Silicon carbide ceramic and preparation method and application thereof

Abstract

The application provides a silicon carbide ceramic and a preparation method and application thereof, the preparation method comprises sequentially performing granulation, molding and sintering; wherein, the powder used in the granulation process comprises silicon-carbon composite micro-nano particles, and the silicon-carbon composite micro-nano particles have any one of the following structures or a combination of two: (A) a core-shell structure of carbon-coated silicon; (B) a silicon-carbon composite structure of heterogeneous combination. The preparation method provided by the application does not need or reduces the silicon infiltration step, simplifies the process and equipment, effectively improves the product purity, reduces or eliminates the existence of free silicon in the finished ceramic, and further improves the high-temperature performance and corrosion resistance of the product, prolongs the service life of the product, and is conducive to large-scale popularization and application.

Description

Technical Field

[0001] This invention belongs to the field of inorganic materials technology, and relates to a silicon carbide ceramic, and more particularly to a silicon carbide ceramic and its preparation method and application. Background Technology

[0002] Silicon carbide is an important engineering ceramic material. It boasts high hardness, second only to diamond, boron nitride, and a few other materials, and exhibits stable chemical properties, resulting in excellent wear and corrosion resistance. Furthermore, silicon carbide possesses advantages such as high strength, high temperature resistance, good thermal conductivity, low density, and good thermal shock resistance. It is an ideal material for mechanical seals, high-load, long-life kiln furniture, heat exchange tubes, high-temperature ceramic radiant burners, aerospace engine combustion chambers, nuclear fuel cooling reactor cladding materials, and high-temperature gas-cooled reactor furnace linings in the petroleum, metallurgical, chemical, machinery, aerospace, and spacecraft industries under extreme environmental conditions such as high temperature, high pressure, corrosion, radiation, and abrasion.

[0003] Silicon carbide ceramics are usually prepared by reaction sintering. This method involves mixing silicon carbide powder and carbon powder in a certain proportion and pressing them into a green body. The green body is then heated to 1600-1900℃, where liquid silicon diffuses into the green body or diffuses into the green body through the gas phase. After carbon and silicon come into contact, they react to generate new silicon carbide, which binds the original silicon carbide particles together, thereby obtaining high-strength silicon carbide ceramic materials.

[0004] However, the reaction between silicon and carbon during the above sintering process is not sufficient, resulting in low product purity. The ceramics sintered by reaction ultimately contain 5-20% free silicon, which in turn affects the high-temperature performance and corrosion resistance of the material.

[0005] Furthermore, existing preparation methods involve mixing silicon powder, carbon powder, and silicon carbide powder (or other materials) to form a slurry, followed by molding and sintering processes. During sintering, a silicon infiltration process is required, which utilizes capillary channels within the green body to infiltrate silicon into the green body. This process suffers from several drawbacks: firstly, the uniformity of infiltration is significantly limited; secondly, due to the limitations of element diffusion within solids, a large amount of infiltrated silicon does not react with carbon; and thirdly, the capillary infiltration process is prone to clogging, and the silicon infiltration process significantly increases the complexity and cost of the sintering equipment.

[0006] For the reasons mentioned above, silicon carbide ceramics prepared by traditional reaction sintering methods have a relatively high content of unreacted silicon, resulting in lower product purity. Ceramic parts require regular cleaning during use, but cleaning agents typically contain highly corrosive substances such as hydrofluoric acid. Although silicon carbide has extremely strong corrosion resistance, free silicon is easily eroded, leading to a shortened product lifespan.

[0007] Therefore, it is evident that providing a silicon carbide ceramic and its preparation method that eliminates or reduces silicon infiltration operations, simplifies the process and equipment, effectively improves product purity, reduces or eliminates the presence of free silicon in the finished ceramic, thereby improving the high-temperature performance and corrosion resistance of the product and extending its service life has become an urgent problem to be solved by those skilled in the art. Summary of the Invention

[0008] The purpose of this invention is to provide a silicon carbide ceramic, its preparation method, and its application. The preparation method eliminates or reduces the need for silicon infiltration steps, simplifies the process and equipment, effectively improves product purity, reduces or eliminates the presence of free silicon in the finished ceramic, thereby improving the high-temperature performance and corrosion resistance of the product, extending the product's service life, and facilitating large-scale promotion and application.

[0009] To achieve this objective, the present invention adopts the following technical solution:

[0010] In a first aspect, the present invention provides a method for preparing silicon carbide ceramics, the method comprising granulation, molding and sintering performed sequentially.

[0011] The powder used in the granulation process includes silicon-carbon composite micro / nano particles, and the silicon-carbon composite micro / nano particles have any one or a combination of two of the following structures:

[0012] (A) Core-shell structure of carbon-coated silicon;

[0013] (B) Heterogeneous silicon-carbon composite structure.

[0014] The preparation method provided by this invention encapsulates or attaches carbon elements to the surface of silicon particles in situ during the raw material stage, enabling the two to undergo an effective chemical reaction within a short diffusion range. This eliminates or reduces the need for silicon infiltration, simplifies the process and equipment, and improves production efficiency. At the same time, it can effectively control the Si / C ratio in the micro-region during ceramic production, optimize the reaction sintering process, improve product purity, reduce or eliminate the presence of free silicon in the finished ceramic, thereby improving the high-temperature performance and corrosion resistance of the product, extending the product's service life, and facilitating large-scale promotion and application.

[0015] Preferably, the preparation method of the silicon-carbon composite micro / nano particles includes the following steps:

[0016] (1) Obtain silicon particles and coat or attach carbon-containing organic matter on the surface of the silicon particles to obtain a silicon-carbon-containing organic matter composite.

[0017] (2) The silicon-carbon organic composite obtained in step (1) is carbonized in a reducing atmosphere to obtain carbon-coated silicon particles or silicon-carbon composite powder.

[0018] Alternatively, the method for preparing the silicon-carbon composite micro / nano particles includes: directly depositing carbon elements on the surface of silicon particles to obtain carbon-encapsulated silicon particles.

[0019] Preferably, the deposition method includes chemical vapor deposition.

[0020] Preferably, the average particle size of the silicon-carbon composite micro / nano particles is 0.01-300 μm, for example, it can be 0.01 μm, 0.02 μm, 0.05 μm, 0.1 μm, 1 μm, 10 μm, 20 μm, 40 μm, 60 μm, 80 μm, 100 μm, 120 μm, 140 μm, 160 μm, 180 μm, 200 μm, 220 μm, 240 μm, 260 μm, 280 μm or 300 μm, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0021] Preferably, the method for preparing the silicon carbide ceramic further includes the following steps:

[0022] (3) Mix silicon carbide particles, dispersant and silicon-carbon composite micro-nano particles obtained in step (2), and stir evenly to obtain a slurry;

[0023] (4) Inject the slurry obtained in step (3) into the mold to form a green body;

[0024] (5) The green body obtained in step (4) is dried and sintered in sequence to obtain silicon carbide ceramic.

[0025] Preferably, the average particle size of the silicon particles in step (1) is 0.01-300 μm, for example, it can be 0.01 μm, 0.1 μm, 1 μm, 10 μm, 20 μm, 40 μm, 60 μm, 80 μm, 100 μm, 120 μm, 140 μm, 160 μm, 180 μm, 200 μm, 220 μm, 240 μm, 260 μm, 280 μm or 300 μm, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0026] Preferably, the carbon-containing organic material in step (1) includes any one or a combination of at least two of phenolic resin, resorcinol-formaldehyde resin, polystyrene, polyaniline, glucose, oleic acid, polydopamine, polypyrrole, or polyvinylidene fluoride. Typical but non-limiting combinations include combinations of phenolic resin and resorcinol-formaldehyde resin, combinations of resorcinol-formaldehyde resin and polystyrene, combinations of polyaniline and glucose, combinations of glucose and oleic acid, combinations of oleic acid and polydopamine, combinations of polydopamine and polypyrrole, or combinations of polypyrrole and polyvinylidene fluoride.

[0027] Preferably, the encapsulation method of the carbon-containing organic matter in step (1) includes solution mixing, ball milling mixing, or hydrothermal reaction.

[0028] Preferably, the temperature of the hydrothermal reaction is 90-200℃, for example, it can be 90℃, 100℃, 110℃, 120℃, 130℃, 140℃, 150℃, 160℃, 170℃, 180℃, 190℃ or 200℃, but it is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0029] Preferably, the hydrothermal reaction time is 1-48 hours, for example, it can be 1 hour, 2 hours, 4 hours, 6 hours, 8 hours, 10 hours, 12 hours, 14 hours, 16 hours, 18 hours, 20 hours, 22 hours, 24 hours, 26 hours, 28 hours, 30 hours, 32 hours, 34 hours, 36 hours, 38 hours, 40 hours, 42 hours, 44 hours, 46 hours, or 48 hours, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0030] Preferably, the reducing atmosphere in step (2) includes any one or a combination of at least two of nitrogen, argon or hydrogen. Typical but non-limiting combinations include a combination of nitrogen and hydrogen, a combination of argon and hydrogen, a combination of nitrogen and argon, or a combination of nitrogen, argon and hydrogen.

[0031] Preferably, the silicon-carbon organic composite in step (2) is dried before carbonization.

[0032] Preferably, the carbonization temperature in step (2) is 350-800℃, for example, it can be 350℃, 400℃, 450℃, 500℃, 550℃, 600℃, 650℃, 700℃, 750℃ or 800℃, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0033] Preferably, the carbonization time in step (2) is 0.1-48h, for example, it can be 0.1h, 1h, 2h, 4h, 6h, 8h, 10h, 12h, 14h, 16h, 18h, 20h, 22h, 24h, 26h, 28h, 30h, 32h, 34h, 36h, 38h, 40h, 42h, 44h, 46h or 48h, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0034] Preferably, the dispersant in step (3) includes any one or a combination of at least two of polyethylene glycol, polyacrylic acid, ammonium citrate or tetramethylammonium hydroxide. Typical but non-limiting combinations include combinations of polyethylene glycol and polyacrylic acid, combinations of polyacrylic acid and ammonium citrate, combinations of ammonium citrate and tetramethylammonium hydroxide, combinations of polyethylene glycol, polyacrylic acid and ammonium citrate, or combinations of polyacrylic acid, ammonium citrate and tetramethylammonium hydroxide.

[0035] Preferably, the total mass of the slurry is used as the calculation basis, and the mixing amount of silicon carbide particles in step (3) is 79-96 wt%, for example, it can be 79 wt%, 80 wt%, 81 wt%, 82 wt%, 83 wt%, 84 wt%, 85 wt%, 86 wt%, 87 wt%, 88 wt%, 89 wt%, 90 wt%, 91 wt%, 92 wt%, 93 wt%, 94 wt%, 95 wt%, or 96 wt%, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0036] Preferably, the total mass of the slurry is used as the calculation basis, and the mixing amount of the dispersant in step (3) is 1-5 wt%, for example, it can be 1 wt%, 1.5 wt%, 2 wt%, 2.5 wt%, 3 wt%, 3.5 wt%, 4 wt%, 4.5 wt%, or 5 wt%, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0037] Preferably, the total mass of the slurry is used as the calculation basis, and the mixing amount of carbon-coated silicon particles or silicon-carbon composite powder in step (3) is 0.5-20 wt%, for example, it can be 0.5 wt%, 1 wt%, 2 wt%, 3 wt%, 4 wt%, 5 wt%, 6 wt%, 7 wt%, 8 wt%, 9 wt%, 10 wt%, 11 wt%, 12 wt%, 13 wt%, 14 wt%, 15 wt%, 16 wt%, 17 wt%, 18 wt%, 19 wt%, or 20 wt%, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0038] Preferably, the drying in step (5) is carried out in an oven, and the drying temperature is 40-100℃, for example, it can be 40℃, 45℃, 50℃, 55℃, 60℃, 65℃, 70℃, 75℃, 80℃, 85℃, 90℃, 95℃ or 100℃, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0039] Preferably, the sintering in step (5) is carried out in a vacuum sintering furnace, and the sintering temperature is 1500-1900℃, for example, it can be 1500℃, 1550℃, 1600℃, 1650℃, 1700℃, 1750℃, 1800℃, 1850℃ or 1900℃, and the time is 0.1-48h, for example, it can be 0.1h, 1h, 2h, 4h, 6h, 8h, 10h, 12h, 14h, 16h, 18h, 20h, 22h, 24h, 26h, 28h, 30h, 32h, 34h, 36h, 38h, 40h, 42h, 44h, 46h or 48h, but it is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0040] As a preferred embodiment of the first aspect of the present invention, the preparation method includes the following steps:

[0041] (1) Obtain silicon particles with an average particle size of 0.01-300 μm, and coat or attach carbon-containing organic matter on the surface of the silicon particles by solution mixing, ball milling or hydrothermal reaction to obtain a silicon-carbon-containing organic matter composite; the carbon-containing organic matter includes any one or a combination of at least two of phenolic resin, resorcinol-formaldehyde resin, polystyrene, polyaniline, glucose, oleic acid, polydopamine, polypyrrole or polyvinylidene fluoride;

[0042] (2) After drying the silicon-carbon organic composite obtained in step (1), carbonize it at 350-800℃ for 0.1-48h in a reducing atmosphere to obtain carbon-coated silicon particles or silicon-carbon composite powder.

[0043] (3) Mix silicon carbide particles, dispersant and silicon-carbon composite micro-nano particles obtained in step (2), and stir evenly to obtain a slurry; the dispersant includes any one or a combination of at least two of polyethylene glycol, polyacrylic acid, ammonium citrate or tetramethylammonium hydroxide; based on the total mass of the slurry, the mixing amount of silicon carbide particles is 79-96 wt%, the mixing amount of dispersant is 1-5 wt%, and the mixing amount of silicon-carbon composite micro-nano particles is 0.5-20 wt%;

[0044] (4) Inject the slurry obtained in step (3) into the mold to form a green body;

[0045] (5) The green body obtained in step (4) is dried in an oven at 40-100℃, and then sintered in a vacuum sintering furnace. The sintering temperature is controlled at 1500-1900℃ and the time is 0.1-48h to obtain silicon carbide ceramic.

[0046] In a second aspect, the present invention provides a silicon carbide ceramic, which is prepared by the preparation method described in the first aspect.

[0047] Thirdly, the present invention provides an application of silicon carbide ceramics as described in the second aspect, wherein devices manufactured from the silicon carbide ceramics include mechanical seals, kiln furniture, heat exchange tubes, radiant burners, or aerospace engine combustion chambers.

[0048] The numerical range described in this invention includes not only the point values ​​listed above, but also any point values ​​within the numerical ranges not listed above. Due to space limitations and for the sake of brevity, this invention will not exhaustively list all the specific point values ​​included in the range.

[0049] Compared with the prior art, the present invention has the following beneficial effects:

[0050] The preparation method provided by this invention encapsulates or attaches carbon elements to the surface of silicon particles in situ during the raw material stage, enabling the two to undergo an effective chemical reaction within a short diffusion range. This eliminates or reduces the need for silicon infiltration steps, simplifies the process and equipment, and improves production efficiency. At the same time, it can effectively control the Si / C ratio in the micro-region during ceramic production, optimize the reaction sintering process, improve product purity, reduce or eliminate the presence of free silicon in the finished ceramic, thereby improving the high-temperature performance and corrosion resistance of the product, extending the product's service life, and facilitating large-scale promotion and application. Attached Figure Description

[0051] Figure 1 This is a schematic diagram of the silicon-carbon composite micro / nano particle structure in the preparation method provided by the present invention.

[0052] Figure 2 This is a flowchart of the preparation method of silicon carbide ceramics provided by the present invention;

[0053] Figure 3 These are optical microscope images of silicon carbide ceramics provided in Example 1;

[0054] Figure 4 This is a photograph of the finished silicon carbide ceramic product provided in Example 1;

[0055] Figure 5 This is a flowchart of the preparation method of silicon carbide ceramics provided in Comparative Example 1. Detailed Implementation

[0056] The technical solution of the present invention will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention and should not be construed as limiting the invention in any way.

[0057] This invention provides a method for preparing silicon carbide ceramics, comprising granulation, molding and sintering performed sequentially.

[0058] The powder used in the granulation process includes silicon-carbon composite micro / nano particles, and the silicon-carbon composite micro / nano particles have any one or a combination of two of the following structures:

[0059] (A) Core-shell structure of carbon-coated silicon (see) Figure 1 a);

[0060] (B) Heterogeneous silicon-carbon composite structure (see...) Figure 1 b).

[0061] Specifically, the preparation method includes the following steps:

[0062] (1) Obtain silicon particles with an average particle size of 0.01-200 μm, and coat or attach carbon-containing organic matter on the surface of the silicon particles by solution mixing, ball milling or hydrothermal reaction to obtain a silicon-carbon-containing organic matter composite; the carbon-containing organic matter includes any one or a combination of at least two of phenolic resin, resorcinol-formaldehyde resin, polystyrene, polyaniline, glucose, oleic acid, polydopamine, polypyrrole or polyvinylidene fluoride;

[0063] (2) After drying the silicon-carbon organic composite obtained in step (1), carbonize it at 350-800℃ for 0.1-48h in a reducing atmosphere to obtain carbon-coated silicon particles or silicon-carbon composite powder.

[0064] (3) Mix silicon carbide particles, dispersant and carbon-coated silicon particles or silicon-carbon composite powder obtained in step (2), and stir evenly to obtain a slurry; the dispersant includes any one or a combination of at least two of polyethylene glycol, polyacrylic acid, ammonium citrate or tetramethylammonium hydroxide; based on the total mass of the slurry, the mixing amount of silicon carbide particles is 80-90 wt%, and the mixing amount of carbon-coated silicon particles or silicon-carbon composite powder is 5-20 wt%;

[0065] (4) Inject the slurry obtained in step (3) into the mold to form a green body;

[0066] (5) The green body obtained in step (4) is dried in an oven at 40-100℃, and then sintered in a vacuum sintering furnace. The sintering temperature is controlled at 1500-1900℃ and the time is 0.1-48h to obtain silicon carbide ceramic.

[0067] Example 1

[0068] This embodiment provides a silicon carbide ceramic and its preparation method, such as... Figure 2 As shown, the preparation method includes the following steps:

[0069] (1) Obtain silicon particles with an average particle size of 100 μm, and coat the surface of the silicon particles with polystyrene and polyaniline by ball milling to obtain a silicon-carbon organic composite.

[0070] (2) After drying, the silicon-carbon organic composite obtained in step (1) is carbonized at 600°C for 24 hours in a nitrogen-hydrogen mixed atmosphere to obtain carbon-coated silicon particles.

[0071] (3) Mix silicon carbide particles, polyethylene glycol and carbon-coated silicon particles obtained in step (2), and stir evenly to obtain a slurry; using the total mass of the slurry as the calculation basis, the mixing amount of silicon carbide particles is 85wt%, the mixing amount of polyethylene glycol is 5wt%, and the mixing amount of carbon-coated silicon particles is 10wt%.

[0072] (4) Inject the slurry obtained in step (3) into the mold to form a green body;

[0073] (5) The green body obtained in step (4) is first dried at 40°C for 2 hours, then dried in an oven at 80°C for 8 hours, and then sintered in a vacuum sintering furnace. The sintering temperature is controlled at 1600°C for 10 hours, and then kept at the temperature for 8 hours to obtain silicon carbide ceramic.

[0074] The optical microscope images and finished product images of the silicon carbide ceramics obtained in this embodiment are shown below. Figure 3 and Figure 4 .

[0075] Depend on Figure 3 It can be seen that the silicon carbide ceramic obtained in this embodiment has a high appearance density.

[0076] Example 2

[0077] This embodiment provides a silicon carbide ceramic and its preparation method, such as... Figure 2 As shown, the preparation method includes the following steps:

[0078] (1) Obtain silicon particles with an average particle size of 20 μm, and attach glucose to the surface of the silicon particles by hydrothermal reaction, while controlling the temperature of the hydrothermal reaction to be 120℃ and the time to be 24h, to obtain silicon-carbon organic complex.

[0079] (2) After drying, the silicon-carbon organic composite obtained in step (1) is carbonized at 400°C for 48 hours in a nitrogen-hydrogen mixed atmosphere to obtain silicon-carbon composite powder.

[0080] (3) Mix silicon carbide particles, polyacrylic acid and silicon-carbon composite powder obtained in step (2), and stir evenly to obtain a slurry; using the total mass of the slurry as the calculation basis, the mixing amount of silicon carbide particles is 80wt%, the mixing amount of polyacrylic acid is 5wt%, and the mixing amount of silicon-carbon composite powder is 15wt%.

[0081] (4) Inject the slurry obtained in step (3) into the mold to form a green body;

[0082] (5) The green blank obtained in step (4) is first dried in an oven at 40°C for 8 hours, then heated to 70°C for 8 hours, and then sintered in a vacuum sintering furnace. The sintering temperature is controlled at 1500°C for 24 hours, and then kept at the temperature for 24 hours to obtain silicon carbide ceramic.

[0083] The optical microscope images and finished product images of the silicon carbide ceramics obtained in this embodiment are similar to those in Example 1, so they will not be described again here.

[0084] Example 3

[0085] This embodiment provides a silicon carbide ceramic and its preparation method, such as... Figure 2 As shown, the preparation method includes the following steps:

[0086] (1) Obtain silicon particles with an average particle size of 200 μm, and coat the surface of the silicon particles with oleic acid by hydrothermal reaction, while controlling the temperature of the hydrothermal reaction to be 150 °C and the time to be 24 h, to obtain a silicon-carbon-containing organic composite.

[0087] (2) After drying, the silicon-carbon organic composite obtained in step (1) is carbonized at 800°C for 6 hours in a nitrogen-hydrogen mixed atmosphere to obtain carbon-coated silicon particles.

[0088] (3) Mix silicon carbide particles, ammonium citrate and carbon-coated silicon particles obtained in step (2), stir evenly to obtain a slurry; take the total mass of the slurry as the calculation basis, the mixing amount of silicon carbide particles is 90wt%, the mixing amount of ammonium citrate is 5wt%, and the mixing amount of carbon-coated silicon particles is 5wt%.

[0089] (4) Inject the slurry obtained in step (3) into the mold to form a green body;

[0090] (5) The green blank obtained in step (4) is first dried in an oven at 50°C for 8 hours, then heated to 80°C for 6 hours, and then sintered in a vacuum sintering furnace. The sintering temperature is controlled at 1900°C and the time is 6 hours to obtain silicon carbide ceramic.

[0091] The optical microscope images and finished product images of the silicon carbide ceramics obtained in this embodiment are similar to those in Example 1, so they will not be described again here.

[0092] Example 4

[0093] This embodiment provides a silicon carbide ceramic and its preparation method. The preparation method is the same as that in Example 2, except that the carbon-containing organic matter coating the silicon particles is replaced with phenolic resin. Therefore, it will not be described in detail here.

[0094] Example 5

[0095] This embodiment provides a silicon carbide ceramic and its preparation method. The preparation method is the same as that in Example 1 except that the dispersant is replaced with tetramethylammonium hydroxide. Therefore, it will not be described in detail here.

[0096] Example 6

[0097] This embodiment provides a silicon carbide ceramic and its preparation method. The preparation method is based on Embodiment 1, with steps (1) and (2) modified as follows: carbon-encapsulated silicon particles are obtained by directly depositing carbon elements on the surface of silicon particles with an average particle size of 100 μm using chemical vapor deposition. Specifically, the silicon particles are laid flat in the vacuum chamber of a PECVD deposition equipment, and methane and hydrogen are introduced under vacuum conditions at 500°C for deposition. Through plasma action, the carbon source gas is decomposed at low temperature, thereby generating a carbon encapsulation layer on the surface of the silicon particles. The methane flow rate is 85 sccm, the hydrogen flow rate is 45 sccm, the pressure is 300 Pa, the radio frequency power is 200 W, and the deposition time is 20 min.

[0098] The remaining steps and conditions are the same as in Example 1, so they will not be repeated here.

[0099] Comparative Example 1

[0100] This comparative example provides a silicon carbide ceramic and its preparation method, such as... Figure 5 As shown, the preparation method includes the following steps:

[0101] (1) Mix silicon carbide particles, polyethylene glycol and carbon black powder, and stir evenly to obtain a slurry; using the total mass of the slurry as the calculation basis, the mixing amount of silicon carbide particles is 85wt%, the mixing amount of polyethylene glycol is 5wt%, and the mixing amount of carbon black powder is 10wt%.

[0102] (2) The slurry obtained in step (1) is injected into the mold to form a green body;

[0103] (3) The green blank obtained in step (2) is solidified and sintered. Specifically, it is dried at 40°C for 2 hours, then dried at 70°C for 8 hours, and then heated to 250°C under the protection of high-purity nitrogen and solidified at a constant temperature for 4 hours. After that, it is heated to 1900°C and sintered for 4 hours to obtain the green blank.

[0104] (4) Immerse the green blank obtained in step (3) in liquid polycarbosilane, and then embed it with high-purity silicon powder to obtain the carburized green blank.

[0105] (5) The blank obtained in step (4) is sintered in a vacuum sintering furnace. First, the temperature is raised to 900°C, heated for 6 hours and held for 3 hours, then the temperature is raised to 1900°C, heated for 8 hours and held for 8 hours, and then cooled to room temperature with the furnace to obtain silicon carbide ceramic.

[0106] Compared to Example 1, this comparative example uses the traditional reaction sintering method to prepare silicon carbide ceramics. During the sintering process, silicon infiltration is required, and the uniformity of infiltration is difficult to control. Due to the limitations of element diffusion in solids, a large amount of silicon that has penetrated into the interior does not react with carbon. Furthermore, the infiltration process in capillaries is prone to clogging. At the same time, the silicon infiltration process significantly increases the complexity and cost of the sintering equipment.

[0107] Performance testing

[0108] The silicon carbide ceramics obtained in Examples 1-6 and Comparative Example 1 were subjected to density, SiC content and flexural strength tests, respectively. The relevant test results are shown in Table 1 below.

[0109] Table 1

[0110] silicon carbide ceramics <![CDATA[Density (g / cm 3 )]]> SiC content (%) Flexural strength (MPa) Example 1 3.03 97.6 343 Example 2 3.08 98.4 352 Example 3 3.12 99.3 387 Example 4 3.05 97.5 360 Example 5 3.00 96.3 315 Example 6 3.12 98.9 389 Comparative Example 1 2.95 94.2 303

[0111] Therefore, the preparation method provided by this invention encapsulates carbon elements in situ onto the surface of silicon particles during the raw material stage, enabling the two to undergo an effective chemical reaction within a short diffusion range. This eliminates or reduces the need for silicon infiltration steps, simplifies the process and equipment, and improves production efficiency. At the same time, it can effectively control the Si / C ratio in the micro-region during ceramic production, optimize the reaction sintering process, improve product purity, reduce or eliminate the presence of free silicon in the finished ceramic, thereby improving the high-temperature performance and corrosion resistance of the product, extending the product's service life, and facilitating large-scale promotion and application.

[0112] The applicant declares that the above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. A method for preparing silicon carbide ceramics, characterized in that, The preparation method includes the following steps: (1) Obtain silicon particles with an average particle size of 100 μm, and coat the surface of the silicon particles with polystyrene and polyaniline by ball milling to obtain a silicon-carbon organic composite. (2) After drying, the silicon-carbon organic composite obtained in step (1) is carbonized at 600°C for 24 hours in a nitrogen-hydrogen mixed atmosphere to obtain carbon-coated silicon particles. (3) Mix silicon carbide particles, polyethylene glycol and carbon-coated silicon particles obtained in step (2), and stir evenly to obtain a slurry; using the total mass of the slurry as the calculation basis, the mixing amount of silicon carbide particles is 85wt%, the mixing amount of polyethylene glycol is 5wt%, and the mixing amount of carbon-coated silicon particles is 10wt%; (4) The slurry obtained in step (3) is injected into the mold to form a green body; (5) The green body obtained in step (4) is first dried at 40°C for 2 hours, then dried in an oven at 80°C for 8 hours, and then sintered in a vacuum sintering furnace. The sintering temperature is controlled at 1600°C for 10 hours, and then kept at the temperature for 8 hours to obtain silicon carbide ceramic.

2. A method for preparing silicon carbide ceramics, characterized in that, The preparation method includes the following steps: (1) Obtain silicon particles with an average particle size of 20 μm, and attach glucose to the surface of the silicon particles by hydrothermal reaction, while controlling the temperature of the hydrothermal reaction to be 120 °C and the time to be 24 h, to obtain silicon-carbon organic composite. (2) After drying, the silicon-carbon organic composite obtained in step (1) is carbonized at 400°C for 48 hours in a nitrogen-hydrogen mixed atmosphere to obtain silicon-carbon composite powder. (3) Mix silicon carbide particles, polyacrylic acid and silicon-carbon composite powder obtained in step (2), and stir evenly to obtain a slurry; using the total mass of the slurry as the calculation basis, the mixing amount of silicon carbide particles is 80wt%, the mixing amount of polyacrylic acid is 5wt%, and the mixing amount of silicon-carbon composite powder is 15wt%; (4) The slurry obtained in step (3) is injected into the mold to form a green body; (5) The green blank obtained in step (4) is first dried in an oven at 40°C for 8 hours, then heated to 70°C for 8 hours, and then sintered in a vacuum sintering furnace. The sintering temperature is controlled at 1500°C for 24 hours, and then kept at the temperature for 24 hours to obtain silicon carbide ceramic.

3. A method for preparing silicon carbide ceramics, characterized in that, The preparation method includes the following steps: (1) Obtain silicon particles with an average particle size of 200 μm, and coat the surface of the silicon particles with oleic acid by hydrothermal reaction, while controlling the temperature of the hydrothermal reaction to be 150 °C and the time to be 24 h, to obtain a silicon-carbon-containing organic composite. (2) After drying the silicon-carbon organic composite obtained in step (1), carbonization was carried out at 800°C for 6 hours in a nitrogen-hydrogen mixed atmosphere to obtain carbon-coated silicon particles. (3) Mix silicon carbide particles, ammonium citrate and carbon-coated silicon particles obtained in step (2), and stir evenly to obtain a slurry; using the total mass of the slurry as the calculation basis, the mixing amount of silicon carbide particles is 90wt%, the mixing amount of ammonium citrate is 5wt%, and the mixing amount of carbon-coated silicon particles is 5wt%; (4) The slurry obtained in step (3) is injected into the mold to form a green body; (5) The green blank obtained in step (4) is first dried in an oven at 50°C for 8 hours, then heated to 80°C for 6 hours, and then sintered in a vacuum sintering furnace. The sintering temperature is controlled at 1900°C and the time is 6 hours to obtain silicon carbide ceramic.

4. A method for preparing silicon carbide ceramics, characterized in that, The preparation method includes the following steps: (1) Obtain silicon particles with an average particle size of 20 μm, and attach phenolic resin to the surface of the silicon particles by hydrothermal reaction, while controlling the temperature of the hydrothermal reaction to be 120℃ and the time to be 24h, to obtain a silicon-carbon-containing organic composite. (2) After drying, the silicon-carbon organic composite obtained in step (1) is carbonized at 400°C for 48 hours in a nitrogen-hydrogen mixed atmosphere to obtain silicon-carbon composite powder. (3) Mix silicon carbide particles, polyacrylic acid and silicon-carbon composite powder obtained in step (2), and stir evenly to obtain a slurry; using the total mass of the slurry as the calculation basis, the mixing amount of silicon carbide particles is 80wt%, the mixing amount of polyacrylic acid is 5wt%, and the mixing amount of silicon-carbon composite powder is 15wt%; (4) The slurry obtained in step (3) is injected into the mold to form a green body; (5) The green blank obtained in step (4) is first dried in an oven at 40°C for 8 hours, then heated to 70°C for 8 hours, and then sintered in a vacuum sintering furnace. The sintering temperature is controlled at 1500°C for 24 hours, and then kept at the temperature for 24 hours to obtain silicon carbide ceramic.

5. A method for preparing silicon carbide ceramics, characterized in that, The preparation method includes the following steps: (1) Obtain silicon particles with an average particle size of 100 μm, and coat the surface of the silicon particles with polystyrene and polyaniline by ball milling to obtain a silicon-carbon organic composite. (2) After drying, the silicon-carbon organic composite obtained in step (1) is carbonized at 600°C for 24 hours in a nitrogen-hydrogen mixed atmosphere to obtain carbon-coated silicon particles. (3) Mix silicon carbide particles, tetramethylammonium hydroxide and carbon-coated silicon particles obtained in step (2), and stir evenly to obtain a slurry; using the total mass of the slurry as the calculation basis, the mixing amount of silicon carbide particles is 85wt%, the mixing amount of tetramethylammonium hydroxide is 5wt%, and the mixing amount of carbon-coated silicon particles is 10wt%; (4) The slurry obtained in step (3) is injected into the mold to form a green body; (5) The green body obtained in step (4) is first dried at 40°C for 2 hours, then dried in an oven at 80°C for 8 hours, and then sintered in a vacuum sintering furnace. The sintering temperature is controlled at 1600°C for 10 hours, and then kept at the temperature for 8 hours to obtain silicon carbide ceramic.

6. A method for preparing silicon carbide ceramics, characterized in that, The preparation method includes the following steps: (1) Carbon-coated silicon particles were prepared by directly depositing carbon on the surface of silicon particles with an average particle size of 100 μm using chemical vapor deposition. The specific operation was as follows: the silicon particles were laid flat in the vacuum chamber of the PECVD deposition equipment, and methane and hydrogen were introduced under vacuum conditions and at 500 °C for deposition. The carbon source gas was decomposed at low temperature by plasma action, thereby generating a carbon coating layer on the surface of the silicon particles. The methane flow rate was 85 sccm, the hydrogen flow rate was 45 sccm, the pressure was 300 Pa, the radio frequency power was 200 W, and the deposition time was 20 min. (2) Mix silicon carbide particles, polyethylene glycol and carbon-coated silicon particles obtained in step (1), and stir evenly to obtain a slurry; using the total mass of the slurry as the calculation basis, the mixing amount of silicon carbide particles is 85wt%, the mixing amount of polyethylene glycol is 5wt%, and the mixing amount of carbon-coated silicon particles is 10wt%; (3) The slurry obtained in step (2) is injected into the mold to form a green body; (4) The green body obtained in step (3) is first dried at 40°C for 2 hours, then dried in an oven at 80°C for 8 hours, and then sintered in a vacuum sintering furnace. The sintering temperature is controlled at 1600°C for 10 hours, and then kept at the temperature for 8 hours to obtain silicon carbide ceramic.

7. A silicon carbide ceramic, characterized in that, The silicon carbide ceramic is prepared by the preparation method according to any one of claims 1-6.

8. An application of the silicon carbide ceramic as described in claim 7, characterized in that, Devices made of silicon carbide ceramics include mechanical seals, kiln furniture, heat exchange tubes, radiant burners, or aerospace engine combustion chambers.

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