A high-temperature resistant, thermally insulating, and electrically controllable fiber-reinforced aerogel composite material and its preparation method.

Abstract

This invention discloses a high-temperature resistant, heat-insulating, and electrically controllable fiber-reinforced aerogel composite material and its preparation method. Silicon carbide fibers are subjected to plasma surface treatment and then added to a nano-dispersion liquid to obtain a fiber suspension. The fiber suspension is then dehydrated, shaped, dried, and cured to obtain silicon carbide fiber felt. Tetraethyl orthosilicate and ethanol are mixed to obtain a mixed solution. Concentrated sulfuric acid and ammonia are added sequentially to the mixed solution to form a sol. The silicon carbide fiber felt is immersed in the sol and allowed to stand, followed by gel aging to obtain a silicon carbide fiber felt-silica wet gel composite material. This silicon carbide fiber felt-silica wet gel composite material is then immersed in an organic solvent for hydrophobic modification, followed by drying to obtain the fiber-reinforced aerogel composite material. The composite material of this invention possesses high temperature resistance, high sound insulation, low density, and low thermal conductivity.

Description

Technical Field

[0001] This invention relates to a high-temperature resistant, heat-insulating, and electrically controllable fiber felt-reinforced aerogel composite material and its preparation method, belonging to the field of aerogel composite material preparation technology. Background Technology

[0002] Silica aerogel is an amorphous solid material composed of nanoscale particles dispersed in air. It possesses excellent properties such as high porosity, high specific surface area, low density, low refractive index, high visible light transmittance, low thermal conductivity, and low dielectric constant. Furthermore, its fine structure and macroscopic properties can be adjusted through process control, resulting in superior characteristics in thermal insulation, fire retardancy, sound insulation, optics, and electrical applications. However, because aerogels are composed of nanoscale SiO2 particles with high porosity, their strength is very low and they are quite brittle, significantly limiting their applications in various fields. Based on existing patented technologies (US patents US 7,078,359 B2, US 8,214,980 B2 and Chinese patents CN 101698584A, CN 102531540A, etc.) and literature reports (Nano Letters, 2002, 9(2): 957-960; Applied Materials & Interfaces, 2011, 3: 4796-4803, etc.), the main method for reinforcing aerogel materials is currently fiber reinforcement. The fibers that can be incorporated include glass fibers, high-silica fibers, aluminosilicate fibers, mullite fibers, and basalt fibers. Although these methods provide some reinforcement, the fiber diameter is much larger than the aerogel pores, resulting in an uneven mesh structure and certain defects in the composite material. Furthermore, the compatibility of the fiber material with the matrix material and the temperature and corrosion resistance of the fibers also affect the overall performance of the composite material.

[0003] Existing glass fiber and pre-oxidized fiber have a temperature resistance of 400-600℃. When exposed to high-temperature flames, they will burn through within 0.5-4 minutes and deform, thus failing to provide fire protection. Furthermore, the electrical properties of existing glass fiber and pre-oxidized fiber cannot be controlled. In contrast, silicon carbide fiber can withstand temperatures up to 1300℃, and its electrical properties can be freely adjusted. It can be widely used in the aerospace, aviation, and new energy vehicle industries. Summary of the Invention

[0004] In view of the shortcomings of the prior art, the first objective of this invention is to provide a method for preparing a fiber felt reinforced aerogel composite material with controllable high-temperature resistant, thermal insulation and electrical properties.

[0005] The second objective of this invention is to provide a high-temperature resistant, heat-insulating, and electrically controllable fiber-reinforced aerogel composite material prepared by the above-described method. The fiber-reinforced aerogel composite material of this invention is obtained by combining silicon carbide fibers and silica aerogel. The silicon carbide fiber felt possesses excellent mechanical properties and can withstand temperatures above 1300℃. Furthermore, it exhibits excellent chemical, physical, and electrical properties at high temperatures, as well as resistance to acid and alkali corrosion. When combined with silica aerogel, it possesses high-temperature resistance, high sound insulation, low density, and low thermal conductivity.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] This invention provides a method for preparing a high-temperature resistant, thermally insulating, and electrically controllable fiber-reinforced aerogel composite material. The method involves plasma surface treatment of silicon carbide fibers, followed by addition to a nano-dispersion liquid to obtain a fiber suspension. The fiber suspension is then dehydrated, shaped, dried, and cured to obtain silicon carbide fiber felt. Tetraethyl orthosilicate and ethanol are mixed to obtain a mixed solution. An acid solution and ammonia are added sequentially to the mixed solution to form a sol. The silicon carbide fiber felt is immersed in the sol and allowed to stand, followed by gel aging to obtain a silicon carbide fiber felt-silica wet gel composite material. This silicon carbide fiber felt-silica wet gel composite material is then immersed in an organic solvent for hydrophobic modification, followed by drying to obtain the fiber-reinforced aerogel composite material.

[0008] The nano-dispersion is composed of the following components by weight: 0.5-25 parts surfactant, 0.2-15 parts fumed silica, 0.1-10 parts thickener, 0.1-0.5 parts defoamer, 0.5-10 parts softener, and 39.5-98.6 parts water.

[0009] The preparation method of this invention first involves surface treatment of short-cut fibers using low-temperature plasma. This process only alters the physical and chemical properties of the material surface, introducing hydrophilic groups such as carboxyl, hydroxyl, and carbonyl groups onto the surface of silicon carbide fibers. This improves the wettability of the silicon carbide fiber surface, which is beneficial for fiber dispersion in nano-dispersion liquid. Compared with conventional oxidation methods, the surface etching effect is more significant, which can reduce the rigidity of silicon carbide fibers to a certain extent, improve fiber flexibility, and reduce flocculation problems during dispersion to a certain extent. It also helps to increase the contact area between fibers and resin materials, improve the bonding strength, and enhance the performance of composite materials. In addition, the amount of hydrophilic groups introduced by plasma treatment is not significantly different, and it also helps to improve the bonding force between aerogel particles and fibers.

[0010] Then, silicon carbide fibers are placed in a nano-dispersion liquid. In this invention, fumed silica powder is incorporated into the dispersion liquid, which further plays a role in surface modification, promoting the dispersibility of silicon carbide in water, and also providing skeletal support. First, fumed silica forms a mesh structure during the composite felt forming process. This structure provides a robust support framework, preventing deformation and breakage of the composite fibers during forming. This skeletal support makes the overall structure of the composite felt more stable, increasing its mechanical strength and tensile properties. Furthermore, this structure helps the thin felt maintain a certain thickness and shape, making it more suitable for various applications. Second, fumed silica can form a silica coating layer on the surface of the silicon carbide fibers, thereby modifying the fiber surface. This surface modification can improve the chemical stability and oxidation resistance of the silicon carbide fibers, extending their service life. Simultaneously, this coating layer can reduce the friction between fibers, improving the fiber flexibility and wear resistance. In addition, the surface modification of silica can also affect the bonding performance between the fibers and the matrix, enhancing the overall stability of the fiber composite felt. The surfactants in the nano-dispersion can improve the viscosity and flowability of the dispersion, and promote the wetting and dispersion of the fiber material. They possess dispersion, wetting, and surface tension reduction properties, and can form a thin film between the fiber material and the liquid, improving the compatibility of the fiber material with the mixture. Thickeners also help to change the viscosity and thixotropic properties of the dispersion, preventing fiber dispersion and sedimentation. Softeners can improve the antistatic properties and hydrophilicity of the fibers, improving their softness. The combination of fumed silica and aerogel can improve the thermal insulation effect of the material under high-temperature conditions to a certain extent.

[0011] Finally, the obtained silicon carbide fiber felt was immersed in a solution containing tetraethyl orthosilicate for gel aging. Since the silicon carbide fiber itself has a layer of silicon oxide coating, it can be completely wetted by the solution containing tetraethyl orthosilicate, so that the silicon carbide fiber felt and aerogel can be uniformly composited. Finally, the silicon carbide fiber felt-silica wet gel composite material is hydrophobically modified to improve the thermal insulation performance. The resulting fiber felt reinforced aerogel composite material has the performance characteristics of high temperature resistance, high sound insulation, low density, and low thermal conductivity.

[0012] As a preferred embodiment, the nano-dispersion comprises the following components by weight: 15-20 parts surfactant, 1-5 parts fumed silica, 4-10 parts thickener, 0.1-0.5 parts defoamer, 5-10 parts softener, and 39.5-98.6 parts water.

[0013] As a preferred embodiment, the length of the silicon carbide fiber is 4–15 mm. Controlling the length of the silicon carbide fiber in this invention is beneficial for subsequent dispersion. In this invention, the silicon carbide fiber is a short-cut carbon fiber obtained by cutting long silicon carbide fibers using a fiber cutting machine.

[0014] As a preferred embodiment, the conditions for the plasma surface hydrophilic modification treatment are: time of 5–90 min, power of 600–900 W, and pressure of 0.1–0.2 MPa. Higher power and pressure during the plasma surface hydrophilic treatment result in a more pronounced surface etching effect on the silicon carbide fibers. Controlling these conditions within the aforementioned range ensures the introduction of functional groups into the silicon carbide fibers, improving hydrophilicity, while avoiding a decrease in mechanical properties.

[0015] In practice, the inventors also tried other hydrophilic modifications, such as acid oxidation treatment, but the dispersion effect after modification was far inferior to that of the present invention. More importantly, the inventors found that plasma treatment is also beneficial to improve the bonding strength between the fiber and the aerogel particles.

[0016] As a preferred embodiment, the preparation process of the nano-dispersion is as follows: surfactant, fumed silica, thickener, defoamer, and softener are added to water, and the pH is adjusted to 2–12, preferably 3–6, followed by sand milling and pulping. In this invention, the pH can be adjusted according to the fiber dispersion rate; the faster the dispersion rate, the better, as a suitable pH value can accelerate the dispersion process.

[0017] As a preferred embodiment, the softener is a polyether-modified silicone oil and / or a hydrophilic amino silicone oil.

[0018] As a preferred embodiment, the surfactant is at least one selected from sodium hexametaphosphate, fatty alcohol polyoxyethylene ether, fatty amine polyoxyethylene ether, alkyl ammonium salt, fatty alcohol and ethylene oxide condensate, polyethylene glycol, polyoxyethylene sorbitan monostearate, polyvinylpyrrolidone, and cetearyl alcohol polyoxyethylene ether; and the thickener is at least one selected from carboxymethyl cellulose, hydroxypropyl methyl cellulose, hydroxyethyl cellulose, and polyethylene oxide.

[0019] As a preferred embodiment, the defoamer is at least one selected from butyl phosphate, silicone, alkyl polyether, and polyether siloxane. Examples of butyl phosphate used in this invention include tributyl phosphate, silicone such as Defeng 2854, alkyl polyether such as Xinwancheng S-717, and polyether siloxane such as Tego 902W.

[0020] As a preferred embodiment, the viscosity of the fiber suspension is 5–400 mPa·s; the air content is 2–20%. The viscosity of the nano-dispersion can affect the stability of silicon carbide fibers in the slurry, while the air content affects the unit area weight during fiber mat forming. More preferably, the viscosity is 185–300 mPa·s, and the air content is 2–5%.

[0021] As a preferred embodiment, the sand milling and pulping time is 20–180 min.

[0022] In actual operation, the fiber suspension is sent to the grid for dehydration and molding.

[0023] As a preferred embodiment, after dehydration and molding, an adhesive is added to the felt body, and then it is dried and cured. The amount of adhesive added is 5-15% of the mass of the felt body.

[0024] As a further preferred embodiment, the adhesive is selected from one of acrylic resin, polyurethane, silicone resin, phenolic resin, and epoxy resin. The adhesive is added by dip coating.

[0025] As a further preferred embodiment, the molar ratio of the tetraethyl orthosilicate to ethanol is 1:2-8.

[0026] As a further preferred option, tetraethyl orthosilicate is mixed with ethanol to obtain a mixed solution, an acid solution is added to the mixed solution to adjust the pH value to 2-4, and then ammonia is added to adjust the pH value to 5-8.

[0027] In a further preferred embodiment, the acid solution is selected from hydrochloric acid, oxalic acid, acetic acid, and sulfuric acid.

[0028] In actual operation, after obtaining the sol, the silicon carbide fiber felt is immersed in the sol.

[0029] As a preferred embodiment, the gel aging temperature is 40-80℃, and the gel aging time is 10-24 hours. In actual operation, the silicon carbide fiber felt impregnated with sol is placed in an oven for gel aging.

[0030] As a preferred embodiment, the organic solvent is obtained by mixing solvent A and solvent B, wherein the volume ratio of solvent A to solvent B is 5-15:1; solvent A is selected from at least one of n-hexane and n-butane, and solvent B is selected from at least one of hexamethyldisilazane, trimethylchlorosilane, and hexamethyldisiloxane.

[0031] As a preferred embodiment, the soaking temperature is 15-50℃ and the soaking time is 18-30h.

[0032] As a preferred method, the silicon carbide fiber felt-silica wet gel composite material after soaking is dried at 45-110℃ under normal pressure for 1-8 hours.

[0033] The present invention also provides a fiber felt reinforced aerogel composite material with controllable high temperature resistance, thermal insulation and electrical properties prepared by the above preparation method.

[0034] The composite material prepared by this invention has the following advantages:

[0035] (1) The present invention uses silicon carbide short-cut fibers to prepare silicon carbide fiber felt products directly by wet felting technology, and the raw materials of silicon carbide fiber felt can be obtained in batches.

[0036] (2) Using silicon carbide fiber felt as raw material, the fiber is resistant to temperature up to 1300℃, and its chemical, physical, electrical properties and acid and alkali corrosion resistance are excellent at high temperatures.

[0037] (3) The prepared silicon carbide fiber felt has stable quality, and thus the silicon carbide fiber felt composite silica aerogel composite material also has stable product quality.

[0038] (4) Silicon carbide fiber felt has adjustable electrical properties, and the electrical properties of silicon carbide fiber felt composite silica aerogel composite material can be freely controlled, and composite materials with multiple functions such as heat insulation and electromagnetic shielding can be made.

[0039] (5) The silicon carbide fiber felt composite silica aerogel composite material has the properties of high temperature resistance, high sound insulation, low density and low thermal conductivity. Attached Figure Description

[0040] Figure 1 This is a photograph of the silicon carbide fiber aerogel felt product prepared in Example 1.

[0041] Figure 2 A physical image of the silicon carbide fiber felt product prepared for Comparative Example 1. Detailed Implementation

[0042] Example 1:

[0043] 1) Cut the silicon carbide fiber into 4mm short fibers using a fiber cutter;

[0044] 2) The short-cut fibers obtained in step 1) were surface treated for 30 minutes using a low-temperature plasma surface treatment machine with a power of 800W and a working pressure of 0.101Mpa.

[0045] 3) Add 74.9g of water to the dispersion tank, then add 10g of sodium hexametaphosphate, 5g of polyethylene glycol, 1g of hydrophilic fumed silica, 4g of carboxymethyl cellulose, 0.1g of GTE 902w and 5g of polyether silicone modified silicone oil in sequence. Adjust the pH value to 3-6, and after sand milling for 1 hour, the nano-dispersion is ready.

[0046] 4) Weigh a certain amount of silicon carbide fiber from step 2) and add it to the nano-dispersion prepared in step 3). Stir and disperse the mixture in a dispersion tank to prepare a uniform silicon carbide fiber suspension with a viscosity of 185 mPa·s and an air content of 5%.

[0047] 5) The silicon carbide fiber suspension prepared in step 4) is transported to a grid for dehydration and molding. Then, an acrylic adhesive is added, with the content of the adhesive being 10% of the product mass. The mixture is then dried, cured, and cut in a forced-air oven to obtain the silicon carbide fiber felt product.

[0048] 6) In the preparation of a mixed solution of tetraethyl orthosilicate / ethanol with a molar ratio of 1:5, 98% concentrated sulfuric acid solution was added as a catalyst to adjust the pH value to 3. After stirring continuously for 11 hours, 0.05 mol / L ammonia solution was added to adjust the pH value to 6. After stirring continuously for 30 minutes to form a sol, the silicon carbide fiber felt obtained in step 5 was immersed in the sol and allowed to stand.

[0049] 7): Place the material impregnated in step 6) in an oven at 45°C for 24 hours to age. The resulting silicon carbide fiber felt-silica wet gel composite material is then soaked in a mixed solution of n-hexane and hexamethyldisilazane at a volume ratio of 8:1 for 24 hours. The soaking solution is then filtered out.

[0050] 8): The silicon carbide fiber felt soaked in step 7) and the silica wet gel composite material are dried at 80℃ and normal pressure for 5 hours to obtain silicon carbide fiber aerogel felt. The final physical image of the silicon carbide fiber aerogel felt is shown below. Figure 1 As shown in Table 1, the performance is as follows.

[0051] Comparative Example 1

[0052] All other conditions were the same as in Example 1, except that plasma surface treatment was not performed. The results showed that the prepared silicon carbide fiber suspension was transported to a grid for dehydration and molding, then an adhesive was added, and the fiber felt product was dried and cured in a forced-air oven. The surface of the cut fiber felt product was as... Figure 1 The presence of fiber agglomeration indicates that the silicon carbide fiber felt product is substandard.

[0053] The properties of the final silicon carbide fiber aerogel felt are shown in Table 1.

[0054] Comparative Example 2

[0055] Other conditions were the same as in Example 1. The silicon carbide fibers were not subjected to low-temperature plasma treatment. Instead, the obtained short-cut silicon carbide fibers were added to a mixed aqueous solution of hydrofluoric acid and phosphoric acid in a ratio of 5:2, heated to 120°C, and held for 2 hours. After removal, the fibers were washed four times with alcohol and then dried in a 60°C oven for 3 hours before being added to a nano-dispersion. The results showed that the acid-modified silicon carbide fibers agglomerated during washing and drying, increasing the difficulty of fiber dispersion and manufacturing costs. The final felt still exhibited uneven agglomeration on the surface. The properties of the final silicon carbide fiber aerogel felt are shown in Table 1.

[0056] Comparative Example 3

[0057] The only difference between this comparative example and Example 1 is that hydrophilic fumed silica was not added to the nano-dispersion. As a result, it was found in the experiment that bundles easily formed during the dispersion process. The properties of the silicon carbide fiber aerogel felt obtained in the end are shown in Table 1.

[0058] The performance of the silicon carbide fiber aerogel felt obtained in Example 1 was tested using the comparative example, and the results are shown in Table 1.

[0059] Table 1

[0060]

Claims

1. A method for preparing a fiber-reinforced aerogel composite material with controllable high-temperature resistant, thermally insulating, and electrical properties, characterized in that: Silicon carbide fibers were subjected to plasma surface hydrophilic modification treatment and then added to a nano-dispersion liquid to obtain a fiber suspension. The fiber suspension was dehydrated, shaped, dried, and cured to obtain silicon carbide fiber felt. Tetraethyl orthosilicate and ethanol were mixed to obtain a mixed solution. An acid solution and ammonia were added to the mixed solution in sequence to form a sol. The silicon carbide fiber felt was immersed in the sol and allowed to stand. Then, it was gel aged to obtain a silicon carbide fiber felt-silica wet gel composite material. The silicon carbide fiber felt-silica wet gel composite material was then immersed in an organic solvent for hydrophobic modification and then dried to obtain a fiber felt reinforced aerogel composite material. The length of the silicon carbide fiber is 4~15mm; The conditions for plasma surface hydrophilic modification treatment are: time 5~90min, power 600~900W, and pressure 0.1~0.2Mpa; The nano-dispersion is composed of the following components by weight: 0.5-25 parts surfactant, 0.2-15 parts fumed silica, 0.1-10 parts thickener, 0.1-0.5 parts defoamer, 0.5-10 parts softener, and 39.5-98.6 parts water.

2. The preparation method of a high-temperature resistant, thermally insulating, and electrically controllable fiber-reinforced aerogel composite material according to claim 1, characterized in that: The preparation process of the nano-dispersion is as follows: after adding surfactant, fumed silica, thickener, defoamer and softener to water, the pH is adjusted to 2~12 and then sand milling is performed; the sand milling time is 20~180min.

3. The method for preparing a high-temperature resistant, thermally insulating, and electrically controllable fiber-reinforced aerogel composite material according to claim 1 or 2, characterized in that: The softener is a polyether-modified silicone oil and / or a hydrophilic amino silicone oil; The surfactant is at least one of sodium hexametaphosphate, fatty alcohol polyoxyethylene ether, fatty amine polyoxyethylene ether, alkyl ammonium salt, polyethylene glycol, polyoxyethylene sorbitan monostearate, and polyvinylpyrrolidone; the thickener is at least one of carboxymethyl cellulose, hydroxypropyl methyl cellulose, hydroxyethyl cellulose, and polyethylene oxide. The defoamer is at least one of butyl phosphate, organosilicon, and alkyl polyether.

4. The preparation method of a high-temperature resistant, thermally insulating, and electrically controllable fiber-reinforced aerogel composite material according to claim 1, characterized in that: The viscosity of the fiber suspension is 5~400 mPa·s; the air content is 2~20%; After dehydration and molding, the resulting felt is mixed with an adhesive and then dried and cured. The amount of adhesive added is 5-15% of the mass of the felt. The adhesive is selected from one of acrylic resin, polyurethane, silicone resin, phenolic resin, and epoxy resin.

5. The method for preparing a high-temperature resistant, thermally insulating, and electrically controllable fiber-reinforced aerogel composite material according to claim 1, characterized in that: The molar ratio of tetraethyl orthosilicate to ethanol is 1:2-8; Ethyl orthosilicate and ethanol are mixed to obtain a mixed solution. An acid solution is added to the mixed solution to adjust the pH value to 2-4, and then ammonia is added to adjust the pH value to 5-8.

6. The method for preparing a high-temperature resistant, thermally insulating, and electrically controllable fiber-reinforced aerogel composite material according to claim 1, characterized in that: The gel aging temperature is 40-80℃, and the gel aging time is 10-24h.

7. The method for preparing a high-temperature resistant, thermally insulating, and electrically controllable fiber-reinforced aerogel composite material according to claim 1, characterized in that: The organic solvent is obtained by mixing solvent A and solvent B, wherein the volume ratio of solvent A to solvent B is 5-15:1; solvent A is selected from at least one of n-hexane and n-butane, and solvent B is selected from at least one of hexamethyldisilazane, trimethylchlorosilane, and hexamethyldisiloxane.

8. The method for preparing a high-temperature resistant, thermally insulating, and electrically controllable fiber-reinforced aerogel composite material according to claim 1, characterized in that: The soaking temperature is 15-50℃ and the soaking time is 18-30h; the silicon carbide fiber felt-silica wet gel composite material after soaking is dried at 45-110℃ under normal pressure for 1-8h.

9. A high-temperature resistant, thermally insulating, and electrically controllable fiber-reinforced aerogel composite material prepared by the preparation method according to any one of claims 1-8.

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