Production of Si by vacuum carbothermal reduction of SiO2 using concentrated solar energy

Using concentrated solar radiation as the energy source of high-temperature process heat, the carbothermal reduction of silica to silicon was examined thermodynamically and demonstrated experimentally at vacuum pressures. Reducing the system pressure favors Si(g) formation, enabling its vacuum distillation. Experimentation in a solar reactor was performed in the range 1,997–2,263 K at ∼3×10−3 bar with mixtures of charcoal and silica directly exposed to radiative flux intensities equivalent to 6,500 suns, yielding Si purities ranging from 66.1–79.2 wt.%. The Si purity increased with temperature. Solid characterizations showed SiC and SiO as important reaction intermediaries.