Effects of SnO<sub>2</sub>-SiO<sub>2</sub>-MgO-Bi<sub>2</sub>O<sub>3</sub>-Y<sub>2</sub>O<sub>3</sub> Additions on Liquid Phase Sintering Silicon Nitride

Si 3 N 4 ceramics were sintered at relatively low temperature of 1400-1650 °C with additives from the SnO 2 -SiO 2 -MgO-Bi 2 O 3 -Y 2 O 3 system. The degree of densification, α-β transformation, mass loss and microstructure were measured as a function of additives composition, sintering temperature, and nitrogen gas pressure. Specimen prepared from 3 mass% SnO 2 , 3 mass% SiO 2 , 3 mass% MgO, 6 mass% Bi 2 O 3 , and 5 mass% Y 2 O 3 as the sintering additive could be sintered to almost full density at relatively low temperature as 1550 °C for 2 h under ambient pressure of nitrogen atmosphere. The α-β transformation was not completed at this condition. The mass loss was relatively high due to the evaporation of SiO 2 , MgO and Bi 2 O 3 . However, the resulted dense materials have high bending strength.