Diffusion Processes

processes that occur during the displacement of the smallest particles of matter (atoms, ions, and molecules) or of their complexes because of the tendency toward an equilibrium distribution of the migrating particle concentrations within a given volume.

The exchange of particles between materials in different states of aggregation may take place during diffusion processes—that is, the phenomena of adsorption and desorption, solution and crystallization, and drying may occur. Diffusion processes also form the basis of such industrial operations as powder sintering (for example, in powder metallurgy), thermal treatment of metals, chemical-thermal treatment of metals (case hardening and nitriding), homogenization of alloys, and diffusion coating. The importance of diffusion processes increases in connection with the necessity of producing special materials for the developing areas of technology, such as atomic power engineering and space travel. Knowledge of the relationships governing the diffusion processes makes it possible to avoid undesirable changes in structures that occur under the influence of high temperatures, large loads, and irradiation.