A gradient aerogel composite material and preparation method thereof

Abstract

The present invention discloses a gradient aerogel composite material and its preparation method. The gradient aerogel composite material is prepared by preparing a sunscreen slurry, applying the slurry, hot-pressing fibers, impregnating and aging the sol, supercritical drying, and heat treating. The gradient aerogel composite material prepared using the present invention is ultra-lightweight, high-temperature resistant, exhibits ultra-low thermal conductivity over a wide temperature range, and can be formed into large-scale thermal insulation components. It can be used as a thermal insulation material in aerospace, nuclear power, shipbuilding, and other fields.

Description

Technical Field

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

[0002] Aerogel, a nanoporous material, boasts an extremely low room-temperature thermal conductivity (0.012 W / (m·K)), promising broad applications in thermal insulation. Aerogel composite products, made with fiber as the reinforcement and silica aerogel as the matrix, have already found applications in aerospace, petrochemical pipelines, and new energy vehicles.

[0003] However, the silica aerogel composites prepared by the existing method have a low density (usually greater than 0.30 g / cm2) in applications that have extremely stringent requirements on the weight, thermal insulation performance and mechanical properties of thermal insulation materials (such as aircraft and spacecraft). 3 The high-temperature thermal conductivity (typical value of 0.045 W / (m·K) at 800°C) and high-temperature thermal conductivity (typical value of 0.045 W / (m·K) at 800°C) are still too high to meet application requirements, and the operating temperature is also limited to below 800°C. Reducing the volume fraction of fibers and the density of the aerogel in aerogel composites can effectively reduce the density of the composite, but at the same time, the high-temperature thermal insulation performance and mechanical strength are significantly sacrificed. Introducing a sunscreen into aerogel composites can reduce their high-temperature thermal conductivity, but the high solid-state thermal conductivity of the sunscreen increases the thermal conductivity of the composite in the medium and low temperature ranges, making it impossible to maintain a very low thermal conductivity over a wide temperature range. Furthermore, current processing methods make it difficult to ensure the uniform introduction of the sunscreen into the composite, making it impossible to stably form large, complex components.

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

[0005] To address the lack of ultra-lightweight, wide-temperature-range, and ultra-low thermal conductivity aerogel composite materials in the prior art, the present invention provides a gradient aerogel composite material and a method for preparing it. This method utilizes a sunscreen slurry preparation, slurry coating, fiber hot pressing, sol-gel impregnation, supercritical drying, and heat treatment process to prepare the gradient aerogel composite material with excellent thermal insulation properties. The gradient aerogel composite material prepared using this invention exhibits ultra-lightweight, high-temperature resistance, ultra-low thermal conductivity over a wide temperature range, and the ability to form large-scale thermal insulation components. It is suitable for use as a thermal insulation material in aerospace, nuclear power, shipbuilding, and other fields.

[0006] The technical solutions of the present invention are as follows:

[0007] The preparation method of the gradient aerogel composite material described in the present invention includes six steps: preparing a sunscreen slurry, slurry coating, fiber hot pressing molding, sol impregnation and aging, supercritical drying, and heat treatment.

[0008] The purpose of the present invention is achieved through the following technical solutions:

[0009] A method for preparing a gradient aerogel composite material comprises the following steps:

[0010] S1. Prepare sunscreen slurry:

[0011] The dispersant, the viscous component and water are mixed and stirred at 25° C. to 50° C. to form a mixed solution, the sunscreen is added to the mixed solution and stirred rapidly at 25° C. to 50° C. to form a sunscreen slurry having a viscosity of 500 mPa·s to 3000 mPa·s, wherein the mass ratio of the dispersant, the viscous component, the sunscreen and the water is (0.5-3):(3-10):(5-30):100;

[0012] The dispersant is one of lauryl glucoside, fatty alcohol polyoxyethylene ether glucoside, lauryl betaine, fatty alcohol polyoxyethylene ether and laurylphenol polyoxyethylene ether;

[0013] The viscous component is one of starch, gelatin and polyvinyl alcohol;

[0014] The sunscreen is one of silicon carbide, zirconium oxide, titanium oxide, potassium hexatitanate, carbon black, iron oxide, and ferrosoferric oxide, and the average diameter of the sunscreen particles ranges from 0.5 μm to 5 μm;

[0015] S2. Slurry coating:

[0016] The layered fibers are laid flat, and the obtained sunscreen slurry is evenly sprayed on the fiber surface at a pressure of 0.1 MPa to 0.5 MPa, and dried at 120° C. to 200° C. for 2 to 6 hours to form a sunscreen coating with a thickness of 0.05 mm to 0.3 mm on the layered fiber surface to obtain a sunscreen modified layered fiber;

[0017] The layered fibers are selected from any one of rock wool, glass fiber, quartz fiber, aluminum silicate fiber, zirconium oxide fiber, lanthanum zirconate fiber, aluminum oxide fiber, and mullite fiber;

[0018] The natural density of the layered fibers is 0.02 g / cm 3 ~0.1 g / cm 3 , thickness is 0.1mm~5mm, average diameter is 0.5μm~8μm;

[0019] S3, Fiber hot pressing molding:

[0020] The opacifying agent-modified layered fibers are sequentially stacked and laid on a high-temperature resistant metal mold, and after the laying is completed, the fiber preform with the mold is tightened and pressed to obtain a fiber preform with the mold, and the fiber preform with the mold is maintained at 600° C. to 1000° C. for 6 hours to 24 hours and then naturally cooled to obtain a gradient fiber preform;

[0021] S4. Sol impregnation and aging:

[0022] Under a pressure of -0.1 MPa to 0 MPa, the gradient fiber preform is immersed in the sol for 1 to 4 hours to obtain a sol-preform mixture, and the sol-preform mixture is maintained at 40°C to 70°C for 8 to 24 hours to form a gel-preform composite.

[0023] The sol is one of silicon oxide, aluminum oxide and zirconium oxide sol, the solid content of the sol is 6% to 15%, and the average particle size of the sol particles is in the range of 5nm to 50nm;

[0024] S5. Supercritical drying:

[0025] Alcohols are used as a medium for supercritical drying. The gel-preform composite is placed in an autoclave, and after adding the alcohol, it is kept sealed. The volume ratio of the gel-preform composite to the alcohol is 1:(0.3-3). The autoclave is heated to above the critical point of the alcohol, maintained at 8.0 MPa-15.0 MPa for 1 hour-10 hours, and the gas in the autoclave is slowly discharged until the pressure is 0 to obtain a gradient aerogel composite body.

[0026] S6. Heat treatment:

[0027] The gradient aerogel composite material blank is placed in a high-temperature furnace, heated from room temperature to 600°C to 1000°C, maintained for 1h to 5h, and naturally cooled to obtain a 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 have low density and wide temperature range thermal conductivity, as well as mechanical properties. Their typical properties are as follows:

[0028] (1) Composite material with a service temperature of 800°C: density of 0.19 g / cm 3 The thermal conductivity at room temperature is 0.016 W / (m·K), the thermal conductivity at 800℃ is 0.022 W / (m·K), the compressive strength (3% deformation) is 0.12 MPa, the flexural strength is 1.2 MPa, the material (thickness 10mm) is heated at 800℃ for 1h on one side, the shrinkage in the thickness direction is 0.3%, and the temperature rise on the cold side is 63℃;

[0029] (2) Composite material with a service temperature of 1200°C: density of 0.27 g / cm 3 The thermal conductivity at room temperature is 0.020 W / (m·K), the thermal conductivity at 1200℃ is 0.030 W / (m·K), the compressive strength (3% deformation) is 0.17 MPa, the flexural strength is 1.1 MPa, and the material (thickness 12.5mm) is heated on one side at 1200℃ for 1h. The shrinkage in the thickness direction is 0.4%, and the temperature rise on the cold side is 176℃.

[0030] (3) Composite material with a service temperature of 1600°C: density of 0.31 g / cm 3 The thermal conductivity at room temperature is 0.026 W / (m·K), the thermal conductivity at 1600℃ is 0.056 W / (m·K), the compressive strength (3% deformation) is 0.16 MPa, the bending strength is 0.95 MPa, and the material (thickness 18mm) is heated on one side at 1600℃ for 1h. The shrinkage in the thickness direction is 0.9%, and the temperature rise on the cold side is 262℃.

[0031] Furthermore, the solvent used in the sol described in S4 is one of ethanol, isopropanol, n-propanol, n-butanol, sec-butanol, and tert-butanol.

[0032] Furthermore, the alcohol substance described in S5 is one of ethanol, methanol, isopropanol, n-propanol, n-butanol, sec-butanol, and tert-butanol.

[0033] Furthermore, the heating from room temperature to 600° C. to 1000° C. in S6 is completed at a heating rate of 0.5° C. / min to 3° C. / min.

[0034] 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 have low density and wide temperature range thermal conductivity, as well as mechanical properties. Their typical properties are as follows:

[0035] (1) Composite material with a service temperature of 800°C: density of 0.19 g / cm 3 The thermal conductivity at room temperature is 0.016 W / (m·K), the thermal conductivity at 800℃ is 0.022 W / (m·K), the compressive strength (3% deformation) is 0.12 MPa, the flexural strength is 1.2 MPa, the material (thickness 10mm) is heated at 800℃ for 1h on one side, the shrinkage in the thickness direction is 0.3%, and the temperature rise on the cold side is 63℃;

[0036] (2) Composite material with a service temperature of 1200°C: density of 0.27 g / cm 3 The thermal conductivity at room temperature is 0.020 W / (m·K), the thermal conductivity at 1200℃ is 0.030 W / (m·K), the compressive strength (3% deformation) is 0.17 MPa, the flexural strength is 1.1 MPa, and the material (thickness 12.5mm) is heated on one side at 1200℃ for 1h. The shrinkage in the thickness direction is 0.4%, and the temperature rise on the cold side is 176℃.

[0037] (3) Composite material with a service temperature of 1600°C: density of 0.31 g / cm 3 The thermal conductivity at room temperature is 0.026 W / (m·K), the thermal conductivity at 1600℃ is 0.056 W / (m·K), the compressive strength (3% deformation) is 0.16 MPa, the bending strength is 0.95 MPa, and the material (thickness 18mm) is heated on one side at 1600℃ for 1h. The shrinkage in the thickness direction is 0.9%, and the temperature rise on the cold side is 262℃.

[0038] Compared with the prior art, the present invention has the following beneficial effects:

[0039] 1. The present invention discloses a method for preparing a gradient aerogel composite material, wherein a sunscreen is gradiently distributed from the hot side to the cold side of the composite material, achieving optimal sunscreening effects tailored to actual high-temperature operating conditions. Within the composite's temperature field through its thickness, a sunscreen coating with a size comparable to the wavelength of the most energetic infrared radiation is gradiently distributed, effectively shielding the radiation and inhibiting radiative heat conduction. As the temperature increases, the wavelength of the most energetic infrared radiation decreases. Therefore, a high-temperature-resistant, smaller-diameter sunscreen coating is applied near and near the hot side of the composite material; a medium-temperature-resistant, medium-diameter sunscreen coating is applied near and near the middle layer of the composite material; and a larger-diameter sunscreen coating, or no sunscreen coating, is applied near and near the cold side of the composite material. Ceramics with high specific extinction coefficients (such as zirconium oxide, silicon carbide, titanium oxide, and iron oxide) are used as the sunscreen component. These ceramics exhibit excellent thermal stability even in aerobic environments, thus avoiding the oxidation failure common in metal reflective screens.

[0040] 2. The preparation method of a gradient aerogel composite material described in the present invention introduces a sunscreen in the form of a coating, which can minimize the effect of the sunscreen on the thermal insulation performance of the composite material in the medium and low temperature ranges. When the sunscreen component is introduced into the aerogel composite material by conventional methods, the sunscreen exists in a homogeneous form, and a relatively high total amount of sunscreen must be ensured to achieve the effect of reducing high-temperature thermal conductivity. The intrinsic thermal conductivity of the sunscreen is usually 2-3 orders of magnitude higher than that of aerogel and fiber, which will eventually lead to an increase in the thermal conductivity of the aerogel composite material in the medium and low temperature ranges. The present invention proposes to introduce multiple layers of sunscreen in the form of a coating, and the coating is distributed in a gradient form and has a thickness of less than 0.3 mm, so that the content of the sunscreen in the aerogel composite material is significantly reduced, and the efficiency of the sunscreen is greatly improved. While effectively exerting the effect of the sunscreen, the increase in the thermal conductivity of the aerogel composite material by the sunscreen itself is minimized.

[0041] 3. The preparation method of a gradient aerogel composite material described in the present invention pre-introduces a sunscreen into the fiber, which has a simple process and is easy to prepare large-scale thermal insulation components in batches and stably. The common way of introducing sunscreen is to add the sunscreen to the sol, stir and disperse it, and then infiltrate it into the fiber. The sunscreen is easy to settle in the sol, and the uniformity is poor, which significantly weakens the actual light-shielding effect. The present invention proposes to prepare a sunscreen slurry and apply the slurry to the layered fiber by spraying. By maintaining a high viscosity of the slurry and adding a viscous component, the sunscreen is stably attached to the fiber surface without leaking and settling in the fiber, which effectively ensures the uniformity of the sunscreen. At the same time, the layered fiber containing the sunscreen coating is conducive to minimizing the thermal bridge effect of the sunscreen between layers and the solid-state heat conduction of the fiber in the thickness direction, and can form thermal insulation components of complex shapes.

[0042] 4. The present invention discloses a method for preparing a gradient aerogel composite material. The fiber preform is formed by hot pressing and then subjected to a heat treatment and sintering process, ensuring that the composite material has excellent mechanical properties. Under hot pressing conditions, physical overlap, entanglement, and certain chemical bonding occur between the layered fibers, significantly strengthening the interlayer bonding force. The heat treatment and sintering process further physically and chemically bonds the three components of the aerogel skeleton particles, fibers, and sunscreen, significantly strengthening the overall structure. Furthermore, the introduction of a high-rigidity sunscreen enhances the pressure-bearing properties of the aerogel composite material. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] The accompanying drawings are used to provide further understanding of the present invention and constitute a part of the specification. They are used to explain the present invention together with the embodiments of the present invention and do not constitute a limitation of the present invention.

[0044] Figure 1 This is a process flow chart of a method for preparing a gradient aerogel composite material according to the present invention;

[0045] Figure 2 This is a schematic diagram of layered fiber placement in the method for preparing a gradient aerogel composite material described in Example 1 of the present invention;

[0046] Figure 3 This is a photograph of layered alumina fibers in the method for preparing a gradient aerogel composite material described in Example 3 of the present invention;

[0047] Figure 4 This is a photo of a gradient aerogel composite material prepared by the preparation method of a gradient aerogel composite material described in Example 7 of the present invention. DETAILED DESCRIPTION

[0048] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention.

[0049] Figure 1 This is a process flow chart of a method for preparing a gradient aerogel composite material described in an embodiment;

[0050] Example 1:

[0051] A method for preparing a gradient aerogel composite material comprises the following steps:

[0052] S1. Prepare two sunscreen slurries:

[0053] Sunscreen slurry No. 1: Lauryl glucoside, starch, and water are mixed and stirred at 40°C to form a mixed solution. Silicon carbide particles are added to the mixed solution and stirred rapidly at 40°C to form a sunscreen slurry having a viscosity of 1600 mPa·s. The mass ratio of lauryl glucoside, starch, silicon carbide, and water in the sunscreen slurry is 1.8:6.0:12:100.

[0054] The average diameter of silicon carbide particles is 2.5 μm;

[0055] Sunscreen slurry No. 2: Lauryl glucoside, starch, and water were mixed and stirred at 40°C to form a mixed solution. Silicon carbide particles were added to the mixed solution and stirred rapidly at 40°C to form a sunscreen slurry with a viscosity of 1400 mPa·s. The mass ratio of lauryl glucoside, starch, silicon carbide, and water in the sunscreen slurry was 1.6:6.0:9:100.

[0056] The average diameter of silicon carbide particles is 3.5 μm;

[0057] S2. Slurry coating:

[0058] This embodiment uses three types of fibers, the first type of fiber is coated with the first type of sunscreen slurry, the second type of fiber is coated with the second type of sunscreen slurry, and the third type of fiber is not coated with the sunscreen slurry;

[0059] First fiber: Lay the layered quartz fiber flat, spray the obtained first sunscreen slurry evenly on the fiber surface at a pressure of 0.15 MPa, and dry it at 170°C for 4.5 hours to form a sunscreen coating with a thickness of 0.05 mm on the layered quartz fiber surface, thereby obtaining the first silicon carbide-modified layered quartz fiber;

[0060] The natural density of layered quartz fiber is 0.06 g / cm 3 , thickness 1.5 mm, average diameter 3 μm;

[0061] The second type of fiber: the layered rock wool fiber is laid flat, and the second sunscreen slurry obtained is evenly sprayed on the fiber surface at a pressure of 0.15 MPa, and is kept at 170°C for 4.5 hours to dry it, so that a sunscreen coating with a thickness of 0.02 mm is formed on the surface of the layered rock wool fiber, thereby obtaining the second type of silicon carbide modified layered rock wool fiber;

[0062] The natural density of layered rock wool fiber is 0.06 g / cm 3 , thickness 1.5 mm, average diameter 1.5 μm;

[0063] Type 3 fiber: layered glass fiber, not coated with opacifier sizing;

[0064] The natural density of laminated glass fiber is 0.06 g / cm 3 , thickness 1.5 mm, average diameter 0.8 μm;

[0065] S3, Fiber hot pressing molding:

[0066] The opacifying agent-modified layered fibers are sequentially stacked and laid on a high-temperature resistant metal mold. After the laying is completed, the fiber preform with the mold is tightened and pressed to obtain a fiber preform. The fiber preform with the mold is maintained at 650° C. for 12 hours and then naturally cooled to obtain a gradient fiber preform.

[0067] The order of laying the opacifier-modified layered fibers, from the hot side to the cold side, is as follows: first, silicon carbide-modified layered quartz fiber, second, silicon carbide-modified layered rock wool fiber, and third, layered glass fiber. The total thickness of the three fibers after lamination and molding is 10 mm, with a thickness ratio of 2:2:6.

[0068] S4. Sol impregnation and aging:

[0069] The gradient fiber preform was immersed in silica sol under a pressure of -0.1 MPa for 2 hours to obtain a sol-preform mixture, and the sol-preform mixture was kept at 50°C for 16 hours to form a gel-preform composite.

[0070] The solid content of the silica sol is 9%, and the average particle size of the sol particles is 8 nm;

[0071] S5. Supercritical drying:

[0072] Ethanol was used as a medium for supercritical drying. The gel-preform composite was placed in an autoclave, and after adding ethanol, it was kept sealed. The volume ratio of the gel-preform composite to ethanol was 1:1. The autoclave was heated to above the critical point of ethanol and maintained at 12.5 MPa for 6 hours. The gas in the autoclave was slowly discharged until the pressure was 0 to obtain a gradient aerogel composite body.

[0073] S6. Heat treatment:

[0074] The gradient aerogel composite material body was placed in a high-temperature furnace, heated from room temperature to 650°C, maintained for 2 hours, and naturally cooled to obtain the gradient aerogel composite material.

[0075] The prepared gradient aerogel composite material has the following properties:

[0076] The operating temperature is 800℃; 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℃ is 0.022 W / (m·K). The compressive strength (3% deformation) is 0.12 MPa, and the flexural strength is 1.8 MPa. When the material (10 mm thick) is heated on one side at 800℃ for 1 hour, the shrinkage in the thickness direction is 0.3%, and the temperature rise on the cold side is 63℃.

[0077] Figure 2 This is a schematic diagram of layered fiber placement in the preparation method of a gradient aerogel composite material described in Example 1.

[0078] Example 2:

[0079] A method for preparing a gradient aerogel composite material comprises the following steps:

[0080] S1. Prepare three sunscreen slurries:

[0081] Sunscreen slurry No. 1: Lauryl betaine, gelatin, and water were mixed and stirred at 45°C to form a mixed solution. Titanium oxide particles were added to the mixed solution and stirred rapidly at 45°C to form a sunscreen slurry with a viscosity of 1500 mPa·s. The mass ratio of lauryl betaine, gelatin, titanium oxide, and water in the sunscreen slurry was 2.0:6.5:20:100.

[0082] The average diameter of titanium oxide particles is 2.0 μm;

[0083] Second sunscreen slurry: Lauryl betaine, gelatin, and water were mixed and stirred at 45°C to form a mixed solution. Silicon carbide particles were added to the mixed solution and stirred rapidly at 45°C to form a sunscreen slurry with a viscosity of 1400 mPa·s. The mass ratio of lauryl betaine, gelatin, silicon carbide, and water in the sunscreen slurry was 1.3:6.5:15:100.

[0084] The average diameter of silicon carbide particles is 2.5 μm;

[0085] The third sunscreen slurry was prepared by mixing dodecyl betaine, gelatin, and water, stirring at 45°C to form a mixed solution, adding silicon carbide particles to the mixed solution, and rapidly stirring at 45°C to form a sunscreen slurry with a viscosity of 1200 mPa·s. The mass ratio of dodecyl betaine, gelatin, silicon carbide, and water in the sunscreen slurry was 1.0:6.0:8:100.

[0086] The average diameter of silicon carbide particles is 4.0 μm;

[0087] S2. Slurry coating:

[0088] This embodiment uses four types of fibers, the first type of fiber is coated with the first type of sunscreen slurry, the second type of fiber is coated with the second type of sunscreen slurry, the third type of fiber is coated with the third type of sunscreen slurry, and the fourth type of fiber is not coated with the sunscreen slurry;

[0089] First fiber: Lay the layered zirconia fiber flat, spray the obtained first sunscreen slurry evenly on the fiber surface at a pressure of 0.22 MPa, and dry it at 180°C for 6 hours to form a sunscreen coating with a thickness of 0.15 mm on the surface of the layered zirconia fiber, thereby obtaining the first titanium oxide-modified layered zirconia fiber;

[0090] The natural density of layered zirconia fibers is 0.08 g / cm 3 , thickness 1.5 mm, average diameter 2.0 μm;

[0091] Second fiber: Lay the layered quartz fiber flat, spray the obtained second sunscreen slurry evenly on the fiber surface at a pressure of 0.22 MPa, and dry it at 180°C for 6 hours to form a sunscreen coating with a thickness of 0.08 mm on the layered quartz fiber surface, thereby obtaining the second silicon carbide-modified layered quartz fiber;

[0092] The natural density of layered quartz fiber is 0.06 g / cm 3 , thickness 1.5 mm, average diameter 1.5 μm;

[0093] The third type of fiber: the layered rock wool fiber is laid flat, and the third type of sunscreen slurry is evenly sprayed on the fiber surface at a pressure of 0.22 MPa. The slurry is kept at 180°C for 6 hours to dry it, so that a sunscreen coating with a thickness of 0.02 mm is formed on the surface of the layered rock wool fiber, thereby obtaining the third type of silicon carbide modified layered rock wool fiber;

[0094] The natural density of layered rock wool fiber is 0.06 g / cm 3 , thickness 1.5 mm, average diameter 1.0 μm;

[0095] Type 4 fiber: layered glass fiber, not coated with opacifier sizing;

[0096] The natural density of laminated glass fiber is 0.06 g / cm 3 , thickness 1.5 mm, average diameter 1.0 μm;

[0097] S3, Fiber hot pressing molding:

[0098] The opacifying agent-modified layered fibers are sequentially stacked and laid on a high-temperature resistant metal mold. After the laying is completed, the fiber preform with the mold is tightened and pressed to obtain a fiber preform. The fiber preform with the mold is maintained at 650° C. for 12 hours and then naturally cooled to obtain a gradient fiber preform.

[0099] The order of laying the opacifier-modified layered fibers, from the hot side to the cold side, is: first, titanium oxide-modified layered zirconia fiber; second, silicon carbide-modified layered quartz fiber; third, silicon carbide-modified layered rock wool fiber; and fourth, layered glass fiber. The total thickness of the four fibers after laminate molding is 12.5 mm, with a thickness ratio of 2:2:3:5.5.

[0100] S4. Sol impregnation and aging:

[0101] The gradient fiber preform was immersed in silica sol under a pressure of -0.1 MPa for 3 hours to obtain a sol-preform mixture, and the sol-preform mixture was kept at 55°C for 20 hours to form a gel-preform composite.

[0102] The solid content of the silica sol is 11%, and the average particle size of the sol particles is 20 nm;

[0103] S5. Supercritical drying:

[0104] Isopropyl alcohol was used as the medium for supercritical drying. The gel-preform composite was placed in an autoclave, which was kept airtight after adding isopropyl alcohol. The volume ratio of the gel-preform composite to isopropyl alcohol was 1:1.4. The autoclave was heated to above the critical point of isopropyl alcohol and maintained at 8.0 MPa for 4.5 hours. The gas in the autoclave was slowly discharged until the pressure reached 0, thereby obtaining a gradient aerogel composite body.

[0105] S6. Heat treatment:

[0106] The gradient aerogel composite material body was placed in a high-temperature furnace, heated from room temperature to 650°C, maintained for 2 hours, and naturally cooled to obtain the gradient aerogel composite material.

[0107] The prepared gradient aerogel composite material has the following properties:

[0108] The operating temperature is 1200℃; 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℃ 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 (thickness 12.5mm) is heated on one side at 1200℃ for 1h, the shrinkage in the thickness direction is 0.4%, and the temperature rise on the cold side is 176℃.

[0109] Example 3:

[0110] A method for preparing a gradient aerogel composite material comprises the following steps:

[0111] S1. Prepare 4 kinds of sunscreen slurries:

[0112] Sunscreen slurry No. 1: Fatty alcohol polyoxyethylene ether, polyvinyl alcohol, and water are mixed and stirred at 50°C to form a mixed solution. Zirconium oxide particles are added to the mixed solution and stirred rapidly at 50°C to form a sunscreen slurry with a viscosity of 1800 mPa·s. The mass ratio of fatty alcohol polyoxyethylene ether, polyvinyl alcohol, zirconium oxide, and water in the sunscreen slurry is 2.5:5.0:28:100.

[0113] The average diameter of the zirconium oxide particles is 1.5 μm;

[0114] Second sunscreen slurry: Fatty alcohol polyoxyethylene ether, polyvinyl alcohol, and water were mixed and stirred at 50°C to form a mixed solution. Titanium oxide particles were added to the mixed solution and rapidly stirred at 50°C to form a sunscreen slurry with a viscosity of 1600 mPa·s. The mass ratio of fatty alcohol polyoxyethylene ether, polyvinyl alcohol, titanium oxide, and water in the sunscreen slurry was 2.1:5.8:23:100.

[0115] The average diameter of titanium oxide particles is 2.0 μm;

[0116] A third sunscreen slurry was prepared by mixing fatty alcohol polyoxyethylene ether, polyvinyl alcohol, and water, stirring the mixture at 50°C to form a mixed solution, adding silicon carbide particles to the mixed solution, and rapidly stirring the mixture at 50°C to form a sunscreen slurry having a viscosity of 1400 mPa·s. The mass ratio of fatty alcohol polyoxyethylene ether, polyvinyl alcohol, silicon carbide, and water in the sunscreen slurry was 1.6:6.0:16:100.

[0117] The average diameter of silicon carbide particles is 2.5 μm;

[0118] A fourth sunscreen slurry was prepared by mixing fatty alcohol polyoxyethylene ether, polyvinyl alcohol, and water, stirring the mixture at 50°C to form a mixed solution, adding silicon carbide particles to the mixed solution, and rapidly stirring the mixture at 50°C to form a sunscreen slurry having a viscosity of 1300 mPa·s. The mass ratio of fatty alcohol polyoxyethylene ether, polyvinyl alcohol, silicon carbide, and water in the sunscreen slurry was 1.2:6.0:8:100.

[0119] The average diameter of silicon carbide particles is 4.0 μm;

[0120] S2. Slurry coating:

[0121] This embodiment uses five types of fibers, the first type of fiber is coated with the first sunscreen slurry, the second type of fiber is coated with the second sunscreen slurry, the third type of fiber is coated with the third sunscreen slurry, the fourth type of fiber is coated with the fourth sunscreen slurry, and the fifth type of fiber is not coated with the sunscreen slurry;

[0122] First fiber: Lay the layered alumina fiber flat, spray the obtained first sunscreen slurry evenly on the fiber surface at a pressure of 0.30 MPa, and dry it at 180°C for 10 hours to form a sunscreen coating with a thickness of 0.20 mm on the layered alumina fiber surface, thereby obtaining the first zirconia-modified layered alumina fiber;

[0123] The natural density of layered alumina fibers is 0.06 g / cm 3 , thickness 1.5 mm, average diameter 3.5 μm;

[0124] Second type of fiber: Lay the layered zirconia fiber flat, spray the obtained second sunscreen slurry evenly on the fiber surface at a pressure of 0.30 MPa, and maintain it at 180°C for 10 hours to dry it, so that a sunscreen coating with a thickness of 0.10 mm is formed on the surface of the layered zirconia fiber, thereby obtaining the second type of titanium oxide modified layered zirconia fiber;

[0125] The natural density of layered zirconia fibers is 0.08 g / cm 3 , thickness 1.5 mm, average diameter 1.5 μm;

[0126] Fiber Type 3: Lay the layered quartz fiber flat, and evenly spray the obtained third sunscreen slurry onto the fiber surface at a pressure of 0.30 MPa. Maintain the slurry at 180°C for 10 hours to dry it, so that a sunscreen coating with a thickness of 0.08 mm is formed on the surface of the layered quartz fiber, thereby obtaining the third silicon carbide-modified layered quartz fiber.

[0127] The natural density of layered quartz fiber is 0.06 g / cm 3 , thickness 1.5 mm, average diameter 1.5 μm;

[0128] The fourth type of fiber: the layered rock wool fibers were laid flat, and the fourth type of sunscreen slurry was evenly sprayed on the fiber surface at a pressure of 0.30 MPa. The slurry was kept at 180° C. for 10 hours to dry it, so that a sunscreen coating with a thickness of 0.04 mm was formed on the surface of the layered rock wool fibers, thereby obtaining the fourth type of silicon carbide modified layered rock wool fibers;

[0129] The natural density of layered rock wool fiber is 0.06 g / cm 3 , thickness 1.5 mm, average diameter 1.0 μm;

[0130] Type 5 fiber: layered glass fiber, not coated with opacifier sizing;

[0131] The natural density of laminated glass fiber is 0.06 g / cm 3 , thickness 1.5 mm, average diameter 1.0 μm;

[0132] S3, Fiber hot pressing molding:

[0133] The opacifying agent-modified layered fibers are sequentially stacked and laid on a high-temperature resistant metal mold. After the laying is completed, the fiber preform with the mold is tightened and pressed to obtain a fiber preform. The fiber preform with the mold is maintained at 650° C. for 12 hours and then naturally cooled to obtain a gradient fiber preform.

[0134] The order of laying the opacifier-modified layered fibers, from the hot side to the cold side, is: first, zirconium oxide-modified layered alumina fibers; second, titanium oxide-modified layered zirconium oxide fibers; third, silicon carbide-modified layered quartz fibers; fourth, silicon carbide-modified layered rock wool fibers; and fifth, layered glass fibers. The total thickness of the five fiber stacks after molding is 18.0 mm, with a thickness ratio of 3:3:3:4:5.

[0135] S4. Sol impregnation and aging:

[0136] The gradient fiber preform was immersed in alumina sol under a pressure of -0.1 MPa for 3 hours to obtain a sol-preform mixture, and the sol-preform mixture was kept at 65°C for 20 hours to form a gel-preform composite.

[0137] The solid content of the alumina sol is 15%, and the average particle size of the sol particles is 35 nm;

[0138] S5. Supercritical drying:

[0139] Tert-butanol was used as a medium for supercritical drying. The gel-preform composite was placed in an autoclave, and after adding tert-butanol, it was kept sealed. The volume ratio of the gel-preform composite to tert-butanol was 1:1.6. The autoclave was heated to above the critical point of tert-butanol and maintained at 10.0 MPa for 6.5 hours. The gas in the autoclave was slowly discharged until the pressure was 0 to obtain a gradient aerogel composite body.

[0140] S6. Heat treatment:

[0141] The gradient aerogel composite material body was placed in a high-temperature furnace, heated from room temperature to 650°C, maintained for 2 hours, and naturally cooled to obtain the gradient aerogel composite material;

[0142] The prepared gradient aerogel composite material has the following properties:

[0143] The operating temperature is 1600℃; 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℃ 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 (thickness 18mm) is heated on one side at 1600℃ for 1h, the shrinkage in the thickness direction is 0.9%, and the temperature rise on the cold side is 262℃.

[0144] Figure 3 This is a photograph of layered alumina fibers in the method for preparing a gradient aerogel composite material described in Example 3.

[0145] Example 4:

[0146] A method for preparing a gradient aerogel composite material comprises the following steps:

[0147] S1. Prepare two sunscreen slurries:

[0148] Sunscreen slurry No. 1: Lauryl glucoside, starch, and water are mixed and stirred at 25°C to form a mixed solution. Silicon carbide particles are added to the mixed solution and stirred rapidly at 25°C to form a sunscreen slurry having a viscosity of 500 mPa·s. The mass ratio of lauryl glucoside, starch, silicon carbide, and water in the sunscreen slurry is 0.5:3:5:100.

[0149] The average diameter of silicon carbide particles is 2.5 μm;

[0150] Second sunscreen slurry: dodecyl glucoside, starch, and water were mixed and stirred at 40°C to form a mixed solution. Silicon carbide particles were added to the mixed solution and stirred rapidly at 40°C to form a sunscreen slurry with a viscosity of 1400 mPa·s. The mass ratio of dodecyl glucoside, starch, silicon carbide, and water in the sunscreen slurry was 1.6:6.0:9:100.

[0151] The average diameter of silicon carbide particles is 5.0 μm;

[0152] S2. Slurry coating:

[0153] This embodiment uses three types of fibers, the first type of fiber is coated with the first type of sunscreen slurry, the second type of fiber is coated with the second type of sunscreen slurry, and the third type of fiber is not coated with the sunscreen slurry;

[0154] First fiber: Lay the layered aluminum silicate fiber flat, spray the obtained first sunscreen slurry evenly on the fiber surface at a pressure of 0.1 MPa, and dry it at 200°C for 2 hours to form a sunscreen coating with a thickness of 0.05 mm on the surface of the layered aluminum silicate fiber, thereby obtaining the first silicon carbide-modified layered quartz fiber;

[0155] The natural density of layered aluminum silicate fiber is 0.06 g / cm 3 , thickness 1.5 mm, average diameter 8 μm;

[0156] The second type of fiber: the layered rock wool fiber is laid flat, and the second sunscreen slurry is evenly sprayed on the fiber surface at a pressure of 0.10 MPa, and the slurry is kept at 120° C. for 6 hours to dry the layered rock wool fiber, so that a sunscreen coating with a thickness of 0.02 mm is formed on the surface of the layered rock wool fiber, thereby obtaining the second type of silicon carbide modified layered rock wool fiber;

[0157] The natural density of layered rock wool fiber is 0.06 g / cm 3, thickness 1.5 mm, average diameter 1.5 μm;

[0158] Type 3 fiber: layered glass fiber, not coated with opacifier sizing;

[0159] The natural density of laminated glass fiber is 0.06 g / cm 3 , thickness 1.5 mm, average diameter 0.8 μm;

[0160] S3, Fiber hot pressing molding:

[0161] The opacifier-modified layered fibers are sequentially stacked and laid on a high-temperature resistant metal mold. After the laying is completed, the fiber preform with the mold is tightened and pressed to obtain a fiber preform. The fiber preform with the mold is kept at 600° C. for 24 hours and then naturally cooled to obtain a gradient fiber preform.

[0162] The order of laying the opacifier-modified layered fibers, from the hot side to the cold side, is: first, silicon carbide-modified layered aluminum silicate fiber, second, silicon carbide-modified layered rock wool fiber, and third, layered glass fiber. The total thickness of the three fibers after lamination and molding is 10 mm, with a thickness ratio of 2:3:5.

[0163] S4. Sol impregnation and aging:

[0164] Under a pressure of 0 MPa, the gradient fiber preform was immersed in silica sol for 4 hours to obtain a sol-preform mixture, and the sol-preform mixture was kept at 40°C for 24 hours to form a gel-preform composite.

[0165] The solid content of the silica sol is 6%, and the average particle size of the sol particles is 5 nm;

[0166] S5. Supercritical drying:

[0167] Ethanol was used as a medium for supercritical drying. The gel-preform composite was placed in an autoclave, and after adding ethanol, it was kept airtight. The volume ratio of the gel-preform composite to ethanol was 1:0.3. The autoclave was heated to above the critical point of ethanol and maintained at 15.0 MPa for 10 hours. The gas in the autoclave was slowly discharged until the pressure was 0 to obtain a gradient aerogel composite body.

[0168] S6. Heat treatment:

[0169] The gradient aerogel composite material green body was placed in a high-temperature furnace, heated from room temperature to 600°C, maintained for 5 hours, and naturally cooled to obtain the gradient aerogel composite material.

[0170] The prepared gradient aerogel composite material has the following properties:

[0171] The operating temperature is 800℃; 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℃ 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 (10 mm thick) is heated on one side at 800℃ for 1 hour, the shrinkage in the thickness direction is 0.1%, and the temperature rise on the cold side is 74℃.

[0172] Example 5:

[0173] A method for preparing a gradient aerogel composite material comprises the following steps:

[0174] S1. Prepare two sunscreen slurries:

[0175] Sunscreen slurry No. 1: Lauryl glucoside, starch, and water are mixed and stirred at 40°C to form a mixed solution. Silicon carbide particles are added to the mixed solution and stirred rapidly at 40°C to form a sunscreen slurry having a viscosity of 1600 mPa·s. The mass ratio of lauryl glucoside, starch, silicon carbide, and water in the sunscreen slurry is 1.8:6.0:15:100.

[0176] The average diameter of silicon carbide particles is 5 μm;

[0177] Second sunscreen slurry: dodecyl glucoside, starch, and water were mixed and stirred at 40°C to form a mixed solution. Silicon carbide particles were added to the mixed solution and stirred rapidly at 40°C to form a sunscreen slurry with a viscosity of 1400 mPa·s. The mass ratio of dodecyl glucoside, starch, silicon carbide, and water in the sunscreen slurry was 1.6:6.0:9:100.

[0178] The average diameter of silicon carbide particles is 3.5 μm;

[0179] S2. Slurry coating:

[0180] This embodiment uses three types of fibers, the first type of fiber is coated with the first type of sunscreen slurry, the second type of fiber is coated with the second type of sunscreen slurry, and the third type of fiber is not coated with the sunscreen slurry;

[0181] First fiber: Lay the layered quartz fiber flat, spray the obtained first sunscreen slurry evenly on the fiber surface at a pressure of 0.15 MPa, and dry it at 170°C for 4.5 hours to form a sunscreen coating with a thickness of 0.05 mm on the layered quartz fiber surface, thereby obtaining the first silicon carbide-modified layered quartz fiber;

[0182] The natural density of layered quartz fiber is 0.06 g / cm 3, thickness 1.5 mm, average diameter 5 μm;

[0183] The second type of fiber: the layered rock wool fiber is laid flat, and the second sunscreen slurry obtained is evenly sprayed on the fiber surface at a pressure of 0.15 MPa, and is kept at 170°C for 4.5 hours to dry it, so that a sunscreen coating with a thickness of 0.02 mm is formed on the surface of the layered rock wool fiber, thereby obtaining the second type of silicon carbide modified layered rock wool fiber;

[0184] The natural density of layered rock wool fiber is 0.06 g / cm 3 , thickness 1.5 mm, average diameter 3 μm;

[0185] Type 3 fiber: layered glass fiber, not coated with opacifier sizing;

[0186] The natural density of laminated glass fiber is 0.06 g / cm 3 , thickness 1.5 mm, average diameter 0.8 μm;

[0187] S3, Fiber hot pressing molding:

[0188] The opacifying agent-modified layered fibers are sequentially stacked and laid on a high-temperature resistant metal mold. After the laying is completed, the fiber preform with the mold is tightened and pressed to obtain a fiber preform. The fiber preform with the mold is maintained at 650° C. for 12 hours and then naturally cooled to obtain a gradient fiber preform.

[0189] The order of laying the opacifier-modified layered fibers, from the hot side to the cold side, is as follows: first, silicon carbide-modified layered quartz fiber, second, silicon carbide-modified layered rock wool fiber, and third, layered glass fiber. The total thickness of the three fibers after lamination and molding is 10 mm, with a thickness ratio of 2:2:6.

[0190] S4. Sol impregnation and aging:

[0191] The gradient fiber preform was immersed in zirconia sol under a pressure of -0.1 MPa for 2 hours to obtain a sol-preform mixture, and the sol-preform mixture was kept at 50°C for 16 hours to form a gel-preform composite.

[0192] The solid content of the zirconium oxide sol is 12%, and the average particle size of the sol particles is 8 nm;

[0193] S5. Supercritical drying:

[0194] Ethanol was used as a medium for supercritical drying. The gel-preform composite was placed in an autoclave, and after adding ethanol, it was kept airtight. The volume ratio of the gel-preform composite to ethanol was 1:0.3. The autoclave was heated above the critical point of ethanol and maintained at 13.0 MPa for 6 hours. The gas in the autoclave was slowly discharged until the pressure was 0 to obtain a gradient aerogel composite body.

[0195] S6. Heat treatment:

[0196] The gradient aerogel composite material body was placed in a high-temperature furnace, heated from room temperature to 650°C, maintained for 2 hours, and naturally cooled to obtain the gradient aerogel composite material.

[0197] The prepared gradient aerogel composite material has the following properties:

[0198] The operating temperature is 800℃; 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℃ 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 (10 mm thick) is heated on one side at 800℃ for 1 hour, the shrinkage in the thickness direction is 0.4%, and the temperature rise on the cold side is 76℃.

[0199] Example 6:

[0200] A method for preparing a gradient aerogel composite material comprises the following steps:

[0201] S1. Prepare three sunscreen slurries:

[0202] Sunscreen slurry No. 1: Lauryl betaine, gelatin, and water were mixed and stirred at 45°C to form a mixed solution. Titanium oxide particles were added to the mixed solution and stirred rapidly at 45°C to form a sunscreen slurry with a viscosity of 1500 mPa·s. The mass ratio of lauryl betaine, gelatin, titanium oxide, and water in the sunscreen slurry was 2.0:6.5:20:100.

[0203] The average diameter of titanium oxide particles is 2.0 μm;

[0204] Second sunscreen slurry: Lauryl betaine, gelatin, and water were mixed and stirred at 45°C to form a mixed solution. Silicon carbide particles were added to the mixed solution and stirred rapidly at 45°C to form a sunscreen slurry with a viscosity of 1400 mPa·s. The mass ratio of lauryl betaine, gelatin, silicon carbide, and water in the sunscreen slurry was 1.3:6.5:15:100.

[0205] The average diameter of silicon carbide particles is 2.5 μm;

[0206] The third sunscreen slurry was prepared by mixing dodecyl betaine, gelatin, and water, stirring the mixture at 45°C to form a mixed solution, adding iron oxide particles to the mixed solution, and rapidly stirring the mixture at 45°C to form a sunscreen slurry with a viscosity of 1200 mPa·s. The mass ratio of dodecyl betaine, gelatin, silicon carbide, and water in the sunscreen slurry was 1.0:6.0:8:100.

[0207] The average diameter of the iron oxide particles is 4.0 μm;

[0208] S2. Slurry coating:

[0209] This embodiment uses four types of fibers, the first type of fiber is coated with the first type of sunscreen slurry, the second type of fiber is coated with the second type of sunscreen slurry, the third type of fiber is coated with the third type of sunscreen slurry, and the fourth type of fiber is not coated with the sunscreen slurry;

[0210] First fiber: Lay the layered lanthanum zirconate fiber flat, spray the obtained first sunscreen slurry evenly on the fiber surface at a pressure of 0.25 MPa, and dry it at 180°C for 6 hours to form a sunscreen coating with a thickness of 0.15 mm on the surface of the layered lanthanum zirconate fiber, thereby obtaining the first titanium oxide-modified layered lanthanum zirconate fiber;

[0211] The natural density of layered lanthanum zirconate fibers is 0.10 g / cm 3 , thickness 0.5 mm, average diameter 2.0 μm;

[0212] Second fiber: Lay the layered quartz fiber flat, spray the obtained second sunscreen slurry evenly on the fiber surface at a pressure of 0.22 MPa, and dry it at 180°C for 6 hours to form a sunscreen coating with a thickness of 0.08 mm on the layered quartz fiber surface, thereby obtaining the second silicon carbide-modified layered quartz fiber;

[0213] The natural density of layered quartz fiber is 0.06 g / cm 3 , thickness 1.5 mm, average diameter 1.5 μm;

[0214] The third type of fiber: the layered rock wool fiber is laid flat, and the third type of sunscreen slurry is evenly sprayed on the fiber surface at a pressure of 0.22 MPa. The slurry is kept at 180°C for 6 hours to dry it, so that a sunscreen coating with a thickness of 0.02 mm is formed on the surface of the layered rock wool fiber, thereby obtaining the third type of silicon carbide modified layered rock wool fiber;

[0215] The natural density of layered rock wool fiber is 0.06 g / cm 3 , thickness 1.5 mm, average diameter 1.0 μm;

[0216] Type 4 fiber: layered glass fiber, not coated with opacifier sizing;

[0217] The natural density of laminated glass fiber is 0.02 g / cm 3 , thickness 5 mm, average diameter 0.5 μm;

[0218] S3, Fiber hot pressing molding:

[0219] The opacifying agent-modified layered fibers are sequentially stacked and laid on a high-temperature resistant metal mold. After the laying is completed, the fiber preform with the mold is tightened and pressed to obtain a fiber preform. The fiber preform with the mold is maintained at 650° C. for 12 hours and then naturally cooled to obtain a gradient fiber preform.

[0220] The order of laying the opacifier-modified layered fibers, from the hot side to the cold side, is: first, titanium oxide-modified layered lanthanum zirconate fiber, second, silicon carbide-modified layered quartz fiber, third, iron oxide-modified layered rock wool fiber, and fourth, layered glass fiber. The total thickness of the four fibers after laminate molding is 12.5 mm, with a thickness ratio of 2:2:3:5.5.

[0221] S4. Sol impregnation and aging:

[0222] The gradient fiber preform was immersed in silica sol under a pressure of -0.1 MPa for 3 hours to obtain a sol-preform mixture, and the sol-preform mixture was kept at 55°C for 20 hours to form a gel-preform composite.

[0223] The solid content of the silica sol is 11%, and the average particle size of the sol particles is 20 nm;

[0224] S5. Supercritical drying:

[0225] Isopropyl alcohol was used as the medium for supercritical drying. The gel-preform composite was placed in an autoclave, which was kept sealed after adding isopropyl alcohol. The volume ratio of the gel-preform composite to isopropyl alcohol was 1:1.4. The autoclave was heated to above the critical point of isopropyl alcohol and maintained at 12.5 MPa for 4.5 hours. The gas in the autoclave was slowly discharged until the pressure reached 0, thereby obtaining a gradient aerogel composite body.

[0226] S6. Heat treatment:

[0227] The gradient aerogel composite material body was placed in a high-temperature furnace, heated from room temperature to 650°C, maintained for 2 hours, and naturally cooled to obtain the gradient aerogel composite material;

[0228] The prepared gradient aerogel composite material has the following properties:

[0229] The operating temperature is 1200℃; 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℃ 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 (thickness 12.5mm) is heated on one side at 1200℃ for 1h, the shrinkage in the thickness direction is 0.5%, and the temperature rise on the cold side is 181℃.

[0230] Example 7:

[0231] A method for preparing a gradient aerogel composite material comprises the following steps:

[0232] S1. Prepare two sunscreen slurries:

[0233] Sunscreen slurry No. 1: Lauryl betaine, gelatin, and water were mixed and stirred at 45°C to form a mixed solution. Titanium oxide particles were added to the mixed solution and stirred rapidly at 45°C to form a sunscreen slurry with a viscosity of 1500 mPa·s. The mass ratio of lauryl betaine, gelatin, titanium oxide, and water in the sunscreen slurry was 2.0:6.5:20:100.

[0234] The average diameter of titanium oxide particles is 2.0 μm;

[0235] Second sunscreen slurry: Lauryl betaine, gelatin, and water were mixed and stirred at 45°C to form a mixed solution. Zirconium oxide particles were added to the mixed solution and stirred rapidly at 45°C to form a sunscreen slurry with a viscosity of 1400 mPa·s. The mass ratio of lauryl betaine, gelatin, zirconium oxide, and water in the sunscreen slurry was 1.3:6.5:14:100.

[0236] The average diameter of silicon carbide particles is 2.5 μm;

[0237] S2. Slurry coating:

[0238] This embodiment uses three types of fibers, the first type of fiber is coated with the first type of sunscreen slurry, the second type of fiber is coated with the second type of sunscreen slurry, and the third type of fiber is not coated with the sunscreen slurry;

[0239] First fiber: Lay the layered zirconia fiber flat, spray the obtained first sunscreen slurry evenly on the fiber surface at a pressure of 0.22 MPa, and maintain it at 180°C for 6 hours to dry it, so that a sunscreen coating with a thickness of 0.12 mm is formed on the surface of the layered zirconia fiber, thereby obtaining the first titanium oxide-modified layered zirconia fiber;

[0240] The natural density of layered zirconia fibers is 0.08 g / cm3 , thickness 1.5 mm, average diameter 2.0 μm;

[0241] Second fiber: Lay the layered quartz fiber flat, spray the obtained second sunscreen slurry evenly on the fiber surface at a pressure of 0.22 MPa, and dry it at 180°C for 6 hours to form a sunscreen coating with a thickness of 0.07 mm on the layered quartz fiber surface, thereby obtaining the second silicon carbide-modified layered quartz fiber;

[0242] The natural density of layered quartz fiber is 0.06 g / cm 3 , thickness 1.5 mm, average diameter 1.5 μm;

[0243] Type 3 fiber: layered rock wool fiber, not coated with sunscreen slurry;

[0244] The natural density of layered rock wool fiber is 0.06 g / cm 3 , thickness 1.5 mm, average diameter 1.0 μm;

[0245] S3, Fiber hot pressing molding:

[0246] The opacifying agent-modified layered fibers are sequentially stacked and laid on a high-temperature resistant metal mold. After the laying is completed, the fiber preform with the mold is tightened and pressed to obtain a fiber preform. The fiber preform with the mold is maintained at 650° C. for 12 hours and then naturally cooled to obtain a gradient fiber preform.

[0247] The order of laying the opacifier-modified layered fibers, from the hot side to the cold side, is: first, titanium oxide-modified layered zirconia fibers, second, zirconium oxide-modified layered quartz fibers, and third, layered rock wool fibers. The total thickness of the three fibers after laminate molding is 12.5 mm, with a thickness ratio of 3:4:5.5.

[0248] S4. Sol impregnation and aging:

[0249] The gradient fiber preform was immersed in silica sol under a pressure of -0.1 MPa for 3 hours to obtain a sol-preform mixture, and the sol-preform mixture was kept at 55°C for 20 hours to form a gel-preform composite.

[0250] The solid content of the silica sol is 11%, and the average particle size of the sol particles is 20 nm;

[0251] S5. Supercritical drying:

[0252] Isopropanol was used as the medium for supercritical drying. The gel-preform composite was placed in an autoclave, which was kept sealed after adding isopropanol. The volume ratio of the gel-preform composite to isopropanol was 1:1.4. The autoclave was heated to above the critical point of isopropanol and maintained at 11.0 MPa for 4.5 hours. The gas in the autoclave was slowly discharged until the pressure reached 0 to obtain a gradient aerogel composite body.

[0253] S6. Heat treatment:

[0254] The gradient aerogel composite material body was placed in a high-temperature furnace, heated from room temperature to 650°C, maintained for 2 hours, and naturally cooled to obtain the gradient aerogel composite material.

[0255] The prepared gradient aerogel composite material has the following properties:

[0256] The operating temperature is 1200℃; 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℃ 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 (thickness 12.5 mm) is heated on one side at 1200℃ for 1 hour, the shrinkage in the thickness direction is 0.2%, and the temperature rise on the cold side is 178℃.

[0257] Figure 4 This is a photo of a gradient aerogel composite material prepared by the preparation method of a gradient aerogel composite material described in Example 7.

[0258] Example 8:

[0259] A method for preparing a gradient aerogel composite material comprises the following steps:

[0260] S1. Prepare two sunscreen slurries:

[0261] Sunscreen slurry No. 1: Fatty alcohol polyoxyethylene ether, polyvinyl alcohol, and water are mixed and stirred at 50°C to form a mixed solution. Zirconium oxide particles are added to the mixed solution and stirred rapidly at 50°C to form a sunscreen slurry having a viscosity of 3000 mPa·s. The mass ratio of fatty alcohol polyoxyethylene ether, polyvinyl alcohol, zirconium oxide, and water in the sunscreen slurry is 3.0:10.0:30:100.

[0262] The average diameter of the zirconium oxide particles is 1.5 μm;

[0263] Second sunscreen slurry: Fatty alcohol polyoxyethylene ether, polyvinyl alcohol, and water were mixed and stirred at 50°C to form a mixed solution. Titanium oxide particles were added to the mixed solution and rapidly stirred at 50°C to form a sunscreen slurry with a viscosity of 1600 mPa·s. The mass ratio of fatty alcohol polyoxyethylene ether, polyvinyl alcohol, titanium oxide, and water in the sunscreen slurry was 2.1:5.8:23:100.

[0264] The average diameter of titanium oxide particles is 2.0 μm;

[0265] S2. Slurry coating:

[0266] This embodiment uses three types of fibers, the first type of fiber is coated with the first type of sunscreen slurry, the second type of fiber is coated with the second type of sunscreen slurry, and the third type of fiber is not coated with the sunscreen slurry;

[0267] First fiber: Lay the layered mullite fiber flat, spray the obtained first opacifier slurry evenly on the fiber surface at a pressure of 0.50 MPa, and dry it at 180°C for 10 hours to form a 0.20 mm thick opacifier coating on the surface of the layered alumina fiber, thereby obtaining the first zirconia-modified layered mullite fiber;

[0268] The natural density of layered mullite fiber is 0.06 g / cm 3 , thickness 1.5 mm, average diameter 4.5 μm;

[0269] Second type of fiber: Lay the layered zirconia fiber flat, spray the obtained second sunscreen slurry evenly on the fiber surface at a pressure of 0.30 MPa, and maintain it at 180°C for 10 hours to dry it, so that a sunscreen coating with a thickness of 0.10 mm is formed on the surface of the layered zirconia fiber, thereby obtaining the second type of titanium oxide modified layered zirconia fiber;

[0270] The natural density of layered zirconia fibers is 0.08 g / cm 3 , thickness 1.5 mm, average diameter 1.5 μm;

[0271] Type 3 fiber: layered quartz fiber, not coated with sunscreen slurry;

[0272] The natural density of layered quartz fiber is 0.06 g / cm 3 , thickness 1.5 mm, average diameter 1.5 μm;

[0273] S3, Fiber hot pressing molding:

[0274] The opacifying agent-modified layered fibers are sequentially stacked and laid on a high-temperature resistant metal mold. After the laying is completed, the fiber preform with the mold is tightened and pressed to obtain a fiber preform. The fiber preform with the mold is kept at 1000° C. for 6 hours and then naturally cooled to obtain a gradient fiber preform.

[0275] The order of laying the opacifier-modified layered fibers, from the hot side to the cold side, is: zirconia-modified layered mullite fiber (first), titania-modified layered zirconia fiber (second), and layered quartz fiber (third). The total thickness of the three fibers after laminate molding is 18.0 mm, with a thickness ratio of 4:5:9.

[0276] S4. Sol impregnation and aging:

[0277] The gradient fiber preform was immersed in alumina sol under a pressure of -0.1 MPa for 3 hours to obtain a sol-preform mixture, and the sol-preform mixture was kept at 65°C for 20 hours to form a gel-preform composite.

[0278] The solid content of the alumina sol is 14%, and the average particle size of the sol particles is 50 nm;

[0279] S5. Supercritical drying:

[0280] Tert-butanol was used as the medium for supercritical drying. The gel-preform composite was placed in an autoclave, which was kept airtight after tert-butanol was added. The volume ratio of the gel-preform composite to tert-butanol was 1:3. The autoclave was heated above the critical point of tert-butanol and maintained at 12.5 MPa for 10 hours. The gas in the autoclave was slowly discharged until the pressure reached 0, thereby obtaining a gradient aerogel composite body.

[0281] S6. Heat treatment:

[0282] The gradient aerogel composite material body was placed in a high-temperature furnace, heated from room temperature to 1000°C, maintained for 1 hour, and naturally cooled to obtain the gradient aerogel composite material.

[0283] The prepared gradient aerogel composite material has the following properties:

[0284] The operating temperature is 1600℃; 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℃ 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 (thickness 18mm) is heated on one side at 1600℃ for 1h, the shrinkage in the thickness direction is 0.6%, and the temperature rise on the cold side is 281℃.

[0285] Comparative Example 1:

[0286] The difference between Comparative Example 1 and Example 1 is that in the step "S1, preparing sunscreen slurry", the average diameter of the silicon carbide particles used in the first sunscreen slurry and the second sunscreen slurry is 10 μm, and the rest is the same as Example 1.

[0287] 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℃. When the material (10mm thick) was heated on one side at 800℃ for 1h, the shrinkage in the thickness direction was 0.3%, and the temperature rise on the cold side was 88℃.

[0288] This shows that due to the high intrinsic thermal conductivity of the sunscreen particles, when their average diameter is relatively large, solid-state heat conduction will be significantly increased, the overall thermal conductivity will increase, and the thermal insulation performance will decrease.

[0289] Comparative Example 2:

[0290] The difference between Comparative Example 2 and Example 1 is that the average particle size of the silica sol particles in the step of "S4, sol impregnation and aging" is 20 nm, and the rest is the same as Example 1.

[0291] The prepared aerogel composite material has an operating 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.

[0292] It shows that as the particle size of silica sol particles increases, the temperature resistance of the composite material improves, the thermal conductivity increases, and the mechanical properties decrease.

[0293] Comparative Example 3:

[0294] The difference between Comparative Example 3 and Example 1 is that the heat treatment temperature in the step "S6, heat treatment" is 900°C, and the rest is the same as Example 1.

[0295] The prepared aerogel composite material shrinks by 8.3% in thickness during heat treatment, with a thermal conductivity of 0.030 W / (m·K) at room temperature and 0.043 W / (m·K) at 800°C. When the material (10 mm thick) was heated on one side at 800°C for 1 hour, the shrinkage in the thickness direction was 0.3%, and the temperature rise on the cold side was 108°C.

[0296] It shows that too high heat treatment temperature will cause the pore structure of silica aerogel to collapse, the composite material to shrink, and the thermal insulation performance to decrease.

[0297] Comparative Example 4:

[0298] The difference between Comparative Example 4 and Example 2 is that in the step “S1, preparing sunscreen slurry”, the mass ratio of titanium oxide to water in the first sunscreen slurry is 50:100, and the rest is the same as Example 2.

[0299] The viscosity of the prepared sunscreen slurry is too high (above 4500 mPa·s), and it cannot be sprayed evenly on the layered fibers, and the spraying thickness is greater than 0.5 mm.

[0300] This indicates that too high a sunscreen content in the sunscreen slurry will significantly affect the spraying effect.

[0301] Comparative Example 5:

[0302] The difference between Comparative Example 5 and Example 3 is that in the "S2, slurry coating" step, the average diameters of the first layered alumina fiber and the second layered zirconia fiber are 9 μm and 6 μm, respectively, and the rest are the same as Example 3.

[0303] The prepared aerogel composite material has a thermal conductivity of 0.029 W / (m·K) at room temperature and 0.072 W / (m·K) at 1600°C. When the material (18 mm thick) was heated on one side at 1600°C for 1 hour, the shrinkage in the thickness direction was 0.4%, and the temperature rise on the cold side was 315°C.

[0304] It shows that the increase in fiber diameter will lead to a significant increase in comprehensive thermal conductivity and a decrease in thermal insulation performance.

[0305] In addition, it should be understood that although this specification is described in terms of implementation methods, not every implementation method contains only one independent technical solution. This narrative method of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment can also be appropriately combined to form other implementation methods that can be understood by those skilled in the art.

Claims

1. A method for preparing a gradient aerogel composite material, characterized in that: The following steps are involved: S1. Prepare sunscreen slurry: The dispersant, the viscous component and water are mixed and stirred at 25° C. to 50° C. to form a mixed solution, the sunscreen is added to the mixed solution and stirred rapidly at 25° C. to 50° C. to form a sunscreen slurry having a viscosity of 500 mPa·s to 3000 mPa·s, wherein the mass ratio of the dispersant, the viscous component, the sunscreen and the water is (0.5-3):(3-10):(5-30):100; The dispersant is one of lauryl glucoside, fatty alcohol polyoxyethylene ether glucoside, lauryl betaine, fatty alcohol polyoxyethylene ether and laurylphenol polyoxyethylene ether; The viscous component is one of starch, gelatin and polyvinyl alcohol; The sunscreen is one of silicon carbide, zirconium oxide, titanium oxide, potassium hexatitanate, carbon black, iron oxide, and ferrosoferric oxide, and the average diameter of the sunscreen particles ranges from 0.5 μm to 5 μm; S2. Slurry coating: The layered fibers are laid flat, and the obtained sunscreen slurry is evenly sprayed on the fiber surface at a pressure of 0.1 MPa to 0.5 MPa, and dried at 120° C. to 200° C. for 2 to 6 hours to form a sunscreen coating with a thickness of 0.01 mm to 0.3 mm on the layered fiber surface to obtain a sunscreen modified layered fiber; The layered fibers are selected from any one of rock wool, glass fiber, quartz fiber, aluminum silicate fiber, zirconium oxide fiber, lanthanum zirconate fiber, aluminum oxide fiber, and mullite fiber; The natural density of the layered fibers is 0.02 g / cm 3 ~0.1 g / cm 3 , thickness is 0.1mm~5mm, average diameter is 0.5μm~8μm; S3, Fiber hot pressing molding: The opacifying agent-modified layered fibers are sequentially stacked and laid on a high-temperature resistant metal mold, and after the laying is completed, the fiber preform with the mold is tightened and pressed to obtain a fiber preform with the mold, and the fiber preform with the mold is maintained at 600° C. to 1000° C. for 6 hours to 24 hours and then naturally cooled to obtain a gradient fiber preform; S4. Sol impregnation and aging: Under a pressure of -0.1 MPa to 0 MPa, the gradient fiber preform is immersed in the sol for 1 to 4 hours to obtain a sol-preform mixture, and the sol-preform mixture is maintained at 40°C to 70°C for 8 to 24 hours to form a gel-preform composite. The sol is one of silicon oxide, aluminum oxide and zirconium oxide sol, the solid content of the sol is 6% to 15%, and the average particle size of the sol particles is in the range of 5nm to 50nm; S5. Supercritical drying: Alcohols are used as a medium for supercritical drying. The gel-preform composite is placed in an autoclave, and after adding the alcohol, it is kept sealed. The volume ratio of the gel-preform composite to the alcohol is 1:(0.3-3). The autoclave is heated to above the critical point of the alcohol, maintained at 8.0 MPa-15.0 MPa for 1 hour-10 hours, and the gas in the autoclave is slowly discharged until the pressure is 0 to obtain a gradient aerogel composite body. S6. Heat treatment: The gradient aerogel composite material blank is placed in a high-temperature furnace, heated from room temperature to 600°C to 1000°C, maintained for 1h to 5h, and naturally cooled to obtain a 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 have low density and wide temperature range thermal conductivity, as well as mechanical properties. Their typical properties are as follows: (1) Composite material with a service temperature of 800°C: density of 0.19 g / cm 3 The thermal conductivity at room temperature is 0.016 W / (m·K), the thermal conductivity at 800℃ is 0.022 W / (m·K), the compressive strength at 3% deformation is 0.12 MPa, the flexural strength is 1.2 MPa, and the shrinkage in the thickness direction of a 10mm thick composite material after being heated at 800℃ for 1h is 0.3%, and the temperature rise on the cold side is 63℃. (2) Composite material with a service temperature of 1200°C: density of 0.27 g / cm 3 The thermal conductivity at room temperature is 0.020 W / (m·K), the thermal conductivity at 1200℃ is 0.030 W / (m·K), the compressive strength at 3% deformation is 0.17 MPa, the flexural strength is 1.1 MPa, and the shrinkage in the thickness direction of the composite material with a thickness of 12.5 mm is 0.4% after being heated on one side at 1200℃ for 1 hour, and the temperature rise on the cold side is 176℃. (3) Composite material with a service temperature of 1600°C: density of 0.31 g / cm 3 The thermal conductivity at room temperature is 0.026 W / (m·K), the thermal conductivity at 1600℃ is 0.056 W / (m·K), the compressive strength at 3% deformation is 0.16 MPa, the flexural strength is 0.95 MPa, and the 18mm thick composite material is heated at 1600℃ on one side for 1h. The shrinkage in the thickness direction is 0.9%, and the temperature rise on the cold side is 262℃.

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

3. The method for preparing a gradient aerogel composite material according to claim 1, wherein: The alcohol substance described in S5 is one of ethanol, methanol, isopropanol, n-propanol, n-butanol, sec-butanol, and tert-butanol.

4. The method for preparing a gradient aerogel composite material according to claim 1, wherein: The heating from room temperature to 600° C. to 1000° C. in S6 is completed at a heating rate of 0.5° C. / min to 3° C. / min.

5. A gradient aerogel composite material, characterized in that: The preparation method of a gradient aerogel composite material according to any one of claims 1 to 4 is obtained, wherein 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 have low density and wide temperature range thermal conductivity, as well as mechanical properties, and their typical properties are as follows: (1) Composite material with a service temperature of 800°C: density of 0.19 g / cm 3 The thermal conductivity at room temperature is 0.016 W / (m·K), the thermal conductivity at 800℃ is 0.022 W / (m·K), the compressive strength at 3% deformation is 0.12 MPa, the flexural strength is 1.2 MPa, and the shrinkage in the thickness direction of a 10mm thick composite material after being heated at 800℃ for 1h is 0.3%, and the temperature rise on the cold side is 63℃. (2) Composite material with a service temperature of 1200°C: density of 0.27 g / cm 3 The thermal conductivity at room temperature is 0.020 W / (m·K), the thermal conductivity at 1200℃ is 0.030 W / (m·K), the compressive strength at 3% deformation is 0.17 MPa, the flexural strength is 1.1 MPa, and the shrinkage in the thickness direction of the composite material with a thickness of 12.5 mm is 0.4% after being heated on one side at 1200℃ for 1 hour, and the temperature rise on the cold side is 176℃. (3) Composite material with a service temperature of 1600°C: density of 0.31 g / cm 3 The thermal conductivity at room temperature is 0.026 W / (m·K), the thermal conductivity at 1600℃ is 0.056 W / (m·K), the compressive strength at 3% deformation is 0.16 MPa, the flexural strength is 0.95 MPa, and the 18mm thick composite material is heated at 1600℃ on one side for 1h. The shrinkage in the thickness direction is 0.9%, and the temperature rise on the cold side is 262℃.

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