Anisotropy of Wetting of PB Crystals By Their Own Melt and By Liquid GA-PB Alloys

Abstract

In a first set of experiments, observations of anisotropic wetting of different orientations of a macroscopic (milimeter-sized) solid single crystal of Pb by pure liquid Pb have been made at the melting point. It was found that the surface orientations which undergo premelting transitions below the bulk melting point are perfectly wetted by the liquid, whereas the {100} and {111} facets, which do not premelt, are only partially wetted. On those surfaces, wetting improves with decreasing atomic density of the surface. In a second set of observations on Pb-Ga alloys, wetting of a mezoscopic (micronsized) solid single crystal of Pb by liquid Ga was studied in a scanning Auger microprobe. At relatively low temperatures, below the premelting of the solid Pb surfaces, liquid Ga droplets are found to reside only at the {210} orientations of Pb surface. As the temperature is raised above that where most Pb surface orientations undergo premelting, the anisotropic distribution of Ga droplets disappears. In both cases, the anisotropy of wetting is driven by the anisotropy of surface energy of the solid. The degree of wetting is shown to be strongly correlated to the degree of premelting at the solid surface.