CN113999046B - A kind of preparation method of low temperature reaction sintering silicon carbide ceramic film - Google Patents

Abstract

The invention discloses a preparation method of a low-temperature reaction sintered silicon carbide ceramic membrane. The silicon carbide ceramic membrane is prepared from raw materials such as silicon carbide powder, silicon powder, carbon black, naCl-KCl fused salt, kaolin, sodium carboxymethylcellulose, PVP, glycerol, water and the like through the processes of batching, mixing, forming, drying, sintering, soaking in water and desalting. The invention bonds SiC raw material particles into a continuous porous ceramic support body through a beta-SiC new phase generated by silicon and carbon solid phase reaction and a molten salt liquid phase reaction, nano pores constructed by interweaving SiC nano fibers are formed on the surface, the volume density is small, and the invention has the characteristics of low sintering temperature, low oxide content, high internal porosity, nano pores on the surface, acid and alkali resistance and the like.

Description

A kind of preparation method of low temperature reaction sintering silicon carbide ceramic film

technical field

The invention belongs to the technical field of inorganic membrane separation materials and relates to a method for preparing a porous ceramic material, in particular to a method for preparing a low-temperature reaction sintered silicon carbide ceramic membrane.

Background technique

Ceramic membrane separation technology is a high-efficiency and energy-saving separation technology, and its application fields involve chemical industry, petroleum and petrochemical industry, biochemical industry, food, electronics, medicine and other industries. Ceramic membranes on the market are mainly made of alumina, titanium oxide, silicon oxide, zirconia and silicon carbide. Among them, silicon carbide ceramic membranes have received high attention due to their excellent performance, especially the rapid development of their applications in the field of water treatment. The silicon carbide ceramic membrane is mainly composed of a silicon carbide ceramic support body, a silicon carbide transition layer and a silicon carbide film layer.

At present, the preparation of SiC ceramic supports mainly includes liquid phase sintering, reaction sintering, pressureless sintering and recrystallization sintering. Pressureless sintering and recrystallization sintering of silicon carbide ceramic membranes require high temperature, high energy consumption, high requirements for sintering furnace equipment, and high cost; liquid phase sintering usually uses oxides with low melting points as sintering aids, and the sintering temperature is low, but The oxide content is high; the reaction and sintering temperature is relatively low, but the quality of the ceramic film is poor and the cost is relatively high. Each process method has its advantages and disadvantages. The patent "a preparation method of low-temperature sintering acid and alkali-resistant porous silicon carbide ceramic support (application number: CN201710656733.4)" uses an acid-alkali-resistant sintering aid to sinter below 1400°C with high mechanical strength and high porosity , acid and alkali resistant porous silicon carbide ceramic support body. The raw material of the support described in the patent "liquid phase sintered multi-channel silicon carbide ceramic membrane and its preparation method (application number: CN201810075180.8)" contains kaolin and talc, and the sintering temperature is effectively reduced by liquid phase sintering. The sintering temperature is Below 1500°C. "Multi-channel silicon carbide ceramic membrane and its preparation method (application number: CN201810075202.0)", mixing different silicon carbide powder I, silicon carbide powder II and the pore-forming agent mixture to obtain mud, and Extrusion molding, the green body obtained is dried and then fired to obtain a multi-channel silicon carbide ceramic membrane. The patent "a silicon carbide ceramic film and its preparation method (application number: CN201510449442.9)" mixes SiC aggregates, sintering aids, toughening aids, and polymer binders in a certain proportion, and after stirring and ball milling, Forming, high-temperature sintering, coating and sintering to obtain a porous silicon carbide ceramic membrane. The patent "A normal-pressure solid-phase sintered silicon carbide film support and its preparation method (application number: CN201811564686.1)" combines submicron silicon carbide powder or nanometer silicon carbide powder, micron silicon carbide powder , carbon powder, sintering aid and organic binder are mixed to obtain a mixed powder, and after mixing with plasticizer, lubricant and water in the obtained mixed powder, a water-based silicon carbide mud is obtained; the obtained water-based The silicon carbide sludge is extruded and dried, and then heated to 1750° C. to 2200° C. for sintering to obtain a silicon carbide film support. The patent "a high temperature and corrosion resistant reaction sintered silicon carbide film support and its preparation method (application number: CN201911039324.5)" combines submicron or micron silicon carbide powder, submicron or micron silicon nitride powder, The carbon precursor is fully mixed to obtain a mixed powder; molded to obtain a green body; the green body is sintered to obtain a high-temperature-resistant and corrosion-resistant reaction-sintered silicon carbide film support.

The above method has high equipment requirements for high-temperature sintering (above 1700° C.) silicon carbide ceramic support body, high energy consumption and high cost. Low-temperature sintering (about 1500°C) silicon carbide ceramic supports often use low-melting point oxide sintering aids, etc., which have problems such as poor acid and alkali resistance or low strength.

Contents of the invention

In order to solve the problems existing in the background technology, the present invention proposes a method for preparing a low-temperature reaction sintered silicon carbide ceramic film. The new SiC phase generated by the solid phase reaction of silicon powder and carbon black is co-sintered with the SiC powder raw material. The silicon-carbon reaction in the NaCl-KCl molten salt system bonds the SiC raw material particles into a continuous porous ceramic support. The surface of the silicon carbide ceramic membrane is composed of nanofibers interwoven with silicon carbide nanofibers to construct uniform pores. The preparation process of the silicon carbide ceramic film is simple and convenient, the sintering temperature is low, the oxide content is small, and the pores are uniform.

In view of the problems existing in the prior art such as high temperature, high equipment requirements, large energy consumption and large pores of the surface ceramic membrane, in this application, the sintering of the newly formed silicon carbide phase and the silicon carbide raw material is highlighted to obtain a silicon carbide ceramic support body preparation.

In order to achieve the above object of the invention, the present invention provides the following technical solutions:

The present invention uses raw materials such as silicon carbide powder, silicon powder, carbon black, NaCl-KCl molten salt, kaolin, sodium carboxymethyl cellulose, PVP, glycerin and water, through batching, mixing into mud, molding, drying, sintering and SiC ceramic membranes were prepared by water immersion desalination and other processes.

The invention relies on the β-SiC new phase generated by the sintering of silicon and carbon solid phase reaction and molten salt liquid phase reaction to bond SiC raw material particles into a porous ceramic support body, and uses silicon carbide nanofiber slurry to coat and sinter to prepare silicon carbide Ceramic Membrane.

Described method specifically comprises:

(1) Batching and kneading into mud, extruding and drying to prepare dry green body: silicon carbide powder, silicon powder, carbon powder, NaCl-KCl molten salt, kaolin, carboxymethyl cellulose and glycerin, etc. according to the formula Weigh the ingredients, add water to stir the mixture, and then knead it into a mud, extrude the kneaded mud, control the molding temperature, and obtain a high-quality wet silicon carbide support body green body, the wet silicon carbide support body green body Drying in an oven to obtain a silicon carbide blank;

(2) Place the dried silicon carbide green body in a high-temperature furnace and heat it in a vacuum, so that the organic matter such as the bonding molding agent in the silicon carbide green body is completely cracked, so as to realize cracking and debinding;

(3) Sintering of silicon carbide support body: put the silicon carbide biscuit into a sintering furnace, sinter at high temperature to obtain porous silicon carbide, soak in water to remove salt, and obtain a porous silicon carbide support body;

(4) Mix silicon carbide nanofibers and polyvinyl alcohol (PVA) according to a certain concentration to obtain silicon carbide nanofiber water slurry, apply the silicon carbide nanofiber water slurry on the porous silicon carbide support, and then apply the slurry The porous silicon carbide support after feeding is dried in an oven;

(5) Sintering the silicon carbide support body coated with silicon carbide nanofibers in a high-temperature furnace to obtain a silicon carbide ceramic film.

In the above (1), the silicon powder and carbon black are mixed at a molar ratio of 1: (1 to 3) to obtain a silicon-carbon composite powder, and the uniform mixing of the raw materials can be achieved by closed stirring and mixing with a mixer ; Then silicon carbide powder, silicon-carbon composite powder, NaCl-KCl molten salt, kaolin, carboxymethyl cellulose and glycerin are 70-80:6-15:2-5:5-10 in parts by mass: 1~4: 0.2~0.5.

In this way, the silicon carbide ceramic film is prepared by adding carbon black and silicon powder to the silicon carbide particles and sintering by low-temperature liquid phase reaction, so that the silicon carbide ceramic film has the characteristics of low sintering temperature, low oxide content, corrosion resistance, and high strength.

And the mixed raw material NaCl-KCl molten salt obtained in step (1) has a refinement effect on the original powder, the molten salt ratio is 1:1.2, the molten salt method is adopted, and NaCl-KCl is used as the molten salt medium, and Si powder and The carbon reaction generates a new SiC phase on the surface of the silicon carbide raw material powder.

The particle diameter of the silicon carbide powder is 0.1-10 μm, and the purity is above 99%.

In the above (1), the specific process of adding water and mixing is as follows: the raw materials are dry-mixed in the mixer for 10-30 minutes, then wet-mixed with water for 40-60 minutes, and then muddled and placed at room temperature for 24 hours.

In the above (1), the drying in the oven is carried out according to the following specific step temperature control method:

Dry the mud at room temperature for 12-24 hours, then transfer it to an oven, start to heat up from room temperature to 50°C, the heating rate is 1-5°C/min, and keep warm for 3-5 hours;

Start to heat up from 50°C to 80°C, the heating rate is 1-5°C/min, and keep warm for 3-5 hours;

Start to heat up from 80°C to 120°C, the heating rate is 1-5°C/min, and keep warm for 5-10h.

The aforementioned stepwise temperature control method for drying treatment can avoid cracks in the silicon carbide green body, and the preparation of high-quality crack-free green body can be realized through gradually and slowly raising the temperature to volatilize water.

The above (2) is specifically: placing the dried silicon carbide blank in a tube furnace and vacuuming it, and then raising the temperature from room temperature to 800°C at a rate of 3-5°C/min to make the silicon carbide blank Organic substances such as molding agents, binders and lubricants in the furnace are completely decomposed.

In the sintering in (3), a sintering aid is also added, and the sintering aid is composed of kaolin or Al ₂ O ₃ and SiO ₂ composite powder.

In (3), the high-temperature sintering is specifically processed according to the following specific stepwise heating method:

From room temperature to 200°C, the heating rate is 5-10°C/min, and the temperature is kept for 1-3h;

From 200°C to 900°C, the heating rate is 5-10°C/min, and the temperature is kept for 1-3 hours;

From 900°C to 1350-1600°C, the heating rate is 1-5°C/min;

At a temperature of 1350-1600°C, keep warm for 1-5 hours;

Then cool down with the furnace.

The above-mentioned high-temperature sintering treatment using such a stepwise temperature control method can control the formation of liquid phase and the bonding between ceramic particles in sequence at different temperatures corresponding to the high-temperature sintering process, so as to realize porous ceramic sintering.

In the above (3), desalination by soaking in water involves soaking the porous silicon carbide in water for 30-60 minutes, and then changing the water, repeating this for 3-5 times.

In the above (4), the silicon carbide nanofiber aqueous slurry is prepared according to the mass percentage of silicon carbide nanofibers at a concentration of 0.5wt% to 5wt% and polyvinyl alcohol at a concentration of 0.2wt% to 0.5wt%.

In the above (5), the silicon carbide ceramic film is obtained by sintering at 900-1600° C. for 0.5-2 hours in a high-temperature furnace.

The sintering temperature of the support body of the present invention is 1350-1600°C. Since the raw materials contain silicon powder and carbon black, the SiC phase newly generated by the solid phase reaction of silicon powder and carbon black is used to co-sinter with the SiC raw material powder to prepare porous SiC ceramics. The use of NaCl-KCl molten salt liquid phase is beneficial to the shaping, low-temperature sintering and pore formation of SiC raw material particles. The β-SiC new phase generated by the solid-state reaction of silicon and carbon sintering and the liquid-phase reaction of molten salt bond the SiC raw material particles into a continuous porous ceramic support, and the surface forms nanopores constructed by interweaving SiC nanofibers.

Aiming at the problems in the background technology, the present invention adopts raw materials containing silicon powder and carbon black, utilizes the SiC phase newly generated by the solid phase reaction of silicon powder and carbon black to co-sinter with SiC powder raw materials to prepare porous SiC ceramics, and simultaneously uses NaCl-KCl Molten salt is beneficial to shaping, low-temperature sintering and pore creation of SiC raw materials. Relying on the new phase of β-SiC formed by the solid phase reaction of silicon and carbon and the liquid phase reaction of molten salt, the SiC raw material particles are bonded into a continuous porous ceramic support. The surface pores of the silicon carbide ceramic membrane coated with silicon carbide nanofibers are constructed by interwoven nanofibers, and the pores are small and uniform.

Beneficial effects of the present invention:

The present invention adopts the silicon-carbon reaction of NaCl-KCl molten salt system to bond the SiC raw material particles into a continuous porous ceramic support body, and the silicon carbide nanofibers are sintered at 900-1600°C. Under bonding, the surface pores of the silicon carbide ceramic membrane covered with silicon carbide nanofibers are constructed by interwoven nanofibers, and the pores are small and uniform. The sintering temperature is 1350-1600°C, the raw materials are easy to obtain, the preparation is simple, the molding is easy, the production cost is low, the requirement for the kiln is low, the energy consumption is low, and it is suitable for the preparation method of industrial customized porous silicon carbide ceramic materials.

The product of the invention has the characteristics of less oxide content, high purity, high porosity, and acid and alkali resistance (the oxide content mainly depends on the amount of kaolin added in the raw material). The process has the advantages of low sintering temperature, simple molding process, low production cost, no need of ultra-high temperature equipment, and is suitable for industrial scale production.

The low-temperature reaction sintered silicon carbide ceramic membrane produced by the present invention has a porosity of 30% to 52%, a volume density of 1.0-1.5g/cm ³ , low sintering temperature, low oxide content and high internal porosity , The surface is characterized by nanoporosity and acid and alkali resistance.

Description of drawings

FIG. 1 is a flow chart of the preparation of low temperature reaction sintered silicon carbide ceramic film in Example 1.

FIG. 2 is a SEM microstructure diagram of the silicon carbide green body in Example 1. FIG.

FIG. 3 is a SEM microstructure diagram of the silicon carbide ceramic film in Example 1. FIG.

FIG. 4 is a SEM microstructure diagram of the silicon carbide nanowire ceramic film in Example 1. FIG.

Detailed ways

The present invention will be further described below through the following embodiments. It should be understood that the following embodiments are only used to illustrate the present invention, not to limit the present invention.

Embodiments of the present invention are as follows:

Example 1

(1) Ingredients and kneading into mud: silicon carbide powder, silicon-carbon composite powder, NaCl-KCl molten salt, kaolin, carboxymethyl cellulose and glycerin are weighed according to the formula, and the mass ratio is 78:10:3 :6:2.8:0.2. Put it into a closed mixer, add water to stir the mixture, and then knead it into mud.

Specifically, the raw materials are dry-mixed in the mixer for 25 minutes, then wet-mixed with water for 50 minutes, and then the mud is smelted and placed at room temperature for 24 hours.

(2) Extrusion molding: the kneaded mud material is extruded and formed in an extrusion molding machine, and the molding temperature is controlled at normal temperature to obtain a wet silicon carbide support body blank, which is cut into sheet-shaped mud blanks.

Then dry in an oven to obtain a silicon carbide green compact;

(3) Ceramic biscuit drying and cracking:

The wet silicon carbide support body mud is shaped in an oven to remove moisture, and it is specifically processed according to the following specific step temperature control method:

Put the mud base at room temperature to dry for 18 hours, then transfer it to an oven, start heating from room temperature to 50°C, the heating rate is 3°C/min, and keep warm for 3h;

Start to heat up from 50°C to 80°C with a heating rate of 3°C/min and hold for 4 hours;

The temperature was raised from 80°C to 120°C, the heating rate was 3°C/min, and the temperature was kept for 8h.

Obtain silicon carbide biscuit after drying;

The dried silicon carbide blank was placed in a tube furnace and evacuated, and then the temperature was raised from room temperature to 800°C at a rate of 4°C/min to completely decompose the molding agent and lubricant therein.

(4) Sintering of silicon carbide support body: put the biscuit after drying and cracking into the sintering furnace, the sintering procedure: from normal temperature to 600°C, the heating rate is 5°C/min, and keep for 1h; from 600°C to 900°C, The heating rate is 5°C/min, keep warm for 1h; from 900°C to 1450°C, the heating rate is 3°C/min; at 1450°C, hold for 2h; then cool with the furnace;

The porous silicon carbide was then soaked in water for 40 minutes, and then the water was changed. This was repeated 4 times to obtain a porous silicon carbide ceramic membrane.

(5) Preparation of silicon carbide nanofiber slurry, coating and drying and sintering: the silicon carbide nanofiber and polyvinyl alcohol PVA are prepared according to the mass percentage of 5wt% and 0.5wt% concentration of silicon carbide nanofiber water slurry, Brush coating on the porous silicon carbide support, and then dry the coating layer in an oven at 100°C for 5h.

(6) Sintering of silicon carbide ceramic film: the silicon carbide support body coated with silicon carbide nanofibers was sintered in a high temperature furnace at 1200° C. for 2 hours to obtain a silicon carbide ceramic film.

The SEM microstructures of the silicon carbide ceramic film obtained in Example 1 before and after sintering, and the silicon carbide nanofiber ceramic film are shown in FIG. 2 , FIG. 3 and FIG. 4 , respectively. Through testing, it is calculated that the porosity of the silicon carbide ceramic membrane obtained in Example 2 is 40.5%, the bulk density is 1.25 g/cm ³ , and the oxide content is about 6%.

Example 2

(1) Ingredients and kneading into mud: Silicon carbide powder, silicon-carbon composite powder, NaCl-KCl molten salt, kaolin, carboxymethyl cellulose and glycerin are weighed and ingredients according to the formula, and the mass ratio is 70:14: 2:10:3.5:0.5. Put it into a closed mixer, add water to stir the mixture, and then knead it into mud.

Specifically, the raw materials are dry-mixed in the mixer for 30 minutes, then wet-mixed with water for 60 minutes, and then the mud is kneaded, and placed at room temperature for 24 hours.

(2) Extrusion molding: the kneaded mud material is extruded and formed in a vacuum extrusion molding machine, and the molding temperature is controlled to obtain a wet silicon carbide support body blank, which is cut into sheet-shaped mud blanks.

(3) Ceramic biscuit drying and cracking:

The wet silicon carbide support body mud is shaped in an oven to remove moisture, and it is specifically processed according to the following specific step temperature control method:

Put the mud base at room temperature to dry for 24 hours, then transfer it to an oven, start heating from room temperature to 50°C, the heating rate is 5°C/min, and keep warm for 3h;

Start to heat up from 50°C to 80°C with a heating rate of 5°C/min and hold for 5 hours;

Start to heat up from 80°C to 120°C at a heating rate of 5°C/min and hold for 10 hours.

Obtain silicon carbide biscuit after drying;

The dried silicon carbide blank was placed in a tube furnace and evacuated, and then the temperature was raised from room temperature to 800°C at a rate of 4°C/min to completely decompose the molding agent and lubricant therein.

(4) Sintering of silicon carbide support body: put the biscuit after drying and cracking into the sintering furnace, the sintering procedure: from normal temperature to 600°C, the heating rate is 5°C/min, and keep for 1h; from 600°C to 900°C, The heating rate is 5°C/min, keep warm for 1h; from 900°C to 1450°C, the heating rate is 3°C/min; at 1450°C, hold for 2h; then cool with the furnace;

The porous silicon carbide was then soaked in water for 60 minutes, and then the water was changed. This was repeated 5 times to obtain a porous silicon carbide ceramic membrane.

(5) Preparation of silicon carbide nanofiber slurry, coating and drying and sintering: silicon carbide nanofiber and polyvinyl alcohol PVA are prepared according to the mass percentage of 0.5wt% and 0.2wt% concentration of silicon carbide nanofiber water slurry , brush-coated on the porous silicon carbide support, and then dry the coating layer in an oven at 100°C for 5h.

(6) Sintering of silicon carbide ceramic membrane: the silicon carbide support body coated with silicon carbide nanofibers was sintered in a high-temperature furnace at 900° C. for 2 hours to obtain a silicon carbide ceramic membrane.

Through testing, it is calculated that the porosity of the silicon carbide ceramic membrane obtained in Example 2 is 33.4%, the bulk density is 1.286 g/cm ³ , and the oxide content is about 10%.

Example 3

(1) Ingredients and kneading into mud: Weigh silicon carbide powder, silicon-carbon composite powder, NaCl-KCl molten salt, kaolin, carboxymethyl cellulose and glycerin according to the formula, and the mass ratio is 75:12: 2.5:6.5:3.7:0.3. Put it into a closed mixer, add water to stir the mixture, and then knead it into mud.

Specifically, the raw materials are dry mixed in the mixer for 10 minutes, then wet mixed with water for 40 minutes, and then the mud is smelted and placed at room temperature for 24 hours.

(2) Extrusion molding: the kneaded mud material is extruded and formed in a vacuum extrusion molding machine, and the molding temperature is controlled to obtain a wet silicon carbide support body blank, which is cut into sheet-shaped mud blanks.

(3) Ceramic biscuit drying and cracking:

The wet silicon carbide support body mud is shaped in an oven to remove moisture, and it is specifically processed according to the following specific step temperature control method:

Put the mud body at room temperature to dry for 12 hours, then transfer it to an oven, start heating from room temperature to 50°C, the heating rate is 1°C/min, and keep warm for 3h;

Start to heat up from 50°C to 80°C with a heating rate of 1°C/min and hold for 3 hours;

The temperature was raised from 80°C to 120°C at a heating rate of 1°C/min and kept for 5 hours.

Obtain silicon carbide biscuit after drying;

The dried silicon carbide blank was placed in a tube furnace and evacuated, and then the temperature was raised from room temperature to 800°C at a rate of 3°C/min to completely crack the molding agent and lubricant therein.

(4) Sintering of silicon carbide support body: put the biscuit after drying and cracking into the sintering furnace, the sintering procedure: from normal temperature to 600°C, the heating rate is 5°C/min, and keep for 1h; from 600°C to 900°C, The heating rate is 5°C/min, keep warm for 1h; from 900°C to 1500°C, the heating rate is 3°C/min; at 1500°C, keep warm for 2h; then cool with the furnace;

The porous silicon carbide was then soaked in water for 30 minutes, and then the water was changed. This was repeated 5 times to obtain a porous silicon carbide ceramic membrane.

(5) SiC nanofiber slurry preparation, film coating and drying and sintering: silicon carbide nanofiber and polyvinyl alcohol PVA are respectively prepared according to the mass percentage of 2.5wt% and 0.3wt% concentration of silicon carbide nanofiber water slurry , brush-coated on the porous silicon carbide support, and then dry the coating layer in an oven at 100°C for 4h.

(6) Sintering of silicon carbide ceramic film: the silicon carbide support body coated with silicon carbide nanofibers was sintered in a high temperature furnace at 1000° C. for 2 hours to obtain a silicon carbide ceramic film.

Through testing, it is calculated that the porosity of the silicon carbide ceramic membrane obtained in Example 2 is 33.5%, the bulk density is 1.29 g/cm ³ , and the oxide content is about 6.5%.

Example 4

(1) Batching and kneading into mud: weigh silicon carbide powder, silicon-carbon composite powder, NaCl-KCl molten salt, kaolin, carboxymethyl cellulose and glycerin according to the formula, and the mass ratio is 80:6: 4:8:1.5:0.5. Put it into a closed mixer, add water to stir the mixture, and then knead it into mud.

Specifically, the raw materials are dry-mixed in the mixer for 20 minutes, then wet-mixed with water for 45 minutes, and then the mud is smelted and placed at room temperature for 24 hours.

(2) Extrusion molding: the kneaded mud material is extruded and formed in a vacuum extrusion molding machine, and the molding temperature is controlled to obtain a green silicon carbide support body, which is cut into sheet-shaped mud billets.

(3) Ceramic biscuit drying and cracking: the wet silicon carbide support body mud blank is removed from the moisture in the oven to shape, and it is specifically processed according to the following specific step temperature control method:

Dry the mud at room temperature for 20 hours, then transfer it to an oven, start to heat up from room temperature to 50°C, the heating rate is 4°C/min, and keep warm for 4h;

Start to heat up from 50°C to 80°C with a heating rate of 4°C/min and hold for 3 hours;

The temperature was raised from 80°C to 120°C at a heating rate of 4°C/min and kept for 8 hours.

Obtain silicon carbide biscuit after drying;

The dried silicon carbide blank was placed in a tube furnace and evacuated, and then the temperature was raised from room temperature to 800°C at a rate of 3°C/min to completely crack the molding agent and lubricant therein.

(4) Sintering of silicon carbide support body: put the biscuit after drying and cracking into the sintering furnace, the sintering procedure: from normal temperature to 600°C, the heating rate is 5°C/min, and keep for 1h; from 600°C to 900°C, The heating rate is 5°C/min, keep warm for 1h; from 900°C to 1500°C, the heating rate is 3°C/min; at 1500°C, keep warm for 2h; then cool with the furnace;

The porous silicon carbide was then soaked in water for 45 minutes, and then the water was changed. This was repeated 4 times to obtain a porous silicon carbide ceramic membrane.

(5) Preparation of silicon carbide nanofiber slurry, coating and drying and sintering: the silicon carbide nanofiber and polyvinyl alcohol PVA are respectively prepared according to the mass percentage of 3wt% and 0.4wt% concentration of silicon carbide nanofiber water slurry, Brush coating on the porous silicon carbide support, and then dry the coating layer in an oven at 100°C for 5h.

(6) Sintering of silicon carbide ceramic membrane: the silicon carbide support body coated with silicon carbide nanofibers was sintered in a high-temperature furnace at 1100° C. for 2 hours to obtain a silicon carbide ceramic membrane.

Through testing, it is calculated that the porosity of the silicon carbide ceramic membrane obtained in Example 2 is 51.23%, the bulk density is 1.19 g/cm ³ , and the oxide content is about 8%.

Example 5

(1) Batching and kneading into mud: weigh silicon carbide powder, silicon-carbon composite powder, NaCl-KCl molten salt, kaolin, carboxymethyl cellulose and glycerin according to the formula, and the mass ratio is 75:8: 4:10:2.5:0.5. Put it into a closed mixer, add water to stir the mixture, and then knead it into mud.

Specifically, the raw materials are dry-mixed in the mixer for 25 minutes, then wet-mixed with water for 40 minutes, and then the mud is kneaded, and placed at room temperature for 24 hours.

(2) Extrusion molding: the kneaded mud material is extruded and formed in a vacuum extrusion molding machine, and the molding temperature is controlled to obtain a wet silicon carbide support body blank, which is cut into sheet-shaped mud blanks.

(3) Ceramic biscuit drying and cracking: the wet silicon carbide support body mud blank is removed from the moisture in the oven to shape, and it is specifically processed according to the following specific step temperature control method:

Put the mud body at room temperature to dry for 12 hours, then transfer it to an oven, start heating from room temperature to 50°C, the heating rate is 1°C/min, and keep warm for 3h;

Start to heat up from 50°C to 80°C with a heating rate of 2°C/min and hold for 4 hours;

The temperature was raised from 80°C to 120°C at a heating rate of 2°C/min and kept for 7 hours.

Obtain silicon carbide biscuit after drying;

The dried silicon carbide blank was placed in a tube furnace and evacuated, and then the temperature was raised from room temperature to 800°C at a rate of 3°C/min to completely crack the molding agent and lubricant therein.

(4) Sintering of silicon carbide support body: put the biscuit after drying and cracking into the sintering furnace, the sintering procedure: from normal temperature to 600°C, the heating rate is 5°C/min, and keep for 1h; from 600°C to 900°C, The heating rate is 5°C/min, keep warm for 1h; from 900°C to 1500°C, the heating rate is 3°C/min; at 1500°C, keep warm for 2h; then cool with the furnace;

The porous silicon carbide was then soaked in water for 40 minutes, and then the water was changed. This was repeated 4 times to obtain a porous silicon carbide ceramic membrane.

(5) Preparation of silicon carbide nanofiber slurry, coating and drying and sintering: the silicon carbide nanofiber and polyvinyl alcohol PVA are respectively prepared according to the mass percentage of 3wt% and 0.4wt% concentration of silicon carbide nanofiber water slurry, Brush coating on the porous silicon carbide support, and then dry the coating layer in an oven at 100°C for 5h.

(6) Sintering of silicon carbide ceramic membrane: the silicon carbide support body coated with silicon carbide nanofibers was sintered in a high-temperature furnace at 1600° C. for 2 hours to obtain a silicon carbide ceramic membrane.

Through testing, it is calculated that the porosity of the silicon carbide ceramic membrane obtained in Example 2 is 48.20%, the bulk density is 1.20 g/cm ³ , and the oxide content is about 10%.

Claims (7)

1. A preparation method of a low-temperature reaction sintered silicon carbide ceramic membrane is characterized by comprising the following steps: the method specifically comprises the following steps:

(1) Proportioning and kneading into mud, extruding and molding, and drying to prepare a dry biscuit: weighing and mixing silicon carbide powder, silicon powder, carbon powder, naCl-KCl fused salt, kaolin, carboxymethyl cellulose and glycerol according to a formula, adding water, stirring and mixing the materials, kneading the materials into mud, extruding and molding the kneaded mud material, controlling the molding temperature to obtain a wet silicon carbide support body biscuit, and drying the wet silicon carbide support body biscuit in an oven to obtain a silicon carbide biscuit;

in the step (1), the silicon powder and the carbon black are mixed in a ratio of 1: (1 to 3) mixing the raw materials according to the molar ratio to obtain silicon-carbon composite powder; then, mixing 70-80 parts of silicon carbide powder, silicon-carbon composite powder, naCl-KCl fused salt, kaolin, carboxymethyl cellulose and glycerol in parts by weight: 6-15: 2 to 5:5 to 10:1 to 4:0.2 to 0.5;

(2) Placing the dried silicon carbide biscuit in a high-temperature furnace, and vacuumizing and heating;

(3) Putting the silicon carbide biscuit into a sintering furnace, sintering at high temperature to obtain porous silicon carbide, soaking in water to remove salt, and obtaining a porous silicon carbide support;

(4) Mixing silicon carbide nanofibers and polyvinyl alcohol (PVA) according to a certain concentration to obtain silicon carbide nanofiber water slurry, coating the silicon carbide nanofiber water slurry on a porous silicon carbide support, and drying the porous silicon carbide support coated with the slurry in an oven;

in the step (4), the silicon carbide nanofiber water slurry is prepared according to the concentration of 0.5wt% -5 wt% of silicon carbide nanofiber and 0.2wt% -0.5 wt% of polyvinyl alcohol in percentage by mass;

(5) And sintering the silicon carbide support body coated with the silicon carbide nano fibers in a high-temperature furnace to obtain the silicon carbide ceramic membrane.

2. The method for preparing a low-temperature reaction sintered silicon carbide ceramic film according to claim 1, wherein: in the step (1), the concrete processes of adding water, stirring and mixing materials are as follows: the raw materials are dry-mixed in a mixer for 10 to 30min, then water is added for wet mixing for 40 to 60min, pugging is carried out, and the mixture is placed at normal temperature for aging for 24 hours.

3. The method for preparing a low-temperature reaction sintered silicon carbide ceramic film according to claim 1, wherein: in the step (1), drying is carried out in an oven according to the following specific step temperature control mode:

airing the mud blank at normal temperature for 12 to 24h, then transferring the mud blank into an oven, heating the mud blank from the normal temperature to 50 ℃, wherein the heating rate is 1 to 5 ℃/min, and keeping the temperature for 3 to 5h;

heating from 50 ℃ to 80 ℃, wherein the heating rate is 1 to 5 ℃/min, and keeping the temperature for 3 to 5 hours;

heating from 80 ℃ to 120 ℃, wherein the heating rate is 1-5 ℃/min, and the heat preservation is 5-10 h.

4. The method for preparing a low-temperature reaction sintered silicon carbide ceramic film according to claim 1, wherein: the step (2) is specifically as follows: and (3) placing the dried silicon carbide biscuit in a tube furnace, vacuumizing, and heating to 800 ℃ from the normal temperature at a heating rate of 3-5 ℃/min for treatment.

5. The method for preparing a low-temperature reaction sintered silicon carbide ceramic film according to claim 1, wherein: in the step (3), the high-temperature sintering is specifically carried out according to the following specific step heating manner:

heating from normal temperature to 200 ℃, wherein the heating rate is 5 to 10 ℃/min, and the heat preservation is carried out for 1 to 3 hours;

heating from 200 ℃ to 900 ℃, wherein the heating rate is 5 to 10 ℃/min, and keeping the temperature for 1 to 3h;

heating from 900 ℃ to 1350-1600 ℃, wherein the heating rate is 1-5 ℃/min;

keeping the temperature at 1350 to 1600 ℃ for 1 to 5h;

and then cooling along with the furnace.

6. The method for preparing a low-temperature reaction sintered silicon carbide ceramic film according to claim 1, wherein: in the step (3), the step of soaking and desalting is to soak the porous silicon carbide in water for 30 to 60min, then change the water, and repeat the process for 3 to 5 times.

7. The method according to claim 1, wherein the method comprises the steps of: and (5) sintering the ceramic film in a high-temperature furnace at 900-1600 ℃ for 0.5-2 hours to obtain the silicon carbide ceramic film.

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