A silicon carbide ceramic membrane and its preparation method

Abstract

This invention belongs to the field of ceramic filtration membrane technology, and particularly relates to a silicon carbide ceramic membrane and its preparation method, including the following steps: (1) preparation of a support layer blank; (2) primary vapor deposition of the support layer blank; (3) secondary vapor deposition of the support layer blank; (4) post-treatment of the support layer blank; (5) preparation of a separation layer; (6) surface hydrophobic modification treatment. The silicon carbide ceramic membrane prepared by this invention has the advantages of high throughput, high filtration and separation effect, good mechanical strength and stability, and good surface hydrophobicity and is not easily contaminated.

Description

Technical Field

[0001] This invention belongs to the field of ceramic filtration membrane technology, and particularly relates to a silicon carbide ceramic membrane and its preparation method. Background Technology

[0002] Traditional silicon carbide ceramic filter membranes typically employ a sandwich structure, consisting of a support layer, an intermediate layer, and a separation layer arranged sequentially. The support layer is usually formed by stacking and firing layers of large-particle raw materials, resulting in large pores between the particles and exhibiting high strength and porosity. In silicon carbide ceramic filter membranes, the support layer acts as the membrane carrier, primarily ensuring the membrane's mechanical strength and providing structural support. It effectively supports and fixes the membrane layer, maintaining a stable structure and performance during filtration. Simultaneously, the high porosity and large pore size of the support layer help reduce filtration resistance, increase filtration flux, and thus improve filtration efficiency. The separation layer is the thinnest layer in the silicon carbide ceramic filter membrane, typically tens of micrometers thick, and has the smallest pores. It can screen and separate substances, acting as a filtration sieve. Therefore, the performance of the separation layer directly determines the filtration precision and efficiency of the silicon carbide ceramic filter membrane. However, since the pore size of the support layer can typically be at least 25 times larger than that of the separation layer particles, an intermediate layer is usually placed between the support layer and the separation layer in existing processes to prevent the separation layer particles from penetrating into the support layer during the preparation of the separation layer. At the same time, since the transition layer covers the support layer and its pore size is between that of the support layer and the separation layer, it can form an effective pore size transition. Therefore, the transition layer also acts as a bridge between the support layer and the separation layer. It can effectively support and fix the separation layer, improve the structural stability of the silicon carbide ceramic filter membrane, and protect the separation layer from damage.

[0003] However, the presence of the intermediate layer objectively reduces the flux of the silicon carbide ceramic filter membrane. Furthermore, the difference in micropore size between the support layer, intermediate layer, and separation layer in traditional processes is small, typically varying by a factor of 1 to 5, further contributing to the low flux of the filter membrane and making improvement difficult. Moreover, as... Figure 1As shown, the traditional process for preparing silicon carbide films requires at least three sintering processes, making the process relatively complex and costly. Furthermore, the multiple coating processes result in low yield and low throughput. In addition, after each high-temperature sintering coating in the traditional process (typically at 2000-2400℃ under inert gas protection such as argon), a high-temperature oxidation process (at 700-1200℃ under air circulation) is required to remove residual carbon from the high-temperature sintering. This carbon originates from the preform or coating slurry containing binders, dispersants, and other organic matter. If the carbon is not removed, because carbon is hydrophobic, the solvent / water in the slurry has difficulty entering the carrier pores through capillary force during coating, thus preventing the final formation of the coating film. Therefore, in the traditional process, oxidation treatment is necessary after high-temperature sintering. After oxidation, the removal of carbon from the carrier makes the surface hydrophilic and the pore size relatively larger. This facilitates the entry of the slurry solvent / water into the carrier pores through capillary force to eventually form a coating film. However, this requires the coating particles in the coating slurry to be large enough so that they do not enter the carrier due to capillary force.

[0004] To address the aforementioned issues, Chinese Patent Publication No. CN113121241B discloses a high-throughput silicon carbide ceramic filter membrane and its preparation method, which employs a single-stage direct coating separation layer process on a carrier, such as... Figure 2 As shown, after the carrier is sintered, a separation layer is directly coated, and then decarburization is performed after the separation layer is sintered. By optimizing the sintering process and the film-forming solution formulation, it is possible to prevent fine silicon carbide particles from entering the micropores of the carrier during film formation due to capillary action. This allows for the direct coating of a separation layer with an average pore size of less than 0.2 μm onto a silicon carbide carrier with an average pore size of more than 10 μm, effectively preventing fine silicon carbide particles from entering the micropores of the carrier during coating. This avoids the shortcomings of traditional ceramic membrane preparation processes that require multiple coatings (at least two coatings and three sinterings), thereby reducing production costs and improving product yield. Due to the removal of the intermediate layer, the flux of ceramic membranes with the same pore size can be significantly increased.

[0005] However, research has revealed the following defects in this high-flux silicon carbide ceramic filter membrane:

[0006] First, after the separation layer is oxidized, the pore size (average pore size of 10 μm or more) of the silicon carbide carrier, i.e. the support layer, is much larger than the particle size of the silicon carbide powder in the slurry used for the separation layer (particle size of about 0.1~6 μm). It is difficult to form a dense and uniform separation layer membrane structure during the coating process, which easily leads to defects such as voids and cracks inside the separation layer. However, during the filtration process, the separation layer membrane also needs to withstand a certain pressure and stress. Defects are prone to become stress concentration points, leading to membrane rupture or failure. In addition, due to the mismatch between pore size and particle size, the support layer carrier cannot provide effective support for the separation layer membrane, making the separation layer membrane prone to rupture and collapse during use. As a result, the mechanical strength and stability of the high-flux silicon carbide ceramic filter membrane are poor.

[0007] Secondly, during the preparation of the support layer carrier, the amount of carbon remaining after high-temperature sintering is small and the particle size is fine, and a considerable portion of it adheres to the pores inside the support layer. Therefore, it is difficult for the carbon remaining after high-temperature sintering of the carrier to effectively seal the pores of the support layer. This is also why the Chinese patent with publication number CN113121241B had to optimize the membrane liquid formulation so that the particles of the membrane slurry and the surface of the support layer carrier carry the same charge. Although this operation method can utilize the repulsion effect of the same charge between the two to a certain extent to inhibit the entry of fine particles into the micropores of the carrier due to capillary action during coating, the effect is still unsatisfactory. It will also lead to a weakening of the bonding between the support layer and the separation layer, and defects such as cracking, collapse, and detachment of the separation layer.

[0008] Third, this high-flux silicon carbide ceramic filter membrane has poor surface hydrophobicity. In some applications, such as oil-water separation and industrial wastewater treatment, pollutants such as organic matter and microorganisms can easily adhere to and grow on the membrane surface, leading to membrane fouling. Summary of the Invention

[0009] The purpose of this invention is to address the aforementioned technical problems by providing a silicon carbide ceramic membrane with high throughput, high filtration and separation efficiency, good mechanical strength and stability, excellent surface hydrophobicity, and resistance to contamination, as well as a method for its preparation.

[0010] In view of this, the present invention provides a method for preparing a silicon carbide ceramic film, comprising the following steps:

[0011] (1) Preparation of support layer blank: Mix the raw materials of support layer blank and stir evenly. Then put the mixture into an extrusion molding machine and extrude to obtain a wet blank of support layer. Then dry and sinter the wet blank of support layer to obtain support layer blank.

[0012] (2) Primary vapor deposition of the support layer preform: The support layer preform obtained in step (1) is placed in a vapor deposition apparatus, and silicon vapor is directed into the support layer preform from the feed side under the action of a carrier gas, and then discharged from the discharge side of the support layer preform.

[0013] (3) Secondary vapor deposition of the support layer blank: The support layer blank obtained in step (2) is placed in a vapor deposition apparatus, and silicon carbide vapor is directed into the support layer blank from the feed side under the action of the carrier gas, and then discharged from the discharge side of the support layer blank.

[0014] (4) Post-processing of the support layer blank: Place the support layer blank in a sealed container, pressurize the pressure in the sealed container to 0.5~3MPa using an air pressurization device, maintain the pressure for 1~3min, then open the discharge valve to reduce the pressure in the sealed container to normal pressure at a rate of 0.03~0.1MPa / min; repeat the above pressurization, pressure maintenance and pressure reduction process 3~5 times, then open the sealed container and take out the support layer blank;

[0015] (5) Preparation of the separation layer: The raw materials of the separation layer are mixed and prepared into a film slurry. The film slurry is then coated on the feed side surface of the support layer blank to form a separation layer film and a wet blank of silicon carbide ceramic film is obtained. The wet blank of silicon carbide ceramic film is then dried, sintered and oxidized to obtain the original film of silicon carbide ceramic film.

[0016] (6) Surface hydrophobic modification treatment: Mix the raw materials of the surface hydrophobic modifier and prepare a surface hydrophobic modifier mixture. Then, the silicon carbide ceramic film obtained in step (5) is dried in a vacuum at a temperature of 100~200℃ for 10~30h. After being fully immersed in the surface hydrophobic modifier mixture, it is taken out and kept at 500~800℃ for 0.5~3h to obtain the silicon carbide ceramic film of the present invention.

[0017] Furthermore, by weight, the raw materials for the support layer blank include:

[0018] Silicon carbide powder I: 30-50 parts;

[0019] Silicon carbide powder II, 10-20 parts;

[0020] 8-15 parts carbon black;

[0021] 5-10 parts of silicon powder;

[0022] 1-5 parts of dispersant;

[0023] Plasticizer 0.5-3 parts;

[0024] Sintering aid 0.5-10 parts;

[0025] 10-25 parts water.

[0026] Furthermore, the average particle size of silicon carbide powder I and silicon carbide powder II is 5~20 μm, the density of silicon carbide powder II is 30%~60% of that of silicon carbide powder I, the average particle size of carbon black is 1~5 μm, and the average particle size of silicon powder is 0.1~1 μm.

[0027] Furthermore, in step (1), the process of drying and sintering the wet blank of the support layer is as follows:

[0028] After drying the wet blank of the support layer at 30~50℃ for 20~30h, the green blank of the support layer is obtained. Then, the green blank of the support layer is sintered at high temperature under an argon protective atmosphere. The high temperature sintering process is as follows: first, the temperature is raised to 600~800℃ at a heating rate of 60~100℃ / h and held at this temperature for 1~2h for debinding treatment. Then, the temperature is raised to 2000~2500℃ at a heating rate of 100~200℃ / h and held at this temperature for 3~6h. After that, the blank is cooled to room temperature in the furnace to obtain the support layer blank.

[0029] Furthermore, in step (2), the primary vapor deposition process of the support layer blank is as follows:

[0030] The support layer preform obtained in step (1) is placed in a chemical vapor deposition apparatus. Then, silicon powder is evaporated to form silicon vapor, and the silicon vapor is directed into the support layer preform from the feed side by a carrier gas and then discharged from the discharge side of the support layer preform. The parameters for the first vapor deposition are: the silicon vapor is drawn through the support layer preform at a rate of 0.5~2g / min using negative pressure suction, and the carrier gas flows through the support layer preform at a rate of 50~100mL / min. The temperature of the first vapor deposition is 1300~1500℃.

[0031] Furthermore, after step (1) and before step (2), the support layer blank is subjected to carbon deposition treatment, as follows:

[0032] The support layer preform prepared in step (1) is placed in a chemical vapor deposition furnace for the deposition of pyrolytic carbon. The carbon source gas is propane, propylene or butene. The carbon deposition process is carried out under negative pressure suction environment. The flow rate of the carbon source gas is 10~20 mL / min. The volume ratio of carbon source gas to dilution gas is 1:1~1:3. The deposition temperature is 500~800℃. The deposition time is 10~30 min. The carbon source gas flows into the support layer preform from the feed side and then exits from the discharge side of the support layer preform.

[0033] Furthermore, in step (3), the secondary vapor deposition process of the support layer blank is as follows:

[0034] The support layer preform obtained in step (2) is placed in a vapor deposition apparatus. Using negative pressure suction, silicon carbide vapor is directed into the support layer preform from the feed side under the action of the carrier gas, and then discharged from the discharge side of the support layer preform. Silicon carbide particles are deposited on the surface of the support layer preform to obtain a support layer preform after secondary vapor deposition treatment. The parameters of the secondary vapor deposition are: deposition temperature of 1000-1300℃, growth gas source of trichloromethylsilane gas, volume ratio of growth gas source to carrier gas of 1:1-1:3, flow rate of growth gas source of 10-30mL / min, and secondary vapor deposition treatment time of 30-60min.

[0035] Furthermore, in step (5), the raw materials of the separation layer, by weight, include:

[0036] Silicon carbide powder III, 5-10 parts;

[0037] Silicon carbide powder IV, 10-15 parts;

[0038] 1-5 parts adhesive;

[0039] 4-9 parts of dispersant;

[0040] 70-90 parts water;

[0041] The average particle size of silicon carbide powder III is 3 to 5 times that of silicon carbide powder IV, and the average particle size of silicon carbide powder III is 1 to 3 μm.

[0042] Furthermore, by weight, the surface hydrophobic modifier mixture comprises:

[0043] 10-20 parts of polydimethylsiloxane;

[0044] 30-50 parts organic solvent;

[0045] 3-5 parts linear silicone oil;

[0046] 5-8 parts of amino silicone oil;

[0047] 1-3 parts epoxy silicone oil;

[0048] Surfactant 0.3~1 part.

[0049] The beneficial effects of the present invention are: the silicon carbide ceramic membrane prepared by the present invention has the advantages of high throughput, high filtration and separation effect, good mechanical strength and stability, and good surface hydrophobicity and is not easily contaminated. Attached Figure Description

[0050] Figure 1This is a schematic diagram of the process for preparing ceramic filter membranes using the three-step sintering and oxidation method employed in existing traditional processes;

[0051] Figure 2 This is a schematic diagram of the process for preparing ceramic filter membranes using the single-layer separation process adopted in Chinese patent publication (announcement) number CN113121241B;

[0052] Figure 3 This is a schematic diagram of the preparation process of the silicon carbide ceramic film according to the present invention;

[0053] Figure 4 This is a schematic diagram of the A, B, C, and D partitions of the silicon carbide ceramic membrane described in this invention during detection. Detailed Implementation

[0054] The technical solutions of the embodiments of this application will be clearly described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this application. All other embodiments obtained by those skilled in the art based on the embodiments of this application are within the scope of protection of this application.

[0055] In the description of this application, it should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the exemplary embodiments according to this application. For ease of description, techniques, methods, and devices known to those skilled in the art may not be discussed in detail, but where appropriate, such techniques, methods, and devices should be considered part of the specification. In all examples shown and discussed herein, any specific values ​​should be interpreted as merely exemplary and not as limitations. Therefore, other examples of exemplary embodiments may have different values. It should be noted that similar reference numerals and letters in the following figures denote similar items, and therefore, once an item is defined in one figure, it need not be further discussed in subsequent figures.

[0056] It should be noted that, in this application, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes that element. Furthermore, it should be noted that the scope of the methods and apparatuses in the embodiments of this application is not limited to performing functions in the order shown or discussed, but may also include performing functions substantially simultaneously or in the reverse order, depending on the functions involved. For example, the described methods may be performed in a different order than described, and various steps may be added, omitted, or combined. Additionally, features described with reference to certain examples may be combined in other examples.

[0057] A method for preparing a silicon carbide ceramic film includes the following steps:

[0058] (1) Preparation of support layer blank: Mix the raw materials of support layer blank and stir evenly. Then put the mixture into an extrusion molding machine and extrude to obtain a wet blank of support layer. Then dry and sinter the wet blank of support layer to obtain support layer blank.

[0059] (2) Primary vapor deposition of the support layer preform: The support layer preform obtained in step (1) is placed in a vapor deposition apparatus, and silicon vapor is directed into the support layer preform from the feed side under the action of a carrier gas, and then discharged from the discharge side of the support layer preform.

[0060] (3) Secondary vapor deposition of the support layer blank: The support layer blank obtained in step (2) is placed in a vapor deposition apparatus, and silicon carbide vapor is directed into the support layer blank from the feed side under the action of the carrier gas, and then discharged from the discharge side of the support layer blank.

[0061] (4) Post-processing of the support layer blank: Place the support layer blank in a sealed container, pressurize the pressure in the sealed container to 0.5~3MPa using an air pressurization device, maintain the pressure for 1~3min, then open the discharge valve to reduce the pressure in the sealed container to normal pressure at a rate of 0.03~0.1MPa / min; repeat the above pressurization, pressure maintenance and pressure reduction process 3~5 times, then open the sealed container and take out the support layer blank;

[0062] (5) Preparation of the separation layer: The raw materials of the separation layer are mixed and prepared into a film slurry. The film slurry is then coated on the surface of the support layer blank to form a separation layer film. The wet blank of the silicon carbide ceramic film is then dried, sintered and oxidized to obtain the original silicon carbide ceramic film.

[0063] (6) Surface hydrophobic modification treatment: Mix the raw materials of the surface hydrophobic modifier and prepare a surface hydrophobic modifier mixture. Then, the silicon carbide ceramic film obtained in step (5) is dried in a vacuum at a temperature of 100~200℃ for 10~30h. After being fully immersed in the surface hydrophobic modifier mixture, it is taken out and kept at 500~800℃ for 0.5~3h to obtain the silicon carbide ceramic film of the present invention.

[0064] Preferably, the raw materials for the support layer blank, by weight, include:

[0065] Silicon carbide powder I: 30-50 parts;

[0066] Silicon carbide powder II, 10-20 parts;

[0067] 8-15 parts carbon black;

[0068] 5-10 parts of silicon powder;

[0069] 1-5 parts of dispersant;

[0070] Plasticizer 0.5-3 parts;

[0071] Sintering aid 0.5-10 parts;

[0072] 10-25 parts water.

[0073] More preferably, the average particle size of silicon carbide powder I and silicon carbide powder II is 5~20 μm, wherein silicon carbide powder I is spherical solid silicon carbide particles or porous silicon carbide particles, and silicon carbide powder II is porous silicon carbide particles with open channels, i.e., three-dimensional interconnected channels. The porosity of silicon carbide powder II can be adjusted as needed, specifically such that, for the same volume, the weight of silicon carbide powder II is 30%~60% of the weight of silicon carbide powder I, that is, the density of silicon carbide powder II is 30%~60% of that of silicon carbide powder I.

[0074] As some examples of the present invention, in the same silicon carbide ceramic film, the average particle size of silicon carbide powder I and silicon carbide powder II may be the same or different.

[0075] Preferably, in the same silicon carbide ceramic film, the average particle size of silicon carbide powder I and silicon carbide powder II is close, or the average particle size of silicon carbide powder II is slightly larger than the average particle size of silicon carbide powder I, such as the average particle size of silicon carbide powder II being 1.1 to 1.3 times the average particle size of silicon carbide powder I.

[0076] In the raw materials of the support layer blank described in this invention, due to the use of silicon carbide powder I with a high density and silicon carbide powder II with a porous structure, the silicon carbide powder I with a high density can provide strong mechanical properties, while the silicon carbide powder II can provide high porosity, so that the support layer blank has high throughput and high filtration efficiency.

[0077] Furthermore, by adding silicon carbide powder II to the support layer blank, in the subsequent primary and secondary vapor deposition processes, compared with the gaps between silicon carbide particles, silicon carbide powder II has more and smaller vapor channels and is more likely to trap vapor deposits. It can quickly trap vapor deposits through the subsequent primary and secondary vapor deposition processes, thereby achieving rapid reduction of pore size. In this way, it can lay the foundation for obtaining a support layer structure with rapid reduction of feed-side pore size but small overall throughput reduction through primary and secondary vapor deposition.

[0078] As some examples of the present invention, the dispersant is selected from one or more of nitric acid, polyammonium methacrylate, polyvinyl alcohol, and polyethylene glycol.

[0079] As some examples of the present invention, the plasticizer is selected from one or more of cellulose, polyvinyl alcohol, polysaccharides, starch, and dextrin.

[0080] As some examples of the present invention, the sintering aid is selected from one or more of zirconium oxide, alumina, titanium dioxide, silicon dioxide, calcium carbonate, and barium titanate.

[0081] Preferably, the carbon black has an average particle size of 1~5 μm, and the silicon powder has an average particle size of 0.1~1 μm.

[0082] In the support layer, since the particle size of carbon black and silicon powder is much smaller than the average particle size of silicon carbide powder I and silicon carbide powder II, after stirring, mixing and extrusion molding, carbon black and silicon powder will fill the gaps between large silicon carbide particles or coat the surface of large silicon carbide particles. They can react during the subsequent high-temperature sintering process to generate silicon carbide microparticles that are bonded to the gaps between large silicon carbide particles or coat the surface of large silicon carbide particles, thereby further improving the physical strength of the support layer.

[0083] Furthermore, in step (1), the process of drying and sintering the wet blank of the support layer is as follows:

[0084] After drying the wet blank of the support layer at 30~50℃ for 20~30h, the green blank of the support layer is obtained. Then, the green blank of the support layer is sintered at high temperature under an argon protective atmosphere. The high temperature sintering process is as follows: first, the temperature is raised to 600~800℃ at a heating rate of 60~100℃ / h and held at this temperature for 1~2h for debinding treatment. Then, the temperature is raised to 2000~2500℃ at a heating rate of 100~200℃ / h and held at this temperature for 3~6h. After that, the blank is cooled to room temperature in the furnace to obtain the support layer blank.

[0085] Furthermore, in step (2), the primary vapor deposition process of the support layer blank is as follows:

[0086] The support layer preform obtained in step (1) is placed in a chemical vapor deposition apparatus. Then, silicon powder is evaporated to form silicon vapor, and the silicon vapor is directed into the support layer preform from the feed side by a carrier gas and then discharged from the discharge side of the support layer preform. The parameters for the first vapor deposition are: the silicon vapor is drawn through the support layer preform at a rate of 0.5~2g / min using negative pressure suction, and the carrier gas flows through the support layer preform at a rate of 50~100mL / min. The temperature of the first vapor deposition is 1300~1500℃. The time of the first vapor deposition is preferably such that most of the carbon remaining in the support layer preform can be converted into silicon carbide, such as such that 50~80% of the carbon remaining in the support layer preform can be converted into silicon carbide.

[0087] As some examples of the present invention, in step (2), the carrier gas is selected from one or more of nitrogen, argon, hydrogen, etc.

[0088] In step (2), silicon carbide can be generated directly in situ by reacting silicon vapor and residual carbon on the surface of the support layer blank. This eliminates the adverse effects of the hydrophobicity of carbon on the subsequent coating process. At the same time, a layer of silicon carbide can be formed on the surface of the support layer blank. These silicon carbide particles formed by one vapor deposition can block the pores on the surface of the support layer blank, especially on the feed side, thereby reducing the probability of small silicon carbide particles in the separation layer entering the carrier pores and maintaining its throughput at a high level.

[0089] Furthermore, after step (1) and before step (2), the support layer blank can be subjected to carbon deposition treatment.

[0090] Specifically, the carbon deposition process for the support layer preform is as follows:

[0091] The support layer preform prepared in step (1) is placed in a chemical vapor deposition furnace for the deposition of pyrolytic carbon. The carbon source gas is propane, propylene or butene. The carbon deposition process is carried out under negative pressure suction environment. The flow rate of the carbon source gas is 10~20 mL / min. The volume ratio of carbon source gas to dilution gas is 1:1~1:3. The deposition temperature is 500~800℃. The deposition time is 10~30 min. The carbon source gas flows into the support layer preform from the feed side and then exits from the discharge side of the support layer preform.

[0092] As some examples of the present invention, in actual implementation, the carbon deposition process on the support layer blank can be repeated multiple times as needed to obtain carbon deposition layers of different thicknesses.

[0093] Preferably, in this invention, the thickness of the carbon deposition layer on the feed side of the support layer blank is controlled to be 0.1~0.3 μm.

[0094] By performing carbon deposition on the support layer blank, a carbon deposition layer with a rapidly decreasing concentration or thickness from the feed side to the discharge side can be formed on the surface of the support layer blank, providing a basis for obtaining a silicon carbide deposition layer with a rapidly decreasing concentration or thickness from the feed side to the discharge side through a subsequent vapor phase deposition process.

[0095] It is understandable that when carbon deposition is performed on the support layer blank, the deposition time needs to be appropriately extended in the subsequent vapor deposition process.

[0096] Furthermore, in step (3), the secondary vapor deposition process of the support layer blank is as follows:

[0097] The support layer preform obtained in step (2) is placed in a vapor deposition apparatus. Using negative pressure suction, silicon carbide vapor is directed into the support layer preform from the feed side under the action of the carrier gas, and then discharged from the discharge side of the support layer preform. Silicon carbide particles are deposited on the surface of the support layer preform to obtain a support layer preform after secondary vapor deposition treatment. The parameters of the secondary vapor deposition are: deposition temperature of 1000-1300℃, growth gas source of trichloromethylsilane gas, volume ratio of growth gas source to carrier gas of 1:1-1:3, flow rate of growth gas source of 10-30mL / min, and secondary vapor deposition treatment time of 30-60min.

[0098] As some examples of the present invention, in step (3), the carrier gas is selected from one or more of nitrogen, argon, hydrogen, etc.

[0099] Furthermore, in step (4), the support layer blank can be post-processed according to the throughput requirements of the usage environment. Generally, when the throughput requirements of the support layer blank are large, the number of times the pressurization and depressurization processes are repeated can be appropriately increased.

[0100] Furthermore, in step (5), the raw materials of the separation layer, by weight, include:

[0101] Silicon carbide powder III, 5-10 parts;

[0102] Silicon carbide powder IV, 10-15 parts;

[0103] 1-5 parts adhesive;

[0104] 4-9 parts of dispersant;

[0105] 70-90 parts water.

[0106] As some examples of the present invention, the binder is selected from one or more of cellulose, polyvinyl alcohol, polysaccharides, starch, dextrin, etc.

[0107] As some examples of the present invention, the dispersant is selected from one or more of sodium hexametaphosphate, sodium pyrophosphate, ammonium citrate, sodium citrate, sodium polyacrylate, hydroxymethyl cellulose, polyvinyl alcohol, etc.

[0108] Preferably, the average particle size of the silicon carbide powder III is 3 to 5 times that of the average particle size of the silicon carbide powder IV.

[0109] Preferably, the average particle size of the silicon carbide powder III is 1~3 μm.

[0110] Furthermore, in step (5), the drying process of the silicon carbide ceramic film wet blank is as follows: drying at 30~40℃ for 5~10h.

[0111] Furthermore, in step (5), the sintering process is as follows: under the protection of argon atmosphere, the temperature is first raised to 600-800℃ at a heating rate of 60-100℃ / h, and held at this temperature for 1-2h for degumming treatment. Then, the temperature is raised to 1800-2200℃ at a heating rate of 100-200℃ / h, and held at this temperature for 2-4h. After that, the furnace is cooled to room temperature to obtain the support layer blank.

[0112] Furthermore, in step (5), the oxidation process is as follows: under air-permeable conditions, the sintered support layer blank is subjected to high-temperature oxidation sintering at 700~1000℃ to remove residual carbon.

[0113] Furthermore, in step (6), the surface hydrophobic modifier mixture comprises, by weight, the following components:

[0114] 10-20 parts of polydimethylsiloxane;

[0115] 30-50 parts organic solvent;

[0116] 3-5 parts linear silicone oil;

[0117] 5-8 parts of amino silicone oil;

[0118] 1-3 parts epoxy silicone oil;

[0119] Surfactant 0.3~1 part.

[0120] Preferably, the linear silicone oil is a modified linear silicone oil that has undergone modification treatment.

[0121] As some examples of the present invention, the organic solvent is selected from one or more of hydrofluoroether, dichloromethane, chloroform, hexane, toluene, methanol, ethanol, etc.

[0122] Furthermore, the preparation process of the modified linear silicone oil is as follows:

[0123] First, 10-15 parts by weight of linear hydroxyl silicone oil, 3-5 parts by weight of chain extender and 0.1-0.3 parts by weight of catalyst are added to a reactor. After heating to 60-70°C with stirring, the reaction is carried out for 3-5 hours to obtain the modified linear silicone oil.

[0124] As some examples of the present invention, the chain extender is selected from carboxyl chain extenders, epoxy chain extenders, etc.

[0125] As some examples of the present invention, the catalyst is cobalt trioxide.

[0126] Preferably, the amino silicone oil is a primary amino silicone oil, a secondary amino silicone oil, etc.

[0127] Preferably, the epoxy silicone oil is a side-chain epoxy silicone oil in which the epoxy group is located on the side chain of polymethylsiloxane.

[0128] Preferably, the surfactant is an anionic surfactant.

[0129] As some examples of the present invention, the surfactant is selected from sodium dodecylbenzenesulfonate, sodium oleate, sodium rosinate, etc.

[0130] In the surface hydrophobic modifier mixture, the organic solvent can dilute other components, reducing the viscosity of the surface hydrophobic modifier mixture and improving its wetting ability, making it easy to coat and quickly spread on the surface of the silicon carbide ceramic film. The addition of the linear silicone oil can improve the bonding ability between the surface hydrophobic modifier mixture and the silicon carbide ceramic film by utilizing the chemical cross-linking effect of the reactive groups on its linear segments with other components or the physical entanglement effect of the long chains. The amino silicone oil can further improve the bonding ability between the surface hydrophobic modifier mixture and the silicon carbide ceramic film through electrostatic adsorption with surfactants. At the same time, the amino silicone oil can react with epoxy silicone oil to form a network structure, further improving the bonding ability between the surface hydrophobic modifier mixture and the silicon carbide ceramic film.

[0131] Furthermore, after the silicon carbide ceramic film is impregnated with a mixture of surface hydrophobic modifiers, it can be subjected to high-temperature pyrolysis treatment to form hydrophobic substances on the surface of the silicon carbide ceramic film, thereby improving the surface hydrophobicity of the silicon carbide ceramic film.

[0132] Furthermore, in the silicon carbide ceramic film of the present invention, a silicon carbide nano-modification structure is formed on the feed side of the support layer preform through primary vapor deposition and secondary vapor deposition. The silicon carbide nano-modification structure includes in-situ grown primary silicon carbide particles formed by primary vapor deposition and secondary silicon carbide particles formed by physical vapor deposition. The primary and secondary silicon carbide particles can form tiny granular protrusions on the surface or in the pores of the support layer preform. These granular protrusions can improve the hydrophobic and antifouling properties of the support layer preform. At the same time, the surface hydrophobic modifier mixture can further coat the surface of these silicon carbide nano-modification structures with a silane hydrophobic layer, further improving the hydrophobic and antifouling properties of the silicon carbide ceramic film, especially the support layer preform.

[0133] More importantly, in the primary and secondary vapor deposition processes described in this invention, the gas enters from the feed side and exits from the discharge side of the support layer preform. Therefore, the vapor deposition product will preferentially deposit on the feed side of the support layer preform, forming a structure in which the thickness of the vapor deposition product decreases rapidly from the feed side to the discharge side of the support layer preform. Ultimately, in the support layer described in this invention, a support layer structure with rapidly increasing pore size from the feed side to the discharge side of the support layer preform is formed. This structure has the advantages of high integration, high strength, strong stability, and the ability to provide good support for the separation layer membrane.

[0134] Furthermore, this application employs porous silicon carbide particles, which can increase the flux of the silicon carbide ceramic membrane. Simultaneously, the method of reducing the pore size at the junction of the support layer preform and the separation layer through vapor deposition in this application can rapidly reduce the pore size on the feed side of the support layer preform while maintaining a relatively large pore size on the discharge side. Therefore, the flux reduction of the silicon carbide ceramic membrane described in this invention can be controlled to a low level. Based on this, this invention also employs high-pressure gas for post-processing of the support layer preform. The impact force generated during gas release can purge and unblock the pore channels within the support layer preform, thereby improving the connectivity of the pores within the support layer preform and ultimately increasing the flux of the silicon carbide ceramic membrane.

[0135] The structure of the silicon carbide ceramic film described in this invention differs from that of the traditional three-layer structure:

[0136] By reducing the transition layer, this invention forms a pore structure on the support layer through vapor deposition, where the pore size rapidly increases from the feed side to the discharge side. This not only enables a rapid transition in pore size, effectively supporting the separation layer membrane and improving its stability and service life, but also reduces the number of layers, does not increase the overall thickness of the ceramic filter membrane, and improves the hydrophobic and antifouling properties of the support layer.

[0137] Structurally more stable, this integrated support layer structure and transition layer function can reduce the number of silicon carbide ceramic film layers and improve the structural stability of silicon carbide ceramic film.

[0138] The structure of the silicon carbide ceramic membrane described in this invention is compared with the single-layer coating separation process provided in Chinese Patent Publication No. CN113121241B:

[0139] First, by increasing the vapor deposition process, a pore structure that rapidly increases from the feed side to the discharge side can be formed on the support layer. This results in a small pore size on the side where the support layer blank is connected to the separation layer, which can prevent particles in the separation layer slurry from entering the support layer blank and can form a good bond and support for the separation layer.

[0140] Second, by using gas to post-process the support layer preform after vapor deposition, the impact force generated when the gas is released can be used to purge and clear the pores in the support layer preform, thereby improving the connectivity of the pores in the support layer preform and ultimately increasing the flux of the silicon carbide ceramic film.

[0141] Third, by using a mixture of surface hydrophobic modifiers to perform hydrophobic modification on silicon carbide ceramic films, the hydrophobic properties of silicon carbide ceramic films can be improved.

[0142] The following specific embodiments illustrate the silicon carbide ceramic film and its preparation method according to the present invention:

[0143] Example 1

[0144] The preparation of silicon carbide ceramic films includes the following steps:

[0145] (1) Preparation of the support layer blank: By weight, the raw materials of the support layer blank include: 30 parts of silicon carbide powder I; 20 parts of silicon carbide powder II; 8 parts of carbon black; 5 parts of silicon powder; 1 part of dispersant; 0.5 parts of plasticizer; 0.5 parts of sintering aid; 10 parts of water; the average particle size of silicon carbide powder I is 20 μm, the average particle size of silicon carbide powder II is 20 μm, the density of silicon carbide powder II is 30% of that of silicon carbide powder I, the average particle size of carbon black is 1 μm, and the average particle size of silicon powder is 0.1 μm.

[0146] The raw materials for the support layer preform are mixed and stirred evenly. The mixture is then placed in an extrusion molding machine and extruded to obtain a wet preform of the support layer. The wet preform of the support layer is dried at 30°C for 30 hours to obtain a green preform of the support layer. The green preform of the support layer is then sintered at high temperature under an argon protective atmosphere. The high temperature sintering process is as follows: first, the temperature is raised to 800°C at a heating rate of 100°C / h and held at this temperature for 1 hour for debinding treatment. Then, the temperature is raised to 2500°C at a heating rate of 200°C / h and held at this temperature for 3 hours. Finally, the preform is cooled to room temperature in the furnace to obtain the support layer preform.

[0147] (2) Primary vapor deposition of the support layer preform: The support layer preform is placed in a chemical vapor deposition apparatus, and then silicon powder is evaporated to form silicon vapor. The silicon vapor is directed into the support layer preform from the feed side by a carrier gas and then discharged from the discharge side of the support layer preform. The primary vapor deposition parameters are: the silicon vapor is drawn through the support layer preform at a rate of 0.5 g / min and the carrier gas at a rate of 50 mL / min using negative pressure suction. The temperature of the primary vapor deposition is 1300 °C and the time is 10 min.

[0148] (3) Secondary vapor deposition of the support layer blank: The support layer blank is placed in a vapor deposition apparatus. The silicon carbide vapor is directed into the support layer blank from the feed side under the action of the carrier gas by the negative pressure suction. Then it is discharged from the discharge side of the support layer blank. Silicon carbide particles are deposited on the surface of the support layer blank to obtain the support layer blank after secondary vapor deposition treatment. The parameters of the secondary vapor deposition are: deposition temperature is 1000℃, the growth gas source is trichloromethylsilane gas, the volume ratio of growth gas source to carrier gas is 1:1, the flow rate of the growth gas source is 10mL / min, and the secondary vapor deposition treatment time is 30min.

[0149] (4) Post-processing of the support layer blank: Place the support layer blank in a sealed container, pressurize the pressure in the sealed container to 0.5MPa using an air pressurization device, maintain the pressure for 3 minutes, and then open the discharge valve to reduce the pressure in the sealed container to normal pressure at a rate of 0.03MPa / min; repeat the above pressurization, pressure maintenance and pressure reduction process 5 times, then open the sealed container and take out the support layer blank;

[0150] (5) Preparation of the separation layer: By weight, the raw materials of the separation layer include: 5 parts of silicon carbide powder III; 15 parts of silicon carbide powder IV; 1 part of binder; 4 parts of dispersant; 70 parts of water; the average particle size of silicon carbide powder III is 1 μm, and the average particle size of silicon carbide powder IV is 0.25 μm.

[0151] The raw materials of the separation layer are mixed and prepared into a film slurry. The film slurry is then coated on the feed side surface of the support layer blank to form a separation layer film, resulting in a wet blank of silicon carbide ceramic film. The wet blank of silicon carbide ceramic film is then dried, sintered and oxidized to obtain the original film of silicon carbide ceramic film.

[0152] (6) Surface hydrophobic modification treatment: By weight, the surface hydrophobic modifier mixture includes: 20 parts of polydimethylsiloxane; 50 parts of organic solvent; 3 parts of linear silicone oil; 5 parts of amino silicone oil; 1 part of epoxy silicone oil; and 0.3 parts of surfactant.

[0153] The raw materials of the surface hydrophobic modifier are mixed and formulated into a surface hydrophobic modifier mixture. Then, the original silicon carbide ceramic film is dried in a vacuum at 100°C for 30 hours, and then immersed in the surface hydrophobic modifier mixture for full wetting. After being taken out, it is kept at 800°C for 0.5 hours to obtain the silicon carbide ceramic film.

[0154] Example 2

[0155] The preparation of silicon carbide ceramic films includes the following steps:

[0156] (1) Preparation of the support layer blank: By weight, the raw materials of the support layer blank include: 40 parts of silicon carbide powder I; 15 parts of silicon carbide powder II; 10 parts of carbon black; 8 parts of silicon powder; 3 parts of dispersant; 1 part of plasticizer; 5 parts of sintering aid; 15 parts of water; the average particle size of silicon carbide powder I is 16 μm, the average particle size of silicon carbide powder II is 20 μm, the density of silicon carbide powder II is 50% of that of silicon carbide powder I, the average particle size of carbon black is 5 μm, and the average particle size of silicon powder is 0.5 μm.

[0157] The raw materials for the support layer preform are mixed and stirred evenly. The mixture is then placed in an extrusion molding machine and extruded to obtain a wet preform of the support layer. The wet preform of the support layer is dried at 40°C for 25 hours to obtain a green preform of the support layer. The green preform of the support layer is then sintered at high temperature under an argon protective atmosphere. The high temperature sintering process is as follows: first, the temperature is raised to 700°C at a heating rate of 80°C / h and held at this temperature for 1.5 hours for debinding treatment. Then, the temperature is raised to 2200°C at a heating rate of 150°C / h and held at this temperature for 4 hours. Finally, the preform is cooled to room temperature in the furnace to obtain the support layer preform.

[0158] (2) Primary vapor deposition of the support layer preform: The support layer preform is placed in a chemical vapor deposition apparatus, and then silicon powder is evaporated to form silicon vapor. The silicon vapor is directed into the support layer preform from the feed side by a carrier gas and then discharged from the discharge side of the support layer preform. The primary vapor deposition parameters are: the silicon vapor is drawn through the support layer preform at a rate of 1 g / min and the carrier gas at a rate of 80 mL / min using negative pressure suction. The temperature of the primary vapor deposition is 1400℃ and the time is 18 min.

[0159] (3) Secondary vapor deposition of the support layer blank: The support layer blank is placed in a vapor deposition apparatus. The silicon carbide vapor is directed into the support layer blank from the feed side under the action of the carrier gas by the negative pressure suction. Then it is discharged from the discharge side of the support layer blank. Silicon carbide particles are deposited on the surface of the support layer blank to obtain the support layer blank after secondary vapor deposition. The parameters of the secondary vapor deposition are: deposition temperature is 1200℃, the growth gas source is trichloromethylsilane gas, the volume ratio of growth gas source to carrier gas is 1:2, the flow rate of the growth gas source is 20mL / min, and the secondary vapor deposition time is 40min.

[0160] (4) Post-processing of the support layer blank: Place the support layer blank in a sealed container, pressurize the pressure in the sealed container to 1MPa through an air pressurization device, maintain the pressure for 2 minutes, and then open the discharge valve to reduce the pressure in the sealed container to normal pressure at a rate of 0.08MPa / min; repeat the above pressurization, pressure maintenance and pressure reduction process 3 times, then open the sealed container and take out the support layer blank;

[0161] (5) Preparation of the separation layer: by weight, the raw materials of the separation layer include: 8 parts of silicon carbide powder III; 10 parts of silicon carbide powder IV; 3 parts of binder; 5 parts of dispersant; 80 parts of water; the average particle size of silicon carbide powder III is 1.5 μm, and the average particle size of silicon carbide powder IV is 0.3 μm.

[0162] The raw materials of the separation layer are mixed and prepared into a film slurry. The film slurry is then coated on the feed side surface of the support layer blank to form a separation layer film, resulting in a wet blank of silicon carbide ceramic film. The wet blank of silicon carbide ceramic film is then dried, sintered and oxidized to obtain the original film of silicon carbide ceramic film.

[0163] (6) Surface hydrophobic modification treatment: By weight, the surface hydrophobic modifier mixture includes: 10 parts of polydimethylsiloxane; 30 parts of organic solvent; 4 parts of linear silicone oil; 6 parts of amino silicone oil; 2 parts of epoxy silicone oil; and 0.6 parts of surfactant.

[0164] The raw materials of the surface hydrophobic modifier are mixed and formulated into a surface hydrophobic modifier mixture. Then, the original silicon carbide ceramic film is dried in a vacuum at 180°C for 20 hours, and then immersed in the surface hydrophobic modifier mixture for full wetting. After being taken out, it is kept at 600°C for 2 hours to obtain the silicon carbide ceramic film.

[0165] Example 3

[0166] The preparation of silicon carbide ceramic films includes the following steps:

[0167] (1) Preparation of the support layer blank: By weight, the raw materials of the support layer blank include: 50 parts of silicon carbide powder I; 10 parts of silicon carbide powder II; 15 parts of carbon black; 10 parts of silicon powder; 5 parts of dispersant; 3 parts of plasticizer; 10 parts of sintering aid; 25 parts of water; the average particle size of silicon carbide powder I is 10 μm, the average particle size of silicon carbide powder II is 15 μm, the density of silicon carbide powder II is 60% of that of silicon carbide powder I, the average particle size of carbon black is 3 μm, and the average particle size of silicon powder is 1 μm.

[0168] The raw materials for the support layer preform are mixed and stirred evenly. The mixture is then placed in an extrusion molding machine and extruded to obtain a wet preform of the support layer. The wet preform of the support layer is dried at 50°C for 20 hours to obtain a green preform of the support layer. The green preform of the support layer is then sintered at high temperature under an argon protective atmosphere. The high temperature sintering process is as follows: first, the temperature is raised to 600°C at a heating rate of 60°C / h and held at this temperature for 2 hours for debinding treatment. Then, the temperature is raised to 2000°C at a heating rate of 100°C / h and held at this temperature for 6 hours. Finally, the preform is cooled to room temperature in the furnace to obtain the support layer preform.

[0169] After step (1) and before step (2), carbon deposition treatment is performed on the support layer blank. The process is as follows: The support layer blank is placed in a chemical vapor deposition furnace to deposit pyrolytic carbon. The carbon source gas is propane. The carbon deposition treatment is carried out under negative pressure suction environment. The flow rate of the carbon source gas is 15 mL / min. The volume ratio of carbon source gas to dilution gas is 1:1. The deposition temperature is 600℃ and the deposition time is 20 min. The carbon source gas flows into the support layer blank from the feed side and then exits from the discharge side of the support layer blank.

[0170] (2) Primary vapor deposition of the support layer preform: The support layer preform is placed in a chemical vapor deposition apparatus, and then silicon powder is evaporated to form silicon vapor. The silicon vapor is directed into the support layer preform from the feed side by a carrier gas and then discharged from the discharge side of the support layer preform. The primary vapor deposition parameters are: the silicon vapor is drawn through the support layer preform at a rate of 2 g / min and the carrier gas at a rate of 100 mL / min using negative pressure suction. The temperature of the primary vapor deposition is 1500 °C and the time is 23 min.

[0171] (3) Secondary vapor deposition of the support layer blank: The support layer blank is placed in a vapor deposition apparatus. The silicon carbide vapor is directed into the support layer blank from the feed side under the action of the carrier gas by the negative pressure suction. Then it is discharged from the discharge side of the support layer blank. Silicon carbide particles are deposited on the surface of the support layer blank to obtain the support layer blank after secondary vapor deposition. The parameters of the secondary vapor deposition are: deposition temperature is 1300℃, the growth gas source is trichloromethylsilane gas, the volume ratio of growth gas source to carrier gas is 1:3, the flow rate of the growth gas source is 30mL / min, and the secondary vapor deposition time is 60min.

[0172] (4) Post-processing of the support layer blank: Place the support layer blank in a sealed container, pressurize the pressure in the sealed container to 3MPa through an air pressurization device, maintain the pressure for 1min, and then open the discharge valve to reduce the pressure in the sealed container to normal pressure at a rate of 0.1MPa / min; repeat the above pressurization, pressure maintenance and pressure reduction process 4 times, then open the sealed container and take out the support layer blank;

[0173] (5) Preparation of the separation layer: By weight, the raw materials of the separation layer include: 10 parts of silicon carbide powder III; 12 parts of silicon carbide powder IV; 5 parts of binder; 9 parts of dispersant; 90 parts of water; the average particle size of silicon carbide powder III is 3 μm, and the average particle size of silicon carbide powder IV is 1 μm.

[0174] The raw materials of the separation layer are mixed and prepared into a film slurry. The film slurry is then coated on the feed side surface of the support layer blank to form a separation layer film, resulting in a wet blank of silicon carbide ceramic film. The wet blank of silicon carbide ceramic film is then dried, sintered and oxidized to obtain the original film of silicon carbide ceramic film.

[0175] (6) Surface hydrophobic modification treatment: By weight, the surface hydrophobic modifier mixture includes: 15 parts of polydimethylsiloxane; 40 parts of organic solvent; 5 parts of linear silicone oil; 8 parts of amino silicone oil; 3 parts of epoxy silicone oil; and 1 part of surfactant.

[0176] The raw materials of the surface hydrophobic modifier are mixed and formulated into a surface hydrophobic modifier mixture. Then, the original silicon carbide ceramic film is dried in a vacuum at 200°C for 10 hours, and then immersed in the surface hydrophobic modifier mixture for full wetting. After being taken out, it is kept at 500°C for 3 hours to obtain the silicon carbide ceramic film.

[0177] Comparative Example 1

[0178] Preparation of silicon carbide ceramic film: The only difference between it and Example 2 above is that it does not include the secondary vapor deposition process in step (3).

[0179] Comparative Example 2

[0180] Preparation of silicon carbide ceramic film: The only difference between it and Example 2 above is that it does not include the first vapor deposition process in step (2).

[0181] Comparative Example 3

[0182] Preparation of silicon carbide ceramic film: The only difference between it and the above Example 2 is that it does not include the post-processing of the support layer blank in step (4).

[0183] Comparative Example 4

[0184] Preparation of silicon carbide ceramic film: The only difference between it and Example 2 above is that in step (6), the surface hydrophobic modifier mixture used contains only polydimethylsiloxane and organic solvent.

[0185] Experimental Example 1

[0186] The silicon carbide ceramic films prepared in Examples 1-3 and Comparative Examples 1-4 were tested. The pore sizes of regions A, B, C, and D of the support layer were measured by dividing the support layer into four equal regions from the feed side to the discharge side. Region A is located on the feed side of the support layer, and region D is located on the discharge side. The surface pore size and water contact angle of the support layer were measured after post-processing of the support layer preform. The results are shown in Table 1 below.

[0187] Table 1 Performance test results of silicon carbide ceramic membrane

[0188]

[0189] The embodiments of this application have been described above with reference to the accompanying drawings. Unless otherwise specified, the embodiments and features in the embodiments of this application can be combined with each other. This application is not limited to the specific embodiments described above. The specific embodiments described above are merely illustrative and not restrictive. Those skilled in the art can make many other forms under the guidance of this application without departing from the spirit and scope of the claims, and all of these forms are within the protection scope of this application.

Claims

1. A method for preparing a silicon carbide ceramic film, characterized in that, Including the following steps: (1) Preparation of support layer blank: Mix the raw materials of support layer blank and stir evenly. Then put the mixture into an extrusion molding machine and extrude to obtain a wet blank of support layer. Then dry and sinter the wet blank of support layer to obtain support layer blank. (2) Primary vapor deposition of the support layer preform: The support layer preform obtained in step (1) is placed in a vapor deposition apparatus, and silicon vapor is directed into the support layer preform from the feed side under the action of a carrier gas, and then discharged from the discharge side of the support layer preform. (3) Secondary vapor deposition of the support layer blank: The support layer blank obtained in step (2) is placed in a vapor deposition apparatus, and silicon carbide vapor is directed into the support layer blank from the feed side under the action of the carrier gas, and then discharged from the discharge side of the support layer blank. (4) Post-processing of the support layer blank: Place the support layer blank in a sealed container, pressurize the pressure in the sealed container to 0.5~3MPa using an air pressurization device, maintain the pressure for 1~3min, then open the discharge valve to reduce the pressure in the sealed container to normal pressure at a rate of 0.03~0.1MPa / min; repeat the above pressurization, pressure maintenance and pressure reduction process 3~5 times, then open the sealed container and take out the support layer blank; (5) Preparation of the separation layer: The raw materials of the separation layer are mixed and prepared into a film slurry. The film slurry is then coated on the feed side surface of the support layer blank to form a separation layer film and a wet blank of silicon carbide ceramic film is obtained. The wet blank of silicon carbide ceramic film is then dried, sintered and oxidized to obtain the original film of silicon carbide ceramic film. (6) Surface hydrophobic modification treatment: Mix the raw materials of the surface hydrophobic modifier and prepare a surface hydrophobic modifier mixture. Then, the silicon carbide ceramic film obtained in step (5) is dried in a vacuum at a temperature of 100~200℃ for 10~30h. After being fully wetted in the surface hydrophobic modifier mixture, it is taken out and kept at 500~800℃ for 0.5~3h to obtain the silicon carbide ceramic film. The raw materials of the support layer blank, by weight, include: Silicon carbide powder I 30-50 parts; Silicon carbide powder II, 10-20 parts; 8-15 parts carbon black; 5-10 parts of silicon powder; 1-5 parts of dispersant; Plasticizer 0.5-3 parts; Sintering aid 0.5-10 parts; 10-25 parts water; Wherein, silicon carbide powder I is spherical solid silicon carbide particles or porous silicon carbide particles, silicon carbide powder II is porous silicon carbide particles with open channels, and the density of silicon carbide powder II is 30% to 60% of that of silicon carbide powder I.

2. The method for preparing a silicon carbide ceramic film according to claim 1, characterized in that, The average particle size of silicon carbide powder I and silicon carbide powder II is 5~20 μm, the average particle size of carbon black is 1~5 μm, and the average particle size of silicon powder is 0.1~1 μm.

3. The method for preparing a silicon carbide ceramic film according to claim 1, characterized in that, In step (1), the process of drying and sintering the wet blank of the support layer is as follows: After drying the wet blank of the support layer at 30~50℃ for 20~30h, the green blank of the support layer is obtained. Then, the green blank of the support layer is sintered at high temperature under an argon protective atmosphere. The high temperature sintering process is as follows: first, the temperature is raised to 600~800℃ at a heating rate of 60~100℃ / h and held at this temperature for 1~2h for debinding treatment. Then, the temperature is raised to 2000~2500℃ at a heating rate of 100~200℃ / h and held at this temperature for 3~6h. After that, the blank is cooled to room temperature in the furnace to obtain the support layer blank.

4. The method for preparing a silicon carbide ceramic film according to claim 1, characterized in that, In step (2), the primary vapor deposition process of the support layer preform is as follows: The support layer preform obtained in step (1) is placed in a chemical vapor deposition apparatus. Then, silicon powder is evaporated to form silicon vapor, and the silicon vapor is directed into the support layer preform from the feed side by a carrier gas and then discharged from the discharge side of the support layer preform. The parameters for the first vapor deposition are: the silicon vapor is drawn through the support layer preform at a rate of 0.5~2g / min using negative pressure suction, and the carrier gas flows through the support layer preform at a rate of 50~100mL / min. The temperature of the first vapor deposition is 1300~1500℃.

5. The method for preparing a silicon carbide ceramic film according to claim 1, characterized in that, After step (1) and before step (2), the support layer blank is subjected to carbon deposition treatment, as follows: The support layer preform prepared in step (1) is placed in a vapor deposition furnace for the deposition of pyrolytic carbon. The carbon source gas is propane, propylene or butene. The carbon deposition process is carried out under negative pressure suction environment. The flow rate of the carbon source gas is 10~20 mL / min. The volume ratio of the carbon source gas to the dilution gas is 1:1~1:

3. The deposition temperature is 500~800℃. The deposition time is 10~30 min. The carbon source gas flows into the support layer preform from the feed side and then exits from the discharge side of the support layer preform.

6. The method for preparing a silicon carbide ceramic film according to claim 1, characterized in that, In step (3), the secondary vapor deposition process of the support layer blank is as follows: The support layer preform obtained in step (2) is placed in a vapor deposition apparatus. The silicon carbide vapor is directed into the support layer preform from the feed side by the negative pressure suction under the action of the carrier gas, and then discharged from the discharge side of the support layer preform. Silicon carbide particles are deposited on the surface of the support layer preform to obtain a support layer preform after secondary vapor deposition treatment. The parameters of the secondary vapor deposition are: deposition temperature of 1000-1300℃, growth gas source of trichloromethylsilane gas, volume ratio of growth gas source to carrier gas of 1:1-1:3, flow rate of growth gas source of 10-30mL / min, and secondary vapor deposition treatment time of 30-60min.

7. The method for preparing a silicon carbide ceramic film according to claim 1, characterized in that, In step (5), the raw materials of the separation layer, by weight, include: Silicon carbide powder III, 5-10 parts; Silicon carbide powder IV, 10-15 parts; 1-5 parts adhesive; 4-9 parts of dispersant; 70-90 parts water; The average particle size of silicon carbide powder III is 3 to 5 times that of silicon carbide powder IV, and the average particle size of silicon carbide powder III is 1 to 3 μm.

8. The method for preparing a silicon carbide ceramic film according to claim 1, characterized in that, The surface hydrophobic modifier mixture comprises, by weight: 10-20 parts of polydimethylsiloxane; 30-50 parts organic solvent; 3-5 parts linear silicone oil; 5-8 parts of amino silicone oil; 1-3 parts epoxy silicone oil; Surfactant 0.3~1 part; The linear silicone oil is a modified linear silicone oil that has undergone modification treatment. The preparation process of the modified linear silicone oil is as follows: First, 10-15 parts by weight of linear hydroxyl silicone oil, 3-5 parts by weight of chain extender and 0.1-0.3 parts by weight of catalyst are added to a reactor. After heating to 60-70°C with stirring, the reaction is carried out for 3-5 hours to obtain the modified linear silicone oil.

9. A silicon carbide ceramic membrane, characterized in that, The silicon carbide ceramic film is prepared by the preparation method described in any one of claims 1 to 8.

Images