Inorganic thermal control coating and method for forming coating on aerospace metal substrate

Abstract

The present invention discloses an inorganic thermal control coating and a method for forming a coating on an aerospace metal substrate, and relates to the field of new material technology. An inorganic thermal control coating, the raw materials of which include by weight: 25%-40% modified nano-silica sol, 25%-40% white pigment, 5%-12% two-dimensional flaky filler, 2.5%-6% dispersant, 0.5%-1.5% defoamer, and the remainder solvent. The method for forming a coating on an aerospace metal substrate is implemented by spraying the above-mentioned inorganic thermal control coating on the surface of the aerospace metal substrate and thermally curing it. The coating disclosed by the present invention can be directly sprayed onto aerospace metal substrates without pre-treating the metal substrate, thereby avoiding deformation of the metal substrate during pre-treatment, which affects the stability of the equipment. At the same time, the direct spraying method without pre-treatment has lower processing difficulty.

Description

Technical Field

[0001] The present invention relates to the technical field of new materials, and in particular to an inorganic thermal control coating and a method for forming a coating thereon on an aerospace metal substrate. Background Art

[0002] Coating-type thermal control white paint plays a vital role in spacecraft thermal control systems. Through its unique thermal radiation and reflection properties, this type of paint effectively regulates the temperature of the spacecraft's surface, ensuring stable operation in environments with extreme temperature differences. Compared to traditional thermal control methods, coating-type thermal control white paint offers advantages such as light weight, easy construction, and strong adaptability, making it an essential component of modern aerospace thermal control technology. Coating-type thermal control white paints are generally divided into organic and inorganic thermal control white paints, depending on the weight of the binder used. In contrast, inorganic white paints exhibit unique advantages in the field of aerospace thermal control, thanks to their superior heat resistance, radiation resistance, and long-term stability. Inorganic white paints can withstand the extreme temperature fluctuations and cosmic ray radiation experienced by spacecraft in the space environment for extended periods of time, ensuring the long-term, reliable operation of spacecraft thermal control systems.

[0003] However, inorganic thermal control white paint faces numerous challenges during its practical application. Due to its high rigidity, poor flexibility, and different thermal expansion coefficients compared to metal substrates commonly used in aerospace applications (such as titanium alloys and aluminum-based silicon carbide), inorganic white paint exhibits weak adhesion to the metal substrate. To improve the adhesion between inorganic white paint and the metal substrate, surface roughening treatments such as grinding or sandblasting are often required to ensure a secure adhesion of the inorganic white paint to the substrate. This treatment typically requires a surface roughness Ra of at least 3.2 to provide sufficient mechanical adhesion. However, surface roughening is significantly more challenging for harder metal substrates, such as titanium alloys and aluminum-based silicon carbide. These materials are not only hard but also highly wear-resistant, making traditional roughening methods difficult to achieve optimal results. Furthermore, for certain soft metal substrates, such as magnesium alloys, sandblasting and other roughening methods can cause deformation, potentially impacting the overall performance and structural stability of the spacecraft. Summary of the Invention

[0004] A first aspect of the present invention is to provide an inorganic thermal control coating, which solves the problem of poor adhesion of inorganic white paint on metal substrates in the prior art.

[0005] In order to achieve the above object, the technical solution adopted by the present invention is as follows:

[0006] An inorganic thermal control coating comprises the following raw materials by weight: 25%-40% modified nano-silica sol, 25%-40% white pigment, 5%-12% two-dimensional flaky filler, 2.5%-6% dispersant, 0.5%-1.5% defoamer, and the balance solvent.

[0007] Furthermore, the solvent is ethanol, isopropanol or acetone.

[0008] Furthermore, the white pigment is one or more of zinc oxide, titanium dioxide and zirconium dioxide.

[0009] Furthermore, the two-dimensional flake filler has excellent mechanical properties and wettability, and is boron nitride, mica powder, kaolin or talc.

[0010] Furthermore, the dispersant is polyacrylate or polymethyl methacrylate.

[0011] Furthermore, the defoaming agent is polydimethylsiloxane or polyether polysiloxane.

[0012] Furthermore, the preparation method of the modified nano-silica sol comprises the following steps:

[0013] Step S10: Nano-silica powder is dispersed in a solvent, with a weight ratio of nano-silica powder to solvent of 2:3; a uniform nano-silica suspension is obtained by high-speed stirring at a stirring rate of 1200 rpm for 5 hours;

[0014] Step S20: mixing the nano-silica suspension and the polyurethane prepolymer solution in a weight ratio of 10:1, stirring and reacting at 60° C. for 5 hours at a stirring rate of 300 rpm; allowing the polyurethane prepolymer to fully react with the active sites on the surface of the nano-silica to form modified nano-silica;

[0015] Step S30: After the reaction in step S02 is completed, the product is washed, filtered, and dried to obtain modified nano-silica.

[0016] Step S40: Re-dispersing the modified nano-silica in the solvent, with the weight ratio of the modified nano-silica to the solvent being 2:3; obtaining a uniform modified nano-silica sol by high-speed stirring, with a stirring rate of 1200 rpm and a stirring time of 5 h.

[0017] In this invention, polyurethane prepolymer is used to chemically bond and modify nano-silica. By strictly controlling the reaction conditions (temperature, stirring speed, and time), the chemical reaction between the surface active groups of the nano-silica and the reactive functional groups in the polyurethane prepolymer is promoted. Compared to physical adsorption modification of the nano-silica binder by polyurethane prepolymer, this method has higher stability.

[0018] Furthermore, in step S10, the average particle size of the nano-silica powder is 50 nm.

[0019] Furthermore, in step S10, the weight ratio of the nano-silica powder to the solvent is 2:3.

[0020] Furthermore, in step S30, the product is washed with anhydrous ethanol, filtered by suction, and dried at 60°C.

[0021] The second aspect of the present invention is to provide a method for preparing an inorganic thermal control white paint, the implementation process of which is: mixing the modified nano-silica sol with the white pigment, two-dimensional flaky filler, dispersant, defoaming agent, and solvent in the above-mentioned weight ratio, and fully dispersing them using a high-speed stirrer to obtain an inorganic thermal control coating.

[0022] The third aspect of the present invention is to provide a method for forming a coating on an aerospace metal substrate, which is implemented by spraying the above-mentioned inorganic thermal control coating on the surface of the aerospace metal substrate and thermally curing it to obtain an aerospace inorganic thermal control coating with excellent adhesion to the metal substrate.

[0023] Furthermore, the aerospace metal substrate is a magnesium alloy substrate, an aluminum alloy substrate or a titanium alloy substrate.

[0024] Furthermore, spraying was performed using a spray gun with a nozzle diameter of 1.0 mm, an air pressure of 2 atm, a spraying distance of 20 cm, and 5 spraying passes.

[0025] Furthermore, the thermal curing process is: thermal curing at a temperature of 80° C. for 12 hours.

[0026] Compared with the prior art, the present invention has the following beneficial effects:

[0027] In this invention, a nanosilica sol modified by chemical bonding with a polyurethane prepolymer is used as the matrix for the inorganic thermal control coating. This promotes a chemical reaction between the surface active groups of the nanosilica and the reactive functional groups in the polyurethane prepolymer. Compared to methods where the polyurethane prepolymer is modified by physical adsorption onto the nanosilica binder, this method offers greater stability.

[0028] The isocyanate groups (-NCO) in the polyurethane prepolymer are activated under heating and undergo a condensation reaction with the hydroxyl groups (-OH) on the surface of the nanosilica, forming urethane bonds (-NHCOO-). These urethane bonds anchor the polyurethane chains to the nanosilica surface, creating a "core-shell" structure. The silica serves as the "core" at the rigid end, while the polyurethane segments serve as the "shell" at the flexible end. The steric hindrance of the polyurethane chains prevents the silica nanoparticles from agglomerating, allowing for uniform dispersion. Furthermore, the flexibility of the polyurethane chains imparts elasticity to the coating. When subjected to external forces, the chain segments move to disperse stress, preventing brittle cracking.

[0029] The surface of the two-dimensional flaky filler is rich in hydroxyl groups or polar groups, which can be combined with the ester groups in the polyurethane chain through hydrogen bonds or van der Waals forces. At the same time, the polyurethane segments can be interspersed in the interlayer gaps of the two-dimensional flaky filler, forming a physical interlaced network structure with the modified silica. When the coating is subjected to external forces, the flaky filler absorbs energy through slip and interlayer shear, while the elastic segments of the modified silica disperse stress through deformation. When the content of the two-dimensional flaky filler is too low, the filler cannot form a continuous reinforced network structure and the stress dispersion ability is weak; when the content is too high, the filler agglomerates, resulting in a decrease in the density of the coating, increased light scattering, and a weakening of the interfacial bonding force.

[0030] Through the synergistic effect of polyurethane prepolymer-modified nano-silica and two-dimensional flaky fillers, a composite structure of "elastic chain segments + rigid skeleton" of the coating is constructed, which jointly inhibits the expansion of cracks in the coating, improves the coating's crack resistance, and breaks through the bottleneck of traditional inorganic coatings with strong rigidity and poor adhesion.

[0031] The present invention provides a new inorganic thermal control coating, a thermally controlled inorganic white paint that can be directly thermally cured to bond with aerospace metal substrates, exhibiting strong adhesion. This eliminates the need, in the prior art, to pretreat the metal substrate (e.g., polishing, sandblasting, etc.) to ensure adhesion when spraying the thermally controlled inorganic white paint onto aerospace metal substrates to form a coating. This simplifies the process flow and reduces production costs. Traditional pretreatment steps are not only time-consuming and labor-intensive, but may also cause damage or deformation to the metal substrate. However, the present invention, through the introduction of modified nano-silica adhesives and two-dimensional flaky fillers, achieves direct and strong bonding between the coating and the metal substrate, eliminating the need for additional pretreatment steps. This simplified process flow effectively improves production efficiency. Furthermore, the elimination of pretreatment steps also reduces the requirements for the production environment and equipment, further reducing production costs and energy consumption. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1This is the integrating sphere reflectivity spectrum of the inorganic thermal control coating in Example 1 of the present invention in the visible light-near infrared band of 0.2-2 μm;

[0033] Figure 2 This is the infrared reflectivity spectrum of the inorganic thermal control coating in Example 1 of the present invention in the mid-to-far infrared band of 2.5-20 μm;

[0034] Figure 3 This is an optical photograph of the coating adhesion tested on a smooth aluminum alloy substrate surface using the cross-grid method in Example 1 of the present invention;

[0035] Figure 4 This is an optical photograph of the smooth aluminum alloy substrate after thermal curing treatment in Comparative Example 1 of the present invention;

[0036] Figure 5 This is an optical photograph of the smooth aluminum alloy substrate after thermal curing treatment in Comparative Example 2 of the present invention. DETAILED DESCRIPTION

[0037] The following description is provided in the context of specific applications and their requirements to enable those skilled in the art to make and use the present application. It will be apparent to those skilled in the art that various modifications may be made to the disclosed embodiments, and that the general principles defined herein may be applied to other embodiments and application scenarios without departing from the principles and scope of the present application. Therefore, the present application is not limited to the described embodiments, but should be accorded the broadest scope consistent with the claims.

[0038] It should be understood that the expression "one or more of" includes individually each of the items recited after the expression and various combinations of two or more of the recited items, unless otherwise apparent from the context and usage. The expression "and / or" in conjunction with three or more recited items should be understood to have the same meaning, unless otherwise apparent from the context.

[0039] The terms "comprising", "having" or "containing", including their grammatical synonyms, should generally be understood as open and non-restrictive, e.g., not excluding other unrecited elements or steps, unless otherwise specifically stated or understood from the context.

[0040] It should be understood that the order of steps or the order in which certain actions are performed are not important as long as the present invention remains operable. Additionally, two or more steps or actions may be performed simultaneously.

[0041] The use of any and all examples or exemplary language, such as "such as" or "including," herein is intended merely to better illustrate the invention and does not limit the scope of the invention unless otherwise claimed. No language in this specification should be construed as indicating any non-claimed element as essential to the practice of the invention.

[0042] The invention provides an inorganic thermal control coating. The raw materials of the inorganic thermal control coating include, by weight, 25%-40% of modified nano-silica sol, 25%-40% of white pigment, 5%-12% of two-dimensional flaky filler, 2.5%-6% of dispersant, 0.5%-1.5% of defoamer, and the balance of solvent.

[0043] Example 1

[0044] Preparation of modified nano-silica sol:

[0045] Disperse 50 g of nano-silica powder with an average size of 50 nm in 75 g of anhydrous ethanol and stir at 1200 rpm for 5 hours to obtain a nano-silica suspension with a mass fraction of 40%;

[0046] 100 g of nano-silica suspension and 10 g of polyurethane prepolymer were weighed and mixed, and stirred at 60°C for 5 hours at a stirring rate of 300 rpm. The polyurethane prepolymer had a functionality of 2 and a molecular weight of 5000 g / mol.

[0047] After the reaction is completed, the product is washed with anhydrous ethanol, filtered, and dried at 60°C to obtain modified nano-silica;

[0048] Weigh 40g of modified nano-silica powder, redisperse it in 60g of anhydrous ethanol, and stir at 1200rpm for 5 hours to obtain a modified nano-silica suspension with a mass fraction of 40%, which is used as the coating matrix;

[0049] Preparation of inorganic thermal control coatings:

[0050] In the coating matrix, white pigment zinc oxide, two-dimensional sheet material boron nitride, dispersant polyacrylate, defoamer polydimethylsiloxane and solvent anhydrous ethanol were added in sequence. The mass of each component was 30g of silica binder, 40g of zinc oxide, 8g of boron nitride, 3g of polyacrylate, 1g of polydimethylsiloxane and 18g of anhydrous ethanol. The mixture was stirred at 1500 rpm for 5 hours to obtain an inorganic thermal control coating.

[0051] Formation of inorganic thermal control coatings on aerospace metal substrates:

[0052] The inorganic thermal control coating prepared in Step 5 was sprayed onto a smooth aluminum alloy metal substrate. Five coats were applied using a 1.0 mm nozzle diameter, 2 atm air pressure, and a spray distance of 20 cm. The coating was then thermally cured at 80°C for 12 hours, resulting in a final coating thickness of 120 μm.

[0053] The inorganic thermal control coating has a solar absorption ratio of 0.13 in the 200~2000nm band, an infrared emissivity of 0.91 in the 2.5~20um band, and an adhesion grade of 1.

[0054] Example 2

[0055] Preparation of modified nano-silica sol:

[0056] Disperse 50 g of nano-silica powder with an average particle size of 50 nm in 50 g of isopropanol and stir at 1200 rpm for 5 hours to obtain a nano-silica suspension with a mass fraction of 50%;

[0057] 100 g of nano-silica suspension and 10 g of polyurethane prepolymer were weighed and mixed, and stirred at 60°C for 5 hours at a stirring rate of 300 rpm. The polyurethane prepolymer had a functionality of 3 and a molecular weight of 8000 g / mol.

[0058] After the reaction is completed, the product is washed with anhydrous ethanol, filtered, and dried at 60°C to obtain modified nano-silica;

[0059] 50 g of modified nano-silica powder was weighed, redispersed in 50 g of isopropanol, and stirred at 1200 rpm for 5 hours to obtain a modified nano-silica sol with a mass fraction of 50%, which was used as a coating matrix.

[0060] Preparation of inorganic thermal control coatings:

[0061] In the coating matrix, white pigment zinc oxide, two-dimensional sheet material boron nitride, dispersant polyacrylate, defoamer polydimethylsiloxane and solvent anhydrous ethanol were added in sequence. The mass of each component was 35g of silica binder, 40g of zinc oxide, 8g of boron nitride, 3g of polyacrylate, 1g of polydimethylsiloxane and 13g of isopropyl alcohol. The mixture was stirred at 1500 rpm for 5 hours to obtain an inorganic thermal control coating.

[0062] Formation of inorganic thermal control coatings on aerospace metal substrates:

[0063] The prepared inorganic thermal control coating was sprayed onto a smooth magnesium alloy metal substrate. Six coats were applied using a 1.0 mm nozzle diameter, 2 atm air pressure, and a 20 cm spray distance. The coating was then thermally cured at 80°C for 12 hours, resulting in a final coating thickness of 140 μm.

[0064] In this embodiment, the inorganic thermal control coating has a solar absorption ratio of 0.138 in the 200-2000 nm band, an infrared emissivity of 0.902 in the 2.5-20 μm band, and an adhesion level of 0.

[0065] Example 3

[0066] Preparation of modified nano-silica sol:

[0067] Disperse 50 g of nano-silica powder with an average particle size of 50 nm in 75 g of anhydrous ethanol and stir at 1200 rpm for 5 hours to obtain a nano-silica suspension with a mass fraction of 40%;

[0068] 100 g of nano-silica suspension and 10 g of polyurethane prepolymer were weighed and mixed, and stirred at 60°C for 5 hours at a stirring rate of 300 rpm. The polyurethane prepolymer had a functionality of 2 and a molecular weight of 5000 g / mol.

[0069] After the reaction is completed, the product is washed with anhydrous ethanol, filtered, and dried at 60°C to obtain modified nano-silica;

[0070] Weigh 40 g of modified nano-silica powder, redisperse it in 60 g of anhydrous ethanol, and stir at 1200 rpm for 5 hours to obtain a modified nano-silica sol with a mass fraction of 40%, which is used as the coating matrix;

[0071] Preparation of inorganic thermal control coatings:

[0072] In the coating matrix, white pigment zinc oxide, two-dimensional sheet material boron nitride, dispersant polyacrylate, defoamer polydimethylsiloxane and solvent anhydrous ethanol were added in sequence. The mass of each component was 35g of silica binder, 40g of zinc oxide, 5g of mica powder, 3g of polyacrylate, 1g of polydimethylsiloxane and 16g of anhydrous ethanol. The mixture was stirred at 1500 rpm for 5 hours to obtain an inorganic thermal control coating.

[0073] Formation of inorganic thermal control coatings on aerospace metal substrates:

[0074] The prepared inorganic thermal control coating was sprayed onto a smooth aluminum alloy metal substrate. Five coats were applied using a 1.0 mm nozzle diameter, 2 atm air pressure, and a spray distance of 20 cm. The coating was then thermally cured at 80°C for 12 hours.

[0075] In this embodiment, the inorganic thermal control coating has a solar absorption ratio of 0.133 in the 200-2000 nm band, an infrared emissivity of 0.913 in the 2.5-20 μm band, and an adhesion level of 1.

[0076] Example 4

[0077] Preparation of modified nano-silica sol:

[0078] Disperse 50 g of nano-silica powder with an average particle size of 50 nm in 75 g of anhydrous ethanol and stir at 1200 rpm for 5 hours to obtain a nano-silica suspension with a mass fraction of 40%;

[0079] 100 g of nano-silica suspension and 10 g of polyurethane prepolymer were weighed and mixed, and stirred at 60°C for 5 hours at a stirring rate of 300 rpm. The polyurethane prepolymer had a functionality of 2 and a molecular weight of 5000 g / mol.

[0080] After the reaction is completed, the product is washed with anhydrous ethanol, filtered, and dried at 60°C to obtain modified nano-silica;

[0081] Weigh 40 g of modified nano-silica powder, redisperse it in 60 g of anhydrous ethanol, and stir at 1200 rpm for 5 hours to obtain a modified nano-silica sol with a mass fraction of 40%, which is used as the coating matrix;

[0082] Preparation of inorganic thermal control coatings:

[0083] In the coating matrix, white pigment zinc oxide, two-dimensional sheet material boron nitride, dispersant polyacrylate, defoamer polydimethylsiloxane and solvent anhydrous ethanol were added in sequence. The mass of each component was 30g of silica binder, 40g of zinc oxide, 8g of boron nitride, 3g of polyacrylate, 1g of polydimethylsiloxane and 18g of anhydrous ethanol. The mixture was stirred at 1500 rpm for 5 hours to obtain an inorganic thermal control coating.

[0084] Formation of inorganic thermal control coatings on aerospace metal substrates:

[0085] The prepared inorganic thermal control coating was sprayed onto a smooth titanium alloy metal substrate. Three passes were applied using a 1.0 mm nozzle diameter, 2 atm air pressure, and a spray distance of 20 cm. The coating was then thermally cured at 80°C for 12 hours, resulting in a final coating thickness of 100 μm.

[0086] In this embodiment, the inorganic thermal control coating has a solar absorption ratio of 0.143 in the 200-2000 nm band, an infrared emissivity of 0.905 in the 2.5-20 μm band, and an adhesion level of 0.

[0087] The test methods for the solar absorption ratio, infrared emissivity, and adhesion level in Examples 1 to 4 are described in the following experimental examples.

[0088] Experimental example:

[0089] The coating formed on the aerospace metal substrate was subjected to solar absorption ratio test experiments, infrared emissivity test experiments, and coating adhesion test experiments.

[0090] 1. The solar absorption ratio test method is the spectral reflectance method in the national standard (GJB 2502.3-2015), and the test band is 200~2000nm.

[0091] The infrared emissivity test experimental method is: the steady-state calorimeter method in the national standard (GJB 2502.3-2015), and the test band is 2.5~20um.

[0092] The coating adhesion test method is the scratching method.

[0093] The test conditions are as follows:

[0094] The average particle size of the nano-silica powder is 50 nm; the functionality of the polyurethane prepolymer is 2 and the molecular weight is 5000 g / mol;

[0095] Test sample preparation method:

[0096] Coating Preparation Method: The prepared coating was sprayed onto a smooth titanium alloy substrate (roughness Ra: 0.9-1.6 μm). Three passes were applied using a 1.0 mm nozzle diameter, 2 atm air pressure, and a spray distance of 20 cm. The coating was then thermally cured at 80°C for 12 hours, resulting in a final coating thickness of 100 μm.

[0097] (2) Preparation method of nano-silica sol: Weigh 40g of nano-silica powder, disperse it in 60g of anhydrous ethanol, and stir it at 1200rpm for 5 hours to obtain a nano-silica sol with a mass fraction of 40%, which is used as the coating matrix.

[0098] The experimental results are as follows:

[0099] Table 1: Effects of different coating compositions on the solar absorption ratio, emissivity and adhesion of the coating.

[0100]

[0101] As shown in Table 1, when the base material is a chemically bonded modified nano-silica sol, its solar absorption ratio is significantly lower than that of the physically modified nano-silica sol, and its infrared emissivity is higher. The solar absorption ratio means that the coating can emit more solar radiation and reduce heat absorption. The high infrared emissivity means that the coating can quickly dissipate the heat generated by the equipment in the form of infrared radiation. Therefore, chemically modified nano-silica sol is better at regulating temperature than physically modified nano-silica sol. In addition, chemically modified nano-silica has stronger adhesion than physically modified nano-silica. When the base material is an ordinary nano-silica sol, it is impossible to form a complete coating on the titanium alloy substrate by spraying. The coating cracks and cannot be applied, and the solar absorption and infrared emissivity cannot be accurately measured.

[0102] Table 1 shows that two-dimensional fillers (boron nitride, mica powder, kaolin, and talc) exhibit stronger adhesion than one-dimensional fillers (glass fiber) and three-dimensional fillers (hollow glass microspheres and calcium carbonate). This is because one-dimensional fillers tend to generate stress concentration at their ends, making it difficult to form a uniform reinforcement network. Fiber breakage can lead to rapid crack propagation. Three-dimensional fillers, on the other hand, lack in-plane reinforcement, have a smaller interfacial bonding area with the substrate, and suffer from low stress transfer efficiency. Two-dimensional plate-like fillers have a layered structure, with weak van der Waals forces between the layers. Under external forces, the layers can slip and shear, dissipating stress through friction and interfacial energy dissipation, thus preventing stress concentration-induced crack propagation. Furthermore, two-dimensional fillers exhibit anisotropy and a large specific surface area in the in-plane direction, forming a continuous network structure within the coating and increasing the contact area with the substrate, effectively improving the coating's rigidity and deformation resistance.

[0103] Table 2: Effect of chemically modified nano-silica sol on the solar absorptivity, emissivity and adhesion of the coating.

[0104]

[0105] As shown in Table 2, when the modified nano-silica sol content is less than 25%, it is impossible to form a complete coating on the titanium alloy substrate directly by spraying. When its content exceeds 40%, the modified nano-silica sol is too high, and the zinc oxide content is relatively reduced, resulting in a decrease in optical properties, especially the solar absorption ratio, which is 0.205 and the infrared emissivity is 0.885.

[0106] When the modified nano-silica is dissolved to about 30%, its usage is small, the cost is low, the solar absorption ratio is relatively low, the infrared emissivity is relatively high, and the adhesion is strong.

[0107] Table 3: Effect of boron nitride on coating solar absorptivity, emissivity and adhesion.

[0108]

[0109] Table 3 shows that when the boron nitride content is less than 5%, it is impossible to form a complete coating directly on the titanium alloy substrate by spraying. When its content exceeds 12%, the coating adhesion is significantly reduced. When the modified nano-silica content is around 8%, its dosage is small, the cost is low, the solar absorption ratio is relatively low, the infrared emissivity is relatively high, and the adhesion is strong.

[0110] Table 4: Effect of zinc oxide on the solar absorptivity, emissivity and adhesion of the coating.

[0111]

[0112] Table 4 shows that when the zinc oxide content is less than 25%, its infrared emissivity is low, its solar absorptivity is high, and its temperature regulation ability is poor. When the content exceeds 40%, the coating adhesion is significantly reduced. When the zinc oxide content is around 40%, its solar absorptivity is relatively low, its infrared emissivity is relatively high, and its adhesion is strong. Table 5: Effect of polyacrylate on the solar absorptivity, emissivity, and adhesion of the coating.

[0113]

[0114] Table 5 shows that when the polyacrylate content is less than 2.5%, it is impossible to form a complete coating directly on the titanium alloy substrate by spraying. When the content exceeds 6%, the coating adhesion is significantly reduced. When the polyacrylate content is around 3%, its solar absorption ratio is relatively low, the infrared emissivity is relatively high, and the adhesion is strong.

[0115] Table 6: Effect of polydimethylsiloxane on the solar absorptivity, emissivity and adhesion of coatings.

[0116]

[0117] As can be seen from Table 6 and Table 5, when the polydimethylsiloxane content is less than 0.5%, the coating adhesion is significantly reduced. When the content exceeds 1.5%, the coating adhesion is also significantly reduced. When the polydimethylsiloxane content is around 13%, its solar absorption ratio is relatively low, the infrared emissivity is relatively high, and the adhesion is strong.

[0118] It is worth noting that, based on the above structural design, in order to solve the same technical problem, even if some insubstantial changes or modifications are made to the present invention, the essence of the technical solution adopted is still the same as that of the present invention, and therefore it should also be within the scope of protection of the present invention.

Claims

1. An inorganic thermal control coating, characterized in that: The raw materials include, by weight: modified nano-silica sol 25%-40%, white pigment 25%-40%, two-dimensional flake filler 5%-12%, dispersant 2.5%-6%, defoamer 0.5%-1.5%, and the balance solvent; The preparation method of modified nano-silica sol comprises the following steps: Step S10: dispersing nano-silica powder in a solvent and obtaining a uniform nano-silica suspension by high-speed stirring; Step S20: mixing the nano-silica suspension with the polyurethane prepolymer solution to allow the polyurethane prepolymer to fully react with the active sites on the surface of the nano-silica to form modified nano-silica; Step S30: After the reaction in step S20 is completed, the product is washed, filtered, and dried to obtain modified nano-silica; Step S40: Re-dispersing the modified nano-silica in the solvent, and obtaining a uniform modified nano-silica sol by high-speed stirring.

2. The inorganic thermal control coating according to claim 1, characterized in that: The solvent is ethanol, isopropanol or acetone.

3. The inorganic thermal control coating according to claim 1, characterized in that: The white pigment is one or more of zinc oxide, titanium dioxide and zirconium dioxide.

4. The inorganic thermal control coating according to claim 1, characterized in that: The two-dimensional flake filler is boron nitride, mica powder, kaolin or talc.

5. The inorganic thermal control coating according to claim 1, characterized in that: The dispersant is polyacrylate or polymethyl methacrylate.

6. The inorganic thermal control coating according to claim 1, characterized in that: The defoaming agent is polydimethylsiloxane or polyether polysiloxane.

7. The inorganic thermal control coating according to claim 1, characterized in that: The preparation method of modified nano-silica sol comprises the following steps: Step S10: Nano-silica powder is dispersed in a solvent, with a weight ratio of nano-silica powder to solvent of 2:3; a uniform nano-silica suspension is obtained by high-speed stirring at a stirring rate of 1200 rpm for 5 hours; Step S20: mixing the nano-silica suspension and the polyurethane prepolymer solution in a weight ratio of 10:1, stirring and reacting at 60° C. for 5 hours at a stirring rate of 300 rpm; allowing the polyurethane prepolymer to fully react with the active sites on the surface of the nano-silica to form modified nano-silica; Step S30: After the reaction in step S20 is completed, the product is washed, filtered, and dried to obtain modified nano-silica; Step S40: Re-dispersing the modified nano-silica in the solvent, with the weight ratio of the modified nano-silica to the solvent being 2:3; obtaining a uniform modified nano-silica sol by high-speed stirring, with a stirring rate of 1200 rpm and a stirring time of 5 h.

8. The inorganic thermal control coating according to claim 7, characterized in that: In step S10, the average particle size of the nano-silica powder is 50 nm.

9. A method for forming a coating of an inorganic thermal control coating on an aerospace metal substrate, characterized in that: The inorganic thermal control coating according to any one of claims 1 to 8 is sprayed on the surface of an aerospace metal substrate and thermally cured to obtain an aerospace inorganic thermal control coating adhered to the metal substrate.

10. The method for forming a coating on an aerospace metal substrate using an inorganic thermal control coating according to claim 9, characterized in that: The spray gun was used for spraying, the nozzle diameter of the spray gun was 1.0 mm, the air pressure was 2 atm, and the spraying distance was 20 cm; The thermal curing process is: thermal curing at a temperature of 80°C for 12 hours.

Images