A high-temperature-resistant coating containing composite alumina and a preparation method thereof

Abstract

The application discloses a high-temperature-resistant coating containing composite alumina and a preparation method thereof, and relates to the technical field of coatings. In the application, under the high-temperature service environment, the alpha phase crystal nucleus of corundum phase alumina provides structural support as a rigid skeleton, and the anisotropic compressive stress generated by the gamma phase forces the condensation reaction of the particle surface and the silicate matrix to form a high bond energy covalent bond. At the same time, the magnesium hydroxide microcrystals in the matrix are thermally decomposed to generate a forsterite reinforced phase with silica sol, so that the coating realizes high heat resistance. Then, the epoxy modified methyl silicate is introduced to build a dense barrier in the coating, and the epoxy group is crosslinked with the solidification network of the silica sol, and the silane coupling agent is double-anchored on the surface of the active alumina, so that the corrosion resistance of the coating is improved. Then, the low-temperature pre-activation is combined with the high-temperature in-situ strengthening and solidification of the coating, so that the high-temperature resistance and corrosion resistance of the coating are further improved.

Description

Technical Field

[0001] This invention relates to the field of coating technology, specifically to a high-temperature resistant coating containing composite alumina and its preparation method. Background Technology

[0002] With the rapid development of aerospace, new energy vehicles, high-temperature metallurgy, thermal power generation, and petrochemical industries, the demand for high-temperature protective coatings is increasing. Among them, inorganic high-temperature resistant coatings have become the preferred protective material for various high-temperature service metal components (such as the combustion chamber shell of aero-engines, the thermal management system of power batteries in new energy vehicles, the steel structure of metallurgical furnaces and kilns, the pipelines of thermal power generation boilers, and the inner wall of chemical reaction vessels) due to their excellent high-temperature resistance, non-flammability, low VOC emissions, and good chemical stability. Their high-temperature resistance, mechanical properties, and resistance to media corrosion directly determine the protective effectiveness of the metal substrate, the operational reliability of the equipment, and its service life.

[0003] In the production and application of high-temperature resistant inorganic coatings, long-term high-temperature resistance is the core indicator for evaluating their protective performance, directly determining the structural integrity and protective continuity of the coating under extreme high-temperature environments. Simultaneously, the adhesion between the coating and the substrate, impact resistance, and thermal shock stability are key performance indicators determining whether the coating will crack and detach under temperature alternation and mechanical loads. Furthermore, inorganic high-temperature resistant coatings prepared using existing technologies exhibit poor high-temperature mechanical properties. Moreover, existing composite inorganic coatings often incorporate large amounts of organic binders to improve flexibility; however, organic components decompose and carbonize above 300℃, significantly reducing the coating's high-temperature resistance and generating toxic and harmful gases, causing environmental pollution and safety hazards.

[0004] Patent CN103113768A discloses a high-temperature resistant coating for engine exhaust systems. This coating uses silica sol as the main film-forming base material and adds 5-30 parts of low-melting-point glass powder as a sintering aid, raising the long-term service temperature of the coating to around 600℃. It is mainly designed for medium- and low-temperature protection of ordinary industrial steel structures and engine exhaust systems. However, this coating has poor high-temperature mechanical properties and thermal shock stability, and it is not optimized for coastal and industrial corrosive environments. Its salt spray corrosion resistance is insufficient, and it cannot meet the long-term protection requirements under extreme high-temperature and highly corrosive environments. Therefore, it is particularly necessary to invent a high-temperature resistant inorganic coating with high heat resistance and excellent corrosion resistance. Summary of the Invention

[0005] The purpose of this invention is to provide a high-temperature resistant coating containing composite alumina and its preparation method, so as to solve the problems existing in the prior art.

[0006] To solve the above-mentioned technical problems, the present invention provides the following technical solution: a high-temperature resistant coating containing composite alumina, wherein the high-temperature resistant coating containing composite alumina is composed of component A and component B, wherein component A contains composite alumina powder, silicon dioxide, mica powder, alkaline silica sol and silane coupling agent KH-560, and component B contains epoxy-modified methylsilicate solution, magnesium hydroxide and deionized water.

[0007] Furthermore, a high-temperature resistant coating containing composite alumina is characterized by comprising the following preparation steps: s1. Disperse corundum phase alumina and anhydrous ethanol under ultrasonic power of 300W for 20min, add activated alumina, stir and disperse at 200rpm for 50min, add silane coupling agent KH-560, heat to 50℃, stir and react at 300rpm for 3h, after the reaction is completed, centrifuge to separate, take the solid, wash twice with anhydrous ethanol, dry at 90℃ and nitrogen flow rate of 75mL / min for 5h, finally grind and pass through a 200-mesh sieve to obtain composite alumina powder; s2. The composite alumina powder is mixed with silica and mica powder and wet-milled to obtain a mixed slurry; deionized water and alkaline silica sol are mixed, the mixed slurry and silane coupling agent KH-560 are added, and the mixture is dispersed at high speed of 1200 rpm for 50 min. After filtration through a 200-mesh sieve, component A is obtained. s3. Mix epoxy-modified methylsilicate solution with deionized water, add magnesium hydroxide, and stir at 800 rpm for 30 min to obtain component B; s4. Mix component A and component B evenly to obtain a high-temperature resistant coating containing composite alumina.

[0008] Furthermore, the mass ratio of corundum phase alumina, anhydrous ethanol, activated alumina, and silane coupling agent KH-560 in step s1 is 18:200:10:(0.8~0.9).

[0009] Furthermore, the corundum phase alumina in step s1 is α-Al2O3 with a particle size of 50 nm; the active alumina is γ-Al2O3 with a particle size of 20 nm.

[0010] Furthermore, the mass ratio of the composite alumina powder, silicon dioxide, mica powder, deionized water, alkaline silica sol, and silane coupling agent KH-560 in step s2 is 28:8:5:45:7.5:0.35.

[0011] Furthermore, the wet milling process parameters in step s2 are as follows: the liquid medium is deionized water, the amount is 25% of the mass of the composite alumina powder, the ball milling medium is zirconia balls, the ball-to-material ratio is 4:1, the rotation speed is 400 rpm, and the time is 1.5 h.

[0012] Furthermore, in step s3, the mass ratio of the epoxy-modified methylsilicate solution, deionized water, and magnesium hydroxide is 14:5:2.

[0013] Further, the preparation method of the epoxy-modified methylsilicate solution in step s3 is as follows: deionized water, anhydrous ethanol, and silane coupling agent KH-560 are stirred and mixed at a speed of 300~400 rpm, then glacial acetic acid is added to adjust the pH of the solution to 4. Next, the temperature is raised to 40~45℃ and stirred at 200 rpm for 1~2 hours. After the reaction is completed, 40wt% methylsilicate aqueous solution is added, and the temperature is raised to 50~65℃ and stirred at 300 rpm for 3 hours to obtain the solution. The mass ratio of deionized water, anhydrous ethanol, silane coupling agent KH-560, and 40wt% methylsilicate aqueous solution is 50:5:8.5:100.

[0014] Furthermore, the 40wt% methylsilicate aqueous solution is composed of methylsilicate and deionized water, wherein the methylsilicate is at least one of potassium methylsilicate, lithium methylsilicate, sodium methylsilicate, and calcium methylsilicate.

[0015] Furthermore, in step s4, the mass ratio of component A to component B is 1:0.15.

[0016] Compared with the prior art, the beneficial effects achieved by the present invention are: This invention utilizes the confined geometric configuration of corundum-phase alumina and activated alumina to reverse the volume shrinkage during the γ-phase to α-phase transformation into a densification driving force for interfacial chemical bond rearrangement. Under high-temperature service conditions, the α-phase nuclei provide structural support as a rigid framework, while the anisotropic compressive stress generated by the γ-phase forces the particle surface to undergo a condensation reaction with the silicate matrix, forming high-bond-energy silica-alumina covalent bonds. Simultaneously, the magnesium hydroxide microcrystals in the matrix undergo thermal decomposition, generating highly reactive magnesium oxide that reacts in situ with the silica sol matrix to form a forsterite reinforcing phase. This results in a coating that achieves superior high efficiency. The coating improves heat resistance by introducing epoxy-modified methylsilicate to construct a dense barrier within the coating. The hydrophobic methyl groups of the methylsilicate self-assemble in the nanopores and on the surface to form a low surface energy hydrophobic layer, which blocks the capillary adsorption and penetration pathways of corrosive media through steric hindrance. On the other hand, the curing and cross-linking network of epoxy groups and silica sol, as well as the dual anchoring effect of silane coupling agent on the surface of activated alumina, significantly reduce the free volume and defect density inside the coating. This synergistic effect of hydrophobic interface barrier and highly dense cross-linking network significantly improves the corrosion resistance of the coating.

[0017] This invention combines low-temperature pre-activation with high-temperature in-situ reinforced curing of the coating. The pre-crosslinked network formed in the substrate at low temperature avoids the initiation of microcracks caused by sudden high-temperature heating, while the microporous channels formed by the escape of trace amounts of water vapor generated by the decomposition of magnesium hydroxide at high temperature release thermal stress. This allows the coating to maintain a dense structure and excellent interfacial adhesion even under extreme heat and corrosion environments, further enhancing the coating's high-temperature resistance and corrosion resistance. Detailed Implementation

[0018] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0019] To more clearly illustrate the method provided by the present invention, the following embodiments are provided in detail. The test methods for various indicators of the high-temperature resistant coating containing composite alumina prepared in the following embodiments are as follows: A high-temperature resistant coating containing composite alumina was applied to the surface of a polished 304 stainless steel substrate with a coating thickness of 250 μm per coat. After standing for 8 hours, the coating was held at 80°C for 1 hour, then heated to 180°C at a rate of 5°C / min and held for 1 hour. The coating was then cooled with the furnace and tested.

[0020] High temperature resistance: Take the same size examples and comparative examples, and place the coating samples in a muffle furnace according to GB / T 1735. Hold them at 400℃, 600℃ and 800℃ for 2 hours respectively. After cooling with the furnace, observe the appearance of the coating (no cracking or peeling is acceptable).

[0021] Salt spray resistance: Using examples and comparative examples of the same size, the corrosion of the coating was tested after 300 hours according to GB / T 10125.

[0022] Example 1; s1. Alumina phase corundum and anhydrous ethanol were dispersed under ultrasonic power of 300W for 20 min, activated alumina was added, and the mixture was stirred and dispersed at 200 rpm for 50 min. Silane coupling agent KH-560 was added, and the mixture was heated to 50℃ and stirred at 300 rpm for 3 h. After the reaction, the mixture was centrifuged, the solid was collected, washed twice with anhydrous ethanol, and dried at 90℃ under a nitrogen atmosphere of 75 mL / min for 5 h. Finally, the solid was ground through a 200-mesh sieve to obtain composite alumina powder. The mass ratio of alumina phase corundum, anhydrous ethanol, activated alumina, and silane coupling agent KH-560 was 18:200:10:0.8. The alumina phase corundum was α-Al2O3 with a particle size of 50 nm, and the activated alumina was γ-Al2O3 with a particle size of 20 nm. s2. The composite alumina powder is mixed with silica and mica powder, and then wet-milled. The process parameters are: deionized water as the liquid medium, the amount of which is 25% of the mass of the composite alumina powder; zirconia balls as the ball milling medium, the ball-to-powder ratio is 4:1; the rotation speed is 400 rpm; and the time is 1.5 h to obtain a mixed slurry. The deionized water is mixed with alkaline silica sol, and the mixed slurry and silane coupling agent KH-560 are added. The mixture is dispersed at high speed at 1200 rpm for 50 min, and then passed through a 200-mesh sieve. The slurry under the sieve is collected. The material was processed to obtain component A; the mass ratio of the composite alumina powder, silicon dioxide, mica powder, deionized water, alkaline silica sol, and silane coupling agent KH-560 was 28:8:5:45:7.5:0.35; the silicon dioxide had a particle size of 3 μm; the mica powder was in flake form with a particle size of 10 μm; the alkaline silica sol contained 35 wt% silicon dioxide, had a pH of 10, a modulus of 3.2, a particle size of 15 nm, and a Na₂O content of 0.2%. s3. Deionized water, anhydrous ethanol, and silane coupling agent KH-560 were mixed by stirring at 300 rpm. Glacial acetic acid was then added to adjust the pH of the solution to 4. The mixture was then heated to 40°C and stirred at 200 rpm for 1 hour. After the reaction, a 40 wt% methylsilicate aqueous solution was added, and the temperature was raised to 50°C and stirred at 300 rpm for 3 hours to obtain an epoxy-modified methylsilicate solution. The mass ratio of the deionized water, anhydrous ethanol, silane coupling agent KH-560, and 40 wt% methylsilicate aqueous solution was 50:5:8.5:100. The 40 wt% methylsilicate aqueous solution was composed of potassium methylsilicate and deionized water. The epoxy-modified methylsilicate solution was mixed with deionized water, and magnesium hydroxide was added. The mixture was stirred at 800 rpm for 30 minutes to obtain component B. The mass ratio of the epoxy-modified methylsilicate solution, deionized water, and magnesium hydroxide was 14:5:2. The particle size of the magnesium hydroxide was 1 μm. s4. Mix component A and component B evenly to obtain a high-temperature resistant coating containing composite alumina; the mass ratio of component A to component B is 1:0.15.

[0023] Example 2; s1. Alumina phase corundum and anhydrous ethanol were dispersed under ultrasonic power of 300W for 20 min. Activated alumina was added, and the mixture was stirred and dispersed at 200 rpm for 50 min. Silane coupling agent KH-560 was added, and the mixture was heated to 50℃ and stirred at 300 rpm for 3 h. After the reaction, the mixture was centrifuged, and the solid was washed twice with anhydrous ethanol. It was then dried at 90℃ under a nitrogen atmosphere with a flow rate of 75 mL / min for 5 h. Finally, it was ground through a 200-mesh sieve to obtain composite alumina powder. The mass ratio of alumina phase corundum, anhydrous ethanol, activated alumina, and silane coupling agent KH-560 was 18:200:10:0.85. The alumina phase corundum was α-Al2O3 with a particle size of 50 nm. The activated alumina was γ-Al2O3 with a particle size of 20 nm. s2. The composite alumina powder is mixed with silica and mica powder, and then wet-milled. The process parameters are: deionized water as the liquid medium, the amount of which is 25% of the mass of the composite alumina powder; zirconia balls as the ball milling medium, the ball-to-powder ratio is 4:1; the rotation speed is 400 rpm; and the time is 1.5 h to obtain a mixed slurry. The deionized water is mixed with alkaline silica sol, and the mixed slurry and silane coupling agent KH-560 are added. The mixture is dispersed at high speed at 1200 rpm for 50 min, and then passed through a 200-mesh sieve. The slurry under the sieve is collected. The material was processed to obtain component A; the mass ratio of the composite alumina powder, silicon dioxide, mica powder, deionized water, alkaline silica sol, and silane coupling agent KH-560 was 28:8:5:45:7.5:0.35; the silicon dioxide had a particle size of 3 μm; the mica powder was in flake form with a particle size of 10 μm; the alkaline silica sol contained 35 wt% silicon dioxide, had a pH of 10, a modulus of 3.2, a particle size of 15 nm, and a Na₂O content of 0.2%. s3. Deionized water, anhydrous ethanol, and silane coupling agent KH-560 were mixed by stirring at 350 rpm. Glacial acetic acid was then added to adjust the pH of the solution to 4. The mixture was then heated to 43°C and stirred at 200 rpm for 1.5 hours. After this, a 40 wt% methylsilicate aqueous solution was added, and the mixture was heated to 58°C and stirred at 300 rpm for 3 hours to obtain an epoxy-modified methylsilicate solution. The mass ratio of the deionized water, anhydrous ethanol, silane coupling agent KH-560, and 40 wt% methylsilicate aqueous solution was 50:5:8.5:100. The 40 wt% methylsilicate aqueous solution was composed of potassium methylsilicate and deionized water. The epoxy-modified methylsilicate solution was mixed with deionized water, and magnesium hydroxide was added. The mixture was stirred at 800 rpm for 30 minutes to obtain component B. The mass ratio of the epoxy-modified methylsilicate solution, deionized water, and magnesium hydroxide was 14:5:2. The particle size of the magnesium hydroxide was 1 μm. s4. Mix component A and component B evenly to obtain a high-temperature resistant coating containing composite alumina; the mass ratio of component A to component B is 1:0.15.

[0024] Example 3; s1. Alumina phase corundum and anhydrous ethanol were dispersed under ultrasonic power of 300W for 20 min, activated alumina was added, and the mixture was stirred and dispersed at 200 rpm for 50 min. Silane coupling agent KH-560 was added, and the mixture was heated to 50℃ and stirred at 300 rpm for 3 h. After the reaction, the mixture was centrifuged, the solid was collected, washed twice with anhydrous ethanol, and dried at 90℃ under a nitrogen atmosphere of 75 mL / min for 5 h. Finally, the solid was ground through a 200-mesh sieve to obtain composite alumina powder. The mass ratio of alumina phase corundum, anhydrous ethanol, activated alumina, and silane coupling agent KH-560 was 18:200:10:0.9. The alumina phase corundum was α-Al2O3 with a particle size of 50 nm; the activated alumina was γ-Al2O3 with a particle size of 20 nm. s2. The composite alumina powder is mixed with silica and mica powder, and then wet-milled. The process parameters are: deionized water as the liquid medium, the amount of which is 25% of the mass of the composite alumina powder; zirconia balls as the ball milling medium, the ball-to-powder ratio is 4:1; the rotation speed is 400 rpm; and the time is 1.5 h to obtain a mixed slurry. The deionized water is mixed with alkaline silica sol, and the mixed slurry and silane coupling agent KH-560 are added. The mixture is dispersed at high speed at 1200 rpm for 50 min, and then passed through a 200-mesh sieve. The slurry under the sieve is collected. The material was processed to obtain component A; the mass ratio of the composite alumina powder, silicon dioxide, mica powder, deionized water, alkaline silica sol, and silane coupling agent KH-560 was 28:8:5:45:7.5:0.35; the silicon dioxide had a particle size of 3 μm; the mica powder was in flake form with a particle size of 10 μm; the alkaline silica sol contained 35 wt% silicon dioxide, had a pH of 10, a modulus of 3.2, a particle size of 15 nm, and a Na₂O content of 0.2%. s3. Deionized water, anhydrous ethanol, and silane coupling agent KH-560 were mixed by stirring at 400 rpm. Glacial acetic acid was then added to adjust the pH of the solution to 4. The mixture was then heated to 45°C and stirred at 200 rpm for 2 hours. After the reaction, a 40 wt% methylsilicate aqueous solution was added, and the temperature was raised to 65°C and stirred at 300 rpm for 3 hours to obtain an epoxy-modified methylsilicate solution. The mass ratio of the deionized water, anhydrous ethanol, silane coupling agent KH-560, and 40 wt% methylsilicate aqueous solution was 50:5:8.5:100. The 40 wt% methylsilicate aqueous solution was composed of potassium methylsilicate and deionized water. The epoxy-modified methylsilicate solution was mixed with deionized water, and magnesium hydroxide was added. The mixture was stirred at 800 rpm for 30 minutes to obtain component B. The mass ratio of the epoxy-modified methylsilicate solution, deionized water, and magnesium hydroxide was 14:5:2. The particle size of the magnesium hydroxide was 1 μm. s4. Mix component A and component B evenly to obtain a high-temperature resistant coating containing composite alumina; the mass ratio of component A to component B is 1:0.15.

[0025] Example 4; s1. Alumina phase corundum and anhydrous ethanol were dispersed under ultrasonic power of 300W for 20 min, activated alumina was added, and the mixture was stirred and dispersed at 200 rpm for 50 min. Silane coupling agent KH-560 was added, and the mixture was heated to 50℃ and stirred at 300 rpm for 3 h. After the reaction, the mixture was centrifuged, the solid was taken, washed twice with anhydrous ethanol, and dried at 90℃ under a nitrogen atmosphere of 75 mL / min for 5 h. Finally, the solid was ground and passed through a 200-mesh sieve to obtain composite alumina powder. The mass ratio of alumina phase corundum, anhydrous ethanol, activated alumina, and silane coupling agent KH-560 was 18:200:10:0.85. The alumina phase corundum was α-Al2O3 with a particle size of 50 nm; the activated alumina was γ-Al2O3 with a particle size of 20 nm. s2. The composite alumina powder is mixed with silica and mica powder, and then wet-milled. The process parameters are: deionized water as the liquid medium, the amount of which is 25% of the mass of the composite alumina powder; zirconia balls as the ball milling medium, the ball-to-powder ratio is 4:1; the rotation speed is 400 rpm; and the time is 1.5 h to obtain a mixed slurry. The deionized water is mixed with alkaline silica sol, and the mixed slurry and silane coupling agent KH-560 are added. The mixture is dispersed at high speed at 1200 rpm for 50 min, and then passed through a 200-mesh sieve. The slurry under the sieve is collected. The material was processed to obtain component A; the mass ratio of the composite alumina powder, silicon dioxide, mica powder, deionized water, alkaline silica sol, and silane coupling agent KH-560 was 28:8:5:45:7.5:0.35; the silicon dioxide had a particle size of 3 μm; the mica powder was in flake form with a particle size of 10 μm; the alkaline silica sol contained 35 wt% silicon dioxide, had a pH of 10, a modulus of 3.2, a particle size of 15 nm, and a Na₂O content of 0.2%. s3. Deionized water, anhydrous ethanol, and silane coupling agent KH-560 were mixed by stirring at 350 rpm. Glacial acetic acid was then added to adjust the pH of the solution to 4. The mixture was then heated to 43°C and stirred at 200 rpm for 1.5 hours. After this, a 40 wt% methylsilicate aqueous solution was added, and the temperature was raised to 58°C and stirred at 300 rpm for 3 hours to obtain an epoxy-modified methylsilicate solution. The mass ratio of the deionized water, anhydrous ethanol, silane coupling agent KH-560, and 40 wt% methylsilicate aqueous solution was 50:5:8.5:100. The 40 wt% methylsilicate aqueous solution was composed of potassium methylsilicate and deionized water. The epoxy-modified methylsilicate solution was mixed with deionized water, and magnesium hydroxide was added. The mixture was stirred at 800 rpm for 30 minutes to obtain component B. The mass ratio of the epoxy-modified methylsilicate solution, deionized water, and magnesium hydroxide was 7:5:2. The particle size of the magnesium hydroxide was 1 μm. s4. Mix component A and component B evenly to obtain a high-temperature resistant coating containing composite alumina; the mass ratio of component A to component B is 1:0.15.

[0026] Comparative Example 1; The difference between Comparative Example 1 and Example 2 is that no activated alumina is added; the remaining steps are the same as in Example 2.

[0027] Comparative Example 2; The difference between Comparative Example 2 and Example 2 is that corundum phase alumina is not added; the remaining steps are the same as in Example 2.

[0028] Comparative Example 3; The difference between Comparative Example 3 and Example 2 is that step s3 is different. Step s3 is changed to: mixing 40wt% methylsilicate aqueous solution with deionized water, adding magnesium hydroxide, and stirring at 800 rpm for 30 min to obtain component B; the mass ratio of the 40wt% methylsilicate aqueous solution, deionized water, and magnesium hydroxide is 14:5:2; the 40wt% methylsilicate aqueous solution is composed of potassium methylsilicate and deionized water; the particle size of the magnesium hydroxide is 1 μm; the remaining steps are the same as in Example 2.

[0029] Comparative Example 4; The difference between Comparative Example 4 and Example 2 is that no epoxy-modified methylsilicate solution is added; the remaining steps are the same as in Example 2.

[0030] Example of effect Table 1 below shows the performance analysis results of the high-temperature resistant coatings containing composite alumina used in Examples 1 to 4 and Comparative Examples 1 to 4 of the present invention.

[0031] Table 1 A comparison of the experimental results of the embodiments and comparative examples in Table 1 reveals that, under high-temperature service conditions, the present invention utilizes corundum phase alumina and activated alumina. The α-phase nuclei serve as a rigid framework to provide structural support, while the anisotropic compressive stress generated by the γ-phase forces the particle surface to undergo a condensation reaction with the silicate matrix, forming high-bond-energy silicon-aluminum covalent bonds. This results in excellent high heat resistance of the coating. Subsequently, by introducing epoxy-modified methyl silicate, a dense barrier is constructed inside the coating. The hydrophobic methyl groups of methyl silicate self-assemble in the nanopores and on the surface to form a low surface energy hydrophobic layer. On the other hand, the curing and cross-linking network of epoxy groups and silica sol, as well as the dual anchoring effect of silane coupling agents on the surface of activated alumina, significantly reduce the free volume and defect density inside the coating, thereby improving the corrosion resistance of the coating.

[0032] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from its spirit or essential characteristics. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of equivalents of the claims are intended to be included within the present invention. No markings in the claims should be construed as limiting the scope of the claims.

Claims

1. A method for preparing a high-temperature resistant coating containing composite alumina, characterized in that, Includes the following steps: s1. After ultrasonically dispersing corundum phase alumina and anhydrous ethanol, add activated alumina and continue stirring and dispersing. Add silane coupling agent KH-560, heat and stir to react, and then centrifuge, wash, dry and grind and sieve to obtain composite alumina powder. The corundum phase alumina is α-Al2O3 with a particle size of 50 nm; the active alumina is γ-Al2O3 with a particle size of 20 nm. s2. The composite alumina powder is mixed with silica and mica powder, and wet-milled to obtain a mixed slurry; deionized water and alkaline silica sol are mixed, the mixed slurry and silane coupling agent KH-560 are added, the mixture is dispersed at high speed and filtered, and the solid is collected to obtain component A; s3. Mix epoxy-modified methylsilicate solution with deionized water, add magnesium hydroxide to disperse, and obtain component B; s4. Mix component A and component B evenly to obtain a high-temperature resistant coating containing composite alumina.

2. The method for preparing a high-temperature resistant coating containing composite alumina according to claim 1, characterized in that, The mass ratio of corundum phase alumina, anhydrous ethanol, activated alumina, and silane coupling agent KH-560 in step s1 is 18:200:10:(0.8~0.9).

3. The method for preparing a high-temperature resistant coating containing composite alumina according to claim 1, characterized in that, The mass ratio of the composite alumina powder, silicon dioxide, mica powder, deionized water, alkaline silica sol, and silane coupling agent KH-560 in step s2 is 28:8:5:45:7.5:0.

35.

4. The method for preparing a high-temperature resistant coating containing composite alumina according to claim 1, characterized in that, The process parameters for wet milling in step s2 are as follows: the liquid medium is deionized water, the amount is 25% of the mass of the composite alumina powder, the ball milling medium is zirconia balls, the ball-to-material ratio is 4:1, the rotation speed is 400 rpm, and the time is 1.5 h.

5. The method for preparing a high-temperature resistant coating containing composite alumina according to claim 1, characterized in that, The mass ratio of the epoxy-modified methylsilicate solution, deionized water, and magnesium hydroxide in step s3 is 14:5:

2.

6. The method for preparing a high-temperature resistant coating containing composite alumina according to claim 1, characterized in that, The preparation method of the epoxy-modified methylsilicate solution in step s3 is as follows: Deionized water, anhydrous ethanol, and silane coupling agent KH-560 are stirred and mixed at a speed of 300~400 rpm, then glacial acetic acid is added to adjust the pH of the solution to 4. Next, the temperature is raised to 40~45℃ and stirred at 200 rpm for 1~2 hours. After the reaction is completed, 40wt% methylsilicate aqueous solution is added, and the temperature is raised to 50~65℃ and stirred at 300 rpm for 3 hours to obtain the solution. The mass ratio of the deionized water, anhydrous ethanol, silane coupling agent KH-560, and 40wt% methylsilicate aqueous solution is 50:5:8.5:

100.

7. The method for preparing a high-temperature resistant coating containing composite alumina according to claim 1, characterized in that, The 40wt% methylsilicate aqueous solution is composed of methylsilicate and deionized water, wherein the methylsilicate is at least one of potassium methylsilicate, lithium methylsilicate, sodium methylsilicate, and calcium methylsilicate.

8. The method for preparing a high-temperature resistant coating containing composite alumina according to claim 1, characterized in that, The mass ratio of component A to component B in step s4 is 1:0.

15.

9. A high-temperature resistant coating prepared by the method for preparing a high-temperature resistant coating containing composite alumina as described in any one of claims 1-8, characterized in that, The high-temperature resistant coating containing composite alumina is composed of component A and component B. Component A includes composite alumina powder, silicon dioxide, mica powder, alkaline silica sol and silane coupling agent KH-560, and component B includes epoxy-modified methylsilicate solution, magnesium hydroxide and deionized water.

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