Hybrid fiber mat reinforced carbon aerogel composite and method of making same

Abstract

The present application relates to a kind of mixed fiber felt reinforced carbon aerogel composite material and its preparation method, composite material, comprising: mixed fiber felt, the mixed fiber felt includes textile fiber cloth layer and non-woven fiber felt layer, textile fiber cloth layer and non-woven fiber felt layer are alternately stacked along the thickness direction;Carbon aerogel, fill in the internal pore and interlayer gap of textile fiber cloth layer and non-woven fiber felt layer;The thickness of non-woven fiber felt layer and the ratio of fiber length in non-woven fiber felt layer is less than 1:2.Introduce low thermal conductivity fiber, so that low thermal conductivity fiber and carbon aerogel carbonization molding process is synchronized shrinkage, in turn effectively improve the thickness direction compression strength of material, solve the high thermal conductivity, high cost, low strength, difficult to meet the performance demand under complex stress condition, difficult to design strength specifically existing in prior art.

Description

Technical Field

[0001] This invention relates to the field of heat-insulating composite materials, specifically to a hybrid fiber felt reinforced carbon aerogel composite material and its preparation method. Background Technology

[0002] During high-speed entry into the atmosphere, an aircraft experiences intense friction with its surface, creating a shock layer on its outer surface. As the high-speed airflow passes through this shock layer, it is compressed, converting a significant amount of kinetic energy into heat, which is then transferred to the aircraft's surface, creating a harsh aerodynamic heating environment. Thermal protection materials are crucial for preventing heat transfer and ensuring aircraft safety.

[0003] Aerogel materials are porous materials formed by the interconnected stacking of nanoscale particles. Their unique nanonetwork and nanopore structure effectively suppress gas-phase heat conduction and reduce solid-phase heat conduction, making them important in thermal protection. Among all aerogel materials, carbon aerogels possess the highest thermal stability, maintaining a basic mesoporous structure even at inert atmospheres up to 2800°C, thus exhibiting excellent performance in high-temperature insulation. Pure carbon aerogels are brittle and have low mechanical strength, often requiring fiber reinforcement to improve their mechanical properties. However, traditional carbon fibers have the following drawbacks:

[0004] The high cost of carbon fiber and the significant increase in the overall thermal conductivity of the material due to its use limit the practical application of carbon aerogel composites.

[0005] In addition, since conventional carbon aerogels are mostly homogeneous isotropic materials with uniform material properties in all directions, the cracking direction is uncontrollable and unpredictable, making it difficult to design and improve the mechanical properties of composite materials in a targeted manner.

[0006] Furthermore, ordinary carbon fibers are stable at high temperatures and do not shrink during carbonization, while carbon aerogel precursors (such as phenolic resins) exhibit about 20% linear shrinkage during high-temperature curing and carbonization, which is mismatched with the thermal shrinkage of the carbon fiber matrix and greatly limits the improvement of compressive strength.

[0007] There is currently an urgent need in the market for a carbon aerogel composite material with low thermal conductivity, high strength, and low cost. Summary of the Invention

[0008] Based on the above analysis, the present invention aims to provide a method for preparing a hybrid fiber felt reinforced carbon aerogel composite material, in order to solve one of the problems of high thermal conductivity, high cost, and low strength in the existing technology.

[0009] On one hand, the present invention provides a hybrid fiber felt reinforced carbon aerogel composite material, comprising:

[0010] A mixed fiber felt, comprising a woven fiber cloth layer and a non-woven fiber felt layer, wherein the woven fiber cloth layer and the non-woven fiber felt layer are alternately stacked along the thickness direction;

[0011] Carbon aerogel is used to fill the internal pores and interlayer gaps of the textile fiber fabric layer and the nonwoven fiber felt layer.

[0012] The ratio of the thickness of the nonwoven fiber felt layer to the fiber length in the nonwoven fiber felt layer is <1:2.

[0013] Furthermore, the ratio of the thickness of the nonwoven fiber felt layer to the fiber length in the nonwoven fiber felt layer satisfies: (1~3):7.

[0014] Furthermore, the thickness of the nonwoven fiber felt layer is 10mm~30mm.

[0015] Furthermore, the nonwoven fiber felt layer is made of low thermal conductivity fiber or carbon fiber and a mixture of one or more low thermal conductivity fibers. The low thermal conductivity fiber has a non-graphite crystal structure, and the precursor of the low thermal conductivity fiber has a greater linear shrinkage rate than carbon fiber during the carbonization molding process.

[0016] Furthermore, the precursor of the low thermal conductivity fiber is one or more of viscose fiber, viscose fiber pre-oxidized yarn, polyacrylonitrile fiber, polyacrylonitrile fiber pre-oxidized yarn, and phenolic fiber.

[0017] Furthermore, the number of textile fiber fabric layers and nonwoven fiber felt layers is ≥5.

[0018] A method for preparing a hybrid fiber felt reinforced carbon aerogel composite material, comprising:

[0019] S1: Select a low thermal conductivity fiber precursor to prepare a nonwoven fiber felt preform alone or select a low thermal conductivity fiber precursor to mix with carbon fiber to prepare a nonwoven fiber felt preform.

[0020] S2: Prepare a mixed fiber felt preform by layering and knitting a non-woven fiber felt preform and a textile fiber cloth layer;

[0021] S3: Prepare a composite material intermediate by pre-impregnating and curing the mixed fiber felt with a carbon aerogel precursor solution of the first concentration;

[0022] S4: The composite material intermediate is impregnated with a second-concentration carbon aerogel precursor solution and cured to prepare a composite material precursor; the carbon aerogel precursor concentration in the second-concentration carbon aerogel precursor solution is higher than that in the first-concentration carbon aerogel precursor solution.

[0023] S5: High-temperature carbonization of composite material precursors to prepare finished composite materials with a mixed fiber felt reinforcement structure.

[0024] Furthermore, in step S3, the carbon aerogel precursor content in the mixture is 2wt%~8wt%.

[0025] Furthermore, in step S4, the carbon aerogel precursor content in the mixture is 20wt%~55wt%.

[0026] Furthermore, the impregnation pressure in step S4 is 0.1 MPa to 0.4 MPa.

[0027] Compared with the prior art, the present invention can achieve at least one of the following beneficial effects:

[0028] 1. This invention comprises a multi-layer structure consisting of alternating layers of textile fiber fabric and non-woven fiber felt along the thickness direction, wherein the ratio of the thickness of the non-woven fiber felt layer to the fiber length therein is controlled to be less than 1:2 (preferably (1~3):7). ​​Simultaneously, low thermal conductivity fibers (whose precursor carbonization shrinkage rate is greater than that of carbon fibers) are introduced into the non-woven fiber felt layer. Through anisotropic structural design, the material possesses high compressive strength (10% strain compressive strength reaches 16.3~21.9 MPa) and fracture toughness in the thickness direction, overcoming the shortcomings of traditional isotropic materials that are difficult to target with specific mechanical designs. Furthermore, the low thermal conductivity fibers and carbon aerogel shrink synchronously during carbonization, effectively reducing internal microcracks and lowering interfacial thermal resistance, thereby significantly improving thermal insulation performance (room temperature thermal conductivity as low as 0.16~0.31 W·(m·K)). -1 At 800℃, its thermal conductivity is as low as 0.35~0.60 W·(m·K). -1 Ultimately, this achieved a synergistic optimization of low density, high strength, and low thermal conductivity.

[0029] 2. This invention introduces low thermal conductivity fibers into the nonwoven fiber felt layer, so that the low thermal conductivity fibers shrink synchronously with the carbon aerogel carbonization process, thereby effectively reducing cracks (delamination cracks) in the matrix along the planar direction (XY direction) and effectively improving the compressive strength of the material in the thickness direction. The 10% strain compressive strength is between 16.3 and 21.9 MPa, preferably ≥21.0 MPa.

[0030] 3. This invention employs carbon aerogel precursor solutions of varying concentrations for sequential pre-impregnation and impregnation. Low-concentration pre-impregnation effectively maintains the fiber's structural shape, preventing bending and deformation during high-concentration impregnation and improving the impregnation effect. During impregnation, the carbon aerogel precursor forms a complete aerogel structure within the fiber gaps, further enhancing thermal insulation performance, with a thermal conductivity of 0.35~0.60 W·(m·K) at 800℃. -1 Preferably, the concentration is ≤0.38 W·(m·K). -1 .

[0031] 4. This invention achieves multiple synergistic technological effects by sequentially executing a series of process steps: "preparing a nonwoven felt layer by mixing a low thermal conductivity fiber precursor with carbon fiber → alternating layering and needle punching with a woven fabric layer → pre-impregnation with a low concentration carbon aerogel precursor under normal pressure → impregnation with a high concentration carbon aerogel precursor under vacuum pressure → step-by-step high-temperature carbonization".

[0032] On the one hand, low-concentration pre-impregnation protects the fluffy structure of the fiber felt and the micro- and nanopores of the fibers themselves, while high-concentration impregnation constructs a complete aerogel network in the fiber gaps. This combination not only avoids the damage to the nanopores caused by atmospheric pressure drying (thus eliminating the need for supercritical drying and significantly reducing costs), but also causes the low thermal conductivity fiber precursor and carbon aerogel to shrink synchronously during carbonization, effectively suppressing delamination cracks. On the other hand, the stepped carbonization heating (holding at 300℃, then slowly heating at 1℃ / min~5℃ / min to 700℃~1000℃) reduces microcracks caused by thermal stress, ensuring a dense and uniform material structure. Ultimately, this method can stably prepare materials with both low density (0.72 g / cm³~0.81 g / cm³) and high aerogel density. 3 It possesses high compressive strength (10% strain compressive strength reaches 16.3MPa~21.9MPa) and excellent thermal insulation performance (room temperature thermal conductivity as low as 0.16W·(m·K)). -1 ~0.31 W·(m·K) -1 Its thermal conductivity at 800℃ is as low as 0.35 W·(m·K). -1 ~0.60 W / (m·K) -1 ) Hybrid fiber felt reinforced carbon aerogel composite material.

[0033] 5. The hybrid fiber felt reinforced carbon aerogel composite material and its preparation method provided by this invention have the following significant features and advantages compared with the prior art:

[0034] Product Structure

[0035] Low thermal conductivity fiber reinforcement system: The nonwoven fiber felt layer is made of low thermal conductivity fibers (such as viscose fiber, polyacrylonitrile fiber, phenolic fiber, etc.) or a mixture thereof with carbon fiber. The carbonization shrinkage rate of this type of fiber precursor is greater than that of carbon fiber.

[0036] Complete carbon aerogel filling: Carbon aerogel fills the internal pores and interlayer gaps of the fiber cloth layer and felt layer, forming a continuous nanoporous network.

[0037] Core advantages

[0038] (1) Excellent mechanical properties and designability:

[0039] The anisotropic structure gives the material high compressive strength and high fracture toughness in the thickness direction (Z direction), with a 10% strain compressive strength of 16.3~21.9 MPa (preferably ≥21.0 MPa), which is much higher than that of traditional isotropic carbon aerogels.

[0040] Multi-layer symmetrical ply structure (≥5 layers) ensures uniform stress distribution, reduces peak stress by 30%~50%, avoids warping deformation, and provides good dimensional stability.

[0041] When cracks propagate, a large number of fibers need to be pulled out or broken, resulting in high energy dissipation and significantly improved resistance to delamination.

[0042] (2) Excellent thermal insulation performance:

[0043] The room temperature thermal conductivity is as low as 0.16~0.37 W·(m·K). -1 At 800℃, its thermal conductivity is as low as 0.35~0.60 W·(m·K). -1 It reduces carbon aerogel by about 50% compared to traditional carbon fiber reinforced carbon aerogel.

[0044] (3) The preparation process is economical and efficient:

[0045] By adopting a two-step method of "low-concentration pre-impregnation + high-concentration impregnation", the high cost of supercritical drying is avoided, and atmospheric pressure drying is achieved, which significantly reduces production costs.

[0046] The low thermal conductivity fiber precursor shrinks synchronously with the carbon aerogel, reducing internal microcracks and improving yield.

[0047] (4) Low density and excellent overall performance:

[0048] The density of the composite material is 0.72~0.81 g·cm³. -3 It achieves a synergistic optimization of high strength and low thermal conductivity at low density.

[0049] (5) Meets the requirements of complex working conditions:

[0050] Differentiated strength designs can be made for thickness-direction compression and complex stress conditions, making it suitable for harsh environments such as aircraft thermal protection systems and high-temperature insulation components.

[0051] The above-described technical solutions can also be combined with each other to achieve more preferred combinations. Other features and advantages of the present invention will be set forth in the following description, and some advantages may become apparent from the description or be learned by practicing the invention. The objects and other advantages of the invention can be realized and obtained from what is particularly pointed out in the description and drawings. Attached Figure Description

[0052] The accompanying drawings are for illustrative purposes only and are not intended to limit the invention. Throughout the drawings, the same reference numerals denote the same parts.

[0053] Figure 1 High-magnification photograph of the surface (XY plane) of the mixed fiber felt in Example 2;

[0054] Figure 2 High-magnification photograph of the surface (XY plane) of the composite material in Example 2;

[0055] Figure 3 This is a high-magnification photograph of the side (XZ plane) of the composite material in Example 2;

[0056] Figure 4 This is a SEM image of the matrix of the composite material in Example 2. Detailed Implementation

[0057] The preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings, which constitute a part of the present invention and are used together with the embodiments of the present invention to illustrate the principles of the present invention, but are not intended to limit the scope of the present invention.

[0058] On one hand, the present invention provides a hybrid fiber felt reinforced carbon aerogel composite material, comprising:

[0059] A mixed fiber felt, comprising a woven fiber cloth layer and a non-woven fiber felt layer, wherein the woven fiber cloth layer and the non-woven fiber felt layer are alternately stacked along the thickness direction;

[0060] Carbon aerogel is used to fill the internal pores and interlayer gaps of the textile fiber fabric layer and the nonwoven fiber felt layer.

[0061] The ratio of the thickness of the nonwoven fiber felt layer to the fiber length in the nonwoven fiber felt layer is <1:2.

[0062] During implementation, the textile fiber fabric layer can provide directional reinforcement in the XY plane. The ratio of the thickness of the nonwoven fiber felt layer to the fiber length is <1:2, ensuring that the length of a single fiber in the felt layer is much greater than the thickness of the felt layer. The fibers are fully spread in the XY plane, forming large-area interlayer anchoring points. The proportion of Z-direction (thickness direction) oriented fibers is extremely low, making the nonwoven fiber felt layer anisotropic in both the XY plane and the Z direction. When a Z-direction crack (matrix crack) initiates, overcoming the large-area interlayer anchoring points requires pulling out or breaking a large number of fibers to propagate, thereby obtaining high fracture toughness in the Z direction. When the Z-direction crack (matrix crack) propagates, it requires pulling out or breaking a large number of fibers, resulting in high energy dissipation and increased resistance to crack propagation, which in turn improves the compressive strength in the compression direction.

[0063] In addition, the textile fiber fabric layer and the non-woven fiber felt layer are alternately stacked along the thickness direction to form a periodic layered structure. The fabric layer provides directional load-bearing in the XY plane (perpendicular to the thickness direction), and the felt layer acts as a "crack arresting layer" to force cracks to deflect or branch at the interlayer interface. The felt layer provides interlayer bonding and anti-delamination ability. As a "structural adhesive layer" and "crack blocking layer", the felt layer not only connects the fabric layer, but also inhibits the propagation of cracks in the Z direction, so that the composite material as a whole also constitutes anisotropic material in the XY plane and Z direction.

[0064] Compared with existing technologies, this invention constructs anisotropic composite materials in the XY plane and Z direction by alternating layers of nonwoven fiber felt and textile fiber cloth, and by controlling the ratio of nonwoven fiber felt thickness to fiber length. This allows the material to exhibit differentiated mechanical responses in the thickness direction and in the direction perpendicular to the thickness plane, meeting the performance requirements under complex stress conditions (such as strong compression environments with pressure applied in the thickness direction) while imparting high deformation toughness in the Z direction and reducing Z-direction cracks (matrix cracks). This makes differentiated design for the XY plane and Z direction possible, avoiding the defect of uniform and indistinguishable performance effects in all directions of existing isotropic materials. It also solves the problems of traditional isotropic aerogel materials that are difficult to meet the performance requirements under complex stress conditions and difficult to conduct targeted strength design.

[0065] Preferably, the ratio of the thickness of the nonwoven fiber felt layer to the fiber length in the nonwoven fiber felt layer satisfies the following condition: (1~3):7, which can be 1:7, 1.1:7, 1.2:7, 1.3:7, 1.4:7, 1.5:7, 1.6:7, 1.7:7, 1.8:7, 1.9:7, 2.0:7, 2.1:7, 2.2:7, 2.3:7, 2.4:7, 2.5:7, 2.6:7, 2.7:7, 2.8:7, 2.9:7 or 3:7.

[0066] During implementation, the ratio of nonwoven fiber felt layer thickness to fiber length is (1~3):7. On the one hand, this ensures that the length of a single fiber in the felt layer is much greater than the thickness of the felt layer, and that the fibers are fully spread in the XY plane to form large-area interlayer anchoring points, with a very low proportion of Z-oriented fibers. When Z-direction cracks (matrix cracks) initiate, overcoming the large-area interlayer anchoring points requires pulling out or breaking a large number of fibers to propagate, thus obtaining high Z-direction fracture toughness. When Z-direction cracks propagate, a large number of fibers need to be pulled out or broken, resulting in high energy dissipation and increased resistance to crack propagation. On the other hand, this avoids the situation where the ratio of nonwoven fiber felt layer thickness to fiber length is too small, causing the fibers to form heat conduction channels on the upper and lower surfaces of the nonwoven fiber felt layer, resulting in increased thermal conductivity and decreased thermal insulation performance.

[0067] Preferably, the nonwoven fiber felt layer is selected from low thermal conductivity fibers or carbon fibers and a mixture of one or more low thermal conductivity fibers. The low thermal conductivity fibers have a non-graphite crystal structure, and the precursor of the low thermal conductivity fibers has a greater linear shrinkage rate than that of carbon fibers during the carbonization process.

[0068] It should be noted that low thermal conductivity fiber precursors can be carbonized at high temperatures to obtain low thermal conductivity fibers.

[0069] The preparation of low thermal conductivity fibers in nonwoven fiber felt layers can be achieved by carbonizing the precursor of low thermal conductivity fibers at high temperature to obtain the finished low thermal conductivity fibers. When the nonwoven fiber felt layer is composed of a mixture of low thermal conductivity fibers and carbon fibers (i.e., when the mass ratio of low thermal conductivity fibers in the nonwoven fiber felt layer is not 0), it is necessary to mix the precursor of low thermal conductivity fibers with carbon fibers and then perform high-temperature carbonization treatment. During the high-temperature carbonization process, the low thermal conductivity fibers obtained from the precursor of low thermal conductivity fibers undergo a certain degree of linear shrinkage, while carbon fibers hardly shrink during the high-temperature carbonization process.

[0070] In practice, the textile fiber fabric layer and the non-woven fiber felt layer are impregnated with the precursor of carbon aerogel, so that the internal pores and interlayer gaps of the textile fiber fabric layer and the non-woven fiber felt layer are filled with the precursor of carbon aerogel. At the same time as the precursor of low thermal conductivity fiber carbonizes to form low thermal conductivity fiber, the precursor of carbon aerogel carbonizes to form carbon aerogel. Simultaneously, because the precursor of low thermal conductivity fiber shrinks and loses weight as it carbonizes to form low thermal conductivity fiber, the shrinkage process is synchronized with the carbon aerogel precursor carbonization process to form carbon aerogel. This effectively reduces the cracks (delamination cracks) in the matrix along the planar direction (XY direction) and effectively improves the mechanical properties of the material.

[0071] Compared with the prior art, the present invention introduces low thermal conductivity fibers into the nonwoven fiber felt layer, so that the low thermal conductivity fibers shrink synchronously with the carbon aerogel carbonization process, thereby effectively reducing cracks (delamination cracks) in the matrix along the planar direction (XY direction) and effectively improving the compressive strength of the material in the thickness direction. The 10% strain compressive strength is between 16.3MPa and 21.9MPa, preferably ≥21.0MPa.

[0072] Specifically, the precursor of the low thermal conductivity fiber can be one or more of viscose fiber, viscose fiber pre-oxidized yarn, polyacrylonitrile fiber, polyacrylonitrile fiber pre-oxidized yarn, and phenolic fiber.

[0073] During implementation, the precursor structures of viscose fiber, polyacrylonitrile fiber, and phenolic fiber determine that they are difficult to form highly ordered graphite crystals even at high temperatures; at the same time, the precursors of viscose fiber, polyacrylonitrile fiber, and phenolic fiber lose weight and shrink during the heating process, which is synchronized with the shrinkage of carbon aerogel carbonization molding process.

[0074] Specifically, the mass content of low thermal conductivity fiber precursor in the nonwoven fiber felt layer is 18% to 100%, which can be 18%, 19%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, or 100%.

[0075] It should be noted that, on the one hand, low thermal conductivity fibers have a non-graphite crystalline structure, which greatly reduces thermal conductivity compared to carbon fibers, thus helping to significantly reduce the thermal conductivity of the system and further improve thermal insulation performance.

[0076] On the other hand, the surface of low thermal conductivity fibers contains abundant active groups, which can form strong chemical bonds with carbon aerogel, thereby forming a strong interface.

[0077] Specifically, the thickness of the nonwoven fiber felt layer is 10mm to 30mm, and can be 10mm, 12mm, 14mm, 16mm, 18mm, 20mm, 22mm, 24mm, 26mm, 28mm, or 30mm, with a density of 270 kg / m³. 3 ~600 kg / m 3 .

[0078] It should be noted that when the thickness is too small (<10mm), the fibers are difficult to form large-area bridging between layers, the pore volume is insufficient, the improvement of interlayer fracture toughness is limited, and the "reinforcement-insulation" synergistic effect of carbon aerogel on the felt layer is weakened; if the felt layer is too thick (>30mm), even if the fiber length is sufficient, some fibers will be forced to align in the Z direction when forming the web, and the proportion of Z-oriented fibers will increase, which is not conducive to anti-delamination and low thermal conductivity.

[0079] Specifically, the thickness of the textile fiber fabric layer is 0.2mm to 2mm, and can be 0.2mm, 0.3mm, 0.4mm, 0.5mm, 0.6mm, 0.7mm, 0.8mm, 0.9mm, 1.0mm, 1.1mm, 1.2mm, 1.3mm, 1.4mm, 1.5mm, 1.6mm, 1.7mm, 1.8mm, 1.9mm or 2.0mm. The material can be carbon fiber or a low thermal conductivity fiber woven structure.

[0080] Specifically, the weaving structure of the textile fiber fabric layer is one or more of plain weave, twill weave, non-weft weave, and satin weave.

[0081] Specifically, the number of textile fiber fabric layers and non-woven fiber felt layers is ≥5.

[0082] It should be noted that the woven fiber cloth layer and the nonwoven fiber felt layer in the composite material of the present invention adopt a symmetrical or near-symmetrical structure. The above structure can eliminate the tensile-shear and bending-torsional coupling effects caused by the asymmetry of the layup, prevent the product from warping or bending unexpectedly during curing or under stress, and ensure the stability of the structural dimensions. With more than 5 layers in the symmetrical structure, the stress can be more evenly distributed on multiple interfaces, the peak stress is reduced by 30%-50%, and the overall load-bearing capacity is significantly improved.

[0083] Preferably, the number of layers of the textile fiber cloth layer and the nonwoven fiber felt layer is 5 to 25, and can be 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, or 25.

[0084] Specifically, the textile fiber fabric layer and the nonwoven fiber felt layer can be connected by needle punching, with a needle punching density of 5 needles / cm. 2 ~10 stitches / cm 2 It can be 5 stitches / cm 2 6 needles / cm 2 7 needles / cm 2 8 needles / cm 2 9 needles / cm 2 Or 10 stitches / cm 2 .

[0085] It should be noted that the needle-punching density is 5 needles / cm² to 10 needles / cm², forming fiber clusters in the thickness direction. This can significantly improve the interlayer stability of the multilayer alternating structure in subsequent processes and service, avoiding layup slippage and delamination; at the same time, it avoids excessive cutting of oriented fibers in the textile fiber layer, maintaining the design strength in the XY plane.

[0086] Specifically, the density of the composite material is 350 kg / m³. 3 ~1100kg / m 3 .

[0087] Compared with existing technologies, this invention consists of a multi-layer structure formed by alternating layers of textile fiber fabric and non-woven fiber felt along the thickness direction, with the thickness-to-fiber length ratio of the non-woven fiber felt layer controlled to be less than 1:2 (preferably (1~3):7). ​​Simultaneously, low thermal conductivity fibers (whose precursor carbonization shrinkage rate is greater than that of carbon fibers) are introduced into the non-woven fiber felt layer. Through anisotropic structural design, the material possesses high compressive strength (10% strain compressive strength reaches 16.3~21.9 MPa) and fracture toughness in the thickness direction, overcoming the shortcomings of traditional isotropic materials that are difficult to target with mechanical design. Furthermore, the low thermal conductivity fibers and carbon aerogel shrink synchronously during carbonization, effectively reducing internal microcracks and lowering interfacial thermal resistance, thereby significantly improving thermal insulation performance (room temperature thermal conductivity as low as 0.16~0.31 W·(m·K)). -1 At 800℃, its thermal conductivity is as low as 0.35~0.60 W·(m·K). -1 Ultimately, this achieved a synergistic optimization of low density, high strength, and low thermal conductivity.

[0088] On the other hand, the present invention provides a method for preparing a hybrid fiber felt reinforced carbon aerogel composite material, comprising:

[0089] S1: The nonwoven fiber felt preform is prepared by using a low thermal conductivity fiber precursor alone or by mixing a low thermal conductivity fiber precursor with carbon fiber.

[0090] S2: Prepare a mixed fiber felt preform by layering and knitting a non-woven fiber felt preform and a textile fiber cloth layer;

[0091] S3: Prepare a composite material intermediate by pre-impregnating and curing the mixed fiber felt with a carbon aerogel precursor solution of the first concentration;

[0092] S4: The composite material intermediate is impregnated with a second-concentration carbon aerogel precursor solution and cured to prepare a composite material precursor; the carbon aerogel precursor concentration in the second-concentration carbon aerogel precursor solution is higher than that in the first-concentration carbon aerogel precursor solution.

[0093] S5: High-temperature carbonization of composite material precursors to prepare finished composite materials with a mixed fiber felt reinforcement structure.

[0094] Specifically, in step S1, the mass content of low thermal conductivity fiber precursor in the nonwoven fiber felt layer is 20%~100%, which can be 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95% or 100%.

[0095] It should be noted that if the mass content of low thermal conductivity fiber precursor in the nonwoven fiber felt layer is too low, the thermal conductivity will increase. The shrinkage of the nonwoven fiber felt layer and the shrinkage during the formation of carbon aerogel are difficult to match, resulting in an increase in cracks (delamination cracks) in the matrix along the planar direction (XY direction) and a decrease in the compressive strength of the material in the thickness direction.

[0096] Specifically, step S1, which involves preparing a nonwoven fiber felt preform by mixing a low thermal conductivity fiber precursor with carbon fiber, includes:

[0097] S101: The low thermal conductivity fiber precursor and carbon fiber filament are broken into single fibers and then fully mixed according to the designed mass ratio.

[0098] S102: Use a roller carding machine or a cover plate carding machine to output a thin fiber web with a thickness of 0.3 mm to 0.8 mm and a suitable areal density;

[0099] S103: Using a cross-laying machine to lay multiple layers of thin fiber web to obtain a nonwoven fiber felt layer of the target thickness.

[0100] Specifically, in step S2, the needle density is 5 needles / cm. 2 ~10 stitches / cm 2 It can be 5 stitches / cm 2 6 needles / cm 2 7 needles / cm 2 8 needles / cm 2 9 needles / cm 2 Or 10 stitches / cm 2 .

[0101] Specifically, step S3, impregnating the felt layer under normal pressure helps maintain the original loose, high-porosity structure, while compressing the felt layer makes the originally loose, high-porosity felt layer compacted.

[0102] To avoid the fibers being forced to reorient in the Z direction and disrupt the main distribution in the XY plane, the main fiber structure is maintained in the XY plane, providing an ideal configuration for subsequent carbon aerogel filling and interlayer anchoring.

[0103] Specifically, in steps S3 and S4, the carbon aerogel precursor solution is a mixture of phenolic resin, curing agent, and polar solvent.

[0104] Specifically, the phenolic resin is one or more of the following: ordinary phenolic resin, boron phenolic resin, and silicon phenolic resin.

[0105] Specifically, the curing agent can be hexamethylenetetramine, and the amount added is 10wt% to 20wt% of the phenolic resin, which can be 10wt%, 12wt%, 14wt%, 16wt%, 18wt%, or 20wt%.

[0106] Specifically, the polar solvent is one or more of n-butanol, isopropanol, ethanol, and ethylene glycol.

[0107] Specifically, step S3 includes: immersing the mixed fiber felt in a first-concentration carbon aerogel precursor solution for 30s~60s, removing the fiber felt and squeezing out the excess solution, and then placing the mixed fiber felt in a mold for atmospheric pressure curing reaction.

[0108] Specifically, the curing temperature in steps S3 and S4 is 80℃~120℃, which can be 80℃, 85℃, 90℃, 95℃, 100℃, 105℃, 110℃, 115℃ or 120℃; the time is 24h~60h, which can be 24h, 26h, 28h, 30h, 32h, 34h, 36h, 38h, 40h, 42h, 44h, 46h, 48h, 50h, 52h, 54h, 56h, 58h or 60h.

[0109] It should be noted that if the temperature is too low, the curing will be incomplete, and the precursor will settle and be unevenly distributed in the felt layer due to gravity. If the temperature is too high, premature pyrolysis or non-uniform cross-linking may occur, resulting in defects in the aerogel structure. At the same time, the low thermal conductivity fiber precursors (especially pre-oxidized fibers) in the felt layer begin to experience significant thermal weight loss at temperatures above 130°C, which affects the subsequent carbonization yield and structural consistency.

[0110] Specifically, in step S3, the carbon aerogel precursor content in the carbon aerogel precursor solution is 2wt%~8wt%, which can be 2wt%, 3wt%, 4wt%, 5wt%, 6wt%, 7wt%, or 8wt%; the curing agent content is 10wt%~20wt% of the amount of carbon aerogel precursor used.

[0111] It should be noted that using a carbon aerogel precursor solution with a content of 2wt%~8wt% can prevent the carbon aerogel precursor concentration from rising excessively, so that it only plays a role in fiber bonding and enhances the overall rigidity of the preform.

[0112] Specifically, in step S4, the carbon aerogel precursor content in the carbon aerogel precursor solution is 20wt%~55wt%, which can be 20wt%, 22wt%, 24wt%, 26wt%, 28wt%, 30wt%, 32wt%, 34wt%, 36wt%, 38wt%, 40wt%, 42wt%, 44wt%, 46wt%, 48wt%, 50wt%, 52wt%, 54wt%, or 55wt%; the curing agent content is 10wt%~20wt% of the amount of carbon aerogel precursor used.

[0113] It should be noted that the carbon aerogel precursor content is 20wt%~55wt% because too low a concentration of carbon aerogel precursor cannot form a complete aerogel structure; too high a concentration results in excessive viscosity, which can easily lead to deformation when wetting the preform.

[0114] It should be noted that the low thermal conductivity fiber precursors (viscose fiber, polyacrylonitrile filament, pre-oxidized fiber, etc.) in the felt layer will generate micropores / mesopores during carbonization, which is the key source of low thermal conductivity. The low concentration and good fluidity of the pre-impregnated carbon aerogel precursor can completely fill the pores between fibers. The low concentration of pre-impregnation can effectively maintain the structural shape of the fibers and avoid bending and deformation during the high concentration impregnation process, thus improving the impregnation effect. During impregnation, the carbon aerogel precursor forms a complete aerogel structure in the fiber gaps, further improving the thermal insulation performance and achieving low thermal conductivity.

[0115] Compared with existing technologies, this invention uses carbon aerogel precursor solutions of different concentrations for pre-impregnation and impregnation in sequence. Low-concentration pre-impregnation can effectively maintain the structural shape of the fiber and avoid bending deformation during high-concentration impregnation, thereby improving the impregnation effect. During impregnation, the carbon aerogel precursor forms a complete aerogel structure in the fiber gaps, further improving the thermal insulation performance and achieving low thermal conductivity.

[0116] Specifically, the impregnation pressure in step S4 is 0.1MPa~0.4MPa, and can be 0.1MPa, 0.12MPa, 0.15MPa, 0.18MPa, 0.2MPa, 0.22MPa, 0.25MPa, 0.28MPa, 0.3MPa, 0.32MPa, 0.35MPa, 0.38MPa, 0.4MPa, 0.42MPa, 0.45MPa, 0.48MPa or 0.2MPa.

[0117] It should be noted that an impregnation pressure of 0.1MPa to 0.4MPa ensures that the low-viscosity precursor penetrates a 10 to 30 mm thick felt layer while greatly shortening the impregnation time; the pressure range is below the fiber deflection threshold, ensuring that the main fiber body of the felt layer is distributed along the XY plane, avoiding the cross-layer fiber clusters formed by the straightening needle punch by high-pressure fluid.

[0118] Preferably, an atmospheric pressure drying step is provided between steps S4 and S5:

[0119] S4.5: Dry the composite material precursor at 80℃~120℃ under normal pressure for 12h~48h to remove polar solvents and obtain a dried composite material precursor.

[0120] It should be noted that during atmospheric pressure drying, when the solvent (such as water or alcohol) in the pores of the wet gel evaporates, the gas-liquid interface moves inside the pores, generating huge capillary forces that damage the nanoporous structure and affect the low thermal conductivity of the carbon aerogel. Compared with existing technologies, this invention achieves the filling and support of the fiber's own micropores by using carbon aerogel precursor solutions of different concentrations for pre-impregnation and impregnation in sequence, avoiding the damage to the nanoporous structure caused by atmospheric pressure drying, and greatly saving costs compared with traditional supercritical drying.

[0121] In step S4.5, the ambient pressure drying temperature can be 80℃, 85℃, 90℃, 95℃, 100℃, 105℃, 110℃, 115℃ or 120℃; the ambient pressure drying time can be 12h, 14h, 16h, 18h, 20h, 22h, 24h, 26h, 28h, 30h, 32h, 34h, 36h, 38h, 40h, 42h, 44h, 46h or 48h.

[0122] Specifically, the high-temperature carbonization atmosphere in step S5 is nitrogen or argon, including:

[0123] S501: Increase the temperature from room temperature to 290℃~310℃ at a rate of 3℃ / min~5℃ / min, and hold for 30min~90min;

[0124] S502: Increase to 700℃~1000℃ at a rate of 1℃ / min~5℃ / min, hold for 30min~120min, and then decrease to room temperature at a rate of 1℃ / min~3℃ / min.

[0125] Specifically, the temperature in step S502 can be 700℃, 750℃, 800℃, 850℃, 900℃, 950℃ or 1000℃.

[0126] It should be noted that phenolic resin begins to pyrolyze at 200℃~300℃, releasing small molecules such as water, phenols, and aldehydes; the low thermal conductivity fiber precursors (viscose, polyacrylonitrile filaments, and pre-oxidized fibers) in the felt layer have not yet undergone violent pyrolysis below 300℃. The heat preservation in step S501 at 290℃~310℃ allows the pre-oxidized fibers to complete the initial cyclization and stabilization, avoiding sudden shrinkage during subsequent high-temperature carbonization that could lead to structural damage.

[0127] In step S501, a heating rate that is too slow (<2℃ / min) is inefficient; a rate that is too fast (>5℃ / min) will cause a violent release of phenolic resin gas, resulting in internal gas pressure accumulation, bubbling, and microcracks. At the same time, the fiber structure is stable at this rate, and the thermal expansion coefficients of the aerogel and fiber at the interlayer interface are significantly different. A rapid heating rate will cause thermal stress concentration at the interface, leading to micro-delamination.

[0128] The heat preservation time of 30min~90min in step S501 can ensure that the initial pyrolysis reaction of phenolic resin and fiber precursor is basically completed, releasing most of the small molecule gas, while avoiding excessive shrinkage of aerogel or fiber oxidation caused by excessive heat preservation time.

[0129] In step S502, the heating rate is 1℃ / min to 5℃ / min in the range of 300℃ to 700℃. The phenolic resin undergoes violent pyrolysis. If the heating rate is too fast, the pore walls of the aerogel will collapse locally due to thermal stress, the specific surface area will decrease, and microcracks will be generated at the fiber / aerogel interface due to asynchronous shrinkage.

[0130] In step S502, the final carbonization temperature is 700℃~1000℃, which can ensure complete carbonization of the aerogel, retain the micropores formed by the carbonization of the fiber precursor, and avoid excessive reaction between the carbon fiber (if present) and the aerogel.

[0131] In step S502, the holding time is 30min~120min, which can ensure that the core temperature reaches the set value and the carbonization reaction is basically completed. At the same time, extending the holding time can make the temperature field uniform and the carbonization complete, avoiding insufficient carbonization of the core.

[0132] In step S502, the cooling rate of 1℃ / min to 3℃ / min can reduce thermal stress, coordinate the shrinkage of each layer, and avoid the thermal stress caused by the temperature difference between the inside and outside during rapid cooling, which could lead to microcracks or delamination.

[0133] Compared with existing technologies, this invention achieves multiple synergistic technological effects by sequentially executing a series of process steps: "preparing a nonwoven felt layer by mixing a low thermal conductivity fiber precursor with carbon fiber → alternately layering and needle-punching with a woven fabric layer → pre-impregnating with a low-concentration carbon aerogel precursor under normal pressure → impregnating with a high-concentration carbon aerogel precursor under vacuum pressure → step-by-step high-temperature carbonization".

[0134] On the one hand, low-concentration pre-impregnation protects the fluffy structure of the fiber felt and the micro- and nanopores of the fibers themselves, while high-concentration impregnation constructs a complete aerogel network in the fiber gaps. This combination not only avoids the damage to the nanopores caused by atmospheric pressure drying (thus eliminating the need for supercritical drying and significantly reducing costs), but also allows the low thermal conductivity fiber precursor and carbon aerogel to shrink synchronously during carbonization, effectively suppressing delamination cracks. On the other hand, the stepped carbonization heating (holding at 300℃, then slowly heating at 1℃ / min~5℃ / min to 700℃~1000℃) reduces microcracks caused by thermal stress, ensuring a dense and uniform material structure. Ultimately, this method can stably prepare materials with low density (0.72 g / cm³~0.81 g / cm³), high compressive strength (10% strain compressive strength reaching 16.3 MPa~21.9 MPa), and excellent thermal insulation performance (room temperature thermal conductivity as low as 0.16 W·(m·K)). -1 ~0.31 W·(m·K)-1 Its thermal conductivity at 800℃ is as low as 0.35 W·(m·K). -1 ~0.60 W / (m·K) -1 ) Hybrid fiber felt reinforced carbon aerogel composite material.

[0135] Compared with existing technologies, the hybrid fiber felt reinforced carbon aerogel composite material and its preparation method provided by this invention have the following significant features and advantages:

[0136] Product Structure

[0137] Anisotropic multilayer alternating structure: Textile fiber cloth layer and non-woven fiber felt layer are alternately stacked along the thickness direction, and the ratio of non-woven fiber felt layer thickness to fiber length is controlled at <1:2 (preferably (1~3):7), forming anisotropic material with different properties in the XY plane and Z direction.

[0138] Low thermal conductivity fiber reinforcement system: The nonwoven fiber felt layer is made of low thermal conductivity fibers (such as viscose fiber, polyacrylonitrile fiber, phenolic fiber, etc.) or a mixture thereof with carbon fiber. The carbonization shrinkage rate of this type of fiber precursor is greater than that of carbon fiber.

[0139] Complete carbon aerogel filling: Carbon aerogel fills the internal pores and interlayer gaps of the fiber cloth layer and felt layer, forming a continuous nanoporous network.

[0140] Core advantages

[0141] (1) Excellent mechanical properties and designability:

[0142] The anisotropic structure gives the material high compressive strength and high fracture toughness in the thickness direction (Z direction), with a 10% strain compressive strength of 16.3~21.9 MPa (preferably ≥21.0 MPa), which is much higher than that of traditional isotropic carbon aerogels.

[0143] Multi-layer symmetrical ply structure (≥5 layers) ensures uniform stress distribution, reduces peak stress by 30%~50%, avoids warping deformation, and provides good dimensional stability.

[0144] When cracks propagate, a large number of fibers need to be pulled out or broken, resulting in high energy dissipation and significantly improved resistance to delamination.

[0145] (2) Excellent thermal insulation performance:

[0146] The room temperature thermal conductivity is as low as 0.16~0.31 W·(m·K). -1 At 800℃, its thermal conductivity is as low as 0.35~0.60 W·(m·K). -1 It reduces carbon aerogel by about 50% compared to traditional carbon fiber reinforced carbon aerogel.

[0147] (3) The preparation process is economical and efficient:

[0148] By adopting a two-step method of "low-concentration pre-impregnation + high-concentration impregnation", the high cost of supercritical drying is avoided, and atmospheric pressure drying is achieved, which significantly reduces production costs.

[0149] The low thermal conductivity fiber precursor shrinks synchronously with the carbon aerogel, reducing internal microcracks and improving yield.

[0150] (4) Low density and excellent overall performance:

[0151] The density of the composite material is 0.72~0.81 g·cm³. -3 It achieves a synergistic optimization of high strength and low thermal conductivity at low density.

[0152] (5) Meets the requirements of complex working conditions:

[0153] Differentiated strength designs can be made for thickness-direction compression and complex stress conditions, making it suitable for harsh environments such as aircraft thermal protection systems and high-temperature insulation components.

[0154] To more clearly describe the present invention, the following embodiments and comparative examples are provided for further illustration.

[0155] Example 1

[0156] This embodiment provides a method for preparing a hybrid fiber felt reinforced carbon aerogel composite material, including:

[0157] S1: Select a low thermal conductivity fiber precursor to prepare a nonwoven fiber felt preform alone or select a low thermal conductivity fiber precursor to mix with carbon fiber to prepare a nonwoven fiber felt preform.

[0158] Specifically, it includes:

[0159] S101: Cut polyacrylonitrile pre-oxidized fiber and ordinary carbon fiber into 70mm pieces, break them apart into single fibers, and then mix them evenly in a mass ratio of 1:3.

[0160] S102: Outputs 0.3 mm to 0.8 mm and a surface density of 170 g / m² using a roller carding machine. 2 Thin fiber web;

[0161] S103: Using a cross-laying machine, multiple layers of thin fiber web are laid to obtain a 10mm nonwoven fiber felt layer. The ratio of the thickness of the nonwoven fiber felt layer to the length of the fiber filaments therein is 1:7.

[0162] S2: Prepare a mixed fiber felt preform by layering and knitting a non-woven fiber felt preform and a textile fiber cloth layer;

[0163] Specifically, this includes: laying a 220mm×220mm non-woven fiber felt layer on a foam board, with a fiber felt layer density of 170g / m². 2 Subsequently, a sample with dimensions of 220mm × 220mm, a thickness of 1mm, and a surface density of 220g / m³ was prepared. 2 Carbon fiber fabric is laid on a nonwoven fiber felt layer; then carbon fiber fabric and nonwoven fiber felt layer are laid in a cyclical manner, with 23 layers of carbon fiber fabric and 24 layers of nonwoven fiber felt layer laid; the mixed fiber laminate structure is needle-punched using a needle-punching process with a needle-punching density of 10 needles / cm. 2 A mixed fiber reinforced body with dimensions of 220mm×220mm×20mm and a carbon fiber content of approximately 75wt% was obtained, with a bulk density of 450kg / m³. 3 ;

[0164] S3: Prepare a composite material intermediate by pre-impregnating and curing the mixed fiber felt with a carbon aerogel precursor solution of the first concentration;

[0165] Specifically, this involves dissolving 4 parts of phenolic resin in 95 parts of isopropanol solution, and adding 20% ​​hexamethylenetetramine curing agent based on the mass of the phenolic resin to obtain a 4wt% dilute phenolic resin solution.

[0166] A density of 450 kg / m³ 3 The mixed fiber felt was placed in an open container, and a 4wt% dilute phenolic solution was poured in. The mixture was immersed for 30 seconds, then the fiber felt was removed, and excess solution was squeezed out. The fiber felt was then placed in a custom-made 220×220×20mm drying fixture and placed in an oven for curing and drying at 120℃ for 24 hours, resulting in a composite material intermediate with dimensions of 220×220×20mm.

[0167] S4: The composite material intermediate is impregnated with a second-concentration carbon aerogel precursor solution and then cured to prepare the composite material precursor;

[0168] Specifically, this involves dissolving 45 parts of phenolic resin in 55 parts of isopropanol solution, and adding 20% ​​hexamethylenetetramine curing agent (based on the mass of the phenolic resin) to obtain a 45wt% dilute phenolic resin solution.

[0169] The rigid hybrid fiber reinforcement was placed in a custom-made stainless steel mold and sealed. After installing the inlet and outlet valves, the airtightness of the device was checked. At room temperature, the prepared phenolic resin solution was slowly injected into the mold from bottom to top using a vacuum-low-pressure infusion method. Initially, the infusion pressure was set to 0.1 MPa. When a continuous flow of resin solution appeared at the mold outlet, the pressure was increased to 0.2 MPa. When the solution at the outlet valve was continuously homogeneous, the pressure was increased to 0.4 MPa and infusion continued for 10 minutes. Finally, the outlet and inlet valves of the mold were closed. The mold was then sealed and placed at 90°C. o Phenolic aerogel composite material was prepared in a C oven based on sol-gel reaction. After 48 h of molding, the composite material was cooled to room temperature to obtain the final product.

[0170] S4.5: Demold the composite material and then place it at 80°C. o Dry in a C oven for 6 hours, then raise the temperature to 100°C. o Dry at 0°C for 24 hours, at which point the sample is almost completely dry. After drying, allow the oven to cool to room temperature, then remove the sample to prepare a dried composite intermediate with a density of approximately 0.9 g / cm³. 3 ;

[0171] S5: A composite material with a mixed fiber felt reinforcement structure was prepared by high-temperature carbonization of the composite precursor. The dried phenolic aerogel composite material was placed in a box furnace for high-temperature carbonization under nitrogen or argon atmosphere. First, the temperature was increased from room temperature to 300℃ at 3℃ / min and held for 60 min. Then, the temperature was increased to 700℃ at 1.5℃ / min and held for 60 min. Finally, the temperature was decreased to room temperature at a rate of 1℃ / min. The material was then removed, yielding a mixed fiber felt reinforced carbon aerogel composite material with a density of approximately 0.75 g / cm³. 3 .

[0172] This embodiment provides a hybrid fiber felt reinforced carbon aerogel composite material, prepared by the method described above.

[0173] Example 2

[0174] This embodiment provides a method for preparing a mixed fiber felt reinforced carbon aerogel composite material, which is largely the same as the preparation process in Example 1. The difference is that the nonwoven fiber felt layer prepared in step S1 only contains viscose fiber pre-oxidized filaments; the mixed fiber felt prepared in step S2 contains approximately 55 wt% carbon fiber.

[0175] This embodiment provides a hybrid fiber felt reinforced carbon aerogel composite material, prepared by the above method, with the resulting hybrid fiber felt having a density of 0.45 g / cm³. 3 A mixed fiber felt reinforced carbon aerogel composite material with a density of approximately 0.81 g / cm³ was obtained. 3.

[0176] Example 3

[0177] This embodiment provides a method for preparing a mixed fiber felt reinforced carbon aerogel composite material, which is largely the same as the preparation process in Example 1. The difference is that in step S1, the ratio of carbon fiber to polyacrylonitrile pre-oxidized fiber in the nonwoven fiber felt layer is controlled so that the carbon fiber content in the resulting mixed fiber felt is about 25 wt%.

[0178] This embodiment provides a hybrid fiber felt reinforced carbon aerogel composite material, prepared by the above method, with a density of 0.45 g / cm³. 3 .

[0179] Example 4

[0180] This embodiment provides a method for preparing a mixed fiber felt reinforced carbon aerogel composite material, which is largely the same as the preparation process in Example 1. The difference is that all the carbon fiber cloth in the mixed fiber felt prepared in step S2 is replaced with polyacrylonitrile pre-oxidized fiber cloth with the same weaving parameters, and the carbon fiber content of the non-woven fiber felt layer is controlled to be 0, and the non-woven fiber felt layer is entirely composed of polyacrylonitrile pre-oxidized fibers.

[0181] This embodiment provides a hybrid fiber felt reinforced carbon aerogel composite material, prepared by the above method, with a density of 0.45 g / cm³. 3 .

[0182] Example 5

[0183] This embodiment provides a method for preparing a mixed fiber felt reinforced carbon aerogel composite material, which is largely the same as the preparation process in Example 1. The difference is that the thickness of the nonwoven fiber felt layer is 20 mm, the length of the acrylonitrile pre-oxidized fiber and the ordinary carbon fiber fiber in the nonwoven fiber felt layer is 70 mm, and the ratio of the thickness of the nonwoven fiber felt layer to the length of the fiber is 2:7.

[0184] This embodiment provides a hybrid fiber felt reinforced carbon aerogel composite material, prepared by the method described above.

[0185] Example 6

[0186] This embodiment provides a method for preparing a mixed fiber felt reinforced carbon aerogel composite material, which is largely the same as the preparation process in Example 1. The difference is that the thickness of the nonwoven fiber felt layer is 10 mm, the length of the acrylonitrile pre-oxidized fiber and the ordinary carbon fiber fiber in the nonwoven fiber felt layer is 80 mm, and the ratio of the thickness of the nonwoven fiber felt layer to the length of the fiber is 1:8.

[0187] This embodiment provides a hybrid fiber felt reinforced carbon aerogel composite material, prepared by the method described above.

[0188] Example 7

[0189] This embodiment provides a method for preparing a mixed fiber felt reinforced carbon aerogel composite material, which is largely the same as the preparation process in Example 1, except that the carbon aerogel precursor content in the carbon aerogel precursor solution in step S3 is 6 wt%.

[0190] This embodiment provides a hybrid fiber felt reinforced carbon aerogel composite material, prepared by the method described above.

[0191] Example 8

[0192] This embodiment provides a method for preparing a mixed fiber felt reinforced carbon aerogel composite material, which is largely the same as the preparation process in Example 1, except that the carbon aerogel precursor content in the carbon aerogel precursor solution in step S3 is 8 wt%.

[0193] This embodiment provides a hybrid fiber felt reinforced carbon aerogel composite material, prepared by the method described above.

[0194] Example 9

[0195] This embodiment provides a method for preparing a mixed fiber felt reinforced carbon aerogel composite material, which is largely the same as the preparation process in Example 1, except that: first, the temperature is raised from room temperature to 310°C at a rate of 5°C / min and held for 60 min; then, the temperature is raised to 800°C at a rate of 3°C / min and held for 90 min; and then, the temperature is lowered to room temperature at a rate of 1°C / min.

[0196] This embodiment provides a hybrid fiber felt reinforced carbon aerogel composite material, prepared by the method described above.

[0197] Example 10

[0198] This embodiment provides a method for preparing a mixed fiber felt reinforced carbon aerogel composite material, which is largely the same as the preparation process in Example 1, except that: the temperature is increased from room temperature to 290°C at a rate of 3°C / min and held for 40 min; then the temperature is increased to 750°C at a rate of 2°C / min and held for 40 min; and then the temperature is decreased to room temperature at a rate of 2°C / min.

[0199] This embodiment provides a hybrid fiber felt reinforced carbon aerogel composite material, prepared by the method described above.

[0200] Comparative Example 1

[0201] This comparative example provides a method for preparing a mixed fiber felt reinforced carbon aerogel composite material. The preparation process of Comparative Example 1 is largely the same as that of Example 2, except that the length of the viscose fiber pre-oxidized filament in the nonwoven fiber felt layer of Comparative Example 1 is 20 mm, and the rest is the same as that of Example 2.

[0202] Comparative Example 2

[0203] This comparative example provides a method for preparing a mixed fiber felt reinforced carbon aerogel composite material. The preparation process of comparative example 2 is largely the same as that of example 2, except that comparative example 2 does not include step S3 pre-impregnation treatment. After step S2, step S4 is directly performed with impregnation using a 45wt% phenolic solution. The rest is the same as in example 2.

[0204] Comparative Example 3

[0205] This comparative example provides a method for preparing a mixed fiber felt reinforced carbon aerogel composite material. The preparation process of Comparative Example 3 is largely the same as that of Example 2, except that the final carbonization temperature of step S5 in Comparative Example 3 is 1100℃, and the rest is the same as that in Example 2.

[0206] Comparative Example 4

[0207] This comparative example provides a method for preparing a mixed fiber felt reinforced carbon aerogel composite material. The preparation process of Comparative Example 4 is largely the same as that of Example 2, except that the phenolic resin mass concentration in the precursor solution in step S4 of Comparative Example 4 is 15 wt%, and the rest is the same as in Example 2.

[0208] Comparative Example 5

[0209] This comparative example provides a method for preparing a mixed fiber felt reinforced carbon aerogel composite material. The preparation process of Comparative Example 5 is largely the same as that of Example 2, except that the content of the nonwoven fiber felt layer prepared in step S1 is 0, that is, the fiber preform is composed of 100% carbon fiber.

[0210] This comparative example provides a hybrid fiber felt reinforced carbon aerogel composite material, prepared by the above method, with a density of 0.45 g / cm³. 3 .

[0211] Performance testing

[0212] The performance testing of the above embodiments and comparative examples mainly includes:

[0213] Compression performance test: The compressive strength of the composite material along the Z-axis (thickness direction) was tested using an electronic universal testing machine MTS E44.304-30 kN, in accordance with the test method for compression performance of carbon-carbon composite materials GB / T34559-2017.

[0214] Thermal conductivity testing: The room temperature thermal conductivity of the composite material along the Z-axis (thickness direction) was tested using the flat plate heat flow method (NETZSCH HFM 436), and the standard GB / T10295-2008 for testing the steady-state thermal resistance and related properties of insulation materials was adopted.

[0215] The test results are shown in Table 1.

[0216] Table 1 Performance Test Results

[0217]

[0218] Based on Examples 1-10 and Comparative Examples 1-5, and referring to Table 1, it can be seen that the carbonized densities of the composite materials with mixed fiber felt reinforcement structures prepared in Examples 1-4 are not significantly different, ranging from 0.72 to 0.81 g·cm³. -3 In Example 2, pure low thermal conductivity felt was used instead of carbon fiber felt, which improved the matching degree of carbonization shrinkage between the matrix and the fiber reinforcement along the thickness direction (Z), effectively reducing micro-defects inside the composite material, making the matrix more continuous in the thickness direction. Therefore, the 10% strain compressive strength is higher than that of Examples 1 and 3. The preferred 10% strain compressive strength is between 16.3 and 21.9 MPa, and preferably ≥ 21.0 MPa, which is much higher than the 15.5 MPa of Comparative Example 5. Figure 1-3 As shown, high-magnification photographs of the surfaces of the finished product in Example 2 show no obvious delamination defects. Figure 4 As shown, the aerogel micropores in the finished product of Example 2 are uniform.

[0219] Examples 1-10 show that the finished composite materials with a mixed fiber felt reinforcement structure have a room temperature thermal conductivity of 0.16~0.33 W·(m·K). -1 Preferably, the concentration is ≤0.19 W·(m·K). -1 This is far lower than the 0.35 W·(m·K) of Comparative Example 5. -1 The thermal conductivity was reduced by nearly 50%; the composite materials with mixed fiber felt reinforcement structures prepared in Examples 1-10 had a thermal conductivity of 0.35~0.68 W·(m·K) at 800℃. -1 Preferably, the concentration is ≤0.38 W·(m·K). -1 This is far lower than the 0.69 W·(m·K) of Comparative Example 5. -1 This represents a reduction of nearly 50%.

[0220] The strength of Comparative Example 1 is lower than that of Example 2. This is because short fibers (20 mm) are prone to slippage and buckling due to insufficient entanglement and interlacing between fibers, resulting in poor support of the network structure and thus lower compressive strength and modulus. Medium-length fibers (70 mm) exhibit enhanced interlacing and entanglement, forming a more stable three-dimensional network structure. During compression, the fibers can better cooperate in bearing load, improving interfacial shear transfer efficiency. Simultaneously, the buckling resistance of the fibers themselves increases because the fiber length is sufficient to prevent bending or slippage, thus significantly improving compressive strength and modulus.

[0221] The strength and room temperature thermal conductivity of Comparative Examples 2 and 3 are significantly higher than those of Example 2. Due to the poor toughness of the low thermal conductivity fibers, Comparative Example 2 lacks a pre-impregnation treatment, which causes the fiber felt to be compressed and deformed as a whole, increasing its bulk density. Furthermore, the fiber orientation gradually shifts from the planar XY direction to the thickness direction (Z direction), providing more heat transfer channels along the thickness direction. Therefore, the composite material of Comparative Example 2 has increased strength and thermal conductivity.

[0222] Comparative Example 3 exhibits a higher carbonization temperature, resulting in more complete pyrolysis of the matrix and low thermal conductivity fibers, leading to a denser structure and thus higher strength. Simultaneously, the matrix and low thermal conductivity fibers show a higher degree of graphitization, significantly increasing their solid-state thermal conductivity and consequently, a significant increase in the thermal conductivity of the composite material.

[0223] The resin concentration in Comparative Example 4 was too low (15wt%), resulting in an excessively low density of the composite material, which in turn resulted in low thermal conductivity and compressive strength.

[0224] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing a hybrid fiber felt-reinforced carbon aerogel composite material, characterized in that, include: S1: The nonwoven fiber felt preform is prepared by using a low thermal conductivity fiber precursor alone or by mixing a low thermal conductivity fiber precursor with carbon fiber. S2: Prepare a mixed fiber felt preform by layering and knitting a non-woven fiber felt preform and a textile fiber cloth layer; S3: The mixed fiber felt preform is pre-impregnated and cured with a carbon aerogel precursor solution of the first concentration to prepare a composite material intermediate; S4: The composite material intermediate is impregnated with a second-concentration carbon aerogel precursor solution and then cured to prepare the composite material precursor; The carbon aerogel precursor concentration in the second concentration carbon aerogel precursor solution is higher than that in the first concentration carbon aerogel precursor solution. S5: High-temperature carbonization of composite material precursors to prepare finished composite materials with mixed fiber felt reinforcement structure; Step S5 includes: S501: Increase the temperature from room temperature to 290℃~310℃ at a rate of 3℃ / min~5℃ / min, and hold for 30min~90min; S502: Increase to 700℃~1000℃ at a rate of 1℃ / min~5℃ / min, hold for 30min~120min, and then decrease to room temperature at a rate of 1℃ / min~3℃ / min; The hybrid fiber felt reinforced carbon aerogel composite material includes: A mixed fiber felt, comprising a woven fiber cloth layer and a non-woven fiber felt layer, wherein the woven fiber cloth layer and the non-woven fiber felt layer are alternately stacked along the thickness direction; Carbon aerogel is used to fill the internal pores and interlayer gaps of the textile fiber fabric layer and the nonwoven fiber felt layer. The ratio of the thickness of the nonwoven fiber felt layer to the fiber length in the nonwoven fiber felt layer is <1:2; The nonwoven fiber felt layer is made of low thermal conductivity fiber or a mixture of carbon fiber and one or more low thermal conductivity fibers. The low thermal conductivity fiber has a non-graphite crystal structure, and the precursor of the low thermal conductivity fiber has a greater linear shrinkage rate than carbon fiber during the carbonization process.

2. The method for preparing a hybrid fiber felt-reinforced carbon aerogel composite material according to claim 1, characterized in that, The ratio of the thickness of the nonwoven fiber felt layer to the fiber length in the nonwoven fiber felt layer satisfies the following condition: (1~3):

7.

3. The method for preparing a hybrid fiber felt-reinforced carbon aerogel composite material according to claim 1, characterized in that, The thickness of the nonwoven fiber felt layer is 10mm~30mm.

4. The method for preparing a mixed fiber felt reinforced carbon aerogel composite material according to claim 1, characterized in that, The precursor of the low thermal conductivity fiber is one or more of viscose fiber, viscose fiber pre-oxidized yarn, polyacrylonitrile fiber, polyacrylonitrile fiber pre-oxidized yarn, and phenolic fiber.

5. A method for preparing a mixed fiber felt reinforced carbon aerogel composite material according to any one of claims 1-4, characterized in that, The number of layers in both the textile fiber fabric layer and the nonwoven fiber felt layer is ≥5.

6. The method for preparing a mixed fiber felt reinforced carbon aerogel composite material according to claim 1, characterized in that, In step S3, the carbon aerogel precursor content in the mixture is 2wt%~8wt%.

7. The method for preparing a mixed fiber felt reinforced carbon aerogel composite material according to claim 1, characterized in that, In step S4, the carbon aerogel precursor content in the mixture is 20wt%~55wt%.

8. The method for preparing a mixed fiber felt reinforced carbon aerogel composite material according to claim 7, characterized in that, The impregnation pressure in step S4 is 0.1 MPa to 0.4 MPa.

9. A hybrid fiber felt reinforced carbon aerogel composite material, characterized in that, Prepared by the preparation method according to any one of claims 1-8.

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