Silicon carbide special ceramic and preparation method thereof

Abstract

The invention discloses silicon carbide special ceramic and a preparation method thereof, and belongs to the technical field of silicon carbide ceramic. The preparation method comprises the following steps: mixing silicon carbide powder with rare earth coated PAN carbon fibers, titanium disilicide, titanium aluminum carbon powder, silicon hexaboride, hafnium carbide, tantalum carbide and a carbon source, adding a binder and a dispersant, carrying out ball milling to prepare slurry, carrying out compression molding to obtain a porous biscuit, and finally carrying out a two-step sintering process to prepare the silicon carbide special ceramic. According to the invention, the defects of low fracture toughness, low high-temperature strength and low oxidation resistance of a traditional reaction sintered silicon carbide material are overcome, and the prepared silicon carbide special ceramic has high hardness and toughness, is high in bending strength retention rate and excellent in oxidation resistance under the ultrahigh-temperature condition of 1400 DEG C, and can meet the application requirements of more working scenes.

Description

Technical Field

[0001] This invention belongs to the field of silicon carbide ceramic technology, specifically relating to a special silicon carbide ceramic and its preparation method. Background Technology

[0002] Silicon carbide is an important advanced ceramic material. Its unique bonding mode (extremely high proportion of covalent bonds) endows it with a series of excellent physical and chemical properties, including: extremely high hardness and wear resistance, excellent chemical stability, and good high-temperature mechanical and thermal properties. Based on this, silicon carbide materials are widely used in many technical fields such as metallurgy, chemical industry, aerospace, wear resistance, sealing, and semiconductors, such as kiln furniture, chemical pumps and valves, engines, gas turbines, pipelines, reactors, and linings.

[0003] Currently, the main methods for preparing silicon carbide ceramic materials include pressureless sintering, reaction sintering, hot pressing sintering, gas pressure sintering, and precursor pyrolysis conversion. Among these, reaction sintering holds an irreplaceable position in the preparation of complex shapes and large-size components due to its advantages of low cost and high efficiency. However, its inherent process characteristics also lead to some defects in the prepared materials. For example, reaction sintering products typically contain 10%-20% free silicon, which significantly reduces material performance when the operating temperature exceeds the melting point of silicon, thus limiting its application in high-temperature environments. Furthermore, the pore structure, uniformity of distribution, and compatibility of the raw materials all affect the microstructure and performance stability of the final material, making product consistency control difficult.

[0004] In view of this, it is of great significance to research and develop a high-performance reaction-sintered silicon carbide special ceramic material in order to improve the shortcomings of the traditional reaction sintering method and expand its application range. Summary of the Invention

[0005] In response to the problems mentioned in the background art, the purpose of this invention is to provide a special silicon carbide ceramic and its preparation method. Through research and improvement of raw materials and preparation process, this invention effectively improves the performance defects of traditional reaction sintered silicon carbide ceramics and can meet the application needs of more working scenarios.

[0006] To achieve the above objectives, the present invention specifically adopts the following technical solution: This invention provides a method for preparing silicon carbide special ceramics, comprising the following steps: S1. Take silicon carbide powder and mix it with carbon fiber, titanium disilicide, titanium aluminum carbon powder, silicon hexaboride, hafnium carbide, tantalum carbide and carbon source, then disperse it in a solvent, ultrasonically stir it, then add binder and dispersant, and ball mill it to obtain a mixed slurry for later use; the carbon fiber is rare earth coated PAN carbon fiber, and the carbon source is composed of carbon black and needle coke, with a mass ratio of (6.5-7.5):(2.5-3.5); S2. Vacuum casting and isostatic pressing of the mixed slurry obtained in S1, followed by drying and curing, yields a porous preform for later use. S3. Under the protection of inert gas, the obtained porous green blank is sintered once, and then the porous green blank is embedded in silicon powder for secondary sintering. After the heat preservation is completed, silicon carbide special ceramics are obtained.

[0007] Furthermore, by weight, the amounts of each raw material in S1 are as follows: 100 parts silicon carbide powder, 4.0-6.4 parts carbon fiber, 1.8-4.2 parts titanium disilicide, 1.2-3.5 parts titanium aluminum carbon powder, 3-6 parts silicon hexaboride, 0.1-0.4 parts hafnium carbide, 0.3-0.6 parts tantalum carbide, and 8-12 parts carbon source.

[0008] Further, the silicon carbide powder mentioned in S1 is 6H-SiC with a particle size of 30-120 μm; wherein the particle size of 30-80 μm accounts for 30%-70%, and the particle size of 80-120 μm accounts for 70%-30%; preferably, the particle size of 30-80 μm accounts for 50%, and the particle size of 80-120 μm accounts for 50%. This invention uses ordinary silicon carbide powder (97% purity) with a particle size of 30-120 μm as the basic framework material, without the need for nano- or submicron-sized high-purity silicon carbide powder.

[0009] Further, the method for preparing the rare earth-coated PAN carbon fiber described in S1 is as follows: PAN carbon fiber is placed in concentrated sulfuric acid solution and heated at 50-70℃ under inert gas protection for 15-20 min, and then washed until neutral; the treated PAN carbon fiber is transferred into rare earth nitrate solution and stirred evenly, reacted at 120-160℃ for 6-8 h, and finally washed and vacuum dried to obtain the rare earth-coated PAN carbon fiber.

[0010] Furthermore, the rare earth nitrate solution is prepared using lanthanum nitrate and cerium nitrate, with the mass ratio of PAN carbon fiber, lanthanum nitrate, and cerium nitrate being 10:(0.1-0.2):(0.2-0.3).

[0011] The rare earth-coated PAN carbon fiber of this invention not only has the toughening effect of fiber pull-out and bridging, but also the rare earth coating can further improve its interfacial bonding with the basic skeleton and other dopants, avoiding adverse interfacial reactions at high temperatures. At the same time, it can also enhance the diffusion effect between dopants, provide additional micro-reaction channels, and facilitate the full occurrence of silicon-carbon reaction during sintering. It effectively solves the problem of inconsistent microstructure caused by uneven mixing or local pore blockage, avoids the defect of local weak bonding areas becoming crack sources, and improves the overall strength and reliability of the material.

[0012] This invention uses carbon black and needle coke as carbon sources. The high reactivity of carbon black ensures the rate of the silicon-carbon reaction, while needle coke, on the one hand, inhibits excessively high reaction rates to prevent large amounts of new silicon carbide from clogging capillary channels; on the other hand, its needle-like and lamellar structure also hinders crack propagation, thus playing a certain toughening role. The carbon source combination selected in this invention allows silicon to continuously and stably penetrate into the material during the melting and infiltration process, ensuring the reaction rate while avoiding the problem of excessive residual carbon.

[0013] In addition, this invention adds other exogenous reinforcing phases: titanium disilicide forms a eutectic liquid phase during silicon infiltration, promoting sintering and densification, increasing hardness and strength, and strengthening grain boundaries and oxidation resistance; titanium aluminum carbon can promote the migration between doped phases, activating sintering and toughening, which is beneficial to the uniformity of the performance of the prepared silicon carbide ceramic material; and trace amounts of hafnium carbide and tantalum carbide can improve grain boundary strength, improve the hardness, strength and oxidation resistance of the material under ultra-high temperature environment, and give the material stability at higher temperatures.

[0014] Furthermore, the binder in S1 is phenolic resin, and the dispersant is polyvinylpyrrolidone, both of which are added at 2%-4% of the mass of silicon carbide powder.

[0015] Furthermore, the isostatic pressing pressure value described in S2 is 50-70 MPa, the holding time is 40-60 s, and the porosity of the obtained porous preform needs to be controlled to be 22%-28%.

[0016] Further, the temperature of the first sintering in S3 is 1420-1460℃, the heating rate is 5-10℃ / min, and the holding time is 0.5-1 h; the temperature of the second sintering is 1510-1590℃, the heating rate is 2-4℃ / min, and the holding time is 2-3 h. This invention employs a two-step sintering process: the first sintering (pre-sintering of the green body) removes the binder and dispersant from the porous green body, while simultaneously allowing some of the doped components in the green body to undergo a preliminary reaction, forming a certain skeletal strength, and further controlling the open pores, porosity, and connectivity of the green body, laying the groundwork for the second step of silicon-carbon infiltration reaction; in the second sintering (silicon-carbon infiltration reaction sintering), the molten silicon liquid spontaneously infiltrates into the pores of the porous green body under capillary force, reacting with the carbon source to fill the pores, achieving densification, and obtaining silicon carbide ceramic material. This invention can effectively reduce the free silicon content through two-step sintering, eliminating the need for subsequent heat treatment and significantly reducing energy consumption and overall process costs.

[0017] The present invention also provides silicon carbide special ceramics prepared by the above method.

[0018] Compared with the prior art, the beneficial effects of the present invention are: This invention not only effectively improves the high-temperature strength and oxidation resistance of silicon carbide materials, breaking through the limitations of traditional reaction-sintered ceramic materials in high-temperature applications, but also produces silicon carbide special ceramic materials with high hardness and fracture toughness, meeting the application requirements of more working scenarios. This invention effectively reduces energy consumption and cost, has a simple preparation process, and produces products with good consistency, making it suitable for industrial production. Detailed Implementation

[0019] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below in conjunction with embodiments. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0020] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. The terminology used in this specification is for the purpose of describing particular embodiments only and is not intended to limit the invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0021] Example 1 A method for preparing silicon carbide special ceramics, comprising the following steps: 1. Under nitrogen protection, 10 parts of PAN carbon fiber (length-to-diameter ratio 5-10:1) were dispersed in 10 parts of concentrated sulfuric acid solution (98% concentration), heated at 60℃ for 20 min, and then washed with water until neutral. Separately, 0.15 parts of lanthanum nitrate and 0.25 parts of cerium nitrate were dissolved in 20 parts of nitric acid solution (60% concentration) to prepare a rare earth nitrate solution. The treated PAN carbon fiber was transferred into the rare earth nitrate solution and stirred until homogeneous. 0.05 parts of alkylphenol polyoxyethylene ether were added, and the mixture was heated to 140℃ for 7 h. After washing and vacuum drying, rare earth-coated PAN carbon fiber was obtained.

[0022] 2. Weigh out 100 parts by weight of silicon carbide powder (6H-SiC, purity 97%; 50% of particles with a diameter of 30-80 μm and 50% of particles with a diameter of 80-120 μm), 5.2 parts of rare earth-coated PAN carbon fiber, 2.8 parts of titanium disilicide, 2.5 parts of titanium aluminum carbon powder, 4.5 parts of silicon hexaboride, 0.25 parts of hafnium carbide, 0.42 parts of tantalum carbide, and 10 parts of carbon source (composed of carbon black and needle coke in a mass ratio of 7:3). Mix the above raw materials and then disperse them in a solvent (ethanol + 0.1% triethyl phosphate, solid-liquid ratio 1:1.8). Stir ultrasonically for 30 min, then add 3 parts of phenolic resin and 2 parts of polyvinylpyrrolidone, and ball mill for 2 h (ball-to-material ratio 1:1, speed 500 rpm) to obtain a mixed slurry.

[0023] 3. The obtained mixed slurry is transferred to a pressure vessel for vacuum treatment, and then injected into a mold for isostatic pressing (60 MPa for 50 s). After drying and curing, a porous green body with a porosity of 26% is obtained. The porous green body is placed in a furnace and heated to 1440℃ at 8℃ / min under nitrogen protection, and held for 0.8 h. Then, the porous green body is embedded in half of its mass of silicon powder, heated to 1560℃ at 3℃ / min, held for 2.5 h, and cooled with the furnace to obtain silicon carbide special ceramics.

[0024] Example 2 A method for preparing silicon carbide special ceramics, comprising the following steps: 1. Under nitrogen protection, 10 parts of PAN carbon fiber (length-to-diameter ratio 5-10:1) were dispersed in 10 parts of concentrated sulfuric acid solution (98% concentration), heated at 60℃ for 20 min, and then washed with water until neutral. Separately, 0.12 parts of lanthanum nitrate and 0.2 parts of cerium nitrate were dissolved in 20 parts of nitric acid solution (60% concentration) to prepare a rare earth nitrate solution. The treated PAN carbon fiber was transferred into the rare earth nitrate solution and stirred until homogeneous. 0.05 parts of alkylphenol polyoxyethylene ether were added, and the mixture was heated to 140℃ for 7 h. After washing and vacuum drying, rare earth-coated PAN carbon fiber was obtained.

[0025] 2. Weigh out 100 parts by weight of silicon carbide powder (6H-SiC, purity 97%; 70% of particles with a diameter of 30-80 μm and 30% of particles with a diameter of 80-120 μm), 4.0 parts of rare earth-coated PAN carbon fiber, 1.8 parts of titanium disilicide, 3.5 parts of titanium aluminum carbon powder, 3 parts of silicon hexaboride, 0.4 parts of hafnium carbide, 0.3 parts of tantalum carbide, and 12 parts of carbon source (composed of carbon black and needle coke in a mass ratio of 6.5:3.5). Mix the above raw materials and then disperse them in a solvent (ethanol + 0.1% triethyl phosphate, solid-liquid ratio 1:1.8). Stir ultrasonically for 30 min, then add 3 parts of phenolic resin and 2 parts of polyvinylpyrrolidone, and ball mill for 2 h (ball-to-material ratio 1:1, speed 500 rpm) to obtain a mixed slurry.

[0026] 3. The obtained mixed slurry is transferred to a pressure vessel for vacuum treatment, and then injected into a mold for isostatic pressing (70 MPa for 40 s). After drying and curing, a porous green body with a porosity of 28% is obtained. The porous green body is placed in a furnace and heated to 1460℃ at 10℃ / min under nitrogen protection, and held for 0.5 h. Then, the porous green body is embedded in half of its mass of silicon powder, heated to 1510℃ at 2℃ / min, held for 3 h, and cooled with the furnace to obtain silicon carbide special ceramics.

[0027] Example 3 A method for preparing silicon carbide special ceramics, comprising the following steps: 1. Under nitrogen protection, 10 parts of PAN carbon fiber (length-to-diameter ratio 5-10:1) were dispersed in 10 parts of concentrated sulfuric acid solution (98% concentration), heated at 60℃ for 20 min, and then washed with water until neutral. Separately, 0.2 parts of lanthanum nitrate and 0.3 parts of cerium nitrate were dissolved in 20 parts of nitric acid solution (60% concentration) to prepare a rare earth nitrate solution. The treated PAN carbon fiber was transferred into the rare earth nitrate solution and stirred until homogeneous. 0.05 parts of alkylphenol polyoxyethylene ether were added, and the mixture was heated to 140℃ for 7 h. After washing and vacuum drying, rare earth-coated PAN carbon fiber was obtained.

[0028] 2. Weigh out 100 parts by weight of silicon carbide powder (6H-SiC, purity 97%; 30% of particles with a diameter of 30-80 μm and 70% of particles with a diameter of 80-120 μm), 6.4 parts of rare earth-coated PAN carbon fiber, 4.2 parts of titanium disilicide, 1.2 parts of titanium aluminum carbon powder, 6 parts of silicon hexaboride, 0.1 parts of hafnium carbide, 0.6 parts of tantalum carbide, and 8 parts of carbon source (composed of carbon black and needle coke in a mass ratio of 7.5:2.5). Mix the above raw materials and then disperse them in a solvent (ethanol + 0.1% triethyl phosphate, solid-liquid ratio 1:1.8). Stir ultrasonically for 30 min, then add 3 parts of phenolic resin and 2 parts of polyvinylpyrrolidone, and ball mill for 2 h (ball-to-material ratio 1:1, speed 500 rpm) to obtain a mixed slurry.

[0029] 3. The obtained mixed slurry is transferred to a pressure vessel for vacuum treatment, and then injected into a mold for isostatic pressing (50 MPa for 60 s). After drying and curing, a porous green body with a porosity of 22% is obtained. The porous green body is placed in a furnace and heated to 1420℃ at 5℃ / min under nitrogen protection, and held for 1 h. Then, the porous green body is embedded in half of its mass of silicon powder, heated to 1590℃ at 4℃ / min, held for 2 h, and cooled with the furnace to obtain silicon carbide special ceramics.

[0030] Comparative Example 1 Referring to Embodiment 1 of the present invention, the only difference is that ordinary PAN carbon fiber without rare earth coating is used instead.

[0031] Comparative Example 2 Referring to Comparative Example 1 of the present invention, the only difference is that 0.05 parts of lanthanum nitrate and 0.08 parts of cerium nitrate are added as doping materials to the ordinary PAN carbon fiber.

[0032] Comparative Example 3 Referring to Embodiment 1 of the present invention, the only difference is that titanium disilicide is not added.

[0033] Comparative Example 4 Referring to Embodiment 1 of the present invention, the only difference is that titanium aluminum carbon powder is not added.

[0034] Comparative Example 5 Referring to Embodiment 1 of the present invention, the only difference is that the carbon source is changed to be composed of carbon black and graphite in a mass ratio of 1:1.

[0035] Comparative Example 6 Referring to Embodiment 1 of the present invention, the only difference is that the sintering process is adjusted to a one-step process: under nitrogen protection, the porous blank is buried in half of its mass of silicon powder, heated to 1560°C at 3°C / min, and held for 2.5 h.

[0036] Test case The silicon carbide special ceramic samples prepared in the above embodiments and comparative examples were tested, and the results are shown in Table 1 (hardness test according to GB / T 16534-2009, fracture toughness test according to GB / T 23806-2009, flexural strength test according to GB / T 6569-2006, and oxidation weight gain test using a thermogravimetric analyzer).

[0037] Table 1. Performance test results of silicon carbide special ceramic samples

[0038] Based on the above sample test results, it can be seen that the silicon carbide special ceramic material prepared by this invention effectively overcomes the shortcomings of low fracture toughness in traditional reaction-sintered silicon carbide materials, and ensures high hardness while improving the fracture toughness of the material. As for the problem of residual free silicon in traditional reaction-sintered products limiting high-temperature applications, this invention combines multiple doping phases and optimized sintering processes to make silicon melting and infiltration efficient and stable, without excessive silicon infiltration and effectively reducing the free silicon content. At the same time, it can ensure high reaction density and product consistency, and has high flexural strength retention and excellent oxidation resistance under ultra-high temperature conditions of 1400℃.

[0039] The embodiments described above are merely preferred embodiments of the present invention, and while the descriptions are specific and detailed, they are not intended to limit the present invention. It should be noted that various changes and modifications can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the concept and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing silicon carbide special ceramics, characterized in that, Includes the following steps: S1. Take silicon carbide powder and mix it with carbon fiber, titanium disilicide, titanium aluminum carbon powder, silicon hexaboride, hafnium carbide, tantalum carbide and carbon source, then disperse it in a solvent, ultrasonically stir it, then add binder and dispersant, and ball mill it to obtain a mixed slurry for later use; the carbon fiber is rare earth coated PAN carbon fiber, and the carbon source is composed of carbon black and needle coke, with a mass ratio of (6.5-7.5):(2.5-3.5); S2. Vacuum casting and isostatic pressing of the mixed slurry obtained in S1, followed by drying and curing, yields a porous preform for later use. S3. Under the protection of inert gas, the obtained porous green blank is sintered once, and then the porous green blank is embedded in silicon powder for secondary sintering. After the heat preservation is completed, silicon carbide special ceramics are obtained.

2. The method for preparing silicon carbide special ceramics according to claim 1, characterized in that, By weight, the amounts of each raw material in S1 are as follows: 100 parts silicon carbide powder, 4.0-6.4 parts carbon fiber, 1.8-4.2 parts titanium disilicide, 1.2-3.5 parts titanium aluminum carbon powder, 3-6 parts silicon hexaboride, 0.1-0.4 parts hafnium carbide, 0.3-0.6 parts tantalum carbide, and 8-12 parts carbon source.

3. The method for preparing silicon carbide special ceramics according to claim 1, characterized in that, The silicon carbide powder mentioned in S1 is 6H-SiC with a particle size of 30-120 μm; of which 30%-70% have a particle size of 30-80 μm and 70%-30% have a particle size of 80-120 μm.

4. The method for preparing silicon carbide special ceramics according to claim 1, characterized in that, The method for preparing rare earth-coated PAN carbon fiber described in S1 is as follows: PAN carbon fiber is placed in concentrated sulfuric acid solution and heated at 50-70℃ under inert gas protection for 15-20 min, and then washed until neutral; the treated PAN carbon fiber is transferred into rare earth nitrate solution and stirred evenly, reacted at 120-160℃ for 6-8 h, and finally washed and vacuum dried to obtain rare earth-coated PAN carbon fiber.

5. The method for preparing silicon carbide special ceramics according to claim 4, characterized in that, The rare earth nitrate solution is prepared using lanthanum nitrate and cerium nitrate, with the mass ratio of PAN carbon fiber, lanthanum nitrate and cerium nitrate being 10:(0.1-0.2):(0.2-0.3).

6. The method for preparing silicon carbide special ceramics according to claim 1, characterized in that, The binder in S1 is phenolic resin, and the dispersant is polyvinylpyrrolidone. The amount of both added is 2%-4% of the mass of silicon carbide powder.

7. The method for preparing silicon carbide special ceramics according to claim 1, characterized in that, The isostatic pressing pressure value described in S2 is 50-70 MPa, the holding time is 40-60 s, and the porosity of the obtained porous preform needs to be controlled to be 22%-28%.

8. The method for preparing silicon carbide special ceramics according to claim 1, characterized in that, The first sintering temperature of S3 is 1420-1460℃, the heating rate is 5-10℃ / min, and the holding time is 0.5-1 h. The second sintering temperature is 1510-1590℃, the heating rate is 2-4℃ / min, and the holding time is 2-3 h.

9. The silicon carbide special ceramics prepared by the method according to any one of claims 1-8.

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