A method for preparing a recrystallized silicon carbide-silicon carbonitride ceramic membrane

Abstract

The application belongs to the technical field of nanofiltration, and provides a preparation method of recrystallized silicon carbide-silicon carbon nitride ceramic membrane. The application obtains a pyrolytic material by first applying a polysilazane solution on a porous base and then performing first pyrolysis; and obtains the recrystallized silicon carbide-silicon carbon nitride ceramic membrane by second applying the polysilazane solution on the pyrolytic material and then performing second pyrolysis. The application uses a solution containing propargyl polysilazane or an organic polysilazane Durazane 1500 rapid cure fast-drying resin as a precursor to prepare the ceramic membrane, and the ceramic membrane has high ceramic yield, excellent high-temperature stability, high rejection rate and controllable microstructure, and is suitable for separation and protection applications in extreme environments.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of nanofiltration, and particularly relates to a preparation method of recrystallized silicon carbide-silicon carbon nitride ceramic membrane. BACKGROUND

[0002] The filtering precision of the membrane is divided into ultrafiltration membrane, nanofiltration membrane, reverse osmosis membrane and the like. The material of the existing nanofiltration membrane is generally divided into organic nanofiltration membrane and inorganic nanofiltration membrane, and the inorganic nanofiltration membrane is widely applied due to excellent corrosion resistance and high strength. The material of the inorganic nanofiltration membrane is generally ceramic membrane such as silicon carbide (SiC), aluminum oxide (Al2O3), zirconium oxide (ZrO2), titanium oxide (TiO2), silicon oxide (SiO2) and silicon nitride.

[0003] At present, the method for preparing the silicon nitride ceramic membrane is generally to prepare paint by using inorganic material silicon particles or silicon nitride powder, and then to obtain by sintering; due to the poor dispersibility of the silicon particles and the silicon nitride powder in the oil-based paint or the water-based paint, the obtained ceramic membrane has low interception rate, which needs to be further improved. SUMMARY

[0004] Therefore, the present application aims to provide a preparation method of recrystallized silicon carbide-silicon carbon nitride ceramic membrane. The recrystallized silicon carbide-silicon carbon nitride ceramic membrane prepared by the preparation method has a filtering precision of less than or equal to 1 nm and high interception rate, and has excellent high-temperature resistance.

[0005] In order to achieve the above-mentioned application purposes, the present application provides the following technical solutions:

[0006] The present application provides a preparation method of recrystallized silicon carbide-silicon carbon nitride ceramic membrane, which comprises the following steps:

[0007] The first pyrolysis is performed after the first application of the polysilazane solution on the porous substrate, to obtain a pyrolysis material;

[0008] The second pyrolysis is performed after the second application of the polysilazane solution on the pyrolysis material, to obtain the recrystallized silicon carbide-silicon carbon nitride ceramic membrane;

[0009] The process of the first pyrolysis is as follows:

[0010] The first temperature maintenance is performed at 1-2 ℃ / min from room temperature to 300 ℃;

[0011] The second temperature maintenance is performed at 2-5 ℃ / min from 300 ℃ to 600 ℃;

[0012] The third temperature maintenance is performed at 3-5 ℃ / min from 600 ℃ to 1000 ℃;

[0013] The fourth temperature maintaining is performed at 1200℃ to 1400℃ at a rate of 2℃ / min;

[0014] The process of the first pyrolysis after the first application of the polysilazane solution on the porous substrate is repeated until the pore size of the pyrolyzed material is less than or equal to 1nm;

[0015] The second pyrolysis comprises sequentially performing the first pyrolysis and the recrystallization;

[0016] The process of the recrystallization is:

[0017] The fifth temperature maintaining is performed at 1200℃ to 1400℃ at a rate of 2℃ / min;

[0018] The sixth temperature maintaining is performed at 1400℃ to 1600℃ at a rate of 2~5℃ / min;

[0019] The recrystallization is performed in a nitrogen atmosphere or an ammonia atmosphere;

[0020] The polysilazane solution is a solution containing propargyl polysilazane or an organic polysilazane Durazane 1500 rapid cure resin;

[0021] The content of propargyl in the propargyl polysilazane is 10~30mol%.

[0022] Preferably, the time of the first temperature maintaining is 1~2h, the time of the second temperature maintaining is 2h, the time of the third temperature maintaining is 2h, the time of the fourth temperature maintaining is 1~2h, the time of the fifth temperature maintaining is 1h, and the time of the sixth temperature maintaining is 2h.

[0023] Preferably, the preparation method of the propargyl polysilazane comprises the following steps:

[0024] The propargyl polysilazane is obtained by mixing the polysilazane oligomer, triethylamine and toluene, and then adding bromopropargyl dropwise in the obtained mixture to perform condensation reaction.

[0025] Preferably, the average molecular weight of the polysilazane oligomer is 900~1000, the molar ratio of the polysilazane oligomer to triethylamine is 3:0.8~1.2, and the molar ratio of the polysilazane oligomer to bromopropargyl is 9:0.8~1.2; the temperature of the condensation reaction is 60℃, and the time is 5h.

[0026] Preferably, the concentration of the solution containing propargyl polysilazane is 10~30wt%, and the solvent comprises one or more of ethyl acetate, toluene and acetone;

[0027] The first application and the second application are performed by dip coating; and the speed of the dip coating is 0.1~10mm / s.

[0028] Preferably, the porous matrix comprises a support body and a microfiltration membrane and an ultrafiltration membrane sequentially on the support body; the microfiltration membrane has a pore size of 0.5-1 μm and a thickness of 40-60 μm; the ultrafiltration membrane has a pore size of 20-50 nm and a thickness of 30-50 μm.

[0029] Preferably, the method for preparing the porous matrix comprises the following steps:

[0030] mixing silicon carbide, cellulose, dextran, vegetable oil, water and glycerol, and sequentially performing mud refining, extrusion, degumming and first sintering to obtain a support body;

[0031] applying a microfiltration coating on the support body and performing second sintering to obtain a microfiltration body with a support body-microfiltration membrane;

[0032] applying an ultrafiltration coating on the microfiltration membrane of the microfiltration body and performing third sintering to obtain the porous matrix.

[0033] Preferably, the silicon carbide, cellulose, dextran, vegetable oil, water and glycerol constitute a support body raw material; the mass percentage of each component in the support body raw material is 70% of silicon carbide, 6% of cellulose, 3% of dextran, 1% of vegetable oil, 19% of water and 1% of glycerol;

[0034] The mud refining time is 3-5 h; the degumming temperature is 140-160 ℃ and the degumming time is 8-12 h;

[0035] The first sintering process is as follows:

[0036] from room temperature to 590-610 ℃ at a rate of 1-2 ℃ per minute, and holding for 0.5-1.5 h;

[0037] from 590-610 ℃ to 1590-1610 ℃ at a rate of 5-10 ℃ per minute, and holding for 0.5-1.5 h;

[0038] from 1590-1610 ℃ to 2190-2210 ℃ at a rate of 3-5 ℃ per minute, and holding for 1.5-2.5 h;

[0039] from 2190-2210 ℃ to 2440-2460 ℃ at a rate of 3-5 ℃ per minute, and holding for 1-3 h;

[0040] After the first sintering, the process further comprises cooling to room temperature, and the cooling rate is 2-5 ℃ per minute.

[0041] Preferably, the microfiltration coating comprises the following components by mass percentage:

[0042] Silicon carbide powder 60%, vegetable oil 10%, water 25% and glycerol 5%; the particle size of the silicon carbide powder is 7 μm;

[0043] The process of the second sintering is:

[0044] Raising the temperature from room temperature to 590-610 ℃ at a rate of 1-2 ℃ / min and keeping for 0.5-1.5 h;

[0045] Raising the temperature from 590-610 ℃ to 1590-1610 ℃ at a rate of 5-10 ℃ / min and keeping for 0.5-1.5 h;

[0046] Raising the temperature from 1590-1610 ℃ to 2190-2210 ℃ at a rate of 3-5 ℃ / min and keeping for 1-3 h;

[0047] After the second sintering, cooling to room temperature is further included, and the cooling rate is 2-5 ℃ / min.

[0048] Preferably, the ultrafiltration coating includes the following components in mass percentage:

[0049] Silicon carbide powder 60%, vegetable oil 10%, water 25% and glycerol 5%; the particle size of the silicon carbide powder is 0.5 μm;

[0050] The process of the third sintering is:

[0051] Raising the temperature from room temperature to 590-610 ℃ at a rate of 1-2 ℃ / min and keeping for 0.5-1.5 h;

[0052] Raising the temperature from 590-610 ℃ to 1590-1610 ℃ at a rate of 5-10 ℃ / min and keeping for 0.5-1.5 h;

[0053] Raising the temperature from 1590-1610 ℃ to 2190-2210 ℃ at a rate of 3-5 ℃ / min and keeping for 0.5-1.5 h;

[0054] After the third sintering, cooling to room temperature is further included, and the cooling rate is 2-5 ℃ / min.

[0055] The application provides a preparation method of a recrystallized silicon carbide-silicon carbon nitride ceramic film.

[0056] 1. Compared with the prior art recrystallized silicon carbide ceramic film, the application adopts a porous substrate, performs dip drawing in a solution containing propargyl polysilazane (PPSZ), and then performs first pyrolysis and second pyrolysis to form a film, so that the film layer has better immersion and is more closely combined.

[0057] 2. The present application uses a solution containing propargyl polysilazane or an organic polysilazane Durazane 1500 rapidcure fast-drying resin as a precursor to prepare a ceramic membrane, which has high ceramic yield, excellent high-temperature stability, high retention rate, and controllable microstructure, and is suitable for separation and protection applications in extreme environments.

[0058] 3. Compared with the existing recrystallized silicon carbide ceramic membrane with a filtration precision of ≥0.05 μm, the initial membrane layer pore size of the porous substrate can reach 20-50 nm, and the pores are filled to increase the pore size to below 1 nm through the first pyrolysis.

[0059] 4. In the process of the second pyrolysis, the pyrolysis material is sintered at a high temperature of 1400℃, the neck connection is realized by using the atomic diffusion of the surface of the silicon carbon nitride (SiCN) particles, and the amorphous / crystalline state is realized. That is, a completely recrystallized silicon carbide (SiC)-silicon carbon nitride (SiCN) ceramic membrane is prepared. BRIEF DESCRIPTION OF DRAWINGS

[0060] Figure 1 The preparation method flow chart of the recrystallized silicon carbide-silicon carbon nitride ceramic membrane provided by the present application is provided. DETAILED DESCRIPTION

[0061] Figure 1 The preparation method flow chart of the recrystallized silicon carbide-silicon carbon nitride ceramic membrane provided by the present application is provided, and the following Figure 1 The preparation method of the present application is described in detail.

[0062] The present application provides a preparation method of a recrystallized silicon carbide-silicon carbon nitride ceramic membrane, comprising the following steps:

[0063] After the first application of the polysilazane solution on the porous substrate, the first pyrolysis is performed to obtain a pyrolysis material;

[0064] After the second application of the polysilazane solution on the pyrolysis material, the second pyrolysis is performed to obtain the recrystallized silicon carbide-silicon carbon nitride ceramic membrane;

[0065] The process of the first pyrolysis is:

[0066] The first holding is performed at 1-2℃ / min from room temperature to 300℃;

[0067] The second holding is performed at 2-5℃ / min from 300℃ to 600℃;

[0068] The third holding is performed at 3-5℃ / min from 600℃ to 1000℃;

[0069] The fourth holding is performed at 2℃ / min from 1000℃ to 1200℃;

[0070] repeating the process of applying the polysilazane solution on the porous substrate and then performing the first pyrolysis until the pore size of the pyrolytic material is less than or equal to 1 nm;

[0071] the second pyrolysis comprises sequentially performing the first pyrolysis and the recrystallization;

[0072] the process of the recrystallization is:

[0073] performing the fifth temperature holding at 1400℃ at a rate of 2℃ / min from 1200℃;

[0074] performing the sixth temperature holding at 1600℃ at a rate of 2~5℃ / min from 1400℃;

[0075] the recrystallization is performed in a nitrogen atmosphere or an ammonia atmosphere;

[0076] the polysilazane solution is a solution of propargyl polysilazane or an organic polysilazane Durazane 1500 rapid cure resin;

[0077] the content of propargyl in the propargyl polysilazane is 10~30 mol%.

[0078] The raw materials used in the present application are preferably commercially available products unless otherwise specified.

[0079] The present application performs the first pyrolysis after applying the polysilazane solution on the porous substrate for the first time to obtain a pyrolytic material.

[0080] In the present application, the porous substrate preferably comprises a support body and a microfiltration membrane and an ultrafiltration membrane sequentially arranged on the support body. In the present application, the pore size of the microfiltration membrane is preferably 0.5~1μm, the material is preferably silicon carbide, and the thickness is preferably 40~60μm. In the present application, the pore size of the ultrafiltration membrane is 20~50nm, the material is preferably silicon carbide, and the thickness is preferably 30~50μm.

[0081] In the present application, the preparation method of the porous substrate preferably comprises the following steps:

[0082] Mixing silicon carbide, cellulose, dextran, vegetable oil, water and glycerol, and sequentially performing mud refining, extrusion, degumming and first sintering to obtain a support body;

[0083] Applying a microfiltration coating on the support body and performing second sintering to obtain a microfiltration body with a support body-microfiltration membrane;

[0084] Applying an ultrafiltration coating on the microfiltration membrane of the microfiltration body and performing third sintering to obtain the porous substrate.

[0085] The present application mixes silicon carbide, cellulose, dextran, vegetable oil, water and glycerol, and sequentially carries out mud refining, extrusion, degumming and first sintering to obtain a support body. In the present application, the silicon carbide, cellulose, dextran, vegetable oil, water and glycerol constitute the support body raw material; the mass percentage of each component in the support body raw material is 70% silicon carbide, 6% cellulose, 3% dextran, 1% vegetable oil, 19% water and 1% glycerol. In the present application, the time of mud refining is preferably 3-5h, and is particularly preferably 3h, 4h or 5h. In the present application, the temperature of degumming is preferably 140-160℃, and is particularly preferably 140℃, 150℃ or 160℃; the time is preferably 8-12h, and is particularly preferably 8h, 10h or 12h.

[0086] In the present application, the process of the first sintering is preferably:

[0087] from room temperature to 590-610℃ at a rate of 1-2℃ / min, and holding for 0.5-1.5h;

[0088] from 590-610℃ to 1590-1610℃ at a rate of 5-10℃ / min, and holding for 0.5-1.5h;

[0089] from 1590-1610℃ to 2190-2210℃ at a rate of 3-5℃ / min, and holding for 1.5-2.5h;

[0090] from 2190-2210℃ to 2440-2460℃ at a rate of 3-5℃ / min, and holding for 1-3h;

[0091] The process of the first sintering is further preferably:

[0092] from room temperature to 600℃ at a rate of 1-2℃ / min, and holding for 1h;

[0093] from 600℃ to 1600℃ at a rate of 5-10℃ / min, and holding for 1h;

[0094] from 1600℃ to 2200℃ at a rate of 3-5℃ / min, and holding for 2h;

[0095] from 2200℃ to 2450℃ at a rate of 3-5℃ / min, and holding for 1h.

[0096] In the present application, from room temperature to 590-610℃ at a rate of 1-2℃ / min, and holding for 0.5-1.5h; this process can remove the binder (dextran and glycerol) and solvent; the first heating rate is preferably controlled at 1-2℃ / min to prevent film layer cracking.

[0097] In the present application, the temperature is raised from 590-610℃ to 1590-1610℃ at a rate of 5-10℃ / min and kept for 0.5-1.5h; this process can activate the surface of the particles.

[0098] In the present application, the temperature is raised from 1590-1610℃ to 2190-2210℃ at a rate of 3-5℃ / min and kept for 1.5-2.5h; in this process, the SiC surface evaporates and condenses, the neck is formed; and oxidation can be prevented.

[0099] In the present application, the temperature is raised from 2190-2210℃ to 2440-2460℃ at a rate of 3-5℃ / min and kept for 1-3h, this process can realize densification and promote grain growth, so that the grain size is in a suitable size and the strength is improved.

[0100] After the first sintering, the present application preferably further comprises cooling to room temperature, and the cooling rate is preferably 2-5℃ / min. In the present application, this process can prevent thermal stress cracks.

[0101] In the present application, the first sintering is preferably carried out in vacuum or protective atmosphere, and the protective atmosphere is preferably argon.

[0102] In the present application, the pore size of the support is preferably 5-10μm.

[0103] After obtaining the support, the present application applies a microfiltration coating on the support, carries out second sintering, and obtains a microfiltration body with support-microfiltration membrane. In the present application, the microfiltration coating preferably comprises the following components in mass percentage: 60% of silicon carbide powder, 10% of vegetable oil, 25% of water and 5% of glycerol; and the particle size of the silicon carbide powder is 7μm.

[0104] In the present application, the process of the second sintering is preferably as follows:

[0105] raising the temperature from room temperature to 590-610℃ at a rate of 1-2℃ / min and keeping for 0.5-1.5h;

[0106] raising the temperature from 590-610℃ to 1590-1610℃ at a rate of 5-10℃ / min and keeping for 0.5-1.5h;

[0107] raising the temperature from 1590-1610℃ to 2190-2210℃ at a rate of 3-5℃ / min and keeping for 1-3h;

[0108] The process of the second sintering is further preferably as follows:

[0109] raising the temperature from room temperature to 600℃ at a rate of 1-2℃ / min and keeping for 1h;

[0110] from 600℃ to 1600℃ at a rate of 5-10℃ / min, and holding for 1h;

[0111] from 1600℃ to 2200℃ at a rate of 3-5℃ / min, and holding for 1-3h.

[0112] In the present application, from room temperature to 590-610℃ at a rate of 1-2℃ / min, and holding for 0.5-1.5h, which can remove the binder / solvent and prevent the film layer from cracking.

[0113] In the present application, from 590-610℃ to 1590-1610℃ at a rate of 5-10℃ / min, and holding for 0.5-1.5h, which can activate the surface of the particles.

[0114] In the present application, from 1590-1610℃ to 2190-2210℃ at a rate of 3-5℃ / min, and holding for 1-3h, which can promote the grain growth and form a densified film layer.

[0115] After the second sintering, the present application preferably further comprises cooling to room temperature, and the cooling rate is preferably 2-5℃ / min. In the present application, this process can prevent thermal stress cracking.

[0116] In the present application, the second sintering is preferably carried out under vacuum or a protective atmosphere, and the protective atmosphere is preferably argon.

[0117] After obtaining the microfiltration body with the support-microfiltration membrane, the present application applies an ultrafiltration coating on the microfiltration membrane of the microfiltration body, and carries out a third sintering to obtain the porous matrix. In the present application, the ultrafiltration coating preferably comprises the following components by mass percentage: silicon carbide powder 60%, vegetable oil 10%, water 25% and glycerol 5%; and the particle size of the silicon carbide powder is 0.5μm.

[0118] In the present application, the process of the third sintering is preferably as follows:

[0119] from room temperature to 590-610℃ at a rate of 1-2℃ / min, and holding for 0.5-1.5h;

[0120] from 590-610℃ to 1590-1610℃ at a rate of 5-10℃ / min, and holding for 0.5-1.5h;

[0121] from 1590-1610℃ to 2190-2210℃ at a rate of 3-5℃ / min, and holding for 0.5-1.5h;

[0122] The process of the third sintering is further preferably as follows:

[0123] from room temperature to 600℃ at a rate of 1-2℃ / min, and holding for 1h;

[0124] from 600 °C to 1600 °C at a rate of 5-10 °C / min, and holding for 1 h;

[0125] from 1600 °C to 2200 °C at a rate of 3-5 °C / min, and holding for 0.5-1.5 h.

[0126] In the present application, from room temperature to 590-610 °C at a rate of 1-2 °C / min, and holding for 0.5-1.5 h, which can remove the binder / solvent and prevent the film layer from cracking.

[0127] In the present application, from 590-610 °C to 1590-1610 °C at a rate of 5-10 °C / min, and holding for 0.5-1.5 h, which can activate the surface of the particles.

[0128] In the present application, from 1590-1610 °C to 2190-2210 °C at a rate of 3-5 °C / min, and holding for 0.5-1.5 h, which can promote grain growth and form a densified film layer.

[0129] After the third sintering, the present application further comprises cooling to room temperature, and the cooling rate is preferably 2-5 °C / min.

[0130] In the present application, the third sintering is preferably carried out in vacuum or a protective atmosphere, and the protective atmosphere is preferably argon.

[0131] In the present application, the content of propargyl groups in the propargyl polysilazane is 10-30 mol%, and is specifically preferably 10 mol%, 15 mol%, 20 mol%, 25 mol%, or 30 mol%. In the present application, a content of propargyl groups in the propargyl polysilazane that is too low (<10 mol%) can result in insufficient crosslinking and a decrease in ceramic yield, and a content that is too high (>30 mol%) can result in violent outgassing during pyrolysis and cracking of the film layer.

[0132] In the present application, the polysilazane solution is a solution containing propargyl polysilazane or an organic polysilazane Durazane 1500 rapid cure fast-drying resin. In the present application, the organic polysilazane Durazane 1500 rapid cure fast-drying resin is preferably purchased from Merck, Germany.

[0133] In the present application, the concentration of the solution containing propargyl polysilazane is preferably 10-30 wt%, and is specifically preferably 10 wt%, 15 wt%, 20 wt%, 25 wt%, or 30 wt%. In the present application, the solvent of the solution containing propargyl polysilazane preferably includes one or more of ethyl acetate, toluene, and acetone.

[0134] In the present application, the preparation method of the propargyl polysilazane preferably comprises the following steps:

[0135] The propargyl polysilazane is obtained by adding bromopropargyl dropwise in the obtained mixed system after mixing the polysilazane oligomer, triethylamine and toluene to carry out condensation reaction. In the present application, the average molecular weight of the polysilazane oligomer is preferably 900-1000. In the present application, the molar ratio of the polysilazane oligomer to triethylamine is preferably 3:0.8-1.2, and more preferably 3:0.8, 3:0.9, 3:1, 3:1.1 or 3:1.2. In the present application, the molar ratio of the polysilazane oligomer to bromopropargyl is preferably 9:0.8-1.2, and more preferably 9:0.8, 9:0.9, 9:1, 9:1.1 or 9:1.2. In the present application, the temperature for mixing the polysilazane oligomer, triethylamine and toluene is preferably 60°C, and the mixing of the polysilazane oligomer, triethylamine and toluene is preferably carried out under stirring. In the present application, the bromopropargyl is preferably added dropwise for 120 min. In the present application, the temperature for the condensation reaction is preferably 60°C, and the time is preferably 5 h; and the condensation reaction is preferably carried out under stirring. After the condensation reaction, the present application preferably further comprises: after the obtained condensation reaction system is cooled and reaches room temperature, centrifugal separation is carried out on the cooled condensation reaction system to obtain yellow-brown transparent clear liquid; the yellow-brown transparent clear liquid is washed with toluene, and the washing liquid is recovered; the solvent is removed from the washing liquid under vacuum to obtain dark-brown transparent viscous resin, i.e. the propargyl polysilazane. In the present application, the number of washing is preferably 2 times.

[0136] In the present application, the first application is preferably by dip coating, and the speed of the dip coating is preferably 0.1-10 mm / s, and more preferably 0.1 mm / s, 0.5 mm / s, 1 mm / s, 1.5 mm / s, 2 mm / s, 2.5 mm / s, 3 mm / s, 3.5 mm / s, 4 mm / s, 4.5 mm / s, 5 mm / s, 5.5 mm / s, 6 mm / s, 6.5 mm / s, 7 mm / s, 7.5 mm / s, 8 mm / s, 8.5 mm / s, 9 mm / s, 9.5 mm / s or 10 mm / s. After the first application, the present application preferably comprises curing, and the temperature for the curing is preferably 40°C, and the time is preferably 1 h.

[0137] In the present application, the first pyrolysis is carried out by:

[0138] The temperature is increased to 300°C from room temperature at 1-2°C / min for the first holding;

[0139] The temperature is increased to 600°C from 300°C at 2-5°C / min for the second holding;

[0140] the third temperature holding is performed at a temperature rising rate of 3-5℃ / min from 600℃ to 1000℃;

[0141] the fourth temperature holding is performed at a temperature rising rate of 2℃ / min from 1000℃ to 1200℃.

[0142] In the present application, the first pyrolysis is preferably performed under a protective atmosphere, which is preferably argon.

[0143] After the first pyrolysis, the present application preferably further comprises furnace cooling to room temperature.

[0144] In the present application, the time of the first temperature holding is preferably 1-2h. In the present application, during the first temperature holding at a temperature rising rate of 1-2℃ / min from room temperature to 300℃, the solvent volatilizes and the residual propargyl group further crosslinks.

[0145] In the present application, the time of the second temperature holding is preferably 2h. In the present application, during the second temperature holding at a temperature rising rate of 2-5℃ / min from 300℃ to 600℃, the side chain decomposes (releasing C2H2, H2) and a Si-N network is formed.

[0146] In the present application, the time of the third temperature holding is preferably 2h. In the present application, during the third temperature holding at a temperature rising rate of 3-5℃ / min from 600℃ to 1000℃, amorphous SiCN (β-SiCN) is generated and NH3 is released.

[0147] In the present application, the time of the fourth temperature holding is preferably 1-2h. In the present application, during the fourth temperature holding at a temperature rising rate of 2℃ / min from 1000℃ to 1200℃, preliminary crystallization (nano β-SiC / Si3N4) is performed.

[0148] The process of the first pyrolysis after the first application of the polysilazane solution on the porous substrate is repeated until the pore size of the pyrolyzed material is less than or equal to 1nm.

[0149] After obtaining the pyrolyzed material, the present application performs a second pyrolysis after a second application of a polysilazane solution on the pyrolyzed material, to obtain the recrystallized silicon carbide-silicon carbonitride ceramic film.

[0150] In the present application, the mode and parameters of the second application are consistent with the above technical solution and will not be described here again. In the present application, the parameters of the polysilazane solution are consistent with the above technical solution and will not be described here again.

[0151] In the present application, the second pyrolysis comprises sequentially performing a first pyrolysis and recrystallization.

[0152] The process of the recrystallization is as follows:

[0153] The fifth temperature maintaining is performed at 2℃ / min from 1200℃ to 1400℃;

[0154] The sixth temperature maintaining is performed at 2~5℃ / min from 1400℃ to 1600℃.

[0155] In the present application, the recrystallization is preferably performed under a nitrogen atmosphere or an ammonia (NH3) atmosphere, and is further preferably performed under a nitrogen atmosphere. In the present application, the flow rate of the nitrogen atmosphere or the ammonia atmosphere is independently preferably 50~100mL / min, and is particularly preferably 50mL / min, 60mL / min, 70mL / min, 80mL / min, 90mL / min or 100mL / min. In the present application, the pyrolysis under a nitrogen atmosphere or an ammonia atmosphere can inhibit the generation of free carbon and increase the N content (increase of Si3N4 phase).

[0156] In the present application, the time of the fifth temperature maintaining is preferably 1h.

[0157] In the present application, the time of the sixth temperature maintaining is preferably 2h.

[0158] In the present application, during the recrystallization, the phase evolution is: β-SiCN→a-SiC (1-3nm) + Si3N4 (amorphous / crystalline). Free carbon can form a graphene-like structure (depending on the C / N ratio of the precursor). The densification mechanism is: evaporation-condensation and diffusion together, and the porosity is reduced to <40%.

[0159] In the present application, the process of the second pyrolysis is particularly as follows:

[0160] The first temperature maintaining is performed at 1~2℃ / min from room temperature to 300℃;

[0161] The second temperature maintaining is performed at 2~5℃ / min from 300℃ to 600℃;

[0162] The third temperature maintaining is performed at 3~5℃ / min from 600℃ to 1000℃;

[0163] The fourth temperature maintaining is performed at 2℃ / min from 1000℃ to 1200℃;

[0164] The fifth temperature maintaining is performed at 2℃ / min from 1200℃ to 1400℃;

[0165] The sixth temperature maintaining is performed at 2~5℃ / min from 1400℃ to 1600℃.

[0166] After the second pyrolysis, the present application is preferably cooled to room temperature in the furnace.

[0167] In the present application, during the first pyrolysis and the second pyrolysis, when the temperature reaches 600℃ or above, slow heating (<3℃ / min) is needed to avoid film rupture caused by rapid release of gas.

[0168] In the present application, the propargyl crosslinking in the propargyl polysilazane can inhibit mass loss, and make the ceramic membrane yield 60~80%; meanwhile, the obtained ceramic membrane has excellent high-temperature stability and controllable microstructure, and is suitable for separation and protection applications in extreme environments.

[0169] In the present application, the recrystallized silicon carbide-silicon carbonitride ceramic membrane can be used for nanofiltration of liquid.

[0170] The preparation method of the recrystallized silicon carbide-silicon carbonitride ceramic membrane provided by the present application will be described in detail below in combination with examples, but they should not be understood as limiting the scope of protection of the present application.

[0171] Example 1

[0172] The preparation method of the recrystallized silicon carbide-silicon carbonitride ceramic membrane comprises the following steps:

[0173] Step 1, preparation of the support: the raw materials are mixed according to the following mass percentage: silicon carbide 70%, cellulose 6%, dextran 3%, vegetable oil (specific type: rice oil) 1%, water 19% and glycerol 1%, and the mixture is subjected to mud refining (room temperature, 4h), extrusion, degumming (150℃, 10h) and first sintering in sequence, and then cooled to room temperature at a cooling rate of 2~5℃ / min to obtain the support, and the filtration pore size of the obtained support is 10μm.

[0174] The process of the first sintering is as follows:

[0175] heated from room temperature to 600℃ at a rate of 1~2℃ / min and kept for 1h;

[0176] heated from 600℃ to 1600℃ at a rate of 5~10℃ / min and kept for 1h;

[0177] heated from 1600℃ to 2200℃ at a rate of 3~5℃ / min and kept for 2h;

[0178] heated from 2200℃ to 2450℃ at a rate of 3~5℃ / min and kept for 3h;

[0179] The first sintering is carried out in argon.

[0180] Step 2, preparation of the microfiltration body with support-microfiltration membrane:

[0181] The silicon carbide powder (particle size 7μm), vegetable oil, water and glycerol are mixed according to the mass ratio of 60:10:25:5 to obtain the microfiltration coating.

[0182] The microfiltration coating is coated onto the support, and a second sintering is performed to obtain a microfiltration membrane with a pore size of 1 μm, the thickness of the microfiltration membrane being 40-60 μm.

[0183] The process of the second sintering is as follows:

[0184] Raising the temperature from room temperature to 600°C at a rate of 1-2°C / min, and holding for 1 h;

[0185] Raising the temperature from 600°C to 1600°C at a rate of 5-10°C / min, and holding for 1 h;

[0186] Raising the temperature from 1600°C to 2200°C at a rate of 3-5°C / min, and holding for 2 h;

[0187] Lowering the temperature from 2200°C to room temperature at a rate of 2-5°C / min;

[0188] The second sintering is performed in argon.

[0189] Step 3, preparation of a porous matrix with support-microfiltration membrane-ultrafiltration membrane:

[0190] The silicon carbide powder (particle size 0.5 μm), vegetable oil, water and glycerol are mixed in a mass ratio of 60:10:25:5 to obtain an ultrafiltration coating;

[0191] The ultrafiltration coating is coated onto the microfiltration membrane, and a third sintering is performed to obtain a porous matrix with a pore size of 50 nm, the thickness of the ultrafiltration membrane being 30-50 μm;

[0192] The process of the third sintering is as follows:

[0193] Raising the temperature from room temperature to 600°C at a rate of 1-2°C / min, and holding for 1 h;

[0194] Raising the temperature from 600°C to 1600°C at a rate of 5-10°C / min, and holding for 1 h;

[0195] Raising the temperature from 1600°C to 2200°C at a rate of 3-5°C / min, and holding for 1 h;

[0196] Lowering the temperature from 2200°C to room temperature at a rate of 2-5°C / min;

[0197] The third sintering is performed in argon.

[0198] Step 4, first pyrolysis after applying a solution containing propargyl polysilazane:

[0199] ① Preparation of propargyl polysilazane: put polysilazane oligomer (LSZ, average molecular weight 900-1000), triethylamine and toluene into a flask, stir and heat to 60°C, drop propargyl bromide, drop for about 120 min, then continue stirring for 5 h, a large amount of white salt is generated. After cooling, centrifugal separation is performed on the solution, yellow-brown transparent clear liquid is obtained, the salt is washed with toluene, and the washing liquid is recovered (washed twice). The centrifugal liquid is distilled under vacuum to remove the solvent, and a dark brown transparent viscous resin PPSZ is obtained, wherein the molar ratio of polysilazane oligomer to triethylamine is 3:1, the molar ratio of polysilazane oligomer to propargyl bromide is 9:1, and the content of propargyl in the obtained propargyl polysilazane is 30 mol%.

[0200] ② Dissolve the propargyl polysilazane in ethyl acetate to form a solution containing propargyl polysilazane with a concentration of 30 wt%.

[0201] ③ Coating the solution containing propargyl polysilazane on the porous substrate by dip-coating method, the dip-coating speed is 10 mm / s, after coating, solidify at 40°C for 1 h, then perform the first pyrolysis;

[0202] The process of the first pyrolysis is:

[0203] Ramp from room temperature to 300°C at 1-2°C / min, first hold for 1 h (argon atmosphere);

[0204] Ramp from 300°C to 600°C at 2-5°C / min, second hold for 2 h (argon atmosphere);

[0205] Ramp from 600°C to 1000°C at 3-5°C / min, third hold for 2 h (argon atmosphere);

[0206] Ramp from 1000°C to 1200°C at 2°C / min, fourth hold for 2 h (argon atmosphere);

[0207] Cool down from 1200°C to room temperature in the furnace;

[0208] Repeat step ③ in step 4 for 2 times to obtain the pyrolyzed material.

[0209] Step 5, second pyrolysis after applying the solution containing propargyl polysilazane:

[0210] Coat the solution containing propargyl polysilazane on the pyrolyzed material by dip-coating method, the dip-coating speed is 10 mm / s, after coating, solidify at 40°C for 1 h, then perform the second pyrolysis.

[0211] Ramp from room temperature to 300°C at 1-2°C / min, first hold for 1 h (argon atmosphere);

[0212] The second temperature holding is performed at 600℃ for 2h (argon atmosphere) at a temperature rising rate of 2~5℃ / min from 300℃ to 600℃;

[0213] The third temperature holding is performed at 1000℃ for 2h (nitrogen atmosphere) at a temperature rising rate of 2℃ / min from 1000℃ to 1200℃;

[0214] The fourth temperature holding is performed at 1200℃ for 1h (nitrogen atmosphere) at a temperature rising rate of 2℃ / min from 1200℃ to 1400℃;

[0215] The fifth temperature holding is performed at 1400℃ for 2h (nitrogen atmosphere) at a temperature rising rate of 2~5℃ / min from 1400℃ to 1600℃;

[0216] The sixth temperature holding is performed at 1600℃ for 2h (nitrogen atmosphere) at a temperature rising rate of 2~5℃ / min from 1400℃ to 1600℃;

[0217] Cooling down to room temperature in the furnace, and the ceramic membrane is obtained.

[0218] Performance characterization

[0219] The gas permeability of the obtained ceramic membrane is determined by GB / T 1969-1996 "Porous Ceramics Permeability Test Method", and the results are as follows: He flux is 10 -7 mol / (m²·s·Pa), and H2 / CO2 selectivity is 25 (800℃).

[0220] The liquid interception rate of the obtained ceramic membrane is determined by GB / T 37246-2018 "Fine Ceramic Thermal Shock Resistance Test Method", and the results are as follows: The potassium dichromate (Cr2O7 2- Particle size: 0.48~0.78nm) interception rate is greater than 96%.

[0221] The high temperature stability of the obtained ceramic membrane is determined by GB / T 37246-2018 "Fine Ceramic Thermal Shock Resistance Test Method", and the results are as follows: The weight loss rate is less than 3.7% after 100 hours of oxidation at 1200℃.

[0222] Example 2

[0223] Dissolve the propargyl polysilazane in acetone to form a solution containing propargyl polysilazane with a concentration of 10wt%, and other operations are the same as in Example 1.

[0224] The gas permeability of the obtained ceramic membrane is determined by GB / T 1969-1996 "Porous Ceramics Permeability Test Method", and the results are as follows: He flux is 10 -6 mol / (m²·s·Pa), and H2 / CO2 selectivity is 20 (800℃).

[0225] The liquid interception rate of the obtained ceramic membrane was determined by GB / T32360-2015 "Ultrafiltration membrane test method", and the results were as follows: the interception rate of potassium dichromate (Cr2O7 2- Particle size: 0.48~0.78nm) was greater than 93%.

[0226] The high temperature stability of the obtained ceramic membrane was determined by GB / T 37246-2018 "Fine ceramic thermal shock resistance test method", and the results were as follows: the weight loss rate was less than 5% after 100 hours of oxidation at 1200℃.

[0227] Example 3

[0228] The solution containing propargyl polysilazane with a concentration of 30wt% in Example 1 was replaced with an organic polysilazane Durazane 1500 rapid cure fast-drying resin purchased from Merck, Germany, and other operations were the same as in Example 1.

[0229] The gas permeability of the obtained ceramic membrane was determined by GB / T 1969-1996 "Porous ceramic permeability test method", and the results were as follows: He flux was 10 -7 mol / (m²·s·Pa), and H2 / CO2 selectivity was 40 (800℃).

[0230] The liquid interception rate of the obtained ceramic membrane was determined by GB / T32360-2015 "Ultrafiltration membrane test method", and the results were as follows: the interception rate of potassium dichromate (Cr2O7 2- Particle size: 0.48~0.78nm) was greater than 99%.

[0231] The high temperature stability of the obtained ceramic membrane was determined by GB / T 37246-2018 "Fine ceramic thermal shock resistance test method", and the results were as follows: the weight loss rate was less than 3.5% after 100 hours of oxidation at 1200℃.

[0232] Comparative Example 1

[0233] The propargyl polysilazane in Example 1 was replaced with a domestic ordinary polysilazane resin (molecular weight of 600~1000), and other operations were the same as in Example 1.

[0234] The gas permeability of the obtained ceramic membrane was determined by GB / T 1969-1996 "Porous ceramic permeability test method", and the results were as follows: He flux was 10 -6 mol / (m²·s·Pa), and H2 / CO2 selectivity was 25 (800℃).

[0235] The liquid interception rate of the obtained ceramic membrane was determined by GB / T32360-2015 "Ultrafiltration membrane test method", and the results were as follows: the interception rate of potassium dichromate (Cr2O7 2-Particle size: 0.48~0.78nm) Interception rate is greater than 92%.

[0236] The high temperature stability of the obtained ceramic membrane was determined by GB / T 37246-2018 "Fine Ceramic Thermal Shock Resistance Test Method", and the results were: 1200℃ oxidation for 100 hours, the weight loss rate was less than 4.5%.

[0237] The above only describes the preferred embodiments of the present application, and it should be noted that for those skilled in the art, without departing from the principles of the present application, a number of improvements and refinements can be made, and these improvements and refinements should also be considered as the protection scope of the present application.

Claims

1. A method for preparing a recrystallized silicon carbide-silicon carbon nitride ceramic membrane, comprising the following steps: performing a first pyrolysis after a first application of a polysilazane solution on a porous substrate to obtain a pyrolyzed material; performing a second pyrolysis after a second application of a polysilazane solution on the pyrolyzed material to obtain the recrystallized silicon carbide-silicon carbon nitride ceramic membrane; the first pyrolysis comprises the following process: heating from room temperature to 300 ℃ at a rate of 1-2 ℃ / min and then performing a first holding; heating from 300 ℃ to 600 ℃ at a rate of 2-5 ℃ / min and then performing a second holding; heating from 600 ℃ to 1000 ℃ at a rate of 3-5 ℃ / min and then performing a third holding; heating from 1000 ℃ to 1200 ℃ at a rate of 2 ℃ / min and then performing a fourth holding; repeating the process of performing the first pyrolysis after the first application of the polysilazane solution on the porous substrate until the pore size of the pyrolyzed material is less than or equal to 1 nm; the second pyrolysis comprises sequentially performing a first pyrolysis and recrystallization; the recrystallization comprises the following process: heating from 1200 ℃ to 1400 ℃ at a rate of 2 ℃ / min and then performing a fifth holding; heating from 1400 ℃ to 1600 ℃ at a rate of 2-5 ℃ / min and then performing a sixth holding; the recrystallization is performed in a nitrogen atmosphere or an ammonia atmosphere; the polysilazane solution is a solution containing propargyl polysilazane or an organic polysilazane Durazane 1500 rapidcure fast-drying resin; the content of propargyl in the propargyl polysilazane is 10-30 mol%; the time of the first holding is 1-2 h, the time of the second holding is 2 h, the time of the third holding is 2 h, the time of the fourth holding is 1-2 h, the time of the fifth holding is 1 h, and the time of the sixth holding is 2 h; a method for preparing the propargyl polysilazane comprises the following steps: mixing a polysilazane oligomer, triethylamine and toluene, and then adding bromopropargyl dropwise in the obtained mixture to perform a condensation reaction, thereby obtaining the propargyl polysilazane; the average molecular weight of the polysilazane oligomer is 900-1000, the molar ratio of the polysilazane oligomer to triethylamine is 3:0.8-1.2, and the molar ratio of the polysilazane oligomer to bromopropargyl is 9:0.8-1.2; the condensation reaction is performed at a temperature of 60 ℃ for 5 h; the concentration of the solution containing propargyl polysilazane is 10-30 wt%, and the solvent comprises one or more of ethyl acetate, toluene and acetone; the first application and the second application are performed by dip coating; and the speed of the dip coating is 0.1-10 mm / s; the porous substrate comprises a support body and a microfiltration membrane and an ultrafiltration membrane sequentially arranged on the support body; the pore size of the microfiltration membrane is 0.5-1 μm, and the thickness is 40-60 μm; the pore size of the ultrafiltration membrane is 20-50 nm, and the thickness is 30-50 μm; a method for preparing the porous substrate comprises the following steps: mixing silicon carbide, cellulose, dextran, vegetable oil, water and glycerol, and then sequentially performing mud refining, extrusion, degumming and first sintering to obtain the support body. ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ 2. The production method according to claim 1, characterized by, ​ 3. The preparation method according to claim 1, characterized in that, ​ ​ 4. The production method according to claim 3, characterized by, ​ 5. The production method according to claim 1, 3 or 4, characterized by, ​ ​ 6. The method of claim 1, wherein, ​ 7. The production method according to claim 1 or 6, characterized by, ​ ​ applying microfiltration coating on the support body, performing second sintering to obtain a microfiltration body with support body-microfiltration membrane; applying ultrafiltration coating on the microfiltration membrane of the microfiltration body, performing third sintering to obtain the porous matrix.

8. The preparation method according to claim 7, characterized in that, The silicon carbide, cellulose, dextran, vegetable oil, water and glycerol constitute a support material; the mass percentage of each component in the support material is 70% of silicon carbide, 6% of cellulose, 3% of dextran, 1% of vegetable oil, 19% of water and 1% of glycerol; The time for the mud is 3-5h; the temperature for the degumming is 140-160℃, and the time is 8-12h; The process of the first sintering is: from room temperature to 590-610℃ at a rate of 1-2℃ / min, and holding for 0.5-1.5h; from 590-610℃ to 1590-1610℃ at a rate of 5-10℃ / min, and holding for 0.5-1.5h; from 1590-1610℃ to 2190-2210℃ at a rate of 3-5℃ / min, and holding for 1.5-2.5h; from 2190-2210℃ to 2440-2460℃ at a rate of 3-5℃ / min, and holding for 1-3h; After the first sintering, it further includes cooling to room temperature, and the cooling rate is 2-5℃ / min.

9. The preparation method according to claim 7, characterized in that, The microfiltration coating includes the following mass percentage of components: 60% of silicon carbide powder, 10% of vegetable oil, 25% of water and 5% of glycerol; the particle size of the silicon carbide powder is 7μm; The process of the second sintering is: from room temperature to 590-610℃ at a rate of 1-2℃ / min, and holding for 0.5-1.5h; from 590-610℃ to 1590-1610℃ at a rate of 5-10℃ / min, and holding for 0.5-1.5h; from 1590-1610℃ to 2190-2210℃ at a rate of 3-5℃ / min, and holding for 1-3h; After the second sintering, it further includes cooling to room temperature, and the cooling rate is 2-5℃ / min.

10. The preparation method according to claim 7, characterized in that, The ultrafiltration coating includes the following mass percentage of components: 60% of silicon carbide powder, 10% of vegetable oil, 25% of water and 5% of glycerol; the particle size of the silicon carbide powder is 0.5μm; The process of the third sintering is: from room temperature to 590-610℃ at a rate of 1-2℃ / min, and holding for 0.5-1.5h; from 590-610℃ to 1590-1610℃ at a rate of 5-10℃ / min, and holding for 0.5-1.5h; from 1590-1610℃ to 2190-2210℃ at a rate of 3-5℃ / min, and holding for 0.5-1.5h; After the third sintering, it further includes cooling to room temperature, and the cooling rate is 2-5℃ / min.

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