A method for improving the in-plane thermal conductivity of a c / c composite material

Abstract

The application provides a method for improving in-plane thermal conductivity of C / C composite material, and belongs to the technical field of carbon / carbon composite material; the method comprises the steps of preparing impregnation slurry, preparing carbon fiber mesh tire preform, preparing low-density carbon / carbon composite material blank, preparing suspension, filling and densification; the preparation of the impregnation slurry comprises the steps of silane treatment of carbon nanotubes, pitch pretreatment and slurry preparation; in the slurry preparation, tetraethyl orthosilicate is added into anhydrous ethanol, then the pH is adjusted to 3-4, and the mixture is stirred uniformly at 36-40 DEG C; then methyl triethoxysilane is added and stirred uniformly, and the mixture is added into the mixed solution after stirring at room temperature; the mixed solution is stirred at 50-53 DEG C for 1.0-1.5 h, and the impregnation slurry is obtained through ultrasonic dispersion; the mixed solution is prepared by mixing maleic anhydride modified pitch, anhydrous ethanol, silane modified carbon nanotubes and graphite powder; and the carbon / carbon composite material prepared by the method has high strength and in-plane thermal conductivity and high stability.

Description

Technical Field

[0001] This invention belongs to the field of carbon / carbon composite material technology, and specifically relates to a method for improving the in-plane thermal conductivity of C / C composite materials. Background Technology

[0002] Carbon / carbon composites are a new type of high-performance material composed of carbon fiber reinforcement and carbon matrix. With their low density, high specific strength, high specific modulus, excellent high temperature resistance and good chemical stability, they have shown irreplaceable application value in high-end fields such as aerospace and defense, especially becoming one of the core materials of thermal protection systems. The structural design of thermal protection systems is a core issue of major aerospace equipment such as hypersonic aircraft and launch vehicles. High-performance thermal protection materials generally have ultra-high thermal conductivity, ultra-high load-bearing capacity, ultra-lightweight and high ablation resistance, making them one of the key materials for aerospace equipment.

[0003] Among the many reinforcing fibers, high thermal conductivity mesophase pitch-based carbon fiber (MPCF) is a high-performance product in the field of carbon fiber. It is a key raw material urgently needed for the development of major weapons and equipment such as aerospace, and it is also a key basic raw material for both military and civilian use.

[0004] MPCF (Metal-Plastic Composite) possesses characteristics such as low density, high strength, high modulus, high thermal conductivity, and corrosion resistance. High thermal conductivity C / C composite materials with integrated structural / functional properties developed using MPCF play an irreplaceable role in weaponry and national defense. The level and scale of its application are crucial to the success and leapfrog development of high-performance aerospace equipment. Aerospace engines, as core components of national defense equipment, require their throat liners, nozzles, and other parts to withstand ultra-high temperatures, thermal shock, strong oxidation, and airflow erosion, with temperatures reaching over 2000℃. This places even more stringent technical requirements on their thermal protection materials.

[0005] Currently, the preparation of high thermal conductivity carbon / carbon composites based on MPCF mainly includes chemical vapor infiltration and liquid phase impregnation-carbonization.

[0006] Among them, chemical vapor infiltration is a method that deposits gaseous carbon source in the pores of a preform to form matrix carbon, which can produce composite materials with good structural uniformity. However, this method has a long process cycle, high production cost, and high porosity, resulting in poor material density and ablation resistance.

[0007] The liquid phase impregnation-carbonization method involves immersing the preform in a liquid impregnating agent (asphalt, resin, etc.), using the penetration of the impregnating agent to fill the pores, and then forming the matrix carbon through the curing and carbonization process. The density of the composite material is improved through multiple impregnation-curing-carbonization cycles. The process is simple, low-cost, and easy to scale up.

[0008] However, the MPCF-based carbon / carbon composites obtained by this method often suffer from the problem of not being able to simultaneously achieve good thermal conductivity and other properties. To improve in-plane thermal conductivity, existing technologies typically increase the MPCF content or use high thermal conductivity impregnating agents. However, excessively high fiber content can lead to difficulties in preform molding and poor fiber overlap, resulting in thermal conductivity defects. Furthermore, single bitumen or resin impregnating agents undergo significant volume shrinkage during carbonization, making it difficult to fully fill the pores of the preform. This not only fails to effectively improve density but also creates numerous microcracks within the composite material, reducing its mechanical properties and disrupting heat conduction paths, thus lowering its thermal conductivity. In addition, the impregnating agents used in existing technologies have poor interfacial compatibility with fibers, resulting in low interfacial bonding strength and significant heat conduction resistance at the interface, further reducing the product's thermal conductivity. Simultaneously, while pursuing low in-plane thermal conductivity, existing technologies often result in composites with excessively high Z-direction thermal conductivity, failing to meet the structural design requirements of "lateral thermal conduction and longitudinal thermal insulation" for components such as aero-engine throat liners and nozzles.

[0009] Therefore, providing a method to improve the in-plane thermal conductivity of carbon / carbon composite materials, while ensuring mechanical properties, and improving the thermal conductivity in the XY direction and enhancing the thermal insulation performance in the Z direction, is a technical problem that urgently needs to be solved in the existing technology. Summary of the Invention

[0010] To address the technical problems existing in the prior art, this invention provides a method for improving the in-plane thermal conductivity of C / C composite materials, thereby increasing the thermal conductivity in the XY direction, decreasing the thermal conductivity in the Z direction, and simultaneously improving the mechanical properties of the composite material.

[0011] To address the aforementioned technical problems, the present invention adopts the following technical solution:

[0012] A method for improving the in-plane thermal conductivity of C / C composite materials includes the following steps: preparing an impregnation slurry, preparing a preform containing a carbon fiber mesh, preparing a low-density carbon / carbon composite preform, preparing a suspension, filling, and densification. The specific operations are as follows:

[0013] 1. Preparation of impregnation slurry

[0014] (1) Silane treatment of carbon nanotubes

[0015] Carbon nanotubes were placed in an acid solution, heated to 60-64℃, and stirred at 320-360 rpm for 30-40 min. Then, they were ultrasonically dispersed for 3.0-3.5 h at a power of 100-110 W and a frequency of 40-45 kHz. After ultrasonic dispersion, the nanotubes were filtered, washed, and dried to obtain acid-treated carbon nanotubes. The acid-treated carbon nanotubes were then placed in an ethanol solution, and KH560 silane coupling agent was added. The solution was kept at 68-72℃ for 3.5-4.0 h, filtered, washed, and dried to obtain silane-treated carbon nanotubes.

[0016] The carbon nanotubes have a diameter of 8-12 nm and a length of 15-20 μm;

[0017] The acid solution is a mixture of concentrated sulfuric acid and concentrated nitric acid, and the volume ratio of the concentrated nitric acid solution to the concentrated sulfuric acid solution is 1:3-4.

[0018] The concentrated nitric acid solution has a mass concentration of 48-52%, and the concentrated sulfuric acid solution has a mass concentration of 70-75%.

[0019] The mass ratio of the carbon nanotubes to the acid solution is 10:70-80;

[0020] The mass ratio of the acid-treated carbon nanotubes, ethanol solution, and silane coupling agent is 10:80-90:1.0-1.2.

[0021] The ethanol solution has a mass concentration of 50-55%;

[0022] (2) Asphalt pretreatment

[0023] 70# base asphalt is heated to 150-160℃ to melt, maleic anhydride and benzoyl peroxide are added, and the mixture is stirred at 400-500 rpm for 4-5 hours to obtain maleic anhydride modified asphalt.

[0024] The mass ratio of the base bitumen, maleic anhydride, and benzoyl peroxide is 100:3.5:0.5-1.0;

[0025] (3) Pulp formation

[0026] Maleic anhydride modified asphalt is placed in anhydrous ethanol, the temperature is raised to 50-53℃, and stirred at 450-500 rpm for 30-40 min. Silane modified carbon nanotubes and graphite powder are added, and the mixture is stirred at 780-830 rpm for 1.0-1.5 h to obtain a mixture.

[0027] The particle size of the graphite powder is 3-5 μm;

[0028] The mass ratio of maleic anhydride modified asphalt, anhydrous ethanol, silane modified carbon nanotubes and graphite powder is 15-20:50:6-10:25-30.

[0029] Add tetraethyl orthosilicate to anhydrous ethanol and stir at room temperature for 20-30 min. Add hydrochloric acid solution to adjust the pH to 3-4. After the addition is complete, raise the temperature to 36-40℃ and stir at 300-330 rpm for 10-15 min. Add methyltriethoxysilane and continue stirring for 20-25 min. After naturally cooling to room temperature, continue stirring for 10-15 min. Add the methyltriethoxysilane to the mixture at a rate of 1.0-1.5 g / min while stirring at 400-450 rpm. After the addition is complete, stir for 20-30 min. Raise the temperature to 50-53℃ and stir at the same time for 1.0-1.5 h. Disperse ultrasonically for 25-30 min at an ultrasonic power of 80-100 W and an ultrasonic frequency of 30-36 kHz. After removing large particulate impurities, age at room temperature for 2.0-2.5 h to obtain the impregnating slurry.

[0030] The mass ratio of the anhydrous ethanol, tetraethyl orthosilicate, methyltriethoxysilane, and the mixture is 25-30:10-12:0.8-1.0:140-150.

[0031] The mass concentration of the hydrochloric acid solution is 5-6%.

[0032] 2. Preparation of carbon fiber mesh preform

[0033] The carbon fiber mesh is placed in the impregnation slurry and ultrasonically impregnated at a temperature of 48-52℃, an ultrasonic power of 140-160W, and an impregnation time of 1.8-2.2h to obtain a preform containing carbon fiber mesh.

[0034] In the carbon fiber mesh, the carbon fiber has a thermal conductivity of 800-810 W / m·K, a tensile strength of 3.0-3.2 GPa, an elastic modulus of 840-860 GPa, and a mesh areal density of 78-83 g / m². 2 The thickness is 0.8-1.2mm;

[0035] The mass ratio of the carbon fiber mesh to the impregnation slurry is 10:56-83.

[0036] 3. Preparation of low-density carbon / carbon composite preforms

[0037] Carbon fiber plain weave fabric is laminated with a carbon fiber mesh preform to obtain a sizing carbon fiber fabric with a thickness of 18-20 mm. The sizing carbon fiber fabric is then needle-punched, with the needle-punching density controlled at 200-220 needles / cm. 2The needle-punching depth is 10-13 mm to obtain a needle-punched fabric containing sizing agent. Then, it is dried at 80-90℃ for 5.8-6.2 h, cured at 400-600℃ for 30-36 h, and carbonized at 890-910℃ for 2.0-2.2 h to obtain a low-density carbon / carbon composite preform.

[0038] The carbon fiber plain weave fabric is made of T700 grade PAN-based carbon fiber, with a thickness of 0.15-0.20 mm and an areal density of 200-300 g / m³. 2 ;

[0039] The density of the low-density carbon / carbon composite preform is 0.92-1.10 g / cm³. 3 .

[0040] 4. Preparation of suspension

[0041] Carbon black is added to deionized water and stirred until homogeneous. Then, phenol and formaldehyde solutions are added and stirred at 250-300 rpm for 10-15 min. Ammonia solution is added to adjust the pH to 8.0-8.5. The temperature is raised to 50-52℃ and stirred for 1.0-1.2 h. Then, phenol and formaldehyde solutions are added a second time and stirred at 280-330 rpm for 20-25 min. The temperature is raised to 82-85℃ and stirred for 2.0-2.3 h. Anhydrous ethanol is added and stirred at 400-420 rpm for 20-25 min. Ultrasonic treatment is performed at 14-17℃ for 25-30 min, with an ultrasonic power of 180-200 W and an ultrasonic frequency of 50-55 kHz. After ultrasonic treatment, the mixture is stirred at 400-450 rpm for 20-25 min. Polyethylene glycol 1000 is added and stirred at 240-270 rpm for 15-20 min to remove large particulate impurities, resulting in a suspension.

[0042] The carbon black has a particle size of 50-80 nm;

[0043] The mass concentration of the ammonia solution is 1.0-2.0%;

[0044] The mass ratio of carbon black, deionized water, the first addition of phenol, the first addition of formaldehyde solution, the second addition of phenol, the second addition of formaldehyde solution, anhydrous ethanol, and polyethylene glycol 1000 is 7.5-8.0:100:14.0-14.5:18.5-19.0:4.0-4.3:4.8-5.2:180-200:0.20-0.22.

[0045] The formaldehyde solution has a mass concentration of 37-40%.

[0046] 5. Fill

[0047] The low-density carbon / carbon composite preform is immersed in a suspension of 6-8 times its mass and impregnated under pressure at 1-5 MPa for 5.8-6.3 h. Then it is heated at 80-90℃ for 10-12 h, cured at 400-600℃ for 30-36 h, and carbonized at 890-910℃ for 2.0-2.2 h. The above steps constitute one filling process. The filling process is repeated twice to obtain a filled carbon / carbon composite preform.

[0048] 6. Densification

[0049] The carbon / carbon composite preform is placed in a suspension of 6-8 times its mass and impregnated under pressure of 4.8-5.2 MPa for 5.8-6.3 hours, with the heating temperature controlled at 80-90℃ for 10-12 hours. It is then cured at 400-600℃ for 30-36 hours, followed by carbonization at 890-910℃ for 2.0-2.2 hours. The preform is then placed in a suspension of 6-8 times its mass again and impregnated under pressure of 3.8-4.2 MPa for 5.8-6.3 hours, with the heating temperature controlled at 80-90℃ for 10-12 hours. Finally, it is cured at 400-600℃ for 30-36 hours. Curing at 0℃ for 30-36 hours, carbonizing at 890-910℃ for 2.0-2.2 hours, and then cooling are followed by pressure impregnation in 6-8 times their weight of suspension at 4.8-5.2 MPa for 5.8-6.3 hours. Heating is then carried out at 80-90℃ for 10-12 hours, followed by curing at 400-600℃ for 30-36 hours, carbonizing at 890-910℃ for 2.0-2.2 hours, and finally heat treatment at 1500-1800℃ for 2.0 hours. After natural cooling to room temperature, a density of 1.80-1.85 g / cm³ is obtained. 3 High-density carbon / carbon composite materials.

[0050] Compared with the prior art, the present invention has achieved the following beneficial effects:

[0051] 1. This invention uses low-modulus MPCF as the reinforcing phase in a needle-punched C / C composite material skeleton structure. Low-modulus MPCF (X and Y axes) carbonized at low temperature and high-strength PAN-based carbon fiber (Z axis) are needle-punched into a three-dimensional preform. The C / C composite material is densified by carbon coupling with a pitch / carbon nanotube-derived matrix. The pitch-based carbon fiber mesh significantly improves the transverse thermal conductivity of the composite material. The impregnation slurry uses kH560 silane to treat the carbon nanotubes, enhancing the bonding between the carbon nanotubes and the pitch matrix and preventing agglomeration. The pitch is modified with maleic anhydride, improving the compatibility and reactivity between the pitch and carbon materials. Tetraethyl orthosilicate is added during the slurry-forming step to form a silica sol, which reacts with methyltriethoxysilane. The synergistic effect of silanes constructs an organic-inorganic hybrid network in the slurry, enhancing its adhesion and stability. Then, a carbon fiber mesh preform is impregnated and laminated with carbon fiber plain weave fabric. The asphalt slurry is pyrolyzed to form a carbon matrix, with the carbon fibers forming a continuous dominant thermal network. Combined with silane-modified carbon nanotubes and graphite, a synergistic thermal conductive network is formed, improving the in-plane thermal conductivity of the composite material. Carbon black is used as a nanofiller, dispersed in a phenolic resin precursor, and polymerized with ammonia to form phenolic resin-coated carbon black, enhancing the permeability of the suspension. After carbonization, the density and mechanical properties are significantly improved. Through multiple impregnation, curing, and carbonization cycles, a high-density, high-thermal-conductivity, high-strength, and high-stability carbon / carbon composite material is obtained.

[0052] 2. The carbon / carbon composite material prepared by this invention has a thermal conductivity of 380.2-385.9 W / m·K in the XY direction, a thermal conductivity of 7.6-8.5 W / m·K in the Z direction, a tensile strength of 185-194 MPa, and a compressive strength of 178-185 MPa.

[0053] 3. The carbon / carbon composite material prepared by this invention is heated to 1800℃ at a rate of 40℃ / min, kept at that temperature for 6.0h, and then cooled to 25℃ at a rate of 60℃ / min, kept at that temperature for 6.0h. This process is repeated as one treatment cycle, and 20 treatment cycles are performed continuously. The thermal conductivity in the XY direction is measured to be 361.2-375.1W / m·K, the tensile strength is 175-187MPa, and the compressive strength is 168-177MPa. Detailed Implementation

[0054] To provide a clearer understanding of the technical features, objectives, and effects of the present invention, specific embodiments of the present invention are now described.

[0055] Example 1

[0056] 1. Preparation of impregnation slurry

[0057] (1) Silane treatment of carbon nanotubes

[0058] 10g of carbon nanotubes were placed in 70g of acid solution, the temperature was raised to 60℃, and the mixture was stirred at 320rpm for 30min. Then, ultrasonic dispersion was performed for 3.0h, with an ultrasonic power of 100W and an ultrasonic frequency of 40kHz. After ultrasonic dispersion, the mixture was filtered, washed, and dried to obtain acid-treated carbon nanotubes. 10g of acid-treated carbon nanotubes were placed in 80g of 50wt% ethanol solution, and 1.0g of KH560 silane coupling agent was added. The mixture was kept at 68℃ for 3.5h, filtered, washed, and dried to obtain silane-treated carbon nanotubes.

[0059] The carbon nanotubes have a diameter of 8 nm and a length of 15 μm.

[0060] The acid solution is a mixture of concentrated sulfuric acid and concentrated nitric acid, and the volume ratio of the concentrated nitric acid solution to the concentrated sulfuric acid solution is 1:4.

[0061] The concentrated nitric acid solution has a mass concentration of 48%, and the concentrated sulfuric acid solution has a mass concentration of 70%.

[0062] (2) Asphalt pretreatment

[0063] 100g of 70# base asphalt was heated to 150℃ to melt, 3g of maleic anhydride and 0.5g of benzoyl peroxide were added, and the mixture was stirred at 400rpm for 4h to obtain maleic anhydride modified asphalt.

[0064] (3) Pulp formation

[0065] Add 15g of maleic anhydride modified asphalt to 50g of anhydrous ethanol, raise the temperature to 50℃, stir at 450rpm for 30min, add 6g of silane modified carbon nanotubes and 25g of graphite powder, stir at 780rpm for 1.0h to obtain a mixture.

[0066] Add 10g of tetraethyl orthosilicate to 25g of anhydrous ethanol and stir at room temperature for 20min. Add 6wt% hydrochloric acid solution to adjust the pH to 3. After the addition is complete, raise the temperature to 36℃ and stir at 300rpm for 10min. Add 0.8g of methyltriethoxysilane and continue stirring for 20min. After naturally cooling to room temperature, continue stirring for 10min. Add the mixture to 140g of the mixture at a rate of 1.0g / min while stirring at 400rpm. After the addition is complete, stir for 20min. Raise the temperature to 50℃ and stir for 1.0h. Disperse ultrasonically for 25min at an ultrasonic power of 80W and a frequency of 30kHz. After removing large particulate impurities, age at room temperature for 2.0h to obtain the impregnating slurry.

[0067] The graphite powder has a particle size of 3 μm.

[0068] 2. Preparation of carbon fiber mesh preform

[0069] 10g of carbon fiber mesh was placed into 56g of impregnation slurry and ultrasonically impregnated at a temperature of 48℃, an ultrasonic power of 140W, and an impregnation time of 1.8h to obtain a preform containing carbon fiber mesh.

[0070] The carbon fiber mesh has a thermal conductivity of 800 W / m·K, a tensile strength of 3.0 GPa, an elastic modulus of 840 GPa, and a mesh areal density of 78 g / m². 2 The thickness is 0.8mm.

[0071] 3. Preparation of low-density carbon / carbon composite preforms

[0072] Carbon fiber plain weave fabric is laminated with carbon fiber mesh preform to obtain a sizing carbon fiber fabric with a thickness of 18 mm. The sizing carbon fiber fabric is then needle-punched, with the needle-punching density controlled at 200 needles / cm. 2 The needle-punching depth is 10 mm to obtain a needle-punched fabric containing sizing agent. Then, it is dried at 80℃ for 5.8 h, cured at 400℃ for 30 h, and carbonized at 890℃ for 2.2 h to obtain a low-density carbon / carbon composite preform.

[0073] The carbon fiber plain weave fabric is made of T700 grade PAN-based carbon fiber, with a thickness of 0.15 mm and an areal density of 200 g / m³. 2 ;

[0074] The density of the low-density carbon / carbon composite preform is 0.92 g / cm³. 3 .

[0075] 4. Preparation of suspension

[0076] Add 7.5g of carbon black to 100g of deionized water and stir until homogeneous. Then add 14.0g of phenol and 18.5g of 40wt% formaldehyde solution and stir at 250rpm for 10min. Add ammonia solution to adjust the pH to 8.0, raise the temperature to 50℃, and stir for 1.0h. Add another 4.0g of phenol and 4.8g of 40wt% formaldehyde solution and stir at 280rpm for 20min. Raise the temperature to 82℃ and stir for 2.0h. Add 180g of anhydrous ethanol and stir at 400rpm for 20min. Sonicate at 14℃ for 25min, with an ultrasonic power of 180W and an ultrasonic frequency of 50kHz. After ultrasonication, stir at 400rpm for 20min. Add 0.20g of polyethylene glycol 1000 and stir at 240rpm for 15min to remove large particulate impurities, thus obtaining a suspension.

[0077] The carbon black has a particle size of 50 nm;

[0078] The mass concentration of the ammonia solution is 1.0%.

[0079] 5. Fill

[0080] The low-density carbon / carbon composite preform was immersed in a suspension of 6 times its mass and impregnated under pressure at 4.8 MPa for 5.8 h. Then it was heated to 80 °C for 10 h, cured at 400 °C for 30 h, and carbonized at 890 °C for 2.0 h. The above steps constitute one filling process. The filling process was repeated twice to obtain a filled carbon / carbon composite preform.

[0081] 6. Densification

[0082] The carbon / carbon composite preform was placed in a suspension of 6 times its mass and impregnated under pressure of 4.8 MPa for 5.8 h, followed by heating at 80℃ for 10 h, curing at 400℃ for 30 h, and carbonizing at 890℃ for 2.0 h. It was then placed in a suspension of 6 times its mass again and impregnated under pressure of 3.8 MPa for 5.8 h, followed by heating at 80℃ for 10 h, curing at 400℃ for 30 h, and carbonizing at 890℃ for 2.0 h. After cooling, it was again placed in a suspension of 6 times its mass and impregnated under pressure of 4.8 MPa for 5.8 h, followed by heating at 80℃ for 10 h, curing at 400℃ for 30 h, and carbonizing at 890℃ for 2.0 h. Finally, it was heat-treated at 1500℃ for 2.0 h and allowed to cool naturally to room temperature, yielding a preform with a density of 1.80 g / cm³. 3 High-density carbon / carbon composite materials.

[0083] Example 2

[0084] 1. Preparation of impregnation slurry

[0085] (1) Silane treatment of carbon nanotubes

[0086] 10g of carbon nanotubes were placed in 80g of acid solution, the temperature was raised to 64℃, and the mixture was stirred at 360rpm for 40min. Then, ultrasonic dispersion was performed for 3.5h, with an ultrasonic power of 110W and an ultrasonic frequency of 45kHz. After ultrasonic dispersion, the mixture was filtered, washed, and dried to obtain acid-treated carbon nanotubes. 10g of acid-treated carbon nanotubes were placed in 90g of 55wt% ethanol solution, and 1.2g of KH560 silane coupling agent was added. The mixture was kept at 72℃ for 4.0h, filtered, washed, and dried to obtain silane-treated carbon nanotubes.

[0087] The carbon nanotubes have a diameter of 12 nm and a length of 20 μm;

[0088] The acid solution is a mixture of concentrated sulfuric acid and concentrated nitric acid, and the volume ratio of the concentrated nitric acid solution to the concentrated sulfuric acid solution is 1:3.

[0089] The concentrated nitric acid solution has a mass concentration of 52%, and the concentrated sulfuric acid solution has a mass concentration of 75%.

[0090] (2) Asphalt pretreatment

[0091] 100g of 70# base asphalt was heated to 160℃ to melt, 5g of maleic anhydride and 1.0g of benzoyl peroxide were added, and the mixture was stirred at 500rpm for 5h to obtain maleic anhydride modified asphalt.

[0092] (3) Pulp formation

[0093] Add 20g of maleic anhydride modified asphalt to 50g of anhydrous ethanol, raise the temperature to 53℃, stir at 500rpm for 40min, add 10g of silane modified carbon nanotubes and 30g of graphite powder, stir at 830rpm for 1.5h to obtain a mixture.

[0094] Add 12g of tetraethyl orthosilicate to 30g of anhydrous ethanol and stir at room temperature for 30min. Add 6wt% hydrochloric acid solution to adjust the pH to 4. After the addition is complete, raise the temperature to 40℃ and stir at 330rpm for 15min. Add 1.0g of methyltriethoxysilane and continue stirring for 25min. After naturally cooling to room temperature, continue stirring for 15min. Add the mixture to 150g of the mixture at a rate of 1.5g / min while stirring at 450rpm. After the addition is complete, stir for 30min. Raise the temperature to 53℃ and stir for 1.5h. Disperse the mixture ultrasonically for 30min at a power of 100W and a frequency of 36kHz. After removing large particulate impurities, age the mixture at room temperature for 2.5h to obtain the impregnating slurry.

[0095] The graphite powder has a particle size of 5 μm.

[0096] 2. Preparation of carbon fiber mesh preform

[0097] 10g of carbon fiber mesh was placed into 83g of impregnation slurry and ultrasonically impregnated at a temperature of 52℃, an ultrasonic power of 160W, and an impregnation time of 2.2h to obtain a preform containing carbon fiber mesh.

[0098] The carbon fiber mesh has a thermal conductivity of 810 W / m·K, a tensile strength of 3.2 GPa, an elastic modulus of 860 GPa, and a mesh areal density of 83 g / m². 2 The thickness is 1.2mm.

[0099] 3. Preparation of low-density carbon / carbon composite preforms

[0100] Carbon fiber plain weave fabric is laminated with carbon fiber mesh preform to obtain a sizing carbon fiber fabric with a thickness of 20 mm. The sizing carbon fiber fabric is then needle-punched, with the needle-punching density controlled at 220 needles / cm. 2 The needle-punching depth is 13 mm to obtain a needle-punched fabric containing sizing agent. Then, it is dried at 90℃ for 6.2 h, cured at 600℃ for 36 h, and carbonized at 910℃ for 2.0 h to obtain a low-density carbon / carbon composite preform.

[0101] The carbon fiber plain weave fabric is made of T700 grade PAN-based carbon fiber, with a thickness of 0.20 mm and an areal density of 300 g / m³. 2 ;

[0102] The density of the low-density carbon / carbon composite preform is 1.10 g / cm³. 3 .

[0103] 4. Preparation of suspension

[0104] Add 8.0g of carbon black to 100g of deionized water and stir until homogeneous. Then add 14.5g of phenol and 19.0g of 37wt% formaldehyde solution and stir at 300rpm for 15min. Add ammonia solution to adjust the pH to 8.5, raise the temperature to 52℃, and stir for 1.2h. Add 4.3g of phenol and 5.2g of 37wt% formaldehyde solution again and stir at 330rpm for 25min. Raise the temperature to 85℃ and stir for 2.3h. Add 200g of anhydrous ethanol and stir at 420rpm for 25min. Sonicate at 17℃ for 30min, with an ultrasonic power of 200W and an ultrasonic frequency of 55kHz. After sonication, stir at 450rpm for 25min. Add 0.22g of polyethylene glycol 1000 and stir at 270rpm for 20min to remove large particulate impurities, thus obtaining a suspension.

[0105] The carbon black has a particle size of 80 nm;

[0106] The mass concentration of the ammonia solution is 2.0%.

[0107] 5. Fill

[0108] The low-density carbon / carbon composite preform was immersed in a suspension of 8 times its mass and impregnated under pressure at 1 MPa for 6.3 h. Then it was heated to 90 °C for 12 h, cured at 600 °C for 36 h, and carbonized at 910 °C for 2.2 h. The above steps constitute one filling process. The filling process was repeated twice to obtain a filled carbon / carbon composite preform.

[0109] 6. Densification

[0110] The carbon / carbon composite preform was placed in a suspension equal to its mass and impregnated under pressure of 5.2 MPa for 6.3 h. The impregnation time was 12 h at 90 °C, followed by curing at 600 °C for 36 h and carbonization at 910 °C for 2.2 h. The preform was then placed in a suspension equal to its mass again and impregnated under pressure of 4.2 MPa for 6.3 h. The impregnation time was 12 h at 90 °C, followed by curing at 600 °C for 36 h and carbonization at 910 °C for 2.2 h. After cooling, the preform was again placed in a suspension equal to its mass and impregnated under pressure of 5.2 MPa for 6.3 h. The impregnation time was 12 h at 90 °C, followed by curing at 600 °C for 36 h and carbonization at 910 °C for 2.2 h. Finally, it was heat-treated at 1800 °C for 2.2 h and allowed to cool naturally to room temperature, yielding a preform with a density of 1.83 g / cm³. 3 High-density carbon / carbon composite materials.

[0111] Example 3

[0112] 1. Preparation of impregnation slurry

[0113] (1) Silane treatment of carbon nanotubes

[0114] 10g of carbon nanotubes were placed in 75g of acid solution, the temperature was raised to 62℃, and the mixture was stirred at 340rpm for 35min. Then, ultrasonic dispersion was performed for 3.2h, with an ultrasonic power of 105W and an ultrasonic frequency of 43kHz. After ultrasonic dispersion, the mixture was filtered, washed, and dried to obtain acid-treated carbon nanotubes. 10g of acid-treated carbon nanotubes were placed in 85g of 53wt% ethanol solution, and 1.2g of KH560 silane coupling agent was added. The mixture was kept at 70℃ for 3.8h, filtered, washed, and dried to obtain silane-treated carbon nanotubes.

[0115] The carbon nanotubes have a diameter of 10 nm and a length of 18 μm.

[0116] The acid solution is a mixture of concentrated sulfuric acid and concentrated nitric acid, and the volume ratio of the concentrated nitric acid solution to the concentrated sulfuric acid solution is 1:3.

[0117] The concentrated nitric acid solution has a mass concentration of 50%, and the concentrated sulfuric acid solution has a mass concentration of 73%.

[0118] (2) Asphalt pretreatment

[0119] 100g of 70# base asphalt was heated to 155℃ to melt, 4g of maleic anhydride and 0.8g of benzoyl peroxide were added, and the mixture was stirred at 450rpm for 4.5h to obtain maleic anhydride modified asphalt.

[0120] (3) Pulp formation

[0121] Add 18g of maleic anhydride modified asphalt to 50g of anhydrous ethanol, raise the temperature to 52℃, stir at 480rpm for 35min, add 8g of silane modified carbon nanotubes and 28g of graphite powder, stir at 800rpm for 1.2h to obtain a mixture.

[0122] Add 12g of tetraethyl orthosilicate to 28g of anhydrous ethanol and stir at room temperature for 25min. Add 5wt% hydrochloric acid solution to adjust the pH to 3.5. After the addition is complete, raise the temperature to 38℃ and stir at 320rpm for 12min. Add 0.8g of methyltriethoxysilane and continue stirring for 23min. After naturally cooling to room temperature, continue stirring for 13min. Add the mixture to 145g of the mixture at a rate of 1.2g / min while stirring at 420rpm. After the addition is complete, stir for 25min. Raise the temperature to 52℃ and stir for 1.2h. Disperse ultrasonically for 28min at a power of 90W and a frequency of 33kHz. After removing large particulate impurities, age at room temperature for 2.2h to obtain the impregnated slurry.

[0123] The graphite powder has a particle size of 4 μm.

[0124] 2. Preparation of carbon fiber mesh preform

[0125] 10g of carbon fiber mesh was placed into 75g of impregnation slurry and ultrasonically impregnated at a temperature of 50℃, an ultrasonic power of 150W, and an impregnation time of 2.0h to obtain a preform containing carbon fiber mesh.

[0126] In the carbon fiber mesh, the carbon fiber has a thermal conductivity of 805 W / m·K, a tensile strength of 3.2 GPa, an elastic modulus of 850 GPa, and a mesh areal density of 80 g / m². 2 The thickness is 1.0mm.

[0127] 3. Preparation of low-density carbon / carbon composite preforms

[0128] Carbon fiber plain weave fabric is laminated with carbon fiber mesh preform to obtain a sizing carbon fiber fabric with a thickness of 20 mm. The sizing carbon fiber fabric is then needle-punched, with the needle-punching density controlled at 210 needles / cm. 2 The needle-punching depth is 12 mm to obtain a needle-punched fabric containing sizing agent. Then, it is dried at 85℃ for 6.0 h, cured at 500℃ for 32 h, and carbonized at 900℃ for 2.0 h to obtain a low-density carbon / carbon composite preform.

[0129] The carbon fiber plain weave fabric is made of T700 grade PAN-based carbon fiber, with a thickness of 0.18 mm and an areal density of 250 g / m³. 2 ;

[0130] The density of the low-density carbon / carbon composite preform is 0.97 g / cm³. 3 .

[0131] 4. Preparation of suspension

[0132] Add 7.8g of carbon black to 100g of deionized water and stir well. Then add 14.3g of phenol and 18.7g of 38wt% formaldehyde solution and stir at 280rpm for 13min. Add ammonia solution to adjust the pH to 8.2, raise the temperature to 52℃, and stir for 1.2h. Add another 4.2g of phenol and 5.0g of 38wt% formaldehyde solution and stir at 300rpm for 23min. Raise the temperature to 84℃ and stir for 2.2h. Add 190g of anhydrous ethanol and stir at 410rpm for 23min. Ultrasonic treatment is performed at 15℃ for 28min, with an ultrasonic power of 190W and an ultrasonic frequency of 53kHz. After ultrasonic treatment, stir at 430rpm for 22min. Add 0.22g of polyethylene glycol 1000 and stir at 260rpm for 18min to remove large particulate impurities, resulting in a suspension.

[0133] The carbon black has a particle size of 60 nm;

[0134] The mass concentration of the ammonia solution is 1.5%.

[0135] 5. Fill

[0136] The low-density carbon / carbon composite preform was immersed in a suspension with a mass of 7 times its weight and impregnated under pressure at 5 MPa for 6.0 h. Then it was heated to 85 °C for 11 h, cured at 500 °C for 32 h, and carbonized at 900 °C for 2.0 h. The above steps constitute one filling process. The filling process was repeated twice to obtain a filled carbon / carbon composite preform.

[0137] 6. Densification

[0138] The carbon / carbon composite preform was placed in a suspension of 7 times its mass and impregnated under pressure of 5 MPa for 6.0 h. The impregnation time was 12 h at 85 °C, followed by curing at 500 °C for 32 h and carbonization at 900 °C for 2.0 h. The preform was then placed in a suspension of 7 times its mass again and impregnated under pressure of 4 MPa for 6.0 h. The impregnation time was 12 h at 85 °C, followed by curing at 500 °C for 32 h and carbonization at 900 °C for 2.0 h. After cooling, the preform was again placed in a suspension of 7 times its mass and impregnated under pressure of 5 MPa for 6.0 h. The impregnation time was 12 h at 85 °C, followed by curing at 500 °C for 32 h and carbonization at 900 °C for 2.0 h. Finally, it was heat-treated at 1700 °C for 2.0 h and allowed to cool naturally to room temperature, yielding a preform with a density of 1.85 g / cm³. 3 High-density carbon / carbon composite materials.

[0139] Comparative Example 3.1

[0140] Based on Example 3, the following changes were made:

[0141] In the preparation of the impregnation slurry, in the slurry forming step, silane-treated carbon nanotubes are replaced with acid-treated carbon nanotubes in equal amounts;

[0142] The slurry preparation step is as follows: 18g of maleic anhydride modified asphalt is placed into 50g of anhydrous ethanol, the temperature is raised to 52℃, and the mixture is stirred at 480rpm for 35min. Then, 8g of acid-treated carbon nanotubes and 28g of graphite powder are added, and the mixture is stirred at 800rpm for 1.2h to obtain a mixture, which is the impregnation slurry.

[0143] The rest of the operations are exactly the same.

[0144] Comparative Example 3.2

[0145] Based on Example 3, the following changes were made:

[0146] In the preparation of impregnation slurry, the maleic anhydride modified bitumen step is omitted; in the slurry forming step, the maleic anhydride modified bitumen is replaced in equal amounts with untreated 70# base bitumen.

[0147] The suspension preparation step is as follows: 7.8g of carbon black is added to 100g of deionized water, 21.4g of phenolic resin and 0.22g of polyethylene glycol 1000 are added, and the mixture is stirred at 260rpm for 18min to obtain the suspension.

[0148] The rest of the operations are exactly the same.

[0149] Performance testing

[0150] The high-density carbon / carbon composite materials prepared in Examples 1-3, Comparative Example 3-1, and Comparative Example 3-2 were subjected to performance testing, as detailed below:

[0151] 1. Mechanical and thermal properties

[0152]

[0153] 2. Thermal shock resistance

[0154] The high-density carbon / carbon composite materials prepared in Examples 1-3, Comparative Examples 3-1, and Comparative Examples 3-2 were subjected to a process in which the temperature was increased to 1800°C at a rate of 40°C / min, held at that temperature for 6.0 h, and then decreased to 25°C at a rate of 60°C / min, held at that temperature for 6.0 h. This process was repeated as one treatment cycle, and 20 cycles were performed consecutively. The thermal conductivity and mechanical properties were then tested again, and the results are as follows:

[0155]

[0156] This invention utilizes low-modulus MPCF as the reinforcing phase in a needle-punched C / C composite skeleton structure. It employs low-temperature carbonized low-modulus MPCF (X and Y axes) and high-strength PAN-based carbon fiber (Z axis) needle-punched into a three-dimensional preform. The C / C composite is densified through pitch / carbon nanotube-derived matrix carbon coupling. The pitch-based carbon fiber mesh significantly improves the transverse thermal conductivity of the composite. The impregnation slurry uses kH560 silane to treat the carbon nanotubes, enhancing the bonding between the carbon nanotubes and the pitch matrix and preventing agglomeration. The pitch is modified with maleic anhydride, improving the compatibility and reactivity between the pitch and carbon materials. Tetraethyl orthosilicate is added during the slurry-forming step to form a silica sol, which reacts with methyltriethoxysilane. Synergistic effects are achieved by constructing an organic-inorganic hybrid network in the slurry, enhancing its adhesion and stability. The carbon fiber mesh preform is then impregnated and laminated with carbon fiber plain weave fabric. Pyrolysis of the asphalt slurry forms a carbon matrix, with the carbon fibers forming a continuous dominant thermal network. This, combined with silane-modified carbon nanotubes and graphite, creates a synergistic thermally conductive network, improving the in-plane thermal conductivity of the composite material. Carbon black is used as a nanofiller, dispersed in a phenolic resin precursor, and polymerized with ammonia to form phenolic resin-coated carbon black, enhancing the suspension's permeability. After carbonization, the density and mechanical properties are significantly improved. Through multiple impregnation, curing, and carbonization cycles, a high-density, high-thermal-conductivity, high-strength, and high-stability carbon / carbon composite material is obtained.

[0157] Comparative Example 3-1 shows a weak interface between carbon nanotubes and asphalt, with no silica network to prevent agglomeration. This leads to a breakage of the thermally conductive network, a decrease in in-plane thermal conductivity, and an increase in interfacial defects in the carbon nanotubes. Consequently, the stability of the impregnation slurry decreases, affecting fiber penetration and ultimately reducing the mechanical properties and stability of the composite material. Comparative Example 3.2 omits asphalt modification treatment, resulting in poor compatibility between asphalt and carbon materials, uneven impregnation, and a suspension that is merely physically mixed. This leads to easy agglomeration of carbon black, poor filling effect, and ultimately a significant decrease in thermal conductivity and mechanical properties, as well as a marked reduction in stability.

[0158] Unless otherwise specified, all proportions mentioned in this invention are mass proportions, and all percentages are mass percentages.

[0159] Finally, it should be noted that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for improving the in-plane thermal conductivity of C / C composite materials, characterized in that, The process includes steps such as preparing impregnation slurry, preparing carbon fiber mesh preform, preparing low-density carbon / carbon composite preform, preparing suspension, filling and densification. The preparation of the impregnation slurry includes silane treatment of carbon nanotubes, asphalt pretreatment, and slurry formation steps; The asphalt pretreatment step involves adding maleic anhydride and benzoyl peroxide to the asphalt to obtain maleic anhydride-modified asphalt. The slurry preparation step is as follows: add tetraethyl orthosilicate to anhydrous ethanol, add hydrochloric acid solution, adjust the pH to 3-4, stir at 36-40℃ for 10-15 min, add methyltriethoxysilane, stir for 20-25 min, stir at room temperature for 10-15 min, add to the mixture, stir at 50-53℃ for 1.0-1.5 h, and then disperse by ultrasonication to obtain the impregnation slurry; The mixture is prepared by mixing maleic anhydride modified asphalt, anhydrous ethanol, silane modified carbon nanotubes and graphite powder. The steps for preparing the suspension are as follows: carbon black is added to deionized water, phenol and formaldehyde solutions are added and stirred, ammonia solution is added to adjust the pH to 8.0-8.5, and the mixture is stirred at 50-52℃ for 1.0-1.2h. Phenol and formaldehyde solutions are added a second time, and the mixture is stirred evenly at 82-85℃ for 2.0-2.3h. Anhydrous ethanol is added and stirred for 20-25min. The mixture is then ultrasonically treated at 14-17℃ for 25-30min. Finally, polyethylene glycol 1000 is added to obtain the suspension.

2. The method for improving the in-plane thermal conductivity of C / C composite materials according to claim 1, characterized in that, The steps for treating carbon nanotubes with silane are as follows: Carbon nanotubes are placed in an acid solution, the temperature is raised to 60-64℃, and the mixture is stirred at 320-360 rpm for 30-40 minutes. Then, ultrasonic dispersion is performed for 3.0-3.5 hours, with an ultrasonic power of 100-110 W and an ultrasonic frequency of 40-45 kHz. After ultrasonic dispersion, the nanotubes are filtered, washed, and dried to obtain acid-treated carbon nanotubes. The acid-treated carbon nanotubes are then placed in an ethanol solution, and kH560 silane coupling agent is added. The solution is kept at 68-72℃ for 3.5-4.0 hours, and then filtered, washed, and dried to obtain silane-treated carbon nanotubes. The carbon nanotubes have a diameter of 8-12 nm and a length of 15-20 μm; The acid solution is a mixture of concentrated sulfuric acid and concentrated nitric acid, and the volume ratio of the concentrated nitric acid solution to the concentrated sulfuric acid solution is 1:3-4. The concentrated nitric acid solution has a mass concentration of 48-52%, and the concentrated sulfuric acid solution has a mass concentration of 70-75%. The mass ratio of the carbon nanotubes to the acid solution is 10:70-80; The mass ratio of the acid-treated carbon nanotubes, ethanol solution, and silane coupling agent is 10:80-90:1.0-1.

2. The ethanol solution has a mass concentration of 50-55%.

3. The method for improving the in-plane thermal conductivity of C / C composite materials according to claim 1, characterized in that, The asphalt pretreatment step is as follows: heat 70# base asphalt to 150-160℃ to melt, add maleic anhydride and benzoyl peroxide, stir and react at 400-500 rpm for 4-5 hours to obtain maleic anhydride modified asphalt. The mass ratio of the base bitumen, maleic anhydride, and benzoyl peroxide is 100:3.5:0.5-1.

0.

4. The method for improving the in-plane thermal conductivity of C / C composite materials according to claim 1, characterized in that, In the slurry forming step, the particle size of the graphite powder is 3-5 μm; In the mixture, the mass ratio of maleic anhydride modified asphalt, anhydrous ethanol, silane modified carbon nanotubes and graphite powder is 15-20:50:6-10:25-30. The mass ratio of anhydrous ethanol, tetraethyl orthosilicate, methyltriethoxysilane, and the mixture is 25-30:10-12:0.8-1.0:140-150. The mass concentration of the hydrochloric acid solution is 5-6%.

5. A method for improving the in-plane thermal conductivity of C / C composite materials according to claim 1, characterized in that, The steps for preparing the carbon fiber mesh preform are as follows: the carbon fiber mesh is placed in an impregnation slurry and ultrasonically impregnated at an impregnation temperature of 48-52℃, an ultrasonic power of 140-160W, and an impregnation time of 1.8-2.2h to obtain the carbon fiber mesh preform. In the carbon fiber mesh, the carbon fiber has a thermal conductivity of 800-810 W / m·K, a tensile strength of 3.0-3.2 GPa, an elastic modulus of 840-860 GPa, and a mesh areal density of 78-83 g / m². 2 The thickness is 0.8-1.2mm; The mass ratio of the carbon fiber mesh to the impregnation slurry is 10:56-83.

6. The method for improving the in-plane thermal conductivity of C / C composite materials according to claim 1, characterized in that, The steps for preparing the low-density carbon / carbon composite preform are as follows: carbon fiber plain weave fabric is laminated with a carbon fiber mesh preform to obtain a sizing-containing carbon fiber fabric with a thickness of 18-20 mm; the sizing-containing carbon fiber fabric is then needle-punched, with the needle-punching density controlled at 200-220 needles / cm². 2 The needle-punching depth is 10-13 mm to obtain a needle-punched fabric containing sizing agent. Then, it is dried at 80-90℃ for 5.8-6.2 h, cured at 400-600℃ for 30-36 h, and carbonized at 890-910℃ for 2.0-2.2 h to obtain a low-density carbon / carbon composite preform. The carbon fiber plain weave fabric is made of T700 grade PAN-based carbon fiber, with a thickness of 0.15-0.20 mm and an areal density of 200-300 g / m³. 2 ; The density of the low-density carbon / carbon composite preform is 0.92-1.10 g / cm³. 3 .

7. A method for improving the in-plane thermal conductivity of C / C composite materials according to claim 1, characterized in that, In the step of preparing the suspension, the mass ratio of carbon black, deionized water, the first addition amount of phenol, the first addition amount of formaldehyde solution, the second addition amount of phenol, the second addition amount of formaldehyde solution, anhydrous ethanol, and polyethylene glycol 1000 is 7.5-8.0:100:14.0-14.5:18.5-19.0:4.0-4.3:4.8-5.2:180-200:0.20-0.22; The carbon black has a particle size of 50-80 nm; The mass concentration of the ammonia solution is 1.0-2.0%; The formaldehyde solution has a mass concentration of 37-40%.

8. A method for improving the in-plane thermal conductivity of C / C composite materials according to claim 1, characterized in that, The filling step involves immersing a low-density carbon / carbon composite preform in a suspension of 6-8 times its mass, impregnating it under pressure at 1-5 MPa for 5.8-6.3 hours, then heating it at 80-90°C for 10-12 hours, curing it at 400-600°C for 30-36 hours, and carbonizing it at 890-910°C for 2.0-2.2 hours. This process constitutes one filling step, and the process is repeated twice to obtain a filled carbon / carbon composite preform.

9. A method for improving the in-plane thermal conductivity of C / C composite materials according to claim 1, characterized in that, The carbon / carbon composite preform is placed in a suspension of 6-8 times its mass and impregnated under pressure of 4.8-5.2 MPa for 5.8-6.3 hours, with the heating temperature controlled at 80-90℃ for 10-12 hours. It is then cured at 400-600℃ for 30-36 hours, followed by carbonization at 890-910℃ for 2.0-2.2 hours. The preform is then placed in a suspension of 6-8 times its mass again and impregnated under pressure of 3.8-4.2 MPa for 5.8-6.3 hours, with the heating temperature controlled at 80-90℃ for 10-12 hours. Finally, it is cured at 400-600℃ for 30-36 hours. Curing at 0℃ for 30-36 hours, carbonizing at 890-910℃ for 2.0-2.2 hours, and then cooling are followed by pressure impregnation in 6-8 times their weight of suspension at 4.8-5.2 MPa for 5.8-6.3 hours. Heating is then carried out at 80-90℃ for 10-12 hours, followed by curing at 400-600℃ for 30-36 hours, carbonizing at 890-910℃ for 2.0-2.2 hours, and finally high-temperature heat treatment at 1500-1800℃ for 2.0 hours. After natural cooling to room temperature, a density of 1.80-1.85 g / cm³ is obtained. 3 High-density carbon / carbon composite materials.

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