Carbon aerogel with atomic scale gradient structure as well as preparation method and application of carbon aerogel
By introducing a carbon tube network with atomic scale gradient structure into carbon aerogels, the problems of low mechanical strength and large permanent deformation of traditional carbon aerogels under high compression strain are solved, and high compression elasticity and strength are improved, which is suitable for a variety of high-demand application scenarios.
Patent Information
- Application Number
- CN202510539069.X
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-04-27
- Publication Date
- 2025-06-27
AI Technical Summary
The existing carbon aerogels have low mechanical strength and large permanent deformation under high compression strain, which is difficult to meet the reliability requirements of practical applications.
A carbon aerogel with an atomic scale gradient structure is adopted, a three-dimensional porous network formed by crosslinking carbon tubes with each other, and an orderly gradient structure of carbon atoms is introduced in the thickness direction of the carbon tube wall. A carbon layer with a gradient structure is deposited on the surface of oxide ceramic nanowires through the CVI process, and the template is removed through etching technology to obtain a carbon aerogel with excellent mechanical properties.
It realizes the high compression elasticity and high strength of carbon aerogel, and can return to the initial state without permanent deformation after large strain compression. It is suitable for high-precision sensors and flexible wearable devices and other fields.
Smart Images
Figure CN120208204A_ABST
Abstract
Description
Technical Field
[0001] The invention belongs to the technical field of inorganic nano-carbon materials, and specifically relates to a carbon aerogel with an atomic scale gradient structure and a preparation method and application thereof. Background Art
[0002] Aerogels have high porosity, large specific surface area, low thermal conductivity, excellent optoelectronic and mechanical properties, and are potential candidate materials for catalytic carriers, high-temperature thermal insulation, supercapacitors and pressure sensors. However, traditional aerogels are fragile and have poor flexibility, which greatly limits their practical applications. At present, researchers use graphene, carbon nanotubes, MXene, etc. as building blocks, and gradually overcome the brittleness of traditional aerogels by designing their assembly microstructures such as building honeycomb and layered structures, and obtain graphite-based carbon aerogels with good compression recovery.
[0003] Although the above-mentioned microstructure design effectively overcomes the brittleness problem of traditional aerogels, due to the low crosslinking density and weak bonding force between nano-units such as carbon nanotubes / graphene, the load transfer efficiency is low and its inherent excellent performance cannot be fully exerted. Under high compressive strain, carbon aerogels show low mechanical strength (usually in the range of several kilopascals to tens of kilopascals) and large permanent deformation. The latest research Nature Communications 14.1 (2023): 3178. It is shown that by significantly increasing the degree of crosslinking between the constituent units (carbon tubes), the elasticity and mechanical strength can be improved simultaneously. However, this method of simply increasing the degree of crosslinking between units has obvious limitations in improving the mechanical properties of carbon aerogels: when the degree of crosslinking is increased to a certain extent, for example, when the matrix template density reaches 300 mg / cm 3 When the pressure is too high, the elasticity of carbon aerogel will drop significantly, and a large permanent deformation will be left after large strain compression.
[0004] Therefore, exploring a method that can give both high applicability and achieve high strength and superelasticity of carbon aerogels is the key to ensuring the service reliability of aerogels. Summary of the invention
[0005] In order to overcome the shortcomings of the above-mentioned prior art means, the purpose of the present invention is to provide a carbon aerogel with an atomic scale gradient structure and a preparation method and application thereof, which can solve the technical problems of poor compression resilience, low strength and difficult adjustment of existing carbon aerogels under large deformation, and achieve high applicability to improve the mechanical properties of aerogels with different unit crosslinking degrees, thereby realizing customized preparation of carbon aerogels with required mechanical properties according to actual application needs.
[0006] In order to achieve the above object, the present invention adopts the following technical solutions: The first object of the present invention is to disclose a carbon aerogel with an atomic-scale gradient structure, which is a three-dimensional porous network formed by the cross-linking of carbon nanotubes. The carbon nanotubes have an atomic-scale gradient structure in the thickness direction of the carbon nanotube wall; the gradient structure is that the carbon layer of the carbon nanotube wall has an increasing degree of atomic order from the inner layer to the outer layer of the wall.
[0007] Preferably, the maximum outer diameter of the carbon nanotube wall ranges from 50 to 300 nm, and the maximum wall thickness of the carbon nanotube ranges from 10 to 100 nm; the volume density is 10 mg / cm 3 ~100 mg / cm 3 .
[0008] The second object of the present invention is to disclose a preparation method of the above-mentioned carbon aerogel with an atomic-scale gradient structure, including the following steps: Adopt the chemical vapor infiltration (CVI) process, slow down the carbon source gas flow rate in stages, and deposit and coat a carbon layer on the nanowires of the oxide ceramic nanowire aerogel / foam; etch the nanowires in the core of the carbon layer to obtain the carbon aerogel with an atomic-scale gradient structure.
[0009] Preferably, the deposition temperature of the CVI process is 700~1400 °C, the heating rate of the deposition furnace is 0.1~10 o °C / min, and the gas pressure in the furnace is 1~100 kPa.
[0010] Further preferably, the flow rate of the carbon source gas used in the CVI process is 10~80 mL / min, and the deposition time is 1~30 h.
[0011] Still further preferably, the carbon source gas is selected from one or a mixture of methane, ethane, propane, ethylene, propylene, acetylene, benzene or toluene.
[0012] Preferably, in the CVI process, hydrogen is introduced during the carbon deposition, and the flow rate of the introduced hydrogen is 0~100 mL / min, but does not include 0 mL / min.
[0013] Preferably, the density of the oxide ceramic aerogel / foam is 50~300 mg / cm 3 .
[0014] Preferably, the process of etching the nanowires in the core of the carbon layer is to soak the oxide ceramic nanowire aerogel / foam with a deposited and coated carbon layer on the nanowires in HF for 4~7 h and then dry it.
[0015] The third object of the present invention is to claim the application of the above-mentioned carbon aerogel with an atomic-scale gradient structure in the fields of sensors and flexible wearable devices.
[0016] Compared with the prior art, the present invention has the following beneficial effects: The carbon aerogel with an atomic-scale gradient structure disclosed by the present invention is a three-dimensional network highly cross-linked by carbon nanotubes, which can achieve reversible compression and decompression through cross-linking nodes, thereby realizing rapid load transfer and improving the elastic recovery ability of the carbon aerogel. In this carbon aerogel with an atomic-scale gradient structure, carbon atom layers with different degrees of order are introduced in the carbon layer thickness direction, that is, from the inner layer to the outer layer, the degree of order of the carbon layer gradually increases, rather than the conventional situation where the degree of order of the carbon layer gradually decreases from the inner layer to the outer layer. This gradient change in the degree of order of the carbon layer from the inner layer to the outer layer reduces the stress concentration and defects caused by the sudden change in the cross-linking degree between carbon atom layers. The part with relatively poor order in the inner layer provides strength for the carbon nanotubes, while the part with relatively high order in the outer layer provides good deformation ability for the carbon nanotubes. This synergistic effect endows the carbon aerogel with excellent compression resilience and relatively high strength. By regulating the gradient change range and change rate of the carbon layer order, comprehensive regulation of the mechanical properties of the carbon aerogel can be achieved.
[0017] The preparation method of the carbon aerogel with an atomic-scale gradient structure disclosed by the present invention obtains a ceramic nanowire network with a certain bulk density as a template through hot pressing, deposits a pyrolytic carbon layer with an atomic-scale gradient on the surface of the oxide nanowires by the CVI method, obtains different gradient structure pyrolytic carbons by changing the flow rates of the CVI carbon source gas and hydrogen, and finally obtains the carbon aerogel with an atomic-scale gradient structure through etching. This method can obtain a structure in which the degree of order gradient of carbon atoms increases from the inner to the outer surface of the carbon layer in the carbon layer thickness direction through the gradual change control of the flow rate of the carbon source gas. By changing the change range and change rate of the flow rate of the carbon source gas, the gradient structure change of the carbon layer is regulated, the improvement and regulation of the mechanical properties of the carbon aerogel are realized, and a wide range of regulation of the mechanical properties of the carbon aerogel can be achieved. The mechanical properties include at least one of compression resilience, elastic modulus, and compressive strength.
[0018] Furthermore, by controlling the thickness of the CVI atomic-scale gradient pyrolytic carbon layer, the strength and elasticity of the carbon nanotube aerogel with an atomic-scale gradient structure can be regulated.
[0019] Furthermore, the gradient change of the degree of order of carbon atoms at the atomic scale can also be achieved by introducing hydrogen and controlling the amount of hydrogen. Description of the Drawings
[0020] Figure 1 is the microscopic morphology diagram of the carbon aerogel with an atomic-scale gradient structure prepared in the embodiment of the present invention; wherein, (a) is the low-magnification SEM image, and (b) is the high-magnification SEM image; Figure 2TEM micrograph of carbon nanotubes with atomic-scale gradient prepared in the embodiments of the present invention; among them, (a) low-magnification TEM micrograph; (b) high-magnification TEM micrograph and SAED pattern Figure 3 For the density of 29 mg / cm³ prepared in the embodiments of the present invention 3 Compressive stress-strain curve of carbon aerogel with atomic-scale gradient structure (order increasing from low to high) Figure 4 For the density of 29 mg / cm³ prepared in the embodiments of the present invention 3 Macroscopic compression process of carbon aerogel with atomic-scale gradient structure (order increasing from low to high) prepared in the embodiments of the present invention
[0021] Figure 5 For the density of 52 mg / cm³ prepared in the embodiments of the present invention 3 Compressive stress-strain curve of carbon aerogel with atomic-scale gradient structure (order increasing from low to high) Figure 6 For the density of 55 mg / cm³ prepared in the embodiments of the present invention 3 Compressive stress-strain curve of carbon aerogel with atomic-scale gradient structure (order decreasing from high to low) Figure 7 For the density of 49 mg / cm³ prepared in the comparative examples of the present invention 3 Compressive stress-strain curve of carbon aerogel with uniform carbon layer structure (high order) Figure 8 For the density of 56 mg / cm³ prepared in the comparative examples of the present invention 3 Compressive stress-strain curve of carbon aerogel with uniform carbon layer structure (low order) Figure 9 Compressive stress-strain curve of carbon aerogel with uniform carbon layer structure (low order) prepared in the comparative examples of the present invention Detailed implementation manners
[0022] In order to enable those skilled in the art to better understand the solutions of the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.
[0023] The following is a further detailed description of the present invention: The present invention first proposes a carbon aerogel with an atomic-scale gradient structure. This carbon aerogel is a three-dimensional porous network formed by the cross-linking of carbon nanotubes, and the carbon nanotubes have an atomic-scale gradient structure in the thickness direction of the carbon nanotube wall; the gradient structure is such that the order of carbon atoms gradually increases from the inner layer to the outer layer of the carbon nanotube wall.
[0024] Due to less cross-linking and easy deformation and sliding between the highly ordered pyrolytic carbon layers, when the carbon nanotube aerogel deforms, the carbon layers are prone to dissipate stress through relative sliding or curling deformation, so that the carbon nanotube aerogel has strong deformation ability, but often has low strength and is prone to large permanent deformation under high strain; the low-order pyrolytic carbon has more sp 3 cross-linking between the layer walls, which can effectively enhance the anti-shear and anti-torsion ability between the carbon layers, thereby increasing the resistance to relative slip between the carbon layers. When the carbon nanotube aerogel deforms, a large number of sp 3 cross-links between the carbon layers endow the carbon nanotube aerogel with higher strength and deformation resistance, but excessive sp 3 cross-linking between the carbon layers often causes stress concentration, resulting in carbon nanotube fracture. 3 In some preferred embodiments of the present invention, the maximum outer diameter of the carbon nanotube wall of the carbon aerogel with an atomic-scale gradient structure ranges from 50 to 300 nm, and the maximum wall thickness of the carbon nanotube ranges from 10 to 100 nm; the volume density is 10 to 100 mg / cm
[0025] This carbon aerogel with an atomic-scale gradient structure can have a maximum recoverable compressive strain of up to 99%, and the corresponding maximum stress can be regulated within the range of 4 to 11 MPa, and the carbon aerogel can still return to its initial size after unloading the load. 3 .
[0026] The present invention also provides a preparation method for the above-mentioned carbon aerogel with an atomic-scale gradient structure, including the following steps: using SiC or Si3N4 nanowire aerogel as a raw material, increasing its density to 50 to 300 mg / cm through hot pressing
[0027] , obtaining SiO2 nanowire aerogel through high-temperature oxidation treatment, depositing a carbon layer with an atomic-scale gradient on the surface of SiO2 nanowires by CVI, and removing the SiO2 nanowire template by etching technology to obtain a carbon aerogel with a controllable gradient structure; 3 Specifically: This preparation method can use ceramic nanowire aerogel / foam as a raw material, and through hot pressing, the cross-linking degree between nanowires can be increased to obtain a ceramic nanowire network with a certain volume density.
[0028] If the ceramic nanowire aerogel / foam raw material is an oxide ceramic, it can be directly used as the matrix material for the CVI process. Otherwise, it needs to be treated by high-temperature oxidation to convert the non-oxide ceramic nanowires into oxides.
[0029] In the embodiments of the present invention, the SiC nanowire aerogel of Patent ZL201811626203.6 or the Si3N4 nanowire aerogel of Patent ZL201811626361.1 is used as the raw material.
[0030] In the preferred embodiments of the present invention, the hot pressing temperature is 900~1700 °C, and the volume density of the ceramic nanowire skeleton obtained after hot pressing is 50~300 mg / cm 3 , for non-oxide ceramic nanowires, the principle of high-temperature oxidation is to achieve the transformation from non-oxide to oxide by extending the holding time on the premise of retaining the original high aspect ratio characteristics of the ceramic nanowires.
[0031] In the CVI process of this preparation method, the carbon source gas flow rate is slowed down in stages. Using hydrocarbon gas-phase carbon sources such as methane and ethylene as precursors, pyrolysis occurs at high temperature, and a carbon layer with gradually increasing carbon atom order is deposited on the surface of the nanowires. The deposition pressure is either atmospheric pressure or negative pressure.
[0032] In the preferred embodiments of the present invention, the temperature of CVI is 700~1400 o °C, the heating rate of the deposition furnace is 0.1~10 o °C / min, the pressure in the furnace is 1~100 kPa, the precursors are hydrocarbon gas-phase carbon sources such as methane and ethylene, the precursor flow rate is 10~80 mL / min, the hydrogen flow rate is 0~100 mL / min, the argon flow rate is 50~200 mL / min, and the deposition treatment time is 1~30 h.
[0033] By controlling the CVI process, the deposition of a carbon layer with an atomic-scale gradient can be achieved on the surface of the nanowires. Through the gradual change control of the carbon source gas flow rate, a structure with an increasing gradient of carbon atom order from the inside to the outer surface of the carbon layer in the carbon layer thickness direction can be obtained. By changing the change range and change rate of the carbon source gas flow rate, the gradient structure change of the carbon layer can be regulated. In addition, the gradient change of carbon atom order at the atomic scale can also be achieved by introducing hydrogen and controlling the amount of hydrogen.
[0034] In some preferred embodiments of the present invention, the carbon source gas is selected from one or a mixture of several of methane, ethane, propane, ethylene, propylene, acetylene, benzene or toluene.
[0035] This preparation method uses etching techniques such as hydrofluoric acid etching to remove the oxide ceramic nanowires in the core, and a controllable gradient structure carbon aerogel is obtained.
[0036] In a preferred embodiment of the present invention, the oxide ceramic nanowire aerogel / foam with a carbon layer deposited and coated on the nanowires is soaked in HF for 4 to 7 hours and then dried.
[0037] The preparation of the carbon aerogel with an atomic-scale gradient structure disclosed by the present invention changes the carbon layer structure by regulating the gradient change of the order degree of carbon atoms in the thickness direction of the carbon layer, thereby realizing the improvement and regulation of the mechanical properties of the carbon aerogel. The present invention has a wide range of applications, and is applicable not only to the preparation of carbon aerogel by the CVI method, but also to all preparation methods that can change the order degree of the carbon layer of the carbon aerogel. The adjustable elastic carbon aerogel obtained by the present invention, with the unique combination of strength and elasticity, is expected to be used as materials such as high-temperature dynamic thermal sealing, damping shock absorption, and sound-absorbing materials, meeting the different requirements for materials with properties such as elasticity, strength, and temperature resistance under harsh working conditions in certain scenarios.
[0038] Compared with the organic matter carbonization method, hydrothermal synthesis method, chemical vapor deposition, and ice template method, this preparation method can obtain a carbon aerogel with excellent mechanical properties under large deformation, greatly improving the practical application reliability of the carbon aerogel. Moreover, the preparation process is simple, the mechanical properties of the carbon aerogel can be accurately regulated, and the customized production of the carbon aerogel can be realized. The recoverable compression strain can reach up to 99% at most, and the corresponding maximum stress can be regulated within the range of 4 to 11 MPa. After unloading the load, the elastic carbon tube aerogel can still return to the initial size, and it is suitable for fields such as heat insulation and fire prevention, catalyst carriers, high-temperature filtration, pressure sensors, and flexible wearable devices.
[0039] The following is further described in conjunction with the drawings and embodiments.
[0040] Example 1 This example prepared a carbon aerogel with an atomic-scale gradient structure and a density of 10 mg / cm 3 .
[0041] 1) Select SiO2 nanofiber aerogel with a density of 10 mg / cm 3 as the raw material, and increase its density to 50 mg / cm 3 by hot pressing, and the hot pressing temperature is 1000 - 1200 °C; 2) Place the SiO2 nanofiber aerogel after hot pressing in step 1) in a CVI furnace, evacuate, and raise the temperature to 700 - 1100 o °C at a heating rate of 0.1 - 5 o °C / min; 3) Introduce the gas-phase carbon source precursor methane into the CVI furnace, control the flow rate of methane to be 40 - 80 mL / min, after heat preservation for 0.5 - 1 h, change the flow rate of methane to 20 - 30 mL / min, after heat preservation for 0.1 - 2 h, change the flow rate of methane to 10 - 20 mL / min, heat preservation for 0.1 - 2 h, and deposit pyrolytic carbon with gradually changing carbon atom order on the surface of the nanowires; 4) Immerse it in HF for 6 h, and then conduct drying treatment to obtain a carbon aerogel with an atomic-scale gradient structure and a density of 10 mg / cm 3
[0042] Example 2 In this example, a carbon aerogel with an atomic-scale gradient structure and a density of 25 ± 5 mg / cm 3
[0043] 1) Select SiC nanowire aerogel with a density of 5 - 20 mg / cm 3 as the raw material, and increase its density to 100 mg / cm through hot pressing, the hot pressing temperature is 900 - 1200 °C, and oxidize at 1000 - 1100 °C in an air furnace for 4 - 12 h; 3 2) Place the SiC nanowire aerogel treated in step 1) in the CVI furnace, evacuate to 100 - 1500 Pa, and heat up to 1000 - 1200 o °C at a heating rate of 2 - 10 o °C / min; 3) Introduce the gas-phase carbon source precursor methane into the CVI furnace, maintain atmospheric pressure deposition, control the flow rate of methane to be 20 - 40 mL / min, after heat preservation for 0.2 - 1 h, change the flow rate of methane to 10 - 20 mL / min, after heat preservation for 0.5 h, heat up to 1200 - 1300 o °C at a heating rate of 5 o °C / min, change the flow rate of methane to 5 - 20 mL / min, introduce hydrogen with a flow rate of 10 - 60 mL / min, heat preservation for 0.5 - 2 h, and deposit pyrolytic carbon with gradually increasing carbon atom order from inside to outside on the surface of the nanowires; 4) Immerse it in HF for 4 h, and then conduct atmospheric pressure drying to obtain a carbon aerogel with an atomic-scale gradient structure and a density of 25 ± 5 mg / cm 3
[0044] As Figure 1As shown, it is the microscopic morphology diagram of the carbon aerogel prepared in this embodiment. It can be seen from the figure that the carbon aerogel retains the three-dimensional network structure of the template. Thanks to the hot pressing method and CVI for depositing pyrolytic carbon on the nanowire template, the carbon nanotubes are mutually overlapped and crosslinked.
[0045] As Figure 2 shown, it is the microscopic TEM diagram of the carbon nanotubes of the carbon aerogel prepared in this embodiment. It can be seen from the figure that the wall of the carbon nanotube aerogel is relatively thin, only dozens to hundreds of nanometers. In the figure, ① is the outermost layer and ③ is the innermost layer. From the inside to the outside, the degree of order of the carbon atom arrangement in the carbon nanotubes increases successively in the thickness direction, with an atomic-scale gradient structure. The degree of order of the carbon atom arrangement gradually increases from ③ inside the tube to ① outside the tube, indicating that the crosslinking degree between its walls is different and the mechanical behaviors shown are different. The carbon nanotubes assembled from pyrolytic carbon with a gradient change in the degree of order of carbon atoms and the high crosslinking between the carbon nanotubes make the carbon aerogel with an atomic-scale gradient structure have a significant improvement in both strength and compression elasticity, becoming a super-elastic aerogel: Refer to Figure 3 it, and it can be seen that even when the compression strain of the carbon aerogel is 95%, the corresponding stress is 3.8 MPa, the elastic modulus is 495 kPa, and the carbon nanotube aerogel can still return to its initial size after unloading the load (the macroscopic compression process is shown in Figure 4 ).
[0046] Example 3 This example prepared a carbon aerogel with an atomic-scale gradient structure having a density of 50 ± 10 mg / cm 3 .
[0047] 1) Select SiC nanowire aerogel with a density of 5 - 20 mg / cm 3 as the raw material, and increase its density to 100 mg / cm 3 by the hot pressing method. The hot pressing temperature is 1100 - 1300 °C, and it is oxidized at 1000 °C in an air furnace for 6 h; 2) Place the SiC nanowire aerogel treated in step 1) in a CVI furnace, evacuate to 100 - 3000 Pa, and raise the temperature to 1000 - 1100 o °C at a heating rate of 5 - 10 o °C / min; 3) Introduce the gaseous carbon source precursor propane into the CVI furnace, control the flow rate of propane to be 20 - 60 mL / min, keep the temperature for 0.5 - 2 h, then change the flow rate of propane to 5 - 20 mL / min, keep the temperature for 0.5 - 2 h, and then raise the temperature to 1150 - 1400 o °C at a heating rate of 2 - 10 oC. Change the propane flow rate to 5 - 10 mL / min, introduce hydrogen with a flow rate of 40 - 100 mL / min, keep warm for 1 - 2 h, and deposit pyrolytic carbon with gradually increasing carbon atom order from inside to outside on the surface of the nanowires; 4) Immerse it in HF for 4 h, and then perform atmospheric drying to obtain a carbon aerogel with an atomic-scale gradient structure and a density of 50 ± 10 mg / cm 3 .
[0048] As Figure 5 , for the carbon nanotube aerogel sample prepared in this example, when the compressive strain is 95%, the corresponding stress is 8.07 MPa. When further compressed to 99%, the corresponding stress is 11.20 MPa, no permanent deformation occurs, and the elastic modulus is 750 kPa.
[0049] Compared with the homogeneous carbon aerogel without a gradient structure, the elasticity and strength of the carbon nanotube aerogel prepared in this example are significantly improved, as shown in Table 1.
[0050] Example 4 This example prepared a carbon aerogel with an atomic-scale gradient structure and a matrix density of 300 mg / cm 3 .
[0051] 1) Select SiC nanowire aerogel with a density of 5 - 20 mg / cm 3 as the raw material, and increase its density to 300 mg / cm 3 by hot pressing. The hot pressing temperature is 1200 - 1300 °C, and it is oxidized at 1000 °C in an air furnace for 24 h; 2) Place the SiC nanowire aerogel treated in step 1) in a CVI furnace, evacuate to 100 - 3000 Pa, and heat it to 1000 - 1200 o °C at a heating rate of 5 - 10 o °C / min; 3) Introduce the gaseous carbon source precursor methane into the CVI furnace, control the methane flow rate to be 20 - 60 mL / min, keep warm for 0.1 - 1 h, then change the methane flow rate to 5 - 20 mL / min, keep warm for 0.1 - 1 h, and then heat it to 1150 - 1400 o °C at a heating rate of 2 - 10 o °C / min. Change the methane flow rate to 5 - 10 mL / min, introduce hydrogen with a flow rate of 40 - 100 mL / min, keep warm for 0.5 - 1 h, and deposit pyrolytic carbon with gradually increasing carbon atom order from inside to outside on the surface of the nanowires; 4) Immerse it in HF for 8 h, and then perform atmospheric drying to obtain a carbon aerogel with a density of 30 ± 10 mg / cm 3Carbon aerogel with atomic-scale gradient structure.
[0052] As Figure 6 , for the carbon nanotube aerogel sample prepared in this example, when the compressive strain is 90%, the corresponding stress is 20.11 MPa, and there is basically no permanent deformation, and the elastic modulus is 5185 kPa.
[0053] The carbon nanotube aerogel prepared in this example has significantly improved elasticity compared with the homogeneous carbon aerogel with no gradient structure prepared with a matrix with a density of 300 mg / cm 3 , as shown in Table 1.
[0054] Example 5 This example prepared a carbon aerogel with atomic-scale gradient structure with a density of 100±20 mg / cm 3 ; 1) Select Si3N4 nanowire aerogel with a density of 10~50 mg / cm 3 as the raw material, and increase its density to 300 mg / cm 3 by hot pressing. The hot pressing temperature is 1400~1700 °C, and it is oxidized at 1100~1300 °C in an air furnace for 6~24 h; 2) Place the Si3N4 nanowire aerogel treated in step 1) in a CVI furnace, evacuate to below 200 Pa, and raise the temperature at a rate of 2~10 o °C / min to 1300 o °C; 3) Introduce the gaseous carbon source precursor ethylene into the CVI furnace, control the flow rate of ethylene to be 30~80 mL / min, keep it warm for 1 h, then change the ethylene flow rate to 20~50 mL / min, keep it warm for 0.5~2 h, then change the ethylene flow rate to 10~30 mL / min, keep it warm for 0.5~4 h, then change the ethylene flow rate to 5~20 mL / min, keep it warm for 0.5~4 h, then change the ethylene flow rate to 5~10 mL / min, and keep it warm for 1~8 h to deposit pyrolytic carbon with gradually changing carbon atom order on the nanowire surface; 4) Immerse it in HF for 12 h, and then perform drying treatment to obtain a carbon aerogel with atomic-scale gradient structure with a density of 100±20 mg / cm 3 .
[0055] Comparative Example 1 This comparative example prepared a carbon aerogel with a uniform carbon layer structure with a density of 50±10 mg / cm 3 , as a control group, to prove the advantages of the gradient structure of the carbon aerogel.
[0056] 1) Select 10~50 mg / cm3 Using Si3N4 nanowire aerogel as raw material, its density is increased to 100 mg / cm by hot pressing 3 , the hot pressing temperature is 1200 - 1500 °C, and it is oxidized at 1100 - 1300 °C in an air furnace for 6 - 24 h; 2) Place the Si3N4 nanowire aerogel treated in step 1) in a CVI furnace, evacuate, and heat it at a heating rate of 2 - 10 o °C / min to 1000 - 1200 o °C; 3) Introduce the gaseous carbon source precursor methane into the CVI furnace, control the flow rate of methane to be 5 - 10 mL / min, keep it warm for 3 - 6 h, and deposit homogeneous pyrolytic carbon with a high degree of order on the surface of the nanowires; 4) Immerse it in HF for 6 h, and then perform drying treatment to obtain a carbon aerogel with a density of 50 ± 10 mg / cm 3 and having a uniform carbon layer structure.
[0057] As Figure 8 , for the carbon nanotube aerogel prepared in this comparative example, when the compressive strain is 95%, the corresponding stress is 1.56 MPa, and the elastic modulus is 261 kPa, but it has an obvious permanent deformation (20%), and the highest compression and rebound strain is 40%, and the corresponding stress is 0.043 MPa.
[0058] Comparative Example 2 This comparison prepared a carbon aerogel with a density of 50 ± 10 mg / cm 3 and having a uniform carbon layer structure as a control group to prove the advantages of the gradient structure of the carbon aerogel.
[0059] 1) Select Si3N4 nanowire aerogel with a density of 10 - 50 mg / cm 3 as raw material, and increase its density to 200 mg / cm by hot pressing 3 , the hot pressing temperature is 1200 - 1500 °C, and it is oxidized at 1100 - 1300 °C in an air furnace for 6 - 24 h; 2) Place the Si3N4 nanowire aerogel treated in step 1) in a CVI furnace, evacuate to below 200 Pa, and heat it at a heating rate of 2 - 10 o °C / min to 1300 o °C; 3) Introduce the gaseous carbon source precursor ethylene into the CVI furnace, control the flow rate of ethylene to be 40 - 80 mL / min, keep it warm for 1 h, and deposit homogeneous pyrolytic carbon with a lower degree of order on the surface of the nanowires; 4) Immerse it in HF for 12 h, and then perform drying treatment to obtain a density of 50 ± 10 mg / cm3 Carbon aerogel with a uniform carbon layer structure.
[0060] Such as Figure 9 For the carbon nanotube aerogel prepared in this comparative example, when the compression-rebound strain is 95%, the corresponding stress is 4.8 MPa and the elastic modulus is 442 kPa.
[0061] Comparative Example 3 This comparative example prepared a carbon aerogel with an atomic-scale gradient structure and a density of 50 ± 15 mg / cm 3
[0062] 1) Select SiC nanowire aerogel with a density of 5 - 20 mg / cm 3 as the raw material, and increase its density to 150 mg / cm through hot pressing. The hot pressing temperature is 1200 - 1500 °C, and it is oxidized at 1000 °C in an air furnace for 4 - 12 h; 3 2) Place the SiC nanowire aerogel treated in step 1) in a CVI furnace, evacuate, and maintain the pressure in the furnace at 1000 - 5000 Pa, and raise the temperature to 1150 - 1300 o °C at a heating rate of 2 - 10 o °C / min; 3) Pass propane with a gas-phase carbon source precursor flow rate of 5 - 10 mL / min into the CVI furnace, pass hydrogen with a flow rate of 40 - 100 mL / min, keep the temperature for 1 - 2 h, and lower the temperature to 1000 - 1100 o °C at a cooling rate of 5 o °C / min. Change the propane flow rate to 5 - 20 mL / min, keep the temperature for 0.5 - 2 h, then change the propane flow rate to 20 - 60 mL / min, keep the temperature for 0.5 - 2 h, and deposit pyrolytic carbon with gradually decreasing carbon atom order from inside to outside on the nanowire surface; 4) Immerse it in HF for 6 h, and then dry it using any drying method among atmospheric drying, freeze drying, or supercritical drying to obtain a carbon aerogel with an atomic-scale gradient structure and a density of 50 ± 15 mg / cm 3
[0063] Such as Figure 7 For the carbon nanotube aerogel prepared in this comparative example, when the compression strain is 95%, the corresponding stress is 6.7 MPa and the elastic modulus is 519 kPa, but it has an obvious permanent deformation (1%), the highest compression-rebound strain is 90%, and the corresponding stress is 4.5 MPa.
[0064] Comparative Example 4 In the literature Nature Communications 14.1 (2023): 3178 is Comparative Example 4, and the relevant experimental results can be referred to Fig. 8 in the SI of this literature.
[0065] Table 1 shows the comparison of the specimens prepared in Example 3, Example 4, Comparative Example 1, and Comparative Example 2 of the present invention in terms of large deformation compression resilience, strength, and elastic modulus. It can be seen that the specimens prepared in Example 3 and Example 4 with a gradually changing order degree from low to high from the inside to the outside of the carbon layer have relatively the best performance in terms of compression resilience, strength, and elastic modulus.
[0066] Table 1. Comparison of the mechanical properties of carbon aerogels with atomic-scale gradient structures and homogeneous carbon aerogels without gradient structures
[0067] In summary, by means of CVI, pyrolytic carbon with a gradient change in the order degree of carbon atoms is deposited on the surface of the nanowire aerogel, and a three-dimensional porous network formed by cross-linking carbon nanotubes is obtained by using the ceramic nanowire network as a template. By regulating the gradient structure change of the pyrolytic carbon, the obtained adjustable gradient structure carbon aerogel has a maximum recoverable compression strain of up to 99%, and the corresponding maximum stress can be regulated within the range of 4 - 11 MPa. Moreover, it has excellent compression fatigue resistance, can realize the customized production and preparation of carbon aerogels, and shows considerable application prospects in the fields of high-precision sensors and flexible wearable devices.
[0068] The above content is only to illustrate the technical idea of the present invention and cannot be used to limit the protection scope of the present invention. Any modification made on the basis of the technical solution according to the technical idea proposed by the present invention falls within the protection scope of the claims of the present invention.
Claims
1. A carbon aerogel having an atomic scale gradient structure, characterized in that: It is a three-dimensional porous network formed by cross-linking carbon tubes. The carbon tubes have an atomic-scale gradient structure in the thickness direction of the carbon tube wall. The gradient structure is that the carbon atoms in the carbon tube wall are arranged in an orderly manner from the inner layer to the outer layer of the tube wall.
2. The carbon aerogel having an atomic scale gradient structure according to claim 1, characterized in that: The maximum outer diameter of the carbon tube wall is in the range of 50-300 nm, the maximum wall thickness of the carbon tube is in the range of 10-100 nm; the volume density is 10 mg / cm 3 ~100 mg / cm 3 .
3. A method for preparing the carbon aerogel having an atomic scale gradient structure according to claim 1 or claim 2, characterized in that: The following steps are involved: Using the CVI process, the carbon source gas flow velocity is slowed down in stages to deposit a coating carbon layer on the nanowires of the oxide ceramic nanowire aerogel / foam; The nanowires in the core of the carbon layer are etched to produce a carbon aerogel with an atomic-scale gradient structure.
4. The method for preparing the carbon aerogel having an atomic scale gradient structure according to claim 3, characterized in that: In the CVI process, the deposition temperature is 700~1400 o C, the heating rate of the deposition furnace is 0.1~10 o C / min, and the gas pressure in the furnace is 1~100 kPa.
5. The method for preparing the carbon aerogel having an atomic scale gradient structure according to claim 3 or claim 4, characterized in that: In the CVI process, the carbon source gas flow rate used is 5-80 mL / min, and the deposition time is 1-30 h.
6. The method for preparing the carbon aerogel having an atomic scale gradient structure according to claim 5, characterized in that: The carbon source gas is selected from one or a mixture of methane, ethane, propane, ethylene, propylene, acetylene, benzene or toluene.
7. The method for preparing the carbon aerogel having an atomic scale gradient structure according to claim 3, characterized in that: In the CVI process, hydrogen is introduced during the carbon deposition process, and the flow rate of the introduced hydrogen is 0-100 mL / min, but does not include 0 mL / min.
8. The method for preparing the carbon aerogel having an atomic scale gradient structure according to claim 3, characterized in that: The density of the oxide ceramic aerogel / foam is 50-300 mg / cm 3 .
9. The method for preparing the carbon aerogel having an atomic scale gradient structure according to claim 3, characterized in that: The process of etching the nanowires at the core of the carbon layer is to immerse the oxide ceramic nanowire aerogel / foam deposited on the nanowires and covering the carbon layer in HF for 4 to 7 hours and then dry it.
10. Application of the carbon aerogel with atomic-scale gradient structure as claimed in claim 1 or claim 2 in the field of sensors and flexible wearable devices.