In-situ reaction sintered silicon carbide ceramic and preparation method thereof

Abstract

The invention relates to the technical field of preparation of silicon carbide ceramics, in particular to an in-situ reaction sintered silicon carbide ceramic and a preparation method thereof.The preparation method comprises the following technological stages which are conducted in sequence: S1, preparation of silicon carbide slurry, specifically, organic matter precursor raw materials are weighed according to the mass content percentage to form the silicon carbide slurry; s2, vacuum grouting: injecting the silicon carbide slurry in the vacuum grouting tank into the shaping mold from the bottom of the shaping mold to form a silicon carbide green body; and S3, in-situ reaction sintering is conducted, specifically, the silicon carbide green body is placed in a sintering furnace, heating, heat preservation and cooling are conducted on the silicon carbide green body in the argon atmosphere through a segmented temperature control technology, and the silicon carbide ceramic is obtained. The silicon carbide ceramic prepared by the method disclosed by the invention has relatively high density and excellent mechanical properties.

Description

Technical Field

[0001] This invention relates to the field of silicon carbide ceramic preparation technology, specifically to an in-situ reaction sintering silicon carbide ceramic and its preparation method. Background Technology

[0002] Reaction-bonded silicon carbide ceramics are widely used in high-temperature heat exchangers, semiconductor manufacturing equipment, and aero-engine components due to their excellent high-temperature strength, corrosion resistance, and thermal conductivity. The core preparation principle involves reacting molten silicon with a carbon source at high temperature to generate silicon carbide (SiC), which fills the pores between the original silicon carbide particles, thereby increasing the material's density.

[0003] Traditional reaction sintering technology typically employs the external addition of carbon sources such as carbon black or graphite powder. The carbon source is mixed with silicon carbide powder and then sintered, allowing the molten silicon to react with the carbon source to form SiC. However, this method has several significant drawbacks: First, carbon black or graphite powder tends to agglomerate in the slurry, leading to uneven carbon source distribution and incomplete localized reactions during sintering. Residual carbon black or graphite powder can also reduce the material's mechanical properties. Second, the carbon-to-silicon ratio requires precise control, making process regulation difficult. Third, insufficient carbon source purity can easily introduce impurities such as metal ions and oxides, affecting the material's thermal conductivity and corrosion resistance.

[0004] To address these issues, existing technologies attempt to improve the process through optimization or carbon source replacement. For example, some processes attempt to disperse the carbon source through ball milling, but mechanical ball milling easily leads to the re-agglomeration of graphite powder, and may introduce metallic impurities such as iron and aluminum during the milling process, reducing the material's thermal conductivity. Other processes use starch as a carbon source, generating nano-SiC through in-situ reaction of starch carbonization with metallic silicon. However, after starch carbonization, the carbon distribution is random, resulting in a loose and porous carbon layer that is difficult to preferentially coat the silicon carbide matrix, and the reaction efficiency is low, still exhibiting the problem of uneven carbon source distribution. In summary, the core bottleneck of existing technologies lies in the poor uniformity of carbon source distribution and the introduction of impurities, which limits the density and mechanical properties of silicon carbide ceramic materials. Summary of the Invention

[0005] To address the aforementioned problems in the prior art, this invention provides an in-situ reaction-sintered silicon carbide ceramic and its preparation method. The silicon carbide ceramic prepared by the method of this invention has high density and excellent mechanical properties.

[0006] To achieve the above objectives, a first aspect of the present invention provides a method for preparing in-situ reaction-sintered silicon carbide ceramics, comprising the following steps: S1. Preparation of silicon carbide slurry: Weigh the following raw materials according to the mass percentage: 80wt%-85wt% silicon carbide powder, 10wt%-15wt% organic precursor and 5wt%-7wt% other additives; add a dispersion liquid based on 25wt%-30wt% of the total mass of the raw materials, stir for 36h-48h to form the silicon carbide slurry; S2, Vacuum grouting: The silicon carbide slurry is injected into a vacuum grouting tank, and the silicon carbide slurry in the vacuum grouting tank is injected into the shaping mold from the bottom of the shaping mold. The mold is dried at 80℃~120℃ for 1~2 hours to form the silicon carbide green blank. S3. In-situ reaction sintering: The silicon carbide green blank is placed in a sintering furnace, and silicon particles of 20wt%-40wt% of the total mass of the silicon carbide green blank are evenly sprinkled around it. The silicon carbide green blank is heated, held, and cooled in a segmented temperature control process under an argon atmosphere to obtain silicon carbide ceramics. During the segmented temperature control process, when the temperature inside the sintering furnace is below 1550℃, the pressure of the argon atmosphere in the sintering furnace is 0.05MPa-0.1MPa. When the temperature inside the sintering furnace reaches or exceeds 1550℃, the pressure of the argon atmosphere in the sintering furnace increases to 5MPa-10MPa.

[0007] In one example, the organic precursor in the silicon carbide slurry is coated on the surface of the silicon carbide powder.

[0008] In one example, the particle size of the silicon carbide powder is 3μm-5μm.

[0009] In one example, the organic precursor includes at least one of phenolic resin, polycarbosilane, epoxy resin, isopropanol, glucose, sucrose, and starch.

[0010] In one example, the dispersion comprises at least one of deionized water, ethanol, and acetone.

[0011] In one instance, the other additives include dispersants, binders, and defoamers.

[0012] In one example, the dispersant includes at least one of sodium dodecylbenzenesulfonate, tetramethylammonium hydroxide, polyacrylic acid, ammonium polyacrylate, ammonium citrate, and sodium silicate.

[0013] In one example, the adhesive includes at least one of polyvinyl alcohol and polyethylene glycol.

[0014] In one example, the defoamer includes at least one of polydimethylsiloxane, GP-type glycerol polyether, and GPE-type polyoxyethylene ether.

[0015] In one example, based on the total mass of the raw materials, the mass content of the dispersant is 1.0wt%-4.0wt%, the mass content of the binder is 1.0wt%-4.0wt%, and the mass content of the defoamer is 0.1wt%-1.5wt%.

[0016] In one example, during the S2 vacuum grouting step, the silicon carbide slurry is injected from the bottom of the molding mold at a grouting pressure ranging from 0.3 MPa to 0.5 MPa.

[0017] In one example, the segmented temperature control process specifically includes a segmented heating process, which includes the following steps: (1) First heating stage: The temperature inside the sintering furnace is raised from room temperature to 200℃, the heating time is 30min-60min, and the pressure range of the argon atmosphere is 0.05MPa-0.1MPa; (2) First heat preservation stage: The temperature inside the sintering furnace is kept at 200℃ for 60min-120min, and the pressure range of the argon atmosphere is 0.05MPa-0.1MPa; (3) Second heating stage: The temperature inside the sintering furnace is raised from 200℃ to 400℃, the heating time is 30min-60min, and the pressure range of the argon atmosphere is 0.05MPa-0.1MPa; (4) Second heat preservation stage: The temperature inside the sintering furnace is kept at 400℃ for 60min-120min, and the pressure range of the argon atmosphere is 0.05MPa-0.1MPa; (5) Third heating stage: The temperature inside the sintering furnace is raised from 400℃ to 800℃, the heating time is 60min-180min, and the pressure range of the argon atmosphere is 0.05MPa-0.1MPa; (6) Third heat preservation stage: The temperature inside the sintering furnace is kept at 800℃ for 60min-120min, and the pressure range of the argon atmosphere is 0.05MPa-0.1MPa; (7) Fourth heating stage: The temperature inside the sintering furnace is raised from 800℃ to 1550℃, the heating time is 120min-240min, and the pressure range of the argon atmosphere is 0.05MPa-0.1MPa; when the temperature inside the sintering furnace is 1550℃, the pressure range of the argon atmosphere is increased to 5MPa-10MPa. (8) Fourth heat preservation stage: The temperature inside the sintering furnace is kept at 1550℃ for 60min-150min, and the pressure range of the argon atmosphere is 5MPa-10MPa; (9) Fifth heating stage: The temperature inside the sintering furnace is raised from 1550℃ to 1950℃, the heating time is 60min-180min, and the pressure range of the argon atmosphere is 5MPa-10MPa; (10) Fifth heat preservation stage: The temperature inside the sintering furnace is kept at 1950℃ for 60min-120min, and the pressure range of the argon atmosphere is 5MPa-10MPa.

[0018] In one example, during the stage when the temperature inside the sintering furnace is between 1550℃ and 1950℃ or during the fifth heating stage, the pressure of the argon atmosphere is controlled within the range of 5MPa-10MPa in a periodic manner. The periodic change is a pulsed pressure, wherein the periodic change must meet the following conditions: a peak pressure of 8MPa-10MPa is applied every 30min-60min for a duration of 5min-15min, and the base pressure of 5MPa-8MPa is maintained for the remaining time.

[0019] In one example, the segmented temperature control process further includes a segmented cooling process, which comprises the following steps: (11) Cooling stage: The temperature inside the sintering furnace is reduced from 1950℃ to 800℃, and the cooling time is 480min-600min; (12) Rapid cooling stage: The temperature inside the sintering furnace is reduced from 800°C to room temperature, and the cooling time is 60 min-80 min; The rapid cooling stage employs argon gas forced convection cooling at a rate of 10°C / min to 15°C / min.

[0020] The second aspect of the present invention provides an in-situ reaction sintered silicon carbide ceramic, which is prepared by the preparation method of the in-situ reaction sintered silicon carbide ceramic described in the first aspect of the present invention. The silicon carbide ceramic has a bulk density ≥3.15g / cm³, a flexural strength ≥240MPa, and a porosity ≤1.5%.

[0021] By employing the above technical solution, the present invention has at least the following advantages compared with the prior art: The in-situ reaction sintering method for preparing silicon carbide ceramics of this invention effectively solves the problems of uneven carbon source distribution, impurity introduction, and insufficient density in traditional reaction sintering technology through the synergistic effect of in-situ pyrolysis of organic precursors as carbon sources, vacuum slip casting, and segmented temperature-controlled sintering. Specific beneficial effects are as follows: First, the uniformity of carbon source distribution is significantly improved: using organic precursors (such as phenolic resin) as carbon sources, the precursors are uniformly coated on the surface of silicon carbide powder through long-term stirring. During sintering (400~800℃), the organic precursors undergo in-situ pyrolysis to generate a carbon layer, avoiding the agglomeration problem caused by the traditional external addition of carbon black / graphite powder. The carbon source and silicon carbide matrix have more sufficient contact, resulting in a more complete reaction during sintering, effectively reducing local carbon residue, and thus significantly improving the mechanical properties of the material; the green body has high density and is free of defects. The advantages of this invention are as follows: First, the vacuum grouting process, by injecting grout from the bottom of the mold and combining it with a vacuum environment, reduces the generation of air bubbles in the silicon carbide material. Compared with traditional grouting molding, it provides a more uniform microstructure for the subsequent sintering stage, further improving the density of the final ceramic product. Second, this invention adopts a segmented temperature-controlled sintering process. During the heating stage (<1550℃), a micro-positive pressure argon gas of 0.05MPa-0.1MPa is used for protection, which can protect the material from oxidation, reduce the oxidation loss of silicon particles, avoid a decrease in the density of the material, and promote the uniform deposition of carbon from the decomposition of organic matter. During the high-temperature stage (≥1550℃), the argon gas pressure is increased to 5MPa-10MPa, and the pressure is used to promote the filling of pores by the molten silicon liquid phase, further improving the uniformity and density of the material. In summary, this method solves the core problems of uneven carbon source distribution, impurity introduction, and insufficient density in traditional technologies by synergistically optimizing in-situ carbon source generation, vacuum slurry injection, and segmented pressure-controlled sintering, and significantly improves the density and mechanical properties of silicon carbide ceramics.

[0022] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein. Attached Figure Description

[0023] Figure 1 The diagram shows the process flow chart of the in-situ reaction sintering silicon carbide ceramic preparation method of the present invention.

[0024] Figure 2 The image shown is a microstructure of the in-situ reaction-sintered silicon carbide ceramic of the present invention. Detailed Implementation

[0025] The following provides a detailed description of specific embodiments of the present invention. It should be understood that the specific embodiments described herein are for illustrative and explanatory purposes only and are not intended to limit the scope of the invention.

[0026] The first aspect of this invention provides a method for preparing in-situ reaction-sintered silicon carbide ceramics, the process flow diagram of which is shown below. Figure 1 As shown; The preparation method of the in-situ reaction sintered silicon carbide ceramic includes the following steps: S1. Preparation of silicon carbide slurry: Weigh the following raw materials according to the mass percentage: 80wt%-85wt% silicon carbide powder, 10wt%-15wt% organic precursor and 5wt%-7wt% other additives; add a dispersion liquid based on 25wt%-30wt% of the total mass of the raw materials, stir for 36h-48h to form the silicon carbide slurry; S2, Vacuum grouting: The silicon carbide slurry is injected into a vacuum grouting tank, and the silicon carbide slurry in the vacuum grouting tank is injected into the shaping mold from the bottom of the shaping mold. The mold is dried at 80℃~120℃ for 1~2 hours to form the silicon carbide green blank. S3. In-situ reaction sintering: The silicon carbide green blank is placed in a sintering furnace, and silicon particles of 20wt%-40wt% of the total mass of the silicon carbide green blank are evenly sprinkled around it. The silicon carbide green blank is heated, held, and cooled in a segmented temperature control process under an argon atmosphere to obtain silicon carbide ceramics. During the segmented temperature control process, when the temperature inside the sintering furnace is below 1550℃, the pressure range of the argon atmosphere in the sintering furnace is 0.05MPa-0.1MPa. When the temperature inside the sintering furnace reaches or exceeds 1550℃, the pressure range of the argon atmosphere in the sintering furnace is 5MPa-10MPa.

[0027] In this invention, the S1 silicon carbide slurry is prepared by weighing the following raw materials according to their mass percentages: 80wt%-85wt% silicon carbide powder (e.g., 80wt%, 80.5wt%, 81wt%, 81.5wt%, 82wt%, 82.5wt%, 83wt%, 83.5wt%, 84wt%, 84.5wt%, or 85wt%), 10wt%-15wt% organic precursor (e.g., 10wt%, 10.5wt%, 11wt%, 11.5wt%, 12wt%, 12.5wt%, 13wt%, 13.5wt%, 14wt%, 14.5wt%, or 15wt%), and 5wt%-7wt% other additives (e.g., 5wt%, 5.1wt%). 5.2wt%, 5.3wt%, 5.4wt%, 5.5wt%, 5.6wt%, 5.7wt%, 5.8wt%, 5.9wt%, 6wt%, 6.1wt%, 6.2wt%, 6.3wt%, 6.4wt%, 6.5wt%, 6.6wt%, 6.7wt%, 6.8wt%, 6.9wt%, or 7wt%) of the raw materials are added to a dispersion, and the mixture is stirred for 36h-48h to form the silicon carbide slurry.

[0028] In one example, the organic precursor in the silicon carbide slurry coats the surface of the silicon carbide powder. In step S1, thorough stirring of the silicon carbide powder and organic precursor ensures that the organic precursor uniformly coats the surface of the silicon carbide powder particles, resulting in a more complete in-situ reaction. In traditional methods, externally added carbon black or graphite powder tends to agglomerate, leading to uneven distribution of the carbon source in the slurry and resulting in excessively high or low carbon content in some areas of the green body. This invention, through prolonged stirring, ensures that the organic precursor uniformly coats the surface of the silicon carbide powder particles. During sintering, the carbon layer generated by the decomposition of the organic precursor adheres tightly to the silicon carbide surface, achieving sufficient contact between the carbon source and the silicon carbide matrix. This uniformly distributed carbon source, when reacting with subsequent molten silicon, has a large contact area and a short reaction path, avoiding free silicon residue due to insufficient local carbon source or unreacted carbon residue due to excessive carbon source, significantly improving the completeness of the reaction. Furthermore, this coating structure helps promote sintering densification, increasing the material's density. The carbon layer formed after the decomposition of the uniformly coated carbon source can fill the tiny pores between silicon carbide particles. During the high-temperature sintering stage (800~1950℃), molten silicon penetrates into the pores under pressure (gradual pressure increase from 0.1MPa to 5MPa), reacting with the uniformly distributed carbon to form SiC, resulting in higher pore-filling efficiency. Compared to traditional processes, the silicon carbide ceramics prepared by this method have higher density and more uniform microstructure.

[0029] In one example, the silicon carbide powder has a particle size of 3μm-5μm, for example: 3.0μm, 3.5μm, 4.0μm, 4.5μm or 5.0μm.

[0030] When the particle size of silicon carbide powder is 3μm-5μm, the specific surface area of ​​silicon carbide powder particles is larger, which can make the contact between the carbon source and silicon source more sufficient during in-situ reaction, improve the reaction activity, and the appropriate particle size is conducive to the formation of a coating effect on the organic precursor when it comes into contact with the silicon carbide powder particles, thereby improving the uniformity of carbon source distribution and thus improving the density and mechanical properties of silicon carbide ceramic products.

[0031] In one example, the organic precursor includes at least one of phenolic resin, polycarbosilane, epoxy resin, isopropanol, glucose, sucrose, and starch.

[0032] In one example, the organic precursor is a phenolic resin. Phenolic resin has a high carbon content, and as a carbon source for in-situ reactions, it enables the formation of a more uniform in-situ carbon layer, thereby forming a silicon carbide ceramic product with better density.

[0033] In one example, the dispersion comprises at least one of deionized water, ethanol, and acetone.

[0034] In one instance, the other additives include dispersants, binders, and defoamers.

[0035] In one example, the dispersant includes at least one of sodium dodecylbenzenesulfonate, tetramethylammonium hydroxide, polyacrylic acid, ammonium polyacrylate, ammonium citrate, and sodium silicate. The dispersant can improve the dispersibility of silicon carbide powder and organic precursor slurry, promote uniform coating of organic precursors, prevent the agglomeration of solid particles such as silicon carbide powder and organic precursors, and maintain a stable dispersion of the slurry.

[0036] In one example, the binder includes at least one of polyvinyl alcohol and polyethylene glycol. The binder enhances the strength of the green body, ensures structural stability, binds solid particles in the slurry together, improves the mechanical strength of the green body, and prevents cracking and deformation of the green body due to shrinkage or stress during drying and sintering. The stable green body structure provides a uniform microstructure for subsequent sintering stages, allowing molten silicon to fill pores more effectively and increasing the density of the final ceramic.

[0037] In one example, the defoamer includes at least one of polydimethylsiloxane, GP-type glycerol polyether, and GPE-type polyoxyethylene ether. The defoamer reduces the formation of bubbles in the slurry, thereby increasing the density of the green body. By reducing the surface tension of the slurry, the defoamer inhibits the generation of bubbles during stirring and slurry pouring, accelerates the collapse of existing bubbles, reduces porosity defects inside the green body, and significantly improves the efficiency of pore filling, thus enhancing the density and mechanical properties of silicon carbide ceramics.

[0038] In one example, based on the total mass of the raw materials, the dispersant has a mass content of 1.0 wt%-4.0 wt% (e.g., 1.0 wt%, 1.1 wt%, 1.2 wt%, 1.3 wt%, 1.4 wt%, 1.5 wt%, 1.6 wt%, 1.7 wt%, 1.8 wt%, 1.9 wt%, 2.0 wt%, 2.1 wt%, 2.2 wt%, 2.3 wt%, 2.4 wt%, 2.5 wt%, 2.6 wt%, 2.7 wt%, 2.8 wt%, 2.9 wt%, 3.0 wt%, 3.1 wt%, 3.2 wt%, 3.3 wt%, 3.4 wt%, 3.5 wt%, 3.6 wt%, 3.7 wt%, 3.8 wt%, 3.9 wt% or 4.0 wt%), and the adhesive has a mass content of 1.0 wt%-4.0 wt% (e.g., 1.0 wt%, 1.1 wt%, 1.2 wt%, 1.3 wt%). The defoamer content is 0.4wt%, 1.5wt%, 1.6wt%, 1.7wt%, 1.8wt%, 1.9wt%, 2.0wt%, 2.1wt%, 2.2wt%, 2.3wt%, 2.4wt%, 2.5wt%, 2.6wt%, 2.7wt%, 2.8wt%, 2.9wt%, 3.0wt%, 3.1wt%, 3.2wt%, 3.3wt%, 3.4wt%, 3.5wt%, 3.6wt%, 3.7wt%, 3.8wt%, 3.9wt%, or 4.0wt%), and the defoamer content is 0.1wt%-1.5wt% (e.g., 0.1wt%, 0.2wt%, 0.3wt%, 0.4wt%, 0.5wt%, 0.6wt%, 0.7wt%, 0.8wt%, 0.9wt%, 1wt%, 1.1wt%, 1.2wt%, 1.3wt%, 1.4wt%, or 1.5wt%).

[0039] In one example, the mass content of the dispersant is 2.0 wt% to 3.0 wt% based on the total mass of the raw materials.

[0040] In one example, the adhesive content is 1.8wt%-2.0wt% based on the total mass of the raw materials.

[0041] In one example, the defoamer content is 0.2wt%-0.5wt% based on the total mass of the raw materials.

[0042] In this invention, S2, vacuum slurry injection: the silicon carbide slurry is injected into a vacuum slurry injection tank, and the silicon carbide slurry in the vacuum slurry injection tank is injected into the shaping mold from the bottom of the shaping mold. The mixture is then dried at 80℃~120℃ for 1~2 hours to form the silicon carbide green body. Injecting the slurry from the bottom of the shaping mold ensures that internal air is expelled from the mold. Compared to top injection, the amount of air inside the shaping mold is reduced, resulting in fewer air bubbles in the green body material, which is beneficial for improving the density of the silicon carbide ceramic.

[0043] In one example, during the S2 vacuum grouting step, the silicon carbide slurry is injected into the mold from the bottom at a pressure ranging from 0.3 MPa to 0.5 MPa, for example, 0.3 MPa, 0.31 MPa, 0.32 MPa, 0.33 MPa, 0.34 MPa, 0.35 MPa, 0.36 MPa, 0.37 MPa, 0.38 MPa, 0.39 MPa, 0.4 MPa, 0.41 MPa, 0.42 MPa, 0.43 MPa, 0.44 MPa, 0.45 MPa, 0.46 MPa, 0.47 MPa, 0.48 MPa, 0.49 MPa, or 0.5 MPa. Furthermore, controlling the grouting pressure within a suitable range ensures a more compact packing of solid particles in the slurry, reduces the porosity of the green body, and provides a denser microstructure foundation for subsequent sintering.

[0044] In this invention, S3, in-situ reaction sintering: The silicon carbide green blank is placed in a sintering furnace, and silicon particles of 20wt%-40wt% (e.g., 20wt%, 25wt%, 30wt%, 35wt%, 40wt%) based on the total mass of the silicon carbide green blank are evenly sprinkled around it. When the temperature rises to about 1450℃, the silicon particles around the silicon carbide green blank melt, and the molten silicon in the liquid phase slowly seeps into the sintered blank, reacting with the carbon generated in-situ within the blank to form silicon carbide, thereby achieving densification of the sintered body.

[0045] In this invention, S3, in-situ reaction sintering: the silicon carbide green body is heated, held, and cooled under an argon atmosphere using a segmented temperature control process to obtain silicon carbide ceramics; during the segmented temperature control process, when the temperature inside the sintering furnace is below 1550℃, the pressure range of the argon atmosphere in the sintering furnace is 0.05MPa-0.1MPa (for example, 0.05MPa, 0.055MPa, 0.06MPa, 0.065MPa, 0.07MPa, 0.05MPa, 0.06 ... The pressure range of the argon atmosphere in the sintering furnace is 5MPa-10MPa (e.g., 5MPa, 5.5MPa, 6MPa, 6.5MPa, 7MPa, 7.5MPa, 8MPa, 8.5MPa, 9MPa, 9.5MPa, or 10MPa) when the temperature inside the sintering furnace reaches or exceeds 1550℃. This invention employs a segmented temperature-controlled sintering process. During the heating stage (<1550℃), a micro-positive pressure argon gas of 0.05MPa-0.1MPa is used for protection, which can protect the material from oxidation, reduce the oxidation loss of silicon particles, avoid a decrease in the material's density, and promote the uniform deposition of carbon from the decomposition of organic matter. During the high-temperature stage (≥1550℃), the argon gas pressure is increased to 5MPa-10MPa, and the pressure is used to promote the filling of pores by the molten silicon liquid phase, thereby further improving the uniformity and density of the material.

[0046] In one example, the segmented temperature control process specifically includes a segmented heating process, which includes the following steps: (1) First heating stage: The temperature inside the sintering furnace is raised from room temperature to 200°C for 30 min-60 min, and the pressure range of the argon atmosphere is 0.05 MPa-0.1 MPa.

[0047] (2) First heat preservation stage: The temperature inside the sintering furnace is kept at 200℃ for 60min-120min, and the pressure range of the argon atmosphere is 0.05MPa-0.1MPa. This process mainly removes the binder from the raw materials.

[0048] (3) Second heating stage: The temperature inside the sintering furnace is raised from 200℃ to 400℃, the heating time is 30min-60min, and the pressure range of the argon atmosphere is 0.05MPa-0.1MPa.

[0049] (4) Second holding stage: The temperature inside the sintering furnace is held at 400℃ for 60min-120min, and the pressure of the argon atmosphere is 0.05MPa-0.1MPa. During this process, the carbon-containing organic precursors decompose.

[0050] (5) Third heating stage: The temperature inside the sintering furnace is raised from 400℃ to 800℃, and the heating time is 60min-180min. The pressure range of the argon atmosphere is 0.05MPa-0.1MPa. This process has a long heating time to ensure slow heating, so that the carbon layer from the decomposition of organic precursors is uniformly deposited and coated on the surface of silicon carbide.

[0051] (6) Third heat preservation stage: The temperature inside the sintering furnace is kept at 800℃ for 60min-120min, and the pressure range of the argon atmosphere is 0.05MPa-0.1MPa.

[0052] (7) Fourth heating stage: The temperature inside the sintering furnace is raised from 800℃ to 1550℃ over a period of 120min-240min, with an argon atmosphere pressure range of 0.05MPa-0.1MPa; when the temperature inside the sintering furnace is 1550℃, the argon atmosphere pressure is increased to a range of 5MPa-10MPa. Silicon has a melting point of 1414℃, at which temperature it reacts to generate SiC. When the temperature inside the sintering furnace is 1550℃, increasing the argon atmosphere pressure promotes the uniform filling of the pores of the silicon carbide powder by liquid-phase silicon, resulting in silicon carbide ceramics with higher density.

[0053] (8) Fourth holding stage: The temperature inside the sintering furnace is held at 1550℃ for 60min-150min, and the pressure of the argon atmosphere is 5MPa-10MPa. Holding for a certain period of time allows the liquid silicon to fully penetrate into the sintered body, thereby achieving densification of the sintered body.

[0054] (9) Fifth heating stage: The temperature inside the sintering furnace is raised from 1550℃ to 1950℃, with a heating time of 60min-180min and an argon atmosphere pressure range of 5MPa-10MPa. Continue heating to allow C and Si in the product to react fully.

[0055] (10) Fifth heat preservation stage: The temperature inside the sintering furnace is kept at 1950℃ for 60min-120min, and the pressure range of the argon atmosphere is 5MPa-10MPa.

[0056] This invention employs a segmented temperature-controlled sintering process. During the heating stage (<1550℃), a micro-positive pressure argon gas of 0.05MPa-0.1MPa is used for protection, which can protect the material from oxidation, reduce the oxidation loss of silicon particles, avoid a decrease in the material's density, and promote the uniform deposition of carbon from the decomposition of organic matter. During the high-temperature stage (≥1550℃), the argon gas pressure is increased to 5MPa-10MPa, and the pressure is used to promote the filling of pores by the molten silicon liquid phase, thereby further improving the uniformity and density of the material.

[0057] In one example, the segmented temperature control process further includes a segmented cooling process, which comprises the following steps: (11) Cooling stage: The temperature inside the sintering furnace is reduced from 1950℃ to 800℃, and the cooling time is 480min-600min.

[0058] (12) Rapid cooling stage: The temperature inside the sintering furnace is reduced from 800℃ to room temperature, and the cooling time is 60min-80min; wherein, the rapid cooling stage adopts the argon gas forced convection cooling, and the cooling rate is 10℃ / min-15℃ / min, for example: 5℃ / min, 6℃ / min, 7℃ / min, 8℃ / min, 9℃ / min or 10℃ / min.

[0059] The in-situ reaction sintering step of this invention employs pressure sintering. During the reaction sintering stage, a certain argon pressure promotes the liquid phase to fill the pores, achieving densification. The heating process uses a gradient heating method, which effectively improves the temperature uniformity within the furnace. During cooling, initial furnace cooling followed by rapid cooling effectively avoids the formation of thermal stress cracks.

[0060] In one example, during the stage when the temperature inside the sintering furnace is between 1550℃ and 1950℃ or during the fifth heating stage, the pressure of the argon atmosphere is controlled within the range of 5MPa-10MPa in a periodic manner. The periodic change is a pulsed pressure, wherein the periodic change must meet the following conditions: a peak pressure of 8MPa-10MPa is applied every 30min-60min for a duration of 5min-15min, and the base pressure of 5MPa-8MPa is maintained for the remaining time.

[0061] Building upon this foundation, the present invention further optimizes the fifth heating stage (1550℃~1950℃) with periodically varying pressure control, thereby further promoting the full filling of the pores inside the sintered material by the molten silicon liquid phase. This solves the technical bottleneck of uneven molten silicon penetration in traditional constant high-pressure sintering. The dynamic pressure control of the present invention can promote particle rearrangement and densification. This is because under traditional constant high pressure, silicon carbide particles in the sintered body tend to form a "rigid skeleton," which restricts the sliding and rearrangement between particles, making it difficult for molten silicon to fill some of the micropores. The present invention utilizes the mechanical vibration effect generated by the periodic changes in pressure to increase the penetration rate of the molten silicon liquid phase. The pressure pulse can also form an instantaneous pressure gradient, driving the molten silicon to penetrate into the micropores more efficiently, thereby further improving the uniformity and density of the silicon carbide ceramic material.

[0062] The second aspect of the present invention provides an in-situ reaction sintered silicon carbide ceramic, which is prepared by the preparation method of the in-situ reaction sintered silicon carbide ceramic described in the first aspect of the present invention. The silicon carbide ceramic has a bulk density ≥3.15g / cm³, a flexural strength ≥240MPa, and a porosity ≤1.5%.

[0063] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0064] Unless otherwise specified, all materials and instruments used in the following examples are commercially available.

[0065] Example 1 The preparation method of silicon carbide ceramics specifically includes the following steps: S1. Preparation of silicon carbide slurry: Weigh the following raw materials according to the following percentages by mass: 85wt% silicon carbide powder with a particle size of 5μm, 10wt% epoxy resin, 1.5wt% ammonium polyacrylate dispersant, 3wt% polyethylene glycol binder, and 0.5wt% polydimethylsiloxane defoamer; add 30wt% of deionized water based on the total mass of the raw materials, stir for 48h, and form silicon carbide slurry A1 of this embodiment; S2, Vacuum grouting: The silicon carbide slurry A1 obtained in step S1 is injected into a vacuum grouting tank. The silicon carbide slurry A1 in the vacuum grouting tank is injected into the shaping mold from the bottom of the shaping mold at a grouting pressure of 0.5MPa. It is dried at 80℃ for 2 hours to form silicon carbide green blank B1. S3. In-situ reaction sintering: The silicon carbide green blank B1 obtained in step S2 is placed in a sintering furnace, and silicon particles based on 30 wt% of the total mass of the silicon carbide green blank B1 are evenly sprinkled around it. Under an argon atmosphere, the silicon carbide green blank B1 is heated, held, and cooled using a segmented temperature control process to obtain silicon carbide ceramic C1. Its microstructure is shown in the figure below. Figure 2 As shown; Specifically, in the segmented temperature control process: First heating stage: The temperature inside the sintering furnace is raised from room temperature to 200℃ over 60 minutes, with an argon atmosphere pressure of 0.1 MPa. First holding stage: The temperature inside the sintering furnace is held at 200℃ for 60 minutes, with an argon atmosphere pressure of 0.1 MPa. Second heating stage: The temperature inside the sintering furnace is raised from 200℃ to 400℃ over 60 minutes, with an argon atmosphere pressure of 0.1 MPa. Second holding stage: The temperature inside the sintering furnace is held at 400℃ for 60 minutes, with an argon atmosphere pressure of 0.1 MPa. Third heating stage: The temperature inside the sintering furnace is raised from 400℃ to 800℃ over 150 minutes, with an argon atmosphere pressure of 0.1 MPa. Third holding stage: The temperature inside the sintering furnace is held at 800℃ for 120 minutes, with an argon atmosphere pressure of 0.1 MPa. Fourth heating stage: The temperature inside the sintering furnace is raised from 800℃ to 1550℃ over 180 minutes, with an argon atmosphere pressure of 0.1 MPa. When the furnace temperature reaches 1550℃, the argon atmosphere pressure is increased to 10 MPa. Fourth holding stage: The furnace temperature is held at 1550℃ for 120 minutes, with an argon atmosphere pressure of 10 MPa. Fifth heating stage: The furnace temperature is raised from 1550℃ to 1950℃ over 150 minutes, with an argon atmosphere pressure of 10 MPa. Fifth holding stage: The furnace temperature is held at 1950℃ for 60 minutes, with an argon atmosphere pressure of 10 MPa. Furnace cooling stage: The furnace temperature is reduced from 1950℃ to 800℃ over 600 minutes. Rapid cooling stage: The furnace temperature is reduced from 800℃ to room temperature over 80 minutes.

[0066] Example 2 group Example 2 was conducted in accordance with Example 1, with the only difference being the change in the percentage of the mass content of the raw materials used in the silicon carbide slurry preparation, as shown below: Example 2-1, Preparation of silicon carbide slurry: Weigh the following raw materials according to the following percentages by mass: 80wt% silicon carbide powder with a particle size of 5μm, 15wt% epoxy resin, 1.5wt% ammonium polyacrylate dispersant, 3wt% polyethylene glycol binder, and 0.5wt% polydimethylsiloxane defoamer; add 30wt% of deionized water based on the total mass of the raw materials, stir for 48h to form silicon carbide slurry A1 of this example; Example 2-2, Preparation of silicon carbide slurry: Weigh the following raw materials according to the following percentages by mass: 82wt% silicon carbide powder with a particle size of 5μm, 11wt% epoxy resin, 2.5wt% ammonium polyacrylate dispersant, 3.5wt% polyethylene glycol binder, and 1wt% polydimethylsiloxane defoamer; add 30wt% of deionized water based on the total mass of the raw materials, and stir for 48h to form silicon carbide slurry A1 of this example.

[0067] Example 3 Group Example 3 was performed in accordance with Example 1, with the only difference being that the pressure of the argon atmosphere in the sintering furnace was changed during the segmented temperature control process, as shown below: Example 3-1: In the segmented temperature control process, when the temperature inside the sintering furnace is below 1550°C, the pressure of the argon atmosphere in the sintering furnace is 0.05 MPa, and when the temperature inside the sintering furnace reaches or exceeds 1550°C, the pressure of the argon atmosphere in the sintering furnace is 5 MPa. In Example 3-2, during the segmented temperature control process, when the temperature inside the sintering furnace is below 1550°C, the pressure of the argon atmosphere in the sintering furnace is 0.07 MPa, and when the temperature inside the sintering furnace reaches or exceeds 1550°C, the pressure of the argon atmosphere in the sintering furnace is 7 MPa.

[0068] Example 4 group Example 4 was conducted in accordance with Example 1, with the only difference being the change in the particle size of the silicon carbide powder, as shown below: Example 4-1: The particle size of the silicon carbide powder is 3 μm; Example 4-2: The particle size of the silicon carbide powder is 2 μm; In Examples 4-3, the particle size of silicon carbide powder was 7 μm.

[0069] Example 5 group Example 5 was performed in accordance with Example 1, with the only difference being that the grouting pressure was changed, as detailed below: Example 5-1: Silicon carbide slurry A1 in a vacuum grouting tank is injected into the shaping mold from the bottom of the shaping mold at a grouting pressure of 0.3 MPa; Example 5-2: Silicon carbide slurry A1 in a vacuum grouting tank is injected into the shaping mold from the bottom of the shaping mold at a grouting pressure of 0.7 MPa; In Example 5-3, silicon carbide slurry A1 in a vacuum grouting tank is injected into the shaping mold from the bottom of the shaping mold at a grouting pressure of 0.2 MPa.

[0070] Example 6 Example 6 is performed in accordance with Example 1, except that the argon atmosphere pressure is changed during the temperature rise in the sintering furnace from 1550°C to 1950°C. The argon atmosphere pressure is changed from a constant state to a periodically changing state, as shown below: Example 6: A peak pressure of 10 MPa was applied every 60 minutes for 5 minutes, while the base pressure of 8 MPa was maintained for the rest of the time.

[0071] Comparative Example 1 Comparative Example 1 was conducted in accordance with Example 1, with the only difference being the change in the pressure of the argon atmosphere in the sintering furnace during the segmented temperature control process, as shown below: Comparative Example 1-1: In the segmented temperature control process, when the temperature inside the sintering furnace is below 1550℃, the pressure of the argon atmosphere in the sintering furnace is 1MPa, and when the temperature inside the sintering furnace reaches or exceeds 1550℃, the pressure of the argon atmosphere in the sintering furnace is 10MPa. Comparative Examples 1-2 show that during the segmented temperature control process, when the temperature inside the sintering furnace is below 1550℃, the pressure of the argon atmosphere in the sintering furnace is 0.1MPa, and when the temperature inside the sintering furnace reaches or exceeds 1550℃, the pressure of the argon atmosphere in the sintering furnace is 3MPa.

[0072] Comparative Example 2 Comparative Example 2 was conducted in accordance with Example 1, with the only difference being the change in the pressure of the argon atmosphere in the sintering furnace during the segmented temperature control process, as shown below: Comparative Example 2-1 shows that during the segmented temperature control process, the pressure of the argon atmosphere in the sintering furnace is always maintained at 0.1 MPa. Comparative Example 2-2 shows that during the segmented temperature control process, the pressure of the argon atmosphere in the sintering furnace is always maintained at 10 MPa.

[0073] Test case All the above embodiments and comparative examples specifically include: (1) Method for measuring the density of silicon carbide ceramics: Take a small sample from the silicon carbide product, place it on an analytical balance and weigh it to obtain the mass M. Then, measure the volume V of the sample by the displacement method and divide it to obtain the density (refer to the standard: GB / T25995-2010).

[0074] (2) Measurement method of flexural strength of silicon carbide ceramics: The flexural strength of silicon carbide material is measured by the three-point bending method. The silicon carbide material is processed into 5 specimen strips of 20×3×4. The specimen strips are then clamped on a universal testing machine for testing. The load is applied at a constant rate until the specimen strip breaks. The maximum load is recorded. The test is performed 5 times and the average value is taken (refer to the standard: GB / T 6569-2006).

[0075] (3) Method for measuring the porosity of silicon carbide ceramics: The porosity is measured by Archimedes' drainage method (refer to standard: GB / T 25995-2010).

[0076] Table 1 The in-situ reaction sintering method for preparing silicon carbide ceramics of the present invention effectively solves the problems of uneven carbon source distribution, impurity introduction, and insufficient density in traditional reaction sintering technology through the synergistic effect of in-situ pyrolysis of carbon source from organic precursors, vacuum slip casting, and segmented temperature-controlled sintering. This effectively improves the density and mechanical properties of silicon carbide ceramics; all products in the embodiments achieved a density ≥3.11 g / cm³. 3 The flexural strength is ≥231MPa and the porosity is ≤0.315%. The density and mechanical properties are significantly better than those of the comparative example. This confirms the synergistic effect of the in-situ uniform carbon source coating, vacuum grouting to reduce air bubbles, and segmented pressure control to promote the filling of molten silicon liquid phase in this invention. In particular, the high-pressure and pulse pressure control in the high-temperature section can effectively improve the pore filling efficiency and significantly optimize the density and mechanical properties of silicon carbide ceramics.

[0077] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A method for preparing in-situ reaction-sintered silicon carbide ceramics, characterized in that, Includes the following steps: S1. Preparation of silicon carbide slurry: Weigh the following raw materials according to the mass percentage: 80wt%-85wt% silicon carbide powder, 10wt%-15wt% organic precursor and 5wt%-7wt% other additives; add a dispersion liquid based on 25wt%-30wt% of the total mass of the raw materials, stir for 36h-48h to form the silicon carbide slurry; S2, Vacuum grouting: The silicon carbide slurry is injected into a vacuum grouting tank. The silicon carbide slurry in the vacuum grouting tank is injected from the bottom of the shaping mold. The slurry is dried at 80℃~120℃ for 1~2 hours to form a silicon carbide green blank. S3. In-situ reaction sintering: The silicon carbide green blank is placed in a sintering furnace, and silicon particles of 20wt%-40wt% of the total mass of the silicon carbide green blank are evenly sprinkled around it. The silicon carbide green blank is heated, held, and cooled in a segmented temperature control process under an argon atmosphere to obtain silicon carbide ceramics. During the segmented temperature control process, when the temperature inside the sintering furnace is below 1550℃, the pressure of the argon atmosphere in the sintering furnace is 0.05MPa-0.1MPa. When the temperature inside the sintering furnace reaches or exceeds 1550℃, the pressure of the argon atmosphere in the sintering furnace increases to 5MPa-10MPa.

2. The method for preparing in-situ reaction-sintered silicon carbide ceramics according to claim 1, characterized in that, The organic precursor in the silicon carbide slurry is coated on the surface of the silicon carbide powder; And / or, the particle size of the silicon carbide powder is 3μm-5μm.

3. The method for preparing in-situ reaction-sintered silicon carbide ceramics according to claim 1, characterized in that, The organic precursor includes at least one of phenolic resin, polycarbosilane, epoxy resin, isopropanol, glucose, sucrose, and starch. And / or, the dispersion includes at least one of deionized water, ethanol, and acetone.

4. The method for preparing in-situ reaction-sintered silicon carbide ceramics according to claim 1, characterized in that, The other additives include dispersants, binders, and defoamers, wherein, The dispersant includes at least one of sodium dodecylbenzenesulfonate, tetramethylammonium hydroxide, polyacrylic acid, ammonium polyacrylate, ammonium citrate, and sodium silicate; And / or, the adhesive includes at least one of polyvinyl alcohol and polyethylene glycol; And / or, the defoamer includes at least one of polydimethylsiloxane, GP-type glycerol polyether, and GPE-type polyoxyethylene ether.

5. The method for preparing in-situ reaction-sintered silicon carbide ceramics according to claim 4, characterized in that, Based on the total mass of the raw materials, the mass content of the dispersant is 1.0wt%-4.0wt%, the mass content of the binder is 1.0wt%-4.0wt%, and the mass content of the defoamer is 0.1wt%-1.5wt%.

6. The method for preparing in-situ reaction-sintered silicon carbide ceramics according to claim 1, characterized in that, In the S2 vacuum grouting step, the silicon carbide slurry is injected into the shaping mold from the bottom of the shaping mold at a pressure range of 0.3MPa-0.5MPa.

7. The method for preparing in-situ reaction-sintered silicon carbide ceramics according to claim 1, characterized in that, The segmented temperature control process specifically includes a segmented heating process, which includes the following steps: (1) First heating stage: The temperature inside the sintering furnace is raised from room temperature to 200℃, the heating time is 30min-60min, and the pressure range of the argon atmosphere is 0.05MPa-0.1MPa; (2) First heat preservation stage: The temperature inside the sintering furnace is kept at 200℃ for 60min-120min, and the pressure range of the argon atmosphere is 0.05MPa-0.1MPa; (3) Second heating stage: The temperature inside the sintering furnace is raised from 200℃ to 400℃, the heating time is 30min-60min, and the pressure range of the argon atmosphere is 0.05MPa-0.1MPa; (4) Second heat preservation stage: The temperature inside the sintering furnace is kept at 400℃ for 60min-120min, and the pressure range of the argon atmosphere is 0.05MPa-0.1MPa; (5) Third heating stage: The temperature inside the sintering furnace is raised from 400℃ to 800℃, the heating time is 60min-180min, and the pressure range of the argon atmosphere is 0.05MPa-0.1MPa; (6) Third heat preservation stage: The temperature inside the sintering furnace is kept at 800℃ for 60min-120min, and the pressure range of the argon atmosphere is 0.05MPa-0.1MPa; (7) Fourth heating stage: The temperature inside the sintering furnace is raised from 800℃ to 1550℃, the heating time is 120min-240min, and the pressure range of the argon atmosphere is 0.05MPa-0.1MPa; when the temperature inside the sintering furnace is 1550℃, the pressure range of the argon atmosphere is increased to 5MPa-10MPa. (8) Fourth heat preservation stage: The temperature inside the sintering furnace is kept at 1550℃ for 60min-150min, and the pressure range of the argon atmosphere is 5MPa-10MPa; (9) Fifth heating stage: The temperature inside the sintering furnace is raised from 1550℃ to 1950℃, the heating time is 60min-180min, and the pressure range of the argon atmosphere is 5MPa-10MPa; (10) Fifth heat preservation stage: The temperature inside the sintering furnace is kept at 1950℃ for 60min-120min, and the pressure of the argon atmosphere is 5MPa-10MPa.

8. The method for preparing in-situ reaction-sintered silicon carbide ceramics according to claim 7, characterized in that, During the stage when the temperature in the sintering furnace is between 1550℃ and 1950℃ or during the fifth heating stage, the pressure of the argon atmosphere is controlled within the range of 5MPa-10MPa in a periodic manner. The periodic change is a pulsed pressure, and the periodic change must meet the following conditions: a peak pressure of 8MPa-10MPa is applied every 30min-60min for a duration of 5min-15min, and the base pressure of 5MPa-8MPa is maintained for the rest of the time.

9. The method for preparing in-situ reaction-sintered silicon carbide ceramics according to claim 7, characterized in that, The segmented temperature control process further includes a segmented cooling process, which comprises the following steps: (11) Cooling stage: The temperature inside the sintering furnace is reduced from 1950℃ to 800℃, and the cooling time is 480min-600min; (12) Rapid cooling stage: The temperature inside the sintering furnace is reduced from 800°C to room temperature, and the cooling time is 60 min-80 min; The rapid cooling stage employs argon forced convection cooling at a rate of 10°C / min to 15°C / min.

10. An in-situ reaction-sintered silicon carbide ceramic, prepared by the method for preparing in-situ reaction-sintered silicon carbide ceramic according to any one of claims 1-9, characterized in that, The silicon carbide ceramic has a bulk density ≥3.15 g / cm³, a flexural strength ≥240 MPa, and a porosity ≤1.5%.

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