A C / SiC foam skeleton reinforced SiC aerogel composite material and its preparation method

Abstract

This invention relates to the field of aerogel composite materials technology, and more specifically, to C / SiC foam-reinforced SiC aerogel composite materials and their preparation methods. This invention uses lightweight, high-strength C foam as the skeleton material for the aerogel composite material, and achieves mechanical modification and reinforcement of the C foam skeleton through a SiC coating. The SiC aerogel is obtained by in-situ molding on the surface of the C / SiC foam skeleton using a sol-gel process combined with a carbothermal reduction process, achieving integral molding of the aerogel composite material. Through a gradient structure design, the precursor organic sol solution can better penetrate into the pores of the C foam skeleton. Simultaneously, the porosity can be adjusted to control the proportion of SiC aerogel, optimizing impedance matching characteristics and facilitating surface electromagnetic wave incidence. Furthermore, the internal C foam skeleton also exhibits a gradient distribution, optimizing dielectric loss attenuation and facilitating incident electromagnetic wave absorption, thus synergistically achieving the wave absorption performance of the aerogel composite material.

Description

Technical Field

[0001] This invention relates to the field of aerogel composite materials technology, and more specifically, to a C / SiC foam skeleton reinforced SiC aerogel composite material and its preparation method. Background Technology

[0002] Aerogels are ultraporous materials with a porosity of approximately 90% to 99.9% and a pore size ranging from 1 nm to 100 nm, exhibiting high specific surface area (≥500 m²). 2 Materials with properties such as ultra-lightweight, ultra-insulating, and ultra-low dielectric strength are numerous, but their properties are singular. For example, silica aerogel is not resistant to high temperatures or ablation and cannot be used in high-temperature environments. It mainly enables electromagnetic wave transmission and has virtually no wave absorption properties. Silicon carbide nanowire aerogel has low strength, its network structure is prone to collapse, and the nanowires are prone to entanglement and aggregation. Its performance is unstable, its preparation process is complex, and it requires high equipment investment. Carbon aerogel cannot be used in high-temperature oxygen environments. It has low structural strength, is prone to reacting with oxygen, and mainly shields and reflects electromagnetic waves. It also has no wave absorption properties and cannot meet the requirements of the aerospace field for ablation resistance, heat insulation, and wave absorption stealth.

[0003] Chinese invention patent application CN202211470104.X discloses a lightweight load-bearing multifunctional SiC aerogel composite material and its preparation method. The lightweight load-bearing multifunctional SiC aerogel composite material includes a carbon foam skeleton, a reinforcing coating disposed on the surface of the carbon foam skeleton, and aerogel disposed within the pores of the carbon foam skeleton. The carbon foam skeleton has a three-dimensional open-pore structure, and the aerogel is silicon carbide aerogel with a three-dimensional network structure. The carbon foam skeleton and the aerogel have a double-network coupled nested structure. The lightweight load-bearing multifunctional SiC aerogel composite material of this invention has low density and high strength. The pore structure of the double-network coupled nested structure inhibits air convection and conduction, resulting in excellent thermal insulation performance. It can also control the overall dielectric properties of the material, enabling electromagnetic wave absorption and thus achieving a stealth effect.

[0004] Chinese invention patent application CN201911053850.7 discloses a method for preparing high-temperature resistant SiC aerogel, which aims to solve the technical problems of low yield and easy damage to the microstructure of aerogel in existing methods for preparing SiC aerogel. The method is as follows: 1. Prepare liquid A and liquid B, and mix liquid A and liquid B to obtain a hydrolysate; 2. Prepare a wet gel; 3. Prepare an aerogel; 4. React the aerogel with magnesium powder, then wash and dry to obtain SiC aerogel. This invention uses magnesium thermoelectric reduction, under inert gas protection, to reduce the aerogel precursor to SiC aerogel, successfully avoiding the generation of SiO gas during the reduction process, maintaining the integrity of the product morphology to the greatest extent, and preparing organosilicon aerogels with uniform pore structure and complete shape through supercritical drying.

[0005] Chinese invention patent application number CN202211198954.9 discloses a SiC aerogel high-temperature thermal insulation material and its preparation method, relating to the field of thermal insulation material technology. The preparation method of the SiC aerogel high-temperature thermal insulation material includes the following steps: (1) preparing graphene oxide sol; (2) preparing reduced graphene oxide gel using a solvothermal process; (3) preparing graphene aerogel using a freeze-drying process; and (4) preparing SiC aerogel using a carbothermal reduction process. The preparation method of SiC aerogel high-temperature thermal insulation material provided by this invention has a short production cycle, simple process, and high production efficiency. It avoids the problems of complex process and long production cycle caused by the need to simultaneously introduce silicon source and carbon source in traditional processes. Compared with the traditional preparation method with a production cycle of 6 to 10 days, the preparation method provided by this invention has a cycle of 3 to 5 days. Furthermore, the method for preparing SiC aerogel high-temperature thermal insulation materials provided by this invention uses graphene aerogel as a template to prepare SiC aerogel through a high-temperature vapor-phase silicon infiltration process. This not only simplifies the preparation process but also overcomes the problem of easy cracking during carbothermic reduction of two-phase composite materials. The prepared SiC aerogel thermal insulation material inherits the flexibility of graphene aerogel and will not experience brittle fracture like SiC aerogels prepared by traditional methods. The compressive strength at 20% compressive strain is 0.2-0.8 MPa, and the density is 0.025-0.15 g / cm³. 3 The compressive strength at 20% compressive strain is 0.2-0.8 MPa, and the thermal conductivity at 1000℃ under 0.1 MPa argon atmosphere is 0.205-0.329 W / (m·K). It has good mechanical properties and excellent high-temperature thermal insulation performance. Moreover, the preparation process does not use organic solvents, so it is green and environmentally friendly. In addition, only a small amount of reducing agent is added during the preparation process, resulting in SiC aerogel high-temperature thermal insulation material with low impurity content.

[0006] Chinese invention patent application CN202210189502.8 discloses a SiC nanowire-reinforced SiC ceramic matrix composite material and its preparation method. The preparation method includes the following steps: First, SiC nanowires are prepared by chemical vapor deposition. Then, the SiC nanowires are self-assembled into a layered structure with tightly cross-linked SiC nanowire aerogel using a fiber freeze-forming method. Next, a pyrolytic carbon interface coating is deposited on the surface of the SiC nanowires through chemical vapor infiltration. Finally, a SiC matrix is ​​in-situ composited in the SiC nanowire aerogel using a vacuum pressure-assisted precursor impregnation pyrolysis method. This invention significantly improves the mechanical properties of SiC ceramics by utilizing the cross-linked network structure and micro / nano hierarchical pore distribution of the SiC nanowire aerogel, meeting the demand for lightweight and high-strength structural materials for high-temperature equipment in the aerospace field.

[0007] As shown in the above patents, an aerogel composite material is disclosed, but the preparation process fails to effectively balance structural strength and performance, thus failing to achieve the expected goals. Summary of the Invention

[0008] To address the aforementioned technical problems, this invention provides a C / SiC foam-reinforced SiC aerogel composite material and its preparation method. By modifying and reinforcing SiC aerogel with C / SiC foam, the overall molding of the aerogel composite material is achieved, improving the overall mechanical properties of the composite material. The impedance matching characteristics are optimized through gradient structure design, which is beneficial for the incidence of surface electromagnetic waves. At the same time, the internal C foam skeleton also exhibits a gradient distribution, which optimizes dielectric loss attenuation and is beneficial for the absorption of incident electromagnetic waves. Together, these factors contribute to the wave absorption performance of the aerogel composite material.

[0009] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows:

[0010] A C / SiC foam-reinforced SiC aerogel composite material comprises C foam, a SiC coating, and SiC aerogel. The composite material has a compressive modulus of 3.5-6.5 MPa, a maximum compressive strength of 0.6-1.5 MPa, and a specific strength of 0.04-0.06 MPa / (kg·m²). 3 The average real part of the dielectric constant is 7-12, the average imaginary part of the dielectric constant is 2-4, the absolute value of the reflection loss is 50.0-60.0dB, and the effective absorption bandwidth is 2.0-2.4GHz.

[0011] The C foam is obtained through a high-temperature pyrolysis process, with a porosity of 70-90% and a density of 0.15-0.35 g / cm³. 3 Young's modulus 0.5-2.0 GPa, shear strength 1.0-2.5 MPa, thermal conductivity 0.1-0.2 W / (m·K);

[0012] The SiC coating is obtained by chemical vapor deposition and is uniformly coated on the surface of the C foam skeleton in a continuous structure. The thickness of the SiC coating is 0.1-0.3 μm.

[0013] The SiC aerogel is obtained through a sol-gel process and is uniformly filled within the pores of the C / SiC foam framework. The density of the SiC aerogel is 0.6-0.9 g / cm³. 3 Specific surface area is 150-300 μm 2 / g, porosity 60-80%, average pore size 45-70nm, linear shrinkage 35-45%;

[0014] The C-foam has an open-cell interconnected structure, and the porosity is distributed in a gradient along the central direction of the aerogel, with the porosity of the outermost layer being 85-90% and the porosity of the center being 70-75%.

[0015] The SiC coating and C foam form a dual-network structure.

[0016] A method for preparing a C / SiC foam skeleton reinforced SiC aerogel composite material, characterized by comprising the following steps:

[0017] S1: Cut melamine foam to a certain size, first heat it to 100-150℃ in a muffle furnace, hold it for 2-3 hours to remove surface impurities and unreacted matrix, then place it in a high-temperature pyrolysis furnace, introduce nitrogen to maintain an inert atmosphere, set the temperature rise rate to 1-2℃ / min, the temperature to 900-1000℃, hold it for 2-3 hours, and cool it with the furnace to obtain C foam;

[0018] S2: Place C foam in a chemical vapor deposition furnace, introduce hydrogen, trimethylsilane and argon, set the gas flow rate ratio to 150-180:20-30:150-180sccm, set the reaction time to 2-4h, and obtain C / SiC foam with uniform SiC coating.

[0019] S3: Tetraethyl orthosilicate was selected as the silicon source of the reaction system, resorcinol and formaldehyde were selected as the carbon source of the reaction system, and γ-aminopropyltriethoxysilane was selected as the catalyst and supplementary silicon source. After stirring at 30°C for 30-45 min to mix evenly, the precursor organic sol solution was obtained.

[0020] S4: Place the cut C / SiC foam at the bottom of a polytetrafluoroethylene beaker mold in advance, then pour the precursor organic sol solution into the polytetrafluoroethylene beaker mold. The solution fills the inner diameter of the beaker mold to 50-60 mm and the height to 25-40 mm. Place it in a 60℃ oven for 24-36 h of sol-gel reaction, and then perform an aging treatment. After 48-60 h, organic wet gel is obtained.

[0021] S5: Perform solution displacement treatment on the organic wet gel. Place the organic wet gel into a mold containing the displacement solution and place it in an oven for displacement 2-4 times. The displacement time is 24-36 hours and the displacement temperature is 60℃. After that, take out the wet gel and place it at room temperature until the quality is stable to obtain RF / SiO2 aerogel reinforced with C / SiC foam skeleton.

[0022] S6: The obtained C / SiC foam skeleton reinforced RF / SiO2 aerogel is subjected to carbonization and reduction treatment. First, the C / SiC foam skeleton reinforced RF / SiO2 aerogel is heated to 800-900℃ and held for 1-2 hours under nitrogen atmosphere protection. Finally, it is heated to 1500-1600℃ and held for 2-4 hours. The heating rate is 3-5℃ / min and the nitrogen flow rate is 50-70.00ml / min. The aerogel is cooled in the furnace to obtain the C / SiC foam skeleton reinforced SiC aerogel composite material.

[0023] Compared with the prior art, the beneficial effects of this invention are:

[0024] 1. This invention uses lightweight and high-strength C foam as the skeleton material of aerogel composite material, and achieves mechanical modification and enhancement of C foam skeleton through SiC coating. Furthermore, SiC aerogel is obtained by in-situ molding on the surface of C / SiC foam skeleton through sol-gel process combined with carbothermal reduction process, realizing the overall molding of aerogel composite material and effectively improving the overall load-bearing performance of aerogel composite material.

[0025] 2. This invention adopts a design scheme with a gradient distribution of C foam porosity, that is, the porosity of the outermost layer is 85-90%, and the porosity of the center is 70-75%. On the one hand, this allows the precursor organic sol liquid to enter the interior of the C foam skeleton pores more easily. On the other hand, the porosity can be adjusted to adjust the proportion of SiC aerogel, optimize the impedance matching characteristics, and facilitate the incidence of surface electromagnetic waves. At the same time, the internal C foam skeleton also has a gradient distribution, which optimizes the dielectric loss attenuation and facilitates the absorption of incident electromagnetic waves. This synergistically realizes the wave absorption performance of the aerogel composite material.

[0026] 3. This invention uses tetraethyl orthosilicate, resorcinol, formaldehyde, and γ-aminopropyltriethoxysilane as precursor organic sol solutions, and modifies them by displacement solution treatment. Then, under nitrogen atmosphere protection, the temperature is raised to 800-900℃ and held for 1-2 hours, and finally raised to 1500-1600℃ and held for 2-4 hours. Through gradient pyrolysis process, the cracking degree of SiC aerogel is alleviated, and in-situ molding of SiC aerogel on C / SiC foam skeleton can be realized, which significantly improves the mechanical properties of aerogel composite materials. Detailed Implementation

[0027] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0028] A C / SiC foam-reinforced SiC aerogel composite material comprises C foam, a SiC coating, and SiC aerogel. The composite material has a compressive modulus of 4.5 MPa, a maximum compressive strength of 1.2 MPa, and a specific strength of 0.05 MPa / (kg·m). 3 The average dielectric constant has a real part of 10 and an imaginary part of 3, with an absolute value of 55 dB for reflection loss and an effective absorption bandwidth of 2.2 GHz.

[0029] C foam is obtained through a high-temperature pyrolysis process, with a porosity of 80% and a density of 0.25 g / cm³. 3 Young's modulus 1.5 GPa, shear strength 1.5 MPa, thermal conductivity 0.15 W / (m·K);

[0030] The SiC coating was obtained by chemical vapor deposition and was uniformly coated on the surface of the C foam skeleton in a continuous structure. The SiC coating thickness was 0.2 μm.

[0031] The SiC aerogel was obtained through a sol-gel process, uniformly filling the pores of the C / SiC foam framework. The density of the SiC aerogel was 0.7 g / cm³. 3 Specific surface area is 200m 2 / g, porosity 70%, average pore size 60nm, linear shrinkage 35%;

[0032] The C foam has an open-cell interconnected structure, and the porosity is distributed in a gradient along the center of the aerogel, with the porosity of the outermost layer being 90% and the porosity of the center being 70%.

[0033] The SiC coating forms a dual-network structure with the C foam.

[0034] A method for preparing a C / SiC foam skeleton reinforced SiC aerogel composite material includes the following steps:

[0035] S1: Cut melamine foam to a certain size, first heat it to 100℃ in a muffle furnace, hold it for 2 hours to remove surface impurities and unreacted matrix, then place it in a high-temperature pyrolysis furnace, introduce nitrogen to maintain an inert atmosphere, set the temperature rise rate to 1℃ / min, the temperature to 95℃, hold it for 2 hours, and cool it with the furnace to obtain C foam.

[0036] S2: Place C foam in a chemical vapor deposition furnace, introduce hydrogen, trimethylsilane and argon, set the gas flow rate ratio to 150:20:180 sccm, set the reaction time to 4h, and obtain C / SiC foam with uniform SiC coating.

[0037] S3: Tetraethyl orthosilicate was selected as the silicon source of the reaction system, resorcinol and formaldehyde were selected as the carbon source of the reaction system, and γ-aminopropyltriethoxysilane was selected as the catalyst and supplementary silicon source. After stirring at 30°C for 35 min to mix evenly, the precursor organic sol solution was obtained.

[0038] S4: Place the cut C / SiC foam at the bottom of a polytetrafluoroethylene beaker mold in advance, then pour the precursor organic sol solution into the polytetrafluoroethylene beaker mold, the solution fills the inner diameter 55mm and the height 30mm, and place it in a 60℃ oven for 30h sol-gel reaction, and then perform aging treatment, and obtain organic wet gel after 50h.

[0039] S5: The organic wet gel is subjected to solution displacement treatment. The organic wet gel is placed in a mold containing displacement solution and placed in an oven for displacement 3 times, with a displacement time of 24 hours and a displacement temperature of 60℃. After that, the wet gel is taken out and placed at room temperature until the quality is stable to obtain RF / SiO2 aerogel reinforced with C / SiC foam skeleton.

[0040] S6: The obtained C / SiC foam skeleton reinforced RF / SiO2 aerogel was subjected to carbonization and reduction treatment. First, the C / SiC foam skeleton reinforced RF / SiO2 aerogel was heated to 850℃ and held for 1h under nitrogen atmosphere protection. Finally, it was heated to 1500℃ and held for 4h. The heating rate was 3℃ / min and the nitrogen flow rate was 50.00ml / min. The C / SiC foam skeleton reinforced SiC aerogel composite material was obtained by furnace cooling.

[0041] The above description only illustrates the preferred embodiments of the present invention. However, the present invention is not limited to the above embodiments. Within the scope of knowledge possessed by those skilled in the art, various changes can be made without departing from the spirit of the present invention, and all such changes should be included within the protection scope of the present invention.

Claims

1. A C / SiC foam-reinforced SiC aerogel composite material, comprising C foam, a SiC coating, and SiC aerogel, wherein the composite material has a compressive modulus of 3.5-6.5 MPa, a maximum compressive strength of 0.6-1.5 MPa, and a specific strength of 0.04-0.06 MPa / (kg·m³). 3 The average real part of the dielectric constant is 7-12, the average imaginary part of the dielectric constant is 2-4, the absolute value of the reflection loss is 50.0-60.0dB, and the effective absorption bandwidth is 2.0-2.4GHz. The C foam is obtained through a high-temperature pyrolysis process, with a porosity of 70-90% and a density of 0.15-0.35 g / cm³. 3 Young's modulus 0.5-2.0 GPa, shear strength 1.0-2.5 MPa, thermal conductivity 0.1-0.2 W / (m·K); The SiC coating is obtained by chemical vapor deposition and is uniformly coated on the surface of the C foam skeleton in a continuous structure. The thickness of the SiC coating is 0.1-0.3 μm. The SiC aerogel is obtained through a sol-gel process and is uniformly filled within the pores of the C / SiC foam framework. The density of the SiC aerogel is 0.6-0.9 g / cm³. 3 Specific surface area is 150-300 μm 2 / g, porosity 60-80%, average pore size 45-70nm, linear shrinkage 35-45%; The C-foam has an open-cell interconnected structure, and is distributed in a gradient along the central direction of the aerogel. The porosity of the outermost layer is 85-90%, and the porosity of the center is 70-75%. The SiC coating and C foam form a dual-network structure.

2. A method for preparing the C / SiC foam skeleton reinforced SiC aerogel composite material according to claim 1, characterized in that, Includes the following steps: S1: Cut melamine foam to a certain size, first heat it to 100-150℃ in a muffle furnace, hold it for 2-3 hours to remove surface impurities and unreacted matrix, then place it in a high-temperature pyrolysis furnace, introduce nitrogen to maintain an inert atmosphere, set the temperature rise rate to 1-2℃ / min, the temperature to 900-1000℃, hold it for 2-3 hours, and cool it with the furnace to obtain C foam; S2: Place C foam in a chemical vapor deposition furnace, introduce hydrogen, trimethylsilane and argon, set the gas flow rate ratio to 150-180:20-30:150-180sccm, set the reaction time to 2-4h, and obtain C / SiC foam with uniform SiC coating. S3: Tetraethyl orthosilicate was selected as the silicon source of the reaction system, resorcinol and formaldehyde were selected as the carbon source of the reaction system, and γ-aminopropyltriethoxysilane was selected as the catalyst and supplementary silicon source. After stirring at 30°C for 30-45 min to mix evenly, the precursor organic sol solution was obtained. S4: Place the cut C / SiC foam at the bottom of a polytetrafluoroethylene beaker mold in advance, then pour the precursor organic sol solution into the polytetrafluoroethylene beaker mold. The solution fills the inner diameter of the beaker mold to 50-60 mm and the height to 25-40 mm. Place it in a 60℃ oven for 24-36 h of sol-gel reaction, and then perform an aging treatment. After 48-60 h, organic wet gel is obtained. S5: The organic wet gel is subjected to solution displacement treatment. The organic wet gel is placed in a mold containing displacement solution and placed in an oven for displacement 2-4 times. The displacement time is 24-36 hours and the displacement temperature is 60℃. After that, the wet gel is taken out and placed at room temperature until the quality is stable to obtain RF / SiO2 aerogel reinforced with C / SiC foam skeleton. S6: The obtained C / SiC foam skeleton reinforced RF / SiO2 aerogel is subjected to carbonization and reduction treatment. First, the C / SiC foam skeleton reinforced RF / SiO2 aerogel is heated to 800-900℃ and held for 1-2 hours under nitrogen atmosphere protection. Finally, it is heated to 1500-1600℃ and held for 2-4 hours. The heating rate is 3-5℃ / min and the nitrogen flow rate is 50-70.00ml / min. The aerogel is cooled in the furnace to obtain the C / SiC foam skeleton reinforced SiC aerogel composite material.