Formation of SiO and Related Si-Based Materials Through Carbothermic Reduction of Silica-Containing Slag

Silicon based nanoparticulates of various composition and morphology have been produced by smelting reduction method which includes a carbothermic reduction of SiO2-Al2O3-CaO starting materials to SiO vapor at 2073 K and transfer of the vapor with a carrier-gas to cooler surfaces inside the experimental reactor where the nanoparticulates were deposited. The chemical composition of the starting materials was matched to the basic composition of silica-rich coal ash which is considered as a potential source of Si in this study. Special emphasis was placed upon examining the degree of SiO2 reduction from starting materials, purity and morphology of the as-obtained nanomaterials. It is shown that up to 20% of Si can be converted from the silica-based melt into rounded nanoparticles, nanoparticle chains and nanowires containing Si,O and C in variable proportions depending on deposition temperature and gas flow conditions. The diameter of nanoparticulates was estimated to be in the range of 20 similar to 100 nm. The nanoparticles and chains were found to be deposited at lower temperature locations (293 similar to 1320 K) while the nanowires were obtained at higher temperatures (1320 similar to 1570 K). There was a tendency for an increase in Si concentration in order of nanowires, nanoparticles chains and nanoparticles. The carbon concentration, on the contrary, was much higher in nanowires as compared to that in nanoparticles. Although the degree Of SiO2 reduction from silica-containing melt to SiO vapor is limited because a part Of SiO2 reacts with C producing SiC, its good controllability, high productivity and possibility for processing cheap starting materials make the smelting reduction a very attractive technique for production of silicon based nanostructured materials.