Abstract
The degassing kinetics of niobium-nitrogen solid solutions were determined by annealing in high vacuum between 1630 and 1970° C. Nitrogenated niobium wires of 0.5 mm dia, containing about 3 at % N, were resistance-heated by dc. Continuous resistance measurements during annealing served to follow the degassing process. In order to interpret the degassing experiments, the rate and degassing laws and also the expressions for the rate constants and half-times were computed for various rate-determining sub-processes. Detectable degassing begins above 1600° C; above 2000° C a few minutes sufficed to achieve complete degassing. The degassing can be described by a rate law of second order with an activation energy of 124 kcal/mole N 2. The rate-determining factor is taken to be the recombination of nitrogen atoms at the metal surface and their subsequent desorption. A relationship is quoted for the temperature dependence of the degassing rate which is valid for nitrogenated niobium samples which are thin but otherwise of arbitrary shape.
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