다공성 Si3N4/BN 복합체의 제조 및 특성에 관한 연구

Abstract

Radome is the microwave transmission window that is used in a harsh working condition such as a high speed and high temperature environment. Current radome materials demand a series of critical properties such as high mechanical strength, electrical properties, low dielectric constant, excellent thermal shock resistance and rain erosion resistance, etc. These properties are used to suggest that silicon nitride (Si3N4) ceramics is regarded as one of the most promising candidate materials for radome materials due to its combination of excellent mechanical properties at both room and elevated temperature and good resistance to corrosion. However, the dielectric constant of Si3N4 is still relatively high for practical application (7.9 – 8.2 for hot-pressed Si3N4 at 8 – 10 GHz). In this study, porous Si3N4/BN composite ceramics were fabricated by pressureless sintering in order to reduce the dielectric constant. Spherical-shaped pore-former agent, PMMA was employed to Si3N4/BN composite. We controlled the amount of both PMMA and BN contents in order to control the porosity of Si3N4/BN composite and tune the properties; moderately high flexural strength and low dielectric property.