Low-temperature preparation of β- Si ₃ N ₄ porous ceramics with a small amount of Li ₂ O - Y ₂ O ₃

Porous β-Si₃N₄ ceramics are sintered at 1600°C in N₂ and postheat treated at 1500°C under vacuum using Li₂O and Y₂O₃ as the sintering additives. The partial sintering and phase transformation are promoted at low temperature by the addition of Li₂O. The addition of Y₂O₃ is advantageous for the formation of high aspect ratio β-Si ₃N₄ grains. After postheat treatment, a large amount of intergranular glassy phase is removed, and the Li content in the samples is decreased. By this method, the β-Si₃N₄ porous ceramic with a porosity of 54.1% and high flexural strength of 110 ± 8.1 MPa can be prepared with a small amount of sintering additives, 0.66 wt% Li ₂O and 0.33 wt% Y₂O₃, and it is suitable for high-temperature applications.