Silicon carbide cladding as well as preparation method and application thereof

Abstract

The invention discloses a silicon carbide cladding as well as a preparation method and application thereof, and relates to the technical field of silicon carbide cladding preparation. The preparation method comprises the following steps: weaving the fiber ribs on the outer side of the rib-free silicon carbide cladding; the fiber ribs are fixed and formed, densification treatment and silicon carbide deposition are conducted on the end plug portions of the rib-free silicon carbide cladding, and the silicon carbide cladding is obtained; the outer side of the silicon carbide cladding is provided with ribs. According to the preparation method, the problem that a rib type structure is difficult to prepare due to brittleness of silicon carbide is solved, the reliability between the obtained silicon carbide cladding fiber rib and the body is high, the stability is good, and the radial positioning stability of the silicon carbide cladding in a small-spacing fuel assembly is remarkably enhanced when the silicon carbide cladding fiber rib is used for the nuclear reactor fuel assembly.

Description

Technical Field

[0001] This invention relates to the field of silicon carbide cladding technology, and particularly to a silicon carbide cladding, its preparation method, and its application. Background Technology

[0002] In nuclear reactor fuel assemblies, the cladding tubes, as critical structural components, play a crucial role in preventing fissile material leakage, protecting fuel pellets from coolant corrosion, and maintaining the geometry and strength of the fuel rods. With increasing demands for reactor safety and efficiency, silicon carbide, due to its superior high-temperature resistance, radiation resistance, and corrosion resistance, has become a preferred material to replace traditional zirconium alloy cladding, attracting widespread research attention. However, stable operation of fuel assemblies depends on effective positioning structures to maintain the coolant flow channel clearance between rods. Especially in miniaturized or high-power-density reactors, when the fuel rod spacing decreases, the radial positioning effect of traditional metal positioning grids is significantly weakened, making it difficult to reliably constrain the fuel rod positions.

[0003] To address this challenge, zirconium alloy cladding has evolved with ribbed designs (such as straight or spiral ribs) and formed using plastic processing techniques, but this is highly dependent on the ductility of the metallic material. In contrast, ceramic-based silicon carbide materials are inherently brittle and have extremely low ductility, making traditional rib-forming processes based on plastic deformation completely unsuitable. However, current research and development on silicon carbide cladding focuses on the fabrication of smooth tubes. Due to the high brittleness of silicon carbide cladding, complex geometries are difficult to form, thus posing a significant obstacle to the precision forming of ribbed structures on the outer side of silicon carbide cladding. This has become a core bottleneck restricting the engineering application of silicon carbide cladding in small-pitch fuel assemblies. Summary of the Invention

[0004] The present invention aims to at least solve one of the aforementioned technical problems existing in the prior art. Therefore, one objective of the present invention is to provide a method for preparing a silicon carbide cladding, overcoming the limitation of traditional silicon carbide cladding being difficult to form due to its brittleness, and producing a silicon carbide cladding with high strength and high integrity, featuring an outer ribbed surface.

[0005] The second objective of this invention is to provide a silicon carbide cladding.

[0006] The third objective of this invention is to provide a method for preparing a silicon carbide clad tube.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is as follows: The first aspect of this invention provides a method for preparing a silicon carbide coating, comprising the following steps: Fiber ribs are woven on the outside of the ribless silicon carbide shell; the fiber ribs are fixed and shaped, and the end plug of the ribless silicon carbide shell is densified and silicon carbide is deposited to obtain the silicon carbide shell; the silicon carbide shell is a silicon carbide shell with ribs on the outside.

[0008] This invention directly weaves fiber ribs onto the surface of a pre-formed, unribbed silicon carbide cladding. After fixing and shaping, local densification and silicon carbide deposition are performed to obtain a silicon carbide cladding with external ribs. This overcomes the limitation of silicon carbide's brittleness making it difficult to form complex ribbed structures. Furthermore, the process eliminates the need for secondary processing such as bonding and thermal spraying, avoiding the risk of rib-body interface (interface between fiber ribs and silicon carbide cladding) separation caused by secondary processing. This results in a silicon carbide cladding with external ribs that possesses high strength and high integrity. The externally ribbed silicon carbide cladding prepared by this invention is a continuous ceramic matrix composite material rib structure. When used in nuclear reactor fuel assemblies, it can significantly enhance the radial positioning stability of silicon carbide cladding in small-pitch fuel assemblies, achieving precise radial positioning of fuel rods under small-pitch conditions. It eliminates the failure risk caused by interface delamination, significantly enhancing the overall reliability and stability of the fuel assembly structure, and solving the problems of insufficient constraint force of traditional metal positioning grids and the difficulty in reliably forming external positioning ribs of silicon carbide cladding. Meanwhile, the fiber ribs obtained by the present invention through a specific process are not easy to crack or break off upon impact. Furthermore, the fixed steps further prevent the fiber rib interface from delaminating and becoming unstable.

[0009] It should be understood that densification and silicon carbide deposition at the end plug of a ribless silicon carbide shell are local densification and local silicon carbide deposition. That is, densification and silicon carbide deposition are carried out on the fibrous ribs at the end plug location (end plug surface and the connection between end plug and shell). This process will make the entire area densified, including the fibrous ribs, the connection between the fibrous ribs and the end plug, and the connection between the fibrous ribs and the shell. Finally, only the ribs in the end area of ​​the silicon carbide shell are ceramicized.

[0010] Specifically, fiber ribs are woven on the outside of the ribless silicon carbide shell, including weaving on the outside of the silicon carbide shell body and the outside of the end plug.

[0011] In some embodiments, the method for preparing the rib-free silicon carbide cladding includes the following steps: Silicon carbide fibers are woven on the surface of the core mold to prepare a preform; the preform undergoes carbon deposition to form an interface layer, followed by curing and densification treatment, then silicon carbide deposition, and finally end plug connection to obtain the ribless silicon carbide shell.

[0012] In some preferred embodiments, the end plug connection includes the following steps: connecting the end plug to the silicon carbide casing using a bonding agent. Specifically, the bonding agent is applied to the surfaces of the silicon carbide casing and the end plug to be encapsulated, and after connecting the two, the end plug is kept at 1300~1600℃ for 1~5 hours to complete the end plug connection.

[0013] In some preferred embodiments, the steps of weaving fiber ribs and weaving silicon carbide fibers on the mandrel surface include at least one of weaving, braiding, and loop winding. Specifically, the weaving of the fiber ribs and the weaving of the silicon carbide fibers on the mandrel surface may be the same or different.

[0014] It should be understood that the number of weaving layers can be one or more, such as 1 to 3 layers.

[0015] In some preferred embodiments, the densification process in the preparation of the externally ribbed silicon carbide cladding and the unribbed silicon carbide cladding includes chemical vapor infiltration of silicon carbide and / or impregnation pyrolysis of silicon carbide. The densification processes in the preparation of the externally ribbed silicon carbide cladding and the unribbed silicon carbide cladding can be the same or different.

[0016] Specifically, the densification treatment temperature is 900~1300℃; the densification treatment time is 10~600h. In some preferred embodiments, the densification treatment temperature is 1000~1100℃; the densification treatment time is 100~300h.

[0017] In some preferred embodiments, the silicon carbide deposition in the preparation of the outer ribbed silicon carbide shell and the ribless silicon carbide shell includes chemical vapor deposition.

[0018] In some preferred embodiments, in the preparation of the ribbed silicon carbide cladding and the ribless silicon carbide cladding, the silicon carbide deposition temperature is 1100~1500℃, and the silicon carbide deposition time is 10~100h.

[0019] In some preferred embodiments, in the preparation of the outer ribbed silicon carbide shell and the ribless silicon carbide shell, the silicon carbide deposition temperature is 1200~1400℃, and the silicon carbide deposition time is 40~60h.

[0020] In some preferred embodiments, the silicon carbide deposition yields a silicon carbide coating; the thickness of the silicon carbide coating is 100~200 nm.

[0021] In some preferred embodiments, the thickness of the interface layer is 100~600nm.

[0022] In some embodiments, the fiber ribs include straight ribs and / or spiral ribs.

[0023] In some embodiments, the width of the fiber rib is 0.5 to 1.5 mm; the length of the fiber rib is 1 to 4.5 mm.

[0024] In some embodiments, the fixing includes the following steps: forming a rib mesh on a silicon carbide cladding using silicon carbide fibers, and fixing the fiber ribs.

[0025] In some preferred embodiments, the rib mesh is formed by needle punching or weaving to fix the fiber ribs. Specifically, the mesh structure of the rib mesh is rhomboid.

[0026] In some preferred embodiments, the thickness of the rib mesh is 20~50μm.

[0027] In some embodiments, the curing includes the following steps: filling the preform forming the interface layer with silicon carbide; the filling includes chemical vapor infiltration of silicon carbide, and / or impregnation pyrolysis of silicon carbide.

[0028] In some preferred embodiments, the curing temperature is 900~1200℃; the curing time is 50~200h.

[0029] In some embodiments, the carbon deposition is pyrolytic carbon deposition. Specifically, the carbon deposition temperature is 900~1100℃; the carbon deposition time is 5~20h.

[0030] A second aspect of the present invention provides a silicon carbide cladding shell, which is prepared by the preparation method described in the first aspect of the present invention.

[0031] In some embodiments, the outer side of the silicon carbide cladding includes fibrous ribs, which are fixed to the surface of the silicon carbide cladding body by a rib mesh. Further, the fibrous ribs at the end plug portion of the silicon carbide cladding are ceramicized.

[0032] A third aspect of the present invention provides a process for preparing a silicon carbide clad tube, the process comprising the preparation method described in the first aspect of the present invention.

[0033] In some embodiments, during the fabrication of the silicon carbide cladding tube, the outer diameter of the mandrel is 7-9 mm.

[0034] In some embodiments, the density of the silicon carbide clad tube is >2.7 g / cm³. 3 Outer diameter is 9~11mm; inner diameter is 7~9mm; length is >100mm.

[0035] Compared with the prior art, the beneficial effects of the present invention are: This invention provides a method for preparing a silicon carbide cladding. Fiber ribs are woven onto the outside of a ribless silicon carbide cladding, fixed, and then locally densified and deposited with silicon carbide to obtain a silicon carbide cladding with an outer ribbed structure. This solves the problem that the brittleness of silicon carbide makes it difficult to prepare ribbed structures. Furthermore, the obtained silicon carbide cladding with outer ribs exhibits high reliability and stability with the fibrous ribs of the cladding and the cladding itself. When used in nuclear reactor fuel assemblies, it significantly enhances the radial positioning stability of silicon carbide cladding in small-pitch fuel assemblies, improves the radial positioning effect of silicon carbide-clad fuel rods, avoids the risk of failure due to interface delamination, and solves the problem of insufficient constraint force in traditional metal positioning grids. Attached Figure Description

[0036] Figure 1 This is a cross-sectional view of the end of the silicon carbide cladding tube and the end plug connection area in Embodiment 1 of the present invention.

[0037] Figure 2 This is a cross-sectional view of the silicon carbide cladding tube end plug section in Embodiment 1 of the present invention.

[0038] right Figure 1 , Figure 2 The numbering in the code is explained as follows: 01-Silicon carbide coating; 02-Rib mesh; 03-Fiber rib; 04-Silicon carbide fiber braided layer; 05-Core mold; 06-Binder layer; 07-End plug. Detailed Implementation

[0039] The present invention will be further described in detail below through specific embodiments. Unless otherwise specified, the raw materials, reagents, or apparatus used in the embodiments and comparative examples are all available from conventional commercial sources or can be obtained by existing technical methods. Unless otherwise specified, the test or experimental methods are conventional methods in the art.

[0040] An embodiment of the first aspect of the present invention provides a method for preparing a silicon carbide coating, comprising the following steps: Fiber ribs are woven on the outside of the ribless silicon carbide shell; the fiber ribs are fixed and shaped, and the end plug of the ribless silicon carbide shell is densified and silicon carbide is deposited to obtain the silicon carbide shell; the silicon carbide shell is a silicon carbide shell with ribs on the outside.

[0041] In this invention, densification and silicon carbide deposition are performed on the end plug portion of the unribbed silicon carbide cladding. This densification and deposition are localized, specifically targeting the fiber ribs at the end plug location (end plug surface and the connection between the end plug and the cladding). This process densifies the entire area, including the fiber ribs, the connection between the fiber ribs and the end plug, and the connection between the fiber ribs and the cladding. Ultimately, only the ribs in the end region of the silicon carbide cladding are ceramicized. The fiber ribs of this invention are fixed to the end plug and the connection area between the end plug and the cladding through densification and silicon carbide deposition at the interface between the fiber ribs and the silicon carbide cladding body. Since the fiber ribs are woven after the end plug is connected, and the silicon carbide cladding already contains fuel, the localized densification and silicon carbide deposition process, which only affects the end plug portion, minimizes the impact on other areas of the silicon carbide cladding (the central fuel-containing area), thus avoiding thermal damage.

[0042] It should be understood that localized deposition can be achieved by setting up a localized gas flow field for deposition, or by using tooling to place only the end plug portion that needs to be densified or deposited in the deposition furnace for densification and deposition.

[0043] Specifically, the fiber ribs include straight ribs and / or helical ribs. The width of the fiber ribs is 0.5 to 1.5 mm, for example, 0.5 mm, 0.8 mm, 1 mm, 1.2 mm, or 1.5 mm. The height of the fiber ribs is 1 to 4.5 mm, for example, 1 mm, 2 mm, 3 mm, 4 mm, or 4.5 mm. It is understood that the helical ribs are shaped similarly to the threads of a screw.

[0044] In some embodiments, fixing the fiber ribs includes the following steps: forming a rib mesh on a silicon carbide cladding using silicon carbide fibers to fix the fiber ribs. The rib mesh is formed by needle punching or weaving to fix the fiber ribs. The thickness of the rib mesh is 20~50μm. For example, the thickness of the rib mesh is 20μm, 30μm, 40μm or 50μm.

[0045] Furthermore, the preparation method of the ribless silicon carbide shell includes the following steps: silicon carbide fiber weaving is performed on the surface of the core mold to prepare a preform; the preform is subjected to carbon deposition to form an interface layer, and after curing and densification treatment, silicon carbide deposition is performed, and the preform is connected by end plugs to obtain the ribless silicon carbide shell.

[0046] In some embodiments, the silicon carbide cladding, after silicon carbide deposition, is finished before being connected to the end plug. Alternatively, the end plug may also be finished before being connected to the silicon carbide cladding.

[0047] The end-plug connection includes the following steps: connecting the end-plug to the silicon carbide casing using a bonding agent. In some preferred embodiments, the bonding agent is applied to the surfaces of the silicon carbide casing and the end-plug to be encapsulated, and after connecting them, the connection is completed by holding the mixture at 1300~1600℃ for 1~5 hours. For example, the bonding agent used can be a ceramic slurry.

[0048] It is important to understand that in the preparation of both rib-free and ribbed silicon carbide cladding, the weaving, densification, and silicon carbide deposition processes are selected from the same technology, or from the same range of technologies, only differing in specific steps or process conditions. For example, the weaving process may be selected from machine weaving, braiding, or loop winding, but may not be machine weaving, braiding, or loop winding simultaneously.

[0049] Specifically, in the steps of fiber rib weaving and silicon carbide fiber weaving on the mandrel surface (i.e., fiber rib weaving and preform weaving), the weaving includes at least one of machine weaving, braiding, and loop winding. The weaving of the fiber ribs and the weaving of the silicon carbide fibers on the mandrel surface may be the same or different.

[0050] It should be understood that the number of weaving layers can be one or more, such as 1 to 3 layers.

[0051] In the preparation of externally ribbed silicon carbide cladding and unribbed silicon carbide cladding, the densification treatment includes chemical vapor infiltration (CVI) of silicon carbide and / or impregnation pyrolysis of silicon carbide. The densification treatments in the preparation of externally ribbed silicon carbide cladding and unribbed silicon carbide cladding can be the same or different. When using chemical vapor infiltration (CVI) for densification, the gas pressure is 500~3000 Pa; the reaction gas is trichloromethylsilane, the carrier gas is hydrogen, the dilution gas is argon, the molar ratio of hydrogen to trichloromethylsilane is (9~20):1; the flow rate of hydrogen is 500~3000 mL / min; and the flow rate of argon is 1000~4000 mL / min.

[0052] Specifically, the densification treatment temperature is 900~1300℃; the densification treatment time is 10~600h. For example, the densification temperature can be 900℃, 1000℃, 1050℃, 1100℃, 1200℃ or 1300℃, and the densification time can be 10h, 100h, 150h, 200h, 250h, 300h, 400h, 500h or 600h. In some preferred embodiments, the densification treatment temperature is 1000~1100℃; the densification treatment time is 100~300h.

[0053] In the preparation method of this invention, in the preparation of the outer ribbed silicon carbide shell and the unribbed silicon carbide shell, silicon carbide deposition can be performed by chemical vapor deposition. A silicon carbide coating is deposited on the densified silicon carbide shell or the end plug by chemical vapor deposition. When using chemical vapor deposition, the gas pressure for silicon carbide deposition is 1000~5000 Pa; the reaction gas is trichloromethylsilane, the carrier gas is hydrogen, the dilution gas is argon, the molar ratio of hydrogen to trichloromethylsilane is (9~20):1; the flow rate of hydrogen is 1000~7000 mL / min; and the flow rate of argon is 2000~9000 mL / min.

[0054] Specifically, the silicon carbide deposition temperature is 1100~1500℃. The silicon carbide deposition time is 10~100h. For example, the silicon carbide deposition temperature can be 1100℃, 1200℃, 1300℃, 1400℃ or 1500℃, and the silicon carbide deposition time can be 10h, 30h, 40h, 50h, 60h, 70h, 90h or 100h. In some preferred embodiments, the silicon carbide deposition temperature is 1200~1400℃, and the silicon carbide deposition time is 40~60h.

[0055] The thickness of the silicon carbide coating formed by silicon carbide deposition is 100~200nm.

[0056] In the preparation of the rib-free silicon carbide cladding, a carbon deposition process is performed on the preform to form an interface layer before silicon carbide deposition. Specifically, carbon deposition is achieved by depositing pyrolytic carbon via chemical vapor deposition. The carbon deposition temperature is 900–1100 °C; the carbon deposition time is 5–20 h. The thickness of the carbon-deposited interface layer is 100–600 nm. For example, the thickness of the interface layer can be 100 nm, 200 nm, 300 nm, 400 nm, 500 nm, or 600 nm, or other thickness ranges composed of these values, such as 200–600 nm, 300–600 nm, 400–600 nm, or 500–600 nm.

[0057] In some embodiments, the thickness of the interface layer is 300~500nm.

[0058] Furthermore, after the interface layer is prepared, the fiber layer is cured. The curing includes the following steps: filling the preform forming the interface layer with silicon carbide; the filling includes chemical vapor infiltration of silicon carbide, and / or impregnation pyrolysis of silicon carbide. In some preferred embodiments, the curing temperature is 900~1200℃; the curing time is 50~200h.

[0059] After curing, the mandrel is removed as needed. For example, when the mandrel is a graphite tube, it can be removed by oxidation at 600~700℃. When the mandrel is a metal tube, the mandrel removal step is not required.

[0060] For ribless silicon carbide cladding that has undergone densification and silicon carbide deposition, it is then connected to the end plug after finishing. Alternatively, the end plug can also be connected to the silicon carbide cladding after finishing.

[0061] A second aspect of the present invention provides a silicon carbide cladding shell, which is prepared by the preparation method described in the first aspect of the present invention.

[0062] In some embodiments, the outer side of the silicon carbide cladding includes fibrous ribs, which are fixed to the surface of the silicon carbide cladding body by a rib mesh. Further, the fibrous ribs at the end plug portion of the silicon carbide cladding are ceramicized.

[0063] A third aspect of the present invention provides a process for preparing a silicon carbide clad tube, the process comprising the preparation method described in the first aspect of the present invention.

[0064] Specifically, during the fabrication of the silicon carbide clad tube, the outer diameter of the mandrel is 7-9 mm. The density of the silicon carbide clad tube is >2.7 g / cm³. 3 Outer diameter is 9~11mm; inner diameter is 7~9mm; length is >100mm.

[0065] The preparation method of the present invention will be described in detail below using the preparation of silicon carbide clad tubes as an example through specific embodiments.

[0066] Example 1 A method for preparing a silicon carbide coating, such as Figure 1 and Figure 2 As shown, the silicon carbide cladding obtained in this embodiment is a silicon carbide clad tube, containing a silicon carbide coating 01, a ribbed mesh 02, fiber ribs 03, a silicon carbide fiber rib braided layer 04, a mandrel 05, a binder layer 06, and an end plug 07. Its preparation method specifically includes the following steps: S1. Preparation of the core mold: Take a commercially available graphite tube with an outer diameter of 8mm and a length of 200mm as the core mold 05; S2. Preform preparation: The core mold 05 from step S1 is placed in a three-dimensional braiding device, and the outer side of the third-generation SiC fiber is braided. The number of braiding layers is 2, the thickness of each layer is 0.2~0.4mm, the average fiber diameter is 12μm, forming a silicon carbide fiber rib braided layer 04, and the preform is obtained. S3. Interface layer preparation: The preform in step S2 is subjected to pyrolytic carbon deposition in a pyrolytic carbon deposition furnace. The carbon source is methane. The deposition is carried out at 1000℃ for 10h to form an interface layer with a thickness of 400nm. S4. Fiber layer curing: The preform containing the interface layer in step S3 is placed in a deposition furnace and filled with silicon carbide by chemical vapor infiltration at 1050°C in a trichloromethylsilane atmosphere for 100 hours to solidify and shape the fiber layer. S5. Core mold removal: The graphite tubes in the cured preform from step S4 are removed by oxidation at 650°C; S6. Densification treatment: The core mold removed in step S5 is placed in a deposition furnace and subjected to chemical vapor infiltration of silicon carbide at 1050℃ and 1000Pa for 200h. The reaction gas is trichloromethylsilane, the carrier gas is hydrogen (1000mL / min), and the dilution gas is argon (2000mL / min). The molar ratio of hydrogen to trichloromethylsilane is 10:1, resulting in a densified tube. S7. Deposition of silicon carbide coating: The densified tube from step S6 is placed in a deposition furnace and subjected to chemical vapor deposition at 1300℃ and 4000Pa for 50 hours to obtain a silicon carbide clad tube with a silicon carbide coating 01 deposited on its surface. The thickness of the silicon carbide coating is 150μm. During the deposition process, the reaction gas is trichloromethylsilane, the carrier gas is hydrogen (5000 mL / min), and the dilution gas is argon (7000 mL / min). The molar ratio of hydrogen to trichloromethylsilane is 10:1. S8. Precision machining: The silicon carbide end plug 07 is prepared by machining, and the silicon carbide shell tube fitting of step S7 and the end plug 07 are precision machined so that the end plug and the end size of the silicon carbide shell tube correspond to each other, and the end plug can be inserted into the end of the silicon carbide shell tube and seal it. S9: End plug connection: The mixed powder is mixed with acetone and used as a binder. This mixture is then evenly applied to the surfaces to be encapsulated on the silicon carbide clad tube and the end plug after the finishing process in step S8, forming a binder layer 06. The two surfaces to be encapsulated are then brought into contact and aligned. Excess slurry is removed to complete the connection. The joined parts are placed in a spark plasma sintering furnace and heated to 1450°C in a nitrogen atmosphere. The temperature is maintained for 15 minutes, and then cooled to room temperature to obtain a rib-free silicon carbide clad tube. The mixed powder is prepared according to the mixed powder in Example 3 of CN118063232A. The specific preparation method is as follows: Powder B (Pr3S) at a mass ratio of 1:10 i2 C2 (particle size 100nm) and powder A (SiC, particle size 30nm) were ground thoroughly in an agate grinding bowl for 30 minutes to obtain a uniform mixed powder. The mixed powder and acetone were mixed by planetary ball milling (milling speed 300 r / min, milling time 30 min) to obtain the binder; the mass ratio of the mixed powder to acetone in the binder was 1:4. S10. Fiber rib weaving: Using the unribbed silicon carbide cladding tube from step S9, fiber ribs 03 are formed on the outside of the unribbed silicon carbide cladding tube, including the end plug of the unribbed silicon carbide cladding tube, by a ring winding method, which are spiral ribs. S11. Fiber Rib Fixation: The fiber ribs 03 from step S10 are fixed by loop winding with silicon carbide fiber bundles. The silicon carbide fiber bundles form a fixing rib mesh 02 tightly attached to the silicon carbide cladding tube. The average single fiber diameter of the silicon carbide fiber bundle is 12 μm, and one bundle is 50 μm. Root fibers ; S12. Fiber rib forming: Repeat steps S10 and S11 until the fiber ribs reach the required width and height; in this embodiment, the fiber rib width is 1 mm and the height is 3 mm; S13. Local densification and silicon carbide deposition: A local deposition airflow field is set at the end plug. Through the processes of steps S3, S4, S6 and S7, the end plugs at both ends of the tube formed in step S12 are subjected to interface layer preparation, densification treatment and silicon carbide coating deposition to obtain a silicon carbide cladding with external ribs, which is a silicon carbide cladding tube with external ribs.

[0067] The silicon carbide density of the silicon carbide-clad tube obtained in this embodiment is 2.9 g / cm³. 3 The outer diameter of the silicon carbide clad tube is 10mm, the inner diameter is 8mm, and the length is 200mm.

[0068] In Example 1, the spiral ribs formed through weaving, fixing, and densification prevent radial displacement, vibration, or bending of the silicon carbide clad tube during operation, achieving precise positioning. The ribs and the base tube form a robust integral structure through CVD / CVI processes, avoiding the risk of loosening caused by mechanical assembly and ensuring long-term reliability of positioning.

[0069] Example 2 Referring to the preparation method of Example 1, the core mold is replaced by a tantalum metal tube instead of a graphite tube, and there is no need to remove the core mold afterwards.

[0070] In Example 2, a tantalum metal tube is used as the mandrel, which can serve as part of the cladding tube. The externally formed silicon carbide ribs retain their original function, still used to engage with external components for precise positioning. The presence of the metal mandrel makes the tube less prone to deformation when the ribs bear positioning loads.

[0071] Example 3 Referring to the preparation method of Example 1, in step S10, the woven fiber ribs are straight ribs by adjusting the angle of the loop winding.

[0072] In Example 3, the woven fiber ribs are straight ribs. As an optimized variant of the positioning scheme, straight ribs are more suitable for specific grid designs that require axial positioning and anti-rotation.

[0073] Example 4 Referring to the preparation method of Example 1, by adjusting the number of repetitions of steps S10 and S11, fiber ribs of different widths were obtained. In this example, the width of the fiber ribs is 1 mm.

[0074] In Example 4, the width of the ribs is precisely controlled by repeating the weaving and fixing of the fiber ribs, thereby fine-tuning the fit gap between the shell tube and the support grid.

[0075] Comparative Example 1 The preparation method is the same as in Example 1, but steps S11 and S12 are omitted. In Comparative Example 1, the fiber ribs were not fixed or formed, resulting in loose fiber ribs, boundary areas that did not meet design requirements, and large errors, leading to inaccurate positioning and low density in the fiber rib area.

[0076] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. A method for preparing a silicon carbide coating, characterized in that, Includes the following steps: Fiber ribs are woven on the outside of the ribless silicon carbide cladding. The fiber ribs are fixed and shaped, and densification and silicon carbide deposition are performed on the end plug of the unribbed silicon carbide shell to obtain the silicon carbide shell; the silicon carbide shell is a silicon carbide shell with ribs on the outside.

2. The preparation method according to claim 1, characterized in that, The method for preparing the rib-free silicon carbide cladding includes the following steps: Silicon carbide fibers are woven on the surface of the core mold to prepare a preform; the preform undergoes carbon deposition to form an interface layer, followed by curing and densification treatment, then silicon carbide deposition, and finally end plug connection to obtain the ribless silicon carbide shell.

3. The preparation method according to claim 1 or 2, characterized in that, The weaving includes at least one of machine weaving, braiding, and loop wrapping.

4. The preparation method according to claim 1 or 2, characterized in that, The densification process includes chemical vapor infiltration of silicon carbide and / or impregnation pyrolysis of silicon carbide.

5. The preparation method according to claim 1 or 2, characterized in that, The silicon carbide deposition includes chemical vapor deposition; and / or, the temperature of the silicon carbide deposition is 1100~1500℃.

6. The preparation method according to claim 1, characterized in that, The fibrous ribs include straight ribs and / or spiral ribs.

7. The preparation method according to claim 1, characterized in that, The fixing process includes the following steps: forming a rib mesh on a silicon carbide cladding using silicon carbide fibers, and fixing the fiber ribs.

8. The preparation method according to claim 2, characterized in that, The curing process includes the following steps: filling the preform forming the interface layer with silicon carbide; the filling includes chemical vapor infiltration of silicon carbide, and / or impregnation pyrolysis of silicon carbide.

9. A silicon carbide cladding, characterized in that, The silicon carbide cladding is prepared by the preparation method according to any one of claims 1 to 8.

10. A process for preparing a silicon carbide clad tube, characterized in that, The preparation process includes the preparation method according to any one of claims 1 to 8.

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