Thermodynamic studies of liquid copper alloys by electromotive force method: Part II. The Cu−Ni−O and Cu−Ni systems

Abstract

Oxygen activities in liquid Cu−Ni melts have been measured at 1100°, 1200°, and 1300°C by the solid electrolyte electromotive force method. Addition of nickel lowers the activity coefficient of oxygen in liquid copper. The temperature dependence of$\in _{\rm O}^{(Ni)}$ can be represented as follows:

$$ \in _{\rm O}^{(Ni)} = 17.0 - (3.60 \times 10^4 / T)$$

(1)

The solubility and activity of oxygen in liquid Cu−Ni alloys in equilibrium with NiO were measured at 1400°C. Oxygen solubility decreases with increasing nickel in the alloys. Nickel activities in the liquid Cu−Ni system were also calculated from the electromotive force data. Copper activities were evaluated by the Gibbs-Duhem integration. Activities of copper and nickel deviate positively from ideality. The activity coefficient of nickel in the liquid Cu−Ni system at 1400°C can be represented by the Darken's formulation: In

$$\gamma _{Ni} = 1.323 (1 - N_{Ni} )^2 ; N_{Ni} = 0.55 to 0.77$$

(2)

In

$$\gamma _{Ni} = 1.000 (1 - N_{Ni} )^2 + 0.005; N_{Ni} = 0.0 to 0.3$$

(3)

Excess entropies in the liquid Cu−Ni system are less than 0.1 eu. A complete set of thermodynamic properties of the system can be calculated by combining the free energy data of this study with the estimated enthalpy data from literature sources.