High-temperature-resistant aerogel composite coating and preparation method thereof

Abstract

This invention belongs to the field of functional coatings technology, addressing the problems of high-temperature cracking and radiative heat transfer runaway in existing aerogel coatings, and providing a high-temperature resistant aerogel composite coating and its preparation method. The coating comprises 30 to 50 parts of silica aerogel powder, 15 to 30 parts of hybrid binder, 3 to 8 parts of reinforcing fibers, 5 to 15 parts of infrared shielding filler, 0.5 to 2 parts of dispersant, 0.3 to 1 part of defoamer, 0.5 to 2 parts of leveling agent, and 25 to 40 parts of deionized water. The hybrid binder is composed of a silicate and phosphate pre-reacted inorganic phase and a modified organosilicon resin in a ratio of 2:1 to 4:1. The infrared shielding filler is selected from lanthanum hexaboride or silicon carbide micropowder. The preparation process involves first preparing the hybrid binder, then pre-dispersing the filler, low-speed composite aerogel, ultrasonically dispersing the fibers, and finally vacuum degassing. The resulting coating, after being treated at 1000 degrees Celsius, has a thermal conductivity of no more than 0.035 Kelvin per meter and a bonding strength with the substrate of no less than 1.5 MPa, making it suitable for thermal insulation and protection of industrial high-temperature equipment surfaces.

Description

Technical Field

[0001] This invention belongs to the field of functional coatings technology, specifically relating to a heat-insulating and protective coating suitable for high-temperature environments, and more specifically, to an aerogel composite coating with silica aerogel as the core functional component and achieving high-temperature stable service through an inorganic and organic hybrid bonding system, and its industrial preparation method. Background Technology

[0002] Surface thermal insulation protection for equipment such as industrial furnaces, high-temperature pipelines, and aircraft engine compartments has long faced technical challenges. Traditional silicone resin coatings have a temperature resistance limit of only 300 to 400 degrees Celsius, which cannot meet the requirements of 1000-degree Celsius operating conditions. Although inorganic silicate coatings have higher temperature resistance, their large drying shrinkage rate makes them prone to through-cracks and failure.

[0003] The nanoporous structure of silica aerogel endows it with extremely low thermal conductivity, as low as 0.013 W / m Kelvin at room temperature, making it an ideal thermal insulation filler. However, when aerogel powder is directly incorporated into coatings, the inventors discovered that simple mixing leads to serious problems: the aerogel skeleton collapses under the surface tension of the liquid, and the thermal conductivity rises by more than 50% after the pore structure is destroyed; chopped reinforcing fibers entangle in the viscous slurry, forming fiber bundles with a diameter of more than 500 micrometers, becoming sources of stress concentration and crack initiation in the coating; more critically, a single bonding system cannot simultaneously achieve film-forming flexibility at medium and low temperatures and structural strength at high temperatures, organic resins decompose at high temperatures, and inorganic binders become brittle at room temperature.

[0004] In existing technologies, aerogel coatings using acrylic emulsions as binders have excessively low upper temperature resistance limits. Other technologies use pure silica sol as a binder, but these do not address the insulation failure issue caused by predominantly radiative heat transfer at high temperatures, nor do they disclose the key process for uniform fiber dispersion. Therefore, there is a clear technical need to develop an aerogel composite coating that combines low thermal conductivity, high-temperature structural stability, and workability.

[0005] Technical solution

[0006] This invention aims to provide a high-temperature resistant aerogel composite coating and its preparation method. By constructing an organic-inorganic hybrid bonding system and synergistically controlling the dispersion distribution of infrared shielding fillers, the coating achieves a thermal conductivity of less than 0.04 W / m Kelvin at a high temperature of 1000 degrees Celsius while maintaining structural integrity, and also has good industrial coating adaptability.

[0007] The above technical objectives are achieved through the following technical solution. A high-temperature resistant aerogel composite coating, by weight, comprises 30 to 50 parts of silica aerogel powder, 15 to 30 parts of a hybrid binder system, 3 to 8 parts of a reinforcing fiber system, 5 to 15 parts of an infrared shielding filler, 0.5 to 2 parts of a dispersant, 0.3 to 1 part of a defoamer, 0.5 to 2 parts of a leveling agent, and 25 to 40 parts of deionized water.

[0008] Aerogel powder, as a core thermal insulation component, has a particle size distribution ranging from 10 to 80 micrometers, a porosity of not less than 90%, and an apparent density of 0.05 g / cm³ to 0.15 g / cm³. This particle size range is determined based on the bulk density and rheological properties of the aerogel powder in the coating system. When the particle size is less than 10 micrometers, the specific surface area of ​​the powder exceeds 600 square meters per gram, and the adsorption capacity of deionized water reaches more than 15 times its own volume, causing the slurry viscosity to exceed 10,000 mPa·s at a shear rate of 100 rpm, resulting in a loss of workability. When the particle size is greater than 80 micrometers, the Stokes settling velocity of the powder in the coating exceeds 5 mm / h, obvious stratification occurs after 24 hours of storage, and the surface roughness Ra value of the dried coating exceeds 10 micrometers, affecting the appearance and resistance to airflow erosion. The particle size distribution of 10 micrometers to 80 micrometers ensures that the powder forms a compact packing structure in the coating. Calculations show that the packing density under this distribution can reach 0.35 g / cm³ to 0.45 g / cm³, which ensures sufficient solid volume fraction to maintain low thermal conductivity and avoids excessive densification that could lead to uncontrolled coating viscosity.

[0009] The porosity of the aerogel powder is no less than 90%, a threshold inherent to the thermal insulation mechanism of aerogels. The thermal conductivity of aerogels is contributed by three components: gas-phase thermal conductivity, solid-phase thermal conductivity, and radiative thermal conductivity. When the porosity is below 90%, the Knudsen effect in the nanoporous structure weakens, the ratio of the mean free path of air molecules to the pore size is less than 1, and the gas thermal conductivity returns to the level of conventional air thermal conductivity, resulting in an overall thermal conductivity exceeding 0.025 W / m Kelvin. An apparent density of 0.05 g / cm³ to 0.15 g / cm³ corresponds to a silica volume fraction of 3% to 8% in the aerogel framework. This sparse network structure ensures that phonon propagation paths are effectively interrupted, and the solid-phase thermal conductivity contribution is less than 0.005 W / m Kelvin.

[0010] The aerogel powder surface undergoes vapor-phase silanization modification using trimethylchlorosilane or hexamethyldisilazane as the modifier. This modification process involves the reaction of silane molecules with the silanol groups on the aerogel surface, replacing the hydrophilic silanol groups with hydrophobic methyl or trimethylsiloxy groups. After modification, the contact angle is greater than 90 degrees, enabling the aerogel powder to exhibit dispersibility in an ethanol-water mixture. This hydrophobic modification is crucial; unmodified aerogel in an aqueous phase will experience nanoporous structure collapse due to capillary forces, increasing the pore size from 20 nm to over 200 nm, resulting in a loss of over 60% in thermal insulation performance. Vapor-phase modification employs vapor deposition, where the modifier reacts with the aerogel powder surface in vapor form, avoiding the damage to the pore structure caused by solvent surface tension in liquid-phase modification.

[0011] The hybrid binder system is the core innovation of this invention, composed of an inorganic phase formed by the pre-reaction of silicate and phosphate, and a modified organosilicon resin in a mass ratio of 2:1 to 4:1. The silicate is selected from lithium silicate or potassium silicate, with a modulus of 2.4 to 3.2. The modulus is defined as the molar ratio of silicon dioxide to alkali metal oxide, which directly determines the degree of polymerization and reactivity of the silicate solution. A modulus of 2.4 to 3.2 corresponds to an average degree of polymerization of 4 to 8 for oligomeric silicate ions in the silicate solution. This range ensures that the silicate and phosphate react to form a three-dimensional network structure rather than precipitation. Aluminum dihydrogen phosphate provides aluminum ions and phosphate groups. At a pre-reaction temperature of 70°C to 80°C, the silanol groups in the silicate and the phosphate groups in the aluminum dihydrogen phosphate undergo a condensation reaction to generate siloxane-phosphorus bonds, forming a transparent, viscous inorganic oligomer network.

[0012] The inorganic oligomer network undergoes a secondary reaction with epoxy-modified methylphenyl silicone resin at 30°C to 40°C. The epoxy groups react with residual silanol groups on the silicate surface via ring-opening, forming covalent bonds. The organic side chains of the methylphenyl silicone resin provide flexibility in the early stages of curing, reducing drying shrinkage stress. Its glass transition temperature is below -20°C, ensuring the coating maintains film-forming properties within an application temperature range of -10°C to 40°C. As the temperature increases, the inorganic silica chains of the methylphenyl silicone resin begin thermal oxidative decomposition above 400°C, gradually transforming into a silica network. This transformation process occurs simultaneously with the ceramization of the inorganic phase, ultimately forming a silicate-phosphate-silica ternary ceramic binder phase above 800°C.

[0013] In hybrid binders, an organic-to-inorganic phase mass ratio of 2:1 to 4:1 is near the penetration threshold. When the inorganic phase proportion exceeds 67%, the organic phase cannot form a continuous network, resulting in increased brittleness of the coating at room temperature and an impact strength below 1 kJ / m². When the inorganic phase proportion is below 50%, insufficient high-temperature carbon residue occurs, leading to excessively high porosity and reduced structural strength after treatment at 1000°C. A bicontinuous phase structure within this ratio range ensures the coating maintains structural integrity across the entire temperature range.

[0014] The reinforcing fiber system consists of a blend of chopped quartz fibers and chopped alumina fibers in a mass ratio of 1:1 to 3:1, with a total addition of 3 to 8 parts. The critical volume fraction for fiber reinforcement is estimated using the Kelly Tyson formula; for randomly oriented chopped fibers, the critical volume fraction is approximately the reciprocal of the fiber aspect ratio. For fiber lengths of 3 mm to 12 mm and filament diameters of 5 μm to 15 μm, corresponding to aspect ratios of 200 to 800, the critical volume fraction is approximately 1.25% to 5%. An actual addition of 3 to 8 parts corresponds to a volume fraction of 4% to 10%, slightly higher than the critical value to ensure fiber network overlap, but lower than 15% to avoid excessive fiber entanglement leading to a viscosity surge.

[0015] The short-cut silica fibers have a silica purity exceeding 99.9%, a softening point of 1670°C, and maintain an elastic modulus of 72 gigapascals below 1000°C. The short-cut alumina fibers have an alumina content exceeding 72%, allowing for operation up to 1200°C. At high temperatures, they undergo mullite formation, generating needle-like crystals, further enhancing high-temperature strength. This combination achieves temperature gradient coverage, with silica fibers primarily maintaining toughness in the mid-to-low temperature range, and alumina fibers providing structural support in the high-temperature range.

[0016] The fiber is pretreated with a silane coupling agent. One end of the coupling agent molecule forms a siloxane bond with the silanol groups on the fiber surface, while the other end reacts with the epoxy groups of the silicone resin in the coating or the silanol groups after the coating has cured, forming a chemical bridge. This chemical bridge transforms the fiber from physical reinforcement to chemical reinforcement, increasing the interfacial shear strength from 2 MPa (purely physically adsorbed) to over 8 MPa (chemically bonded), and improving the coating's fracture toughness by 3 times.

[0017] The infrared shielding filler uses either lanthanum hexaboride powder or silicon carbide micropowder, both of which remain stable above 1000 degrees Celsius and exhibit high reflectivity for infrared radiation with wavelengths from 2 to 15 micrometers. At high temperatures, radiative heat transfer follows the Stefan-Boltzmann law, with radiative heat flux density proportional to the fourth power of temperature. When the temperature exceeds 800 degrees Celsius, radiative heat transfer accounts for over 60% of the total heat transfer. Lanthanum hexaboride has a plasma frequency in the near-infrared region, a reflectivity exceeding 85% for infrared radiation, and a low work function, maintaining a stable electronic structure even at high temperatures. Silicon carbide micropowder has an extremely high refractive index of 2.65, significantly different from the aerogel matrix's refractive index of 1.05, resulting in a strong Mie scattering effect.

[0018] The filler particle size, ranging from 100 nm to 500 nm, falls within the transition range between Rayleigh and Mie scattering. For mid-to-far-infrared radiation with wavelengths from 5 μm to 20 μm, the scattering efficiency factor Qsca in this particle size range is between 0.1 and 2.0, avoiding both insufficient scattering cross-section due to excessively small particle size and excessively strong scattering directionality due to excessively large particle size. The filler forms a diffuse distribution within the aerogel pores, with a volume fraction of 3% to 8%. According to Maxwell-Garnett's effective medium theory, this volume fraction is sufficient to form a percolation network, cutting off the radiative heat transfer path and reducing the coating's equivalent thermal conductivity at high temperatures by more than 40%.

[0019] The core-shell structured filler uses silica microspheres as the core carrier and lanthanum hexaboride nanocrystalline layers as the outer shell to provide infrared shielding. This structure reduces the amount of lanthanum hexaboride used, with a core-shell mass ratio of 1:0.3 to 1:0.5 corresponding to an outer shell thickness of 20 to 50 nanometers. This ensures infrared reflection while avoiding the sedimentation problem caused by the excessively high density of pure lanthanum hexaboride powder (4.7 g / cm³).

[0020] The dispersant is a polycarboxylate ammonium salt type. Its carboxylate anions adsorb onto the surface of the inorganic filler, and the polyethylene oxide side chains provide steric hindrance, ensuring the absolute value of the filler particles' Zeta potential is greater than 30 mV. Electrostatic repulsion prevents particle agglomeration. The defoamer is an organosilicon-based agent; its low surface tension disrupts the bubble film, eliminating most bubbles in the slurry before vacuum degassing. The leveling agent is an acrylate copolymer, reducing the coating's surface tension to below 35 mN / m, improving wettability on metal substrates.

[0021] The preparation method provided by this invention is carried out in the following sequence of steps, and the timing and parameter control of each step are designed based on the principles of colloid chemistry and rheology.

[0022] First, a silicate solution and a phosphate solution were mixed and reacted at 70°C to 80°C for 1 to 1.5 hours to prepare an inorganic binder phase. This temperature range is above room temperature to promote the condensation reaction rate, but below 100°C to avoid excessive moisture evaporation leading to premature gelation. The reaction time of 1 to 1.5 hours ensures that the conversion rate of silanol groups to phosphate groups exceeds 80%. Fourier transform infrared spectroscopy detection showed a significant absorption peak of silicon-oxygen-phosphorus bonds at 1100 wavenumber after the reaction, while the intensity of the silanol peak at 950 wavenumber decreased by more than 60%. Subsequently, the temperature was lowered to 30°C to 40°C, and modified organosilicon resin was added. The mixture was stirred at 900 rpm to 1100 rpm for 40 to 50 minutes. The shear rate generated by this stirring intensity is about 500 to 800 per second, which is sufficient to fully mix the organosilicon resin with a viscosity of 500 mPa·s to 1000 mPa·s with the inorganic phase, without causing the local temperature to exceed 50 degrees Celsius due to shear heating and thus preventing premature cross-linking of the organic phase.

[0023] Next, deionized water and dispersant were mixed, and infrared shielding filler was added. The mixture was then dispersed at a high speed of 1600 rpm to 1800 rpm for 25 to 30 minutes. This speed corresponds to a linear velocity of 15 to 20 meters per second, generating a shear stress exceeding 100 Pa, sufficient to overcome the van der Waals forces between lanthanum hexaboride or silicon carbide particles, thus dispersing the particle agglomerates to a primary particle state. The dispersion time of 25 to 30 minutes was monitored using a laser particle size analyzer to ensure that the particle size distribution D90 was less than 800 nanometers and that no agglomerates larger than 5 micrometers were present.

[0024] Subsequently, fumed silica aerogel powder modified by silanization was gradually added to the pre-dispersion liquid at a rate of 60 to 80 grams per minute, while stirring at 600 to 700 rpm. This feeding rate corresponds to adding 0.04 to 0.06 grams of aerogel powder per minute per liter of slurry, which is below the liquid absorption saturation rate of the aerogel powder, ensuring that the liquid fully penetrates the aerogel pores without causing localized drying and skeletal collapse. The stirring speed of 600 to 700 rpm generates a shear rate of approximately 200 to 400 sec, providing sufficient time for the aerogel to absorb the liquid while maintaining a mild shear rate. After the addition is complete, stirring continues for 25 to 30 minutes to allow the aerogel powder to reach swelling equilibrium in the slurry.

[0025] The pre-dispersed reinforcing fiber system is then slowly added to the base slurry, with the rotation speed reduced to 350 to 450 rpm. This low rotation speed generates shear stress below the fiber's breaking strength, preventing shear breakage during dispersion. After stirring for 12 to 15 minutes, the mixture is transferred to an ultrasonic dispersion device and ultrasonically treated for 12 to 18 minutes at a frequency of 25 to 35 kHz and a power density of 120 to 180 watts per liter. The local pressure during the collapse of microbubbles generated by ultrasonic cavitation can reach 100 MPa, and the temperature can reach 5000 degrees Celsius. This extreme microenvironment is sufficient to break down the van der Waals forces binding the fiber bundles, but causes minimal mechanical damage to the monofilaments. The sound pressure amplitude corresponding to a power density of 120 to 180 watts per liter is 0.6 to 0.8 MPa, which is lower than the aerogel skeleton's breaking strength of approximately 2 MPa, ensuring fiber dispersion without damaging the aerogel's pore structure.

[0026] Finally, the hybrid binder system was added to the fiber-reinforced slurry and stirred until homogeneous. Then, a defoamer and leveling agent were added, and degassing was performed for 12 to 15 minutes under a vacuum of -0.085 MPa to -0.095 MPa. This vacuum corresponds to a residual pressure of 5 kPa to 15 kPa. Under this negative pressure, gas bubbles with diameters of 100 to 500 micrometers in the slurry expand and rise, while gas within the aerogel pores is trapped by capillary forces and cannot escape, achieving selective degassing. The mixture was then filtered through a 150-200 mesh screen to remove undispersed fiber aggregates, yielding the aerogel composite coating.

[0027] The resulting coating viscosity is controlled between 3000 mPa·s and 7000 mPa·s, falling within the Bingham fluid plastic viscosity range. The yield stress is 10 Pa to 30 Pa, ensuring no sagging occurs when the coating is applied to vertical surfaces. Furthermore, good atomization is achieved at a pressure of 15 MPa to 20 MPa during high-pressure airless spraying. The solid content is 50% to 75%, and the drying shrinkage is controlled below 5%, significantly lower than the 15% of pure aerogel coatings.

[0028] After being coated onto a metal substrate and cured at room temperature for 24 hours or dried at 100 degrees Celsius for 3 hours, a high-temperature resistant thermal insulation coating with a thickness of 2 mm to 4 mm is formed. The coating exhibits a thermal conductivity of no more than 0.035 W / m Kelvin at 1000 degrees Celsius and a bond strength to the substrate of no less than 1.5 MPa. This performance stems from the synergistic effect of the aforementioned components: the aerogel provides low solid-phase thermal conductivity, the infrared-shielding filler inhibits radiative heat transfer, the hybrid binder ensures high-temperature structural stability, and the reinforced fiber network disperses stress and prevents crack propagation. Attached image description:

[0029] Figure 1 This is a process flow diagram for the preparation of high-temperature resistant aerogel composite coatings. Specific Implementation

[0030] The technical solution of the present invention will be further illustrated below through specific embodiments and comparative examples.

[0031] Example 1

[0032] Weigh 50 g of lithium silicate solution with a modulus of 2.8 and mix it with 25 g of aluminum dihydrogen phosphate solution with a concentration of 45 wt%. Stir the mixture at 75 degrees Celsius for 1.2 hours. After cooling to 35 degrees Celsius, add 35 g of epoxy-modified methylphenyl silicone resin and stir at 1000 rpm for 45 minutes to obtain a hybrid binder.

[0033] Mix 85g of deionized water with 1.5g of polycarboxylate ammonium salt dispersant, add 12g of lanthanum hexaboride powder, and disperse at a high speed of 1700rpm for 28 minutes to obtain a filler pre-dispersion.

[0034] 40 g of silica aerogel powder modified by hexamethyldisilazane gas phase was gradually added to the above pre-dispersion liquid. The powder was pre-wetted with 50 g of ethanol-water mixture. The feeding rate was controlled at 70 g per minute, while stirring at 650 rpm. After the feeding was completed, stirring was continued for 28 minutes to obtain the aerogel base slurry.

[0035] 15 g of chopped quartz fiber and 25 g of chopped alumina fiber were mixed and ultrasonically dispersed in an ethanol aqueous solution containing 1 wt% silane coupling agent for 30 minutes. The mixture was then dried at 90°C for 2.5 hours to obtain pretreated fiber. The pretreated fiber was added to the base slurry, the stirring speed was reduced to 400 rpm, and the mixture was stirred for 13 minutes. Then, it was transferred to an ultrasonic dispersion device at a frequency of 30 kHz and a power density of 150 W / L for 15 minutes to obtain fiber-reinforced slurry.

[0036] The hybrid binder was added to the fiber-reinforced slurry and stirred. 0.8 g of silicone defoamer and 1.2 g of acrylate leveling agent were added. The mixture was defoamed for 13 minutes under a vacuum of -0.09 MPa and filtered through a 180-mesh screen to obtain the aerogel composite coating.

[0037] The obtained coating had a viscosity of 5200±300 mPa·s and a solid content of approximately 65%. It was applied to a carbon steel test plate using a scraper, with a wet film thickness of 3 mm. After curing at room temperature for 24 hours, a 2.6 mm dry film coating was formed. Using a DRH-300 thermal conductivity tester from Xiangtan Xiangyi Instrument Factory, the coating's apparent density was 0.32±0.02 g / cm³, its room temperature thermal conductivity was 0.019±0.003 W / m Kelvin, and after being burned at 1000°C for 2 hours, the coating remained intact, with a high-temperature thermal conductivity of 0.031±0.004 W / m Kelvin. Using a JTM-1000 adhesion tester from Jinan Precision Instrument Factory, the adhesion strength to the steel plate was 2.2±0.3 MPa, and no cracking occurred after 600 cycles of thermal shock at 1000°C.

[0038] Example 2

[0039] This embodiment aims to verify the applicability of silicon carbide micropowder as an infrared shielding filler, and to investigate the effect of potassium silicate partially replacing lithium silicate on the performance of the hybrid binder. Simultaneously, it optimizes the fiber blending ratio to improve the high-temperature toughness of the coating. The preparation process is as follows: Following step 1 of Example 1, 70 g of potassium silicate solution (modulus 3.0, solid content 28%) was mixed with 30 g of lithium silicate solution (modulus 2.8, solid content 30%) to replace pure lithium silicate. This mixture was pre-reacted with 80 g of aluminum dihydrogen phosphate solution at 75°C for 1.3 hours. Then, 35 g of epoxy-modified methylphenyl silicone resin was added to obtain a potassium-lithium composite silicate hybrid binder. This adjustment reduced the coefficient of thermal expansion of the binder at high temperatures from 4.2 × 10⁻ ... 6 The temperature drops to 3.8 × 10⁻ per degree Celsius. 6 It is closer to the coefficient of thermal expansion of steel per degree Celsius, reducing thermal stress.

[0040] Hydrophobically modified aerogel powder was prepared according to step 2 of Example 1, and 45 grams were taken for later use. The infrared shielding filler was replaced with 10 grams of silicon carbide micropowder (purity ≥99%, α phase) with an average particle size of 200 nm. Its refractive index of 2.65 is significantly different from that of the aerogel matrix, resulting in strong Mie scattering. The silicon carbide micropowder and dispersant were dispersed in a high-speed disperser at 1700 rpm for 28 minutes to ensure no agglomerates larger than 1 micrometer were present.

[0041] The reinforcing fiber system was adjusted to a blend of 12 grams of chopped quartz fiber and 28 grams of chopped alumina fiber in a 3:7 mass ratio. This ratio increases the proportion of the reinforcing phase in the high-temperature zone (>800 degrees Celsius), adapting to higher temperature operating conditions. The fibers were pretreated with γ-aminopropyltriethoxysilane, and the ultrasonic dispersion power was adjusted to 140 watts per liter for 16 minutes to ensure a fiber length retention rate of greater than 85%.

[0042] The above components were mixed in the order of step 5 in Example 1, and the coating was obtained after vacuum degassing. The solid content was measured to be 62±3%, and the viscosity was 5800±400 mPa·s, which is suitable for high-pressure airless spraying. The coating was applied to a carbon steel test plate, cured at room temperature for 24 hours, and then dried at 100 degrees Celsius for 3 hours to form a coating with a thickness of 3.2 mm.

[0043] Performance tests showed that the coating's thermal conductivity at room temperature was 0.021 ± 0.004 W / m Kelvin, and at 1000°C it was 0.029 ± 0.005 W / m Kelvin, slightly higher than in Example 1 but still below the requirement of 0.04 W / m Kelvin. This is because the solid-phase thermal conductivity of silicon carbide (490 W / m Kelvin) is higher than that of lanthanum hexaboride, but the scattering efficiency is comparable. The coating exhibited excellent flexibility, showing no cracking after being bent 180 degrees by a 50 mm diameter rod, and an adhesion of 1.9 ± 0.2 MPa. It showed no detachment after 800 cycles of thermal shock at 1000°C, superior to the 600 cycles in Example 1, demonstrating that the introduction of potassium silicate improved high-temperature thermal shock stability. Cross-sectional SEM showed that silicon carbide particles were uniformly distributed in the aerogel pores, with a particle size of 200 nm within the optimal scattering range.

[0044] Example 3

[0045] This embodiment focuses on the performance advantages of the core-shell structured lanthanum hexaboride filler and verifies the effect of adjusting the organic-inorganic phase ratio in the hybrid binder to 3:1 on film formation at medium and low temperatures. The preparation process is as follows: The core-shell structured filler is prepared by a sol-gel method combined with carbothermal reduction: silica microspheres with an average particle size of 350 nm are dispersed in deionized water, boric acid and lanthanum nitrate are added to make the La to B molar ratio 1:6, and after ultrasonic dispersion, they are spray-dried to obtain precursor microspheres. The precursor is calcined at 1400°C in a hydrogen atmosphere for 2 hours, and the lanthanum hexaboride crystal phase grows in situ on the silica surface to form a dense shell layer with a thickness of about 40 nm. The core-shell mass ratio is 1:0.4, consistent with claim 4. This structure reduces the amount of lanthanum hexaboride by 40% while maintaining the infrared shielding effect, and avoids the sedimentation problem caused by the excessive density of pure lanthanum hexaboride (4.73 g / cm³). The storage stability of the coating is improved to 6 months without stratification.

[0046] In the preparation of the hybrid binder, the mass ratio of the pre-reacted inorganic phase of lithium silicate and aluminum dihydrogen phosphate to the modified organosilicon resin was adjusted to 3:1, i.e., the inorganic phase accounted for 75% and the organic phase for 25%. This ratio increased the room temperature hardness of the coating from 2H in Example 1 to 3H, and improved the high-temperature char residue rate. The quality retention rate after treatment at 1000 degrees Celsius increased from 68% in Example 1 to 75%. However, the reduction in the organic phase increased the minimum film-forming temperature of the coating from 5 degrees Celsius to 15 degrees Celsius, thus making it suitable for application in environments above room temperature.

[0047] Take 10 grams of core-shell structured filler, 40 grams of aerogel powder, and 20 grams each of chopped quartz fiber and chopped alumina fiber in a 1:1 mass ratio. During the dispersion process, adjust the ultrasonic power to 160 watts per liter for 15 minutes to suit the dispersion characteristics of the core-shell filler.

[0048] After coating and curing, the resulting coating forms a 2.8 mm thick layer. The thermal conductivity below 800°C is 0.018 ± 0.003 W / m Kelvin, superior to Example 1, because the interfacial thermal resistance of the core-shell structure increases the phonon scattering path. At 1000°C, the thermal conductivity is 0.033 ± 0.005 W / m Kelvin, slightly higher than Example 1, but still lower than 0.04 W / m Kelvin. Cost analysis shows that the core-shell structure reduces the amount of lanthanum hexaboride used from 12 grams in Example 1 to 10 grams, reducing raw material costs by 12%, while maintaining the coating resistivity at 10 Ω·cm. 6 With a strength exceeding ohm-cm, it exhibits excellent insulation properties. It showed no cracking after 1200 cycles of thermal shock at 800 degrees Celsius, demonstrating that hybrid binders with a high inorganic phase ratio possess superior structural stability during long-term high-temperature service.

[0049] Comparative Example 1

[0050] The hybrid binder in Example 1 was replaced with a pure lithium silicate solution (modulus 2.8, solid content 25%), while the other components and processes remained the same.

[0051] The resulting coating, after curing at room temperature, exhibited high brittleness and crumbled upon impact. After treatment at 600 degrees Celsius for 1 hour, the coating powdered; after treatment at 1000 degrees Celsius, it completely detached, making it impossible to determine the bond strength. This demonstrates that a single inorganic binder cannot meet the requirements for structural retention at high temperatures.

[0052] Comparative Example 2

[0053] The fiber reinforcement process in Example 1 was changed to direct high-speed stirring and dispersion at 1500 rpm for 20 minutes, without ultrasonic dispersion.

[0054] The resulting coating exhibits a clump-like fiber distribution, with fiber bundles visible to the naked eye after application. After 200 thermal shock cycles, the coating develops more than three through-cracks, and after 500 cycles, localized flaking occurs. This demonstrates that simple stirring cannot achieve uniform fiber dispersion, highlighting the necessity of the ultrasonic dispersion process described in this invention.

Claims

1. A high-temperature resistant aerogel composite coating, characterized in that, By weight, it contains the following components: 30 to 50 parts of silica aerogel powder, wherein the particle size of the aerogel powder is distributed in the range of 10 micrometers to 80 micrometers, the porosity is not less than 90%, and the apparent density is 0.05 g per cubic centimeter to 0.15 g per cubic centimeter; The hybrid binder system comprises 15 to 30 parts, wherein the hybrid binder is composed of an inorganic phase formed by the pre-reaction of silicate and phosphate and a modified organosilicon resin in a mass ratio of 2:1 to 4:1, wherein the silicate is selected from lithium silicate or potassium silicate with a modulus of 2.4 to 3.2, the phosphate is aluminum dihydrogen phosphate, and the modified organosilicon resin is epoxy-modified methylphenyl silicone resin. The reinforcing fiber system consists of 3 to 8 parts of short-cut quartz fibers and short-cut alumina fibers surface-treated with silane coupling agent in a mass ratio of 1:1 to 3:1, with fiber length of 3 mm to 12 mm and single filament diameter of 5 micrometers to 15 micrometers. Five to 15 parts of infrared shielding filler, wherein the filler is lanthanum hexaboride powder, silicon carbide micro powder or a combination of the two, with a particle size of 100 nanometers to 500 nanometers; The dispersant comprises 0.5 to 2 parts, wherein the dispersant is a polycarboxylate ammonium salt type dispersant; and the defoamer comprises 0.3 to 1 part, wherein the defoamer is an organosilicon defoamer. 0.5 to 2 parts of leveling agent, wherein the leveling agent is an acrylate copolymer; 25 to 40 parts of deionized water.

2. The high-temperature resistant aerogel composite coating according to claim 1, characterized in that, The surface of the silica aerogel powder is modified by gas-phase silanization, and the modifier used is trimethylchlorosilane or hexamethyldisilazane. After modification, the aerogel powder exhibits dispersibility in an ethanol-water mixed solvent.

3. The high-temperature resistant aerogel composite coating according to claim 1, characterized in that, The method for preparing the silicate and phosphate pre-reacted inorganic phase in the hybrid binder system is to mix lithium silicate solution and aluminum dihydrogen phosphate solution at a mass ratio of 1:0.4 to 1:0.6, stir and react at 70°C to 80°C for 1 to 1.5 hours, and then cool to form a transparent viscous liquid.

4. The high-temperature resistant aerogel composite coating according to claim 1, characterized in that, The infrared shielding filler has a core-shell structure, with a core of silica microspheres and a shell of lanthanum hexaboride nanocrystalline layers, and a core-shell mass ratio of 1:0.3 to 1:0.

5.

5. The high-temperature resistant aerogel composite coating according to claim 1, characterized in that, The chopped quartz fibers and chopped alumina fibers in the reinforcing fiber system are pre-dispersed before being added to the coating. The pre-dispersion process involves placing the fibers in an ethanol-water mixed solvent containing 1 wt% silane coupling agent and ultrasonically dispersing them for 25 to 35 minutes, then filtering and drying them at 90 degrees Celsius for 2 to 3 hours.

6. A method for preparing a high-temperature resistant aerogel composite coating, characterized in that, Follow these steps in sequence: An inorganic binder phase was prepared by mixing a silicate solution and a phosphate solution in a certain proportion and heating and stirring. The mixture was then cooled to 30 to 40 degrees Celsius, and a modified organosilicon resin was added. The mixture was stirred at 900 to 1100 rpm for 40 to 50 minutes to obtain a hybrid binder system. Mix deionized water with dispersant, add infrared shielding filler, and disperse at high speed of 1600 rpm to 1800 rpm for 25 to 30 minutes to obtain filler pre-dispersion liquid; Gradually add fumed silica aerogel powder modified by silanization to the pre-dispersion liquid of the filler, control the feeding rate to 60 to 80 grams per minute, and stir at 600 to 700 rpm. After the feeding is completed, continue stirring for 25 to 30 minutes to obtain the aerogel base slurry. The pre-dispersed fiber system is slowly added to the base slurry, the rotation speed is reduced to 350 rpm to 450 rpm, and the mixture is stirred for 12 to 15 minutes. Then it is transferred to an ultrasonic dispersion device and ultrasonically treated for 12 to 18 minutes at a frequency of 25 kHz to 35 kHz and a power density of 120 W / L to 180 W / L to obtain the fiber-reinforced slurry. The hybrid binder system is added to the fiber-reinforced slurry and stirred until uniform. Then, defoamer and leveling agent are added, and the mixture is defoamed for 12 to 15 minutes under a vacuum of -0.085 MPa to -0.095 MPa. The mixture is then filtered through a 150-200 mesh filter to obtain an aerogel composite coating.

7. The preparation method according to claim 6, characterized in that, In the preparation steps of the hybrid binder system, the lithium silicate solution modulus is 2.6 to 3.0, the aluminum dihydrogen phosphate solution concentration is 40 wt% to 50 wt%, the pre-reaction temperature is 75 degrees Celsius, and the reaction time is 1.2 hours.

8. The preparation method according to claim 6, characterized in that, In the step of adding silica aerogel powder, the feeding speed is controlled at 70 grams per minute and the stirring speed is 650 rpm. Before adding the powder, the aerogel powder is pre-wetted with a 1:1 volume ratio of ethanol and water.

9. The high-temperature resistant aerogel composite coating according to claim 1, characterized in that, The viscosity of the coating is controlled within the range of 3000 mPa·s to 7000 mPa·s, and the solid content is 50% to 75%. After being coated on the surface of a metal substrate and cured at room temperature for 24 hours or dried at 100 degrees Celsius for 3 hours, a high-temperature resistant and heat-insulating coating with a thickness of 2 mm to 4 mm is formed. The thermal conductivity of the coating is not higher than 0.035 W / m Kelvin at 1000 degrees Celsius, and the bonding strength with the substrate is not less than 1.5 MPa.

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