Thermodynamic and kinetic studies of oxygen behavior in tantalum-based alloys

The experimental study of equilibrium and kinetic properties of oxygen in tantalum-based alloys was made by EMF measurements on solid electrolytic cells over the temperature range of 600-11000C. The terminal solubility of oxygen in tantalum was determined to be c/sub s/ = 12.4 exp (-(15.5 kJ/mole)/RT) over the experimental temperature range. It was concluded that oxygen obeys Henry's law for concentrations up to the terminal solubility in tantalum for the temperature range 600 to 11000C. The oxygen activity coefficient increased with Mo content in Ta-Mo alloys and decreased with V content in Ta-V alloys. The equilibrium results showed virtually no disturbance in thermodynamic behavior of oxygen solution by adding Nb to Ta-O alloys. The oxygen diffusion in tantalum was not significantly modified by small addition of Nb, V, Mo, Ni and Ti. The addition of W in tantalum had a larger effect in lowering oxygen diffusivity in Ta-W alloys. By alloying Cr with Ta, the oxygen diffusivity was lowered by more than an order of magnitude