This paper introduces the characteristics of silicon nitride combined silicon carbide bricks. Silicon carbide bricks belong to special refractory brick. It not only has the characteristics of high density, high strength, good thermal shock stability, high load softening point, good thermal conductivity, and high resistance value, but also has excellent anti-cryolite properties. , aluminum fluoride, sodium fluoride and calcium fluoride and other melting corrosion and oxidation resistance. Mainly used in building sanitary ceramics, daily-use porcelain, electric porcelain, aluminum, copper, zinc, steelmaking and rolling, ironmaking, metal heat treatment, environmental protection and other fields.
1 Introduction
Silicon nitride bonded silicon carbide brick is an advanced special refractory brick material with silicon carbide sand as the main raw material and silicon nitride as the binding phase. Since SiC and Si3N4 are both covalent bond compounds, sintering is difficult, so they are usually prepared by reaction sintering in industrial production. Using SiC as the aggregate, adding metal silicon powder, selecting reasonable particle gradation, mixing system and molding process, the dried green body is fired in a special firing equipment in a nitrogen atmosphere. During the firing process, the generated Si3N4 (matrix binding phase) is a gray-white crystal, which can effectively bind the SiC particles (aggregate) together to form a spatial network structure, so that the brick has incomparable characteristics of other refractory materials. Silicon nitride combined with silicon carbide materials are foreign developed countries such as Norton and Carborundum companies in the United States, An-nawevrk and HTK companies in Germany, and TKR and NGK companies in Japan. Silicon carbide special brick. This material was introduced into my country in the mid-1980s. After years of promotion and application, the superior properties of special refractory brick silicon nitride combined with silicon carbide have been gradually understood.
2. Performance
The high-temperature flexural strength of silicon nitride combined with silicon carbide is 4 to 8 times that of ordinary refractories; the thermal expansion coefficient is half of that of high-aluminum refractories; the thermal conductivity is 7 to 8 times that of ordinary refractories, and the strength increases with temperature. When the temperature rises to 1400 °C, the strength begins to decrease; but when the temperature drops to 1500 °C, it still maintains the flexural strength index at room temperature. The thermal conductivity of the material gradually decreases with the increase of temperature. It has the characteristics of good thermal shock stability, high load softening point, good thermal conductivity and high resistance value, and has excellent resistance to melting corrosion and oxidation resistance of cryolite, aluminum fluoride, sodium fluoride and calcium fluoride. Its performance is described as follows:
1) Silicon nitride combined with silicon carbide bricks are hard in texture, with a Mohs hardness of about 9. They are high-hardness materials among non-metallic materials, and their hardness is second only to diamond.
2) The normal temperature strength of the silicon nitride combined silicon carbide brick is high, and it almost maintains the same strength and hardness as the normal temperature at a high temperature of 1200-1400 °C. With the use of different atmospheres, the maximum safe use temperature can reach 1650 ~ 1750 ℃.
3) The thermal expansion coefficient is small, the thermal conductivity is high compared to silicon carbide and other bricks, it is not easy to generate thermal stress, has good thermal shock stability, and has a long service life. High temperature creep resistance, corrosion resistance, extreme cold and heat resistance, oxidation resistance, easy to be made into special refractory bricks with high dimensional accuracy and requirements.
In the next article, we will talk about the application range of silicon nitride combined with silicon carbide bricks.
