Reaction-sintered silicon carbide sintering plate and its preparation method

Abstract

This invention discloses a reaction-sintered silicon carbide firing plate and its preparation method. The reaction-sintered silicon carbide firing plate product is obtained through powder granulation, pressing, and reaction sintering. The silicon carbide powder is mixed in four particle size ranges, resulting in uniform particle size distribution, more reasonable packing, and a relatively compact powder structure where coarse particles form the framework and fine particles fill the spaces between the coarse particles, ensuring the density of the green body after pressing. Ball milling followed by spray granulation ensures uniform mixing of all raw materials. The green body, pressed using a pre-designed hydraulic mold, also has an uneven surface structure, reducing the contact area between the firing plate and the bottom of the ceramic piece, increasing air circulation, and effectively preventing adhesion. This product has the advantages of long lifespan, high strength, and rapid thermal conductivity, solving the problems of low strength, low thermal conductivity, and short service life of mullite, while also addressing the industry pain point of adhesion in reaction-sintered silicon carbide firing plates.

Description

Technical Field

[0001] This invention belongs to the field of silicon carbide composite material technology, specifically relating to reaction-sintered silicon carbide sintering plates and their preparation methods. Background Technology

[0002] Currently, mullite is mainly used for firing plates in daily-use ceramics. However, mullite firing plates suffer from low strength and insufficient thermal conductivity, a major pain point in the industry. Theoretically, mullite firing plates can only be used about 150 times, resulting in a short service life. Their low strength and bending strength (below 200 MPa) mean that under full-load production conditions, their lifespan is less than one month, with approximately 100 uses. To meet load-bearing requirements, the thickness of the mullite firing plate is designed between 1cm and 1.2cm, occupying a significant amount of kiln space and absorbing a large amount of heat. Due to the low strength of mullite, the firing plates are prone to breakage, causing kiln blockage. If the kiln is shut down for cleaning, the indirect costs can exceed 100,000 yuan per instance. Furthermore, after prolonged friction between the mullite firing plate and the alumina rollers, the mullite in the high-temperature zone can stick to the alumina rollers, causing blistering on the roller surface and significantly affecting the normal operation of the kiln.

[0003] In existing technologies, silicon carbide firing plates prepared by reaction sintering experience the release of free silicon during continuous high-temperature use. This free silicon can adhere to the bottom of the ceramic ware at high temperatures, affecting the product quality. Therefore, existing reaction-sintered silicon carbide firing plates require an alumina slurry to be applied to the surface before use. The alumina slurry forms a protective coating to prevent the free silicon in the firing plate from adhering to the ceramic ware base. However, the need to apply the slurry and dry it before each use increases the number of steps and production costs.

[0004] Therefore, there is an urgent need to develop a reaction-sintered silicon carbide sintering plate that has good performance, long service life, strong load-bearing capacity, and does not require the application of slurry. Summary of the Invention

[0005] To address the lack of reaction-sintered silicon carbide sintering plates in existing technologies that offer good performance, long service life, strong load-bearing capacity, and require no slurry application, this invention provides a reaction-sintered silicon carbide sintering plate and its preparation method. The reaction-sintered silicon carbide sintering plate product is obtained through powder granulation, compaction, and reaction sintering.

[0006] The objective of this invention is achieved through the following technical solution:

[0007] A method for preparing reaction-sintered silicon carbide sintering plates includes the following steps:

[0008] S1. Granulation powder preparation:

[0009] The silicon carbide powders of four particle size ranges are mixed in a mass ratio of (1μm-3μm):(5μm-8μm):(10μm-15μm):(20μm-25μm)=2:3:2:3;

[0010] Prepare other auxiliary materials: molding agent PEG (polyethylene glycol), polyvinyl alcohol, carbon black with an average particle size of 0.01μm to 1μm, and graphite; wherein PEG is 3%-5% of the weight of silicon carbide powder, polyvinyl alcohol is 1%-3% of the weight of silicon carbide powder, carbon black is 15%-20% of the weight of silicon carbide powder, and graphite is 5%-10% of the weight of silicon carbide powder;

[0011] The prepared silicon carbide powder and other auxiliary materials are mixed together and then ball-milled, followed by spray granulation to obtain granulated powder with a moisture content of 1-2%.

[0012] S2, Hydraulic pressure:

[0013] The granulated powder is placed in a hydraulic mold and pressed into a green body of a predetermined shape and size, with a green body density of 1.8 g / cm³. 3 -2.0g / cm 3 ;

[0014] S3. Pre-firing: Place the green blank at 300℃-500℃ for 1-2 hours, and remove it after cooling;

[0015] S4. Impregnation: Place the pre-fired green body in a resin solution and impregnate it at 2MPa-4MPa for 4-8 hours, then remove and dry it.

[0016] S5, Reaction Sintering:

[0017] Multiple green blanks are horizontally stacked, and silicon particles are filled between adjacent green blanks. The total weight of silicon particles is 25-30% of the weight of the green blanks. The mass ratio of silicon particles with two particle sizes, (3-5) mm and (2-3) μm, is 1:2.

[0018] Sintering parameters: Vacuum degree <30Pa, heat up to 800℃-900℃ at a rate of 15℃ / min, hold for 1h-1.5h, heat up to 1200℃-1400℃ at a rate of 12℃ / min, hold for 1h-1.5h, then heat up to 1600℃-1800℃ at a rate of 10℃ / min and hold for 21-24h.

[0019] S6, Secondary sintering reaction:

[0020] After the S5 heat preservation stage is completed, the secondary sintering stage is entered to generate a silicon nitride film. The temperature is reduced to 1500℃ at a cooling rate of 5℃ / min. After vacuuming, high-purity nitrogen gas with a purity ≥99.99% is introduced. The flow rate of high-purity nitrogen gas ≥ is 0.5L / min-1L / min. The reaction temperature is maintained at 1500℃-1300℃ for 1h-2h. The high-purity nitrogen gas reacts with elemental silicon to generate a silicon nitride film. The silicon nitride film can prevent adhesion between the film and daily-use ceramic products.

[0021] S7. After heat preservation, the temperature is reduced to below 100℃ at a rate of 10℃ / min. After cooling to room temperature, the product is taken out and finally sandblasted to increase the surface smoothness of the product, thus obtaining the reaction sintered silicon carbide sintering plate.

[0022] Furthermore, step S5 reaction sintering also includes: covering the bottom and surface of the impregnated green blank with a support, placing multiple green blanks horizontally in layers, separating adjacent green blanks with a support, filling the support with silicon particles, and the support is a graphite ring or graphite rod coated with boron nitride.

[0023] Furthermore, the firing plate prepared using the aforementioned steps has the following properties:

[0024] ① Density is 2.9 g / cm³ 3 -3.1g / cm 3 The flexural strength is 280MPa-320MPa, and the fracture toughness is 3.0MPa / m. 1 / 2 -4.1MPa / m 1 / 2 ;

[0025] ② It is resistant to high temperatures, with a working temperature of ≥1250℃ for medium-temperature kilns and ≥1380℃ for high-temperature kilns, and it has strong thermal shock resistance.

[0026] ③Long service life, with over 1000 uses;

[0027] ④ Curvature < 2mm, thickness 4mm-6mm, flatness deviation of large board < ±0.1%;

[0028] ⑤ The long-term load-bearing capacity of the firing plate is 5kg-50kg;

[0029] ⑥ After sintering in a high-temperature environment, the sintering plate and the product do not stick together and do not corrode each other.

[0030] Furthermore, the spherical ink treatment in step S1 specifically includes: adding two types of silicon carbide grinding balls with sizes of 6mm-8mm and 1mm-2mm in a mass ratio of 1:1 as grinding media, the mass ratio of grinding balls to the total amount of powder raw materials is 2:1, the rotation speed is 100r / min-200r / min, grinding for 6h-10h, and then filtering out the grinding media.

[0031] Furthermore, the inner cavity surface of the hydraulic mold described in step S2 is provided with a concave-convex structure, such as a concave circle, a flat groove structure, a triangular prism structure, a square grid structure, etc. After hydraulic pressing, a raised symmetrical structure will be generated on the surface of the green blank.

[0032] Furthermore, the hydraulic pressing step in step S2 specifically includes: for large-sized green blanks, after hydraulic pressing, isostatic pressing is performed to improve the strength of the product. The green blank is placed in a waterproof sleeve and placed in an isostatic pressing device, and isostatic pressing is performed at 150MPa-200MPa at room temperature for 2min-6min to obtain the green blank after isostatic pressing.

[0033] In step S6, a mass flow controller is installed on the nitrogen pipeline to precisely control the flow rate of high-purity nitrogen at 1 L / min, with a purity ≥99.99%. By precisely controlling the flow rate of nitrogen during the reaction, the uniformity of the reaction atmosphere and the sufficiency of the reaction are ensured. The nitrogen flow rate is 1 L / min, and a slight positive pressure is maintained in the reaction chamber to prevent air infiltration.

[0034] Furthermore, in step S6, the nitrogen gas is preheated to above 800°C via a preheating pipe before entering the sintering furnace. This ensures the entire gas delivery system is well-sealed to prevent gas leakage and guarantee the accuracy of the gas flow rate.

[0035] This invention also relates to a reaction-sintered silicon carbide sintering plate, which is prepared using the above-described method for preparing a reaction-sintered silicon carbide sintering plate. The prepared sintering plate has the following properties:

[0036] ① Density is 2.9 g / cm³ 3 -3.1g / cm 3 The flexural strength is 280MPa-320MPa, and the fracture toughness is 3.0MPa / m. 1 / 2 -4.1MPa / m 1 / 2 ;

[0037] ② It is resistant to high temperatures, with a maximum temperature of ≥1250℃ for medium-temperature kilns and ≥1380℃ for high-temperature kilns, and it also has strong thermal shock resistance.

[0038] ③Long service life, with over 1000 uses (over 1 year).

[0039] ④ Curvature < 2mm, thickness 4mm-6mm, flatness deviation of large board < ±0.1%;

[0040] ⑤ The long-term load-bearing capacity of the firing plate is 5kg-50kg;

[0041] ⑥ After sintering in a high-temperature environment, the firing plate does not stick to the daily-use ceramic products and they do not corrode each other.

[0042] Compared with the prior art, the present invention has the following beneficial effects:

[0043] 1. The method for preparing the reaction sintering silicon carbide sintering plate of the present invention uses silicon carbide powder of four particle size ranges, with uniform particle size distribution and good performance of the sintered product after gradation; the use of silicon carbide grinding balls for ball milling can avoid the contamination of powder by stainless steel grinding balls.

[0044] 2. The method for preparing the reaction-sintered silicon carbide sintering plate of the present invention, in the silicon carbide reaction sintering process, the added carbon black and graphite not only participate in the sintering reaction, but also affect the microstructure and macroscopic properties of the material, mainly with the following effects:

[0045] ① As a carbon source participating in the reaction: The preparation principle of reaction sintered silicon carbide is to use α-SiC and C as raw materials, add an appropriate amount of binder for molding and drying, and then put it into a Si-containing embedded material; when the billet is heated in the furnace, the Si around the billet melts and penetrates into the capillary of the billet to react with the C in the billet to generate SiC. The generated SiC gradually fills the pores in the billet and connects the original α-SiC, finally achieving densification of the product and obtaining a finished product with the required strength.

[0046] ② Affects the viscosity and pH value of the slurry: The addition of carbon black will affect the viscosity and pH value of the slurry. As the carbon black content increases, the viscosity of the slurry increases and the pH value also gradually increases, which will affect the stability of the slurry and the molding process. Adding an appropriate amount of carbon black will allow the stability of the entire slurry and the molding process to reach the optimal state.

[0047] ③ Affects the bulk density and flexural strength of sintered bodies: The increase of carbon black content will increase the bulk density and flexural strength of sintered bodies, but when the carbon black content is too high, the sintered body will crack and black "undercooked" areas will appear inside, resulting in a sharp decrease in bulk density and flexural strength. Therefore, an appropriate amount of carbon black content plays an important role in the density and strength of the finished product.

[0048] ④ Affects the microstructure of sintered bodies: The addition of carbon black and graphite will affect the microstructure of sintered bodies, and thus affect their mechanical properties. An appropriate ratio of carbon black and graphite can optimize the structure of sintered bodies and improve their mechanical properties.

[0049] ⑤ Improve the bulk density of the green body and reduce the apparent porosity of the fired sample: Replacing a certain amount of graphite with carbon black as the carbon source for reaction sintering silicon carbide can improve the bulk density of the green body and reduce the apparent porosity of the fired sample, thereby improving the mechanical properties of the sample.

[0050] ⑥ Reduce the content of free Si: The addition of carbon black can reduce the content of free Si in the sintered product, thereby improving the mechanical properties of the product.

[0051] ⑦ Improve the sintering performance and mechanical properties of ceramics: During ball milling, graphite coats the surface of silicon carbide particles, significantly reducing the friction between silicon carbide particles, improving the flowability of the powder, thereby reducing the forming pressure of ceramic green bodies, avoiding damage to molds and presses by hard powder, ensuring production safety, and improving the density and internal structure uniformity of green bodies, further improving the sintering performance of ceramics and the mechanical properties of ceramic products.

[0052] ⑧ Generate β-silicon carbide to improve the density and service life of ceramics: During the silicon infiltration sintering stage, the graphite layer on the surface of silicon carbide reacts with metallic silicon to generate β-silicon carbide, which is firmly adsorbed onto the raw material α-silicon carbide. This makes the sintered silicon carbide ceramics more dense and reduces defects between particles, further improving the mechanical properties of the ceramics and extending their service life.

[0053] 3. The method for preparing the reaction-sintered silicon carbide sintering plate of the present invention uses a steel mold with concave-convex textures on one inner surface during hydraulic pressing. After pressing, the surface of one side of the green blank forms a corresponding concave-convex structure. After sintering, a sintering plate with a concave-convex structure is obtained, which has excellent anti-slip and anti-stick properties. By selecting a suitable type of concave-convex texture, the heat conduction, friction, airflow channels, anti-adhesion, and structural strength of the sintering plate can be optimized according to specific application requirements. The concave-convex structure can be a dotted pattern, a grid pattern, a striped pattern, a honeycomb pattern, a wave pattern, or a spiral pattern, etc.; depending on the application requirements, the sintering plate can be rectangular, fish-shaped, or other shapes. Spiral concave-convex textures are arranged along the spiral direction, providing a special stress distribution and airflow channel effect; honeycomb concave-convex textures provide hexagonal support units, which have high strength and stability, and are suitable for applications requiring high load-bearing capacity and deformation resistance. The prepared firing plate has a textured surface with undulating dotted patterns, forming multiple independent support points on the surface. This reduces the contact area with the ceramic and prevents adhesion to the bottom of the ceramic, making it suitable for the sintering process of easily adhered materials.

[0054] 4. In the preparation method of the reaction sintering silicon carbide support plate of the present invention, a support is laid between each layer of green blanks during sintering. On the one hand, it can provide good support for the green blanks and avoid surface deformation of the support plate during reaction sintering. On the other hand, the use of graphite rings or graphite rods coated with boron nitride as support members will not cause adhesion to the support plate or silicon particles, will not affect the melting and penetration of silicon particles into the green body, and will not affect the adhesion of silicon to the surface of the support plate after reaction with nitrogen.

[0055] 5. The method for preparing the reaction-sintered silicon carbide sintering plate of the present invention involves placing silicon particles of two sizes during reaction sintering: (3-5) mm and (2-3) μm in a mass ratio of 1:2. The total weight of the silicon particles is 25%-30% of the total weight of the green blank to be sintered. First, the silicon particles react with the elemental carbon (i.e., carbon black and graphite) in the green blank of the sintering plate. During the reaction, the silicon particles in the sintering furnace melt at high temperature and penetrate into the green blank to react with carbon. By using two different sizes of silicon particles, the degree of melting of silicon particles of different sizes is different. By adjusting the appropriate particle size ratio, the degree of silicon melting in the furnace at different times is adjusted to ensure that in the reaction sintering step S5, the carbon black and graphite in the sintering plate react completely with silicon. At the same time, all the remaining silicon reacts with the high-purity nitrogen gas in the secondary sintering step S6 to generate silicon nitride, avoiding excess and unreacted silicon adhering to the surface of the sintering plate. Then, silicon particles undergo a secondary sintering reaction with high-purity nitrogen to produce a silicon nitride film. By generating a silicon nitride film on the surface of the silicon carbide firing plate, the silicon carbide firing plate is isolated from the surface, preventing trace amounts of free silicon or silicon dioxide in the firing plate from floating to the surface in an extreme high-temperature working environment and then sticking between the daily-use porcelain and the firing plate.

[0056] 6. In the preparation method of the reaction-sintered silicon carbide sintering plate of the present invention, the heating rate in step S5 is a key factor affecting the reaction process. Too fast or too slow heating rates may cause the degree of transformation of silicon nitride α phase to β phase to exceed the degree of internal reaction, thereby affecting the completeness of silicon powder reaction. The reaction time in step S5 affects the formation of silicon nitride and the uniformity of reaction. If the reaction time is too short, the surface of the sintering plate cannot be completely covered with a complete silicon nitride layer. If the reaction time is too long, the silicon nitride layer on the surface of the sintering plate is prone to uneven thickness. The present invention has found the optimal sintering heating rate and reaction time through multiple experiments. Attached Figure Description

[0057] The accompanying drawings are provided to further illustrate the invention and form part of the specification. They are used together with the embodiments of the invention to explain the invention and do not constitute a limitation thereof.

[0058] Figure 1 A sample image of the silicon carbide sintering plate prepared in Example 1 of the present invention;

[0059] Figure 2 A sample image of the silicon carbide sintering plate prepared in Example 2 of the present invention;

[0060] Figure 3 This is a sample image of the silicon carbide sintering plate prepared in Example 3 of the present invention;

[0061] Figure 4This is a diagram of the steel mold used to prepare the silicon carbide sintering plate in Example 3 of the present invention (a recessed circular hole is provided on one side of the inner surface of the steel mold, which will generate a raised dotted texture structure on the surface of the green blank after hydraulic pressure).

[0062] Figure 5 This is a sample image of the silicon carbide sintering plate prepared in Embodiment 4 of the present invention, in which a flat groove structure is set on the surface of the sintering plate by means of a hydraulic mold. Detailed Implementation

[0063] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the 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] Example 1:

[0065] A method for preparing silicon carbide sintering plates by reaction sintering was used to prepare small plates with dimensions of 300×300×5mm, including the following steps:

[0066] S1. Granulation powder preparation:

[0067] The silicon carbide powder is mixed in four particle size ranges: 1-3μm: 5-8μm: 10-15μm: 20-25μm = 2:3:2:3;

[0068] Other auxiliary materials: molding agent PEG is 3% of the weight of silicon carbide powder, polyvinyl alcohol is 1% of the weight of silicon carbide powder, carbon black with an average particle size of 0.01μm to 1μm is 18% of the weight of silicon carbide powder, and graphite is 5% of the weight of silicon carbide powder;

[0069] The granulated powder was obtained by ball milling and spray granulation, and the moisture content of the granulated powder was 2%.

[0070] S2, density of hydraulically pressed green body: 1.91 g / cm³ 3 ;

[0071] S3, pre-fire the green body at 300℃ for 1.5 hours;

[0072] S4. Immerse in resin solution at 3 MPa for 6 hours, then remove and dry.

[0073] S5. Reaction sintering: Multiple green blanks are horizontally stacked, and silicon particles are filled between adjacent green blanks. The total weight of silicon particles is 26% of the weight of the green blanks. The mass ratio of silicon particles with two sizes, (3-5) mm and (2-3) μm, is 1:2. The vacuum degree is 28-30 Pa, the temperature is increased to 900℃ at a rate of 15℃ / min, held for 1 h, and then increased to 1700℃ at a rate of 10℃ / min and held for 21 h.

[0074] S6. After the heat preservation stage, the secondary sintering stage is entered to generate silicon nitride. The temperature is reduced to 1500℃ at a rate of 5℃ / min. Vacuum is drawn and nitrogen is introduced. The flow rate of high-purity nitrogen (purity ≥99.99%) is 1 L / min. The temperature is maintained for 1.5h.

[0075] Test results:

[0076] Finished product density: 3.02 g / cm³ 3 Fracture toughness 3.82 MPa / m 1 / 2 The bending strength is 305 MPa, the flatness deviation is <±0.16%, and after 20 trials, it does not stick to daily-use ceramic products.

[0077] Example 2:

[0078] A method for preparing silicon carbide sintering plates by reaction sintering was used to prepare small plates with dimensions of 300×300×5mm, including the following steps:

[0079] S1, The silicon carbide powder ratio is the same as in Example 1;

[0080] Other auxiliary materials: molding agent PEG is 4% of the weight of silicon carbide powder, polyvinyl alcohol is 3% of the weight of silicon carbide powder, carbon black with an average particle size of 0.01μm to 1μm is 20% of the weight of silicon carbide powder, and graphite is 10% of the weight of silicon carbide powder;

[0081] The granulated powder preparation is the same as in Example 1;

[0082] S2, density of hydraulically pressed green body: 1.93 g / cm³ 3 The difference from Example 1 is that the mold used has a corrugated surface structure;

[0083] S3. Pre-fire the green body at 300℃ for 2 hours;

[0084] S4. Impregnation: The green body is impregnated in a resin solution at 3MPa for 4 hours, then removed and dried.

[0085] S5. Reaction Sintering: Multiple green blanks are horizontally stacked, with silicon particles filling the spaces between adjacent green blank layers. The total weight of the silicon particles is 28% of the weight of the green blanks. The mass ratio of the two particle sizes, (3-5) mm and (2-3) μm, is 1:2. The vacuum degree is 28-30 Pa, and the temperature is increased to 900℃ at a rate of 15℃ / min, held for 1.5 h, and then increased to 1700℃ at a rate of 10℃ / min and held for 22-24 h.

[0086] S6. Secondary sintering: Cool down to 1500℃ at a rate of 5℃ / min, evacuate and fill with nitrogen gas, with a flow rate of 1 L / min for high-purity nitrogen gas (purity ≥99.99%), and hold for 2 hours.

[0087] Test results:

[0088] Finished product density: 3.05 g / cm³ 3 Fracture toughness 3.79 MPa / m 1 / 2 It has a bending strength of 298 MPa, a flatness deviation of <±0.15%, and after 20 trials, it does not adhere to daily-use ceramic products.

[0089] Example 3:

[0090] A fish-shaped flat plate (280×408×5mm) was prepared using a reaction-sintered silicon carbide sintering method, comprising the following steps:

[0091] S1, The silicon carbide powder ratio is the same as in Example 1;

[0092] Other auxiliary materials: molding agent PEG is 1% of the weight of silicon carbide powder, polyvinyl alcohol is 2% of the weight of silicon carbide powder, carbon black with an average particle size of 0.01-1μm is 15% of the weight of silicon carbide powder, and graphite is 8% of the weight of silicon carbide powder;

[0093] The granulated powder preparation is the same as in Example 1;

[0094] S2, density of hydraulically pressed green body: 1.89 g / cm³ 3 The difference from Example 1 is that the overall structure is fish-shaped;

[0095] S3. Pre-fire the green body at 350℃ for 2 hours;

[0096] S4. The green body is immersed in the resin solution at 2 MPa for 8 hours, then removed and dried.

[0097] S5. Reaction sintering: Multiple green blanks are horizontally stacked, and silicon particles are filled between adjacent green blanks. The total weight of silicon particles is 30% of the weight of the green blanks. The mass ratio of silicon particles with two particle sizes, (3-5) mm and (2-3) μm, is 1:2. The vacuum degree is 28-30 Pa, the temperature is increased to 800℃ at a rate of 15℃ / min, held for 1.5 h, and then increased to 1800℃ at a rate of 10℃ / min and held for 22-24 h.

[0098] S6. Secondary sintering: Cool down to 1500℃ at a rate of 5℃ / min, evacuate and fill with nitrogen gas, with a flow rate of 1 L / min for high-purity nitrogen gas (purity ≥99.99%), and hold for 1 hour.

[0099] Test results:

[0100] Finished product density: 3.08 g / cm³ 3 Fracture toughness 3.84 MPa / m 1 / 2 Flexural strength 311 MPa, flatness deviation < ±0.18%, tested 20 times, no adhesion to daily-use ceramic products, such as... Figure 4 The image shown is a diagram of the steel mold used to prepare the silicon carbide sintering plate in Example 3 (a recessed circular hole is provided on one side of the inner surface of the steel mold, which will generate a raised dotted texture structure on the surface of the green blank after hydraulic pressure).

[0101] Example 4:

[0102] A rectangular plate measuring 400×450×5mm was prepared using a reaction-sintered silicon carbide sintering plate preparation method, including the following steps:

[0103] The difference from Example 1 is:

[0104] Step S2: Place the granulated powder into a hydraulic mold and press it into a green body of the set shape and size. The hydraulic green body is then subjected to isostatic pressing treatment, resulting in a final product of 1.92 g / cm³. 3 ;

[0105] like Figure 5 The image shown is a sample of the silicon carbide sintering plate prepared in Example 4, in which a flat groove structure is set on the surface of the sintering plate using a hydraulic mold.

[0106] Step S5: The bottom and surface of the impregnated green blank are covered with the support. Multiple green blanks are stacked horizontally, and adjacent green blanks are separated by the support. The support is filled with silicon particles. The support is a graphite ring coated with boron nitride. Adjacent graphite rings are closely attached to each other. The total weight of silicon particles is 30% of the weight of the green blank. The mass ratio of the two particle sizes of silicon particles (3-5) mm and (2-3) μm is 1:2.

[0107] Test results:

[0108] The density of the finished product is 3.04 g / cm³. 3 Fracture toughness 3.69 MPa / m 1 / 2 The bending strength is 285 MPa, the flatness deviation is <±0.2%, and after 20 trials, the silicon carbide firing plate does not adhere to the daily ceramic products.

[0109] Comparative Example 1:

[0110] The small plate has a size of 300*300*5mm. The main preparation steps are the same as in Example 1, except that: there are no steps S3 pre-firing, S4 impregnation and S6 secondary sintering. In step S5, the total weight of silicon particles with a particle size of 2-3μm is 26% of the weight of the green blank. After the heat preservation is completed, the temperature is directly reduced to the furnace opening temperature before the furnace is opened.

[0111] Test results:

[0112] Density 2.58 g / cm³ 3 Fracture toughness 2.79 MPa / m 1 / 2 The bending strength is 268 MPa, the flatness deviation is ±0.2%, and the surface of the firing plate shows obvious adhesion to the daily ceramic products during the third trial.

[0113] Compared with the test results of the firing plate of Example 1, it can be seen that Comparative Example 1, which lacks steps S3 pre-firing, S4 impregnation and S6 secondary sintering, has significantly lower density, fracture toughness and bending strength than Example 1. Moreover, it showed obvious adhesion to daily ceramic products after the third trial. This indicates that using a scheme similar to the reaction sintering steps in the prior art (i.e., directly sintering the green body after hydraulic pressing to obtain the silicon carbide firing plate) results in low density and low strength of the product, and adhesion cannot be avoided without additional alumina slurry during use.

[0114] Comparative Example 2:

[0115] The small plate has a size of 300*300*5mm. The main preparation steps are the same as in Example 1. The difference is that there is no pre-firing step S3 and no secondary sintering step S6. In step S5, the total weight of silicon particles with a particle size of 2-3μm is 26% of the weight of the green blank. After the heat preservation is completed, the temperature is directly reduced to the furnace opening temperature before the furnace is opened.

[0116] Test results:

[0117] The density of the finished product is 2.72 g / cm³. 3 Fracture toughness 2.99 MPa / m 1 / 2 The bending strength is 282, the flatness deviation is ±0.18%, and the surface of the firing plate shows obvious adhesion to the daily ceramic products during the third trial.

[0118] Compared with the test results of the firing plate in Example 1, it can be seen that Comparative Example 2, which did not have the pre-firing in step S3 and the secondary sintering in step S6, had significantly lower density, fracture toughness and bending strength than Example 1, and showed obvious adhesion to daily ceramic products after the third trial. The density and strength of Comparative Example 2 were higher than those of Comparative Example 1, indicating that impregnation of the green body followed by reaction sintering can improve the density and strength of the finished product.

[0119] Comparative Example 3:

[0120] The small plate has a size of 300*300*5mm. The main preparation steps are the same as in Example 1, except that there is no secondary sintering in step S6. In step S5, the total weight of silicon particles with a particle size of 2-3μm is 26% of the weight of the green blank. After the heat preservation is completed, the temperature is directly reduced to the furnace opening temperature before the furnace is opened.

[0121] Test results:

[0122] The density of the finished product is 2.92 g / cm³. 3 Fracture toughness 3.62 MPa / m 1 / 2 The bending strength is 298 MPa, the flatness is ±0.2%, and the firing plate adheres to the daily ceramic products during the fourth trial.

[0123] Compared with the test results of the firing plate of Example 1, it can be seen that Comparative Example 3 only has silicon particles of one size and does not have the secondary sintering step S6. The density, fracture toughness and bending strength of the finished product are slightly lower than those of Example 1. Moreover, it showed obvious adhesion to daily ceramic products after the fourth trial, indicating that the absence of the secondary sintering step S6 will reduce the anti-adhesion performance of the finished product. The density and strength of Comparative Example 3 are significantly higher than those of Comparative Example 1. The anti-adhesion performance during the trial is not much different from that of Comparative Example 1, indicating that adding the pre-firing step S3 and the impregnation treatment step S4 can effectively improve the density and strength of the finished product.

[0124] Comparative Example 4:

[0125] The small plate has a size of 300*300*5mm. The main preparation steps are the same as in Example 1, except that: in step S5, the total weight of silicon particles with a particle size of 2-3μm is 26% of the weight of the green blank, and the nitrogen purity in the secondary sintering in step S6 is 85-90%.

[0126] Test results:

[0127] The density of the finished product is 2.95 g / cm³. 3 Fracture toughness 3.65 MPa / m 1 / 2 The bending strength is 299 MPa, the flatness is ±0.27%, the thickness of the silicon nitride film layer on the surface of the firing plate is uneven, and the firing plate and the daily ceramic products showed local adhesion during the 8th trial.

[0128] Compared with the test results of the firing plate in Example 1, it can be seen that Comparative Example 4 only has silicon particles of one size. The nitrogen purity in the secondary sintering in step S6 is lower than that in Example 1. The density, fracture toughness and bending strength of the finished product are slightly lower than those in Example 1. Moreover, local adhesion to daily ceramic products occurs when it is tested for the 8th time. The density, fracture toughness and strength of Comparative Example 4 are higher than those of Comparative Example 1. The anti-adhesion performance of Comparative Example 4 is better than that of Comparative Example 1 when it is tested. This indicates that after the reaction sintering treatment in step S5, the addition of the secondary sintering in step S6, when the nitrogen purity is 85-90%, can generate a silicon nitride film layer on the surface of the finished product as a protective isolation layer, which effectively improves the anti-adhesion performance of the finished product.

[0129] Comparative Example 5:

[0130] The small plate size is 300*300*5mm. The main preparation steps are the same as in Example 1, except that: in step S5, the total weight of silicon particles with a particle size of 2-3μm is 26% of the weight of the green blank, and the nitrogen purity in step S6 is 95%.

[0131] Test results:

[0132] Density 2.89 g / cm³ 3 Fracture toughness 2.99 MPa / m 1 / 2 The bending strength is 289 MPa, the flatness is ±0.3%, the thickness of the silicon nitride film layer on the surface of the firing plate is uneven, and the firing plate and the daily ceramic products show local adhesion during the 10th trial.

[0133] Compared with the test results of the firing plate in Example 1, it can be seen that Comparative Example 5 has only one type of silicon particle size. The nitrogen purity in the secondary sintering step S6 is slightly lower than that in Example 1. The density, fracture toughness, and bending strength of the prepared product are slightly lower than those in Example 1, and local adhesion occurs with the daily-use ceramic product after the 7th trial. The density, fracture toughness, and strength of Comparative Example 5 are all higher than those of Comparative Example 1 and Comparative Example 4. The anti-adhesion performance is better than that of Comparative Example 1 and Comparative Example 4 during the trial. This indicates that the nitrogen purity is increased to 95% during the secondary sintering step S6. The silicon nitride film layer formed on the surface of the finished product is more stable and reliable, which effectively improves the anti-adhesion performance of the finished product.

[0134] Comparative Example 6:

[0135] The rectangular plate is 400*450*5mm. The main preparation steps are the same as in Example 4, except that no support is placed. A total of 4 green blanks are stacked horizontally. The surface and bottom of each green blank are covered with two types of silicon particles. The green blanks are separated by silicon particles.

[0136] Test results:

[0137] The density of the finished product is 2.94 g / cm³. 3 Fracture toughness 3.60 MPa / m 1 / 2The bending strength is 275 MPa. The flatness is large, with a bending degree of 5mm-6mm. The area of ​​the silicon nitride film layer attached to the surface accounts for less than 20% of the area of ​​the firing plate. During the third trial, the firing plate and the daily ceramic products showed local adhesion.

[0138] Compared with the test results of the firing plate in Example 4, it can be seen that in Comparative Example 6, no support was placed between the green bodies, and silicon particles were spread between each layer of green bodies. The density, fracture toughness, and bending strength of the finished product were slightly lower than those in Example 1, but the deformation was large, with a bending degree of 5mm-6mm. The amount of silicon nitride film was very small, and local adhesion to daily ceramic products occurred after the third trial. This indicates that the absence of support between the green bodies significantly affects the flatness of the finished product because the silicon particles spread between the silicon carbide green bodies melt and penetrate at high temperature, thereby affecting the horizontal state of the silicon carbide green bodies and thus affecting the flatness of the finished product. Moreover, when multiple green bodies are horizontally stacked, after the silicon melting and penetration are completed in step S5, nitrogen cannot react with silicon and uniformly adhere to the entire surface of the firing plate.

[0139] By comparing the embodiments and comparative examples, the advantages of the present invention can be seen:

[0140] 1. The reaction-sintered silicon carbide sintering plate product prepared by this invention, such as... Figure 1 The image shown is a sample diagram of the silicon carbide sintering plate prepared in Example 1; as shown... Figure 2 The image shown is a sample diagram of the silicon carbide sintering plate prepared in Example 2; as shown... Figure 3 The image shown is a sample of the silicon carbide sintering plate prepared in Example 3. The reaction-sintered silicon carbide sintering plate product prepared by this invention has the advantages of long life, high strength, and fast thermal conductivity, solving the problems of low strength, low thermal conductivity, and short service life that exist in the prior art when using mullite as a sintering plate. At the same time, it solves the industry pain point that reaction-sintered silicon carbide sintering plates in the prior art are prone to adhesion to daily-use ceramic products.

[0141] 2. This invention uses silicon carbide powder with four particle size ranges, resulting in uniform particle size, more reasonable packing, and a relatively compact powder structure where coarse particles form a framework and fine particles fill the spaces between them, ensuring the density of the green body after pressing. Ball milling followed by spray granulation ensures uniform mixing of all raw materials and auxiliary materials. Two different silicon particle sizes are used in proportion to adjust the degree of silicon melting in the furnace at different stages, ensuring that in step S5 (reaction sintering), the carbon black and graphite in the sintering plate react completely with silicon, while the remaining silicon reacts with the high-purity nitrogen in step S6 (secondary sintering) to form silicon nitride, preventing excess, unreacted silicon from adhering to the surface of the sintering plate.

[0142] 3. The green body obtained by pressing with a set hydraulic mold also has a concave-convex structure on its surface. The surface of the silicon carbide firing plate product prepared has a concave-convex structure. This concave-convex structure does not affect the overall levelness of the product. After placing the daily-use porcelain product, there will be no problem of skewing. The concave-convex structure can significantly reduce the contact area between the daily-use porcelain product and the firing plate, greatly increase the air circulation between the daily-use porcelain and the bottom of the firing plate, and further avoid the daily-use porcelain and the firing plate from sticking together.

[0143] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A method for preparing a reaction-sintered silicon carbide sintering plate, characterized in that: Includes the following steps: S1. Granulation powder preparation: The silicon carbide powders of four particle size ranges are mixed in a mass ratio of (1μm-3μm):(5μm-8μm):(10μm-15μm):(20μm-25μm)=2:3:2:3; Prepare other auxiliary materials: molding agent PEG, polyvinyl alcohol, carbon black with an average particle size of 0.01μm to 1μm, and graphite; wherein PEG is 3%-5% of the weight of silicon carbide powder, polyvinyl alcohol is 1%-3% of the weight of silicon carbide powder, carbon black is 15%-20% of the weight of silicon carbide powder, and graphite is 5%-10% of the weight of silicon carbide powder; The prepared powder raw materials and other auxiliary materials are mixed together and then ball-milled, followed by spray granulation to obtain granulated powder with a moisture content of 1-2%. S2, Hydraulic pressure: The granulated powder is placed in a hydraulic mold and pressed into a green body of a predetermined shape and size, with a green body density of 1.8 g / cm³. 3 -2.0g / cm 3 ; S3. Pre-firing: Place the green blank at 300℃-500℃ for 1-2 hours, and remove it after cooling; S4. Impregnation: Place the pre-fired green body in a resin solution and impregnate it at 2MPa-4MPa for 4-8 hours, then remove and dry it. S5, Reaction Sintering: Multiple green blanks are horizontally stacked, and silicon particles are filled between adjacent green blanks. The total weight of silicon particles is 25-30% of the weight of the green blanks. The mass ratio of silicon particles with two sizes, (3-5) mm and (2-3) μm, is 1:

2. Sintering parameters: Vacuum degree <30Pa, heat up to 800℃-900℃ at a rate of 15℃ / min, hold for 1h-1.5h, heat up to 1200℃-1400℃ at a rate of 12℃ / min, hold for 1h-1.5h, then heat up to 1600℃-1800℃ at a rate of 10℃ / min and hold for 21-24h. S6, Secondary sintering reaction: After the S5 heat preservation stage is completed, the temperature is reduced to 1500℃ at a cooling rate of 5℃ / min. After vacuuming, high-purity nitrogen is introduced at a flow rate of 0.5L / min-1L / min. The reaction temperature is maintained at 1500℃-1300℃ for 1-2 hours. The high-purity nitrogen reacts with elemental silicon to form a silicon nitride film on the surface of the sintering plate. S7. After heat preservation, the temperature is reduced to below 100℃ at a rate of 10℃ / min. After cooling to room temperature, the product is taken out and finally sandblasted to increase the surface smoothness of the product, thus obtaining the reaction sintered silicon carbide sintering plate.

2. The method for preparing the reaction-sintered silicon carbide sintering plate according to claim 1, characterized in that: Step S5 reaction sintering also includes: covering the bottom and surface of the impregnated green blank with a support, placing multiple green blanks horizontally in layers, separating adjacent green blanks with a support, and filling the support with silicon particles of two different sizes. The support is a graphite ring or graphite rod coated with boron nitride.

3. The method for preparing the reaction-sintered silicon carbide sintering plate according to claim 1, characterized in that: The ball milling process described in step S1 specifically includes: adding two types of silicon carbide grinding balls with particle sizes of 6mm-8mm and 1mm-2mm at a mass ratio of 1:1 as grinding media, with a mass ratio of grinding balls to the total amount of powder raw materials of 2:1, a rotation speed of 100r / min-200r / min, grinding for 6h-10h, and then filtering out the grinding media.

4. The method for preparing the reaction-sintered silicon carbide sintering plate according to claim 1, characterized in that: The inner cavity surface of the hydraulic mold described in step S2 is provided with a concave-convex structure, which includes one of the following: a recessed circular hole, a flat groove structure, a triangular prism structure, or a square grid structure.

5. The method for preparing the reaction-sintered silicon carbide sintering plate according to claim 1, characterized in that: The hydraulic pressing step in step S2 further includes: for large-sized green blanks, after hydraulic pressing, isostatic pressing is performed. The green blank is placed in a waterproof sleeve and placed in an isostatic pressing device. It is subjected to isostatic pressing at 150MPa-200MPa at room temperature for 2min-6min to obtain the green blank after isostatic pressing.

6. The method for preparing the reaction-sintered silicon carbide sintering plate according to claim 1, characterized in that: In step S6, a mass flow controller is installed on the nitrogen pipeline to precisely control the flow rate of high-purity nitrogen to 1 L / min, with a purity ≥99.99%.

7. The method for preparing the reaction-sintered silicon carbide sintering plate according to claim 1, characterized in that: In step S6, nitrogen gas is first heated to above 800°C through a preheating pipe before entering the sintering furnace.

8. A reaction-sintered silicon carbide sintering plate, characterized in that: The silicon carbide sintering plate prepared by the reaction sintering method according to any one of claims 1-7 has the following properties: ① Density is 2.9 g / cm³ 3 -3.1g / cm 3 The flexural strength is 280MPa-320MPa, and the fracture toughness is 3.0MPa / m. 1 / 2 -4.1MPa / m 1 / 2 ; ② High temperature resistance, operating temperature ≥1380℃; ③Long service life, with over 1000 uses; ④ Curvature < 2mm, thickness 4mm-6mm, flatness deviation of large board < ±0.1%; ⑤ The long-term load-bearing capacity of the firing plate is 5kg-50kg; ⑥ After sintering in a high-temperature environment, the sintering plate and the product do not stick together and do not corrode each other.

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