Interdiffusion and Moving Boundaries in NiO‐CaO and NiO‐MgO Single‐Crystal Couples

For single‐crystal NiO‐CaO diffusion anneals in air at 1346° to 1527°C, the chemical interdiffusion coefficient increased exponentially with increasing Ni concentration; for NiO‐MgO at 1342° to 1346°C, a similar relation was found for [Ni] <0.41. The higher diffusivity and correspondingly greater flux in the NiO‐rich phase resulted in reaction at the interface and movement of the crystallographic boundary with the growth of the NiO at the expense of the other crystal. The crystallographic orientation of the volume swept out transformed to that of the growing crystal.