The synthesis of silicon nitride whiskers from SiO2-N2-Na3AlF6 system

Abstract

Silicon nitride (Si3N4) whiskers were synthesized from SiO2-N2-Na3AlF6 system. Whiskers, which were synthesized when the molar ratio of SiO2 to Na3AlF6 (SiO2/Na3AlF6) ranged from 2 to 8, were prismatic with a stable diameter ranging from 0.1 to 0.5 μm. Therefore, the whiskers were considered to have grown by a VS mechanism. The effect of the addition of iron oxide (Fe2O3 : SiO2 = 1.5–7.5 : 100) was examined when SiO2/Na3AlF6 was 3, at which the maximum amount of whiskers was obtained. Since some of the whiskers, synthesized when the weight of Fe2O3 to that of SiO2 ranged from 3.0 to 6.25 (Fe2O3 : SiO2 = 3.0–6.25 : 100), have droplets on their tips, they were assumed to have grown by VS and VLS mechanisms. The composition of the droplets were found to be Al-Si by elemental analysis by EDAX. Since droplets composed of Al-Si have never been reported, we performed a detailed analysis of the droplets in this study.