Preparation method of blocky mullite aerogel

Abstract

The invention provides a preparation method of blocky mullite aerogel, and belongs to the technical field of aerogel materials. The preparation method provided by the invention comprises the following steps: mixing a silicon source, an aluminum source, a solvent, a polymer solution and a gelling agent, and gelatinizing to obtain gel; mixing the gel with a reinforcing agent, and reinforcing to obtain reinforced gel; and soaking the reinforced gel in a replacement liquid, carrying out solvent replacement, and drying at normal pressure to obtain the blocky mullite aerogel. A silicon source, an aluminum source and a solvent are added to form mullite sol, a polymer solution is added, the polymer solution and aluminum atoms in the mullite sol can form chemical bonds such as coordinate bonds or covalent bonds, a gel skeleton is enhanced, capillary stress in the drying process is resisted, and then blocky mullite aerogel can be prepared during normal-pressure drying; expensive equipment and a supercritical or vacuum environment are not needed, and the cost and the energy consumption are low.

Description

Technical Field

[0001] The invention belongs to the technical field of aerogel materials, and in particular relates to a method for preparing blocky mullite aerogel. 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. During the drying process, the aerogel will produce capillary stress due to the evaporation of the solvent in the gel pores, causing the gel skeleton to shrink and crack, making it difficult to obtain block aerogel. In the prior art, supercritical drying or vacuum freeze drying is mainly used to obtain block aerogels, but supercritical drying or vacuum freeze drying equipment is expensive and energy-intensive, which is not conducive to large-scale production.

[0003] Therefore, how to prepare blocky mullite aerogel under normal pressure drying to reduce cost and energy consumption has become a difficult problem in the prior art. Summary of the invention

[0004] The object of the present invention is to provide a method for preparing blocky mullite aerogel. The preparation method provided by the present invention can obtain blocky mullite aerogel under normal pressure drying, with low cost and energy consumption.

[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 blocky 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) The strengthened gel obtained in step (2) is immersed in a replacement liquid, and then the solvent is replaced and then dried at normal pressure to obtain a block of 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, in step (1), the volume ratio of the total volume of the silicon source, the aluminum source and the solvent after mixing to the volume of the polymer solution is 1:(0.5-2).

[0009] Preferably, the gelling agent in step (1) comprises propylene oxide or aqueous ammonia.

[0010] Preferably, the molar ratio of the propylene oxide to the aluminum source is (8-20):1.

[0011] Preferably, the gelation temperature in step (1) is 25-100° C., and the gelation time is 1-5 days.

[0012] Preferably, the strengthening temperature in step (2) is 40-100° C., and the strengthening time is 1-10 days.

[0013] Preferably, the temperature of the solvent replacement in step (3) is 25-100° C., and the time of the solvent replacement is 1-11 days.

[0014] Preferably, in step (3), the temperature of the atmospheric pressure drying is 25-150° C., and the time of the atmospheric pressure drying is 1-100 h.

[0015] The present invention provides a method for preparing a block mullite aerogel, comprising the following steps: (1) mixing a silicon source, an aluminum source, a solvent, a polymer solution and a gelling agent, gelling, and obtaining 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, reinforcing, and obtaining 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 block mullite aerogel. The silicon source, aluminum source and solvent added in the present invention form a mullite sol, and the polymer solution is added, which can form chemical bonds such as coordination bonds or covalent bonds with aluminum atoms in the mullite sol, strengthen the gel skeleton, and resist capillary stress during the drying process, so that the block mullite aerogel can be prepared when drying at normal pressure, without the need for expensive equipment and a supercritical or vacuum environment, and with low cost and energy consumption. The results of the examples show that the present invention can prepare blocky mullite aerogel under normal pressure drying conditions. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 A schematic diagram of the process for preparing the blocky mullite aerogel provided by the present invention; Figure 2 This is a macroscopic image of the blocky mullite aerogel prepared in Example 2. DETAILED DESCRIPTION

[0017] The present invention provides a method for preparing a blocky 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) The strengthened gel obtained in step (2) is immersed in a replacement liquid, and then the solvent is replaced and then dried at normal pressure to obtain a block of 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, 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 aqueous acid 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 includes glacial acetic acid or concentrated hydrochloric acid; the mass concentration of the concentrated hydrochloric acid is preferably 36-38%.

[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 includes glacial acetic acid or concentrated hydrochloric acid; the mass concentration of the concentrated hydrochloric acid is preferably 36-38%.

[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 can further cross-link the gel network and remove the 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 a blocky 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, the atmospheric pressure drying can be carried out at a single temperature, or can be carried out in steps at different temperatures. In an embodiment of the present invention, the atmospheric pressure drying can be first dried at 40°C for 12 hours, then dried at 60°C for 12 hours; it can also be first dried at 25°C for 40 hours, then dried at 80°C for 20 hours, and finally dried at 150°C for 20 hours; it can also be dried at 60°C for 10 hours; it can also be first dried at 30°C for 48 hours, and then dried at 100°C for 24 hours.

[0088] The present invention adds a polymer solution to strengthen the gel skeleton and resist the capillary stress in the drying process, so that block mullite aerogel can be prepared during normal pressure drying, without expensive equipment and supercritical or vacuum environment, and the raw materials used are cheap and widely available, with low cost and energy consumption. The preparation method is simple and safe, and can be mass-produced. The prepared mullite aerogel has low density, high specific surface area and low thermal conductivity.

[0089] The schematic flow diagram of the method for preparing the blocky 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 a silica sol; an aluminum source and deionized water are mixed to obtain an aluminum sol; the silica sol, the aluminum sol and a polymer solution are mixed and stirred to obtain a mullite sol, which is gelled to obtain a mullite gel, and after aging, strengthening, solvent replacement and normal pressure drying, a mullite aerogel is obtained.

[0090] 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.

[0091] Example 1 A method for preparing a blocky 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 the mixture at room temperature to obtain an aluminum sol; and mixing a silicon source (ethyl orthosilicate) with a solvent (the molar ratio of the silicon 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) Mix carboxymethyl chitosan (degree of substitution ≥ 90%, isoelectric point 3-4, MacLean) and water, and place in a 60°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 1:1.5), 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) The gel obtained in step (3) is immersed in anhydrous ethanol and aged at 60° C. for 2 days, with the anhydrous ethanol being replaced 3 times a day. The gel is then immersed in a strengthening solution (composed of tetraethyl orthosilicate, aluminum chloride hexahydrate and anhydrous ethanol in a molar ratio of 1:3:30) and strengthened at 60° C. for 2 days, with the strengthening solution being replaced twice a day to obtain a strengthened gel. The strengthened gel is then immersed in anhydrous ethanol and solvent replaced at 60° C. for 1 day, with the anhydrous ethanol being replaced twice. The gel is then immersed in n-hexane and solvent replaced at room temperature for 1 day, with the n-hexane being replaced twice. Finally, the gel is dried at 40° C. for 12 hours and then at 60° C. for 12 hours to obtain a blocky mullite aerogel.

[0092] Example 2 The step (2) of Example 1 was replaced by: (2) chitosan (viscosity <200 mPa.s, Aladdin) and glacial acetic acid aqueous solution were mixed and placed in a water bath 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 5%. The other steps and parameters were the same as those in Example 1.

[0093] Example 3 The carboxymethyl chitosan in step (2) of Example 1 was replaced by hydroxypropyl cellulose (hydroxypropoxyl group: 5-16 wt %, McLean), and the other steps and parameters were the same as those in Example 1.

[0094] Example 4 The aluminum source in step (1) of Example 1 was replaced with aluminum nitrate nonahydrate, and the other steps and parameters were the same as those of Example 1.

[0095] Example 5 The aluminum source in step (1) of Example 1 was replaced by boehmite, and the other steps and parameters were the same as those of Example 1.

[0096] Example 6 The silicon source in step (1) of Example 1 was replaced by a mixed silicon source of ethyl orthosilicate and vinyl triethoxysilane in a molar ratio of 1:1. The other steps and parameters were the same as those in Example 1.

[0097] Example 7 A method for preparing a blocky mullite aerogel comprises: (1) mixing an aluminum source (aluminum chloride hexahydrate), a silicon source (ethyl orthosilicate, dimethyl dimethoxysilane and polysilsesquioxane in a molar ratio of 1:1:1) and a solvent (in a molar ratio of 1:0.8:7×10 -4 water, anhydrous ethanol and concentrated hydrochloric acid) and hydrolyzed at room temperature to obtain a single-phase mullite sol, wherein the molar ratio of the silicon source, the aluminum source and the solvent is 1:3:75; (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 10%; (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 1:1), 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 60°C in a mold for 3 days, and then demolding to obtain a gel; (4) The gel obtained in step (3) is immersed in anhydrous ethanol and aged at 25° C. for 10 days, with the anhydrous ethanol being replaced once a day. The gel is then immersed in a strengthening solution (composed of tetraethyl orthosilicate, aluminum chloride hexahydrate and anhydrous ethanol in a molar ratio of 1:3:30) and strengthened at 40° C. for 10 days, with the strengthening solution being replaced once a day to obtain a strengthened gel. The strengthened gel is then immersed in anhydrous ethanol and solvent replaced at 25° C. for 10 days, with the anhydrous ethanol being replaced 5 times a day. The gel is then immersed in n-hexane and solvent replaced at 25° C. for 1 day, with the n-hexane being replaced once. Finally, the gel is dried at 25° C. for 40 hours, 80° C. for 20 hours and 150° C. for 20 hours to obtain a blocky mullite aerogel.

[0098] Example 8 A method for preparing a blocky 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, methyltrimethoxysilane and vinyltrimethoxysilane in a molar ratio of 1:1:1) with a solvent (the molar ratio of 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) Chitosan (viscosity <200 mPa.s, Aladdin) and glacial acetic acid aqueous solution were mixed, and ultrasonicated at 50°C to obtain a chitosan solution, wherein the mass concentration of chitosan was 8% 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 1:2), adding the drying control additive N,N-dimethylformamide (the molar ratio of N,N-dimethylformamide to the aluminum source in the mullite sol is 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 14:1), stirring at room temperature for 10 minutes, standing in a mold at 80°C for 2 days, and then demolding to obtain a gel; (4) The gel obtained in step (3) is immersed in anhydrous ethanol and aged at 100° C. for 1 day, with the anhydrous ethanol being replaced 5 times a day. The gel is then immersed in a strengthening solution (composed of tetraethyl orthosilicate, aluminum chloride hexahydrate and anhydrous ethanol in a molar ratio of 1:3:30) and strengthened at 100° C. for 1 day, with the strengthening solution being replaced 3 times a day to obtain a strengthened gel. The strengthened gel is then immersed in anhydrous ethanol and solvent replaced at 100° C. for 8 days, with the anhydrous ethanol being replaced once a day. The gel is then immersed in n-hexane and solvent replaced at 25° C. for 1 day, with the n-hexane being replaced once. Finally, the gel is dried at 60° C. for 10 hours to obtain a blocky mullite aerogel.

[0099] Example 9 A method for preparing a blocky 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, methyltrimethoxysilane and vinyltrimethoxysilane in a molar ratio of 1:1:1) with a solvent (the molar ratio of 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) 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 1%; (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 drying control additive N,N-dimethylformamide (the molar ratio of N,N-dimethylformamide to the aluminum source in the mullite sol is 0.5:1), and then adding the gelling agent propylene oxide (the molar ratio of propylene oxide to the aluminum source in the mullite sol is 11:1), stirring at room temperature for 40 minutes, standing in a mold at 100°C for 1 day, and then demolding to obtain a gel; (4) The gel obtained in step (3) is immersed in anhydrous ethanol and aged at 80° C. for 4 days, with the anhydrous ethanol being replaced twice a day. The gel is then immersed in a strengthening solution (composed of ethyl orthosilicate and anhydrous ethanol in a molar ratio of 1:50) and strengthened at 80° C. for 2 days. The strengthening solution is replaced 5 times a day to obtain a strengthened gel. The strengthened gel is then immersed in n-hexane and solvent replacement is performed at 35° C. for 1 day. The n-hexane is replaced twice. Finally, the gel is dried at 30° C. for 48 hours and at 100° C. for 24 hours to obtain a block of mullite aerogel.

[0100] Comparative Example 1 A method for preparing a mullite aerogel comprises: (1) obtaining a dual-phase mullite sol as in Example 1; (2) adding a drying control additive N,N-dimethylformamide (the molar ratio of N,N-dimethylformamide to the aluminum source in the mullite sol is 1:1) to the mullite sol in step (1), and then adding a 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; (3) The gel obtained in step (2) is immersed in anhydrous ethanol and aged at 60° C. for 2 days, the anhydrous ethanol is replaced 3 times a day, and then the gel is immersed in a strengthening solution (composed of tetraethyl orthosilicate, aluminum chloride hexahydrate and anhydrous ethanol in a molar ratio of 1:3:30) and strengthened at 60° C. for 2 days, the strengthening solution is replaced twice a day, and a strengthened gel is obtained. The strengthened gel is then immersed in anhydrous ethanol and solvent replacement is performed at 60° C. for 1 day, the anhydrous ethanol is replaced twice, and then the gel is immersed in n-hexane and solvent replacement is performed at room temperature for 1 day, the n-hexane is replaced twice, and finally the gel is dried at 40° C. for 12 hours and then at 60° C. for 12 hours to obtain a mullite aerogel.

[0101] Comparative Example 2 The aluminum source in step (1) of Comparative Example 1 was replaced with aluminum nitrate nonahydrate, and the other steps and parameters were the same as those of Comparative Example 1.

[0102] Comparative Example 3 The aluminum source in step (1) of Comparative Example 1 was replaced with boehmite, and the other steps and parameters were the same as those of Comparative Example 1.

[0103] Comparative Example 4 The silicon source in step (1) of comparative example 1 was replaced with a mixed silicon source of tetraethyl orthosilicate, dimethyldimethoxysilane and polysilsesquioxane in a molar ratio of 1:1:1. The other steps and parameters were the same as those of comparative example 1.

[0104] The macroscopic image of the mullite aerogel prepared in Example 2 is as follows: Figure 2 As shown. Figure 2It can be seen that the present invention obtains blocky mullite aerogel under normal pressure drying conditions.

[0105] The appearance morphology of the mullite aerogels in Examples 1 to 9 and Comparative Examples 1 to 4 was observed and the density, drying shrinkage, specific surface area, average pore size and thermal conductivity of the mullite aerogels in Examples 1 to 9 and Comparative Examples 1 to 4 were tested. The results are shown in Table 1, where the drying shrinkage refers to the degree of shrinkage of the diameter of the aerogel from the wet gel before drying to the aerogel after drying. The drying shrinkage is calculated according to the following formula: , Where ε is the drying shrinkage, d 0 is the diameter of the wet gel, d 1 is the diameter of the aerogel.

[0106] The specific surface area and average pore size were measured by ASAP 2460 specific surface area and porosity analyzer from Micromeritics.

[0107] The thermal conductivity was obtained by using the transient plane heat source method using a Swedish Hot Disk TPS2500 thermal constant analyzer.

[0108] Table 1 Density, appearance, drying shrinkage, specific surface area, average pore size and thermal conductivity of mullite aerogel in Examples 1 to 9 and Comparative Examples 1 to 4

[0109] According to the data in Table 1, it can be seen from the comparison example 1 and Examples 1 to 3 that when no polymer is added, the aerogel obtained by drying at normal pressure is in the form of broken pieces, while when the polymer is added, a block-shaped mullite aerogel can be obtained by drying at normal pressure, and the aerogel has low density, high specific surface area and low thermal conductivity; it can be seen from Examples 1, 4 and 5 that changing the type of aluminum source does not affect the beneficial effects of the polymer, and a block-shaped mullite aerogel with low density, high specific surface area and low thermal conductivity can still be obtained; it can be seen from Examples 1 and 6 that changing the type of silicon source does not affect the beneficial effects of the polymer, and a block-shaped mullite aerogel with low density, high specific surface area and low thermal conductivity can still be obtained.

[0110] In summary, the present invention adds polymers to obtain blocky mullite aerogel under normal pressure drying conditions without supercritical or vacuum environment, with lower cost and energy consumption, and the prepared mullite aerogel has low density, high specific surface area and low thermal conductivity.

[0111] 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 blocky 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) The strengthened gel obtained in step (2) is immersed in a replacement liquid, and then the solvent is replaced and then dried at normal pressure to obtain a block of 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 3, characterized in that: In the step (1), the volume ratio of the total volume of the silicon source, the aluminum source and the solvent after mixing to the volume ratio of the polymer solution is 1:(0.5-2).

5. The preparation method according to claim 1, characterized in that: The gelling agent in step (1) includes propylene oxide or ammonia water.

6. The preparation method according to claim 5, characterized in that: The molar ratio of the propylene oxide to the aluminum source is (8-20):

1.

7. 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.

8. The preparation method according to claim 1, characterized in that: The strengthening temperature in step (2) is 40-100° C., and the strengthening time is 1-10 days.

9. The preparation method according to claim 1, characterized in that: The temperature of the solvent replacement in step (3) is 25-100° C., and the time of the solvent replacement is 1-11 days.

10. The preparation method according to claim 1, characterized in that: The temperature of the atmospheric pressure drying in the step (3) is 25-150° C., and the time of the atmospheric pressure drying is 1-100 h.

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