Process for preparing high-compactness silicon carbide ceramic material based on reaction sintering method

Abstract

The invention belongs to the technical field of ceramic material preparation, and particularly relates to a process for preparing a high-compactness silicon carbide ceramic material based on a reaction sintering method, and the process comprises the steps of raw material preparation, material mixing, spray granulation, cold press molding, drying and glue discharging, mold filling, reaction sintering, demolding and grinding. The nano silicon carbide ceramic comprises the following raw materials in parts by weight: 88-92 parts of nano silicon carbide, 8-12 parts of a sintering aid, 2-4 parts of organic polyvinylpyrrolidone, 0.3-0.5 part of polycarboxylic acid and 0.2-0.3 part of a release agent. The sintering aid is a mixture of carbon black and graphite powder in a mass ratio of 3: 2. By optimizing the raw material ratio and the reaction sintering process and organically combining the raw material ratio and the reaction sintering process, the obtained silicon carbide ceramic material is good in compactness, high in toughness and bending resistance and excellent in overall performance, the reaction sintering process is low in energy consumption, the preparation cost is effectively reduced, and remarkable economic benefits and social benefits are achieved.

Description

Technical Field

[0001] The present invention belongs to the technical field of ceramic material preparation, and specifically relates to a process for preparing high-density silicon carbide ceramic materials based on reaction sintering method. Background Art

[0002] Reaction sintering technology has been widely used in many fields, especially in the new energy and photovoltaic industries. Reaction-sintered silicon carbide is an important material with excellent properties such as high strength, high wear resistance, high thermal conductivity, and low thermal expansion coefficient. It performs well under harsh working conditions of high temperature, acid-base, and molten metal, and is widely used in fields such as metallurgy, environmental protection, photovoltaic, and aerospace.

[0003] Reaction sintering is carried out by reacting a raw material mixture with an external gas (such as nitrogen) or liquid to form a new compound and release heat, thereby promoting the sintering process. Traditional hot pressing sintering requires ultra-high temperature (>2000°C) and high-pressure conditions for sintering, which not only has high costs, but also is difficult to prepare complex parts. At the same time, the material structure has coarse particles and pores, and low mechanical strength, and increasingly cannot meet the market's demand for product performance. Therefore, it is of great significance to develop a process technology that can prepare products to meet the modern market demand and has low costs based on the existing reaction sintering technology. Summary of the Invention

[0004] Aiming at the above defects or improvement requirements of the prior art, the present invention provides a process for preparing high-density silicon carbide ceramic materials based on reaction sintering method. The silicon carbide prepared by this preparation process has good density, excellent mechanical properties, low energy consumption, and can effectively reduce costs.

[0005] To achieve the above object, the present invention provides a process for preparing high-density silicon carbide ceramic materials based on reaction sintering method, including preparing raw materials, mixing, spray granulation, cold pressing molding, drying and debinding, loading into a mold, reaction sintering, demolding, and grinding and processing; The raw materials include, by weight, 88-92 parts of nano-silicon carbide, 8-12 parts of sintering aid, 2-4 parts of organic polyvinylpyrrolidone, 0.3-0.5 parts of polycarboxylic acid, and 0.2-0.3 parts of demolding agent; The sintering aid is a mixture of carbon black and graphite powder with a mass ratio of 3:2.

[0006] By optimizing the raw material ratio and using two highly active carbon sources, carbon black and graphite, as sintering aids, the present invention can not only penetrate into the gaps between silicon carbide particles through the capillary action of liquid-phase silicon to form a continuous β-SiC skeleton structure, while the residual silicon fills the pores to achieve material densification, but also the two can reduce the grain boundary diffusion coefficient of silicon carbide, promote grain boundary movement and grain growth, accelerate the sintering process, and the high-temperature resistance of graphite can reduce the risk of thermal stress cracking of the material during high-temperature sintering; using organic polyvinylpyrrolidone as a binder can evenly disperse silicon carbide particles, reduce sintering defects, and the formed three-dimensional network structure improves the green body toughness, further avoiding cracking during drying and demolding; using polycarboxylic acid as a dispersant can inhibit the agglomeration of silicon carbide particles by its dual mechanisms of electrostatic repulsion and steric hindrance, and at the same time, after sintering, it forms a dense skeleton, which can also improve the flexural strength; in addition, by optimizing the reaction sintering process, after mixing the materials into a suspension state, spray granulation can effectively control the uniformity of the powder, and at the same time, the obtained particles have good fluidity, which is beneficial to subsequent cold pressing forming and reduces pore defects; then cold pressing forming is carried out to form a uniform and dense green body, which can further reduce the sintering temperature and sintering cost. At the same time, the combination of the two can also reduce the silicon infiltration time and improve the flexural strength of the material. The obtained silicon carbide ceramic material has good densification and strong toughness, and the overall performance is excellent.

[0007] Further, in the above technical solution, the particle size of the nano-silicon carbide is 3-5 μm; the particle size of the carbon black is 0.4-1 μm; the particle size of the graphite powder is 2-4 μm.

[0008] Further, in the above technical solution, for the mixing of materials, each raw material is sequentially added into a ball mill, and deionized water accounting for 20% of the total weight of the added raw materials is added, and wet ball milling is carried out until a semi-dry mixing state is achieved.

[0009] Further, in the above technical solution, the process of the wet ball milling is as follows: the ball-to-material ratio is 5:1, the rotation speed is 200-250 rpm, and the time is 3-5 h.

[0010] Further, in the above technical solution, the process parameters of the spray granulation are: the inlet temperature is 150 °C, and the outlet temperature is 300 °C.

[0011] Further, in the above technical solution, the process parameters of the cold pressing forming are: the pressure is 460-550 MPa, and the pressure holding time is 3-5 min. In this technical solution, by strictly controlling the forming pressure and time, the density, strength and dimensional accuracy of the green body can be ensured.

[0012] Further, in the above technical solution, the process parameters of the drying are: the temperature is 100 °C, and the time is 10-14 h.

[0013] Further, in the above technical solution, the process of loading the mold is as follows: placing the cold-pressed formed green body in a special graphite mold crucible for reaction-sintered silicon carbide sintering, and laying a layer of silicon metal particles on the surface of the green body; the particle size of the silicon metal particles is 60-120 mesh, and the laying ratio is 1.5 times the weight of the green body. In this technical solution, laying a layer of silicon metal powder on the surface of the green body during mold loading can make the liquid phase penetrate into the pores of silicon carbide during sintering, further improving its density.

[0014] Further, in the above technical solution, the process of reaction sintering is to put the loaded graphite mold crucible into a reaction sintering furnace, evacuate to below 10 Mpa, and keep the nitrogen condition throughout the process by introducing nitrogen, and then carry out the steps of heating, heat preservation, and cooling, specifically including: The first stage: heating from room temperature to 350 °C at a heating rate of 5 °C / min, and keeping the temperature for 30 min after reaching 350 °C; The second stage: heating from 350 °C to 550 °C at a heating rate of 2 °C / min, and keeping the temperature for 60 min after reaching 650 °C; The third stage: heating from 650 °C to 900 °C at a heating rate of 2 °C / min, and keeping the temperature for 30 min after reaching 900 °C; The fourth stage: heating from 900 °C to 1100 °C at a heating rate of 1.6 °C / min, and keeping the temperature for 60 min after reaching 1100 °C; The fifth stage: heating from 1100 °C to 1300 °C at a heating rate of 1 °C / min, and keeping the temperature for 30 min after reaching 1300 °C; The sixth stage: heating from 1300 °C to 1550 °C at a heating rate of 1 °C / min, and keeping the temperature for 3-5 h after reaching 1550 °C; After the heat preservation is completed, turn off the heating system, cool down to 900 °C at a rate of 2 °C / min, and take out the mold after naturally cooling down to below 50 °C. Too fast heating rate may cause the green body to crack, and insufficient heat preservation time will lead to incomplete reaction, affecting the product performance. The present invention adopts a sintering process of multi-stage slow heating and heat preservation, which can not only effectively prevent the sintered ceramic material from cracking, but also make the liquid silicon penetrate into the green body and in-situ generate silicon carbide to fill the pores, further improving the density.

[0015] The present invention also provides a silicon carbide ceramic material prepared by the above preparation process.

[0016] Compared with the prior art, the beneficial effects of the present invention are: By optimizing the raw material ratio, using carbon black and graphite dual-carbon source sintering aids in combination with organic polyvinylpyrrolidone and polycarboxylic acid, the raw materials are uniformly and densely mixed, and the sintering temperature can also be reduced; at the same time, the reactive sintering process is optimized. By combining spray granulation and cold pressing forming processes, a uniform and dense green body can be obtained while further reducing the sintering temperature, reducing the silicon infiltration time, lowering the sintering cost, and improving the flexural strength of the material; by optimizing the sintering heating process and adopting multi-stage slow heating and increasing the heat preservation nodes, the cracking problem of reactive sintered ceramic materials can be solved.

[0017] Compared with traditional hot pressing sintering which requires ultra-high temperature (>2000°C) and high pressure, is costly and difficult to prepare complex parts, the present invention organically combines the optimization of raw material ratio and reactive sintering process. Through chemical reaction combined with liquid-phase silicon infiltration, densification is achieved at a lower temperature while retaining the performance advantages of high-purity SiC. The sintering temperature (1400 - 1600°C) is lower than the traditional sintering temperature, with low energy consumption and no need for high-pressure equipment. The material density can reach more than 95% of the theoretical value, significantly superior to that of traditional process sintering; the obtained silicon carbide ceramic material not only has good densification but also has characteristics such as high hardness (>2700 HV) and high strength (flexural strength >300 MPa), with excellent overall performance. Brief Description of the Drawings

[0018] Figure 1 It is a 1000-fold magnified SEM image of the cross-section of the finished silicon carbide ceramic material obtained in Example 1 of the present invention; Figure 2 It is a 3000-fold magnified SEM image of the cross-section of the finished silicon carbide ceramic material obtained in Example 1 of the present invention. Detailed Description of the Invention

[0019] The experimental methods in the following examples are all conventional methods unless otherwise specified. The raw materials involved in the following examples are all ordinary commercially available products and can be obtained through market purchase unless otherwise specified.

[0020] The above-mentioned technical features of the present invention and the technical features specifically described below (such as in the implementation cases) can be combined with each other to form new or preferred technical solutions.

[0021] Example 1 A process for preparing a high-density silicon carbide ceramic material based on reactive sintering method, comprising the following steps: (1) Prepare raw materials: The raw materials include 90 parts of 3N nano silicon carbide with a particle size of 3.6 μm, 10 parts of sintering aid, 3 parts of organic polyvinylpyrrolidone K30, 0.4 parts of polycarboxylic acid CE-64, and 0.2 parts of mold release agent AO by weight; wherein the sintering aid is a mixture of carbon black (0.5 μm) and graphite powder (3 μm) with a mass ratio of 3:2; (2) Mixing: Add each raw material into a ball mill in sequence, add deionized water accounting for 20% of the total weight of the added raw materials, and perform wet ball milling (ball-to-material ratio of 5:1, rotation speed of 230 rpm, time of 4 h) to mix until it reaches a semi-dry mixing state; (3) Spray granulation: Inlet temperature is 150 °C, outlet temperature is 300 °C; (4) Cold pressing: Pressure is 500 MPa, pressure holding time is 4 min; (5) Drying and debinding: Dry the formed green body, drying temperature is 100 °C, time is 12 hours; (6) Molding: Place the cold-pressed formed green body into a special graphite mold crucible for reaction sintered silicon carbide sintering, and lay a layer of silicon metal particles on the surface of the green body; the particle size of the silicon metal particles is 60 - 120 mesh, and the laying ratio is 1.5 times the weight of the green body; (7) Reaction sintering: Put the graphite mold crucible after molding into a reaction sintering furnace, evacuate to below 10 Mpa, and keep the nitrogen condition throughout the process by introducing nitrogen, then perform the steps of heating up, holding temperature, and cooling down. Specifically, it includes: the first stage, raise the temperature from room temperature to 350 °C, heating rate is 5 °C / min, hold the temperature for 30 min after reaching 350 °C; the second stage, raise the temperature from 350 °C to 550 °C, heating rate is 2 °C / min, hold the temperature for 60 min after reaching 650 °C; the third stage, raise the temperature from 650 °C to 900 °C, heating rate is 2 °C / min, hold the temperature for 30 min after reaching 900 °C; the fourth stage, raise the temperature from 900 °C to 1100 °C, heating rate is 1.6 °C / min, hold the temperature for 60 min after reaching 1100 °C; the fifth stage, raise the temperature from 1100 °C to 1300 °C, heating rate is 1 °C / min, hold the temperature for 30 min after reaching 1300 °C; the sixth stage, raise the temperature from 1300 °C to 1550 °C, heating rate is 1 °C / min, hold the temperature for 4 h after reaching 1550 °C; after the holding temperature ends, turn off the heating system, cool down to 900 °C at a rate of 2 °C / min, and take out the mold after naturally cooling to below 50 °C; (8) Demolding: Take out the sintered body from the special graphite mold crucible for reaction sintered silicon carbide; (9) Grinding process: Grind the plane of the sintered body to the corresponding size, and perform surface grinding and polishing to obtain the required flatness and parallelism.

[0022] Example 2 A process for preparing a high-density silicon carbide ceramic material based on the reaction sintering method, including the following steps: (1) Prepare raw materials: The raw materials include 88 parts of 3N nano silicon carbide with a size of 3μm, 12 parts of sintering aids, 2 parts of organic polyvinylpyrrolidone K30, 0.5 part of polycarboxylic acid CE-64, and 0.3 part of mold release agent AO by weight; among them, the sintering aids are a mixture of carbon black (0.4μm) and graphite powder (2μm) with a mass ratio of 3:2; (2) Mix the materials: Add each raw material into a ball mill in sequence, add deionized water accounting for 20% of the total weight of the raw materials, and wet ball mill (ball-to-material ratio 5:1, rotation speed 200rpm, time 5h) to mix until it reaches a semi-dry mixing state; (3) Spray granulation: The inlet temperature is 150°C and the outlet temperature is 300°C; (4) Cold pressing: The pressure is 460MPa and the pressure holding time is 5min; (5) Drying and debinding: Dry the formed green body, with the drying temperature at 100°C and the time at 12 hours; (6) Loading the mold: Place the cold-pressed formed green body into a special graphite mold crucible for reaction sintering of silicon carbide, and lay a layer of metallic silicon particles on the surface of the green body; among them, the particle size of the metallic silicon particles is 60-120 mesh, and the laying ratio is 1.5 times the weight of the green body; (7) Reaction sintering: Place the graphite mold crucible after loading into a reaction sintering furnace, evacuate to below 10Mpa, and keep the nitrogen condition throughout the process by introducing nitrogen, and then carry out the steps of heating, holding, and cooling, specifically including: In the first stage, heat from room temperature to 350°C at a heating rate of 5°C / min, and hold for 30min after reaching 350°C; in the second stage, heat from 350°C to 550°C at a heating rate of 2°C / min, and hold for 60min after reaching 650°C; in the third stage, heat from 650°C to 900°C at a heating rate of 2°C / min, and hold for 30min after reaching 900°C; in the fourth stage, heat from 900°C to 1100°C at a heating rate of 1.6°C / min, and hold for 60min after reaching 1100°C; in the fifth stage, heat from 1100°C to 1300°C at a heating rate of 1°C / min, and hold for 30min after reaching 1300°C; in the sixth stage, heat from 1300°C to 1550°C at a heating rate of 1°C / min, and hold for 3h after reaching 1550°C; after the holding is completed, turn off the heating system, cool down to 900°C at a rate of 2°C / min, and take out the mold after naturally cooling to below 50°C; (8) Demolding: Take out the sintered body from the special graphite mold crucible for reaction sintering of silicon carbide; (9) Grinding process: Grind the plane of the sintered body to the corresponding size, and polish the surface to obtain the required flatness and parallelism.

[0023] Example 3 A process for preparing high-density silicon carbide ceramic materials by reaction sintering method, comprising the following steps: (1) Prepare raw materials: The raw materials include 92 parts of 3N nano silicon carbide with a particle size of 35μm, 8 parts of sintering aid, 4 parts of organic polyvinylpyrrolidone K30, 0.3 parts of polycarboxylic acid CE-64, and 0.3 parts of mold release agent AO by weight; The sintering aid is a mixture of carbon black (0.8μm) and graphite powder (4μm) with a mass ratio of 3:2; (2) Mixing: Add each raw material into a ball mill in turn, add deionized water accounting for 20% of the total weight of the raw materials, and wet ball mill (ball-to-material ratio 5:1, rotation speed 250rpm, time 3h) to mix to a semi-dry mixing state; (3) Spray granulation: The inlet temperature is 150°C and the outlet temperature is 300°C; (4) Cold pressing: The pressure is 550MPa and the pressure holding time is 3min; (5) Drying and debinding: Dry the formed green body, the drying temperature is 100°C and the time is 12 hours; (6) Loading the mold: Place the cold-pressed formed green body in a special graphite mold crucible for reaction sintering of silicon carbide, and lay a layer of metallic silicon particles on the surface of the green body; The particle size of the metallic silicon particles is 60-120 mesh, and the laying ratio is 1.5 times the weight of the green body; (7) Reaction sintering: Place the loaded graphite mold crucible into a reaction sintering furnace, evacuate to below 10Mpa, and keep the nitrogen condition throughout the process by introducing nitrogen, and then carry out the steps of heating, heat preservation, and cooling, specifically including: In the first stage, raise the temperature from room temperature to 350°C at a heating rate of 5°C / min, and keep it at 350°C for 30min; In the second stage, raise the temperature from 350°C to 550°C at a heating rate of 2°C / min, and keep it at 650°C for 60min; In the third stage, raise the temperature from 650°C to 900°C at a heating rate of 2°C / min, and keep it at 900°C for 30min; In the fourth stage, raise the temperature from 900°C to 1100°C at a heating rate of 1.6°C / min, and keep it at 1100°C for 60min; In the fifth stage, raise the temperature from 1100°C to 1300°C at a heating rate of 1°C / min, and keep it at 1300°C for 30min; In the sixth stage, raise the temperature from 1300°C to 1550°C at a heating rate of 1°C / min, and keep it at 1550°C for 5h; After the heat preservation is completed, turn off the heating system, cool down to 900°C at a rate of 2°C / min, and take out the mold after naturally cooling to below 50°C; (8) Demolding: Take out the sintered body from the special graphite mold crucible for reaction sintering of silicon carbide; (9) Grinding process: Grind the plane of the sintered body to the corresponding size, and polish the surface to obtain the required flatness and parallelism.

[0024] Comparative Example 1 A process for preparing high-density silicon carbide ceramic materials by reaction sintering method, which is different from Example 1 in that the sintering aids are all carbon black.

[0025] Comparative Example 2 A process for preparing high-density silicon carbide ceramic materials by reaction sintering method, which is different from Example 1 in that organic polyvinylpyrrolidone is replaced by phenolic resin.

[0026] Comparative Example 3 A process for preparing high-density silicon carbide ceramic materials by reaction sintering method, which is different from Example 1 in that there is no spray granulation process.

[0027] Comparative Example 4 A process for preparing high-density silicon carbide ceramic materials by reaction sintering method, which is different from Example 1 in that the cold pressing forming process is replaced by an injection molding process, the forming pressure is 1 MPa, the temperature is 60 °C, and the time is 5 min.

[0028] Comparative Example 5 A process for preparing high-density silicon carbide ceramic materials by reaction sintering method, which is different from Example 1 in that the sintering process is as follows: after being put into the reaction sintering furnace, the temperature is directly raised to 1550 °C, kept warm for 4 h, and then naturally cooled to 50 °C and taken out.

[0029] Test Example 1. The appearance, density (Archimedes drainage method), density (Archimedes drainage method, metallographic analysis method), hardness (indentation method), fracture toughness (indentation method), and strength (universal testing machine) of the products (width 4 mm, thickness 3 mm) obtained in Examples 1-3 and Comparative Examples 1-5 were tested, and the results are shown in Table 1.

[0030] Table 1

[0031] It can be seen from the results in Table 1 that the density of the silicon carbide ceramic materials prepared by using the raw material formula and reaction sintering process of the present invention is 2.95 - 3.1 g / cm 3, with a relative density above 95%, a hardness above 2700 HV, good fracture toughness and flexural strength, and excellent comprehensive properties. In Comparative Example 1, since graphite was not added, even though the reactive sintering process of the present invention was used, due to insufficient reaction temperature and incomplete reaction, its relative density, hardness, and mechanical properties were all affected to a certain extent; in Comparative Example 2, phenolic resin was used as the binder, and due to its high residual rate and many pores, it directly affected the relative density and other properties; in Comparative Example 3, spray granulation was not used, and its uniformity and fluidity were poor, affecting cold pressing forming and thus the densification; in Comparative Example 4, the cold pressing forming process was not used, and the product had poor densification and uniformity, directly affecting its mechanical properties; in Comparative Example 5, the segmented heating and holding process was not used, and the densification was poor, and the blank had cracking phenomenon due to too fast heating rate.

[0032] 2. The cross-section of the finished silicon carbide ceramic material obtained in Example 1 was photographed using a scanning electron microscope, and the results are as Figure 1 (1000 times) and Figure 2 (3000 times) as shown. It can be seen that the cross-section of the silicon carbide ceramic material prepared by the present invention is dense, and no pores are seen even under a 3000-fold microscope, indicating good densification.

[0033] In summary, by optimizing the raw material ratio and the reactive sintering process and organically combining the two, the silicon carbide ceramic material obtained by the present invention has good densification, strong toughness and flexural resistance, and excellent overall performance. The reactive sintering process has low energy consumption, effectively reduces costs, and has significant economic and social benefits.

[0034] Finally, it should be emphasized that the above are only the preferred embodiments of the present invention and are not used to limit the present invention. For those skilled in the art, the present invention can have various changes and modifications. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A process for preparing high-density silicon carbide ceramic material based on reaction sintering method, characterized in that: Including raw material preparation, mixing, spray granulation, cold pressing, drying and debinding, mold installation, reaction sintering, demoulding, grinding; The raw materials include 88-92 parts of nano silicon carbide, 8-12 parts of sintering aid, 2-4 parts of organic polyvinyl pyrrolidone, 0.3-0.5 parts of polycarboxylic acid, and 0.2-0.3 parts of release agent by weight; The sintering aid is a mixture of carbon black and graphite powder in a mass ratio of 3:

2.

2. The process for preparing high-density silicon carbide ceramic material based on reaction sintering method according to claim 1 is characterized in that: The particle size of the nano silicon carbide is 3-5 μm; the particle size of the carbon black is 0.4-1 μm; and the particle size of the graphite powder is 2-4 μm.

3. The process for preparing high-density silicon carbide ceramic material based on reaction sintering method according to claim 1 is characterized in that: For the mixing, each raw material is sequentially added into a ball mill, and deionized water accounting for 20% of the total weight of the raw materials is added, and wet ball milling is performed to mix the raw materials to a semi-dry mixed state.

4. The process for preparing high-density silicon carbide ceramic material based on reaction sintering method according to claim 3 is characterized in that: The wet ball milling process is as follows: ball-to-material ratio 5:1, rotation speed 200-250 rpm, time 3-5 h.

5. The process for preparing high-density silicon carbide ceramic material based on reaction sintering method according to claim 1 is characterized in that: The process parameters of the spray granulation are: inlet temperature 150°C, outlet temperature 300°C.

6. The process for preparing high-density silicon carbide ceramic material based on reaction sintering method according to claim 1, characterized in that: The process parameters of the cold pressing forming are: pressure 460-550 MPa, holding time 3-5 min.

7. The process for preparing high-density silicon carbide ceramic material based on reaction sintering method according to claim 1, characterized in that: The drying process parameters are: temperature 100° C., time 10-14 h.

8. The process for preparing high-density silicon carbide ceramic material based on reaction sintering method according to claim 1, characterized in that: The molding process is as follows: placing the cold pressed green body in a graphite mold sagger dedicated for reaction sintering of silicon carbide, and laying a layer of metal silicon particles on the surface of the green body; the particle size of the metal silicon particles is 60-120 meshes, and the laying ratio is 1.5 times the weight of the green body.

9. The process for preparing high-density silicon carbide ceramic material based on reaction sintering method according to claim 1, characterized in that: The process of the reaction sintering is to place the graphite mold sagger after the mold is placed in the reaction sintering furnace, evacuate to below 10Mpa, introduce nitrogen and maintain nitrogen conditions throughout the process, and then perform heating, heat preservation and cooling steps, specifically including: In the first stage, the temperature was raised from room temperature to 350°C at a rate of 5°C / min, and then kept at 350°C for 30 minutes; In the second stage, the temperature was increased from 350°C to 550°C at a rate of 2°C / min, and then kept at 650°C for 60 minutes; The third stage, the temperature was increased from 650℃ to 900℃, the heating rate was 2℃ / min, and the temperature was kept at 900℃ for 30min; In the fourth stage, the temperature was increased from 900°C to 1100°C at a heating rate of 1.6°C / min, and then kept at 1100°C for 60 minutes; The fifth stage, from 1100℃ to 1300℃, the heating rate is 1℃ / min, and after reaching 1300℃, it is kept warm for 30min; The sixth stage, from 1300℃ to 1550℃, the heating rate is 1℃ / min, and after reaching 1550℃, keep warm for 3-5h; After the insulation is completed, turn off the heating system and cool down to 900℃ at a rate of 2℃ / min. Then take out the mold after naturally cooling down to below 50℃.

10. The silicon carbide ceramic material obtained by the preparation process according to any one of claims 1 to 9.

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