ABSTRACT
When the reaction that takes place is one of diffusion as a movement of atoms within a chemically uniform material, it is called self-diffusion. When a permanent displacement of chemical species occurs, causing local composition change, it is called interdiffusion or chemical diffusion. The driving force for chemical diffusion is a chemical potential gradient (concentration gradient). When two dissimilar materials are in contact, chemical diffusion of the two materials in opposite directions forms an interface reaction layer. Once this layer has been formed, additional reaction can take place only by the diffusion of chemical species through this layer.
