Silicon carbide-based composite ceramic coating and slurry sintering preparation method and application thereof

Abstract

The application provides a silicon carbide-based composite ceramic coating and a slurry sintering preparation method and application thereof, the silicon carbide-based composite ceramic coating comprises a mullite underlayer arranged on the surface of silicon carbide and a high-entropy rare earth silicate composite surface layer located on the mullite underlayer; the high-entropy rare earth silicate composite surface layer comprises a main phase and a second phase, the main phase is a high-entropy rare earth monosilicate, and the second phase is a high-entropy rare earth disilicate; and the mullite underlayer comprises a mullite phase and amorphous silicon dioxide. The silicon carbide-based composite ceramic coating is obtained by a slurry sintering method, the coating preparation method has the advantages of simplicity, low one-time investment cost of equipment and suitability for large-scale production, and a burner with the coating has excellent high-temperature water-oxygen corrosion resistance at 1300 DEG C or above.

Description

Technical Field

[0001] This invention relates to the field of porous media combustion technology, and in particular to a silicon carbide-based composite ceramic coating, its slurry sintering preparation method, and its application. Background Technology

[0002] Porous media combustion technology is a combustion technology that achieves ultra-low emissions and stable combustion of pollutants. The porous media combustion plate, as its core component, needs to possess excellent thermal shock resistance and high-temperature oxidation resistance. Compared with other materials, silicon carbide porous ceramics have advantages such as a low coefficient of thermal expansion, high thermal conductivity and emissivity, and excellent thermal shock resistance, making them the preferred material for porous media burners. However, silicon carbide porous ceramics face dual oxidation from high-temperature water vapor and combustion-supporting gases in the combustion environment. The SiO2 generated from silicon carbide oxidation reacts with water vapor to form highly volatile Si(OH)4, severely affecting the service life of the silicon carbide.

[0003] Therefore, porous media materials have become the main bottleneck restricting the widespread application of porous media burners in medium and high temperature industries.

[0004] Applying a coating resistant to high-temperature water-oxygen corrosion to the surface of silicon carbide can isolate the substrate from the corrosive environment, which is an effective way to improve the surface stability of silicon carbide in combustion environments. Furthermore, the coating can increase the service temperature of the burner, meeting its usage requirements under different operating conditions and extending the burner's service life.

[0005] Therefore, it is necessary to develop silicon carbide-based coatings that can meet the requirements of medium and high temperature fields, thereby improving the application prospects of porous media materials. Summary of the Invention

[0006] To address the aforementioned technical problems, this invention provides a silicon carbide-based composite ceramic coating, its slurry sintering preparation method, and its application. This invention, by sequentially setting a mullite underlayer and a high-entropy rare-earth silicate composite top layer on a silicon carbide substrate, can provide a coating system with excellent bonding to the silicon carbide substrate, thermal shock resistance, and resistance to water and oxygen corrosion at high temperatures above 1300℃. This improves the reliability and stability of silicon carbide in high-temperature combustion environments and effectively enhances the retention rate of silicon carbide's mechanical properties at high temperatures.

[0007] To achieve this objective, the present invention adopts the following technical solution:

[0008] In a first aspect, the present invention provides a silicon carbide-based composite ceramic coating, the silicon carbide-based composite ceramic coating comprising a mullite underlayer disposed on the surface of silicon carbide, and a high-entropy rare earth silicate composite surface layer disposed on the mullite underlayer; the high-entropy rare earth silicate composite surface layer comprises a main phase and a second phase, the main phase being a high-entropy rare earth monosilicate, and the second phase being a high-entropy rare earth disilicate.

[0009] The mullite substrate comprises a mullite phase and amorphous silicon dioxide.

[0010] The design concept of this invention is that mullite and silicon carbide substrates have similar coefficients of thermal expansion and chemical compatibility, and mullite possesses excellent chemical stability and resistance to high-temperature oxidation. Therefore, the mullite underlayer can isolate the top layer from the substrate while ensuring the overall performance of the coating, preventing element diffusion between the coating and the substrate. However, the silica in mullite is highly reactive; in a water-oxygen environment, SiO2 reacts with water vapor to generate volatile Si(OH)4, leading to pores in the coating. Rare earth silicate ceramics have good resistance to high-temperature water-oxygen corrosion. However, monocomponent rare earth silicates exhibit poor structural stability in long-term, high-temperature environments. Rare earth disilicates are prone to crystal transformation and abnormal grain growth, while rare earth monosilicates readily react with SiO2 to form rare earth disilicates, which have a large coefficient of thermal expansion and are incompatible with mullite. This can lead to cracking and coating failure during the start-up and shutdown process of cyclic combustion.

[0011] High-entropy materials are a class of multi-component solid solutions composed of five or more components, exhibiting high-entropy effects, retarded diffusion effects, lattice distortion effects, and the "cocktail effect." Compared to single-component rare-earth silicates, high-entropy rare-earth silicates exhibit superior phase structure stability due to their high configurational entropy. To enable high-entropy rare-earth silicates to possess a thermal expansion coefficient matching that of the mullite substrate and better resistance to high-temperature water-oxygen corrosion, this invention designs a high-entropy rare-earth monosilicate... and high-entropy rare earth disilicates By combining different materials, a high-entropy rare earth silicate composite ceramic coating with excellent resistance to high-temperature water-oxygen corrosion and thermal shock was prepared, thereby enabling the large-scale application of silicon carbide-based porous ceramic burners at temperatures above 1300℃.

[0012] Preferably, the content of amorphous silica in the mullite base layer is 5% to 20%, for example, it can be 5%, 7%, 9%, 10%, 12%, 14%, 15%, 17%, 19% or 20%, etc., but is not limited to the listed values. Other unlisted values ​​within this range are also applicable, preferably 5% to 10%.

[0013] The present invention further optimizes the content of amorphous silica in the mullite substrate to be 5-20%, which can better improve the adhesion to the substrate and ensure the density of the mullite substrate.

[0014] Preferably, the content of high-entropy rare-earth disilicate in the high-entropy rare-earth silicate composite surface layer is 10-25%, for example, it can be 10%, 12%, 14%, 15%, 17%, 19%, 20%, 22%, 24% or 25%, etc., but is not limited to the listed values. Other unlisted values ​​within this range are also applicable, preferably 10-20%.

[0015] The present invention further optimizes the content of high-entropy rare earth disilicate in the high-entropy rare earth silicate composite surface layer to be 10-25%, which has a thermal expansion coefficient that is more compatible with the mullite bottom layer, thereby improving its resistance to high-temperature water and oxygen corrosion and thermal shock resistance.

[0016] Preferably, the chemical formula of the high-entropy rare-earth monosilicate is: The chemical formula of the high-entropy rare-earth disilicate is: Among them, RE i They are any one of the rare earth elements Sc, Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb or Lu, where n≥5 and 1≤i≤n.

[0017] Preferably, the thickness of the mullite base layer is 50–200 μm, for example, it can be 50 μm, 67 μm, 84 μm, 100 μm, 117 μm, 134 μm, 150 μm, 167 μm, 184 μm or 200 μm, but is not limited to the listed values, and other unlisted values ​​within this range are also applicable; the thickness of the high-entropy rare earth silicate composite surface layer is 100–200 μm, for example, it can be 100 μm, 112 μm, 123 μm, 134 μm, 145 μm, 156 μm, 167 μm, 178 μm, 189 μm or 200 μm, but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0018] Preferably, the density of the mullite base layer is 96% to 99%, for example, it can be 96%, 96.2%, 96.5%, 96.6%, 96.8%, 97%, 97.2%, 97.5%, 97.8%, 98%, 98.2%, 98.5%, 98.8%, or 99%, etc.

[0019] In a second aspect, the present invention provides a method for preparing a slurry sintering of the silicon carbide-based composite ceramic coating as described in the first aspect, the slurry sintering preparation method comprising:

[0020] (1) The silicon carbide substrate is impregnated in the mullite base slurry and then subjected to removal of excess slurry and drying.

[0021] (2) Repeat step (1) at least once to obtain a precursor containing a mullite coating;

[0022] (3) The mullite-coated precursor described in step (2) is subjected to a first calcination and a first cooling to obtain a first silicon carbide ceramic material containing a mullite bottom layer;

[0023] (4) In step (3), the first silicon carbide ceramic material is impregnated in a high-entropy rare earth silicate composite surface slurry, and then the excess slurry is removed and dried in sequence.

[0024] (5) Repeat step (4) at least once to obtain a precursor material containing high-entropy rare earth silicate composite ceramics.

[0025] (6) The precursor material containing high-entropy rare earth silicate composite ceramic in step (5) is subjected to a second calcination and a second cooling to obtain silicon carbide ceramic with silicon carbide-based composite ceramic coating.

[0026] This invention utilizes a slurry sintering method to prepare mullite coatings and high-entropy rare-earth silicate composite ceramic coatings on the surface of silicon carbide-based ceramics. This method has the advantages of being simple and easy to implement, requiring less initial equipment investment, and being suitable for large-scale production.

[0027] Preferably, the raw materials of the mullite bottom layer slurry include andalusite powder of 250-450 mesh, corundum powder of 700-900 mesh, and silica powder of 7500-9500 mesh.

[0028] It is worth noting that currently, high-temperature environmental barrier coatings are generally prepared using plasma spraying, but this method requires sophisticated equipment and is costly. This invention optimizes the particle size distribution of the main powders in the mullite underlayer slurry, enabling the formation of a well-bonded mullite underlayer on the surface of a silicon carbide substrate via slurry sintering. Furthermore, the subsequent impregnation with a high-entropy rare-earth silicate composite toplayer slurry further enhances the phase stability of rare-earth silicates and their corrosion resistance in high-temperature, water-oxygen environments.

[0029] Studies have found that when the particle size of each component is too large, the sintered coating has more pores and lower resistance to oxygen penetration. When the powder particles are all ball-milled to a particle size of about 7500-8000 mesh, the sintered coating is too dense with no stress release space, and the coating shrinks and cracks, failing to completely cover the silicon carbide matrix. Only when the andalusite powder, corundum powder, and silica powder are compounded according to the above particle size requirements, the sintered coating has moderate pores and appropriate space for stress release. It is not easy to crack in the high-temperature combustion environment, and the coating does not shrink. It can better cover the silicon carbide matrix and play a protective role against oxidation.

[0030] Specifically, andalusite powder with a mesh size of 250 to 450 can be, for example, 250 mesh, 273 mesh, 295 mesh, 317 mesh, 339 mesh, 362 mesh, 384 mesh, 406 mesh, 428 mesh, or 450 mesh, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0031] Corundum powder with a mesh size of 700 to 900, such as 700 mesh, 723 mesh, 745 mesh, 767 mesh, 789 mesh, 812 mesh, 834 mesh, 856 mesh, 878 mesh or 900 mesh, etc., but not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0032] Silica powder with a mesh size of 7500 to 9500, such as 7500 mesh, 7723 mesh, 7945 mesh, 8167 mesh, 8389 mesh, 8612 mesh, 8834 mesh, 9056 mesh, 9278 mesh or 9500 mesh, etc., but not limited to the listed values, and other unlisted values ​​in this range are also applicable.

[0033] Preferably, the preparation of the mullite bottom layer slurry includes: first ball milling of andalusite raw material with a particle size of 250-450 mesh to obtain andalusite powder; mixing andalusite powder, corundum powder, silica powder, first binder, first curing agent, first dispersant and ethanol, and then performing a second ball milling and sieve filtration to obtain the mullite bottom layer slurry.

[0034] The present invention preferably involves ball milling the andalusite raw material and matching the particle size of the corundum powder and silica powder. This ensures that the coating porosity is moderate to improve the resistance to oxygen penetration, while avoiding the problem of the coating being too dense and lacking stress release space. Ultimately, the coating is not prone to cracking in high-temperature combustion environments and does not shrink. It can better cover the silicon carbide substrate and play a protective role against oxidation.

[0035] Preferably, the mass ratio of andalusite powder: corundum powder: silica powder: first binder: first curing agent: first dispersant: ethanol is (40-70):(10-30):(2-10):(20-60):(1-6):(2-10):(30-70).

[0036] Specifically, the andalusite powder is 40-70, for example, 40, 44, 47, 50, 54, 57, 60, 64, 67, or 70, but not limited to the listed values; other unlisted values ​​within this range also apply. The corundum powder is 10-30, for example, 10, 13, 15, 17, 19, 22, 24, 26, 28, or 30, but not limited to the listed values; other unlisted values ​​within this range also apply. The silica powder is 2-10, for example, 2, 2.9, 3.8, 4.7, 5.6, 6.5, 7.4, 8.3, 9.2, or 10, but not limited to the listed values; other unlisted values ​​within this range also apply. The first binder is 20-60, for example, 20, 25, 29, 34, 38, 43, 47, etc. 52, 56, or 60, etc., but not limited to the listed values; other unlisted values ​​within this range also apply; first curing agent 1 to 6, for example, 1, 1.6, 2.2, 2.7, 3.3, 3.8, 4.4, 4.9, 5.5, or 6, etc., but not limited to the listed values; other unlisted values ​​within this range also apply; first dispersant 2 to 10, for example, 2, 2.9, 3.8, 4.7, 5.6, 6.5, 7.4, 8.3, 9.2, or 10, etc., but not limited to the listed values; other unlisted values ​​within this range also apply; ethanol 30 to 70, for example, 30, 35, 39, 44, 48, 53, 57, 62, 66, or 70, etc., but not limited to the listed values; other unlisted values ​​within this range also apply.

[0037] Preferably, the first ball milling is carried out in a pot mill.

[0038] Preferably, the rotational speed of the first ball mill is 180 to 220 r / min, for example, it can be 180 r / min, 185 r / min, 189 r / min, 194 r / min, 198 r / min, 203 r / min, 207 r / min, 212 r / min, 216 r / min or 220 r / min, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0039] Preferably, the first ball milling time is 24 to 48 hours, for example, it can be 24 hours, 27 hours, 30 hours, 32 hours, 35 hours, 38 hours, 40 hours, 43 hours, 46 hours or 48 hours, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0040] Preferably, the particle size of the first ball-milled andalusite is 1000-5000 mesh, for example, it can be 1000 mesh, 1200 mesh, 1300 mesh, 1400 mesh, 1500 mesh, 1600 mesh, 1700 mesh, 1800 mesh, 2000 mesh, 2200 mesh, 2300 mesh, 2500 mesh, 2800 mesh, 3000 mesh, 3200 mesh, 3500 mesh, 4000 mesh, 4500 mesh or 5000 mesh, etc.

[0041] The particle size distribution of andalusite after the first ball milling is within the above-mentioned range. This allows the ball-milled andalusite to be better combined with other raw materials, ultimately improving the thermal shock resistance and oxidation corrosion resistance of the silicon carbide-based composite ceramic coating.

[0042] Preferably, the second ball milling time is 6 to 24 hours, for example, it can be 6 hours, 8 hours, 10 hours, 12 hours, 14 hours, 16 hours, 18 hours, 20 hours, 22 hours or 24 hours, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0043] Preferably, the rotational speed of the second ball mill is 180 to 220 r / min, for example, it can be 180 r / min, 185 r / min, 189 r / min, 194 r / min, 198 r / min, 203 r / min, 207 r / min, 212 r / min, 216 r / min or 220 r / min, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0044] Preferably, the mesh size of the sieve used for filtration in step (1) is 100 to 200 mesh, for example, it can be 100 mesh, 112 mesh, 123 mesh, 134 mesh, 145 mesh, 156 mesh, 167 mesh, 178 mesh, 189 mesh or 200 mesh, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0045] Preferably, the removal of excess slurry in step (1) includes centrifugation and purging performed sequentially.

[0046] Preferably, the drying in step (1) includes baking.

[0047] Preferably, the drying temperature in step (1) is 80 to 120°C, for example, it can be 80°C, 85°C, 89°C, 94°C, 98°C, 103°C, 107°C, 112°C, 116°C or 120°C, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0048] Preferably, the number of repetitions in step (2) is 1 to 5 times, for example, 1 time, 2 times, 3 times, 4 times or 5 times.

[0049] Preferably, the temperature of the first calcination in step (3) is 1500 to 1600°C, for example, it can be 1500°C, 1512°C, 1523°C, 1534°C, 1545°C, 1556°C, 1567°C, 1578°C, 1589°C or 1600°C, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0050] Preferably, the first calcination time in step (3) is 3 to 10 hours, for example, it can be 3 hours, 3.8 hours, 4.6 hours, 5.4 hours, 6.2 hours, 6.9 hours, 7.7 hours, 8.5 hours, 9.3 hours or 10 hours, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0051] Preferably, the preparation of the high-entropy rare-earth silicate composite surface slurry in step (4) includes:

[0052] High-entropy rare earth monosilicate powder, high-entropy rare earth disilicate powder, a second binder, a second curing agent, a second dispersant, and ethanol are mixed, and then subjected to a third ball milling and sieve filtration to obtain the high-entropy rare earth silicate composite surface slurry.

[0053] Preferably, the mass ratio of the high-entropy rare earth monosilicate powder, the high-entropy rare earth disilicate powder, the second binder, the second curing agent, the second dispersant and ethanol is (70-90):(10-30):(20-60):(1-6):(2-10):(30-70).

[0054] Specifically, the high-entropy rare-earth monosilicate powder has a content of 70–90, for example, 70, 73, 75, 77, 79, 82, 84, 86, 88, or 90, but is not limited to the listed values; other unlisted values ​​within this range also apply. The high-entropy rare-earth disilicate powder has a content of 10–30, for example, 10, 13, 15, 17, 19, 22, 24, 26, 28, or 30, but is not limited to the listed values; other unlisted values ​​within this range also apply. The second binder has a content of 20–60, for example, 20, 25, 29, 34, 38, 43, 47, 52, 56, or 60, but is not limited to the listed values; other unlisted values ​​within this range also apply. The following applies: Second curing agent 1-6, for example, can be 1, 1.6, 2.2, 2.7, 3.3, 3.8, 4.4, 4.9, 5.5, or 6, but is not limited to the listed values; other unlisted values ​​within this range also apply; Second dispersant 2-10, for example, can be 2, 2.9, 3.8, 4.7, 5.6, 6.5, 7.4, 8.3, 9.2, or 10, but is not limited to the listed values; other unlisted values ​​within this range also apply; Ethanol 30-70, for example, can be 30, 35, 39, 44, 48, 53, 57, 62, 66, or 70, but is not limited to the listed values; other unlisted values ​​within this range also apply.

[0055] Preferably, the rotational speed of the third ball mill is 180 to 220 r / min, for example, it can be 180 r / min, 185 r / min, 189 r / min, 194 r / min, 198 r / min, 203 r / min, 207 r / min, 212 r / min, 216 r / min or 220 r / min, etc., but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0056] Preferably, the third ball milling time is 6 to 24 hours, for example, it can be 6 hours, 8 hours, 10 hours, 12 hours, 14 hours, 16 hours, 18 hours, 20 hours, 22 hours or 24 hours, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0057] Preferably, the mesh size of the sieve used for filtration in step (4) is 100 to 200 mesh, for example, it can be 100 mesh, 112 mesh, 123 mesh, 134 mesh, 145 mesh, 156 mesh, 167 mesh, 178 mesh, 189 mesh or 200 mesh, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0058] Preferably, the preparation processes of the high-entropy rare-earth monosilicate powder and the high-entropy rare-earth disilicate powder each independently include:

[0059] S1, rare earth oxides and the third dispersant are mixed and then ball-milled to form a precursor slurry.

[0060] S2. The precursor slurry is dried and sieved in sequence, and then sintered to obtain high-entropy rare earth silicate particles.

[0061] S3. The high-entropy rare earth silicate particles are ball-milled and sieved in air to obtain high-entropy rare earth silicate powder.

[0062] Preferably, the rare earth oxide satisfies a RE:Si:O molar ratio of 1:2:5 in the chemical formula of high-entropy rare earth monosilicate particles, or the rare earth oxide satisfies a RE:Si:O molar ratio of 2:2:7 in the chemical formula of high-entropy rare earth disilicate particles.

[0063] Preferably, the third dispersant comprises water and / or ethanol.

[0064] Preferably, the fourth ball milling time is 6 to 24 hours, for example, it can be 6 hours, 8 hours, 10 hours, 12 hours, 14 hours, 16 hours, 18 hours, 20 hours, 22 hours or 24 hours, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0065] Preferably, the rotational speed of the fourth ball mill is 300-400 r / min, for example, it can be 300 r / min, 310 r / min, 320 r / min, 330 r / min, 340 r / min, 345 r / min, 350 r / min, 360 r / min, 380 r / min, 390 r / min or 400 r / min, etc.

[0066] Preferably, the heating rate of the sintering process is 5 to 10 °C / min, for example, it can be 5 °C / min, 5.6 °C / min, 6.2 °C / min, 6.7 °C / min, 7.3 °C / min, 7.8 °C / min, 8.4 °C / min, 8.9 °C / min, 9.5 °C / min or 10 °C / min, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0067] Preferably, the sintering temperature is 1500–1650°C, for example, 1500°C, 1517°C, 1534°C, 1550°C, 1567°C, 1584°C, 1600°C, 1617°C, 1634°C, or 1650°C, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0068] Preferably, the sintering synthesis time is 0.5 to 20 hours, for example, it can be 0.5 hours, 2.7 hours, 4.9 hours, 7 hours, 9.2 hours, 11.4 hours, 13.5 hours, 15.7 hours, 17.9 hours or 20 hours, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0069] Preferably, the fifth ball milling time is 6 to 20 hours, for example, it can be 6 hours, 8 hours, 10 hours, 11 hours, 13 hours, 14 hours, 16 hours, 17 hours, 19 hours or 20 hours, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0070] Preferably, the rotational speed of the fifth ball mill is 300-400 r / min, for example, it can be 300 r / min, 312 r / min, 323 r / min, 334 r / min, 345 r / min, 356 r / min, 367 r / min, 378 r / min, 389 r / min or 400 r / min, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0071] Preferably, the sieving in step S3 is sieving through a 400-mesh sieve.

[0072] Preferably, the first adhesive and the second adhesive each independently comprise a resin with a residual carbon value greater than 35%, said resin comprising any one or a combination of at least two of epoxy resin, phenolic resin, polyacrylic resin, polyvinyl butyral, furfural resin, or phenol-furfural resin, wherein typical but not limiting combinations are combinations of epoxy resin and phenolic resin, combinations of polyacrylic resin and phenolic resin, combinations of epoxy resin and polyacrylic resin, combinations of polyvinyl butyral and phenolic resin, and combinations of polyvinyl butyral and phenol-furfural resin.

[0073] Preferably, the first curing agent and the second curing agent each independently comprise any one or a combination of at least two of citric acid, p-toluenesulfonic acid, pentosulfonate, or oxalic acid, wherein typical but non-limiting combinations are combinations of citric acid and p-toluenesulfonic acid, combinations of oxalic acid and p-toluenesulfonic acid, combinations of citric acid and oxalic acid, and combinations of pentosulfonate and p-toluenesulfonic acid.

[0074] Preferably, the first dispersant and the second dispersant each independently comprise any one or a combination of at least two of castor oil, trioleic acid glyceride, Tween 20, or organobentonite, wherein typical but non-limiting combinations are a combination of castor oil and trioleic acid glyceride, a combination of Tween 20 and trioleic acid glyceride, a combination of castor oil and Tween 20, a combination of organobentonite and trioleic acid glyceride, or a combination of castor oil and organobentonite.

[0075] Preferably, the silicon carbide substrate has a porous structure, and the shape of the pores includes any one or a combination of at least two of the following: triangles, rounded triangles at vertexes, circles, ellipses, regular polygons, variant polygons, or hierarchical polygons. Typical but non-limiting combinations are the combination of triangles and rounded triangles at vertexes, circles and rounded triangles at vertexes, triangles and ellipses, triangles and regular polygons, variant polygons and regular polygons, and hierarchical polygons and regular polygons.

[0076] Thirdly, the present invention provides an application of the silicon carbide-based composite ceramic coating described in the first aspect in a porous medium burner in a medium-high temperature field, preferably wherein the temperature in the medium-high temperature field is ≥1300℃.

[0077] The silicon carbide-based composite ceramic coating provided by the first aspect of the present invention has excellent performance, strong resistance to thermal shock and high-temperature water-oxygen corrosion, and can be effectively applied in fields with temperatures ≥1300℃.

[0078] Compared with the prior art, the present invention has at least the following beneficial effects:

[0079] (1) The silicon carbide-based composite ceramic coating provided by the present invention uses andalusite, white corundum and nano-SiO2 as raw materials. The mullite prepared contains a part of the SiO2 glass phase, which can improve the density of the mullite coating and its adhesion to the substrate.

[0080] (2) The silicon carbide-based composite ceramic coating high-entropy rare earth silicate provided by the present invention has high configuration entropy, which can further improve the phase stability of rare earth silicate and its corrosion resistance in high temperature water and oxygen environment; moreover, through the composite of high-entropy rare earth double silicate and high-entropy rare earth single silicate, it has a thermal expansion coefficient that is more matched with the mullite bottom layer, thereby simultaneously improving its resistance to high temperature water and oxygen corrosion and thermal shock performance. Under preferred conditions, it can achieve more than 30 times above 1500℃ without cracking, and the oxidation weight gain rate is within 0.782%, which can better meet the requirements of burners for high temperature water and oxygen corrosion resistance above 1300℃.

[0081] (3) The method for preparing silicon carbide-based composite ceramic coating provided by the present invention uses slurry sintering to prepare mullite coating and high entropy rare earth silicate composite ceramic coating on silicon carbide-based ceramic surface. This method has the advantages of being simple and easy to implement, requiring less initial equipment investment and being suitable for large-scale production. Moreover, it can achieve excellent bonding between the coating and the substrate. Attached Figure Description

[0082] Figure 1 This is the surface XRD pattern of the silicon carbide-based composite ceramic coating obtained in Example 2 of the present invention.

[0083] Figure 2This is an SEM elemental analysis image of the mullite substrate obtained in Example 2 of the present invention.

[0084] Figure 3 This is a SEM image of andalusite after ball milling in Embodiment 1 of the present invention.

[0085] Figure 4 This is a SEM image of the mullite substrate obtained in Example 1 of the present invention.

[0086] Figure 5 This is a SEM image of andalusite that has not been ball-milled in Embodiment 4 of the present invention.

[0087] Figure 6 This is a SEM image of the mullite substrate obtained in Example 4 of the present invention.

[0088] Figure 7 This is a SEM image of andalusite after ball milling in Embodiment 5 of the present invention.

[0089] Figure 8 This is a SEM image of the mullite substrate obtained in Embodiment 5 of the present invention. Detailed Implementation

[0090] To facilitate understanding of the present invention, the following embodiments are provided. Those skilled in the art should understand that these embodiments are merely illustrative and should not be construed as limiting the scope of the invention.

[0091] It should be understood that in the description of this invention, the terms "first," "second," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Therefore, a feature defined with "first," "second," etc., may explicitly or implicitly include one or more of that feature. In the description of this invention, unless otherwise stated, "a plurality of" means two or more.

[0092] Example 1

[0093] This embodiment provides a method for preparing a silicon carbide-based composite ceramic coating, the method comprising the following steps:

[0094] S1, Preparation of the mullite substrate

[0095] S1.1, Preparation of mullite underlayer slurry:

[0096] Andalusite raw material with a particle size of 250 mesh was ball-milled at 180 r / min for 48 h in a ball mill to obtain andalusite powder with a particle size of 1200-3000 mesh.

[0097] The materials were uniformly mixed according to the mass ratio of andalusite powder: corundum powder: silica powder: first binder: first curing agent: first dispersant: ethanol = 70:20:10:20:4:6:50, ball milled at 200 r / min for 10 h in a can mill, and filtered through a 200 mesh sieve to obtain the mullite bottom slurry.

[0098] The corundum powder has a particle size of 200 mesh, and the silica powder has a particle size of 8000 mesh; the first binder is a resin with a residual carbon value greater than 35%, which is a mixture of epoxy resin (specific brand: E-20) and polyacrylic acid resin (specific brand: PPB-MP-300-M) in a mass ratio of epoxy resin: polyacrylic acid resin = 1:1; the first curing agent is p-toluenesulfonic acid; and the first dispersant is trioleic acid glyceride.

[0099] S1.2, Slurry coating and curing: The porous silicon carbide skeleton is immersed in the mullite bottom slurry. After complete immersion, it is taken out and centrifuged to remove excess slurry. It is then blown evenly with compressed air at a pressure of 0.5 MPa and dried and cured at 100°C to obtain a porous skeleton with a first bottom slurry coating.

[0100] Repeat step S1.2 above 5 times to obtain a precursor containing a mullite coating;

[0101] S1.3, Heat treatment: The precursor containing mullite substrate is heat-treated at 1500℃ for 4 hours and then cooled to room temperature to obtain the first silicon carbide ceramic material containing mullite substrate.

[0102] S2, Preparation of high-entropy ytterbium silicate composite ceramic coating

[0103] S2.1, Preparation of high-entropy rare-earth silicate composite surface layer slurry:

[0104] S2.1.1, 6.73g of neodymium oxide, 7.25g of gadolinium oxide, 7.46g of dysprosium oxide, 7.65g of erbium oxide, 7.88g of ytterbium oxide, and 12.02g of silicon oxide were mixed evenly and placed in an agate ball mill jar. Anhydrous ethanol was added as a medium, and the mixture was ball-milled at 350 r / min for 12 hours. The dried powder was then subjected to pressureless sintering in a muffle furnace. The parameters were as follows: the temperature was increased to 1550℃ at a rate of 10℃ / min and held for 4 hours. After the reaction, the mixture was cooled to room temperature with the furnace to obtain high-entropy rare earth monosilicate particles. The high-entropy rare earth monosilicate particles were then ball-milled in air at 350 r / min for 12 hours and sieved to obtain high-entropy rare earth monosilicate powder. The particle size of the high-entropy rare earth monosilicate powder was 350 mesh, and the purity was greater than 99.9%.

[0105] S2.1.2, 6.73g neodymium oxide, 7.25g g gadolinium oxide, 7.46g dysprosium oxide, 7.65g erbium oxide, 7.88g ytterbium oxide, and 6g silicon oxide were mixed evenly and placed in an agate ball mill jar. Anhydrous ethanol was added as a medium, and the mixture was ball-milled at 350 r / min for 12 hours. The dried powder was then subjected to pressureless calcination in a muffle furnace. The parameters were as follows: the temperature was increased to 1550℃ at a rate of 10℃ / min and held for 4 hours. After the reaction, the mixture was cooled to room temperature with the furnace to obtain high-entropy rare earth disilicate particles. The high-entropy rare earth disilicate particles were then ball-milled in air at 350 r / min for 12 hours and sieved to obtain high-entropy rare earth disilicate powder. The particle size of the high-entropy rare earth disilicate powder was 350 mesh, and the purity was greater than 99.9%.

[0106] S2.1.3, according to the mass ratio of high entropy rare earth monosilicate powder: high entropy rare earth disilicate powder: second binder: second curing agent: second dispersant: ethanol = 80:20:30:2:8:60, the materials are uniformly mixed, ball-milled at 200 r / min for 12 h, and filtered through a 200 mesh sieve to obtain the surface slurry;

[0107] The second binder is a resin with a residual carbon value greater than 35%, and the resin is an alcohol-soluble phenolic resin (specific brand: FQ-9); the second curing agent is p-toluenesulfonic acid; and the second dispersant is organic bentonite.

[0108] S2.2, Slurry application and curing: The first silicon carbide ceramic material is immersed in the high entropy rare earth silicate composite surface slurry, excess slurry is removed, and it is blown evenly with compressed air at a pressure of 0.5 MPa. It is then dried and cured at 80°C to obtain a porous structure skeleton of the first surface slurry coating.

[0109] Repeat step S2.2 three times to obtain a precursor material containing high-entropy rare-earth silicate composite ceramics.

[0110] S2.3, Heat treatment: The precursor material containing high-entropy rare earth silicate composite ceramic is heat-treated at 1550℃ for 3h, and then cooled to room temperature to obtain silicon carbide ceramic material coated with mullite-high-entropy rare earth silicate composite material.

[0111] Thermal shock resistance test: First, heat the muffle furnace to 1500℃. Then, place the following silicon carbide ceramic materials—mullite-high entropy rare earth silicate composite coated, mullite-Yb2Si2O7 coated, mullite-Yb2SiO5 coated, mullite-coated, and uncoated—into the furnace and hold for 10 minutes. After holding, remove them and immerse them in cold water below 20℃ for 30 minutes. Remove them, dry them, and observe them under a high-powered microscope for cracks. If no cracks appear, continue the water-cooling thermal shock process. Repeat the thermal shock 50 times and observe the results.

[0112] Antioxidant performance test: Silicon carbide ceramic samples coated with mullite-high entropy rare earth silicate composite material (size: 800mm×30mm×20mm, weight 18.59g), mullite-Yb2Si2O7 coated silicon carbide ceramic material (size: 800mm×30mm×20mm, weight 17.25g), mullite-Yb2SiO5 coated silicon carbide ceramic material (size: 800mm×30mm×20mm, weight 17.25g), and mullite-coated silicon carbide ceramic material and uncoated silicon carbide ceramic material (size: 800mm×30mm×20mm, weight 15.63g) were burned for 200h (working frequency 42.08Hz, working air opening degree 33.0%, working gas opening degree: 2.5%), and the oxidation weight gain rate was calculated.

[0113] The results are shown in Table 1.

[0114] Table 1

[0115]

[0116] Example 2

[0117] This embodiment provides a method for preparing a silicon carbide-based composite ceramic coating, the method comprising the following steps:

[0118] S1, Preparation of the mullite substrate

[0119] S1.1, Preparation of mullite underlayer slurry:

[0120] Andalusite raw material with a particle size of 450 mesh was ball-milled at 200 r / min for 30 h in a ball mill to obtain andalusite powder with a particle size of 2100-4500 mesh;

[0121] The materials were uniformly mixed according to the mass ratio of andalusite powder: corundum powder: silica powder: first binder: first curing agent: first dispersant: ethanol = 45:10:2:20:4:6:60, ball milled at 200 r / min for 16 h in a ball mill, and filtered through a 100 mesh sieve to obtain the mullite bottom slurry.

[0122] The corundum powder has a particle size of 325 mesh, and the silica powder has a particle size of 800 mesh; the first binder is a resin with a carbon residue value greater than 35%, and the resin is acrylic resin (specific brand: BR-80); the first curing agent is citric acid; and the first dispersant is trioleic acid glyceride.

[0123] S1.2, Slurry Coating and Curing: The porous silicon carbide skeleton is immersed in the mullite bottom slurry. After complete immersion, it is taken out and centrifuged to remove excess slurry. It is then blown evenly with compressed air at a pressure of 0.5 MPa and dried and cured at 120°C to obtain a porous skeleton with a first-layer bottom slurry coating.

[0124] Repeat step S1.2 three times to obtain a precursor containing a mullite coating;

[0125] S1.3, Heat treatment: The precursor containing mullite substrate is heat-treated at 1550℃ for 3 hours and then cooled to room temperature to obtain the first silicon carbide ceramic material containing mullite substrate.

[0126] S2, Preparation of high-entropy ytterbium silicate composite ceramic coating

[0127] S2.1, Preparation of high-entropy rare-earth silicate composite surface layer slurry:

[0128] S2.1.1, 1.38g scandium oxide, 2.26g yttrium oxide, 3.83g erbium oxide, 3.86g thulium oxide, 3.94g ytterbium oxide, 3.98g lutetium oxide, and 7.21g silicon oxide were mixed evenly and placed in an agate ball mill jar. Anhydrous ethanol was added as a medium, and the mixture was ball-milled at 350 r / min for 6 hours. The dried powder was then subjected to pressureless sintering in a muffle furnace. The parameters were as follows: the temperature was increased to 1600℃ at a rate of 5℃ / min and held for 2 hours. After the reaction, the mixture was cooled to room temperature with the furnace to obtain high-entropy rare earth monosilicate particles. The high-entropy rare earth monosilicate particles were then ball-milled in air at 400 r / min for 10 hours and sieved to obtain high-entropy rare earth monosilicate powder. The particle size of the high-entropy rare earth monosilicate powder was 325 mesh, and the purity was greater than 99.9%.

[0129] S2.1.2, 1.38g scandium oxide, 2.26g yttrium oxide, 3.83g erbium oxide, 3.86g thulium oxide, 3.94g ytterbium oxide, 3.98g lutetium oxide, and 3.61g silicon oxide were mixed evenly and placed in an agate ball mill jar. Anhydrous ethanol was added as a medium, and the mixture was ball-milled at 350r / min for 6 hours. The dried powder was then subjected to pressureless calcination in a muffle furnace. The parameters were as follows: the temperature was increased to 1600℃ at a rate of 5℃ / min and held for 2 hours. After the reaction, the mixture was cooled to room temperature with the furnace to obtain high-entropy rare earth disilicate particles. The high-entropy rare earth disilicate particles were then ball-milled in air at 400r / min for 10 hours and sieved to obtain high-entropy rare earth disilicate powder. The particle size of the high-entropy rare earth disilicate powder was 325 mesh, and the purity was greater than 99.9%.

[0130] S2.1.3, according to the mass ratio of high entropy rare earth monosilicate powder: high entropy rare earth disilicate powder: second binder: second curing agent: second dispersant: ethanol = 90:10:40:6:5:40, the materials are uniformly mixed, ball-milled at 220 r / min for 12 h, and filtered through a 200 mesh sieve to obtain the surface slurry;

[0131] The second binder is a resin with a carbon residue value greater than 35%, and the resin is an alcohol-soluble phenolic resin (specific brand: 2123); the second curing agent is p-toluenesulfonic acid; and the second dispersant is organic bentonite.

[0132] S2.2, Slurry application and curing: The first silicon carbide ceramic material is immersed in the high entropy rare earth silicate composite surface slurry. After complete immersion, it is taken out and centrifuged to remove excess slurry. It is then blown evenly with compressed air at a pressure of 0.5 MPa and dried and cured at 80°C to obtain a porous structure skeleton of the first surface slurry coating.

[0133] Repeat step S2.2 three times to obtain a precursor material containing high-entropy rare-earth silicate composite ceramics.

[0134] S2.3, Heat treatment: The precursor material containing high-entropy rare earth silicate composite ceramic was heat-treated at 1475℃ for 4 hours and then cooled to room temperature to obtain silicon carbide ceramic material coated with mullite-high-entropy rare earth silicate composite material.

[0135] The surface XRD pattern of the silicon carbide ceramic material coated with mullite-high entropy rare earth silicate composite ceramic prepared in this embodiment is as follows: Figure 1 As shown, based on the diffraction pattern, the rare-earth ytterbium silicate composite coating can be calculated to consist of 90 mol.% rare-earth monosilicate phase and 10 mol.% rare-earth disilicate phase. The SEM image of the mullite substrate is shown below. Figure 2 As shown, number 8 indicates amorphous material, indicating that the mullite substrate in this embodiment contains amorphous silicon dioxide, and number 9 indicates the mullite phase. The mullite-rare earth silicate composite ceramic-coated silicon carbide ceramic material prepared in this embodiment was subjected to thermal shock resistance testing: First, the muffle furnace was heated to 1550℃. Then, the mullite-high entropy rare earth silicate composite coated silicon carbide ceramic material, the mullite-Yb2SiO5 coated silicon carbide ceramic material, and the uncoated silicon carbide ceramic material were placed in the furnace and held at that temperature for 10 minutes. Afterward, they were removed and immersed in cold water below 20℃ for 30 minutes. They were then removed, dried, and observed under a high-powered microscope for cracks. If no cracks were found, the water-cooling thermal shock process was continued. Test results: After 30 cycles of repeated thermal shock at 1550℃, no cracks were observed.

[0136] Antioxidant performance test: Silicon carbide ceramic material coated with mullite-high entropy rare earth silicate composite material (size: 800mm×30mm×20mm, weight 15.63g), silicon carbide ceramic material coated with mullite-Yb2SiO5 (size: 800mm×30mm×20mm, weight 16.38g), and uncoated silicon carbide ceramic material (size: 800mm×30mm×20mm, weight 14.11g) were burned for 100h (working frequency 40Hz, working air opening 30%, working gas opening: 2.7%), and the oxidation weight gain rate was calculated.

[0137] Table 2

[0138]

[0139] Example 3

[0140] This embodiment provides a method for preparing a silicon carbide-based composite ceramic coating, the method comprising the following steps:

[0141] S1, Preparation of the mullite substrate

[0142] S1.1, Preparation of mullite underlayer slurry:

[0143] Andalusite raw material with a particle size of 300 mesh was ball-milled at 220 r / min for 24 h in a ball mill to obtain andalusite powder with a particle size of 1000-1800 mesh;

[0144] The materials were mixed uniformly according to the mass ratio of andalusite powder: corundum powder: silica powder: first binder: first curing agent: first dispersant: ethanol = 60:15:2:50:4:8:60, ball milled at 180 r / min for 24 h in a can mill, and filtered through a 100 mesh sieve to obtain the mullite bottom slurry.

[0145] The corundum powder has a particle size of 325 mesh, and the silica powder has a particle size of 800 mesh; the first binder is a resin with a carbon residue value greater than 35%, and the resin is acrylic resin (brand name ACR201); the first curing agent is oxalic acid; and the first dispersant is castor oil.

[0146] S1.2, Slurry Coating and Curing: The porous silicon carbide skeleton is immersed in the mullite bottom slurry. After complete immersion, it is taken out and centrifuged to remove excess slurry. It is then blown evenly with compressed air at a pressure of 0.5 MPa and dried and cured at 120°C to obtain a porous skeleton with a first-layer bottom slurry coating.

[0147] Repeat step S1.2 three times to obtain a precursor containing a mullite coating;

[0148] S1.3, Heat treatment: The precursor containing mullite substrate was heat-treated at 1525℃ for 4 hours and then cooled to room temperature to obtain the first silicon carbide ceramic material containing mullite substrate.

[0149] S2, Preparation of high-entropy ytterbium silicate composite ceramic coating

[0150] S2.1, Preparation of high-entropy rare-earth silicate composite surface layer slurry:

[0151] S2.1.1, 10.09g neodymium oxide, 10.46g samarium oxide, 10.56g europium oxide, 10.88g gadolinium oxide, 11.19g dysprosium oxide, 11.34g holmium oxide, 11.48g erbium oxide, 11.58g thulium oxide and 28.84g silicon oxide are mixed evenly and placed in an agate ball mill jar, with anhydrous ethanol added as a medium, and ball milled at 300r / min for 12 hours. The dried powder is then calcined in a muffle furnace without pressure. The parameters are as follows: the temperature is increased to 1650℃ at a rate of 8℃ / min, held for 1 hour, and then cooled to room temperature in the furnace after pressureless sintering to obtain high-entropy rare earth monosilicate particles; the high-entropy rare earth monosilicate particles are ball-milled in air at 300r / min for 12h and sieved to obtain high-entropy rare earth monosilicate powder with a particle size of 325 mesh and a purity greater than 99.9%.

[0152] S2.1.2, 10.09g neodymium oxide, 10.46g samarium oxide, 10.56g europium oxide, 10.88g gadolinium oxide, 11.19g dysprosium oxide, 11.34g holmium oxide, 11.48g erbium oxide, 11.58g thulium oxide and 14.42g silicon oxide are mixed evenly and placed into an agate ball mill jar, with anhydrous ethanol added as a medium, and ball milled at 300r / min for 12 hours. The dried powder is then calcined in a muffle furnace without pressure. The parameters are as follows: the temperature is increased to 1650℃ at a rate of 8℃ / min, held for 1 hour, and then cooled to room temperature with the furnace after the reaction to obtain high-entropy rare earth disilicate particles; the high-entropy rare earth disilicate particles are ball-milled in air at 300r / min for 12h and sieved to obtain high-entropy rare earth disilicate powder with a particle size of 325 mesh and a purity greater than 99.9%.

[0153] S2.1.3, according to the mass ratio of high entropy rare earth monosilicate powder: high entropy rare earth disilicate powder: second binder: second curing agent: second dispersant: ethanol = 70:10:50:2:8:55, the materials are uniformly mixed, ball-milled at 200 r / min for 18 h, and filtered through a 200 mesh sieve to obtain the surface slurry;

[0154] The second binder is a resin with a residual carbon value greater than 35%, and the resin is phenol-furfural resin (specifically brand F15); the second curing agent is pentosol; and the second dispersant is organic bentonite.

[0155] S2.2, Slurry application and curing: The first silicon carbide ceramic material is immersed in the high entropy rare earth silicate composite surface slurry. After complete immersion, it is taken out and centrifuged to remove excess slurry. It is then blown evenly with compressed air at a pressure of 0.5 MPa and dried and cured at 110°C to obtain a porous structure skeleton of the first surface slurry coating.

[0156] Repeat step S2.2 three times to obtain a precursor material containing high-entropy rare-earth silicate composite ceramics.

[0157] S2.3, Heat treatment: The precursor material containing high-entropy rare earth silicate composite ceramic is heat-treated at 1550℃ for 2h, and then cooled to room temperature to obtain silicon carbide ceramic material coated with mullite-high-entropy rare earth silicate composite material.

[0158] The mullite-rare earth silicate composite material coated silicon carbide ceramic materials prepared in this embodiment were subjected to thermal shock resistance tests: First, the muffle furnace was heated to 1600℃. Then, the mullite-rare earth silicate composite material coated silicon carbide ceramic materials, the mullite-90wt.%Yb2SiO5+10wt.%Yb2Si2O7 coated silicon carbide ceramic materials, and the uncoated silicon carbide ceramic materials were placed in the furnace and kept at that temperature for 10 minutes. After that, they were removed and immersed in cold water below 20℃ for 30 minutes. They were then taken out, dried, and observed under a high-powered microscope for the appearance of cracks. If no cracks appeared, the water-cooling thermal shock process was continued. The thermal shock was repeated 20 times at 1600℃.

[0159] Antioxidant performance test: The oxidation weight gain rate of silicon carbide ceramic material coated with mullite-rare earth silicate composite material (size: 800mm×30mm×20mm, weight 20.18g), silicon carbide ceramic material coated with mullite-90wt.%Yb2SiO5+10wt.%Yb2Si2O7 (size: 800mm×30mm×20mm, weight 20.25g), and uncoated silicon carbide ceramic material (size: 800mm×30mm×20mm, weight 18.35g) was calculated after 100h of combustion (working frequency 41.8Hz, working air opening degree 31.0%, working gas opening degree: 2.8%).

[0160] The results are shown in Table 3.

[0161] Table 3

[0162]

[0163] Example 4

[0164] This embodiment provides a method for preparing a silicon carbide-based composite ceramic coating. The preparation method is the same as in Example 1, except that the andalusite raw material is not ball-milled and is directly made of 250-mesh andalusite powder. It will not be described again here.

[0165] Example 5

[0166] This embodiment provides a method for preparing a silicon carbide-based composite ceramic coating. Except for the andalusite raw material being ball-milled to a particle size of 7500 mesh using a planetary ball mill, the preparation method is the same as in Example 1 and will not be repeated here.

[0167] The SEM image of andalusite after ball milling in Example 1 is shown below. Figure 3 As shown, the SEM image of unmilled andalusite in Example 4 is as follows. Figure 5 As shown, the SEM image of andalusite after ball milling in Example 5 is as follows. Figure 7 As shown, the SEM images of the mullite substrates obtained in Examples 1, 4, and 5 are respectively as follows: Figure 4 , Figure 6 and Figure 8 As shown above, by ball milling only andalusite powder into a coarse-fine mixed powder state, this invention can, on the one hand, increase the density of the mullite substrate, reduce pores, and improve the thermal shock resistance of the coating; on the other hand, it can also avoid the situation where the coating is too dense due to all the powder being too small, leaving no room for thermal expansion and contraction during the thermal shock test, ultimately leading to the coating peeling off.

[0168] Example 6

[0169] This embodiment provides a method for preparing a silicon carbide-based composite ceramic coating. Except for the mass ratio of high-entropy rare earth monosilicate powder to high-entropy rare earth disilicate powder being 1:1, the preparation method is the same as in Example 1, and will not be repeated here.

[0170] Example 7

[0171] This embodiment provides a method for preparing a silicon carbide-based composite ceramic coating. Except for the mass ratio of high-entropy rare earth monosilicate powder to high-entropy rare earth disilicate powder being 10:1, the preparation method is the same as in Example 1, and will not be repeated here.

[0172] Example 8

[0173] This embodiment provides a method for preparing a silicon carbide-based composite ceramic coating. Except for the mass fraction of andalusite powder being 30%, the preparation method is the same as in Example 1, and will not be repeated here.

[0174] Example 9

[0175] This embodiment provides a method for preparing a silicon carbide-based composite ceramic coating. Except for the mass fraction of andalusite powder being 80%, the preparation method is the same as in Example 1, and will not be repeated here.

[0176] Example 10

[0177] This embodiment provides a method for preparing a silicon carbide-based composite ceramic coating, wherein the method replaces the high-entropy rare-earth monosilicate powder with Y particles of the same size. 0.25 Nd 0.25 Eu 0.25 Er 0.25 Except for the SiO5 powder, everything else is the same as in Example 1, and will not be repeated here.

[0178] Example 11

[0179] This embodiment provides a method for preparing a silicon carbide-based composite ceramic coating, wherein the method replaces the high-entropy rare-earth disilicate powder with Dy particles of the same size. 0.25 Sc 0.25 Eu 0.25 Er 0.25 Except for the Si2O7 powder, everything else is the same as in Example 1, and will not be repeated here.

[0180] In Examples 4-11, the thermal shock resistance and oxidation weight gain were tested using the same method as in Example 1, and the results are shown in Table 4.

[0181] Table 4

[0182] Example 4 Coating peeling -2.3％ Example 5 Cracks 0.8％ Example 6 Cracks 1.3％ Example 7 There are cracks and the coating is peeling off. -3.1％ Example 8 Cracks 2.1％ Example 9 Cracks 1.2％ Example 10 No cracks 1.5％ Example 11 No cracks 1.3％

[0183] The following points can be observed from Tables 1 to 4:

[0184] (1) As can be seen from the comprehensive examples 1 to 3, the method for preparing silicon carbide-based composite ceramic coating provided by the present invention is to prepare silicon carbide-based composite ceramic coating by slurry coating. It not only has low investment cost and low equipment requirements, but also can achieve more than 30 times without cracking at temperatures above 1500℃, and the oxidation weight gain rate is within 0.782%. It can better meet the requirements of burners for high temperature water and oxygen corrosion resistance at temperatures above 1300℃.

[0185] (2) It can be seen from the combined examples 1 and 4-5 that in example 1, only the andalusite powder was ball-milled. Compared with example 4, which directly used 250 mesh andalusite powder without ball milling, and example 5, which ball-milled the andalusite raw material, corundum powder and silica powder to a particle size of 7500 mesh, example 2 did not produce cracks after 50 thermal shocks at 1500℃, and the oxidation weight gain rate was only 0.25%. In example 4, the coating peeled off after 50 thermal shocks at 1500℃, and the oxidation weight gain rate was -2.3% (due to the coating peeling, the self-weight was reduced). In example 5, the coating cracked after 50 thermal shocks at 1500℃, and the oxidation weight gain rate reached 0.8%. This shows that the present invention preferably only ball-mills the andalusite powder and controls it within a specific particle size range, while other powders still maintain a larger particle size range, which can better improve the bonding strength between the coating and the ceramic, avoid the occurrence of cracks at high temperature and prevent the coating from falling off.

[0186] (3) It can be seen from the combined examples 1 and 6-7 that the content of high entropy rare earth disilicate in example 6 is too high. After corrosion, the surface of the coating is prone to forming porous and cracked rare earth monosilicate. The corrosive medium diffuses into the interior of the coating along the defects, which reduces the resistance to high temperature water and oxygen corrosion. The content of high entropy rare earth monosilicate in example 7 is too high. It is easy to react with SiO2 to form high disilicate, and the coefficient of thermal expansion increases. It is not compatible with the mullite coating and eventually leads to the failure of the coating peeling off. This shows that the present invention needs to use high entropy rare earth monosilicate as the main phase and high entropy rare earth disilicate as the second phase, and the mass ratio of the two should be controlled within a specific range in order to better improve the performance of the coating.

[0187] (4) As can be seen from the combined examples 1 and 8-9, in example 1, the ratio of andalusite: corundum powder: silica powder: first binder: first curing agent: first dispersant: ethanol was controlled to 70:20:10:20:4:6:50. In example 1, no cracks were generated after 50 thermal shocks at 1500℃, and the oxidation weight gain rate was only 0.25%. However, in examples 8-9, with all other factors remaining unchanged, the mass fraction of andalusite was adjusted to 30 or 80, which ultimately resulted in cracks being generated after 50 thermal shocks at 1500℃. The oxidation weight gain rates in examples 8-9 were 2.1% and 1.2%, respectively. This shows that the amount of andalusite added in this invention has a significant impact on the thermal shock resistance and oxidation corrosion resistance of the coating. It is preferable to control the amount of andalusite added within a specific range to better improve the thermal shock resistance and oxidation corrosion resistance of the coating.

[0188] (5) It can be seen from the combined examples 1 and 10-11 that Example 1 is a high-entropy rare earth silicate containing 5 rare earth elements, while Examples 10-11 each contain only 4 rare earth elements. The data shows that Examples 10-11 did not produce cracks after 50 thermal shocks at 1500℃, but the oxidation weight gain rate was higher than that of Example 1. This indicates that the present invention further preferably uses high-entropy rare earth silicates with at least 5 rare earth elements, which has better oxidation and corrosion resistance.

[0189] The present invention has been illustrated with the above embodiments to illustrate its detailed features, but the present invention is not limited to the above detailed features, that is, it does not mean that the present invention must rely on the above detailed features to be implemented. Those skilled in the art should understand that any improvements to the present invention, equivalent substitutions for the selected technical features, additions of auxiliary technical features, and selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present invention.

Claims

1. A silicon carbide-based composite ceramic coating, characterized in that, The silicon carbide-based composite ceramic coating includes a mullite underlayer disposed on the silicon carbide surface and a high-entropy rare earth silicate composite surface layer disposed on the mullite underlayer; the high-entropy rare earth silicate composite surface layer includes a main phase and a second phase, the main phase being a high-entropy rare earth monosilicate and the second phase being a high-entropy rare earth disilicate; the content of high-entropy rare earth disilicate in the high-entropy rare earth silicate composite surface layer is 10~25%; The mullite substrate comprises a mullite phase and amorphous silicon dioxide; The preparation of the mullite bottom layer slurry used in the preparation of the mullite bottom layer includes: first ball milling of andalusite raw material with a particle size of 250-450 mesh to obtain andalusite powder; mixing andalusite powder, corundum powder, silica powder, first binder, first curing agent, first dispersant and ethanol, and then ball milling and sieve filtration to obtain the mullite bottom layer slurry; the mass ratio of andalusite powder:corundum powder:silica powder:first binder:first curing agent:first dispersant:ethanol is (40-70):(10-30):(2-10):(20-60):(1-6):(2-10):(30-70); the particle size of the andalusite after the first ball milling is 1000-5000 mesh.

2. The silicon carbide-based composite ceramic coating according to claim 1, characterized in that, The content of amorphous silica in the mullite base layer is 5-20%.

3. The silicon carbide-based composite ceramic coating according to claim 2, characterized in that, The content of amorphous silica in the mullite base layer is 5-10%.

4. The silicon carbide-based composite ceramic coating according to claim 1, characterized in that, The content of high-entropy rare earth disilicate in the high-entropy rare earth silicate composite surface layer is 10-20%.

5. The silicon carbide-based composite ceramic coating according to claim 1, characterized in that, The chemical formula of the high-entropy rare-earth monosilicate is: … The chemical formula of the high-entropy rare-earth disilicate is 2SiO5. … )2Si2O7, where, RE i They are any one of the rare earth elements Sc, Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb or Lu, where n≥5 and 1≤i≤n.

6. The silicon carbide-based composite ceramic coating according to claim 1, characterized in that, The thickness of the mullite base layer is 50~200μm; the thickness of the high-entropy rare earth silicate composite surface layer is 100~200μm.

7. The silicon carbide-based composite ceramic coating according to claim 1, characterized in that, The density of the mullite substrate is 96%~99%.

8. A method for preparing a silicon carbide-based composite ceramic coating by slurry sintering according to any one of claims 1 to 7, characterized in that, The slurry sintering preparation method includes: (1) A silicon carbide substrate is impregnated in a mullite bottom slurry and then subjected to removal of excess slurry and drying. The preparation of the mullite bottom slurry includes: first ball milling of andalusite raw material with a particle size of 250-450 mesh to obtain andalusite powder; mixing andalusite powder, corundum powder, silica powder, first binder, first curing agent, first dispersant and ethanol, and then ball milling and sieve filtration to obtain the mullite bottom slurry; the particle size of andalusite after the first ball milling is 1000-5000 mesh; the mass ratio of andalusite powder: corundum powder: silica powder: first binder: first curing agent: first dispersant: ethanol is (40-70):(10-30):(2-10):(20-60):(1-6):(2-10):(30-70). (2) Repeat step (1) at least once to obtain a precursor containing a mullite coating; (3) The mullite-coated precursor described in step (2) is subjected to a first calcination and a first cooling to obtain a first silicon carbide ceramic material containing a mullite bottom layer; (4) In step (3), the first silicon carbide ceramic material is impregnated in a high-entropy rare earth silicate composite surface slurry, and then the excess slurry is removed and dried in sequence. (5) Repeat step (4) at least once to obtain a precursor material containing high-entropy rare earth silicate composite ceramics. (6) The precursor material containing high-entropy rare earth silicate composite ceramic in step (5) is subjected to a second calcination and a second cooling to obtain silicon carbide ceramic with silicon carbide-based composite ceramic coating.

9. The preparation method according to claim 8, characterized in that, The raw materials for the mullite bottom slurry include andalusite powder of 250-450 mesh, corundum powder of 700-900 mesh, and silica powder of 7500-9500 mesh.

10. The preparation method according to claim 8, characterized in that, The first ball milling is carried out in a pot mill.

11. The preparation method according to claim 8, characterized in that, The rotational speed of the first ball mill is 180~220 r / min.

12. The preparation method according to claim 8, characterized in that, The first ball milling time is 24~48 hours.

13. The preparation method according to claim 8, characterized in that, The second ball milling time is 6~24 hours.

14. The preparation method according to claim 8, characterized in that, The rotational speed of the second ball mill is 180~220 r / min.

15. The preparation method according to claim 8, characterized in that, The mesh size of the sieve used for filtration in step (1) is 100~200 mesh.

16. The preparation method according to claim 8, characterized in that, The removal of excess slurry in step (1) includes centrifugation and purging performed sequentially.

17. The preparation method according to claim 8, characterized in that, The drying described in step (1) includes baking.

18. The preparation method according to claim 8, characterized in that, The drying temperature in step (1) is 80~120℃.

19. The preparation method according to claim 8, characterized in that, The number of repetitions in step (2) is 1 to 5 times.

20. The preparation method according to claim 8, characterized in that, In step (3), the temperature of the first calcination is 1500~1600℃.

21. The preparation method according to claim 8, characterized in that, The first calcination time in step (3) is 3~10h.

22. The preparation method according to claim 8, characterized in that, The preparation of the high-entropy rare-earth silicate composite surface slurry in step (4) includes: High-entropy rare earth monosilicate powder, high-entropy rare earth disilicate powder, a second binder, a second curing agent, a second dispersant, and ethanol are mixed, and then subjected to a third ball milling and sieve filtration to obtain the high-entropy rare earth silicate composite surface slurry.

23. The preparation method according to claim 22, characterized in that, The mass ratio of the high-entropy rare earth monosilicate powder, the high-entropy rare earth disilicate powder, the second binder, the second curing agent, the second dispersant and ethanol is (70~90):(10~30):(20~60):(1~6):(2~10):(30~70).

24. The preparation method according to claim 22, characterized in that, The rotational speed of the third ball mill is 180~220 r / min.

25. The preparation method according to claim 22, characterized in that, The third ball milling time is 6~24 hours.

26. The preparation method according to claim 22, characterized in that, The mesh size of the sieve used for filtration in step (4) is 100~200 mesh.

27. The preparation method according to claim 22, characterized in that, The preparation processes of the high-entropy rare-earth monosilicate powder and the high-entropy rare-earth disilicate powder each independently include: S1, rare earth oxides and the third dispersant are mixed and then ball-milled to form a precursor slurry; S2. The precursor slurry is dried and sieved in sequence, and then sintered to obtain high-entropy rare earth silicate particles. S3. The high-entropy rare earth silicate particles are ball-milled and sieved in air to obtain high-entropy rare earth silicate powder.

28. The preparation method according to claim 27, characterized in that, The third dispersant includes water and / or ethanol.

29. The preparation method according to claim 27, characterized in that, The fourth ball milling time is 6~24 hours.

30. The preparation method according to claim 27, characterized in that, The rotational speed of the fourth ball mill is 300~400 r / min.

31. The preparation method according to claim 27, characterized in that, The heating rate of the sintering process is 5~10℃ / min.

32. The preparation method according to claim 27, characterized in that, The sintering temperature is 1500~1650℃.

33. The preparation method according to claim 27, characterized in that, The sintering synthesis time is 0.5~20h.

34. The preparation method according to claim 27, characterized in that, The fifth ball milling time is 6~20 hours.

35. The preparation method according to claim 27, characterized in that, The rotational speed of the fifth ball mill is 300~400 r / min.

36. The preparation method according to claim 22, characterized in that, The first adhesive and the second adhesive each independently comprise a resin with a carbon residue value greater than 35%, wherein the resin comprises any one or a combination of at least two of epoxy resin, phenolic resin, polyacrylic resin, polyvinyl butyral, furfural resin or phenol-furfural resin.

37. The preparation method according to claim 22, characterized in that, The first curing agent and the second curing agent each independently comprise any one or a combination of at least two of citric acid, p-toluenesulfonic acid, pentachlorophenate, or oxalic acid.

38. The preparation method according to claim 22, characterized in that, The first dispersant and the second dispersant each independently comprise any one or a combination of at least two of castor oil, trioleic acid glyceride, Tween 20, or organobentonite.

39. The preparation method according to claim 8, characterized in that, The silicon carbide substrate has a porous structure.

40. The application of a silicon carbide-based composite ceramic coating according to any one of claims 1 to 7 in a porous medium burner in a medium-high temperature field, wherein the temperature in the medium-high temperature field is ≥1300℃.

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