Calcium Vapor Reduction of Group V and VI Metal Oxide Compounds

Abstract

We have studied calcium vapor reduction of Group V and VI metal oxide compounds (Ta2O5, Nb2O5, WO3, MoO3, MgWO4, MgMoO4, and CaMoO4) at temperatures from 800 to 860°C and residual argon pressures from 5 to 10 kPa. The products of the reduction of the Group V metal compounds had the form of a homogeneous mixture corresponding to the reaction stoichiometry. After the reduction of the Group VI compounds under similar conditions, we observed spatial separation of the reaction products: most of the reductant metal oxide was located beyond the reaction zone. In the initial stage of the reduction of MgWO4 and MgMoO4, calcium substitutes for magnesium in these compounds. Together with calcium oxide, the magnesium oxide forms a layer on the surface of the reactants. Analysis of our results suggests that the calcium vapor reduction of the Group VI metal oxide compounds is likely to follow the electronically-mediated reaction mechanism.