Silicon nitride attracts attention as a high-temperature engineering material. Silicon nitride ceramics have a series of characteristics, namely light density (3. 19g/cm3), hardness (Vickers hardness ~ 19GPa), high strength (elastic modulus ~ 300GPa ), small coefficient of thermal expansion (about 3×10-6/℃). The high-temperature creep of Si3N4 is small, especially after adding an appropriate amount of SiC, the high-temperature creep resistance is significantly improved. Si3N4 has good oxidation resistance, which can withstand oxidation up to 1400°C, and the actual use temperature can reach 1200°C. Si3N4 has good corrosion resistance and can resist the corrosion of most acids, but it cannot resist the corrosion of concentrated NaOH and HF. The friction coefficient of Si3N4 is small, only 0.1, which is similar to the metal surface with oil. Due to the excellent properties of silicon nitride ceramics, it has been widely used in many industrial fields and has many potential uses. Utilizing its high temperature resistance and wear resistance, it is used in ceramic engines for rotors, stators and scroll tubes of gas turbines; spark plugs, piston covers, cylinder liners, auxiliary combustion chambers, and parts of piston-turbine combined aeroengines. Taking advantage of its good thermal shock resistance, corrosion resistance, small friction coefficient, and small thermal expansion coefficient, it is widely used in the metallurgical and thermal processing industries for temperature measurement thermocouple casings, casting molds, crucibles, muffle furnace furnaces, Burners, heating element fixtures, aluminum furnace linings, aluminum liquid conduits, aluminum cladding linings, aluminum electrolytic cell linings, heat radiation tubes, transfer rollers, high-temperature blowers and valves, etc.; used in steelmaking horizontal continuous casting machines in the iron and steel industry The shunt ring; the electronic industry is used as a crucible for pulling single crystal silicon, etc. Taking advantage of its corrosion resistance, good wear resistance and good thermal conductivity, it is widely used in the chemical industry as ball valves, sealing rings, filters and heat exchanger components. Taking advantage of its good wear resistance, high strength, and small friction coefficient, it is widely used in the machinery industry as bearing balls, rollers, ball races, high-temperature bolts, molds, plunger pumps, and sealing materials. In addition, it is also used in electronics, military heavy and nuclear industries, such as switch circuit substrates, film capacitors, high-temperature insulators, radars, radomes, missile tail nozzles, barrel linings, nuclear reactor supports, spacers and The carrier of nuclear fission material, etc.