THE STRUCTURE AND PROPERTIES OF MELT AND CONCENTRATED-SOLUTIONS

The crystallization process is determined by the properties of the solid and of the properties of the liquid state. The properties of the solid at the melting temperature T(m) can be scaled by so-called melting rules. These rules are based on the similarity laws of interatomic forces and provide scaling laws for substances with similar crystal lattices and similar molecular bonds. Scaling laws can also be developed for the properties of simple liquids. Their applicability is more limited, because most liquids are not simple liquids. Their application to crystal growth is even more limited because a crystal does not grow into bulk liquid but into a surface layer. This surface layer has always long range correlations. Long range correlations in liquids and surface layers lead to density fluctuations. Light scattering is a powerful tool to study density fluctuations. The most important results from light scattering experiments during crystal growth are: The solid- liquid interface is not sharp. There is a thick (mum) layer of preordered material in front of the growing crystal. The crystal grows into the interface layer - not into bulk melt. The diffusion constant for the molecules in the solid- liquid interface layer is much smaller than the constant of self diffusion in the melt. Light scattering is a useful technique-for the study of the dynamics of the solidification process and for the characterization of crystal surfaces.