Nitride ceramics, such as silicon nitride ceramics in sintering will react with oxygen to produce silicon dioxide, so good quality silicon nitride products, generally in the protective atmosphere of nitrogen sintering, silicon nitride sintering more ways, as described below:
1) Reaction sintering (RS)
Taking Si3N4 ceramics as an example, reactive sintering Si3N4 ceramics is to mix Si powder or Si powder with Si3N4 powder, and then
pre-nitride through nitrogen at about 1200 degrees, and then process the required products. Finally, the final nitride sintering is carried out at about 1400 degrees. In this process, there is no need to add sintering aid, so the strength of the material will not be significantly reduced at high temperature Silicide has no shrinkage and can prepare products with complex shapes. However, due to low density (70%-90%) and large number of pores, the mechanical properties are greatly affected.
2) Atmospheric sintering (PLS)
Atmospheric pressure sintered silicon nitride is prepared by mixing high-purity, ultra-fine, high-A-phase silicon nitride powder with a small amount of sintering aid through forming, sintering and other processes. In the sintering process,a dissolves into liquid phase, and then precipitates into B Si3N4 crystal nucleus, which is conducive to the sintering process. Nitrogen must be injected during sintering to inhibit the decomposition of Si3N4 at high temperature. The ceramic with complex shape and excellent performance can be obtained by atmospheric sintering. Its disadvantage is that the shrinkage rate of sintering is large, generally 16%~26%, which is easy to crack and deform the product.