Silicon nitride bonded silicon carbide brick is a new type of refractory material, which contains finer categories, such as silicon nitride bonded silicon carbide radiation tube, silicon nitride bonded silicon carbide brick and so on. Because this kind of material has a variety of excellent performance, silicon nitride bonded silicon carbide brick stands out from many products with the same performance due to its energy-saving and environmental protection characteristics, and has a good market development prospect in the future.

1, the impact of the nature of raw materials

Silicon nitride bonded silicon carbide brick involves the main production raw materials: silicon carbide, silicon powder, nitrogen and other additives. Different from ordinary silicon nitride material products, silicon nitride combined with silicon carbide products required raw materials must have higher purity. 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 strict control of the purity of raw materials, the production process also needs strict control of the particle size and particle grading of raw materials. Too high particle size of raw material will directly affect the volume density of the embryo forming, resulting in the reduction of the density of the embryo body, affecting the final product quality. In terms of raw material particle size distribution, to pay attention to the grain size of silicon powder, silicon powder granularity control can ensure the silicon powder and the reaction efficiency of nitrogen, but blindly reduce silicon powder particle size also has certain negative effects, namely, silicon powder and nitrogen reaction rate is too fast, intense reaction causing rising heat concentration in the reaction device, once the temperature exceeds 1400 ℃, Will induce silicon carbide surface flow phenomenon, but not conducive to product quality control. In addition, adding ZrSiO4 into the raw materials of silicon nitride bonded silicon carbide products can improve the oxidation resistance of the products.

2, the influence of binding agent

In the production process of silicon nitrite bonded silicon carbide brick, temporary binding agent needs to be added. The addition of binding agent has two main effects. One is to help the fusion of raw materials to achieve homogenization, improve the dispersion of raw material particle surface, and create good conditions for embryo body forming. Second, silicon nitride bonded silicon carbide products in a dry and into the process of facing the process of heating up, and under the condition of high temperature, silicon nitride combined with silicon carbide products the temporary binder will decompose, gaseous substances volatile process to the silicon nitride combined with silicon carbide products leaving lots of reticular pores channel, not only is more advantageous to the nitrogen filling the, The reaction efficiency between silicon powder and nitrogen is improved, and the stability of the final product is also improved. Temporary binders mainly include: organic dextrin, calcium lignosulfonate and German sima chemical dispersants and so on. At present, the mass percentage of temporary binders added in the industry is usually within 5%.

3, the impact of molding process

At present, the forming process of silicon nitride bonded silicon carbide brick mainly includes semi-dry forming and grouting forming. Among them, semi-dry forming is more common because of its advantages of higher production efficiency. The grouting method is mainly used in China, which requires that the slurry performance must be good, there are many factors that determine the quality of the slurry, among which the surface treatment of silicon carbide powder plays a very important role. The source of raw material basic imports - French saint-gobain company, in 2018, shenyang long letter of silicon carbide powder co., LTD., through independent research and development, achievements to overcome the difficulties, developed specifically for silicon nitride combined with silicon carbide micro powder, silicon carbide products not only get rid of the dependence on foreign products, also had the very big enhancement on product performance, The volume density increased from 2.52g/mL to 2.57g/mL. The average bending strength at 20℃ increased from 90P to 100MP. No matter which process, the bulk density of the body will directly affect the quality of nitriding.

4, the effect of drying system

Temperature and time in drying process have great influence on product quality. Too low temperature or too short time will lead to residual water in the embryo body, which will induce the oxidation reaction of silicon powder in the subsequent nitriding reaction process, thus reducing the nitriding reaction efficiency and affecting the product quality. The rate of temperature rise can also affect product quality. Too high temperature increase is not conducive to the control of high temperature environment, too high temperature will cause cracks on the surface of embryo body.

5. Influence of kiln loading method

One of the factors that may affect the quality of the kiln before the nitrogen process is the gap interval between the embryos. A certain space should be left between the embryonic bodies to provide favorable conditions for smooth permeation and filling of nitrogen, and to avoid the phenomenon of silicon flow caused by excessive amount of kiln loading.

6. Influence of nitriding system

The raw material of silicon nitride bonded silicon carbide brick is mixed and molded and fired in the nitriding furnace at a high temperature of about 1400℃. The quality and performance of the final product are closely related to the temperature of the nitriding reaction. In the process of reaction between silicon powder and nitrogen, there are roughly two temperature stages: the first is the heating stage, and then the nitriding reaction stage of the raw material. In the heating stage, the temperature in the device increases from the initial temperature to about 1100℃, while the temperature in the nitriding reaction stage of raw materials is between 1100 ~ 1350℃.