Thermodynamic Study of Liquid Cu-Ni-O Alloys by Electromotive Force Method

Using the cell, Pt/Ni, NiO/ZrO2(+CaO)/Cu-Ni-O or Cu-Ni-O, NiO/Cr-cermet, Pt, the activities of unsaturated oxygen in the liquid Cu-3.5 wt%Ni alloy and the activities of oxygen and nickel in the liquid Cu-Ni alloys in equilibrium with NiO were measured in the temperature range 1200 to 1350°C. The samples were taken at 1300°C and analyzed for oxygen and nickel contents. The activities of oxygen in the liquid Cu-3.5 wt%Ni alloy followed Henry’s law and its activity coefficient was found to be 0.21. The activities of copper were evaluated by the Gibbs-Duhem integration at 1300°C. The activities of nickel and copper deviated positively from ideality. The solubility of oxygen in the liquid Cu-Ni alloys at 1300°C decreased rapidly with increasing nickel to about 0.1 mol nickel and then became nearly constant. The liquidus curve of the Cu-Ni diagram was obtained from the flection point on the emf-temperature curves. The valve of εONi at 1300°C evaluated by extraporation was −7.2.