High-performance multi-spectral-band adaptive white inorganic coating and preparation method thereof

Abstract

The invention discloses a white inorganic coating with high performance and multispectral adaptability and a preparation method of the white inorganic coating, and belongs to the technical field of thermal control coatings of spacecrafts. The invention aims to solve the problems that the solar reflectivity of a ZnO inorganic thermal control coating is only about 85% and the thermal control capability is poor. A white inorganic coating with the pore diameter matched with the solar spectrum energy distribution rule is manufactured through the spraying technology, a white powder material, an alkali solution and silicate resin are bonded and mixed to be uniform to prepare white slurry, finally, the slurry is sprayed to an alloy substrate through the spraying technology, and after drying, the white inorganic coating is obtained. And a white inorganic coating with high-performance light area adaptability is formed on the alloy substrate. The white coating is low in solar absorptivity and high in emissivity, and the coating is stable in structural performance and excellent in mechanical property under extreme conditions (pressure, temperature and irradiation) due to the fact that silicate resin and a high-stability ZnO material are selected, so that the white coating is suitable for the actual task environment of spacecrafts and can be used in the fields of deep space exploration and the like.

Description

Technical Field

[0001] The present invention relates to the technical field of spacecraft thermal control coatings, and particularly relates to a high-performance multi-spectrum adaptable white inorganic coating and a preparation method thereof, which have very important application values. Background Art

[0002] In deep space exploration missions, the unobstructed sunlight in the universe will cause the temperature of the spacecraft shell to rise rapidly, affecting the normal operation of the spacecraft. A thermal control system is required to ensure the stable operation of the spacecraft. In the thermal control system, compared with the complex and high-cost active thermal control, covering a layer of thermal control coating on the surface of the spacecraft shell for protection is the most economical and effective method. Among them, white paint-based thermal control coatings have become the most widely used type of thermal control materials due to their low cost, simple operation, and suitability for various complex-shaped surfaces. White paint-based thermal control coatings often have high solar reflectivity and high infrared emissivity to control the temperature of the spacecraft surface thermal balance.

[0003] White paint type thermal control coatings can be divided into inorganic thermal control coatings and organic thermal control coatings according to the type of binder. The structures of inorganic coatings and organic coatings are similar, and the difference lies in whether the binder used is organic or inorganic. In the extreme environment of space, the use of organic thermal control coatings will be restricted. The chemical bonds of organic binders are vulnerable to the influence of space environmental conditions, such as auto-oxidation, degradation, and fracture, and the coatings will also crack, peel off, and yellow, seriously affecting their thermal control ability. Compared with organic thermal control coatings, inorganic thermal control coatings have higher reliability in space missions and have become the focus of research in the field of thermal control coatings. In inorganic thermal control coatings, ZnO has become a commonly used pigment due to its wide bandgap, high refractive index, and stable performance. However, it is still limited by its optical properties. The solar reflectivity of commonly used ZnO inorganic thermal control coatings is only about 85%, and the thermal control ability is poor. To achieve higher thermal control efficiency, it is particularly important to develop a white inorganic coating with high solar reflectivity.

[0004] An optical structure with excellent thermal management capabilities should have both high solar reflectivity and high solar emissivity. Multiple scattering of sunlight can achieve high solar reflectivity. According to Fresnel's law: ρ = (1 - √(ε_r)) / (1 + √(ε_r)), when the dielectric constant ε of the medium r≥1. When the Fresnel coefficient ρ is negative, it means that the incident light will undergo a phase change of 2π before backscattering. Two strategies can be adopted to promote the multiple scattering behavior of sunlight after it enters the material, namely, introducing an interface with a high dielectric contrast and fine particles similar in wavelength to sunlight. The pore structure of the inorganic coating often comes from the accumulation of pigment particles after the binder cures. The pore structure formed by the particle accumulation is random and cannot accurately match the optimal size of the scattered light. Therefore, a method needs to be proposed to regulate the pore structure of the inorganic thermal control coating to match the energy distribution of each spectral band of the solar spectrum, so as to achieve better thermal management capabilities of the inorganic coating. Summary of the Invention

[0005] Traditional inorganic thermal control materials often only consider the overall reflection ability of the material itself to the solar spectrum, while ignoring the influence of the coating structure on the reflection of the solar spectrum. Compared with the simplicity of the design of traditional thermal control materials, the present invention realizes a higher solar light reflectivity by designing the internal structure of the coating.

[0006] The pore structure in the existing inorganic coatings often comes from the random accumulation of pigments, and the formed pore structure is random and cannot accurately match the optimal size of the scattered light. The present invention prepares a pore structure with a pore size distribution matching the energy distribution law of the solar spectrum, improves the solar spectrum reflectivity of the white inorganic thermal control coating, and thus improves the thermal control ability of the inorganic thermal control coating.

[0007] Some researchers have studied the pore-forming methods for coatings, but these methods often have problems such as high requirements for production conditions and pollution, and their applications are limited. The present invention adopts a simple spraying technique to assemble a hierarchical porous structure inside the coating by changing the dynamic flow process of the internal pigments in the paint droplets, and finally prepares a white inorganic coating adaptable to the optical region. The manufacturing method is simple and environmentally friendly, which greatly improves the possibility of its practical application.

[0008] The present invention provides a high-performance multi-spectrum adaptable white inorganic coating and a preparation method thereof. A white inorganic coating with pores matching the energy distribution law of the solar spectrum is manufactured by spraying technology. A white powder material, an alkali solution and a silicate resin binder are mixed evenly to form a white slurry, and finally the slurry is sprayed on an alloy substrate by spraying technology. After drying, a high-performance multi-spectrum adaptable white inorganic coating is formed on the alloy substrate.

[0009] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0010] The object of the present invention is to provide a preparation method of a high-performance multi-spectrum adaptable white inorganic coating, which is characterized by including the following steps: mixing a white pigment, an alkali solution with a pH value of 10 - 13, and a silicate resin evenly to obtain a white slurry; then spraying it on the surface of an alloy substrate and curing to obtain the coating.

[0011] Further defined, it is mixed evenly by a cutting mixer.

[0012] Further defined, the stirring rate is 1000 rpm - 3000 rpm; for example, 1000 rpm, 1500 rpm, 2000 rpm, 2500 rpm, 3000 rpm, etc.

[0013] Further defined, the stirring time is 1 - 3 h; for example, 1 h, 1.5 h, 2 h, 2.5 h, 3 h, etc.

[0014] Further defined, the silicate resin is one of lithium silicate resin, sodium silicate resin, and potassium silicate resin.

[0015] Further defined, the alkali solution is lithium hydroxide, sodium hydroxide, or potassium hydroxide; the mass ratio of the white pigment to the volume of the alkali solution is 10 g∶50 ml.

[0016] Further defined, the pigment - binder ratio is 1∶(1 - 15); for example, 1∶1, 1∶2, 1∶3, 1∶4, 1∶5, etc.

[0017] Further defined, the white pigment is ZnO.

[0018] Further defined, the alloy substrate is aluminum alloy, titanium alloy, magnesium alloy, etc.

[0019] Further defined, the spraying distance is 10 cm - 30 cm; for example, 10 cm, 15 cm, 20 cm, 25 cm, 30 cm.

[0020] Further defined, the spraying pressure is 0.4 MPa - 1 MPa; for example, 0.4 MPa, 0.6 MPa, 0.8 MPa, 1 MPa.

[0021] Further defined, the curing temperature is 80°C - 200°C; for example, 80°C, 120°C, 160°C, 200°C.

[0022] Another object of the present invention is to provide a high-performance multi-spectrum adaptable white inorganic coating. The coating is a white inorganic coating with pore sizes matching the solar spectrum energy distribution law manufactured by spraying technology. Specifically, a white powder material, an alkali solution, and a silicate resin are bonded and mixed evenly to form a white slurry. Finally, the slurry is sprayed on an alloy substrate by spraying technology. After drying, a high-performance multi-spectrum adaptable white inorganic coating is formed on the alloy substrate. The coating as a whole presents a porous structure, and the pore size distribution is at the nanometer and micrometer levels. The nanometer size is 200 nm to 800 nm, and the micrometer size is 1 μm to 3 μm, with an average reflectivity of 94.2%.

[0023] Based on the Mie multiple scattering law, the present invention has developed a hierarchical porous coating construction strategy. In this strategy, an alkali solution is ingeniously introduced into the paint system to change the chemical microenvironment of the binder, thereby inducing the silicate resin to exist in the form of oligomers, and then regulating the dynamic flow of the internal pigment dispersion in the paint droplets during the water evaporation stage, realizing the assembly of the internal structure of the coating, and finally preparing a high-performance light-region adaptable white inorganic coating.

[0024] The present invention introduces pores as the second scatterer into the inorganic white coating, cooperates with ZnO to jointly achieve multiple scattering of light, and at the same time regulates the pore structure of the coating to make its size characteristics match the energy distribution law of the solar spectrum, realizing a high reflectivity of the solar spectrum, thereby improving the thermal management ability of the coating. The present invention adopts a simple pore-forming method, only regulates the alkaline environment of the slurry to control the pore structure of the coating. The coating preparation method is simple, has high experimental repeatability, and is low in cost, greatly improving the possibility of its practical application.

[0025] Compared with the prior art, the present invention has the following beneficial effects:

[0026] The present invention uses spraying technology to prepare a light-region adaptable white inorganic coating with a high solar reflectivity. ZnO powder, an alkali solution, and a resin are bonded and mixed evenly to form a white slurry, creating a suitable alkaline environment to induce the silicate binder to form a specific oligomer form, significantly reducing the flow resistance of the internal pigment dispersion in the white paint droplets during the spraying process, promoting pigment positioning and assembly, and forming a pore structure with both nano- and micrometer-scale hierarchical pores after the white paint film is formed under the action of capillary force. After curing, a light-region adaptable white inorganic coating with a high solar reflectivity is formed on the alloy substrate. By adjusting the pigment-binder ratio of the slurry and the spraying process conditions, the pore structure inside the coating material can be controlled.

[0027] In addition, the white coating has a low solar absorptance and a high emissivity. Due to the selection of silicate resin and highly stable ZnO material, the coating has stable structural properties and excellent mechanical properties under extreme conditions (pressure, temperature, irradiation), making it suitable for the actual mission environment of spacecraft and can be used in fields such as deep space exploration.

[0028] In order to further understand the features and technical content of the present invention, please refer to the following detailed description of the present invention and the attached drawings. However, the attached drawings are only for reference and illustration purposes and are not used to limit the present invention. Brief Description of the Drawings

[0029] Figure 1 White light interference test diagram of the white slurry droplets prepared in Example 1 of the present invention;

[0030] Figure 2 SEM diagram of the ZnO-Li-200°C coating prepared in Example 1 of the present invention;

[0031] Figure 3 Solar spectrum absorption test results of the white coating of the ZnO-Li-200°C coating prepared in Example 1 of the present invention;

[0032] Figure 4 Spectral emission test results of the white coating of the ZnO-Li-200°C coating prepared in Example 1 of the present invention;

[0033] Figure 5 Macroscopic morphology test results of the white coating of the ZnO-Li-200°C coating prepared in Example 1 of the present invention before and after ultraviolet irradiation and thermal cycling tests;

[0034] Figure 6 XPS test results of the white coating of the ZnO-Li-200°C coating prepared in Example 1 of the present invention before and after ultraviolet irradiation;

[0035] Figure 7 Solar reflectance test results of the white coating of the ZnO-Li-200°C coating prepared in Example 1 of the present invention before and after ultraviolet irradiation and after thermal cycling tests;

[0036] Figure 8 Actual cooling effect test results of the white coating of the ZnO-Li-200°C coating prepared in Example 1 of the present invention;

[0037] Figure 9 Absorption and irradiation ratio test results of the white coatings of the ZnO-Li-200°C, ZnO-Na-200°C, and ZnO-K-200°C coatings prepared in Examples 1, 2, and 3 of the present invention;

[0038] Figure 10Infrared emission test results of the ZnO-Li-200°C, ZnO-Na-200°C, and ZnO-K-200°C coatings prepared in Example 1, Example 2, and Example 3 of the present invention;

[0039] Figure 11 Solar reflectance test results of the ZnO-Li-200°C, ZnO-Na-200°C, and ZnO-K-200°C coatings prepared in Example 1, Example 2, and Example 3 of the present invention. Detailed implementation manners

[0040] The present invention will be described in detail below in conjunction with specific embodiments. The following embodiments will help those skilled in the art to further understand the present invention, and at the same time do not limit the present invention in any form. It should be noted that for those of ordinary skill in the art, without departing from the inventive concept of the present invention, several modifications and improvements can still be made. These all belong to the protection scope of the present invention.

[0041] Example 1: In this example, an inorganic white coating ZnO-Li-200°C with high solar reflectivity and light zone adaptability is prepared. This coating is obtained by spraying a slurry formed by mixing ZnO pigment, lithium hydroxide solution as an alkali solution, and lithium silicate resin on an alloy substrate. Its preparation method is carried out according to the following steps:

[0042] Step 1: Preparation of white slurry:

[0043] Mix ZnO pigment, lithium hydroxide solution with pH = 12, and lithium silicate resin, and stir evenly at a speed of 2000 rpm for 2 hours (time-consuming 2h) at room temperature using a cutting mixer. The pigment-volume ratio (ZnO pigment to lithium silicate resin) is 3:1; a colored slurry is obtained.

[0044] The mass ratio of the white pigment to the volume of the alkali solution is 10g:50ml;

[0045] Step 2: Spray the slurry on the alloy substrate:

[0046] Select aluminum alloy as the metal substrate. Ultrasonically clean the sandblasted aluminum alloy substrate with acetone and absolute ethanol, dry it and then place it in the spraying chamber. Control the spraying distance to be 20 cm, the spraying pressure to be 0.6 Mpa. After the spraying thickness reaches 200 μm, dry it in an oven at 200°C for 2 hours to obtain a high-performance coating.

[0047] Example 2: In this example, an inorganic white coating ZnO-Na-200°C with high solar reflectivity and light zone adaptability is prepared. This coating is obtained by spraying a slurry formed by mixing ZnO pigment, sodium hydroxide solution as an alkali solution, and sodium silicate resin on an alloy substrate. Its preparation method is carried out according to the following steps:

[0048] Step 1: Preparation of white slurry:

[0049] Mix ZnO pigment, sodium hydroxide solution with pH = 11, and sodium silicate resin, and stir evenly at room temperature using a cutting mixer at a speed of 2500 rpm (for 2 hours). The pigment-binder ratio (ZnO pigment to lithium silicate resin) is 3:1 to obtain a colored slurry.

[0050] The mass ratio of the white pigment to the volume of the alkali solution is 10 g:50 ml;

[0051] Step 2: Spray the slurry on the alloy substrate:

[0052] Select aluminum alloy as the metal substrate. Ultrasonically clean the sandblasted aluminum alloy substrate with acetone and absolute ethanol, dry it, and then place it in the spraying chamber. Control the spraying distance to be 20 cm, the spraying pressure to be 0.4 Mpa. After the spraying thickness reaches 200 μm, dry it in an oven at 200 °C for 2 hours to obtain a high-performance coating.

[0053] Example 3: In this example, the inorganic white coating ZnO-K-200 °C with high solar reflectivity and light zone adaptability is obtained by spraying a slurry formed by mixing ZnO pigment, potassium hydroxide solution as the alkali solution, and potassium silicate resin on an alloy substrate. Its preparation method is carried out according to the following steps:

[0054] Step 1: Preparation of white slurry:

[0055] Mix ZnO pigment, potassium hydroxide solution with pH = 10, and potassium silicate resin, and stir evenly at room temperature using a cutting mixer at a speed of 2500 rpm (for 2 hours). The pigment-binder ratio (ZnO pigment to lithium silicate resin) is 4:1 to obtain a white slurry.

[0056] The mass ratio of the white pigment to the volume of the alkali solution is 10 g:50 ml;

[0057] Step 2: Spray the slurry on the alloy substrate:

[0058] Select aluminum alloy as the metal substrate. Ultrasonically clean the sandblasted aluminum alloy substrate with acetone and absolute ethanol, dry it, and then place it in the spraying chamber. Control the spraying distance to be 15 cm, the spraying pressure to be 0.4 Mpa. After the spraying thickness reaches 200 μm, dry it in an oven at 200 °C for 2 hours to obtain a high-performance coating.

[0059] Example 4: In this example, the inorganic white coating ZnO-K-80 °C with high solar reflectivity and light zone adaptability is obtained by spraying a slurry formed by mixing ZnO pigment, potassium hydroxide solution as the alkali solution, and potassium silicate resin on an alloy substrate. Its preparation method is carried out according to the following steps:

[0060] Step 1: Preparation of white slurry:

[0061] Mix ZnO pigment, potassium hydroxide solution with pH = 10 and potassium silicate resin, and stir evenly at room temperature with a cutting mixer at a speed of 2500 rpm (for 2 h). The pigment-binder ratio (ZnO pigment to lithium silicate resin) is 2:1; obtain white slurry.

[0062] The mass ratio of white pigment to the volume of alkali solution is 10 g:50 ml;

[0063] Step 2: Spray the slurry on the alloy substrate:

[0064] Select aluminum alloy as the metal substrate. Ultrasonically clean the sandblasted aluminum alloy substrate with acetone and absolute ethanol, and put it into the spraying chamber after drying. Control the spraying distance to be 15 cm, the spraying pressure to be 0.8 Mpa. After the spraying thickness reaches 200 μm, dry it in an oven at 80 °C for 2 h to obtain a high-performance coating.

[0065] For the coating prepared in the above embodiment, the following tests were carried out:

[0066] White light interference test: The ZnO-Li-200 °C coating prepared in Example 1 of the present invention was used for white light interference test. As Figure 1 shown, the surface morphology characteristics after droplet drying are intuitively displayed through the measurement data of the white light interferometer. After the liquid in the droplet is completely evaporated, the range of particle deposition is about 200 μm. The particles are closely packed at the edge of the original droplet, while only loosely stacked particles exist inside the droplet. As approaching the edge contour of the droplet, the characteristics become denser and denser. Smaller-scale pores, namely nanoscale pores, are formed inside the closely packed particles, and larger-scale pores, namely micron-scale pores, are formed inside the loosely stacked particles. Through the stacking of particles inside the droplet layer by layer, the coating will finally achieve the assembly of a hierarchical porous structure.

[0067] SEM test: The ZnO-Li-200 °C coating prepared in Example 1 of the present invention was used for SEM test. As Figure 1 shown, the coating as a whole presents a porous structure. The pore sizes are distributed in the nano and micron levels. The pores and pigments jointly form a multiple scatterer network. Most of the pore sizes in the coating are in the VIS wavelength range with high energy flux, and there are also pores with pore diameters in the UV and NIR wavelength ranges, corresponding to the energy distribution law of the solar spectrum.

[0068] Solar spectrum reflectance test: The ZnO-Li-200 °C coating prepared in Example 1 of the present invention was used to test the solar light reflection performance. As Figure 2As shown, the test shows that the ZnO-Li-200°C coating has good reflection performance in the solar spectrum band, with an average reflectivity of 89.5%, which has reached the reflection performance of commercial coatings in the solar spectrum band.

[0069] Infrared emission measurement: The ZnO-Li-200°C coating prepared in Example 1 of the present invention was used to test the absorption of sunlight. As Figure 3 shown, the test shows that the ZnO-Li-200°C coating has good spectral emission performance, with an average reflectivity of 94.2%, which has reached the infrared emission performance of commercial coatings.

[0070] Ultraviolet measurement: A spatial ultraviolet irradiation simulation device was used to conduct an ultraviolet irradiation test on the ZnO-Li-200°C white coating prepared in Example 4, and the surface morphology of the white coating before and after ultraviolet irradiation was compared (as Figure 4 shown). The comparison before and after irradiation shows that after the ZnO-Li-200°C coating undergoes ultraviolet irradiation testing, there is no peeling, no exposure of the base, and no yellowing on the coating surface. Moreover, by comparing the solar reflectivity of the coating before and after ultraviolet irradiation, it is found that the optical properties of the coating have not deteriorated, indicating that the prepared ZnO-Li-200°C coating has excellent environmental stability.

[0071] Thermal cycling test: In fifty thermal cycling tests up to 200°C and down to -196°C, there is no peeling, no exposure of the base, and no yellowing on the coating surface. Moreover, by comparing the solar reflectivity of the coating before and after the thermal cycling test, it is found that the optical properties of the coating remain stable and basically unchanged, indicating that the prepared ZnO-Li-200°C coating has excellent heat resistance and can resist extreme temperature environments in space.

[0072] XPS test: The ZnO-Li-200°C coating prepared in Example 1 of the present invention was used for XPS test, and the test results are as Figure 5 shown. Before and after ultraviolet irradiation, the bond composition of the material of the white inorganic coating has not changed. The Zn2p orbit can be mainly divided into Zn2p3 / 2 and Zn2p1 / 2, and after irradiation, it slightly changes from 1021.26 and 1044.34 eV to 1021 and 1044.23 eV. The characteristic peaks of the O1s spectrum mainly appear near 529.59, 531.68, and 532.8 eV and 529.95, 531.73, and 532.57 eV before and after ultraviolet irradiation, corresponding to Zn-O, Li-O, and Si-O bonds respectively. In addition, the binding energy of Si 2p is 102.54 eV and 102.53 eV before and after ultraviolet irradiation respectively.

[0073] Coating Thermal Control Ability Test: To visualize the thermal control performance of the coating, in the present invention, a solar simulator and an infrared thermal imager are simultaneously used to simulate the thermal control performance of the ZnO-Li-200°C coating. The test results are as follows Figure 8 shown. After being irradiated by the solar simulator for 600 s, the temperature of the ZnO-Li-200°C coating only rises from 25°C to 34.8°C, which is ~7°C lower than that of the substrate without coating protection. This confirms the effective thermal control ability of the light-region adaptable white inorganic coating prepared in the present invention.

[0074] Mass Loss Test: After the ultraviolet irradiation test, a high-precision balance was used to measure the mass loss of the ZnO-Li-200°C white coating prepared in Example 1 before and after irradiation. From the numerical value of the mass loss rate, the mass loss rate of the coating under the action of ultraviolet irradiation is extremely small and basically unchanged.

[0075] Solar Spectral Reflectance Test: In the present invention, the ZnO-Li-200°C coating prepared in Example 1 was used to test the sunlight reflection performance. As follows Figure 2 shown. The test shows that the ZnO-Li-200°C coating has good reflection performance in the solar spectral band, with an average reflectance of 89.5%, which has reached the reflection performance of commercial coatings in the solar spectral band.

[0076] Absorption-Radiation Ratio Test: To evaluate the energy absorption and radiation characteristics of materials in a specific radiation environment, the absorption-radiation ratio tests were carried out on the ZnO-Li-200°C, ZnO-Na-200°C, and ZnO-K-200°C white coatings prepared in Example 1, Example 2, and Example 3. The test results are as follows Figure 9 shown. ZnO-Li-200°C has the lowest absorption-radiation ratio of about 13.23%. The absorption-radiation ratio of ZnO-Na-200°C is lower than that of ZnO-K-200°C because the high pH has a greater impact on the binder, forming more pores inside the coating.

[0077] Infrared Emission Test: In the present invention, the ZnO-Li-200°C, ZnO-Na-200°C, and ZnO-K-200°C white coatings prepared in Example 1, Example 2, and Example 3 were used to test the sunlight absorption. As follows Figure 9 shown. The test shows that the ZnO-Li-200°C, ZnO-Na-200°C, and ZnO-K-200°C white coatings all have good spectral emission performance, with an average reflectance of 94.2%, which has reached the infrared emission performance of commercial coatings.

[0078] Solar spectral reflectance test: The present invention uses the ZnO-Li-200°C, ZnO-Na-200°C, and ZnO-K-200°C white coatings prepared in Example 1, Example 2, and Example 3 to test the reflection performance of sunlight. As Figure 11 shown, the test shows that the ZnO-Li-200°C coating has the highest reflection performance in the solar spectral band, and has reached the reflection performance of commercial coatings in the solar spectral band, indicating that the influence of high pH on the binder is greater, and high-performance coatings can be prepared.

[0079] The specific embodiments of the present invention have been described above. It should be noted that the present invention is not limited to the above specific embodiments, and those skilled in the art can make various deformations or modifications within the scope of the claims, which does not affect the essence of the present invention.

Claims

1. A preparation method of a high-performance multi-spectrum adaptable white inorganic coating, characterized in that, It includes the following steps: uniformly mixing a white pigment, an alkali solution with a pH value of 10 - 13, and a silicate resin to obtain a white slurry; then spraying it on the surface of an alloy substrate and curing to obtain the coating.

2. The method according to claim 1, wherein Mix uniformly using a cutting mixer; the stirring rate is 1000 - 3000 rpm.

3. The method according to claim 1, wherein The silicate resin is lithium silicate resin, sodium silicate resin, or potassium silicate resin.

4. The method according to claim 1, characterized in that, The alkali solution is lithium hydroxide, sodium hydroxide, or potassium hydroxide; the mass ratio of the white pigment to the volume of the alkali solution is 10 g∶50 ml.

5. The method according to claim 1, characterized in that The pigment - binder ratio is 1∶(1 - 15).

6. The method according to claim 1, wherein The white pigment is ZnO.

7. The method according to claim 1, wherein The alloy substrate is aluminum alloy, titanium alloy, or magnesium alloy.

8. The method according to claim 1, characterized in that The spraying distance is 10 cm - 30 cm, and the spraying pressure is 0.4 MPa - 1 MPa.

9. The method according to claim 1, characterized in that The curing temperature is 80 °C - 200 °C.

10. A coating prepared by the method according to any one of claims 1 - 9, the coating as a whole presents a porous structure, the size of the pores is distributed at the nano and micron levels, the nano - size is 200 nm - 800 nm, the micron - size is 1 μm - 3 μm, and the average solar - spectrum reflectivity is 94.2%.

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