Preparation method of SiC porous ceramic material with three-dimensional interconnected hierarchical pore structure

Abstract

The invention belongs to the technical field of ceramic materials, and particularly relates to a preparation method of a SiC porous ceramic material with a three-dimensional interconnected hierarchical pore structure. In order to realize hierarchical pore structure and three-dimensional network interconnection, SiC powder, ammonia water, acrylamide, N, N-methylenebisacrylamide and water are subjected to ball milling and uniform mixing to prepare slurry, a surfactant, a pore forming agent, a foaming agent and a binder are added, uniform stirring is performed, an initiator is added for gelatinization foaming, a sintering precursor is obtained, the sintering precursor is subjected to heat preservation, and the porous silicon carbide composite material is prepared. And performing carbonization treatment and sintering treatment on the precursor to obtain the SiC porous ceramic material with the three-dimensional interconnected hierarchical pore structure. By controlling the addition amount of the surfactant, the pore-forming agent and the KOH solution, the pore size and the distribution uniformity can be accurately controlled. The method is simple and reliable in process route, free of complex equipment, low in equipment investment, short in production period and suitable for large-scale mass production, and has a good application prospect.

Description

Technical Field

[0001] This invention belongs to the field of ceramic materials technology, specifically relating to a method for preparing SiC porous ceramic materials with a three-dimensional interconnected hierarchical pore structure. Background Technology

[0002] Silicon carbide porous ceramics are a novel type of ceramic material that combines the advantages of both SiC and porous materials. They possess the high hardness, high melting point, good chemical stability, and excellent thermal conductivity of SiC, as well as the high porosity, large specific surface area, and good thermal shock resistance of porous materials. This makes them suitable for applications in various fields such as high-temperature filtration, catalyst support, sound absorption and noise reduction, thermal insulation, and biomedical applications.

[0003] Currently, the main method for preparing hierarchical porous structures is to introduce micropores or mesopores into macropores to obtain hierarchical porous structures. This requires first preparing the macropore structure and then introducing the micropore structure through methods such as freeze-drying, hydrothermal / solvothermal methods, etching, and template methods. However, traditional preparation methods often struggle to achieve precise control over multi-level pore size, high porosity, and three-dimensional network structure simultaneously, resulting in limitations in material properties. For example, when preparing porous ceramics by freeze-drying, the requirements for the solid content and fluidity of the slurry are stringent, requiring expensive low-temperature vacuum equipment and a long preparation cycle. It is also prone to pore collapse due to ice crystal sublimation, and the connectivity and uniformity are difficult to control. Hydrothermal / solvothermal methods require a high-temperature, high-pressure, and closed reaction environment, making parameter control and process monitoring difficult. They are only suitable for small-scale ceramic powders, and macroscopic block preparation is prone to agglomeration and densification. Some solvents are also toxic and volatile. Etching methods are difficult to select and control the concentration of etchants, which can easily lead to matrix damage or substandard pores. It is difficult to achieve pore orientation and gradient distribution, and chemical etchants are highly corrosive, requiring additional waste liquid treatment. In template methods, the organic template releases toxic gases during sintering, and the hard template method is difficult to separate from the matrix, easily leaving impurities. Furthermore, the template morphology and size limit the pore structure, and custom-made irregular or large-size templates are costly and have low reuse rates. Simple traditional preparation methods, such as pore-forming agent methods, direct foaming methods, and organic foam impregnation methods, have weak ability to precisely control the pore structure, making it difficult to achieve directional or gradient pore size distribution. Moreover, the processes are complex and can easily lead to resource pollution and waste. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention employs a gel casting method combined with a pore-forming agent to prepare SiC porous ceramic materials with a three-dimensional interconnected hierarchical porous structure in one step. The aim is to achieve precise construction of multi-level pores, balance high porosity and mechanical stability, while broadening the process adaptability range and optimizing environmental protection and cost-effectiveness.

[0005] This invention discloses a method for preparing SiC porous ceramic materials with a three-dimensional interconnected hierarchical pore structure, comprising the following:

[0006] (1) The SiC powder is ball-milled with ammonia, acrylamide, N,N-methylenebisacrylamide and water to form a SiC mixed slurry;

[0007] (2) Add surfactant, pore-forming agent and binder to SiC mixed slurry, mix well under alkaline conditions, add initiator to carry out gelation foaming, and obtain sintering precursor;

[0008] (3) After carbonization of the sintering precursor, sintering is performed to obtain SiC porous ceramic material with a three-dimensional interconnected hierarchical pore structure.

[0009] In step (1):

[0010] The amount of ammonia added is 1%-3% of the mass of the SiC mixed slurry, the amount of acrylamide added is 5%-7% of the mass of the SiC mixed slurry, the amount of N,N-methylenebisacrylamide added is 0.3%-0.5% of the mass of the SiC mixed slurry, the average particle size of the SiC powder is 0.5µm, and the solid content of the SiC powder in the mixed slurry is controlled in the range of 55%~65%.

[0011] In step (2):

[0012] The surfactant is sodium dodecyl sulfate (SDS), and the surfactant accounts for 1%-4% of the mass of the SiC mixed slurry.

[0013] The pore-forming agent is starch, and it accounts for 15%-19% of the mass of the SiC mixed slurry.

[0014] The binder is polyvinyl alcohol. When using the binder, it is prepared as a polyvinyl alcohol aqueous solution with a mass concentration of 7%-9%. The degree of polymerization of polyvinyl alcohol is 2000 and the degree of alcoholysis is 99%. The mass ratio of SiC mixed slurry to polyvinyl alcohol aqueous solution is 1:(0.70-1.3).

[0015] KOH is used to adjust the alkalinity of the mixed slurry. When using KOH, it is prepared as a 50% (w / w) aqueous solution, and the KOH aqueous solution accounts for 8%-11% of the mass of the SiC mixed slurry.

[0016] The initiator is ammonium persulfate. When using the initiator, a 10% (w / w) ammonium persulfate aqueous solution is prepared. The amount of ammonium persulfate aqueous solution added is 0.1%-0.5% of the mass of the SiC mixed slurry.

[0017] After adding the initiator, continue stirring for 30-60 seconds to foam the material. Pour the foamed slurry into a mold and dry it in a box-type drying oven at 65℃-80℃ for 24 hours to obtain the sintering precursor.

[0018] In step (3):

[0019] The carbonization process includes the following steps: under an inert atmosphere, the sintering precursor is heated from room temperature to 800°C at a rate of 5°C / min, held at 800°C for 2 hours, and then cooled in the furnace.

[0020] The sintering process includes the following steps: After carbonization, the temperature is raised from room temperature to 1200℃ at a rate of 3℃ / min under an inert atmosphere and held for 30 min. Then, the temperature is raised to 1950℃-2100℃ at a rate of 1℃ / min and held for sintering for 1-3 h. Finally, the temperature is cooled in the furnace to obtain SiC porous ceramic material with a three-dimensional interconnected hierarchical pore structure.

[0021] Using the above heating rate can ensure that the carbothermic reduction reaction proceeds uniformly, avoid "overheating" in local areas due to excessively rapid heating, and prevent abnormal growth of SiC grains. Abnormally grown grains will block hierarchical channels and destroy the three-dimensional interconnect structure.

[0022] Compared with the prior art, the features and beneficial effects of the present invention are as follows:

[0023] (l) The present invention uses starch as a pore-forming agent. By changing the amount of starch added, the number of starch particles uniformly dispersed in SiC ceramics can be controlled, thereby controlling the size of the pores formed after starch decomposition.

[0024] (2) The present invention uses a gelation method to gel during the foaming process, forming a gel structure that can prevent the foam from collapsing, thereby fixing the air bubbles and effectively improving the strength of the green body;

[0025] (3) The present invention uses polyvinyl alcohol as a binder. Its concentration and addition amount can effectively adjust the pore size, porosity and connectivity of macroporous SiC ceramics, and can increase the viscosity of the slurry, and have a long-term stabilizing effect on bubbles.

[0026] (4) The present invention can conveniently and effectively adjust the porosity and connectivity of macroporous SiC ceramics by adding surfactants. In the present invention, only a small amount of surfactant is used, but it can significantly improve the connectivity and pore size of the pores.

[0027] (5) The present invention also controls the carbonization and sintering temperature of the sample, as well as the heating rate, to prevent incomplete pyrolysis of starch particles and other organic matter, which would affect the porosity and mechanical properties of the material.

[0028] (6) Since the starch, organic monomers and polyvinyl alcohol in this invention are readily available, and the preparation path does not involve complex chemical reactions or the use of sacrificial template agents except for the sintering process, this invention is easy to organize for production, pollution-free and low in cost.

[0029] (7) The process route of the present invention is simple and reliable, and does not require complex equipment. Compared with the sol-gel method and hot pressing sintering method, the equipment investment is reduced by more than 30%, and the production cycle is shortened to 48 hours. It is suitable for large-scale mass production and has good application prospects. Attached Figure Description

[0030] Figure 1 These are scanning electron microscope images of the SiC porous ceramic material with a three-dimensional interconnected hierarchical pore structure prepared in Example 1;

[0031] Figure 2 This is an X-ray diffraction pattern of the SiC porous ceramic material with a three-dimensional interconnected hierarchical pore structure prepared in Example 1;

[0032] Figure 3 These are pore size distribution diagrams of SiC porous ceramic materials with three-dimensional interconnected hierarchical pore structures prepared in various embodiments;

[0033] Figure 4 These are scanning electron microscope images of the SiC porous ceramic material with a three-dimensional interconnected hierarchical pore structure prepared in Example 2;

[0034] Figure 5 These are scanning electron microscope images of the SiC porous ceramic material with a three-dimensional interconnected hierarchical pore structure prepared in Example 3;

[0035] Figure 6 These are scanning electron microscope images of the SiC porous ceramic material with a three-dimensional interconnected hierarchical pore structure prepared in Example 4;

[0036] Figure 7 These are scanning electron microscope images of the SiC porous ceramic material with a three-dimensional interconnected hierarchical pore structure prepared in Example 5;

[0037] Figure 8 These are scanning electron microscope images of the SiC porous ceramic material with a three-dimensional interconnected hierarchical pore structure prepared in Example 6;

[0038] Figure 9 These are scanning electron microscope images of the SiC porous ceramic material with a three-dimensional interconnected hierarchical pore structure prepared in Example 7;

[0039] In each figure, (1) is a SEM image of the first-order pore structure, (2) is a SEM image of the second-order pore structure, and (3) is a SEM image of the third-order pore structure. Detailed Implementation

[0040] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments and accompanying drawings. It should be noted that the embodiments described in this invention are only for further explanation and illustration, and not for limiting their application scope. Based on this invention, all other embodiments obtained by those skilled in the art without inventive effort are within the protection scope of this invention.

[0041] In this invention, the primary pores are formed by introducing air into the slurry through mechanical stirring to create bubbles. The anionic surfactant sodium dodecyl sulfate (SDS) spontaneously accumulates at the gas-liquid interface and aligns in a specific direction, forming a molecular film with its hydrophobic terminal -C. 12 H 25 Inserted into the bubble, hydrophilic end—OSO3 - Na + Extending into the slurry, the hydrophilic end reduces the surface tension of the slurry, hindering the coalescence and collapse of bubbles. Furthermore, the negatively charged hydrophilic end repels bubbles through electrostatic repulsion, preventing the liquid film from thinning and breaking, thus stabilizing the bubbles within the slurry. After gelation, drying, and sintering, the bubbles disappear, leaving behind spherical pores. Secondary pores are formed by the addition of starch particles, which decompose into volatile products such as CO2 and H2O during carbonization and sintering, leaving starch pores. These pores are mainly distributed along the walls of the primary pores. Tertiary pores are primarily formed by the thermal decomposition of organic matter in the green body. The resulting small gas molecules escape from the gaps between SiC particles, forming initial micropores. As the sintering temperature increases, neck-like connections form on the surface of the SiC particles, and the gaps between particles in the incompletely densified areas eventually form a microporous structure.

[0042] In the examples, the electron microscope used for scanning the SiC ceramic material was a CX-100S; the X-ray diffractometer was a DF911-DX-2500; the pore size distribution was determined using a Micromeritics AutoPore V 9620; the average particle size of the SiC powder was 0.5µm; the degree of polymerization of polyvinyl alcohol was 2000, and the degree of alcoholysis was 99%; the mass fraction of the KOH solution was 50%.

[0043] Example 1

[0044] (1) The SiC powder is ball-milled with ammonia, acrylamide, N,N-methylenebisacrylamide and water to form a SiC mixed slurry. The amount of ammonia added is 1% of the mass of the SiC mixed slurry, the amount of acrylamide added is 5% of the mass of the SiC mixed slurry, the amount of N,N-methylenebisacrylamide added is 0.4% of the mass of the SiC mixed slurry, and the solid content of SiC powder in the slurry is 60%.

[0045] (2) Add 1% of surfactant SDS, 15% starch as pore-forming agent, 8% KOH solution and 7% polyvinyl alcohol aqueous solution as binder to SiC mixed slurry. The mass ratio of SiC mixed slurry to polyvinyl alcohol aqueous solution is 1:0.75. Stir evenly, then add 10% ammonium persulfate aqueous solution as initiator. The amount of ammonium persulfate aqueous solution added is 0.2% of the mass of SiC mixed slurry. Continue stirring for 30s-60s to foam. Pour the foamed slurry into a mold and dry it in a box-type drying oven at 80℃ for 24h to obtain the sintering precursor.

[0046] (3) The sintering precursor is first carbonized: Under the protection of argon atmosphere, the sintering precursor is heated from room temperature to 800℃ at a heating rate of 5℃ / min, held at 800℃ for 2h, and then cooled with the furnace to complete the carbonization treatment. Then the sintering treatment is carried out: Under the protection of argon atmosphere, the carbonized sintering precursor is heated from room temperature to 1200℃ at a heating rate of 3℃ / min, held for 30min, then heated to 1950℃ and held for 1h at a heating rate of 1℃ / min, and then cooled with the furnace to obtain SiC porous ceramic material with a three-dimensional interconnected hierarchical pore structure.

[0047] Scanning electron microscope images of SiC porous ceramic materials are shown below. Figure 1 As shown, from Figure 1 (1) Figure 1 (2) and Figure 1 As can be seen from (3), SiC ceramic material has a hierarchical pore structure, and the pores are interconnected, forming a three-dimensional network. Figure 1 (2) It can be seen that secondary pores are evenly distributed on the wall of the primary pore; its X-ray diffraction pattern is as follows. Figure 2 As shown, from Figure 2 As can be seen from the diagram, the SiC porous ceramic material is a SiC phase with high purity; its pore size distribution is shown in the figure below. Figure 3 As shown, from Figure 3 As can be seen, the primary pore size is distributed between 10μm and 500μm, accounting for 71% of the total pore size of the sample; the secondary pore size is distributed between 100nm and 500nm, accounting for 11% of the total pore size of the sample; and the tertiary pore size is distributed between 1nm and 50nm, accounting for 18% of the total pore size of the sample.

[0048] Example 2

[0049] (1) The SiC powder is ball-milled with ammonia, acrylamide, N,N-methylenebisacrylamide and water to form a SiC mixed slurry. The amount of ammonia added is 1% of the mass of the SiC mixed slurry, the amount of acrylamide added is 5% of the mass of the SiC mixed slurry, the amount of N,N-methylenebisacrylamide added is 0.4% of the mass of the SiC mixed slurry, and the solid content of SiC powder in the slurry is 60%.

[0050] (2) Add 3% of surfactant SDS, 15% starch as pore-forming agent, 8% KOH solution and 7% polyvinyl alcohol aqueous solution as binder to SiC mixed slurry. The mass ratio of SiC mixed slurry to polyvinyl alcohol aqueous solution is 1:0.75. Stir evenly, then add 10% ammonium persulfate aqueous solution as initiator. The amount of ammonium persulfate aqueous solution added is 0.2% of the mass of SiC mixed slurry. Continue stirring for 30s-60s to foam. Pour the foamed slurry into a mold and dry it in a box-type drying oven at 80℃ for 24h to obtain the sintering precursor.

[0051] (3) The sintering precursor is first carbonized: Under the protection of argon atmosphere, the sintering precursor is heated from room temperature to 800℃ at a heating rate of 5℃ / min, held at 800℃ for 2h, and then cooled with the furnace to complete the carbonization treatment. Then the sintering treatment is carried out: Under the protection of argon atmosphere, the carbonized sintering precursor is heated from room temperature to 1200℃ at a heating rate of 3℃ / min, held for 30min, and then heated to 1950℃ and held for sintering for 1h at a heating rate of 1℃ / min, and then cooled with the furnace to obtain SiC porous ceramic material with a three-dimensional interconnected hierarchical pore structure.

[0052] Scanning electron microscope images of SiC porous ceramic materials are shown below. Figure 4 As shown, from Figure 4 (1) Figure 4 (2) and Figure 4As can be seen from (3), SiC ceramic materials have a hierarchical porous structure, with interconnected primary pores and secondary pores uniformly distributed on the walls of the primary pores, forming a three-dimensional network structure. Compared to Example 1, without changing other conditions, this example optimizes the addition of surfactant (SDS) to 3%. The higher concentration of surfactant significantly reduces the gas-liquid interfacial tension of the slurry, enhancing the viscoelasticity and Gibbs-Marangoni effect of the liquid film. This enhanced interfacial stability effectively inhibits the merger and disproportionation of bubbles during foaming and gel solidification, thereby significantly improving the dispersion uniformity and retention rate of bubbles in the slurry matrix, ultimately forming a highly interconnected primary pore network with uniform pore size distribution. Secondly, in terms of controlling the matrix and micropores (secondary and tertiary pores), an appropriate amount of anionic surfactant (SDS) improves the electrostatic repulsion of SiC particles in the aqueous system, optimizing the rheological properties and dispersion uniformity of the slurry. This makes the ceramic skeleton that forms the pore walls more compact and structurally complete, providing a uniformly distributed matrix for the starch particles (secondary pore-forming agent). It also makes the intergranular morphology (tertiary pores) formed by particle accumulation more regular, greatly reducing structural defects caused by agglomeration.

[0053] Example 3

[0054] (1) The SiC powder is ball-milled with ammonia, acrylamide, N,N-methylenebisacrylamide and water to form a SiC mixed slurry. The amount of ammonia added is 1% of the mass of the SiC mixed slurry, the amount of acrylamide added is 5% of the mass of the SiC mixed slurry, the amount of N,N-methylenebisacrylamide added is 0.4% of the mass of the SiC mixed slurry, and the solid content of SiC powder in the slurry is 60%.

[0055] (2) Add 4% of surfactant SDS, 15% starch as pore-forming agent, 8% KOH solution and 7% polyvinyl alcohol aqueous solution as binder to SiC mixed slurry. The mass ratio of SiC mixed slurry to polyvinyl alcohol aqueous solution is 1:0.75. Stir evenly, then add 10% ammonium persulfate aqueous solution as initiator. The amount of ammonium persulfate aqueous solution added is 0.2% of the mass of SiC mixed slurry. Continue stirring for 30s-60s to foam. Pour the foamed slurry into a mold and dry it in a box-type drying oven at 80℃ for 24h to obtain the sintering precursor.

[0056] (3) Carbonization treatment of sintering precursor: Under the protection of argon atmosphere, the sintering precursor is heated from room temperature to 800℃ at a heating rate of 5℃ / min, held at 800℃ for 2h, and then cooled with the furnace to complete the carbonization treatment. Then sintering treatment is carried out: Under the protection of argon atmosphere, the carbonized sintering precursor is heated from room temperature to 1200℃ at a heating rate of 3℃ / min, held for 30min, and then heated to 1950℃ and held for sintering for 1h at a heating rate of 1℃ / min, and then cooled with the furnace to obtain SiC porous ceramic material with a three-dimensional interconnected hierarchical pore structure.

[0057] Scanning electron microscope images of SiC porous ceramic materials are shown below. Figure 5 As shown, from Figure 5 (1) Figure 5 (2) and Figure 5 As can be seen in (3), without changing other conditions, compared with Example 2, this example further increases the amount of surfactant (SDS) to 4%. First, the primary pore structure exhibits a significant refinement effect. The high concentration of surfactant further reduces the gas-liquid interfacial tension of the slurry, resulting in smaller and more stable bubble sizes. This enhanced interfacial stabilization inhibits the coalescence and growth of bubbles during gelation, leading to a significant reduction in the primary pore diameter compared to Example 2. Second, porosity and connectivity undergo microscopic reconstruction. Due to the refinement of bubble size, the number of bubbles per unit volume increases, resulting in a relatively thicker liquid film between bubbles (i.e., the pore walls after sintering). This increase in microscopic packing density narrows the connecting throats of some pores, macroscopically manifested as a moderate reduction in porosity and a structural adjustment in connectivity. Finally, the hierarchical pore distribution exhibits a densification characteristic. In the thicker pore wall matrix, the distribution of secondary pores (starch-based pores) and tertiary pores (packing gap pores) is more dispersed, and the number of visible pores is relatively reduced. This embodiment demonstrates that by adjusting the surfactant concentration, the pore structure of SiC ceramics can be precisely customized: while maintaining the core "three-dimensional interconnected hierarchical structure" of this invention, smaller pore sizes and a denser framework structure are obtained by sacrificing some porosity, thereby meeting the differentiated requirements of material microstructure for different application scenarios.

[0058] Example 4

[0059] (1) The SiC powder is ball-milled with ammonia, acrylamide, N,N-methylenebisacrylamide and water to form a SiC mixed slurry. The amount of ammonia added is 1% of the mass of the SiC mixed slurry, the amount of acrylamide added is 5% of the mass of the SiC mixed slurry, the amount of N,N-methylenebisacrylamide added is 0.4% of the mass of the SiC mixed slurry, and the solid content of SiC powder in the slurry is 60%.

[0060] (2) Add 1% of surfactant SDS, 17% starch as pore-forming agent, 8% KOH solution and 7% polyvinyl alcohol aqueous solution as binder to SiC mixed slurry. The mass ratio of SiC mixed slurry to polyvinyl alcohol aqueous solution is 1:0.75. Stir evenly, then add 10% ammonium persulfate aqueous solution as initiator. The amount of ammonium persulfate aqueous solution added is 0.2% of the mass of SiC mixed slurry. Continue stirring for 30s-60s to foam. Pour the foamed slurry into a mold and dry it in a box-type drying oven at 80℃ for 24h to obtain the sintering precursor.

[0061] (3) Carbonization treatment of sintering precursor: Under the protection of argon atmosphere, the sintering precursor is heated from room temperature to 800℃ at a heating rate of 5℃ / min, held at 800℃ for 2h, and then cooled with the furnace to complete the carbonization treatment. Then sintering treatment is carried out: Under the protection of argon atmosphere, the carbonized sintering precursor is heated from room temperature to 1200℃ at a heating rate of 3℃ / min, held for 30min, and then heated to 1950℃ and held for sintering for 1h at a heating rate of 1℃ / min, and then cooled with the furnace to obtain SiC porous ceramic material with a three-dimensional interconnected hierarchical pore structure.

[0062] Scanning electron microscope images of SiC porous ceramic materials are shown below. Figure 6 As shown, from Figure 6 (1) Figure 6 (2) and Figure 6 As can be seen from (3), SiC ceramic material has a multi-level pore structure, and the primary pores are interconnected. The secondary pores are uniformly distributed on the pore walls of the primary pores to form a three-dimensional network structure. Compared with Example 1, this example achieves significant optimization of the pore structure by appropriately increasing the proportion of starch added: the incremental introduction of starch particles not only effectively improves the overall porosity of the material, but also synergistically induces the reasonable expansion of the pore size of the primary and secondary pores, thereby further enhancing the connectivity efficiency and distribution uniformity of the multi-level pore network in three-dimensional space.

[0063] Example 5

[0064] (1) The SiC powder is ball-milled with ammonia, acrylamide, N,N-methylenebisacrylamide and water to form a SiC mixed slurry. The amount of ammonia added is 1% of the mass of the SiC mixed slurry, the amount of acrylamide added is 5% of the mass of the SiC mixed slurry, the amount of N,N-methylenebisacrylamide added is 0.4% of the mass of the SiC mixed slurry, and the solid content of SiC powder in the slurry is 60%.

[0065] (2) Add 1% of surfactant SDS, 19% starch as pore-forming agent, 8% KOH solution and 7% polyvinyl alcohol aqueous solution as binder to SiC mixed slurry. The mass ratio of SiC mixed slurry to polyvinyl alcohol aqueous solution is 1:0.75. Stir evenly, then add 10% ammonium persulfate aqueous solution as initiator. The amount of ammonium persulfate aqueous solution added is 0.2% of the mass of SiC mixed slurry. Continue stirring for 30s-60s to foam. Pour the foamed slurry into a mold and dry it in a box-type drying oven at 80℃ for 24h to obtain the sintering precursor.

[0066] (3) Carbonization treatment of sintering precursor: Under the protection of argon atmosphere, the sintering precursor is heated from room temperature to 800℃ at a heating rate of 5℃ / min, held at 800℃ for 2h, and then cooled with the furnace to complete the carbonization treatment. Then sintering treatment is carried out: Under the protection of argon atmosphere, the carbonized sintering precursor is heated from room temperature to 1200℃ at a heating rate of 3℃ / min, held for 30min, and then heated to 1950℃ and held for sintering for 1h at a heating rate of 1℃ / min, and then cooled with the furnace to obtain SiC porous ceramic material with a three-dimensional interconnected hierarchical pore structure.

[0067] Scanning electron microscope images of SiC porous ceramic materials are shown below. Figure 7 As shown, from Figure 7 (1) Figure 7 (2) and Figure 7 As can be seen from (3), compared with Example 4, this example further increases the amount of starch added, so that the material exhibits differentiated performance in terms of pore structure parameters: the porosity is reduced, the primary pore structure is more compact, and the number of secondary and tertiary pores is slightly reduced. However, the core invention effect of "three-dimensional interconnection and pore structure hierarchy" is still fully preserved, and only targeted optimization is achieved in the structural details.

[0068] Example 6

[0069] (1) The SiC powder is ball-milled with ammonia, acrylamide, N,N-methylenebisacrylamide and water to form a SiC mixed slurry. The amount of ammonia added is 1% of the mass of the SiC mixed slurry, the amount of acrylamide added is 5% of the mass of the SiC mixed slurry, the amount of N,N-methylenebisacrylamide added is 0.4% of the mass of the SiC mixed slurry, and the solid content of SiC powder in the slurry is 60%.

[0070] (2) Add 1% of surfactant SDS, 15% starch as pore-forming agent, 9% KOH solution and 7% polyvinyl alcohol aqueous solution as binder to SiC mixed slurry. The mass ratio of SiC mixed slurry to polyvinyl alcohol aqueous solution is 1:0.75. Stir evenly, then add 10% ammonium persulfate aqueous solution as initiator. The amount of ammonium persulfate aqueous solution added is 0.2% of the mass of SiC mixed slurry. Continue stirring for 30s-60s to foam. Pour the foamed slurry into a mold and dry it in a box-type drying oven at 80℃ for 24h to obtain the sintering precursor.

[0071] (3) Carbonization treatment of sintering precursor: Under the protection of argon atmosphere, the sintering precursor is heated from room temperature to 800℃ at a heating rate of 5℃ / min, held at 800℃ for 2h, and then cooled with the furnace to complete the carbonization treatment. Then sintering treatment is carried out: Under the protection of argon atmosphere, the carbonized sintering precursor is heated from room temperature to 1200℃ at a heating rate of 3℃ / min, held for 30min, and then heated to 1950℃ and held for sintering for 1h at a heating rate of 1℃ / min, and then cooled with the furnace to obtain SiC porous ceramic material with a three-dimensional interconnected hierarchical pore structure.

[0072] Scanning electron microscope images of SiC porous ceramic materials are shown below. Figure 8 As shown, from Figure 8 (1) Figure 8 (2) and Figure 8 As can be seen from (3), compared with Example 1, without changing other conditions, increasing the KOH solution content can improve the pH environment of the slurry, enhance the electrostatic repulsion of the double electric layer on the surface of SiC particles, improve the dispersion uniformity of particles in the aqueous system, and effectively inhibit particle agglomeration. This reduces the thickening of pore walls and pore blockage caused by particle agglomeration during the foaming and gelation process of the slurry, making the constructed primary pore walls thinner, more transparent and uniform, which can improve the porosity of the material and enhance the connectivity between primary pores.

[0073] Example 7

[0074] (1) The SiC powder is ball-milled with ammonia, acrylamide, N,N-methylenebisacrylamide and water to form a SiC mixed slurry. The amount of ammonia added is 1% of the mass of the SiC mixed slurry, the amount of acrylamide added is 5% of the mass of the SiC mixed slurry, the amount of N,N-methylenebisacrylamide added is 0.4% of the mass of the SiC mixed slurry, and the solid content of SiC powder in the slurry is 60%.

[0075] (2) Add 1% of surfactant SDS, 15% starch as pore-forming agent, 11% KOH solution and 7% polyvinyl alcohol aqueous solution as binder to SiC mixed slurry. The mass ratio of SiC mixed slurry to polyvinyl alcohol aqueous solution is 1:0.75. Stir evenly, then add 10% ammonium persulfate aqueous solution as initiator. The amount of ammonium persulfate aqueous solution added is 0.2% of the mass of SiC mixed slurry. Continue stirring for 30s-60s to foam. Pour the foamed slurry into a mold and dry it in a box-type drying oven at 80℃ for 24h to obtain the sintering precursor.

[0076] (3) Carbonization treatment of sintering precursor: Under the protection of argon atmosphere, the sintering precursor is heated from room temperature to 800℃ at a heating rate of 5℃ / min, held at 800℃ for 2h, and then cooled with the furnace to complete the carbonization treatment. Then sintering treatment is carried out: Under the protection of argon atmosphere, the carbonized sintering precursor is heated from room temperature to 1200℃ at a heating rate of 3℃ / min, held for 30min, and then heated to 1950℃ and held for sintering for 1h at a heating rate of 1℃ / min, and then cooled with the furnace to obtain SiC porous ceramic material with a three-dimensional interconnected hierarchical pore structure.

[0077] Scanning electron microscope images of SiC porous ceramic materials are shown below. Figure 9 As shown, from Figure 9 (1) Figure 9 (2) and Figure 9 As can be seen from (3), compared with Example 6, when the KOH solution is added at a higher level without changing other conditions, the distance between SiC particles will decrease, the number of primary pores will decrease and the pore size will increase, the number of secondary and tertiary pores will increase and the pore size will decrease, thereby making the pore structure of the generated SiC porous ceramic material more compact and its compressive strength, flexural strength and wear resistance better.

[0078] In summary, this invention successfully prepares three-dimensional interconnected porous SiC ceramics with uniform pore distribution, adjustable pore size, high porosity, and excellent mechanical properties. This method is simple, reliable, requires no large fixed investment, and has promising application prospects.

Claims

1. A method for preparing a SiC porous ceramic material with a three-dimensional interconnected hierarchical pore structure, characterized in that, The process includes the following steps: SiC powder is ball-milled and mixed uniformly with ammonia, acrylamide, N,N-methylenebisacrylamide, and water to form a SiC mixed slurry; surfactant, pore-forming agent, and binder are added to the SiC mixed slurry, and after mixing under alkaline conditions, an initiator is added for foaming to obtain a sintering precursor; the sintering precursor is carbonized and then sintered to obtain a SiC porous ceramic material with a three-dimensional interconnected hierarchical pore structure.

2. The method for preparing a SiC porous ceramic material with a three-dimensional interconnected hierarchical pore structure according to claim 1, characterized in that, The amount of ammonia added is 1%-3% of the mass of the SiC mixed slurry, the amount of acrylamide added is 5%-7% of the mass of the SiC mixed slurry, and the amount of N,N-methylenebisacrylamide added is 0.3%-0.5% of the mass of the SiC mixed slurry.

3. The method for preparing a SiC porous ceramic material with a three-dimensional interconnected hierarchical pore structure according to claim 1, characterized in that, The average particle size of the SiC powder is 0.5µm; the solid content of the SiC powder in the SiC mixed slurry is 55%~65%.

4. The method for preparing a SiC porous ceramic material with a three-dimensional interconnected hierarchical pore structure according to claim 1, characterized in that, The surfactant is sodium dodecyl sulfate, and its dosage is 1%-4% of the mass of the SiC mixed slurry; the pore-forming agent is starch, and its dosage is 15%-19% of the mass of the SiC mixed slurry; the initiator is ammonium persulfate, which is prepared as a 10% ammonium persulfate aqueous solution, and the amount of the ammonium persulfate aqueous solution added is 0.1%-0.5% of the mass of the SiC mixed slurry.

5. The method for preparing a SiC porous ceramic material with a three-dimensional interconnected hierarchical pore structure according to claim 1, characterized in that, The binder is polyvinyl alcohol, and when used, it is prepared as a polyvinyl alcohol aqueous solution with a mass concentration of 7%-9%. The mass ratio of the SiC mixed slurry to the polyvinyl alcohol aqueous solution is 1:(0.70-1.3).

6. The method for preparing a SiC porous ceramic material with a three-dimensional interconnected hierarchical pore structure according to claim 1, characterized in that, The SiC mixed slurry is adjusted to be alkaline using KOH, and a KOH aqueous solution with a mass fraction of 50% is prepared for use. The KOH aqueous solution accounts for 8%-11% of the mass of the SiC mixed slurry.

7. The method for preparing a SiC porous ceramic material with a three-dimensional interconnected hierarchical pore structure according to claim 1, characterized in that, After adding the initiator, continue stirring for 30-60 seconds to foam the material. Then, dry the foamed slurry at 65-80℃ for 24 hours to obtain the sintering precursor.

8. The method for preparing a SiC porous ceramic material with a three-dimensional interconnected hierarchical pore structure according to claim 1, characterized in that, The carbonization process includes the following steps: under an inert atmosphere, the sintering precursor is heated from room temperature to 800°C at a rate of 5°C / min, held at 800°C for 2 hours, and then cooled in the furnace.

9. The method for preparing a SiC porous ceramic material with a three-dimensional interconnected hierarchical pore structure according to claim 1, characterized in that, The sintering process includes the following: After the carbonization treatment, under the protection of an inert atmosphere, the temperature is raised from room temperature to 1200℃ at a rate of 3℃ / min and held for 30min. Then, the temperature is raised to 1950℃-2100℃ at a rate of 1℃ / min and held for 1h-3h. Finally, the temperature is cooled with the furnace to obtain the SiC porous ceramic material.

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