Silicon carbide ceramic composite for nuclear energy safety structure and method for manufacturing the same

Abstract

The application belongs to the technical field of nuclear energy key structure materials, and relates to a silicon carbide ceramic composite material for a nuclear energy safety structure and a preparation method thereof.In raw material selection, conventional beta-SiC powder is used as a basic raw material, and Al4C3-C with a low neutron absorption cross section is introduced on the surface of the SiC powder in situ through a molten salt method, so that low-temperature densification of the SiC ceramic is successfully realized without introducing any high neutron absorption cross section element.The SiC ceramic prepared in this way has the characteristics of low porosity, uniform microstructure and pure grain boundary phase, and thus exhibits excellent mechanical properties.

Description

Technical Field

[0001] This invention belongs to the field of key structural materials technology for nuclear energy, and relates to a silicon carbide ceramic composite material for nuclear energy safety structures and its preparation method. Background Technology

[0002] Silicon carbide (SiC) ceramics possess excellent properties such as low density, high hardness, high strength, and high chemical stability, and have been widely used in aerospace and defense fields. Silicon carbide fiber-reinforced silicon carbide (SiC) f The SiC composite material effectively overcomes the inherent brittleness of traditional SiC ceramics while maintaining its excellent properties such as light weight, high temperature resistance, corrosion resistance, and radiation resistance. This makes it a promising candidate material for advanced nuclear energy applications and has become one of the ideal materials for nuclear fuel cladding components.

[0003] But SiC f SiC composite materials, when used as core-shell components, suffer from problems such as long densification cycles, low densification levels, low crystallinity, and excessive residual phases. Currently, the preparation of SiC... f The main methods for preparing SiC composites include precursor impregnation pyrolysis (PIP), chemical vapor infiltration (CVI), reactive melting infiltration (RMI), and nano-infiltration transient eutectic (NITE). PIP has a preparation cycle of over 20 days and results in high residual carbon content, high porosity, and poor crystallinity in the matrix. CVI can obtain a high-purity SiC matrix, but faces challenges of high porosity and low crystallinity. RMI produces composites with low porosity but high residual silicon content, and molten silicon at high temperatures easily corrodes SiC fibers. In contrast, NITE has significant advantages such as short cycle time, high densification, and high crystallinity. However, NITE has a high densification temperature and residual sintering aids, which often lead to thermal damage and sintering aid corrosion of SiC fibers, thus reducing their service performance. Furthermore, sintering aids with high residual neutron absorption cross-sections directly reduce the effective utilization of neutrons under reactor conditions, shortening the fuel cycle and increasing operating costs.

[0004] Chinese patent application document (publication number: CN112374902A) discloses a composite process for preparing SiC using CVI process for preforming and NITE process for filling residual pores. f / SiC composite materials have effectively achieved high density in complex components. However, the CVI process used in this method significantly increases the preparation cost of the composite material and extends the preparation cycle. Furthermore, the NITE process still uses a sintering aid system of yttrium oxide and alumina containing elements with high neutron absorption cross sections. Therefore, this method is not suitable for the preparation of core-shell components.

[0005] Chinese patent application document (publication number: CN114907127B) discloses a method for preparing SiC by adding polycarbosilane to NITE-SiC slurry to reduce sintering difficulty and using alumina or zirconium oxide as sintering aid. f / SiC composite materials effectively improve the mechanical properties of composite materials. However, the polycarbosilane used in this method will produce residual carbon in the matrix after cracking, which may potentially affect the radiation resistance and corrosion resistance of the composite material.

[0006] Chinese patent application document (publication number: CN1119661244A) discloses a method for growing a rare earth (RE) silicon-carbon (RE3Si2C2) coating layer on the surface of SiC powder using a molten salt method, and using this SiC@RE3Si2C2 powder directly as the initial powder for NITE-SiC slurry, thereby promoting the low-temperature sintering of composite materials and effectively utilizing SiC. f The densification temperature of the SiC composite material was reduced to 1600℃, which can avoid thermal damage to SiC fibers at high temperatures. However, the rare earth elements used in this method, such as Pr, Gd, and Y, all have high neutron absorption cross sections, so they are still not suitable for the preparation of core-shell components. Summary of the Invention

[0007] The purpose of this invention is to address the aforementioned problems in the existing technology by proposing a silicon carbide ceramic composite material for nuclear energy safety structures. Al4C3-C is in situ coated on the surface of SiC powder using the molten salt method, and densification of the SiC ceramic composite material is successfully achieved without introducing any high neutron absorption cross-section elements.

[0008] The objective of this invention can be achieved through the following technical solutions: A method for preparing a silicon carbide ceramic composite material for nuclear energy safety structures, the method comprising the following steps: S1. SiC powder, aluminum chloride and carbon black are ground in a molten salt medium and then subjected to high temperature treatment to obtain composite powder; S2. Add dispersant and solvent to the composite powder and ball mill, then add polyvinyl butyral and ball mill to obtain SiC ceramic slurry; S3. SiC fibers and SiC ceramic slurry are laminated, then impregnated, and then dried to obtain SiC prepreg sheets; S4. The SiC prepreg is heat-treated and then subjected to spark plasma sintering to obtain the SiC. f / SiC ceramic matrix composites.

[0009] This invention proposes a novel strategy for in-situ coating of Al4C3-C composite phase onto the surface of silicon carbide (SiC) powder using a molten salt method. This method successfully achieves efficient densification of SiC ceramic composites while completely avoiding the introduction of high neutron absorption cross-section elements such as boron and cadmium. The method utilizes molten salt as a reaction and transport medium, enabling highly uniform adsorption and coating of the Al4C3-C precursor on the SiC particle surface, fundamentally overcoming the compositional inhomogeneity problem caused by powder agglomeration in traditional mechanical mixing methods. Furthermore, by precisely controlling the molten salt system, the thickness, phase composition, and uniformity of the Al4C3-C coating layer on the powder surface can be effectively adjusted, thereby significantly improving the stability and repeatability of subsequent sintering processes. During sintering, the uniformly dispersed Al4C3-C phase can not only effectively suppress the migration of SiC grain boundaries and prevent abnormal grain growth, but also help to form a fine and uniform microstructure, significantly enhancing the strength, hardness and fracture toughness of the material. At the same time, this coating layer can also promote the shrinkage, filling and closure of pores, greatly improve the matrix density, and effectively reduce the risk of microcracks initiation during sintering or service. This provides a reliable technical path for developing high-performance SiC-based structural ceramics suitable for harsh environments such as nuclear energy.

[0010] Aluminum chloride, with its low melting point in molten salt systems, rapidly dissociates into aluminum ions and disperses uniformly within the molten salt medium, significantly reducing the activation energy of the reaction. Carbon black, as a highly active carbon source, possesses a large specific surface area and abundant surface active sites due to its nano-sized particles, enabling it to undergo a directional in-situ synthesis reaction with aluminum ions on the SiC powder surface. This generates the Al4C3 phase, while unreacted carbon black can be directly adsorbed and deposited on the SiC surface, forming a uniform and continuous Al4C3-C composite coating layer. This avoids the defects of localized overheating and runaway reactions common in traditional solid-phase reactions. Furthermore, no solid impurities remain after the raw material reaction; chlorine in aluminum chloride is removed in gaseous form, and carbon black does not introduce nitrogen- or oxygen-containing byproducts, effectively improving the purity of the SiC powder and the density of the composite coating layer, preventing performance degradation caused by impurities and porosity. In addition, the ratio of aluminum chloride to carbon black can be precisely controlled to determine the proportion of Al4C3 and C in the composite coating layer, flexibly adapting to the differentiated performance requirements of various applications.

[0011] In the above-mentioned method for preparing a silicon carbide ceramic composite material for nuclear energy safety structures, in step S1, the mass ratio of SiC powder, aluminum chloride, carbon black, and molten salt medium is (85-94):(5-10):(1-5):(150-200). This invention, by controlling the raw material ratio, can minimize the enrichment of sintering aids at the composite material interface, thereby effectively reducing the impact of sintering aids at grain boundaries on the thermal conductivity of the composite material. Aluminum chloride can directly provide aluminum ions in the molten salt. Aluminum ions are uniformly distributed on the surface of SiC powder through ion migration, resulting in more comprehensive and uniform coating of the SiC powder. Conventional aluminum powder requires additional redox reactions, and side reactions can affect the reaction rate and may lead to uneven distribution of the final aids. However, excessive addition of aluminum chloride can cause aluminum-rich phases at the matrix or fiber interface after sintering, affecting the thermal conductivity and mechanical properties of the composite material. Excessive sintering aids may also corrode the fibers, thereby reducing the strength and toughness of the composite material; insufficient addition will prevent the composite material from achieving dense sintering. Excessive carbon black will accumulate in local areas, reducing the uniformity of sintering aids introduced by the molten salt method, and the final composite material will also have reduced performance due to excessive carbon in some areas; insufficient carbon black will prevent the composite material from sintering densely.

[0012] In the above-mentioned method for preparing a silicon carbide ceramic composite material for nuclear safety structures, the average particle size of SiC powder is 30nm-2μm, the aluminum chloride is anhydrous AlCl3 with a purity of over 98%, and the average particle size of carbon black is 10-50nm.

[0013] Preferably, the SiC powder is β-SiC powder.

[0014] In the above-mentioned method for preparing a silicon carbide ceramic composite material for nuclear energy safety structures, in step S1, the molten salt medium is a sodium salt and a potassium salt with a molar ratio of 1:(0.5-1.5), wherein the sodium salt is one of NaCl, NaNO3, and Na2SO4, and the potassium salt is one of KCl, KNO3, and K2SO4.

[0015] This invention utilizes the fact that the melting point of the molten salt medium formed by mixing sodium and potassium salts is much lower than the individual melting points of each component, thereby effectively reducing the process temperature required for the entire coating and reaction process. This low-temperature advantage not only helps reduce energy consumption and improve process economy, but also avoids adverse side reactions such as pre-sintering or surface oxidation of SiC powder at high temperatures, ensuring the high activity and uniformity of the powder during subsequent sintering. At the same time, the lower processing temperature also provides convenience for equipment material selection and operational safety, making it particularly suitable for nuclear ceramic material preparation systems that are heat-sensitive or require strict control of impurity introduction, demonstrating good engineering application prospects and sustainability.

[0016] In the above-mentioned method for preparing a silicon carbide ceramic composite material for nuclear energy safety structures, in step S1, the high-temperature treatment temperature is 900-1200℃, the heating rate is 5-20℃ / min, and the holding time is 200-250min.

[0017] Preferably, in step S1, after the high-temperature treatment, a demolten salt treatment is also performed, which specifically includes stirring the composite powder in an organic solvent, rinsing it with the organic solvent, and finally drying it under vacuum.

[0018] Further preferably, the organic solvent includes at least one selected from formamide, N-methylpyrrolidone, ethylene glycol, anhydrous ethanol, and acetone.

[0019] In the above-mentioned method for preparing a silicon carbide ceramic composite material for nuclear energy safety structures, in step S2, the dispersant is at least one of polyethyleneimine, tetramethylammonium hydroxide, and polyethylene glycol. And / or the solvent is at least one of ethanol, isopropanol, and acetone.

[0020] In the above-mentioned method for preparing a silicon carbide ceramic composite material for nuclear energy safety structures, in step S2, the amount of dispersant added is 0.5-1.5% of the composite powder mass, the amount of solvent added is 70-80% of the composite powder mass, and the amount of polyvinyl butyral added is 5-15% of the composite powder mass. This invention utilizes the excellent film-forming properties, flexibility, and bonding strength of polyvinyl butyral, which plays a crucial role in this process. It enables the uniformly coated SiC powder (Al4C3-C) to firmly adhere to the surface of SiC fibers, forming a stable fiber-matrix interface structure. This provides good structural support for subsequent molding and sintering processes. This design not only helps to achieve uniform densification of fiber-reinforced ceramic matrix composites but also effectively suppresses defects caused by powder shedding or uneven distribution during sintering, significantly improving the mechanical properties and structural reliability of the final material.

[0021] In the above-mentioned method for preparing a silicon carbide ceramic composite material for nuclear energy safety structures, in step S3, the impregnation treatment is vacuum pressure impregnation, wherein the impregnation pressure is 2-3 MPa and the time is 10-20 min.

[0022] In the above-mentioned method for preparing a silicon carbide ceramic composite material for nuclear energy safety structures, in step S4, the heat treatment temperature is 850-950℃ and the time is 1-3h. The sintering temperature and / or discharge plasma sintering temperature is 1600-1900℃, the heating rate is 20-50℃ / min, the pressure is 20-30MPa, and the holding time is 20-60min.

[0023] The purpose of the heat treatment in this invention is to remove the polyvinyl butyral introduced in the previous process through low-temperature pyrolysis, thereby avoiding the introduction of additional carbon sources. However, if the heat treatment temperature is too high, the composite material may be pre-sintered at a lower temperature, affecting the densification effect of the subsequent sintering process. If the heat treatment temperature is too low, the decomposition temperature of the binder may not be reached, resulting in incomplete decomposition.

[0024] Meanwhile, the temperature during spark plasma sintering (SPCS) also needs to be strictly optimized. Too low a temperature leads to insufficient densification, high porosity, and poor mechanical properties; while too high a temperature severely damages the SiC fibers, which act as the reinforcing phase, causing grain coarsening or even breakage, significantly weakening the strength and toughness of the composite material. Therefore, this invention, by precisely matching pyrolysis and sintering parameters, ensures complete removal of the binder while maximizing the protection of the fiber structure and achieving a highly dense matrix, providing a key process guarantee for the preparation of high-performance, high-reliability nuclear-grade SiC ceramic composite materials.

[0025] The present invention also provides a silicon carbide ceramic composite material for nuclear energy safety structures, wherein the silicon carbide ceramic composite material is prepared by the above-described preparation method.

[0026] Compared with the prior art, the present invention has the following beneficial effects: 1. In terms of raw material selection, this invention uses conventional β-SiC powder as the basic raw material, and innovatively introduces Al4C3-C with a low neutron absorption cross section in situ on the surface of SiC powder through the molten salt method. Without introducing any elements with a high neutron absorption cross section, the low-temperature densification of SiC ceramics is successfully achieved. The SiC ceramics prepared in this way have the characteristics of low porosity, uniform microstructure and pure grain boundary phase, thus exhibiting excellent mechanical properties.

[0027] 2. This invention, through sintering using the NITE process, effectively promotes the interfacial bonding between the matrix and fibers, as well as the densification of the matrix itself, resulting in SiC... f The fracture strength of the / SiC composite material was significantly improved, while maintaining the overall low neutron toxicity of the composite material.

[0028] 3. The composite material of this invention is densified using spark plasma sintering technology. The β-SiC raw material, as well as NaCl, KCl, AlCl3, and C, used are all commercially available unmodified raw materials, eliminating the need for complex processes such as additional surface treatment, activation, or pre-synthesis. Therefore, the overall preparation process is reduced, production efficiency and process controllability are improved, which is conducive to industrialization and promotion. Attached Figure Description

[0029] Figure 1 The image shows the XRD pattern of the composite powder prepared in Example 1.

[0030] Figure 2 The image shows the SEM image of the composite powder prepared in Example 1.

[0031] Figure 3 SiC prepared in Example 1 f SEM image of the / SiC composite material after polishing.

[0032] Figure 4 SiC prepared in Comparative Example 1 f SEM image of the / SiC composite material after polishing. Detailed Implementation

[0033] The following are specific embodiments of the present invention, which further describe the technical solution of the present invention. However, the present invention is not limited to these embodiments. The following embodiments further illustrate the content of the present invention, but should not be construed as limiting the present invention. Modifications and substitutions made to the inventive methods, steps, or conditions without departing from the essence of the invention are all within the scope of the present invention.

[0034] The following examples use the following raw material selection: The SiC powder was β-SiC powder purchased from Qinhuangdao Yinuo New Material Technology Co., Ltd.

[0035] The SiC fiber cloth, model S01 / 3H290-120 / 88, was purchased from Fujian Liya New Materials Co., Ltd.

[0036] The aluminum chloride was anhydrous AlCl3 purchased from Shanghai Aladdin Biochemical Technology Co., Ltd.

[0037] The carbon black had an average particle size of 20 nm and was purchased from Qinhuangdao Yinuo New Material Technology Co., Ltd.

[0038] The alumina had an average particle size of 3 μm and was purchased from Shanghai Aladdin Biochemical Technology Co., Ltd.

[0039] Polyethyleneimine (PEI), with a molecular weight of 10,000, was purchased from Shanghai Aladdin Biochemical Technology Co., Ltd.

[0040] Polyvinyl butyral (PVB) was purchased from Sinopharm Chemical Reagent Co., Ltd.

[0041] Ethanol (C2H5OH), analytical grade, purchased from Sinopharm Chemical Reagent Co., Ltd.

[0042] In this embodiment of the invention, the heat treatment equipment used is a pyrolysis furnace.

[0043] In this embodiment of the invention, the sintering equipment used is a spark plasma sintering furnace.

[0044] In this embodiment of the invention, the thermal conductivity is tested using the laser thermal conductivity method, and the test is performed using a Netzsch LFA 467 laser thermal conductivity meter.

[0045] In this embodiment of the invention, the Archimedes' method of water displacement is used to test the open porosity and bulk density.

[0046] Example 1: S1. Prepare powder raw materials with the following mass percentages: 91wt% SiC powder, 6wt% aluminum chloride and 3wt% carbon black; SiC powder, aluminum chloride, and carbon black were ground in a molten salt medium. The total mass of sodium chloride and potassium chloride in the molten salt medium was twice that of the powder raw material, and the molar ratio of the two was 1:1. The powder was then placed in a tube furnace and heated to 1000℃ at a rate of 5℃ / min and held for 240min. The composite powder was then added to formamide and magnetically stirred for 120 minutes, then rinsed with anhydrous ethanol, and finally vacuum dried to obtain the composite powder. Then add 1 wt% polyethyleneimine of the total mass of the composite powder and 75 wt% ethanol of the total mass of the slurry system, so that the total mass fraction of the solid phase is about 25 wt%. Then ball mill for 2 hours, add 10 wt% polyvinyl butyral of the total mass of the powder, and continue ball milling for 12 hours to form SiC ceramic slurry. S2. Pour the slurry into the plastic cup to cover the bottom layer. Then, add a layer of SiC fiber cloth and a layer of the above-mentioned SiC ceramic slurry into the plastic cup. The last layer of SiC ceramic slurry should be about 1cm higher than the fiber cloth. A total of 5 pieces of SiC fiber cloth and 6 layers of the above-mentioned SiC ceramic slurry are set in the plastic cup. The thickness of each layer of SiC ceramic slurry is 0.5cm. S3. Place the plastic cup into the impregnation tank for vacuum pressure impregnation. Set the vacuum to 4500Pa, the pressure to 3MPa, and the time to 10min to obtain a pre-impregnated sheet. S4. Remove the pre-impregnated sheet, air dry it at room temperature, and cut it to a size of 30×30mm. S5. Place the cut prepreg sheet into a graphite mold and heat-treat it at 900℃ for 1 hour. S6. Finally, the pre-impregnated sheet and the graphite mold are passed together through a spark plasma sintering furnace at 1700℃ and 20MPa for 30 minutes to obtain SiC. f / SiC ceramic matrix composites.

[0047] Figure 1-2 The images show the XRD and SEM images of the composite powder prepared in step S1 of the embodiment. As can be seen from the images, the present invention successfully generated an in-situ coated Al4C3-C composite phase on the surface of silicon carbide powder.

[0048] Figure 3 SiC prepared in Example 1 f SEM image of the SiC composite material after polishing. The image shows that the SiC fiber surface is smooth, the matrix has few pores, and the interface layer is intact.

[0049] Example 2: S1. Prepare the following powder raw materials by weight percentage: 85wt% SiC powder, 10wt% aluminum chloride and 5wt% carbon black; SiC powder, aluminum chloride, and carbon black were ground in a molten salt medium. The total mass of sodium chloride and potassium chloride in the molten salt medium was twice that of the powder raw material, and the molar ratio of the two was 1:1. The powder was then placed in a tube furnace and heated to 1000℃ at a rate of 5℃ / min and held for 240min. The composite powder was then added to formamide and magnetically stirred for 120 minutes, then rinsed with anhydrous ethanol, and finally vacuum dried to obtain the composite powder. Then add 1 wt% polyethyleneimine of the total mass of the composite powder and 75 wt% ethanol of the total mass of the slurry system, so that the total mass fraction of the solid phase is about 25 wt%. Then ball mill for 2 hours, add 10 wt% polyvinyl butyral of the total mass of the powder, and continue ball milling for 12 hours to form SiC ceramic slurry. S2. Pour the slurry into the plastic cup to cover the bottom layer. Then, add a layer of SiC fiber cloth and a layer of the above-mentioned SiC ceramic slurry into the plastic cup. The last layer of SiC ceramic slurry should be about 1cm higher than the fiber cloth. The plastic cup is equipped with a total of 5 pieces of SiC fiber cloth and 6 layers of the above-mentioned SiC ceramic slurry. The thickness of each layer of SiC ceramic slurry is about 0.5cm. S3. Place the plastic cup into the impregnation tank for vacuum pressure impregnation. Set the vacuum to 4500Pa, the pressure to 3MPa, and the time to 10min to obtain a pre-impregnated sheet. S4. Remove the pre-impregnated sheet, air dry it at room temperature, and cut it to a size of 30×30mm. S5. Place the cut prepreg sheet into a graphite mold and heat-treat it at 900℃ for 1 hour. S6. Finally, the pre-impregnated sheet and the graphite mold are passed together through a spark plasma sintering furnace at 1850℃ and 20MPa for 30 minutes to obtain SiC. f / SiC ceramic matrix composites.

[0050] Example 3: S1. Prepare the following powder raw materials by weight percentage: 94wt% SiC powder, 5wt% aluminum chloride and 1wt% carbon black; SiC powder, aluminum chloride, and carbon black were ground in a molten salt medium. The total mass of sodium chloride and potassium chloride in the molten salt medium was twice that of the powder raw material, and the molar ratio of the two was 1:1. The powder was then placed in a tube furnace and heated to 1000℃ at a rate of 5℃ / min and held for 240min. The composite powder was then added to formamide and magnetically stirred for 120 minutes, then rinsed with anhydrous ethanol, and finally vacuum dried to obtain the composite powder. Then add 1 wt% polyethyleneimine of the total mass of the composite powder and 75 wt% ethanol of the total mass of the slurry system, so that the total mass fraction of the solid phase is about 25 wt%. Then ball mill for 2 hours, add 10 wt% polyvinyl butyral of the total mass of the powder, and continue ball milling for 12 hours to form SiC ceramic slurry. S2. Pour the slurry into the plastic cup to cover the bottom layer. Then, add a layer of SiC fiber cloth and a layer of the above-mentioned SiC ceramic slurry into the plastic cup. The last layer of SiC ceramic slurry should be about 1cm higher than the fiber cloth. The plastic cup is equipped with a total of 5 pieces of SiC fiber cloth and 6 layers of the above-mentioned SiC ceramic slurry. The thickness of each layer of SiC ceramic slurry is about 0.5cm. S3. Place the plastic cup into the impregnation tank for vacuum pressure impregnation. Set the vacuum to 4500Pa, the pressure to 3MPa, and the time to 10min to obtain a pre-impregnated sheet. S4. Remove the pre-impregnated sheet, air dry it at room temperature, and cut it to a size of 30×30mm. S5. Place the cut prepreg sheet into a graphite mold and heat-treat it at 900℃ for 1 hour. S6. Finally, the pre-impregnated sheet and the graphite mold are passed together through a spark plasma sintering furnace at 1650℃ and 20MPa for 30 minutes to obtain SiC. f / SiC ceramic matrix composites.

[0051] Example 4: The difference from Example 1 is only that in step S1, the following powder raw materials are prepared in weight percentages: 96 wt% SiC powder, 1 wt% aluminum chloride and 3 wt% carbon black.

[0052] Example 5: The difference from Example 1 is only that, in step S1, the following powder raw materials are prepared in weight percentages: 82wt% SiC powder, 15wt% aluminum chloride and 3wt% carbon black.

[0053] Example 6: The difference from Example 1 is only that, in step S1, the following powder raw materials are prepared in weight percentages: 93.9 wt% SiC powder, 6 wt% aluminum chloride and 0.1 wt% carbon black; Example 7: The difference from Example 1 is only that, in step S1, the following powder raw materials are prepared in weight percentages: 84 wt% SiC powder, 6 wt% aluminum chloride and 10 wt% carbon black; Example 8: The only difference from Example 1 is that in step S1, the molten salt medium is sodium chloride.

[0054] Example 9: The only difference from Example 1 is that in step S1, the molten salt medium is potassium chloride.

[0055] Example 10: The difference from Example 1 is that in step S1, the composite powder is prepared by heating the powder in a tube furnace at a rate of 5°C / min to 800°C and holding it at that temperature for 240 min.

[0056] Example 11: The difference from Example 1 is that in step S1, the composite powder is prepared by heating the powder in a tube furnace at a rate of 5°C / min to 1500°C and holding it at that temperature for 240 min.

[0057] Example 12: The difference from Example 1 is only that step S5 does not involve heat treatment; instead, the cut pre-impregnated sheet and graphite mold are passed together through a spark plasma sintering furnace at 1700°C and 20 MPa for 30 minutes to obtain SiC. f / SiC ceramic matrix composites.

[0058] Comparative Example 1: S1. Add 90wt% SiC powder and 10wt% alumina to a ball mill jar, then add 1wt% polyethyleneimine (based on the total mass of the powder) and 75wt% ethanol (based on the total mass of the slurry system), so that the total mass fraction of the solid phase is about 25wt%. Then ball mill for 2 hours, add 10wt% polyvinyl butyral (based on the total mass of the powder), and continue ball milling for 12 hours to form SiC ceramic slurry. S2. Pour the slurry into the plastic cup to cover the bottom layer. Then, add a layer of SiC fiber cloth and a layer of the above-mentioned SiC ceramic slurry into the plastic cup. The last layer of SiC ceramic slurry should be about 1cm higher than the fiber cloth. The plastic cup is equipped with a total of 5 pieces of SiC fiber cloth and 6 layers of the above-mentioned SiC ceramic slurry. The thickness of each layer of SiC ceramic slurry is about 0.5cm. S3. Place the plastic cup into the impregnation tank for vacuum pressure impregnation. Set the vacuum to 4500Pa, the pressure to 3MPa, and the time to 10min to obtain a pre-impregnated sheet. S4. Remove the pre-impregnated sheet, air dry it at room temperature, and cut it to a size of 30×30mm. S5. Place the cut prepreg sheet into a graphite mold and heat-treat it at 900℃ for 1 hour to remove the adhesive. S6. Finally, the pre-impregnated sheet and the graphite mold are passed together through a spark plasma sintering furnace at 1700℃ and 20MPa for 30 minutes to obtain SiC. f / SiC ceramic matrix composites.

[0059] Figure 4 SiC prepared in Comparative Example 1 f SEM image of the SiC composite material after polishing. The image shows that the SiC fiber edges are blurred, the matrix has many pores, and the interface is largely eroded.

[0060] Comparative Example 2: S1. Prepare powder raw materials with the following mass percentages: 91wt% SiC powder, 6wt% aluminum powder and 3wt% carbon black; SiC powder, aluminum powder, and carbon black are ground in a molten salt medium. The total mass of sodium chloride and potassium chloride in the molten salt medium is twice that of the powder raw materials, and the molar ratio of the two is 1:1. The powder is then placed in a tube furnace and heated to 1000℃ at a rate of 5℃ / min and held for 240min to produce powder. The composite powder was then added to formamide and magnetically stirred for 120 minutes, then rinsed with anhydrous ethanol, and finally vacuum dried to obtain the composite powder. Then add 1 wt% polyethyleneimine of the total mass of the composite powder and 75 wt% ethanol of the total mass of the slurry system, so that the total mass fraction of the solid phase is about 25 wt%. Then ball mill for 2 hours, add 10 wt% polyvinyl butyral of the total mass of the powder, and continue ball milling for 12 hours to form SiC ceramic slurry. S2. Pour the slurry into the plastic cup to cover the bottom layer. Then, add a layer of SiC fiber cloth and a layer of the above-mentioned SiC ceramic slurry into the plastic cup. The last layer of SiC ceramic slurry should be about 1cm higher than the fiber cloth. The plastic cup is equipped with a total of 5 pieces of SiC fiber cloth and 6 layers of the above-mentioned SiC ceramic slurry. The thickness of each layer of SiC ceramic slurry is about 0.5cm. S3. Place the plastic cup into the impregnation tank for vacuum pressure impregnation. Set the vacuum to 4500Pa, the pressure to 3MPa, and the time to 10min to obtain a pre-impregnated sheet. S4. Remove the pre-impregnated sheet, air dry it at room temperature, and cut it to a size of 30×30mm. S5. Place the cut prepreg sheet into a graphite mold and heat-treat it at 900℃ for 1 hour. S6. Finally, the pre-impregnated sheet and the graphite mold are passed together through a spark plasma sintering furnace at 1700℃ and 20MPa for 30 minutes to obtain SiC. f / SiC ceramic matrix composites.

[0061] Comparative Example 3: S1. Prepare powder raw materials with the following mass percentages: 97wt% SiC powder, 3wt% carbon black; SiC powder and carbon black were ground in a molten salt medium. The total mass of sodium chloride and potassium chloride in the molten salt medium was twice that of the powder raw material, and the molar ratio of the two was 1:1. The powder was then placed in a tube furnace and heated to 1000℃ at a rate of 5℃ / min and held for 240min to produce powder. The composite powder was then added to formamide and magnetically stirred for 120 minutes, then rinsed with anhydrous ethanol, and finally vacuum dried to obtain the composite powder. Then add 1 wt% polyethyleneimine of the total mass of the composite powder and 75 wt% ethanol of the total mass of the slurry system, so that the total mass fraction of the solid phase is about 25 wt%. Then ball mill for 2 hours, add 10 wt% polyvinyl butyral of the total mass of the powder, and continue ball milling for 12 hours to form SiC ceramic slurry. S2. Pour the slurry into the plastic cup to cover the bottom layer. Then, add a layer of SiC fiber cloth and a layer of the above-mentioned SiC ceramic slurry into the plastic cup. The last layer of SiC ceramic slurry should be about 1cm higher than the fiber cloth. The plastic cup is equipped with a total of 5 pieces of SiC fiber cloth and 6 layers of the above-mentioned SiC ceramic slurry. The thickness of each layer of SiC ceramic slurry is about 0.5cm. S3. Place the plastic cup into the impregnation tank for vacuum pressure impregnation. Set the vacuum to 4500Pa, the pressure to 3MPa, and the time to 10min to obtain a pre-impregnated sheet. S4. Remove the pre-impregnated sheet, air dry it at room temperature, and cut it to a size of 30×30mm. S5. Place the cut prepreg sheet into a graphite mold and heat-treat it at 900℃ for 1 hour. S6. Finally, the pre-impregnated sheet and the graphite mold are passed together through a spark plasma sintering furnace at 1700℃ and 20MPa for 30 minutes to obtain SiC. f / SiC ceramic matrix composites.

[0062] Comparative Example 4: S1. Prepare powdered raw materials with the following mass percentages: 94wt% SiC powder, 6wt% aluminum chloride; SiC powder and aluminum chloride were ground in a molten salt medium. The total mass of sodium chloride and potassium chloride in the molten salt medium was twice that of the powder raw material, and the molar ratio of the two was 1:1. The powder was then placed in a tube furnace and heated to 1000℃ at a rate of 5℃ / min and held for 240min to produce powder. The composite powder was then added to formamide and magnetically stirred for 120 minutes, then rinsed with anhydrous ethanol, and finally vacuum dried to obtain the composite powder. Then add 1 wt% polyethyleneimine of the total mass of the composite powder and 75 wt% ethanol of the total mass of the slurry system, so that the total mass fraction of the solid phase is about 25 wt%. Then ball mill for 2 hours, add 10 wt% polyvinyl butyral of the total mass of the powder, and continue ball milling for 12 hours to form SiC ceramic slurry. S2. Pour the slurry into the plastic cup to cover the bottom layer. Then, add a layer of SiC fiber cloth and a layer of the above-mentioned SiC ceramic slurry into the plastic cup. The last layer of SiC ceramic slurry should be about 1cm higher than the fiber cloth. The plastic cup is equipped with a total of 5 pieces of SiC fiber cloth and 6 layers of the above-mentioned SiC ceramic slurry. The thickness of each layer of SiC ceramic slurry is about 0.5cm. S3. Place the plastic cup into the impregnation tank for vacuum pressure impregnation. Set the vacuum to 4500Pa, the pressure to 3MPa, and the time to 10min to obtain a pre-impregnated sheet. S4. Remove the pre-impregnated sheet, air dry it at room temperature, and cut it to a size of 30×30mm. S5. Place the cut prepreg sheet into a graphite mold and heat-treat it at 900℃ for 1 hour. S6. Finally, the pre-impregnated sheet and the graphite mold are passed together through a spark plasma sintering furnace at 1700℃ and 20MPa for 30 minutes to obtain SiC. f / SiC ceramic matrix composites.

[0063] Performance test results of composite materials prepared in Examples 1-12 and Comparative Examples 1-4 In summary, this invention addresses the problems of high sintering temperature and high neutron absorption cross-section of sintering aids in existing technologies, and proposes a SiC... f A method for the low-temperature and rapid densification of SiC composite materials is proposed. This technical solution completely avoids the use of traditional additives with high neutron absorption cross-sections and successfully achieves low-temperature densification of the material. The resulting material has the characteristics of low porosity, uniform microstructure, and pure grain boundary phase. At the same time, the prepared material not only maintains low neutron toxicity as a whole, but also has excellent mechanical properties.

[0064] The embodiments herein cover any points not exhaustively within the scope of the technical claims of this invention, as well as new technical solutions formed by equivalent substitutions of one or more technical features in the embodiments. These are all within the scope of the claims of this invention. Furthermore, in all listed or unlisted embodiments of this invention, each parameter in the same embodiment merely represents an instance (i.e., a feasible solution) of its technical solution, and there is no strict coordination or limitation relationship between the parameters. The parameters can be substituted for each other without violating axioms and the claims of this invention, unless otherwise stated.

[0065] The technical means disclosed in this invention are not limited to those described above, but also include technical solutions composed of any combination of the above technical features. The above descriptions are specific embodiments of this invention. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of this invention, and these improvements and modifications are also considered within the scope of protection of this invention.

[0066] The specific embodiments described herein are merely illustrative of the spirit of the invention. Those skilled in the art to which this invention pertains may make various modifications or additions to the described specific embodiments or use similar methods to substitute them, without departing from the spirit of the invention or exceeding the scope defined by the appended claims.

Claims

1. A method for preparing a silicon carbide ceramic composite material for nuclear energy safety structures, characterized in that, The method includes the following steps: S1. SiC powder, aluminum chloride and carbon black are ground in a molten salt medium and then subjected to high temperature treatment to obtain composite powder; S2. Add dispersant and solvent to the composite powder and ball mill, then add polyvinyl butyral and ball mill to obtain SiC ceramic slurry; S3. SiC fibers and SiC ceramic slurry are laminated, then impregnated, and then dried to obtain SiC prepreg sheets; S4. The SiC prepreg is heat-treated and then subjected to spark plasma sintering to obtain the SiC. f / SiC ceramic matrix composites.

2. The method for preparing a silicon carbide ceramic composite material for nuclear energy safety structures according to claim 1, characterized in that, In step S1, the mass ratio of SiC powder, aluminum chloride, carbon black and molten salt medium is (85-94):(5-10):(1-5):(150-200).

3. The method for preparing a silicon carbide ceramic composite material for nuclear energy safety structures according to claim 1, characterized in that, The average particle size of SiC powder is 30nm-2μm, aluminum chloride is anhydrous AlCl3 with a purity of over 98%, and carbon black has an average particle size of 10-50nm.

4. The method for preparing a silicon carbide ceramic composite material for nuclear energy safety structures according to claim 1, characterized in that, In step S1, the molten salt medium is a sodium salt and a potassium salt with a molar ratio of 1:(0.5-1.5), wherein the sodium salt is one of NaCl, NaNO3, and Na2SO4, and the potassium salt is one of KCl, KNO3, and K2SO4.

5. The method for preparing a silicon carbide ceramic composite material for nuclear energy safety structures according to claim 1, characterized in that, In step S1, the high-temperature treatment temperature is 900-1200℃, the heating rate is 5-20℃ / min, and the holding time is 200-250min.

6. The method for preparing a silicon carbide ceramic composite material for nuclear energy safety structures according to claim 1, characterized in that, In step S2, the amount of dispersant added is 0.5-1.5% of the mass of the composite powder, the amount of solvent added is 70-80% of the mass of the composite powder, and the amount of polyvinyl butyral added is 5-15% of the mass of the composite powder.

7. The method for preparing a silicon carbide ceramic composite material for nuclear energy safety structures according to claim 1, characterized in that, In step S2, the dispersant is at least one of polyethyleneimine, tetramethylammonium hydroxide, and polyethylene glycol; And / or the solvent is at least one of ethanol, isopropanol, and acetone.

8. The method for preparing a silicon carbide ceramic composite material for nuclear energy safety structures according to claim 1, characterized in that, In step S3, the impregnation process is vacuum pressure impregnation, wherein the impregnation pressure is 2-3 MPa and the time is 10-20 min.

9. The method for preparing a silicon carbide ceramic composite material for nuclear energy safety structures according to claim 1, characterized in that, In step S4, the heat treatment temperature is 850-950℃ and the time is 1-3h; The sintering temperature and / or discharge plasma sintering temperature is 1600-1900℃, the heating rate is 20-50℃ / min, the pressure is 20-30MPa, and the holding time is 20-60min.

10. A silicon carbide ceramic composite material for nuclear safety structures, characterized in that, The silicon carbide ceramic composite material is prepared by the preparation method described in any one of claims 1-9.

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