Lightweight and high-strength textured fibrous Si3N4 3D scaffold seeded with β-Si3N4 particles prepared via freeze casting

Highly porous Si 3 N 4 ceramics with unidirectionally aligned pore channels are gaining significant attention across various fields due to their outstanding functional capabilities. However, achieving high strength in such unidirectional highly porous Si 3 N 4 ceramics remains challenging. Herein, we design and fabricate a novel β-Si 3 N 4 scaffold composed of directionally aligned lamellar walls with a textured microstructure by directionally freeze casting of α-Si 3 N 4 suspensions with fine elongated β-Si 3 N 4 seeds addition, followed by liquid phase sintering. During the sintering, the scaffold exhibited anisotropic shrinkage, and fibrous β-Si 3 N 4 grains were synthesized through epitaxial growth on the seeds preferentially oriented or the nuclei originated from α-Si 3 N 4 powders, resulting in the grains aligned parallel to lamellar walls and bridged the walls. Seed additions of 7 to 15 wt% were beneficial for the optimized distribution of the two types of β-Si 3 N 4 grains, which contributed to the excellent resistance to bucking-induced fracture for the walls. Compared with other unidirectional porous Si 3 N 4 prepared by freeze-casting in the literature, the Si 3 N 4 scaffold exhibited outstanding compressive strength, ranging from 2.8 to 22.0 MPa, as the porosity decreased from 94.4% to 88.0% and the density increased from 175 to 365 mg/cm 3 . The lightweight and strong Si 3 N 4 scaffolds are promising candidates for engineering applications in harsh environments.