The effect of Y₂O₃ on the properties of porous Si₃N₄ ceramic prepared by reactive sintering

Porous Si₃N₄ ceramic were fabricated via reactive sintering of Si/Si₃N₄ compacts. The influence of sintering additives Y₂O₃ on the phase composition, microstructures, porosity and flexural strength was studied. The result indicates that Si/Si₃N₄ compacts with 5% Y₂O₃ are completely nitrided with the condition of high purity nitrogen flow at temperature 1350°C for 12 hours. During the nitridation process, the crystalline secondary phase is formed on the interfaces between particles, which leads to the completely phase transformation from Si to Si₃N₄. The newly formed Si₃N₄ efficiently connects to the original Si₃N₄ powders, thus making the flexural strength increase from 28.1 MPa (no sintering additive Y₂O₃) to 45.2 MPa, while the porosity decreases little.