Factors influencing the quality of silicon nitride combined with silicon carbide bricks and their control measures

Silicon nitride combined with silicon carbide brick is a new type of refractory material, which contains finer categories, such as silicon nitride combined with silicon carbide radiant tube, silicon nitride combined with silicon carbide brick and so on. Due to the excellent properties of this kind of materials, silicon nitride combined with silicon carbide bricks stands out from many products with the same performance due to their energy-saving and environmental protection characteristics, and the future market development prospects are good.

1. The influence of the properties of raw materials

The main raw materials involved in the production of silicon nitride combined with silicon carbide bricks are: silicon carbide, silicon powder, nitrogen and other additives. Different from ordinary silicon nitride material products, silicon nitride combined with silicon carbide products requires higher purity of raw materials. The purity of silicon carbide should reach more than 98.5%, the purity of silicon powder should reach more than 99%, and the purity of nitrogen should reach more than 99.9%. In addition to the purity of the raw materials that need to be strictly controlled, the particle size and particle gradation of the raw materials need to be strictly controlled during the production process. The high particle size of the raw material will directly affect the bulk density of the embryo body molding, resulting in the reduction of the compactness of the embryo body, and affecting the final product quality. In terms of raw material particle gradation, we should pay attention to the particle size of silicon powder, the particle size control of silicon powder can ensure the reaction efficiency of silicon powder and nitrogen, but blindly reducing the particle size of silicon powder will also have a certain negative impact, that is, the reaction rate of silicon powder and nitrogen is too fast, and the violent reaction causes the heat accumulation in the reaction device to rise, once the temperature exceeds 1400 °C, it will induce the phenomenon of silicon flow on the surface of silicon carbide, which is not conducive to the quality control of the product. In addition, the addition of ZrSiO4 to the raw materials of silicon nitride combined with silicon carbide products can play a role in improving the oxidation resistance of the product.

2. The effect of binders

In the production process of silicon nitride combined with silicon carbide bricks, it is necessary to add a temporary binder, which has two main effects: one is to help the fusion between raw materials to achieve homogeneity, improve the dispersion of the surface of raw material particles, and create good conditions for embryo body molding; Second, silicon nitride combined with silicon carbide products in the drying and firing process to face the process of heating up, and under high temperature conditions, silicon nitride combined with silicon carbide products in the temporary binder will decompose, gaseous substances volatilization process to silicon nitride combined with silicon carbide products to leave a large number of network porous channels, not only more conducive to nitrogen filling, improve the reaction efficiency between silicon powder and nitrogen, but also more conducive to the stability of the final product. Temporary binders mainly include: organic dextrin, calcium lignosulfonate and German Sima Chemical dispersant, etc., at present, the mass percentage of the added amount of temporary binder in the industry is usually within 5%.

3. The influence of the 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 molding is more commonly used due to the advantages of high production efficiency. The main use of grouting molding in China requires that the performance of the slurry must be good, and there are many factors that determine the quality of the slurry, among which the surface treatment of silicon carbide powder occupies a very important position. The source of this raw material is basically imported - Saint-Gobain of France, Shenyang Changxin Silicon Carbide Micropowder Co., Ltd. passed independent research in 2018