There are many methods to prepare silicon nitride ceramic powder. Direct nitridation of silicon powder and reduction nitridation of silicon dioxide are briefly introduced.

The direct nitridation of silicon powder is realized by the direct reaction of chemically pure silicon powder (analytical purity: more than 95%) with nitrogen in NH3, N2+H2 or N2 atmosphere. The reaction equation is as follows: The advantages of synthesizing Si3N4 fine powder by direct nitridation of silicon powder are simple technological process and low cost, but the disadvantages are high reaction temperature, long reaction time and slow reaction speed. The prepared Si3N4 has a wide particle size distribution and needs further crushing, grinding and purification.

Silicon dioxide reduction nitridation method, after mixing silicon dioxide fine powder with carbon powder, first generates silicon monoxide through thermal reduction, and then nitrides silicon dioxide to generate massive silicon nitride. The general chemical reaction formula is as follows: SiO _ 2 reduction nitriding method is characterized by rich raw materials, and the reaction product is loose powder, which does not need to be crushed together with the silicon powder nitriding product, thus avoiding the reintroduction of impurities, so the Si3N4 powder prepared by this method has regular particle shape and narrow particle size distribution.

As an excellent high-temperature engineering material, Si3N4 ceramic material can give full play to its advantages in the high-temperature field. Its strength can be maintained at the high temperature of 1200℃, and it will not melt into a melt after heating, and it will not decompose until 1900℃. It has amazing chemical resistance, and can tolerate almost all inorganic acids and caustic soda solutions below 30%, as well as many. At the same time, it is a high-performance electrical insulating material, and silicon nitride hardly reacts with water; Slowly hydrolyze in concentrated strong acid solution to generate ammonium salt and silicon dioxide; Strong alkali solution is easily soluble in hydrofluoric acid, does not react with dilute acid, can slowly corrode silicon nitride, and molten alkali can quickly transform silicon nitride into silicate and aminosilicon nitride. These properties are similar to those of superalloys, but as a high-temperature structural material, it also has some shortcomings such as low mechanical impact strength and easy brittle fracture. Therefore, it is widely used in the research of making complex materials with silicon nitride, especially silicon nitride combined with silicon carbide, and toughening silicon nitride ceramics with whiskers and adding other compounds.