Inorganic thermal control coating and method for forming coating on spaceflight metal substrate by using inorganic thermal control coating

Abstract

The invention discloses an inorganic thermal control coating and a method for forming a coating on a spaceflight metal substrate by using the inorganic thermal control coating, and relates to the technical field of new materials. The inorganic thermal control coating comprises the following raw materials in percentage by weight: 25%-40% of modified nano silicon dioxide sol, 25%-40% of white pigment, 5%-12% of two-dimensional flaky filler, 2.5%-6% of a dispersing agent, 0.5%-1.5% of a defoaming agent and the balance of a solvent. The method for forming the coating on the spaceflight metal base material by the coating comprises the following steps: spraying the inorganic thermal control coating on the surface of the spaceflight metal base material, and carrying out thermal curing. The coating disclosed by the invention can be directly sprayed onto a metal base material for aerospace, the metal base material does not need to be pretreated, the situation that the metal base material deforms during pretreatment and influences the stability of equipment is avoided, and meanwhile, the processing difficulty is lower due to the fact that the coating is directly sprayed without pretreatment.

Description

Technical Field

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

[0002] In the thermal control system of spacecraft, the paint-type thermal control white paint plays a crucial role. Through its unique thermal radiation and reflection properties, this type of paint effectively regulates the temperature of the spacecraft surface, ensuring the stable operation of the spacecraft in an extreme temperature difference environment. Compared with traditional thermal control means, the paint-type thermal control white paint has the advantages of light weight, convenient construction, strong adaptability, etc., and has become an important part of modern aerospace thermal control technology. In the paint-type thermal control white paint, it can usually be divided into organic thermal control white paint and inorganic thermal control white paint according to the weight of the binder used. In contrast, inorganic white paint shows unique advantages in the field of aerospace thermal control due to its excellent heat resistance, radiation resistance, and long-term stability. Inorganic white paint can withstand the extreme temperature changes of the spacecraft in the space environment and the radiation of cosmic rays for a long time, ensuring the long-term reliable operation of the spacecraft thermal control system.

[0003] However, the inorganic thermal control white paint also faces many challenges in the actual construction process. Due to its strong rigidity, poor flexibility, and different thermal expansion coefficients from the commonly used metal substrates in the aerospace field (such as titanium alloy, aluminum matrix silicon carbide, etc.), the bonding force between the inorganic white paint and the metal substrate is weak. In order to improve the bonding force between the inorganic white paint and the metal substrate, it is usually necessary to perform surface roughening treatment on the metal substrate, such as metal grinding or sandblasting, to ensure that the inorganic white paint can firmly adhere to the substrate surface. This treatment usually requires the surface roughness Ra of the metal substrate to be not less than 3.2 to provide sufficient mechanical biting force. However, for metal substrates with high hardness, such as titanium alloy and aluminum matrix silicon carbide, the difficulty of surface roughening treatment increases significantly. These materials not only have high hardness but also strong wear resistance, making it difficult for traditional roughening treatment methods to achieve the ideal treatment effect. At the same time, for some soft metal substrates, such as magnesium alloy, roughening treatment methods such as sandblasting may cause deformation of the substrate, thus affecting the overall performance and structural stability of the spacecraft. Summary of the Invention

[0004] The 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 to metal substrates in the prior art.

[0005] To achieve the above object, the technical solution adopted by the present invention is as follows: An inorganic thermal control coating, the raw materials of which by weight ratio include: 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.

[0006] Further, the solvent is ethanol, isopropanol or acetone.

[0007] Further, the white pigment is one or more of zinc oxide, titanium dioxide and zirconium dioxide.

[0008] Further, the two-dimensional flaky filler has excellent mechanical properties and wettability, and it is boron nitride, mica powder, kaolin or talc powder.

[0009] Further, the dispersant is polyacrylate or polymethyl methacrylate.

[0010] Further, the defoamer is polydimethylsiloxane or polyether polysiloxane.

[0011] Further, the preparation method of the modified nano-silica sol includes the following steps: Step S10: Disperse nano-silica powder in a solvent, and the weight ratio of nano-silica powder to the solvent is 2:3; obtain a uniform nano-silica suspension by high-speed stirring, with a stirring rate of 1200 rpm and a stirring time of 5 h; Step S20: Mix the nano-silica suspension and the polyurethane prepolymer solution in a weight ratio of 10:1, and stir and react at 60°C for 5 h, with a stirring rate of 300 rpm; make the polyurethane prepolymer fully react with the active sites on the surface of nano-silica to form modified nano-silica; Step S30: After the reaction in step S02 is completed, wash, filter and dry the product to obtain modified nano-silica.

[0012] Step S40: Redisperse the modified nano-silica in a solvent, and the weight ratio of modified nano-silica to the solvent is 2:3; obtain a uniform modified nano-silica sol by high-speed stirring, with a stirring rate of 1200 rpm and a stirring time of 5 h.

[0013] In the present invention, polyurethane prepolymer is used to carry out chemical bonding modification on nano-silica. By strictly controlling the reaction conditions (temperature, stirring speed and time), the chemical reaction between the surface active groups of nano-silica and the reactive functional groups in the polyurethane prepolymer is promoted. Compared with the physical adsorption modification method of polyurethane prepolymer on nano-silica adhesive, it has higher stability.

[0014] Further, in step S10, the average particle size of the nano-silica powder is 50 nm.

[0015] Further, in step S10, the weight ratio of the nano-silica powder to the solvent is 2:3.

[0016] Further, in step S30, the product is washed with absolute ethanol, the filtration method is suction filtration, and the drying temperature is 60 °C.

[0017] The second aspect of the present invention lies in providing a preparation method of an inorganic thermal control white paint, and the implementation process is as follows: mixing the modified nano-silica sol with white pigment, two-dimensional flaky filler, dispersant, defoamer, and solvent according to the above weight ratio, and fully dispersing them by using a high-speed stirrer to obtain an inorganic thermal control coating.

[0018] The third aspect of the present invention lies in providing a method for forming a coating on an aerospace metal substrate with the coating, and the implementation process is as follows: spraying the above inorganic thermal control coating on the surface of the aerospace metal substrate and performing thermal curing to obtain an aerospace inorganic thermal control coating with excellent adhesion to the metal substrate.

[0019] Further, the aerospace metal substrate is a magnesium alloy substrate, an aluminum alloy substrate, or a titanium alloy substrate.

[0020] Further, spray gun spraying is adopted, the nozzle diameter of the spray gun is 1.0 mm, the air pressure is 2 atm, the spraying distance is 20 cm, and spraying is performed 5 times.

[0021] Further, the thermal curing process is: thermal curing for 12 h at a temperature of 80 °C.

[0022] Compared with the prior art, the present invention has the following beneficial effects: In the present invention, the modified nano-silica sol chemically bonded by the polyurethane prepolymer is used as the matrix of the inorganic thermal control coating to promote the chemical reaction between the surface active groups of nano-silica and the reactive functional groups in the polyurethane prepolymer. Compared with the physical adsorption modification method of the nano-silica binder by the polyurethane prepolymer, it has higher stability.

[0023] The isocyanate groups (-NCO) in the polyurethane prepolymer are activated under heating conditions and undergo a condensation reaction with the hydroxyl groups (-OH) on the surface of nano-silica to form urethane bonds (-NHCOO-). The polyurethane chains are anchored on the surface of nano-silica through the formed urethane bonds, forming a "core-shell" structure. Among them, silica acts as the "core" and belongs to the rigid end, while the polyurethane chain segment acts as the "shell" and belongs to the flexible end. On the one hand, the steric hindrance effect of the polyurethane chains can prevent the aggregation of silica nanoparticles, enabling them to be evenly dispersed; on the other hand, the flexibility of the polyurethane chains endows the coating with elasticity. When subjected to external forces, the stress of the coating is dispersed through the movement of the chain segments, avoiding brittle cracking of the coating.

[0024] The surface of two-dimensional flaky fillers is rich in hydroxyl groups or polar groups, which can bind to the ester groups in the polyurethane chains through hydrogen bonds or van der Waals forces. At the same time, the polyurethane chain segments can penetrate into the interlayer voids of the two-dimensional flaky fillers, forming a physical interpenetrating network structure with the modified silica. When the coating is subjected to external forces, the flaky fillers absorb energy through slip and interlayer shear, while the elastic chain segments of the modified silica disperse the stress through deformation. When the content of the two-dimensional flaky fillers is too low, the fillers cannot form a continuous reinforcing network structure, and the stress dispersion ability is weak; when the content is too high, the fillers agglomerate, resulting in a decrease in the denseness of the coating, an increase in light scattering, and a weakening of the interfacial bonding force at the same time.

[0025] Through the synergistic effect of nano-silica modified by polyurethane prepolymer and two-dimensional flaky fillers, a composite structure of "elastic chain segments + rigid skeleton" of the coating is constructed to jointly inhibit the crack propagation of the coating and improve the crack resistance of the coating, breaking through the bottleneck of traditional inorganic coatings with strong rigidity and poor adhesion.

[0026] In the present invention, a new inorganic thermal control coating is provided. This coating is a thermal control inorganic white paint, which can be directly thermally cured and combined with aerospace metal substrates with strong adhesion. Thus, in the prior art, when spraying the thermal control inorganic white paint on the aerospace metal substrate to form a coating, in order to ensure the adhesion effect, the steps of pre-treating the metal substrate (such as grinding, sandblasting, etc.) are also required. Thereby, the process flow is simplified and the production cost is reduced. The traditional pre-treatment steps are not only time-consuming and laborious, but may also cause certain damage or deformation to the metal substrate. However, in the present invention, through the introduction of modified nano-silica adhesives and two-dimensional flaky fillers, a direct and firm combination of the coating and the metal substrate is achieved without additional pre-treatment steps. This simplified process flow effectively improves the production efficiency. At the same time, due to the reduction of the pre-treatment steps, the requirements for the production environment and equipment are also reduced, further reducing the production cost and energy consumption. Description of the Drawings

[0027] Figure 1It is the integrating sphere reflectance spectrum of the inorganic thermal control coating in the 0.2 - 2μm visible - near infrared band in Embodiment 1 of the present invention; Figure 2 It is the infrared reflectance spectrum of the inorganic thermal control coating in the 2.5 - 20μm mid - far infrared band in Embodiment 1 of the present invention; Figure 3 It is the optical photograph after the cross - cut test of the coating adhesion on the surface of the smooth aluminum alloy substrate in Embodiment 1 of the present invention; Figure 4 It is the optical photograph after the heat - curing treatment on the surface of the smooth aluminum alloy substrate in Comparative Example 1 of the present invention; Figure 5 It is the optical photograph after the heat - curing treatment on the surface of the smooth aluminum alloy substrate in Comparative Example 2 of the present invention. Detailed implementation manners

[0028] The following description is provided in the context of a particular application and its requirements, by which those skilled in the art can make and use this application. For those of ordinary skill in the art, it is obvious that various changes can be made to the disclosed embodiments, and without departing from the principles and scope of this application, the general principles defined in this application can be applied to other embodiments and application scenarios. Therefore, this application is not limited to the described embodiments, but should be given the broadest scope consistent with the claims.

[0029] It should be understood that the expression “one or more of...” individually includes each of the objects recited after the expression and various different combinations of two or more of the recited objects, unless otherwise understood from the context and usage. The expression “and / or” in combination with three or more recited objects should be understood to have the same meaning, unless otherwise understood from the context.

[0030] The terms “comprising”, “having” or “containing”, including the use of their grammatical synonyms, should generally be understood as open - ended and non - restrictive, for example, not excluding other unrecited elements or steps, unless otherwise specifically stated or understood from the context.

[0031] It should be understood that as long as the present invention is still operable, the order of steps or the order of performing certain actions is not important. In addition, two or more steps or actions can be performed simultaneously.

[0032] The use of any and all examples or exemplary language such as “for example” or “including” in this document is only intended to better illustrate the present invention and does not limit the scope of the present invention unless a claim is made. No language in this specification should be construed as indicating that any unclaimed element is essential for the practice of the present invention.

[0033] The present invention provides an inorganic thermal control coating, and its raw materials include, by weight ratio: 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.

[0034] Example 1 Prepare modified nano-silica sol: Disperse 50 g of nano-silica powder with an average size of 50 nm into 75 g of absolute ethanol, and stir at 1200 rpm for 5 hours to obtain a nano-silica suspension with a mass fraction of 40%; Weigh 100 g of nano-silica suspension and 10 g of polyurethane prepolymer respectively and mix them, stir at 60 °C for 5 hours, and the stirring rate is 300 rpm, where the functionality of the polyurethane prepolymer is 2 and the molecular weight is 5000 g / mol; After the reaction is completed, wash with absolute ethanol, filter by suction and then dry at 60 °C to obtain modified nano-silica; Weigh 40 g of modified nano-silica powder, redisperse it in 60 g of absolute ethanol, and stir at 1200 rpm for 5 hours to obtain a modified nano-silica suspension with a mass fraction of 40% as the coating matrix; Prepare inorganic thermal control coating: In the coating matrix, sequentially add white pigment zinc oxide, two-dimensional flaky material boron nitride, dispersant polyacrylate, defoamer polydimethylsiloxane and solvent absolute ethanol. The masses of each component are 30 g of silica binder, 40 g of zinc oxide, 8 g of boron nitride, 3 g of polyacrylate, 1 g of polydimethylsiloxane, and 18 g of absolute ethanol. Stir at 1500 rpm for 5 hours to obtain an inorganic thermal control coating; Form an inorganic thermal control coating on the aerospace metal substrate: Spray the inorganic thermal control coating prepared in step 5 on the metal substrate. The metal substrate is selected as an aluminum alloy substrate with a smooth surface. During spraying, the nozzle diameter of the spray gun is 1.0 mm, the air pressure is 2 atm, the spraying distance is 20 cm, and spray 5 times. Then thermally cure at 80 °C for 12 hours, and the finally prepared coating thickness is 120 μm.

[0035] The solar absorptance of the inorganic thermal control coating in the 200-2000 nm band is 0.13, the infrared emissivity in the 2.5-20 μm band is 0.91, and the adhesion grade is grade 1.

[0036] Example 2 Prepare modified nano-silica sol: Disperse 50 g of nano-silica powder with an average particle size of 50 nm into 50 g of isopropanol, and stir at 1200 rpm for 5 hours to obtain a nano-silica suspension with a mass fraction of 50%; Weigh 100 g of the nano-silica suspension and 10 g of the polyurethane prepolymer respectively and mix them. Stir at 60 °C for 5 hours with a stirring rate of 300 rpm. The functionality of the polyurethane prepolymer is 3 and the molecular weight is 8000 g / mol; After the reaction is completed, wash with absolute ethanol, filter by suction and then dry at 60 °C to obtain modified nano-silica; Weigh 50 g of the modified nano-silica powder, redisperse it in 50 g of isopropanol, and stir at 1200 rpm for 5 hours to obtain a modified nano-silica sol with a mass fraction of 50%, which is used as the coating matrix.

[0037] Prepare an inorganic thermal control coating: In the coating matrix, sequentially add white pigment zinc oxide, two-dimensional flaky material boron nitride, dispersant polyacrylate, defoamer polydimethylsiloxane and solvent absolute ethanol. The masses of each component are 35 g of silica binder, 40 g of zinc oxide, 8 g of boron nitride, 3 g of polyacrylate, 1 g of polydimethylsiloxane, and 13 g of isopropanol. Stir at 1500 rpm for 5 hours to obtain the inorganic thermal control coating; Form an inorganic thermal control coating on the aerospace metal substrate: Spray the prepared inorganic thermal control coating on the metal substrate. The metal substrate is selected as a magnesium alloy substrate with a smooth surface. When spraying, the nozzle diameter of the spray gun is 1.0 mm, the air pressure is 2 atm, the spraying distance is 20 cm, and spray 6 times. Then thermally cure at 80 °C for 12 hours, and the final thickness of the prepared coating is 140 μm.

[0038] In this example, the solar absorptance of the inorganic thermal control coating in the 200 - 2000 nm band is 0.138, the infrared emissivity in the 2.5 - 20 μm band is 0.902, and the adhesion grade is 0 grade.

[0039] Example 3 Prepare a modified nano-silica sol: Disperse 50 g of nano-silica powder with an average particle size of 50 nm into 75 g of absolute ethanol, and stir at 1200 rpm for 5 hours to obtain a nano-silica suspension with a mass fraction of 40%; Weigh 100 g of the nano-silica suspension and 10 g of the polyurethane prepolymer respectively and mix them. Stir at 60 °C for 5 hours with a stirring rate of 300 rpm. The functionality of the polyurethane prepolymer is 2 and the molecular weight is 5000 g / mol; After the reaction was completed, it was washed with absolute ethanol, filtered by suction, and then dried at 60 °C to obtain modified nano-silica; 40 g of the modified nano-silica powder was weighed and redispersed in 60 g of absolute ethanol, and stirred at 1200 rpm for 5 hours to obtain a modified nano-silica sol with a mass fraction of 40%, which was used as the coating matrix; Prepare an inorganic thermal control coating: In the coating matrix, zinc oxide as a white pigment, two-dimensional flaky boron nitride, a dispersant polyacrylate, an antifoaming agent polydimethylsiloxane, and a solvent absolute ethanol were added in sequence. The masses of each component were 35 g of silica binder, 40 g of zinc oxide, 5 g of mica powder, 3 g of polyacrylate, 1 g of polydimethylsiloxane, and 16 g of absolute ethanol. It was stirred at 1500 rpm for 5 hours to obtain an inorganic thermal control coating; Form an inorganic thermal control coating on the aerospace metal substrate: The prepared inorganic thermal control coating was sprayed on the metal substrate. The metal substrate was an aluminum alloy substrate with a smooth surface. During spraying, the nozzle diameter of the spray gun was 1.0 mm, the air pressure was 2 atm, the spraying distance was 20 cm, and it was sprayed 5 times. Then it was thermally cured at 80 °C for 12 hours respectively.

[0040] In this example, the solar absorptance of the inorganic thermal control coating in the 200 - 2000 nm band was 0.133, the infrared emissivity in the 2.5 - 20 μm band was 0.913, and the adhesion grade was 1.

[0041] Example 4 Prepare a modified nano-silica sol: 50 g of nano-silica powder with an average particle size of 50 nm was dispersed in 75 g of absolute ethanol and stirred at 1200 rpm for 5 hours to obtain a nano-silica suspension with a mass fraction of 40%; 100 g of the nano-silica suspension and 10 g of polyurethane prepolymer were weighed and mixed, and stirred at 60 °C for 5 hours with a stirring rate of 300 rpm. The functionality of the polyurethane prepolymer was 2 and the molecular weight was 5000 g / mol; After the reaction was completed, it was washed with absolute ethanol, filtered by suction, and then dried at 60 °C to obtain modified nano-silica; 40 g of the modified nano-silica powder was weighed and redispersed in 60 g of absolute ethanol, and stirred at 1200 rpm for 5 hours to obtain a modified nano-silica sol with a mass fraction of 40%, which was used as the coating matrix; Prepare an inorganic thermal control coating: In the coating matrix, zinc oxide as a white pigment, boron nitride as a two-dimensional flaky material, polyacrylate as a dispersant, polydimethylsiloxane as an antifoaming agent, and anhydrous ethanol as a solvent are added in sequence. The masses of each component are 30 g of silica binder, 40 g of zinc oxide, 8 g of boron nitride, 3 g of polyacrylate, 1 g of polydimethylsiloxane, and 18 g of anhydrous ethanol. Stir at 1500 rpm for 5 hours to obtain an inorganic thermal control coating; Form an inorganic thermal control coating on the aerospace metal substrate: Spray the prepared inorganic thermal control coating on the metal substrate. The metal substrate is selected as a titanium alloy substrate with a smooth surface. When spraying, the nozzle diameter of the spray gun is 1.0 mm, the air pressure is 2 atm, the spraying distance is 20 cm, and spray 3 times. Then thermally cure at 80 °C for 12 hours, and the finally prepared coating thickness is 100 μm.

[0042] In this example, the solar absorptance of the inorganic thermal control coating in the 200 - 2000 nm band is 0.143, the infrared emissivity in the 2.5 - 20 μm band is 0.905, and the adhesion grade is 0 grade.

[0043] The test methods for the solar absorptance, infrared emissivity, and adhesion grade in Examples 1 - 4 are as described in the following experimental example.

[0044] Experimental example: Conduct solar absorptance test experiments, infrared emissivity test experiments, and coating adhesion test experiments on the coatings formed on the aerospace metal substrate respectively.

[0045] 1. The test method for solar absorptance is the spectral reflectance method in the national standard (GJB 2502.3 - 2015), and the test band is 200 - 2000 nm.

[0046] The test method for infrared emissivity is the steady - state calorimeter method in the national standard (GJB 2502.3 - 2015), and the test band is 2.5 - 20 μm.

[0047] The test method for coating adhesion is the scratch - off method.

[0048] The test conditions are as follows: The average particle size of nano - silica powder is 50 nm; the functionality of the polyurethane prepolymer is 2, and the molecular weight is 5000 g / mol; Test sample preparation method: Coating preparation method: The prepared coating is sprayed on a smooth surface of a titanium alloy substrate (roughness Ra: 0.9 - 1.6 μm). During spraying, the nozzle diameter of the spray gun is 1.0 mm, the air pressure is 2 atm, the spraying distance is 20 cm, and it is sprayed 3 times. Then it is thermally cured at 80 °C for 12 hours, and the finally prepared coating thickness is 100 μm.

[0049] (2)Preparation method of nano-silica sol: Weigh 40 g of nano-silica powder, disperse it in 60 g of absolute ethanol, and stir it at 1200 rpm for 5 hours to obtain a nano-silica sol with a mass fraction of 40%, which is used as the coating matrix.

[0050] The experimental results are as follows: Table 1: Effects of coatings with different compositions on the solar absorptance, emissivity, and adhesion of the coating.

[0051]

[0052] From Table 1, it can be seen that when the matrix material is the nano-silica sol modified by chemical bonding, its solar absorptance is significantly lower than that of the nano-silica sol modified physically, and the infrared emissivity is higher. The solar absorptance means that the coating can emit more solar radiation and reduce heat absorption. A high infrared emissivity means that the coating can quickly dissipate the heat generated by the equipment in the form of infrared radiation. Therefore, compared with the nano-silica sol modified physically, the nano-silica sol modified chemically has a better temperature regulation performance. And the nano-silica modified chemically has stronger adhesion than the nano-silica modified physically. When the matrix material is the ordinary nano-silica sol, a complete coating cannot be formed on the titanium alloy substrate by spraying at this time, the coating cracks and cannot be applied, and the solar absorptance and infrared emissivity cannot be accurately measured.

[0053] From Table 1, it can be seen that when the filler is selected as two-dimensional fillers (boron nitride, mica powder, kaolin, talc powder) compared with one-dimensional fillers (glass fiber) and three-dimensional fillers (hollow glass microspheres, calcium carbonate), the adhesion is stronger; the reason is as follows: One-dimensional fillers are prone to stress concentration at the ends and it is difficult to form a uniform reinforcement network, and crack rapid propagation may be triggered after fiber fracture. While the spherical fillers of three-dimensional fillers lack the reinforcement ability in the plane direction, and the interfacial bonding area with the matrix is small, and the stress transfer efficiency is low. Two-dimensional flaky fillers have a layered structure and are bonded by weak van der Waals forces between layers. Under the action of external forces, slip and shear deformation can occur between the lamellae, and the stress is dispersed through friction and interfacial energy dissipation to avoid crack propagation caused by stress concentration. At the same time, two-dimensional fillers have anisotropy and a large specific surface area in the plane direction, can form a continuous network structure in the coating, and increase the contact area with the matrix, thus effectively improving the rigidity and anti-deformation ability of the coating.

[0054] Table 2: Influence of Chemically Modified Nano-Silica Sol on Solar Absorptance, Emissivity, and Adhesion of the Coating.

[0055]

[0056] As can be seen from Table 2, when the content of the modified nano-silica sol is less than 25%, a complete coating cannot be directly formed on the titanium alloy substrate by spraying. When its content exceeds 40%, with the excessive content of the modified nano-silica sol, the content of zinc oxide decreases relatively, resulting in a decline in optical properties, especially having a greater impact on the solar absorptance, with the solar absorptance being 0.205 and the infrared emissivity being 0.885.

[0057] When the modified nano-silica sol is about 30%, its dosage is small, the cost is low, the solar absorptance is relatively low, the infrared emissivity is relatively high, and the adhesion is strong.

[0058] Table 3: Influence of Boron Nitride on Solar Absorptance, Emissivity, and Adhesion of the Coating.

[0059]

[0060] As can be seen from Table 3, when the content of boron nitride is less than 5%, a complete coating cannot be directly formed on the titanium alloy substrate by spraying. When its content exceeds 12%, the adhesion of the coating decreases significantly. When the modified nano-silica sol is about 8%, its dosage is small, the cost is low, the solar absorptance is relatively low, the infrared emissivity is relatively high, and the adhesion is strong.

[0061] Table 4: Influence of Zinc Oxide on Solar Absorptance, Emissivity, and Adhesion of the Coating.

[0062]

[0063] As can be seen from Table 4, when the content of zinc oxide is less than 25%, its infrared emissivity is low, the solar absorptance is high, and the temperature regulation ability is poor. When its content exceeds 40%, the adhesion of the coating decreases significantly. When zinc oxide is about 40%, its solar absorptance is relatively low, the infrared emissivity is relatively high, and the adhesion is strong. Table 5: Influence of Polyacrylate on Solar Absorptance, Emissivity, and Adhesion of the Coating.

[0064]

[0065] As can be seen from Table 5, when the content of polyacrylate is less than 2.5%, a complete coating cannot be directly formed on the titanium alloy substrate by spraying. When its content exceeds 6%, the adhesion of the coating decreases significantly. When polyacrylate is about 3%, its solar absorptance is relatively low, the infrared emissivity is relatively high, and the adhesion is strong.

[0066] Table 6: Influence of polydimethylsiloxane on the solar absorptance, emissivity and adhesion of the coating.

[0067]

[0068] It can be seen from Table 6 that, as can be seen from Table 5, when the content of polydimethylsiloxane is less than 0.5%, the adhesion of the coating decreases significantly. When its content exceeds 1.5%, the adhesion of the coating decreases significantly. When the polydimethylsiloxane is about 13%, its solar absorptance is relatively low, the infrared emissivity is relatively high, and the adhesion is strong.

[0069] According to the above embodiments, the present invention can be well implemented. It should be noted that on the premise of the above structural design, in order to solve the same technical problems, even if some non-substantive changes or polishing are made to the present invention, the essence of the technical solution adopted is still the same as that of the present invention, so it should also be within the protection scope of the present invention.

Claims

1. An inorganic thermal control coating, characterized in that, Its raw materials include, by weight ratio: 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.

2. The inorganic thermal control coating according to claim 1, wherein, The solvent is ethanol, isopropanol or acetone.

3. An 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. An inorganic thermal control coating according to claim 1, wherein, The two-dimensional flaky filler is boron nitride, mica powder, kaolin or talc powder.

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

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

7. An inorganic thermal control coating according to claim 1, wherein The preparation method of the modified nano-silica sol includes the following steps: Step S10: Disperse nano-silica powder in the solvent, and the weight ratio of nano-silica powder to the solvent is 2:3; obtain a uniform nano-silica suspension by high-speed stirring, with a stirring rate of 1200 rpm and a stirring time of 5 h; Step S20: Mix the nano-silica suspension and the polyurethane prepolymer solution in a weight ratio of 10:1, and stir and react at 60°C for 5 h, with a stirring rate of 300 rpm; make the polyurethane prepolymer fully react with the active sites on the surface of nano-silica to form modified nano-silica; Step S30: After the reaction in Step S02 ends, wash, filter and dry the product to obtain modified nano-silica; Step S40: Redisperse the modified nano-silica in the solvent, and the weight ratio of modified nano-silica to the solvent is 2:3; obtain 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. An 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 on an aerospace metal substrate with an inorganic thermal control coating, characterized in that Spray the inorganic thermal control coating according to any one of claims 1-8 on the surface of the aerospace metal substrate, and perform thermal curing to obtain an aerospace inorganic thermal control coating attached to the metal substrate.

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

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