Ultralow-density carbon foam material and preparation method thereof

Abstract

The invention relates to an ultralow-density carbon foam material and a preparation method thereof, belongs to thermal insulation materials, and solves the problems that in the prior art, carbon foam is high in density, complex in process, large in heat conductivity coefficient, incapable of meeting the requirements of the high-temperature thermal insulation field, prone to scaling, insufficient in mechanical property and the like. The preparation method of the ultralow-density carbon foam material comprises the following steps: S1, uniformly mixing a carbon source matrix and a compatibilizer to obtain a modified carbon source matrix; s2, adding a carbon nanomaterial into the modified carbon source matrix to form a carbon nanomaterial reinforced carbon source matrix; s3, preparation of a carbonaceous precursor solution; s4, permeation and swelling: putting the porous polymer foam into the carbonaceous precursor solution, and performing permeation and swelling to form a uniformly distributed composite structure; s5, regulating and controlling the distribution of the carbonaceous precursor solution; s6, carrying out curing reaction; and S7, carrying out high-temperature gradient pyrolysis to obtain the ultralow-density carbon foam with a compact carbon skeleton. The thermal insulation property and the mechanical property of the foamy carbon material are improved.

Description

Technical Field

[0001] The present invention relates to the technical field of thermal insulation materials, and particularly to an ultra-low density carbon foam material and a preparation method thereof. Background Art

[0002] With the rapid development of aerospace technology, the performance requirements for thermal protection materials are becoming increasingly stringent. During the re-entry process of a spacecraft, its surface needs to withstand extremely high thermal loads. Therefore, it has become an urgent task to develop materials that combine lightweight and excellent thermal protection performance. Traditional thermal protection systems have a large weight, which has an adverse impact on flight performance and fuel efficiency, prompting researchers to actively explore new lightweight and high-performance thermal protection materials.

[0003] Carbon foam materials, with their three-dimensional porous structure, ultra-low density, high porosity, high specific surface area, high temperature resistance (up to 3000 °C in an inert atmosphere), low thermal conductivity, low coefficient of thermal expansion, and excellent chemical and thermal stability, etc., show broad application prospects in many fields such as aerospace thermal protection systems. However, existing carbon foam materials have deficiencies in terms of structural uniformity, mechanical properties, and thermal stability, and are difficult to meet the application requirements in extreme environments.

[0004] To solve the above problems, a number of domestic patents have disclosed preparation methods for carbon foam materials. For example, carbon foam is prepared by electrospinning, freeze-drying, impregnation with phenolic resin, and carbonization treatment. Although this material has good mechanical properties, it has problems such as high density, complex process, and high cost, which limit its large-scale application; another example is that a foam carbon material with excellent heat insulation performance and mechanical properties is prepared by mixing phenolic resin, silane foaming agent, and short-cut carbon fiber, followed by preliminary curing, foaming curing, chemical vapor deposition, and high-temperature impurity removal. However, this method results in high graphitization of the material due to high-temperature impurity removal, with a large thermal conductivity, and it is difficult to meet the application requirements in the field of high-temperature thermal insulation. Summary of the Invention

[0005] In view of the above analysis, embodiments of the present invention aim to provide an ultra-low density carbon foam material and a preparation method thereof, to solve at least one of the problems such as high density of existing carbon foam, complex process, large thermal conductivity, easy chipping of carbon foam, insufficient mechanical properties, difficulty in balancing low density and high strength, and inability to meet the requirements in the field of high-temperature thermal insulation.

[0006] On the one hand, embodiments of the present invention provide a preparation method for an ultra-low density carbon foam material, including the preparation of a carbonaceous precursor, specifically including the following steps:

[0007] S1. Pretreatment of the carbon source matrix: Mix the carbon source matrix and the compatibilizer evenly to obtain a modified carbon source matrix;

[0008] S2. Preparation of carbon nanomaterial-reinforced carbon source matrix: Add carbon nanomaterials to the modified carbon source matrix obtained in S1, and make them uniformly dispersed through mechanical stirring and ultrasonic treatment to form a carbon nanomaterial-reinforced carbon source matrix;

[0009] S3. Preparation of carbonaceous precursor solution: Mix the carbon nanomaterial-reinforced carbon source matrix obtained in S2 with a curing agent, and carry out a pre-reaction in a water bath environment to obtain a carbonaceous precursor solution.

[0010] Specifically, the carbon source matrix is an organic solution of a thermosetting resin prepolymer or a polymer monomer; the thermosetting resin prepolymer in the organic solution of the thermosetting resin prepolymer includes one or more composite systems of phenolic resin, epoxy resin, bismaleimide resin, furanone resin or furfural resin; the polymer monomer includes furfuryl alcohol.

[0011] Preferably, the carbon nanomaterials include one or several of carbon nanofibers, carbon nanotubes, graphene, and graphene oxide.

[0012] It should be noted that the temperature of the water bath environment in S3 is 25-45°C, the pre-reaction process is carried out under stirring, and the pre-reaction time is 2-10h.

[0013] Furthermore, the preparation method further includes the following steps:

[0014] S4. Osmotic swelling: Place the porous polymer foam in the carbonaceous precursor solution obtained in S3 for osmotic swelling to form a uniformly distributed composite structure;

[0015] S5. Regulation of carbonaceous precursor solution distribution: Regulate the distribution of the carbonaceous precursor solution, and remove the excess carbonaceous precursor solution in the pores of the composite structure to obtain a wet composite foam with a carbonaceous precursor solution-rich skeleton;

[0016] S6. Curing reaction: Place the wet composite foam obtained in S5 in an oven for gradient temperature rise curing, and after the reaction is completed, cool it to room temperature to obtain a high-strength rigid composite foam with an open-cell structure;

[0017] S7. High-temperature gradient pyrolysis: Place the high-strength rigid composite foam prepared in S6 in a high-temperature carbonization furnace, carry out high-temperature gradient pyrolysis in an inert atmosphere, and finally cool it to room temperature to obtain an ultra-low density carbon foam with a dense carbon skeleton.

[0018] Specifically, the osmotic swelling in S4 is carried out at 25-50°C, and the osmotic swelling time is 0.5-3h.

[0019] Illustratively, the high-temperature pyrolysis temperature described in S7 is: increasing from 25°C to 300-500°C at a heating rate of 1-5°C / min, maintaining at 300-500°C for 2-5 hours, and then increasing to 700-1200°C at a heating rate of 0.5-5°C / min, and maintaining for 1-3 hours.

[0020] On the other hand, an embodiment of the present invention also provides an ultra-low density carbon foam material, which uses an open-cell polymer foam as a supporting skeleton, a thermosetting resin or a polymer monomer as a carbon source matrix, and introduces carbon nanomaterials into the carbon source matrix to serve as a reinforcing phase.

[0021] It is worth noting that the volume density of the carbon foam material is 0.042-0.053 g / cm 3 , porosity ≥ 97%, thermal conductivity of 0.041 ~ 0.053W / (m·K), and compressive strength of 0.43 ~ 0.67MPa.

[0022] On the other hand, an embodiment of the present invention also provides an application of an ultra-low density carbon foam material, an application of the carbon foam material or the carbon foam material prepared by the preparation method, and the ultra-low density carbon foam material is applied to the field of high-temperature heat-insulating materials.

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

[0024] 1. The present invention significantly improves the compressive strength and specific strength of the carbon foam product by introducing carbon nanomaterials into the carbon source matrix, solving the problems of easy slagging and insufficient mechanical properties of traditional carbon foam.

[0025] 2. When preparing the carbonaceous precursor in the present invention, the viscosity of the carbonaceous precursor solution is adjusted to an appropriate range (30 to 80 mPa·s) by precisely controlling the temperature and time of the pre-reaction; on the one hand, this facilitates the subsequent distribution control of the carbonaceous precursor solution in the composite foam; on the other hand, it can ensure that a high-strength composite foam structure is formed after the curing reaction.

[0026] 3. The present invention prepares carbon foam materials through the methods of osmotic swelling, solidification, and high-temperature gradient pyrolysis. The preparation process is simple to operate, suitable for preparing large-size products, and suitable for industrial production. It has important application value in the fields of aerospace high-temperature thermal protection, molten metal filtration, etc., and solves the problems of traditional thermal protection materials such as heavy weight, uneven structure and insufficient high-temperature performance.

[0027] 4. The present invention uses open-cell polymer foam as the support framework, selects a thermosetting resin with a high char yield as the carbon source matrix, and introduces carbon nanomaterials as the reinforcing phase. By precisely controlling process parameters such as infiltration swelling, regulation of the distribution of the carbonaceous precursor solution, gradient curing, and high-temperature gradient pyrolysis, the prepared carbon foam has properties such as ultra-low density, excellent thermal stability, low thermal conductivity, and high strength, effectively solving the problem that it is difficult for existing carbon foams to simultaneously achieve low density and high strength, and can fully meet the requirements of the high-temperature insulation field.

[0028] The ultra-low density carbon foam material prepared by the present invention has a uniform open-cell structure, with a bulk density of 0.042 - 0.053 g / cm 3 , a thermal conductivity lower than 0.053 W / (m·K), and a compressive strength of 0.43 - 0.67 MPa, having broad application prospects in the field of lightweight high-temperature thermal protection.

[0029] In the present invention, the above technical solutions can also be combined with each other to achieve more preferred combined solutions. Other features and advantages of the present invention will be described in the subsequent description, and some advantages can be made obvious from the description, or understood by implementing the present invention. The objectives and other advantages of the present invention can be achieved and obtained from the content specifically pointed out in the description and the drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] The drawings are only for the purpose of showing specific embodiments and are not considered to be a limitation of the present invention. Throughout the drawings, the same reference signs denote the same components.

[0031] Figure 1 is a physical photograph of the ultra-low density carbon foam of the present invention;

[0032] Figure 2 is a stitched scanning electron microscope (SEM) image of the ultra-low density carbon foam of Example 5 of the present invention magnified 110 times;

[0033] Figure 3 is a scanning electron microscope (SEM) image of the ultra-low density carbon foam of Example 5 of the present invention magnified 300 times;

[0034] Figure 4 is the compression stress-strain diagram of the ultra-low density carbon foam of Example 5 of the present invention;

[0035] Figure 5 is a scanning electron microscope (SEM) image of the carbon foam of Comparative Example 2 of the present invention magnified 300 times. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0036] The preferred embodiments of the present invention will be specifically described below in conjunction with the accompanying drawings. The accompanying drawings form a part of this application and are used together with the embodiments of the present invention to explain the principles of the present invention, rather than to limit the scope of the present invention.

[0037] On the one hand, a specific embodiment of the present invention discloses a method for preparing an ultra-low density carbon foam material, including the preparation of a carbonaceous precursor, specifically including the following steps:

[0038] S1. Pretreatment of the carbon source matrix: Mix the carbon source matrix and the compatibilizer evenly to obtain a modified carbon source matrix;

[0039] S2. Preparation of the carbon nanomaterial-reinforced carbon source matrix: Add the carbon nanomaterial to the modified carbon source matrix prepared in S1, and make it evenly dispersed through mechanical stirring and ultrasonic treatment to form a carbon nanomaterial-reinforced carbon source matrix;

[0040] S3. Preparation of the carbonaceous precursor solution: Mix the carbon nanomaterial-reinforced carbon source matrix prepared in S2 with the curing agent, and carry out a pre-reaction in a water bath environment to obtain a carbonaceous precursor solution.

[0041] Specifically, in S1, the carbon source matrix is an organic solution of a thermosetting resin prepolymer or a polymer monomer; the thermosetting resin prepolymer in the organic solution of the thermosetting resin prepolymer includes one or more composite systems of phenolic resin, epoxy resin, bismaleimide resin, furanone resin or furfural resin; the polymer monomer includes furfuryl alcohol.

[0042] It should be noted that when the carbon source matrix is a polymer monomer, it is directly applied to the preparation process without introducing an organic solvent. When the carbon source matrix is an organic solution of a thermosetting resin prepolymer, the solid content of the thermosetting resin is 50-90 wt.%, and the organic solvent includes one or more of isopropanol, ethanol, ethylene glycol, and n-butanol. Preferably, the organic solvent is ethanol. The polymer monomer (such as furfuryl alcohol) itself is a low-viscosity liquid with good fluidity and processability, so there is no need to introduce an organic solvent. The thermosetting resin prepolymer is solid or high-viscosity liquid at room temperature (such as phenolic resin), and an organic solvent needs to be added to reduce the viscosity to meet the processing requirements.

[0043] Preferably, when the carbon source matrix is an organic solution of a phenolic resin prepolymer, the solid content of the phenolic resin is 50-90 wt.%; the organic solvent includes one or more of isopropanol, ethanol, ethylene glycol, and n-butanol. Preferably, the organic solvent is ethanol. Preferably, the solid content of the phenolic resin is 50 wt.%, 70 wt.%, 80 wt.%, 90 wt.%.

[0044] Exemplarily, the compatibilizer includes one or several of polyvinylidene fluoride (PVDF), polyethylene glycol (PEG), and polyacrylic acid (PAA); preferably, the compatibilizer is PVDF.

[0045] It should be noted that during the preparation process of the carbonaceous precursor solution, the carbon nanomaterials do not participate in the reaction, and the reaction process will not significantly affect the uniformity of the carbon nanomaterials in the carbon source matrix.

[0046] It is worth noting that the order of S1, S2, and S3 cannot be reversed and cannot be combined: If the carbon nanomaterials, carbon source matrix, and compatibilizer are mixed and stirred evenly together (i.e., S1 and S2 are combined into one step), it will cause the carbon nanomaterials and the compatibilizer to be mixed together first, and the carbon nanomaterials will agglomerate together, resulting in poor dispersibility and affecting the product performance; If a curing agent is first added to the carbon source matrix for a pre-reaction and then carbon nanomaterials are introduced for reinforcement, it will cause the reaction time between the carbon source matrix and the curing agent to be too long, resulting in too high viscosity of the carbonaceous precursor solution, poor dispersibility of the subsequently added carbon nanomaterials, and difficult discharge of the excess carbonaceous precursor solution. Eventually, the distribution of the carbonaceous precursor solution is uneven, and the density and thermal conductivity of the carbon foam will increase significantly, but the compressive strength will not be significantly improved.

[0047] Further, in S1, the carbon source matrix and the compatibilizer are mixed in a mass ratio of 100:(0.05 - 0.5). Too little addition of the compatibilizer may result in poor dispersibility of the carbon nanomaterials in the carbon source matrix, causing agglomeration of the carbon nanomaterials in the matrix. Preferably, the mass ratio of the carbon source matrix to the compatibilizer is 100:0.05, 100:0.1, 100:0.2, 100:0.3, 100:0.4, 100:0.5.

[0048] Preferably, during the mixing process of the carbon source matrix and the compatibilizer in S1, after mechanical stirring for 3 - 4 h, ultrasonic treatment is carried out for 2 - 3 h. Preferably, mechanical stirring is carried out for 3 h and ultrasonic treatment is carried out for 2 h.

[0049] Further, the carbon nanomaterials include one or several of carbon nanofibers, carbon nanotubes, graphene, and graphene oxide; preferably, the carbon nanomaterials are single-layer graphene oxide, and the particle size of the single-layer graphene oxide < 50 nm. Too large a particle size is likely to cause uneven dispersion.

[0050] Specifically, the addition amount of the carbon nanomaterial in S2 is 0.1-1.0 wt% of the mass of the carbon source matrix. If the addition amount of the carbon nanomaterial is too much, its dispersibility in the carbon source matrix may be poor, resulting in agglomeration; if the addition amount is too little, there will be no obvious improvement in the performance of the carbon foam material. Preferably, the addition amount of the carbon nanomaterial is 0.1 wt%, 0.2 wt%, 0.3 wt%, 0.4 wt%, 0.5 wt%, 0.6 wt%, 0.7 wt%, 0.8 wt%, 0.9 wt%, 1.0 wt% of the mass of the carbon source matrix.

[0051] Preferably, during the mixing process of the carbon nanomaterial and the modified carbon source matrix in S2, after mechanical stirring for 3-4 h, ultrasonic treatment is carried out for 2-3 h. Preferably, mechanical stirring is carried out for 3 h and ultrasonic treatment is carried out for 2 h.

[0052] It should be noted that the curing agent in S3 is selected according to the type of the carbon source matrix. Thermosetting resins are cured through cross-linking reactions, and the selection of the curing agent needs to match the chemical structure and reaction mechanism of the resin; the selection of the curing agent for polymer monomers depends on the chemical structure of the monomers and their polymerization reaction mechanisms.

[0053] Exemplarily, when the carbon source matrix is a phenolic resin prepolymer organic solution, the curing agent includes one of hexamethylenetetramine, ammonia water, and urea; preferably, the curing agent is hexamethylenetetramine, and the addition amount is 5-15% of the mass of the phenolic resin prepolymer, preferably 5%, 10%, 15%.

[0054] Specifically, when the carbon source matrix is furfuryl alcohol, the curing agent includes one of oxalic acid, citric acid, p-toluenesulfonic acid, or methyl p-toluenesulfonate; preferably, the curing agent is methyl p-toluenesulfonate. Compared with medium-strong acids such as oxalic acid, p-toluenesulfonic acid, and citric acid, using an ester compound with weak acidity as the curing agent can catalyze the stable self-polymerization pre-reaction of the carbonaceous polymer monomer (furfuryl alcohol), effectively avoiding the common foaming phenomenon when using medium-strong acid curing agents, and making the reaction process more stable and controllable. The furfuryl alcohol reinforced with carbon nanomaterials and the curing agent are mixed at a mass ratio of 100:(0.5-2), preferably, the mass ratio is 100:0.5, 100:0.8, 100:1, 100:1.2, 100:1.4, 100:1.5, 100:1.8, 100:2.

[0055] It should be noted that if the addition amount of the curing agent is too much, the reaction between the carbon source matrix and the curing agent will be too violent, making the reaction uncontrollable and causing foaming; if the addition amount of the curing agent is too little, the polymerization rate will be slow, and the reaction time needs to be greatly extended.

[0056] It should be noted that the organic solution of the thermosetting resin prepolymer and the pre-reaction of the polymer monomer both form a three-dimensional cross-linked network through polycondensation reactions. Since the activation energies and reaction kinetic conditions of these reactions are similar, the temperature of the water bath environment described in S3 is 25-45°C, the pre-reaction process is carried out under stirring, and the pre-reaction duration is 2-10h. Preferably, the temperature of the water bath environment is 25°C, 30°C, 35°C, 40°C, 45°C, and the pre-reaction duration is 2h, 3h, 4h, 5h, 6h, 7h, 8h, 9h, 10h.

[0057] Too high a pre-reaction temperature will also cause the reaction between the carbon source matrix and the curing agent to be intense, resulting in uncontrollable foaming. Too low a pre-reaction temperature leads to a slow pre-polymerization reaction and requires a greatly extended reaction time. A short pre-reaction time will result in a low degree of pre-polymerization, and it is difficult to form a high-strength composite foam structure after the curing reaction; too long a pre-polymerization time will cause the viscosity of the carbonaceous precursor to be too high, making it difficult to control the distribution of the carbonaceous precursor solution in the composite foam and causing a large number of pores in the final carbon foam to be blocked.

[0058] Preferably, the viscosity range of the carbonaceous precursor solution is controlled to be 30-80 mPa·s.

[0059] In a possible design, the carbon source matrix is furfuryl alcohol and the curing agent is methyl p-toluenesulfonate. In S3, the ester hydrolysis generates a weak acid, and the weak acid catalyzes the self-polymerization of furfuryl alcohol. The solute of the obtained carbonaceous precursor solution is polyfurfuryl alcohol formed by the self-polymerization of furfuryl alcohol.

[0060] Furthermore, the preparation method further includes the following steps:

[0061] S4. Osmotic swelling: Place the porous polymer foam in the carbonaceous precursor solution prepared in S3 for osmotic swelling to form a uniformly distributed composite structure;

[0062] S5. Regulation of the distribution of the carbonaceous precursor solution: Regulate the distribution of the carbonaceous precursor solution to remove the excess carbonaceous precursor solution in the pores of the composite structure to obtain a wet composite foam with a carbonaceous precursor solution-rich skeleton;

[0063] S6. Curing reaction: Place the wet composite foam obtained in S5 in an oven for gradient temperature rise curing. After the reaction is completed, cool it to room temperature to obtain a high-strength rigid composite foam with an open-cell structure;

[0064] S7. High-temperature gradient pyrolysis: Place the high-strength rigid composite foam prepared in S6 in a high-temperature carbonization furnace for high-temperature gradient pyrolysis in an inert atmosphere, and finally cool it to room temperature to obtain an ultra-low-density carbon foam with a dense carbon skeleton.

[0065] Specifically, the porous polymer foam is a foam material with an open-cell structure. The lightweight open-cell foam enables the final carbon foam to maintain a high open-cell ratio, ultra-low density, and low thermal conductivity. Moreover, the open-cell structure can promote the formation of a uniform open-cell structure for the final carbon foam material. The porous polymer foam includes one of polyurethane foam, melamine foam, and polyimide foam, preferably polyurethane foam. The density of the porous polymer foam is 0.01 - 0.04 g / cm 3 , and the thickness is 5 - 50 mm.

[0066] Preferably, the size of the porous polymer foam is determined according to actual production requirements, which can widely adapt to different production needs, especially having significant advantages in terms of large-size requirements.

[0067] It should be noted that the mass ratio of the porous polymer foam to the carbonaceous precursor solution in S4 is 1:(70 - 100), preferably 1:70, 1:80, 1:90, 1:100. If the amount of the carbonaceous precursor solution is too small, the polymer foam cannot be fully penetrated and swollen in the carbonaceous precursor solution, resulting in an uneven internal structure of the composite foam. If the amount is too large, it will not cause an adverse impact on the subsequent reaction process but will cause unnecessary waste.

[0068] Preferably, the penetration and swelling are carried out at 25 - 50 °C, and the penetration and swelling time is 0.5 - 3 h. Specifically, the penetration and swelling temperature is 25 °C, 30 °C, 35 °C, 40 °C, 45 °C, 50 °C, and the penetration and swelling time is 0.5 h, 1 h, 1.5 h, 2 h, 2.5 h, 3 h.

[0069] During the penetration and swelling process, the carbonaceous precursor and its solvent diffuse and penetrate into the interior of the polymer foam skeleton. Through the swelling effect, the volume and mass of the polymer foam increase, enabling the carbonaceous precursor solution to uniformly fill the foam skeleton and form a uniformly distributed composite structure.

[0070] It should be noted that the temperature and time of penetration and swelling are selected according to the different carbon source matrices. When the carbon source matrix is furfuryl alcohol, the penetration and swelling temperature is slightly higher, at 40 - 50 °C, which can accelerate the penetration and swelling of the carbonaceous precursor solution into the polymer foam. When the carbon source matrix is an organic solution of phenolic resin prepolymer, the viscosity of the high-solid-content phenolic resin is relatively high at room temperature, and increasing the temperature will reduce the viscosity of the phenolic resin, which is beneficial to the penetration and swelling of the phenolic resin into the polymer foam, preferably 40 - 50 °C. The penetration time is determined according to the volume expansion of the foam in the carbonaceous precursor solution. When the volume of the foam does not increase significantly after a certain period of penetration and swelling, it is considered that the penetration and swelling have reached the saturation state.

[0071] Further, the method for regulating the distribution of the carbonaceous precursor solution in S5 includes centrifugation, the method of absorbing glue with absorbent paper, or the two-roll pressing method.

[0072] Preferably, the distribution of the carbonaceous precursor solution is regulated to no liquid enrichment in the composite foam: when regulating the distribution of the carbonaceous precursor solution by centrifugation technology, the rotation speed is 600 - 1000 r / min, and the centrifugation time is controlled within 5 - 20 min; when regulating the distribution of the carbonaceous precursor solution by the two-roll pressing method, the pressure is 0.1 - 0.5 MPa or the roll spacing is 0.05 - 0.1% of the foam thickness, and the speed is 500 - 800 mm / min.

[0073] Further, the curing temperature in S6 needs to be determined according to the type of carbon source matrix and its curing reaction mechanism. First, determine the basic temperature range based on the thermal stability (decomposition temperature, crosslinking activity) of the carbon source matrix and the reaction activation energy under the catalysis of the curing agent; then, combined with the target crosslinking density and the requirements of the subsequent pyrolysis process, optimize the heating rate gradient to avoid material defects.

[0074] The curing heating rate gradient is as follows: from 25°C to the pre-curing temperature at a heating rate of 0.5 - 5°C / min, and hold at the pre-curing temperature for 1 - 15 h to achieve initial crosslinking and / or slow evaporation of the solvent; then, from the pre-curing temperature to the curing temperature at a heating rate of 0.5 - 5°C / min, and hold for 0.5 - 10 h to promote the formation of a three-dimensional network.

[0075] It should be noted that the pre-curing temperature is 70 - 90°C, and the curing temperature is 120 - 170°C. Preferably, in the gradient curing process, the heating rate to the pre-curing temperature is 0.5°C / min, 1°C / min, 2°C / min, 3°C / min, 4°C / min, 5°C / min, and the holding time at the pre-curing temperature is 1 h, 2 h, 3 h, 4 h, 5 h, 6 h, 7 h, 8 h, 9 h, 10 h, 11 h, 12 h, 13 h, 14 h, 15 h; the heating rate to any temperature of 120°C, 130°C, 140°C, 150°C, 160°C or 170°C is 0.5°C / min, 1°C / min, 2°C / min, 3°C / min, 4°C / min, 5°C / min, and the holding time at this temperature is 0.5 h, 1 h, 1.5 h, 2 h, 2.5 h, 3 h, 4 h, 5 h, 6 h, 7 h, 8 h, 9 h, 10 h.

[0076] Specific parameters need to be adjusted accordingly: for the furfuryl alcohol system without solvent, the pre-curing temperature is 70 °C (maintained for 1 - 5 h), and during the curing stage, the heating rate (0.5 - 5 °C / min) and holding time (0.5 - 3 h) need to be strictly controlled to inhibit cracks caused by intense exothermic reactions; for the phenolic resin system with solvent, pre-curing needs to be maintained at 90 °C for 10 - 15 h to ensure sufficient volatilization of the solvent, and during the curing stage, it is maintained at 150 °C for 6 - 10 h to enhance network densification. The entire curing process needs to balance the reaction rate and structural integrity through gradient heating to provide an ideal precursor structure for subsequent carbonization.

[0077] Specifically, when the carbon source matrix is furfuryl alcohol, the curing temperature gradient is as follows: heating from 25 °C to 70 °C at a heating rate of 0.5 - 5 °C / min, maintaining at 70 °C for 1 - 5 h, and then heating to 120 - 170 °C at a heating rate of 0.5 - 5 °C / min and maintaining for 0.5 - 3 h. For the reaction system with furfuryl alcohol as the carbon source matrix, the curing reaction is highly exothermic at 70 °C and above. If the temperature is raised too quickly in one step, it is easy to generate bubbles or excessive internal stress, resulting in cracks, which will affect the strength of the final carbon foam material. Therefore, gradient heating is required. Preferably, when the carbon source matrix is furfuryl alcohol, during the gradient curing process, the heating rate to 70 °C is 0.5 °C / min, 1 °C / min, 2 °C / min, 3 °C / min, 4 °C / min, 5 °C / min, and the holding time at 70 °C is 1 h, 2 h, 3 h, 4 h, 5 h; the heating rate to any temperature of 120 °C, 130 °C, 140 °C, 150 °C, 160 °C or 170 °C is 0.5 °C / min, 1 °C / min, 2 °C / min, 3 °C / min, 4 °C / min, 5 °C / min, and the holding time at this temperature is 0.5 h, 1 h, 1.5 h, 2 h, 2.5 h, 3 h.

[0078] When the carbon source matrix is an organic solution of phenolic resin prepolymer, the curing temperature rising gradient is as follows: rising to 90 °C at a heating rate of 0.5 - 5 °C / min, holding at 90 °C for 10 - 15 h, then rising to 150 °C at a heating rate of 0.5 - 5 °C / min and holding for 6 - 10 h. For the reaction system with an organic solution of phenolic resin prepolymer as the carbon source matrix, the curing reaction exotherms violently at 90 °C and above. If the temperature is raised too quickly at one time, it is easy to generate bubbles or excessive internal stress, resulting in cracks, which will affect the strength of the final carbon foam material. Therefore, gradient heating is required. Preferably, when the carbon source matrix is an organic solution of phenolic resin prepolymer, in the gradient curing process, the heating rate to 90 °C is 0.5 °C / min, 1 °C / min, 2 °C / min, 3 °C / min, 4 °C / min, 5 °C / min, and the holding time at 90 °C is 10 h, 11 h, 12 h, 13 h, 14 h, 15 h; the heating rate to 150 °C is 0.5 °C / min, 1 °C / min, 2 °C / min, 3 °C / min, 4 °C / min, 5 °C / min, and the holding time at this temperature is 6 h, 7 h, 8 h, 9 h, 10 h.

[0079] Furthermore, in the S7 high-temperature pyrolysis process, temperature control has a crucial impact on the material properties. High temperature promotes the formation of a more ordered graphite microcrystalline structure, and at the same time enables the residual organic components to be fully pyrolyzed, thereby constructing a dense three-dimensional carbon network and significantly improving the hardness and compressive properties of the material; however, too high a carbonization temperature will lead to an excessive increase in the degree of carbonization, reducing phonon scattering in the carbon skeleton (especially along the graphite layer plane direction), and thus significantly increasing the thermal conductivity.

[0080] Preferably, to meet the requirements of high mechanical properties and low thermal conductivity, the high-temperature pyrolysis temperature in S7 is as follows: rising from 25 °C to 300 - 500 °C at a heating rate of 1 - 5 °C / min, holding at 300 - 500 °C for 2 - 5 h, then rising to 700 - 1200 °C at a heating rate of 0.5 - 5 °C / min and holding for 1 - 3 h.

[0081] Preferably, in the S7 high-temperature gradient pyrolysis process: the heating rate to any one of the temperatures of 300 °C, 400 °C or 500 °C is 1 °C / min, 2 °C / min, 3 °C / min, 4 °C / min, 5 °C / min, and the holding time at this temperature is 2 h, 3 h, 4 h, 5 h; the heating rate to any one of the temperatures of 700 °C, 800 °C, 900 °C, 1000 °C, 1100 °C or 1200 °C is 0.5 °C / min, 1 °C / min, 2 °C / min, 3 °C / min, 4 °C / min, 5 °C / min, and the holding time at this temperature is 1 h, 2 h, 3 h.

[0082] It should be noted that during the carbonization process of the composite foam, a large amount of small molecules such as CO2 and H2O are released. The composite foam shows obvious weight loss at 300-500 °C. Gradient heating can make the small molecules slowly discharged to prevent the material from cracking and pulverizing, and can prevent obvious defects in the foam caused by too fast heating rate and too large thermal stress.

[0083] On the other hand, a specific embodiment of the present invention also discloses an ultra-low density carbon foam material, which uses an open-cell polymer foam as a supporting skeleton, a thermosetting resin or a polymer monomer as a carbon source matrix, and a carbon nanomaterial is introduced into the carbon source matrix as a reinforcing phase.

[0084] Preferably, the volume density of the carbon foam material is 0.042-0.053 g / cm3, and the porosity of the carbon foam material is ≥97%.

[0085] Furthermore, the thermal conductivity of the carbon foam material is 0.041-0.053 W / (m·K).

[0086] It should be noted that the compressive strength of the carbon foam material is 0.43-0.67 MPa.

[0087] Exemplarily, the carbon foam material prepared with a thermosetting resin prepolymer organic solution as the carbon source matrix presents a three-dimensional through-network structure, and the carbon skeleton presents the composite characteristics of graphite microcrystals / vitreous carbon; the carbon skeleton of the carbon foam material prepared with a polymer monomer as the carbon source matrix is mainly vitreous carbon, and the pore walls are thinner and the structure is more uniform.

[0088] On the other hand, a specific embodiment of the present invention also discloses an application of the ultra-low density carbon foam material, and the ultra-low density carbon foam material is applied to the field of high-temperature thermal insulation materials.

[0089] In summary, the present invention uses an open-cell polymer foam as a supporting skeleton, selects a thermosetting resin or a polymer monomer furfuryl alcohol with a high char yield as the carbon source matrix, and introduces a carbon nanomaterial as a reinforcing phase. While improving the compressive strength, it maintains a low volume density, thus achieving a significant improvement in specific strength and providing a new idea for the research and development of lightweight and high-strength materials; by precisely controlling process parameters such as infiltration swelling, carbonaceous precursor solution distribution regulation, gradient curing, and high-temperature gradient pyrolysis, the carbon foam prepared by the present invention has properties such as ultra-low density, low thermal conductivity, and high strength, effectively solving the problem that it is difficult for existing carbon foams to achieve low density and high strength at the same time. Its low thermal conductivity can effectively block heat transfer, reduce thermal expansion and delay thermal decomposition, thereby endowing the material with high thermal stability and enabling it to fully meet the requirements of the high-temperature adiabatic field. The ultra-low density carbon foam material prepared by the present invention has a uniform open-cell structure, and the volume density is 0.042-0.053 g / cm 3, with a thermal conductivity lower than 0.053 W / (m·K) and a compressive strength of 0.43 - 0.67 MPa, it has broad application prospects in the field of lightweight high-temperature thermal protection.

[0090] The following specifically describes the ultra-low density carbon foam material and its preparation method of the present invention with reference to specific embodiments.

[0091] Example 1

[0092] This example provides an ultra-low density carbon foam material and its preparation method.

[0093] Ultra-low density carbon foam material: It includes a porous polymer foam skeleton and a carbonaceous precursor carbonized thereon; the carbonaceous precursor is a carbon source matrix enhanced with carbon nanomaterials.

[0094] The porous polymer foam is a polyurethane foam with dimensions of 100 mm * 100 mm * 20 mm and a density of 0.025 g / cm 3 ; the carbon source matrix is 500 g of furfuryl alcohol; the carbon nanomaterial is 2.5 g of graphene oxide.

[0095] The compatibilizer is 0.5 g of PVDF; the curing agent is 5.0 g of methyl p-toluenesulfonate.

[0096] The specific preparation process is as follows:

[0097] S1. Pretreatment of the carbon source matrix: After mixing the carbon source matrix and the compatibilizer, perform ultrasonic treatment for 2 h and mechanical stirring for 3 h at room temperature to fully disperse and form a uniform mixed solution, obtaining a modified carbon source matrix;

[0098] S2. Preparation of the carbon nanomaterial-reinforced carbon source matrix: Add the carbon nanomaterial to the modified carbon source matrix prepared in S1, perform ultrasonic treatment for 2 h and mechanical stirring for 3 h at room temperature to form a carbon nanomaterial-reinforced carbon source matrix;

[0099] S3. Preparation of the carbonaceous precursor solution: Mix the carbon nanomaterial-reinforced carbon source matrix prepared in S2 with the curing agent, perform pre-reaction by stirring in a 35°C water bath for 5 h to obtain a carbonaceous precursor solution;

[0100] S4. Penetration and swelling: Place the porous polymer foam in the carbonaceous precursor solution prepared in S3, perform penetration and swelling at 25°C for 1 h to form a uniformly distributed composite structure;

[0101] S5. Regulation of the carbonaceous precursor solution distribution: Place the wet composite structure prepared in S4 in a roller press for extrusion, set the distance between the two rollers to 1 mm, and the speed of the two rollers to 800 mm / min to remove the excess solution in the pores of the composite structure foam, obtaining a wet composite foam with a carbonaceous precursor solution-rich skeleton;

[0102] S6, Curing reaction: Place the wet composite foam obtained in S5 in an oven, heat it to 70 °C at a heating rate of 1 °C / min, and hold for 3 h to allow the complete exothermic curing of furfuryl alcohol. Then, heat it to 170 °C at a heating rate of 0.5 °C / min and hold for 2 h. After the reaction is completed, cool it to room temperature to obtain a high-strength rigid foam with an open-cell structure;

[0103] S7, High-temperature gradient pyrolysis: Place the high-strength rigid foam prepared in S6 in a high-temperature carbonization furnace. Under an argon atmosphere, heat it from room temperature to 350 °C at a heating rate of 2 °C / min and hold for 2 h. Then, heat it to 1000 °C at a heating rate of 1 °C / min and hold for 2 h. Subsequently, cool it to room temperature with the furnace, and finally cool it to room temperature to obtain an ultra-low-density carbon foam with a dense carbon skeleton, as Figure 1 shown.

[0104] The density of the prepared carbon foam material is 0.045 g / cm 3 , the thermal conductivity is 0.043 W / (m·K), and the compressive strength is 0.47 MPa, as shown in Table 2.

[0105] Example 2

[0106] This example provides an ultra-low-density carbon foam material and a preparation method.

[0107] The difference from Example 1 is that multi-walled carbon nanotubes are selected as the carbon nanomaterial, and the final carbonization temperature is set at 800 °C. See Table 1 for details.

[0108] The density of the prepared carbon foam material is 0.044 g / cm 3 , the thermal conductivity is 0.041 W / (m·K), and the compressive strength is 0.43 MPa, as shown in Table 2.

[0109] Example 3

[0110] This example provides an ultra-low-density carbon foam material and a preparation method.

[0111] The difference from Example 1 is that the addition amount of graphene oxide is 5.0 g, the addition amount of methyl p-toluenesulfonate is 7.5 g, the pre-reaction temperature is 45 °C, the osmotic swelling temperature is 40 °C, and the osmotic swelling time is 2.5 h. See Table 1 for details.

[0112] The density of the prepared carbon foam material is 0.053 g / cm 3 , the thermal conductivity is 0.047 W / (m·K), and the compressive strength is 0.67 MPa, as shown in Table 2.

[0113] Example 4

[0114] This example provides an ultra-low-density carbon foam material and a preparation method.

[0115] It is different from Example 1 in that the addition amount of graphene oxide is 5.0 g, the pre-reaction temperature is 40 °C, the osmotic swelling temperature is 40 °C, and the osmotic swelling time is 2 h. See Table 1 for details.

[0116] The density of the prepared carbon foam material is 0.047 g / cm 3 , the thermal conductivity is 0.042 W / (m·K), and the compressive strength is 0.60 MPa. See Table 2 for details.

[0117] Example 5

[0118] This example provides an ultra-low density carbon foam material and a preparation method.

[0119] It is different from Example 1 in that the addition amount of methyl p-toluenesulfonate is 7.5 g, the pre-reaction temperature is 40 °C, the pre-reaction time is 6 h, the swelling and osmosis temperature is 40 °C, and the osmotic swelling time is 2 h. See Table 1 for details.

[0120] The density of the prepared carbon foam material is 0.049 g / cm 3 , the thermal conductivity is 0.043 W / (m·K), and the compressive strength is 0.54 MPa. See Table 2 for details. The spliced scanning electron microscope (SEM) image of the ultra-low density carbon foam in this example magnified 110 times is as Figure 2 shown; the scanning electron microscope (SEM) image of the ultra-low density carbon foam in this example magnified 300 times is as Figure 3 shown; the compression stress-strain diagram of the ultra-low density carbon foam in this example is as Figure 4 shown.

[0121] Example 6

[0122] This example provides an ultra-low density carbon foam material and a preparation method.

[0123] Ultra-low density carbon foam material: including a porous polymer foam skeleton and a carbonaceous precursor carbonized thereon; the carbonaceous precursor is a carbon source matrix reinforced with carbon nanomaterials.

[0124] The porous polymer foam is a polyurethane foam with dimensions of 100 mm * 100 mm * 20 mm and a density of 0.025 g / cm 3 ; the carbon source matrix is 500 g of 70 wt.% phenolic resin (prepared in advance); the carbon nanomaterial is 5.0 g of graphene oxide.

[0125] The compatibilizer is 0.5 g of PVDF; the curing agent is 35.0 g of hexamethylenetetramine (350 g of pure phenolic resin, and the addition amount of the curing agent is 10 wt.%).

[0126] S1, S2, S3, S4, and S5 are the same as in Example 1.

[0127] S6, Curing reaction: Place the wet composite foam obtained in S5 in an oven, heat it to 90°C at a heating rate of 2°C / min, and hold for 12 h. Then heat it to 150°C at a heating rate of 2°C / min and hold for 6 h. After the reaction is completed, cool it to room temperature to obtain a high-strength rigid foam with an open-cell structure;

[0128] S7, High-temperature gradient pyrolysis: Place the high-strength rigid foam prepared in S6 in a high-temperature carbonization furnace. Under an argon atmosphere, heat it from room temperature to 300°C at a heating rate of 2°C / min and hold for 1 h. Then heat it to 1000°C at a heating rate of 1°C / min and hold for 2 h. Subsequently, cool it to room temperature with the furnace, and finally cool it to room temperature to obtain an ultra-low-density carbon foam with a dense carbon skeleton.

[0129] The density of the prepared carbon foam material is 0.042 g / cm 3 , the thermal conductivity is 0.050 W / (m·K), and the compressive strength is 0.56 MPa. See Table 2.

[0130] Example 7

[0131] This example provides an ultra-low-density carbon foam material and a preparation method.

[0132] The difference from Example 6 is that the osmotic swelling temperature is 35°C and the osmotic swelling time is 2 h. See Table 1 for details.

[0133] The density of the prepared carbon foam material is 0.045 g / cm 3 , the thermal conductivity is 0.052 W / (m·K), and the compressive strength is 0.60 MPa. See Table 2.

[0134] Example 8

[0135] This example provides an ultra-low-density carbon foam material and a preparation method.

[0136] The difference from Example 6 is that the concentration of the phenolic resin used is 90 wt.%, the addition amount of hexamethylenetetramine is 45.0 g, the osmotic swelling temperature is 50°C, and the osmotic swelling time is 2 h. See Table 1 for details.

[0137] The density of the prepared carbon foam material is 0.051 g / cm 3 , the thermal conductivity is 0.053 W / (m·K), and the compressive strength is 0.67 MPa. See Table 2.

[0138] Example 9

[0139] This example provides an ultra-low-density carbon foam material and a preparation method.

[0140] The difference from Example 6 is that the final carbonization temperature is set at 800 °C. See Table 1 for details.

[0141] The density of the prepared carbon foam material is 0.042 g / cm 3 , the thermal conductivity is 0.044 W / (m·K), and the compressive strength is 0.45 MPa. See Table 2 for details.

[0142] Example 10

[0143] This example provides an ultra-low density carbon foam material and a preparation method.

[0144] The difference from Example 6 is that the carbon nanomaterial selected is multi-walled carbon nanotubes. See Table 1 for details.

[0145] The density of the prepared carbon foam material is 0.044 g / cm 3 , the thermal conductivity is 0.045 W / (m·K), and the compressive strength is 0.54 MPa. See Table 2 for details.

[0146] Comparative Example 1

[0147] This comparative example provides a carbon foam material and a preparation method.

[0148] Compared with Example 1, step S2 is not carried out (i.e., no carbon nanomaterial is introduced).

[0149] The density of the prepared carbon foam material is 0.043 g / cm 3 , the thermal conductivity is 0.042 W / (m·K), and the compressive strength is 0.31 MPa. See Table 2 for details.

[0150] Comparative Example 2

[0151] This comparative example provides a carbon foam material and a preparation method.

[0152] Compared with Example 1, in the curing reaction process of step S6, the temperature is not increased in a gradient manner, but directly increased to the required temperature at a heating rate of 0.5 °C / min. Without gradient heating, it is directly heated to 170 °C.

[0153] The density of the prepared carbon foam material is 0.044 g / cm 3 , the thermal conductivity is 0.047 W / (m·K), and the compressive strength is 0.37 MPa. See Table 2 for details. And there are defects in the microstructure, there are bubbles on the surface of the foam skeleton, and obvious fractures exist in the skeleton. See Figure 5 .

[0154] Comparative Example 3

[0155] This comparative example provides a carbon foam material and a preparation method.

[0156] Compared with Example 1, in the carbonization process of step S7, no gradient heating is carried out, and it is directly heated to the required temperature at a heating rate of 1 °C / min.

[0157] The density of the prepared carbon foam material is 0.044 g / cm 3 , the thermal conductivity is 0.046 W / (m·K), the compressive strength is 0.38 MPa, as shown in Table 2. And there are defects in the microstructure and fractures in the skeleton.

[0158] Comparative Example 4

[0159] This comparative example provides a carbon foam material and a preparation method.

[0160] Compared with Example 1, in the preparation process of the carbonaceous precursor solution, the carbon nanomaterial, the carbon source matrix, and the compatibilizer are mixed and stirred evenly together (that is, S1 and S2 are combined into one step).

[0161] The density of the prepared carbon foam material is 0.046 g / cm 3 , the thermal conductivity is 0.042 W / (m·K), the compressive strength is 0.38 MPa, as shown in Table 2.

[0162] Comparative Example 5

[0163] This comparative example provides a carbon foam material and a preparation method.

[0164] Compared with Example 1, in the process of steps S1 to S3, the carbon source matrix is first pre-reacted with a curing agent, and then the carbon nanomaterial is added.

[0165] The density of the prepared carbon foam material is 0.070 g / cm 3 , the thermal conductivity is 0.063 W / (m·K), the compressive strength is 0.45 MPa, as shown in Table 2.

[0166] Comparative Example 6

[0167] This comparative example provides a carbon foam material and a preparation method.

[0168] Compared with Example 1, in the process of regulating the distribution of the carbonaceous precursor solution in step S5, the removal amount of the carbonaceous precursor solution is too small, and the operation stops before reaching the state where there is no liquid enrichment in the composite foam, resulting in partial blockage of the pores of the final carbon foam.

[0169] The density of the prepared carbon foam material is 0.066 g / cm 3 , the thermal conductivity is 0.060 W / (m·K), the internal composition distribution of the material is uneven, and the measured result of the compressive strength cannot truly reflect its mechanical properties, as shown in Table 2.

[0170] Comparative Example 7

[0171] This comparative example provides a carbon foam material and a preparation method.

[0172] Compared with Example 1, the pre-reaction time in step S3 is 1.5 h, and the reaction duration is too short.

[0173] The density of the prepared carbon foam material is 0.030 g / cm 3 , the thermal conductivity is 0.033 W / (m·K), and the compressive strength is 0.34 MPa, as shown in Table 2.

[0174] Table 1 Important parameters of examples and comparative examples

[0175]

[0176]

[0177] Table 2 Summary table of sample properties obtained from examples and comparative examples

[0178]

[0179]

[0180] It can be seen from Example 2, Example 1, Example 9 and Example 10 that the higher the carbonization temperature, the better the mechanical properties of the material, but the thermal conductivity will also increase accordingly; compared with Example 1, 2 and Example 3-5, and Example 6, 9, 10 and Example 7, 8, it can be known that the higher the infiltration swelling temperature and the longer the infiltration swelling time (within the scope of the present invention), the more sufficient the infiltration of the carbonaceous precursor into the foam, the higher the weight gain, and the stronger the compressive strength; compared with Example 8 and Example 6, 7, 9, 10, it can be seen that when the carbon source matrix is a phenolic resin prepolymer organic solution, the higher the solid content of the phenolic resin, the higher the compressive strength of the product carbon foam.

[0181] It can be seen from the comparison between Comparative Example 1 and Example 1 that the absence of carbon nanomaterials will lead to a significant decrease in the compressive strength of the product carbon foam material; compared with Example 1, Comparative Examples 2 and 3 do not adopt a gradient heating strategy during the curing or high-temperature carbonization process, which both lead to a significant decrease in the mechanical properties of the product foam material.

[0182] Compared with Example 1, in Comparative Example 4, the carbon nanomaterials, carbon source matrix, and compatibilizer are mixed and stirred evenly together (i.e., steps S1 and S2 are combined into one step), resulting in the prior mixing of the carbon nanomaterials and the compatibilizer, and the carbon nanomaterials agglomerate together, with poor dispersibility, affecting the product performance;

[0183] Comparative Example 5 compared with Example 1, the curing agent was first added to the carbon source matrix for pre-reaction, and then the carbon nanomaterials were introduced for enhancement. This led to an excessively long reaction time between the carbon source matrix and the curing agent, resulting in an overly high viscosity of the carbonaceous precursor solution. The dispersion of the subsequently added carbon nanomaterials was poor, and the excess carbonaceous precursor solution was not easily discharged. Ultimately, the distribution of the carbonaceous precursor solution was uneven, the density and thermal conductivity of the carbon foam increased significantly, and there was no obvious improvement in the compressive strength.

[0184] Comparative Example 6 compared with Example 1, the removal amount of the carbonaceous precursor solution was too small, and the operation stopped before the composite foam reached the state without liquid enrichment. There was liquid enrichment, resulting in an uneven density distribution and poor performance of the final carbon foam.

[0185] Comparative Example 7 compared with Example 1, the pre-reaction time was too short, resulting in a low degree of pre-polymerization. Although the open-cell rate was high, the density and thermal conductivity were low, but the strength of the composite foam structure after the curing reaction was extremely low.

[0186] In summary, the present invention uses an open-cell polymer foam as the support framework, selects a thermosetting resin or polymer monomer furfuryl alcohol with a high char yield as the carbon source matrix, and introduces carbon nanomaterials as the reinforcing phase. While improving the compressive strength, it maintains a low bulk density, thereby achieving a significant improvement in specific strength and providing a new idea for the research and development of lightweight and high-strength materials; the present invention precisely controls process parameters such as osmotic swelling, carbonaceous precursor solution distribution regulation, gradient curing, and high-temperature gradient pyrolysis. The prepared carbon foam has properties such as ultra-low density, low thermal conductivity, and high strength, effectively solving the problem that existing carbon foams are difficult to achieve low density and high strength simultaneously. Its low thermal conductivity can effectively block heat transfer, reduce thermal expansion, and delay thermal decomposition, thereby endowing the material with high thermal stability and enabling it to fully meet the requirements of the high-temperature insulation field. The ultra-low density carbon foam material prepared by the present invention has a uniform open-cell structure, with a bulk density of 0.042 - 0.053 g / cm 3 , a thermal conductivity lower than 0.053 W / (m·K), and a compressive strength of 0.43 - 0.67 MPa, having broad application prospects in the field of lightweight high-temperature thermal protection.

[0187] The above is only a preferred specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention should be covered within the protection scope of the present invention.

Claims

1. A preparation method of an ultra-low density carbon foam material, characterized in that, It includes the preparation of a carbonaceous precursor, specifically including the following steps: S1. Pretreatment of the carbon source matrix: Mix the carbon source matrix and the compatibilizer evenly to obtain a modified carbon source matrix; S2. Preparation of the carbon nanomaterial-reinforced carbon source matrix: Add the carbon nanomaterial to the modified carbon source matrix obtained in S1, and make it evenly dispersed through mechanical stirring and ultrasonic treatment to form a carbon nanomaterial-reinforced carbon source matrix; S3. Preparation of the carbonaceous precursor solution: Mix the carbon nanomaterial-reinforced carbon source matrix obtained in S2 with the curing agent, and carry out a pre-reaction in a water bath environment to obtain a carbonaceous precursor solution.

2. The preparation method according to claim 1, characterized in that, The carbon source matrix is an organic solution of a thermosetting resin prepolymer or a polymer monomer; the thermosetting resin prepolymer in the organic solution of the thermosetting resin prepolymer includes one or more composite systems of phenolic resin, epoxy resin, bismaleimide resin, furanone resin or furfural resin; the polymer monomer includes furfuryl alcohol.

3. The preparation method according to claim 1, characterized in that, The carbon nanomaterial includes one or several of carbon nanofibers, carbon nanotubes, graphene, and graphene oxide.

4. The carbon foam material according to claim 1, wherein The temperature of the water bath environment in S3 is 25-45°C, the pre-reaction process is carried out under stirring, and the pre-reaction time is 2-10h.

5. The preparation method according to claim 1, characterized in that, The preparation method further includes the following steps: S4. Osmotic swelling: Place the porous polymer foam in the carbonaceous precursor solution obtained in S3 for osmotic swelling to form a uniformly distributed composite structure; S5. Regulation of the carbonaceous precursor solution distribution: Regulate the distribution of the carbonaceous precursor solution, and remove the excess carbonaceous precursor solution in the pores of the composite structure to obtain a wet composite foam with a carbonaceous precursor solution-rich skeleton; S6. Curing reaction: Place the wet composite foam obtained in S5 in an oven for gradient temperature rise curing, and cool to room temperature after the reaction ends to obtain a high-strength rigid composite foam with an open-cell structure; S7. High-temperature gradient pyrolysis: Place the high-strength rigid composite foam prepared in S6 in a high-temperature carbonization furnace for high-temperature gradient pyrolysis in an inert atmosphere, and finally cool to room temperature to obtain an ultra-low-density carbon foam with a dense carbon skeleton.

6. The preparation method according to claim 5, wherein The osmotic swelling in S4 is carried out at 25-50°C, and the osmotic swelling time is 0.5-3h.

7. The preparation method according to claim 5, characterized in that The high-temperature pyrolysis temperature in S7 is: rising from 25°C to 300-500°C at a heating rate of 1-5°C / min, maintaining at 300-500°C for 2-5h, and then rising to 700-1200°C at a heating rate of 0.5-5°C / min and maintaining for 1-3h.

8. An ultra-low density carbon foam material, characterized in that, Prepared by the method according to any one of claims 1-7, the carbon foam material uses an open-cell polymer foam as a support skeleton, a thermosetting resin or a polymer monomer as a carbon source matrix, and a carbon nanomaterial is introduced into the carbon source matrix as a reinforcing phase.

9. The carbon foam material according to claim 8, characterized in that, The volume density of the carbon foam material is 0.042 to 0.053 g / cm 3 , the porosity is ≥97%, the thermal conductivity is 0.041 to 0.053 W / (m·K), and the compressive strength is 0.43 to 0.67 MPa.

10. Application of an ultra-low density carbon foam material, characterized in that, Application of the carbon foam material prepared by the preparation method according to any one of claims 1-7 or the carbon foam material according to any one of claims 8-9, the ultra-low-density carbon foam material is applied to the field of high-temperature heat insulation materials.

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