Fabrication and properties of porous boron nitride/silicon oxynitride ceramic composites via gas pressure sintering

摘要

Silicon oxynitride (Si_2N_2O) based wave transparent composites with different volumes of hexagonal boron nitride (h-BN) were prepared by gas pressure sintering at 1700 ℃ with 5.0-10.0 mol% Li_2O as additive. The effects of Li_2O and BN contents on phase, microstructure, mechanical and dielectric properties of the composites were investigated. The decomposition of Si_2N_2O and pore structures was influenced by Li_2O content, while the incorporation of h-BN effectively alleviated Si_2N_2O decomposition. The BN/Si_2N_2O composites could withstand a thermal shock of 1100 ℃ without strength degradation in N_2, while only the samples with adequate porosity exhibited high thermal shock resistance in air. The high thermal shock resistance was attributed to the crack-healing ability of the composites. The as-sintered BN/Si_2N_2O ceramics showed both low dielectric constant (ε ＜ 4.49) and loss tangent (tanδ ＜ 0.0056) with good mechanical properties and thermal shock resistance, indicating that the as-sintered BN/Si_2N_2O composites could be used as promising high temperature wave transparent material.