Thermal Oxidation of Metallic Niobium by Water Vapor

The behavior of metallic niobium in pure water vapor (without added oxygen) was studied between 800 and 1000°C. Linear kinetics curves were observed (except for a short initial period) with a homographic influence of H2O pressure. Hydrogen additions in the gas phase largely modified the reaction rates. The oxide formed (NbO2) is different from that predicted by thermodynamics (Nb2O5). Taking into account all these experimental observations, a mechanism is proposed in which the limiting step is oxygen incorporation into the oxide lattice.