Hole sealing agent and application thereof, thermal control protective coating and preparation method thereof, and thermal control component

Abstract

The invention relates to the field of surface engineering, and discloses a hole sealing agent and application thereof, a thermal control protective coating and a preparation method thereof, and a thermal control component. The hole sealing agent comprises soluble organic acid lanthanum salt, a weakly acidic buffer pair, an oxidation auxiliary agent and water, and the pH value of the hole sealing agent is weakly acidic. According to the lanthanum metal salt composite hole sealing agent suitable for the space environment, the organic acid lanthanum salt and the oxidation auxiliary agent are adopted, the pH value of a system is kept in a weak acid environment, and the composition of the composite hole sealing agent is optimized, so that the corrosion resistance, the thermal control optical performance and the surface compactness of a coating subjected to soaking treatment are remarkably improved, and the service life of the coating is prolonged. And the product and the process do not need high-temperature, vacuum or complex equipment, the process is green, simple and convenient, and the method is suitable for batch treatment of large spacecraft components.

Description

Technical Field

[0001] This application relates to the field of surface engineering, and more particularly to a sealing agent and its application, a thermal control protective coating and its preparation method, and a thermal control component. Background Technology

[0002] In low Earth orbit and deep space missions, spacecraft exteriors are exposed to harsh environments such as atomic oxygen, ultraviolet radiation, alternating extreme temperatures, and trace contaminants. To maintain the normal operating temperature of internal equipment, materials with low solar absorptivity (α) are often fabricated on the surfaces of lightweight structural components. S A white functional coating with high hemispherical emissivity (ε).

[0003] Micro-arc oxidation (MAO) technology is widely used for thermal protection because it can generate high-emissivity ceramic coatings in situ on the surfaces of light metals such as magnesium and aluminum. However, MAO coatings generally contain micron-sized pores and penetrating microcracks, which become channels for corrosive media to penetrate, leading to localized corrosion of the substrate during ground storage or early-stage operation in orbit. Furthermore, the porous structure easily adsorbs space contaminants and accelerates surface photochemical reactions under ultraviolet irradiation, causing α-corrosion. S Changes disrupt the thermal balance. Traditional sealing methods such as boiling water sealing and chromate passivation can partially block pores, but the former has limited effectiveness, and the latter has been banned by international aerospace standards due to its hexavalent chromium content. Summary of the Invention

[0004] In view of this, the purpose of this application is to provide a sealing agent that can simultaneously improve the corrosion resistance, thermal optical properties and surface density of the thermal protection coating; Another objective of this application is to provide the application of the above-mentioned sealing agent in the preparation of thermal control protective coatings; Another objective of this application is to provide a thermal control protective coating based on the above-mentioned sealing agent and a method for preparing the same, such that the thermal control protective coating has high corrosion resistance, thermal control optical properties and surface density. Another objective of this application is to provide a thermal control component based on the above-mentioned thermal control protective coating, so that the thermal control component possesses the excellent performance brought by the above-mentioned thermal control protective coating and is suitable for long-term on-orbit operation.

[0005] In order to solve the above-mentioned technical problems / achieve the above-mentioned objectives, or at least partially solve the above-mentioned technical problems / achieve the above-mentioned objectives, as a first aspect of this application, a sealing agent is provided, comprising: a soluble organic acid lanthanum salt, a weakly acidic buffer pair, an oxidizing agent, and water, wherein the pH value is weakly acidic.

[0006] Optionally, it includes: 0.05 mol / L of a soluble organic acid lanthanum salt, 0.2-0.8% by volume of an oxidizing agent, wherein the weakly acidic buffer maintains the pH of the sealing agent at a weakly acidic level, and the balance is water.

[0007] Further optionally, the soluble organic acid lanthanum salt includes lanthanum acetate monohydrate and / or lanthanum citrate; the weak acid buffer pair includes an acetate-sodium acetate buffer pair or a citrate-sodium citrate buffer pair; and the oxidizing agent includes hydrogen peroxide.

[0008] Further optionally, the pH value is 5.5-6.8.

[0009] As a second aspect of this application, the use of the sealing agent in the preparation of thermally protective coatings is provided.

[0010] As a third aspect of this application, a thermal control protective coating is provided, comprising a porous coating and a sealing agent as described in this application, wherein the sealing agent seals the pores in the coating.

[0011] Optionally, the porous coating includes a coating formed by micro-arc oxidation.

[0012] As a fourth aspect of this application, a method for preparing the thermal control protective coating is provided, comprising: Provides a porous coating; The coating is immersed in the sealing agent described in this application for soaking treatment; After soaking, the surface is cleaned of residual ions and dried to obtain the thermal control protective coating.

[0013] As a fifth aspect of this application, a thermal control component is provided, including a metal substrate and a thermal control protective coating disposed on the surface of the metal substrate, the thermal control protective coating including the thermal control protective coating described in this application.

[0014] Optionally, the metal matrix includes magnesium alloys and / or aluminum alloys.

[0015] This application provides a lanthanum metal salt composite sealing agent suitable for space environments. By using organic acid lanthanum salt, oxidizing agent, and maintaining the pH value of the system in a weakly acidic environment, the composition of the composite sealing agent is optimized, resulting in significant improvements in corrosion resistance, thermal control and optical properties, and surface density of the coating after immersion treatment. Moreover, the product and process of this application do not require high temperature, vacuum, or complex equipment, and the process is green and simple, making it suitable for the mass production of large spacecraft components. Attached Figure Description

[0016] Figure 1The images shown are XRD comparison spectra of the basic micro-arc oxidation coating (MAO, unsealed) and the micro-arc oxidation coating solutions in the examples and comparative examples after sealing. Figure 2 The image shows cross-sectional views of the basic micro-arc oxidation coating (MAO, unsealed) at different magnifications in Example 1; Figure 3 The images shown are SEM and SEM-mapping images of the micro-arc oxidation coating solution after sealing the pores in Example 1. Detailed Implementation

[0017] This application discloses a sealing agent and its application, a thermal control protective coating and its preparation method, and a thermal control component. Those skilled in the art can refer to the content of this application and appropriately modify the process parameters to achieve the desired results. It should be particularly noted that all similar substitutions and modifications are obvious to those skilled in the art and are considered to be included in this application. The products, processes, and applications described in this application have been described through preferred embodiments. Those skilled in the art can obviously modify or appropriately change and combine the preparation methods described herein without departing from the content, spirit, and scope of this application to realize and apply the technology of this application. Obviously, the described embodiments are only some, not all, of the embodiments of this application. All other embodiments obtained by those skilled in the art based on the embodiments of this application without creative effort are within the scope of protection of this application.

[0018] It should be noted that, in this document, relational terms such as "first" and "second," "step 1" and "step 2," and "(1)" and "(2)" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element. Moreover, the embodiments and features described in this application can be combined with each other without conflict.

[0019] Existing lanthanum salt sealing systems mostly use a single aqueous solution of lanthanum nitrate or lanthanum chloride, which suffers from problems such as low sealing efficiency, porous film, and weak UV resistance. Furthermore, some formulations, while reducing porosity, introduce light-absorbing impurities, which in turn increases α-growth rate. SThis approach is insufficient to meet the stringent requirements of thermal protection coatings for long-life spacecraft. Furthermore, current technologies have not yet achieved a synergistic improvement in three properties—significantly enhanced corrosion resistance, actively reduced solar absorptivity, and effective porosity suppression—through a single chemical sealing agent immersion treatment.

[0020] In view of the deficiencies of the prior art, in the first aspect of this application, a sealing agent is provided, comprising: a soluble organic acid lanthanum salt, a weakly acidic buffer pair, an oxidizing agent and water, wherein the pH value is weakly acidic.

[0021] This application regulates La through organic acid ligands. 3+ The hydrolysis rate is optimized to avoid surface roughness caused by rapid precipitation; a buffer system is used to maintain a near-neutral weakly acidic environment to prevent the micro-arc oxide film from dissolving under acidic conditions; a trace amount of oxidizing agent is introduced to promote the generation of highly reflective and chemically inert lanthanum hydroxyl oxides (such as LaOOH) in the pores. This product not only effectively blocks the pores, but its wide bandgap characteristics can also reduce the absorption of electron transitions in the ultraviolet-visible region, thereby reducing the solar absorptivity and improving the infrared radiation efficiency.

[0022] In some embodiments of this application, the sealing agent comprises: 0.03-0.07 mol / L of a soluble organic acid lanthanum salt, 0.2-0.8% by volume of an oxidizing agent, a weakly acidic buffer to maintain the pH of the sealing agent at a weakly acidic level, and the remainder being water.

[0023] In the sealing agent of this application, an excessively high concentration of lanthanum salt in the solution will cause rapid hydrolysis on the coating surface, generating a large amount of La(OH)3 / LaOOH precipitate, rather than slowly depositing within the pores. If these precipitates cover the coating surface as coarse particles or continuous film layers, they will increase light scattering, causing the white coating to turn yellow or dull. Therefore, in some embodiments of this application, the sealing agent includes 0.03-0.07 mol / L of a soluble organic acid lanthanum salt, such as 0.03 mol / L, 0.04 mol / L, 0.05 mol / L, 0.06 mol / L, 0.07 mol / L, or any value between the two. Soluble organic lanthanum salts within this range can have a better deposition rate, effectively blocking pores and preventing excessive precipitate formation on the coating surface. In other embodiments of this application, the soluble organic acid lanthanum salt includes lanthanum acetate monohydrate and / or lanthanum citrate.

[0024] In the sealing agent of this application, the concentration of the oxidizing agent is particularly optimal. If the concentration is too high, its strong oxidizing properties may trigger an excessively vigorous reaction within the micropores, damaging the integrity of the sealing structure. Simultaneously, some of the oxidizing agent (or its reaction byproducts) may be introduced into an acidic environment, corroding phases such as MgO and Mg2SiO4 in the coating. This not only enlarges the existing micropores but may even create new defects, ultimately leading to coating weight loss, chalking, or a decrease in whiteness. If the concentration is too low, it cannot effectively drive the La... 3+ The oxidation-hydrolysis process mainly produces La(OH)3, which has poor thermal stability. This substance is prone to dehydration and cracking during subsequent drying or thermal cycling, resulting in a loss of sealing effect. Simultaneously, at low concentrations, the sealing material does not deposit sufficiently within the micropores, leading to a low sealing rate and limited improvement in the coating's corrosion resistance. Therefore, in some embodiments of this application, the sealing agent includes an oxidation aid with a volume percentage of 0.2-0.8%, such as 0.2%, 0.25%, 0.3%, 0.35%, 0.4%, 0.45%, 0.5%, 0.55%, 0.6%, 0.65%, 0.7%, 0.75%, 0.8%, or any value between these two. Considering the special characteristics of thermally controlled protective coatings, colored oxidants and oxidants that may introduce impurity ions (such as chloride ions or cerium ions), thereby causing ionic corrosion or leading to yellowing of the coating, cannot be used as the oxidation aid. In other embodiments of this application, the oxidation aid is preferably hydrogen peroxide, such as 30% hydrogen peroxide.

[0025] In the sealing agent of this application, during the sealing process of the lanthanum salt solution, the pH value of the solution can affect the La 3+ The hydrolysis behavior, precipitation morphology, and ability to deposit in micropores are considered. This application controls the sealing agent solution to be weakly acidic; deviations to neutral or alkaline conditions significantly disrupt the ordered, site-specific precipitation of lanthanum ions. When the solution is neutral, ion hydrolysis reactions occur rapidly on the coating surface and in the solution bulk. The colloidal substances produced by these hydrolysis reactions do not penetrate deep into the pores, but merely form a loose layer on the pore surface, offering limited improvement to the coating's corrosion resistance. In an alkaline environment, La... 3+ A large amount of La(OH)3 precipitate will be generated immediately, forming flocculent suspension. The precipitate only adheres to the coating surface by physical adsorption, without clear selectivity or density, which also has the disadvantage of reducing the absorption ratio and having limited effect on improving the coating's corrosion resistance. Therefore, in some embodiments of this application, the pH value is 5.5-6.8, for example, 5.5, 5.6, 5.7, 5.8, 5.9, 6.0, 6.1, 6.2, 6.3, 6.4, 6.5, 6.6, 6.7, 6.8, or any value between any two. In other embodiments of this application, the weakly acidic buffer pair includes an acetate-sodium acetate buffer pair or a citrate-sodium citrate buffer pair.

[0026] In the second aspect of this application, the sealing agent described in this application is used to seal the white micro-arc oxidation ceramic coating, resulting in significant improvements in the following three aspects of the micro-arc oxidation ceramic coating after immersion treatment: (1) The electrochemical impedance modulus in 3.5% NaCl solution increases by an order of magnitude, resulting in a significant enhancement in corrosion resistance; (2) The solar absorptivity decreased by 0.06±0.01 in the 200-2600 nm solar spectrum band, while the hemispherical emissivity increased by 0.04±0.01. (3) The surface porosity is significantly reduced and the microstructure is more compact.

[0027] Based on the aforementioned superior performance, this application provides the application of the sealing agent in the preparation of thermally controlled protective coatings. Specifically, the thermally controlled protective coating uses a micro-arc oxidation coating as the base coating, and more specifically, it is a micro-arc oxidation ceramic coating formed using a silicate system as the electrolyte, such as an electrolyte prepared with Na₂SiO₃·9H₂O and NaOH. More specifically, it includes 10-15 g / L of Na₂SiO₃·9H₂O and 1-3 g / L of NaOH.

[0028] In a third aspect of this application, a thermal protection coating is provided, comprising a porous coating and a sealing agent as described in this application, the sealing agent sealing the pores in the coating.

[0029] In some embodiments of this application, the porous coating includes a coating formed by micro-arc oxidation.

[0030] In a fourth aspect of this application, a method for preparing the thermal control protective coating is provided, comprising: Provides a porous coating; The coating is immersed in the sealing agent described in this application for soaking treatment; After soaking, the surface is cleaned of residual ions and dried to obtain the thermal control protective coating.

[0031] In some embodiments of this application, the porous coating is obtained by micro-arc oxidation; more specifically, a ceramic coating with micron-sized pores is deposited on a metal substrate by micro-arc oxidation using a silicate electrolyte, wherein the micro-arc oxidation is performed in a constant current mode.

[0032] In some embodiments of this application, the metal substrate undergoes pretreatment steps such as degreasing, alkali washing, acid washing, water washing, and drying before micro-arc oxidation.

[0033] In some embodiments of this application, the operating parameters of the micro-arc oxidation include: The silicate electrolyte formula is Na2SiO3·9H2O (12 g / L) and NaOH (1.5 g / L).

[0034] The power supply is a bipolar pulse power supply, using constant current mode, with a current density of 6A / dm. 2 Frequency 600Hz, duty cycle 10%, working time 15 minutes.

[0035] In some embodiments of this application, the soaking treatment may be assisted by heating, stirring, or ultrasonication to ensure that the sealing agent contacts and reacts with the coating uniformly and fully, effectively sealing the pores. In other embodiments of this application, the heating temperature is 50-70°C, and the stirring speed is 100-500 rpm.

[0036] In some embodiments of this application, the soaking time is 30-60 min, for example 30 min, 35 min, 40 min, 45 min, 50 min, 55 min, 60 min or any value between the two.

[0037] In a fifth aspect of this application, a thermal control component is provided, comprising a metal substrate and a thermal control protective coating disposed on the surface of the metal substrate, wherein the thermal control protective coating includes the thermal control protective coating described in this application. The thermal control protective coating on the surface of the metal substrate can be first coated or deposited using conventional methods to form a porous coating (e.g., a white ceramic coating deposited by micro-arc oxidation), and then the entire coating is immersed in the sealing agent described in this application for treatment, thereby obtaining the thermal control component.

[0038] In some embodiments of this application, the metal matrix includes, but is not limited to, magnesium alloys and / or aluminum alloys; in other embodiments of this application, the magnesium alloy may be AZ91D magnesium alloy.

[0039] In certain embodiments of this application, magnesium alloy components with the thermal control protective coating of this application were tested. After the white micro-arc oxidation coating on their surface was sealed, the following synergistic performance improvements were observed: (1) Significantly enhanced corrosion resistance: Electrochemical impedance spectroscopy (EIS) was performed in 3.5% NaCl solution, and its low-frequency impedance modulus |Z| was significantly enhanced. 0.01Hz The resistance to corrosive media penetration is more than an order of magnitude higher than that of unsealed samples, indicating a significant increase in resistance to corrosive media penetration. (2) Optimization of thermal control optical performance: The solar absorptivity (200-2600 nm) is reduced and the hemispherical emissivity is increased simultaneously, realizing the anomalous effect of "sealing the aperture without increasing absorption and compacting the aperture to increase radiation", which is conducive to long-term thermal balance stability; (3) Improved surface density: SEM observation showed that the number of surface micropores was significantly reduced and the porosity was significantly decreased, providing a physical barrier against atomic oxygen erosion and pollutant adsorption; In the comparative experiments provided in this application, unless otherwise specified, all experimental conditions and materials are kept consistent to ensure comparability. Unless otherwise specified, all experimental materials and reagents used in the examples are commercially available.

[0040] The following provides further details regarding a sealing agent, its application, a thermal control protective coating, its preparation method, and a thermal control component provided in this application.

[0041] Example 1: 1. Substrate material and preparation of micro-arc oxidation film Typical aerospace-grade AZ91D magnesium alloy sheet was selected and machined into 40 mm × 40 mm × 3 mm test pieces. The following pretreatment processes were then performed sequentially: a) Degreasing: Place the sample in analytical grade acetone and ultrasonically clean for 10 minutes to remove machining oil stains; b) Alkaline washing: Immerse in a 60℃, 2 wt% sodium hydroxide aqueous solution for 3 minutes to remove surface oxides and residual grease; c) Acid washing and activation: Immerse in room temperature, 5 g / L citric acid aqueous solution for 45 seconds, and lightly etch to improve the film adhesion; d) Washing and drying: Rinse three times with running deionized water for at least one minute each time, then dry with cold air and set aside.

[0042] The pretreated sample was used as the anode and subjected to micro-arc oxidation in a conventional silicate electrolyte system (12 g / L Na2SiO3·9H2O, 1.5 g / L NaOH) (a bipolar pulse power supply was used in constant current mode with a current density of 6 A / dm³). 2 A uniform, high-whiteness ceramic film was obtained by operating at a frequency of 600 Hz, a duty cycle of 10%, and for 15 minutes. The resulting coating showed no obvious cracks or discoloration, and its thickness was controlled within the range of 40-50 μm. This sample served as a reference sample for subsequent pore sealing. The absorption of this sample remained at 0.38±0.01, and the emission remained at 0.85±0.01.

[0043] 2. Preparation of composite organic acid lanthanum metal salt sealing solution Prepare 1 L of sealing solution in a clean glass beaker in the following order: a) Add 800 mL of deionized water; b) Slowly add 16.7 g of lanthanum acetate solid (corresponding to 0.05 mol / L) while stirring until completely dissolved; c) Add 4.1 g of analytical grade sodium acetate (CH3COONa), and then add glacial acetic acid (CH3COOH) dropwise to adjust the pH to 6.3 ± 0.1 to form an acetate-sodium acetate buffer system; d) While stirring continuously, slowly add 15 mL of 30% hydrogen peroxide (H2O2) solution (approximately 0.45 vol%). e) Add deionized water to a total volume of 1 L, and continue stirring for 10 minutes to ensure that there is no precipitate in the solution; 3. Sealing process a) After rapidly rinsing the MAO reference sample prepared in step 1 with deionized water, hang it vertically on a polytetrafluoroethylene hanger to ensure complete immersion and no air bubbles adhering to it. b) Immerse the test piece in the above sealing solution, place it in a constant temperature water bath, and heat it to 60°C. o C, and turn on the magnetic stirrer (at a speed of about 300 rpm) to ensure the homogeneity of the solution; c) The constant temperature soaking time is 45 min. During this period, avoid frequent opening of the lid to reduce the decomposition of H2O2. d) After soaking, quickly remove the sample and immediately rinse it with running deionized water for at least 3 minutes to thoroughly remove residual ions from the surface; e) Place the test piece at 80°C o Dry in a forced-air oven for 2 hours, cool to room temperature, and then seal and store for testing.

[0044] Example 2: The preparation was carried out according to the process in Example 1, except that lanthanum acetate monohydrate was replaced with lanthanum citrate, the buffer pair was replaced with sodium citrate-citric acid, and the pH was maintained at 6.3±0.1.

[0045] 1. Substrate material and preparation of micro-arc oxidation film Typical aerospace-grade AZ91D magnesium alloy sheet was selected and machined into 40 mm × 40 mm × 3 mm test pieces. The following pretreatment processes were then performed sequentially: a) Degreasing: Place the sample in analytical grade acetone and ultrasonically clean for 10 minutes to remove machining oil stains; b) Alkali washing: Transfer to 60 o C. Soak in a 2 wt% sodium hydroxide aqueous solution for 3 minutes to remove surface oxides and residual grease; c) Acid washing and activation: Immerse in room temperature, 5 g / L citric acid aqueous solution for 45 seconds, and lightly etch to improve the film adhesion; d) Washing and drying: Rinse three times with running deionized water for at least one minute each time, then dry with cold air and set aside.

[0046] The pretreated sample was used as the anode and subjected to micro-arc oxidation in a conventional silicate electrolyte system (a bipolar pulse power supply was used in constant current mode with a current density of 6 A / dm³). 2 A uniform, high-whiteness ceramic film was obtained by operating at a frequency of 600 Hz, a duty cycle of 10%, and for 15 minutes. The resulting coating showed no obvious cracks or discoloration, and its thickness was controlled within the range of 40-50 μm. This sample served as a reference sample for subsequent pore sealing. The absorption of this sample remained at 0.363±0.02, and the emission remained at 0.864±0.02.

[0047] 2. Preparation of composite organic acid lanthanum metal salt sealing solution Prepare 1 L of sealing solution in a clean glass beaker in the following order: a) Add 800 mL of deionized water; b) Slowly add 16.6 g of lanthanum citrate (corresponding to 0.05 mol / L), stirring constantly until completely dissolved; c) Add 14.7 g of analytical grade sodium citrate Na3C6H5O7, and then add citric acid (C6H8O7) dropwise to adjust the pH to 6.3 ± 0.1 to form a citric acid-sodium citrate buffer system; d) While stirring continuously, slowly add 15 mL of 30% hydrogen peroxide (H2O2) solution (approximately 0.45 vol% hydrogen peroxide). e) Add deionized water to a total volume of 1 L, and continue stirring for 10 minutes to ensure that there is no precipitate in the solution; 3. Sealing process a) After rapidly rinsing the MAO reference sample prepared in step 1 with deionized water, hang it vertically on a polytetrafluoroethylene hanger to ensure complete immersion and no air bubbles adhering to it. b) Immerse the test piece in the above sealing solution, place it in a constant temperature water bath, and heat it to 60°C. o C, and turn on the magnetic stirrer (at a speed of about 300 rpm) to ensure the homogeneity of the solution; c) The constant temperature soaking time is 45 min. During this period, avoid frequent opening of the lid to reduce the decomposition of H2O2. d) After soaking, quickly remove the sample and immediately rinse it with running deionized water for at least 3 minutes to thoroughly remove residual ions from the surface; e) Place the test piece at 80°C o Dry in a forced-air oven for 2 hours, cool to room temperature, and then seal and store for testing.

[0048] Comparative Example 1: The MAO reference sample prepared in Example 1 was used for pore sealing with a 0.1 mol / L lanthanum nitrate aqueous solution (pH≈4.6, without buffer and oxidizing agent), and the other conditions were the same as in Example 1.

[0049] Comparative Example 2: Prepared according to the process in Example 1, except that hydrogen peroxide is replaced with nitric acid.

[0050] 1. Substrate material and preparation of micro-arc oxidation film Typical aerospace-grade AZ91D magnesium alloy sheet was selected and machined into 40 mm × 40 mm × 3 mm test pieces. The following pretreatment processes were then performed sequentially: a) Degreasing: Place the sample in analytical grade acetone and ultrasonically clean for 10 minutes to remove machining oil stains; b) Alkali washing: Transfer to 60 o C. Soak in a 2 wt% sodium hydroxide aqueous solution for 3 minutes to remove surface oxides and residual grease; c) Acid washing and activation: Immerse in room temperature, 5 g / L citric acid aqueous solution for 45 seconds, and lightly etch to improve the film adhesion; d) Washing and drying: Rinse three times with running deionized water for at least one minute each time, then dry with cold air and set aside.

[0051] The pretreated sample was used as the anode and subjected to micro-arc oxidation in a conventional silicate electrolyte system (a bipolar pulse power supply was used in constant current mode with a current density of 6 A / dm³). 2 A uniform, high-whiteness ceramic film was obtained by operating at a frequency of 600 Hz, a duty cycle of 10%, and for 15 minutes. The resulting coating showed no obvious cracks or discoloration, and its thickness was controlled within the range of 40-50 μm. This sample served as a reference sample for subsequent pore sealing. The absorption of this sample remained at 0.363±0.02, and the emission remained at 0.864±0.02.

[0052] 2. Preparation of composite organic acid lanthanum metal salt sealing solution Prepare 1 L of sealing solution in a clean glass beaker in the following order: a) Add 800 mL of deionized water; b) Slowly add 16.7 g of lanthanum acetate solid (corresponding to 0.05 mol / L) while stirring until completely dissolved; c) Add 4.1 g of analytical grade sodium acetate (CH3COONa), and then add glacial acetic acid (CH3COOH) dropwise to adjust the pH to 6.3 ± 0.1 to form an acetate-sodium acetate buffer system; d) While stirring continuously, slowly add 4.5 mL of concentrated nitric acid (approximately 0.45 vol%). e) Add deionized water to a total volume of 1 L, and continue stirring for 10 minutes to ensure that there is no precipitate in the solution; 3. Sealing process a) After rapidly rinsing the MAO reference sample prepared in step 1 with deionized water, hang it vertically on a polytetrafluoroethylene hanger to ensure complete immersion and no air bubbles adhering to it. b) Immerse the test piece in the above sealing solution, place it in a constant temperature water bath, and heat it to 60°C. o C, and turn on the magnetic stirrer (at a speed of about 300 rpm) to ensure the homogeneity of the solution; c) The constant temperature soaking time is 45 minutes. During this period, avoid frequently opening the lid to prevent the solution temperature from dropping. d) After soaking, quickly remove the sample and immediately rinse it with running deionized water for at least 3 minutes to thoroughly remove residual ions from the surface; e) Place the test piece at 80°C o Dry in a forced-air oven for 2 hours, cool to room temperature, and then seal and store for testing.

[0053] Experimental example: (1) X-ray diffraction (XRD) test: The material composition and crystal structure of the coating surface were observed using an X-ray diffractometer.

[0054] It is evident that Examples 1 and 2, compared to the unsealed MAO coating, exhibit distinct LaOOH / La(OH)3 diffraction peaks at 27°, but the peak intensity in Example 2 is significantly weaker. Comparative Examples 1 and 2 do not show obvious LaOOH / La(OH)3 diffraction peaks, as shown in the attached figure. Figure 1 As shown.

[0055] (2) Electrochemical impedance spectroscopy (EIS) test: A three-electrode system was used, and the test was conducted in a 3.5 wt% NaCl solution, with a frequency range of 10. 5 -10 -2 Hz, disturbance voltage 10 mV.

[0056] The results show that the impedance modulus |Z| of the unsealed MAO coating at 0.01 Hz is... 0.01Hz ≈ 8.31×10 4 Ω·cm 2 ; After sealing the hole in Example 1, |Z| 0.01Hz Increased to 1.26×10 6 Ω·cm 2The increase of more than an order of magnitude indicates that the corrosion channels were effectively blocked. The increase in impedance modulus in Example 2 was within one order of magnitude. Meanwhile, the EIS impedance of Comparative Example 1 at 0.01 Hz was only about 3 times higher than that of the unsealed MAO coating, which was significantly less effective than the improvement in Example 1; the impedance modulus of Comparative Example 2 not only did not increase, but also decreased, which reflects that nitric acid, as an oxidizing agent, would damage the magnesium silicate structure on the coating surface.

[0057] (3) Optical thermal control performance test: Based on ASTM E903 (Solar Absorbance) and ASTM E408 (Hemispherical Emissivity) standards, the solar absorptivity α is calculated by integration in the 200-2600 nm wavelength band. S And the hemispherical emissivity ε in the 8-14 μm infrared band was measured.

[0058] The results show that after sealing the holes in Example 1, α S The value decreased from 0.38 to 0.32, a decrease of approximately 0.06. Simultaneously, ε increased from 0.85 to 0.90, an increase of approximately 0.04, and α... S The / ε ratio is 0.36, achieving synergistic optimization of thermal control performance; Example 2: α after sealing. S The value decreased from 0.38 to 0.35, a decrease of approximately 0.03; simultaneously, ε increased from 0.85 to 0.88, an increase of approximately 0.03, and α... S The / ε ratio is 0.40; while in Comparative Example 1α S No decrease, α S The value around 0.38 reflects the shortcomings of single inorganic acid lanthanum salts in sealing pores; in Comparative Example 2, after sealing, α... S The value decreased from 0.38 to 0.37, a reduction of only 0.01; additionally, the emission value also decreased to 0.83, α S The / ε ratio increased to 0.45, indicating that the strong acid oxidant had a negative impact on thermal control performance.

[0059] (4) Surface morphology and porosity analysis: The surface morphology was observed using a scanning electron microscope (SEM).

[0060] Numerous open pores with diameters of 0.5-14 μm were visible on the surface of the unsealed MAO samples; after sealing in Example 1, most micropores were filled with dense deposits, and SEM mapping revealed that La element was enriched in the micropores, such as... Figure 3 As shown in the image analysis software, the surface porosity decreased from approximately 18% to below 6%, confirming a significant sealing effect. Figure 2 As shown in the illustration. In contrast, the coating surface in Comparative Example 1 shows localized graying and uneven pore filling.

[0061] (5) Space environment simulation verification: a) Vacuum ultraviolet irradiation experiment (wavelength: 115 nm-400 nm; total fluence: 5000 ESH; 100 h): Before and after irradiation, the thermal control protective coating Δα of Example 1... S <0.015, no powdering or peeling; Thermal control protective coating Δα of Example 2 S <0.03, no chalking or peeling; unsealed coating Δα S <0.062; Comparative Example 1 thermal control protective coating Δα S <0.081, Comparative Example 2 thermal control protective coating Δα S <0.113, and there is obvious powdering phenomenon; b) Thermal cycling test (-196°C to 100°C, 100 cycles): The thermal protection coating of Example 1 maintained an adhesion grade of 0 in the cross-cut adhesion test. The adhesion grade of Example 2 remained at 0; the adhesion grade of the unsealed coating remained at 0; the adhesion grade of the coating in Comparative Example 1 remained at 0; in Comparative Example 2, after the solution sealed the pores, the surface coating structure became loose, and the adhesion grade dropped to 1 in the cross-cut adhesion test, which indirectly illustrates the damage of strong acid oxidants to the coating surface. The above description is merely a specific embodiment of this application, enabling those skilled in the art to understand or implement this application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of this application. Therefore, this application is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features claimed herein.

Claims

1. A sealing agent, characterized in that, include: The mixture consists of a soluble organic acid lanthanum salt, a weakly acidic buffer pair, an oxidizing agent, and water, with a pH of weakly acidic.

2. The sealing agent according to claim 1, characterized in that, include: The 0.03-0.07 mol / L soluble organic acid lanthanum salt, the 0.2-0.8% (v / v) oxidizing agent, the weakly acidic buffer to maintain the pH of the sealing agent as weakly acidic, and the balance being water.

3. The sealing agent according to claim 1 or 2, characterized in that, The soluble organic acid lanthanum salt includes lanthanum acetate monohydrate and / or lanthanum citrate; the weakly acidic buffer pair includes an acetate-sodium acetate buffer pair or a citrate-sodium citrate buffer pair; the oxidizing agent includes hydrogen peroxide.

4. The sealing agent according to claim 1 or 2, characterized in that, The pH value is 5.5-6.

8.

5. The application of the sealing agent according to any one of claims 1-4 in the preparation of thermal control protective coatings.

6. A thermal control protective coating, characterized in that, The coating includes a porous coating and a sealing agent according to any one of claims 1-4, wherein the sealing agent seals the pores in the coating.

7. The thermal control protective coating according to claim 6, characterized in that, The porous coating includes coatings formed by micro-arc oxidation.

8. The method for preparing the thermal control protective coating according to claim 6, characterized in that, include: Provides a porous coating; The coating is immersed in the sealing agent according to any one of claims 1-4 for soaking treatment; After soaking, the surface is cleaned of residual ions and dried to obtain the thermal control protective coating.

9. A thermal control component, characterized in that, It includes a metal substrate and a thermal control protective coating disposed on the surface of the metal substrate, wherein the thermal control protective coating includes the thermal control protective coating as described in claim 6 or 7.

10. The thermal control component according to claim 9, characterized in that, The metal matrix includes magnesium alloys and / or aluminum alloys.

Images