PROTONIC DEFECTS IN OXIDES AND THEIR POSSIBLE ROLE IN HIGH-TEMPERATURE OXIDATION

Protons from hydrogen or water vapour may dissolve in oxides and other corrosion products, and may affect, and in some cases, dominate their defect structures. Defect-dependent properties like scale growth and plastic deformation them become dependent on the ambient hydrogen or water vapour pressure. Small concentrations of protons may enhance the transport of oxygen in the form of hydroxide ion diffusion. Furthermore, the transport of protons through a scale (dissolving as hydrogen in the metal), can replace the outward transport of electrons during scale growth. Recent literature results indicate that protons can be dominant defects in Y2O3, Al2O3 and Cr2O3 under certain conditions.