A high-density, high-strength three-layer carbon-based composite material and its preparation method

Abstract

This invention discloses a high-density, high-strength "three-layer structure" carbon-based composite material and its preparation method. The method includes: mixing activated coke with a D50 of 3-6 μm and microcrystalline graphite powder with a D50 of 10-60 μm to obtain a mixed powder; kneading the mixed powder in a kneading pan, removing moisture, heating to 160-240℃, then adding a molten binder or modified binder, and simultaneously adding a modifier, followed by kneading with the lid closed; after kneading, pouring the mixture into a rolling mill for rolling, then crushing and sieving to obtain pressed powder; vacuum-treating the pressed powder, then molding and isostatically pressing to obtain green blocks, and finally calcining to obtain the carbon-based composite material. This invention has a short production cycle and low cost. The carbon-based composite material obtained has a one-layer interface structure, a two-layer brazed structure, and a three-layer steel-concrete structure. The special "three-layer" structure design achieves a dual effect of "reinforced aggregate complementarity + micro-active layer construction," which can effectively improve the bulk density, mechanical strength, homogeneity, and stability of the carbon-based composite material.

Description

Technical Field

[0001] This invention belongs to the field of carbon-based composite material technology, and specifically relates to a high-density, high-strength "three-layer structure" carbon-based composite material and its preparation method. Background Technology

[0002] Carbon-based composite materials possess a series of excellent properties, including isotropy, good lubricity and wear resistance, excellent machinability, low coefficient of thermal expansion, and high chemical stability. They are widely used in semiconductors, nuclear reactors, aerospace sealing, machinery, powder metallurgy, continuous casting steel, bioengineering and other fields.

[0003] Currently, carbon-based composite materials are mainly produced through the following process: using petroleum coke, artificial graphite powder, or calcined pitch coke as aggregates, and coal tar pitch, anthracene oil, or phenolic resin as binders, the process involves grinding, primary kneading, sheet rolling, cooling, preforming, semi-carbonization, crushing, screening, secondary kneading, sheet rolling, cooling, preforming, isostatic pressing, calcination, impregnation, secondary calcination, secondary impregnation, tertiary calcination, and graphitization to prepare high-performance carbon-based composite materials that meet the requirements. However, the aforementioned processes have poor mechanical properties, poor structural homogeneity, long production cycles, high costs, low yields, and the isotropy of the products does not meet expectations. During heat treatment processes such as calcination and graphitization, the poor consolidation effect of the binder leads to the decomposition and overflow of a large amount of volatiles, and the green body is at risk of bulging and cracking during heat treatment. The carbon-based composite block has a large volume shrinkage rate and uneven shrinkage at various locations, resulting in high porosity and poor uniformity of the carbon-based composite material, which in turn reduces its density and mechanical properties.

[0004] Compared to traditional aggregates, activated coke is a novel carbon material with a unique spherical active structure and special properties. It boasts excellent mechanical and thermal properties, large shrinkage, excellent compressibility, good structural stability, high purity, good lubrication and anti-wear properties, isotropy, excellent self-sintering properties, and high added value. It has been widely used in high-tech fields such as solar photovoltaics, metallurgy, chemical industry, nuclear energy, aerospace, mechanical seals, semiconductor industry, and nuclear industry. However, as a typical low-density, high-strength material, activated coke-based aggregates result in low densification of bulk materials. Furthermore, the significant volume shrinkage leads to cracking of the green body during firing, severely hindering the development of larger-sized products and resulting in poor overall performance of the final product. Therefore, it is urgent to optimize the aggregate composition, particle size, and proportion to improve the density and overall performance of the finished product, including flexural and compressive strength. Summary of the Invention

[0005] In view of the above-mentioned shortcomings of the existing technology, the purpose of this invention is to provide a high-density and high-strength "three-layer structure" carbon-based composite material and its preparation method. The present invention has a short production cycle and low cost, and can effectively improve the bulk density, mechanical strength, homogeneity and stability of carbon-based composite materials.

[0006] The technical solution of this invention is implemented as follows:

[0007] A method for preparing a high-density, high-strength "three-layer structure" carbon-based composite material includes the following steps:

[0008] S1: Mix activated coke with a D50 of 3~6 μm and microcrystalline graphite powder with a D50 of 10~60 μm to obtain mixed powder;

[0009] S2: Put the mixed powder into a kneading pot and knead to remove moisture. Then heat it to 160~240 ℃, add molten binder or modified binder, and add modifier at the same time. Then close the lid and knead. After kneading, a paste is obtained.

[0010] S3: Pour the paste into a rolling mill and roll it into sheets. Then crush and sieve the sheets to obtain pressed powder. After vacuum pretreatment, the pressed powder is sealed and stored to maintain the moisture content of the pressed powder. Then, it is molded and isostatically pressed to obtain green blocks. Finally, it is placed in a graphite crucible for calcination to obtain the carbon-based composite material.

[0011] Furthermore, in step S1, the mass ratio of activated coke to microcrystalline graphite powder is 40~80:1~20.

[0012] Furthermore, the modified binder is prepared according to the following steps:

[0013] (1) After crushing the adhesive, pass it through a 50-500 mesh sieve to obtain adhesive powder;

[0014] (2) Add the binder powder to the organic solvent, wherein the mass ratio of the binder powder to the organic solvent is 1~10:30~300; then place it in a constant temperature magnetic stirrer and sonicate at 40~80 ℃ for 30~120 min. After solid-liquid separation, rotary evaporate at 60~100 ℃ under vacuum for 30~60 min to remove the organic solvent in the soluble part and obtain the soluble substance.

[0015] (3) Mix 1 to 5 parts of soluble substance and 20 to 40 parts of binder powder to obtain the modified binder.

[0016] Furthermore, the binder is one or more of phenolic resin, mesophase coal tar pitch, high-temperature coal tar pitch, medium-temperature coal tar pitch, or low-temperature coal tar pitch.

[0017] Further, the organic solvent is one or more of acetone, methyl acetal, tetrahydrofuran, toluene, petroleum ether, dichloromethane, or quinoline.

[0018] Furthermore, the modifier is one or two of coal tar, oleic acid, anthracene oil, and pyrolysis slurry.

[0019] Further, the specific steps of step S2 are as follows: set the kneading temperature to 100~120 ℃, adjust the rotation speed to 1~10 r / min, open the lid and reverse the direction; when the kneading temperature reaches the predetermined temperature, put the mixed powder into the kneading pot, dry mix at 120~160℃ for 20~40 min, adjust the rotation speed to 5~50 r / min, open the lid and rotate in the forward direction; when the temperature of the mixed powder reaches the set temperature, adjust the rotation speed to 20~40 r / min, close the lid and reverse the direction; when the moisture is completely removed, set the kneading temperature to 160~240℃, and put the molten binder or modified binder into the mixed powder, while adding the modifier, adjust the rotation speed to 20~50 r / min, close the lid, wet mix for 0.5~2 h, alternating between forward and reverse rotation, and obtain a paste after kneading.

[0020] Further, the specific steps for preparing the pressed powder from the paste in step S3 are as follows: the paste is poured into a rolling mill and rolled 1 to 5 times, with a rolling thickness of 1 to 5 mm. The rolling temperature is set to 160 to 240 ℃ and the rotation speed is adjusted to 5 to 50 r / min. After rolling, the obtained sheet powder is placed at room temperature to cool for 6 to 12 hours, crushed, and passed through a 100 to 500 mesh sieve. After resting for 6 to 12 hours, the pressed powder is obtained.

[0021] Further, the specific steps for preparing the green block by pressing powder in step S3 are as follows: the pressed powder is subjected to vacuum treatment, and then pre-formed into a green block at 1~10 MPa, wherein the forming temperature is set to 20~200 ℃ and the pressure is held for 1~30 s; then it is allowed to stand for 6~12 h, and then placed in an isostatic press and pressed at 100~200 MPa for 0.5~1 h, with gradient depressurization, and the isostatic pressing-gradient depressurization is repeated 1~3 times before the sample is taken out and allowed to stand for another 6~12 h to obtain a density of 1.45~1.55 g / cm³. 3 The green blank.

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] 1. The present invention uses activated coke with a D50 of 3~6 μm as the main aggregate and microcrystalline graphite powder with a D50 of 10~60 μm as the secondary aggregate. The small particles of activated coke have a larger specific surface area, which coats the surface of the large particles of microcrystalline graphite and fills the gaps between the stacked microcrystalline graphite. Activated coke possesses a unique spherical active structure with high isotropy and excellent pressing performance. It can effectively improve the pore structure of carbon-based composite materials, enhancing their mechanical strength and thermal conductivity. Microcrystalline graphite powder, with its high isotropy, excellent electrical conductivity, and low coefficient of thermal expansion, when combined with activated coke, allows for the simultaneous superposition of isotropy between aggregates, effectively controlling the coefficient of thermal expansion of carbon-based composite materials and preventing cracking. Simultaneously, activated coke's unique spherical structure and weakly acidic, oxygen-rich, low-hydrogen functional group activity promote interfacial bonding, effectively limiting destructive cracks and improving the pore structure of carbon-based composite materials. This results in pores that are mostly independent circular rather than acute-angled, and are not interconnected. The gas within the micropores exhibits a rotational dynamic effect, circulating in a "rolling bearing" manner (the mechanism is shown in the diagram). Figure 13 (As shown) This suppresses the formation of pore channels and cracks when volatiles escape. By effectively combining the two aggregate particle sizes, the thermal synergy of the particles can be controlled, thereby achieving a "synergistic enhancement" of the bulk density and mechanical strength of the calcined block.

[0024] 2. The organic solvent used in this invention is rich in polar molecules and contains a small amount of non-polar hydroxyl groups, which can efficiently dissolve the light components such as β and γ components, as well as oxygen-containing functional groups such as C=O, COO, and CO, and nitrogen-containing functional groups such as CN in the binder. The organic solvent is a low-boiling-point substance, easily removed and recovered through rotary evaporation, avoiding environmental pollution. It also facilitates the improvement of the purity of the light components, oxygen-containing functional groups, and nitrogen-containing functional groups. This mixture is then mixed with the binder to obtain a modified binder, which effectively increases the content of oxygen-containing functional groups such as C=O, COO, and CO, and nitrogen-containing functional groups such as CN in the binder. The increased content of oxygen- and nitrogen-containing groups is beneficial for molecular cross-linking during sintering. Compared to the binder, the modified binder has a higher content of oxygen-containing functional groups such as C=O, COO, and CO, and nitrogen-containing functional groups such as CN, and a lower volatile content, thereby improving the wettability of the binder to aggregate particles, the plasticity of the paste during molding, and the coking residue value.

[0025] Meanwhile, the abundant β-components, γ-components, and other lightweight components, as well as oxygen-containing functional groups such as C=O, COO, and CO, and nitrogen-containing functional groups such as CN, on the surface of the modified binder act as active interface suppliers, coating the aggregate particle surface to achieve tight bonding of the aggregate particles and forming a micro-active layer between the aggregate particles. The modifier can effectively reduce the viscosity of the binder and the modified binder, improve the flowability of the binder and the modified binder, and promote the uniform distribution of the micro-active layer.

[0026] 3. This invention performs vacuum pretreatment on the pressed powder and maintains the moisture content of the pressed powder, eliminating pores within and between the pressed powder particles, effectively increasing the interfacial chelating force during molding, improving the isotropy and density of the carbon-based composite material, and promoting the construction of the cross-linked network skeleton between the activated coke-modified binder-microcrystalline graphite interface; at the same time, the formation of the micro-active layer can simultaneously enhance the interfacial bonding force between aggregates and the interfacial wettability between aggregates and modified binder, improve the homogeneity of the carbon-based composite material, and inhibit the formation of cracks, forming an interfacial structure.

[0027] By utilizing the active groups on the surface of activated coke and the active interface suppliers abundant in the micro-active layer, a reserved deformation zone is provided for the interface between activated coke, modified binder, and microcrystalline graphite. This disperses stress concentration and shields against cracks. Simultaneously, the reserved deformation zone also promotes the strengthening and toughening of brittle microcrystalline graphite powder, filling interface defects in a layered plugging manner. This achieves a "brazing" effect, resulting in a strong bond between different components, further improving the density and mechanical strength of the carbon-based composite material, thus creating a two-layer brazed structure.

[0028] Low-density, high-strength activated coke is used as the main aggregate, and high-density, low-strength microcrystalline graphite is used as the secondary aggregate. The two aggregate structures complement each other, achieving a synergistic effect of 1+1>2, serving as the "steel reinforcement" of the carbon-based composite material. The modified binder is tightly bonded to the aggregate particles, promoting the formation of an excellent micro-active layer on the aggregate surface, serving as the "concrete" of the carbon-based composite material, resulting in a three-layer steel-concrete structure.

[0029] The special "three-layer" structure design achieves a two-pronged approach of "reinforced aggregate complementarity + micro-active layer construction", which can produce a high-density and high-strength carbon-based composite material.

[0030] 4. This invention does not require semi-carbonization, impregnation, or graphitization treatment. It is formed by one-time calcination, which is simple. The carbon-based composite material prepared has high bulk density, excellent mechanical properties, and good homogeneity and stability. Attached Figure Description

[0031] Figure 1 - Flexural strength, compressive strength, microstructure of the flexural cross section, and scanning electron microscope image of the flexural surface of the carbon-based composite material obtained in Example 1.

[0032] Figure 2 -Metallographic image of the flexural surface of the carbon-based composite material obtained in Example 1.

[0033] Figure 3 - The flexural strength, compressive strength, microstructure of the flexural cross section, and scanning electron microscope image of the flexural surface of the carbon-based composite material obtained in Example 2.

[0034] Figure 4 -Metallographic image of the flexural surface of the carbon-based composite material obtained in Example 2.

[0035] Figure 5 - The flexural strength, compressive strength, microstructure of the flexural cross section, and scanning electron microscope image of the flexural surface of the carbon-based composite material obtained in Example 3.

[0036] Figure 6 -Metallographic image of the flexural surface of the carbon-based composite material obtained in Example 3.

[0037] Figure 7 - The flexural strength, compressive strength, microstructure of the flexural cross section, and scanning electron microscope image of the flexural surface of the carbon-based composite material obtained in Example 4.

[0038] Figure 8 -Metallographic image of the flexural surface of the carbon-based composite material obtained in Example 4.

[0039] Figure 9 - Comparative Example 1: flexural strength, compressive strength, microstructure of the flexural cross section, and scanning electron microscope image of the flexural surface of the carbon-based composite material.

[0040] Figure 10 - Metallographic image of the flexural surface of the carbon-based composite material obtained in Comparative Example 1.

[0041] Figure 11 - Comparative Example 2: flexural strength, compressive strength, microstructure of the flexural cross section, and scanning electron microscope image of the flexural surface of the carbon-based composite material.

[0042] Figure 12 - Metallographic image of the flexural surface of the carbon-based composite material obtained in Comparative Example 2.

[0043] Figure 13 - A diagram illustrating the mechanism by which gas circulates in micropores in the form of "rolling bearings". Detailed Implementation

[0044] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments.

[0045] Example 1

[0046] 1) Accurately weigh 72 parts of activated coke with a D50 of 4 μm and 18 parts of microcrystalline graphite powder with a D50 of 14 μm, and mix the activated coke and microcrystalline graphite powder in a powder mixer for 30 min to obtain mixed micro powder.

[0047] 2) Accurately weigh 30 parts of high-temperature coal tar pitch and 3 parts of coal tar.

[0048] 3) Set the kneading temperature to 100℃ and the rotation speed to 3 r / min, open the lid and reverse the direction. When the kneading temperature reaches the predetermined temperature, slowly add the mixed powder obtained in step 1) into the kneading pot and dry mix at 160℃ for 40 minutes, adjusting the rotation speed to 10 r / min, open the lid and rotate forward. When the temperature of the mixed powder reaches the set temperature, adjust the rotation speed to 30 r / min, close the lid and reverse the direction. When the moisture is completely removed, set the kneading temperature to 200℃ and cook the high-temperature coal tar pitch obtained in step 4). After it melts, add it to the mixed powder, along with coal tar, adjust the rotation speed to 50 r / min, close the lid, and wet mix for 1.5 hours, alternating between forward and reverse rotation. After kneading, slowly pour the resulting paste-like powder into a rolling mill, roll it twice, and roll it to a thickness of 1.5 mm. The rolling temperature is set to 210℃ and the rotation speed is adjusted to 30 r / min. After the rolling process is completed, the resulting flake powder is placed at room temperature to cool for 8 hours, then crushed and passed through a 150-mesh sieve, and left to stand for 8 hours to obtain pressed powder.

[0049] 4) The pressed powder obtained in step 3) is subjected to vacuum treatment, then stored in a sealed container to maintain the moisture content of the pressed powder. It is then placed under 3 MPa to pre-form a preliminary blank, with the forming temperature set at 30℃ and the pressure held for 30 seconds. After standing for 8 hours, it is placed in an isostatic press and pressed at 200 MPa for 0.5 hours, followed by gradient depressurization. This isostatic pressing-gradient depressurization process is repeated twice. The sample is then removed and allowed to stand for 12 hours to obtain a density of 1.50 g / cm³. 3 The green blank.

[0050] 5) Place the green block obtained in step 4) into a crucible filled with sintering material, ensuring that the green block is in the center of the sintering material, and place the crucible in a calcining furnace to calcine to obtain the carbon-based composite material.

[0051] The flexural strength, compressive strength, microstructure of the flexural cross-section, and scanning electron microscope image of the flexural surface of the carbon-based composite material obtained in this embodiment are shown below. Figure 1 As shown, the metallographic image of the flexural surface is as follows: Figure 2 As shown. Figure 1 (a) and Figure 1 (c) shows the flexural strength and compressive strength of the carbon-based composite material, respectively. Figure 1 (b) and Figure 1 (d) shows the microstructure of the flexural fracture surface and the scanning electron microscope image of the flexural surface of the carbon-based composite material, respectively. Figure 1As shown in (a) and 1(c), the flexural strength and compressive strength of the graphite material are 73.3 MPa and 215.9 MPa, respectively. Microscopic morphology of the cross-section, scanning electron microscopy (SEM) image of the surface, and surface metallographic image reveal that the aggregates are tightly bonded to each other and to the binder. There are few interparticle pores, no large pores or microcracks, and fractures mostly occur within the particles rather than between particles. The fracture surface is bright, neat, and without undulations. Therefore, the prepared carbon-based composite material exhibits excellent flexural and compressive strength.

[0052] Example 2

[0053] 1) Accurately weigh 72 parts of activated coke with a D50 of 4 μm and 18 parts of microcrystalline graphite powder with a D50 of 14 μm, and mix the activated coke and microcrystalline graphite powder in a powder mixer for 30 min to obtain mixed micro powder.

[0054] 2) 60 parts of high-temperature coal tar pitch were crushed and passed through a 200-mesh sieve to obtain binder powder. 100 parts of toluene and 100 parts of tetrahydrofuran were accurately weighed to obtain a mixed solvent. 10 parts of binder powder were added to this mixed solvent and ultrasonically vibrated at 55 °C for 80 min in a constant-temperature magnetic stirrer. The soluble and insoluble portions were then separated. The soluble portion was rotary evaporated under vacuum at 80 °C for 40 min to completely remove toluene and tetrahydrofuran, yielding a pure soluble substance.

[0055] 3) Take 1 part of the pure soluble substance obtained in step 2) and mix it thoroughly with 29 parts of adhesive powder to obtain the modified adhesive.

[0056] 4) Accurately weigh 30 parts of modified binder and 3 parts of coal tar.

[0057] 5) Set the kneading temperature to 100 ℃ and the rotation speed to 3 r / min. Open the lid and reverse the rotation. When the kneading temperature reaches the predetermined temperature, slowly add the mixed powder obtained in step 3) into the kneading pot and dry mix at 160 ℃ for 40 min. Adjust the rotation speed to 10 r / min and open the lid, rotating in the forward direction. When the temperature of the mixed powder reaches the set temperature, adjust the rotation speed to 30 r / min, close the lid, and reverse the rotation. When the moisture is completely removed, set the kneading temperature to 200 ℃ and cook the modified binder obtained in step 3). After it melts, add it to the mixed powder, along with the coal tar modifier. Adjust the rotation speed to 50 r / min, close the lid, and wet mix for 1.5 h, alternating between forward and reverse rotation. After kneading, slowly pour the resulting paste-like powder into a rolling mill and roll it twice to a thickness of 1.5 mm. The rolling temperature is set to 210 ℃ and the rotation speed is adjusted to 30 r / min. After the rolling process is completed, the resulting flake powder is placed at room temperature to cool for 8 hours, then crushed and passed through a 150-mesh sieve, and left to stand for 8 hours to obtain pressed powder.

[0058] 6) The pressed powder obtained in step 5) is subjected to vacuum treatment, then stored in a sealed container to maintain the moisture content of the pressed powder. It is then placed under 3 MPa to pre-form a preliminary blank, with the forming temperature set at 30℃ and the pressure held for 30 seconds. After standing for 8 hours, it is placed in an isostatic press and pressed at 200 MPa for 0.5 hours, followed by gradient depressurization. This isostatic pressing-gradient depressurization process is repeated twice. The sample is then removed and allowed to stand for 12 hours to obtain a density of 1.50 g / cm³. 3 The green blank.

[0059] 7) Place the green block obtained in step 6) into a crucible filled with sintering material, ensuring that the green block is in the center of the sintering material, and place the crucible in a calcining furnace to calcine and obtain carbon-based composite material.

[0060] The flexural strength, compressive strength, microstructure of the flexural cross-section, and scanning electron microscope image of the flexural surface of the carbon-based composite material obtained in this embodiment are shown below. Figure 3 As shown, Figure 3 (a) and Figure 3 (c) shows the flexural strength and compressive strength of the carbon-based composite material, and the metallographic image of the flexural surface is shown below. Figure 4 As shown. Figure 3 (b) and Figure 3 (d) shows the microstructure of the flexural fracture surface and the scanning electron microscope image of the flexural surface of the carbon-based composite material, respectively. Figure 3 As shown in (a) and 3(c), the flexural strength and compressive strength of the graphite material are 76.6 MPa and 245.4 MPa, respectively. Microscopic morphology of the cross-section, scanning electron microscopy (SEM) image, and surface metallographic image reveal that the aggregates are tightly bonded to each other and to the binder. The interparticle pores are few in size, mostly circular, with no large pores or microcracks. Furthermore, fractures mostly occur within the particles rather than between particles. The fracture surface is bright, neat, and without undulations. Therefore, the resulting carbon-based composite material exhibits excellent flexural and compressive strength.

[0061] Example 3

[0062] This embodiment is the same as embodiment 2, except that the modified binder in this embodiment is composed of 2 parts of soluble substance and 28 parts of binder powder.

[0063] The flexural strength, compressive strength, microstructure of the flexural cross-section, and scanning electron microscope image of the flexural surface of the carbon-based composite material obtained in this embodiment are shown below. Figure 5 As shown, the metallographic image of the flexural surface is as follows: Figure 6 As shown. Figure 5 (a) and Figure 5 (c) shows the flexural strength and compressive strength of the carbon-based composite material, respectively. Figure 5 (b) and Figure 5 (d) shows the microstructure of the flexural fracture surface and the scanning electron microscope image of the flexural surface of the carbon-based composite material, respectively. Figure 5 As shown in (a) and 5(c), the flexural strength and compressive strength of the graphite material are 80.1 MPa and 249.3 MPa, respectively. Microscopic morphology of the cross-section, scanning electron microscopy (SEM) image, and surface metallographic image reveal that the aggregates are tightly bonded to each other and to the binder. The interparticle pores are few in size, mostly circular, with no large pores or microcracks. Furthermore, fractures mostly occur within the particles rather than between particles. The fracture surface is bright, neat, and without undulations. Therefore, the resulting carbon-based composite material exhibits excellent flexural and compressive strength.

[0064] Example 4

[0065] This embodiment is the same as embodiment 2, except that the modified binder in this embodiment is composed of 3 parts of soluble matter and 27 parts of binder powder.

[0066] The flexural strength, compressive strength, microstructure of the flexural cross-section, and scanning electron microscope image of the flexural surface of the carbon-based composite material obtained in this embodiment are shown below. Figure 7 As shown, the metallographic image of the flexural surface is as follows: Figure 8 As shown. Figure 7 (a) and Figure 7 (c) shows the flexural strength and compressive strength of the carbon-based composite material, respectively. Figure 7 (b) and Figure 7 (d) shows the microstructure of the flexural fracture surface and the scanning electron microscope image of the flexural surface of the carbon-based composite material, respectively. Figure 7 As shown in (a) and 7(c), the flexural strength and compressive strength of the graphite material are 70.8 MPa and 205.4 MPa, respectively. Microscopic morphology of the cross-section, scanning electron microscopy (SEM) image, and surface metallographic image reveal that the aggregates are tightly bonded to each other and to the binder. There are few interparticle pores, no large pores or microcracks, and fractures mostly occur within the particles rather than between them. The fracture surface is bright, neat, and without undulations. Therefore, the resulting carbon-based composite material exhibits excellent flexural and compressive strength.

[0067] Comparative Example 1

[0068] This embodiment is the same as Embodiment 1, except that in this embodiment, all aggregates are activated coke with a D50 of 4 μm.

[0069] The flexural strength, compressive strength, microstructure of the flexural cross-section, and scanning electron microscope image of the flexural surface of the carbon-based composite material obtained in this embodiment are shown below. Figure 9 As shown, the metallographic image of the flexural surface is as follows: Figure 10 As shown. Figure 9 (a) and Figure 9 (c) shows the flexural strength and compressive strength of the carbon-based composite material, respectively. Figure 9 (b) and Figure 9(d) shows the microstructure of the flexural fracture surface and the scanning electron microscope image of the flexural surface of the carbon-based composite material, respectively. Figure 9 As shown in (a) and 9(c), the flexural strength and compressive strength of the graphite material are 67.1 MPa and 188.4 MPa, respectively. From the cross-sectional microstructure, surface scanning electron microscope image, and surface metallographic image, it can be seen that, compared to Examples 1-4, the bonding between aggregates and between aggregates and binder is relatively loose, the pore size between particles is randomly distributed, there are no obvious microcracks, but there are a small number of large pores, and fractures mostly occur between particles. Therefore, the flexural strength and compressive strength of the prepared carbon-based composite material are generally poor.

[0070] Comparative Example 2

[0071] This embodiment is the same as Embodiment 1, except that the D50 of the activated coke in this embodiment is 2 μm and the D50 of the microcrystalline graphite powder is 30 μm.

[0072] The flexural strength, compressive strength, microstructure of the flexural cross-section, and scanning electron microscope image of the flexural surface of the carbon-based composite material obtained in this embodiment are shown below. Figure 11 As shown, the metallographic image of the flexural surface is as follows: Figure 12 As shown. Figure 11 (a) and Figure 11 (c) shows the flexural strength and compressive strength of the carbon-based composite material, respectively. Figure 11 (b) and Figure 11 (d) shows the microstructure of the flexural fracture surface and the scanning electron microscope image of the flexural surface of the carbon-based composite material, respectively. Figure 11 As shown in (a) and 11(c), the flexural strength and compressive strength of the graphite material are 70.1 MPa and 201.0 MPa, respectively. From the cross-sectional microstructure, surface scanning electron microscope image, and surface metallographic image, it can be seen that, compared to Examples 1-4, the bonding between aggregates and between aggregates and binder is relatively loose, the pore size between particles is randomly distributed, there are no obvious microcracks, but there are a small number of large pores, and the fracture mostly occurs between particles. Therefore, the flexural strength and compressive strength of the prepared carbon-based composite material are generally poor.

[0073] The performance parameters of the carbon-based composite materials obtained in Examples 1-4 and Comparative Examples 1-3 are shown in the table below:

[0074]

[0075] As shown in the table above, without impregnation, multiple calcination, or graphitization processes, by optimizing the aggregate mix and combining two fine aggregates of different particle sizes and proportions, a bulk density of 1.62 g / cm³ can be obtained. 3A high-density, high-strength carbon-based composite material with a flexural strength of 73.3 MPa and a compressive strength of 215.9 MPa was obtained. Furthermore, a comparison between Examples 1 and Examples 2-4 shows that by using a modified binder, the calcined blocks were further densified and reinforced based on aggregate optimization, resulting in a "homogeneous rigid" carbon-based composite material. This promotes the formation of an excellent micro-active layer on the aggregate surface, achieving a two-pronged approach of "reinforced aggregate complementarity + micro-active layer construction," thus obtaining a high-density, high-strength carbon-based composite material.

[0076] Finally, it should be noted that the above embodiments of the present invention are merely illustrative examples and not intended to limit the implementation of the invention. Those skilled in the art can make other variations and modifications based on the above description. It is impossible to exhaustively list all possible implementations here. All obvious variations or modifications derived from the technical solutions of this invention are still within the scope of protection of this invention.

Claims

1. A method for preparing a high-density, high-strength "three-layer structure" carbon-based composite material, characterized in that, Includes the following steps: S1: Mix activated coke with a D50 of 3~6 μm and microcrystalline graphite powder with a D50 of 10~60 μm to obtain a mixed powder; wherein the mass ratio of activated coke to microcrystalline graphite powder is 40~80:1~20. S2: Add the mixed powder into a kneading pot and knead to remove moisture. Then heat the pot to 160~240 ℃, add the molten modified binder and modifier at the same time, and then close the lid and knead. After kneading, a paste is obtained. The modifier is one or two of coal tar, oleic acid, anthracene oil and cracked oil slurry. S3: Pour the paste into a rolling mill and roll it into sheets. Then crush and sieve to obtain pressed powder. After vacuum pretreatment, the pressed powder is sealed and stored to maintain the moisture content of the pressed powder. Then, it is molded and isostatically pressed to obtain green blocks. Finally, it is placed in a graphite crucible for calcination to obtain the carbon-based composite material. The modified binder is prepared according to the following steps: (1) After crushing the adhesive, pass it through a 50-500 mesh sieve to obtain adhesive powder; (2) Add the binder powder to the organic solvent, wherein the mass ratio of the binder powder to the organic solvent is 1~10:30~300; then place it in a constant temperature magnetic stirrer and sonicate at 40~80 ℃ for 30~120 min. After solid-liquid separation, rotary evaporate at 60~100 ℃ under vacuum for 30~60 min to remove the organic solvent in the soluble part and obtain the soluble substance. (3) Mix 1 to 5 parts of soluble substance and 20 to 40 parts of binder powder to obtain the modified binder.

2. The method for preparing a high-density, high-strength "three-layer structure" carbon-based composite material according to claim 1, characterized in that, The binder is one or more of phenolic resin, mesophase coal tar pitch, high-temperature coal tar pitch, medium-temperature coal tar pitch, or low-temperature coal tar pitch.

3. The method for preparing a high-density, high-strength "three-layer structure" carbon-based composite material according to claim 1, characterized in that, The organic solvent is one or more of acetone, methyl acetal, tetrahydrofuran, toluene, petroleum ether, dichloromethane, or quinoline.

4. The method for preparing a high-density, high-strength "three-layer structure" carbon-based composite material according to claim 1, characterized in that, The specific steps of step S2 are as follows: Set the kneading temperature to 100~120 ℃, adjust the rotation speed to 1~10 r / min, open the lid and reverse the direction; when the kneading temperature reaches the predetermined temperature, put the mixed powder into the kneading pot, dry mix at 120~160℃ for 20~40 min, adjust the rotation speed to 5~50 r / min, open the lid and rotate in the forward direction; when the temperature of the mixed powder reaches the set temperature, adjust the rotation speed to 20~40 r / min, close the lid and reverse the direction; when the moisture is completely removed, set the kneading temperature to 160~240℃, add the molten modified binder into the mixed powder, add the modifier at the same time, adjust the rotation speed to 20~50 r / min, close the lid, wet mix for 0.5~2 h, alternating between forward and reverse rotation, and obtain a paste after kneading.

5. A method for preparing a high-density, high-strength "three-layer structure" carbon-based composite material according to claim 1 or 4, characterized in that, The specific steps for preparing the pressed powder from the paste in step S3 are as follows: Pour the paste into a rolling mill and roll it 1 to 5 times, with a rolling thickness of 1 to 5 mm. The rolling temperature is set to 160 to 240 ℃ and the rotation speed is adjusted to 5 to 50 r / min. After rolling, place the obtained sheet powder at room temperature to cool for 6 to 12 hours, crush it, pass it through a 100 to 500 mesh sieve, and let it stand for 6 to 12 hours to obtain the pressed powder.

6. The method for preparing a high-density, high-strength "three-layer structure" carbon-based composite material according to claim 1, characterized in that, The specific steps for preparing the green block by pressing powder in step S3 are as follows: The powder is vacuum-treated, then pre-formed at 1-10 MPa to prepare the initial green block, with the forming temperature set at 20-200 ℃ and the pressure held for 1-30 s; then it is allowed to stand for 6-12 hours, and then placed in an isostatic press and pressed at 100-200 MPa for 0.5-1 hours, with gradual depressurization. This isostatic pressing-gradient depressurization process is repeated 1-3 times before the sample is removed and allowed to stand for another 6-12 hours to obtain a density of 1.45-1.55 g / cm³. 3 The green blank.

7. A high-density, high-strength "three-layer structure" carbon-based composite material, characterized in that, The high-density, high-strength "three-layer structure" carbon-based composite material was prepared using any one of claims 1 to 6.

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