In-situ self-grown carbon nanotube reinforced nanoporous carbon aerogel composite material and preparation method thereof

Abstract

The present application relates to a kind of in-situ autogenous carbon nanotube reinforced nanopore carbon aerogel composite material and its preparation method, belong to the field of thermal protection materials, at least one of the problems in the prior art carbon aerogel material, such as low mechanical property, high temperature stability, in the promotion of mechanical property, cause its basic performance (such as heat insulation performance, low density, etc.) decline, preparation process is complex and cost is higher and so on is solved.The preparation method comprises: the solution of linear phenol formaldehyde resin is mixed with curing agent, to obtain the phenol formaldehyde resin solution after curing;Add metal cobalt powder, magnesium chloride and zinc acetate as catalyst;By heating and stirring, to obtain resin liquid;Resin liquid is sequentially cured, dried and carbonized.The present application realizes the promotion of carbon aerogel material mechanical property, has excellent heat insulation performance and high temperature stability, guarantees low density and light weight.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of heat protection materials, and particularly relates to a kind of in-situ self-grown carbon nanotube reinforced nanoporous carbon aerogel composite material and a preparation method thereof. BACKGROUND

[0002] Carbon aerogel is a kind of porous material with low density, high porosity, high specific surface area and low thermal conductivity, but its mechanical properties have short board, such as brittle and fragile, low strength, etc., which limits its wide application in engineering field. In the prior art, the main methods to improve the mechanical properties of carbon aerogel are: skeleton strengthening (such as improving sol-gel method, changing catalyst, introducing crosslinking agent, etc.), composite material strengthening, heteroatom doping, etc. Compared with the above methods, composite material strengthening is a better choice to improve the comprehensive performance of carbon aerogel, because it has comprehensive advantages in mechanical property improvement, process complexity and cost control, designability and thermal insulation performance, etc.

[0003] Composite material strengthening is to improve the mechanical properties of carbon aerogel by adding reinforcing phase (such as fiber, nanomaterial, etc.) in the carbon aerogel. Common reinforcing phases include: carbon fiber, organic fiber (phenolic fiber, etc.), carbon nanotube, graphene, metal particles, ceramic particles, etc. However, at present, the carbon aerogel composite material obtained by composite material strengthening still has problems in agglomeration, interface bonding and high temperature stability, etc. For example, the reinforcing phase is easy to agglomerate in the carbon aerogel matrix, which leads to uneven reinforcing effect, and the mechanical properties of local area are reduced due to agglomeration, which not only affects the strength of the material, but also may lead to uneven distribution of thermal conductivity, and further affect the high temperature stability. In addition, the interface between the reinforcing phase and the carbon aerogel matrix is easy to peel off under high temperature or complex stress conditions, which further affects the mechanical properties and high temperature stability.

[0004] Therefore, how to further improve the mechanical properties of carbon aerogel and have excellent thermal insulation performance, etc. has become a key problem to be solved in the current field. SUMMARY

[0005] In view of the above analysis, the present application aims to provide a kind of in-situ self-grown carbon nanotube reinforced nanoporous carbon aerogel composite material and a preparation method thereof, to solve at least one of the problems of the existing carbon aerogel material, such as low mechanical properties, insufficient high temperature stability, basic performance (such as thermal insulation performance, low density, etc.) decline when improving mechanical properties, complex preparation process, and high cost, etc.

[0006] The purpose of the present application is achieved by the following technical scheme:

[0007] The present application provides a kind of in-situ self-grown carbon nanotube reinforced nanoporous carbon aerogel composite material and a preparation method thereof, comprising the following steps:

[0008] (1) mixing a solution of linear phenolic resin with a curing agent to obtain a cured phenolic resin solution;

[0009] (2) adding metal cobalt powder, magnesium chloride and zinc acetate as catalysts to the phenolic resin solution;

[0010] (3) after adding the catalysts, heating and stirring to obtain a resin liquid;

[0011] (4) sequentially curing, drying and carbonizing the resin liquid to obtain an in-situ self-grown carbon nanotube reinforced nanoporous carbon aerogel composite material.

[0012] Further, in step (2), the adding of the metal cobalt powder, magnesium chloride and zinc acetate includes: adding the metal cobalt powder for heterogeneous surface catalysis, the magnesium chloride for synergistic auxiliary catalysis and the zinc acetate for homogeneous catalysis in batches every 10-60 min.

[0013] Further, in step (2), the mass of the catalysts accounts for 3%-7% of the mass of the linear phenolic resin.

[0014] Further, in the catalysts, the molar ratio of the metal cobalt powder, magnesium chloride and zinc acetate is (0.5-1.5):(0.5-1.5):(0.5-1.5).

[0015] Further, in step (3), the heating and stirring include: gradually increasing the temperature and gradually increasing the rotation speed in the temperature range of 50-70℃ and the rotation speed range of 600-800 rpm.

[0016] Further, in the gradual temperature increase, the temperature increase amplitude is 4-8% of the initial temperature, and the interval time of the temperature increase is 3-7 min; and / or,

[0017] in the gradual rotation speed increase, the rotation speed increase amplitude is 5-9% of the initial rotation speed, and the interval time of the rotation speed increase is 3-7 min.

[0018] Further, in step (1), the mixing of the solution of linear phenolic resin with the curing agent includes: under the conditions of heating and stirring, first adding hexamethylenetetramine to the solution of linear phenolic resin, and then adding benzoyl peroxide as the curing agent.

[0019] Further, in step (1), the heating temperature is 45-65℃; and / or,

[0020] the total mass of the hexamethylenetetramine and benzoyl peroxide accounts for 3%-7% of the mass of the linear phenolic resin.

[0021] Further, in step (4), the drying includes: first performing microwave drying, and then performing vacuum drying.

[0022] The in-situ self-grown carbon nanotube reinforced nanoporous carbon aerogel composite material prepared by the preparation method has a compression strength of ≥10 MPa, a permanent deformation of less than 1.5% after 99% strain cycle for 1000 times, a linear ablation rate of ≤0.04 mm / s, and a thermal conductivity of ≤0.3 W·m -1 ·K -1 , and a density of ≤25 mg / cm 3 .

[0023] Compared with the prior art, the present application can at least achieve one of the following beneficial effects:

[0024] (1) The carbon aerogel material is reinforced by the in-situ self-grown carbon nanotubes, effectively solving the problem of poor mechanical properties of traditional porous carbon aerogel materials.

[0025] The principle of in-situ self-grown carbon nanotubes in the present application mainly lies in that the cured phenolic resin acts as a "matrix", which not only acts as a carrier but also provides a carbon source (C). The inventors utilize the synergistic catalytic effect of cobalt powder, magnesium chloride and zinc acetate to efficiently and uniformly activate, rearrange, grow and extend the carbon atoms in the phenolic resin, thereby realizing the in-situ generation of carbon nanotubes on the matrix.

[0026] The carbon aerogel composite material obtained by the above principle has at least the following advantages: the in-situ self-grown carbon nanotubes are uniformly distributed in the matrix and are combined with the matrix through firm chemical bonds, which not only significantly improves the overall strength of the material but also reduces internal defects. In addition, the in-situ self-grown carbon nanotubes can deform cooperatively with the matrix, effectively reducing the generation of micro-cracks, thereby significantly improving the fatigue resistance of the material and achieving overall improvement of the mechanical properties.

[0027] (2) In some specific embodiments, the in-situ self-grown carbon nanotube reinforced carbon aerogel composite material prepared by the present application has a compression strength of 10 MPa or more, and further, the compression strength is 18 MPa or more, which is significantly improved compared with the existing several to several hundred kilopascals. At the same time, the carbon aerogel composite material prepared by the present application has excellent fatigue resistance, for example, the permanent deformation is less than 1.5% after 99% strain cycle for 1000 times. The bending strength of the carbon aerogel composite material prepared by the present application is 6.5 MPa or more.

[0028] (3) The present application strengthens the carbon aerogel material by in-situ self-grown carbon nanotubes, significantly improving the high-temperature stability and thermal insulation performance of the carbon aerogel. Specifically, carbon nanotubes have excellent thermal stability and low thermal conductivity. Compared with the traditional method of adding reinforcing phase (such as carbon nanotubes) in carbon aerogel, the present application uses in-situ self-grown method, so that the carbon nanotubes are uniformly distributed in the three-dimensional porous network structure of the matrix, effectively avoiding the problem of easy agglomeration of carbon nanotubes in the traditional method. At the same time, the in-situ self-grown carbon nanotubes form a stronger interface with the aerogel matrix, thereby enhancing the thermal stability of the carbon aerogel material at high temperature and ensuring that the material as a whole has excellent thermal insulation performance.

[0029] (4) In some embodiments, the in-situ self-grown carbon nanotube reinforced carbon aerogel composite material prepared by the present application has a linear ablation rate of ≤0.04 mm / s and a thermal conductivity of ≤0.3 W·m -1 ·K -1 .

[0030] (5) The present application constructs a three-dimensional network with a porous structure through the curing of phenolic resin, the synergistic effect of the catalyst, and the curing, drying and carbonization process, realizing the low density and lightweight characteristics of the carbon aerogel material.

[0031] (6) In some embodiments, the in-situ self-grown carbon nanotube reinforced carbon aerogel composite material prepared by the present application has a density of ≤25 mg / cm 3 .

[0032] (7) The preparation method of the present application has a simple process flow, mild reaction conditions, a wide source of raw materials, and economical cost.

[0033] In the present application, the above technical solutions can be combined with each other to realize more preferred combination solutions. Other features and advantages of the present application will be described in the subsequent specification, and some advantages will become apparent from the specification or be understood through the implementation of the present application. The purpose and other advantages of the present application can be achieved and obtained through the specific indications in the specification and the drawings. BRIEF DESCRIPTION OF DRAWINGS

[0034] The accompanying drawings are included to provide a further understanding of the application and are incorporated in and constitute a part of this specification, illustrate embodiments of the application and together with the description serve to explain the principles of the application. In the drawings:

[0035] Figure 1 SEM image of the in-situ self-grown carbon nanotube reinforced nanoporous carbon aerogel composite material prepared in Example 1 of the present application;

[0036] Figure 2SEM image of the in-situ self-grown carbon nanotube reinforced nanoporous carbon aerogel composite material prepared in Example 1 of the present application;

[0037] Figure 3 SEM image of the in-situ self-grown carbon nanotube reinforced nanoporous carbon aerogel composite material prepared in Example 1 of the present application;

[0038] Figure 4 SEM image of the in-situ self-grown carbon nanotube reinforced nanoporous carbon aerogel composite material prepared in Example 1 of the present application;

[0039] Figure 5 Sem-eds spectrum of the in-situ self-grown carbon nanotube reinforced nanoporous carbon aerogel composite material prepared in Example 1 of the present application;

[0040] Figure 6 SEM image of the carbon aerogel material prepared in Comparative Example 5. DETAILED DESCRIPTION

[0041] The preferred embodiments of the present application will be described in detail below with reference to the drawings, which form a part of this application, and together with the embodiments of the present application serve to explain the principles of the present application, but are not intended to limit the scope of the present application.

[0042] Carbon aerogel material is a lightweight, porous and high specific surface area nanomaterial, which has a significant advantage in thermal stability, especially in high temperature environment, and can still maintain structural integrity and is not easy to decompose, and has a wide application prospect in national defense, energy and intelligent sensing, etc. However, the brittleness limits its wide application. In recent years, researchers have developed aerogels with certain compression and rebound characteristics by taking graphene, carbon nanofiber, carbon nanotube and other flexible nanostructures as basic component units, but the compression strength is generally low (a few to a few hundred kilopascals), and the bearing capacity is insufficient. In addition, improving the bearing capacity of carbon aerogel often sacrifices its lightweight, heat insulation performance or thermal stability, etc. Therefore, how to maintain the unique advantages of carbon aerogel while breaking the contradiction between mechanical properties and lightweight, heat insulation performance, and further improving the comprehensive mechanical properties, is still a great challenge currently.

[0043] Based on this, the present application provides a preparation method of an in-situ self-grown carbon nanotube reinforced nanoporous carbon aerogel composite material, comprising the following steps:

[0044] (1) mixing a solution of linear phenolic resin with a curing agent to obtain a cured phenolic resin solution;

[0045] (2) adding metal cobalt powder, magnesium chloride and zinc acetate as catalysts into the phenolic resin solution;

[0046] (3) After adding the catalyst, resin liquid is obtained by heating and stirring;

[0047] (4) The resin liquid is sequentially solidified, dried and carbonized to obtain an in-situ self-grown carbon nanotube reinforced nanoporous carbon aerogel composite material.

[0048] Compared with the prior art, the present application proposes a preparation method of an in-situ self-grown carbon nanotube reinforced nanoporous carbon aerogel composite material, which strengthens the carbon aerogel material in the form of in-situ self-grown carbon nanotubes, effectively solving the problem of poor mechanical properties of traditional porous carbon aerogel materials.

[0049] The principle of in-situ self-grown carbon nanotubes in the present application mainly lies in that the solidified phenolic resin is used as a "matrix", which not only serves as a carrier but also provides a carbon source (C). The inventors utilize the synergistic catalytic effect of cobalt powder, magnesium chloride and zinc acetate to efficiently and uniformly activate, rearrange, grow and extend the carbon atoms in the phenolic resin, thereby realizing the in-situ generation of carbon nanotubes on the matrix.

[0050] It should be noted that the inventors have analyzed the synergistic catalytic effect of cobalt powder, magnesium chloride and zinc acetate and believe that the internal mechanism mainly includes the following points:

[0051] (a) The role of cobalt powder: Based on the electronic structure and surface properties of cobalt, cobalt powder can provide active sites for phenolic resin, adsorb reactants and reduce the activation energy of the reaction, thereby promoting the reaction and facilitating the in-situ formation of carbon nanotubes on the polymer molecular chains of the matrix.

[0052] (b) The role of magnesium chloride: Based on the catalysis of cobalt powder, magnesium chloride is added for synergistic catalysis. Magnesium chloride can increase the active sites of cobalt powder and adjust the electronic structure of cobalt powder, thereby improving the selectivity of reactants and increasing the number of in-situ self-grown carbon nanotubes.

[0053] (c) The role of zinc acetate: The carboxyl group of zinc acetate can form hydrogen bonds with the hydroxyl group in the reactant (such as phenolic resin), thereby further realizing mixing at the microscale, enhancing the interaction between reactant molecules, and also forming a more efficient catalytic system with cobalt powder and magnesium chloride through synergistic catalysis, further improving the selectivity and efficiency of the reaction, reducing the activation energy of the reaction, and thereby increasing the amount of carbon nanotubes generated.

[0054] (d) The synergistic effect of metal cobalt powder, magnesium chloride and zinc acetate in the catalytic reaction realizes the effect of 1+1>2. This synergistic mechanism not only improves the selectivity and efficiency of the catalytic reaction, but also increases the number of active sites and the uniformity of distribution, reduces the activation energy of the reaction, and realizes multifunctional catalysis. This not only increases the amount of carbon nanotubes generated, but also makes the distribution of carbon nanotubes in the matrix more uniform, while greatly improving the overall reaction rate.

[0055] The carbon aerogel composite material obtained by the above principle has at least the following advantages: the in-situ self-grown carbon nanotubes are uniformly distributed in the matrix and are combined with the matrix through a firm chemical bond, which not only significantly improves the overall strength of the material, but also reduces internal defects. In addition, the in-situ self-grown carbon nanotubes can cooperate with the matrix to deform, effectively reducing the generation of micro-cracks, thereby significantly improving the fatigue resistance of the material and achieving overall improvement of the mechanical properties.

[0056] In some specific embodiments, the in-situ self-grown carbon nanotube reinforced nanoporous carbon aerogel composite material prepared by the present application has a compressive strength of 10 MPa or more, and further, the compressive strength is 18 MPa or more, which is significantly improved compared to the existing several to several hundred kilopascals; at the same time, the carbon aerogel composite material prepared by the present application has excellent fatigue resistance, for example, the permanent deformation is less than 1.5% after 99% strain cycle for 1000 times. The bending strength of the carbon aerogel composite material prepared by the present application is 6.5 MPa or more.

[0057] The present application strengthens the carbon aerogel material by in-situ self-grown carbon nanotubes, significantly improves the high-temperature stability and thermal insulation performance of the carbon aerogel. Specifically, carbon nanotubes themselves have excellent thermal stability and low thermal conductivity. Compared with the traditional method of adding reinforcing phases (such as carbon nanotubes) in carbon aerogel, the present application uses in-situ self-grown method to achieve uniform distribution of carbon nanotubes in the three-dimensional porous network structure of the matrix, effectively avoiding the problem of easy agglomeration of carbon nanotubes in the traditional method. At the same time, the in-situ self-grown carbon nanotubes form a stronger interface with the aerogel matrix, thereby enhancing the thermal stability of the carbon aerogel material at high temperature and ensuring that the material as a whole has excellent thermal insulation performance.

[0058] In some specific embodiments, the in-situ self-grown carbon nanotube reinforced nanoporous carbon aerogel composite material prepared by the present application has a linear ablation rate of ≤0.04 mm / s and a thermal conductivity of ≤0.3 W·m -1 ·K -1 .

[0059] The present application constructs a three-dimensional network of porous structure through the curing of phenolic resin, the synergistic effect of the catalyst and the curing, drying and carbonization process, and realizes the low density and lightweight characteristics of the carbon aerogel material.

[0060] In some embodiments, the in-situ self-grown carbon nanotube reinforced nanoporous carbon aerogel composite material prepared by the present application has a density ≤ 25 mg / cm 3 .

[0061] The inventors have found that, in the step (2), controlling the parameters such as the order and interval time of adding the catalyst, the amount of the catalyst added, the specific composition of the catalyst, the temperature during the process of adding the catalyst, and the rotation speed, can better exert the multifunctional synergistic catalytic effect of the metal cobalt powder, magnesium chloride and zinc acetate, achieve more uniform and efficient catalytic effect, and further promote the improvement of the comprehensive performance of the carbon aerogel composite material.

[0062] In some embodiments, in the step (2), the adding of the metal cobalt powder, magnesium chloride and zinc acetate comprises: adding the metal cobalt powder for multiphase surface catalysis, the magnesium chloride for synergistic auxiliary catalysis, and the zinc acetate for homogeneous catalysis, in batches and sequentially, every 10-60 min. Preferably, adding the metal cobalt powder for multiphase surface catalysis, the magnesium chloride for synergistic auxiliary catalysis, and the zinc acetate for homogeneous catalysis, in batches and sequentially, every 20-40 min.

[0063] For example, the adding in batches and sequentially herein refers to: first adding the metal cobalt powder, then adding the magnesium chloride, and finally adding the zinc acetate.

[0064] In some embodiments, in the step (2), the mass of the catalyst accounts for 3%-7% of the mass of the linear phenolic resin, and preferably accounts for 4%-6% of the mass of the linear phenolic resin; for example, the mass percentage of the catalyst in the mass of the linear phenolic resin is 3.0%, 3.5%, 4.0%, 4.5%, 5.0%, 5.5%, 6.0%, 6.5%, or 7.0%.

[0065] In some embodiments, in the catalyst, the molar ratio of the metal cobalt powder, the magnesium chloride and the zinc acetate is (0.5-1.5):(0.5-1.5):(0.5-1.5). Preferably, the molar ratio of the metal cobalt powder, the magnesium chloride and the zinc acetate is (0.9-1.1):(0.9-1.1):(0.9-1.1).

[0066] Specifically, in the catalyst, the molar ratio of the metal cobalt powder, the magnesium chloride and the zinc acetate is ([a1]-[a2]):([a3]-[a4]):([a5]-[a6]); a1, a2, a3, a4, a5, and a6 each independently take a value such as 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, and a1

[0067] In some embodiments, in step (2), the temperature of the system is controlled at 45-65 °C during the process of adding the cobalt powder, magnesium chloride and zinc acetate; for example, the temperature of the system is 45 °C, 48 °C, 50 °C, 52 °C, 55 °C, 57 °C, 60 °C, 65 °C; preferably, the temperature of the system is controlled at 50-60 °C.

[0068] In some embodiments, in step (2), the stirring speed is 500-700 rpm during the process of adding the cobalt powder, magnesium chloride and zinc acetate. Preferably, the stirring speed is 550-650 rpm.

[0069] The inventors have found that, in the process of the dissolution reaction in step (3), by using the step-by-step heating and step-by-step increasing of the stirring speed within a suitable temperature range and stirring speed interval, and further by finely controlling the change amplitude and time interval of the heating and stirring speed, the reaction rate and uniformity can be better controlled, the micro defects and unnecessary by-products can be effectively reduced, the microstructure of the carbon aerogel can be improved, and the in-situ growth of carbon nanotubes can be accelerated, thereby helping to prepare carbon aerogel composite materials with excellent comprehensive performance.

[0070] In some embodiments, in step (3), the heating and stirring include: step-by-step heating and step-by-step increasing of the stirring speed within a temperature range of 50-70 °C and a stirring speed interval of 600-800 rpm. Preferably, the temperature range is 50-65 °C; and the stirring speed interval is 600-750 rpm.

[0071] In some embodiments, in the step-by-step heating, the heating amplitude is 4-8% of the initial temperature; and the interval time of heating is 3-7 min. In the step-by-step heating, the initial temperature is T0, and the final target temperature is T f , satisfying T0 < T f , and T0 and T f are both controlled at 50-70 °C.

[0072] Preferably, the heating amplitude is 5-7% of the initial temperature. Preferably, the interval time of heating is 4-6 min. Preferably, the initial temperature T0 is 50-55 °C, and the final target temperature T f is 55-65 °C.

[0073] In some embodiments, in the step-by-step increasing of the stirring speed, the increasing amplitude of the stirring speed is 5-9% of the initial stirring speed; and the interval time of increasing the stirring speed is 3-7 min. In the step-by-step increasing of the stirring speed, the initial stirring speed is R0, and the final target stirring speed is R f , satisfying R0 < R f , and R0 and R f are both controlled at 600-800 rpm.

[0074] Preferably, the amplitude of each increase in rotation speed is 6-8% of the initial rotation speed. Preferably, the interval time of increasing rotation speed is 4-6 min.

[0075] Preferably, the initial rotation speed R0 is 550-650 rpm; the final target rotation speed R f is 650-750 rpm.

[0076] In some embodiments, when both the temperature and the rotation speed reach the final target temperature T f and the final target rotation speed R f , the reaction is continued for 3-10 min. Illustratively, the time of continuing the reaction is the same as the interval time of the temperature rising, and / or the interval time of increasing the rotation speed.

[0077] In some embodiments, in step (1), the mixing of the solution of linear phenolic resin with the curing agent comprises: under the condition of heating and stirring, first adding hexamethylenetetramine to the solution of linear phenolic resin, and then adding benzoyl peroxide as the curing agent.

[0078] It should be noted that the batch addition of the curing agent can effectively control the reaction rate. Under the condition of heating, the first added hexamethylenetetramine is rapidly activated by thermal activation, promoting the preliminary formation of the three-dimensional network structure. The subsequently added benzoyl peroxide is chemically activated, and its amine group reacts with the active groups in the phenolic resin, further accelerating the chain growth and cross-linking curing. The synergistic effect of thermal curing and chemical curing builds a uniform and stable three-dimensional network structure, significantly improves the mechanical properties of the material, provides a stable matrix for the subsequent in-situ generation of carbon nanotubes, and helps to form a uniform and porous network of carbon aerogel, achieving an optimized balance between the mechanical properties and lightweight of the thermal insulation material.

[0079] The inventors found that, in step (1), by controlling the reaction conditions of linear phenolic resin curing, the addition amount of the curing agent, the composition of the curing agent, and the addition timing and other parameters, the rate and uniformity of the curing reaction can be better controlled, and the generation of micro defects and by-products can be reduced. This helps to improve the microstructure of the cured phenolic resin, form a more uniform and stable three-dimensional network structure, provide a good foundation for the subsequent formation of a uniform and porous structure and in-situ self-grown carbon nanotubes, while ensuring the efficiency of the phenolic resin curing reaction, and thus preparing a carbon aerogel composite material with excellent comprehensive performance.

[0080] In some embodiments, in step (1), the heating temperature is 45-65°C. Preferably, the heating temperature is 50-60°C. Illustratively, the heating temperature is 45°C, 48°C, 50°C, 52°C, 55°C, 58°C, 60°C, or 65°C.

[0081] In some embodiments, in step (1), the stirring speed is 400-600 rpm. Preferably, the stirring speed is 450-550 rpm. Illustratively, the stirring speed is 400 rpm, 420 rpm, 450 rpm, 470 rpm, 500 rpm, 520 rpm, 550 rpm, 570 rpm, 600 rpm.

[0082] In some embodiments, in step (1), the total mass of hexamethylenetetramine and benzoyl peroxide is 3-7% of the mass of the linear phenolic resin. Preferably, the total mass of hexamethylenetetramine and benzoyl peroxide is 4-6% of the mass of the linear phenolic resin.

[0083] In some embodiments, in step (1), the molar ratio of hexamethylenetetramine to benzoyl peroxide is (0.7-1.3):(0.7-1.3). Preferably, the molar ratio of hexamethylenetetramine to benzoyl peroxide is (0.9-1.1):(0.9-1.1). Illustratively, the molar ratio of hexamethylenetetramine to benzoyl peroxide is ([b1]-[b2]):([b3]-[b4]), b1

[0084] In some embodiments, in step (1), hexamethylenetetramine is first added, followed by benzoyl peroxide after 20-40 min, and the curing is completed after 40-60 min.

[0085] In some embodiments, in step (1), the mass average molecular weight of the cured phenolic resin is greater than 1000. Preferably, the mass average molecular weight of the cured phenolic resin is 1500-8000.

[0086] In some embodiments, in step (1), the preparation of the linear phenolic resin solution comprises mixing the linear phenolic resin and the solvent uniformly.

[0087] Illustratively, the solvent is at least one of isopropyl alcohol, n-hexane, methanol, and tetrahydrofuran. Preferably, the solvent is one or a combination of isopropyl alcohol and tetrahydrofuran.

[0088] Illustratively, the mass average molecular weight of the linear phenolic resin is 300-500.

[0089] Illustratively, the mass of the solvent is 40-60% of the total mass of the linear phenolic resin solution.

[0090] In some embodiments, in step (4), the temperature for the solidification is 80-100°C. Preferably, the temperature for the solidification is 85-95°C.

[0091] In some embodiments, in step (4), the time for the solidification is >24h. Preferably, the time for the solidification is 25-34h.

[0092] Preferably, in step (4), the solidification process is started within 10h after the resin liquid is obtained.

[0093] In some embodiments, in step (4), the drying is performed by microwave-assisted vacuum drying. Specifically, the drying includes: first microwave drying, and then vacuum drying. Through the synergistic effect of the two drying methods, the respective advantages are fully played, for example, microwave drying is efficient and fast, which can significantly shorten the drying period and improve the uniformity of drying; vacuum drying further accelerates the drying process while maintaining the integrity of the material form; through microwave-assisted vacuum drying, energy saving and environmental protection are achieved, which is conducive to the preparation of carbon aerogel materials with excellent comprehensive performance such as porous structure and low thermal conductivity, while the drying efficiency is taken into account.

[0094] Illustratively, the parameters of the microwave drying include: microwave frequency of 1600-3400Mhz, microwave power of 1000-2000W, drying temperature of 60-90°C, and drying time of 10-14h.

[0095] Illustratively, in the process of microwave drying, the microwave frequency is 1600Mhz, 1800Mhz, 2000Mhz, 2200Mhz, 2500Mhz, 2800Mhz, 3000Mhz, 3200Mhz, or 3400Mhz. The microwave power is 1000W, 1200W, 1400W, 1600W, 1800W, or 2000W. The drying temperature is 60°C, 65°C, 70°C, 75°C, 80°C, 85°C, or 90°C.

[0096] Preferably, in the process of microwave drying, the microwave frequency is 2000-3000Mhz; the microwave power is 1400-1600W; the drying temperature is 70-80°C; and the drying time is 11-13h.

[0097] Illustratively, the parameters of the vacuum drying include: vacuum degree of 0.7-1.3mbar, power of the vacuum drying instrument of 800-1000W, drying temperature of 80-120°C, and drying time of 10-12h.

[0098] Preferably, the vacuum drying is performed at a vacuum degree of 0.9-1.1 mbar, a power of 850-950 W, a drying temperature of 95-105℃, and a drying time of 10.5-11.5 h.

[0099] In some embodiments, in step (4), the carbonizing comprises: under the protection of inert gas, sequentially incubating the dried sample at three gradient temperatures; wherein low-temperature pyrolysis is performed at the first gradient temperature, then medium-temperature pyrolysis is performed at the second gradient temperature, and finally high-temperature carbonization is performed at the third gradient temperature.

[0100] In some embodiments, the first gradient temperature is 150-200℃, the second gradient temperature is 400-600℃, and the third gradient temperature is 1000-1200℃. Preferably, the first gradient temperature is 165-185℃, the second gradient temperature is 450-550℃, and the third gradient temperature is 1050-1150℃.

[0101] Illustratively, the incubation time at the first gradient is 0.8-1.2 h, the incubation time at the second gradient is 1.7-2.3 h, and the incubation time at the third gradient is 3.5-4.5 h.

[0102] Illustratively, the heating rate to the first gradient is 3.7-4.3℃ / min, such as 3.7℃ / min, 3.9℃ / min, 4℃ / min, 4.1℃ / min, 4.3℃ / min. The heating rate from the first gradient to the second gradient is 3.6-4.4℃ / min, such as 3.6℃ / min, 3.8℃ / min, 4℃ / min, 4.2℃ / min, 4.4℃ / min. The heating rate from the second gradient to the third gradient is 3.5-4.5℃ / min, such as 3.5℃ / min, 3.8℃ / min, 4℃ / min, 4.2℃ / min, 4.5℃ / min. After carbonization, the cooling rate from the third gradient to room temperature is 5-10℃ / min, such as 5℃ / min, 6℃ / min, 7℃ / min, 8℃ / min, 9℃ / min, 10℃ / min.

[0103] Illustratively, the inert gas is argon. For example, the volume purity of argon is ≥99.995%. The carbonization is performed in a tube furnace, such as a horizontal tube furnace. The rate of argon flowing into the tube furnace is 0.7-1.3 L / min, such as 0.7 L / min, 0.9 L / min, 1.1 L / min, 1.3 L / min.

[0104] By controlling the parameters (such as temperature, time, heating rate, cooling rate, etc.) in the curing and carbonization process, the mechanical properties of the carbon aerogel composite material are ensured, and the lightweight, high-temperature stability, heat insulation performance, etc. are better achieved.

[0105] The application provides an in-situ self-grown carbon nanotube reinforced nanoporous carbon aerogel composite material obtained by the preparation method, and in specific embodiment modes, the obtained in-situ self-grown carbon nanotube reinforced nanoporous carbon aerogel composite material has a compressive strength of ≥10 Mpa, a permanent deformation of less than 1.5% in 99% strain cycle for 1000 times, a linear ablation rate of ≤0.04 mm / s, and a thermal conductivity of ≤0.3 W·m -1 ·K -1 , and a density of ≤25 mg / cm 3 .

[0106] Therefore, the in-situ self-grown carbon nanotube reinforced nanoporous carbon aerogel composite material obtained by the preparation method has excellent mechanical properties, high-temperature stability and heat insulation performance, and meanwhile, the low density and lightweight characteristics of the carbon aerogel are ensured.

[0107] The technical solutions of the application are further described in detail below in combination with specific examples and comparative examples.

[0108] Example 1

[0109] The embodiment provides a preparation method of an in-situ self-grown carbon nanotube reinforced nanoporous carbon aerogel composite material, and the method comprises the following steps:

[0110] (1) mixing a solution of linear phenolic resin with a curing agent to obtain a cured phenolic resin solution;

[0111] The solution of linear phenolic resin is prepared by uniformly mixing linear phenolic resin with isopropyl alcohol, and the solution of linear phenolic resin is obtained; wherein the mass average molecular weight of the linear phenolic resin is 400-430, and the mass of the isopropyl alcohol accounts for 50% of the total mass of the solution of linear phenolic resin.

[0112] In a water bath magnetic stirring instrument, hexamethylenetetramine is first added to the solution of linear phenolic resin, and then benzoyl peroxide is added after 10 min, and the solution of cured phenolic resin is obtained after 40 min, and the molecular weight of the cured phenolic resin is 2500-2600; wherein the temperature of the water bath magnetic stirring instrument is set to 45℃, and the stirring speed is 600 rpm. The total mass of the hexamethylenetetramine and the benzoyl peroxide accounts for 3% of the mass of the linear phenolic resin, and the molar ratio of the hexamethylenetetramine to the benzoyl peroxide is 0.7:1.3.

[0113] (2) adding metal cobalt powder, magnesium chloride and zinc acetate as catalysts to the phenolic resin solution;

[0114] The metal cobalt powder, magnesium chloride, and zinc acetate are added into the phenolic resin solution as catalysts in batches every 10 minutes. The temperature of the system in step (2) is 65°C, the stirring speed is 500 rpm, the total mass of the catalysts (metal cobalt powder, magnesium chloride, and zinc acetate) accounts for 2% of the mass of the linear phenolic resin, and the molar ratio of the metal cobalt powder, magnesium chloride, and zinc acetate is 1.5:0.5:0.5.

[0115] (3) After the catalyst is added, the resin liquid is obtained by heating and stirring.

[0116] Specifically, the heating and stirring include: setting the initial temperature of the water bath to 50°C and the initial speed to 600 rpm, increasing the temperature by 5.0°C every 10 minutes (the temperature increase is 10% of the initial temperature each time), and increasing the speed by 60 rpm every 10 minutes (the speed increase is 10% of the initial speed each time), until the temperature and speed reach the final target temperature of 65°C and the final target speed of 780 rpm, and continue to react for 10 minutes.

[0117] (4) The resin liquid is sequentially solidified, dried, and carbonized to obtain an in-situ self-grown carbon nanotube reinforced nanoporous carbon aerogel composite material.

[0118] Solidification: The resin liquid obtained in step (3) is placed in a hydrothermal synthesis reactor, and the hydrothermal synthesis reactor is placed in an oven. The solidification temperature is set to 100°C, and the solidification time is 25 hours to obtain a solidified product.

[0119] Drying: The solidified product is placed in a microwave generator for microwave drying. The microwave frequency is 1600 Mhz, the microwave power is 2000 W, the drying temperature is 90°C, and the drying time is 10 hours. The sample after microwave drying is placed in a vacuum drying instrument for vacuum drying. The vacuum degree is set to 1.3 mbar, the power of the vacuum drying instrument is 800 W, the drying temperature is 120°C, and the drying time is 12 hours.

[0120] Carbonization: The dried sample is placed in a horizontal tube furnace, pure argon gas (volume purity ≥ 99.995%) is introduced at a rate of 1.2 L / min, and heated to 150°C at a heating rate of 3.5°C / min for 1.2 hours for low-temperature pyrolysis, then heated to 400°C at a heating rate of 3.5°C / min and kept at this temperature for 1.7 hours for medium-temperature pyrolysis, and then heated to 1000°C at a heating rate of 3.5°C / min and kept at this temperature for 4.5 hours to complete carbonization.

[0121] Example 2

[0122] The difference between this embodiment and embodiment 1 is that in step (2), magnesium chloride, cobalt powder and zinc acetate are added into the phenolic resin solution as catalysts in turn every 10 minutes. The other steps and parameters are similar to those of embodiment 1.

[0123] Embodiment 3

[0124] The difference between this embodiment and embodiment 1 is that in step (2), magnesium chloride, zinc acetate and cobalt powder are added into the phenolic resin solution as catalysts in turn every 10 minutes. The other steps and parameters are similar to those of embodiment 1.

[0125] Embodiment 4

[0126] The difference between this embodiment and embodiment 1 is that in step (2), cobalt powder, magnesium chloride and zinc acetate are added into the phenolic resin solution as catalysts in turn every 30 minutes. The system temperature is 55°C and the stirring speed is 600 rpm. The other steps and parameters are similar to those of embodiment 1.

[0127] Embodiment 5

[0128] The difference between this embodiment and embodiment 4 is that in step (2), the total mass of the catalysts cobalt powder, magnesium chloride and zinc acetate accounts for 3% of the mass of the linear phenolic resin, and the molar ratio of cobalt powder, magnesium chloride and zinc acetate is 0.9:1.1:0.9. The other steps and parameters are similar to those of embodiment 4.

[0129] Embodiment 6

[0130] The difference between this embodiment and embodiment 5 is that in step (2), the total mass of the catalysts cobalt powder, magnesium chloride and zinc acetate accounts for 5% of the mass of the linear phenolic resin, and the molar ratio of cobalt powder, magnesium chloride and zinc acetate is 1:1:1. The other steps and parameters are similar to those of embodiment 5.

[0131] Embodiment 7

[0132] The difference between this embodiment and embodiment 1 is that in step (3), the reaction is carried out at a constant temperature of 60°C and a constant speed of 750 rpm for 40 minutes. The other steps and parameters are similar to those of embodiment 1.

[0133] Embodiment 8

[0134] The difference between this example and Example 1 is that in step (3), the initial temperature of the water bath is set to 50°C, the initial rotation speed is 600 rpm, the temperature is increased by 4.0°C every 7 min (the increase amplitude is 8% of the initial temperature), and the rotation speed is increased by 30 rpm every 7 min (the increase amplitude is 5% of the initial rotation speed) until the temperature and rotation speed reach the final target temperature of 66°C and the final target rotation speed of 720 rpm, and the reaction is continued for 7 min. The other steps and parameters are similar to those of Example 1.

[0135] Example 9

[0136] The difference between this example and Example 1 is that in step (3), the initial temperature of the water bath is set to 50°C, the initial rotation speed is 600 rpm, the temperature is increased by 3°C every 5 min (the increase amplitude is 6% of the initial temperature), and the rotation speed is increased by 40 rpm every 5 min (the increase amplitude is 6.7% of the initial rotation speed) until the temperature and rotation speed reach the final target temperature of 65°C and the final target rotation speed of 720 rpm, and the reaction is continued for 7 min. The other steps and parameters are similar to those of Example 1.

[0137] Example 10

[0138] The difference between this example and Example 1 is that in step (1), in the water bath magnetic stirring instrument, the hexamethylenetetramine is first added to the solution of linear phenolic resin, and then the benzoyl peroxide is added after 30 min, and the cured phenolic resin solution is obtained after 50 min. The other steps and parameters are similar to those of Example 1.

[0139] Example 11

[0140] The difference between this example and Example 1 is that in step (1), the temperature of the water bath magnetic stirring instrument is set to 50°C, and the stirring rotation speed is 550 rpm. The other steps and parameters are similar to those of Example 1.

[0141] Example 12

[0142] The difference between this example and Example 1 is that in step (1), the temperature of the water bath magnetic stirring instrument is set to 55°C, the stirring rotation speed is 500 rpm, the total mass of the hexamethylenetetramine and benzoyl peroxide accounts for 4% of the mass of the linear phenolic resin, and the molar ratio of hexamethylenetetramine to benzoyl peroxide is 0.9:1.1. The other steps and parameters are similar to those of Example 1.

[0143] Example 13

[0144] The difference between this example and Example 12 is that in step (1), the total mass of hexamethylenetetramine and benzoyl peroxide accounts for 5% of the mass of the linear phenolic resin, and the molar ratio of hexamethylenetetramine to benzoyl peroxide is 1:1. The remaining steps and parameters are similar to those of Example 12.

[0145] Example 14

[0146] The difference between this example and Example 1 is that in step (4), microwave drying is performed first, the microwave frequency is 2500 Mhz, the microwave power is 1500 W, the drying temperature is 75°C, and the drying time is 12 h. The remaining steps and parameters are similar to those of Example 1.

[0147] Example 15

[0148] The difference between this example and Example 1 is that in step (4), the drying only includes vacuum drying, and the specific parameters of vacuum drying are the same as those of Example 1, but does not include microwave drying. The remaining steps and parameters are similar to those of Example 1.

[0149] Example 16

[0150] The difference between this example and Example 1 is that in step (4), carbonization: pure argon gas (volume purity ≥ 99.995%) is passed at a rate of 1.2 L / min, and heated to 175°C at a heating rate of 4°C / min first, and low-temperature pyrolysis is performed for 1.0 h, then heated to 500°C at a heating rate of 4°C / min, and medium-temperature pyrolysis is performed for 2.0 h at this temperature, and then heated to 1100°C at a heating rate of 4°C / min, and carbonization is completed by keeping the temperature at this temperature for 4.0 h. The remaining steps and parameters are similar to those of Example 1.

[0151] Comparative Example 1

[0152] The difference between this comparative example and Example 1 is that in step (2), metal cobalt powder is added to the phenolic resin solution as a catalyst; the total mass of the catalyst, i.e. metal cobalt powder, accounts for 2% of the mass of the linear phenolic resin. The remaining steps and parameters are similar to those of Example 1.

[0153] Comparative Example 2

[0154] The difference between this comparative example and Example 1 is that in step (2), metal cobalt powder and magnesium chloride are added to the phenolic resin solution as catalysts, with metal cobalt powder and magnesium chloride being added in batches every 10 min; the total mass of the catalysts, i.e. metal cobalt powder and magnesium chloride, accounts for 2% of the mass of the linear phenolic resin, and the molar ratio of metal cobalt powder to magnesium chloride is 1.5:1.0. The remaining steps and parameters are similar to those of Example 1.

[0155] Comparative Example 3

[0156] The difference between the present comparative example and example 1 is that in step (2), metal cobalt powder and zinc acetate are sequentially added into the phenolic resin solution in batches every 10 minutes as catalysts; the total mass of the catalysts metal cobalt powder and zinc acetate accounts for 2% of the mass of the linear phenolic resin, and the molar ratio of the metal cobalt powder and zinc acetate is 1.5:1.0. The remaining steps and parameters are similar to those of example 1.

[0157] Comparative example 4

[0158] The difference between the present comparative example and example 1 is that in step (2), magnesium chloride and zinc acetate are sequentially added into the phenolic resin solution in batches every 10 minutes as catalysts; the total mass of the catalysts magnesium chloride and zinc acetate accounts for 2% of the mass of the linear phenolic resin, and the molar ratio of the magnesium chloride and zinc acetate is 1.0:1.0. The remaining steps and parameters are similar to those of example 1.

[0159] Comparative example 5

[0160] The difference between the present comparative example and example 1 is that step (2) is omitted, that is, no metal cobalt powder, magnesium chloride and zinc acetate are added as catalysts. The remaining steps and parameters are similar to those of example 1.

[0161] The carbon aerogel materials obtained in the above examples and comparative examples are subjected to performance tests, wherein the test method for density adopts GB 1463-2005, the test method for thermal conductivity adopts GBT 10295-2008, the test method for linear ablation rate adopts GJB 323B-2018 (the heat flow density is 4.18 WM / m 2 ), the test method for compressive strength adopts GJB 10246.2-2021, the test method for fatigue performance adopts GJB 2637A-2019, the fatigue performance in Table 1 refers to the permanent deformation after 1000 times of 99% strain cycles, and the test method for bending strength adopts GB / T 1449-2005.

[0162] Table 1: Performance test results of examples and comparative examples

[0163]

[0164]

[0165] From Figures 1-5 It can be seen that by adding metal cobalt powder, magnesium chloride and zinc acetate as catalysts, in-situ self-grown carbon nanotubes in the carbon aerogel composite material are realized. From the microstructure, Figures 1 to 3 It is shown that the diameter of the in-situ self-grown carbon nanotubes in example 1 is 40-60 nm, Figure 4 It is shown that the in-situ self-grown carbon nanotubes are uniformly distributed and grow well. Figure 6No carbon nanotubes were produced in Displayed Comparative Example 5.

[0166] The above descriptions are only the preferred embodiments of the present application, not intended to limit the scope of the present application. Any modification or replacement within the technical scope of the present application should be covered within the scope of the present application.

Claims

1. A method for preparing in-situ self-grown carbon nanotube reinforced nanoporous carbon aerogel composites, characterized in that, The method comprises the following steps: (1) mixing a solution of linear phenolic resin with a curing agent to obtain a cured phenolic resin solution; The mixing of the solution of linear phenolic resin with the curing agent comprises: under the conditions of heating and stirring, first adding hexamethylenetetramine to the solution of linear phenolic resin, and then adding benzoyl peroxide as the curing agent; (2) adding metal cobalt powder, magnesium chloride and zinc acetate as catalysts to the phenolic resin solution; (3) after adding the catalysts, heating and stirring to obtain a resin liquid; (4) sequentially curing, drying and carbonizing the resin liquid to obtain an in-situ self-grown carbon nanotube reinforced nanoporous carbon aerogel composite material.

2. The production method according to claim 1, characterized by, In step (2), the adding of the metal cobalt powder, magnesium chloride and zinc acetate comprises: adding the metal cobalt powder to perform multiphase surface catalysis, adding the magnesium chloride to perform synergistic auxiliary catalysis, and adding the zinc acetate to perform homogeneous catalysis, in batches and sequentially, every 10-60 min.

3. The preparation method according to claim 1, characterized in that, In step (2), the mass of the catalysts accounts for 3%-7% of the mass of the linear phenolic resin.

4. The production method according to claim 1, characterized by, In the catalysts, the molar ratio of the metal cobalt powder, magnesium chloride and zinc acetate is (0.5-1.5):(0.5-1.5):(0.5-1.5).

5. The method of claim 1, wherein, In step (3), the heating and stirring comprise: gradually increasing the temperature and gradually increasing the rotation speed in the temperature range of 50-70℃ and the rotation speed range of 600-800 rpm.

6. The production method according to claim 5, wherein In the gradual temperature increase, the temperature increase amplitude is 4-8% of the initial temperature, and the interval time of temperature increase is 3-7 min.

7. The preparation method according to claim 5, characterized in that, In the gradual rotation speed increase, the rotation speed increase amplitude is 5-9% of the initial rotation speed, and the interval time of rotation speed increase is 3-7 min.

8. The method of claim 1, wherein, In step (1), the heating temperature is 45-65℃; and / or, The total mass of the hexamethylenetetramine and benzoyl peroxide accounts for 3%-7% of the mass of the linear phenolic resin.

9. The method of claim 1, wherein, In step (4), the drying comprises: first performing microwave drying, and then performing vacuum drying.

10. The in-situ carbon nanotube reinforced nanoporous carbon aerogel composite material obtained by the production process according to any one of claims 1 to 9, characterized in that, Compression strength ≥ 10 MPa, permanent deformation after 99% strain cycle 1000 times less than 1.5%, linear ablation rate ≤ 0.04 mm / s, thermal conductivity ≤ 0.3 W·m -1 · K -1 , density ≤ 25 mg / cm 3 .

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