Nucleation

Abstract

Nuclei are intermediates in the formation of new phases and the stochastic character of nucleation gives rise to relatively large fluctuations in the rate of phase growth when this is measured on microelectrodes. It is shown that the rate of three-dimensional nucleation of α-lead dioxide and of two-dimensional nucleation of layer planes of calomel may be determined by a statistical analysis of transients. The formation and removal of kink sites at the edges of layer planes of calomel also gives rise to observable fluctuations; lattice formation is shown to be a non-Markovian process.

Clusters of subcritical size are intermediates in the formation of nuclei. Relaxation times for the establishment of the steady state distribution of clusters are measured for the nucleation of mercury. The data cannot be interpreted using currently accepted theory; it is suggested that clusters change in shape in the region of the critical nucleus so that the variation of the free energy of formation of the clusters with size is less rapid than that given by the Kelvin equation.