Mechanical, dielectric properties and thermal shock resistance of porous silicon oxynitride ceramics by gas pressure sintering

摘要

Porous silicon oxynitride (Si_2N_2O) ceramics were prepared by gas pressure sintering with 2.5-10.0 mol% Li_2O as additive. The influences of Li_2O content on phase, microstructure, mechanical and dielectric properties of the Si_2N_2O ceramics were investigated. XRD analysis showed that the increase of Li_2O content facilitate both the densification and the decomposition of Si_2N_2O into Si_3N_4. The elongated Si_2N_2O crystals contribute to the high flexural strength (161.3-228.4 MPa at room temperature) of the products. The thermal shock resistance was greatly influenced by the sample porosity, and the highest critical temperature difference (ΔT_C) could be up to 1300 ℃. The dielectric properties were mainly affected by the sample porosity. The as-sintered Si_2N_2O ceramics showed both low dielectric constant (ε ＜ 4.59) and loss tangent (tan δ ＜ 0.0049) with good mechanical properties and excellent thermal shock resistance, indicating the gas pressure sintered Si_2N_2O ceramics could be used as promising high temperature wave transparent material.