Silicon carbide reticulated porous ceramic filter and method of making same

Abstract

The application provides a silicon carbide reticular porous ceramic filter and a preparation method thereof. The method adopts a one-step filling polymer template technology of silicon-carbon slurry, and realizes fine regulation and control of the performance and microstructure of the silicon carbide reticular porous ceramic by precisely controlling a carbon source, so as to overcome the hollow pillar problem caused by insufficient filling of slurry in the preparation of the ceramic filter, and the defect problem possibly caused in the polymer decomposition process.

Description

Technical Field

[0001] This invention relates to the field of ceramic material preparation technology, and more specifically to a silicon carbide mesh porous ceramic filter and its preparation method. Background Technology

[0002] Ceramic filters are indispensable in metal casting, especially in precision casting, for removing solid inclusions from molten metal. Besides requiring chemical stability and freedom from contaminating chemicals, filters must also possess good mechanical properties and thermal shock resistance, preventing peeling or detachment during casting to ensure and improve the performance of the casting. Silicon carbide mesh porous ceramics, with their superior mechanical properties, chemical stability, high-temperature strength, and corrosion resistance, occupy an important position in numerous filter applications, playing a crucial role, especially in the purification of molten metals in the metal smelting industry.

[0003] Currently, methods for preparing porous silicon carbide ceramics include foaming, 3D printing, and polymer template methods. Polymer template methods are the preferred method for manufacturing industrial filters because they can produce porous silicon carbide ceramics with a network pore structure, high permeability, and large specific surface area, while also offering advantages such as low cost, high efficiency, and ease of operation.

[0004] Nevertheless, the preparation of high-performance porous network ceramics using polymer templates still faces numerous challenges. Among these, the formation of hollow pillars and defects generated during polymer template combustion significantly impact the strength, thermal shock resistance, and resistance to molten metal erosion of silicon carbide ceramics. Therefore, many studies have focused on reducing these voids and defects to improve the performance of silicon carbide porous network ceramics.

[0005] One technique to improve the strength and thermal shock resistance of mesh porous ceramics is to refill them with slurry of different viscosities. However, although the multiple filling process can partially fill the voids in the support, it cannot completely eliminate defects, and repeated filling may introduce new interface defects, thereby adversely affecting the mechanical properties of the final product.

[0006] Another approach is to use vacuum infiltration technology to reduce voids and defects. Low-viscosity slurry is used to fill the voids in silicon carbide pillars in a vacuum environment, which can enhance the strength of silicon carbide mesh porous ceramics. However, due to high cost, complex operation and low efficiency, the application of vacuum infiltration in industrial production is greatly limited. Summary of the Invention

[0007] The purpose of this invention is to address the problems existing in the prior art by providing a silicon carbide mesh porous ceramic filter and its preparation method. This method uses a one-step polymer template filling technology with silicon carbide slurry and achieves fine control of the performance and microstructure of silicon carbide mesh porous ceramic by precisely controlling the carbon source. This overcomes the problem of hollow pillars caused by insufficient slurry filling in the ceramic filter preparation process and the defects that may occur during polymer decomposition.

[0008] According to a first aspect of the present invention, a method for preparing a silicon carbide mesh porous ceramic filter is provided, comprising the following steps:

[0009] S1. Preparation of the first carbon sphere-PVA composite sol

[0010] PVA powder was completely dissolved in deionized water to obtain a PVA solution, which was then cooled for later use.

[0011] The first carbon ball powder is dispersed in deionized water, and the agglomeration of the first carbon balls is broken by ultrasonic treatment or mechanical stirring to obtain the first carbon ball dispersion.

[0012] A coupling agent is added to the first carbon sphere dispersion to react with the functional groups on the surface of the first carbon spheres and form chemical bonds, thus obtaining a modified first carbon sphere dispersion.

[0013] Under ultrasonic treatment or mechanical stirring conditions, the modified first carbon ball dispersion is slowly added to the PVA solution, and ultrasonic treatment or mechanical stirring is continued until the first carbon ball is evenly dispersed to obtain the first carbon ball-PVA composite sol.

[0014] S2. In the first carbon ball-PVA composite sol obtained in step S1, mixed silicon carbide powder, metallic silicon powder, second carbon ball powder, dispersant and plasticizer are added in sequence and stirred evenly to obtain a mixed wet material; wherein, the average particle size of the first carbon ball is much smaller than the average particle size of the second carbon ball.

[0015] S3. The mixed wet material obtained in step S2 is ball-milled, sieved, and defoamed to obtain silicon carbide slurry.

[0016] S4. Immerse the polymer mold in the silicon carbide slurry obtained in step S3, remove it and use a rotating disk to remove excess slurry, then perform drying treatment to obtain ceramic green body.

[0017] S5. The ceramic blank obtained in step S4 is sintered to obtain a silicon carbide mesh porous ceramic filter.

[0018] As an optional implementation, the first carbon sphere has an average particle size of 50 nm to 200 nm, a sphericity > 0.8, and a specific surface area > 200 m² / g; the second carbon sphere has an average particle size of 1 μm to 10 μm.

[0019] As an optional implementation, the mass concentration of the PVA solution is 5% to 10%, and the mass concentration of the first carbon sphere dispersion is 60% to 80%.

[0020] As an optional implementation, the amount of coupling agent added is 1% to 5% of the weight of the first carbon sphere.

[0021] As an optional implementation, the coupling agent includes one or more of the following: γ-aminopropyltriethoxysilane (APTES), γ-methacryloyloxypropyltrimethoxysilane (MPTS), γ-glycidoxypropyltrimethoxysilane (GPTMS), vinyltrimethoxysilane (VTMS), bis(butoxyacetylacetylacetonate)diisopropoxytitanate (Tyzor AA-75), isopropoxytriacryloyloxytitanate (IPT), isopropoxyzirconia acrylate, and polyethylene glycol diglycidyl ether (PEGDE).

[0022] As an optional implementation, the specific proportions of each component in the mixed wet material, by mass percentage, are as follows: 25%~45% mixed silicon carbide powder, 15%~35% metallic silicon powder, 5%~15% compounded carbon ball powder, 0.5%~2% dispersant, 1%~5% plasticizer, and 20%~40% deionized water; wherein, the compounded carbon ball powder includes first carbon ball powder and second carbon ball powder.

[0023] As an optional implementation, the first carbon ball powder accounts for 30% to 50% of the mass of the compound carbon ball powder, and the second carbon ball powder accounts for 50% to 70% of the mass of the compound carbon ball powder.

[0024] As an optional implementation, the mixed silicon carbide powder includes a first silicon carbide powder and a second silicon carbide powder, wherein the average particle size of the first silicon carbide powder is smaller than the average particle size of the second silicon carbide powder.

[0025] As an optional implementation, the average particle size of the first silicon carbide powder is 1 μm to 5 μm, and the average particle size of the second silicon carbide powder is 20 μm to 40 μm.

[0026] As an optional implementation, the mass ratio of the first silicon carbide powder to the second silicon carbide powder is (3:7) to (5:5).

[0027] As an optional implementation, the average particle size of the silicon metal powder is 5 μm to 15 μm.

[0028] As an optional implementation, the dispersant includes one or more of polyvinylpyrrolidone K30 (PVP-K30), polycarboxylate, tetramethylammonium hydroxide, and isobutylene maleic anhydride copolymer.

[0029] As an optional implementation, the plasticizer includes one or more of ethylene glycol, glycerol, polyethylene glycol, and ethylene glycol monoethyl ether.

[0030] As an optional implementation, the polymer template has a porosity >80% and a pore size of 0.5 cm to 2 cm, including polyurethane honeycomb foam, polystyrene honeycomb foam or polyethylene honeycomb foam.

[0031] In a second aspect of the present invention, a silicon carbide mesh porous ceramic filter prepared by the aforementioned method is provided.

[0032] As an optional implementation, the filter has a porosity greater than 80%, a compressive strength greater than 3 MPa, and a tensile strength greater than 3000 J / m. 2 .

[0033] As can be seen from the above technical solution of the present invention, the preparation method of the silicon carbide mesh porous ceramic filter proposed in the present invention uses carbon balls of different particle sizes as the core carbon source. First, carbon ball-PVA sol is prepared by in-situ one-step chemical coupling agent modification to improve the dispersibility of small-diameter carbon balls, so that small-diameter carbon balls are evenly distributed between large-diameter carbon balls. Combined with the combination of carbon balls of different particle sizes, the stability and thixotropy of the slurry are improved, and the distribution and filling of the slurry in the polymer matrix are more balanced, thereby achieving a balance between reaction rate and density during subsequent sintering.

[0034] During sintering, the excellent thixotropic properties of the slurry allow it to fill the polymer matrix uniformly, preventing large defects during sintering. Simultaneously, large-diameter carbon spheres generate coarser SiC whiskers, enhancing the strength and toughness of the final product. Small-diameter carbon spheres uniformly fill the pores between the large-diameter spheres, providing more carbon sources to react with silicon and form more fine SiC whiskers, resulting in a denser sintered body. This improves the strength and hardness of the final product, thereby enhancing its mechanical properties. Furthermore, the combination of carbon spheres of different sizes can regulate the reaction rate, making the reaction more uniform and allowing for the uniform removal of gases during sintering, avoiding defects caused by pore blockage and agglomeration.

[0035] This overcomes the problem of hollow pillars caused by insufficient slurry filling in the preparation of ceramic filters, as well as the defects that may occur during polymer decomposition.

[0036] The preparation method of the present invention is simple to operate, easy to control, low in cost, and highly efficient, and has broad application prospects. Attached Figure Description

[0037] Figure 1 This is a macroscopic view of a silicon carbide mesh porous ceramic filter as an example of the present invention.

[0038] Figure 2 These are SEM images of the silicon carbide mesh porous ceramic filter exemplified by this invention; wherein, 2a and 2b are SEM images at different magnifications, respectively.

[0039] Figure 3 This is an XRD pattern of a silicon carbide mesh porous ceramic filter, an example of the present invention.

[0040] Figure 4 This is a rheological property diagram of the silicon carbide slurry as an example of the present invention. Detailed Implementation

[0041] To better understand the technical content of the present invention, specific embodiments are described below in conjunction with the accompanying drawings.

[0042] Various aspects of the invention are described in this disclosure with reference to the accompanying drawings, in which numerous illustrative embodiments are shown. The embodiments of this disclosure are not necessarily intended to encompass all aspects of the invention. It should be understood that the various concepts and embodiments described above, as well as those described below in more detail, can be implemented in any of a number of ways.

[0043] Compared to traditional carbon black and flake graphite, carbon spheres possess superior dispersion and rheological properties. The addition of carbon spheres improves rheological properties, ensuring a more balanced distribution of the carbon source within the polymer matrix. Furthermore, the high specific surface area and chemical activity of carbon spheres facilitate the in-situ reaction between silicon and carbon, resulting in more and more uniformly distributed SiC whiskers. This effectively compensates for material defects and enhances the mechanical strength of the ceramic material.

[0044] However, traditional processes using single-size carbon spheres as a carbon source cannot completely solve the problems of slurry dispersion and stability. Therefore, they cannot effectively address the hollow pillar problem caused by insufficient slurry filling, or the defects that may occur during polymer decomposition.

[0045] Therefore, this invention overcomes the above problems by mismatching carbon spheres of different particle sizes and modifying small-sized carbon spheres. By changing the properties of the slurry and combining the mismatched carbon spheres, a balance between reaction rate and density during sintering is achieved, thereby improving the mechanical properties of silicon carbide mesh porous ceramic filters while maintaining high porosity through a simple and low-cost method.

[0046] In one exemplary embodiment of the present invention, a method for preparing a silicon carbide mesh porous ceramic filter is provided, comprising the following steps:

[0047] S1. Preparation of the first carbon sphere-PVA composite sol

[0048] PVA solution preparation: Dissolve an appropriate amount of PVA (polyvinyl alcohol) powder in deionized water, heat at about 90°C and stir constantly until the PVA is completely dissolved to form a uniform and transparent solution, and then cool to room temperature for later use.

[0049] First carbon ball powder pre-dispersion treatment: The first carbon ball powder is dispersed in deionized water and subjected to ultrasonic treatment or mechanical stirring for 2-4 hours to break up the agglomeration of the first carbon balls and obtain the first carbon ball dispersion.

[0050] In-situ introduction of coupling agent: The coupling agent is added to the first carbon sphere dispersion and stirred at 60~80℃ for 2~4h to allow the coupling agent to react with the functional groups on the surface of the first carbon sphere to form chemical bonds, thereby obtaining the modified first carbon sphere dispersion.

[0051] Preparation of composite sol: Under ultrasonic treatment or mechanical stirring, the modified first carbon ball dispersion is slowly added to the PVA solution, and ultrasonic treatment or mechanical stirring (500~1000rpm) is continued for 1~2h until the first carbon ball is evenly dispersed to obtain the first carbon ball-PVA composite sol.

[0052] S2. In the first carbon ball-PVA composite sol obtained in step S1, mixed silicon carbide powder, metallic silicon powder, second carbon ball powder, dispersant and plasticizer are added in sequence and stirred evenly to obtain a mixed wet material; wherein, the average particle size of the first carbon ball is much smaller than the average particle size of the second carbon ball.

[0053] S3. Pour the mixed wet material obtained in step S2 into a ball mill jar and ball mill at a speed of 200 r / min for 3~6 hours. Then filter the slurry with a 100-mesh sieve and defoam using a vacuum centrifugal stirrer to obtain silicon carbide slurry.

[0054] S4. Immerse the polymer mold in the silicon carbide slurry obtained in step S3, remove it and use a rotating disk to remove excess slurry, and then dry it at 100°C for 12 hours to obtain a ceramic green body.

[0055] S5. The ceramic green body obtained in step S4 is sintered at 1450~1600℃ for 1~3h to obtain a silicon carbide mesh porous ceramic filter.

[0056] As an optional example, the average particle size of the first carbon sphere is in the nanometer range, and the average particle size of the second carbon sphere is in the micrometer range.

[0057] As an optional example, the first carbon sphere has an average particle size of 50 nm to 200 nm, a sphericity > 0.8, and a specific surface area > 200 m² / g; the second carbon sphere has an average particle size of 1 μm to 10 μm.

[0058] As an optional example, the mass concentration of the PVA solution is 5% to 10%, and the mass concentration of the first carbon sphere dispersion is 60% to 80%.

[0059] As an optional example, the amount of coupling agent added is 1% to 5% of the weight of the first carbon sphere.

[0060] As optional examples, coupling agents include one or more of the following: γ-aminopropyltriethoxysilane (APTES), γ-methacryloyloxypropyltrimethoxysilane (MPTS), γ-glycidoxypropyltrimethoxysilane (GPTMS), vinyltrimethoxysilane (VTMS), bis(butoxyacetylacetylacetonate)diisopropoxytitanate (Tyzor AA-75), isopropoxytriacryloyloxytitanate (IPT), isopropoxyzirconia acrylate, and polyethylene glycol diglycidyl ether (PEGDE).

[0061] As an optional example, the specific proportions of each component in the mixed wet material, by mass percentage, are as follows: 25%~45% mixed silicon carbide powder, 15%~35% metallic silicon powder, 5%~15% compounded carbon ball powder, 0.5%~2% dispersant, 1%~5% plasticizer, and 20%~40% deionized water; wherein, the compounded carbon ball powder includes first carbon ball powder and second carbon ball powder.

[0062] As an optional example, the first carbon ball powder accounts for 30% to 50% of the mass of the compound carbon ball powder, and the second carbon ball powder accounts for 50% to 70% of the mass of the compound carbon ball powder.

[0063] As an optional example, the mixed silicon carbide powder includes a first silicon carbide powder and a second silicon carbide powder, wherein the average particle size of the first silicon carbide powder is smaller than the average particle size of the second silicon carbide powder.

[0064] In a more specific example, the average particle size of the first silicon carbide powder is 1 μm to 5 μm, and the average particle size of the second silicon carbide powder is 20 μm to 40 μm.

[0065] As an optional example, the mass ratio of the first silicon carbide powder to the second silicon carbide powder is (3:7) to (5:5).

[0066] As an optional example, the average particle size of the metallic silicon powder is 5 μm to 15 μm.

[0067] As an optional example, the dispersant includes one or more of polyvinylpyrrolidone K30 (PVP-K30), polycarboxylates, tetramethylammonium hydroxide, and isobutylene maleic anhydride copolymers.

[0068] As an optional example, the plasticizer includes one or more of ethylene glycol, glycerol, polyethylene glycol, and ethylene glycol monoethyl ether.

[0069] As an optional example, the polymer template has a porosity >80% and a pore size of 0.5 cm to 2 cm, including polyurethane honeycomb foam, polystyrene honeycomb foam or polyethylene honeycomb foam.

[0070] In the preparation method of this invention, during the silicon carbide slurry preparation stage, small-diameter carbon spheres, due to their larger specific surface area, can increase the viscosity of the slurry, reduce sedimentation, and thus enhance stability. Furthermore, the intermolecular forces between the active groups on the surface of the small-diameter carbon spheres and the binder PVA are strong. These forces can weaken under external force and recover in a static state, thus endowing the slurry with excellent thixotropic properties. However, the dispersibility of small-diameter carbon spheres is poor. Therefore, by using some large-diameter carbon spheres as substitutes, it is ensured that the slurry can be stably and uniformly dispersed while maintaining a constant total carbon content, thereby giving the slurry good stability and thixotropic properties.

[0071] During the sintering stage, small-diameter carbon spheres, due to their larger specific surface area, exhibit higher reactivity and can generate more fine silicon carbide whiskers, thereby improving the strength of the ceramic. However, using small-diameter carbon spheres alone may lead to uneven reaction and defects due to uneven dispersion of the carbon spheres. Simultaneously, the rapid reaction between small-diameter carbon spheres and silicon can easily form dense silicon carbide regions locally, which is detrimental to the removal of gases generated during the reaction, also leading to defects. Therefore, introducing some large-diameter carbon spheres into the system can, on the one hand, regulate the reaction rate, making the reaction more uniform, allowing for more uniform gas removal and reducing the likelihood of defects, and ensuring more uniform filling of the polymer template by the slurry, thus reducing structural defects; on the other hand, large-diameter carbon spheres can form more robust silicon carbide whiskers, thereby enhancing the toughness of the ceramic.

[0072] In another exemplary embodiment of the present invention, a silicon carbide mesh porous ceramic filter prepared by the aforementioned method is provided. This filter has a porosity greater than 80%, a compressive strength greater than 3 MPa, and a tensile strength greater than 3000 J / m. 2 It possesses excellent mechanical properties while maintaining high porosity.

[0073] To facilitate better understanding, the present invention will be further illustrated below with several specific examples, but the preparation process is not limited to these examples, and the content of the present invention is not limited to these examples.

[0074] Unless otherwise specified, the materials in the examples are prepared according to existing methods or purchased directly from the market.

[0075] Example 1

[0076] (1) Preparation of small-diameter carbon sphere-PVA composite sol

[0077] a. Dissolve 2g of PVA (polyvinyl alcohol) powder in 25g of deionized water, heat at around 90°C and stir constantly until the PVA is completely dissolved to form a uniform and transparent solution, then cool to room temperature for later use.

[0078] b. Disperse 3.15g of 100nm carbon spheres in 4.5g of water and stir mechanically for 3h. Then add 0.09g of APTES and stir at 60℃ for 2h.

[0079] c. The PVA solution prepared in step a and cooled to room temperature is added to the small-particle-size carbon sphere suspension prepared in step b while stirring, and then stirred at 600 rpm for 2 hours to obtain the small-particle-size carbon sphere-PVA composite sol.

[0080] (2) Add 21g of 30μm silicon carbide, 9g of 5μm silicon carbide, 25g of 10μm metallic silicon powder, 6.85g of 5μm carbon ball powder, 0.5g of PVP-K30 and 3g of polyethylene glycol 400 to the composite sol prepared in step (1) and stir mechanically for 2h.

[0081] (3) The wet material prepared in step (2) is poured into a ball mill jar and ball milled at 200 r / min for 4 h. The slurry is filtered with a 100-mesh sieve and defoamed using a vacuum centrifugal stirrer to prepare silicon carbide slurry.

[0082] (4) Immerse polyurethane honeycomb foam with an average pore size of 1 cm and a porosity of >85% into the slurry prepared in step (3). After taking it out, use a rotating disk to remove excess slurry from the foam surface at a speed of 60 rpm. Then, dry it at 100°C for 12 h to obtain a ceramic blank.

[0083] (5) The ceramic blank was sintered at 1500℃ under a nitrogen atmosphere for 2 hours to prepare a silicon carbide mesh porous ceramic filter.

[0084] Comparative Example 1

[0085] [Preparation of slurry by direct blending of carbon spheres of varying particle sizes]

[0086] The composition of the raw materials is as follows:

[0087] Mixed silicon carbide powder: 30g silicon carbide powder (21g 30μm silicon carbide, 9g 5μm silicon carbide);

[0088] 10μm metallic silicon powder: 25g;

[0089] 3.15g of 100nm carbon sphere powder and 6.85g of 5μm carbon sphere powder;

[0090] PVA: 2g

[0091] PVP-K30: 0.5g

[0092] Polyethylene glycol 400: 3g

[0093] Deionized water: 29.5g

[0094] (1) Dissolve PVA powder in deionized water, heat at about 90°C and stir constantly until PVA is completely dissolved to form a uniform and transparent solution, and then cool to room temperature for later use.

[0095] (2) Add the weighed silicon carbide powder, metallic silicon powder, carbon ball powder, PVP-K30 and polyethylene glycol 400 to the PVA solution prepared in step (1) and stir mechanically for 2 hours.

[0096] (3) The wet material prepared in step (2) is poured into a ball mill jar and ball milled at 200 r / min for 4 hours. The slurry is filtered with a 100-mesh sieve and defoamed using a vacuum centrifugal stirrer to prepare silicon carbide slurry.

[0097] (4) Immerse polyurethane honeycomb foam with an average pore size of 1 cm and a porosity of >85% into the slurry prepared in step (3). After removing it, use a rotating disk to remove excess slurry from the foam surface at a speed of 60 rpm. Then, dry it at 100°C for 12 h to obtain a ceramic green body.

[0098] (5) The ceramic blank was sintered at 1500℃ under a nitrogen atmosphere for 2 hours to prepare a silicon carbide mesh porous ceramic filter.

[0099] Comparative Example 2

[0100] [Using large-diameter carbon balls alone]

[0101] The composition of the raw materials is as follows:

[0102] Mixed silicon carbide powder: 30g silicon carbide powder (21g 30μm silicon carbide, 9g 5μm silicon carbide)

[0103] 10μm metallic silicon powder: 25g

[0104] 10g of 5μm carbon ball powder

[0105] PVA: 2g

[0106] PVP-K30: 0.5g

[0107] Polyethylene glycol 400: 3g

[0108] Deionized water: 29.5g

[0109] The preparation process is the same as in Example 2, resulting in a silicon carbide mesh porous ceramic filter.

[0110] Comparative Example 3

[0111] [Using small-diameter carbon balls alone]

[0112] The composition of the raw materials is as follows:

[0113] Mixed silicon carbide powder: 30g silicon carbide powder (21g 30μm silicon carbide, 9g 5μm silicon carbide)

[0114] 10μm metallic silicon powder: 25g

[0115] 100nm carbon ball powder 10g

[0116] PVA: 2g

[0117] PVP-K30: 0.5g

[0118] Polyethylene glycol 400: 3g

[0119] Deionized water: 29.5g

[0120] The preparation process is the same as in Example 2, resulting in a silicon carbide mesh porous ceramic filter.

[0121] Comparative Example 4

[0122] [Carbon black as a carbon source]

[0123] The composition of the raw materials is as follows:

[0124] Mixed silicon carbide powder: 30g silicon carbide powder (21g 30μm silicon carbide, 9g 5μm silicon carbide)

[0125] 10μm metallic silicon powder: 25g

[0126] 1μm carbon black powder: 10g (carbon black powder: specific surface area 50~200 m² / g, bulk density: about 150~300 kg / m³, particle size D50: 1μm)

[0127] PVA: 2g

[0128] PVP-K30: 0.5g

[0129] Polyethylene glycol 400: 3g

[0130] Deionized water: 29.5g

[0131] The ceramic preparation process is the same as in Example 2, resulting in a silicon carbide mesh porous ceramic filter.

[0132] Comparative Example 5

[0133] [Flake graphite as a carbon source]

[0134] The composition of the raw materials is as follows:

[0135] Mixed silicon carbide powder: 30% silicon carbide powder (21g of 30μm silicon carbide, 9g of 5μm silicon carbide)

[0136] 10μm metallic silicon powder: 25g

[0137] 1μm flake graphite: 10g (Graphite powder: specific surface area: 3~20 m² / g, bulk density: 200~600 kg / m³, particle size D50: 1μm)

[0138] PVA: 2g

[0139] PVP-K30: 0.5g

[0140] Polyethylene glycol 400: 3g

[0141] Deionized water: 29.5g

[0142] The ceramic preparation process is the same as in Example 2, resulting in a silicon carbide mesh porous ceramic filter.

[0143] test

[0144] [SEM]

[0145] The morphology of the filter in Example 1 was tested, and the results are as follows: Figure 1 and Figure 2 As shown.

[0146] Combining macroscopic and microscopic images, it can be seen that the filter has a mesh structure with a pore size of about 1 cm, indicating that the prepared filter has a large throughput and can effectively filter large-scale impurities in molten metal.

[0147] [XRD]

[0148] The filter of Example 1 was subjected to XRD testing, and the results are as follows: Figure 3 As shown.

[0149] As can be seen from the figure, the prepared filter has the characteristic peaks of silicon carbide, which proves that a silicon carbide ceramic filter has been obtained.

[0150] [Rheological properties of silicon carbide slurry]

[0151] The rheological properties of the slurry were measured using a rotational viscometer, and the results are as follows: Figure 4 As shown.

[0152] As shown in the figure, the slurry prepared after in-situ one-step chemical coupling agent modification of small-particle carbon spheres-PVA sol in Example 1 exhibits high viscosity at low shear rates, preventing particle sedimentation and ensuring the stability of the slurry. With increasing shear rate, the slurry viscosity decreases rapidly, exhibiting good thixotropy. This characteristic promotes rapid dilution of the slurry and rapid filling of the foam pore walls during impregnation.

[0153] Although the slurry prepared by direct blending of carbon spheres of different sizes in Comparative Example 1 exhibits high viscosity at low shear rates and good thixotropy at high shear rates, the viscosity of the slurry is unstable due to the uneven dispersion of small-sized carbon spheres, which affects the consistency during actual filling.

[0154] Comparative Example 2 shows that the overall viscosity of the large-particle-size carbon ball slurry is low and the thixotropy is poor when used alone.

[0155] Comparative Example 3 shows that the overall viscosity of the slurry made with small-diameter carbon balls alone is high, and the viscosity of the slurry is very unstable due to the poor dispersion of the small-diameter carbon balls.

[0156] Comparative Example 4 uses carbon black alone, resulting in a slurry with lower overall viscosity and poor thixotropy.

[0157] Comparative Example 5 uses flake graphite alone, resulting in a slurry with low overall viscosity and poor thixotropy.

[0158] [Porosity and Mechanical Properties]

[0159] The porosity, compressive strength, and fracture strength of silicon carbide mesh porous ceramics were tested respectively, and the results are shown in the table below.

[0160] Example 1 81.5 3.14 3200 Comparative Example 1 83 2.5 2400 Comparative Example 2 89 1.14 1900 Comparative Example 3 86 1.21 1800 Comparative Example 4 87 1.12 1760 Comparative Example 5 89 1.04 1610

[0161] As can be seen from the table, the porosity of all samples reached or exceeded 80%, thus exhibiting excellent permeability.

[0162] Among them, the ceramic filter prepared in Example 1 has the lowest porosity and the highest compressive strength and fracture strength.

[0163] The increased porosity of the ceramic filter in Comparative Example 1 resulted in a decrease in both compressive strength and fracture strength. This was because direct blending led to uneven distribution of small-diameter carbon spheres in some areas. However, the compressive strength and fracture strength were higher than those in Comparative Examples 2 and 3, indicating that the combination of carbon spheres of different diameters can effectively improve the strength of ceramics.

[0164] Comparative Example 2 directly uses large-diameter carbon spheres alone, resulting in poor slurry stability and thixotropy, low reactivity, and the generation of more large-sized silicon carbide whiskers. Therefore, it has the highest porosity and low compressive strength.

[0165] Comparative Example 3 uses small-diameter carbon spheres alone, but the uneven dispersion leads to uneven local reactions and residual defects, resulting in high porosity and low strength.

[0166] In Comparative Example 4, carbon black was used alone. The uneven dispersion of the slurry led to incomplete carbon reaction in some areas, resulting in defects such as high porosity and low strength.

[0167] Comparative Example 5 uses flake graphite alone. The uneven dispersion of the slurry leads to insufficient local carbon reaction and residual defects, which are manifested as high porosity and low strength.

[0168] Therefore, it can be seen that a silicon carbide ceramic filter with high porosity and high strength has been successfully prepared by the method of the present invention.

[0169] While the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the invention. Those skilled in the art can make various modifications and refinements without departing from the spirit and scope of the invention. Therefore, the scope of protection of the present invention shall be determined by the claims.

Claims

1. A method for preparing a silicon carbide mesh porous ceramic filter, characterized in that, Includes the following steps: S1. Preparation of the first carbon sphere-PVA composite sol PVA powder was completely dissolved in deionized water to obtain a PVA solution, which was then cooled for later use. The first carbon ball powder is dispersed in deionized water, and the agglomeration of the first carbon balls is broken by ultrasonic treatment or mechanical stirring to obtain the first carbon ball dispersion. A coupling agent is added to the first carbon sphere dispersion to allow the coupling agent to react with the functional groups on the surface of the first carbon spheres to form chemical bonds, thereby obtaining a modified first carbon sphere dispersion. Under ultrasonic treatment or mechanical stirring conditions, the modified first carbon ball dispersion is slowly added to the PVA solution, and ultrasonic treatment or mechanical stirring is continued until the first carbon ball is evenly dispersed to obtain the first carbon ball-PVA composite sol. S2. Add mixed silicon carbide powder, metallic silicon powder, second carbon ball powder, dispersant and plasticizer sequentially to the first carbon ball-PVA composite sol obtained in step S1, and stir evenly to obtain a mixed wet material; wherein, the average particle size of the first carbon ball is 50 nm~200 nm, and the average particle size of the second carbon ball is 1 μm~10 μm; S3. The mixed wet material obtained in step S2 is ball-milled, sieved, and defoamed to obtain silicon carbide slurry. S4. Immerse the polymer mold in the silicon carbide slurry obtained in step S3, remove it and use a rotating disk to remove excess slurry, then perform drying treatment to obtain ceramic green body. S5. Sinter the ceramic blank obtained in step S4 to obtain a silicon carbide mesh porous ceramic filter.

2. The preparation method according to claim 1, characterized in that, The first carbon sphere has a sphericity > 0.8 and a specific surface area > 200 μm. 2 / g.

3. The preparation method according to claim 1, characterized in that, The mass concentration of the PVA solution is 5%~10%, and the mass concentration of the first carbon ball dispersion is 60%~80%.

4. The preparation method according to claim 1, characterized in that, The amount of coupling agent added is 1% to 5% of the weight of the first carbon sphere.

5. The preparation method according to claim 1, characterized in that, The coupling agent includes one or more of γ-aminopropyltriethoxysilane, γ-methacryloxypropyltrimethoxysilane, γ-glycidyl etheroxypropyltrimethoxysilane, vinyltrimethoxysilane, diisopropyl di(acetylacetonyl)titanate, and polyethylene glycol diglycidyl ether.

6. The preparation method according to claim 1, characterized in that, The specific proportions of each component in the mixed wet material, by mass percentage, are as follows: 25%~45% mixed silicon carbide powder, 15%~35% metallic silicon powder, 5%~15% compound carbon ball powder, 0.5%~2% dispersant, 1%~5% plasticizer, and 20%~40% deionized water; wherein, the compound carbon ball powder includes first carbon ball powder and second carbon ball powder.

7. The preparation method according to claim 6, characterized in that, The first carbon ball powder accounts for 30% to 50% of the mass of the compound carbon ball powder, and the second carbon ball powder accounts for 50% to 70% of the mass of the compound carbon ball powder.

8. The preparation method according to claim 6, characterized in that, The mixed silicon carbide powder includes a first silicon carbide powder and a second silicon carbide powder, wherein the average particle size of the first silicon carbide powder is smaller than the average particle size of the second silicon carbide powder.

9. The preparation method according to claim 8, characterized in that, The average particle size of the first silicon carbide powder is 1 μm to 5 μm, and the average particle size of the second silicon carbide powder is 20 μm to 40 μm.

10. The preparation method according to claim 8, characterized in that, The mass ratio of the first silicon carbide powder to the second silicon carbide powder is (3:7) to (5:5).

11. The preparation method according to claim 1, characterized in that, The average particle size of the silicon metal powder is 5 μm to 15 μm.

12. The preparation method according to claim 1, characterized in that, The dispersant includes one or more of polyvinylpyrrolidone K30, polycarboxylate, tetramethylammonium hydroxide, and isobutylene maleic anhydride copolymer.

13. The preparation method according to claim 1, characterized in that, The plasticizer includes one or more of ethylene glycol, glycerol, polyethylene glycol, and ethylene glycol monoethyl ether.

14. The preparation method according to claim 1, characterized in that, The polymer template has a porosity >80% and a pore size of 0.5 cm to 2 cm, including polyurethane honeycomb foam, polystyrene honeycomb foam or polyethylene honeycomb foam.

15. A silicon carbide mesh porous ceramic filter prepared by the method according to any one of claims 1-14.

16. The silicon carbide mesh porous ceramic filter according to claim 15, characterized in that, The filter has a porosity greater than 80% and a compressive strength greater than 3 MPa.

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