An antioxidant gradient coating for C / C composite material and its preparation method

Abstract

This invention discloses an antioxidant gradient coating for C / C composite materials and its preparation method, comprising preparing suspensions A, B, and C respectively: after preheating the C / C-SiC sample, it is sequentially immersed in suspensions A, B, and C from step 1 for 10-20 seconds, then removed, cleaned, and dried to obtain a B2O3@SiO2 / SiB6@Al2O3-SiC coating sample. This preparation method increases the toughness of the SiC-B2O3@SiO2 / SiB6@Al2O3 coating sample, and the SiC-B2O3@SiO2 / SiB6@Al2O3 coating sample can form flowing SiO2·B2O3 at high temperatures, which can provide high-temperature protection for the C / C composite matrix and self-repair cracks appearing on the SiC-B2O3@SiO2 / SiB6@Al2O3 coating sample, thereby improving the protective effect of the coating.

Description

Technical Field

[0001] This invention belongs to the field of composite material technology, specifically to an antioxidant gradient coating on the surface of a C / C composite material and its preparation method. Background Technology

[0002] Carbon-carbon composites are composite materials prepared by high-temperature pyrolysis of carbon fibers and carbon matrix. The literature [Huang Jianfeng, Zhang Yutao, Li Hejun, Zeng Xierong, Cao Liyun. New progress in the research of high-temperature anti-oxidation coatings of carbon / carbon composites in China [J]. Journal of Aeronautical Materials, 2007(02):74-78.] mentions that carbon-carbon composites are widely used in aviation, aerospace, and shipbuilding due to their advantages such as high-temperature anti-oxidation properties, high strength, and good thermal conductivity. However, it has been found that due to the relatively weak chemical bond structure between carbon atoms in carbon-carbon composites, they are prone to oxidation reactions at high temperatures. This oxidation reaction leads to a decrease in the mechanical properties of the material, a shortened lifespan, and even damage to the material structure, resulting in poor performance of coatings prepared from this composite material. Therefore, anti-oxidation technology has become an important direction in the research of carbon-carbon composites.

[0003] Currently, silicon carbide (SiC) is commonly used in the market. Due to its extremely high melting point and thermal stability, SiC exhibits excellent physicochemical compatibility with C / C composite matrices and forms good interfacial adhesion with the C / C matrix. Therefore, SiC has always been a fundamental material for anti-oxidation coatings on C / C composites. However, simply coating a C / C composite matrix with SiC alone cannot provide long-term effective protection.

[0004] To address the limitations of single-component SiC coatings, the use of boron oxide (B₂O₃), with its excellent antioxidant properties, has been proposed. Due to its low melting point (450℃), the resulting glassy phase exhibits good fluidity and can fill defects such as cracks and pores, making it a common choice for anti-oxidation coatings on C / C composite matrices. However, the rapid volatilization rate of boron oxide (B₂O₃) at high temperatures limits its antioxidant applications.

[0005] Meanwhile, silicon boride (SiB6), which has a high melting point (2503K) and excellent oxidation resistance, is also used in the market. Silicon boride (SiB6) forms a borosilicate glass phase at temperatures exceeding 823K. This glass phase exhibits excellent oxidation resistance and can heal defects such as cracks in the sealing coating at high temperatures. However, SiB6 has a low initial oxidation temperature and cannot generate enough glass phase within a specific temperature range to heal cracks, easily leading to the destruction of the C / C composite matrix.

[0006] Two core-shell structured coatings, SiB6@Al2O3 and B2O3@SiO2, have been proposed for the market. The core-shell structure is an ordered, nanoscale assembly formed by one nanomaterial encapsulating another through chemical bonds or other interactions. This structure can endow many new properties that cannot be obtained from single nanoparticles. Since SiO2 nanomaterials are simple to synthesize and have easily controllable particle size, combined with its good mechanical properties and excellent thermal and chemical stability, they can protect the encapsulated particles. Using Al2O3 as a suitable shell material, two coatings can be prepared by reacting with B2O3, the oxidation product of SiB6, at 900-1300℃. These two coatings can not only generate abundant glass-phase healed cracks but also achieve the purpose of toughening. However, while both coatings can protect the C / C composite matrix, they cannot self-repair, resulting in limited protection for the C / C composite matrix. After repeated use, the protective effect gradually decreases, leading to the destruction of the C / C composite matrix. Summary of the Invention

[0007] To address the problem that existing protective coatings on C / C composite matrices cannot self-repair and their protective effect decreases with repeated use, leading to damage to the C / C composite matrix, this invention provides an antioxidant gradient coating for the surface of C / C composite materials and its preparation method.

[0008] To achieve the above objectives, the present invention provides the following technical solution:

[0009] This invention discloses a method for preparing an antioxidant gradient coating on the surface of a C / C composite material, comprising the following steps:

[0010] Step 1: Prepare suspensions A, B, and C separately.

[0011] SiB6@Al2O3 core-shell powder and B2O3@SiO2 core-shell powder are mixed to obtain a mixed powder A1 with a SiB6@Al2O3 core-shell powder content of 5% to 40%. The mixed powder A1 is added to a first mixture prepared by silica sol and water in a volume ratio of 1:2 to 4, and the mixture is stirred to obtain a suspension A.

[0012] SiB6@Al2O3 core-shell powder and B2O3@SiO2 core-shell powder are mixed to obtain mixed powder B1 with SiB6@Al2O3 core-shell powder accounting for 20% to 60%. The mixed powder B1 is added to a first mixture prepared by silica sol and water in a volume ratio of 1:2 to 4, and the mixture is stirred to obtain suspension B.

[0013] SiB6@Al2O3 core-shell powder and B2O3@SiO2 core-shell powder are mixed to obtain a mixed powder C1 with a SiB6@Al2O3 core-shell powder ratio of 40% to 80%. The mixed powder C1 is added to a first mixture prepared by silica sol and water in a volume ratio of 1:2 to 4, and the mixture is stirred to obtain a suspension C.

[0014] Step 2: After preheating the C / C-SiC sample, immerse it sequentially in suspension A, suspension B and suspension C from step 1 for 10-20 seconds, then remove it, clean and dry it to obtain the B2O3@SiO2 / SiB6@Al2O3-SiC coating sample.

[0015] Furthermore, the C / C-SiC sample is prepared by embedding a C / C sample.

[0016] Furthermore, the embedding process includes:

[0017] The C / C sample was embedded in the first powder and kept at a temperature of 2000-2400℃ under a protective gas for 2-8 hours to obtain a single-embedded C / C sample.

[0018] The C / C sample that was first embedded is then embedded in a second powder and kept at a temperature of 2000-2400℃ under a protective gas for 2-8 hours to obtain the C / C-SiC sample.

[0019] Furthermore, in the encapsulation process, the first powder is obtained by mixing silicon powder, carbon powder and yttrium oxide powder in a mass percentage ratio of 70%:20%:10%;

[0020] The second powder is obtained by mixing silicon powder, carbon powder and zirconium oxide powder in a mass percentage ratio of 60%:35%:5%.

[0021] Furthermore, the protective gas is one or more of argon, helium, and nitrogen.

[0022] Further, the preparation of SiB6@Al2O3 core-shell powder and B2O3@SiO2 core-shell powder in step 1 includes:

[0023] Preparation of the SiB6@Al2O3 core-shell powder: Silicon boride is added to deionized water to prepare a first solution of 2-5 g / L. The solution is magnetically stirred for 12-16 h. An aqueous solution of aluminum nitrate nonahydrate is added to the first solution, and a first pH adjuster is added to adjust the pH value of the first solution to 7-9. The solution is magnetically stirred for 16-24 h to obtain a SiB6@Al(OH)3 suspension. Then, the suspension is sequentially filtered, dried, and calcined to obtain the SiB6@Al2O3 powder.

[0024] Preparation of the B2O3@SiO2 core-shell powder: Boron oxide is added to a third solution prepared by deionized water and anhydrous ethanol to prepare a second solution with a concentration of 5-10 g / L. Then, a second mixture and a second pH adjuster are slowly added to the second solution to adjust the pH value of the second solution to 7-8. The mixture is stirred for 16-24 h to obtain a B2O3@Si(OH)4 suspension. After centrifugation and washing with water, B2O3@Si(OH)4 powder is obtained. The B2O3@Si(OH)4 powder is calcined for 3-8 h to obtain the B2O3@SiO2 powder.

[0025] Furthermore, in the preparation of SiB6@Al2O3 core-shell powder, the mass ratio of aluminum nitrate nonahydrate to silicon boride is 6-9:1.

[0026] Furthermore, in the preparation of the B2O3@SiO2 core-shell powder, the third solution is prepared by mixing deionized water and anhydrous ethanol in a volume ratio of 1:2 to 4; the second mixture is prepared by mixing tetraethyl orthosilicate and anhydrous ethanol in a volume ratio of 1:5 to 7.

[0027] Furthermore, the first pH adjuster is one or both of ammonia and sodium carbonate; the second pH adjuster is ammonia.

[0028] The present invention also discloses an antioxidant gradient coating on the surface of a C / C composite material prepared by the above method.

[0029] Compared with the prior art, the present invention has the following beneficial technical effects:

[0030] This invention discloses a method for preparing an antioxidant gradient coating on the surface of a C / C composite material. The method involves mixing SiB6@Al2O3 core-shell powder with B2O3@SiO2 core-shell powder to obtain a mixed powder A1 with 5%–40% SiB6@Al2O3 core-shell powder, a mixed powder B1 with 20%–60% SiB6@Al2O3 core-shell powder, and a mixed powder C1 with 40%–80% SiB6@Al2O3 core-shell powder. Suspensions A, B, and C are then prepared. A C / C-SiC sample is sequentially immersed in suspensions A, B, and C for impregnation, thereby forming a coating structure distributed according to an objective temperature profile. The outermost layer, with its higher temperature, contains SiB6@Al2O3 core-shell microcolloids. The high content of B2O3@SiO2 core-shell microcapsules in the SiC-B2O3@SiO2 / SiB6@Al2O3 coating samples, with a relatively low innermost temperature, results in a gradient coating within the sample. This increases the toughness of the SiC-B2O3@SiO2 / SiB6@Al2O3 coating. Furthermore, the SiC-B2O3@SiO2 / SiB6@Al2O3 coating samples can form flowing SiO2·B2O3 at high temperatures, providing high-temperature protection for the C / C composite matrix and enabling self-repair of cracks appearing on the SiC-B2O3@SiO2 / SiB6@Al2O3 coating samples, thus enhancing the protective effect of the SiC-B2O3@SiO2 / SiB6@Al2O3 coating on the C / C composite matrix.

[0031] Furthermore, in the preparation method proposed in this invention, the C / C-SiC sample is coated by impregnation, resulting in mild reaction conditions. During the impregnation process, only the impregnation temperature and cleaning time need to be adjusted. Therefore, the method is simple to operate, easy to implement, effectively improves the preparation efficiency, reduces the production cost, and generates no waste, making it environmentally friendly.

[0032] Furthermore, in the preparation method proposed in this invention, the C / C-SiC sample is prepared by embedding the C / C sample. In this embedding process, the C / C sample is sequentially embedded in a first powder and a second powder, and kept at a temperature of 2000-2400℃ under a protective gas for 2-8 hours. This method is simple and convenient, and can improve the preparation efficiency of B2O3@SiO2 / SiB6@Al2O3-SiC coating samples.

[0033] Furthermore, the preparation of the B2O3@SiO2 core-shell powder involves adding boron oxide to a third solution prepared from deionized water and anhydrous ethanol, then adding a second pH adjuster to adjust the pH value, and finally centrifuging and washing to obtain B2O3@Si(OH)4 powder. The B2O3@Si(OH)4 powder is then calcined for 3–8 hours to obtain B2O3@SiO2 powder. Similarly, the preparation of B6@Al2O3 core-shell powder involves adding silicon boride to deionized water, then adding a second pH adjuster to adjust the pH value, and finally sequentially filtering, drying, and calcining to obtain SiB6@Al2O3 powder. The preparation of both B2O3@SiO2 and SiB6@Al2O3 powders is environmentally friendly and simple, as no waste gas is generated during the process.

[0034] The present invention also discloses an antioxidant gradient coating on the surface of C / C composite material. This antioxidant gradient coating can form flowing SiO2·B2O3 at high temperature, thereby providing high-temperature protection for the C / C composite material matrix and automatically repairing cracks generated on the SiC-B2O3@SiO2 / SiB6@Al2O3 antioxidant gradient coating. Attached Figure Description

[0035] Figure 1 SEM image of the B2O3@SiO2 / SiB6@Al2O3-SiC coating surface prepared by the method for preparing an antioxidant gradient coating on the surface of a C / C composite material provided by the present invention;

[0036] Figure 2 XRD pattern of the B2O3@SiO2 / SiB6@Al2O3-SiC coating surface prepared by the method for preparing an antioxidant gradient coating on the surface of a C / C composite material provided by the present invention;

[0037] Figure 3 Thermal shock resistance curves of B2O3@SiO2 / SiB6@Al2O3-SiC coating samples prepared by the method for preparing an antioxidant gradient coating on the surface of a C / C composite material provided by the present invention in air at 1573K. Detailed Implementation

[0038] In the following description, only certain exemplary embodiments are briefly described. As those skilled in the art will recognize, the described embodiments can be modified in various ways without departing from the spirit or scope of the invention. Therefore, the drawings and description are considered to be exemplary in nature and not restrictive.

[0039] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," "counterclockwise," "axial," "radial," and "circumferential" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0040] Furthermore, the terms "first" and "second" 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. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this invention, "a plurality of" means two or more, unless otherwise explicitly specified.

[0041] In this invention, unless otherwise explicitly specified and limited, "above" or "below" the second feature can include direct contact between the first and second features, or contact between the first and second features through another feature between them. Furthermore, "above," "over," and "on top" of the second feature includes the first feature being directly above or diagonally above the second feature, or simply indicates that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature includes the first feature being directly above or diagonally above the second feature, or simply indicates that the first feature is at a lower horizontal level than the second feature.

[0042] The embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

[0043] This invention discloses a method for preparing an antioxidant gradient coating on the surface of a C / C composite material, specifically including the following steps:

[0044] Step 1: Prepare suspensions A, B, and C separately.

[0045] C / C-SiC samples were prepared by embedding C / C samples.

[0046] Specifically, the C / C composite material was polished with 400-grit, 800-grit, and 1500-grit sandpaper to remove its surface sharp edges, ultrasonically cleaned with ethanol for 30 minutes, and then placed in a forced-air drying oven at 60°C for 3 hours to obtain the C / C sample.

[0047] The C / C sample was embedded in a graphite crucible filled with the first powder. The temperature of the graphite crucible was adjusted to 2000-2400℃. Then, a protective gas was introduced into the graphite crucible and kept at the temperature for 2-8 hours to obtain a first-embedded C / C sample.

[0048] The C / C sample was then embedded in a graphite crucible filled with a second powder. The temperature of the graphite crucible was adjusted to 2000–2400 °C. A protective gas was then introduced into the graphite crucible and kept at that temperature for 2–8 hours to obtain the C / C-SiC sample.

[0049] The first mixture is prepared by mixing silica sol and water in a volume ratio of 1:2 to 4; the first powder is prepared by mixing silicon powder, carbon powder and yttrium oxide powder in a mass percentage ratio of 70%:20%:10%; the second powder is prepared by mixing silicon powder, carbon powder and zirconium oxide powder in a mass percentage ratio of 60%:35%:5%; and the protective gas is one or more of argon, helium and nitrogen.

[0050] Preparation of SiB6@Al2O3 core-shell powder and B2O3@SiO2 core-shell powder;

[0051] Specifically,

[0052] Preparation of B6@Al2O3 core-shell powder:

[0053] Silicon boride was added to deionized water to prepare a first solution of 2-5 g / L. The solution was magnetically stirred for 12-16 h. An aqueous solution of aluminum nitrate nonahydrate was added to the first solution, and a first pH adjuster was added to adjust the pH value of the first solution to 7-9. The solution was magnetically stirred for 16-24 h to obtain a SiB6@Al(OH)3 suspension. The suspension was then subjected to filtration, drying, and calcination at 300 °C to obtain SiB6@Al2O3 powder.

[0054] The mass ratio of aluminum nitrate nonahydrate to silicon borate is 6–9:1, and the first pH adjuster is one or both of ammonia and sodium carbonate.

[0055] Preparation of B2O3@SiO2 core-shell powder:

[0056] Boron oxide was added to a third solution prepared from deionized water and anhydrous ethanol to prepare a second solution with a concentration of 5–10 g / L. Then, a second mixture prepared from tetraethyl orthosilicate and anhydrous ethanol at a volume ratio of 1:5–7 and a second pH adjuster were slowly added to the second solution. The pH value of the second solution prepared from deionized water and anhydrous ethanol at a volume ratio of 1:2–4 was adjusted to 7–8. The mixture was stirred for 16–24 h to obtain a B2O3@Si(OH)4 suspension. After centrifugation and washing with water, B2O3@Si(OH)4 powder was obtained. The B2O3@Si(OH)4 powder was calcined at 300 °C for 3–8 h to obtain B2O3@SiO2 powder.

[0057] The second pH adjuster is ammonia.

[0058] Preparation of suspension A:

[0059] The prepared SiB6@Al2O3 core-shell powder was mixed with B2O3@SiO2 core-shell powder to obtain a mixed powder A1 with a SiB6@Al2O3 core-shell powder content of 5% to 40%. The mixed powder A1 was added to a first mixture prepared by silica sol and water in a volume ratio of 1:2 to 4, and the mixture was magnetically stirred for 15 to 20 hours to obtain suspension A.

[0060] Preparation of suspension B:

[0061] The prepared SiB6@Al2O3 core-shell powder was mixed with B2O3@SiO2 core-shell powder to obtain mixed powder B1 with a SiB6@Al2O3 core-shell powder ratio of 20% to 60%. Mixed powder B1 was added to a first mixture prepared by silica sol and water in a volume ratio of 1:2 to 4, and magnetically stirred for 15 to 20 hours to obtain suspension B.

[0062] Preparation of suspension C:

[0063] The prepared SiB6@Al2O3 core-shell powder was mixed with B2O3@SiO2 core-shell powder to obtain a mixed powder C1 with a SiB6@Al2O3 core-shell powder ratio of 40% to 80%. The mixed powder C1 was added to a first mixture prepared by silica sol and water in a volume ratio of 1:2 to 4, and the mixture was magnetically stirred for 15 to 20 hours to obtain a suspension C.

[0064] Step 2: After preheating the C / C-SiC sample, immerse it sequentially in suspension A, suspension B and suspension C from step 1 for 10-20 seconds, then remove it, clean and dry it to obtain the B2O3@SiO2 / SiB6@Al2O3-SiC coating sample.

[0065] Specifically, the C / C-SiC sample is preheated to 200-300°C, then directly immersed in the suspension A prepared in step 2 for 10-20 seconds, then removed and ultrasonically cleaned for 10-20 seconds. After ultrasonic cleaning, it is placed in an oven at 60-70°C and dried for 1-2 minutes. The above operation is repeated until a first coating with a thickness of 10-20 μm appears on the C / C-SiC sample, thus obtaining the first coating sample.

[0066] The first coating sample is preheated to 200-300°C and then immersed in the suspension B prepared in step 2 for 10-20 seconds. After immersion, it is ultrasonically cleaned for 10-20 seconds and then placed in an oven at 60-70°C for 1-2 minutes. The above operation is repeated until a second coating with a thickness of 10-20 μm appears on the first coating sample, thus obtaining the second coating sample.

[0067] The second coating sample is preheated to 200-300°C, immersed in the suspension C prepared in step 2 for 10-20 seconds, then removed and ultrasonically cleaned for 10-20 seconds. After ultrasonic cleaning, it is placed in an oven at 60-70°C and dried for 1-2 minutes. The above operation is repeated until a third coating with a thickness of 10-20 μm appears on the first coating sample, thus obtaining the B2O3@SiO2 / SiB6@Al2O3-SiC coating sample.

[0068] The B2O3@SiO2 / SiB6@Al2O3 anti-oxidation coating prepared by the above method can form flowing SiO2·B2O3 at high temperature for high-temperature protection and crack self-repair of C / C composite matrix, and the generated mullite whiskers can toughen the coating.

[0069] The above method will be further explained and illustrated below with reference to the embodiments:

[0070] Example 1:

[0071] Step 1: Prepare suspensions A, B, and C separately.

[0072] The C / C composite material was polished with 400-grit, 800-grit, and 1500-grit sandpaper to remove its surface sharp edges. It was then ultrasonically cleaned with ethanol for 30 minutes. The sample was placed in a forced-air drying oven at 60°C and dried for 3 hours to obtain the C / C sample.

[0073] The C / C sample was embedded in a graphite crucible filled with a first powder material obtained by mixing silicon powder, carbon powder and yttrium oxide powder in a mass percentage ratio of 70%:20%:10%. The temperature of the graphite crucible was adjusted to 2100℃, and then argon gas was introduced into the graphite crucible for protection. The temperature was maintained for 8 hours to obtain a first-embedded C / C sample.

[0074] The C / C sample was then embedded in a graphite crucible filled with a second powder mixture of silicon powder, carbon powder and zirconium oxide powder in a mass percentage ratio of 60%:35%:5%. The temperature of the graphite crucible was adjusted to 2100℃, and then argon gas was introduced into the graphite crucible for protection. The crucible was kept at this temperature for 8 hours to obtain the C / C-SiC sample.

[0075] Preparation of B6@Al2O3 core-shell powder:

[0076] 3.6 g of silicon boride was added to deionized water to prepare a first solution with a concentration of 4 g / L. The solution was magnetically stirred for 15 h. Aluminum nitrate nonahydrate was added to the first solution, with a mass ratio of aluminum nitrate nonahydrate to silicon boride of 8:1. Then, ammonia was added to the solution to adjust the pH value of the first solution to 7.5. The solution was magnetically stirred for 20 h to obtain a SiB6@Al(OH)3 suspension. The suspension was then subjected to filtration, drying, and calcination at 300 °C to obtain SiB6@Al2O3 powder.

[0077] Preparation of B2O3@SiO2 core-shell powder:

[0078] A third solution of 0.25 L was prepared by mixing deionized water and anhydrous ethanol at a volume ratio of 1:3. Boron oxide was added to the third solution to prepare a second solution of 8 g / L. Then, a second mixture of 0.024 L prepared by mixing tetraethyl orthosilicate and anhydrous ethanol at a volume ratio of 1:5 was slowly added dropwise to the second solution, and ammonia was added simultaneously to adjust the pH of the second solution to 8. The mixture was stirred for 20 h to obtain a B2O3@Si(OH)4 suspension. After centrifugation and washing with water, B2O3@Si(OH)4 powder was obtained. The B2O3@Si(OH)4 powder was calcined at 300℃ for 5 h to obtain B2O3@SiO2 powder.

[0079] Preparation of suspension A:

[0080] The prepared SiB6@Al2O3 core-shell powder was mixed with B2O3@SiO2 core-shell powder to obtain a mixed powder A1 with a mass ratio of 10% SiB6@Al2O3 core-shell powder. 4g of mixed powder A1 was added to 0.04L of a first mixed liquid prepared by silica sol and water in a volume ratio of 1:3. The mixture was magnetically stirred for 20h to obtain suspension A.

[0081] Preparation of suspension B:

[0082] The prepared SiB6@Al2O3 core-shell powder was mixed with B2O3@SiO2 core-shell powder to obtain mixed powder B1 with a mass ratio of 30% SiB6@Al2O3 core-shell powder. 4g of mixed powder B1 was added to 0.04L of the first mixture prepared by silica sol and water in a volume ratio of 1:3. The mixture was magnetically stirred for 20h to obtain suspension B.

[0083] Preparation of suspension C:

[0084] The prepared SiB6@Al2O3 core-shell powder was mixed with B2O3@SiO2 core-shell powder to obtain a mixed powder C1 with a mass ratio of 50% SiB6@Al2O3 core-shell powder. 4g of the mixed powder C1 was added to 0.04L of a first mixed liquid prepared by silica sol and water in a volume ratio of 1:3. The mixture was magnetically stirred for 20h to obtain a suspension C.

[0085] Step 2: After preheating the C / C-SiC sample, immerse it sequentially in suspension A, suspension B and suspension C from step 1 for 10-20 seconds, then remove it, clean and dry it to obtain the B2O3@SiO2 / SiB6@Al2O3-SiC coating sample.

[0086] The C / C-SiC sample prepared in step 1 is preheated to 260°C, then directly immersed in the prepared suspension A for 15 seconds and then taken out. After ultrasonic cleaning for 15 seconds, it is placed in an oven at 70°C and dried for 1 minute. The above operation is repeated until a first coating with a thickness of 10 μm appears on the C / C-SiC sample, thus obtaining the first coating sample.

[0087] The first coating sample was preheated to 260°C, then immersed directly in the prepared suspension B for 15 seconds and then removed. After ultrasonic cleaning for 15 seconds, it was placed in an oven at 70°C and dried for 1 minute. The above operation was repeated until a second coating with a thickness of 10 μm appeared on the first coating sample, thus obtaining the second coating sample.

[0088] The obtained second coating sample was preheated to 260°C, then directly immersed in the prepared suspension C for 15 seconds, and then ultrasonically cleaned for 15 seconds. After ultrasonic cleaning, it was placed in an oven at 70°C and dried for 1 minute. The above operation was repeated until a third coating with a thickness of 10 μm appeared on the first coating sample, thus obtaining the B2O3@SiO2 / SiB6@Al2O3-SiC coating sample.

[0089] Example 2:

[0090] Step 1: Prepare suspensions A, B, and C separately.

[0091] The C / C composite material was polished with 400-grit, 800-grit, and 1500-grit sandpaper to remove its surface sharp edges. It was then ultrasonically cleaned with ethanol for 30 minutes. The sample was placed in a forced-air drying oven at 60°C and dried for 3 hours to obtain the C / C sample.

[0092] The C / C sample was embedded in a graphite crucible filled with a first powder material obtained by mixing silicon powder, carbon powder and yttrium oxide powder in a mass percentage ratio of 70%:20%:10%. The temperature of the graphite crucible was adjusted to 2100℃, and then argon gas was introduced into the graphite crucible for protection. The temperature was maintained for 8 hours to obtain a first-embedded C / C sample.

[0093] The C / C sample was then embedded in a graphite crucible filled with a second powder mixture of silicon powder, carbon powder and zirconium oxide powder in a mass percentage ratio of 60%:35%:5%. The temperature of the graphite crucible was adjusted to 2100℃, and then argon gas was introduced into the graphite crucible for protection. The crucible was kept at this temperature for 8 hours to obtain the C / C-SiC sample.

[0094] Preparation of B6@Al2O3 core-shell powder:

[0095] 3.6 g of silicon boride was added to deionized water to prepare a first solution with a concentration of 4 g / L. The solution was magnetically stirred for 15 h. Aluminum nitrate nonahydrate was added to the first solution, with a mass ratio of aluminum nitrate nonahydrate to silicon boride of 8:1. Sodium carbonate was then added to the solution to adjust the pH value of the first solution to 7.5. The solution was magnetically stirred for 20 h to obtain a SiB6@Al(OH)3 suspension. The suspension was then subjected to filtration, drying, and calcination at 300 °C to obtain SiB6@Al2O3 powder.

[0096] Preparation of B2O3@SiO2 core-shell powder:

[0097] A third solution of 0.25 L was prepared by mixing deionized water and anhydrous ethanol at a volume ratio of 1:3. Boron oxide was added to the third solution to prepare a second solution of 8 g / L. Then, a second mixture of 0.024 L prepared by mixing tetraethyl orthosilicate and anhydrous ethanol at a volume ratio of 1:5 was slowly added dropwise to the second solution, and ammonia was added simultaneously to adjust the pH of the second solution to 8. The mixture was stirred for 20 h to obtain a B2O3@Si(OH)4 suspension. After centrifugation and washing with water, B2O3@Si(OH)4 powder was obtained. The B2O3@Si(OH)4 powder was calcined at 300℃ for 5 h to obtain B2O3@SiO2 powder.

[0098] Preparation of suspension A:

[0099] The prepared SiB6@Al2O3 core-shell powder was mixed with B2O3@SiO2 core-shell powder to obtain a mixed powder A1 with a SiB6@Al2O3 core-shell powder mass ratio of 20%. 4g of mixed powder A1 was added to 0.04L of a first mixed liquid prepared by silica sol and water in a volume ratio of 1:3. The mixture was magnetically stirred for 15h to obtain suspension A.

[0100] Preparation of suspension B:

[0101] The prepared SiB6@Al2O3 core-shell powder was mixed with B2O3@SiO2 core-shell powder to obtain mixed powder B1 with a mass ratio of 40% SiB6@Al2O3 core-shell powder. 4g of mixed powder B1 was added to 0.04L of the first mixture prepared by silica sol and water in a volume ratio of 1:3. The mixture was magnetically stirred for 15h to obtain suspension B.

[0102] Preparation of suspension C:

[0103] The prepared SiB6@Al2O3 core-shell powder was mixed with B2O3@SiO2 core-shell powder to obtain a mixed powder C1 with a SiB6@Al2O3 core-shell powder mass ratio of 60%. 4g of mixed powder C1 was added to 0.04L of a first mixed liquid prepared by silica sol and water in a volume ratio of 1:3. The mixture was magnetically stirred for 15h to obtain a suspension C.

[0104] Step 2: After preheating the C / C-SiC sample, immerse it sequentially in suspension A, suspension B and suspension C from step 1 for 10-20 seconds, then remove it, clean and dry it to obtain the B2O3@SiO2 / SiB6@Al2O3-SiC coating sample.

[0105] The C / C-SiC sample prepared in step 1 is preheated to 260°C, then directly immersed in the prepared suspension A for 15 seconds and then taken out. After ultrasonic cleaning for 15 seconds, it is placed in an oven at 70°C and dried for 1 minute. The above operation is repeated until a first coating with a thickness of 12 μm appears on the C / C-SiC sample, thus obtaining the first coating sample.

[0106] The first coating sample was preheated to 260°C, then immersed directly in the prepared suspension B for 15 seconds and then removed. After ultrasonic cleaning for 15 seconds, it was placed in an oven at 70°C and dried for 1 minute. The above operation was repeated until a second coating with a thickness of 12 μm appeared on the first coating sample, thus obtaining the second coating sample.

[0107] The obtained second coating sample was preheated to 260°C, then directly immersed in the prepared suspension C for 15 seconds, and then ultrasonically cleaned for 15 seconds. After ultrasonic cleaning, it was placed in an oven at 70°C and dried for 1 minute. The above operation was repeated until a third coating with a thickness of 12 μm appeared on the first coating sample, thus obtaining the B2O3@SiO2 / SiB6@Al2O3-SiC coating sample.

[0108] Example 3:

[0109] Step 1: Prepare suspensions A, B, and C separately.

[0110] The C / C composite material was polished with 400-grit, 800-grit, and 1500-grit sandpaper to remove its surface sharp edges. It was then ultrasonically cleaned with ethanol for 30 minutes. The sample was placed in a forced-air drying oven at 60°C and dried for 3 hours to obtain the C / C sample.

[0111] The C / C sample was embedded in a graphite crucible filled with a first powder material obtained by mixing silicon powder, carbon powder and yttrium oxide powder in a mass percentage ratio of 70%:20%:10%. The temperature of the graphite crucible was adjusted to 2100℃, and then argon gas was introduced into the graphite crucible for protection. The temperature was maintained for 8 hours to obtain a first-embedded C / C sample.

[0112] The C / C sample was then embedded in a graphite crucible filled with a second powder mixture of silicon powder, carbon powder and zirconium oxide powder in a mass percentage ratio of 60%:35%:5%. The temperature of the graphite crucible was adjusted to 2100℃, and then argon gas was introduced into the graphite crucible for protection. The crucible was kept at this temperature for 8 hours to obtain the C / C-SiC sample.

[0113] Preparation of B6@Al2O3 core-shell powder:

[0114] 3.6 g of silicon boride was added to deionized water to prepare a first solution with a concentration of 4 g / L. The solution was magnetically stirred for 15 h. Aluminum nitrate nonahydrate was added to the first solution, with a mass ratio of aluminum nitrate nonahydrate to silicon boride of 8:1. Then, ammonia was added to the solution to adjust the pH value of the first solution to 7.5. The solution was magnetically stirred for 20 h to obtain a SiB6@Al(OH)3 suspension. The suspension was then subjected to filtration, drying, and calcination at 300 °C to obtain SiB6@Al2O3 powder.

[0115] Preparation of B2O3@SiO2 core-shell powder:

[0116] A third solution of 0.25 L was prepared by mixing deionized water and anhydrous ethanol at a volume ratio of 1:3. Boron oxide was added to the third solution to prepare a second solution of 8 g / L. Then, a second mixture of 0.024 L prepared by mixing tetraethyl orthosilicate and anhydrous ethanol at a volume ratio of 1:5 was slowly added dropwise to the second solution, and ammonia was added simultaneously to adjust the pH of the second solution to 8. The mixture was stirred for 20 h to obtain a B2O3@Si(OH)4 suspension. After centrifugation and washing with water, B2O3@Si(OH)4 powder was obtained. The B2O3@Si(OH)4 powder was calcined at 300℃ for 5 h to obtain B2O3@SiO2 powder.

[0117] Preparation of suspension A:

[0118] The prepared SiB6@Al2O3 core-shell powder was mixed with B2O3@SiO2 core-shell powder to obtain a mixed powder A1 with a mass ratio of 30% SiB6@Al2O3 core-shell powder. 4g of mixed powder A1 was added to 0.04L of a first mixed liquid prepared by silica sol and water in a volume ratio of 1:3. The mixture was magnetically stirred for 18h to obtain suspension A.

[0119] Preparation of suspension B:

[0120] The prepared SiB6@Al2O3 core-shell powder was mixed with B2O3@SiO2 core-shell powder to obtain a mixed powder B1 with a mass ratio of 50% SiB6@Al2O3 core-shell powder. 4g of mixed powder B1 was added to 0.04L of a first mixed liquid prepared by silica sol and water in a volume ratio of 1:3. The mixture was magnetically stirred for 18h to obtain suspension B.

[0121] Preparation of suspension C:

[0122] The prepared SiB6@Al2O3 core-shell powder was mixed with B2O3@SiO2 core-shell powder to obtain a mixed powder C1 with a SiB6@Al2O3 core-shell powder mass ratio of 70%. 4g of mixed powder C1 was added to 0.04L of a first mixed liquid prepared by silica sol and water in a volume ratio of 1:3. The mixture was magnetically stirred for 18h to obtain a suspension C.

[0123] Step 2: After preheating the C / C-SiC sample, immerse it sequentially in suspension A, suspension B and suspension C from step 1 for 10-20 seconds, then remove it, clean and dry it to obtain the B2O3@SiO2 / SiB6@Al2O3-SiC coating sample.

[0124] The C / C-SiC sample prepared in step 1 is preheated to 250°C, then directly immersed in the prepared suspension A for 15 seconds and then taken out. After ultrasonic cleaning for 15 seconds, it is placed in an oven at 70°C and dried for 1 minute. The above operation is repeated until a first coating with a thickness of 14 μm appears on the C / C-SiC sample, thus obtaining the first coating sample.

[0125] The first coating sample was preheated to 250°C, then immersed directly in the prepared suspension B for 15 seconds and then removed. After ultrasonic cleaning for 15 seconds, it was placed in an oven at 70°C and dried for 1 minute. The above operation was repeated until a second coating with a thickness of 14 μm appeared on the first coating sample, thus obtaining the second coating sample.

[0126] The obtained second coating sample was preheated to 250°C, then directly immersed in the prepared suspension C for 15 seconds, and then ultrasonically cleaned for 15 seconds. After ultrasonic cleaning, it was placed in an oven at 70°C and dried for 1 minute. The above operation was repeated until a third coating with a thickness of 10-20 μm appeared on the first coating sample, thus obtaining the B2O3@SiO2 / SiB6@Al2O3-SiC coating sample.

[0127] See Figure 2 By testing the B2O3@SiO2 / SiB6@Al2O3-SiC coating sample prepared in Example 3 above, SEM images of the surface morphology of the B2O3@SiO2 / SiB6@Al2O3-SiC coating sample were obtained. It can be seen from the images that there are some pores on the coating surface. These pores exist in the silica sol and can be filled after heat treatment. The overall density of the coating is good, which reduces the diffusion channels of oxygen during thermal shock resistance, so that the prepared coating can have better thermal shock resistance.

[0128] See Figure 1 The B2O3@SiO2 / SiB6@Al2O3-SiC coating sample prepared in Example 3 was tested, and the surface XRD pattern of the B2O3@SiO2 / SiB6@Al2O3-SiC coating sample was obtained. It can be seen from the pattern that the peaks of each substance in the B2O3@SiO2 / SiB6@Al2O3-Si coating sample prepared by this method are very narrow, and the peak intensity of SiC is very high. This means that the prepared coating material has high crystallinity, the crystal arrangement is relatively complete, the crystal quality is good, and the prepared coating has better thermal shock resistance.

[0129] Thermal shock resistance tests were conducted on the B2O3@SiO2 / SiB6@Al2O3-SiC coating samples prepared in Example 3. The samples were placed in a silicon carbide rod high-temperature furnace, and the furnace temperature was adjusted to 1300℃. The resulting spectral data are shown below. Figure 3 As shown in the figure, the mass loss rate of the B2O3@SiO2 / SiB6@Al2O3-SiC coating sample gradually decreases within 0 to 150 cycles. The mass loss rate gradually reaches its maximum value of 0.3% at 150 cycles. After 150 to 250 cycles, the mass loss rate gradually increases, but it is still lower than that at 0 cycles. After 250 cycles, the mass loss is only -0.14%. Therefore, this coating material has strong wear resistance, self-repair function, and high toughness.

[0130] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. It will be apparent to those skilled in the art that the invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from its spirit or essential characteristics. Therefore, the embodiments should be considered illustrative and non-limiting in all respects, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of equivalents of the claims are intended to be included within the scope of the invention. No reference numerals in the claims should be construed as limiting the scope of the claims.

[0131] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can be appropriately combined to form other embodiments that can be understood by those skilled in the art. The above content is only for illustrating the technical concept of the present invention and should not be construed as limiting the scope of protection of the present invention. Any modifications made based on the technical concept proposed in this invention shall fall within the scope of protection of the claims of this invention.

Claims

1. A method for producing a surface oxidation-resistant gradient coating of a C / C composite material, characterized by, Comprising the following steps: Step 1, respectively preparing suspension A, suspension B and suspension C: Mixing SiB6@Al2O3 core-shell powder and B2O3@SiO2 core-shell powder to obtain mixed powder A1 with SiB6@Al2O3 core-shell powder accounting for 5% to 40%, adding the mixed powder A1 into a first mixed liquid prepared by mixing silica sol and water in a volume ratio of 1:2 to 4, and stirring to obtain suspension A; Mixing SiB6@Al2O3 core-shell powder and B2O3@SiO2 core-shell powder to obtain mixed powder B1 with SiB6@Al2O3 core-shell powder accounting for 20% to 60%, adding the mixed powder B1 into a first mixed liquid prepared by mixing silica sol and water in a volume ratio of 1:2 to 4, and stirring to obtain suspension B; Mixing SiB6@Al2O3 core-shell powder and B2O3@SiO2 core-shell powder to obtain mixed powder C1 with SiB6@Al2O3 core-shell powder accounting for 40% to 80%, adding the mixed powder C1 into a first mixed liquid prepared by mixing silica sol and water in a volume ratio of 1:2 to 4, and stirring to obtain suspension C; Step 2, preheating the C / C-SiC sample, and then sequentially immersing it in the suspensions A, B and C in step 1 for 10 to 20 seconds, taking it out, cleaning and drying to obtain a B2O3@SiO2 / SiB6@Al2O3-SiC coated sample, wherein the outermost layer contains more SiB6@Al2O3 core-shell powder and the innermost layer contains more B2O3@SiO2 core-shell powder, so that the coating in the prepared B2O3@SiO2 / SiB6@Al2O3-SiC coated sample presents a gradient.

2. The method for preparing an antioxidant gradient coating on the surface of a C / C composite material according to claim 1, characterized in that, The C / C-SiC sample is prepared by embedding treatment of a C / C sample.

3. The method for preparing an antioxidant gradient coating on the surface of a C / C composite material according to claim 2, characterized in that, The embedding treatment comprises: Embedding the C / C sample in a first powder, and heat treating at a temperature of 2000 to 2400 DEG C and under a protective gas for 2 to 8 hours to obtain a primary embedded C / C sample; Then embedding the primary embedded C / C sample in a second powder, and heat treating at a temperature of 2000 to 2400 DEG C and under a protective gas for 2 to 8 hours to obtain the C / C-SiC sample.

4. The method of claim 3, wherein the C / C composite material surface oxidation resistant gradient coating is prepared by the steps of: In the embedding treatment, the first powder is obtained by mixing silicon powder, carbon powder and yttrium oxide powder in a mass percentage ratio of 70%:20%:10%; The second powder is obtained by mixing silicon powder, carbon powder and zirconium oxide powder in a mass percentage ratio of 60%:35%:5%.

5. The method for preparing an antioxidant gradient coating on the surface of a C / C composite material according to claim 3, characterized in that, The protective gas is one or more of argon, helium and nitrogen.

6. The method of claim 1, wherein the C / C composite material surface oxidation resistant gradient coating is prepared by the steps of: The preparation of SiB6@Al2O3 core-shell powder and B2O3@SiO2 core-shell powder in step 1 comprises: Preparation of the SiB6@Al2O3 core-shell powder: silicon boride is added to deionized water to prepare a first solution with a concentration of 2-5 g / L, and the first solution is stirred magnetically for 12-16 h; an aqueous solution of aluminum nitrate nonahydrate is added to the first solution, and a first pH adjusting agent is added to adjust the pH of the first solution to 7-9, and the first solution is stirred magnetically for 16-24 h to obtain a SiB6@Al(OH)3 suspension, which is then subjected to filtration, drying, and calcination in sequence to obtain the SiB6@Al2O3 powder; Preparation of the B2O3@SiO2 core-shell powder: boron oxide is added to a third solution of deionized water and anhydrous ethanol to prepare a second solution with a concentration of 5-10 g / L, and then a second mixed solution and a second pH adjusting agent are slowly added to the second solution to adjust the pH of the second solution to 7-8, and the second solution is stirred for 16-24 h to obtain a B2O3@Si(OH)4 suspension, which is subjected to centrifugation and water washing to obtain a B2O3@Si(OH)4 powder, and the B2O3@Si(OH)4 powder is calcined for 3-8 h to obtain the B2O3@SiO2 powder.

7. The method for preparing an antioxidant gradient coating on the surface of a C / C composite material according to claim 6, characterized in that, In the preparation of the SiB6@Al2O3 core-shell powder, the mass ratio of aluminum nitrate nonahydrate to silicon boride is 6-9:

1.

8. The method for preparing an antioxidant gradient coating on the surface of a C / C composite material according to claim 6, characterized in that, In the preparation of the B2O3@SiO2 core-shell powder, the third solution is prepared by mixing deionized water and anhydrous ethanol in a volume ratio of 1:2-4; and the second mixed solution is prepared by mixing tetraethyl orthosilicate and anhydrous ethanol in a volume ratio of 1:5-7.

9. The method of claim 6, wherein the C / C composite material surface oxidation resistant gradient coating is prepared by the steps of: The first pH adjusting agent is one or both of ammonia and sodium carbonate; and the second pH adjusting agent is ammonia.

10. A C / C composite material surface oxidation-resistant gradient coating prepared by the method of any one of claims 1-9.

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