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) M(x)O(y) + C (+ N-2;) -> {M(x)'N-y', M(x)''C-y'', 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 (AIN, TIN, Si3N4, ZrN) were formed for systems run in N-2: 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 beat al very high temperatures may make alternative processes economically feasible.