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 degreesC. Linear kinetics curves were obs erved (except for a short initial period) with a homographic influence of H 2O pressure. Hydrogen additions in the gas phase largely modified the react ion rates. The oxide formed (NbO2) is different from that predicted by ther modynamics (Nb2O5). Taking into account all these experimental observations , a mechanism is proposed in which the limiting step is oxygen incorporatio n into the oxide lattice.