Structure and melting of Pb nanocrystals produced by mechanical alloying of Fe/Pb powder mixtures Original Research Article

The melting of Pb nanocrystals produced by milling mixtures of elemental Fe and Pb powders and their structural transformations upon thermal treatments are investigated using differential scanning calorimetry (DSC) and in situ X-ray diffraction (XRD). The DSC curves of milled samples exhibit a strong broadening and a low-temperature shift of the Pb crystal–liquid transition peak. For severely milled powders, the Pb melting endotherm splits into two well-defined sub-peaks. Comparison of DSC and XRD data allows the attribution of the low-temperature transition to nanometer-sized Pb aggregates in interfacial regions with Fe, whereas the high-temperature one is associated with Pb crystals with relatively large average crystallite size. Under heating and cooling treatments, a number of concomitant processes show up, such as relaxation of structural defects, crystallite growth, migration of Pb atoms out of the interfacial regions, and size-dependent melting/freezing of different types of Pb-containing crystals.