Silicon carbide whisker surface modified alumina particle ceramic membrane and low-temperature in-situ synthesis method thereof

Abstract

The invention relates to the technical field of ceramic membranes, in particular to a silicon carbide whisker surface modified aluminum oxide particle ceramic membrane and a low-temperature in-situ synthesis method thereof. The silicon carbide whisker surface modified alumina particle ceramic membrane is prepared from the following raw materials in percentage by mass: 70 to 90 weight percent of alpha-Al2O3 powder, 5 to 15 weight percent of silicon source, 5 to 15 weight percent of carbon source, 1 to 5 weight percent of sintering aid and 0.1 to 1 weight percent of catalyst. On one hand, the initial synthesis temperature of the SiC whiskers is reduced by adopting the combined catalyst, and the method adapts to a low-temperature sintering schedule of an aluminum oxide ceramic flat sheet membrane. On the other hand, a low-temperature in-situ synthesis method for modifying the aluminum oxide particles on the surfaces of the silicon carbide whiskers is adopted, the aluminum oxide particles are wrapped by the SiC whiskers to form a core-shell structure, and the hydrophilicity and chemical stability of the aluminum oxide ceramic membrane are improved.

Description

Technical Field

[0001] This solution relates to the field of ceramic membrane technology, and in particular to a ceramic membrane of silicon carbide whisker surface modified alumina particles and its low-temperature in-situ synthesis method. Background Technology

[0002] Ceramic membrane separation technology is a highly efficient and energy-saving separation technology with applications in industries such as chemical, petroleum and petrochemical, biochemical, food, electronics, and pharmaceuticals. The ceramic membranes on the market are mainly made of materials such as alumina, titanium dioxide, silicon dioxide, zirconium oxide, and silicon carbide. Currently, the widely used alumina membrane material is susceptible to damage from strong acids and alkalis, and exhibits poor high-temperature thermal stability. Under these harsh environmental conditions, its service life is significantly shortened, leading to increased wastewater treatment costs. Furthermore, alumina membrane materials generally have low hydrophilicity, with a wetting angle of approximately 30° with pure water, resulting in low wastewater treatment efficiency and further increasing treatment costs.

[0003] Silicon carbide exhibits excellent chemical stability, resisting strong acids and alkalis, and can be used within a pH range of 0-14. It also demonstrates good high-temperature stability and hydrophilicity. These characteristics give silicon carbide ceramic membranes a natural advantage in wastewater treatment, making them an important direction for the future development of inorganic ceramic membranes. Invention patent CN200910141221.X discloses "An In-situ Toughened Alumina Ceramics with Silicon Carbide Whiskers," which generates nanoscale silicon carbide whiskers through in-situ reaction. This overcomes the problems of severe silicon carbide whisker agglomeration, poor compatibility with the alumina ceramic matrix, and significant impact on the sintering rate of alumina ceramics. This method primarily addresses the poor toughness of alumina ceramics, improving the mechanical properties of alumina materials. Invention patent CN202211456738.X discloses "A Low-Temperature In-Situ Synthesis Method of Cordierite Honeycomb Ceramic with Silicon Carbide Whisker Coating and the Product Obtained Therefrom". This method employs a stepped, segmented pore-forming scheme to create three types of pores (large, medium, and small) inside and on the surface of the honeycomb ceramic, effectively improving porosity and specific surface area. Invention patent CN201810075191.6 discloses "Liquid-Phase Sintering Multi-Channel Silicon Carbide Ceramic Membrane Element and its Preparation Method". This method uses kaolin and talc as fluxes, and obtains a silicon carbide ceramic membrane by high-temperature sintering at 1300℃~1500℃. The wetting angle between the silicon carbide ceramic membrane and water is only 0.3°. Although the above-mentioned silicon carbide materials have advantages such as a small wetting angle and high mechanical strength, the high production cost due to the sintering temperature of 1300℃~1500℃ results in a relatively high production cost.

[0004] Achieving low-cost production of ceramic membranes, combined with developing membrane material design and preparation methods oriented towards application processes, will solve the bottleneck problems in the widespread application of ceramic membranes and represent a major future development trend. Summary of the Invention

[0005] The main objective of this solution is to provide a ceramic membrane of silicon carbide whisker-modified alumina particles and its low-temperature in-situ synthesis method, aiming to improve the technical problems of low wastewater treatment efficiency caused by the general hydrophilicity and low membrane flux of existing alumina ceramic membranes.

[0006] To achieve the above objectives, this solution proposes a ceramic film with silicon carbide whisker surface modified with alumina particles, comprising the following raw materials by mass percentage: 70wt%–90wt% α-Al2O3 powder, 5wt%–15wt% silicon source, 5wt%–15wt% carbon source, 1wt%–5wt% sintering aid, and 0.1wt%–1wt% catalyst.

[0007] Preferably, the catalyst may be a transition metal, specifically including at least one of Fe powder with a particle size of 0.5~10 μm, Co powder with a particle size of 10~50 nanometers, Ni powder with a particle size of 10~50 nanometers, and Cu powder with a particle size of 0.5~10 μm.

[0008] Preferably, the silicon source includes at least one of silicon micropowder, kaolin, and quartz; the carbon source includes at least one of carbon black, starch, graphite, HPMC, CMC, vegetable oil, and glycerol; and the sintering aid includes at least one of kaolin, magnesium oxide, calcium carbonate, silicon micropowder, zinc oxide, and quartz.

[0009] Preferably, the particle size range of the α-Al2O3 powder is 0.5–50 μm.

[0010] In addition, this scheme also proposes a low-temperature in-situ synthesis method for ceramic films of silicon carbide whisker surface modified alumina particles, including the following steps: α-Al2O3 powder, silicon source, carbon source, catalyst and sintering aid are mixed by a layer-by-layer coating method, and the ceramic films of silicon carbide whisker surface modified alumina particles are obtained after aging of mud, drying and shaping, vacuum sintering and surface coating.

[0011] Preferably, the "layer-by-layer coating method for mixing" process includes the following steps: first, α-Al2O3 powder is added to a mixing device, and HPMC solution from the carbon source is added during stirring to coat the surface of the α-Al2O3 powder with a layer of HPMC solution; then, a pre-mixed and uniformly mixed dry powder raw material of silicon source, dry powder carbon source and catalyst is added and mixed for 1 to 10 minutes; then, a sintering aid is added and mixed for 1 to 10 minutes; liquid carbon source raw material is added and mixed evenly to obtain mud; then, pure water is added to make the water content of the mud 13% to 18%; wherein, the dry powder carbon source includes at least one of carbon black, starch, graphite, HPMC or CMC; and the liquid carbon source includes at least one of glycerol or vegetable oil.

[0012] Preferably, the "mud aging" process includes the following steps: kneading the mixed raw materials for 10-60 minutes; kneading the mud 1-3 times on a mud-kneading device, then kneading it 1-3 times under a vacuum of ≥-0.095MPa; and finally aging it for 12-72 hours at a temperature of 20-25℃ and a humidity of 50-80%.

[0013] Preferably, the "drying and shaping" process includes the following steps: after the aged clay is extruded, cut, microwave-shaped, and dried, an alumina support is obtained; wherein, during extrusion, the vacuum degree of the extrusion equipment is ≥-0.095MPa, the extrusion speed is 0.1~5m / min, and the extrusion pressure is 1~10MPa; after being cut to the required length, it is transferred to a microwave device for shaping, the power of the microwave device is 350~900W, and the conveying speed is 0.1~5m / min; during drying, it is dried at 40~110℃ for 1~24h; The alumina support can be a single-channel tubular alumina support, a multi-channel flat alumina support, or a multi-channel tubular alumina support.

[0014] Preferably, the "vacuum sintering" process includes the following steps: transporting the dried and shaped green blank to a high-temperature vacuum furnace for firing; the firing regime is as follows: heating from room temperature to 200°C at a heating rate of 10-50°C / h; heating from 200°C to 600°C at a heating rate of 5-20°C / h, holding at that temperature for 1-5 hours; heating from 600°C to 800°C at a heating rate of 5-20°C / h; heating from 800°C to the firing temperature, holding at that temperature for 3-5 hours at a heating rate of 10-30°C / h; wherein the firing temperature range is 1200-1450°C.

[0015] Preferably, the "surface spraying film layer" process includes the following steps: uniformly spraying a film layer slurry onto the surface of the sintered alumina ceramic support, drying it, and then firing it, wherein the firing temperature is 1100~1200℃, and the temperature is maintained at the firing temperature for 1~3 hours; the film layer slurry is prepared by mixing nano-zirconia, nano-alumina or nano-silicon carbide with 1% PVA solution in a mass ratio of 1~2:8~9.

[0016] Compared with existing technologies, the ceramic film of silicon carbide whisker surface modified with alumina particles and the low-temperature in-situ synthesis method of this solution have the following advantages: 1. A low-temperature in-situ synthesis method is adopted to modify alumina particles with silicon carbide whiskers. The SiC whiskers encapsulate the alumina particles to form a core-shell structure, which improves the hydrophilicity and chemical stability of the alumina ceramic film.

[0017] 2. The use of a combined catalyst lowers the initial synthesis temperature of SiC whiskers, making it compatible with the low-temperature sintering process of alumina ceramic flat film. Detailed Implementation

[0018] The technical solutions in the embodiments of this solution will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of this solution, and not all of them. Based on the embodiments of this solution, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of this solution.

[0019] Furthermore, the technical solutions of the various embodiments can be combined with each other, but this must be based on the ability of those skilled in the art to implement them. When the combination of technical solutions is contradictory or cannot be implemented, it should be considered that such combination of technical solutions does not exist and is not within the scope of protection claimed by this solution.

[0020] A ceramic film with silicon carbide whisker surface modified with alumina particles, comprising the following raw materials by mass percentage: 70wt% to 90wt% α-Al2O3 powder, 5wt% to 15wt% silicon source, 5wt% to 15wt% carbon source, 1wt% to 5wt% sintering aid and 0.1wt% to 1wt% catalyst.

[0021] The catalyst comprises at least one of Fe powder, nano-Co powder, nano-Ni powder, and Cu powder; the silicon source comprises at least one of silica powder, kaolin, and quartz; the carbon source comprises at least one of carbon black, starch, graphite, HPMC, CMC, vegetable oil, and glycerol; the sintering aid comprises at least one of kaolin, magnesium oxide, calcium carbonate, silica powder, zinc oxide, and quartz; and the α-Al2O3 powder has a particle size range of 0.5–50 μm.

[0022] In this scheme, a relatively large amount of α-Al₂O₃ powder is used in the raw materials, mainly to provide high hardness and thermal stability as a matrix framework, ensuring the basic strength of the ceramic film. In addition, silicon source and carbon source are added, each at 5%~15%, to generate silicon carbide whiskers in situ during the high-temperature reaction during sintering, thereby improving fracture toughness through a fiber toughening mechanism. The addition of sintering aids can promote the sintering reaction, promote grain boundary diffusion, and control the porosity of the ceramic film product. In particular, to reduce the synthesis temperature of SiC whiskers, this scheme preferably uses a combination catalyst—a transition metal powder of Fe powder, nano Co powder, nano Ni powder, and Cu powder—which melts into a liquid phase at the sintering temperature. The above-mentioned combination catalyst can promote the dissolution and precipitation of SiO, Si, and C, thereby reducing the initial synthesis temperature of SiC whiskers. On the other hand, by promoting various reduction reactions, the amount of silicon carbide whiskers is further increased, making the SiC content >10wt%.

[0023] In addition, this scheme also proposes a low-temperature in-situ synthesis method for ceramic films of silicon carbide whisker surface modified alumina particles, including the following steps: α-Al2O3 powder, silicon source, carbon source, catalyst and sintering aid are mixed by a layer-by-layer coating method, and the ceramic films of silicon carbide whisker surface modified alumina particles are obtained after aging of mud, drying and shaping, vacuum sintering and surface coating.

[0024] The "layer-by-layer coating method for mixing" process specifically includes the following steps: First, α-Al2O3 powder is put into a mixing device (high-power mixer), and 0.5%~1% HPMC solution from the carbon source is added under high-speed stirring to coat the surface of the α-Al2O3 powder with a layer of HPMC solution; then, a pre-mixed and uniformly mixed dry powder raw material of silicon source, dry carbon source and catalyst is added and mixed for 1~10 minutes, with the temperature not exceeding 34°C during the mixing process; then, sintering aid and liquid carbon source raw material are added and mixed evenly to obtain mud; then, pure water is added to make the water content of the mud 13%~18%; wherein, the dry carbon source includes at least one of carbon black, starch, graphite, HPMC or CMC; the liquid carbon source includes at least one of glycerol or vegetable oil.

[0025] The above-mentioned "layer-by-layer coating method" can significantly improve the uniformity of raw material dispersion and reactivity. First, α-Al2O3 powder is mixed with HPMC solution (0.5%~1%) under high-speed stirring to form an organic-inorganic hybrid interface. The hydroxyl groups of HPMC are bonded to the surface of Al2O3 to construct a 3D steric hindrance effect and prevent subsequent powder agglomeration. Then, a dry powder premix of silicon source / carbon source / catalyst is added in stages. The HPMC adhesion layer is used to achieve nanoscale in-situ adsorption to ensure that Si and C elements are in atomic-level contact at the Al2O3 grain boundaries. Finally, the sintering aid and liquid raw materials are mixed at a relatively low temperature (≤34℃) to inhibit the decomposition of organic components and maintain the rheological properties of HPMC solution. After sintering, the final mixture can form interwoven silicon carbide whiskers.

[0026] The "mud aging" process specifically includes the following steps: after mixing, the raw materials are kneaded in a kneader for 10-60 minutes; then kneaded 1-3 times on a mud-making equipment (a coarse mud-making machine with cooling water); then kneaded 1-3 times under a vacuum of ≥-0.095MPa; finally, aged for 12-72 hours at a temperature of 20-25℃ and a humidity of 50-80%.

[0027] The "drying and shaping" process specifically includes the following steps: After aging, the clay material is extruded, cut, microwave-shaped, and dried to obtain a single-channel tubular alumina support, a multi-channel flat alumina support, or a multi-channel tubular alumina support; during extrusion molding, the vacuum degree of the extrusion equipment (extruder) is ≥-0.095MPa, the extrusion speed is 0.1~5m / min, and the extrusion pressure is 1~10MPa; after being cut to the required length, it is transferred to microwave equipment (continuous microwave) for shaping, the power of each chamber in the microwave equipment is 350~900W, and the conveyor belt speed during conveying is 0.1~5m / min; during drying in a forced-air drying oven, it is dried at 40~110℃ for 1~24h.

[0028] In the "drying and forming" process, vacuum extrusion under a pressure of ≥-0.095MPa can eliminate air bubbles inside the clay material. Combined with a pressure of 1~10MPa, the green body becomes more compact, giving the tubular / flat alumina support a uniform skeletal structure. Then, microwave rapid shaping is used. Utilizing the selective heating characteristics of microwaves, moisture is allowed to migrate from the core of the green body to the outer layer in a gradient, avoiding surface cracking caused by traditional hot air shaping. The shaping time is shortened to 3~5 minutes. The final drying step is carried out at 40~110℃, and residual moisture is slowly evaporated through air circulation, reducing the moisture content of the green body.

[0029] The "vacuum sintering" process specifically includes the following steps: transporting the dried and shaped green blank to a high-temperature vacuum furnace, and sintering it at a vacuum degree ≤10. -1 The firing process is as follows: heating from room temperature to 200℃ at a rate of 10–50℃ / h, primarily to remove adsorbed water; heating from 200℃ to 600℃ at a rate of 5–20℃ / h, holding for 1–5 hours; heating from 600℃ to 800℃ at a rate of 5–20℃ / h to avoid phase transformation cracking; heating from 800℃ to the firing temperature, holding for 3–5 hours at a rate of 10–30℃ / h, during which the raw materials gradually heat up and form a melt; the firing temperature range is 1200–1400℃, where the transition metal catalyst melts into a liquid phase, promoting the dissolution and precipitation of SiO, Si, and C, forming SiC whiskers that cover the surface and neck of the alumina particles, achieving thermal equilibrium throughout the kiln. The material is then naturally cooled to room temperature to obtain the low-temperature sintered alumina ceramic support.

[0030] The "surface coating" process includes the following steps: a layer of film slurry is uniformly sprayed onto the surface of the sintered alumina ceramic support, dried, and then sintered in vacuum or air at a temperature of 1100~1200℃ for 1~3 hours; the film slurry is prepared by mixing nano-zirconia, nano-alumina or nano-silicon carbide with 1% PVA solution in a mass ratio of 1~2:8~9.

[0031] In summary, this scheme employs a low-temperature in-situ synthesis method to synergistically grow SiC whiskers on the neck and surface of α-Al₂O₃ particles. The SiC whiskers in the neck contribute to improving the mechanical strength (flexural strength ≥ 40 MPa) and chemical stability of the material. Simultaneously, the in-situ growth of SiC whiskers encapsulating α-alumina particles during the firing of the alumina ceramic film (i.e., forming a core-shell structure) helps improve the hydrophilicity of the material (wetting angle with water ≤ 5°). Furthermore, the SiC whiskers on the neck and surface of the alumina ceramic film intertwine, playing a self-anchoring role, thus resulting in excellent adhesion to the ceramic matrix. At the same time, the entire firing temperature can be controlled below 1450℃, which is lower than the traditional 1500℃ firing temperature of silicon carbide ceramic films, reducing raw material costs and fuel consumption, while significantly reducing raw material costs.

[0032] The ceramic membrane prepared by the low-temperature in-situ synthesis method of the above-mentioned silicon carbide whisker surface modified alumina particles has the following properties: wetting angle with water ≤5°, porosity ≥40%, flexural strength ≥40MPa, and pure water flux of 100 nm pore size membrane ≥600 L / (m²) under 40 kPa suction. 2 ·h).

[0033] The technical solution of this solution will be further described in detail below with reference to specific embodiments. It should be understood that the following embodiments are only used to explain this solution and are not intended to limit this solution.

[0034] Example 1 A low-temperature in-situ synthesis method for a ceramic film of silicon carbide whisker surface modified with alumina particles includes the following steps: First, 78 wt% of α-Al₂O₃ powder is added to the mixing equipment. While stirring, 1 wt% of HPMC solution from the carbon source is added to coat the surface of the α-Al₂O₃ powder with a layer of HPMC solution. Then, a mixture of 9 wt% pre-mixed silicon source (silicon micro powder: kaolin = 1:3), 5 wt% dry carbon source (carbon black: HPMC = 2:3), and 0.5 wt% catalyst (Fe powder: nano Co powder: nano Ni powder = 1:1:1) is added and mixed for 10 min. Then, 3.5 wt% sintering aid (magnesium oxide: calcium carbonate: quartz = 1:1:1) is added and mixed for 10 min. Finally, 3 wt% liquid carbon source (vegetable oil: glycerol = 1:2) is added and mixed evenly. Pure water is added to make the moisture content of the mud 15%.

[0035] After kneading the above-mentioned raw materials for 30 minutes, knead them once on a kneading machine, then knead them three times under a vacuum of ≥-0.095MPa; finally, age them for 48 hours at a temperature of 22℃ and a humidity of 75%. After aging, the clay material is extruded, cut, microwave-set, and dried to obtain an alumina support. During extrusion, the vacuum degree of the extrusion equipment is ≥-0.095MPa, the extrusion speed is 2m / min, and the extrusion pressure is 5.8MPa. After being cut to the required length, it is transferred to a microwave device for setting. The power of the microwave device is 550W, and the conveying speed is 2m / min. During drying, it is dried at 90℃ for 24 hours. The dried and shaped green body is transported to a high-temperature vacuum furnace for firing. The specific firing regime is as follows: heating from room temperature to 200℃ at a rate of 10℃ / h; heating from 200℃ to 600℃ at a rate of 5℃ / h, holding at that temperature for 3h; heating from 600℃ to 800℃ at a rate of 20℃ / h; heating from 800℃ to 1450℃, holding at that temperature for 3h, and finally cooling to room temperature. A film slurry composed of nano-silicon carbide and 1% PVA solution in a ratio of 1.5:8.5 was uniformly sprayed onto the surface of the sintered alumina ceramic support. After drying, it was sintered at a temperature of 1200℃ and held at the sintering temperature for 2 hours. After sintering, a ceramic film of alumina particles modified with silicon carbide whiskers was obtained.

[0036] Example 2 A low-temperature in-situ synthesis method for a ceramic film of silicon carbide whisker surface modified with alumina particles includes the following steps: First, 72 wt% of α-Al₂O₃ powder is added to the mixing equipment. While stirring, 0.5 wt% of HPMC solution from the carbon source is added to coat the surface of the α-Al₂O₃ powder with a layer of HPMC solution. Then, a mixture of pre-mixed silicon source (silicon micro powder: kaolin = 1:3) 9 wt%, dry carbon source (carbon black: starch: HPMC = 1:3:2) 12.5 wt%, and catalyst (Cu powder: Fe powder: nano Ni powder = 1:1:1) 0.5 wt% is added and mixed for 10 min. Then, sintering aid (magnesium oxide: calcium carbonate: zinc oxide = 1:1:1) 3.5 wt% is added and mixed for 10 min. Finally, 2% of liquid carbon source glycerol is added and mixed evenly. Pure water is added to make the moisture content of the mud 16%.

[0037] After kneading the above-mentioned raw materials for 30 minutes, knead them once on a kneading machine, then knead them three times under a vacuum of ≥-0.095MPa; finally, age them for 48 hours at a temperature of 22℃ and a humidity of 75%. After aging, the clay material is extruded, cut, microwave-set, and dried to obtain an alumina support. During extrusion, the vacuum degree of the extrusion equipment is ≥-0.095MPa, the extrusion speed is 2m / min, and the extrusion pressure is 5.8MPa. After being cut to the required length, it is transferred to a microwave device for setting. The microwave device has a power of 550W and a conveying speed of 2m / min. During drying, it is dried at 100℃ for 24 hours. The dried and shaped green body is transported to a high-temperature vacuum furnace for firing. The specific firing regime is as follows: heating from room temperature to 200℃ at a rate of 10℃ / h; heating from 200℃ to 600℃ at a rate of 5℃ / h, holding at that temperature for 3h; heating from 600℃ to 800℃ at a rate of 20℃ / h; heating from 800℃ to 1350℃, holding at that temperature for 3h, and finally cooling to room temperature. A film slurry composed of nano-zirconia and 1% PVA solution in a ratio of 1.5:8.5 was uniformly sprayed onto the surface of the sintered alumina ceramic support. After drying, it was sintered at a temperature of 1200℃ and held at the sintering temperature for 2 hours. After sintering, a ceramic film of alumina particles modified with silicon carbide whiskers was obtained.

[0038] Example 3 A low-temperature in-situ synthesis method for a ceramic film of silicon carbide whisker surface modified with alumina particles includes the following steps: First, 70 wt% of α-Al₂O₃ powder is added to the mixing equipment by mass percentage. While stirring, 1 wt% of HPMC solution from the carbon source is added to coat the surface of the α-Al₂O₃ powder with a layer of HPMC solution. Then, a mixture of 9 wt% pre-mixed silicon source (silicon micro powder: kaolin: quartz = 1:2:1), 12 wt% dry carbon source (carbon black: starch: HPMC = 1:3:2), and 1 wt% catalyst (Fe powder: Cu powder = 1:1) is added and mixed for 10 min. Next, 5 wt% sintering aid (magnesium oxide: calcium carbonate: zinc oxide = 1:1:1) is added and mixed for 10 min. Finally, 2% liquid carbon source glycerol is added and mixed evenly. Pure water is added to make the moisture content of the mud 16%.

[0039] After kneading the above-mentioned raw materials for 30 minutes, knead them once on a kneading machine, then knead them three times under a vacuum of ≥-0.095MPa; finally, age them for 48 hours at a temperature of 22℃ and a humidity of 75%. After aging, the clay material is extruded, cut, microwave-set, and dried to obtain an alumina support. During extrusion, the vacuum degree of the extrusion equipment is ≥-0.095MPa, the extrusion speed is 2m / min, and the extrusion pressure is 5.8MPa. After being cut to the required length, it is transferred to a microwave device for setting. The microwave device has a power of 550W and a conveying speed of 2m / min. During drying, it is dried at 100℃ for 24 hours. The dried and shaped green body is transported to a high-temperature vacuum furnace for firing. The specific firing regime is as follows: heating from room temperature to 200℃ at a rate of 10℃ / h; heating from 200℃ to 600℃ at a rate of 5℃ / h, holding at that temperature for 3h; heating from 600℃ to 800℃ at a rate of 20℃ / h; heating from 800℃ to 1200℃, holding at that temperature for 3h, and finally cooling to room temperature. A film slurry composed of nano-alumina and 1% PVA solution in a ratio of 1.5:8.5 was uniformly sprayed onto the surface of the sintered alumina ceramic support. After drying, it was sintered at a temperature of 1100℃ and held at the sintering temperature for 2 hours. After sintering, a ceramic film of silicon carbide whisker-modified alumina particles was obtained.

[0040] Comparative Example 1 Traditional silicon carbide ceramic membrane preparation process: 1) Preparation of liquid-phase sintered silicon carbide ceramic membrane element support.

[0041] A1 Weighing raw materials: Sodium carboxymethyl cellulose is used as the first binder and carbon black is used as the pore-forming agent. Weigh silicon carbide powder I with a particle size of 40um, kaolin, talc, sodium carboxymethyl cellulose and carbon black in a mass ratio of 100:7:4:10:8.

[0042] B1 Raw material mixing: First, the sodium carboxymethyl cellulose weighed in A1 is stirred and dissolved in warm water at 40°C. Then, silicon carbide powder I and carbon black are added in sequence and mixed evenly with a high-speed mixer. The solid content is 62%.

[0043] C1 Raw Material Mixing: Add the above mixture to a vacuum ply mill and mix repeatedly for 8 hours. During plying, the extrusion pressure is 0.10 MPa and the vacuum degree is 0.08 MPa. Aging is carried out for 16 hours. Plying is carried out again during the day and aging is carried out at night to obtain the ply material for later use.

[0044] D1 Support preform extrusion: The clay material from step C1 is placed into a vacuum extrusion molding machine with an extrusion pressure of 5.8 MPa and an extrusion die of a 19-hole tubular extrusion head to obtain a 19-hole multi-channel tubular silicon carbide support preform.

[0045] E1 Support Preform Drying: Place the extruded support preform in a room temperature and allow it to dry naturally.

[0046] In winter (November to April in northern China), the workshop temperature is below 20℃ and the relative humidity is below 50%, making the support structure very prone to cracking and difficult to dry naturally. To avoid cracking, in this comparative example, the extruded support structure was left to dry naturally at room temperature (above 20℃, relative humidity greater than 50%) for 8 minutes, and then forced to dry with warm air through a simple ventilation pipe.

[0047] F1 Support Blank Drying: After the support blank is dried at room temperature, it is placed in a drying oven and slowly heated from room temperature to 110°C over 3 hours, and held at that temperature for 1 hour; then it is cooled naturally. G1 Support Firing: The support blank dried in step F1 is loaded into a sintering furnace, the temperature is set to 800℃ and held for 2 hours, and then the temperature is raised to 1300℃ and held for 2 hours to obtain a liquid phase sintered multichannel silicon carbide support with high bonding strength.

[0048] 2) Preparation of the transition layer A2 accurately weighs silicon carbide powder II with a particle size of 5 μm, kaolin, polyvinyl alcohol as the second binder, and polyacrylic acid as the first dispersant in a mass ratio of 100:20:20:4. B2 adds deionized water to the above-weighed material and places it in a planetary ball mill. Using silicon carbide balls as the grinding media, it is ball-milled at high speed for 10 hours to obtain a highly stable transition layer slurry with a solid content as high as 40%. C2. The slurry obtained in step B2 is transferred into a slurry tank and injected into the coating device by a diversion pump. The flow time of the slurry in the multi-channel ceramic membrane support is controlled at 12s, thereby forming a transition layer on the surface of the inner pore of the support. D2 After drying the support with the transition layer formed on the surface obtained in step C2, it is transferred to a sintering furnace and sintered at 1250℃ for 1 hour, thereby preparing a dense and uniform silicon carbide intermediate transition layer on the surface of the silicon carbide support.

[0049] 3) Preparation of surface film A3 accurately weighs silicon carbide powder III with a particle size of 0.5 mm, polyvinyl alcohol, and polyacrylic acid at a mass ratio of 100:20:8; B3 adds deionized water to the above-weighed material and puts it into a planetary ball mill. Using silicon carbide balls as the grinding medium, it is ball-milled at high speed for 8 hours to obtain a highly stable coating liquid with a solid content of 35%. C3. The coating liquid obtained in step B3 is transferred into the slurry tank, and the coating liquid is injected into the coating device by the diversion pump. The flow time of the coating liquid in the internal pore of the multi-channel support is controlled at 12s, so as to form a film layer on the surface of the internal pore of the support. D3 After drying the support with the film layer formed on the surface obtained in step C3, it is transferred to a sintering furnace and sintered at 1100℃ for 1 hour, thereby preparing a dense and uniform silicon carbide film layer on the surface of the silicon carbide support.

[0050] Comparative Example 2 In this comparative example, all preparation steps and parameters are the same as in Example 1. The difference is that in the mixing process, all raw materials are directly put into the mixing equipment and mixed evenly.

[0051] Comparative Example 3 In this comparative example, all preparation steps and parameters are the same as in Example 1. The difference is that in the mixing process, the α-Al2O3 powder was not pre-coated with HPMC solution, but was added directly along with the other carbon sources.

[0052] Comparative Example 4 In this comparative example, all preparation steps and parameters are the same as in Example 1, except that no catalyst is added.

[0053] The ceramic membranes prepared in Examples 1-3 and Comparative Examples 1-4 were subjected to the following performance tests, and the specific test results are shown in the table below:

[0054] The ceramic membrane with silicon carbide whisker surface modified with alumina particles obtained in Examples 1-3 of this scheme can maintain a wetting angle with water of ≤5°, indicating good hydrophilicity; the porosity is maintained at ≥40%; the flexural strength is ≥40MPa, and it can withstand high-pressure backflush, particle erosion, and high-temperature environments; the pure water flux of the 100 nm pore size membrane under 40 kPa suction is ≥800 L / (m²). 2 ·h), with good penetration ability.

[0055] As can be seen from the test results of Comparative Example 1 in the table above, if conventional silicon carbide ceramic membranes are directly sintered at low temperature (1300℃), the resulting membrane products have too low flexural strength (20MPa), are easy to break, and cannot be used normally.

[0056] The test results of Comparative Examples 2 and 3 show that when the raw materials are mixed together directly during the mixing process, the wetting angle with water increases, and the pure water flux and flexural strength decrease. When the Al2O3 is not pre-coated with HPMC solution, the uniformity of the subsequent raw material mixing is relatively poor, the wetting angle with water increases, and the pure water flux and flexural strength also decrease to varying degrees.

[0057] As can be seen from the test results of Comparative Example 4 in the table above, since no catalyst was added to the raw materials and the product was obtained directly by low-temperature sintering, its flexural strength, pure water flux and other properties decreased to varying degrees, while the wetting angle with water increased.

[0058] Example 4 In this embodiment, all preparation steps and parameters are the same as in Example 1, except that the catalyst used is different. Specifically:

[0059] The ceramic film with modified alumina particles on the surface of silicon carbide whiskers prepared in Example 4 was subjected to performance testing. The specific test results are shown in the table below:

[0060] As shown in the test data in the table above, the adjustment of the catalyst mainly affects the pure water flux and wetting angle with water of the ceramic membrane product. The preferred catalyst combination in this scheme is Fe powder + nano Co powder + nano Ni powder, and the preferred mass ratio of each is 1:1:1, which results in a ceramic membrane product with better performance.

[0061] Example 5 In this embodiment, all preparation steps and parameters are the same as in Example 1. The difference lies in the firing regime used, specifically:

[0062] The ceramic film with modified alumina particles on the surface of silicon carbide whiskers prepared in Example 5 was subjected to performance testing. The specific test results are shown in the table below:

[0063] As shown in the test data above, adjustments to the firing regime mainly affect the pure water flux, flexural strength, and wetting angle with water of the ceramic membrane product. The preferred firing regime in this scheme is as follows: heating from room temperature to 200℃ at a rate of 10℃ / h; heating from 200℃ to 600℃ at a rate of 5℃ / h, holding for 3 hours; heating from 600℃ to 800℃ at a rate of 20℃ / h; and heating from 800℃ to 1450℃, holding for 3 hours, at a rate of 20℃ / h. The resulting ceramic membrane product exhibits superior performance.

[0064] Example 6 In this embodiment, all preparation steps and parameters are the same as in Example 1. The difference lies in the slurry used for spraying, specifically:

[0065] The ceramic film with modified alumina particles on the surface of silicon carbide whiskers prepared in Example 6 was subjected to performance testing. The specific test results are shown in the table below:

[0066] As shown in the test data in the table above, the slurry used during spraying mainly affects the pure water flux and wetting angle performance with water of the ceramic membrane product. The preferred slurry in this scheme is a membrane slurry prepared solely from nano-silicon carbide particles, which results in a ceramic membrane product with better performance.

[0067] Example 7 A low-temperature in-situ synthesis method for a ceramic film of silicon carbide whisker surface modified with alumina particles includes the following steps: First, 72 wt% of α-Al₂O₃ powder is added to the mixing equipment. While stirring, 0.5 wt% of HPMC solution from the carbon source is added to coat the surface of the α-Al₂O₃ powder with a layer of HPMC solution. Then, a mixture of pre-mixed silicon source (silicon micro powder: kaolin = 1:3) 9 wt%, dry carbon source (carbon black: starch: HPMC = 2:5:4) 11.5 wt%, and catalyst (Fe powder: nano Co powder: nano Ni powder = 1:1:1) 0.5 wt% is added and mixed for 10 min. Then, 3.5 wt% of sintering aid (magnesium oxide: calcium carbonate: quartz = 1:1:2) is added and mixed for 10 min. Finally, 3% of liquid carbon source (vegetable oil: glycerol = 1:2) is added and mixed evenly. Pure water is added to make the moisture content of the mud 15.5%.

[0068] After kneading the above-mentioned raw materials for 30 minutes, knead them once on a kneading machine, then knead them three times under a vacuum of ≥-0.095MPa; finally, age them for 48 hours at a temperature of 22℃ and a humidity of 75%. After aging, the clay material is extruded, cut, microwave-set, and dried to obtain an alumina support. During extrusion, the vacuum degree of the extrusion equipment is ≥-0.095MPa, the extrusion speed is 2m / min, and the extrusion pressure is 5.8MPa. After being cut to the required length, it is transferred to a microwave device for setting. The power of the microwave device is 550W, and the conveying speed is 2m / min. During drying, it is dried at 105℃ for 24 hours. The dried and shaped green body is transported to a high-temperature vacuum furnace for firing. The specific firing regime is as follows: heating from room temperature to 200℃ at a rate of 10℃ / h; heating from 200℃ to 600℃ at a rate of 5℃ / h, holding at that temperature for 3h; heating from 600℃ to 800℃ at a rate of 20℃ / h; heating from 800℃ to 1450℃, holding at that temperature for 3h, and finally cooling to room temperature. A film slurry composed of nano-silicon carbide and 1% PVA solution in a ratio of 1.5:8.5 was uniformly sprayed onto the surface of the sintered alumina ceramic support. After drying, it was sintered at a temperature of 1200℃ and held at the sintering temperature for 2 hours. After sintering, a ceramic film of alumina particles modified with silicon carbide whiskers was obtained.

[0069] The ceramic film with modified alumina particles on the surface of silicon carbide whiskers prepared in Example 7 was subjected to performance testing. The specific test results are shown in the table below:

[0070] The test results in the table above show that, by comprehensively adjusting the catalyst type, sintering regime, slurry used in spraying, and the proportions of each raw material, even with the sintering temperature of the ceramic membrane reduced to 1200℃, the wetting angle between the ceramic membrane and water obtained under these low-temperature sintering conditions can be maintained at 2°; the porosity can be maintained at 41%; the flexural strength can be increased to 60MPa; and the pure water flux of the 100nm pore size membrane under 40KPa suction is 1150L / (m²). 2 ·h), with excellent performance in all aspects.

[0071] The above description is only a preferred embodiment of this solution and does not limit the patent scope of this solution. All equivalent structural transformations made using the content of this specification under the inventive concept of this solution, or direct / indirect applications in other related technical fields, are included within the patent protection scope of this solution.

Claims

1. A ceramic film with silicon carbide whisker surface modified with alumina particles, characterized in that, By weight percentage, it includes the following raw materials: 70wt% to 90wt% α-Al2O3 powder, 5wt% to 15wt% silicon source, 5wt% to 15wt% carbon source, 1wt% to 5wt% sintering aid and 0.1wt% to 1wt% catalyst.

2. The ceramic film of silicon carbide whisker surface modified with alumina particles according to claim 1, characterized in that, The catalyst includes at least one of Fe powder, nano-Co powder, nano-Ni powder, and Cu powder.

3. The ceramic film of silicon carbide whisker surface modified with alumina particles according to claim 1, characterized in that, The silicon source includes at least one of silicon micropowder, kaolin, and quartz; The carbon source includes at least one of carbon black, starch, graphite, HPMC, CMC, vegetable oil, and glycerin; The sintering aid includes at least one of kaolin, magnesium oxide, calcium carbonate, silica powder, zinc oxide, and quartz.

4. The ceramic film of silicon carbide whisker surface modified with alumina particles according to claim 1, characterized in that, The particle size range of the α-Al2O3 powder is 0.5–50 μm.

5. A method for low-temperature in-situ synthesis of a ceramic film of silicon carbide whisker surface-modified alumina particles as described in claim 3, characterized in that, The process includes the following steps: mixing α-Al2O3 powder, silicon source, carbon source, catalyst and sintering aid by a layer-by-layer coating method according to mass percentage; and then preparing a ceramic film of silicon carbide whisker surface modified alumina particles by aging, drying and shaping, vacuum sintering and surface coating.

6. The low-temperature in-situ synthesis method of a ceramic film of silicon carbide whisker surface modified alumina particles according to claim 5, characterized in that, The "layer-by-layer coating method for mixing" process includes the following steps: First, α-Al2O3 powder is added to a mixing device, and HPMC solution from the carbon source is added during stirring to coat the surface of the α-Al2O3 powder with a layer of HPMC solution; then, a pre-mixed mixture of silicon source, dry carbon source, and catalyst is added and mixed for 1-10 minutes; then, sintering aid and liquid carbon source are added and mixed evenly to obtain a slurry; finally, pure water is added to make the slurry moisture content 13%-18%. The dry carbon source includes at least one of carbon black, starch, graphite, HPMC, or CMC; the liquid carbon source includes at least one of glycerol or vegetable oil.

7. The low-temperature in-situ synthesis method of a ceramic film of silicon carbide whisker surface modified alumina particles according to claim 5, characterized in that, The "mud aging" process includes the following steps: kneading the mixed raw materials for 10-60 minutes; kneading the mud 1-3 times on a mud-kneading machine, then kneading it 1-3 times under a vacuum of ≥-0.095MPa; and finally aging it for 12-72 hours at a temperature of 20-25℃ and a humidity of 50-80%.

8. The low-temperature in-situ synthesis method of a ceramic film of silicon carbide whisker surface modified alumina particles according to claim 5, characterized in that, The "drying and molding" process includes the following steps: after the aged clay is extruded, cut, microwave-shaped and dried, an alumina support is obtained; During extrusion molding, the vacuum degree of the extrusion equipment is ≥-0.095MPa, the extrusion speed is 0.1~5m / min, and the extrusion pressure is 1~10MPa; after being cut into the required length, it is transferred to microwave equipment for shaping, the power of the microwave equipment is 350~900W, and the conveying speed is 0.1~5m / min; during drying, it is dried at 40~110℃ for 1~24h. The alumina support can be a single-channel tubular alumina support, a multi-channel flat alumina support, or a multi-channel tubular alumina support.

9. The low-temperature in-situ synthesis method of a ceramic film of silicon carbide whisker surface modified alumina particles according to claim 5, characterized in that, The "vacuum sintering" process includes the following steps: transporting the dried and shaped green blank to a high-temperature vacuum furnace for firing; The firing process is as follows: heating from room temperature to 200℃ at a rate of 10–50℃ / h; heating from 200℃ to 600℃ at a rate of 5–20℃ / h, holding at that temperature for 1–5h; heating from 600℃ to 800℃ at a rate of 5–20℃ / h; heating from 800℃ to the firing temperature, holding at that temperature for 3–5h, at a rate of 10–30℃ / h; wherein the firing temperature range is 1200–1450℃.

10. The low-temperature in-situ synthesis method of a ceramic film of silicon carbide whisker surface modified alumina particles according to claim 5, characterized in that, The "surface coating" process includes the following steps: uniformly spraying a film slurry onto the surface of the sintered alumina ceramic support, drying it, and then firing it. The firing temperature is 1100~1200℃, and the temperature is maintained at the firing temperature for 1~3 hours; The film slurry is prepared by mixing nano-zirconia, nano-alumina or nano-silicon carbide with 1% PVA solution in a mass ratio of 1~2:8~9.

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