Efficient preparation method of high-temperature radiation resistant aerogel thermal insulation material

Abstract

The present application relates to a kind of efficient preparation methods of high-temperature radiation resistant aerogel thermal insulation material, the method is: the preparation of a certain length-diameter ratio alumina nanowire cluster by hydrothermal method;A certain proportion of radiation resistant agent is uniformly mixed using kneader, alumina nanowire cluster containing radiation resistant agent is formed by moulding, the block after forming is placed in silane-based precursor solution containing catalyst;Then aging process is carried out;Gradient solvent replacement is carried out;Then subcritical drying and heat treatment process under inert atmosphere are carried out.The present application uses high length-diameter ratio alumina nanowire to carry out three-dimensional jointing, and is modified using silane-based precursor, realizes the preparation of low-cost, lightweight and efficient thermal insulation aerogel.Under high temperature, the radiation resistant agent in aerogel can effectively resist infrared radiation, substantially reduce the high-temperature thermal conductivity of aerogel, so that nano-aerogel has the characteristics of low cost, ultra-light, low thermal conductivity, high temperature resistance and the like.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of aerogel preparation, and particularly relates to a high-efficiency preparation method of a high-temperature-resistant aerogel thermal insulation material. BACKGROUND

[0002] Aerogel material is a gel material with a gas dispersion medium, which is a kind of nanometer porous solid material with a network structure formed by mutual accumulation of colloidal particles or polymer molecules. The size of the pores in the material is in the nanometer range. The porosity of the material is as high as 80-99.8%, the typical size of the pores is 1-100 nm, the specific surface area is 200-1000 m 2 / g, and the density can be as low as 3 kg / m 3 , and the thermal conductivity at room temperature can be as low as 0.012 W / m·k. Due to these characteristics, aerogel material has a wide application potential in the fields of thermal, acoustic, optical, microelectronic and particle detection. At present, the most widely used field of aerogel is still the thermal insulation field. Due to the unique nanometer structure of aerogel, the convection and solid conduction can be effectively reduced. It is needless to say that aerogel is the most efficient thermal insulation material at low and medium temperature, but the infrared radiation is serious at high temperature, and the thermal conductivity of some near-infrared transparent aerogel materials will be greatly improved at high temperature. Therefore, for the system with high infrared transmittance, a certain light shielding agent needs to be doped to reduce the thermal conductivity at high temperature and improve the overall thermal insulation efficiency of the material.

[0003] Chinese patent application CN201810068117.1 discloses a preparation method of a high-temperature-resistant aerogel material. Although the aerogel prepared by the method has good high-temperature-resistant characteristics, the heat-resistant temperature is above 1000 DEG C, and the aerogel can even withstand a high temperature above 1300 DEG C, the aerogel material will still produce a series of phase changes at a high temperature above 1200 DEG C, so that the specific surface area of the aerogel after high-temperature heat treatment is small and does not exceed 100 m 2 / g. Therefore, the high-temperature thermal insulation performance of the aerogel material is not very good.

[0004] Chinese patent CN201910630467.7 discloses a preparation method of a high-temperature-resistant special-shaped nanocrystal aerogel material. The special-shaped nanocrystal aerogel material is prepared by assembling nanorods and silica sol. The material has good temperature resistance and can withstand a temperature limit of 1400 DEG C. However, the material preparation process needs a sol-gel process, aging and solvent replacement, supercritical drying and other steps, which greatly increases the complexity of the preparation and prolongs the material preparation period. Therefore, the present application can make up for the shortcomings of the patent and prepare a high-temperature-resistant alumina nanometer aerogel in a simple preparation process.

[0005] From the cost point of view, the preparation of traditional aerogel materials mostly depends on supercritical drying equipment, and the process is complex and high in cost, which restricts the batch production of the product to some extent. Due to the high cost of supercritical drying, researchers have tried to explore other drying methods, such as atmospheric drying and freeze drying method for the preparation of aerogel. The ordinary atmospheric drying method, due to the weak aerogel skeleton, the skeleton collapses seriously under the action of liquid surface tension, so that the porosity and specific surface area of the material decrease significantly, and the bulk density and heat insulation efficiency of the material are greatly reduced. Some researchers start from the aspects of roughening the skeleton and reducing the surface energy, on the one hand, to improve the strength of the skeleton to resist the surface tension of the liquid, and on the other hand, to modify the skeleton to be hydrophobic to reduce the surface energy caused by the escape of solvent molecules. However, these two paths often result in a relatively strong skeleton of the aerogel, which is insufficient in heat insulation efficiency. Compared with atmospheric drying, freeze drying method can well maintain the pore structure. This method uses low-temperature freezing and sublimation to retain the pores occupied by ice crystals, while the skeleton does not collapse. Some researchers have combined nanofiber and aluminum-boron-silicon sol through freeze drying method to construct nanofiber aerogel, which has a temperature resistance of 1100 DEG C. The temperature resistance of this one-dimensional nanostructured porous material is improved compared with traditional nanometer aerogel, which provides an important reference for the preparation of high-temperature resistant aerogel materials. However, the skeleton and pore size of the aerogel prepared by this method exceed the typical aerogel structure characteristics (1-100 nm), especially the 10-20 mu m pores will lead to serious gas phase heat conduction and heat convection of the material, and the overall thermal insulation performance of the material is lower than that of the typical aerogel material, which limits its engineering application in aerospace and other fields.

[0006] With the development of science and technology, the heat insulation materials in various fields are required to have high temperature resistance and high temperature insulation performance. At present, there is no method that can simultaneously realize the preparation of aerogel heat insulation materials with high temperature and high efficiency, light weight and low cost. Therefore, under the strict restrictions on cost and period, it is very necessary to develop an effective method to prepare aerogel materials with low cost, light weight and high efficiency. SUMMARY

[0007] In order to solve the technical problems existing in the prior art, the application provides a high-efficiency preparation method of high-temperature-resistant radiation aerogel heat insulation material.

[0008] The application provides a high-efficiency preparation method of high-temperature-resistant radiation aerogel heat insulation material in the first aspect, and the method comprises the following steps:

[0009] (1) 1-30 g of alumina nanopowder (particle size 5-50 nm) is dissolved in 10-200 mL of water, 0.1-2 g of a mixture of 0.001-1 mol / L hydrochloric acid and 0.001-1 mol / L sulfuric acid (weight ratio 1:1) is added as an adsorbent, and the reaction is carried out at 100-300°C for 1-7 h to obtain alumina nanowire clusters with a diameter of 10-100 nm and a length of 100-800 μm.

[0010] (2) The alumina nanowire clusters obtained in step (1) are mixed with an anti-radiation agent, and homogenously dispersed by using a kneader, which is bidirectional rotation, at a speed of 10-100 r / min, to obtain a wet gel, wherein the anti-radiation agent accounts for 0.1-3% of the mass of the wet gel.

[0011] (3) The wet gel obtained in step (2) is pre-laid in a mold and then molded, which is divided into two steps, i.e., preliminary forming at a pressure of 0.1-2 MPa for 5-30 min, and shaping at a pressure of 1-5 MPa for 1-20 min, to obtain a wet gel block.

[0012] (4) The wet gel in step (3) is immersed in a mixed solution of methyltrimethoxysilane, ethanol, ammonia water (solution A) and ammonium fluoride (solution B) (the amount of the mixed solution is 2-5 times the volume of the block, and the mass ratio of solution A to solution B is 100:1-100:20), a stirring magnet is arranged at the lower part of the bracket, and stirring is carried out at a speed of 100-300 r / min to promote solvent replacement and catalysis, to obtain a composite gel, which is left to stand for 6-24 h.

[0013] In step (4) above, the concentration of methyltrimethoxysilane in the mixed solution (A) is 0.5-20 mass%, and the concentration of ammonia is 0.1-5 mass%, and the concentration of ammonium fluoride in solution (B) is 0.05-0.5 mol / L.

[0014] (5) The composite gel obtained in step (4) is replaced in 5-15 times of solvent, i.e., ethanol solution, a mixed solvent of ethanol and a low surface energy solvent, and pure low surface energy solvent, respectively, for 3-5 days, to carry out solvent replacement. The low surface energy solvent can be, but is not limited to, petroleum ether, n-hexane, cyclohexane, etc.

[0015] (6) The composite gel obtained in step (5) is subjected to a subcritical drying process in a special container, which is a pressure-resistant closed structure, made of metal, provided with instruments for regulating pressure, and provided with a gas outlet. The container with the wet gel block is sealed and placed in an oven at 40-80°C for heating for 1-12 h, and then the exhaust valve is opened for 5-30 min for gas exchange. The steps of heating and exhausting are repeated for 5-10 times. Then the dried gel is taken out and left to stand at room temperature and normal pressure for 24-72 h.

[0016] (7) The aerogel obtained in step (6) is subjected to a low-temperature heat treatment process, and the heat treatment atmosphere is nitrogen or argon atmosphere, to obtain a lightweight radiation-resistant aerogel.

[0017] (8) The prepared aerogel has a heat-resistant temperature of 1100-1400℃, a room temperature thermal conductivity of 0.028-0.038 W / m·K, a 1000℃ thermal conductivity of 0.05-0.1 W / m·K, and a density of 0.1-0.3 g / cm 3 .

[0018] The application provides, in a second aspect, a high-temperature radiation-resistant aerogel thermal insulation material prepared by the method of the first aspect.

[0019] Compared with the prior art, the application has at least the following beneficial effects:

[0020] (1) Unlike other doping modifications and other high-temperature-resistant aerogel thermal insulation materials prepared by doping modification, the long nanowires are used as the main unit in the assembly process in the present research. The nanowires prepared in the typical examples have a diameter of 20-50 nm and a length of 100-800 μm, which not only ensures a low thermal conductivity, but also improves the overall temperature resistance of the material due to the self-supporting effect of the three-dimensional network structure.

[0021] (2) The nanowire clusters with a large aspect ratio can realize physical cross-linking of the wet gel network structure, rather than chemical cross-linking. The wet gel can be repeatedly shaped, and the process has strong applicability and high utilization rate.

[0022] (3) The kneading method is used to combine the viscous nanocluster with the radiation-resistant agent powder, which solves the problem of sedimentation of the radiation-resistant agent in the solution in the traditional doping process, thereby effectively improving the thermal insulation efficiency of the material.

[0023] (4) The present application uses silane-based precursors and nanowire skeletons to construct hierarchical micro-nano structures. The hydrophobic secondary structure formed by the nanoparticles effectively fills the pores between the nanowires, which not only improves the heat transfer path and reduces the gas phase heat conduction process, but also effectively improves the thermal insulation efficiency of the nanometer aerogel. On the other hand, the hydrophobic skeleton can reduce the interfacial tension in the drying process, which is beneficial to the subcritical drying process.

[0024] (5) The nanowires have the functions of self-supporting and self-toughening, which eliminates the need for fiber reinforcement in traditional aerogel composites, and the lightweight performance of the nanowires is improved by more than 50% compared with similar aerogel products.

[0025] (6) The self-supporting effect of the nanowire framework determines that it can be dried by a subcritical drying process, which is different from atmospheric drying and supercritical drying, and it can maintain a fine framework while realizing the construction of a high porosity framework. The subcritical drying process can effectively reduce costs and reduce dependence on large equipment. BRIEF DESCRIPTION OF DRAWINGS

[0026] Figure 1 is a preparation flow chart of the present application.

[0027] Figure 2 is a real object diagram of the nanogel prepared in Example 1.

[0028] Figure 3 is a SEM diagram of the aerogel prepared in Example 1.

[0029] Figure 4 is an EDS spectrum diagram of the aerogel prepared in Example 1. DETAILED DESCRIPTION

[0030] In order to make the purpose, technical scheme and advantages of the present application clearer, the technical scheme of the present application will be described clearly and completely below in combination with the embodiments of the present application. Obviously, the described embodiments are part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without making creative efforts fall within the scope of protection of the present application.

[0031] The present application provides in a first aspect an efficient preparation method of a high-temperature radiation-resistant aerogel thermal insulation material, which comprises the following steps:

[0032] The present application will be further described below by way of examples, but the scope of protection of the present application is not limited to these examples.

[0033] Example 1

[0034] (1) 6 g of alumina nano powder (particle size 20 nm) was dissolved in 100 mL of water, 1 g of 0.02 mol / L hydrochloric acid and sulfuric acid (1:1) was added as an adsorbent, and reacted at 220°C for 7 h to obtain alumina nanowire clusters with a diameter of 50 nm and a length of 100-800 μm.

[0035] (2) The alumina nanocluster obtained in step (1) was mixed with a radiation-resistant agent, and a kneader was used for uniform dispersion, the kneader was bidirectional rotation, the rotation speed was 20 r / min, thereby obtaining a wet gel, the radiation-resistant agent accounted for 1% of the mass of the wet gel. The radiation-resistant agent is a 1:1 mixture of silicon carbide and titanium oxide.

[0036] (3) The wet gel obtained in step (2) is placed in a mold for pre-laying and then molded in two steps, i.e., preliminary forming at a pressure of 0.5 MPa for 30 min and then shaping at a pressure of 2 MPa for 20 min, so as to obtain a wet gel block;

[0037] (4) Methyltrimethoxysilane is dissolved in ethanol (mass ratio 2%) and ammonia water is added as a catalyst (mass fraction 0.1%) to obtain solution A, and 0.1 mol / L of ammonium fluoride is added as a catalyst (solution B), and the above solutions are stirred, the mass ratio of solution A and solution B is 100:1, and the stirring time is 10 min, to obtain a mixed solution C, and the wet gel in step (3) is immersed in solution C for gelation reaction. A stirring magnet is arranged at the lower part of the bracket, and stirring is carried out at 100 r / min, and the gelation reaction is carried out for 12 h, so as to promote solvent replacement and catalysis, thereby obtaining a composite gel;

[0038] (5) The composite gel obtained in step (4) is replaced in 10 times of solvent respectively, and the solvents are ethanol solution, ethanol and cyclohexane mixed solvent, and cyclohexane respectively for 3 days.

[0039] (6) The composite gel obtained in step (5) is placed in a special container for a subcritical drying process. The container is a pressure-resistant closed structure made of metal, and instruments for regulating pressure are arranged, and a gas outlet is arranged. The container with the wet gel block is sealed and placed in a 50℃ oven for heating for 2 h, and then the exhaust valve is opened for 20 min for gas exchange. The heating and exhaust steps are repeated 6 times. Then the dried gel is taken out and placed at room temperature and normal pressure for 24 h.

[0040] (7) The aerogel obtained in step (6) is subjected to a heat treatment process at 500℃ to obtain a high-temperature-resistant aluminum oxide aerogel.

[0041] (8) The prepared aerogel has a heat-resistant temperature of 1300℃, a room-temperature thermal conductivity of 0.03 W / m·K, a high-temperature thermal conductivity of 0.05 W / m·K, and a density of 0.15 g / cm 3 .

[0042] Example 2

[0043] Example 2 is basically the same as Example 1, except that the aluminum oxide nano-powder in step 1 is 20 g.

[0044] The thermal insulation performance test of the aluminum oxide aerogel material in Example 2 shows that the surface of the aerogel material has no discoloration and no shedding when touched lightly, and other performance indicators are shown in Table 1.

[0045] Comparative Example 1

[0046] Comparative Example 1 is substantially the same as Example 1, except that the shaping process in Step 2 is not carried out in a multi-step process.

[0047] The thermal insulation performance of the alumina aerogel material in Comparative Example 1 was tested, and it was found that the surface of the aerogel material had micro-cracks, and the bulk fell off when touched gently. The other performance indicators are shown in Table 1.

[0048] Comparative Example 2

[0049] Comparative Example 2 is substantially the same as Example 1, except that Step 2 is not carried out in the preparation process.

[0050] The thermal insulation performance of the alumina aerogel material in Comparative Example 2 was tested, and it was found that the aerogel material had a large shrinkage during the drying process and had a certain degree of deformation. The other performance indicators are shown in Table 1.

[0051] Comparative Example 3

[0052] Comparative Example 3 is substantially the same as Example 1, except that Step 4 is not carried out in a multi-solvent replacement process, but a single ethanol solvent replacement is used.

[0053] The thermal insulation performance of the alumina aerogel material in Comparative Example 3 was tested, and it was found that the surface of the aerogel material had cracks, and the overall shape was deformed compared to the wet gel. The other performance indicators are shown in Table 1.

[0054] Comparative Example 4

[0055] Comparative Example 4 is substantially the same as Example 1, except that the drying process in Step 5 is carried out at normal pressure instead of a subcritical drying process.

[0056] The thermal insulation performance of the alumina aerogel material in Comparative Example 4 was tested, and it was found that the surface of the aerogel material had cracks, and the overall shape was deformed compared to the wet gel. The other performance indicators are shown in Table 1.

[0057] Comparative Example 5

[0058] Comparative Example 5 is substantially the same as Example 1, except that the prepared aerogel does not undergo a final heat treatment process.

[0059] The surface of the alumina aerogel in Comparative Example 5 is smooth, without cracking and falling off problems.

[0060] Comparative Example 6

[0061] Comparative Example 6 is substantially the same as Example 1, except that the prepared aerogel does not undergo a kneading process of the radiation resistance agent in Step 2.

[0062] The surface of the alumina aerogel in Comparative Example 6 is smooth, without cracking and falling off problems.

[0063] Comparative Example 7

[0064] Comparative Example 7 is substantially the same as Example 1, except that in Step 1, a solution of spherical nanocrystals with a diameter of 13 nm is used instead of nanowire clusters for the shaping process, and the subsequent steps are the same.

[0065] The results show that the material obtained is a powder rather than an aerogel bulk.

[0066] Comparative Example 8

[0067] Comparative Example 8 is substantially the same as Example 1, except that in Step 2, the molding process is not performed.

[0068] The material prepared is found to have a large number of pores inside the material when subjected to SEM testing, resulting in defects.

[0069] Comparative Example 9

[0070] ① Sol preparation

[0071] Take 160 g of methyl orthosilicate and 160 g of acetonitrile in a 500 mL beaker, seal it with plastic wrap and magnetically stir for 1 min. After mixing evenly, add 60 g of hydrochloric acid with a concentration of 0.003 mol / L as a catalyst. This process needs to be added slowly and stirred magnetically for 5 min; add the above mixture to a 1000 mL three-necked flask, heat and magnetically stir under the condition of 70°C, and reflux for 30 min, to obtain the first solution of siliceous sol precursor; add 160 g of methyl orthosilicate to the obtained first solution of siliceous sol precursor, continue to heat and magnetically stir under the condition of 70°C, and react for 16 h to obtain a siliceous sol (silica sol). Dilute the siliceous sol, evaporate 300 g of solvent contained in the siliceous sol, and then add 600 g of acetonitrile to mix evenly to obtain the diluted siliceous sol, and the diluted siliceous sol is ready for use after cold storage.

[0072] ② Nanocrystal assembly process

[0073] Dissolve 3.7 g of aluminum oxide nano powder in 34 g of acetonitrile and stir evenly to obtain a first mixture, then add 8 g of the above diluted silica sol as an adhesive to the first mixture, ultrasonically disperse for 20 min to obtain a second mixture, and then add 2 g of ammonia with a concentration of 0.43 mol / L to the second mixture, continue to ultrasonically disperse for 20 min to prepare an aerogel wet gel with oxide nanocrystals as the skeleton.

[0074] ③ Gelation and aging

[0075] Place the prepared aerogel wet gel in a mold, stand for 24 h, and then place it in a 60°C oven for 48 h to complete the gelation and aging process.

[0076] ④ solvent exchange

[0077] The above gels after completion of gelation and aging were taken out and placed in 10 volumes of ethanol for solvent exchange, and the solvent exchange time was 3d, and the solvent exchange process was repeated 3 times.

[0078] ⑤ supercritical drying to obtain aerogel materials.

[0079] ⑥ heat treatment process

[0080] The above aerogel materials were heated to 1200℃ (heat treatment temperature) at a heating rate of 10℃ / min, and then cooled to room temperature after heat preservation for 1h (heat treatment time) to obtain high-temperature-resistant aerogel materials.

[0081] The performance indicators of the high-temperature-resistant aerogel materials in Examples 1-2 and Comparative Examples 1-10 are shown in Table 1.

[0082] Comparative Example 10 was designed according to patent CN19100410

[0083] Table 1: Performance indicators of the radiation-resistant aerogel materials prepared in Examples 1-2 and the high-temperature-resistant aerogel materials in Comparative Examples 1-10.

[0084]

[0085] Finally, it should be noted that the above examples are only used to illustrate the technical solutions of the present application, and not to limit them; although the present application has been described in detail with reference to the foregoing examples, those skilled in the art should understand that they can still modify the technical solutions recorded in the foregoing examples, or make equivalent replacements for part of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present application.

Claims

1. A method for efficient production of high temperature radiation resistant aerogel thermal insulation material, characterized by, The method comprises the following steps: (1) using a mixture of hydrochloric acid and sulfuric acid as an adsorbent, preparing alumina nanowire clusters with a diameter of 10-100 nm and a length of 100-800 μm through high-temperature hydrothermal reaction; (2) mixing the alumina nanowire clusters obtained in step (1) with an anti-radiation agent, homogeneously dispersing the mixture by using a kneader, rotating the kneader in two directions at a speed of 10-100 r / min, thereby obtaining a wet gel, wherein the anti-radiation agent accounts for 0.1-3% of the mass of the wet gel; (3) molding the alumina nanowire clusters containing the anti-radiation agent obtained in step (2), wherein the molding is performed in two steps, i.e., preliminarily forming by using a pressure of 0.5 MPa for 30 min and then shaping by using a pressure of 2 MPa for 20 min, thereby obtaining a wet gel block; (4) immersing the wet gel in step (3) in a mixed solution of methyltrimethoxysilane, ethanol, ammonia water and a solution of ammonium fluoride, setting a stirring magnet in the lower part of a bracket, and stirring at a speed of 100-300 r / min to promote solvent replacement and catalysis, thereby obtaining a composite gel, and standing for 6-24 h; (5) placing the composite gel obtained in step (4) in a 5-15-fold ethanol solution, a mixed solution of ethanol and a low-surface-energy solvent, and a pure low-surface-energy solvent respectively for 3-5 days to perform solvent replacement; (6) placing the composite gel obtained in step (5) in a special container to perform a subcritical drying process, thereby obtaining an aerogel material; (7) performing a low-temperature heat treatment process on the aerogel material obtained in step (6) in a nitrogen or argon atmosphere, thereby obtaining a lightweight anti-radiation aerogel, i.e., a high-temperature radiation-resistant aerogel thermal insulation material.

2. The production method according to claim 1, characterized by, In step (1), 1-30 g of alumina nanopowder with a particle size of 5-50 nm is dissolved in 10-200 mL of water, 0.1-2 g of a mixture of 0.001-1 mol / L hydrochloric acid and 0.001-1 mol / L sulfuric acid with a weight ratio of 1:1 is added as an adsorbent, and the mixture is reacted at 100-300 ℃ for 1-7 h, thereby obtaining alumina nanowires with a diameter of 10-100 nm and a length of 100-800 μm.

3. The preparation method according to claim 1, characterized in that The anti-radiation agent is a 1:1 mixture of silicon carbide and titanium oxide.

4. The method of claim 1, wherein, In step (4), the amount of the mixed solution is 2-5 times the volume of the block.

5. The preparation method according to claim 1, characterized in that The low-surface-energy solvent is petroleum ether, n-hexane or cyclohexane.

6. The method of claim 1, wherein, The special container in step (6) is made of metal, has a pressure-resistant closed structure, is provided with instruments and apparatus for regulating pressure, and is provided with a gas outlet.

7. The preparation method according to claim 1, characterized in that In step (4), in the mixed solution A, the concentration of methyltrimethoxysilane is 0.5-20 mass%, and the concentration of ammonia is 0.1-5 mass%; in the solution B, the concentration of ammonium fluoride is 0.05-0.5 mol / L.

8. The preparation method according to claim 1, characterized in that In step (4), the mass ratio of the mixed solution A to the solution B is 100:1-100:

20.

9. A high temperature resistant radiation aerogel thermal insulation material, characterized in that, It is prepared by the preparation method in any one of claims 1-8, and has a heat-resistant temperature of 1100-1400℃, a room-temperature thermal conductivity of 0.028-0.038 W / m·K, a 1000℃ thermal conductivity of 0.05-0.1 W / m·K, and a density of 0.1-0.3 g / cm 3 .

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