Wide-spectrum infrared emission transparent thermal control coating for spacecraft, preparation method of wide-spectrum infrared emission transparent thermal control coating and optical device

Abstract

The invention discloses a wide-spectrum infrared emission transparent thermal control coating for a spacecraft, a preparation method of the wide-spectrum infrared emission transparent thermal control coating and an optical device. The wide-spectrum infrared emission transparent thermal control coating comprises a transparent polymer matrix as well as modified SiO2 nanoparticles, modified ZrO2 nanoparticles and boron nitride nanosheets which are dispersed in the matrix. Based on 100 parts by mass of the transparent polymer matrix, the addition amount of the modified SiO2 nanoparticles is 0.1 to 5 parts, the addition amount of the modified ZrO2 nanoparticles is 0.1 to 3 parts, and the addition amount of the boron nitride nanosheets is 0.1 to 2 parts. Preferably, the modified ZrO2 nano particles are subjected to MgO doping treatment. According to the coating, through the synergistic effect of the three nanofillers, high light transmittance is kept, meanwhile, an infrared emission window is expanded to a wide spectrum region of 8-20 microns from traditional 8-14 microns, and the coating has good mechanical properties.

Description

Technical Field

[0001] This invention relates to the field of spacecraft thermal control materials technology, specifically to a broadband infrared-emitting transparent thermal control coating for spacecraft, its preparation method, and optical devices. This transparent thermal control coating possesses both high light transmittance and a wide infrared emission window, enabling it to effectively improve the heat dissipation performance of spacecraft in the space environment. Background Technology

[0002] Spacecraft primarily rely on radiation to dissipate heat into deep space during their orbital operation to maintain thermal equilibrium. For critical components such as optical observation windows, detector protective covers, and solar concentrators, the surface coatings not only need to have high light transmittance to meet optical performance requirements, but also should possess good infrared emission capabilities to achieve effective heat dissipation.

[0003] In existing technologies, transparent thermal control coatings mostly use transparent polymers as the matrix and add a small amount of inorganic nanofillers (such as SiO2) to maintain high transmittance in the visible to near-infrared bands, and rely on the intrinsic vibrational modes of the material to provide a certain emissivity in the mid-infrared region. However, the infrared emission of this type of coating is mainly concentrated in a narrow band of 8-14 μm, and the radiation contribution beyond this range is limited, resulting in insufficient heat dissipation efficiency.

[0004] From the perspective of thermal radiation mechanisms, extending the high-emission band from 8-14 μm to a broader spectral range of 8-20 μm can significantly enhance the overlap with blackbody radiation in the typical temperature range of 250-350 K, thereby increasing the net radiative flux per unit area. For example, under blackbody radiation at 300 K, the radiative power in the 8-14 μm band accounts for approximately 37.6% of the total radiation, while the 8-20 μm band accounts for 59.8%, representing an increase in radiative power of approximately 60%.

[0005] Although existing transparent thermal control coatings have achieved a certain balance between light transmittance and partial infrared emissivity, their limited infrared emission window width and insufficient heat dissipation capacity restrict the long-term stable operation of spacecraft in complex space environments. Therefore, how to simultaneously achieve high light transmittance and broadband infrared high emissivity through reasonable material design and structural control has become a key technical problem that urgently needs to be solved in the field of aerospace thermal control coatings. Summary of the Invention

[0006] This invention aims to provide a broadband infrared emission transparent thermal control coating for spacecraft, its preparation method, and optical devices, to solve the problems of narrow infrared emission windows and insufficient heat dissipation capacity in existing transparent thermal control coatings. This coating, while maintaining high visible light transmittance, can widen the infrared emission window, improve radiative heat dissipation efficiency, and enhance the coating's toughness and crack resistance.

[0007] To achieve the above objectives, the present invention adopts the following technical solution: On one hand, the present invention provides a broadband infrared emission transparent thermal control coating for spacecraft, which includes a transparent polymer matrix and modified SiO2 nanoparticles, modified ZrO2 nanoparticles and boron nitride nanosheets dispersed in the matrix; Based on 100 parts by weight of the transparent polymer matrix, the amount of modified SiO2 nanoparticles added is 0.1-5 parts, the amount of modified ZrO2 nanoparticles added is 0.1-3 parts, and the amount of boron nitride nanosheets added is 0.1-2 parts.

[0008] In a preferred embodiment, the modified ZrO2 nanoparticles are doped with MgO, and the doping amount of MgO is 0.01-2 mol.

[0009] In a preferred embodiment, the modified SiO2 nanoparticles have an average particle size of 5-30 nm; the modified ZrO2 nanoparticles have an average particle size of 10-50 nm.

[0010] In a preferred embodiment, the boron nitride nanosheets have a lateral dimension of 1-50 nm and a thickness of 1-50 nm.

[0011] In a preferred embodiment, both the modified SiO2 nanoparticles and the modified ZrO2 nanoparticles are surface-modified with a silane coupling agent.

[0012] In a preferred embodiment, the silane coupling agent is selected from at least one of vinylsilane, epoxysilane, aminosilane, or methacryloxysilane.

[0013] In a preferred embodiment, the transparent polymer matrix is ​​a polysiloxane with reactive functional groups on its side chains or at its ends, wherein the reactive functional groups include vinyl groups, silane-hydrogen bonds, or epoxy groups.

[0014] In a preferred embodiment, the coating thickness is 0.1-100 μm.

[0015] On the other hand, the present invention also provides a method for preparing the transparent thermal control coating, comprising the following steps: The first step is to modify the surface of SiO2 nanoparticles with a silane coupling agent to obtain modified SiO2 nanoparticles. The second step is to modify the surface of ZrO2 nanoparticles with silane coupling agent to obtain modified ZrO2 nanoparticles. The third step is to exfoliate boron nitride nanosheets in an organic solvent to prepare a dispersion. The fourth step involves mixing the modified SiO2 nanoparticles, the modified ZrO2 nanoparticles, and the boron nitride nanosheet dispersion with a transparent polymer matrix, crosslinking agent, solvent, and additives in a specific ratio, and then dispersing the mixture to obtain a uniform coating slurry. The fifth step involves applying the coating slurry onto the substrate, which is then cured to form the transparent thermal control coating.

[0016] In a preferred embodiment, in the second step described above, after obtaining the modified ZrO2 nanoparticles, the modified ZrO2 nanoparticles are further subjected to MgO doping treatment to obtain MgO-doped modified ZrO2 nanoparticles.

[0017] In a preferred embodiment, the MgO doping of the modified ZrO2 nanoparticles is achieved by a co-precipitation method, comprising: dissolving a zirconium source and a magnesium source together in a stoichiometric ratio, co-precipitating under alkaline conditions, and obtaining MgO-doped ZrO2 nanoparticles after aging, washing, drying and calcination.

[0018] In a preferred embodiment, the liquid-phase exfoliation of the boron nitride nanosheets includes: dispersing the boron nitride nanosheets in a solvent, followed by ultrasonic disruption and centrifugation, and then collecting the supernatant for later use.

[0019] In another aspect, the present invention also provides an optical device for spacecraft, wherein the transparent thermal control coating is disposed on the optical working surface of the optical device.

[0020] In a preferred embodiment, the optical device is a reflector, a reflective layer is provided on the substrate of the reflector, and a transparent thermal control coating is provided on top of the reflective layer. The transparent thermal control coating is used to radiate the heat absorbed by the reflector substrate into the space environment in the form of infrared radiation.

[0021] Compared with existing technologies, the broadband infrared emission transparent thermal control coating for spacecraft, its preparation method, and optical devices provided by this invention have the following beneficial effects: 1) Widening the infrared emission window: Through the synergistic effect of phonon polariton coupling and lattice vibration between modified ZrO2 nanoparticles and boron nitride nanosheets, the coating exhibits high and balanced infrared emissivity in the 8-20 μm band, effectively improving the radiation heat dissipation efficiency in a vacuum environment.

[0022] 2) Enhanced mechanical properties of coating: Modified ZrO2 nanoparticles and boron nitride nanosheets form a synergistic toughening effect in the polymer matrix, which significantly improves the fracture toughness and crack resistance of the coating through crack deflection, bridging and pull-out mechanisms.

[0023] 3) Maintaining high optical transmittance: By controlling the particle size, amount of nanoparticles and surface modification, the light transmittance of the coating at 550nm is not less than 90%, achieving a balance between high light transmittance and high infrared emission.

[0024] 4) Strong process adaptability: It adopts conventional wet coating and low temperature thermosetting process, which is suitable for complex curved surfaces and large-area uniform coating, and has good engineering application prospects. Attached Figure Description

[0025] The accompanying drawings, which form part of this specification, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings: Figure 1 This is a schematic diagram of a method for preparing a transparent thermal control coating provided by the present invention. Detailed Implementation

[0026] The technical solutions in the embodiments of the present invention will now be clearly and completely described with reference to the accompanying drawings. The described embodiments are only a part of the implementation of the present invention, not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0027] It should be noted that, in the description of this invention, "an embodiment" or "an embodiment of the invention" refers to a specific feature, structure, or characteristic that can be included in at least one implementation of the invention. The phrase "in one embodiment" appearing in different places in the specification does not necessarily refer to the same embodiment, nor are they mutually exclusive individual or selective embodiments. This invention can also be implemented in ways other than those described herein, and any equivalent modifications made by those skilled in the art without departing from the concept of the invention fall within the scope of protection of this invention.

[0028] In the field of spacecraft thermal control technology, surface coatings for optical devices need to simultaneously meet the dual requirements of high light transmittance and efficient infrared radiation heat dissipation. Existing transparent thermal control coating systems mostly employ single or limited types of nanofillers, and their infrared emission characteristics primarily depend on the intrinsic vibrational modes of the material, with the emission window typically limited to the traditional atmospheric window band of 8-14 μm. Studies have shown that in the typical operating temperature range of spacecraft (250-350 K), the distribution of blackbody radiation energy in the 8-20 μm band can reach approximately 60%, significantly higher than the approximately 38% in the 8-14 μm band. Existing coatings contribute limited radiation within this broad spectral range, restricting further improvements in heat dissipation efficiency.

[0029] Based on the aforementioned technological status, this invention provides a design concept for achieving broadband infrared emission through material combination and structural control. This design uses a transparent polymer as a matrix and constructs a multi-component composite system by introducing modified SiO2 nanoparticles, modified ZrO2 nanoparticles, and boron nitride nanosheets with specific particle sizes and surface properties. Specifically, the modified ZrO2 nanoparticles and boron nitride nanosheets extend the infrared emission band through phonon polariton coupling and synergistic lattice vibrations; simultaneously, the three nanofillers form a multi-level toughening mechanism within the polymer matrix, improving the mechanical reliability of the coating while maintaining high light transmittance. This design aims to achieve a performance balance between broadband high emission and high light transmittance.

[0030] Based on the above design concept, the present invention provides a broadband infrared emission transparent thermal control coating for spacecraft, comprising a transparent polymer matrix and modified SiO2 nanoparticles, modified ZrO2 nanoparticles and boron nitride nanosheets dispersed in the matrix. Based on 100 parts by weight of the transparent polymer matrix, the amount of modified SiO2 nanoparticles added is 0.1-5 parts, the amount of modified ZrO2 nanoparticles added is 0.1-3 parts, and the amount of boron nitride nanosheets added is 0.1-2 parts.

[0031] The transparent thermal control coating provided by this invention abandons single or two-component filler systems and, for the first time, synergistically combines three specific inorganic nanofillers—modified SiO2 nanoparticles, modified ZrO2 nanoparticles, and boron nitride nanosheets—in a transparent polymer matrix. These three fillers differ fundamentally in chemical composition, morphology, and physical properties, and their combination constitutes a novel material system.

[0032] Furthermore, the transparent thermal control coating provided by this invention is not simply a mixture of three fillers. Instead, a specific range of addition amounts (based on 100 parts of polymer matrix) was determined through extensive experiments to achieve the best synergistic effect among the three: modified SiO2 nanoparticles: 0.1-5 parts, modified ZrO2 nanoparticles: 0.1-3 parts, and boron nitride nanosheets: 0.1-2 parts. This formulation design aims to balance the function of each filler and avoid the degradation of optical or mechanical properties due to an excess of any one filler.

[0033] Modified ZrO2 nanoparticles and boron nitride nanosheets exert a synergistic effect in the coating through the following mechanism: In terms of infrared performance, phonon polaritons excited on the surface of boron nitride nanosheets couple with the optical phonon modes of ZrO2 nanoparticles, forming a phonon-polariton hybrid mode. This coupling produces localized field enhancement and resonant absorption in the 8–20 μm band, thereby broadening and planarizing the emission spectrum of the coating. Simultaneously, the high in-plane thermal conductivity of boron nitride nanosheets facilitates the construction of a two-dimensional thermally conductive network within the coating, synergistically reducing interfacial thermal resistance, promoting phonon transport, and improving overall heat dissipation efficiency with the ZrO2 nanoparticles.

[0034] In terms of mechanical properties, modified ZrO2 nanoparticles act as primary barriers, consuming some energy by inducing crack deflection and pinning; boron nitride nanosheets, acting as toughening units, further promote crack deflection, bypassing, and bifurcation, and constrain crack opening through bridging. The strong interfacial bonding between the two helps to uniformly transfer and disperse the load. Boron nitride nanosheets dissipate energy through interlayer slip, while ZrO2 nanoparticles assist in stress transfer to the boron nitride layer, jointly inhibiting microcrack initiation. In the later stages of crack propagation, the pull-out process of boron nitride nanosheets needs to overcome interfacial friction and van der Waals forces to further absorb fracture energy, thereby transforming the failure mode into pseudo-plastic fracture and improving the fracture toughness of the coating.

[0035] It is evident that the composite introduction of modified ZrO2 nanoparticles and boron nitride nanosheets, through the synergistic effect of phonon polariton coupling and lattice vibration, extends the infrared emission window of the coating from the traditional 8-14 μm to a broad 8-20 μm region, thereby improving its radiative heat dissipation efficiency in a vacuum environment. In terms of mechanical properties, the two form a synergistic toughening mechanism: the modified ZrO2 nanoparticles act as a primary barrier to induce crack deflection, while the boron nitride nanosheets further dissipate fracture energy through crack bridging, stress dispersion, and lamellar pull-out mechanisms, effectively inhibiting crack initiation and propagation, and jointly enhancing the fracture toughness of the coating.

[0036] Based on the above design improvements, the technical solution of the present invention is expected to achieve the following technical effects: First, it achieves high infrared emissivity across a broad spectrum. The three nanofillers possess different intrinsic infrared absorption characteristics. Modified SiO2, modified ZrO2, and boron nitride nanosheets may contribute to phonon vibrations and phonon polaritons at different characteristic frequencies in the mid-to-far infrared band of 8-20 μm, respectively. Their synergistic effect can cover a wider infrared band, filling the emission blind spots of single-material systems, thereby jointly achieving and maintaining high infrared emissivity within this broad spectrum.

[0037] Secondly, it maintains high light transmittance. By controlling the total amount of the three types of nanofillers at a low level (maximum 10 parts) and preferably using nanoscale, it helps to reduce light scattering and enable the coating to maintain high transmittance at a wavelength of 550 nm.

[0038] Third, it enhances the mechanical properties and durability of the coating. Particle-like SiO2 / ZrO2 and plate-like boron nitride are dispersed in the polymer matrix, and these three nanofillers with different morphologies and sizes can construct a multi-scale reinforcing and toughening network. Nanoparticles can act as stress concentration points, inducing microcrack deflection; boron nitride nanosheets, with their two-dimensional structure and high strength, hinder crack propagation through bridging, synergistically improving the fracture toughness and crack resistance of the coating.

[0039] In summary, this invention achieves an optimized balance between infrared emission performance, optical transparency, and mechanical reliability at low addition levels by compounding specific types and proportions of ternary nanofillers, providing a novel material solution for addressing the simultaneous high light transmittance and efficient heat dissipation requirements of spacecraft optical devices.

[0040] In one embodiment, the modified ZrO2 nanoparticles are doped with MgO, and the doping amount of MgO is 0.01-2 mol.

[0041] In this embodiment, modified ZrO2 nanoparticles are doped with MgO. This doping treatment affects the material properties through the following mechanism: 1) Regarding infrared performance, MgO doping introduces lattice distortion and oxygen vacancy defects. Lattice distortion may alter the phonon vibration modes of ZrO2, while oxygen vacancy defects generate additional light absorption in the 2.5–8 μm wavelength range. These effects, combined with the infrared characteristics of components such as SiO2 and boron nitride, positively impact the broad-spectrum emission performance of the coating in the 8–20 μm wavelength range.

[0042] 2) In terms of material processability, appropriate MgO doping helps to suppress the grain growth and agglomeration tendency of ZrO2 nanoparticles. Improved dispersibility is conducive to the formation of a more uniform composite structure in the polymer matrix, reducing light scattering caused by agglomeration, and at the same time, it supports the maintenance of the light transmittance of the coating.

[0043] 3) In terms of mechanical properties, the improved dispersibility of MgO-doped ZrO2 nanoparticles allows for a more uniform distribution within the matrix, forming a more effective synergistic toughening structure with boron nitride nanosheets. This structure positively impacts the fracture toughness of the coating through mechanisms such as crack deflection and bridging.

[0044] In summary, the embodiments of the present invention improve the functionality of the ZrO2 component from the intrinsic material property level by doping ZrO2 nanoparticles with a specific amount of MgO. Through microstructure regulation, the broadband infrared emission performance of the coating is synergistically enhanced, and its optical performance and mechanical reliability are indirectly consolidated by optimizing the dispersibility.

[0045] In one embodiment, the modified SiO2 nanoparticles have an average particle size of 5-30 nm; the modified ZrO2 nanoparticles have an average particle size of 10-50 nm.

[0046] The physical dimensions of the modified SiO2 nanoparticles and modified ZrO2 nanoparticles in this embodiment are limited as described above, based on the following technical considerations: In terms of optical properties, controlling the particle size of modified SiO2 nanoparticles within the range of 5–30 nm helps reduce their scattering of light, thus supporting the maintenance of the coating's high transmittance at 550 nm. Simultaneously, setting the particle size of modified ZrO2 nanoparticles to 10–50 nm aligns with their phonon vibration characteristics in the mid- and far-infrared bands, which helps enhance phonon coupling between them and boron nitride nanosheets, thereby positively impacting the broadening of the infrared emission band.

[0047] In terms of structural properties, the aforementioned nanoscale particle size helps to suppress filler agglomeration and sedimentation, promoting its uniform dispersion in the polymer matrix and providing a foundation for the uniformity of the coating's optical and mechanical properties. Furthermore, nanoparticles of different sizes, together with plate-like boron nitride, construct a multi-scale composite structure. When the coating is subjected to stress, this structure can dissipate energy through crack deflection and bifurcation, thereby enhancing the coating's fracture toughness.

[0048] In summary, by limiting the average particle size range of modified SiO2 and modified ZrO2 nanoparticles, the embodiments of the present invention help to control the visible light transmittance, infrared emission characteristics and mechanical behavior of the coating.

[0049] In one embodiment, the boron nitride nanosheets have a lateral dimension of 1-50 nm and a thickness of 1-50 nm.

[0050] The size range of boron nitride nanosheets, especially their thickness which is much smaller than the wavelength of visible light, helps to reduce the scattering and blocking of visible light by the boron nitride nanosheets, thereby playing a positive role in maintaining the overall high light transmittance of the coating.

[0051] At this nanoscale, boron nitride nanosheets can effectively excite phonon polaritons and couple with the lattice vibrations of modified ZrO2 nanoparticles. This may broaden the infrared emission band of the coating and contribute to achieving broadband infrared emission in the 8-20 μm band.

[0052] Boron nitride nanosheets, confined to this size range, facilitate uniform dispersion within the polymer matrix and form a multi-scale composite structure with modified SiO2 and modified ZrO2 nanoparticles. This structure provides conditions for energy dissipation through mechanisms such as crack deflection and bridging, thereby influencing the improvement of the coating's fracture toughness.

[0053] In summary, the boron nitride nanosheets in this embodiment of the invention are limited by the above-mentioned size based on considerations of the influence of the coating on optical transmittance, infrared emission characteristics and mechanical properties.

[0054] In one embodiment, both the modified SiO2 nanoparticles and the modified ZrO2 nanoparticles are surface-modified with a silane coupling agent. This modification treatment can reduce the surface energy of the nanoparticles, weaken their aggregation tendency, and thus promote their uniform dispersion in the polymer matrix.

[0055] Based on this, one end of the silane coupling agent molecule can bind to the surface of inorganic nanoparticles, while the other end is compatible with or reacts with the organic polymer matrix, thereby establishing an interfacial connection between the filler and the matrix and enhancing the bonding force between them. The resulting technical effects include: uniform dispersion of the filler helps reduce light scattering centers caused by agglomerate formation, thus supporting the maintenance of high transmittance of the coating in the visible light region; simultaneously, improved interfacial bonding facilitates more effective stress transfer from the matrix to the nanofiller, allowing the nanoparticles to participate more fully in the load-bearing and toughening process, thereby positively impacting the stability of the coating's mechanical properties.

[0056] In summary, the surface modification of SiO2 and ZrO2 nanoparticles in this embodiment of the invention is a key step in achieving uniform dispersion and enhanced interfacial bonding, which helps to synergistically optimize the overall performance of the coating.

[0057] In one embodiment, the silane coupling agent is selected from at least one of vinylsilane, epoxysilane, aminosilane, or methacryloxysilane. Preferably, it is one of vinyltrimethoxysilane (VTMS), 3-glycidyl etheroxypropyltrimethoxysilane (GPTMS), or 3-aminopropyltriethoxysilane (APTES).

[0058] These silane coupling agents contain specific organic functional groups, including vinyl, epoxy, amino, or methacryloxy groups. When the matrix polymer is a polysiloxane with corresponding reactive functional groups (such as vinyl, silane-hydrogen bonds, or epoxy groups), these functional groups can chemically react with the matrix to form covalent bonds between the inorganic filler and the organic polymer.

[0059] Based on this, by selecting the aforementioned silane coupling agents with well-defined reactive properties, it is possible to design interfacial layers that are specifically compatible with the polymer matrix. This helps improve the compatibility between the filler and the matrix, and has a positive effect on enhancing the interfacial bonding strength and stability.

[0060] In summary, by limiting the use of the specific types of silane coupling agents described above, the embodiments of the present invention provide a feasible technical approach for achieving effective interfacial modification in polymer matrices with different chemical properties.

[0061] In one embodiment, the transparent polymer matrix is ​​a polysiloxane with reactive functional groups on its side chains or at its ends, the reactive functional groups including vinyl, silane-hydrogen bonds, or epoxy groups.

[0062] These reactive functional groups (vinyl groups, silane bonds, epoxy groups) provide clear chemical reaction sites between polysiloxane alkyl bodies and crosslinking agents, as well as between the matrix and surface-modified fillers, enabling the coating to form a three-dimensional network structure through specific crosslinking reactions (such as hydrosilylation, epoxy ring-opening polymerization, etc.).

[0063] This cross-linked structure helps improve the density, mechanical strength, and thermal stability of the coating, thereby enhancing its resistance to aerospace thermal cycling environments. Simultaneously, when the functional groups of surface-modified fillers (such as SiO2 and ZrO2) chemically bond with the reactive functional groups of the matrix, a covalent bridge can be formed between the filler and the matrix, which is beneficial for improving interfacial stress transmission and enhancing the mechanical properties of the composite coating.

[0064] In summary, the embodiments of the present invention provide the necessary chemical basis for constructing a stable coating crosslinking structure and a robust filler-matrix interface by using polysiloxanes with specific reactive functional groups as the matrix.

[0065] In one embodiment, the coating thickness is 0.1-100 μm, preferably 10-30 μm. This thickness range is set based on the following considerations: When the coating thickness is insufficient, a continuous and complete infrared functional layer may not be formed, affecting its radiative heat dissipation efficiency; while excessive thickness may adversely affect light transmittance due to enhanced absorption by the substrate material or increased interface reflection. The preferred range of 10-30 μm ensures both infrared emission function and good light transmittance.

[0066] From a structural performance perspective, this thickness range facilitates the formation of a continuous and complete film layer, ensuring both the adhesion strength between the coating and the substrate and preventing stress buildup caused by excessive thickness, thus supporting the long-term reliability of the coating. Furthermore, this thickness range is compatible with the film-forming capabilities of conventional coating processes, providing conditions for achieving uniform and controllable coating preparation in practical applications.

[0067] It should be noted that the coating composition may also contain 5-10 parts of a crosslinking agent containing silicon-hydrogen bonds (Si-H), 0.1-5 parts of other additives, and 20-40 parts of solvent. The other additives may be leveling agents, defoamers, dispersants, and other commonly used additives. The solvent may be anhydrous ethanol, isopropanol, ethyl acetate, or a mixture thereof.

[0068] In summary, by limiting the coating thickness to the range of 0.1-100 μm, the embodiments of the present invention are beneficial to coordinating its optical performance, thermal radiation function and structural reliability.

[0069] It should be noted that the coating composition also contains 5-10 parts of a crosslinking agent containing silicon-hydrogen bonds (Si-H), 0.1-5 parts of other additives, and 20-40 parts of solvent. The other additives may be leveling agents, defoamers, dispersants, and other commonly used additives. The solvent may be anhydrous ethanol, isopropanol, ethyl acetate, or a mixture thereof.

[0070] The "Si-H crosslinking agent" mentioned above corresponds to the polysiloxane matrix containing reactive functional groups such as vinyl groups. The two can form a strong three-dimensional network structure through a hydrosilylation reaction, which is the chemical basis for the coating to achieve certain mechanical strength, adhesion, and durability. Limiting its dosage range (5-10 parts) aims to ensure a moderate crosslinking density, avoiding insufficient crosslinking leading to an overly soft coating, or excessive crosslinking leading to embrittlement.

[0071] The "other additives" (leveling agents, defoamers, and dispersants) are mainly used to solve process problems in coating formulation and application. Dispersants promote the uniform dispersion and stability of nanofillers in the slurry, preventing sedimentation and agglomeration, which is a prerequisite for achieving uniform coating function. Defoamers eliminate air bubbles during high-speed dispersion and application, preventing defects such as pinholes after coating curing. Leveling agents improve the leveling properties of the slurry on the substrate, helping to form a smooth and uniform film. These additives work together to play a crucial supporting role in obtaining a defect-free, high-performance final coating product.

[0072] The main functions of the "solvent" system (anhydrous ethanol, isopropanol, ethyl acetate, etc.) are: to adjust the viscosity and solid content of the slurry so that it is suitable for specific coating processes such as spraying and spin coating; to ensure the full dissolution and dispersion of each component (polymer, filler, additives); and to achieve the shaping and curing of the coating through evaporation after coating.

[0073] Based on the above design concept, see Figure 1 The present invention also provides a method for preparing the above-mentioned transparent thermal control coating, characterized by comprising the following steps: The first step is to modify the surface of SiO2 nanoparticles with a silane coupling agent to obtain modified SiO2 nanoparticles. The second step is to modify the surface of ZrO2 nanoparticles with silane coupling agent to obtain modified ZrO2 nanoparticles. The third step is to exfoliate boron nitride nanosheets in an organic solvent to prepare a dispersion. The fourth step involves mixing the modified SiO2 nanoparticles, the modified ZrO2 nanoparticles, and the boron nitride nanosheet dispersion with a transparent polymer matrix, crosslinking agent, solvent, and additives in a specific ratio, and then dispersing the mixture to obtain a uniform coating slurry. The fifth step involves applying the coating slurry onto the substrate, which is then cured to form the transparent thermal control coating.

[0074] The first step involves dispersing nano-SiO2 in an alcohol solvent, followed by the addition of a silane coupling agent, and then stirring at 60-80°C for 2-4 hours for modification. The modified particles are then centrifuged, washed, and vacuum dried to obtain modified nano-SiO2 powder. The dispersion process is first ultrasonicated for 10-30 minutes, followed by high-speed shearing at 500-3000 r / min for 10-30 minutes to achieve stable dispersion.

[0075] The second step involves dispersing nano-ZrO2 in an alcohol solvent, then adding a silane coupling agent, stirring at room temperature for 2-3 hours, and refluxing at 70-80°C for 3-4 hours; the modified particles are then centrifuged, washed, and vacuum dried to obtain modified nano-ZrO2.

[0076] The third step involves dispersing boron nitride nanosheets in an organic solvent, and then using an ultrasonic cell disruptor at 500W power for 1-2 hours under ice-water bath conditions. Afterward, the mixture is centrifuged at 3000 rpm for 20-30 minutes, and the supernatant is collected for later use.

[0077] The fifth step involves applying the coating slurry obtained in the fourth step onto the substrate, forming a film on the substrate surface using spraying, spin coating, dip coating, or jet printing methods, and then curing it at a low temperature to obtain the transparent thermal control coating. Specifically, it is cured at 50-120℃ for 0.5-3 hours to obtain a dense, low-defect transparent film layer.

[0078] The method for preparing the aforementioned transparent thermally controlled coating provided by this invention involves surface modification of SiO2 nanoparticles and ZrO2 nanoparticles in steps one through three, and liquid-phase exfoliation of boron nitride nanosheets, aiming to improve the dispersibility, surface activity, and compatibility with the polymer matrix of each nanofiller in advance. This provides the necessary material basis for constructing a uniform composite structure. In step four, the pretreated components are mixed with the matrix, crosslinking agent, etc., in proportion and dispersed to promote uniform distribution of various nanofillers in the polymer solution, forming a stable slurry system. In step five, the slurry is transformed into a solid coating through coating and curing steps. The summarized coating methods (such as spraying, spin coating, etc.) and curing processes provide a general process route for forming continuous and complete functional films on substrates of different shapes and materials.

[0079] In summary, the preparation method defined in this invention supports and corresponds to the components and structural features defined in the aforementioned product claims. Through a systematic and sequential process, it provides an operable and controllable preparation guarantee for realizing the structural construction and functional realization of the transparent thermal control coating.

[0080] In one embodiment, after obtaining the modified ZrO2 nanoparticles in the second step, the modified ZrO2 nanoparticles are further subjected to MgO doping treatment to obtain MgO-doped modified ZrO2 nanoparticles.

[0081] This step, through pre-treatment with MgO at the nanopowder stage, introduces lattice distortion and oxygen vacancies at the material synthesis level, providing a bulk-modified core filler for the coating to achieve broadband infrared emission. The MgO-doped ZrO2 nanoparticles exhibit improved dispersibility and synergistic effects with boron nitride nanosheets in phonon coupling and toughening.

[0082] Compared to postponing the doping step or adding the magnesium source directly to the slurry, this pilot doping treatment helps to obtain MgO-ZrO2 composite powders with more uniform composition and structure at the nanoscale. This provides a material basis for achieving stable and repeatable infrared emission properties and mechanical enhancement effects in subsequent coatings.

[0083] In summary, the preparation steps defined in the embodiments of the present invention, by completing the key MgO doping modification in advance during the powder synthesis stage, provide a methodological guarantee for achieving the required broadband infrared emission characteristics and optimized mechanical properties of the coating.

[0084] In one embodiment, MgO doping of modified ZrO2 nanoparticles is achieved via a co-precipitation method. This method involves dissolving a zirconium source and a magnesium source in a stoichiometric ratio, co-precipitating under alkaline conditions, and then obtaining MgO-doped ZrO2 nanoparticles after aging, washing, drying, and calcination.

[0085] The MgO doping treatment specifically employs a co-precipitation method. The previously prepared modified ZrO2 and magnesium chloride are weighed in a molar ratio, dissolved in deionized water, and ammonia is added dropwise under stirring until the pH reaches 9-10. After co-precipitation, the mixture is aged for 10-14 hours, filtered, washed until Cl⁻-free, dried at 70-80℃, and then calcined at 900℃ for 2-3 hours to obtain MgO-doped modified ZrO2 nanopowder.

[0086] In this doping process, Mg²⁺ ions enter the ZrO₂ lattice during the early stages of nucleation and growth, which helps to achieve a uniform distribution of MgO in the ZrO₂ bulk phase. Compared with later surface modification or physical mixing, this method can reduce component segregation and provides a basis for obtaining nanopowders with consistent lattice properties.

[0087] By controlling the stoichiometry of the precursor solution, the MgO doping level of the final product can be adjusted. Subsequent aging, washing, drying, and calcination steps help form structurally stable MgO-doped ZrO2 nanocrystals. This method features adjustable process parameters, providing the technical conditions for obtaining doped powders with consistent performance.

[0088] In summary, the embodiments of the present invention provide a specific process path for achieving uniform and controllable ion doping by using the co-precipitation method for MgO doping, which helps to support the implementation of optimizing filler function through lattice control.

[0089] In one embodiment, the liquid phase exfoliation process of boron nitride nanosheets includes: dispersing boron nitride nanosheets in a solvent, followed by ultrasonic disruption and centrifugation, and then collecting the supernatant for later use.

[0090] The cavitation effect generated during ultrasonic disruption helps overcome the van der Waals forces between hexagonal boron nitride layers, promoting their exfoliation into thinner nanosheets. Subsequent centrifugation removes insufficiently exfoliated thick sheets or large particles, resulting in a suspension of smaller, more stable nanosheets.

[0091] This pretreatment method helps reduce optical scattering and stress concentration caused by the presence of large particles, providing a material basis for the subsequent preparation of a uniform and stable coating slurry. Simultaneously, this standardized process provides a controllable process route for obtaining boron nitride nanosheets that meet specific size requirements, playing a positive role in maintaining the consistency of coating performance.

[0092] In summary, the embodiments of the present invention, through the above-described liquid phase exfoliation method, can provide the necessary material pretreatment support for boron nitride nanosheets to achieve their infrared functionality and mechanical enhancement in composite coatings.

[0093] It should be noted that the key properties of the transparent thermal control coating obtained by the above preparation method are: light transmittance ≥90% at 550 nm; apparent infrared emissivity ≥0.8 in the 8-20 μm band, thereby achieving broadband radiative heat dissipation in the 8-20 μm range. This transparent thermal control coating can form good adhesion with spacecraft substrates, such as quartz glass, polyimide film, aluminum alloy, etc.; if necessary, plasma or silane primer treatment can be performed on the substrate surface to improve adhesion and resistance to thermal shock.

[0094] The above coating methods can employ any of the following: spraying, spin coating, dip coating, or jet printing. These are all existing, mature film-forming processes, each with its own technical characteristics: spraying is suitable for large-sized substrates and those with complex curved surfaces; spin coating is beneficial for forming a uniform film on flat surfaces; dip coating can achieve overall coverage of complex structural components; and jet printing is suitable for applications requiring precise localized coating. The appropriate coating process can be selected based on the substrate's geometry and size.

[0095] The transparent thermal control coating of the present invention is applicable to spacecraft optical devices, including but not limited to optical observation windows, detector protective covers, solar concentrators, solar cells and other parts that need to simultaneously meet the requirements of high light transmittance and high radiation heat dissipation.

[0096] Therefore, the present invention also provides an optical device for spacecraft, wherein the aforementioned broadband infrared emitting transparent thermal control coating is disposed on the optical working surface.

[0097] In one embodiment, the optical device is a reflector, and a reflective layer is provided on the substrate of the reflector. The aforementioned transparent thermal control coating is also provided on the reflective layer. The transparent thermal control coating is used to radiate the heat absorbed by the reflector substrate into the space environment in the form of infrared radiation.

[0098] The following examples illustrate the implementation of the present invention in detail, thereby enabling a full understanding and implementation of how the present invention uses technical means to solve technical problems and achieve technical effects.

[0099] Test equipment and test methods (1) Light transmittance Test equipment: UV-Vis-NIR spectrophotometer (model: PerkinElmer Lambda 1050+).

[0100] Test method: Following standard ASTM E903, the coating was uniformly applied to a transparent quartz glass substrate and cured. The transmittance was measured at a wavelength of 550 nm using the integrating sphere attachment provided with the instrument. Baseline calibration was performed using a standard reference plate prior to testing.

[0101] (2) Infrared emissivity Test equipment: Fourier transform infrared spectrometer (model: Bruker Vertex 70) equipped with a gold integrating sphere reflectance accessory (PIKE Technologies IntegratIR).

[0102] Test Method: Emissivity was indirectly calculated using the reflectance method, referring to standard ASTM E408. The coating was applied to a polished aluminum sheet (low-emissivity substrate) and cured. First, the hemispherical spectral reflectance R(λ) of the coating in the 8-14 μm and 14-20 μm bands was measured. Then, according to Kirchhoff's law of thermal radiation, under thermal equilibrium, the spectral emissivity ε(λ) = 1 − R(λ). The final result is the integral average of the spectral emissivity for each band.

[0103] (3) Adhesion Testing equipment: cross-cut tester (tooth spacing: 1mm or 2mm), soft brush, 3M 610 pressure-sensitive tape.

[0104] Test Method: Refer to standard GB / T 9286-2021 "Cross-cut Test for Paints and Varnishes". Apply the coating to a standard aluminum alloy plate LY12 and cure. Use a cross-cut tester to cut 6×6 squares with a spacing of 1mm into the substrate. After lightly brushing with a soft brush, firmly adhere pressure-sensitive adhesive tape to the square area and quickly peel it off. Rating is based on the proportion of paint film that has peeled off from the substrate.

[0105] (4) Fracture toughness Testing equipment: Universal testing machine (model: Instron 5944), nanoindenter (model: Keysight G200).

[0106] Test Method: Following standard ISO 14577, a quasi-static indentation test was performed at multiple points on the coating surface using a Berkovich diamond indenter. The elastic modulus (E) and hardness (H) of the material were obtained by analyzing the load-displacement curves, and the fracture toughness (KIC) was calculated using continuous stiffness measurement (CSM) technology and a specific mechanical model, Lawn / Evans / Marshall. This method effectively evaluates the crack resistance of brittle coatings.

[0107] Example 1 (1) Nano SiO2 modification 100 g of nano-SiO2 was dispersed in 2 kg of anhydrous ethanol, and 5 g of 3-aminopropyltriethoxysilane was added. The mixture was stirred at room temperature for 2 h and refluxed at 70 °C for 3 h. After centrifugation and washing with ethanol three times, the mixture was dried under vacuum at 60 °C for 12 h to obtain modified nano-SiO2 with an average particle size of 25 nm.

[0108] (2) Nano ZrO2 modification 100g of nano-zirconia was dispersed in 2kg of anhydrous ethanol, and 5g of methyltriethoxysilane (MTES) was added. The mixture was stirred at room temperature for 2 h and refluxed at 70℃ for 3 h. After centrifugation and washing with ethanol three times, the mixture was vacuum dried at 60℃ for 12 h to obtain modified nano-ZrO2 powder with an average particle size of 30 nm.

[0109] (3) Preparation of two-dimensional nanomaterial dispersion Boron nitride nanosheets were dispersed in N-methylpyrrolidone (NMP) at a concentration of 1 mg / mL and sonicated at 500 W for 1.5 hours under ice-water bath conditions using an ultrasonic cell disruptor. The mixture was then centrifuged at 8000 rpm for 20 minutes, and the supernatant was collected to obtain the boron nitride nanosheet dispersion.

[0110] (4) Dispersion and slurry preparation Add 1 kg of transparent polysiloxane prepolymer (PDMS, vinyl-terminated), 100 g of crosslinking agent and 300 g of solvent to a clean beaker. The solvent is anhydrous ethanol / isopropanol in a volume ratio of 1:1. Stir magnetically at 500 r / min for 10 min to obtain a homogeneous solution.

[0111] Add 30 g of the previously prepared modified SiO2 powder, 10 g of modified ZrO2 powder, and a supernatant containing 10 g of boron nitride nanosheets to the above solution in sequence. Then add 5 g of dispersant BYK-163, 2 g of leveling agent BYK-333, and 2 g of defoamer BYK-055. The mixture is then ultrasonically treated (400 W, 30 min). Immediately after ultrasonication, the mixture is transferred to a high-speed shear disperser and sheared at 3000 r / min for 20 minutes to obtain a homogeneous dispersion. The slurry is then degassed under vacuum (-0.1 MPa) for 15 min to obtain a final transparent slurry suitable for coating.

[0112] (5) Film formation and curing The quartz glass was wiped once with anhydrous ethanol and once with deionized water, dried with nitrogen, and treated with air plasma at 200W for 30 seconds to enhance adhesion. The transparent slurry prepared earlier was then sprayed onto the quartz substrate to form a film. The air pressure was 5 MPa, the nozzle diameter was 0.3 mm, the spray distance was 15 cm, and the spraying was repeated twice. The target thickness was about 30 μm. The film was allowed to stand at room temperature for 10 min to level, and then the temperature was programmed to cure: the film was kept at 60℃ for 1 hour, and then the temperature was increased to 100℃ and kept at 2 hours. The film was then allowed to cool naturally to room temperature to obtain the coated sample.

[0113] Example 2 The difference from Example 1 is that, in the dispersion and slurry preparation steps, the modified SiO2 powder, modified ZrO2 powder, and the amount of boron nitride nanosheets with solid content added sequentially to the transparent polysiloxane prepolymer solution are all reduced compared to Example 1. In Example 2, the amount of modified SiO2 powder is 10 g, the amount of modified ZrO2 powder is 5 g, and the amount of boron nitride nanosheet supernatant containing 3 g of solid content is 1 g. The remaining steps and components are the same as in Example 1.

[0114] Example 3 The difference from Example 1 is that in the second step, after the ZrO2 nanoparticles underwent surface modification treatment with a silane coupling agent, they were also subjected to doping treatment. The remaining steps and components are the same as in Example 1.

[0115] Modified ZrO2 doping 100 mol of modified ZrO2 prepared in Example 1 and 1 mol of magnesium chloride (MgCl2) were weighed according to the stoichiometric ratio and dissolved together in deionized water. Ammonia was added dropwise with stirring until the pH reached 9-10. After co-precipitation, the mixture was aged for 12 h. The powder was filtered and washed until Cl⁻-free, dried at 80 °C, and then calcined at 900 °C for 2 h to obtain 1 mol% MgO-doped modified ZrO2 nanoparticles with an average particle size of 30 nm.

[0116] Comparative Example 1 The difference from Example 1 is that only 30g of the modified SiO2 prepared in Example 1 was added, and no modified ZrO2 nanoparticles and boron nitride nanosheets were added. The rest is the same as in Example 1.

[0117] Comparative Example 2 The difference from Example 1 is that only 30g of modified SiO2 and 20g of modified ZrO2 nanoparticles prepared in Example 1 were added, and boron nitride nanosheets were not added. The rest is the same as in Example 1.

[0118] Comparative Example 3 The difference from Example 1 is that only 30g of modified SiO2 and 20g of boron nitride nanosheets prepared in Example 1 were added, and no modified ZrO2 nanoparticles were added. The rest is the same as in Example 1.

[0119] The results are shown in Table 1, the performance comparison table.

[0120] Table 1 Performance Comparison Table

[0121] Regarding light transmittance, all samples exhibited excellent optical performance (≥90%), with Comparative Example 1 showing the highest transmittance (92%), which is related to its relatively simple composition and low particle packing density. Examples 1, 2, and 3, after introducing various modified functional nanoparticles, still maintained high transmittance levels of 91% and 90%, respectively. This indicates that through optimized nanodispersion technology and a "dot doping" composite strategy, a large number of phonon scattering sources were successfully introduced to enhance infrared radiation while minimizing the impact on light scattering, thus achieving an ideal balance of "high infrared emission - high light transmittance." In particular, Example 3, with its MgO doping, improved infrared and mechanical properties without sacrificing optical transparency, and reduced light scattering centers by suppressing agglomeration.

[0122] Regarding achieving high emissivity in the broadband infrared band, Comparative Example 1 exhibits a high emissivity of 0.86 in the 8-14 μm band, but its emissivity drops sharply to 0.60 in the 14-20 μm band. Comparative Example 2 differs from Comparative Example 1, exhibiting an emissivity of 0.85 in the 8-14 μm band and a high emissivity of 0.80 in the 14-20 μm band. This demonstrates that modified SiO2 and modified ZrO2 respectively dominate the radiative enhancement in the mid-near-infrared and mid-far-infrared bands, exhibiting natural spectral complementarity.

[0123] Example 1 achieved a balanced high infrared emissivity of 0.85 for 8-14 μm and 0.83 for 14-20 μm. This is because boron nitride nanosheets can effectively bridge the absorption valleys between different materials through phonon-polaritrile coupling with modified ZrO2 nanoparticles, thus broadening and flattening the emission spectrum. Therefore, Example 1 outperforms any single or two-component formulation.

[0124] Compared to Example 1, Example 2 exhibits the same light transmittance and full-band (8-20 μm) infrared emissivity. However, Example 3, while maintaining a high light transmittance of 90%, further enhances its infrared emissivity to 0.86 in the 8-14 μm band and 0.85 in the 14-20 μm band, achieving superior and more balanced high infrared emission performance across the entire 8-20 μm band. MgO doping, by introducing lattice distortion and oxygen vacancies, not only enhances the intrinsic infrared activity of modified ZrO2 but also effectively suppresses the aggregation of its nanoparticles, making Example 3 the optimal solution for achieving broad-spectrum high emission.

[0125] Regarding the improvement of coating mechanical reliability, the fracture toughness of Comparative Example 3 (0.86 MPa·m¹ / ²) is significantly higher than that of Comparative Examples 1 and 2. This is because boron nitride nanosheets achieve toughening through mechanisms such as interlayer slip, crack deflection, bridging, and pull-out. The fracture toughnesses of Examples 1 and 2 are 0.89 MPa·m¹ / ² and 0.88 MPa·m¹ / ², respectively, both superior to all two-component systems, while Example 3 achieves the optimal 0.90 MPa·m¹ / ². This indicates that uniformly dispersed modified ZrO₂ nanoparticles can act as primary crack deflection points, synergistically working with boron nitride nanosheets, which serve as the main toughening centers, at multiple levels to jointly construct a more efficient energy dissipation network. MgO doping further enhances this synergistic toughening effect by improving the dispersion of modified ZrO₂ and optimizing the interface.

[0126] The above are merely preferred embodiments of the present invention and are not intended to limit the scope of protection of the present invention. For those skilled in the art, the present invention can have various modifications and variations. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A wide-spectrum infrared emission transparent thermal control coating for spacecraft, characterized in that, The transparent polymer matrix, modified SiO2 nanoparticles, modified ZrO2 nanoparticles and boron nitride nanosheets are dispersed in the matrix. The amount of the modified SiO2 nanoparticles is 0.1-5 parts, the amount of the modified ZrO2 nanoparticles is 0.1-3 parts, and the amount of the boron nitride nanosheets is 0.1-2 parts, based on 100 parts of the transparent polymer matrix.

2. The transparent thermal control coating according to claim 1, characterized in that The modified ZrO2 nanoparticles are doped with MgO, and the doping amount of MgO is 0.01-2 mol%.

3. The transparent thermal control coating according to claim 1 or 2, characterized in that The average particle size of the modified SiO2 nanoparticles is 5-30 nm, and the average particle size of the modified ZrO2 nanoparticles is 10-50 nm.

4. The transparent thermal control coating according to claim 1 or 2, characterized in that, The lateral size of the boron nitride nanosheets is 1-50 nm, and the thickness is 1-50 nm.

5. The transparent thermal control coating according to claim 1 or 2, wherein Both the modified SiO2 nanoparticles and the modified ZrO2 nanoparticles are surface-modified with a silane coupling agent.

6. The transparent thermal control coating of claim 5, wherein, The silane coupling agent is at least one of vinyl silane, epoxy silane, amino silane or methacryloxy silane.

7. The transparent thermal control coating of claim 1, wherein, The transparent polymer matrix is polysiloxane with reactive functional groups on the side chain or terminal, and the reactive functional groups include vinyl, silicon-hydrogen bond or epoxy.

8. The transparent thermal control coating according to claim 1 or 2, characterized in that, The coating thickness is 0.1-100 μm.

9. A method for producing the transparent thermal control coating according to any one of claims 1 to 8, characterized in that The method comprises the following steps: In the first step, the SiO2 nanoparticles are surface-modified with a silane coupling agent to obtain modified SiO2 nanoparticles. In the second step, the ZrO2 nanoparticles are surface-modified with a silane coupling agent to obtain modified ZrO2 nanoparticles. In the third step, the boron nitride nanosheets are subjected to liquid-phase exfoliation in an organic solvent to prepare a dispersion. In the fourth step, the modified SiO2 nanoparticles, the modified ZrO2 nanoparticles and the boron nitride nanosheet dispersion are mixed with the transparent polymer matrix, a crosslinking agent, a solvent and an additive in a certain proportion, and then subjected to dispersion treatment to obtain a uniform coating slurry. In the fifth step, the coating slurry is coated on a substrate, and the transparent thermal control coating is formed after curing.

10. The method of claim 9, wherein, In the second step, after obtaining the modified ZrO2 nanoparticles, the modified ZrO2 nanoparticles are further subjected to MgO doping treatment to obtain MgO-doped modified ZrO2 nanoparticles.

11. The method of claim 10, wherein, The MgO doping of the modified ZrO2 nanoparticles is realized by a coprecipitation method, which comprises: dissolving a zirconium source and a magnesium source in a stoichiometric ratio, and then coprecipitating under alkaline conditions to obtain MgO-doped ZrO2 nanopowder after aging, washing, drying and calcination.

12. The method of claim 9, wherein, The liquid-phase exfoliation of the boron nitride nanosheets comprises: dispersing the boron nitride nanosheets in a solvent, and then subjecting to ultrasonic crushing and centrifugation to obtain a supernatant for standby use.

13. An optical device for a spacecraft, characterized by, The optical working surface of the optical device is provided with the transparent thermal control coating as claimed in any one of claims 1-8.

14. The optical device for a spacecraft of claim 13, wherein, The optical device is a mirror, and a reflective layer is arranged on the substrate of the mirror, and the transparent thermal control coating is further arranged on the reflective layer.

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