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Introduction to Silicon Carbide Ceramic Product Types

Release Time:

2015-05-15 15:47

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Silicon Carbide Ceramics
　　
　　silicon carbide ceramics
　　
　　Silicon carbide ceramics have excellent high-temperature properties such as high strength, high thermal conductivity, good shock resistance, oxidation resistance, wear resistance, and corrosion resistance, making it a high-quality ceramic material. It is widely used in metallurgy, energy, chemical, and other industries. Initially, silicon carbide ceramic materials used clay, SiO2, silicate, mullite, and other binders. With the application of high-tech methods, new types of silicon carbide products have been widely developed, such as silicon nitride-bonded silicon carbide, oxynitride-bonded silicon carbide, reaction-sintered silicon carbide, recrystallized silicon carbide, and silicon infiltration silicon carbide materials.
　　
　　Due to different binders in silicon carbide ceramics, their properties, usage conditions, and service life vary greatly. The various types of silicon carbide ceramic materials are introduced as follows:
　　1. Silicon Carbide Ceramics with Different Binders
　　1. Clay Binder
　　Clay-bonded products are the most common, lowest in price, and simplest in process. Currently, clay-bonded silicon carbide kilns have a large usage in China's ceramic industry.
　　Due to the reaction of aluminum and oxygen in clay with silicon carbide at 1120–1150°C, the products have low refractoriness and weak oxidation resistance, limiting their application fields. The clay content in the product generally does not exceed 15%, and the amount of fine powder in the mix should not be too high to avoid oxidation. Silicon carbide content ranges from 50% to 93%. Generally used to manufacture crucibles, supports, and flame barriers.
　　2. SiO2 Binder
　　Adding about 10% SiO2 (micropowder) to silicon carbide, during firing, an SiO2 film forms on the surface of silicon carbide particles, bonding them together. Due to the high purity of raw materials and low impurities, its high-temperature performance is much better than clay-bonded products, but its performance is also affected by forming processes. It can be used in high oxygen atmospheres above 1200°C. Generally used to make shelves and supports.
　　3. Mullite-Bonded Silicon Carbide
　　Using mullite (5%–8%) and silicon carbide as raw materials, with pulp or dextrin as binder, formed and fired at 1380°C to firmly bond mullite and silicon carbide. This product has better performance than clay-bonded and SiO2-bonded silicon carbide products, with good thermal shock and oxidation resistance. Its application in ceramic kilns in China is gradually increasing.
　　4. Reaction-Sintered Silicon Carbide
　　Adding metallic silicon powder and carbon (graphite, carbon black, etc.) to silicon carbide, firing at 1450°C in a carbon-embedded environment causes silicon to react with carbon to form low-temperature β-SiC, bonding the original silicon carbide particles. Another method is direct reaction of carbon with metallic silicon to form silicon carbide products, i.e., forming with carbon or carbon and silicon carbide, then firing with silicon embedded. Both methods produce silicon carbide products with good properties. Since the product generally contains 8%–15% free silicon and a small amount of free carbon, its service temperature is below 1400°C. It has good thermal conductivity and impact resistance but poor strength, hardness, and corrosion resistance. Reaction-sintered silicon carbide products have almost no dimensional change before and after sintering, so they can be machined into any shape and size after forming, especially suitable for large-scale, complex-shaped products.
　　5. Silicon Nitride-Bonded Silicon Carbide
　　Silicon nitride has excellent high-temperature properties and can be used as a binder for silicon carbide products. Silicon nitride-bonded silicon carbide products have developed as a high-tech silicon carbide ceramic material in the past 20 years. The manufacturing process involves adding 15%–25% fine silicon powder to the silicon carbide particle mixture, introducing high-purity nitrogen gas in a nitriding furnace, and performing nitriding reaction sintering under certain temperature and pressure conditions. Silicon and nitrogen form α-Si3N4 and β-Si3N4, bonding the hard silicon carbide to form a dense network structure. Therefore, silicon nitride-bonded silicon carbide products have good physical and chemical properties, high-temperature performance, and can be used up to 1500°C. They are widely used in abrasives, metallurgy, daily use, and electronic ceramics industries, with broad prospects as kiln materials.
　　6. Silicon Oxynitride-Bonded Silicon Carbide
　　Its performance is close to silicon nitride-bonded silicon carbide products, with even better oxidation resistance. The production method involves forming green bodies from silicon carbide, silicon dioxide, clay, and additives, then firing under different temperature and pressure conditions with carbon embedding or nitrogen introduction. The reaction produces plate-like silicon oxynitride distributed around silicon carbide particles, tightly bonding them and maintaining excellent oxidation resistance of silicon carbide.
　　
　　7. Recrystallized Silicon Carbide Ceramics
　　Purified silicon carbide micro-powder and ultra-fine powder mixed with a certain amount of binder are formed and fired at 2200–2400°C. Silicon carbide particles recrystallize and bond directly, with silicon carbide content reaching 99%. Compared to the above various binder silicon carbide products, recrystallized silicon carbide products have higher hot mechanical strength, thermal conductivity, thermal shock resistance, and oxidation resistance, making it a high-quality silicon carbide ceramic. The United States developed recrystallized silicon carbide products in the late 1930s. For decades, the US, Germany, and the UK have produced them in large quantities. China has also made great progress in this field and has started mass production.
　　8. Silicon Infiltration Silicon Carbide Ceramics
　　Silicon infiltration silicon carbide products are based on recrystallized silicon carbide products, where liquid or gas phase silicon infiltration fills the pores of recrystallized silicon carbide with silicon, forming denser SiSiC with better performance. China is currently researching SiSiC processes and properties and has achieved small-batch production.
　　In summary, the excellent performance of silicon carbide ceramics is well recognized and widely applied. Currently, high-performance silicon carbide ceramics are still in the research and development stage. To fully utilize the superior properties of silicon carbide and reduce costs, it is essential to thoroughly understand the relationship between material composition, microstructure, and performance, which will ensure future production. As research continues to deepen, its application fields will gradually expand, and the market prospects are extremely broad.
　　
　　SiC ceramics have been widely applied in industrial fields such as petroleum, chemical engineering, microelectronics, automotive, aerospace, aviation, papermaking, laser technology, mining, and atomic energy.

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