A microwave-absorbing aerogel with a toughened ceramic coating and a preparation method thereof

Abstract

The present invention discloses an absorbing aerogel with a toughened ceramic coating and a preparation method thereof, belonging to the technical field of thermal protection materials. The method comprises: surface activating chopped carbon fibers and coating them with a p-xylene polymer coating to obtain surface carbon fibers C; then laying carbon fibers C between layers of quartz needle felt to obtain an aerogel needle-punched preform A; treating the surface of aerogel needle-punched preform A with paraffin wax to obtain an aerogel needle-punched preform B; vacuum impregnating the preform with alkaline silica sol to obtain aerogel D; and uniformly coating the surface of aerogel D with a ceramic slurry to obtain an absorbing aerogel with a magnesium boroaluminate ceramic anti-scour coating toughened with Mg2B2O5 whiskers. The present invention can produce a thermal protection material with absorbing stealth capabilities and airflow scour resistance.

Description

Technical Field

[0001] The invention provides a wave-absorbing aerogel with a toughened ceramic coating and a preparation method thereof, belonging to the technical field of thermal protection materials. Background Art

[0002] Silica aerogel has better thermal insulation effect than thermal insulation tiles and thermal insulation felts. It can be used for external heat protection after being coated with an erosion-resistant ceramic coating on the surface. It is one of the important thermal protection materials for high-speed aircraft. Carbon fiber is a dielectric loss material and can have a good wave absorbing effect at a low mass fraction. However, the nanoporous structure of the aerogel prevents traditional micron-sized coating particles from entering its interior. In addition, the strength of the aerogel is relatively low, resulting in poor adhesion of the coating. At the same time, a higher sintering temperature may reduce the thermal insulation performance of the aerogel. Therefore, the sintering temperature of the ceramic coating should not be too high. At the same time, considering the expansion coefficient matching, the types of erosion-resistant ceramic coatings that can be prepared on the surface are limited, and the coating strength and toughness are not high. If the carbon fiber used as a wave absorbing functional material is continuous in the material system, it will form a conductor path under the action of the electromagnetic field, thereby becoming a strong reflector of radar waves. Therefore, the volume density of carbon fiber used as a wave absorbing material generally does not exceed 0.015g / cm 3 Increasing the amount of addition requires effective control of its conductor path. To solve the above problems, it is necessary to further study the preparation method of stealth aerogel with toughened ceramic coating. Summary of the Invention

[0003] The purpose of the present invention is to provide a wave-absorbing aerogel with a toughened ceramic coating and a preparation method thereof, so that the aerogel thermal protection material can resist airflow erosion and have wave-absorbing stealth functions, and the strength and toughness of the ceramic coating can be improved.

[0004] To achieve the above object, the present invention adopts the following technical solutions:

[0005] A method for preparing a microwave-absorbing aerogel with a toughened ceramic coating comprises the following steps:

[0006] 1) heating the chopped carbon fibers in an air muffle furnace for surface activation, turning off the heating, cooling to room temperature, and then removing the fibers. A p-xylene polymer coating is then applied to the surface of the chopped carbon fibers using a Parylene vacuum coating device to obtain a surface-treated carbon fiber C.

[0007] 2) Needling the quartz needle felt layers of the quartz needle felt preform, laying surface-treated carbon fibers C between the quartz needle felt layers, and obtaining an aerogel needle-punched preform A with a microwave absorbing function after mixed needling;

[0008] 3) placing the side of the aerogel needle-punched preform A on which the ceramic coating is to be prepared into heated and melted paraffin liquid, controlling the immersion depth so that a certain thickness of the surface of the aerogel needle-punched preform A is immersed in the paraffin to form a placeholder, thereby obtaining an aerogel needle-punched preform B with a surface placeholder;

[0009] 4) placing the aerogel needle-punched preform B in a mold and sealing it, preparing an alkaline silica sol, injecting the gel through a vacuum impregnation-pressure injection composite process, gelling, and aging to obtain a wet gel. After opening the mold and removing the wet gel, the wet gel is heated in hot water to remove paraffin, exposing the occupied quartz preform fibers on the surface. After replacing the alcohol solvent, the preform is supercritically dried with carbon dioxide to obtain aerogel D with microwave absorbing function.

[0010] 5) MgO, H3BO3, Al, Ti, KOH, and CoO powders are added to an appropriate amount of water to prepare a ceramic slurry, which is brushed onto the surface of aerogel D having an absorbing function multiple times and dried until the surface is evenly covered with the ceramic slurry; the aerogel D is then heated and maintained in an air muffle furnace for a period of time, the heating is turned off, and the aerogel is taken out after cooling to room temperature to obtain an absorbing aerogel having a magnesium boroaluminate ceramic scour-resistant coating toughened with Mg2B2O5 whiskers.

[0011] Furthermore, in step 1), the length of the chopped carbon fibers is 1.8 to 2.5 mm.

[0012] Furthermore, in step 1), the temperature is raised to 280-320° C. in an air muffle furnace and kept at this temperature for 1.5-2 hours to perform surface activation.

[0013] Furthermore, in step 1), the thickness of the p-xylene polymer coating is 25 to 30 μm.

[0014] Furthermore, the density of the quartz needle-punched preform in step 2) is 0.09-0.11 g / cm 3 .

[0015] Furthermore, in step 2), surface-treated carbon fibers C accounting for 30% to 40% of the weight of the quartz needle felt are laid between the layers of quartz needle felt.

[0016] Furthermore, in step 2), the volume density of carbon fiber C is 0.03 to 0.04 g / cm 3 .

[0017] Furthermore, in step 3), the paraffin wax is 85# paraffin wax with a melting point of 82-87°C.

[0018] Furthermore, in step 3), paraffin is immersed in the aerogel needle-punched preform A with a surface thickness of 3 to 8 mm to form a placeholder.

[0019] Furthermore, the solid content of the alkaline silica sol in step 4) is 20%.

[0020] Furthermore, in step 4), the wet gel is prepared by gelling at room temperature for 12 hours and aging at 55-60° C. for 24 hours.

[0021] Furthermore, in step 4), the paraffin is removed by heating in hot water at 92-98° C. for 1 hour.

[0022] Furthermore, in step 4), after the alcohol solvent is replaced for 36 hours, supercritical carbon dioxide drying is carried out at 42° C. and 13 MPa for 48 hours.

[0023] Furthermore, in step 5), the molar ratio of MgO, H3BO3, Al, Ti, KOH, and CoO powders is 1:1.8:0.4:0.05:0.08:0.1, and the powder particle size is 1 to 10 μm.

[0024] Furthermore, in step 5), the temperature is kept at 550-600° C. in an air muffle furnace for 2-3 hours.

[0025] A wave-absorbing aerogel with a toughened ceramic coating is prepared by the above preparation method.

[0026] The beneficial effects achieved by the present invention are as follows:

[0027] The toughened ceramic-coated stealth aerogel prepared by this invention exhibits strong adhesion. In tensile tests at both room temperature and 1200°C, the coating and substrate remained intact, with all fractures occurring within the aerogel. This indicates that the coating's adhesion strength is superior to the aerogel's strength. The preparation process has no effect on the aerogel's thermal insulation properties, with the aerogel's thermal conductivity at room temperature being no less than 0.02 W / (m·K).

[0028] 2. In the present invention, through step 1), the surface activation of the carbon fiber reduces the viscosity of the carbon fiber, improves the dispersion of the fiber, and ensures the uniformity and adhesion of the polymer coating. During the subsequent sintering process of the anti-scour coating at 550-600°C, the polyparaxylene insulating coating will be burned off. However, the 25-30 μm coating ensures that no conductor path is formed between the carbon fibers to reduce the wave absorption performance, and protects the carbon fibers from excessive ablation.

[0029] 3. In the present invention, after the paraffin wax takes place, the surface in contact with the aerogel is rough, and there are many gaps on the aerogel surface. The ceramic slurry can partially penetrate into the gaps to form a mechanical connection, and the quartz reinforcement in the aerogel and ceramic layer is a continuous structure, which ensures the adhesion strength of the coating.

[0030] 4. The present invention prepares a whisker-toughened ceramic coating on the aerogel surface through step 5). The added Al powder and Ti powder in the sintering aid can lower the sintering temperature, preventing the degradation of aerogel performance caused by high-temperature calcination. The CoO in the sintering aid acts as a catalyst to reduce the viscosity of liquid B2O3 at high temperatures, allowing Mg2B2O5 crystals to grow along the dominant crystal direction, resulting in in-situ grown whiskers with an aspect ratio of 15 to 20. DETAILED DESCRIPTION

[0031] In order to make the various technical features and advantages or technical effects of the above technical solutions of the present invention more obvious and easy to understand, they are described in detail below in conjunction with embodiments.

[0032] Example 1

[0033] 1) The short carbon fiber (length 2 mm) was heated to 300° C. in an air muffle furnace and kept at this temperature for 1.8 hours for surface activation. The heating was turned off and the carbon fiber was cooled to room temperature and then taken out. Subsequently, a 27 μm thick p-xylene polymer coating was coated on the carbon fiber surface using a Parylene vacuum coating device to obtain a surface-treated carbon fiber C.

[0034] 2) Quartz needle punching preform (density 0.1g / cm 3 ) ply needle punching, 35% of the weight of the quartz needle felt is covered between the quartz needle felt ply layers with surface treated carbon fiber C (the volume density of carbon fiber C is 0.03 g / cm 3 ), and after mixed needling, an aerogel needling preform A with wave absorbing function is obtained.

[0035] 3) The side of the preform A to be prepared with the ceramic coating is placed in heated and melted 85# paraffin wax (melting point 85°C) liquid, and the immersion depth is controlled so that the paraffin wax is immersed in the preform with a thickness of 5 mm on the surface to form a placeholder, thereby obtaining an aerogel needle-punched preform B with a surface placeholder.

[0036] 4) Preform B was placed in a mold and sealed, and an alkaline silica sol with a solid content of 20% by mass was prepared. The gel was injected through a vacuum impregnation-pressure injection composite process, and the gel was gelled at room temperature for 12 hours and aged at 58°C for 24 hours to obtain a wet gel. After the mold was opened and the wet gel was removed, it was heated in 95°C hot water for 1 hour to remove the paraffin, exposing the occupied quartz preform fibers on the surface. After alcohol solvent replacement for 36 hours, the aerogel D with microwave absorbing function was obtained by supercritical carbon dioxide drying at 42°C and 13 MPa for 48 hours.

[0037] 5) A ceramic slurry was prepared by mixing 5 μm MgO, H₃BO₃, Al, Ti, KOH, and CoO powders in a molar ratio of 1:1.8:0.4:0.05:0.08:0.1 with an appropriate amount of water. The slurry was applied to the surface of the microwave-absorbing aerogel D by brushing multiple times and dried until the surface was evenly covered with the slurry. After being heated at 580°C in an air muffle furnace for 2.5 hours, the heat was turned off, and the aerogel was cooled to room temperature before removal. This yielded a microwave-absorbing aerogel with a magnesium boroaluminate ceramic scour-resistant coating toughened with Mg₂B₂O₅ whiskers.

[0038] Example 2

[0039] 1) The chopped carbon fiber (length 1.8 mm) was heated to 280° C. in an air muffle furnace and kept warm for 2 hours for surface activation. The heating was turned off and the mixture was cooled to room temperature before being taken out. Subsequently, a p-xylene polymer coating with a thickness of 25 to 30 μm was coated on the surface of the carbon fiber using a Parylene vacuum coating device to obtain a surface-treated carbon fiber C.

[0040] 2) Quartz needle punching preform (density 0.09g / cm 3 ) ply needle punching, 30% of the weight of the quartz needle felt is covered between the quartz needle felt ply layers with surface treated carbon fiber C (the volume density of carbon fiber C is 0.03 g / cm 3 ), and after mixed needling, an aerogel needling preform A with wave absorbing function is obtained.

[0041] 3) The side of the preform A to be prepared with the ceramic coating is placed in heated and melted 85# paraffin wax (melting point 82°C) liquid, and the immersion depth is controlled so that the paraffin wax is immersed in the preform with a thickness of 3 mm on the surface to form a placeholder, thereby obtaining an aerogel needle-punched preform B with a surface placeholder.

[0042] 4) Preform B was placed in a mold and sealed, and an alkaline silica sol with a solid content of 20% by mass was prepared. The gel was injected through a vacuum impregnation-pressure injection composite process, and the gel was gelled at room temperature for 12 hours and aged at 55°C for 24 hours to obtain a wet gel. After the mold was opened and the wet gel was removed, it was heated in 92°C hot water for 1 hour to remove the paraffin, exposing the occupied quartz preform fibers on the surface. After alcohol solvent replacement for 36 hours, the aerogel D with microwave absorbing function was obtained by supercritical carbon dioxide drying at 42°C and 13 MPa for 48 hours.

[0043] 5) A ceramic slurry was prepared by mixing 1 μm MgO, H₃BO₃, Al, Ti, KOH, and CoO powders in a molar ratio of 1:1.8:0.4:0.05:0.08:0.1 with an appropriate amount of water. The slurry was applied to the surface of the microwave-absorbing aerogel D by brushing multiple times and dried until the surface was evenly covered with the slurry. After being heated at 550°C in an air muffle furnace for 3 hours, the heat was turned off, and the aerogel was cooled to room temperature and removed to obtain a microwave-absorbing aerogel with a magnesium boroaluminate ceramic scour-resistant coating toughened with Mg₂B₂O₅ whiskers.

[0044] Example 3

[0045] 1) The chopped carbon fiber (length 2.5 mm) was heated to 320° C. in an air muffle furnace and kept warm for 1.5 hours for surface activation. The heating was turned off and the mixture was cooled to room temperature before being taken out. Subsequently, a p-xylene polymer coating with a thickness of 25 to 30 μm was coated on the surface of the carbon fiber using a Parylene vacuum coating device to obtain a surface-treated carbon fiber C.

[0046] 2) Quartz needle punching preform (density 0.11g / cm 3 ) ply needle punching, 40% of the weight of the quartz needle felt is covered between the quartz needle felt ply layers with surface treated carbon fiber C (the volume density of carbon fiber C is 0.04 g / cm 3 ), and after mixed needling, an aerogel needling preform A with wave absorbing function is obtained.

[0047] 3) The side of the preform A to be prepared with the ceramic coating is placed in heated and melted 85# paraffin wax (melting point 87°C) liquid, and the immersion depth is controlled so that the paraffin wax is immersed in the preform with a thickness of 8 mm on the surface to form a placeholder, thereby obtaining an aerogel needle-punched preform B with a surface placeholder.

[0048] 4) Preform B was placed in a mold and sealed, and an alkaline silica sol with a solid content of 20% by mass was prepared. The gel was injected through a vacuum impregnation-pressure injection composite process, and the gel was gelled at room temperature for 12 hours and aged at 60°C for 24 hours to obtain a wet gel. After the mold was opened and the wet gel was removed, it was heated in hot water at 98°C for 1 hour to remove the paraffin, exposing the occupied quartz preform fibers on the surface. After alcohol solvent replacement for 36 hours, the aerogel D with microwave absorbing function was obtained by supercritical carbon dioxide drying at 42°C and 13 MPa for 48 hours.

[0049] 5) A ceramic slurry was prepared by mixing 10 μm MgO, H₃BO₃, Al, Ti, KOH, and CoO powders in a molar ratio of 1:1.8:0.4:0.05:0.08:0.1 with an appropriate amount of water. The slurry was applied to the surface of the microwave-absorbing aerogel D by brushing multiple times and dried until the surface was evenly covered with the slurry. After being heated at 600°C for 2 hours in an air muffle furnace, the furnace was turned off, cooled to room temperature, and removed to obtain a microwave-absorbing aerogel with a magnesium boroaluminate ceramic scour-resistant coating toughened with Mg₂B₂O₅ whiskers.

[0050] The density, strength and thermal conductivity of the microwave-absorbing aerogel of the embodiment were tested. The test results are shown in Table 1.

[0051] Table 1 Density, strength and thermal conductivity performance test data of absorbing aerogel

[0052] <![CDATA[Density (g / cm 3 )]]> Strength (MPA) Thermal conductivity (W / (m·K)) Example 1 0.305 0.42 0.024 Example 2 0.312 0.48 0.026 Example 3 0.314 0.51 0.025

[0053] The absorbing performance of the absorbing aerogel product prepared in Example 2 was tested. The test results showed that the reflectivity was lower than -10 dB in the 10-18 GHz frequency range and lower than -15 dB in the 11-15 GHz frequency range.

[0054] Although the present invention has been disclosed as above by way of embodiments, they are not intended to limit the present invention. Any appropriate modification or equivalent substitution of the technical solution of the present invention by a person skilled in the art should be included in the protection scope of the present invention. The protection scope of the present invention shall be based on that defined in the claims.

Claims

1. A method for preparing a microwave-absorbing aerogel with a toughened ceramic coating, characterized in that: The following steps are involved: 1) heating the chopped carbon fibers in an air muffle furnace for surface activation, turning off the heating, cooling to room temperature, and then removing the fibers. A p-xylene polymer coating is then applied to the surface of the chopped carbon fibers using a Parylene vacuum coating device to obtain a surface-treated carbon fiber C. 2) Needling the quartz needle felt layers of the quartz needle felt preform, laying surface-treated carbon fibers C between the quartz needle felt layers, and obtaining an aerogel needle-punched preform A with a microwave absorbing function after mixed needling; 3) placing the side of the aerogel needle-punched preform A on which the ceramic coating is to be prepared into heated and melted paraffin liquid, controlling the immersion depth so that a certain thickness of the surface of the aerogel needle-punched preform A is immersed in the paraffin to form a placeholder, thereby obtaining an aerogel needle-punched preform B with a surface placeholder; 4) placing the aerogel needle-punched preform B in a mold and sealing it, preparing an alkaline silica sol, injecting the gel through a vacuum impregnation-pressure injection composite process, gelling, and aging to obtain a wet gel. After opening the mold and removing the wet gel, the wet gel is heated in hot water to remove paraffin, exposing the occupied quartz preform fibers on the surface. After replacing the alcohol solvent, the preform is supercritically dried with carbon dioxide to obtain aerogel D with microwave absorbing function. 5) MgO, H3BO3, Al, Ti, KOH, and CoO powders are added to an appropriate amount of water to prepare a ceramic slurry, which is brushed onto the surface of aerogel D having an absorbing function multiple times and dried until the surface is evenly covered with the ceramic slurry; the aerogel D is then heated and maintained in an air muffle furnace for a period of time, the heating is turned off, and the aerogel is taken out after cooling to room temperature to obtain an absorbing aerogel having a magnesium boroaluminate ceramic scour-resistant coating toughened with Mg2B2O5 whiskers.

2. The preparation method according to claim 1, wherein In step 1), the length of the chopped carbon fibers is 1.8 to 2.5 mm; the temperature is raised to 280 to 320° C. in an air muffle furnace and kept at this temperature for 1.5 to 2 hours for surface activation.

3. The preparation method according to claim 1, wherein The thickness of the p-xylene polymer coating in step 1) is 25 to 30 μm.

4. The preparation method according to claim 1, wherein The density of the quartz needle-punched preform in step 2) is 0.09-0.11 g / cm 3 Surface-treated carbon fiber C, which accounts for 30% to 40% of the weight of the quartz needle felt, is laid between the quartz needle felt layers; the volume density of the carbon fiber C is 0.03 to 0.04 g / cm 3 .

5. The preparation method according to claim 1, wherein In step 3), 85# paraffin wax is selected, with a melting point of 82-87° C.; the aerogel needle-punched preform A with a surface thickness of 3-8 mm is immersed in the paraffin wax to form a placeholder.

6. The preparation method according to claim 1, wherein In step 4), the solid content of the alkaline silica sol is 20%; the gel is allowed to gel at room temperature for 12 hours, and then aged at 55-60° C. for 24 hours to obtain a wet gel; and the gel is heated in hot water at 92-98° C. for 1 hour to remove the paraffin.

7. The preparation method according to claim 1, wherein In step 4), the alcohol solvent was replaced for 36 hours and then supercritical drying with carbon dioxide was carried out at 42° C. and 13 MPa for 48 hours.

8. The preparation method according to claim 1, wherein In step 5), the molar ratio of MgO, H3BO3, Al, Ti, KOH, and CoO powders is 1:1.8:0.4:0.05:0.08:0.1, and the powder particle size is 1 to 10 μm.

9. The preparation method according to claim 1, wherein In step 5), the mixture is kept at 550-600° C. in an air muffle furnace for 2-3 hours.

10. A microwave-absorbing aerogel with a toughened ceramic coating, characterized in that: The invention is prepared by the preparation method according to any one of claims 1 to 9.