Fundamental aspects of reactions at the metal/scale interface during scaling

The interactions between interfacial reactions and interfacial defects during scale growth is illustrated by the effect of alkaline-earth elements on the growth of NiO scale on pure nickel at temperatures lower than 1000 C. Indeed, a very small amount of these elements segregated at the NiO/Ni interface induces a decrease of one to two orders of magnitude in the growth kinetics of NiO scales. Moreover, the alkaline-earth elements also induced large decrease in the dislocation and pore density within NiO grains. These experimental observations are in agreement with the ''poisoned interface model'' (PIM), but they cannot be interpreted as the effect of grain boundary segregation on diffusion through the scale. (orig.)