Brownian motion in spinodal decomposition

Abstract The flux from random solute movements, Brownian motion, is added to the diffusion equation for spinodal decomposition. The resulting equation for the time dependence of the diffuse intensity accounts for the several discrepancies between theory and experiment which have been observed during the very early stages of spinodal decomposition. The influence of Brownian motion on the rate of change of the diffuse intensity is characterized by a thermal driving force proportional to k B T where k B is Boltzmann's constant and T is the temperature. The observed critical wave vector depends on the initial intensity distribution and occurs at the wave vector for which the thermal driving force is balanced by the usual thermodynamic driving force. The equation can also be used to study the early stages of homogeneous nucleation (G-P zone formation) on aging a quenched specimen outside the spinodal.