Silicon nitride has stable chemical properties and can resist the corrosion of almost all inorganic acids (except hydrogen fluoride) and caustic soda (sodium hydroxide) solutions with a concentration below 30 degrees, and can also resist the corrosion of many organic substances. The non-wetting properties of various non-ferrous metal melts (especially aluminum solutions) withstand strong radiation 4, and the high temperature creep is small. Especially after adding an appropriate amount of silicon carbide, the high temperature creep resistance performance is obviously improved, and the oxidation resistance performance is good. It can resist oxidation up to 1400 degrees, the actual use temperature reaches 1200 degrees 5, the friction coefficient is very small, only 0.1, which is similar to the metal surface full of oil. Silicon nitride ceramics and silicon nitride combined with silicon carbide ceramics are special high-temperature structural materials developed in recent years. With the development of silicon nitride and fine processing, silicon nitride structural ceramics have been widely used in industry to manufacture ball valves, pump bodies, sealing rings, heat exchangers and other components.

Silicon nitride ceramics is an important structural ceramic material and a superhard material. It has lubricity, wear resistance, and high temperature resistance; it can resist oxidation at high temperatures and resist cold and heat shocks. It can be heated to 1000°C in the air. Above, it will not break when heated sharply after cooling.

Silicon nitride ceramics have high toughness and high mechanical strength. Silicon nitride has high hardness, Hv=18GPa～21Gpa, HRA=91～93, second only to a few superhard materials such as diamond, cubic BN, B4C, etc., and the friction coefficient is small ( O.1), self-lubricating, similar to the oiled metal surface (0.1--0.2). Si3N4+12HF==3SiF4+4NH3F- has no oxidizing property, the oxidizing property of H+ is weak, and there is no strong reducing atom in Si3N4, so redox reaction is impossible, only the double decomposition reaction is considered, and the valence remains unchanged. There are a total of four elements Si, N, H, and F in the reaction, which are relatively easy to determine. Silicon nitride + hydrofluoric acid = silicon tetrafluoride + ammonia (it is common sense that silicon is easily combined with F to produce silicon tetrafluoride. Remember (it is also the reason why hydrofluoric acid is not stored in glass containers (silicon dioxide)), the valence states of silicon and fluorine in the reaction can be determined unchanged, and if H and N undergo redox, hydrogen and nitrogen will be generated. unlikely, so there is no valence change in the reaction). .