Synthesis of one-dimensional nanostructures - beta-SiC nanorods with and without amorphous SiO2 wrapping layers

Synthesis of one-dimensional nanostructures-beta-SiC nanorods with and with out amorphous SiO2 wrapping layers-was achieved by controlling carbothermal reduction of sol-gel derived silica xerogels with carbon nanoparticles emb edded in the network. The beta-SiC nanorods with amorphous SiO2 wrapping la yers were obtained by carboreduction at 1650 degrees C for 1.5 hours and th en heating at 1800 degrees C for 30 minutes. The composite nanorods are typ ically up to 20 mu m in length. The diameters of the center, thinner beta-S iC nanorods are in the range of 10 to 30 nm while the outside diameters of the corresponding amorphous SiO2 wrapping layers are between 20 and 70 nm. Monolithic beta-SiC nanorods were produced by only carbothermal reduction a t 1650 degrees C for 2.5 hours. The diameters of the monolithic beta-SiC na norods are in agreement with those at the center of the thinner beta-SiC na norods wrapped up in amorphous SiO2 layers. The large quantities of SiC rod nuclei and the nanometer-sized nucleus sites on carbon nanoparticles are f avorable to the formation of much thinner beta-SiC nanorods. The formation of the outside amorphous SiO2 wrapping layer is due to the combination reac tion of decomposed SiO vapor and O-2 during cooling. The monolithic beta-Si C nanorods may be used as reinforcing and toughening elements in ceramic, m etal, and polymer matrix nanocomposites. The beta-SiC nanorods with amorpho us SiO2 wrapping layers might offer opportunities for both fundamental rese arch and technological applications.