In Situ Measurement of Shrinkage During Postreaction Sintering of Reaction-Bonded Silicon Nitride

The reaction‐bonding technique is one of the major fabrication processes of silicon nitride (Si3N4) ceramics, which has received much attention as a cost‐effective process due to the use of cheap Si powder as a raw material. Many studies on the development of this method have been performed in order to improve their properties; however, the sintering shrinkage behavior, which is a very important information to optimize the firing condition, has not been well clarified. In this study, we focused on the reaction‐bonding technique of the Si–Y2O3–Al2O3 system. At first, reaction‐bonded body of the Si–Y2O3–Al2O3 system was prepared, and then its postreaction sintering shrinkage behavior was investigated by in situ dilatometry. It was found that no shrinkage occurred from 1400° to 1600°C due to grain rearrangement in the reaction‐bonded Si3N4 body. Furthermore, the shrinkage of the reaction‐bonded Si3N4 started around 1750°C, which is a higher temperature compared with the green body of conventional Si3N4 powder. The restriction of shrinkage seems to result from neck growth and strong aggregation among reacted Si3N4 particles.