A method for preparing a silicon carbide film based on a difference in wettability to construct a hollow interface

Abstract

The application discloses a preparation method of a silicon carbide membrane based on wettability difference induced hollow interface construction. The method introduces a carbon powder pore former with wettability difference from silicon carbide particles into a green support body, realizes slurry preferential spreading in the hydrophilic region and local retention in the hydrophobic region during the dip-coating process, and then induces the formation of an ordered hollow channel structure at the membrane-support interface. During the co-sintering process, the structure can effectively inhibit the penetration of the membrane slurry into the large pores of the support body, enhance the integrity of the membrane layer, and significantly reduce the interface mass transfer resistance. The obtained membrane layer has adjustable pore size and highly continuous surface structure, significantly improving the gas flux and dust filtration performance compared with traditional membranes, while shortening the preparation period and reducing the sintering energy consumption. The method is suitable for the construction of various asymmetric membrane structures, has good scalability and process compatibility, and provides a new way for the large-scale preparation of low-cost and high-performance silicon carbide membranes.

Description

Technical Field

[0001] This invention relates to a method for preparing silicon carbide films with hollow interfaces based on wettability differences, belonging to the field of ceramic film material preparation. Background Technology

[0002] High-efficiency high-temperature flue gas purification is a key step in achieving energy conservation and pollutant emission reduction, particularly suitable for energy-intensive industries such as chemical, petrochemical, and metallurgical processing. It can achieve both fine particulate matter removal and waste heat recovery, possessing significant economic and environmental implications. Among numerous gas separation membrane materials, silicon carbide (SiC) has become a promising choice for industrial gas-solid separation due to its excellent thermal stability, chemical inertness, and mechanical strength. Despite the superior performance of silicon carbide membranes, their practical engineering applications are still constrained by both high manufacturing costs and low gas flux. Especially in high-flow-rate flue gas treatment scenarios, low membrane flux significantly increases equipment size and investment costs, limiting its large-scale promotion.

[0003] Currently, traditional SiC membrane structures often employ multilayer configurations with three or more layers to balance separation accuracy while suppressing slurry infiltration into the support structure. However, this strategy requires multiple dip-coating and sintering processes, which are not only complex and time-consuming but also energy-intensive, leading to increased manufacturing costs. Furthermore, multilayer structures introduce more membrane-membrane or membrane-support interfaces, increasing the risk of slurry infiltration into lower layers, thereby exacerbating interfacial resistance and reducing the overall membrane permeability. Existing research indicates that up to 40% of the total pressure drop in ceramic membranes originates from the interfacial region between the membrane layer and the support [Ceram. Int., 2021, 47(9): 12357–12365]. Therefore, interfacial structure design has become one of the key directions for improving membrane flux and overall performance.

[0004] A relatively effective strategy is to construct SiC membrane structures without intermediate layers, that is, to directly deposit the membrane layer onto the surface of a macroporous support through a single dip-coating process. This method reduces the number of process steps and lowers costs to some extent, but problems such as slurry penetration, membrane sintering defects, and insufficient membrane-substrate bonding still exist. To alleviate these problems, some literature has attempted to prefill the support with organic / inorganic barrier agents such as polyvinyl alcohol (PVA) and butyraldehyde resin (PVB) to seal macropores and reduce the risk of slurry seepage [J. Membr. Sci., 2024, 695, 122496]; however, the tight bonding between the membrane layer and the support skeleton still results in significant interfacial resistance, which is difficult to overcome fundamentally using conventional methods. To further optimize the interface structure, researchers have proposed constructing a porous intermediate layer [Sep. Purif. Technol., 2023, 305: 122400] or introducing sacrificial pore-forming agents [Chinese Invention Patent CN201910668952.3]. However, these methods often introduce randomly distributed or excessively large interlayer voids, which are detrimental to interfacial bonding. Therefore, there is an urgent need to construct interface cavity structures with clear directionality and controllable dimensions to effectively reduce interfacial resistance while ensuring bonding strength.

[0005] In contrast, directly co-sintering the film onto the green support is a more efficient construction method [Sep.Purif. Technol.]. [2024;338:126441]. This method eliminates the need for intermediate layers and multiple sintering steps, creating local cavities at the membrane-support interface through the burn-off of pore-forming agents. This oriented hollow structure provides preferential gas channels, significantly alleviating interfacial mass transfer limitations while reducing local stress, thus helping to maintain membrane structural integrity and preserving excellent interfacial bonding performance while improving membrane flux.

[0006] This invention proposes a novel method for constructing asymmetric silicon carbide membranes based on a wettability-induced strategy. The core of this method lies in achieving directional construction of hollow interfacial channels through differential wettability. Specifically, a crosslinking system is constructed using polyvinyl alcohol (PVA) and citric acid (CA), resulting in heterogeneous wettability on the support surface. This enhances the selectivity of slurry distribution and improves the mechanical strength of the green body. During the dip-coating process, the wettability difference between SiC particles and activated carbon pore-forming agents is utilized to achieve preferential spreading of the slurry in hydrophilic regions and localized hindrance in hydrophobic regions, thereby inducing the formation of directional hollow interfacial structures and effectively reducing interfacial resistance. Combined with a one-step co-firing process, this method offers advantages such as low cost, structural stability, and ease of scale-up, providing a high-performance, scalable new solution for industrial gas-solid separation under high-temperature conditions. Summary of the Invention

[0007] This invention provides a hollow interface construction method based on wettability difference. By introducing regions with significant wettability differences between the surface and capillary structure in the silicon carbide support green body, the membrane slurry is induced to undergo orderly redistribution during the film formation process, forming a directional cavity structure at the interface between the membrane layer and the support. This effectively reduces the interfacial mass transfer resistance and improves the flux performance and structural stability of the membrane material under high-temperature gas-solid separation conditions.

[0008] The technical solution of this invention is as follows: A method for preparing silicon carbide films with hollow interfaces based on wettability differences, the specific steps of which are as follows: Preparation of the support green body: Polyvinyl alcohol (PVA) and citric acid (CA) are uniformly mixed at a set ratio and a set rotation speed to form a green body binder; silicon carbide powder is mixed uniformly with sintering aid, activated carbon pore-forming agent and the binder, and then the support green body is prepared by cold isostatic pressing; heat treatment is carried out at a set crosslinking temperature and crosslinking time to obtain a structurally stable support green body; Preparation of membrane slurry and film formation: Silicon carbide film powder and sintering aid are dispersed in an aqueous solution of methyl cellulose (MC) and a defoamer is added. After adding an appropriate amount of defoamer, the film is subjected to vacuum stirring and degassing treatment to obtain a stable membrane slurry. The membrane slurry is uniformly coated onto the surface of the green support under set dip coating parameters (dip rate, pull-out rate, holding time). After drying and high-temperature co-sintering, a silicon carbide ceramic membrane with asymmetric structure and hollow interface characteristics is obtained.

[0009] Preferably, the adhesive is a water-soluble system prepared with pure water as the solvent, containing 5–25 wt% PVA and 0–20 wt% CA, with a crosslinking temperature of 25–170 ℃ and a crosslinking time of 4–24 h.

[0010] Preferably, the average particle size of the silicon carbide powder in the slurry is 10-40 μm, and the proportion is 30 wt%.

[0011] The amount of MC added to the membrane slurry is preferably 0.25–1.75 wt%, and more preferably 1.0 wt%.

[0012] The preferred dip-coating parameters are an immersion rate of 500-2000 μm / s, a pull-out rate of 125-2000 μm / s, and a dip-coating time of 20-160 s.

[0013] The preferred co-sintering temperature is 1250-1450 ℃, and the holding time is 1-4 h.

[0014] Compared with the prior art, the beneficial effects of the present invention are as follows: The asymmetric silicon carbide ceramic membrane prepared by this invention possesses a directional interfacial hollow channel structure, effectively overcoming the trade-off between separation accuracy and flux caused by the increase in the number of traditional membrane layers. Utilizing the heterogeneous wettability of the green body structure, selective spreading and localized retardation of the membrane slurry are induced during film formation, achieving an ordered particle distribution and retaining cavities in the carbon powder region. During sintering, this cavity structure further develops, significantly reducing the membrane-support interface contact area, thereby lowering mass transfer resistance. Furthermore, under high MC content control, the membrane structure forms a complete and dense top layer and a low-resistance intermediate cavity transition layer, inhibiting slurry penetration into the support. Compared to traditional multilayer structures, this method, combined with a one-step co-firing process, significantly shortens the preparation cycle, reduces energy and material consumption, and possesses advantages such as high flux, low cost, and easy scale-up, making it suitable for large-scale application in industrial scenarios such as high-temperature flue gas filtration, particle capture, and heat recovery. Attached Figure Description

[0015] Figure 1 This is an electron microscope image of the surface of the green support prepared in Example 3.

[0016] Figure 2 This is an electron microscope image of the surface of the ceramic film prepared in Example 3.

[0017] Figure 3 This is an electron microscope image of the cross-section of the ceramic film prepared in Example 3.

[0018] Figure 4 This is a pore size distribution diagram of the ceramic membrane prepared in Example 3.

[0019] Figure 5 This refers to the air permeability of the ceramic membrane prepared in Example 3.

[0020] Figure 6 This is a comparison of the air permeability of the ceramic membrane prepared in Example 3 with that of other studies. Detailed Implementation Example 1

[0021] A support was prepared using PVA and CA as the bonding system, with a ratio of 5 wt% PVA and 0 wt% CA. The mixture was stirred at 150 rpm for 2 h. 200 μm SiC, CaO, ZrO2, 3Al2O3⋅2SiO2, activated carbon pore-forming agent, and binder were uniformly mixed at a mass ratio of 49:0.6:0.6:1.2:9:4.5. The mixture was then cold isostatically pressed at 10 MPa and allowed to stand at 25 ℃ for 12 h to crosslink and obtain a support green body. A film powder was prepared by mixing 40 μm silicon carbide with CaO, ZrO2, and mullite whiskers at a mass ratio of 96:1:1:2. This powder was then mixed with 0.25 wt% MC aqueous solution at a ratio of 3:7 and stirred at 150 rpm for degassing for 4 h (vacuum degree −0.1 MPa) to form a homogeneous film slurry. The support was fixed in the dip coating device, and the immersion rate was set to 3000 μm / s, held for 10s, and the lifting rate was set to 3000 μm / s for coating. After drying at room temperature for 12 h, it was sintered at 1450 ℃ for 4 h and then cooled naturally.

[0022] Testing revealed that the green strength of the obtained silicon carbide support was 1.19 MPa, the average pore size of the silicon carbide film was 14.4 μm, and the gas permeation flux was 676.2 m³. 3 ·m -2 ·h -1 ·kPa. Example 2

[0023] PVA (10 wt%) and CA (5 wt%) were used as binders, and the mixture was stirred at 300 rpm for 2 h. The pre-sintering crosslinking heat treatment temperature was 90 ℃ for 4 h. 20 μm SiC was used as the film-forming powder, with the ratio of SiC to sintering aids remaining constant. MC was added at 0.5 wt%, the degassing time was 6 h, and the dip-coating parameters were: immersion 2000 μm / s, holding for 40 s, pull-out 500 μm / s, drying for 2 h, and sintering at 1450 ℃ for 1 h. The resulting silicon carbide support green body strength was 2.48 MPa, the average pore size of the silicon carbide film was 9.70 μm, and the gas permeation flux was 553.5 m³. 3 ·m -2 ·h -1 ·kPa. Example 3

[0024] Using 15 wt% PVA and 10 wt% CA as binders, the mixture was stirred for 4 h (300 rpm). The green body underwent crosslinking heat treatment at 110℃ for 12 h. The film-forming powder was 20 μm SiC with 1.0 wt% MC content, and degassing was performed for 12 h. Dip-coating was performed with an immersion speed of 2000 μm / s, a holding time of 20 s, a pull-out speed of 125 μm / s, followed by drying for 4 h and sintering at 1450℃ for 4 h. The resulting silicon carbide support green body had a strength of 4.39 MPa, an average pore size of 7.5 μm in the silicon carbide film, and a gas permeation flux of 521.8 m³. 3 ·m -2 ·h -1 ·kPa.

[0025] Figure 1 This is an electron microscope image of the surface of the green support prepared in Example 3. Figure 2 This is an electron microscope image of the surface of the ceramic film prepared in Example 3. Figure 3 This is an electron microscope image of the cross-section of the ceramic film prepared in Example 3. Figure 4 This is a pore size distribution diagram of the ceramic membrane prepared in Example 3. Figure 5 This refers to the air permeability of the ceramic membrane prepared in Example 3. Figure 6 This is a comparison of the air permeability of the ceramic membrane prepared in Example 3 with that of other studies. Example 4

[0026] Using 25wt% PVA and 20wt% CA as binders, the green carbide was cross-linked and heat-treated at 170 °C for 24 h. The film powder had a particle size of 10 μm, an MC concentration of 1.5 wt%, a rotation speed of 150 rpm, and a degassing time of 12 h. The dip-coating parameters were: immersion speed of 2000 μm / s, holding time of 20 s, and a pulling speed of 31.25 μm / s. Drying was carried out for 4 h, and sintering was performed at 1250 °C for 4 h. The resulting silicon carbide support green body had a strength of 2.24 MPa, an average pore size of 4.6 μm, and a gas permeation flux of 291.0 m³. 3 ·m -2 ·h -1 ·kPa.

Claims

1. A method for preparing silicon carbide films with hollow interfaces based on wettability differences, characterized in that, The specific steps are as follows: (1) Preparation of support green body: Polyvinyl alcohol and citric acid are mixed in proportion to prepare binder. Silicon carbide support powder, sintering aid, carbon powder pore-forming agent and binder are mixed evenly. After cold isostatic pressing, heat treatment is carried out at the set crosslinking temperature and crosslinking time to obtain a structurally stable support green body. The binder is a water-soluble system prepared with pure water as solvent, containing 5-25 wt% polyvinyl alcohol and 5-20 wt% citric acid, with a crosslinking temperature of 25-170 ℃ and a crosslinking time of 4-24 h. (2) Preparation of film slurry and film formation: Silicon carbide powder with a certain solid content and sintering aid are added to a methylcellulose aqueous solution of a certain concentration, mixed evenly, and then an appropriate amount of defoamer is added. The mixture is stirred and stirred to disperse it fully. Then, vacuum degassing is performed to obtain a homogeneous film slurry. The film slurry is uniformly dipped onto the surface of the support green body. During the dip-coating process, the dip-in rate is 500-2000 μm / s, the pull-out rate is 31.25-8000 μm / s, and the dip-coating time is 20-160 s. After the drying process, high-temperature co-sintering is performed at a temperature of 1250-1450 ℃ to obtain an asymmetric silicon carbide film with hollow interface characteristics.

2. The method for preparing a silicon carbide film based on wettability differences to construct a hollow interface according to claim 1, characterized in that, The average particle size of the silicon carbide powder in the slurry is 10-40 μm, and the amount added is 20-40 wt%.

3. The method for preparing a silicon carbide film based on wettability differences to construct a hollow interface according to claim 1, characterized in that, The amount of methylcellulose added to the membrane slurry is 0.25–1.75 wt%.

4. The method for preparing a silicon carbide film based on wettability differences to construct a hollow interface according to claim 1, characterized in that, The holding time for the co-sintering process is 1-4 h.

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