An ultra-low density carbon foam material and method of making

Abstract

The application relates to an ultralow-density carbon foam material and a preparation method, and belongs to the field of heat insulation materials, and solves the problems of high density, complex process, large thermal conductivity, inability to meet the demand of the high-temperature insulation field, easy slagging of carbon foam, and insufficient mechanical properties in the prior art. 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 carbon nanomaterials into the modified carbon source matrix to form a carbon nanomaterial-reinforced carbon source matrix; S3, preparation of a carbon precursor solution; S4, osmotic swelling: placing a porous polymer foam in the carbon precursor solution to perform osmotic swelling and form a uniformly-distributed composite structure; S5, distribution regulation of the carbon precursor solution; S6, solidification reaction; S7, high-temperature gradient pyrolysis, and the ultralow-density carbon foam with a dense carbon skeleton is obtained. The heat preservation performance and the mechanical properties of the foam carbon material are improved.

Description

TECHNICAL FIELD

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

[0002] With the rapid development of aerospace technology, the performance requirements of thermal protection materials are increasingly stringent. During reentry, the surface of a spacecraft needs to withstand extremely high thermal loads. Therefore, it is urgent to develop materials that are both lightweight and have excellent thermal protection performance. Traditional thermal protection systems are heavy, which adversely affects flight performance and fuel efficiency, prompting researchers to actively explore new lightweight, high-performance thermal protection materials.

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

[0004] To solve the above problems, several patents have been disclosed in China for the preparation of carbon foam materials. For example, carbon foam is prepared by electrospinning, freeze-drying, phenolic resin impregnation, 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. For another example, by mixing phenolic resin, silane foaming agent, and chopped carbon fibers, and through preliminary curing, foaming curing, chemical vapor deposition, and high-temperature impurity removal, a foam carbon material with excellent thermal insulation performance and mechanical properties is prepared. However, this method results in high graphitization of the material due to high-temperature impurity removal, resulting in a large thermal conductivity, which makes it difficult to meet the application requirements in the high-temperature insulation field. SUMMARY

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

[0006] In one aspect, the embodiments of the present application provide a preparation method of an ultra-low-density carbon foam material, which comprises the preparation of a carbon precursor, specifically comprising the following steps:

[0007] S1, pretreatment of the carbon source matrix: uniformly mix the carbon source matrix and the compatibilizer to obtain a modified carbon source matrix;

[0008] S2, preparation of carbon nanomaterials reinforced carbon source matrix: carbon nanomaterials are added to the modified carbon source matrix prepared in S1, and are uniformly dispersed by mechanical stirring and ultrasonic treatment to form a carbon nanomaterials reinforced carbon source matrix;

[0009] S3, preparation of carbon precursor solution: the carbon nanomaterials reinforced carbon source matrix prepared in S2 is mixed with a curing agent, and pre-reaction is carried out in a water bath environment to obtain a carbon precursor solution.

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

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

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

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

[0014] S4, osmotic swelling: the porous polymer foam is placed in the carbon precursor solution prepared in S3 to perform osmotic swelling to form a uniformly distributed composite structure;

[0015] S5, carbon precursor solution distribution regulation: the distribution of the carbon precursor solution is regulated, and the excess carbon precursor solution in the pores of the composite structure is removed to obtain a wet composite foam rich in carbon precursor solution;

[0016] S6, curing reaction: the wet composite foam obtained in S5 is placed in an oven for gradient temperature rising curing, and after the reaction is completed, it is cooled to room temperature to obtain a high-strength hard composite foam with an open-cell structure;

[0017] S7, high-temperature gradient pyrolysis: the high-strength hard composite foam prepared in S6 is placed in a high-temperature carbonization furnace for high-temperature gradient pyrolysis under an inert atmosphere, and finally cooled 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℃, and the osmotic swelling time is 0.5-3h.

[0019] Exemplarily, the high-temperature pyrolysis temperature in S7 is: increasing from 25 DEG C to 300-500 DEG C at a temperature increasing rate of 1-5 DEG C / min, keeping at 300-500 DEG C for 2-5 h, then increasing to 700-1200 DEG C at a temperature increasing rate of 0.5-5 DEG C / min, keeping for 1-3 h.

[0020] In another aspect, the embodiment of the present application further provides an ultra-low density carbon foam material, which takes open-cell polymer foam as a support skeleton, takes thermosetting resin or polymer monomer as a carbon source matrix, and introduces carbon nanomaterials as a reinforcing phase in the carbon source matrix.

[0021] Notably, the volume density of the carbon foam material is 0.042-0.053 g / cm 3 , the porosity is greater than or equal to 97%, the thermal conductivity is 0.041-0.053 W / (m*K), and the compressive strength is 0.43-0.67 MPa.

[0022] In another aspect, the embodiment of the present application further provides an application of the ultra-low density carbon foam material, the application of the carbon foam material prepared by the preparation method, and the application of the ultra-low density carbon foam material in the field of high-temperature heat insulation materials.

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

[0024] 1. By introducing carbon nanomaterials into the carbon source matrix, the present application significantly improves the compressive strength and specific strength of the product carbon foam material, and solves the problems of slagging and insufficient mechanical properties of traditional carbon foam.

[0025] 2. When preparing the carbonaceous precursor, the present application precisely controls the temperature and time of pre-reaction, and adjusts the viscosity of the carbonaceous precursor solution to a suitable range (30-80 mPa*s), which on the one hand facilitates subsequent distribution control of the composite foam with the carbonaceous precursor solution, and on the other hand ensures the formation of a high-strength composite foam structure after solidification reaction.

[0026] 3. The present application prepares the carbon foam material by the method of penetration swelling, solidification, and high-temperature gradient pyrolysis, which has the advantages of simple preparation process, suitability for preparing large-size products, and suitability for industrial production, and has important application value in the fields of aerospace high-temperature heat protection and molten metal filtration, and solves the problems of heavy weight, uneven structure, and insufficient high-temperature performance of traditional heat protection materials.

[0027] 4, The application adopts open-cell polymer foam as a supporting framework, selects a high-residual-carbon-rate thermosetting resin as a carbon source matrix, and introduces carbon nanomaterials as a reinforcing phase; by precisely controlling process parameters such as permeation swelling, carbon precursor solution distribution regulation, gradient curing, and high-temperature gradient pyrolysis, the prepared carbon foam has the performances of ultralow density, excellent thermal stability, low thermal conductivity, and high strength, effectively solves the problem that existing carbon foams are difficult to simultaneously realize low density and high strength, and can fully meet the needs of the high-temperature insulation field.

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

[0029] The above technical solutions in the application can also be combined with each other to realize more preferred combination solutions. Other features and advantages of the application will be described in the subsequent specification, and some advantages will become apparent from the specification or be understood by implementing the application. The purposes and other advantages of the application can be realized and obtained from the contents specifically pointed out in the specification and the drawings. BRIEF DESCRIPTION OF DRAWINGS

[0030] The accompanying drawings are included to provide a further understanding of the application and are incorporated herein and constitute a part of the application. The drawings illustrate embodiments of the application and, together with the description, serve to explain the principles of the application. In the drawings:

[0031] Figure 1 It is a physical photo of the ultralow-density carbon foam of the application;

[0032] Figure 2 It is a scanning electron microscope (SEM) splicing graph of the ultralow-density carbon foam of Example 5 of the application, magnified by 110 times;

[0033] Figure 3 It is a scanning electron microscope (SEM) graph of the ultralow-density carbon foam of Example 5 of the application, magnified by 300 times;

[0034] Figure 4 It is a compressive stress-strain graph of the ultralow-density carbon foam of Example 5 of the application;

[0035] Figure 5 It is a scanning electron microscope (SEM) graph of the carbon foam of Comparative Example 2 of the application, magnified by 300 times. DETAILED DESCRIPTION

[0036] Preferred embodiments of the present application are described in detail below with reference to the attached drawing figures, wherein the application is shown as currently constructed and arranged. It is to be understood that the application is not limited to the embodiments described below, but can be carried out in various ways.

[0037] In one aspect, one specific embodiment of the present application discloses a method for preparing an ultra-low density carbon foam material, comprising the preparation of a carbonaceous precursor, specifically comprising the following steps:

[0038] S1, pretreatment of the carbon source matrix: uniformly mix the carbon source matrix and the compatibilizer to obtain a modified carbon source matrix;

[0039] S2, preparation of the carbon nanomaterial reinforced carbon source matrix: add carbon nanomaterial to the modified carbon source matrix prepared in S1, and uniformly disperse it by 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 pre-react in a water bath environment to obtain a carbonaceous precursor solution.

[0041] Specifically, in S1, the carbon source matrix is an organic solution of thermosetting resin prepolymer or a polymer monomer; the thermosetting resin prepolymer in the organic solution of thermosetting resin prepolymer includes one or more composite systems of phenolic resin, epoxy resin, bismaleimide resin, furfural 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 used in the preparation process without the need to introduce an organic solvent. When the carbon source matrix is an organic solution of thermosetting resin prepolymer, the solid content of the thermosetting resin is 50-90 wt.%, and the organic solvent includes one or more of isopropyl alcohol, ethanol, ethylene glycol, n-butanol, and preferably the organic solvent is ethanol. The polymer monomer (such as furfuryl alcohol) itself is a low-viscosity liquid with good flowability and processability, so there is no need to introduce an organic solvent. The thermosetting resin prepolymer is solid or a high-viscosity liquid (such as phenolic resin) at room temperature, 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 phenolic resin prepolymer, the solid content of the phenolic resin is 50-90 wt.%; the organic solvent includes one or more of isopropyl alcohol, ethanol, ethylene glycol, n-butanol, and preferably the organic solvent is ethanol. Preferably, the solid content of the phenolic resin is 50 wt.%, 70 wt.%, 80 wt.%, or 90 wt.%.

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

[0045] It should be noted that the carbon nanomaterial does not participate in the reaction during the preparation of the carbonaceous precursor solution, and the reaction process does not have a significant impact on the uniformity of the carbon nanomaterial in the carbon source matrix.

[0046] It should be noted that the order of S1, S2 and S3 cannot be changed and cannot be combined: if the carbon nanomaterial, the carbon source matrix and the compatibilizer are mixed and stirred uniformly together (i.e., S1 and S2 are combined into one step), the carbon nanomaterial and the compatibilizer will be mixed together first, the carbon nanomaterial will agglomerate together, the dispersibility will be poor, and the product performance will be affected; if the curing agent is first added to the carbon source matrix for pre-reaction, and then the carbon nanomaterial is introduced for reinforcement, the carbon source matrix will react with the curing agent for too long a time, the viscosity of the carbonaceous precursor solution will be too large, the dispersibility of the carbon nanomaterial added later will be poor, and the excess carbonaceous precursor solution will not be easily discharged, the carbonaceous precursor solution will finally be distributed unevenly, the density and thermal conductivity of the carbon foam will be significantly increased, but the compressive strength will not be significantly improved.

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

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

[0049] Further, the carbon nanomaterial comprises one or more of carbon nanofibers, carbon nanotubes, graphene and graphene oxide; preferably, the carbon nanomaterial is single-layer graphene oxide, and the particle size of the single-layer graphene oxide is <50 nm, and a particle size that is too large can easily result in uneven dispersion.

[0050] Specifically, the amount of carbon nanomaterials added in S2 is 0.1-1.0wt% of the mass of the carbon source matrix. Too much carbon nanomaterials may not be well dispersed in the carbon source matrix, causing agglomeration; too little carbon nanomaterials has no obvious effect on the performance of the carbon foam material. Preferably, the amount of carbon nanomaterials added is 0.1wt%, 0.2wt%, 0.3wt%, 0.4wt%, 0.5wt%, 0.6wt%, 0.7wt%, 0.8wt%, 0.9wt%, 1.0wt% of the mass of the carbon source matrix.

[0051] Preferably, in the process of mixing carbon nanomaterials and modified carbon source matrix in S2, mechanical stirring is performed for 3-4h, followed by ultrasonic treatment for 2-3h. Preferably, mechanical stirring is performed for 3h, followed by ultrasonic treatment for 2h.

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

[0053] For example, when the carbon source matrix is a phenolic resin prepolymer organic solution, the curing agent includes one of hexamethylenetetramine, ammonia, 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%, or 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 p-toluenesulfonic acid methyl ester; preferably, the curing agent is p-toluenesulfonic acid methyl ester. Compared with medium-strong acids such as oxalic acid, p-toluenesulfonic acid, and citric acid, the use of weakly acidic ester compounds as curing agents catalyzes the stable self-polymerization pre-reaction of carbon-based polymer monomers (furfuryl alcohol), effectively avoiding the foaming phenomenon often caused by the use of medium-strong acid curing agents, and the reaction process is more stable and controllable. The carbon nanomaterial-enhanced furfuryl alcohol and the curing agent are mixed in a mass ratio of 100:(0.5-2), preferably a mass ratio of 100:0.5, 100:0.8, 100:1, 100:1.2, 100:1.4, 100:1.5, 100:1.8, or 100:2.

[0055] It should be noted that too much curing agent will cause the reaction between the carbon source matrix and the curing agent to be too violent, making the reaction uncontrollable and causing foaming; too little curing agent will result in a slow polymerization rate, requiring a significantly longer reaction time.

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

[0057] Too high pre-reaction temperature will also cause the reaction between the carbon source matrix and the curing agent to be violent, resulting in uncontrollable foaming. Too low pre-reaction temperature will cause the prepolymerization reaction to be slow, which requires a significant extension of the reaction time. Short pre-reaction time will result in low degree of prepolymerization, making it difficult to form a high-strength composite foam structure after the curing reaction. Too long prepolymerization time will result in too high viscosity of the carbon precursor solution, making it difficult to control the distribution of the carbon precursor solution in the composite foam, resulting in a large number of pore blockages in the final carbon foam.

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

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

[0060] Further, the preparation method further comprises the following steps:

[0061] S4, osmotic swelling: placing the porous polymer foam in the carbon precursor solution prepared in S3 to perform osmotic swelling, forming a uniformly distributed composite structure;

[0062] S5, carbon precursor solution distribution control: controlling the distribution of the carbon precursor solution, removing excess carbon precursor solution in the pores of the composite structure, and obtaining a wet composite foam rich in carbon precursor solution in the skeleton;

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

[0064] S7, high-temperature gradient pyrolysis: placing the high-strength hard composite foam prepared in S6 in a high-temperature carbonization furnace for high-temperature gradient pyrolysis under an inert atmosphere, and finally cooling 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 light open-cell foam can enable the final carbon foam to maintain a high open-cell rate, ultra-low density and low thermal conductivity, and the open-cell structure can promote the provision of a uniform open-cell structure for the final carbon foam material. The porous polymer foam comprises one of a polyurethane foam, a melamine foam and a polyimide foam, and preferably is a polyurethane foam. The porous polymer foam has a density of 0.01-0.04 g / cm 3 and a thickness of 5-50 mm.

[0066] Preferably, the size of the porous polymer foam is determined according to actual production requirements, and the porous polymer foam can be widely adapted to different production requirements, and has a significant advantage in large-size requirements.

[0067] It should be noted that the mass ratio of the porous polymer foam to the carbon precursor solution in S4 is 1:(70-100), and preferably is 1:70, 1:80, 1:90 or 1:100. Too little amount of the carbon precursor solution will cause the polymer foam to be unable to be sufficiently infiltrated and swollen by the carbon precursor solution, resulting in an uneven internal structure of the composite foam. Too much amount of the carbon precursor solution will not cause adverse effects on the subsequent reaction process, but will cause unnecessary waste.

[0068] Preferably, the infiltration and swelling is performed at 25-50℃, and the infiltration and swelling time is 0.5-3 h. Specifically, the infiltration and swelling temperature is 25℃, 30℃, 35℃, 40℃, 45℃ or 50℃, and the infiltration and swelling time is 0.5 h, 1 h, 1.5 h, 2 h, 2.5 h or 3 h.

[0069] During the infiltration and swelling, the carbon precursor and the solvent thereof diffuse and infiltrate into the polymer foam skeleton, and the volume of the polymer foam is expanded and the mass thereof is increased through the swelling effect, so that the carbon precursor solution uniformly fills the foam skeleton, and a uniformly distributed composite structure is formed.

[0070] It should be noted that the temperature and time of the infiltration and swelling are selected according to the different carbon source matrixes. When the carbon source matrix is furfuryl alcohol, the infiltration and swelling temperature is slightly high, i.e. 40-50℃, which can accelerate the infiltration and swelling of the polymer foam by the carbon precursor solution. When the carbon source matrix is an organic solution of a phenol-formaldehyde resin prepolymer, the viscosity of the phenol-formaldehyde resin with high solid content is high at room temperature, and the viscosity of the phenol-formaldehyde resin is reduced by heating, which is beneficial to the infiltration and swelling of the polymer foam by the phenol-formaldehyde resin, and the infiltration and swelling temperature is preferably 40-50℃. The infiltration time is determined according to the volume expansion of the foam in the carbon precursor solution. When the volume of the foam does not significantly increase after a certain infiltration and swelling time, it is considered that the infiltration and swelling has reached a saturation state.

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

[0072] Preferably, the distribution of the carbon precursor solution is regulated without liquid enrichment in the composite foam: when the distribution of the carbon precursor solution is regulated by centrifugation, the rotation speed is 600-1000 r / min, and the centrifugation time is controlled to be 5-20 min; when the distribution of the carbon precursor solution is regulated by two-roller pressing, the pressure is 0.1-0.5 MPa or the distance between the rollers is 0.05-0.1% of the thickness of the foam, and the speed is 500-800 mm / min.

[0073] Further, the solidification temperature in S6 needs to be determined according to the type of the carbon source matrix and the solidification reaction mechanism thereof. First, the basic temperature range is determined according to 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, the heating gradient is optimized to avoid material defects in combination with the target crosslinking density and the subsequent pyrolysis process requirements.

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

[0075] It should be noted that the pre-solidification temperature is 70-90℃, and the solidification temperature is 120-170℃. Preferably, in the gradient solidification process, the rate of temperature rise to the pre-solidification temperature is 0.5℃ / min, 1℃ / min, 2℃ / min, 3℃ / min, 4℃ / min, or 5℃ / min, the temperature is maintained at the pre-solidification temperature for 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, or 15 h; the rate of temperature rise to 120℃, 130℃, 140℃, 150℃, 160℃, or 170℃ is 0.5℃ / min, 1℃ / min, 2℃ / min, 3℃ / min, 4℃ / min, or 5℃ / min, and the temperature is maintained at the temperature for 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, or 10 h.

[0076] Specific parameters need to be adjusted: for the solvent-free furfuryl alcohol system, the pre-curing temperature is 70°C (1-5h), the curing stage needs to strictly control the heating rate (0.5-5°C / min) and holding time (0.5-3h) to inhibit the crack caused by the intense exothermic; for the solvent-containing phenolic resin system, the pre-curing needs to be kept at 90°C for 10-15h to ensure the solvent is fully volatilized, and the curing stage is kept at 150°C for 6-10h to enhance the network density. The whole 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 heating gradient is: from 25°C to 70°C at a heating rate of 0.5-5°C / min, keeping at 70°C for 1-5h, then heating to 120-170°C at a heating rate of 0.5-5°C / min, keeping at 0.5-3h. For the reaction system with furfuryl alcohol as the carbon source matrix, the curing reaction is intense exothermic at 70°C and above, if the temperature is raised too fast, it is easy to produce bubbles or internal stress too large to cause cracks, affecting the strength of the final carbon foam material, so gradient heating is needed. Preferably, when the carbon source matrix is furfuryl alcohol, the gradient curing process, the rate of heating to 70°C is 0.5°C / min, 1°C / min, 2°C / min, 3°C / min, 4°C / min, 5°C / min, the holding time at 70°C is 1h, 2h, 3h, 4h, 5h; the rate of heating to 120°C, 130°C, 140°C, 150°C, 160°C or 170°C is any one of 0.5°C / min, 1°C / min, 2°C / min, 3°C / min, 4°C / min, 5°C / min, the holding time at this temperature is 0.5h, 1h, 1.5h, 2h, 2.5h, 3h.

[0078] When the carbon source matrix is an organic solution of phenolic resin prepolymer, the curing temperature gradient is: increasing to 90°C at a rate of 0.5-5°C / min, maintaining at 90°C for 10-15h, and then increasing to 150°C at a rate of 0.5-5°C / min, maintaining at 150°C for 6-10h. For the reaction system in which the carbon source matrix is an organic solution of phenolic resin prepolymer, the curing reaction is exothermic at 90°C and above, and if the temperature is increased too quickly at one time, bubbles or excessive internal stress causing cracks are likely to occur, affecting the strength of the final carbon foam material, so gradient heating is required. Preferably, when the carbon source matrix is an organic solution of phenolic resin prepolymer, the rate of temperature increase to 90°C in the gradient curing process 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 10h, 11h, 12h, 13h, 14h, 15h; the rate of temperature increase 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 6h, 7h, 8h, 9h, 10h.

[0079] Further, the temperature regulation in the S7 high-temperature pyrolysis process has a key influence on the material performance. High temperature promotes the formation of more ordered graphite crystalline structure, and at the same time makes the residual organic components fully pyrolyze, thereby constructing a dense three-dimensional carbon network, significantly improving the hardness and compression resistance of the material; however, excessively high carbonization temperature can lead to excessive carbonization, reducing phonon scattering in the carbon skeleton (especially along the plane direction of the graphite layer), and thus significantly increasing the thermal conductivity coefficient.

[0080] Preferably, in order to balance the requirements of high mechanical performance and low thermal conductivity coefficient, the high-temperature pyrolysis temperature in S7 is: increasing from 25°C to 300-500°C at a rate of 1-5°C / min, maintaining at 300-500°C for 2-5h, and then increasing to 700-1200°C at a rate of 0.5-5°C / min, maintaining at 700-1200°C for 1-3h.

[0081] Preferably, the high-temperature gradient pyrolysis process in S7 is: the rate of temperature increase to any one 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 2h, 3h, 4h, 5h; the rate of temperature increase to any one 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 1h, 2h, 3h.

[0082] It should be noted that the carbonization process of the composite foam is accompanied by the release of a large amount of small molecules such as CO2 and H2O, and the composite foam obviously loses weight at 300-500 DEG C. The gradient heating can slowly release the small molecules to prevent the material from bursting and pulverizing, and can prevent the foam from having obvious defects caused by excessive thermal stress due to rapid heating.

[0083] In another aspect, the embodiment of the present application also discloses an ultra-low density carbon foam material, which takes open-cell polymer foam as a support skeleton, takes thermosetting resin or polymer monomer as a carbon source matrix, and introduces carbon nanomaterial as a reinforcing phase in the carbon source matrix.

[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 greater than or equal to 97%.

[0085] Further, 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 by taking the thermosetting resin prepolymer organic solution as the carbon source matrix presents a three-dimensional through network structure, and the carbon skeleton presents a graphite microcrystal / glassy carbon composite feature; the carbon foam material prepared by taking the polymer monomer as the carbon source matrix mainly has a glassy carbon carbon skeleton, and the pore wall is thinner and the structure is more uniform.

[0088] In another aspect, the embodiment of the present application 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 heat insulation materials.

[0089] To sum up, the present application takes open-cell polymer foam as a support skeleton, selects high-residual-carbon-rate thermosetting resin or polymer monomer furfuryl alcohol as a carbon source matrix, and introduces carbon nanomaterial as a reinforcing phase, thereby improving the compressive strength while maintaining the low volume density, so that the specific strength is significantly improved, and a new idea is provided for the research and development of light-weight high-strength materials; the present application precisely controls the process parameters such as penetration swelling, carbon precursor solution distribution regulation, gradient curing and high-temperature gradient pyrolysis, and the prepared carbon foam has the performances of ultra-low density, low thermal conductivity and high strength, thereby effectively solving the problem that the existing carbon foam is difficult to simultaneously realize low density and high strength, the low thermal conductivity can effectively block heat transfer, reduce thermal expansion and delay thermal decomposition, thereby endowing the material with high thermal stability, and the material can fully meet the needs of the high-temperature insulation field. The ultra-low density carbon foam material prepared by the present application has a uniform open-cell structure, the volume density is 0.042-0.053 g / cm 3The carbon foam material has a low thermal conductivity of less than 0.053 W / (m*K), a compression strength of 0.43-0.67 MPa, and a wide application prospect in the field of light high-temperature thermal protection.

[0090] The present application is described below in combination with specific examples.

[0091] Example 1

[0092] The present application provides a kind of ultra-low density carbon foam material and preparation method.

[0093] The ultra-low density carbon foam material includes a porous polymer foam skeleton and a carbonized carbon precursor on the skeleton; the carbon precursor is a carbon source matrix reinforced by carbon nanomaterials.

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

[0095] The compatibilizer is 0.5g of PVDF; and the curing agent is 5.0g 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, ultrasonic treatment is performed at room temperature for 2h, and mechanical stirring is performed for 3h, so that the carbon source matrix is fully dispersed and a uniform mixed solution is formed, to obtain a modified carbon source matrix;

[0098] S2, preparation of the carbon source matrix reinforced by carbon nanomaterials: the carbon nanomaterials are added to the modified carbon source matrix prepared in S1, ultrasonic treatment is performed at room temperature for 2h, and mechanical stirring is performed for 3h, to form a carbon source matrix reinforced by carbon nanomaterials;

[0099] S3, preparation of the carbon precursor solution: the carbon source matrix reinforced by carbon nanomaterials prepared in S2 is mixed with the curing agent, water bath stirring is performed at 35°C for 5h, and pre-reaction is performed to obtain a carbon precursor solution;

[0100] S4, osmotic swelling: the porous polymer foam is placed in the carbon precursor solution prepared in S3, and osmotic swelling is performed at 25°C for 1h, to form a composite structure with uniform distribution;

[0101] S5, distribution regulation of the carbon precursor solution: the wet composite structure prepared in S4 is placed in a roller press for extrusion, the distance between the two rollers is set to 1mm, and the speed of the two rollers is set to 800mm / min, to remove the excess solution in the foam pores of the composite structure, and obtain a wet composite foam with a skeleton rich in carbon precursor solution;

[0102] S6, curing reaction: the wet composite foam obtained in S5 is placed in an oven, and the temperature is raised to 70 DEG C at a rate of 1 DEG C / min and kept for 3 h to make the complete exothermic reaction of furfuryl alcohol, and then the temperature is raised to 170 DEG C at a rate of 0.5 DEG C / min and kept for 2 h, and after the reaction is completed, it is cooled to room temperature to obtain a high-strength rigid foam with an open-cell structure;

[0103] S7, high-temperature gradient pyrolysis: the high-strength rigid foam prepared in S6 is placed in a high-temperature carbonization furnace, and the temperature is raised to 350 DEG C at a rate of 2 DEG C / min from room temperature under an argon atmosphere, kept for 2 h, and then the temperature is raised to 1000 DEG C at a rate of 1 DEG C / min, kept for 2 h, and then cooled to room temperature with the furnace, and finally cooled to room temperature to obtain an ultra-low density carbon foam with a dense carbon skeleton, as shown in Figure 1 .

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

[0105] Example 2

[0106] The present embodiment provides an ultra-low density carbon foam material and a preparation method.

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

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

[0109] Example 3

[0110] The present embodiment 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 DEG C, the osmotic swelling temperature is 40 DEG C, and the osmotic swelling time is 2.5 h. See Table 1 for details.

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

[0113] Example 4

[0114] The present embodiment provides an ultra-low density carbon foam material and a preparation method.

[0115] The difference from Example 1 is that the added amount of graphene oxide is 5.0 g, the pre-reaction temperature is 40℃, the osmotic swelling temperature is 40℃, 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, as shown in Table 2.

[0117] Example 5

[0118] The present embodiment provides an ultra-low density carbon foam material and a preparation method.

[0119] The difference from Example 1 is that the added amount of methyl p-toluenesulfonate is 7.5 g, the pre-reaction temperature is 40℃, the pre-reaction time is 6 h, the swelling osmotic temperature is 40℃, 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, as shown in Table 2. The 110-fold scanning electron microscope (SEM) splicing image of the ultra-low density carbon foam of the present embodiment is shown in Figure 2 , the 300-fold scanning electron microscope (SEM) image of the ultra-low density carbon foam of the present embodiment is shown in Figure 3 , and the compressive stress-strain graph of the ultra-low density carbon foam of the present embodiment is shown in Figure 4 .

[0121] Example 6

[0122] The present embodiment provides an ultra-low density carbon foam material and a preparation method.

[0123] The ultra-low density carbon foam material comprises a porous polymer foam skeleton and a carbonized carbon precursor thereon; the carbon precursor is a carbon source matrix reinforced with carbon nanomaterials.

[0124] The porous polymer foam is a polyurethane foam with a size 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.% phenol formaldehyde resin (pre-configured); and the carbon nanomaterials are 5.0 g of graphene oxide.

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

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

[0127] S6, curing reaction: the wet composite foam obtained in S5 was placed in an oven, and raised to 90°C at a temperature raising rate of 2°C / min, and kept for 12 h, then raised to 150°C at a temperature raising rate of 2°C / min, kept for 6 h, and cooled to room temperature after the reaction was completed, to obtain a high-strength rigid foam with open-cell structure;

[0128] S7, high-temperature gradient pyrolysis: the high-strength rigid foam prepared in S6 was placed in a high-temperature carbonization furnace, and raised from room temperature to 300°C at a temperature raising rate of 2°C / min under an argon atmosphere, kept for 1 h, then raised to 1000°C at a temperature raising rate of 1°C / min, kept for 2 h, then cooled to room temperature with the furnace, and finally cooled to room temperature, to obtain an ultra-low density carbon foam with a dense carbon skeleton.

[0129] The prepared carbon foam material has a density of 0.042 g / cm 3 , a thermal conductivity of 0.050 W / (m·K), and a compressive strength of 0.56 MPa, as shown in 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 penetration swelling temperature is 35°C, and the penetration swelling time is 2 h. See Table 1 for details.

[0133] The prepared carbon foam material has a density of 0.045 g / cm 3 , a thermal conductivity of 0.052 W / (m·K), and a compressive strength of 0.60 MPa, as shown in 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 phenolic resin concentration used is 90 wt.%, the addition amount of hexamethylenetetramine is 45.0 g, the penetration swelling temperature is 50°C, and the penetration swelling time is 2 h. See Table 1 for details.

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

[0138] Example 9

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

[0140] The difference between this example and example 6 is that the carbonization final temperature is set to 800℃. See Table 1 for details.

[0141] The prepared carbon foam material has a density of 0.042 g / cm 3 , a thermal conductivity of 0.044 W / (m·K), and a compressive strength of 0.45 MPa, as shown in Table 2.

[0142] Example 10

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

[0144] The difference between this example and example 6 is that the carbon nanomaterial is multi-walled carbon nanotubes. See Table 1 for details.

[0145] The prepared carbon foam material has a density of 0.044 g / cm 3 , a thermal conductivity of 0.045 W / (m·K), and a compressive strength of 0.54 MPa, as shown in Table 2.

[0146] Comparative Example 1

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

[0148] Compared with example 1, step S2 (i.e. not introducing carbon nanomaterial) is not performed.

[0149] The prepared carbon foam material has a density of 0.043 g / cm 3 , a thermal conductivity of 0.042 W / (m·K), and a compressive strength of 0.31 MPa, as shown in Table 2.

[0150] Comparative Example 2

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

[0152] Compared with example 1, during the curing reaction process of step S6, the temperature is not raised in a gradient, but is directly raised to the required temperature at a rate of 0.5℃ / min. The temperature is not raised in a gradient, but is directly raised to 170℃.

[0153] The prepared carbon foam material has a density of 0.044 g / cm 3 , a thermal conductivity of 0.047 W / (m·K), and a compressive strength of 0.37 MPa, as shown in Table 2. There are defects in the microstructure, bubbles on the surface of the foam skeleton, and obvious fractures in the skeleton, as shown in Figure 5 .

[0154] Comparative Example 3

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

[0156] Compared with Example 1, the carbonization process in step S7 is directly heated to the required temperature at a heating rate of 1℃ / min without gradient heating.

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

[0158] Comparative Example 4

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

[0160] Compared with Example 1, the carbon nanomaterial, carbon source matrix, and compatibilizer are mixed and stirred uniformly during the preparation of the carbonaceous precursor solution (i.e., S1 and S2 are combined into one step).

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

[0162] Comparative Example 5

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

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

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

[0166] Comparative Example 6

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

[0168] Compared with Example 1, during the distribution regulation process of the carbonaceous precursor solution in step S5, the amount of the carbonaceous precursor solution removed is too small, and the process is stopped before the composite foam reaches the state of no liquid enrichment. This leads to partial blockage of the pores of the final carbon foam.

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

[0170] Comparative Example 7

[0171] The present 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, which is too short.

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

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

[0175]

[0176]

[0177] Table 2: Summary of properties of samples obtained in examples and comparative examples

[0178]

[0179]

[0180] As can be seen from Example 2 and Example 1 and Example 9 and Example 10, the higher the carbonization temperature, the better the mechanical properties of the material, but the thermal conductivity will also increase accordingly; as can be seen from Example 1, 2 and Example 3-5 and Example 6, 9, 10 and Example 7, 8, the higher the osmotic swelling temperature and the longer the osmotic swelling time (within the scope of the present application), the more sufficient the penetration of the carbonaceous precursor into the foam, the higher the weight gain, and the stronger the compressive strength; as can be seen from Example 8 and Example 6, 7, 9, 10, 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] As can be seen from Comparative Example 1 and Example 1, the addition of carbon nanomaterials will significantly reduce the compressive strength of the product carbon foam material; as can be seen from Comparative Examples 2 and 3 and Example 1, the gradient temperature rising strategy is not used in the curing or high-temperature carbonization process, which will significantly reduce the mechanical properties of the product foam material.

[0182] Comparative Example 4 and Example 1, the carbon nanomaterials, carbon source matrix, and compatibilizer are mixed and stirred uniformly (i.e., S1 and S2 are combined into one step), which causes the carbon nanomaterials and the compatibilizer to be mixed together first, and the carbon nanomaterials to agglomerate together, resulting in poor dispersibility and affecting the product performance.

[0183] Compared with Example 1, the pre-reaction of the curing agent in the carbon source matrix is carried out first, and then the carbon nanomaterial is introduced for reinforcement in Comparative Example 5, which results in too long reaction time of the carbon source matrix with the curing agent, too large viscosity of the carbon precursor solution, poor dispersibility of the carbon nanomaterial added later, and difficulty in removing the excess carbon precursor solution, and finally, uneven distribution of the carbon precursor solution, significantly increased density and thermal conductivity of the carbon foam, and no obvious improvement in compressive strength.

[0184] Compared with Example 1, the amount of the carbon precursor solution removed is too small in Comparative Example 6, and the process is stopped without reaching the state of liquid-free composite foam, and there is liquid enrichment, which results in uneven density distribution of the final carbon foam and poor performance.

[0185] Compared with Example 1, the pre-reaction time is too short in Comparative Example 7, resulting in low degree of pre-polymerization, although the open porosity is high, the density and thermal conductivity are low, but the strength of the composite foam structure after the curing reaction is extremely low.

[0186] In summary, the present application uses open-cell polymer foam as a support skeleton, selects a high-residual-carbon-rate thermosetting resin or polymer monomer furfuryl alcohol as a carbon source matrix, and introduces carbon nanomaterial as a reinforcing phase, which improves the compressive strength while maintaining a low bulk density, thereby significantly improving the specific strength and providing a new idea for the research and development of lightweight high-strength materials. The present application precisely controls the parameters such as penetration swelling, carbon precursor solution distribution regulation, gradient curing, and high-temperature gradient pyrolysis, and the prepared carbon foam has the properties of ultra-low density, low thermal conductivity, and high strength, effectively solving the problem that the existing carbon foam is difficult to simultaneously achieve low density and high strength. The low thermal conductivity can effectively block heat transfer, reduce thermal expansion, and delay thermal decomposition, thereby endowing the material with high thermal stability, so that it can fully meet the needs of the high-temperature insulation field. The ultra-low density carbon foam material prepared by the present application has a uniform open-cell structure, a bulk density of 0.042-0.053 g / cm 3 , a thermal conductivity of less than 0.053 W / (m·K), and a compressive strength of 0.43-0.67 MPa, which has a broad application prospect in the field of lightweight high-temperature thermal protection.

[0187] The above description is only a preferred specific embodiment of the present application, but the protection scope of the present application is not limited thereto, and any changes or replacements within the technical scope disclosed by the present application can be easily thought of by those skilled in the art, which should be covered within the protection scope of the present application.

Claims

1. A method for preparing an ultra-low density carbon foam material, characterized in that, The preparation of carbonaceous precursors includes the following steps: S1. Pretreatment of carbon source matrix: Mix the carbon source matrix and compatibilizer evenly to obtain the modified carbon source matrix; S2. Preparation of carbon nanomaterial-reinforced carbon source matrix: Carbon nanomaterials are added to the modified carbon source matrix prepared in S1, and the carbon nanomaterials are uniformly dispersed by mechanical stirring and ultrasonic treatment to form a carbon nanomaterial-reinforced carbon source matrix. S3. Preparation of carbon precursor solution: The carbon nanomaterial-reinforced carbon source matrix obtained in S2 is mixed with a curing agent and pre-reacted in a water bath to obtain a carbon precursor solution. The compatibilizer includes one or more of polyvinylidene fluoride (PVDF), polyethylene glycol (PEG), and polyacrylic acid (PAA); The preparation method further includes the following steps: S4. Permeation and swelling: The porous polymer foam is placed in the carbonaceous precursor solution prepared in S3 to permeate and swell, forming a uniformly distributed composite structure. S5. Control of carbon precursor solution distribution: Control the distribution of carbon precursor solution to remove excess carbon precursor solution from the pores of the composite structure and obtain a wet composite foam with a framework rich in carbon precursor solution. S6. Curing reaction: The wet composite foam obtained in S5 is placed in an oven for gradient heating and curing. After the reaction is completed, it is cooled to room temperature to obtain a high-strength rigid composite foam with an open-cell structure. S7. High-temperature gradient pyrolysis: The high-strength rigid composite foam prepared in S6 is placed in a high-temperature carbonization furnace and subjected to high-temperature gradient pyrolysis in an inert atmosphere. Finally, it is cooled to room temperature to obtain ultra-low-density carbon foam with a dense carbon skeleton.

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, furfuryl ketone resin or furfural resin; the polymer monomer includes furfuryl alcohol.

3. The preparation method according to claim 1, characterized in that, The carbon nanomaterials include one or more of carbon nanofibers, carbon nanotubes, graphene, and graphene oxide.

4. The preparation method according to claim 1, characterized in that, The water bath temperature in S3 is 25~45℃, and the pre-reaction process is carried out under stirring for 2~10h.

5. The preparation method according to claim 1, characterized in that, The permeation and swelling described in S4 is carried out at 25~50℃, and the permeation and swelling time is 0.5~3h.

6. The preparation method according to claim 1, characterized in that, The high-temperature gradient pyrolysis temperature described in S7 is as follows: the temperature is increased from 25°C to 300-500°C at a heating rate of 1-5°C / min, and held at 300-500°C for 2-5 hours. Then, the temperature is increased to 700-1200°C at a heating rate of 0.5-5°C / min and held for 1-3 hours.

7. An ultra-low density carbon foam material, characterized in that, The carbon foam material is prepared by the method according to any one of claims 1 to 6, wherein the carbon foam material uses an open-cell polymer foam as a supporting skeleton, a thermosetting resin or polymer monomer as a carbon source matrix, and carbon nanomaterials are introduced into the carbon source matrix to act as a reinforcing phase.

8. The carbon foam material according to claim 7, characterized in that, The bulk density of the carbon foam material is 0.042~0.053 g / cm³. 3 It has a porosity ≥97%, a thermal conductivity of 0.041~0.053W / (m·K), and a compressive strength of 0.43~0.67MPa.

9. An application of an ultra-low density carbon foam material, characterized in that, The application of the carbon foam material prepared by the preparation method according to any one of claims 1 to 6 or the carbon foam material according to any one of claims 7 to 8, wherein the ultra-low density carbon foam material is applied in the field of high-temperature heat insulation materials.

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