Gradient core-shell structure composite material and preparation method thereof

Abstract

The invention discloses a gradient core-shell structure composite material and a preparation method thereof. The preparation method comprises the following steps: preparing a core layer structure; preparing an interface isolation layer; preparing a middle layer structure; preparing an outer layer structure; carrying out carbonization treatment; the invention has the following characteristics: 1, a gradient core-shell structure: through gradient change of thermal expansion coefficient and heat conductivity coefficient of a layer-by-layer material, interface thermal stress concentration is avoided, and the service life of the material is prolonged; 2, multifunctional compounding: the core layer is light and heat-insulating, the middle layer is over-buffered, and the outer layer is high-temperature-resistant and protective, so that multifunctional integration of the material is realized; 3, process controllability: gradient carbonization is adopted, so that structural collapse is avoided, and uniform generation of a carbon layer and a silicon carbide layer is protected; seamless connection of core-shell layers is achieved through freeze drying and in-situ polymerization, self-supporting of the material is achieved, and the layering problem of a traditional composite material is solved. And 4, environmental adaptability: the chemical inertness of the outer silicon carbide aerogel can resist acid and alkali corrosion, and the material is suitable for complex environments and the fields of aerospace high-temperature heat insulation and the like.

Description

Technical Field

[0001] The present invention belongs to the technical field of composite material preparation, and in particular relates to a gradient core-shell structure composite material and a preparation method thereof. Background Art

[0002] Aircraft encounter transient ultra-high temperatures (>1000°C) upon entering the atmosphere, requiring materials that combine high-temperature insulation, lightweight construction, and thermal shock resistance. A single aerogel cannot meet the technical challenges of lightweight, high strength, and high-temperature stability. Existing composite structural designs suffer from weak interfacial bonding, lack gradient thermal conductivity, and mechanical transition design, making them difficult to handle thermal stress gradients. Therefore, achieving high performance in gradient core-shell composites through rational material selection and process design remains a technical challenge.

[0003] For example, compared with Patent 1 (CN 105801156B), the porous alumina-silica aerogel spheres effectively increase the insulation temperature, but lack mechanical strength and are difficult to meet the practical application requirements in the field of high-temperature insulation. Compared with Patent 2 (CN 115611288B), the enclosed silica aerogel microsphere thermal insulation coating lacks a gradient thermal conductivity design at the interface, and coating cracking has occurred. Summary of the Invention

[0004] In view of the above problems, the purpose of the present invention is to provide a gradient core-shell structure composite material and a preparation method thereof that can achieve material self-support and solve the delamination problem of traditional composite materials.

[0005] The present invention is achieved through the following technical solutions: A gradient core-shell structure composite material and a preparation method thereof, comprising the following steps: Step a: Preparation of core layer structure: ① Clean the surface of the hollow glass microspheres to remove impurities and dry them for later use; ② Prepare SiO2 sol, immerse the microspheres in the sol, and form a SiO2 gel layer on the surface of the microspheres through the sol-gel method. After solvent replacement and drying, SiO2 aerogel-coated hollow glass microspheres are formed.

[0006] Step b: Preparation of interface isolation layer: Wrapping the isolation layer by chemical deposition to protect the SiO2 gel layer on the hollow glass microspheres in step a; Step c: Preparation of the middle layer structure: dissolving a phenolic resin precursor in a solvent, adding an appropriate amount of catalyst, and stirring to form a phenolic resin sol, immersing the hollow glass microspheres obtained in step b in the phenolic resin sol, and forming a SiO2 gel layer on the hollow glass microspheres described in step b by a sol-gel method, and drying to form a phenolic resin gel layer; Step d: Preparation of the outer layer structure: Phenolic resin sol and silane coupling agent are mixed in proportion and stirred to form a silicon carbide precursor sol. The hollow glass microspheres obtained in step c are immersed in the silicon carbide precursor sol to form a silicon carbide gel layer on the outer layer by a sol-gel method, which is then dried to form the outer layer structure. Step e: Carbonization treatment: After drying the material obtained in step d, place it in a carbonization furnace, and carbonize the phenolic resin gel layer described in step c into a carbon aerogel layer under atmosphere protection conditions; under the same conditions, the silicon carbide gel layer described in step d is converted into a silicon carbide aerogel layer.

[0007] The hollow microspheres described in step a are high-temperature-resistant glass microspheres such as borosilicate glass microspheres or surface-modified glass microspheres, or hollow ceramic microspheres; the hollow microspheres described in step a have a diameter of 10 to 50 μm, and the thickness of the SiO2 aerogel layer is 100 to 500 nm.

[0008] The raw materials of the SiO2 aerogel described in step a include a silicon source, a solvent, water, a catalyst and a high-temperature stabilizer; the silicon source includes ethyl orthosilicate, polyethyl orthosilicate or methyl orthosilicate; the solvent includes methanol or ethanol; the catalyst is hydrochloric acid, nitric acid or oxalic acid; the high-temperature stabilizer includes ZrO2, TiO2 or Al2O3; the viscosity of the hollow microspheres immersed in the SiO2 sol is 10 to 50 mPa•s.

[0009] The hollow microspheres in step a have a diameter of 10 to 50 μm, and the thickness of the SiO2 aerogel layer is 100 to 500 nm.

[0010] The SiO2 gel layer in step a is dried by supercritical drying or freeze drying, wherein the supercritical drying temperature is 45-55°C, the pressure is 10-16 MPa, the CO2 flow rate is 2000-2500 kg / h, and the drying time is 6-12 hours; the freeze drying temperature is -50°C, the pressure is <10 Pa, the drying time is 24-48 hours, and the temperature is increased at a rate of 1-2°C / h.

[0011] The interface isolation layer in step b is boron nitride, aluminum oxide or silicon nitride.

[0012] The phenolic resin aerogel raw materials described in step c include phenolic compounds, aldehyde compounds, catalysts, solvents, and barriers; the phenolic compounds are phenol, resorcinol, or bisphenol; the aldehyde compounds are formaldehyde, acetaldehyde, or furfural; the catalyst is an alkaline catalyst or an acidic catalyst; the solvent is ethanol, methanol, acetone, or deionized water; the barrier is carbon nanotubes or graphene; the viscosity of the hollow glass microspheres immersed in the phenolic resin sol is 50 to 200 mPa•s.

[0013] The raw materials of the outer layer structure in step d include phenolic resin sol and silane coupling agent; the raw materials of the phenolic resin aerogel include phenolic compounds, aldehyde compounds, catalysts and solvents; the silane coupling agent includes one or two of KH550, KH560, KH570 and SCA-αA42M; the viscosity of the sol immersed in silicon carbide precursor in step d is 50 to 200 mPa•s.

[0014] The thickness of the carbon aerogel layer in step e is 1 to 2 μm; the thickness of the silicon carbide aerogel layer in step e is 500 nm to 1 μm.

[0015] The drying method of the phenolic resin gel layer in step c and the silicon carbide gel layer in step d is freeze drying at a temperature of -50°C, a pressure of <10 Pa, a time of 24 to 48 hours, and a heating rate of 1 to 2°C / h.

[0016] The carbonization treatment step described in step e is to first pre-carbonize at a low temperature, heat to 300°C to 400°C at a heating rate of 2 to 5°C / min, pre-carbonize for 1 to 2 hours, and then heat to 800°C to 900°C at a heating rate of 5 to 10°C / min, and carbonize for 2 to 3 hours; the protective gas in the atmosphere protection conditions described in step e is ultrapure argon or nitrogen, and the flow rate is 300 to 500 ml / min.

[0017] Beneficial effects of the present invention: 1. Gradient core-shell structure: By changing the thermal expansion coefficient and thermal conductivity of each layer, the thermal stress concentration at the interface is avoided and the material life is extended; 2. Multifunctional composite: the core layer is lightweight and heat-insulating, the middle layer is over-buffered, and the outer layer is high-temperature resistant and protective, realizing the multifunctional integration of materials.

[0018] 3. Process controllability: Gradient carbonization (pre-carbonization at 300-400°C + high-temperature carbonization at 800-900°C) is used to avoid structural collapse and ensure uniform growth of the protective carbon layer and silicon carbide layer. Freeze drying and in-situ polymerization are used to achieve seamless connection between the core and shell layers, making the material self-supporting and solving the delamination problem of traditional composite materials.

[0019] 4. Environmental adaptability: The chemical inertness of the outer layer of silicon carbide aerogel can resist acid and alkali corrosion, and is suitable for complex environments (such as high temperature, high humidity, and corrosive media). It is suitable for aerospace high-temperature insulation (high-temperature resistant insulation materials such as aircraft thermal protection systems and rocket engine insulation linings) and other fields. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] The present invention will be described in further detail below with reference to the accompanying drawings.

[0021] Figure 1 It is a process flow chart of the present invention. DETAILED DESCRIPTION

[0022] The following describes the implementation of the present invention through specific embodiments. People skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification.

[0023] It should be noted that the structures, proportions, sizes, etc. depicted in the drawings of this specification are only used to match the contents disclosed in the specification for people familiar with this technology to understand and read, and are not used to limit the conditions for the implementation of the present invention. Therefore, they have no substantial technical significance. Any modification of the structure, change in the proportional relationship, or adjustment of the size should still fall within the scope of the technical content disclosed by the present invention without affecting the efficacy and purpose of the present invention. At the same time, the terms such as "upper", "lower", "left", "right", "middle", etc. quoted in this specification are only for the convenience of description and are not used to limit the scope of the implementation of the present invention. Changes or adjustments in their relative relationships should also be regarded as the scope of the implementation of the present invention without substantially changing the technical content.

[0024] In the description of the present invention, it should be noted that, unless otherwise expressly specified and limited, the terms "connected" and "connected" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to the specific circumstances. It should be noted that the terms "include", "comprise" or any other variants are intended to cover non-exclusive inclusion, so that a process, method, article or device that includes a series of elements includes not only those elements, but also other elements that are not explicitly listed, or also includes elements that are inherent to such process, method, article or device. Example 1

[0025] Step a: Wash the hollow glass microspheres of borosilicate with deionized water to remove surface impurities, and dry them for later use; mix ethyl orthosilicate with ethanol and deionized water in a ratio of 1:4:4, add a small amount of hydrochloric acid (pH=3~4) as a catalyst, add 5wt% ZrO2, and stir to form a solution with a viscosity of 10~50mPa•s; immerse the hollow microspheres in the solution, and form a SiO2 aerogel layer on the surface of the microspheres by a sol-gel method. The coated microspheres are supercritically dried in CO2 at a temperature of 55°C, a pressure of 14MPa, and a CO2 flow rate of 250kg / h for 5h.

[0026] Step b: Install the boron nitride (BN) isolation layer using chemical deposition, specifically: place the pre-treated silica aerogel in a quartz boat, place it in the constant temperature zone of the CVD reactor, evacuate the reactor and introduce argon gas with a flow rate of 100 sccm to clean the residual oxygen; gradually increase the temperature to 1000°C at a rate of 5°C / min, maintain the argon flow rate at 50 sccm, and introduce a mixed gas with a flow rate of BCl3 of 20 sccm and a flow rate of NH3 of 200 sccm in a volume ratio of 1:10, maintain for 60 minutes, and gradually cool to room temperature to form a BN isolation layer of 50-200nm.

[0027] Step c: mixing resorcinol and formaldehyde at a molar ratio of 1:2, adding methanol at a molar ratio of 200:1 and sodium carbonate as a catalyst, and stirring until the viscosity reaches 100-200 mPa·s; The hollow glass microspheres were immersed in phenolic resin sol and gelled at 60°C for 48 hours. After gelling, they were freeze-dried at -50°C, pressure <10Pa, time 48 hours, and temperature was increased at a rate of 2°C / h).

[0028] Step d: mixing the phenolic resin sol and the silane coupling agent in a ratio of 10:1 to form a silicon carbide precursor solution, and stirring for 2 hours until the viscosity of the silicon carbide precursor solution is 100-200 mPa·s; The middle layer is immersed in a silicon carbide precursor solution, forming a silicon carbide gel layer on the outer layer via a sol-gel method. This is followed by freeze drying at -50°C, a pressure of <10 Pa, and a time of 24 to 48 hours, with the temperature increased at a rate of 1 to 2°C / hour, to obtain the outer layer of the self-supporting gradient core-shell structure.

[0029] Step e: First, the dried material was placed in a tube furnace and heated to 300°C at a heating rate of 2°C / min under nitrogen protection for pre-carbonization for 2 hours. The material was then heated to 900°C at a heating rate of 5°C / min and carbonized for 3 hours. After carbonization, the material was naturally cooled to room temperature to obtain a gradient core-shell composite material.

[0030] Table 1 shows the effect of different ratios of SiO2 aerogel coating on the performance of gradient core-shell structure composite materials

[0031] Table 1 It can be seen from Table 1 that when the proportion of ethanol increases, although the density decreases, the thermal insulation capacity also decreases. Experiments have found that when the ratio of ethyl orthosilicate to ethanol is 1:4, the thermal insulation capacity and overall lightweight are the best.

[0032] Table 2 shows the effect of isolation layer deposition time on thickness and performance of gradient core-shell composite materials.

[0033] Table 2 It can be seen from Table 2 that as the deposition time and the thickness of the isolation layer increase, the thermal conductivity of the gradient core-shell structure composite material becomes an inverse parabola, and the density increases accordingly. Experiments have found that when the deposition time is 60 minutes and the thickness of the isolation layer is 156 nm, the thermal conductivity is at the lowest point of the inverse parabola. At this time, the individual performance and overall lightweight of the gradient core-shell structure composite material are the best.

[0034] Table 3 shows the effect of carbonization temperature on the performance of gradient core-shell structure composite materials

[0035] Table 3 It can be seen from Table 3 that when the carbonization time remains unchanged and the carbonization temperature increases, the compressive strength of the gradient core-shell structure composite material increases accordingly, and the thermal insulation temperature of the gradient core-shell structure composite material at 1200℃ forms an inverse parabola. The experiment found that when the carbonization temperature is 900℃, the thermal insulation temperature of the gradient core-shell structure composite material at 1200℃ is at the lowest point of the inverse parabola, and at this time the compressive strength and thermal insulation effect of the gradient core-shell structure composite material are the best.

[0036] Table 4 Effect of carbonization time on the properties of gradient core-shell structure composites

[0037] Table 4 It can be seen from Table 4 that when the carbonization temperature remains unchanged and the carbonization time increases, the compressive strength of the gradient core-shell structure composite material increases accordingly, and the thermal insulation temperature of the gradient core-shell structure composite material at 1200℃ forms an inverse parabola. The experiment found that when the carbonization time is 3h, the thermal insulation temperature of the gradient core-shell structure composite material at 1200℃ is at the lowest point of the inverse parabola, and at this time the compressive strength and thermal insulation effect of the gradient core-shell structure composite material are the best.

[0038] Table 5 Properties of gradient core-shell structure composite materials

[0039] Table 5 In summary, the core-shell structure composite material properties in Table 5 can be obtained. It can be seen that the preparation method of the present invention can obtain a gradient core-shell structure composite material with lightweight thermal insulation, middle layer excessive buffering, and outer layer high temperature protection, realizing multifunctional integrated materials.

[0040] The protection scope of the present invention is not limited to the technical solutions disclosed in the specific implementation methods. Any modifications, equivalent replacements, improvements, etc. made to the above embodiments based on the technical essence of the present invention fall within the protection scope of the present invention.

Claims

1. A gradient core-shell structure composite material and a preparation method thereof, characterized in that The following steps are involved: Step a: Preparation of the core layer structure: ① Clean the surface of the hollow glass microspheres to remove impurities and dry them for later use; ② Prepare SiO2 sol, immerse the microspheres in the sol, form a SiO2 gel layer on the surface of the microspheres by the sol-gel method, and then form SiO2 aerogel-coated hollow glass microspheres through solvent replacement and drying; Step b: Preparation of interface isolation layer: Wrapping the isolation layer by chemical deposition to protect the SiO2 gel layer on the hollow glass microspheres in step a; Step c: Preparation of the middle layer structure: dissolving a phenolic resin precursor in a solvent, adding an appropriate amount of catalyst, and stirring to form a phenolic resin sol, immersing the hollow glass microspheres obtained in step b in the phenolic resin sol, and forming a SiO2 gel layer on the hollow glass microspheres described in step b by a sol-gel method, and drying to form a phenolic resin gel layer; Step d: Preparation of the outer layer structure: Phenolic resin sol and silane coupling agent are mixed in proportion and stirred to form a silicon carbide precursor sol. The hollow glass microspheres obtained in step c are immersed in the silicon carbide precursor sol to form a silicon carbide gel layer on the outer layer by a sol-gel method, which is then dried to form the outer layer structure. Step e: Carbonization treatment: After drying the material obtained in step d, place it in a carbonization furnace, and carbonize the phenolic resin gel layer described in step c into a carbon aerogel layer under atmosphere protection conditions; under the same conditions, the silicon carbide gel layer described in step d is converted into a silicon carbide aerogel layer.

2. The gradient core-shell structure composite material and the preparation method thereof according to claim 1, characterized in that: The hollow microspheres described in step a are borosilicate glass microspheres, surface-modified glass microspheres, high-temperature-resistant glass microspheres, or hollow ceramic microspheres; the hollow microspheres described in step a have a diameter of 10 to 50 μm, and the thickness of the SiO2 aerogel layer is 100 to 500 nm.

3. The gradient core-shell structure composite material and the preparation method thereof according to claim 1, characterized in that: The raw materials of the SiO2 aerogel described in step a include a silicon source, a solvent, water, a catalyst and a high-temperature stabilizer; the silicon source includes ethyl orthosilicate, polyethyl orthosilicate or methyl orthosilicate; the solvent includes methanol or ethanol; the catalyst is hydrochloric acid, nitric acid or oxalic acid; the high-temperature stabilizer includes ZrO2, TiO2 or Al2O3; the viscosity of the hollow microspheres immersed in the SiO2 sol is 10 to 50 mPa•s.

4. The gradient core-shell structure composite material and the preparation method thereof according to claim 1, characterized in that: The SiO2 gel layer in step a is dried by supercritical drying or freeze drying, wherein the supercritical drying temperature is 45-55°C, the pressure is 10-16 MPa, the CO2 flow rate is 2000-2500 kg / h, and the drying time is 6-12 hours; the freeze drying temperature is -50°C, the pressure is <10 Pa, the drying time is 24-48 hours, and the temperature is increased at a rate of 1-2°C / h.

5. The gradient core-shell structure composite material and the preparation method thereof according to claim 1, characterized in that: The interface isolation layer in step b is boron nitride, aluminum oxide or silicon nitride.

6. The gradient core-shell structure composite material and the preparation method thereof according to claim 1, characterized in that: The phenolic resin aerogel raw materials described in step c include phenolic compounds, aldehyde compounds, catalysts, solvents, and barriers; the phenolic compounds are phenol, resorcinol, or bisphenol; the aldehyde compounds are formaldehyde, acetaldehyde, or furfural; the catalyst is an alkaline catalyst or an acidic catalyst; the solvent is ethanol, methanol, acetone, or deionized water; the barrier is carbon nanotubes or graphene; the viscosity of the hollow glass microspheres immersed in the phenolic resin sol is 50 to 200 mPa•s.

7. The gradient core-shell structure composite material and the preparation method thereof according to claim 1, characterized in that: The raw materials of the outer layer structure in step d include phenolic resin sol and silane coupling agent; the raw materials of the phenolic resin aerogel include phenolic compounds, aldehyde compounds, catalysts and solvents; the silane coupling agent includes one or two of KH550, KH560, KH570 and SCA-αA42M; the viscosity of the sol immersed in silicon carbide precursor in step d is 50 to 200 mPa•s.

8. The gradient core-shell structure composite material and the preparation method thereof according to claim 1, characterized in that: The thickness of the carbon aerogel layer in step e is 1 to 2 μm; the thickness of the silicon carbide aerogel layer in step e is 500 nm to 1 μm.

9. The gradient core-shell structure composite material and the preparation method thereof according to claim 1, characterized in that: The drying method of the phenolic resin gel layer in step c and the silicon carbide gel layer in step d is freeze drying at a temperature of -50°C, a pressure of <10 Pa, a time of 24 to 48 hours, and a heating rate of 1 to 2°C / h.

10. The gradient core-shell structure composite material and the preparation method thereof according to claim 1, characterized in that: The carbonization treatment step described in step e is to first pre-carbonize at a low temperature, heat to 300°C to 400°C at a heating rate of 2 to 5°C / min, pre-carbonize for 1 to 2 hours, and then heat to 800°C to 900°C at a heating rate of 5 to 10°C / min, and carbonize for 2 to 3 hours; the protective gas in the atmosphere protection conditions described in step e is ultrapure argon or nitrogen, and the flow rate is 300 to 500 ml / min.

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