Thermodynamics of the Interaction of Niobium and Tantalum with Oxygen and Nitrogen at Temperatures near the Melting Point

The concentration of nitrogen and oxygen present in niobium and tantalum in equilibrium with the pure gas has been determined as a function of pressure at each of three temperatures near the melting point, and in the liquid phase at the melting point. A curious solubility inversion was noted in the tantalumoxygen system where the oxygen concentration in equilibrium with a specified pressure of oxygen is lower at 2850° than at 2960°C. Data were used to calculate the partial molar and integral values of the free energy, enthalpy, and entropy of dissociation of solutions of nitrogen in niobium and tantalum, and partial molar free energy and enthalpy of dissociation of solutions of oxygen in niobium and tantalum.