PREPARATION OF BETA-SIC NANORODS WITH AND WITHOUT AMORPHOUS SIO2 WRAPPING LAYERS

Preparation of beta-SiC nanorods with and without amorphous SiO2 wrapp ing layers was achieved by carbothermal reduction of sol-gel derived s ilica 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 typica lly 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 rang e 10-30 nm, while the outer diameters of the corresponding amorphous S iO2 wrapping layers are between 20 and 70 nm. The beta-SIC nanorods wi thout amorphous SiO2 wrapping layers were produced by carbothermal red uction only at 1650 degrees C for 2.5 h, and their diameters are in ag reement with those of the center thinner beta-SiC nanorods wrapped in amorphous SiO2 layers. Large quantities of SiC rod nuclei and the nano meter-sized nucleus sites on carbon nanoparticles are both favorable t o the formation of much thinner beta-SiC nanorods. The formation of th e outer amorphous SiO2 wrapping layer is from the combination reaction of decomposed SiO vapor and O-2.