Oxygen potentials, Gibbs' energies and phase relations in the Cu-Cr-O system

Abstract

Thermodynamic properties of ternary compounds, cuprous and cupric chromites (CuCrO₂, CuCr₂0₄), and oxygen potentials corresponding to three three-phase regions in the Cu-Cr-O system have been measured in the temperature range 900 to 1350 K using a solid state galvanic cell incorporating calcia-stabilized zirconia. Cuprous chromite was found to be nearly stoichiometric. The compositions of non-stoichiometric cupric chromite saturated with CuO and Cr₂0₃ have been determined using electron microprobe and energy dispersive X-ray analysis. The results of this study resolve discrepancies in Gibbs" energies of cuprous and cupric chromites reported in the literature. A ternary phase diagram for the Cu-Cr-O system at 1150 K and phase relations in air for the Cu₂0-CuO-Cr₂0₃ system as a function of temperature have been derived based on the new thermodynamic data. The phase diagram given in the literature is found to be inaccurate.