Thermodynamic and Kinetic Studies of Oxygen Behavior in Tantalum-Based Alloys

摘要

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 to 1100 exp 0 C. The terminal solubility of oxygen in tantalum was determined to be c/sub s/ = 12.4 exp (-(5.5 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 1100 exp 0 C. 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 positive modifications of the oxygen activity coefficient in Ta-Mo alloys were believed to be due to repulsive interactions between molybdenum and oxygen atoms up to third nearest neighbors and probably to fourth or fifth nearest neighbor shells. 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 Ta with Cr, the oxygen diffusivity was lowered by more than an order of magnitude. Oriani's model was used to fit diffusion data in tantalum-based alloys and the values of trap energy were calculated. The binding energies, delta E/sub X/, obtained from diffusion measurements in Ta-Nb-O alloys and Ta-V-O alloys were compared with the difference in nearest neighbor pairwise interaction energies epsilon/sub iu/ and epsilon/sub iv/ derived from equilibrium measurement on these two alloys, there was very good agreement between these two terms in Ta-Nb-O and Ta-V-O alloys. 113 references, 50 figures, 11 tables. (ERA citation 09:014196)