Low-temperature sintered silicon carbide ceramic and production process thereof

Abstract

The invention relates to a low-temperature sintered silicon carbide ceramic and a production process thereof, and belongs to the technical field of ceramic production. A preparation method of the low-temperature sintered silicon carbide ceramic comprises the following steps: S1, mixing and grinding nano calcium fluoride, nano titanium carbide, nano magnesium oxide and borax to prepare a composite sintering aid; s2, submicron SiC powder, a composite sintering aid, carbon black and polyvinyl alcohol are subjected to ball milling for 1-2 h to form a mixture, a polycarboxylic acid amine salt dispersing agent, deionized water and glycerin are added, ball milling continues for 0.5 h, slurry is obtained, the slurry is granulated, and granulated powder is obtained; s3, filling the granulated powder into a mold, and maintaining the pressure for 10-15 minutes under the hydraulic pressure of 150-180 MPa to obtain a green body; and S4, preheating the green body in an industrial microwave oven for 1-2 hours, transferring the green body into a vacuum hot pressing furnace, introducing argon protection for sintering, cooling and releasing pressure after sintering is finished, and separating the mold to obtain a silicon carbide ceramic finished product. The method is low in sintering temperature, energy consumption is reduced compared with a traditional sintering method, and considerable economic benefits are achieved.

Description

Technical Field

[0001] This invention relates to a low-temperature sintered silicon carbide ceramic and its production process, belonging to the field of ceramic production technology. Background Technology

[0002] Silicon carbide ceramics possess high flexural strength, excellent oxidation resistance, good corrosion resistance, high wear resistance, and a low coefficient of friction. Furthermore, its strength and creep resistance at high temperatures are the best among known ceramic materials, and its oxidation resistance is the best among all non-oxide ceramics. As a representative of third-generation semiconductor materials, silicon carbide ceramics have a bandgap three times that of silicon and can withstand a breakdown voltage ten times that of silicon, while maintaining its electrical properties at high temperatures. Due to its unique physical properties, silicon carbide ceramics are gradually becoming a necessity in the fields of new energy vehicles, photovoltaic energy storage, 5G communications, medical devices, and defense and aerospace.

[0003] However, SiC, as a strongly covalent compound, has an extremely low self-diffusion coefficient. Traditional methods for sintering SiC ceramics require temperatures around 2000℃, resulting in high energy consumption and potential grain coarsening. Prior art, disclosed in CN104030721B, describes a method for preparing porous silicon carbide ceramics through low-temperature sintering. This method introduces a phosphate bonding system of Al2O3, ZrO2, and H3PO4, achieving a porosity >40% during sintering at 1300℃, making it difficult to achieve high density. Prior art with publication number CN107619281A discloses a method for preparing a low-temperature sintered acid and alkali resistant porous silicon carbide ceramic support. The raw materials used are silicon carbide powder, sintering aid, forming agent, pore-forming agent, lubricant, and solvent. The sintering aid is composed of zircon, high borosilicate, potassium feldspar, quartz sand, Suzhou clay, calcined talc, chalk, and fluorite. This method uses readily available raw materials, is simple to prepare, easy to form, and has low production costs, but the resulting ceramic has low compressive strength, only 22.3~27.4 MPa. Prior art with publication number CN107935598B discloses a low-temperature sintering method for high-performance silicon carbide ceramic materials. Its sintering aid is made from the following raw materials in parts by weight: 40~45 parts zinc powder, 4~7 parts zinc fluorosilicate, and 0.6~1.0 parts strontium aluminoborate. Although this technology can reduce the sintering temperature to 1720~1740℃, the corrosion resistance of the grain boundary phase is not ideal.

[0004] In summary, existing low-temperature sintering technologies for silicon carbide ceramics still suffer from drawbacks such as low mechanical properties and poor corrosion resistance. Furthermore, current processes mostly employ traditional resistance furnace sintering, which results in low mass transfer efficiency, further limiting the densification effect under low-temperature sintering conditions. Summary of the Invention

[0005] To address the aforementioned problems in the existing technology, this invention provides a low-temperature sintered silicon carbide ceramic and its production process, achieving the following objectives: through improvements and innovations in silicon carbide ceramic sintering aids and production processes, a silicon carbide ceramic production process with a lower sintering temperature than traditional methods is provided. The silicon carbide ceramic produced using this process achieves low-temperature sintering at 1350~1480℃, while simultaneously improving the ceramic's density, mechanical properties, and high-temperature stability.

[0006] To achieve the above objectives, the following technical solution is adopted: This invention provides a low-temperature sintered silicon carbide ceramic, the raw materials of which include submicron-sized SiC powder, composite sintering aid, carbon black, polyvinyl alcohol (PVA), polycarboxylate amine salt dispersant, and glycerol; wherein the mass ratio of submicron-sized SiC powder to composite sintering aid is (96.5~98.0):(5.0~7.5); the amount of carbon black is 0.5~1.0% of the mass of SiC powder, the amount of polyvinyl alcohol is 5~10% of the mass of SiC powder, the amount of polycarboxylate amine salt dispersant is 0.2~0.6% of the mass of SiC powder, and the amount of glycerol is 0.3~0.5% of the mass of SiC powder.

[0007] The submicron-sized SiC powder used in this invention has a particle size of 0.2~0.7μm.

[0008] The carbon black used in this invention has a particle size of 30~60nm and its amount is 0.5~1.0% of the mass of SiC powder.

[0009] The polyvinyl alcohol used in this invention has a degree of polymerization of 400-700 and is used in an amount of 5-10% of the mass of SiC powder.

[0010] The amount of polycarboxylic acid amine salt dispersant used in this invention is 0.2~0.6% of the mass of SiC powder.

[0011] The polycarboxylic acid amine salt dispersant is one or more of polycarboxylic acid amine salt dispersant 5023, polycarboxylic acid amine salt dispersant 5027, and polycarboxylic acid amine salt dispersant 5029.

[0012] The preferred polycarboxylate amine salt dispersant is polycarboxylate amine salt dispersant 5023.

[0013] The amount of glycerol used in this invention is 0.3~0.5% of the mass of SiC powder.

[0014] The composite sintering aid used in this invention comprises, by weight, 10-15 parts calcium fluoride (CaF2), 3-6 parts nano-titanium carbide (TiC), 2-3 parts nano-magnesium oxide (MgO), and borax (Na2B4O7). 10H2O) 3.5~6.5 parts.

[0015] The nano-calcium fluoride particles used in this invention have a particle size of 30~50nm; the calcium fluoride melts to form a highly active liquid phase, which fills the gaps between SiC particles and promotes particle rearrangement and diffusion.

[0016] The nano-titanium carbide particles used in this invention have a particle size of 50~70nm; the high lattice matching degree between titanium carbide and SiC can promote diffusion on the surface of SiC particles, inhibit abnormal grain growth, and improve density.

[0017] The nano-magnesium oxide used in this invention has a particle size of 30~60nm; magnesium oxide is used to modify the SiC grain boundary phase, reduce the grain boundary energy, and improve the high-temperature stability and oxidation resistance of ceramics.

[0018] The borax used in this invention has the chemical formula Na2B4O7·10H2O. Borax decomposes to produce a liquid phase of B2O3, which forms a composite low-melting-point liquid phase with CaF2, which is beneficial to reducing the overall sintering temperature.

[0019] This invention also provides a production process for low-temperature sintered silicon carbide ceramics, comprising the following steps: S1. Mix nano-calcium fluoride, nano-titanium carbide, nano-magnesium oxide and borax evenly, and grind for 0.5~1h to obtain a composite sintering aid.

[0020] S2. Add submicron-sized SiC powder, composite sintering aid, carbon black, and polyvinyl alcohol (PVA) to a ball mill and ball mill for 1-2 hours to form a mixture. Add deionized water, polycarboxylate amine salt dispersant, and glycerol to the mixture and continue ball milling for 0.5 hours to obtain a slurry. Use a centrifugal spray dryer to granulate the slurry to obtain granulated powder.

[0021] The ball milling process uses silicon carbide balls with a ball-to-material ratio of 3-4:1 and a milling speed of 300-500 r / min.

[0022] The amount of deionized water used is 0.5 to 0.65 times the total mass of the mixture.

[0023] The centrifugal spray dryer controls the inlet air temperature to 200~220℃, the outlet air temperature to 80~90℃, and the feed rate to 60~90mL / min.

[0024] S3. Load the granulated powder into the mold and hold it under hydraulic pressure at 150~180MPa for 10~15min, with a holding temperature of 80~90℃. The resulting green body density is ≥2.0g / cm³. 3 .

[0025] S4. Preheat the green body in an industrial microwave oven at 600-700℃ and 915MHz. After preheating for 1-2 hours, transfer it to a vacuum hot press furnace, where argon gas is introduced for protection. Sinter at a vacuum of ≤-0.095MPa, pressure of 22-36MPa, and temperature of 1350-1480℃ for 2-3 hours. After sintering, maintain pressure and cool to below 800℃. Begin depressurizing at a rate ≤5MPa / min to prevent cracking of the green body due to sudden pressure drops. Continue cooling to below 200℃, remove the mold, and separate the mold to obtain the finished silicon carbide ceramic product.

[0026] The beneficial effects of this invention are as follows: The low-temperature sintered silicon carbide ceramic provided by this invention has a bulk density of 3.06~3.11 g / cm³. 3 The silicon carbide ceramic exhibits a flexural strength of 396~423 MPa and a thermal conductivity of 153.7~160.2 W / (m·K). After a 200-hour high-temperature oxidation test at 1200℃, its mass retention rate is >99.2%. The low-temperature sintering process for silicon carbide ceramics provided by this invention can produce silicon carbide ceramics with high bulk density, high flexural strength, good thermal conductivity, and strong high-temperature oxidation resistance at 1350~1480℃. Due to its low firing temperature, energy consumption is reduced compared to traditional sintering methods, resulting in considerable economic benefits. Detailed Implementation

[0027] To make the objectives, technical solutions, and advantages of the present invention clearer, the embodiments of the present invention will be described in further detail below. It should be understood that the specific embodiments described herein are for illustrative and explanatory purposes only and are not intended to limit the scope of the invention.

[0028] Example 1: A low-temperature sintered silicon carbide ceramic A low-temperature sintered silicon carbide ceramic, the raw materials for which include submicron-sized SiC powder, composite sintering aid, carbon black, polyvinyl alcohol (PVA), polycarboxylate amine dispersant 5029, and glycerol; The mass ratio of submicron-sized SiC powder to composite sintering aid is 97:5; the amount of carbon black is 0.8% of the mass of SiC powder, the amount of polyvinyl alcohol is 8% of the mass of SiC powder, the amount of polycarboxylate amine dispersant 5029 is 0.3% of the mass of SiC powder, and the amount of glycerol is 0.5% of the mass of SiC powder. The composite sintering aid is prepared by means of 10 parts by weight of calcium fluoride (CaF2), 3 parts by weight of nano titanium carbide (TiC), 3 parts by weight of nano magnesium oxide (MgO), and 6.5 parts by weight of borax. A low-temperature sintering process for silicon carbide ceramics includes the following steps: S1. Mix nano-calcium fluoride, nano-titanium carbide, nano-magnesium oxide, and borax evenly and grind for 1 hour to obtain a composite sintering aid.

[0029] S2. Submicron-sized SiC powder, composite sintering aid, carbon black, and polyvinyl alcohol (PVA) are added to a ball mill and ball-milled for 2 hours to form a mixture. Polycarboxylate amine salt dispersant 5029, deionized water, and glycerol are added to the mixture, and ball milling is continued for 0.5 hours to obtain a slurry. The slurry is granulated using a centrifugal spray dryer to obtain granulated powder.

[0030] The ball mill uses silicon carbide balls at a ball-to-material ratio of 4:1 and a rotation speed of 300 r / min.

[0031] The amount of deionized water used is 0.65 times the total mass of the mixture.

[0032] The centrifugal spray dryer controls the inlet air temperature at 200℃, the outlet air temperature at 80℃, and the feed rate at 60mL / min.

[0033] S3. Load the granulated powder into the mold and hold it under 180MPa hydraulic pressure for 10 minutes. The holding temperature is 90℃ to obtain the green body.

[0034] S4. Preheat the green body in an industrial microwave oven at 700℃ and 915MHz for 1 hour. Then transfer it to a vacuum hot press furnace, where argon gas is introduced for protection. Sinter at a vacuum of ≤-0.095MPa, pressure of 22MPa, and temperature of 1350℃ for 3 hours. After sintering, maintain pressure and cool to below 800℃, then begin depressurizing. The depressurization rate should be ≤5MPa / min to avoid sudden pressure drops that could cause cracking. Continue cooling to below 200℃, remove the mold, and separate the mold from the ceramic body to obtain the silicon carbide ceramic product.

[0035] Example 2: A low-temperature sintered silicon carbide ceramic A low-temperature sintered silicon carbide ceramic, the raw materials for which include submicron-sized SiC powder, composite sintering aid, carbon black, polyvinyl alcohol (PVA), polycarboxylate amine dispersant 5023, and glycerol; The mass ratio of submicron-sized SiC powder to composite sintering aid is 98:7.5; the amount of carbon black is 1.0% of the mass of SiC powder, the amount of polyvinyl alcohol is 10% of the mass of SiC powder, the amount of polycarboxylate amine dispersant 5023 is 0.6% of the mass of SiC powder, and the amount of glycerol is 0.3% of the mass of SiC powder. The composite sintering aid is prepared by means of 12 parts calcium fluoride (CaF2), 6 parts nano titanium carbide (TiC), 2 parts nano magnesium oxide (MgO), and 4 parts borax by weight. A low-temperature sintering process for silicon carbide ceramics includes the following steps: S1. Mix nano-calcium fluoride, nano-titanium carbide, nano-magnesium oxide and borax evenly and grind for 0.5 h to obtain a composite sintering aid.

[0036] S2. Submicron-sized SiC powder, composite sintering aid, carbon black, and polyvinyl alcohol (PVA) are added to a ball mill and ball-milled for 2 hours to form a mixture. Polycarboxylate amine salt dispersant 5023, deionized water, and glycerol are added to the mixture, and ball milling is continued for 0.5 hours to obtain a slurry. The slurry is granulated using a centrifugal spray dryer to obtain granulated powder.

[0037] The ball mill uses silicon carbide balls at a ball-to-material ratio of 3:1 and a rotation speed of 400 r / min.

[0038] The amount of deionized water used is 0.60 times the total mass of the mixture.

[0039] The centrifugal spray dryer controls the inlet air temperature at 200℃, the outlet air temperature at 80℃, and the feed rate at 70mL / min.

[0040] S3. Load the granulated powder into the mold and hold it under 150MPa hydraulic pressure for 10 minutes. The holding temperature is 90℃ to obtain the green body.

[0041] S4. Preheat the green body in an industrial microwave oven at 600℃ and 915MHz for 2 hours. Then transfer it to a vacuum hot press furnace and sinter it at 1400℃ under argon gas protection for 2 hours at a vacuum of ≤-0.095MPa, a pressure of 30MPa, and a temperature of 1400℃. After sintering, maintain the pressure and cool to below 800℃. Begin to release the pressure at a rate ≤5MPa / min to avoid cracking of the green body due to a sudden drop in pressure. Continue cooling to below 200℃, remove the mold, and separate the mold to obtain the silicon carbide ceramic product.

[0042] Example 3: A low-temperature sintered silicon carbide ceramic A low-temperature sintered silicon carbide ceramic, the raw materials for which include submicron-sized SiC powder, composite sintering aid, carbon black, polyvinyl alcohol (PVA), polycarboxylate amine dispersant 5027, and glycerol; The mass ratio of submicron-sized SiC powder to composite sintering aid is 96.5:6; the amount of carbon black is 0.5% of the mass of SiC powder, the amount of polyvinyl alcohol is 5% of the mass of SiC powder, the amount of polycarboxylate amine dispersant 5027 is 0.2% of the mass of SiC powder, and the amount of glycerol is 0.3% of the mass of SiC powder. The composite sintering aid is prepared by means of 14 parts calcium fluoride (CaF2), 3 parts nano titanium carbide (TiC), 2 parts nano magnesium oxide (MgO), and 3.5 parts borax by weight. A low-temperature sintering process for silicon carbide ceramics includes the following steps: S1. Mix nano-calcium fluoride, nano-titanium carbide, nano-magnesium oxide and borax evenly and grind for 0.5 h to obtain a composite sintering aid.

[0043] S2. Submicron-sized SiC powder, composite sintering aid, carbon black, and polyvinyl alcohol (PVA) are added to a ball mill and ball-milled for 1 hour to form a mixture. Polycarboxylate amine salt dispersant 5027, deionized water, and glycerol are added to the mixture, and ball milling is continued for 0.5 hours to obtain a slurry. The slurry is granulated using a centrifugal spray dryer to obtain granulated powder.

[0044] The ball mill uses silicon carbide balls at a ball-to-material ratio of 3:1 and a rotation speed of 300 r / min.

[0045] The amount of deionized water used is 0.50 times the total mass of the mixture.

[0046] The centrifugal spray dryer controls the inlet air temperature at 220℃, the outlet air temperature at 90℃, and the feed rate at 90mL / min.

[0047] S3. Load the granulated powder into the mold and hold it under 150MPa hydraulic pressure for 15 minutes. The holding temperature is 80℃ to obtain the green body.

[0048] S4. Preheat the green body in an industrial microwave oven at 700℃ and 915MHz. After 1 hour of preheating, transfer it to a vacuum hot press furnace and purge it with argon gas for protection. Sinter at a vacuum of ≤-0.095MPa, pressure of 36MPa, and temperature of 1480℃ for 2 hours. After sintering, maintain the pressure and cool to below 800℃. Begin to release the pressure at a rate ≤5MPa / min to prevent cracking of the green body due to sudden pressure drops. Continue cooling to below 200℃, remove the mold, and separate the mold to obtain the silicon carbide ceramic product.

[0049] Comparative Example 1 Compared with Example 2, the operation is the same except that no composite sintering aid is added to the mixture.

[0050] Comparative Example 2 Compared with Example 2, the green body was not preheated and was directly sintered at atmospheric pressure under argon atmosphere protection at a sintering temperature of 2000℃ for 3 hours; all other operations were the same.

[0051] Performance testing The silicon carbide ceramics obtained in Examples 1-3 and Comparative Examples 1-2 were subjected to performance tests. The test standards and methods are as follows, and the test results are shown in Table 1.

[0052] Bulk density was determined according to GB / T 25995-2010 "Test Method for Density and Apparent Porosity of Fine Ceramics" at room temperature (25℃). Bending strength was tested according to GB / T 6569-2006 "Test Method for Bending Strength of Fine Ceramics", using the three-point bending method (span 30 mm, loading rate 0.5 mm / min, test temperature 25℃). High-temperature oxidation resistance was tested by keeping silicon carbide ceramic samples at 1200℃ in air for 200h and measuring the mass retention rate. Thermal conductivity was tested using the laser flash method (referring to GB / T 22588-2008 "Measuring Thermal Diffusion Coefficient or Thermal Conductivity by Flash Method"). The silicon carbide ceramic sample size was Φ10mm×2mm, and the test temperature was room temperature (25℃).

[0053] Table 1. Performance test results of silicon carbide ceramics According to the data in Table 1, the bulk density of the low-temperature sintered silicon carbide ceramic provided by this invention reaches 3.06~3.11 g / cm³. 3 The flexural strength is 396~423MPa, and the thermal conductivity is 153.7~160.2 W / (m·K). After a 200-hour high-temperature oxidation test at 1200℃, the mass retention rate is 99.20~99.46%. The low-temperature sintering process for silicon carbide ceramics provided by this invention can produce silicon carbide ceramics with high bulk density, high flexural strength, good thermal conductivity, and strong high-temperature oxidation resistance at 1350~1480℃. Due to the low firing temperature, energy consumption can be reduced by more than 15% compared to traditional sintering methods, resulting in considerable economic benefits.

[0054] Obviously, there are many other specific implementation methods that can be varied under the concept of this invention. It should be stated here that any changes made under the inventive concept of this invention will fall within the protection scope of this invention.

Claims

1. A process for the production of a low temperature sintered silicon carbide ceramic, characterized in that: The method comprises the following steps: S1, mixing and grinding nano calcium fluoride, nano titanium carbide, nano magnesium oxide and borax to obtain a composite sintering aid; S2, ball milling submicron SiC powder, the composite sintering aid, carbon black and polyvinyl alcohol to form a mixture, then adding polycarboxylic acid amine salt dispersant, deionized water and glycerol to continue ball milling for 0.5 h to obtain a slurry, and granulating the slurry to obtain granulated powder; S3, loading the granulated powder into a mold, and pressurizing at 150-180 MPa for 10-15 min to obtain a green body; S4, preheating the green body in an industrial microwave oven for 1-2 h, then transferring it into a vacuum hot pressing furnace, and sintering under argon protection, and cooling and unloading after sintering to separate the mold to obtain a silicon carbide ceramic product.

2. The method according to claim 1, characterized in that: The mass ratio of the submicron SiC powder to the composite sintering aid is (96.5-98.0):(5.0-7.5); The amount of the carbon black is 0.5-1.0% of the mass of the SiC powder, the amount of the polyvinyl alcohol is 5-10% of the mass of the SiC powder, the amount of the polycarboxylic acid amine salt dispersant is 0.2-0.6% of the mass of the SiC powder, and the amount of the glycerol is 0.3-0.5% of the mass of the SiC powder; The composite sintering aid is prepared from calcium fluoride 10-15 parts, nano titanium carbide 3-6 parts, nano magnesium oxide 2-3 parts and borax 3.5-6.5 parts by weight.

3. The process for producing a low temperature sintered silicon carbide ceramic according to claim 1, characterized by: The sintering is performed at a temperature of 1350-1480℃ for 2-3 h.

4. The process for producing a low temperature sintered silicon carbide ceramic according to claim 1, characterized by: The cooling and unloading is performed at a rate of ≤5 MPa / min after the sintering is completed and the temperature is cooled to below 800℃.

5. The process for producing a low temperature sintered silicon carbide ceramic according to claim 1, characterized by: The preheating is performed at a temperature of 600-700℃.

6. The process for producing a low temperature sintered silicon carbide ceramic according to claim 1, characterized by: The granulation is performed by using a centrifugal spray dryer.

7. The process for producing a low temperature sintered silicon carbide ceramic according to claim 6, characterized by: The control conditions of the centrifugal spray dryer are as follows: the inlet air temperature is 200-220℃, the outlet air temperature is 80-90℃, and the feeding rate is 60-90 mL / min.

8. The process for producing a low temperature sintered silicon carbide ceramic according to claim 1, characterized by: The amount of the deionized water is 0.5-0.65 times the total mass of the mixture.

9. The process for producing a low temperature sintered silicon carbide ceramic according to Claim 1, characterized by: The particle size of the submicron SiC powder is 0.2-0.7 μm, the particle size of the carbon black is 30-60 nm, the polymerization degree of the polyvinyl alcohol is 400-700, the polycarboxylic acid amine salt dispersant is one or more of polycarboxylic acid amine salt dispersant 5023, polycarboxylic acid amine salt dispersant 5027 and polycarboxylic acid amine salt dispersant 5029, the particle size of the nano calcium fluoride is 30-50 nm, the particle size of the nano titanium carbide is 50-70 nm, and the particle size of the nano magnesium oxide is 30-60 nm.

10. A low temperature sintered silicon carbide ceramic, characterized by: Prepared by any one of the preparation methods of claims 1-9.

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