dense coating on the surface of a high-temperature resistant carbon fiber electric heating felt sample according to Example 1 of the present invention;

[0048] Figure 5 is the normal spectral emissivity of the original carbon fiber electric heating felt without any treatment;

[0049] Figure 6 is the normal spectral emissivity of the high temperature resistant carbon fiber electric heating felt sample of Example 1 of the present invention;

[0050] Figure 7 is the normal spectral emissivity of the high-temperature resistant carbon fiber electric heating felt sample of Example 2 of the present invention;

[0051] Figure 8 is the normal spectral emissivity of the high-temperature resistant carbon fiber electric heating felt sample of Example 3 of the present invention;

[0052] Figure 9 The electric heating curves of different carbon fiber electric heating felt samples (input power 100W);

[0053] Figure 10 is the resistivity of different carbon fiber electric heating felt samples;

[0054] Figure 11 This is a photo of the flexible bending of the high-temperature resistant carbon fiber electric heating felt sample of Example 1 of the present invention. DETAILED DESCRIPTION

[0055] The present invention is described in detail below with reference to the accompanying drawings and specific embodiments. This embodiment is implemented based on the technical solution of the present invention, and provides a detailed implementation method and specific operation process, but the protection scope of the present invention is not limited to the following embodiments.

[0056] The present invention provides a method for preparing a high-temperature resistant carbon fiber electric heating felt, comprising the following steps:

[0057] S1, silicon oxide, titanium oxide, silicon carbide, titanium carbide nanopowders with a mass ratio of (0.5-2): (0.5-2): (0.5-2): (0.5-2) are ball-milled at a speed of 200 r / min to 500 r / min for 0.5 h to 3 h to obtain a mixed nanopowder, and then water, a coupling agent, a thickener, and a dispersant are added, and shear stirring is carried out at a speed of 600 r / min to 1500 r / min for 0.5 h to 1 h to obtain a nanocomposite emulsion, wherein the particle size range of the silicon oxide, titanium oxide, silicon carbide, and titanium carbide nanopowders is 20nm~80nm, the mass ratio of water to mixed nanopowder is 1:1~3:1, the mass of coupling agent is 1~5% of the total mass of water and mixed nanopowder, the mass of thickener is 5~15% of the total mass of water and mixed nanopowder, the mass of dispersant is 1~3% of the total mass of water and mixed nanopowder, the coupling agent is selected from at least one of KH550, KH560 or KH570, the thickener is selected from at least one of sodium carboxymethyl cellulose, polyacrylic acid or sodium alginate, and the dispersant is selected from at least one of polyacrylamide or sodium lauryl sulfate;

[0058] S2, Preparation of Carbon Fiber Felt Nanocomposite Lining Layer:

[0059] S2-1, immersing the carbon fiber felt in concentrated nitric acid at 75° C. for oxidation activation for 3 to 8 hours, washing with water, and then drying to obtain an activated carbon fiber felt, wherein the carbon fiber felt is selected from at least one of polyacrylonitrile-based carbon fiber felt, asphalt-based carbon fiber felt, and viscose-based carbon fiber felt, and the thickness of the carbon fiber felt is 0.2 to 50 mm;

[0060] S2-2, immersing the activated carbon fiber felt obtained in step S2-1 into the nanocomposite emulsion obtained in step S1, heating to 50-60° C., and ultrasonically treating for 30 minutes at an ultrasonic power of 50-100 W and a frequency of 20-60 kHz;

[0061] S2-3, taking out the carbon fiber felt treated in step S2-2, drying it at 60-80°C for 1-3 hours, and then performing a heat treatment. The heat treatment conditions are: nitrogen atmosphere, heating rate of 3-5°C / min, heating to 1300-1600°C, keeping the temperature for 2-3 hours, and cooling naturally;

[0062] S2-4, heating the carbon fiber felt treated in step S2-3 to 50-60° C., and ultrasonically cleaning the felt for 0.5-3 hours at an ultrasonic power of 80-120 W and a frequency of 30-80 kHz to obtain a carbon fiber felt with a nanocomposite lining layer coated on the fiber surface;

[0063] S3, silanization treatment of the carbon fiber felt: immersing the carbon fiber felt with the nanocomposite liner coated on the fiber surface obtained in step S2-4 in water, and then adding a coupling agent with a mass of 1-3% of the mass of water and an organic silane with a mass of 1-3% of the mass of water, stirring thoroughly, and then standing for 20-30 hours. The mixture is taken out and dried to obtain a carbon fiber felt with a silanized fiber surface;

[0064] S4, silanization treatment of the emissivity-enhancing powder: fully stir water, emissivity-enhancing powder, coupling agent, and organosilane in a mass ratio of 100:(5-15):(1-3):(1-3), let stand for 20-30 hours, take out, and dry to obtain a silanized emissivity-enhancing powder;

[0065] S5, silanization treatment of the conductive enhancing powder: fully stir water, conductive enhancing powder, coupling agent, and organosilane in a mass ratio of 100:(5-15):(1-3):(1-3), let stand for 20-30 hours, take out, and dry to obtain silanized conductive enhancing powder;

[0066] In some specific embodiments, in steps S3, S4, and S5, the coupling agent is selected from at least one of KH550, KH560, and KH570, and the organosilane is selected from at least one of ethyl orthosilicate and methyl orthosilicate;

[0067] In some specific embodiments, in step S4, the emissivity enhancing powder is selected from at least one of silicon carbide and aluminum oxide;

[0068] In some specific embodiments, in step S5, the conductive reinforcing powder is selected from at least one of titanium carbide and zirconium boride;

[0069] S6, preparation of silicon oxide-aluminum oxide-titania composite sol:

[0070] S6-1, uniformly mixing a silicon oxide precursor, an aluminum oxide precursor, and a titanium oxide precursor in a molar ratio of (2-3):(1-1.5):(1-1.5), then adding anhydrous ethanol in a ratio of anhydrous ethanol volume to the total volume of the precursors = (2:1) to (3:1), and thoroughly mixing to obtain a precursor mixed solution, wherein the silicon oxide precursor is selected from at least one of ethyl silicate or methyl silicate, the aluminum oxide precursor is aluminum isopropoxide, and the titanium oxide precursor is selected from at least one of titanium tetrachloride or tetrabutyl titanate;

[0071] S6-2, slowly adding water dropwise to the precursor mixed solution prepared in step S6-1 while stirring, wherein the molar ratio of the total amount of precursor to the added water is 3:1 to 4:1;

[0072] S6-3, adjusting the pH of the solution obtained in step S6-2 to 5-6 with glacial acetic acid, aging at room temperature to 60° C. for 20-30 hours to obtain a silicon oxide-aluminum oxide-titania composite sol;

[0073] S7, outer coating self-assembly step:

[0074] S7-1, dispersing the silanized emissivity enhancing powder obtained in step S4 and the silanized conductivity enhancing powder obtained in step S5 in the silica-alumina-titania composite sol obtained in step S6-3, wherein the mass ratio of the silanized emissivity enhancing powder, the silanized conductivity enhancing powder, and the silica-alumina-titania composite sol is (2-5):1:(3-10). After thorough stirring, the carbon fiber felt with silanized fiber surface obtained in step S3 is added thereto, and the mixture is reacted for 1-3 days under slow stirring.

[0075] S7-2, every 6 to 8 hours during the reaction, 5 g of a 3 to 5 wt.% aqueous solution of an alkali metal carbonate is added dropwise, wherein the aqueous solution of the alkali metal carbonate is selected from at least one of an aqueous lithium carbonate solution, an aqueous sodium carbonate solution, or an aqueous potassium carbonate solution. After the reaction is completed, the pH of the reaction system is adjusted to 8 to 12 with 5 to 20 wt.% aqueous ammonia. The carbon fiber felt is then taken out, rinsed 1 to 2 times with anhydrous ethanol, and dried at 60 to 80° C. for 2 hours to obtain a carbon fiber felt with a surface self-assembled outer layer coating.

[0076] S8, densification of the self-assembled outer coating: heat-treat the carbon fiber felt with the surface self-assembled outer coating obtained in step S7-2 under the following conditions: nitrogen atmosphere, heating to 800-1200°C at 3-10°C / min, keeping warm for 1-3h, and naturally cooling to obtain a high-temperature resistant carbon fiber electric heating felt with a double-layer coating on the fiber surface.

[0077] A high-temperature resistant carbon fiber electric heating felt is prepared by the preparation method, and the high-temperature resistant performance of the carbon fiber electric heating felt is enhanced based on a double-layer coating.

[0078] The high-temperature-resistant carbon fiber electric heating felt produced above can be used in the electric heating field. While maintaining its original lightweight, flexible, stable conductive properties and high emissivity, the initial oxidation temperature of the produced high-temperature carbon fiber electric heating felt exceeds 650°C, raising the upper temperature limit of electric heating applications to 600°C. This significantly expands its application range in the electric heating field and can be used in electric heating applications with a temperature limit of around 600°C, such as industrial heating, special material processing, and high-temperature experimental equipment. It has good application prospects and economic benefits.

[0079] Unless otherwise specified, the reagents, methods, instruments and equipment used in the present invention are conventional reagents, methods, instruments and equipment in the art. Unless otherwise specified, the reagents and materials used in the following examples are commercially available.

[0080] Example 1

[0081] A method for preparing a high-temperature resistant carbon fiber electric heating felt is as follows:

[0082] S1, weighing 2.5g of silicon oxide, 5g of titanium oxide, 6g of silicon carbide, and 8g of titanium carbide nanopowders, ball milling and mixing at a speed of 200r / min for 0.5h to obtain a mixed nanopowder, then adding water, KH550, sodium carboxymethyl cellulose, and polyacrylamide, and shear stirring at a speed of 600r / min for 0.5h to obtain a nanocomposite emulsion, wherein the particle size of the silicon oxide, titanium oxide, silicon carbide, and titanium carbide nanopowders is 20nm, the mass ratio of water to the mixed nanopowder is 1:1, the mass of KH550 is 1% of the total mass of the water and the mixed nanopowder, the mass of sodium carboxymethyl cellulose is 5% of the total mass of the water and the mixed nanopowder, and the mass of polyacrylamide is 1% of the total mass of the water and the mixed nanopowder;

[0083] S2, preparation of polyacrylonitrile-based carbon fiber felt nanocomposite lining layer:

[0084] S2-1, immersing a polyacrylonitrile-based carbon fiber felt having a thickness of 0.2 mm in concentrated nitric acid at 75° C. for oxidation activation for 3 h, washing with water, and then drying to obtain an activated polyacrylonitrile-based carbon fiber felt;

[0085] S2-2, immersing the activated polyacrylonitrile-based carbon fiber felt obtained in step S2-1 into the nanocomposite emulsion prepared in step S1, heating to 50° C., and ultrasonically treating for 30 minutes at an ultrasonic power of 50 W and a frequency of 30 kHz;

[0086] S2-3, taking out the polyacrylonitrile-based carbon fiber felt treated in step S2-2, drying it at 60° C. for 3 hours, and then performing a heat treatment under the following conditions: nitrogen atmosphere, heating rate of 3° C. / min, heating to 1300° C., holding at this temperature for 2 hours, and cooling naturally;

[0087] S2-4, heating the polyacrylonitrile-based carbon fiber felt treated in step S2-3 to 50° C., and ultrasonically cleaning the felt for 0.5 h at an ultrasonic power of 80 W and a frequency of 60 kHz to remove excess inorganic powder in the pores of the carbon fiber felt, thereby obtaining a polyacrylonitrile-based carbon fiber felt having a nanocomposite lining layer coated on the fiber surface;

[0088] S3, silanization treatment of polyacrylonitrile-based carbon fiber felt: immerse the polyacrylonitrile-based carbon fiber felt with the nanocomposite liner coated on the fiber surface obtained in step S2-4 in 100 mL of water, and then add 1.5% of KH550 by weight of water and 1.5% of ethyl orthosilicate by weight of water. After thorough stirring, let it stand for 24 hours, take it out, and dry it to obtain a polyacrylonitrile-based carbon fiber felt with silanized fiber surface;

[0089] S4, silanization treatment of emissivity enhancing powder: 800 g of water, 40 g of emissivity enhancing powder (emissivity enhancing powder is 20 g of silicon carbide and 20 g of aluminum oxide), 12 g of KH550, and 12 g of ethyl orthosilicate are fully stirred and allowed to stand for 24 hours, taken out, and dried to obtain silanized emissivity enhancing powder, wherein the mass ratio of water, emissivity enhancing powder, KH550, and ethyl orthosilicate is 100:5:1.5:1.5;

[0090] S5, silanization treatment of conductive enhancing powder: 400 g of water, 20 g of conductive enhancing powder (the conductive enhancing powder is 10 g of titanium carbide and 10 g of zirconium boride), 6 g of KH550, and 6 g of ethyl orthosilicate are fully stirred and allowed to stand for 24 hours, taken out, and dried to obtain silanized conductive enhancing powder, wherein the mass ratio of water, conductive enhancing powder, KH550, and ethyl orthosilicate is 100:5:1.5:1.5;

[0091] S6, preparation of silicon oxide-aluminum oxide-titania composite sol:

[0092] S6-1, 0.2 mol of ethyl silicate, 0.1 mol of aluminum isopropoxide, and 0.1 mol of titanium tetrachloride are uniformly mixed, and then anhydrous ethanol is added in a ratio of anhydrous ethanol volume to the total volume of the precursor (ethyl silicate + aluminum isopropoxide + titanium tetrachloride) = 2:1, and the mixture is thoroughly mixed to obtain a precursor mixed solution;

[0093] S6-2, slowly adding water dropwise to the precursor mixed solution prepared in step S6-1 while stirring, wherein the molar ratio of the total amount of precursor (ethyl silicate + aluminum isopropoxide + titanium tetrachloride) to the added water is 3:1;

[0094] S6-3, adjusting the pH of the solution obtained in step S6-2 to 5 with glacial acetic acid, and aging at room temperature for 24 hours to obtain a silicon oxide-aluminum oxide-titania composite sol;

[0095] S7, outer coating self-assembly step:

[0096] S7-1, dispersing 40 g of the silanized emissivity enhancing powder obtained in step S4 and 20 g of the silanized conductivity enhancing powder obtained in step S5 in 60 g of the silica-alumina-titania composite sol obtained in step S6-3, wherein the mass ratio of the silanized emissivity enhancing powder, the silanized conductivity enhancing powder, and the silica-alumina-titania composite sol is 2:1:3. After thorough stirring, the polyacrylonitrile-based carbon fiber felt with silanized fiber surface obtained in step S3 is added thereto, and the mixture is reacted for 2 days under slow stirring;

[0097] S7-2, during the reaction process, 5 g of a 3 wt.% lithium carbonate aqueous solution was added dropwise every 6 h. After the reaction, the pH of the reaction system was adjusted to 8 with 5 wt.% ammonia water. The polyacrylonitrile-based carbon fiber felt was then taken out and rinsed twice with anhydrous ethanol to remove excess sol and powder in the pores of the carbon fiber felt. The felt was then dried at 60° C. for 2 h to obtain a polyacrylonitrile-based carbon fiber felt with a surface self-assembled outer layer coating.

[0098] S8, densification of the self-assembled outer coating: The polyacrylonitrile-based carbon fiber felt with the surface self-assembled outer coating obtained in step S7-2 is heat-treated under the following conditions: nitrogen atmosphere, heating to 800°C at 3°C / min, keeping warm for 1 hour, and naturally cooling to obtain a high-temperature resistant polyacrylonitrile-based carbon fiber electric heating felt with a double-layer coating on the fiber surface.

[0099] Example 2

[0100] A method for preparing a high-temperature resistant carbon fiber electric heating felt is as follows:

[0101] S1, weighing 3g of silicon oxide, 6g of titanium oxide, 2.5g of silicon carbide, and 2.5g of titanium carbide nanopowders, ball milling and mixing at a speed of 300r / min for 1h to obtain a mixed nanopowder, then adding water, KH560, polyacrylic acid, and sodium lauryl sulfate, and shear stirring at a speed of 800r / min for 0.8h to obtain a nanocomposite emulsion, wherein the particle size of the silicon oxide, titanium oxide, silicon carbide, and titanium carbide nanopowders is 50nm, the mass ratio of water to the mixed nanopowder is 2:1, the mass of KH560 is 3% of the total mass of the water and the mixed nanopowder, the mass of polyacrylic acid is 10% of the total mass of the water and the mixed nanopowder, and the mass of sodium lauryl sulfate is 2% of the total mass of the water and the mixed nanopowder;

[0102] S2, preparation of polyacrylonitrile-based carbon fiber felt nanocomposite lining layer:

[0103] S2-1, immersing a 20 mm thick polyacrylonitrile-based carbon fiber felt in concentrated nitric acid at 75° C. for oxidation activation for 6 h, washing with water, and then drying to obtain an activated polyacrylonitrile-based carbon fiber felt;

[0104] S2-2, immersing the activated polyacrylonitrile-based carbon fiber felt obtained in step S2-1 into the nanocomposite emulsion prepared in step S1, heating to 55° C., and ultrasonically treating for 30 minutes at an ultrasonic power of 80 W and a frequency of 50 kHz;

[0105] S2-3, taking out the polyacrylonitrile-based carbon fiber felt treated in step S2-2, drying it at 70°C for 2 hours, and then performing a heat treatment under the following conditions: nitrogen atmosphere, heating rate of 4°C / min, heating to 1500°C, holding at this temperature for 2.5 hours, and cooling naturally;

[0106] S2-4, heating the polyacrylonitrile-based carbon fiber felt treated in step S2-3 to 55° C., and ultrasonically cleaning the felt for 2 hours at an ultrasonic power of 100 W and a frequency of 60 kHz to remove excess inorganic powder in the pores of the carbon fiber felt, thereby obtaining a polyacrylonitrile-based carbon fiber felt having a nanocomposite lining layer coated on the fiber surface;

[0107] S3, silanization treatment of polyacrylonitrile-based carbon fiber felt: immerse the polyacrylonitrile-based carbon fiber felt with the nanocomposite liner coated on the fiber surface obtained in step S2-4 in 100 mL of water, and then add 2% KH560 and 2% methyl orthosilicate by weight of the water to the felt. After thorough stirring, let it stand for 24 hours, remove it, and dry it to obtain a polyacrylonitrile-based carbon fiber felt with silanized fiber surface;

[0108] S4, silanization treatment of emissivity enhancing powder: 400 g of water, 40 g of emissivity enhancing powder (emissivity enhancing powder is 20 g of silicon carbide and 20 g of aluminum oxide), 8 g of KH560, and 8 g of methyl orthosilicate are fully stirred and allowed to stand for 24 hours, taken out, and dried to obtain silanized emissivity enhancing powder, wherein the mass ratio of water, emissivity enhancing powder, KH560, and methyl orthosilicate is 100:10:2:2;

[0109] S5, silanization treatment of conductive enhancing powder: 200 g of water, 20 g of conductive enhancing powder (the conductive enhancing powder is 10 g of titanium carbide and 10 g of zirconium boride), 5 g of KH560, and 5 g of methyl orthosilicate are fully stirred and allowed to stand for 24 hours, taken out, and dried to obtain silanized conductive enhancing powder, wherein the mass ratio of water, conductive enhancing powder, KH560, and methyl orthosilicate is 100:10:2.5:2.5;

[0110] S6, preparation of silicon oxide-aluminum oxide-titania composite sol:

[0111] S6-1, 0.25 mol of methyl silicate, 0.1 mol of aluminum isopropoxide, and 0.1 mol of titanium tetrachloride are uniformly mixed, and then anhydrous ethanol is added in a ratio of anhydrous ethanol volume to the total volume of the precursor (methyl silicate + aluminum isopropoxide + titanium tetrachloride) = 2.5:1, and the mixture is thoroughly mixed to obtain a precursor mixed solution;

[0112] S6-2, slowly adding water dropwise to the precursor mixed solution prepared in step S6-1 while stirring, wherein the molar ratio of the total amount of precursor (methyl silicate + aluminum isopropoxide + titanium tetrachloride) to the added water is 3.5:1;

[0113] S6-3, adjusting the pH of the solution obtained in step S6-2 to 5.5 with glacial acetic acid, and aging at 40° C. for 24 hours to obtain a silicon oxide-aluminum oxide-titania composite sol;

[0114] S7, outer coating self-assembly step:

[0115] S7-1, dispersing 40 g of the silanized emissivity enhancing powder obtained in step S4 and 10 g of the silanized conductivity enhancing powder obtained in step S5 in 50 g of the silica-alumina-titania composite sol obtained in step S6-3, wherein the mass ratio of the silanized emissivity enhancing powder, the silanized conductivity enhancing powder, and the silica-alumina-titania composite sol is 4:1:5. After thorough stirring, the polyacrylonitrile-based carbon fiber felt with silanized fiber surface obtained in step S3 is added thereto, and the mixture is reacted for 2 days under slow stirring;

[0116] S7-2, during the reaction process, 5 g of a 4 wt.% sodium carbonate aqueous solution was added dropwise every 7 h. After the reaction, the pH of the reaction system was adjusted to 10 with 12 wt.% ammonia water. The polyacrylonitrile-based carbon fiber felt was then taken out and rinsed twice with anhydrous ethanol to remove excess sol and powder in the pores of the carbon fiber felt. The felt was then dried at 70° C. for 2 h to obtain a polyacrylonitrile-based carbon fiber felt with a surface self-assembled outer layer coating.

[0117] S8, densification of the self-assembled outer coating: The polyacrylonitrile-based carbon fiber felt with the surface self-assembled outer coating obtained in step S7-2 is heat-treated under the following conditions: nitrogen atmosphere, heating to 1000°C at 5°C / min, keeping warm for 2 hours, and naturally cooling to obtain a high-temperature resistant polyacrylonitrile-based carbon fiber electric heating felt with a double-layer coating on the fiber surface.

[0118] Example 3

[0119] A method for preparing a high-temperature resistant carbon fiber electric heating felt is as follows:

[0120] S1, weighing 5g of silicon oxide, 3.5g of titanium oxide, 6g of silicon carbide, and 8g of titanium carbide nanopowders, ball milling and mixing at a speed of 500r / min for 3h to obtain a mixed nanopowder, then adding water, KH570, sodium alginate, and sodium lauryl sulfate, and shear stirring at a speed of 1400r / min for 1h to obtain a nanocomposite emulsion, wherein the particle size of the silicon oxide, titanium oxide, silicon carbide, and titanium carbide nanopowders is 80nm, the mass ratio of water to the mixed nanopowder is 3:1, the mass of KH570 is 5% of the total mass of the water and the mixed nanopowder, the mass of sodium alginate is 15% of the total mass of the water and the mixed nanopowder, and the mass of sodium lauryl sulfate is 3% of the total mass of the water and the mixed nanopowder;

[0121] S2, preparation of polyacrylonitrile-based carbon fiber felt nanocomposite lining layer:

[0122] S2-1, immersing a 50 mm thick polyacrylonitrile-based carbon fiber felt in concentrated nitric acid at 75° C. for oxidative activation for 8 h, washing with water, and then drying to obtain an activated polyacrylonitrile-based carbon fiber felt;

[0123] S2-2, immersing the activated polyacrylonitrile-based carbon fiber felt obtained in step S2-1 into the nanocomposite emulsion prepared in step S1, heating to 60° C., and ultrasonically treating for 30 minutes at an ultrasonic power of 100 W and a frequency of 60 kHz;

[0124] S2-3, taking out the polyacrylonitrile-based carbon fiber felt treated in step S2-2, drying it at 80°C for 3 hours, and then heat treating it under the following conditions: nitrogen atmosphere, heating rate of 5°C / min, heating to 1600°C, holding at this temperature for 3 hours, and cooling naturally;

[0125] S2-4, heating the polyacrylonitrile-based carbon fiber felt treated in step S2-3 to 60° C. and ultrasonically cleaning the felt for 3 hours at an ultrasonic power of 120 W and a frequency of 80 kHz to remove excess inorganic powder in the pores of the carbon fiber felt, thereby obtaining a polyacrylonitrile-based carbon fiber felt having a nanocomposite lining layer coated on the fiber surface;

[0126] S3, silanization treatment of polyacrylonitrile-based carbon fiber felt: immerse the polyacrylonitrile-based carbon fiber felt with the nanocomposite liner coated on the fiber surface obtained in step S2-4 in 100 mL of water, and then add 3% of KH570 and 3% of methyl orthosilicate by weight of water to the felt. After thorough stirring, let it stand for 24 hours, take it out, and dry it to obtain a polyacrylonitrile-based carbon fiber felt with silanized fiber surface;

[0127] S4, silanization treatment of emissivity enhancing powder: 400 g of water, 60 g of emissivity enhancing powder (emissivity enhancing powder is 30 g of silicon carbide and 30 g of aluminum oxide), 12 g of KH570, and 12 g of methyl orthosilicate are fully stirred and allowed to stand for 24 hours, taken out, and dried to obtain silanized emissivity enhancing powder, wherein the mass ratio of water, emissivity enhancing powder, KH570, and methyl orthosilicate is 100:15:3:3;

[0128] S5, silanization treatment of conductive enhancing powder: 200 g of water, 30 g of conductive enhancing powder (the conductive enhancing powder is 15 g of titanium carbide and zirconium boride), 6 g of KH570, and 6 g of methyl orthosilicate are fully stirred and allowed to stand for 24 hours, taken out, and dried to obtain silanized conductive enhancing powder, wherein the mass ratio of water, conductive enhancing powder, KH570, and methyl orthosilicate is 100:15:3:3;

[0129] S6, preparation of silicon oxide-aluminum oxide-titania composite sol:

[0130] S6-1, 0.3 mol of ethyl silicate, 0.15 mol of aluminum isopropoxide, and 0.1 mol of tetrabutyl titanate are uniformly mixed, and then anhydrous ethanol is added in a ratio of anhydrous ethanol volume to the total volume of the precursor (ethyl silicate + aluminum isopropoxide + tetrabutyl titanate) = 3:1, and the mixture is thoroughly mixed to obtain a precursor mixed solution;

[0131] S6-2, slowly adding water dropwise to the precursor mixed solution prepared in step S6-1 while stirring, wherein the molar ratio of the total amount of precursor (ethyl silicate + aluminum isopropoxide + tetrabutyl titanate) to the added water is 4:1;

[0132] S6-3, adjusting the pH of the solution obtained in step S6-2 to 6 with glacial acetic acid, and aging at 60° C. for 24 hours to obtain a silicon oxide-aluminum oxide-titania composite sol;

[0133] S7, outer coating self-assembly step:

[0134] S7-1, dispersing 50 g of the silanized emissivity enhancing powder obtained in step S4 and 10 g of the silanized conductivity enhancing powder obtained in step S5 in 100 g of the silica-alumina-titania composite sol obtained in step S6-3, wherein the mass ratio of the silanized emissivity enhancing powder, the silanized conductivity enhancing powder, and the silica-alumina-titania composite sol is 5:1:10. After thorough stirring, the polyacrylonitrile-based carbon fiber felt with silanized fiber surface obtained in step S3 is added thereto, and the mixture is reacted for 3 days under slow stirring;

[0135] S7-2, during the reaction process, 5 g of a 4 wt.% potassium carbonate aqueous solution was added dropwise every 8 hours. After the reaction was completed, the pH of the reaction system was adjusted to 12 with 15 wt.% ammonia water. The polyacrylonitrile-based carbon fiber felt was then taken out and rinsed twice with anhydrous ethanol to remove excess sol and powder in the pores of the carbon fiber felt. The felt was then dried at 80° C. for 2 hours to obtain a polyacrylonitrile-based carbon fiber felt with a surface self-assembled outer layer coating.

[0136] S8, densification of the self-assembled outer coating: The polyacrylonitrile-based carbon fiber felt with the surface self-assembled outer coating obtained in step S7-2 is heat-treated under the following conditions: nitrogen atmosphere, heating to 1200°C at 10°C / min, keeping warm for 3 hours, and naturally cooling to obtain a high-temperature resistant polyacrylonitrile-based carbon fiber electric heating felt with a double-layer coating on the fiber surface.

[0137] Comparative Example 1

[0138] This comparative example is commercially available polyacrylonitrile-based carbon fiber felt that has not been treated in any way.

[0139] The carbon fiber felt samples of the above examples and comparative examples were characterized as follows:

[0140] (1) Thermogravimetric Analysis (TGA) is a thermal analysis technique that measures the weight change of a sample at elevated or constant temperature to investigate its thermal, chemical, and structural properties. Its principle is based on the mass change of a sample at elevated or constant temperature, and can be used to analyze reactions such as thermal decomposition, desorption, and oxidation.

[0141] Test conditions:

[0142] Test 1: Air atmosphere, 20°C / min, room temperature to 800°C.

[0143] Test 2: Air atmosphere, 20℃ / min, 600℃ for 10min.

[0144] (2) Characterization of coating micromorphology: The coating micromorphology was analyzed using a FlexSEM 1000 scanning electron microscope.

[0145] (3) Normal spectral emissivity test: The thermal radiation performance is measured using an automatic spectroscopic radiation test system.

[0146] (4) Electric heating performance test:

[0147] The experimental setup includes an electric heating element, electrodes, a conductive circuit, and an input power supply. The test used the carbon fiber electric heating felt with enhanced high-temperature resistance, prepared in this invention, as the electric heating element, conductive copper foil as the electrode material, and an adjustable DC power supply.

[0148] A K-type thermocouple is used for real-time temperature testing.

[0149] The test process includes three stages: heating process, constant temperature process, and power-off cooling process.

[0150] (5) Resistivity test

[0151] Required equipment: DC regulated power supply, digital multimeter or voltmeter, ammeter or current probe and sample fixture (for fixing carbon fiber felt sample).

[0152] Measurement steps:

[0153] 1. Sample preparation: Cut samples of a certain size from the carbon fiber felt, measure and record the length (L), width (W) and thickness (T) of the sample.

[0154] 2. Sample installation: Fix the sample on the sample fixture to ensure good electrode contact.

[0155] 3. Current-voltage measurement:

[0156] a. Use a DC regulated power supply to apply a constant current (I) to the sample.

[0157] b. Use a digital multimeter or voltmeter to measure the voltage (V) across the sample.

[0158] 4. Resistance calculation: Calculate the resistance (R) of the sample according to Ohm's law: R = V / I.

[0159] 5. Resistivity calculation: Calculate the resistivity (ρ) of the sample based on its geometric dimensions: ρ = R × A / L, where A is the cross-sectional area of ​​the sample (A = W × T).

[0160] The above characterization results are as follows:

[0161] like Figure 1 、 Figure 2 As shown, the weight loss rates of the high-temperature resistant carbon fiber electric heating felt samples prepared by the formula and process of Example 1, Example 2 or Example 3 of the present invention after being kept at 600°C for 10 minutes were 0.16%, 0.21% and 0.22% respectively, which were significantly lower than the weight loss rate of the untreated carbon fiber electric heating felt sample in Comparative Example 1 (35%). Figure 1 、 Figure 9 As shown, after the untreated carbon fiber electric heating felt sample of Comparative Example 1 of the present invention was rapidly heated to 550°C, the material oxidized, the structure was destroyed, and the performance became unstable, resulting in a sharp drop in temperature. Conversely, the high-temperature resistant carbon fiber electric heating felt samples prepared using the formula and process of Example 1, Example 2, or Example 3 had an initial oxidation temperature increased by 150-200°C and were able to generate heat stably between 600-650°C, indicating that the high-temperature resistant carbon fiber felt samples of the present invention can withstand temperatures of 600°C. The carbon fibers have been modified with a nano-liner, the self-assembly process has been promoted, and the alkali metal elements have been introduced, so that the outer coating can evenly coat the surface of each carbon fiber, densely isolating oxygen, and the carbon fibers are not oxidized, providing a structural basis for the use of the carbon fiber electric heating felt at high temperatures of 600°C. The above results show that the high-temperature resistant carbon fiber electric heating felt of the present invention can be widely used in various electric heating scenarios requiring a temperature upper limit of 600°C, such as industrial heating, special material processing, high-temperature experimental equipment, etc., providing a new solution for high-temperature electric heating applications.

[0162] like Figure 3 As shown, the nanocomposite lining layer of the high-temperature resistant carbon fiber electric heating felt sample of Example 1 of the present invention is stably coated on the carbon fiber surface, changing the originally smooth and inert carbon fiber surface into a rough and active nano lining, which is beneficial to the uniform adhesion of subsequent coatings.

[0163] like Figure 4 As shown, the carbon fiber surface of the high-temperature resistant carbon fiber electric heating felt sample of Example 1 of the present invention is evenly coated with a double-layer coating, which is dense and oxygen-isolated, and provides a structural basis for the use of the carbon fiber electric heating felt at a high temperature of 600°C.

[0164] like Figure 5-8 As shown, the high-temperature resistant carbon fiber electric heating felt samples prepared by the formula and process in Example 1, Example 2 or Example 3 have high infrared emissivity, and the infrared emissivity is higher than 0.8. It can be seen that the high-temperature resistant carbon fiber electric heating felt samples of Examples 1-3 self-assemble on the carbon fiber surface to form an outer coating by selecting silicon carbide and aluminum oxide with high infrared radiation emissivity as emissivity enhancing powders. The densification of the coating provides good coating and fixation for the emissivity enhancing powder, weakening the negative impact of the dense coating on the infrared emissivity of the original carbon fiber felt, thereby maintaining the high emissivity of the original carbon fiber felt.

[0165] like Figure 10 As shown, the resistivity of the carbon fiber electric heating felt samples in Example 1, Example 2 or Example 3 of the present invention are 19.9mΩ·cm, 20.2mΩ·cm and 20.02mΩ·cm respectively, while the resistivity of the carbon fiber electric heating felt sample in Comparative Example 1 without any treatment is 20.1mΩ·cm, indicating that conductive nanopowders such as titanium carbide and zirconium boride serve as conductive reinforcing powders to construct a conductive network in the dense coating. The densification of the coating provides good coating and fixation for the conductive reinforcing powder, ensuring the high conductive properties of the carbon fiber electric heating felt as a whole, so that the carbon fiber electric heating felt can still maintain stable conductive properties under the coating of the dense coating.

[0166] like Figure 11 As shown, the high-temperature resistant carbon fiber electric heating felt sample of Example 1 of the present invention has good flexibility, and after being coated, it retains the lightness and flexibility of the original carbon fiber electric heating felt.

[0167] In summary, the preparation method of the high-temperature resistant carbon fiber electric heating felt proposed in the present invention, while maintaining the original performance advantages of the carbon fiber electric heating felt, greatly improves the high-temperature resistance, significantly expands its application field, and embodies good process stability and performance stability. The carbon fiber electric heating felts prepared in Examples 1, 2, and 3 of the present invention have stable processes, reliable quality, and excellent performance. Compared with the prior art, the high-temperature resistant carbon fiber electric heating felt of the present invention, while maintaining its original light weight, flexibility, stable conductive properties and high emissivity, raises the upper limit of the electric heating application temperature to about 600°C, significantly expanding its application range in the electric heating field.

[0168] The above description of the embodiments is intended to facilitate understanding and use of the invention by those skilled in the art. It will be apparent that those skilled in the art can readily make various modifications to these embodiments and apply the general principles described herein to other embodiments without requiring inventive effort. Therefore, the present invention is not limited to the above-described embodiments. Improvements and modifications made by those skilled in the art based on the disclosure of the present invention, without departing from the scope of the present invention, should be within the scope of protection of the present invention.

Claims

1. A method for preparing a high-temperature resistant carbon fiber electric heating felt, characterized in that: The following steps are involved: S1, mixing silicon oxide, titanium oxide, silicon carbide, and titanium carbide nanopowders uniformly to obtain a mixed nanopowder, then adding water, a coupling agent, a thickener, and a dispersant, and shearing and stirring to obtain a nanocomposite emulsion; S2, preparation of a carbon fiber felt nanocomposite lining layer: immersing the carbon fiber felt in concentrated nitric acid for oxidation activation, immersing the activated carbon fiber felt in the nanocomposite emulsion prepared in step S1, and performing heat treatment to obtain a carbon fiber felt with a nanocomposite lining layer coated on the fiber surface; S3, silanization treatment of the carbon fiber felt: immersing the carbon fiber felt with the nanocomposite lining layer coated on the fiber surface obtained in step S2 in water, then adding a coupling agent and an organic silane thereto, stirring thoroughly, allowing to stand, and drying to obtain a carbon fiber felt with silanized fiber surface; S4, silanization treatment of the emissivity-enhancing powder: thoroughly stirring water, the emissivity-enhancing powder, the coupling agent, and the organic silane, and then standing and drying to obtain a silanized emissivity-enhancing powder; S5, silanization treatment of the conductive enhancing powder: water, conductive enhancing powder, coupling agent, and organosilane are fully stirred, allowed to stand, and dried to obtain silanized conductive enhancing powder; S6, preparation of silica-alumina-titania composite sol: uniformly mixing a silica precursor, an alumina precursor, and a titania precursor, adding anhydrous ethanol, and mixing thoroughly to obtain a precursor mixed solution, adding water to the precursor mixed solution, adjusting the pH to 5-6, and aging to obtain a silica-alumina-titania composite sol; S7, outer coating self-assembly step: dispersing the silanized emissivity enhancement powder obtained in step S4 and the silanized conductivity enhancement powder obtained in step S5 in the silicon oxide-aluminum oxide-titania composite sol obtained in step S6, and after sufficient stirring, adding the carbon fiber felt with silanized fiber surface obtained in step S3 therein, reacting under slow stirring, and adding an alkali metal carbonate aqueous solution dropwise during the reaction process. After the reaction is completed, adjusting the pH of the reaction system to 8-12, and then taking out the carbon fiber felt, washing it, and drying it to obtain a carbon fiber felt with a surface self-assembled outer coating; S8, densification of the self-assembled outer coating: heat-treating the carbon fiber felt with the self-assembled outer coating obtained in step S7, and naturally cooling the carbon fiber felt to obtain a high-temperature resistant carbon fiber electric heating felt with a double-layer coating on the fiber surface; In steps S3, S4, and S5, the coupling agent is selected from at least one of KH550, KH560, and KH570, and the organosilane is selected from at least one of ethyl orthosilicate and methyl orthosilicate; In step S4, the emissivity enhancing powder is selected from at least one of silicon carbide and aluminum oxide; In step S5, the conductive reinforcing powder is selected from at least one of titanium carbide and zirconium boride.

2. The method for preparing a high-temperature resistant carbon fiber electric heating felt according to claim 1, characterized in that: In step S1, the mass ratio of silicon oxide, titanium oxide, silicon carbide and titanium carbide nanopowders is (0.5-2): (0.5-2): (0.5-2): (0.5-2); The mass ratio of water to mixed nanopowder is 1:1~3:1; The mass of the coupling agent is 1-5% of the total mass of water and mixed nanopowders; The mass of the thickener is 5-15% of the total mass of water and mixed nanopowder; The mass of the dispersant is 1-3% of the total mass of water and mixed nanopowder.

3. The method for preparing a high temperature resistant carbon fiber electric heating felt according to claim 1, characterized in that: In step S1, the particle size of the silicon oxide, titanium oxide, silicon carbide, and titanium carbide nanopowders is in the range of 20 nm to 80 nm; the coupling agent is selected from at least one of KH550, KH560, or KH570; the thickener is selected from at least one of sodium carboxymethyl cellulose, polyacrylic acid, or sodium alginate; and the dispersant is selected from at least one of polyacrylamide or sodium lauryl sulfate.

4. The method for preparing a high temperature resistant carbon fiber electric heating felt according to claim 1, characterized in that: In step S2, the carbon fiber felt is selected from at least one of polyacrylonitrile-based carbon fiber felt, asphalt-based carbon fiber felt, and viscose-based carbon fiber felt; and the thickness of the carbon fiber felt is 0.2 to 50 mm.

5. The method for preparing a high temperature resistant carbon fiber electric heating felt according to claim 1, characterized in that: In step S2, the heat treatment is specifically: heating and ultrasonic treatment in the nanocomposite emulsion, drying after taking out, heating to 1300-1600°C for heat treatment, cooling naturally and then heating and ultrasonic cleaning.

6. The method for preparing a high temperature resistant carbon fiber electric heating felt according to claim 1, characterized in that: In step S3, the mass of the coupling agent is 1-3% of the mass of water, and the mass of the organosilane is 1-3% of the mass of water; In step S4, the mass ratio of water, emissivity enhancing powder, coupling agent, and organosilane is 100:(5-15):(1-3):(1-3); In step S5, the mass ratio of water, conductive reinforcing powder, coupling agent, and organosilane is 100:(5-15):(1-3):(1-3).

7. The method for preparing a high temperature resistant carbon fiber electric heating felt according to claim 1, characterized in that: In step S6, the silicon oxide precursor is selected from at least one of ethyl silicate or methyl silicate; the aluminum oxide precursor is aluminum isopropoxide; and the titanium oxide precursor is selected from at least one of titanium tetrachloride or tetrabutyl titanate; The molar ratio of the silicon oxide precursor, the aluminum oxide precursor, and the titanium oxide precursor is (2~3): (1~1.5): (1~1.5).

8. The method for preparing a high temperature resistant carbon fiber electric heating felt according to claim 1, characterized in that: In step S7, the mass ratio of the silanized emissivity enhancing powder, the silanized conductivity enhancing powder, and the silicon oxide-aluminum oxide-titanium oxide composite sol is (2-5):1:(3-10); The alkali metal carbonate aqueous solution is selected from at least one of a lithium carbonate aqueous solution, a sodium carbonate aqueous solution or a potassium carbonate aqueous solution.

9. A high-temperature resistant carbon fiber electric heating felt prepared by the preparation method according to any one of claims 1 to 8.

10. Use of the high-temperature resistant carbon fiber electric heating felt according to claim 9 in the field of electric heating.

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