1 Introductory Remarks

Clustering processes in first-order phase transformations play an important role in a huge variety of processes in nature, and in scientific and technological applications. An adequate theoretical description of such processes is therefore of considerable interest. One of the tools allowing the theoretical description of such processes is the nucleation theory. The theoretical approach predominantly employed so far in the interpretation of experimental results of nucleation-growth processes is based on the classical nucleation theory, its extensions and modifications. It is supplemented by density functional computations, statistical mechanical model analyses, and computer modeling of model systems allowing us to gain additional insights into the respective processes and to specify the possible limitations of the classical approaches. Although the basic concepts of the classical approach to the description of nucleation processes were developed about 80 years ago, a number of problems remain, however, unsettled till now which are partly of fundamental character. Several of these problems are analyzed in the present book. One of these analyzes is directed to the method of determination of the coefficients of emission in nucleation theory avoiding the concept of constraint equilibrium distributions (Chap. 3). A second such topic is the proper determination of the work of critical cluster formation for the different processes under investigation. It is discussed in detail in Chaps. 4 (in application to crystallization) and 5 (in application to boiling of binary liquid– gas solutions). A third topic, a relatively recent development of the nucleation theory with a wide spectrum of possible applications, consists in the theoretical description of nucleation and growth processes in solid solutions with sharp concentration gradients (Chap. 10). The majority of theoretical approaches to the description of nucleation and growth processes rely, as far as thermodynamic aspects are involved, on Gibbs’ classical thermodynamic theory of interfacial phenomena. In recent years it has been shown that, by generalizing Gibbs’ thermodynamic approach, a number of problems of the classical theory can be resolved. In particular, as is shown in Chap. 11, the generalized Gibbs’ approach leads to predictions for the properties of the critical clusters and the work of critical cluster formation, which are equivalent to the results of van der Waals’ square gradient and more sophisticated density functional approaches. Some additional new insights, which have been obtained recently employing the generalized Gibbs’ approach, are sketched in Chap. 12. The nucleation theory has the unique advantage that its basic principles are equally well applicable to quite a variety of different systems. As a reflection of this general applicability, the spectrum of analyses, presented in the monograph, includes condensation and boiling, crystallization and melting, self-organization of ferroelectric domains and nanofilms, for-