Oxidation Behavior and Mechanical Property of Si_3N_4 Ceramics with Rare Earth Oxide Addition

摘要

The effects of rare earth oxides (Lu_2O_3 and La_2O_3) on the property, microstructure and oxidation behavior of hot-pressing sintered Si_3N_4 ceramics were investigated. The silicon nitride ceramics with Lu_2O_3 and La_2O_3 as addition have been fabricated by hot-pressed at 1800℃ for 1h under a pressure of 25MPa. Oxidation test was carried out at 1400℃ in air for 100 hours. Mechanical properties, SEM and XRD were measured before and after oxidation. The results showed that Si_3N_4 ceramics doped Lu_2O_3 had good microstructure and mechanical properties than those doped La_2O_3. Oxidation test showed a parabolic weight gain with oxidation time at 1400℃ in air and the oxidation products of the ceramics were SiO_2, Re_2Si_2O_7 and Re_2SiO_5 confirmed by XRD and EDS. The rate-controlling step was the diffusion of ion. The samples doped Lu_2O_3 showed superior oxidation resistance to those doped La_2O_3.