Kinetics and Thermodynamics of the Interaction of Niobium and Tantalum Base-Alloys with Nitrogen; Introduction to the Reaction Behavior of Niobium and Tantalum in Various Gas Atmospheres.

The reaction behavior of niobium and tantalum towards nitrogen, oxygen, water vapor, carbon monoxide, and hydrocarbons at high temperatures and low gas pressures is first reviewed and the influence of adsorbed species on the reaction kinetics is briefly considered. The kinetics and thermodynamics of the solution of nitrogen in alloys of niobium with molybdenum, rhenium, or ruthenium and in alloys of tantalum with niobium, tungsten, or rhenium at temperatures between 1600 and 2300 degree C and at nitrogen pressures between 10** minus **4 and 5 multiplied by 10**2 Torr are considered at length. It is shown that on alloying niobium or tantalum with elements of higher groups, the initial rate of nitrogen solution, the nitrogen solubility, and the solubility limit for nitrogen markedly decrease, whereas the heat and entropy of solution of nitrogen increase (become less negative). The influence of the alloying element increases with increasing group number of the element in the sequence: Mo(W), Re, Ru. From these results a correlation between the kinetic and thermodynamic data for the solution of nitrogen in niobium- and tantalum-based alloys is derived. Refs.