VACUUM CARBOTHERMIC REDUCTION OF Al2O3, BeO, MgO-CaO, TiO2, ZrO2, HfO2 + ZrO2, SiO2, SiO2 + Fe2O3, AND GeO2 TO THE METALS. A THERMODYNAMIC STUDY

Thermochemical equilibrium calculations are carried out to elucidate improved conditions for the production of Al, Si, FeSi, Ti, Mg, Hf, Zr, Be, and Ge by the high-temperature carbothermic reduction of their oxides, and for the production of Mg by the silicothermic reduction of MgO-CaO. The onset temperature for the formation of free Al, Be, Si, Ti, Mg, Hf, and Zr in the gas phase is considerably lowered by decreasing the total pressure, enabling their vacuum distillation. An important prediction of vacuum operation is the suppression of undesired by-products, such as Al-carbide, Al4C3, and the Al-oxycarbides Al2OC and Al4O4C. These species considerably interfere in the carbothermic Al production at an ambient pressure, as shown in preliminary experiments using induction furnace irradiation. CO coproduced in these reactions may be water-gas shifted to syngas and further processed to hydrogen and liquid fuels.