· 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.