Aerogel with sintering-free high-emissivity panel and preparation method thereof

Abstract

The invention discloses aerogel with a sintering-free high-emissivity panel and a preparation method of the aerogel, and belongs to the technical field of thermal protection materials. In order to solve the technical problems that an aerogel panel and a core layer are not firmly connected, a high-emissivity coating is difficult to permeate, and the radiation capacity is insufficient at high temperature, and the like, the technical means of TPU occupation, silica sol injection, supercritical drying, repeated coating of high-emissivity slurry and the like are mainly adopted. The panel and the aerogel core layer can be tightly connected, the heat insulation performance of aerogel is not affected, meanwhile, the infrared radiation capacity and the high-temperature stability of the panel are improved, and the service life of the aerogel in a high-temperature environment is effectively prolonged.

Description

Technical Field

[0001] The present invention belongs to the technical field of thermal protection materials, and particularly relates to an aerogel with a sintering-free high-emissivity panel and a preparation method thereof. Background Art

[0002] At present, the thermal protection structures widely used in the outer surface scoured by air flow are mostly composite structures, which are composed of an erosion-resistant panel with high strength and density and a core layer with low strength but good heat insulation performance. The materials used as the core layer mainly include several types such as thermal insulation tiles, aerogels, and fiber thermal insulation felts. Among them, aerogels have become one of the research hotspots in the current application fields due to their relatively excellent heat insulation performance.

[0003] The excellent heat insulation performance of aerogels stems from their internal nano-scale microstructure. However, this characteristic also results in loose tissue connection and poor strength of aerogels. Generally, high-temperature-resistant ceramic fabric preforms are compounded inside to improve the strength. These factors pose challenges to the preparation of a panel structure that is tightly connected to the core layer on the surface of the aerogel core layer. Currently, the main preparation methods of the panel include the suture fabric-impregnation curing method and the in-situ secondary brush coating densification method. The suture fabric-impregnation curing method is to suture ceramic fiber cloth on the surface of the aerogel and then brush ceramic precursors on the surface of the fiber cloth to prepare the panel. The panel and the aerogel are intermittently connected by sutures, and the bonding force is discontinuous. The in-situ secondary brush coating densification method is to brush ceramic precursors on the surface of the aerogel to form a densified panel. However, the nano-pore structure of the aerogel will prevent the micron functional particles added in the precursors from penetrating, and it is difficult to customize more functions for the panel.

[0004] High-emissivity coatings are a type of high-infrared-emissivity materials prepared on the surface of materials, which can effectively improve the ability of high-temperature objects to radiate heat to the environment, and the higher the object temperature, the more significant the effect. So far, the preparation of high-emissivity coatings on rigid thermal insulation tiles has been studied and reported many times at home and abroad, but there are few reports on the preparation methods of high-emissivity coatings on aerogels. To solve the above problems, it is necessary to further carry out research on the preparation method of aerogels with sintering-free high-emissivity panels. Summary of the Invention

[0005] The object of the present invention is to propose an aerogel with a sintering-free high-emissivity panel and a preparation method thereof. By adopting processes such as TPU occupation, silica sol injection, and supercritical drying, technical problems such as the insecure connection between the aerogel panel and the core layer, the difficulty in penetration of the high-emissivity coating, and the insufficient radiation ability at high temperatures are solved. At the same time, the heat insulation performance of the aerogel and the infrared radiation ability at high temperatures are improved.

[0006] To achieve the above object, the present invention adopts the following technical solutions:

[0007] A preparation method of an aerogel with a sintering-free high-emissivity panel, comprising the following steps:

[0008] 1) Prepare an aerogel fabric preform using quartz fiber or alumina fiber. Immerse one side of the aerogel fabric preform to be coated into molten thermoplastic polyurethane elastomer (TPU) to a predetermined thickness, and take it out after cooling to the point where the TPU is shaped, to obtain a preform A with surface occupancy;

[0009] 2) Place the preform A into a molding die, carry out silica sol injection impregnation, and then carry out gel aging to obtain a wet gel. After supercritical drying, obtain an aerogel B with surface TPU occupancy;

[0010] 3) Place the aerogel B in a muffle furnace for heat treatment for a period of time, then continue heating after raising the temperature for a period of time, fully burn off the surface-occupying TPU, expose the aerogel fabric preform on the surface, and then carry out a hydrophobic treatment to obtain a hydrophobic core layer aerogel C with exposed fabric;

[0011] 4) Mix alumina sol with TaSi 2 , SiC, CoO evenly, and obtain a high-emissivity slurry D after ball milling;

[0012] 5) Adopt a spraying or brushing method to coat the high-emissivity slurry D on the surface of the exposed fabric of the hydrophobic core layer aerogel C, and then dry it in an oven to complete one coating; repeat the coating several times, and finally obtain an aerogel with a sintering-free high-emissivity panel.

[0013] Furthermore, in step 1), the volume density of the aerogel fabric preform should not be lower than 0.15 g / cm 3 .

[0014] Furthermore, in step 1), the melting temperature of the TPU is 230 - 235 °C, and take it out after cooling to below 150 °C when the TPU is shaped.

[0015] Furthermore, in step 2), the solid content of the silica sol is 32% - 45%.

[0016] Furthermore, in step 2), the gel aging temperature is 85 - 90 °C.

[0017] Furthermore, in step 3), place the aerogel B in a muffle furnace at 260 - 280 °C for heat preservation for 1 - 1.5 h, and then raise the temperature to 550 - 570 °C and heat for not less than 4 h.

[0018] Furthermore, in step 4), the solid content of the alumina sol is 40% - 50%, and the mass ratio of the alumina sol to TaSi 2 , SiC, CoO is 100:(35 - 45):13x:0.2x, where the value range of x is 0.8 - 1.3.

[0019] Further, in step 5), the temperature in the oven is 60-65°C, and the drying duration is not less than 15 h.

[0020] Further, the total number of coating times in step 5) is not less than 3 times.

[0021] An aerogel with a sintering-free high-emissivity panel is prepared by the above preparation method.

[0022] The beneficial effects obtained by the present invention are as follows:

[0023] 1. The sintering-free high-emissivity panel prepared by the present invention is connected to the aerogel core layer through a continuous fabric rather than a suture, and the panel is continuously attached with strong adhesion. This preparation process avoids the high-temperature calcination of the panel and has no influence on the heat insulation performance of the aerogel. The thermal conductivity of the aerogel at room temperature is 0.02 W / (m·K).

[0024] 2. The present invention uses TPU, which is an elastomer at room temperature and has a very low coefficient of thermal expansion, to occupy the preform, avoiding the risk of pulling deformation of the preform caused by the shrinkage of the occupying agent after cooling, and also avoiding the risk of cracking of the brittle occupying agent during the production process, which may cause damage to the fabric or occupying failure. Moreover, the viscosity of polyurethane in the molten state is extremely high, and its surface with the ceramic fiber fabric is non-wetting, so there is no risk of internal inclusion of the aerogel caused by capillary action penetrating into the fabric interior.

[0025] 3. The present invention prepares a sintering-free high-emissivity panel on the surface of the aerogel. Compared with the in-situ secondary brush coating densification process, micron high-emissivity powder can be evenly introduced into the panel interior.

[0026] 4. The high-emissivity powder used in the present invention greatly improves the infrared radiation ability of the panel at high temperatures and reduces the tendency of the alumina panel to crystallize and fail at high temperatures for a long time. TaSi 2 The hemispherical emissivity of the TaSi-SiC panel from room temperature to 1200°C is higher than 0.92, and the surface emissivity is increased by 15% compared with that of the pure alumina panel, effectively improving the infrared radiation ability of the panel and effectively extending the service life of the alumina panel at high temperatures.

[0027] 5. By introducing CoO in the two-component emitter, the present invention can form a molten CoO·SiO 2 glass phase with a lower viscosity when TaSi starts to oxidize above 900°C, 2 and make it tend to coat on the surface of TaSi 2 particles to prevent the further oxidation of TaSi 2 . Specific embodiments

[0028] In order to make the technical features, advantages or technical effects in the above technical solutions of the present invention more obvious and understandable, the following will be described in detail with reference to embodiments.

[0029] Example 1

[0030] 1) Prepare an aerogel fabric preform using quartz fiber or alumina fiber through textile and needling processes, with a bulk density of 0.15 g / cm 3 ; Immerse one side of the aerogel fabric preform to be coated into molten TPU at 230 °C for a predetermined thickness, and take it out after cooling to 150 °C for TPU shaping to obtain preform A with surface occupancy.

[0031] 2) Place preform A into a forming mold, inject and impregnate it with silica sol with a solid content of 40%, then carry out gel aging at 85 °C to obtain a wet gel, and after supercritical drying, obtain aerogel B with surface TPU occupancy.

[0032] 3) Place aerogel B in a muffle furnace, keep it at 270 °C for 1.5 h, then raise the temperature to 560 °C and heat for 5 h to fully burn off the surface-occupying TPU, expose the surface aerogel fabric preform, and then carry out hydrophobic treatment to obtain hydrophobic core-layer aerogel C with exposed fabric.

[0033] 4) Mix alumina sol with a solid content of 45% with TaSi 2 , SiC, and CoO evenly according to a mass ratio of 100:40:13:0.2, and obtain high-emissivity agent slurry D after ball milling.

[0034] 5) Adopt a spraying method to coat high-emissivity agent slurry D on the surface of the exposed fabric of hydrophobic core-layer aerogel C, and then dry it in an oven at 62 °C for 17 h to complete one coating; a total of 4 coatings are carried out, and finally an aerogel material with a 2-mm-thick sinter-free high-emissivity panel is obtained.

[0035] Test the prepared aerogel material with a sinter-free high-emissivity panel. The test results show that the spherical emissivity of this material is not less than 0.93, and in a wind tunnel test under a heat flux condition of 2.1 MW / m 2 for 300 s, the recession thickness of the panel is less than 0.5 mm, and the temperature rise of the back panel is lower than 95 °C.

[0036] Example 2

[0037] 1) Prepare an aerogel fabric preform using quartz fiber or alumina fiber through textile and needling processes, with a bulk density not being 0.18 g / cm 3 ; Immerse one side of the aerogel fabric preform to be coated into molten TPU at 232 °C for a predetermined thickness, and take it out after cooling to 140 °C for TPU shaping to obtain preform A with surface occupancy.

[0038] 2) Place the preform A into a forming mold, impregnate it with 32% silica sol by injection, then carry out gel aging at 87 °C to obtain a wet gel, and after supercritical drying, obtain the aerogel B with TPU occupying the surface positions.

[0039] 3) Place the aerogel B in a muffle furnace, keep it at 260 °C for 1.5 h, then raise the temperature to 550 °C and heat for 5 h to fully burn off the TPU occupying the surface positions, expose the aerogel fabric preform on the surface, and then carry out hydrophobic treatment to obtain the hydrophobic core layer aerogel C with the fabric exposed.

[0040] 4) Mix alumina sol with a solid content of 40% with TaSi 2 , SiC, and CoO in a mass ratio of 100:45:10:0.16 and mix evenly. After ball milling, obtain the high-emissivity agent slurry D.

[0041] 5) Using the brush coating method, coat the high-emissivity agent slurry D on the surface of the exposed fabric of the hydrophobic core layer aerogel C, and then dry it in an oven at 60 °C for 18 h to complete one coating; coat a total of 5 times, and finally obtain the aerogel material with a non-sintered high-emissivity panel with a thickness of 3.5 mm.

[0042] Example 3

[0043] 1) Use quartz fiber or alumina fiber to prepare an aerogel fabric preform through textile and needling processes, with a bulk density of 0.17 g / cm 3 ; Immerse one side of the aerogel fabric preform to be coated into molten TPU at 235 °C to a predetermined thickness, take it out after cooling to 130 °C for TPU shaping, and obtain the preform A with TPU occupying the surface positions.

[0044] 2) Place the preform A into a forming mold, impregnate it with 45% silica sol by injection, then carry out gel aging at 90 °C to obtain a wet gel, and after supercritical drying, obtain the aerogel B with TPU occupying the surface positions.

[0045] 3) Place the aerogel B in a muffle furnace, keep it at 280 °C for 1 h, then raise the temperature to 570 °C and heat for 4 h to fully burn off the TPU occupying the surface positions, expose the aerogel fabric preform on the surface, and then carry out hydrophobic treatment to obtain the hydrophobic core layer aerogel C with the fabric exposed.

[0046] 4) Mix alumina sol with a solid content of 50% with TaSi 2 , SiC, and CoO in a mass ratio of 100:35:16.9:0.26 and mix evenly. After ball milling, obtain the high-emissivity agent slurry D.

[0047] 5) By means of spraying, the high-emissivity agent slurry D is coated on the surface of the exposed fabric of the hydrophobic core layer aerogel C, and then dried in an oven at 65 °C for 15 h to complete one coating; a total of 3 coatings are applied, and finally an aerogel material with a non-sintered high-emissivity panel with a thickness of 1.5 mm is obtained.

[0048] Although the present invention has been disclosed above by way of examples, it is not intended to limit the present invention. Any appropriate modifications or equivalent replacements made by those of ordinary skill in the art to the technical solutions of the present invention shall be covered by the protection scope of the present invention. The protection scope of the present invention shall be subject to what is defined by the claims.

Claims

1. A method for preparing an aerogel with a sinter-free high emissivity panel, characterized in that: The following steps are involved: 1) using quartz fiber or alumina fiber to prepare an aerogel fabric preform, immersing one side of the aerogel fabric preform to be coated into molten thermoplastic polyurethane elastomer TPU to a predetermined thickness, and taking it out after cooling to TPU to be shaped, to obtain a preform A with surface occupation; 2) placing the preform A into a molding mold, performing silica sol injection and impregnation, and then performing gel aging to obtain a wet gel, and after supercritical drying, obtaining an aerogel B with TPU occupying the surface; 3) placing aerogel B in a muffle furnace for heating treatment for a period of time, and then heating for a period of time after the temperature is raised to fully burn off the TPU occupying the surface, exposing the aerogel fabric preform on the surface, and then performing a hydrophobic treatment to obtain a hydrophobic core layer aerogel C with exposed fabric; 4) mixing alumina sol with TaSi2, SiC and CoO uniformly, and obtaining high-emissivity slurry D after ball milling; 5) The high emissivity slurry D is applied to the exposed fabric surface of the hydrophobic core aerogel C by spraying or brushing, and then dried in an oven to complete one coating; the coating is repeated several times to finally obtain an aerogel with a sinter-free high emissivity panel.

2. The preparation method according to claim 1, characterized in that The volume density of the aerogel fabric preform in step 1) should not be less than 0.15 g / cm 3 .

3. The preparation method according to claim 1, characterized in that: In step 1), the melting temperature of TPU is 230-235° C., and the TPU is taken out after being cooled to below 150° C. and fixed.

4. The preparation method according to claim 1, characterized in that: The solid content of the silica sol in step 2) is 32% to 45%.

5. The preparation method according to claim 1, characterized in that: In step 2), the gel aging temperature is 85-90°C.

6. The preparation method according to claim 1, characterized in that: In step 3), aerogel B is placed in a muffle furnace and kept at 260-280° C. for 1-1.5 hours, and then heated to 550-570° C. and heated for not less than 4 hours.

7. The preparation method according to claim 1, characterized in that: In step 4), the solid content of alumina sol is 40% to 50%, and the mass ratio of alumina sol to TaSi2, SiC, and CoO is 100:(35 to 45):13x:0.2x, where the value range of x is 0.8 to 1.

3.

8. The preparation method according to claim 1, characterized in that: In step 5), the temperature in the oven is 60-65° C., and the drying time is not less than 15 hours.

9. The preparation method according to claim 1, characterized in that: The total number of coatings in step 5) is not less than 3 times.

10. An aerogel with a sinter-free high emissivity panel, characterized in that: Prepared by the preparation method according to any one of claims 1 to 9.