Application of Silicon Carbide in Refractory Materials

    Silicon carbide is second only to diamond in hardness and has strong wear resistance. It is an ideal material for wear-resistant pipelines, impellers, pump chambers, cyclones, and mine hopper linings. Its wear resistance is 5% of the service life of cast iron and rubber. -20 times, it is also one of the ideal materials for aviation flight runways. The silicon carbide powder is coated on the inner wall of the turbine impeller or cylinder block by a special process, which can improve its wear resistance and prolong the service life by 1 to 2 times.

    Due to the high thermal conductivity and small thermal expansion coefficient of silicon carbide, the thermal shock resistance of silicon carbide refractories is very good. The thermal shock resistance of silicon carbide products is also closely related to the type and properties of the bonding base.

    The test proves: put the sample into the electric furnace at 1200℃ and heat it for 20min, then take it out and cool it in the air and measure the change of elastic modulus. The elastic modulus of silicate-bonded silicon carbide products shows a relatively gentle and gradual downward trend with the increase of the number of cold and thermal shock tests, while silicon nitride-bonded silicon carbide products are different. Before 30 cold cycle tests, its elasticity The modulus changes very little with the increase of the number of thermal shock tests, and can maintain a fairly constant value. However, after 31 thermal shock tests, the elastic modulus of the sample drops rapidly and breaks suddenly. Silicon oxynitride-bonded silicon carbide products are similar to silicate-bonded silicon carbide products, and there is no sudden failure. The elastic modulus shows a gentle downward trend with the increase of the number of thermal shock tests.

    In the actual application process, since the silicate-bonded silicon carbide product can be observed to expand, crack and deform after being subjected to thermal shock, the service life of the material can be easily predicted.

    Due to the good thermal conductivity of silicon carbide itself, the thermal conductivity of refractory materials with high silicon carbide content is higher, and the thermal conductivity is mostly more than 14.4W/(m•K). Used for heat exchangers, saggars, water walls of coal gasifiers, indirect heating kiln furniture products, etc. The thermal conductivity of the particle surface of silicon carbide products will gradually decrease during use. The properties of the bonding base material have a certain influence on the thermal conductivity of silicon carbide products.

    Silicon carbide has good oxidation resistance. The oxidation is weak below 1300 °C, and the obvious oxidation occurs above 1300 °C. The oxidation produces a SiO2 glass protective film, which can inhibit the oxidation of silicon carbide.

    The oxidation resistance of silicon carbide refractory products also varies significantly with the type of bonding base material. The low oxidation resistance of silicon nitride combined silicon carbide products can be explained by their microstructural characteristics. Because the base material of silicon nitride-bonded silicon carbide products is in the form of interwoven fibers, the gas permeability is high, and the protective effect on silicon carbide particles is small; while in silicate-bonded and silicon oxynitride-bonded silicon carbide products, The surface of the silicon carbide particles is covered by a continuous base material, so it has strong anti-oxidation properties. The oxidation resistance properties of silicate-bonded silicon carbide and silicon oxynitride-bonded silicon carbide show similar behavior in the above tests, but can clearly show differences between them in long-term use.

    SiC is a compound with strong covalent bonding, which still maintains high bonding strength at high temperature, so SiC has good chemical stability and will not be eroded by most acid-base solutions. Silicon carbide has a larger wetting angle with molten metal and slag. Compared with oxide refractories, it has good corrosion resistance to various solids, liquids and gases. For example, Al2O3-SiC-C castables and products used in iron-making systems, silicon-molded bricks for cement kilns and castables containing silicon carbide, various acid-base reaction vessels, etc.

    Silicon carbide is a typical covalently bonded compound with many excellent properties, such as abrasion resistance, high temperature resistance, corrosion resistance, high thermal conductivity, high chemical stability, wide band gap and high electron mobility. It is widely used in abrasives, refractories, functional ceramics, metallurgical accessories and other industries. With the development of social economy and technology, silicon carbide will also be used in more fields.