High-temperature-resistant coating and preparation method thereof

Abstract

The invention relates to a preparation method of a high-temperature-resistant coating, and belongs to the technical field of thermal insulation coatings, aluminum oxide, zirconium oxide and silicon carbide form main body powder, the main body powder, bentonite and yttrium oxide are mixed and subjected to ball milling to form slurry, silicon dioxide, aluminum dihydrogen phosphate, polyvinylpyrrolidone and sodium alginate are prepared into a binder, and the binder is prepared into the high-temperature-resistant coating. And sequentially adding dimeticone and the slurry into the binder, and sequentially carrying out homogenization treatment and ultrasonic treatment to obtain the coating. A coating prepared by spraying the coating prepared by the invention on an aluminum alloy substrate in surface second has excellent high temperature resistance, can bear a working environment at the temperature of 1400 DEG C or above for a long time, and does not peel off after more than 30 seconds through an oxyacetylene flame test; the bonding strength of the coating and a matrix is 18.2 Mpa; the substrate sprayed with the coating is heated to 1200 DEG C and rapidly taken out to the room temperature to be subjected to water quenching, the falling phenomenon does not exist after more than 30 times of circulation, the excellent thermal shock resistance is achieved, the thickness of the coating is uniform, and the relative standard deviation RSD of the thickness is 1.28%.

Description

Technical Field

[0001] The present invention relates to the technical field of heat-insulating and heat-preserving coatings, and particularly to a high-temperature resistant coating and a preparation method thereof. Background Art

[0002] Coatings (paint), what we usually call paint is just one of them. It refers to a class of liquid or solid materials that can form a thin film on the surface of an object under certain conditions to play a role in protection, decoration or other special functions (insulation, rust prevention, mildew prevention, heat resistance, etc.). Because most early coatings were mainly made of vegetable oils, they were also called paints. Now synthetic resins have replaced vegetable oils, so they are called coatings. Coatings are not all liquid, and powder coatings are a major category of coating varieties. Coatings belong to organic chemical engineering polymer materials, and the formed coating film belongs to the type of polymer compounds. According to the modern classification of chemical industrial products, coatings belong to fine chemical products. Modern coatings are gradually becoming a class of multifunctional engineering materials and are an important industry in the chemical industry. The main functions are four points: protection, decoration, covering up product defects and other special functions, and enhancing the value of products. China has become the world's second largest coating producer and consumer and has entered the mainstream of the world coating industry development.

[0003] High-temperature resistant coatings are a special functional coating material that can maintain stable physical and chemical properties in high-temperature environments (usually ≥200°C) and provide protection or specific functions for the substrate. Its core function is to resist high-temperature oxidation, corrosion, wear and thermal shock, extend the service life of equipment, and have characteristics such as heat insulation, wear resistance, conductivity or insulation to meet diverse needs. There are also significant differences in the performance of different types of high-temperature resistant coatings. Depending on the type, they can withstand extreme high temperatures from 200°C to over 1600°C. Organosilicon-based coatings mainly contain organosilicon resins, have good flexibility and strong weather resistance, and are suitable for complex surfaces, but have relatively low high-temperature resistance, usually with a temperature resistance range of 400 - 600°C. Silicate-based coatings have high hardness, low cost, and a temperature resistance range of 600 - 800°C, but are brittle and prone to cracking. Phosphate-based coatings can reach a temperature resistance of 800 - 1200°C and have strong adhesion, but require high-temperature curing. Ceramic coatings have excellent temperature resistance performance, can reach a temperature resistance of over 1200°C, and have excellent chemical stability. However, due to poor ductility, ceramic coatings will produce cracks when the substrate expands and contracts thermally, and the adhesion on the substrate surface is not ideal. Summary of the Invention

[0004] The purpose of the present invention is to provide a preparation method of a high-temperature resistant coating. By adding specific binders, it effectively solves the problems of the main powder body stratifying and settling during the spraying process, resulting in a decrease in the denseness of the formed coating and easy cracking, as well as the poor bonding force between the coating and the substrate and easy peeling off.

[0005] Another purpose of the present invention is to provide a high-temperature resistant ceramic coating.

[0006] The object of the present invention is achieved by the following technical solutions: A preparation method of a high-temperature resistant coating, characterized in that: the main powder is composed of alumina, zirconia, and silicon carbide, and is mixed and ball-milled with bentonite and yttrium oxide to form a slurry. A binder is prepared from silica, aluminum dihydrogen phosphate, polyvinylpyrrolidone, and sodium alginate. Dimethyl silicone oil and the slurry are successively added to the binder, and homogenization treatment and ultrasonic treatment are successively carried out to obtain the coating.

[0007] Furthermore, in terms of parts by weight, the components are 60-80 parts of alumina, 20-25 parts of zirconia, 8-10 parts of silicon carbide, 15-20 parts of silica, 10-12 parts of polyvinylpyrrolidone, 12-15 parts of aluminum dihydrogen phosphate, 5-7 parts of sodium alginate, 3-5 parts of bentonite, and 2-3 parts of yttrium oxide.

[0008] Furthermore, for the ball milling, yttrium oxide and bentonite are added to the main powder, zirconia balls are added, the ball-to-material ratio is 3:1, wet milling is carried out with ethanol for 6-8 h, and then ammonia water is added to adjust the pH of the slurry to 8-9 to obtain the slurry. The total mass of the main powder, yttrium oxide, bentonite, and zirconia balls and the mass of ethanol are 1:1-2.

[0009] Furthermore, for the binder, silica and aluminum dihydrogen phosphate are crushed into powders, added to a dispersion medium composed of polyvinylpyrrolidone and sodium alginate, and stirred and homogenized for 1-2 h, with a stirring speed of 20-30 rpm and a homogenization speed of 2000-2500 rpm.

[0010] Furthermore, for the dispersion medium, polyvinylpyrrolidone and sodium alginate are taken and added to water at 50-60 °C and stirred to dissolve. The mass ratio of the total mass of polyvinylpyrrolidone and sodium alginate to the mass of water is 3-5:100.

[0011] Furthermore, in the homogenization and ultrasonic treatment, the homogenization time is 20-30 min, the homogenization speed is 2000-2500 rpm. After homogenization, ultrasonic treatment is carried out for 30-60 min, the ultrasonic frequency is 25-40 kHz, and the amount of dimethyl silicone oil is 0.5%-0.8% of the total mass of the coating.

[0012] Most specifically, a preparation method of a high-temperature resistant coating, characterized by including the following steps: (1) Design the formula: In terms of parts by weight, it is 60-80 parts of alumina, 20-25 parts of zirconia, 8-10 parts of silicon carbide, 15-20 parts of silica, 10-12 parts of polyvinylpyrrolidone, 12-15 parts of aluminum dihydrogen phosphate, 5-7 parts of sodium alginate, 3-5 parts of bentonite, and 2-3 parts of yttrium oxide; (2) Ball milling treatment Crush alumina, zirconia and silicon carbide and sieve them through a 400-mesh sieve to obtain the main powder. Add yttrium oxide, bentonite and zirconia balls with a particle size of 1.2 - 1.8 mm, with a ball-to-material ratio of 3:1. Then add ethanol as the wet grinding medium and wet grind for 6 - 8 h. Then add ammonia water to adjust the pH value to 8 - 9 to obtain a slurry. The total mass of the mixed powder, yttrium oxide, bentonite and zirconia balls is 1:1 - 2 with the mass of the wet grinding medium; (3)Binder preparation Take the formula amount of silica and aluminum dihydrogen phosphate, mix them, crush and sieve them through a 400-mesh sieve. Add the dispersion medium and place it in a stirring homogenizer. Stir and homogenize at a stirring speed of 20 - 30 rpm and a homogenizing speed of 2000 - 2500 rpm for 1 - 2 h to obtain the binder. The dispersion medium is obtained by taking the formula amount of polyvinylpyrrolidone and sodium alginate, placing them in hot water at 50 - 60 °C, stirring and dissolving, and cooling to room temperature. The mass ratio of the total mass of polyvinylpyrrolidone (PVP-K90) and sodium alginate to the total mass of hot water is 3 - 5:100; (4)Mix and prepare the coating Under stirring at 15 - 25 rpm, add the slurry prepared in step (2) to the binder, then add dimethyl silicone oil, and continue stirring for 20 - 30 min. Stir and homogenize at 2000 - 2500 rpm for 20 - 30 min. After homogenization, perform ultrasonic treatment. The ultrasonic frequency is 25 - 40 kHz and the ultrasonic time is 30 - 60 min to obtain the coating. The amount of dimethyl silicone oil is 0.5% - 0.8% of the total mass of the coating.

[0013] The density difference of insoluble alumina and zirconia in the coating is large. During the deposition process of spraying the coating, due to the long time, under the action of gravity, alumina and zirconia will show obvious sedimentation stratification. The effect of only a high thixotropic agent is not enough to resist particle sedimentation. Moreover, the surface energy of nano-alumina and zirconia is high, and they are prone to agglomeration. The sedimentation of nano-particles will exacerbate the agglomeration. The poorly dispersed agglomerates are prone to form closed pores during high-temperature sintering, reducing the coating density. Secondly, the thermal expansion coefficients of alumina and zirconia are quite different, so the coating prepared by spraying is prone to cracking problems.

[0014] In the process of formulating the adhesive in the present invention, a dispersion medium prepared by dissolving PVP and sodium alginate in hot water is added to the high-temperature binder, which plays two roles. On the one hand, the dispersion medium itself plays a suspending role. After spraying the coating on the substrate surface, it effectively inhibits the sedimentation of the ceramic matrix powder particles in the coating, supports the uniform suspension of the matrix powder particles in the coating, and further inhibits the agglomeration of the matrix powder particles. At the same time, PVP and sodium alginate decompose at the specified sintering temperature, delaying the closure of pores and inhibiting the generation of cracks, thereby improving the densification of the coating sintered at high temperature. On the other hand, the two compounds synergistically form a low-temperature binder. After the coating is sprayed onto the substrate surface, the polar groups of PVP-K90 and the carboxylate groups of sodium alginate form hydrogen bonds or ionic bonds at low temperature, enhancing the interfacial bonding force between the coating and the substrate, improving the adhesion of the coating on the substrate surface, and enabling the coating to stably adhere to the substrate surface before high-temperature sintering. In addition, the linear molecular chain of PVP-K90 and the rigid polysaccharide chain of sodium alginate interpenetrate each other to form a three-dimensional network structure. This structure can effectively transfer stress and reduce the risk of shrinkage cracking of the coating during sintering.

[0015] The coating prepared by spraying the coating prepared by the above method has the following specific steps: (1) Take a common metal aluminum alloy substrate of appropriate size, perform sandblasting treatment according to Sa3 level, ultrasonically clean it with acetone 2-3 times, take it out, dry it, and then spray the coating by high-velocity oxygen fuel. The slurry feeding rate is 20-30 g / min, the spraying distance is 15-17 cm, spray repeatedly for multiple times until the thickness reaches 220-280 μm, let it stand for 12 h, and naturally volatilize to dryness; (2) Place the substrate with the coating attached in a muffle furnace, set the heating rate to 80-100 °C / min, heat up to 350-400 °C, keep it warm for 1-2 hours, continue to heat up at a heating rate of 50-80 °C / min to 1100-1200 °C, continue to keep it warm for 3-4 hours, turn off the muffle furnace, naturally cool to room temperature, take it out, and that's it.

[0016] Before sintering, the coating relies on the synergy of PVP-K90 and sodium alginate as a low-temperature binder, enabling the coating to uniformly adhere to the substrate surface. During the first heat preservation process, the low-temperature binder decomposes, and the decomposition process can simultaneously release stress, reduce stress concentration, and avoid cracking of the coating and the substrate due to the difference in thermal expansion coefficients during high-temperature treatment. In this process, due to the adjustment of pH by ammonia water, the premature reaction of phosphates at lower temperatures is inhibited. After high-temperature sintering, an AlPO4-SiC eutectic structure will be formed in the coating, enhancing the adhesion ability of the coating on the substrate surface.

[0017] A high-temperature resistant ceramic coating is composed of a main powder, a binder, an auxiliary agent and a solvent. It is characterized in that: the main powder is composed of alumina, zirconia and silicon carbide; the binder is composed of silicon dioxide, aluminum dihydrogen phosphate, polyvinylpyrrolidone and sodium alginate; the auxiliary agent includes a thixotropic agent bentonite and a stabilizer yttrium oxide.

[0018] This coating is composed of a main powder, a binder, an auxiliary agent and a solvent. The core components of the main powder are alumina, zirconia and silicon carbide. Among them, alumina is a refractory phase, which improves the hardness of the coating; zirconia is a toughening phase, which improves the coating strength; silicon carbide enhances the thermal conductivity and improves the thermal shock resistance. The composite of silicon dioxide and aluminum dihydrogen phosphate is used as a high-temperature binder, bentonite is used as a thixotropic agent to improve the rheological properties of the coating, and yttrium oxide is used as a stabilizer to prevent ZrO2 phase transformation cracking. In addition, the composite of PVP and sodium alginate synergistically produces a suspending effect and a low-temperature bonding effect.

[0019] Furthermore, the components are in parts by weight: 60-80 parts of alumina, 20-25 parts of zirconia, 8-10 parts of silicon carbide, 15-20 parts of silicon dioxide, 10-12 parts of polyvinylpyrrolidone, 12-15 parts of aluminum dihydrogen phosphate, 5-7 parts of sodium alginate, 3-5 parts of bentonite, and 2-3 parts of yttrium oxide.

[0020] Furthermore, the coating is prepared by mixing and ball-milling the main powder, the auxiliary agent yttrium oxide and bentonite, then adding the binder and dimethyl silicone oil, and performing homogenization and ultrasonic treatment in sequence.

[0021] Furthermore, for the ball-milling, yttrium oxide and bentonite are added to the main powder, zirconia balls are added, the ball-to-material ratio is 3:1, wet-milled with ethanol for 6-8 h, and then ammonia water is added to adjust the pH of the slurry to 8-9 to obtain a slurry. The total mass of the main powder, yttrium oxide, bentonite and zirconia balls and the mass of ethanol are 1:1-2.

[0022] Furthermore, for the binder, silicon dioxide and aluminum dihydrogen phosphate are crushed into powders, added to a dispersion medium composed of polyvinylpyrrolidone and sodium alginate, and stirred and homogenized for 1-2 h, with a stirring speed of 20-30 rpm and a homogenization speed of 2000-2500 rpm.

[0023] Furthermore, for the dispersion medium, polyvinylpyrrolidone and sodium alginate are taken and added to water at 50-60 °C and stirred until dissolved. The mass ratio of the total mass of polyvinylpyrrolidone and sodium alginate to the mass of water is 3-5:100.

[0024] Further, in the homogenization and ultrasonic treatment, the homogenization time is 20 - 30 min, the homogenization rotation speed is 2000 - 2500 rpm. After the homogenization is completed, ultrasonic treatment is carried out for 30 - 60 min, the ultrasonic frequency is 25 - 40 kHz, and the amount of dimethyl silicone oil is 0.5% - 0.8% of the total mass of the coating.

[0025] The present invention has the following technical effects: The coating prepared by the coating of the present invention on the surface of the aluminum alloy matrix has excellent high-temperature resistance, can withstand the working environment with a temperature above 1400 °C for a long time, and there is no peeling after being tested by oxyacetylene flame for more than 30 s; the bonding strength between the coating and the matrix is 18.2 Mpa; the matrix with the sprayed coating is heated to 1200 °C, quickly taken out to room temperature and quenched in water, and there is no peeling phenomenon after cycling more than 30 times, having excellent thermal shock resistance, the coating thickness is uniform, and the relative standard deviation RSD of the thickness is 1.28%. Specific embodiments

[0026] The present invention will be specifically described below through examples. It is necessary to point out here that the following examples are only used to further illustrate the present invention and cannot be understood as limiting the protection scope of the present invention. Those skilled in the art can make some non-essential improvements and adjustments to the present invention according to the above content of the present invention.

[0027] Example 1 A preparation method of a high-temperature resistant coating, characterized by comprising the following steps: (1) Design the formula: By weight, it is 70 parts of alumina, 24 parts of zirconia, 9 parts of silicon carbide, 18 parts of silica, 10 parts of polyvinylpyrrolidone, 12 parts of aluminum dihydrogen phosphate, 6 parts of sodium alginate, 4 parts of bentonite, and 2 parts of yttrium oxide; (2) Ball milling treatment The alumina, zirconia and silicon carbide are crushed and passed through a 400-mesh sieve to obtain the main powder body. Yttrium oxide, bentonite and zirconia balls with a particle size of 1.2 mm are added, the ball-to-material ratio is 3:1, and then wet grinding medium ethanol is added for wet grinding for 6 h, and then ammonia water is added to adjust the pH value to 8.5 to obtain a slurry. The total mass of the mixed powder, yttrium oxide, bentonite and zirconia balls and the mass of the wet grinding medium is 1:1.5; (3) Preparation of the binder Take the formula amount of silica and aluminum dihydrogen phosphate, mix them, crush and pass through a 400-mesh sieve, add a dispersion medium, place it in a stirring homogenizer, and stir and homogenize at a stirring speed of 25 rpm and a homogenizing speed of 2200 rpm for 1.5 h to obtain a binder; the dispersion medium is prepared by taking the formula amount of PVP-K90 and sodium alginate, placing them in hot water at 55 °C, stirring and dissolving, and cooling to room temperature. The mass ratio of the total mass of PVP-K90 and sodium alginate to the total mass of hot water is 4:100. (4) Mix and prepare the coating Under stirring at 20 rpm, add the slurry prepared in step (2) to the binder, then add dimethyl silicone oil, continue stirring for 25 min, stir and homogenize at 2200 rpm for 25 min. After homogenization, perform ultrasonic treatment. The ultrasonic frequency is 30 kHz and the ultrasonic time is 50 min to obtain the coating. The amount of dimethyl silicone oil is 0.6% of the total mass of the coating.

[0028] Spray the coating prepared in Example 1 to form a coating. The specific operation is as follows: (1) Take a common metal aluminum alloy substrate of appropriate size, perform sandblasting treatment according to Sa3 level, ultrasonically clean it with acetone 3 times, take it out, dry it, and then spray the coating prepared in Example 1 by high-velocity oxygen fuel spraying (parameters: dye propane pressure 0.8 MPa, oxygen pressure 0.8 MPa). The slurry feeding rate is 25 g / min, the spraying distance is 16 cm, spray repeatedly for multiple times until the thickness reaches 250 μm, let it stand for 12 h, and naturally volatilize to dryness. (2) Place the substrate with the attached coating in a muffle furnace, set the heating rate to 90 °C / min, heat up to 380 °C, keep it warm for 1.5 hours, continue to heat up at a heating rate of 60 °C / min to 1150 °C, continue to keep it warm for 3.5 hours, turn off the muffle furnace, naturally cool to room temperature, take it out, and that's it.

[0029] Perform the following performance tests on the coating of Example 1: High-temperature resistance test: The coating prepared in this example has excellent high-temperature resistance and can withstand a working environment with a temperature above 1400 °C for a long time. It does not peel off after being tested by an oxyacetylene flame for more than 30 s. Adhesion strength test: The adhesion strength between the coating and the substrate is 18.2 Mpa tested by the tensile method according to ASTM C633 standard. Thermal shock resistance test: Heat the substrate with the sprayed coating to 1200 °C, quickly take it out to room temperature and perform water quenching. It has excellent thermal shock resistance with no peeling phenomenon after cycling more than 30 times.

[0030] All the performance test steps for the comparative examples and examples are the same as those in Example 1.

[0031] Comparative Example 1 During the preparation of the binder, only PVP-90 is contained in the dispersion medium, and sodium alginate is not added. The remaining steps are the same as those in Example 1.

[0032] Comparative Example 2 Compared with Example 1, PVP-K90 and sodium alginate are added to normal temperature water to prepare a dispersion medium, and the remaining steps are the same as those in Example 1.

[0033] Comparative Example 3 Compared with Example 1, PVP-90 is replaced with PVP-K30, and the remaining steps are the same as those in Example 1.

[0034] For the coatings prepared in Comparative Examples 1-3, the dispersion medium is prepared into a coating with an equal thickness according to the same spraying method as in Example 1. By testing the coating properties of the coatings prepared in Example 1 and each comparative example, the blank group is a coating sprayed with a coating prepared by directly mixing silica and aluminum dihydrogen phosphate and adding them to hot water to prepare a binder without PVP-K90 and sodium alginate. The specific results are shown in Table 1.

[0035] Table 1: It can be seen that in the oxyacetylene flame test, spalling occurred in the blank group at 22 s, and spalling also occurred in Comparative Examples 1-3 within 20-30 s, while no spalling occurred in Example 1 until more than 30 s. During the thermal shock resistance test, no spalling occurred in the coating of Example 1 after more than 30 cycles, while spalling occurred in other comparative examples during the cycle within 30 times.

[0036] Thickness uniformity test: Six different sites were taken on the substrates with ceramic coatings sintered in Example 1 and each comparative example for thickness detection to determine the thickness of each point, and the relative standard deviation RSD was calculated. The results are shown in Table 2.

[0037] Table 2: It can be seen that the coating thickness uniformity effect of the blank group is poor, and each comparative example has different degrees of improvement compared with the blank group, but the uniformity effect is still not ideal, and the RSD is greater than 2%. The coating thickness uniformity of the example is excellent, and the RSD is as low as 1.28%.

[0038] Example 2 A preparation method of a high-temperature resistant coating, characterized by comprising the following steps: (1) Design the formula: By weight, it is 60 parts of alumina, 20 parts of zirconia, 8 parts of silicon carbide, 15 parts of silica, 11 parts of polyvinylpyrrolidone, 14 parts of aluminum dihydrogen phosphate, 5 parts of sodium alginate, 3 parts of bentonite, and 2.5 parts of yttrium oxide; (2)Ball milling treatment Alumina, zirconia and silicon carbide are pulverized and screened through a 400-mesh sieve to obtain the main powder. Yttrium oxide, bentonite and zirconia balls with a particle size of 1.8 mm are added, and the ball-to-material ratio is 3:1. Then, wet grinding medium ethanol is added for wet grinding for 8 h, and ammonia water is added to adjust the pH value to 9 to obtain a slurry. The total mass of the mixed powder, yttrium oxide, bentonite and zirconia balls and the mass of the wet grinding medium is 1:1; (3)Binder preparation Take the formulated amounts of silica and aluminum dihydrogen phosphate, mix them, pulverize and screen through a 400-mesh sieve, add a dispersion medium, place it in a stirring homogenizer, and stir and homogenize for 2 h at a stirring speed of 30 rpm and a homogenizing speed of 2000 rpm to obtain a binder; the dispersion medium is obtained by taking the formulated amounts of PVP-K90 and sodium alginate, placing them in hot water at 50 °C, stirring and dissolving, and cooling to room temperature. The ratio of the total mass of PVP-K90 and sodium alginate to the total mass of hot water is 3:100; (4)Mix and prepare the coating Under stirring at 25 rpm, add the slurry prepared in step (2) to the binder, then add dimethyl silicone oil, continue stirring for 20 min, stir and homogenize at 2000 rpm for 30 min. After homogenization, perform ultrasonic treatment with an ultrasonic frequency of 40 kHz and an ultrasonic time of 60 min to obtain a coating. The amount of dimethyl silicone oil is 0.5% of the total mass of the coating.

[0039] Spray the coating prepared in Example 2 to form a coating. The specific operation is as follows: (1)Take a common metal aluminum alloy substrate of appropriate size, perform sandblasting treatment according to Sa3 level, ultrasonically clean it with acetone 2 - 3 times, take it out, dry it, and then spray the coating prepared in Example 2 by high-velocity oxygen fuel spraying (parameters: dye propane pressure 0.7 MPa, oxygen pressure 0.9 MPa), with a slurry feeding rate of 30 g / min and a spraying distance of 17 cm. Spray repeatedly for multiple times until the thickness reaches 220 μm, let it stand for 12 h, and naturally volatilize; (2)Place the substrate with the coating attached in a muffle furnace, set the heating rate to 80 °C / min, heat up to 350 °C, keep it warm for 2 hours, continue to heat up at a heating rate of 50 °C / min to 1200 °C, continue to keep it warm for 3 hours, turn off the muffle furnace, naturally cool to room temperature, take it out, and that's it.

[0040] High-temperature resistance test: The coating prepared in this example has excellent high-temperature resistance and can withstand a working environment with a temperature above 1400 °C for a long time. There is no peeling after 30 s of testing with an oxyacetylene flame; Adhesion strength test: The adhesion strength between the coating and the substrate was tested by the tensile method according to ASTM C633 standard, and it was 17.7 Mpa. Thermal shock resistance test: The substrate with the sprayed coating was heated to 1200 °C, quickly taken out to room temperature and quenched with water. After 30 cycles, there was no peeling phenomenon, indicating excellent thermal shock resistance.

[0041] The coating has a uniform thickness, and the relative standard deviation RSD of the thickness is 1.25%.

[0042] Example 3 A preparation method of a high-temperature resistant coating, characterized by comprising the following steps: (1) Design the formula: By weight, it is 80 parts of alumina, 25 parts of zirconia, 10 parts of silicon carbide, 20 parts of silica, 12 parts of polyvinylpyrrolidone, 15 parts of aluminum dihydrogen phosphate, 7 parts of sodium alginate, 5 parts of bentonite, and 3 parts of yttrium oxide; (2) Ball milling treatment Alumina, zirconia and silicon carbide were crushed and passed through a 400-mesh sieve to obtain the main powder. Yttrium oxide, bentonite and zirconia balls with a particle size of 1.5 mm were added, and the ball-to-material ratio was 3:1. Then, wet milling medium ethanol was added for wet milling for 7 h, and ammonia water was added to adjust the pH value to 8 to obtain a slurry. The total mass of the mixed powder, yttrium oxide, bentonite and zirconia balls and the mass of the wet milling medium was 1:2; (3) Preparation of the binder Take the formulated amounts of silica and aluminum dihydrogen phosphate, mix them, crush them through a 400-mesh sieve, add a dispersion medium, place them in a stirring homogenizer, and stir and homogenize at a stirring speed of 20 rpm and a homogenization speed of 2500 rpm for 1 h to obtain the binder; the dispersion medium is obtained by taking the formulated amounts of PVP-K90 and sodium alginate, placing them in hot water at 60 °C, stirring and dissolving, and cooling to room temperature. The ratio of the total mass of PVP-K90 and sodium alginate to the total mass of hot water is 5:100; (4) Mix and prepare the coating Under stirring at 15 rpm, the slurry prepared in step (2) was added to the binder, then dimethyl silicone oil was added, and stirring continued for 30 min. Stirring and homogenizing were carried out at 2500 rpm for 20 min. After homogenization, ultrasonic treatment was carried out. The ultrasonic frequency was 25 kHz and the ultrasonic time was 30 min to obtain the coating. The amount of dimethyl silicone oil was 0.5% of the total mass of the coating.

[0043] The coating prepared in Example 1 was sprayed to form a coating. The specific operation is as follows: (1)Take a common metal aluminum alloy substrate of appropriate size, perform sandblasting treatment at Sa3 level, ultrasonically clean it with acetone 2 - 3 times, take it out, after drying, spray the coating prepared in Example 3 by high velocity oxygen fuel spraying (parameters: dye propane pressure 0.6 MPa, oxygen pressure 0.9 MPa), the slurry feeding rate is 20 g / min, the spraying distance is 15 cm, spray repeatedly for multiple times until the thickness reaches 280 μm, let it stand for 12 h, and naturally volatilize to dryness; (2)Place the substrate with the coating attached in a muffle furnace, set the heating rate at 100℃ / min, heat up to 400℃, keep it warm for 1 hour, continue to heat up at a heating rate of 80℃ / min to 1100℃, continue to keep it warm for 4 hours, turn off the muffle furnace, naturally cool it to room temperature, take it out, and it is obtained.

[0044] High temperature resistance test: The coating prepared in this example has excellent high temperature resistance, can withstand a working environment with a temperature above 1400℃ for a long time, and there is no peeling after 30 s of oxy - acetylene flame test; Adhesion strength test: The adhesion strength between the coating and the substrate is 17.1 Mpa tested by the tensile method according to ASTM C633 standard; Thermal shock resistance test: Heat up the substrate with the sprayed coating to 1200℃, quickly take it out to room temperature and perform water quenching, and there is no peeling phenomenon after 30 cycles, showing excellent thermal shock resistance. The coating thickness is uniform, and the relative standard deviation RSD of the thickness is 1.31%.

Claims

1. A method for preparing a high temperature resistant coating, characterized in that: Alumina, zirconium oxide and silicon carbide are used as main powders, which are mixed with bentonite and yttrium oxide and ball-milled to form slurry. Silicon dioxide, aluminum dihydrogen phosphate, polyvinyl pyrrolidone and sodium alginate are used as a binder. Dimethyl silicone oil and slurry are added to the binder in sequence, and homogenization and ultrasonic treatment are carried out in sequence to obtain the coating.

2. The method for preparing a high temperature resistant coating according to claim 1, characterized in that: The components are, by weight, 60 to 80 parts of aluminum oxide, 20 to 25 parts of zirconium oxide, 8 to 10 parts of silicon carbide, 15 to 20 parts of silicon dioxide, 10 to 12 parts of polyvinyl pyrrolidone, 12 to 15 parts of aluminum dihydrogen phosphate, 5 to 7 parts of sodium alginate, 3 to 5 parts of bentonite, and 2 to 3 parts of yttrium oxide.

3. A method for preparing a high temperature resistant coating according to claim 1 or 2, characterized in that: The ball milling comprises adding yttrium oxide and bentonite to the main powder, adding zirconium oxide balls, the ball-to-material ratio being 3:1, adding ethanol for wet milling for 6-8 hours, and then adding ammonia water to adjust the slurry pH to 8-9 to obtain a slurry, wherein the total mass of the main powder, yttrium oxide, bentonite and zirconium oxide balls is 1:1-2 to the mass of ethanol.

4. A method for preparing a high temperature resistant coating according to any one of claims 1 to 3, characterized in that: The binder is prepared by crushing silicon dioxide and aluminum dihydrogen phosphate into powder, adding a dispersion medium consisting of polyvinyl pyrrolidone and sodium alginate, stirring and homogenizing for 1 to 2 hours, stirring at a speed of 20 to 30 rpm, and homogenizing at a speed of 2000 to 2500 rpm.

5. The method for preparing a high temperature resistant coating according to claim 4, characterized in that: The dispersion medium is prepared by adding polyvinyl pyrrolidone and sodium alginate into water at 50-60° C. and stirring to dissolve the mixture. The mass ratio of the total mass of polyvinyl pyrrolidone and sodium alginate to water is 3-5:

100.

6. A method for preparing a high temperature resistant coating according to claim 5, characterized in that: During the homogenization and ultrasonic treatment, the homogenization time is 20 to 30 minutes, the homogenization speed is 2000 to 2500 rpm, after the homogenization, the ultrasonic treatment is carried out for 30 to 60 minutes, the ultrasonic frequency is 25 to 40 kHz, and the amount of dimethicone is 0.5% to 0.8% of the total mass of the coating.

7. A method for preparing a high temperature resistant coating, characterized in that: The steps include: (1) Design formula: In parts by weight, it comprises 60 to 80 parts of aluminum oxide, 20 to 25 parts of zirconium oxide, 8 to 10 parts of silicon carbide, 15 to 20 parts of silicon dioxide, 10 to 12 parts of polyvinyl pyrrolidone, 12 to 15 parts of aluminum dihydrogen phosphate, 5 to 7 parts of sodium alginate, 3 to 5 parts of bentonite, and 2 to 3 parts of yttrium oxide; (2) Ball milling Alumina, zirconium oxide and silicon carbide are crushed through a 400-mesh sieve to obtain a main powder, yttrium oxide, bentonite and zirconium oxide balls with a particle size of 1.2 to 1.8 mm are added, and the ball-to-material ratio is 3:1, and then wet grinding medium ethanol is added for wet grinding for 6 to 8 hours, and then ammonia water is added to adjust the pH value to 8 to 9 to obtain a slurry, and the total mass of the mixed powder, yttrium oxide, bentonite and zirconium oxide balls and the mass of the wet grinding medium are 1:1 to 2; (3) Binder preparation Take the formulated amount of silicon dioxide and aluminum dihydrogen phosphate, mix them, crush them through a 400-mesh sieve, add a dispersion medium, place them in a stirring homogenizer, stir them for 1 to 2 hours at a stirring speed of 20 to 30 rpm and a homogenizing speed of 2000 to 2500 rpm, and obtain a binder; the dispersion medium is a formulated amount of polyvinylpyrrolidone and sodium alginate placed in 50 to 60°C hot water, stirred to dissolve, and cooled to room temperature, and the total mass ratio of the polyvinylpyrrolidone (PVP-K90) and sodium alginate to the total mass of hot water is 3 to 5:100; (4) Mixing and preparing coatings Under stirring at 15-25 rpm, add the slurry obtained in step (2) to the adhesive, then add dimethyl silicone oil, continue stirring for 20-30 min, stir and homogenize at 2000-2500 rpm for 20-30 min, and after homogenization, perform ultrasonic treatment at an ultrasonic frequency of 25-40 kHz and an ultrasonic time of 30-60 min to obtain a coating, wherein the amount of dimethyl silicone oil is 0.5%-0.8% of the total mass of the coating.

8. A method for preparing a coating by spraying the coating prepared by the method of claim 7, the specific steps being as follows: (1) Take a commonly used metal aluminum alloy substrate of appropriate size, sandblast it according to Sa3 level, ultrasonically clean it with acetone for 2 to 3 times, take it out, dry it, and then use high-speed oxygen fuel to spray the coating. The slurry feeding rate is 20 to 30 g / min, the spraying distance is 15 to 17 cm, and the spraying is repeated many times until the thickness is 220 to 280 μm. Let it stand for 12 hours and evaporate naturally; (2) Place the substrate with the coating in a muffle furnace, set the heating rate to 80-100°C / min, heat it to 350-400°C, keep it warm for 1-2 hours, continue to heat it to 1100-1200°C at a heating rate of 50-80°C / min, keep it warm for 3-4 hours, close the muffle furnace, cool it naturally to room temperature, and take it out.

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