Self-sintering antioxidant carbon-graphite sealing material and preparation method thereof

Abstract

The application discloses a kind of self-sintering oxidation-resistant carbon graphite sealing materials and preparation method thereof, its method includes: activated agent, catalyst and hexagonal boron nitride are mixed and reacted, after washing, dry modified hexagonal boron nitride is obtained;Subsequently, it is put into mixing kettle, again and molten pitch impregnation kneading, then it is broken and sieved to obtain pitch-coated hexagonal boron nitride powder;Again, it is pressed into shape, and physical pressure semi-carbonization treatment is carried out under inert atmosphere, again it is broken and sieved to obtain green coke coated hexagonal boron nitride powder;Crosslinking agent is dissolved in solvent, then add mesocarbon microbead, heat reaction under inert atmosphere, obtain crosslinking modified mesocarbon microbead;Green coke coated hexagonal boron nitride powder and crosslinking modified mesocarbon microbead are mixed uniformly according to the mass ratio of 5-30:70-95, to obtain pressed powder;The pressed powder is pressed into block, then cold isostatic pressing forming is carried out to obtain green body block;Green body block is calcined, then graphitization treatment is carried out under inert atmosphere, and carbon graphite sealing material is obtained.

Description

Technical Field

[0001] This invention belongs to the field of carbon materials technology, specifically relating to a self-sintering antioxidant carbon graphite sealing material and its preparation method. Background Technology

[0002] Carbon graphite sealing materials, with their excellent properties such as self-lubrication and corrosion resistance, are the core sealing materials for bearing cavities and accessory transmission systems of aero-engines. Their performance directly determines the reliability of engine operation, and conducting high-performance research is a key requirement to ensure the safe service of core aero-engine components.

[0003] Currently, carbon-graphite sealing materials are mainly prepared using a solid-state method. This method uses calcined coke, delayed coke, etc., as aggregates, coal tar pitch, modified pitch, and medium-temperature pitch as binders, and adds auxiliary materials such as carbon black, needle coke, or artificial graphite. The process involves kneading, rolling, crushing, grinding, pressing, calcining, impregnation, multiple calcinations, and graphitization to finally obtain a carbon-graphite sealing material that meets performance requirements. However, this process is cumbersome, requiring multiple "impregnation-calcination" processes to achieve material densification. This not only leads to poor material homogeneity but also easily causes a gradient densification problem of "dense on the outside and loose on the inside." Furthermore, the impregnated inorganic salts are prone to deliquescence, leading to abnormal wear of the seals and significantly shortening their service life. Currently, self-sintering processes are often used to improve the homogeneity defects of carbon-graphite sealing materials. However, this process typically uses a single aggregate (such as raw petroleum coke, raw pitch coke, or mesophase carbon microspheres (MCMBs)) as raw material, and the material is prepared through crushing, pressing, calcination, and graphitization. Although the pure raw coke aggregate used has high chemical activity and good self-sintering properties, its inherent plasticity is poor, and harmful sintering components are difficult to remove precisely. This makes it difficult to shape during the pressing process, and the temperature field control requirements during the calcination process are extremely stringent. The severe volume shrinkage easily causes the carbon blocks to crack, ultimately resulting in limited product size specifications and low yield. In addition, due to the severe volume shrinkage, the resulting self-sintering carbon graphite material has a low open porosity, making it difficult to further improve the antioxidant properties of the matrix material by impregnating it with phosphate antioxidants. Summary of the Invention

[0004] To address the aforementioned shortcomings of existing technologies, the present invention aims to provide a self-sintering, antioxidant carbon-graphite sealing material and its preparation method. The present invention can produce carbon-graphite sealing materials through a single calcination and graphitization process with a high yield. At the same time, the carbon-graphite sealing material obtained has high homogeneity, low porosity, and excellent antioxidant and mechanical properties.

[0005] The technical solution of this invention is implemented as follows:

[0006] A method for preparing a self-sintering antioxidant carbon-graphite sealing material includes the following steps:

[0007] (1) The activator, catalyst and hexagonal boron nitride powder are mixed and reacted, and after washing and drying, modified hexagonal boron nitride is obtained;

[0008] (2) Add the modified hexagonal boron nitride into a kneading pot, heat it to 120-140℃, remove the moisture, then heat it to 175-185℃, add the molten impregnated asphalt and knead, and then crush and sieve to obtain asphalt-coated hexagonal boron nitride powder.

[0009] (3) The asphalt-coated boron nitride is pressed into shape and subjected to semi-carbonization under pressure in an inert atmosphere, and then crushed and sieved to obtain coke-like coated hexagonal boron nitride powder.

[0010] (4) Dissolve the crosslinking agent in an organic solvent, then add mesophase carbon microspheres, and heat the mixture under an inert atmosphere to obtain crosslinked modified mesophase carbon microspheres;

[0011] (5) The coke-like coated hexagonal boron nitride powder from step (3) and the cross-linked modified mesophase carbon microspheres from step (4) are mixed evenly at a mass ratio of 5-30:70-95 to obtain pressed powder; wherein the preferred mass ratio of coke-like coated hexagonal boron nitride powder to cross-linked modified mesophase carbon microspheres is 10:90.

[0012] (6) Press the powder into blocks, and then cold isostatically press to obtain green blocks;

[0013] (7) The green block is calcined and then graphitized under an inert atmosphere to obtain the carbon graphite sealing material.

[0014] Further, the activator is one or more of phosphorus oxychloride, carbon tetrachloride and thionyl chloride; the catalyst is one or two of aluminum trichloride and ferric trichloride; and the mass ratio of hexagonal boron nitride powder, activator and catalyst is 1:5-10:0.01-0.04, preferably 1:5:0.03.

[0015] Furthermore, in step (1), the reaction temperature is 60-80℃, and the reaction time is 3-6h. Studies have shown that when the temperature is below 60℃, the reaction activity between the catalyst and the inert chemical bonds on the surface of hexagonal boron nitride is low, while when the temperature is above 80℃, the decomposition rate of the activator is accelerated, generating a large amount of gas and causing material waste. Controlling the temperature at 60-80℃ helps to control the decomposition rate of the activator, promotes the reaction activity between the catalyst and the inert chemical bonds on the surface of hexagonal boron nitride, and ensures that the hexagonal boron nitride is fully activated and modified.

[0016] Further, in step (2), the impregnated asphalt is a low-quinoline-insoluble medium-temperature asphalt, wherein the quinoline-insoluble content is <0.3%, the toluene-insoluble content is ≥12%, the softening point is 85~90 ℃, the ash content is <0.01%, and the volatile content is 65-67%; and the mass ratio of modified hexagonal boron nitride to impregnated asphalt is 50-60:40-50.

[0017] Further, the specific steps in step (3) are as follows: the asphalt-coated hexagonal boron nitride powder is pressed into shape at 5-10 MPa, and then heated to 300-600℃ under an inert atmosphere and treated at 3-5 MPa for 4-6 hours. After crushing and grinding, the powder is obtained by passing it through a 200-325 mesh sieve.

[0018] Further, the crosslinking agent is one or more of terephthalic acid, trioxymethylene, and paraoxymethylene; its addition amount is 1-5% of the mass of the mesophase carbon microspheres; the β resin content in the crosslinked modified mesophase carbon microspheres is 4-6%.

[0019] Furthermore, in step (4), the reaction temperature is 150-180℃ and the reaction time is 2-6h.

[0020] Further, in step (6), the specific steps for preparing the green block are as follows: the powder from step (5) is pressed into a block at 1-5 MPa, vacuum sealed in a bag, and left for 2-10 h; then it is placed in a cold isostatic pressing device and pressed at 150-200 MPa for 10-30 min, then the pressure is gradually released, the sample is taken out, the sealing bag is peeled off, and the green block is obtained after being left for 2-10 h.

[0021] Further, in step (7), the specific steps of calcination and graphitization are as follows: the green block is placed in a graphite crucible, filled with calcining material, and then placed in a calcination tube furnace. Inert gas is introduced, and the temperature is raised to 800-1000℃ for calcination for 2-4 hours. The temperature is then reduced to 400-500℃ and allowed to cool naturally to room temperature. The calcined block is then placed in a graphitization furnace and graphitized at 1500-2000℃ for 0.5-2 hours under inert atmosphere protection to obtain the carbon graphite sealing material.

[0022] The present invention also provides a self-sintering antioxidant carbon graphite sealing material, which is prepared by the preparation method of the self-sintering antioxidant carbon graphite sealing material described above.

[0023] Compared with the prior art, the present invention has the following beneficial effects:

[0024] 1. This invention employs activators and catalysts to activate and modify hexagonal boron nitride (h-BN), followed by coating and semi-carbonization treatment with molten impregnated bitumen. This process forms a dense, uniform, and strongly bonded coke-like coating layer on the surface and within the pores of hexagonal boron nitride. Specifically, the edges or defects of hexagonal boron nitride often contain a small number of hydroxyl (-OH) or amino (-NH2) groups, which can be converted into chlorine (-Cl) groups using activators such as phosphorus oxychloride, carbon tetrachloride, and thionyl chloride. The introduction of chlorine atoms can alter the polarity of the hexagonal boron nitride surface. Since impregnated bitumen also contains polar functional groups, according to the principle of "like dissolves like," this effectively improves the wettability of the impregnated bitumen, allowing it to fully penetrate the surface and micropores of the hexagonal boron nitride and undergo a cross-linking reaction with the chlorine groups on the surface, forming a dense, uniform, and firmly bonded bitumen coating. Simultaneously, the chlorine groups are effectively removed during the semi-carbonization process, preventing impurities from interfering with the bonding between the impregnated bitumen and the hexagonal boron nitride interface. Catalysts such as aluminum trichloride and ferric chloride not only catalyze the dissociation of the activator to form an active complex but also catalyze the condensation of the impregnated bitumen on the hexagonal boron nitride surface during the semi-carbonization process, forming a firmly bonded coke layer. Furthermore, in the subsequent graphitization process, the catalysts can catalyze graphitization, lower the graphitization temperature, accelerate the graphitization rate, form a locally highly ordered graphite layer, optimize the interfacial bonding, and improve the mechanical properties of the carbon-graphite sealing material.

[0025] 2. The hexagonal boron nitride used in this invention has excellent lubrication properties. Therefore, when hexagonal boron nitride coated with coke-like material is mixed with mesophase carbon microsphere aggregate, it can effectively reduce friction between aggregate particles, alleviate local stress concentration, and improve the flowability of aggregate particles, thereby increasing the yield of carbon-graphite sealing materials. Simultaneously, hexagonal boron nitride has excellent thermal conductivity. Its uniform dispersion in the aggregate particles can effectively regulate the heat distribution of the product's exterior and core during sintering, releasing thermal stress and further improving the yield. Furthermore, hexagonal boron nitride has a lamellar structure and is chemically stable and oxidation-resistant at high temperatures (up to 1000℃ and above). Adding it to carbon-graphite sealing materials can form an oxygen-barrier film in an oxygen-rich environment, effectively improving the oxidation resistance of the carbon-graphite sealing materials while reducing their porosity and increasing their pressure resistance.

[0026] 3. The crosslinking agents used in this invention, such as terephthalic acid, paraformaldehyde, and paraformaldehyde, can generate highly active intermediates (carbocations) during the heating reaction. These intermediates have strong electrophilicity and selectively undergo substitution reactions with aromatic molecules on the active sites of the mesophase carbon microspheres, forming methylene bridges (-CH2-) or ether bridges. This connects adjacent linear or small-molecule aromatic structures, forming planar macromolecules (i.e., β-resin) with larger molecular weights and moderate degrees of condensation. Since the reaction temperature (150-180 ℃) is much lower than the thermal condensation temperature (>400 ℃), and the reaction is achieved through chemical bridging rather than dehydrogenation condensation at high temperatures, deep condensation of the system to form quinoline insolubles can be effectively avoided. This results in crosslinked modified mesophase carbon microspheres with good thermal fluidity, thereby effectively improving the homogeneity, orderliness, and mechanical properties of the carbon-graphite sealing material.

[0027] 4. This invention uses low-quinoline medium-temperature asphalt as the impregnation asphalt. During the impregnation process, the impregnated asphalt can penetrate more thoroughly into the surface of hexagonal boron nitride and the interior of the aggregates, forming a uniform, continuous, and defect-free coating layer. Simultaneously, the thiol (-SH) and amino (-NH2) functional groups in the impregnated asphalt can break down to form free radicals upon heating, or react with active hydrogen and unsaturated bonds in the impregnated asphalt molecules to form intramolecular cyclization structures or intermolecular covalent cross-linking bridges, significantly increasing the molecular weight and cross-linking density of the impregnated asphalt during thermal conversion.

[0028] 5. This invention applies pressure during the semi-carbonization process, which promotes the uniform spreading and migration of impregnated asphalt on the surface of hexagonal boron nitride particles and within agglomerates. This provides a stable static pressure environment for the orderly formation and growth of the mesophase, significantly reducing the porosity of the coating layer and the overall powder structure, effectively inhibiting the loss of pyrolysis volatiles, and improving the coking value. By precisely controlling the low-temperature carbonization temperature and time, the coating layer remains in the semi-carbonization stage. This preserves the heteroatom functional groups and unclosed aromatic structures in the asphalt coking layer, thereby forming a carbonaceous surface with high surface energy and high reactivity.

[0029] 6. This invention uses mesophase carbon microspheres as the main aggregate. These spherical particles can be tightly packed during pressing, increasing both the green body density and the contact points between particles, thus improving the bulk density of the carbon-graphite sealing material. Furthermore, during heating, the mesophase carbon microspheres soften and undergo plastic deformation, fusing together like droplets, driving the material's volume shrinkage. This improves the sintering driving force and densification efficiency, ensuring uniform shrinkage and ultimately enhancing the mechanical properties of the carbon-graphite sealing material. Mesophase carbon microspheres are mostly prepared from refined coal tar pitch or petroleum pitch, with ash content and impurity elements such as sulfur and metals far lower than in raw petroleum coke, facilitating the preparation of high-performance, high-purity carbon-graphite products.

[0030] 7. The carbon-graphite sealing material prepared by this invention does not require repeated impregnation and densification; only a single calcination and graphitization are needed, which can effectively reduce the production cycle and carbon emissions. Furthermore, the carbon-graphite sealing material prepared by this invention has excellent antioxidant properties, eliminating the need for further impregnation with phosphate antioxidants. Attached Figure Description

[0031] Figure 1 -Photos of the mixed paste before it was removed from the pot and the semi-carbonized blocks in Example 1.

[0032] Figure 2 - Transmission electron microscope (TEM) images and scanning electron microscope (SEM) images of hexagonal boron nitride powder and carbonaceous hexagonal boron nitride powder coated with coke in Example 1.

[0033] Figure 3 - XRD patterns, Raman spectra, infrared spectra, and XRS full spectrum of hexagonal boron nitride powder and coke-coated hexagonal boron nitride powder in Example 1.

[0034] Figure 4 - The bending and compressive strength diagrams and corresponding cross-sectional morphology diagrams of the carbon graphite sealing material prepared in Example 1.

[0035] Figure 5 - Example 2 shows the flexural and compressive strength diagrams and corresponding cross-sectional morphology diagrams of the carbon-graphite sealing material prepared.

[0036] Figure 6 - Example 3 shows the flexural and compressive strength diagrams and corresponding cross-sectional morphology diagrams of the carbon-graphite sealing material prepared.

[0037] Figure 7 - Comparative Example 1: flexural and compressive strength diagrams and corresponding cross-sectional morphology diagrams of the carbon-graphite sealing material.

[0038] Figure 8 - Comparative Example 2: flexural and compressive strength diagrams and corresponding cross-sectional morphology diagrams of the carbon-graphite sealing material prepared. Detailed Implementation

[0039] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings.

[0040] Example 1

[0041] A method for preparing a self-sintering antioxidant carbon-graphite sealing material includes the following steps:

[0042] 1) Hexagonal boron nitride powder was placed in a 100℃ oven for drying pretreatment. Then, hexagonal boron nitride powder, sulfoxide (SOCl2), and ferric chloride (FeCl3) were added to a double-walled glass reactor in a mass ratio of 1:5:0.03, and reacted at a constant temperature of 80℃ for 4 h. After surface activation treatment, the powder was washed four times with anhydrous ethanol, and then dried in an 80℃ oven for 3 h to obtain activated and modified hexagonal boron nitride.

[0043] 2) Weigh 3% of the mass of mesophase carbon microspheres of terephthalic acid and dissolve it in anhydrous ethanol to obtain a crosslinking solution; add the mesophase carbon microspheres and crosslinking solution to a reaction vessel, introduce nitrogen gas, and react at 160℃ for 4 h to obtain crosslinked modified mesophase carbon microspheres with 5% β resin content.

[0044] 3) Add the activated and modified hexagonal boron nitride powder from step 1) to a kneading pot and mix at 120 ℃ for 1 h to remove moisture. The kneading pot rotates at 20 r / min in the forward direction. After moisture removal, heat the powder to 175 ℃ and introduce molten low-quinoline insoluble medium-temperature asphalt (where the mass ratio of low-quinoline insoluble medium-temperature asphalt to activated and modified hexagonal boron nitride is 42:58). Knead for 1 h at 50 r / min, alternating between forward and reverse rotation, and intermittently opening and closing the lid for mixing. After kneading, pour out the paste and let it cool to room temperature. After 10 h, crush and grind the powder, pass it through a 100-mesh sieve, and let it stand for another 10 h to obtain asphalt-coated hexagonal boron nitride powder.

[0045] 4) The asphalt-coated hexagonal boron nitride powder obtained in step 3) is pressed into shape at 10 MPa by compression molding process. After being left to stand for 10 h, it is placed in a box-type atmosphere furnace, nitrogen is introduced to maintain an oxygen-free environment, and the temperature is raised to 400 ℃ by program. After semi-carbonization treatment at 3 MPa for 6 h, it is cooled to room temperature with the furnace to complete the semi-carbonization process. The semi-carbonized block is crushed and ground into powder, and after passing through a 200-mesh sieve, coke-like coated hexagonal boron nitride powder is obtained, denoted as h-BN@SC.

[0046] 5) The coke-like coated hexagonal boron nitride powder obtained in step 4) and the mesophase carbon microspheres obtained in step 2) are mixed mechanically at a mass ratio of 10:90. After passing through a 140-mesh sieve, the mixture is left to stand for 10 hours to obtain pressed powder.

[0047] 6) Press the powder obtained in step 5) at 1 MPa to a density of 1.30 g / cm³. 3 The block was vacuum-sealed in a bag and left to stand for 10 hours. Then, it was placed in a cold isostatic pressing apparatus and pressed at 200 MPa for 30 minutes. After gradual depressurization, the sample was removed, the sealing bag was peeled off, and it was left to stand for another 10 hours to obtain a sample with a density of 1.40 g / cm³.3 The green blank.

[0048] 7) Place the green body obtained in step 6) in a graphite crucible, fill all six sides of the green body with the calcining material, and then place it in a calcining tube furnace. Argon gas is introduced during the calcination process, and the furnace is calcined at 1000℃ for 4 hours. Then, the temperature is reduced to 500℃ and then naturally cooled to room temperature to obtain a density of 1.72 g / cm³. 3 The calcined blocks were placed in a vacuum graphitization furnace under an argon atmosphere and treated at 1800 °C for 1 h. The temperature was then programmed to decrease to 500 °C and allowed to cool naturally to room temperature, yielding a density of 1.95 g / cm³. 3 Graphitized bulk material, namely carbon graphite sealing material.

[0049] Example 2

[0050] This embodiment is the same as Embodiment 1, except that in step 5) of this embodiment, the mass ratio of coke-like coated hexagonal boron nitride powder to cross-linked modified mesophase carbon microspheres is 20:80.

[0051] Example 3

[0052] This embodiment is the same as Embodiment 1, except that in step 5) of this embodiment, the mass ratio of coke-like coated hexagonal boron nitride powder to cross-linked modified mesophase carbon microspheres is 30:70.

[0053] Example 4

[0054] This embodiment is the same as Embodiment 1, except that in step 5) of this embodiment, the mass ratio of coke-like coated hexagonal boron nitride powder to mesophase carbon microspheres is 5:95.

[0055] Example 5

[0056] This embodiment is the same as Embodiment 1, except that in step 1) of this embodiment, the mass ratio of hexagonal boron nitride powder, thionyl chloride and ferric chloride is 1:5:0.01.

[0057] Example 6

[0058] This embodiment is the same as Embodiment 1, except that in step 1) of this embodiment, the mass ratio of hexagonal boron nitride powder, thionyl chloride and ferric chloride is 1:10:0.03.

[0059] Example 7

[0060] This embodiment is the same as Embodiment 1, except that in step 1) of this embodiment, the mass ratio of hexagonal boron nitride powder, thionyl chloride and ferric chloride is 1:5:0.02.

[0061] Example 8

[0062] This embodiment is the same as Embodiment 1, except that in step 1) of this embodiment, the mass ratio of hexagonal boron nitride powder, thionyl chloride and ferric chloride is 1:5:0.04.

[0063] Example 9

[0064] This embodiment is the same as Embodiment 1, except that in step 2) of this embodiment, the amount of p-phenylenediethanol added is 1% of the mesophase carbon microspheres, and the β resin content of the obtained crosslinked modified mesophase carbon microspheres is 4%.

[0065] Example 10

[0066] This embodiment is the same as Embodiment 1, except that in step 2) of this embodiment, the amount of p-phenylenediethanol added is 5% of the mesophase carbon microspheres, and the β resin content of the obtained crosslinked modified mesophase carbon microspheres is 6%.

[0067] Comparative Example 1

[0068] A method for preparing a self-sintering antioxidant carbon-graphite sealing material includes the following steps:

[0069] 1) Weigh hexagonal boron nitride powder and mesophase carbon microspheres in a mass ratio of 10:90 and set aside for later use.

[0070] 2) The material obtained in step 1) is mechanically mixed and then passed through a 140-mesh sieve. After being left to stand for 10 hours, pressed powder is obtained.

[0071] 3) The powder obtained in step 2) is pressed at 1 MPa to a density of 1.42 g / cm³. 3 The block was vacuum-sealed in a bag and left to stand for 10 hours. Then, it was placed in a cold isostatic pressing apparatus and pressed at 200 MPa for 30 minutes. After gradual depressurization, the sample was removed, the sealing bag was peeled off, and it was left to stand for another 10 hours to obtain a sample with a density of 1.52 g / cm³. 3 The green blank.

[0072] 4) Place the green body obtained in step 3) in a graphite crucible, fill all six sides of the green body with the calcining material, and then place it in a calcining tube furnace. Argon gas is introduced during the calcination process, and the furnace is calcined at 1000℃ for 4 hours. Then, the temperature is reduced to 500℃ and then naturally cooled to room temperature to obtain a density of 1.68 g / cm³. 3 The calcined blocks were placed in a vacuum graphitization furnace under an argon atmosphere and treated at 1800 °C for 1 h. The temperature was then programmed to decrease to 500 °C and allowed to cool naturally to room temperature, yielding a density of 1.80 g / cm³. 3 Graphitized bulk material.

[0073] Comparative Example 2

[0074] A method for preparing a self-sintering antioxidant carbon-graphite sealing material includes the following steps:

[0075] 1) Weigh out hexagonal boron nitride powder and low-quinoline insoluble medium-temperature asphalt in a mass ratio of 58:42, and set aside for use.

[0076] 2) Hexagonal boron nitride powder was added to a kneading pot and mixed at 120 ℃ for 1 h to remove moisture. The kneading pot rotated at 20 r / min in the forward direction. After moisture removal, the powder was heated to 175 ℃, and molten low-quinoline insoluble medium-temperature asphalt was introduced and kneaded for 1 h. The kneading pot rotated at 50 r / min, alternating between forward and reverse rotation, with the lid opened and closed intermittently. After kneading, the paste was poured out, and after the material temperature dropped to room temperature, it was left to stand for 10 h before being crushed and ground. After passing through a 100-mesh sieve, it was left to stand for 10 h to obtain asphalt-coated hexagonal boron nitride powder.

[0077] 3) The asphalt-coated hexagonal boron nitride powder obtained in step 2) is pressed into shape at 10 MPa by compression molding process. After being left to stand for 10 h, it is placed in a box-type atmosphere furnace, nitrogen is introduced to maintain an oxygen-free environment, and the temperature is raised to 400℃ by program temperature control. After semi-carbonization treatment at 3 MPa for 6 h, it is cooled to room temperature with the furnace to complete the semi-carbonization process. The semi-carbonized block is crushed and ground into powder, and after passing through a 200-mesh sieve, coke-like coated hexagonal boron nitride powder is obtained.

[0078] 4) The coke-like coated hexagonal boron nitride powder obtained in step 3) and mesophase carbon microspheres are mixed mechanically at a mass ratio of 10:90, passed through a 140-mesh sieve, and left to stand for 10 hours to obtain pressed powder.

[0079] 5) Press the powder obtained in step 4) at 1 MPa to a density of 1.39 g / cm³. 3 The block was vacuum-sealed in a bag and left to stand for 10 hours. Then, it was placed in a cold isostatic pressing apparatus and pressed at 200 MPa for 30 minutes. After gradual depressurization, the sample was removed, the sealing bag was peeled off, and it was left to stand for another 10 hours to obtain a sample with a density of 1.47 g / cm³. 3 The green blank.

[0080] 4) Place the green body obtained in step 3) in a graphite crucible, fill all six sides of the green body with the calcining material, and then place it in a calcining tube furnace. Argon gas is introduced during the calcination process, and the furnace is calcined at 1000℃ for 4 hours. Then, the temperature is reduced to 500℃ and then naturally cooled to room temperature to obtain a density of 1.67 g / cm³. 3 The calcined blocks were placed in a vacuum graphitization furnace under an argon atmosphere and treated at 1800 °C for 1 h. The temperature was then programmed to decrease to 500 °C and allowed to cool naturally to room temperature, yielding a density of 1.83 g / cm³. 3 Graphitized bulk material.

[0081] Comparative Example 3

[0082] A method for preparing a self-sintering antioxidant carbon-graphite sealing material includes the following steps:

[0083] 1) Weigh out hexagonal boron nitride powder and low-quinoline insoluble medium-temperature asphalt in a mass ratio of 58:42, and set aside for use.

[0084] 2) Hexagonal boron nitride powder was added to a kneading pot and mixed at 120 ℃ for 1 h to remove moisture. The kneading pot rotated at 20 r / min in the forward direction. After moisture removal, the powder was heated to 175 ℃, and molten low-quinoline insoluble medium-temperature asphalt was introduced and kneaded for 1 h. The kneading pot rotated at 50 r / min, alternating between forward and reverse rotation, with the lid opened and closed intermittently. After kneading, the paste was poured out, and after the material temperature dropped to room temperature, it was left to stand for 10 h before being crushed and ground. After passing through a 100-mesh sieve, it was left to stand for 10 h to obtain asphalt-coated hexagonal boron nitride powder.

[0085] 3) The asphalt-coated hexagonal boron nitride powder obtained in step 2) is pressed into shape at 10 MPa by compression molding process. After being left to stand for 10 h, it is placed in a box-type atmosphere furnace, nitrogen is introduced to maintain an oxygen-free environment, and the temperature is raised to 400℃ by program temperature control. After semi-carbonization treatment at 3 MPa for 6 h, it is cooled to room temperature with the furnace to complete the semi-carbonization process. The semi-carbonized block is crushed and ground into powder, and after passing through a 200-mesh sieve, coke-like coated hexagonal boron nitride powder is obtained.

[0086] 4) Weigh 3% of the mass of mesophase carbon microspheres of terephthalic acid and dissolve it in anhydrous ethanol to obtain a crosslinking solution. Add the mesophase carbon microspheres and the crosslinking solution to the reaction vessel, introduce nitrogen gas, and react at 160 °C for 4 h to obtain crosslinked modified mesophase carbon microspheres with 5% β resin content.

[0087] 5) The coke-like coated hexagonal boron nitride powder obtained in step 3) and the modified mesophase carbon microspheres obtained in step 4) are mixed mechanically at a mass ratio of 10:90. After passing through a 140-mesh sieve, the mixture is left to stand for 10 hours to obtain pressed powder.

[0088] 5) Press the powder obtained in step 4) at 1 MPa to a density of 1.37 g / cm³. 3 The block was vacuum-sealed in a bag and left to stand for 10 hours. Then, it was placed in a cold isostatic pressing apparatus and pressed at 200 MPa for 30 minutes. After gradual depressurization, the sample was removed, the sealing bag was peeled off, and it was left to stand for another 10 hours to obtain a sample with a density of 1.49 g / cm³. 3 The green blank.

[0089] 4) Place the green body obtained in step 3) in a graphite crucible, fill all six sides of the green body with the calcining material, and then place it in a calcining tube furnace. Argon gas is introduced during the calcination process, and the furnace is calcined at 1000℃ for 4 hours. Then, the temperature is reduced to 500℃ and then naturally cooled to room temperature to obtain a density of 1.69 g / cm³. 3 The calcined blocks were placed in a vacuum graphitization furnace under an argon atmosphere and treated at 1800 °C for 1 h. The temperature was then programmed to decrease to 500 °C and allowed to cool naturally to room temperature, yielding a density of 1.84 g / cm³. 3 Graphitized bulk material.

[0090] Comparative Example 4

[0091] This embodiment is the same as Embodiment 1, except that in step 1) of this embodiment, the mass ratio of hexagonal boron nitride powder, thionyl chloride and ferric chloride is 1:5:0.05.

[0092] Comparative Example 5

[0093] This embodiment is the same as Embodiment 1, except that in step 2) of this embodiment, the amount of p-phenylenediethanol added is 6% of the mesophase carbon microspheres, and the β resin content of the obtained crosslinked modified mesophase carbon microspheres is 8%.

[0094] Comparative Example 6

[0095] This embodiment is the same as embodiment 1, except that in step 3) of this embodiment, modified asphalt is used instead of low-quinoline insoluble medium-temperature asphalt.

[0096] 1. Photos of the actual product before the mixed paste is removed from the pot in step 3) of Example 1 and photos of the semi-carbonized block obtained in step 4) are shown below. Figure 1 (a) and Figure 1 As shown in (b).

[0097] 2. Transmission electron microscopy (TEM) images and scanning electron microscopy (SEM) images of hexagonal boron nitride powder (h-BN) and coke-coated hexagonal boron nitride powder (h-BN@SC) in Example 1 are shown below. Figure 2 As shown, the XRD pattern, Raman spectrum, infrared spectrum, and XRS full spectrum are respectively as follows: Figure 3 (a) Figure 3 (b) Figure 3 (c) and Figure 3 As shown in (d).

[0098] Transmission electron microscopy image of hexagonal boron nitride powder as shown below Figure 2 As shown in (a), by Figure 2(a) Clear layered lattice fringes can be seen. High-resolution insets and line scan profiles show a characteristic interlayer spacing of 0.216 nm, which is a typical crystallographic feature of hexagonal boron nitride powder (corresponding to the interface spacing of crystal plane (100)). The hexagonal boron nitride has sharp edges, a pure layered structure, and clear interfaces. Transmission electron microscopy image of carbonized hexagonal boron nitride powder is shown below. Figure 2 As shown in (e), a distinct "interfacial transition layer" appears in the coke-coated hexagonal boron nitride. This layer exhibits amorphous characteristics and forms a clear boundary with the lattice fringes of hexagonal boron nitride, directly proving that the bitumen successfully formed a coating layer on the surface of hexagonal boron nitride. The presence of the transition layer alters the surface state of hexagonal boron nitride, indicating that the coating process introduced a new interfacial structure. Scanning electron microscope images of hexagonal boron nitride powder at different magnifications are shown below. Figure 2 (c) and Figure 2 As shown in (d), hexagonal boron nitride exhibits a typical lamellar, stacked morphology. The particle surface is smooth, and the stacking relationship between layers is clear, displaying the inherent lamellar aggregation characteristics of hexagonal boron nitride. The particle size is relatively uniform. Scanning electron microscope images of coke-coated hexagonal boron nitride powder at different magnifications are shown below. Figure 2 (h) and Figure 2 As shown in (i), the morphology of hexagonal boron nitride particles changed significantly after coating. The original thin lamellar structure was covered by the asphalt coating layer, the surface became rough, the adhesion between particles was enhanced, and the whole particle exhibited an aggregated blocky morphology. This indicates that asphalt not only changed the surface roughness of hexagonal boron nitride, but also affected the aggregation state of the particles, making the originally loose lamellar structure more tightly bound together.

[0099] Depend on Figure 3 visible, Figure 3 (a) shows typical characteristic diffraction peaks of hexagonal boron nitride, with the strongest peak being the (002) crystal plane (2θ≈26°), corresponding to the layered stacking structure of hexagonal boron nitride; at the same time, characteristic peaks such as (100), (101), (102), and (004) appear, indicating that pure hexagonal boron nitride has high crystallinity and a complete hexagonal crystal system structure. The characteristic diffraction peaks of hexagonal boron nitride coated with carbonaceous material (such as (100), (101), etc.) are significantly weakened in intensity and the peak shape becomes wider; the (002) peak is still retained but the peak shape is slightly broadened, indicating that the crystal structure of hexagonal boron nitride is not destroyed, but the surface is covered by a carbon layer derived from pitch (amorphous / low crystallinity carbon), which reduces the exposure of hexagonal boron nitride grains, and the disorder introduced by the carbon layer reduces the XRD signal intensity of the crystallinity of hexagonal boron nitride. Figure 3(b) In the sample, hexagonal boron nitride shows no obvious carbon characteristic peaks, only background signals. Pure hexagonal boron nitride has weak Raman activity and no carbon components. The carbon-coated hexagonal boron nitride exhibits the typical characteristic peaks of carbon materials, D and G. These two peaks directly prove that a carbon coating layer is formed on the surface of hexagonal boron nitride after pitch pyrolysis, and the carbon layer has a certain degree of disorder and graphitization structure. Figure 3 (c) shows only the characteristic vibrational peaks of hexagonal boron nitride in h-BN, including in-plane stretching vibrations of the BN bond and out-of-plane bending vibrations of the BNB bond, with no other functional group signals, indicating that pure hexagonal boron nitride has a simple chemical composition. While retaining the characteristic BN peaks, the carbon-coated hexagonal boron nitride retains the characteristic peaks of BN, and adds new carbon-related functional group peaks, including stretching vibrations of the CH bond (from alkyl structure residues in bitumen) and vibrations of the C=C bond (characteristic of sp² hybrid carbon). These new peaks prove that the bitumen-derived carbon layer contains sp² / sp³ hybrid carbon and organic functional groups, further verifying the chemical composition of the carbon coating layer. Figure 3 In (d), only B1s and N1s peaks were detected in hexagonal boron nitride, which is completely consistent with the chemical composition of hexagonal boron nitride (containing only B and N elements). The newly enhanced signal C1s peak and the weak signal O1s peak of the coke-like coated hexagonal boron nitride show that the C1s peak intensity is significantly higher than the B and N peaks, indicating that carbon is the main component of the coating layer and has a high content; the O1s peak comes from oxygen-containing functional groups in the asphalt or surface oxidation during the preparation process; the B and N peaks are still present, indicating that the main structure of hexagonal boron nitride has not been destroyed, and only the surface is coated with a carbon layer.

[0100] 3. The carbon-graphite sealing materials prepared in Examples 1-10 and Comparative Examples 1-6 were tested for bulk density, open porosity, resistivity, flexural strength, compressive strength, and Shore hardness according to JB / T8133 standard. Their basic performance parameters are shown in Table 1. The flexural and compressive strength diagrams and corresponding cross-sectional morphology diagrams of the carbon-graphite sealing materials prepared in Examples 1-3 and Comparative Examples 1-2 are shown below. Figure 4-8 As shown.

[0101] Table 1. Basic Performance Parameters

[0102]

[0103] As can be seen from the table above: (1) Through Examples 1, 5, 7, 8 and Comparative Example 4, it can be seen that as the amount of catalyst increases, the performance of carbon-graphite sealing material shows a trend of first increasing and then decreasing, indicating that both insufficient and excessive catalyst will affect the performance of carbon-graphite sealing material. This is because insufficient catalyst will reduce the reaction rate between the activator and the active groups on the surface of hexagonal boron nitride, affecting the conversion rate and the uniformity of the surface grafting density, which will affect the interfacial bonding effect, thereby affecting the performance of the subsequent carbon-graphite sealing material. Excessive catalyst will trigger the disproportionation or decomposition reaction of the activator, the excessive reaction of the acyl chloride group and the local overheating damage of the h-BN surface; at the same time, too much residual catalyst will be introduced into the material system as a metallic impurity, which will catalyze the oxidation reaction of h-BN and its surrounding matrix, and abnormal dehydrogenation condensation will occur during the subsequent heat treatment process, resulting in cracks, pores or uneven local graphitization inside the material, weakening the strength of the material.

[0104] Meanwhile, as can be seen from Examples 1 and 6, the amount of activator needs to be controlled within a reasonable range. When the activator is excessive, it will excessively corrode the surface of the hexagonal boron nitride powder, destroy its lamellar integrity and form structural defects, thereby weakening the mechanical support and thermal stability of hexagonal boron nitride.

[0105] (2) As can be seen from Examples 1, 9 and 10, when the content of β resin in the crosslinked modified mesophase carbon microspheres is low, there is insufficient β resin to connect adjacent aromatic molecules into a network. This reduces the compactness of the aromatic molecule sheets and their aggregates formed by the layered arrangement between and inside the mesophase carbon microspheres. After sintering, a loose structure is easily formed, affecting the overall density and airtightness of the carbon graphite sealing material. On the other hand, when the content of β resin is too high, the excessive rigid crosslinking layer may make the "shell" on the particle surface too thick and too stiff, resulting in poor modulus matching with the mesophase carbon microspheres. This leads to stress concentration at the interface, resulting in a decrease in bonding strength.

[0106] (3) As can be seen from Comparative Examples 1-3 and Example 1, the simultaneous activation modification of hexagonal boron nitride and crosslinking modification of mesophase carbon microspheres can effectively improve the performance of carbon-graphite sealing materials. Activation modification can introduce active groups on the surface of hexagonal boron nitride, enhancing its subsequent chemical compatibility with impregnated bitumen. Using impregnated bitumen to construct a "coke-like" interface transition layer on the surface of the activated and modified hexagonal boron nitride significantly improves the interfacial bonding strength with the matrix, and improves the problems of difficult dispersion and low efficiency in raw materials. Crosslinking modification of mesophase carbon microspheres increases the β-resin content on their surface. The high β-resin char content reduces pores left by small molecule volatilization, forming a continuous network structure and improving material density. Simultaneously, a thicker and more continuous binder phase forms around the mesophase carbon microspheres, which not only strengthens the interfacial bonding force between particles but also more fully "welds" the h-BN-coated carbon layer to the entire carbon skeleton, achieving a strong bond between the two and leveraging their synergistic effect. This process produces a self-sintering graphite composite material with uniform hexagonal boron nitride distribution, good interfacial bonding strength, and excellent overall performance.

[0107] (4) As can be seen from Example 1 and Comparative Example 6, compared with modified asphalt, the use of low-quinoline insoluble medium-temperature asphalt can significantly improve the performance of carbon graphite sealing materials.

[0108] (5) Combination Figures 4-8 It can be seen that the flexural strength and compressive strength of the carbon-graphite sealing material prepared in Comparative Example 1 are 54.21 MPa and 106.66 MPa, respectively; Figure 7 (b) and Figure 7 (d) It can be seen that the cross-section of the carbon-graphite sealing material prepared in Comparative Example 1 shows a clear hexagonal boron nitride lamellar structure, with obvious gaps and interfaces between particles, and relatively loose bonding. At the same time, severe hexagonal boron nitride agglomeration also occurs. This loose interface is prone to cracking under stress, leading to stress concentration. Therefore, the carbon-graphite sealing material prepared has low flexural and compressive strength.

[0109] Compared to the carbon-graphite sealing material prepared in Comparative Example 1, the carbon-graphite sealing material prepared in Comparative Example 2 showed improved flexural strength and compressive strength, but due to... Figure 8 (b) and Figure 8 (d) It can be seen that the cross-section of the carbon-graphite sealing material prepared in Comparative Example 2 shows a clear hexagonal boron nitride lamellar structure, with large gaps between particles and severe hexagonal boron nitride agglomeration, resulting in a loose structure. This will lead to stress concentration and interface cracking in the carbon-graphite sealing material under stress.

[0110] Compared to the carbon-graphite sealing material prepared in Comparative Example 1, the carbon-graphite sealing material prepared in Example 1 showed an increase in flexural strength of approximately 48.59% and an increase in compressive strength of approximately 64.90%; Figure 4 (b) and Figure 4 (d) It can be seen that the cross-sectional particles of the carbon graphite sealing material prepared in Example 1 exhibit a tightly bonded blocky morphology with blurred interparticle interfaces and no obvious lamellar separation or voids. This indicates that the hexagonal boron nitride coated with coke-like material is firmly bonded to the mesophase carbon microspheres, with strong interfacial bonding force, uniform stress transmission, and reduced stress concentration.

[0111] Compared to the carbon-graphite sealing material prepared in Comparative Example 1, the carbon-graphite sealing material prepared in Example 2 showed an increase in flexural strength of approximately 40.20% and an increase in compressive strength of approximately 58.82%; Figure 5 (b) and Figure 5 (d) It can be seen that, compared with Example 1, the particle bonding tightness of the cross-section is slightly reduced, a small number of lamellar structures are exposed locally, and the interface clarity is slightly improved. This indicates that the interface bonding force is slightly weaker and the stress transfer efficiency is reduced.

[0112] Depend on Figure 6 (a) and Figure 6 (b) As can be seen, the flexural strength and compressive strength of the carbon-graphite sealing material prepared in Example 3 are 67.40 MPa and 150.59 MPa, respectively. Compared with the carbon-graphite sealing material prepared in Comparative Example 1, the flexural strength of the carbon-graphite sealing material prepared in Example 3 is increased by approximately 24.33%, and the compressive strength is increased by approximately 28.81%. Figure 6 (b) and Figure 6 (d) It can be seen that, compared with Example 1, the number of lamellar structures in the cross-section is significantly increased, the particle bonding becomes looser, and the interfacial gaps are larger. This indicates that the interfacial bonding force between hexagonal boron nitride and mesophase carbon microspheres is further weakened, the stress concentration phenomenon is intensified, and the mechanical properties are significantly reduced.

[0113] As can be seen from the above, as the content of hexagonal boron nitride coated with bio-coated carbon increases, the bonding tightness between the mesophase carbon microspheres and hexagonal boron nitride decreases, and the interfacial bonding force between the hexagonal boron nitride and the mesophase carbon microspheres decreases. Therefore, it is necessary to strictly control the mass ratio of bio-coated hexagonal boron nitride and cross-linked modified mesophase carbon microspheres.

[0114] 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 self-sintering antioxidant carbon-graphite sealing material, characterized in that, Includes the following steps: (1) The activator, catalyst and hexagonal boron nitride powder are mixed and reacted, and after washing and drying, modified hexagonal boron nitride is obtained; (2) Add the modified hexagonal boron nitride into a kneading pot, heat it to 120-140℃, remove the moisture, then heat it to 175-185℃, add the molten impregnated asphalt and knead, and then crush and sieve to obtain asphalt-coated hexagonal boron nitride powder. (3) The asphalt-coated boron nitride is pressed into shape and subjected to semi-carbonization under pressure in an inert atmosphere, and then crushed and sieved to obtain coke-like coated hexagonal boron nitride powder. (4) Dissolve the crosslinking agent in an organic solvent, then add mesophase carbon microspheres, and heat the mixture under an inert atmosphere to obtain crosslinked modified mesophase carbon microspheres; (5) Mix the coke-like coated hexagonal boron nitride powder from step (3) and the cross-linked modified mesophase carbon microspheres from step (4) at a mass ratio of 5-30:70-95 to obtain pressed powder; (6) Press the powder into blocks, and then cold isostatically press to obtain green blocks; (7) The green block is calcined and then graphitized under an inert atmosphere to obtain the carbon graphite sealing material.

2. The method for preparing a self-sintering antioxidant carbon-graphite sealing material according to claim 1, characterized in that, The activator is one or more of phosphorus oxychloride, carbon tetrachloride and thionyl chloride; the catalyst is one or two of aluminum trichloride and ferric trichloride; and the mass ratio of hexagonal boron nitride powder, activator and catalyst is 1:5-10:0.01-0.

04.

3. The method for preparing a self-sintering antioxidant carbon-graphite sealing material according to claim 1, characterized in that, In step (1), the reaction temperature is 60-80℃ and the reaction time is 3-6h.

4. The preparation method of a self-sintering antioxidant carbon-graphite sealing material according to claim 1, characterized in that, In step (2), the impregnated asphalt is a low-quinoline-insoluble medium-temperature asphalt, wherein the quinoline-insoluble content is <0.3%, the toluene-insoluble content is ≥12%, the softening point is 85~90 ℃, the ash content is <0.01%, and the volatile content is 65-67%; and the mass ratio of modified hexagonal boron nitride to impregnated asphalt is 50-60:40-50.

5. The preparation method of a self-sintering antioxidant carbon-graphite sealing material according to claim 1, characterized in that, The specific steps in step (3) are as follows: the asphalt-coated hexagonal boron nitride powder is pressed into shape at 5-10 MPa, and then heated to 300-600℃ under an inert atmosphere and treated at 3-5 MPa for 4-6 hours. After crushing and grinding, the powder is obtained by passing it through a 200-325 mesh sieve.

6. The preparation method of a self-sintering antioxidant carbon-graphite sealing material according to claim 1, characterized in that, The crosslinking agent is one or more of terephthalic acid, trioxymethylene, and paraoxymethylene; its addition amount is 1-5% of the mass of the mesophase carbon microspheres; the β resin content in the crosslinked modified mesophase carbon microspheres is 4-6%.

7. A method for preparing a self-sintering antioxidant carbon-graphite sealing material according to claim 1 or 6, characterized in that, In step (4), the reaction temperature is 150-180℃ and the reaction time is 2-6h.

8. The method for preparing a self-sintering antioxidant carbon-graphite sealing material according to claim 1, characterized in that, In step (6), the specific steps for preparing the green block are as follows: the powder from step (5) is pressed into a block at 1-5 MPa, vacuum sealed in a bag, and left for 2-10 h; then it is placed in a cold isostatic pressing device and pressed at 150-200 MPa for 10-30 min, then the pressure is gradually released, the sample is taken out, the sealing bag is peeled off, and the green block is obtained after being left for 2-10 h.

9. The method for preparing a self-sintering antioxidant carbon-graphite sealing material according to claim 1, characterized in that, In step (7), the specific steps of calcination and graphitization are as follows: the green block is placed in a graphite crucible, filled with calcining material, and then placed in a calcination tube furnace. Inert gas is introduced, and the temperature is raised to 800-1000℃ for calcination for 2-4 hours. The temperature is then reduced to 400-500℃ and allowed to cool naturally to room temperature. The calcined block is then placed in a graphitization furnace and graphitized at 1500-2000℃ for 0.5-2 hours under inert atmosphere protection to obtain the carbon graphite sealing material.

10. A self-sintering, antioxidant carbon-graphite sealing material, characterized in that, The material was prepared using the method described in any one of claims 1-9 for preparing a self-sintering antioxidant carbon-graphite sealing material.

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