A low solar light absorption rate, high infrared emissivity aerospace thermal control film and its preparation method

Abstract

The present invention relates to the field of spacecraft thermal control technology, and more specifically to a low solar light absorptivity, high infrared emissivity aerospace thermal control film and its preparation method. The present invention utilizes atomic deposition technology to coat silicon oxide on the surface of a self-supporting anodic aluminum oxide nanotube array film, and then deposits an aluminum foil having a nanosilver layer on one side of the bonding surface of the silicon oxide / anodic aluminum oxide film to form a thermal control film. The anodic aluminum oxide nanotube array provides the silicon oxide deposition coating with infrared emission points having a high specific surface area, thereby enabling the thermal control film to exhibit high infrared emissivity; the metallic aluminum film provides the thermal control film with high solar spectrum reflectivity; and the nanotube array structure further enhances the film's infrared radiation characteristics through a localized electromagnetic wave resonance mechanism. The prepared thermal control film has a solar spectrum reflectivity of 0.86 and an infrared emissivity of 0.96 at the atmospheric window, resulting in the thermal control film exhibiting good cooling efficiency.

Description

Technical Field

[0001] The present invention relates to the field of spacecraft thermal control technology, and in particular to an aerospace thermal control film with low solar light absorption rate and high infrared emissivity and a preparation method thereof. Background Art

[0002] Spacecraft face an extremely complex thermal environment in space. To ensure the proper functioning of instruments and crew, the internal temperature of the spacecraft must be strictly maintained. Thermal radiation is the only means by which spacecraft dissipate heat in space. Given that the maximum surface temperature of a spacecraft in the sunlit region typically ranges from 100°C to 150°C, the surface materials of the spacecraft have low radiative heat exchange efficiency within this temperature range. Therefore, the spacecraft surface must be coated with a coating with high infrared emissivity and low solar absorption to maintain the desired ratio of heat energy from the sun and the Earth to heat energy radiated from the spacecraft surface into space. With the advancement of aerospace technology, my country has established a relatively comprehensive and diverse portfolio of thermal control coatings that can meet diverse needs. For example, in my country's lunar and Mars exploration projects, in order to meet the thermal control needs of new missions, new thermal control coatings have been developed one after another: the low-absorption / low-emission coating developed in the Mars rover mission has a solar absorption ratio of 0.19±0.02 and a hemispherical emissivity of 0.2~0.4; the Al-AlN composite film structure heat-absorbing coating has a solar absorption ratio of 0.92 and a hemispherical emissivity of 0.08.

[0003] On the other hand, with the further extension of my country's space exploration, new requirements have been put forward for the performance of thermal control coatings, including: (1) Given that the infrared emissivity of thermal control materials is positively correlated with the mass per unit area of ​​the material, increasing the coating thickness is a common technical means to make the thermal control coating have a higher infrared emissivity. A higher coating thickness undoubtedly reduces the payload of the spacecraft. Constructing a thermal control coating with low thickness (≤50μm), low solar absorption ratio (<0.1), and high infrared emissivity (>0.85) has become a key development direction in the future; (2) For a thermal control material with a certain infrared radiation characteristic, constructing it into a periodic microstructure is an effective means to enhance its infrared emissivity. At present, 3D printing, nanoimprinting, lithography and other technologies have been developed to prepare high infrared emissivity films, but the related technologies have disadvantages such as high cost and difficulty in large-scale preparation. Therefore, developing a new low-cost, large-scale production periodic microstructure preparation technology can become the key to developing new thermal control coatings.

[0004] Given that metal anodization is a technology that can produce large-area metal oxide thin films, anodized films have been developed into highly infrared-emitting oxide thermal control coatings (CN115305549A, CN110098120B). However, their emissivity characteristics have been found to be significantly affected by the environment. Under high temperature, humidity, or space vacuum conditions, the films are prone to discoloration, reddening, water absorption and deliquesce, and crystal structure degradation, which affect their emissivity. Therefore, the preservation of anodized films and their long-term on-orbit service currently face certain technical limitations (CN115961321A, CN115948782A, CN113981501A). Furthermore, the current development of anodized films into high-performance infrared-radiating coatings relies on the infrared radiation properties of the anodized metal oxide material itself, but ignores the periodic nanotube array structure inherent in the anodized layer, which can enhance infrared radiation through localized electromagnetic resonance (CN111676501B, CN103243368A). It can be seen that relying on the advantages of anodized films and targeting the current shortcomings of such films during use, the radiation enhancement mechanism of the periodic micro-nano structure of anodized films is added to consider. The present invention designs a new silicon oxide / anodized aluminum oxide / metal aluminum composite structure with low solar light absorption rate and high infrared emissivity thermal control film and improves the relevant preparation technical parameters, which has profound positive significance for promoting the progress of my country's spacecraft thermal control technology. Summary of the Invention

[0005] The purpose of the present invention is to provide a low solar light absorption rate, high infrared emissivity aerospace thermal control film and preparation method, coupled with the high specific area characteristics of the anodized nanotube array, the electromagnetic wave local resonance mechanism of the nanotube array, the high infrared radiation characteristics of the silicon oxide material and the high visible spectrum reflection characteristics of the metal aluminum film. The film has a low thickness and achieves high solar reflectivity, high solar emissivity and good cooling efficiency.

[0006] In order to achieve the above technical objectives and the above technical effects, the present invention is implemented through the following technical solutions:

[0007] A low solar absorptivity, high infrared emissivity aerospace thermal control film comprising, from the sun-facing side toward the inside, a silicon oxide / anodized aluminum oxide layer, a nanometer-thick silver layer, and a micrometer-thick aluminum layer; wherein the silicon oxide / anodized aluminum oxide layer is composed of a silicon oxide coating layer and an anodized nanotube array layer;

[0008] After depositing a coating silicon oxide layer on the surface of a self-supporting anodic aluminum oxide nanotube array film with a periodic structure, a nanometer-thick silver layer / micrometer-thick aluminum layer laminate film is hot-pressed on one side of the composite film to produce a thermal control film with low solar light absorption and high infrared emissivity. When the film is in use, the side not bonded with the micrometer-thick aluminum layer serves as the sun-facing side.

[0009] In another aspect, the present invention provides a method for preparing the thermal control film, comprising the following steps:

[0010] S1: A 1 mm thick aluminum foil with a purity of 99.99% was electrochemically polished by electrolysis in a perchloric acid / ethanol mixture at 20 V for 30 min, and then rinsed with deionized water to obtain a clean electropolished aluminum foil.

[0011] S2: placing the electropolished aluminum foil in a 0.1 mol / L phosphoric acid solution, electrolyzing it at 195 V for 12 h at a temperature of 0°C to obtain a primary electrolytic sample; washing the preliminary electrolytic sample with deionized water, immersing it in a 65°C chromic acid / phosphoric acid etching mixed electrolyte for 5 h, and then washing it with deionized water to obtain an etched primary electrolytic sample; placing the etched primary electrolytic sample again in a 0.1 mol / L phosphoric acid solution, electrolyzing it at 195 V for 10 h at a temperature of 0°C, then raising the electrolyte temperature to 30°C and keeping the sample without power for 12 hours to obtain an anodized aluminum nanotube array layer on the aluminum foil surface, i.e., an anodized aluminum nanotube array / aluminum film;

[0012] S3: Filling the anodic aluminum oxide nanotube array / aluminum film with a polystyrene (PS) / toluene solution, removing the solvent in an 80°C oven after filling to obtain a polystyrene / anodic aluminum oxide nanotube array / aluminum film, then removing the metallic aluminum with a saturated HgCl2 aqueous solution, then washing with deionized water to remove components, and then removing the aluminum oxide end sealing layer with a 3 mol / L phosphoric acid solution. Then, removing the polystyrene in the nanotube pores with toluene to obtain a 25 μm thick self-supporting anodic aluminum oxide nanotube array film;

[0013] S4: Using atomic deposition technology with bis(diethylamino)silane as a silicon source, a 15 nm silicon oxide coating layer was deposited on the surface of the self-supporting anodic aluminum oxide nanotube array film at 100°C to prepare a self-supporting silicon oxide / anodic aluminum oxide nanotube array film;

[0014] S5: Using a 20-micron aluminum foil as a high solar spectrum reflective substrate, a 500-nanometer-thick silver film is deposited on the aluminum foil surface by electron evaporation deposition to produce a nanometer-thick silver / micrometer-thick aluminum laminate film;

[0015] S6: Using hot rolling means, a self-supporting silicon oxide / anodized aluminum oxide nanotube array film is attached to the nano-thick silver side of the nano-thick silver / micron-thick aluminum laminate film, and the two films are hot-statically pressed together under hot static pressing conditions to finally produce a thermal control film.

[0016] Furthermore, the volume ratio of perchloric acid to ethanol in step S1 is 1:4.

[0017] Furthermore, the chromic acid / phosphoric acid etching mixed electrolyte in step S2 is 1.8wt% H2CrO4 / 6wt% H3PO4.

[0018] Furthermore, the polystyrene mass content of the polystyrene (PS) / toluene solution in step S3 is 5 wt %.

[0019] Beneficial effects of the present invention

[0020] (1) The thermal control film of the present invention exhibits extremely low solar light absorption rate, and its solar spectrum reflectivity is as high as 0.86. This effect is mainly due to the composite structure design of the film. The high reflectivity of aluminum allows most of the solar radiation energy to be reflected rather than absorbed, thereby reducing the heat load. In addition, the design of the silicon oxide / anodized aluminum oxide composite layer further optimizes the overall optical properties. Silicon oxide exhibits low light absorption characteristics in the visible light range, and its optical band gap makes it highly reflective in the ultraviolet to visible light range. Combined with the structural advantages of anodized aluminum oxide, the film can form an effective optical heat insulation layer to ensure that the spacecraft maintains a low temperature in space, thereby protecting the normal operation of the instruments in the cabin and the safety of the occupants.

[0021] (2) The film of the present invention has an excellent infrared emissivity of 0.96, which is crucial, especially in spacecraft thermal control, as it can effectively dissipate internal heat to prevent overheating. The realization of high infrared emissivity depends on the unique structure of the alumina nanotube array. This structure not only has a high specific surface area, which significantly improves the thermal radiation efficiency, but also utilizes the local resonance mechanism of electromagnetic waves, thereby enhancing the coupling effect on infrared radiation. Through the design of the periodic nanotube array, when infrared radiation interacts with the material, it can produce strong resonance, effectively improving the radiation efficiency. Therefore, the film can not only quickly radiate heat into space, but also maintain a stable temperature in a high-temperature environment.

[0022] (3) The silicon oxide / anodized aluminum oxide film is combined with the silver-coated aluminum foil by hot static pressing using hot rolling technology, so that the silicon oxide / anodized aluminum oxide / metal aluminum composite film has good structural stability; the self-supporting structural design of the film greatly enhances its mechanical strength and durability, allowing the material to remain stable under extreme environmental conditions. The self-supporting anodized aluminum oxide nanotube array can effectively avoid film cracks or peeling caused by mechanical stress or thermal expansion during spacecraft operation. This design not only improves the overall stability and toughness of the film and reduces the failure rate, but also reduces maintenance costs during long-term on-orbit service, providing a guarantee for the long-term operation of the spacecraft.

[0023] (4) The preparation method of the present invention has high feasibility and economy. It adopts a two-step anodizing process and atomic layer deposition technology, which have been widely used and mature in industry. The aluminum substrate is treated by electrolytic polishing to obtain a highly uniform surface, which lays a good foundation for subsequent anodizing and silicon oxide deposition. By controlling the thickness of the aluminum oxide film and the silver-plated aluminum film, the composite film is guaranteed to have a low thickness (< 50 microns); the atomic layer deposition technology is used for uniform coating of silicon oxide to ensure precise control at the nanometer level. Such process settings not only improve the performance consistency of the film, but also reduce production costs. In addition, the application of the hot pressing bonding process makes the bonding between different materials stronger, ensuring that the various layers of the film can work together effectively, further improving the overall performance of the film. Combined with the selection of high-purity aluminum and appropriate reaction conditions, the reliability and durability of the film in practical applications are guaranteed, making it have broad application prospects in fields such as spacecraft and building radiant cooling.

[0024] Of course, any product implementing the present invention does not necessarily need to achieve all of the advantages described above at the same time. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for describing the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0026] Figure 1 Schematic diagram of the thermal control film structure of the present invention. Including: 1-silicon oxide / anodized aluminum oxide layer, 2-silicon oxide coating layer, 3-anodized nanotube array layer, 4-nanometer-thick silver layer, 5-micron-thick aluminum layer;

[0027] Figure 2 Schematic diagram of the preparation process of self-supporting silicon oxide / aluminum oxide nanotube array film;

[0028] Figure 3 Schematic diagram of the preparation process of the thermal control film of the present invention;

[0029] Figure 4 This is a schematic diagram of the thermal control film of the present invention;

[0030] Figure 5 Schematic diagram of the solar spectrum reflection spectrum and infrared spectrum emission spectrum of the thermal control film of the present invention;

[0031] Figure 6 is the solar spectrum reflectance spectrum of the self-supporting aluminum oxide / silicon dioxide film of the present invention;

[0032] Figure 7 is the infrared emission spectrum of the self-supporting aluminum oxide / silicon dioxide film of the present invention;

[0033] Figure 8 This is the solar spectrum reflectance spectrum of the S781 aerospace white paint currently in service in my country;

[0034] Figure 9 The infrared emission spectrum of the S781 aerospace white paint currently in service in China;

[0035] Figure 10 This is the solar spectrum reflectance spectrum of KS-Z inorganic white paint currently in service in my country;

[0036] Figure 11 The infrared emission spectrum of KS-Z inorganic white paint currently in service in China; DETAILED DESCRIPTION

[0037] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts shall fall within the scope of protection of the present invention.

[0038] To demonstrate the technical advantages of the thermal control coating described in this invention, the authors tested the solar reflectance and infrared emission spectra of a self-supporting alumina / silica film and existing Chinese white paint coatings (S781 and KS-Z inorganic white paint). The thermal control coating described in this invention exhibited superior solar reflectance and infrared emission characteristics compared to the self-supporting alumina / silica film and existing Chinese white paint coatings (S781 and KS-Z inorganic white paint), demonstrating the technical advantages of the thermal control coating described in this invention. Example 1

[0039] By coupling the high specific area characteristics of the anodized nanotube array, the electromagnetic wave local resonance mechanism of the nanotube array, the high infrared radiation characteristics of the silicon oxide material, and the high visible spectrum reflectivity of the metal aluminum film, the film has a low thickness and achieves high solar reflectivity, high solar emissivity, and good cooling efficiency. The thermal control coating structure of this embodiment is as follows Figure 1 As shown, from the sun-facing side to the inside, there is a silicon oxide / anodized aluminum oxide layer, a nanometer-thick silver layer, and a micrometer-thick aluminum layer. The silicon oxide / anodized aluminum oxide layer is composed of a silicon oxide coating layer and an anodized nanotube array layer.

[0040] As described in this embodiment, the thermal control film is made by hot rolling bonding a self-supporting silicon oxide / anodized aluminum oxide film and a silver-coated aluminum film; the self-supporting silicon oxide / anodized aluminum oxide film is prepared by coating silicon oxide on the surface of a self-supporting anodized aluminum oxide nanotube array film;

[0041] After depositing a silicon oxide layer on the surface of a self-supporting anodic aluminum oxide nanotube array film with a periodic structure, a nanosilver / metal aluminum film is hot-pressed onto one side of the composite film to form a thermal control coating with low solar light absorption and high infrared emissivity. When the film is in use, the aluminum oxide / silicon dioxide nanotube array film side serves as the sun-facing side. Example 2

[0042] As described in this embodiment, the method for preparing a thermal control film with low solar absorption rate and high infrared emissivity is to prepare a self-supporting periodic anodic oxide aluminum nanotube array film by treating a metal aluminum plate with a two-step anodic oxidation method, and then fill the nanotube pores with a high molecular polymer, remove the unreacted metal aluminum and part of the aluminum oxide end sealing layer, and then remove the polymer filler to obtain ( Figure 2 and Figure 3 The two-step anodization method is necessary to ensure that the alumina nanotube array has high periodicity. The silicon oxide coating layer is prepared by atomic layer deposition technology; the silver coating on the aluminum foil surface is prepared by electron beam thermal evaporation; the self-supporting silicon oxide / anodized aluminum oxide film is combined with the silver-coated aluminum foil by hot roller pressing and hot static pressing. Figure 3 ).

[0043] The specific steps include:

[0044] S1: A 1mm thick aluminum foil with 99.99% purity was electrochemically polished in a perchloric acid / ethanol mixture (perchloric acid:ethanol volume ratio of 1:4) at 20V for 30min. The foil was then rinsed with deionized water to obtain a clean electropolished aluminum foil.

[0045] S2: Place the electropolished aluminum foil in a 0.1 mol / L phosphoric acid solution, electrolyze it at 0°C and 195V for 12 hours to obtain a primary electrolytic sample. Wash the preliminary electrolytic sample with deionized water, immerse it in a 65°C chromic acid / phosphoric acid etching mixed electrolyte (1.8wt% H2CrO4 / 6wt% H3PO4) for 5 hours, and then wash it with deionized water to obtain an etched primary electrolytic sample. Place the etched primary electrolytic sample again in a 0.1 mol / L phosphoric acid solution, electrolyze it at 0°C and 195V for 10 hours, then increase the electrolyte temperature to 30°C and keep the sample without power for 12 hours to obtain an anodic aluminum oxide nanotube array layer on the aluminum foil surface, i.e., an anodic aluminum oxide nanotube array / aluminum film.

[0046] S3: Filling the anodic aluminum oxide nanotube array / aluminum film with a polystyrene (PS) / toluene solution (polystyrene content 5 wt%), removing the solvent in an 80°C oven after filling to obtain a polystyrene / anodic aluminum oxide nanotube array / aluminum film, then removing the metallic aluminum with a saturated HgCl2 aqueous solution, then washing with deionized water to remove components, and then removing the aluminum oxide end sealing layer with a 3 mol / L phosphoric acid solution. Then, removing the polystyrene in the nanotube pores with toluene to obtain a 25 μm thick self-supporting anodic aluminum oxide nanotube array film;

[0047] S4: Using atomic deposition technology with bis(diethylamino)silane as a silicon source, a 15 nm silicon oxide coating layer was deposited on the surface of the self-supporting anodic aluminum oxide nanotube array film at 100°C to prepare a self-supporting silicon oxide / anodic aluminum oxide nanotube array film;

[0048] S5: Using a 20-micron aluminum foil as a high solar spectrum reflective substrate, a 500-nanometer-thick silver film is deposited on the aluminum foil surface by electron evaporation deposition to produce a nanometer-thick silver / micrometer-thick aluminum laminate film;

[0049] S6: Using hot rolling means, a self-supporting silicon oxide / anodized aluminum oxide nanotube array film is attached to the nano-thick silver side of the nano-thick silver / micron-thick aluminum laminate film, and the two films are hot-statically pressed together under hot static pressing conditions to finally produce a thermal control film. Example 3

[0050] The silicon oxide / anodized aluminum oxide / metal aluminum composite structure thermal control film prepared in Example 2 has high solar spectrum reflectivity and high infrared spectrum emissivity ( Figure 5Spectral testing shows that the solar spectrum reflectivity is 0.86 and the infrared emissivity at the atmospheric window is 0.96, resulting in the thermally controllable film exhibiting good cooling efficiency. Under direct sunlight conditions, the temperature difference between the sun-facing and sun-facing sides can reach 6.1°C. This makes the thermally controllable film of the present invention suitable for use in architectural radiant cooling, aerospace, and military fields.

[0051] Comparative Example 1

[0052] The self-supporting silicon oxide / aluminum oxide nanotube array film in Example 2 was tested for solar spectrum reflection spectrum and infrared emission spectrum. The test data were as follows: Figure 6 and Figure 7 Spectral testing shows that the solar spectrum reflectance is <0.65 and the infrared emissivity at the atmospheric window is <0.85.

[0053] Comparative Example 2

[0054] We purchased the S781 aerospace white paint currently in service in my country and conducted solar spectrum reflection spectrum and infrared emission spectrum tests. The test data are as follows: Figure 8 and Figure 9 Spectral testing shows that the solar spectrum reflectance is <0.82 and the infrared emissivity at the atmospheric window is <0.90.

[0055] Comparative Example 3

[0056] We purchased KS-Z inorganic white paint currently in service in my country and conducted solar spectrum reflection spectrum and infrared emission spectrum tests. The test data are as follows: Figure 10 and Figure 11 Spectral tests show that the solar spectrum reflectance is <0.8 and the infrared emissivity at the atmospheric window is <0.92.

[0057] In summary, the present invention proposes a thermal control film with low solar absorptivity and high infrared emissivity, and a method for its preparation. The present invention utilizes atomic deposition technology to coat silicon oxide on the surface of a self-supporting anodic aluminum oxide nanotube array film. Furthermore, aluminum foil with a nanosilver layer is deposited on one side of the silicon oxide / anodic aluminum oxide film's bonding surface to form the thermal control film. The anodic aluminum oxide nanotube array imparts a high specific surface area to the silicon oxide coating, resulting in high infrared emissivity for the thermal control film. The metallic aluminum film imparts high solar spectrum reflectivity to the thermal control film. The nanotube array structure further enhances the film's infrared radiation properties through a mechanism of localized electromagnetic resonance.

[0058] The preferred embodiments of the present invention disclosed above are intended only to help illustrate the present invention. These preferred embodiments do not exhaustively describe all details, nor do they limit the present invention to the specific embodiments described. Obviously, many modifications and variations are possible based on the content of this specification. These embodiments are selected and described in detail in this specification to better explain the principles and practical applications of the present invention, thereby enabling those skilled in the art to better understand and utilize the present invention. The present invention is limited only by the claims and their full scope and equivalents.

Claims

1. A low solar absorptivity, high infrared emissivity aerospace thermal control film, characterized in that: From the sun-facing side to the inside, it includes: a silicon oxide / anodized aluminum oxide layer, a nanometer-thick silver layer, and a micrometer-thick aluminum layer; wherein the silicon oxide / anodized aluminum oxide layer is composed of a silicon oxide coating layer and an anodic oxide nanotube array layer; After depositing a coating silicon oxide layer on the surface of a self-supporting anodic aluminum oxide nanotube array film with a periodic structure, a nanometer-thick silver layer / micrometer-thick aluminum layer laminate film is hot-pressed on one side of the composite film to produce a thermal control film with low solar light absorption and high infrared emissivity. When the film is in use, the side not bonded with the micrometer-thick aluminum layer serves as the sun-facing side.

2. The method for preparing a thermal control film according to claim 1, wherein: The following steps are involved: S1: A 1 mm thick aluminum foil with a purity of 99.99% was electrochemically polished by electrolysis in a perchloric acid / ethanol mixture at 20 V for 30 min, and then rinsed with deionized water to obtain a clean electropolished aluminum foil. S2: Place the electropolished aluminum foil in 0.1 mol / L phosphoric acid solution and electrolyze at 195 V for 12 h at 0°C to prepare the primary electrolysis sample; The preliminary electrolysis sample was washed with deionized water, immersed in a 65°C chromic acid / phosphoric acid etching mixed electrolyte for 5 hours, and then washed with deionized water to obtain an etched primary electrolysis sample; the etched primary electrolysis sample was again placed in a 0.1 mol / L phosphoric acid solution, electrolyzed at 0°C and 195V for 10 hours, and then the electrolyte temperature was increased to 30°C and the sample was kept without power for 12 hours to obtain an anodic aluminum oxide nanotube array layer on the aluminum foil surface, i.e., an anodic aluminum oxide nanotube array / aluminum thin film; S3: Filling the anodic aluminum oxide nanotube array / aluminum film with a polystyrene (PS) / toluene solution, removing the solvent in an 80°C oven after filling to obtain a polystyrene / anodic aluminum oxide nanotube array / aluminum film, then removing the metallic aluminum with a saturated HgCl2 aqueous solution, then washing with deionized water to remove components, and then removing the aluminum oxide end sealing layer with a 3 mol / L phosphoric acid solution. Then, removing the polystyrene in the nanotube pores with toluene to obtain a 25 μm thick self-supporting anodic aluminum oxide nanotube array film; S4: Using atomic deposition technology with bis(diethylamino)silane as a silicon source, a 15 nm silicon oxide coating layer was deposited on the surface of the self-supporting anodic aluminum oxide nanotube array film at 100°C to prepare a self-supporting silicon oxide / anodic aluminum oxide nanotube array film; S5: Using a 20-micron aluminum foil as a high solar spectrum reflective substrate, a 500-nanometer-thick silver film is deposited on the aluminum foil surface by electron evaporation deposition to produce a nanometer-thick silver / micrometer-thick aluminum laminate film; S6: Using hot rolling means, a self-supporting silicon oxide / anodized aluminum oxide nanotube array film is attached to the nano-thick silver side of the nano-thick silver / micron-thick aluminum laminate film, and the two films are hot-statically pressed together under hot static pressing conditions to finally produce a thermal control film.

3. The preparation method according to claim 2, wherein: The volume ratio of perchloric acid to ethanol in step S1 is 1:

4.

4. The preparation method according to claim 2, wherein: The chromic acid / phosphoric acid etching mixed electrolyte in step S2 is 1.8wt% H2CrO4 / 6wt% H3PO4.

5. The preparation method according to claim 2, wherein: The polystyrene mass content of the polystyrene (PS) / toluene solution in step S3 is 5 wt %.

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