Here in this lecture, we only focus on the kinetics of nucleation. Occurs at preferential sites such as grain boundaries, dislocations or impurities. Homogeneous nucleation occurs when there are no special objects inside a phase which can cause nucleation. Pdf heterogeneous versus homogeneous crystal nucleation. Homogeneous nucleation occurs spontaneously and randomly, but it requires superheating or supercooling of the medium. Heterogeneous nucleation may occur under driving forces much less than that required for detectable homogeneous nucleation, and nucleation control normally implies control of some distribution of heterogeneities.
Heterogeneous nucleation is the process of nucleation that takes place at the surface of the system in which the nucleation occurs. Nucleation occurs at some structural imperfections such as foreign surface and hence with reduced surface energy. Homogeneous nucleation is the process by which nuclei that are randomly and spontaneously generated grow irreversibly to form a new phase. For nucleation to occur, the cluster size must be greater than the critical nucleus size, r, at which the activation barrier is. Likewise, the microscopically rough surface of a champagne glass offers nucleation. Dust or atmospheric aerosols can serve as heterogeneous nucleation centers for water condensation in the atmosphere. Further, this type of nucleation occurs at nucleation sites. Moreover, by means of the nucleation rate expressed as j z. Homogeneous nucleation an overview sciencedirect topics. Gases and to a great extent liquids are intrinsically devoid of microstructure, and the uniformity necessary to ensure that. Suspended particles or minute bubbles also provide nucleation sites. Nucleation without preferential nucleation sites is. Heterogeneous nucleation an overview sciencedirect topics.