Characterization of si-based nanoparticulates produced by carbothermic reduction of silica-containing slag

Si-based nanoparticles, nanochains and nanowires were synthesized by smelting reduction method which includes a high temperature carbothermic reduction of silica-rich melt to SiO vapor and transfer of the vapor with Ar carrier-gas to cooler surfaces inside the experimental reactor where the nanoparticulates were deposited. Features of the process have been discussed in our previous paper. In this paper, the synthesized nanoparticulates were characterized by using XRD, XPS, EDX, TEM and HRTEM analysis. The deposition temperature was found to be the crucial parameter governing the nanoparticulate morphology and phase composition. The nanowires were obtained in the high temperature range of 1320-1570 K. It is found that the as-obtained nanowires were composed of a SiC core and an amorphous sheath of silicon suboxide. The nanowires had diameter ranging from 20 to 60 nm and length up to several microns. The rounded nanoparticles of 30-50 nm in diameter were deposited at locations under temperatures lower than 920 K. They were mainly composed of amorphous silicon suboxide which could be decomposed under certain conditions yielding Si nanocrystallites embedded into the oxygen enriched suboxide matrix. The nanocrystallite size was estimated to be of 3-8 nm although much larger, up to 50 nm, Si crystals were detected at high temperature locations.