Highly thermally conductive unidirectional carbon / carbon composite material and method for manufacturing the same

Abstract

The application discloses a kind of high thermal conductivity unidirectional carbon / carbon composite material and preparation method thereof, carbon fiber bundle is spread, carbon fiber bundle is flat, and flat carbon fiber bundle is obtained;Flat carbon fiber bundle is arranged in parallel, and weaving is carried out, and carbon fiber cloth is obtained;Pyrolytic carbon is deposited to carbon fiber cloth;The carbon fiber cloth of pyrolytic carbon deposition is pre-graphitized;Pre-graphitized carbon fiber cloth of preset layer number is laminated, and preform is obtained;Flat carbon fiber bundle is arranged in imitation bricklaying structure;Preform is clamped along the thickness direction, and pyrolytic carbon is deposited to preform densification, then graphitization treatment is carried out, and high thermal conductivity unidirectional carbon / carbon composite material is obtained.The structure and arrangement mode of fiber bundle and unidirectional fiber cloth are controlled and designed, cross-scale structure design on micro-mesoscopic-macro scale is realized, and unidirectional C / C composite material with high thermal conductivity, high bearing and ultra-light is obtained.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of carbon / carbon composite material preparation, and particularly relates to a high-thermal-conductivity unidirectional carbon / carbon composite material and a preparation method thereof. BACKGROUND

[0002] Carbon / carbon (C / C) composite material is an important candidate material for the thermal protection system of a spacecraft due to its low density, high specific strength, low thermal expansion coefficient and excellent high-temperature mechanical properties. However, the aerodynamic heating of the spacecraft is severe, and a large amount of heat is accumulated on the surface of the material, which easily causes the material to be damaged too fast and fail. Therefore, improving the thermal conductivity of the material used in the thermal protection system and reducing the surface temperature and thermal gradient of the material are considered as one of the effective means to improve the structural stability and service life of the material. The use of mesophase pitch-based carbon fiber with high thermal conductivity as a reinforcing material can significantly improve the thermal conductivity of the C / C composite material.

[0003] At present, researchers have carried out a large number of explorations in the design and preparation of high-thermal-conductivity C / C composite materials. Among them, unidirectional high-thermal-conductivity C / C composite material has a very high thermal conductivity along the axial direction of the fiber, and can fully exert its directional high-thermal-conductivity capacity and is therefore concerned. Snead et al. (Snead L L, Burchell T D. Thermal conductivity degradation of graphites due to neutron irradiation at low temperature [J]. Journal of Nuclear Materials, 1995, 224(3): 222-229) prepared unidirectional high-thermal-conductivity C / C composite material by using chemical vapor infiltration and pitch impregnation, and the room-temperature thermal conductivity can reach 746 W·m -1 ·K -1 ; Fan Zhen et al. (Fan Zhen, Yu Lijiong, Li Wei, et al. Design and preparation of high-thermal-conductivity C / C composite material [J]. China Materials Progress, 2017, 36(5): 369-376) prepared unidirectional high-thermal-conductivity C / C composite material by using a process combining hot pressing molding, high-pressure liquid-phase impregnation densification and high-temperature graphitization, and the room-temperature thermal conductivity can reach 740 W·m -1 ·K -1However, it can be found that the unidirectional high-thermal-conductivity C / C composite material is difficult to densify and prone to closed pores due to the large-size pore structure in the fiber bundle used in the preform, and the large-size structure between the fiber bundles is mainly filled with pyrolytic carbon, which leads to the mechanical properties of the composite material along the radial direction of the fiber bundle being obviously insufficient. Therefore, it is an urgent problem to be solved to design the structure of the high-thermal-conductivity unidirectional preform to improve the densification efficiency and strengthen the mechanical properties. SUMMARY

[0004] To solve the problems in the prior art, the purpose of the present application is to provide a high-thermal-conductivity unidirectional carbon / carbon composite material and a preparation method thereof, which realizes the cross-scale structure design on the micro-meso-macro scale by regulating and designing the structure and arrangement mode of the fiber bundle and the unidirectional fiber cloth, and obtains a unidirectional C / C composite material with high thermal conductivity, high bearing capacity and ultra-light quality.

[0005] The technical scheme adopted by the present application is as follows:

[0006] A preparation method of a high-thermal-conductivity unidirectional carbon / carbon composite material, comprising the following processes:

[0007] The carbon fiber bundle is spread to make the carbon fiber bundle flat, and a flat carbon fiber bundle is obtained;

[0008] The flat carbon fiber bundles are arranged in parallel and woven to obtain a carbon fiber cloth;

[0009] The carbon fiber cloth is pre-deposited with pyrolytic carbon;

[0010] The carbon fiber cloth pre-deposited with pyrolytic carbon is subjected to a pre-graphitization treatment;

[0011] The carbon fiber cloth subjected to the pre-graphitization treatment is stacked in a predetermined number of layers to obtain a preform; for the adjacent two layers of carbon fiber cloth, the junctions of the adjacent flat carbon fiber bundles in one layer of carbon fiber cloth and the junctions of the adjacent flat carbon fiber bundles in the other layer of carbon fiber cloth are staggered with each other;

[0012] The preform is clamped along the thickness direction, and the preform is densified by depositing pyrolytic carbon, and then subjected to a graphitization treatment to obtain the high-thermal-conductivity unidirectional carbon / carbon composite material.

[0013] Preferably, the number of carbon fiber bundles is 2k.

[0014] Preferably, the width of the flat carbon fiber bundle is 7-9mm, and the height is 0.15-0.25mm.

[0015] Preferably, the width of the carbon fiber cloth is 12-14 cm, and the height is 0.15-0.25 mm.

[0016] Preferably, when depositing pyrolytic carbon on the carbon fiber cloth, the pyrolytic carbon is deposited by using a low-pressure chemical vapor infiltration process, the deposition temperature is 1000-1100℃, the pressure is 2-5 kPa, the flow rate of natural gas is 15-18 L / min, and the deposition time is 30-50 min.

[0017] Preferably, when pre-graphitizing the carbon fiber cloth on which the pyrolytic carbon is deposited, the carbon fiber cloth on which the pyrolytic carbon is deposited is kept at 2400-2500℃ for 90-120 min.

[0018] Preferably, when stacking the carbon fiber cloths on which the pyrolytic carbon is deposited and which are pre-graphitized, the total number of the carbon fiber cloths on which the pyrolytic carbon is deposited and which are pre-graphitized is 12-15 layers.

[0019] When clamping the preform along the thickness direction, the clamping force is 50-60 kPa.

[0020] Preferably, when densifying the preform on which the pyrolytic carbon is deposited, the pyrolytic carbon is deposited by using a chemical vapor infiltration process, the deposition temperature is 1000-1100℃, the pressure is 8-15 kPa, the flow rate of natural gas is 15-18 L / min, and the deposition time is 150-180 h.

[0021] The temperature for graphitizing is 2500-2600℃, and the time is 80-100 min.

[0022] Preferably, the carbon fiber bundle is a mesophase pitch-based carbon fiber bundle.

[0023] The application further provides a high-thermal-conductivity unidirectional carbon / carbon composite material, which is prepared by the preparation method of the high-thermal-conductivity unidirectional carbon / carbon composite material.

[0024] The application has the following beneficial effects:

[0025] The carbon fiber bundle is spread in the application, and the carbon fiber bundle is in a flat shape. The flat carbon fiber bundles are arranged in parallel and woven into cloth. The carbon fiber cloth obtained through the above process has high adhesion between the flat carbon fiber bundles and relatively few and relatively uniform pore structures, which is beneficial to the deposition of pyrolytic carbon and enhances the bonding strength between the flat carbon fiber bundles. In the preform, the junctions of adjacent flat carbon fiber bundles in one layer of carbon fiber cloth are staggered with the junctions of adjacent flat carbon fiber bundles in another layer of carbon fiber cloth. This layering method is a kind of wall brick laying type layering structure, which can enhance the interfacial bonding strength between the carbon fibers and the flat carbon fiber bundles. The wall brick laying type layering structure enables each layer of unidirectional fiber cloth to effectively bear load, and the combined action of the two improves the bending resistance of the unidirectional high-thermal-conductivity C / C composite material along the radial direction. In the application, the carbon fiber cloth is pre-deposited with pyrolytic carbon, which can fill the pores between the carbon fiber bundles, which is beneficial to the densification of the preform after subsequent lamination. Pre-graphitizing the carbon fiber cloth with pre-deposited pyrolytic carbon can make the carbon fiber cloth with densified pyrolytic carbon not shrink during subsequent graphitization, and the force generated when the post-deposited pyrolytic carbon shrinks can effectively clamp the carbon fiber bundle, thereby forming a compressive stress interface layer on the side of the carbon fiber bundle between the layers, and improving the overall reinforcing effect of the carbon fiber bundle. In summary, the application controls and designs the structure and arrangement of the carbon fiber bundle and the unidirectional fiber cloth, realizes the cross-scale structure design on the micro-mesoscopic-macroscopic scale, and obtains a unidirectional C / C composite material with high thermal conductivity, high load bearing and ultra-light weight. BRIEF DESCRIPTION OF DRAWINGS

[0026] Figure 1(a) is a schematic diagram of the spreading process used in the embodiment of the application;

[0027] Figure 1(b) is a pore distribution diagram of the composite material prepared before and after the spreading process used in the embodiment of the application;

[0028] Figure 2(a) is a mechanical mechanism diagram of a conventional unidirectional C / C composite material;

[0029] Figure 2(b) is a mechanical strengthening mechanism diagram of the wall brick laying structure in the embodiment of the application;

[0030] Figure 3 Figure 3 is a schematic diagram of the preform clamping in the embodiment of the application;

[0031] Figure 4 Figure 4 is a partial photo of the unidirectional high-thermal-conductivity C / C composite material prepared in Example 1 of the application;

[0032] Figure 5A photograph of the unidirectional high-thermal-conductivity C / C composite material prepared from the unexpanded fiber bundle in Inventive Comparative Example 4.

[0033] In the figure, 1 is a carbon fiber bundle, 2 is a flat carbon fiber bundle, 3 is a carbon fiber cloth, 4 is the junction of adjacent flat carbon fiber bundles, 5 is a preform, and 6 is a graphite jig with holes. DETAILED DESCRIPTION

[0034] The application will be further described below in conjunction with the accompanying drawings and examples.

[0035] The application proposes a structure design and preparation method of a brick-like structure light-weight high-strength high-thermal-conductivity unidirectional C / C composite material, aiming to realize cross-scale structure design on micro-meso-macro scales by regulating pyrolytic carbon, carbon fiber bundles, fiber cloths, and the size and arrangement of the fiber cloths, and finally prepare high-thermal-conductivity high-load-bearing and ultra-lightweight unidirectional C / C composite materials.

[0036] The preparation method of the high-thermal-conductivity unidirectional carbon / carbon composite material of the application comprises the following steps:

[0037] Step one: design mesophase pitch-based carbon fiber bundles: referring to FIG. 1(a), the 2k mesophase pitch-based carbon fiber bundles are expanded by the fiber expansion process to flatten the “elliptical cylindrical” fiber bundles, and the expansion becomes “flat cuboid-like” fiber bundles, which are used as “bricks” in the brick-like structure of the application. The specific size of the flat carbon fiber bundle is as follows: the width is 7-9 mm, and the height is 0.15-0.25 mm (along the radial direction of the carbon fiber).

[0038] Step two: prepare unidirectional mesophase pitch-based carbon fiber cloth: arrange the flat carbon fiber bundles after expansion along the radial direction of the fiber to weave the cloth, and prepare the unidirectional mesophase pitch-based carbon fiber cloth, referring to FIG. 2(a) and FIG. 2(b). The flat carbon fiber bundles arranged along the horizontal direction form a layer of fiber cloth, and all the fiber bundles in the obtained fiber cloth are parallel, the thickness of the fiber cloth is 0.15-0.25 mm, and the width of the fiber cloth along the radial direction is 12-14 cm.

[0039] Step three: pre-deposit pyrolytic carbon: the prepared mesophase pitch-based carbon fiber cloth is used to deposit pyrolytic carbon by the low-pressure chemical vapor infiltration process. The deposition temperature is 1000-1100℃, the pressure is 2-5kPa, the flow rate of natural gas is 15-18L / min, and the deposition time is 30-50min.

[0040] Step four: pre-graphitization treatment: the fiber cloth after pre-deposition in step three is subjected to heat treatment at 2400-2500℃ for 90-120min.

[0041] Step five: preparation of unidirectional preform: as shown in Figure 2(b), the unidirectional fiber cloth after step four is laid, the displacement of adjacent two layers of fiber cloth in the horizontal direction is 4-5mm, forming a brick-like structure, the total number of layers is 12-15, after laying, a customized graphite clamp with holes is used for clamping ( Figure 3 ), and a bolt is used for pressing and fastening, the clamping force is 50-60kPa.

[0042] Step six: preparation of unidirectional high thermal conductivity carbon / carbon composite material: the prepared unidirectional preform is densified by chemical vapor infiltration process to deposit pyrolytic carbon, which is the "mud layer" in the application. The deposition temperature is 1000-1100℃, the pressure is 8-15kPa, the flow rate of natural gas is 15-18L / min, and the deposition time is 150-180h. Finally, graphitization heat treatment at 2500-2600℃ is carried out, and the graphitization time is 80-100min. After graphitization, the specific characteristics of the unidirectional high thermal conductivity C / C composite material are as follows: the density is 1.85-1.88g / cm 3 , the thickness is 2.0-3.5mm, and the width is 12-14cm.

[0043] In the above scheme of the application, the 2k fiber bundle is spread by the spreading process, and the "elliptical cylindrical" fiber bundle is changed into a "cuboid-like" fiber bundle, as shown in Figure 1(a). Before spreading, the width of the elliptical cylindrical carbon fiber bundle 1 is small, and the fiber bundles are not closely attached to each other, showing a tangent state, and there is a large pore structure, making the densification process difficult, as shown in Figure 1(b). In addition, the large-size structure between the fiber bundles lacks carbon fiber reinforcement, which is mainly filled with pyrolytic carbon, resulting in that the mechanical properties between the fiber bundles are mainly dominated by pyrolytic carbon. The combination of the two factors causes the problem of obvious strength deficiency of the composite material in the direction between the fiber bundles. After spreading, each cuboid-like flat carbon fiber bundle 1-1 can be compared to a brick, and the bricks are closely attached to each other, and the pore distribution is relatively uniform, which is beneficial to the deposition of pyrolytic carbon and enhances the bonding strength between the fiber bundles, as shown in Figure 1(b).

[0044] In the above scheme of the application, the width of the fiber cloth along the radial direction is 12-14cm, which limits the width of the unidirectional carbon fiber cloth, avoids the generation of large thermal stress due to the mismatch of the thermal expansion coefficient during the deposition process, and thus causes cracks between the fiber bundles and interlaminar delamination between the fiber cloths.

[0045] ​In the above scheme of the present application, the unidirectional fiber cloth is pre-deposited with high-texture pyrolytic carbon before the preparation of the preform, which mainly plays a role of pre-densification and shaping: firstly, the high-texture pyrolytic carbon is pre-deposited between the fibers and the fiber bundles by using a low-pressure chemical vapor infiltration process, so as to prevent the problem of difficult deposition between the fibers or the fiber bundles in the subsequent overall densification process; secondly, the shape of each fiber bundle after the fiber spreading is maintained, the interface bonding between the fiber bundles is increased, and the compression force generated during the clamping of the graphite clamp does not break the shape and structure of the "brick", thereby affecting the strength.

[0046] In the above scheme of the present application, the unidirectional fiber cloth pre-deposited with pyrolytic carbon is subjected to a pre-graphitization heat treatment at 2400-2500 DEG C before the preparation of the preform. The pre-graphitization can make the structure in the fiber bundle not shrink after the densification of the composite material, and the force generated when the post-deposited pyrolytic carbon, i.e. the "mud layer between the bricks", shrinks can effectively clamp the brick layer, thereby forming an interface layer on the side close to the fiber bundle between the layers and improving the overall reinforcing effect of the fiber bundle. During the preparation of the preform, the distance between the fiber cloth layers is controlled by controlling the fastening force. If the fastening force is too strong, the distance between the fiber cloths is too short, the volume of the deposited pyrolytic carbon is limited, i.e. the "mud layer" is weak; if the fastening force is too weak, the distance between the fiber cloths is too large, the volume of the deposited pyrolytic carbon is too large, i.e. the "mud layer" is too strong, and the "brick layer" cannot effectively bear the load.

[0047] In the above scheme of the present application, as shown in FIG. 2(b), the fiber cloth of the present application is laid in a wall brick-like structure, which can effectively improve the mechanical properties. As shown in FIG. 2(a), when the fiber cloth is laid in a parallel alternating manner to prepare a composite material, the crack rapidly expands along the interface, so that the material rapidly breaks and fails. As shown in FIG. 2(b), when the fiber cloth is laid in a wall brick-like structure to prepare a composite material, the crack deflects after expanding along the interface, the crack propagation path is increased, and the mechanical properties of the composite material are improved.

[0048] In the above scheme of the present application, the fiber spreading design makes the fibers and the fibers between the fibers be arranged in the radial direction of the fibers, and the interface bonding strength between the fibers and the fiber bundles is enhanced; the wall brick-like laying structure makes each layer of unidirectional fiber cloth be able to effectively bear the load, and the bending resistance of the unidirectional high-thermal-conductivity C / C composite material in the radial direction is improved under the combined action of the two.

[0049] In the above scheme of the present application, the densified unidirectional high-thermal-conductivity C / C composite material is subjected to a heat treatment at 2500-2600 DEG C, which improves the overall thermal conductivity of the composite material and avoids the significant decrease of the strength of the composite material due to the excessively high heat treatment temperature.

[0050] Example 1:

[0051] The preparation method of the high-thermal-conductivity unidirectional carbon / carbon composite material of the embodiment comprises the following steps:

[0052] (1) The 2k carbonized mesophase pitch-based carbon fiber bundle is subjected to a fiber spreading process to spread the fiber bundle from an elliptical cylindrical shape into a cuboid shape. The specific size of the cuboid-shaped fiber bundle is: a width of 8 mm and a height of 0.20 mm (along the radial direction of the carbon fiber).

[0053] (2) The fiber bundle after the spreading is arranged along the radial direction of the fiber to prepare a mesophase pitch-based carbon fiber cloth. The width of the fiber cloth along the radial direction is 12 cm, and the thickness is 0.20 mm.

[0054] (3) The prepared mesophase pitch-based carbon fiber cloth is pre-deposited with pyrolytic carbon by using a chemical vapor infiltration process. The deposition temperature is 1000℃, the pressure is 2kPa, the flow rate of natural gas is 15L / min, and the deposition time is 30min.

[0055] (4) Pre-graphitization treatment: the fiber cloth after the pre-deposition in step three is subjected to heat treatment at 2400℃ for 90min.

[0056] (5) The unidirectional fiber cloth after the pre-graphitization treatment is subjected to an alternative layering as shown in FIG. 2(b). The displacement of the adjacent two layers of fiber cloth in the horizontal direction is 4mm. The total number of layers is 12. After the layering, a customized graphite clamp with holes is used for clamping, and a bolt is used for compression and fastening. The clamping force is 50kPa.

[0057] (6) The prepared unidirectional preform is densified by using a chemical vapor process. The deposition temperature is 1000℃, the pressure is 8kPa, the flow rate of natural gas is 15L / min, and the deposition time is 150h. Finally, graphitization heat treatment is performed at 2600℃ for 80min.

[0058] It is detected that the high-thermal-conductivity unidirectional carbon / carbon composite material obtained in the embodiment has a density of 1.85g / cm 3 , a thickness of 2.7mm, and a width of 12cm. The thermal conductivity along the fiber axis is 750W·m -1 ·K -1 , the inter-bundle (radial) bending strength is 18MPa, the inter-bundle (radial) tensile strength is 10MPa, the axial bending strength is 500MPa, and the axial tensile strength is 700MPa.

[0059] Embodiment 2:

[0060] The preparation method of the high-thermal-conductivity unidirectional carbon / carbon composite material of the embodiment comprises the following steps:

[0061] (1) The 2k mesophase pitch-based carbon fiber bundle was drawn by a drawing process, and the elliptical cylindrical fiber bundle was drawn into a cuboid-like fiber bundle. The specific size of the cuboid-like fiber bundle was 9 mm in width and 0.15 mm in height (along the radial direction of the carbon fiber).

[0062] (2) The fiber bundle after drawing was arranged along the radial direction of the fiber to prepare a mesophase pitch-based carbon fiber cloth. The width of the fiber cloth along the radial direction was 14 cm, and the thickness was 0.15 mm.

[0063] (3) The prepared mesophase pitch-based carbon fiber cloth was pre-deposited with pyrolytic carbon by a chemical vapor infiltration process. The deposition temperature was 1050°C, the pressure was 5kPa, the flow rate of natural gas was 16L / min, and the deposition time was 50min.

[0064] (4) Pre-graphitization treatment: the fiber cloth after pre-deposition in step three was heat treated at 2500°C for 120min.

[0065] (5) The unidirectional fiber cloth after pre-graphitization treatment was alternately laid as shown in Figure 2(b). The displacement of the adjacent two layers of fiber cloth in the horizontal direction was 5mm, the total number of layers was 15, and after laying, a customized graphite clamp with holes was used for clamping, and a bolt was used for compression and fastening. The clamping force was 60kPa.

[0066] (6) The prepared unidirectional preform was densified by a chemical vapor process, the deposition temperature was 1050°C, the pressure was 15kPa, the flow rate of natural gas was 18L / min, and the deposition time was 180h. Finally, a graphitization heat treatment was carried out at 2500°C for 100min.

[0067] It was detected that the unidirectional high thermal conductivity carbon / carbon composite material obtained in the embodiment had a density of 1.88g / cm 3 , a thickness of 2.6mm, and a width of 14cm. The thermal conductivity along the fiber axis was 700W·m -1 ·K -1 , the inter-bundle (radial) bending strength was 16MPa, the inter-bundle (radial) tensile strength was 8MPa, the axial bending strength was 400MPa, and the axial tensile strength was 500MPa.

[0068] Example 3:

[0069] The preparation method of the high thermal conductivity unidirectional carbon / carbon composite material of the embodiment comprises the following steps:

[0070] (1) The carbonized mesophase pitch-based carbon fiber bundle of 2k is subjected to a fiber spreading process to spread the fiber bundle from an elliptical cylindrical shape into a cuboid shape. The cuboid-shaped fiber bundle has a width of 7 mm and a height of 0.25 mm (in the radial direction of the carbon fiber).

[0071] (2) The fiber bundle of 2k after the spreading process is arranged in the radial direction of the fiber to prepare a mesophase pitch-based carbon fiber cloth. The fiber cloth has a width of 13 cm in the radial direction and a thickness of 0.25 mm.

[0072] (3) The prepared mesophase pitch-based carbon fiber cloth is subjected to a chemical vapor infiltration process to pre-deposit pyrolytic carbon. The deposition temperature is 1100°C, the pressure is 4 kPa, the flow rate of natural gas is 18 L / min, and the deposition time is 40 min.

[0073] (4) Pre-graphitization treatment: the fiber cloth after pre-deposition in step three is subjected to heat treatment at 2450°C for 100 min.

[0074] (5) The unidirectional fiber cloth after the pre-graphitization treatment is subjected to an alternating layering as shown in FIG. 2(b). The displacement of the adjacent two layers of fiber cloth in the horizontal direction is 4.5 mm. The total number of layers is 13. After the layering, a customized graphite clamp with holes is used for clamping, and a bolt is used for compression and fastening. The clamping force is 55 kPa.

[0075] (6) The prepared unidirectional preform is subjected to densification by a chemical vapor process. The deposition temperature is 1100°C, the pressure is 10 kPa, the flow rate of natural gas is 13 L / min, and the deposition time is 170 h. Finally, a graphitization heat treatment is performed at 2550°C for 90 min.

[0076] It is detected that the unidirectional high-thermal-conductivity carbon / carbon composite material obtained in the embodiment has a density of 1.88 g / cm 3 , a thickness of 3.5 mm, and a width of 13 cm. The thermal conductivity in the fiber axial direction is 730 W·m -1 ·K -1 , the inter-bundle (radial) bending strength is 17 MPa, the inter-bundle (radial) tensile strength is 9 MPa, the axial bending strength is 450 MPa, and the axial tensile strength is 600 MPa.

[0077] As can be seen from the results of the above embodiment, after the preform structure is optimized and designed, it is beneficial to use a chemical vapor infiltration process to deposit pyrolytic carbon, so that the density of the unidirectional high-thermal-conductivity C / C composite material reaches 1.85-1.88 g / cm 3 , and the thermal conductivity in the fiber axial direction is 700-750 W·m -1 ·K -1, the inter-bundle (radial) bending strength is 16-18 MPa, the inter-bundle (radial) tensile strength is 8-10 MPa, the axial bending strength is 400-500 MPa, and the axial tensile strength is 500-700 MPa, realizing the preparation of the unidirectional C / C composite material with high thermal conductivity, high bearing capacity and ultra-light quality.

[0078] Comparative Example 1

[0079] The comparative example includes the following steps:

[0080] (1) The 2k mesophase pitch-based carbon fiber bundle is subjected to a fiber spreading process to spread the elliptical cylindrical fiber bundle into a cuboid-shaped fiber bundle. The specific size of the cuboid-shaped fiber bundle is: the width is 8 mm, and the height is 0.20 mm (along the radial direction of the carbon fiber).

[0081] (2) The fiber bundle after the spreading is arranged along the radial direction of the fiber to prepare a mesophase pitch-based carbon fiber cloth. The width of the fiber cloth along the radial direction is 12 cm, and the thickness is 0.20 mm.

[0082] (3) The prepared mesophase pitch-based carbon fiber cloth is pre-deposited with pyrolytic carbon by a chemical vapor infiltration process. The deposition temperature is 1000°C, the pressure is 2kPa, the flow rate of natural gas is 15L / min, and the deposition time is 30min.

[0083] (4) The unidirectional fiber cloth pre-deposited with pyrolytic carbon is subjected to an alternating type of lamination as shown in FIG. 2(b). The displacement of the adjacent two layers of fiber cloth in the horizontal direction is 4mm, the total number of layers is 12, and after lamination, a customized graphite clamp with holes is used for clamping, and a bolt is used for compression and fastening. The fastening force is 30kPa.

[0084] (5) The prepared unidirectional preform is densified by a chemical vapor process. The deposition temperature is 1000°C, the pressure is 8kPa, the flow rate of natural gas is 15L / min, and the deposition time is 150h. Finally, a graphitization heat treatment at 2600°C is performed, and the heat treatment time is 80min.

[0085] The unidirectional high-thermal-conductivity carbon / carbon composite material obtained in the comparative example has a density of 1.80g / cm 3 , and a thickness of 2.9mm. The thermal conductivity along the fiber bundle axial direction is 620W·m -1 ·K -1 , the inter-bundle (radial) bending strength is 12MPa, the inter-bundle (radial) tensile strength is 6MPa, the axial bending strength is 350MPa, and the axial tensile strength is 443MPa.

[0086] Compared with Example 1, the pre-deposited pre-graphitization heat treatment is not performed in this comparative example, and the fastening force is too small and the distance between the fiber cloths is too large, thus resulting in a large porosity and a reduced strength.

[0087] Comparative Example 2:

[0088] This comparative example includes the following steps:

[0089] (1) The 2k carbonized mesophase pitch-based carbon fiber bundle is subjected to a fiber spreading process to spread the elliptical cylindrical fiber bundle into a cuboid-shaped fiber bundle, and the specific size of the cuboid-shaped fiber bundle is: a width of 8 mm and a height of 0.20 mm (along the radial direction of the carbon fiber).

[0090] (2) The 2k fiber bundle after the spreading is arranged along the radial direction of the fiber to prepare a mesophase pitch-based carbon fiber cloth, and the width of the fiber cloth along the radial direction is 18 cm and the thickness is 0.20 mm.

[0091] (3) The prepared mesophase pitch-based carbon fiber cloth is pre-deposited with pyrolytic carbon by a chemical vapor infiltration process. The deposition temperature is 1000°C, the pressure is 2kPa, the flow rate of natural gas is 15L / min, and the deposition time is 30min.

[0092] (4) Pre-graphitization treatment: the fiber cloth after pre-deposition in step three is subjected to a heat treatment at 2400°C for 90min.

[0093] (5) The unidirectional fiber cloth after the pre-graphitization treatment is subjected to an alternating layering as shown in FIG. 2(b), the displacement of the adjacent two layers of fiber cloths in the horizontal direction is 4mm, the total layering number is 12 layers, and after the layering, a customized hole graphite clamp is used for clamping and a bolt is used for compression and fastening, and the clamping force is 50kPa.

[0094] (5) The prepared unidirectional preform is densified by a chemical vapor process, the deposition temperature is 1000°C, the pressure is 8kPa, the flow rate of natural gas is 15L / min, and the deposition time is 150h. Finally, a graphitization heat treatment at 2600°C is performed for 80min.

[0095] The unidirectional high-thermal-conductivity carbon / carbon composite material obtained in this comparative example has a density of 1.83g / cm 3 , a thickness of 2.7mm, and a width of 18cm. The thermal conductivity along the fiber axis is 700W·m -1 ·K -1 , the inter-bundle (radial) bending strength is 10MPa, the inter-bundle (radial) tensile strength is 5MPa, the axial bending strength is 320MPa, and the axial tensile strength is 440MPa.

[0096] Compared with Example 1, the fiber cloth used in this comparative example has a larger width, and the prepared composite material has a large width, so that obvious cracks and other defects can be seen on the surface of the composite material, thereby leading to a decrease in performance.

[0097] Comparative Example 3

[0098] This comparative example includes the following steps:

[0099] (1) The 2k carbonized mesophase pitch-based carbon fiber bundle was subjected to a fiber spreading process to spread the elliptical cylindrical fiber bundle into a cuboid-shaped fiber bundle. The specific size of the cuboid-shaped fiber bundle was 8 mm in width and 0.20 mm in height (along the radial direction of the carbon fiber).

[0100] (2) The fiber bundle after spreading was arranged along the radial direction of the fiber to prepare a mesophase pitch-based carbon fiber cloth. The width of the fiber cloth along the radial direction was 12 cm, and the thickness was 0.20 mm.

[0101] (3) The prepared mesophase pitch-based carbon fiber cloth was pre-deposited with pyrolytic carbon using a chemical vapor infiltration process. The deposition temperature was 1000°C, the pressure was 2kPa, the flow rate of natural gas was 15L / min, and the deposition time was 30min.

[0102] (4) Pre-graphitization treatment: the fiber cloth after pre-deposition in step three was subjected to heat treatment at 2400°C for 90min.

[0103] (5) The unidirectional fiber cloth after pre-graphitization treatment was subjected to parallel alternating layering as shown in FIG. 2(a). The total number of layers was 12. After layering, a customized graphite clamp with holes was used for clamping, and a bolt was used for compression and fastening. The clamping force was 50kPa.

[0104] (5) The prepared unidirectional preform was densified using a chemical vapor process. The deposition temperature was 1000°C, the pressure was 8kPa, the flow rate of natural gas was 15L / min, and the deposition time was 150h. Finally, graphitization heat treatment was performed at 2600°C for 80min.

[0105] The unidirectional high-thermal-conductivity carbon / carbon composite material obtained in this comparative example had a density of 1.85g / cm 3 , a thickness of 2.7mm, and a width of 12cm. The thermal conductivity along the fiber axis was 740W·m -1 ·K -1 , the inter-bundle (radial) bending strength was 8MPa, the inter-bundle (radial) tensile strength was 4MPa, the axial bending strength was 380MPa, and the axial tensile strength was 490MPa.

[0106] Compared with Example 1, this comparative example does not use brick structure for laying, resulting in a significant decrease in the strength between the composite bundles.

[0107] Comparative Example 4:

[0108] This comparative example includes the following steps:

[0109] (1) The 2k fiber bundles without spreading were arranged along the radial direction of the fibers to prepare mesophase pitch-based carbon fiber cloth, and the width of the fiber cloth along the radial direction was 12 cm.

[0110] (2) The prepared mesophase pitch-based carbon fiber cloth was pre-deposited with pyrolytic carbon using a chemical vapor infiltration process. The deposition temperature was 1000°C, the pressure was 2kPa, the flow rate of natural gas was 15L / min, and the deposition time was 30min.

[0111] (4) Pre-graphitization treatment: the fiber cloth after pre-deposition in step three was heat treated at 2400°C for 90min.

[0112] (5) The unidirectional fiber cloth pre-deposited with pyrolytic carbon was alternately laid as shown in Figure 2(b), the displacement of adjacent two layers of fiber cloth in the horizontal direction was 4mm, the total number of layers was 12, after laying, a customized graphite clamp with holes was used for clamping, and a bolt was used for compression and fastening, the clamping force was 50kPa.

[0113] (6) The prepared unidirectional preform was densified using a chemical vapor process, the deposition temperature was 1000°C, the pressure was 8kPa, the flow rate of natural gas was 15L / min, and the deposition time was 150h. Finally, a graphitization heat treatment was carried out at 2600°C for 80min.

[0114] The unidirectional high-thermal-conductivity carbon / carbon composite material obtained in this comparative example has a density of 1.78g / cm 3 , a thickness of 3.3mm, and a width of 12cm. The thermal conductivity along the fiber axis is 700W·m -1 ·K -1 , the inter-bundle (radial) bending strength is 10MPa, the inter-bundle (radial) tensile strength is 5MPa, the axial bending strength is 430MPa, and the axial tensile strength is 610MPa.

[0115] Compared with Example 1, Figure 4 this comparative example does not spread the fiber bundles used, and Figure 5 therefore, after densification, there are large grooves on the surface, which reduces the density and strength of the composite material.

Claims

1. A method for preparing a high thermal conductivity unidirectional carbon / carbon composite material, characterized in that, The process includes the following: The carbon fiber bundle is spread into a flat shape to obtain a flat carbon fiber bundle. Flat carbon fiber bundles are arranged in parallel and woven into a fabric to obtain carbon fiber cloth; the width of the carbon fiber cloth is 12-14cm and the height is 0.15-0.25mm. Pyrolytic carbon is pre-deposited onto the carbon fiber cloth; The carbon fiber cloth with pre-deposited pyrolytic carbon is pre-graphitized. A pre-graphitized carbon fiber cloth of a predetermined number of layers is stacked to obtain a preform; in the preform, for two adjacent layers of carbon fiber cloth, the boundary of adjacent flat carbon fiber bundles in one layer of carbon fiber cloth is staggered from the boundary of adjacent flat carbon fiber bundles in the other layer of carbon fiber cloth. The preform is clamped along its thickness direction, and pyrolytic carbon is deposited on the preform to densify it. Then, graphitization is performed to obtain the high thermal conductivity unidirectional carbon / carbon composite material.

2. The method for preparing a high thermal conductivity unidirectional carbon / carbon composite material according to claim 1, characterized in that, The carbon fiber bundles used are 2 k carbon fiber bundles.

3. The method for preparing a high thermal conductivity unidirectional carbon / carbon composite material according to claim 1, characterized in that, The flat carbon fiber bundle has a width of 7-9 mm and a height of 0.15-0.25 mm.

4. The method for preparing a high thermal conductivity unidirectional carbon / carbon composite material according to claim 1, characterized in that, When depositing pyrolytic carbon on carbon fiber cloth, a low-pressure chemical vapor infiltration process is used to deposit the pyrolytic carbon. The deposition temperature is 1000-1100℃, the pressure is 2-5kPa, the natural gas flow rate is 15-18L / min, and the deposition time is 30-50min.

5. The method for preparing a high thermal conductivity unidirectional carbon / carbon composite material according to claim 1, characterized in that, When pre-graphitizing carbon fiber cloth with deposited pyrolytic carbon, the carbon fiber cloth with deposited pyrolytic carbon is kept at 2400-2500℃ for 90-120 minutes.

6. The method for preparing a high thermal conductivity unidirectional carbon / carbon composite material according to claim 1, characterized in that, When stacking pre-graphitized carbon fiber cloth with a preset number of layers, the total number of pre-graphitized carbon fiber cloth layers is 12-15. When the preform is clamped along the thickness direction, the clamping force is 50-60 kPa.

7. The method for preparing a high thermal conductivity unidirectional carbon / carbon composite material according to claim 1, characterized in that, When densifying the preform by depositing pyrolytic carbon, a chemical vapor infiltration process is used to deposit pyrolytic carbon for densification. The deposition temperature is 1000-1100℃, the pressure is 8-15kPa, the natural gas flow rate is 15-18L / min, and the deposition time is 150-180h. The temperature for graphitization is 2500-2600℃, and the time is 80-100 min.

8. The method for preparing a high thermal conductivity unidirectional carbon / carbon composite material according to claim 1, characterized in that, The carbon fiber bundles are mesophase pitch-based carbon fiber bundles.

9. A high thermal conductivity unidirectional carbon / carbon composite material, characterized in that, The high thermal conductivity unidirectional carbon / carbon composite material is prepared by the preparation method of the high thermal conductivity unidirectional carbon / carbon composite material according to any one of claims 1-8.

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