Time-dependent melting and superheating of lead crystallites

The melting of small lead particles was studied by in situ electron microscopy. Particles of different shapes were examined and found to have qualitatively different melting behaviours. In particular, a thin platelet form with extensive {111} surfaces had a probability of melting per unit time near the bulk melting point, a phenomenon previously reported in bismuth particles (Peppiatt 1975). Some particles could be superheated by up to 2 K above the bulk melting point as a consequence. In contrast, polyhedral lead particles showed no anomalous effects. The time-dependent behaviour is attributed to the difficulty in nucleating the liquid on the {111} surface. The observation could be used as the basis for a study of surface melting.