Equilibrium phase relationships in the system Cu-O under high oxygen pressure

The equilibrium phase relationships near the liquidus line of the system Cu2O-CuO-O2 (a part of wider system Cu-O) were determined under pure oxygen pressure from 0.001 to 11 MPa by three experimental methods: differential thermal analysis (DTA), thermogravimetry (TG), and thermobarometry (TB). The coordinates of the eutectic point between solid Cu2O and CuO were found to be PO2=0.069±0.001 MPa and T=1364±1 K. It was proved experimentally that, at least at temperatures up to 1526 K and oxygen pressures up to 11 MPa, CuO melts incongruently with liberation of gaseous oxygen and with the temperature dependence of PO2 obeying an Arrheniustype equation. The conditions for congruent melting of CuO were analyzed using the model, and it was found that congruent melting of CuO should occur at ≈ 1620 K under oxygen pressure ∼1000 MPa.