Metals, nitrides, and carbides via solar carbothermal reduction of metal oxides

We have examined the thermodynamics of the carbothermic reduction of metal oxides in either nitrogen or argon atmospheres. The reaction, which is given generally by (where the M denotes metal) MxOy + C (+ N2;) → {Mx′Ny′, Mx″Cy″, M} + CO, is highly endothermic and proceeds at temperatures from 1300 to 2350 K for the systems considered. Exploratory experimental studies were conducted in a solar furnace using concentrated solar radiation. The nature of the solid-phase products was determined by X-ray powder diffraction. Nitrides (AlN, TiN, Si3N4, ZrN) were formed for systems run in N2; carbides (Al4C3, TiC, SiC, CaC2) were formed for runs in Ar; and metals (Mg, Zn) were obtained from their oxides in an Ar atmosphere. The use of solar energy as the source of high-temperature process heat offers the possibility of reducing emissions of greenhouse gases and other pollutants to the environment when it replaces the burning of a fuel for process heat. Furthermore, the availability of process heat at very high temperatures may make alternative processes economically feasible.