Gradient aerogel composite material and preparation method thereof

Abstract

The invention discloses a gradient aerogel composite material and a preparation method thereof, and the gradient aerogel composite material is prepared by adopting the processes of opacifying agent slurry preparation, slurry coating, fiber hot press molding, sol dipping and aging, supercritical drying and heat treatment. The gradient aerogel composite material prepared by the method has the characteristics of ultra-light weight, high temperature resistance, wide temperature range, ultra-low thermal conductivity and capability of forming a large-size thermal insulation component, and can be used as a thermal insulation material in the fields of aerospace, nuclear power, ships and the like.

Description

Technical Field

[0001] The present invention belongs to the technical field of thermal insulation materials, and particularly relates to a gradient aerogel composite material and a preparation method thereof. Background Art

[0002] As a nano-porous material, aerogel has an extremely low room-temperature thermal conductivity (0.012 W / (m·K)), and has broad application prospects in the field of thermal insulation. Aerogel composite products prepared with fibers as the reinforcing phase and silica aerogel as the matrix have been applied in the fields of aerospace, petrochemical pipelines, new energy vehicles, etc.

[0003] However, for silica aerogel composite materials prepared by existing methods, in application scenarios with extremely strict requirements for the weight, thermal insulation performance and mechanical properties of thermal insulation materials (such as aircraft, spacecraft, etc.), their density (usually greater than 0.30 g / cm 3 above) and high-temperature thermal conductivity (the typical value of thermal conductivity at 800°C is 0.045 W / (m·K)) are still relatively high and cannot meet the use requirements, and the use temperature is also limited to below 800°C. By reducing the volume fraction of fibers and the density of aerogel in the aerogel composite material, the density of the composite material can be effectively reduced, but at the same time, the high-temperature thermal insulation performance and mechanical strength are sacrificed to a large extent. Introducing a light-shielding agent into the aerogel composite material can reduce its high-temperature thermal conductivity, but the relatively high solid thermal conductivity of the light-shielding agent will cause the thermal conductivity of the composite material to increase in the medium and low temperature ranges, and it is impossible to maintain a very low wide-temperature-range thermal conductivity. Moreover, the current process methods are difficult to ensure that the light-shielding agent is uniformly introduced into the composite material, and it is impossible to stably form large-size complex components.

[0004] Therefore, there is an urgent need to develop a preparation technology for ultra-lightweight, wide-temperature-range ultra-low thermal conductivity aerogel composite materials to meet the thermal insulation requirements in the fields of aircraft, spacecraft, etc. Summary of the Invention

[0005] Aiming at the problem of the lack of ultra-lightweight, wide-temperature-range ultra-low thermal conductivity aerogel composite materials in the prior art, the present invention provides a gradient aerogel composite material and a preparation method thereof, to prepare a gradient aerogel composite material with excellent thermal insulation performance. By adopting the processes of preparing a light-shielding agent slurry, slurry coating, fiber hot pressing, sol impregnation, supercritical drying, and heat treatment, the preparation of the gradient aerogel composite material is realized. The gradient aerogel composite material prepared by the present invention has the characteristics of ultra-lightweight, high temperature resistance, wide-temperature-range ultra-low thermal conductivity, and can form large-size thermal insulation components, and can be used as a thermal insulation material in the fields of aerospace, nuclear power, ships, etc.

[0006] The technical solution of the present invention is as follows: A preparation method of a gradient aerogel composite material according to the present invention comprises six steps: preparing a light-shielding agent slurry, coating the slurry, hot pressing and forming fibers, sol impregnation and aging, supercritical drying, and heat treatment.

[0007] The object of the present invention is achieved by the following technical solutions: A preparation method of a gradient aerogel composite material comprises the following steps: S1. Preparing a light-shielding agent slurry: Mix a dispersant, a viscous component and water, stir evenly at 25°C to 50°C to form a mixed solution, add a light-shielding agent to the mixed solution, and stir evenly quickly at 25°C to 50°C to form a light-shielding agent slurry with a viscosity of 500 mPa·s to 3000 mPa·s. In the light-shielding agent slurry, the mass ratio of the dispersant, the viscous component, the light-shielding agent and water is (0.5 - 3):(3 - 10):(5 - 30):100; The dispersant is one of dodecyl glucoside, fatty alcohol polyoxyethylene ether glucoside, dodecyl betaine, fatty alcohol polyoxyethylene ether and dodecylphenol polyoxyethylene ether; The viscous component is one of starch, gelatin and polyvinyl alcohol; The light-shielding agent is one of silicon carbide, zirconia, titanium oxide, potassium hexa-titanate, carbon black, iron oxide and ferric ferrocyanide, and the average diameter range of the light-shielding agent particles is 0.5 μm to 5 μm; S2. Coating the slurry: Lay the layered fibers flat, spray the obtained light-shielding agent slurry evenly on the fiber surface under a pressure of 0.1 MPa to 0.5 MPa, and keep it at 120°C to 200°C for 2 h to 6 h to dry it, so as to form a light-shielding agent coating with a thickness of 0.05 mm to 0.3 mm on the surface of the layered fibers, and obtain light-shielding agent-modified layered fibers; The layered fibers are selected from any one of rock wool, glass fiber, quartz fiber, aluminum silicate fiber, zirconia fiber, lanthanum zirconate fiber, alumina fiber and mullite fiber; The natural density of the layered fibers is 0.02 g / cm 3 ~0.1 g / cm 3 , with a thickness of 0.1 mm to 5 mm and an average diameter of 0.5 μm to 8 μm; S3. Hot pressing and forming fibers: Stack and lay the light-shielding agent-modified layered fibers on a high-temperature resistant metal mold in sequence. After the laying is completed, fasten and press through the high-temperature resistant metal mold to obtain a fiber preform with a mold. Keep the fiber preform with a mold at 600°C to 1000°C for 6 h to 24 h and then cool it naturally to obtain a gradient fiber preform; S4. Sol impregnation and aging: Under the pressure condition of -0.1 MPa to 0 MPa, immerse the gradient fiber preform in the sol for 1 h to 4 h to obtain a sol-preform mixture, and keep the sol-preform mixture at 40°C to 70°C for 8 h to 24 h to form a gel-preform composite; The sol described above is one of silica sol, alumina sol, and zirconia sol. The solid content of the sol is 6% to 15%, and the average particle size range of the sol particles is 5 nm to 50 nm; S5. Supercritical drying: Use an alcohol substance as the medium for supercritical drying. Place the gel-preform composite in an autoclave, add the alcohol substance and keep it airtight. The volume ratio of the gel-preform composite to the alcohol substance is 1:(0.3 to 3). Heat it above the critical point of the alcohol and keep it at 8.0 MPa to 15.0 MPa for 1 h to 10 h. Slowly discharge the gas in the autoclave until the pressure is 0 to obtain a gradient aerogel composite blank; S6. Heat treatment: Place the gradient aerogel composite blank in a high-temperature furnace, heat it from room temperature to 600°C to 1000°C, keep it for 1 h to 5 h, and naturally cool it to obtain a gradient aerogel composite. The gradient aerogel composite is a composite material with a service temperature of 800°C, or a composite material with a service temperature of 1200°C, or a composite material with a service temperature of 1600°C. These three composite materials take into account low density, wide-temperature-range thermal conductivity, and mechanical properties. Their typical properties are as follows: (1) The composite material with a service temperature of 800°C: The density is 0.19 g / cm 3 , the thermal conductivity at room temperature is 0.016 W / (m·K), the thermal conductivity at 800°C is 0.022 W / (m·K), the compressive strength (3% deformation) is 0.12 MPa, the flexural strength is 1.2 MPa. The material (with a thickness of 10 mm) is heated on one side at 800°C for 1 h, and the shrinkage rate in the thickness direction is 0.3%, and the temperature rise on the cold surface is 63°C; (2) The composite material with a service temperature of 1200°C: The density is 0.27 g / cm 3 , the thermal conductivity at room temperature is 0.020 W / (m·K), the thermal conductivity at 1200°C is 0.030 W / (m·K), the compressive strength (3% deformation) is 0.17 MPa, the flexural strength is 1.1 MPa. The material (with a thickness of 12.5 mm) is heated on one side at 1200°C for 1 h, and the shrinkage rate in the thickness direction is 0.4%, and the temperature rise on the cold surface is 176°C; (3) The composite material with a service temperature of 1600°C: The density is 0.31 g / cm 3, its thermal conductivity at room temperature is 0.026 W / (m·K), its thermal conductivity at 1600 °C is 0.056 W / (m·K), its compressive strength (3% deformation) is 0.16 MPa, its flexural strength is 0.95 MPa. The material (with a thickness of 18 mm) is heated on one side at 1600 °C for 1 h, and the shrinkage rate in the thickness direction is 0.9%, and the temperature rise on the cold side is 262 °C.

[0008] Furthermore, the solvent used for the sol described in S4 is one of ethanol, isopropanol, n-propanol, n-butanol, sec-butanol, and tert-butanol.

[0009] Furthermore, the alcohol substance described in S5 is one of ethanol, methanol, isopropanol, n-propanol, n-butanol, sec-butanol, and tert-butanol.

[0010] Furthermore, the temperature increase from room temperature to 600 °C to 1000 °C described in S6 is completed at a heating rate of 0.5 °C / min to 3 °C / min.

[0011] The present invention also relates to a gradient aerogel composite material, which is obtained according to the preparation method of the above-mentioned gradient aerogel composite material. The gradient aerogel composite material is a composite material with a service temperature of 800 °C, or a composite material with a service temperature of 1200 °C, or a composite material with a service temperature of 1600 °C. These three composite materials take into account low density, wide-temperature-range thermal conductivity, and mechanical properties, and their typical properties are as follows: (1) The composite material with a service temperature of 800 °C: The density is 0.19 g / cm 3 , its thermal conductivity at room temperature is 0.016 W / (m·K), its thermal conductivity at 800 °C is 0.022 W / (m·K), its compressive strength (3% deformation) is 0.12 MPa, its flexural strength is 1.2 MPa. The material (with a thickness of 10 mm) is heated on one side at 800 °C for 1 h, and the shrinkage rate in the thickness direction is 0.3%, and the temperature rise on the cold side is 63 °C; (2) The composite material with a service temperature of 1200 °C: The density is 0.27 g / cm 3 , its thermal conductivity at room temperature is 0.020 W / (m·K), its thermal conductivity at 1200 °C is 0.030 W / (m·K), its compressive strength (3% deformation) is 0.17 MPa, its flexural strength is 1.1 MPa. The material (with a thickness of 12.5 mm) is heated on one side at 1200 °C for 1 h, and the shrinkage rate in the thickness direction is 0.4%, and the temperature rise on the cold side is 176 °C; (3) The composite material with a service temperature of 1600 °C: The density is 0.31 g / cm 3, its thermal conductivity at room temperature is 0.026 W / (m·K), the thermal conductivity at 1600 °C is 0.056 W / (m·K), the compressive strength (3% deformation) is 0.16 MPa, the flexural strength is 0.95 MPa. The material (with a thickness of 18 mm) is heated unidirectionally at 1600 °C for 1 h, the shrinkage rate in the thickness direction is 0.9%, and the temperature rise on the cold side is 262 °C.

[0012] Compared with the prior art, the present invention has the following beneficial effects: 1. In the preparation method of the gradient aerogel composite material according to the present invention, the light-shielding agent is gradiently distributed from the hot surface to the cold surface of the composite material, which can enable it to exert the optimal light-shielding effect matching the actual high-temperature working conditions. In the temperature field of the composite material along the thickness direction, a light-shielding agent coating with a gradient arrangement and a wavelength size equivalent to the most energetic infrared radiation wave is capable of blocking the radiation wave to the greatest extent and suppressing radiative heat conduction. The higher the temperature, the shorter the wavelength of the most energetic infrared radiation wave. Therefore, at the hot surface position and its vicinity of the composite material, a light-shielding agent coating with high temperature resistance and a smaller diameter is arranged; at the middle layer position and its vicinity of the composite material, a light-shielding agent coating with medium temperature resistance and a medium diameter is arranged; at the cold surface position and its vicinity of the composite material, a light-shielding agent coating with a larger diameter or no light-shielding agent coating is arranged. Using ceramics with a high specific extinction coefficient as the light-shielding agent component (such as zirconia, silicon carbide, titanium oxide, iron oxide, etc.), it also has good thermal stability in an oxygen-containing environment, avoiding the oxidation failure problem of metal reflective screen substances.

[0013] 2. In the preparation method of the gradient aerogel composite material according to the present invention, introducing the light-shielding agent in the form of a coating can minimize the influence of the light-shielding agent on the heat insulation performance of the composite material in the medium-temperature and low-temperature sections. When introducing the light-shielding agent component into the aerogel composite material by a conventional method, the light-shielding agent exists in a homogeneous form, and a relatively high total amount of the light-shielding agent must be ensured to achieve the effect of reducing the high-temperature thermal conductivity. However, the intrinsic thermal conductivity of the light-shielding agent is usually 2 - 3 orders of magnitude higher than that of the aerogel and fiber, which will ultimately lead to an increase in the thermal conductivity of the aerogel composite material in the medium-temperature and low-temperature sections. The present invention proposes to introduce a multi-layer light-shielding agent in the form of a coating, with a gradient distribution of the coating and a thickness of less than 0.3 mm. As a result, the content of the light-shielding agent in the aerogel composite material decreases significantly, the efficiency of the light-shielding agent is greatly improved, and while effectively exerting the effect of the light-shielding agent, the increase in the heat conduction of the aerogel composite material caused by the light-shielding agent itself is minimized.

[0014] 3. The preparation method of a gradient aerogel composite material according to the present invention pre-introduces a light-shielding agent into the fibers. The process is simple and it is easy to batch and stably prepare large-sized heat-insulating components. The common existing method of introducing a light-shielding agent is to add the light-shielding agent to the sol, stir and disperse it, and then infiltrate it into the fibers. The light-shielding agent is prone to sedimentation in the sol, and the uniformity is poor, significantly weakening the actual light-shielding effect. The present invention proposes to prepare a light-shielding agent slurry and use a spraying method to coat the slurry on the layered fibers. By keeping the slurry at a relatively high viscosity and adding a viscous component, the light-shielding agent is stably attached to the fiber surface without leaking and sedimenting in the fibers, effectively ensuring the uniformity of the light-shielding agent. At the same time, the layered fibers with a light-shielding agent coating are beneficial to minimizing the thermal bridge effect of the light-shielding agent between layers and the solid-state heat conduction of the fibers in the thickness direction, and can form heat-insulating components with complex shapes.

[0015] 4. The preparation method of a gradient aerogel composite material according to the present invention uses a hot pressing molding method and subsequent heat treatment sintering process for the fiber preform to ensure that the composite material has good mechanical properties. Under hot pressing conditions, physical lapping, entanglement, and certain chemical bonding occur between the layered fibers, and the interlayer bonding force is significantly enhanced. The heat treatment sintering process further causes physical bonding and chemical bonding between the three components of the aerogel skeleton particles, fibers, and light-shielding agent, resulting in overall significant strengthening. At the same time, the introduction of a high-rigidity light-shielding agent enhances the pressure-bearing performance of the aerogel composite material. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] The drawings are used to provide a further understanding of the present invention and constitute a part of the specification. They are used together with the embodiments of the present invention to explain the present invention and do not constitute a limitation to the present invention.

[0017] Figure 1 is a process flow chart of the preparation method of a gradient aerogel composite material according to the present invention; Figure 2 is a schematic diagram of the laying of layered fibers in the preparation method of a gradient aerogel composite material according to Embodiment 1 of the present invention; Figure 3 is a photograph of layered alumina fibers in the preparation method of a gradient aerogel composite material according to Embodiment 3 of the present invention; Figure 4 is a photograph of the gradient aerogel composite material prepared by the preparation method of a gradient aerogel composite material according to Embodiment 7 of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0018] 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 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 scope of protection of the present invention.

[0019] Figure 1 It is a process flow chart of a preparation method of a gradient aerogel composite material described in the embodiment; Example 1: A preparation method of a gradient aerogel composite material includes the following steps: S1. Prepare 2 kinds of light-shielding agent slurries: The first kind of light-shielding agent slurry: Mix dodecyl glucoside, starch and water, stir evenly at 40 °C to form a mixed solution, add silicon carbide particles to the mixed solution, and stir quickly at 40 °C to form a light-shielding agent slurry with a viscosity of 1600 mPa·s; in the light-shielding agent slurry, the mass ratio of dodecyl glucoside, starch, silicon carbide and water is 1.8:6.0:12:100; The average diameter of the silicon carbide particles is 2.5 μm; The second kind of light-shielding agent slurry: Mix dodecyl glucoside, starch and water, stir evenly at 40 °C to form a mixed solution, add silicon carbide particles to the mixed solution, and stir quickly at 40 °C to form a light-shielding agent slurry with a viscosity of 1400 mPa·s. In the light-shielding agent slurry, the mass ratio of dodecyl glucoside, starch, silicon carbide and water is 1.6:6.0:9:100; The average diameter of the silicon carbide particles is 3.5 μm; S2. Slurry coating: In this embodiment, 3 kinds of fibers are used. The first kind of fiber is coated with the first kind of light-shielding agent slurry, the second kind of fiber is coated with the second kind of light-shielding agent slurry, and the third kind of fiber is not coated with the light-shielding agent slurry; The first kind of fiber: Lay the layered quartz fiber flat, spray the obtained first kind of light-shielding agent slurry evenly on the fiber surface at a pressure of 0.15 MPa, and keep it at 170 °C for 4.5 h to dry it, so as to form a light-shielding agent coating with a thickness of 0.05 mm on the surface of the layered quartz fiber, and obtain the first kind of silicon carbide modified layered quartz fiber; The natural density of the layered quartz fiber is 0.06 g / cm 3 , the thickness is 1.5 mm, and the average diameter is 3 μm; The second type of fiber: Lay the layered rock wool fiber flat, and spray the obtained second type of light-shielding agent slurry evenly on the fiber surface at a pressure of 0.15 MPa, and keep it at 170 °C for 4.5 h to dry it, so as to form a light-shielding agent coating with a thickness of 0.02 mm on the surface of the layered rock wool fiber, and obtain the second type of silicon carbide modified layered rock wool fiber; The natural density of the layered rock wool fiber is 0.06 g / cm 3 , with a thickness of 1.5 mm and an average diameter of 1.5 μm; The third type of fiber: layered glass fiber, without coating the light-shielding agent slurry; The natural density of the layered glass fiber is 0.06 g / cm 3 , with a thickness of 1.5 mm and an average diameter of 0.8 μm; S3. Fiber hot pressing and forming: Stack and lay the light-shielding agent modified layered fibers on the high-temperature resistant metal mold in sequence. After the laying is completed, tighten and press through the high-temperature resistant metal mold to obtain a fiber preform with a mold. Keep the fiber preform with a mold at 650 °C for 12 h and then cool it naturally to obtain a gradient fiber preform; The laying order of the light-shielding agent modified layered fibers, from the hot surface to the cold surface, is as follows: the first type of silicon carbide modified layered quartz fiber, the second type of silicon carbide modified layered rock wool fiber, the third type of layered glass fiber; the total thickness after the lamination and molding of the three types of fibers is 10 mm, and the thickness ratio is 2:2:6; S4. Sol impregnation and aging: Under the pressure condition of -0.1 MPa, immerse the gradient fiber preform in the silica sol for 2 h to obtain a sol-preform mixture. Keep the sol-preform mixture at 50 °C for 16 h to form a gel-preform composite; The solid content of the silica sol is 9%, and the average particle size of the sol particles is 8 nm; S5. Supercritical drying: Use ethanol as the medium for supercritical drying. Place the gel-preform composite in an autoclave, add ethanol and keep it airtight. The volume ratio of the gel-preform composite to ethanol is 1:1. Heat it above the critical point of ethanol and keep it at 12.5 MPa for 6 h. Slowly discharge the gas in the autoclave until the pressure is 0 to obtain a gradient aerogel composite blank; S6. Heat treatment: Place the gradient aerogel composite blank in a high-temperature furnace, heat it from room temperature to 650 °C, keep it for 2 h, and cool it naturally to obtain a gradient aerogel composite.

[0020] The prepared gradient aerogel composite has the following properties: The use temperature is 800 °C; the density is 0.19 g / cm 3 ; the thermal conductivity at room temperature is 0.016 W / (m·K), and the thermal conductivity at 800 °C is 0.022 W / (m·K); the compressive strength (3% deformation) is 0.12 MPa, and the flexural strength is 1.8 MPa; the material (with a thickness of 10 mm) is heated on one side at 800 °C for 1 h, the shrinkage rate in the thickness direction is 0.3%, and the temperature rise on the cold surface is 63 °C.

[0021] Figure 2 It is a schematic diagram of the layered fiber placement in the preparation method of a gradient aerogel composite material described in Example 1.

[0022] Example 2: A preparation method of a gradient aerogel composite material, comprising the following steps: S1. Prepare 3 kinds of light-shielding agent slurries: The first kind of light-shielding agent slurry: Mix dodecyl betaine, gelatin and water, stir evenly at 45 °C to form a mixed solution, add titanium oxide particles to the mixed solution, and stir quickly at 45 °C to form a light-shielding agent slurry with a viscosity of 1500 mPa·s; in the light-shielding agent slurry, the mass ratio of dodecyl betaine, gelatin, titanium oxide, and water is 2.0:6.5:20:100; The average diameter of the titanium oxide particles is 2.0 μm; The second kind of light-shielding agent slurry: Mix dodecyl betaine, gelatin and water, stir evenly at 45 °C to form a mixed solution, add silicon carbide particles to the mixed solution, and stir quickly at 45 °C to form a light-shielding agent slurry with a viscosity of 1400 mPa·s; in the light-shielding agent slurry, the mass ratio of dodecyl betaine, gelatin, silicon carbide, and water is 1.3:6.5:15:100; The average diameter of the silicon carbide particles is 2.5 μm; The third kind of light-shielding agent slurry: Mix dodecyl betaine, gelatin and water, stir evenly at 45 °C to form a mixed solution, add silicon carbide particles to the mixed solution, and stir quickly at 45 °C to form a light-shielding agent slurry with a viscosity of 1200 mPa·s; in the light-shielding agent slurry, the mass ratio of dodecyl betaine, gelatin, silicon carbide, and water is 1.0:6.0:8:100; The average diameter of the silicon carbide particles is 4.0 μm; S2. Slurry coating: In this example, 4 kinds of fibers are used. The first kind of fiber is coated with the first kind of light-shielding agent slurry, the second kind of fiber is coated with the second kind of light-shielding agent slurry, the third kind of fiber is coated with the third kind of light-shielding agent slurry, and the fourth kind of fiber is not coated with the light-shielding agent slurry; The first type of fiber: Lay the laminated zirconia fiber flat, spray the obtained first type of light-shielding agent slurry evenly on the fiber surface at a pressure of 0.22 MPa, and keep it at 180 °C for 6 h to dry it, so as to form a light-shielding agent coating with a thickness of 0.15 mm on the surface of the laminated zirconia fiber, and obtain the first type of titanium oxide-modified laminated zirconia fiber; The natural density of the laminated zirconia fiber is 0.08 g / cm 3 , with a thickness of 1.5 mm and an average diameter of 2.0 μm; The second type of fiber: Lay the laminated quartz fiber flat, spray the obtained second type of light-shielding agent slurry evenly on the fiber surface at a pressure of 0.22 MPa, and keep it at 180 °C for 6 h to dry it, so as to form a light-shielding agent coating with a thickness of 0.08 mm on the surface of the laminated quartz fiber, and obtain the second type of silicon carbide-modified laminated quartz fiber; The natural density of the laminated quartz fiber is 0.06 g / cm 3 , with a thickness of 1.5 mm and an average diameter of 1.5 μm; The third type of fiber: Lay the laminated rock wool fiber flat, spray the obtained third type of light-shielding agent slurry evenly on the fiber surface at a pressure of 0.22 MPa, and keep it at 180 °C for 6 h to dry it, so as to form a light-shielding agent coating with a thickness of 0.02 mm on the surface of the laminated rock wool fiber, and obtain the third type of silicon carbide-modified laminated rock wool fiber; The natural density of the laminated rock wool fiber is 0.06 g / cm 3 , with a thickness of 1.5 mm and an average diameter of 1.0 μm; The fourth type of fiber: Laminated glass fiber, without coating the light-shielding agent slurry; The natural density of the laminated glass fiber is 0.06 g / cm 3 , with a thickness of 1.5 mm and an average diameter of 1.0 μm; S3. Fiber hot pressing and forming: Stack and lay the light-shielding agent-modified laminated fibers on the high-temperature resistant metal mold in sequence. After the laying is completed, tighten and press through the high-temperature resistant metal mold to obtain a fiber preform with the mold. Keep the fiber preform with the mold at 650 °C for 12 h and then cool it naturally to obtain a gradient fiber preform; The laying order of the light-shielding agent-modified laminated fibers, from the hot surface to the cold surface, is as follows: the first type of titanium oxide-modified laminated zirconia fiber, the second type of silicon carbide-modified laminated quartz fiber, the third type of silicon carbide-modified laminated rock wool fiber, the fourth type of laminated glass fiber; the total thickness after the lamination and molding of the 4 types of fibers is 12.5 mm, and the thickness ratio is 2:2:3:5.5; S4. Sol impregnation and aging: Under a pressure condition of -0.1 MPa, the gradient fiber preform was immersed in silica sol for 3 h to obtain a sol-preform mixture, and the sol-preform mixture was kept at 55 °C for 20 h to form a gel-preform composite; The solid content of the silica sol was 11%, and the average particle size of the sol particles was 20 nm; S5. Supercritical drying: Isopropanol was used as the medium for supercritical drying. The gel-preform composite was placed in an autoclave, and after adding isopropanol, it was kept airtight. The volume ratio of the gel-preform composite to isopropanol was 1:1.4. It was heated above the critical point of isopropanol and kept at 8.0 MPa for 4.5 h, and then the gas in the autoclave was slowly discharged until the pressure was 0 to obtain a gradient aerogel composite blank; S6. Heat treatment: The gradient aerogel composite blank was placed in a high-temperature furnace, heated from room temperature to 650 °C, kept for 2 h, and then naturally cooled to obtain a gradient aerogel composite.

[0023] The prepared gradient aerogel composite has the following properties: The use temperature is 1200 °C; the density is 0.27 g / cm 3 ; the thermal conductivity at room temperature is 0.020 W / (m·K), and the thermal conductivity at 1200 °C is 0.030 W / (m·K); the compressive strength (3% deformation) is 0.17 MPa, and the flexural strength is 1.4 MPa; when the material (with a thickness of 12.5 mm) is heated on one side at 1200 °C for 1 h, the shrinkage rate in the thickness direction is 0.4%, and the temperature rise on the cold side is 176 °C.

[0024] Example 3: A preparation method of a gradient aerogel composite, comprising the following steps: S1. Prepare 4 kinds of light-shielding agent slurries: The first light-shielding agent slurry: Mix fatty alcohol polyoxyethylene ether, polyvinyl alcohol and water, stir evenly at 50 °C to form a mixed solution, add zirconia particles to the mixed solution, and stir evenly quickly at 50 °C to form a light-shielding agent slurry with a viscosity of 1800 mPa·s; in the light-shielding agent slurry, the mass ratio of fatty alcohol polyoxyethylene ether, polyvinyl alcohol, zirconia and water is 2.5:5.0:28:100; The average diameter of the zirconia particles is 1.5 μm; The second light-shielding agent slurry: Mix fatty alcohol polyoxyethylene ether, polyvinyl alcohol and water, stir evenly at 50°C to form a mixed solution, add titanium oxide particles to the mixed solution, and stir quickly at 50°C to form a light-shielding agent slurry with a viscosity of 1600 mPa·s; in the light-shielding agent slurry, the mass ratio of fatty alcohol polyoxyethylene ether, polyvinyl alcohol, titanium oxide and water is 2.1:5.8:23:100; The average diameter of the titanium oxide particles is 2.0 μm; The third light-shielding agent slurry: Mix fatty alcohol polyoxyethylene ether, polyvinyl alcohol and water, stir evenly at 50°C to form a mixed solution, add silicon carbide particles to the mixed solution, and stir quickly at 50°C to form a light-shielding agent slurry with a viscosity of 1400 mPa·s; in the light-shielding agent slurry, the mass ratio of fatty alcohol polyoxyethylene ether, polyvinyl alcohol, silicon carbide and water is 1.6:6.0:16:100; The average diameter of the silicon carbide particles is 2.5 μm; The fourth light-shielding agent slurry: Mix fatty alcohol polyoxyethylene ether, polyvinyl alcohol and water, stir evenly at 50°C to form a mixed solution, add silicon carbide particles to the mixed solution, and stir quickly at 50°C to form a light-shielding agent slurry with a viscosity of 1300 mPa·s; in the light-shielding agent slurry, the mass ratio of fatty alcohol polyoxyethylene ether, polyvinyl alcohol, silicon carbide and water is 1.2:6.0:8:100; The average diameter of the silicon carbide particles is 4.0 μm; S2. Slurry coating: In this embodiment, 5 kinds of fibers are used. The first kind of fiber is coated with the first kind of light-shielding agent slurry, the second kind of fiber is coated with the second kind of light-shielding agent slurry, the third kind of fiber is coated with the third kind of light-shielding agent slurry, the fourth kind of fiber is coated with the fourth kind of light-shielding agent slurry, and the fifth kind of fiber is not coated with the light-shielding agent slurry; The first kind of fiber: Lay the layered alumina fiber flat, spray the obtained first kind of light-shielding agent slurry evenly on the fiber surface at a pressure of 0.30 MPa, and keep it at 180°C for 10 h to dry it, so as to form a light-shielding agent coating with a thickness of 0.20 mm on the surface of the layered alumina fiber, and obtain the first kind of zirconia-modified layered alumina fiber; The natural density of the layered alumina fiber is 0.06 g / cm 3 , the thickness is 1.5 mm, and the average diameter is 3.5 μm; The second kind of fiber: Lay the layered zirconia fiber flat, spray the obtained second kind of light-shielding agent slurry evenly on the fiber surface at a pressure of 0.30 MPa, and keep it at 180°C for 10 h to dry it, so as to form a light-shielding agent coating with a thickness of 0.10 mm on the surface of the layered zirconia fiber, and obtain the second kind of titanium oxide-modified layered zirconia fiber; The natural density of the layered zirconia fiber is 0.08 g / cm 3 , the thickness is 1.5 mm, and the average diameter is 1.5 μm; The 3rd fiber: Lay the layered quartz fiber flat, and evenly spray the obtained 3rd light-shielding agent slurry on the fiber surface at a pressure of 0.30 MPa, and keep it at 180 °C for 10 h to dry it, so that a light-shielding agent coating with a thickness of 0.08 mm is formed on the surface of the layered quartz fiber, and the 3rd silicon carbide-modified layered quartz fiber is obtained; The natural density of the layered quartz fiber is 0.06 g / cm 3 , the thickness is 1.5 mm, and the average diameter is 1.5 μm; The 4th fiber: Lay the layered rock wool fiber flat, and evenly spray the obtained 4th light-shielding agent slurry on the fiber surface at a pressure of 0.30 MPa, and keep it at 180 °C for 10 h to dry it, so that a light-shielding agent coating with a thickness of 0.04 mm is formed on the surface of the layered rock wool fiber, and the 4th silicon carbide-modified layered rock wool fiber is obtained; The natural density of the layered rock wool fiber is 0.06 g / cm 3 , the thickness is 1.5 mm, and the average diameter is 1.0 μm; The 5th fiber: Layered glass fiber, without coating the light-shielding agent slurry; The natural density of the layered glass fiber is 0.06 g / cm 3 , the thickness is 1.5 mm, and the average diameter is 1.0 μm; S3. Fiber hot pressing and forming: Stack and lay the light-shielding agent-modified layered fibers on a high-temperature resistant metal mold in sequence. After the laying is completed, tighten and press through the high-temperature resistant metal mold to obtain a fiber preform with a mold. Keep the fiber preform with a mold at 650 °C for 12 h and then cool it naturally to obtain a gradient fiber preform; The laying order of the light-shielding agent-modified layered fibers, from the hot surface to the cold surface, is as follows: the 1st zirconia-modified layered alumina fiber, the 2nd titanium oxide-modified layered zirconia fiber, the 3rd silicon carbide-modified layered quartz fiber, the 4th silicon carbide-modified layered rock wool fiber, the 5th layered glass fiber; the total thickness after the 5 kinds of fibers are laminated and molded is 18.0 mm, and the thickness ratio is 3:3:3:4:5; S4. Sol impregnation and aging: Under the pressure condition of -0.1 MPa, immerse the gradient fiber preform in the alumina sol and keep it for 3 h to obtain a sol-preform mixture. Keep the sol-preform mixture at 65 °C for 20 h to form a gel-preform composite; The solid content of the alumina sol is 15%, and the average particle size of the sol particles is 35 nm; S5. Supercritical drying: Supercritical drying was carried out using tert-butanol as the medium. The gel-preform composite was placed in an autoclave, and after adding tert-butanol, it was kept airtight. The volume ratio of the gel-preform composite to tert-butanol was 1:1.6. It was heated above the critical point of tert-butanol and maintained at 10.0 MPa for 6.5 h. Then, the gas in the autoclave was slowly discharged until the pressure reached 0, obtaining a gradient aerogel composite blank. S6. Heat treatment: The gradient aerogel composite blank was placed in a high-temperature furnace, heated from room temperature to 650 °C, maintained for 2 h, and then naturally cooled to obtain the gradient aerogel composite. The prepared gradient aerogel composite has the following properties: The use temperature is 1600 °C; the density is 0.31 g / cm 3 ; the thermal conductivity at room temperature is 0.026 W / (m·K), and the thermal conductivity at 1600 °C is 0.059 W / (m·K); the compressive strength (3% deformation) is 0.16 MPa, and the flexural strength is 1.1 MPa; when the material (with a thickness of 18 mm) is heated unidirectionally at 1600 °C for 1 h, the shrinkage rate in the thickness direction is 0.9%, and the temperature rise on the cold surface is 262 °C.

[0025] Figure 3 It is a photograph of layered alumina fibers in the preparation method of a gradient aerogel composite described in Example 3.

[0026] Example 4: A preparation method of a gradient aerogel composite, comprising the following steps: S1. Prepare 2 kinds of light-shielding agent slurries: The first kind of light-shielding agent slurry: Mix dodecyl glucoside, starch and water, stir evenly at 25 °C to form a mixed solution, add silicon carbide particles to the mixed solution, and stir evenly rapidly at 25 °C to form a light-shielding agent slurry with a viscosity of 500 mPa·s; in the light-shielding agent slurry, the mass ratio of dodecyl glucoside, starch, silicon carbide, and water is 0.5:3:5:100; The average diameter of the silicon carbide particles is 2.5 μm; The second kind of light-shielding agent slurry: Mix dodecyl glucoside, starch and water, stir evenly at 40 °C to form a mixed solution, add silicon carbide particles to the mixed solution, and stir evenly rapidly at 40 °C to form a light-shielding agent slurry with a viscosity of 1400 mPa·s; in the light-shielding agent slurry, the mass ratio of dodecyl glucoside, starch, silicon carbide, and water is 1.6:6.0:9:100; The average diameter of the silicon carbide particles is 5.0 μm; S2. Slurry coating: In this embodiment, three types of fibers are used. The first type of fiber is coated with the first type of light-shielding agent slurry, the second type of fiber is coated with the second type of light-shielding agent slurry, and the third type of fiber is not coated with light-shielding agent slurry; The first type of fiber: Lay the layered aluminosilicate fiber flat, and evenly spray the obtained first type of light-shielding agent slurry on the fiber surface at a pressure of 0.1 MPa, and keep it drying at 200 °C for 2 h to form a light-shielding agent coating with a thickness of 0.05 mm on the surface of the layered aluminosilicate fiber, obtaining the first type of silicon carbide-modified layered quartz fiber; The natural density of the layered aluminosilicate fiber is 0.06 g / cm 3 , the thickness is 1.5 mm, and the average diameter is 8 μm; The second type of fiber: Lay the layered rock wool fiber flat, and evenly spray the obtained second type of light-shielding agent slurry on the fiber surface at a pressure of 0.10 MPa, and keep it drying at 120 °C for 6 h to form a light-shielding agent coating with a thickness of 0.02 mm on the surface of the layered rock wool fiber, obtaining the second type of silicon carbide-modified layered rock wool fiber; The natural density of the layered rock wool fiber is 0.06 g / cm 3 , the thickness is 1.5 mm, and the average diameter is 1.5 μm; The third type of fiber: Layered glass fiber, not coated with light-shielding agent slurry; The natural density of the layered glass fiber is 0.06 g / cm 3 , the thickness is 1.5 mm, and the average diameter is 0.8 μm; S3. Fiber hot pressing and forming: Stack and lay the light-shielding agent-modified layered fibers on the high-temperature resistant metal mold in sequence. After the laying is completed, tighten and press through the high-temperature resistant metal mold to obtain a fiber preform with a mold. Keep the fiber preform with a mold at 600 °C for 24 h and then cool it naturally to obtain a gradient fiber preform; The laying order of the light-shielding agent-modified layered fibers, from the hot surface to the cold surface, is as follows: the first type of silicon carbide-modified layered aluminosilicate fiber, the second type of silicon carbide-modified layered rock wool fiber, the third type of layered glass fiber; the total thickness after the three types of fibers are laminated and molded is 10 mm, and the thickness ratio is 2:3:5; S4. Sol impregnation and aging: Under the pressure condition of 0 MPa, immerse the gradient fiber preform in the silica sol for 4 h to obtain a sol-preform mixture, and keep the sol-preform mixture at 40 °C for 24 h to form a gel-preform complex; The solid content of the silica sol is 6%, and the average particle size of the sol particles is 5 nm; S5. Supercritical drying: Supercritical drying is carried out using ethanol as the medium. The gel-preform composite is placed in an autoclave, and after adding ethanol, it is kept airtight. The volume ratio of the gel-preform composite to ethanol is 1:0.3. It is heated to above the critical point of ethanol and maintained at 15.0 MPa for 10 h. Then, the gas in the autoclave is slowly discharged until the pressure is 0 to obtain a gradient aerogel composite blank. S6. Heat treatment: The gradient aerogel composite blank is placed in a high-temperature furnace and heated from room temperature to 600 °C, maintained for 5 h, and then naturally cooled to obtain the gradient aerogel composite.

[0027] The prepared gradient aerogel composite has the following properties: The use temperature is 800 °C; the density is 0.17 g / cm 3 ; the thermal conductivity at room temperature is 0.019 W / (m·K), and the thermal conductivity at 800 °C is 0.025 W / (m·K); the compressive strength (3% deformation) is 0.15 MPa, and the flexural strength is 1.6 MPa; when the material (with a thickness of 10 mm) is heated on one side at 800 °C for 1 h, the shrinkage rate in the thickness direction is 0.1%, and the temperature rise on the cold side is 74 °C.

[0028] Example 5: A preparation method of a gradient aerogel composite includes the following steps: S1. Prepare 2 kinds of light-shielding agent slurries: The first kind of light-shielding agent slurry: Mix dodecyl glucoside, starch and water, stir evenly at 40 °C to form a mixed solution, add silicon carbide particles to the mixed solution, and stir quickly at 40 °C to form a light-shielding agent slurry with a viscosity of 1600 mPa·s; in the light-shielding agent slurry, the mass ratio of dodecyl glucoside, starch, silicon carbide, and water is 1.8:6.0:15:100; The average diameter of the silicon carbide particles is 5 μm; The second kind of light-shielding agent slurry: Mix dodecyl glucoside, starch and water, stir evenly at 40 °C to form a mixed solution, add silicon carbide particles to the mixed solution, and stir quickly at 40 °C to form a light-shielding agent slurry with a viscosity of 1400 mPa·s; in the light-shielding agent slurry, the mass ratio of dodecyl glucoside, starch, silicon carbide, and water is 1.6:6.0:9:100; The average diameter of the silicon carbide particles is 3.5 μm; S2. Slurry coating: In this example, 3 kinds of fibers are used. The first kind of fiber is coated with the first kind of light-shielding agent slurry, the second kind of fiber is coated with the second kind of light-shielding agent slurry, and the third kind of fiber is not coated with the light-shielding agent slurry; The first type of fiber: Lay the layered quartz fiber flat, and evenly spray the obtained first type of light-shielding agent slurry on the fiber surface at a pressure of 0.15 MPa, and keep it at 170 °C for 4.5 h to dry it, so as to form a light-shielding agent coating with a thickness of 0.05 mm on the surface of the layered quartz fiber, and obtain the first type of silicon carbide-modified layered quartz fiber; The natural density of the layered quartz fiber is 0.06 g / cm 3 , with a thickness of 1.5 mm and an average diameter of 5 μm; The second type of fiber: Lay the layered rock wool fiber flat, and evenly spray the obtained second type of light-shielding agent slurry on the fiber surface at a pressure of 0.15 MPa, and keep it at 170 °C for 4.5 h to dry it, so as to form a light-shielding agent coating with a thickness of 0.02 mm on the surface of the layered rock wool fiber, and obtain the second type of silicon carbide-modified layered rock wool fiber; The natural density of the layered rock wool fiber is 0.06 g / cm 3 , with a thickness of 1.5 mm and an average diameter of 3 μm; The third type of fiber: Layered glass fiber, without coating the light-shielding agent slurry; The natural density of the layered glass fiber is 0.06 g / cm 3 , with a thickness of 1.5 mm and an average diameter of 0.8 μm; S3. Fiber hot pressing and forming: Stack and lay the light-shielding agent-modified layered fibers on a high-temperature resistant metal mold in sequence. After the laying is completed, tighten and press through the high-temperature resistant metal mold to obtain a fiber preform with a mold. Keep the fiber preform with a mold at 650 °C for 12 h and then cool it naturally to obtain a gradient fiber preform; The laying order of the light-shielding agent-modified layered fibers, from the hot surface to the cold surface, is as follows: the first type of silicon carbide-modified layered quartz fiber, the second type of silicon carbide-modified layered rock wool fiber, and the third type of layered glass fiber; the total thickness after the three types of fibers are laminated and molded is 10 mm, and the thickness ratio is 2:2:6; S4. Sol impregnation and aging: Under the pressure condition of -0.1 MPa, immerse the gradient fiber preform in zirconia sol for 2 h to obtain a sol-preform mixture, and keep the sol-preform mixture at 50 °C for 16 h to form a gel-preform composite; The solid content of the zirconia sol is 12%, and the average particle size of the sol particles is 8 nm; S5. Supercritical drying: Supercritical drying is carried out using ethanol as the medium. The gel-preform composite is placed in an autoclave, ethanol is added and kept airtight. The volume ratio of the gel-preform composite to ethanol is 1:0.3. It is heated above the critical point of ethanol and kept at 13.0 MPa for 6 h. Then the gas in the autoclave is slowly discharged until the pressure is 0, obtaining a gradient aerogel composite blank. S6. Heat treatment: The gradient aerogel composite blank is placed in a high-temperature furnace, heated from room temperature to 650 °C, kept for 2 h, and then naturally cooled to obtain the gradient aerogel composite.

[0029] The prepared gradient aerogel composite has the following properties: The use temperature is 800 °C; the density is 0.23 g / cm 3 ; the thermal conductivity at room temperature is 0.020 W / (m·K), and the thermal conductivity at 800 °C is 0.028 W / (m·K); the compressive strength (3% deformation) is 0.21 MPa, and the flexural strength is 1.5 MPa; when the material (with a thickness of 10 mm) is heated on one side at 800 °C for 1 h, the shrinkage rate in the thickness direction is 0.4%, and the temperature rise on the cold side is 76 °C.

[0030] Example 6: A preparation method of a gradient aerogel composite, comprising the following steps: S1. Prepare 3 kinds of light-shielding agent slurries: The first kind of light-shielding agent slurry: Mix dodecyl betaine, gelatin and water, stir evenly at 45 °C to form a mixed solution, add titanium oxide particles to the mixed solution, and stir quickly at 45 °C to form a light-shielding agent slurry with a viscosity of 1500 mPa·s; in the light-shielding agent slurry, the mass ratio of dodecyl betaine, gelatin, titanium oxide and water is 2.0:6.5:20:100; The average diameter of the titanium oxide particles is 2.0 μm; The second kind of light-shielding agent slurry: Mix dodecyl betaine, gelatin and water, stir evenly at 45 °C to form a mixed solution, add silicon carbide particles to the mixed solution, and stir quickly at 45 °C to form a light-shielding agent slurry with a viscosity of 1400 mPa·s; in the light-shielding agent slurry, the mass ratio of dodecyl betaine, gelatin, silicon carbide and water is 1.3:6.5:15:100; The average diameter of the silicon carbide particles is 2.5 μm; The 3rd light-shielding agent slurry: Mix dodecyl betaine, gelatin and water, stir evenly at 45°C to form a mixed solution, add iron oxide particles to the mixed solution, and stir quickly at 45°C to mix evenly, forming a light-shielding agent slurry with a viscosity of 1200 mPa·s; in the light-shielding agent slurry, the mass ratio of dodecyl betaine, gelatin, silicon carbide and water is 1.0:6.0:8:100; The average diameter of the iron oxide particles is 4.0 μm; S2. Slurry coating: In this embodiment, 4 types of fibers are used. The 1st fiber is coated with the 1st light-shielding agent slurry, the 2nd fiber is coated with the 2nd light-shielding agent slurry, the 3rd fiber is coated with the 3rd light-shielding agent slurry, and the 4th fiber is not coated with the light-shielding agent slurry; The 1st fiber: Lay the layered lanthanum zirconate fiber flat, spray the obtained 1st light-shielding agent slurry evenly on the fiber surface under a pressure of 0.25 MPa, and keep it at 180°C for 6 h to dry it, so that a light-shielding agent coating with a thickness of 0.15 mm is formed on the surface of the layered lanthanum zirconate fiber, obtaining the 1st titanium oxide-modified layered lanthanum zirconate fiber; The natural density of the layered lanthanum zirconate fiber is 0.10 g / cm 3 , the thickness is 0.5 mm, and the average diameter is 2.0 μm; The 2nd fiber: Lay the layered quartz fiber flat, spray the obtained 2nd light-shielding agent slurry evenly on the fiber surface under a pressure of 0.22 MPa, and keep it at 180°C for 6 h to dry it, so that a light-shielding agent coating with a thickness of 0.08 mm is formed on the surface of the layered quartz fiber, obtaining the 2nd silicon carbide-modified layered quartz fiber; The natural density of the layered quartz fiber is 0.06 g / cm 3 , the thickness is 1.5 mm, and the average diameter is 1.5 μm; The 3rd fiber: Lay the layered rock wool fiber flat, spray the obtained 3rd light-shielding agent slurry evenly on the fiber surface under a pressure of 0.22 MPa, and keep it at 180°C for 6 h to dry it, so that a light-shielding agent coating with a thickness of 0.02 mm is formed on the surface of the layered rock wool fiber, obtaining the 3rd silicon carbide-modified layered rock wool fiber; The natural density of the layered rock wool fiber is 0.06 g / cm 3 , the thickness is 1.5 mm, and the average diameter is 1.0 μm; The 4th fiber: Layered glass fiber, not coated with the light-shielding agent slurry; The natural density of the layered glass fiber is 0.02 g / cm 3 , the thickness is 5 mm, and the average diameter is 0.5 μm; S3. Fiber hot pressing and forming: The light-shielding agent modified laminated fibers are stacked and laid on a high-temperature resistant metal mold in sequence. After the laying is completed, the high-temperature resistant metal mold is used to fasten and press, obtaining a fiber preform with the mold. The fiber preform with the mold is maintained at 650 °C for 12 h and then naturally cooled to obtain a gradient fiber preform; The laying sequence of the light-shielding agent modified laminated fibers, from the hot surface to the cold surface, is as follows: the first titanium oxide modified laminated lanthanum zirconate fiber, the second silicon carbide modified laminated quartz fiber, the third iron oxide modified laminated rock wool fiber, and the fourth laminated glass fiber; the total thickness after the lamination and molding of the 4 fibers is 12.5 mm, and the thickness ratio is 2:2:3:5.5; S4. Sol impregnation and aging: Under a pressure condition of -0.1 MPa, the gradient fiber preform is immersed in silica sol for 3 h to obtain a sol-preform mixture. The sol-preform mixture is maintained at 55 °C for 20 h to form a gel-preform composite; The solid content of the silica sol is 11%, and the average particle size of the sol particles is 20 nm; S5. Supercritical drying: Isopropanol is used as the medium for supercritical drying. The gel-preform composite is placed in an autoclave, and after adding isopropanol, it is kept airtight. The volume ratio of the gel-preform composite to isopropanol is 1:1.4. It is heated to above the critical point of isopropanol and maintained at 12.5 MPa for 4.5 h. The gas in the autoclave is slowly discharged until the pressure is 0 to obtain a gradient aerogel composite blank; S6. Heat treatment: The gradient aerogel composite blank is placed in a high-temperature furnace, heated from room temperature to 650 °C, maintained for 2 h, and then naturally cooled to obtain a gradient aerogel composite; The prepared gradient aerogel composite has the following properties: The use temperature is 1200 °C; the density is 0.28 g / cm 3 ; the thermal conductivity at room temperature is 0.021 W / (m·K), and the thermal conductivity at 1200 °C is 0.032 W / (m·K); the compressive strength (3% deformation) is 0.18 MPa, and the flexural strength is 1.5 MPa; when the material (with a thickness of 12.5 mm) is heated unidirectionally at 1200 °C for 1 h, the shrinkage rate in the thickness direction is 0.5%, and the temperature rise on the cold surface is 181 °C.

[0031] Example 7: A preparation method of a gradient aerogel composite, comprising the following steps: S1. Prepare 2 kinds of light-shielding agent slurries: The first type of light-shielding agent slurry: Mix dodecyl betaine, gelatin, and water, stir evenly at 45 °C to form a mixed solution, add titanium oxide particles to the mixed solution, and stir quickly at 45 °C to form a light-shielding agent slurry with a viscosity of 1500 mPa·s; in the light-shielding agent slurry, the mass ratio of dodecyl betaine, gelatin, titanium oxide, and water is 2.0:6.5:20:100; The average diameter of the titanium oxide particles is 2.0 μm; The second type of light-shielding agent slurry: Mix dodecyl betaine, gelatin, and water, stir evenly at 45 °C to form a mixed solution, add zirconium oxide particles to the mixed solution, and stir quickly at 45 °C to form a light-shielding agent slurry with a viscosity of 1400 mPa·s; in the light-shielding agent slurry, the mass ratio of dodecyl betaine, gelatin, zirconium oxide, and water is 1.3:6.5:14:100; The average diameter of the silicon carbide particles is 2.5 μm; S2. Slurry coating: In this embodiment, 3 types of fibers are used. The first type of fiber is coated with the first type of light-shielding agent slurry, the second type of fiber is coated with the second type of light-shielding agent slurry, and the third type of fiber is not coated with the light-shielding agent slurry; The first type of fiber: Lay the layered zirconia fiber flat, spray the obtained first type of light-shielding agent slurry evenly on the fiber surface at a pressure of 0.22 MPa, and keep it at 180 °C for 6 h to dry it, so that a light-shielding agent coating with a thickness of 0.12 mm is formed on the surface of the layered zirconia fiber, and the first type of titanium oxide-modified layered zirconia fiber is obtained; The natural density of the layered zirconia fiber is 0.08 g / cm 3 , the thickness is 1.5 mm, and the average diameter is 2.0 μm; The second type of fiber: Lay the layered quartz fiber flat, spray the obtained second type of light-shielding agent slurry evenly on the fiber surface at a pressure of 0.22 MPa, and keep it at 180 °C for 6 h to dry it, so that a light-shielding agent coating with a thickness of 0.07 mm is formed on the surface of the layered quartz fiber, and the second type of silicon carbide-modified layered quartz fiber is obtained; The natural density of the layered quartz fiber is 0.06 g / cm 3 , the thickness is 1.5 mm, and the average diameter is 1.5 μm; The third type of fiber: Layered rock wool fiber, not coated with light-shielding agent slurry; The natural density of the layered rock wool fiber is 0.06 g / cm 3 , the thickness is 1.5 mm, and the average diameter is 1.0 μm; S3. Fiber hot pressing and forming: The light-shielding agent-modified laminated fibers are sequentially stacked and laid on a high-temperature-resistant metal mold. After the laying is completed, the high-temperature-resistant metal mold is used to fasten and press, obtaining a fiber preform with the mold. The fiber preform with the mold is maintained at 650 °C for 12 h and then naturally cooled to obtain a gradient fiber preform; The laying sequence of the light-shielding agent-modified laminated fibers, from the hot surface to the cold surface, is as follows: the first titanium oxide-modified laminated zirconia fiber, the second zirconia-modified laminated quartz fiber, and the third laminated rock wool fiber; the total thickness after the lamination and molding of the three fibers is 12.5 mm, and the thickness ratio is 3:4:5.5; S4. Sol impregnation and aging: Under a pressure condition of -0.1 MPa, the gradient fiber preform is immersed in silica sol for 3 h to obtain a sol-preform mixture. The sol-preform mixture is maintained at 55 °C for 20 h to form a gel-preform composite; The solid content of the silica sol is 11%, and the average particle size of the sol particles is 20 nm; S5. Supercritical drying: Isopropyl alcohol is used as the medium for supercritical drying. The gel-preform composite is placed in an autoclave, and after adding isopropyl alcohol, it is kept airtight. The volume ratio of the gel-preform composite to isopropyl alcohol is 1:1.4. It is heated to above the critical point of isopropyl alcohol and maintained at 11.0 MPa for 4.5 h. The gas in the autoclave is slowly discharged until the pressure is 0 to obtain a gradient aerogel composite blank; S6. Heat treatment: The gradient aerogel composite blank is placed in a high-temperature furnace, heated from room temperature to 650 °C, maintained for 2 h, and naturally cooled to obtain a gradient aerogel composite.

[0032] The prepared gradient aerogel composite has the following properties: The use temperature is 1200 °C; the density is 0.28 g / cm 3 ; the thermal conductivity at room temperature is 0.020 W / (m·K), and the thermal conductivity at 1200 °C is 0.031 W / (m·K); the compressive strength (3% deformation) is 0.16 MPa, and the flexural strength is 1.3 MPa; when the material (with a thickness of 12.5 mm) is heated unidirectionally at 1200 °C for 1 h, the shrinkage rate in the thickness direction is 0.2%, and the temperature rise on the cold surface is 178 °C.

[0033] Figure 4 It is a physical photo of the gradient aerogel composite prepared by the preparation method of the gradient aerogel composite described in Example 7.

[0034] Example 8: A preparation method of a gradient aerogel composite, comprising the following steps: S1. Prepare 2 kinds of light-shielding agent slurries: The first kind of light-shielding agent slurry: Mix fatty alcohol polyoxyethylene ether, polyvinyl alcohol and water, stir evenly at 50 °C to form a mixed solution, add zirconia particles to the mixed solution, and stir quickly at 50 °C to form a light-shielding agent slurry with a viscosity of 3000 mPa·s; in the light-shielding agent slurry, the mass ratio of fatty alcohol polyoxyethylene ether, polyvinyl alcohol, zirconia, and water is 3.0:10.0:30:100; The average diameter of the zirconia particles is 1.5 μm; The second kind of light-shielding agent slurry: Mix fatty alcohol polyoxyethylene ether, polyvinyl alcohol and water, stir evenly at 50 °C to form a mixed solution, add titanium oxide particles to the mixed solution, and stir quickly at 50 °C to form a light-shielding agent slurry with a viscosity of 1600 mPa·s; in the light-shielding agent slurry, the mass ratio of fatty alcohol polyoxyethylene ether, polyvinyl alcohol, titanium oxide, and water is 2.1:5.8:23:100; The average diameter of the titanium oxide particles is 2.0 μm; S2. Slurry coating: In this embodiment, 3 kinds of fibers are used. The first kind of fiber is coated with the first kind of light-shielding agent slurry, the second kind of fiber is coated with the second kind of light-shielding agent slurry, and the third kind of fiber is not coated with the light-shielding agent slurry; The first kind of fiber: Lay the layered mullite fiber flat, spray the obtained first kind of light-shielding agent slurry evenly on the fiber surface at a pressure of 0.50 MPa, and keep it at 180 °C for 10 h to dry it, so that a light-shielding agent coating with a thickness of 0.20 mm is formed on the surface of the layered alumina fiber, and the first kind of zirconia-modified layered mullite fiber is obtained; The natural density of the layered mullite fiber is 0.06 g / cm 3 , the thickness is 1.5 mm, and the average diameter is 4.5 μm; The second kind of fiber: Lay the layered zirconia fiber flat, spray the obtained second kind of light-shielding agent slurry evenly on the fiber surface at a pressure of 0.30 MPa, and keep it at 180 °C for 10 h to dry it, so that a light-shielding agent coating with a thickness of 0.10 mm is formed on the surface of the layered zirconia fiber, and the second kind of titanium oxide-modified layered zirconia fiber is obtained; The natural density of the layered zirconia fiber is 0.08 g / cm 3 , the thickness is 1.5 mm, and the average diameter is 1.5 μm; The third kind of fiber: Layered quartz fiber, not coated with the light-shielding agent slurry; The natural density of the layered quartz fiber is 0.06 g / cm 3 , the thickness is 1.5 mm, and the average diameter is 1.5 μm; S3. Fiber hot pressing and forming: The light-shielding agent modified laminated fibers are stacked and laid on a high-temperature resistant metal mold in sequence. After the laying is completed, it is further fastened and pressed by the high-temperature resistant metal mold to obtain a fiber preform with a mold. The fiber preform with a mold is kept at 1000 °C for 6 h and then naturally cooled to obtain a gradient fiber preform; The laying sequence of the light-shielding agent modified laminated fibers from the hot surface to the cold surface is as follows: the first kind of zirconia-modified laminated mullite fiber, the second kind of titanium oxide-modified laminated zirconia fiber, and the third kind of laminated quartz fiber; the total thickness after the lamination and molding of the three kinds of fibers is 18.0 mm, and the thickness ratio is 4:5:9; S4, Sol impregnation and aging: Under the pressure condition of -0.1 MPa, the gradient fiber preform is immersed in alumina sol for 3 h to obtain a sol-preform mixture. The sol-preform mixture is kept at 65 °C for 20 h to form a gel-preform composite; The solid content of the alumina sol is 14%, and the average particle size of the sol particles is 50 nm; S5, Supercritical drying: Tert-butanol is used as the medium for supercritical drying. The gel-preform composite is placed in an autoclave, and after adding tert-butanol, it is kept airtight. The volume ratio of the gel-preform composite to tert-butanol is 1:3. It is heated above the critical point of tert-butanol and kept at 12.5 MPa for 10 h. The gas in the autoclave is slowly discharged until the pressure is 0 to obtain a gradient aerogel composite blank; S6, Heat treatment: The gradient aerogel composite blank is placed in a high-temperature furnace, heated from room temperature to 1000 °C, kept for 1 h, and naturally cooled to obtain a gradient aerogel composite.

[0035] The prepared gradient aerogel composite has the following properties: The use temperature is 1600 °C; the density is 0.30 g / cm 3 ; the thermal conductivity at room temperature is 0.027 W / (m·K), and the thermal conductivity at 1600 °C is 0.062 W / (m·K); the compressive strength (3% deformation) is 0.17 MPa, and the flexural strength is 1.2 MPa; when the material (with a thickness of 18 mm) is heated unidirectionally at 1600 °C for 1 h, the shrinkage rate in the thickness direction is 0.6%, and the temperature rise on the cold surface is 281 °C.

[0036] Comparative example 1: The difference between Comparative example 1 and Example 1 is that in the step of "S1, Preparing the light-shielding agent slurry", the average diameter of the silicon carbide particles used in the first kind of light-shielding agent slurry and the second kind of light-shielding agent slurry is 10 μm, and the others are the same as in Example 1.

[0037] The prepared aerogel composite material has a thermal conductivity of 0.024 W / (m·K) at room temperature and 0.030 W / (m·K) at 800 °C; when the material (with a thickness of 10 mm) is heated unidirectionally at 800 °C for 1 h, the shrinkage rate in the thickness direction is 0.3%, and the temperature rise on the cold side is 88 °C.

[0038] It shows that due to the high intrinsic thermal conductivity of the particles of the light-shielding agent, when its average diameter is relatively large, it will significantly increase the solid-state heat conduction, increase the comprehensive thermal conductivity, and reduce the heat insulation performance.

[0039] Comparative Example 2: The difference between Comparative Example 2 and Example 1 lies in that the average particle size of the silica sol particles in the "S4, Sol Impregnation and Aging" step is 20 nm, and the others are the same as in Example 1.

[0040] The prepared aerogel composite material has a service temperature of 1000 °C; the thermal conductivity at room temperature is 0.021 W / (m·K), and the thermal conductivity at 800 °C is 0.026 W / (m·K); the compressive strength (3% deformation) is 0.08 MPa, and the flexural strength is 1.4 MPa.

[0041] It shows that as the particle size of the silica sol particles increases, the heat resistance of the composite material improves, the thermal conductivity increases, and the mechanical properties decrease.

[0042] Comparative Example 3: The difference between Comparative Example 3 and Example 1 lies in that the heat treatment temperature in the "S6, Heat Treatment" step is 900 °C, and the others are the same as in Example 1.

[0043] The prepared aerogel composite material shrinks by 8.3% in thickness during the heat treatment process, the thermal conductivity at room temperature is 0.030 W / (m·K), and the thermal conductivity at 800 °C is 0.043 W / (m·K); when the material (with a thickness of 10 mm) is heated unidirectionally at 800 °C for 1 h, the shrinkage rate in the thickness direction is 0.3%, and the temperature rise on the cold side is 108 °C.

[0044] It shows that too high heat treatment temperature will cause the pore structure of the silica aerogel to collapse, the composite material to shrink, and the heat insulation performance to decrease.

[0045] Comparative Example 4: The difference between Comparative Example 4 and Example 2 lies in that the mass ratio of titanium oxide to water in the first light-shielding agent slurry in the "S1, Preparation of Light-Shielding Agent Slurry" step is 50:100, and the others are the same as in Example 2.

[0046] The prepared light-shielding agent slurry has a relatively high viscosity (above 4500 mPa·s), cannot be sprayed evenly on the layered fibers, and the sprayed thickness is greater than 0.5 mm.

[0047] It shows that too high a light-shielding agent content in the light-shielding agent slurry will significantly affect the spraying effect.

[0048] Comparative Example 5: The difference between Comparative Example 5 and Example 3 is that in the step of "S2, slurry coating", the average diameters of the first type of layered alumina fiber and the second type of layered zirconia fiber are 9 μm and 6 μm respectively, and the others are the same as in Example 3.

[0049] The prepared aerogel composite material has a thermal conductivity of 0.029 W / (m·K) at room temperature and a thermal conductivity of 0.072 W / (m·K) at 1600 °C; the material (with a thickness of 18 mm) is heated unidirectionally at 1600 °C for 1 h, and the shrinkage rate in the thickness direction is 0.4%, and the temperature rise on the cold side is 315 °C.

[0050] It shows that the increase in fiber diameter will lead to a significant increase in the comprehensive thermal conductivity and a decrease in the heat insulation performance.

[0051] In addition, it should be understood that although this specification is described according to the 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 preparation method of a gradient aerogel composite material, characterized in that: It includes the following steps: S1. Prepare the light-shielding agent slurry: Mix the dispersant, the viscous component and water, stir evenly at 25°C to 50°C to form a mixed solution, add the light-shielding agent to the mixed solution, and stir quickly at 25°C to 50°C to form a light-shielding agent slurry with a viscosity of 500 mPa·s to 3000 mPa·s. In the light-shielding agent slurry, the mass ratio of the dispersant, the viscous component, the light-shielding agent and water is (0.5 to 3):(3 to 10):(5 to 30):100; The dispersant is one of dodecyl glucoside, fatty alcohol polyoxyethylene ether glucoside, dodecyl betaine, fatty alcohol polyoxyethylene ether and dodecyl phenol polyoxyethylene ether; The viscous component is one of starch, gelatin and polyvinyl alcohol; The light-shielding agent is one of silicon carbide, zirconia, titanium oxide, potassium hexatitanate, carbon black, iron oxide and magnetite, and the average diameter range of the light-shielding agent particles is 0.5 μm to 5 μm; S2. Coating the slurry: Lay the layered fiber flat, spray the obtained light-shielding agent slurry evenly on the fiber surface at a pressure of 0.1 MPa to 0.5 MPa, and keep it at 120°C to 200°C for 2 h to 6 h to dry it, so as to form a light-shielding agent coating with a thickness of 0.01 mm to 0.3 mm on the surface of the layered fiber, and obtain the light-shielding agent-modified layered fiber; The layered fiber is selected from any one of rock wool, glass fiber, quartz fiber, aluminum silicate fiber, zirconia fiber, lanthanum zirconate fiber, alumina fiber and mullite fiber; The natural density of the layered fiber is 0.02 g / cm 3 ~0.1 g / cm 3 , the thickness is 0.1 mm to 5 mm, and the average diameter is 0.5 μm to 8 μm; S3. Hot pressing and forming of the fiber: Stack and lay the light-shielding agent-modified layered fiber on the high-temperature-resistant metal mold in sequence. After the laying is completed, tighten and press through the high-temperature-resistant metal mold to obtain a fiber preform with a mold. Keep the fiber preform with a mold at 600°C to 1000°C for 6 h to 24 h and then cool it naturally to obtain a gradient fiber preform; S4. Sol impregnation and aging: Under the pressure condition of -0.1 MPa to 0 MPa, immerse the gradient fiber preform in the sol for 1 h to 4 h to obtain a sol-preform mixture. Keep the sol-preform mixture at 40°C to 70°C for 8 h to 24 h to form a gel-preform complex; The sol is one of silica sol, alumina sol and zirconia sol, the solid content of the sol is 6% to 15%, and the average particle size range of the sol particles is 5 nm to 50 nm; S5. Supercritical drying: Use an alcohol substance as the medium for supercritical drying. Place the gel-preform complex in an autoclave, add the alcohol substance and keep it airtight. The volume ratio of the gel-preform complex to the alcohol substance is 1:(0.3 to 3). Heat it above the critical point of the alcohol, keep it at 8.0 MPa to 15.0 MPa for 1 h to 10 h, and slowly discharge the gas in the autoclave until the pressure is 0 to obtain a gradient aerogel composite blank; S6. Heat treatment: Place the gradient aerogel composite blank in a high-temperature furnace, heat it from room temperature to 600 °C to 1000 °C, hold for 1 h to 5 h, and then cool it naturally to obtain the gradient aerogel composite. The gradient aerogel composite is a composite material with a service temperature of 800 °C, or a composite material with a service temperature of 1200 °C, or a composite material with a service temperature of 1600 °C. These three composite materials take into account low density, wide-temperature-range thermal conductivity, and mechanical properties. Their typical properties are as follows: (1)Composite material used at a temperature of 800 °C: density is 0.19 g / cm 3 , thermal conductivity at room temperature is 0.016 W / (m·K), thermal conductivity at 800 °C is 0.022 W / (m·K), 3% deformation compressive strength is 0.12 MPa, flexural strength is 1.2 MPa. The composite material with a thickness of 10 mm is heated unidirectionally at 800 °C for 1 h, the shrinkage rate in the thickness direction is 0.3%, and the temperature rise on the cold surface is 63 °C; (2)Composite material used at a temperature of 1200 °C: density is 0.27 g / cm 3 , the thermal conductivity at room temperature is 0.020 W / (m·K), the thermal conductivity at 1200 °C is 0.030 W / (m·K), the 3% deformation compression strength is 0.17 MPa, the flexural strength is 1.1 MPa. The composite material with a thickness of 12.5 mm is heated on one side at 1200 °C for 1 h, the shrinkage rate in the thickness direction is 0.4%, and the temperature rise on the cold surface is 176 °C; (3)Composite material used at a temperature of 1600 °C: density is 0.31 g / cm 3 , thermal conductivity at room temperature is 0.026 W / (m·K), thermal conductivity at 1600 °C is 0.056 W / (m·K), 3% deformation compressive strength is 0.16 MPa, flexural strength is 0.95 MPa. The composite material with a thickness of 18 mm is heated unidirectionally at 1600 °C for 1 h, the shrinkage rate in the thickness direction is 0.9%, and the temperature rise on the cold surface is 262 °C.

2. The preparation method of a gradient aerogel composite material according to claim 1, wherein: For the sol described in S4, the solvent used is one of ethanol, isopropanol, n-propanol, n-butanol, sec-butanol, and tert-butanol.

3. The preparation method of a gradient aerogel composite material according to claim 1, characterized in that: For the alcohol substance described in S5, it is one of ethanol, methanol, isopropanol, n-propanol, n-butanol, sec-butanol, and tert-butanol.

4. The preparation method of a gradient aerogel composite material according to claim 1, characterized in that: For the heating from room temperature to 600 °C to 1000 °C described in S6, the heating rate is completed at a rate of 0.5 °C / min to 3 °C / min.

5. A gradient aerogel composite material, characterized in that: Obtained according to the preparation method of a gradient aerogel composite material described in any one of claims 1-4. The gradient aerogel composite is a composite material with a service temperature of 800 °C, or a composite material with a service temperature of 1200 °C, or a composite material with a service temperature of 1600 °C. These three composite materials take into account low density, wide-temperature-range thermal conductivity, and mechanical properties. Their typical properties are as follows: (1) Composite material used at a temperature of 800 °C: density is 0.19 g / cm 3 , thermal conductivity at room temperature is 0.016 W / (m·K), thermal conductivity at 800 °C is 0.022 W / (m·K), 3% deformation compression strength is 0.12 MPa, flexural strength is 1.2 MPa. The composite material with a thickness of 10 mm is heated unidirectionally at 800 °C for 1 h, the shrinkage rate in the thickness direction is 0.3%, and the temperature rise on the cold surface is 63 °C; (2)Composite material used at a temperature of 1200 °C: density is 0.27 g / cm 3 , thermal conductivity at room temperature is 0.020 W / (m·K), thermal conductivity at 1200 °C is 0.030 W / (m·K), 3% deformation compressive strength is 0.17 MPa, flexural strength is 1.1 MPa. The composite material with a thickness of 12.5 mm is heated on one side at 1200 °C for 1 h, the shrinkage rate in the thickness direction is 0.4%, and the temperature rise on the cold side is 176 °C; (3)Composite material used at a temperature of 1600°C: density is 0.31 g / cm 3 , thermal conductivity at room temperature is 0.026 W / (m·K), thermal conductivity at 1600°C is 0.056 W / (m·K), 3% deformation compressive strength is 0.16 MPa, flexural strength is 0.95 MPa. The composite material with a thickness of 18 mm is heated on one side at 1600°C for 1 h, the shrinkage rate in the thickness direction is 0.9%, and the temperature rise on the cold surface is 262°C.

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