A carbon fiber reinforced silicon carbide ceramic and its preparation method

Abstract

The present invention provides a carbon fiber reinforced silicon carbide ceramic and a preparation method thereof, belonging to the technical field of silicon carbide ceramics; the preparation method includes steps of preparing functional carbon fibers, preparing modified silicon carbide microspheres, preparing a mixture, forming and calcining; the step of preparing modified silicon carbide microspheres is as follows: placing silicon carbide in an ethanol solution, adding sodium dodecyl aminopropionate for ball milling treatment, after the ball milling ends, filtering and drying to obtain ball milled silicon carbide; placing the ball milled silicon carbide in dimethyl sulfoxide, stirring evenly, adding modified sodium alginate and hydroxyethyl cellulose, heating to 70 - 74 °C, adding tetrabutylammonium bromide, carrying out a heat preservation reaction for 10.0 - 11.5 h, after the reaction ends, filtering, washing and drying to obtain modified silicon carbide microspheres; the ceramic product prepared by the present invention has high strength performance and toughness, a low thermal expansion coefficient, and excellent high temperature oxidation resistance.

Description

Technical Field

[0001] The present invention belongs to the technical field of silicon carbide ceramics, and particularly relates to a carbon fiber reinforced silicon carbide ceramic and a preparation method thereof. Background Art

[0002] Ceramics are the general term for pottery and porcelain. Traditional ceramics are mainly materials and various products obtained by crushing, mixing, molding, and calcining clay as the main raw material and various natural minerals; modern ceramics, also known as new ceramics, are commonly made of non-silicate chemical raw materials or synthetic raw materials, such as oxides (aluminum oxide, zirconium oxide, titanium oxide, etc.) and non-oxides (silicon nitride, boron nitride, etc.); traditional ceramics are mainly used in daily necessities, building sanitation, chemical industry, electrical and other fields. With the development of the economy and the rise of high-tech industries, various new ceramics have also developed rapidly. Compared with traditional ceramics, they have better mechanical properties, temperature resistance, and chemical corrosion resistance, and are widely used in various fields.

[0003] Silicon carbide ceramics are ceramics mainly composed of silicon carbide, which have advantages such as good high-temperature resistance, wear resistance, high hardness, and low relative density, and are widely used in aerospace, microelectronics, automobiles, atomic energy, and petrochemical industries, etc. It is a ceramic material with great development potential and application prospects; however, due to the bonding characteristics of the molecular structure of silicon carbide itself, it lacks the ability of plastic deformation, showing greater brittleness, being sensitive to defects, and having poor reliability, thus seriously affecting its use performance as a structural material.

[0004] As a new fiber material with high strength and high modulus, carbon fiber has many excellent properties. The axial strength and modulus of carbon fiber are high, the density is low, the specific performance is high, it has excellent chemical corrosion resistance, heat conduction and electrical conductivity, a small thermal expansion coefficient, and excellent electromagnetic shielding performance. It is an important ceramic reinforcement and has wide applications in mechanical manufacturing, aerospace, nuclear power, and national defense industries, etc.

[0005] When carbon fiber is used as the reinforcing phase in silicon carbide ceramics, when the silicon carbide ceramics are subjected to external forces, the carbon fiber can connect the two sides of the crack like a bridge, preventing the further expansion of the crack, thus significantly improving the fracture resistance of the ceramics; during the fracture process, the carbon fiber can consume the fracture energy through mechanisms such as fiber pull-out, fiber bridging, and crack deflection, thereby exerting the strengthening and toughening effect of the carbon fiber, which can not only ensure the toughness of the carbon fiber reinforced silicon carbide ceramics but also make them have good strength performance.

[0006] However, when carbon fiber is used as the reinforcing phase in silicon carbide ceramics, the following problems exist:

[0007] First, the force between silicon carbide powders is strong, resulting in severe agglomeration, poor powder dispersibility. Moreover, the surface wettability of carbon fibers is poor, with high inertness and fewer surface active groups, leading to weak bonding between carbon fibers and the silicon carbide matrix and poor interfacial compatibility. As a result, macroscopic defects and unnecessary microstructural defects are likely to occur during the preparation of ceramic products, thus reducing the strength performance of ceramic products.

[0008] Second, the high-temperature oxidation resistance of carbon fibers is poor. When the temperature exceeds 400 °C, the oxidation of carbon fibers is particularly obvious, and the mass loss gradually increases. This not only affects the dimensional stability of the fibers but also significantly reduces the mechanical properties of ceramic products and increases the linear expansion coefficient, leading to stress concentration and fatigue fracture, ultimately limiting the use of ceramic products in high-temperature environments.

[0009] CN118047621A discloses a fiber-reinforced silicon carbide composite material and its preparation method. The raw material components include modified silicon carbide powder, silicon powder, modified carbon fiber, phenolic resin, graphite powder, stabilizing additives, and sintering additives. Among them, the modified silicon carbide powder is obtained by coating and modifying the surface of silicon carbide powder with a dispersant, hydroxyethyl cellulose, calcium carbonate, and polyacrylic acid, which improves problems such as the easy agglomeration of silicon carbide powder and enhances the sintering performance of the composite material. The modified carbon fiber is a modified carbon fiber coated with graphene oxide layer, silicon carbide layer, and carbon nanotube layer from the inside out, which improves the high-temperature oxidation resistance, fracture toughness, and flexural strength of the composite material.

[0010] The ceramic composite material prepared by this patent improves the fracture toughness and flexural strength, and the weight loss rate is 0.88% when kept at 1500 °C for 30 min. Although it reduces the mass loss at high temperatures, its retention rates of strength performance and toughness are poor in a high-temperature aerobic environment, also limiting the use range of ceramic products. Summary of the Invention

[0011] To solve the technical problems existing in the prior art, the present invention provides a carbon fiber-reinforced silicon carbide ceramic and its preparation method, which can improve the strength performance and toughness of ceramic products, reduce the thermal expansion coefficient, and enhance the high-temperature oxidation resistance.

[0012] In view of the above technical problems, the present invention adopts the following technical solutions:

[0013] A preparation method of a carbon fiber-reinforced silicon carbide ceramic includes steps of preparing functional carbon fibers, preparing modified silicon carbide microspheres, preparing a mixture, forming, and calcining. The specific operations are as follows:

[0014] 1. Preparation of functional carbon fibers

[0015] (1) Primary functionalization

[0016] Place the carbon fiber in acetone, raise the temperature to 86 - 90 °C, soak it for 3.7 - 4.2 h while maintaining the temperature, take it out and wash it, dry it at 63 - 67 °C for 9.5 - 11.0 h, then put it into deionized water, add citric acid solution, raise the temperature to 38 - 42 °C, stir while maintaining the temperature for 37 - 44 min, add kH550, raise the temperature to 62 - 67 °C at a rate of 0.8 - 1.3 °C / min, stir while maintaining the temperature for 4.3 - 4.7 h. After the stirring while maintaining the temperature is completed, filter it out and wash it, dry it at 78 - 82 °C for 9.0 - 12.0 h to obtain the primary functionalized carbon fiber;

[0017] The carbon fiber has a length of 0.4 - 0.6 μm and a diameter of 140 - 170 nm;

[0018] The mass ratio of the carbon fiber, acetone, deionized water, citric acid solution, and kH550 is 9.7 - 10.3:78 - 83:95 - 106:24.3 - 25.4:1.30 - 1.35;

[0019] The mass concentration of the citric acid solution is 16 - 20%;

[0020] (2)Secondary functionalization

[0021] Place the primary functionalized carbon fiber in N,N - dimethylformamide, stir evenly under a nitrogen atmosphere, add acrylamide, control the temperature at 58 - 63 °C, then add ammonium persulfate and N,N’ - methylenebisacrylamide, carry out ultrasonic dispersion, control the ultrasonic time at 37 - 45 min, the ultrasonic power at 216 - 223 W, and the ultrasonic frequency at 23 - 26 kHz. After the ultrasonic treatment is completed, stir and react at 142 - 155 rpm for 15.5 - 16.3 h. After the reaction is completed, filter, wash, and dry to obtain the functional carbon fiber;

[0022] The mass ratio of the primary functionalized carbon fiber, N,N - dimethylformamide, acrylamide, ammonium persulfate, and N,N’ - methylenebisacrylamide is 10.3 - 10.8:180 - 210:3.2 - 3.5:0.10 - 0.12:0.25 - 0.28.

[0023] 2. Preparation of modified silicon carbide microspheres

[0024] Put silicon carbide into an ethanol solution, add sodium dodecyl aminopropionate and conduct ball milling treatment. The ball milling time is 28 - 32 min, the ball milling speed is 164 - 175 rpm, and the ball-to-material ratio is 3 - 5:1. After ball milling, filter it out and dry it at 76 - 80 °C for 11.0 - 13.0 h to obtain ball-milled silicon carbide; put the ball-milled silicon carbide into dimethyl sulfoxide, stir evenly, add modified sodium alginate and hydroxyethyl cellulose, heat it up to 70 - 74 °C at a rate of 1.7 - 2.4 °C / min, add tetrabutylammonium bromide, keep the temperature for reaction for 10.0 - 11.5 h. After the reaction is completed, filter, wash and dry to obtain modified silicon carbide microspheres;

[0025] The particle size of the silicon carbide is 120 - 150 nm;

[0026] The mass ratio of the silicon carbide, ethanol solution and sodium dodecyl aminopropionate is 12.3 - 12.6:115 - 125:1.30 - 1.34;

[0027] The mass concentration of the ethanol solution is 27 - 32%;

[0028] The mass-to-volume ratio of the ball-milled silicon carbide, dimethyl sulfoxide, modified sodium alginate, hydroxyethyl cellulose and tetrabutylammonium bromide is 11.2 - 11.7 g:115 - 124 mL:2.0 - 2.3 g:1.0 - 1.5 g:0.3 - 0.5 g;

[0029] The preparation method of the modified sodium alginate is as follows: put sodium alginate into deionized water, stir evenly, add kH560, raise the temperature to 62 - 65 °C, keep stirring for 2.3 - 2.6 h. After stirring is completed, filter, wash and dry to obtain modified sodium alginate;

[0030] The mass ratio of the sodium alginate, deionized water and kH560 is 9.7 - 10.2:105 - 114:1.2 - 1.5.

[0031] 3. Prepare the mixture

[0032] Add functional carbon fiber and modified silicon carbide microspheres to dimethyl sulfoxide, raise the temperature to 68 - 72 °C, keep stirring for 5.7 - 6.2 h, filter it out, wash and dry to obtain the preliminary mixture; put the preliminary mixture into an ethanol solution, then add silicon nitride, graphite, zirconia, phenolic resin, titanium dioxide and sodium dioctyl sulfosuccinate, and conduct homogenization treatment. The homogenization pressure is 4.7 - 5.3 MPa, the homogenization time is 4.0 - 6.0 min, and the number of homogenization times is 3 times. After the homogenization treatment is completed, filter, wash and dry to obtain the mixture;

[0033] The volume mass ratio of the dimethyl sulfoxide, functional carbon fiber, and modified silicon carbide microspheres is 1000 mL: 10.5 - 11.0 g: 52.0 - 52.7 g;

[0034] The mass ratio of the premixed material, ethanol solution, silicon nitride, graphite, zirconia, phenolic resin, titanium dioxide, and sodium dioctyl sulfosuccinate is 62.4 - 63.5: 214 - 225: 3.4 - 3.7: 4.4 - 4.6: 5.0 - 5.3: 8.4 - 8.7: 1.2 - 1.6: 0.8 - 1.1;

[0035] The mass concentration of the ethanol solution is 23 - 27%.

[0036] 4. Molding and Calcination

[0037] Place the mixed material in a mold, perform a pre-tightening treatment under a pressure of 7.8 - 8.2 MPa for 10 - 12 s, and then perform a cold pressing molding treatment at 34 - 36 MPa for 7.5 - 8.5 min to obtain a ceramic green body; place the ceramic green body in a sintering furnace, under an argon atmosphere, heat it at a rate of 6.0 - 7.0 °C / min to 860 - 880 °C, hold for 23 - 28 min, then heat it at a rate of 1.7 - 2.3 °C / min to 1572 - 1586 °C, hold for 2.4 - 2.6 h, and cool naturally to obtain carbon fiber reinforced silicon carbide ceramic.

[0038] A carbon fiber reinforced silicon carbide ceramic is prepared by the above preparation method.

[0039] Compared with the prior art, the present invention has achieved the following beneficial effects:

[0040] 1. The present invention uses silicon carbide as the ceramic matrix and carbon fiber as the ceramic reinforcing phase. First, the carbon fiber is subjected to functional treatment. Specifically, the carbon fiber is first soaked in acetone to remove the colloid and impurities on the surface of the carbon fiber, and then treated with a citric acid solution and a KH550 silane coupling agent. The citric acid solution contains hydroxyl groups, which can adhere to the surface of the carbon fiber and enhance the binding performance with the KH550 silane coupling agent, so that the surface of the carbon fiber contains more amino groups to obtain primary functionalized carbon fiber. The primary functionalized carbon fiber is mixed with acrylamide monomer, and under the action of an initiator and a crosslinking agent, a polyacrylamide chain is formed through a polymerization reaction, which forms a tight network structure with the carbon fiber through a crosslinking reaction, and the interfacial bonding strength between them is good, thereby improving the strength performance and stability performance of the ceramic material, and enabling the functional carbon fiber to have good high-temperature oxidation resistance; in the step of preparing silicon carbide microspheres, specifically, the silicon carbide is first subjected to ball milling treatment. Under the action of a surfactant, the silicon carbide is uniformly dispersed, and under the physical impact of ball milling, the crystal lattice generates defects, improving the surface activity of the silicon carbide. Then, the silicon carbide is mixed with modified sodium alginate and hydroxyethyl cellulose. The modified sodium alginate is prepared by modifying with an epoxy silane coupling agent, and it contains epoxy groups on it. When mixed with silicon carbide, the epoxy groups of the modified sodium alginate can crosslink with the hydroxyethyl cellulose and the hydroxyl groups on the surface of the silicon carbide, and there is also good binding performance between the hydroxyethyl cellulose and the silicon carbide, so that the modified sodium alginate and hydroxyethyl cellulose are uniformly coated on the surface of the silicon carbide, improving the uniform dispersion of the silicon carbide; the present invention conducts functional treatment on the carbon fiber and microsphere modification treatment on the silicon carbide, so that the carbon fiber has good dispersion in the silicon carbide matrix. In the step of preparing the mixture, the amino groups of the functional carbon fiber crosslink with the epoxy groups of the modified silicon carbide microspheres, thereby realizing the uniform dispersion of the carbon fiber in the silicon carbide matrix, improving the homogeneity of the mixture, and better exerting the strengthening and toughening effect of the carbon fiber on the silicon carbide, thereby improving the toughness and strength performance of the ceramic product, ensuring the stability and high-temperature oxidation resistance of the ceramic product, and improving the comprehensive performance of the product;

[0041] 2. The carbon fiber reinforced silicon carbide ceramic prepared by the present invention has a flexural strength of 574 - 579 MPa, a fracture toughness of 11.9 - 12.3 Mpa·m 1 / 2 , a thermal expansion coefficient of 1.0 - 1.2×10 -6 / °C, and a tensile strength of 282 - 289 MPa;

[0042] 3. The carbon fiber reinforced silicon carbide ceramic prepared by the present invention, in an air environment, is heated to 1200 °C at a rate of 20 °C / min, and then heated to 2000 °C at a rate of 40 °C / min, held at 2000 °C for 6.0 h. After the heat preservation ends, it is cooled to room temperature at a rate of 40 °C / min; the above operation is taken as one cycle, and the above operation is repeated 10 cycles. The flexural strength is measured again to be 559 - 568 MPa, and the fracture toughness is 11.5 - 12.0 Mpa·m 1 / 2 , and the tensile strength is 271 - 281 MPa. Detailed implementation manners

[0043] For a clearer understanding of the technical features, objectives, and effects of the present invention, the detailed implementation manners of the present invention are described as follows:

[0044] Example 1

[0045] 1. Preparation of functional carbon fiber

[0046] (1) Primary functionalization

[0047] Place 10.0 g of carbon fiber in 80 g of acetone, raise the temperature to 88 °C, keep it warm and soak for 4.0 h, take it out and wash it, dry it at 65 °C for 10.0 h, then put it into 100 g of deionized water, add 25.0 g of 18 wt% citric acid solution, raise the temperature to 40 °C, keep it warm and stir for 40 min, add 1.32 g of kH550, raise the temperature to 64 °C at a rate of 1.0 °C / min, keep it warm and stir for 4.5 h. After the heat preservation and stirring end, filter it out and wash it, and dry it at 80 °C for 10.0 h to obtain primary functionalized carbon fiber;

[0048] The carbon fiber has a length of 0.5 μm and a diameter of 160 nm;

[0049] (2) Secondary functionalization

[0050] Place 10.5 g of primary functionalized carbon fiber in 200 g of N, N-dimethylformamide, stir evenly under a nitrogen atmosphere, add 3.4 g of acrylamide, control the temperature at 60 °C, then add 0.11 g of ammonium persulfate and 0.26 g of N,N'-methylenebisacrylamide, carry out ultrasonic dispersion, control the ultrasonic time at 40 min, the ultrasonic power at 220 W, and the ultrasonic frequency at 25 kHz. After the ultrasonic treatment ends, stir and react at 150 rpm for 16.0 h. After the reaction ends, filter, wash, and dry to obtain functional carbon fiber.

[0051] 2. Preparation of modified silicon carbide microspheres

[0052] 12.5 g of silicon carbide was placed in 120 g of 30 wt% ethanol solution, and 1.32 g of sodium dodecyl aminopropionate was added for ball milling. The ball milling time was 30 min, the ball milling speed was 170 rpm, and the ball-to-material ratio was 4:1. After ball milling, it was filtered out and dried at 78 °C for 12.0 h to obtain ball-milled silicon carbide; 11.4 g of ball-milled silicon carbide was placed in 120 mL of dimethyl sulfoxide, stirred evenly, then 2.1 g of modified sodium alginate and 1.3 g of hydroxyethyl cellulose were added, heated to 72 °C at a rate of 2.0 °C / min, 0.4 g of tetrabutylammonium bromide was added, and the reaction was carried out under insulation for 11.0 h. After the reaction, it was filtered, washed, and dried to obtain modified silicon carbide microspheres;

[0053] The particle size of the silicon carbide is 140 nm;

[0054] The preparation method of the modified sodium alginate is as follows: 10.0 g of sodium alginate was placed in 110 g of deionized water, stirred evenly, then 1.4 g of kH560 was added, the temperature was raised to 64 °C, and the mixture was stirred under insulation for 2.5 h. After stirring, it was filtered, washed, and dried to obtain modified sodium alginate.

[0055] 3. Preparation of the mixture

[0056] 10.7 g of functional carbon fiber and 52.3 g of modified silicon carbide microspheres were added to 1000 mL of dimethyl sulfoxide, the temperature was raised to 70 °C, and the mixture was stirred under insulation for 6.0 h. After filtering, it was washed and dried to obtain a preliminary mixture; 63.0 g of the preliminary mixture was put into 220 g of 25 wt% ethanol solution, then 3.6 g of silicon nitride, 4.5 g of graphite, 5.2 g of zirconia, 8.6 g of phenolic resin, 1.4 g of titanium dioxide, and 1.0 g of sodium dioctyl sulfosuccinate were added, and homogenization treatment was carried out. The homogenization pressure was 5.0 MPa, the homogenization time was 5.0 min, and the number of homogenization times was 3 times. After the homogenization treatment, it was filtered, washed, and dried to obtain the mixture.

[0057] 4. Molding and calcination

[0058] The mixture was placed in a mold, pre-tightened under a pressure of 8.0 MPa for 11 s, and then cold-pressed and formed under 35 MPa for 8.0 min to obtain a ceramic green body; the ceramic green body was placed in a sintering furnace, and under an argon atmosphere, it was heated to 870 °C at a rate of 6.5 °C / min, held for 25 min, then heated to 1580 °C at a rate of 2.0 °C / min, held for 2.5 h, and cooled naturally to obtain carbon fiber-reinforced silicon carbide ceramics.

[0059] Example 2

[0060] 1. Preparation of functional carbon fiber

[0061] (1)Primary functionalization

[0062] Place 9.7 g of carbon fiber in 78 g of acetone, raise the temperature to 86 °C, soak for 3.7 h while maintaining the temperature, take it out and wash it, dry it at 63 °C for 11.0 h, then put it into 95 g of deionized water, add 24.3 g of 16 wt% citric acid solution, raise the temperature to 38 °C, stir while maintaining the temperature for 37 min, add 1.30 g of kH550, raise the temperature to 62 °C at a rate of 0.8 °C / min, stir while maintaining the temperature for 4.3 h. After the stirring while maintaining the temperature is completed, filter it out and wash it, and dry it at 78 °C for 12.0 h to obtain primary functionalized carbon fiber;

[0063] The carbon fiber has a length of 0.4 μm and a diameter of 140 nm;

[0064] (2)Secondary functionalization

[0065] Place 10.3 g of primary functionalized carbon fiber in 180 g of N,N-dimethylformamide, stir evenly under a nitrogen atmosphere, add 3.2 g of acrylamide, control the temperature at 58 °C, then add 0.10 g of ammonium persulfate and 0.25 g of N,N'-methylenebisacrylamide, carry out ultrasonic dispersion, control the ultrasonic time at 37 min, the ultrasonic power at 216 W, and the ultrasonic frequency at 23 kHz. After the ultrasonic treatment is completed, stir and react at 142 rpm for 15.5 h. After the reaction is completed, filter, wash, and dry to obtain functionalized carbon fiber.

[0066] 2. Preparation of modified silicon carbide microspheres

[0067] Place 12.3 g of silicon carbide in 115 g of 27 wt% ethanol solution, add 1.30 g of sodium dodecylaminopropionate for ball milling treatment, the ball milling time is 28 min, the ball milling speed is 164 rpm, the ball-to-material ratio is 3:1. After the ball milling is completed, filter it out and dry it at 76 °C for 13.0 h to obtain ball-milled silicon carbide; place 11.2 g of ball-milled silicon carbide in 115 mL of dimethyl sulfoxide, stir evenly, add 2.0 g of modified sodium alginate and 1.0 g of hydroxyethyl cellulose, raise the temperature to 70 °C at a rate of 1.7 °C / min, add 0.3 g of tetrabutylammonium bromide, and react while maintaining the temperature for 10.0 h. After the reaction is completed, filter, wash, and dry to obtain modified silicon carbide microspheres;

[0068] The particle size of the silicon carbide is 120 nm;

[0069] The preparation method of the modified sodium alginate is as follows: place 9.7 g of sodium alginate in 105 g of deionized water, stir evenly, add 1.2 g of kH560, raise the temperature to 62 °C, stir while maintaining the temperature for 2.3 h. After the stirring is completed, filter, wash, and dry to obtain modified sodium alginate.

[0070] 3. Preparation of the mixture

[0071] 10.5 g of functional carbon fiber and 52.0 g of modified silicon carbide microspheres were added to 1000 mL of dimethyl sulfoxide. The temperature was raised to 68 °C and stirred for 5.7 h while maintaining the temperature. After filtration, washing and drying, a preliminary mixture was obtained. 62.4 g of the preliminary mixture was put into 214 g of 23 wt% ethanol solution, and then 3.4 g of silicon nitride, 4.4 g of graphite, 5.0 g of zirconia, 8.4 g of phenolic resin, 1.2 g of titanium dioxide and 0.8 g of sodium dioctyl sulfosuccinate were added, and homogenization treatment was carried out. The homogenization pressure was 4.7 MPa, the homogenization time was 6.0 min, and the number of homogenization times was 3 times. After the homogenization treatment, filtration, washing and drying were carried out to obtain a mixed material.

[0072] 4. Molding and calcination

[0073] The mixed material was placed in a mold and pre-tightened at a pressure of 7.8 MPa for 12 s, and then cold-pressed and formed at 34 MPa for 8.5 min to obtain a ceramic green body. The ceramic green body was placed in a sintering furnace, and under an argon atmosphere, the temperature was raised to 860 °C at a rate of 6.0 °C / min, held for 23 min, then the temperature was raised to 1572 °C at a rate of 2.3 °C / min, held for 2.6 h, and cooled naturally to obtain carbon fiber reinforced silicon carbide ceramic.

[0074] Example 3

[0075] 1. Preparation of functional carbon fiber

[0076] (1)Primary functionalization

[0077] 10.3 g of carbon fiber was placed in 83 g of acetone, the temperature was raised to 90 °C, and soaked for 4.2 h while maintaining the temperature. After taking out, it was washed and dried at 67 °C for 9.5 h, and then put into 106 g of deionized water. 25.4 g of 20 wt% citric acid solution was added, the temperature was raised to 42 °C, and stirred for 44 min while maintaining the temperature. 1.35 g of kH550 was added, and the temperature was raised to 67 °C at a rate of 1.3 °C / min, and stirred for 4.7 h while maintaining the temperature. After the stirring ended, it was filtered, washed and dried at 82 °C for 9.5 h to obtain primary functionalized carbon fiber;

[0078] The carbon fiber has a length of 0.6 μm and a diameter of 170 nm;

[0079] (2)Secondary functionalization

[0080] 10.8 g of primary functionalized carbon fiber was placed in 210 g of N,N-dimethylformamide, stirred evenly under a nitrogen atmosphere, 3.5 g of acrylamide was added, the temperature was controlled at 63 °C, then 0.12 g of ammonium persulfate and 0.28 g of N,N'-methylenebisacrylamide were added, and ultrasonic dispersion was carried out. The ultrasonic time was controlled at 45 min, the ultrasonic power was 223 W, and the ultrasonic frequency was 26 kHz. After the ultrasonic treatment, the reaction was stirred at 155 rpm for 16.3 h. After the reaction was completed, it was filtered, washed, and dried to obtain functionalized carbon fiber.

[0081] 2. Preparation of modified silicon carbide microspheres

[0082] 12.6 g of silicon carbide was placed in 125 g of 32 wt% ethanol solution, 1.34 g of sodium dodecylaminopropionate was added for ball milling. The ball milling time was 32 min, the ball milling speed was 175 rpm, and the ball-to-material ratio was 5:1. After the ball milling was completed, it was filtered out and dried at 80 °C for 11.0 h to obtain ball-milled silicon carbide; 11.7 g of ball-milled silicon carbide was placed in 124 mL of dimethyl sulfoxide, stirred evenly, 2.3 g of modified sodium alginate and 1.5 g of hydroxyethyl cellulose were added, and the temperature was raised to 74 °C at a rate of 2.4 °C / min. 0.5 g of tetrabutylammonium bromide was added, and the reaction was kept warm for 11.5 h. After the reaction was completed, it was filtered, washed, and dried to obtain modified silicon carbide microspheres;

[0083] The particle size of the silicon carbide is 150 nm;

[0084] The preparation method of the modified sodium alginate is as follows: 10.2 g of sodium alginate was placed in 114 g of deionized water, stirred evenly, 1.5 g of kH560 was added, the temperature was raised to 65 °C, and the mixture was stirred at a constant temperature for 2.6 h. After the stirring was completed, it was filtered, washed, and dried to obtain modified sodium alginate.

[0085] 3. Preparation of the mixture

[0086] 11.0 g of functionalized carbon fiber and 52.7 g of modified silicon carbide microspheres were added to 1000 mL of dimethyl sulfoxide, the temperature was raised to 72 °C, and the mixture was stirred at a constant temperature for 6.2 h. After filtration, it was washed and dried to obtain a preliminary mixture; 63.5 g of the preliminary mixture was put into 225 g of 27 wt% ethanol solution, then 3.7 g of silicon nitride, 4.6 g of graphite, 5.3 g of zirconia, 8.7 g of phenolic resin, 1.6 g of titanium dioxide, and 1.1 g of sodium dioctyl sulfosuccinate were added, and homogenization treatment was carried out. The homogenization pressure was 5.3 MPa, the homogenization time was 4.0 min, and the number of homogenization times was 3 times. After the homogenization treatment was completed, it was filtered, washed, and dried to obtain the mixture.

[0087] 4. Molding and calcination

[0088] Place the mixture in a mold, perform pre-tightening treatment under a pressure of 8.2 MPa for 10 s, and then perform cold pressing and forming treatment at 36 MPa for 7.5 min to obtain a ceramic green body; place the ceramic green body in a sintering furnace, under an argon atmosphere, heat it at a rate of 7.0 °C / min to 880 °C, hold for 28 min, then heat it at a rate of 1.7 °C / min to 1586 °C, hold for 2.4 h, and cool naturally to obtain carbon fiber reinforced silicon carbide ceramics.

[0089] Comparative Example 1

[0090] Based on Example 1, the changes are as follows:

[0091] Omit the preparation of functional carbon fibers; in the step of preparing the mixture, replace the functional carbon fibers with carbon fibers without any treatment in equal amounts;

[0092] The preparation method of the initial mixture is to mix 10.7 g of carbon fibers and 52.3 g of modified silicon carbide microspheres, stir evenly to obtain the initial mixture; the carbon fibers have a length of 0.5 μm and a diameter of 160 nm;

[0093] The remaining operations are the same.

[0094] Comparative Example 2

[0095] Based on Example 1, the changes are as follows:

[0096] Omit the step of preparing modified silicon carbide microspheres; in the step of preparing the mixture, replace the modified silicon carbide microspheres with silicon carbide without any treatment in equal amounts;

[0097] The preparation method of the initial mixture is to mix 10.7 g of functional carbon fibers and 52.3 g of silicon carbide, stir evenly to obtain the initial mixture; the particle size of the silicon carbide is 140 nm;

[0098] The remaining operations are the same.

[0099] Performance Test

[0100] Perform performance tests on the carbon fiber reinforced silicon carbide ceramics prepared in Examples 1-3 and Comparative Examples 1-2, specifically as follows:

[0101]

[0102] Among them, for the high-temperature oxidation resistance performance, the carbon fiber-reinforced silicon carbide ceramics prepared in Examples 1-3 and Comparative Examples 1-2 were heated in an air environment at a rate of 20 °C / min to 1200 °C, and then heated at a rate of 40 °C / min to 2000 °C, and held at 2000 °C for 6.0 h. After the holding was completed, the temperature was decreased to room temperature at a rate of 40 °C / min; the above operations were taken as one cycle, and the above operations were repeated 10 cycles, and then the performance of the product was tested again.

[0103] In the present invention, silicon carbide is used as the ceramic matrix and carbon fiber is used as the ceramic reinforcing phase. First, the carbon fiber is subjected to functional treatment. Specifically, the carbon fiber is first soaked in acetone to remove the colloid and impurities on the surface of the carbon fiber, and then treated with a citric acid solution and a KH550 silane coupling agent. The citric acid solution contains hydroxyl groups, which can adhere to the surface of the carbon fiber and enhance the binding performance with the KH550 silane coupling agent, so that the surface of the carbon fiber contains more amino groups to obtain primary functionalized carbon fiber. The primary functionalized carbon fiber is mixed with acrylamide monomer, and under the action of an initiator and a crosslinking agent, a polyacrylamide chain is formed through a polymerization reaction, which forms a tight network structure with the carbon fiber through a crosslinking reaction, and the interfacial bonding strength between them is good, so that the strength performance and stability performance of the ceramic material can be improved, and the functional carbon fiber has good high-temperature oxidation resistance; in the step of preparing silicon carbide microspheres, specifically, the silicon carbide is first subjected to ball milling treatment. Under the action of a surfactant, the silicon carbide is uniformly dispersed, and under the physical impact of ball milling, the crystal lattice generates defects, improving the surface activity of the silicon carbide. Then, the silicon carbide is mixed with modified sodium alginate and hydroxyethyl cellulose. The modified sodium alginate is prepared by modifying with an epoxy silane coupling agent, and it contains epoxy groups on it. When mixed with silicon carbide, the epoxy groups of the modified sodium alginate can crosslink with the hydroxy groups on the surface of hydroxyethyl cellulose and silicon carbide, and there is also good binding performance between hydroxyethyl cellulose and silicon carbide, so that the modified sodium alginate and hydroxyethyl cellulose are uniformly coated on the surface of the silicon carbide, improving the uniform dispersion of the silicon carbide; in the present invention, the carbon fiber is subjected to functional treatment and the silicon carbide is subjected to microsphere modification treatment, so that the carbon fiber has good dispersion in the silicon carbide matrix. In the step of preparing the mixture, the amino groups of the functional carbon fiber crosslink with the epoxy groups of the modified silicon carbide microspheres, thus realizing the uniform dispersion of the carbon fiber in the silicon carbide matrix, improving the homogeneity of the mixture, and better exerting the strengthening and toughening effect of the carbon fiber on the silicon carbide, thereby improving the toughness and strength performance of the ceramic product, ensuring the stability and high-temperature oxidation resistance of the ceramic product, and improving the comprehensive performance of the product.

[0104] Comparative Example 1 omitted the step of preparing functional carbon fibers. The carbon fibers had strong inertness, poor surface wettability, and poor surface activity. In the step of preparing the mixture, their compatibility with the silicon carbide matrix was poor, and they were not evenly dispersed in the silicon carbide matrix, which affected the homogeneity of the mixture, and the reinforcing and toughening effects of the carbon fibers could not be fully exerted. Moreover, the carbon fibers had poor high-temperature oxidation resistance, and their strength and toughness decreased rapidly in a high-temperature aerobic environment, resulting in poor stability. Comparative Example 2 omitted the preparation of modified silicon carbide microspheres. In the step of preparing the mixture, the agglomeration force between the silicon carbide particles was strong. When mixed with the functional carbon fibers, the binding property between them was poor, and sufficient and effective cross-linking could not be achieved, thus affecting the homogeneous stability of the mixture and ultimately the comprehensive performance of the ceramic product.

[0105] Unless otherwise specified, the percentages used in the present invention are all mass percentages.

[0106] Finally, it should be noted that the above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or perform equivalent replacements for some of the technical features. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for preparing carbon fiber reinforced silicon carbide ceramics, characterized in that: The method includes the steps of preparing functional carbon fiber, preparing modified silicon carbide microspheres, preparing a mixture, molding and calcining; The preparation of functional carbon fibers includes primary functionalization and secondary functionalization; The primary functionalization step comprises placing the carbon fiber in acetone, raising the temperature to 86-90° C., soaking in the acetone for 3.7-4.2 hours, taking it out and washing it, drying it at 63-67° C. for 9.5-11.0 hours, then putting it into deionized water, adding citric acid solution, raising the temperature to 38-42° C., stirring in the acetone for 37-44 minutes, adding kH550, raising the temperature to 62-67° C. at a rate of 0.8-1.3° C. / min, stirring in the acetone for 4.3-4.7 hours, filtering it out and washing it, and drying it at 78-82° C. for 9.0-12.0 hours to obtain primary functionalized carbon fiber; The secondary functionalization step comprises placing the primary functionalized carbon fiber in N,N-dimethylformamide, stirring evenly under a nitrogen atmosphere, adding acrylamide, controlling the temperature to 58-63° C., then adding ammonium persulfate and N,N'-methylenebisacrylamide, and performing ultrasonic dispersion. After the ultrasonic dispersion is completed, stirring and reacting for 15.5-16.3 hours, filtering, washing, and drying after the reaction is completed to obtain the functional carbon fiber. The mass ratio of the primary functionalized carbon fiber, N,N-dimethylformamide, acrylamide, ammonium persulfate and N,N'-methylenebisacrylamide is 10.3-10.8:180-210:3.2-3.5:0.10-0.12:0.25-0.28; The steps of preparing the modified silicon carbide microspheres are as follows: placing silicon carbide in an ethanol solution, adding sodium dodecylaminopropionate for ball milling, filtering out and drying after the ball milling to obtain ball-milled silicon carbide; placing the ball-milled silicon carbide in dimethyl sulfoxide, stirring evenly, adding modified sodium alginate and hydroxyethyl cellulose, heating to 70-74° C., adding tetrabutylammonium bromide, keeping the temperature for reaction for 10.0-11.5 hours, filtering, washing and drying after the reaction to obtain modified silicon carbide microspheres; The mass ratio of the silicon carbide, ethanol solution and sodium dodecylaminopropionate is 12.3-12.6:115-125:1.30-1.34; The mass volume ratio of the ball-milled silicon carbide, dimethyl sulfoxide, modified sodium alginate, hydroxyethyl cellulose and tetrabutylammonium bromide is 11.2-11.7 g: 115-124 mL: 2.0-2.3 g: 1.0-1.5 g: 0.3-0.5 g; The preparation method of the modified sodium alginate is as follows: placing sodium alginate in deionized water, stirring evenly, adding KH560, raising the temperature to 62-65° C., keeping the temperature and stirring for 2.3-2.6 hours, filtering, washing and drying after the stirring is completed to obtain the modified sodium alginate; The mass ratio of sodium alginate, deionized water and kH560 is 9.7-10.2:105-114:1.2-1.5; The steps of preparing the mixture are: adding functional carbon fiber and modified silicon carbide microspheres to dimethyl sulfoxide, raising the temperature to 68-72° C., keeping the mixture warm and stirring for 5.7-6.2 hours, filtering out, washing and drying to obtain a primary mixture; putting the primary mixture into an ethanol solution, then adding silicon nitride, graphite, zirconium oxide, phenolic resin, titanium dioxide and sodium dioctyl succinate sulfonate, and homogenizing the mixture at a homogenizing pressure of 4.7-5.3 MPa, a homogenizing time of 4.0-6.0 minutes, and three homogenizing times; after the homogenization is completed, filtering, washing and drying to obtain a mixture.

2. The method for preparing carbon fiber reinforced silicon carbide ceramics according to claim 1, characterized in that: In the primary functionalization step, the carbon fiber has a length of 0.4-0.6 μm and a diameter of 140-170 nm; The mass ratio of the carbon fiber, acetone, deionized water, citric acid solution, and Kh550 is 9.7-10.3:78-83:95-106:24.3-25.4:1.30-1.35; The mass concentration of the citric acid solution is 16-20%.

3. The method for preparing carbon fiber reinforced silicon carbide ceramics according to claim 1, characterized in that: In the secondary functionalization step, the ultrasonic dispersion has an ultrasonic time of 37-45 min, an ultrasonic power of 216-223 W, and an ultrasonic frequency of 23-26 kHz.

4. The method for preparing carbon fiber reinforced silicon carbide ceramics according to claim 1, characterized in that: In the step of preparing modified silicon carbide microspheres, the ball milling time is 28-32 min, the ball milling speed is 164-175 rpm, and the ball-to-material ratio is 3-5:1; The particle size of the silicon carbide is 120-150nm; The mass concentration of the ethanol solution is 27-32%.

5. The method for preparing carbon fiber reinforced silicon carbide ceramics according to claim 1, characterized in that: In the step of preparing the mixture, the volume mass ratio of the dimethyl sulfoxide, the functional carbon fiber and the modified silicon carbide microspheres is 1000 mL: 10.5-11.0 g: 52.0-52.7 g; The mass ratio of the primary mixture, ethanol solution, silicon nitride, graphite, zirconium oxide, phenolic resin, titanium dioxide and dioctyl sodium sulfosuccinate is 62.4-63.5:214-225:3.4-3.7:4.4-4.6:5.0-5.3:8.4-8.7:1.2-1.6:0.8-1.1; The mass concentration of the ethanol solution is 23-27%.

6. The method for preparing carbon fiber reinforced silicon carbide ceramics according to claim 1, characterized in that: The molding and calcining steps are as follows: placing the mixture in a mold, performing a pre-tightening treatment at a pressure of 7.8-8.2 MPa for 10-12 seconds, and then performing a cold pressing molding treatment at 34-36 MPa for 7.5-8.5 minutes to obtain a ceramic body; placing the ceramic body in a sintering furnace, heating the temperature to 860-880°C at a rate of 6.0-7.0°C / min in an argon atmosphere, keeping the temperature for 23-28 minutes, then heating the temperature to 1572-1586°C at a rate of 1.7-2.3°C / min, keeping the temperature for 2.4-2.6 hours, and cooling naturally to obtain carbon fiber reinforced silicon carbide ceramics.

7. Carbon fiber reinforced silicon carbide ceramics prepared according to the preparation method according to any one of claims 1 to 6.

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