Adsorption, Absorption, and Degassing in the Oxygen-Niobium System at Very Low Pressure

Abstract

The interaction of low‐pressure oxygen with niobium has been investigated at temperatures between 300° to 2100°K. Four main kinetic patterns can be distinguished. At temperatures close to 300°K adsorption proceeds to the formation of a saturated surface layer. At intermediate temperatures (about 500°–800°K) a thin oxide layer is formed; simultaneously oxygen dissolves and diffuses into the metal. At higher temperatures (800°–170°K) oxygen dissolves rapidly and irreversibly; the observed kinetics can be explained by a surface mechanism involving two adsorption states. Finally, at very high temperatures (1700°K and higher) niobium oxides evaporate from an oxygen‐niobium solution. The kinetics of evaporation indicates that a mixture of and evolves, the composition of which shifts from the former to the latter with decreasing oxygen concentration.