Silicon carbide ceramic slurry slip casting method based on plaster mold
By combining plaster molds with particle size distribution design and dispersant selection, the problems of slurry stability and strength in silicon carbide ceramic slurry casting were solved, realizing the efficient industrial production of silicon carbide ceramic products and obtaining high density and excellent mechanical properties.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- 浙江富乐德半导体材料科技有限公司
- Filing Date
- 2025-12-31
- Publication Date
- 2026-05-08
AI Technical Summary
Existing silicon carbide ceramic slip casting methods suffer from poor slurry stability, low green body strength, poor compatibility with molds, and low sintering activity, resulting in low yield and making them unsuitable for industrial production.
A slurry casting method for silicon carbide ceramics based on gypsum molds was adopted. By designing particle size distribution and selecting dispersants, a water-based slurry with high solid content and low viscosity was prepared. The dehydration rate and ambient humidity were controlled. The slurry was solidified in situ by utilizing the capillary force of the gypsum mold. Combined with segmented drying and protective atmosphere sintering, the green body strength and sintering performance were optimized.
A high-density, uniform green body was obtained, which improved the strength and sintering performance of the green body, making it suitable for industrial production. The relative density of the finished product reached over 95%, and its mechanical properties were superior to those of traditional methods.
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Figure CN121990830A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of advanced ceramic material forming technology, and specifically to a slip casting method based on plaster molds for preparing silicon carbide ceramics. Background Technology
[0002] Silicon carbide ceramics are widely used in mechanical seals, aerospace, chemical metallurgy, electronic semiconductors and other fields due to their excellent properties such as high strength, high hardness, excellent wear resistance, corrosion resistance, high thermal conductivity and high chemical stability.
[0003] One of the key processes in the preparation of silicon carbide ceramic products is forming. Research reveals that common forming methods include dry pressing, isostatic pressing, injection molding, and slip casting. Among these, slip casting, especially using porous plaster molds, is highly favored due to its simple equipment, low cost, and ability to produce complex and large parts.
[0004] However, there are many technical difficulties in applying slip casting to silicon carbide ceramics: (1) Slurry stability problem: Silicon carbide particles have high surface energy and are prone to agglomeration in water, making it difficult to prepare slurries with high solid content, low viscosity and long-term stability. Poor slurry stability will lead to uneven density of the green body, and deformation and cracking are likely to occur after sintering. (2) Green body strength problem: The green body formed after the solidification of pure silicon carbide slurry has very low strength and is easily damaged during demolding and subsequent processing, resulting in low yield. (3) Matching problem with mold: If the water absorption rate and capillary structure of the gypsum mold do not match the solidification characteristics of the slurry, it will lead to stress concentration inside the green body and cracks. (4) Sintering activity problem: Pure silicon carbide is a strong covalent compound, which is extremely difficult to sinter (i.e., low sintering activity). Usually, sintering aids need to be added and the sintering density needs to be improved by optimizing the particle size distribution.
[0005] While some existing technologies involve slip casting of silicon carbide (SiC), most suffer from complex processes (requiring large amounts of organic binders), poor green body performance, or are limited to laboratory scale. Therefore, developing a simple, high-quality SiC plaster mold slip casting method suitable for industrial production is of great significance. Summary of the Invention
[0006] To address the shortcomings of existing slip casting techniques for silicon carbide (SiC), this invention provides a slip casting method for silicon carbide ceramics based on gypsum molds, which is simple, low-cost, produces high-strength green bodies, and exhibits good sintering performance.
[0007] To achieve the above objectives, the present invention provides the following technical solution: a method for casting silicon carbide ceramic slurry based on a plaster mold, comprising the following steps: (1) Slurry preparation: Silicon carbide micro powder, sintering aid, dispersant and deionized water are mixed and ball-milled to obtain a uniform, stable water-based slurry with high solid content; Preferably, the silicon carbide micro powder has particle sizes of 10-30 μm and 80-100 μm, respectively, and the mass ratio of fine powder to coarse powder is 0.3-0.6:0.4-0.7.
[0008] Preferably, the sintering aid is selected from carboxymethyl cellulose (CMC), and the amount used is 5-20% of the mass of silicon carbide micro powder. The addition of the sintering aid not only promotes subsequent sintering densification, but also plays a certain role in binding in the slurry, improving the strength of the green body and reducing the breakage rate during demolding and handling.
[0009] Preferably, the dispersant is sodium silicate, and the amount used is 1-8% of the mass of silicon carbide micro powder.
[0010] Preferably, the water-based slurry has a solid content of 80-90% and a low viscosity of <1000mPa•s.
[0011] By designing particle size distribution and selecting dispersants, a slurry with high solid content (mass fraction 80-90%), low viscosity (<1000 mPa•s), and good stability was prepared, laying the foundation for obtaining high-density, uniform preforms and final products.
[0012] (2) Grouting and curing: After vacuum degassing, the grout is injected into a porous gypsum mold to form a blank; Preferably, the temperature and humidity of the mold environment is 60-80%RH.
[0013] Preferably, the porosity of the porous plaster mold is 30-50%, and the dehydration rate is controlled at 0.1-0.5 L / min to avoid stress cracking. The plaster mold utilizes capillary force to absorb water, allowing the slurry to solidify in situ within the mold cavity. By limiting the pore characteristics of porous gypsum molds and controlling environmental conditions, the curing process of the slurry is made smooth and uniform, effectively avoiding cracking and deformation of the blank caused by excessive dehydration.
[0014] Preferably, the porous gypsum mold is made of a mixed gypsum powder formed by mixing α-type and β-type gypsum powders.
[0015] (3) Demolding and drying: After the blank reaches a sufficient strength of 7-15 MPa, demold it and then perform segmented drying to remove residual moisture and prevent drying cracking.
[0016] As a preferred option, the product is aged for 24 hours at 20-25°C and high humidity (above 85%RH) before the segmented drying process to release internal stress. As a preferred method, after aging, the temperature is increased to 35°C at a rate of 1-2°C / min, then increased to 50°C at a rate of 2-4°C / min, and finally increased to 150°C at a rate of 3-6°C / min. The temperature is then slowly decreased to 25-30°C at a rate of 1-2°C / min to remove residual moisture and prevent drying and cracking.
[0017] (4) Sintering: The dried green body is sintered at high temperature under a protective atmosphere. By passing the sintering curve, a dense silicon carbide ceramic product is finally obtained.
[0018] Preferably, the protective gas is selected from nitrogen or argon.
[0019] Preferably, the sintering temperature is 2200~2300℃ and the sintering time is 48~55h.
[0020] More preferably, the sintering curve is as follows: first, under nitrogen protection, the temperature is increased from 25°C to 1000°C at a rate of 1~2°C / min; then, under N2 protection, the temperature is increased to 1500°C at a rate of 2~3°C / min; then, under argon protection, the temperature is increased to 2000°C at a rate of 4~5°C / min; and finally, under argon protection, the temperature is increased to 2200~2300°C at a rate of 1~2°C / min.
[0021] Compared with existing technologies, the advantages of this invention are: the forming method of this invention yields green bodies with high density and good uniformity; the relative density of the silicon carbide ceramic products obtained after sintering can reach over 95%, and their mechanical properties and microstructure are superior to those of products prepared by traditional slip casting methods. The entire process requires no expensive equipment, has low raw material costs, and is very suitable for large-scale industrial production of complex-shaped silicon carbide ceramic components. Attached Figure Description
[0022] Figure 1 This is a microstructure diagram of the silicon carbide ceramic product obtained in Example 1. Detailed Implementation
[0023] The present invention will be further described in detail below through specific embodiments. The raw materials used in the embodiments can be commercially available or prepared by conventional methods.
[0024] However, it should be understood that the examples given are intended to help illustrate the methods and beneficial effects of the present invention, and are not intended to limit the scope of protection of the present invention.
[0025] In this embodiment, the porous gypsum mold is made by mixing α-type and β-type gypsum powders in a mass ratio of 1:1 using a conventional method. The porosity of the porous gypsum mold is 40%.
[0026] Example 1 A method for casting silicon carbide ceramic slurry based on plaster molds includes the following steps: (1) Slurry preparation: 200g of silicon carbide micro powder (including 66g of 20um micro powder and 134g of 90um micro powder), 30g of sintering aid CMC, 10g of dispersant sodium silicate and 30g of deionized water were mixed and ball-milled to obtain a uniform, stable water-based slurry with a solid content of 88.9% and a low viscosity of <1000mPa•s; (2) Grouting and curing: After vacuum degassing, the water-based grout is injected into the porous gypsum mold. By controlling the ambient temperature and humidity to 80%RH and adjusting the dehydration rate (0.3L / min), the gypsum mold is used to adsorb water by capillary force, so that the grout solidifies in situ in the mold cavity to form a blank and avoid stress cracking.
[0027] (3) Demolding and drying: After the green body reaches a strength of 10 MPa, carefully demold it and then keep it at 20℃ and 85%RH for 24 hours for aging. Then, carry out segmented slow drying: raise the temperature to 35℃ at 1℃ / min, then raise the temperature to 50℃ at 3℃ / min, and finally raise the temperature to 150℃ at 5℃ / min. Then, slowly lower the temperature to 25℃ at 1℃ / min to slowly remove residual moisture and prevent drying cracking.
[0028] (4) Sintering: The dried blank is sintered at high temperature under a protective atmosphere: first, under nitrogen protection, the temperature is increased from 25℃ to 1000℃ at 2℃ / min, then under N2 protection, the temperature is increased to 1500℃ at 2℃ / min, then under argon protection, the temperature is increased to 2000℃ at 4℃ / min, and finally under argon protection, the temperature is increased to 2300℃ at 2℃ / min. The blank is sintered for 50 hours to obtain a dense silicon carbide ceramic product 1.
[0029] The microstructure diagram of silicon carbide ceramic product 1 is shown below. Figure 1 As shown, the density is 3.02 g / cm³. 3 Bending strength 399 MPa.
[0030] Example 2 A method for casting silicon carbide ceramic slurry based on plaster molds includes the following steps: (1) Slurry preparation: 200g of silicon carbide micro powder (including 66g of 15um micro powder and 134g of 95um micro powder), 20g of sintering aid CMC, 16g of dispersant sodium silicate and 30g of deionized water were mixed and ball-milled to obtain a uniform, stable water-based slurry with a solid content of 88.7% and a low viscosity of <1000mPa•s; (2) Grouting and curing: After vacuum degassing, the water-based grout is injected into the porous gypsum mold. By controlling the ambient temperature and humidity to 70%RH and adjusting the dehydration rate (0.2L / min), the gypsum mold is used to absorb water by capillary force, so that the grout solidifies in situ in the mold cavity to form a blank and avoid stress cracking.
[0031] (3) Demolding and drying: After the green body reaches a strength of 12 MPa, carefully demold it and then keep it at 25℃ and 85%RH for 24 hours for aging. Then, carry out segmented slow drying: raise the temperature to 35℃ at 1℃ / min, then raise the temperature to 50℃ at 3℃ / min, and finally raise the temperature to 150℃ at 5℃ / min. Then, slowly lower the temperature to 25℃ at 1℃ / min to slowly remove residual moisture and prevent drying cracking.
[0032] (4) Sintering: The dried blank is sintered at high temperature under a protective atmosphere: first, under nitrogen protection, the temperature is increased from 25℃ to 1000℃ at 2℃ / min, then under N2 protection, the temperature is increased to 1500℃ at 2℃ / min, then under argon protection, the temperature is increased to 2000℃ at 4℃ / min, and finally under argon protection, the temperature is increased to 2300℃ at 2℃ / min. The blank is sintered for 53 hours to obtain a dense silicon carbide ceramic product 2.
[0033] The density of silicon carbide ceramic product 2 is 3.03 g / cm³. 3 Bending strength 372 MPa.
[0034] Example 3 A method for casting silicon carbide ceramic slurry based on plaster molds includes the following steps: (1) Slurry preparation: 200g of silicon carbide micro powder (including 66g of 20um micro powder and 134g of 80um micro powder), 40g of sintering aid CMC, 10g of dispersant sodium silicate and 30g of deionized water were mixed and ball-milled to obtain a uniform, stable water-based slurry with a solid content of 89.3% and a low viscosity of <1000mPa•s; (2) Grouting and curing: After vacuum degassing, the water-based grout is injected into the porous gypsum mold. By controlling the ambient temperature and humidity to 60%RH and adjusting the dehydration rate (0.4L / min), the gypsum mold is used to adsorb water by capillary force, so that the grout solidifies in situ in the mold cavity to form a blank and avoid stress cracking.
[0035] (3) Demolding and drying: After the green body reaches a strength of 15 MPa, carefully demold it and then keep it at 25℃ and 85%RH for 24 hours for aging. Then, carry out segmented slow drying: raise the temperature to 35℃ at 1℃ / min, then raise the temperature to 50℃ at 3℃ / min, and finally raise the temperature to 150℃ at 5℃ / min. Then, slowly lower the temperature to 25℃ at 1℃ / min to slowly remove residual moisture and prevent drying cracking.
[0036] (4) Sintering: The dried blank is sintered at high temperature under a protective atmosphere: first, under nitrogen protection, the temperature is increased from 25℃ to 1000℃ at 2℃ / min, then under N2 protection, the temperature is increased to 1500℃ at 2℃ / min, then under argon protection, the temperature is increased to 2000℃ at 4℃ / min, and finally under argon protection, the temperature is increased to 2300℃ at 2℃ / min. The blank is sintered for 55 hours to obtain a dense silicon carbide ceramic product 3.
[0037] The density of silicon carbide ceramic product 3 is 3.14 g / cm³. 3 Bending strength 385 MPa.
[0038] Example 4 A method for casting silicon carbide ceramic slurry based on plaster molds includes the following steps: (1) Slurry preparation: 200g of silicon carbide micro powder (including 66g of 10um micro powder and 134g of 80um micro powder), 15g of sintering aid CMC, 10g of dispersant sodium silicate and 30g of deionized water were mixed and ball-milled to obtain a uniform, stable water-based slurry with a solid content of 88.2% and a low viscosity of <1000mPa•s; (2) Grouting and curing: After vacuum degassing, the water-based grout is injected into the porous gypsum mold. By controlling the ambient temperature and humidity to 70%RH and adjusting the dehydration rate (0.5L / min), the gypsum mold is used to adsorb water by capillary force, so that the grout solidifies in situ in the mold cavity to form a blank and avoid stress cracking.
[0039] (3) Demolding and drying: After the green body reaches a strength of 10 MPa, carefully demold it and then keep it at 20℃ and 85%RH for 24 hours for aging. Then, carry out segmented slow drying: raise the temperature to 35℃ at 1℃ / min, then raise the temperature to 50℃ at 3℃ / min, and finally raise the temperature to 150℃ at 5℃ / min. Then, slowly lower the temperature to 25℃ at 1℃ / min to slowly remove residual moisture and prevent drying cracking.
[0040] (4) Sintering: The dried green body is sintered at high temperature under a protective atmosphere: first, under nitrogen protection, the temperature is increased from 25℃ to 1000℃ at 2℃ / min, then under N2 protection, the temperature is increased to 1500℃ at 2℃ / min, then under argon protection, the temperature is increased to 2000℃ at 4℃ / min, and finally under argon protection, the temperature is increased to 2300℃ at 2℃ / min. The sintering time is 50 hours to finally obtain dense silicon carbide ceramic products 4.
[0041] The density of silicon carbide ceramic product 4 is 3.06 g / cm³. 3 Bending strength 397 MPa.
[0042] Example 5 A method for casting silicon carbide ceramic slurry based on plaster molds includes the following steps: (1) Slurry preparation: 200g of silicon carbide micro powder (including 86g of 20um micro powder and 114g of 90um micro powder), 20g of sintering aid CMC, 10g of dispersant sodium silicate and 30g of deionized water were mixed and ball-milled to obtain a uniform, stable water-based slurry with a solid content of 88.5% and a low viscosity of <1000mPa•s; (2) Grouting and curing: After vacuum degassing, the water-based grout is injected into the porous gypsum mold. By controlling the ambient temperature and humidity to 80%RH and adjusting the dehydration rate (0.2L / min), the gypsum mold is used to absorb water by capillary force, so that the grout solidifies in situ in the mold cavity to form a blank and avoid stress cracking.
[0043] (3) Demolding and drying: After the green body reaches a strength of 10 MPa, carefully demold it and then keep it at 20℃ and 85%RH for 24 hours for aging. Then, carry out segmented slow drying: raise the temperature to 35℃ at 1℃ / min, then raise the temperature to 50℃ at 3℃ / min, and finally raise the temperature to 150℃ at 5℃ / min. Then, slowly lower the temperature to 25℃ at 1℃ / min to slowly remove residual moisture and prevent drying cracking.
[0044] (4) Sintering: The dried blank is sintered at high temperature under a protective atmosphere: first, under nitrogen protection, the temperature is increased from 25℃ to 1000℃ at 2℃ / min, then under N2 protection, the temperature is increased to 1500℃ at 2℃ / min, then under argon protection, the temperature is increased to 2000℃ at 4℃ / min, and finally under argon protection, the temperature is increased to 2300℃ at 2℃ / min. The blank is sintered for 50 hours to obtain a dense silicon carbide ceramic product 5.
[0045] The density of silicon carbide ceramic product 5 is 3.15 g / cm³. 3 Bending strength 401 MPa.
[0046] Example 6 A method for casting silicon carbide ceramic slurry based on plaster molds includes the following steps: (1) Slurry preparation: 200g of silicon carbide micro powder (including 106g of 20um micro powder and 94g of 90um micro powder), 30g of sintering aid CMC, 10g of dispersant sodium silicate and 30g of deionized water were mixed and ball-milled to obtain a uniform, stable water-based slurry with a solid content of 88.9% and a low viscosity of <1000mPa•s; (2) Grouting and curing: After vacuum degassing, the water-based grout is injected into the porous gypsum mold. By controlling the ambient temperature and humidity to 80%RH and adjusting the dehydration rate (0.3L / min), the gypsum mold is used to adsorb water by capillary force, so that the grout solidifies in situ in the mold cavity to form a blank and avoid stress cracking.
[0047] (3) Demolding and drying: After the green body reaches a strength of 10 MPa, carefully demold it and then keep it at 20℃ and 85%RH for 24 hours for aging. Then, carry out segmented slow drying: raise the temperature to 35℃ at 1℃ / min, then raise the temperature to 50℃ at 3℃ / min, and finally raise the temperature to 150℃ at 5℃ / min. Then, slowly lower the temperature to 25℃ at 1℃ / min to slowly remove residual moisture and prevent drying cracking.
[0048] (4) Sintering: The dried blank is sintered at high temperature under a protective atmosphere: first, under nitrogen protection, the temperature is increased from 25℃ to 1000℃ at 2℃ / min, then under N2 protection, the temperature is increased to 1500℃ at 2℃ / min, then under argon protection, the temperature is increased to 2000℃ at 4℃ / min, and finally under argon protection, the temperature is increased to 2300℃ at 2℃ / min. The blank is sintered for 50 hours to obtain a dense silicon carbide ceramic product 6.
[0049] The density of silicon carbide ceramic product 6 is 3.17 g / cm³. 3 Bending strength 423 MPa.
[0050] Example 7 A method for casting silicon carbide ceramic slurry based on plaster molds includes the following steps: (1) Slurry preparation: 200g of silicon carbide micro powder (including 74g of 20um micro powder and 126g of 90um micro powder), 30g of sintering aid CMC, 4g of dispersant sodium silicate and 30g of deionized water were mixed and ball-milled to obtain a uniform, stable water-based slurry with a solid content of 88.6% and a low viscosity of <1000mPa•s; (2) Grouting and curing: After vacuum degassing, the water-based grout is injected into the porous gypsum mold. By controlling the ambient temperature and humidity to 80%RH and adjusting the dehydration rate (0.4L / min), the gypsum mold is used to absorb water by capillary force, so that the grout solidifies in situ in the mold cavity to form a blank and avoid stress cracking.
[0051] (3) Demolding and drying: After the green body reaches a strength of 10 MPa, carefully demold it and then keep it at 20℃ and 85%RH for 24 hours for aging. Then, carry out segmented slow drying: raise the temperature to 35℃ at 1℃ / min, then raise the temperature to 50℃ at 3℃ / min, and finally raise the temperature to 150℃ at 5℃ / min. Then, slowly lower the temperature to 25℃ at 1℃ / min to slowly remove residual moisture and prevent drying cracking.
[0052] (4) Sintering: The dried blank is sintered at high temperature under a protective atmosphere: first, under nitrogen protection, the temperature is increased from 25℃ to 1000℃ at 2℃ / min, then under N2 protection, the temperature is increased to 1500℃ at 2℃ / min, then under argon protection, the temperature is increased to 2000℃ at 4℃ / min, and finally under argon protection, the temperature is increased to 2300℃ at 2℃ / min. The blank is sintered for 50 hours to obtain a dense silicon carbide ceramic product 7.
[0053] The density of silicon carbide ceramic product 7 is 3.12 g / cm³. 3 Bending strength 398 MPa.
[0054] Example 8 A method for casting silicon carbide ceramic slurry based on plaster molds includes the following steps: (1) Slurry preparation: 200g of silicon carbide micro powder (including 60g of 20um micro powder and 140g of 90um micro powder), 20g of sintering aid CMC, 12g of dispersant sodium silicate and 30g of deionized water were mixed and ball milled to obtain a uniform, stable water-based slurry with a solid content of 88.5% and a low viscosity of <1000mPa•s; (2) Grouting and curing: After vacuum degassing, the water-based grout is injected into the porous gypsum mold. By controlling the ambient temperature and humidity to 80%RH and adjusting the dehydration rate (0.2L / min), the gypsum mold is used to absorb water by capillary force, so that the grout solidifies in situ in the mold cavity to form a blank and avoid stress cracking.
[0055] (3) Demolding and drying: After the green body reaches a strength of 7 MPa, carefully demold it and then keep it at 25℃ and 85%RH for 24 hours for aging. Then, carry out segmented slow drying: raise the temperature to 35℃ at 1℃ / min, then raise the temperature to 50℃ at 3℃ / min, and finally raise the temperature to 150℃ at 5℃ / min. Then, slowly lower the temperature to 25℃ at 1℃ / min to slowly remove residual moisture and prevent drying cracking.
[0056] (4) Sintering: The dried blank is sintered at high temperature under a protective atmosphere: first, under nitrogen protection, the temperature is increased from 25℃ to 1000℃ at 2℃ / min, then under N2 protection, the temperature is increased to 1500℃ at 2℃ / min, then under argon protection, the temperature is increased to 2000℃ at 4℃ / min, and finally under argon protection, the temperature is increased to 2300℃ at 2℃ / min. The blank is sintered for 50 hours to obtain a dense silicon carbide ceramic product 8.
[0057] The density of silicon carbide ceramic product 8 is 3.05 g / cm³. 3 Bending strength 367 MPa.
[0058] Comparative Example 1: No particle size distribution design A method for casting silicon carbide ceramic slurry based on plaster molds includes the following steps: (1) Slurry preparation: 200g of silicon carbide micro powder (with a particle size of 90um), 30g of sintering aid CMC, 10g of dispersant sodium silicate and 30g of deionized water were mixed and ball-milled to obtain a uniform, stable water-based slurry with a solid content of 88.9% and a low viscosity of <1000mPa•s; (2) Grouting and curing: After vacuum degassing, the water-based grout is injected into the porous gypsum mold. By controlling the ambient temperature and humidity to 80%RH and adjusting the dehydration rate (0.3L / min), the gypsum mold is used to adsorb water by capillary force, so that the grout solidifies in situ in the mold cavity to form a blank.
[0059] (3) Demolding and drying: After the green body reaches a strength of 10 MPa, carefully demold it and then keep it at 20℃ and 85%RH for 24 hours for aging. Then, perform segmented slow drying: raise the temperature to 35℃ at 1℃ / min, then raise the temperature to 50℃ at 3℃ / min, and finally raise the temperature to 150℃ at 5℃ / min. Then, slowly lower the temperature to 25℃ at 1℃ / min to slowly remove residual moisture.
[0060] (4) Sintering: The dried green body is sintered at high temperature under a protective atmosphere: first, under nitrogen protection, the temperature is increased from 25℃ to 1000℃ at 2℃ / min, then under N2 protection, the temperature is increased to 1500℃ at 2℃ / min, then under argon protection, the temperature is increased to 2000℃ at 4℃ / min, and finally under argon protection, the temperature is increased to 2300℃ at 2℃ / min. The sintering time is 50 hours to finally obtain silicon carbide ceramic product a.
[0061] The result was that the product could not be sintered, had poor density, and a density of 2.06 g / cm³. 3 Bending strength 132 MPa.
[0062] Comparative Example 2: Other Dispersant Options A method for casting silicon carbide ceramic slurry based on plaster molds includes the following steps: (1) Slurry preparation: 200g of silicon carbide micro powder (including 106g of 20um micro powder and 94g of 90um micro powder), 30g of sintering aid (CMC), 10g of dispersant (TMAH) and 30g of deionized water were mixed and ball-milled to obtain a uniform, stable, water-based slurry with a solid content of 88.9% and a low viscosity of <1000mPa•s; (2) Grouting and curing: After vacuum degassing, the water-based grout is injected into the porous gypsum mold. By controlling the ambient temperature and humidity to 80%RH and adjusting the dehydration rate (0.3L / min), the gypsum mold is used to adsorb water by capillary force, so that the grout solidifies in situ in the mold cavity to form a blank.
[0063] (3) Demolding and drying: After the green body reaches a strength of 10 MPa, carefully demold it and then keep it at 20℃ and 85%RH for 24 hours for aging. Then, perform segmented slow drying: raise the temperature to 35℃ at 1℃ / min, then raise the temperature to 50℃ at 3℃ / min, and finally raise the temperature to 150℃ at 5℃ / min. Then, slowly lower the temperature to 25℃ at 1℃ / min to slowly remove residual moisture.
[0064] (4) Sintering: The dried green body is sintered at high temperature under a protective atmosphere: first, under nitrogen protection, the temperature is increased from 25℃ to 1000℃ at 2℃ / min, then under N2 protection, the temperature is increased to 1500℃ at 2℃ / min, then under argon protection, the temperature is increased to 2000℃ at 4℃ / min, and finally under argon protection, the temperature is increased to 2300℃ at 2℃ / min. The sintering time is 50 hours to finally obtain silicon carbide ceramic product b.
[0065] The results showed that the slurry viscosity was low, the dispersion effect was poor, the product was uneven, fine particles were aggregated inside the product, and the flexural strength was 236 MPa.
[0066] Comparative Example 3: No sintering aids added A method for casting silicon carbide ceramic slurry based on plaster molds includes the following steps: (1) Slurry preparation: 200g of silicon carbide micro powder (including 106g of 20um micro powder and 94g of 90um micro powder), 10g of sodium silicate dispersant and 30g of deionized water were mixed and ball-milled to obtain a uniform, stable, water-based slurry with a solid content of 87.5% and a low viscosity of <1000mPa•s. (2) Grouting and curing: After vacuum degassing, the water-based grout is injected into the porous gypsum mold. By controlling the ambient temperature and humidity to 80%RH and adjusting the dehydration rate (0.3L / min), the gypsum mold is used to adsorb water by capillary force, so that the grout solidifies in situ in the mold cavity to form a blank.
[0067] (3) Demolding and drying: After the green body reaches a strength of 10 MPa, carefully demold it and then keep it at 20℃ and 85%RH for 24 hours for aging. Then, perform segmented slow drying: raise the temperature to 35℃ at 1℃ / min, then raise the temperature to 50℃ at 3℃ / min, and finally raise the temperature to 150℃ at 5℃ / min. Then, slowly lower the temperature to 25℃ at 1℃ / min to slowly remove residual moisture.
[0068] (4) Sintering: The dried green body is sintered at high temperature under a protective atmosphere: first, under nitrogen protection, the temperature is increased from 25℃ to 1000℃ at 2℃ / min, then under N2 protection, the temperature is increased to 1500℃ at 2℃ / min, then under argon protection, the temperature is increased to 2000℃ at 4℃ / min, and finally under argon protection, the temperature is increased to 2300℃ at 2℃ / min. The sintering time is 50 hours to finally obtain silicon carbide ceramic product c.
[0069] The result was: incomplete sintering, density 2.88 g / cm³. 3 Flexural strength 169 MPa.
[0070] The above are merely preferred embodiments of the present invention and do not limit the patent scope of the present invention. Any equivalent structural or procedural transformations made using the present invention specification, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of the present invention.
Claims
1. A method for slip casting of silicon carbide ceramic slurry based on plaster molds, characterized in that, The molding method includes the following steps: (1) Silicon carbide micro powder, sintering aid, dispersant and deionized water are mixed and ball-milled to obtain a uniform, stable water-based slurry with high solid content; (2) After vacuum degassing, the slurry is injected into a porous gypsum mold to form a blank; (3) After the green body reaches a strength of 7-15 MPa, it is demolded and then dried in sections; (4) The dried blank is sintered at high temperature under a protective atmosphere, and a dense silicon carbide ceramic product is obtained by passing the sintering curve.
2. The method for casting silicon carbide ceramic slurry based on plaster molds according to claim 1, characterized in that, The particle sizes of the silicon carbide micro powder mentioned in step (1) are 10-30um and 80-100um, respectively, and the mass ratio of fine powder to coarse powder is 0.3-0.6:0.4-0.
7.
3. The method for casting silicon carbide ceramic slurry based on plaster molds according to claim 1, characterized in that, The sintering aid mentioned in step (1) is selected from carboxymethyl cellulose, and the amount used is 5-20% of the mass of silicon carbide micro powder.
4. The method for casting silicon carbide ceramic slurry based on plaster molds according to claim 1, characterized in that, The dispersant mentioned in step (1) is selected from sodium silicate, and the amount used is 1-8% of the mass of silicon carbide micro powder.
5. The method for casting silicon carbide ceramic slurry based on plaster molds according to claim 1 or 2, characterized in that, In step (1), the solid content of the water-based slurry is 80-90%, and the viscosity is <1000mPa•s.
6. The method for casting silicon carbide ceramic slurry based on plaster molds according to claim 1, characterized in that, In step (2), the ambient temperature and humidity of the mold environment is 60-80%RH.
7. The method for casting silicon carbide ceramic slurry based on plaster molds according to claim 1, characterized in that, Before the segmented drying in step (3), the product is aged for 24 hours at 20~25℃ and high humidity (above 85%RH).
8. The method for casting silicon carbide ceramic slurry based on plaster molds according to claim 1, characterized in that, In step (3), the segmented drying process is as follows: the temperature is increased to 35°C at 1~2°C / min, then increased to 50°C at 2~4°C / min, and finally increased to 150°C at 3~6°C / min, and then decreased to 25~30°C at 1~2°C / min.
9. The method for casting silicon carbide ceramic slurry based on plaster molds according to claim 1, characterized in that, The sintering curve in step (4) is as follows: first, under nitrogen protection, the temperature is increased from 25℃ to 1000℃ at 1~2℃ / min, then under N2 protection, the temperature is increased to 1500℃ at 2~3℃ / min, then under argon protection, the temperature is increased to 2000℃ at 4~5℃ / min, and finally under argon protection, the temperature is increased to 2200~2300℃ at 1~2℃ / min.
10. The method for casting silicon carbide ceramic slurry based on plaster molds according to claim 1, characterized in that, In step (4), the sintering temperature is 2200~2300℃ and the sintering time is 48~55h.