SUPERHEATING AND MELTING-POINT DEPRESSION OF PB NANOPARTICLES EMBEDDED IN AL MATRICES

Two kinds of Pb-Al granular sample (with nanometre-sized Pb particles embedded in an Al matrix) were prepared by using melt-spinning and bal l-milling techniques. The Pb particles were synthesized with similar p article sizes, about 5-30 nm in diameter, but were observed to have di fferent Pb-Al interfaces for samples prepared using different approach es. In the melt-spun Pb-Al samples, the Pb nanoparticles were seen to have an epitaxial relationship with the Al matrix, while the Pb partic les in the ball-milled sample were seen to be randomly oriented with r espect to the Al matrix. The melting behaviour of the Pb particles was investigated by differential scanning calorimetry. It was found that the faceted Pb nanoparticles in the melt-spun sample could be superhea ted by about 11-40 K, whereas the irregularly shaped Pb particles in t he ball-milled sample melted about 13 K below its equilibrium point. W e suggest that different interface structures, which cause variations in energy differences between solid-Pb-solid-Al and liquid-Pb-solid-Al interfaces, are responsible for the different melting behaviour of Pb nanoparticles.