Silicon carbide special ceramics and method for preparing the same

Abstract

The application discloses a kind of silicon carbide special ceramics and preparation method thereof, belong to silicon carbide ceramic technical field.The application mixes silicon carbide powder with rare earth coated PAN carbon fiber, titanium disilicide, titanium aluminum carbon powder, silicon hexaboride, hafnium carbide, tantalum carbide and carbon source, adds binder and dispersing agent ball milling to form slurry, then compaction forming is obtained Porous green body, finally through two-step sintering process is made silicon carbide special ceramics.The application overcomes the low fracture toughness of traditional reaction sintering silicon carbide material, the deficiency of high temperature strength and oxidation resistance, and the prepared silicon carbide special ceramics has high hardness and toughness, high bending strength retention rate under 1400 DEG C ultra-high temperature condition, excellent oxidation resistance, can satisfy the application demand of more working scene.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of silicon carbide ceramics, and particularly relates to a special silicon carbide ceramic and a preparation method thereof. BACKGROUND

[0002] Silicon carbide is an important advanced ceramic material, and its unique bonding mode (the proportion of covalent bonds is extremely high) endows it with a series of excellent physical and chemical properties, including: extremely high hardness and wear resistance, excellent chemical stability, 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, semiconductor, etc., such as kiln furniture, chemical pump valves, engines, gas turbines, pipelines, reaction kettles, inner linings, etc.

[0003] At present, 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 which the reaction sintering method has an irreplaceable position in the preparation of complex shapes and large-size parts due to its low cost and high efficiency. However, at the same time, its inherent process characteristics also lead to some problems and defects in the prepared materials, such as the reaction sintering product usually contains 10%-20% of free silicon, which will significantly reduce the material performance when the use temperature exceeds the silicon melting point, thereby limiting the application in high-temperature environments. In addition, the pore structure, distribution uniformity and matching combination of raw materials will all affect the microstructure and performance stability of the final material, making it difficult to control the consistency of the product.

[0004] Therefore, in order to improve the defects of the traditional reaction sintering method and expand its application range, it is of great significance to research and develop a high-performance reaction sintering special silicon carbide ceramic material. SUMMARY

[0005] In view of the problems in the background art, the purpose of the present application is to provide a special silicon carbide ceramic and a preparation method thereof. Through research and improvement of raw materials and preparation process, the performance defects of traditional reaction sintered silicon carbide ceramics are effectively improved, and the application requirements of more working scenarios can be met.

[0006] In order to achieve the above purpose, the technical scheme adopted by the present application is as follows:

[0007] The present application provides a preparation method of a special silicon carbide ceramic, comprising the following steps:

[0008] S1, take silicon carbide powder and carbon fiber, titanium disilicide, titanium aluminum carbon powder, silicon hexaboride, hafnium carbide, tantalum carbide and carbon source are mixed, then dispersed in solvent, ultrasonic stirring, then adding binder and dispersant, ball milling to obtain mixed slurry for standby; the carbon fiber is rare earth coated PAN carbon fiber, the carbon source is composed of carbon black and needle coke, the mass ratio of the two is (6.5-7.5):(2.5-3.5);

[0009] S2, the mixed slurry obtained in S1 is vacuum, injection molding, isostatic pressing, drying and curing to obtain a porous green body for standby;

[0010] S3, under the protection of inert gas, the obtained porous green body is sintered once, then the porous green body is buried in silicon powder for secondary sintering, and the silicon carbide special ceramic is obtained after heat preservation.

[0011] Further, the amount of each raw material in S1 is as follows by weight fraction: silicon carbide powder 100 parts, carbon fiber 4.0-6.4 parts, titanium disilicide 1.8-4.2 parts, titanium aluminum carbon powder 1.2-3.5 parts, silicon hexaboride 3-6 parts, hafnium carbide 0.1-0.4 parts, tantalum carbide 0.3-0.6 parts, and carbon source 8-12 parts.

[0012] Further, the silicon carbide powder in S1 is 6H-SiC, the particle size is 30-120 μm; wherein the particle size of 30-80 μm accounts for 30%-70%, the particle size of 80-120 μm accounts for 70%-30%; preferably the particle size of 30-80 μm accounts for 50%, the particle size of 80-120 μm accounts for 50%. The ordinary silicon carbide powder (purity 97%) with particle size of 30-120 μm can be used as the basic framework raw material, without the need for nano or sub-micron high-purity silicon carbide powder.

[0013] Further, the preparation method of the rare earth coated PAN carbon fiber in S1 is as follows: take PAN carbon fiber and put it into concentrated sulfuric acid solution, heat at 50-70℃ under inert gas protection for 15-20 min, then wash to neutral; the treated PAN carbon fiber is transferred into rare earth nitrate solution and stirred, reacted at 120-160℃ for 6-8 h, and finally washed and vacuum dried to obtain the rare earth coated PAN carbon fiber.

[0014] Further, the rare earth nitrate solution is prepared by lanthanum nitrate and cerium nitrate, and the mass ratio of PAN carbon fiber, lanthanum nitrate and cerium nitrate is 10:(0.1-0.2):(0.2-0.3).

[0015] The rare earth coated PAN carbon fiber in the application not only has the toughening effect of fiber pull-out and bridging, but also can further improve the interface bonding property with the base framework and other doped raw materials, avoid the adverse interface reaction generated at high temperature, and can also strengthen the diffusion effect between the doped raw materials, provide an additional micro-reaction channel, which is beneficial to the full reaction of the silicon-carbon reaction in the sintering process, effectively solves the problem of inconsistent microstructure caused by uneven mixing or local pore blockage, avoids the defect that the local weakly bonded area becomes a crack source, and improves the overall strength and reliability of the material.

[0016] The carbon black has high activity to ensure the reaction rate of silicon-carbon, and the needle coke can inhibit the excessively high reaction rate to avoid the blockage of the capillary channel by a large amount of new-phase silicon carbide, and on the other hand, the needle-like and flaky structure of the needle coke can also hinder the crack propagation, thereby playing a certain toughening effect. The selected combination of carbon sources in the application can make silicon continuously and stably infiltrate into the material during the infiltration process, ensure the reaction rate, and avoid the problem of excessively high residual carbon content.

[0017] In addition, the application also adds other exogenous reinforcing phases: titanium disilicide can form a eutectic liquid phase during the silicon infiltration process, promote sintering and densification, improve hardness and strength, and play the role of strengthening the grain boundary and oxidation resistance; titanium aluminum carbide can promote the migration between the doped phases, has the effects of activating sintering and toughening, and is beneficial to the uniformity of the properties of the prepared silicon carbide ceramic material; and a small amount of hafnium carbide and tantalum carbide can improve the grain boundary strength, improve the hardness, strength and oxidation resistance of the material in the ultrahigh temperature environment, and endow the material with the use stability at a higher temperature.

[0018] Further, the binder in S1 is phenolic resin, and the dispersant is polyvinylpyrrolidone, and the addition amount of both is 2%-4% of the mass of the silicon carbide powder.

[0019] Further, the pressure value of the isostatic pressing forming in S2 is 50-70 MPa, the pressure holding time is 40-60 s, and the porosity of the obtained porous green body needs to be controlled to be 22%-28%.

[0020] Further, the temperature of the first sintering is 1420-1460 DEG C, the heating rate is 5-10 DEG C / min, and the holding time is 0.5-1 h, and the temperature of the second sintering is 1510-1590 DEG C, the heating rate is 2-4 DEG C / min, and the holding time is 2-3 h. The present application adopts a two-step sintering preparation process: the first sintering (green body pre-sintering) removes the binder and dispersant in the porous green body, and at the same time, the preliminary reaction of part of the doped components in the green body occurs to form a certain skeleton strength, which further controls the open porosity, porosity and connectivity of the green body, and makes good preparation for the second step of silicon infiltration reaction; in the second sintering (melting silicon reaction sintering), the molten silicon liquid spontaneously infiltrates into the pores of the porous green body under the action of capillary force, reacts with the carbon source to fill the pores, realizes densification, and obtains the silicon carbide ceramic material. The two-step sintering of the present application can effectively reduce the content of free silicon, and does not need subsequent heat treatment, thereby significantly reducing the energy consumption and comprehensive process cost.

[0021] The present application also provides a silicon carbide special ceramic prepared by the above method.

[0022] Compared with the prior art, the present application has the following beneficial effects:

[0023] The process of the present application not only effectively improves the high-temperature strength and oxidation resistance of the silicon carbide material, breaks the high-temperature application limitation of the traditional reaction sintering ceramic material, but also makes the prepared silicon carbide special ceramic material have high hardness and fracture toughness, which can meet the application requirements of more working scenarios. The present application effectively reduces the energy consumption and cost, and has simple preparation process, good product consistency and is suitable for industrial production. DETAILED DESCRIPTION

[0024] In order to make the purpose, technical scheme and advantages of the present application clearer, the technical scheme of the present application will be described clearly and completely below in combination with examples. If the specific conditions are not indicated in the examples, the conventional conditions or the conditions recommended by the manufacturer are used. If the reagents or instruments used are not indicated by the manufacturer, they are all conventional products that can be purchased on the market.

[0025] 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 to which this application belongs. The terminology used in the description of the application merely for the purpose of describing a specific embodiment is not intended to limit the application. The term "and / or" used herein includes any and all combinations of one or more of the associated listed items.

[0026] Example 1

[0027] A preparation method of a silicon carbide special ceramic, comprising the following steps:

[0028] 1. Under nitrogen protection, 10 parts of PAN carbon fiber (aspect ratio 5-10:1) is dispersed in 10 parts of concentrated sulfuric acid solution (concentration 98%), heated at 60°C for 20 min, and then washed with water to neutral. Another 0.15 parts of lanthanum nitrate and 0.25 parts of cerium nitrate are dissolved in 20 parts of nitric acid solution (concentration 60%) to prepare a rare earth nitrate solution. The treated PAN carbon fiber is transferred into the rare earth nitrate solution and stirred, 0.05 parts of alkylphenol polyoxyethylene ether is added, heated to 140°C for 7 h, washed, vacuum dried to obtain rare earth coated PAN carbon fiber.

[0029] 2. 100 parts of silicon carbide powder (6H-SiC, purity 97%; 50% of particle size 30-80 μm, 50% of particle size 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, 10 parts of carbon source (consisting of carbon black and needle coke in a mass ratio of 7:3) are weighed. The above raw materials are mixed, then dispersed in a solvent (ethanol + 0.1% triethyl phosphate, solid-liquid ratio 1:1.8), ultrasonic stirring for 30 min, then 3 parts of phenolic resin and 2 parts of polyvinylpyrrolidone are added, ball milling for 2 h (ball-to-material ratio 1:1, rotation speed 500 rpm) to obtain a mixed slurry.

[0030] 3. The obtained mixed slurry is transferred into a pressure tank for vacuum treatment, then injected into a mold for isostatic pressing (60 MPa for 50 s), dried and solidified to obtain a porous green body with a porosity of 26%; the porous green body is placed in a furnace, heated to 1440°C at a rate of 8°C / min under nitrogen protection, and held for 0.8 h; then the porous green body is buried in silicon powder with half of its mass, heated to 1560°C at a rate of 3°C / min, held for 2.5 h, and cooled in the furnace to obtain a silicon carbide special ceramic.

[0031] Example 2

[0032] A method for preparing a silicon carbide special ceramic, comprising the following steps:

[0033] 1. Under nitrogen protection, 10 parts of PAN carbon fiber (aspect ratio 5-10:1) is dispersed in 10 parts of concentrated sulfuric acid solution (concentration 98%), heated at 60°C for 20 min, and then washed with water to neutral. Another 0.12 parts of lanthanum nitrate and 0.2 parts of cerium nitrate are dissolved in 20 parts of nitric acid solution (concentration 60%) to prepare a rare earth nitrate solution. The treated PAN carbon fiber is transferred into the rare earth nitrate solution and stirred, 0.05 parts of alkylphenol polyoxyethylene ether is added, heated to 140°C for 7 h, washed, vacuum dried to obtain rare earth coated PAN carbon fiber.

[0034] 2. Take 100 parts of silicon carbide powder (6H-SiC, purity 97%; 70% of particle size 30-80 μm, 30% of particle size 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 (consisting of carbon black and needle coke in a mass ratio of 6.5:3.5) by weight; mix the above raw materials, then disperse them in a solvent (ethanol + 0.1% triethyl phosphate, solid-liquid ratio 1:1.8), ultrasonic stir for 30 min, then add 3 parts of phenolic resin and 2 parts of polyvinylpyrrolidone, ball mill for 2 h (ball-to-material ratio 1:1, rotation speed 500 rpm) to obtain a mixed slurry.

[0035] 3. Transfer the obtained mixed slurry into a pressure tank for vacuum treatment, then inject into a mold for isostatic pressing (70 MPa for 40 s), dry and solidify to obtain a porous green body with a porosity of 28%; place the porous green body into a furnace, heat to 1460℃ at a rate of 10℃ / min under nitrogen protection, and keep the temperature for 0.5 h; then bury the porous green body in silicon powder with a mass of half of the porous green body, heat to 1510℃ at a rate of 2℃ / min, keep the temperature for 3 h, and cool down with the furnace to obtain a silicon carbide special ceramic.

[0036] Example 3

[0037] A method for preparing a silicon carbide special ceramic, comprising the following steps:

[0038] 1. Under nitrogen protection, disperse 10 parts of PAN carbon fiber (aspect ratio 5-10:1) in 10 parts of concentrated sulfuric acid solution (concentration 98%), heat at 60℃ for 20 min, then wash with water until neutral; separately dissolve 0.2 parts of lanthanum nitrate and 0.3 parts of cerium nitrate in 20 parts of nitric acid solution (concentration 60%) to prepare a rare earth nitrate solution. Stir the treated PAN carbon fiber in the rare earth nitrate solution, add 0.05 parts of alkylphenol polyoxyethylene ether, heat to 140℃ for 7 h, wash and vacuum dry to obtain rare earth coated PAN carbon fiber.

[0039] 2. Take 100 parts of silicon carbide powder (6H-SiC, purity 97%; 30-80 μm in particle size accounts for 30%, 80-120 μm in particle size accounts for 70%) by weight, 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 part of hafnium carbide, 0.6 part of tantalum carbide, 8 parts of carbon source (consisting of carbon black and needle coke in a mass ratio of 7.5:2.5); mix the above raw materials, then disperse in a solvent (ethanol + 0.1% triethyl phosphate, solid-liquid ratio 1:1.8), ultrasonic stirring for 30 min, then add 3 parts of phenolic resin and 2 parts of polyvinylpyrrolidone, ball milling for 2 h (ball-to-material ratio 1:1, rotation speed 500 rpm) to obtain a mixed slurry.

[0040] 3. The obtained mixed slurry is transferred into a pressure tank for vacuum treatment, then injected into a mold for isostatic pressing (50 MPa for 60 s), dried and solidified to obtain a porous green body with a porosity of 22%; the porous green body is placed in a furnace, heated to 1420℃ at a rate of 5℃ / min under nitrogen protection, and kept for 1 h; then the porous green body is buried in silicon powder with a mass of half of the porous green body, heated to 1590℃ at a rate of 4℃ / min, and kept for 2 h, and cooled in the furnace to obtain a silicon carbide special ceramic.

[0041] Comparative Example 1

[0042] Referring to Example 1 of the present application, the only difference is that the ordinary PAN carbon fiber without rare earth coating is used instead.

[0043] Comparative Example 2

[0044] Referring to Comparative Example 1 of the present application, the only difference is that 0.05 parts of lanthanum nitrate and 0.08 parts of cerium nitrate are additionally added as doping raw materials on the basis of ordinary PAN carbon fiber.

[0045] Comparative Example 3

[0046] Referring to Example 1 of the present application, the only difference is that titanium disilicide is not added.

[0047] Comparative Example 4

[0048] Referring to Example 1 of the present application, the only difference is that titanium aluminum carbon powder is not added.

[0049] Comparative Example 5

[0050] Referring to Example 1 of the present application, the only difference is that the carbon source is changed to consist of carbon black and graphite in a mass ratio of 1:1.

[0051] Comparative Example 6

[0052] Referring to Example 1 of the present application, the only difference is that the sintering process is adjusted to one-step treatment: the porous green body is buried in half of the mass of silicon powder under nitrogen protection, and heated to 1560℃ at a rate of 3℃ / min, and kept for 2.5h.

[0053] Test Example

[0054] The silicon carbide special ceramic samples prepared in the above examples and comparative examples are detected, and the results are shown in Table 1 (the hardness detection is based on GB / T 16534-2009, the fracture toughness detection is based on GB / T 23806-2009, the bending strength detection is based on GB / T 6569-2006, and the oxidation weight gain detection is performed by using a thermal gravimetric analyzer).

[0055] Table 1: Performance detection results of silicon carbide special ceramic samples

[0056]

[0057] According to the sample detection results, it can be seen that the silicon carbide special ceramic material prepared by the present application effectively overcomes the low fracture toughness of the traditional reaction sintered silicon carbide material, and improves the fracture toughness of the material while ensuring its high hardness; and for the problem of high-temperature application of residual free silicon in the traditional reaction sintered product, the present application combines various doped phases and optimizes the sintering process, so that the silicon infiltration is efficient and stable, without excessive silicon infiltration and effectively reducing the free silicon content, while ensuring the high density of the reaction and the consistency of the product, the bending strength retention rate is high under the condition of 1400℃ ultra-high temperature, and the oxidation resistance is excellent.

[0058] The above-described embodiments only express several preferred embodiments of the present application, and the description is more specific and detailed, but is not used to limit the present application. It should be noted that for those skilled in the art, the present application can also have various changes and modifications, and any modification, equivalent replacement, improvement, etc. made within the concept and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A method of producing a silicon carbide special ceramic, characterized by, It comprises the following steps: S1, taking silicon carbide powder and carbon fiber, titanium disilicide, titanium aluminum carbon powder, silicon hexaboride, hafnium carbide, tantalum carbide and carbon source are mixed, then dispersed in solvent, ultrasonic stirring, then adding binder and dispersant, ball milling to obtain mixed slurry for standby; Wherein, the amount of each raw material is as follows: silicon carbide powder 100 parts, carbon fiber 4.0-6.4 parts, titanium disilicide 1.8-4.2 parts, titanium aluminum carbon powder 1.2-3.5 parts, silicon hexaboride 3-6 parts, hafnium carbide 0.1-0.4 parts, tantalum carbide 0.3-0.6 parts, carbon source 8-12 parts by weight; The carbon fiber is rare earth coated PAN carbon fiber, and its preparation method is as follows: taking PAN carbon fiber into concentrated sulfuric acid solution, heating at 50-70℃ under inert gas protection for 15-20 min, then washing to neutral; the treated PAN carbon fiber is transferred into rare earth nitrate solution, stirring, reacting at 120-160℃ for 6-8 h, and finally washing, vacuum drying to obtain rare earth coated PAN carbon fiber; The carbon source is composed of carbon black and needle coke, and the mass ratio of the two is (6.5-7.5):(2.5-3.5); S2, the mixed slurry obtained in S1 is vacuumed, injection molded, isostatic pressing formed, dried and solidified to obtain a porous green body for standby; S3, the obtained porous green body is sintered once under inert gas protection, and then buried in silicon powder for secondary sintering, and the silicon carbide special ceramic is obtained after the end of heat preservation.

2. The method of making silicon carbide special ceramics according to claim 1, characterized in that, The silicon carbide powder in S1 is 6H-SiC, and the particle size is 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%.

3. The method of making a silicon carbide special ceramic according to claim 1, wherein The rare earth nitrate solution is prepared by lanthanum nitrate and cerium nitrate, and the mass ratio of PAN carbon fiber, lanthanum nitrate and cerium nitrate is 10:(0.1-0.2):(0.2-0.3).

4. The method of making a silicon carbide special ceramic according to claim 1, wherein The binder in S1 is phenolic resin, and the dispersant is polyvinylpyrrolidone, and the addition amount of both is 2%-4% of the mass of silicon carbide powder.

5. The method of making a silicon carbide special ceramic according to claim 1, wherein The pressure value of isostatic pressing forming in S2 is 50-70 MPa, and the pressure holding time is 40-60 s, and the porosity of the obtained porous green body needs to be controlled at 22%-28%.

6. The method of making silicon carbide special ceramics according to claim 1, wherein 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, and the temperature of the second sintering is 1510-1590℃, the heating rate is 2-4℃ / min, and the holding time is 2-3 h.

7. The silicon carbide special ceramic prepared by the method of any one of claims 1-6.

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