Porous Si ₃ N ₄ Ceramics Prepared via Nitridation of Si Powder with Si ₃ N ₄ Filler and Postsintering

Porous silicon nitride (Si ₃ N ₄ ) ceramics with high porosity were prepared via nitridation of Si powder, using Si ₃ N ₄ as filler and Y ₂ O ₃ as sintering additive. After nitridation, samples with high Si ₃ N ₄ filler content showed high porosity, low flexural strength, and low grain size. A porosity of 50–62% a flexural strength of 16–49 MPa were obtained. After postsintering at 1750°C, sample with Si ₃ N ₄ filler content of 50% exhibited a bimodal grain size distribution of elongated β‐Si ₃ N ₄ grains with high aspect ratio embedded in fine‐grained matrix. Porous Si ₃ N ₄ ceramics with a porosity of 48–60% and a flexural strength of 100–145 MPa were obtained.