Phase Equilibria in the System Vanadium Oxide-Niobium Oxide

Abstract

The phase diagram for the pseudo-binary system V₂O₅-Nb₂O₅ was constructed from fusion characteristics and x-ray diffraction data. Three compounds were postulated for the system. The compound VNb₉O₂₅ and V₂Nb₂₃O₆₂ were found to melt incongruently at about 129O °C and 1322 °C respectively. The third compound occurring at about 93 to 94 mole percent Nb₂O₅ melted incongruently at approximately 1332 °C. Apparently,Nb₂O₅ accepted up to 5 mole percent V₂O₅ in solid solution, however, V₂O₅ did not accept any appreciable Nb₂O₅ in solid solution. In addition, the Nb₂O₅ rich portions of the following binary systems were reinvestigated: ZnO - Nb₂O₅, NiO - Nb₂O₅, A1₂O₃ - Nb₂O₅, TiO₂ - Nb₂O₅, and ZrO₂ - Nb₂O₅. In each case an Nb₂O₅ solid solution had been reported previously in excess of 9O mole percent Nb₂O₅.However, subsequent data indicated that these Nb₂O₅ solid solutions contained discrete compounds which are related to those found in the pseudo-binary V₂O₅ - Nb₂O₅.

Figure 1.. Phase equilibrium diagram for the system vanadium oxide-niobium-oxide.

●—no melting. ◑—partial melting. ○—complete melting. ◉—cannot be interpreted from fusion characteristics. Liq.—liquid. X—unknown phase Nb₂O₅₈₈—Nb₂O₅ solid solution. For clarity, not all experimental data appearing in table 4 are plot ted on this diagram.

Figure 2.. Expanded view of the high Nb₂O₅ region of the phase diagram for the system vanadium oxide-niobium oxide.

●—no melting. ◑—partial melting. Liq.—liquid. X—unknown phase Nb₂O₅₈₈—Nb₂O₅ solid solution.