Phase relationships in the system Cr-W-O and thermodynamic properties of CrWO₄ and Cr₂WO₆

Abstract

The phase diagram of the Cr-W-O system at 1000 ° C was established by metallographic and X-ray identification of the phases present after equilibration in evacuated silica capsules. Two ternary oxide phases, CrWO₄ and Cr₂WO₆ were detected. The oxygen potential over the three-phase mixtures, W+Cr₂O₃ s+CrWO₄, WO_2.90+CrWO₄+Cr₂WO₆ and Cr₂O₃+Cr_WO₄+Cr₂WO₆, were measured by solid state cells incorporating Y₂O₃ stabilized ZrO₂ electrolyte and Ni+NiO reference electrode. The Gibbs' energies of formation of the two ternary phases can be represented by the following equations W(s) + ½Cr₂0₃(s) + 5/4 0₂(g) → CrWO₄(s). ΔG° =- 172 047 + 48.725T(±230) cal mo1^-1. Cr₂0₃ (s) + WO₃(s) → Cr₂WO₆ (s). ΔG± = -3 835 + 0.235T(±500) cal mol^-1.