Carbothermal solid state reduction of stable metal oxides
The paper considers carbothermal solid state reduction of manganese, titanium and aluminium oxides in argon, helium and hydrogen. The difference in reduction in helium and argon was reflected by different diffusion coefficients of gaseous reactants and products, which are much higher in helium than in argon. When carbothermal reduction took place in hydrogen, it was involved in the reduction process by reducing oxides to suboxides and forming methane.
Manganese and titanium oxides were reduced to carbide Mn7C3 and oxycarbide Ti(OxC1-x) correspondingly, while products of alumina reduction included carbide Al4C3 and vapours of Al and Al2O, which were re-oxidised to Al4O4C outside the reactor and deposited in the lower temperature zone. Gas atmosphere had a profound effect on the extent and rate of reduction. This effect was different in reduction of different oxides. Reduction of manganese oxides was the fastest in hydrogen, and faster in helium than in argon. Reduction of titania in argon and helium proceeded with about the same rate and was much faster in hydrogen than in the inert atmospheres. The rate and extent of alumina reduction in hydrogen and helium were higher than in argon, although no significant difference was observed in alumina reduction in hydrogen and helium. This reflects differences in reduction mechanisms, which are discussed in the paper.