ABSTRACT
This chapter explains diffusion was restricted to neutral atoms and was considered to be due to changes in concentration. It discusses the various diffusion coefficients. The idea of diffusion in a gas or a liquid is well known. If some heavily perfumed flowers are placed in a room the scent is soon noticeable everywhere in the room due to the diffusion of molecules from the flowers through the gas molecules of the air. Diffusion also takes place in solids, although at a much slower rate than in gases or liquids. Solid-state diffusion is quite easy in iron oxide and so corrosion continues quite rapidly at room temperature. There are a number of experimental methods which allow tracer diffusion coefficients to be determined. The crystal sandwich is heated for a known time at the temperature for which the diffusion coefficient is required. Atomic movement through the crystalline lattice is called volume, lattice or bulk diffusion.
