A high-temperature and corrosion-resistant inorganic phosphate-based composite coating and its preparation method

Abstract

This invention discloses a high-temperature and corrosion-resistant inorganic phosphate-based composite coating and its preparation method, belonging to the field of material surface modification technology. The composite coating consists of a modified aluminum dihydrogen phosphate solution and an inorganic composite filler. The modified aluminum dihydrogen phosphate solution is obtained by mixing aluminum dihydrogen phosphate and methyltriethoxysilane; the modified aluminum dihydrogen phosphate solution is present in an amount of 15-25 wt%; the inorganic composite filler includes copper oxide, aluminum oxide, silicon carbide, zirconium oxide, alumina, and nano-alumina-hybrid carbon nanotubes. The coating of this invention exhibits excellent high-temperature resistance and corrosion resistance, thereby effectively solving the technical problems of oxidation and corrosion of heat-resistant steel components in high-temperature corrosive environments, and reliably improving the service life of heat-resistant steel components in high-temperature corrosive environments.

Description

Technical Field

[0001] This invention belongs to the field of material surface modification technology, specifically relating to a high-temperature and corrosion-resistant inorganic phosphate-based composite coating and its preparation method. Background Technology

[0002] With the development of ultra-supercritical power generation technology, the increased steam temperature in ultra-supercritical turbine units leads to more severe high-temperature corrosion of metallic materials. This necessitates higher requirements for high-temperature resistance and corrosion prevention than for creep strength. Therefore, the corrosion resistance of ferritic heat-resistant steels at high temperatures deserves special attention. Studies show that in environments above 600℃, the chromium oxide film formed on the surface of ferritic heat-resistant steel is prone to peeling and volatilization in supercritical water environments. Furthermore, the higher the temperature, the greater the corrosion weight gain, and the more prone the oxide layer is to cracking and other defects, further exacerbating corrosion. Therefore, high-temperature resistance and corrosion prevention should be fully considered when developing new ferritic / martensitic heat-resistant steels.

[0003] In order to promote the development of ultra-supercritical power generation technology and effectively solve the problems of oxidation and corrosion of heat-resistant steel components used in ultra-supercritical steam turbine units in high-temperature and corrosive environments, it is necessary to develop high-temperature resistant and corrosion-resistant coatings.

[0004] Inorganic coatings are environmentally friendly, have good heat resistance, and long service life, making them a focus of attention in industrial applications. Among them, inorganic phosphate-based coatings are particularly favored due to their good adhesion, excellent thermal and chemical stability, and environmental friendliness. Current inorganic phosphate binders generally use chromium phosphate or aluminum chromium phosphate. While coatings prepared from these materials exhibit excellent high-temperature resistance, the preparation process and the resulting solution system contain chromium (Cr). 6+ Contact with skin can cause allergies and even cancer; and Cr ions have a persistent environmental hazard and are not easily decomposed or absorbed. Summary of the Invention

[0005] The purpose of this section is to outline some aspects of embodiments of the present invention and to briefly describe some preferred embodiments. Simplifications or omissions may be made in this section, as well as in the abstract and title of this application, to avoid obscuring the purpose of these documents; however, such simplifications or omissions should not be construed as limiting the scope of the invention.

[0006] In view of the problems existing in the above and / or prior art, the present invention is proposed.

[0007] One objective of this invention is to provide a method for preparing a high-temperature and corrosion-resistant inorganic phosphate-based composite coating.

[0008] To solve the above-mentioned technical problems, the present invention provides the following technical solution: a high-temperature and corrosion-resistant inorganic phosphate-based composite coating, which is composed of a modified aluminum dihydrogen phosphate solution and an inorganic composite filler;

[0009] The modified aluminum dihydrogen phosphate solution is obtained by mixing aluminum dihydrogen phosphate and methyltriethoxysilane; the modified aluminum dihydrogen phosphate solution exists in an amount of 15-25 wt% by mass.

[0010] The inorganic composite filler comprises copper oxide, aluminum oxide, silicon carbide, zirconium oxide, alumina, and nano-alumina-hybrid carbon nanotubes; by mass fraction, copper oxide 3-5 wt%, aluminum oxide 15-25 wt%, silicon carbide 20-25 wt%, zirconium oxide 3-5 wt%, alumina 8-12 wt%, and nano-alumina-hybrid carbon nanotubes 0.1-0.3 wt%.

[0011] As a preferred embodiment of the high-temperature and corrosion-resistant inorganic phosphate-based composite coating of the present invention, the coating comprises, by mass fraction: 15-20 wt% modified aluminum dihydrogen phosphate solution, 4-5 wt% copper oxide, 15-20 wt% aluminum oxide, 20-23 wt% silicon carbide, 3-4 wt% zirconium oxide, 8-10 wt% aluminum sulfate, and 0.1-0.2 wt% nano-alumina-hybrid carbon nanotubes.

[0012] As a preferred embodiment of the high-temperature and corrosion-resistant inorganic phosphate-based composite coating of the present invention, the coating comprises, by mass fraction: 20 wt% modified aluminum dihydrogen phosphate solution, 4 wt% copper oxide, 20 wt% aluminum oxide, 22.8 wt% silicon carbide, 3 wt% zirconium oxide, 10 wt% aluminum sulfate, and 0.2 wt% nano-alumina-hybrid carbon nanotubes.

[0013] As a preferred embodiment of the high-temperature and corrosion-resistant inorganic phosphate-based composite coating of the present invention, the diameter of the alumina is 3-5 μm, the diameter of the silicon carbide is 2-5 μm, and the diameter of the zirconium oxide is 50-70 nm.

[0014] As a preferred embodiment of the high-temperature and corrosion-resistant inorganic phosphate-based composite coating of the present invention, wherein: the nano-alumina-hybrid carbon nanotube is obtained by loading nano-alumina onto a hybrid carbon nanotube carrier, and the hybrid carbon nanotube is a hydroxylated multi-walled carbon nanotube with 3-aminopropyltriethoxysilane loaded on its surface.

[0015] Another object of the present invention is to provide a method for preparing the high-temperature and corrosion-resistant inorganic phosphate-based composite coating as described above, comprising,

[0016] We provide nano-alumina-hybrid carbon nanotubes;

[0017] Provide modified aluminum dihydrogen phosphate solution;

[0018] Inorganic composite filler is uniformly dispersed in modified aluminum dihydrogen phosphate solution to form a homogeneous inorganic phosphate-based composite solution, which is then uniformly coated onto the surface of a substrate and cured.

[0019] As a preferred embodiment of the preparation method of the high-temperature and corrosion-resistant inorganic phosphate-based composite coating of the present invention, the curing process includes: curing at room temperature for 6-7 hours, curing at 50°C for 60-80 minutes, curing at 90°C for 30-40 minutes, curing at 200°C for 15-20 minutes, and curing at 300°C for 30-40 minutes.

[0020] As a preferred embodiment of the preparation method of the high-temperature and corrosion-resistant inorganic phosphate-based composite coating of the present invention, the curing process includes: curing at room temperature for 6 hours, curing at 50°C for 1 hour, curing at 90°C for 30 minutes, curing at 200°C for 15 minutes, and curing at 300°C for 30 minutes.

[0021] As a preferred embodiment of the preparation method of the high temperature and corrosion resistant inorganic phosphate-based composite coating of the present invention, wherein: the provision of nano-alumina-hybrid carbon nanotubes involves fully hydrolyzing 3-aminopropyltriethoxysilane, adding hydroxylated multi-walled carbon nanotubes for full reaction, and centrifuging to obtain the precursor;

[0022] Alumina was dissolved in an aqueous ethanol solution, a precursor was added, and the mixture was ultrasonicated, centrifuged, washed, and dried.

[0023] In a preferred embodiment of the preparation method of the high-temperature and corrosion-resistant inorganic phosphate-based composite coating of the present invention, the method for providing nano-alumina-hybrid carbon nanotubes involves dissolving 0.01 g of 3-aminopropyltriethoxysilane (APTES, 99 wt%) in an ethanol-water solution (v:v = 3:1), adjusting the pH of the solution to 5 with acetic acid, and stirring at room temperature for 30 min to allow complete hydrolysis of APTES. Subsequently, 1 g of hydroxylated multi-walled carbon nanotubes (MWCNTs, 30-50 nm, length less than 10 μm, hydroxyl content 1.06 wt%, 95 wt%) are added, and the mixture is stirred at 60°C for 6 hours at a medium speed (300-500 r / min), followed by sonication for 1 hour. Ammonia is then added to adjust the pH to 9, ensuring that APTES and hydroxyl groups react fully and are uniformly loaded onto the surface of the MWCNTs. Finally, the solution was centrifuged to obtain a precipitate, washed twice with anhydrous ethanol, and dried in a forced-air drying oven at 60°C for 24 hours to obtain the APTES-MWCNTs precursor. The precursor was then sieved through a 10μm sieve to ensure good dispersibility.

[0024] 0.5 g of alumina (60–100 nm, 99 wt%) was dissolved in 20 g (5:1) of an aqueous ethanol solution and stirred at room temperature for 30 minutes. Subsequently, 0.5 g of the precursor was added, and the mixture was sonicated for 1 hour. The precipitate was obtained by centrifugation, washed twice with anhydrous ethanol, and dried in a forced-air drying oven at 60 °C for 24 hours to obtain Al2O3-MWCNTs hybrid material.

[0025] As a preferred embodiment of the preparation method of the high-temperature and corrosion-resistant inorganic phosphate-based composite coating of the present invention, wherein: the modified aluminum dihydrogen phosphate solution is provided by stirring and mixing aluminum dihydrogen phosphate and methyltriethoxysilane until the color of the solution changes from transparent to semi-transparent milky white, and after standing, the solution separates into layers, and the semi-transparent viscous liquid precipitated in the lower half is the modified aluminum dihydrogen phosphate solution.

[0026] In a preferred embodiment of the preparation method of the high-temperature and corrosion-resistant inorganic phosphate-based composite coating of the present invention, 100 ml of aluminum dihydrogen phosphate (AP) and 5 wt% methyltriethoxysilane (MTES) are stirred at 350 r / min at room temperature for 30-40 minutes using a magnetic stirrer until the MTES and AP are uniformly mixed and no longer separate into layers. As the stirring time increases, the viscosity of the solution increases, and the color gradually changes from transparent to translucent milky white. After standing for 15-20 minutes, the solution separates into layers, and the translucent viscous liquid precipitated in the lower layer is the modified aluminum dihydrogen phosphate solution.

[0027] In a preferred embodiment of the preparation method of the high-temperature and corrosion-resistant inorganic phosphate-based composite coating of the present invention, the coating is uniformly applied to the surface of the substrate, and the coating thickness is 80-100 μm.

[0028] As a preferred embodiment of the preparation method of the high-temperature and corrosion-resistant inorganic phosphate-based composite coating of the present invention, the coating is uniformly coated on the substrate surface by air spraying with an air pressure of 0.3 MPa. The distance between the nozzle and the substrate is about 30 cm, and the spray gun is perpendicular to the substrate surface. The left and right movement speed of the spray gun is 15-20 cm / s, and the spraying is repeated 2-3 times to uniformly coat the treated substrate surface.

[0029] In a preferred embodiment of the preparation method of the high-temperature and corrosion-resistant inorganic phosphate-based composite coating of the present invention, the substrate is selected from CB2 or IBN heat-resistant steel.

[0030] As a preferred embodiment of the preparation method of the high-temperature and corrosion-resistant inorganic phosphate-based composite coating of the present invention, the substrate undergoes pretreatment by immersing it in a beaker containing acetone and alcohol and ultrasonically cleaning it for 15-20 minutes to remove oil stains and impurities from the substrate surface; after drying, it is cross-polished with 200, 600 and 1200 grit sandpaper to roughen the substrate surface; then it is rinsed with flowing deionized water, and finally the substrate surface is wiped with alcohol to ensure that the surface cleanliness of the substrate reaches Sa3 level, and then dried at low temperature for later use.

[0031] This invention applies a high-temperature resistant and corrosion-resistant coating to the heat-resistant steel components of a steam turbine unit. This coating structure reliably solves the oxidation and corrosion problems of heat-resistant steel components used in high-temperature corrosive environments in steam turbine units, improving their high-temperature corrosion resistance, extending their service life, and ensuring safe operation of the steam turbine unit. The invention is highly operable, with a simple process, low cost, and is easy to industrialize. The resulting coating structure is dense and stable, providing reliable protection for heat-resistant steel components in the corrosive environment of high-temperature steam.

[0032] Compared with the prior art, the present invention has the following beneficial effects:

[0033] The coating of this invention has excellent high temperature resistance and corrosion resistance, thereby effectively solving the technical problems of oxidation and corrosion of heat-resistant steel components in high temperature and corrosion environments, and reliably improving the service life of heat-resistant steel components in high temperature and corrosion environments.

[0034] The coating of this invention is highly operable, simple in process, low in cost, easy to industrialize, pollution-free, and environmentally friendly; the obtained coating structure is dense and stable, and provides reliable protection for heat-resistant steel components in the corrosive environment of high-temperature steam. Attached Figure Description

[0035] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort. Wherein:

[0036] Figure 1 The kinetic curves of the coated CB2 heat-resistant steel substrate and the pure CB2 heat-resistant steel substrate in Examples 1-3 and Comparative Examples 1-3 in a 650°C water vapor environment are shown.

[0037] Figure 2The kinetic curves of the IBN heat-resistant steel substrates coated with the coating and the pure IBN heat-resistant steel substrates in Examples 1-3 and Comparative Examples 1-3 in a 650°C water vapor environment are shown.

[0038] Figure 3 The microstructure of the CB2 heat-resistant steel substrate coated with the coating in Comparative Example 2 and Example 3 after high-temperature ablation for 1500 hours is shown.

[0039] Figure 4 The macroscopic images are of the CB2 heat-resistant steel substrates coated with the coating in Comparative Example 2, Comparative Example 3, and Example 3 after being kept at a high temperature of 650°C for 20 minutes and then placed in room temperature water for water quenching and impact.

[0040] Figure 5 This is a photograph of the CB2 heat-resistant steel substrate coated with the coating in Comparative Example 4;

[0041] Figure 6 This is a photograph of the CB2 heat-resistant steel substrate coated with the coating in Comparative Example 5;

[0042] Figure 7 This is a photograph of the CB2 heat-resistant steel substrate coated with the coating in Comparative Example 6;

[0043] Figure 8 A photograph of the paint used in Comparative Example 8;

[0044] Figure 9 The images show a comparison between the sample obtained in Comparative Example 9 and the physical specimen of Example 1. Detailed Implementation

[0045] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the specific embodiments of the present invention will be described in detail below with reference to the examples in the specification.

[0046] Many specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways different from those described herein, and those skilled in the art can make similar extensions without departing from the spirit of the invention. Therefore, the invention is not limited to the specific embodiments disclosed below.

[0047] Secondly, the term "one embodiment" or "embodiment" as used herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the present invention. The phrase "in one embodiment" appearing in different places in this specification does not necessarily refer to the same embodiment, nor is it a single or selective embodiment that is mutually exclusive with other embodiments.

[0048] Unless otherwise specified, all raw materials used in the examples are commercially available.

[0049] Comparative Example 1

[0050] The high-temperature / corrosion-resistant inorganic phosphate-based composite coating of Comparative Example 1 is composed of the following raw materials by mass fraction:

[0051] The mixture consists of 20 wt% aluminum dihydrogen phosphate solution, 20 wt% alumina, 27 wt% silicon carbide, 3 wt% zirconium oxide, 10 wt% aluminum sulfate, and 20 wt% deionized water.

[0052] Step (1): Immerse the substrate in a beaker containing acetone and alcohol, and ultrasonically clean for 15 minutes to remove oil stains and impurities from the substrate surface; after drying, use 200, 600 and 1200 grit sandpaper to cross-polish the substrate surface to roughen it; then rinse with running deionized water, and finally wipe the substrate surface with alcohol to ensure that the substrate surface cleanliness reaches Sa3 level, and dry at low temperature for later use.

[0053] Step (2): Mix alumina, silicon carbide, zirconium oxide and aluminum alum in the above proportions until uniform. Add aluminum dihydrogen phosphate solution and stir at room temperature for 5 minutes. Then add deionized water and stir at room temperature for 1 hour. Apply the coating to the substrate surface by spraying. After step curing, the sample is obtained.

[0054] Comparative Example 2

[0055] The high-temperature / corrosion-resistant inorganic phosphate-based composite coating of Comparative Example 2 is composed of the following raw materials by mass fraction:

[0056] The mixture consists of 20 wt% aluminum dihydrogen phosphate solution, 20 wt% aluminum oxide, 23 wt% silicon carbide, 3 wt% zirconium oxide, 10 wt% aluminum sulfate, 4 wt% copper oxide, and 20 wt% deionized water.

[0057] Step (1): Immerse the substrate in a beaker containing acetone and alcohol, and ultrasonically clean for 15 minutes to remove oil stains and impurities from the substrate surface; after drying, use 200, 600 and 1200 grit sandpaper to cross-polish the substrate surface to roughen it; then rinse with running deionized water, and finally wipe the substrate surface with alcohol to ensure that the substrate surface cleanliness reaches Sa3 level, and dry at low temperature for later use.

[0058] Step (2): Mix aluminum oxide, silicon carbide, zirconium oxide, aluminum alum and copper oxide evenly according to the above ratio, add aluminum dihydrogen phosphate solution, stir at room temperature for 5 minutes, add deionized water and stir at room temperature for 1 hour, then apply the coating to the substrate surface by spraying, and obtain the sample after step curing.

[0059] Comparative Example 3

[0060] The high-temperature / corrosion-resistant inorganic phosphate-based composite coating of Comparative Example 3 is composed of the following raw materials by mass fraction:

[0061] The composition consists of 20 wt% aluminum dihydrogen phosphate solution, 20 wt% alumina, 22.8 wt% silicon carbide, 3 wt% zirconium oxide, 10 wt% aluminum sulfate, 4 wt% copper oxide, 0.2 wt% nano-alumina-hybrid carbon nanotubes, and 20 wt% deionized water.

[0062] Step (1): Immerse the substrate in a beaker containing acetone and alcohol, and ultrasonically clean for 15 minutes to remove oil stains and impurities from the substrate surface; after drying, use 200, 600 and 1200 grit sandpaper to cross-polish the substrate surface to roughen it; then rinse with running deionized water, and finally wipe the substrate surface with alcohol to ensure that the substrate surface cleanliness reaches Sa3 level, and dry at low temperature for later use.

[0063] Step (2): Mix alumina, silicon carbide, zirconium oxide, aluminum sulfate, copper oxide, and nano alumina-hybrid carbon nanotubes according to the above ratio. Add aluminum dihydrogen phosphate solution and stir at room temperature for 5 minutes. Then add deionized water and stir at room temperature for 1 hour. Apply the coating to the substrate surface by spraying. After step curing, the sample is obtained.

[0064] Example 1

[0065] The high-temperature / corrosion-resistant inorganic phosphate-based composite coating of this Example 1 is composed of the following raw materials by mass fraction:

[0066] A modified aluminum dihydrogen phosphate solution (15 wt%), alumina (25 wt%), silicon carbide (24.7 wt%), zirconium oxide (5 wt%), aluminum sulfate (12 wt%), copper oxide (5 wt%), nano-alumina-hybrid carbon nanotubes (0.3 wt%), and deionized water (13 wt%).

[0067] (1) Dissolve 0.01 g of 3-aminopropyltriethoxysilane (APTES, 99 wt%) in an ethanol-water solution (v:v = 3:1), add acetic acid to adjust the pH of the solution to 5, and stir at room temperature for 30 min to allow APTES to be fully hydrolyzed. Then, add 1 g of hydroxylated multi-walled carbon nanotubes (MWCNTs, 30-50 nm, length less than 10 μm, hydroxyl content 1.06 wt%, 95 wt%), stir at 60 °C for 6 hours at medium speed (300-500 r / min), sonicate for 1 hour, add ammonia to adjust the pH to 9, so that APTES and hydroxyl groups can react fully and be uniformly loaded onto the surface of MWCNTs. Finally, centrifuge the solution to obtain a precipitate, wash twice with anhydrous ethanol, and dry in a forced-air drying oven at 60 °C for 24 hours to obtain the APTES-MWCNTs precursor, and sieve the precursor through a 10 μm sieve.

[0068] 0.5 g of alumina (60–100 nm, 99 wt%) was dissolved in 20 g (5:1) of an aqueous ethanol solution and stirred at room temperature for 30 minutes. Subsequently, 0.5 g of the precursor was added, and the mixture was sonicated for 1 hour. The precipitate was obtained by centrifugation, washed twice with anhydrous ethanol, and dried in a forced-air drying oven at 60 °C for 24 hours to obtain Al2O3-MWCNTs hybrid material.

[0069] (2) Using a magnetic stirrer, stir 100 ml of aluminum dihydrogen phosphate (AP) and 5 wt% methyltriethoxysilane (MTES) at 350 r / min at room temperature for 30-40 minutes until the MTES and AP are evenly mixed and no longer separate into layers. As the stirring time increases, the viscosity of the solution increases, and the color of the solution gradually changes from transparent to translucent milky white. After standing for 15-20 minutes, the solution separates into layers, and the translucent viscous liquid that precipitates in the lower half is the modified aluminum dihydrogen phosphate solution.

[0070] (3) Immerse the substrate in a beaker containing acetone and alcohol and ultrasonically clean it for 15 minutes to remove oil stains and impurities from the substrate surface. After drying, use 200, 600 and 1200 grit sandpaper to cross-polish the substrate surface to roughen it. Then rinse with running deionized water and wipe the substrate surface with alcohol to ensure that the surface cleanliness reaches Sa3 level. Dry it at low temperature for later use.

[0071] (4) Mix alumina, silicon carbide, zirconium oxide, aluminum sulfate, copper oxide, and nano alumina-hybrid carbon nanotubes in the above proportions until uniform. Add modified aluminum dihydrogen phosphate solution and stir at room temperature for 5 minutes. Then add deionized water and stir at room temperature for 30 minutes. Apply the coating to the substrate surface by spraying. After step curing, the sample is obtained.

[0072] Example 2

[0073] This Example 2 is basically the same as Example 1, except that it is composed of the following raw materials by mass fraction:

[0074] b. Modified aluminum dihydrogen phosphate solution 25wt%, alumina 15wt%, silicon carbide 20.9wt%, zirconium oxide 3wt%, aluminum sulfate 8wt%, copper oxide 3wt%, nano-alumina-hybrid carbon nanotubes 0.1wt%, deionized water 25wt%.

[0075] Example 3

[0076] This Example 3 is basically the same as Example 1, except that it is composed of the following raw materials by mass fraction:

[0077] c-modified aluminum dihydrogen phosphate solution 20wt%, alumina 20wt%, silicon carbide 22.8wt%, zirconium oxide 3wt%, aluminum sulfate 10wt%, copper oxide 4wt%, nano-alumina-hybrid carbon nanotubes 0.2wt%, deionized water 20wt%.

[0078] The substrates used in this experiment were CB2 heat-resistant steel and IBN heat-resistant steel. The CB2 heat-resistant steel coating samples and IBN heat-resistant steel coating samples obtained from Comparative Examples 1-3 and Examples 1-3 were subjected to the following tests:

[0079] Oxidation kinetic curve: The sample was placed in a water vapor oxidation / corrosion apparatus heated to 650℃, with a flow rate of 50 ml / min, and an oxidation / corrosion test was conducted for 1500 h. The mass change was recorded periodically using a balance to calculate the oxidation / corrosion rate.

[0080] Water quenching shock test: After heating the sample to 650℃ and holding it at that temperature for 20 minutes, quickly immerse it in room temperature water and observe the changes on the coating surface.

[0081] Test results are as follows Figures 1-4 As shown. Figure 1 The figures show the kinetic curves of the coated CB2 heat-resistant steel substrates and the pure CB2 heat-resistant steel substrates in a 650℃ water vapor environment in Examples 1-3 and Comparative Examples 1-3. It can be seen from the figures that the mass growth rate of the bare metal substrate is significantly faster than that of the coated sample, and its oxidation kinetic curve exhibits a linear trend. It can be inferred that the Cr2O3 oxide film formed due to the low Cr content in the CB2 heat-resistant steel has defects such as easy peeling and cracking, and may even be volatile and unable to block the diffusion of oxygen and metal ions. In this case, the oxidation rate still depends on the oxidation reaction rate, maintaining the original linear trend. (Observation) Figure 1 As can be seen from (a) and (b), the coatings exhibited different oxidation kinetic characteristics in the initial and continuous oxidation stages during the 1500-hour test period. The samples of Comparative Example 1 and Comparative Example 2 showed strong oxidation in the initial stage, with an oxidation kinetic parabolic rate constant of 4.4 × 10⁻⁶. -4 mg 2 ·cm -4 ·h -1 After the formation of the protective oxide layer, the rate of mass increase slows down significantly, and the parabolic rate constant of the oxidation kinetics reaches 2.318 × 10⁻⁶. -4 mg 2 ·cm -4 ·h -1Within 600 hours of high-temperature oxidation, the oxidation kinetic curves of Comparative Example 1 and Comparative Example 2 maintained a parabolic trend, indicating that the coating was relatively dense and provided some protection, hindering the oxidation process. However, when the oxidation time exceeded 600 hours, the oxidation kinetic curves of the coatings showed a linear trend. This is consistent with the phenomenon observed in previous experiments where the coatings of Comparative Example 1 and Comparative Example 2 easily peeled off from the metal substrate. When the oxidation time increased to a certain value, the coating partially lost its protective effect on the substrate. The above analysis data proves that the coatings of Comparative Example 1 and Comparative Example 2 have the ability to protect CB2 steel from high-temperature oxidation, but the effect is not ideal.

[0082] observe Figure 1 As shown in (c) and (d), the coated samples experienced rapid weight loss in the initial stage of oxidation, due to the evaporation of free water within the coating. After approximately 300 hours, the mass of the samples coated in Comparative Example 3 and Example 1 stabilized. The oxidation kinetics of both samples exhibited a logarithmic law in the later stages, indicating that the oxide film was very dense and firmly adhered to the metal substrate surface. The entire oxidation process depended on the phase diffusion rate of oxygen and metal ions within the film, and oxidation essentially ceased. This demonstrates that the samples in Comparative Example 3 and Example 1 possess good resistance to high-temperature oxidation. Among them, the mass increase of the Example 3 sample was more stable, and the final mass loss of the coated portion was less than that of the Comparative Example 3 sample, suggesting that Example 3 is more likely to be applied practically. It is expected that the high-temperature protection performance of the Sample 3 coated with the Oxidation Time will be even more outstanding after 1500 hours of oxidation.

[0083] Figure 2 The figures show the kinetic curves of the IBN heat-resistant steel substrates coated with the coating and the pure IBN heat-resistant steel substrates in Examples 1-3 and Comparative Examples 1-3 in a 650℃ water vapor environment. It can be seen from the figures that the mass gain rate of the IBN heat-resistant steel is higher than that of the CB2 heat-resistant steel, possibly because the Cr and Ti contents in the IBN heat-resistant steel are lower, making it difficult to form a stable protective metal oxide film. The oxidation kinetic curves of the two heat-resistant steels after being coated with the phosphate composite coating are basically the same. The good high-temperature protective performance of the coatings in Examples 1-3 is still applicable to IBN heat-resistant steel.

[0084] Figure 3 The figures show the microstructure of the CB2 heat-resistant steel substrates coated with the coatings in Comparative Example 2 and Example 3 after 1500 hours of high-temperature ablation; as can be seen from the figures, the coating in Comparative Example 2 ( Figure 3 a) The surface exhibits a molten porous state. Coatings in this state lack a dense surface layer and therefore lose their ability to prevent corrosive media and oxygen, which can damage the metal substrate, from penetrating. The coating in Example 3 ( Figure 3(b) After high-temperature ablation, the surface density of the coating was not significantly affected. It is noteworthy that fine debris was distributed on the surface. Carbon nanotubes possess excellent thermal conductivity and can act as sacrificial modules and heat sinks, stabilizing small inorganic particles during calcination. However, under air conditions and high-temperature ablation at 650°C, carbon nanotubes would have already thermally decomposed or lost their original structure, thus losing their superior properties. The alumina-grafted carbon nanotubes used in this invention exhibit high-temperature stability, and the addition of alumina also increases the overall structural hardness. It is this function that allows the coating to retain its basic functions after high-temperature ablation.

[0085] Figure 4 The figures show macroscopic images of the CB2 heat-resistant steel substrates coated with the thermal shock agent in Comparative Examples 2, 3, and 3 after being heated at 650°C for 20 minutes and then immersed in room-temperature water. As can be seen from the figures, in Comparative Example 2, the original coating was completely intact and of uniform thickness. After five repeated water-quenching shock tests, obvious fine cracks appeared, which was due to the thermal stress generated during the thermal shock exceeding the bending strength of the surface coating. After 25 cycles of water-quenching shock tests, the surface coating showed large-area peeling, with very thin coating remaining at the peeled areas. After 50 cycles of water-quenching shock tests, the peeling state of the surface coating was not significantly different from that after 25 cycles. In Comparative Example 3, the surface quality of the coating remained intact after 30 cycles of water-quenching shock tests, and no obvious cracks appeared on the surface. After 65 repeated water-quenching shock tests, the surface quality of the coating deteriorated, the peeling was severe, and it lost its protective function for the metal substrate. The macroscopic failure mechanism of the coating manifests as crack initiation at the circumference of the sample, which extends under continuous thermal shock stress until the coating peels off over a large area; then new crack initiation occurs, and this process repeats. In Example 3, the coating initially detached at the edge, exhibiting the high-temperature / corrosion-resistant inorganic phosphate composite coating peeling off from the metal adhesive layer. As the number of test cycles increased, the number of detachment sites increased, but after reaching a certain point, the peeling stabilized without further deterioration.

[0086] Comparative Example 4

[0087] Comparative Example 4 is essentially the same as Example 1, except that it consists of the following raw materials by mass fraction:

[0088] The modified aluminum dihydrogen phosphate solution contains 28 wt% aluminum oxide, 25 wt% aluminum oxide, 24.7 wt% silicon carbide, 5 wt% zirconium oxide, 12 wt% aluminum sulfate, 5 wt% copper oxide, and 0.3 wt% nano-alumina-hybrid carbon nanotubes.

[0089] The other steps are the same as in Example 1, except that the substrate is CB2 heat-resistant steel, and a CB2 heat-resistant steel coating sample is obtained.

[0090] The physical image of the obtained sample is as follows Figure 5 As shown, when the modified aluminum dihydrogen phosphate solution exceeds 25%, the chemical reaction between the coating and the substrate is intense, and pores are generated on the coating surface, which seriously affects the surface quality of the coating. It is judged that the sample preparation was unsuccessful and no subsequent performance test was carried out.

[0091] Comparative Example 5

[0092] Comparative Example 5 is basically the same as Example 1, except that it is composed of the following raw materials in the following mass fractions: 15 wt% modified aluminum dihydrogen phosphate solution, 25 wt% alumina, 24.6 wt% silicon carbide, 5 wt% zirconium oxide, 12 wt% aluminum sulfate, 5 wt% copper oxide, 0.4 wt% nano-alumina-hybrid carbon nanotubes, and 13 wt% deionized water.

[0093] The other steps are the same as in Example 1, except that the substrate is CB2 heat-resistant steel, and a CB2 heat-resistant steel coating sample is obtained.

[0094] The physical image of the obtained sample is as follows Figure 6 As shown, when the content of the nano-alumina hybrid carbon nanotube reinforcing phase exceeds 0.3%, the excessively high content of the reinforcing phase leads to agglomeration in the coating, resulting in severe surface cracking after the coating is cured. Therefore, the sample preparation was deemed unsuccessful and no further performance tests were conducted.

[0095] Comparative Example 6

[0096] Comparative Example 6 is essentially the same as Example 1, except that it consists of the following raw materials by mass fraction:

[0097] The mixture consists of 15 wt% modified aluminum dihydrogen phosphate solution, 25 wt% alumina, 25 wt% silicon carbide, 5 wt% zirconium oxide, 12 wt% aluminum sulfate, 5 wt% copper oxide, and 13 wt% deionized water.

[0098] The other steps are the same as in Example 1, except that the substrate is CB2 heat-resistant steel, and a CB2 heat-resistant steel coating sample is obtained.

[0099] The physical image of the obtained sample is as follows Figure 7 As shown, the nano-alumina hybrid carbon nanotubes are the reinforcing phase. Without the addition of the reinforcing phase in Example 1, the coating will crack after heating at 650°C. The presence of the reinforcing phase can increase the toughness of the coating and improve its high-temperature resistance.

[0100] Comparative Example 7

[0101] Comparative Example 7 is basically the same as Example 1, except that the conditions in step (2) of preparing modified aluminum dihydrogen phosphate were adjusted. Experiments showed that when the stirring speed in step 2 exceeded 350 r / min or the stirring time exceeded 40 min, the hybrid solution would polymerize, the solution would gradually become viscous, and even solidify into blocks. If the stirring speed was too low or the stirring time was too short, the solution would be in a layered state, and the color of the solution would not change.

[0102] Comparative Example 8

[0103] Comparative Example 8 is basically the same as Example 1, except that MTES in step (2) is replaced with silicate for doping and mixing. The specific experimental method is as follows: 100 ml of aluminum dihydrogen phosphate and 5 wt% potassium silicate are stirred at room temperature using a magnetic stirrer.

[0104] The results showed that solid particles were generated after the two were mixed, and the coating cured directly with increasing stirring time (e.g., Figure 8 ).

[0105] Comparative Example 9

[0106] Comparative Example 9 is basically the same as Example 1, except that in step (1) of hybrid material preparation, the prepared APTES-MWCNTs precursor is not sieved. Other steps are the same as in Example 1, and CB2 heat-resistant steel substrate is used to obtain CB2 heat-resistant steel coated samples.

[0107] The obtained sample is compared with the physical image of Example 1, for example. Figure 9 As shown, it can be seen that Figure 9 a represents the coating prepared without sieving the precursor. Due to the varying particle sizes of the precursor, APTES-MWCNTs exhibit agglomeration, resulting in a rough coating surface with uneven solid particles. Figure 9 b represents the coating prepared after sieving the precursor. The coating surface is smooth and flat, and there are no macroscopic defects.

[0108] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A high-temperature and corrosion-resistant inorganic phosphate-based composite coating, characterized in that: It is composed of modified aluminum dihydrogen phosphate solution and inorganic composite filler; The modified aluminum dihydrogen phosphate solution is obtained by mixing aluminum dihydrogen phosphate and methyltriethoxysilane; the inorganic composite filler is composed of copper oxide, aluminum oxide, silicon carbide, zirconium oxide, aluminum sulfate and nano-alumina-hybrid carbon nanotubes. The modified aluminum dihydrogen phosphate solution contains 20 wt% copper oxide, 4 wt% copper oxide, 20 wt% aluminum oxide, 22.8 wt% silicon carbide, 3 wt% zirconium oxide, 10 wt% aluminum sulfate, 0.2 wt% nano-alumina-hybrid carbon nanotubes, and 20 wt% deionized water by mass fraction. The preparation method of the nano-alumina-hybrid carbon nanotubes is as follows: 3-aminopropyltriethoxysilane is fully hydrolyzed, hydroxylated multi-walled carbon nanotubes are added and reacted fully, centrifuged to obtain the precursor, and the precursor is sieved through a 10 μm sieve. Alumina was dissolved in an aqueous ethanol solution, a precursor was added, and the mixture was ultrasonicated, centrifuged, washed, and dried. The modified aluminum dihydrogen phosphate solution is prepared by stirring aluminum dihydrogen phosphate and methyltriethoxysilane until the color of the solution changes from transparent to semi-transparent milky white. After standing, the solution separates into layers, and the semi-transparent viscous liquid that precipitates in the lower half is the modified aluminum dihydrogen phosphate solution.

2. The high-temperature and corrosion-resistant inorganic phosphate-based composite coating as described in claim 1, characterized in that: The diameter of alumina is 3–5 μm, that of silicon carbide is 2–5 μm, and that of zirconium oxide is 50–70 nm.

3. The method for preparing the high-temperature and corrosion-resistant inorganic phosphate-based composite coating according to claim 1 or 2, characterized in that: include, We provide nano-alumina-hybrid carbon nanotubes; Provide modified aluminum dihydrogen phosphate solution; Inorganic composite filler is uniformly dispersed in modified aluminum dihydrogen phosphate solution to form a homogeneous inorganic phosphate-based composite solution, which is then uniformly coated onto the surface of a substrate and cured.

4. The method for preparing the high-temperature and corrosion-resistant inorganic phosphate-based composite coating as described in claim 3, characterized in that: The curing process involves curing at room temperature for 6–7 hours, at 50°C for 60–80 minutes, at 90°C for 30–40 minutes, at 200°C for 15–20 minutes, and at 300°C for 30–40 minutes.

5. The method for preparing the high-temperature and corrosion-resistant inorganic phosphate-based composite coating as described in claim 3, characterized in that: The coating is uniformly applied to the surface of the substrate, with a thickness of 80–100 μm.

Images