High Pressure Oxidation of Niobium

Niobium oxidizes according to the linear rate law from 400°–800°C (14.7–605 psia O2). The oxidation rate is extremely pressure sensitive above 550°C. Theoretical considerations indicate that an equilibrium adsorption process occurs prior to the rate‐determining step. It was necessary to include a term in the rate equation for the interaction between the adsorbed molecules to interpret results above 650°C. The interaction energy is influenced by the initial orientation of the metal surface. The activation energy for the oxidation process is approximately 9 to 10 kcal (500°–800°C).