The role of the metal/oxide interface in the growth of passive films in aqueous environments

A mechanistic methodology has been developed to understand the role of the metal/scale interface in the growth of scales at high temperatures. Specifically, cation vacancies arriving at the metal/scale interface are annihilated by the climb of misfit and misorientation interfacial dislocations. If this mechanism is blocked, e.g. by the tangling of dislocations within the metal, then cation diffusion cannot continue to support the growth of an adherent oxide. To the extent that adherent, crystalline and epitaxial passive or anodic films formed in aqueous environments also grow by cation diffusion over vacancies, the same mechanisms must apply. The segregation of large reactive element cations to the metal/scale interface and their importance in enhancing scale adherence by blocking vacancy annihilation, also constitute concepts that might find relevance for passive films in aqueous solutions.