Preparation of β-SiC nanorods with and without amorphous SiO2 wrapping layers

Preparation of beta-SiC nanorods with and without amorphous SiO2 wrapping layers was achieved by carbothermal reduction of sol-gel derived silica xerogels containing carbon nanoparticles. The beta-SiC nanorods with amorphous SiO2 wrapping layers were obtained by carboreduction at 1650 degrees C for 1.5 h, and at the end of 1.5 h the temperature was steeply raised to 1800 degrees C and held for 30 min; they are typically up to 20 mu m in length. The diameters of the center thinner beta-SiC nanorods within the amorphous SiO2 wrapping layers are in the range 10-30 nm, while the outer diameters of the corresponding amorphous SiO2 wrapping layers are between 20 and 70 nm. The beta-SIC nanorods without amorphous SiO2 wrapping layers were produced by carbothermal reduction only at 1650 degrees C for 2.5 h, and their diameters are in agreement with those of the center thinner beta-SiC nanorods wrapped in amorphous SiO2 layers. Large quantities of SiC rod nuclei and the nanometer-sized nucleus sites on carbon nanoparticles are both favorable to the formation of much thinner beta-SiC nanorods. The formation of the outer amorphous SiO2 wrapping layer is from the combination reaction of decomposed SiO vapor and O-2.