A functional filler and its preparation method, an inorganic thermal control coating and its application

Abstract

This invention provides a functional filler and its preparation method, an inorganic thermal control coating, and its application, belonging to the field of coating technology. The preparation method of the functional filler includes using zinc acetate aqueous solution as a raw material, adding indium nitrate and aluminum nitrate, stirring to dissolve, then sequentially adding a complexing agent and a stabilizer, heating in a water bath to form a transparent gel, and finally sintering at high temperature. This invention uses a sol-gel method and high-temperature sintering process to dope indium and aluminum elements into zinc oxide to obtain indium-aluminum co-doped zinc oxide. Then, the indium-aluminum co-doped zinc oxide is added as a functional filler to inorganic silicate resin to prepare an inorganic thermal control coating. Aluminum and indium elements can synergistically improve the temperature resistance of the coating, thereby obtaining an inorganic silicate coating with protective and thermal control effects, which can be used on spacecraft surfaces and achieve good thermal control and temperature resistance.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of coatings, and particularly relates to a functional filler, a preparation method thereof, an inorganic thermal control coating, and application. BACKGROUND

[0002] The temperature on the sun-facing side of a spacecraft (such as a satellite or a spaceship) is high, and the temperature on the non-sun-facing side is low, with a temperature difference of several hundred degrees Celsius. The materials of the body and the equipment of the spacecraft often cannot withstand such severe temperature changes. Thermal control coating is the most commonly used, most convenient to apply, and most effective protective and thermal control material for spacecraft.

[0003] Thermal control coating is a light scattering material mainly composed of a functional filler and a binder. The purpose of thermal control is achieved by means of the diffuse reflection of sunlight by the finely dispersed functional filler in the coating and the radiation characteristics of the coating in the infrared band. The coating formed by applying the thermal control coating controls the thermal balance of the object by adjusting the solar absorptivity (or solar absorptance) α s and the infrared emissivity (or hemispherical emissivity) ε of the surface of the object; wherein the solar absorptivity α s is the ratio of the solar radiation energy absorbed by the surface of the coating to the total incident solar radiation energy, directly determines the warming speed and steady temperature of the object under sunlight, and the absorbed solar energy will be converted into internal energy of the object, causing the temperature to rise; the infrared emissivity ε H is the ratio of the infrared radiation energy emitted by the surface of the object to the infrared radiation energy emitted by an ideal radiator (referred to as a "black body") at the same temperature; the infrared emissivity ε is a physical quantity that measures the ability of the surface of the base to release energy in the form of thermal radiation (infrared rays); the average temperature of the outer surface of the spacecraft is determined by the absorption-emission ratio α s / ε H of the surface of the coating, the greater the value of αs / ε H , the faster the temperature rises, and the smaller the value of α s / ε H , the faster the temperature drops; the inorganic thermal control coating on the surface of the spacecraft generally requires that the solar absorptivity α s be 0.14-0.21, the infrared emissivity ε ε is be 0.92-0.94, and the value of α s / ε H be controlled to be between 0.14 and 0.15, so that the thermal control temperature of the coating is ±200°C, thereby ensuring that the inorganic coating has good thermal control effect at different temperatures. Therefore, the value of α s / ε HThe value is crucial for ensuring that spacecraft operate within their normal operating temperature range. Summary of the Invention

[0004] Based on the problems existing in the prior art, the present invention provides a functional filler and its preparation method, an inorganic thermal control coating and its application, so as to improve the comprehensive performance of the inorganic thermal control coating, such as temperature resistance and infrared emissivity.

[0005] As one of the objectives of this invention, this invention provides a method for preparing a functional filler, which includes using a sol-gel method to chemically dope zinc oxide to obtain indium-aluminum co-doped zinc oxide powder, which is the functional filler.

[0006] In a preferred embodiment, the chemical doping includes: using an aqueous solution of zinc acetate as a raw material, adding indium nitrate and aluminum nitrate, stirring to dissolve, then sequentially adding a complexing agent and a stabilizer, heating in a water bath to form a transparent gel, and finally sintering at high temperature to obtain the product.

[0007] In a preferred embodiment, the molar ratio of indium oxide, aluminum oxide and zinc oxide in the indium-aluminum co-doped zinc oxide powder is (1~2):(1~8):100.

[0008] In a preferred embodiment, the high-temperature sintering includes sintering for 5 to 10 hours under inert gas and at 500 to 650°C, followed by annealing to obtain the indium-aluminum co-doped zinc oxide.

[0009] In a preferred embodiment, the complexing agent is citric acid.

[0010] In a preferred embodiment, the stabilizer is polyvinylpyrrolidone.

[0011] In a preferred embodiment, the chemical doping further includes the addition of a pH adjuster to adjust the pH of the solution to ~5.0.

[0012] Preferably, the pH adjuster is ammonia or monoethanolamine.

[0013] In a preferred embodiment, the inert gas is argon.

[0014] As a second objective of the invention, the present invention also provides a functional filler prepared by the preparation method described above.

[0015] As a third objective of the invention, the present invention also provides an inorganic thermal control coating comprising at least the functional fillers described above.

[0016] In a preferred embodiment, the inorganic thermal control coating includes at least the functional filler, additives, deionized water, and inorganic silicate resin.

[0017] In a preferred embodiment, the additives include one or a combination of the anti-settling agent bentonite and the dispersant Solsperse 20000.

[0018] Preferably, the mass ratio of the functional filler to the inorganic silicate resin is 1~1.5:1.

[0019] Preferably, the inorganic silicate resin is one or a combination of inorganic sodium silicate resin and inorganic potassium silicate resin.

[0020] Preferably, the inorganic silicate resin has a modulus of 3.2 to 3.5 and a solid content of 25% to 40%.

[0021] In a preferred embodiment, the inorganic thermal control coating comprises, by weight, 30-40 parts of the inorganic silicate resin, 30-45 parts of the functional filler, 10-20 parts of deionized water, and 0.5-2.0 parts of additives.

[0022] As a fourth objective of the invention, the present invention also provides a method for preparing the inorganic thermal control coating as described above, comprising the following specific steps:

[0023] S1. Dissolve the inorganic silicate resin in deionized water and stir until homogeneous to obtain solution A;

[0024] S2. Add the auxiliary agent to the solution A and stir until homogeneous to obtain mixture B;

[0025] S3. Add the functional filler to the mixture B, stir evenly, and grind to obtain the inorganic thermal control coating.

[0026] As a fifth objective of the invention, the present invention also provides an inorganic thermal control coating, which includes spraying the inorganic thermal control coating as described above onto the surface of a spacecraft substrate, and curing it to form a paint film, which is the inorganic thermal control coating.

[0027] Preferably, the thickness of the inorganic thermal control coating is 20~80μm.

[0028] Preferably, the inorganic thermal control coating has an infrared emissivity of 0.92~0.96 and a solar absorptivity of 0.14~0.15.

[0029] The inorganic thermal control coating does not change color or peel off after being eroded by acetylene flame for 30 minutes; after being heated in a vacuum environment of 950℃ for 72 hours, the coating does not peel off, blister, or corrode, and the inorganic thermal control coating can still play a good protective and thermal control role.

[0030] This invention employs the sol-gel method to prepare indium-aluminum co-doped zinc oxide. By doping the zinc oxide base with rare dispersed metals indium and heat-resistant aluminum oxide, which have photoelectric properties, the temperature resistance and infrared emissivity of zinc oxide can be improved. Then, the indium-aluminum co-doped zinc oxide is added as a functional filler to an inorganic resin to prepare an inorganic thermal control coating. The coating has an infrared emissivity of 0.92~0.94 and a solar absorptivity of 0.14~0.21. After 30 minutes of acetylene flame ablation, the coating film does not change color or peel off. After heating in a vacuum tube furnace at 950℃ for 72 hours, the coating film does not peel off, blister, or corrode, and the inorganic thermal control coating still provides good protection and thermal control.

[0031] As a sixth objective of the invention, the present invention also provides an application of the inorganic thermal control coating as described above in the surface protection of spacecraft (spacecraft, satellites, etc.).

[0032] The beneficial technical effects obtained by this invention are as follows:

[0033] 1. This invention uses the sol-gel method and high-temperature sintering process to dope indium and aluminum into zinc oxide to obtain indium-aluminum co-doped zinc oxide. Then, the indium-aluminum co-doped zinc oxide is added as a functional filler to inorganic silicate resin to prepare an inorganic thermal control coating. Indium can improve the temperature resistance and infrared emissivity of the inorganic thermal control coating, while aluminum and indium can synergistically improve the temperature resistance of the coating. The temperature resistance of the inorganic thermal control coating prepared by adding functional fillers of indium and aluminum can reach above 800℃.

[0034] 2. The inorganic thermal control coating prepared by this invention has an infrared emissivity of 0.92~0.94 and a solar absorptivity of 0.14. After 30 minutes of acetylene flame ablation, the coating film does not change color or peel off. After heating in a vacuum environment of 950℃ for 72 hours, the coating film does not peel off, blister, or corrode. The inorganic thermal control coating can still play a good protective and thermal control role.

[0035] 3. The inorganic thermal control coating prepared by this invention is a water-based coating product, which is environmentally friendly and has no VOC emissions. Attached Figure Description

[0036] Figure 1 This is a scanning electron microscope (SEM) image of indium-aluminum co-doped zinc oxide powder provided in Example 1 of the present invention.

[0037] Figure 2 for Figure 1 Enlarged image.

[0038] Figure 3 and Figure 4 These are comparative photos showing the results of the inorganic thermal control coating prepared in Example 1 of the present invention before and after ablation using an acetylene flame gun at a flame temperature of 1300°C and an ablation time of 30 min.

[0039] Figure 5 and Figure 6 These are comparative photographs of the inorganic thermal control coating prepared in Example 1 of the present invention before and after heating at 950°C for 72 hours in a vacuum tube furnace. Detailed Implementation

[0040] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0041] This invention provides a method for preparing functional fillers, which uses the sol-gel method and high-temperature sintering technology to prepare indium-aluminum co-doped zinc oxide by chemical doping of indium and aluminum.

[0042] Further, the chemical doping steps include: using zinc acetate aqueous solution as raw material, adding indium nitrate and aluminum nitrate, stirring to dissolve, then adding complexing agent, pH adjuster and stabilizer in sequence, heating in a water bath to form a transparent gel, and finally sintering the transparent gel at high temperature to obtain indium-aluminum co-doped zinc oxide powder.

[0043] Furthermore, the indium-aluminum co-doped zinc oxide powder contains indium oxide, aluminum oxide and zinc oxide, and the molar ratio of indium oxide:aluminum oxide:zinc oxide is (1~2):(1~8):100.

[0044] Furthermore, the high-temperature sintering includes sintering under inert gas and at 500~650℃ for 5~10 hours, followed by annealing to obtain the indium-aluminum co-doped zinc oxide.

[0045] Furthermore, the complexing agent is citric acid.

[0046] Furthermore, the pH adjuster is ammonia or monoethanolamine, used to adjust the pH of the solution to approximately 5.0.

[0047] Furthermore, the stabilizer is polyvinylpyrrolidone.

[0048] Furthermore, the mass ratio of the complexing agent to the stabilizer is 10~15:1.

[0049] Furthermore, the water bath heating temperature is 50~70℃.

[0050] Furthermore, the inert gas is argon.

[0051] Furthermore, the inorganic thermal control coating includes at least: additives, deionized water, and inorganic silicate resin.

[0052] Preferably, the additives include one or a combination of the anti-settling agent bentonite and the dispersant Solsperse 20000.

[0053] Preferably, the mass ratio of functional filler to inorganic silicate resin is 1~1.5:1.

[0054] Preferably, the inorganic silicate resin is one or a combination of inorganic sodium silicate resin and inorganic potassium silicate resin.

[0055] More preferably, the inorganic silicate resin has a modulus of 3.2 to 3.5 and a solid content of 25% to 40%.

[0056] Furthermore, by weight, the inorganic thermal control coating comprises: 30-40 parts of inorganic silicate resin, 35-40 parts of functional filler, 10-20 parts of deionized water, and 0.5-2.0 parts of additives.

[0057] In some specific embodiments, the preparation method of the inorganic thermal control coating includes the following steps:

[0058] S1. Dissolve the inorganic silicate resin in deionized water and stir until homogeneous to obtain mixture A;

[0059] S2. Add the additive to the mixture A, stir until homogeneous, and obtain mixture B;

[0060] S3. Add the functional filler to the mixture B, stir evenly, and grind to a fineness of 20 micrometers to obtain the inorganic thermal control coating.

[0061] Furthermore, inorganic thermal control coatings are sprayed onto the surface of spacecraft, and after curing, they form a paint film, which is the inorganic thermal control coating.

[0062] Furthermore, the thickness of the inorganic thermal control coating is 20~80μm.

[0063] Furthermore, the inorganic thermal control coating exhibits a cross-cut adhesion rating of 0-1, and a solar absorptivity α. s The infrared emissivity is 0.14. ε H The absorption-emission ratio α is 0.92~0.94. s / ε H The value is 0.14~0.15.

[0064] Furthermore, the inorganic thermal control coating does not change color or peel off after 30 minutes of acetylene flame ablation.

[0065] Furthermore, after heating in a vacuum environment of 950℃ for 72 hours, the paint film did not peel off, bubble, or corrode, and the inorganic thermal control coating still provided good protection and thermal control.

[0066] Furthermore, the maximum temperature resistance is ≥800℃.

[0067] Unless otherwise specified, all test materials and reagents used in the following examples are commercially available.

[0068] Unless otherwise specified in the embodiments, the techniques or conditions described in the literature in this field or in accordance with the product manual may be followed.

[0069] Example 1

[0070] This embodiment provides a method for preparing an inorganic thermal control coating, the specific steps of which include:

[0071] 1. Preparation of Indium-Aluminum Co-doped Oxide

[0072] First, measure 100 mL of 0.1 mol / L zinc acetate solution into a 200 mL beaker, then add 0.030 g of indium nitrate powder and 0.021 g of aluminum nitrate powder. Add 15 g of citric acid complexing agent to prevent metal ion precipitation. Then, add 1 mol / L ammonia water to adjust the pH of the mixed solution to about 5.0. Add 1.0 g of polyvinylpyrrolidone stabilizer to improve the stability of the sol. Stir in a 70℃ water bath for 5 h to form a transparent sol. Let it stand at room temperature to 25℃ for 24 h to allow the sol to further polymerize and form a more stable gel.

[0073] The gel was calcined in an argon atmosphere in a muffle furnace at 600℃ for 4 h to crystallize ZnO and co-dope it with indium-aluminum. The final white powder was indium-aluminum co-doped zinc oxide.

[0074] See Figure 1 and Figure 2 The images shown are scanning electron microscope (SEM) images and magnified views of the indium-aluminum co-doped zinc oxide powder prepared in this embodiment. As can be seen from the images, cylindrical and needle-like structures coexist in the indium-aluminum co-doped zinc oxide powder.

[0075] 2. Preparation of Inorganic Thermal Control Coatings

[0076] The specific steps include:

[0077] (1) Dissolve 30g of inorganic potassium silicate resin (purchased from Zhejiang Yuda Chemical Co., Ltd., with a modulus of 3.3 and a solid content of 35wt%) in 20g of deionized water and stir until homogeneous to obtain solution A;

[0078] (2) Add 0.5g of bentonite anti-settling agent and 0.5g of dispersant Solsperse 20000 to solution A, stir well to obtain mixture B;

[0079] (3) Add 38g of indium-aluminum co-doped zinc oxide powder to the mixture B, stir evenly, and grind to a fineness of 20 micrometers to obtain the inorganic thermal control coating.

[0080] Performance characterization:

[0081] The coating prepared in Example 1 was sprayed onto a stainless steel plate (2.5 mm thick, the substrate was first sandblasted to Sa2.5 grade) using compressed air, and cured at room temperature (25°C) for 24 hours, controlling the film thickness to be 50 ± 2 μm, thus obtaining the coating test plate. An acetylene flame gun was used to conduct an ablation test on the coating test plate, using an acetylene outer flame with an outer flame temperature of approximately 1500°C and an ablation time of 60 seconds. See [link / reference] Figure 3 and Figure 4 The images show photos before and after acetylene flame ablation. As can be seen from the images, the inorganic thermal control coating remains white after 60 seconds of ablation, without discoloration, peeling, or corrosion.

[0082] The coating prepared in Example 1 was sprayed onto a stainless steel disc (30 mm in diameter, 2.5 mm thick, with the substrate pre-blasted to Sa2.5 grade) using compressed air. It was cured at room temperature (25°C) for 24 hours, with the film thickness controlled at 50 ± 2 μm. Several perpendicular cross-cut lines were made on the film surface using a cross-cutting tool, each line reaching the bottom layer of the film, thus obtaining the cross-cut coating test panel. The cross-cut coating test panel was then heated in a vacuum tube furnace at 950°C for 72 hours. The results are as follows... Figure 5 The image shows the product before vacuum high-temperature heating. Figure 6 After high-temperature heating, a comparison shows that the paint film does not peel off or bubble, and there is no corrosion expansion at the marked areas. The inorganic thermal control coating still provides good corrosion protection and heat dissipation for the stainless steel substrate. However, the white paint film shows a significant graying phenomenon, mainly because ZnO loses some lattice oxygen (O) under vacuum high-temperature conditions. 2- Oxygen vacancies and free electrons are formed, which occupy the conduction band, causing ZnO to exhibit n-type semiconductor properties and making its color gray or darker.

[0083] Furthermore, this embodiment also used cross-cut coating test panels to conduct high temperature resistance evaluation tests. The method included: placing the cross-cut coating test panels in a muffle furnace, setting the temperature, heating for 240 hours, and then observing whether the paint film peeled off or changed color.

[0084] The solar absorptivity, infrared emissivity, temperature resistance, and test results of the coatings prepared in the examples are shown in Table 1.

[0085] Example 2

[0086] The preparation method of the inorganic thermal control coating provided in this embodiment is basically the same as that in Example 1, the only difference being the amount of indium-aluminum co-doped zinc oxide powder added. Specifically, the preparation method of the inorganic thermal control coating includes:

[0087] (1) Dissolve 30g of inorganic potassium silicate resin (purchased from Zhejiang Yuda Chemical Co., Ltd., with a modulus of 3.3 and a solid content of 35wt%) in 20g of deionized water and stir until homogeneous to obtain mixture A;

[0088] (2) Add 0.5g of bentonite anti-settling agent and 0.5g of dispersant Solsperse 20000 to the mixture A, stir evenly to obtain mixture B;

[0089] (3) Add 35g of indium-aluminum co-doped zinc oxide powder to the mixture B, stir evenly, and grind to a fineness of 20 micrometers to obtain the inorganic thermal control coating.

[0090] The solar absorptivity, infrared emissivity, temperature resistance, and test results of the inorganic thermal control coating prepared in this embodiment are shown in Table 1.

[0091] Example 3

[0092] The preparation method of the inorganic thermal control coating provided in this embodiment is basically the same as that in Example 1, the only difference being the amount of indium-aluminum co-doped zinc oxide powder added. Specifically, the preparation method of the inorganic thermal control coating includes:

[0093] (1) Dissolve 30g of inorganic potassium silicate resin (purchased from Zhejiang Yuda Chemical Co., Ltd., with a modulus of 3.3 and a solid content of 35wt%) in 20g of deionized water and stir until homogeneous to obtain mixture A;

[0094] (2) Add 0.5g of bentonite anti-settling agent and 0.5g of dispersant Solsperse 20000 to the mixture A, stir evenly to obtain mixture B;

[0095] (3) Add 40g of indium-aluminum co-doped zinc oxide powder to the mixture B, stir evenly, and grind to a fineness of 20 micrometers to obtain the inorganic thermal control coating.

[0096] The solar absorptivity, infrared emissivity, temperature resistance, and test results of the inorganic thermal control coating prepared in this embodiment are shown in Table 1.

[0097] Example 4

[0098] This embodiment provides a method for preparing an inorganic thermal control coating, which is basically the same as the preparation method in Example 1, except that the amount of aluminum oxide doping is different in step (1) in the preparation of indium-aluminum co-doped zinc oxide. Specifically, 100 mL of 0.1 mol / L zinc acetate solution is measured into a 200 mL beaker, and 0.030 g of indium nitrate powder and 0.042 g of aluminum nitrate powder are added in sequence. 15 g of citric acid complexing agent is added to prevent metal ion precipitation. Then, 1 mol / L ammonia water is added dropwise to adjust the pH of the mixed solution to about 5.0. 1.0 g of polyvinylpyrrolidone stabilizer is added to improve the stability of the sol. The mixture is stirred in a 70°C water bath for 5 h to form a transparent sol. It is then allowed to stand at room temperature to 25°C for 24 h to allow the sol to further polymerize and form a stable colloid. The gel is then calcined in a muffle furnace at 600°C under an argon atmosphere for 4 h to crystallize ZnO and co-dopide it with indium-aluminum. The final white powder obtained is indium-aluminum co-doped zinc oxide.

[0099] The test results of various film properties of the coating prepared in this embodiment are shown in Table 1.

[0100] Example 5

[0101] This embodiment provides a method for preparing an inorganic thermal control coating, which is basically the same as the preparation method in Example 1, except that the amount of aluminum oxide doping is different in step (1) in the preparation of indium-aluminum co-doped zinc oxide. Specifically, 100 mL of 0.1 mol / L zinc acetate solution is measured into a 200 mL beaker, and 0.030 g of indium nitrate powder and 0.168 g of aluminum nitrate powder are added in sequence. 15 g of citric acid complexing agent is added to prevent metal ion precipitation. Then, 1 mol / L ammonia water is added dropwise to adjust the pH of the mixed solution to about 5.0. 1.0 g of polyvinylpyrrolidone stabilizer is added to improve the stability of the sol. The mixture is stirred in a 70°C water bath for 5 h to form a transparent sol. It is then allowed to stand at room temperature to 25°C for 24 h to allow the sol to further polymerize and form a stable colloid. The gel is then calcined in a muffle furnace at 600°C under an argon atmosphere for 4 h to crystallize ZnO and co-dopide it with indium-aluminum. The final white powder obtained is indium-aluminum co-doped zinc oxide.

[0102] The test results of various film properties of the coating prepared in this embodiment are shown in Table 1.

[0103] Comparative Example 1

[0104] This comparative example provides a method for preparing an inorganic thermal control coating, which is basically the same as the preparation method in Example 1. The only difference is that 0.030g of indium nitrate powder was not added in the indium-aluminum co-doped zinc oxide step. All other steps are the same.

[0105] The solar absorptivity, infrared emissivity, temperature resistance, and test results of the inorganic thermal control coating prepared in this comparative example are shown in Table 1.

[0106] Comparative Example 2

[0107] This comparative example provides a method for preparing an inorganic thermal control coating, which is basically the same as the preparation method in Example 1. The only difference is that 0.021g of aluminum nitrate powder was not added in the indium-aluminum co-doped zinc oxide step. All other steps are the same.

[0108] The solar absorptivity, infrared emissivity, temperature resistance, and test results of the inorganic thermal control coating prepared in this comparative example are shown in Table 1.

[0109] Comparative Example 3

[0110] This comparative example provides a method for preparing an inorganic thermal control coating, which is basically the same as the preparation method in Example 1. The only difference is that in the indium-aluminum co-doped zinc oxide step, 0.030g of indium nitrate powder and 0.21g of aluminum nitrate powder are not added. All other steps are the same.

[0111] The test results of various physical properties of the coating prepared in this comparative example are shown in Table 1.

[0112] Comparative Example 4

[0113] This comparative example provides a method for preparing an inorganic thermal control coating, which is basically the same as the preparation method in Example 1, except that the amount of indium oxide doping is different in step 1, in the preparation of indium-aluminum co-doped zinc oxide.

[0114] Specifically, 100 mL of 0.1 mol / L zinc acetate solution was measured into a 200 mL beaker, and 0.10 g of indium nitrate powder and 0.021 g of aluminum nitrate powder were added sequentially. 15 g of citric acid complexing agent was added to prevent metal ion precipitation. Then, 1 mol / L ammonia water was added dropwise to adjust the pH of the mixed solution to about 5.0. 1.0 g of polyvinylpyrrolidone stabilizer was added to improve the stability of the sol. The mixture was stirred in a 70℃ water bath for 5 h to form a transparent sol. The mixture was then allowed to stand at room temperature to 25℃ for 24 h to allow the sol to further polymerize and form a stable colloid. The gel was then calcined in a muffle furnace at 600℃ under an argon atmosphere for 4 h to crystallize ZnO and co-dope it with indium-aluminum. The final white powder obtained was indium-aluminum co-doped zinc oxide.

[0115] The test results of various film properties of the coating prepared in this comparative example are shown in Table 1.

[0116] Comparative Example 5

[0117] The preparation method of the inorganic thermal control coating provided in this comparative example is basically the same as that in Example 1, except that the amount of indium-aluminum co-doped zinc oxide powder added is different.

[0118] Specifically, the preparation methods of inorganic thermal control coatings include:

[0119] (1) Dissolve 30g of inorganic potassium silicate resin (purchased from Zhejiang Yuda Chemical Co., Ltd., with a modulus of 3.3 and a solid content of 35wt%) in 20g of deionized water and stir until homogeneous to obtain mixture A;

[0120] (2) Add 0.5g of bentonite anti-settling agent and 0.5g of dispersant Solsperse 20000 to the mixture A, stir evenly to obtain mixture B;

[0121] (3) Add 30g of indium-aluminum co-doped zinc oxide powder to the mixture B, stir evenly, and grind to a fineness of 20 micrometers to obtain the inorganic thermal control coating.

[0122] The solar absorptivity, infrared emissivity, temperature resistance, and test results of the inorganic thermal control coating prepared in this comparative example are shown in Table 1.

[0123] Comparative Example 6

[0124] The preparation method of the inorganic thermal control coating provided in this comparative example is basically the same as that in Example 1, the only difference being the amount of indium-aluminum co-doped zinc oxide powder added. Specifically, the preparation method of the inorganic thermal control coating includes:

[0125] (1) Dissolve 30g of inorganic potassium silicate resin (purchased from Zhejiang Yuda Chemical Co., Ltd., with a modulus of 3.3 and a solid content of 35wt%) in 20g of deionized water and stir until homogeneous to obtain mixture A;

[0126] (2) Add 0.5g of bentonite anti-settling agent and 0.5g of dispersant Solsperse 20000 to the mixture A, stir evenly to obtain mixture B;

[0127] (3) Add 45g of indium-aluminum co-doped zinc oxide powder to the mixture B, stir evenly, and grind to a fineness of 20 micrometers to obtain the inorganic thermal control coating.

[0128] The solar absorptivity, infrared emissivity, temperature resistance, and test results of the inorganic thermal control coating prepared in this comparative example are shown in Table 1.

[0129] Comparative Example 7

[0130] This comparative example provides a method for preparing an inorganic thermal control coating, which is basically the same as the preparation method in Example 1, except that the amount of aluminum oxide doping is different in step 1 in the preparation of indium-aluminum co-doped zinc oxide. Specifically, 100 mL of 0.1 mol / L zinc acetate solution is measured into a 200 mL beaker, and 0.030 g of indium nitrate powder and 0.20 g of aluminum nitrate powder are added sequentially. 15 g of citric acid complexing agent is added to prevent metal ion precipitation, and then 1 mol / L ammonia water is added dropwise to adjust the pH of the mixed solution to about 5.0. 1.0 g of polyvinylpyrrolidone stabilizer is added to improve the stability of the sol. The mixture is stirred in a 70°C water bath for 5 h to form a transparent sol. It is then allowed to stand at room temperature to 25°C for 24 h to allow the sol to further polymerize and form a stable colloid. The gel is then calcined in a muffle furnace at 600°C under an argon atmosphere for 4 h to crystallize ZnO and co-dopant it with indium-aluminum. The final white powder obtained is indium-aluminum co-doped zinc oxide.

[0131] The test results of various film properties of the coating prepared in this comparative example are shown in Table 1.

[0132] Table 1. Comprehensive physical properties of the inorganic thermal control coatings provided in the examples and comparative examples.

[0133]

[0134] As shown in Table 1, the inorganic thermal control coating prepared in Example 1 has an adhesion grade of 0 and a solar absorptivity α. s The infrared emissivity is 0.14. ε H The absorption-emission ratio α is 0.94. s / ε H The value is 0.149, the thermal control temperature of the coating is ±200℃, and the long-term temperature resistance is 800℃. This indicates that the inorganic thermal control coating provided in Example 1 has good thermal control performance and temperature resistance performance, which meets the requirements for use on the surface of spacecraft under extreme conditions and ensures that it can work normally within the operating temperature range of spacecraft.

[0135] By comparing the test results of the examples and comparative examples in Table 1, it is shown that the higher the amount of indium-aluminum co-doped zinc oxide added, the greater the solar absorptivity and infrared emissivity. This is because in the inorganic white paint, the higher the content of indium-aluminum co-doped zinc oxide, the rougher the paint film surface. A rough surface increases the multiple emission and internal scattering of light, prolongs the light path, thereby increasing the absorption opportunities and improving the solar absorptivity α. s At the same time, the rough surface increases the effective radiation area, which easily forms a cavity effect of multiple reflections and absorptions, leading to a decrease in infrared emissivity. ε HThe pigment-to-binder ratio increases. However, when the amount of indium-aluminum co-doped zinc oxide added is too high (Comparative Example 6), the pigment-to-binder ratio in the coating increases, leading to a decrease in the adhesion performance of the paint film (adhesion level 2 in the cross-cut adhesion test). This indicates that when the pigment-to-binder ratio of the inorganic thermal control coating increases, the content of inorganic resin decreases relatively, resulting in a decrease in adhesion to the substrate. Conversely, when the amount of indium-aluminum co-doped zinc oxide added is too low (Comparative Example 5), the thermal control performance of the coating decreases.

[0136] By comparing the test results of Example 1 and Comparative Example 1, it is shown that indium doping of zinc oxide can improve the infrared emissivity of the coating.

[0137] By comparing the test results of Example 1 and Comparative Examples 1, 2, and 3, the coating prepared without aluminum has a maximum temperature resistance of 650℃, and the coating prepared without indium has a maximum temperature resistance of 700℃. In Comparative Example 3, with only zinc oxide, the maximum temperature resistance is only 600℃. However, in Example 1, when both indium and aluminum are doped, the resulting filler significantly improves the temperature resistance of the coating, and the inorganic thermal control coating can withstand a high temperature of 800℃ for a long time. This indicates that co-doping with indium and aluminum can significantly improve the temperature resistance of the filler. Clearly, compared to pure zinc oxide, adding indium-aluminum co-doped zinc oxide as a functional filler to inorganic silicate resin to prepare an inorganic thermal control coating allows indium to increase the infrared emissivity of the coating, and aluminum to improve its temperature resistance. In particular, aluminum and indium have a synergistic effect in improving the temperature resistance of the inorganic thermal control coating. Only by simultaneously adding indium and aluminum can the temperature resistance of the prepared inorganic thermal control coating reach 800℃.

[0138] By comparing the test results of Examples 1, 4, and 5 with Comparative Examples 3 and 7, it was found that during the preparation of indium-aluminum co-doped zinc oxide, when the aluminum content increased, adding the same mass of indium-aluminum co-doped zinc oxide to the inorganic thermal control coating improved the coating's temperature resistance to 850℃; however, the infrared emissivity decreased. Simultaneously, the adhesion of the coating film in Example 4 became grade 1, indicating that the amount of aluminum doping in the functional filler has a significant impact on the coating's adhesion. Further referring to the test results of Comparative Example 7, when the proportion of aluminum doping was further increased, the coating adhesion further decreased, and the infrared emissivity also decreased significantly. s / ε H The value is greater than 0.15.

[0139] By comparing Example 1 and Comparative Example 4, the same mass of indium-aluminum co-doped zinc oxide was added to the inorganic thermal control coating. In Example 1, the molar ratio of indium, aluminum, and zinc was 1:1:100, and in Comparative Example 4, the molar ratio of indium, aluminum, and zinc was 3:1:100. The test results showed that as the indium doping amount increased, the infrared emissivity of the coating increased, the adhesion of the paint film decreased, and the temperature resistance decreased. In particular, the increase in indium doping amount also led to a corresponding increase in the cost of the coating.

[0140] In summary, the functional filler prepared using the technical solution of Example 1 of this invention, on the one hand, by adjusting the ratio of indium and aluminum, the inorganic thermal control coating prepared using it as a functional filler has an infrared emissivity of 0.92~0.94, a solar absorptivity of 0.14~0.21, and an α... s / ε H With a value of 0.14~0.15, the paint film does not change color or peel off after 30 minutes of acetylene flame ablation; after heating in a vacuum environment of 950℃ for 72 hours, the paint film does not peel off, blister, or corrode, and the inorganic thermal control coating can still play a good role in corrosion prevention and thermal control; on the other hand, in indium-aluminum co-doped zinc oxide, indium and aluminum co-doping can play a synergistic role in improving the temperature resistance of the coating, with a temperature resistance of ≥800℃.

[0141] Obviously, the inorganic thermal control coating provided by this invention is a coating product with excellent comprehensive performance, which can be applied to the surface of spacecraft (satellites, spacecraft, etc.) to achieve the functions of thermal control and protection.

[0142] The above description of the embodiments is intended to enable those skilled in the art to understand and use the invention. It will be apparent to those skilled in the art that various modifications can be made to these embodiments, and the general principles described herein can be applied to other embodiments without inventive effort. Therefore, the present invention is not limited to the above embodiments, and any improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the scope of the invention should be within the protection scope of the present invention.

Claims

1. A method for the preparation of a functional filler, characterized in that, The functional filler is prepared by doping zinc oxide with indium and aluminum by a sol-gel method. The chemical doping comprises: using zinc acetate aqueous solution as raw material, adding indium nitrate and aluminum nitrate, stirring and dissolving, then adding complexing agent and stabilizer in sequence, heating in water bath to form transparent gel, and finally sintering the gel under inert gas atmosphere at high temperature. In the indium-aluminum co-doped zinc oxide powder, the molar ratio of indium, aluminum and zinc is 1:1:

100. The complexing agent is citric acid. The stabilizer is polyvinylpyrrolidone. The chemical doping further comprises adding pH regulator to adjust the pH value of the solution to 5.

0.

2. The method of claim 1, wherein the functional filler is prepared by the steps of: The high-temperature sintering comprises sintering at 500-650℃ for 5-10h under inert gas to obtain the indium-aluminum co-doped zinc oxide powder.

3. The method of claim 1, wherein the functional filler is prepared by the steps of: The inert gas is argon.

4. The method of making a functional filler according to any one of claims 1-3, characterized in that, The pH regulator is ammonia or monoethanolamine.

5. A functional filler prepared by the preparation method of any one of claims 1-4.

6. An inorganic thermal control paint, characterized by, At least comprising the functional filler prepared by the preparation method of any one of claims 1-4, or comprising the functional filler of claim 5. The inorganic thermal control coating at least comprises the functional filler, auxiliary agent, deionized water and inorganic silicate resin. The auxiliary agent comprises one or a combination of anti-settling agent bentonite and dispersant Solsperse 20000. The inorganic silicate resin is one or a combination of inorganic sodium silicate resin and inorganic potassium silicate resin.

7. The inorganic thermal control paint according to claim 6, wherein The mass ratio of the functional filler to the inorganic silicate resin is 1-1.5:

1.

8. The inorganic thermal control paint according to claim 6, wherein The modulus of the inorganic silicate resin is 3.2-3.5, and the solid content of the inorganic silicate resin is 25%-40%.

9. The inorganic thermal control paint according to any one of claims 6 to 8, characterized in that, The inorganic thermal control coating comprises, in parts by mass, 30-40 parts of the inorganic silicate resin, 30-45 parts of the functional filler, 10-20 parts of deionized water, and 0.5-2.0 parts of auxiliary agent.

10. A method for the preparation of an inorganic thermal control paint according to any one of claims 6 to 9, characterized in that, The method comprises the following specific steps: S1. Dissolving inorganic silicate resin in deionized water to obtain solution A; S2. Adding auxiliary agent to the solution A to obtain mixture B; S3. Adding functional filler to the mixture B, stirring and grinding to obtain inorganic thermal control coating.

11. An inorganic thermal control coating, which is prepared by spraying the inorganic thermal control coating of any one of claims 6-9 on the surface of a metal or carbon steel substrate, and curing to form a paint film, thereby obtaining the inorganic thermal control coating.

12. The inorganic thermal control coating of claim 11, wherein, The thickness of the inorganic thermal control coating is 20-80μm.

13. The inorganic thermal control coating of claim 11, wherein, The ratio a of the infrared emissivity and the solar absorptance of the inorganic thermal control coating s ε H is 0.14 to 0.15.​ 14. Use of the inorganic thermal control coating of any one of claims 6-9 or the inorganic thermal control coating of any one of claims 11-13 in spacecraft surface protection.

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