Silicon carbide ceramic sealing material and preparation method thereof

Abstract

The present invention provides a silicon carbide ceramic sealing material and a preparation method thereof. The silicon carbide ceramic sealing material comprises a silicon carbide phase and a graphite phase; the silicon carbide ceramic sealing material has a bimodal distribution microstructure. The preparation method of the silicon carbide ceramic sealing material comprises: (1) mixing a carbon source, a silicon carbide powder, a boron source and a solvent to obtain a mixed slurry; (2) subjecting the mixed slurry to spray granulation and drying to obtain a granulated powder; (3) pressing the granulated powder into a desired shape to obtain a sealing material blank; (4) subjecting the obtained sealing material blank to two-step sintering to obtain the silicon carbide ceramic sealing material.

Description

Technical Field

[0001] The invention relates to a silicon carbide ceramic sealing material and a preparation method thereof, and belongs to the field of ceramic materials. Background Art

[0002] With the development of technology, more and more mechanical seals have replaced traditional packing seals with their unique advantages. They have the advantages of reliable operation, good sealing performance, long service life, and low power consumption. Mechanical seals have a pair of friction pairs consisting of a sealing dynamic ring and a static ring. The temperature of the friction pair has a great influence on the performance, so the selection of friction pair materials is crucial. Silicon carbide ceramics have become the preferred material for high-end mechanical seals in recent years due to their excellent mechanical properties, chemical corrosion resistance, high thermal conductivity, and low expansion. Silicon carbide ceramics are mainly divided into reactive silicon carbide, solid-phase sintered silicon carbide, and liquid-phase sintered silicon carbide according to their components.

[0003] Solid-phase sintered silicon carbide ceramic materials are composed of two phases of silicon carbide and graphite. They have excellent mechanical properties, chemical corrosion resistance, and are suitable for industrial production. As seals, they are widely used in various industries such as automobiles, chemicals, petroleum, and printing and dyeing. However, in the preparation of traditional solid-phase sintered silicon carbide materials, the graphite phase comes from the added carbon particles and the residual carbon particles from the cracking of the binder. Due to the pinning effect of the added carbon particles during the sintering process, the silicon carbide grains will not grow abnormally during the sintering process. Therefore, the silicon carbide grain size in the prepared solid-phase sintered silicon carbide material is relatively uniform, usually 1 to 3 μm, and the maximum will not exceed 10 μm. However, in hot water application environments, conventional solid-phase sintered silicon carbide ceramic materials are not resistant to hot water corrosion, and corrosion pits are easily formed, resulting in leakage of the seal, affecting the efficiency and life of the seal. Therefore, it is urgent to develop a solid-phase sintered silicon carbide ceramic sealing material with excellent hot water corrosion resistance. Summary of the invention

[0004] In view of the defect that the above-mentioned traditional solid-phase sintered silicon carbide sealing material is not resistant to hot water corrosion, the present invention has developed a solid-phase sintered silicon carbide ceramic material with a bimodal distribution characteristic. This material not only retains the excellent mechanical properties and chemical corrosion resistance of the traditional solid-phase sintered silicon carbide material, but also generates a new bimodal distribution microstructure, that is, one part has a grain size of 3μm to 10μm, which is the grain size of the conventional solid-phase sintered silicon carbide material, and the other part has a grain size of 10μm to 1000μm, which is a large-grained silicon carbide, so that it has hot water corrosion resistance.

[0005] In one aspect, the present invention provides a silicon carbide ceramic sealing material, wherein the silicon carbide ceramic sealing material comprises a silicon carbide phase and a graphite phase; the silicon carbide ceramic sealing material has a bimodal distribution microstructure.

[0006] Preferably, the content of the graphite phase is 3.0-6.0wt%;

[0007] Preferably, the silicon carbide ceramic sealing material further comprises a boron carbide phase, and the content of the boron carbide phase does not exceed 0.6 wt % (due to the low content, it cannot be measured by XRD).

[0008] Preferably, the grain size of the silicon carbide phase in the silicon carbide ceramic sealing material is 3 μm to 1000 μm; wherein the grain size of a part is 3 μm to 10 μm, and the grain size of another part is 10 μm to 1000 μm.

[0009] Preferably, the relative density of the silicon carbide ceramic sealing material is 98.5-99.8%, the flexural strength is 390-435 MPa, and the fracture toughness is 4.50-4.99 MPa. 1 / 2 .

[0010] On the other hand, the present invention also provides a method for preparing a silicon carbide ceramic sealing material, comprising:

[0011] (1) mixing a carbon source, silicon carbide powder, a boron source and a solvent to obtain a mixed slurry;

[0012] (2) spray granulating and drying the mixed slurry to obtain granulated powder;

[0013] (3) pressing the granulated powder into a shape to obtain a sealing material blank of a desired shape;

[0014] (4) The obtained sealing material blank is sintered in two steps to obtain the silicon carbide ceramic sealing material.

[0015] Preferably, the carbon source is a thermosetting phenolic resin.

[0016] Preferably, the particle size of the silicon carbide powder is 0.3-0.8 μm.

[0017] Preferably, the boron source is boron carbide; and the solvent is ethanol.

[0018] Preferably, taking the total mass of the carbon source, silicon carbide powder and boron source as 100wt%, the mass of the carbon source is calculated as the residual carbon amount of the phenolic resin cracking, and its content is 3-6wt%, the content of silicon carbide powder accounts for 93.4-96.7wt% of the total mass of the powder, and the content of the boron source accounts for 0.3-0.6wt% of the total mass of the powder; the solid content of the mixed slurry is 55-60wt%.

[0019] Preferably, the parameters of the spray granulation include: an inlet temperature of 165-180°C and an outlet temperature of 60-80°C.

[0020] Preferably, the compression molding method is isostatic pressing; the pressure of the isostatic pressing is 150-250 MPa.

[0021] Preferably, the atmosphere of the two-step sintering is an inert atmosphere, preferably argon.

[0022] Preferably, the parameters of the two-step sintering include: firstly keeping the temperature at 1800-1950°C for 0.5-1h, and then keeping the temperature at 2100-2200°C for 1-3h.

[0023] Preferably, the parameters of the two-step sintering include: first heating to 1800-1950°C at a heating rate of 3-5°C / min and keeping warm for 0.5-1h, then heating to 2100-2200°C at a heating rate of 0.5-2°C / min and keeping warm for 1-3h. Low-temperature rapid sintering and short-term heat preservation can improve production efficiency while discharging pores in the blank, quickly realize the rearrangement of solid particles, and ensure the uniform distribution of each component, so as to avoid the phenolic resin cross-linked on the surface of silicon carbide particles at low temperature from flowing and aggregating again during the slow heating process, resulting in a large amount of agglomeration of carbon sources and reducing material properties, and ensure that the carbon source generated by the cracking of part of the phenolic resin exists in the silicon carbide matrix in a submicron manner, and its sintering pinning effect is weak in the subsequent high-temperature sintering, and it is easy to be jumped and wrapped by the rapidly growing silicon carbide particles, so that some silicon carbide particles can grow abnormally. High-temperature slow sintering and long-term heat preservation promote the rapid growth of some silicon carbide particles, and further promote material densification.

[0024] In the present invention, a thermosetting phenolic resin is used as a carbon source to prepare a silicon carbide ceramic sealing material, because the thermosetting phenolic resin has excellent cross-linking properties at low temperatures, which helps to maintain the strength of the formed blank. At the same time, the phenolic resin, as an organic matter, can be uniformly wrapped on the surface of silicon carbide particles during the mixing and drying process, and cracked into highly active nano-carbon particles during the subsequent heat treatment process, which has high sintering activity and promotes rapid densification during the sintering process of silicon carbide ceramics. On the other hand, the phenolic resin has a high content of residual carbon after thermal cracking and can be used as a carbon source in the solid phase sintering process. However, since the particles produced by thermal cracking are relatively small, the pinning effect that hinders the further growth of silicon carbide particles during the solid phase sintering of silicon carbide is relatively weak. As a result, some silicon carbide particles in the sintered body can grow abnormally, and the silicon carbide grains in the obtained silicon carbide sealing material have a bimodal distribution characteristic, that is, the grain size of the silicon carbide phase in the silicon carbide ceramic sealing material is 3μm to 1000μm, a portion of the grains are relatively small in size between 3μm and 10μm, and another portion of the grains are relatively large in size between 10μm and 1000μm.

[0025] In the prior art, silicon carbide ceramic sealing materials are prepared by one-step sintering, and silicon carbide particles usually have a single microstructure feature at the micron level. The present invention realizes the sintering densification of silicon carbide ceramic sealing materials by two-step temperature-controlled sintering: in the low-temperature heat treatment stage, the temperature is quickly raised to suppress the growth rate of silicon carbide grains, achieve uniform distribution of silicon carbide particles and carbon particles, avoid aggregation of carbon particles, and ensure that part of the carbon source generated by the decomposition of phenolic resin exists in the silicon carbide matrix in a submicron manner; in the high-temperature heat treatment stage, the temperature is slowly raised to promote the growth of silicon carbide particles and achieve a bimodal distribution structure of silicon carbide grains.

[0026] Beneficial effects:

[0027] The present invention uses thermosetting phenolic resin as a carbon source for solid-phase sintering of silicon carbide ceramic sealing materials, which weakens the significant pinning effect of traditional direct addition of inorganic carbon sources, so that the silicon carbide particles in the material form a bimodal distribution microstructure feature, thereby having hot water corrosion resistance. Another significant feature of the present invention is that its preparation process is consistent with that of traditional atmospheric solid-phase sintered silicon carbide sealing materials, and it also has the characteristics of simple process and suitability for large-scale production. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 The morphology of the granulated powder prepared in Example 1;

[0029] Figure 2 The microstructure morphology of the polished surface of the sample with a residual carbon content of 5 wt% after pyrolysis of the phenolic resin in Example 2;

[0030] Figure 3 The microstructure of the polished surface of the sample with a residual carbon content of 6 wt% after pyrolysis of the phenolic resin in Example 3;

[0031] Figure 4 The microstructure morphology of the polished surface of the sample with a residual carbon content of 3 wt% after pyrolysis of the phenolic resin in Comparative Example 1;

[0032] Figure 5 This is the microstructural morphology of the polished surface of the sample in Comparative Example 2 whose carbon source is carbon black (6wt%). DETAILED DESCRIPTION

[0033] To further explain the content, features and practical effects of the present invention, the present invention is described in detail below in conjunction with the embodiments. It should be pointed out that the modification method of the design of the present invention is not limited to these specific implementation methods. Without departing from the spirit and connotation of the design of the present invention, the equivalent replacement and modification made by those skilled in the art on the basis of reading the content of the present invention are also within the scope of the present invention.

[0034] The following is an exemplary description of the method for preparing the silicon carbide ceramic sealing material provided by the present invention.

[0035] Ingredients: Phenolic resin is used as a carbon source, and silicon carbide powder and a boron source are used as raw material powders. The raw material powders and the solvent are uniformly mixed to obtain a mixed slurry.

[0036] In optional embodiment, described phenolic resin is thermosetting phenolic resin, and thermosetting phenolic resin has excellent crosslinking property at low temperature, helps to keep the intensity of forming blank.Simultaneously, phenolic resin can be evenly wrapped in the surface of silicon carbide particles in batch mixing and drying process as a kind of organic matter, is cracked into highly active nano carbon particles in subsequent heat treatment process, has higher sintering activity, promotes rapid densification in silicon carbide ceramic sintering process.On the other hand, phenolic resin thermal cracking residual carbon content is high, can be used as the carbon source in solid phase sintering process, but because its thermal cracking particle is less, in silicon carbide solid phase sintering process, hindering the pinning effect that silicon carbide particles further grow up is weak, thereby part of silicon carbide particles can be abnormally grown up in sintered body.

[0037] In the prior art, carbon black is used as the carbon source, and its pinning effect during the sintering process is significant. The obtained silicon carbide material has low density and the silicon carbide grains are fine and basically equiaxed. Using carbon black and phenolic resin as mixed carbon sources, the material is dense and the microstructure is uniform, and the mechanical properties are excellent, but the size of the silicon carbide grains is usually 1 to 3 μm, and the maximum will not exceed 10 μm. In the present invention, only thermosetting phenolic resin is used as the carbon source, and the thermosetting phenolic resin is added in a liquid state. During the mixing process, it can be uniformly wrapped on the surface of the silicon carbide powder particles, and compared with inorganic carbon sources, it is more evenly distributed in the sample. Rapidly solidify on the surface of silicon carbide particles during spray granulation to ensure its uniform distribution in the granulated powder, which is beneficial to the uniform consistency molding of each part of the sample blank during the isostatic pressing process, improve the blank strength, and avoid defects such as cracking or delamination of the blank. In the subsequent cracking process, part of the cracking into fine nano-carbon particles has high sintering activity, which is beneficial to the sintering densification of the material. In the present invention, the pinning effect of nano-carbon on silicon carbide particles is relatively weak, which is conducive to the abnormal growth of some silicon carbide particles, thereby forming the characteristics of a bimodal distribution of silicon carbide grain sizes.

[0038] In an optional embodiment, taking the total mass of the carbon source, silicon carbide powder and boron source as 100wt%, the mass of the carbon source is calculated based on the residual carbon amount of the phenolic resin cracking, and its content is 3-6wt%, the content of silicon carbide powder accounts for 93.4-96.7wt% of the total mass of the powder, and the content of the boron source accounts for 0.3-0.6wt% of the total mass of the powder.

[0039] In an optional embodiment, if the residual carbon amount produced by the pyrolysis of the phenolic resin is less than 3wt%, the carbon is mainly used to consume silicon dioxide on the surface of the silicon carbide powder, which makes it difficult to promote the densification of the solid-phase sintered silicon carbide ceramics, and the prepared ceramics have poor performance. If the residual carbon amount produced by the pyrolysis of the phenolic resin is greater than 6wt%, the pinning effect of carbon in the sintering and densification process of the silicon carbide ceramics is obvious, the silicon carbide particles grow uniformly, it is difficult to form long columnar silicon carbide grains, and a typical bimodal distribution microstructure cannot be formed.

[0040] The mixed slurry is spray granulated and dried to obtain granulated powder.

[0041] In an optional embodiment, the outlet temperature of the spray granulation is controlled at 60-80° C. If the outlet temperature is too low, the moisture content in the granulated powder is too high, and the powder is easy to stick to the mold during the molding process, resulting in sample damage; if the outlet temperature is too high, it is easy to cause the bonding performance of the binder in the granulated powder to decrease, resulting in sample cracking.

[0042] Molding: The granulated powder is molded by isostatic pressing to obtain a silicon carbide ceramic sealing material blank of the desired shape.

[0043] In an optional embodiment, the isostatic pressing pressure is 150-250 MPa. The green blank obtained by isostatic pressing in the present invention has a higher green blank strength, which is usually more than twice that of the dry pressed green blank, thus avoiding cracking and breakage of the green blank after dry pressing.

[0044] Two-step sintering: The obtained silicon carbide ceramic sealing material blank is sintered in two steps under an inert atmosphere to obtain the silicon carbide ceramic sealing material.

[0045] In an optional embodiment, the inert atmosphere is argon.

[0046] In an optional embodiment, the parameters of the two-step sintering include: first heating to 1800-1950°C, keeping warm for 0.5-1h, then heating to 2100-2200°C, and keeping warm for 1-3h. The present invention achieves sintering densification of the material by a two-step temperature control method. In the low-temperature heat treatment stage, the temperature is rapidly increased (the first heating rate is 3-5°C / min) to suppress the growth rate of silicon carbide grains, achieve uniform distribution of silicon carbide particles and carbon particles, and avoid aggregation of carbon particles; in the high-temperature heat treatment stage, the temperature is slowly increased (the second heating rate is 0.5-2°C / min) to promote the growth of silicon carbide particles and achieve a bimodal distribution structure. Among them, the second heating rate is less than the first heating rate.

[0047] In the present invention, the relative density of the silicon carbide ceramic sealing material measured by the Archimedes method is 98.5-99.8%. The flexural strength of the silicon carbide ceramic sealing material measured by the three-point bending method is 390-4530 MPa. The fracture toughness of the silicon carbide ceramic sealing material measured by the slotting method is 4.50-4.99 M·Pam 1 / 2 .

[0048] In the present invention, SEM is used to test or judge whether the silicon carbide ceramic sealing material has a bimodal distribution microstructure.

[0049] The following further examples are given to illustrate the present invention in detail. It should also be understood that the following examples are only used to further illustrate the present invention and cannot be understood as limiting the scope of protection of the present invention. Some non-essential improvements and adjustments made by those skilled in the art based on the above content of the present invention belong to the scope of protection of the present invention. The specific process parameters and the like in the following examples are also only examples within a suitable range, that is, those skilled in the art can make a selection within a suitable range through the description herein, and are not limited to the specific values ​​​​exemplified below.

[0050] Example 1

[0051] 96.4g SiC powder, 10ml phenolic resin solution (the residual carbon content after phenolic resin cracking is 3.0wt%), 0.6g boron carbide, 200g anhydrous ethanol and 200g silicon carbide grinding balls are placed in a ball mill, ball milled and mixed for 4h to obtain slurry, and then the slurry is sprayed and granulated to obtain granulated powder (inlet temperature 170℃, outlet temperature 68℃); the granulated powder is isostatically pressed at 150MPa to obtain a blank; the formed blank is heated to 1900℃ at a heating rate of 5℃ / min in an Ar gas atmosphere, kept warm for 0.5h, and then heated to 2100℃ at a heating rate of 0.5℃ / min, kept warm for 3h, and fired to obtain a silicon carbide ceramic sealing material with a phenolic resin content of 3wt%. The content of graphite phase in the obtained silicon carbide ceramic sealing material is 3wt%.

[0052] Figure 1 This is a morphology diagram of the granulated powder in Example 1. As can be seen from the figure, the granulated powder has good sphericity, and the particle size of the granulated powder is between 20 and 100 μm.

[0053] The silicon carbide grains in the silicon carbide ceramic sealing material obtained in Example 1 have a typical bimodal distribution microstructure, and the particle size of the silicon carbide grains is 3 to 1000 μm. The relative density of the sample is 98.5%, the flexural strength is 390 MPa, and the fracture toughness is 4.50 M·Pam 1 / 2 .

[0054] Example 2

[0055] 94.4g SiC powder, 18.8ml phenolic resin solution (the residual carbon content after phenolic resin cracking is 5.0wt%), 0.6g boron carbide, 200g anhydrous ethanol and 200g silicon carbide grinding balls are placed in a ball mill, and ball milled for 4h to obtain slurry; then the slurry is spray granulated to obtain granulated powder (inlet temperature is 180℃, outlet temperature is 63℃); the granulated powder is isostatically pressed at 250MPa to obtain a blank; the formed blank is heated to 1850℃ at a heating rate of 3℃ / min in an Ar gas atmosphere, kept warm for 1 hour, and then heated to 2200℃ at a heating rate of 2℃ / min, kept warm for 2h, and sintered to obtain a silicon carbide ceramic sealing material with a phenolic resin content of 5wt%. The content of graphite phase in the obtained silicon carbide ceramic sealing material is 5wt%.

[0056] Figure 2 This is the microstructure morphology of the polished surface of the sample with a phenolic resin content of 5wt% in Example 2. As can be seen from the figure, the sample has a dense microstructure, in which the black and dot-like phase is the graphite phase, and the gray-brown and gray-white long columns, rods, etc. are silicon carbide phases. As can be seen from the figure, the silicon carbide grain size has the characteristics of a bimodal distribution, with a large number of slender silicon carbides staggered and distributed, with a length of more than 500μm, and many relatively small silicon carbide grains distributed between the long rod-shaped silicon carbide grains, with a grain size of less than 50μm, and most of them are less than 10μm. The relative density of the sample is 99.8%, the flexural strength is 430.5±33.0MPa, and the fracture toughness is 4.82MPa·m 1 / 2 .

[0057] Example 3

[0058] 93.4g SiC powder, 20ml phenolic resin solution (the residual carbon content after phenolic resin cracking is 6wt%), 0.6g boron carbide, 200g anhydrous ethanol and 200g silicon carbide grinding balls are placed in a ball mill, ball milled and mixed for 4h to obtain slurry, and then the slurry is sprayed and granulated to obtain granulated powder (inlet temperature 165℃, outlet temperature 75℃); the granulated powder is isostatically pressed at 200MPa to obtain a blank; the formed blank is heated to 1950℃ at a heating rate of 4℃ / min in an Ar gas atmosphere, kept warm for 1h, and then heated to 2150℃ at a heating rate of 1℃ / min, kept warm for 3h, and sintered to obtain a silicon carbide ceramic sealing material with a phenolic resin content of 6wt%. The content of graphite phase in the obtained silicon carbide ceramic sealing material is 6wt%.

[0059] Figure 3The microstructure of the polished surface of the sample with a phenolic resin content of 6wt%. As can be seen from the figure, the sample has a dense microstructure, and the silicon carbide particles have a bimodal distribution. Most of the silicon carbide particles have a particle size range below 10μm, and a small number of silicon carbide particles have a particle size above 100μm. The relative density of the sample is 99.5%, the flexural strength is 411.2MPa, and the fracture toughness is 4.99MPa·m 1 / 2 .

[0060] Comparative Example 1

[0061] The preparation process of the silicon carbide ceramic sealing material in this comparative example 1 is as in Example 3, except that 94.4 g of SiC powder, 10 ml of phenolic resin solution (the residual carbon content after pyrolysis of phenolic resin is 3 wt%), 3 g of carbon black, 0.6 g of boron carbide, 200 g of anhydrous ethanol and 200 g of silicon carbide grinding balls are put into a ball mill, and ball milled for 4 hours to obtain a slurry. The content of graphite phase in the obtained silicon carbide ceramic sealing material is 6 wt%.

[0062] Figure 4 The microstructure of the polished surface of the sample in comparative example 1, where the mass ratio of carbon black to phenolic resin (total mass of carbon source is 6wt%) is 1:1. As can be seen from the figure, the size of silicon carbide particles in the sample is relatively uniform, the grain size of silicon carbide is below 5μm, the microstructure of silicon carbide is uniform, and there is no bimodal distribution. The relative density of the sample is 99.9%, the flexural strength is 450.7±25.0MPa, and the fracture toughness is 4.0MPa·m 1 / 2 .

[0063] Comparative Example 2

[0064] The preparation process of the silicon carbide ceramic sealing material (or silicon carbide ceramic sealing material whose carbon source is carbon black) in this comparative example 2 refers to that in Example 3, except that 93.4 g of SiC powder, 6 g of carbon black, 0.6 g of boron carbide, 200 g of anhydrous ethanol and 200 g of silicon carbide grinding balls are put into a ball mill, and the mixture is milled for 4 hours to obtain a slurry.

[0065] Figure 5 This is the microstructure of the polished surface of the sample in comparative example 2 where the carbon source is carbon black (6wt%). As can be seen from the figure, the carbon in the sample is mainly distributed at the grain boundaries of the silicon carbide particles. The grain size of the silicon carbide particles is relatively uniform and the grains are small. The grain size of the silicon carbide grains is below 10μm, and there is no bimodal distribution. The relative density of the sample is 80.0%, the flexural strength is 253.4MPa, and the fracture toughness is 3.0~3.5M·Pam 1 / 2 .

[0066] Comparative Example 3

[0067] The preparation process of the silicon carbide ceramic sealing material in this comparative example 3 refers to that of Example 2 (or other embodiments are also acceptable), with the difference that the formed blank is directly heated to 2200°C at a heating rate of 2°C / min under an Ar gas atmosphere, kept warm for 2 hours, and sintered to obtain a silicon carbide ceramic sealing material with a phenolic resin content of 5wt%.

[0068] The grain size of silicon carbide in the sample obtained in this comparative example 3 is less than 100 μm, the abnormally grown silicon carbide grains are small, and the bimodal distribution characteristics are not obvious. The relative density of the sample is 98.5%, the flexural strength is 380 MPa, and the fracture toughness is 4.8 M·Pam 1 / 2 .

[0069] Comparative Example 4

[0070] The preparation process of the silicon carbide ceramic sealing material in this comparative example 4 refers to that of Example 2, with the difference that: the formed blank is heated to 1850°C at a heating rate of 3°C / min under Ar gas atmosphere without being kept warm, and then heated to 2200°C at a heating rate of 2°C / min, kept warm for 2h, and sintered to obtain a silicon carbide ceramic sealing material with a phenolic resin content of 5wt%.

[0071] The silicon carbide grain size in the sample obtained in this comparative example 4 is less than 200 μm, and there is a bimodal distribution, but the maximum silicon carbide grain size is less than 200 μm. The relative density of the sample is 99.0%, the flexural strength is 390 MPa, and the fracture toughness is 4.0 M·Pam 1 / 2 .

Claims

1. A silicon carbide ceramic sealing material, characterized in that: The silicon carbide ceramic sealing material comprises a silicon carbide phase and a graphite phase; the content of the graphite phase is 5.0 wt%; the silicon carbide ceramic sealing material has a bimodal distribution microstructure, the bimodal distribution microstructure comprises long rod-shaped silicon carbide grains and relatively fine silicon carbide grains distributed between the long rod-shaped silicon carbide grains, the length of the long rod-shaped silicon carbide grains is more than 500 μm, and the grain size of the relatively fine silicon carbide grains is less than 50 μm; the preparation method of the silicon carbide ceramic sealing material comprises: (1) mixing a carbon source, silicon carbide powder, a boron source and a solvent to obtain a mixed slurry; wherein the carbon source is a thermosetting phenolic resin; (2) spray granulating and drying the mixed slurry to obtain granulated powder; (3) Pressing the granulated powder into a shape to obtain a sealing material blank of a desired shape; (4) Sintering the obtained sealing material blank in two steps to obtain the silicon carbide ceramic sealing material; wherein the parameters of the two-step sintering include: first heating the temperature to 1800-1950°C at a heating rate of 3-5°C / min and keeping the temperature for 0.5-1 h, and then heating the temperature to 2100-2200°C at a heating rate of 0.5-2°C / min and keeping the temperature for 1-3 h.

2. The silicon carbide ceramic sealing material according to claim 1, characterized in that: The silicon carbide ceramic sealing material further comprises a boron carbide phase, and the content of the boron carbide phase does not exceed 0.6 wt %.

3. The silicon carbide ceramic sealing material according to claim 1, characterized in that: The silicon carbide ceramic sealing material has a relative density of 98.5-99.8%, a flexural strength of 390-435 MPa, and a fracture toughness of 4.50-4.99 MPa. 1 / 2 .

4. The silicon carbide ceramic sealing material according to claim 1, characterized in that: The particle size of the silicon carbide powder is 0.3 to 0.8 μm; The boron source is boron carbide; and the solvent is ethanol.

5. The silicon carbide ceramic sealing material according to claim 1, characterized in that: Taking the total mass of the carbon source, silicon carbide powder and boron source as 100wt%, the mass of the carbon source is calculated based on the residual carbon content of the cracking of the thermosetting phenolic resin, and its content is 5wt%, the content of the silicon carbide powder is 94.4-96.7wt%, and the content of the boron source is 0.3-0.6wt%; the solid content of the mixed slurry is 55-60wt%.

6. The silicon carbide ceramic sealing material according to claim 1, characterized in that: The parameters of the spray granulation include: an inlet temperature of 165-180°C and an outlet temperature of 60-80°C.

7. The silicon carbide ceramic sealing material according to claim 1, characterized in that: The pressing method is isostatic pressing; the pressure of the isostatic pressing is 150-250 MPa.

8. The silicon carbide ceramic sealing material according to claim 1, characterized in that: The atmosphere of the two-step sintering is an inert atmosphere.

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