Microstructure control and optimization of low temperature pressureless sintered silicon nitride - barium aluminosilicate composites

Silicon nitride-barium aluminosilicate (Si3N4/BAS) composites are promising materials for high temperature engineering applications. However, BAS is usually present in Si3N4 in the form of hexacelsian, which is an undesirable composition. In this work, the Si3N4/BAS composites containing both monoclinic-celsian and in-situ beta-Si3N4 was prepared successfully. And the critical condition for coexistence of beta-Si3N4 and monoclinic-celsian was also ascertained for the first time. Various methods were used to analyze the crystallization process of BAS in Si3N4 and the key factors affecting the crystallization process. Furthermore, all the prepared Si3N4/BAS composites have relatively high mechanical strength, low thermal expansion coefficient of 3.850 x 10(-6)/degrees C (32, 1000 degrees C) and good dielectric performance. It provides more implementation space for the structural control and optimization of Si3N4/BAS composites according to the application environment of material. This study will contribute to promote application of Si3N4/BAS composites in high temperature engineering fields such as radar radome and coating.