J. Korean Ceram. Soc. > Volume 51(5); 2014 > Article
 Journal of the Korean Ceramic Society 2014;51(5): 386. doi: https://doi.org/10.4191/kcers.2014.51.5.386
 반응소결된 Si3N4-SiO2-BN 복합체의 기계적 강도 및 유전물성에 관한 연구 이현민, 이승준1, 백승수1, 김도경 한국과학기술원 (KAIST)1국방과학연구소 Flexural Strength and Dielectric Properties of in-situ Si3N4-SiO2-BN Composite Ceramics Hyun Min Lee, Seung Jun Lee1, Seungsu Baek1, Do Kyung Kim Korea Advanced Institute of Science and Technology (KAIST)1Agency for Defense Development (ADD) ABSTRACT Silicon nitride ($Si_3N_4$) is regarded as one of the most promising materials for high temperature structural applications due to its excellent mechanical properties at both room and elevated temperatures. However, one high-temperature $Si_3N_4$ material intended for use in radomes has a relatively high dielectric constant of 7.9 - 8.2 at 8 - 10 GHz. In order to reduce the dielectric constant of the $Si_3N_4$, an in-situ reaction process was used to fabricate $Si_3N_4-SiO_2$-BN composites. In the present study, an in-situ reaction between $B_2O_3$ and $Si_3N_4$, with or without addition of BN in the starting powder mixture, was used to form the composite. The in-situ reaction process resulted in the uniform distribution of the constituents making up the composite ceramic, and resulted in good flexural strength and dielectric constant. The composite was produced by pressure-less sintering and hot-pressing at $1650^{circ}C$ in a nitrogen atmosphere. Microstructure, flexural strength, and dielectric properties of the composites were evaluated with respect to their compositions and sintering processes. The highest flexural strength (193 MPa) and lowest dielectric constant (5.4) was obtained for the hot-pressed composites. The strength of these $Si_3N_4-SiO_2$-BN composites decreased with increasing BN content. Key words: $Si_3N_4$, Porous ceramic, In-situ reaction, Dielectric property
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