Low-cost lightweight high-strength aerogel thermal insulation material and preparation method thereof

Abstract

The present application relates to a kind of low-cost light high-strength aerogel thermal insulation material and its preparation method, the method is: the preparation of a certain length-diameter ratio alumina nanowire cluster by hydrothermal method;Alumina nanowire cluster is molded into shape, and the block after molding is placed in silane-based precursor solution containing catalyst;Subsequently, aging process is carried out;Gradient solvent replacement is carried out;Subsequently, subcritical drying and heat treatment process are carried out.The present application uses high length-diameter ratio alumina nanowire to carry out three-dimensional jointing, and uses silane-based precursor to be modified, realizes the preparation of low-cost, light, efficient thermal insulation and high-temperature resistant aerogel.Under the action of high temperature, the self-supporting effect of nanometer skeleton makes nanometer aerogel have the characteristics of low cost, ultra-light, high porosity, 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 low-cost light-weight high-strength aerogel thermal insulation material and a preparation method thereof. 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 conduction, solid phase conduction and thermal radiation can be effectively reduced. It has been proved in the existing research that aerogel is an effective thermal insulation material.

[0003] The existing high-temperature-resistant aerogels mainly include carbon aerogel, ceramic aerogel, silica aerogel, alumina aerogel and zirconia aerogel. Carbon aerogel and ceramic aerogel have good high-temperature resistance, but their application is limited, i.e. they can only be used for thermal insulation above 1400℃ in an oxygen-free environment, and there is no effective way to overcome the oxidation resistance of carbon aerogel and ceramic aerogel. The oxide aerogels such as silica, alumina and zirconia will undergo serious crystal transformation and sintering at high temperature, resulting in structure collapse, nanometer particle growth and pore reduction, thereby causing the specific surface area of the aerogel to decrease sharply and the thermal insulation performance to weaken greatly, resulting in thermal insulation failure. At the same time, the traditional aerogel is brittle, and the mechanical strength needs to be improved through fiber reinforcement, so the light-weight characteristics of the aerogel composite material in actual application cannot be fully played.

[0004] 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 resistance, the heat-resistant temperature is above 1000℃, and it can even withstand high temperature above 1300℃, the aerogel material will still undergo a series of phase changes above 1200℃, so that the specific surface area after high-temperature heat treatment is less than 100 m 2 / g, and therefore the high-temperature thermal insulation performance of the aerogel material is not very good.

[0005] Chinese patent CN201910630467.7 discloses a preparation method of a high-temperature-resistant special-shaped nanocrystal aerogel material. The method uses nanorods and silica sol to prepare a special-shaped nanocrystal aerogel material. The material has good temperature resistance and can withstand a temperature limit of 1400°C. However, the material preparation process requires sol-gel process, aging and solvent replacement, supercritical drying and other steps, greatly increasing the complexity of preparation and prolonging the material preparation cycle. Therefore, the present invention can make up for the shortcomings of the patent and prepare high-temperature-resistant aluminum oxide nanometer aerogel under simple preparation steps.

[0006] From the cost point of view, the preparation of traditional aerogel materials mostly depends on supercritical drying equipment, and the process is complex and the cost is high, 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, which makes the porosity and specific surface area of the material decrease significantly, and the bulk density and heat insulation efficiency of the material decrease greatly. 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 nanofibers with aluminum boron silica sol to construct nanofiber aerogel through freeze drying method, and the temperature resistance can reach 1100°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 μm pores will cause serious gas phase heat conduction and heat convection of the material, and the overall heat insulation performance is lower than that of typical aerogel materials, which limits its engineering application in aerospace and other fields.

[0007] 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. In addition, strict restrictions are also put on cost and cycle. Therefore, it is very necessary to develop an effective method to prepare aerogel materials with low cost, light weight and high efficient heat insulation. SUMMARY

[0008] In order to solve the technical problems in the prior art, the application provides a low-cost, material high-temperature-resistant, light aerogel thermal insulation material and a preparation method thereof.

[0009] The application provides a low-cost, light, high-strength aerogel thermal insulation material and a preparation method thereof in a first aspect.

[0010] (1) Dissolve 1-30 g of aluminum oxide nano powder (particle size 5-50 nm) in 10-200 mL of water, add 0.001-1 mol / L of a mixed solution of hydrochloric acid and sulfuric acid (weight ratio 1:1) as a catalyst (0.1-2 g) at 100-300 DEG C for 1-7 h to obtain aluminum oxide nanowires with a diameter of 10-100 nm and a length of 100-800 μm.

[0011] (2) Place the aluminum oxide nanoclusters obtained in step (1) in a mold for pre-laying and then perform mold pressing, which is divided into two steps, i.e., first, preliminary forming is performed at a pressure of 0.1-2 MPa for 5-30 min, and then, setting is performed at a pressure of 1-5 MPa for 1-20 min.

[0012] (3) Dip the wet gel in step (2) 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), set a stirring magnet in the lower part of the bracket, and stir at 100-300 r / min to promote solvent replacement and catalysis, so as to obtain a composite gel, and then stand for 6-24 h.

[0013] In step (3), 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 the solution (B) is 0.05-0.5 mol / L.

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

[0015] (5) Put the composite gel obtained in step (4) into a specific container for a subcritical drying process, the container is a pressure-resistant closed structure, metal material, and is provided with instruments for regulating pressure and a gas exhaust port. The container with the wet gel block is sealed and placed in an oven at 40-80 DEG C for heating for 1-12h, then the exhaust valve is opened for 5-30min for gas exchange. The heating and degassing steps are repeated for 5-10 times. Then the dried gel is taken out and placed at room temperature and normal pressure for 24-72h.

[0016] (6) The aerogel obtained in step (5) is subjected to a heat treatment process at 400-800 DEG C to obtain a high-temperature-resistant alumina aerogel.

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

[0018] The present application provides a low-cost lightweight high-strength aerogel thermal insulation material prepared by the preparation method described in the first aspect of the present application.

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

[0020] (1) Unlike other doping modification and other high-temperature-resistant aerogel thermal insulation materials prepared by doping modification, the present study uses long nanowires as the main unit for assembly process. The nanowires prepared in the typical examples have a diameter of 20-50 nm and a length of 100-800 mu m, 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 cluster 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 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 on the one hand improves the heat transfer path, reduces the gas phase heat conduction process, and effectively improves the thermal insulation efficiency of the nanometer aerogel; on the other hand, the hydrophobic skeleton can reduce the interfacial tension during the drying process, which is beneficial to the subcritical drying process.

[0023] (4) The nanowire has a self-supporting and self-toughening effect, which eliminates the fiber reinforcement process of traditional aerogel composites, and the lightweight performance of the present application is improved by more than 50% compared with similar aerogel products.

[0024] (5) The self-supporting effect of the nanowire skeleton 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 skeleton while realizing the construction of a high porosity skeleton. The subcritical drying process can effectively reduce costs and reduce dependence on large equipment. BRIEF DESCRIPTION OF DRAWINGS

[0025] Figure 1 is a preparation flow chart of the present application.

[0026] Figure 2 is a real object diagram of the nanogel prepared in Example 1.

[0027] Figure 3 is a SEM diagram of the aerogel prepared in Example 1.

[0028] Figure 4 is an EDS spectrum diagram of the aerogel prepared in Example 1. DETAILED DESCRIPTION

[0029] In order to make the objects, technical solutions and advantages of the present application clearer, the technical solutions 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 of ordinary skill in the art without making creative efforts fall within the scope of protection of the present application.

[0030] The present application provides, in a first aspect, a low-cost lightweight high-strength aerogel thermal insulation material and a preparation method thereof, the method comprising the following steps:

[0031] 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.

[0032] Example 1

[0033] (1) Dissolve 6 g of alumina nano powder (particle size 20 nm) in 100 mL of water, add 1 g of 0.02 mol / L hydrochloric acid and sulfuric acid (1:1) as a catalyst, and react at 220°C for 7 h to obtain clusters of alumina nanowires with a diameter of 50 nm and a length of 100-800 μm.

[0034] (2) The alumina nanowire clusters obtained in step (1) are placed in a mold for pre-laying and then molded, which is carried out in two steps, first preliminary forming at a pressure of 0.5 MPa for 30 min, and then shaping at a pressure of 2 MPa for 20 min;

[0035] (3) methyltrimethoxysilane was dissolved in ethanol (2% by mass) and ammonia water was added as a catalyst (0.1% by mass) and stirred for 10 min to obtain solution A, 0.1 mol / L ammonium fluoride was added as a catalyst (solution B), the above solution was stirred, the mass ratio of solution A and solution B was 100:1, and stirring was performed for 10 min to obtain a mixed solution C, the wet gel in (2) was immersed in solution C for gelation reaction. A stirring magnet was arranged at the lower part of the bracket, and stirring was performed at 100 r / min, and the gel was left to stand for 12 h to promote solvent replacement and catalysis, thereby obtaining a composite gel;

[0036] (4) the composite gel obtained in step (3) was replaced with 10 times the solvent, and the solvent was an ethanol solution, an ethanol and cyclohexane mixed solvent, and a cyclohexane mixed solvent, respectively, for 3 days.

[0037] (5) the composite gel obtained in step (4) was placed in a special container for a subcritical drying process, the container was a pressure-resistant closed structure made of metal, instruments for regulating pressure were arranged, and a gas outlet was arranged. The container with the wet gel block was sealed and placed in an oven at 50°C for heating for 2 h, then the exhaust valve was opened for 20 min for gas exchange. The heating and exhaust steps were repeated 6 times. Then the dried gel was taken out and left to stand at room temperature and normal pressure for 24 h.

[0038] (6) the aerogel obtained in step (5) was subjected to a 500°C heat treatment process to obtain a high-temperature-resistant aluminum oxide aerogel.

[0039] The prepared aerogel has a heat-resistant temperature of 1400°C, a room-temperature thermal conductivity of 0.028 W / m·K, and a density of 0.12 g / cm 3 .

[0040] Example 2

[0041] Example 2 is basically the same as Example 1, except that the aluminum oxide nano-powder in step 1 is 20 g.

[0042] The thermal insulation performance of the aluminum oxide aerogel material in Example 2 was tested, and it was found that the surface of the aerogel material had no discoloration, and no block fell off when touched lightly, and other performance indicators are shown in Table 1.

[0043] Comparative Example 1

[0044] Comparative Example 1 is basically the same as Example 1, except that the molding process in step 2 does not go through a step-by-step molding.

[0045] The thermal insulation performance of the aluminum oxide aerogel material in Comparative Example 1 was tested, and it was found that the surface of the aerogel material had micro-cracks, and block fell off when touched lightly, and other performance indicators are shown in Table 1.

[0046] Comparative Example 2

[0047] Comparative Example 2 is substantially the same as Example 1, except that step 2 is not performed.

[0048] 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 was deformed to some extent. Other performance indicators are shown in Table 1.

[0049] Comparative Example 3

[0050] Comparative Example 3 is substantially the same as Example 1, except that step 4 is not performed with multiple solvent replacement, but with single ethanol solvent replacement.

[0051] The thermal insulation performance of the alumina aerogel material in Comparative Example 3 was tested, and it was found that the aerogel material had cracks on the surface and the overall shape was deformed compared to the wet gel. Other performance indicators are shown in Table 1.

[0052] Comparative Example 4

[0053] Comparative Example 4 is substantially the same as Example 1, except that the drying process in step 5 is performed at normal pressure instead of a subcritical drying process.

[0054] The thermal insulation performance of the alumina aerogel material in Comparative Example 4 was tested, and it was found that the aerogel material had cracks on the surface and the overall shape was deformed compared to the wet gel. Other performance indicators are shown in Table 1.

[0055] Comparative Example 5

[0056] Comparative Example 5 is substantially the same as Example 1, except that the prepared aerogel does not undergo the final heat treatment process.

[0057] The alumina aerogel in Comparative Example 5 has a smooth surface without cracking and falling off problems.

[0058] Comparative Example 6

[0059] Comparative Example 6 is substantially the same as Example 1, except that a 13 nm diameter spherical nanocrystal solution is used instead of nanowire clusters in step 1 for the molding process, and the subsequent steps are the same.

[0060] The results show that the material obtained is a powder rather than an aerogel block.

[0061] Comparative Example 7

[0062] Comparative Example 7 is substantially the same as Example 1, except that the molding process in step 2 is not performed.

[0063] The prepared material was found to have a large number of pores inside the material during SEM testing, causing defects.

[0064] Comparative Example 8

[0065] ① Sol preparation

[0066] 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, which 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 at 70°C, and reflux for 30 min to obtain a siliceous sol precursor first solution; add 160 g of methyl orthosilicate to the obtained siliceous sol precursor first solution, continue to heat and magnetically stir at 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 obtain a diluted siliceous sol, which is stored in the refrigerator for later use.

[0067] ② Nanocrystal assembly process

[0068] Dissolve 3.7 g of alumina 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 a binder to the first mixture, ultrasonically disperse for 20 min to obtain a second mixture, and then add 2 g of ammonia water 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.

[0069] ③ Gelation and aging

[0070] Place the prepared aerogel wet gel in a mold and let it stand for 24 h, then place it in a 60°C oven for 48 h to complete the gelation and aging process.

[0071] ④ Solvent replacement

[0072] After the above gelation and aging process is completed, take out the gel and place it in 10 times the volume of ethanol for solvent replacement, and the solvent replacement time is 3 d, and the solvent replacement process is repeated 3 times.

[0073] ⑤ Supercritical drying to prepare an aerogel material.

[0074] ⑥ Heat treatment process

[0075] Heat the above aerogel material to 1200°C (heat treatment temperature) at a rate of 10°C / min, and then cool to room temperature after holding for 1 h (heat treatment time) to obtain a high-temperature-resistant aerogel material.

[0076] The performance indexes of the aerogel materials in Examples 1-2 and Comparative Examples 1-8 are shown in Table 1.

[0077] Comparative Example 9 is designed according to patent CN19100410

[0078] Table 1: Performance indexes of the alumina aerogel materials prepared in Examples 1-2 and the high-temperature-resistant aerogel materials in Comparative Examples 1-9.

[0079]

[0080] 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 substitutions for part of the technical features; and these modifications or substitutions 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 of making an aerogel thermal insulation material, characterized by, The method comprises the following steps: (1) using a mixed solution of hydrochloric acid and sulfuric acid as a catalyst, preparing alumina nanowire clusters with a diameter of 10-100 nm and a length of 100-800 μm through high-temperature hydrothermal reaction at 100-300 °C; (2) performing die pressing on the alumina nanowire clusters obtained in step (1), which is performed in two steps, i.e., first performing preliminary forming by pressing at a pressure of 0.5 MPa for 30 min, and then performing setting by pressing at a pressure of 2 MPa for 20 min, so as to obtain a wet gel block; (3) immersing the wet gel in step (2) in a mixed solution of a mixed solution A of methyltrimethoxysilane, ethanol and ammonia water and a solution B of ammonium fluoride, setting a stirring magnet in the lower part of a bracket, and stirring at 100-300 r / min to promote solvent replacement and catalysis, so as to obtain a composite gel, and standing for 6-24 h; (4) placing the composite gel obtained in step (3) in 5-15 times of ethanol solution, a mixed solution of ethanol and a low-surface-energy solvent, and pure low-surface-energy solvent respectively for 3-5 days to perform solvent replacement; (5) placing the composite gel obtained in step (4) in a specific container to perform a subcritical drying process, so as to obtain an aerogel material; (6) performing a low-temperature heat treatment process at 400-800 °C on the aerogel material obtained in step (5), so as to obtain a high-temperature-resistant alumina aerogel, i.e., an aerogel thermal insulation material.

2. The production method according to claim 1, characterized by, In the 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 mixed solution 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 a catalyst, and reaction is performed at 100-300 °C for 1-7 h, so as to obtain alumina nanowire clusters 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, In step (3), the amount of the mixed solution of methyltrimethoxysilane, ethanol and ammonia water in solution A and the solution B of ammonium fluoride is 2-5 times of the volume of the block.

4. The method of claim 1, wherein, The low-surface-energy solvent is petroleum ether, n-hexane or cyclohexane.

5. The preparation method according to claim 1, characterized in that, The specific container in step (5) is made of metal, has a pressure-resistant closed structure, is provided with instruments and meters for regulating pressure, and is provided with a gas discharge port.

6. The method of claim 1, wherein, In step (3), in the mixed solution A, the concentration of methyltrimethoxysilane is 0.5-20 mass%, and the concentration of ammonia is 0.1-5 mass%, and in the solution B, the concentration of ammonium fluoride is 0.05-0.5 mol / L.

7. The preparation method according to claim 1, characterized in that, In step (3), the mass ratio of the mixed solution A to the solution (B) is 100:1-100:

20.

8. Aerogel thermal insulation material, characterized in that The aerogel thermal insulation material obtained by the preparation method in any one of claims 1-7 has a heat-resistant temperature of 1100-1400℃, a room-temperature thermal conductivity of 0.028-0.038 W / m·K, and a density of 0.1-0.3 g / cm 3 .

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