Phase Equilibria and Thermodynamic Properties in the V_nO_2n−1 System

Abstract

The phase equilibria of the V₂O₃–VO₂ system in connection with the oxygen activity were established in the temperature range from 600° to 1200°C. A quenching method was applied to the experiments from 1000° to 1200°C under controlled oxygen atmosphere with the use of a CO₂–H₂ gas mixture. For the temperature range from 600° to 1000°C, a solid electrolyte cell of the type; Pt/adjacent two-phase mixture (V_nO_2n−1+V_n+1O_2(n+1)−1)/(ZrO₂)_0.85(CaO)_0.15/O₂ (air reference electrode)/Pt, was utilized to measure the oxygen activity. The standard free energy changes of the reactions (n+1)V_nO_2n−1+1⁄2O₂\ ightleftarrowsnV_n+1O_2(n+1)−1 were calculated from the electromotive force developed by the cell.