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摘要
SiO2((activated or mesoporous silica))/Mg-(magnesiothermic or metal sintering aid)/C-(activated or polymeric carbon)/N-2(atmosphere) systems were used in the one-step synthesis of beta-SiC and beta-Si3N4 whiskers. In this study, a mixture of the active precursors was allowed to react via a self-sustaining reaction (hig-henergy ball milling process). Scanning electron micrographs and X-ray diffraction (XRD) analysis showed that the rod-like SiC whiskers (similar to 800 mu m) were synthesized in situ by the direct carbothermal reduction of silicon nitride (or silicon) with activated carbon in N-2 (or Ar) atmosphere. The results show that beta-Si3N4 (without beta-SiC) was fully formed after 5 h of milling with four different morphologies, namely whisker tip (droplet/no droplet) and nonuniform whiskers (short hexagonal/rhombohedral/rod-like) with a length of 0.1-400 mu m. By adding metal sintering aids, the liquid phase Mg-Si-O-N and the rate of carbothermal reduction increased (enhanced densification via particle rearrangement) and their hexagonal whiskers tended to assume a rod-like shape. The effect of the concentration of CO (reduction of alpha-Fe2O3 to Fe by CO) on the whisker synthesis suggests that, in addition to the concentration of CO, the nature of the family of mesoporous silica/carbon template is an important factor in the synthesis of beta-SiC and beta-Si3N4 whiskers. The possible chemical reactions were investigated by studying the unwanted phases (MgO, Si, SiC, Fe2O3, Fe3O4, FeO, Fe, Fe3C, MgCO3) of comparable XRD graphs.
- 出版日期2017-8
