High-temperature-resistant mullite aerogel as well as preparation method and application thereof

Abstract

The invention provides high-temperature-resistant mullite aerogel as well as a preparation method and application thereof, and belongs to the technical field of aerogel materials. According to the invention, the polymer solution is added, and the carbonized polymer not only can improve the high temperature resistance of the mullite aerogel, but also can be used as an infrared opacifying agent to reduce the thermal conductivity of the mullite aerogel at high temperature; the carbonized aerogel is impregnated with ceramic sol and is subjected to ceramic treatment, so that a ceramic coating layer and a micro-nano sheet layer can be constructed on the surface and in a network structure of a mullite aerogel nano skeleton, and the high-temperature resistance of the mullite aerogel is further improved. The result of the embodiment shows that the high temperature resistance of the mullite aerogel prepared by the invention is above 1400 DEG C and can reach 1500 DEG C.

Description

Technical Field

[0001] The invention belongs to the technical field of aerogel materials, and in particular relates to a high-temperature resistant mullite aerogel and a preparation method and application thereof. Background Art

[0002] Mullite is often used to prepare high-temperature resistant aerogel thermal protection materials due to its high melting point, low thermal expansion coefficient, excellent high-temperature mechanical properties and no polycrystalline transformation at high temperatures. However, the high-temperature resistance of mullite aerogel prepared in the prior art is generally 1300°C, which still needs to be further improved.

[0003] Therefore, how to further improve the high temperature resistance of mullite aerogel has become a difficult problem in the prior art. Summary of the invention

[0004] The purpose of the present invention is to provide a high temperature resistant mullite aerogel and its preparation method and application. The mullite aerogel prepared by the preparation method provided by the present invention has a high temperature resistance of above 1400°C and can reach 1500°C.

[0005] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions: The present invention provides a method for preparing a high temperature resistant mullite aerogel, comprising the following steps: (1) mixing a silicon source, an aluminum source, a solvent, a polymer solution and a gelling agent, and performing gelation to obtain a gel; the polymer in the polymer solution comprises one or more of hydroxypropyl cellulose, hydroxypropyl methyl cellulose, carboxymethyl cellulose, hydroxyethyl cellulose, chitosan, carboxymethyl chitosan, polyvinyl alcohol and polyvinyl pyrrolidone; (2) mixing the gel obtained in step (1) with a strengthening agent to strengthen the gel to obtain a strengthened gel; (3) soaking the strengthened gel obtained in step (2) in a replacement liquid, performing solvent replacement, and then drying at normal pressure to obtain a mullite aerogel; (4) carbonizing the mullite aerogel obtained in step (3) to obtain a carbonized aerogel; (5) The carbonized aerogel obtained in step (4) is impregnated in a ceramic sol, and then dried and ceramicized in sequence to obtain a high temperature resistant mullite aerogel.

[0006] Preferably, in step (1), the molar ratio of silicon in the silicon source to aluminum in the aluminum source is 1:(0.2-5).

[0007] Preferably, the mass concentration of the polymer solution in step (1) is 1-10%.

[0008] Preferably, the gelation temperature in step (1) is 25-100° C., and the gelation time is 1-5 days.

[0009] Preferably, in step (4), the carbonization temperature is 800-1400° C., and the carbonization time is 1-50 h.

[0010] Preferably, the immersion time in step (5) is 1 to 50 hours.

[0011] Preferably, the drying temperature in step (5) is 25-150° C., and the drying time is 1-50 h.

[0012] Preferably, the temperature of the ceramic treatment in step (5) is 600-1200° C., and the time of the ceramic treatment is 1-10 h.

[0013] The present invention also provides high temperature resistant mullite aerogel prepared by the preparation method described in the above technical solution.

[0014] The present invention also provides application of the high temperature resistant mullite aerogel described in the above technical solution in the field of thermal protection.

[0015] The invention provides a method for preparing a high-temperature resistant mullite aerogel, comprising the following steps: (1) mixing a silicon source, an aluminum source, a solvent, a polymer solution and a gelling agent, and gelling them to obtain a gel; the polymer in the polymer solution comprises one or more of hydroxypropyl cellulose, hydroxypropyl methyl cellulose, carboxymethyl cellulose, hydroxyethyl cellulose, chitosan, carboxymethyl chitosan, polyvinyl alcohol and polyvinyl pyrrolidone; (2) mixing the gel obtained in the step (1) with a reinforcing agent, and reinforcing them to obtain a reinforced gel; (3) soaking the reinforced gel obtained in the step (2) in a displacement liquid, performing solvent displacement, and then drying at normal pressure to obtain a mullite aerogel; (4) carbonizing the mullite aerogel obtained in the step (3) to obtain a carbonized aerogel; and (5) immersing the carbonized aerogel obtained in the step (4) in a ceramic sol, and then drying and ceramicizing them in sequence to obtain a high-temperature resistant mullite aerogel. The present invention adds a polymer solution, and the polymer can not only inhibit the growth of mullite grains after carbonization, improve the thermal stability of mullite aerogel, but also can act as an infrared sunscreen to reduce the transmittance of mullite aerogel to infrared light, improve the extinction performance of infrared light, reduce its thermal radiation at high temperature, and thus reduce the high-temperature thermal conductivity of mullite aerogel; the carbonized aerogel is impregnated with ceramic sol and ceramicized, and a ceramic coating layer and a micro-nano sheet layer can be constructed on the surface of the nano-skeleton and the network structure of the mullite aerogel, further improving the high-temperature resistance of the mullite aerogel. The results of the embodiment show that the high-temperature resistance of the mullite aerogel prepared by the present invention is above 1400°C and can reach 1500°C. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 A schematic flow chart of a method for preparing high temperature resistant mullite aerogel provided by the present invention; Figure 2 This is a macroscopic image of the mullite aerogel prepared in step (4) of Example 2; Figure 3 This is a SEM image of the mullite aerogel prepared in step (4) of Example 2; Figure 4 This is a macroscopic image of the high temperature resistant mullite aerogel prepared in step (6) of Example 2; Figure 5 This is a SEM image of the high temperature resistant mullite aerogel prepared in step (6) of Example 2. DETAILED DESCRIPTION

[0017] The present invention provides a method for preparing a high temperature resistant mullite aerogel, comprising the following steps: (1) mixing a silicon source, an aluminum source, a solvent, a polymer solution and a gelling agent, and performing gelation to obtain a gel; the polymer in the polymer solution comprises one or more of hydroxypropyl cellulose, hydroxypropyl methyl cellulose, carboxymethyl cellulose, hydroxyethyl cellulose, chitosan, carboxymethyl chitosan, polyvinyl alcohol and polyvinyl pyrrolidone; (2) mixing the gel obtained in step (1) with a strengthening agent to strengthen the gel to obtain a strengthened gel; (3) soaking the strengthened gel obtained in step (2) in a replacement liquid, performing solvent replacement, and then drying at normal pressure to obtain a mullite aerogel; (4) carbonizing the mullite aerogel obtained in step (3) to obtain a carbonized aerogel; (5) The carbonized aerogel obtained in step (4) is impregnated in a ceramic sol, and then dried and ceramicized in sequence to obtain a high temperature resistant mullite aerogel.

[0018] Unless otherwise specified, the present invention has no particular limitation on the sources of the raw materials, and commercially available products known to those skilled in the art may be used.

[0019] The present invention mixes a silicon source, an aluminum source, a solvent, a polymer solution and a gelling agent, performs gelation, and obtains a gel.

[0020] In the present invention, the silicon source preferably includes one or more of dimethyldimethoxysilane, dimethyldiethoxysilane, methyltrimethoxysilane, methyltriethoxysilane, tetramethyl silicate, tetraethyl silicate, tetraisopropyl silicate, tetrabutyl silicate, tetraphenyl silicate, aminopropyltrimethoxysilane, aminopropyltriethoxysilane, polysilsesquioxane, vinyl silane, triacetoxyvinylsilane, dimethoxydivinylsilane, trivinylsilane, vinylmethylsilane, vinyltrimethoxysilane, vinyltriethoxysilane, vinyltri(trimethylsiloxy)silane, tetravinylsilane, methylvinyldimethoxysilane, diethoxymethylvinylsilane and tri(trimethylsilyl)oxyvinylsilane.

[0021] In the present invention, the aluminum source preferably includes one or more of aluminum nitrate nonahydrate, anhydrous aluminum nitrate, aluminum chloride hexahydrate, anhydrous aluminum chloride and boehmite.

[0022] In the present invention, the molar ratio of silicon in the silicon source to aluminum in the aluminum source is preferably 1:(0.2-5). As an embodiment, the molar ratio of silicon in the silicon source to aluminum in the aluminum source may be specifically 1:0.2, 1:0.5, 1:1, 1:2, 1:3, 1:4 or 1:5. The present invention controls the molar ratio of silicon in the silicon source to aluminum in the aluminum source within the above range, which can further increase the specific surface area of ​​the mullite aerogel and reduce the thermal conductivity.

[0023] In the present invention, the polymer in the polymer solution includes one or more of hydroxypropyl cellulose, hydroxypropyl methyl cellulose, carboxymethyl cellulose, hydroxyethyl cellulose, chitosan, carboxymethyl chitosan, polyvinyl alcohol and polyvinyl pyrrolidone.

[0024] In the present invention, the solvent in the polymer solution is preferably water or an acid aqueous solution.

[0025] In the present invention, the acid aqueous solution preferably includes one or more of hydrochloric acid, sulfuric acid, nitric acid, hydrofluoric acid or glacial acetic acid aqueous solution.

[0026] In the present invention, when the solvent is an acid aqueous solution, the volume concentration of the acid aqueous solution is preferably 0.1 to 10%.

[0027] In the present invention, the mass concentration of the polymer solution is preferably 1-10%. As an embodiment, the mass concentration of the polymer solution can be specifically 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9% or 10%.

[0028] In the present invention, the method for preparing the polymer solution is preferably: mixing a polymer with a solvent to obtain a polymer solution.

[0029] In the present invention, the mixing temperature is preferably 25-90°C; the mixing is preferably carried out under stirring or ultrasonic conditions. The present invention has no particular limitation on the stirring and ultrasonic conditions, and the stirring or ultrasonic conditions well known to those skilled in the art can be used to ensure that the polymer is fully dissolved in the solvent.

[0030] In the present invention, the gelling agent preferably includes propylene oxide or ammonia water.

[0031] In the present invention, when the gelling agent is propylene oxide, the molar ratio of the propylene oxide to the aluminum source is preferably (8-20): 1. As an embodiment, the molar ratio of the propylene oxide to the aluminum source may be specifically 8:1, 9:1, 10:1, 11:1, 12:1, 13:1, 14:1, 15:1, 16:1, 17:1, 18:1, 19:1 or 20:1.

[0032] In the present invention, when the gelling agent is ammonia water, the pH value after the silicon source, aluminum source, solvent, polymer solution and ammonia water are mixed is preferably 6 to 10. As an embodiment, the pH value after the silicon source, aluminum source, solvent, polymer solution and ammonia water are mixed can be specifically 6, 7, 8, 9 or 10. In the present invention, the ammonia water is preferably obtained by mixing concentrated ammonia water with a solvent; the mass concentration of the concentrated ammonia water is preferably 25 to 28%; the solvent is preferably water or ethanol; the ratio of the volume of the concentrated ammonia water to the total volume of the concentrated ammonia water and the solvent is preferably (0.5 to 10): 100. The addition of a gelling agent in the present invention is more conducive to the formation of a gel.

[0033] In the present invention, the mixture of the silicon source, aluminum source, solvent, polymer solution and gelling agent is preferably: A silicon source, an aluminum source and a solvent are mixed and subjected to a first hydrolysis to obtain a single-phase mullite sol; and the single-phase mullite sol is then mixed with a polymer solution and a gelling agent.

[0034] In the present invention, the solvent preferably includes water, a mixed solution of water and ethanol, a mixed solution of water and acid, or a mixed solution of water, ethanol and acid.

[0035] In the present invention, the molar ratio of water, ethanol and acid in the solvent is preferably (4-200): (0-30): (0-0.01).

[0036] In the present invention, the acid preferably comprises glacial acetic acid.

[0037] In the present invention, the molar ratio of the silicon source, the aluminum source and the solvent is preferably 1: (0.2-5): (4-240). The present invention controls the molar ratio of the silicon source, the aluminum source and the solvent within the above range, so that the silicon source and the aluminum source are fully hydrolyzed to obtain a single-phase mullite sol.

[0038] The present invention has no special limitation on the operation of mixing the silicon source, the aluminum source and the solvent, and a technical solution for mixing materials well known to those skilled in the art may be adopted.

[0039] In the present invention, the temperature of the first hydrolysis is preferably room temperature. The present invention has no special limitation on the time of the first hydrolysis, as long as the silicon source and the aluminum source are fully hydrolyzed to obtain the sol.

[0040] In the present invention, the mixing of the silicon source, aluminum source, solvent, polymer solution and gelling agent is also preferably as follows: the silicon source and part of the solvent are mixed, and a second hydrolysis is performed to obtain a silica sol; the aluminum source and the remaining solvent are mixed, and a third hydrolysis is performed to obtain an aluminum sol; the silica sol and the aluminum sol are mixed to obtain a dual-phase mullite sol, and the dual-phase mullite sol is mixed with the polymer solution and the gelling agent; or: the silicon source and part of the solvent are mixed, and a second hydrolysis is performed to obtain a silica sol; the aluminum source and the remaining solvent are mixed, and a third hydrolysis is performed to obtain an aluminum sol; the silica sol, the aluminum sol and the polymer solution are mixed to obtain a mullite gel, and the mullite gel is mixed with the gelling agent; or: the silicon source and part of the solvent are mixed, and a second hydrolysis is performed to obtain a silica sol; the aluminum source and the remaining solvent are mixed, and a third hydrolysis is performed to obtain an aluminum sol; after the aluminum sol and the polymer solution are mixed, the silica sol is added to obtain a mullite gel, and the mullite gel is mixed with the gelling agent.

[0041] In the present invention, the partial solvent preferably includes water, a mixed solution of water and ethanol, a mixed solution of water and acid, or a mixed solution of water, ethanol and acid.

[0042] In the present invention, the acid preferably comprises glacial acetic acid.

[0043] In the present invention, the molar ratio of water, ethanol and acid in the partial solvent is preferably (1-50): (0-30): (0-0.01).

[0044] In the present invention, the molar ratio of the silicon source to a portion of the solvent is preferably 1:(1-90).

[0045] The present invention has no special limitation on the operation of mixing the silicon source and part of the solvent, and a technical solution for mixing materials well known to those skilled in the art may be adopted.

[0046] In the present invention, the temperature of the second hydrolysis is preferably room temperature. The present invention has no particular limitation on the time of the second hydrolysis, as long as the silicon source is fully hydrolyzed to obtain the sol.

[0047] In the present invention, the residual solvent is preferably water or a mixed solution of water and ethanol.

[0048] In the present invention, the molar ratio of water to ethanol in the residual solvent is preferably (1-150):(0-30).

[0049] In the present invention, the molar ratio of the aluminum source to the remaining solvent is preferably 1:(1-180).

[0050] The present invention has no special limitation on the operation of mixing the aluminum source and the remaining solvent, and a technical solution for mixing materials well known to those skilled in the art may be adopted.

[0051] In the present invention, the temperature of the third hydrolysis is preferably room temperature. The present invention has no special limitation on the time of the third hydrolysis, as long as the aluminum source is fully hydrolyzed to obtain the sol.

[0052] In the present invention, the molar ratio of silicon to aluminum in the silica sol and alumina sol is preferably 1:(0.2-5). As an embodiment, the molar ratio of silicon to aluminum in the silica sol and alumina sol may be specifically 1:0.2, 1:0.5, 1:1, 1:2, 1:3, 1:4 or 1:5.

[0053] In the present invention, the volume ratio of the two-phase mullite sol and the polymer solution or the volume ratio of the total volume of the silica sol and the aluminum sol to the polymer solution is preferably 1: (0.5~2). In the present invention, the polymer solution can form chemical bonds such as coordination bonds or covalent bonds with the aluminum atoms in the mullite sol, strengthen the gel skeleton, resist the capillary stress during the drying process, and then prepare a block mullite aerogel when dried at normal pressure. The present invention controls the amount of the polymer solution within the above range, which can further strengthen the gel skeleton, ensure that the block mullite aerogel is obtained when dried at normal pressure, and ensure that the mullite aerogel has a higher specific surface area and a lower thermal conductivity.

[0054] In the present invention, a drying control additive is preferably added when the silicon source, aluminum source, solvent, polymer solution and gelling agent are mixed.

[0055] In the present invention, the drying control additive preferably includes one or more of glycerol, formamide, N,N-dimethylformamide, N,N-dimethylacetamide, polyethylene glycol, glycerol, oxalic acid and tetramethylammonium hydroxide. In the present invention, the molecular weight of the polyethylene glycol is preferably 2000-20000.

[0056] In the present invention, the molar ratio of the drying control additive to the aluminum source is preferably (0.1~3):1. As an embodiment, the molar ratio of the drying control additive to the aluminum source may be specifically 0.1:1, 0.5:1, 1:1, 2:1 or 3:1. In the present invention, the drying control additive is used to adjust the pore size to make the pore size distribution more uniform, thereby reducing the capillary stress during drying, and being able to obtain block aerogel when drying at normal pressure, and maintaining a low shrinkage rate and a high specific surface area. The present invention controls the molar ratio of the drying control additive to the aluminum source within the above range, which can further increase the specific surface area of ​​the mullite aerogel and reduce its shrinkage rate.

[0057] In the present invention, when a drying control additive is added, the pH value of the mixture of the silicon source, the aluminum source, the solvent, the polymer solution, the drying control additive and the ammonia water is preferably 6-10.

[0058] In the present invention, the gelation temperature is preferably 25-100° C. As an embodiment, the gelation temperature may be specifically 25° C., 30° C., 40° C., 50° C., 60° C., 70° C., 80° C., 90° C. or 100° C.

[0059] In the present invention, the gelation time is preferably 1 to 5 days. As an embodiment, the gelation time can be specifically 1 day, 2 days, 3 days, 4 days or 5 days. The present invention controls the gelation temperature and time within the above range to fully form a gel.

[0060] In the present invention, the gelation is preferably carried out in a mold. The present invention has no particular limitation on the size of the mold, which can be selected according to actual needs.

[0061] After gelation is completed, the gelled product is preferably demolded. The demolding operation is not particularly limited in the present invention, as long as the gel can be removed from the mold without destroying the shape of the gel.

[0062] After obtaining the gel, the present invention mixes the gel with a strengthening agent to strengthen the gel to obtain the strengthened gel.

[0063] In the present invention, the gel is preferably aged and then mixed with a strengthening agent for strengthening.

[0064] In the present invention, the gel is preferably immersed in an aging liquid for aging.

[0065] In the present invention, the aging solution preferably includes one or more of water, ethanol, acetone, acetonitrile and tetrahydrofuran.

[0066] In the present invention, the water is preferably deionized water.

[0067] The present invention has no particular limitation on the amount of the aging liquid, as long as it can soak the gel.

[0068] In the present invention, the aging temperature is preferably 25-100° C. As an embodiment, the aging temperature may be specifically 25° C., 30° C., 40° C., 50° C., 60° C., 70° C., 80° C., 90° C. or 100° C.

[0069] In the present invention, the aging time is preferably 0.1 to 10 days. As an embodiment, the aging time may be specifically 0.1 days, 1 days, 2 days, 3 days, 4 days, 5 days, 6 days, 7 days, 8 days, 9 days or 10 days. In the present invention, during the aging process, the aging liquid is preferably replaced 1 to 5 times a day. The present invention has no special limitation on the replacement time, and the technical solutions familiar to those skilled in the art can be adopted. In the present invention, the aging process can further cross-link the gel network and remove unreacted raw materials, thereby improving the various properties of the gel. The present invention controls the various parameters of aging within the above range, which can further improve the various properties of the gel, and thus improve the comprehensive performance of the mullite aerogel.

[0070] In the present invention, the strengthening agent preferably includes a silicon source or a mixture of a silicon source and an aluminum source.

[0071] In the present invention, the silicon source and the aluminum source are preferably the same as the silicon source and the aluminum source mentioned above, and will not be described in detail here.

[0072] In the present invention, anhydrous ethanol is preferably added when the gel is mixed with the enhancer.

[0073] In the present invention, the strengthening agent is preferably mixed with anhydrous ethanol to obtain a strengthening liquid, and then the gel is immersed in the strengthening liquid for strengthening.

[0074] In the present invention, the ratio of the amount of silicon source, aluminum source and anhydrous ethanol in the strengthening solution is preferably 1: (0-5): (0.1-100). The present invention has no particular limitation on the amount of the strengthening solution, as long as it can soak the gel.

[0075] In the present invention, the strengthening temperature is preferably 40-100° C. As an embodiment, the strengthening temperature may be specifically 40° C., 50° C., 60° C., 70° C., 80° C., 90° C. or 100° C.

[0076] In the present invention, the strengthening time is preferably 1 to 10 days. As an embodiment, the strengthening time can be specifically 1 day, 2 days, 3 days, 4 days, 5 days, 6 days, 7 days, 8 days, 9 days or 10 days.

[0077] In the present invention, during the strengthening process, the strengthening liquid is preferably replaced 1 to 5 times a day. The present invention has no special limitation on the time of the replacement, and a technical solution familiar to those skilled in the art can be adopted. In the present invention, the strengthening is used to strengthen the gel skeleton. The present invention controls the parameters of the strengthening within the above range, which can fully strengthen the gel skeleton, is more conducive to obtaining blocky mullite aerogel and further increasing the specific surface area of ​​the mullite aerogel and reducing its thermal conductivity.

[0078] After obtaining the strengthened gel, the present invention immerses the strengthened gel in a replacement liquid, performs solvent replacement, and then dries at normal pressure to obtain the mullite aerogel.

[0079] In the present invention, the replacement fluid preferably includes one or more of n-hexane, n-heptane, cyclohexane, methanol, anhydrous ethanol, isopropanol, n-butanol, benzene and toluene.

[0080] In the present invention, the solvent replacement is preferably completed in one step or in steps, that is, the solvent replacement is performed in a single replacement liquid, or the solvent replacement is first performed in one replacement liquid and then in another replacement liquid. In an embodiment of the present invention, the solvent replacement can be first performed in anhydrous ethanol and then in n-hexane; or it can be performed only in n-hexane.

[0081] The present invention has no particular limitation on the amount of the replacement fluid, as long as it can soak the strengthened gel.

[0082] In the present invention, the temperature of the solvent replacement is preferably 25-100° C. As an embodiment, the temperature of the solvent replacement can be specifically 25° C., 30° C., 40° C., 50° C., 60° C., 70° C., 80° C., 90° C. or 100° C.

[0083] In the present invention, the time for the solvent replacement is preferably 1 to 11 days. As an embodiment, the time for the solvent replacement can be specifically 1 day, 2 days, 3 days, 4 days, 5 days, 6 days, 7 days, 8 days, 9 days, 10 days or 11 days.

[0084] In the present invention, during the solvent replacement process, the replacement fluid is preferably replaced 1 to 5 times a day. The present invention has no special limitation on the replacement time, and the technical solutions familiar to those skilled in the art can be used. The present invention performs solvent replacement, which can replace the solvent in the gel with a solvent with low surface tension, reduce the capillary stress during normal pressure drying, avoid structural collapse or damage of the gel during the drying process, and obtain block aerogel with a higher specific surface area. The present invention controls the various parameters in the solvent replacement process within the above range, which can further increase the specific surface area of ​​the mullite aerogel.

[0085] In the present invention, the temperature of the atmospheric drying is preferably 25-150° C. As an embodiment, the temperature of the atmospheric drying can be 25° C., 30° C., 50° C., 70° C., 90° C., 100° C., 120° C. or 150° C.

[0086] In the present invention, the time of the atmospheric drying is preferably 1 to 100 hours. As an embodiment, the time of the atmospheric drying can be specifically 1 hour, 10 hours, 20 hours, 30 hours, 40 hours, 50 hours, 60 hours, 70 hours, 80 hours, 90 hours or 100 hours. The present invention controls the temperature and time of atmospheric drying within the above range, so that the drying can be sufficient.

[0087] In the present invention, the atmospheric pressure drying is preferably completed in one step or in steps, that is, atmospheric pressure drying is performed at a single temperature, or atmospheric pressure drying is performed in steps at different temperatures. The present invention has no special limitation on the operation of the stepwise atmospheric pressure drying, which can be selected according to actual needs.

[0088] After obtaining the mullite aerogel, the present invention carbonizes the mullite aerogel to obtain the carbonized aerogel.

[0089] In the present invention, the mullite aerogel is preferably pre-oxidized before carbonization.

[0090] In the present invention, the pre-oxidation temperature is preferably 200-400° C. As an embodiment, the pre-oxidation temperature may be specifically 200° C., 250° C., 300° C., 350° C. or 400° C.

[0091] In the present invention, the pre-oxidation time is preferably 0.1 to 10 hours. As an embodiment, the pre-oxidation time can be specifically 0.1 hours, 1 hours, 2 hours, 3 hours, 4 hours, 5 hours, 6 hours, 7 hours, 8 hours, 9 hours or 10 hours.

[0092] In the present invention, the pre-oxidation is preferably carried out in an air environment. The pre-oxidation of the present invention improves the thermal stability of the polymer in the mullite aerogel and avoids the rupture or collapse of the mullite aerogel structure during the subsequent carbonization process.

[0093] In the present invention, the carbonization temperature is preferably 800-1400° C. As an embodiment, the carbonization temperature may be specifically 800° C., 900° C., 1000° C., 1100° C., 1200° C., 1300° C. or 1400° C.

[0094] In the present invention, the carbonization time is preferably 1 to 50 hours. As an embodiment, the carbonization time can be specifically 1 hour, 10 hours, 20 hours, 30 hours, 40 hours or 50 hours.

[0095] In the present invention, the carbonization is preferably carried out in an inert atmosphere; the inert atmosphere is preferably nitrogen, helium or argon. In the carbonization process, the polymer is carbonized at high temperature, which can not only improve the high temperature resistance of the mullite aerogel, but also act as an infrared shading agent to reduce the thermal conductivity of the mullite aerogel at high temperature. The present invention controls the temperature and time of carbonization within the above range, so that the polymerization can be fully carbonized.

[0096] After the carbonization is completed, the present invention preferably cools the carbonized product to obtain a carbonized aerogel.

[0097] The present invention has no special limitation on the cooling operation, and any cooling technical solution well known to those skilled in the art may be used.

[0098] After obtaining the carbonized aerogel, the present invention immerses the carbonized aerogel in a ceramic sol, and then performs drying and ceramicization treatments in sequence to obtain a high-temperature resistant mullite aerogel.

[0099] In the present invention, the ceramic sol is preferably a sol containing one or more elements of lithium, boron, silicon, aluminum, zirconium, titanium, calcium, magnesium, iron, yttrium and lanthanum.

[0100] In the present invention, the method for preparing the ceramic sol is preferably: mixing the ceramic sol raw material with a solvent, and stirring for 0.5 to 10 hours to obtain the ceramic sol.

[0101] In the present invention, the ceramic sol raw material preferably includes one or more of lithium-containing compounds, boron-containing compounds, silicon-containing compounds, aluminum-containing compounds, zirconium-containing compounds, titanium-containing compounds, calcium-containing compounds, magnesium-containing compounds, iron-containing compounds, yttrium-containing compounds and lanthanum-containing compounds.

[0102] In the present invention, the lithium-containing compound preferably includes one or more of lithium acetate, lithium nitrate and lithium hydroxide; the boron-containing compound is preferably boric acid; the silicon-containing compound preferably includes dimethyldimethoxysilane, dimethyldiethoxysilane, methyltrimethoxysilane, methyltriethoxysilane, tetramethyl silicate, tetraethyl silicate, tetraisopropyl silicate, tetrabutyl silicate, tetraphenyl silicate, aminopropyltriethoxysilane, polysilsesquioxane, vinyl silane, triacetoxyvinylsilane, dimethoxydivinylsilane, trivinylsilane, vinylmethylsilane, vinyltrimethoxysilane, vinyltriethoxysilane, vinyltri(trimethylsiloxy)silane, tetravinylsilane, methylvinyldimethoxysilane, diethoxysilane, One or more of methylvinylsilane and tris(trimethylsilyl)oxyvinylsilane; the aluminum-containing compound preferably includes one or more of aluminum nitrate nonahydrate, anhydrous aluminum nitrate, aluminum chloride hexahydrate, anhydrous aluminum chloride and boehmite; the zirconium-containing compound preferably includes one or more of zirconium acetate, zirconium tetrachloride, zirconium nitrate pentahydrate and zirconium oxychloride octahydrate; the titanium-containing compound preferably includes one or both of tetrabutyl titanate and isopropyl titanate; the calcium-containing compound is preferably calcium nitrate tetrahydrate; the magnesium-containing compound is preferably magnesium chloride hexahydrate; the iron-containing compound is preferably ferric sulfate hexahydrate; the yttrium-containing compound is preferably yttrium chloride hexahydrate; the lanthanum-containing compound is preferably one or both of lanthanum nitrate hexahydrate and lanthanum chloride hexahydrate.

[0103] In the present invention, the solvent preferably includes a mixture of water and anhydrous ethanol or water.

[0104] In the present invention, the molar ratio of water to anhydrous ethanol in the solvent is preferably (1-50):(0-30).

[0105] In the present invention, the molar ratio of the ceramic sol raw material to the solvent is preferably 1:(1-80). The present invention controls the molar ratio of the ceramic sol raw material to the solvent within the above range, so that the ceramic sol raw material can fully form a sol.

[0106] The present invention has no special limitation on the stirring operation, and any stirring technical solution well known to those skilled in the art may be used.

[0107] In the present invention, the impregnation temperature is preferably 25-100°C; the impregnation time is preferably 1-50h. As an embodiment, the impregnation temperature may be specifically 25°C, 30°C, 40°C, 50°C, 60°C, 70°C, 80°C, 90°C or 100°C; the impregnation time may be specifically 1h, 10h, 20h, 30h, 40h or 50h. The present invention controls the impregnation temperature and time within the above range, so that more ceramic sol can be impregnated in the mullite aerogel, and the high temperature resistance of the mullite aerogel can be further improved after subsequent ceramic treatment.

[0108] In the present invention, the drying temperature is preferably 25-150°C; the drying time is preferably 1-50h; and the drying is preferably carried out under normal pressure. As an embodiment, the drying temperature can be specifically 25°C, 30°C, 50°C, 70°C, 90°C, 100°C, 120°C or 150°C; the drying time can be specifically 1h, 10h, 20h, 30h, 40h or 50h.

[0109] In the present invention, the temperature of the ceramic treatment is preferably 600-1200° C. As an embodiment, the temperature of the ceramic treatment may be specifically 600° C., 700° C., 800° C., 900° C., 1000° C., 1100° C. or 1200° C.

[0110] In the present invention, the ceramic treatment time is preferably 1 to 10 hours. As an embodiment, the ceramic treatment time can be specifically 1 hour, 2 hours, 3 hours, 4 hours, 5 hours, 6 hours, 7 hours, 8 hours, 9 hours or 10 hours.

[0111] In the present invention, the ceramicization treatment is preferably performed in air.

[0112] The present invention impregnates the ceramic sol and performs a ceramic treatment, which can construct a ceramic coating layer and a micro-nano sheet layer on the surface and network structure of the mullite aerogel nano-skeleton, improve the high temperature resistance of the mullite aerogel, and also improve the anti-oxidation performance, mechanical properties and infrared shielding performance of the mullite aerogel. The present invention controls the temperature and time of the ceramic treatment within the above range, which can further improve the high temperature resistance and other properties of the mullite aerogel.

[0113] After the ceramic treatment is completed, the present invention preferably cools the product of the ceramic treatment to obtain a high temperature resistant mullite aerogel.

[0114] The present invention has no special limitation on the cooling operation, and any cooling technical solution well known to those skilled in the art may be used.

[0115] The invention adds polymer, impregnates ceramic sol and performs ceramic treatment, and controls various process parameters at the same time, thereby improving the high temperature resistance of mullite aerogel. At the same time, the preparation method of the invention is efficient and controllable, the raw materials are cheap and widely available, and the operation is safe and simple, the equipment requirements are low, and the invention has the potential for large-scale production.

[0116] The schematic flow chart of the method for preparing the high temperature resistant mullite aerogel provided by the present invention is preferably as follows: Figure 1 As shown: a silicon source, deionized water, anhydrous ethanol and an acid are mixed to obtain a silica sol, an aluminum source and deionized water are mixed to obtain an aluminum sol, the silica sol, the aluminum sol and the polymer solution are mixed and stirred to obtain a mullite sol, which is gelled to obtain a mullite gel, which is aged, strengthened, solvent replaced and dried at normal pressure to obtain a mullite aerogel, which is heat treated (carbonized) with argon to obtain a carbonized mullite aerogel (carbonized aerogel), which is impregnated with a ceramic sol and then dried to obtain a ceramic-coated mullite aerogel, which is subjected to a ceramic heat treatment to obtain a high temperature resistant mullite aerogel.

[0117] The present invention also provides high temperature resistant mullite aerogel prepared by the preparation method described in the above technical solution.

[0118] The high temperature resistant mullite aerogel prepared by the invention has excellent high temperature resistance.

[0119] The present invention also provides application of the high temperature resistant mullite aerogel described in the above technical solution in the field of thermal protection.

[0120] The present invention has no special limitation on the operation of the application, and the technical solutions of the application well known to those skilled in the art may be adopted.

[0121] The technical solutions in the present invention will be described clearly and completely below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0122] Example 1 A method for preparing a high temperature resistant mullite aerogel comprises: (1) mixing an aluminum source (aluminum chloride hexahydrate) with water (the molar ratio of the aluminum source to water is 1:22), and hydrolyzing at room temperature to obtain an aluminum sol; mixing a silicon source (ethyl orthosilicate) with a solvent (the molar ratio of the aluminum source to water is 1:7×10 -4 water and concentrated hydrochloric acid) (the molar ratio of silicon source to solvent is 1:5), and hydrolyzed at room temperature to obtain silica sol; aluminum sol and silica sol are mixed to obtain dual-phase mullite sol, and the molar ratio of silicon to aluminum in the silica sol and aluminum sol is 1:3; (2) Mixing hydroxypropyl cellulose (hydroxypropoxyl group: 5-16 wt%, MacLean) and water, and placing in a water bath at 60°C to obtain a hydroxypropyl cellulose solution, wherein the mass concentration of the hydroxypropyl cellulose is 1%; (3) adding the mullite sol in step (1) dropwise to the hydroxypropyl cellulose solution in step (2) (the volume ratio of the mullite sol to the hydroxypropyl cellulose solution is 1:1.5), adding the drying control additive N,N-dimethylformamide (the molar ratio of N,N-dimethylformamide to the aluminum source in the mullite sol is 1:1), and then adding the gelling agent propylene oxide (the molar ratio of propylene oxide to the aluminum source in the mullite sol is 11:1), stirring at room temperature for 30 minutes, standing in a mold at 40°C for 3 days, and then demolding to obtain a gel; (4) soaking the gel obtained in step (3) in anhydrous ethanol and aging at 50° C. for 3 days, replacing the anhydrous ethanol twice a day, then soaking the gel in a strengthening solution (composed of ethyl orthosilicate and anhydrous ethanol in a molar ratio of 1:30) and strengthening at 50° C. for 3 days, replacing the strengthening solution once a day to obtain a strengthened gel, then soaking the strengthened gel in n-hexane and performing solvent replacement at 40° C. for 3 days, replacing the n-hexane twice a day, and finally drying the gel at 60° C. for 24 hours to obtain a mullite aerogel; (5) placing the mullite aerogel obtained in step (4) in a muffle furnace for pre-oxidation at 200° C. for 2 h, then placing it in a tubular furnace for carbonization at 800° C. for 2 h in an argon atmosphere, and cooling to obtain a carbonized aerogel; (6) Aluminum chlorohexahydrate and tetraethyl orthosilicate are mixed with water and stirred for 2 h to obtain a silica-alumina ceramic sol, wherein the molar ratio of tetraethyl orthosilicate, aluminum chlorohexahydrate and water is 1:3:72, and the carbonized aerogel obtained in step (5) is impregnated in the silica-alumina ceramic sol at a temperature of 60° C. for 8 h, and then dried at 80° C. under normal pressure for 6 h, and then placed in a muffle furnace for ceramic treatment at 800° C. for 2 h to obtain a high-temperature resistant mullite aerogel.

[0123] The high temperature resistant mullite aerogel prepared in Example 1 has a stable and complete structure and a blocky morphology. After being treated with argon at 1400° C. for 2 h, it still has a stable structure.

[0124] Example 2 A method for preparing a high temperature resistant mullite aerogel comprises: (1) obtaining a dual-phase mullite sol as in Example 1; (2) Chitosan (viscosity <200 mPa.s, Aladdin) and glacial acetic acid aqueous solution were mixed, and ultrasonicated at 60°C to obtain a chitosan solution, wherein the mass concentration of chitosan was 1.5% and the volume concentration of glacial acetic acid was 3%; (3) adding the mullite sol in step (1) dropwise to the chitosan solution in step (2) (the volume ratio of the mullite sol to the chitosan solution is 1:1.5), adding the drying control additive N,N-dimethylformamide (the molar ratio of N,N-dimethylformamide to the aluminum source in the mullite sol is 1:1), and then adding the gelling agent propylene oxide (the molar ratio of propylene oxide to the aluminum source in the mullite sol is 11:1), stirring at room temperature for 30 minutes, standing in a mold at 25°C for 5 days, and then demolding to obtain a gel; (4) soaking the gel obtained in step (3) in anhydrous ethanol, aging at 60° C. for 2 days, replacing the anhydrous ethanol 3 times a day, then soaking the gel in a strengthening solution (composed of ethyl orthosilicate and anhydrous ethanol in a molar ratio of 1:30), strengthening at 60° C. for 3 days, replacing the strengthening solution twice a day, to obtain a strengthened gel, then soaking the strengthened gel in anhydrous ethanol, performing solvent replacement at 60° C. for 2 days, replacing the anhydrous ethanol twice a day, then soaking the gel in n-hexane, performing solvent replacement at 30° C. for 1 day, replacing the n-hexane once a day, and finally drying the gel at 40° C. for 12 hours and 60° C. for 12 hours to obtain a mullite aerogel; (5) placing the mullite aerogel obtained in step (4) in a muffle furnace, pre-oxidizing at 300° C. for 5 h, then placing it in a tubular furnace, carbonizing at 800° C. for 2 h in an argon atmosphere, and cooling to obtain a carbonized aerogel; (6) Aluminum chlorohexahydrate and tetraethyl orthosilicate are mixed with water and stirred for 2 h to obtain a silica-alumina ceramic sol, wherein the molar ratio of tetraethyl orthosilicate, aluminum chlorohexahydrate and water is 1:3:72, and the carbonized aerogel obtained in step (5) is impregnated in the silica-alumina ceramic sol at a temperature of 25° C. for 8 h, and then dried at 80° C. under normal pressure for 6 h, and then placed in a muffle furnace for ceramic treatment at 800° C. for 2 h to obtain a high-temperature resistant mullite aerogel.

[0125] The high temperature resistant mullite aerogel prepared in Example 2 has a stable and complete structure and a blocky morphology. After being treated with argon at 1400° C. for 2 h, it still has a stable structure.

[0126] Example 3 A method for preparing a high temperature resistant mullite aerogel comprises: (1) obtaining a dual-phase mullite sol as in Example 1; (2) Carboxymethyl cellulose ( M w is 90000, DS is 0.7, 50~100mPa.s, MacLean) and water are mixed and a carboxymethyl cellulose solution is obtained in a 50℃ water bath, wherein the mass concentration of the carboxymethyl cellulose is 2%; (3) adding the mullite sol in step (1) dropwise to the carboxymethyl cellulose solution in step (2) (the volume ratio of the mullite sol to the carboxymethyl cellulose solution is 1:1.5), adding the drying control additive N,N-dimethylformamide (the molar ratio of N,N-dimethylformamide to the aluminum source in the mullite sol is 1:1), and then adding the gelling agent propylene oxide (the molar ratio of propylene oxide to the aluminum source in the mullite sol is 11:1), stirring at room temperature for 30 minutes, standing in a mold at 60°C for 2 days, and then demolding to obtain a gel; (4) soaking the gel obtained in step (3) in anhydrous ethanol, aging at 70°C for 1 day, replacing the anhydrous ethanol 5 times a day, then soaking the gel in a strengthening solution (composed of ethyl orthosilicate and anhydrous ethanol in a molar ratio of 1:30), strengthening at 80°C for 2 days, replacing the strengthening solution 4 times a day, to obtain a strengthened gel, then soaking the strengthened gel in anhydrous ethanol, solvent replacement at 50°C for 4 days, replacing the anhydrous ethanol 3 times a day, then soaking the gel in n-hexane, solvent replacement at 40°C for 1 day, replacing the n-hexane once a day, finally drying the gel at 40°C for 24 hours and 80°C for 24 hours, to obtain a mullite aerogel; (5) placing the mullite aerogel obtained in step (4) in a muffle furnace, pre-oxidizing at 400° C. for 10 h, then placing it in a tubular furnace, carbonizing it at 800° C. for 2 h in an argon atmosphere, and cooling it to obtain a carbonized aerogel; (6) Aluminum chlorohexahydrate and tetraethyl orthosilicate are mixed with water and stirred for 2 h to obtain a silicon-aluminum ceramic sol, wherein the molar ratio of tetraethyl orthosilicate, aluminum chlorohexahydrate and water is 1:3:72, and the carbonized aerogel obtained in step (5) is impregnated in the silicon-aluminum ceramic sol at a temperature of 80° C. for 8 h, and then dried at 80° C. under normal pressure for 6 h, and then placed in a muffle furnace for ceramic treatment at 800° C. for 2 h to obtain a high-temperature resistant mullite aerogel.

[0127] The high temperature resistant mullite aerogel prepared in Example 3 has a stable and complete structure and a blocky morphology. After being treated with argon at 1400° C. for 2 h, it still has a stable structure.

[0128] Example 4 A method for preparing a high temperature resistant mullite aerogel comprises: (1) replacing the aluminum source in Example 1 with boehmite, and keeping other parameters the same as those in Example 1, to obtain a dual-phase mullite sol; (2) Mix hydroxypropyl methylcellulose (Type I, 100 mPa.s, McLean) and water, and place in a water bath at 25°C to obtain a hydroxypropyl methylcellulose solution, wherein the mass concentration of the hydroxypropyl methylcellulose is 4%; (3) adding the mullite sol in step (1) dropwise to the hydroxypropyl methylcellulose solution in step (2) (the volume ratio of the mullite sol to the hydroxypropyl methylcellulose solution is 1:0.5), adding a drying control additive N,N-dimethylformamide (the molar ratio of N,N-dimethylformamide to the aluminum source in the mullite sol is 2:1), and then adding a gelling agent propylene oxide (the molar ratio of propylene oxide to the aluminum source in the mullite sol is 14:1), stirring at room temperature for 30 minutes, standing in a mold at 80°C for 1 day, and then demolding to obtain a gel; (4) soaking the gel obtained in step (3) in anhydrous ethanol, aging at 80°C for 1 day, replacing the anhydrous ethanol 4 times a day, then soaking the gel in a strengthening solution (composed of ethyl orthosilicate and anhydrous ethanol in a molar ratio of 1:30), strengthening at 50°C for 8 days, replacing the strengthening solution once a day, to obtain a strengthened gel, then soaking the strengthened gel in anhydrous ethanol, performing solvent replacement at 70°C for 2 days, replacing the anhydrous ethanol 3 times a day, then soaking the gel in n-hexane, performing solvent replacement at 30°C for 1 day, replacing the n-hexane twice a day, finally drying the gel at 30°C for 48 hours and at 100°C for 12 hours, to obtain a mullite aerogel; (5) placing the mullite aerogel obtained in step (4) in a tubular furnace, carbonizing it at 1000° C. for 5 h in an argon atmosphere, and cooling it to obtain a carbonized aerogel; (6) Aluminum chlorohexahydrate and tetraethyl orthosilicate are mixed with water and stirred for 2 h to obtain a silica-alumina ceramic sol, wherein the molar ratio of tetraethyl orthosilicate, aluminum chlorohexahydrate and water is 1:3:72, and the carbonized aerogel obtained in step (5) is impregnated in the silica-alumina ceramic sol at a temperature of 60° C. for 8 h, and then dried at 80° C. under normal pressure for 6 h, and then placed in a muffle furnace for ceramic treatment at 800° C. for 2 h to obtain a high-temperature resistant mullite aerogel.

[0129] The high temperature resistant mullite aerogel prepared in Example 4 has a stable and complete structure and a blocky morphology. After being treated with argon at 1400° C. for 2 h, it still has a stable structure.

[0130] Example 5 A method for preparing a high temperature resistant mullite aerogel comprises: (1) replacing the silicon source in Example 4 with ethyl orthosilicate and vinyltrimethoxysilane in a molar ratio of 1:1, and the other parameters are the same as those in Example 4, to obtain a dual-phase mullite sol; (2) Mix carboxymethyl chitosan (degree of substitution ≥ 90%, isoelectric point 3-4, MacLean) and water, and place in a 70°C water bath to obtain a carboxymethyl chitosan solution, wherein the mass concentration of carboxymethyl chitosan is 5%; (3) adding the mullite sol in step (1) dropwise to the carboxymethyl chitosan solution in step (2) (the volume ratio of the mullite sol to the carboxymethyl chitosan solution is 1:2), adding the drying control additive N,N-dimethylformamide (the molar ratio of N,N-dimethylformamide to the aluminum source in the mullite sol is 3:1), and then adding the gelling agent propylene oxide (the molar ratio of propylene oxide to the aluminum source in the mullite sol is 14:1), stirring at room temperature for 30 minutes, standing in a mold at 100°C for 1 day, and then demolding to obtain a gel; (4) soaking the gel obtained in step (3) in anhydrous ethanol, aging at 100° C. for 1 day, replacing the anhydrous ethanol twice a day, then soaking the gel in a strengthening solution (composed of ethyl orthosilicate and anhydrous ethanol in a molar ratio of 1:30), strengthening at 70° C. for 2 days, replacing the strengthening solution once a day, to obtain a strengthened gel, then soaking the strengthened gel in anhydrous ethanol, performing solvent replacement at 80° C. for 5 days, replacing the anhydrous ethanol twice a day, then soaking the gel in n-hexane, performing solvent replacement at 25° C. for 1 day, replacing the n-hexane once a day, and finally drying the gel at 25° C. for 60 hours and 150° C. for 40 hours to obtain a mullite aerogel; (5) placing the mullite aerogel obtained in step (4) in a muffle furnace, pre-oxidizing at 300° C. for 5 h, then placing it in a tubular furnace, carbonizing it at 1200° C. for 10 h in an argon atmosphere, and cooling it to obtain a carbonized aerogel; (6) Aluminum chlorohexahydrate and tetraethyl orthosilicate are mixed with water and stirred for 2 h to obtain a silicon-aluminum ceramic sol, wherein the molar ratio of tetraethyl orthosilicate, aluminum chlorohexahydrate and water is 1:3:72, and the carbonized aerogel obtained in step (5) is impregnated in the silicon-aluminum ceramic sol at a temperature of 100° C. for 8 h, and then dried at 80° C. under normal pressure for 6 h, and then placed in a muffle furnace for ceramic treatment at 800° C. for 2 h to obtain a high-temperature resistant mullite aerogel.

[0131] The high temperature resistant mullite aerogel prepared in Example 5 has a stable and complete structure and a blocky morphology. After being treated with argon at 1400° C. for 2 h, it still has a stable structure.

[0132] Example 6 A method for preparing a high temperature resistant mullite aerogel comprises: (1) obtaining a dual-phase mullite sol as in Example 1; (2) Mix hydroxyethyl cellulose (250-450 mPa.s, McLean) and water, and place in a 40°C water bath to obtain a hydroxyethyl cellulose solution, wherein the mass concentration of the hydroxyethyl cellulose is 3%; (3) adding the mullite sol in step (1) dropwise to the hydroxyethyl cellulose solution in step (2) (the volume ratio of the mullite sol to the hydroxyethyl cellulose solution is 1:1.5), adding the drying control additive N,N-dimethylformamide (the molar ratio of N,N-dimethylformamide to the aluminum source in the mullite sol is 1.5:1), and then adding the gelling agent propylene oxide (the molar ratio of propylene oxide to the aluminum source in the mullite sol is 17:1), stirring at room temperature for 30 minutes, standing in a mold at 50°C for 3 days, and then demolding to obtain a gel; (4) soaking the gel obtained in step (3) in anhydrous ethanol and aging at 40°C for 5 days, replacing the anhydrous ethanol twice a day, then soaking the gel in a strengthening solution (composed of ethyl orthosilicate and anhydrous ethanol in a molar ratio of 1:30) and strengthening at 100°C for 1 day, replacing the strengthening solution twice a day to obtain a strengthened gel, then soaking the strengthened gel in anhydrous ethanol and performing solvent replacement at 100°C for 1 day, replacing the anhydrous ethanol three times a day, and finally drying the gel at 50°C for 24 hours and 120°C for 24 hours to obtain a mullite aerogel; (5) placing the mullite aerogel obtained in step (4) in a muffle furnace, pre-oxidizing at 300° C. for 5 h, then placing it in a tubular furnace, carbonizing it at 1200° C. for 10 h in an argon atmosphere, and cooling it to obtain a carbonized aerogel; (6) Aluminum chlorohexahydrate, tetraethyl orthosilicate, calcium nitrate tetrahydrate and water are mixed and stirred for 2 hours to obtain a calcium-aluminum-silica ceramic sol, wherein the molar ratio of tetraethyl orthosilicate, aluminum chlorohexahydrate, calcium nitrate tetrahydrate and water is 1:3:0.5:72. The carbonized aerogel obtained in step (5) is impregnated in the calcium-aluminum-silica ceramic sol at a temperature of 40°C for 8 hours, and then dried at 80°C under normal pressure for 6 hours, and then placed in a muffle furnace for ceramic treatment at 1000°C for 5 hours to obtain a high-temperature resistant mullite aerogel.

[0133] The high temperature resistant mullite aerogel prepared in Example 6 has a stable and complete structure and a blocky morphology. After being treated with argon at 1450° C. for 2 h, it still has a stable structure.

[0134] Example 7 A method for preparing a high temperature resistant mullite aerogel comprises: (1) replacing the silicon source in Example 1 with tetraethyl orthosilicate and polysilsesquioxane in a molar ratio of 1:1, and the other parameters are the same as those in Example 1, to obtain a dual-phase mullite sol; (2) Mix hydroxypropyl methylcellulose (Type I, 100 mPa.s, McLean) and water, and place in a water bath at 25°C to obtain a hydroxypropyl methylcellulose solution, wherein the mass concentration of the hydroxypropyl methylcellulose is 3%; (3) adding the mullite sol in step (1) dropwise to the hydroxypropyl methylcellulose solution in step (2) (the volume ratio of the mullite sol to the hydroxypropyl methylcellulose solution is 1:1.5), adding a drying control additive N,N-dimethylformamide (the molar ratio of N,N-dimethylformamide to the aluminum source in the mullite sol is 2.5:1), and then adding a gelling agent propylene oxide (the molar ratio of propylene oxide to the aluminum source in the mullite sol is 17:1), stirring at room temperature for 30 minutes, standing at 50°C in a mold for 3 days, and then demolding to obtain a gel; (4) soaking the gel obtained in step (3) in anhydrous ethanol, aging at 70°C for 2 days, replacing the anhydrous ethanol twice a day, then soaking the gel in a strengthening solution (composed of ethyl orthosilicate and anhydrous ethanol in a molar ratio of 1:30) at 90°C for 2 days, replacing the strengthening solution 5 times a day, to obtain a strengthened gel, then soaking the strengthened gel in anhydrous ethanol, performing solvent replacement at 90°C for 2 days, replacing the anhydrous ethanol 3 times a day, then soaking the gel in n-hexane, performing solvent replacement at 40°C for 2 days, replacing the n-hexane once a day, and finally drying the gel at 40°C for 40 hours and 60°C for 30 hours to obtain a mullite aerogel; (5) placing the mullite aerogel obtained in step (4) in a muffle furnace, pre-oxidizing at 300° C. for 5 h, then placing it in a tubular furnace, carbonizing it at 1000° C. for 5 h in an argon atmosphere, and cooling it to obtain a carbonized aerogel; (6) Aluminum chlorohydrate, tetraethyl orthosilicate and water are mixed and stirred for 2 hours to obtain a silicon-aluminum ceramic sol, wherein the molar ratio of tetraethyl orthosilicate, aluminum chlorohydrate and water is 1:3:72, and the carbonized aerogel obtained in step (5) is impregnated in the silicon-aluminum ceramic sol at a temperature of 50°C for 8 hours, and then dried at 80°C under normal pressure for 6 hours, and then placed in a muffle furnace for ceramic treatment at 600°C for 2 hours to obtain a high-temperature resistant mullite aerogel.

[0135] The high temperature resistant mullite aerogel prepared in Example 7 has a stable and complete structure and a blocky morphology. After being treated with argon at 1400° C. for 2 h, it still has a stable structure.

[0136] Example 8 A method for preparing a high temperature resistant mullite aerogel comprises: (1) replacing the silicon source in Example 1 with ethyl orthosilicate, vinyl trimethoxysilane and aminopropyl trimethoxysilane in a molar ratio of 1:1:1, and other parameters are the same as those in Example 1, to obtain a dual-phase mullite sol; (2) Chitosan (viscosity <200 mPa.s, Aladdin) and glacial acetic acid aqueous solution were mixed, and ultrasonicated at 60°C to obtain a chitosan solution, wherein the mass concentration of chitosan was 5% and the volume concentration of glacial acetic acid was 10%; (3) adding the mullite sol in step (1) dropwise to the chitosan solution in step (2) (the volume ratio of the mullite sol to the chitosan solution is 1:1.5), adding the drying control additive N,N-dimethylformamide (the molar ratio of N,N-dimethylformamide to the aluminum source in the mullite sol is 2:1), and then adding the gelling agent propylene oxide (the molar ratio of propylene oxide to the aluminum source in the mullite sol is 17:1), stirring at room temperature for 30 minutes, standing in a mold at 30°C for 5 days, and then demolding to obtain a gel; (4) soaking the gel obtained in step (3) in anhydrous ethanol, aging at 25° C. for 10 days, replacing the anhydrous ethanol once a day, then soaking the gel in a strengthening solution (composed of ethyl orthosilicate and anhydrous ethanol in a molar ratio of 1:30) at 40° C. for 10 days, replacing the strengthening solution once a day, to obtain a strengthened gel, then soaking the strengthened gel in anhydrous ethanol, performing solvent replacement at 25° C. for 7 days, replacing the anhydrous ethanol once a day, then soaking the gel in n-hexane, performing solvent replacement at 30° C. for 3 days, replacing the n-hexane once a day, and finally drying the gel at 60° C. for 24 hours and 100° C. for 48 hours to obtain a mullite aerogel; (5) placing the mullite aerogel obtained in step (4) in a muffle furnace, pre-oxidizing at 300° C. for 5 h, then placing it in a tubular furnace, carbonizing it at 1000° C. for 5 h in an argon atmosphere, and cooling it to obtain a carbonized aerogel; (6) Aluminum chlorohexahydrate, tetraethyl orthosilicate and water are mixed and stirred for 2 hours to obtain a silicon-aluminum ceramic sol, wherein the molar ratio of tetraethyl orthosilicate, aluminum chlorohexahydrate and water is 1:3:72, and the carbonized aerogel obtained in step (5) is impregnated in the silicon-aluminum ceramic sol at a temperature of 70°C for 8 hours, and then dried at 80°C under normal pressure for 6 hours, and then placed in a muffle furnace for ceramic treatment at 800°C for 2 hours to obtain a high-temperature resistant mullite aerogel.

[0137] The high temperature resistant mullite aerogel prepared in Example 8 has a stable and complete structure and a blocky morphology. After being treated with argon at 1400° C. for 2 h, it still has a stable structure.

[0138] Example 9 A method for preparing a high temperature resistant mullite aerogel comprises: (1) replacing the silicon source in Example 1 with ethyl orthosilicate, methyltrimethoxysilane and vinyltriethoxysilane in a molar ratio of 1:1:1, and other parameters are the same as those in Example 1, to obtain a dual-phase mullite sol; (2) polyvinyl pyrrolidone (average molecular weight 8000, MacLean) and water were mixed and ultrasonicated at 90°C to obtain a polyvinyl pyrrolidone solution, wherein the mass concentration of polyvinyl pyrrolidone was 10%; (3) adding the mullite sol in step (1) dropwise to the polyvinyl pyrrolidone solution in step (2) (the volume ratio of the mullite sol to the polyvinyl pyrrolidone solution is 1:1.5), adding the gelling agent propylene oxide (the molar ratio of propylene oxide to the aluminum source in the mullite sol is 11:1), stirring at room temperature for 30 minutes, standing in a mold at 70°C for 2 days, and then demolding to obtain a gel; (4) soaking the gel obtained in step (3) in anhydrous ethanol and aging at 60° C. for 4 days, replacing the anhydrous ethanol three times a day, then soaking the gel in a strengthening solution (composed of ethyl orthosilicate and anhydrous ethanol in a molar ratio of 1:30) and strengthening at 60° C. for 5 days, replacing the strengthening solution once a day, to obtain a strengthened gel, then soaking the strengthened gel in anhydrous ethanol and performing solvent replacement at 30° C. for 6 days, replacing the anhydrous ethanol twice a day, then soaking the gel in n-hexane and performing solvent replacement at 30° C. for 2 days, replacing the n-hexane once a day, and finally drying the gel at 25° C. for 12 hours and at 60° C. for 24 hours to obtain a mullite aerogel; (5) placing the mullite aerogel obtained in step (4) in a muffle furnace, pre-oxidizing at 300° C. for 5 h, then placing it in a tubular furnace, carbonizing it at 1000° C. for 5 h in an argon atmosphere, and cooling it to obtain a carbonized aerogel; (6) Aluminum chlorohydrate, tetraethyl orthosilicate, magnesium chloride hexahydrate and water are mixed and stirred for 2 hours to obtain a silicon-aluminum-magnesium ceramic sol, wherein the molar ratio of tetraethyl orthosilicate, aluminum chlorohydrate, magnesium chloride hexahydrate and water is 1:3:0.5:72. The carbonized aerogel obtained in step (5) is impregnated in the silicon-aluminum-magnesium ceramic sol at a temperature of 90° C. for 8 hours, and then dried at 80° C. under normal pressure for 6 hours, and then placed in a muffle furnace for ceramic treatment at 1000° C. for 5 hours to obtain a high-temperature resistant mullite aerogel.

[0139] The high temperature resistant mullite aerogel prepared in Example 9 has a stable and complete structure and a blocky morphology. After being treated with argon at 1450° C. for 2 h, it still has a stable structure.

[0140] Example 10 A method for preparing a high temperature resistant mullite aerogel comprises: (1) replacing the silicon source in Example 1 with ethyl orthosilicate, vinyl tri(trimethylsiloxy)silane and polysilsesquioxane in a molar ratio of 1:1:1, and other parameters are the same as those in Example 1, to obtain a dual-phase mullite sol; (2) polyvinyl alcohol (polyvinyl alcohol type 105, Macklin) and water were mixed and placed in a water bath at 80°C to obtain a polyvinyl alcohol solution, wherein the mass concentration of the polyvinyl alcohol was 8%; (3) adding the mullite sol in step (1) dropwise to the polyvinyl alcohol solution in step (2) (the volume ratio of the mullite sol to the polyvinyl alcohol solution is 1:1.5), adding the drying control additive N,N-dimethylformamide (the molar ratio of N,N-dimethylformamide to the aluminum source in the mullite sol is 1:1), and then adding the gelling agent propylene oxide (the molar ratio of propylene oxide to the aluminum source in the mullite sol is 14:1), stirring at room temperature for 30 minutes, standing in a mold at 40°C for 3 days, and then demolding to obtain a gel; (4) soaking the gel obtained in step (3) in anhydrous ethanol, aging at 90° C. for 2 days, replacing the anhydrous ethanol twice a day, then soaking the gel in a strengthening solution (composed of ethyl orthosilicate and anhydrous ethanol in a molar ratio of 1:30) at 70° C. for 2 days, replacing the strengthening solution twice a day, to obtain a strengthened gel, then soaking the strengthened gel in anhydrous ethanol, performing solvent replacement at 60° C. for 3 days, replacing the anhydrous ethanol four times a day, then soaking the gel in n-hexane, performing solvent replacement at 30° C. for 1 day, replacing the n-hexane once a day, and finally drying the gel at 80° C. for 24 hours to obtain a mullite aerogel; (5) placing the mullite aerogel obtained in step (4) in a muffle furnace, pre-oxidizing at 300° C. for 5 h, then placing it in a tubular furnace, carbonizing it at 1000° C. for 5 h in an argon atmosphere, and cooling it to obtain a carbonized aerogel; (6) Aluminum chlorohydrate, tetraethyl orthosilicate, zirconium oxychloride octahydrate and water are mixed and stirred for 2 hours to obtain a silicon-aluminum-zirconium ceramic sol, wherein the molar ratio of tetraethyl orthosilicate, aluminum chlorohydrate, zirconium oxychloride octahydrate and water is 1:3:0.5:72. The carbonized aerogel obtained in step (5) is impregnated in the silicon-aluminum-zirconium ceramic sol at a temperature of 60° C. for 8 hours, and then dried at 80° C. under normal pressure for 6 hours, and then placed in a muffle furnace for ceramic treatment at 1200° C. for 10 hours to obtain a high-temperature resistant mullite aerogel.

[0141] The high temperature resistant mullite aerogel prepared in Example 10 has a stable and complete structure and a blocky morphology. After being treated with argon at 1450° C. for 2 h, it still has a stable structure.

[0142] Embodiment 11 A method for preparing a high temperature resistant mullite aerogel comprises: (1) mixing an aluminum source (aluminum chloride hexahydrate), a silicon source (ethyl orthosilicate, dimethyl diethoxysilane and polysilsesquioxane in a molar ratio of 1:1:1) and water, and hydrolyzing the mixture at room temperature to obtain a single-phase mullite sol, wherein the molar ratio of the silicon source, the aluminum source and the water is 1:3:72; (2) Mix carboxymethyl chitosan (degree of substitution ≥ 90%, isoelectric point 3-4, MacLean) and water, and place in a 70°C water bath to obtain a carboxymethyl chitosan solution, wherein the mass concentration of carboxymethyl chitosan is 6%; (3) adding the mullite sol in step (1) dropwise to the carboxymethyl chitosan solution in step (2) (the volume ratio of the mullite sol to the carboxymethyl chitosan solution is 1:1.5), adding the drying control additive N,N-dimethylformamide (the molar ratio of N,N-dimethylformamide to the aluminum source in the mullite sol is 3:1), and then adding the gelling agent propylene oxide (the molar ratio of propylene oxide to the aluminum source in the mullite sol is 14:1), stirring at room temperature for 30 minutes, standing in a mold at 90°C for 1 day, and then demolding to obtain a gel; (4) soaking the gel obtained in step (3) in anhydrous ethanol and aging at 30° C. for 6 days, replacing the anhydrous ethanol twice a day, then soaking the gel in a strengthening solution (composed of ethyl orthosilicate and anhydrous ethanol in a molar ratio of 1:30) and strengthening at 80° C. for 3 days, replacing the strengthening solution twice a day to obtain a strengthened gel, then soaking the strengthened gel in anhydrous ethanol and performing solvent replacement at 40° C. for 4 days, replacing the anhydrous ethanol once a day, then soaking the gel in n-hexane and performing solvent replacement at 40° C. for 1 day, replacing the n-hexane twice a day, and finally drying the gel at 40° C. for 80 hours to obtain a mullite aerogel; (5) placing the mullite aerogel obtained in step (4) in a muffle furnace, pre-oxidizing at 300° C. for 5 h, then placing it in a tubular furnace, carbonizing it at 1000° C. for 5 h in an argon atmosphere, and cooling it to obtain a carbonized aerogel; (6) Aluminum chloride hexahydrate, tetraethyl orthosilicate, zirconium oxychloride octahydrate, magnesium chloride hexahydrate, yttrium chloride hexahydrate and water are mixed and stirred for 2 hours to obtain a silicon-aluminum-zirconium-magnesium-yttrium ceramic sol, wherein the molar ratio of tetraethyl orthosilicate, aluminum chloride hexahydrate, zirconium oxychloride octahydrate, magnesium chloride hexahydrate, yttrium chloride hexahydrate and water is 1:3:0.5:0.5:0.5:72. The carbonized aerogel obtained in step (5) is impregnated in the silicon-aluminum-zirconium-magnesium-yttrium ceramic sol at a temperature of 60° C. for 8 hours, and then dried at 80° C. under normal pressure for 6 hours, and then placed in a muffle furnace for ceramic treatment at 1200° C. for 10 hours to obtain a high-temperature resistant mullite aerogel.

[0143] The high temperature resistant mullite aerogel prepared in Example 11 has a stable and complete structure and a blocky morphology. After being treated with argon at 1500° C. for 2 h, it still has a stable structure.

[0144] Comparative Example 1 Step (6) of Example 1 is omitted, that is, ceramic sol impregnation and ceramicization treatment are not performed, and other steps and parameters are the same as those of Example 1.

[0145] The mullite aerogel prepared in Comparative Example 1 has a stable and complete structure and a blocky morphology, and still has a stable structure after being treated with argon at 1300° C. for 2 h.

[0146] Comparative Example 2 Step (5) of Example 1 is omitted, i.e., pre-oxidation and carbonization are not performed, and other steps and parameters are the same as those of Example 1.

[0147] The mullite aerogel prepared in Comparative Example 2 has a stable and complete structure and a blocky morphology, and still has a stable structure after being treated with argon at 1300° C. for 2 h.

[0148] Comparative Example 3 Steps (5) and (6) of Example 1 are omitted, that is, the pre-oxidation, carbonization, ceramic sol impregnation and ceramicization treatments are not performed, and the other steps and parameters are the same as those of Example 1.

[0149] The mullite aerogel prepared in Comparative Example 3 has a stable and complete structure and a blocky morphology. After being treated with argon at 1300° C. for 2 h, it still has a stable structure.

[0150] The macroscopic image of the mullite aerogel prepared in step (4) of Example 2 is as follows: Figure 2 As shown in the SEM images Figure 3 shown.

[0151] The macroscopic image of the high temperature resistant mullite aerogel prepared in step (6) of Example 2 is as follows: Figure 4 As shown in the SEM images Figure 5 As shown. Figures 2~5 It can be seen that after pre-oxidation, carbonization and ceramicization, the aerogel can still maintain a complete block structure without cracks or breakage. The SEM image shows that after the above treatment, the constituent particles of the aerogel do not show rapid growth, melting and agglomeration, and still have a good pore structure, indicating that it has good high temperature resistance.

[0152] The density, specific surface area, average pore size, thermal conductivity, compressive strength and high temperature resistance of the mullite aerogels in Examples 1 to 11 and Comparative Examples 1 to 3 were tested. The results are shown in Table 1, where the specific surface area and average pore size were obtained by testing with an ASAP 2460 specific surface and porosity analyzer from Micromeritics.

[0153] The thermal conductivity was obtained by using the transient plane heat source method using a Swedish Hot Disk TPS2500 thermal constant analyzer.

[0154] High temperature resistance is evaluated by whether the aerogel continues to maintain a complete block morphology after being treated at a certain temperature. For example, if the aerogel can maintain a complete block structure after being treated at 1400°C, but after being treated at 1450°C, the block structure is destroyed and cracks and breaks into pieces appear, then the high temperature resistance of the aerogel is 1400°C.

[0155] Table 1 Density, specific surface area, average pore size, thermal conductivity, pressure resistance and high temperature resistance of mullite aerogels in Examples 1 to 11 and Comparative Examples 1 to 3

[0156] According to the data in Table 1, it can be seen from the comparison example 1 and Example 1 that the high temperature resistance, specific surface area and compressive strength of the mullite aerogel can be effectively improved by impregnation with ceramic sol and ceramicization treatment; it can be seen from Example 1 and Example 6 that the high temperature resistance and compressive strength of the mullite aerogel can be further improved by changing the composition of the ceramic sol; it can be seen from the comparison example 2 and Example 1 that the high temperature resistance of the mullite aerogel can be effectively improved by pre-oxidation and carbonization treatment; it can be seen from the comparison example 3 and Example 1 that the pre-oxidation and carbonization in the present invention can synergize with the impregnation with ceramic sol and ceramicization treatment to further improve the high temperature resistance and compressive strength of the mullite aerogel.

[0157] In summary, the present invention adds a polymer for carbonization and simultaneously impregnates the ceramic sol and performs a ceramicization treatment, which can improve the high temperature resistance of the mullite aerogel and simultaneously improve its specific surface area and compression strength.

[0158] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for preparing a high temperature resistant mullite aerogel, characterized in that: The following steps are involved: (1) mixing a silicon source, an aluminum source, a solvent, a polymer solution and a gelling agent, and performing gelation to obtain a gel; the polymer in the polymer solution comprises one or more of hydroxypropyl cellulose, hydroxypropyl methyl cellulose, carboxymethyl cellulose, hydroxyethyl cellulose, chitosan, carboxymethyl chitosan, polyvinyl alcohol and polyvinyl pyrrolidone; (2) mixing the gel obtained in step (1) with a strengthening agent to strengthen the gel to obtain a strengthened gel; (3) soaking the strengthened gel obtained in step (2) in a replacement liquid, performing solvent replacement, and then drying at normal pressure to obtain a mullite aerogel; (4) carbonizing the mullite aerogel obtained in step (3) to obtain a carbonized aerogel; (5) The carbonized aerogel obtained in step (4) is impregnated in a ceramic sol, and then dried and ceramicized in sequence to obtain a high temperature resistant mullite aerogel.

2. The preparation method according to claim 1, characterized in that: In the step (1), the molar ratio of silicon in the silicon source to aluminum in the aluminum source is 1:(0.2-5).

3. The preparation method according to claim 1, characterized in that: The mass concentration of the polymer solution in step (1) is 1-10%.

4. The preparation method according to claim 1, characterized in that: The gelation temperature in step (1) is 25-100° C., and the gelation time is 1-5 days.

5. The preparation method according to claim 1, characterized in that: In the step (4), the carbonization temperature is 800-1400° C., and the carbonization time is 1-50 h.

6. The preparation method according to claim 1, characterized in that: The immersion time in step (5) is 1 to 50 hours.

7. The preparation method according to claim 1, characterized in that: The drying temperature in step (5) is 25-150° C., and the drying time is 1-50 h.

8. The preparation method according to claim 1, characterized in that: The temperature of the ceramic treatment in step (5) is 600-1200° C., and the time of the ceramic treatment is 1-10 hours.

9. The high temperature resistant mullite aerogel prepared by the preparation method according to any one of claims 1 to 8.

10. Use of the high temperature resistant mullite aerogel according to claim 9 in the field of thermal protection.

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