High-mechanical-strength carbon aerogel composite material and preparation method thereof

Abstract

The invention discloses a high-mechanical-strength carbon aerogel composite material and a preparation method thereof. According to the method, homogeneous z-direction fibers are introduced into a polyacrylonitrile-based pre-oxidized fiber needled felt by means of a sewing process, the distribution proportion of the z-direction fibers is increased, and after the sewn needled felt and phenolic sol are compounded and cracked, the carbon aerogel composite material with high mechanical strength can be obtained. In the stress process of the composite material, the z-direction fibers introduced through sewing can provide numerous stress supporting column points, and the mechanical strength of the composite material is greatly improved. The method has the characteristics of simplicity in operation, no need of solvent replacement, suitability for large-scale production and the like, and is expected to be applied to bearing / thermal insulation materials in the field of light thermal protection.

Description

Technical Field

[0001] The invention relates to a high mechanical strength carbon aerogel composite material and a preparation method thereof, belongs to the field of composite material preparation, and is expected to be applied to load-bearing / heat-insulating materials in the field of lightweight thermal protection. Background Art

[0002] Aerogel is a type of nanoporous material formed by the accumulation of nanoparticles. It has properties such as high specific surface area, high porosity, and low thermal conductivity. The temperature resistance of aerogel varies depending on the preparation material. The temperature resistance of general organic aerogels (such as phenolic aerogels, polyimide aerogels, etc.) is lower than 500°C, mainly because the organic matter begins to decompose when the temperature is too high, resulting in skeleton damage. The temperature resistance of inorganic oxide aerogels (such as silica aerogels, alumina aerogels, etc.) can reach about 1000°C. As the temperature rises, the inorganic oxide particle skeleton will undergo sintering or phase transition, causing volume changes, resulting in material collapse and fragmentation. In contrast to the above-mentioned aerogels, the temperature resistance of carbon aerogels is as high as 2000°C or more. In an inert or vacuum environment, carbon aerogels can still maintain a mesoporous structure after long-term high-temperature treatment. Therefore, carbon aerogels are regarded as ideal thermal protection materials in ultra-high temperature environments, especially for high heat flow and high enthalpy service environments.

[0003] Similar to other aerogel properties, carbon aerogel is brittle and weak in strength, and requires the introduction of fiber reinforcements to prepare composite materials to achieve the effect of strengthening and toughening. Patent application CN118405935A discloses the preparation of carbon aerogel composite materials by silicon-boron diatomic doping and modification and its preparation. By introducing silicon and boron atoms into linear phenolic resin, the strength of the carbon aerogel skeleton is greatly improved, and further compounded with 2.5D polyacrylonitrile-based preoxidized silk fiber reinforcement, a silicon-boron diatomic doped toughened carbon aerogel composite material is prepared. Wu Kede et al. composited silicon-modified carbon aerogel with needle-punched carbon fiber reinforcement to obtain a carbon aerogel composite material with a compressive strain of more than 40%, and a 10% compressive strain strength of 50MPa (KedeWu, Qi Zhou, Junxiang Cao, et al. Ultrahigh-strength carbon aerogels for hightemperature thermal insulation. Journal of Colloid and Interface Science, 2022, 609, 667–675.). Li Jian et al. composited and pyrolyzed linear phenolic and phenolic fiber needle felt to prepare a carbon aerogel composite material with a compressive strength of 80 MPa (Jian Li, Penglei Guo, Chenglong Hu, et al. Fabrication of Large Aerogel-Like Carbon / Carbon Composites with excellent load-bearing capacity and thermal-insulating performance at 1800°C. ACS Nano, 2022, 16, 6565-6577.). The existing methods have the following defects:

[0004] 1. The existing methods require the use of 2.5D fiber reinforcements with long production cycles and high costs, which is not conducive to the promotion and application of carbon aerogel composites.

[0005] 2. In the existing methods, in order to achieve the effect of doping and modification to improve the strength of the carbon aerogel skeleton, it is necessary to perform cracking and carbonization treatment at a high temperature of 1600°C.

[0006] 3. In the existing methods, when preparing the organic precursor of the carbon aerogel composite material, it is necessary to cure at 120-200°C, and solvent replacement is required before drying. Summary of the invention

[0007] In order to improve the mechanical strength and preparation method of the above-mentioned carbon aerogel composite materials, the present invention provides a high mechanical strength carbon aerogel composite material and a preparation method thereof. By compounding and pyrolyzing phenolic aerogel and stitched needle-punched fiber felt, the preparation of lightweight and high-strength carbon aerogel composite materials is achieved, which makes up for the defects of existing carbon aerogel composite materials such as insufficient mechanical strength, complicated preparation process and high cost, and is expected to be applied to load-bearing / thermal insulation integrated materials in the field of lightweight thermal protection.

[0008] To achieve the above object, the specific technical solution of the present invention is a method for preparing a high mechanical strength carbon aerogel composite material, comprising the following steps:

[0009] (1) preparing phenolic sol;

[0010] (2) vacuum impregnating the phenolic sol in (1) into the stitched needle-punched fiber felt, and then curing it;

[0011] (3) placing the sample cured in (2) in the air at room temperature and heating to dry, thereby obtaining an organic precursor of a carbon aerogel composite material;

[0012] (4) The organic precursor of the carbon aerogel composite material in (3) is cracked and carbonized under a high temperature inert atmosphere to obtain a carbon aerogel composite material.

[0013] Furthermore, the phenolic sol system used in step (1) can be one or more phenolic sols such as resorcinol-formaldehyde phenolic sol, resorcinol-furfural sol, and linear phenolic sol.

[0014] Furthermore, the stitched needle-punched fiber felt is a stitched polyacrylonitrile-based pre-oxidized fiber needle-punched felt, and the stitching density ranges from 2mm×2mm to 20mm×20mm.

[0015] Furthermore, the density of the stitched polyacrylonitrile-based preoxidized filament needle felt is in the range of 0.1 g / cm 3 ~0.25g / cm 3 .

[0016] Furthermore, the temperature range of the cracking and carbonization is 800°C to 1000°C.

[0017] Furthermore, the heating rate of the cracking and carbonization is 0.5°C / min to 5°C / min.

[0018] Furthermore, the curing temperature ranges from 80°C to 120°C.

[0019] The present invention also provides a carbon aerogel composite material prepared according to the method.

[0020] The principle of the present invention is: the traditional carbon fiber precursor needle-punched felt adopts a multiple-layer stacking needle-punching process, and has good strength in the xy plane, but lacks support in the z-axis direction and has weak strength. The present invention introduces homogeneous z-direction fibers through a suturing process, thereby increasing the distribution ratio of the z-direction fibers. During the stress process of the composite material, these z-direction fibers introduced by suturing will provide numerous stress support points, thereby greatly improving the mechanical strength of the composite material.

[0021] Due to the application of the above technical solution, the present invention has the following advantages compared with the prior art:

[0022] 1. The reinforcement used in the present invention is stitched polyacrylonitrile-based pre-oxidized filament needle-punched felt, and no complicated reinforcement design is required.

[0023] 2. In the process of preparing the organic precursor of the carbon aerogel composite material, the present invention does not require solvent replacement and can be directly dried at normal pressure.

[0024] 3. In the process of preparing the carbon aerogel composite material, there is no need to deliberately increase the pyrolysis carbonization temperature to increase the strength of the aerogel skeleton. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 This is a physical schematic diagram of the steps for preparing the high mechanical strength carbon aerogel composite material in Example 1;

[0026] Figure 2 This is the compressive stress-strain curve of the high mechanical strength carbon aerogel composite material in Example 1. DETAILED DESCRIPTION

[0027] The following is combined with Figures 1-2 The present invention is further described with examples:

[0028] Embodiment 1:

[0029] A high mechanical strength carbon aerogel composite material and a preparation method thereof, comprising the following steps:

[0030] (1) Weigh 2200 g of resorcinol and 3840 g of furfural, add them to a mixture of 6000 g of anhydrous ethanol and 4000 g of purified water, and stir to dissolve. Then, add 55 g of hexamethylenetetramine, and stir to dissolve to obtain a phenolic sol.

[0031] (2) The phenolic sol in (1) was impregnated and stitched into polyacrylonitrile-based pre-oxidized needle felt (size 450 mm×450 mm×60 mm, stitching density 5 mm×5 mm) under vacuum until no more bubbles were discharged, and then placed in a 90° C. oven for curing for 48 h.

[0032] (3) The sample cured in (2) is placed at room temperature until its mass does not change, and then placed in an oven at 80° C. for drying until its mass does not change, thereby obtaining an organic precursor of a carbon aerogel composite material.

[0033] (4) The organic precursor of the carbon aerogel composite material in (3) was heated to 800°C at a heating rate of 1°C / min in a nitrogen atmosphere and kept warm for 3 hours for cracking and carbonization to obtain a carbon aerogel composite material with high mechanical strength.

[0034] The density of the high mechanical strength carbon aerogel composite material prepared was 0.68 g / cm 3 The compression strength (implemented in accordance with GB / T13480-2014) is 102MPa, and the shear strength (implemented in accordance with GJB 10311-2021) is 12MPa.

[0035] Figure 1 This is a schematic diagram of the steps for preparing a high mechanical strength carbon aerogel composite material. It can be seen that the carbon aerogel composite material finally prepared has a complete structure and no delamination on the surface or inside. Figure 1 The rightmost image is a non-destructive CT test image of the sample, which is used to detect the internal quality of the sample. It shows photos of the sample at four different positions, proving that there is no stratification inside the sample.

[0036] Figure 2 The compressive stress-strain curve of the high mechanical strength carbon aerogel composite material is shown in Figure 1. It can be seen that the 10% strain compressive strength is 102 MPa and the failure compressive strength is 109 MPa.

[0037] Embodiment 2:

[0038] A high mechanical strength carbon aerogel composite material and a preparation method thereof, comprising the following steps:

[0039] (1) Weigh 5400 g of linear phenolic acid and add it to 9862 g of anhydrous ethanol, stir and dissolve, then add 1000 g of hexamethylenetetramine and stir and dissolve to obtain a phenolic acid sol.

[0040] (2) The phenolic sol in (1) was impregnated and stitched into polyacrylonitrile-based pre-oxidized needle felt (size 450 mm×450 mm×60 mm, stitching density 10 mm×10 mm) under vacuum until no more bubbles were discharged, and then placed in an 80°C oven for curing for 48 hours.

[0041] (3) The sample cured in (2) is placed at room temperature until its mass does not change, and then placed in an oven at 80° C. for drying until its mass does not change, thereby obtaining an organic precursor of a carbon aerogel composite material.

[0042] (4) The organic precursor of the carbon aerogel composite material in (3) is heated to 1000°C at a heating rate of 3°C / min in a nitrogen atmosphere and kept warm for 3 hours for cracking and carbonization to obtain a carbon aerogel composite material with high mechanical strength.

[0043] The density of the finally prepared high mechanical strength carbon aerogel composite material is 0.73 g / cm 3 The compression strength (implemented in accordance with GB / T13480-2014) is 135MPa, and the shear strength (implemented in accordance with GJB 10311-2021) is 17MPa.

[0044] Embodiment 3:

[0045] A high mechanical strength carbon aerogel composite material and a preparation method thereof, comprising the following steps:

[0046] (1) Weigh 2200 g of resorcinol and 3200 g of formaldehyde (formalin solution) and add them to a mixture of 6000 g of anhydrous ethanol and 2000 g of purified water, stirring to dissolve, and then add 5 g of anhydrous sodium carbonate and stir to dissolve to obtain a phenolic sol.

[0047] (2) The phenolic sol in (1) was impregnated and stitched into polyacrylonitrile-based pre-oxidized needle felt (size 450 mm×450 mm×60 mm, stitching density 3 mm×3 mm) under vacuum until no more bubbles were discharged, and then placed in a 95°C oven for curing for 72 hours.

[0048] (3) The sample cured in (2) is placed at room temperature until its mass does not change, and then placed in an oven at 80° C. for drying until its mass does not change, thereby obtaining an organic precursor of a carbon aerogel composite material.

[0049] (4) The organic precursor of the carbon aerogel composite material in (3) was heated to 900°C at a heating rate of 5°C / min in a nitrogen atmosphere and kept warm for 3 hours for cracking and carbonization to obtain a carbon aerogel composite material with high mechanical strength.

[0050] The density of the high mechanical strength carbon aerogel composite material prepared was 0.65 g / cm 3 The compression strength (implemented in accordance with GB / T13480-2014) is 95MPa, and the shear strength (implemented in accordance with GJB 10311-2021) is 10MPa.

[0051] The specific embodiments of the present invention disclosed above are intended to help understand the content of the present invention and implement it accordingly. It can be understood by those skilled in the art that various replacements, changes and modifications are possible without departing from the spirit and scope of the present invention. The present invention should not be limited to the contents disclosed in the embodiments of this specification, and the scope of protection of the present invention shall be subject to the scope defined in the claims.

Claims

1. A method for preparing a high mechanical strength carbon aerogel composite material, characterized in that: The following steps are involved: Prepare phenolic sol; The stitched needle-punched fiber mat is vacuum impregnated with a phenolic sol and then cured; The cured sample is left to air at room temperature and then heated to dry to obtain an organic precursor of a carbon aerogel composite material. The organic precursor of the carbon aerogel composite material is cracked and carbonized in a high-temperature inert atmosphere to obtain the carbon aerogel composite material.

2. The preparation method according to claim 1, characterized in that: The phenolic sol is one or more of resorcinol-formaldehyde phenolic sol, resorcinol-furfural sol and linear phenolic sol.

3. The preparation method according to claim 1, characterized in that: The stitched needle-punched fiber felt is a stitched polyacrylonitrile-based pre-oxidized fiber needle-punched felt, and the stitching density ranges from 2mm×2mm to 20mm×20mm.

4. The preparation method according to claim 3, characterized in that: The density of the stitched polyacrylonitrile-based pre-oxidized filament needle-punched felt is in the range of 0.1 g / cm3 to 0.25 g / cm3.

5. The preparation method according to claim 1, characterized in that: The temperature range of the cracking and carbonization is 800°C to 1000°C.

6. The preparation method according to claim 1, characterized in that: The heating rate of the cracking and carbonization is 0.5°C / min to 5°C / min.

7. The preparation method according to claim 1, characterized in that: The curing temperature ranges from 80°C to 120°C.

8. A carbon aerogel composite material prepared according to the method according to any one of claims 1 to 7.

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