Nitridation of Silicon Powders Catalyzed by Cobalt Nanoparticles

The effect of Co nanoparticles (NPs) on the nitridation of silicon (Si) was studied. Co NPs were deposited homogeneously on the surfaces of Si powders using an in situ reduction method using NaBH4 as a reducing reagent. Si powders impregnated with 0.5-2.0 wt% Co NPs were nitrided in 1200 degrees C-1400 degrees C for 2h. The resultant silicon nitride powders were characterized by XRD, FE-SEM, TEM, and EDS. The results showed that: (1) Co NPs significantly decreased the Si nitridation temperature, and the nitridation could be completed at 1300 degrees C upon using 2 wt% Co NPs as catalysts. For comparison, the Si conversion could not be completed even at a temperature as high as 1400 degrees C in the case without using a catalyst; (2) many Si3N4 whiskers with 80-320nm in diameter and tens micrometers in length were generated and uniformly distributed in the final products. They were single-crystalline -Si3N4 grown along the [101] direction. The enhanced nitridation in the case of using Co NPs as a catalyst was attributed two following factors, the increased bond length and weakened bond strength in N-2 caused by the electron donation from the Co atoms to the N atoms.