Determination of Activities of Niobium in Cu-Nb Melts Containing Dilute Nb

Abstract

The activity coefficients of niobium in Cu-Nb melts were measured by equilibrating solid NbO₂ with liquid copper under controlled oxygen potentials in the temperature range of 1773 K to 1898 K (1500 °C to 1625 °C). Either CO-CO₂ gas mixture or H₂-CO₂ gas mixture was employed to obtain the desired oxygen partial pressures. Cu-Nb system was found to follow Henry’s law in the composition range studied. The temperature dependence of Henry’s constant in the Cu-Nb melts could be expressed as follows:

$$ \log \gamma_{{{\text{Nb(l}})}}^{0} = \frac{3305}{T} + 0.72. $$

The partial molar excess Gibbs energy change of niobium in Cu-Nb melts can be expressed as follows:

$$ \Delta \overline{G}_{\text{Nb}}^{\text{ex}} = 63,280 + 13.2T \left( {\text{J/mol}} \right) $$