Co-catalyzed nitridation of silicon and in-situ growth of α-Si3N4 nanorods

The catalytic effects of cobalt (Co) on the direct nitridation of silicon (Si) and morphologies of the nitridation products were investigated, and the relevant reaction mechanisms were proposed. The overall conversion of Si to silicon nitride (Si3N4) was dramatically improved with increasing the nitridation temperature from 1300 to 1350 °C. Co played an important role in accelerating the Si nitridation as well as the in-situ growth of α-Si3N4 nanorods, via the formation of Cosingle bondSi liquid phase. At 1350 °C, the overall conversion in the reference sample without Co was only 54%, whereas it exceeded 90% in the sample containing 1.25 wt% Co. When the Co addition was more than 7.5 wt%, α-Si3N4 nanorods of 80–120 nm in diameter and 800–1600 nm in length became the main product phase. The growth processes of the nanorods with and without nanoparticles (caps) at their tips were governed respectively by vapor–liquid–solid and vapor–vapor–solid mechanisms.