Oxidation behaviour of the sintered Si3N4-Y2O3-Al2O3 system

The oxidation behaviour of silicon nitride composed of Si₃N₄, Y₂O₃, Al₂O₃, AlN and TiO₂ was investigated in dry and wet air at 1100–1400 °C. The oxidation rates were confirmed to obey the parabolic law. An activation energy of 255 kJ mol^–1 was calculated from the Arrhenius plots of the results of oxidation in an air flow. In still air the oxidation rate was larger than that in an air flow, but the oxidation rate in flowing air was not affected by the air flow rate. -cristobalite and Y₂O₃·2SiO₂ were formed in oxidized surface layers. These crystal phases increased with increasing oxidation temperature. In particular, a higher content of -cristobalite was obtained in still air oxidation. The existence of water vapour in flowing air greatly promoted the oxidation.Concurrent with Kanagawa Academy of Science and Technology.