A high-temperature and high-pressure synthesis method of carbon fiber reinforced and toughened ceramic composite material

Abstract

The high-temperature and high-pressure preparation method of the carbon fiber reinforced and toughened ceramic composite material belongs to the technical field of ceramic composite material preparation. First, nickel-plated carbon fibers are subjected to surface coating treatment: silane coupling agent is added to an alcohol water solution, after sufficient hydrolysis, nickel-plated PAN-based carbon fibers and nano silicon powder are added, after the reaction is completed, the solution is subjected to suction filtration and drying to obtain modified carbon fibers with a surface film layer structure of Ni-Si-SiO2, the modified carbon fibers are loaded in an assembly block of a six-surface pressing machine, and the six-surface pressing machine is placed in the six-surface pressing machine, sintering and pressing are carried out at 1100-1500 DEG C and 1-5 GPa for 10-30 minutes, and a block-shaped reinforced and toughened ceramic composite material is obtained. By adding nano silicon powder to adjust the phase structure and coating thickness of the gel layer on the surface of the carbon fiber, the brittleness of the ceramic phase material is improved, and a silicon oxide-based ceramic composite material with a nano-grain overall structure and self-lubricating / abrasion-reducing, heat-resistant / corrosion-resistant properties is synthesized.

Description

Technical Field

[0001] This invention belongs to the field of ceramic composite material preparation technology, and relates to a reinforced / toughened / self-lubricating ceramic composite material prepared by high temperature and high pressure (HTHP) technology, using nickel-plated polyacrylonitrile (PAN) carbon fibers with surface metal-nonmetallization composite modification treatment as toughening and reinforcing phase, in-situ generated silica as ceramic matrix phase, and nano-silica powder as coating increment and reaction adjustment phase. Background Technology

[0002] Ceramic materials are a class of inorganic non-metallic materials made from natural or synthetic compounds through shaping and high-temperature sintering. They possess excellent properties such as high melting point, high hardness, high wear resistance, and oxidation resistance, and are widely used in machinery, chemical, aerospace, and other fields. With the continuous expansion of application scenarios, higher requirements are being placed on the strength, toughness, temperature resistance, and wear resistance of ceramic materials. Ceramic materials prepared using traditional raw materials and high-temperature-atmospheric-pressure processes struggle to overcome the shortcomings of coarse grains, high brittleness, and low toughness. Therefore, researchers have conducted a series of studies to strengthen and toughen ceramic materials. For example, optimizing processes and designing fine microstructures can reduce the number of pores / cracks in ceramics to improve brittleness; refining grains can improve toughness; adding appropriate functional additives to the matrix material can promote densification, inhibit abnormal grain growth, and improve strength and toughness; and adding suitable reinforcing / toughening phases to the ceramic matrix can also enhance strength and toughness. Among commonly used toughening materials, carbon fiber is a filamentous carbon material with a carbon content of over 90%. It possesses characteristics such as lightweight, high specific elasticity, high specific strength, high temperature resistance, friction resistance, and corrosion resistance. Therefore, it is often selected as a reinforcing material to be composited with resins, metals, or ceramics to improve the overall mechanical properties of the material. However, carbon fiber has poor surface activity and does not wet with heterogeneous ceramic matrices. The bonding ability between heterogeneous phases in composite materials is a key factor limiting material performance. Therefore, improving the surface activity of carbon fiber and enhancing its interfacial bonding ability with heterogeneous materials is crucial to fully realizing the reinforcing / toughening effect of carbon fiber. To address this, surface modification treatment of the carbon fiber raw material is necessary before composite processing to increase the number of surface active sites, which can effectively improve its interfacial wettability and bonding ability with heterogeneous materials.

[0003] Patent CN 113185313 B discloses a carbon fiber reinforced ceramic matrix composite material and its preparation method. It involves impregnating a carbon fiber preform with boron carbide colloid, followed by aging treatment and then re-immersing it in a pre-reaction solution containing silicon carbide and an ultra-high temperature ceramic precursor. The resulting carbon fiber preform is then heat-treated. The resulting carbon fiber reinforced ceramic matrix composite material exhibits advantages such as ultra-high temperature resistance, high overall strength, and good fracture toughness. However, the precursor, after high-temperature pyrolysis, forms a particle accumulation structure on the fiber surface, resulting in poor bonding with the fiber. It still cannot completely avoid the problem of large ceramic phase particle size and high interparticle porosity after the ultra-high temperature ceramic precursor pyrolysis, which becomes more pronounced after high-temperature ablation of the composite material. Patent CN117326880 A discloses a high-temperature, high-pressure preparation method for nickel-plated carbon fiber / silica composite material. It involves surface modification of nickel-plated carbon fibers using a silane coupling agent, followed by high-temperature, high-pressure synthesis to obtain a high-strength, high-toughness carbon fiber reinforced silica ceramic composite material. However, the gel film layer coated on the surface of nickel-plated carbon fiber using only the polycondensation effect of tetraethyl orthosilicate is thin, and a large number of residual active oxygen groups reduce the phase transformation rate of the coating layer during high temperature and high pressure processes and cause oxidation damage to the nickel plating layer, thus reducing the strength of the composite material. Therefore, it is necessary to solve the problem of effectively thickening the gel coating layer in order to further adjust the quantity, structure and properties of the ceramic matrix phase.

[0004] This invention involves adding nano-silica powder to the precursor solution during the sol-gel method for coating amorphous nano-silica films onto nickel-plated carbon fibers using a silane coupling agent as a reaction precursor. This increases the coating thickness, consumes free oxygen in the silane film, and improves the ratio of carbon fibers to the ceramic matrix, thereby controlling the structure and properties of the composite material. Specifically, this invention employs high-temperature, high-pressure (HTHP) synthesis technology. The addition of nano-silica powder increases the number of in-situ silicon oxide nucleation cores, significantly reduces the synthesis temperature, and inhibits grain coarsening under high temperature and pressure. This achieves the effects of improving the in-situ generation reaction ratio, refining the matrix structure, and enhancing the density and toughness of the ceramic composite material. It solves the application technical challenges of carbon fiber reinforcement / toughening and can further be used to prepare novel superhard material products such as high-temperature resistant abrasives with diamond / boron nitride and other superhard abrasive particles as the hard phase. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a high-temperature and high-pressure (HTHP) preparation method for carbon fiber reinforced and toughened ceramic composites. This method involves adjusting the phase structure and coating thickness of the gel layer on the carbon fiber surface, refining the gel layer microstructure, enhancing the gel layer's reactivity, improving the brittleness of the ceramic matrix phase, and increasing the bonding strength and overall toughness / temperature resistance of the heterogeneous phase interfaces in the ceramic composite material. First, carbon fibers are coated with a carboxyphilic element, nickel (Ni), establishing a carboxyphilic active metal layer on the carbon fiber surface. Then, an amorphous silica gel film containing elemental nano-silica powder is coated onto the nickel-plated carbon fiber surface using a sol-gel method. The thickness of the amorphous film layer is controlled by adjusting the quantity and distribution of the nano-silica powder. Finally, a high-temperature and high-pressure (HTHP) synthesis method is used, and the composite sheet sample with dimensions of φ10×1mm is sintered in a six-sided press. This process prepares a carbon fiber reinforced and toughened silica-based ceramic composite material with self-lubrication / friction reduction, heat resistance / corrosion resistance. The dimensions of the sintered products prepared by this method can be adjusted according to the actual workpiece requirements.

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

[0007] A high-temperature and high-pressure preparation method for carbon fiber reinforced and toughened ceramic composite materials includes the following steps: adding a silane coupling agent to an alcohol-water solution and stirring continuously at 40–100°C for 2–12 hours until fully hydrolyzed; then adding nickel-plated PAN-based carbon fibers and nano-silica powder and stirring continuously at 40–100°C for 2–12 hours; after the reaction is complete, filtering and drying the solution to obtain nano-amorphous silica-coated modified carbon fibers; loading the obtained modified carbon fibers into an assembly block of a six-sided press and placing it into the six-sided press; sintering and pressing at 1100–1500°C and 1–5 GPa for 10–30 minutes to obtain a bulk reinforced and toughened ceramic composite material.

[0008] Preferably, the alcohol-water solution is a mixture of ethanol and deionized water in a volume ratio of 3:1, and the volume ratio of the silane coupling agent to the alcohol-water solution is 1:10 to 100.

[0009] Preferably, the silane coupling agent is tetraethyl orthosilicate (TEOS).

[0010] Preferably, the nickel-plated PAN-based carbon fiber is 100-mesh nickel-plated polyacrylonitrile (PAN) carbon fiber with a nickel layer thickness of 1.0–1.5 μm.

[0011] Preferably, the mass ratio of the added nano-silicon powder to carbon fiber is 1:5 to 20, and the thickness of the amorphous silicon oxide coating is >10μm.

[0012] Beneficial effects:

[0013] This invention utilizes nickel-plated PAN-based carbon fibers modified with tetraethyl orthosilicate (TEPS) to prepare reinforced and toughened ceramic composites via sintering on a six-sided press. A uniformly thick amorphous silica gel film containing nano-silica powder is coated onto the surface of the nickel-plated carbon fibers using a sol-gel method, forming a Ni-Si-SiO2 composite coating film. This increases the number and roughness of active sites on the carbon fiber surface, improving the material's dispersibility and surface wettability, and particularly enhancing the interfacial bonding strength between the carbon fibers and the silica-based ceramic matrix. This fully leverages the high strength and high modulus of carbon fibers in the composite material, providing reinforcement and toughening advantages. Employing HTHP technology, which introduces high-pressure driving force, reduces the sintering temperature from >1700℃ in traditional atmospheric pressure processes to 1100℃, saving energy, shortening preparation time, and improving production efficiency. The addition of nano-silica particles inhibits grain growth during synthesis, refines the sintered microstructure, and improves the microstructure properties. Through high-temperature and high-pressure treatment, nano-silica powder combines with active oxygen in the gel film to form new chemical bonds. The generated SiO2 co-grows / crystallizes in situ with the amorphous silica in the gel film. Together with atomic nickel that migrates and diffuses long distances to the grain boundaries of silica particles under high-temperature and high-pressure conditions, a densely woven cross-linked ceramic crystal network is formed, effectively improving the material's density and toughness. Simultaneously, the addition of nano-silica powder allows for flexible and convenient control of the coating thickness to regulate the proportion of the silica matrix ceramic phase, and also increases the number of heterogeneous nucleation sites during the crystallization process, refining the grains. This results in a fine microstructure with nanocrystalline particles throughout, further improving the strength, toughness, and temperature resistance of the ceramic composite material. Attached image description:

[0014] Figure 1 The images show the XRD patterns of the ceramic composite material HTHP before and after sintering in Example 1.

[0015] Figure 2 This is a SEM image of the fracture surface of the ceramic composite material in Example 1. Detailed Implementation

[0016] Example 1

[0017] 5 mL of tetraethyl orthosilicate was added to 200 mL of a 3:1 mixture of ethanol and deionized water. The mixture was hydrolyzed at 50 °C on a magnetic stirrer for 2 hours. Then, 2 g of 300-mesh nickel-plated PAN-based carbon fiber and 0.2 g of nano-silica powder were added. Finally, the mixture was reacted at 90 °C on a magnetic stirrer for 4 hours. The resulting product was then filtered and dried to obtain nickel-plated PAN-based carbon fiber with a non-metallic surface modification. This was then placed in an assembly block of a six-sided press and sintered at 5 GPa and 1100 °C for 20 minutes to prepare a ceramic composite material.

[0018] Figure 1 The X-ray diffraction (XRD) pattern of the phase structure of the prepared sintered sample shows that the diffraction peaks of elemental Si in the sintered sample almost completely disappeared, and the diffraction peaks of α-SiO2 appeared. This indicates that most of the elemental Si participated in the reaction, combined with the free oxygen groups in the gel coating to form silicon oxide, and together with the amorphous silicon oxide generated in situ in the gel film, it underwent a crystallization transformation under high temperature and high pressure. This process greatly increased the number of heterogeneous nucleation cores, which refined the microstructure of the ceramic composite material. Figure 2 The scanning electron microscope (SEM) image of the cross-section of the prepared sintered sample shows that the material grains are at the nanoscale and the fracture characteristics are ductile fracture.

[0019] Example 2

[0020] 3 mL of tetraethyl orthosilicate was added to 200 mL of a 3:1 mixture of ethanol and deionized water. Hydrolysis was carried out at 50 °C on a magnetic stirrer for 2 hours. Then, 2 g of 300-mesh nickel-plated PAN-based carbon fiber and 0.1 g of nano-silica powder were added. Finally, the mixture was reacted at 80 °C on a magnetic stirrer for 5 hours. The mixture was then filtered and dried to obtain nickel-plated PAN-based carbon fiber with a non-metallic surface modification. This was then placed in an assembly block of a six-sided press and sintered at 4 GPa and 1250 °C for 20 minutes to prepare a ceramic composite material. Scanning electron microscopy revealed good interfacial bonding between the carbon fiber and the ceramic matrix, with no obvious cracks or pores. The microstructure exhibited fine grains and typical ductile fracture characteristics, indicating that the composite material possesses good toughness and strength.

[0021] Example 3

[0022] 5 mL of tetraethyl orthosilicate was added to 200 mL of a 3:1 mixture of ethanol and deionized water. Hydrolysis was carried out at 50 °C on a magnetic stirrer for 4 hours. Then, 2 g of 300-mesh nickel-plated PAN-based carbon fiber and 0.4 g of nano-silica powder were added. Finally, the mixture was reacted at 70 °C on a magnetic stirrer for 6 hours. The mixture was then filtered and dried to obtain nickel-plated PAN-based carbon fiber with a non-metallic surface modification. This was then placed in an assembly block of a six-sided press and sintered at 3 GPa and 1350 °C for 25 minutes to prepare a ceramic composite material. Scanning electron microscopy revealed good interfacial bonding between the carbon fiber and the ceramic matrix, with no obvious cracks or pores. The microstructure exhibited fine grains and typical ductile fracture characteristics, indicating that the composite material possesses good toughness and strength.

[0023] Example 4

[0024] 5 mL of tetraethyl orthosilicate was added to 200 mL of a 3:1 mixture of ethanol and deionized water. Hydrolysis was carried out at 50 °C on a magnetic stirrer for 4 hours. Then, 2 g of 300-mesh nickel-plated PAN-based carbon fiber and 0.05 g of nano-silica powder were added. Finally, the mixture was reacted at 60 °C on a magnetic stirrer for 8 hours. The mixture was then filtered and dried to obtain nickel-plated PAN-based carbon fiber with a non-metallic surface modification. This was then placed in an assembly block of a six-sided press and sintered at 2 GPa and 1400 °C for 30 minutes to prepare a ceramic composite material. Scanning electron microscopy revealed good interfacial bonding between the carbon fiber and the ceramic matrix, with no obvious cracks or pores. The microstructure exhibited fine grains and typical ductile fracture characteristics, indicating that the composite material possesses good toughness and strength.

[0025] Example 5

[0026] 5 mL of tetraethyl orthosilicate was added to 200 mL of a 3:1 mixture of ethanol and deionized water. Hydrolysis was carried out at 50 °C on a magnetic stirrer for 2 hours. Then, 2 g of 300-mesh nickel-plated PAN-based carbon fiber and 0.2 g of nano-silica powder were added. The mixture was then reacted at 50 °C on a magnetic stirrer for 8 hours. The resulting product was filtered and dried to obtain nickel-plated PAN-based carbon fiber with a non-metallic surface modification. This was then placed in an assembly block of a six-sided press and sintered at 1 GPa and 1500 °C for 10 minutes to prepare a ceramic composite material. Scanning electron microscopy revealed good interfacial bonding between the carbon fiber and the ceramic matrix, with no obvious cracks or pores. The microstructure exhibited fine grains and typical ductile fracture characteristics, indicating good toughness and strength.

[0027] In addition to the aforementioned benefits, this invention innovatively proposes a method for toughening composite materials: adding nanoparticles that grow in situ as part of the material matrix during synthesis. Simultaneously, the thermal strength of the ceramic matrix material synthesized using HTHP technology is significantly improved, with its temperature resistance under dry friction conditions exceeding 1200℃. This allows for the further fabrication of novel superhard material products such as high-temperature resistant abrasives using diamond / boron nitride and other superhard abrasive particles as the hard phase. In summary, by using surface-coated carbon fibers as a toughening agent, coated silica as the ceramic matrix, and further adding hard particle phases such as diamond, boron nitride, and silicon nitride, a reinforced and toughened ceramic composite material with high strength, toughness, wear resistance, and high-temperature resistance can be prepared using high-temperature and high-pressure technology.

Claims

1. A high-temperature and high-pressure preparation method for carbon fiber reinforced and toughened ceramic composite materials, comprising the following steps: adding a silane coupling agent to an alcohol-water solution, stirring continuously at 40–100°C for 2–12 hours, and after complete hydrolysis, adding nickel-plated PAN-based carbon fibers and nano-silica powder, stirring continuously at 40–100°C for 2–12 hours, filtering and drying the solution after the reaction is complete to obtain nano-amorphous silica-coated modified carbon fibers, loading the obtained modified carbon fibers into an assembly block of a six-sided press, placing it into the six-sided press, and sintering and pressing at 1100–1500°C and 1–5 GPa for 10–30 minutes to obtain a bulk reinforced and toughened ceramic composite material.

2. The high-temperature and high-pressure preparation method of carbon fiber reinforced and toughened ceramic composite material according to claim 1, characterized in that, The alcohol-water solution is a mixed solution of ethanol and deionized water in a volume ratio of 3:1, and the volume ratio of the silane coupling agent to the alcohol-water solution is 1:10 to 100.

3. The high-temperature and high-pressure preparation method for carbon fiber reinforced and toughened ceramic composite materials according to claim 1, characterized in that, The silane coupling agent is tetraethyl orthosilicate.

4. The high-temperature and high-pressure preparation method for carbon fiber reinforced and toughened ceramic composite materials according to claim 1, characterized in that, The nickel-plated PAN-based carbon fiber is 100-mesh nickel-plated polyacrylonitrile-based carbon fiber with a nickel layer thickness of 1.0-1.5 μm.

5. The high-temperature and high-pressure preparation method for carbon fiber reinforced and toughened ceramic composite materials according to claim 1, characterized in that, The mass ratio of the added nano-silicon powder to carbon fiber is 1:5 to 20, and the thickness of the amorphous silicon oxide coating is >10μm.

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