Preparation method of high-strength high-thermal-conductivity silicon carbide ceramics

Abstract

This invention discloses a method for preparing high-strength, high-thermal-conductivity silicon carbide ceramics, relating to the field of advanced ceramic processing technology. The method includes the following steps: adding PEG to deionized water, then adding hydrophilically modified mesophase pitch-based carbon fibers and hydroxylated modified α-SiC, followed by adding monomers and crosslinking agents, and finally adding an initiator; stirring and pouring the mixture into a mold; heating and curing to obtain HTC. f - SiC green embryo; drying and degreasing; introducing carbon matrix using polymer impregnation pyrolysis process to obtain HTC. f A SiC-C intermediate is prepared by using a reactive melt infiltration process to infiltrate molten Si and react it with the carbon matrix, resulting in high-strength, high-thermal-conductivity silicon carbide ceramics. This invention significantly reduces the manufacturing cost of SiC ceramics, lowers equipment energy consumption, and improves the thermal conductivity, mechanical properties, and fracture toughness of SiC ceramics. This invention solves the problems of complex preparation processes and poor performance of silicon carbide ceramics in existing technologies.

Description

Technical Field

[0001] This invention relates to the field of advanced ceramic processing technology, specifically to a method for preparing high-strength, high-thermal-conductivity silicon carbide ceramics. Background Technology

[0002] Silicon carbide (SiC) ceramics are widely used in numerous fields such as petroleum, metallurgy, chemical industry, machinery, aerospace, and aviation due to their lightweight, high hardness, excellent high temperature resistance, oxidation resistance, corrosion resistance, wear resistance, wide bandgap, high breakdown voltage, high thermal conductivity, and excellent thermochemical stability. Theoretically, single-crystal SiC can achieve a thermal conductivity as high as 490 W / m·K at room temperature. However, its preparation process is complex and costly, and it is currently mainly used in high-frequency, high-voltage, high-temperature, and high-power applications such as integrated circuits, aerospace systems, and MOSFETs. In general industrial applications, polycrystalline SiC ceramics are more commonly used. However, the grain orientation, lattice defects, complex grain boundary structure, and the presence of pores and second phases at grain boundaries in polycrystalline SiC result in a significantly lower overall thermal conductivity compared to single-crystal SiC ceramics. The conventional preparation process for SiC ceramics mainly includes green forming and sintering densification. In industrial applications, the main forming methods for SiC ceramic preforms include slip casting, molding, and isostatic pressing. Slip casting is a complex process, resulting in low green strength (10-30 MPa) and high shrinkage (10-20%). Molding and isostatic pressing are primarily suitable for preparing preforms with regular shapes, but their post-sintering processing costs are relatively high. Regarding sintering processes, reaction sintering, pressureless sintering, hot pressing, and spark plasma sintering are currently the main methods. Reaction sintering has attracted attention due to its low cost, short cycle time, and relatively low sintering temperature, and it can achieve near-dense structures. However, the presence of free silicon significantly reduces the creep properties, flexural strength, and resistance to strong acids and alkalis of SiC ceramics. In contrast, pressureless sintering requires less sophisticated equipment, but it typically necessitates higher sintering temperatures or the introduction of suitable sintering aids to achieve the desired sintering effect. Watari et al. prepared silicon carbide ceramics with a thermal conductivity as high as 270 W / (m·K) using a hot-pressing sintering process by adding 2 wt.% BeO as a sintering aid. This is the highest thermal conductivity reported for SiC ceramics to date. However, due to the extremely toxicity of Be and its compound powders, this process has significant limitations in industrial applications. Therefore, researchers have been committed to exploring environmentally friendly sintering aids, such as Y2O3, CaO, MgO, rare earth oxides, Al2O3, and AlN, either alone or in combination. Although introducing liquid-phase sintering aids can effectively reduce the sintering temperature and increase the density of SiC ceramics, phonons must overcome the "phonon barrier" formed by the liquid phase at grain boundaries during phonon thermal conduction. The more complex the composition and the higher the content of the liquid phase, the higher this "barrier" becomes, thus having a more significant adverse effect on thermal conductivity. Patent CN202510519863.8 discloses a sintering process using extremely low amounts of boric acid and fructose as additives, wherein during the sintering process, boric acid and fructose are thermally decomposed to generate products B and C.Although the content of these two products is only 0.4 wt.%, their in-situ formation and excellent dispersibility significantly enhance the densification effect of the ceramic body, ultimately yielding SiC ceramics with a thermal conductivity as high as 180.94 W / (m·K) at room temperature. However, the sintering temperature remains as high as 2150℃. On the other hand, patent CN117865705A proposes a new process for preparing SiC ceramics. This process first involves grafting carbon nanofibers onto a mixture of modified zirconium silicate, and then combining cold isostatic pressing (150–180 MPa) and pressureless sintering (2050–2100℃) techniques to achieve ceramic densification. Experimental results show that the prepared SiC ceramics possess a tensile strength of 275 MPa, a thermal conductivity of 142 W / (m·K), and a fracture toughness as high as 8.23 ​​MPa·m1 / 2. Nevertheless, this method still relies on cold isostatic pressing equipment and high-temperature sintering at 2100℃.

[0003] In summary, existing technologies suffer from drawbacks such as high cost, high sintering energy consumption, low forming accuracy, and difficulty in balancing thermal conductivity and mechanical properties, which in turn limit the manufacturing of complex structural products. Summary of the Invention

[0004] To address the aforementioned technical problems, the present invention aims to provide a method for preparing high-strength, high-thermal-conductivity silicon carbide ceramics, thereby solving the problems of complex preparation processes and poor performance of silicon carbide ceramics in the prior art.

[0005] The technical solution of this invention to solve the above-mentioned technical problems is as follows: A method for preparing high-strength, high-thermal-conductivity silicon carbide ceramics is provided, comprising the following steps: (1) PEG was added to deionized water to adjust the pH value. Then, hydrophilic modified mesophase pitch-based carbon fiber and hydroxylated modified α-SiC were added to prepare a water-based slurry. The slurry was ball-milled, and monomers and crosslinking agents were added. The slurry was continued to be ball-milled. Finally, an initiator was added, the mixture was stirred and poured into a mold, and then heated to cure in order to obtain HTC. f -SiC embryo; (2) The HTC obtained in step (1) f -SiC green embryos are dried and degreased to produce porous HTC. f -SiC embryo; (3) The porous HTC obtained in step (2) f -SiC green embryos are prepared by introducing a carbon matrix using a polymer impregnation and pyrolysis process to obtain HTC. f -SiC-C intermediate; (4) The HTC obtained in step (3) f -The SiC-C intermediate is prepared by using a reactive melt infiltration process to infiltrate molten Si and react it with the carbon matrix, thereby obtaining high-strength and high-thermal-conductivity silicon carbide ceramics.

[0006] Based on the above technical solution, the present invention can be further improved as follows: Furthermore, in step (1), PEG is a mixture of PEG-400, PEG-600 and PEG-1000.

[0007] Furthermore, in the deionized water, the mass fraction of PEG-400 is 1%, the mass fraction of PEG-600 is 0.5%, and the mass fraction of PEG-1000 is 0.5%.

[0008] Furthermore, in step (1), tetramethylammonium hydroxide is used to adjust the pH value to 10-12.

[0009] Further, in step (1), the hydrophilic modified mesophase pitch-based carbon fiber is prepared by the following method: dopamine is added to Tris-HCl buffer solution, stirred for the first time to obtain a mixed solution, then the mesophase pitch-based carbon fiber is added, stirred for the second time, centrifuged, washed and dried to obtain polydopamine-coated mesophase pitch-based carbon fiber, that is, hydrophilic modified mesophase pitch-based carbon fiber.

[0010] The beneficial effects of adopting the above-mentioned further technical solutions are as follows: It can improve hydrophilicity and dispersibility. The hydroxyl group (-OH) has strong hydrophilicity, which can significantly improve the wettability and dispersion stability of SiC powder in water-based gel systems and prevent particle agglomeration. Hydroxylation treatment can effectively regulate the surface electrochemical properties of SiC powder, thereby greatly improving the dispersibility and stability of the slurry. Only a small amount of dispersant is needed to achieve a stable slurry with high solid phase and low viscosity.

[0011] Furthermore, Tris-HCl buffer is prepared by adding tris(hydroxymethyl)aminomethane and tris(hydroxymethyl)aminomethane hydrochloride to deionized water and stirring for 1-2 hours to obtain Tris-HCl buffer.

[0012] Furthermore, the mass-to-volume ratio of tris(hydroxymethyl)aminomethane, tris(hydroxymethyl)aminomethane hydrochloride, and deionized water is 0.1-10 mg: 1 mg: 10-100 mL.

[0013] Furthermore, in the mixed solution, the mass ratio of Tris-HCl buffer to dopamine is (0.1-100):(1-50).

[0014] Furthermore, the first stirring should last 1-3 hours.

[0015] Furthermore, the mass ratio of the mixed solution to the mesophase pitch-based carbon fiber is (1-100):(0.1-10).

[0016] Furthermore, the length of the mesophase pitch-based carbon fiber is 1-3 mm.

[0017] Further, the mixture is stirred for a second time for 12-48 hours.

[0018] Further, dry at 50-150℃ for 10-40 hours.

[0019] Further, in step (1), the hydroxylated modified α-SiC is prepared by the following method: the α-SiC powder is pretreated to obtain pure α-SiC powder, and then kept at 600℃ for 2h to obtain hydroxylated modified α-SiC.

[0020] Furthermore, the pretreatment method is as follows: α-SiC powder is added to a mixed acid solution of HCl and HF to obtain a slurry, which is then ball-milled, diluted, sieved, and washed; the above steps are repeated, and the powder is dried to obtain pure α-SiC powder.

[0021] Furthermore, the mass-to-volume ratio of α-SiC powder to mixed acid solution is 1g:5-10mL.

[0022] Furthermore, the mass of HCl in the mixed acid solution is 5-20%, and the mass of HF is 5-20%.

[0023] Furthermore, the balls were ball-milled at 80 rpm for 24-48 hours.

[0024] Furthermore, deionized water is used for dilution and washing.

[0025] Furthermore, in step (1), the volume fraction of hydrophilic modified mesophase pitch-based carbon fiber and hydroxylated modified α-SiC in the water-based slurry is 40-50%.

[0026] Furthermore, the volume ratio of hydrophilic modified mesophase pitch-based carbon fiber to hydroxylated modified α-SiC is 10-30:70-90.

[0027] Furthermore, in step (1), the water-based slurry is ball-milled for 6-24 hours.

[0028] Furthermore, in step (1), ball milling continues for 3-6 hours.

[0029] Furthermore, in step (1), the mass of the monomer is 5-10% of the water-based slurry, the mass of the crosslinking agent is 0.1-0.6% of the water-based slurry, and the mass of the initiator is 0.1-0.6% of the water-based slurry. Furthermore, in step (1), the monomer is at least one of acrylamide, methacrylamide, N-vinylpyrrolidone, 2-hydroxyethyl methacrylate, and dimethacrylamide, and the monomer may be gelatin, agarose, or protein powder.

[0030] Furthermore, in step (1), the monomer is acrylamide. Further, in step (1), the monomer is at least one of acrylamide (AM), methacrylamide (MAM), N-vinylpyrrolidone (NVP), 2-hydroxyethyl methacrylate (HEMA), and dimethacrylamide (DMAA), or the monomer is gelatin, agarose, or protein powder.

[0031] Furthermore, in step (1), the crosslinking agent is N,N-methylenebisacrylamide, polyethylene glycol diacrylate, or ethylene glycol dimethacrylate.

[0032] Furthermore, in step (1), the crosslinking agent is N,N-methylenebisacrylamide (MBAM), polyethylene glycol diacrylate (PEGDA), or ethylene glycol dimethacrylate (EGDMA).

[0033] Furthermore, in step (1), the initiator is a redox system, a thermal initiator, or a photoinitiator.

[0034] Furthermore, the redox system consists of ammonium persulfate and TEMED.

[0035] TEMED is N,N,N',N'-tetramethylethylenediamine.

[0036] Furthermore, in step (1), the initiator is ammonium persulfate.

[0037] Furthermore, in step (1), the mold material is 3D printed metal, 3D printed silicone or 3D printed photocurable resin.

[0038] Furthermore, in step (1), the product is heated and cured at 30-80℃ for 10-60 minutes.

[0039] Furthermore, in step (1), deionized water can be replaced with tert-butanol to prepare a non-aqueous slurry.

[0040] Furthermore, in step (1), when preparing the non-aqueous slurry, the crosslinking agent is ethylene glycol dimethacrylate.

[0041] Furthermore, in step (2), drying is achieved by the following method: [The text abruptly ends here, likely due to an incomplete sentence or missing information.] f -SiC green embryos are immersed in PEG solution, then in ethanol, drained, dried in a ventilated environment, and then kept warm to complete the drying process.

[0042] Furthermore, the PEG solution is prepared by mixing PEG-2000, PEG600, PEG-1000 and deionized water in a volume ratio of (20-40):(10-30):(10-20):10.

[0043] Furthermore, soak in PEG solution for 24-48 hours.

[0044] Furthermore, when soaking in ethanol, first soak for 4 hours, then soak in fresh ethanol for another 4 hours, repeating the soaking process 3-5 times to complete the soaking process.

[0045] Furthermore, dry in a ventilated environment at a constant temperature of 25 ℃ and a humidity of 25% for 24-48 hours.

[0046] Furthermore, the temperature is maintained at 60 ℃ for 12-24 hours, then raised to 80 ℃ and maintained for 12-24 hours, and then raised to 100 ℃ and maintained for 12-24 hours to complete the heat preservation process.

[0047] Furthermore, in step (2), degreasing is achieved by the following method: drying the HTC... f -The SiC green embryo is heated from room temperature to 200℃ and held for 1 hour under the protection of argon or nitrogen atmosphere, then heated to 300℃ and held for 1 hour, then heated to 400℃ and held for 1 hour, then heated to 500℃ and held for 1 hour, and finally heated to 600℃ and held for 2 hours to complete the degreasing process.

[0048] Furthermore, the heating rate is 1℃ / min.

[0049] Furthermore, in step (3), the introduction of a carbon matrix is ​​achieved by the following method: [The text abruptly ends here, likely due to an incomplete sentence or missing information.] f - A SiC green embryo is suspended above phenolic resin without being immersed, and a vacuum is applied; then it is completely immersed in the phenolic resin and vacuum impregnated for 30-60 minutes; followed by pressure impregnation for 10-30 minutes; then cured at 200℃ for 2 hours, and finally pyrolyzed at 900-1500℃ for 2-4 hours; repeating the above operation yields HTC. f -SiC-C intermediate. Furthermore, inert gas was used to pressurize the pressure to 1.5 MPa.

[0050] Furthermore, in step (4), HTC f High-strength, high-thermal-conductivity silicon carbide ceramics are prepared by reacting SiC-C intermediates and Si powder with melt infiltration.

[0051] Furthermore, in step (4), a reactive melt infiltration treatment is carried out at 1500-1600℃.

[0052] The present invention has the following beneficial effects: 1. This invention first employs a gel casting process to form a SiC ceramic preform reinforced with high thermal conductivity carbon fiber (HTC). The preform shrinkage is precisely controlled through a multi-step combined drying and two-step degreasing process. Then, a carbon matrix is ​​introduced into the preform through a polymer impregnation pyrolysis (PIP) process to obtain a porous HTCf-SiC-C intermediate. Finally, the intermediate and silicon (Si) powder are placed together in a graphite crucible, and molten Si is infiltrated and reacted with the carbon matrix through a reactive melt infiltration (RMI) process to achieve complete densification of the material. Through the above combined process, the net-size forming and preparation of isotropic, high-precision (±10 μm), high-strength (456±20 MPa), and high thermal conductivity (approximately 212 W / (m·K) at room temperature) silicon carbide ceramics are successfully achieved. This invention is particularly suitable for applications such as semiconductor manufacturing, new energy, high-temperature industry, thermal management, aerospace, and precision instruments.

[0053] 2. Adding high thermal conductivity fibers (HTC, mesophase pitch-based carbon fiber) can broaden the phonon transport channels of SiC ceramics, overcome the phonon thermal conductivity barriers caused by defects such as pores, impurities and grain boundaries inside SiC ceramics, and thus improve the thermal conductivity of SiC ceramics.

[0054] 3. By adding high thermal conductivity fiber reinforcement, the number and distribution of defects such as pores, impurities and grain boundaries in SiC ceramics are greatly optimized, improving the fracture toughness of SiC ceramics by more than 2 times.

[0055] 4. The SiC ceramic prepared by this invention has high thermal conductivity, high strength and high fracture toughness, which are 214.05 W / m·K, 439±13 MPa and 5.11±0.07 MPa·m1 / 2, respectively.

[0056] 5. The SiC ceramics prepared by this invention can achieve net-size forming of complex structures. Starting from injection molding, through green forming, debinding, pyrolysis, and melting densification, the linear shrinkage rate of the material throughout the entire process is less than 2%.

[0057] 6. The implementation process of this invention has a low dependence on equipment. The reaction sintering temperature is less than 1600℃. No high-pressure sintering furnace or press is used. Equipment energy consumption is reduced by more than 50%, manufacturing cost is reduced by more than 50%, and the production process is safe and controllable. Attached Figure Description

[0058] Figure 1 SEM image of the high thermal conductivity silicon carbide ceramic prepared in Example 1. Detailed Implementation

[0059] The principles and features of the present invention are described below with reference to the accompanying drawings. The examples given are for illustrative purposes only and are not intended to limit the scope of the invention. Unless otherwise specified in the examples, conventional conditions or conditions recommended by the manufacturer should be followed. Reagents or instruments whose manufacturers are not specified are all commercially available products.

[0060] PEG stands for polyethylene glycol.

[0061] The silicone capsule is from patent 202510605813.1.

[0062] Example 1: A method for preparing high-strength, high-thermal-conductivity silicon carbide ceramics includes the following steps: (1) Green embryo gel injection molding A mixture of PEG-400, PEG-600, and PEG-1000 was added to deionized water, with PEG-400 at a mass fraction of 1%, PEG-600 at a mass fraction of 0.5%, and PEG-1000 at a mass fraction of 0.5%. Tetramethylammonium hydroxide was added to adjust the pH to 11. Then, hydrophilic modified mesophase pitch-based carbon fibers and hydroxylated modified α-SiC were added at a volume ratio of 10:90 to prepare a water-based slurry. The volume fraction of hydrophilic modified mesophase pitch-based carbon fibers and hydroxylated modified α-SiC in the water-based slurry was 45%. The slurry was ball-milled for 20 hours at a speed maintained at 70 rpm. The mixture was ball-milled at rpm for 4 hours. Then, monomers (acrylamide, 8% of the water-based slurry by mass) and crosslinking agent (N,N-methylenebisacrylamide, 0.5% of the water-based slurry by mass) were added. Finally, initiator (ammonium persulfate, 0.5% of the water-based slurry by mass) was added, and the mixture was rapidly stirred and poured into a mold (3D printing photocurable resin). The mixture was then heated and cured at 50°C for 50 minutes in a hot air oven to obtain HTC. f -SiC embryo; The hydrophilic modified mesophase pitch-based carbon fiber was prepared by the following method: Tris(hydroxymethyl)aminomethane and tris(hydroxymethyl)aminomethane hydrochloride were added to deionized water at a mass-volume ratio of 8 mg: 1 mg: 100 mL and magnetically stirred for 1.5 h to prepare Tris-HCl buffer solution; Dopamine was added to Tris-HCl buffer solution at a mass ratio of 50:25 and stirred for 1.5 h to obtain a mixed solution; then, short-cut mesophase pitch-based carbon fiber with an average length of 1-3 mm was added at a mass ratio of 50:5 and stirred for 25 h; centrifuged and washed three times with alcohol and deionized water until the supernatant was colorless and transparent; the bottom powder was placed in an oven and dried at 80 °C for 25 h to obtain polydopamine-coated mesophase pitch-based carbon fiber, i.e., hydrophilic modified mesophase pitch-based carbon fiber; Hydroxylated modified α-SiC was prepared by the following method: α-SiC powder (average particle size 1-3 μm, purity 99%) was added to a mixed acid solution of HCl and HF (HCl and HF were 15% by mass and HF by mass) at a mass-to-volume ratio of 1 g: 8 mL to obtain a slurry. The slurry was ball-milled at 80 rpm for 30 h, diluted with deionized water, and sieved to remove unsuitable particles. The slurry was repeatedly washed with deionized water to replace the HCl and HF. The above steps were repeated (the acid addition and washing process were repeated), and the slurry was dried to obtain pure α-SiC powder. The α-SiC powder was pretreated to obtain pure α-SiC powder, and then kept at 600℃ for 2 h to obtain hydroxylated modified α-SiC. (2) Drying and defatting of the embryo The HTC obtained in step (1) f -SiC green embryos are dried and degreased to produce porous HTC. f -SiC embryo; specifically: the HTC obtained in step (1) f -SiC green embryos were soaked in a PEG solution (prepared by mixing PEG-2000, PEG600, PEG-1000 and deionized water in a volume ratio of 30:15:15:10) for 30 hours, then soaked in ethanol for 4 hours, followed by soaking in fresh ethanol for another 4 hours. This process of soaking in ethanol was repeated 4 times. The embryos were then drained and dried in a ventilated environment at a constant temperature of 25 ℃ and a humidity of 25% for 30 hours. They were then placed in a hot air oven and kept at 60 ℃ for 18 hours, then heated to 80 ℃ and kept at 80 ℃ for 18 hours, and finally heated to 100 ℃ and kept at 100 ℃ for 18 hours to complete the drying process. After drying HTC f -The SiC green embryo is heated at a rate of 1℃ / min from room temperature to 200℃ and held for 1 hour, then heated to 300℃ and held for 1 hour, then heated to 400℃ and held for 1 hour, then heated to 500℃ and held for 1 hour, and finally heated to 600℃ and held for 2 hours to complete the degreasing process. (3) HTC f Preparation of SiC-C intermediates The porous HTC obtained in step (2) f -SiC green embryos are prepared by introducing a carbon matrix using a polymer impregnation pyrolysis (PIP) process to obtain HTC. f -SiC-C intermediate; specifically: porous HTC f- SiC green embryos are placed in an impregnation tank containing phenolic resin, suspended above the resin without being submerged, and a vacuum is applied. Then, the embryos are completely immersed in the phenolic resin under vacuum for 40 minutes. Next, the impregnation tank is pressurized to 1.5 MPa using an inert gas and impregnated under pressure for 20 minutes. Finally, the embryos are transferred to an oven and cured at 200°C for 2 hours, followed by pyrolysis at 1000°C for 3 hours. This process of vacuuming and pyrolysis is repeated twice to obtain HTC. f -SiC-C intermediate; (4) Densification The HTC obtained in step (3) f -The SiC-C intermediate is prepared by reactive melt infiltration (RMI) to infiltrate molten Si and react with the carbon matrix, resulting in high-strength, high-thermal-conductivity silicon carbide ceramics. Specifically, the mixture (molten-infiltrated silicon capsules) is loaded into a crucible lined with graphite paper and leveled. It is first roughly pressed, then compacted with a pressure feeder, then leveled again with a scraper, and finally compacted with a pressure feeder. The powder thickness under the part is 15mm. HTC... f- The SiC-C intermediate is placed in a crucible containing the mixture, and then the mixture is added on top of the part. After compaction by a pressure feeder, the powder thickness on the part is ensured to be 13 mm. The part is then subjected to reactive melt infiltration treatment at 1500 ℃ to obtain high-strength and high-thermal-conductivity silicon carbide ceramic.

[0063] Example 2: A method for preparing high-strength, high-thermal-conductivity silicon carbide ceramics includes the following steps: In step (3), the PIP loop is repeated once; The rest is the same as in Example 1.

[0064] Example 3: A method for preparing high-strength, high-thermal-conductivity silicon carbide ceramics includes the following steps: In step (4), the RMI reaction temperature is 1600 ℃; The rest is the same as in Example 1.

[0065] Example 4: A method for preparing high-strength, high-thermal-conductivity silicon carbide ceramics includes the following steps: In step (2), the volume ratio of hydrophilic modified mesophase pitch-based carbon fiber to hydroxylated modified α-SiC is 20:80; The rest is the same as in Example 1.

[0066] Example 5: A method for preparing high-strength, high-thermal-conductivity silicon carbide ceramics includes the following steps: (1) Green embryo gel injection molding A mixture of PEG-400, PEG-600, and PEG-1000 was added to deionized water, with PEG-400 at a mass fraction of 1%, PEG-600 at a mass fraction of 0.5%, and PEG-1000 at a mass fraction of 0.5%. Tetramethylammonium hydroxide was added to adjust the pH to 10. Then, hydrophilic modified mesophase pitch-based carbon fibers and hydroxylated modified α-SiC were added at a volume ratio of 30:70 to prepare a water-based slurry. The volume fraction of hydrophilic modified mesophase pitch-based carbon fibers and hydroxylated modified α-SiC in the water-based slurry was 40%. The slurry was ball-milled for 6 hours at a speed maintained at 80 rpm. The mixture was ball-milled at rpm for 3 hours. Then, monomers (acrylamide, 5% of the water-based slurry by mass) and crosslinking agent (N,N-methylenebisacrylamide, 0.1% of the water-based slurry by mass) were added. Finally, initiator (ammonium persulfate, 0.1% of the water-based slurry by mass) was added, and the mixture was rapidly stirred and poured into a mold (3D printing photocurable resin). The mixture was then heated and cured at 30°C for 60 minutes in a hot air oven to obtain HTC. f -SiC embryo; The hydrophilic modified mesophase pitch-based carbon fiber was prepared by the following method: Tris(hydroxymethyl)aminomethane and tris(hydroxymethyl)aminomethane hydrochloride were added to deionized water at a mass-volume ratio of 0.1 mg: 1 mg: 100 mL and magnetically stirred for 1 h to prepare Tris-HCl buffer solution; Dopamine was added to Tris-HCl buffer solution at a mass ratio of 0.1: 1 and stirred for 1 h to obtain a mixed solution; then, short-cut mesophase pitch-based carbon fiber with an average length of 1-3 mm was added at a mass ratio of 1: 0.1 and stirred for 12 h; centrifuged; and washed twice with alcohol and deionized water until the supernatant was colorless and transparent; the bottom powder was placed in an oven and dried at 50 °C for 40 h to obtain polydopamine-coated mesophase pitch-based carbon fiber, i.e., hydrophilic modified mesophase pitch-based carbon fiber; Hydroxylated modified α-SiC was prepared by the following method: α-SiC powder (average particle size 1-3 μm, purity 99%) was added to a mixed acid solution of HCl and HF (HCl mass 5%, HF mass 5%) at a mass-to-volume ratio of 1 g: 5 mL to obtain a slurry. The slurry was ball-milled at 80 rpm for 24 h, diluted with deionized water, and sieved to remove unsuitable particles. The slurry was repeatedly washed with deionized water to replace the HCl and HF. The above steps were repeated (repeated acid addition and washing process), and the slurry was dried to obtain pure α-SiC powder. The α-SiC powder was pretreated to obtain pure α-SiC powder, and then kept at 600℃ for 2 h to obtain hydroxylated modified α-SiC. (2) Drying and defatting of the embryo The HTC obtained in step (1) f -SiC green embryos are dried and degreased to produce porous HTC. f -SiC embryo; specifically: the HTC obtained in step (1) f -SiC green embryos were soaked in a PEG solution (prepared by mixing PEG-2000, PEG600, PEG-1000 and deionized water in a volume ratio of 20:10:10:10) for 24 hours, then soaked in ethanol for 4 hours, followed by soaking in fresh ethanol for another 4 hours. This process of soaking in ethanol was repeated 3 times. The embryos were then drained and dried in a ventilated environment at a constant temperature of 25 ℃ and 25% humidity for 24 hours. They were then placed in a hot air oven and kept at 60 ℃ for 12 hours, then heated to 80 ℃ and kept at 80 ℃ for 12 hours, and finally heated to 100 ℃ and kept at 100 ℃ for 12 hours to complete the drying process. After drying HTC f -The SiC green embryo is heated at a rate of 1℃ / min from room temperature to 200℃ and held for 1 hour, then heated to 300℃ and held for 1 hour, then heated to 400℃ and held for 1 hour, then heated to 500℃ and held for 1 hour, and finally heated to 600℃ and held for 2 hours to complete the degreasing process. (3) HTC f Preparation of SiC-C intermediates The porous HTC obtained in step (2) f -SiC green embryos are prepared by introducing a carbon matrix using a polymer impregnation pyrolysis (PIP) process to obtain HTC. f -SiC-C intermediate; specifically: porous HTC f - SiC green embryos are placed in an impregnation tank containing phenolic resin, suspended above the resin without being submerged, and a vacuum is applied. Then, the embryos are completely immersed in the phenolic resin under vacuum for 30 minutes. Next, the impregnation tank is pressurized to 1.5 MPa using an inert gas and impregnated under pressure for 10 minutes. Finally, the embryos are transferred to an oven and cured at 200°C for 2 hours, followed by pyrolysis at 900°C for 4 hours. This process of vacuuming and pyrolysis is repeated twice to obtain HTC. f -SiC-C intermediate; (4) Densification The HTC obtained in step (3) f -The SiC-C intermediate is prepared by reactive melt infiltration (RMI) to infiltrate molten Si and react with the carbon matrix, resulting in high-strength, high-thermal-conductivity silicon carbide ceramics. Specifically, the mixture (molten-infiltrated silicon capsules) is loaded into a crucible lined with graphite paper and leveled. It is first roughly pressed, then compacted with a pressure feeder, then leveled again with a scraper, and finally compacted with a pressure feeder. The powder thickness under the part is 15mm. HTC... f-The SiC-C intermediate is placed in a crucible containing the mixture, and then the mixture is added on top of the part. After compaction by a pressure feeder, the powder thickness on the part is ensured to be 13 mm. The part is then subjected to reactive melt infiltration treatment at 1550 ℃ to obtain high-strength and high-thermal-conductivity silicon carbide ceramic.

[0067] Example 6: A method for preparing high-strength, high-thermal-conductivity silicon carbide ceramics includes the following steps: (1) Green embryo gel injection molding A mixture of PEG-400, PEG-600, and PEG-1000 was added to deionized water, with PEG-400 at a mass fraction of 1%, PEG-600 at a mass fraction of 0.5%, and PEG-1000 at a mass fraction of 0.5%. Tetramethylammonium hydroxide was added to adjust the pH to 12. Then, hydrophilic modified mesophase pitch-based carbon fibers and hydroxylated modified α-SiC were added at a volume ratio of 20:80 to prepare a water-based slurry. The volume fraction of hydrophilic modified mesophase pitch-based carbon fibers and hydroxylated modified α-SiC in the water-based slurry was 50%. The slurry was ball-milled for 24 hours at a speed maintained at 80 rpm. The mixture was ball-milled at rpm for 6 hours. Then, monomers (acrylamide, 10% of the water-based slurry by mass) and crosslinking agent (N,N-methylenebisacrylamide, 0.6% of the water-based slurry by mass) were added. Finally, initiator (ammonium persulfate, 0.6% of the water-based slurry by mass) was added, and the mixture was rapidly stirred and poured into a mold (3D printing photocurable resin). The mixture was then heated and cured at 80°C for 10 minutes in a hot air oven to obtain HTC. f -SiC embryo; The hydrophilic modified mesophase pitch-based carbon fiber was prepared by the following method: Tris(hydroxymethyl)aminomethane and tris(hydroxymethyl)aminomethane hydrochloride were added to deionized water at a mass ratio of 10 mg: 1 mg: 100 mL and magnetically stirred for 2 h to prepare Tris-HCl buffer solution; Dopamine was added to Tris-HCl buffer solution at a mass ratio of 100: 50 and stirred for 3 h to obtain a mixed solution; then, short-cut mesophase pitch-based carbon fiber with an average length of 1-3 mm was added at a mass ratio of 100: 10 and stirred for 48 h; centrifuged and washed 5 times with alcohol and deionized water until the supernatant was colorless and transparent; the bottom powder was placed in an oven and dried at 150 °C for 10-40 h to obtain polydopamine-coated mesophase pitch-based carbon fiber, i.e., hydrophilic modified mesophase pitch-based carbon fiber; Hydroxylated modified α-SiC was prepared by the following method: α-SiC powder (average particle size 1-3 μm, purity 99%) was added to a mixed acid solution of HCl and HF (HCl and HF accounted for 20% by mass and HF by mass) at a mass-to-volume ratio of 1 g: 10 L to obtain a slurry. The slurry was ball-milled at 80 rpm for 48 h, diluted with deionized water, and sieved to remove unsuitable particles. The slurry was repeatedly washed with deionized water to replace the HCl and HF. The above steps were repeated (the acid addition and washing process were repeated), and the slurry was dried to obtain pure α-SiC powder. The α-SiC powder was pretreated to obtain pure α-SiC powder, and then kept at 600℃ for 2 h to obtain hydroxylated modified α-SiC. (2) Drying and defatting of the embryo The HTC obtained in step (1) f -SiC green embryos are dried and degreased to produce porous HTC. f -SiC embryo; specifically: the HTC obtained in step (1) f -SiC green embryos are soaked in a PEG solution (prepared by mixing PEG-2000, PEG600, PEG-1000 and deionized water in a volume ratio of 40:30:20:10) for 48 hours, then soaked in ethanol for 4 hours, followed by soaking in fresh ethanol for another 4 hours. This process of soaking in ethanol is repeated 5 times. After soaking, the embryos are drained and dried in a ventilated environment at a constant temperature of 25 ℃ and a humidity of 25% for 48 hours. Then, they are placed in a hot air oven and kept at 60 ℃ for 24 hours, followed by raising the temperature to 80 ℃ and keeping it at that temperature for 12-24 hours, and then raising the temperature to 100 ℃ and keeping it at that temperature for 24 hours to complete the drying process. After drying HTC f -The SiC green embryo is heated at a rate of 1℃ / min from room temperature to 200℃ and held for 1 hour, then heated to 300℃ and held for 1 hour, then heated to 400℃ and held for 1 hour, then heated to 500℃ and held for 1 hour, and finally heated to 600℃ and held for 2 hours to complete the degreasing process. (3) HTC f Preparation of SiC-C intermediates The porous HTC obtained in step (2) f -SiC green embryos are prepared by introducing a carbon matrix using a polymer impregnation pyrolysis (PIP) process to obtain HTC. f -SiC-C intermediate; specifically: porous HTC f- SiC green embryos are placed in an impregnation tank containing phenolic resin, suspended above the resin without being submerged, and a vacuum is applied. Then, the embryos are completely immersed in the phenolic resin under vacuum for 60 minutes. Next, the impregnation tank is pressurized to 1.5 MPa using an inert gas and impregnated under pressure for 30 minutes. Finally, the embryos are transferred to an oven and cured at 200°C for 2 hours, followed by pyrolysis at 1500°C for 2 hours. This process of vacuuming and pyrolysis is repeated twice to obtain HTC. f -SiC-C intermediate; (4) Densification The HTC obtained in step (3) f -The SiC-C intermediate is prepared by reactive melt infiltration (RMI) to infiltrate molten Si and react with the carbon matrix, resulting in high-strength, high-thermal-conductivity silicon carbide ceramics. Specifically, the mixture (molten-infiltrated silicon capsules) is loaded into a crucible lined with graphite paper and leveled. It is first roughly pressed, then compacted with a pressure feeder, then leveled again with a scraper, and finally compacted with a pressure feeder. The powder thickness under the part is 15mm. HTC... f- The SiC-C intermediate was placed in a crucible containing the mixture, and then the mixture was added on top of the part. After compaction by a pressure feeder, the powder thickness on the part was ensured to be 13 mm. The part was then subjected to reactive melt infiltration treatment at 1600 ℃ to obtain high-strength and high-thermal-conductivity silicon carbide ceramics.

[0068] Comparative Example 1: A method for preparing high-strength, high-thermal-conductivity silicon carbide ceramics includes the following steps: In step (1), no hydrophilic modified mesophase pitch-based carbon fiber is added; The rest is the same as in Example 1.

[0069] Comparative Example 2: A method for preparing high-strength, high-thermal-conductivity silicon carbide ceramics includes the following steps: In step (1), no hydrophilic modified mesophase pitch-based carbon fiber is added; In step (2), a 60 ℃ hot air drying method is directly used; The rest is the same as in Example 1.

[0070] Comparative Example 3: A method for preparing high-strength, high-thermal-conductivity silicon carbide ceramics includes the following steps: In step (1), the hydrophilic modified mesophase pitch-based carbon fiber is replaced with unmodified mesophase pitch-based carbon fiber; In step (2), a 60 ℃ hot air drying method is directly used; The rest is the same as in Example 1.

[0071] Comparative Example 4: A method for preparing high-strength, high-thermal-conductivity silicon carbide ceramics includes the following steps: In step (2), a 60 ℃ hot air drying method is directly used; The rest is the same as in Example 1.

[0072] Test case I. Morphological Detection The high-strength, high-thermal-conductivity silicon carbide ceramic prepared in Example 1 was subjected to morphological analysis. The specific analysis method was as follows: a) After sample preparation, the sample was cut into 1cm*1cm*1cm pieces, then resin-insulated. After resin curing, it was polished with diamond suspension and observed by SEM; b) A 3*4*36mm bending specimen was processed from the sample and subjected to three-point bending mechanical property testing, resulting in a SEM image of the fracture surface; c) SEM observation of the same sample at different locations, with c showing the fibrous portion; d) A macroscopic image of the fracture surface of the sample, showing the fibers and fracture morphology. The results are shown in […]. Figure 1 (a) Morphology of the sample after polishing; b) SEM image of the fracture surface of the bent sample; c) Morphology of fiber pull-out at the fracture surface of the bent sample; d) SEM image of the fracture surface of the bent sample.

[0073] Depend on Figure 1 As shown in Figure a: Surface morphology of the original sample after polishing (untested area), observation scale: low magnification (scale bar 200μm), reflecting the overall distribution of carbon fibers in the ceramic matrix. Key features: Carbon fiber distribution characteristics: The black dotted / clump-like areas are the cross-sections of carbon fibers, showing uneven distribution characteristics: there are both single dispersed fibers and obvious fiber bundle aggregation areas (such as the black clumps in the lower left corner and lower middle); Matrix density: The ceramic matrix itself has extremely high density, with no obvious process pores and cracks, proving that the process was successful and the matrix quality is excellent; Fiber volume fraction: The volume fraction of carbon fibers is about 10%-15%, which is a medium fiber content; Surface quality: The polished surface is flat and smooth, with no obvious scratches and processing damage. The diamond suspension polishing process has an ideal effect, clearly showing the interface bonding state between the fiber and the matrix.

[0074] Figure b: High-magnification morphology of the matrix region at the three-point bending fracture. Observation scale: high magnification (scale bar 10 μm). It reflects the intrinsic fracture behavior of the ceramic matrix. The core feature is that it exhibits typical ceramic brittle cleavage fracture: a large number of clear cleavage planes, cleavage steps and river lines are visible. The grains are irregular polyhedral in shape. The fracture surface is flat and sharp. The grain size is uniformly distributed, about 2-5 μm. The grains are tightly bonded. There is no obvious intergranular fracture and intergranular porosity. There are no traces of plastic deformation. It is consistent with the intrinsic characteristics of ceramic materials: "rapid crack propagation and instantaneous fracture". This region is a pure matrix region with extremely low fiber content. Its fracture behavior represents the failure mode of the matrix phase in the composite material.

[0075] Figure c: Morphology of the carbon fiber reinforced region at a three-point bending fracture. Observation scale: medium to high magnification (scale bar 50 μm). This reflects the carbon fiber-matrix interface behavior and core toughening mechanism. Core features: Extremely significant fiber pull-out phenomenon: a large number of continuous carbon fibers are pulled out from the matrix, forming a staggered columnar structure. The yellow markings indicate that the pull-out length of a single fiber can reach 22 μm. Carbon fiber size characteristics: The fiber diameter is uniform, approximately 7-8 μm, which is consistent with the typical size of commercial T700 / T800 grade carbon fibers. Interface bonding state: The fiber surface is very clean, with almost no matrix adhesion, indicating that the carbon fiber-ceramic matrix interface bonding strength is moderate: it can effectively transfer loads and also allows for interface debonding during crack propagation. Crack deflection and bridging: Radial microcracks are generated around the fibers in the matrix, proving that the cracks are significantly deflected when they encounter the fibers during propagation; some unbroken fibers bridge the cracks on both sides and continue to bear the load. Toughening mechanism analysis: Carbon fiber pull-out is the most important toughening mechanism of this composite material. Debonding occurs when the crack propagates to the fiber-matrix interface. During the process of the fibers being pulled out of the matrix, a large amount of fracture energy is consumed through interfacial friction; at the same time, fiber bridging and crack deflection further consume energy, making the toughness of the material 1-2 orders of magnitude higher than that of pure ceramics.

[0076] Figure d: Macroscopic morphology of the three-point bending fracture surface. Observation scale: macroscopic low magnification (scale bar 500μm). It reflects the overall fracture characteristics and performance uniformity of the material. The core feature is that the fracture surface is rough and uneven, which is in stark contrast to the smooth cleavage fracture surface of pure ceramics. This is a macroscopic manifestation of the toughening effect of carbon fiber. The area marked by the yellow box is the carbon fiber bundle aggregation and pull-out area. This directly corresponds to the high magnification observation results in Figure c. The fracture surface simultaneously has a smooth area of ​​matrix cleavage fracture and a rough area of ​​fiber pull-out, indicating that the fracture of the material is the result of the synergistic effect of matrix brittle fracture and carbon fiber toughening mechanism.

[0077] II. Performance Testing The silicon carbide ceramics prepared in Examples 1-4 and Comparative Examples 1-4 were subjected to performance testing. The specific testing methods were as follows: density was tested according to the method specified in GBT 25995-2010; flexural strength was tested according to the method specified in GBT 6569-2006; fracture toughness was tested according to the method specified in JISR 1607-2015; thermal conductivity was tested according to the method specified in ASTM E1530; and residual silicon was tested by HF acid etching.

[0078] The results are shown in Table 1.

[0079] Table 1 Performance data results of Examples 1-4 and Comparative Examples 1-4

[0080] Table 1 shows that adding HTC fibers can directly improve the thermal conductivity and fracture toughness of SiC. Multi-step drying and degreasing processes can reduce the porosity and residual silicon content of SiC. Increasing the number of PIP-C cycles can increase density and reduce porosity and residual silicon content. Increasing the reaction temperature will improve the strength of SiC ceramics, but decrease its fracture toughness.

[0081] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing high-strength, high-thermal-conductivity silicon carbide ceramic, characterized in that, Includes the following steps: (1) PEG was added to deionized water to adjust the pH value. Then, hydrophilic modified mesophase pitch-based carbon fiber and hydroxylated modified α-SiC were added to prepare a water-based slurry. The slurry was ball-milled, and monomers and crosslinking agents were added. The slurry was continued to be ball-milled. Finally, an initiator was added, the mixture was stirred and poured into a mold, and then heated to cure in order to obtain HTC. f -SiC embryogenesis; (2) The HTC obtained in step (1) f -SiC green embryos are dried and degreased to produce porous HTC. f -SiC embryogenesis; (3) The porous HTC obtained in step (2) f -SiC green embryos are prepared by introducing a carbon matrix using a polymer impregnation and pyrolysis process to obtain HTC. f -SiC-C intermediate; (4) The HTC obtained in step (3) f -The SiC-C intermediate is prepared by using a reactive melt infiltration process to infiltrate molten Si and react it with the carbon matrix, thereby obtaining high-strength and high-thermal-conductivity silicon carbide ceramics.

2. The method for preparing high-strength, high-thermal-conductivity silicon carbide ceramic according to claim 1, characterized in that, In step (1), the hydrophilic modified mesophase pitch-based carbon fiber is prepared by the following method: dopamine is added to Tris-HCl buffer, stirred for the first time to obtain a mixed solution, then the mesophase pitch-based carbon fiber is added, stirred for the second time, centrifuged, washed and dried to obtain polydopamine-coated mesophase pitch-based carbon fiber, that is, hydrophilic modified mesophase pitch-based carbon fiber.

3. The method for preparing high-strength, high-thermal-conductivity silicon carbide ceramic according to claim 1, characterized in that, In step (1), the hydroxylated modified α-SiC is obtained by the following method: the α-SiC powder is pretreated to obtain pure α-SiC powder, and then kept at 600℃ for 2h to obtain hydroxylated modified α-SiC.

4. The method for preparing high-strength, high-thermal-conductivity silicon carbide ceramic according to claim 1, characterized in that, In step (1), the volume fraction of hydrophilic modified mesophase pitch-based carbon fiber and hydroxylated modified α-SiC in the water-based slurry is 40-50%.

5. The method for preparing high-strength, high-thermal-conductivity silicon carbide ceramic according to claim 1, characterized in that, In step (1), the volume ratio of hydrophilic modified mesophase pitch-based carbon fiber to hydroxylated modified α-SiC is 10-30:70-90.

6. The method for preparing high-strength, high-thermal-conductivity silicon carbide ceramic according to claim 1, characterized in that, In step (1), the monomer is at least one of acrylamide, methacrylamide, N-vinylpyrrolidone, 2-hydroxyethyl methacrylate, and dimethacrylamide, or the monomer is gelatin, agarose, or protein powder; the crosslinking agent is N,N-methylenebisacrylamide, polyethylene glycol diacrylate, or ethylene glycol dimethacrylate; and the initiator is a redox system, a thermal initiator, or a photoinitiator.

7. The method for preparing high-strength, high-thermal-conductivity silicon carbide ceramic according to claim 1, characterized in that, In step (2), drying is achieved by the following method: HTC f -SiC green embryos are immersed in PEG solution, then in ethanol, drained, dried in a ventilated environment, and then kept warm to complete the drying process.

8. The method for preparing high-strength, high-thermal-conductivity silicon carbide ceramic according to claim 1, characterized in that, In step (3), the introduction of a carbon matrix is ​​achieved by the following method: porous HTC f - A SiC green embryo is suspended above phenolic resin without being immersed, and a vacuum is applied; then it is completely immersed in the phenolic resin under vacuum for 30-60 minutes; followed by pressure impregnation for 10-30 minutes; then cured at 200℃ for 2 hours, and finally pyrolyzed at 900-1500℃ for 2-4 hours; this process is repeated to obtain HTC. f -SiC-C intermediate.

9. The method for preparing high-strength, high-thermal-conductivity silicon carbide ceramic according to claim 1, characterized in that, In step (4), reactive melt infiltration treatment is carried out at 1500-1600℃ to obtain high-strength and high-thermal-conductivity silicon carbide ceramics.

10. The high-strength, high-thermal-conductivity silicon carbide ceramic prepared by the method according to any one of claims 1-9.

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