| Abstract Scope |
Refractory metals are candidates for hypersonic and propulsion components, where survival depends on forming a protective oxide rather than degrading. However, existing stability descriptors, including Pourbaix and maximum driving force (MDF) maps, target aqueous corrosion and do not address oxidation under temperature, oxygen pressure, and applied field. Here, we reformulate the MDF for metal/oxide/gas systems, with oxygen pressure and temperature replacing pH, volatile oxides replacing dissolved ions as the metal-loss channel, and applied bias entering through the voltage drop across the growing oxide film. We validate the descriptor against measured thermochemistry and oxidation experiments, reproducing the observed oxidation-susceptibility ranking of Ta, Nb, Mo, and W and their protective versus volatile behavior. We further examine bias-dependent stability, including a possible reordering of tungsten and niobium. Although our use case is specific to refractory metals, the framework applies broadly to other metal/oxide/gas system. |