Mass Transport

This chapter introduces mathematical models for describing mass transport by atomic diffusion under steady-state and transient conditions as defined by the Fick’s laws of diffusion, by ionic migration, and by convective motion of a fluid in a certain environment. In solid-sate diffusion, crystal structures of some crystalline materials are sensitive to heat treatment processes in specific gaseous environments. This is attributed to the atomic structure of thin surface layers, which can be altered by diffusion of interstitial atoms during heat treatment at relatively high temperatures and time \(t > 0\) . Atomic diffusion is a mass transport mechanism due to the random motion of particles (atoms, molecules, or ions) within a medium. The random walk model gives insight of the random collisions of species while traveling to a destination within a solid, liquid, and gas media. In physics and materials science, the mass transport by diffusion mechanism is fundamentally a random thermally activated motion of atoms in a solid crystal structure. Thus, solid–solid or gas–solid diffusion is the most common terminology in the fields of materials science.