High-strength, low-thermal-conductivity and high-temperature-resistant silicon oxide aerogel-fiber composite material and preparation method thereof

Abstract

The invention discloses a high-strength, low-thermal-conductivity and high-temperature-resistant silicon oxide aerogel-fiber composite material and a preparation method thereof. The preparation method comprises the following steps: uniformly mixing large-particle-size acidic silicon oxide sol, an organic silicon source, an alcoholic solution and water; adding a catalyst into the obtained composite silicon oxide sol to promote gel polycondensation; laying a fiber felt in a mold, and dipping and filling the obtained composite silicon oxide sol into the fiber felt under a negative pressure condition; putting the obtained silicon oxide sol-fiber felt under a high-temperature condition for gelling and aging to obtain a silicon oxide gel-fiber composite material; and carrying out supercritical drying on the silicon oxide gel-fiber composite material to obtain the high-strength high-temperature-resistant silicon oxide aerogel composite material. The large-particle-size acidic alcohol silicon oxide sol and the organic silicon source are used as raw materials, and the prepared silicon oxide aerogel is low in heat conductivity coefficient, high in strength and good in temperature resistance.

Description

Technical Field

[0001] The present invention belongs to the technical field of aerogel materials, and particularly relates to a high-strength, low-thermal-conductivity, high-temperature-resistant silica aerogel-fiber composite material and a preparation method thereof. Background Art

[0002] Silica aerogel material is one of the several aerogel materials with the broadest applications in the field of thermal insulation materials at present. Silica aerogel material has an extremely low thermal conductivity and good heat preservation and insulation properties, and has good development prospects in many fields such as aerospace, automobile manufacturing, thermal insulation and sound insulation materials, nuclear energy, and military industry.

[0003] However, although silica aerogel has excellent heat insulation performance, currently, for conventional silica aerogel products, since the particle size of the formed nano-skeleton particles is usually only a few nanometers, the material will undergo relatively serious shrinkage when the temperature is above 650 °C, and the mechanical strength of the silica aerogel is relatively low, especially the compressive strength within 5% deformation, which is usually within 0.5 MPa. Therefore, its practical use is restricted.

[0004] In order to improve the mechanical properties of aerogel composite materials, the currently commonly used method is to increase the content of the reinforcing body (such as ceramic fibers) or increase the density of silica sol. The negative effect brought is that the overall density of the aerogel composite material is increased, and the thermal conductivity of the aerogel composite material increases significantly. How to balance high strength and low thermal conductivity is an urgent problem to be solved. Summary of the Invention

[0005] Aiming at the problems of easy sintering shrinkage and low mechanical strength of silica aerogel-fiber composite materials in the prior art at high temperatures, the present invention provides a high-strength, low-thermal-conductivity, high-temperature-resistant silica aerogel-fiber composite material and a preparation method thereof. The prepared aerogel composite material has good mechanical strength and low thermal conductivity, and has good high-temperature resistance in a high-temperature environment of 800 °C to 1100 °C.

[0006] The purpose of the present invention is achieved through the following technical solutions: A preparation method of a high-strength, low-thermal-conductivity, high-temperature-resistant silica aerogel-fiber composite material, comprising the following steps: S1. Mix a large-particle-size acidic alcohol-based silica sol, an organosilicon source, an alcohol solvent, and an acid catalyst, stir evenly, and stand for 0.5 h to 3 h to prepare a composite silica sol with alcohol as the solvent and containing two types of silica sols, wherein the solid content of the large-particle-size acidic alcohol-based silica sol is 5 wt% to 40 wt%, and the particle size of silica in the large-particle-size acidic alcohol-based silica sol is 15 nm to 50 nm; The ratio of the silicon content in the acidic alcohol-based silica sol to that in the organosilicon source is controlled at 1:(0.5 - 5), and the concentration of the acid solution is 0.1 mol / L - 1 mol / L; The molar ratio of the organosilicon source, water, and alcohol solvent is controlled at 1:(3 - 20):(3 - 30); The organosilicon source is one of tetraethyl orthosilicate, tetramethyl orthosilicate, tetrabutyl orthosilicate, and isopropyl orthosilicate; The alcohol solvent is selected from one of ethanol, isopropanol, n-propanol, sec-butanol, n-butanol, and methanol; The acid catalyst is selected from one of hydrochloric acid, oxalic acid, and hydrofluoric acid; S2. Add an alkali catalyst to the composite silica sol of the silica sol obtained in the upward step to promote gel polycondensation, and stir evenly to obtain a composite silica sol; The alkali catalyst is ammonia water or sodium hydroxide, and the concentration of the alkali catalyst solution is 0.1 mol / L - 2 mol / L; S3. Impregnate and fill the composite silica sol obtained in the above step into the laid fiber preform with a mold under negative pressure conditions, and maintain the pressure condition for ≥0.5 h to obtain a silica sol-fiber composite material; S4. Place the silica sol-fiber composite material obtained in the above step under high-temperature conditions for gelation and aging to obtain a silica gel-fiber composite material; S5. Perform supercritical drying on the silica gel-fiber composite material obtained in the above step to obtain a high-strength, low-thermal-conductivity, high-temperature-resistant silica aerogel-fiber composite material, which has the following properties: ① It has good mechanical strength. The compressive strength of the aerogel composite material with 3% deformation is 1.2 MPa - 4.5 MPa, and the compressive strength of the aerogel composite material with 5% deformation is 2.5 MPa - 6 MPa, which is 10 - 15 times that of the conventional silica aerogel composite material; ② The thermal conductivity at room temperature is 0.035 W / (m·K) - 0.041 W / (m·K), which is only increased by 1.3 - 2.2 times compared with the conventional silica aerogel composite material; ③ It has good heat resistance in a high-temperature environment of 800°C - 1100°C. After heat treatment at 1100°C for 2 h, the thickness shrinkage rate ≤5%.

[0007] Further, in step S3, the fiber in the fiber preform is one of glass fiber, aluminosilicate fiber, quartz fiber, mullite fiber, alumina fiber, and zirconia fiber.

[0008] Further, in step S4, the conditions for gelation and aging are as follows: the gel aging temperature is 40°C to 60°C, and the constant temperature is maintained for 12h to 72h.

[0009] The present invention also relates to a high-strength, low-thermal-conductivity, high-temperature-resistant silica aerogel-fiber composite material, which is obtained according to the preparation method of the above-mentioned high-strength, low-thermal-conductivity, high-temperature-resistant silica aerogel-fiber composite material, and has the following properties: ① It has good mechanical strength. The compressive strength of the aerogel composite material with 3% deformation is 1.2 MPa to 4.5 MPa, and the compressive strength of the aerogel composite material with 5% deformation is 2.5 MPa to 6 MPa, which is 10 to 15 times that of the conventional silica aerogel composite material; ② The thermal conductivity at room temperature is 0.035 W / (m·K) to 0.041 W / (m·K), which is only increased by 1.3 to 2.2 times compared with the conventional silica aerogel composite material; ③ It has good heat resistance in a high-temperature environment of 800°C to 1100°C. After heat treatment at 1100°C for 2h, the thickness shrinkage rate ≤ 5%.

[0010] Compared with the prior art, the present invention has the following advantages: 1. The preparation method of the high-strength, low-thermal-conductivity, high-temperature-resistant silica aerogel-fiber composite material of the present invention uses large-particle-size acidic alcohol-based silica sol, organosilicon source and ceramic fiber as raw materials. The preparation process of the method mainly includes sol preparation, sol impregnation, aging, and supercritical drying. The process is simple and easy to operate.

[0011] 2. The high-strength, low-thermal-conductivity, high-temperature-resistant silica aerogel-fiber composite material of the present invention has a low thermal conductivity, good mechanical strength, and good heat resistance in a high-temperature environment of 800 - 1100°C. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] The drawings are used to provide a further understanding of the present invention, and constitute a part of the specification. Together with the embodiments of the present invention, they are used to explain the present invention, and do not constitute a limitation to the present invention.

[0013] Figure 1 It is a process flow diagram of the preparation method of the high-strength, low-thermal-conductivity, high-temperature-resistant silica aerogel-fiber composite material of the present invention; Figure 2 It is a scanning electron micrograph (500 times) of the high-strength, low-thermal-conductivity, high-temperature-resistant silica aerogel-fiber composite material prepared in Example 1 of the present invention after heat treatment at 1100°C for 2h; Figure 3It is the scanning electron microscope image (10,000 times magnification) of the high-strength, low-thermal conductivity, high-temperature resistant silica aerogel-fiber composite prepared in Example 1 of the present invention after heat treatment at 1100 °C for 2 h; Figure 4 It is the scanning electron microscope image (500 times magnification) of the high-strength, low-thermal conductivity, high-temperature resistant silica aerogel-fiber composite prepared in Example 2 of the present invention after heat treatment at 1100 °C for 2 h; Figure 5 It is the scanning electron microscope image (10,000 times magnification) of the high-strength, low-thermal conductivity, high-temperature resistant silica aerogel-fiber composite prepared in Example 2 of the present invention after heat treatment at 1100 °C for 2 h. Detailed implementation manners

[0014] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0015] Example 1: As Figure 1 shown, a preparation method of a high-strength, low-thermal conductivity, high-temperature resistant silica aerogel-fiber composite includes the following steps: S1. Mix large-particle-size acidic alcohol-based silica sol, organosilicon source, alcohol solvent, and acid catalyst, stir evenly, and let stand for 0.5 h to prepare a composite silica sol with alcohol as the solvent and containing two types of silica sols. The solid content of the large-particle-size acidic alcohol-based silica sol is 5 wt%, and the particle size of silica in the large-particle-size acidic alcohol-based silica sol is 15 nm to 50 nm; The ratio of the silicon content in the acidic alcohol-based silica sol and the organosilicon source is controlled at 1:1, and the concentration of the acid solution is 0.1 mol / L; The molar ratio of the organosilicon source, water, and alcohol solvent is controlled at 1:16:10; The organosilicon source is tetraethyl orthosilicate; The alcohol solvent is selected from ethanol solvent; The acid catalyst is hydrochloric acid; S2. Add an alkali catalyst to the composite silica sol obtained in the previous step to promote gel polycondensation, stir evenly, and obtain a composite silica sol; The alkali catalyst is an ammonia water solution with a concentration of 0.1 mol / L; S3. Impregnate and fill the composite silica sol obtained in the above step into the laid fiber preform with a mold under negative pressure conditions, and maintain the pressure condition for ≥0.5 h to obtain a silica sol-fiber composite material; The fiber in the fiber preform is mullite fiber; S4. Place the silica sol-fiber composite material obtained in the above step under high-temperature conditions for gelation and aging. The conditions for gelation and aging are: the gel aging temperature is 40 °C, and keep the temperature constant for 72 h to obtain a silica gel-fiber composite material; S5. Perform supercritical drying on the silica gel-fiber composite material obtained in the above step to obtain a high-strength, low-thermal conductivity, high-temperature resistant silica aerogel-fiber composite material.

[0016] The obtained high-strength, low-thermal conductivity, high-temperature resistant silica aerogel-fiber composite material has good mechanical strength. The compressive strength of the aerogel composite material with a 3% deformation is 3.5 MPa to 4 MPa, the thermal conductivity at room temperature is 0.041 W / (m·K), and it has good heat resistance in a high-temperature environment of 800 °C to 1100 °C; Figure 2 and Figure 3 are the scanning electron microscope images with magnifications of 500 and 10,000 times respectively of the high-strength, low-thermal conductivity, high-temperature resistant silica aerogel-fiber composite material prepared in Example 1 after heat treatment at 1100 °C for 2 h. The thickness shrinkage rate after heat treatment at 1100 °C for 2 hours is 2.8%.

[0017] Example 2: A preparation method of a high-strength, low-thermal conductivity, high-temperature resistant silica aerogel-fiber composite material, comprising the following steps: S1. Mix large-particle-size acidic alcohol-based silica sol, organosilicon source, alcohol solvent, and acid catalyst, stir evenly, and let stand for 3 h to prepare a composite silica sol containing two types of silica sols with alcohol as the solvent. The solid content of the large-particle-size acidic alcohol-based silica sol is 30 wt%, and the particle size of silica in the large-particle-size acidic alcohol-based silica sol is 15 nm to 50 nm; The ratio of the silicon content in the acidic alcohol-based silica sol to the organosilicon source is controlled at 1:2.5, and the concentration of the acid solution is 0.5 mol / L; The molar ratio of the organosilicon source, water, and alcohol solvent is controlled at 1:12:10; The organosilicon source is tetraethyl orthosilicate; The alcohol solvent is selected from isopropyl alcohol; The acid catalyst is oxalic acid; S2. Add an alkali catalyst to the composite silica sol of the silica sol obtained in the upward step to promote gel polycondensation, stir evenly to obtain a composite silica sol; The alkali catalyst is a sodium hydroxide solution with a concentration of 2 mol / L; S3. Impregnate and fill the composite silica sol obtained in the above step into the laid fiber preform with a mold under negative pressure conditions, and maintain the pressure condition for ≥ 0.5 h to obtain a silica sol-fiber composite material; The fiber in the fiber preform is a zirconia fiber; S4. Place the silica sol-fiber composite material obtained in the above step under high temperature conditions for gelation and aging. The conditions for gelation and aging are: the gel aging temperature is 60 °C, and keep the temperature constant for 12 h to obtain a silica gel-fiber composite material; S5. Perform supercritical drying on the silica gel-fiber composite material obtained in the above step to obtain a high-strength, low thermal conductivity, high-temperature resistant silica aerogel-fiber composite material.

[0018] The obtained high-strength, low thermal conductivity, high-temperature resistant silica aerogel-fiber composite material has good mechanical strength. The compressive strength of the aerogel composite material with 5% deformation is between 1.2 MPa and 1.8 MPa, the thermal conductivity at room temperature is 0.037 W / (m·K), and the prepared composite material has good heat resistance in a high-temperature environment of 800 °C to 1100 °C; Figure 4 and Figure 5 are the scanning electron microscope images with magnifications of 500 and 10,000 times respectively of the high-strength, low thermal conductivity, high-temperature resistant silica aerogel-fiber composite material prepared in Example 1 after heat treatment at 1100 °C for 2 h. The thickness shrinkage rate after heat treatment at 1100 °C for 2 hours is 4.6%.

[0019] Example 3: A preparation method of a high-strength, low thermal conductivity, high-temperature resistant silica aerogel-fiber composite material, comprising the following steps: S1. Mix a large-particle-size acidic alcohol-based silica sol, an organosilicon source, an alcohol solvent, and an acid catalyst, stir evenly, and stand for 2 h to prepare a composite silica sol containing two types of silica sols with alcohol as the solvent. The solid content of the large-particle-size acidic alcohol-based silica sol is 15 wt%, and the particle size of silica in the large-particle-size acidic alcohol-based silica sol is 15 nm to 50 nm; The ratio of the silicon content in the acidic alcohol-based silica sol to the organosilicon source is controlled at 1:5, and the concentration of the acid solution is 1 mol / L; The molar ratio of the organosilicon source, water, and alcohol solvent is controlled at 1:8:5; The silicone source described above is isopropyl orthosilicate; The alcohol solvent described above is selected from n-butanol; The acid catalyst described above is hydrofluoric acid; S2. Add an alkali catalyst to the composite silica sol of the silica sol obtained in the upward step to promote gel condensation, and stir evenly to obtain a composite silica sol; The alkali catalyst described above is a sodium hydroxide solution with a concentration of 1 mol / L; S3. Impregnate and fill the composite silica sol obtained in the above step into the laid fiber preform with a mold under negative pressure conditions, and maintain the pressure conditions for ≥ 0.5 h to obtain a silica sol-fiber composite material; The fiber in the fiber preform described above is quartz fiber; S4. Place the silica sol-fiber composite material obtained in the above step under high temperature conditions for gelation and aging. The conditions for gelation and aging are: the gel aging temperature is 50 °C, and keep the temperature constant for 48 h to obtain a silica gel-fiber composite material; S5. Perform supercritical drying on the silica gel-fiber composite material obtained in the above step to obtain a high-strength, low-thermal conductivity, high-temperature resistant silica aerogel-fiber composite material.

[0020] The obtained high-strength, low-thermal conductivity, high-temperature resistant silica aerogel-fiber composite material has good mechanical strength. The compressive strength of the aerogel composite material with 5% deformation is 1.8 MPa - 2.3 MPa, the thermal conductivity at room temperature is 0.035 W / (m·K), and the prepared composite material has good temperature resistance in a high-temperature environment of 800 °C - 1100 °C. The thickness shrinkage rate after heat treatment at 1100 °C for 2 hours is 3.2%.

[0021] Comparative Example 1: The difference between Comparative Example 1 and Example 1 is that the particle size of silica in step S1 is 3 nm - 5 nm, and the others are the same as in Example 1; For the obtained silica aerogel-fiber composite material, the compressive strength of the aerogel composite material with 3% deformation is 1.2 MPa - 2 MPa, the thermal conductivity at room temperature is 0.040 W / (m·K), and obvious collapse occurred in the thickness direction of the prepared composite material after heat treatment at 1100 °C for 2 hours.

[0022] The results show that: in Comparative Example 1, replacing the large-particle-size silica sol in Example 1 with a small-particle-size silica sol, the temperature resistance of the prepared thermal insulation material is significantly reduced, and the compressive performance shows an obvious decline. Finally, when the particle sizes of the formed silica aerogel particles are similar, they cannot play a role in supporting each other, resulting in a decline in the compressive performance of the thermal insulation material.

[0023] Comparative Example 2: The difference between Comparative Example 2 and Example 1 lies in the different molar ratios (1:21:31) of the silicone source, water, and alcohol solvent in step S1, and the others are the same as in Example 1; The results show that the intact and blocky silica aerogel-fiber composite material cannot be obtained in Comparative Example 2, indicating that the molar ratios of the silicone source, water, and alcohol have a significant impact on the cross-linking, polycondensation, and final structure of the silica aerogel.

[0024] Comparative Example 3: The difference between Comparative Example 3 and Example 1 lies in that no silicone source is added in step S1, and an acidic silica sol with a particle size of 15 - 50 nm and the same silicon content is used to replace the silicone source, and the others are the same as in Example 1; For the obtained silica aerogel-fiber composite material, the compressive strength of the aerogel composite material with 3% deformation is within 0.3 MPa, the thermal conductivity at room temperature is 0.047 W / (m·K), and the thickness shrinkage rate of the composite material after heat treatment at 1100 °C for 2 hours is 2.1%.

[0025] The results show that using only large-particle-size silica sol to prepare the aerogel thermal insulation material in Comparative Example 3 has good heat resistance, but the compressive performance and thermal insulation performance of the material are significantly lower than those of the aerogel thermal insulation material prepared by combining silica sols with different particle sizes.

[0026] Results and Discussion: 1. In the examples of the present invention, large-particle-size alcohol-based acidic silica sol and silicone sol of two types are used as raw materials. The ratio of water and alcohol solvent (any one of ethanol, isopropanol, n-propanol, sec-butanol, n-butanol, and methanol) is adjusted, and then an acid catalyst is added to fully hydrolyze the silicone source (one of tetraethyl orthosilicate, tetramethyl orthosilicate, tetrabutyl orthosilicate, and isopropyl orthosilicate). Then, an appropriate amount of base catalyst is added to promote the polycondensation of the sol. Under negative pressure conditions, it is impregnated and filled into the laid fiber preform with a mold. After aging the gel, it is directly subjected to high-temperature supercritical drying without a solvent replacement process. The process is simple and easy to operate. The prepared high-strength and high-temperature-resistant silica aerogel-fiber composite material has good mechanical properties and good heat resistance in a high-temperature environment of 800 - 1100 °C.

[0027] 2. In step S1 of the present invention, large-particle-size alcohol-based acidic silica sol is used. The particle size of silica in the large-particle-size acidic alcohol-based silica sol is 15 - 50 nm, which is much larger than the particle size of conventional silica aerogel (about 3 - 5 nm). Introducing large-particle-size silica sol can increase the size of the unit particles in the finally prepared silica aerogel, reduce the surface energy of the material, so that it is not easy to sinter at high temperatures, inhibit the structural shrinkage of small-particle-size silica, and increase the use temperature of the silica aerogel, having more excellent high-temperature resistance.

[0028] 3. In step S1 of the present invention, a large-particle-size alcohol-based acidic silica sol and an organosilicon source (any one of tetraethyl orthosilicate, tetramethyl orthosilicate, tetrabutyl orthosilicate, and isopropyl orthosilicate) are compounded. By controlling the ratio of water, alcohol, and the organosilicon source, the particle size and pore structure of the gel formed after hydrolysis and polycondensation of the organosilicon source are adjusted. Using an alcohol-based silica sol instead of an aqueous silica sol is because the alcohol-based solvent can ensure that it will not directly undergo a hydrolysis reaction with the organosilicon source after mixing, but rather controls the hydrolysis rate of the silicon source by subsequently controlling the amount and addition method of water. On the other hand, the alcohol-based solvent can directly undergo supercritical drying without a solvent replacement process, simplifying the production process. Selecting an acidic silica sol and adding an appropriate amount of acid catalyst after mixing the organosilicon source, solvent, and water is to maintain the stability of the solvent and avoid obvious changes in the pH value of the sol, which may lead to the gelation or precipitation of silica. Additionally, an acidic condition is beneficial to the hydrolysis of the organosilicon source. If the added acid concentration is too low, an excessive amount of solvent will be introduced, and if the concentration is too high, it is easy to cause a too-high local concentration. Therefore, in step S1 of the present invention, the molar ratio of the organosilicon source, water, and alcohol solvent is controlled at 1:(3 - 8):(3 - 30); the acid solution concentration is 0.1 - 1 mol / L.

[0029] The composite silica sol (large-particle-size alcohol-based acidic silica sol and organosilicon source) can prevent the silica aerogel finally prepared from undergoing structural collapse at high temperatures, improving its heat resistance; at the same time, the structure formed by the interlaced and mutually supported filling of large particles of silica and small particles of silica greatly improves the mechanical strength of the aerogel and its composites; furthermore, the aerogel with a complete chain structure formed by the hydrolysis and polycondensation of the organosilicon source ensures the low thermal conductivity and blockability of the composite aerogel. When the proportion of one of the two types of silica sols is too high, the improvement of the mechanical strength of the prepared aerogel and its composites is limited; the higher the proportion of silica in the acidic alcohol-based silica sol and the larger the particle size, the higher the heat resistance of the aerogel and its composites, but too large a particle size of silica is not conducive to the formation of a stable sol, and the thermal conductivity of the prepared aerogel and its composites is higher. Therefore, the solid content of silica in the alcohol-based silica sol used in the present invention is 5 - 40 wt%, the particle size of silica is 15 - 50 nm, and the ratio of the silica content in the acidic alcohol-based silica sol to the organosilicon source is controlled at 1:(0.5 - 5).

[0030] 4. In step S3 of the present invention, one or more of glass fiber, quartz fiber, mullite fiber, alumina fiber, and zirconia fiber are selected as the reinforcement. For the aerogel composite material, the heat resistance of the fiber and the aerogel should both meet the usage requirements. Therefore, ceramic fibers that can withstand 800 - 1100 °C for a long time are selected as the reinforcement phase to prepare the composite material.

[0031] In addition, it should be understood that although this specification is described according to embodiments, not every embodiment only contains an independent technical solution. This narrative way of the specification is only for clarity. Those skilled in the art should regard the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A method for preparing a high-strength, low-thermal-conductivity, high-temperature-resistant silica aerogel-fiber composite material, characterized in that: The following steps are involved: S1. A large-particle acidic alcohol-based silica sol, an organic silicon source, an alcohol solvent and an acid catalyst are mixed, stirred evenly, and allowed to stand for 0.5 h to 3 h to prepare a composite silica sol containing two types of silica sols with alcohol as a solvent, wherein the large-particle acidic alcohol-based silica sol has a solid content of 5 wt% to 40 wt%, and the particle size of silicon oxide in the large-particle acidic alcohol-based silica sol is 15 nm to 50 nm; The ratio of the silicon content in the acidic alcohol-based silica sol to that in the organic silicon source is controlled at 1:(0.5-5), and the concentration of the acid solution is 0.1 mol / L-1 mol / L; The molar ratio of the organic silicon source, water and alcohol solvent is controlled at 1:(3-20):(3-30); The organic silicon source is one of ethyl orthosilicate, methyl orthosilicate, butyl orthosilicate and isopropyl orthosilicate; The alcohol solvent is selected from ethanol, isopropanol, n-propanol, sec-butanol, n-butanol and methanol; The acid catalyst is selected from one of hydrochloric acid, oxalic acid and hydrofluoric acid; S2, adding a base catalyst to the composite silica sol of the silica sol obtained in the above step to promote gel polycondensation, stirring evenly to obtain a composite silica sol; The alkaline catalyst is ammonia water or sodium hydroxide, and the concentration of the alkaline catalyst solution is 0.1 mol / L to 2 mol / L; S3, impregnating the composite silica sol obtained in the previous step into the laid fiber preform with a mold under negative pressure conditions, maintaining the pressure conditions for ≥0.5h, to obtain a silica sol-fiber composite material; S4, placing the silica sol-fiber composite material obtained in the above step under high temperature conditions for gelation and aging to obtain a silica gel-fiber composite material; S5. Supercritical drying the silica gel-fiber composite material obtained in the above step to obtain a high-strength, low-thermal-conductivity, high-temperature-resistant silica aerogel-fiber composite material having the following properties: ① It has good mechanical strength. The compressive strength of the aerogel composite material with 3% deformation is 1.2MPa~4.5MPa, and the compressive strength of the aerogel composite material with 5% deformation is 2.5MPa~5MPa; ②The thermal conductivity at room temperature is 0.035 W / (m·K)~0.041 W / (m·K); ③ It has good heat resistance in high temperature environment of 800℃~1100℃. After heat treatment at 1100℃ for 2h, the thickness shrinkage rate is ≤5%.

2. The method for preparing a high-strength, low-thermal-conductivity, high-temperature-resistant silica aerogel-fiber composite material according to claim 1, characterized in that: In step S3, the fiber in the fiber preform is one of glass fiber, aluminum silicate fiber, quartz fiber, mullite fiber, alumina fiber and zirconia fiber.

3. The method for preparing a high-strength, low-thermal-conductivity, high-temperature-resistant silica aerogel-fiber composite material according to claim 1, characterized in that: In step S4, the gelling and aging conditions are as follows: the gelling aging temperature is 40° C. to 60° C. and the temperature is kept constant for 12 h to 72 h.

4. A high-strength, low-thermal-conductivity, high-temperature-resistant silica aerogel-fiber composite material, characterized in that: The method for preparing a high-strength, low-thermal-conductivity, high-temperature-resistant silica aerogel-fiber composite material according to any one of claims 1 to 3 has the following properties: ① It has good mechanical strength. The compressive strength of the aerogel composite material with 3% deformation is 1.2MPa~4.5MPa, and the compressive strength of the aerogel composite material with 5% deformation is 2.5MPa~6MPa; ②The thermal conductivity at room temperature is 0.035 W / (m·K)~0.041 W / (m·K); ③ It has good heat resistance in high temperature environment of 800℃~1100℃. After heat treatment at 1100℃ for 2h, the thickness shrinkage rate is ≤5%.

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