Kinetics and Microstructural Control


· Thermodynamic equilibrium requires that processes take place quasi-statically.
· In the discussion of phase diagrams, the time scale has been assumed to be slow enough that diffusion processes can maintain uniform compositions of all the phases present.
· In general, solid state diffusion processes will determine the cooling or heating rates required to maintain equilibrium.
· These diffusion processes are slower than the convective transport that can occur in liquids and gasses. The solid-gas or liquid-gas interface may be in thermodynamic equilibrium, but the bulk solid will have concentration gradients, and therefore not be in equilibrium.