1. The influence of raw material properties
The main production materials involved in the combination of silicon nitride and silicon carbide bricks include additives such as silicon carbide, silicon powder, and nitrogen gas. Unlike ordinary silicon nitride material products, the raw materials required for silicon nitride combined with silicon carbide products must have higher purity. The purity of silicon carbide should be above 98.5%, the purity of silicon powder should be above 99%, and the purity of nitrogen should be above 99.9%. In addition to strict control over the purity of raw materials, strict control over the particle size and grading of raw materials is also required during the production and processing process. Excessive particle size of raw materials will directly affect the bulk density of the formed embryo, resulting in a decrease in the density of the embryo and affecting the quality of the final product. In terms of particle size distribution of raw materials, attention should be paid to the particle size of silicon powder. Particle size control of silicon powder can ensure the reaction efficiency between silicon powder and nitrogen gas. However, blindly reducing the particle size of silicon powder will also have certain negative effects, that is, the reaction rate between silicon powder and nitrogen gas is too fast, and the violent reaction will cause heat accumulation and increase in the reaction device. Once the temperature exceeds 1400 ℃, it will induce silicon flow on the surface of silicon carbide, which is not conducive to product quality control. In addition, adding ZrSiO4 to the raw materials of silicon nitride combined with silicon carbide products can improve the oxidation resistance of the products.
2. The influence of binders
In the production process of silicon nitride combined with silicon carbide bricks, temporary binders need to be added. The addition of binders has two main effects: firstly, it can help the fusion of raw materials to achieve homogeneity, improve the dispersion of raw material particle surfaces, and create favorable conditions for embryo formation; Secondly, silicon nitride bonded silicon carbide products face a heating process during the drying and firing processes. Under high temperature conditions, the temporary binder in the silicon nitride bonded silicon carbide products will decompose, leaving a large number of network like pore channels for the volatilization of gaseous substances. This not only facilitates the filling of nitrogen gas and improves the reaction efficiency between silicon powder and nitrogen gas, but also contributes to the stability of the final product. Temporary binders mainly include organic dextrins, calcium lignosulfonate, and German Sima Chemical dispersants. Currently, the mass percentage of temporary binders added in the industry is usually within 5%.
3. The impact of molding process
At present, the molding process of silicon nitride combined with silicon carbide bricks mainly includes two categories: semi dry molding and grouting molding. Among them, semi dry forming is more commonly used due to its high production efficiency advantage. The main method used domestically is injection molding, which requires good performance of the slurry. There are many factors that determine the quality of the slurry, among which the surface treatment of silicon carbide micro powder plays a very important role.
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