A thermodynamic approach to homogeneous nucleation via fluctuations of concentration in binary liquid alloys

A thermodynamic approach to homogeneous crystalline nucleation in binary liquid alloys is presented, which is based on a two-step mechanism for critical embryo formation. It postulates that suitable concentration fluctuations in the undercooled liquid state can provide favoured sites for nucleation. Thus, a distinction is operated between local chemical order fluctuations and structure fluctuations, as opposed to the classical nucleation theory approach. To quantify the importance of concentration fluctuations, the proposed mechanism is applied to binary liquids exhibiting a tendency towards phase separation. The energy required to form a relevant fluctuation in the liquid, prior to nucleation, is calculated as a function of the undercooling amount. Furthermore, the ratio between the population of relevant fluctuations and that of critical nuclei is assessed statisticallyt the probability for a fluctuation to become a critical embryo increases with the amount of undercooling. Finally, the two-step mechanism for nucleation is supported from a kinetic point of view.