GENERALIZED GIBBS' THERMODYNAMICS AND NUCLEATION -GROWTH PHENOMENA

摘要

Nucleation processes – the formation of aggregates of critical sizes allowing their further deterministic growth - are one of the basic mechanisms first-order phase transitions (like condensation and boiling, segregation in solutions or crystallization and melting) may proceed. In order to describe theoretically the kinetics of nucleation-growth processes, the so-called work of cluster formation – the change of the thermodynamic potential due to the formation of a cluster of a given size and composition - has to be known. This quantity is conventionally determined in the framework of Gibbs' thermo-dynamic theory of heterogeneous systems employing certain additional assumptions. However, Gibbs restricted his analysis exclusively to "equilibrium states of heterogeneous substances" and, already by this limitation, does not supply us with a fully satisfactory solution of mentioned problem. Generalizing Gibbs' method, recently a thermodynamic description of non-equilibrium states consisting of clusters of arbitrary sizes and composition in the otherwise homogeneous ambient phase was developed by us. This approach leads not only to a sound foundation of the thermodynamic aspects of the theoretical description of cluster growth processes but also to a variety of principally new insights into the course of nucleation-growth or spinodal decomposition processes, in general. In particular, it leads to a different set of thermodynamic equilibrium conditions for the determination of the properties of the critical clusters as compared with Gibbs' classical treatment. Some of the most important consequences of this new approach in application both to nucleation and growth-dissolution processes are analyzed in the present contribution.