This article introduces the characteristics of nitride bonded silicon carbide bricks. 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 cryolite resistance. , Aluminum fluoride, sodium fluoride and calcium fluoride, etc. Melting corrosion and oxidation resistance. Mainly used in building and 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 refractory material with silicon carbide sand as the main raw material and silicon nitride as the bonding phase. Since SiC and Si3N4 are covalent bond compounds, sintering is difficult, and reaction sintering methods are usually used in industrial production. SiC is used as aggregate, metal silicon powder is added, reasonable particle grading, mixing system and forming process are selected, and the dried body is fired in a special firing equipment in a nitrogen atmosphere. During the firing process, the resulting Si3N4 (matrix binding phase) is off-white crystals, which can effectively combine SiC particles (aggregate) together to form a spatial network structure, which makes the bricks have incomparable characteristics with other refractory materials. Silicon nitride bonded silicon carbide material is a kind of 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, which are used in grinding wheels, ceramics, electric porcelain and other industries in the 1970s. Special silicon carbide bricks. The material was introduced to my country in the mid-1980s. After years of promotion and application, we gradually understand the superior properties of silicon nitride combined with silicon carbide.
2. Performance
The high temperature flexural strength of silicon nitride combined with silicon carbide is 4 to 8 times that of ordinary refractory materials; the thermal expansion coefficient is half that of high aluminum refractory materials; the thermal conductivity is 7 to 8 times that of general refractory materials, and the strength increases with temperature When the temperature rises to 1400℃, the strength begins to decrease; but when the temperature drops to 1500℃, the normal temperature flexural strength index is still maintained. The thermal conductivity of the material gradually decreases with the increase of temperature. It has high density, high strength, It has the characteristics of good thermal shock stability, high softening point under load, good thermal conductivity, high resistance value, etc., and has excellent resistance to melting corrosion and oxidation of cryolite, aluminum fluoride, sodium fluoride and calcium fluoride. Now its performance is described as follows:
1) Silicon nitride bonded silicon carbide bricks are hard, with a Mohs hardness of about 9, which is a high-hardness material among non-metallic materials, and its hardness is second only to diamond.
2) The room temperature strength of the silicon nitride bonded silicon carbide brick is high, and it maintains almost the same strength and hardness as room temperature at a high temperature of 1200-1400°C. With the use of different atmosphere, the highest safe use temperature can reach 1650 ~ 1750 ℃.
3) The coefficient of thermal expansion is small, and the thermal conductivity is higher than that of silicon carbide and other bricks. It is not easy to generate thermal stress, has good thermal shock stability and long service life. High temperature creep resistance, corrosion resistance, extreme cold and extreme heat resistance, oxidation resistance, easy to make bricks with high dimensional accuracy and meeting requirements.
3. Application
3.1 Ceramic industry
3.1.1 Building and Sanitary Ceramics Industry
At this stage, in the firing of ceramic products, most of the roller kiln is used to fire sanitary ceramics and wall and floor tiles, and the rollers of the roller kiln are basically made of silicon nitride combined with silicon carbide. The application of silicon nitride combined with silicon carbide rollers solves the problem of high firing temperature and heavy load, effectively reducing product energy consumption and improving product quality.
3.1.2 Daily ceramic industry
There are two ways of firing daily-use ceramics: one is to use a sagger or similar kiln furniture to use a shuttle kiln; the other is to use a roller kiln in the same way as building sanitary ware. The use of silicon nitride combined with silicon carbide kiln furniture can significantly reduce the quality ratio of kiln furniture to bricks, save energy and reduce consumption, and at the same time improve product quality and qualification rate. The use of roller kiln to burn daily ceramics, and the use of silicon nitride combined with silicon carbide rollers to increase the service life of the kiln.
3.1.3 Electric porcelain and electronic ceramic industry
The electric porcelain and electronic ceramic industries require kiln furniture materials with high temperature, high strength, good thermal stability, long service life, and affordable prices. This provides a broad market for the application of silicon nitride combined with silicon carbide kiln furniture.
3.2 Metallurgical industry
3.2.1 Aluminum, copper, zinc and other industries
Use high-quality silicon nitride combined with silicon carbide materials to replace traditional carbon materials on the side walls of the electrolytic cell. It can also be used as a thermowell for temperature measurement, aluminum smelting furnace lining, aluminum liquid "bun" lining, crucible , Pumps, pipes, valves for conveying molten aluminum, molds for casting aluminum, and risers for forming automobile wheels, etc.
3.2.2 Steelmaking and rolling industry
The application of new steelmaking technology and new technology puts forward higher requirements on refractory materials for ladle. Ladle lining has changed from the original high-alumina bricks, which dominated the original, to silicon nitride combined with silicon carbide with better corrosion resistance. material. It has been applied to ladle in developed countries such as Europe and America successively, and has achieved significant economic benefits. The most important application of silicon nitride as a refractory material in the steelmaking industry is as a separating ring for horizontal continuous casting. In addition, there are many industrial furnaces, in order to prevent some of their parts from overheating and damage, water cooling measures are often used. The best material for the water-cooled tube slide system is silicon nitride combined with silicon carbide material bricks.
3.2.3 Ironmaking industry
In recent years, silicon nitride bonded silicon carbide bricks for blast furnaces have developed rapidly. About 61% of blast furnaces abroad have adopted them, especially 68% of large blast furnaces with a hearth diameter of 12-15m. According to statistics, in the past 10 years, there have been 127 blast furnaces with more than 3,500 tons of such high-quality bricks, and most of the blast furnaces use 270-800 tons per blast furnace. The use parts are from tuyere, furnace belly, furnace waist to furnace body. Lower middle and so on.
3.2.4 Metal heat treatment industry
There are various working conditions for metal heat treatment, and the working conditions are relatively harsh. Although silicon nitride ceramics are not necessarily suitable for various conditions, under certain conditions, silicon nitride ceramics have good results. For example: the gear is quenched into the mandrel on the equipment, used as the fixture of the workpiece and the hook of the heating element in the vacuum heat treatment.
4. Environmental protection industry
At present, in the environmental protection industry, most of the nozzles in the desulfurization and denitration projects are made of silicon nitride combined with silicon carbide materials. The nozzles formed by using this material have precise dimensions, corrosion resistance, good erosion resistance, and fog. Excellent chemical performance and long service life. At present, the consumption of desulfurization and denitration nozzles at home and abroad is increasing year by year.
5 Conclusion
Silicon nitride bonded silicon carbide material has high density, high strength, good thermal shock stability, high load softening point, good thermal conductivity, high resistance value, and has excellent resistance to cryolite, aluminum fluoride, sodium fluoride and Calcium fluoride and other properties such as melting corrosiveness and oxidation resistance are becoming more and more irreplaceable in such industries as building and sanitary ceramics, daily-use ceramics, electric porcelain, non-ferrous smelting, steelmaking and rolling, ironmaking, heat treatment, and environmental protection. effect.
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