Porous silicon carbide ceramic based on skeleton support and chemical vapor deposition homogeneous coating as well as preparation method and application of porous silicon carbide ceramic
By growing a nanoscale β-SiC coating layer on the surface of porous silicon carbide ceramic particles, a micron core-nano shell structure is constructed, which solves the contradiction between high porosity and high strength in porous silicon carbide ceramics and realizes the preparation of high-performance porous SiC ceramics, which are suitable for catalysts, high-temperature devices and membrane reaction devices.
Patent Information
- Application Number
- CN202511727213.9
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-11-24
- Publication Date
- 2026-02-10
AI Technical Summary
Existing methods for preparing porous silicon carbide ceramics cannot simultaneously achieve high porosity, high strength, and high toughness without introducing foreign impurities, and their high-temperature performance is insufficient.
A nanoscale β-SiC coating layer was grown in situ on the surface of porous silicon carbide ceramic particles using a framework support and chemical vapor deposition homogeneous coating method, constructing a micron core-nano shell structure. The nanoshell layer was used as a sintering activation layer to promote the strengthening of the interparticle interface during pressureless sintering.
A pure porous SiC ceramic with high porosity, high strength, high fracture toughness and excellent high-temperature performance was prepared. The material has high purity and can be used stably in high-temperature oxidizing or corrosive environments, reducing production costs and equipment dependence.
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Figure CN121494597A_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of advanced ceramic material preparation technology, and relates to a porous silicon carbide ceramic based on skeleton support and chemical vapor deposition homogeneous coating, its preparation method and application. Background Technology
[0002] Porous silicon carbide (SiC) ceramics have broad application prospects in high-temperature filtration, catalyst support, membrane reactor, thermal management, and semiconductor manufacturing processes due to their excellent high-temperature stability, high thermal conductivity, three-dimensional interconnected pore structure, and high specific surface area.
[0003] However, the traditional preparation methods of porous SiC ceramics face a fundamental contradiction: it is difficult to achieve both high porosity and high strength / toughness. Common improvement methods include the following: (1) Partial sintering method: introducing sintering aids (such as Al2O3, Y2O3, etc.) to lower the sintering temperature and promote densification. However, these metal oxide phases will form a low melting point glass phase at high temperature, which seriously degrades the high-temperature mechanical properties, creep resistance and corrosion resistance of the material. (2) Organic precursor conversion method: This method has disadvantages such as large shrinkage, low product purity and limited improvement in mechanical properties. (3) Direct stacking sintering method: if fine particles are used to improve strength, it will lead to a sharp decrease in porosity and poor permeability; if coarse particles are used to maintain high porosity, there are few contact points between particles, and the sintering neck is difficult to grow, resulting in low material strength and high brittleness.
[0004] In existing technologies, surface modification is used to improve the sintering activity of large SiC particles forming porous silicon carbide ceramic frameworks. This often involves heterogeneous coating or physical mixing of nanoparticles, which suffers from weak interfacial bonding and uneven distribution of the modified material.
[0005] Therefore, developing a method that can maintain high porosity and significantly enhance the mechanical and high-temperature properties of porous SiC ceramics without introducing any foreign impurities has become a technical bottleneck that urgently needs to be overcome in this field. Summary of the Invention
[0006] The purpose of this invention is to provide a porous silicon carbide ceramic based on skeleton support and chemical vapor deposition homogeneous coating, as well as its preparation method and application. By optimizing the preparation process of porous silicon carbide ceramic materials and reducing the sintering temperature of the materials, pure porous SiC ceramics with high porosity, high strength, high fracture toughness and excellent high temperature performance are prepared.
[0007] To achieve this objective, the present invention adopts the following technical solution:
[0008] In a first aspect, the present invention provides a method for preparing porous silicon carbide ceramics based on framework support and homogeneous coating by chemical vapor deposition, the preparation method comprising:
[0009] Silicon carbide raw material is placed in a fluidized bed chemical vapor deposition apparatus, and silicon carbide source, carrier gas and dilution gas are introduced to perform fluidized bed chemical vapor deposition (CVD) to form a homogeneous nanoscale coating layer on the surface of the silicon carbide raw material, thereby obtaining modified silicon carbide material;
[0010] The average particle size of the silicon carbide raw material is 20μm-50μm, for example, it can be 22μm, 24μm, 25μm, 26μm, 28μm, 30μm, 32μm, 34μm, 35μm, 36μm, 38μm, 40μm, 42μm, 44μm, 45μm, 46μm or 48μm, etc.
[0011] The pressureless granulation powder and the modified silicon carbide material are mixed and then pressed and sintered in a pressureless manner to obtain porous silicon carbide ceramics.
[0012] The preparation method provided by this invention involves growing a homogeneous nanoscale coating layer with high sintering activity in situ on the surface of micron-sized SiC particles using CVD technology, thereby constructing a unique "micron core-nano shell" structural unit. This structural unit utilizes the nanoshell layer as a sintering activation layer, which greatly promotes the formation and growth of sintering necks during pressureless sintering, achieving intrinsic strengthening of the interparticle interface, and thus preparing pure porous SiC ceramics with high porosity, high strength, high fracture toughness, and excellent high-temperature performance.
[0013] It should be noted that coarse-grained SiC with a specific particle size range is selected as a rigid skeleton to ensure that the material has high porosity and a through-hole structure after molding. Then, a nanoscale β-SiC crystal layer is uniformly coated on its surface by CVD process. This nano-coating layer is a homogeneous material with the core skeleton and has extremely high sintering activity due to its nanoscale size and the high surface energy of the β phase.
[0014] It should also be noted that during pressureless sintering, the β-SiC nanoscale coating at the particle contact point becomes a "short-circuit path" for rapid atomic diffusion. The material transport rate is several orders of magnitude higher than that of bulk diffusion. This allows for the rapid formation and full growth of the sintering neck at temperatures lower than those of traditional sintering. The resulting sintering neck is dense and pure, and is completely crystalline with the particle body, thus achieving intrinsic strengthening of the interface.
[0015] Preferably, the silicon carbide raw material further includes surface activation treatment before fluidized bed chemical vapor deposition.
[0016] In this invention, surface activation treatment is used to remove surface oxides and contaminants from silicon carbide raw materials, thereby enhancing the adhesion of the CVD coating layer. The surface activation treatment includes acid washing and / or ultrasonic cleaning.
[0017] Preferably, the silicon carbide raw material includes α-SiC.
[0018] Preferably, the average particle size of the silicon carbide raw material is 22μm-40μm, for example, it can be 24μm, 25μm, 26μm, 28μm, 30μm, 32μm, 34μm, 35μm, 36μm or 38μm, etc.
[0019] In this invention, the macroscopic pore size and porosity of the material can be controlled by adjusting the particle size range of the silicon carbide raw material.
[0020] Preferably, the carbon silicon source includes silicon chloride (SiCl4) and methane (CH4).
[0021] Preferably, the carrier gas includes hydrogen (H2).
[0022] Preferably, the diluting gas includes nitrogen (N2).
[0023] Preferably, the molar ratio of silicon chloride, methane, carrier gas and dilution gas is 1:(0.5-0.8):3.5:(8-10), for example, it can be 1:0.5:3.5:8, 1:0.6:3.5:8.5, 1:0.7:3.5:9 or 1:0.8:3.5:10, etc.
[0024] Preferably, the temperature of the fluidized bed chemical vapor deposition is 900℃-1300℃, for example, it can be 920℃, 940℃, 950℃, 960℃, 980℃, 1000℃, 1020℃, 1040℃, 1050℃, 1060℃, 1080℃, 1100℃, 1120℃, 1140℃, 1150℃, 1160℃, 1180℃, 1200℃, 1220℃, 1240℃, 1250℃, 1260℃ or 1280℃, etc., preferably 1100℃-1250℃.
[0025] Preferably, the pressure of the fluidized bed chemical vapor deposition is 500Pa-1500Pa, for example, it can be 500Pa, 600Pa, 700Pa, 800Pa, 900Pa, 1000Pa, 1100Pa, 1200Pa, 1300Pa or 1400Pa, and more preferably 500Pa-1000Pa.
[0026] Preferably, the fluidized bed chemical vapor deposition time is 0.5h-3h, for example, it can be 0.6h, 0.7h, 0.8h, 0.9h, 1h, 1.1h, 1.2h, 1.3h, 1.4h, 1.5h, 1.6h, 1.7h, 1.8h, 2h, 2.1h, 2.2h, 2.3h, 2.4h, 2.5h, 2.6h, 2.7h, 2.8h or 2.9h, and preferably 0.5h-1.5h.
[0027] It should be noted that by precisely controlling the CVD process parameters, the thickness, grain size, and crystallinity of the nanoscale coating can be controlled, thereby achieving precise design of material properties. Controlling the temperature range of fluidized bed chemical vapor deposition (CVD) is beneficial for generating highly sinterable β-SiC nanoscale coatings, rather than coarse α-SiC coatings; controlling the pressure range of CVD can significantly improve the uniformity of coating thickness; and adjusting the deposition time range of CVD allows for control of the coating thickness range.
[0028] Preferably, the homogeneous nanoscale coating layer is a β-SiC nanoscale coating layer.
[0029] It should be noted that the "short-circuit diffusion" effect provided by the nano-coating layer makes the sintering neck more robust, greatly increasing the bonding area and bonding strength between particles, thereby significantly improving the flexural strength and compressive strength of the material. In addition, the highly active β-SiC at the interface can achieve low-temperature sintering, effectively suppressing grain coarsening of fine powder in the matrix and large particles in the skeleton, helping the material to form a finer and more uniform micro-grain structure after sintering. This helps to induce toughening mechanisms such as crack deflection, bridging, and pull-out effect of the nanoshell, significantly improving the fracture toughness of the material and overcoming the disadvantage of high brittleness of traditional porous ceramics.
[0030] Preferably, the thickness of the homogeneous nanoscale coating layer is 50nm-200nm, for example, it can be 60nm, 70nm, 80nm, 90nm, 100nm, 110nm, 120nm, 130nm, 140nm, 150nm, 160nm, 170nm, 180nm or 190nm, and more preferably 100nm-200nm.
[0031] It should be noted that the silicon carbon source is decomposed at high temperature, and heterogeneous nucleation and growth occur on the surface of micron-sized α-SiC framework particles through gas-phase mass transfer, forming a uniform and dense β-SiC nanoscale coating layer.
[0032] Preferably, the average particle size of the pressureless granulated powder is 10μm-200μm, for example, it can be 20μm, 30μm, 40μm, 50μm, 60μm, 70μm, 80μm, 90μm, 100μm, 110μm, 120μm, 130μm, 140μm, 150μm, 160μm, 170μm, 180μm or 190μm, etc.
[0033] In this invention, the pressureless granulation powder is pressureless sintered silicon carbide ceramic granulation powder. No specific requirements or limitations are placed on the pressureless granulation powder; it can be obtained commercially by those skilled in the art or prepared independently.
[0034] Preferably, the mass ratio of the pressureless granulation powder to the modified silicon carbide material is (1:20):1, for example, it can be 1:1, 2:1, 4:1, 6:1, 8:1, 10:1, 11:1, 12:1, 13:1, 14:1, 15:1, 16:1, 17:1, 18:1 or 19:1, etc.
[0035] Preferably, the pressing pressure is 35MPa-45MPa, for example, it can be 36MPa, 37MPa, 38MPa, 39MPa, 40MPa, 41MPa, 42MPa, 43MPa or 44MPa, etc.
[0036] Preferably, the pressureless sintering is carried out under a protective atmosphere.
[0037] In this invention, the protective atmosphere includes argon.
[0038] Preferably, the heating rate of the pressureless sintering is 3℃ / min-5℃ / min, for example, it can be 3.2℃ / min, 3.5℃ / min, 3.8℃ / min, 4℃ / min, 4.2℃ / min, 4.5℃ / min or 4.8℃ / min, etc.; the final temperature is 1750℃-2110℃, for example, it can be 1800℃, 1850℃, 1900℃, 1950℃, 2000℃ or 2050℃, etc.; the holding time is 0.5h-2h, for example, it can be 0.6h, 0.8h, 1h, 1.2h, 1.5h, 1.6h or 1.8h, etc.
[0039] In this invention, by utilizing the high sintering activity of the β-SiC nanoscale coating layer, the sintering temperature can be reduced, thereby reducing energy consumption and production costs, as well as reducing reliance on and wear and tear on high-temperature equipment.
[0040] In this invention, the pressureless sintering is followed by furnace cooling to room temperature.
[0041] In a second aspect, the present invention provides a porous silicon carbide ceramic, which is prepared by the preparation method described in the first aspect.
[0042] The porous SiC ceramic material provided by this invention exhibits excellent mechanical and high-temperature properties while maintaining high porosity. Under preferred conditions, the porous silicon carbide ceramic material has a flexural strength exceeding 130 MPa and a fracture toughness reaching 3 MPa·m. 1 / 2 The samples exhibited high strength retention after high-temperature treatment.
[0043] Thirdly, the present invention provides an application of porous silicon carbide ceramic as described in the second aspect, wherein the porous silicon carbide ceramic is used in the fields of catalysts, high-temperature devices, membrane reaction devices or semiconductor devices.
[0044] 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.
[0045] Compared with the prior art, the present invention has the following beneficial effects:
[0046] (1) The preparation method provided by the present invention grows a homogeneous nanoscale coating layer with high sintering activity in situ on the surface of micron-sized SiC particles by CVD process, and constructs a unique “micron core-nano shell” structural unit. This structural unit uses the nano shell as a sintering activation layer, which greatly promotes the formation and growth of sintering necks during pressureless sintering, and realizes the intrinsic strengthening of the interparticle interface, thereby preparing a pure porous SiC ceramic with high porosity, high strength, high fracture toughness and excellent high temperature performance.
[0047] (2) The preparation method provided by the present invention does not introduce any metal or oxide sintering aids in the entire preparation process, which improves the purity of the material and enables the porous SiC ceramic material to be used stably for a long time in an oxidizing or corrosive environment above 1600℃.
[0048] (3) The preparation method provided by the present invention separates the "strength contributing phase - nanoscale active coating layer" and the "structural support phase - micron skeleton" in space. The micron skeleton ensures the high porosity and macroscopic pore structure of the material. The dense sintered neck formed by the β-SiC nanoscale coating layer through high temperature sintering and combined with the particle body as a complete crystal is responsible for providing strong connection force, which solves the problem of high porosity and high strength contradiction in the prior art.
[0049] (4) The porous SiC ceramic material obtained by this invention has excellent mechanical and high-temperature properties. Under preferred conditions, its flexural strength is above 130 MPa and its fracture toughness reaches 3 MPa·m.1 / 2 The samples exhibited high strength retention after high-temperature treatment. Attached Figure Description
[0050] Figure 1 SEM image (×100 μm) of porous silicon carbide ceramic prepared by the preparation method provided in Example 3.
[0051] Figure 2 SEM image (×2μm) of porous silicon carbide ceramic prepared by the preparation method provided in Example 3. Detailed Implementation
[0052] 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.
[0053] All materials used in the specific embodiments of this invention are commercially available or prepared using conventional methods in the prior art. All methods employed are conventional techniques in the field. In the following specific embodiments, the silicon carbide raw materials were sequentially cleaned with an 8% HF solution, ultrasonically cleaned with deionized water, and dried before being placed in the fluidized bed chemical vapor deposition apparatus. The pressureless granulated powder is a product obtained by sintering silicon carbide with an average particle size of 20 μm at atmospheric pressure and a temperature of 2050°C for 1 hour.
[0054] Example 1
[0055] This embodiment provides a method for preparing porous silicon carbide ceramics based on framework support and homogeneous coating by chemical vapor deposition. The preparation method includes the following steps:
[0056] (1) 100g of silicon carbide raw material with an average particle size of 25μm was placed in a fluidized bed chemical vapor deposition device, and SiCl4, CH4, H2 and N2 were introduced at a molar ratio of 1:0.6:3.5:9. Fluidized bed chemical vapor deposition was carried out for 0.7h at a temperature of 1200℃ and a pressure of 900Pa to form a β-SiC nanoscale coating layer with a thickness of 120nm on the surface of the silicon carbide raw material, thereby obtaining modified silicon carbide material;
[0057] (2) Mix the pressureless granulation powder with an average particle size of 120 μm and the modified silicon carbide material described in step (1) at a mass ratio of 15:1, press them into Φ50×5 mm circular green blanks under a pressure of 40 MPa, and then heat the circular green blanks to 2110 °C at a heating rate of 5 °C / min under an argon atmosphere for pressureless sintering and hold for 1 h. After cooling to room temperature in the furnace, porous silicon carbide ceramics are obtained.
[0058] Example 2
[0059] This embodiment provides a method for preparing porous silicon carbide ceramics based on framework support and homogeneous coating by chemical vapor deposition. The preparation method includes the following steps:
[0060] (1) 100g of silicon carbide raw material with an average particle size of 40μm was placed in a fluidized bed chemical vapor deposition device, and SiCl4, CH4, H2 and N2 were introduced at a molar ratio of 1:0.7:3.5:9.5. Fluidized bed chemical vapor deposition was carried out at a temperature of 1000℃ and a pressure of 1kPa for 0.6h to form a β-SiC nanoscale coating layer with a thickness of 100nm on the surface of the silicon carbide raw material, thereby obtaining modified silicon carbide material;
[0061] (2) Mix the pressureless granulated powder with an average particle size of 80 μm and the modified silicon carbide material described in step (1) at a mass ratio of 15:1, press them into Φ50×5mm round green blanks under a pressure of 40MPa, and then heat the round green blanks to 1950℃ under an argon atmosphere at a heating rate of 3℃ / min for pressureless sintering and hold for 1h. After cooling to room temperature in the furnace, porous silicon carbide ceramics are obtained.
[0062] Example 3
[0063] This embodiment provides a method for preparing porous silicon carbide ceramics based on skeleton support and chemical vapor deposition homogeneous coating. Except for adjusting the fluidized bed chemical vapor deposition time in step (1) to 0.8h, and forming a β-SiC nanoscale coating layer with a thickness of 135nm on the surface of the silicon carbide raw material, all other conditions are the same as in Example 1.
[0064] In this embodiment, the SEM image of the obtained porous silicon carbide ceramic is as follows: Figure 1-2 As shown, by Figure 1-2 It can be seen that in the prepared porous silicon carbide ceramic, large particles form a ceramic skeleton, the grain boundaries at the joints are tightly attached, and there is a three-dimensional through-hole structure inside.
[0065] Example 4
[0066] This embodiment provides a method for preparing porous silicon carbide ceramics based on skeleton support and chemical vapor deposition homogeneous coating. Except for adjusting the fluidized bed chemical vapor deposition time in step (1) to 0.4h and forming a β-SiC nanoscale coating layer with a thickness of 70nm on the surface of the silicon carbide raw material, all other conditions are the same as in Example 1.
[0067] Example 5
[0068] This embodiment provides a method for preparing porous silicon carbide ceramics based on skeleton support and chemical vapor deposition homogeneous coating. Except for adjusting the fluidized bed chemical vapor deposition time in step (1) to 2h and forming a β-SiC nanoscale coating layer with a thickness of 300nm on the surface of the silicon carbide raw material, all other conditions are the same as in Example 1.
[0069] Example 6
[0070] This embodiment provides a method for preparing porous silicon carbide ceramics based on skeleton support and homogeneous coating by chemical vapor deposition. Except for adjusting the temperature of fluidized bed chemical vapor deposition in step (1) to 800°C, the other conditions are the same as in Example 1.
[0071] Example 7
[0072] This embodiment provides a method for preparing porous silicon carbide ceramics based on skeleton support and homogeneous coating by chemical vapor deposition. Except for adjusting the temperature of fluidized bed chemical vapor deposition in step (1) to 1300℃, the other conditions are the same as in Example 1.
[0073] Example 8
[0074] This embodiment provides a method for preparing porous silicon carbide ceramics based on skeleton support and homogeneous coating by chemical vapor deposition. Except for adjusting the pressure of fluidized bed chemical vapor deposition in step (1) to 1.5 kPa, the other conditions are the same as in Example 1.
[0075] Comparative Example 1
[0076] This comparative example provides a method for preparing porous silicon carbide ceramics based on skeleton support and chemical vapor deposition homogeneous coating. Except for the average particle size of silicon carbide raw material in step (1) being 5 μm, all other conditions are the same as in Example 1.
[0077] Comparative Example 2
[0078] This comparative example provides a method for preparing porous silicon carbide ceramics based on skeleton support and chemical vapor deposition homogeneous coating. Except for the average particle size of the silicon carbide raw material in step (1) being 60 μm, all other conditions are the same as in Example 1.
[0079] Comparative Example 3
[0080] This comparative example provides a method for preparing a porous silicon carbide ceramic material, the method comprising the following steps:
[0081] 100g of silicon carbide raw material with an average particle size of 25μm and 5g of composite sintering aid were mixed and sintered at 2150℃ for 1h to obtain porous silicon carbide ceramic material.
[0082] The composite sintering aids are B and C.
[0083] The porous silicon carbide ceramic materials obtained in the above embodiments and comparative examples were tested for porosity, mechanical properties, and high-temperature performance. The results are shown in Table 1. Porosity was determined using the gas adsorption method, flexural strength was determined using the three-point bending method, fracture toughness was determined using the single-sided notched beam (SENB) method, and the high-temperature performance was tested by heat-treating the porous silicon carbide ceramic material in air at 1500℃ for 100 hours, followed by testing the flexural strength.
[0084] Table 1
[0085]
[0086] As shown in Table 1:
[0087] The preparation method provided by this invention involves in-situ growth of a homogeneous nanoscale coating layer with high sintering activity on the surface of micron-sized SiC particles using CVD technology, constructing a unique "micron core-nano shell" structural unit. The nanoshell layer is then used as a sintering activation layer, greatly promoting the formation and growth of sintering necks during pressureless sintering, achieving intrinsic strengthening of the interparticle interface. This results in the preparation of porous SiC ceramics that simultaneously possess high porosity, high strength, high fracture toughness, and excellent high-temperature performance. Under preferred conditions, the obtained porous silicon carbide ceramic material exhibits a porosity of 36%-41%, a flexural strength exceeding 130 MPa, and a fracture toughness reaching 3 MPa·m. 1 / 2 The samples exhibited high strength retention after high-temperature treatment.
[0088] A comparison of Examples 3-5 shows that when the β-SiC nanoscale coating layer is within a more preferred range, it provides sufficient active material to fully react with the pressureless granulation powder, forming a robust and smooth sintering neck. The neck size matches the particle size well, the stress distribution is uniform, and it can effectively passivate crack tips, achieving the best balance between strength and toughness. When the thickness of the β-SiC nanoscale coating layer is slightly thin, due to the limited volume of active material, although a continuous sintering neck can be formed, the neck size is small and the cross-section is weak. Under stress, cracks easily propagate rapidly in the small neck, leading to brittle fracture. When the thickness of the β-SiC nanoscale coating layer is slightly thick, it may experience significant shrinkage and grain growth during sintering, generating large internal stress, which may cause the coating layer to peel off from the α-SiC core or form microcracks inside the sintering neck. Although the neck size is large, its actual load-bearing capacity decreases due to the presence of defects.
[0089] A comparison of Examples 1 and 6-7 reveals that if the fluidized bed chemical vapor deposition temperature is too low (e.g., 800℃ in Example 6), the precursor SiCl4 molecules lack sufficient kinetic energy, resulting in incomplete decomposition and extremely low surface atomic mobility, forming an amorphous, non-stoichiometric nanoscale coating layer. This coating layer exhibits poor mass transport during subsequent sintering, leading to poor development of sintering necks between porous silicon carbide ceramic particles and a significant decrease in macroscopic mechanical properties (flexural strength, fracture toughness). If the fluidized bed chemical vapor deposition temperature is slightly higher (e.g., 1300℃ in Example 7), the homogeneous nucleation in the gas phase intensifies, and the deposition rate is too fast, resulting in a nanoscale coating layer with coarse crystals, a loose structure, and poor uniformity. This coating layer is prone to defects during pressing and cannot form strong and uniform connecting necks during sintering, leading to a decrease in the uniformity and reliability of the mechanical properties of the porous silicon carbide ceramic material.
[0090] A comparison of Examples 1 and 8 shows that if the pressure of fluidized bed chemical vapor deposition is too high (e.g., 1.5 kPa in Example 8), the mean free path of the reactant gas molecules becomes shorter, making it difficult for reaction byproducts to diffuse and be discharged. This leads to homogeneous nucleation in the gas phase, which consumes precursors and is not conducive to the formation of a uniform nanoscale coating layer. Consequently, the effective thickness of the coating layer is reduced, and its density decreases. Ultimately, this results in insufficient particle bonding strength, flexural strength, and fracture toughness of the porous silicon carbide ceramic material under the same sintering regime.
[0091] A comparison of Example 1 and Comparative Examples 1-2 shows that if the average particle size of the core silicon carbide raw material is too small (e.g., 5 μm in Comparative Example 1), the specific surface area increases sharply, resulting in too many contact points between particles per unit volume and excessive sintering driving force. This leads to over-densification during the sintering process, causing a decrease in the porosity and three-dimensional interconnected channel structure of the porous silicon carbide ceramic material, which are key characteristics, thus deviating from the design target. Conversely, if the average particle size of the core silicon carbide raw material is too large (e.g., 60 μm in Comparative Example 2), the specific surface area decreases, reducing the number of contact points between particles. Furthermore, the increased radius of curvature of the particles leads to a decrease in sintering driving force and mass transfer rate. Consequently, the porous silicon carbide ceramic material exhibits small interparticle neck sizes and weak bonding forces after sintering, resulting in a decrease in macroscopic mechanical strength and toughness.
[0092] A comparison of Example 1 and Comparative Example 3 shows that the mechanical and high-temperature properties of the porous silicon carbide ceramic materials obtained by the traditional preparation method are difficult to meet the requirements for high quality.
[0093] The present invention has been illustrated with the above embodiments to illustrate its detailed structural features. However, the present invention is not limited to the above detailed structural features, that is, it does not mean that the present invention must rely on the above detailed structural features to be implemented. Those skilled in the art should understand that any improvements to the present invention, equivalent substitutions for the components used in the present invention, additions of auxiliary components, and selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present invention.
Claims
1. A method for preparing porous silicon carbide ceramics based on framework support and chemical vapor deposition homogeneous coating, characterized in that, The preparation method includes: Silicon carbide raw material is placed in a fluidized bed chemical vapor deposition apparatus, and silicon carbide source, carrier gas and dilution gas are introduced to perform fluidized bed chemical vapor deposition, forming a homogeneous nanoscale coating layer on the surface of the silicon carbide raw material to obtain modified silicon carbide material. The average particle size of the silicon carbide raw material is 20μm-50μm; The pressureless granulation powder and the modified silicon carbide material are mixed and then pressed and sintered in a pressureless manner to obtain porous silicon carbide ceramics.
2. The preparation method according to claim 1, characterized in that, Before fluidized bed chemical vapor deposition, the silicon carbide raw material further includes: surface activation treatment of the silicon carbide raw material; Preferably, the silicon carbide raw material includes α-SiC; Preferably, the average particle size of the silicon carbide raw material is 22μm-40μm.
3. The preparation method according to claim 1, characterized in that, The silicon carbide source includes silicon chloride and methane; Preferably, the carrier gas includes hydrogen; Preferably, the diluting gas includes nitrogen; Preferably, the molar ratio of silicon chloride, methane, carrier gas and dilution gas is 1:(0.5-0.8):3.5:(8-10).
4. The preparation method according to claim 1, characterized in that, The temperature of the fluidized bed chemical vapor deposition is 900℃-1300℃, preferably 1100℃-1250℃; Preferably, the pressure of the fluidized bed chemical vapor deposition is 500 Pa to 1500 Pa, more preferably 500 Pa to 1000 Pa; Preferably, the fluidized bed chemical vapor deposition time is 0.5h-3h, and more preferably 0.5h-1.5h.
5. The preparation method according to claim 1, characterized in that, The homogeneous nanoscale coating layer is a β-SiC nanoscale coating layer; Preferably, the thickness of the homogeneous nanoscale coating layer is 50nm-200nm, and more preferably 100nm-200nm.
6. The preparation method according to claim 1, characterized in that, The average particle size of the pressureless granulated powder is 10μm-200μm; Preferably, the mass ratio of the pressureless granulation powder to the modified silicon carbide material is (1-20):
1.
7. The preparation method according to claim 1, characterized in that, The pressing pressure is 35MPa-45MPa.
8. The preparation method according to claim 1, characterized in that, The pressureless sintering is carried out under a protective atmosphere; Preferably, the heating rate of the pressureless sintering is 3℃ / min-5℃ / min, the final temperature is 1750℃-2110℃, and the holding time is 0.5h-2h.
9. A porous silicon carbide ceramic, characterized in that, The porous silicon carbide ceramic is prepared by the preparation method according to any one of claims 1-8.
10. An application of the porous silicon carbide ceramic as described in claim 9, characterized in that, The porous silicon carbide ceramics are used in the fields of catalysts, high-temperature devices, membrane reaction devices, or semiconductor devices.