Silicon capsule and preparation method thereof, and preparation method of continuous fiber toughened ceramic matrix composite material

Abstract

The invention discloses a silicon capsule and a preparation method thereof as well as a preparation method of a continuous fiber toughened ceramic matrix composite material, and solves the problems that in a traditional melt siliconizing process, when the reaction temperature rises, due to direct contact between silicon powder and lower heat conductivity of liquid silicon, a remarkable temperature gradient is formed in the embedded silicon powder, and the heat conductivity of the silicon powder is reduced. The silicon powder melting process is not uniform due to the temperature difference; according to the preparation method, polyvinyl alcohol is taken through a water-soluble binder, carbon powder is uniformly wrapped on the surfaces of silicon particles, then the taken polyvinyl alcohol is removed at a high temperature, the carbon powder on the surfaces and the silicon particles react to form a SiC thin layer, and finally the silicon particles with the surfaces wrapped with the polyvinyl alcohol solution are cracked at the high temperature and uniformly permeate into a porous intermediate, so that the silicon-carbon composite material is obtained. And the infiltration uniformity of liquid silicon and the compactness of the material can be effectively improved, large-area silicon blocks formed when traditional silicon melt is cooled and damage to surface fibers of products in the processing and breaking process are reduced, and net size forming is achieved.

Description

Technical Field

[0001] The invention relates to a preparation process of a dense material, in particular to a silicon capsule and a preparation method thereof, and a preparation method of a continuous fiber-reinforced ceramic-based composite material. Background Art

[0002] Continuous fiber-reinforced ceramic matrix composites (CFCCs) overcome the brittleness of traditional ceramic materials, exhibiting excellent properties in high-temperature strength, toughness, thermal shock resistance, and oxidation resistance. Consequently, they hold broad application prospects in aerospace, energy, and defense sectors. CFCC composite manufacturing processes include chemical vapor deposition (CVI), polymer infusion pyrolysis (PIP), slurry infusion (SI), sol-gel (Sol-Gel), and reactive melt infiltration (RMI). Except for RMI, these manufacturing processes struggle to achieve full density, typically leaving 10-15% porosity. RMI offers a short production cycle, improving production efficiency, lower raw material costs such as silicon and silicon-zirconium alloys, unrestricted component geometry, and low residual porosity (<5%). However, in traditional melt siliconization, as the reaction temperature increases, significant temperature gradients develop within the embedded silicon powder due to direct contact between the silicon powders and the low thermal conductivity of the liquid silicon. This temperature difference leads to uneven melting of the silicon powder, which in turn causes the following problems: First, the liquid silicon in direct contact with the product surface penetrates quickly and unevenly; second, due to the lack of effective control, the volume expansion generated during the reaction between carbon and silicon will cause the pores on the product surface to close rapidly; this phenomenon further leads to the insufficient size of the peripheral liquid silicon penetration channel, limiting the smooth progress of the subsequent siliconization process.

[0003] Patent publication number CN112457027A discloses that direct contact between silicon powder and silicon powder can be avoided by mixing SiC powder and silicon powder. However, this still fails to control the asynchronicity of the embedded silicon powder melting. Although the uniformity of the infiltration and the density of the material are improved, the effect is relatively limited. There are also methods that attempt to solve the problem of uneven infiltration and improve product consistency through tooling. For example, patent publication number CN109176832B discloses a siliconizing tooling. This method is to open a cavity in the container body and place a support member with a receiving structure for accommodating silicon powder in the cavity. The carbon workpiece is placed on the support member and then covered with a container cover to carry out the siliconizing process. The support member and the carbon workpiece are tightly pressed against each other, achieving a good siliconizing effect. The support member combines the supporting function and the receiving function into one. After the reaction, there is no residual silicon slag to adhere to, which is convenient for cleaning. At the same time, the siliconizing can be uniform and reduce the weight imbalance. Although this type of tooling can reduce the cleaning work on the surface of the product after RMI, it has limited effect on improving the uniformity and density of the infiltration, because the RMI process is essentially controlled by reaction-diffusion dynamics and wetting dynamics. Patent publication number CN113773094B discloses a method for treating molten silicon-infiltrated silicon powder, including chemical vapor deposition of carbon on the surface of the silicon powder, and mixing phenolic resin or other types of resin with the silicon powder, and pre-treating at around 900-1100°C to form a core-shell structure of the silicon powder. The purpose is to form a thin shell on its surface, and to utilize the volume change effect during the melting and heating process to enable silicon to break the shell and quickly enter the porous body, avoiding problems such as reaction clogging. Although it effectively improves the uniformity of the infiltration, the invention has the following problems. First, the pre-treatment steps are too complicated, which invisibly increases the manufacturing cost and production cycle. Second, whether silicon is coated via chemical vapor deposition (CVD) or phenolic resin conversion, its surface microstructure is a hard glassy carbon layer, which reacts with silicon at high temperatures to form a thin SiC layer. Due to the presence of a hard carbon layer on the outside of the silicon powder, thermal stress management is difficult, leading to poor quality and premature breakage. Third, chemical vapor deposition (CVD) carbon coating of silicon powder is affected by the flow field, making deposition uniformity and yield difficult to guarantee. Phenolic resin coating of carbon leaves phenolic resin residue in the silicon powder, which forms larger SiC blocks inside, affecting the subsequent infiltration of the entire liquid silicon. Fourth, both the CVI and PIP methods cause adhesion between silicon particles, making it difficult to achieve a "one-by-one" effect. Summary of the Invention

[0004] The purpose of the present invention is to solve the problem that in the traditional melt siliconization process, when the reaction temperature rises, a significant temperature gradient is formed inside the embedded silicon powder due to direct contact between the silicon powders and the low thermal conductivity of the liquid silicon. This temperature difference leads to an uneven melting process of the silicon powder. The present invention provides a silicon capsule and a preparation method thereof, as well as a preparation method of a continuous fiber-reinforced ceramic-based composite material.

[0005] In order to achieve the above object, the present invention adopts the following technical solutions:

[0006] A method for preparing a silicon capsule is characterized in that it comprises the following steps:

[0007] Step 1, weighing polyvinyl alcohol and adding it to deionized water, stirring and dissolving it with a magnetic rotor and a magnetic stirrer to obtain a polyvinyl alcohol solution with a concentration of 2% to 8%;

[0008] Step 2: Weigh silicon particles and pour them into a ball mill, add polyvinyl alcohol solution until the silicon particles are completely immersed, ball mill, and sieve to obtain silicon particles with the polyvinyl alcohol solution coated on the surface;

[0009] Step 3: Weigh silicon carbide powder, silicon particles coated with polyvinyl alcohol solution, and carbon powder and add them into a ball mill. After ball milling, sieve them, and continue ball milling and sieving to obtain silicon capsules.

[0010] Furthermore, in step 3, the mass proportion of the silicon carbide powder is 10%-20%, the mass proportion of the silicon particles coated with polyvinyl alcohol solution is 70%-80%, and the mass proportion of carbon powder is 5%-10%. The sum of the mass percentages of the above components is 100%.

[0011] Furthermore, step 2 is specifically as follows:

[0012] Pour silicon particles with a particle size of 0.5μm to 10μm into a ball mill, add polyvinyl alcohol solution until the silicon particles are completely immersed, ball mill for 4h to 6h, and pass through a 5000-10000 mesh sieve to obtain silicon particles with the surface coated with polyvinyl alcohol solution.

[0013] Furthermore, the silicon particles are silicon powder coated with polydopamine on the surface, and the preparation method is:

[0014] Step a, mixing tris(hydroxymethyl)aminomethane and tris(hydroxymethyl)aminomethane hydrochloride in a mass ratio of 1 to 10:1 to obtain a mixture, dissolving the mixture in deionized water at a mass ratio of deionized water to the mixture of 10 to 30:1, and magnetically stirring for 1 to 2 hours to obtain a buffer solution; weighing 10 to 100 ml of the buffer solution, adding dopamine at a mass ratio of dopamine to the buffer solution of 1 to 50:1 to 100, and magnetically stirring for 1 to 3 hours to obtain a dopamine solution;

[0015] Step b, weighing silicon powder with a particle size of 0.4 μm to 1 μm and a dopamine solution in a mass ratio of 1 to 10:1 to 100, magnetically stirring for 20 to 200 hours to obtain a suspension, centrifuging the suspension, and centrifugally washing it 2 to 5 times with alcohol and deionized water respectively until the supernatant is colorless and transparent to obtain a precipitate, placing the precipitate in a crucible, and drying it in an oven to obtain polydopamine-coated silicon particles with a particle size of 0.5 μm to 10 μm.

[0016] Furthermore, in step b, the drying temperature in the oven is 50° C. to 150° C., and the drying time is 10 h to 40 h.

[0017] Furthermore, step 3 is specifically as follows:

[0018] Step 3.1, weighing silicon carbide powder with a particle size of 5 μm to 25 μm, silicon particles coated with polyvinyl alcohol solution, and carbon powder, adding them to a ball mill, ball milling for 2 h to 10 h, passing through a 10-mesh sieve, and adding them to the ball mill again;

[0019] Step 3.2: ball mill for 2 h to 4 h, and pass through a 10-mesh sieve to obtain silicon capsules.

[0020] A silicon capsule is special in that it is prepared based on the above-mentioned preparation method of the silicon capsule.

[0021] A method for preparing a continuous fiber-reinforced ceramic matrix composite material, which is special in that it comprises the following steps:

[0022] Step A: placing the porous intermediate into a graphite crucible or a graphite paper box, and evenly embedding the silicon capsules prepared by the above silicon capsule preparation method on the surface of the porous intermediate;

[0023] Step B: placing the graphite crucible in a vacuum sintering furnace, sintering, and cooling to room temperature to obtain a continuous fiber-reinforced ceramic matrix composite material.

[0024] Furthermore, in step A, the porous intermediate is one of a porous carbon fiber, a porous silicon carbide fiber preform, a porous ceramic whisker preform, a porous tape-cast ceramic embryo, and a porous gel-injection molded ceramic embryo prepared by one of the CVI, PIP, SI, and So-Gel methods.

[0025] Furthermore, step B is specifically as follows: placing the graphite crucible into a vacuum sintering furnace, adjusting the reaction temperature to between 1450° C. and 1600° C., sintering for 2 h to 3 h, and cooling to obtain a continuous fiber-reinforced ceramic-based composite material.

[0026] When the temperature rises to between 300 and 600°C, polyvinyl alcohol takes advantage of its good film-forming properties and is evenly mixed with carbon powder and spread on the surface of silicon particles; when the temperature rises to 800°C, due to the low residual carbon rate of the polyvinyl alcohol film, the dense carbon layer on the surface will be transformed into a porous carbon film, alleviating the thermal stress mismatch between silicon and carbon caused by the difference in thermal expansion coefficient. At the same time, the porous carbon film reacts with silicon to obtain a relatively dense SiC thin layer; when the temperature rises to above 1412°C, silicon melts in the SiC thin shell. Due to the wrapping effect of the porous thin shell, the silicon particles will not melt at low temperatures. When the temperature is further increased, the silicon particles coated with polyvinyl alcohol solution exert stress on the thin shell through the volume expansion effect, and a small amount of silicon particles preferentially seep out from the micro-nano pores, making the temperature field distribution of the embedded particles close to synchronization, thereby controlling the silicon to penetrate into the porous intermediate at a higher temperature, lower viscosity and more uniformly, thereby significantly improving the melt infiltration uniformity of the continuous fiber reinforced ceramic matrix composite material.

[0027] Beneficial effects of the present invention:

[0028] (1) The present invention provides a method for preparing silicon capsules. This method utilizes the excellent viscosity and wettability of a polyvinyl alcohol aqueous solution to uniformly disperse carbon powder onto the surface of silicon particles, avoiding the uneven coating and interparticle adhesion associated with CVI and PIP methods. Water-soluble polyvinyl alcohol, as a binder and dispersion medium for the carbon powder, has a moderate saturated vapor pressure compared to ethanol and acetone solvents, making it easy to store for long periods and non-toxic and environmentally friendly.

[0029] (2) The present invention provides a method for preparing silicon capsules, in which polydopamine and a buffer solution are coated on the surface of silicon powder to obtain polydopamine-coated silicon particles with a particle size of 0.5 μm to 10 μm, and then the carbon powder and SiC powder are uniformly coated on the surface of the nanocarbon layer using the polyvinyl alcohol in the above step to prepare a small-sized capsule multi-level shell structure. For ultra-thin, special-shaped, and high-precision components, the multi-level shell silicon capsule method can reduce the residual stress inside the material, improve the toughness of the material, control the deformation and stress concentration of the material, and greatly improve the consistency and qualified rate of the product.

[0030] (3) The present invention provides a method for preparing a continuous fiber-reinforced ceramic-based composite material. During the sintering process, stress is applied to the thin shell through the volume expansion effect of temperature increase, and a small amount of silicon particles with a surface coated with polyvinyl alcohol solution preferentially seep out from the micro-nano pores, so that the temperature field distribution of the embedded particles approaches synchronization, thereby controlling the silicon to infiltrate the porous intermediate at a higher temperature, lower viscosity, and more uniformly, thereby significantly improving the melt infiltration uniformity of the material.

[0031] (4) The present invention provides a method for preparing a silicon capsule. For ultra-thick components, a layer of silicon capsules can be used to avoid the "black core" phenomenon and improve the density of the product. The density of the continuous fiber-reinforced ceramic matrix composite material prepared by the present invention can reach 2.0g / cm 3 above.

[0032] (5) The present invention provides a method for preparing a continuous fiber-reinforced ceramic-based composite material, which can complete the preparation of silicon capsules in an oven, has low equipment requirements, and can be manufactured on a large scale at low cost.

[0033] (6) The material prepared by the method for preparing a continuous fiber-reinforced ceramic-based composite material provided by the present invention has no residual silicon blocks on the surface and the fibers are intact and undamaged. Only slight polishing is required, avoiding damage to the product surface caused by using tools to break the silicon blocks. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 This is a morphology diagram of the continuous fiber-reinforced ceramic matrix composite material prepared in Example 3 of the present invention;

[0035] Figure 2 CT scan photos of the continuous fiber-reinforced ceramic matrix composite prepared in Example 3 of the present invention and a CT scan photo of the C / SiC composite material using traditional silicon powder-embedded RMI;

[0036] Among them, (a) is a CT scan photo of the continuous fiber-reinforced ceramic matrix composite prepared in Example 3 of the present invention; (b) is a CT scan photo of the C / SiC composite material using traditional silicon powder embedded RMI;

[0037] Figure 3 This is a SEM photograph of the fracture surface of the continuous fiber-reinforced ceramic matrix composite material prepared in Example 3;

[0038] Figure 4 The morphology photos of the surface of the RMI after embedding with traditional silicon powder and the surface of the continuous fiber toughened ceramic matrix composite material prepared in Example 3 after being broken are shown;

[0039] (a) is a morphological photograph of the surface of the RMI after being embedded with traditional silicon powder and then subjected to a breaking process; (b) is a morphological photograph of the surface of the continuous fiber-reinforced ceramic matrix composite material prepared in Example 3 after being subjected to a breaking process. DETAILED DESCRIPTION

[0040] The following will clearly and completely describe the technical solutions of the present invention in conjunction with the accompanying drawings and embodiments. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0041] Example 1

[0042] A method for preparing a silicon capsule comprises the following steps:

[0043] Step 1, weighing polyvinyl alcohol and adding it to deionized water, stirring and dissolving it with a magnetic rotor and a magnetic stirrer to obtain a polyvinyl alcohol solution with a concentration of 2%;

[0044] Step 2: Pour silicon particles with a particle size of 0.5 μm to 10 μm into a ball mill, add polyvinyl alcohol solution until the silicon particles are completely immersed, ball mill for 4 hours, and pass through a 5000 mesh sieve to obtain silicon particles with the surface coated with polyvinyl alcohol solution.

[0045] Step 3: Weigh silicon carbide powder with a particle size of 5 μm to 25 μm, silicon particles coated with polyvinyl alcohol solution, and carbon powder, add them to a ball mill, ball mill for 4 hours, pass through a 10-mesh sieve, and add them to the ball mill again; ball mill for 2 hours, pass through a 10-mesh sieve, and obtain silicon capsules.

[0046] The mass proportion of silicon carbide powder is 20%, the mass proportion of silicon particles coated with polyvinyl alcohol solution is 70%, and the mass proportion of carbon powder is 10%.

[0047] This embodiment also provides a method for preparing a continuous fiber-reinforced ceramic matrix composite material, comprising the following steps:

[0048] Step A: placing the porous carbon fiber prepared by the CVI method as a porous intermediate into a graphite crucible or a graphite paper box, and evenly embedding the silicon capsules on the surface of the porous intermediate;

[0049] Step B: placing the graphite crucible into a vacuum sintering furnace, adjusting the reaction temperature to 1450° C., sintering for 2 hours, and cooling to room temperature to obtain a continuous fiber-reinforced ceramic matrix composite material.

[0050] Example 2

[0051] A method for preparing a silicon capsule comprises the following steps:

[0052] Step 1, weighing polyvinyl alcohol and adding it to deionized water, stirring and dissolving it with a magnetic rotor and a magnetic stirrer to obtain a polyvinyl alcohol solution with a concentration of 2%;

[0053] Step 2: Pour silicon particles with a particle size of 0.5 μm to 10 μm into a ball mill, add polyvinyl alcohol solution until the silicon particles are completely immersed, ball mill for 6 hours, and pass through an 8000 mesh sieve to obtain silicon particles with the surface coated with polyvinyl alcohol solution.

[0054] The silicon particles are silicon powder coated with polydopamine on the surface, and the preparation method is as follows:

[0055] Step a: taking tris(hydroxymethyl)aminomethane and tris(hydroxymethyl)aminomethane hydrochloride in a mass ratio of 2:1, dissolving 5 g of the obtained mixture in 100 ml of deionized water, and stirring magnetically for 1 hour to obtain a buffer solution; weighing 50 ml of the buffer solution, and adding dopamine, with a mass ratio of dopamine to buffer solution of 1:3, and stirring magnetically for 1 hour to obtain a dopamine solution;

[0056] Step b, weighing silicon powder with a particle size of 0.4 μm to 1 μm and a dopamine solution in a mass ratio of 1:5, magnetically stirring for 20 hours to obtain a suspension, centrifuging the suspension, and centrifuging and washing it three times with alcohol and deionized water respectively until the supernatant is colorless and transparent to obtain a precipitate, placing the precipitate in a crucible, and placing it in an oven to dry at a drying temperature of 100° C. and a drying time of 10 hours to obtain polydopamine-coated silicon particles with a particle size of 0.5 μm to 10 μm.

[0057] Step 3: Weigh silicon carbide powder with a particle size of 5 μm to 25 μm, silicon particles coated with polyvinyl alcohol solution, and carbon powder, add them to a ball mill, ball mill for 2 h to 10 h, pass through a 10-mesh sieve, and add them to the ball mill again; ball mill for 2 h to 4 h, pass through a 10-mesh sieve to obtain silicon capsules.

[0058] The mass proportion of silicon carbide powder is 15%, the mass proportion of silicon particles coated with polyvinyl alcohol solution is 78%, and the mass proportion of carbon powder is 7%.

[0059] This embodiment also provides a method for preparing a continuous fiber-reinforced ceramic matrix composite material, comprising the following steps:

[0060] Step A: placing the porous silicon carbide fiber preform prepared by the So-Gel method into a graphite crucible or a graphite paper box, and evenly embedding the silicon capsules on the surface of the porous intermediate;

[0061] Step B: placing the graphite crucible in a vacuum sintering furnace, adjusting the reaction temperature to 1500° C., sintering for 2.5 hours, and cooling to room temperature to obtain a continuous fiber-reinforced ceramic matrix composite material.

[0062] Example 3

[0063] A method for preparing a silicon capsule comprises the following steps:

[0064] Step 1, weighing polyvinyl alcohol and adding it to deionized water, stirring and dissolving it with a magnetic rotor and a magnetic stirrer to obtain a polyvinyl alcohol solution with a concentration of 8%;

[0065] Step 2: Pour silicon particles with a particle size of 0.5 μm to 10 μm into a ball mill, add polyvinyl alcohol solution until the silicon particles are completely immersed, ball mill for 6 hours, and pass through a 10,000 mesh sieve to obtain silicon particles with the surface coated with polyvinyl alcohol solution.

[0066] The silicon particles are silicon powder coated with polydopamine on the surface, and the preparation method is as follows:

[0067] Step a, taking tris (hydroxymethyl) aminomethane and tris (hydroxymethyl) aminomethane hydrochloride in a mass ratio of 10:1, taking 4g of the obtained mixture into 100ml of deionized water, and magnetically stirring for 2h to obtain a buffer solution; weighing 100ml of the buffer solution, and adding dopamine, the mass ratio of dopamine to buffer solution is 5:1, and magnetically stirring for 3h to obtain a dopamine solution;

[0068] Step b, weighing silicon powder with a particle size of 0.4 μm to 1 μm and a dopamine solution in a mass ratio of 1:1, magnetically stirring for 40 hours to obtain a suspension, centrifuging the suspension, and centrifuging and washing with alcohol and deionized water for 5 times respectively until the supernatant is colorless and transparent to obtain a precipitate, placing the precipitate in a crucible, and placing it in an oven to dry at a drying temperature of 150° C. for 40 hours to obtain polydopamine-coated silicon particles with a particle size of 0.5 μm to 10 μm.

[0069] Step 3: Weigh silicon carbide powder with a particle size of 5 μm to 25 μm, silicon particles coated with polyvinyl alcohol solution, and carbon powder, add them to a ball mill, ball mill for 10 hours, pass through a 10-mesh sieve, and add them to the ball mill again; ball mill for 4 hours, pass through a 10-mesh sieve, and obtain silicon capsules.

[0070] The mass proportion of silicon carbide powder is 20%, the mass proportion of silicon particles coated with polyvinyl alcohol solution is 70%, and the mass proportion of carbon powder is 10%.

[0071] This embodiment also provides a method for preparing a continuous fiber-reinforced ceramic matrix composite material, comprising the following steps:

[0072] Step A, placing a porous ceramic whisker preform prepared by the So-Gel method into a graphite crucible or a graphite paper box, and evenly embedding silicon capsules on the surface of the porous ceramic whisker preform;

[0073] Step B: placing the graphite crucible in a vacuum sintering furnace, adjusting the reaction temperature to 1600° C., sintering for 3 hours, and cooling to room temperature to obtain a continuous fiber-reinforced ceramic matrix composite material.

[0074] Figure 1 This is the appearance morphology of the continuous fiber toughened ceramic matrix composite material prepared in Example 3. Figure 1 It can be seen that there are no extra silicon pieces on the surface; only slight polishing is required to obtain a product with net size.

[0075] The continuous fiber toughened ceramic matrix composite material prepared in Example 3 was subjected to CT scanning, and the scanned photos obtained are as follows: Figure 2 As shown in (a). Figure 2 (b) shows the density of 1.3-1.4 g / cm obtained by using traditional silicon powder to embed RMI. 3 CT scan of semi-dense C / SiC composite material. Figure 2 Comparison between (a) and (b) shows that the CT scan photograph of the continuous fiber-reinforced ceramic matrix composite material prepared in Example 3 in (a) shows very uniform infiltration; while in (b) the infiltration is uneven and there is an obvious "black core" area.

[0076] Figure 3 This is a SEM photo of the fracture of the continuous fiber toughened ceramic matrix composite material prepared in Example 3. Figure 3 It can be seen that the continuous fiber reinforced ceramic matrix composite prepared in this embodiment has a dense interior, extremely small pore size and low porosity. The density of RMI-siliconized C / SiC can reach 2.6g / cm 3 , the porosity is 1.9%.

[0077] Figure 4 (a) is a photo of the surface of the RMI after the traditional silicon powder embedding process. It can be seen that due to the adhesion of large areas of silicon melt, silicon blocks are formed during cooling and are combined with the SiC on the surface through chemical reactions. The bonding force is too strong, resulting in large areas of fibers being peeled off after the blocks are broken, and the product surface is seriously damaged. The continuous fiber-reinforced ceramic matrix composite prepared in Example 3, such as Figure 4 As shown in (b), after surface polishing, the surface fibers of the product are well preserved.

[0078] The above description is merely a specific embodiment of the present invention, and a comparison of the effects of the specific embodiment with the relevant comparative examples. However, the scope of protection of the present invention is not limited thereto. Any changes or substitutions within the technical scope disclosed in the present invention shall be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention shall be based on the scope of protection of the claims.

Claims

1. A method for preparing a silicon capsule, characterized in that: The following steps are involved: Step 1, weighing polyvinyl alcohol and adding it to deionized water, stirring and dissolving it with a magnetic rotor and a magnetic stirrer to obtain a polyvinyl alcohol solution with a concentration of 2% to 8%; Step 2: Weigh silicon particles and pour them into a ball mill, add polyvinyl alcohol solution until the silicon particles are completely immersed, ball mill, and sieve to obtain silicon particles with the polyvinyl alcohol solution coated on the surface; Step 3: Weigh silicon carbide powder, silicon particles coated with polyvinyl alcohol solution, and carbon powder and add them into a ball mill. After ball milling, sieve them, and continue ball milling and sieving to obtain silicon capsules.

2. The method for preparing a silicon capsule according to claim 1, characterized in that: In step 3, the mass proportion of the silicon carbide powder is 10%-20%, the mass proportion of the silicon particles coated with polyvinyl alcohol solution is 70%-80%, and the mass proportion of carbon powder is 5%-10%. The sum of the mass percentages of the above components is 100%.

3. The method for preparing a silicon capsule according to claim 1, characterized in that: Step 2 is as follows: Pour silicon particles with a particle size of 0.5μm to 10μm into a ball mill, add polyvinyl alcohol solution until the silicon particles are completely immersed, ball mill for 4h to 6h, and pass through a 5000-10000 mesh sieve to obtain silicon particles with the surface coated with polyvinyl alcohol solution.

4. The method for preparing a silicon capsule according to claim 1 or 3, characterized in that: The silicon particles in step 2 are silicon powder coated with polydopamine, and the preparation method is: Step a, mixing tris(hydroxymethyl)aminomethane and tris(hydroxymethyl)aminomethane hydrochloride in a mass ratio of 1 to 10:1 to obtain a mixture, dissolving the mixture in deionized water at a mass ratio of deionized water to the mixture of 10 to 30:1, and magnetically stirring for 1 to 2 hours to obtain a buffer solution; weighing 10 to 100 ml of the buffer solution, adding dopamine at a mass ratio of dopamine to the buffer solution of 1 to 50:1 to 100, and magnetically stirring for 1 to 3 hours to obtain a dopamine solution; Step b, weighing silicon powder with a particle size of 0.4 μm to 1 μm and a dopamine solution in a mass ratio of 1 to 10:1 to 100, magnetically stirring for 20 to 200 hours to obtain a suspension, centrifuging the suspension, and centrifugally washing it 2 to 5 times with alcohol and deionized water respectively until the supernatant is colorless and transparent to obtain a precipitate, placing the precipitate in a crucible, and drying it in an oven to obtain polydopamine-coated silicon particles with a particle size of 0.5 μm to 10 μm.

5. The method for preparing a silicon capsule according to claim 4, characterized in that: In step b, the drying temperature in the oven is 50° C. to 150° C., and the drying time is 10 h to 40 h.

6. The method for preparing a silicon capsule according to claim 1 or 2, characterized in that: Step 3 is as follows: Step 3.1, weighing silicon carbide powder with a particle size of 5 μm to 25 μm, silicon particles coated with polyvinyl alcohol solution, and carbon powder, adding them to a ball mill, ball milling for 2 h to 10 h, passing through a 10-mesh sieve, and adding them to the ball mill again; Step 3.2: ball mill for 2 h to 4 h, and pass through a 10-mesh sieve to obtain silicon capsules.

7. A silicon capsule, characterized in that: The silicon capsule is prepared using the preparation method of any one of claims 1 to 6.

8. A method for preparing a continuous fiber-reinforced ceramic matrix composite material, characterized in that: The following steps are involved: Step A, placing the porous intermediate into a graphite crucible or a graphite paper box, and uniformly embedding the silicon capsules prepared by the silicon capsule preparation method according to any one of claims 1 to 6 on the surface of the porous intermediate; Step B: placing the graphite crucible in a vacuum sintering furnace, sintering, and cooling to room temperature to obtain a continuous fiber-reinforced ceramic-based composite material.

9. The method for preparing a continuous fiber-reinforced ceramic matrix composite material according to claim 8, characterized in that: In step A, the porous intermediate is one of a porous carbon fiber, a porous silicon carbide fiber preform, a porous ceramic whisker preform, a porous tape-cast ceramic embryo, and a porous gel-injection-molded ceramic embryo prepared by one of the CVI, PIP, SI, and So-Gel methods.

10. The method for preparing a continuous fiber-reinforced ceramic matrix composite material according to claim 8, characterized in that: Step B is specifically as follows: placing a graphite crucible into a vacuum sintering furnace, adjusting the reaction temperature to between 1450° C. and 1600° C., sintering for 2 h to 3 h, and cooling to obtain a dense silicon capsule for reactive melt infiltration with low porosity.

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