Homogeneous crystal nucleation kinetics in small closed systems

Nuclei of a new phase are formed within metastable parent phase due to fluctuations. During this process it is necessary to overcome a certain nucleation barrier. At appropriate conditions the supercritical clusters (called... [ view full abstract ]

Nuclei of a new phase are formed within metastable parent phase due to fluctuations. During this process it is necessary to overcome a certain nucleation barrier. At appropriate conditions the supercritical clusters (called nuclei) of nanometer size are formed. A better understanding to the nucleation and growth processes enables to develop materials with targeted properties.
We have numerically solved the nucleation kinetic equations to determine the size distribution of nuclei and nucleation rates in small confined volumes. [1] As a model system crystal nucleation of Ni droplets was chosen due to availability of experimental data. [2] In smaller volumes one needs higher supercooling to form crystal nuclei and the depletion of liquid phase is not negligible. It is necessary to take into account the size dependence of the interfacial energy to explain satisfactorily experimental data. At lower supercooling number of formed nuclei is relatively low, as the nucleation barrier is higher, and the classical nucleation theory gives reasonable approach to nucleation rate. However in smaller volumes (< cubic micrometer) higher supercooling is needed to form nuclei and the decrease of the number of molecules within liquid phase plays important role in nucleation process. The number of nuclei increases with time, at a certain time reaches some maximum value, and continues to decrease as a consequence of liquid phase depletion. Similarly, nucleation rate reaches at a certain time some maximum value, which depends on nucleus size.

This work was supported by the Project no. LD1504 of the Ministry of Education, Youth and Sports of the Czech Republic (COST Action CM1402).

[1] Z. Kožíšek: CrystEngComm 15 (2013) 2269.
[2] J. Bokeloh, R.E. Rozas, J. Horbach, G. Wilde: Phys. Rev. Lett. 107 (2011) 145701.