CN106431491A - Preparation method of blocky mullite-silicon carbide composite aerogel material with high specific surface area - Google Patents

Abstract

The invention relates to a preparation method of a blocky mullite-silicon carbide composite aerogel material with a high specific surface. The preparation method comprises the steps of mixing a carbon source and an aluminum source, introducing a silane coupling agent which can be used as a coagulant or a silicon source after hydrolysis reaction, obtaining the organic/silicon oxide/aluminum oxide composite aerogel through sol-gel, aging and supercritical drying, then carrying out carbonization treatment and high-temperature carbothermic reduction under the protection of inert atmosphere gas, and finally preparing the blocky mullite/silicon carbide anti-oxidation composite aerogel material through in-situ reaction and subsequent air thermic calcination. The invention has the advantages of simple material and simple process, and the process is simple to operate and easy to realize mass production.

Description

Preparation method of bulk high specific surface mullite-silicon carbide composite airgel material

technical field

The invention belongs to the field of preparation technology of airgel materials, and relates to a preparation method of blocky high-specification mullite-silicon carbide composite airgel materials; in particular, a one-step sol-gel method combined with supercritical drying is designed Process and heat treatment process conditions A method for preparing blocky high specific mullite/SiC anti-oxidation composite airgel.

Background technique

Silicon carbide porous material is a new type of functional material with excellent characteristics of high temperature resistance, wear resistance, low thermal expansion coefficient, large specific surface area and excellent chemical stability. It can be widely used in catalyst carrier, high temperature gas filter, membrane separation, sensor and other fields. However, silicon carbide materials often encounter serious oxidation problems during the application process, and a silicon oxide layer is formed on the surface at around 700 ° C, which reduces its application to a certain extent. Mullite material is a general term for a series of minerals composed of aluminosilicates. Mullite is the only stable binary compound in the Al ₂ O ₃ -SiO ₂ system. It has high temperature resistance, high strength, small thermal conductivity, and high Creep resistance and thermal stability, while having a similar coefficient of thermal expansion to SiC materials. Therefore, the research on mullite composite silicon carbide porous materials will have broad prospects. Many researchers at home and abroad have carried out research on this porous material, but the current research mainly uses the in-situ generation method of mullite, by introducing silicon carbide material into the raw material, so as to utilize the oxidation formed by the surface oxidation of silicon carbide at high temperature. The silicon layer reacts with the aluminum source in the raw material to form the final silicon carbide/mullite composite porous material.

As a lightweight porous material with a three-dimensional nanoporous structure, airgel also has the characteristics of low density, high specific surface area, and high porosity. It has broad application prospects in adsorption, catalysis, heat insulation, and impedance coupling. If silicon carbide material and mullite material can be prepared into a porous airgel structure, it will have more excellent performance. At present, there are relevant reports about silicon carbide airgel at home and abroad, (such as the Chinese patent of patent No. CN102910926A ), there are also similar reports about mullite airgel materials, (Cluzel F, Larnac G, Phalippou J.Structure and thermalevolution of mullite aerogels[J].Journal of materials science, 1991,26(22):5979-5984 ), but there is no relevant literature report on silicon carbide/mullite composite airgel materials. In this patent, mullite and silicon carbide airgel are combined, and a block-shaped high-temperature-resistant high-specification mullite/SiC anti-oxidation composite airgel is prepared by a one-step sol-gel method combined with supercritical drying process and heat treatment process conditions. In this way, the agglomeration performance of the silicon carbide material can be improved (the agglomeration performance of the silicon carbide aerogel is extremely poor), and secondly, the oxidation resistance of the silicon carbide material can be better improved.

Contents of the invention

The purpose of the present invention is to provide a method for preparing a blocky high-specification mullite-silicon carbide composite airgel material in order to improve the deficiencies in the prior art. The method uses simple materials and processes, and the microstructure is controllable Well, the prepared airgel material has the characteristics of low density, high specific surface area, oxidation resistance, and high temperature resistance. At the same time, it can be prepared into samples of various shapes after being combined with fibers. Applications in fields such as gas filters, membrane separation, and sensors have positive production significance.

The technical scheme of the present invention is: the preparation method of massive high specific surface mullite-silicon carbide composite airgel material, and its specific steps are as follows:

(1) After uniformly mixing carbon source, formaldehyde, ethanol, water and aluminum source, uniformly stirring at a temperature of 20-50°C to obtain a hydrolyzed organic/alumina binary sol system;

(2) adding the silicon source to the binary sol system obtained in step (1), and continuing to stir evenly at a temperature of 20-50° C. to obtain a cross-linked ternary sol system;

(3) Pour the ternary sol system obtained in step (2) into a mold to react to gel, and place it for 10 to 30 hours;

(4) Add the aging solution in step (3), and replace it in an oven at 25-75°C;

(5) the wet gel obtained in the step (4) is carried out with _CO supercritical drying treatment to obtain organic/formaldehyde/silicon oxide/alumina composite airgel;

(6) heat-treating the composite airgel obtained in step (5) under the protection of an inert atmosphere gas, thereby obtaining C/mullite/SiC composite airgel;

(7) placing the C/mullite/SiC composite airgel obtained in step (6) in an air atmosphere for calcination to remove carbon, thereby obtaining the final massive porous mullite/SiC composite airgel material;

Wherein: the carbon source, ethanol, water, aluminum source in the step (1) are uniformly mixed according to the molar ratio of 1: (1～4): (10～30): (1～5): (0.1～0.5); The silicon source and the carbon source in (2) are mixed according to the molar ratio (0.5-5):1.

Preferably, the carbon source described in step (1) is one of catechol-formaldehyde, resorcinol-formaldehyde, cresol-formaldehyde, pyroglucinol-formaldehyde or phenolic resin or a mixture thereof. Preferably, the aluminum source described in step (1) is one of aluminum chloride hexahydrate, aluminum nitrate nonahydrate, aluminum sec-butoxide or aluminum isopropoxide or a mixture thereof.

Preferably, the silicon source described in step (2) is triaminopropyl triethoxysilane, vinyl triperoxy tert-butyl silane, butadienyl triethoxy silane or γ-glycidyl ether oxypropyl One or a mixture of trimethoxysilanes.

Preferably, the stirring speed in step (1) is 400-600 rpm, and the stirring time is 0.5-4 h; the stirring speed in step (2) is 400-600 rpm, and the stirring time is 0.1-2 h.

Preferably, the aging solution described in step (4) is one of ethanol, methanol, acetone, ether, n-pentanol or isopropanol or a mixture thereof.

Preferably, the drying method described in step (5) is as follows: the drying temperature is 50-70° C., the pressure in the autoclave is 8-12 MPa, the gas release rate is 5-20 L/min, and the drying time is 8-20 hours.

Preferably, the number of replacements in step (5) is 3 to 6 times, and the time for each replacement is 12 to 24 hours.

Preferably, the heat treatment temperature in step (6) is between 1000-1500° C.; the heating rate is 2-10° C./min, and the heat treatment time is 3-10 hours; the inert atmosphere protection gas is argon, nitrogen or helium.

Preferably, the air heat calcination temperature in step (7) is between 400-800°C; the heating rate is 3-5°C/min, and the heat treatment time is 2-5h.

Beneficial effect:

(1) The process is simple. Using a one-step sol-gel method, introducing carbon source, aluminum source and silicon source at the same time, and through the subsequent supercritical drying, carbonization and carbothermal reduction process, the silicon source and aluminum source can generate mullite phase at high temperature, silicon source and carbon source to form a silicon carbide phase, and finally the carbon template is removed by air heat calcination, so as to finally obtain a blocky high specific surface mullite/silicon carbide composite aerogel.

(2) In situ generation of silicon carbide phase. At present, when preparing silicon carbide/mullite composite materials, silicon carbide micropowder and alumina micropowder are used as reaction raw materials, and the silicon oxide layer formed by the silicon carbide phase at high temperature reacts with alumina to form a mullite phase. In this solution, silicon carbide is also generated in situ, which is obtained through the carbothermal reduction process of silicon source and carbon source at high temperature, so the structure is finer. At the same time, due to the existence of carbon template, the porosity of the prepared material is higher. Higher, larger specific surface area.

(3) The silicon carbide/mullite airgel material prepared in this method is a complete block, and the oxidation resistance of the silicon carbide material is further improved due to the introduction of the mullite phase, which is helpful for realizing the airgel material in The application in the fields of catalyst carrier, high temperature gas filter, membrane separation and sensor has positive significance.

Description of drawings

Fig. 1 is the physical photo of the massive high specific surface mullite/silicon carbide composite airgel material that example 1 makes;

Fig. 2 is the XRD diffraction pattern of the ternary airgel system after carbothermal reduction at 1400°C under different reactant concentrations (the sum of aluminum source, silicon source and carbon source) obtained after adjusting the ethanol content in Example 2.

detailed description

Example 1

After uniformly mixing catechol, formaldehyde, ethanol, water, and aluminum chloride hexahydrate in a molar ratio of 1:2:17.4:2:0.18, stir evenly at a temperature of 20°C and a speed of 600rpm for 0.5h to obtain partially hydrolyzed organic/alumina binary sol system. Then add triaminopropyltriethoxysilane to the above-mentioned binary sol system at a molar ratio of 0.77:1 to catechol, continue to stir evenly at a temperature of 20°C at a speed of 600rpm for 0.1h, and then pour React to gel in the mold, add ethanol aging solution after standing for 10 hours, and replace in an oven at 25°C for 3 times, each time for 12 hours. Then the wet gel was subjected to _CO2 supercritical drying treatment, and the supercritical reaction temperature was 50 °C. The pressure of the reactor was 10 MPa, the degassing rate was 5 L/min, and the drying time was 20 hours to obtain catechol/formaldehyde/silica/alumina composite airgel. The composite airgel was heat-treated at 1000°C under the protection of argon atmosphere, the heating rate was 3°C/min, and the holding time was 3h, so as to obtain the C/mullite/SiC composite airgel. Finally, the obtained C/mullite/SiC composite airgel is placed in the air atmosphere at 500°C for calcination to remove carbon, the heating rate is 3°C/min, and the holding time is 3h, so as to obtain the final blocky porous mullite/SiC composite airgel glue material. After characterization, it was found that the bulk high specific surface mullite/silicon carbide composite airgel material has a density of 0.25g/cm ³ and a specific surface area of 134m ² /g, which is 98°C higher than that of pure silicon carbide materials. . The physical photo of the obtained massive high specific surface mullite/silicon carbide composite airgel material is shown in Figure 1, as can be seen from Figure 1, the prepared mullite/silicon carbide composite airgel material It is a block material with the light green color of silicon carbide on the surface. Although the strength is poor, it has high porosity and large specific surface area.

Example 2

After uniformly mixing catechol, formaldehyde, ethanol, water, and aluminum chloride hexahydrate in a molar ratio of 1:3:25.3:3:0.32, stir evenly at a temperature of 30°C and a speed of 500 rpm for 1 hour to obtain partially hydrolyzed Organic/alumina binary sol system. Then add butadienyltriethoxysilane to the above-mentioned binary sol system at a molar ratio of 2:1 to catechol, continue to stir evenly at 30°C and 500rpm for 0.5h, and then pour React to gel in the mold, add acetone aging solution after standing for 20 hours, and replace it in an oven at 60°C for 4 times, each time for 18 hours. Then the wet gel was subjected to _CO2 supercritical drying treatment, and the supercritical reaction temperature was 60 °C. The pressure of the reactor was 12MPa, the degassing rate was 10L/min, and the drying time was 10h to obtain the catechol/formaldehyde/silica/alumina composite airgel. The composite airgel was heat-treated at 1400°C under the protection of argon atmosphere, the heating rate was 5°C/min, and the holding time was 5h, so as to obtain the C/mullite/SiC composite airgel. Finally, the obtained C/mullite/SiC composite airgel is placed in the air atmosphere at 700°C for calcination to remove carbon, the heating rate is 5°C/min, and the holding time is 4h, so as to obtain the final blocky porous mullite/SiC composite airgel glue material. After characterization, it is found that the density of the blocky high specific surface mullite/silicon carbide composite airgel material is 0.32g/cm ³ , the specific surface area is 156m ² /g, and the oxidation resistance temperature of the pure silicon carbide material is 94°C higher. . The XRD diffraction pattern of the ternary airgel system after carbothermal reduction at 1400 °C under different reactant concentrations (the sum of aluminum source, silicon source and carbon source) obtained after adjusting the ethanol content is shown in Figure 2. It can be seen from the figure that , after carbothermal reduction at 1400°C, when the concentration of the reactants was between 20% and 45%, relatively obvious silicon carbide and mullite phases appeared in the material, and the material also contained a large amount of carbon templates, but after subsequent After the air calcination heat treatment, the structure did not collapse, and the material still showed a complete block in Figure 1.

Example 3

After uniformly mixing resorcinol, formaldehyde, ethanol, water, and aluminum nitrate nonahydrate in a molar ratio of 1:4:30:5:0.46, stir evenly at a temperature of 35°C and a speed of 500rpm for 2 hours to obtain partially hydrolyzed organic /alumina binary sol system. Then add triaminopropyltriethoxysilane to the above-mentioned binary sol system at a molar ratio of 5:1 to resorcinol, continue to stir evenly at a temperature of 35°C and a speed of 400rpm for 1.5h, and then pour React to gel in the mold, place it for 25 hours, add ethanol aging solution, and replace it in an oven at 70°C for 5 times, 24 hours each time. Then the wet gel was subjected to _CO2 supercritical drying treatment, and the supercritical reaction temperature was 55 °C. The pressure of the reactor was 9 MPa, the degassing rate was 20 L/min, and the drying time was 13 hours to obtain resorcinol/formaldehyde/silica/alumina composite airgel. The composite airgel was heat-treated at 1350°C under the protection of nitrogen atmosphere, the heating rate was 8°C/min, and the holding time was 6h, so as to obtain the C/mullite/SiC composite airgel. Finally, the obtained C/mullite/SiC composite airgel is placed in the air atmosphere at 800°C for calcination to remove carbon, the heating rate is 5°C/min, and the holding time is 2h, so as to obtain the final blocky porous mullite/SiC composite airgel glue material. After characterization, it is found that the density of the blocky high specific surface mullite/silicon carbide composite airgel material is 0.22g/cm ³ , the specific surface area is 156m ² /g, and the oxidation resistance temperature of the pure silicon carbide material is 125°C higher. .

Example 4

After uniformly mixing pyroglucinol, formaldehyde, ethanol, water, and aluminum sec-butoxide in a molar ratio of 1:1.4:12:1.6:0.25, uniformly stirring at a temperature of 40°C and a speed of 400 rpm for 3 hours, the partially hydrolyzed organic /alumina binary sol system. Then add vinyl triperoxy tert-butylsilane to the above-mentioned binary sol system at a molar ratio of 3:1 to pyroglucinol, continue to stir evenly at 40°C and 400rpm for 1.3h, and then pour React to gel in the mold, place it for 15 hours, add n-amyl alcohol aging solution, and replace it in an oven at 50°C for 3 times, each time for 18 hours. Then the wet gel was subjected to _CO2 supercritical drying treatment, and the supercritical reaction temperature was 70 °C. The pressure of the reactor was 9.5 MPa, the degassing rate was 15 L/min, and the drying time was 8 hours to obtain the composite airgel of pyroglucinol/formaldehyde/silica/alumina. The composite airgel was heat-treated at 1500°C under the protection of helium atmosphere, the heating rate was 5°C/min, and the holding time was 10h, so as to obtain the C/mullite/SiC composite airgel. Finally, the obtained C/mullite/SiC composite airgel was calcined to remove carbon at 600°C in the air atmosphere, the heating rate was 3°C/min, and the holding time was 5h, so as to obtain the final blocky porous mullite/SiC composite airgel glue material. After characterization, it is found that the density of the blocky high specific surface mullite/silicon carbide composite airgel material is 0.26g/cm ³ , the specific surface area is 186m ² /g, and the oxidation resistance temperature of the pure silicon carbide material is 156°C higher. .

Claims (10)

1. The preparation method of block high specific surface mullite-silicon carbide composite airgel material, its specific steps are as follows: (1) After uniformly mixing carbon source, formaldehyde, ethanol, water and aluminum source, uniformly stirring at a temperature of 20-50°C to obtain a hydrolyzed organic/alumina binary sol system; (2) adding the silicon source to the binary sol system obtained in step (1), and continuing to stir evenly at a temperature of 20-50° C. to obtain a cross-linked ternary sol system; (3) Pour the ternary sol system obtained in step (2) into a mold to react to gel, and place it for 10 to 30 hours; (4) Add the aging solution in step (3), and replace it in an oven at 25-75°C; (5) the wet gel obtained in the step (4) is carried out with _CO supercritical drying treatment to obtain organic/formaldehyde/silicon oxide/alumina composite airgel; (6) heat-treating the composite airgel obtained in step (5) under the protection of an inert atmosphere gas, thereby obtaining C/mullite/SiC composite airgel; (7) placing the C/mullite/SiC composite airgel obtained in step (6) in an air atmosphere for calcination to remove carbon, thereby obtaining the final massive porous mullite/SiC composite airgel material; Wherein: the carbon source, ethanol, water, aluminum source in the step (1) are uniformly mixed according to the molar ratio of 1: (1～4): (10～30): (1～5): (0.1～0.5); The silicon source and the carbon source in (2) are mixed according to the molar ratio (0.5-5):1. 2. preparation method according to claim 1, is characterized in that the carbon source described in step (1) is pyrocatechol-formaldehyde, resorcinol-formaldehyde, mixed cresol-formaldehyde, pyroglucinol - one or a mixture of formaldehyde or phenolic resins. 3. The preparation method according to claim 1, wherein the aluminum source described in step (1) is one of aluminum chloride hexahydrate, aluminum nitrate nonahydrate, aluminum sec-butoxide or aluminum isopropoxide or a mixture thereof. 4. The preparation method according to claim 1, characterized in that the silicon source described in step (2) is triaminopropyl triethoxysilane, vinyl triperoxy tert-butyl silane, butadienyl One of triethoxysilane or γ-glycidyloxypropyltrimethoxysilane or a mixture thereof. 5. The preparation method according to claim 1, characterized in that in the step (1), the stirring speed is 400～600rpm, and the stirring time is 0.5～4h; in the step (2), the stirring speed is 400～600rpm, and the stirring time is 0.1 ~2h. 6. The preparation method according to claim 1, characterized in that the aging solution described in step (4) is one of ethanol, methanol, acetone, ether, n-pentanol or isopropanol or a mixture thereof. 7. The preparation method according to claim 1, characterized in that the drying method described in step (5) is that the drying temperature is 50～70°C, the pressure in the autoclave is 8～12MPa, and the gas release rate is 5～70℃. 20L/min, drying time is 8~20h. 8. The preparation method according to claim 1, characterized in that the number of replacements in step (5) is 3 to 6 times, and the time for each replacement is 12 to 24 hours. 9. The preparation method according to claim 1, characterized in that the heat treatment temperature described in step (6) is between 1000-1500°C; the heating rate is 2-10°C/min, and the heat-treatment time is 3-10h; The inert atmosphere protection gas is argon, nitrogen or helium. 10. The preparation method according to claim 1, characterized in that the air heat calcination temperature described in step (7) is between 400-800° C.; the heating rate is 3-5° C./min, and the heat treatment time is 2-5° C. 5h.