Research on Morphology and Processing Methods of Mixed Fire-resistant Products

The self-made sialon combined with aluminum carbon bricks is developed by incorporating silicon nitride and ultra-fine alumina powders, which are then fired in a nitrogen-rich atmosphere. This process results in the formation of a sialon phase within the carbon bricks, characterized by a significant presence of nitrogen. This suggests that using silicon nitride as an intermediate to produce sialon-bonded refractories is a viable approach, especially when certain industrial conditions are not available. Sialon can be derived from aluminosilicate materials like kaolin, where nitrogen, along with carbon or aluminum powder, replaces part of the oxygen, leading to a more cost-effective production method. While the use of aluminum powder is relatively low-cost, it can make controlling the brick size challenging. In the case of silicon nitride-bonded silicon carbide bricks, a special type of sialon-based material, the production involves mixing high-purity silicon powder with silicon carbide in specific proportions. Under high-pressure vacuum conditions and at temperatures ranging from 1300°C to 1352°C, the mixture is nitrided and sintered (with nitrogen purity up to 99.99%). The addition of alumina powder helps form a more stable bonding phase, but this also makes it harder to control the product's size and density. Using aluminum powder or silicon nitride for cerium bonding can lead to higher costs, limiting its practical application. Most users in the industry prefer these products for blast furnaces, where large-sized bricks are commonly used. However, manufacturing such large components under high-temperature and high-pressure nitriding conditions is expensive and often economically unfeasible. Many traditional refractory plants lack nitriding furnaces, making alternative methods—such as adding specific additives or burning carbon—more practical. Some studies have explored the use of sialon in producing sialon-bonded corundum products. By adding 5% Y₂O₃ as a sintering aid, a network of sialon is formed to cross-link the dispersed corundum particles, resulting in a dense sintered body through liquid-phase sintering. Although this method achieves good laboratory performance, the industrial environment poses challenges. The products are often exposed to acidic or alkaline slags, or alkali vapor, which can cause corrosion. Y₂O₃ tends to react with aluminosilicates, forming a low-melting glass phase that negatively affects performance at high temperatures. From a microstructural perspective, the bonding between sialon-bonded silicon carbide and corundum bricks consists of an amorphous sialon phase. When the production process is well-designed, the nitrogen content in the sialon phase is high, ensuring better stability. Otherwise, if the process is not optimized, the nitrogen content may be too low. In the case of self-made sialon combined with aluminum carbon bricks, the use of silicon nitride as an additive during nitriding and firing leads to the formation of a strong sialon bonding phase. The nitrogen peak is clearly visible, and the matrix can generate sialon in situ, enhancing the overall performance of the brick.

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