Types and preparation methods of nitride bonded silicon carbide refractory materials

Nitrides are a type of non oxide materials that have been extensively studied in engineering ceramics. Si3N4, BN, TiN, etc. are commonly used in this type of material. They are covalent or ionic bonding compounds with strong bonds, high hardness, high melting point, stable chemical properties, and resistance to chemical corrosion. Compared with traditional oxide ceramics, nitride ceramics also have relatively high toughness. In refractory materials, the current application of nitrides is mainly limited to serving as binding phases and additives.

Nitride bonded refractory materials are refractory materials that use nitrides as the bonding phase. The most common nitride bonding phases include Si3N4, Si2N2O, and Theron, with particles such as SiC or corundum as aggregates. According to different bonding methods, it can be divided into Si3N4 bonded SiC products, Sialon bonded SiC products, Sialon bonded corundum products, and Si2N2O bonded SiC products.

1. Silicon oxynitride combined with silicon carbide

The performance of Si2N2O is similar to that of Si3N4, which can serve as a binding phase for SiC at high temperatures, and its oxidation resistance is better than that of Si3N4. The preparation of silicon oxynitride combined with silicon carbide products is completed in a nitriding furnace, using silicon powder, silicon dioxide, and silicon carbide as raw materials. After the reaction, Si2N2O is generated to combine SiC particles, forming silicon carbide products with Si2N2O as the binding phase. The main reactions that occur are as follows:

SiO2+3Si+2N2 → 2Si2N2O

The main crystal phase of the product after reaction is SiC, and the secondary crystal phase is Si2N2O. The plate-like Si2N2O is uniformly dispersed in the matrix, enveloping SiC particles in the form of [SiN3O] tetrahedra, forming Si2N2O bound SiC materials. This microstructure can to some extent hinder the oxidation of SiC to SiO2, and the antioxidant performance is improved. Moreover, the volume density of Si2N2O-SiC after oxidation is also increasing.

Research has shown that materials such as Si2N2O combined with SiC and Si3N4 combined with SiC do not directly react with metal melts such as magnesium and aluminum at higher temperatures. Instead, the oxide film on the surface of the material reacts with the metal melt. After the oxide film on the surface of the material is eroded by the metal melt, the resistance to metal melt erosion of the material is improved due to the non wetting of Si3N4, SiC, and Si2N2O on the melt. The oxidation resistance of Si2N2O is better than that of Si3N4, and the degree of reaction with the metal melt is lower, which improves the resistance to metal melt erosion of silicon oxynitride combined with silicon carbide materials; At the same time, the pollution of materials on the melt is reduced, which is beneficial for controlling the composition of the smelting metal.