Preparation method for constructing multi-size light absorption coating by doping low-refractive-index particles

Abstract

The invention discloses a preparation method for constructing a multi-size light absorption coating by doping low-refractive-index particles, and relates to a preparation method of a light absorption coating. The purpose of the present invention is to increase the absorptivity and emissivity of black coatings used in existing thermal protection fields. According to the preparation method, SiO2 nano-particles are used as doping particles, and the coating is obtained through a plasma electrolytic oxidation method; siO2 NPs is doped into the coating, so that the surface of the coating has a low effective refractive index, and reflection can be effectively reduced; the coating has a multi-size micro-nano surface structure, and the nano structure can enhance forward scattering and promote the coating to absorb and scatter light in a solar spectral range; the micron protruding structures promote light scattering of the coating on the infrared band, the optical path is increased, and the infrared emission performance of the coating is improved. The coating has good thermal control performance due to excellent absorption performance and emission performance, and has huge potential for long-term application under outdoor and extreme environment conditions.

Description

Technical Field

[0001] This invention relates to a method for preparing a light-absorbing coating, specifically a method for preparing a multi-size light-absorbing coating by doping with low-refractive-index particles. Background Technology

[0002] Coating the surface of spacecraft components with black thermal control coatings exhibiting high light absorption and emissivity can be widely used to enhance their heat absorption or dissipation capabilities. Various processes exist for preparing black thermal control coatings, including laser cladding, chemical vapor deposition, hydrothermal methods, and plasma electrolytic oxidation (PEO). Among these, PEO has attracted significant attention due to its low cost, low pollution, ease of operation, and the excellent thermal control performance, reliable mechanical strength, good thermal stability, and sufficient bonding strength of the resulting coatings.

[0003] Plasma electrolytic oxidation (PEO) is a surface treatment technology applicable to aluminum, magnesium, titanium, and their alloys, and can be used to prepare various types of thermally controlled coatings. A significant advantage of PEO technology is its ability to control the morphology of the resulting coating by adjusting process parameters, thereby affecting its light absorption properties. However, the ability to adjust the light absorption characteristics of the coating by changing process parameters is limited. Under certain conditions, such as high voltage or low frequency, the coating composition may become uneven, or even blistering may occur, which can adversely affect the optical and mechanical properties of the coating.

[0004] Another significant advantage of PEO technology lies in its ability to introduce elemental doping from the electrolyte. By adding iron, copper, and nickel salts to the electrolyte, corresponding oxides are generated on the coating surface. Besides ion doping, particle doping can also be performed in the electrolyte. Adding particles such as TiO2, Cr2O3, and graphene (rGO) to the electrolyte improves the coating composition and modulates its morphology. Compared to adjusting process parameters, elemental doping offers significant advantages in enhancing light absorption performance by altering the coating's composition and structure. However, the rational and precise selection of dopants is crucial for improving coating performance and currently faces considerable challenges. Summary of the Invention

[0005] The purpose of this invention is to improve the absorption and emissivity of black coatings used in the field of existing thermal protection, and to provide a method for preparing multi-size light-absorbing coatings by low-refractive-index particle doping.

[0006] A method for preparing a multi-size light-absorbing coating by doping with low-refractive-index particles is specifically carried out according to the following steps:

[0007] 1. Use sandpaper to sand the TC4 board, then clean it to obtain the treated TC4 board;

[0008] II. Preparation of electrolyte:

[0009] The electrolyte is prepared by dissolving SiO2 nanoparticles, sodium polyphosphate, EDTA, sodium hexametaphosphate, FeSO4, sodium metasilicate, nickel acetate and ammonium metavanadate in deionized water.

[0010] 3. Connect the treated TC4 plate to the positive terminal of the power supply and the electrolytic cell to the negative terminal of the power supply. Pour the electrolyte into the electrolytic cell and stir continuously. Use plasma electrolytic oxidation technology to prepare a coating on the TC4 plate. After the reaction is complete, wash and dry to obtain a multi-size light-absorbing coating constructed by low refractive index particle doping.

[0011] The principle of this invention:

[0012] This invention uses SiO2 nanoparticles (SiO2 NPs) as dopants to obtain a PEO-50-1.0 coating via plasma electrolytic oxidation (PEO). The doping of SiO2 NPs into the coating results in a low equivalent refractive index on the PEO-50-1.0 surface, effectively reducing reflection. The PEO-50-1.0 coating possesses multi-sized micro / nano surface structures; these nanostructures enhance forward scattering, promoting the absorption and scattering of light across the solar spectrum. Micron-sized protrusions further enhance light scattering in the infrared band, increasing the optical path and improving the infrared emission performance of the PEO-50-1.0 coating. These excellent absorption and emission properties give the PEO-50-1.0 coating good thermal control performance.

[0013] This invention uses TC4 as a substrate and prepares a multi-sized micro / nano-structured ceramic coating on the TC4 surface using PEO technology and low-refractive-index SiO2 NPs. Its advantages are as follows:

[0014] 1. The coating exhibits an amorphous structure, mainly composed of oxides such as ferric oxide, titanium dioxide, vanadium pentoxide, nickel oxide, silicates, and silicon dioxide; it has good light absorption properties and also has advantages such as being green, efficient, stable, and low-cost.

[0015] 2. The doping of SiO2 NPs into the coating can effectively reduce the equivalent refractive index of the PEO coating surface and reduce light scattering.

[0016] Third, SiO2 NPs also construct multi-scale micro- and nano-structures on the PEO coating surface, manifested as micro-structures with high protrusions on the coating surface and nano-structures with particle distribution of different sizes; these micro- and nano-particles interact with light of corresponding wavelengths, enhancing forward scattering and improving light absorption; the high protrusions also increase light scattering and absorption in the infrared spectral range.

[0017] IV. This invention prepares a PEO coating doped with low-refractive-index silica nanoparticles (SiO2 NPs) to adjust the refractive index, morphology, and structure of the composite coating. The doped SiO2 NPs reduce the effective refractive index of the coating, thereby reducing light reflection from the PEO coating and enhancing multi-band light scattering. The micron / nano-scale particles and micron-scale protrusions on the coating surface enhance multiple light scattering and increase the optical path. A coating with excellent optical properties is prepared through a silica-doped PEO process. When 50 nm of SiO2 is added to the electrolyte... At NPs, the PEO-50-1.0 coating exhibits the best performance, demonstrating an ultra-high solar absorptivity of 96.1% in the 0.25–2.5 μm spectral range and a thermal emissivity of 95.6% in the 2.5–16 μm infrared region. Furthermore, even at an incident angle of 70°, the absorptivity remains as high as 94.3%, meeting the requirements for multi-angle applications. During the heating experiment, the temperature of the PEO-50-1.0 coating rapidly increased, reaching 130°C in 400 seconds. In the subsequent cooling phase, under ambient conditions, the coating temperature decreased from 130°C to 74.5°C within 200 seconds.

[0018] V. The low-refractive-index particle-doped multi-size light-absorbing coatings prepared by this invention have high solar absorptivity, excellent thermal emissivity and robust mechanical properties, and have great potential for long-term application in outdoor and extreme environmental conditions. Attached Figure Description

[0019] Figure 1 In the diagram, a represents the refractive index and extinction coefficient of SiO2NPs, and b is a schematic diagram of the preparation of a multi-size light-absorbing coating constructed by low-refractive-index particle doping according to the present invention.

[0020] Figure 2 The following are bar charts showing the thickness and roughness of the coatings prepared in Comparative Example 1 and Examples 1-7;

[0021] Figure 3 The images show SEM images of the coatings prepared in Comparative Example 1 and Examples 1-4. Figure 3 In the examples, (a.1), (a.2), and (a.3) are PEO-0-0 coatings prepared in Comparative Example 1; (b.1), (b.2), and (b.3) are PEO-15-1.0 coatings prepared in Example 2; (c.1), (c.2), and (c.3) are PEO-50-1.0 coatings prepared in Example 1; (d.1), (d.2), and (d.3) are PEO-100-1.0 coatings prepared in Example 3; and (e.1), (e.2), and (e.3) are PEO-200-1.0 coatings prepared in Example 4.

[0022] Figure 4SEM image of the PEO-50-1.0 coating prepared in Example 1 and the size distribution of non-uniform particles;

[0023] Figure 5 SEM images of the PEO-0-0 coating prepared in Comparative Example 1 and the size distribution of non-uniform particles;

[0024] Figure 6 (a) is a transmission electron microscope image of the PEO-50-1.0 coating prepared in Example 1, and (b) is...

[0025] High-resolution transmission electron microscope image, with the inset showing its Fourier transform.

[0026] Figure 7 EDS image of the surface of the PEO-50-1.0 coating prepared in Example 1;

[0027] Figure 8 EDS image of the cross-section of the PEO-50-1.0 coating prepared in Example 1, scale bar: 10 μm;

[0028] Figure 9 XRD patterns of SiO2, PEO-0-0 coating prepared in Comparative Example 1, and PEO-50-1.0 coating prepared in Example 1;

[0029] Figure 10 FT-IR characterization images of SiO2, PEO-0-0 coating prepared in Comparative Example 1, and PEO-50-1.0 coating prepared in Example 1;

[0030] Figure 11 Raman spectra of SiO2, PEO-0-0 coating prepared in Comparative Example 1, and PEO-50-1.0 coating prepared in Example 1;

[0031] Figure 12 The first XPS spectra of the PEO-0-0 coating prepared in Comparative Example 1 and the PEO-50-1.0 coating prepared in Example 1 are shown, where (a) is the full spectrum, (b) is the Ni 2p spectrum, (c) is the Ti 2p spectrum, and (d) is the V 2p spectrum.

[0032] Figure 13 The second XPS spectra of the PEO-0-0 coating prepared in Comparative Example 1 and the PEO-50-1.0 coating prepared in Example 1 are shown, where (a) is Fe 2p, (b) is Si 2p, and (c) is O 1s spectrum.

[0033] Figure 14 (a) shows the comparison between the absorption spectrum of TC4 and the solar irradiance, and (b) shows the infrared emissivity characteristics of TC4.

[0034] Figure 15 (a) and (d) are comparison diagrams of the absorption spectrum of the PEO coating and the solar irradiance, (b) and (e) are the infrared emissivity characteristics of the PEO coating, and (c) and (f) are the solar weighted absorptivity of the PEO coating in the wavelength range of 200-2500 nm and the average infrared emissivity in the wavelength range of 2.5-16 μm.

[0035] Figure 16 A schematic diagram of the variable angle absorption performance testing device is shown.

[0036] Figure 17 The absorption performance of different PEO coatings varies with angle, where (a) is PEO-0-0 coating, (b) is PEO-15-1.0 coating, (c) is PEO-50-1.0 coating, (d) is PEO-100-1.0 coating, (e) is PEO-200-1.0 coating, and (f) is the solar weighted absorptivity of different PEO coatings varying with incident angle.

[0037] Figure 18 (a) shows the illumination intensity at 500 mW / cm². -2 The curves showing the surface temperature of TC4, PEO-15-1.0 and PEO-50-1.0 samples over time (in a dry state) are shown. The right side shows the infrared thermal image of PEO-50-1.0, PEO-0-0 and TC4 at 400 s. Figure 18 (b) shows the curve of sample surface temperature decreasing over time in the absence of light source, while the right side shows the infrared thermal image of PEO-50-1.0, PEO-0-0, and TC4 at 400 s.

[0038] Figure 19 In the middle (a) and (b), optical photographs were taken before and after the cross-cut test of the PEO-50-1.0 coating, respectively. Detailed Implementation

[0039] Specific Implementation Method 1: This implementation method is a preparation method for multi-size light-absorbing coatings constructed by low-refractive-index particle doping, specifically completed according to the following steps:

[0040] 1. Use sandpaper to sand the TC4 board, then clean it to obtain the treated TC4 board;

[0041] II. Preparation of electrolyte:

[0042] The electrolyte is prepared by dissolving SiO2 nanoparticles, sodium polyphosphate, EDTA, sodium hexametaphosphate, FeSO4, sodium metasilicate, nickel acetate and ammonium metavanadate in deionized water.

[0043] 3. Connect the treated TC4 plate to the positive terminal of the power supply and the electrolytic cell to the negative terminal of the power supply. Pour the electrolyte into the electrolytic cell and stir continuously. Use plasma electrolytic oxidation technology to prepare a coating on the TC4 plate. After the reaction is complete, wash and dry to obtain a multi-size light-absorbing coating constructed by low refractive index particle doping.

[0044] Specific Implementation Method Two: This implementation method differs from Specific Implementation Method One in that: in step one, the TC4 board is polished sequentially using 600#, 800#, 1200#, and 1500# sandpaper, and then cleaned sequentially using anhydrous ethanol and acetone to obtain the treated TC4 board. Other steps are the same as in Specific Implementation Method One.

[0045] Specific Implementation Method 3: This implementation method differs from Specific Implementation Method 1 or 2 in that: the particle size of the SiO2 nanoparticles mentioned in step 2 is 15nm~200nm; the concentration of SiO2 nanoparticles in the electrolyte mentioned in step 2 is 0.25g / L~1.5g / L. Other steps are the same as in Specific Implementation Method 1 or 2.

[0046] Specific Implementation Method Four: This implementation method differs from Specific Implementation Methods One to Three in that the concentration of sodium polyphosphate in the electrolyte described in step two is 0.5 g / L to 2 g / L. The other steps are the same as in Specific Implementation Methods One to Three.

[0047] Specific Implementation Method Five: This implementation method differs from Specific Implementation Methods One to Four in that the concentration of EDTA in the electrolyte described in step two is 15 g / L to 25 g / L. The other steps are the same as in Specific Implementation Methods One to Four.

[0048] Specific Implementation Method Six: This implementation method differs from Specific Implementation Methods One to Five in that the concentration of sodium hexametaphosphate in the electrolyte described in step two is 4 g / L to 5 g / L. The other steps are the same as in Specific Implementation Methods One to Five.

[0049] Specific Implementation Method Seven: This implementation method differs from Specific Implementation Methods One to Six in that the concentration of FeSO4 in the electrolyte described in step two is 4 g / L to 6 g / L. The other steps are the same as in Specific Implementation Methods One to Six.

[0050] Specific Implementation Method Eight: This implementation method differs from Specific Implementation Methods One to Seven in that the concentration of sodium metasilicate in the electrolyte described in step two is 5 g / L to 7 g / L. The other steps are the same as in Specific Implementation Methods One to Seven.

[0051] Specific Implementation Method Nine: This implementation method differs from Specific Implementation Methods One to Eight in that: the concentration of nickel acetate in the electrolyte in step two is 4 g / L to 6 g / L; the concentration of ammonium metavanadate in the electrolyte in step two is 2 g / L to 4 g / L. The other steps are the same as in Specific Implementation Methods One to Eight.

[0052] Specific Implementation Method Ten: This implementation method differs from Specific Implementation Methods One through Nine in that: the plasma electrolytic oxidation technology described in step three uses a voltage of 350V~450V, a duty cycle of 20%~30%, a frequency of 800Hz~1000Hz, and a reaction time of 10min~20min; the washing described in step three involves sequential washing with distilled water and anhydrous ethanol. Other steps are the same as in Specific Implementation Methods One through Nine.

[0053] The beneficial effects of the present invention are verified using the following embodiments:

[0054] Example 1: A method for constructing multi-size light-absorbing coatings by doping with low-refractive-index particles, specifically performed according to the following steps:

[0055] First, the TC4 board is polished with 600#, 800#, 1200# and 1500# sandpaper in sequence, and then cleaned with anhydrous ethanol and acetone once each to obtain the treated TC4 board.

[0056] II. Preparation of electrolyte:

[0057] The electrolyte was prepared by dissolving SiO2 nanoparticles (SiO2 NPs), sodium polyphosphate, EDTA, sodium hexametaphosphate, FeSO4, sodium metasilicate, nickel acetate and ammonium metavanadate in deionized water.

[0058] In step two, the electrolyte contains 1 g / L SiO2 nanoparticles, 1 g / L sodium polyphosphate, 20 g / L EDTA, 4.5 g / L sodium hexametaphosphate, 5 g / L FeSO4, 6 g / L sodium metasilicate, 5 g / L nickel acetate, and 3 g / L ammonium metavanadate.

[0059] The SiO2 nanoparticles mentioned in step two have a particle size of 50 nm;

[0060] 3. Connect the treated TC4 plate to the positive terminal of the power supply and the electrolytic cell to the negative terminal of the power supply. Pour the electrolyte into the electrolytic cell and stir continuously. Use plasma electrolytic oxidation technology to prepare a coating on the TC4 plate. After the reaction is complete, wash and dry to obtain a low refractive index particle doped multi-size light-absorbing coating (denoted as PEO-50-1.0).

[0061] The plasma electrolytic oxidation technology described in step three uses a voltage of 400V, a duty cycle of 30%, a frequency of 1000Hz, and a reaction time of 10min.

[0062] Example 2: The difference between this example and Example 1 is that the particle size of the SiO2 nanoparticles in step two is 15 nm; the low refractive index particle doping to construct a multi-size light-absorbing coating in step three is denoted as PEO-15-1.0. All other steps and parameters are the same as in Example 1.

[0063] Example 3: The difference between this example and Example 1 is that the SiO2 nanoparticles in step two have a particle size of 100 nm; the low refractive index particle doping layer obtained in step three is denoted as PEO-100-1.0. All other steps and parameters are the same as in Example 1.

[0064] Example 4: The difference between this example and Example 1 is that the particle size of the SiO2 nanoparticles in step two is 200 nm; the low refractive index particle doping layer obtained in step three is denoted as PEO-200-1.0. All other steps and parameters are the same as in Example 1.

[0065] Example 5: The difference between this example and Example 1 is that the concentration of SiO2 nanoparticles in the electrolyte in step two is 0.25 g / L; the low refractive index particle doping multi-size light-absorbing coating obtained in step three is denoted as PEO-50-0.25. All other steps and parameters are the same as in Example 1.

[0066] Example 6: The difference between this example and Example 1 is that the concentration of SiO2 nanoparticles in the electrolyte in step two is 0.5 g / L; the low refractive index particle doping multi-size light-absorbing coating obtained in step three is denoted as PEO-50-0.5. All other steps and parameters are the same as in Example 1.

[0067] Example 7: The difference between this example and Example 1 is that the concentration of SiO2 nanoparticles in the electrolyte in step two is 1.5 g / L; the low refractive index particle doping multi-size light-absorbing coating obtained in step three is designated as PEO-50-1.5. All other steps and parameters are the same as in Example 1.

[0068] Comparative Example 1: This embodiment does not include SiO2 nanoparticles, i.e., the preparation method of the PEO-0-0 coating is carried out according to the following steps:

[0069] First, the TC4 board is polished with 600#, 800#, 1200# and 1500# sandpaper in sequence, and then cleaned twice with anhydrous ethanol and acetone respectively to obtain the treated TC4 board.

[0070] II. Preparation of electrolyte:

[0071] Sodium polyphosphate, EDTA, sodium hexametaphosphate, FeSO4, sodium metasilicate, nickel acetate and ammonium metavanadate are dissolved in deionized water to obtain an electrolyte.

[0072] In step two, the electrolyte contains sodium polyphosphate at a concentration of 1 g / L, EDTA at a concentration of 20 g / L, sodium hexametaphosphate at a concentration of 4.5 g / L, FeSO4 at a concentration of 5 g / L, sodium metasilicate at a concentration of 6 g / L, nickel acetate at a concentration of 5 g / L, and ammonium metavanadate at a concentration of 3 g / L.

[0073] 3. Connect the treated TC4 plate to the positive terminal of the power supply and the electrolytic cell to the negative terminal of the power supply. Pour the electrolyte into the electrolytic cell and stir continuously. Use plasma electrolytic oxidation technology to prepare a coating on the TC4 plate. After the reaction is complete, wash and dry to obtain the PEO-0-0 coating.

[0074] The plasma electrolytic oxidation technology described in step three uses a voltage of 400V, a duty cycle of 30%, a frequency of 1000Hz, and a reaction time of 10min.

[0075] Figure 1 In the diagram, a represents the refractive index and extinction coefficient of SiO2NPs, and b is a schematic diagram of the preparation of a multi-size light-absorbing coating constructed by low-refractive-index particle doping according to the present invention.

[0076] from Figure 1 From a, we can see that SiO2 NPs have a low refractive index, less than 1.5 in the 0.2-8 μm range and less than 2 in the 10-16 μm range; from Figure 1 As shown in b, SiO2 NPs are incorporated into the coating through plasma electrolytic oxidation (PEO) technology to obtain a PEO coating with a multi-level light absorption structure.

[0077] Figure 2 The following are bar charts showing the thickness and roughness of the coatings prepared in Comparative Example 1 and Examples 1-7;

[0078] from Figure 2 As shown in (a), with the increase of SiO2 NPs particle size, the thickness and roughness first increase and then decrease. The coating prepared from 50nm SiO2 NPs has the largest thickness and roughness, with PEO-50-1.0 exhibiting the largest thickness and roughness. Figure 2As shown in (b), when the particle size is 50 nm, the concentration of SiO2 NPs particles is adjusted. It is found that as the concentration increases, the thickness and roughness of the PEO coating change in the same way, first increasing and then decreasing. Among them, when the doped particle size is 50 nm and the concentration is 1 g / L, the roughness and thickness are the largest, which are 2.5 μm and 18 μm, respectively.

[0079] Figure 3 The images show SEM images of the coatings prepared in Comparative Example 1 and Examples 1-4. Figure 3 In the examples, (a.1), (a.2), and (a.3) are PEO-0-0 coatings prepared in Comparative Example 1; (b.1), (b.2), and (b.3) are PEO-15-1.0 coatings prepared in Example 2; (c.1), (c.2), and (c.3) are PEO-50-1.0 coatings prepared in Example 1; (d.1), (d.2), and (d.3) are PEO-100-1.0 coatings prepared in Example 3; and (e.1), (e.2), and (e.3) are PEO-200-1.0 coatings prepared in Example 4.

[0080] from Figure 3 Images (a.1), (a.2), and (a.3) show SEM images of the PEO-0-0 coating without SiO2 NPs doping. This coating has a smooth surface without obvious protrusions. After SiO2 NPs doping, the surface roughness of the PEO coating increases, and the obvious protrusions become more pronounced, as shown in the PEO-15-1.0 coating (b.1), (b.2), and (b.3). However, with the increase in the size of the silica nanoparticles, the protrusion morphology on the coating surface first increases and then decreases, as shown in the PEO-50-1.0, PEO-100-1.0, and PEO-200-1.0 coatings (cd). The PEO-50-1.0 coating exhibits the highest roughness when the particle radius is 50 nm, a trend consistent with the surface roughness measurement results.

[0081] Figure 4 SEM image of the PEO-50-1.0 coating prepared in Example 1 and the size distribution of non-uniform particles;

[0082] Figure 4The effective diameter histograms are based on probability distributions across different length scales. Scanning electron microscopy images reveal nanostructures (a.1, a.2) and micron-sized particle diameters (a.3, a.4, and a.5). The PEO-50-1.0 coating exhibits a rich array of scale structures, with the main size ranges as follows: 90–200 nm, 200–500 nm, 500–1100 nm, 1.7–3.1 μm, 3.7–8.7 μm, and 15–25 μm. These size ranges encompass both nanoscale features (a.1, a.2) and micron-sized features (a.3, a.4, a.5).

[0083] Figure 5 SEM images of the PEO-0-0 coating prepared in Comparative Example 1 and the size distribution of non-uniform particles;

[0084] Figure 5 The effective diameter histogram, based on probability distributions across different length scales, reveals the morphological characteristics of the coated surface. Scanning electron microscopy images show micrometer-scale particle diameters (a and b). Figure 4 In contrast, the surface of the PEO-0-0 coating mainly exhibits a micron-scale structure with a size distribution of 7-14 μm and 19-29 μm.

[0085] Figure 6 (a) is a transmission electron microscope image of the PEO-50-1.0 coating prepared in Example 1, and (b) is...

[0086] High-resolution transmission electron microscope image, with the inset showing its Fourier transform.

[0087] from Figure 6 The transmission electron microscope (TEM) images clearly show that silica nanoparticles (SiO2 NPs) are randomly distributed within the coating (in a spherical shape), with an average size of approximately 50 nm. These SiO2 NPs are encapsulated in an irregular morphology, likely due to localized surface melting of the silica nanoparticles during plasma electrolytic oxidation (PEO). High-resolution TEM images of the nanoparticles (…) Figure 6 In (b), crystal lattice fringes are clearly observed, indicating a high degree of crystallinity. The selected lattice spacing corresponds to the (011), (110), (121), and (112) crystal planes of SiO2 NPs.

[0088] Figure 7 EDS image of the surface of the PEO-50-1.0 coating prepared in Example 1;

[0089] Figure 7This indicates that the coating matrix contains elements such as silicon, titanium, iron, nickel, oxygen, and vanadium. Areas with higher silicon content correspond to the locations of SiO2 NPs.

[0090] Figure 8 EDS image of the cross-section of the PEO-50-1.0 coating prepared in Example 1, scale bar: 10 μm;

[0091] from Figure 8 The cross-sectional morphology of the intermediate coating shows that the coating thickness is approximately 10 μm, indicating that a strong bonding interface has been formed between the coating and the substrate.

[0092] Figure 9 XRD patterns of SiO2, PEO-0-0 coating prepared in Comparative Example 1, and PEO-50-1.0 coating prepared in Example 1;

[0093] Figure 9 XRD patterns of PEO-50-1.0, PEO-0-0 coatings, and SiO2 NPs are shown. For the PEO-0-0 coating, broad diffraction peaks between 10° and 40° indicate the presence of an amorphous phase. The diffraction peaks observed at 70.9° and 76.7° originate from the TC4 substrate. For the PEO-50-1.0 coating, the diffraction peaks in the range of 20° to 25° are significantly enhanced and can be attributed to the diffraction peaks of SiO2 NPs.

[0094] Figure 10 FT-IR characterization images of SiO2, PEO-0-0 coating prepared in Comparative Example 1, and PEO-50-1.0 coating prepared in Example 1;

[0095] from Figure 10 It can be seen that in the PEO coating, the vibrational modes related to the Fe-O bond are at 583 cm⁻¹. -1 It was observed at 638 cm. -1 The absorption peak at 950 cm⁻¹ is attributed to the stretching vibration of Ni-O. Furthermore, the absorption peak at 950 cm⁻¹... -1 There is a strong absorption peak at 700-500 cm⁻¹, corresponding to the stretching vibration of VO. Additionally, there is an absorption peak at 700-500 cm⁻¹. -1 There are distinct absorption bands within the range, corresponding to the stretching vibrations of Ti-O and Ti-O-Ti bonds, respectively. Furthermore, compared to the PEO-0-0 coating, the PEO-50-1.0 coating exhibits significant absorption at 1070 cm⁻¹. -1 Up to 895cm -1 A distinct absorption peak is observed between the two peaks. This peak can be attributed to the stretching vibration of the silicon-oxygen-silicon bonds in the SiO2 NPs, as well as the symmetric and asymmetric bending vibrations of the silicate material present in the coating structure. This indicates that the coating contains both silicate material and SiO2 NPs.

[0096] Figure 11 Raman spectra of SiO2, PEO-0-0 coating prepared in Comparative Example 1, and PEO-50-1.0 coating prepared in Example 1;

[0097] Figure 11 Approximately 689cm -1 The peak value at 226 cm⁻¹ corresponds to the Alg vibrational mode of Fe-O. -1 The spectral band detected at 996 cm⁻¹ is attributed to the bending vibration of the nickel-oxygen bond. Furthermore, at 996 cm⁻¹... -1 The observed bands indicate the V=O stretching vibration in the V₂O₅ structure. Additionally, the observed bands at 600 cm⁻¹... -1 The A1g vibrational mode at this location corresponds to the vibration of the O-Ti-O bond. Furthermore, the Raman spectrum also shows a vibration at 462 cm⁻¹. -1 The peak observed in silica nanoparticles is attributed to the bending vibrations of the Si-O-Si bonds. At 336 cm⁻¹ -1 A broad, weak peak in the vicinity is attributed to silicate vibrations. SiO2 NPs have been successfully integrated into the coating, influencing its surface structure and morphology, thereby promoting the formation of micro / nano hierarchical surface structures.

[0098] Figure 12 The first XPS spectra of the PEO-0-0 coating prepared in Comparative Example 1 and the PEO-50-1.0 coating prepared in Example 1 are shown, where (a) is the full spectrum, (b) is the Ni 2p spectrum, (c) is the Ti 2p spectrum, and (d) is the V 2p spectrum.

[0099] from Figure 12 It can be seen that the full spectra of both PEO-50-1.0 and PEO-0-0 coatings show characteristic peaks corresponding to Fe 2p, Si 2p, O1s, Ti 2p, V 2p, and Ni 2p. Figure 12 In (b), the XPS spectrum of Ni 2p in the PEO-0-0 coating is at 855.8 eV (Ni 2+ ) and 858.04 eV (Ni 3+ Two distinct peaks were observed at 856.10 eV (Ni). Similarly, the Ni 2p spectrum of the PEO-50-1.0 coating showed two distinct peaks at 856.10 eV (Ni). 2+ Peaks are observed at 860.83 eV (Ni³⁺). In Figure 12(c), the Ti 2p XPS spectrum in the PEO-0-0 coating shows two distinct peaks, located at 458.68 eV (Ti 2p⁺) and 860.83 eV (Ni³⁺). 1 / 2 ) and 464.35 eV (Ti 2p 3 / 2 ), corresponding to Ti in TiO2 4+Similarly, the Ti 2p spectrum of the PEO-50-1.0 coating is at 458.65 eV (Ti 2p). 1 / 2 ) and 464.8 eV (Ti 2p 3 / 2 The peak value is shown at (), which is also attributed to the Ti in TiO2. 4+ substance. Figure 12 The V 2p value of (d) indicates that its corresponding binding energy value corresponds to V 2p. 3 / 2 and V 2p 1 / 2 For V2p 3 / 2 In the PEO-50-1.0 coating, a similarity to V was observed. 5+ V 4+ and V 3+ The substance-related peaks are located at 517.08 eV, 516.34 eV, and 515.58 eV, respectively, while in the PEO-0-0 coating they are located at 517.19 eV, 516.4 eV, and 515.60 eV, respectively. These findings confirm the presence of V2O5, V2O3, and VO.

[0100] Figure 13 The second XPS spectra of the PEO-0-0 coating prepared in Comparative Example 1 and the PEO-50-1.0 coating prepared in Example 1 are shown, where (a) is Fe 2p, (b) is Si 2p, and (c) is O 1s spectrum.

[0101] Figure 13(a) shows the high-resolution Fe 2p spectra of the PEO-0-0 and PEO-50-1.0 coatings, revealing four distinct peaks corresponding to Fe 2p. 3 / 2 (approximately 710.9 eV), its associated satellite peaks, Fe 2p 1 / 2 (Approximately 724.4 eV) and its corresponding satellite peaks. Furthermore, the spin-orbit splitting of Fe 2p is approximately 13.5 eV. Due to spin-orbit coupling, the Fe 2p3 / 2 peak was used to determine the peak splitting mode and Fe... 2+ and Fe 3+ The relative proportions. For the PEO-50-1.0 coating, Fe 3+ / Fe 2+The ratio of 1.6 confirms that the previously characterized oxide is primarily Fe3O4, with trace amounts of other iron oxides. As shown in Figure 13b, the XPS spectrum of Si 2p in the PEO-50-1.0 coating exhibits two distinct peaks: one at 103.65 eV, corresponding to the Si-O bonds in SiO2 NPs, and the other at 102.54 eV, attributed to the Si-O bonds in the silicate compound. Similarly, the Si 2p spectrum in the PEO-0-0 coating shows two peaks at 103.5 eV and 102.41 eV, corresponding to SiO2 and silicates, respectively. The increased peak area at 103.65 eV in the PEO-50-1.0 coating further indicates that SiO2 NPs have been effectively integrated into the coating structure. As shown in Figure 13(c), the high-resolution O 1s spectrum of the PEO-50-1.0 coating can be decomposed into three distinct peaks located at approximately 530.77 eV, 531.83 eV, and 532.53 eV. The lowest binding energy peak is associated with non-bridging oxygen in the silicate or MO bonds in the metal oxide. The middle peak is attributed to M-OH substances, corresponding to hydroxyl groups, while the highest binding energy peak is designated as Si-O, representing bridging oxygen in the silicate structure. Compared to the O 1s spectrum of the PEO-0-0 coating (peaks at 530.96 eV, 531.66 eV, and 532.22 eV), the area and intensity of the Si-O peak in the PEO-50-1.0 coating are significantly increased. This observation provides strong evidence for the successful integration of SiO2 NPs into the coating structure.

[0102] Figure 14 (a) shows the comparison between the absorption spectrum of TC4 and the solar irradiance, and (b) shows the infrared emissivity characteristics of TC4.

[0103] Figure 14 Figures 14(a) and 14(b) show the solar absorption spectrum of TC4 in the wavelength range of 200–2500 nm and the infrared emission spectrum in the wavelength range of 2.5–16 μm. Based on these figures, the solar weighted absorptivity and average emissivity of TC4 were calculated to be 50.4% and 16.1%, respectively.

[0104] Figure 15 (a) and (d) are comparison diagrams of the absorption spectrum of the PEO coating and the solar irradiance, (b) and (e) are the infrared emissivity characteristics of the PEO coating, and (c) and (f) are the solar weighted absorptivity of the PEO coating in the wavelength range of 200-2500 nm and the average infrared emissivity in the wavelength range of 2.5-16 μm.

[0105] Figures 15(a) and 15(b) show the absorptivity and infrared emissivity spectra of coatings prepared using different SiO2 NP sizes, respectively. Based on Figures 15(a) and 15(b), the solar-weighted absorptivity and average emissivity of the coatings were calculated, as shown in Figure 15(c). The absorptivity and infrared emissivity of the coatings initially increased and then decreased with increasing SiO2 NP size. PEO-50-1.0 exhibited the highest absorptivity and emissivity, at 96.1% and 95.6%, respectively, higher than PEO-15-1.0 (95.9% and 94.7%), PEO-100-1.0 (95.3% and 93.1%), and PEO-200-1.0 (95.1% and 92.9%). PEO-0-0 showed the lowest absorptivity and emissivity, at 93.9% and 90.7%, respectively. Furthermore, the effect of SiO2 NPs concentration on coating performance was systematically studied. For example... Figure 15 As shown in (d)-(f), the absorption and emission properties of the coating initially improved as the concentration of 50 nm SiO2 NPs increased from 0 to 1.5 g / L, and then reached a stable state. Optimal performance was observed at a silica concentration of 1.5 g / L, where the absorption and emission efficiencies reached 96.1% and 95.6%, respectively. Compared to TC4 in Figure 14, the prepared PEO-50-1.0 coating exhibited superior light absorption and infrared emission properties.

[0106] Figure 16 A schematic diagram of the variable angle absorption performance testing device is shown.

[0107] from Figure 16 It can be seen that: as the incident angle θ inc As the angle of incident light changes, so too will the angle of incident light change.

[0108] Figure 17 The absorption performance of different PEO coatings varies with angle, where (a) is PEO-0-0 coating, (b) is PEO-15-1.0 coating, (c) is PEO-50-1.0 coating, (d) is PEO-100-1.0 coating, (e) is PEO-200-1.0 coating, and (f) is the solar weighted absorptivity of different PEO coatings varying with incident angle.

[0109] Figure 17The absorption spectra of different PEO coatings at various incident angles from 0° to 70° are shown in the spectral range of 250–2500 nm. The red and purple dashed lines represent isopleths with absorption intensities of 93% and 95%, respectively. Figure 17(f) shows the solar-weighted absorptivity of different PEO coatings at different incident angles. The results indicate that the wide-angle absorption performance initially increases with the increase in the size of the SiO2-doped NPs, but then decreases. The PEO-50-1.0 coating exhibits excellent spectral absorption performance. When the incident angle is less than 50°, its absorptivity exceeds 95% across the entire wavelength range, while the absorptivity of other coatings is below 95%. At a measurable 70° angle, PEO-50-1.0 achieved an absorption rate of 94.3%, which is superior to PEO-0-0 (91.7%), PEO-15-1.0 (93.1%), PEO-100-1.0 (92.4%) and PEO-200-1.0 (92.6%).

[0110] Figure 18 (a) shows the illumination intensity at 500 mW / cm². -2 The curves showing the surface temperature of TC4, PEO-15-1.0 and PEO-50-1.0 samples over time (in a dry state) are shown. The right side shows the infrared thermal image of PEO-50-1.0, PEO-0-0 and TC4 at 400 s. Figure 18 (b) shows the curve of sample surface temperature decreasing over time in the absence of light source, while the right side shows the infrared thermal image of PEO-50-1.0, PEO-0-0, and TC4 at 400 s.

[0111] from Figure 18 As shown in (a), after 400 s of illumination, the surface temperature of PEO-50-1.0 reached 127.8 °C, while the PEO-0-0 coating and TC4 reached 124.1 °C and 51.5 °C, respectively, under five solar irradiances. The faster temperature rise observed in PEO-50-1.0 indicates its stronger heat absorption capacity during illumination. In the cooling experiment (… Figure 18 In (b), after 200 s, the temperature of the PEO-50-1.0 coating dropped from 130℃ to 74.5℃, lower than TC4 (115℃) and PEO-15-1.0 (75.4℃), indicating its superior thermal emission performance. The PEO-50-1.0 coating, with its excellent heat absorption capacity and superior thermal emission performance, enables thermal control in space environments, improving the accuracy of instrument use.

[0112] Figure 19In the middle (a) and (b), optical photographs are taken before and after the cross-cut test of PEO-50-1.0 coating, respectively;

[0113] Figure 19 Optical photographs of the PEO-50-1.0 coating before and after the cross-cut test are shown. No coating peeling occurred after the cross-cut test, proving that the PEO-50-1.0 coating has good adhesion.

Claims

1. A method for preparing a multi-size light-absorbing coating by doping with low-refractive-index particles, characterized in that... The preparation method is specifically carried out according to the following steps:

1. Use sandpaper to sand the TC4 board, then clean it to obtain the treated TC4 board; II. Preparation of electrolyte: The electrolyte is prepared by dissolving SiO2 nanoparticles, sodium polyphosphate, EDTA, sodium hexametaphosphate, FeSO4, sodium metasilicate, nickel acetate and ammonium metavanadate in deionized water.

3. Connect the treated TC4 plate to the positive terminal of the power supply and the electrolytic cell to the negative terminal of the power supply. Pour the electrolyte into the electrolytic cell and stir continuously. Use plasma electrolytic oxidation technology to prepare a coating on the TC4 plate. After the reaction is complete, wash and dry to obtain a multi-size light-absorbing coating constructed by low refractive index particle doping.

2. The method for preparing a multi-size light-absorbing coating by low-refractive-index particle doping according to claim 1, characterized in that... In step one, the TC4 board is polished with 600#, 800#, 1200# and 1500# sandpaper in sequence, and then cleaned with anhydrous ethanol and acetone in sequence to obtain the treated TC4 board.

3. The method for preparing a multi-size light-absorbing coating by low-refractive-index particle doping according to claim 1, characterized in that... The particle size of the SiO2 nanoparticles mentioned in step two is 15nm~200nm; the concentration of SiO2 nanoparticles in the electrolyte mentioned in step two is 0.25g / L~1.5g / L.

4. The method for preparing a multi-size light-absorbing coating by low-refractive-index particle doping according to claim 1, characterized in that... The concentration of sodium polyphosphate in the electrolyte mentioned in step two is 0.5 g / L to 2 g / L.

5. The method for preparing a multi-size light-absorbing coating by low-refractive-index particle doping according to claim 1, characterized in that... The concentration of EDTA in the electrolyte mentioned in step two is 15 g / L to 25 g / L.

6. The method for preparing a multi-size light-absorbing coating by low-refractive-index particle doping according to claim 1, characterized in that... The concentration of sodium hexametaphosphate in the electrolyte mentioned in step two is 4 g / L to 5 g / L.

7. The method for preparing a multi-size light-absorbing coating by low-refractive-index particle doping according to claim 1, characterized in that... The concentration of FeSO4 in the electrolyte mentioned in step two is 4 g / L to 6 g / L.

8. The method for preparing a multi-size light-absorbing coating by low-refractive-index particle doping according to claim 1, characterized in that... The concentration of sodium metasilicate in the electrolyte mentioned in step two is 5 g / L to 7 g / L.

9. The method for preparing a multi-size light-absorbing coating by low-refractive-index particle doping according to claim 1, characterized in that... The concentration of nickel acetate in the electrolyte in step two is 4 g / L to 6 g / L; the concentration of ammonium metavanadate in the electrolyte in step two is 2 g / L to 4 g / L.

10. The method for preparing a multi-size light-absorbing coating by low-refractive-index particle doping according to claim 1, characterized in that... The plasma electrolytic oxidation technology described in step three uses a voltage of 350V~450V, a duty cycle of 20%~30%, a frequency of 800Hz~1000Hz, and a reaction time of 10min~20min; the washing described in step three involves washing with distilled water and anhydrous ethanol in sequence.

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