稀土Sm₂O₃对多孔Si₂N₂O陶瓷显微结构和性能的影响

Porous Si₂N₂O ceramics with different porosities were fabricated using Si₃N₄ and SiO₂ as starting materials and Sm₂O₃ as a sintering additive by a gas pressure sintering process under N₂ atmosphere. The influences of sintering temperature and Sm₂O₃ content on the phase for Si₂N₂O ceramics were investigated. The XRD analysis shows that the increase of either sintering temperature or Sm₂O₃ content will facilitate the decomposition of Si₂N₂O into Si₃N₄. The content of sintering aids has an effect on the microstructure, and the morphology of Si₂N₂O grains varies from lamellar grains through plate-like grains to short fiber lapped plate-like grains when the sintering addictive content increases. The elongated Si₂N₂O crystals contribute to the high flexural strength (i.e., 220–356 MPa at room temperature). The dielectric properties are mainly affected due to the porosity. The as-sintered Si₂N₂O ceramics show both better mechanical properties and more excellent oxidation resistance with low dielectric constant (ε=4.1) and loss tangent (tanδ<0.005), compared to Si₃N₄. The weight gains of Si₂N₂O and Si₃N₄ are 0.6% and 2.1%, respectively, after oxidation at 1 400 ℃ for 10 h, indicating that the gas pressure sintered Si₂N₂O ceramic could be used as a promising high-temperature wave transparent material.