Porous ceramic tube and method for producing the same

Abstract

The application discloses a porous ceramic tube and a preparation method thereof. The preparation method of the porous ceramic tube comprises the following steps: mixing ceramic powder, a binder and a solvent to obtain a casting solution; coating an organic solution on the inner wall of a mold, and compounding ceramic particles on the organic solution, and drying to obtain a pretreated mold; injecting the casting solution into the pretreated mold, and shaping to obtain a blank; and drying and sintering the blank to obtain the porous ceramic tube. The application has the advantages of simple process and high stability, and can realize efficient and stable preparation of the ultra-thin porous ceramic tube with uniform wall thickness, high porosity and low defects.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of ceramic pipes, and particularly relates to a porous ceramic pipe and a preparation method thereof. BACKGROUND

[0002] Ultra-thin porous ceramic pipes have excellent chemical stability, high temperature resistance, high mechanical strength, and controllable pore structure, and are widely used in technical fields such as chemical industry, petrochemical industry, pharmaceutical industry, and food industry. In terms of mass transfer performance, the ultra-thin porous structure can reduce fluid transmission resistance, and the gas permeation flux thereof can be increased by 3-5 times compared with traditional materials, and the separation selectivity thereof is particularly excellent in solid-liquid separation and high-temperature gas separation applications. In the prior art, the thickness of the separation layer is controlled, and the chemical modification of sol-gel is used to reduce the mass transfer resistance in the separation process, but the packing density of the porous ceramic pipe and the additional investment cost caused by the subsequent complex process also limit its application. Therefore, researchers continue to improve the technical process.

[0003] Patent CN120365075A discloses a recrystallized silicon carbide ceramic pipe, which is prepared by mixing, aging, kneading, extrusion forming, microwave drying, and vacuum sintering processes using recrystallized silicon carbide powder, 100F powder, and D50 20-25 μm silicon carbide powder. The recrystallized silicon carbide ceramic pipe prepared by the method has excellent mechanical properties and is suitable for key equipment in semiconductor and photovoltaic production processes. However, the preparation and classification of multi-component powder (especially D50 fine powder) increase the cost of raw materials, the energy consumption of the microwave process is high, and the process is complex, and the green body is prone to defects.

[0004] Patent CN108264338A discloses a high-porosity porous ceramic pipe formed by uniform mullite whisker interlocking and a preparation method thereof. Three kinds of powders, i.e., an aluminum source, a silicon source, and a whisker growth catalyst, are uniformly mixed and then dispersed into an organic solution (PESF and PVP are dissolved in NMP solvent to obtain an organic solution). After being uniformly mixed and ball milled, the mixture is placed in a mold and extrusion phase inversion molding is performed to obtain a ceramic pipe green body. The green body is sintered at 1300-1500℃, the whiskers grow in situ and form an interlocking structure, thereby obtaining a high-porosity mullite whisker porous ceramic pipe with a porosity of >70% and a breaking strength of about >3 MPa. The mullite whisker porous ceramic pipe prepared by the method has high porosity and high mechanical strength, but the growth of the whiskers is difficult to control in the process, and the organic solvent (NMP) in the raw material is toxic and difficult to recover, increasing the environmental treatment cost.

[0005] So far, researchers have carried out a large amount of research work in the preparation direction of the ultra-thin porous ceramic tube. However, the porous ceramic tube prepared by the existing process still has problems such as large wall thickness, complex preparation process, embryo body prone to defects and low yield, which restricts its application in a wider field. Therefore, according to the actual industrial demand, improving the preparation process of the ultra-thin porous ceramic tube, controlling the wall thickness and porosity of the ceramic tube, and improving the yield have become key technical problems to be solved at present. SUMMARY

[0006] The purpose of the present application is to provide a porous ceramic tube and a preparation method thereof, which has a simple process, combines embryo body forming and drying, does not need to remove or move the formed wet blank body for drying, and realizes efficient and stable preparation of the porous ceramic tube with ultra-thin wall thickness, high porosity, low defects and high performance.

[0007] In order to achieve the above-mentioned purpose, the technical scheme provided by one specific embodiment of the present application is as follows:

[0008] A preparation method of a porous ceramic tube, the preparation method of the porous ceramic tube comprises the following steps:

[0009] Mixing ceramic powder, binder and solvent to obtain a casting solution;

[0010] Coating an organic solution on the inner wall of the mold, and compounding ceramic particles on the organic solution, and drying to obtain a pretreated mold;

[0011] Injecting the casting solution into the pretreated mold to form an embryo body;

[0012] Drying and sintering the embryo body to obtain a porous ceramic tube.

[0013] In one or more embodiments of the present application, the organic solution is at least one of a polyvinyl alcohol solution and a polyvinyl butyral alcohol solution; and / or,

[0014] The mass concentration of the organic solution is 5%-8%; and / or,

[0015] The coating thickness of the organic solution is 5-20 mu m.

[0016] In one or more embodiments of the present application, the ceramic particles are at least one of alumina particles, zirconia particles, titanium oxide particles and silicon nitride particles; and / or,

[0017] The average particle size of the ceramic particles is 20 nm-1 mu m.

[0018] In one or more embodiments of the present application, the mass ratio of the organic solution to the ceramic particles is 1: (0.5-1.5).

[0019] In one or more embodiments of the present application, the roughness Ra of the pre-processed inner wall of the mold is 3.2 μm-12.5 μm.

[0020] In one or more embodiments of the present application, the ceramic powder is at least one of alumina, zirconia, titania, silicon nitride; and / or,

[0021] The particle size of the ceramic powder is 20 nm-1 μm; and / or,

[0022] The binder is at least one of polyvinyl alcohol, polyacrylic acid, polyethylene glycol, methyl cellulose; and / or,

[0023] The solvent is at least one of water, ethanol.

[0024] In one or more embodiments of the present application, in the casting solution, the mass fraction of the ceramic powder is 40%-70%; and / or,

[0025] In the casting solution, the mass fraction of the binder is 5%-10%; and / or,

[0026] In the casting solution, the mass fraction of the solvent is 20%-55%; and / or,

[0027] The viscosity of the casting solution is 1000 cp-2000 cp.

[0028] In one or more embodiments of the present application, the mold is tubular, the material of the mold is quartz, stainless steel or ceramic, and the inner diameter of the mold is 0.8 mm-20 mm.

[0029] In one or more embodiments of the present application, after the ceramic particles are compounded on the organic solution, drying is performed at 30°C-50°C for 5 min-20 min; and / or,

[0030] After the ceramic powder, the binder and the solvent are mixed, ball milling is performed for 6 h-12 h to obtain the casting solution; and / or,

[0031] When the casting solution is injected into the pre-processed mold, the casting solution is previously stirred at a speed of 300 r / min-600 r / min at 20°C-50°C; and / or,

[0032] The drying conditions of the embryo are: temperature 35°C-75°C, time 0.5 h-3 h; and / or,

[0033] The sintering conditions are as follows: under an inert atmosphere, first, heating at a heating rate of 1-3 DEG C / min to 400-600 DEG C, and keeping for 1-2 h; then, heating at a heating rate of 3-5 DEG C / min to 800-1000 DEG C, and keeping for 0.5-1 h; finally, heating at a heating rate of 5-10 DEG C / min to 1200-1400 DEG C, and keeping for 1-2 h.

[0034] In one or more embodiments of the present application, the vacuum-driven operation is: using a vacuum pump to generate negative pressure in the pretreated mold, so that the casting solution is injected into the pretreated mold; and / or,

[0035] The in-situ drying operation is: drying the embryo and the mold together.

[0036] Another specific embodiment of the present application provides a technical solution as follows:

[0037] A porous ceramic tube is prepared by the above method.

[0038] In one or more embodiments of the present application, the wall thickness of the porous ceramic tube is 90-110 μm.

[0039] Compared with the prior art, the present application has the following beneficial effects:

[0040] (1) The present application combines vacuum-driven filling forming and in-situ drying process to form integrated continuous operation, which is simple and controllable. After forming, the wet embryo can be dried without moving, which reduces the risk of embryo damage and improves production efficiency and yield.

[0041] (2) The present application uses a vacuum pump to drive the casting solution to form in the mold, so that the casting solution uniformly fills the mold, avoiding the problem of uneven wall thickness caused by unstable flow of the casting solution, and improving the yield. Combined with the inner wall of the mold pretreated by organic solution and ceramic particle coating, the casting solution is uniformly spread and adhered, successfully preparing a ceramic tube green body with small wall thickness and uniform thickness and complete structure, solving the problems of uneven wall thickness and easy to produce pinholes in traditional methods.

[0042] (3) The present application uses mold outer wall heating method to dry the wet embryo in-situ, so that the wet embryo is uniformly heated and dried from the outside to the inside in the forming mold, relieving the internal stress caused by water gradient evaporation, and avoiding defects such as cracking and bending deformation in the drying process. Combined with subsequent stepwise heat treatment, the complete decomposition of organic matter and the uniform shrinkage of ceramic particles are ensured, preventing cracking and deformation in the high-temperature sintering stage, realizing the synergistic regulation of ultra-thin wall thickness and high porosity, and stable process.

[0043] (4) The process is simple, efficient and has high product yield, and the prepared porous ceramic pipe has an ultrathin wall thickness, high porosity, uniform and stable structure and good mechanical properties. BRIEF DESCRIPTION OF DRAWINGS

[0044] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the drawings needed to be used in the embodiments or the prior art description will be briefly introduced below. Obviously, the drawings described below are only some embodiments described in the present application, and other drawings can be obtained by those skilled in the art without creative labor.

[0045] Figure 1 Flow chart for the preparation method of the porous ceramic pipe in an embodiment of the present application;

[0046] Figures 2-3 Sample photo of the porous ceramic pipe in Example 1 of the present application;

[0047] Figure 4 Metallographic microscope photo of the cross section of the porous ceramic pipe in Example 1 of the present application. DETAILED DESCRIPTION

[0048] In order to make the person skilled in the art better understand the technical solutions in the present disclosure, the technical solutions in the embodiments of the present disclosure will be clearly and completely described below. Obviously, the described embodiments are only some of the embodiments of the present disclosure, not all. Based on the embodiments in the present disclosure, all other embodiments obtained by those skilled in the art without creative labor should be within the scope of protection of the present disclosure.

[0049] Traditional porous ceramic pipe preparation processes (such as extrusion molding, slip casting, etc.) are difficult to realize the synergistic regulation of ultrathin wall thickness and high porosity, and have problems such as low product yield, easy drying and cracking of pipe embryo body, and sintering deformation, which limits their application in the fields of efficient separation and catalysis.

[0050] Patent CN119499891A provides an asymmetric ceramic hollow fiber nanofiltration membrane and a preparation method thereof. The asymmetric ceramic hollow fiber nanofiltration membrane has a ceramic hollow fiber membrane base, a gamma-mesoporous intermediate layer and a microporous separation layer from inside to outside. The asymmetric ceramic hollow fiber nanofiltration membrane prepared by the method can provide greater packing density and specific surface area while reducing the mass transfer resistance in the separation process. However, this process requires multiple coating, the interlayer bonding force is weak, and the precursor required for sol-gel is expensive, increasing the cost.

[0051] Patent CN108686524A discloses a method for preparing silicon carbide ceramic hollow fiber membranes reinforced and toughened with silicon carbide whiskers. First, raw materials are mixed in a certain proportion and ball-milled into a casting slurry. Then, the slurry is extruded and spun to obtain a green body. Finally, a phase transformation / high-temperature sintering technique is used to obtain the finished silicon carbide ceramic hollow fiber membrane reinforced and toughened with silicon carbide whiskers. Due to the combined effect of pull-out bridging and crack redirection mechanisms of silicon carbide whiskers, the finished hollow fiber membrane has a self-supporting asymmetric structure and exhibits high strength, high packing density, large permeation flux, and good thermal shock resistance. However, silicon carbide whiskers are an expensive raw material, resulting in high costs. Furthermore, whiskers are prone to agglomeration, leading to poor slurry uniformity and stability, which can cause uneven shape and wall thickness of the hollow fiber green body, and even blockage of the spinning head, resulting in a low yield.

[0052] Patent CN105536559A discloses a mullite ceramic hollow fiber membrane and its preparation method. The resulting mullite ceramic hollow fiber membrane has high strength, high porosity, and high water flux, and can be directly used as the substrate of microfiltration or ultrafiltration membranes or as a catalyst support in membrane reactors. However, this method requires a high sintering temperature for mullite, typically above 1500℃, placing high demands on sintering equipment, resulting in high energy consumption. Furthermore, the phase transformation spinning process is difficult to control, leading to poor wall thickness uniformity, and the membrane is prone to cracking, bubbles, and even collapse during subsequent sintering.

[0053] Patent CN103349918A discloses a method for preparing multi-channel ceramic hollow fiber membranes, which involves uniformly mixing ceramic powder, polymer, organic solvent, and dispersant in a specific ratio to prepare a casting solution. The multi-channel ceramic hollow fiber membrane prepared by this method possesses its own asymmetric structure and an internal skeletal structure, simultaneously meeting the strength and flux requirements of ceramic hollow fiber membranes. However, this method requires sophisticated mold design and processing, involves complex manufacturing processes, and the prepared green bodies are prone to issues such as inconsistent wall thickness, channel deformation, and even blockage, resulting in a low yield.

[0054] Patent CN103111192A provides a method for microstructure modulation of ceramic hollow fiber membranes. This method is simple to operate and low in cost. It can utilize the different gelation rates between the inner and outer coagulation baths and the solvent during phase transformation to prepare hollow fiber membranes with different asymmetric structures. However, this method can result in pinholes or pores during phase transformation, and the process control is relatively complex, with poor process repeatability.

[0055] In view of the deficiencies of the prior art, the present application first prepares a casting solution with high solid content and high viscosity; a layer of organic solution is first coated on the inner wall of the mold, and then a layer of ceramic powder is added for pretreatment, so as to increase the roughness of the mold wall, improve the adhesion between the mold and the casting solution, and facilitate the forming of the ultra-thin body; then the casting solution is stably transported into the pretreated mold by using a vacuum pump, so as to avoid the defects of the body caused by unstable flow of the casting solution in the traditional extrusion or grouting process, thereby realizing the forming of the high-quality body with ultra-thin wall thickness and uniform wall thickness; after forming, the wet body does not need to be moved, and is directly dried in situ by the heating device on the outer wall of the mold, so as to avoid the cracking and deformation problems caused by the movement and drying stress concentration; finally, multi-stage programmed temperature sintering is carried out in an inert atmosphere, so as to realize the densification and stabilization of the pore structure of the ultra-thin porous ceramic pipe body, and improve the mechanical properties while maintaining high porosity.

[0056] The present application has the advantages of simple process, combination of body forming and drying, no need to remove the formed wet body or move the formed wet body for drying, realization of efficient and stable preparation of the porous ceramic pipe with ultra-thin wall thickness, high porosity, low defects and high performance.

[0057] A specific embodiment of the present application provides a preparation method of a porous ceramic pipe, as shown in the following formula (I): Figure 1 The preparation method of the porous ceramic pipe comprises the following steps:

[0058] Step 1: mixing ceramic powder, a binder and a solvent to obtain a casting solution.

[0059] Specifically, the ceramic powder, the binder and the solvent are mixed, and then ball-milled by a planetary ball mill for 6h-12h to obtain a casting solution with a viscosity of 1000cp-2000cp. The ball-milling can realize the full dispersion of the ceramic powder, and prepare the casting solution with high solid content and high viscosity, thereby providing a basis for subsequent forming.

[0060] Further, the ceramic powder is at least one of alumina, zirconia, titania and silicon nitride, and the particle size of the ceramic powder is 20nm-1μm. The binder is at least one of polyvinyl alcohol, polyacrylic acid, polyethylene glycol and methyl cellulose, and the solvent is water, ethanol or a mixed solution of water and ethanol with a volume ratio of 1:1-3:1.

[0061] Further, in the casting solution, the mass fraction of the ceramic powder is 40%-70%, the mass fraction of the binder is 5%-10%, and the mass fraction of the solvent is 20%-55%.

[0062] Step 2: coating an organic solution on the inner wall of the mold, scattering ceramic particles on the organic solution, and drying the mold in an oven at 30℃-50℃ for 5min-20min to obtain a pretreated mold.

[0063] Specifically, the mold is a rigid tubular mold, which is made of quartz, stainless steel or ceramic, and the inner diameter of the mold is 0.8mm-20mm.

[0064] Further, the organic solution is at least one of polyvinyl alcohol solution and polyvinyl butyral alcohol solution, the mass concentration of the organic solution is 5%-8%, and the coating thickness of the organic solution is 5μm-20μm, which can be specifically 5μm, 8μm, 10μm, 15μm, 18μm or 20μm.

[0065] Specifically, the inner wall of the mold is coated with an organic solution first, and then a layer of ceramic particles is added for pretreatment, so that the organic solution forms a bonding film on the inner surface of the mold to fix the ceramic particles, the ceramic particles are attached to the inner wall of the mold, a rough surface is formed, the roughness of the mold pipe wall is increased, the adhesion between the mold and the casting solution is improved, and the ultra-thin embryo is conveniently formed. The above-mentioned organic solution is residue-free after sintering and does not pollute the sample, and is cheap and easy to obtain.

[0066] The polyvinyl alcohol solution is specifically a polyvinyl alcohol aqueous solution. If the casting solution is a water-based casting solution, the organic solution is polyvinyl alcohol solution; if the casting solution is an organic solvent-based casting solution, such as using ethanol as a solvent to prepare the casting solution, the organic solution is polyvinyl butyral alcohol solution, so as to avoid the bonding film formed by dissolving the polyvinyl alcohol solution in the organic solvent-based casting solution, and increase the adhesion.

[0067] Further, the ceramic particles are at least one of alumina particles, zirconia particles, titania particles and silicon nitride particles, the average particle size of the ceramic particles is 20nm-1μm, and the mass ratio of the organic solution to the ceramic particles is 1: (0.5-1.5). The same type of ceramic particles as the ceramic powder is selected, in the sintering process, the bonding film formed by the organic solution is removed, and the ceramic particles can participate in the sintering process of the embryo, and finally form a finished product together with the embryo.

[0068] In the present application, after coating an organic solution on the inner wall of the mold, ceramic particles are scattered on the organic solution. Compared with the method of mixing ceramic particles in the organic solution in advance and then coating, the method in the present application uses the organic solution to bond the ceramic particles on the surface of the mold to form a rough structure, so that the surface of the mold has a high roughness, the casting solution flows into the gap between the ceramic particles, prevents flow and slip, and facilitates molding.

[0069] Further, the roughness Ra of the pretreated inner wall of the mold is 3.2μm-12.5μm, according to the inner diameter of the mold, such as the inner diameter of the mold is less than 2mm, the roughness Ra is controlled to be 3.2μm-6.3μm; if the inner diameter of the mold is 2mm-20mm, the roughness Ra is controlled to be 6.3μm-12.5μm.

[0070] The roughness of the inner wall of the pre-processed mold is tested as follows: the pre-processed mold is cut along the axial direction, the mold is cleaned with anhydrous ethanol, and after drying, the mold is fixed on a measuring platform, and the roughness of the mold is measured at three different positions along the axial direction by using a stylus surface roughness measuring instrument (model: BC200-S).

[0071] In step 3, the casting solution is injected into the casting solution tank, the stirrer at the bottom of the casting solution tank is first started, the rotating speed is controlled to be 300 r / min-600 r / min, and the temperature is controlled to be 20℃-50℃, so as to prevent the casting solution from settling by stirring; then the vacuum pump is started, the casting solution is injected into the pre-processed mold through the casting solution conveying pipeline, and the ceramic body is formed after molding, and the casting solution overflowing from the port of the mold is collected by the recovery tank.

[0072] Specifically, the vacuum pump provides power to uniformly fill the mold with the casting solution, the flow rate of the casting solution is stable, the defect of uneven wall thickness caused by unstable flow of the casting solution is avoided, and the stability and high repeatability of the molding are ensured.

[0073] In step 4, the electric heating sleeve of the heating device on the outer wall of the mold is started to dry the body, the drying temperature is 35℃-75℃, and the drying time is 0.5h-3h.

[0074] Specifically, the electric heating sleeve on the outer side of the mold is used to dry the body in situ, so as to avoid cracking or deformation of the body due to movement and uneven shrinkage.

[0075] In step 5, the dried body is placed in a sintering furnace together with the mold, and heat treatment is performed in an inert atmosphere, and after the heat treatment is completed, the porous ceramic tube is obtained after cooling to room temperature.

[0076] Specifically, the operation of heat treatment is as follows: in an inert atmosphere, first, the temperature is raised to 400℃-600℃ at a heating rate of 1℃ / min-3℃ / min, and the temperature is kept for 1h-2h; then the temperature is raised to 800℃-1000℃ at a heating rate of 3℃ / min-5℃ / min, and the temperature is kept for 0.5h-1h; finally, the temperature is raised to 1200℃-1400℃ at a heating rate of 5℃ / min-10℃ / min, and the temperature is kept for 1h-2h. Through the staged heat treatment, the sintering of the ultra-thin porous ceramic tube is completed in an inert atmosphere. The slow heating program is beneficial to the discharge of the binder, and avoids the cracking of the body caused by rapid heating. Finally, high-temperature sintering makes the ceramic particles firmly combined, ensuring high porosity while obtaining good mechanical strength.

[0077] Another specific embodiment of the present application provides a porous ceramic tube prepared by the preparation method of the porous ceramic tube.

[0078] Specifically, the preparation method of the present application can prepare the ultra-thin porous ceramic tube with a wall thickness of 90-110 μm, and the wall thickness is uniform and the porosity is high.

[0079] Example 1

[0080] The specific steps of the preparation method of the porous ceramic tube in the present example are as follows:

[0081] (1) Preparation of the casting solution: the alumina ceramic powder with an average particle size of 500 nm (60% by mass), polyvinyl alcohol binder (8% by mass) and deionized water solvent (32% by mass) are mixed, and placed in a planetary ball mill at a rotation speed of 300 r / min for 8 h to obtain a uniform casting solution with a viscosity of about 1500 cp.

[0082] (2) Mold pretreatment: a quartz glass mold with an inner diameter of 2 mm is selected, and a 5% by mass polyvinyl alcohol aqueous solution is uniformly coated on the inner wall to a thickness of 5 μm, and then a layer of alumina ceramic powder with an average particle size of 200 nm is immediately sprinkled, and the mass ratio of the organic solution to the ceramic particles is 1:0.5, so that the powder is uniformly attached and the inner wall roughness is increased, and the roughness of the pretreated mold is 6.3 μm.

[0083] (3) Casting forming: the casting solution prepared in step (1) is injected into the casting solution tank, the stirrer at the bottom of the tank is turned on, the rotation speed is controlled at 400 r / min, and the temperature is controlled at 25℃ to prevent the powder from settling. The vacuum pump is turned on, and the casting solution is smoothly injected into the pretreated mold until it is filled, and the casting solution overflowing from the port of the mold is collected by the recovery tank to obtain a ceramic tube wet embryo.

[0084] (4) Embryo drying: the electric heating jacket arranged on the outer wall of the mold is turned on, and the temperature is set to 50℃, and the ceramic tube wet embryo in the mold is dried in situ, and the drying time is 2 h.

[0085] (5) Sintering and demolding: the dried ceramic tube embryo is placed in a high-temperature sintering furnace together with the quartz mold, and the temperature is raised in the following program: first, the temperature is raised to 500℃ at a rate of 2℃ / min, and the temperature is kept for 1.5 h; then the temperature is raised to 900℃ at a rate of 4℃ / min, and the temperature is kept for 1 h; finally, the temperature is raised to 1300℃ at a rate of 8℃ / min, and the temperature is kept for 1.5 h. The sintered ultra-thin porous ceramic tube is taken out from the mold after the furnace is cooled to room temperature.

[0086] The sample photo of the porous ceramic tube prepared in the present example is shown in Figures 2-3 , and the cross-section metallographic microscope photo is shown in Figure 4 .

[0087] Example 2

[0088] The preparation method of the porous ceramic tube in this embodiment has the following specific steps:

[0089] (1) Preparation of casting solution: zirconium oxide ceramic powder with an average particle size of 20 nm (mass fraction 55%), polyethylene glycol binder (mass fraction 7%) and ethanol solvent (mass fraction 38%) were mixed, and placed in a planetary ball mill at a speed of 350 r / min for 10 h to obtain a uniform casting solution with a viscosity of about 1800 cp.

[0090] (2) Mold pretreatment: a stainless steel mold with an inner diameter of 5 mm was selected, and a layer of polyvinyl butyl alcohol ethanol solution with a mass fraction of 6% was uniformly coated on the inner wall, with a coating thickness of 10 μm. Then, a layer of zirconium oxide ceramic powder with an average particle size of 20 nm was immediately sprinkled, and the mass ratio of organic solution to ceramic particles was 1:1. The powder was uniformly attached to increase the roughness of the inner wall. The roughness of the pretreated mold was 8.2 μm.

[0091] (3) The casting solution prepared in step (1) was injected into the casting solution tank, the stirrer at the bottom of the tank was turned on, the speed was controlled at 500 r / min, and the temperature was controlled at 30℃ to prevent the powder from settling. The vacuum pump was turned on, and the casting solution was smoothly injected into the pretreated mold until it was filled. The casting solution overflowing from the mold port was collected by the recovery tank, and the ceramic tube wet embryo was obtained.

[0092] (4) Embryo drying: the electric heating jacket set on the outer wall of the mold was turned on, and the temperature was set to 60℃. The ceramic tube wet embryo in the mold was dried in situ, and the drying time was 1.5 h.

[0093] (5) Sintering and demolding: the dried ceramic tube embryo was placed in a high-temperature sintering furnace together with the mold, and the program temperature rising sintering was carried out in argon atmosphere: first, the temperature was raised to 550℃ at a rate of 3℃ / min, and the temperature was kept for 1 h; then the temperature was raised to 900℃ at a rate of 5℃ / min, and the temperature was kept for 1 h; finally, the temperature was raised to 1250℃ at a rate of 8℃ / min, and the temperature was kept for 2 h. The sintered ultra-thin porous ceramic tube was taken out from the mold after the furnace was cooled to room temperature.

[0094] Example 3

[0095] The preparation method of the porous ceramic tube in this embodiment has the following specific steps:

[0096] (1) Preparation of casting solution: zirconium oxide ceramic powder with an average particle size of 20 nm (mass fraction 55%), polyethylene glycol binder (mass fraction 7%) and ethanol solvent (mass fraction 38%) were mixed, and placed in a planetary ball mill at a speed of 350 r / min for 10 h to obtain a uniform casting solution with a viscosity of about 1800 cp.

[0097] (2) Mold pretreatment: an alumina ceramic mold with an inner diameter of 10 mm was selected, and a layer of polyvinyl alcohol solution with a mass fraction of 7% was uniformly coated on the inner wall, with a coating thickness of 15 μm, and then a layer of titanium oxide powder with an average particle size of 500 nm was immediately sprinkled, with a mass ratio of organic solution to ceramic particles of 1:1.5, so that the powder was uniformly attached and the inner wall roughness was increased. The roughness of the pretreated mold was 10.6 μm.

[0098] (3) Casting film forming: the casting film solution prepared in step (1) was injected into the casting film solution tank, the stirrer at the bottom of the tank was turned on, the rotating speed was controlled at 350 r / min, and the temperature was controlled at 40℃ to prevent the powder from settling. The vacuum pump was turned on, and the casting film solution was smoothly injected into the pretreated mold until it was filled. The casting film solution overflowing from the mold port was collected by the recovery tank, and the ceramic tube wet embryo was obtained.

[0099] (4) Embryo drying: the electric heating jacket set on the outer wall of the mold was turned on, and the temperature was set at 45℃. The ceramic tube wet embryo in the mold was dried in situ, and the drying time was 2.5 h.

[0100] (5) Sintering and demolding: the dried ceramic tube embryo was placed in a high-temperature sintering furnace together with the mold, and sintered in a nitrogen atmosphere: heated to 400℃ at a rate of 3℃ / min, kept for 2 h; heated to 800℃ at a rate of 5℃ / min, kept for 1 h; heated to 1200℃ at a rate of 10℃ / min, kept for 1 h. The sintered ultra-thin porous ceramic tube was taken out of the mold after the furnace was cooled to room temperature.

[0101] Example 4

[0102] The preparation method of the porous ceramic tube in this embodiment is as follows:

[0103] (1) Preparation of casting film solution: alumina ceramic powder with an average particle size of 200 nm (mass fraction 70%), polyvinyl alcohol binder (mass fraction 10%) and deionized water solvent (mass fraction 20%) were mixed and placed in a planetary ball mill at a rotating speed of 320 r / min for 9 h to obtain a uniform casting film solution with a viscosity of about 1900 cp.

[0104] (2) Mold pretreatment: a stainless steel mold with an inner diameter of 0.8 mm was selected, and a layer of polyvinyl alcohol aqueous solution with a mass fraction of 5% was uniformly coated on the inner wall, with a coating thickness of 20 μm, and then a layer of alumina powder with an average particle size of 100 nm was immediately sprinkled, with a mass ratio of organic solution to ceramic particles of 1:0.7, so that the powder was uniformly attached and the inner wall roughness was increased. The roughness of the pretreated mold was 3.2 μm.

[0105] (3) Casting film forming: the casting film solution prepared in step (1) is injected into a casting film solution tank, the bottom agitator is turned on, the rotating speed is controlled at 300 r / min, and the temperature is controlled at 50°C to prevent the powder from settling. The vacuum pump is turned on, the casting film solution is smoothly injected into the pretreated mold until it is filled, the overflowed casting film solution at the mold port is collected by the recovery tank, and a ceramic tube wet embryo is obtained.

[0106] (4) Embryo drying: the electric heating jacket arranged on the outer wall of the mold is turned on, the temperature is set at 35°C, the ceramic tube wet embryo in the mold is dried in situ, and the drying time is 3 h.

[0107] (5) Sintering and demolding: the dried ceramic tube embryo is placed in a high-temperature sintering furnace together with the mold, and sintering is performed in a nitrogen atmosphere: the temperature is raised to 450°C at a rate of 2.5°C / min, the temperature is kept for 2 h; the temperature is raised to 850°C at a rate of 4°C / min, the temperature is kept for 1 h; the temperature is raised to 1350°C at a rate of 6°C / min, and the temperature is kept for 2 h. The sintered ultra-thin porous ceramic tube is taken out of the mold after the furnace is cooled to room temperature.

[0108] Example 5

[0109] The specific steps of the preparation method of the porous ceramic tube in this example are as follows:

[0110] (1) Preparation of casting film solution: silicon nitride ceramic powder with an average particle size of 1 μm (mass fraction 50%), polyacrylic acid binder (mass fraction 6%) and deionized water solvent (mass fraction 44%) are mixed, placed in a planetary ball mill at a rotating speed of 400 r / min for 6 h, and a uniform casting film solution with a viscosity of about 1200 cp is obtained.

[0111] (2) Mold pretreatment: a quartz mold with an inner diameter of 20 mm is selected, a layer of polyvinyl alcohol aqueous solution with a mass fraction of 8% is uniformly coated on the inner wall, the coating thickness is 18 μm, then a layer of silicon nitride powder with an average particle size of 400 nm is immediately sprinkled, the mass ratio of organic solution to ceramic particles is 1:1.2, the powder is uniformly attached, the roughness of the inner wall is increased, and the roughness of the pretreated mold is 12.5 μm.

[0112] (3) Casting film forming: the casting film solution prepared in step (1) is injected into a casting film solution tank, the bottom agitator is turned on, the rotating speed is controlled at 300 r / min, and the temperature is controlled at 50°C to prevent the powder from settling. The vacuum pump is turned on, the casting film solution is smoothly injected into the pretreated mold until it is filled, the overflowed casting film solution at the mold port is collected by the recovery tank, and a ceramic tube wet embryo is obtained.

[0113] (4) Embryo drying: the electric heating jacket arranged on the outer wall of the mold is turned on, the temperature is set at 35°C, the ceramic tube wet embryo in the mold is dried in situ, and the drying time is 3 h.

[0114] (5) Sintering demolding: the dried ceramic tube blank is placed in a high-temperature sintering furnace together with the mold, and sintered under an argon atmosphere: heated to 600°C at 1°C / min, kept for 1 h; heated to 1000°C at 3°C / min, kept for 0.5 h; heated to 1400°C at 5°C / min, kept for 1 h. The sintered ultra-thin porous ceramic tube is taken out of the mold after the furnace cools to room temperature.

[0115] Comparative Example 1

[0116] The preparation method of the porous ceramic tube in this comparative example is basically the same as that in Example 1, except that the casting solution is extruded into the spinneret, and the membrane extruded from the spinneret is immersed in an external coagulation bath (water, temperature 20-30°C) to gel and solidify to form a ceramic membrane green body, and then naturally dried and placed in a high-temperature furnace; heated to 700°C to remove organic polymers, and then heated to 1400°C for sintering, and then naturally cooled to obtain the porous ceramic tube.

[0117] Comparative Example 2

[0118] The preparation method of the porous ceramic tube in this comparative example is basically the same as that in Example 1, except that the step (2) mold pretreatment operation is not performed, and a smooth inner wall quartz glass mold is directly used.

[0119] The porosity, average pore size, wall thickness, nitrogen permeability, and pure water flux of the samples prepared in Examples 1-5 and Comparative Examples 1-2 are tested, and the specific test methods are as follows:

[0120] (1) Porosity test: the porosity is tested by the Archimedes principle method (drainage method): the porosity is calculated according to the change in mass of the sample before and after being immersed in alcohol, and the calculation formula is:

[0121]

[0122] Wherein, p is the porosity / %, m0 is the original weight of the sample, m1 is the suspended weight of the sample in the liquid, and m2 is the wet weight of the sample.

[0123] (2) Pore size analyzer test: the sample is fully wetted with a wetting agent, one end of the sample is placed in a PVC tube for sealing, and the other end is placed in the pore size analyzer mold port, a test gas cylinder (nitrogen) is opened, and the upper limit of the test pressure is set to 80 KPa. As the test pressure rises, the wetting liquid in the pores is pushed out in turn, allowing the gas to pass through, until all the pores are opened, reaching the same permeability as the dry membrane; the test results are recorded according to the instrument analysis.

[0124] (3) Wall thickness test: a cross section of the ultra-thin porous ceramic tube is taken to prepare a metallographic sample, and the wall thickness is directly observed and measured under a metallographic microscope.​

[0125] (4) Nitrogen permeability test: The membrane tube is installed in the test pool by the permeability test device built in the laboratory, and the sealing is ensured. The nitrogen inlet pressure is adjusted to the set value, and after the system is stable, the transmembrane pressure difference, temperature and gas volume flow rate on the permeation side are recorded. Change the pressure and repeat the measurement, and record the data.

[0126] Gas permeation flux calculation formula: J= ;

[0127] J: mol·m -2 ·s -1 ·Pa -1 ; Q: volume flow rate (converted to flow rate at standard temperature and pressure, such as mol / s); A: effective permeation area of the membrane (m 2 ); ΔP: transmembrane pressure difference (Pa).

[0128] (5) Pure water flux test: At 1 MPa and 25°C, the volume of pure water permeating per unit membrane area per unit time is measured.

[0129] The pure water flux (Jw) calculation formula is: Jw= , wherein Jw: pure water flux (m 3 ·m -2 ·h -1 ); V: volume of permeate collected in time t (m 3 ); A: effective filtration area (m 2 ); t: collection time (h).

[0130] The sample test data of Examples 1-5 and Comparative Example 1 are recorded as shown in the following table.

[0131] Table 1 Porosity, average pore size, wall thickness, nitrogen permeation flux, pure water flux, and product yield of samples in each example and each comparative example

[0132]

[0133] Compared with the sample of Example 1, the sample prepared by Comparative Example 1 has a higher wall thickness, and the higher wall thickness increases the gas permeation resistance, and the nitrogen permeation flux is significantly lower than that of Example 1. At the same time, the process product yield of Comparative Example 1 is low, and the green body is easy to crack. The traditional phase inversion spinning process itself is complex, including dry spinning process, coagulation bath and other process variable control. Embodiments are prone to defects such as pinholes, cracking and uneven wall thickness during solidification and drying. The process combination of the present application by forming and drying integration is beneficial to improve the product yield, repeatability and uniform sample thickness.

[0134] The sample prepared by Comparative Example 2 has poor uniformity of wall thickness, embryo body is easy to crack and deform, surface has stripes, and the yield is less than 30%. Compared with Example 1, Comparative Example 2 does not perform the mold pretreatment operation, resulting in insufficient adhesion between the inner wall of the mold and the casting solution. During the filling and drying of the casting solution, the embryo body and the inner wall of the mold have a relative "slip", resulting in problems such as uneven wall thickness, surface stripes, and easy cracking.

[0135] From the results of the above examples and comparative example tests, it can be seen that the process of the present application is simple, has high yield, and has high controllability of conditions. The ultra-thin porous ceramic pipe prepared has a wall thickness of 90 μm-110 μm, uniform wall thickness, high porosity, and effectively reduces the permeation resistance. Moreover, the process combination of molding and drying integration is adopted, which improves the yield and the repeatability of production, and solves the problems of easy cracking of green body and low yield of existing processes.

[0136] It is apparent to those skilled in the art that the present disclosure is not limited to the details of the foregoing exemplary embodiments, and that the present disclosure can be implemented in other specific forms without departing from the spirit or essential characteristics of the present disclosure. Therefore, the embodiments should be considered in all respects as illustrative and not restrictive, and the scope of the present disclosure is defined by the appended claims rather than the foregoing description, and it is intended to include all changes falling within the meaning and range of equivalents of the elements of the claims. Therefore, the scope of the present disclosure should be defined by the appended claims rather than the foregoing description, and it is intended to include all changes falling within the meaning and range of equivalents of the elements of the claims.

[0137] Furthermore, it should be understood that, although the present specification is described in terms of embodiments, not every embodiment contains only one independent technical solution, and the description of the specification is only for the sake of clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can be appropriately combined to form other embodiments that those skilled in the art can understand.

Claims

1. A method for producing a porous ceramic tube, characterized by, The preparation method of the porous ceramic tube comprises the following steps: The ceramic powder, the binder and the solvent are mixed to obtain a casting solution; in the casting solution, the mass fraction of the ceramic powder is 40%-70%, and the viscosity of the casting solution is 1000cp-2000cp; An organic solution is coated on the inner wall of the mold, the ceramic particles are compounded on the organic solution, and drying is performed to obtain a pretreated mold; the mass concentration of the organic solution is 5%-8%, the coating thickness of the organic solution is 5-20μm, the average particle size of the ceramic particles is 20nm-1μm, the mass ratio of the organic solution to the ceramic particles is 1:(0.5-1.5), and the roughness Ra of the inner wall of the pretreated mold is 3.2-12.5μm; The casting solution is injected into the pretreated mold by vacuum driving to form a green body; The green body is dried and sintered in situ to obtain the porous ceramic tube.

2. The method of producing a porous ceramic tube according to claim 1, characterized by, The organic solution is at least one of a polyvinyl alcohol solution and a polyvinyl butyral alcohol solution.

3. The method of producing a porous ceramic tube according to claim 1, wherein The ceramic particles are at least one of alumina particles, zirconia particles, titania particles and silicon nitride particles.

4. The method of producing a porous ceramic tube according to claim 1, characterized by, The ceramic powder is at least one of alumina, zirconia, titania and silicon nitride; and / or, The particle size of the ceramic powder is 20nm-1μm; and / or, The binder is at least one of polyvinyl alcohol, polyacrylic acid, polyethylene glycol and methyl cellulose; and / or, The solvent is at least one of water and ethanol.

5. The method of producing a porous ceramic tube according to claim 1, wherein In the casting solution, the mass fraction of the binder is 5%-10%; and / or, In the casting solution, the mass fraction of the solvent is 20%-55%.

6. The method of producing a porous ceramic tube according to claim 1, wherein The mold is tubular, the material of the mold is quartz, stainless steel or ceramic, and the inner diameter of the mold is 0.8-20mm.

7. The method of producing a porous ceramic tube according to claim 1, wherein After the ceramic particles are compounded on the organic solution, drying is performed at 30-50℃ for 5-20min; and / or, After the ceramic powder, the binder and the solvent are mixed, ball milling is performed for 6-12h to obtain the casting solution; and / or, When the casting solution is injected into the pretreated mold, the casting solution is stirred at a speed of 300-600r / min at 20-50℃ in advance; and / or, The drying conditions of the green body are as follows: the temperature is 35-75℃, and the time is 0.5-3h; and / or, The sintering conditions are as follows: in an inert atmosphere, first, the temperature is raised to 400-600℃ at a temperature raising rate of 1-3℃ / min, and the temperature is kept for 1-2h; then, the temperature is raised to 800-1000℃ at a temperature raising rate of 3-5℃ / min, and the temperature is kept for 0.5-1h; finally, the temperature is raised to 1200-1400℃ at a temperature raising rate of 5-10℃ / min, and the temperature is kept for 1-2h.

8. The method of producing a porous ceramic tube according to claim 1, wherein The operation of the vacuum driving is as follows: a vacuum pump is used to generate negative pressure in the pretreated mold, so that the casting solution is injected into the pretreated mold; and / or, The operation of the in-situ drying is as follows: the green body and the mold are heated together for drying.

9. A porous ceramic tube, characterized by, The porous ceramic tube is prepared by the preparation method of the porous ceramic tube according to any one of claims 1-8.

10. The porous ceramic tube according to claim 9, characterized in that The porous ceramic tube has a wall thickness of 90-110 μm. The porous ceramic tube has a wall thickness of 90-110 μm.

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