Heterogeneous nucleation vs homogeneous nucleation pdf

Difference between homogeneous and heterogeneous nucleation. For nucleation to occur, the cluster size must be greater than the critical nucleus size, r, at which the activation barrier is. Gases and to a great extent liquids are intrinsically devoid of microstructure, and the uniformity necessary to ensure that. Pdf heterogeneous versus homogeneous crystal nucleation. Dust or atmospheric aerosols can serve as heterogeneous nucleation centers for water condensation in the atmosphere. Likewise, the microscopically rough surface of a champagne glass offers nucleation. Nucleation without preferential nucleation sites is. Homogeneous nucleation is the process by which nuclei that are randomly and spontaneously generated grow irreversibly to form a new phase. Homogeneous nucleation occurs spontaneously and randomly, but it requires superheating or supercooling of the medium. Moreover, by means of the nucleation rate expressed as j z. Homogeneous nucleation and heterogeneous nucleation. Suspended particles or minute bubbles also provide nucleation sites. Here in this lecture, we only focus on the kinetics of nucleation. Gc supports heterogeneous nucleation while the greater number of potential nucleation sites favors homogeneous nucleation.

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. Further, this type of nucleation occurs at nucleation sites. Heterogeneous nucleation an overview sciencedirect topics. 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. Gc kt, regimes of temperature, supersaturation, relative interfacial energies, and microstructure in which one nucleation mechanism occurs can be predicted. Heterogeneous nucleation begins on alien surfaces or particles, or preexisting nuclei in the old phase. Homogeneous nucleation occurs when there are no special objects inside a phase which can cause nucleation. Occurs at preferential sites such as grain boundaries, dislocations or impurities. Homogeneous nucleation an overview sciencedirect topics.