ROLE OF INTERFACE STRUCTURE AND INTERFACIAL DEFECTS IN OXIDE SCALE GROWTH

Recent studies of the structure and dynamics of solid-solid interfaces have provided some understanding about the role of the scale-metal in terface in the growth of reaction product scales on pure metals. The a ction of interfacial defects (misfit dislocations, misorientation disl ocations and disconnections) in the creation and annihilation of the p oint defects supporting the diffusional growth of scales is considered . Anion point defects (vacancies/interstitials) supporting scale growt h by anion diffusion are annihilated/created by the climb of misorient ation dislocations or disconnections in the scale at the interface. Fo r scale growth by cation diffusion, cation point defects (vacancies/in terstitials) can be annihilated/created by the climb of interfacial mi sfit or misorientation dislocations in the metal. Because of their nec essarily high density, in most cases, the dominant climb of misfit dis locations would be favored. The blocking of interfacial reaction steps can be a means to retard the scaling kinetics and to alter the fundam ental scaling mode. For instance, the interfacial segregation of large reactive element ions can pin the interface dislocations, an action w hich poisons the usual interfacial reaction step. Such considerations are consistent with the well-known phenomena ascribed to the reactive element effect (REE).