A method for growing nanofibers in the pore wall of a porous silicon carbide ceramic membrane carrier

Abstract

The application discloses a method for growing nanofibers in the pore wall of a porous silicon carbide ceramic membrane carrier. The preparation process comprises the following steps: 1) weighing a certain amount of aluminum sol solution, adding a proper amount of silicon carbide particles into the aluminum sol solution, uniformly mixing and then performing drying treatment to obtain silicon carbide particles coated with an aluminum sol layer; 2) performing dry pressing forming on the pretreated silicon carbide particles to obtain a green body; 3) sintering the green body in a high-temperature muffle furnace, converting the aluminum sol into aluminum oxide, and reacting the aluminum oxide with silicon dioxide formed on the surface of the silicon carbide to form a support body with needle-like mullite nanofibers; and 4) etching the surface silicon dioxide by using an alkali solution to obtain a porous silicon carbide ceramic with mullite fibers grown on the pore wall surface. The preparation process has the advantages of simple process, low sintering temperature, low energy consumption, low preparation cost and the like, improves the internal structure of the pore channel, and has application potential in industrial flue gas purification.

Description

Technical Field

[0001] This invention belongs to the field of porous ceramic material preparation technology, and relates to a method for growing nanofibers within the pore walls of a porous silicon carbide ceramic membrane carrier. Background Technology

[0002] Porous silicon carbide ceramics, with their excellent mechanical strength, good chemical resistance, high thermal conductivity, low coefficient of thermal expansion, and high thermal shock resistance, are the preferred materials for high-temperature flue gas filtration processes. However, silicon carbide is a strong covalent compound, so its sintering temperature typically exceeds 2000 °C. Therefore, reducing the sintering temperature of porous silicon carbide ceramics and improving their filtration performance is of great significance. In-situ reaction sintering is used to prepare porous silicon carbide ceramic membrane supports, and sintering aids are usually introduced, which can significantly reduce the sintering temperature of the silicon carbide porous ceramic support. To further control the properties and pore structure of porous silicon carbide ceramics, most research cases involve growing fibers or whiskers in the porous ceramic pores or directly adding whiskers to modify the pores.

[0003] Chinese invention patent CN112759418B reports the use of modified porous corundum ceramic powder as aggregate, with the addition of elemental silicon powder and αAl2O3 micro powder as additives, to enhance porous corundum ceramics by sintering silicon nitride whiskers grown in the necks and channels between particles. Chinese invention patent CN112876280B prepares a silicon carbide whisker-reinforced porous alumina-carbon ceramic with excellent mechanical properties, good purification effect, and long service life; the silicon carbide whiskers grow inside the channels of the alumina-carbon porous ceramic. Chinese invention patent CN114853493A uses zirconia whiskers as reinforcement incorporated into a slurry and prepares zirconia whisker-reinforced zirconia ceramics using 3D printing technology. Xu et al. (Ceramics International, 2021, 47, 8150–8160) obtained mullite whisker-reinforced porous silicon carbide ceramics by adding kaolin and alumina to silicon carbide aggregate, and then using the reaction and sintering of silicon dioxide and alumina to form mullite whiskers. Therefore, previous studies have mostly focused on adding or growing whiskers within the ceramic channels or at the neck joints to enhance the mechanical properties of porous ceramics. Furthermore, existing research has shown that the fibers or whiskers prepared in this way all grow in a divergent manner within the channels, meaning they grow out of plane relative to the channel walls. Summary of the Invention

[0004] The purpose of this invention is to provide a novel method for growing nanofibers on the surface of porous silicon carbide ceramic particles within the pore walls. By modifying the surface of the silicon carbide particles, the method utilizes the reaction and restricted growth of silica formed from the oxidation of the silicon carbide particles with the surface-coated alumina sol, increasing the surface roughness and specific surface area of ​​the silicon carbide particles. This not only benefits catalyst loading but also improves dust retention. This invention uses an in-situ reaction sintering method to grow mullite nanofibers on the surface of silicon carbide particles, which is beneficial for increasing the specific surface area of ​​the carrier and reducing filtration resistance. Furthermore, the preparation process is simple and economical.

[0005] To achieve the above objectives, the technical solution of the present invention is as follows: (1) Weigh a certain amount of aluminum sol solution and place it in a beaker; (2) Weigh a certain amount of silicon carbide powder, slowly pour it into the aluminum sol solution, and stir it evenly with a glass rod; (3) The mixed slurry obtained in step (2) is placed in an oven and dried to obtain pretreated silicon carbide particles; (4) Pour the pretreated silicon carbide particles from step (3) into a mortar, add activated carbon powder to obtain a mixed powder, and grind until there are no lumps; wherein, the mass of aluminum sol is 1~13% of the mass of the mixed powder, and the mass of silicon carbide powder is 72~85 wt.% of the mass of the mixed powder; (5) The powder obtained in step (4) is pressed into a sheet or strip shape by a tablet press under a pressure of 8 MPa. (6) Place the billet in a muffle furnace for sintering, raise the temperature to 1250~1450 ℃ according to a certain sintering program, hold for 4 h, and finally cool to room temperature with the furnace. (7) Place the sintered sample in an alkaline solution for alkaline etching.

[0006] Furthermore, after sintering, the aluminum sol solution is transformed into nano-alumina, which reacts with the silica formed by oxidation on the silicon carbide surface to form needle-like nano-mullite fibers.

[0007] Furthermore, in step (2), the silicon carbide powder needs to be added to the aluminum sol solution while stirring.

[0008] Furthermore, in step (3), the mixed slurry needs to be dried at 120 ℃ for a time of 0.5~1 h.

[0009] Furthermore, the alkaline solution in step (7) is NaOH with a concentration of 10 wt.%.

[0010] Furthermore, the alkaline etching time in step (7) is 0.5~1 h.

[0011] Compared with the prior art, the present invention has the following advantages: (1) The process of the present invention is simple, which greatly reduces the sintering temperature of silicon carbide ceramic support and reduces the energy consumption of silicon carbide ceramic support preparation.

[0012] (2) Dense nano-mullite fibers were grown on the surface of the prepared silicon carbide porous ceramic, which enhanced the utilization rate of the silicon carbide particle surface and strengthened the bending strength and thermal shock resistance of the ceramic support.

[0013] (3) The nano-mullite fibers generated by the in-situ reaction on the silicon carbide surface greatly increase the surface roughness of the silicon carbide ceramic support and increase its specific surface area, which is beneficial to particle interception and catalyst loading. Attached Figure Description

[0014] Figure 1 This is a SEM image of silicon carbide particles after pretreatment in Example 1 of the present invention.

[0015] Figure 2 This is a SEM image of the surface of silicon carbide particles after sintering and alkaline etching in Example 1 of the present invention.

[0016] Figure 3 The images shown are transmission electron microscope (TEM) images and elemental distribution diagrams of the fibers in Example 1 of this invention.

[0017] Figure 4 This refers to the thermal shock resistance of the silicon carbide ceramic support prepared in Example 1 of the present invention. Detailed Implementation

[0018] The present invention will be further described below with reference to the accompanying drawings and embodiments, but the implementation and protection scope of the present invention are not limited thereto. Example 1

[0019] 24 g of silicon carbide powder with an average particle size of 200 μm was poured into 1.5 g of aluminum sol solution and stirred with a glass rod for 10 min to coat the silicon carbide particles with a layer of aluminum sol. The mixed silicon carbide particles were then placed in a 120 ℃ oven and baked for 30 min to remove moisture from the aluminum sol, thus obtaining pretreated silicon carbide particles. A scanning electron microscope image of the pretreated silicon carbide particles is shown below. Figure 1As shown. 4.5 g of activated carbon powder was added to the pretreated silicon carbide particles and mixed evenly to obtain a lumpy state, yielding the raw material powder. Under a pressure of 8 MPa, the raw material powder was pressed into sheet-like (Φ 30 mm × 3 mm) and strip-like (50 mm × 6 mm × 6 mm) green bodies using a mold. The prepared silicon carbide ceramic film support green bodies were placed in a muffle furnace for sintering, heated to 1350 ℃ and held for 4 h, and finally cooled to room temperature with the furnace. The silicon carbide ceramic film support sample was removed and cooled to room temperature. A 10 wt.% NaOH solution was prepared, and the sample was placed in the NaOH solution. The solution was heated to a slight boiling state for alkaline etching, with an etching time of 0.5 h. From Figure 2 As can be seen, needle-like nanofibers exist on the surface of silicon carbide. The structure of these nanofibers was characterized using transmission electron microscopy (TEM). Figure 3 It can be seen from the data that its selected electron diffraction pattern is consistent with that of mullite, and it is mainly composed of Si, Al, and O. Figure 4 It can be seen that the prepared silicon carbide film support does not show significant decrease in flexural strength after 20 cycles from room temperature to 800 °C, exhibiting good thermal shock resistance. Example 2

[0020] 23.4 g of silicon carbide powder with an average particle size of 200 μm was poured into 2.1 g of alumina sol solution and stirred with a glass rod for 10 min to coat the silicon carbide particles with a layer of alumina sol. The mixed silicon carbide particles were then placed in an oven at 120 ℃ and baked for 30 min to remove moisture from the alumina sol, thus obtaining pretreated silicon carbide particles. 4.5 g of activated carbon powder was added to the pretreated silicon carbide particles and mixed evenly to obtain a lump-free raw material powder. Under a pressure of 8 MPa, the raw material powder was pressed into sheet-like (Φ 30 mm × 3 mm) and strip-like (50 mm × 6 mm × 6 mm) green bodies using a mold. The prepared silicon carbide ceramic support green bodies were placed in a muffle furnace for sintering, heated to 1350 ℃ and held for 4 h, and finally cooled to room temperature with the furnace. Remove the silicon carbide ceramic film support sample and cool it to room temperature. Prepare a 10 wt.% NaOH solution, place the sample in the NaOH solution, and heat the solution to a slight boiling state for alkaline etching. The etching time is 0.5 h. Example 3

[0021] 22.8 g of silicon carbide powder with an average particle size of 200 μm was poured into 2.7 g of alumina sol solution and stirred with a glass rod for 10 min to coat the silicon carbide particles with a layer of alumina sol. The mixed silicon carbide particles were then placed in an oven at 120 ℃ and baked for 30 min to remove moisture from the alumina sol, thus obtaining pretreated silicon carbide particles. 4.5 g of activated carbon powder was added to the pretreated silicon carbide particles and mixed evenly to obtain a lump-free raw material powder. Under a pressure of 8 MPa, the raw material powder was pressed into sheet-like (Φ 30 mm × 3 mm) and strip-like (50 mm × 6 mm × 6 mm) green bodies using a mold. The prepared silicon carbide ceramic support green bodies were placed in a muffle furnace for sintering, heated to 1350 ℃ and held for 4 h, and finally cooled to room temperature with the furnace. Remove the silicon carbide ceramic film support sample and cool it to room temperature. Prepare a 10 wt.% NaOH solution, place the sample in the NaOH solution, and heat the solution to a slight boiling state for alkaline etching. The etching time is 0.5 h. Example 4

[0022] 22.2 g of silicon carbide powder with an average particle size of 200 μm was poured into 3.3 g of alumina sol solution and stirred with a glass rod for 10 min to coat the silicon carbide particles with a layer of alumina sol. The mixed silicon carbide particles were then placed in an oven at 120 ℃ and baked for 30 min to remove moisture from the alumina sol, thus obtaining pretreated silicon carbide particles. 4.5 g of activated carbon powder was added to the pretreated silicon carbide particles and mixed evenly to obtain a lump-free raw material powder. Under a pressure of 8 MPa, the raw material powder was pressed into sheet-like (Φ 30 mm × 3 mm) and strip-like (50 mm × 6 mm × 6 mm) green bodies using a mold. The prepared silicon carbide ceramic support green bodies were placed in a muffle furnace for sintering, heated to 1450 ℃ and held for 4 h, and finally cooled to room temperature with the furnace. Remove the silicon carbide ceramic film support sample and cool it to room temperature. Prepare a 10 wt.% NaOH solution, place the sample in the NaOH solution, and heat the solution to a slight boiling state for alkaline etching. The etching time is 0.5 h. Example 5

[0023] 21.6 g of silicon carbide powder with an average particle size of 200 μm was poured into 3.9 g of alumina sol solution and stirred with a glass rod for 10 min to coat the silicon carbide particles with a layer of alumina sol. The mixed silicon carbide particles were then placed in an oven at 120 ℃ and baked for 30 min to remove moisture from the alumina sol, thus obtaining pretreated silicon carbide particles. 4.5 g of activated carbon powder was added to the pretreated silicon carbide particles and mixed evenly to obtain a lump-free raw material powder. Under a pressure of 8 MPa, the raw material powder was pressed into sheet-like (Φ 30 mm × 3 mm) and strip-like (50 mm × 6 mm × 6 mm) green bodies using a mold. The prepared silicon carbide ceramic support green bodies were placed in a muffle furnace for sintering, heated to 1250 ℃ and held for 4 h, and finally cooled to room temperature with the furnace. Remove the silicon carbide ceramic film support sample and cool it to room temperature. Prepare a 10 wt.% NaOH solution, place the sample in the NaOH solution, heat the solution to a slight boiling state for alkaline etching, and the etching time is 1 h.

[0024] The above embodiments of the present invention are merely illustrative examples to clearly illustrate the present invention, and are not intended to limit the implementation of the present invention. Any modifications, equivalent substitutions, and improvements made within the principles of the present invention should be included within the protection scope of the claims of the present invention.

Claims

1. A method for growing nanofibers within the pore walls of a porous silicon carbide ceramic membrane carrier, characterized in that, The specific preparation steps are as follows: (1) Weigh out the aluminum sol solution and place it in a beaker; (2) Weigh out silicon carbide powder and slowly pour it into aluminum sol solution, stirring evenly with a glass rod; (3) The mixed slurry obtained in step (2) is placed in an oven and dried to obtain pretreated silicon carbide particles; (4) Pour the pretreated silicon carbide particles from step (3) into a mortar, add activated carbon powder to obtain a mixed powder, and grind until there are no lumps; wherein, the mass of aluminum sol is 1~13 wt.% of the mass of the mixed powder, and the mass of silicon carbide powder is 72~85 wt.% of the mass of the mixed powder; (5) The powder obtained in step (4) is pressed into a sheet or strip shape by a tablet press under a pressure of 8 MPa. (6) Place the billet in a muffle furnace for sintering, heat it to 1250~1450 ℃, hold it for 4 h, and finally cool it to room temperature with the furnace. (7) Place the sintered sample in an alkaline solution for alkaline etching; the alkaline solution is NaOH with a concentration of 10 wt.% and an alkaline etching time of 0.5 to 1 h.

2. The method for growing nanofibers within the pore walls of a porous silicon carbide ceramic membrane carrier according to claim 1, characterized in that: In step (2), the silicon carbide powder needs to be added to the aluminum sol solution while stirring.

3. The method for growing nanofibers within the pore walls of a porous silicon carbide ceramic membrane carrier according to claim 1, characterized in that: In step (3), the mixed slurry needs to be dried at 120 ℃, and the drying time needs to be controlled within 0.5~1 h.

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