Diffusion in Solid‐State Systems

This chapter is confined to diffusion in condensed matter, namely, in metals, binary alloys, and oxides. Emphasis is on very basic fundamental aspects, the contents being roughly characterized by the general theory of diffusion, diffusion coefficients, Matano-Boltzmann analysis, Kirkendall effect, Darken analysis, factors influencing diffusion, impurity diffusion in metals, grain boundary (GB) diffusion in metals, diffusion in solid oxides, morphology of reaction products, and measurement of diffusion parameters. In the solid state systems, diffusion manifests itself as the migration of “solute” atoms through a host lattice via the defect structure of that lattice. Since the rate of formation of defects increases with the vibrational energy of the atoms, the diffusion process is enhanced at elevated temperatures. The two basic parameters, which specify a given diffusion distribution, are the surface concentration and the diffusion coefficient at any point within the material.