Self-propagating high-temperature synthesis of silicon carbide nanofibers

Abstract

The article presents the results of studies into the gas-phase synthesis of silicon carbide fibers using silicon powder, polytetrafluoroethylene (PTFE) energy additive and polyethylene (PE) powder by self-propagating high-temperature synthesis (SHS). Stoichiometric mixtures were used for experiments. Green mixture components were mixed in a 3 liter drum with tungsten carbide balls for 30 min. The green mixture weight was 500 g. Experiments were conducted in the SHS-30 industrial reactor. Silicon + PTFE mixture combustion was accompanied by a rapid increase in pressure from 0.5 to 4.0 MPa in less than 1 s, and a relatively rapid pressure drop to 1.5 MPa in 1.5 min. The combustion rate was more than 50 cm/s. It was established that there was a spread of the mixture components during the combustion due to the high combustion rate and intense gas emission. A cottonlike material of light blue color was obtained; it consisted of 100-500 nm thick silicon carbide fibers. The maximum pressure in the reactor reached 3.1 MPa in 1 s during the silicon + PTFE + PE combustion and then decreased to 1.5 MPa in 3 min. The combustion rate was about 40 cm/s. The entire volume of the reactor was filled with blue-grey cotton-like silicon carbide and SiC powder with equiaxed 0.5-3,0 μ m particles merged into conglomerates. Needle-like silicon crystals were formed in the transition layer between the powder and silicon carbide fibers. The results of experiments proved the possibility of obtaining silicon carbide nanofibers in relatively large quantities during the combustion of exothermic mixtures.