Preparation of rod-like β-Si3N4 seeds with tailored morphology

•The increased Y2O3 content led to the higher aspect ratio of β-Si3N4 seeds.•The decreased N2 pressure led to the higher aspect ratio of β-Si3N4 seeds.•β-Si3N4 seeds with moderate aspect ratio and few agglomerations were obtained.

Microstructures of β-Si3N4 seeds prepared by the heat treatment of α-Si3N4 powders were tailored by controlling the amount of Y2O3 additives and the N2 pressure. Based on the previous studies on rare earth (RE) distribution in Si3N4 ceramics doped with RE2O3, the Y2O3 existed in the two forms: (1) Y-containing phase such as Y2Si3O3N4, and (2) the adsorption of Si3N4 grain surfaces. The Y-containing phase resulted in the agglomeration of the seeds, and the Y adsorption promoted the growth anisotropy. Both the increased Y2O3 content and the decreased N2 pressure led to the increased Y adsorption and the higher aspect ratio of β-Si3N4 seeds. By the combination of low N2 pressure and low Y2O3 content, the β-Si3N4 seeds with moderate and uniform aspect ratio (~4.23), and few agglomerations were obtained.