Pressureless sintering refers to the process of sintering a ceramic blank with a certain shape at high temperature and normal pressure (0. 1MPa), and making it a dense, hard, stable volume and consolidated body with certain properties through physical and chemical reactions. Compared with "hot pressing" and "atmosphere pressurization", sintering is carried out in MPa atmosphere (such as air, hydrogen, argon and nitrogen) without external driving force. The driving force of sintering comes from the change of free energy, that is, the surface area of powder decreases and the surface energy decreases. In the pressureless sintering process, mass transfer can be carried out by solid phase diffusion or evaporation and condensation. Gas-phase mass transfer needs to heat the material to a high enough temperature to form a high enough vapor pressure, which has little effect on general ceramic materials. Ceramic materials that cannot be densified by solid state sintering can be sintered by adding appropriate sintering AIDS to generate liquid phase at high temperature. The properties of materials obtained by pressureless sintering are lower than those obtained by hot pressing. But the process is simple, the equipment is easy to manufacture, and the cost is low, so it is suitable for preparing ceramic products with complex shapes and mass production.

In order to reduce the cost of silicon nitride materials, cheap low-purity β-Si3N4 powder was used to prepare silicon nitride ceramic materials by pressureless sintering. The results show that β-Si3N4 powder has good sintering performance, and a nested structure composed of columnar particles and small spherical particles is obtained. The structural composition is relatively uniform, and there is no abnormal growth of grains. The bending strength of the obtained material is 587M Pa, and the toughness reaches 5.3M Pa*m 1/2, which shows that it is acceptable.

As a practical method, pressureless sintering of silicon nitride ceramics has attracted more and more attention. It can economically mass-produce various products. Compared with the past few years, the performance of pressureless sintered silicon nitride ceramics has been greatly improved, which makes silicon nitride ceramics widely used.

Silicon nitride has a strong valence bond structure, and its sintering is very difficult. It is difficult for pressureless sintering process to meet certain performance requirements. Even at high temperature, the bulk diffusion coefficients of nitrogen and silicon are small, and above 1600℃, silicon nitride will decompose obviously, and it is difficult to densify silicon nitride ceramics without some special measures. The key to pressureless sintering of silicon nitride ceramics lies in the selection of sintering AIDS, for which people have done a lot of research work and made great progress.

There are few pressureless sintered silicon nitride products on the market now. You can ask this manufacturer of silicon nitride ceramics, Baidu search Hangzhou Remotel Technology Co., Ltd., starting number 182, the middle four digits are 5847, and the last four digits are 5005. They can help you.