Self-Propagating High-Temperature Synthesis of Silicon Carbide Nanofibers

The results of investigations into the organization of the synthesis of silicon carbide fibers in the gas phase using silicon powder, an energy additive of polytetrafluoroethylene (PTFE), and polyethylene (PE) powder by self-propagating high-temperature synthesis (SHS) are presented. Mixtures of the stoichiometric composition are used for experiments. Charge components are mixed in a drum with 3 L in volume with tungsten carbide balls for 30 min. The charge weight is 500 g. Experiments are performed in an SVS-30 industrial reactor. The combustion of the charge of the silicon + PTFE composition is accompanied by a rapid pressure rise from 0.5 to 4.0 MPa for a time shorter than 1 s and relatively rapid pressure drop to 1.5 MPa for 1.5 min. The combustion speed exceeds 50 cm/s. It is established that the combustion is accompanied by the spread of charge components, which is a consequence of the high process speed and intense gas liberation. A cottony light blue material, which consists of silicon carbide fibers 100-500 nm in thickness, is fabricated. The maximal reactor pressure during the combustion of the silicon + PTFE + PE composition reaches 3.1 MPa for 1 s and decreases to 1.5 MPa for 3 min. The combustion speed is about 40 cm/s. The entire accessory volume is filled by cottony blue-gray silicon carbide and SiC powder with equiaxial particles 0.5-3.0 mu m in size combined into conglomerates. Silicon needlelike crystals are formed in a transient layer between the powder and silicon carbide fibers. The results of the experiments show the possibility of fabricating silicon carbide nanofibers in relatively large amounts under the combustion of exothermic mixtures.