A frame-reinforced, wave-transparent, heat-insulating aerogel material and a method for preparing the same

Abstract

The application discloses a kind of frame reinforced wave-transparent heat-insulating aerogel materials and preparation method thereof, belong to composite material technical field.The application disperses aluminium oxide nano powder in water, adds adsorbent solution, wave-transparent-light-shielding dual-function auxiliary nano particles, obtains precursor mixed solution after being mixed uniformly;Put ceramic frame into reaction kettle, add precursor mixed solution, make precursor mixed solution fully soak ceramic frame, place reaction kettle in heating environment and carry out reaction to obtain wet gel;Wet gel is taken out, remove wet gel on the surface of ceramic frame, solvent replacement is carried out using organic solvent, and supercritical drying is carried out to obtain aerogel;The aerogel is heat treated to obtain frame reinforced wave-transparent heat-insulating aerogel material.The application introduces wave-transparent-light-shielding dual-function auxiliary and rigid frame structure, and obtains aerogel composite material with good overall formability, high temperature resistance, excellent dielectric properties and excellent mechanical strength.

Description

Technical Field

[0001] This invention belongs to the field of composite material technology, specifically relating to a frame-reinforced, wave-transparent, heat-insulating aerogel material and its preparation method. Background Technology

[0002] In the aerodynamic heating environment of long-endurance flight, the surface temperature can quickly reach 1000-1500℃ or even higher, requiring the thermal protection system to provide efficient thermal insulation without affecting signal transmission and reception. This places demands on thermal insulation materials that are high-temperature resistant, highly efficient in thermal insulation, and lightweight, based on low dielectric constant and low dielectric loss.

[0003] Currently, commonly used microwave-transparent thermal insulation materials mainly include ceramic thermal insulation tiles, fiberglass mats, and aerogel composites. The main problems with ceramic thermal insulation tiles are their high density and poor dielectric properties; fiberglass mats have significant drawbacks in thermal conductivity and poor formability; aerogel composites, as a novel porous nanomaterial, have unique advantages in density and dielectric properties, but urgently need to address the problem of rapidly increasing thermal conductivity due to infrared radiation transparency at high temperatures and their inherent structural fragility. Patent CN112552064A introduces a lightweight microwave-transparent thermal insulation tile material using a semi-dry-wet two-step fiber dispersion method, which improves density and dielectric constant compared to traditional rigid thermal insulation tiles, but its dielectric loss and thermal conductivity remain relatively high. Patent CN106630931A introduces a fiber-reinforced alumina-silica aerogel material, which prepares an integrated microwave-transparent thermal insulation aerogel material through a one-step sol-gel method, but its density and dielectric constant are relatively high. Patent CN108383486A describes a chromium-containing fiber-reinforced silica aerogel material. Chromium oxide is introduced into the aerogel system through the complexation and hydrolysis of chromium salts to improve the material's thermal insulation performance; however, it has a high density and insufficient temperature resistance. Patent CN111043450A describes a novel wave-transparent thermal insulation component that combines thermal insulation tiles and aerogel materials. It combines the thermal insulation and dielectric properties of aerogel materials with the mechanical properties of thermal insulation tiles; however, its structure is complex and prone to delamination and aging during use.

[0004] In summary, there is an urgent need to develop a material that combines good thermal insulation and wave transmission properties to meet the requirements of wave transmission and thermal insulation. Summary of the Invention

[0005] The purpose of this invention is to obtain an aerogel composite material with good overall formability, high temperature resistance, excellent dielectric properties, and excellent mechanical strength by introducing a dual-functional additive for wave transmission and light shielding and a rigid frame structure, thereby applying traditional materials to the field of lightweight, high-temperature resistant, high-efficiency heat insulation and wave transmission.

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

[0007] A method for preparing a frame-reinforced, microwave-transparent, and thermally insulating aerogel material includes the following steps:

[0008] 1) Disperse 1 part by weight of alumina nanopowder in 20-40 parts of water, add 0.2-2 parts of adsorbent solution and 0.05-0.3 parts of wave-transmitting and light-shielding dual-functional auxiliary nanoparticles, mix evenly to obtain a precursor mixture;

[0009] 2) Place the ceramic frame into the reactor, add the precursor mixture obtained in step 1), and allow the precursor mixture to fully saturate the ceramic frame. Place the reactor in a heating environment to carry out the reaction and obtain a wet gel.

[0010] 3) Take out the wet gel obtained in step 2), remove the wet gel from the surface of the ceramic frame, perform solvent replacement several times with 5-10 times the volume equivalent of organic solvent, and then perform supercritical drying to obtain aerogel.

[0011] 4) Heat-treat the aerogel obtained in step 3) to obtain a frame-reinforced, wave-transparent, and heat-insulating aerogel material.

[0012] Furthermore, the alumina nanoparticles have a particle size of 20-500 nm.

[0013] Furthermore, the adsorbent is one of nitric acid, hydrochloric acid, sulfuric acid, phosphoric acid, and oxalic acid, and the concentration of the adsorbent is 0.5-1.5M.

[0014] Furthermore, the wave-transmitting and light-shielding dual-functional additive nanoparticles are one of aluminum phosphate, chromium phosphate, chromium oxide, and aluminum chromium phosphate, with a particle size of 50-500 nm.

[0015] Furthermore, the ceramic frame is made of alumina ceramic or silicon nitride ceramic, the frame type is corrugated or honeycomb, and the wall thickness is 0.5-2mm.

[0016] Furthermore, the reaction vessel is incubated at 200-250℃ for 4-24 hours.

[0017] Furthermore, the organic solvent is one of ethanol, cyclohexane, and acetone.

[0018] Furthermore, the solvent is replaced 3-5 times.

[0019] Furthermore, the aerogel is subjected to heat treatment at 500-700℃ for 0.5-20 hours.

[0020] A frame-reinforced, wave-transparent, and thermally insulating aerogel material is prepared by the above method.

[0021] The technical effects achieved by this invention are as follows:

[0022] This invention employs a novel one-step hydrothermal method to grow aerogels within a ceramic framework, simultaneously introducing a microwave-transparent and light-shielding bifunctional additive uniformly into the system. The ceramic framework is fully wetted when the precursor mixture has low viscosity and good flowability. Then, alumina nanowires are controllably grown under heating conditions through the electrostatic forces of the adsorbent, achieving complete filling of the hollow portions of the framework structure. Suitable microwave-transparent and light-shielding bifunctional additives were selected, and nanoscale particles were used to facilitate their dispersion in the precursor, ensuring they do not react with other components in the system under hydrothermal conditions. Compared to previous related works that used soluble salt precursors that were subsequently converted into target additive molecules, this invention's strategy does not involve the species transformation and growth process of the additive particles, thus better preserving the size and physicochemical properties of the additive itself.

[0023] This invention is based on the framework-reinforced aerogel material system. It uses a one-step hydrothermal method to construct an alumina nanowire system. During the hydrothermal process, a wave-transmitting and light-shielding dual-functional auxiliary nanoparticle is introduced in situ. At the same time, the aerogel is uniformly and fully filled into the framework structure. It has the advantages of simple process and good doping effect.

[0024] This invention selects lightweight, high-strength alumina nanowire aerogel and combines it with corrugated and honeycomb ceramic framework structures, and incorporates a dual-functional additive for wave transmission and heat insulation into the system, so as to give full play to the temperature resistance and heat insulation performance of the aerogel material while ensuring the strength of the material.

[0025] The microwave-transparent thermal insulation aerogel material obtained through the technical solution of this invention has a temperature resistance rating above 1200℃. Its dielectric constant in the Ku band remains stable within the range of 1.2-1.26 from room temperature to 1200℃, and its dielectric loss is within the range of 0.002-0.007, demonstrating excellent dielectric properties. Its room temperature thermal conductivity is ≤0.045W / m·K, and its thermal conductivity at 1000℃ is ≤0.103W / m·K, meeting the requirements for high-efficiency thermal insulation. Its compressive strength (10%) reaches 4.9MPa, its flexural strength reaches 4.2MPa, and its in-plane tensile strength reaches 2.4MPa, exhibiting significantly superior mechanical strength compared to aerogel materials. Attached Figure Description

[0026] Figure 1 This is a flowchart of the preparation method for a frame-composite microwave-transparent thermal insulation aerogel material.

[0027] Figure 2 This is a diagram of a corrugated ceramic frame.

[0028] Figure 3 This is a sample image of a frame-composite microwave-transparent thermal insulation aerogel plate.

[0029] Figure 4This is a SEM image of the frame-composite microwave-transparent thermal insulation aerogel material in Example 1, showing the combination of alumina nanowires and the frame. Detailed Implementation

[0030] To make the various technical features, advantages, or effects of the present invention more apparent and understandable, a detailed description is provided below in conjunction with the accompanying drawings.

[0031] Example 1

[0032] 1) Disperse 100g of alumina nanoparticles (20nm particle size) evenly in 2000g of water, add 20ml of 0.5M nitric acid, and stir until the viscosity of the mixture increases slightly. While stirring, add 5g of aluminum phosphate nanoparticles (50nm particle size) to the mixture and mix thoroughly.

[0033] 2) Add 1 / 5 volume of the precursor mixture obtained in step 1) to the hydrothermal reactor, place a honeycomb alumina ceramic frame with a hexagonal side length of 15 mm and a wall thickness of 0.5 mm on it, and continue to add the precursor mixture obtained in step 1) to ensure that the liquid level covers the ceramic frame, and react at 200℃ for 24 h.

[0034] 3) Take out the wet gel obtained in step 2), remove the wet gel from the surface of the ceramic frame, replace it with 5 times the volume of ethanol solvent 5 times, and then perform supercritical carbon dioxide drying.

[0035] 4) The aerogel obtained in step 3) is heat-treated at 500℃ for 20h to obtain a wave-transparent and heat-insulating aerogel material.

[0036] The microwave-transparent thermal insulation aerogel material prepared under the conditions of this embodiment has a room temperature thermal conductivity of 0.039 W / m·K, a 1000℃ thermal conductivity of 0.103 W / m·K, a dielectric constant of 1.21-1.24 from room temperature to 1200℃ at 10 GHz, a room temperature dielectric loss of 0.002, a 1200℃ dielectric loss of 0.006, a compressive strength (10%) of 4.0 MPa, a flexural strength of 3.5 MPa, and an in-plane tensile strength of 2.0 MPa.

[0037] Example 2

[0038] 1) Disperse 100g of alumina nanoparticles (100nm particle size) evenly in 3000g of water, add 100ml of 1.2M phosphoric acid, and stir until the viscosity of the mixture increases slightly. While stirring, add 20g of chromium phosphate nanoparticles (100nm particle size) to the mixture and mix thoroughly.

[0039] 2) Add 1 / 5 volume of the precursor mixture obtained in step 1) to the hydrothermal reactor, place a hexagonal honeycomb alumina ceramic frame with a side length of 15 mm and a wall thickness of 1 mm on it, and continue to add the precursor mixture obtained in step 1) to ensure that the liquid level covers the ceramic frame, and react at 220℃ for 12 h.

[0040] 3) Take out the wet gel obtained in step 2), remove the wet gel from the surface of the ceramic frame, replace it with 8 times the volume of cyclohexane solvent 5 times, and then perform supercritical carbon dioxide drying.

[0041] 4) The aerogel obtained in step 3) is heat-treated at 600℃ for 12 hours to obtain a wave-transparent and heat-insulating aerogel material.

[0042] The microwave-transparent thermally insulating aerogel material prepared under the conditions of this embodiment has a room temperature thermal conductivity of 0.042 W / m·K, a 1000℃ thermal conductivity of 0.095 W / m·K, a dielectric constant of 1.21-1.25 from room temperature to 1200℃ at 10 GHz, a room temperature dielectric loss of 0.002, a 1200℃ dielectric loss of 0.007, a compressive strength (10%) of 4.3 MPa, a flexural strength of 3.7 MPa, and an in-plane tensile strength of 2.1 MPa.

[0043] Example 3

[0044] 1) Disperse 100g of alumina nanoparticles (500nm particle size) evenly in 4000g of water, add 200ml of 1.5M oxalic acid, and stir until the viscosity of the mixture increases slightly. While stirring, add 30g of aluminum chromium phosphate nanoparticles (500nm particle size) to the mixture and mix thoroughly.

[0045] 2) Add 1 / 5 volume of the precursor mixture obtained in step 1) to the hydrothermal reactor, place a hexagonal honeycomb alumina ceramic frame with a side length of 15 mm and a wall thickness of 2 mm on it, and continue to add the precursor mixture obtained in step 1) to ensure that the liquid level covers the ceramic frame, and react at 250℃ for 4 hours.

[0046] 3) Take out the wet gel obtained in step 2), remove the wet gel from the surface of the ceramic frame, replace it three times with 10 times the volume of acetone solvent, and then perform supercritical carbon dioxide drying.

[0047] 4) The aerogel obtained in step 3) is heat-treated at 700℃ for 5 hours to obtain a wave-transparent and heat-insulating aerogel material.

[0048] The microwave-transparent thermally insulating aerogel material prepared under the conditions of this embodiment has a room temperature thermal conductivity of 0.045 W / m·K, a 1000℃ thermal conductivity of 0.083 W / m·K, a dielectric constant of 1.22-1.25 from room temperature to 1200℃ at 10 GHz, a room temperature dielectric loss of 0.003, a 1200℃ dielectric loss of 0.008, a compressive strength (10%) of 4.9 MPa, a flexural strength of 4.2 MPa, and an in-plane tensile strength of 2.4 MPa.

[0049] Example 4

[0050] 1) Disperse 100g of alumina nanoparticles (200nm particle size) evenly in 3000g of water, add 100ml of 0.8M sulfuric acid, and stir until the viscosity of the mixture increases slightly. While stirring, add 15g of chromium oxide nanoparticles (100nm particle size) to the mixture and mix evenly.

[0051] 2) Add 1 / 5 volume of the precursor mixture obtained in step 1) to the hydrothermal reactor, place a corrugated silicon nitride ceramic frame with a wall thickness of 1 mm on it, and continue to add the precursor mixture obtained in step 1) to ensure that the liquid level covers the ceramic frame. React at 240℃ for 8 hours.

[0052] 3) Take out the wet gel obtained in step 2), remove the wet gel from the surface of the ceramic frame, replace it with 10 times the volume of ethanol solvent 5 times, and then perform supercritical carbon dioxide drying.

[0053] 4) The aerogel obtained in step 3) is heat-treated at 700℃ for 0.5h to obtain a wave-transparent and heat-insulating aerogel material.

[0054] The microwave-transparent thermally insulating aerogel material prepared under the conditions of this embodiment has a room temperature thermal conductivity of 0.04 W / m·K, a 1000℃ thermal conductivity of 0.091 W / m·K, a dielectric constant of 1.21-1.25 from room temperature to 1200℃ at 10 GHz, a room temperature dielectric loss of 0.002, a 1200℃ dielectric loss of 0.006, a compressive strength (10%) of 4.4 MPa, a flexural strength of 3.8 MPa, and an in-plane tensile strength of 2 MPa.

[0055] Example 5

[0056] 1) Disperse 100g of alumina nanoparticles (100nm particle size) evenly in 2000g of water, add 50ml of 1M hydrochloric acid, and stir until the viscosity of the mixture increases slightly. While stirring, add 20g of chromium phosphate nanoparticles (200nm particle size) to the mixture and mix thoroughly.

[0057] 2) Add 1 / 5 volume of the precursor mixture obtained in step 1) to the hydrothermal reactor, place a corrugated silicon nitride ceramic frame with a wall thickness of 1.5 mm on it, and continue to add the precursor mixture obtained in step 1) to ensure that the liquid level covers the ceramic frame. React at 220℃ for 12 h.

[0058] 3) Take out the wet gel obtained in step 2), remove the wet gel from the surface of the ceramic frame, replace it with acetone solvent 8 times and then perform supercritical carbon dioxide drying.

[0059] 4) The aerogel obtained in step 3) is heat-treated at 600℃ for 8 hours to obtain a wave-transparent and heat-insulating aerogel material.

[0060] The microwave-transparent thermally insulating aerogel material prepared under the conditions of this embodiment has a room temperature thermal conductivity of 0.043 W / m·K, a 1000℃ thermal conductivity of 0.094 W / m·K, a dielectric constant of 1.22-1.26 from room temperature to 1200℃ at 10 GHz, a room temperature dielectric loss of 0.002, a 1200℃ dielectric loss of 0.007, a compressive strength (10%) of 4.7 MPa, a flexural strength of 4.1 MPa, and an in-plane tensile strength of 2.2 MPa.

[0061] Comparative Example 1

[0062] Comparative Example 1 was prepared according to Example 1 disclosed in CN 107032736 A.

[0063] Chromium nitrate was dissolved in ethanol at a ratio of 1:2 and stirred for approximately 20 minutes until completely dissolved. Then, a 1M ammonia solution was slowly added dropwise to the chromium nitrate solution until the pH reached 8. Stirring continued for 30 minutes to obtain a chromium salt complex solution. This complex was then injected using a vacuum method to obtain a solution with a density of 0.1 g / cm³. 3 In a quartz fiber reinforced matrix, after the sol-gel process, it is dried in a 100℃ oven and then treated in a muffle furnace at 600℃ for 2 hours. The fiber preform is then placed in a mold, and the silica sol and preform are composited using a vacuum pressing method. After that, it is aged at room temperature for 36 hours and at 90℃ for 36 hours. After aging, it is replaced with acetone solvent twice, then dried with supercritical carbon dioxide, and finally treated with methyltrimethoxysilane for vapor phase hydrophobic and moisture-proof properties to obtain a heat-insulating sample.

[0064] Comparative Example 2

[0065] Comparative Example 2 was prepared according to Example 1 disclosed in CN 111410549 A.

[0066] (1) Prepare fiber pulp according to the mass ratio of silicon nitride short chopped fiber, starch, boron nitride and water of 1:0.2:0.03:40;

[0067] (2) Pour the fiber slurry into the mold and dehydrate it by filtration to obtain a wet blank, and then press it to a thickness of 30mm on a pressure forming machine;

[0068] (3) Dry the wet blank in an oven at 100℃ for 12 hours to obtain the dry blank;

[0069] (4) Place the dry blank into a high-temperature furnace and sinter at 1200℃ for 1 hour to obtain a high-temperature resistant, low thermal conductivity heat-insulating and wave-transparent material.

[0070] Comparative Example 3

[0071] Comparative Example 3 was prepared according to Example 1 disclosed in CN 112552064 A.

[0072] (1) Mix short-cut quartz fibers with water at a mass ratio of 100:1, put them into a dispersion tank, set the dispersion speed to 3000 r / min and disperse for 20 min to obtain initially dispersed fibers;

[0073] (2) Add water to the initially dispersed fibers so that the mass ratio of the dispersed short fibers to water is 1:50. Then add 2wt% boron nitride relative to the mass of the short fibers and disperse again for 2 hours at a dispersion speed of 2000 r / min to obtain fiber slurry.

[0074] (3) After pouring all the prepared fiber slurry into the material forming fixture (internal cavity size 300×300mm), turn on the water valve and set the water valve to level 3, and wait for the water in the slurry to flow out; after it has initially become regularized, remove the fixture and press the pre-formed blank. Control the material density to 0.1g / cm³ by controlling the pressing thickness. 3 A wet blank of thermal insulation material is obtained;

[0075] (4) The wet blank of the thermal insulation material is clamped and dried in an oven at 150°C for 48 hours. Then the dried material is placed in a muffle furnace for sintering at 1100°C for 3 hours to obtain the dry blank of the thermal insulation material.

[0076] (5) The dry blank of the heat insulation material is placed in an organosiloxane solution for moisture protection to obtain a lightweight microwave-transparent ceramic heat insulation material.

[0077] Table 1. Performance comparison of the wave-transparent thermal insulation aerogel materials prepared in Examples 1-5 and Comparative Examples 1-3

[0078]

[0079] As can be seen from Table 1, the thermal conductivity of the embodiments of the present invention is no greater than 0.1 W / m·K at 1000℃, exhibiting excellent high-temperature thermal insulation performance. The comparison of dielectric constant and dielectric loss at room temperature and high temperature also demonstrates the significant advantage of the dielectric properties of the aerogel material prepared by the present invention. Mechanical strength is also significantly improved due to the introduction of a rigid ceramic framework.

[0080] Although the present invention has been disclosed above with reference to embodiments, it is not intended to limit the present invention. Appropriate modifications or equivalent substitutions made by those skilled in the art to the technical solutions of the present invention should be covered within the protection scope of the present invention, which is defined by the claims.

Claims

1. A method for preparing a frame-reinforced, wave-transparent, and heat-insulating aerogel material, characterized in that, Includes the following steps: 1) Disperse 1 part by weight of alumina nanopowder in 20-40 parts of water, add 0.2-2 parts of adsorbent solution and 0.05-0.3 parts of wave-transparent and light-shielding dual-functional auxiliary nanoparticles, and mix evenly to obtain a precursor mixture; the alumina nanopowder has a particle size of 20-500 nm, the adsorbent is one of nitric acid, hydrochloric acid, sulfuric acid, phosphoric acid, and oxalic acid, and the concentration of the adsorbent is 0.5-1.5 M, and the wave-transparent and light-shielding dual-functional auxiliary nanoparticles are one of aluminum phosphate, chromium phosphate, chromium oxide, and chromium aluminum phosphate, and the particle size is 50-500 nm; 2) Place the ceramic frame into the reactor, add the precursor mixture obtained in step 1), and allow the precursor mixture to fully saturate the ceramic frame. Place the reactor in a heating environment to carry out the reaction and obtain a wet gel. 3) Take out the wet gel obtained in step 2), remove the wet gel from the surface of the ceramic frame, perform solvent replacement several times with 5-10 times the volume equivalent of organic solvent, and then perform supercritical drying to obtain aerogel. 4) Heat-treat the aerogel obtained in step 3) to obtain a frame-reinforced, wave-transparent, and heat-insulating aerogel material.

2. The preparation method according to claim 1, characterized in that, The ceramic frame is made of alumina ceramic or silicon nitride ceramic, and the frame type is corrugated or honeycomb, with a wall thickness of 0.5-2mm.

3. The preparation method according to claim 1, characterized in that, The reaction vessel is kept at 200-250℃ for 4-24 hours.

4. The preparation method according to claim 1, characterized in that, The organic solvent is one of ethanol, cyclohexane, and acetone.

5. The preparation method according to claim 1, characterized in that, Solvent replacement 3-5 times.

6. The preparation method according to claim 1, characterized in that, The aerogel is subjected to heat treatment at 500-700℃ for 0.5-20 hours.

7. A frame-reinforced, wave-transparent, heat-insulating aerogel material, characterized in that, It is prepared by the preparation method according to any one of claims 1-6.

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