SURFACE MELTING OF SMALL PARTICLES, AND THE EFFECTS OF SURFACE IMPURITIES

This paper considers three situations in which surface melting may occur on small particles. The first is of small particles embedded in an inert matrix, where the surface melting is driven by a reduced surface energy of the liquid phase. We discuss the nature of the melting transition as the solid particle is warmed to the bulk melting point, and we show that the region over which the particle exists in a mixed solid-liquid phase becomes smaller as the particle is reduced in size. Secondly, we consider the effects of this surface layer on the stability of a particle if the particle was in the presence of its vapour, and show that this is essentially unaffected by the layer. though the amount of supersaturation needed to nucleate from the vapour phase is substantially smaller when surface melting is present. Thirdly, we show that even when the surface energy is unfavourable, surface melting may be driven by impurities in the liquid phase, and as in the first case we consider the nature of the phase transitions, and how it scales with the particle size.