Calcium Vapor Reduction of Group V and VI Metal Oxide Compounds

• Published in: Inorganic materials Vol. 56; no. 1; pp. 35 - 41
• Main Authors: Kolosov, V. N., Orlov, V. M., Miroshnichenko, M. N.
• Format: Journal Article
• Language: English
• Published: Moscow Pleiades Publishing 01.01.2020; Springer Nature B.V
• Subjects: Argon; Calcium compounds; Calcium oxide; Chemistry; Chemistry and Materials Science; Homogeneous mixtures; Industrial Chemistry/Chemical Engineering; Inorganic Chemistry; Lime; Magnesium oxide; Materials Science; Metal compounds; Metal oxides; Molybdenum oxides; Molybdenum trioxide; Niobium oxides; Oxidation; Reaction mechanisms; Reaction products; Stoichiometry; Superconductors (materials); Tantalum; Tantalum oxides; Vapors; tungsten; powder; reduction; tantalum; niobium; molybdenum
• ISSN: 0020-1685; 1608-3172
• DOI: 10.1134/S0020168520010069

— We have studied calcium vapor reduction of Group V and VI metal oxide compounds (Ta 2 O 5 , Nb 2 O 5 , WO 3 , MoO 3 , MgWO 4 , MgMoO 4 , and CaMoO 4 ) 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 MgWO 4 and MgMoO 4 , 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.