Silicon nitride – Improving the properties of one of the world’s most important structural materials

Tape-cast silicon nitride for high temperature applications

With excellent high temperature strength, good resistance to oxidation and low coefficient of thermal expansion Si3N4 ceramic is one of the most important structural materials. However, the pure silicon nitride ceramics are difficult to densify and the addition of various oxides is used to improve sinterability.

Previous work has shown Lu2O3-SiO2 additives are useful in improving the bending strength of Si3N4 at elevated temperature. The bending strength of the tape-cast Si3N4 with rod-like â-Si3N4 seed can be further improved because the elongated grains from seeds were preferentially oriented parallel to the casting direction. In this study from the National Institute of Advanced Industrial Science and Technology (AIST) and published in AZojomo*, Lu2O3-SiO2 additives were selected as sintering additives, and tape casting was used to prepare the unidirectional aligned â-Si3N4 elongated grain Si3N4 ceramics.

The researchers Yu-Ping Zeng, Jian-Feng Yang, Naoki Kondo, Kiyoshi Hirao, Tatsuki Ohji, Hideki Kita and Shuzo Kanzaki found that the seeded and tape-cast Si3N4 materials showed anisotropic microstructures and bending strength with the thickness of green tape having some effect on the bending strength. Due to the formation of a high melting point grain boundary phase Lu2Si2O7N2 and the unidirectionally aligned â-Si3N4 elongated grains, the seeded and tape-cast Si3N4 shows good bending strength at elevated temperature.