A high-temperature resistant mullite aerogel and its preparation method and application

Abstract

The present invention provides a high-temperature resistant mullite aerogel, its preparation method, and application, belonging to the technical field of aerogel materials. The present invention adds a polymer solution, which, after carbonization, not only improves the high-temperature resistance of the mullite aerogel but also acts as an infrared shading agent to reduce the thermal conductivity of the mullite aerogel at high temperatures. The carbonized aerogel is impregnated with a ceramic sol and ceramicized, which can construct a ceramic coating layer and micro-nanosheet layers on the surface of the mullite aerogel nanoskeleton and within its network structure, further improving the high-temperature resistance of the mullite aerogel. The results of the examples show that the mullite aerogel prepared by the present invention has a high-temperature resistance of above 1400°C and can reach 1500°C.

Description

Technical Field

[0001] The present 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 aerogel thermal protection materials due to its high melting point, low thermal expansion coefficient, excellent high-temperature mechanical properties, and resistance to polycrystalline transformation at high temperatures. However, the high-temperature resistance of mullite aerogels prepared in existing technologies generally only reaches 1300°C, and further improvement is needed.

[0003] Therefore, how to further improve the high temperature resistance of mullite aerogel has become a difficult problem in the existing technology. 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:

[0006] The present invention provides a method for preparing a high-temperature resistant mullite aerogel, comprising the following steps:

[0007] (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;

[0008] (2) mixing the gel obtained in step (1) with a strengthening agent to strengthen the gel to obtain a strengthened gel;

[0009] (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;

[0010] (4) carbonizing the mullite aerogel obtained in step (3) to obtain a carbonized aerogel;

[0011] (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.

[0012] Preferably, in step (1), the molar ratio of silicon in the silicon source to aluminum in the aluminum source is 1:(0.2-5).

[0013] Preferably, the mass concentration of the polymer solution in step (1) is 1-10%.

[0014] Preferably, the gelation temperature in step (1) is 25-100° C., and the gelation time is 1-5 days.

[0015] Preferably, the carbonization temperature in step (4) is 800-1400° C., and the carbonization time is 1-50 h.

[0016] Preferably, the immersion time in step (5) is 1 to 50 hours.

[0017] Preferably, the drying temperature in step (5) is 25-150° C., and the drying time is 1-50 h.

[0018] 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.

[0019] The present invention also provides high-temperature resistant mullite aerogel prepared by the preparation method described in the above technical solution.

[0020] The present invention also provides the application of the high-temperature resistant mullite aerogel described in the above technical solution in the field of thermal protection.

[0021] 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 methylcellulose, 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 performing reinforcing to obtain a reinforced gel; (3) immersing the reinforced gel obtained in the step (2) in a displacement fluid, 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 performing drying and ceramicization treatment in sequence to obtain a high-temperature resistant mullite aerogel. The present invention adds a polymer solution. After carbonization, the polymer not only inhibits the growth of mullite grains and improves the thermal stability of the mullite aerogel, but also acts as an infrared sunscreen to reduce the transmittance of the mullite aerogel to infrared light, improve its extinction performance for infrared light, reduce its thermal radiation at high temperatures, and thus reduce the high-temperature thermal conductivity of the mullite aerogel. The carbonized aerogel is impregnated with a ceramic sol and ceramicized. A ceramic coating layer and micro-nanosheet layers can be constructed on the surface of the mullite aerogel nanoskeleton and in the network structure, further improving the high-temperature resistance of the mullite aerogel. The results of the examples show that the mullite aerogel prepared by the present invention has a high-temperature resistance of above 1400°C and can reach 1500°C. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 A schematic flow chart of the method for preparing high-temperature resistant mullite aerogel provided by the present invention;

[0023] Figure 2 This is a macroscopic image of the mullite aerogel prepared in step (4) of Example 2;

[0024] Figure 3 This is the SEM image of the mullite aerogel prepared in step (4) of Example 2;

[0025] Figure 4 This is a macroscopic image of the high-temperature resistant mullite aerogel prepared in step (6) of Example 2;

[0026] Figure 5 This is the SEM image of the high-temperature resistant mullite aerogel prepared in step (6) of Example 2. DETAILED DESCRIPTION

[0027] The present invention provides a method for preparing a high-temperature resistant mullite aerogel, comprising the following steps:

[0028] (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;

[0029] (2) mixing the gel obtained in step (1) with a strengthening agent to strengthen the gel to obtain a strengthened gel;

[0030] (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;

[0031] (4) carbonizing the mullite aerogel obtained in step (3) to obtain a carbonized aerogel;

[0032] (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.

[0033] 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.

[0034] 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.

[0035] 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.

[0036] 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.

[0037] 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). In one embodiment, the molar ratio of silicon in the silicon source to aluminum in the aluminum source can be specifically 1:0.2, 1:0.5, 1:1, 1:2, 1:3, 1:4, or 1:5. By controlling the molar ratio of silicon in the silicon source to aluminum in the aluminum source within the above range, the present invention can further increase the specific surface area of the mullite aerogel and reduce the thermal conductivity.

[0038] In the present invention, the polymer in the polymer solution includes one or more of hydroxypropyl cellulose, hydroxypropyl methylcellulose, carboxymethyl cellulose, hydroxyethyl cellulose, chitosan, carboxymethyl chitosan, polyvinyl alcohol and polyvinyl pyrrolidone.

[0039] In the present invention, the solvent in the polymer solution is preferably water or an acid aqueous solution.

[0040] 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.

[0041] 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%.

[0042] In the present invention, the mass concentration of the polymer solution is preferably 1% to 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%.

[0043] In the present invention, the method for preparing the polymer solution is preferably: mixing a polymer with a solvent to obtain a polymer solution.

[0044] In the present invention, the mixing temperature is preferably 25-90°C; the mixing is preferably performed under stirring or ultrasonic conditions. The stirring and ultrasonic conditions are not particularly limited in the present invention; 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.

[0045] In the present invention, the gelling agent preferably includes propylene oxide or ammonia water.

[0046] 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 can 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.

[0047] In the present invention, when the gelling agent is ammonia water, the pH value of the mixture of the silicon source, aluminum source, solvent, polymer solution, and ammonia water is preferably 6 to 10. In one embodiment, the pH value of the mixture of the silicon source, aluminum source, solvent, polymer solution, and ammonia water 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; and the ratio of the volume of the concentrated ammonia water to the total volume of the concentrated ammonia water and solvent is preferably (0.5 to 10):100. Adding a gelling agent to the present invention further facilitates gel formation.

[0048] In the present invention, the mixture of the silicon source, aluminum source, solvent, polymer solution and gelling agent is preferably:

[0049] 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.

[0050] 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.

[0051] In the present invention, the molar ratio of water, ethanol and acid in the solvent is preferably (4-200): (0-30): (0-0.01).

[0052] In the present invention, the acid preferably comprises glacial acetic acid.

[0053] In the present invention, the molar ratio of the silicon source, aluminum source, and solvent is preferably 1:(0.2-5):(4-240). By controlling the molar ratio of the silicon source, aluminum source, and solvent within the above range, the silicon source and aluminum source are fully hydrolyzed to obtain a single-phase mullite sol.

[0054] The present invention has no special limitation on the operation of mixing the silicon source, aluminum source and solvent, and a technical solution for mixing materials well known to those skilled in the art can be used.

[0055] In the present invention, the temperature of the first hydrolysis is preferably room temperature. The present invention has no particular 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.

[0056] 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 silica sol; the aluminum source and the remaining solvent are mixed, and a third hydrolysis is performed to obtain aluminum sol; the silica sol and the aluminum sol are mixed to obtain a two-phase mullite sol, and the two-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 silica sol; the aluminum source and the remaining solvent are mixed, and a third hydrolysis is performed to obtain aluminum sol; the silica sol, the aluminum sol and the polymer solution are mixed to obtain 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 silica sol; the aluminum source and the remaining solvent are mixed, and a third hydrolysis is performed to obtain aluminum sol; after the aluminum sol and the polymer solution are mixed, the silica sol is added to obtain mullite gel, and the mullite gel is mixed with the gelling agent.

[0057] 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.

[0058] In the present invention, the acid preferably comprises glacial acetic acid.

[0059] 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).

[0060] In the present invention, the molar ratio of the silicon source to a portion of the solvent is preferably 1:(1-90).

[0061] 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 can be used.

[0062] 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.

[0063] In the present invention, the residual solvent is preferably water or a mixed solution of water and ethanol.

[0064] In the present invention, the molar ratio of water to ethanol in the residual solvent is preferably (1-150): (0-30).

[0065] In the present invention, the molar ratio of the aluminum source to the remaining solvent is preferably 1:(1-180).

[0066] 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 can be used.

[0067] In the present invention, the temperature of the third hydrolysis is preferably room temperature. The present invention has no particular limitation on the time of the third hydrolysis, as long as the aluminum source is fully hydrolyzed to obtain the sol.

[0068] In the present invention, the molar ratio of silicon to aluminum in the silica sol and alumina sol is preferably 1:(0.2-5). In one embodiment, the molar ratio of silicon to aluminum in the silica sol and alumina sol can be specifically 1:0.2, 1:0.5, 1:1, 1:2, 1:3, 1:4, or 1:5.

[0069] In the present invention, the volume ratio of the dual-phase mullite sol to the polymer solution, or the volume ratio of the combined volume of the silica sol and alumina 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, strengthening the gel skeleton and resisting capillary stress during the drying process. Consequently, a monolithic mullite aerogel can be produced when dried at ambient pressure. By controlling the amount of polymer solution within the aforementioned range, the present invention further strengthens the gel skeleton, ensuring a monolithic mullite aerogel when dried at ambient pressure, while also ensuring the mullite aerogel has a high specific surface area and low thermal conductivity.

[0070] 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.

[0071] 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 to 20000.

[0072] In the present invention, the molar ratio of the drying control additive to the aluminum source is preferably (0.1-3):1. In one embodiment, the molar ratio of the drying control additive to the aluminum source can be 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, making the pore size distribution more uniform, thereby reducing capillary stress during drying. This allows for the production of monolithic aerogels with low shrinkage and high specific surface area during atmospheric drying. By controlling the molar ratio of the drying control additive to the aluminum source within the above range, the specific surface area of the mullite aerogel can be further increased and its shrinkage reduced.

[0073] In the present invention, when a drying control additive is added, the pH value of the mixture of the silicon source, aluminum source, solvent, polymer solution, drying control additive and ammonia water is preferably 6-10.

[0074] In the present invention, the gelation temperature is preferably 25-100° C. As an embodiment, the gelation temperature can be specifically 25° C., 30° C., 40° C., 50° C., 60° C., 70° C., 80° C., 90° C. or 100° C.

[0075] 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 ranges to fully form a gel.

[0076] 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.

[0077] 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.

[0078] After obtaining the gel, the present invention mixes the gel with a strengthening agent to strengthen the gel to obtain a strengthened gel.

[0079] In the present invention, the gel is preferably aged and then mixed with a strengthening agent for strengthening.

[0080] In the present invention, the gel is preferably immersed in an aging solution for aging.

[0081] In the present invention, the aging solution preferably includes one or more of water, ethanol, acetone, acetonitrile and tetrahydrofuran.

[0082] In the present invention, the water is preferably deionized water.

[0083] The present invention has no particular limitation on the amount of the aging liquid, as long as it can soak the gel.

[0084] In the present invention, the aging temperature is preferably 25-100° C. As an embodiment, the aging temperature can be specifically 25° C., 30° C., 40° C., 50° C., 60° C., 70° C., 80° C., 90° C. or 100° C.

[0085] In the present invention, the aging time is preferably 0.1~10d. As an embodiment, the aging time can be specifically 0.1d, 1d, 2d, 3d, 4d, 5d, 6d, 7d, 8d, 9d or 10d. In the present invention, during the aging process, the aging liquid is preferably replaced 1~5 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 aging parameters within the above range, which can further improve the various properties of the gel, and thus improve the comprehensive performance of the mullite aerogel.

[0086] In the present invention, the strengthening agent preferably includes a silicon source or a mixture of a silicon source and an aluminum source.

[0087] In the present invention, the silicon source and aluminum source are preferably the same as the above-mentioned silicon source and aluminum source, and will not be described in detail here.

[0088] In the present invention, anhydrous ethanol is preferably added when the gel is mixed with the enhancer.

[0089] 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.

[0090] In the present invention, the molar ratio of the 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.

[0091] In the present invention, the strengthening temperature is preferably 40-100° C. As an embodiment, the strengthening temperature can be specifically 40° C., 50° C., 60° C., 70° C., 80° C., 90° C. or 100° C.

[0092] 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.

[0093] In the present invention, the strengthening liquid is preferably replaced 1 to 5 times per day during the strengthening process. The present invention does not specifically limit the replacement time, and technical solutions familiar to those skilled in the art can be employed. In the present invention, the strengthening is used to strengthen the gel skeleton. By controlling the strengthening parameters within the aforementioned ranges, the present invention can fully strengthen the gel skeleton, further facilitating the production of bulk mullite aerogel, and further increasing the specific surface area and reducing the thermal conductivity of the mullite aerogel.

[0094] 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.

[0095] 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.

[0096] In the present invention, the solvent exchange is preferably performed in a single step or in multiple steps. For example, the solvent exchange can be performed in a single replacement fluid, or first in one replacement fluid and then in another replacement fluid. In an embodiment of the present invention, the solvent exchange can be performed first in anhydrous ethanol and then in n-hexane, or can be performed only in n-hexane.

[0097] The present invention has no particular limitation on the amount of the replacement fluid, as long as it can soak the strengthened gel.

[0098] 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.

[0099] In the present invention, the solvent replacement time is preferably 1 to 11 days. As an embodiment, the solvent replacement time 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.

[0100] 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 particular limitation on the time of replacement, and a technical solution well known to those skilled in the art may be used. The present invention performs solvent replacement, which can replace the solvent in the gel with a solvent having low surface tension, thereby reducing the capillary stress during normal pressure drying, avoiding structural collapse or destruction of the gel during the drying process, and obtaining a block aerogel having a higher specific surface area. The present invention controls the various parameters in the solvent replacement process within the above ranges, which can further increase the specific surface area of the mullite aerogel.

[0101] 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.

[0102] In the present invention, the normal pressure drying time is preferably 1 to 100 hours. As an embodiment, the normal pressure drying time can specifically be 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 normal pressure drying within the above ranges to achieve sufficient drying.

[0103] In the present invention, the atmospheric drying is preferably completed in one step or in steps, that is, atmospheric drying is performed at a single temperature or in steps at different temperatures. The present invention has no particular limitation on the operation of the stepwise atmospheric drying, and the method can be selected according to actual needs.

[0104] After obtaining the mullite aerogel, the present invention carbonizes the mullite aerogel to obtain carbonized aerogel.

[0105] In the present invention, the mullite aerogel is preferably pre-oxidized before carbonization.

[0106] In the present invention, the pre-oxidation temperature is preferably 200-400° C. As an embodiment, the pre-oxidation temperature can be specifically 200° C., 250° C., 300° C., 350° C. or 400° C.

[0107] 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 hour, 1 hour, 2 hours, 3 hours, 4 hours, 5 hours, 6 hours, 7 hours, 8 hours, 9 hours or 10 hours.

[0108] In the present invention, the pre-oxidation is preferably performed in an air environment. The pre-oxidation of the present invention improves the thermal stability of the polymer in the mullite aerogel and prevents the mullite aerogel structure from cracking or collapsing during the subsequent carbonization process.

[0109] In the present invention, the carbonization temperature is preferably 800-1400° C. As an embodiment, the carbonization temperature can be specifically 800° C., 900° C., 1000° C., 1100° C., 1200° C., 1300° C. or 1400° C.

[0110] 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.

[0111] In the present invention, the carbonization is preferably performed in an inert atmosphere; the inert atmosphere is preferably nitrogen, helium, or argon. During the carbonization process, the polymer is carbonized at high temperature, which not only improves the high-temperature resistance of the mullite aerogel but also acts as an infrared shading agent to reduce the thermal conductivity of the mullite aerogel at high temperatures. By controlling the carbonization temperature and time within the above ranges, the polymer is fully carbonized.

[0112] After the carbonization is completed, the present invention preferably cools the carbonized product to obtain a carbonized aerogel.

[0113] 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.

[0114] After obtaining the carbonized aerogel, the present invention immerses the carbonized aerogel in a ceramic sol, and then sequentially performs drying and ceramicization treatments to obtain the high-temperature resistant mullite aerogel.

[0115] 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.

[0116] In the present invention, the ceramic sol is preferably prepared by mixing ceramic sol raw materials with a solvent, and stirring for 0.5 to 10 hours to obtain the ceramic sol.

[0117] 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.

[0118] 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, vinylsilane, triacetoxyvinylsilane, dimethoxydivinylsilane, trivinylsilane, vinylmethylsilane, vinyltrimethoxysilane, vinyltriethoxysilane, vinyltris(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.

[0119] In the present invention, the solvent preferably includes a mixture of water and anhydrous ethanol or water.

[0120] In the present invention, the molar ratio of water to anhydrous ethanol in the solvent is preferably (1-50): (0-30).

[0121] 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.

[0122] 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.

[0123] In the present invention, the impregnation temperature is preferably 25-100°C; the impregnation time is preferably 1-50 hours. As an embodiment, the impregnation temperature can be specifically 25°C, 30°C, 40°C, 50°C, 60°C, 70°C, 80°C, 90°C, or 100°C; and the impregnation time can be specifically 1 hour, 10 hours, 20 hours, 30 hours, 40 hours, or 50 hours. The present invention controls the impregnation temperature and time within the above ranges, which enables more ceramic sol to be impregnated into the mullite aerogel, further improving the high-temperature resistance of the mullite aerogel after subsequent ceramicization treatment.

[0124] In the present invention, the drying temperature is preferably 25-150°C; the drying time is preferably 1-50 hours; 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; and the drying time can be specifically 1 hour, 10 hours, 20 hours, 30 hours, 40 hours, or 50 hours.

[0125] In the present invention, the temperature of the ceramic treatment is preferably 600-1200° C. As an embodiment, the temperature of the ceramic treatment can be specifically 600° C., 700° C., 800° C., 900° C., 1000° C., 1100° C. or 1200° C.

[0126] 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.

[0127] In the present invention, the ceramicization treatment is preferably performed in air.

[0128] The present invention impregnates the mullite aerogel with a ceramic sol and then performs a ceramicization treatment, thereby constructing a ceramic coating layer and micro-nanosheet layers on the surface and within the network structure of the mullite aerogel nanoskeleton. This improves the mullite aerogel's high-temperature resistance, while also enhancing its antioxidant, mechanical, and infrared shielding properties. By controlling the temperature and time of the ceramicization treatment within the aforementioned ranges, the present invention can further enhance the mullite aerogel's high-temperature resistance and other properties.

[0129] After the ceramic treatment is completed, the present invention preferably cools the ceramic treatment product to obtain a high temperature resistant mullite aerogel.

[0130] 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.

[0131] The invention adds a polymer, impregnates a ceramic sol, and performs a ceramic treatment while controlling various process parameters, thereby improving the high-temperature resistance of the mullite aerogel. 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, with low requirements on equipment, and has the potential for large-scale production.

[0132] The flow diagram of the preparation method of 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 acid are mixed to obtain silica sol, an aluminum source and deionized water are mixed to obtain aluminum sol, the silica sol, aluminum sol and polymer solution are mixed and stirred to obtain mullite sol, which is gelled to obtain mullite gel, which is aged, strengthened, solvent replaced and dried at normal pressure to obtain mullite aerogel, which is heat treated (carbonized) with argon to obtain carbonized mullite aerogel (carbonized aerogel), which is impregnated with ceramic sol and dried to obtain ceramic-coated mullite aerogel, which is subjected to ceramic heat treatment to obtain high-temperature resistant mullite aerogel.

[0133] The present invention also provides high-temperature resistant mullite aerogel prepared by the preparation method described in the above technical solution.

[0134] The high-temperature resistant mullite aerogel prepared by the invention has excellent high-temperature resistance.

[0135] The present invention also provides the application of the high-temperature resistant mullite aerogel described in the above technical solution in the field of thermal protection.

[0136] The present invention has no special limitation on the operation of the application, and the application technical solutions well known to those skilled in the art can be adopted.

[0137] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions of the present invention. Obviously, the embodiments described are only some 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 making creative efforts are within the scope of protection of the present invention.

[0138] Example 1

[0139] A method for preparing a high-temperature resistant mullite aerogel is as follows: (1) mixing an aluminum source (aluminum chloride hexahydrate) with water (the molar ratio of the aluminum source to water is 1:22), and hydrolyzing the mixture at room temperature to obtain an aluminum sol; mixing a silicon source (ethyl orthosilicate) with a solvent (the molar ratio of the silicon source to water is 1:7×10 -4 The silica sol is prepared by mixing water and concentrated hydrochloric acid (the molar ratio of silicon source to solvent is 1:5) and hydrolyzing at room temperature; the aluminum sol and the silica sol are mixed to obtain a dual-phase mullite sol, and the molar ratio of silicon to aluminum in the silica sol and the aluminum sol is 1:3;

[0140] (2) Mixing hydroxypropyl cellulose (hydroxypropoxyl group: 5-16 wt%, Maclean) and water, and placing in a 60°C water bath to obtain a hydroxypropyl cellulose solution, wherein the mass concentration of the hydroxypropyl cellulose is 1%;

[0141] (3) The mullite sol in step (1) is added 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), and a drying control additive N,N-dimethylformamide is added (the molar ratio of N,N-dimethylformamide to the aluminum source in the mullite sol is 1:1), and then a gelling agent propylene oxide is added (the molar ratio of propylene oxide to the aluminum source in the mullite sol is 11:1), stirred at room temperature for 30 minutes, and allowed to stand in a mold at 40°C for 3 days before demolding to obtain a gel;

[0142] (4) The gel obtained in step (3) was immersed in anhydrous ethanol and aged at 50°C for 3 days, with the anhydrous ethanol replaced twice a day. The gel was then immersed in a strengthening solution (composed of ethyl orthosilicate and anhydrous ethanol in a molar ratio of 1:30) and strengthened at 50°C for 3 days, with the strengthening solution replaced once a day to obtain a strengthened gel. The strengthened gel was then immersed in n-hexane and solvent exchanged at 40°C for 3 days, with the n-hexane replaced twice a day. Finally, the gel was dried at 60°C for 24 hours to obtain a mullite aerogel.

[0143] (5) The mullite aerogel obtained in step (4) was placed in a muffle furnace and pre-oxidized at 200°C for 2 hours, and then placed in a tubular furnace and carbonized at 800°C for 2 hours in an argon atmosphere, and cooled to obtain a carbonized aerogel;

[0144] (6) Aluminum chloride hexahydrate and ethyl orthosilicate are mixed with water and stirred for 2 hours to obtain a silicon-aluminum ceramic sol, wherein the molar ratio of ethyl orthosilicate, aluminum chloride hexahydrate and water is 1:3:72. The carbonized aerogel obtained in step (5) is impregnated in the silicon-aluminum ceramic sol at a temperature of 60°C for 8 hours, and then dried at 80°C under normal pressure for 6 hours. The aerogel is then placed in a muffle furnace for ceramic treatment at 800°C for 2 hours to obtain a high-temperature resistant mullite aerogel.

[0145] 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.

[0146] Example 2

[0147] A method for preparing a high-temperature resistant mullite aerogel comprises: (1) obtaining a dual-phase mullite sol in the same manner as in Example 1;

[0148] (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%;

[0149] (3) adding the mullite sol in step (1) dropwise to the chitosan solution in step (2) (the volume ratio of mullite sol to 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;

[0150] (4) The gel obtained in step (3) was immersed in anhydrous ethanol and aged at 60°C for 2 days, with the anhydrous ethanol replaced 3 times a day. The gel was then immersed in a strengthening solution (composed of ethyl orthosilicate and anhydrous ethanol in a molar ratio of 1:30) and strengthened at 60°C for 3 days. The strengthening solution was replaced twice a day to obtain a strengthened gel. The strengthened gel was then immersed in anhydrous ethanol and solvent replaced at 60°C for 2 days. The anhydrous ethanol was replaced twice a day. The gel was then immersed in n-hexane and solvent replaced at 30°C for 1 day. The n-hexane was replaced once a day. Finally, the gel was dried at 40°C for 12 hours and 60°C for 12 hours to obtain a mullite aerogel.

[0151] (5) The mullite aerogel obtained in step (4) was placed in a muffle furnace and pre-oxidized at 300°C for 5 hours, and then placed in a tubular furnace and carbonized at 800°C for 2 hours in an argon atmosphere, and cooled to obtain a carbonized aerogel;

[0152] (6) Aluminum chloride hexahydrate and ethyl orthosilicate are mixed with water and stirred for 2 h to obtain a silicon-aluminum ceramic sol, wherein the molar ratio of ethyl orthosilicate, aluminum chloride hexahydrate and water is 1:3:72. The carbonized aerogel obtained in step (5) is impregnated in the silicon-aluminum ceramic sol at a temperature of 25°C for 8 h, and then dried at 80°C under normal pressure for 6 h. The aerogel is then placed in a muffle furnace for ceramic treatment at 800°C for 2 h to obtain a high-temperature resistant mullite aerogel.

[0153] 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.

[0154] Example 3

[0155] A method for preparing a high-temperature resistant mullite aerogel comprises: (1) obtaining a dual-phase mullite sol in the same manner as in Example 1;

[0156] (2) Carboxymethyl cellulose ( M w is 90000, DS is 0.7, 50~100mPa.s, McLean) and water, and a carboxymethyl cellulose solution is obtained in a 50℃ water bath, wherein the mass concentration of the carboxymethyl cellulose is 2%;

[0157] (3) The mullite sol in step (1) is added 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), and a drying control additive N,N-dimethylformamide is added (the molar ratio of N,N-dimethylformamide to the aluminum source in the mullite sol is 1:1), and then a gelling agent propylene oxide is added (the molar ratio of propylene oxide to the aluminum source in the mullite sol is 11:1), stirred at room temperature for 30 minutes, and allowed to stand in a mold at 60°C for 2 days before demolding to obtain a gel;

[0158] (4) The gel obtained in step (3) was immersed in anhydrous ethanol and aged at 70°C for 1 day, with the anhydrous ethanol replaced 5 times a day. The gel was then immersed in a strengthening solution (composed of ethyl orthosilicate and anhydrous ethanol in a molar ratio of 1:30) and strengthened at 80°C for 2 days. The strengthening solution was replaced 4 times a day to obtain a strengthened gel. The strengthened gel was then immersed in anhydrous ethanol and solvent replaced at 50°C for 4 days. The anhydrous ethanol was replaced 3 times a day. The gel was then immersed in n-hexane and solvent replaced at 40°C for 1 day. The n-hexane was replaced once a day. Finally, the gel was dried at 40°C for 24 hours and 80°C for 24 hours to obtain a mullite aerogel.

[0159] (5) The mullite aerogel obtained in step (4) was placed in a muffle furnace and pre-oxidized at 400°C for 10 hours, and then placed in a tubular furnace and carbonized at 800°C for 2 hours in an argon atmosphere, and cooled to obtain a carbonized aerogel;

[0160] (6) Aluminum chloride hexahydrate and ethyl orthosilicate are mixed with water and stirred for 2 h to obtain a silicon-aluminum ceramic sol, wherein the molar ratio of ethyl orthosilicate, aluminum chloride hexahydrate and water is 1:3:72. 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. The aerogel is then placed in a muffle furnace for ceramic treatment at 800°C for 2 h to obtain a high-temperature resistant mullite aerogel.

[0161] 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.

[0162] Example 4

[0163] A method for preparing a high-temperature resistant mullite aerogel comprises: (1) replacing the aluminum source in Example 1 with boehmite, with other parameters being the same as those in Example 1, to obtain a dual-phase mullite sol;

[0164] (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 hydroxypropyl methylcellulose is 4%;

[0165] (3) The mullite sol in step (1) is added 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), and a drying control additive N,N-dimethylformamide is added (the molar ratio of N,N-dimethylformamide to the aluminum source in the mullite sol is 2:1), and then a gelling agent propylene oxide is added (the molar ratio of propylene oxide to the aluminum source in the mullite sol is 14:1), stirred at room temperature for 30 minutes, and allowed to stand in a mold at 80°C for 1 day before demolding to obtain a gel;

[0166] (4) The gel obtained in step (3) was immersed in anhydrous ethanol and aged at 80°C for 1 day, with the anhydrous ethanol replaced 4 times a day. The gel was then immersed in a strengthening solution (composed of ethyl orthosilicate and anhydrous ethanol in a molar ratio of 1:30) and strengthened at 50°C for 8 days, with the strengthening solution replaced once a day to obtain a strengthened gel. The strengthened gel was then immersed in anhydrous ethanol and solvent replaced at 70°C for 2 days, with the anhydrous ethanol replaced 3 times a day. The gel was then immersed in n-hexane and solvent replaced at 30°C for 1 day, with the n-hexane replaced 2 times a day. Finally, the gel was dried at 30°C for 48 hours and at 100°C for 12 hours to obtain a mullite aerogel.

[0167] (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;

[0168] (6) Aluminum chloride hexahydrate and ethyl orthosilicate are mixed with water and stirred for 2 hours to obtain a silicon-aluminum ceramic sol, wherein the molar ratio of ethyl orthosilicate, aluminum chloride hexahydrate and water is 1:3:72. The carbonized aerogel obtained in step (5) is impregnated in the silicon-aluminum ceramic sol at a temperature of 60°C for 8 hours, and then dried at 80°C under normal pressure for 6 hours. The aerogel is then placed in a muffle furnace for ceramic treatment at 800°C for 2 hours to obtain a high-temperature resistant mullite aerogel.

[0169] 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.

[0170] Example 5

[0171] 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, with other parameters being the same as in Example 4, to obtain a dual-phase mullite sol;

[0172] (2) Carboxymethyl chitosan (degree of substitution ≥ 90%, isoelectric point 3-4, MacLean) and water were mixed and incubated in a 70°C water bath to obtain a carboxymethyl chitosan solution, wherein the mass concentration of carboxymethyl chitosan was 5%;

[0173] (3) adding the mullite sol in step (1) dropwise to the carboxymethyl chitosan solution in step (2) (the volume ratio of mullite sol to 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;

[0174] (4) The gel obtained in step (3) was immersed in anhydrous ethanol and aged at 100°C for 1 day, with the anhydrous ethanol replaced twice a day. The gel was then immersed in a strengthening solution (composed of ethyl orthosilicate and anhydrous ethanol in a molar ratio of 1:30) and strengthened at 70°C for 2 days, with the strengthening solution replaced once a day to obtain a strengthened gel. The strengthened gel was then immersed in anhydrous ethanol and solvent replaced at 80°C for 5 days, with the anhydrous ethanol replaced twice a day. The gel was then immersed in n-hexane and solvent replaced at 25°C for 1 day, with the n-hexane replaced once a day. Finally, the gel was dried at 25°C for 60 hours and at 150°C for 40 hours to obtain a mullite aerogel.

[0175] (5) The mullite aerogel obtained in step (4) was placed in a muffle furnace and pre-oxidized at 300°C for 5 hours, then placed in a tubular furnace and carbonized at 1200°C for 10 hours in an argon atmosphere, and cooled to obtain a carbonized aerogel;

[0176] (6) Aluminum chloride hexahydrate and ethyl orthosilicate are mixed with water and stirred for 2 hours to obtain a silicon-aluminum ceramic sol, wherein the molar ratio of ethyl orthosilicate, aluminum chloride hexahydrate and water is 1:3:72. The carbonized aerogel obtained in step (5) is impregnated in the silicon-aluminum ceramic sol at a temperature of 100°C for 8 hours, and then dried at 80°C under normal pressure for 6 hours. The mixture is then placed in a muffle furnace for ceramic treatment at 800°C for 2 hours to obtain a high-temperature resistant mullite aerogel.

[0177] 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.

[0178] Example 6

[0179] A method for preparing a high-temperature resistant mullite aerogel comprises: (1) obtaining a dual-phase mullite sol in the same manner as in Example 1;

[0180] (2) Mix hydroxyethyl cellulose (250-450 mPa.s, MacLean) and water, and place in a 40°C water bath to obtain a hydroxyethyl cellulose solution, wherein the mass concentration of hydroxyethyl cellulose is 3%;

[0181] (3) The mullite sol in step (1) is added 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), and the drying control additive N, N-dimethylformamide is added (the molar ratio of N, N-dimethylformamide to the aluminum source in the mullite sol is 1.5:1), and then the gelling agent propylene oxide is added (the molar ratio of propylene oxide to the aluminum source in the mullite sol is 17:1), stirred at room temperature for 30 minutes, and allowed to stand in a mold at 50°C for 3 days before demolding to obtain a gel;

[0182] (4) The gel obtained in step (3) was immersed in anhydrous ethanol and aged at 40°C for 5 days, with the anhydrous ethanol replaced twice a day. The gel was then immersed in a strengthening solution (composed of ethyl orthosilicate and anhydrous ethanol in a molar ratio of 1:30) and strengthened at 100°C for 1 day. The strengthening solution was replaced twice a day to obtain a strengthened gel. The strengthened gel was then immersed in anhydrous ethanol and solvent replaced at 100°C for 1 day. The anhydrous ethanol was replaced three times a day. Finally, the gel was dried at 50°C for 24 hours and 120°C for 24 hours to obtain a mullite aerogel.

[0183] (5) The mullite aerogel obtained in step (4) was placed in a muffle furnace and pre-oxidized at 300°C for 5 hours, then placed in a tubular furnace and carbonized at 1200°C for 10 hours in an argon atmosphere, and cooled to obtain a carbonized aerogel;

[0184] (6) Aluminum chloride hexahydrate, 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 chloride hexahydrate, 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. The aerogel is then placed in a muffle furnace for ceramic treatment at 1000°C for 5 hours to obtain a high-temperature resistant mullite aerogel.

[0185] 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.

[0186] Example 7

[0187] A method for preparing a high-temperature resistant mullite aerogel comprises: (1) replacing the silicon source in Example 1 with ethyl orthosilicate and polysilsesquioxane in a molar ratio of 1:1, with other parameters being the same as in Example 1, to obtain a dual-phase mullite sol;

[0188] (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 hydroxypropyl methylcellulose is 3%;

[0189] (3) The mullite sol in step (1) is added 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), and a drying control additive N,N-dimethylformamide is added (the molar ratio of N,N-dimethylformamide to the aluminum source in the mullite sol is 2.5:1), and then a gelling agent propylene oxide is added (the molar ratio of propylene oxide to the aluminum source in the mullite sol is 17:1), stirred at room temperature for 30 minutes, and allowed to stand in a mold at 50°C for 3 days before demolding to obtain a gel;

[0190] (4) The gel obtained in step (3) was immersed in anhydrous ethanol and aged at 70°C for 2 days, with the anhydrous ethanol replaced twice a day. The gel was then immersed in a strengthening solution (composed of ethyl orthosilicate and anhydrous ethanol in a molar ratio of 1:30) and strengthened at 90°C for 2 days, with the strengthening solution replaced 5 times a day to obtain a strengthened gel. The strengthened gel was then immersed in anhydrous ethanol and solvent replaced at 90°C for 2 days, with the anhydrous ethanol replaced 3 times a day. The gel was then immersed in n-hexane and solvent replaced at 40°C for 2 days, with the n-hexane replaced once a day. Finally, the gel was dried at 40°C for 40 hours and 60°C for 30 hours to obtain a mullite aerogel.

[0191] (5) The mullite aerogel obtained in step (4) was placed in a muffle furnace and pre-oxidized at 300°C for 5 hours, then placed in a tubular furnace and carbonized at 1000°C for 5 hours in an argon atmosphere, and cooled to obtain a carbonized aerogel;

[0192] (6) Aluminum chloride hexahydrate, ethyl orthosilicate and water are mixed and stirred for 2 hours to obtain a silicon-aluminum ceramic sol, wherein the molar ratio of ethyl orthosilicate, aluminum chloride hexahydrate and water is 1:3:72. 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. The aerogel is then placed in a muffle furnace for ceramic treatment at 600°C for 2 hours to obtain a high-temperature resistant mullite aerogel.

[0193] 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.

[0194] Example 8

[0195] A method for preparing a high-temperature resistant mullite aerogel comprises: (1) replacing the silicon source in Example 1 with ethyl orthosilicate, vinyltrimethoxysilane, and aminopropyltrimethoxysilane in a molar ratio of 1:1:1, with other parameters being the same as in Example 1, to obtain a dual-phase mullite sol;

[0196] (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%;

[0197] (3) adding the mullite sol in step (1) dropwise to the chitosan solution in step (2) (the volume ratio of mullite sol to 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;

[0198] (4) The gel obtained in step (3) was immersed in anhydrous ethanol and aged at 25°C for 10 days, with the anhydrous ethanol replaced once a day. The gel was then immersed in a strengthening solution (composed of ethyl orthosilicate and anhydrous ethanol at a molar ratio of 1:30) and strengthened at 40°C for 10 days, with the strengthening solution replaced once a day to obtain a strengthened gel. The strengthened gel was then immersed in anhydrous ethanol and solvent replaced at 25°C for 7 days, with the anhydrous ethanol replaced once a day. The gel was then immersed in n-hexane and solvent replaced at 30°C for 3 days, with the n-hexane replaced once a day. Finally, the gel was dried at 60°C for 24 hours and 100°C for 48 hours to obtain a mullite aerogel.

[0199] (5) The mullite aerogel obtained in step (4) was placed in a muffle furnace and pre-oxidized at 300°C for 5 hours, then placed in a tubular furnace and carbonized at 1000°C for 5 hours in an argon atmosphere, and cooled to obtain a carbonized aerogel;

[0200] (6) Aluminum chloride hexahydrate, ethyl orthosilicate and water are mixed and stirred for 2 hours to obtain a silicon-aluminum ceramic sol, wherein the molar ratio of ethyl orthosilicate, aluminum chloride hexahydrate and water is 1:3:72. 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. The aerogel is then placed in a muffle furnace for ceramic treatment at 800°C for 2 hours to obtain a high-temperature resistant mullite aerogel.

[0201] 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.

[0202] Example 9

[0203] 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, with other parameters being the same as in Example 1, to obtain a dual-phase mullite sol;

[0204] (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%;

[0205] (3) The mullite sol in step (1) is added 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), and the gelling agent propylene oxide is added (the molar ratio of propylene oxide to the aluminum source in the mullite sol is 11:1), stirred at room temperature for 30 minutes, and allowed to stand in a mold at 70°C for 2 days before demolding to obtain a gel;

[0206] (4) The gel obtained in step (3) was immersed in anhydrous ethanol and aged at 60°C for 4 days, with the anhydrous ethanol replaced 3 times a day. The gel was then immersed in a strengthening solution (composed of ethyl orthosilicate and anhydrous ethanol in a molar ratio of 1:30) and strengthened at 60°C for 5 days, with the strengthening solution replaced once a day to obtain a strengthened gel. The strengthened gel was then immersed in anhydrous ethanol and solvent replaced at 30°C for 6 days, with the anhydrous ethanol replaced twice a day. The gel was then immersed in n-hexane and solvent replaced at 30°C for 2 days, with the n-hexane replaced once a day. Finally, the gel was dried at 25°C for 12 hours and 60°C for 24 hours to obtain a mullite aerogel.

[0207] (5) The mullite aerogel obtained in step (4) was placed in a muffle furnace and pre-oxidized at 300°C for 5 hours, then placed in a tubular furnace and carbonized at 1000°C for 5 hours in an argon atmosphere, and cooled to obtain a carbonized aerogel;

[0208] (6) Aluminum chloride hexahydrate, ethyl 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 ethyl orthosilicate, aluminum chloride hexahydrate, 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. The aerogel is then placed in a muffle furnace for ceramic treatment at 1000°C for 5 hours to obtain a high-temperature resistant mullite aerogel.

[0209] 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.

[0210] Example 10

[0211] A method for preparing a high-temperature resistant mullite aerogel comprises: (1) replacing the silicon source in Example 1 with ethyl orthosilicate, vinyl tris(trimethylsiloxy)silane, and polysilsesquioxane in a molar ratio of 1:1:1, with other parameters being the same as in Example 1, to obtain a dual-phase mullite sol;

[0212] (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 polyvinyl alcohol was 8%;

[0213] (3) The mullite sol in step (1) is added 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), and a drying control additive N,N-dimethylformamide is added (the molar ratio of N,N-dimethylformamide to the aluminum source in the mullite sol is 1:1), and then a gelling agent propylene oxide is added (the molar ratio of propylene oxide to the aluminum source in the mullite sol is 14:1), stirred at room temperature for 30 minutes, and allowed to stand in a mold at 40°C for 3 days before demolding to obtain a gel;

[0214] (4) The gel obtained in step (3) was immersed in anhydrous ethanol and aged at 90°C for 2 days, with the anhydrous ethanol replaced twice a day. The gel was then immersed in a strengthening solution (composed of ethyl orthosilicate and anhydrous ethanol in a molar ratio of 1:30) and strengthened at 70°C for 2 days, with the strengthening solution replaced twice a day to obtain a strengthened gel. The strengthened gel was then immersed in anhydrous ethanol and solvent replaced at 60°C for 3 days, with the anhydrous ethanol replaced four times a day. The gel was then immersed in n-hexane and solvent replaced at 30°C for 1 day, with the n-hexane replaced once a day. Finally, the gel was dried at 80°C for 24 hours to obtain a mullite aerogel.

[0215] (5) The mullite aerogel obtained in step (4) was placed in a muffle furnace and pre-oxidized at 300°C for 5 hours, then placed in a tubular furnace and carbonized at 1000°C for 5 hours in an argon atmosphere, and cooled to obtain a carbonized aerogel;

[0216] (6) Aluminum chloride hexahydrate, 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 chloride hexahydrate, 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. The aerogel is then placed in a muffle furnace for ceramic treatment at 1200°C for 10 hours to obtain a high-temperature resistant mullite aerogel.

[0217] 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.

[0218] Example 11

[0219] A method for preparing a high-temperature resistant mullite aerogel comprises: (1) mixing an aluminum source (aluminum chloride hexahydrate), a silicon source (ethyl orthosilicate, dimethyldiethoxysilane, 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;

[0220] (2) Carboxymethyl chitosan (degree of substitution ≥ 90%, isoelectric point 3-4, MacLean) and water were mixed and incubated in a 70°C water bath to obtain a carboxymethyl chitosan solution, wherein the mass concentration of carboxymethyl chitosan was 6%;

[0221] (3) adding the mullite sol in step (1) dropwise to the carboxymethyl chitosan solution in step (2) (the volume ratio of mullite sol to 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 at 90°C in a mold for 1 day, and then demolding to obtain a gel;

[0222] (4) The gel obtained in step (3) was immersed in anhydrous ethanol and aged at 30°C for 6 days, with the anhydrous ethanol replaced twice a day. The gel was then immersed in a strengthening solution (composed of ethyl orthosilicate and anhydrous ethanol in a molar ratio of 1:30) and strengthened at 80°C for 3 days, with the strengthening solution replaced twice a day to obtain a strengthened gel. The strengthened gel was then immersed in anhydrous ethanol and solvent replaced at 40°C for 4 days, with the anhydrous ethanol replaced once a day. The gel was then immersed in n-hexane and solvent replaced at 40°C for 1 day, with the n-hexane replaced twice a day. Finally, the gel was dried at 40°C for 80 hours to obtain a mullite aerogel.

[0223] (5) The mullite aerogel obtained in step (4) was placed in a muffle furnace and pre-oxidized at 300°C for 5 hours, then placed in a tubular furnace and carbonized at 1000°C for 5 hours in an argon atmosphere, and cooled to obtain a carbonized aerogel;

[0224] (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 an immersion temperature of 60°C for 8 hours, and then dried at 80°C under normal pressure for 6 hours. The aerogel is then placed in a muffle furnace for ceramic treatment at 1200°C for 10 hours to obtain a high-temperature resistant mullite aerogel.

[0225] 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.

[0226] Comparative Example 1

[0227] Step (6) of Example 1 was omitted, i.e., ceramic sol impregnation and ceramicization treatment were not performed, and the other steps and parameters were the same as those of Example 1.

[0228] The mullite aerogel prepared in Comparative Example 1 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.

[0229] Comparative Example 2

[0230] Step (5) of Example 1 was omitted, i.e., pre-oxidation and carbonization were not performed, and the other steps and parameters were the same as those in Example 1.

[0231] The mullite aerogel prepared in Comparative Example 2 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.

[0232] Comparative Example 3

[0233] Steps (5) and (6) of Example 1 are omitted, that is, pre-oxidation, carbonization, ceramic sol impregnation and ceramicization treatment are not performed, and other steps and parameters are the same as those in Example 1.

[0234] 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.

[0235] 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.

[0236] 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 to 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, etc., and still have a good pore structure, indicating that it has good high temperature resistance.

[0237] 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. The specific surface area and average pore size were obtained by testing using a Micromeritics ASAP 2460 surface area and porosity analyzer.

[0238] The thermal conductivity was measured using a Swedish Hot Disk TPS2500 thermal constant analyzer using the transient plane heat source method.

[0239] 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 occur, then it means that the high temperature resistance of the aerogel is 1400°C.

[0240] 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

[0241]

[0242] According to the data in Table 1, in combination with Comparative Example 1 and Example 1, it can be seen 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 ceramic treatment; in combination with Example 1 and Example 6, it can be seen that by changing the composition of the ceramic sol, the high temperature resistance and compressive strength of the mullite aerogel can be further improved; in combination with Comparative Example 2 and Example 1, it can be seen that the high temperature resistance of the mullite aerogel can be effectively improved by pre-oxidation and carbonization treatment; in combination with Comparative Example 3 and Example 1, it can be seen that the pre-oxidation and carbonization in the present invention can synergistically act with the impregnation with ceramic sol and ceramic treatment to further improve the high temperature resistance and compressive strength of the mullite aerogel.

[0243] 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 increase its specific surface area and compressive strength.

[0244] 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 principles of the present invention. These improvements and modifications should also be regarded as within the scope of protection of the present invention.

Claims

1. A method for preparing 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) impregnating the carbonized aerogel obtained in step (4) in a ceramic sol, and then drying and ceramicizing the aerogel in sequence to obtain a high-temperature resistant mullite aerogel; In the step (1), the molar ratio of silicon in the silicon source to aluminum in the aluminum source is 1:(0.2-5); the mass concentration of the polymer solution in the step (1) is 1-10%; the solvent in the step (1) is water or a mixed solution of water and acid; the reinforcing agent in the step (2) is a silicon source or a mixture of a silicon source and an aluminum source; the ceramic sol in the step (5) is a sol containing one or more elements of lithium, boron, silicon, aluminum, zirconium, titanium, calcium, magnesium, iron, yttrium and lanthanum; and the immersion time in the step (5) is 1-50 hours.

2. 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.

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

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

5. 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.

6. 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.

7. The high temperature resistant mullite aerogel prepared by the preparation method according to any one of claims 1 to 6.

8. Use of the high-temperature resistant mullite aerogel according to claim 7 in the field of thermal protection.

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