Published online by Cambridge University Press: 26 February 2011
For crystals that melt into fluid liquids, superheating of the solid has been detected in only a few cases. In these cases, a crystal was subjected to focused heating in the center. Under a high thermal gradient some interior superheating was possible, but usually only a few degrees or less. A new approach is reported for preparing samples which can exhibit superheating under more uniform thermal conditions. To exclude the vapor from contact with the crystal a continuous coating is developed with a melting temperature in excess of that for the pure core crystal. For single crystal spherical Ag samples with a diameter of about 130 μm the free surface was coated with a continuous higher melting point layer of Au to inhibit surface initiated melting of silver at its melting point. The coated Ag crystals were observed to exhibit superheating of at least 7.5 K above the melting point of pure Ag for time periods of the order of one minute. Under the experimental conditions used, internal stresses could be excluded as the reason for the observed increase in the melting onset temperature of Ag. The superheating duration is related to the interdiffusion between the coating layer and the core crystal. Some microstructural observations and electron microprobe composition scans also relate to the observed superheating behavior. The results seem to disagree with lattice stability models of melting and may open the way to the study of crystals in the metastable superheated state.