The reaction sintering method of SiC was first successfully studied in the United States. The process of reaction sintering is as follows: firstly α－ SiC powder and graphite powder are mixed in proportion, and the porous green body is made by dry pressing, extrusion or grouting. When contacted with liquid Si at high temperature, C in the green body reacts with infiltrated Si to form β－ SiC, and with α－ SiC is combined, and excess Si is filled in the pores, thereby obtaining a non porous and dense reaction sintered body. Reaction sintered SiC usually contains 8% free Si. Therefore, in order to ensure complete Si infiltration, the blank should have sufficient porosity. Generally, by adjusting the initial mixture α－ The content of SiC and C, α－ The particle size distribution of SiC, the shape and particle size of C, and the molding pressure can be used to obtain the appropriate green density.
The experiments show that the SiC ceramics with pressureless sintering, hot pressing sintering, hot isostatic pressing sintering and reaction sintering have different performance characteristics. If hot press sintering and hot isostatic pressing sintering SiC ceramics are relatively high in terms of sintering density and bending strength, Reaction Sintering SiC is relatively low. On the other hand, the mechanical properties of SiC ceramics are also different with different sintering additives. Pressureless sintering, hot pressing and Reaction Sintering SiC ceramics have good resistance to strong acids and alkalis, but Reaction Sintering SiC ceramics have poor resistance to ultra strong acids such as HF. When the temperature is lower than 900 ℃, the strength of almost all SiC ceramics is improved; When the temperature exceeds 1400 ℃, the bending strength of reaction sintered SiC ceramics decreases sharply. (this is because the sintered body contains a certain amount of free Si, and the bending strength drops sharply when it exceeds a certain temperature.) for SiC ceramics sintered by pressureless sintering and hot isostatic pressing, the high-temperature resistance is mainly affected by the type of additives
